Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

Pair your accounts.

Export articles to Mendeley

Get article recommendations from ACS based on references in your Mendeley library.

You’ve supercharged your research process with ACS and Mendeley!

STEP 1:
Click to create an ACS ID

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

Please note: If you switch to a different device, you may be asked to login again with only your ACS ID.

MENDELEY PAIRING EXPIRED
Your Mendeley pairing has expired. Please reconnect
ACS Publications. Most Trusted. Most Cited. Most Read
Revisiting Reduction of CO2 to Oxalate with First-Row Transition Metals: Irreproducibility, Ambiguous Analysis, and Conflicting Reactivity
More

OR SEARCH CITATIONS

My Activity
Publications

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:JACS Au 2022, 2, 3, 731-744
  • Open Access
Article

Revisiting Reduction of CO2 to Oxalate with First-Row Transition Metals: Irreproducibility, Ambiguous Analysis, and Conflicting Reactivity
Click to copy article linkArticle link copied!

  • Maximilian Marx
    Maximilian Marx
    Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
    More by Maximilian Marx
    Orcidhttps://orcid.org/0000-0001-7047-1615
  • Holm Frauendorf
    Holm Frauendorf
    Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
    More by Holm Frauendorf
  • Anke Spannenberg
    Anke Spannenberg
    Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
    More by Anke Spannenberg
  • Helfried Neumann
    Helfried Neumann
    Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
    More by Helfried Neumann
  • Matthias Beller*
    Matthias Beller
    Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
    *Email: [email protected]
    More by Matthias Beller
    Orcidhttps://orcid.org/0000-0001-5709-0965
Open PDFSupporting Information (1)

JACS Au

Cite this: JACS Au 2022, 2, 3, 731–744
Click to copy citationCitation copied!
https://doi.org/10.1021/jacsau.2c00005
Published February 14, 2022

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0 .

Abstract

Click to copy section linkSection link copied!
High Resolution Image
Download MS PowerPoint Slide

Construction of higher C≥2 compounds from CO2 constitutes an attractive transformation inspired by nature’s strategy to build carbohydrates. However, controlled C–C bond formation from carbon dioxide using environmentally benign reductants remains a major challenge. In this respect, reductive dimerization of CO2 to oxalate represents an important model reaction enabling investigations on the mechanism of this simplest CO2 coupling reaction. Herein, we present common pitfalls encountered in CO2 reduction, especially its reductive coupling, based on established protocols for the conversion of CO2 into oxalate. Moreover, we provide an example to systematically assess these reactions. Based on our work, we highlight the importance of utilizing suitable orthogonal analytical methods and raise awareness of oxidative reactions that can likewise result in the formation of oxalate without incorporation of CO2. These results allow for the determination of key parameters, which can be used for tailoring of prospective catalytic systems and will promote the advancement of the entire field.

This publication is licensed under

CC-BY-NC-ND 4.0 .
  • cc licence
  • by licence
  • nc licence
  • nd licence
Copyright © 2022 The Authors. Published by American Chemical Society

Keywords

what are keywords

Introduction

Click to copy section linkSection link copied!
Nature’s ability to convert carbon dioxide (CO2) into higher carbon compounds, mainly via photosynthesis, has inspired researchers for decades to evaluate the feasibility of constructing value-added C≥2 materials from CO2 as the starting material. (1,2) Various catalytic approaches enabling carbonylation, (3,4) carboxylation, (5−8) or copolymerization reactions (9,10) were developed based on CO2 as a C1 building block (Figure 1). (11) Moreover, the direct conversion into C≥2 compounds, such as ethane, (12,13) ethylene, (14) ethanol and higher alcohols, (15−17) hydrocarbons, (18−20) and even aromatic compounds (21) has been achieved. Nonetheless, the selective formation of a C≥2 product utilizing CO2 under mild reaction conditions remains a significant challenge. This lack of development contrasts the significant progress for the CO2 reduction to C1 products, namely, methanol, carbon monoxide, formic acid, and methane via thermal, electrochemical, and photochemical approaches. (22−27) One of the major difficulties in the development of selective processes toward C≥2 products resides in the C–C bond forming step. (18,19,21) Prior reduction of CO2 to CO or methanol (MeOH) and subsequent conversion thereof to the final C≥2 products circumvents this step. (16−19) However, a comprehensive understanding of the C–C bond formation starting from CO2 might facilitate the development of tailored catalytic systems which could enable more selective transformations.

Figure 1

Figure 1. Selected examples highlighting the progress in CO2 utilization as a C1 building block or reduction into C1 and C≥2 products as well as potential products derived from oxalic acid.

High Resolution Image
Download MS PowerPoint Slide
Dimerization of two CO2 molecules upon two-electron reduction resulting in oxalate, coined CO2 reductive coupling, provides an ideal model reaction to investigate the C–C bond formation of interest. In addition, oxalic acid was recently suggested as a platform chemical for the preparation of sustainable polymers and its conversion into reduced C2 compounds, such as glycolic acid and ethylene glycol. (28,29) Moreover, it is frequently applied in the purification and recycling of actinides by the nuclear industry. (30)
Early reports highlighted the formation of oxalate during electrochemical CO2 reduction on inert electrodes (Hg and Pb). (31−34) Moreover, aromatic esters or nitriles, (33) as well as transition metal complexes, (35−41) were reported to be efficient electrocatalysts for this transformation. (25)
Nearly 40 years ago, a well-defined oxalate complex was isolated by Fröhlich and Schreer from the reaction of a titanium alkyl complex with CO2. (42) Since this pivotal discovery, various oxalate complexes based on Mg, (43) Ti, (42,44) Sc, (45) Sm, (46−49) Yb, (48,50,51) Lu, (52) U, (53−55) Th, (56) Ni, (57,58) Fe, (59,60) and Cu (e.g., 2 and 3) (39,61,62) were obtained from reaction with CO2 (Figure 2). Moreover, CO2 reductive coupling with the help of strong chemical reductants, such as KC8, was reported for complexes based on U, (55) Yb, (50) Fe (1 and 5), (63,64) Ni (4), (58) and Cu (6a,b). (65) Although all these studies were of limited practical relevance, they allowed for the identification of intriguing reaction pathways, e.g., dimetalloxycarbenes undergoing nucleophilic attack onto CO2. (44,48,56) In addition, their homogeneous nature facilitated evaluation of the impact of steric and electronic parameters of the corresponding catalytic system onto oxalate formation. (47,48,60,65) However, the influence of reaction parameters, such as employed solvents or ligand properties, displayed major variations between different examples.

Figure 2

Figure 2. Selected examples for the formation of oxalate complexes from CO2 and CO2 reductive coupling with strong reductants. (58,61−65) The reactions with complexes 1–3 are discussed herein.

High Resolution Image
Download MS PowerPoint Slide
Likewise, the reaction mechanism for C–C bond formation appears to be rather specific for a respective system. Moreover, analysis of oxalate in the presence of additional CO2 reduction products via NMR or IR spectroscopy can be challenging (66) and common analytic techniques for oxalate quantification (67−70) have scarcely been adopted within this field. These obstacles hamper systematic development of novel and refinement of existing protocols for the coupling of CO2. Hence, the small number of reports on CO2 reductive coupling compared to well-established CO2 reduction to CO, formic acid, and MeOH (22−25) comes as no surprise. Further complication arises from undesired side reactions and irreproducibility of experimental results. (66,71,72) As an example, in situ analysis by Knope et al. on the formation of a Nd-based oxalate coordination polymer suggested that oxalate formation under hydrothermal conditions arose from oxidative decomposition of 2,3-pyrazinedicarboxylic acid without previously suggested incorporation of CO2. (72) Similarly, in a joint cooperation with Maverick and co-workers, the oxidative decomposition of ascorbate, utilized as reductant for the formation of a CuI species, was identified as the source of the observed oxalate. (66) In this case, isolation of a dinuclear Cu oxalate complex in combination with a misleading difference IR spectrum and air contamination of reactions under CO2 atmosphere caused misinterpretation of the experimental data. Such conflicting reactions provide the basis for incorrect interpretation of data and exacerbate the unsteady progress within this field.
Here, we present a guideline for investigations on the simplest C–C bond formation from CO2 and showcase common pitfalls associated with this reaction. For this, three exemplary protocols based on first-row transition metals that have been reported to facilitate the reductive coupling of CO2 were revisited in detail.
As a first example, the reaction of carbon dioxide and [Fe(tmtaa)] (1, tmtaa = 4,11-dihydro-5,7,12,14-tetramethyldibenzo[b,i]-[1,4,8,11]-tetraazacyclotetradecine) in combination with strong reductants (Na, K, NaC10H8) is reexamined (Figure 2). (63) [FeI(tmtaa)Na(THF)3] (7), obtained by reduction of [FeII(tmtaa)] with Na (−3.04 V vs Fc/Fc+) (73) in THF, was reported to show a decisive solvent effect for its reaction with CO2. (63) Reductive disproportionation of CO2 to [FeII(tmtaa)(CO)(THF)] (8) and Na2CO3 was described for the reaction in THF, while in toluene, the formation of oxalate (alongside 1) was claimed based on titration with KMnO4.
The coupling of CO2 to oxalate in the absence of strong chemical reductants is evaluated on the example of a triazacyclononane-derived CuI complex. The allylated tridentate ligand L1 was reported to facilitate the formation of dinuclear complex [(L1)Cu(μ-C2O4)Cu(L1)](BPh4)2 (2) upon reaction of the in situ formed [Cu(L1)]BPh4 complex with exhaled air, CO2 (21%), and CsHCO3 (53%) (Figure 2). (61)
Finally, the incorporation of CO2 into oxalate starting from a CuII α-ketocarboxylate complex [Cu(TpiPr,iPr)(O2CC(O)CH(CH3)2)] (9) under oxidative conditions with air, O2, or CO2/O2 via a proposed CO2•– is reviewed. (62) Incorporation of CO2 into the product 3 (Figure 2) was reported based on a reaction with 13CO2/O2 and vibrational spectroscopy.
In all these cases, incorporation of CO2 into oxalate proved to be irreproducible.

Results

Click to copy section linkSection link copied!

Reactions with [Fe(tmtaa)]

Based on the previous work, we initiated our investigations by studying the reaction of in situ formed 7 with CO2 in toluene (Scheme 1). In our hands, we were unable to identify oxalate by 13C NMR spectroscopy (Figures S52 and S53) and capillary electrophoresis (<0.5% yield based on [Fe]; Figures S349 and S350) after aqueous extraction of the reaction mixture, despite the utilization of excess sodium (Table S1, detailed procedures and results are presented in the Supporting Information). To rule out the insufficient solubility of Na causing the lack of C2O42– formation, further reactions were conducted utilizing NaC10H8 (−3.10 V vs Fc/Fc+) (73) in THF as the reductant for in situ formation of 7. Again, no C2O42– was observed by NMR spectroscopic (Figures S50 and S51) and CE analysis (Figures S347 and S348). To complement the data obtained with Na-based reductants, analogous reactions were performed with K.

Scheme 1

Scheme 1. Reduction of [Fe(tmtaa)] to Complex 7 and Observed Products of Subsequent Reaction with CO2 Highlighting the Absence of Oxalate
High Resolution Image
Download MS PowerPoint Slide
In these cases, reaction in THF and toluene also provided no evidence for the reductive coupling of CO2. However, a signal in the 13C NMR spectra located between 162 and 164 ppm was observed for all reactions (Figures S50–S59), which was assigned to CO32– by adjustment of the pH value of the NMR sample (with 1 M NaOH) and comparison with Na2CO3 (Figure S49). The formation of carbonate in both THF and toluene suggests an accompanied CO2 reduction to CO regardless of the solvent. This was indeed confirmed by the presence of the distinct CO vibration (63) (1911–1912 cm–1) of iron carbonyl complex 8 in the IR spectra of the solid product from the reaction of 1 with K in THF and subsequent treatment with CO2 in THF or toluene (Figures S190–S196). Interestingly, no gaseous CO was found during gas chromatographic analysis of the reaction headspace (Figure S456). NMR analysis of the residue after treatment with K and CO2 revealed the presence of 1 (63) for the reaction in toluene, while line broadening, presumably due to paramagnetism, prohibited assignment to 1 or 8 for the reaction in THF (Figure S48).
Based on these results, we found no evidence for the formation of oxalate utilizing complex 1 and strong chemical reductants while reductive disproportionation was confirmed in both THF and toluene.

CO2 Reductive Coupling by tacn-Derived Cu Complexes [Cu(L)]X

We initiated our investigations on the oxalate formation with L1 reported by Peacock and co-workers by following the literature protocols. (61) In our hands, CO2 bubbling through a suspension of CuI, L1, and NaBPh4 in MeOH resulted in a color change, indicating oxidation of the CuI complex. However, the residue obtained from this experiment featured an IR band at 1628 cm–1 (Figure S197), significantly shifted compared to the literature value of 1660 cm–1, (61) and recrystallization from MeNO2 did not provide the desired oxalate complex. Interestingly, when CO2 bubbling was paused after an initial saturation of the reaction mixture over 2 h and the mixture was stirred overnight under an Ar/CO2 atmosphere, a decolorization was observed that was repeatable for the same reaction mixture (up to six times, see Figure S1). This color change indicated a reversible oxidation of the CuI complex during CO2 bubbling, possibly accompanied by reduction of a CuII complex by NaBPh4. (74) Reaction with NaPF6 instead of NaBPh4 did not cause a decolorization upon paused CO2 bubbling, thus corroborating the role of BPh4– in the reduction. The color change during reactions with CO2 in the presence of NaBPh4 was accompanied by precipitation of a yellow solid. NMR spectroscopic analysis of this precipitate (in THF-d8) indicated the formation of a CuI complex different from [Cu(L1)I] (75) (Figure S61), presumably [Cu(L1)]BPh4 based on the absence of additional signals in the 13C NMR and the integral ratio in the 1H NMR spectrum. Contact of the THF-d8 solution to air resulted in crystallization of [(L1)Cu(μ-OH)2Cu(L1)](BPh4)2 (10, Figure 3), which is in good accordance with analogous compounds formed via aerial oxidation of the CuI complexes. (76,77) However, the desired oxalate complex was not obtained from these experiments, and IR vibrations were observed around 1630 cm–1, thus shifted by 30 cm–1.

Figure 3

Figure 3. Compound 10 and the molecular structure of [(L1)Cu(μ-OH)2Cu(L1)]2+ in 10 (thermal ellipsoids displayed at 30% probability and C-bound H atoms omitted for clarity; symmetry operator for generating equivalent atoms: −x + 1, −y + 1, −z + 1).

High Resolution Image
Download MS PowerPoint Slide
Inspired by the possibility of removing potentially formed oxalate from the product complex, (62) we attempted the synthesis of complex 2 starting from Na2C2O4. While a reaction utilizing in situ formed [Cu(L1)(NO3)2] (11) provided a mononuclear complex [Cu(L1)(κ2-C2O4)] (12), we were able to obtain blue needles of [(L1)Cu(μ-C2O4)Cu(L1)](BF4)2 (13) in 62% yield utilizing Cu(BF4)2·6H2O and Na2C2O4 in MeOH/H2O. As expected, the coordination geometry in 13 is similar to that of 2 (Figure 4). Moreover, its distinct C–O stretching vibration is observed at 1651 cm–1 (Figure S178).

Figure 4

Figure 4. Molecular structure of [(L1)Cu(μ-C2O4)Cu(L1)]2+ in 13 (thermal ellipsoids displayed at 30% probability and H atoms omitted for clarity; symmetry operator for generating equivalent atoms: −x, −y + 1, −z + 1).

High Resolution Image
Download MS PowerPoint Slide
With [(L1)Cu(μ-C2O4)Cu(L1)](BF4)2 in hand, we assessed the removal of C2O42– by stirring in toluene/1 M NaOH (2:1, v:v). (62) To our delight, we detected C2O42– with a yield of 47% by CE for two reactions on 24 μmol scale (1, 48%; 2, 47%). On this scale, the 13C NMR signal of C2O42– at 173 ppm (Figure S60 provides 13C NMR shifts for common CO2 reduction products in D2O) was not observable (however, a minor broadening of the baseline for reaction 1 was noticed).
Having established the possibility of oxalate removal from the desired dinuclear Cu complex, we turned our attention to the reaction with solid bicarbonates, which was supposed to yield higher quantities of complex 2. (61) It is noteworthy that we isolated [Cu(L1)Cl2] (14) from an initial reaction of CuI/L1/NaBPh4 (1:1:1) with CsHCO3 (1.3 equiv) in MeOH following filtration, column chromatographic separation (SiO2, MeOH/MeNO2/2 M NH4Cl, 7:1:2), and recrystallization from hot MeNO2. 14, which can be independently prepared from CuCl2, presumably results from oxidation of the initial CuI complex during the aerial workup and subsequent ligand exchange with NH4Cl during purification.
Additional reactions (Table 1) with CsHCO3 or NaHCO3 in combination with CuI or [Cu(MeCN)4]PF6 in MeOH did not result in notable oxalate formation (according to NMR and CE analysis). Notably, a broad signal coinciding with the oxalate signal was observed for the reactions with CuI in the absence of NaBPh4 (Table 1, entries 5–6; Figures S368 and S369). However, no oxalate was detected by ESI-HRMS analysis for entry 6 (Figure S305), suggesting the presence of another compound with a similar migration time. In this case, most likely the iodide anion was detected as the mobility constants for oxalate and I– are comparable. (78) Indeed, control measurements confirm this behavior (Figure S357).
Table 1. Treatment of In Situ Formed Cu-tacn Complexes with Bicarbonatesa
entry[Cu] [μmol][MHCO3] [μmol]t [h]13C NMR (C2O42–)CE (C2O42– (?)) [%]b
1CuI (126)CsHCO3 (133)16n.d.<1
2CuI (120)CsHCO3 (126)117n.d.<1
3cCuI (150)CsHCO3 (300)168n.d.<0.5
4dCuI (296)NaHCO3 (214)210n.d.<1
5eCuI (126)CsHCO3 (134)17n.d.11
6eCuI (122)CsHCO3 (129)122n.d.7
7f[Cu] (120)CsHCO3 (127)118n.d.<0.5
8f[Cu] (120)NaHCO3 (127)118n.d.<1
a

Reaction conditions: [Cu]/L1/NaBPh4 (1:1:1) combinations were utilized in degassed MeOH. n.d. = not detected.

b

Oxalate yields were calculated for signals coinciding with Na2C2O4 added as internal standard after initial measurement and were found to overlap with the signal of iodide.

c

NaPF6 (1.2 equiv) instead of NaBPh4 was utilized.

d

1.7 equiv of CuI was utilized.

e

Reaction in the absence of NaBPh4.

f

Reaction with [Cu(MeCN)4]PF6.

Due to the lack of oxalate formation by CO2 bubbling and reaction with MHCO3, we evaluated the exposure of in situ formed [Cu(L1)]X (X = I, BPh4) to air to rule out an oxidative origin of oxalate. However, leaving a suspension of CuI, L1, and NaBPh4 in MeOH or MeOH/EtOH (1:4, v:v) in air over 41 and 1 d, respectively, did not result in substantial C2O42– formation according to CE (Table S4).
Likewise, treatment of the in situ formed CuI complex with O2 did not cause formation of oxalate. Interestingly, peaks likely belonging to I– with integrals corresponding to C2O42– yields of 7% and 6% were observed for the exposure of solutions of in situ formed [Cu(L1)I] to air in the absence of NaBPh4 (Figures S375 and S376).
Due to the absence of oxalate formation in all these experiments, we investigated the impact of reaction parameters to possibly facilitate CO2 reductive coupling (Table 2).
Table 2. Treatment of CuI, NaBPh4, and L1 with CO2 under Varying Reactions Conditionsa
entryCuI [μmol]parametert [h]13C NMR (C2O42–)CE (C2O42– (?)) [%]b
1120-24n.d.<1
2120-118n.d.<0.5
3182-120n.d.<0.5
4120MeOH/THF (9:1)118n.d.<0.5
5124THF120n.d.<0.5
6123toluene121n.d.<1
712040 °C114n.d.3
812240 °C123n.d.8
9133400–700 nm (0.09 W)18n.d.<0.5
1013010 bar116n.d.16
1113210 bar116n.d.12
a

Reaction conditions: CuI/L1/NaBPh4 (1:1:1) was utilized in degassed MeOH under constant CO2 atmosphere, unless indicated by the varied parameter. n.d. = not detected.

b

Oxalate yields were calculated for signals coinciding with Na2C2O4 added as internal standard after initial measurement and were found to overlap with the signal of iodide.

Prolonged stirring under a constant CO2 atmosphere for 5 days (Table 2, entries 2 and 3) did not provide detectable quantities of oxalate. Likewise, changing the solvent to a mixture of MeOH and THF (Table 2, entry 4), THF (Table 2, entry 5), or toluene (Table 2, entry 6) as well as illuminating the reaction mixture with visible light (400–700 nm, 0.09 W; Table 2, entry 9) remained unsuccessful. Interestingly, elevated temperature (40 °C, entries 7 and 8) and elevated CO2 pressure (10 bar, entries 10 and 11) facilitated the appearance of a signal of fitting migration time in the CE analysis (Figures S384–S386, S388, S389), corresponding to 5% and 14% C2O42– yield, respectively (average of two reactions). Again, no oxalate was found by ESI-HRMS analysis, indicating yet again overlapping with the signal of iodide. However, ion suppression during the electrospray ionization process has to be considered and can be controlled by further dilution, adding an internal standard ion, or by coupling with CE.
Various additives, namely, Mg(OTf)2, LiBF4, HCO2Na, and KPF6, showed no improvement of the reactivity when combined with CuI or [Cu(MeCN)4]PF6 and ligand L1 (Table S6). Since iodide exchange with NaBPh4 was found to be incomplete, indicated by the crystallization of [Cu(L1)I] (15) from a THF solution of CuI, NaBPh4, and L1, dehalogenation with AgBPh4 was conducted. However, no improvement of the reaction was detected by CE/NMR analysis after NaOH treatment (2% yield by CE, but integration hampered by partial overlapping; Figure S391), despite an IR signal at 1665 cm–1 (Figure S235). Interestingly, oxalate in low yields was detected for reactions with NaC10H8 in THF, even in the absence of any Cu complex (2–7% yield).
Next, other tridentate N-based ligands were evaluated instead of L1 (Table 3). Unfortunately, dipicolylamine (dpa), 1,4,7-benzylated (L2), and 1,4,7-propylated (L3) tacn showed no evidence for CO2 reductive coupling reactivity. In contrast, diethylenetriamine (dien) clearly showcased the limits of CE analysis. A signal that would correspond to a 28% C2O42– yield was observed for a reaction of CO2 with dien, CuI, and NaBPh4 in MeOH over 5 d (Table 3, entry 4). No intense C–O vibration was observed above 1600 cm–1 (Figures S255 and S256), and doubling the reaction scale caused a noticeable decrease in the potential C2O42– yield to 10% (Table 3, entry 5). Moreover, performing the reaction under an argon atmosphere resulted in the same CE signal (Figure S414), meaning that the CE signal is most likely corresponding to I– rather than a CO2 reduction product.
Table 3. Treatment of CuI, NaBPh4, and Different Ligands with CO2 in MeOHa
entryCuI [μmol]ligandt [h]13C NMR (C2O42–)CE (C2O42– (?)) [%]b
1123L2120n.d.<0.5
2124L3120n.d.<0.5
3151dpa120n.d.2
4184dien119n.d.28
5409dien119n.d.10
6c180dien120n.d.26
753L4114n.d.5
8d63L4118n.d.29
9d187L4119n.d.19
10d,e187L4119n.d.28
11d,f94L4118n.d.32
12c,d63L4124n.d.3
13c,d94L4118n.d.<0.5
a

Reaction conditions: CuI/ligand/NaBPh4 (1:1:1) was utilized in degassed MeOH under constant CO2 atmosphere, unless stated otherwise. n.d. = not detected.

b

Oxalate yields were calculated for signals coinciding with Na2C2O4 added as internal standard after initial measurement and were found to overlap with the signal of iodide.

c

Reaction conducted under Ar.

d

A total of 0.5 equiv of L4 was utilized.

e

Reaction conducted with 13CO2.

f

Reaction conducted without NaBPh4.

To evaluate if dinuclear Cu complexes might offer an intrinsic advantage for the reductive coupling of two CO2 molecules, we envisaged ligand L4 as a prime candidate. Thus, we targeted the allyl-derivative L4 which was prepared by reaction of 1,4,7-triazatricyclo[5.2.1.04,10]decane (16) (79) with 1,8-bis(bromomethyl)naphthalene (17) (80) and subsequent allylation (Scheme 2). Isolation of [Cu2(L4)I2] (19) further showcased the ability of L4 to coordinate to two Cu centers.

Scheme 2

Scheme 2. Synthesis of Ligand L4 and Its Derived CuI Complex 19 and (Left) Molecular Structure of 19a
High Resolution Image
Download MS PowerPoint Slide

aThermal ellipsoids are displayed at 30% probability, and H atoms are omitted for clarity.

Reactions of L4, CuI, and NaBPh4 toward CO2 in MeOH resulted in the appearance of a CE signal corresponding to 29% C2O42– yield (Table 3, entry 8; 32% in the absence of NaBPh4, entry 11) which decreased to 19% upon increase of the reaction scale (Table 3, entry 9). Contrary to previous experiments with dien, blank experiments under argon did not result in the appearance of this CE peak (≤3% yield; Table 3, entries 12 and 13; Figures S421 and S422). However, no oxalate was detected by ESI-HRMS analysis (Figure S312). Moreover, an experiment with 13CO2 (formed from Na213CO3 and H2SO4), yielding a signal suggesting a 28% C2O42– yield by CE, displayed no observable oxalate signal in the 13C NMR spectrum (Figure S127).
Hence, we exclude the formation of substantial quantities of oxalate with novel ligand L4 as well as L1, L2, L3, dien, and dpa under the studied reaction conditions.

Reactions of α-Ketocarboxylates and Derived CuTp Complexes toward CO2

To evaluate the third literature example, we prepared complex 9 and its 13C5-labeled congener 20 (84%) following the same procedure (62) but utilizing sodium 13C5-3-methyl-2-oxobutyrate (21). 13C-labeling resulted in the expected shift of the C–O stretching frequencies from 1666/1687 cm–1 (9) to 1625/1644 cm–1 (20) (Figure 5).

Figure 5

Figure 5. FTIR spectra from reaction of complexes 9 and 20 with air and CO2/O2 in DCM and toluene, respectively (FTIR spectra of 9 and 20 are displayed for comparison).

High Resolution Image
Download MS PowerPoint Slide
Exposure of 9 and 20 to air (Scheme 3) caused an alteration of the IR spectra resulting in new bands at 1655 cm–1 and a broad band at 1602 cm–1 for 9, the former being in accordance with the initial report. (62) For 20, signals at 1609 and 1644 cm–1 were observed in addition to a broadened band at 1562 cm–1 (Figure 5). The former is in agreement with the isotopic shift observed by Takisawa et al. while the latter two remained inconclusive.

Scheme 3

Scheme 3. Reaction of Complexes 9 or 20 with Air or CO2/O2 and Subsequent Treatment with NaOH in H2O/Toluene
High Resolution Image
Download MS PowerPoint Slide
Therefore, the obtained products were extracted with NaOH and analyzed by NMR spectroscopy and CE. Indeed, the formation of oxalate could be verified (Figures S133–S134 and S423–S425); however, the observed yields (9: 7% [18 h], 54% [48 h]; 20: 23% [18 h]) were significantly decreased in comparison to the literature (89%). (62) It is noteworthy that these yields are determined by CE and calculated assuming a bimolecular mechanism with one oxalate being formed from two α-ketocarboxylate complexes. 13C NMR spectroscopy for the reaction of 20 allowed for the identification of two major byproducts, namely, 2-hydroxy-2-methylpropanoic acid (confirmed by ESI-HRMS; Figure S317) and 2-methylpropanoic acid (Figure 6).

Figure 6

Figure 6. 13C NMR spectroscopic analysis of the NaOH extract from the reaction of 20 with air.

High Resolution Image
Download MS PowerPoint Slide
When reactions of 9 and 20 were conducted in toluene under an O2/CO2 atmosphere, analogous IR spectra were obtained (Figure 5). Again, C2O42– yields quantified by CE were significantly reduced (9: 7%; 20: 2%), and 2-hydroxy-2-methylpropanoic acid as well as 2-methylpropanoic acid were detected as the primary products by 13C NMR spectroscopy after NaOH extraction (Figure S149–S151). Interestingly, addition of minor quantities of D2O to the reaction of 20 with CO2/O2 in toluene-d8 and analysis by 13C NMR spectroscopy revealed the formation of 13C3-acetone (203.7 ppm [t], 30.3 ppm [d], Figure S131). Subsequent extraction with NaOH and analysis by NMR spectroscopy suggested higher selectivities for C2O42– formation (compare Figure S151 and Figures S153 and S155), while yields assessed by CE were poorly reproducible (25% and 3% for two reactions). Nonetheless, the higher selectivity for C2O42– in the presence of D2O appears to be in accordance with the literature. (62) In addition, ESI-HRMS analysis for reactions of 20 in air and under CO2/O2 atmosphere showed no evidence for the presence of 13C12CO42–, while 13C2O42– was detected for the former and the reaction with CO2/O2 in toluene-d8/D2O (Section S9.2).
Next, in situ formation of 20 starting from CuCl2, sodium 13C5-3-methyl-2-oxobutyrate (21), and KTpiPr,iPr in DCM/heptane and exposure to air was attempted and resulted in an oxalate yield of 38% (CE) after 27 h.
To gain further insight into the oxalate formation and evaluate the necessity of defined complexes 9/20, analogous reactions were conducted in the absence of the TpiPr,iPr ligand (Scheme 4). For this purpose, a Cu precursor and sodium 3-methyl-2-oxobutyrate (21a) were suspended in DCM containing 10% MeOH and left in air (layered with heptane). Subsequent NaOH treatment revealed the formation of oxalate as the major product with 1 equiv of Cu(BF4)2·6H2O (38–59% by CE, Table S8) or CuCl2 (55–82%). Note that oxalate yields from here on are monomolecular yields assuming one C2O42– per α-ketocarboxylate. In addition, substoichiometric quantities of Cu(BF4)2·6H2O (0.2 equiv) were sufficient to provide 48% C2O42–. In the absence of Cu, 4% C2O42– was detected by CE (Figure S446), while only the starting material was observed by IR spectroscopy (Figure S292).

Scheme 4

Scheme 4. Reactions of Different Sodium α-Ketocarboxylates in Combination with a Cu2+ Source under Oxidative Conditions and Subsequent NaOH Treatment for Analysis via NMR and CE
High Resolution Image
Download MS PowerPoint Slide
In addition to these aerial oxidations, Cu(BF4)2·6H2O and 21 were stirred under a CO2/O2 atmosphere in CD2Cl2/CD3OD (10:1, v:v) and C6D6/CD3OD (10:1, v:v) for 4 d. In these cases, 13C NMR spectroscopic analysis confirmed the formation of 13C3-acetone (Figure S131). Subsequent NaOH treatment provided oxalate in 19% (CD2Cl2) and 39% (C6D6) yield, respectively. The former was lower due to a noticeable amount of 2-methylpropionic acid resulting from decarboxylation (Figures S156 and S158). The reason for the favored decarboxylation in CD2Cl2 is not clear and might be a result of DCl traces. It should be noted that in no case mixed isotopic constitutions of C2O42– were detected by ESI-HRMS analysis (Section S9.2), substantiating the lack of CO2 incorporation starting from both, defined complexes 9/20, or a CuII salt combined with the α-ketocarboxylate.
Interestingly, NaOH treatment under an Ar atmosphere decreased the oxalate yield to 17% (from 49% in air, Tables S8 and S10), and significant quantities of starting material were observed by 13C NMR spectroscopy (Figures S163 and S164).
Finally, evaluation of different α-ketocarboxylates was performed to complement the results of our investigation. The reaction of sodium phenylpyruvate with Cu(BF4)2·6H2O in DCM/MeOH in air over 46 h resulted in 29% oxalate (CE). In contrast, sodium pyruvate gave only 6% by CE after 16 h, close to the blank experiment. However, we observed oxidative decarboxylation to acetate by 13C NMR spectroscopy (Figure S165). Moreover, 2-hydroxy-3-methylbutyric acid did not undergo oxidative degradation to oxalate.
While the formation of oxalate was confirmed for defined complexes 9 and 20 as well as for reactions in the absence of TpiPr,iPr, we found no evidence for the incorporation of CO2 into the product oxalate and, thus, cannot confirm the reported conversion of CO2 into oxalate.

Discussion

Click to copy section linkSection link copied!
Reduction of [FeII(tmtaa)] with Na in THF, yielding [FeI(tmtaa)Na(THF)3] (7), and subsequent reaction with CO2 was reported to result in two distinct reactions depending on the employed solvent. (63) Formation of [FeII(tmtaa)(CO)(THF)] (8) and Na2CO3 via reductive disproportionation of CO2 was observed in THF. In contrast, oxalate was the claimed product from the reaction in toluene assessed by titration with KMnO4.
Based on the previous work, we investigated the reaction starting from 1 and Na, NaC10H8, and K followed by treatment with CO2 in toluene or THF (Scheme 5). For the reactions with K, we were able to confirm the formation of CO, in the form of complex 8, and CO23– resulting from reductive disproportionation of CO2. Yet, we did not observe the reported solvent effect and identified the distinct CO band of complex 8 (1911–1912 cm–1) for reactions in both toluene and THF. Interestingly, we did not detect any oxalate by NMR spectroscopy or CE analysis (<0.5% based on 1) after aqueous extraction of the resulting reaction products regardless of the utilized reductant, thus ruling out insufficient solubility preventing CO2 reductive coupling.

Scheme 5

Scheme 5. Revised Reaction of [Fe(tmtaa)] with Strong Reductants Followed by CO2 Treatment Yielding “CO” and M2CO3 but Not M2C2O4
High Resolution Image
Download MS PowerPoint Slide
This lack of oxalate formation highlights two major hurdles associated with studying the reduction of CO2 into oxalate, namely, irreproducibility and ambiguous analysis. Standardization of KMnO4 with the help of oxalate constitutes an established procedure. (81) However, KMnO4 is likewise able to oxidize the metal catalyst (in this case Fe2+) and most organic compounds. (82,83) Therefore, oxidation of residual Fe2+ or an organic impurity could have resulted in a false positive for the KMnO4 titration. Thus, our results emphasized the importance of combining different analytical methods to confirm the presence of C2O42–. Furthermore, the reactions with [Fe(tmtaa)] showcased that strong reductants capable of facilitating CO2•– formation do not guarantee reductive coupling to oxalate.
Our investigations on the second selected literature example further corroborate that both of these pitfalls are not limited to the single example of [Fe(tmtaa)]. Peacock and co-workers reported a CuI complex bearing an allylated tridentate ligand (L1) that was converted into the dinuclear complex [(L1)Cu(μ-C2O4)Cu(L1)](BPh4)2 (2) upon reaction with exhaled air, CO2 (21%), or CsHCO3 (53%) in MeOH. (61) Besides a characteristic IR signal at 1660 cm–1, a crystal structure of the oxalate complex and its magnetic moment were reported to prove the reductive coupling of carbon dioxide. A major advantage of this approach seems to be the absence of additional reductant. Surprisingly, despite the interest in the chemistry of tacn-derived Cu complexes, (80,84−91) no further developments of this system were reported, possibly highlighting the unique properties of allyl-substituted L1.
In our hands, initial experiments with CO2 bubbling indicated an oxidation of the CuI complex formed from CuI, NaBPh4, and L1. However, isolation of a μ-hydroxo CuII complex (10) highlighted that trace O2 might compromise the distinct color change associated with CuI oxidation as an analytical tool. Moreover, IR bands in the 1630 cm–1 region observed for the products from these CO2 bubbling experiments might indicate the formation of a CO2 reduction product, despite the 30 cm–1 difference with respect to desired complex 2. Given the proximity of C–O vibrations of CO2 derived compounds, such as NaHCO3 or HCO2Na in the 1550–1700 cm–1 range (Figure S197), additional analytical data for the identification of CO2 reduction products was desirable. Therefore, we prepared the BF4– analogue of complex 2 and confirmed the possibility of oxalate removal by extraction with aqueous NaOH. This extraction after initial FTIR analysis allowed for detection of oxalate by CE and 13C NMR as well as quantification by CE. With this methodology in hand, the conversion of solid bicarbonates into oxalate with a CuI source and L1 was evaluated but provided no evidence for the reaction of interest. Likewise, evaluation of various reaction parameters, such as solvents, temperature, CO2 pressure, light, or different additives did not yield competing quantities of oxalate. As part of these experiments, a shortcoming of the CE analysis was encountered. Due to similar mobility constants of iodide and oxalate, (78) overlapping of their signals during CE analysis could be expected and was confirmed by control measurements. Moreover, we observed signals coinciding with oxalate especially for reactions in the absence of NaBPh4 or at elevated temperature or pressure. Nonetheless, ESI-HRMS showed no evidence for oxalate formation, substantiating that these signals result from I– rather than C2O42–.
Thus, for a precise determination of oxalate in such and related processes, the use of different analytical methods is essential.
Aside from extensive investigations with L1, we employed our approach with initial FTIR analysis and subsequent NaOH treatment prior to NMR and CE to tridentate N-based ligands, namely, dpa, dien, and two triazacyclononane derivatives. Likewise, these ligands were incapable of promoting the formation of oxalate when combined with CuI and NaBPh4 under the studied conditions. For reactions with dien, a blank experiment in the absence of CO2 was performed to demonstrate that the observed signal in the CE likely corresponded to I–, thereby highlighting another valuable tool for studying CO2 reductive coupling.
Finally, we investigated whether a structurally similar dinuclear Cu complex derived from L4 might be active in the conversion of CO2 into oxalate. Analogous 1,8-bis((1,4,7-triazacyclononanyl)methyl)naphthalene (18) was reported to serve as a valuable ligand for the detection of C2O42– via fluorescence spectroscopy in combination with Eosin-Y due to selective binding to the derived Cu complex. (92) The ability of L4 to coordinate two Cu centers was established by the synthesis of [Cu2(L4)I2] (19). However, L4 did not facilitate the formation of oxalate when combined with CuI or CuI/NaBPh4. Again, ESI-HRMS was employed to assign the CE signal with fitting migration time to I– rather than oxalate. In addition, a reaction with 13CO2 was conducted to further corroborate this assignment by the absence of the 13C NMR signal of C2O42–.
Moreover, GC analysis of the reaction headspace for selected examples combined with 13C NMR spectroscopy provided no evidence for substantial CO2 reduction with the investigated CuI complexes, albeit formate traces were identified for few reactions (also under oxidative conditions in air─see Table S4, entry 4). Finally, to rule out the possibility of an oxidative process yielding μ-C2O4 complex 2, we treated the in situ formed [CuI(L1)X] (X = I, BPh4) with air or O2. Neither of these reactions resulted in oxalate formation.
In conclusion, the results from our extensive investigations with various ligands, additives, and reaction conditions (Scheme 6) highlight the problems arising from irreproducibility of CO2 reductive coupling by a Cu complex. (71) While we cannot entirely exclude the formation of small quantities of oxalate sufficient for crystallization of the complex of interest based on the combination of analytical methods employed by us, we cannot confirm the previously reported yields for oxalate complex 2.

Scheme 6

Scheme 6. Irreproducibility in the Formation of Oxalate from CO2 or MHCO3 with [CuI(NNN)]+ Complexes Studied under Various Conditions, with Multiple Ligands and Different Additives
High Resolution Image
Download MS PowerPoint Slide
Besides irreproducibility and ambiguous analysis, conflicting reactivity causing the formation of oxalate without incorporation of CO2 can be misleading and constitutes another major pitfall for investigations on the reductive dimerization of CO2. (66,72) This is showcased by the third selected example based on Cu α-ketocarboxylate complexes. In 2014, Fujisawa and co-workers reported the unusual formation of a dinuclear oxalate complex 3 ligated by TpiPr,iPr which was isolated from the reaction of [Cu(TpiPr,iPr)(O2CC(O)CH(CH3)2)] (9) with air, O2, or CO2/O2. (62) The reaction was proposed to proceed via formation of a CO2•– intermediate resulting from decomposition of the α-ketocarboxylate in the presence of O2. Incorporation of CO2 into the product was evaluated with 13CO2/O2 causing an isotopic shift in the C–O vibration of 49 cm–1. However, the demand for oxidative reaction conditions to facilitate a reduction paired with our experience on the oxidative degradation of ascorbate encouraged us to gain additional insight in the underlying reaction mechanism.
To evaluate CO2 incorporation into oxalate, we prepared complex 9 and its 13C labeled analogue 20. It is noteworthy that our initial attempt to utilize [(TpiPr,iPr)CuBr] (22) was impeded by the formation of an undesired byproduct ([(HpziPr)2CuBr], 23) indicating the decomposition of the TpiPr,iPr ligand, an infamous property of these scorpionate ligands. (93−99)
Our initial reactions of 9 and 20 with air in CH2Cl2/heptane or CO2/O2 in toluene indeed produced oxalate. However, the obtained yields (by CE) were significantly reduced compared to the literature, and analysis by 13C NMR revealed the formation of 2-hydroxy-2-methylpropanoic acid and 2-methylpropanoic acid. These products likely resulted from oxidative decarboxylation of the α-ketocarboxylate and account for the decreased C2O42– yield. Formation of 2-hydroxy-2-methylpropanoic acid was mentioned in the original report and ascribed to dry air, highlighting the necessity of water. (62) Thus, reaction of 20 with CO2/O2 in toluene-d8 with addition of D2O was conducted and displayed enhanced selectivity for oxalate over decarboxylation products by 13C NMR analysis, albeit the oxalate yield showed poor reproducibility according to CE. Interestingly, 13C3-acetone was detected by 13C NMR for this reaction prior to treatment with NaOH. This hints at a different mechanism for the formation of oxalate, namely, oxidative C2–C3 bond scission rather than the reported C1–C2 cleavage. This is further corroborated by the observation of decarboxylation products resulting from oxidative C1–C2 scission in combination with poor C2O42– yields. Moreover, ESI-HRMS analysis was found to be a valuable tool in combination with isotopic labeling. ESI-HRMS measurements confirmed the presence of 13C2O42– for reactions of 20 with air or CO2/O2 (in toluene-d8/D2O) while no mixed isotopic constitutions of oxalate were observed.
Incorporation of CO2 via the originally proposed mechanism should partially result in mixed isotope oxalate. In contrast, should oxalate formation proceed via oxidative C2–C3 bond cleavage, one would not expect any CO2 incorporation and, thus, no formation of 13C12CO42–. Oxidative decarboxylation of α-ketocarboxylates via C1–C2 bond cleavage is well-known for Tp complexes of Fe. (100,101) Likewise, the oxidative C2–C3 cleavage of phenylpyruvate yielding oxalate has been observed for Fe and Co complexes ligated by a trispyridylamine derivative. (100,102) Furthermore, Fe-based enzymes Dke1 (acetylacetone-cleaving enzyme) and HPPD (4-hydroxyphenylpyruvate dioxygenase) were found to convert 4-hydroxyphenylpyruvate into 4-hydroxybenzaldehyde and oxalate or 2,5-dihydroxyphenylacetic acid and CO2, respectively. (103) These differences in reactivity are influenced by the electronic structure of the respective metal center and the ability of the α-ketocarboxylate to undergo enolization. (100,102,103)
Based on our experimental data from complexes 9 and 20, a C2–C3 bond scission mechanism explains the formation of oxalate. These results contrast with the initially reported CO2 incorporation based on an isotopic shift to 1607 cm–1 upon utilization of 13CO2/O2. (62) In addition, considerable quantities of decarboxylation products and low oxalate yields beg the question of how the high reported yields were obtained. Based on the selectivity enhancement upon addition of D2O and improved C2O42– yield after prolonged exposure to air, we envisaged that decomposition of the complexes and perhaps even TpiPr,iPr, as in our synthesis of [(TpiPr,iPr)CuBr], could occur. (93−99) The resulting Cu2+ might then facilitate the oxidative decomposition of the α-ketocarboxylate in analogy to its activity in the oxidation of ascorbic acid. (104,105)
Indeed, exposing a CuII precursor (CuCl2 or Cu(BF4)2·6H2O) and 21a in CH2Cl2/MeOH/heptane to air and extracting the resulting residue with NaOH gave significantly higher oxalate yields by CE (38–82%; mononuclear yield), in accordance with the higher signal intensity in the 13C NMR. Even substoichiometric quantities of Cu(BF4)2·6H2O produced 48% oxalate (by CE), while blank experiments without Cu2+ confirmed its role in the oxalate formation. NMR experiments with Cu(BF4)2·6H2O and 21 in CD2Cl2/CD3OD or C6D6/CD3OD confirmed the formation of 13C3-acetone, which is in accordance with the proposed oxidative C2–C3 bond cleavage (Figure S131). Again, no 13C12CO42– was detected by ESI-HRMS for reactions with 21, highlighting the lack of CO2 incorporation into oxalate.
For a better understanding of the proposed C2–C3 bond cleavage, the NaOH treatment was conducted under an Ar atmosphere. This resulted in a notable decrease in the oxalate yield from 48% to 17%, and unconverted α-ketocarboxylate was detected by NMR spectroscopic analysis. Hence, the basic pH facilitates the oxidative C2–C3 bond scission in the presence of Cu2+. This indicates that enolization of the α-ketocarboxylate might be essential for the formation of oxalate via C2–C3 bond cleavage. To gather additional evidence for this hypothesis, further experiments were conducted with related α-ketocarboxylates. Replacement of 21a with sodium phenylpyruvate, which would likewise allow for enolization, provided oxalate in 29% yield. In contrast, sodium pyruvate gave only 6% C2O42–, which is close to that of the blank experiment. These results further corroborate that the structure of the α-ketocarboxylate, allowing for enolization or stabilization of an intermediate radical species, is another key parameter determining the selectivity for C1–C2 vs C2–C3 bond cleavage.
Based on our experimental results, we propose the following reaction pathways for 9/20 (Scheme 7): Well-defined [Cu(TpiPr,iPr)(O2CC(O)CH(CH3)2)] complexes facilitate primarily oxidative decarboxylation via C1–C2 bond scission. Low quantities of oxalate should be a result of C2–C3 bond cleavage by [Cu(TpiPr,iPr)]+ or by its decomposition products, possibly resulting from hydrolysis in the presence of H2O. In contrast, Cu2+ facilitates the oxidative degradation of suitable α-ketocarboxylates into oxalate. Here, the oxidation under basic pH plays an integral part. Besides these primary reactions, the underlying oxidative degradation processes appear to be more complicated and might involve follow-up condensation reactions during NaOH treatment, as indicted by the 13C NMR spectroscopic analysis (Section S7.4).

Scheme 7

Scheme 7. Proposed Reaction Pathway for the Formation of Oxalate and Acetone via Oxidative C2–C3 Bond Cleavagea
High Resolution Image
Download MS PowerPoint Slide

aIsobutyric acid and 2-hydroxyisobutyric acid were identified, presumably resulting from oxidative decarboxylation upon C1–C2 bond scission.

In conclusion, this example highlights that oxidative processes resulting in the formation of oxalate can readily be misinterpreted. Therefore, cautious analysis with a combination of analytical techniques as well as suitable control experiments to evaluate the incorporation of CO2 are required to avoid this pitfall.

Conclusions

Click to copy section linkSection link copied!
The use of renewable energy to produce organic matter has remained a central challenge for many decades. In this context, the reductive dimerization of carbon dioxide to oxalate can be considered as a first step. Hence, this apparently simple reaction continues to be of interest for basic science as well as more recently in the context of alternative energy technologies, highlighted by the “OCEAN” project of the European Union, which explores the conversion of CO2 into oxalic acid and its utilization as a platform chemical. (28)
While investigating the desired CO2 reductive dimerization, we faced significant problems and describe here the potential pitfalls based on our studies. Looking exemplarily at three previously published works, we identified irreproducibility, insufficient analysis, misleading analytical data, and conflicting reactivity as the main hurdles, which arguably hamper the development of novel and enhancement of established protocols for CO2 reduction to oxalate.
Specifically, using [Fe(tmtaa)] and alkali metal-based reductants, we could not verify the formation of oxalate in toluene or THF previously claimed by titration with KMnO4. Yet, the importance of suitable analytical methods became apparent.
Similarly, in the presence of triazacyclonone-ligated Cu complexes, no CO2 reductive coupling was observed. Here, various reaction parameters, additives, and tridentate ligands were used without providing C2O42–. However, the limitations of single analytical methods, namely, IR and NMR spectroscopy as well as CE, were highlighted. Fortunately, the combination of these methods and suitable control experiments offered a reliable approach to investigate CO2 reductive coupling.
Finally, in the reaction of [Cu(TpiPr,iPr)(O2CC(O)CH(CH3)2)] (9) with air or CO2/O2, oxalate results from oxidative cleavage of the substrate with no evidence for CO2 incorporation. Interestingly, formation of oxalate via oxidative decomposition of the α-ketocarboxylate was enhanced in the presence of Cu2+ without any additional ligand. As part of these investigations, we presented the second (66) example for a potentially misleading outcome of an isotopic labeling study with 13CO2 within this field. Ambiguous results can arise from the formation of additional CO2 reduction or hydration products (formate or bicarbonate), oxidative decomposition reactions resulting in the formation of carboxylic acid or carbonyl compounds, and variable solvent contamination with, e.g., DMF.
Based on all these results, we advise the following guidelines to enhance future progress in this cutting-edge field:
(a)

Utilization of a combination of orthogonal analytical methods, for instance, FTIR spectroscopy combined with NMR spectroscopy and CE analysis, is indispensable. In addition, electrospray mass spectrometry, especially coupled with CE, should allow for appropriate validation of experimental results. Suitable alternatives to CE represent ion chromatography, high-performance liquid chromatography, or gas chromatography in combination with derivatization or oxidative decomposition of oxalic acid (the latter being less compatible with studying CO2 reduction). (67,106−110) These techniques have proven reliable in the quantification of oxalate in biological samples, foods, or waters from pulp and paper processes.

(b)

In general, a cautious strategy for reaction design and implementation of control reactions to exclude oxidative processes should be made. We highly encourage researchers working in this area to examine oxidative conditions or reactions under exclusion of CO2 to validate that a reductive process accounts for the formation of C2O42–.

(c)

While isotopic labeling with 13CO2 in combination with IR spectroscopic analysis can provide valuable insight into the mechanism of oxalate formation, we would like to raise awareness of the limited significance of the assignment of a CO2 reductive coupling mechanism based on isotopic labeling with vibrational spectroscopy as the sole analytical tool. Here, NMR spectroscopy and ESI-HRMS offer great compatibility and provide additional information to ensure the validity of the proposed mechanism and correct identification of the reaction product.

Albeit the interest in CO2 reductive coupling seems to suffer from the variety of complications highlighted herein, we believe the area offers great potential for the fundamental understanding of the reactivity of carbon dioxide. One of the apparently simplest C–C bond formations certainly deserves more attention, because a mechanistic understanding allowing for a general design of suitable catalysts enabling this transformation would be highly desirable in view of the need for efficient CO2 utilization. We believe the lessons presented throughout this article will contribute to paving the way for reliable progress within this field and, hopefully, promote the development of guiding principles for the construction of C≥2 compounds from CO2.

Supporting Information

Click to copy section linkSection link copied!

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacsau.2c00005.

  • General information, experimental procedures, detailed experimental results, and analytical data (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

Click to copy section linkSection link copied!
  • Corresponding Author
  • Authors
    • Maximilian Marx - Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany;  Orcidhttps://orcid.org/0000-0001-7047-1615
    • Holm Frauendorf - Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
    • Anke Spannenberg - Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
    • Helfried Neumann - Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, 18059 Rostock, Germany
  • Author Contributions

    The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

    Crystallographic data for 10 (2092312), 11 (2092313), 12 (2092314), 13 (2092315), 14 (2092316), 15 (2092311), 19 (2092317), 22 (2092318), and 23 (2092319) can be obtained free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe via www.ccdc.cam.ac.uk/structures

Acknowledgments

Click to copy section linkSection link copied!

The authors are grateful for funding by the European Research Council as part of the H2020 project (NoNaCat, ID: 670986) and the Danish National Research Foundation (CADIAC). M.M. is grateful to the Fonds der Chemischen Industrie for a Kekulé fellowship (No. 102241). We thank Dr. Anastasiya Agapova (LIKAT), Dr. Elisabetta Alberico (LIKAT and Instituto di Chimica Biomolecolare, CNR, Sassari), Dr. Alexander Léval (LIKAT), Prof. Andrew W. Maverick (Louisiana State University), and Dr. Jacob Schneidewind (LIKAT) for scientific discussions and valuable suggestions. The analytical department of LIKAT is gratefully acknowledged for conducting NMR measurements.

Abbreviations

Click to copy section linkSection link copied!
CE

capillary electrophoresis

DCM

dichloromethane

Dipp

2,6-di-iso-propylphenyl

ESI

electrospray ionization

HRMS

high resolution mass spectrometry

IR

infrared spectroscopy

NMR

nuclear magnetic resonance

tacn

1,4,7-triazacyclononane

THF

tetrahydrofuran

H2tmtaa

4,11-dihydro-5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]-tetraazacyclotetradecine

TpiPr,iPr

tris(3,5-di-iso-propylpyrazolyl)borate

HpziPr

3,5-di-iso-propylpyrazole

References

Click to copy section linkSection link copied!

This article references 110 other publications.

  1. 1
    Appel, A. M.; Bercaw, J. E.; Bocarsly, A. B.; Dobbek, H.; DuBois, D. L.; Dupuis, M.; Ferry, J. G.; Fujita, E.; Hille, R.; Kenis, P. J. A.; Kerfeld, C. A.; Morris, R. H.; Peden, C. H. F.; Portis, A. R.; Ragsdale, S. W.; Rauchfuss, T. B.; Reek, J. N. H.; Seefeldt, L. C.; Thauer, R. K.; Waldrop, G. L. Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation. Chem. Rev. 2013, 113, 6621– 6658,  DOI: 10.1021/cr300463y
    Google Scholar
    1
    Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation
    Appel, Aaron M.; Bercaw, John E.; Bocarsly, Andrew B.; Dobbek, Holger; DuBois, Daniel L.; Dupuis, Michel; Ferry, James G.; Fujita, Etsuko; Hille, Russ; Kenis, Paul J. A.; Kerfeld, Cheryl A.; Morris, Robert H.; Peden, Charles H. F.; Portis, Archie R.; Ragsdale, Stephen W.; Rauchfuss, Thomas B.; Reek, Joost N. H.; Seefeldt, Lance C.; Thauer, Rudolf K.; Waldrop, Grover L.
    Chemical Reviews (Washington, DC, United States) (2013), 113 (8), 6621-6658CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atm. CO2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atm. CO2. Providing a future energy supply that is secure and CO2-neutral will require switching to non-fossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored,transported, and used upon demand. This Review describes the results of a workshop held to explore these concepts in regard to the development of new and more efficient catalytic processes for the conversion of CO2 to a variety of carbon-based fuels.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsFWqsLs%253D&md5=f8e57b72f24de79c3ec80ffe95eacd34
  2. 2
    Aresta, M.; Dibenedetto, A.; Angelini, A. Catalysis for the Valorization of Exhaust Carbon: From CO2 to Chemicals, Materials, and Fuels. Technological Use of CO2. Chem. Rev. 2014, 114, 1709– 1742,  DOI: 10.1021/cr4002758
    Google Scholar
    2
    Catalysis for the Valorization of Exhaust Carbon: from CO2 to Chemicals, Materials, and Fuels. Technological Use of CO2
    Aresta, Michele; Dibenedetto, Angela; Angelini, Antonella
    Chemical Reviews (Washington, DC, United States) (2014), 114 (3), 1709-1742CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFegsrfP&md5=a773e4deabc012c1c86caf70f43239a4
  3. 3
    Liu, Q.; Wu, L.; Fleischer, I.; Selent, D.; Franke, R.; Jackstell, R.; Beller, M. Development of a Ruthenium/Phosphite Catalyst System for Domino Hydroformylation–Reduction of Olefins with Carbon Dioxide. Chem. Eur. J. 2014, 20, 6888– 6894,  DOI: 10.1002/chem.201400358
    Google Scholar
    3
    Development of a ruthenium/phosphite catalyst system for domino hydroformylation-reduction of olefins with carbon dioxide
    Liu, Qiang; Wu, Lipeng; Fleischer, Ivana; Selent, Detlef; Franke, Robert; Jackstell, Ralf; Beller, Matthias
    Chemistry - A European Journal (2014), 20 (23), 6888-6894CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    An efficient domino ruthenium-catalyzed reverse water-gas-shift-hydroformylation-redn. reaction of olefins to alcs. was reported. Key to success was the use of specific bulky phosphite ligands and triruthenium dodecacarbonyl as the catalyst. Compared to the known ruthenium/chloride system, the new catalyst allows for a more efficient hydrohydroxymethylation of terminal and internal olefins with carbon dioxide at lower temp. Unwanted hydrogenation of the substrate was prevented. Preliminary mechanism investigations uncovered the homogeneous nature of the active catalyst and the influence of the ligand and additive in individual steps of the reaction sequence.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXnslWgtLo%253D&md5=b01c278c53ad6911bf0624d8980797ff
  4. 4
    Wu, L.; Liu, Q.; Fleischer, I.; Jackstell, R.; Beller, M. Ruthenium-Catalysed Alkoxycarbonylation of Alkenes with Carbon Dioxide. Nat. Commun. 2014, 5, 3091,  DOI: 10.1038/ncomms4091
    Google Scholar
    4
    Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide
    Wu Lipeng; Liu Qiang; Fleischer Ivana; Jackstell Ralf; Beller Matthias
    Nature communications (2014), 5 (), 3091 ISSN:.
    Alkene carbonylations represent a major technology for the production of value-added bulk and fine chemicals. Nowadays, all industrial carbonylation processes make use of highly toxic and flammable carbon monoxide. Here we show the application of abundantly available carbon dioxide as C1 building block for the alkoxycarbonylations of industrially important olefins in the presence of a convenient and inexpensive ruthenium catalyst system. In our system, carbon dioxide works much better than the traditional combination of carbon monoxide and alcohols. The unprecedented in situ formation of carbon monoxide from carbon dioxide and alcohols permits an efficient synthesis of carboxylic acid esters, which can be used as detergents and polymer-building blocks. Notably, this transformation allows the catalytic formation of C-C bonds with carbon dioxide as C1 source and avoids the use of sensitive and/or expensive reducing agents (for example, Grignard reagents, diethylzinc or triethylaluminum).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2cvksVShtg%253D%253D&md5=cc752afda0372405681f067b7459d762
  5. 5
    Hong, J.; Li, M.; Zhang, J.; Sun, B.; Mo, F. C-H Bond Carboxylation with Carbon Dioxide. ChemSusChem 2019, 12, 6– 39,  DOI: 10.1002/cssc.201802012
    Google Scholar
    5
    C-H Bond Carboxylation with Carbon Dioxide
    Hong, Junting; Li, Man; Zhang, Jianning; Sun, Beiqi; Mo, Fanyang
    ChemSusChem (2019), 12 (1), 6-39CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Carbon dioxide is a nontoxic, renewable, and abundant C1 source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chem. transformation of CO2 with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivs. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp2)-H bonds of (hetero)arenes, vinylic C(sp2)-H bonds, the ipso-C(sp2)-H bonds of the diazo group, aldehyde C(sp2)-H bonds, α-C(sp3)-H bonds of the carbonyl group, γ-C(sp3)-H bonds of the carbonyl group, C(sp3)-H bonds adjacent to nitrogen atoms, C(sp3)-H bonds of o-alkyl Ph ketones, allylic C(sp3)-H bonds, C(sp3)-H bonds of methane, and C(sp3)-H bonds of halogenated aliph. hydrocarbons. In addn., multicomponent reactions, tandem reactions, and key theor. studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochem., and light-driven methods are highlighted.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktFSlsw%253D%253D&md5=450d45909060f4bea4db3b1d0c103653
  6. 6
    Li, H.-R.; He, L.-N. Construction of C–Cu Bond: A Useful Strategy in CO2 Conversion. Organometallics 2020, 39, 1461– 1475,  DOI: 10.1021/acs.organomet.9b00642
    Google Scholar
    6
    Construction of C-Cu Bond: A Useful Strategy in CO2 Conversion
    Li, Hong-Ru; He, Liang-Nian
    Organometallics (2020), 39 (9), 1461-1475CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
    A review. Carbon dioxide is not only one of the greenhouse gas but also an appealing renewable C1 source. To reconcile the environment benefit with chem. industry development, CO2 conversion into valuable chems. is proposed and tremendous efforts have been devoted to developing new synthetic protocols and highly efficient catalytic systems, wherein copper catalysis is attractive and features effective, inexpensive and diverse transformation of CO2. Considering the ubiquity of C-Cu bond in org. chem. and the wide application of the resulting carbocuprate species in reductive coupling with electrophiles, the C-Cu formation and subsequent CO2 insertion has been developed as an important strategy for CO2 chem. fixation, thereby resulting in prepg. a variety of valuable chems. To arouse broad concern of this strategy, we summarize the recent advances and give an overview on CO2 transformations via the carbocuprate species on the basis of the C-Cu bond formation mechanism, including copper-promoted alkyne and halide activation, transmetalation of some specific chems. with copper and hydrocupration, borocupration, silylcupration of unsatd. substrates. It is hoped that this review can provide some clues for the further exploration in this field.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVygs7%252FL&md5=a9c4a88526d5b5390b1df16d00e157ed
  7. 7
    Juhl, M.; Laursen, S. L. R.; Huang, Y.; Nielsen, D. U.; Daasbjerg, K.; Skrydstrup, T. Copper-Catalyzed Carboxylation of Hydroborated Disubstituted Alkenes and Terminal Alkynes with Cesium Fluoride. ACS Catal. 2017, 7, 1392– 1396,  DOI: 10.1021/acscatal.6b03571
    Google Scholar
    7
    Copper-Catalyzed Carboxylation of Hydroborated Disubstituted Alkenes and Terminal Alkynes with Cesium Fluoride
    Juhl, Martin; Laursen, Simon L. R.; Huang, Yuxing; Nielsen, Dennis U.; Daasbjerg, Kim; Skrydstrup, Troels
    ACS Catalysis (2017), 7 (2), 1392-1396CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    In the presence of CuI and imidazolylidene or benzimidazolylidene ligands, boranes generated in situ from di- and trisubstituted alkenes (cyclohexenes, styrene, and stilbenes) and from terminal alkynes underwent chemo- and diastereoselective carboxylation with CO2 mediated by CsF to yield carboxylic acids and malonic acids. Five terpene-derived natural products and cholesteryl Me ether were used as reactants for copper-catalyzed carboxylations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKhsbo%253D&md5=f2011c6252eb763569e327d43f70cdef
  8. 8
    Ukai, K.; Aoki, M.; Takaya, J.; Iwasawa, N. Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2. J. Am. Chem. Soc. 2006, 128, 8706– 8707,  DOI: 10.1021/ja061232m
    Google Scholar
    8
    Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2
    Ukai, Kazutoshi; Aoki, Masao; Takaya, Jun; Iwasawa, Nobuharu
    Journal of the American Chemical Society (2006), 128 (27), 8706-8707CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    When the esters of arylboronic acids with 2,2-dimethyl-1,3-propanol were treated with a catalytic amt. of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60 °C under carbon dioxide atm., the benzoic acid derivs. were obtained in good yields. Reactions of alkenylboronic esters also proceeded under similar conditions to give α,β-unsatd. carboxylic acids. As these boronic esters are now easily available through coupling or direct borylation reactions, this method would be a useful method for the prepn. of various functionalized aryl- and alkenyl carboxylic acids. For example, the rhodium-catalyzed reaction of a boronic acid ester, i.e., 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane, with carbon dioxide gave benzoic acid.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmtVSjsbo%253D&md5=0c880ab4e3f61a8cf0f5e6ddab46953c
  9. 9
    Coates, G. W.; Moore, D. R. Discrete Metal-Based Catalysts for the Copolymerization of CO2 and Epoxides: Discovery, Reactivity, Optimization, and Mechanism. Angew. Chem., Int. Ed. 2004, 43, 6618– 6639,  DOI: 10.1002/anie.200460442
    Google Scholar
    9
    Discrete metal-based catalysts for the copolymerization of CO2 and epoxides: Discovery, reactivity, optimization, and mechanism
    Coates, Geoffrey W.; Moore, David R.
    Angewandte Chemie, International Edition (2004), 43 (48), 6618-6639CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review on discovery, reactivity, optimization, and mechanism of discrete metal-based catalysts for polymn. of CO2 and epoxides. Given the non-renewable nature of these materials, there is increasing interest in developing routes to polymeric materials from renewable resources. There is a growing demand for biodegradable polymeric materials. Polycarbonates made from CO2 and epoxides have the potential to meet these goals. Since the discovery of catalysts for the copolymn. of CO2 and epoxides in the late 1960's by Inoue, a significant amt. of research has been directed toward the development of catalysts of improved activity and selectivity.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXos1yh&md5=c7aa69fd7ae451f8d02a9330c92b07ea
  10. 10
    Darensbourg, D. J. Making Plastics from Carbon Dioxide: Salen Metal Complexes as Catalysts for the Production of Polycarbonates from Epoxides and CO2. Chem. Rev. 2007, 107, 2388– 2410,  DOI: 10.1021/cr068363q
    Google Scholar
    10
    Making plastics from carbon dioxide: Salen metal complexes as catalysts for the production of polycarbonates from epoxides and CO2
    Darensbourg, Donald J.
    Chemical Reviews (Washington, DC, United States) (2007), 107 (6), 2388-2410CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review is given on the prepn. of polycarbonates (and some cyclic carbonates) from epoxides and carbon dioxide. The use of salicylaldimine-based complexes of chromium, cobalt, and aluminum is discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXksVSmurY%253D&md5=098c95c8b9de54de4c6c123c5f9c2ef7
  11. 11
    Liu, Q.; Wu, L.; Jackstell, R.; Beller, M. Using Carbon Dioxide as a Building Block in Organic Synthesis. Nat. Commun. 2015, 6, 5933,  DOI: 10.1038/ncomms6933
    Google Scholar
    11
    Using carbon dioxide as a building block in organic synthesis
    Liu, Qiang; Wu, Lipeng; Jackstell, Ralf; Beller, Matthias
    Nature Communications (2015), 6 (), 5933pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    A review. The most recent advances made in the area of CO2 valorization-turning CO2 into a useful chem. feedstock-under mild conditions has been reviewed. A special focus is given on the reaction modes for the CO2 activation and its application as C1 building block in org. synthesis. The following subjects will be addressed in this review : (1) novel transformations using carbon dioxide (briefly summarized); (2) different reaction modes for CO2 activation (main focus of this review); and (3) potential new applications of CO2 valorization.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtF2lurjM&md5=e3ba6b5612253c0c6ebec3d937f137f8
  12. 12
    Adachi, K.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of Carbon Dioxide to Hydrocarbon Using Copper-Loaded Titanium Dioxide. Sol. Energy 1994, 53, 187– 190,  DOI: 10.1016/0038-092X(94)90480-4
    Google Scholar
    12
    Photocatalytic reduction of carbon dioxide to hydrocarbon using copper-loaded titanium dioxide
    Adachi, Kenji; Ohta, Kiyohisa; Mizuno, Takayuki
    Solar Energy (1994), 53 (2), 187-90CODEN: SRENA4; ISSN:0038-092X.
    The photocatalytic redn. of CO2 using Cu-loaded TiO2 powd. catalyst was studied at ambient temp. The Cu-TiO2 powders suspended in the soln., which was pressurized with CO2 of 28 kg/cm2, were illuminated with a Xe lamp. The catalyst, Cu(≤5 wt.%)/TiO2, is specific for the products (i.e., the main products were CH4 and C2H4, and not MeOH and formaldehyde). Using the photochem. redn., the yields for CH4, C2H4, and C2H6 were 21.8, 26.2, and 2.7 μL/g, resp., under optimum conditions. The CO2 redn. system developed might be of practical interest for photochem. fuel prodn., storage of solar energy, and prodn. of raw materials for the photochem. industry.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXmvVentbs%253D&md5=836fcbce77926988c421a2145c2c1335
  13. 13
    Li, N.; Wang, B.; Si, Y.; Xue, F.; Zhou, J.; Lu, Y.; Liu, M. Toward High-Value Hydrocarbon Generation by Photocatalytic Reduction of CO2 in Water Vapor. ACS Catal. 2019, 9, 5590– 5602,  DOI: 10.1021/acscatal.9b00223
    Google Scholar
    13
    Toward High-Value Hydrocarbon Generation by Photocatalytic Reduction of CO2 in Water Vapor
    Li, Naixu; Wang, Bingbing; Si, Yitao; Xue, Fei; Zhou, Jiancheng; Lu, Youjun; Liu, Maochang
    ACS Catalysis (2019), 9 (6), 5590-5602CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    Semiconductor crystals with well-defined morphol., porous nanostructure, and spatially sepd. active sites are attractive for use in photocatalysis. This paper describes a controlled synthesis of cake-like porous TiO2 photocatalyst with surface-localized doping of copper and cobalt by using a well-defined MIL-125(Ti) metal org. framework as template precursor. The series of the modified TiO2 photocatalysts present the improved activity for photocatalytic CO2 redn. with water vapor. It is found that 1%Cu-doped TiO2 shows an enhanced behavior for breaking C=O bonds. In this case, the outcomes are primarily CO and CH4, yielding up to 135.94 and 127.05 μmol, resp., under the irradn. of simulated sunlight for 3 h. The performance can be further improved by incorporating trace cobalt. Besides the improved property for CO and CH4 prodn., the selectivity also shifts to high-value hydrocarbons (C2+). The yields for C2H6 and C3H8 can be up to 267.60 and 10.07 μmol, resp., by using 0.02%Co-1%Cu/TiO2. Our in situ Fourier transform IR spectra together with theor. calcns. indicate that efficient charge sepn. on copper and cobalt ions is achieved. This altered charge behavior leads to the generation and enrichment of Me radicals on the surface of cobalt ions, giving rise to the prodn. of C2+ hydrocarbons. This work demonstrates a vibrant catalyst platform for solar fuel generation by photocatalytic CO2 conversion in water.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXptFymurs%253D&md5=1134fbae7d8ae6bbea17cba4c5a3cca8
  14. 14
    Xia, Y.; Xiao, K.; Cheng, B.; Yu, J.; Jiang, L.; Antonietti, M.; Cao, S. Improving Artificial Photosynthesis over Carbon Nitride by Gas–Liquid–Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2. ChemSusChem 2020, 13, 1730– 1734,  DOI: 10.1002/cssc.201903515
    Google Scholar
    14
    Improving Artificial Photosynthesis over Carbon Nitride by Gas-Liquid-Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2
    Xia, Yang; Xiao, Kai; Cheng, Bei; Yu, Jiaguo; Jiang, Lei; Antonietti, Markus; Cao, Shaowen
    ChemSusChem (2020), 13 (7), 1730-1734CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The activity and selectivity of simple photocatalysts for CO2 redn. remain limited by the insufficient photophysics of the catalysts, as well as the low soly. and slow mass transport of gas mols. in/through aq. soln. In this study, these limitations are overcome by constructing a triphasic photocatalytic system, in which polymeric carbon nitride (CN) is immobilized onto a hydrophobic substrate, and the photocatalytic redn. reaction occurs at a gas-liq.-solid (CO2-water-catalyst) triple interface. CN anchored onto the surface of a hydrophobic substrate exhibits an approx. 7.2-fold enhancement in total CO2 conversion, with a rate of 415.50μmol m-2 h-1 under simulated solar light irradn. This value corresponds to an overall photosynthetic efficiency for full water-CO2 conversion of 0.33%, which is very close to biol. systems. A remarkable enhancement of direct C2 hydrocarbon prodn. and a high CO2 conversion selectivity of 97.7% are obsd. Going from water oxidn. to phosphate oxidn., the quantum yield is increased to 1.28%.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFOqtr0%253D&md5=1fe17fc278f45e3e7c1cc3f368067afb
  15. 15
    Wang, L.; Wang, L.; Zhang, J.; Liu, X.; Wang, H.; Zhang, W.; Yang, Q.; Ma, J.; Dong, X.; Yoo, S. J.; Kim, J.-G.; Meng, X.; Xiao, F.-S. Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts. Angew. Chem., Int. Ed. 2018, 57, 6104– 6108,  DOI: 10.1002/anie.201800729
    Google Scholar
    15
    Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts
    Wang, Lingxiang; Wang, Liang; Zhang, Jian; Liu, Xiaolong; Wang, Hai; Zhang, Wei; Yang, Qi; Ma, Jingyuan; Dong, Xue; Yoo, Seung Jo; Kim, Jin-Gyu; Meng, Xiangju; Xiao, Feng-Shou
    Angewandte Chemie, International Edition (2018), 57 (21), 6104-6108CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Methods for the hydrogenation of CO2 into valuable chems. are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non-noble cobalt catalysts (CoAlOx), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the compn. of the catalysts through the use of different preredn. temps., the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g-1 h-1. Operando FT-IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx, a key intermediate in the prodn. of ethanol by CO2 hydrogenation.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXosVWnt7Y%253D&md5=0e5782f8b1b9d3adff17a187617e2019
  16. 16
    Qian, Q.; Cui, M.; He, Z.; Wu, C.; Zhu, Q.; Zhang, Z.; Ma, J.; Yang, G.; Zhang, J.; Han, B. Highly Selective Hydrogenation of CO2 into C2+ Alcohols by Homogeneous Catalysis. Chem. Sci. 2015, 6, 5685– 5689,  DOI: 10.1039/C5SC02000J
    Google Scholar
    16
    Highly selective hydrogenation of CO2 into C2+ alcohols by homogeneous catalysis
    Qian, Qingli; Cui, Meng; He, Zhenhong; Wu, Congyi; Zhu, Qinggong; Zhang, Zhaofu; Ma, Jun; Yang, Guanying; Zhang, Jingjing; Han, Buxing
    Chemical Science (2015), 6 (10), 5685-5689CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The hydrogenation of CO2 to produce alcs. with two or more carbons (C2+ alcs.) is of great importance, but is challenging. In this work, we found that a Ru3(CO)12/Rh2(CO)4Cl2-LiI system could catalyze the reaction effectively in 1,3-dimethyl-2-imidazolidinone (DMI) under mild conditions. Methanol, ethanol, propanol, 2-Me propanol, butanol, and 2-Me butanol were produced in the homogeneous catalytic reaction. The C2+ alcs. could be generated at 160 °C, which is the lowest temp. reported so far for producing C2+ alcs. via CO2 hydrogenation. The selectivity for the C2+ alcs. could be as high as 96.4% at the optimized conditions, which is higher than those reported in the literature. In addn., the catalytic system could be easily recycled. The route of the reaction for forming the C2+ alcs. was discussed on the basis of control expts.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFCqtb3F&md5=70809ef59e10a8440eae3f0da15bc6b6
  17. 17
    Cui, M.; Qian, Q.; He, Z.; Zhang, Z.; Ma, J.; Wu, T.; Yang, G.; Han, B. Bromide Promoted Hydrogenation of CO2 to Higher Alcohols Using Ru–Co Homogeneous Catalyst. Chem. Sci. 2016, 7, 5200– 5205,  DOI: 10.1039/C6SC01314G
    Google Scholar
    17
    Bromide promoted hydrogenation of CO2 to higher alcohols using Ru-Co homogeneous catalyst
    Cui, Meng; Qian, Qingli; He, Zhenhong; Zhang, Zhaofu; Ma, Jun; Wu, Tianbin; Yang, Guanying; Han, Buxing
    Chemical Science (2016), 7 (8), 5200-5205CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Iodides are commonly used promoters in C2+OH synthesis from CO2/CO hydrogenation. Here we report the highly efficient synthesis of C2+OH from CO2 hydrogenation over a Ru3(CO)12-Co4(CO)12 bimetallic catalyst with bis(triphenylphosphoranylidene)ammonium chloride (PPNCl) as the cocatalyst and LiBr as the promoter. Methanol, ethanol, propanol and isobutanol were formed at milder conditions. The catalytic system had a much better overall performance than those of reported iodide promoted systems because PPNCl and LiBr cooperated very well in accelerating the reaction. LiBr enhanced the activity and PPNCl improved the selectivity, and thus both the activity and selectivity were very high when both of them were used simultaneously. In addn., the catalyst could be reused for at least five cycles without an obvious change of catalytic performance.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Krsrg%253D&md5=34a9b14869134f5a5581081486ee98ea
  18. 18
    Gao, P.; Dang, S.; Li, S.; Bu, X.; Liu, Z.; Qiu, M.; Yang, C.; Wang, H.; Zhong, L.; Han, Y.; Liu, Q.; Wei, W.; Sun, Y. Direct Production of Lower Olefins from CO2 Conversion via Bifunctional Catalysis. ACS Catal. 2018, 8, 571– 578,  DOI: 10.1021/acscatal.7b02649
    Google Scholar
    18
    Direct Production of Lower Olefins from CO2 Conversion via Bifunctional Catalysis
    Gao, Peng; Dang, Shanshan; Li, Shenggang; Bu, Xianni; Liu, Ziyu; Qiu, Minghuang; Yang, Chengguang; Wang, Hui; Zhong, Liangshu; Han, Yong; Liu, Qiang; Wei, Wei; Sun, Yuhan
    ACS Catalysis (2018), 8 (1), 571-578CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    Direct conversion of carbon dioxide (CO2) into lower olefins (C2=-C4=), generally referring to ethylene, propylene, and butylene, is highly attractive as a sustainable prodn. route for its great significance in greenhouse gas control and fossil fuel substitution, but such a route always tends to be low in selectivity toward olefins. Here we present a bifunctional catalysis process that offers C2=-C4= selectivity as high as 80% and C2-C4 selectivity around 93% at more than 35% CO2 conversion. This is achieved by a bifunctional catalyst composed of indium-zirconium composite oxide and SAPO-34 zeolite, which is responsible for CO2 activation and selective C-C coupling, resp. We demonstrate that both the precise control of oxygen vacancies on the oxide surface and the integration manner of the components are crucial in the direct prodn. of lower olefins from CO2 hydrogenation. No obvious deactivation is obsd. over 150 h, indicating a promising potential for industrial application.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFaqtrfK&md5=4178d134b8b214f7178551eea2733a55
  19. 19
    Gao, P.; Li, S.; Bu, X.; Dang, S.; Liu, Z.; Wang, H.; Zhong, L.; Qiu, M.; Yang, C.; Cai, J.; Wei, W.; Sun, Y. Direct Conversion of CO2 into Liquid Fuels with High Selectivity over a Bifunctional Catalyst. Nat. Chem. 2017, 9, 1019– 1024,  DOI: 10.1038/nchem.2794
    Google Scholar
    19
    Direct conversion of CO2 into liquid fuels with high selectivity over a bifunctional catalyst
    Gao, Peng; Li, Shenggang; Bu, Xianni; Dang, Shanshan; Liu, Ziyu; Wang, Hui; Zhong, Liangshu; Qiu, Minghuang; Yang, Chengguang; Cai, Jun; Wei, Wei; Sun, Yuhan
    Nature Chemistry (2017), 9 (10), 1019-1024CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)
    Although considerable progress was made in CO2 hydrogenation to various C1 chems., it is still a great challenge to synthesize value-added products with ≥2 carbons, such as gasoline, directly from CO2 because of the extreme inertness of CO2 and a high C-C coupling barrier. Here the authors present a bifunctional catalyst composed of reducible In oxides (In2O3) and zeolites that yields a high selectivity to gasoline-range hydrocarbons (78.6%) with a very low methane selectivity (1%). The O vacancies on the In2O3 surfaces activate CO2 and H to form MeOH, and C-C coupling subsequently occurs inside zeolite pores to produce gasoline-range hydrocarbons with a high octane no. The proximity of these 2 components plays a crucial role in suppressing the undesired reverse water gas shift reaction and giving a high selectivity for gasoline-range hydrocarbons. Also, the pellet catalyst exhibits a much better performance during an industry-relevant test, which suggests promising prospects for industrial applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVSjt7bI&md5=4ef37e087edf5dfbaf26bcd93105f584
  20. 20
    Wang, H.; Zhao, Y.; Wu, Y.; Li, R.; Zhang, H.; Yu, B.; Zhang, F.; Xiang, J.; Wang, Z.; Liu, Z. Hydrogenation of Carbon Dioxide to C2–C4 Hydrocarbons Catalyzed by Pd(PtBu3)2–FeCl2 with Ionic Liquid as Cocatalyst. ChemSusChem 2019, 12, 4390– 4394,  DOI: 10.1002/cssc.201901820
    Google Scholar
    20
    Hydrogenation of Carbon Dioxide to C2-C4 Hydrocarbons Catalyzed by Pd(PtBu3)2-FeCl2 with Ionic Liquid as Cocatalyst
    Wang, Huan; Zhao, Yanfei; Wu, Yunyan; Li, Ruipeng; Zhang, Hongye; Yu, Bo; Zhang, Fengtao; Xiang, Junfeng; Wang, Zhenpeng; Liu, Zhimin
    ChemSusChem (2019), 12 (19), 4390-4394CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Direct hydrogenation of CO2 to C2+ hydrocarbons is very interesting, but achieving this transformation <200° is challenging and seldom reported. A homogeneous catalytic system was developed composed of the ionic liq. 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), Pd(P(tert-Bu)3)2, FeCl2, and the ligand 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) for hydrogenation of CO2 under mild conditions, which resulted in C2-C4 hydrocarbons in selectivities up to 98.3 C-mol % at 180°. The combination of ([BMIm][PF6]) with Xantphos endowed the Pd-Fe catalysts with the ability of activating CO2 and H2 simultaneously via [HPd(PCMe33)(BMIm-COO)(BMIm)(PF6)Fe]+ species, thus catalyzing the formation of C2-C4 hydrocarbons through CO2 hydrogenation. This catalytic system is stable and recyclable, which may have promising applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslWjtLrN&md5=d943a6b6ee8dd523921e85d1f267a668
  21. 21
    Ni, Y.; Chen, Z.; Fu, Y.; Liu, Y.; Zhu, W.; Liu, Z. Selective Conversion of CO2 and H2 into Aromatics. Nat. Commun. 2018, 9, 3457,  DOI: 10.1038/s41467-018-05880-4
    Google Scholar
    21
    Selective conversion of CO2 and H2 into aromatics
    Ni Youming; Chen Zhiyang; Fu Yi; Liu Yong; Zhu Wenliang; Liu Zhongmin; Ni Youming; Chen Zhiyang; Fu Yi; Liu Yong; Zhu Wenliang; Liu Zhongmin; Chen Zhiyang; Fu Yi
    Nature communications (2018), 9 (1), 3457 ISSN:.
    Transformation of greenhouse gas CO2 and renewable H2 into fuels and commodity chemicals is recognized as a promising route to store fluctuating renewable energy. Although several C1 chemicals, olefins, and gasoline have been successfully synthesized by CO2 hydrogenation, selective conversion of CO2 and H2 into aromatics is still challenging due to the high unsaturation degree and complex structures of aromatics. Here we report a composite catalyst of ZnAlOx and H-ZSM-5 which yields high aromatics selectivity (73.9%) with extremely low CH4 selectivity (0.4%) among the carbon products without CO. Methanol and dimethyl ether, which are synthesized by hydrogenation of formate species formed on ZnAlOx surface, are transmitted to H-ZSM-5 and subsequently converted into olefins and finally aromatics. Furthermore, 58.1% p-xylene in xylenes is achieved over the composite catalyst containing Si-H-ZSM-5. ZnAlOx&H-ZSM-5 suggests a promising application in manufacturing aromatics from CO2 and H2.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3c3itlymtg%253D%253D&md5=35f495bb04ebe5f758359084ee8240d6
  22. 22
    Wang, W.-H.; Himeda, Y.; Muckerman, J. T.; Manbeck, G. F.; Fujita, E. CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction. Chem. Rev. 2015, 115, 12936– 12973,  DOI: 10.1021/acs.chemrev.5b00197
    Google Scholar
    22
    CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction
    Wang, Wan-Hui; Himeda, Yuichiro; Muckerman, James T.; Manbeck, Gerald F.; Fujita, Etsuko
    Chemical Reviews (Washington, DC, United States) (2015), 115 (23), 12936-12973CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. CO2 hydrogenation to formate and methanol, formic acid dehydrogenation with various metal complexes, H2 green fuel prodn. and storage, and interconversion of CO2 and formic acid.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCgu7rK&md5=9e39dcc06a0e334b3a891ce797de5f9f
  23. 23
    Yamazaki, Y.; Takeda, H.; Ishitani, O. Photocatalytic Reduction of CO2 Using Metal Complexes. J. Photochem. Photobiol. C 2015, 25, 106– 137,  DOI: 10.1016/j.jphotochemrev.2015.09.001
    Google Scholar
    23
    Photocatalytic reduction of CO2 using metal complexes
    Yamazaki, Yasuomi; Takeda, Hiroyuki; Ishitani, Osamu
    Journal of Photochemistry and Photobiology, C: Photochemistry Reviews (2015), 25 (), 106-137CODEN: JPPCAF; ISSN:1389-5567. (Elsevier B.V.)
    A review. Developing photocatalytic systems for CO2 redn. will provide useful and energy-rich compds. and would be one of the most important focuses in the field of "artificial photosynthesis" and "solar fuels". Such studies have been conducted in the past three decades from the perspective of basic science and for solving the shortage of fossil resources, which include both energy and carbon sources. More recently, focus has been placed on the mitigation of global warming through the redn. of atm. CO2. This review summarizes the enormous body of reported literature in this field, particularly studies that describe photocatalytic systems that use transition metal complexes as key players, i.e., as catalysts (Cat) and/or photosensitizers (PS). In addn., we briefly describe the evaluation of various photocatalytic systems, esp. the performance of reductants (D) and solvents. Furthermore, we analyze the types of photocatalytic systems and classify each component in these systems according to their role: (1) PS, (2) Cat for CO2 redn. catalysts, and (3) D. Briefly, we summarize the important features of each component and provide typical examples. The next section discusses the photocatalytic abilities of each of the three categories of photocatalytic systems: multicomponent systems comprising PS and Cat, supramol. photocatalysts comprising a multinuclear complex, and hybrid systems constructed with metal-complex photocatalysts and inorg. materials, such as semiconductors or electrodes.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs12ltLbJ&md5=da5f207bbb4d735eccf20cdd5cd129f6
  24. 24
    Takeda, H.; Cometto, C.; Ishitani, O.; Robert, M. Electrons, Photons, Protons and Earth-Abundant Metal Complexes for Molecular Catalysis of CO2 Reduction. ACS Catal. 2017, 7, 70– 88,  DOI: 10.1021/acscatal.6b02181
    Google Scholar
    24
    Electrons, Photons, Protons and Earth-Abundant Metal Complexes for Molecular Catalysis of CO2 Reduction
    Takeda, Hiroyuki; Cometto, Claudio; Ishitani, Osamu; Robert, Marc
    ACS Catalysis (2017), 7 (1), 70-88CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    A review. Electrochem. and photochem. redn. of CO2, or a smart combination of both, are appealing approaches for the storage of renewable, intermittent energies and may lead to the prodn. of fuels and of value added chems. By using only earth abundant metal (Cu, Ni, Co, Mn, Fe) complexes, cheap electrodes and/or cheap sacrificial electron donors and visible light sensitizers, systems functioning with mol. catalysts have been recently designed, showing promising results in particular for the two electrons redn. of the carbon dioxide. By combining exptl. and mechanistic studies, key parameters controlling the catalysis efficiency have been deciphered, opening the way to the design of future, more efficient and durable catalysts, as well as to the development of electrochem. or photo-electrochem. cells, all being key steps for the emergence of applied devices. The most recent advances related to these issues are discussed in this review.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGhu7zF&md5=032874cb48f7a230e25fd72a4f4628e5
  25. 25
    Francke, R.; Schille, B.; Roemelt, M. Homogeneously Catalyzed Electroreduction of Carbon Dioxide─Methods, Mechanisms, and Catalysts. Chem. Rev. 2018, 118, 4631– 4701,  DOI: 10.1021/acs.chemrev.7b00459
    Google Scholar
    25
    Homogeneously Catalyzed Electroreduction of Carbon Dioxide-Methods, Mechanisms, and Catalysts
    Francke, Robert; Schille, Benjamin; Roemelt, Michael
    Chemical Reviews (Washington, DC, United States) (2018), 118 (9), 4631-4701CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. The utilization of CO2 via electrochem. redn. constitutes a promising approach toward prodn. of value-added chems. or fuels using intermittent renewable energy sources. For this purpose, mol. electrocatalysts are frequently studied and the recent progress both in tuning of the catalytic properties and in mechanistic understanding is truly remarkable. While in earlier years research efforts were focused on complexes with rare metal centers such as Re, Ru, and Pd, the focus has recently shifted toward earth-abundant transition metals such as Mn, Fe, Co, and Ni. By application of appropriate ligands, these metals have been rendered more than competitive for CO2 redn. compared to the heavier homologues. In addn., the important roles of the second and outer coordination spheres in the catalytic processes have become apparent, and metal-ligand cooperativity has recently become a well-established tool for further tuning of the catalytic behavior. Surprising advances have also been made with very simple organocatalysts, although the mechanisms behind their reactivity are not yet entirely understood. Herein, the developments of the last three decades in electrocatalytic CO2 redn. with homogeneous catalysts are reviewed. A discussion of the underlying mechanistic principles is included along with a treatment of the exptl. and computational techniques for mechanistic studies and catalyst benchmarking. Important catalyst families are discussed in detail with regard to mechanistic aspects, and recent advances in the field are highlighted.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXlsVWqsw%253D%253D&md5=4161321252762123a970f3cb93e62cac
  26. 26
    Windle, C. D.; Perutz, R. N. Advances in Molecular Photocatalytic and Electrocatalytic CO2 Reduction. Coord. Chem. Rev. 2012, 256, 2562– 2570,  DOI: 10.1016/j.ccr.2012.03.010
    Google Scholar
    26
    Advances in molecular photocatalytic and electrocatalytic CO2 reduction
    Windle, Christopher D.; Perutz, Robin N.
    Coordination Chemistry Reviews (2012), 256 (21-22), 2562-2570CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    This review describes recent developments in photocatalytic and electrocatalytic CO2 redn. On the electrocatalytic side, there have been advances in optimization of known rhenium motifs sometimes in conjunction with silicon photoelectrodes giving enhanced catalytic current and stability. Complexes of copper capable of absorbing atm. CO2 have been incorporated into an electrocatalytic cycle and metal-free electrocatalysis of CO2 to methanol has been achieved with pyridinium ions. A complete cell with two photoelectrodes, one for water oxidn. and the other for CO2 redn. to formate has been set up successfully. The cathode employs ruthenium catalysts on InP. Progress in photocatalytic CO2 redn. has been made with osmium complexes exhibiting good selectivity and stability. The sepn. between Ru and Re centers in light-harvesting donor-acceptor dyads has been investigated providing some inspiration for design. A ruthenium catalyst has been sensitized by tantalum oxide particles. Metalloporphyrin-rhenium dyads have also been studied for photocatalytic CO2 redn. In the biol. arena, a ruthenium complex has been used to sensitize carbon monoxide dehydrogenase on titanium dioxide particles.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xlslyls74%253D&md5=2f9fc91d331b52f8f2f667daffa3dbc5
  27. 27
    Morris, A. J.; Meyer, G. J.; Fujita, E. Molecular Approaches to the Photocatalytic Reduction of Carbon Dioxide for Solar Fuels. Acc. Chem. Res. 2009, 42, 1983– 1994,  DOI: 10.1021/ar9001679
    Google Scholar
    27
    Molecular Approaches to the Photocatalytic Reduction of Carbon Dioxide for Solar Fuels
    Morris, Amanda J.; Meyer, Gerald J.; Fujita, Etsuko
    Accounts of Chemical Research (2009), 42 (12), 1983-1994CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review concerning mol. approaches to the photocatalytic redn. of CO2 in homogenous soln. for solar fuels, i.e., photochem. transformation of CO2 into a fuel source as an attractive way to decrease atm. CO2 concns., is given. One way to accomplish this conversion is via light-driven CO2 redn. to gaseous CH4 or liq. CH3OH with electrons and protons derived from water. Existing infrastructure already supports the delivery of natural gas and liq. fuels, making these possible CO2 redn. products particularly appealing. A favorable pathway is to reduce CO2 by proton-assisted, multiple-electron transfer. CO and formate are the primary CO2 redn. products; a HCO3-/CO32- prodn. process is also discussed. Topics covered include: common terms; type 1 reaction (Co and Ni tetraaza-macrocyclic compds., supramol. complexes); type 2 reaction (metalloporphyrins and related metallomacrocycles, Re(CO3)3(bpy)X-based complexes); and summary and future outlook.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVGntr3F&md5=4d5ba24aecb183119ed2ed6cff3959dd
  28. 28
    Schuler, E.; Demetriou, M.; Shiju, N. R.; Gruter, G.-J. M. Towards Sustainable Oxalic Acid from CO2 and Biomass. ChemSusChem 2021, 14, 3636– 3664,  DOI: 10.1002/cssc.202101272
    Google Scholar
    28
    Towards Sustainable Oxalic Acid from CO2 and Biomass
    Schuler, Eric; Demetriou, Marilena; Shiju, N. Raveendran; Gruter, Gert-Jan M.
    ChemSusChem (2021), 14 (18), 3636-3664CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2. A promising route is the electrochem. redn. of CO2 to formic acid derivs. that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chem. for material prodn. as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid prodn. processes with a focus on CO2-based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVehtrrO&md5=c1b6f036df6ddb0275323e9bb175a52a
  29. 29
    Murcia Valderrama, M. A.; van Putten, R.-J.; Gruter, G.-J. M. The Potential of Oxalic – and Glycolic Acid Based Polyesters (Review). Towards CO2 as a Feedstock (Carbon Capture and Utilization – CCU). Eur. Polym. J. 2019, 119, 445– 468,  DOI: 10.1016/j.eurpolymj.2019.07.036
    Google Scholar
    29
    The potential of oxalic - and glycolic acid based polyesters (review). Towards CO2 as a feedstock (Carbon Capture and Utilization - CCU)
    Murcia Valderrama, Maria A.; van Putten, Robert-Jan; Gruter, Gert-Jan M.
    European Polymer Journal (2019), 119 (), 445-468CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
    A review. Plastic materials are indispensable in everyday life because of their versatility, high durability, lightness and cost-effectiveness. As a consequence, worldwide plastic consumption will continue to grow from around 350 million metric tons per annum today to an estd. 1 billion metric tons per annum in 2050. For applications where polymers are applied in the environment or for applications where polymers have a bigger chance of ending up in the environment, (bio)degradable polymers need to be developed to stop endless accumulation of non-degradable polymers irreversibly littering our planet. As monomers and polymers represent more than 80% of the chem. industry's total prodn. vol., a transition from fossil feedstock today (99% of the current feedstock for polymers is fossil-based) to a significantly larger percentage of renewable feedstock in the future (carbon that is already "above the ground") will be required to meet the greenhouse gas redn. targets of the Paris Agreement (>80% CO2 redn. target for the European Chem. Industry sector in 2050). The combination of the predicted polymer market growth and the emergence of new feedstocks creates a fantastic opportunity for novel sustainable polymers. To replace fossil based feedstock, there are only three sustainable alternative sources: biomass, CO2 and existing plastics (via recycling). The ultimate circular feedstock would be CO2: it can be electrochem. reduced to formic acid derivs. that can subsequently be converted into useful monomers such as glycolic acid and oxalic acid. In order to assess the future potential for these polyester building blocks, we will review the current field of polyesters based on these two monomers. Representative synthesis methods, general properties, general degrdn. mechanisms, and recent applications will be discussed in this review. The application potential of these polyesters for a wide range of purposes, as a function of prodn. cost, will also be assessed. It is important to note that polymers derived from CO2 do not necessarily always lead to lower net overall CO2 emissions (during prodn. of after use, e.g. degrdn. in landfills). This needs to be evaluated using robust LCA's and this information is currently not available for the materials discussed in this review.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs1CisLnI&md5=9aa39ae2d5c94cffeb53515e43c00c43
  30. 30
    Abraham, F.; Arab-Chapelet, B.; Rivenet, M.; Tamain, C.; Grandjean, S. Actinide Oxalates, Solid State Structures and Applications. Coord. Chem. Rev. 2014, 266–267, 28– 68,  DOI: 10.1016/j.ccr.2013.08.036
    Google Scholar
    30
    Actinide oxalates, solid state structures and applications
    Abraham, Francis; Arab-Chapelet, Benedicte; Rivenet, Murielle; Tamain, Christelle; Grandjean, Stephane
    Coordination Chemistry Reviews (2014), 266-267 (), 28-68CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    A review. Actinide oxalates are an important class of materials mainly for the nuclear industry. This review presents the crystal growth methods addressed to non-sol. actinide (III) and (IV) oxalates and to sol. actinyl oxalates. Actinide-oxalate discrete ions, one-dimensional coordination polymers and two- or three-dimensional frameworks are described for the different oxidn. states of actinides in simple, double or triple actinide oxalates together with mixed actinide (IV)-lanthanide (III) or -actinide (III) and mixed ligands actinide oxalates. The main applications of actinide oxalates, particularly for radioactive waste management and nuclear fuel treatment and recycling are also reported.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFCju7fO&md5=8e24daab735abe8292b782131b111d33
  31. 31
    Tyssee, D. A.; Wagenknecht, J. H.; Baizer, M. M.; Chruma, J. L. Some Cathodic Organic Syntheses Involving Carbon Dioxide. Tetrahedron Lett. 1972, 13, 4809– 4812,  DOI: 10.1016/S0040-4039(01)94435-1
    Google Scholar
    There is no corresponding record for this reference.
  32. 32
    Amatore, C.; Saveant, J. M. Mechanism and Kinetic Characteristics of the Electrochemical Reduction of Carbon Dioxide in Media of Low Proton Availability. J. Am. Chem. Soc. 1981, 103, 5021– 5023,  DOI: 10.1021/ja00407a008
    Google Scholar
    32
    Mechanism and kinetic characteristics of the electrochemical reduction of carbon dioxide in media of low proton availability
    Amatore, Christian; Saveant, Jean Michel
    Journal of the American Chemical Society (1981), 103 (17), 5021-3CODEN: JACSAT; ISSN:0002-7863.
    The mechanism of the redn. of CO2 in solvents of low proton availability such as DMF was investigated on the basis of the variation of the electrolysis product distribution with c.d. and concn. of CO2 and H2O. It was shown to involve 3 competing pathways: oxalate formation through self-coupling of the CO2 anion radicals, CO formation via O-C coupling of CO2 anion radicals with CO2, and formate formation through protonation of CO2 anion radicals by residual or added H2Oter followed by an homogeneous electron transfer from CO2 anion radicals. Using the product distribution data together with the kinetic data obtained by fast microelectrolytic techniques allows the characterization of the key-steps of the redn. process: initial electron transfer and the rate detg. steps of the 3 competing reactions leading to oxalate, CO and formate.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXkvVyjurg%253D&md5=dd0b1dc1a7a49f0bc50ae23406e778ac
  33. 33
    Gennaro, A.; Isse, A. A.; Savéant, J.-M.; Severin, M.-G.; Vianello, E. Homogeneous Electron Transfer Catalysis of the Electrochemical Reduction of Carbon Dioxide. Do Aromatic Anion Radicals React in an Outer-Sphere Manner?. J. Am. Chem. Soc. 1996, 118, 7190– 7196,  DOI: 10.1021/ja960605o
    Google Scholar
    33
    Homogeneous Electron Transfer Catalysis of the Electrochemical Reduction of Carbon Dioxide. Do Aromatic Anion Radicals React in an Outer-Sphere Manner?
    Gennaro, Armando; Isse, Abdirisak A.; Saveant, Jean-Michel; Severin, Maria-Gabriella; Vianello, Elio
    Journal of the American Chemical Society (1996), 118 (30), 7190-7196CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Electrochem. generated anion radicals of arom. nitriles and esters possess the remarkable property to reduce carbon dioxide to oxalate with negligible formation of carboxylated products. They may thus serve as selective homogeneous catalysts for the redn. of CO2 in an aprotic medium. The catalytic enhancement of the cyclic voltammetric peaks of these catalysts was used to det. the rate const. of the electron transfer from these arom. anion radicals to CO2 as a function of the catalyst std. potential. Substituted benzoic esters allowed a particularly detailed study of the resulting activation-driving force relation. Using 14 different catalysts in this series made it possible to finely scan a range of reaction std. free energies of 0.4 eV. Detailed anal. of the resulting data indicated that the reaction is not a simple outer-sphere electron transfer. It rather consists in a nucleophilic addn. of the anion radical on CO2, forming an oxygen (or nitrogen for the nitriles)-carbon bond, which successively breaks homolytically, generating the parent ester (or nitrile) and the anion radical of CO2, which eventually dimerizes to oxalate.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XktFOqurY%253D&md5=33597bbe7b66ef3c9cbdcf1adb349918
  34. 34
    Gennaro, A.; Isse, A. A.; Severin, M.-G.; Vianello, E.; Bhugun, I.; Saveant, J.-M. Mechanism of the Electrochemical Reduction of Carbon Dioxide at Inert Electrodes in Media of Low Proton Availability. J. Chem. Soc., Faraday Trans. 1996, 92, 3963– 3968,  DOI: 10.1039/FT9969203963
    Google Scholar
    34
    Mechanism of the electrochemical reduction of carbon dioxide at inert electrodes in media of low proton availability
    Gennaro, Armando; Isse, Abdirisak A.; Severin, Maria-Gabriella; Vianello, Elio; Bhugun, Iqbal; Saveant, Jean-Michel
    Journal of the Chemical Society, Faraday Transactions (1996), 92 (20), 3963-3968CODEN: JCFTEV; ISSN:0956-5000. (Royal Society of Chemistry)
    Direct electrolysis of CO2 in DMF at an inert electrode, such as mercury, produces mixts. of CO and oxalate, whereas electrolysis catalyzed by radical anions of arom. esters and nitriles produces exclusively oxalate in the same medium. Examn. of previous results concerning the direct electrochem. redn. and the redn. by photoinjected electrons reveals that there are no significant specific interactions between reactant, intermediates and products on the one hand, and the electrode material on the other, when this is Hg or Pb. These observations and a systematic study of the variations of the oxalate and CO yields with temp. and CO2 concn., allow the derivation of a consistent mechanistic model of the direct electrochem. redn. It involves the formation of oxalate from the coupling of two CO2 radical anions in soln. CO (and an equimolar amt. of carbonate) is produced by redn. at the electrode of a CO2-CO2.- adduct, the formation of which, at the electrode surface, is rendered exothermic by nonspecific electrostatic interactions.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmvVymtrw%253D&md5=0e561d234957e6c009ff7c426f26b1b2
  35. 35
    Kushi, Y.; Nagao, H.; Nishioka, T.; Isobe, K.; Tanaka, K. Oxalate Formation in Electrochemical CO2 Reduction Catalyzed by Rhodium-Sulfur Cluster. Chem. Lett. 1994, 23, 2175– 2178,  DOI: 10.1246/cl.1994.2175
    Google Scholar
    There is no corresponding record for this reference.
  36. 36
    Tanaka, K.; Kushi, Y.; Tsuge, K.; Toyohara, K.; Nishioka, T.; Isobe, K. Catalytic Generation of Oxalate through a Coupling Reaction of Two CO2 Molecules Activated on [(Ir(η5-C5Me5))2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]. Inorg. Chem. 1998, 37, 120– 126,  DOI: 10.1021/ic9702328
    Google Scholar
    36
    Catalytic Generation of Oxalate through a Coupling Reaction of Two CO2 Molecules Activated on [[Ir(η5-C5Me5)]2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]
    Tanaka, Koji; Kushi, Yoshinori; Tsuge, Kiyoshi; Toyohara, Kiyotuna; Nishioka, Takanori; Isobe, Kiyoshi
    Inorganic Chemistry (1998), 37 (1), 120-126CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Electrochem. redn. of [[Ir(η5-C5Me5)]3(μ3-S)2](BPh4)2 ([Ir3S2](BPh4)2) in CO2-satd. MeCN at -1.30 V (vs. Ag/AgCl) produced C2O42- and [[Ir(η5-C5Me5)]2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]+ ([Ir3S2CH2CN]+). The crystal structure of [Ir3S2CH2CN](BPh4) by x-ray anal. revealed that a linear CH2CN group is linked at the exo-position of a C5Me5 ligand, and the C5Me5CH2CN ligand coordinates to an Ir atom with an η4-mode. The cyclic voltammogram of [Ir3S2CH2CN]+ in MeCN under CO2 exhibited a strong catalytic current due to the redn. of CO2, while that of [Ir3S2]2+ did not show an interaction with CO2 in the same solvent. The reduced form of [Ir3S2CH2CN]+ works as the active species in the redn. of CO2. The IR spectra of [Ir3S2CH2CN]+ in CD3CN showed a reversible adduct formation with CO2 and also evidenced the oxalate generation through the reduced form of the CO2 adduct under the controlled potential electrolysis of the soln. at -1.55 V. A coupling reaction of two CO2 mols. bonded on adjacent μ3-S and Ir in [Ir3S2CH2CN]0 is proposed for the 1st catalytic generation of C2O42- without accompanying CO evolution.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXotVCjurY%253D&md5=52b328027efdf28b67342689f85a7909
  37. 37
    Ali, M. M.; Sato, H.; Mizukawa, T.; Tsuge, K.; Haga, M.; Tanaka, K. Selective Formation of HCO2– and C2O42– in Electrochemical Reduction of CO2 Catalyzed by Mono- and Di-Nuclear Ruthenium Complexes. Chem. Commun. 1998, 249– 250,  DOI: 10.1039/a707363a
    Google Scholar
    37
    Selective formation of HCO2- and C2O42- in electrochemical reduction of CO2 catalyzed by mono- and dinuclear ruthenium complexes
    Ali, Md. Meser; Sato, Hiroyasu; Mizukawa, Tetsunori; Tsuge, Kiyoshi; Haga, Masa-aki; Tanaka, Koji
    Chemical Communications (Cambridge) (1998), (2), 249-250CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Electrochem. redn. of carbon dioxide catalyzed by mono- and di-nuclear ruthenium complexes produced HCO2H with trace amts. of CO and C2O42- in the presence and absence of H2O, resp., in MeCN.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXhtFert7o%253D&md5=e29eb2a4bc748296e505da21fe173a2c
  38. 38
    Rudolph, M.; Dautz, S.; Jäger, E.-G. Macrocyclic [N42-] Coordinated Nickel Complexes as Catalysts for the Formation of Oxalate by Electrochemical Reduction of Carbon Dioxide. J. Am. Chem. Soc. 2000, 122, 10821– 10830,  DOI: 10.1021/ja001254n
    Google Scholar
    38
    Macrocyclic [N42-] Coordinated Nickel Complexes as Catalysts for the Formation of Oxalate by Electrochemical Reduction of Carbon Dioxide
    Rudolph, Manfred; Dautz, Sylvana; Jaeger, Ernst-Gottfried
    Journal of the American Chemical Society (2000), 122 (44), 10821-10830CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The macrocyclic nickel complexes are able to catalyze the electrochem. redn. of CO2 to oxalate. In the case of the macrocyclic nickel complexes with substituents COOEt or COMe, the overall reaction can be interpreted in terms of an outer-sphere electron-transfer reaction followed by a dimerization of the CO2•- radical anions, but the variation of the electron-transfer rate consts. with the std. potentials points to a coordinative interaction between the complexes and the CO2 mol. Complexes without COOEt or COMe substitution in undergo a fast deactivation reaction (1st order with respect to [CO2]) that is even visible in the time scale of the cyclic voltammetric expts. The results of the cyclic voltammetric studies could be confirmed in preparative-scale electrolyzes the Ni macrocyclic complex with Me and COOEt substituents proved to be the most active and persistent redox catalyst for the electrochem. redn. of CO2 to oxalate that was described so far.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnsVGgu7g%253D&md5=d5ed4fe2a630709594fb61955fe099ea
  39. 39
    Angamuthu, R.; Byers, P.; Lutz, M.; Spek, A. L.; Bouwman, E. Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex. Science 2010, 327, 313– 315,  DOI: 10.1126/science.1177981
    Google Scholar
    39
    Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex
    Angamuthu, Raja; Byers, Philip; Lutz, Martin; Spek, Anthony L.; Bouwman, Elisabeth
    Science (Washington, DC, United States) (2010), 327 (5963), 313-315CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Global warming concern has dramatically increased interest in using CO2 as a feedstock for prepn. of value-added compds., thereby helping to reduce its atm. concn. Here, the authors describe a dinuclear Cu(I) complex that is oxidized in air by CO2 rather than O2; the product is a tetranuclear Cu(II) complex contg. 2 bridging CO2-derived oxalate groups. Treatment of the Cu(II) oxalate complex in MeCN with a sol. Li salt results in quant. pptn. of Li oxalate. The Cu(II) complex can then be nearly quant. electrochem. reduced at a relatively accessible potential, regenerating the initial dinuclear Cu(I) compd. Preliminary results demonstrate 6 turnovers (producing 12 equiv of oxalate) during 7 h of catalysis at an applied potential of -0.03 V vs. the normal H electrode.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXktlWnsg%253D%253D&md5=7bc869762ac853e6f4b22436e052db56
  40. 40
    Udugala-Ganehenege, M. Y.; Dissanayake, N. M.; Liu, Y.; Bond, A. M.; Zhang, J. Electrochemistry of Nickel(II) and Copper(II) N,N′-Ethylenebis(acetylacetoniminato) Complexes and Their Electrocatalytic Activity for Reduction of Carbon Dioxide and Carboxylic Acid Protons. Transit. Metal Chem. 2014, 39, 819– 830,  DOI: 10.1007/s11243-014-9864-3
    Google Scholar
    40
    Electrochemistry of nickel(II) and copper(II) N,N'-ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons
    Udugala-Ganehenege, Manawadevi Y.; Dissanayake, N. M.; Liu, Yuping; Bond, Alan M.; Zhang, Jie
    Transition Metal Chemistry (Dordrecht, Netherlands) (2014), 39 (7), 819-830CODEN: TMCHDN; ISSN:0340-4285. (Springer)
    The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N'-ethylenebis(acetylacetoniminato)] on their electrochem. and electrocatalytic activity for the redn. of CO2 and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO2 redn., due to the higher stability of the electrochem. generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coeff. of [NiL] calcd. from the steady-state diffusion limiting current is 3.0 × 10-6 cm2 s-1. The catalytic efficiency of [NiL] in non-aq. solvents in terms of ip(CO2)/ip(N2) per nickel center is smaller than that of [Ni(cyclam)]2+, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane)]2+ or multinuclear [Ni3(X)]6+ where X = 8,8',8''-{2,2',2''(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1)) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the redn. of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN. Both [NiL] and [CuL] are also electrocatalysts for the redn. of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GqsbjJ&md5=85b783d8201adbb061560d2a9162f924
  41. 41
    Becker, J. Y.; Vainas, B.; Eger, R.; Kaufman, L. Electrocatalytic Reduction of CO2 to Oxalate by Ag and Pd Porphyrins. J. Chem. Soc., Chem. Commun. 1985, 1471– 1472,  DOI: 10.1039/C39850001471
    Google Scholar
    41
    Electrocatalytic reduction of carbon dioxide to oxalate by silver(II) and palladium(II) porphyrins
    Becker, James Y.; Vainas, Baruch; Eger, Rivka; Kaufman, Leah
    Journal of the Chemical Society, Chemical Communications (1985), (21), 1471-2CODEN: JCCCAT; ISSN:0022-4936.
    The electrochem. redn. of CO2 was catalyzed by Ag(II) or Pd(II) metalloporphyrins in homogeneous soln. in CH2Cl2. The products detected were (HO2C)2 [144-62-7] and H2.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XhtFyntbY%253D&md5=ef895f8af6cecae2e54ce0f8c2eb461f
  42. 42
    Fröhlich, H.-O.; Schreer, H. Einschub Und Reduktive Kopplung von CO2; Zur Bildung von Cp2TiIIIC2O4TiIIICp2 Und Cp2TiIV(−O2C(CH2)3NRCH2CH2NR(CH2)3CO2–) (R = i-C4H9). Z. Chem. 1983, 23, 348– 349,  DOI: 10.1002/zfch.19830230922
    Google Scholar
    There is no corresponding record for this reference.
  43. 43
    Lalrempuia, R.; Stasch, A.; Jones, C. The Reductive Disproportionation of CO2 Using a Magnesium(I) Complex: Analogies with Low Valent f-Block Chemistry. Chem. Sci. 2013, 4, 4383– 4388,  DOI: 10.1039/c3sc52242c
    Google Scholar
    43
    The reductive disproportionation of CO2 using a magnesium(I) complex: analogies with low valent f-block chemistry
    Lalrempuia, Ralte; Stasch, Andreas; Jones, Cameron
    Chemical Science (2013), 4 (12), 4383-4388CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The dimeric magnesium(i) complex, [{(DipNacnac)Mg}2] (DipNacnac = [(DipNCMe)2CH]-, Dip = C6H3Pri2-2,6), reacts with 2 equiv of CO2 to give a high yield of the MgII carbonate complex, [{(DipNacnac)Mg}2(μ-κ2:κ2-CO3)], and CO via a reductive disproportionation process. The MgII oxalate, [{(DipNacnac)Mg}2(μ-C2O4)], is a very low yield byproduct of the reaction. Reducing the carbonate complex with elemental potassium regenerates the MgI starting material. The carbonate complex is shown to form via a stepwise process involving the oxo-bridged intermediate, [{(DipNacnac)Mg}2(μ-O)], which rapidly reacts with stoichiometric CO2 to give [{(DipNacnac)Mg}2(μ-κ2:κ2-CO3)]. The oxo-bridged intermediate has been rationally synthesized via the reaction of [{(DipNacnac)Mg}2] with N2O, and treated with THF to give the adduct, [{(THF)(DipNacnac)Mg}2(μ-O)]. The complex, [{(DipNacnac)Mg}2(μ-O)], reacts with the CO2 isoelectronic analogs, CS2 and CyNCNCy (Cy = cyclohexyl) to give the complexes, [{(DipNacnac)Mg}2(μ-κ2:κ2-CS2O)] and [{(DipNacnac)Mg}2{μ-κ2:κ2-C(NCy)2O}]. Rearrangement of the dithiocarbonate coordination mode of the former occurs upon treatment with di-Et ether, giving the unsym. complex, [{(DipNacnac)Mg}(μ-κ2(S,S'):κ1(O)-CS2O){Mg(DipNacnac)(OEt2)}]. The majority of the complexes prepd. in this study were crystallog. characterized. Taken as a whole, this study demonstrates that magnesium(i) dimers can display very similar reactivity, with respect to small mols. activations, as do SmII and UIII compds. Accordingly, magnesium(i) compds. hold considerable potential as cheaper, less toxic, non-radioactive and diamagnetic alternatives to low valent f-block metal complexes in this realm.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1yis77M&md5=36c9f515dc4821768bdfc8a460307df6
  44. 44
    Paparo, A.; Silvia, J. S.; Kefalidis, C. E.; Spaniol, T. P.; Maron, L.; Okuda, J.; Cummins, C. C. A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2. Angew. Chem., Int. Ed. 2015, 54, 9115– 9119,  DOI: 10.1002/anie.201502532
    Google Scholar
    44
    A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2
    Paparo, Albert; Silvia, Jared S.; Kefalidis, Christos E.; Spaniol, Thomas P.; Maron, Laurent; Okuda, Jun; Cummins, Christopher C.
    Angewandte Chemie, International Edition (2015), 54 (31), 9115-9119CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Authors describe the stable and isolable dimetalloxycarbene [(TiX3)2(μ2-CO2-κ2C,O:κO')] 5, where X = N-(tert-butyl)-3,5-dimethylanilide, which is stabilized by fluctuating μ2-κ2C,O:κ1O' coordination of the carbene carbon to both titanium centers of the dinuclear complex 5, as shown by variable-temp. NMR studies. Quantum chem. calcns. on the unmodified mol. indicated a higher energy of only +10.5 kJ mol-1 for the μ2-κ1O:κ1O' bonding mode of the free dimetalloxycarbene compared to the μ2-κ2C,O:κ1O' bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX3)2(μ2-OCHO-κO:κO')][B(C6F5)4], 4[B(C6F5)4], was simply deprotonated with the strong base K(N(SiMe3)2) to give 5. Complex 5 reacts smoothly with CO2 to generate the bridging oxalate complex [(TiX3)2(μ2-C2O4-κO:κO'')], 6, in a C-C bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO2 on low-valent transition-metal complexes.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVKmsL7M&md5=007e10b53383c159af9da31236269ca2
  45. 45
    Woen, D. H.; Chen, G. P.; Ziller, J. W.; Boyle, T. J.; Furche, F.; Evans, W. J. Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−. Angew. Chem., Int. Ed. 2017, 56, 2050– 2053,  DOI: 10.1002/anie.201611758
    Google Scholar
    45
    Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}-
    Woen, David H.; Chen, Guo P.; Ziller, Joseph W.; Boyle, Timothy J.; Furche, Filipp; Evans, William J.
    Angewandte Chemie, International Edition (2017), 56 (8), 2050-2053CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The first crystallog. characterizable complex of Sc2+, [Sc(NR2)3]- (R = SiMe3), was obtained by LnA3/M reactions (Ln = rare earth metal; A = anionic ligand; M = alkali metal) involving redn. of Sc(NR2)3 with K in the presence of 2.2.2-cryptand (crypt) and 18-crown-6 (18-c-6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]+, [K(18-c-6)]+, and [Cs(crypt)]+ salts of the [Sc(NR2)3]- anion are formed, resp. The formation of this oxidn. state of Sc is also indicated by the eight-line EPR spectra arising from the I = 7/2 45Sc nucleus. The Sc(NR2)3 redn. differs from Ln(NR2)3 reactions (Ln = Y and lanthanides) in that it occurs under N2 without formation of isolable reduced dinitrogen species. [K(18-c-6)][Sc(NR2)3] reacts with CO2 to produce an oxalate complex, {K2(18-c-6)3}{[(R2N)3Sc]2(μ-C2O4-κ1O:κ1O'')}, and a CO2- radical anion complex, [(R2N)3Sc(μ-OCO-κ1O:κ1O')K(18-c-6)]n.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Oitb0%253D&md5=3c6dbaae4983f345cee2224340a1f7dc
  46. 46
    Evans, W. J.; Seibel, C. A.; Ziller, J. W. Organosamarium-Mediated Transformations of CO2 and COS: Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO2 to [O2CCO2]2-. Inorg. Chem. 1998, 37, 770– 776,  DOI: 10.1021/ic971381t
    Google Scholar
    46
    Organosamarium-Mediated Transformations of CO2 and COS: Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO2 to [O2CCO2]2-
    Evans, William J.; Seibel, Christopher A.; Ziller, Joseph W.
    Inorganic Chemistry (1998), 37 (4), 770-776CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The reactivity of CO2 and COS with divalent and trivalent organosamarium complexes has been investigated. (C5Me5)2Sm(THF)2 reductively couples CO2 in THF at room temp. to form the oxalate complex, [(C5Me5)2Sm]2(μ-η2:η2-O2CCO2), 1, in >90% yield. The metal centers in 1 are formally eight-coordinate. The reaction of COS with (C5Me5)2Sm(THF)2 is more complicated and generates a disproportionation product, (C5Me5)2Sm(μ-η2:η1-S2CO)Sm(C5Me5)2(THF), 2, which has one (C5Me5)2Sm unit involved in a four-membered SmSCS ring, while the other (C5Me5)2Sm unit is bound to THF and the oxygen of the S2CO ligand. CO2 reacts with [(C5Me5)2Sm]2(μ-η1:η1-N2Ph2) in >90% yield to form the asym. monoinsertion product, (C5Me5)2Sm[μ-η2:η1-PhNN(CO2)Ph]Sm(C5Me5)2(THF), 3. One (C5Me5)2Sm unit is involved in a five-membered SmNNCO ring, and the other is attached to THF and the other oxygen originating from CO2. 1-3 Were characterized by anal. methods, x-ray diffraction, and NMR and IR spectroscopy.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXns1KjsA%253D%253D&md5=3e2b006426a486f755f4e119c9c81f4d
  47. 47
    Evans, W. J.; Perotti, J. M.; Brady, J. C.; Ziller, J. W. Tethered Olefin Studies of Alkene versus Tetraphenylborate Coordination and Lanthanide Olefin Interactions in Metallocenes. J. Am. Chem. Soc. 2003, 125, 5204– 5212,  DOI: 10.1021/ja020957x
    Google Scholar
    47
    Tethered Olefin Studies of Alkene versus Tetraphenylborate Coordination and Lanthanide Olefin Interactions in Metallocenes
    Evans, William J.; Perotti, Jeremy M.; Brady, Jason C.; Ziller, Joseph W.
    Journal of the American Chemical Society (2003), 125 (17), 5204-5212CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The tethered olefin cyclopentadienyl ligand, [(C5Me4)SiMe2(CH2CH:CH2)]-, forms unsolvated metallocenes, [(C5Me4)SiMe2(CH2CH:CH2)]2Ln (Ln = Sm, 1; Eu, 2; Yb, 3), from [(C5Me4)SiMe2(CH2CH:CH2)]K and LnI2(THF)2 in good yield. Each complex in the solid state has both tethered olefins oriented toward the Ln metal center with the Ln-C(terminal alkene C) distances 0.2-0.3 Å shorter than the Ln-C(internal alkene C) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5) Å, resp., are normal. Like its permethyl analog, (C5Me5)2Sm(THF)2, complex 1 reductively couples CO2 to form the oxalate-bridged dimer {[(C5Me4)SiMe2(CH2CH:CH2)]2Sm}2(μ-η2:η2-O2CCO2), 4, in which the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh4 to form an unsolvated cation that has the option of coordinating [BPh4]- or a pendant olefin, a competition common in olefin polymn. catalysis. The structure of {[(C5Me4)SiMe2(CH2CH:CH2)]2Sm}[BPh4], 5, shows that both pendant olefins are located near Sm rather than the [BPh4]- counterion.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXisFWhur4%253D&md5=15e0f9353262a5aae2df13c7daef9293
  48. 48
    Willauer, A. R.; Toniolo, D.; Fadaei-Tirani, F.; Yang, Y.; Laurent, M.; Mazzanti, M. Carbon Dioxide Reduction by Dinuclear Yb(II) and Sm(II) Complexes Supported by Siloxide Ligands. Dalton Trans. 2019, 48, 6100– 6110,  DOI: 10.1039/C9DT00554D
    Google Scholar
    48
    Carbon dioxide reduction by dinuclear Yb(II) and Sm(II) complexes supported by siloxide ligands
    Willauer, Aurelien R.; Toniolo, Davide; Fadaei-Tirani, Farzaneh; Yang, Yan; Laurent, Maron; Mazzanti, Marinella
    Dalton Transactions (2019), 48 (18), 6100-6110CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    Two dinuclear homoleptic complexes of lanthanides(II) supported by the polydentate tris(tertbutoxy) siloxide ligand ([Yb2L4], 1-Yb and [Sm2L4], 1-Sm, (L = (OtBu)3SiO-)) were synthesized in 70-80% yield and 1-Sm was crystallog. characterized. 1-Yb and 1-Sm are stable in soln. at -40 °C but cleave the DME C-O bond over time at room temp. affording the crystal of [Yb2L4(μ-OMe)2(DME)2], 2. The 1-Yb and 1-Sm complexes effect the redn. of CO2 under ambient conditions leading to carbonate and oxalate formation. The selectivity of the redn. towards oxalate or carbonate changes depend on the solvent polarity and on the nature of the ion. For both the lanthanides, carbonate formation is favored but oxalate formation increases if a non-polar solvent is used. Computational studies suggest that the formation of oxalate is favored with respect to carbonate formation in the reaction of the dimeric lanthanide complexes with CO2. Crystals of the tetranuclear mixed-valence oxalate intermediate [Yb4L8(C2O4)], 3 were isolated from hexane and the presence of a C2O42- ligand bridging two [YbIIL2YbIIIL2] dinuclear moieties was shown. Crystals of the tetranuclear di-carbonate product [Sm4L8(μ3-CO3-κ4-O,O',O'')2], 4 were isolated from hexane. The structures of 3 and 4 suggest that the CO2 activation in non-polar solvents involves the interaction of two dimers with CO2 mols. at least to some extent. Such a cooperative interaction results in both oxalate and carbonate formation.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXkvVWhu70%253D&md5=a157f42609ae8fdd7c54aedf14658204
  49. 49
    Castro, L.; Mills, D. P.; Jones, C.; Maron, L. Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex. Eur. J. Inorg. Chem. 2016, 2016, 792– 796,  DOI: 10.1002/ejic.201501346
    Google Scholar
    49
    Activation of Heteroallenes COxS2-x (x = 0-2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex
    Castro, Ludovic; Mills, David P.; Jones, Cameron; Maron, Laurent
    European Journal of Inorganic Chemistry (2016), 2016 (6), 792-796CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A joint exptl./theor. (DFT) study of the activation of heteroallenes COxS2-x (x = 0-2) by [Sm(Giso)2] {Giso- = [(ArN)2CNCy2]-, Cy = cyclohexyl, Ar = 2,6-diisopropylphenyl} is reported. All heteroallenes are reduced in a different manner. Indeed, while activation of CS2 yields a bimetallic CS2 coupled product through C-S bond formation, CO2 forms an oxalate complex through C-C bond formation. This subsequently undergoes CO2 insertion into one of its Sm-N bonds. Finally, COS activation is predicted to yield a dithiocarbonate complex, through the formation of an intermediate sulfido complex [(Giso)2Sm(μ-S)Sm(Giso)2]. Therefore, [Sm(Giso)2] is a very versatile reagent, since it is a rare example of a complex that allows formation of several activation products involving valence isoelectronic substrates. This is rationalized by DFT calcns., and the latter emphasizes both the lack of kinetic stability of CS vs. CO and the high thermodn. stability of the oxalate.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWhsbw%253D&md5=204afb626174e84e520cb9ced9ad0bd6
  50. 50
    Andrez, J.; Pécaut, J.; Bayle, P.-A.; Mazzanti, M. Tuning Lanthanide Reactivity Towards Small Molecules with Electron-Rich Siloxide Ligands. Angew. Chem., Int. Ed. 2014, 53, 10448– 10452,  DOI: 10.1002/anie.201405031
    Google Scholar
    50
    Tuning Lanthanide Reactivity Towards Small Molecules with Electron-Rich Siloxide Ligands
    Andrez, Julie; Pecaut, Jacques; Bayle, Pierre-Alain; Mazzanti, Marinella
    Angewandte Chemie, International Edition (2014), 53 (39), 10448-10452CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The synthesis, structure, and reactivity of stable homoleptic heterometallic LnL4K2 complexes of divalent lanthanide ions with electron-rich tris(tert-butoxy)siloxide ligands are reported. The [Ln(OSi(OtBu)3)4K2] complexes (Ln = Eu, Yb) are stable at room temp., but they promote the redn. of azobenzene to yield the KPhNNPh radical anion as well as the reductive cleavage of CS2 to yield CS32- as the major product. The EuIII complex of the radical anion PhNNPh is structurally characterized. Moreover, [Yb(OSi(OtBu)3)4K2] can reduce CO2 at room temp. Release of the redn. products in D2O shows the quant. formation of both oxalate and carbonate in a 1:2.2 ratio. The bulky siloxide ligands enforce the labile binding of the redn. products providing the opportunity to establish a closed synthetic cycle for the YbII-mediated CO2 redn. The presence of four electron-rich siloxide ligands renders their EuII and YbII complexes highly reactive.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GksLfO&md5=1af647bd06843e9162e82fb55d068359
  51. 51
    Wong, W.-K.; Zhang, L.-L.; Xue, F.; Mak, T. C. W. Synthesis and X-Ray Crystal Structure of an Unexpected Neutral Oxalate-Bridged Ytterbium(III) Porphyrinate Dimer. J. Chem. Soc., Dalton Trans. 2000, 2245– 2246,  DOI: 10.1039/b003434g
    Google Scholar
    There is no corresponding record for this reference.
  52. 52
    Evans, W. J.; Lorenz, S. E.; Ziller, J. W. Investigating Metal Size Effects in the Ln2(μ-η2:η2-N2) Reduction System: Reductive Reactivity with Complexes of the Largest and Smallest Trivalent Lanthanide Ions, La3+ and Lu3+. Inorg. Chem. 2009, 48, 2001– 2009,  DOI: 10.1021/ic801853d
    Google Scholar
    52
    Investigating metal size effects in the Ln2(μ-η2:η2-N2) reduction system: reductive reactivity with complexes of the largest and smallest trivalent lanthanide ions, La3+ and Lu3+
    Evans, William J.; Lorenz, Sara E.; Ziller, Joseph W.
    Inorganic Chemistry (2009), 48 (5), 2001-2009CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Metal size effects in reductive chem. using [[(C5Me4H)2Ln(THF)]2(μ-η2:η2-N2)] (1, 2; Ln = La, Lu) complexes were evaluated using the extremes in ionic radii of the lanthanide series. Comparisons of reactivity towards 1,3,5,7-cyclooctatetraene, phenazine, carbon dioxide, and anthracene substrates are made. Complexes 1 and 2 react similarly with 1,3,5,7-cyclooctatetraene to form previously known (C5Me4H)Ln(C8H8)(THF)x (Ln = La, x = 2; Ln = Lu, x = 0) in a reaction analogous to the redn. of this substrate with divalent (C5Me5)2Sm. Complexes 1 and 2 differ in their reactions with phenazine in which 1 forms at least three products, including [(C5Me4H)2La](μ-η4:η2-C12H8N2)[La(THF)(C5Me4H)2] (3), and (C5Me4H)3La, whereas 2 forms a single product, [(C5Me4H)2Lu]2(μ-η3:η3-C12H8N2) (4), in quant. yield. Complexes 3 and 4 are similar to the product obtained from the reaction of (C5Me5)2Sm and phenazine, [(C5Me5)2Sm]2(μ-η3:η3-C12H8N2), since all three complexes contain a reduced phenazine dianion, but the phenazine ligand displays structural variations depending on the size of the metal. With CO2, complex 1 forms multiple products, but 2 reacts cleanly to form the reductively coupled oxalate complex, [(C5Me4H)2Lu]2(μ-η2:η2-C2O4) (5) in high yield. With anthracene, 1 forms a complex product mixt. from which only (C5Me4H)3La(THF) (9), characterized by x-ray crystallog., could be identified. In contrast, 2 is unreactive toward anthracene even upon heating to 75° after 24 h.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFeitbc%253D&md5=8ad87fb526902e73043d206129fb2de9
  53. 53
    Tsoureas, N.; Castro, L.; Kilpatrick, A. F. R.; Cloke, F. G. N.; Maron, L. Controlling Selectivity in the Reductive Activation of CO2 by Mixed Sandwich Uranium(III) Complexes. Chem. Sci. 2014, 5, 3777– 3788,  DOI: 10.1039/C4SC01401D
    Google Scholar
    53
    Controlling selectivity in the reductive activation of CO2 by mixed sandwich uranium(III) complexes
    Tsoureas, Nikolaos; Castro, Ludovic; Kilpatrick, Alexander F. R.; Cloke, F. Geoffey N.; Maron, Laurent
    Chemical Science (2014), 5 (10), 3777-3788CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The synthesis and mol. structures of a range of uranium(III) mixed sandwich complexes of the type [U(η8-C8H6(1,4-SiMe3)2)(η5-CpMe4R)] (R = Me, Et, iPr, tBu) and their reactivity towards CO2 are reported. The nature of the R group on the cyclopentadienyl ring in the former has a significant effect on the outcome of CO2 activation: when R = Me, the products are the bridging oxo complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe5)}2(μ-O) and the bridging oxalate complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe5)}2(μ-η2:η2-C2O4); for R = Et or iPr, bridging carbonate {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4R)}2(μ-η1:η2-CO3) and bridging oxalate complexes {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4R)}2(μ-η2:η2-C2O4) are formed in both cases; and when R = tBu the sole product is the bridging carbonate complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4tBu)}2(μ-η1:η2-CO3). Electrochem. studies on both the uranium(III) complexes and the dimeric uranium(IV) CO2 redn. products have been carried out and all exhibit quasi reversible redox processes; in particular, the similarities in the U(III)/U(IV) redox couples suggest that the selectivity in the outcome of CO2 reductive activation by these complexes is steric in origin rather than electronic. The latter conclusion is supported by a detailed computational DFT study on the potential mechanistic pathways for redn. of CO2 by this system.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSltrrE&md5=14a29feb3e3507a1f7593e526763fd45
  54. 54
    Inman, C. J.; Frey, A. S. P.; Kilpatrick, A. F. R.; Cloke, F. G. N.; Roe, S. M. Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand. Organometallics 2017, 36, 4539– 4545,  DOI: 10.1021/acs.organomet.7b00263
    Google Scholar
    54
    Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand
    Inman, Christopher J.; Frey, Alistair S. P.; Kilpatrick, Alexander F. R.; Cloke, F. Geoffrey N.; Roe, S. Mark
    Organometallics (2017), 36 (23), 4539-4545CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
    The new dianionic ligand C6H4{p-CMe2C6H2Me2O-}2 (p-Me2bp), featuring two aryloxide donors and a central arene ring, was synthesized and used to prep. the mixed-ligand U(III) compd. [U(Cp*)(p-Me2bp)] (Cp* = pentamethylcyclopentadienyl), which exhibits an η6 interaction with the U center. Reductive activation of CO2 was studied using [U(Cp*)(p-Me2bp)] in supercrit. CO2, which gave a dinuclear U carbonate complex, {U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3), cleanly and selectively. Reactivity studies in conventional solvents using lower pressures of CO2 showed the formation of a rare U(IV) oxalate complex, {U(Cp*)(p-Me2bp)}2(μ-η2:η2-C2O2), alongside {U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3). The relative ratio of the last two products is temp. dependent: at low temps. (-78°) oxalate formation is favored, while at room temp. the carbonate is the dominant product. The U(IV) iodide [U(Cp*)(p-Me2bp)I] was also synthesized and used as part of an electrochem. study, the results of which showed that [U(Cp*)(p-Me2bp)] has a U(IV)/U(III) redox couple of -2.18 V vs. FeCp2+/0 as well as a possible electrochem. accessible U(III)/U(II) redn. process at -2.56 V vs. FeCp2+/0.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXos1Wrsr4%253D&md5=1bb9cf1e2decd0ea9f715dbc740d3338
  55. 55
    Schmidt, A.-C.; Heinemann, F. W.; Kefalidis, C. E.; Maron, L.; Roesky, P. W.; Meyer, K. Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes. Chem. Eur. J. 2014, 20, 13501– 13506,  DOI: 10.1002/chem.201404400
    Google Scholar
    55
    Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes
    Schmidt, Anna-Corina; Heinemann, Frank W.; Kefalidis, Christos E.; Maron, Laurent; Roesky, Peter W.; Meyer, Karsten
    Chemistry - A European Journal (2014), 20 (42), 13501-13506CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The first sulfite [{((nP,MeArO)3tacn)UIV}2(μ-κ1:κ2-SO3)] (tacn = triazacyclononane) and dithionite [{((nP,MeArO)3tacn)UIV}2(μ-κ2:κ2-S2O4)] of uranium from reaction with gaseous SO2 were prepd. Addnl., the reductive activation of CO2 was investigated with respect to the rare oxalate [{((nP,MeArO)3tacn)UIV}2(μ-κ2:κ2-C2O4)] formation. This ultimately provides the unique S2O42-/C2O42- and SO32-/CO32- complex pairs. All new complexes were characterized by a combination of single-crystal x-ray diffraction, elemental anal., UV/visible/NIR electronic absorption, IR vibrational, and 1H NMR spectroscopy, as well as magnetization (VT SQUID) studies. Also, d. functional theory (DFT) calcns. were carried out to gain further insight into the reaction mechanisms. All observations, together with DFT, support the assumption that SO2 and CO2 show similar (dithionite/oxalate) to analogous (sulfite/carbonate) activation behavior with uranium complexes.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVSnur3J&md5=7069498fd07aeb33ca4387fc4945cfff
  56. 56
    Formanuik, A.; Ortu, F.; Inman, C. J.; Kerridge, A.; Castro, L.; Maron, L.; Mills, D. P. Concomitant Carboxylate and Oxalate Formation From the Activation of CO2 by a Thorium(III) Complex. Chem. Eur. J. 2016, 22, 17976– 17979,  DOI: 10.1002/chem.201604622
    Google Scholar
    56
    Concomitant carboxylate and oxalate formation from the activation of CO2 by a thorium(III) complex
    Formanuik, Alasdair; Ortu, Fabrizio; Inman, Christopher J.; Kerridge, Andrew; Castro, Ludovic; Maron, Laurent; Mills, David P.
    Chemistry - A European Journal (2016), 22 (50), 17976-17979CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Carbon dioxide and carbon disulfide reacts with tris-cyclopentadienylthorium complex, yielding binuclear thorium complexes [(Cp'3Th)2(μ-CS2)] and [(Cp'2Th)2(μ-C2O4)(Cp''CO2-O,O')] [Cp' = 1,3-(Me3Si)2C5H3; Cp'' = 5,5-(Me3Si)2C5H3-2], bridged by dithiocarbonylate and oxalate ligands. Improving our comprehension of diverse CO2 activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. Carbon dioxide activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO2 is readily reduced to CO, but isolated thorium(III) CO2 activation is unprecedented. We show that the thorium(III) complex, [Th(Cp')3] (1), reacts with CO2 to give the mixed oxalate-carboxylate thorium(IV) complex [{ThCp'2[κ2-2-O2CC5H3-5,5-(SiMe3)2]}2(μ-κ2:κ2-C2O4)] (3). The concomitant formation of oxalate and carboxylate is unique for CO2 activation, as in previous examples either redn. or insertion is favored to yield a single product. Therefore, thorium(III) CO2 activation can differ from better understood uranium(III) chem.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslKns7jI&md5=28ff1c89e42f0bbb7f19095b9403199a
  57. 57
    Aresta, M.; Gobetto, R.; Quaranta, E.; Tommasi, I. A Bonding-Reactivity Relationship for Ni(PCy3)2(CO2): A Comparative Solid-State-Solution Nuclear Magnetic Resonance Study (31P, 13C) as a Diagnostic Tool to Determine the Mode of Bonding of CO2 to a Metal Center. Inorg. Chem. 1992, 31, 4286– 4290,  DOI: 10.1021/ic00047a015
    Google Scholar
    57
    A bonding-reactivity relationship for (carbon dioxide)bis(tricyclohexylphosphine)nickel: a comparative solid-state-solution nuclear magnetic resonance study (phosphorus-31, carbon-13) as a diagnostic tool to determine the mode of bonding of carbon dioxide to a metal center
    Aresta, Michele; Gobetto, Roberto; Quaranta, Eugenio; Tommasi, Immacolata
    Inorganic Chemistry (1992), 31 (21), 4286-90CODEN: INOCAJ; ISSN:0020-1669.
    31P and 13C NMR spectra in the solid state and in soln., at variable temp., were used to det. a direct correlation of the modes of bonding of CO2 in Ni(PCy3)2(CO2) in the 2 states. In soln., at 173 K, CO2 is η2-CO bonded to Ni and 31P and 13C chem. shifts are almost identical with the value found for the solid complex, while a dynamic process avs., in soln., the 2 P atoms (ΔG≠ = 39.3 kJ mol-1) at room temp. through an intramol. motion. The modification of the mode of bonding of CO2 to a metal center that occurs when a solid sample is dissolved in a solvent may be relevant to the reactivity of CO2-transition metal complexes, as shown by the reaction of coordinated CO2 with electrophiles (H+, Ag+) and H2. The temp. can play a role.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XlvVelt7c%253D&md5=2e35e7cac444b595f8fd9c9a0cddcf02
  58. 58
    Horn, B.; Limberg, C.; Herwig, C.; Braun, B. Nickel(I)-Mediated Transformations of Carbon Dioxide in Closed Synthetic Cycles: Reductive Cleavage and Coupling of CO2 Generating NiICO, NiIICO3 and NiIIC2O4NiII Entities. Chem. Commun. 2013, 49, 10923– 10925,  DOI: 10.1039/c3cc45407j
    Google Scholar
    58
    Nickel(I)-mediated Transformations of Carbon Dioxide in Closed Synthetic Cycles: Reductive Cleavage and Coupling of CO2 Generating NiICO, NiIICO3 and NiIIC2O4NiII Entities
    Horn, Bettina; Limberg, Christian; Herwig, Christian; Braun, Beatrice
    Chemical Communications (Cambridge, United Kingdom) (2013), 49 (93), 10923-10925CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The β-diketiminato nickel(I) complex K2[LtBuNiI(N22-)NiILtBu] (LtBu = [HC(C(tBu)NC6H3(iPr)2)2]-) reacts with CO2 via reductive disproportionation to form CO and CO32- contg. products, whereas after employment of the NiI precursor [LtBuNiI(N2)NiILtBu] reductive coupling of CO2 was obsd. giving an oxalate bridged dinickel(II) complex [LtBuNi(C2O4)NiLtBu]. The addn. of KC8 to the carbonate and oxalate compds. formed leads to the regeneration of the initial NiI complexes in an N2 atmosphere, thus closing synthetic cycles.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslSgtL%252FL&md5=f49d8b42410edafc1971c8c14dbd9248
  59. 59
    Lu, C. C.; Saouma, C. T.; Day, M. W.; Peters, J. C. Fe(I)-Mediated Reductive Cleavage and Coupling of CO2: An FeII(μ-O,μ-CO)FeII Core. J. Am. Chem. Soc. 2007, 129, 4– 5,  DOI: 10.1021/ja065524z
    Google Scholar
    59
    Fe(I)-Mediated Reductive Cleavage and Coupling of CO2: An FeII(μ-O,μ-CO)FeII Core
    Lu, Connie C.; Saouma, Caroline T.; Day, Michael W.; Peters, Jonas C.
    Journal of the American Chemical Society (2007), 129 (1), 4-5CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    THF solns. of a new iron(I) source, [PhBPCH2Cy3]Fe ([PhBPCH2Cy3] = [PhBP(CH2P(CH2Cy)2)3]-), effect the reductive cleavage of CO2 via O-atom transfer at ambient temp. The dominant reaction pathway is bimetallic and gives a structurally unprecedented diiron FeII(μ-O)(μ-CO)FeII core. X-ray data are also available to suggest that bimetallic reductive CO2 coupling to generate oxalate occurs as a minor reaction pathway. These initial observations forecast a diverse reaction landscape between CO2 and iron(I) synthons. Addnl. [PhBPCH2Cy3]Fe complexes were prepd. and characterized by x-ray crystallog.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xhtlantr7M&md5=6c20af616e63d2dc42e03e60788416fd
  60. 60
    Saouma, C. T.; Lu, C. C.; Day, M. W.; Peters, J. C. CO2 Reduction by Fe(I): Solvent Control of C-O Cleavage versus C-C Coupling. Chem. Sci. 2013, 4, 4042– 4051,  DOI: 10.1039/c3sc51262b
    Google Scholar
    60
    CO2 reduction by Fe(I): solvent control of C-O cleavage versus C-C coupling
    Saouma, Caroline T.; Lu, Connie C.; Day, Michael W.; Peters, Jonas C.
    Chemical Science (2013), 4 (10), 4042-4051CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    This manuscript explores the product distribution of the reaction of carbon dioxide with reactive iron(I) complexes supported by tris(phosphino)borate ligands, [PhBPR3]- ([PhBPR3]- = [PhB(CH2PR2)3]-; R = CH2Cy, Ph, iPr, 3,5-meta-terphenyl). These studies reveal an interesting and unexpected role for the solvent medium with respect to the CO2 activation reaction. For instance, exposure of methylcyclohexane (MeCy) solns. of [PhBP3CH2Cy]Fe(PR'3) to CO2 yields the partial decarbonylation product {[PhBP3CH2Cy]Fe}2(μ-O)(μ-CO). When the reaction is instead carried out in benzene or THF, reductive coupling of CO2 occurs to give the bridging oxalate species {[PhBP3CH2Cy]Fe}2(μ-κOO':κOO'-oxalato). Reaction studies aimed at understanding this solvent effect are presented, and suggest that the product profile is ultimately detd. by the ability of the solvent to coordinate the iron center. When more sterically encumbering auxiliary ligands are employed to support the iron(I) center (i.e., [PhBPPh3]- and [PhBPiPr3]-), complete decarbonylation is obsd. to afford structurally unusual diiron(II) products {[PhBPR3]Fe}2(μ-O). A mechanistic hypothesis that is consistent with the collection of results described is offered, and suggests that reductive coupling of CO2 likely occurs from an electronically satd. FeII-CO2- species.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlent77N&md5=aae0d67884fbfee1232287dc0d4832bf
  61. 61
    Farrugia, L. J.; Lopinski, S.; Lovatt, P. A.; Peacock, R. D. Fixing Carbon Dioxide with Copper: Crystal Structure of [LCu(μ-C2O4)CuL][Ph4B]2 (L = N,N′,N″-triallyl-1,4,7-triazacyclononane). Inorg. Chem. 2001, 40, 558– 559,  DOI: 10.1021/ic000418y
    Google Scholar
    61
    Fixing Carbon Dioxide with Copper: Crystal Structure of [LCu(μ-C2O4)CuL][Ph4B]2 (L = N,N',N''-Triallyl-1,4,7-triazacyclononane)
    Farrugia, Louis J.; Lopinski, Stefan; Lovatt, Paul A.; Peacock, Robert D.
    Inorganic Chemistry (2001), 40 (3), 558-559CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The reaction of carbon dioxide with a soln. of CuI, NaBPh4 and N,N',N''-triallyl-1,4,7-triazacyclononane (L) resulted in the formation of the oxalato bridged dinuclear copper(II) complex [LCu(μ-C4O4)CuL](BPh4)2. The complex can be prepd. in higher yields using CsHCO3 in place of CO2. The crystal structure of the complex was detd. showing square pyramidal geometries for the copper atoms with nitrogen atoms in the axial positions. Variable temp. magnetic susceptibility measurements show it to be antiferromagnetic (J = -274 cm-1) as expected for this type of structure.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXptV2rtLc%253D&md5=5108a2a912fc7a2992f489f0eb9ee73d
  62. 62
    Takisawa, H.; Morishima, Y.; Soma, S.; Szilagyi, R. K.; Fujisawa, K. Conversion of Carbon Dioxide to Oxalate by α-Ketocarboxylatocopper(II) Complexes. Inorg. Chem. 2014, 53, 8191– 8193,  DOI: 10.1021/ic5006242
    Google Scholar
    62
    Conversion of Carbon Dioxide to Oxalate by α-Ketocarboxylatocopper(II) Complexes
    Takisawa, Hideyuki; Morishima, Yui; Soma, Shoko; Szilagyi, Robert K.; Fujisawa, Kiyoshi
    Inorganic Chemistry (2014), 53 (16), 8191-8193CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CHMe2}] (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate) can be spontaneously converted into the binuclear oxalatocopper(II) complex [{Cu(L1)}2(μ-C2O4)] upon exposure to O2/CO2 gas. 13C-labeling expts. revealed that oxalate ions partially incorporated 13CO2 mols. Also, the bicarbonatocopper(I) complex (NEt4)[Cu(L1){O2C(OH)}] in an Ar atm. and the α-ketocarboxylatocopper(I) complex Na[Cu(L1){O2CC(O)CHMe2}] in an O2 atmosphere were also transformed spontaneously into the oxalato complex [{Cu(L1)}2(μ-C2O4)].
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtlaju7nN&md5=40e281a8318b682c866319af10f16a65
  63. 63
    Klose, A.; Hesschenbrouck, J.; Solari, E.; Latronico, M.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C. The Metal–Carbon Multiple Bond in Iron(I)– and Iron(II)–Dibenzotetramethyltetra-[14]azaannulene: Carbene, Carbonyl, and Isocyanide Derivatives. J. Organomet. Chem. 1999, 591, 45– 62,  DOI: 10.1016/S0022-328X(99)00354-X
    Google Scholar
    63
    The metal-carbon multiple bond in iron(I)- and iron(II)-dibenzotetramethyltetra[14]azaannulene: carbene, carbonyl, and isocyanide derivatives
    Klose, A.; Hesschenbrouck, J.; Solari, E.; Latronico, M.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C.
    Journal of Organometallic Chemistry (1999), 591 (1-2), 45-62CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science S.A.)
    The two parent compds. used for studying the iron-carbon multiple bond interactions are [Fe(tmtaa)] (1), and [Fe(tmtaa)Na(THF)3] (2) [tmtaa = dibenzotetramethyltetraaza[14]annulene dianion], the latter being obtained by redn. of 1. The reaction of 1 with CO led to the corresponding monocarbonyl deriv. [Fe(tmtaa)(CO)(L)] [L = THF, 3; L = Py, 4], while the reaction with RNC allowed the isolation of mono-isocyanide [Fe(tmtaa)(o-Me3Si-C6H4NC)(THF)] (5), [Fe(tmtaa)(BuNC)(THF)] (6), and bis-isocyanide [Fe(tmtaa)(tBuNC)2] (7) derivs. Redn. of 6 with sodium metal or the reaction of 1 with NaCN led to a monocyano deriv. bridged into a dimeric form by sodium cations in [{Fe(tmtaa)(CN)}2(μ-NaLn)2] [L = THF, n = 3, 8a; L = DME, n = 2, 8b], while the reaction of 1 with Bu4N+CN- led to the monomeric form [Fe(tmtaa)(CN)]-(Bu4N)+ (9). A detailed magnetic anal. of 1-10, the last one being the bis-pyridine deriv. [Fe(tmtaa)(Py)2] (10) showed a variety of low and intermediate spin states, and spin crossovers (with a minor role played by high spin states) as a function of the axial ligands. A remarkable difference was obsd. with the analogous porphyrin derivs. The d7 iron(I) deriv. 2 occurs in tight ion-pair form, both iron and sodium being bonded to the tmtaa ligand. The reaction of 2 with carbon monoxide led to a monocarbonyl deriv. bridged in a dimeric form by sodium cations bonded to the oxygen atoms in [{Fe(tmtaa)}2{μ-CONa(THF)2}2] (11). Both 2 and 11 showed a spin conversion between S = 1/2 and S = 3/2, with a small antiferromagnetic coupling in the latter case, due to the dimeric form. The reaction of 1 with diazoalkane RR'CN2 led to the corresponding low-spin diamagnetic carbene derivs. [Fe(tmtaa)(CRR')] [R = R' = Ph, 12; R = Ph, R' = H, 13], the 1st one being by far more thermally stable, while the 2nd one decomps. at room temp. to 1 and a mixt. of cis and trans-stilbene. Both react with O2 giving Ph2CO and PhCHO and the μ-oxo dimer [{Fe(tmtaa)}(μ-O)] (14). The proposed structures are supported by the x-ray analyses on complexes 2, 8b, 9, 11b and 12.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXns1Snu70%253D&md5=c4eef53095a38d2789f8596bd8133f44
  64. 64
    Tseng, Y.-T.; Ching, W.-M.; Liaw, W.-F.; Lu, T.-T. Dinitrosyl Iron Complex [K-18-crown-6-ether][(NO)2Fe(MePyrCO2)]: Intermediate for Capture and Reduction of Carbon Dioxide. Angew. Chem., Int. Ed. 2020, 59, 11819– 11823,  DOI: 10.1002/anie.202002977
    Google Scholar
    64
    Dinitrosyl Iron Complex [K-18-crown-6-ether][(NO)2Fe(MePyrCO2)]: Intermediate for Capture and Reduction of Carbon Dioxide
    Tseng, Yu-Ting; Ching, Wei-Min; Liaw, Wen-Feng; Lu, Tsai-Te
    Angewandte Chemie, International Edition (2020), 59 (29), 11819-11823CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Continued efforts are made for the use of CO2 as a C1 feedstock for regeneration of valuable chems. and fuels. Mechanistic study of mol. (electro-/photo-)catalysts disclosed that initial step for CO2 activation involves either nucleophilic insertion or direct redn. of CO2. Nucleophilic activation of CO2 by complex [(NO)2Fe(μ-MePyr)2Fe(NO)2]2- (2, MePyr = 3-methylpyrazolate) gave CO2-captured complex [(NO)2Fe(MePyrCO2)]- (2-CO2, MePyrCO2 = 3-methyl-pyrazole-1-carboxylate). Single-crystal structure, spectroscopic, reactivity, and computational study unravels 2-CO2 as a unique intermediate for reductive transformation of CO2 promoted by Ca2+. Also, sequential reaction of 2 with CO2, Ca(OTf)2, and KC8 established a synthetic cycle, 2 → 2-CO2 → [(NO)2Fe(μ-MePyr)2Fe(NO)2] (1) → 2, for selective conversion of CO2 into oxalate. Presumably, characterization of the unprecedented intermediate 2-CO2 may open an avenue for systematic evaluation of the effects of alternative Lewis acids on redn. of CO2.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXps1Orsrw%253D&md5=1947b1040331e8c2267af1d0560d956c
  65. 65
    Cook, B. J.; Di Francesco, G. N.; Abboud, K. A.; Murray, L. J. Countercations and Solvent Influence CO2 Reduction to Oxalate by Chalcogen-Bridged Tricopper Cyclophanates. J. Am. Chem. Soc. 2018, 140, 5696– 5700,  DOI: 10.1021/jacs.8b02508
    Google Scholar
    65
    Countercations and Solvent Influence CO2 Reduction to Oxalate by Chalcogen-Bridged Tricopper Cyclophanates
    Cook, Brian J.; Di Francesco, Gianna N.; Abboud, Khalil A.; Murray, Leslie J.
    Journal of the American Chemical Society (2018), 140 (17), 5696-5700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    One-electron redn. of Cu3EL (L3- = tris(β-diketiminate)cyclophane, and E = S, Se) affords [Cu3EL]-, which reacts with CO2 to yield exclusively C2O42- (95% yield, TON = 24) and regenerate Cu3EL. Stopped-flow UV/visible data support an A→B mechanism under pseudo-first-order conditions (kobs, 298K = 115(2) s-1), which is 106 larger than those for reported copper complexes. The kobs values are dependent on the countercation and solvent (e.g., kobs is greater for [K(18-crown-6)]+ vs (Ph3P)2N+, and there is a 20-fold decrease in kobs in THF vs DMF). Our results suggest a mechanism in which cations and solvent influence the stability of the transition state.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnvFChsr0%253D&md5=0e7f630edb114f2eaa44dabd2428e601
  66. 66
    Khamespanah, F.; Marx, M.; Crochet, D. B.; Pokharel, U. R.; Fronczek, F. R.; Maverick, A. W.; Beller, M. Oxalate Production via Oxidation of Ascorbate Rather than Reduction of Carbon Dioxide. Nat. Commun. 2021, 12, 1997,  DOI: 10.1038/s41467-021-21817-w
    Google Scholar
    66
    Oxalate production via oxidation of ascorbate rather than reduction of carbon dioxide
    Khamespanah, Fatemeh; Marx, Maximilian; Crochet, David B.; Pokharel, Uttam R.; Fronczek, Frank R.; Maverick, Andrew W.; Beller, Matthias
    Nature Communications (2021), 12 (1), 1997CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Cu complex oxalate forms by oxidative degrdn. of ascorbate. This was evidenced by the reaction conducted under an atm. of O2, giving rise to the same oxalate complex described earlier from which sodium oxalate was removed and identified by NMR spectroscopy. In addn., the same product was obtained from reactions of the Cu(I) complex [Cu2(m-xpt)2]2+ with O2 or air in the presence of DHA. In expts. with [Cu2(m-xpt)2]2+ under 13CO2 + O2, 13C was not incorporated into the oxalate product. In contrast, a new trinuclear Cu(II) carbonate complex, [Cu3(m-xpt)3(μ-CO3)]4+, has been isolated, when [Cu2(m-xpt)2]2+ was treated with CO2 and O2 in the absence of sodium ascorbate or DHA.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXns1akt7c%253D&md5=4155ddc9924ade30a8603243e1a86c31
  67. 67
    Häärä, M.; Sundberg, A.; Willför, S. Calcium Oxalate - a Source of “Hickey” Problems - A Literature Review on Oxalate Formation, Analysis and Scale Control. Nord. Pulp. Paper Res. J. 2011, 26, 263– 282,  DOI: 10.3183/npprj-2011-26-03-p263-282
    Google Scholar
    67
    Calcium oxalate - a source of "hickey" problems - a literature review on oxalate formation, analysis and scale control
    Haara, Matti; Sundberg, Anna; Willfor, Stefan
    Nordic Pulp & Paper Research Journal (2011), 26 (3), 263-282CODEN: NPPJEG; ISSN:0283-2631. (Swedish Association of Pulp and Paper Engineers)
    A review. Calcium oxalate is one of the most problematic scale salts occurring in pulp and paper prodn. processes. Calcium oxalate scaling in a paper machine system often leads to disturbances in the process, prodn. losses due to downtime needed for cleaning, as well as impaired paper quality. This literature review gives a summary of current knowledge and recent research on oxalic acid and calcium oxalate formation esp. in mech. pulping. Methods for oxalate anal., as well as possible ways to control and monitor the scaling in the process, are also discussed. Finally, possibilities to utilize oxalic acid and calcium oxalate in the process are briefly reviewed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFSrtLjJ&md5=3bee1673e006349b047443482306da8d
  68. 68
    Nelson, B. C.; Rockwell, G. F.; Campfield, T.; O’Grady, P.; Hernandez, R. M.; Wise, S. A. Capillary Electrophoretic Determination of Oxalate in Amniotic Fluid. Anal. Chim. Acta 2000, 410, 1– 10,  DOI: 10.1016/S0003-2670(00)00711-X
    Google Scholar
    68
    Capillary electrophoretic determination of oxalate in amniotic fluid
    Nelson, B. C.; Rockwell, G. F.; Campfield, T.; O'Grady, P.; Hernandez, R. M.; Wise, S. A.
    Analytica Chimica Acta (2000), 410 (1-2), 1-10CODEN: ACACAM; ISSN:0003-2670. (Elsevier Science B.V.)
    A capillary electrophoretic (CE) assay for oxalate was applied to the quant. detn. of free oxalate in amniotic fluid. Indirect absorbance detection of oxalate is accomplished with a chromate-based background electrolyte modified with EDTA. Detection interference due to the presence of high levels (≈4 mg/mL) of inorg. chloride is eliminated through a direct sample clean-up procedure based on cation (Ag+-form) resins. Sepn. interference from amniotic fluid proteins is prevented through the use of a simple aq.-based diln. procedure. This method for the detn. of oxalate in amniotic fluid provides precision of ≈5% relative std. deviation. Within-day precisions for the oxalate response and migration time are better than 3% relative std. deviation and 1% relative std. deviation, resp. Between-day precisions for the oxalate response and migration time are better than 6% relative std. deviation and 3% relative std. deviation, resp. The anal. recovery of oxalate (1000 ng/mL) spiked into amniotic fluid was better than 96%. The limit of detection (LOD) for the method is ≈100 ng/mL oxalate. This method also shows promising results for the detn. of oxalate in human blood plasma samples.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitVSmu78%253D&md5=fe338c694aea9aa39ca2a1c9bfb990b9
  69. 69
    Chai, W.; Liebman, M. Oxalate Content of Legumes, Nuts, and Grain-Based Flours. J. Food Compost. Anal. 2005, 18, 723– 729,  DOI: 10.1016/j.jfca.2004.07.001
    Google Scholar
    There is no corresponding record for this reference.
  70. 70
    Sirén, H.; Kokkonen, R.; Hiissa, T.; Särme, T.; Rimpinen, O.; Laitinen, R. Determination of Soluble Anions and Cations from Waters of Pulp and Paper Mills with On-Line Coupled Capillary Electrophoresis. J. Chromatogr. A 2000, 895, 189– 196,  DOI: 10.1016/S0021-9673(00)00586-0
    Google Scholar
    70
    Determination of soluble anions and cations from waters of pulp and paper mills with on-line coupled capillary electrophoresis
    Siren, H.; Kokkonen, R.; Hiissa, T.; Sarme, T.; Rimpinen, O.; Laitinen, R.
    Journal of Chromatography A (2000), 895 (1+2), 189-196CODEN: JCRAEY; ISSN:0021-9673. (Elsevier Science B.V.)
    When the degree of closure of the paper machine wet end waters increases, wet end problems also become more difficult to control without specific and selective online measurements. The need to measure the concns. of individual compds. in order to explain wet end phenomena is growing. This study was performed to set up a CE (capillary electrophoresis) system to a paper machine and to det. sol. inorg. and org. ions in different locations of pulp and paper process waters with real time analyses by 2 online CE methods. A reconstructed com. CE app. was connected to a papermaking machine via an app., which was a combined sampling and sample pretreatment instrument, the role of which was to filter and dil. the samples before online detn. by CE. The online procedures were optimized for simultaneous detn. of anions as chloride, sulfate, oxalate, formate and acetate and for detn. of cations as potassium, calcium, sodium, magnesium and traces of aluminum. The quantification was performed with external std. methods using the programs available in the com. CE instrument. The concns. of the ions were transferred by using a computerized transfer algorithm exporting the results from the anal. instrument to the process control unit. The developed online procedures were tested three times in paper and paperboard mills for 1 mo at a time. Correlations were obsd. between the CE results and changes in the processes.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmvFyltbw%253D&md5=894b1d2e852e19d586d8137d8e43769b
  71. 71
    Thomas, A. M.; Lin, B.-L.; Wasinger, E. C.; Stack, T. D. P. Ligand Noninnocence of Thiolate/Disulfide in Dinuclear Copper Complexes: Solvent-Dependent Redox Isomerization and Proton-Coupled Electron Transfer. J. Am. Chem. Soc. 2013, 135, 18912– 18919,  DOI: 10.1021/ja409603m
    Google Scholar
    71
    Ligand Noninnocence of Thiolate/Disulfide in Dinuclear Copper Complexes: Solvent-Dependent Redox Isomerization and Proton-Coupled Electron Transfer
    Thomas, Andrew M.; Lin, Bo-Lin; Wasinger, Erik C.; Stack, T. Daniel P.
    Journal of the American Chemical Society (2013), 135 (50), 18912-18919CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Copper thiolate/disulfide interconversions are related to the functions of several important proteins such as human Sco1, Cu-Zn superoxide dismutase (SOD1), and mammalian zinc-bonded metallothionein (no data). The synthesis and characterization of well-defined synthetic analogs for such interconversions are challenging yet provide important insights into the mechanisms of such redox processes. Solvent-dependent redox isomerization and proton-coupled electron transfer mimicking these interconversions are obsd. in two structurally related dimeric μ,η2:η2-thiolato Cu(II)-Cu(II) complexes by various methods, including x-ray diffraction, XAS, NMR, and UV-visible. Spectroscopic evidence shows that a solvent-dependent equil. exists between the dimeric μ-thiolato Cu(II)-Cu(II) state and its redox isomeric μ-disulfido Cu(I)-Cu(I) form. Complete formation of μ-disulfido Cu(I)-Cu(I) complexes, however, only occurs after the addn. of 2 equiv of protons, which promote electron transfer from thiolate to Cu(II) and formation of disulfide and Cu(I) via protonation of the coordinating ligand. Proton removal reverses this reaction. The reported unusual reductive protonation/oxidative deprotonation of the metal centers may serve as a new chem. precedent for how related proteins manage Cu ions in living organisms.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVCmur3K&md5=1330a414322b04108d15e78b8bf80193
  72. 72
    Knope, K. E.; Kimura, H.; Yasaka, Y.; Nakahara, M.; Andrews, M. B.; Cahill, C. L. Investigation of in Situ Oxalate Formation from 2,3-Pyrazinedicarboxylate under Hydrothermal Conditions Using Nuclear Magnetic Resonance Spectroscopy. Inorg. Chem. 2012, 51, 3883– 3890,  DOI: 10.1021/ic3000944
    Google Scholar
    72
    Investigation of in Situ Oxalate Formation from 2,3-Pyrazinedicarboxylate under Hydrothermal Conditions Using Nuclear Magnetic Resonance Spectroscopy
    Knope, Karah E.; Kimura, Hiroshi; Yasaka, Yoshiro; Nakahara, Masaru; Andrews, Michael B.; Cahill, Christopher L.
    Inorganic Chemistry (2012), 51 (6), 3883-3890CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The authors have investigated the assembly of a two-dimensional coordination polymer, Nd2(pzdc)2(C2O4)(H2O)2, that was prepd. from the hydrothermal reaction of Nd(NO3)3·6H2O and 2,3-pyrazinedicarboxylic acid (H2pzdc). In situ oxalate formation as obsd. in this system was been investigated using 1H and 13C NMR spectroscopy, and a pathway for C2O42- anion formation under hydrothermal conditions was elucidated. The oxalate ligands found in Nd2(pzdc)2(C2O4)(H2O)2 result from the oxidn. of H2pzdc, which proceeds through intermediates, such as 2-pyrazinecarboxylic acid (2-pzca), 2-hydroxyacetamide, 3-amino-2-hydroxy-3-oxopropanoic acid, 2-hydroxymalonic acid, 2-oxoacetic acid (glyoxylic acid), and glycolic acid. The species are generated through a ring-opening that occurs via cleavage of the C-N bond of the pyrazine ring, followed by hydrolysis/oxidn. of the resulting species.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XivVOhsro%253D&md5=8f9b8078ac11b4b2414fe8b3faba718b
  73. 73
    Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for Organometallic Chemistry. Chem. Rev. 1996, 96, 877– 910,  DOI: 10.1021/cr940053x
    Google Scholar
    73
    Chemical Redox Agents for Organometallic Chemistry
    Connelly, Neil G.; Geiger, William E.
    Chemical Reviews (Washington, D. C.) (1996), 96 (2), 877-910CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review, with >461 refs., showing how one-electron oxidants and reductants have been used in preparative chem. (incorporating both synthetic applications and generation of species for in situ characterization) in nonaq. solns., the usual media for organometallic ET reactions. The authors do not treat photochem.-generated reducing agents which, although generally transient species, may have advantages in some applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhsVGhu7Y%253D&md5=205b204d99818aded3c41067d4bf85e3
  74. 74
    Drew, M. G. B.; Cairns, C.; McFall, S. G.; Nelson, S. M. The Synthesis, Properties, and the Crystal and Molecular Structures of Five-Co-Ordinate Copper(I) and Silver(I) Complexes of a Quinquedentate Macrocyclic Ligand Having an ‘N3S2’ Donor Set. J. Chem. Soc., Dalton Trans. 1980, 2020– 2027,  DOI: 10.1039/DT9800002020
    Google Scholar
    74
    The synthesis, properties, and the crystal and molecular structures of five-coordinate copper(I) and silver(I) complexes of a quinquedentate macrocyclic ligand having an N3S2 donor set
    Drew, Michael G. B.; Cairns, Colin; McFall, Stephen G.; Nelson, S. Martin
    Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1980), (10), 2020-7CODEN: JCDTBI; ISSN:0300-9246.
    The 17-membered macrocyclic ligand 2,15-dimethyl-7,10-dithia-3,14,20-triazabicyclo[14.3.1]icosa-1(20),2,14,16,18-pentaene (L) contg. the N3S2 donor set was synthesized and isolated as the Ag(I) complex by the template action of Ag(I) salts on the cyclic Schiff-base condensation of 2,6-diacetylpyridine with 1,10-diamine-4,7-dithiadecane. Cu2+ was ineffective as a template for the synthesis but CuL2+ could be obtained from AgL+ via metal exchange. NaBPh4 reduces CuL2+ to give CuL+ in good yield. Hydrogenation of AgL+ salts using NaBH4 gives the free reduced macrocycle L1 (formed by hydrogenation of the 2 azomethine bonds), which forms the complexes [CuL1][BPh4] and [CuL1][ClO4]2. The CuL+ complex is unreactive to both O and CO. The crystal and mol. structures of [CuL][ClO4] and [AgL][BPh4] were detd. from x-ray diffractometer data using Patterson and Fourier methods and refined by full-matrix least squares to R 0.077 and 0.071 for 927 and 2621 reflections, resp. Although the coordination geometry of both complexes is a distorted trigonal bipyramid, there are marked differences in the macrocycle conformations in the 2 cases, and, in the Cu(I) complex, in the Cu-N bond lengths. These differences are discussed in relation to the size of the 2 metal ions and of the macrocyclic hole.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXhtVGhtA%253D%253D&md5=df50d952bcb7f513f941ddfa9d081c08
  75. 75

    Crystals of [Cu(L1)I] were obtained from a THF solution of in situ formed [Cu(L1)I] starting from CuI, L1, and NaBPh4. This indicates incomplete iodo exchange with NaBPh4. [Cu(L1)I] was independently synthesized (experimental procedure and analytical data can be found in the Supporting Information).

    There is no corresponding record for this reference.
  76. 76
    Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. Macrocycles with a Single Pendant Arm: Synthesis of N-R-(1,4,7-triazacyclononane) [L, R = 4-but-1-ene; L′, R = 3-prop-1-ene]: Synthesis of the CuI Complex [CuL]I and Synthesis and Crystal Structure of the CuII Complex [CuL2][BPh4]2 and the μ-Hydroxy Bridged CuII Dimer [LCu(μ-OH)2CuL][BPh4]2. Inorg. Chim. Acta 1996, 246, 343– 348,  DOI: 10.1016/0020-1693(96)05081-5
    Google Scholar
    76
    Macrocycles with a single pendant arm: synthesis of N-R-(1,4,7-triazacyclononane) [L, R = 4-but-1-ene; L', R = 3-prop-1-ene]: Synthesis of the CuI complex [CuL]I and synthesis and crystal structure of the CuII complex [CuL2][BPh4]2 and the μ-hydroxy bridged CuII dimer [LCu(μ-OH)2CuL][BPh4]2
    Farrugia, Louis J.; Lovatt, Paul A.; Peacock, Robert D.
    Inorganica Chimica Acta (1996), 246 (1-2), 343-348CODEN: ICHAA3; ISSN:0020-1693. (Elsevier)
    A general method is reported for the prepn. of mono-N-substituted derivs. of [9]aneN3. The method is exemplified by the synthesis of the macrocyclic ligand N-4-but-1-ene-1,4,7-triazacyclononane, L, which has a single pendant butene arm. The propene analog is also reported. Synthesis is reported for [CuIL]I, [CuIIL2][BPh4]2 (1) and [LCuII(OH)2CuIIL][BPh4]2·2MeCN (2). The structures of 1 and 2 were detd.; 1 (C68H82BCuN3) monoclinic, space group P21/n, a 13.0529(8), b 18.008(1), c 13.423(1) Å, β 111.720(6)°, Z = 2; 2 (C72H90B2Cu2N8O2) triclinic, space group P1, a 11.487(1), b 12.870(1), c 12.867(1) Å, α 106.807(6), β 101.833(6), γ 105.859(6)°, Z = 1.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XjvF2rtLg%253D&md5=e404880f17a115f706367c9b4c377613
  77. 77
    Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. Synthesis of a series of novel binucleating ligands based on 1,4,7-triazacyclononane and o-, m- and p-xylene: crystal structure of the μ-hydroxy-bridged dicopper(II) complex [Cu2Lm(OH)2][BPh4]2 [Lm = α,α′-bis(N-1,4,7-triazacyclononane)-m-xylene]. J. Chem. Soc., Dalton Trans. 1997, 911– 912,  DOI: 10.1039/a608058h
    Google Scholar
    77
    Synthesis of a series of novel binucleating ligands based on 1,4,7-triazacyclononane and o-, m- and p-xylene: crystal structure of the μ-hydroxy-bridged dicopper(II) complex [Cu2Lm(OH)2][BPh4]2 [Lm = α,α'-bis(N-1,4,7-triazacyclononane)-m-xylene]
    Farrugia, Louis J.; Lovatt, Paul A.; Peacock, Robert D.
    Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1997), (6), 911-912CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
    Three new binucleating ligands, xylenediylbis(triazacyclononanes) I, based on 1,4,7-triazacyclononane and o-, m- or p-xylene, were prepd. The prepn., crystal structure, and magnetic properties of μ-hydroxy dimer [Cu2Lm(OH)2][BPh4]2 (Lm = m-xylene deriv. I) are described.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXisFCgsrw%253D&md5=81025d13c809bcf103a198a981b05b49
  78. 78
    Agilent Technologies. User Manual: Organic Acids Analysis Kit, PN 5063-6510 https://www.agilent.com/cs/library/usermanuals/public/5968-9047E_print.pdf.pdf (accessed 2021-06-25).
    Google Scholar
    There is no corresponding record for this reference.
  79. 79
    Zhang, X.; Hsieh, W.-Y.; Margulis, T. N.; Zompa, L. J. Binuclear Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands Containing Tri- and Tetramethylene Bridging Groups. An Equilibrium and Structural Study. Inorg. Chem. 1995, 34, 2883– 2888,  DOI: 10.1021/ic00115a015
    Google Scholar
    79
    Binuclear Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands Containing Tri- and Tetramethylene Bridging Groups. An Equilibrium and Structural Study
    Zhang, Xiaoping; Hsieh, Wen-Yuan; Margulis, T. N.; Zompa, Leverett J.
    Inorganic Chemistry (1995), 34 (11), 2883-8CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Two members of a homologous series of bis(triazacyclononane) ligands, 1,3-bis(1,4,7-triaza-1-cyclononyl)propane, EM3, and 1,4-bis(1,4,7-triaza-1-cyclononyl)butane, EM4, form stable 1:1 and 2:1 Cu(II)-L complexes. Dissocn. consts. for the acid salts of the compds. and equil. studies with Cu(II) in aq. 0.1M KNO3 at 25° are reported. Cu(EM3)2+ is more stable than Cu(EM4)2+ while Cu2(EM4)4+ is slightly more stable than Cu2(EM3)4+. Probable reasons for this behavior are discussed in light of the 1:1 complexes existing in soln. as monomeric species. Binuclear Cu(II) complexes of each ligand were isolated and their structures detd. by x-ray crystallog. Cu2(EM3)Cl4·2H2O crystallizes in space group P2/c with a 12.607(3), b 7.589(2), c 12.948 Å, and β 93.71(3)°. Cu2(EM4)Cl4 crystallizes in space group P21/c with a 11.919(2), b 8.468(2), c 11.508(2) Å, and β 99.06(3)°. In both complexes the Cu(II) is 5-coordinate with two secondary amine N atoms of a [9]aneN3 group and two Cl- occupying sites at the base and the tertiary N atom of the same moiety at the apex of a square pyramid. The structures have somewhat different conformations. The pair of Cl- attached to the two Cu(II) are approx. syn for Cu2(EM3)Cl4·2H2O and anti for Cu2(EM4)Cl4.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXls1ykurk%253D&md5=826fdf7b149148e24707e8b19b42a6e9
  80. 80
    Young, M. J.; Chin, J. Dinuclear Copper(II) Complex That Hydrolyzes RNA. J. Am. Chem. Soc. 1995, 117, 10577– 10578,  DOI: 10.1021/ja00147a022
    Google Scholar
    80
    Dinuclear copper(II) complex that hydrolyzes RNA
    Young, Mary Jane; Chin, Jik
    Journal of the American Chemical Society (1995), 117 (42), 10577-8CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A novel ligand (L = 1,8-bis(N-1,4,7-triazacyclononylmethyl)naphthalene) that can bind 2 Cu(II) ions was synthesized. The dinuclear metal complex, [(L)Cu2Cl4] (I), was several hundred-fold more reactive than the mononuclear CuCl2 complex of 1,4,7-triazacyclononane for cleaving ApA and 2',3'-cAMP. The pseudo-1st-order rate consts. for the I (2 mM)-promoted cleavage of ApA (0.05 mM) and 2',3'-cAMP (0.05 mM) at pH 6.0 (10 mM MES) were 2.7 × 10-4 s-1 (at 50°) and 2.8 × 10-3 s-1 (at 25°), resp. These represented about 5 and 8 orders of magnitude rate-accelerations for cleaving ApA and 2',3'-cAMP, resp., over the background hydroxide rates at pH 6.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosVKqtrc%253D&md5=94b11f2ff9a85181a2cb8fcf03ad62bd
  81. 81
    McBride, R. S. The Standardization of Potassium Permanganate Solution by Sodium Oxalate. J. Am. Chem. Soc. 1912, 34, 393– 416,  DOI: 10.1021/ja02205a009
    Google Scholar
    81
    Standardization of Potassium Permanganate Solution by Sodium Oxalate
    McBride, R. S.
    (1912), 34 (), 393-416 ISSN:.
    This paper describes the use of Na2C2O4 in the standardization of KMnO4 soln., its advantages, disadvantages and accuracy.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaC38XhtVartg%253D%253D&md5=3c3e71ba4767a056e6fc2d5506743056
  82. 82
    Knocke, W. R.; van Benschoten, J. E.; Kearney, M. J.; Soborski, A. W.; Reckhow, D. A. Kinetics of Manganese and Iron Oxidation by Potassium Permanganate and Chlorine Dioxide. J. Am. Water Works Assoc. 1991, 83, 80– 87,  DOI: 10.1002/j.1551-8833.1991.tb07167.x
    Google Scholar
    82
    Kinetics of manganese and iron oxidation by potassium permanganate and chlorine dioxide
    Knocke, William R.; Van Benschoten, John E.; Kearney, Maureen J.; Soborski, Andrew W.; Reckhow, David A.
    Journal - American Water Works Association (1991), 83 (6), 80-7CODEN: JAWWA5; ISSN:0003-150X.
    The effects of reduced metal ion concn., pH, temp., and the presence of dissolved org. C on the kinetics of Mn(II) and Fe(II) oxidn. by KMnO4 and ClO2 were studied and modeled. The oxidn. of reduced Mn(II) was rapid except at low temps. The rates of Mn(II) oxidn. are acceptable in the presence of humic or fulvic acids, but Fe(II) oxidn. is strongly inhibited by these acids. Poor Mn removal is attributed to inefficient capture of colloidal Mn oxide. The oxidant addn. sequence is an important design and operation factor.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXls1Khsbs%253D&md5=c8eb876d84ccdbdea538ed763d270b9b
  83. 83
    Singh, N.; Lee, D. G. Permanganate: A Green and Versatile Industrial Oxidant. Org. Process Res. Dev. 2001, 5, 599– 603,  DOI: 10.1021/op010015x
    Google Scholar
    83
    Permanganate: A Green and Versatile Industrial Oxidant
    Singh, Nirmal; Lee, Donald G.
    Organic Process Research & Development (2001), 5 (6), 599-603CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)
    A review with refs. The use of permanganate as an effective oxidant in org. chem. has a long and extensive history. Industrial applications have recently become more attractive environmentally by the introduction of a process for recycling manganese dioxide, a coproduct of these reactions. This recycling approach has reduced the environmental impact of permanganate technol. and made it sustainable as defined by the Brundtland Commission. Several current and potential industrial applications of permanganate oxidns. are discussed along with a description of some emerging technologies.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXmvFGktrk%253D&md5=197d9c2e9e7bdcab49fc60f008eb52ae
  84. 84
    Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Cramer, C. J.; Que, L.; Tolman, W. B. A New Intermediate in Copper Dioxygen Chemistry: Breaking the O-O Bond To Form a {Cu2(μ-O)2}2+ Core. J. Am. Chem. Soc. 1995, 117, 8865– 8866,  DOI: 10.1021/ja00139a026
    Google Scholar
    84
    A New Intermediate in Copper Dioxygen Chemistry: Breaking the O-O Bond To Form a {Cu2(μ-O)2}2+ Core
    Mahapatra, Samiran; Halfen, Jason A.; Wilkinson, Elizabeth C.; Pan, Gaofeng; Cramer, Christopher J.; Que, Lawrence Jr.; Tolman, William B.
    Journal of the American Chemical Society (1995), 117 (34), 8865-6CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The authors report the isolation, spectroscopic and theor. characterization, and C-H bond activation chem. of a new species derived from the reaction of a Cu(I) complex with dioxygen. The proposed {Cu2(μ-O)2}2+ core of this mol. is unprecedented in Cu chem. and may be viewed as a possible intermediate in oxidn. reactions catalyzed by multicopper enzymes and small mol. catalysts. Solns. of [(Bn3TACN)Cu(MeCN)]X (Bn3TACN = 1,4,7-tribenzyl-1,4,7-triazacyclononane; X = ClO4- or SbF6-) in CH2Cl2 absorb 0.5 equiv O2 at -80° to generate an orange-brown species 2 [λmax = 318 (ε 6000 M-1 cm-1) and 430 (7000) nm]. Compd. 2 decomps. to, among other products, the dicopper(II)-bis(μ-hydroxo) complex {[(Bn3TACN)Cu]2(OH)2}(X)2, 3, via rate-detg. attack at ligand benzyl-substituent C-H bonds that was characterized by a large kinetic isotope effect [kH/kD = 50 at -50°; ΔH⧧H = 12.9(5) kcal mol-1, ΔH⧧D = 15.3(5) kcal mol-1, ΔS⧧H = -14(2) e.u., and ΔS⧧D = -11(2) e.u.]. A novel {L2Cu2(μ-O)2}2+ structure with significant covalent character is proposed for 2 from its compn. (EPR, NMR), its oxidizing capability, and similarities of the obsd. resonance Raman (peaks at 602 and 608 cm-1 that shift to one peak at 583 cm-1 upon 18O substitution) and EXAFS (Cu-Cu distance of 2.78 Å) features to those reported for other M2(μ-O)2 (M = Fe, Mn) rhombs. Ab initio calcns. provide support for the proposed ground state structure for 2 and rationalize key exptl. observations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXnsVOjsrk%253D&md5=a096074d355f7850b00c19e9a64811d5
  85. 85
    Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.; Young, V. G.; Cramer, C. J.; Que, L.; Tolman, W. B. Structural, Spectroscopic, and Theoretical Characterization of Bis(μ-oxo)dicopper Complexes, Novel Intermediates in Copper-Mediated Dioxygen Activation. J. Am. Chem. Soc. 1996, 118, 11555– 11574,  DOI: 10.1021/ja962305c
    Google Scholar
    85
    Structural, Spectroscopic, and Theoretical Characterization of Bis(μ-oxo)dicopper Complexes, Novel Intermediates in Copper-Mediated Dioxygen Activation
    Mahapatra, Samiran; Halfen, Jason A.; Wilkinson, Elizabeth C.; Pan, Gaofeng; Wang, Xuedong; Young, Victor G., Jr.; Cramer, Christopher J.; Que, Lawrence, Jr.; Tolman, William B.
    Journal of the American Chemical Society (1996), 118 (46), 11555-11574CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A description of the structure and bonding of novel bis(μ-oxo)dicopper complexes and their bis(μ-hydroxo)dicopper decompn. products was derived from combined x-ray crystallog., spectroscopic, and ab initio theor. studies. [(LCu)2(μ-O)2]X2 were generated from the reaction of solns. of [LCu(MeCN)]X with O2 at -80° [L = 1,4,7-tribenzyl-1,4,7-triazacyclononane (LBn3), 1,4,7-triisopropyl-1,4,7-triazacyclononane (LiPr3), or 1-benzyl-4,7-diisopropyl-1,4,7-triazacyclononane (LiPr2Bn); X = variety of anions]. The geometry of the [Cu2(μ-O)2]2+ core was defined by x-ray crystallog. for [(d21-LBn3Cu)2(μ-O)2](SbF6)2 and by EXAFS spectroscopy for the complexes capped by LBn3 and LiPr3; notable dimensions include short Cu-O (∼1.80 Å) and Cu...Cu (∼2.80 Å) distances like those reported for analogous M2(μ-O)2 (M = Fe or Mn) rhombs. The core geometry is contracted compared to those of the bis(μ-hydroxo)dicopper(II) compds. that result from decompn. of the bis(μ-oxo) complexes upon warming. X-ray structures of the decompn. products [(LBn3Cu)(LBn2HCu)(μ-OH)2](O3SCF3)2.2Me2CO, [(LiPr2HCu)2(μ-OH)2](BPh4)2.2THF, and [(LiPr2BnCu)2(μ-OH)2](O3SCF3)2 showed that they arise from N-dealkylation of the original capping macrocycles. Manometric, electrospray mass spectrometric, and UV-visible, EPR, NMR, and resonance Raman spectroscopic data for the bis(μ-oxo)dicopper complexes in soln. revealed important topol. and electronic structural features of the intact [Cu2(μ-O)2]2+ core. The bis(μ-oxo)dicopper unit is diamagnetic, undergoes a rapid fluxional process involving interchange of equatorial and axial N-donor ligand environments, and exhibits a diagnostic ∼600 cm-1 18O-sensitive feature in Raman spectra. Ab initio calcns. on a model system, [(NH3)6Cu2(μ-O)2]2+, predicted a closed-shell singlet ground-state structure that agrees well with the bis(μ-oxo)dicopper geometry detd. by expt. and helps to rationalize many of its physicochem. properties. From an anal. of the theor. and exptl. results (including a bond valence sum anal.), a formal oxidn. level assignment for the core probably is [CuIII2(μ-O2-)2]2+, although a more complete MO description indicates that the O and Cu fragment orbitals are significantly mixed (i.e., there is a high degree of covalency).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsFOitrw%253D&md5=0d8959439405017cbb104bfeb40ee09d
  86. 86
    Mahapatra, S.; Young, V. G., Jr.; Kaderli, S.; Zuberbühler, A. D.; Tolman, W. B. Tuning the Structure and Reactivity of the [Cu2(μ-O)2]2+ Core: Characterization of a New Bis(μ-oxo)dicopper Complex Stabilized by a Sterically Hindered Dinucleating Bis(triazacylononane) Ligand. Angew. Chem., Int. Ed. 1997, 36, 130– 133,  DOI: 10.1002/anie.199701301
    Google Scholar
    86
    Tuning the structure and reactivity of the [Cu2(μ-O)2]2+ core: characterization of a new bis(μ-oxo)dicopper complex stabilized by a sterically hindered dinucleating bis(triazacyclononane) ligand
    Mahapatra, Samiran; Young, Victor G., Jr.; Kaderli, Susan; Zuberbuehler, Andreas D.; Tolman, William B.
    Angewandte Chemie, International Edition in English (1997), 36 (1/2), 130-133CODEN: ACIEAY; ISSN:0570-0833. (VCH)
    [Cu2(μ-O)2L](ClO4)2 (I) was prepd. and its crystal structure as a solvate detd. in space group P‾1, R1 = 0.0544. The analog of I perdeuterated at iso-Pr (I-D) was also prepd. Kinetics of the oxygenation reaction leading to I were detd. and a mechanism with initial formation of a mono-Cu dioxygen as a rate detg. step is proposed. Kinetics of decompn. of I and I-D show a kinetic isotope effect and a mechanism with intramol. cleavage of a C-H bond of an equatorially disposed iso-Pr substituent is supported. The structure and reactivity of I are compared with related complexes to see the influence of the supporting chelate ligands.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXhtFOjtr0%253D&md5=477e65426533d7762f2856c3e42e29d2
  87. 87
    Dalle, K. E.; Gruene, T.; Dechert, S.; Demeshko, S.; Meyer, F. Weakly Coupled Biologically Relevant CuII2(μ-η1:η1-O2) cis-Peroxo Adduct that Binds Side-On to Additional Metal Ions. J. Am. Chem. Soc. 2014, 136, 7428– 7434,  DOI: 10.1021/ja5025047
    Google Scholar
    87
    Weakly Coupled Biologically Relevant CuII2(μ-η1:η1-O2) cis-Peroxo Adduct that Binds Side-On to Additional Metal Ions
    Dalle, Kristian E.; Gruene, Tim; Dechert, Sebastian; Demeshko, Serhiy; Meyer, Franc
    Journal of the American Chemical Society (2014), 136 (20), 7428-7434CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The ability of many copper metalloenzymes to activate O2 and transfer it to org. substrates has motivated extensive attention in the literature. Studies focusing on synthetic analogs provided a detailed understanding of the structures of potential intermediates, thereby helping to guide mechanistic studies. The authors report herein a crystallog. characterized synthetic CuII2(μ-η1:η1-O2) complex (I) exhibiting cis-peroxo bonding geometry, known in iron chem. but previously unobserved for copper. Detailed study by UV-visible, resonance Raman, and IR spectroscopies provides evidence for a significantly diminished copper-oxygen interaction (ε ≈ 3000 M-1 cm-1, νCu-O = 437 cm-1, νO-O = 799 cm-1) relative to those in known 'coupled' Cu2O2 species, consistent with magnetic measurements which show that the peroxide mediates only weak antiferromagnetic coupling (-2J = 144 cm-1). These characteristics are comparable with those of a computationally predicted transition state for O2 binding to type 3 copper centers, providing exptl. evidence for the proposed mechanism of O2 activation and supporting the biol. relevance of the CuII2(μ-η1:η1-O2) cis-species. The peroxide bonding arrangement also allows binding of sodium cations, obsd. both in the solid state and in soln. Binding induces changes on an electronic level, as monitored by UV-visible spectroscopy (Ka = 1700 M-1), reminiscent of redox-inactive metal binding by iron-oxygen species. The results presented highlight the analogous chem. these reactive oxygen species undergo, with respect to both their mechanism of formation, and the mol. interactions in which they participate.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXntFChtr4%253D&md5=f1507a6458a3d05cdb91ba82bfa0d94b
  88. 88
    Haidar, R.; Ipek, M.; DasGupta, B.; Yousaf, M.; Zompa, L. J. Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands with Polymethylene Bridging Groups: An Equilibrium and Structural Study. Inorg. Chem. 1997, 36, 3125– 3132,  DOI: 10.1021/ic970070f
    Google Scholar
    88
    Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands with Polymethylene Bridging Groups: An Equilibrium and Structural Study
    Haidar, Reem; Ipek, Manus; DasGupta, Barnali; Yousaf, Mohammed; Zompa, Leverett J.
    Inorganic Chemistry (1997), 36 (14), 3125-3132CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Copper(II) complexation by ligands contg. two 1,4,7-triazacyclononane, [9]aneN3, groups conjoined by polymethylene chains two to six carbons in length is described. Equil. modeling studies in aq. soln. using pH-potentiometry indicate that the smallest homolog of the series, EM2, forms only Cu(EM2)2+ in dil. aq. solns. All other ligands of the series form stable 1:1 (protonated and nonprotonated) and 2:1 dicopper(II) (hydroxo and nonhydroxo) complexes. Those ligands that contain bridging chains of four or more carbon atoms likely form dimeric or oligomeric complex species in soln. The EM ligands with the shortest polymethylene bridging groups form the most stable 1:1 species. There is little difference among the ligands (n = 3-6) in complex stability of the protonated, CuH2(EMn)4+, and dicopper(II), Cu2(EMn)4+, species. UV-visible spectroscopic continuous variation studies at pH 4.0 and 7.5 are interpreted from the principal equil. species obtained from the equil. models. Single-crystal x-ray diffraction studies on four complexes ([Cu(EM2)]SO4·6H2O (1), [Cu2(EM2)Cl4]·2H2O (2), [Cu2(EM6)Cl4] (3), and [Cu(EM3)][ZnBr4]·H2O (4)) characterize structural features of several 1:1 monomeric and dicopper(II) complexes in the cryst. solid. The monomeric compds. contain CuN6 chromophores while the dicopper(II) compds. contain square pyramidal CuN2Cl2 coordination geometry. Compd. 1 crystallizes in space group P‾1 with a 7.849(2), b 9.783(2), c 16.919(5) Å, α 78.42(3), β 85.76(3), γ 73.06(3), and Z = 2. 2: Space group P21/n with a 9.689(3), b 11.733(3), c 10.124(3) Å, β 98.20(2), and Z = 2. 3: Space group P21/n with a 7.278(2), b 12.416(3), c 13.781(2) Å, β 90.15(2), and Z = 2. 4: Space group P21/c with a 9.295(3), b 16.233(4), c 16.544(5) Å, β 92.62(2), and Z = 4. Cyclic voltammograms of aq. solns. prepd. by dissolving [Cu(EM2)Cl4]·2H2O confirm its dissocn. to Cu(EM2)2+. Aq. solns. contg. 1:1 molar ratios of Cu(II) and EM2 in 0.1 mol dm-3 KCl at 25° show a 1-electron chem. reversible redn. at scan rates of 500 mV s-1 with E1/2 (Cu(II)-Cu(I)) = -868 mV relative to SCE. EPR (X- and Q- band) spectra of frozen solns. (1:1 DMSO/H2O and glycerol/H2O) of Cu(EM2)2+ at 100 K are typical of axial copper(II) features (X-band parameters: g‖ = 2.225 (A‖ = 164 × 10-4) and g.perp. = 2.045).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXjslOqsrc%253D&md5=34b3d5fc52dc0bdea08d5c04270a281f
  89. 89
    Halfen, J. A.; Young, V. G.; Tolman, W. B. Dioxygen Activation by a Copper(I) Complex of a New Tetradentate Tripodal Ligand: Mechanistic Insights into Peroxodicopper Core Reactivity. J. Am. Chem. Soc. 1996, 118, 10920– 10921,  DOI: 10.1021/ja962344o
    Google Scholar
    89
    Dioxygen Activation by a Copper(I) Complex of a New Tetradentate Tripodal Ligand: Mechanistic Insights into Peroxodicopper Core Reactivity
    Halfen, Jason A.; Young, Victor G., Jr.; Tolman, William B.
    Journal of the American Chemical Society (1996), 118 (44), 10920-10921CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The structurally characterized complex [LPyCu]CF3SO3 (1) (LPy = 1-pyridylmethyl-4,7-diisopropyl-1,4,7-triazacyclononane) binds CO to yield [LPyCuCO]CF3SO3, in which the pyridyl arm of LPy is uncoordinated, and O2 at -78° to yield a trans-1,2-peroxodicopper(II) complex [(LPyCu)2(O2)](CF3SO3)2 (2) {λmax = 550 (ε 10,200 M-1 cm-1), 600 (9700) nm; νO-O = 822 cm-1 [Δν(18O) = 51 cm-1]}. In a 4-electron oxidn. reaction, conversion of the ligand pyridylmethyl group to an amide (LPyO) occurs upon decompn. of 2, with the oxygen in LPyO being derived from the peroxide ligand as shown by isotope labeling. Mechanistic studies indicated that (i) the decompn. follows first order kinetics with ΔH⧧ = 12.6 ± 0.5 kcal mol-1 and ΔS⧧ = -23 ± 2 eu, and (ii) kobsH/kobsD (KIE) = 2.5(5) at -30° (measured for 2 labeled at the pyridylmethyl position). On the basis of this and other evidence, a mechanism for the oxidn. reaction is proposed whereby a unimol. isomerization of the trans-1,2-peroxo unit to a μ-η2:η2-peroxo ligand (a "peroxide shift") precedes C-H bond cleavage.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xmt1Gmuro%253D&md5=fa9dace431cecd114dba6de918b01df7
  90. 90
    Houser, R. P.; Halfen, J. A.; Young, V. G.; Blackburn, N. J.; Tolman, W. B. Structural Characterization of the First Example of a Bis(μ-thiolato)dicopper(II) Complex. Relevance to Proposals for the Electron Transfer Sites in Cytochrome c Oxidase and Nitrous Oxide Reductase. J. Am. Chem. Soc. 1995, 117, 10745– 10746,  DOI: 10.1021/ja00148a018
    Google Scholar
    90
    Structural Characterization of the First Example of a Bis(μ-thiolato)dicopper(II) Complex. Relevance to Proposals for the Electron Transfer Sites in Cytochrome c Oxidase and Nitrous Oxide Reductase
    Houser, Robert P.; Halfen, Jason A.; Young, Victor G., Jr.; Blackburn, Ninian J.; Tolman, William B.
    Journal of the American Chemical Society (1995), 117 (43), 10745-6CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The authors report the use of a new, sterically hindered ligand, sodium 4,7-diisopropyl-1-(2-ethanethiolate)-1,4,7-triazacyclononane (LN3S), for the isolation of the 1st example of a complex with a M2(μ-SR)2 [M = Cu(II)] core, which was subjected to structural studies oriented toward relating its properties to those of the cytochrome c oxidase and nitrous oxide reductase electron transfer sites. [LN3SCu]2(ClO4)2 (3), was isolated as dark green crystals in 62% yield by mixing LN3S and cupric triflate in THF, followed by anion metathesis. Compd.3 was characterized as a solid by elemental anal., x-ray crystallog., and EXAFS spectroscopy and in MeOH soln. by conductance measurements, electrospray mass spectrometry, cyclic voltammetry, and EPR, FTIR, and UV-visible spectroscopy. The complex contains two symmetry related square pyramidal Cu(II) ions liked by the thiolate arms of the LN3S ligands [Cu···Cu = 3.340(3) Å, Cu-S(av.) = 2.33 Å, Cu-S-Cu = 91.52(3)°], with a cis disposition of the axial N donors accompanying a butterfly distortion of the Cu2(μ-SR)2 core (146.5° angle between S-Cu-S planes). A well-resolved Cu-Cu peak at 3.27(7) Å in the EXAFS spectrum establishes that Cu-Cu interactions can be obsd. for dicopper sites with bis(thiolate) connectivity at distances well >3 Å, a result relevant to the interpretation of EXAFS data for CuA sites in proteins. Crystal data for [LN3SCu]2(ClO4)2·MeOCMe3 [3·MeOCMe3]: MW = 959.07, C33H72Cl2Cu2N6O9S2, orthorhombic, space group Pbcm, a 12.5618(8), b 13.4153(9), c 26.312(2) Å, Z = 4, ρcald = 1.437 g cm-2, 2θmax = 48.12°, Mo Kα radiation (λ = 0.71073 Å), T = 193 K. Data were collected using the Siemens SMART system and the structure was solved via direct methods. Full-matrix least squares refinement on F2 using SHELXS-PLUS converged with final R = 0.0386 and Rw = 0.0893 for 3568 independent reflections with I > 2σ(I) and 283 parameters.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosF2jsbs%253D&md5=7caaa7389aeb986d66f935276106884e
  91. 91
    Houser, R. P.; Young, V. G.; Tolman, W. B. A Thiolate-Bridged, Fully Delocalized Mixed-Valence Dicopper(I, II) Complex That Models the CuA Biological Electron-Transfer Site. J. Am. Chem. Soc. 1996, 118, 2101– 2102,  DOI: 10.1021/ja953776m
    Google Scholar
    91
    A Thiolate-Bridged, Fully Delocalized Mixed-Valence Dicopper(I,II) Complex That Models the CuA Biological Electron-Transfer Site
    Houser, Robert P.; Young, Victor G., Jr.; Tolman, William B.
    Journal of the American Chemical Society (1996), 118 (8), 2101-2CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A novel complex, (LCu)2(O3SCF3) (1), that replicates essential elements of the structural and spectroscopic features of the unusual CuA metalloprotein electron transfer site was assembled by mixing the sodium salt of 1-isopropyl-5-mercaptoethyl-1,5-diazacyclooctane (HL) with Cu(O3SCF3)2 in a 3:2 ratio in MeOH. An x-ray crystal structure detn. of 1 revealed it to contain a planar {Cu2(μ-SR)2}1+ core comprised of symmetry-related copper ions in distorted trigonal pyramidal coordination environments (av. Cu···Cu = 2.92 Å, Cu-S = 2.27 Å, Cu-S-Cu = 80.0°). Crystal data: MW = 706.90, C23H46Cu2F3N4O3S3, monoclinic, space group P21/n, a 12.4726(3), b 17.9093(5), c 13.0768(3) Å, β 91.786(1)°, V = 2919.6(1) Å3, Z = 4, ρcalcd = 1.608 g cm-3, 2θmax = 50.14°, Mo Kα radiation (λ = 0.71073 Å), T = 173 K, R1 = 0.0444 and wR2 = 0.0867 for 5149 independent reflections with I > 2σ(I) and 393 parameters. Electrospray MS, cond., magnetic susceptibility, cyclic voltammetry, and optical absorption and EPR spectroscopic data confirmed that the binuclear core remains intact in soln. and that it is best formulated as a class III, fully delocalized mixed-valence species. Notably, the x-band EPR spectrum at 4.2 K contains a nearly axial signal with clearly recognizable 7-line hyperfine splitting in the lower field components (g1 = 2.010, g2 = 2.046, g3 = 2.204, A2Cu = 36.3 G, A2Cu = 49.9 G, as detd. by spectral simulation) that is strikingly similar to the signals reported for the CuA sites in nitrous oxide reductase, cytochrome c oxidase, and engineered proteins.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XovFGiuw%253D%253D&md5=e7eb829c288b115ef0af2f766c423176
  92. 92
    Tang, L.; Park, J.; Kim, H.-J.; Kim, Y.; Kim, S. J.; Chin, J.; Kim, K. M. Tight Binding and Fluorescent Sensing of Oxalate in Water. J. Am. Chem. Soc. 2008, 130, 12606– 12607,  DOI: 10.1021/ja804753n
    Google Scholar
    92
    Tight binding and fluorescent sensing of oxalate in water
    Tang, Lijun; Park, Jinhee; Kim, Hae-Jo; Kim, Youngmee; Kim, Sung Jin; Chin, Jik; Kim, Kwan Mook
    Journal of the American Chemical Society (2008), 130 (38), 12606-12607CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A dinuclear copper complex that binds tightly and selectively to oxalate over other dicarboxylates like malonate, succinate, and glutarate was developed. This receptor can be used for fluorescent detection of oxalate in water at physicol. pH by chemosensing ensemble approach. Crystal structure of oxalate bound to the receptor together with mol. mechanics and DFT computations provide insights into the tight and selective binding of the anion by the receptor.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtVChsLvE&md5=cbff81ccaca34afcfab13bd41cc482f7
  93. 93
    Cano, M.; Heras, J. V.; Santamaria, E.; Pinilla, E.; Monge, A.; Jones, C. J.; McCleverty, J. A. Trispyrazolylborate Degradation and the Crystal Structure of [Mo(NO)(CO)2{HB(OPri)(3-Pri-5-MeC3HN2)2}]. Polyhedron 1993, 12, 1711– 1714,  DOI: 10.1016/S0277-5387(00)87084-9
    Google Scholar
    93
    Trispyrazolylborate degradation and the crystal structure of the molybdenum complex, [Mo(NO)(CO)2{HB(OPr-iso)(3-Pr-iso-5-MeC3HN2)2}]
    Cano, Mercedes; Heras, Jose V.; Santamaria, Elena; Pinilla, Elena; Monge, Angeles; Jones, Christopher J.; McCleverty, Jon A.
    Polyhedron (1993), 12 (13), 1711-14CODEN: PLYHDE; ISSN:0277-5387.
    [Mo(NO){HB(OCHMe2)R2}(CO)2] (R = 3-isopropyl-5-methylpyrazol-1-yl) was isolated from an attempt to prep. [Mo(NO)(HBR3)(CO)2]. A crystal structure shows an isopropoxide group with the alkoxy O bound to the B and Mo atoms [Mo-O = 2.225(5) Å].
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXit1ektg%253D%253D&md5=691d1765a91d36d57b99d2f9f9578546
  94. 94
    Bellachioma, G.; Cardaci, G.; Gramlich, V.; Macchioni, A.; Pieroni, F.; Venanzi, L. M. Synthesis and Characterisation of Bis- and Tris-(pyrazol-1-yl)borate Acetyl Complexes of FeII and RuII and Isolation of an Intermediate of B–N Bond Hydrolysis. J. Chem. Soc., Dalton Trans. 1998, 947– 952,  DOI: 10.1039/a708291f
    Google Scholar
    94
    Synthesis and characterization of bis- and tris-(pyrazol-1-yl)borate acetyl complexes of FeII and RuII and isolation of an intermediate of B-N bond hydrolysis
    Bellachioma, Gianfranco; Cardaci, Giuseppe; Gramlich, Volker; Macchioni, Alceo; Pieroni, Federica; Venanzi, Luigi M.
    Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1998), (6), 947-952CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
    Cis,trans-[MI(Me)(CO)2(PMe3)2] (M = Fe, 1a or Ru, 1b) reacted with K[(pz)2BH2] and Na[(pz)3BH] in CH2Cl2, affording the acetyl complexes trans-[M(COMe){(pz)2BH2}(CO)(PMe3)2] (2a and 2b) and trans-[M(COMe){κ2-(pz)3BH}(CO)(PMe3)2] (3a and 3b), resp. If the reactions are carried out in polar solvents decompn. of both starting materials occurs. Upon standing in n-hexane soln., the free pyrazol-1-yl arm in complex 3a displaces a coordinated PMe3 forming [Fe(COMe){κ3-(pz)3BH}(CO)(PMe3)] (4a). The analogous ruthenium complex was formed directly from the tricarbonyl complex fac-[RuI(Me)(CO)3(PMe3)] (5) with Na[(pz)3BH]. One of the intermediates of the decompn. of a pyrazolyl donor, trans-[Fe(COMe){κ2-(mpz)OB(C8H14)}(CO)(PMe3)2] (6, mpz = 3-methylpyrazolyl), was isolated from the reaction of 1a with K[(mpz)2B(C8H14)]. This complex was fully characterized both in soln. (IR, multinuclear and multidimensional NMR spectroscopy) and in the solid state by x-ray single-crystal diffraction (monoclinic, space group P21/c, R = 0.0671).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXhtlGit7c%253D&md5=1c2a3d3c7bc349a6998faf564421131b
  95. 95
    Lee, C.-L.; Wu, Y.-Y.; Wu, C.-P.; Chen, J.-D.; Keng, T.-C.; Wang, J.-C. Synthesis and Structural Characterization of Face-Sharing Bioctahedral Complexes Containing Poly(pyrazolyl)borate Ligands: [HB(Me2Pz)3BH][X3Mo(μ-X)2(μ-H)MoTp*] (X = Cl or Br; Tp*=HB(Me2Pz)3; Pz = pyrazolyl). Inorg. Chim. Acta 1999, 292, 182– 188,  DOI: 10.1016/S0020-1693(99)00187-5
    Google Scholar
    95
    Synthesis and structural characterization of face-sharing bioctahedral complexes containing poly(pyrazolyl)borate ligands: [HB(Me2Pz)3BH][X3Mo(μ-X)2(μ-H)MoTp*] (X = Cl or Br; Tp* = HB(Me2Pz)3; Pz = pyrazolyl)
    Lee, C.-L.; Wu, Y.-Y.; Wu, C.-P.; Chen, J.-D.; Keng, T.-C.; Wang, J.-C.
    Inorganica Chimica Acta (1999), 292 (2), 182-188CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science S.A.)
    From a soln. prepd. by reaction of Mo2(O2CCH3)4 with KTp* (Tp* = hydridotris(3,5-dimethylpyrazolyl)borate, HB(Me2Pz)3), in glyme at room temp., followed by addn. of Me3SiCl and Me3SiBr to the red soln. in refluxing THF, brown [HB(Me2Pz)3BH][Cl3Mo(μ-Cl)2(μ-H)MoTp*] (1), and [HB(Me2Pz)3BH][Br3Mo(μ-Br)2(μ-H)MoTp*] (2), resp., can be prepd. A pink product [HB(Me2Pz)3BH][MoBr4(Me2PzH)2] (3), was also obtained during the prepn. of 2. Their structures were detd. by x-ray crystallog. The anions of complexes 1 and 2 consist of two octahedra sharing a common triangular face (face-sharing bioctahedral, FSBO), so that the Mo atoms are bridged by one H and two halogen atoms. The unsym. metal centers are also chelated by tridentate Tp* ligands and coordinated by three halogen atoms. In contrast to the sym. [Mo2X8H]3- (X = Cl, Br or I) ions whose Mo-Mo distances are hardly affected by the change in the size of the bridging halide atom, the variation of the Mo-Mo distance from 1 to 2 is ∼0.040 Å. The formation of [HB(Me2Pz)3BH]+ and [MoBr4(Me2PzH)2]- shows the ready B-N bond cleavage of the Tp* ligand.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlt1WlsrY%253D&md5=f32e7d8cef88ee241f1475ceffb456f3
  96. 96
    Chia, L. M. L.; Radojevic, S.; Scowen, I. J.; McPartlin, M.; Halcrow, M. A. Steric Control of the Reactivity of Moderately Hindered Tris(pyrazolyl)borates with Copper(II) Salts. J. Chem. Soc., Dalton Trans. 2000, 133– 140,  DOI: 10.1039/a907258f
    Google Scholar
    There is no corresponding record for this reference.
  97. 97
    Carmona, E.; Cingolani, A.; Marchetti, F.; Pettinari, C.; Pettinari, R.; Skelton, B. W.; White, A. H. Synthesis and Structural Characterization of Mixed-Sandwich Complexes of Rhodium(III) and Iridium(III) with Cyclopentadienyl and Hydrotris(pyrazolyl)borate Ligands. Organometallics 2003, 22, 2820– 2826,  DOI: 10.1021/om020930m
    Google Scholar
    97
    Synthesis and Structural Characterization of Mixed-Sandwich Complexes of Rhodium(III) and Iridium(III) with Cyclopentadienyl and Hydrotris(pyrazolyl)borate Ligands
    Carmona, Ernesto; Cingolani, Augusto; Marchetti, Fabio; Pettinari, Claudio; Pettinari, Riccardo; Skelton, Brian W.; White, Allan H.
    Organometallics (2003), 22 (14), 2820-2826CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
    MCp*(Tp')Cl (M = Rh or Ir, Cp* = pentamethylcyclopentadienyl, Tp' = hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*)) complexes have been synthesized by reaction of the appropriate [(Cp*)MCl2]2 with KTp'. Reaction between MCp*(Tp)Cl and AgNO3 in acetonitrile affords ionic [M(Cp*)Tp]NO3 species, whereas with MCp*(Tp*)Cl B-N bond cleavage within the Tp* ligand occurs. B-N bond scission is also detected during the interaction of [MCp*Cl2]2 complexes with KTp' salts when the reactions are carried out in air for extended periods of time, providing pyrazole derivs., e.g., RhCp*Cl2(pz*H), (pz*H = 3,5-dimethylpyrazole). Two different compds. have been obtained from the reaction of KBp (Bp = dihydrobis(pyrazolyl)borate) and [IrCp*Cl2]2, namely, monomeric IrCp*Cl2(pzH) and the binuclear [IrCp*Cl]2(μ-Cl)(μ-pz), which contains bridging chloride and pyrazolate groups. In contrast, the analogous reaction of [RhCp*Cl2]2 with KBp produces RhCp*(Bp)Cl. Crystal structure detns. have been performed for some of the complexes. IR data indicate κ3-Tp binding for [MCp*Tp]NO3; moreover, the expected correlation between ν(B-H) and the Tp' hapticity is found for MCp*Tp' systems.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjvVWrt7w%253D&md5=de2bc7b92fe42c6babd2de8b8cba71b5
  98. 98
    Morawitz, T.; Zhang, F.; Bolte, M.; Bats, J. W.; Lerner, H.-W.; Wagner, M. Di- and Tritopic Poly(pyrazol-1-yl)borate Ligands: Synthesis, Characterization, and Reactivity toward [Mn(CO)5Br]. Organometallics 2008, 27, 5067– 5074,  DOI: 10.1021/om800504r
    Google Scholar
    98
    Di- and Tritopic Poly(pyrazol-1-yl)borate Ligands: Synthesis, Characterization, and Reactivity toward [Mn(CO)5Br]
    Morawitz, Thorsten; Zhang, Fan; Bolte, Michael; Bats, Jan W.; Lerner, Hans-Wolfram; Wagner, Matthias
    Organometallics (2008), 27 (19), 5067-5074CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
    Treatment of the ditopic phenylene-bridged bis(pyrazol-1-yl)borate K2[m-C6H4(B(tBu)pz2)2] (m-1) with [Mn(CO)5Br] results in ligand degrdn. with formation of the pyrazabole-bridged macrocyclic dimer {m-C6H4(B(tBu)pz)2}2 (2) and the triply pyrazolide-bridged dinuclear complex K[(OC)3Mn(μ-pz)3Mn(CO)3] (3). Even though the Ph-substituted scorpionate ligands Li2[m-C6H4(B(Ph)pz2)2] and Li2[p-C6H4(B(Ph)pz2)2] (m-5, p-5) possess a significantly higher hydrolytic stability than m-1, their reaction with [Mn(CO)5Br] also leads to B-N bond cleavage and gives the 3-type complex Li[(OC)3Mn(μ-pz)2(μ-Br)Mn(CO)3] (6). When, however, the corresponding tris(pyrazol-1-yl)borate ligands Li2[m-C6H4(Bpz3)2] and Li2[p-C6H4(Bpz3)2] (m-8, p-8) are employed, the clean formation of dinuclear Mn(CO)3 complexes Li2[m-C6H4(Bpz3Mn(CO)3)2] and Li2[p-C6H4(Bpz3Mn(CO)3)2] (m-11, p-11) is obsd. The same is true for the novel tritopic scorpionate Li3[1,3,5-C6H3(Bpz3)3] (10), which gives ready access to the trinuclear Mn(CO)3 complex [1,3,5-C6H3(Bpz3Mn(CO)3)3] (12).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtV2lu7bO&md5=333c083d3bae706300a2e7cd972ece04
  99. 99
    Harding, D. J.; Harding, P.; Daengngern, R.; Yimklan, S.; Adams, H. Synthesis and Characterization of Redox-Active Tris(pyrazolyl)borate Cobalt Complexes. Dalton Trans. 2009, 1314– 1320,  DOI: 10.1039/b815001j
    Google Scholar
    99
    Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes
    Harding, David J.; Harding, Phimphaka; Daengngern, Rathawat; Yimklan, Saranphong; Adams, Harry
    Dalton Transactions (2009), (8), 1314-1320CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    The reaction of CoX2 (X = Cl, Br, NO3) with KTpPh2 (hydrotris(3,5-diphenylpyrazolyl)borate) in THF yields the half-sandwich compds. [TpPh2CoX] (X = Cl 1, Br 2, NO3 3). The reaction of [TpPh2CoBr] with NaX (X = N3, NO2) or KSCN (KNCS) permits isolation of [TpPh2CoX] (X = N3 4, NCS 5, NO2 6). In contrast, the reaction of Co(OAc)2 with KTpPh2 yields [TpPh2Co(OAc)(HpzPh2)] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of β-diketones in the presence of NaOMe produces the β-diketonate complexes, [TpPh2Co(β-diketonate)] (β-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the TpPh2 ligands are κ3-coordinated and that the β-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in soln. X-ray crystallog. studies of 7 reveal an intermediate five-coordinate Co center with a H bonding interaction between the pyrazole H and the acetate carbonyl O. The mol. structures of 9 and 10 show Co centers with square pyramidal coordination geometries and κ2-coordinated β-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible 1-electron redn. to Co(I). However, the β-diketonate complexes, 8, 10 and 11 undergo irreversible 1-electron oxidn. The redox potential and reversibility increases as the steric bulk of the substituent on the β-diketonate ligand increases.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhs1eqtLg%253D&md5=9aea75e22909be90619191335621b11a
  100. 100
    Paine, T. K.; Zheng, H.; Que, L. Iron Coordination Chemistry of Phenylpyruvate: An Unexpected κ3-Bridging Mode That Leads to Oxidative Cleavage of the C2-C3 Bond. Inorg. Chem. 2005, 44, 474– 476,  DOI: 10.1021/ic048427k
    Google Scholar
    100
    Iron Coordination Chemistry of Phenylpyruvate: An Unexpected κ3-Bridging Mode That Leads to Oxidative Cleavage of the C2-C3 Bond
    Paine, Tapan K.; Zheng, Hui; Que, Lawrence, Jr.
    Inorganic Chemistry (2005), 44 (3), 474-476CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    One mononuclear Fe(II)-phenylpyruvate complex [TpPh2FeII(PPH)] (1) of the tridentate face-capping TpPh2 ligand and two dinuclear Fe(II)-phenylpyruvate enolate complexes [(6-Me3-TPA)2FeII2(PP)]2+ (2) and [(6-Me3-TPA)2FeII2(2-NO2-PP)]2+ (3) of the tetradentate 6-Me3-TPA ligand are reported to demonstrate two different binding modes of phenylpyruvate to the Fe(II) centers. Phenylpyruvate binds in a κ2-(O,O) manner to the mononuclear FeII(TpPh2) center of 1 but bridges in a κ3-(O,O,O) fashion to the two FeII(6-Me3-TPA) centers of 2 and 3. Mononuclear complex 1 reacts with O2 to undergo oxidative decarboxylation and ortho-hydroxylation of one of the arom. rings of the TpPh2 ligand. In contrast, dinuclear complexes 2 and 3 react with O2 to undergo oxidative cleavage of the C2-C3 bond of phenylpyruvate.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXosFGj&md5=50c438e2a127f6d9e144fd8f86bbfaf3
  101. 101
    Mukherjee, A.; Cranswick, M. A.; Chakrabarti, M.; Paine, T. K.; Fujisawa, K.; Münck, E.; Que, L. Oxygen Activation at Mononuclear Nonheme Iron Centers: A Superoxo Perspective. Inorg. Chem. 2010, 49, 3618– 3628,  DOI: 10.1021/ic901891n
    Google Scholar
    101
    Oxygen Activation at Mononuclear Nonheme Iron Centers: A Superoxo Perspective
    Mukherjee, Anusree; Cranswick, Matthew A.; Chakrabarti, Mrinmoy; Paine, Tapan K.; Fujisawa, Kiyoshi; Munck, Eckard; Que, Lawrence. Jr.
    Inorganic Chemistry (2010), 49 (8), 3618-3628CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Dioxygen (O2) activation by iron enzymes is responsible for many metabolically important transformations in biol. Often a high-valent iron oxo oxidant is proposed to form upon O2 activation at a mononuclear nonheme iron center, presumably via intervening iron superoxo and iron peroxo species. While iron(IV) oxo intermediates have been trapped and characterized in enzymes and models, less is known of the putative iron(III) superoxo species. Utilizing a synthetic model for the 2-oxoglutarate-dependent mono-iron enzymes, [(TpiPr2)FeII(O2CC(O)CH3)], we have obtained indirect evidence for the formation of the putative iron(III) superoxo species, which can undergo one-electron redn., hydrogen-atom transfer, or conversion to an iron(IV) oxo species, depending on the reaction conditions. These results demonstrate the various roles that the iron(III) superoxo species can play in the course of O2 activation at a nonheme iron center.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXkt1Glu74%253D&md5=ba78c62bdd124da8335bd28b67ed1757
  102. 102
    Chakraborty, B.; Halder, P.; Banerjee, P. R.; Paine, T. K. Oxidative C–C Bond Cleavage of α-Keto Acids by Cobalt(II) Complexes of Nitrogen Donor Ligands. Eur. J. Inorg. Chem. 2012, 2012, 5843– 5853,  DOI: 10.1002/ejic.201200663
    Google Scholar
    102
    Oxidative C-C Bond Cleavage of α-Keto Acids by Cobalt(II) Complexes of Nitrogen Donor Ligands
    Chakraborty, Biswarup; Halder, Partha; Banerjee, Priya Ranjan; Paine, Tapan Kanti
    European Journal of Inorganic Chemistry (2012), 2012 (35), 5843-5853CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Four Co(II) complexes, [(6Me3TPA)CoII(BF)](BPh4) (1), [(TPA)CoII(BF)](BPh4) (2), [{(6Me3TPA)CoII}2(PP)](BPh4)2 (3), and [(TPA)CoII(PPH)](BPh4) (4) [where 6Me3TPA = tris(6-methyl-2-pyridylmethyl)amine, TPA = tris(2-pyridylmethyl)amine, BF = monoanionic benzoylformate, PP = dianionic phenylpyruvate, and PPH = monoanionic phenylpyruvate], of α-keto acid derivs. were isolated to show their versatile reactivity with dioxygen. The x-ray crystal structure of 2 suggests a five-coordinate Co(II) center coordinated by a monodentate benzoylformate and a tetradentate N-donor supporting ligand. Conversely, complex 3 is a dinuclear Co complex where two Co(II) centers are bridged by PP. While complex 1 is unreactive towards dioxygen, 2 reacts slowly with O2 to exhibit quant. decarboxylation of coordinated benzoylformate to benzoate. An active Co-O intermediate, intercepted by external substrates, is proposed to initiate the decarboxylation reaction. Complex 3 also reacts with dioxygen, but to cleave the C2-C3 bond of PP with concomitant formation of benzaldehyde and an oxalate-bridged dicobalt(II) complex [{(6Me3TPA)CoII}2(oxalate)](BPh4)2 (5). The mononuclear PPH-Co(II) complex (4), unlike 2 and 3, does not undergo oxidative decarboxylation or C-C bond cleavage of PPH. In the reaction with dioxygen, 4 is oxidized to a PP-Co(III) complex, [(TPA)CoIII(PP)](BPh4) (6), as established from the x-ray single-crystal structure.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsVKqs7bK&md5=3ba622a676780cc1752b49280122d0b9
  103. 103
    Diebold, A. R.; Straganz, G. D.; Solomon, E. I. Spectroscopic and Computational Studies of α-Keto Acid Binding to Dke1: Understanding the Role of the Facial Triad and the Reactivity of β-Diketones. J. Am. Chem. Soc. 2011, 133, 15979– 15991,  DOI: 10.1021/ja203005j
    Google Scholar
    103
    Spectroscopic and Computational Studies of α-Keto Acid Binding to Dke1: Understanding the Role of the Facial Triad and the Reactivity of β-Diketones
    Diebold, Adrienne R.; Straganz, Grit D.; Solomon, Edward I.
    Journal of the American Chemical Society (2011), 133 (40), 15979-15991CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The O2 activating mononuclear nonheme iron enzymes generally have a common facial triad (two histidine and one carboxylate (Asp or Glu) residue) ligating FeII at the active site. Exceptions to this motif have recently been identified in nonheme enzymes, including a 3His triad in the diketone cleaving dioxygenase Dke1. This enzyme is used to explore the role of the facial triad in directing reactivity. A combination of spectroscopic studies (UV-vis absorption, MCD, and resonance Raman) and DFT calcns. is used to define the nature of the binding of the α-keto acid, 4-hydroxyphenylpyruvate (HPP), to the active site in Dke1 and the origin of the atypical cleavage (C2-C3 instead of C1-C2) pattern exhibited by this enzyme in the reaction of α-keto acids with dioxygen. The reduced charge of the 3His triad induces α-keto acid binding as the enolate dianion, rather than the keto monoanion, found for α-keto acid binding to the 2His/1 carboxylate facial triad enzymes. The mechanistic insight from the reactivity of Dke1 with the α-keto acid substrate is then extended to understand the reaction mechanism of this enzyme with its native substrate, acac. This study defines a key role for the 2His/1 carboxylate facial triad in α-keto acid-dependent mononuclear nonheme iron enzymes in stabilizing the bound α-keto acid as a monoanion for its decarboxylation to provide the two addnl. electrons required for O2 activation.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFOmsbrP&md5=15147f9b2dc597e0bbd5c527064be83c
  104. 104
    Davies, M. B. Reactions of L-Ascorbic Acid with Transition Metal Complexes. Polyhedron 1992, 11, 285– 321,  DOI: 10.1016/S0277-5387(00)83175-7
    Google Scholar
    104
    Reactions of L-ascorbic acid with transition metal complexes
    Davies, Michael B.
    Polyhedron (1992), 11 (3), 285-321CODEN: PLYHDE; ISSN:0277-5387.
    A review with 144 refs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xhs1Cqtrs%253D&md5=b901d179216aac0a8022d811500a7ca8
  105. 105
    Shen, J.; Griffiths, P. T.; Campbell, S. J.; Utinger, B.; Kalberer, M.; Paulson, S. E. Ascorbate Oxidation by Iron, Copper and Reactive Oxygen Species: Review, Model Development, and Derivation of Key Rate Constants. Sci. Rep. 2021, 11, 7417,  DOI: 10.1038/s41598-021-86477-8
    Google Scholar
    105
    Ascorbate oxidation by iron, copper and reactive oxygen species: review, model development, and derivation of key rate constants
    Shen, Jiaqi; Griffiths, Paul T.; Campbell, Steven J.; Utinger, Battist; Kalberer, Markus; Paulson, Suzanne E.
    Scientific Reports (2021), 11 (1), 7417CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
    Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biol. response. Because ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical org. mol., reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chem., but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chem. kinetics model, and use seven sets of lab. measurements to constrain mechanisms for the iron and copper reactions and derive key rate consts. We find that micromolar concns. of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH2 and AH-) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II) + AH2/AH- + O2 → Fe(III)/Cu(II) + H2O2 + products. Rate consts. are 5.7 x 104 and 4.7 x 104 M-2 s-1 for Fe(III) + AH2/AH- and 7.7 x 104 and 2.8 x 106 M-2 s-1 for Cu(II) + AH2/AH-, resp.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXot1Gjt74%253D&md5=edd3a64a413681ab66b27fe70f8162ce
  106. 106
    Peldszus, S.; Huck, P. M.; Andrews, S. A. Quantitative Determination of Oxalate and Other Organic Acids in Drinking Water at Low μg/l Concentrations. J. Chromatogr. A 1998, 793, 198– 203,  DOI: 10.1016/S0021-9673(97)00854-6
    Google Scholar
    106
    Quantitative determination of oxalate and other organic acids in drinking water at low μg/l concentrations
    Peldszus, Sigrid; Huck, Peter M.; Andrews, Susan A.
    Journal of Chromatography A (1998), 793 (1), 198-203CODEN: JCRAEY; ISSN:0021-9673. (Elsevier Science B.V.)
    In this research, a recently developed ion chromatog. method for org. acids was expanded to include oxalate. A major challenge was that oxalate elutes between inorg. anions such as sulfate, phosphate, bromide and nitrate, which are often present in much higher concns. than oxalate. Optimization of the previously reported method made it possible to det. oxalate in these matrixes. However, for those samples in which higher inorg. anion concns. caused the oxalate peak to be obscured, a "heart-cut" column switching technique was used as an alternative. The method detection limit for oxalate was 9 μg/L with the direct approach and 6 μg/L for the "heart-cut" technique. These modifications represent a valuable supplement to a recently developed method for monitoring ozonation byproducts in drinking water.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXotVyisbg%253D&md5=7bfdf55d7608336cb65be9a3f85dc5b2
  107. 107
    Li, H.; Liu, Y.; Zhang, Q.; Zhan, H. Determination of the Oxalate Content in Food by Headspace Gas Chromatography. Anal. Methods 2014, 6, 3720– 3723,  DOI: 10.1039/c4ay00032c
    Google Scholar
    107
    Determination of the oxalate content in food by headspace gas chromatography
    Li, Hailong; Liu, Yingying; Zhang, Qian; Zhan, Huaiyu
    Analytical Methods (2014), 6 (11), 3720-3723CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
    A novel method for the detn. of oxalate content in food is developed using headspace gas chromatog. (HS-GC) technol. This method is based on the reaction between oxalate and sodium bromate in an acidic medium, in which oxalate is converted to carbon dioxide that is measured by GC with a thermal conductive detector. It was found that a complete conversion of oxalate to carbon dioxide can be achieved at a temp. of 70 °C within 4 min. The optimal reaction conditions obtained in the present work also minimize the side reactions caused by interfering species, such as org. acid and alcs., with sodium bromate. The present method is simple, rapid, accurate, and very suitable for use in quantification of oxalate content in food.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXotFOhurs%253D&md5=afe8f6f530e8adf85e9eebb437ce8d96
  108. 108
    Li, H.; Chai, X.-S.; DeMartini, N.; Zhan, H.; Fu, S. Determination of Oxalate in Black Liquor by Headspace Gas Chromatography. J. Chromatogr. A 2008, 1192, 208– 211,  DOI: 10.1016/j.chroma.2008.03.066
    Google Scholar
    108
    Determination of oxalate in black liquor by headspace gas chromatography
    Li, Hailong; Chai, Xin-Sheng; DeMartini, Nikolai; Zhan, Huaiyu; Fu, Shiyu
    Journal of Chromatography A (2008), 1192 (2), 208-211CODEN: JCRAEY; ISSN:0021-9673. (Elsevier B.V.)
    This study demonstrated a headspace gas chromatog. method (HS-GC) for the detn. of oxalate content in black liquor (alk. aq. soln. of inorg. chems. and dissolved wood species from the alk. pulping of wood). The method described in this paper is based on the reaction between oxalic and manganese dioxide in an acidic medium, in which oxalic acid is converted to carbon dioxide that is measured with a GC using a thermal cond. detector. The challenge in developing this method was ensuring complete conversion of oxalic acid while minimizing the contribution of side reactions between carbohydrates, lignin and manganese dioxide to the carbon dioxide measured. It was found that a complete conversion of oxalate to carbon dioxide can be achieved within 3 min at a temp. of 70 °C; a MnO2:C oxalate (concn. of H2C2O4 + HC2O4 - + C2O4 2-) mole ratio of 60 and H2SO4 concn. of 0.005-0.01 mol/L in the headspace vial. The method can detect concns. as low as 0.39 μg of oxalate. The std. deviation was found to be 7% while recovery expts. with black liquor showed recoveries of 93-108% which were deemed acceptable for anal. of oxalate in an industrial sample such as black liquor.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlslyntbg%253D&md5=de56b0eadfccaa88ba793e25ba41b230
  109. 109
    Judprasong, K.; Charoenkiatkul, S.; Sungpuag, P.; Vasanachitt, K.; Nakjamanong, Y. Total and Soluble Oxalate Contents in Thai Vegetables, Cereal Grains and Legume Seeds and Their Changes after Cooking. J. Food Compost. Anal. 2006, 19, 340– 347,  DOI: 10.1016/j.jfca.2005.04.002
    Google Scholar
    There is no corresponding record for this reference.
  110. 110
    Clausen, C. A.; Kenealy, W.; Lebow, P. K. Oxalate Analysis Methodology for Decayed Wood. Int. Biodeter. Biodegr. 2008, 62, 372– 375,  DOI: 10.1016/j.ibiod.2008.04.001
    Google Scholar
    There is no corresponding record for this reference.

Cited By

Click to copy section linkSection link copied!

This article is cited by 6 publications.

  1. Florian Keller, Johannes Döhn, Axel Groß, Michael Busch. Exploring the Mechanism of the Electrochemical Polymerization of CO2 to Hard Carbon over CeO2(110). The Journal of Physical Chemistry C 2024, 128 (15) , 6280-6293. https://doi.org/10.1021/acs.jpcc.3c08356
  2. Stella A. Fors, Christian A. Malapit. Homogeneous Catalysis for the Conversion of CO2, CO, CH3OH, and CH4 to C2+ Chemicals via C–C Bond Formation. ACS Catalysis 2023, 13 (7) , 4231-4249. https://doi.org/10.1021/acscatal.2c05517
  3. Vera Boor, Jeannine E. B. M. Frijns, Elena Perez-Gallent, Erwin Giling, Antero T. Laitinen, Earl L. V. Goetheer, Leo J. P. van den Broeke, Ruud Kortlever, Wiebren de Jong, Othonas A. Moultos, Thijs J. H. Vlugt, Mahinder Ramdin. Electrochemical Reduction of CO2 to Oxalic Acid: Experiments, Process Modeling, and Economics. Industrial & Engineering Chemistry Research 2022, 61 (40) , 14837-14846. https://doi.org/10.1021/acs.iecr.2c02647
  4. Rong Zhao, Zhipeng Lin, Isaac Maksso, Julia Struwe, Lutz Ackermann. Electrochemical Cross‐Electrophile‐Coupling for Transition‐Metal‐Free Allylic Carboxylation with Ambient CO 2. ChemElectroChem 2022, 9 (21) https://doi.org/10.1002/celc.202200989
  5. Hong‐Qing Liang, Torsten Beweries, Robert Francke, Matthias Beller. Molecular Catalysts for the Reductive Homocoupling of CO 2 towards C 2+ Compounds. Angewandte Chemie 2022, 134 (19) https://doi.org/10.1002/ange.202200723
  6. Hong‐Qing Liang, Torsten Beweries, Robert Francke, Matthias Beller. Molecular Catalysts for the Reductive Homocoupling of CO 2 towards C 2+ Compounds. Angewandte Chemie International Edition 2022, 61 (19) https://doi.org/10.1002/anie.202200723
Download PDF
Open PDF
Go to JACS Au
Get e-Alerts
Get e-Alerts

JACS Au

Cite this: JACS Au 2022, 2, 3, 731–744
Click to copy citationCitation copied!
https://doi.org/10.1021/jacsau.2c00005
Published February 14, 2022

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY-NC-ND 4.0 .

Article Views

8764

Altmetric

-

Citations

6
Learn about these metrics

Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.

Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.

The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. Selected examples highlighting the progress in CO2 utilization as a C1 building block or reduction into C1 and C≥2 products as well as potential products derived from oxalic acid.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. Selected examples for the formation of oxalate complexes from CO2 and CO2 reductive coupling with strong reductants. (58,61−65) The reactions with complexes 1–3 are discussed herein.

    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 1

    Scheme 1. Reduction of [Fe(tmtaa)] to Complex 7 and Observed Products of Subsequent Reaction with CO2 Highlighting the Absence of Oxalate
    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. Compound 10 and the molecular structure of [(L1)Cu(μ-OH)2Cu(L1)]2+ in 10 (thermal ellipsoids displayed at 30% probability and C-bound H atoms omitted for clarity; symmetry operator for generating equivalent atoms: −x + 1, −y + 1, −z + 1).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. Molecular structure of [(L1)Cu(μ-C2O4)Cu(L1)]2+ in 13 (thermal ellipsoids displayed at 30% probability and H atoms omitted for clarity; symmetry operator for generating equivalent atoms: −x, −y + 1, −z + 1).

    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 2

    Scheme 2. Synthesis of Ligand L4 and Its Derived CuI Complex 19 and (Left) Molecular Structure of 19a
    High Resolution Image
    Download MS PowerPoint Slide

    aThermal ellipsoids are displayed at 30% probability, and H atoms are omitted for clarity.

    Figure 5

    Figure 5. FTIR spectra from reaction of complexes 9 and 20 with air and CO2/O2 in DCM and toluene, respectively (FTIR spectra of 9 and 20 are displayed for comparison).

    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 3

    Scheme 3. Reaction of Complexes 9 or 20 with Air or CO2/O2 and Subsequent Treatment with NaOH in H2O/Toluene
    High Resolution Image
    Download MS PowerPoint Slide

    Figure 6

    Figure 6. 13C NMR spectroscopic analysis of the NaOH extract from the reaction of 20 with air.

    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 4

    Scheme 4. Reactions of Different Sodium α-Ketocarboxylates in Combination with a Cu2+ Source under Oxidative Conditions and Subsequent NaOH Treatment for Analysis via NMR and CE
    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 5

    Scheme 5. Revised Reaction of [Fe(tmtaa)] with Strong Reductants Followed by CO2 Treatment Yielding “CO” and M2CO3 but Not M2C2O4
    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 6

    Scheme 6. Irreproducibility in the Formation of Oxalate from CO2 or MHCO3 with [CuI(NNN)]+ Complexes Studied under Various Conditions, with Multiple Ligands and Different Additives
    High Resolution Image
    Download MS PowerPoint Slide

    Scheme 7

    Scheme 7. Proposed Reaction Pathway for the Formation of Oxalate and Acetone via Oxidative C2–C3 Bond Cleavagea
    High Resolution Image
    Download MS PowerPoint Slide

    aIsobutyric acid and 2-hydroxyisobutyric acid were identified, presumably resulting from oxidative decarboxylation upon C1–C2 bond scission.

  • References

    This article references 110 other publications.

    1. 1
      Appel, A. M.; Bercaw, J. E.; Bocarsly, A. B.; Dobbek, H.; DuBois, D. L.; Dupuis, M.; Ferry, J. G.; Fujita, E.; Hille, R.; Kenis, P. J. A.; Kerfeld, C. A.; Morris, R. H.; Peden, C. H. F.; Portis, A. R.; Ragsdale, S. W.; Rauchfuss, T. B.; Reek, J. N. H.; Seefeldt, L. C.; Thauer, R. K.; Waldrop, G. L. Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation. Chem. Rev. 2013, 113, 6621– 6658,  DOI: 10.1021/cr300463y
      1
      Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation
      Appel, Aaron M.; Bercaw, John E.; Bocarsly, Andrew B.; Dobbek, Holger; DuBois, Daniel L.; Dupuis, Michel; Ferry, James G.; Fujita, Etsuko; Hille, Russ; Kenis, Paul J. A.; Kerfeld, Cheryl A.; Morris, Robert H.; Peden, Charles H. F.; Portis, Archie R.; Ragsdale, Stephen W.; Rauchfuss, Thomas B.; Reek, Joost N. H.; Seefeldt, Lance C.; Thauer, Rudolf K.; Waldrop, Grover L.
      Chemical Reviews (Washington, DC, United States) (2013), 113 (8), 6621-6658CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atm. CO2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atm. CO2. Providing a future energy supply that is secure and CO2-neutral will require switching to non-fossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored,transported, and used upon demand. This Review describes the results of a workshop held to explore these concepts in regard to the development of new and more efficient catalytic processes for the conversion of CO2 to a variety of carbon-based fuels.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsFWqsLs%253D&md5=f8e57b72f24de79c3ec80ffe95eacd34
    2. 2
      Aresta, M.; Dibenedetto, A.; Angelini, A. Catalysis for the Valorization of Exhaust Carbon: From CO2 to Chemicals, Materials, and Fuels. Technological Use of CO2. Chem. Rev. 2014, 114, 1709– 1742,  DOI: 10.1021/cr4002758
      2
      Catalysis for the Valorization of Exhaust Carbon: from CO2 to Chemicals, Materials, and Fuels. Technological Use of CO2
      Aresta, Michele; Dibenedetto, Angela; Angelini, Antonella
      Chemical Reviews (Washington, DC, United States) (2014), 114 (3), 1709-1742CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFegsrfP&md5=a773e4deabc012c1c86caf70f43239a4
    3. 3
      Liu, Q.; Wu, L.; Fleischer, I.; Selent, D.; Franke, R.; Jackstell, R.; Beller, M. Development of a Ruthenium/Phosphite Catalyst System for Domino Hydroformylation–Reduction of Olefins with Carbon Dioxide. Chem. Eur. J. 2014, 20, 6888– 6894,  DOI: 10.1002/chem.201400358
      3
      Development of a ruthenium/phosphite catalyst system for domino hydroformylation-reduction of olefins with carbon dioxide
      Liu, Qiang; Wu, Lipeng; Fleischer, Ivana; Selent, Detlef; Franke, Robert; Jackstell, Ralf; Beller, Matthias
      Chemistry - A European Journal (2014), 20 (23), 6888-6894CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      An efficient domino ruthenium-catalyzed reverse water-gas-shift-hydroformylation-redn. reaction of olefins to alcs. was reported. Key to success was the use of specific bulky phosphite ligands and triruthenium dodecacarbonyl as the catalyst. Compared to the known ruthenium/chloride system, the new catalyst allows for a more efficient hydrohydroxymethylation of terminal and internal olefins with carbon dioxide at lower temp. Unwanted hydrogenation of the substrate was prevented. Preliminary mechanism investigations uncovered the homogeneous nature of the active catalyst and the influence of the ligand and additive in individual steps of the reaction sequence.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXnslWgtLo%253D&md5=b01c278c53ad6911bf0624d8980797ff
    4. 4
      Wu, L.; Liu, Q.; Fleischer, I.; Jackstell, R.; Beller, M. Ruthenium-Catalysed Alkoxycarbonylation of Alkenes with Carbon Dioxide. Nat. Commun. 2014, 5, 3091,  DOI: 10.1038/ncomms4091
      4
      Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide
      Wu Lipeng; Liu Qiang; Fleischer Ivana; Jackstell Ralf; Beller Matthias
      Nature communications (2014), 5 (), 3091 ISSN:.
      Alkene carbonylations represent a major technology for the production of value-added bulk and fine chemicals. Nowadays, all industrial carbonylation processes make use of highly toxic and flammable carbon monoxide. Here we show the application of abundantly available carbon dioxide as C1 building block for the alkoxycarbonylations of industrially important olefins in the presence of a convenient and inexpensive ruthenium catalyst system. In our system, carbon dioxide works much better than the traditional combination of carbon monoxide and alcohols. The unprecedented in situ formation of carbon monoxide from carbon dioxide and alcohols permits an efficient synthesis of carboxylic acid esters, which can be used as detergents and polymer-building blocks. Notably, this transformation allows the catalytic formation of C-C bonds with carbon dioxide as C1 source and avoids the use of sensitive and/or expensive reducing agents (for example, Grignard reagents, diethylzinc or triethylaluminum).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2cvksVShtg%253D%253D&md5=cc752afda0372405681f067b7459d762
    5. 5
      Hong, J.; Li, M.; Zhang, J.; Sun, B.; Mo, F. C-H Bond Carboxylation with Carbon Dioxide. ChemSusChem 2019, 12, 6– 39,  DOI: 10.1002/cssc.201802012
      5
      C-H Bond Carboxylation with Carbon Dioxide
      Hong, Junting; Li, Man; Zhang, Jianning; Sun, Beiqi; Mo, Fanyang
      ChemSusChem (2019), 12 (1), 6-39CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Carbon dioxide is a nontoxic, renewable, and abundant C1 source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chem. transformation of CO2 with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivs. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp2)-H bonds of (hetero)arenes, vinylic C(sp2)-H bonds, the ipso-C(sp2)-H bonds of the diazo group, aldehyde C(sp2)-H bonds, α-C(sp3)-H bonds of the carbonyl group, γ-C(sp3)-H bonds of the carbonyl group, C(sp3)-H bonds adjacent to nitrogen atoms, C(sp3)-H bonds of o-alkyl Ph ketones, allylic C(sp3)-H bonds, C(sp3)-H bonds of methane, and C(sp3)-H bonds of halogenated aliph. hydrocarbons. In addn., multicomponent reactions, tandem reactions, and key theor. studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochem., and light-driven methods are highlighted.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXktFSlsw%253D%253D&md5=450d45909060f4bea4db3b1d0c103653
    6. 6
      Li, H.-R.; He, L.-N. Construction of C–Cu Bond: A Useful Strategy in CO2 Conversion. Organometallics 2020, 39, 1461– 1475,  DOI: 10.1021/acs.organomet.9b00642
      6
      Construction of C-Cu Bond: A Useful Strategy in CO2 Conversion
      Li, Hong-Ru; He, Liang-Nian
      Organometallics (2020), 39 (9), 1461-1475CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
      A review. Carbon dioxide is not only one of the greenhouse gas but also an appealing renewable C1 source. To reconcile the environment benefit with chem. industry development, CO2 conversion into valuable chems. is proposed and tremendous efforts have been devoted to developing new synthetic protocols and highly efficient catalytic systems, wherein copper catalysis is attractive and features effective, inexpensive and diverse transformation of CO2. Considering the ubiquity of C-Cu bond in org. chem. and the wide application of the resulting carbocuprate species in reductive coupling with electrophiles, the C-Cu formation and subsequent CO2 insertion has been developed as an important strategy for CO2 chem. fixation, thereby resulting in prepg. a variety of valuable chems. To arouse broad concern of this strategy, we summarize the recent advances and give an overview on CO2 transformations via the carbocuprate species on the basis of the C-Cu bond formation mechanism, including copper-promoted alkyne and halide activation, transmetalation of some specific chems. with copper and hydrocupration, borocupration, silylcupration of unsatd. substrates. It is hoped that this review can provide some clues for the further exploration in this field.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVygs7%252FL&md5=a9c4a88526d5b5390b1df16d00e157ed
    7. 7
      Juhl, M.; Laursen, S. L. R.; Huang, Y.; Nielsen, D. U.; Daasbjerg, K.; Skrydstrup, T. Copper-Catalyzed Carboxylation of Hydroborated Disubstituted Alkenes and Terminal Alkynes with Cesium Fluoride. ACS Catal. 2017, 7, 1392– 1396,  DOI: 10.1021/acscatal.6b03571
      7
      Copper-Catalyzed Carboxylation of Hydroborated Disubstituted Alkenes and Terminal Alkynes with Cesium Fluoride
      Juhl, Martin; Laursen, Simon L. R.; Huang, Yuxing; Nielsen, Dennis U.; Daasbjerg, Kim; Skrydstrup, Troels
      ACS Catalysis (2017), 7 (2), 1392-1396CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      In the presence of CuI and imidazolylidene or benzimidazolylidene ligands, boranes generated in situ from di- and trisubstituted alkenes (cyclohexenes, styrene, and stilbenes) and from terminal alkynes underwent chemo- and diastereoselective carboxylation with CO2 mediated by CsF to yield carboxylic acids and malonic acids. Five terpene-derived natural products and cholesteryl Me ether were used as reactants for copper-catalyzed carboxylations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVKhsbo%253D&md5=f2011c6252eb763569e327d43f70cdef
    8. 8
      Ukai, K.; Aoki, M.; Takaya, J.; Iwasawa, N. Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2. J. Am. Chem. Soc. 2006, 128, 8706– 8707,  DOI: 10.1021/ja061232m
      8
      Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2
      Ukai, Kazutoshi; Aoki, Masao; Takaya, Jun; Iwasawa, Nobuharu
      Journal of the American Chemical Society (2006), 128 (27), 8706-8707CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      When the esters of arylboronic acids with 2,2-dimethyl-1,3-propanol were treated with a catalytic amt. of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60 °C under carbon dioxide atm., the benzoic acid derivs. were obtained in good yields. Reactions of alkenylboronic esters also proceeded under similar conditions to give α,β-unsatd. carboxylic acids. As these boronic esters are now easily available through coupling or direct borylation reactions, this method would be a useful method for the prepn. of various functionalized aryl- and alkenyl carboxylic acids. For example, the rhodium-catalyzed reaction of a boronic acid ester, i.e., 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane, with carbon dioxide gave benzoic acid.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmtVSjsbo%253D&md5=0c880ab4e3f61a8cf0f5e6ddab46953c
    9. 9
      Coates, G. W.; Moore, D. R. Discrete Metal-Based Catalysts for the Copolymerization of CO2 and Epoxides: Discovery, Reactivity, Optimization, and Mechanism. Angew. Chem., Int. Ed. 2004, 43, 6618– 6639,  DOI: 10.1002/anie.200460442
      9
      Discrete metal-based catalysts for the copolymerization of CO2 and epoxides: Discovery, reactivity, optimization, and mechanism
      Coates, Geoffrey W.; Moore, David R.
      Angewandte Chemie, International Edition (2004), 43 (48), 6618-6639CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review on discovery, reactivity, optimization, and mechanism of discrete metal-based catalysts for polymn. of CO2 and epoxides. Given the non-renewable nature of these materials, there is increasing interest in developing routes to polymeric materials from renewable resources. There is a growing demand for biodegradable polymeric materials. Polycarbonates made from CO2 and epoxides have the potential to meet these goals. Since the discovery of catalysts for the copolymn. of CO2 and epoxides in the late 1960's by Inoue, a significant amt. of research has been directed toward the development of catalysts of improved activity and selectivity.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXos1yh&md5=c7aa69fd7ae451f8d02a9330c92b07ea
    10. 10
      Darensbourg, D. J. Making Plastics from Carbon Dioxide: Salen Metal Complexes as Catalysts for the Production of Polycarbonates from Epoxides and CO2. Chem. Rev. 2007, 107, 2388– 2410,  DOI: 10.1021/cr068363q
      10
      Making plastics from carbon dioxide: Salen metal complexes as catalysts for the production of polycarbonates from epoxides and CO2
      Darensbourg, Donald J.
      Chemical Reviews (Washington, DC, United States) (2007), 107 (6), 2388-2410CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review is given on the prepn. of polycarbonates (and some cyclic carbonates) from epoxides and carbon dioxide. The use of salicylaldimine-based complexes of chromium, cobalt, and aluminum is discussed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXksVSmurY%253D&md5=098c95c8b9de54de4c6c123c5f9c2ef7
    11. 11
      Liu, Q.; Wu, L.; Jackstell, R.; Beller, M. Using Carbon Dioxide as a Building Block in Organic Synthesis. Nat. Commun. 2015, 6, 5933,  DOI: 10.1038/ncomms6933
      11
      Using carbon dioxide as a building block in organic synthesis
      Liu, Qiang; Wu, Lipeng; Jackstell, Ralf; Beller, Matthias
      Nature Communications (2015), 6 (), 5933pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      A review. The most recent advances made in the area of CO2 valorization-turning CO2 into a useful chem. feedstock-under mild conditions has been reviewed. A special focus is given on the reaction modes for the CO2 activation and its application as C1 building block in org. synthesis. The following subjects will be addressed in this review : (1) novel transformations using carbon dioxide (briefly summarized); (2) different reaction modes for CO2 activation (main focus of this review); and (3) potential new applications of CO2 valorization.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtF2lurjM&md5=e3ba6b5612253c0c6ebec3d937f137f8
    12. 12
      Adachi, K.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of Carbon Dioxide to Hydrocarbon Using Copper-Loaded Titanium Dioxide. Sol. Energy 1994, 53, 187– 190,  DOI: 10.1016/0038-092X(94)90480-4
      12
      Photocatalytic reduction of carbon dioxide to hydrocarbon using copper-loaded titanium dioxide
      Adachi, Kenji; Ohta, Kiyohisa; Mizuno, Takayuki
      Solar Energy (1994), 53 (2), 187-90CODEN: SRENA4; ISSN:0038-092X.
      The photocatalytic redn. of CO2 using Cu-loaded TiO2 powd. catalyst was studied at ambient temp. The Cu-TiO2 powders suspended in the soln., which was pressurized with CO2 of 28 kg/cm2, were illuminated with a Xe lamp. The catalyst, Cu(≤5 wt.%)/TiO2, is specific for the products (i.e., the main products were CH4 and C2H4, and not MeOH and formaldehyde). Using the photochem. redn., the yields for CH4, C2H4, and C2H6 were 21.8, 26.2, and 2.7 μL/g, resp., under optimum conditions. The CO2 redn. system developed might be of practical interest for photochem. fuel prodn., storage of solar energy, and prodn. of raw materials for the photochem. industry.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXmvVentbs%253D&md5=836fcbce77926988c421a2145c2c1335
    13. 13
      Li, N.; Wang, B.; Si, Y.; Xue, F.; Zhou, J.; Lu, Y.; Liu, M. Toward High-Value Hydrocarbon Generation by Photocatalytic Reduction of CO2 in Water Vapor. ACS Catal. 2019, 9, 5590– 5602,  DOI: 10.1021/acscatal.9b00223
      13
      Toward High-Value Hydrocarbon Generation by Photocatalytic Reduction of CO2 in Water Vapor
      Li, Naixu; Wang, Bingbing; Si, Yitao; Xue, Fei; Zhou, Jiancheng; Lu, Youjun; Liu, Maochang
      ACS Catalysis (2019), 9 (6), 5590-5602CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      Semiconductor crystals with well-defined morphol., porous nanostructure, and spatially sepd. active sites are attractive for use in photocatalysis. This paper describes a controlled synthesis of cake-like porous TiO2 photocatalyst with surface-localized doping of copper and cobalt by using a well-defined MIL-125(Ti) metal org. framework as template precursor. The series of the modified TiO2 photocatalysts present the improved activity for photocatalytic CO2 redn. with water vapor. It is found that 1%Cu-doped TiO2 shows an enhanced behavior for breaking C=O bonds. In this case, the outcomes are primarily CO and CH4, yielding up to 135.94 and 127.05 μmol, resp., under the irradn. of simulated sunlight for 3 h. The performance can be further improved by incorporating trace cobalt. Besides the improved property for CO and CH4 prodn., the selectivity also shifts to high-value hydrocarbons (C2+). The yields for C2H6 and C3H8 can be up to 267.60 and 10.07 μmol, resp., by using 0.02%Co-1%Cu/TiO2. Our in situ Fourier transform IR spectra together with theor. calcns. indicate that efficient charge sepn. on copper and cobalt ions is achieved. This altered charge behavior leads to the generation and enrichment of Me radicals on the surface of cobalt ions, giving rise to the prodn. of C2+ hydrocarbons. This work demonstrates a vibrant catalyst platform for solar fuel generation by photocatalytic CO2 conversion in water.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXptFymurs%253D&md5=1134fbae7d8ae6bbea17cba4c5a3cca8
    14. 14
      Xia, Y.; Xiao, K.; Cheng, B.; Yu, J.; Jiang, L.; Antonietti, M.; Cao, S. Improving Artificial Photosynthesis over Carbon Nitride by Gas–Liquid–Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2. ChemSusChem 2020, 13, 1730– 1734,  DOI: 10.1002/cssc.201903515
      14
      Improving Artificial Photosynthesis over Carbon Nitride by Gas-Liquid-Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2
      Xia, Yang; Xiao, Kai; Cheng, Bei; Yu, Jiaguo; Jiang, Lei; Antonietti, Markus; Cao, Shaowen
      ChemSusChem (2020), 13 (7), 1730-1734CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The activity and selectivity of simple photocatalysts for CO2 redn. remain limited by the insufficient photophysics of the catalysts, as well as the low soly. and slow mass transport of gas mols. in/through aq. soln. In this study, these limitations are overcome by constructing a triphasic photocatalytic system, in which polymeric carbon nitride (CN) is immobilized onto a hydrophobic substrate, and the photocatalytic redn. reaction occurs at a gas-liq.-solid (CO2-water-catalyst) triple interface. CN anchored onto the surface of a hydrophobic substrate exhibits an approx. 7.2-fold enhancement in total CO2 conversion, with a rate of 415.50μmol m-2 h-1 under simulated solar light irradn. This value corresponds to an overall photosynthetic efficiency for full water-CO2 conversion of 0.33%, which is very close to biol. systems. A remarkable enhancement of direct C2 hydrocarbon prodn. and a high CO2 conversion selectivity of 97.7% are obsd. Going from water oxidn. to phosphate oxidn., the quantum yield is increased to 1.28%.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFOqtr0%253D&md5=1fe17fc278f45e3e7c1cc3f368067afb
    15. 15
      Wang, L.; Wang, L.; Zhang, J.; Liu, X.; Wang, H.; Zhang, W.; Yang, Q.; Ma, J.; Dong, X.; Yoo, S. J.; Kim, J.-G.; Meng, X.; Xiao, F.-S. Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts. Angew. Chem., Int. Ed. 2018, 57, 6104– 6108,  DOI: 10.1002/anie.201800729
      15
      Selective Hydrogenation of CO2 to Ethanol over Cobalt Catalysts
      Wang, Lingxiang; Wang, Liang; Zhang, Jian; Liu, Xiaolong; Wang, Hai; Zhang, Wei; Yang, Qi; Ma, Jingyuan; Dong, Xue; Yoo, Seung Jo; Kim, Jin-Gyu; Meng, Xiangju; Xiao, Feng-Shou
      Angewandte Chemie, International Edition (2018), 57 (21), 6104-6108CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Methods for the hydrogenation of CO2 into valuable chems. are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over non-noble cobalt catalysts (CoAlOx), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the compn. of the catalysts through the use of different preredn. temps., the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g-1 h-1. Operando FT-IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx, a key intermediate in the prodn. of ethanol by CO2 hydrogenation.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXosVWnt7Y%253D&md5=0e5782f8b1b9d3adff17a187617e2019
    16. 16
      Qian, Q.; Cui, M.; He, Z.; Wu, C.; Zhu, Q.; Zhang, Z.; Ma, J.; Yang, G.; Zhang, J.; Han, B. Highly Selective Hydrogenation of CO2 into C2+ Alcohols by Homogeneous Catalysis. Chem. Sci. 2015, 6, 5685– 5689,  DOI: 10.1039/C5SC02000J
      16
      Highly selective hydrogenation of CO2 into C2+ alcohols by homogeneous catalysis
      Qian, Qingli; Cui, Meng; He, Zhenhong; Wu, Congyi; Zhu, Qinggong; Zhang, Zhaofu; Ma, Jun; Yang, Guanying; Zhang, Jingjing; Han, Buxing
      Chemical Science (2015), 6 (10), 5685-5689CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The hydrogenation of CO2 to produce alcs. with two or more carbons (C2+ alcs.) is of great importance, but is challenging. In this work, we found that a Ru3(CO)12/Rh2(CO)4Cl2-LiI system could catalyze the reaction effectively in 1,3-dimethyl-2-imidazolidinone (DMI) under mild conditions. Methanol, ethanol, propanol, 2-Me propanol, butanol, and 2-Me butanol were produced in the homogeneous catalytic reaction. The C2+ alcs. could be generated at 160 °C, which is the lowest temp. reported so far for producing C2+ alcs. via CO2 hydrogenation. The selectivity for the C2+ alcs. could be as high as 96.4% at the optimized conditions, which is higher than those reported in the literature. In addn., the catalytic system could be easily recycled. The route of the reaction for forming the C2+ alcs. was discussed on the basis of control expts.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtFCqtb3F&md5=70809ef59e10a8440eae3f0da15bc6b6
    17. 17
      Cui, M.; Qian, Q.; He, Z.; Zhang, Z.; Ma, J.; Wu, T.; Yang, G.; Han, B. Bromide Promoted Hydrogenation of CO2 to Higher Alcohols Using Ru–Co Homogeneous Catalyst. Chem. Sci. 2016, 7, 5200– 5205,  DOI: 10.1039/C6SC01314G
      17
      Bromide promoted hydrogenation of CO2 to higher alcohols using Ru-Co homogeneous catalyst
      Cui, Meng; Qian, Qingli; He, Zhenhong; Zhang, Zhaofu; Ma, Jun; Wu, Tianbin; Yang, Guanying; Han, Buxing
      Chemical Science (2016), 7 (8), 5200-5205CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Iodides are commonly used promoters in C2+OH synthesis from CO2/CO hydrogenation. Here we report the highly efficient synthesis of C2+OH from CO2 hydrogenation over a Ru3(CO)12-Co4(CO)12 bimetallic catalyst with bis(triphenylphosphoranylidene)ammonium chloride (PPNCl) as the cocatalyst and LiBr as the promoter. Methanol, ethanol, propanol and isobutanol were formed at milder conditions. The catalytic system had a much better overall performance than those of reported iodide promoted systems because PPNCl and LiBr cooperated very well in accelerating the reaction. LiBr enhanced the activity and PPNCl improved the selectivity, and thus both the activity and selectivity were very high when both of them were used simultaneously. In addn., the catalyst could be reused for at least five cycles without an obvious change of catalytic performance.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Krsrg%253D&md5=34a9b14869134f5a5581081486ee98ea
    18. 18
      Gao, P.; Dang, S.; Li, S.; Bu, X.; Liu, Z.; Qiu, M.; Yang, C.; Wang, H.; Zhong, L.; Han, Y.; Liu, Q.; Wei, W.; Sun, Y. Direct Production of Lower Olefins from CO2 Conversion via Bifunctional Catalysis. ACS Catal. 2018, 8, 571– 578,  DOI: 10.1021/acscatal.7b02649
      18
      Direct Production of Lower Olefins from CO2 Conversion via Bifunctional Catalysis
      Gao, Peng; Dang, Shanshan; Li, Shenggang; Bu, Xianni; Liu, Ziyu; Qiu, Minghuang; Yang, Chengguang; Wang, Hui; Zhong, Liangshu; Han, Yong; Liu, Qiang; Wei, Wei; Sun, Yuhan
      ACS Catalysis (2018), 8 (1), 571-578CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      Direct conversion of carbon dioxide (CO2) into lower olefins (C2=-C4=), generally referring to ethylene, propylene, and butylene, is highly attractive as a sustainable prodn. route for its great significance in greenhouse gas control and fossil fuel substitution, but such a route always tends to be low in selectivity toward olefins. Here we present a bifunctional catalysis process that offers C2=-C4= selectivity as high as 80% and C2-C4 selectivity around 93% at more than 35% CO2 conversion. This is achieved by a bifunctional catalyst composed of indium-zirconium composite oxide and SAPO-34 zeolite, which is responsible for CO2 activation and selective C-C coupling, resp. We demonstrate that both the precise control of oxygen vacancies on the oxide surface and the integration manner of the components are crucial in the direct prodn. of lower olefins from CO2 hydrogenation. No obvious deactivation is obsd. over 150 h, indicating a promising potential for industrial application.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFaqtrfK&md5=4178d134b8b214f7178551eea2733a55
    19. 19
      Gao, P.; Li, S.; Bu, X.; Dang, S.; Liu, Z.; Wang, H.; Zhong, L.; Qiu, M.; Yang, C.; Cai, J.; Wei, W.; Sun, Y. Direct Conversion of CO2 into Liquid Fuels with High Selectivity over a Bifunctional Catalyst. Nat. Chem. 2017, 9, 1019– 1024,  DOI: 10.1038/nchem.2794
      19
      Direct conversion of CO2 into liquid fuels with high selectivity over a bifunctional catalyst
      Gao, Peng; Li, Shenggang; Bu, Xianni; Dang, Shanshan; Liu, Ziyu; Wang, Hui; Zhong, Liangshu; Qiu, Minghuang; Yang, Chengguang; Cai, Jun; Wei, Wei; Sun, Yuhan
      Nature Chemistry (2017), 9 (10), 1019-1024CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)
      Although considerable progress was made in CO2 hydrogenation to various C1 chems., it is still a great challenge to synthesize value-added products with ≥2 carbons, such as gasoline, directly from CO2 because of the extreme inertness of CO2 and a high C-C coupling barrier. Here the authors present a bifunctional catalyst composed of reducible In oxides (In2O3) and zeolites that yields a high selectivity to gasoline-range hydrocarbons (78.6%) with a very low methane selectivity (1%). The O vacancies on the In2O3 surfaces activate CO2 and H to form MeOH, and C-C coupling subsequently occurs inside zeolite pores to produce gasoline-range hydrocarbons with a high octane no. The proximity of these 2 components plays a crucial role in suppressing the undesired reverse water gas shift reaction and giving a high selectivity for gasoline-range hydrocarbons. Also, the pellet catalyst exhibits a much better performance during an industry-relevant test, which suggests promising prospects for industrial applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVSjt7bI&md5=4ef37e087edf5dfbaf26bcd93105f584
    20. 20
      Wang, H.; Zhao, Y.; Wu, Y.; Li, R.; Zhang, H.; Yu, B.; Zhang, F.; Xiang, J.; Wang, Z.; Liu, Z. Hydrogenation of Carbon Dioxide to C2–C4 Hydrocarbons Catalyzed by Pd(PtBu3)2–FeCl2 with Ionic Liquid as Cocatalyst. ChemSusChem 2019, 12, 4390– 4394,  DOI: 10.1002/cssc.201901820
      20
      Hydrogenation of Carbon Dioxide to C2-C4 Hydrocarbons Catalyzed by Pd(PtBu3)2-FeCl2 with Ionic Liquid as Cocatalyst
      Wang, Huan; Zhao, Yanfei; Wu, Yunyan; Li, Ruipeng; Zhang, Hongye; Yu, Bo; Zhang, Fengtao; Xiang, Junfeng; Wang, Zhenpeng; Liu, Zhimin
      ChemSusChem (2019), 12 (19), 4390-4394CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Direct hydrogenation of CO2 to C2+ hydrocarbons is very interesting, but achieving this transformation <200° is challenging and seldom reported. A homogeneous catalytic system was developed composed of the ionic liq. 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), Pd(P(tert-Bu)3)2, FeCl2, and the ligand 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) for hydrogenation of CO2 under mild conditions, which resulted in C2-C4 hydrocarbons in selectivities up to 98.3 C-mol % at 180°. The combination of ([BMIm][PF6]) with Xantphos endowed the Pd-Fe catalysts with the ability of activating CO2 and H2 simultaneously via [HPd(PCMe33)(BMIm-COO)(BMIm)(PF6)Fe]+ species, thus catalyzing the formation of C2-C4 hydrocarbons through CO2 hydrogenation. This catalytic system is stable and recyclable, which may have promising applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslWjtLrN&md5=d943a6b6ee8dd523921e85d1f267a668
    21. 21
      Ni, Y.; Chen, Z.; Fu, Y.; Liu, Y.; Zhu, W.; Liu, Z. Selective Conversion of CO2 and H2 into Aromatics. Nat. Commun. 2018, 9, 3457,  DOI: 10.1038/s41467-018-05880-4
      21
      Selective conversion of CO2 and H2 into aromatics
      Ni Youming; Chen Zhiyang; Fu Yi; Liu Yong; Zhu Wenliang; Liu Zhongmin; Ni Youming; Chen Zhiyang; Fu Yi; Liu Yong; Zhu Wenliang; Liu Zhongmin; Chen Zhiyang; Fu Yi
      Nature communications (2018), 9 (1), 3457 ISSN:.
      Transformation of greenhouse gas CO2 and renewable H2 into fuels and commodity chemicals is recognized as a promising route to store fluctuating renewable energy. Although several C1 chemicals, olefins, and gasoline have been successfully synthesized by CO2 hydrogenation, selective conversion of CO2 and H2 into aromatics is still challenging due to the high unsaturation degree and complex structures of aromatics. Here we report a composite catalyst of ZnAlOx and H-ZSM-5 which yields high aromatics selectivity (73.9%) with extremely low CH4 selectivity (0.4%) among the carbon products without CO. Methanol and dimethyl ether, which are synthesized by hydrogenation of formate species formed on ZnAlOx surface, are transmitted to H-ZSM-5 and subsequently converted into olefins and finally aromatics. Furthermore, 58.1% p-xylene in xylenes is achieved over the composite catalyst containing Si-H-ZSM-5. ZnAlOx&H-ZSM-5 suggests a promising application in manufacturing aromatics from CO2 and H2.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3c3itlymtg%253D%253D&md5=35f495bb04ebe5f758359084ee8240d6
    22. 22
      Wang, W.-H.; Himeda, Y.; Muckerman, J. T.; Manbeck, G. F.; Fujita, E. CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction. Chem. Rev. 2015, 115, 12936– 12973,  DOI: 10.1021/acs.chemrev.5b00197
      22
      CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction
      Wang, Wan-Hui; Himeda, Yuichiro; Muckerman, James T.; Manbeck, Gerald F.; Fujita, Etsuko
      Chemical Reviews (Washington, DC, United States) (2015), 115 (23), 12936-12973CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. CO2 hydrogenation to formate and methanol, formic acid dehydrogenation with various metal complexes, H2 green fuel prodn. and storage, and interconversion of CO2 and formic acid.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCgu7rK&md5=9e39dcc06a0e334b3a891ce797de5f9f
    23. 23
      Yamazaki, Y.; Takeda, H.; Ishitani, O. Photocatalytic Reduction of CO2 Using Metal Complexes. J. Photochem. Photobiol. C 2015, 25, 106– 137,  DOI: 10.1016/j.jphotochemrev.2015.09.001
      23
      Photocatalytic reduction of CO2 using metal complexes
      Yamazaki, Yasuomi; Takeda, Hiroyuki; Ishitani, Osamu
      Journal of Photochemistry and Photobiology, C: Photochemistry Reviews (2015), 25 (), 106-137CODEN: JPPCAF; ISSN:1389-5567. (Elsevier B.V.)
      A review. Developing photocatalytic systems for CO2 redn. will provide useful and energy-rich compds. and would be one of the most important focuses in the field of "artificial photosynthesis" and "solar fuels". Such studies have been conducted in the past three decades from the perspective of basic science and for solving the shortage of fossil resources, which include both energy and carbon sources. More recently, focus has been placed on the mitigation of global warming through the redn. of atm. CO2. This review summarizes the enormous body of reported literature in this field, particularly studies that describe photocatalytic systems that use transition metal complexes as key players, i.e., as catalysts (Cat) and/or photosensitizers (PS). In addn., we briefly describe the evaluation of various photocatalytic systems, esp. the performance of reductants (D) and solvents. Furthermore, we analyze the types of photocatalytic systems and classify each component in these systems according to their role: (1) PS, (2) Cat for CO2 redn. catalysts, and (3) D. Briefly, we summarize the important features of each component and provide typical examples. The next section discusses the photocatalytic abilities of each of the three categories of photocatalytic systems: multicomponent systems comprising PS and Cat, supramol. photocatalysts comprising a multinuclear complex, and hybrid systems constructed with metal-complex photocatalysts and inorg. materials, such as semiconductors or electrodes.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs12ltLbJ&md5=da5f207bbb4d735eccf20cdd5cd129f6
    24. 24
      Takeda, H.; Cometto, C.; Ishitani, O.; Robert, M. Electrons, Photons, Protons and Earth-Abundant Metal Complexes for Molecular Catalysis of CO2 Reduction. ACS Catal. 2017, 7, 70– 88,  DOI: 10.1021/acscatal.6b02181
      24
      Electrons, Photons, Protons and Earth-Abundant Metal Complexes for Molecular Catalysis of CO2 Reduction
      Takeda, Hiroyuki; Cometto, Claudio; Ishitani, Osamu; Robert, Marc
      ACS Catalysis (2017), 7 (1), 70-88CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      A review. Electrochem. and photochem. redn. of CO2, or a smart combination of both, are appealing approaches for the storage of renewable, intermittent energies and may lead to the prodn. of fuels and of value added chems. By using only earth abundant metal (Cu, Ni, Co, Mn, Fe) complexes, cheap electrodes and/or cheap sacrificial electron donors and visible light sensitizers, systems functioning with mol. catalysts have been recently designed, showing promising results in particular for the two electrons redn. of the carbon dioxide. By combining exptl. and mechanistic studies, key parameters controlling the catalysis efficiency have been deciphered, opening the way to the design of future, more efficient and durable catalysts, as well as to the development of electrochem. or photo-electrochem. cells, all being key steps for the emergence of applied devices. The most recent advances related to these issues are discussed in this review.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslGhu7zF&md5=032874cb48f7a230e25fd72a4f4628e5
    25. 25
      Francke, R.; Schille, B.; Roemelt, M. Homogeneously Catalyzed Electroreduction of Carbon Dioxide─Methods, Mechanisms, and Catalysts. Chem. Rev. 2018, 118, 4631– 4701,  DOI: 10.1021/acs.chemrev.7b00459
      25
      Homogeneously Catalyzed Electroreduction of Carbon Dioxide-Methods, Mechanisms, and Catalysts
      Francke, Robert; Schille, Benjamin; Roemelt, Michael
      Chemical Reviews (Washington, DC, United States) (2018), 118 (9), 4631-4701CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. The utilization of CO2 via electrochem. redn. constitutes a promising approach toward prodn. of value-added chems. or fuels using intermittent renewable energy sources. For this purpose, mol. electrocatalysts are frequently studied and the recent progress both in tuning of the catalytic properties and in mechanistic understanding is truly remarkable. While in earlier years research efforts were focused on complexes with rare metal centers such as Re, Ru, and Pd, the focus has recently shifted toward earth-abundant transition metals such as Mn, Fe, Co, and Ni. By application of appropriate ligands, these metals have been rendered more than competitive for CO2 redn. compared to the heavier homologues. In addn., the important roles of the second and outer coordination spheres in the catalytic processes have become apparent, and metal-ligand cooperativity has recently become a well-established tool for further tuning of the catalytic behavior. Surprising advances have also been made with very simple organocatalysts, although the mechanisms behind their reactivity are not yet entirely understood. Herein, the developments of the last three decades in electrocatalytic CO2 redn. with homogeneous catalysts are reviewed. A discussion of the underlying mechanistic principles is included along with a treatment of the exptl. and computational techniques for mechanistic studies and catalyst benchmarking. Important catalyst families are discussed in detail with regard to mechanistic aspects, and recent advances in the field are highlighted.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXlsVWqsw%253D%253D&md5=4161321252762123a970f3cb93e62cac
    26. 26
      Windle, C. D.; Perutz, R. N. Advances in Molecular Photocatalytic and Electrocatalytic CO2 Reduction. Coord. Chem. Rev. 2012, 256, 2562– 2570,  DOI: 10.1016/j.ccr.2012.03.010
      26
      Advances in molecular photocatalytic and electrocatalytic CO2 reduction
      Windle, Christopher D.; Perutz, Robin N.
      Coordination Chemistry Reviews (2012), 256 (21-22), 2562-2570CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      This review describes recent developments in photocatalytic and electrocatalytic CO2 redn. On the electrocatalytic side, there have been advances in optimization of known rhenium motifs sometimes in conjunction with silicon photoelectrodes giving enhanced catalytic current and stability. Complexes of copper capable of absorbing atm. CO2 have been incorporated into an electrocatalytic cycle and metal-free electrocatalysis of CO2 to methanol has been achieved with pyridinium ions. A complete cell with two photoelectrodes, one for water oxidn. and the other for CO2 redn. to formate has been set up successfully. The cathode employs ruthenium catalysts on InP. Progress in photocatalytic CO2 redn. has been made with osmium complexes exhibiting good selectivity and stability. The sepn. between Ru and Re centers in light-harvesting donor-acceptor dyads has been investigated providing some inspiration for design. A ruthenium catalyst has been sensitized by tantalum oxide particles. Metalloporphyrin-rhenium dyads have also been studied for photocatalytic CO2 redn. In the biol. arena, a ruthenium complex has been used to sensitize carbon monoxide dehydrogenase on titanium dioxide particles.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xlslyls74%253D&md5=2f9fc91d331b52f8f2f667daffa3dbc5
    27. 27
      Morris, A. J.; Meyer, G. J.; Fujita, E. Molecular Approaches to the Photocatalytic Reduction of Carbon Dioxide for Solar Fuels. Acc. Chem. Res. 2009, 42, 1983– 1994,  DOI: 10.1021/ar9001679
      27
      Molecular Approaches to the Photocatalytic Reduction of Carbon Dioxide for Solar Fuels
      Morris, Amanda J.; Meyer, Gerald J.; Fujita, Etsuko
      Accounts of Chemical Research (2009), 42 (12), 1983-1994CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review concerning mol. approaches to the photocatalytic redn. of CO2 in homogenous soln. for solar fuels, i.e., photochem. transformation of CO2 into a fuel source as an attractive way to decrease atm. CO2 concns., is given. One way to accomplish this conversion is via light-driven CO2 redn. to gaseous CH4 or liq. CH3OH with electrons and protons derived from water. Existing infrastructure already supports the delivery of natural gas and liq. fuels, making these possible CO2 redn. products particularly appealing. A favorable pathway is to reduce CO2 by proton-assisted, multiple-electron transfer. CO and formate are the primary CO2 redn. products; a HCO3-/CO32- prodn. process is also discussed. Topics covered include: common terms; type 1 reaction (Co and Ni tetraaza-macrocyclic compds., supramol. complexes); type 2 reaction (metalloporphyrins and related metallomacrocycles, Re(CO3)3(bpy)X-based complexes); and summary and future outlook.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVGntr3F&md5=4d5ba24aecb183119ed2ed6cff3959dd
    28. 28
      Schuler, E.; Demetriou, M.; Shiju, N. R.; Gruter, G.-J. M. Towards Sustainable Oxalic Acid from CO2 and Biomass. ChemSusChem 2021, 14, 3636– 3664,  DOI: 10.1002/cssc.202101272
      28
      Towards Sustainable Oxalic Acid from CO2 and Biomass
      Schuler, Eric; Demetriou, Marilena; Shiju, N. Raveendran; Gruter, Gert-Jan M.
      ChemSusChem (2021), 14 (18), 3636-3664CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2. A promising route is the electrochem. redn. of CO2 to formic acid derivs. that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chem. for material prodn. as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid prodn. processes with a focus on CO2-based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVehtrrO&md5=c1b6f036df6ddb0275323e9bb175a52a
    29. 29
      Murcia Valderrama, M. A.; van Putten, R.-J.; Gruter, G.-J. M. The Potential of Oxalic – and Glycolic Acid Based Polyesters (Review). Towards CO2 as a Feedstock (Carbon Capture and Utilization – CCU). Eur. Polym. J. 2019, 119, 445– 468,  DOI: 10.1016/j.eurpolymj.2019.07.036
      29
      The potential of oxalic - and glycolic acid based polyesters (review). Towards CO2 as a feedstock (Carbon Capture and Utilization - CCU)
      Murcia Valderrama, Maria A.; van Putten, Robert-Jan; Gruter, Gert-Jan M.
      European Polymer Journal (2019), 119 (), 445-468CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
      A review. Plastic materials are indispensable in everyday life because of their versatility, high durability, lightness and cost-effectiveness. As a consequence, worldwide plastic consumption will continue to grow from around 350 million metric tons per annum today to an estd. 1 billion metric tons per annum in 2050. For applications where polymers are applied in the environment or for applications where polymers have a bigger chance of ending up in the environment, (bio)degradable polymers need to be developed to stop endless accumulation of non-degradable polymers irreversibly littering our planet. As monomers and polymers represent more than 80% of the chem. industry's total prodn. vol., a transition from fossil feedstock today (99% of the current feedstock for polymers is fossil-based) to a significantly larger percentage of renewable feedstock in the future (carbon that is already "above the ground") will be required to meet the greenhouse gas redn. targets of the Paris Agreement (>80% CO2 redn. target for the European Chem. Industry sector in 2050). The combination of the predicted polymer market growth and the emergence of new feedstocks creates a fantastic opportunity for novel sustainable polymers. To replace fossil based feedstock, there are only three sustainable alternative sources: biomass, CO2 and existing plastics (via recycling). The ultimate circular feedstock would be CO2: it can be electrochem. reduced to formic acid derivs. that can subsequently be converted into useful monomers such as glycolic acid and oxalic acid. In order to assess the future potential for these polyester building blocks, we will review the current field of polyesters based on these two monomers. Representative synthesis methods, general properties, general degrdn. mechanisms, and recent applications will be discussed in this review. The application potential of these polyesters for a wide range of purposes, as a function of prodn. cost, will also be assessed. It is important to note that polymers derived from CO2 do not necessarily always lead to lower net overall CO2 emissions (during prodn. of after use, e.g. degrdn. in landfills). This needs to be evaluated using robust LCA's and this information is currently not available for the materials discussed in this review.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs1CisLnI&md5=9aa39ae2d5c94cffeb53515e43c00c43
    30. 30
      Abraham, F.; Arab-Chapelet, B.; Rivenet, M.; Tamain, C.; Grandjean, S. Actinide Oxalates, Solid State Structures and Applications. Coord. Chem. Rev. 2014, 266–267, 28– 68,  DOI: 10.1016/j.ccr.2013.08.036
      30
      Actinide oxalates, solid state structures and applications
      Abraham, Francis; Arab-Chapelet, Benedicte; Rivenet, Murielle; Tamain, Christelle; Grandjean, Stephane
      Coordination Chemistry Reviews (2014), 266-267 (), 28-68CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      A review. Actinide oxalates are an important class of materials mainly for the nuclear industry. This review presents the crystal growth methods addressed to non-sol. actinide (III) and (IV) oxalates and to sol. actinyl oxalates. Actinide-oxalate discrete ions, one-dimensional coordination polymers and two- or three-dimensional frameworks are described for the different oxidn. states of actinides in simple, double or triple actinide oxalates together with mixed actinide (IV)-lanthanide (III) or -actinide (III) and mixed ligands actinide oxalates. The main applications of actinide oxalates, particularly for radioactive waste management and nuclear fuel treatment and recycling are also reported.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFCju7fO&md5=8e24daab735abe8292b782131b111d33
    31. 31
      Tyssee, D. A.; Wagenknecht, J. H.; Baizer, M. M.; Chruma, J. L. Some Cathodic Organic Syntheses Involving Carbon Dioxide. Tetrahedron Lett. 1972, 13, 4809– 4812,  DOI: 10.1016/S0040-4039(01)94435-1
      There is no corresponding record for this reference.
    32. 32
      Amatore, C.; Saveant, J. M. Mechanism and Kinetic Characteristics of the Electrochemical Reduction of Carbon Dioxide in Media of Low Proton Availability. J. Am. Chem. Soc. 1981, 103, 5021– 5023,  DOI: 10.1021/ja00407a008
      32
      Mechanism and kinetic characteristics of the electrochemical reduction of carbon dioxide in media of low proton availability
      Amatore, Christian; Saveant, Jean Michel
      Journal of the American Chemical Society (1981), 103 (17), 5021-3CODEN: JACSAT; ISSN:0002-7863.
      The mechanism of the redn. of CO2 in solvents of low proton availability such as DMF was investigated on the basis of the variation of the electrolysis product distribution with c.d. and concn. of CO2 and H2O. It was shown to involve 3 competing pathways: oxalate formation through self-coupling of the CO2 anion radicals, CO formation via O-C coupling of CO2 anion radicals with CO2, and formate formation through protonation of CO2 anion radicals by residual or added H2Oter followed by an homogeneous electron transfer from CO2 anion radicals. Using the product distribution data together with the kinetic data obtained by fast microelectrolytic techniques allows the characterization of the key-steps of the redn. process: initial electron transfer and the rate detg. steps of the 3 competing reactions leading to oxalate, CO and formate.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXkvVyjurg%253D&md5=dd0b1dc1a7a49f0bc50ae23406e778ac
    33. 33
      Gennaro, A.; Isse, A. A.; Savéant, J.-M.; Severin, M.-G.; Vianello, E. Homogeneous Electron Transfer Catalysis of the Electrochemical Reduction of Carbon Dioxide. Do Aromatic Anion Radicals React in an Outer-Sphere Manner?. J. Am. Chem. Soc. 1996, 118, 7190– 7196,  DOI: 10.1021/ja960605o
      33
      Homogeneous Electron Transfer Catalysis of the Electrochemical Reduction of Carbon Dioxide. Do Aromatic Anion Radicals React in an Outer-Sphere Manner?
      Gennaro, Armando; Isse, Abdirisak A.; Saveant, Jean-Michel; Severin, Maria-Gabriella; Vianello, Elio
      Journal of the American Chemical Society (1996), 118 (30), 7190-7196CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Electrochem. generated anion radicals of arom. nitriles and esters possess the remarkable property to reduce carbon dioxide to oxalate with negligible formation of carboxylated products. They may thus serve as selective homogeneous catalysts for the redn. of CO2 in an aprotic medium. The catalytic enhancement of the cyclic voltammetric peaks of these catalysts was used to det. the rate const. of the electron transfer from these arom. anion radicals to CO2 as a function of the catalyst std. potential. Substituted benzoic esters allowed a particularly detailed study of the resulting activation-driving force relation. Using 14 different catalysts in this series made it possible to finely scan a range of reaction std. free energies of 0.4 eV. Detailed anal. of the resulting data indicated that the reaction is not a simple outer-sphere electron transfer. It rather consists in a nucleophilic addn. of the anion radical on CO2, forming an oxygen (or nitrogen for the nitriles)-carbon bond, which successively breaks homolytically, generating the parent ester (or nitrile) and the anion radical of CO2, which eventually dimerizes to oxalate.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XktFOqurY%253D&md5=33597bbe7b66ef3c9cbdcf1adb349918
    34. 34
      Gennaro, A.; Isse, A. A.; Severin, M.-G.; Vianello, E.; Bhugun, I.; Saveant, J.-M. Mechanism of the Electrochemical Reduction of Carbon Dioxide at Inert Electrodes in Media of Low Proton Availability. J. Chem. Soc., Faraday Trans. 1996, 92, 3963– 3968,  DOI: 10.1039/FT9969203963
      34
      Mechanism of the electrochemical reduction of carbon dioxide at inert electrodes in media of low proton availability
      Gennaro, Armando; Isse, Abdirisak A.; Severin, Maria-Gabriella; Vianello, Elio; Bhugun, Iqbal; Saveant, Jean-Michel
      Journal of the Chemical Society, Faraday Transactions (1996), 92 (20), 3963-3968CODEN: JCFTEV; ISSN:0956-5000. (Royal Society of Chemistry)
      Direct electrolysis of CO2 in DMF at an inert electrode, such as mercury, produces mixts. of CO and oxalate, whereas electrolysis catalyzed by radical anions of arom. esters and nitriles produces exclusively oxalate in the same medium. Examn. of previous results concerning the direct electrochem. redn. and the redn. by photoinjected electrons reveals that there are no significant specific interactions between reactant, intermediates and products on the one hand, and the electrode material on the other, when this is Hg or Pb. These observations and a systematic study of the variations of the oxalate and CO yields with temp. and CO2 concn., allow the derivation of a consistent mechanistic model of the direct electrochem. redn. It involves the formation of oxalate from the coupling of two CO2 radical anions in soln. CO (and an equimolar amt. of carbonate) is produced by redn. at the electrode of a CO2-CO2.- adduct, the formation of which, at the electrode surface, is rendered exothermic by nonspecific electrostatic interactions.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmvVymtrw%253D&md5=0e561d234957e6c009ff7c426f26b1b2
    35. 35
      Kushi, Y.; Nagao, H.; Nishioka, T.; Isobe, K.; Tanaka, K. Oxalate Formation in Electrochemical CO2 Reduction Catalyzed by Rhodium-Sulfur Cluster. Chem. Lett. 1994, 23, 2175– 2178,  DOI: 10.1246/cl.1994.2175
      There is no corresponding record for this reference.
    36. 36
      Tanaka, K.; Kushi, Y.; Tsuge, K.; Toyohara, K.; Nishioka, T.; Isobe, K. Catalytic Generation of Oxalate through a Coupling Reaction of Two CO2 Molecules Activated on [(Ir(η5-C5Me5))2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]. Inorg. Chem. 1998, 37, 120– 126,  DOI: 10.1021/ic9702328
      36
      Catalytic Generation of Oxalate through a Coupling Reaction of Two CO2 Molecules Activated on [[Ir(η5-C5Me5)]2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]
      Tanaka, Koji; Kushi, Yoshinori; Tsuge, Kiyoshi; Toyohara, Kiyotuna; Nishioka, Takanori; Isobe, Kiyoshi
      Inorganic Chemistry (1998), 37 (1), 120-126CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Electrochem. redn. of [[Ir(η5-C5Me5)]3(μ3-S)2](BPh4)2 ([Ir3S2](BPh4)2) in CO2-satd. MeCN at -1.30 V (vs. Ag/AgCl) produced C2O42- and [[Ir(η5-C5Me5)]2(Ir(η4-C5Me5)CH2CN)(μ3-S)2]+ ([Ir3S2CH2CN]+). The crystal structure of [Ir3S2CH2CN](BPh4) by x-ray anal. revealed that a linear CH2CN group is linked at the exo-position of a C5Me5 ligand, and the C5Me5CH2CN ligand coordinates to an Ir atom with an η4-mode. The cyclic voltammogram of [Ir3S2CH2CN]+ in MeCN under CO2 exhibited a strong catalytic current due to the redn. of CO2, while that of [Ir3S2]2+ did not show an interaction with CO2 in the same solvent. The reduced form of [Ir3S2CH2CN]+ works as the active species in the redn. of CO2. The IR spectra of [Ir3S2CH2CN]+ in CD3CN showed a reversible adduct formation with CO2 and also evidenced the oxalate generation through the reduced form of the CO2 adduct under the controlled potential electrolysis of the soln. at -1.55 V. A coupling reaction of two CO2 mols. bonded on adjacent μ3-S and Ir in [Ir3S2CH2CN]0 is proposed for the 1st catalytic generation of C2O42- without accompanying CO evolution.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXotVCjurY%253D&md5=52b328027efdf28b67342689f85a7909
    37. 37
      Ali, M. M.; Sato, H.; Mizukawa, T.; Tsuge, K.; Haga, M.; Tanaka, K. Selective Formation of HCO2– and C2O42– in Electrochemical Reduction of CO2 Catalyzed by Mono- and Di-Nuclear Ruthenium Complexes. Chem. Commun. 1998, 249– 250,  DOI: 10.1039/a707363a
      37
      Selective formation of HCO2- and C2O42- in electrochemical reduction of CO2 catalyzed by mono- and dinuclear ruthenium complexes
      Ali, Md. Meser; Sato, Hiroyasu; Mizukawa, Tetsunori; Tsuge, Kiyoshi; Haga, Masa-aki; Tanaka, Koji
      Chemical Communications (Cambridge) (1998), (2), 249-250CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Electrochem. redn. of carbon dioxide catalyzed by mono- and di-nuclear ruthenium complexes produced HCO2H with trace amts. of CO and C2O42- in the presence and absence of H2O, resp., in MeCN.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXhtFert7o%253D&md5=e29eb2a4bc748296e505da21fe173a2c
    38. 38
      Rudolph, M.; Dautz, S.; Jäger, E.-G. Macrocyclic [N42-] Coordinated Nickel Complexes as Catalysts for the Formation of Oxalate by Electrochemical Reduction of Carbon Dioxide. J. Am. Chem. Soc. 2000, 122, 10821– 10830,  DOI: 10.1021/ja001254n
      38
      Macrocyclic [N42-] Coordinated Nickel Complexes as Catalysts for the Formation of Oxalate by Electrochemical Reduction of Carbon Dioxide
      Rudolph, Manfred; Dautz, Sylvana; Jaeger, Ernst-Gottfried
      Journal of the American Chemical Society (2000), 122 (44), 10821-10830CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The macrocyclic nickel complexes are able to catalyze the electrochem. redn. of CO2 to oxalate. In the case of the macrocyclic nickel complexes with substituents COOEt or COMe, the overall reaction can be interpreted in terms of an outer-sphere electron-transfer reaction followed by a dimerization of the CO2•- radical anions, but the variation of the electron-transfer rate consts. with the std. potentials points to a coordinative interaction between the complexes and the CO2 mol. Complexes without COOEt or COMe substitution in undergo a fast deactivation reaction (1st order with respect to [CO2]) that is even visible in the time scale of the cyclic voltammetric expts. The results of the cyclic voltammetric studies could be confirmed in preparative-scale electrolyzes the Ni macrocyclic complex with Me and COOEt substituents proved to be the most active and persistent redox catalyst for the electrochem. redn. of CO2 to oxalate that was described so far.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXnsVGgu7g%253D&md5=d5ed4fe2a630709594fb61955fe099ea
    39. 39
      Angamuthu, R.; Byers, P.; Lutz, M.; Spek, A. L.; Bouwman, E. Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex. Science 2010, 327, 313– 315,  DOI: 10.1126/science.1177981
      39
      Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex
      Angamuthu, Raja; Byers, Philip; Lutz, Martin; Spek, Anthony L.; Bouwman, Elisabeth
      Science (Washington, DC, United States) (2010), 327 (5963), 313-315CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Global warming concern has dramatically increased interest in using CO2 as a feedstock for prepn. of value-added compds., thereby helping to reduce its atm. concn. Here, the authors describe a dinuclear Cu(I) complex that is oxidized in air by CO2 rather than O2; the product is a tetranuclear Cu(II) complex contg. 2 bridging CO2-derived oxalate groups. Treatment of the Cu(II) oxalate complex in MeCN with a sol. Li salt results in quant. pptn. of Li oxalate. The Cu(II) complex can then be nearly quant. electrochem. reduced at a relatively accessible potential, regenerating the initial dinuclear Cu(I) compd. Preliminary results demonstrate 6 turnovers (producing 12 equiv of oxalate) during 7 h of catalysis at an applied potential of -0.03 V vs. the normal H electrode.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXktlWnsg%253D%253D&md5=7bc869762ac853e6f4b22436e052db56
    40. 40
      Udugala-Ganehenege, M. Y.; Dissanayake, N. M.; Liu, Y.; Bond, A. M.; Zhang, J. Electrochemistry of Nickel(II) and Copper(II) N,N′-Ethylenebis(acetylacetoniminato) Complexes and Their Electrocatalytic Activity for Reduction of Carbon Dioxide and Carboxylic Acid Protons. Transit. Metal Chem. 2014, 39, 819– 830,  DOI: 10.1007/s11243-014-9864-3
      40
      Electrochemistry of nickel(II) and copper(II) N,N'-ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons
      Udugala-Ganehenege, Manawadevi Y.; Dissanayake, N. M.; Liu, Yuping; Bond, Alan M.; Zhang, Jie
      Transition Metal Chemistry (Dordrecht, Netherlands) (2014), 39 (7), 819-830CODEN: TMCHDN; ISSN:0340-4285. (Springer)
      The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N'-ethylenebis(acetylacetoniminato)] on their electrochem. and electrocatalytic activity for the redn. of CO2 and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO2 redn., due to the higher stability of the electrochem. generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coeff. of [NiL] calcd. from the steady-state diffusion limiting current is 3.0 × 10-6 cm2 s-1. The catalytic efficiency of [NiL] in non-aq. solvents in terms of ip(CO2)/ip(N2) per nickel center is smaller than that of [Ni(cyclam)]2+, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane)]2+ or multinuclear [Ni3(X)]6+ where X = 8,8',8''-{2,2',2''(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1)) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the redn. of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN. Both [NiL] and [CuL] are also electrocatalysts for the redn. of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GqsbjJ&md5=85b783d8201adbb061560d2a9162f924
    41. 41
      Becker, J. Y.; Vainas, B.; Eger, R.; Kaufman, L. Electrocatalytic Reduction of CO2 to Oxalate by Ag and Pd Porphyrins. J. Chem. Soc., Chem. Commun. 1985, 1471– 1472,  DOI: 10.1039/C39850001471
      41
      Electrocatalytic reduction of carbon dioxide to oxalate by silver(II) and palladium(II) porphyrins
      Becker, James Y.; Vainas, Baruch; Eger, Rivka; Kaufman, Leah
      Journal of the Chemical Society, Chemical Communications (1985), (21), 1471-2CODEN: JCCCAT; ISSN:0022-4936.
      The electrochem. redn. of CO2 was catalyzed by Ag(II) or Pd(II) metalloporphyrins in homogeneous soln. in CH2Cl2. The products detected were (HO2C)2 [144-62-7] and H2.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XhtFyntbY%253D&md5=ef895f8af6cecae2e54ce0f8c2eb461f
    42. 42
      Fröhlich, H.-O.; Schreer, H. Einschub Und Reduktive Kopplung von CO2; Zur Bildung von Cp2TiIIIC2O4TiIIICp2 Und Cp2TiIV(−O2C(CH2)3NRCH2CH2NR(CH2)3CO2–) (R = i-C4H9). Z. Chem. 1983, 23, 348– 349,  DOI: 10.1002/zfch.19830230922
      There is no corresponding record for this reference.
    43. 43
      Lalrempuia, R.; Stasch, A.; Jones, C. The Reductive Disproportionation of CO2 Using a Magnesium(I) Complex: Analogies with Low Valent f-Block Chemistry. Chem. Sci. 2013, 4, 4383– 4388,  DOI: 10.1039/c3sc52242c
      43
      The reductive disproportionation of CO2 using a magnesium(I) complex: analogies with low valent f-block chemistry
      Lalrempuia, Ralte; Stasch, Andreas; Jones, Cameron
      Chemical Science (2013), 4 (12), 4383-4388CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The dimeric magnesium(i) complex, [{(DipNacnac)Mg}2] (DipNacnac = [(DipNCMe)2CH]-, Dip = C6H3Pri2-2,6), reacts with 2 equiv of CO2 to give a high yield of the MgII carbonate complex, [{(DipNacnac)Mg}2(μ-κ2:κ2-CO3)], and CO via a reductive disproportionation process. The MgII oxalate, [{(DipNacnac)Mg}2(μ-C2O4)], is a very low yield byproduct of the reaction. Reducing the carbonate complex with elemental potassium regenerates the MgI starting material. The carbonate complex is shown to form via a stepwise process involving the oxo-bridged intermediate, [{(DipNacnac)Mg}2(μ-O)], which rapidly reacts with stoichiometric CO2 to give [{(DipNacnac)Mg}2(μ-κ2:κ2-CO3)]. The oxo-bridged intermediate has been rationally synthesized via the reaction of [{(DipNacnac)Mg}2] with N2O, and treated with THF to give the adduct, [{(THF)(DipNacnac)Mg}2(μ-O)]. The complex, [{(DipNacnac)Mg}2(μ-O)], reacts with the CO2 isoelectronic analogs, CS2 and CyNCNCy (Cy = cyclohexyl) to give the complexes, [{(DipNacnac)Mg}2(μ-κ2:κ2-CS2O)] and [{(DipNacnac)Mg}2{μ-κ2:κ2-C(NCy)2O}]. Rearrangement of the dithiocarbonate coordination mode of the former occurs upon treatment with di-Et ether, giving the unsym. complex, [{(DipNacnac)Mg}(μ-κ2(S,S'):κ1(O)-CS2O){Mg(DipNacnac)(OEt2)}]. The majority of the complexes prepd. in this study were crystallog. characterized. Taken as a whole, this study demonstrates that magnesium(i) dimers can display very similar reactivity, with respect to small mols. activations, as do SmII and UIII compds. Accordingly, magnesium(i) compds. hold considerable potential as cheaper, less toxic, non-radioactive and diamagnetic alternatives to low valent f-block metal complexes in this realm.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1yis77M&md5=36c9f515dc4821768bdfc8a460307df6
    44. 44
      Paparo, A.; Silvia, J. S.; Kefalidis, C. E.; Spaniol, T. P.; Maron, L.; Okuda, J.; Cummins, C. C. A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2. Angew. Chem., Int. Ed. 2015, 54, 9115– 9119,  DOI: 10.1002/anie.201502532
      44
      A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2
      Paparo, Albert; Silvia, Jared S.; Kefalidis, Christos E.; Spaniol, Thomas P.; Maron, Laurent; Okuda, Jun; Cummins, Christopher C.
      Angewandte Chemie, International Edition (2015), 54 (31), 9115-9119CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Authors describe the stable and isolable dimetalloxycarbene [(TiX3)2(μ2-CO2-κ2C,O:κO')] 5, where X = N-(tert-butyl)-3,5-dimethylanilide, which is stabilized by fluctuating μ2-κ2C,O:κ1O' coordination of the carbene carbon to both titanium centers of the dinuclear complex 5, as shown by variable-temp. NMR studies. Quantum chem. calcns. on the unmodified mol. indicated a higher energy of only +10.5 kJ mol-1 for the μ2-κ1O:κ1O' bonding mode of the free dimetalloxycarbene compared to the μ2-κ2C,O:κ1O' bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX3)2(μ2-OCHO-κO:κO')][B(C6F5)4], 4[B(C6F5)4], was simply deprotonated with the strong base K(N(SiMe3)2) to give 5. Complex 5 reacts smoothly with CO2 to generate the bridging oxalate complex [(TiX3)2(μ2-C2O4-κO:κO'')], 6, in a C-C bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO2 on low-valent transition-metal complexes.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVKmsL7M&md5=007e10b53383c159af9da31236269ca2
    45. 45
      Woen, D. H.; Chen, G. P.; Ziller, J. W.; Boyle, T. J.; Furche, F.; Evans, W. J. Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−. Angew. Chem., Int. Ed. 2017, 56, 2050– 2053,  DOI: 10.1002/anie.201611758
      45
      Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}-
      Woen, David H.; Chen, Guo P.; Ziller, Joseph W.; Boyle, Timothy J.; Furche, Filipp; Evans, William J.
      Angewandte Chemie, International Edition (2017), 56 (8), 2050-2053CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The first crystallog. characterizable complex of Sc2+, [Sc(NR2)3]- (R = SiMe3), was obtained by LnA3/M reactions (Ln = rare earth metal; A = anionic ligand; M = alkali metal) involving redn. of Sc(NR2)3 with K in the presence of 2.2.2-cryptand (crypt) and 18-crown-6 (18-c-6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]+, [K(18-c-6)]+, and [Cs(crypt)]+ salts of the [Sc(NR2)3]- anion are formed, resp. The formation of this oxidn. state of Sc is also indicated by the eight-line EPR spectra arising from the I = 7/2 45Sc nucleus. The Sc(NR2)3 redn. differs from Ln(NR2)3 reactions (Ln = Y and lanthanides) in that it occurs under N2 without formation of isolable reduced dinitrogen species. [K(18-c-6)][Sc(NR2)3] reacts with CO2 to produce an oxalate complex, {K2(18-c-6)3}{[(R2N)3Sc]2(μ-C2O4-κ1O:κ1O'')}, and a CO2- radical anion complex, [(R2N)3Sc(μ-OCO-κ1O:κ1O')K(18-c-6)]n.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Oitb0%253D&md5=3c6dbaae4983f345cee2224340a1f7dc
    46. 46
      Evans, W. J.; Seibel, C. A.; Ziller, J. W. Organosamarium-Mediated Transformations of CO2 and COS: Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO2 to [O2CCO2]2-. Inorg. Chem. 1998, 37, 770– 776,  DOI: 10.1021/ic971381t
      46
      Organosamarium-Mediated Transformations of CO2 and COS: Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO2 to [O2CCO2]2-
      Evans, William J.; Seibel, Christopher A.; Ziller, Joseph W.
      Inorganic Chemistry (1998), 37 (4), 770-776CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The reactivity of CO2 and COS with divalent and trivalent organosamarium complexes has been investigated. (C5Me5)2Sm(THF)2 reductively couples CO2 in THF at room temp. to form the oxalate complex, [(C5Me5)2Sm]2(μ-η2:η2-O2CCO2), 1, in >90% yield. The metal centers in 1 are formally eight-coordinate. The reaction of COS with (C5Me5)2Sm(THF)2 is more complicated and generates a disproportionation product, (C5Me5)2Sm(μ-η2:η1-S2CO)Sm(C5Me5)2(THF), 2, which has one (C5Me5)2Sm unit involved in a four-membered SmSCS ring, while the other (C5Me5)2Sm unit is bound to THF and the oxygen of the S2CO ligand. CO2 reacts with [(C5Me5)2Sm]2(μ-η1:η1-N2Ph2) in >90% yield to form the asym. monoinsertion product, (C5Me5)2Sm[μ-η2:η1-PhNN(CO2)Ph]Sm(C5Me5)2(THF), 3. One (C5Me5)2Sm unit is involved in a five-membered SmNNCO ring, and the other is attached to THF and the other oxygen originating from CO2. 1-3 Were characterized by anal. methods, x-ray diffraction, and NMR and IR spectroscopy.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXns1KjsA%253D%253D&md5=3e2b006426a486f755f4e119c9c81f4d
    47. 47
      Evans, W. J.; Perotti, J. M.; Brady, J. C.; Ziller, J. W. Tethered Olefin Studies of Alkene versus Tetraphenylborate Coordination and Lanthanide Olefin Interactions in Metallocenes. J. Am. Chem. Soc. 2003, 125, 5204– 5212,  DOI: 10.1021/ja020957x
      47
      Tethered Olefin Studies of Alkene versus Tetraphenylborate Coordination and Lanthanide Olefin Interactions in Metallocenes
      Evans, William J.; Perotti, Jeremy M.; Brady, Jason C.; Ziller, Joseph W.
      Journal of the American Chemical Society (2003), 125 (17), 5204-5212CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The tethered olefin cyclopentadienyl ligand, [(C5Me4)SiMe2(CH2CH:CH2)]-, forms unsolvated metallocenes, [(C5Me4)SiMe2(CH2CH:CH2)]2Ln (Ln = Sm, 1; Eu, 2; Yb, 3), from [(C5Me4)SiMe2(CH2CH:CH2)]K and LnI2(THF)2 in good yield. Each complex in the solid state has both tethered olefins oriented toward the Ln metal center with the Ln-C(terminal alkene C) distances 0.2-0.3 Å shorter than the Ln-C(internal alkene C) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5) Å, resp., are normal. Like its permethyl analog, (C5Me5)2Sm(THF)2, complex 1 reductively couples CO2 to form the oxalate-bridged dimer {[(C5Me4)SiMe2(CH2CH:CH2)]2Sm}2(μ-η2:η2-O2CCO2), 4, in which the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh4 to form an unsolvated cation that has the option of coordinating [BPh4]- or a pendant olefin, a competition common in olefin polymn. catalysis. The structure of {[(C5Me4)SiMe2(CH2CH:CH2)]2Sm}[BPh4], 5, shows that both pendant olefins are located near Sm rather than the [BPh4]- counterion.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXisFWhur4%253D&md5=15e0f9353262a5aae2df13c7daef9293
    48. 48
      Willauer, A. R.; Toniolo, D.; Fadaei-Tirani, F.; Yang, Y.; Laurent, M.; Mazzanti, M. Carbon Dioxide Reduction by Dinuclear Yb(II) and Sm(II) Complexes Supported by Siloxide Ligands. Dalton Trans. 2019, 48, 6100– 6110,  DOI: 10.1039/C9DT00554D
      48
      Carbon dioxide reduction by dinuclear Yb(II) and Sm(II) complexes supported by siloxide ligands
      Willauer, Aurelien R.; Toniolo, Davide; Fadaei-Tirani, Farzaneh; Yang, Yan; Laurent, Maron; Mazzanti, Marinella
      Dalton Transactions (2019), 48 (18), 6100-6110CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      Two dinuclear homoleptic complexes of lanthanides(II) supported by the polydentate tris(tertbutoxy) siloxide ligand ([Yb2L4], 1-Yb and [Sm2L4], 1-Sm, (L = (OtBu)3SiO-)) were synthesized in 70-80% yield and 1-Sm was crystallog. characterized. 1-Yb and 1-Sm are stable in soln. at -40 °C but cleave the DME C-O bond over time at room temp. affording the crystal of [Yb2L4(μ-OMe)2(DME)2], 2. The 1-Yb and 1-Sm complexes effect the redn. of CO2 under ambient conditions leading to carbonate and oxalate formation. The selectivity of the redn. towards oxalate or carbonate changes depend on the solvent polarity and on the nature of the ion. For both the lanthanides, carbonate formation is favored but oxalate formation increases if a non-polar solvent is used. Computational studies suggest that the formation of oxalate is favored with respect to carbonate formation in the reaction of the dimeric lanthanide complexes with CO2. Crystals of the tetranuclear mixed-valence oxalate intermediate [Yb4L8(C2O4)], 3 were isolated from hexane and the presence of a C2O42- ligand bridging two [YbIIL2YbIIIL2] dinuclear moieties was shown. Crystals of the tetranuclear di-carbonate product [Sm4L8(μ3-CO3-κ4-O,O',O'')2], 4 were isolated from hexane. The structures of 3 and 4 suggest that the CO2 activation in non-polar solvents involves the interaction of two dimers with CO2 mols. at least to some extent. Such a cooperative interaction results in both oxalate and carbonate formation.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXkvVWhu70%253D&md5=a157f42609ae8fdd7c54aedf14658204
    49. 49
      Castro, L.; Mills, D. P.; Jones, C.; Maron, L. Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex. Eur. J. Inorg. Chem. 2016, 2016, 792– 796,  DOI: 10.1002/ejic.201501346
      49
      Activation of Heteroallenes COxS2-x (x = 0-2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex
      Castro, Ludovic; Mills, David P.; Jones, Cameron; Maron, Laurent
      European Journal of Inorganic Chemistry (2016), 2016 (6), 792-796CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A joint exptl./theor. (DFT) study of the activation of heteroallenes COxS2-x (x = 0-2) by [Sm(Giso)2] {Giso- = [(ArN)2CNCy2]-, Cy = cyclohexyl, Ar = 2,6-diisopropylphenyl} is reported. All heteroallenes are reduced in a different manner. Indeed, while activation of CS2 yields a bimetallic CS2 coupled product through C-S bond formation, CO2 forms an oxalate complex through C-C bond formation. This subsequently undergoes CO2 insertion into one of its Sm-N bonds. Finally, COS activation is predicted to yield a dithiocarbonate complex, through the formation of an intermediate sulfido complex [(Giso)2Sm(μ-S)Sm(Giso)2]. Therefore, [Sm(Giso)2] is a very versatile reagent, since it is a rare example of a complex that allows formation of several activation products involving valence isoelectronic substrates. This is rationalized by DFT calcns., and the latter emphasizes both the lack of kinetic stability of CS vs. CO and the high thermodn. stability of the oxalate.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslWhsbw%253D&md5=204afb626174e84e520cb9ced9ad0bd6
    50. 50
      Andrez, J.; Pécaut, J.; Bayle, P.-A.; Mazzanti, M. Tuning Lanthanide Reactivity Towards Small Molecules with Electron-Rich Siloxide Ligands. Angew. Chem., Int. Ed. 2014, 53, 10448– 10452,  DOI: 10.1002/anie.201405031
      50
      Tuning Lanthanide Reactivity Towards Small Molecules with Electron-Rich Siloxide Ligands
      Andrez, Julie; Pecaut, Jacques; Bayle, Pierre-Alain; Mazzanti, Marinella
      Angewandte Chemie, International Edition (2014), 53 (39), 10448-10452CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The synthesis, structure, and reactivity of stable homoleptic heterometallic LnL4K2 complexes of divalent lanthanide ions with electron-rich tris(tert-butoxy)siloxide ligands are reported. The [Ln(OSi(OtBu)3)4K2] complexes (Ln = Eu, Yb) are stable at room temp., but they promote the redn. of azobenzene to yield the KPhNNPh radical anion as well as the reductive cleavage of CS2 to yield CS32- as the major product. The EuIII complex of the radical anion PhNNPh is structurally characterized. Moreover, [Yb(OSi(OtBu)3)4K2] can reduce CO2 at room temp. Release of the redn. products in D2O shows the quant. formation of both oxalate and carbonate in a 1:2.2 ratio. The bulky siloxide ligands enforce the labile binding of the redn. products providing the opportunity to establish a closed synthetic cycle for the YbII-mediated CO2 redn. The presence of four electron-rich siloxide ligands renders their EuII and YbII complexes highly reactive.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1GksLfO&md5=1af647bd06843e9162e82fb55d068359
    51. 51
      Wong, W.-K.; Zhang, L.-L.; Xue, F.; Mak, T. C. W. Synthesis and X-Ray Crystal Structure of an Unexpected Neutral Oxalate-Bridged Ytterbium(III) Porphyrinate Dimer. J. Chem. Soc., Dalton Trans. 2000, 2245– 2246,  DOI: 10.1039/b003434g
      There is no corresponding record for this reference.
    52. 52
      Evans, W. J.; Lorenz, S. E.; Ziller, J. W. Investigating Metal Size Effects in the Ln2(μ-η2:η2-N2) Reduction System: Reductive Reactivity with Complexes of the Largest and Smallest Trivalent Lanthanide Ions, La3+ and Lu3+. Inorg. Chem. 2009, 48, 2001– 2009,  DOI: 10.1021/ic801853d
      52
      Investigating metal size effects in the Ln2(μ-η2:η2-N2) reduction system: reductive reactivity with complexes of the largest and smallest trivalent lanthanide ions, La3+ and Lu3+
      Evans, William J.; Lorenz, Sara E.; Ziller, Joseph W.
      Inorganic Chemistry (2009), 48 (5), 2001-2009CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Metal size effects in reductive chem. using [[(C5Me4H)2Ln(THF)]2(μ-η2:η2-N2)] (1, 2; Ln = La, Lu) complexes were evaluated using the extremes in ionic radii of the lanthanide series. Comparisons of reactivity towards 1,3,5,7-cyclooctatetraene, phenazine, carbon dioxide, and anthracene substrates are made. Complexes 1 and 2 react similarly with 1,3,5,7-cyclooctatetraene to form previously known (C5Me4H)Ln(C8H8)(THF)x (Ln = La, x = 2; Ln = Lu, x = 0) in a reaction analogous to the redn. of this substrate with divalent (C5Me5)2Sm. Complexes 1 and 2 differ in their reactions with phenazine in which 1 forms at least three products, including [(C5Me4H)2La](μ-η4:η2-C12H8N2)[La(THF)(C5Me4H)2] (3), and (C5Me4H)3La, whereas 2 forms a single product, [(C5Me4H)2Lu]2(μ-η3:η3-C12H8N2) (4), in quant. yield. Complexes 3 and 4 are similar to the product obtained from the reaction of (C5Me5)2Sm and phenazine, [(C5Me5)2Sm]2(μ-η3:η3-C12H8N2), since all three complexes contain a reduced phenazine dianion, but the phenazine ligand displays structural variations depending on the size of the metal. With CO2, complex 1 forms multiple products, but 2 reacts cleanly to form the reductively coupled oxalate complex, [(C5Me4H)2Lu]2(μ-η2:η2-C2O4) (5) in high yield. With anthracene, 1 forms a complex product mixt. from which only (C5Me4H)3La(THF) (9), characterized by x-ray crystallog., could be identified. In contrast, 2 is unreactive toward anthracene even upon heating to 75° after 24 h.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFeitbc%253D&md5=8ad87fb526902e73043d206129fb2de9
    53. 53
      Tsoureas, N.; Castro, L.; Kilpatrick, A. F. R.; Cloke, F. G. N.; Maron, L. Controlling Selectivity in the Reductive Activation of CO2 by Mixed Sandwich Uranium(III) Complexes. Chem. Sci. 2014, 5, 3777– 3788,  DOI: 10.1039/C4SC01401D
      53
      Controlling selectivity in the reductive activation of CO2 by mixed sandwich uranium(III) complexes
      Tsoureas, Nikolaos; Castro, Ludovic; Kilpatrick, Alexander F. R.; Cloke, F. Geoffey N.; Maron, Laurent
      Chemical Science (2014), 5 (10), 3777-3788CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The synthesis and mol. structures of a range of uranium(III) mixed sandwich complexes of the type [U(η8-C8H6(1,4-SiMe3)2)(η5-CpMe4R)] (R = Me, Et, iPr, tBu) and their reactivity towards CO2 are reported. The nature of the R group on the cyclopentadienyl ring in the former has a significant effect on the outcome of CO2 activation: when R = Me, the products are the bridging oxo complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe5)}2(μ-O) and the bridging oxalate complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe5)}2(μ-η2:η2-C2O4); for R = Et or iPr, bridging carbonate {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4R)}2(μ-η1:η2-CO3) and bridging oxalate complexes {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4R)}2(μ-η2:η2-C2O4) are formed in both cases; and when R = tBu the sole product is the bridging carbonate complex {U[η8-C8H6(1,4-SiMe3)2](η5-CpMe4tBu)}2(μ-η1:η2-CO3). Electrochem. studies on both the uranium(III) complexes and the dimeric uranium(IV) CO2 redn. products have been carried out and all exhibit quasi reversible redox processes; in particular, the similarities in the U(III)/U(IV) redox couples suggest that the selectivity in the outcome of CO2 reductive activation by these complexes is steric in origin rather than electronic. The latter conclusion is supported by a detailed computational DFT study on the potential mechanistic pathways for redn. of CO2 by this system.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSltrrE&md5=14a29feb3e3507a1f7593e526763fd45
    54. 54
      Inman, C. J.; Frey, A. S. P.; Kilpatrick, A. F. R.; Cloke, F. G. N.; Roe, S. M. Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand. Organometallics 2017, 36, 4539– 4545,  DOI: 10.1021/acs.organomet.7b00263
      54
      Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand
      Inman, Christopher J.; Frey, Alistair S. P.; Kilpatrick, Alexander F. R.; Cloke, F. Geoffrey N.; Roe, S. Mark
      Organometallics (2017), 36 (23), 4539-4545CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
      The new dianionic ligand C6H4{p-CMe2C6H2Me2O-}2 (p-Me2bp), featuring two aryloxide donors and a central arene ring, was synthesized and used to prep. the mixed-ligand U(III) compd. [U(Cp*)(p-Me2bp)] (Cp* = pentamethylcyclopentadienyl), which exhibits an η6 interaction with the U center. Reductive activation of CO2 was studied using [U(Cp*)(p-Me2bp)] in supercrit. CO2, which gave a dinuclear U carbonate complex, {U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3), cleanly and selectively. Reactivity studies in conventional solvents using lower pressures of CO2 showed the formation of a rare U(IV) oxalate complex, {U(Cp*)(p-Me2bp)}2(μ-η2:η2-C2O2), alongside {U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3). The relative ratio of the last two products is temp. dependent: at low temps. (-78°) oxalate formation is favored, while at room temp. the carbonate is the dominant product. The U(IV) iodide [U(Cp*)(p-Me2bp)I] was also synthesized and used as part of an electrochem. study, the results of which showed that [U(Cp*)(p-Me2bp)] has a U(IV)/U(III) redox couple of -2.18 V vs. FeCp2+/0 as well as a possible electrochem. accessible U(III)/U(II) redn. process at -2.56 V vs. FeCp2+/0.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXos1Wrsr4%253D&md5=1bb9cf1e2decd0ea9f715dbc740d3338
    55. 55
      Schmidt, A.-C.; Heinemann, F. W.; Kefalidis, C. E.; Maron, L.; Roesky, P. W.; Meyer, K. Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes. Chem. Eur. J. 2014, 20, 13501– 13506,  DOI: 10.1002/chem.201404400
      55
      Activation of SO2 and CO2 by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes
      Schmidt, Anna-Corina; Heinemann, Frank W.; Kefalidis, Christos E.; Maron, Laurent; Roesky, Peter W.; Meyer, Karsten
      Chemistry - A European Journal (2014), 20 (42), 13501-13506CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The first sulfite [{((nP,MeArO)3tacn)UIV}2(μ-κ1:κ2-SO3)] (tacn = triazacyclononane) and dithionite [{((nP,MeArO)3tacn)UIV}2(μ-κ2:κ2-S2O4)] of uranium from reaction with gaseous SO2 were prepd. Addnl., the reductive activation of CO2 was investigated with respect to the rare oxalate [{((nP,MeArO)3tacn)UIV}2(μ-κ2:κ2-C2O4)] formation. This ultimately provides the unique S2O42-/C2O42- and SO32-/CO32- complex pairs. All new complexes were characterized by a combination of single-crystal x-ray diffraction, elemental anal., UV/visible/NIR electronic absorption, IR vibrational, and 1H NMR spectroscopy, as well as magnetization (VT SQUID) studies. Also, d. functional theory (DFT) calcns. were carried out to gain further insight into the reaction mechanisms. All observations, together with DFT, support the assumption that SO2 and CO2 show similar (dithionite/oxalate) to analogous (sulfite/carbonate) activation behavior with uranium complexes.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVSnur3J&md5=7069498fd07aeb33ca4387fc4945cfff
    56. 56
      Formanuik, A.; Ortu, F.; Inman, C. J.; Kerridge, A.; Castro, L.; Maron, L.; Mills, D. P. Concomitant Carboxylate and Oxalate Formation From the Activation of CO2 by a Thorium(III) Complex. Chem. Eur. J. 2016, 22, 17976– 17979,  DOI: 10.1002/chem.201604622
      56
      Concomitant carboxylate and oxalate formation from the activation of CO2 by a thorium(III) complex
      Formanuik, Alasdair; Ortu, Fabrizio; Inman, Christopher J.; Kerridge, Andrew; Castro, Ludovic; Maron, Laurent; Mills, David P.
      Chemistry - A European Journal (2016), 22 (50), 17976-17979CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Carbon dioxide and carbon disulfide reacts with tris-cyclopentadienylthorium complex, yielding binuclear thorium complexes [(Cp'3Th)2(μ-CS2)] and [(Cp'2Th)2(μ-C2O4)(Cp''CO2-O,O')] [Cp' = 1,3-(Me3Si)2C5H3; Cp'' = 5,5-(Me3Si)2C5H3-2], bridged by dithiocarbonylate and oxalate ligands. Improving our comprehension of diverse CO2 activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. Carbon dioxide activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO2 is readily reduced to CO, but isolated thorium(III) CO2 activation is unprecedented. We show that the thorium(III) complex, [Th(Cp')3] (1), reacts with CO2 to give the mixed oxalate-carboxylate thorium(IV) complex [{ThCp'2[κ2-2-O2CC5H3-5,5-(SiMe3)2]}2(μ-κ2:κ2-C2O4)] (3). The concomitant formation of oxalate and carboxylate is unique for CO2 activation, as in previous examples either redn. or insertion is favored to yield a single product. Therefore, thorium(III) CO2 activation can differ from better understood uranium(III) chem.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhslKns7jI&md5=28ff1c89e42f0bbb7f19095b9403199a
    57. 57
      Aresta, M.; Gobetto, R.; Quaranta, E.; Tommasi, I. A Bonding-Reactivity Relationship for Ni(PCy3)2(CO2): A Comparative Solid-State-Solution Nuclear Magnetic Resonance Study (31P, 13C) as a Diagnostic Tool to Determine the Mode of Bonding of CO2 to a Metal Center. Inorg. Chem. 1992, 31, 4286– 4290,  DOI: 10.1021/ic00047a015
      57
      A bonding-reactivity relationship for (carbon dioxide)bis(tricyclohexylphosphine)nickel: a comparative solid-state-solution nuclear magnetic resonance study (phosphorus-31, carbon-13) as a diagnostic tool to determine the mode of bonding of carbon dioxide to a metal center
      Aresta, Michele; Gobetto, Roberto; Quaranta, Eugenio; Tommasi, Immacolata
      Inorganic Chemistry (1992), 31 (21), 4286-90CODEN: INOCAJ; ISSN:0020-1669.
      31P and 13C NMR spectra in the solid state and in soln., at variable temp., were used to det. a direct correlation of the modes of bonding of CO2 in Ni(PCy3)2(CO2) in the 2 states. In soln., at 173 K, CO2 is η2-CO bonded to Ni and 31P and 13C chem. shifts are almost identical with the value found for the solid complex, while a dynamic process avs., in soln., the 2 P atoms (ΔG≠ = 39.3 kJ mol-1) at room temp. through an intramol. motion. The modification of the mode of bonding of CO2 to a metal center that occurs when a solid sample is dissolved in a solvent may be relevant to the reactivity of CO2-transition metal complexes, as shown by the reaction of coordinated CO2 with electrophiles (H+, Ag+) and H2. The temp. can play a role.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XlvVelt7c%253D&md5=2e35e7cac444b595f8fd9c9a0cddcf02
    58. 58
      Horn, B.; Limberg, C.; Herwig, C.; Braun, B. Nickel(I)-Mediated Transformations of Carbon Dioxide in Closed Synthetic Cycles: Reductive Cleavage and Coupling of CO2 Generating NiICO, NiIICO3 and NiIIC2O4NiII Entities. Chem. Commun. 2013, 49, 10923– 10925,  DOI: 10.1039/c3cc45407j
      58
      Nickel(I)-mediated Transformations of Carbon Dioxide in Closed Synthetic Cycles: Reductive Cleavage and Coupling of CO2 Generating NiICO, NiIICO3 and NiIIC2O4NiII Entities
      Horn, Bettina; Limberg, Christian; Herwig, Christian; Braun, Beatrice
      Chemical Communications (Cambridge, United Kingdom) (2013), 49 (93), 10923-10925CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The β-diketiminato nickel(I) complex K2[LtBuNiI(N22-)NiILtBu] (LtBu = [HC(C(tBu)NC6H3(iPr)2)2]-) reacts with CO2 via reductive disproportionation to form CO and CO32- contg. products, whereas after employment of the NiI precursor [LtBuNiI(N2)NiILtBu] reductive coupling of CO2 was obsd. giving an oxalate bridged dinickel(II) complex [LtBuNi(C2O4)NiLtBu]. The addn. of KC8 to the carbonate and oxalate compds. formed leads to the regeneration of the initial NiI complexes in an N2 atmosphere, thus closing synthetic cycles.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhslSgtL%252FL&md5=f49d8b42410edafc1971c8c14dbd9248
    59. 59
      Lu, C. C.; Saouma, C. T.; Day, M. W.; Peters, J. C. Fe(I)-Mediated Reductive Cleavage and Coupling of CO2: An FeII(μ-O,μ-CO)FeII Core. J. Am. Chem. Soc. 2007, 129, 4– 5,  DOI: 10.1021/ja065524z
      59
      Fe(I)-Mediated Reductive Cleavage and Coupling of CO2: An FeII(μ-O,μ-CO)FeII Core
      Lu, Connie C.; Saouma, Caroline T.; Day, Michael W.; Peters, Jonas C.
      Journal of the American Chemical Society (2007), 129 (1), 4-5CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      THF solns. of a new iron(I) source, [PhBPCH2Cy3]Fe ([PhBPCH2Cy3] = [PhBP(CH2P(CH2Cy)2)3]-), effect the reductive cleavage of CO2 via O-atom transfer at ambient temp. The dominant reaction pathway is bimetallic and gives a structurally unprecedented diiron FeII(μ-O)(μ-CO)FeII core. X-ray data are also available to suggest that bimetallic reductive CO2 coupling to generate oxalate occurs as a minor reaction pathway. These initial observations forecast a diverse reaction landscape between CO2 and iron(I) synthons. Addnl. [PhBPCH2Cy3]Fe complexes were prepd. and characterized by x-ray crystallog.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xhtlantr7M&md5=6c20af616e63d2dc42e03e60788416fd
    60. 60
      Saouma, C. T.; Lu, C. C.; Day, M. W.; Peters, J. C. CO2 Reduction by Fe(I): Solvent Control of C-O Cleavage versus C-C Coupling. Chem. Sci. 2013, 4, 4042– 4051,  DOI: 10.1039/c3sc51262b
      60
      CO2 reduction by Fe(I): solvent control of C-O cleavage versus C-C coupling
      Saouma, Caroline T.; Lu, Connie C.; Day, Michael W.; Peters, Jonas C.
      Chemical Science (2013), 4 (10), 4042-4051CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      This manuscript explores the product distribution of the reaction of carbon dioxide with reactive iron(I) complexes supported by tris(phosphino)borate ligands, [PhBPR3]- ([PhBPR3]- = [PhB(CH2PR2)3]-; R = CH2Cy, Ph, iPr, 3,5-meta-terphenyl). These studies reveal an interesting and unexpected role for the solvent medium with respect to the CO2 activation reaction. For instance, exposure of methylcyclohexane (MeCy) solns. of [PhBP3CH2Cy]Fe(PR'3) to CO2 yields the partial decarbonylation product {[PhBP3CH2Cy]Fe}2(μ-O)(μ-CO). When the reaction is instead carried out in benzene or THF, reductive coupling of CO2 occurs to give the bridging oxalate species {[PhBP3CH2Cy]Fe}2(μ-κOO':κOO'-oxalato). Reaction studies aimed at understanding this solvent effect are presented, and suggest that the product profile is ultimately detd. by the ability of the solvent to coordinate the iron center. When more sterically encumbering auxiliary ligands are employed to support the iron(I) center (i.e., [PhBPPh3]- and [PhBPiPr3]-), complete decarbonylation is obsd. to afford structurally unusual diiron(II) products {[PhBPR3]Fe}2(μ-O). A mechanistic hypothesis that is consistent with the collection of results described is offered, and suggests that reductive coupling of CO2 likely occurs from an electronically satd. FeII-CO2- species.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlent77N&md5=aae0d67884fbfee1232287dc0d4832bf
    61. 61
      Farrugia, L. J.; Lopinski, S.; Lovatt, P. A.; Peacock, R. D. Fixing Carbon Dioxide with Copper: Crystal Structure of [LCu(μ-C2O4)CuL][Ph4B]2 (L = N,N′,N″-triallyl-1,4,7-triazacyclononane). Inorg. Chem. 2001, 40, 558– 559,  DOI: 10.1021/ic000418y
      61
      Fixing Carbon Dioxide with Copper: Crystal Structure of [LCu(μ-C2O4)CuL][Ph4B]2 (L = N,N',N''-Triallyl-1,4,7-triazacyclononane)
      Farrugia, Louis J.; Lopinski, Stefan; Lovatt, Paul A.; Peacock, Robert D.
      Inorganic Chemistry (2001), 40 (3), 558-559CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The reaction of carbon dioxide with a soln. of CuI, NaBPh4 and N,N',N''-triallyl-1,4,7-triazacyclononane (L) resulted in the formation of the oxalato bridged dinuclear copper(II) complex [LCu(μ-C4O4)CuL](BPh4)2. The complex can be prepd. in higher yields using CsHCO3 in place of CO2. The crystal structure of the complex was detd. showing square pyramidal geometries for the copper atoms with nitrogen atoms in the axial positions. Variable temp. magnetic susceptibility measurements show it to be antiferromagnetic (J = -274 cm-1) as expected for this type of structure.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXptV2rtLc%253D&md5=5108a2a912fc7a2992f489f0eb9ee73d
    62. 62
      Takisawa, H.; Morishima, Y.; Soma, S.; Szilagyi, R. K.; Fujisawa, K. Conversion of Carbon Dioxide to Oxalate by α-Ketocarboxylatocopper(II) Complexes. Inorg. Chem. 2014, 53, 8191– 8193,  DOI: 10.1021/ic5006242
      62
      Conversion of Carbon Dioxide to Oxalate by α-Ketocarboxylatocopper(II) Complexes
      Takisawa, Hideyuki; Morishima, Yui; Soma, Shoko; Szilagyi, Robert K.; Fujisawa, Kiyoshi
      Inorganic Chemistry (2014), 53 (16), 8191-8193CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The α-ketocarboxylatocopper(II) complex [{Cu(L1)}{O2CC(O)CHMe2}] (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate) can be spontaneously converted into the binuclear oxalatocopper(II) complex [{Cu(L1)}2(μ-C2O4)] upon exposure to O2/CO2 gas. 13C-labeling expts. revealed that oxalate ions partially incorporated 13CO2 mols. Also, the bicarbonatocopper(I) complex (NEt4)[Cu(L1){O2C(OH)}] in an Ar atm. and the α-ketocarboxylatocopper(I) complex Na[Cu(L1){O2CC(O)CHMe2}] in an O2 atmosphere were also transformed spontaneously into the oxalato complex [{Cu(L1)}2(μ-C2O4)].
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtlaju7nN&md5=40e281a8318b682c866319af10f16a65
    63. 63
      Klose, A.; Hesschenbrouck, J.; Solari, E.; Latronico, M.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C. The Metal–Carbon Multiple Bond in Iron(I)– and Iron(II)–Dibenzotetramethyltetra-[14]azaannulene: Carbene, Carbonyl, and Isocyanide Derivatives. J. Organomet. Chem. 1999, 591, 45– 62,  DOI: 10.1016/S0022-328X(99)00354-X
      63
      The metal-carbon multiple bond in iron(I)- and iron(II)-dibenzotetramethyltetra[14]azaannulene: carbene, carbonyl, and isocyanide derivatives
      Klose, A.; Hesschenbrouck, J.; Solari, E.; Latronico, M.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C.
      Journal of Organometallic Chemistry (1999), 591 (1-2), 45-62CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science S.A.)
      The two parent compds. used for studying the iron-carbon multiple bond interactions are [Fe(tmtaa)] (1), and [Fe(tmtaa)Na(THF)3] (2) [tmtaa = dibenzotetramethyltetraaza[14]annulene dianion], the latter being obtained by redn. of 1. The reaction of 1 with CO led to the corresponding monocarbonyl deriv. [Fe(tmtaa)(CO)(L)] [L = THF, 3; L = Py, 4], while the reaction with RNC allowed the isolation of mono-isocyanide [Fe(tmtaa)(o-Me3Si-C6H4NC)(THF)] (5), [Fe(tmtaa)(BuNC)(THF)] (6), and bis-isocyanide [Fe(tmtaa)(tBuNC)2] (7) derivs. Redn. of 6 with sodium metal or the reaction of 1 with NaCN led to a monocyano deriv. bridged into a dimeric form by sodium cations in [{Fe(tmtaa)(CN)}2(μ-NaLn)2] [L = THF, n = 3, 8a; L = DME, n = 2, 8b], while the reaction of 1 with Bu4N+CN- led to the monomeric form [Fe(tmtaa)(CN)]-(Bu4N)+ (9). A detailed magnetic anal. of 1-10, the last one being the bis-pyridine deriv. [Fe(tmtaa)(Py)2] (10) showed a variety of low and intermediate spin states, and spin crossovers (with a minor role played by high spin states) as a function of the axial ligands. A remarkable difference was obsd. with the analogous porphyrin derivs. The d7 iron(I) deriv. 2 occurs in tight ion-pair form, both iron and sodium being bonded to the tmtaa ligand. The reaction of 2 with carbon monoxide led to a monocarbonyl deriv. bridged in a dimeric form by sodium cations bonded to the oxygen atoms in [{Fe(tmtaa)}2{μ-CONa(THF)2}2] (11). Both 2 and 11 showed a spin conversion between S = 1/2 and S = 3/2, with a small antiferromagnetic coupling in the latter case, due to the dimeric form. The reaction of 1 with diazoalkane RR'CN2 led to the corresponding low-spin diamagnetic carbene derivs. [Fe(tmtaa)(CRR')] [R = R' = Ph, 12; R = Ph, R' = H, 13], the 1st one being by far more thermally stable, while the 2nd one decomps. at room temp. to 1 and a mixt. of cis and trans-stilbene. Both react with O2 giving Ph2CO and PhCHO and the μ-oxo dimer [{Fe(tmtaa)}(μ-O)] (14). The proposed structures are supported by the x-ray analyses on complexes 2, 8b, 9, 11b and 12.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXns1Snu70%253D&md5=c4eef53095a38d2789f8596bd8133f44
    64. 64
      Tseng, Y.-T.; Ching, W.-M.; Liaw, W.-F.; Lu, T.-T. Dinitrosyl Iron Complex [K-18-crown-6-ether][(NO)2Fe(MePyrCO2)]: Intermediate for Capture and Reduction of Carbon Dioxide. Angew. Chem., Int. Ed. 2020, 59, 11819– 11823,  DOI: 10.1002/anie.202002977
      64
      Dinitrosyl Iron Complex [K-18-crown-6-ether][(NO)2Fe(MePyrCO2)]: Intermediate for Capture and Reduction of Carbon Dioxide
      Tseng, Yu-Ting; Ching, Wei-Min; Liaw, Wen-Feng; Lu, Tsai-Te
      Angewandte Chemie, International Edition (2020), 59 (29), 11819-11823CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Continued efforts are made for the use of CO2 as a C1 feedstock for regeneration of valuable chems. and fuels. Mechanistic study of mol. (electro-/photo-)catalysts disclosed that initial step for CO2 activation involves either nucleophilic insertion or direct redn. of CO2. Nucleophilic activation of CO2 by complex [(NO)2Fe(μ-MePyr)2Fe(NO)2]2- (2, MePyr = 3-methylpyrazolate) gave CO2-captured complex [(NO)2Fe(MePyrCO2)]- (2-CO2, MePyrCO2 = 3-methyl-pyrazole-1-carboxylate). Single-crystal structure, spectroscopic, reactivity, and computational study unravels 2-CO2 as a unique intermediate for reductive transformation of CO2 promoted by Ca2+. Also, sequential reaction of 2 with CO2, Ca(OTf)2, and KC8 established a synthetic cycle, 2 → 2-CO2 → [(NO)2Fe(μ-MePyr)2Fe(NO)2] (1) → 2, for selective conversion of CO2 into oxalate. Presumably, characterization of the unprecedented intermediate 2-CO2 may open an avenue for systematic evaluation of the effects of alternative Lewis acids on redn. of CO2.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXps1Orsrw%253D&md5=1947b1040331e8c2267af1d0560d956c
    65. 65
      Cook, B. J.; Di Francesco, G. N.; Abboud, K. A.; Murray, L. J. Countercations and Solvent Influence CO2 Reduction to Oxalate by Chalcogen-Bridged Tricopper Cyclophanates. J. Am. Chem. Soc. 2018, 140, 5696– 5700,  DOI: 10.1021/jacs.8b02508
      65
      Countercations and Solvent Influence CO2 Reduction to Oxalate by Chalcogen-Bridged Tricopper Cyclophanates
      Cook, Brian J.; Di Francesco, Gianna N.; Abboud, Khalil A.; Murray, Leslie J.
      Journal of the American Chemical Society (2018), 140 (17), 5696-5700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      One-electron redn. of Cu3EL (L3- = tris(β-diketiminate)cyclophane, and E = S, Se) affords [Cu3EL]-, which reacts with CO2 to yield exclusively C2O42- (95% yield, TON = 24) and regenerate Cu3EL. Stopped-flow UV/visible data support an A→B mechanism under pseudo-first-order conditions (kobs, 298K = 115(2) s-1), which is 106 larger than those for reported copper complexes. The kobs values are dependent on the countercation and solvent (e.g., kobs is greater for [K(18-crown-6)]+ vs (Ph3P)2N+, and there is a 20-fold decrease in kobs in THF vs DMF). Our results suggest a mechanism in which cations and solvent influence the stability of the transition state.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnvFChsr0%253D&md5=0e7f630edb114f2eaa44dabd2428e601
    66. 66
      Khamespanah, F.; Marx, M.; Crochet, D. B.; Pokharel, U. R.; Fronczek, F. R.; Maverick, A. W.; Beller, M. Oxalate Production via Oxidation of Ascorbate Rather than Reduction of Carbon Dioxide. Nat. Commun. 2021, 12, 1997,  DOI: 10.1038/s41467-021-21817-w
      66
      Oxalate production via oxidation of ascorbate rather than reduction of carbon dioxide
      Khamespanah, Fatemeh; Marx, Maximilian; Crochet, David B.; Pokharel, Uttam R.; Fronczek, Frank R.; Maverick, Andrew W.; Beller, Matthias
      Nature Communications (2021), 12 (1), 1997CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Cu complex oxalate forms by oxidative degrdn. of ascorbate. This was evidenced by the reaction conducted under an atm. of O2, giving rise to the same oxalate complex described earlier from which sodium oxalate was removed and identified by NMR spectroscopy. In addn., the same product was obtained from reactions of the Cu(I) complex [Cu2(m-xpt)2]2+ with O2 or air in the presence of DHA. In expts. with [Cu2(m-xpt)2]2+ under 13CO2 + O2, 13C was not incorporated into the oxalate product. In contrast, a new trinuclear Cu(II) carbonate complex, [Cu3(m-xpt)3(μ-CO3)]4+, has been isolated, when [Cu2(m-xpt)2]2+ was treated with CO2 and O2 in the absence of sodium ascorbate or DHA.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXns1akt7c%253D&md5=4155ddc9924ade30a8603243e1a86c31
    67. 67
      Häärä, M.; Sundberg, A.; Willför, S. Calcium Oxalate - a Source of “Hickey” Problems - A Literature Review on Oxalate Formation, Analysis and Scale Control. Nord. Pulp. Paper Res. J. 2011, 26, 263– 282,  DOI: 10.3183/npprj-2011-26-03-p263-282
      67
      Calcium oxalate - a source of "hickey" problems - a literature review on oxalate formation, analysis and scale control
      Haara, Matti; Sundberg, Anna; Willfor, Stefan
      Nordic Pulp & Paper Research Journal (2011), 26 (3), 263-282CODEN: NPPJEG; ISSN:0283-2631. (Swedish Association of Pulp and Paper Engineers)
      A review. Calcium oxalate is one of the most problematic scale salts occurring in pulp and paper prodn. processes. Calcium oxalate scaling in a paper machine system often leads to disturbances in the process, prodn. losses due to downtime needed for cleaning, as well as impaired paper quality. This literature review gives a summary of current knowledge and recent research on oxalic acid and calcium oxalate formation esp. in mech. pulping. Methods for oxalate anal., as well as possible ways to control and monitor the scaling in the process, are also discussed. Finally, possibilities to utilize oxalic acid and calcium oxalate in the process are briefly reviewed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFSrtLjJ&md5=3bee1673e006349b047443482306da8d
    68. 68
      Nelson, B. C.; Rockwell, G. F.; Campfield, T.; O’Grady, P.; Hernandez, R. M.; Wise, S. A. Capillary Electrophoretic Determination of Oxalate in Amniotic Fluid. Anal. Chim. Acta 2000, 410, 1– 10,  DOI: 10.1016/S0003-2670(00)00711-X
      68
      Capillary electrophoretic determination of oxalate in amniotic fluid
      Nelson, B. C.; Rockwell, G. F.; Campfield, T.; O'Grady, P.; Hernandez, R. M.; Wise, S. A.
      Analytica Chimica Acta (2000), 410 (1-2), 1-10CODEN: ACACAM; ISSN:0003-2670. (Elsevier Science B.V.)
      A capillary electrophoretic (CE) assay for oxalate was applied to the quant. detn. of free oxalate in amniotic fluid. Indirect absorbance detection of oxalate is accomplished with a chromate-based background electrolyte modified with EDTA. Detection interference due to the presence of high levels (≈4 mg/mL) of inorg. chloride is eliminated through a direct sample clean-up procedure based on cation (Ag+-form) resins. Sepn. interference from amniotic fluid proteins is prevented through the use of a simple aq.-based diln. procedure. This method for the detn. of oxalate in amniotic fluid provides precision of ≈5% relative std. deviation. Within-day precisions for the oxalate response and migration time are better than 3% relative std. deviation and 1% relative std. deviation, resp. Between-day precisions for the oxalate response and migration time are better than 6% relative std. deviation and 3% relative std. deviation, resp. The anal. recovery of oxalate (1000 ng/mL) spiked into amniotic fluid was better than 96%. The limit of detection (LOD) for the method is ≈100 ng/mL oxalate. This method also shows promising results for the detn. of oxalate in human blood plasma samples.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXitVSmu78%253D&md5=fe338c694aea9aa39ca2a1c9bfb990b9
    69. 69
      Chai, W.; Liebman, M. Oxalate Content of Legumes, Nuts, and Grain-Based Flours. J. Food Compost. Anal. 2005, 18, 723– 729,  DOI: 10.1016/j.jfca.2004.07.001
      There is no corresponding record for this reference.
    70. 70
      Sirén, H.; Kokkonen, R.; Hiissa, T.; Särme, T.; Rimpinen, O.; Laitinen, R. Determination of Soluble Anions and Cations from Waters of Pulp and Paper Mills with On-Line Coupled Capillary Electrophoresis. J. Chromatogr. A 2000, 895, 189– 196,  DOI: 10.1016/S0021-9673(00)00586-0
      70
      Determination of soluble anions and cations from waters of pulp and paper mills with on-line coupled capillary electrophoresis
      Siren, H.; Kokkonen, R.; Hiissa, T.; Sarme, T.; Rimpinen, O.; Laitinen, R.
      Journal of Chromatography A (2000), 895 (1+2), 189-196CODEN: JCRAEY; ISSN:0021-9673. (Elsevier Science B.V.)
      When the degree of closure of the paper machine wet end waters increases, wet end problems also become more difficult to control without specific and selective online measurements. The need to measure the concns. of individual compds. in order to explain wet end phenomena is growing. This study was performed to set up a CE (capillary electrophoresis) system to a paper machine and to det. sol. inorg. and org. ions in different locations of pulp and paper process waters with real time analyses by 2 online CE methods. A reconstructed com. CE app. was connected to a papermaking machine via an app., which was a combined sampling and sample pretreatment instrument, the role of which was to filter and dil. the samples before online detn. by CE. The online procedures were optimized for simultaneous detn. of anions as chloride, sulfate, oxalate, formate and acetate and for detn. of cations as potassium, calcium, sodium, magnesium and traces of aluminum. The quantification was performed with external std. methods using the programs available in the com. CE instrument. The concns. of the ions were transferred by using a computerized transfer algorithm exporting the results from the anal. instrument to the process control unit. The developed online procedures were tested three times in paper and paperboard mills for 1 mo at a time. Correlations were obsd. between the CE results and changes in the processes.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmvFyltbw%253D&md5=894b1d2e852e19d586d8137d8e43769b
    71. 71
      Thomas, A. M.; Lin, B.-L.; Wasinger, E. C.; Stack, T. D. P. Ligand Noninnocence of Thiolate/Disulfide in Dinuclear Copper Complexes: Solvent-Dependent Redox Isomerization and Proton-Coupled Electron Transfer. J. Am. Chem. Soc. 2013, 135, 18912– 18919,  DOI: 10.1021/ja409603m
      71
      Ligand Noninnocence of Thiolate/Disulfide in Dinuclear Copper Complexes: Solvent-Dependent Redox Isomerization and Proton-Coupled Electron Transfer
      Thomas, Andrew M.; Lin, Bo-Lin; Wasinger, Erik C.; Stack, T. Daniel P.
      Journal of the American Chemical Society (2013), 135 (50), 18912-18919CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Copper thiolate/disulfide interconversions are related to the functions of several important proteins such as human Sco1, Cu-Zn superoxide dismutase (SOD1), and mammalian zinc-bonded metallothionein (no data). The synthesis and characterization of well-defined synthetic analogs for such interconversions are challenging yet provide important insights into the mechanisms of such redox processes. Solvent-dependent redox isomerization and proton-coupled electron transfer mimicking these interconversions are obsd. in two structurally related dimeric μ,η2:η2-thiolato Cu(II)-Cu(II) complexes by various methods, including x-ray diffraction, XAS, NMR, and UV-visible. Spectroscopic evidence shows that a solvent-dependent equil. exists between the dimeric μ-thiolato Cu(II)-Cu(II) state and its redox isomeric μ-disulfido Cu(I)-Cu(I) form. Complete formation of μ-disulfido Cu(I)-Cu(I) complexes, however, only occurs after the addn. of 2 equiv of protons, which promote electron transfer from thiolate to Cu(II) and formation of disulfide and Cu(I) via protonation of the coordinating ligand. Proton removal reverses this reaction. The reported unusual reductive protonation/oxidative deprotonation of the metal centers may serve as a new chem. precedent for how related proteins manage Cu ions in living organisms.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVCmur3K&md5=1330a414322b04108d15e78b8bf80193
    72. 72
      Knope, K. E.; Kimura, H.; Yasaka, Y.; Nakahara, M.; Andrews, M. B.; Cahill, C. L. Investigation of in Situ Oxalate Formation from 2,3-Pyrazinedicarboxylate under Hydrothermal Conditions Using Nuclear Magnetic Resonance Spectroscopy. Inorg. Chem. 2012, 51, 3883– 3890,  DOI: 10.1021/ic3000944
      72
      Investigation of in Situ Oxalate Formation from 2,3-Pyrazinedicarboxylate under Hydrothermal Conditions Using Nuclear Magnetic Resonance Spectroscopy
      Knope, Karah E.; Kimura, Hiroshi; Yasaka, Yoshiro; Nakahara, Masaru; Andrews, Michael B.; Cahill, Christopher L.
      Inorganic Chemistry (2012), 51 (6), 3883-3890CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The authors have investigated the assembly of a two-dimensional coordination polymer, Nd2(pzdc)2(C2O4)(H2O)2, that was prepd. from the hydrothermal reaction of Nd(NO3)3·6H2O and 2,3-pyrazinedicarboxylic acid (H2pzdc). In situ oxalate formation as obsd. in this system was been investigated using 1H and 13C NMR spectroscopy, and a pathway for C2O42- anion formation under hydrothermal conditions was elucidated. The oxalate ligands found in Nd2(pzdc)2(C2O4)(H2O)2 result from the oxidn. of H2pzdc, which proceeds through intermediates, such as 2-pyrazinecarboxylic acid (2-pzca), 2-hydroxyacetamide, 3-amino-2-hydroxy-3-oxopropanoic acid, 2-hydroxymalonic acid, 2-oxoacetic acid (glyoxylic acid), and glycolic acid. The species are generated through a ring-opening that occurs via cleavage of the C-N bond of the pyrazine ring, followed by hydrolysis/oxidn. of the resulting species.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XivVOhsro%253D&md5=8f9b8078ac11b4b2414fe8b3faba718b
    73. 73
      Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for Organometallic Chemistry. Chem. Rev. 1996, 96, 877– 910,  DOI: 10.1021/cr940053x
      73
      Chemical Redox Agents for Organometallic Chemistry
      Connelly, Neil G.; Geiger, William E.
      Chemical Reviews (Washington, D. C.) (1996), 96 (2), 877-910CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review, with >461 refs., showing how one-electron oxidants and reductants have been used in preparative chem. (incorporating both synthetic applications and generation of species for in situ characterization) in nonaq. solns., the usual media for organometallic ET reactions. The authors do not treat photochem.-generated reducing agents which, although generally transient species, may have advantages in some applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhsVGhu7Y%253D&md5=205b204d99818aded3c41067d4bf85e3
    74. 74
      Drew, M. G. B.; Cairns, C.; McFall, S. G.; Nelson, S. M. The Synthesis, Properties, and the Crystal and Molecular Structures of Five-Co-Ordinate Copper(I) and Silver(I) Complexes of a Quinquedentate Macrocyclic Ligand Having an ‘N3S2’ Donor Set. J. Chem. Soc., Dalton Trans. 1980, 2020– 2027,  DOI: 10.1039/DT9800002020
      74
      The synthesis, properties, and the crystal and molecular structures of five-coordinate copper(I) and silver(I) complexes of a quinquedentate macrocyclic ligand having an N3S2 donor set
      Drew, Michael G. B.; Cairns, Colin; McFall, Stephen G.; Nelson, S. Martin
      Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1980), (10), 2020-7CODEN: JCDTBI; ISSN:0300-9246.
      The 17-membered macrocyclic ligand 2,15-dimethyl-7,10-dithia-3,14,20-triazabicyclo[14.3.1]icosa-1(20),2,14,16,18-pentaene (L) contg. the N3S2 donor set was synthesized and isolated as the Ag(I) complex by the template action of Ag(I) salts on the cyclic Schiff-base condensation of 2,6-diacetylpyridine with 1,10-diamine-4,7-dithiadecane. Cu2+ was ineffective as a template for the synthesis but CuL2+ could be obtained from AgL+ via metal exchange. NaBPh4 reduces CuL2+ to give CuL+ in good yield. Hydrogenation of AgL+ salts using NaBH4 gives the free reduced macrocycle L1 (formed by hydrogenation of the 2 azomethine bonds), which forms the complexes [CuL1][BPh4] and [CuL1][ClO4]2. The CuL+ complex is unreactive to both O and CO. The crystal and mol. structures of [CuL][ClO4] and [AgL][BPh4] were detd. from x-ray diffractometer data using Patterson and Fourier methods and refined by full-matrix least squares to R 0.077 and 0.071 for 927 and 2621 reflections, resp. Although the coordination geometry of both complexes is a distorted trigonal bipyramid, there are marked differences in the macrocycle conformations in the 2 cases, and, in the Cu(I) complex, in the Cu-N bond lengths. These differences are discussed in relation to the size of the 2 metal ions and of the macrocyclic hole.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXhtVGhtA%253D%253D&md5=df50d952bcb7f513f941ddfa9d081c08
    75. 75

      Crystals of [Cu(L1)I] were obtained from a THF solution of in situ formed [Cu(L1)I] starting from CuI, L1, and NaBPh4. This indicates incomplete iodo exchange with NaBPh4. [Cu(L1)I] was independently synthesized (experimental procedure and analytical data can be found in the Supporting Information).

      There is no corresponding record for this reference.
    76. 76
      Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. Macrocycles with a Single Pendant Arm: Synthesis of N-R-(1,4,7-triazacyclononane) [L, R = 4-but-1-ene; L′, R = 3-prop-1-ene]: Synthesis of the CuI Complex [CuL]I and Synthesis and Crystal Structure of the CuII Complex [CuL2][BPh4]2 and the μ-Hydroxy Bridged CuII Dimer [LCu(μ-OH)2CuL][BPh4]2. Inorg. Chim. Acta 1996, 246, 343– 348,  DOI: 10.1016/0020-1693(96)05081-5
      76
      Macrocycles with a single pendant arm: synthesis of N-R-(1,4,7-triazacyclononane) [L, R = 4-but-1-ene; L', R = 3-prop-1-ene]: Synthesis of the CuI complex [CuL]I and synthesis and crystal structure of the CuII complex [CuL2][BPh4]2 and the μ-hydroxy bridged CuII dimer [LCu(μ-OH)2CuL][BPh4]2
      Farrugia, Louis J.; Lovatt, Paul A.; Peacock, Robert D.
      Inorganica Chimica Acta (1996), 246 (1-2), 343-348CODEN: ICHAA3; ISSN:0020-1693. (Elsevier)
      A general method is reported for the prepn. of mono-N-substituted derivs. of [9]aneN3. The method is exemplified by the synthesis of the macrocyclic ligand N-4-but-1-ene-1,4,7-triazacyclononane, L, which has a single pendant butene arm. The propene analog is also reported. Synthesis is reported for [CuIL]I, [CuIIL2][BPh4]2 (1) and [LCuII(OH)2CuIIL][BPh4]2·2MeCN (2). The structures of 1 and 2 were detd.; 1 (C68H82BCuN3) monoclinic, space group P21/n, a 13.0529(8), b 18.008(1), c 13.423(1) Å, β 111.720(6)°, Z = 2; 2 (C72H90B2Cu2N8O2) triclinic, space group P1, a 11.487(1), b 12.870(1), c 12.867(1) Å, α 106.807(6), β 101.833(6), γ 105.859(6)°, Z = 1.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XjvF2rtLg%253D&md5=e404880f17a115f706367c9b4c377613
    77. 77
      Farrugia, L. J.; Lovatt, P. A.; Peacock, R. D. Synthesis of a series of novel binucleating ligands based on 1,4,7-triazacyclononane and o-, m- and p-xylene: crystal structure of the μ-hydroxy-bridged dicopper(II) complex [Cu2Lm(OH)2][BPh4]2 [Lm = α,α′-bis(N-1,4,7-triazacyclononane)-m-xylene]. J. Chem. Soc., Dalton Trans. 1997, 911– 912,  DOI: 10.1039/a608058h
      77
      Synthesis of a series of novel binucleating ligands based on 1,4,7-triazacyclononane and o-, m- and p-xylene: crystal structure of the μ-hydroxy-bridged dicopper(II) complex [Cu2Lm(OH)2][BPh4]2 [Lm = α,α'-bis(N-1,4,7-triazacyclononane)-m-xylene]
      Farrugia, Louis J.; Lovatt, Paul A.; Peacock, Robert D.
      Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1997), (6), 911-912CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
      Three new binucleating ligands, xylenediylbis(triazacyclononanes) I, based on 1,4,7-triazacyclononane and o-, m- or p-xylene, were prepd. The prepn., crystal structure, and magnetic properties of μ-hydroxy dimer [Cu2Lm(OH)2][BPh4]2 (Lm = m-xylene deriv. I) are described.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXisFCgsrw%253D&md5=81025d13c809bcf103a198a981b05b49
    78. 78
      Agilent Technologies. User Manual: Organic Acids Analysis Kit, PN 5063-6510 https://www.agilent.com/cs/library/usermanuals/public/5968-9047E_print.pdf.pdf (accessed 2021-06-25).
      There is no corresponding record for this reference.
    79. 79
      Zhang, X.; Hsieh, W.-Y.; Margulis, T. N.; Zompa, L. J. Binuclear Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands Containing Tri- and Tetramethylene Bridging Groups. An Equilibrium and Structural Study. Inorg. Chem. 1995, 34, 2883– 2888,  DOI: 10.1021/ic00115a015
      79
      Binuclear Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands Containing Tri- and Tetramethylene Bridging Groups. An Equilibrium and Structural Study
      Zhang, Xiaoping; Hsieh, Wen-Yuan; Margulis, T. N.; Zompa, Leverett J.
      Inorganic Chemistry (1995), 34 (11), 2883-8CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Two members of a homologous series of bis(triazacyclononane) ligands, 1,3-bis(1,4,7-triaza-1-cyclononyl)propane, EM3, and 1,4-bis(1,4,7-triaza-1-cyclononyl)butane, EM4, form stable 1:1 and 2:1 Cu(II)-L complexes. Dissocn. consts. for the acid salts of the compds. and equil. studies with Cu(II) in aq. 0.1M KNO3 at 25° are reported. Cu(EM3)2+ is more stable than Cu(EM4)2+ while Cu2(EM4)4+ is slightly more stable than Cu2(EM3)4+. Probable reasons for this behavior are discussed in light of the 1:1 complexes existing in soln. as monomeric species. Binuclear Cu(II) complexes of each ligand were isolated and their structures detd. by x-ray crystallog. Cu2(EM3)Cl4·2H2O crystallizes in space group P2/c with a 12.607(3), b 7.589(2), c 12.948 Å, and β 93.71(3)°. Cu2(EM4)Cl4 crystallizes in space group P21/c with a 11.919(2), b 8.468(2), c 11.508(2) Å, and β 99.06(3)°. In both complexes the Cu(II) is 5-coordinate with two secondary amine N atoms of a [9]aneN3 group and two Cl- occupying sites at the base and the tertiary N atom of the same moiety at the apex of a square pyramid. The structures have somewhat different conformations. The pair of Cl- attached to the two Cu(II) are approx. syn for Cu2(EM3)Cl4·2H2O and anti for Cu2(EM4)Cl4.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXls1ykurk%253D&md5=826fdf7b149148e24707e8b19b42a6e9
    80. 80
      Young, M. J.; Chin, J. Dinuclear Copper(II) Complex That Hydrolyzes RNA. J. Am. Chem. Soc. 1995, 117, 10577– 10578,  DOI: 10.1021/ja00147a022
      80
      Dinuclear copper(II) complex that hydrolyzes RNA
      Young, Mary Jane; Chin, Jik
      Journal of the American Chemical Society (1995), 117 (42), 10577-8CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A novel ligand (L = 1,8-bis(N-1,4,7-triazacyclononylmethyl)naphthalene) that can bind 2 Cu(II) ions was synthesized. The dinuclear metal complex, [(L)Cu2Cl4] (I), was several hundred-fold more reactive than the mononuclear CuCl2 complex of 1,4,7-triazacyclononane for cleaving ApA and 2',3'-cAMP. The pseudo-1st-order rate consts. for the I (2 mM)-promoted cleavage of ApA (0.05 mM) and 2',3'-cAMP (0.05 mM) at pH 6.0 (10 mM MES) were 2.7 × 10-4 s-1 (at 50°) and 2.8 × 10-3 s-1 (at 25°), resp. These represented about 5 and 8 orders of magnitude rate-accelerations for cleaving ApA and 2',3'-cAMP, resp., over the background hydroxide rates at pH 6.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosVKqtrc%253D&md5=94b11f2ff9a85181a2cb8fcf03ad62bd
    81. 81
      McBride, R. S. The Standardization of Potassium Permanganate Solution by Sodium Oxalate. J. Am. Chem. Soc. 1912, 34, 393– 416,  DOI: 10.1021/ja02205a009
      81
      Standardization of Potassium Permanganate Solution by Sodium Oxalate
      McBride, R. S.
      (1912), 34 (), 393-416 ISSN:.
      This paper describes the use of Na2C2O4 in the standardization of KMnO4 soln., its advantages, disadvantages and accuracy.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaC38XhtVartg%253D%253D&md5=3c3e71ba4767a056e6fc2d5506743056
    82. 82
      Knocke, W. R.; van Benschoten, J. E.; Kearney, M. J.; Soborski, A. W.; Reckhow, D. A. Kinetics of Manganese and Iron Oxidation by Potassium Permanganate and Chlorine Dioxide. J. Am. Water Works Assoc. 1991, 83, 80– 87,  DOI: 10.1002/j.1551-8833.1991.tb07167.x
      82
      Kinetics of manganese and iron oxidation by potassium permanganate and chlorine dioxide
      Knocke, William R.; Van Benschoten, John E.; Kearney, Maureen J.; Soborski, Andrew W.; Reckhow, David A.
      Journal - American Water Works Association (1991), 83 (6), 80-7CODEN: JAWWA5; ISSN:0003-150X.
      The effects of reduced metal ion concn., pH, temp., and the presence of dissolved org. C on the kinetics of Mn(II) and Fe(II) oxidn. by KMnO4 and ClO2 were studied and modeled. The oxidn. of reduced Mn(II) was rapid except at low temps. The rates of Mn(II) oxidn. are acceptable in the presence of humic or fulvic acids, but Fe(II) oxidn. is strongly inhibited by these acids. Poor Mn removal is attributed to inefficient capture of colloidal Mn oxide. The oxidant addn. sequence is an important design and operation factor.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXls1Khsbs%253D&md5=c8eb876d84ccdbdea538ed763d270b9b
    83. 83
      Singh, N.; Lee, D. G. Permanganate: A Green and Versatile Industrial Oxidant. Org. Process Res. Dev. 2001, 5, 599– 603,  DOI: 10.1021/op010015x
      83
      Permanganate: A Green and Versatile Industrial Oxidant
      Singh, Nirmal; Lee, Donald G.
      Organic Process Research & Development (2001), 5 (6), 599-603CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)
      A review with refs. The use of permanganate as an effective oxidant in org. chem. has a long and extensive history. Industrial applications have recently become more attractive environmentally by the introduction of a process for recycling manganese dioxide, a coproduct of these reactions. This recycling approach has reduced the environmental impact of permanganate technol. and made it sustainable as defined by the Brundtland Commission. Several current and potential industrial applications of permanganate oxidns. are discussed along with a description of some emerging technologies.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXmvFGktrk%253D&md5=197d9c2e9e7bdcab49fc60f008eb52ae
    84. 84
      Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Cramer, C. J.; Que, L.; Tolman, W. B. A New Intermediate in Copper Dioxygen Chemistry: Breaking the O-O Bond To Form a {Cu2(μ-O)2}2+ Core. J. Am. Chem. Soc. 1995, 117, 8865– 8866,  DOI: 10.1021/ja00139a026
      84
      A New Intermediate in Copper Dioxygen Chemistry: Breaking the O-O Bond To Form a {Cu2(μ-O)2}2+ Core
      Mahapatra, Samiran; Halfen, Jason A.; Wilkinson, Elizabeth C.; Pan, Gaofeng; Cramer, Christopher J.; Que, Lawrence Jr.; Tolman, William B.
      Journal of the American Chemical Society (1995), 117 (34), 8865-6CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The authors report the isolation, spectroscopic and theor. characterization, and C-H bond activation chem. of a new species derived from the reaction of a Cu(I) complex with dioxygen. The proposed {Cu2(μ-O)2}2+ core of this mol. is unprecedented in Cu chem. and may be viewed as a possible intermediate in oxidn. reactions catalyzed by multicopper enzymes and small mol. catalysts. Solns. of [(Bn3TACN)Cu(MeCN)]X (Bn3TACN = 1,4,7-tribenzyl-1,4,7-triazacyclononane; X = ClO4- or SbF6-) in CH2Cl2 absorb 0.5 equiv O2 at -80° to generate an orange-brown species 2 [λmax = 318 (ε 6000 M-1 cm-1) and 430 (7000) nm]. Compd. 2 decomps. to, among other products, the dicopper(II)-bis(μ-hydroxo) complex {[(Bn3TACN)Cu]2(OH)2}(X)2, 3, via rate-detg. attack at ligand benzyl-substituent C-H bonds that was characterized by a large kinetic isotope effect [kH/kD = 50 at -50°; ΔH⧧H = 12.9(5) kcal mol-1, ΔH⧧D = 15.3(5) kcal mol-1, ΔS⧧H = -14(2) e.u., and ΔS⧧D = -11(2) e.u.]. A novel {L2Cu2(μ-O)2}2+ structure with significant covalent character is proposed for 2 from its compn. (EPR, NMR), its oxidizing capability, and similarities of the obsd. resonance Raman (peaks at 602 and 608 cm-1 that shift to one peak at 583 cm-1 upon 18O substitution) and EXAFS (Cu-Cu distance of 2.78 Å) features to those reported for other M2(μ-O)2 (M = Fe, Mn) rhombs. Ab initio calcns. provide support for the proposed ground state structure for 2 and rationalize key exptl. observations.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXnsVOjsrk%253D&md5=a096074d355f7850b00c19e9a64811d5
    85. 85
      Mahapatra, S.; Halfen, J. A.; Wilkinson, E. C.; Pan, G.; Wang, X.; Young, V. G.; Cramer, C. J.; Que, L.; Tolman, W. B. Structural, Spectroscopic, and Theoretical Characterization of Bis(μ-oxo)dicopper Complexes, Novel Intermediates in Copper-Mediated Dioxygen Activation. J. Am. Chem. Soc. 1996, 118, 11555– 11574,  DOI: 10.1021/ja962305c
      85
      Structural, Spectroscopic, and Theoretical Characterization of Bis(μ-oxo)dicopper Complexes, Novel Intermediates in Copper-Mediated Dioxygen Activation
      Mahapatra, Samiran; Halfen, Jason A.; Wilkinson, Elizabeth C.; Pan, Gaofeng; Wang, Xuedong; Young, Victor G., Jr.; Cramer, Christopher J.; Que, Lawrence, Jr.; Tolman, William B.
      Journal of the American Chemical Society (1996), 118 (46), 11555-11574CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A description of the structure and bonding of novel bis(μ-oxo)dicopper complexes and their bis(μ-hydroxo)dicopper decompn. products was derived from combined x-ray crystallog., spectroscopic, and ab initio theor. studies. [(LCu)2(μ-O)2]X2 were generated from the reaction of solns. of [LCu(MeCN)]X with O2 at -80° [L = 1,4,7-tribenzyl-1,4,7-triazacyclononane (LBn3), 1,4,7-triisopropyl-1,4,7-triazacyclononane (LiPr3), or 1-benzyl-4,7-diisopropyl-1,4,7-triazacyclononane (LiPr2Bn); X = variety of anions]. The geometry of the [Cu2(μ-O)2]2+ core was defined by x-ray crystallog. for [(d21-LBn3Cu)2(μ-O)2](SbF6)2 and by EXAFS spectroscopy for the complexes capped by LBn3 and LiPr3; notable dimensions include short Cu-O (∼1.80 Å) and Cu...Cu (∼2.80 Å) distances like those reported for analogous M2(μ-O)2 (M = Fe or Mn) rhombs. The core geometry is contracted compared to those of the bis(μ-hydroxo)dicopper(II) compds. that result from decompn. of the bis(μ-oxo) complexes upon warming. X-ray structures of the decompn. products [(LBn3Cu)(LBn2HCu)(μ-OH)2](O3SCF3)2.2Me2CO, [(LiPr2HCu)2(μ-OH)2](BPh4)2.2THF, and [(LiPr2BnCu)2(μ-OH)2](O3SCF3)2 showed that they arise from N-dealkylation of the original capping macrocycles. Manometric, electrospray mass spectrometric, and UV-visible, EPR, NMR, and resonance Raman spectroscopic data for the bis(μ-oxo)dicopper complexes in soln. revealed important topol. and electronic structural features of the intact [Cu2(μ-O)2]2+ core. The bis(μ-oxo)dicopper unit is diamagnetic, undergoes a rapid fluxional process involving interchange of equatorial and axial N-donor ligand environments, and exhibits a diagnostic ∼600 cm-1 18O-sensitive feature in Raman spectra. Ab initio calcns. on a model system, [(NH3)6Cu2(μ-O)2]2+, predicted a closed-shell singlet ground-state structure that agrees well with the bis(μ-oxo)dicopper geometry detd. by expt. and helps to rationalize many of its physicochem. properties. From an anal. of the theor. and exptl. results (including a bond valence sum anal.), a formal oxidn. level assignment for the core probably is [CuIII2(μ-O2-)2]2+, although a more complete MO description indicates that the O and Cu fragment orbitals are significantly mixed (i.e., there is a high degree of covalency).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsFOitrw%253D&md5=0d8959439405017cbb104bfeb40ee09d
    86. 86
      Mahapatra, S.; Young, V. G., Jr.; Kaderli, S.; Zuberbühler, A. D.; Tolman, W. B. Tuning the Structure and Reactivity of the [Cu2(μ-O)2]2+ Core: Characterization of a New Bis(μ-oxo)dicopper Complex Stabilized by a Sterically Hindered Dinucleating Bis(triazacylononane) Ligand. Angew. Chem., Int. Ed. 1997, 36, 130– 133,  DOI: 10.1002/anie.199701301
      86
      Tuning the structure and reactivity of the [Cu2(μ-O)2]2+ core: characterization of a new bis(μ-oxo)dicopper complex stabilized by a sterically hindered dinucleating bis(triazacyclononane) ligand
      Mahapatra, Samiran; Young, Victor G., Jr.; Kaderli, Susan; Zuberbuehler, Andreas D.; Tolman, William B.
      Angewandte Chemie, International Edition in English (1997), 36 (1/2), 130-133CODEN: ACIEAY; ISSN:0570-0833. (VCH)
      [Cu2(μ-O)2L](ClO4)2 (I) was prepd. and its crystal structure as a solvate detd. in space group P‾1, R1 = 0.0544. The analog of I perdeuterated at iso-Pr (I-D) was also prepd. Kinetics of the oxygenation reaction leading to I were detd. and a mechanism with initial formation of a mono-Cu dioxygen as a rate detg. step is proposed. Kinetics of decompn. of I and I-D show a kinetic isotope effect and a mechanism with intramol. cleavage of a C-H bond of an equatorially disposed iso-Pr substituent is supported. The structure and reactivity of I are compared with related complexes to see the influence of the supporting chelate ligands.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXhtFOjtr0%253D&md5=477e65426533d7762f2856c3e42e29d2
    87. 87
      Dalle, K. E.; Gruene, T.; Dechert, S.; Demeshko, S.; Meyer, F. Weakly Coupled Biologically Relevant CuII2(μ-η1:η1-O2) cis-Peroxo Adduct that Binds Side-On to Additional Metal Ions. J. Am. Chem. Soc. 2014, 136, 7428– 7434,  DOI: 10.1021/ja5025047
      87
      Weakly Coupled Biologically Relevant CuII2(μ-η1:η1-O2) cis-Peroxo Adduct that Binds Side-On to Additional Metal Ions
      Dalle, Kristian E.; Gruene, Tim; Dechert, Sebastian; Demeshko, Serhiy; Meyer, Franc
      Journal of the American Chemical Society (2014), 136 (20), 7428-7434CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The ability of many copper metalloenzymes to activate O2 and transfer it to org. substrates has motivated extensive attention in the literature. Studies focusing on synthetic analogs provided a detailed understanding of the structures of potential intermediates, thereby helping to guide mechanistic studies. The authors report herein a crystallog. characterized synthetic CuII2(μ-η1:η1-O2) complex (I) exhibiting cis-peroxo bonding geometry, known in iron chem. but previously unobserved for copper. Detailed study by UV-visible, resonance Raman, and IR spectroscopies provides evidence for a significantly diminished copper-oxygen interaction (ε ≈ 3000 M-1 cm-1, νCu-O = 437 cm-1, νO-O = 799 cm-1) relative to those in known 'coupled' Cu2O2 species, consistent with magnetic measurements which show that the peroxide mediates only weak antiferromagnetic coupling (-2J = 144 cm-1). These characteristics are comparable with those of a computationally predicted transition state for O2 binding to type 3 copper centers, providing exptl. evidence for the proposed mechanism of O2 activation and supporting the biol. relevance of the CuII2(μ-η1:η1-O2) cis-species. The peroxide bonding arrangement also allows binding of sodium cations, obsd. both in the solid state and in soln. Binding induces changes on an electronic level, as monitored by UV-visible spectroscopy (Ka = 1700 M-1), reminiscent of redox-inactive metal binding by iron-oxygen species. The results presented highlight the analogous chem. these reactive oxygen species undergo, with respect to both their mechanism of formation, and the mol. interactions in which they participate.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXntFChtr4%253D&md5=f1507a6458a3d05cdb91ba82bfa0d94b
    88. 88
      Haidar, R.; Ipek, M.; DasGupta, B.; Yousaf, M.; Zompa, L. J. Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands with Polymethylene Bridging Groups: An Equilibrium and Structural Study. Inorg. Chem. 1997, 36, 3125– 3132,  DOI: 10.1021/ic970070f
      88
      Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands with Polymethylene Bridging Groups: An Equilibrium and Structural Study
      Haidar, Reem; Ipek, Manus; DasGupta, Barnali; Yousaf, Mohammed; Zompa, Leverett J.
      Inorganic Chemistry (1997), 36 (14), 3125-3132CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Copper(II) complexation by ligands contg. two 1,4,7-triazacyclononane, [9]aneN3, groups conjoined by polymethylene chains two to six carbons in length is described. Equil. modeling studies in aq. soln. using pH-potentiometry indicate that the smallest homolog of the series, EM2, forms only Cu(EM2)2+ in dil. aq. solns. All other ligands of the series form stable 1:1 (protonated and nonprotonated) and 2:1 dicopper(II) (hydroxo and nonhydroxo) complexes. Those ligands that contain bridging chains of four or more carbon atoms likely form dimeric or oligomeric complex species in soln. The EM ligands with the shortest polymethylene bridging groups form the most stable 1:1 species. There is little difference among the ligands (n = 3-6) in complex stability of the protonated, CuH2(EMn)4+, and dicopper(II), Cu2(EMn)4+, species. UV-visible spectroscopic continuous variation studies at pH 4.0 and 7.5 are interpreted from the principal equil. species obtained from the equil. models. Single-crystal x-ray diffraction studies on four complexes ([Cu(EM2)]SO4·6H2O (1), [Cu2(EM2)Cl4]·2H2O (2), [Cu2(EM6)Cl4] (3), and [Cu(EM3)][ZnBr4]·H2O (4)) characterize structural features of several 1:1 monomeric and dicopper(II) complexes in the cryst. solid. The monomeric compds. contain CuN6 chromophores while the dicopper(II) compds. contain square pyramidal CuN2Cl2 coordination geometry. Compd. 1 crystallizes in space group P‾1 with a 7.849(2), b 9.783(2), c 16.919(5) Å, α 78.42(3), β 85.76(3), γ 73.06(3), and Z = 2. 2: Space group P21/n with a 9.689(3), b 11.733(3), c 10.124(3) Å, β 98.20(2), and Z = 2. 3: Space group P21/n with a 7.278(2), b 12.416(3), c 13.781(2) Å, β 90.15(2), and Z = 2. 4: Space group P21/c with a 9.295(3), b 16.233(4), c 16.544(5) Å, β 92.62(2), and Z = 4. Cyclic voltammograms of aq. solns. prepd. by dissolving [Cu(EM2)Cl4]·2H2O confirm its dissocn. to Cu(EM2)2+. Aq. solns. contg. 1:1 molar ratios of Cu(II) and EM2 in 0.1 mol dm-3 KCl at 25° show a 1-electron chem. reversible redn. at scan rates of 500 mV s-1 with E1/2 (Cu(II)-Cu(I)) = -868 mV relative to SCE. EPR (X- and Q- band) spectra of frozen solns. (1:1 DMSO/H2O and glycerol/H2O) of Cu(EM2)2+ at 100 K are typical of axial copper(II) features (X-band parameters: g‖ = 2.225 (A‖ = 164 × 10-4) and g.perp. = 2.045).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXjslOqsrc%253D&md5=34b3d5fc52dc0bdea08d5c04270a281f
    89. 89
      Halfen, J. A.; Young, V. G.; Tolman, W. B. Dioxygen Activation by a Copper(I) Complex of a New Tetradentate Tripodal Ligand: Mechanistic Insights into Peroxodicopper Core Reactivity. J. Am. Chem. Soc. 1996, 118, 10920– 10921,  DOI: 10.1021/ja962344o
      89
      Dioxygen Activation by a Copper(I) Complex of a New Tetradentate Tripodal Ligand: Mechanistic Insights into Peroxodicopper Core Reactivity
      Halfen, Jason A.; Young, Victor G., Jr.; Tolman, William B.
      Journal of the American Chemical Society (1996), 118 (44), 10920-10921CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The structurally characterized complex [LPyCu]CF3SO3 (1) (LPy = 1-pyridylmethyl-4,7-diisopropyl-1,4,7-triazacyclononane) binds CO to yield [LPyCuCO]CF3SO3, in which the pyridyl arm of LPy is uncoordinated, and O2 at -78° to yield a trans-1,2-peroxodicopper(II) complex [(LPyCu)2(O2)](CF3SO3)2 (2) {λmax = 550 (ε 10,200 M-1 cm-1), 600 (9700) nm; νO-O = 822 cm-1 [Δν(18O) = 51 cm-1]}. In a 4-electron oxidn. reaction, conversion of the ligand pyridylmethyl group to an amide (LPyO) occurs upon decompn. of 2, with the oxygen in LPyO being derived from the peroxide ligand as shown by isotope labeling. Mechanistic studies indicated that (i) the decompn. follows first order kinetics with ΔH⧧ = 12.6 ± 0.5 kcal mol-1 and ΔS⧧ = -23 ± 2 eu, and (ii) kobsH/kobsD (KIE) = 2.5(5) at -30° (measured for 2 labeled at the pyridylmethyl position). On the basis of this and other evidence, a mechanism for the oxidn. reaction is proposed whereby a unimol. isomerization of the trans-1,2-peroxo unit to a μ-η2:η2-peroxo ligand (a "peroxide shift") precedes C-H bond cleavage.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xmt1Gmuro%253D&md5=fa9dace431cecd114dba6de918b01df7
    90. 90
      Houser, R. P.; Halfen, J. A.; Young, V. G.; Blackburn, N. J.; Tolman, W. B. Structural Characterization of the First Example of a Bis(μ-thiolato)dicopper(II) Complex. Relevance to Proposals for the Electron Transfer Sites in Cytochrome c Oxidase and Nitrous Oxi