Hydrogen Activation with Ru-PN3P Pincer Complexes for the Conversion of C1 FeedstocksClick to copy article linkArticle link copied!
- Matthew D. MortonMatthew D. MortonDepartment of Chemistry, Imperial College London, Molecular Sciences Research Hub, White City Campus, 82 Wood Lane, London W12 0BZ, United KingdomMore by Matthew D. Morton
- Boon Ying TayBoon Ying TayInstitute of Sustainability for Chemicals, Energy and Environment (ICSE2), Agency for Science, Technology and Research (A*STAR), 1 Pesek Road Jurong Island, Singapore 627833, Republic of SingaporeMore by Boon Ying Tay
- Justin J.Q. MahJustin J.Q. MahInstitute of Sustainability for Chemicals, Energy and Environment (ICSE2), Agency for Science, Technology and Research (A*STAR), 1 Pesek Road Jurong Island, Singapore 627833, Republic of SingaporeMore by Justin J.Q. Mah
- Andrew J.P. WhiteAndrew J.P. WhiteDepartment of Chemistry, Imperial College London, Molecular Sciences Research Hub, White City Campus, 82 Wood Lane, London W12 0BZ, United KingdomMore by Andrew J.P. White
- James D. Nobbs*James D. Nobbs*Email: [email protected]Institute of Sustainability for Chemicals, Energy and Environment (ICSE2), Agency for Science, Technology and Research (A*STAR), 1 Pesek Road Jurong Island, Singapore 627833, Republic of SingaporeMore by James D. Nobbs
- Martin van MeursMartin van MeursInstitute of Sustainability for Chemicals, Energy and Environment (ICSE2), Agency for Science, Technology and Research (A*STAR), 1 Pesek Road Jurong Island, Singapore 627833, Republic of SingaporeMore by Martin van Meurs
- George J.P. Britovsek*George J.P. Britovsek*Email: [email protected]Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, White City Campus, 82 Wood Lane, London W12 0BZ, United KingdomMore by George J.P. Britovsek
Abstract
The hydrogenation of C1 feedstocks (CO and CO2) has been investigated using ruthenium complexes [RuHCl(CO)(PN3P)] as the catalyst. PN3P pincer ligands containing amines in the linker between the central pyridine donor and the phosphorus donors with bulky substituents (tert-butyl (1) or TMPhos (2)) are required to obtain mononuclear single-site catalysts that can be activated by the addition of KOtBu to generate stable five-coordinate complexes [RuH(CO)(PN3P–H)], whereby the pincer ligand has been deprotonated. Activation of hydrogen takes place via heterolytic cleavage to generate [RuH2(CO)(PN3P)], but in the presence of CO, coordination of CO occurs preferentially to give [RuH(CO)2(PN3P–H)]. This complex can be protonated to give the cationic complex [RuH(CO)2(PN3P)]+, but it is unable to activate H2 heterolytically. In the case of the less coordinating CO2, both ruthenium complexes 1 and 2 are highly efficient as CO2 hydrogenation catalysts in the presence of a base (DBU), which in the case of the TMPhos ligand results in a TON of 30,000 for the formation of formate.
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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You are free to share(copy and redistribute) this article in any medium or format and to adapt(remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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Synopsis
Hydrogenation of C1 feedstocks (CO and CO2) has been investigated using ruthenium complexes [RuHCl(CO)(PN3P)] as the catalyst precursor. PN3P ligands with bulky substituents are required to obtain mononuclear single-site hydrogenation catalysts. In the presence of CO, coordination of CO occurs preferentially to give [RuH(CO)2(PN3P−H)], which is unable to activate H2. In the case of the less coordinating CO2, the ruthenium complexes are highly efficient as CO2 hydrogenation catalysts.
Introduction
Results and Discussion
Synthesis and reactivity of PN3P Ru complexes
Hydrogen and CO Activation
Hydrogenation of CO2 to Formate
entry | catalyst | [Ru] μmol | conversiona (%) | TONb |
---|---|---|---|---|
1 | blank | 0 | 0 | 0 |
2 | 1 | 14.2 | 93 | 4400 |
3 | 2 | 14.2 | >99 | 4700 |
4 | 1 | 5.7 | >99 | 11,800 |
5 | 2 | 5.7 | >99 | 11,800 |
6 | 1 | 2.8 | 10 | 2300 |
7 | 2 | 2.8 | 100 | 23,600 |
8 | 1 | 1.4 | 0.3 | 100 |
9 | 2 | 1.4 | 64 | 30,300 |
conversion = DBU-formate/DBU × 100.
TON = mol DBU-formate/mol cat.
Conditions: CO2/H2 (1:1) = 15 bar, temp. = 90 °C, reaction time = 1 h, DBU = 10 mL (66.9 mmol), solvent = DMF (35 mL).
Conclusions
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c04001.
Materials and methods, synthetic procedures, NMR spectra, and SC-XRD (PDF)
CCDC 2260612 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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Acknowledgments
We gratefully acknowledge BP and the Agency for Science, Technology & Research (A*STAR) for funding this work (grant C231218005). We thank Solvay for a generous donation of ClPtBu2 and Johnson Matthey for the donation of RuCl3.
References
This article references 53 other publications.
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- 16Kaithal, A.; Werle, C.; Leitner, W. Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese Catalysts. JACS Au 2021, 1, 130– 136, DOI: 10.1021/jacsau.0c00091Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVyjtrw%253D&md5=0b63eabf0164beb7cb68b4446279d546Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese CatalystsKaithal, Akash; Werle, Christophe; Leitner, WalterJACS Au (2021), 1 (2), 130-136CODEN: JAAUCR; ISSN:2691-3704. (American Chemical Society)Alc.-assisted hydrogenation of carbon monoxide (CO) to methanol was achieved using homogeneous mol. complexes. The mol. manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] ([HN(C2H4PiPr2)2] = MACHO-iPr) revealed the best performance, reaching up to turnover no. = 4023 and turnover frequency 857 h-1 in EtOH/toluene as solvent under optimized conditions (T = 150°C, p(CO/H2) = 5/50 bar, t = 8-12 h). Control expts. affirmed that the reaction proceeds via formate ester as the intermediate, whereby a catalytic amt. of base was found to be sufficient to mediate its formation from CO and the alc. in situ. Selectivity for methanol formation reached >99% with no accumulation of the formate ester. The reaction was demonstrated to work with methanol as the alc. component, resulting in a reactive system that allows catalytic "breeding" of methanol without any coreagents.
- 17Ryabchuk, P.; Stier, K.; Junge, K.; Checinski, M. P.; Beller, M. Molecularly Defined Manganese Catalyst for Low-Temperature Hydrogenation of Carbon Monoxide to Methanol. J. Am. Chem. Soc. 2019, 141, 16923– 16929, DOI: 10.1021/jacs.9b08990Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFSisrvF&md5=c3b36be7511471c1ca3b312931877f22Molecularly Defined Manganese Catalyst for Low-Temperature Hydrogenation of Carbon Monoxide to MethanolRyabchuk, Pavel; Stier, Kenta; Junge, Kathrin; Checinski, Marek P.; Beller, MatthiasJournal of the American Chemical Society (2019), 141 (42), 16923-16929CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Methanol synthesis from syngas (CO/H2 mixts.) is one of the largest man-made chem. processes with annual prodn. reaching 100 million tons. The current industrial method proceeds at high temps. (200-300°C) and pressures (50-100 atm) using a copper-zinc-based heterogeneous catalyst. In contrast, here, we report a molecularly defined manganese catalyst that allows for low-temp./low-pressure (120-150°C, 50 bar) carbon monoxide hydrogenation to methanol. This new approach was evaluated and optimized by quantum mech. simulations virtual high-throughput screenings. Crucial for this achievement is the use of amine-based promoters, which capture carbon monoxide to give formamide intermediates, which then undergo manganese-catalyzed hydrogenolysis, regenerating the promoter. Following this conceptually new approach, high selectivity toward methanol and catalyst turnover nos. (up to 3170) was achieved. The proposed general catalytic cycle for methanol synthesis is supported by model studies and detailed spectroscopic investigations.
- 18Sen, R.; Goeppert, A.; Prakash, G. K. S. Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy. Angew. Chem., Int. Ed. 2022, 61, e202207278 DOI: 10.1002/anie.202207278Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xitl2ntLnF&md5=110cc1d983fd8063a7ecc7bddbc5afd4Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol EconomySen, Raktim; Goeppert, Alain; Surya Prakash, G. K.Angewandte Chemie, International Edition (2022), 61 (42), e202207278CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO2 emissions. Outpacing the natural carbon cycle, atm. CO2 levels increased by 50% since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chem. recycling of CO2 to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO2, CO and their derivs. as potential low-temp. alternatives to the com. processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the crit. assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.
- 19Khusnutdinova, J. R.; Garg, J. A.; Milstein, D. Combining Low-Pressure CO2 Capture and Hydrogenation To Form Methanol. ACS Catal. 2015, 5, 2416– 2422, DOI: 10.1021/acscatal.5b00194Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksVSnur4%253D&md5=b1efdf61ebacb203004cfad8b15d3fa9Combining Low-Pressure CO2 Capture and Hydrogenation To Form MethanolKhusnutdinova, Julia R.; Garg, Jai Anand; Milstein, DavidACS Catalysis (2015), 5 (4), 2416-2422CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)This paper describes a novel approach to CO2 hydrogenation, in which CO2 capture with aminoethanols at low pressure is coupled with hydrogenation of the captured product, oxazolidinone, directly to MeOH. In particular, (2-methylamino)ethanol or valinol captures CO2 at 1-3 bar in the presence of catalytic Cs2CO3 to give the corresponding oxazolidinones in up to 65-70 and 90-95% yields, resp. Efficient hydrogenation of oxazolidinones was achieved using PNN pincer Ru catalysts to give the corresponding aminoethanol (up to 95-100% yield) and MeOH (up to 78-92% yield). We also have shown that both CO2 capture and oxazolidinone hydrogenation can be performed in the same reaction mixt. using a simple protocol that avoids intermediate isolation or purifn. steps. For example, CO2 can be captured by valinol at 1 bar with Cs2CO3 catalyst followed by 4-isopropyl-2-oxazolidinone hydrogenation in the presence of a bipy-based pincer Ru catalyst to produce MeOH in 50% yield after two steps.
- 20Kar, S.; Sen, R.; Kothandaraman, J.; Goeppert, A.; Chowdhury, R.; Munoz, S. B.; Haiges, R.; Prakash, G. K. S. Mechanistic Insights into Ruthenium-Pincer-Catalyzed Amine-Assisted Homogeneous Hydrogenation of CO2 to Methanol. J. Am. Chem. Soc. 2019, 141, 3160– 3170, DOI: 10.1021/jacs.8b12763Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXislOmtLo%253D&md5=492b21aae6c60bd00c70b4bccb34943dMechanistic Insights into Ruthenium-Pincer-Catalyzed Amine-Assisted Homogeneous Hydrogenation of CO2 to MethanolKar, Sayan; Sen, Raktim; Kothandaraman, Jotheeswari; Goeppert, Alain; Chowdhury, Ryan; Munoz, Socrates B.; Haiges, Ralf; Prakash, G. K. SuryaJournal of the American Chemical Society (2019), 141 (7), 3160-3170CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Amine-assisted homogeneous hydrogenation of CO2 to methanol is one of the most effective approaches to integrate CO2 capture with its subsequent conversion to CH3OH. The hydrogenation typically proceeds in two steps. In the first step the amine is formylated via an in situ formed alkylammonium formate salt (with consumption of 1 equiv of H2). In the second step the generated formamide is further hydrogenated with 2 more equiv of H2 to CH3OH while regenerating the amine. In the present study, we investigated the effect of mol. structure of the ruthenium pincer catalysts and the amines that are crit. for a high methanol yield. Surprisingly, despite the high reactivity of several Ru pincer complexes [RuHClPNPR(CO)] (R = Ph/i-Pr/Cy/t-Bu) for both amine formylation and formamide hydrogenation, only catalyst Ru-Macho (R = Ph) provided a high methanol yield after both steps were performed simultaneously in one pot. Among various amines, only (di/poly)amines were effective in assisting Ru-Macho for methanol formation. A catalyst deactivation pathway was identified, involving the formation of ruthenium biscarbonyl monohydride cationic complexes [RuHPNPR(CO)2]+, whose structures were unambiguously characterized and whose reactivities were studied. These reactivities were found to be ligand-dependent, and a trend could be established. With Ru-Macho, the biscarbonyl species could be converted back to the active species through CO dissocn. under the reaction conditions. The Ru-Macho biscarbonyl complex was therefore able to catalyze the hydrogenation of in situ formed formamides to methanol. Complex Ru-Macho-BH was also highly effective for this conversion and remained active even after 10 days of continuous reaction, achieving a max. turnover no. (TON) of 9900.
- 21Rezayee, N. M.; Huff, C. A.; Sanford, M. S. Tandem amine and ruthenium-catalyzed hydrogenation of CO2 to methanol. J. Am. Chem. Soc. 2015, 137, 1028– 1031, DOI: 10.1021/ja511329mGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVChtL4%253D&md5=ed06fe6cf9f8a65bb2443a34dc644b72Tandem Amine and Ruthenium-Catalyzed Hydrogenation of CO2 to MethanolRezayee, Nomaan M.; Huff, Chelsea A.; Sanford, Melanie S.Journal of the American Chemical Society (2015), 137 (3), 1028-1031CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)This Communication describes the hydrogenation of carbon dioxide to methanol via tandem catalysis with dimethylamine and a homogeneous ruthenium complex. Unlike previous examples with homogeneous catalysts, this CO2-to-CH3OH process proceeds under basic reaction conditions. The dimethylamine is proposed to play a dual role in this system. It reacts directly with CO2 to produce dimethylammonium dimethylcarbamate, and it also intercepts the intermediate formic acid to generate DMF. With the appropriate selection of catalyst and reaction conditions, >95% conversion of CO2 was achieved to form a mixt. of CH3OH and DMF.
- 22Kothandaraman, J.; Goeppert, A.; Czaun, M.; Olah, G. A.; Prakash, G. K. Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst. J. Am. Chem. Soc. 2016, 138, 778– 781, DOI: 10.1021/jacs.5b12354Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmsVek&md5=9f708b98d949b119c5bf5aec3f215edaConversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium CatalystKothandaraman, Jotheeswari; Goeppert, Alain; Czaun, Miklos; Olah, George A.; Prakash, G. K. SuryaJournal of the American Chemical Society (2016), 138 (3), 778-781CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A highly efficient homogeneous catalyst system for the prodn. of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h-1 at 145 °C). Ease of sepn. of CH3OH is demonstrated by simple distn. from the reaction mixt. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover no. > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concn. (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.
- 23Curley, J. B.; Hert, C.; Bernskoetter, W. H.; Hazari, N.; Mercado, B. Q. Control of Catalyst Isomers Using an N-Phenyl-Substituted RN(CH2CH2PiPr2)2 Pincer Ligand in CO2 Hydrogenation and Formic Acid Dehydrogenation. Inorg. Chem. 2022, 61, 643– 656, DOI: 10.1021/acs.inorgchem.1c03372Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXivVSrsrrL&md5=da53d392f16826fbf01df4e4dec7d66dControl of Catalyst Isomers Using an N-Phenyl-Substituted RN(CH2CH2PiPr2)2 Pincer Ligand in CO2 Hydrogenation and Formic Acid DehydrogenationCurley, Julia B.; Hert, Clayton; Bernskoetter, Wesley H.; Hazari, Nilay; Mercado, Brandon Q.Inorganic Chemistry (2022), 61 (1), 643-656CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A novel pincer ligand, iPrPNPhP [PhN(CH2CH2PiPr2)2], which is an analog of the versatile MACHO ligand, iPrPNHP [HN(CH2CH2PiPr2)2], was synthesized and characterized. The ligand was coordinated to ruthenium, and a series of hydride-contg. complexes were isolated and characterized by NMR and IR spectroscopies, as well as x-ray diffraction. Comparisons to previously published analogs ligated by iPrPNHP and iPrPNMeP [CH3N(CH2CH2PiPr2)2] illustrate that there are large changes in the coordination chem. that occur when the nitrogen substituent of the pincer ligand is altered. For example, ruthenium hydrides supported by the iPrPNPhP ligand always form the syn isomer (where syn/anti refer to the relative orientation of the group on nitrogen and the hydride ligand on ruthenium), whereas complexes supported by iPrPNHP form the anti isomer and complexes supported by iPrPNMeP form a mixt. of syn and anti isomers. Authors evaluated the impact of the nitrogen substituent of the pincer ligand in catalysis by comparing a series of iPrPNRP (R = H, Me, Ph)-ligated ruthenium hydride complexes as catalysts for formic acid dehydrogenation and carbon dioxide (CO2) hydrogenation to formate. The iPrPNPhP-ligated species is the most active for formic acid dehydrogenation, and mechanistic studies suggest that this is likely because there are kinetic advantages for catalysts that operate via the syn isomer. In CO2 hydrogenation, the iPrPNPhP-ligated species is again the most active under authors optimal conditions, and they report some of the highest turnover frequencies for homogeneous catalysts. Exptl. and theor. insights into the turnover-limiting step of catalysis provide a basis for the obsd. trends in catalytic activity. Addnl., the stability of complexes enabled to detect a previously unobserved autocatalytic effect involving the base that is added to drive the reaction. Overall, by modifying the nitrogen substituent on the MACHO ligand, they have developed highly active catalysts for formic acid dehydrogenation and CO2 hydrogenation and also provided a framework for future catalyst development.
- 24Kar, S.; Sen, R.; Goeppert, A.; Prakash, G. K. S. Integrative CO2 Capture and Hydrogenation to Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol Economy. J. Am. Chem. Soc. 2018, 140, 1580– 1583, DOI: 10.1021/jacs.7b12183Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsVKmt74%253D&md5=53f54a005a5d8a21a0d8850efb1e4487Integrative CO2 Capture and Hydrogenation to Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol EconomyKar, Sayan; Sen, Raktim; Goeppert, Alain; Prakash, G. K. SuryaJournal of the American Chemical Society (2018), 140 (5), 1580-1583CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Herein we report an efficient and recyclable system for tandem CO2 capture and hydrogenation to methanol. After capture in an aq. amine soln., CO2 is hydrogenated in high yield to CH3OH (>90%) in a biphasic 2-MTHF/water system, which also allows for easy sepn. and recycling of the amine and catalyst for multiple reaction cycles. Between cycles, the produced methanol can be conveniently removed in vacuo. Employing this strategy, catalyst Ru-MACHO-BH and polyamine PEHA were recycled three times with 87% of the methanol productivity of the first cycle retained, along with 95% of catalyst activity after four cycles. CO2 from dil. sources such as air can also be converted to CH3OH using this route. We postulate that the CO2 capture and hydrogenation to methanol system presented here could be an important step toward the implementation of the carbon neutral methanol economy concept.
- 25Filonenko, G. A.; van Putten, R.; Schulpen, E. N.; Hensen, E. J. M.; Pidko, E. A. Highly Efficient Reversible Hydrogenation of Carbon Dioxide to Formates Using a Ruthenium PNP-Pincer Catalyst. ChemCatChem. 2014, 6, 1526– 1530, DOI: 10.1002/cctc.201402119Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsVSkur8%253D&md5=4b20b98890b30e5dc80aff978add8271Highly efficient reversible hydrogenation of carbon dioxide to formates using a ruthenium PNP-pincer catalystFilonenko, Georgy A.; van Putten, Robbert; Schulpen, Erik N.; Hensen, Emiel J. M.; Pidko, Evgeny A.ChemCatChem (2014), 6 (6), 1526-1530CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of hydrogen as a fuel requires both safe and robust technologies for its storage and transportation. Formic acid (FA) produced by the catalytic hydrogenation of CO2 is recognized as a potential intermediate H2 carrier. Herein, we present the development of a formate-based H2 storage system that employs a Ru PNP-pincer catalyst. The high stability of this system allows cyclic operation with an exceptionally fast loading and liberation of H2. Kinetic studies highlight the crucial role of the base promoter, which controls the rate-detg. step in FA dehydrogenation and defines the total H2 capacity attainable from the hydrogenation of CO2. The reported findings show promise for the development of practical technologies that use formic acid as a hydrogen carrier.
- 26Guan, C.; Pan, Y.; Ang, E. P. L.; Hu, J.; Yao, C.; Huang, M.-H.; Li, H.; Lai, Z.; Huang, K.-W. Conversion of CO2 from air into formate using amines and phosphorus-nitrogen PN3P-Ru(II) pincer complexes. Green Chem. 2018, 20, 4201– 4205, DOI: 10.1039/C8GC02186DGoogle Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlOrtLnN&md5=246a3c8bf4d82633b21e91a7d461ae83Conversion of CO2 from air into formate using amines and phosphorus-nitrogen PN3P-Ru(II) pincer complexesGuan, Chao; Pan, Yupeng; Ang, Eleanor Pei Ling; Hu, Jinsong; Yao, Changguang; Huang, Mei-Hui; Li, Huaifeng; Lai, Zhiping; Huang, Kuo-WeiGreen Chemistry (2018), 20 (18), 4201-4205CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)Well-defined ruthenium(II) PN3P pincer complexes were developed for the hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF (turnover frequency) and TON (turnover no.) up to 13 000 h-1 and 33 000, resp., in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from air into formate was conducted in the presence of an amine, allowing easy product sepn. and catalyst recycling.
- 27Li, H.; Goncalves, T. P.; Zhao, Q.; Gong, D.; Lai, Z.; Wang, Z.; Zheng, J.; Huang, K. W. Diverse catalytic reactivity of a dearomatized PN3P*-nickel hydride pincer complex towards CO2 reduction. Chem. Commun. 2018, 54, 11395– 11398, DOI: 10.1039/C8CC05948AGoogle Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFCktbbL&md5=465014194f1a362ab4a92771d0e71ec2Diverse catalytic reactivity of a dearomatized PN3P*-nickel hydride pincer complex towards CO2 reductionLi, Huaifeng; Goncalves, Theo P.; Zhao, Qianyi; Gong, Dirong; Lai, Zhiping; Wang, Zhixiang; Zheng, Junrong; Huang, Kuo-WeiChemical Communications (Cambridge, United Kingdom) (2018), 54 (81), 11395-11398CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A dearomatized PN3P*-nickel hydride complex has been prepd. using an oxidative addn. process. The first nickel-catalyzed hydrosilylation of CO2 to methanol has been achieved, with unprecedented turnover nos. Selective methylation and formylation of amines with CO2 were demonstrated by such a PN3P*-nickel hydride complex, highlighting its versatile functions in CO2 redn.
- 28Tanaka, R.; Yamashita, M.; Nozaki, K. Catalytic hydrogenation of carbon dioxide using Ir(III)-pincer complexes. J. Am. Chem. Soc. 2009, 131, 14168– 14169, DOI: 10.1021/ja903574eGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFKktL3J&md5=b3399e3290ced490f3bda0454449bcdbCatalytic Hydrogenation of Carbon Dioxide Using Ir(III)-Pincer ComplexesTanaka, Ryo; Yamashita, Makoto; Nozaki, KyokoJournal of the American Chemical Society (2009), 131 (40), 14168-14169CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Catalytic hydrogenation of carbon dioxide in aq. potassium hydroxide was performed using a newly synthesized isopropyl-substituted PNP-pincer iridium trihydride complex as catalyst. Potassium formate was obtained with turnover no. up to 3,500,000 and turnover frequency of 150,000 h-1.
- 29Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.; Nozaki, K. Mechanistic Studies on the Reversible Hydrogenation of Carbon Dioxide Catalyzed by an Ir-PNP Complex. Organometallics 2011, 30, 6742– 6750, DOI: 10.1021/om2010172Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFertrbP&md5=e16d0147b887b90b737071417163e1e3Mechanistic Studies on the Reversible Hydrogenation of Carbon Dioxide Catalyzed by an Ir-PNP ComplexTanaka, Ryo; Yamashita, Makoto; Chung, Lung Wa; Morokuma, Keiji; Nozaki, KyokoOrganometallics (2011), 30 (24), 6742-6750CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The PNP-ligated iridium(III) trihydride complex 1 exhibited the highest catalytic activity for hydrogenation of carbon dioxide in aq. KOH. The catalytic hydrogenation can be tuned to be a reversible process with the same catalyst at the expense of the activity, when triethanolamine was used as a base. Theor. studies on the hydrogenation of carbon dioxide using DFT calcns. suggested two competing reaction pathways: either the deprotonative dearomatization step or the hydrogenolysis step as the rate-detg. step. The results nicely explain our exptl. observations that the catalytic cycle is dependent on both the strength of the base and hydrogen pressure.
- 30Pan, Y.; Guan, C.; Li, H.; Chakraborty, P.; Zhou, C.; Huang, K. W. CO2 hydrogenation by phosphorus-nitrogen PN3P-pincer iridium hydride complexes: elucidation of the deactivation pathway. Dalton Trans 2019, 48, 12812– 12816, DOI: 10.1039/C9DT01319AGoogle Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVaqsLjL&md5=86544f1ac3b3c8a72ae6888a1411282bCO2 hydrogenation by phosphorus-nitrogen PN3P-pincer iridium hydride complexes: elucidation of the deactivation pathwayPan, Yupeng; Guan, Chao; Li, Huaifeng; Chakraborty, Priyanka; Zhou, Chunhui; Huang, Kuo-WeiDalton Transactions (2019), 48 (34), 12812-12816CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)PN3P-Ir pincer hydride complexes were synthesized and characterized as catalysts and key intermediates in the direct hydrogenation of CO2 to formate under mild conditions. The formation of a dearomatized PN3P*-Ir(I)-CO species was identified as a plausible key process accountable for the loss of catalytic activity in the CO2 hydrogenation.
- 31Khusnutdinova, J. R.; Milstein, D. Metal-ligand cooperation. Angew. Chem., Int. Ed. 2015, 54, 12236– 12273, DOI: 10.1002/anie.201503873Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVOnu7fK&md5=8a302a3f5b0b7a2f5d1faefdf2ed979dMetal-Ligand CooperationKhusnutdinova, Julia R.; Milstein, DavidAngewandte Chemie, International Edition (2015), 54 (42), 12236-12273CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review; metal-ligand cooperation (MLC) has become an important concept in catalysis by transition metal complexes both in synthetic and biol. systems. MLC implies that both the metal and the ligand are directly involved in bond activation processes, by contrast to "classical" transition metal catalysis where the ligand (e.g. phosphine) acts as a spectator, while all key transformations occur at the metal center. In this Review, we will discuss examples of MLC in which 1) both the metal and the ligand are chem. modified during bond activation and 2) bond activation results in immediate changes in the 1st coordination sphere involving the cooperating ligand, even if the reactive center at the ligand is not directly bound to the metal (e.g. via tautomerization). The role of MLC in enabling effective catalysis as well as in catalyst deactivation reactions will be discussed.
- 32Alig, L.; Fritz, M.; Schneider, S. First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands. Chem. Rev. 2019, 119, 2681– 2751, DOI: 10.1021/acs.chemrev.8b00555Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXk&md5=2a22fcda0a1be9ea45c9ecd9094af4c3First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer LigandsAlig, Lukas; Fritz, Maximilian; Schneider, SvenChemical Reviews (Washington, DC, United States) (2019), 119 (4), 2681-2751CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The use of 3d metals in de/hydrogenation catalysis has emerged as a competitive field with respect to "traditional" precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal-ligand cooperativity and ligand redox-activity strongly stimulated this development as a conceptual starting point for rational catalyst design. This review aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodol. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.
- 33Gunanathan, C.; Milstein, D. Bond activation and catalysis by ruthenium pincer complexes. Chem. Rev. 2014, 114, 12024– 12087, DOI: 10.1021/cr5002782Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvFagtrrL&md5=655df14d3f81471371ba5b21d4cc6053Bond Activation and Catalysis by Ruthenium Pincer ComplexesGunanathan, Chidambaram; Milstein, DavidChemical Reviews (Washington, DC, United States) (2014), 114 (24), 12024-12087CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The focus of this Review is limited to a summary of key developments in the area of bond activation and catalysis by defined ruthenium pincer complexes.
- 34Mathis, C. L.; Geary, J.; Ardon, Y.; Reese, M. S.; Philliber, M. A.; VanderLinden, R. T.; Saouma, C. T. Thermodynamic Analysis of Metal-Ligand Cooperativity of PNP Ru Complexes: Implications for CO2 Hydrogenation to Methanol and Catalyst Inhibition. J. Am. Chem. Soc. 2019, 141, 14317– 14328, DOI: 10.1021/jacs.9b06760Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFemtLbJ&md5=b5d9a8c63d1a05b66f22d4e11ad1c14dThermodynamic Analysis of Metal-Ligand Cooperativity of PNP Ru Complexes: Implications for CO2 Hydrogenation to Methanol and Catalyst InhibitionMathis, Cheryl L.; Geary, Jackson; Ardon, Yotam; Reese, Maxwell S.; Philliber, Mallory A.; VanderLinden, Ryan T.; Saouma, Caroline T.Journal of the American Chemical Society (2019), 141 (36), 14317-14328CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The hydrogenation of CO2 in the presence of amines to formate, formamides, and methanol (MeOH) is a promising approach to streamlining carbon capture and recycling. To achieve this, understanding how catalyst design impacts selectivity and performance is crit. Herein we describe a thorough thermochem. anal. of the (de)hydrogenation catalyst, (PNP)Ru-Cl (PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine; Ru = Ru(CO)(H)) and correlate our findings to catalyst performance. Although this catalyst is known to hydrogenate CO2 to formate with a mild base, we show that MeOH is produced when using a strong base. Consistent with pKa measurements, the requirement for a strong base suggests that the deprotonation of a six-coordinate Ru species is integral to the catalytic cycle that produces MeOH. Our studies also indicate that the concn. of MeOH produced is independent of catalyst concn., consistent with a deactivation pathway that is dependent on methanol concn., not equivalency. Our temp.-dependent equil. studies of the dearomatized congener, (*PNP)Ru, with various H-X species (to give (PNP)Ru-X; X = H, OH, OMe, OCHO, OC(O)NMe2) reveal that formic acid equil. is approx. temp.-independent; relative to H2, it is more favored at elevated temps. We also measure the hydricity of (PNP)Ru-H in THF and show how subsequent coordination of the substrate can impact the apparent hydricity. The implications of this work are broadly applicable to hydrogenation and dehydrogenation catalysis and, in particular, to those that can undergo metal-ligand cooperativity (MLC) at the catalyst. These results serve to benchmark future studies by allowing comparisons to be made among catalysts and will pos. impact rational catalyst design.
- 35Nobbs, J. D.; Sugiarto, S.; See, X. Y.; Cheong, C. B.; Aitipamula, S.; Stubbs, L. P.; van Meurs, M. Tetramethylphosphinane as a new secondary phosphine synthon. Nat. Commun. 2023, 6, 85, DOI: 10.1038/s42004-023-00876-8Google ScholarThere is no corresponding record for this reference.
- 36He, L.-P.; Chen, T.; Xue, D.-X.; Eddaoudi, M.; Huang, K.-W. Efficient transfer hydrogenation reaction Catalyzed by a dearomatized PN3P ruthenium pincer complex under base-free Conditions. J. Organomet. Chem. 2012, 700, 202– 206, DOI: 10.1016/j.jorganchem.2011.10.017Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFGgu7k%253D&md5=68caca7956d6277f1cb5bc5ee0ac4a52Efficient transfer hydrogenation reaction catalyzed by a dearomatized PN3P ruthenium pincer complex under base-free conditionsHe, Li-Peng; Chen, Tao; Xue, Dong-Xu; Eddaoudi, Mohamed; Huang, Kuo-WeiJournal of Organometallic Chemistry (2012), 700 (), 202-206CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)A dearomatized complex [RuH(PN3P)(CO)] (PN3P = N,N'-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (I) was prepd. by reaction of the arom. complex [RuH(Cl)(PN3P)(CO)] with t-BuOK in THF. Further treatment of I with formic acid led to the formation of a rearomatized complex (II). These new complexes were fully characterized and the mol. structure of complex II was further confirmed by X-ray crystallog. In complex II, a distorted square-pyramidal geometry around the ruthenium center was obsd., with the CO ligand trans to the pyridinic nitrogen atom and the hydride located in the apical position. The dearomatized complex I displays efficient catalytic activity for hydrogen transfer of ketones in isopropanol.
- 37Benito-Garagorri, D.; Becker, E.; Wiedermann, J.; Lackner, W.; Pollak, M.; Mereiter, K.; Kisala, J.; Kirchner, K. Achiral and Chiral Transition Metal Complexes with Modularly Designed Tridentate PNP Pincer-Type Ligands Based on N-Heterocyclic Diamines. Organometallics 2006, 25, 1900– 1913, DOI: 10.1021/om0600644Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xit1Omurs%253D&md5=58305fac09d0a4afff8d6bf6855df868Achiral and Chiral Transition Metal Complexes with Modularly Designed Tridentate PNP Pincer-Type Ligands Based on N-Heterocyclic DiaminesBenito-Garagorri, David; Becker, Eva; Wiedermann, Julia; Lackner, Wolfgang; Pollak, Martin; Mereiter, Kurt; Kisala, Joanna; Kirchner, KarlOrganometallics (2006), 25 (8), 1900-1913CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The synthesis and characterization of Mo, Fe, Ru, Ni, Pd, and Pt complexes contg. new achiral and chiral PNP pincer-type ligands based on the N-heterocyclic diamines 2,6-diaminopyridine, N,N'-di-10-undecenyl-2,6-diaminopyridine, N,N'-dihexyl-2,6-diaminopyridine, and 2,6-diamino-4-phenyl-1,3,5-triazine are reported. The new PNP ligands were prepd. conveniently in high yield by treatment of the resp. N-heterocyclic diamines with 2 equiv of a variety of achiral and chiral R2PCl compds. in the presence of base. Mo PNP complexes [Mo(PNP)(CO)3PNP] were obtained by treatment of [Mo(CO)3(MeCN)3] with 1 equiv of the resp. PNP ligand. They react with I2 to give novel seven-coordinate pincer complexes [Mo(PNP)(CO)3I]+ and [Mo(PNP)(CO)2(MeCN)I]+ depending of whether the reaction is carried out in CH2Cl2 or MeCN. With [Fe(H2O)6](BF4)2 and 1 equiv of PNP ligand in MeCN dicationic complexes [Fe(PNP)(MeCN)3](BF4)2 were obtained. The cis and trans dichloride complexes [Ru(PNP)(PPh3)Cl2] were prepd. by a ligand exchange reaction of [RuCl2(PPh3)3] with a stoichiometric amt. of the resp. PNP ligand. Cationic PNP complexes of Ni(II), [Ni(PNP)Br]Br, were synthesized by the reaction of [NiBr2(DME)] with 1 equiv of PNP ligand. In similar fashion, treatment of [M(COD)X2] (M = Pd, Pt; X = Cl, Br) with 1 equiv of PNP ligand yields the cationic square-planar complexes [M(PNP)X]X. If the reaction is carried out in the presence of the halide scavenger KCF3SO3, complexes [M(PNP)X]CF3SO3 were obtained, which are better sol. in nonpolar solvents than the analogous halide compds. X-ray structures of representative Mo, Fe, Ru, Ni, and Pd PNP complexes were detd. Finally, the use of the Pd complexes as catalysts for the Suzuki-Miyaura coupling of some aryl bromides and Ph boronic acid was examd.
- 38Salem, H.; Shimon, L. J. W.; Diskin-Posner, Y.; Leitus, G.; Ben-David, Y.; Milstein, D. Formation of Stable trans-Dihydride Ruthenium(II) and 16-Electron Ruthenium(0) Complexes Based on Phosphinite PONOP Pincer Ligands. Reactivity toward Water and Electrophiles. Organometallics 2009, 28, 4791– 4806, DOI: 10.1021/om9004077Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXptFOjsbc%253D&md5=8bc52d256bd1e3c8ce2f727581091b34Formation of Stable trans-Dihydride Ruthenium(II) and 16-Electron Ruthenium(0) Complexes Based on Phosphinite PONOP Pincer Ligands. Reactivity toward Water and ElectrophilesSalem, Hiyam; Shimon, Linda J. W.; Diskin-Posner, Yael; Leitus, Gregory; Ben-David, Yehoshoa; Milstein, DavidOrganometallics (2009), 28 (16), 4791-4806CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The synthesis of a series of new ruthenium complexes based on the new PONOP ligands (1) and (10) (C5H3N-1,3-(OPR2)2: 1, R = iPr; 10, R = tBu) is presented, including the stable trans-dihydride complexes (iPr-PONOP)Ru(H)2(PPh3) (4) and (tBu-PONOP)Ru(H)2(CO) (12) and the stable Ru(0) complexes (R-PONOP)Ru(CO)2 (6, R = iPr; 15, R = tBu). A surprisingly stable 16-electron Ru(0) complex (13) was formed by deprotonation of 12 with KOtBu. Complex 13 reacts with H2 to afford the cis-dihydride complex 12a, which isomerized to the trans-dihydride 12. Complex 13 reacted with CO to afford the satd. Ru(0) complex 15. Reaction of complex 12 with water led to hydrolysis of the phosphinite PONOP ligand and rearrangement to a dimeric product (14). Reaction of the trans-dihydride complex 4 with the electrophiles PhCOCl, MeI, and MeOTf led to abstraction of one of the hydride ligands, forming the monohydride complexes (iPr-PONOP)Ru(H)(PPh3)(X) (X = Cl (2), I (8a), OTf (8b)) together with benzaldehyde in the case of 2. Similarly, 12 afforded the monohydride complexes (tBu-PONOP)Ru(H)(CO)(X) (X = Cl (11), OTf (17), I (18)). Reaction of the Ru(0) complexes 6 and 15 with water resulted in hydrolysis of the O-P bond and formation of the zwitterionic complexes 7 and 16. Treatment of 2 and 11 with MeOTf or MeI resulted in abstraction of the chloride ligand rather than the hydride, forming complexes 8a,b and 17, 18, resp. Addnl. syntheses of complexes based on ligands 1 and 10 are presented.
- 39Ogata, O.; Nara, H.; Fujiwhara, M.; Matsumura, K.; Kayaki, Y. N-Monomethylation of Aromatic Amines with Methanol via PN(H)P-Pincer Ru Catalysts. Org. Lett. 2018, 20, 3866– 3870, DOI: 10.1021/acs.orglett.8b01449Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyisrnO&md5=636ae24a9f7b2f868d600dc09be0da5dN-Monomethylation of Aromatic Amines with Methanol via PNHP-Pincer Ru CatalystsOgata, Osamu; Nara, Hideki; Fujiwhara, Mitsuhiko; Matsumura, Kazuhiko; Kayaki, YoshihitoOrganic Letters (2018), 20 (13), 3866-3870CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)In the presence of 0.02-0.1 mol% ruthenium PNP pincer complex I and in the presence of KOt-Bu at 150°, aryl amines underwent chemoselective and green N-methylation with methanol to give N-methylarylamines. I underwent ionization and assocn. of carbon monoxide to form cationic dicarbonyl pincer ruthenium complexes which also acted as effective catalysts for chemoselective methylation.
- 40Herrmann, W. A. Organometallic Aspects of the Fischer–Tropsch Synthesis. Angew. Chem., Int. Ed. 1982, 21, 117– 130, DOI: 10.1002/anie.198201171Google ScholarThere is no corresponding record for this reference.
- 41Nelson, G. O.; Sumner, C. E. Synthesis and reactivity of pentamethylcyclopentadienylruthenium formyl and α-hydroxy methyl complexes. Organometallics 1986, 5, 1983– 1990, DOI: 10.1021/om00141a009Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XlsFehur4%253D&md5=1760ee6160aaa0ddae6794ecb689fbc2Synthesis and reactivity of pentamethylcyclopentadienylruthenium formyl and α-hydroxy complexesNelson, Gregory O.; Sumner, Charles E.Organometallics (1986), 5 (10), 1983-90CODEN: ORGND7; ISSN:0276-7333.(η-C5Me5)Ru(CO)2CH2OH (I, Cp = cyclopentadienyl), (η-C5Me5)Ru(CO)2CHO (II), and (η-C5Me5)Ru(CO)(PMe2Ph)CHO (III) were synthesized and studied as models for intermediates in the redn. of CO to org. oxygenates by transition metal catalysts. I was prepd. by NaBH3CN redn. of (η-C5Me5)Ru(CO)3+ BF4- (IV). II was synthesized by redn. of IV with [Ph3PCuH]6, but it could not be isolated in pure form. Pure cryst. III was isolated from the redn. of (η-C5Me5)Ru(CO)2(PMe2Ph)+ I- with NaBH4 in THF/H2O. Formyl complexes II and III decompd. by a radical chain mechanism. The intermediate formed from the decompn. of III underwent electron transfer with (η-C5R5)Ru(CO)2I (R = H, Me). An x-ray structure of III was completed.
- 42Nelson, G. O. (Pentamethylcyclopentadienyl)ruthenium compounds. Synthesis and characterization of (η5-C5Me5)Ru(CO)2CH2OH. Organometallics 1983, 2, 1474– 1475, DOI: 10.1021/om50004a046Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXlsVSisbk%253D&md5=ee79562296a7ae88db96e8bc2a63ed8d(Pentamethylcyclopentadienyl)ruthenium compounds. Synthesis and characterization of (η-C5Me5)Ru(CO)2CH2OHNelson, Gregory O.Organometallics (1983), 2 (10), 1474-5CODEN: ORGND7; ISSN:0276-7333.Treatment of (η5-C5Me5)Ru(CO)2I (C5H5 = cyclopentadienyl) in CH2Cl2 with AgBF4 under 60 psi CO produces 82% [(η-C5Me5)Ru(CO)3][BF1], which on redn. with excess NaBH3CN in MeOH gave a mixt. of (η-C5Me2)Ru(CO)2H, (η-C5Me2)Ru(CO)2CH2OMe and (η-C5Me5)Ru(CO)2CH2OH (I) . A soln. of I in THF under 5000 psi CO at 80° does not react. Reaction of I with CF3CON(SiMe3)2 gave (η-C5Me2)Ru(CO)2CH2OSiMe3.
- 43Teets, T. S.; Labinger, J. A.; Bercaw, J. E. A Thermodynamic Analysis of Rhenium(I)–Formyl C–H Bond Formation via Base-Assisted Heterolytic H2 Cleavage in the Secondary Coordination Sphere. Organometallics 2013, 32, 5530– 5545, DOI: 10.1021/om400810vGoogle Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGrsr7E&md5=c387e321ab3624631d99e4305cc39463A Thermodynamic Analysis of Rhenium(I)-Formyl C-H Bond Formation via Base-Assisted Heterolytic H2 Cleavage in the Secondary Coordination SphereTeets, Thomas S.; Labinger, Jay A.; Bercaw, John E.Organometallics (2013), 32 (19), 5530-5545CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)Conversion of synthesis gas, a mixt. of CO and H, into value-added Cn≥2 products requires both C-H and C-C bond-forming events. The authors' group has developed mol. complexes, based on Group 7 (Mn and Re) carbonyl complexes, to interrogate the elementary steps involved in the homogeneous hydrogenative reductive coupling of CO. Here, the authors explore a new mode of H2 activation, in which strong bases in the secondary coordination sphere are positioned to assist in the heterolytic cleavage of H2 to form a formyl C-H bond at a Re-bound carbonyl. Cationic Re(I) complexes [ReI(P∼B:-κ1-P)(CO)5]+1, where P∼B: is a phosphine ligand with a tethered strong base, were prepd. and characterized; measurement of their protonation equil. demonstrates a pronounced attenuation of the basicity upon coordination. Formyl complexes supported by these ligands can be prepd. in 50% to 95% yields by hydride delivery to the parent pentacarbonyl complexes, and several of the free-base formyl complexes can be protonated, generating observable [ReI(P∼BH-κ1-P)(CHO)(CO)4]+1 complexes. Intramol. H bonding is evident for one of the complexes, providing addnl. stabilization to the protonated formyl complex. By measuring both the hydricity of the formyl, ΔG°H-, and its pKa, the overall free energy of H2 cleavage is calcd. from an appropriate cycle and is thermodynamically uphill in all cases (in the best case by only ∼8 kcal/mol), although significantly dependent upon the properties of the supporting ligand.
- 44Elowe, P. R.; West, N. M.; Labinger, J. A.; Bercaw, J. E. Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme. Organometallics 2009, 28, 6218– 6227, DOI: 10.1021/om900804jGoogle Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1CgtrvF&md5=9fec4f86e8fc66763a00a5b97dc408f8Transformations of Group 7 carbonyl complexes: possible intermediates in a homogeneous syngas conversion schemeElowe, Paul R.; West, Nathan M.; Labinger, Jay A.; Bercaw, John E.Organometallics (2009), 28 (21), 6218-6227CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)Redn. of Group VIIB metal phosphine carbonyls by lithium triethylhydroborate gave access to formyl complexes, which were isolated and characterized as borane-stabilized adducts. A variety of C-H and C-C bond forming reactions of Group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C2+ compds. Reaction of [(PPh3)2M(CO)4][BF4] with LiBHEt3 gave neutral formyl complexes [(PPh3)2(CO)3M(CHO)] (2a,b; M = Mn, Re). Attempted silylation of 2b by Me3SiOTf gave unexpected product, [(PPh3)2Re(CO)3(CHO·BF3)] (4b), as a result of fluoride abstraction from BF4- anion and trifluoroborane coordination. Reaction of 2a,b with BX3 gave the stabilized formyl complexes directly, [(PPh3)2(CO)3M(CHO·BX3)] (4a,b, X = F, M = Mn, Re; 5a,b, X = C6F5, M = Mn, Re). The metal formyl complexes 2 are substantially stabilized by coordination to boranes BX3 in the form of novel boroxycarbene complexes M(CO)3(PPh3)2(CHOBX3), but these boron-stabilized carbenes 4 and 5 do not react with hydride sources to undergo further redn. to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)5-x(PPh3)x(CHOMe)]+ (x = 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atm. of CO. The resulting acyls, cis- and trans-Mn(PPh3)(CO)4(C(O)CH2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh3)(CO)4(C(OR)CH2OMe)]+, which undergoes a 1,2-hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or di-Et ether adducts of [Mn(PPh3)(CO)4]+. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh3)(CO)4(CH2COOMe) and is protonolyzed to yield Me acetate and [Mn(PPh3)(CO)4]+; addn. of L (L = PPh3, CO) to the manganese cation regenerates [Mn(PPh3)(CO)4(L)]+. Since the original formyl complex can be obtained by the reaction of [Mn(PPh3)(CO)5]+ with [PtH(dmpe)2]+, which in turn can be generated from H2, this set of transformations amts. to a stoichiometric cycle for selectively converting H2 and CO into a C2 compd. under mild conditions.
- 45Pan, Y.; Pan, C.; Zhang, Y.; Li, H.; Min, S.; Guo, X.; Zheng, B.; Chen, H.; Anders, A.; Lai, Z.; Zheng, J.; Huang, K. Selective Hydrogen Generation from Formic Acid with Well-Defined Complexes of Ruthenium and Phosphorus-Nitrogen PN3 -Pincer Ligand. Chem. - Asian J. 2016, 11, 1357– 1360, DOI: 10.1002/asia.201600169Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Kms7c%253D&md5=9811408b864a042ea6c3ae493d6c97d2Selective Hydrogen Generation from Formic Acid with Well-Defined Complexes of Ruthenium and Phosphorus-Nitrogen PN3-Pincer LigandPan, Yupeng; Pan, Cheng-Ling; Zhang, Yufan; Li, Huaifeng; Min, Shixiong; Guo, Xunmun; Zheng, Bin; Chen, Hailong; Anders, Addison; Lai, Zhiping; Zheng, Junrong; Huang, Kuo-WeiChemistry - An Asian Journal (2016), 11 (9), 1357-1360CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)An unsym. protonated PN3-pincer complex in which ruthenium is coordinated by one nitrogen and two phosphorus atoms was employed for the selective generation of hydrogen from formic acid. Mechanistic studies suggest that the imine arm participates in the formic acid activation/deprotonation step. A long life time of 150 h with a turnover no. over 1 million was achieved.
- 46Ooyama, D.; Tomon, T.; Tsuge, K.; Tanaka, K. Structural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reduction. J. Organomet. Chem. 2001, 619, 299– 304, DOI: 10.1016/S0022-328X(00)00705-1Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhslOksrk%253D&md5=f8bdd0ef09174fb2c177dbf129eb3d6aStructural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reductionOoyama, Dai; Tomon, Takashi; Tsuge, Kiyoshi; Tanaka, KojiJournal of Organometallic Chemistry (2001), 619 (2), 299-304CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science S.A.)The mol. structures of Ru(II) complexes with Me, formyl, and acetyl groups [Ru(bpy)2(CO)L]+ (L = CH3, C(O)H and C(O)CH3) were examd. from the viewpoint of active species in multi-step redn. of CO2 on Ru. The Me complex was prepd. by the reaction of [Ru(bpy)2(OH2)2]2+ with trimethylsilyl acetylene and fully characterized by IR, Raman, 13C NMR and single-crystal x-ray crystallog. Disorder of the Ru-CO and Ru-C(O)H bonds in the crystal structure of the formyl complex made it difficult to det. the bond parameters of the two groups accurately, but the mol. structure of the analogous acetyl complex, which was obtained by the reaction of [Ru(bpy)2(CO3)] with propiolic acid, was detd. by x-ray anal. The Ru-carbonyl (Ru-C-O) bond angles of the Me and acetyl complex with 174(1) and 175.5(5)°, resp., are in the ranges of those of previously characterized [Ru(bpy)2(CO)L]n+ (L = CO2, C(O)OH, CO and CH2OH). However, the Ru-CH3 and Ru-C(O)CH3 bond distances showed unusual relation against the stretching frequency in the Raman spectra.
- 47Toyohara, K.; Nagao, H.; Mizukawa, T.; Tanaka, K. Ruthenium Formyl Complexes as the Branch Point in Two- and Multi-Electron Reductions of CO2. Inorg. Chem. 1995, 34, 5399– 5400, DOI: 10.1021/ic00126a003Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosVarsLc%253D&md5=73b356974881a4dd173c189b7d9149bfRuthenium Formyl Complexes as the Branch Point in Two- and Multi-Electron Reductions of CO2Toyohara, Kiyotsuna; Nagao, Hirotaka; Mizukawa, Tetsunori; Tanaka, KojiInorganic Chemistry (1995), 34 (22), 5399-400CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)Both [Ru(bpy)2(CO)(CHO)]+ and [Ru(bpy)(trpy)(CHO)]+ (bpy = 2,2'-bipyridine; trpy = 2,2',6',2''-terpyridine) were characterized and the latter is the key-intermediate of four- and six-electron redn. of CO2 producing HCHO and CH3OH. Higher reactivity of these formyl complexes than the corresponding hydrides reveals a new pathway of HCOOH formation in electrochem. CO2 redn.
- 48Kelly, J. M.; Vos, J. G. cis-[Ru(bpy)2(CO)H]+: A Possible Intermediate in the Photochemical Production of H2 from Water Catalyzed by [Ru(bpy)3]2+?. Angew. Chem., Int. Ed. 1982, 21 (8), 628– 629, DOI: 10.1002/anie.198206281Google ScholarThere is no corresponding record for this reference.
- 49Dombek, B. D. Hydrogenation of carbon monoxide to methanol and ethylene glycol by homogeneous ruthenium catalysts. J. Am. Chem. Soc. 1980, 102, 6855– 6857, DOI: 10.1021/ja00542a036Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXmtlykt7Y%253D&md5=9325c5615a5476e29cd8eaca9501b0c7Hydrogenation of carbon monoxide to methanol and ethylene glycol by homogeneous ruthenium catalystsDombek, B. DuaneJournal of the American Chemical Society (1980), 102 (22), 6855-7CODEN: JACSAT; ISSN:0002-7863.Solns. of Ru3(CO)12 in carboxylic acids catalyze the hydrogenation of CO at low pressures (100 to 340 atm) to give MeOH (obtained as its ester), with smaller amts. of ethylene glycol diester. At 340 atm and 260° a combined rate to these products of 8.3 × 10-3 turnovers s-1 was obsd. in HOAc solvent. Similar rates to MeOH are obtainable in other polar solvents, but ethylene glycol is not obsd. under these conditions except in the presence of carboxylic acids. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor.
- 50Walker, H. W.; Ford, P. C. Synthesis and characterization of [PPN][HRu(CO)4] and a convenient route to [PPN][HOs(CO)4]. J. Organomet. Chem. 1981, 214, C43– C44, DOI: 10.1016/S0022-328X(81)80019-8Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXls12ns7c%253D&md5=da7fdd77de30f50d95583ee26ff178bdSynthesis and characterization of [PPN][HRu(CO)4] and a convenient route to [PPN][HOs(CO)4]Walker, Howard W.; Ford, Peter C.Journal of Organometallic Chemistry (1981), 214 (3), C43-C44CODEN: JORCAI; ISSN:0022-328X.[PPN][HM(CO)4] (M = Ru, Os; PPN = bis(triphenylphosphine)iminium were prepd. in 60% (M = Ru) yield by treating Na2M(CO)4 with PPN+Cl- in a min. amt. of MeOH at -196° followed by filtration of -78°.
- 51Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Süss, G. The triruthenium cluster anion [Ru3H(CO)11]−: preparation, structure, and fluxionality. J. Chem. Soc., Dalton Trans. 1979, 9, 1356– 1361, DOI: 10.1039/DT9790001356Google ScholarThere is no corresponding record for this reference.
- 52Guntermann, N.; Franciò, G.; Leitner, W. Hydrogenation of CO2 to formic acid in biphasic systems using aqueous solutions of amino acids as the product phase. Green Chem. 2022, 24, 8069– 8075, DOI: 10.1039/D2GC02598AGoogle Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XisFWqsLjF&md5=77846b4ff0482b12f7e1496e1800f4f4Hydrogenation of CO2 to formic acid in biphasic systems using aqueous solutions of amino acids as the product phaseGuntermann, Nils; Francio, Giancarlo; Leitner, WalterGreen Chemistry (2022), 24 (20), 8069-8075CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)Carbon capture and utilization is considered a promising approach for introducing CO2 into the chem. value chain, esp. in combination with bioenergy applications (BECCU). We report here on the catalytic hydrogenation of CO2 to formic acid in a biphasic reaction system using aq. solns. of amino acids as the product phase and possible capture solns. for biogenic CO2. The mol. structure of the ruthenium catalyst and the catalyst phase were matched through a combined design process identifying n-dodecanol (lauryl alc.) as the preferred "green" solvent. A total turnover no. (TON) of over 100 000 mol HCOOH per mol of catalyst (46 582 g HCOOH per g of Ru) with minimal contamination of the aq. phase with metal or org. solvent was obtained. The resulting aq. solns. attained almost quant. conversions with up to 0.94 mol formic acid per mol amino acid (ca. 108 g HCOOH per kg). Such solns. may find use directly, or after upgrading, in agricultural applications without the need for energy intensive and costly isolation of pure formic acid.
- 53Heldebrant, D. J.; Jessop, P. G.; Thomas, C. A.; Eckert, C. A.; Liotta, C. L. The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide. J. Org. Chem. 2005, 70, 5335– 5338, DOI: 10.1021/jo0503759Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXksVertLs%253D&md5=13da346fe0d2d25925ff834f3c173835The Reaction of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) with Carbon DioxideHeldebrant, David J.; Jessop, Philip G.; Thomas, Colin A.; Eckert, Charles A.; Liotta, Charles L.Journal of Organic Chemistry (2005), 70 (13), 5335-5338CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)Amidines have been reported to react with CO2 to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO2 detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO2 and does not indicate that an isolable zwitterionic adduct between DBU and CO2 forms either in the presence or the absence of water.
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- 1Xie, J.; Olsbye, U. The Oxygenate-Mediated Conversion of COx to Hydrocarbons - On the Role of Zeolites in Tandem Catalysis. Chem. Rev. 2023, 123, 11775– 11816, DOI: 10.1021/acs.chemrev.3c000581https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3sXitVSjt7jF&md5=e67a8578a182bc67cc51f9dd7614100eThe oxygenate-mediated conversion of COx to hydrocarbons - on the role of zeolites in tandem catalysisXie, Jingxiu; Olsbye, UnniChemical Reviews (Washington, DC, United States) (2023), 123 (20), 11775-11816CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Decentralised chem. plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorise CO2 and CO with renewable H2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert COx to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodn. and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the sep. processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/ zeotype function in the oxygenate-mediated conversion of COx to hydrocarbons. Use of shape-selective zeolite/zeotype catalysts enables the selective prodn. of fuel components as well as key intermediates for the chem. industry, such as BTX, gasoline, light olefins, and C3+ alkanes. In contrast to the sep. processes which use methanol as a platform, this review examines the potential of methanol, di-Me ether and ketene as possible oxygenate intermediates in sep. chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferrable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from mol. (mechanism, oxygenate mol.), to catalyst, to reactor configuration and finally to process level. Finally we present our perspectives on related emerging technologies, outstanding challenges and potential directions for future research.
- 2Gao, R.; Zhang, C.; Jun, K.-W.; Kim, S. K.; Park, H.-G.; Zhao, T.; Wang, L.; Wan, H.; Guan, G. Transformation of CO2 into liquid fuels and synthetic natural gas using green hydrogen: A comparative analysis. Fuel 2021, 291, 120111 DOI: 10.1016/j.fuel.2020.1201112https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXjvVCqurY%253D&md5=9e8340f4c10b9931b439e8d351dc7cbeTransformation of CO2 into liquid fuels and synthetic natural gas using green hydrogen: A comparative analysisGao, Ruxing; Zhang, Chundong; Jun, Ki-Won; Kim, Seok Ki; Park, Hae-Gu; Zhao, Tiansheng; Wang, Lei; Wan, Hui; Guan, GuofengFuel (2021), 291 (), 120111CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)The power-to-liqs. (P2L) and power-to-gas (P2G) processes which utilize renewable power to convert carbon dioxide and water into value-added syncrude and synthetic natural gas have recently gained much attention as an efficient way for CO2 mitigation. Based on our previously proposed direct P2L and P2L/P2G hybrid processes in the absence of the reverse-water-gas-shift unit, in this work, we developed the indirect P2L and P2L/P2G hybrid processes combined with the reverse-water-gas-shift unit, which produce solely syncrude and the combination of syncrude and synthetic natural gas, resp. A comparative study of the indirect and direct P2L and P2L/P2G hybrid processes via the process modeling and techno-economic anal. was implemented to quant. evaluate their process performance differences, and it was indicated that the indirect P2L and P2L/P2G hybrid processes were also able to be considered as suitable technologies for the transformation of CO2 into high-value hydrocarbons, and the indirect P2L/P2G hybrid process seemed to be more competitive than the indirect P2L process from both tech. and economic aspects. Moreover, compared to the direct P2L and P2L/P2G hybrid processes, the indirect P2L and P2L/P2G hybrid processes produce more syncrude, however, they are less efficient in aspects of energy efficiency and net CO2 redn.
- 3Li, Y.; Zeng, L.; Pang, G.; Wei, X.; Wang, M.; Cheng, K.; Kang, J.; Serra, J. M.; Zhang, Q.; Wang, Y. Direct conversion of carbon dioxide into liquid fuels and chemicals by coupling green hydrogen at high temperature. Appl. Catal. B: Environ. 2023, 324, 122299 DOI: 10.1016/j.apcatb.2022.1222993https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XjtFOqu7%252FL&md5=ce44930d56bcae109d31683a9b98aa5fDirect conversion of carbon dioxide into liquid fuels and chemicals by coupling green hydrogen at high temperatureLi, Yubing; Zeng, Lei; Pang, Ge; Wei, Xueer; Wang, Mengheng; Cheng, Kang; Kang, Jincan; Serra, Jose M.; Zhang, Qinghong; Wang, YeApplied Catalysis, B: Environmental (2023), 324 (), 122299CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)The chem. conversion of CO2 into hydrocarbon fuels and chems. using green hydrogen not only utilizes abundant CO2 as a carbon feedstock but also enables the storage of hydrogen. Herein, we investigate the direct hydrogenation of CO2 to gasoline and olefins over a series of bifunctional iron-zeolite tandem catalysts operated at high temps. (> 300 °C). This process may efficiently utilize CO2 discharged from industrial combustion and green H2 produced by solid oxide electrolytic cells (SOEC). The optimized FeMnK+H-ZSM-5 catalyst offers a 70% selectivity of C5-C11 range hydrocarbons together with a 17% selectivity of C2-C4 lower olefins at 320 °C. The CO2 conversion levels and the aroms. contents could be greatly enhanced as the temp. increases from 320 °C to 400 °C. The hydrocarbon distribution is mainly detd. by the micropore size of the zeolites. The dynamic evolution of bifunctional catalysts and its impact on bifunctional catalysis was systematically investigated.
- 4Federsel, C.; Jackstell, R.; Beller, M. State-of-the-art catalysts for hydrogenation of carbon dioxide. Angew. Chem., Int. Ed. 2010, 49, 6254– 6257, DOI: 10.1002/anie.2010005334https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVOqtLjK&md5=7b93b4a7aaa9d7d675bd95e304208391State-of-the-Art Catalysts for Hydrogenation of Carbon DioxideFedersel, Christopher; Jackstell, Ralf; Beller, MatthiasAngewandte Chemie, International Edition (2010), 49 (36), 6254-6257CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review.
- 5Jessop, P. G.; Joó, F.; Tai, C.-C. Recent advances in the homogeneous hydrogenation of carbon dioxide. Coord. Chem. Rev. 2004, 248, 2425– 2442, DOI: 10.1016/j.ccr.2004.05.0195https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVagsL3M&md5=7b20bd2328b0a94bab5bc750e4ff3bb4Recent advances in the homogeneous hydrogenation of carbon dioxideJessop, Philip G.; Joo, Ferenc; Tai, Chih-ChengCoordination Chemistry Reviews (2004), 248 (21-24), 2425-2442CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)This review covers advances in CO2 hydrogenation published or in press since 1995. The survey of the field shows that while very active catalysts and co-catalysts have been discovered in this period for the prodn. of formic acid and its derivs., there has been only preliminary development of homogeneous catalysts for the prodn. of other oxygenates (e.g. methanol, CO) and Cn-compds. (n > 1). Homogeneous hydrogenation of carbon dioxide continues to attract interest in the hope of finding active and selective catalysts for the prodn. of valuable orgs. based on this cheap and abundant carbon source.
- 6Leitner, W. Carbon Dioxide as a Raw Material: The Synthesis of Formic Acid and Its Derivatives from CO2. Angew. Chem., Int. Ed. 1995, 34, 2207– 2221, DOI: 10.1002/anie.1995220716https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXptlSgu70%253D&md5=1158a3fb43d82a4e51e7ae6a9a98ec0cCarbon dioxide as a raw material: the synthesis of formic acid and its derivatives from CO2Leitner, WalterAngewandte Chemie, International Edition in English (1995), 34 (20), 2207-21CODEN: ACIEAY; ISSN:0570-0833. (VCH)A no. of new approaches to the catalytic redn. of CO2 to formic acid and prospects for industrial-scale operation are reviewed with 100 refs.
- 7Moret, S.; Dyson, P. J.; Laurenczy, G. Direct synthesis of formic acid from carbon dioxide by hydrogenation in acidic media. Nat. Commun. 2014, 5, 4017, DOI: 10.1038/ncomms50177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVShsL3K&md5=7a7e2780125051343cf0bf9b6821a99aDirect synthesis of formic acid from carbon dioxide by hydrogenation in acidic mediaMoret, Severine; Dyson, Paul J.; Laurenczy, GaborNature Communications (2014), 5 (), 4017CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The chem. transformation of carbon dioxide into useful products becomes increasingly important as CO2 levels in the atm. continue to rise as a consequence of human activities. In this article we describe the direct hydrogenation of CO2 into formic acid using a homogeneous ruthenium catalyst, in aq. soln. and in DMSO (DMSO), without any additives. In water, at 40 °C, 0.2 M formic acid can be obtained under 200 bar, however, in DMSO the same catalyst affords 1.9 M formic acid. In both solvents the catalysts can be reused multiple times without a decrease in activity. Worldwide demand for formic acid continues to grow, esp. in the context of a renewable energy hydrogen carrier, and its prodn. from CO2 without base, via the direct catalytic carbon dioxide hydrogenation, is considerably more sustainable than the existing routes.
- 8Rohmann, K.; Kothe, J.; Haenel, M. W.; Englert, U.; Holscher, M.; Leitner, W. Hydrogenation of CO2 to Formic Acid with a Highly Active Ruthenium Acriphos Complex in DMSO and DMSO/Water. Angew. Chem., Int. Ed. 2016, 55, 8966– 8969, DOI: 10.1002/anie.2016038788https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFSisb7J&md5=96073e127409935ca5f9d4a382183bfaHydrogenation of CO2 to Formic Acid with a Highly Active Ruthenium Acriphos Complex in DMSO and DMSO/WaterRohmann, Kai; Kothe, Jens; Haenel, Matthias W.; Englert, Ulli; Hoelscher, Markus; Leitner, WalterAngewandte Chemie, International Edition (2016), 55 (31), 8966-8969CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The novel [Ru(Acriphos)(PPh3)(Cl)(BzO)] [1; Acriphos = 4,5-bis(diphenylphosphino)acridine] is an excellent precatalyst for the hydrogenation of CO2 to give formic acid in DMSO and DMSO/H2O without the need for amine bases as co-reagents. Turnover nos. (TONs) of up to 4200 and turnover frequencies (TOFs) of up to 260 h-1 were achieved, thus rendering 1 among the most active catalysts for CO2 hydrogenations under additive-free conditions reported to date. The thermodn. stabilization of the reaction product by the reaction medium, through H bonds between formic acid and clusters of solvent or H2O, were rationalized by DFT calcns. The relatively low final concn. of formic acid obtained exptl. under catalytic conditions (0.33 mol L-1) is limited by product-dependent catalyst inhibition rather than thermodn. limits, and could be overcome by addn. of small amts. of acetate buffer, leading to a max. concn. of free formic acid of 1.27 mol L-1, which corresponds to optimized values of TON = 16 × 103 and TOFavg ≈103 h-1.
- 9Deka, T. J.; Osman, A. I.; Baruah, D. C.; Rooney, D. W. Methanol fuel production, utilization, and techno-economy: a review. Environ. Chem. Lett. 2022, 20, 3525– 3554, DOI: 10.1007/s10311-022-01485-y9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XitVOltL7L&md5=c09fbaac852b9013256b97b6032d7727Methanol fuel production, utilization, and techno-economy: a reviewDeka, Tanmay J.; Osman, Ahmed I.; Baruah, Debendra C.; Rooney, David W.Environmental Chemistry Letters (2022), 20 (6), 3525-3554CODEN: ECLNBJ; ISSN:1610-3653. (Springer)A review. Climate change and the unsustainability of fossil fuels are calling for cleaner energies such as methanol as a fuel. Methanol is one of the simplest mols. for energy storage and is utilized to generate a wide range of products. Since methanol can be produced from biomass, numerous countries could produce and utilize biomethanol. Here, we review methanol prodn. processes, techno-economy, and environmental viability. Lignocellulosic biomass with a high cellulose and hemicellulose content is highly suitable for gasification-based biomethanol prodn. Compared to fossil fuels, the combustion of biomethanol reduces nitrogen oxide emissions by up to 80%, carbon dioxide emissions by up to 95%, and eliminates sulfur oxide emission. The cost and yield of biomethanol largely depend on feedstock characteristics, initial investment, and plant location. The use of biomethanol as complementary fuel with diesel, natural gas, and di-Me ether is beneficial in terms of fuel economy, thermal efficiency, and redn. in greenhouse gas emissions.
- 10Ulmer, U.; Dingle, T.; Duchesne, P. N.; Morris, R. H.; Tavasoli, A.; Wood, T.; Ozin, G. A. Fundamentals and applications of photocatalytic CO2 methanation. Nat. Commun. 2019, 10, 3169, DOI: 10.1038/s41467-019-10996-210https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3MzovVejsQ%253D%253D&md5=c07d0fb622059bd39e39163ff6e8e4a9Fundamentals and applications of photocatalytic CO2 methanationUlmer Ulrich; Dingle Thomas; Duchesne Paul N; Morris Robert H; Tavasoli Alexandra; Wood Thomas; Ozin Geoffrey A; Dingle Thomas; Tavasoli AlexandraNature communications (2019), 10 (1), 3169 ISSN:.The extraction and combustion of fossil natural gas, consisting primarily of methane, generates vast amounts of greenhouse gases that contribute to climate change. However, as a result of recent research efforts, "solar methane" can now be produced through the photocatalytic conversion of carbon dioxide and water to methane and oxygen. This approach could play an integral role in realizing a sustainable energy economy by closing the carbon cycle and enabling the efficient storage and transportation of intermittent solar energy within the chemical bonds of methane molecules. In this article, we explore the latest research and development activities involving the light-assisted conversion of carbon dioxide to methane.
- 11Bowker, M. Methanol Synthesis from CO2 Hydrogenation. ChemCatChem. 2019, 11, 4238– 4246, DOI: 10.1002/cctc.20190040111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlGktb7L&md5=cfb265c2dbbca73e9d5e638159073715Methanol synthesis from CO2 hydrogenationBowker, MichaelChemCatChem (2019), 11 (17), 4238-4246CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. In the future we will be phasing out the use of fossil fuels in favor of more sustainable forms of energy, esp. solar derived forms such as hydroelec., wind and photovoltaic. However, due to the variable nature of the latter sources which depend on time of day, and season of the year, we also need to have a way of storing such energy at peak prodn. times for use in times of low prodn. One way to do this is to convert such energy into chem. energy, and the principal way considered at present is the prodn. of hydrogen. Although this may be achieved directly in the future via photocatalytic water splitting, at present it is electrolytic prodn. which dominates thinking. In turn, it may well be important to store this hydrogen in an energy dense liq. form such as methanol or ammonia. In this brief review it is emphasized that CO2 is the microscopic carbon source for current industrial methanol synthesis, operating through the surface formate intermediate, although when using CO in the feed, it is CO which is hydrogenated at the global scale. However, methanol can be produced from pure CO2 and hydrogen using conventional and novel types of catalysts. Examples of such processes, and of a demonstrator plant in construction, are given, which utilize CO2 (which would otherwise enter the atm. directly) and hydrogen which can be produced in a sustainable manner. This is a fast-evolving area of science and new ideas and processes will be developed in the near future.
- 12Shulenberger, A. M.; Jonsson, F. R.; Ingolfsson, O.; Tran, K.-C., Process For Producing Liquid Fuel From Carbon Dioxide And Water. US 8198338, 2012.There is no corresponding record for this reference.
- 13Asinger, F. Methanol - Chemie- und Energierohstoff. Springer-Verlag: Berlin, 1986.There is no corresponding record for this reference.
- 14Olah, G. A.; Goeppert, A.; Prakash, G. K. S. Beyond Oil and Gas: The Methanol Economy. Wiley-VCH: Weinheim, 2006.There is no corresponding record for this reference.
- 15Kar, S.; Goeppert, A.; Prakash, G. K. S. Catalytic Homogeneous Hydrogenation of CO to Methanol via Formamide. J. Am. Chem. Soc. 2019, 141, 12518– 12521, DOI: 10.1021/jacs.9b0658615https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFSgu7rM&md5=a6298832ed852fb4e556bd22b6dac67bCatalytic Homogeneous Hydrogenation of CO to Methanol via FormamideKar, Sayan; Goeppert, Alain; Prakash, G. K. SuryaJournal of the American Chemical Society (2019), 141 (32), 12518-12521CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A novel amine-assisted route for low temp. homogeneous hydrogenation of CO to methanol is described. The reaction proceeds through the formation of formamide intermediates. The first amine carbonylation part is catalyzed by K3PO4. Subsequently, the formamides are hydrogenated in situ to methanol in the presence of a com. available ruthenium pincer complex as a catalyst. Under optimized reaction conditions, CO (up to 10 bar) was directly converted to methanol in high yield and selectivity in the presence of H2 (70 bar) and diethylenetriamine. A max. TON of 539 was achieved using the catalyst Ru-Macho-BH. The high yield, selectivity, and TONs obtained for methanol prodn. at low reaction temp. (145 °C) could make this process an attractive alternative over the traditional high temp. heterogeneous catalysis.
- 16Kaithal, A.; Werle, C.; Leitner, W. Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese Catalysts. JACS Au 2021, 1, 130– 136, DOI: 10.1021/jacsau.0c0009116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhvVyjtrw%253D&md5=0b63eabf0164beb7cb68b4446279d546Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese CatalystsKaithal, Akash; Werle, Christophe; Leitner, WalterJACS Au (2021), 1 (2), 130-136CODEN: JAAUCR; ISSN:2691-3704. (American Chemical Society)Alc.-assisted hydrogenation of carbon monoxide (CO) to methanol was achieved using homogeneous mol. complexes. The mol. manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] ([HN(C2H4PiPr2)2] = MACHO-iPr) revealed the best performance, reaching up to turnover no. = 4023 and turnover frequency 857 h-1 in EtOH/toluene as solvent under optimized conditions (T = 150°C, p(CO/H2) = 5/50 bar, t = 8-12 h). Control expts. affirmed that the reaction proceeds via formate ester as the intermediate, whereby a catalytic amt. of base was found to be sufficient to mediate its formation from CO and the alc. in situ. Selectivity for methanol formation reached >99% with no accumulation of the formate ester. The reaction was demonstrated to work with methanol as the alc. component, resulting in a reactive system that allows catalytic "breeding" of methanol without any coreagents.
- 17Ryabchuk, P.; Stier, K.; Junge, K.; Checinski, M. P.; Beller, M. Molecularly Defined Manganese Catalyst for Low-Temperature Hydrogenation of Carbon Monoxide to Methanol. J. Am. Chem. Soc. 2019, 141, 16923– 16929, DOI: 10.1021/jacs.9b0899017https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFSisrvF&md5=c3b36be7511471c1ca3b312931877f22Molecularly Defined Manganese Catalyst for Low-Temperature Hydrogenation of Carbon Monoxide to MethanolRyabchuk, Pavel; Stier, Kenta; Junge, Kathrin; Checinski, Marek P.; Beller, MatthiasJournal of the American Chemical Society (2019), 141 (42), 16923-16929CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Methanol synthesis from syngas (CO/H2 mixts.) is one of the largest man-made chem. processes with annual prodn. reaching 100 million tons. The current industrial method proceeds at high temps. (200-300°C) and pressures (50-100 atm) using a copper-zinc-based heterogeneous catalyst. In contrast, here, we report a molecularly defined manganese catalyst that allows for low-temp./low-pressure (120-150°C, 50 bar) carbon monoxide hydrogenation to methanol. This new approach was evaluated and optimized by quantum mech. simulations virtual high-throughput screenings. Crucial for this achievement is the use of amine-based promoters, which capture carbon monoxide to give formamide intermediates, which then undergo manganese-catalyzed hydrogenolysis, regenerating the promoter. Following this conceptually new approach, high selectivity toward methanol and catalyst turnover nos. (up to 3170) was achieved. The proposed general catalytic cycle for methanol synthesis is supported by model studies and detailed spectroscopic investigations.
- 18Sen, R.; Goeppert, A.; Prakash, G. K. S. Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy. Angew. Chem., Int. Ed. 2022, 61, e202207278 DOI: 10.1002/anie.20220727818https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xitl2ntLnF&md5=110cc1d983fd8063a7ecc7bddbc5afd4Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol EconomySen, Raktim; Goeppert, Alain; Surya Prakash, G. K.Angewandte Chemie, International Edition (2022), 61 (42), e202207278CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO2 emissions. Outpacing the natural carbon cycle, atm. CO2 levels increased by 50% since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chem. recycling of CO2 to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO2, CO and their derivs. as potential low-temp. alternatives to the com. processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the crit. assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.
- 19Khusnutdinova, J. R.; Garg, J. A.; Milstein, D. Combining Low-Pressure CO2 Capture and Hydrogenation To Form Methanol. ACS Catal. 2015, 5, 2416– 2422, DOI: 10.1021/acscatal.5b0019419https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksVSnur4%253D&md5=b1efdf61ebacb203004cfad8b15d3fa9Combining Low-Pressure CO2 Capture and Hydrogenation To Form MethanolKhusnutdinova, Julia R.; Garg, Jai Anand; Milstein, DavidACS Catalysis (2015), 5 (4), 2416-2422CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)This paper describes a novel approach to CO2 hydrogenation, in which CO2 capture with aminoethanols at low pressure is coupled with hydrogenation of the captured product, oxazolidinone, directly to MeOH. In particular, (2-methylamino)ethanol or valinol captures CO2 at 1-3 bar in the presence of catalytic Cs2CO3 to give the corresponding oxazolidinones in up to 65-70 and 90-95% yields, resp. Efficient hydrogenation of oxazolidinones was achieved using PNN pincer Ru catalysts to give the corresponding aminoethanol (up to 95-100% yield) and MeOH (up to 78-92% yield). We also have shown that both CO2 capture and oxazolidinone hydrogenation can be performed in the same reaction mixt. using a simple protocol that avoids intermediate isolation or purifn. steps. For example, CO2 can be captured by valinol at 1 bar with Cs2CO3 catalyst followed by 4-isopropyl-2-oxazolidinone hydrogenation in the presence of a bipy-based pincer Ru catalyst to produce MeOH in 50% yield after two steps.
- 20Kar, S.; Sen, R.; Kothandaraman, J.; Goeppert, A.; Chowdhury, R.; Munoz, S. B.; Haiges, R.; Prakash, G. K. S. Mechanistic Insights into Ruthenium-Pincer-Catalyzed Amine-Assisted Homogeneous Hydrogenation of CO2 to Methanol. J. Am. Chem. Soc. 2019, 141, 3160– 3170, DOI: 10.1021/jacs.8b1276320https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXislOmtLo%253D&md5=492b21aae6c60bd00c70b4bccb34943dMechanistic Insights into Ruthenium-Pincer-Catalyzed Amine-Assisted Homogeneous Hydrogenation of CO2 to MethanolKar, Sayan; Sen, Raktim; Kothandaraman, Jotheeswari; Goeppert, Alain; Chowdhury, Ryan; Munoz, Socrates B.; Haiges, Ralf; Prakash, G. K. SuryaJournal of the American Chemical Society (2019), 141 (7), 3160-3170CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Amine-assisted homogeneous hydrogenation of CO2 to methanol is one of the most effective approaches to integrate CO2 capture with its subsequent conversion to CH3OH. The hydrogenation typically proceeds in two steps. In the first step the amine is formylated via an in situ formed alkylammonium formate salt (with consumption of 1 equiv of H2). In the second step the generated formamide is further hydrogenated with 2 more equiv of H2 to CH3OH while regenerating the amine. In the present study, we investigated the effect of mol. structure of the ruthenium pincer catalysts and the amines that are crit. for a high methanol yield. Surprisingly, despite the high reactivity of several Ru pincer complexes [RuHClPNPR(CO)] (R = Ph/i-Pr/Cy/t-Bu) for both amine formylation and formamide hydrogenation, only catalyst Ru-Macho (R = Ph) provided a high methanol yield after both steps were performed simultaneously in one pot. Among various amines, only (di/poly)amines were effective in assisting Ru-Macho for methanol formation. A catalyst deactivation pathway was identified, involving the formation of ruthenium biscarbonyl monohydride cationic complexes [RuHPNPR(CO)2]+, whose structures were unambiguously characterized and whose reactivities were studied. These reactivities were found to be ligand-dependent, and a trend could be established. With Ru-Macho, the biscarbonyl species could be converted back to the active species through CO dissocn. under the reaction conditions. The Ru-Macho biscarbonyl complex was therefore able to catalyze the hydrogenation of in situ formed formamides to methanol. Complex Ru-Macho-BH was also highly effective for this conversion and remained active even after 10 days of continuous reaction, achieving a max. turnover no. (TON) of 9900.
- 21Rezayee, N. M.; Huff, C. A.; Sanford, M. S. Tandem amine and ruthenium-catalyzed hydrogenation of CO2 to methanol. J. Am. Chem. Soc. 2015, 137, 1028– 1031, DOI: 10.1021/ja511329m21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVChtL4%253D&md5=ed06fe6cf9f8a65bb2443a34dc644b72Tandem Amine and Ruthenium-Catalyzed Hydrogenation of CO2 to MethanolRezayee, Nomaan M.; Huff, Chelsea A.; Sanford, Melanie S.Journal of the American Chemical Society (2015), 137 (3), 1028-1031CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)This Communication describes the hydrogenation of carbon dioxide to methanol via tandem catalysis with dimethylamine and a homogeneous ruthenium complex. Unlike previous examples with homogeneous catalysts, this CO2-to-CH3OH process proceeds under basic reaction conditions. The dimethylamine is proposed to play a dual role in this system. It reacts directly with CO2 to produce dimethylammonium dimethylcarbamate, and it also intercepts the intermediate formic acid to generate DMF. With the appropriate selection of catalyst and reaction conditions, >95% conversion of CO2 was achieved to form a mixt. of CH3OH and DMF.
- 22Kothandaraman, J.; Goeppert, A.; Czaun, M.; Olah, G. A.; Prakash, G. K. Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst. J. Am. Chem. Soc. 2016, 138, 778– 781, DOI: 10.1021/jacs.5b1235422https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmsVek&md5=9f708b98d949b119c5bf5aec3f215edaConversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium CatalystKothandaraman, Jotheeswari; Goeppert, Alain; Czaun, Miklos; Olah, George A.; Prakash, G. K. SuryaJournal of the American Chemical Society (2016), 138 (3), 778-781CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A highly efficient homogeneous catalyst system for the prodn. of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h-1 at 145 °C). Ease of sepn. of CH3OH is demonstrated by simple distn. from the reaction mixt. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover no. > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concn. (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.
- 23Curley, J. B.; Hert, C.; Bernskoetter, W. H.; Hazari, N.; Mercado, B. Q. Control of Catalyst Isomers Using an N-Phenyl-Substituted RN(CH2CH2PiPr2)2 Pincer Ligand in CO2 Hydrogenation and Formic Acid Dehydrogenation. Inorg. Chem. 2022, 61, 643– 656, DOI: 10.1021/acs.inorgchem.1c0337223https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXivVSrsrrL&md5=da53d392f16826fbf01df4e4dec7d66dControl of Catalyst Isomers Using an N-Phenyl-Substituted RN(CH2CH2PiPr2)2 Pincer Ligand in CO2 Hydrogenation and Formic Acid DehydrogenationCurley, Julia B.; Hert, Clayton; Bernskoetter, Wesley H.; Hazari, Nilay; Mercado, Brandon Q.Inorganic Chemistry (2022), 61 (1), 643-656CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)A novel pincer ligand, iPrPNPhP [PhN(CH2CH2PiPr2)2], which is an analog of the versatile MACHO ligand, iPrPNHP [HN(CH2CH2PiPr2)2], was synthesized and characterized. The ligand was coordinated to ruthenium, and a series of hydride-contg. complexes were isolated and characterized by NMR and IR spectroscopies, as well as x-ray diffraction. Comparisons to previously published analogs ligated by iPrPNHP and iPrPNMeP [CH3N(CH2CH2PiPr2)2] illustrate that there are large changes in the coordination chem. that occur when the nitrogen substituent of the pincer ligand is altered. For example, ruthenium hydrides supported by the iPrPNPhP ligand always form the syn isomer (where syn/anti refer to the relative orientation of the group on nitrogen and the hydride ligand on ruthenium), whereas complexes supported by iPrPNHP form the anti isomer and complexes supported by iPrPNMeP form a mixt. of syn and anti isomers. Authors evaluated the impact of the nitrogen substituent of the pincer ligand in catalysis by comparing a series of iPrPNRP (R = H, Me, Ph)-ligated ruthenium hydride complexes as catalysts for formic acid dehydrogenation and carbon dioxide (CO2) hydrogenation to formate. The iPrPNPhP-ligated species is the most active for formic acid dehydrogenation, and mechanistic studies suggest that this is likely because there are kinetic advantages for catalysts that operate via the syn isomer. In CO2 hydrogenation, the iPrPNPhP-ligated species is again the most active under authors optimal conditions, and they report some of the highest turnover frequencies for homogeneous catalysts. Exptl. and theor. insights into the turnover-limiting step of catalysis provide a basis for the obsd. trends in catalytic activity. Addnl., the stability of complexes enabled to detect a previously unobserved autocatalytic effect involving the base that is added to drive the reaction. Overall, by modifying the nitrogen substituent on the MACHO ligand, they have developed highly active catalysts for formic acid dehydrogenation and CO2 hydrogenation and also provided a framework for future catalyst development.
- 24Kar, S.; Sen, R.; Goeppert, A.; Prakash, G. K. S. Integrative CO2 Capture and Hydrogenation to Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol Economy. J. Am. Chem. Soc. 2018, 140, 1580– 1583, DOI: 10.1021/jacs.7b1218324https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsVKmt74%253D&md5=53f54a005a5d8a21a0d8850efb1e4487Integrative CO2 Capture and Hydrogenation to Methanol with Reusable Catalyst and Amine: Toward a Carbon Neutral Methanol EconomyKar, Sayan; Sen, Raktim; Goeppert, Alain; Prakash, G. K. SuryaJournal of the American Chemical Society (2018), 140 (5), 1580-1583CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Herein we report an efficient and recyclable system for tandem CO2 capture and hydrogenation to methanol. After capture in an aq. amine soln., CO2 is hydrogenated in high yield to CH3OH (>90%) in a biphasic 2-MTHF/water system, which also allows for easy sepn. and recycling of the amine and catalyst for multiple reaction cycles. Between cycles, the produced methanol can be conveniently removed in vacuo. Employing this strategy, catalyst Ru-MACHO-BH and polyamine PEHA were recycled three times with 87% of the methanol productivity of the first cycle retained, along with 95% of catalyst activity after four cycles. CO2 from dil. sources such as air can also be converted to CH3OH using this route. We postulate that the CO2 capture and hydrogenation to methanol system presented here could be an important step toward the implementation of the carbon neutral methanol economy concept.
- 25Filonenko, G. A.; van Putten, R.; Schulpen, E. N.; Hensen, E. J. M.; Pidko, E. A. Highly Efficient Reversible Hydrogenation of Carbon Dioxide to Formates Using a Ruthenium PNP-Pincer Catalyst. ChemCatChem. 2014, 6, 1526– 1530, DOI: 10.1002/cctc.20140211925https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmsVSkur8%253D&md5=4b20b98890b30e5dc80aff978add8271Highly efficient reversible hydrogenation of carbon dioxide to formates using a ruthenium PNP-pincer catalystFilonenko, Georgy A.; van Putten, Robbert; Schulpen, Erik N.; Hensen, Emiel J. M.; Pidko, Evgeny A.ChemCatChem (2014), 6 (6), 1526-1530CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)The use of hydrogen as a fuel requires both safe and robust technologies for its storage and transportation. Formic acid (FA) produced by the catalytic hydrogenation of CO2 is recognized as a potential intermediate H2 carrier. Herein, we present the development of a formate-based H2 storage system that employs a Ru PNP-pincer catalyst. The high stability of this system allows cyclic operation with an exceptionally fast loading and liberation of H2. Kinetic studies highlight the crucial role of the base promoter, which controls the rate-detg. step in FA dehydrogenation and defines the total H2 capacity attainable from the hydrogenation of CO2. The reported findings show promise for the development of practical technologies that use formic acid as a hydrogen carrier.
- 26Guan, C.; Pan, Y.; Ang, E. P. L.; Hu, J.; Yao, C.; Huang, M.-H.; Li, H.; Lai, Z.; Huang, K.-W. Conversion of CO2 from air into formate using amines and phosphorus-nitrogen PN3P-Ru(II) pincer complexes. Green Chem. 2018, 20, 4201– 4205, DOI: 10.1039/C8GC02186D26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlOrtLnN&md5=246a3c8bf4d82633b21e91a7d461ae83Conversion of CO2 from air into formate using amines and phosphorus-nitrogen PN3P-Ru(II) pincer complexesGuan, Chao; Pan, Yupeng; Ang, Eleanor Pei Ling; Hu, Jinsong; Yao, Changguang; Huang, Mei-Hui; Li, Huaifeng; Lai, Zhiping; Huang, Kuo-WeiGreen Chemistry (2018), 20 (18), 4201-4205CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)Well-defined ruthenium(II) PN3P pincer complexes were developed for the hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF (turnover frequency) and TON (turnover no.) up to 13 000 h-1 and 33 000, resp., in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from air into formate was conducted in the presence of an amine, allowing easy product sepn. and catalyst recycling.
- 27Li, H.; Goncalves, T. P.; Zhao, Q.; Gong, D.; Lai, Z.; Wang, Z.; Zheng, J.; Huang, K. W. Diverse catalytic reactivity of a dearomatized PN3P*-nickel hydride pincer complex towards CO2 reduction. Chem. Commun. 2018, 54, 11395– 11398, DOI: 10.1039/C8CC05948A27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFCktbbL&md5=465014194f1a362ab4a92771d0e71ec2Diverse catalytic reactivity of a dearomatized PN3P*-nickel hydride pincer complex towards CO2 reductionLi, Huaifeng; Goncalves, Theo P.; Zhao, Qianyi; Gong, Dirong; Lai, Zhiping; Wang, Zhixiang; Zheng, Junrong; Huang, Kuo-WeiChemical Communications (Cambridge, United Kingdom) (2018), 54 (81), 11395-11398CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A dearomatized PN3P*-nickel hydride complex has been prepd. using an oxidative addn. process. The first nickel-catalyzed hydrosilylation of CO2 to methanol has been achieved, with unprecedented turnover nos. Selective methylation and formylation of amines with CO2 were demonstrated by such a PN3P*-nickel hydride complex, highlighting its versatile functions in CO2 redn.
- 28Tanaka, R.; Yamashita, M.; Nozaki, K. Catalytic hydrogenation of carbon dioxide using Ir(III)-pincer complexes. J. Am. Chem. Soc. 2009, 131, 14168– 14169, DOI: 10.1021/ja903574e28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFKktL3J&md5=b3399e3290ced490f3bda0454449bcdbCatalytic Hydrogenation of Carbon Dioxide Using Ir(III)-Pincer ComplexesTanaka, Ryo; Yamashita, Makoto; Nozaki, KyokoJournal of the American Chemical Society (2009), 131 (40), 14168-14169CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Catalytic hydrogenation of carbon dioxide in aq. potassium hydroxide was performed using a newly synthesized isopropyl-substituted PNP-pincer iridium trihydride complex as catalyst. Potassium formate was obtained with turnover no. up to 3,500,000 and turnover frequency of 150,000 h-1.
- 29Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.; Nozaki, K. Mechanistic Studies on the Reversible Hydrogenation of Carbon Dioxide Catalyzed by an Ir-PNP Complex. Organometallics 2011, 30, 6742– 6750, DOI: 10.1021/om201017229https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFertrbP&md5=e16d0147b887b90b737071417163e1e3Mechanistic Studies on the Reversible Hydrogenation of Carbon Dioxide Catalyzed by an Ir-PNP ComplexTanaka, Ryo; Yamashita, Makoto; Chung, Lung Wa; Morokuma, Keiji; Nozaki, KyokoOrganometallics (2011), 30 (24), 6742-6750CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The PNP-ligated iridium(III) trihydride complex 1 exhibited the highest catalytic activity for hydrogenation of carbon dioxide in aq. KOH. The catalytic hydrogenation can be tuned to be a reversible process with the same catalyst at the expense of the activity, when triethanolamine was used as a base. Theor. studies on the hydrogenation of carbon dioxide using DFT calcns. suggested two competing reaction pathways: either the deprotonative dearomatization step or the hydrogenolysis step as the rate-detg. step. The results nicely explain our exptl. observations that the catalytic cycle is dependent on both the strength of the base and hydrogen pressure.
- 30Pan, Y.; Guan, C.; Li, H.; Chakraborty, P.; Zhou, C.; Huang, K. W. CO2 hydrogenation by phosphorus-nitrogen PN3P-pincer iridium hydride complexes: elucidation of the deactivation pathway. Dalton Trans 2019, 48, 12812– 12816, DOI: 10.1039/C9DT01319A30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsVaqsLjL&md5=86544f1ac3b3c8a72ae6888a1411282bCO2 hydrogenation by phosphorus-nitrogen PN3P-pincer iridium hydride complexes: elucidation of the deactivation pathwayPan, Yupeng; Guan, Chao; Li, Huaifeng; Chakraborty, Priyanka; Zhou, Chunhui; Huang, Kuo-WeiDalton Transactions (2019), 48 (34), 12812-12816CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)PN3P-Ir pincer hydride complexes were synthesized and characterized as catalysts and key intermediates in the direct hydrogenation of CO2 to formate under mild conditions. The formation of a dearomatized PN3P*-Ir(I)-CO species was identified as a plausible key process accountable for the loss of catalytic activity in the CO2 hydrogenation.
- 31Khusnutdinova, J. R.; Milstein, D. Metal-ligand cooperation. Angew. Chem., Int. Ed. 2015, 54, 12236– 12273, DOI: 10.1002/anie.20150387331https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVOnu7fK&md5=8a302a3f5b0b7a2f5d1faefdf2ed979dMetal-Ligand CooperationKhusnutdinova, Julia R.; Milstein, DavidAngewandte Chemie, International Edition (2015), 54 (42), 12236-12273CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review; metal-ligand cooperation (MLC) has become an important concept in catalysis by transition metal complexes both in synthetic and biol. systems. MLC implies that both the metal and the ligand are directly involved in bond activation processes, by contrast to "classical" transition metal catalysis where the ligand (e.g. phosphine) acts as a spectator, while all key transformations occur at the metal center. In this Review, we will discuss examples of MLC in which 1) both the metal and the ligand are chem. modified during bond activation and 2) bond activation results in immediate changes in the 1st coordination sphere involving the cooperating ligand, even if the reactive center at the ligand is not directly bound to the metal (e.g. via tautomerization). The role of MLC in enabling effective catalysis as well as in catalyst deactivation reactions will be discussed.
- 32Alig, L.; Fritz, M.; Schneider, S. First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands. Chem. Rev. 2019, 119, 2681– 2751, DOI: 10.1021/acs.chemrev.8b0055532https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXk&md5=2a22fcda0a1be9ea45c9ecd9094af4c3First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer LigandsAlig, Lukas; Fritz, Maximilian; Schneider, SvenChemical Reviews (Washington, DC, United States) (2019), 119 (4), 2681-2751CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The use of 3d metals in de/hydrogenation catalysis has emerged as a competitive field with respect to "traditional" precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal-ligand cooperativity and ligand redox-activity strongly stimulated this development as a conceptual starting point for rational catalyst design. This review aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodol. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.
- 33Gunanathan, C.; Milstein, D. Bond activation and catalysis by ruthenium pincer complexes. Chem. Rev. 2014, 114, 12024– 12087, DOI: 10.1021/cr500278233https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvFagtrrL&md5=655df14d3f81471371ba5b21d4cc6053Bond Activation and Catalysis by Ruthenium Pincer ComplexesGunanathan, Chidambaram; Milstein, DavidChemical Reviews (Washington, DC, United States) (2014), 114 (24), 12024-12087CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. The focus of this Review is limited to a summary of key developments in the area of bond activation and catalysis by defined ruthenium pincer complexes.
- 34Mathis, C. L.; Geary, J.; Ardon, Y.; Reese, M. S.; Philliber, M. A.; VanderLinden, R. T.; Saouma, C. T. Thermodynamic Analysis of Metal-Ligand Cooperativity of PNP Ru Complexes: Implications for CO2 Hydrogenation to Methanol and Catalyst Inhibition. J. Am. Chem. Soc. 2019, 141, 14317– 14328, DOI: 10.1021/jacs.9b0676034https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFemtLbJ&md5=b5d9a8c63d1a05b66f22d4e11ad1c14dThermodynamic Analysis of Metal-Ligand Cooperativity of PNP Ru Complexes: Implications for CO2 Hydrogenation to Methanol and Catalyst InhibitionMathis, Cheryl L.; Geary, Jackson; Ardon, Yotam; Reese, Maxwell S.; Philliber, Mallory A.; VanderLinden, Ryan T.; Saouma, Caroline T.Journal of the American Chemical Society (2019), 141 (36), 14317-14328CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The hydrogenation of CO2 in the presence of amines to formate, formamides, and methanol (MeOH) is a promising approach to streamlining carbon capture and recycling. To achieve this, understanding how catalyst design impacts selectivity and performance is crit. Herein we describe a thorough thermochem. anal. of the (de)hydrogenation catalyst, (PNP)Ru-Cl (PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine; Ru = Ru(CO)(H)) and correlate our findings to catalyst performance. Although this catalyst is known to hydrogenate CO2 to formate with a mild base, we show that MeOH is produced when using a strong base. Consistent with pKa measurements, the requirement for a strong base suggests that the deprotonation of a six-coordinate Ru species is integral to the catalytic cycle that produces MeOH. Our studies also indicate that the concn. of MeOH produced is independent of catalyst concn., consistent with a deactivation pathway that is dependent on methanol concn., not equivalency. Our temp.-dependent equil. studies of the dearomatized congener, (*PNP)Ru, with various H-X species (to give (PNP)Ru-X; X = H, OH, OMe, OCHO, OC(O)NMe2) reveal that formic acid equil. is approx. temp.-independent; relative to H2, it is more favored at elevated temps. We also measure the hydricity of (PNP)Ru-H in THF and show how subsequent coordination of the substrate can impact the apparent hydricity. The implications of this work are broadly applicable to hydrogenation and dehydrogenation catalysis and, in particular, to those that can undergo metal-ligand cooperativity (MLC) at the catalyst. These results serve to benchmark future studies by allowing comparisons to be made among catalysts and will pos. impact rational catalyst design.
- 35Nobbs, J. D.; Sugiarto, S.; See, X. Y.; Cheong, C. B.; Aitipamula, S.; Stubbs, L. P.; van Meurs, M. Tetramethylphosphinane as a new secondary phosphine synthon. Nat. Commun. 2023, 6, 85, DOI: 10.1038/s42004-023-00876-8There is no corresponding record for this reference.
- 36He, L.-P.; Chen, T.; Xue, D.-X.; Eddaoudi, M.; Huang, K.-W. Efficient transfer hydrogenation reaction Catalyzed by a dearomatized PN3P ruthenium pincer complex under base-free Conditions. J. Organomet. Chem. 2012, 700, 202– 206, DOI: 10.1016/j.jorganchem.2011.10.01736https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFGgu7k%253D&md5=68caca7956d6277f1cb5bc5ee0ac4a52Efficient transfer hydrogenation reaction catalyzed by a dearomatized PN3P ruthenium pincer complex under base-free conditionsHe, Li-Peng; Chen, Tao; Xue, Dong-Xu; Eddaoudi, Mohamed; Huang, Kuo-WeiJournal of Organometallic Chemistry (2012), 700 (), 202-206CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)A dearomatized complex [RuH(PN3P)(CO)] (PN3P = N,N'-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (I) was prepd. by reaction of the arom. complex [RuH(Cl)(PN3P)(CO)] with t-BuOK in THF. Further treatment of I with formic acid led to the formation of a rearomatized complex (II). These new complexes were fully characterized and the mol. structure of complex II was further confirmed by X-ray crystallog. In complex II, a distorted square-pyramidal geometry around the ruthenium center was obsd., with the CO ligand trans to the pyridinic nitrogen atom and the hydride located in the apical position. The dearomatized complex I displays efficient catalytic activity for hydrogen transfer of ketones in isopropanol.
- 37Benito-Garagorri, D.; Becker, E.; Wiedermann, J.; Lackner, W.; Pollak, M.; Mereiter, K.; Kisala, J.; Kirchner, K. Achiral and Chiral Transition Metal Complexes with Modularly Designed Tridentate PNP Pincer-Type Ligands Based on N-Heterocyclic Diamines. Organometallics 2006, 25, 1900– 1913, DOI: 10.1021/om060064437https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xit1Omurs%253D&md5=58305fac09d0a4afff8d6bf6855df868Achiral and Chiral Transition Metal Complexes with Modularly Designed Tridentate PNP Pincer-Type Ligands Based on N-Heterocyclic DiaminesBenito-Garagorri, David; Becker, Eva; Wiedermann, Julia; Lackner, Wolfgang; Pollak, Martin; Mereiter, Kurt; Kisala, Joanna; Kirchner, KarlOrganometallics (2006), 25 (8), 1900-1913CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The synthesis and characterization of Mo, Fe, Ru, Ni, Pd, and Pt complexes contg. new achiral and chiral PNP pincer-type ligands based on the N-heterocyclic diamines 2,6-diaminopyridine, N,N'-di-10-undecenyl-2,6-diaminopyridine, N,N'-dihexyl-2,6-diaminopyridine, and 2,6-diamino-4-phenyl-1,3,5-triazine are reported. The new PNP ligands were prepd. conveniently in high yield by treatment of the resp. N-heterocyclic diamines with 2 equiv of a variety of achiral and chiral R2PCl compds. in the presence of base. Mo PNP complexes [Mo(PNP)(CO)3PNP] were obtained by treatment of [Mo(CO)3(MeCN)3] with 1 equiv of the resp. PNP ligand. They react with I2 to give novel seven-coordinate pincer complexes [Mo(PNP)(CO)3I]+ and [Mo(PNP)(CO)2(MeCN)I]+ depending of whether the reaction is carried out in CH2Cl2 or MeCN. With [Fe(H2O)6](BF4)2 and 1 equiv of PNP ligand in MeCN dicationic complexes [Fe(PNP)(MeCN)3](BF4)2 were obtained. The cis and trans dichloride complexes [Ru(PNP)(PPh3)Cl2] were prepd. by a ligand exchange reaction of [RuCl2(PPh3)3] with a stoichiometric amt. of the resp. PNP ligand. Cationic PNP complexes of Ni(II), [Ni(PNP)Br]Br, were synthesized by the reaction of [NiBr2(DME)] with 1 equiv of PNP ligand. In similar fashion, treatment of [M(COD)X2] (M = Pd, Pt; X = Cl, Br) with 1 equiv of PNP ligand yields the cationic square-planar complexes [M(PNP)X]X. If the reaction is carried out in the presence of the halide scavenger KCF3SO3, complexes [M(PNP)X]CF3SO3 were obtained, which are better sol. in nonpolar solvents than the analogous halide compds. X-ray structures of representative Mo, Fe, Ru, Ni, and Pd PNP complexes were detd. Finally, the use of the Pd complexes as catalysts for the Suzuki-Miyaura coupling of some aryl bromides and Ph boronic acid was examd.
- 38Salem, H.; Shimon, L. J. W.; Diskin-Posner, Y.; Leitus, G.; Ben-David, Y.; Milstein, D. Formation of Stable trans-Dihydride Ruthenium(II) and 16-Electron Ruthenium(0) Complexes Based on Phosphinite PONOP Pincer Ligands. Reactivity toward Water and Electrophiles. Organometallics 2009, 28, 4791– 4806, DOI: 10.1021/om900407738https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXptFOjsbc%253D&md5=8bc52d256bd1e3c8ce2f727581091b34Formation of Stable trans-Dihydride Ruthenium(II) and 16-Electron Ruthenium(0) Complexes Based on Phosphinite PONOP Pincer Ligands. Reactivity toward Water and ElectrophilesSalem, Hiyam; Shimon, Linda J. W.; Diskin-Posner, Yael; Leitus, Gregory; Ben-David, Yehoshoa; Milstein, DavidOrganometallics (2009), 28 (16), 4791-4806CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)The synthesis of a series of new ruthenium complexes based on the new PONOP ligands (1) and (10) (C5H3N-1,3-(OPR2)2: 1, R = iPr; 10, R = tBu) is presented, including the stable trans-dihydride complexes (iPr-PONOP)Ru(H)2(PPh3) (4) and (tBu-PONOP)Ru(H)2(CO) (12) and the stable Ru(0) complexes (R-PONOP)Ru(CO)2 (6, R = iPr; 15, R = tBu). A surprisingly stable 16-electron Ru(0) complex (13) was formed by deprotonation of 12 with KOtBu. Complex 13 reacts with H2 to afford the cis-dihydride complex 12a, which isomerized to the trans-dihydride 12. Complex 13 reacted with CO to afford the satd. Ru(0) complex 15. Reaction of complex 12 with water led to hydrolysis of the phosphinite PONOP ligand and rearrangement to a dimeric product (14). Reaction of the trans-dihydride complex 4 with the electrophiles PhCOCl, MeI, and MeOTf led to abstraction of one of the hydride ligands, forming the monohydride complexes (iPr-PONOP)Ru(H)(PPh3)(X) (X = Cl (2), I (8a), OTf (8b)) together with benzaldehyde in the case of 2. Similarly, 12 afforded the monohydride complexes (tBu-PONOP)Ru(H)(CO)(X) (X = Cl (11), OTf (17), I (18)). Reaction of the Ru(0) complexes 6 and 15 with water resulted in hydrolysis of the O-P bond and formation of the zwitterionic complexes 7 and 16. Treatment of 2 and 11 with MeOTf or MeI resulted in abstraction of the chloride ligand rather than the hydride, forming complexes 8a,b and 17, 18, resp. Addnl. syntheses of complexes based on ligands 1 and 10 are presented.
- 39Ogata, O.; Nara, H.; Fujiwhara, M.; Matsumura, K.; Kayaki, Y. N-Monomethylation of Aromatic Amines with Methanol via PN(H)P-Pincer Ru Catalysts. Org. Lett. 2018, 20, 3866– 3870, DOI: 10.1021/acs.orglett.8b0144939https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyisrnO&md5=636ae24a9f7b2f868d600dc09be0da5dN-Monomethylation of Aromatic Amines with Methanol via PNHP-Pincer Ru CatalystsOgata, Osamu; Nara, Hideki; Fujiwhara, Mitsuhiko; Matsumura, Kazuhiko; Kayaki, YoshihitoOrganic Letters (2018), 20 (13), 3866-3870CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)In the presence of 0.02-0.1 mol% ruthenium PNP pincer complex I and in the presence of KOt-Bu at 150°, aryl amines underwent chemoselective and green N-methylation with methanol to give N-methylarylamines. I underwent ionization and assocn. of carbon monoxide to form cationic dicarbonyl pincer ruthenium complexes which also acted as effective catalysts for chemoselective methylation.
- 40Herrmann, W. A. Organometallic Aspects of the Fischer–Tropsch Synthesis. Angew. Chem., Int. Ed. 1982, 21, 117– 130, DOI: 10.1002/anie.198201171There is no corresponding record for this reference.
- 41Nelson, G. O.; Sumner, C. E. Synthesis and reactivity of pentamethylcyclopentadienylruthenium formyl and α-hydroxy methyl complexes. Organometallics 1986, 5, 1983– 1990, DOI: 10.1021/om00141a00941https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XlsFehur4%253D&md5=1760ee6160aaa0ddae6794ecb689fbc2Synthesis and reactivity of pentamethylcyclopentadienylruthenium formyl and α-hydroxy complexesNelson, Gregory O.; Sumner, Charles E.Organometallics (1986), 5 (10), 1983-90CODEN: ORGND7; ISSN:0276-7333.(η-C5Me5)Ru(CO)2CH2OH (I, Cp = cyclopentadienyl), (η-C5Me5)Ru(CO)2CHO (II), and (η-C5Me5)Ru(CO)(PMe2Ph)CHO (III) were synthesized and studied as models for intermediates in the redn. of CO to org. oxygenates by transition metal catalysts. I was prepd. by NaBH3CN redn. of (η-C5Me5)Ru(CO)3+ BF4- (IV). II was synthesized by redn. of IV with [Ph3PCuH]6, but it could not be isolated in pure form. Pure cryst. III was isolated from the redn. of (η-C5Me5)Ru(CO)2(PMe2Ph)+ I- with NaBH4 in THF/H2O. Formyl complexes II and III decompd. by a radical chain mechanism. The intermediate formed from the decompn. of III underwent electron transfer with (η-C5R5)Ru(CO)2I (R = H, Me). An x-ray structure of III was completed.
- 42Nelson, G. O. (Pentamethylcyclopentadienyl)ruthenium compounds. Synthesis and characterization of (η5-C5Me5)Ru(CO)2CH2OH. Organometallics 1983, 2, 1474– 1475, DOI: 10.1021/om50004a04642https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXlsVSisbk%253D&md5=ee79562296a7ae88db96e8bc2a63ed8d(Pentamethylcyclopentadienyl)ruthenium compounds. Synthesis and characterization of (η-C5Me5)Ru(CO)2CH2OHNelson, Gregory O.Organometallics (1983), 2 (10), 1474-5CODEN: ORGND7; ISSN:0276-7333.Treatment of (η5-C5Me5)Ru(CO)2I (C5H5 = cyclopentadienyl) in CH2Cl2 with AgBF4 under 60 psi CO produces 82% [(η-C5Me5)Ru(CO)3][BF1], which on redn. with excess NaBH3CN in MeOH gave a mixt. of (η-C5Me2)Ru(CO)2H, (η-C5Me2)Ru(CO)2CH2OMe and (η-C5Me5)Ru(CO)2CH2OH (I) . A soln. of I in THF under 5000 psi CO at 80° does not react. Reaction of I with CF3CON(SiMe3)2 gave (η-C5Me2)Ru(CO)2CH2OSiMe3.
- 43Teets, T. S.; Labinger, J. A.; Bercaw, J. E. A Thermodynamic Analysis of Rhenium(I)–Formyl C–H Bond Formation via Base-Assisted Heterolytic H2 Cleavage in the Secondary Coordination Sphere. Organometallics 2013, 32, 5530– 5545, DOI: 10.1021/om400810v43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGrsr7E&md5=c387e321ab3624631d99e4305cc39463A Thermodynamic Analysis of Rhenium(I)-Formyl C-H Bond Formation via Base-Assisted Heterolytic H2 Cleavage in the Secondary Coordination SphereTeets, Thomas S.; Labinger, Jay A.; Bercaw, John E.Organometallics (2013), 32 (19), 5530-5545CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)Conversion of synthesis gas, a mixt. of CO and H, into value-added Cn≥2 products requires both C-H and C-C bond-forming events. The authors' group has developed mol. complexes, based on Group 7 (Mn and Re) carbonyl complexes, to interrogate the elementary steps involved in the homogeneous hydrogenative reductive coupling of CO. Here, the authors explore a new mode of H2 activation, in which strong bases in the secondary coordination sphere are positioned to assist in the heterolytic cleavage of H2 to form a formyl C-H bond at a Re-bound carbonyl. Cationic Re(I) complexes [ReI(P∼B:-κ1-P)(CO)5]+1, where P∼B: is a phosphine ligand with a tethered strong base, were prepd. and characterized; measurement of their protonation equil. demonstrates a pronounced attenuation of the basicity upon coordination. Formyl complexes supported by these ligands can be prepd. in 50% to 95% yields by hydride delivery to the parent pentacarbonyl complexes, and several of the free-base formyl complexes can be protonated, generating observable [ReI(P∼BH-κ1-P)(CHO)(CO)4]+1 complexes. Intramol. H bonding is evident for one of the complexes, providing addnl. stabilization to the protonated formyl complex. By measuring both the hydricity of the formyl, ΔG°H-, and its pKa, the overall free energy of H2 cleavage is calcd. from an appropriate cycle and is thermodynamically uphill in all cases (in the best case by only ∼8 kcal/mol), although significantly dependent upon the properties of the supporting ligand.
- 44Elowe, P. R.; West, N. M.; Labinger, J. A.; Bercaw, J. E. Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme. Organometallics 2009, 28, 6218– 6227, DOI: 10.1021/om900804j44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1CgtrvF&md5=9fec4f86e8fc66763a00a5b97dc408f8Transformations of Group 7 carbonyl complexes: possible intermediates in a homogeneous syngas conversion schemeElowe, Paul R.; West, Nathan M.; Labinger, Jay A.; Bercaw, John E.Organometallics (2009), 28 (21), 6218-6227CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)Redn. of Group VIIB metal phosphine carbonyls by lithium triethylhydroborate gave access to formyl complexes, which were isolated and characterized as borane-stabilized adducts. A variety of C-H and C-C bond forming reactions of Group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C2+ compds. Reaction of [(PPh3)2M(CO)4][BF4] with LiBHEt3 gave neutral formyl complexes [(PPh3)2(CO)3M(CHO)] (2a,b; M = Mn, Re). Attempted silylation of 2b by Me3SiOTf gave unexpected product, [(PPh3)2Re(CO)3(CHO·BF3)] (4b), as a result of fluoride abstraction from BF4- anion and trifluoroborane coordination. Reaction of 2a,b with BX3 gave the stabilized formyl complexes directly, [(PPh3)2(CO)3M(CHO·BX3)] (4a,b, X = F, M = Mn, Re; 5a,b, X = C6F5, M = Mn, Re). The metal formyl complexes 2 are substantially stabilized by coordination to boranes BX3 in the form of novel boroxycarbene complexes M(CO)3(PPh3)2(CHOBX3), but these boron-stabilized carbenes 4 and 5 do not react with hydride sources to undergo further redn. to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)5-x(PPh3)x(CHOMe)]+ (x = 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atm. of CO. The resulting acyls, cis- and trans-Mn(PPh3)(CO)4(C(O)CH2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh3)(CO)4(C(OR)CH2OMe)]+, which undergoes a 1,2-hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or di-Et ether adducts of [Mn(PPh3)(CO)4]+. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh3)(CO)4(CH2COOMe) and is protonolyzed to yield Me acetate and [Mn(PPh3)(CO)4]+; addn. of L (L = PPh3, CO) to the manganese cation regenerates [Mn(PPh3)(CO)4(L)]+. Since the original formyl complex can be obtained by the reaction of [Mn(PPh3)(CO)5]+ with [PtH(dmpe)2]+, which in turn can be generated from H2, this set of transformations amts. to a stoichiometric cycle for selectively converting H2 and CO into a C2 compd. under mild conditions.
- 45Pan, Y.; Pan, C.; Zhang, Y.; Li, H.; Min, S.; Guo, X.; Zheng, B.; Chen, H.; Anders, A.; Lai, Z.; Zheng, J.; Huang, K. Selective Hydrogen Generation from Formic Acid with Well-Defined Complexes of Ruthenium and Phosphorus-Nitrogen PN3 -Pincer Ligand. Chem. - Asian J. 2016, 11, 1357– 1360, DOI: 10.1002/asia.20160016945https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xms1Kms7c%253D&md5=9811408b864a042ea6c3ae493d6c97d2Selective Hydrogen Generation from Formic Acid with Well-Defined Complexes of Ruthenium and Phosphorus-Nitrogen PN3-Pincer LigandPan, Yupeng; Pan, Cheng-Ling; Zhang, Yufan; Li, Huaifeng; Min, Shixiong; Guo, Xunmun; Zheng, Bin; Chen, Hailong; Anders, Addison; Lai, Zhiping; Zheng, Junrong; Huang, Kuo-WeiChemistry - An Asian Journal (2016), 11 (9), 1357-1360CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)An unsym. protonated PN3-pincer complex in which ruthenium is coordinated by one nitrogen and two phosphorus atoms was employed for the selective generation of hydrogen from formic acid. Mechanistic studies suggest that the imine arm participates in the formic acid activation/deprotonation step. A long life time of 150 h with a turnover no. over 1 million was achieved.
- 46Ooyama, D.; Tomon, T.; Tsuge, K.; Tanaka, K. Structural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reduction. J. Organomet. Chem. 2001, 619, 299– 304, DOI: 10.1016/S0022-328X(00)00705-146https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhslOksrk%253D&md5=f8bdd0ef09174fb2c177dbf129eb3d6aStructural and spectroscopic characterization of ruthenium(II) complexes with methyl, formyl, and acetyl groups as model species in multi-step CO2 reductionOoyama, Dai; Tomon, Takashi; Tsuge, Kiyoshi; Tanaka, KojiJournal of Organometallic Chemistry (2001), 619 (2), 299-304CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science S.A.)The mol. structures of Ru(II) complexes with Me, formyl, and acetyl groups [Ru(bpy)2(CO)L]+ (L = CH3, C(O)H and C(O)CH3) were examd. from the viewpoint of active species in multi-step redn. of CO2 on Ru. The Me complex was prepd. by the reaction of [Ru(bpy)2(OH2)2]2+ with trimethylsilyl acetylene and fully characterized by IR, Raman, 13C NMR and single-crystal x-ray crystallog. Disorder of the Ru-CO and Ru-C(O)H bonds in the crystal structure of the formyl complex made it difficult to det. the bond parameters of the two groups accurately, but the mol. structure of the analogous acetyl complex, which was obtained by the reaction of [Ru(bpy)2(CO3)] with propiolic acid, was detd. by x-ray anal. The Ru-carbonyl (Ru-C-O) bond angles of the Me and acetyl complex with 174(1) and 175.5(5)°, resp., are in the ranges of those of previously characterized [Ru(bpy)2(CO)L]n+ (L = CO2, C(O)OH, CO and CH2OH). However, the Ru-CH3 and Ru-C(O)CH3 bond distances showed unusual relation against the stretching frequency in the Raman spectra.
- 47Toyohara, K.; Nagao, H.; Mizukawa, T.; Tanaka, K. Ruthenium Formyl Complexes as the Branch Point in Two- and Multi-Electron Reductions of CO2. Inorg. Chem. 1995, 34, 5399– 5400, DOI: 10.1021/ic00126a00347https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosVarsLc%253D&md5=73b356974881a4dd173c189b7d9149bfRuthenium Formyl Complexes as the Branch Point in Two- and Multi-Electron Reductions of CO2Toyohara, Kiyotsuna; Nagao, Hirotaka; Mizukawa, Tetsunori; Tanaka, KojiInorganic Chemistry (1995), 34 (22), 5399-400CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)Both [Ru(bpy)2(CO)(CHO)]+ and [Ru(bpy)(trpy)(CHO)]+ (bpy = 2,2'-bipyridine; trpy = 2,2',6',2''-terpyridine) were characterized and the latter is the key-intermediate of four- and six-electron redn. of CO2 producing HCHO and CH3OH. Higher reactivity of these formyl complexes than the corresponding hydrides reveals a new pathway of HCOOH formation in electrochem. CO2 redn.
- 48Kelly, J. M.; Vos, J. G. cis-[Ru(bpy)2(CO)H]+: A Possible Intermediate in the Photochemical Production of H2 from Water Catalyzed by [Ru(bpy)3]2+?. Angew. Chem., Int. Ed. 1982, 21 (8), 628– 629, DOI: 10.1002/anie.198206281There is no corresponding record for this reference.
- 49Dombek, B. D. Hydrogenation of carbon monoxide to methanol and ethylene glycol by homogeneous ruthenium catalysts. J. Am. Chem. Soc. 1980, 102, 6855– 6857, DOI: 10.1021/ja00542a03649https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3cXmtlykt7Y%253D&md5=9325c5615a5476e29cd8eaca9501b0c7Hydrogenation of carbon monoxide to methanol and ethylene glycol by homogeneous ruthenium catalystsDombek, B. DuaneJournal of the American Chemical Society (1980), 102 (22), 6855-7CODEN: JACSAT; ISSN:0002-7863.Solns. of Ru3(CO)12 in carboxylic acids catalyze the hydrogenation of CO at low pressures (100 to 340 atm) to give MeOH (obtained as its ester), with smaller amts. of ethylene glycol diester. At 340 atm and 260° a combined rate to these products of 8.3 × 10-3 turnovers s-1 was obsd. in HOAc solvent. Similar rates to MeOH are obtainable in other polar solvents, but ethylene glycol is not obsd. under these conditions except in the presence of carboxylic acids. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor.
- 50Walker, H. W.; Ford, P. C. Synthesis and characterization of [PPN][HRu(CO)4] and a convenient route to [PPN][HOs(CO)4]. J. Organomet. Chem. 1981, 214, C43– C44, DOI: 10.1016/S0022-328X(81)80019-850https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3MXls12ns7c%253D&md5=da7fdd77de30f50d95583ee26ff178bdSynthesis and characterization of [PPN][HRu(CO)4] and a convenient route to [PPN][HOs(CO)4]Walker, Howard W.; Ford, Peter C.Journal of Organometallic Chemistry (1981), 214 (3), C43-C44CODEN: JORCAI; ISSN:0022-328X.[PPN][HM(CO)4] (M = Ru, Os; PPN = bis(triphenylphosphine)iminium were prepd. in 60% (M = Ru) yield by treating Na2M(CO)4 with PPN+Cl- in a min. amt. of MeOH at -196° followed by filtration of -78°.
- 51Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Süss, G. The triruthenium cluster anion [Ru3H(CO)11]−: preparation, structure, and fluxionality. J. Chem. Soc., Dalton Trans. 1979, 9, 1356– 1361, DOI: 10.1039/DT9790001356There is no corresponding record for this reference.
- 52Guntermann, N.; Franciò, G.; Leitner, W. Hydrogenation of CO2 to formic acid in biphasic systems using aqueous solutions of amino acids as the product phase. Green Chem. 2022, 24, 8069– 8075, DOI: 10.1039/D2GC02598A52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XisFWqsLjF&md5=77846b4ff0482b12f7e1496e1800f4f4Hydrogenation of CO2 to formic acid in biphasic systems using aqueous solutions of amino acids as the product phaseGuntermann, Nils; Francio, Giancarlo; Leitner, WalterGreen Chemistry (2022), 24 (20), 8069-8075CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)Carbon capture and utilization is considered a promising approach for introducing CO2 into the chem. value chain, esp. in combination with bioenergy applications (BECCU). We report here on the catalytic hydrogenation of CO2 to formic acid in a biphasic reaction system using aq. solns. of amino acids as the product phase and possible capture solns. for biogenic CO2. The mol. structure of the ruthenium catalyst and the catalyst phase were matched through a combined design process identifying n-dodecanol (lauryl alc.) as the preferred "green" solvent. A total turnover no. (TON) of over 100 000 mol HCOOH per mol of catalyst (46 582 g HCOOH per g of Ru) with minimal contamination of the aq. phase with metal or org. solvent was obtained. The resulting aq. solns. attained almost quant. conversions with up to 0.94 mol formic acid per mol amino acid (ca. 108 g HCOOH per kg). Such solns. may find use directly, or after upgrading, in agricultural applications without the need for energy intensive and costly isolation of pure formic acid.
- 53Heldebrant, D. J.; Jessop, P. G.; Thomas, C. A.; Eckert, C. A.; Liotta, C. L. The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide. J. Org. Chem. 2005, 70, 5335– 5338, DOI: 10.1021/jo050375953https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXksVertLs%253D&md5=13da346fe0d2d25925ff834f3c173835The Reaction of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) with Carbon DioxideHeldebrant, David J.; Jessop, Philip G.; Thomas, Colin A.; Eckert, Charles A.; Liotta, Charles L.Journal of Organic Chemistry (2005), 70 (13), 5335-5338CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)Amidines have been reported to react with CO2 to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO2 detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO2 and does not indicate that an isolable zwitterionic adduct between DBU and CO2 forms either in the presence or the absence of water.
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