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ArticleNovember 1, 2021

NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization
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David Sánchez-Roa
David Sánchez-Roa
Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación en Química “Andrés M. del Río” (IQAR) Universidad de Alcalá, Campus Universitario, Alcala de Henares, Madrid 28871, Spain
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Marta E. G. Mosquera*
Marta E. G. Mosquera
Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación en Química “Andrés M. del Río” (IQAR) Universidad de Alcalá, Campus Universitario, Alcala de Henares, Madrid 28871, Spain
*Email: [email protected]
More by Marta E. G. Mosquera
https://orcid.org/0000-0003-2248-3050
Juan Cámpora*
Juan Cámpora
Instituto de Investigaciones Químicas, CSIC-Universidad de Sevilla, C/Américo Vespucio, 49, Sevilla 41092, Spain
*Email: [email protected]
More by Juan Cámpora
https://orcid.org/0000-0001-7305-1296

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The Journal of Organic Chemistry

Cite this: J. Org. Chem. 2021, 86, 23, 16725–16735

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https://doi.org/10.1021/acs.joc.1c01971

Published November 1, 2021

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Abstract

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Zwitterionic adducts of N-heterocyclic carbene and carbodiimide (NHC-CDI) are an emerging class of organic compounds with promising properties for applications in various fields. Herein, we report the use of the ICyCDI(p-Tol) betaine adduct (1a) and its cationic derivatives 2a and 3a as catalyst precursors for the dichloromethane valorization via transformation into high added value products CH₂Z₂ (Z = OR, SR or NR₂). This process implies selective chloride substitution of dichloromethane by a range of nucleophiles Na⁺Z^– (preformed or generated in situ from HZ and an inorganic base) to yield formaldehyde-derived acetals, dithioacetals, or aminals with full selectivity. The reactions are conducted in a multigram-scale under very mild conditions, using dichloromethane both as a reagent and solvent, and very low catalyst loading (0.01 mol %). The CH₂Z₂ derivatives were isolated in quantitative yields after filtration and evaporation, which facilitates recycling the dichloromethane excess. Mechanistic studies for the synthesis of methylal CH₂(OMe)₂ rule out organocatalysis as being responsible for the CH₂ transfer, and a phase-transfer catalysis mechanism is proposed instead. Furthermore, we observed that 1a and 2a react with NaOMe to form unusual isoureate ethers, which are the actual phase-transfer catalysts, with a strong preference for sodium over other alkali metal nucleophiles.

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Subjects

Introduction

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Dichloromethane (DCM) is a relatively inert compound that is widely applied as a solvent in organic synthesis and separation procedures. It can be regarded as a low polarity, nonprotic, and noncoordinating solvent, which, however, dissolves many polar or even ionic species. (1) The heavier dihalomethane congeners, dibromomethane and diiodomethane, are considerably more reactive than DCM. Those are rarely used as a solvent but often employed as a methylene source via nucleophilic substitution reactions. (2) Indeed, along with formaldehyde, dihalomethanes represent an important C1 chemical building block. (3) DCM could be a convenient, readily available, and inexpensive alternative to these compounds; nevertheless, it is seldom used as a chemical reagent. The chemical stability of C–Cl bonds, which makes DCM such an excellent solvent, usually leads to difficult chloride substitution processes. (4) The latter are often plagued by side reactions, such as the HCl elimination whenever the nucleophiles behave as strong bases or free radical chain processes. (4a,5) These unwanted reactions can entail explosion hazards in some cases. (6) Yet, the use of DCM as the source of the CH₂ fragment could help improve many chemical transformations beyond the mere cost reduction. Among other advantages, DCM allows much safer handling than formaldehyde, a widely used CH₂ precursor in classic organic synthesis. (7) Although the intensive usage of organohalogens can lead to environmental issues, there are strategies that can be followed in order to optimize their application and minimize this impact. (8) For instance, DCM can be used simultaneously as solvent and reagent, and due to its low boiling point and its poor miscibility with water and aqueous mixtures, it can be readily separated from polar or heavier substances and recycled for further uses. (9) Among others, clean chlorine substitution in DCM could lead to significant improvements in the syntheses of a wide variety of methylene-bridged derivatives, such as formaldehyde-derived acetals, dithioacetals, or aminals. Formaldehyde acetals or formals are chemicals with many practical applications. Those have proven useful as fuels or fuel additives, (10) and also as reagents for the introduction of an alkoxy- or aryloxymethylene group. (11) On the other hand, dithioacetals and aminals are less used in the industry than formals but have important applications in synthesis (12) and coordination chemistry. (13) Although transition metal catalysts (14) (e.g., Ni (14a) or Cu (14b) complexes) have been occasionally used for coupling dichloromethane with nucleophiles, the usefulness of such processes is usually limited by the need for high metal loadings and relatively low yields.

In this contribution, we disclose a practical application of stable adducts of NHC carbenes and carbodiimides (NHC-CDI) as suitable catalysts for nucleophilic chloride substitution on DCM, providing a convenient route for a variety of symmetrical, methylene-bridged derivatives CH₂Z₂. NHC-CDI’s are an emerging class of dipolar compounds that belong to the chemical class of betaines, electroneutral zwitterions that cannot be represented by any resonance form with full charge cancellation. (15) NHC-CDI’s bearing aryl substituents in the CDI part are readily prepared and exhibit enhanced stability even under the open air, despite the strongly basic and nucleophilic character of their amidinate moiety. (16) Due to these properties, stable NHC-CDI adducts have a promising potential for application in many different fields, including metal ligands in coordination and organometallic chemistry, (17) nanocatalyst design, (18) building blocks for polymers, (19) or in the development of new types of persistent free radicals. (20)

Recently, we have reported that the ICyCDI(p-Tol) betaine adduct (1a), an NHC-CDI derivative containing 1,3-dicyclohexylimidazolylidene (ICy) and di-p-tolylcarbodiimide (CDI(p-Tol)) as the NHC and CDI parts, respectively, reacts in DCM solution to afford the ionic salt [CH₂(1a)₂]²⁺[2Cl^–] (2a·2Cl). Despite the considerable steric bulk of 1a, this process, which implies the cleavage of both C–Cl bonds of DCM, proceeds in quantitative yield and full selectivity, without any detectable byproducts or intermediates (Scheme 1). (21) Compound 2a can be envisaged as a “[CH₂]²⁺” fragment trapped by two neutral 1a units. We were intrigued by the possibility that the central core of the 2a dication could be activated for nucleophilic substitution, delivering this group to mild nucleophiles. In a catalytic version of this process, DCM could be applied as a source of the [CH₂]²⁺ synthon, and 1a (or some other related NHC-CDI derivatives) might act as an organocatalyst in an unusual class of organocatalyzed nucleophilic substitution reaction. Herein we show that this is indeed the case, although further investigation of the details shows that the mechanism of this catalytic transformation differs largely from our initial intuition.

Results and Discussion

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To test our proposal, we first used solid sodium hydroxide as a nucleophile. This reaction led to the substitution of Cl for OH, affording hydrated formaldehyde oligomers, which could be detected in the ¹H NMR spectra of the mixture (22) (broad signal at 4.88 ppm, see Figure S25) and also because of the characteristic smell of free formaldehyde, but the efficiency of the reaction was hard to quantify. Therefore, we shifted our trial to solid sodium methoxide, which would enable the synthesis of methylal through the substitution of chlorine atoms of DCM by methoxy groups (Scheme 2). Methylal or dimethoxymethane is an interesting target since it can be used as a green solvent (23) (far less toxic than DCM itself) or as a safer surrogate of formaldehyde, preventing the use of this toxic substance or its insoluble polymer, paraformaldehyde. (24) Yet, it has been known for a very old time that neat dichloromethane does not react with sodium methoxide, or it does only reluctantly under forcing conditions to afford complex mixtures of products. (25) We performed a series of tests with different amounts of solid sodium methoxide suspended in neat DCM at 25 and 60 °C, using a sealed ampule with a magnetic stirrer as a reactor. We confirmed that, whereas hardly any detectable quantity of methylal was formed in the absence of 2a, the addition of a catalytic amount of the latter (from 2 to 0.2 mol %) led to the quantitative conversion of NaOMe into methylal and NaCl. Due to the similar boiling points of DCM and methylal, we made no attempt to separate the product from the excess solvent. However, spectroscopic analyses of the crude mixtures showed that the transformation is very clean. (26)

Scheme 2. Synthesis of Methylal Using 2a as a Catalyst

The NMR spectrum of a drop of the liquid phase in CDCl₃ displayed only major signals for methylal (3.30 and 4.52 ppm) and unreacted DCM (5.32 ppm), along with very minor signals from the catalyst. We then decided to scale-up the process to show the potential of this reaction. Hence, the synthesis of methylal was carried out starting from 2 g of sodium methoxide and 20 mL of DCM, at 60 °C, using 0.2 mol % of catalyst 2a, and full conversion was achieved. Finally, the catalyst loading was decreased to 0.01 mol % (100 ppm) and NaOMe quantity scaled up to 20 g, leading to an apparent TON figure in the order of 10⁴ without any loss of purity or selectivity. The use of such a small proportion of a metal-free catalyst is remarkable. (27)

NMR analyses of samples removed at regular intervals from a stirred suspension of solid NaOMe in DCM containing 2a (0.2 mol % vs NaOMe) at 40 °C showed that the methylal content of samples increased linearly up to 70% conversion (68% within 7 h) and was consistent with full conversion when a final aliquot was measured after 24 h (Figure 1). These data indicate that the activity of 2a does not show any significant decay over long periods of time, at a turnover frequency (TOF) of 45 h^–1 (referred to DCM, or 90 h^–1 for NaOMe) under such mild conditions. Moreover, the addition of a second 2 g portion of sodium methoxide to a completed reaction mixture containing an excess of unreacted DCM led again to full conversion within the expected 24 h period, suggesting that this catalyst remains indefinitely active under the specified conditions.

Figure 1. Yield vs time plot for the reaction of DCM with NaOMe catalyzed by 2a. Conditions: 40 °C, NaOMe, 2 g (31 mmol); DCM (neat) 40 mL (626 mmol); 2a, 37 mg (0.2 mol % with regard to NaOMe). The last check after 24 h was consistent with full NaOMe consumption.

With this first accomplishment in hand, we set out to explore other suitable nucleophiles to define the scope of this interesting reaction. In particular, we analyzed whether other O, S, or N-based nucleophiles would perform in a similar way in order to obtain formaldehyde-derived acetals, dithioacetals, or aminals, respectively. The results are displayed in Table 1. We first explored the reaction of DCM with solid sodium phenoxide and sodium benzyloxide under the same conditions developed for the synthesis of methylal (entries 2 and 3). We selected these alkoxides because they should exhibit milder reactivity than sodium methoxide. Yet, both of them reacted with DCM under mild conditions, affording the corresponding products in a highly selective manner. Essentially pure products were isolated after a very simple workup involving filtration through a silica pad (to remove NaCl and the remaining catalyst) and evaporation under a vacuum. The purity and quantitative isolated yield confirmed the high selectivity appreciated in the NMR analyses of the crude mixtures.

Table 1. Catalyzed Nucleophilic Substitution Reactions in Dichloromethane with Various Nucleophiles and Conditions^a

entry	product CH₂Z₂^b	substrate/base^c	cat.	conversion^d/yield^e
1	i	NaOMe	2a	>99/>99
2	ii	NaOPh	2a	>99/92
3	iii	NaOBn	2a	>99/87
4	i	MeOH/NaOH	2a	>99/89
5	ii	PhOH/NaOH	2a	>99/89
6	iii	BnOH/NaOH	2a	>99/86
7	iv	PTBP^f/NaOH	2a	>99/85
8	v	AA^g/NaOH	2a	>99/83
9	vi	i-PrOH/NaH	2a	74/67
10	vii	EtSH/NaOH	2a	>99
11	viii	HPz^h/NaH	2a	89/72
12	i	NaOMe	1a	>99/>99
13	ii	NaOPh	1a	>99/86
14	iii	NaOBn	1a	>99/87
15	i	NaOMe	3a	>99/>99

^{^a}

Reaction conditions: catalyst loading 0.2 mol %, 60 °C, 24 h.

^{^b}

See Scheme 3 for the detailed structure of the products.

^{^c}

Insoluble bases (NaOH, NaH), added in excess.

^{^d}

Spectroscopic yield from ¹H NMR.

^{^e}

Isolated yields (calculated on the basis of the starting substrate), unless otherwise specified.

^{^f}

p-tert-Butylphenol.

^{^g}

Allyl alcohol.

^{^h}

Pyrazole.

In view of the excellent results of transformations with solid alkoxides, we examined a more practical setup for this catalytic reaction (Scheme 3). Thus, methylal was obtained using methanol combined with solid sodium hydroxide, a much cheaper and safer base than NaOMe. Although the spectroscopic yield of this reaction was slightly lower, the selectivity was excellent again since methylal was the only organic product detected, along with unreacted DCM. Despite the fact that 2a also catalyzes the reaction of DCM with NaOH, no traces of formaldehyde or formaldehyde oligomers were detected in the NMR spectra of the reaction mixture. The apparent losses in the mass balance can be attributed to the poor mechanical properties of the sticky solid formed by wet sodium salts, which could occlude some methanol.

Scheme 3. Catalytic Transformation of DCM into CH₂Z₂ Using Combinations of Weak Protic Acids and Suitable Bases (NaOH or NaH)

In a similar fashion, 2a efficiently catalyzed the reaction of several alcohols with DCM at 0.2 mol % catalyst loading in the presence of suitable bases. Among the substrates, those that gave the best conversions with NaOH were primary alcohols and phenol derivatives. Thus, benzyl alcohol, allyl alcohol (AA), phenol, and p-tert-butylphenol (PTBP), combined with NaOH, were cleanly transformed into the corresponding acetals with perfect selectivity and excellent yields. NaOH was not effective for 2-propanol, a less acidic secondary alcohol. Nevertheless, when the stronger base NaH was used, the corresponding acetal was produced. Surprisingly enough, the acidic p-chlorophenol turned out to be unreactive, either in the presence of NaOH or as the solid sodium salt, which we attribute to the low nucleophilicity of the corresponding anion. Regarding the synthesis of dithioacetals, we used ethanethiol as a reference for thiols, which was successfully converted to di(ethylthio)methane using NaOH as a base. For the synthesis of aminals, we performed the synthesis of bis(pyrazolyl)methane. This target was selected in view of the wide application of pyrazolyl-based molecules as chelating ligands for metal complexes. (13) Also, in this case, the functionalization of both C–Cl bonds of DCM and the subsequent formation of new C–N was achieved, but NaH was required for the deprotonation of pyrazole (HPz).

Mechanistic Studies

According to our initial ideas, the role of dication 2a would be to act as a source of the [CH₂]²⁺ synthon, regenerating the precursor betaine 1a in each turn of the catalytic cycle. Accordingly, not only 2a but also betaine 1a would be active catalysts for this reaction. Similar reasoning led us to conclude that cationic derivatives, [ZCH₂·1a]⁺, would participate as short-lived intermediates in the catalytic cycle, preceding the introduction of the second Z fragment. To test these hypotheses, we synthesized the salt [MeOCH₂·1a]⁺[Br^–] (3a) as shown in Scheme 4 and compared its catalytic performance with those of 1a and 2a in the synthesis of methylal. Gratifyingly, as can be seen in Table 1, all three compounds perform as catalysts in the synthesis of methylal, with similar efficiency. Moreover, 1a was tested in the synthesis of diphenoxymethane and dibenzyloxymethane with identical results as 2a (Table 1, entries 12–15). However, we realized that the TON and TOF figures of our system were atypical for a regular organocatalytic mechanism involving systematic C–N bond formation and cleavage. On the basis of these data and previous qualitative observations, (21) it can be easily shown that this reaction is at least 2–3 orders of magnitude faster than the reaction of 1a with DCM at the same temperature, (28) which rules out our preliminary proposals.

Scheme 4. Synthesis of the Catalyst Precursor 3a

An alternative phenomenon that would account for the high activity levels observed in our system is solid–liquid phase-transfer catalysis (PTC). PTC allows the solubilization of highly polar or ionic species in nonpolar solvents. Insoluble reagents that normally would be forced to react through the solid–liquid interphase are transported into the solution, where they react under rather diluted conditions. Therefore, solid–liquid PTC enhances the reactivity of solids, and at the same time improves selectivity, by reducing side processes that are common when highly reactive species are dissolved in a higher concentration (Figure 2). (29) Solid–liquid PTC is often regarded as a green methodology, as reagents and saline products are kept in the solid state and can be readily separated by physical methods. (30) Alkylation of alcohols and other nucleophilic substrates under PTC conditions is not a novel procedure, but the potential of this methodology using DCM both as a solvent and as alkylating reagent remains almost unexplored. (31) Although DCM has been found an excellent solvent for liquid–solid PTC, (32) in the rare cases when DCM is used as an electrophile, liquid–liquid PTC methods in biphasic media (with concentrated aqueous NaOH), or highly polar solvents like N-methyl-2-pyrrolidone have been preferred. (33) Interestingly, the above-mentioned transition metal catalysts also used DCM both as electrophile and solvent. (14)

Figure 2. Solid–liquid phase-transfer catalysis.

Several considerations point to PTC as the mechanism that best explains the high activity of our catalysts. First of all, a process controlled by the phase transfer step is consistent with the linear kinetic plot shown in Figure 1, which indicates a zero-order dependency on the reagents well over 50% conversion of NaOMe. Second, to put our results in the correct perspective, we decided to compare the performance of 1a, 2a, or 3a with those of a set of typical phase-transfer agents, like onium-type salts and crown ethers for the synthesis of methylal under the same experimental conditions (Table 2). To enable a more accurate comparison, we ran the experiments under the conditions required by 2a (0.2 mol %) to drive the reaction of DCM with NaOMe to ca. 50% conversion. The only difference with the preparative conditions was that, in order to facilitate data collection, this set of experiments was performed at a slightly lower temperature, 40 °C, at which the half-conversion time would be ca. 4 h. As shown in Table 2, no methylal was formed in the absence of any PTC reagent, confirming the inertness of DCM against solid NaOMe reported in old literature sources cited above. (25) Nevertheless, when we added the same catalyst loading of NBu₄Cl, 18-crown-6, 15-crown-5, or the imidazolium salt ICy·HBF₄ (the precursor of the NHC carbene ICy, one of the constitutive parts of 1a), DCM conversion was observed, albeit with significant differences. Remarkably, 2a proved the most active of the set. NBu₄Cl, one of the best-known and widely used PTC reagents, is also active, with slightly lower activity, and the imidazolium salt showed a rather poor conversion. Moreover, we tested whether CDI(p-Tol), the carbodiimide moiety of 1a, was also active, but no conversion was achieved. At any rate, the efficiency of both 1a and 2a are comparable even to NBu₄Cl and are clearly superior to a typical crown ether, such as 18-crown-6.

Table 2. Catalytic studies of 1a, 2a, 3a, and Other PTC Catalysts toward MOMe (M = Li, Na, K)

entry	substrate	catalyst^a	conversion^b (%)
1	NaOMe
2	NaOMe	NBu₄Cl	44
3	NaOMe	18-crown-6	20
4	NaOMe	15-crown-5	39
5	NaOMe	ICy·HBF₄	8
6	NaOMe	CDI(p-Tol)
7	NaOMe	1a	46
8	NaOMe	3a	43
9	NaOMe	2a	55
10	LiOMe	2a
11	KOMe	2a	5

^{^a}

Catalyst or catalyst precursor (see below).

^{^b}

An aliquot was taken after 4 h to calculate conversion by ¹H NMR.

The mechanism responsible for the solubilization of insoluble nucleophiles depends largely on the nature of the PTC catalyst. Whereas tetraalkylammonium salts, like NBu₄Cl, rely on the high solubility of its cation in low polarity solvents, the action of 18-crown-6 is due to the sequestration of the alkali metal cation in the cavity of the molecule. (29,30) Hence, the lower efficacy of 18-crown-6 in the reaction with NaOMe could be due to its moderate affinity for Na⁺ (e.g., the affinity ratio K⁺/Na⁺ for 18-crown-6 in the gas phase is 10:6). (34) It is well-known that the efficacy of complexing PTCs shows significant dependency on the size of the alkali metal. (35) As shown in entry 4, 15-crown-5, whose smaller cavity is best suited for Na⁺, performs better than 18-crown-6, but it is still inferior to 2a. Similarly, compound 2a shows a strong preference for Na⁺, performing its action in a much more efficient manner with NaOMe than with KOMe, whereas LiOMe turned out to be ineffective (Table 2, entries 9–11). These observations suggest that, in addition to the cation exchange solubilization mechanism, our catalysts may simultaneously be performing as selective ligands for the alkali metal. This conclusion is a somewhat unexpected result since the positive charge of the betaine derivatives (double in the case of 2a) should reduce their capacity to coordinate to cationic alkali metal centers and, in consequence, would be expected to behave in a nonspecific manner, like quaternary ammonium salts.

A significant detail observed during the reaction of NaOMe and DCM catalyzed by either 1a or the cations 2a and 3a is the evident intensification of the color within the initial hours of the reactions, leaving a strong reddish-orange tone that persists once the reaction is finished. Strongly colored reaction mixtures were also observed with other nucleophiles, independently on whether 1a or 2a were used as catalysts, but, revealingly, no color change was observed when the catalysis was unsuccessful, as in the reactions with p-chlorophenoxide or with lithium methoxide. In an attempt to identify the colored materials formed with NaOMe, we recorded the ¹H and ¹³C{¹H} spectra of the deeply colored oils remaining after evaporation of the reaction mixtures catalyzed with either 1a or 2a, by dissolving in CD₂Cl₂. The NMR spectra of the residue left by 2a was particularly clean, showing that the original signals of the methylene-bridged dication had fully disappeared and replaced with a new spectrum of what looked like a mixture containing a strongly prevalent species 2b (see Figure S20). The DOSY spectrum of the mixture (see Figure S19) allows a clear distinction of the signals of the main product, 2b, from those of background species, which have all significantly higher diffusion coefficient or, what is the same, lower molecular weight. The spectra of 2b correspond to a symmetrical species akin to 2a, which has no imidazolium moieties. The broad and ill-defined signals of the cyclohexyl fragments are all associated with the low molecular weight region, consistent with the degradation of the ICy unit under the reaction conditions. Concerning 2b, a single resonance of relative intensity for 6H is found at 3.53 ppm, corresponding to two equivalent methoxy groups, along with another singlet of 2H for the central CH₂ unit at 5.15 ppm. The relative simplicity of the spectra of 2b enabled us to fully assign by ¹H and ¹³C NMR the unusual isoureate ether structure shown in Scheme 5. The NMR spectra of the residue obtained from the 1a-catalyzed reaction (see Figure S17) indicates the presence of the prevalent species, 1b, different from the starting betaine and from 2b, which contains two resonances MeO (3.30 and 3.75 ppm) and a single CH₂ unit at 4.69 ppm. Interestingly, the DOSY spectrum of this mixture (see Figure S16) gave slightly lower size to the molecules of 1b than to the broad background arising from the imidazolium fragment. These data clearly point to the unprecedented processes shown in Scheme 5, giving rise to 1b and 2b, rare examples of isoureate ethers, which are likely responsible for most of the PTC activity in the catalytic reaction. Accordingly, ESI-MS of partially purified extracts in wet MeOH showed intense signals for the corresponding monoprotonated ions (m/z = 299 and 521, respectively), as well as their corresponding Na⁺ complexes (321 and 543). Ion compositions were confirmed in the corresponding HR-ESI spectra (see Experimental part). Note that 1b is the result of trapping the reactive chloromethyl intermediate [ClCH₂·1a]⁺[Cl^–] by a methoxide, giving the same characteristic methoxymethylene fragment, also present in 3a. This was confirmed by comparing the NMR spectra of 3a with the crude residue left after evaporation of DCM/methylal solutions (see Figure S24). Thus, 1b cannot be converted in 2b during the reaction. In consequence (and in contrast with our initial expectations), each of the catalytic reactions initiated by precursors 1a and 2a are due to a different catalytic species. According to this proposal, the catalyst generated from 3a is, very likely the same formed from 1a, namely, 1b.

Scheme 5. Transformation of 2a and 1a into 2b and 1b, Respectively, in Catalytic Media

Attempts to separate 1b and 2b from the mixture of products resulting from the degradation of the NHC units have been unsuccessful so far, apparently due to the sensitivity of the isoureate ethers, which seem to hydrolyze on attempted purification by typical chromatographic workup. However, since the imidazolium precursor ICy·HBF₄ shows very poor activity as a PTC catalyst, the effectivity of both 1a and 2a should be entirely ascribed to the electroneutral isoureate ethers, that, as commented above, must have a significant affinity for the Na⁺ cation. This is in accordance with the facile ionization of the neutral molecules with traces of Na⁺ in the methanol solvent. The low catalytic activity found for the imidazolium salt is consistent with these observations, as this is expected to be deprotonated to the same ICy moiety subsequently degrades under the reaction conditions. Likewise, the experiment performed with CDI(p-Tol) as a catalyst (Table 2, entry 6) demonstrates not only that the free carbodiimide is not be involved in the process, but also that the active isoureate 2b cannot be generated directly by the successive reaction of CDI(p-Tol) with NaOMe and DCM. To confirm this point, we attempted the reaction of CDI(p-Tol) with NaOMe in DCM but, as expected, no reaction was observed. Thus, the only plausible pathway to generate the catalytically active species 1b and 2b is through betaine 1a and its cationic derivatives 2a and 3a.

Conclusions

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In summary, we have shown that efficient catalytic systems generated from betaine 1a or their cationic alkyl derivatives 2a and 3a provide a versatile and clean method for the conversion of DCM in a range of formaldehyde derivatives CH₂Z₂. We have successfully applied this transformation to aliphatic and aromatic alcohols, thiols, and N-heterocycles, which can be used either as insoluble sodium salts or directly, in combination with suitable bases like NaOH or NaH, depending on their acid strengths. This process only generates sodium chloride and water or hydrogen as byproducts, whose straightforward elimination greatly facilitates the purification of the products. Furthermore, DCM transformation was achieved at very low catalyst loadings and required no transition metals. The volatility of dichloromethane allows its facile recovery and recirculation, enabling facile scale-up of the reactions. Mechanistic studies have ruled out an organocatalytic cycle involving the reversible formation and cleavage of C–N bonds of 2a, which rather acts as a precursor for electroneutral, highly efficient Na⁺ complexing isoureate ethers arising from an unusual nucleophilic displacement of the ICy (the NHC fragment of the betaine) by the nucleophilic reagent. We are currently extending our studies to other NHC-CDI derivatives and investigating the potential uses of these compounds in catalysis, either free or complexed to abundant and low-toxicity metals.

Experimental Section

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General Considerations

All manipulations were performed under an inert atmosphere using Schlenk-line techniques (O₂ < 3 ppm) and a glovebox (O₂ < 0.6 ppm) MBraun MB-20G. Solvents were purified using an MBraun Solvent Purification System, except dichloromethane (DCM) and THF, which were distilled with CaH₂ and Na, respectively. All NMR scale experiments were carried out in sample tubes with airtight PTFE valves. Deuterated solvents were degassed and stored in the glovebox in the presence of molecular sieves (4 Å). NMR spectra were recorded with a Bruker 400 Ultrashield (¹H 400 MHz, ¹³C 101 MHz) at 25 °C. All chemical shifts were determined using residual signals of solvents and were referenced with regard to external SiMe₄. Assignments of spectral signals were helped with 2D (¹H–¹³C HSQC and HMBC) and diffusion (DOSY) NMR experiments. Elemental analysis and ESI-MS spectra of samples were carried out by the Analytical Services of the Institute for Chemical Research (Seville, Spain) using an LECO CHNS-TruSpec and Bruker Ion Trap Bruker Esquire 6000, respectively. HR-ESI spectra were recorded by the Mass Spectrometry Service (CITIUS, University of Seville) in a Thermo Scientific Orbitrap Elite hybrid mass spectrometer, operating in direct injection mode with an ESI ion source and ion-trap analyzer. Unless otherwise specified, all commercial reagents were purchased from Sigma-Aldrich and used as received. Imidazolium salt ICy·HBF₄ and catalysts 1a and 2a were prepared according to literature and our synthetic procedures, previously reported. (17a,21,36) Warning! Although dichloromethane does not react vigorously with NaH, NaOH, or sodium alkoxides or aryloxides described in this work, strongly basic reagents like potassium tert-butoxide or neat sodium, which are known to react violently with this solvent, should be avoided.

General Procedure

A regular magnetic bar sufficed to achieve a satisfactory mixing of the suspensions throughout the whole experiment. DCM, containing the required amount of catalyst, was added to a gastight glass Teflon valve glass ampule containing solid Na⁺Z^– (either preformed or generated in situ from HZ and an inorganic base), and the mixture was stirred for a prescribed time in an oil bath preset at the specified temperature. In all experiments, the mixture gradually takes an intense yellow-orange color, as the suspended solid gradually becomes a thinner precipitate (NaCl). At the prescribed time, the mixture was allowed to settle, and a small sample (0.1–0.05 mL) was taken and dissolved in CDCl₃. The conversion was deduced from the relative ratios of the central CH₂ signal of the product and an internal standard (hexamethylbenzene). See below for more details and the purification procedures.

Preliminary Experiments

With NaOH, an excess (1 g) of NaOH was added to a vial, and 10 mL of a solution of 20 mg of catalyst 2a in neat dichloromethane was added to the solid. After 24 h, a free formaldehyde smell was detected, and an aliquot of the mixture was taken. The NMR spectrum of the mixture in CDCl₃ showed a broad signal for hydrated formaldehyde oligomers (see Figure S25), but the efficiency of the reaction was hard to quantify.

With NaOMe in an NMR tube, catalyst 2a (5 mg, 2 mol %) was dissolved in CD₂Cl₂, and then anhydrous NaOMe (27 mg) was added inside the NMR tube. It was not soluble and remained in the bottom of the tube. After 2 h at room temperature, the solution became light orange, and it got more intense over time. It was also perceived a change in the texture of the solid, which became thinner. The ¹H NMR spectrum showed an intense singlet at 3.30 ppm, which was assigned to 1H of methoxy groups from dimethoxymethane (methylal). As the methylene source was CD₂Cl₂, the methylene fragment of the product was not observed.

Optimization of the General Reaction Conditions for the Syntheses of Methylal from DCM and NaOMe with Catalyst 2a

In the general procedure (see Table S1 for details), a regular magnetic bar sufficed to achieve a satisfactory mixing of the suspensions throughout the whole experiment. DCM, containing the required amount of 2a, was added to a Schlenk flask containing solid NaOMe, and the mixture was stirred for a prescribed time. In the experiments conducted at 60 °C, the mixture was transferred to a gastight glass Teflon valve glass ampule, which was closed and magnetically stirred in an oil bath preset at the specified temperature. In all experiments, the mixture gradually takes an intense yellow-orange color, as the suspended solid gradually becomes a thinner precipitate (NaCl). At the prescribed time, the mixture was allowed to settle, and a small sample (0.1–0.05 mL) was taken and dissolved in CDCl₃. The conversion was deduced from the relative ratios of the CH₂ signals of unreacted dichloromethane and methylal. The mixture was then allowed to settle, filtered with a cannula, and vacuum-transferred to a cold trap, which affords a clean, colorless solution of methylal in the remaining dichloromethane. The mixture was a colorless liquid. ¹H NMR (CDCl₃, 400 MHz): δ 4.52 (s, 2H), 3.30 (s, 6H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 97.7, 55.2. Spectroscopic data is in accordance with data reported in literature. (37a)

Monitoring the Reaction of NaOMe with CH₂Cl₂

A 50 mL glass reactor provided with a Young Teflon screw stopcock and a nitrogen-purged liner to allow sample removal was charged with solid NaOMe (2 g, 37 mmol), DCM (35 mL), and 5 mL of a DCM solution containing 37 mg of catalyst 2a (0.2 mol %), and an accurately weighed amount (30 mg) of hexamethylbenzene to be used as an internal standard, weigh to ±0.1 mg accuracy in an analytical balance. The mixture was stirred at 40 °C in an oil bath preset at the specified temperature, taking aliquots of ca. 0.1 mL with a long-needle syringe through the sample removal port. Each sample was diluted with 0.5 mL of CDCl₃, filtered, and analyzed using NMR to determine the reaction advance. The NMR data were positively compared with those listed in the SDBS spectral database in the same solvent (CD₃Cl). (37a)

Comparative Assessment of Catalyst Efficiency in the Methylal Synthesis Using Different Catalysts and Alkali Metal Cations

In order to study the effect of the catalyst in the obtention of methylal, we repeated the reaction under the same conditions described in the previous section, using the same molar amount of a different catalyst in each of them: NBu₄Cl, 18-crown-6, 15-crown-5, 1a, 3a or ICy·HBF₄, CDI(p-Tol). These reactions were not monitored but stopped after a fixed reaction time (4 h at 40 °C, when 50% conversion NaOMe was estimated using 2a), and their progress was determined using the same NMR-based methodology to determine the amount of methylal formed. Likewise, the efficiency of 2a with different alkali metal cations was assessed using equivalent amounts (37 mmol) of the corresponding alkali methoxides MOMe (M = Li, Na, or K) and a 4 h reaction time. The characteristic dark orange color associated with these reactions was not observed when LiOMe was used as the methoxide source.

Procedure for the Generation of Solid Sodium Benzyloxide and Sodium Phenoxide

Sodium benzyloxide or phenoxide was generated prior to use, following a modified procedure taken from the literature: (38) a 100 mL Schlenk flask equipped with a stirring bar was charged with NaH (82.5 mmol) in mineral oil and 25 mL of THF. The flask was brought to an ice–water bath, and the solid was suspended with magnetic stirring. A solution containing 75 mmol of the corresponding alcohol or phenol in 25 mL of THF was kept cool with vigorous stirring. The addition caused the evolution of H₂ gas, more vigorous in the case of phenol. Once the addition was completed, the mixture was kept stirring at room temperature for 4 h. The solvent was removed under a vacuum, and the sticky white solid obtained was washed three times with hexane, in order to remove the mineral oil, to afford a white powder. No further purification was performed.

Synthesis of CH₂(OPh)₂ from Sodium Phenoxide

Sodium phenoxide (3.83 g, 33 mmol), generated from phenol and NaH as described above, was added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. A solution of 33 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. A light white solid (NaCl) remained in the bottom of the flask, leaving the colored solution clear to perform the purification. The solution was separated from the solid by filtration via cannula. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst, and afterward, the solvent was removed under a vacuum to afford a slightly pale-yellow liquid with a yield of 92% (3.04 g). The same procedure was conducted with 16.5 mg of 1a as a catalyst, with a yield of 86% (2.84 g). ¹H NMR (CDCl_3, 400 MHz): δ 7.32 (m, spin system AA′BB′C, 4H), 7.13 (m, spin system AA′BB′C, 4H), 7.05 (tt, J = 7.4 Hz, J = 1.1 Hz, 2H), 5.75 (s, 2H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 157.2, 129.7, 122.6, 116.7, 91.4. IR (cm^–1): 3041 (ν C_Ar─H), 2973 (ν C_sp3─H), 1588 (ν C_Ar═C_Ar), 1490 (ν C_Ar═C_Ar), 1200 (ν_as C_Ar─O-C), 1012 (ν_s C_Ar–O-C). Spectroscopic data is in accordance with data reported in literature. (37b)

Synthesis of CH₂(OBn)₂ from Sodium Benzyloxide

Sodium benzyloxide (2.18 g, 16.5 mmol), generated from benzyl alcohol and NaH as described above, was added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. A solution of 16.5 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. After a few minutes at 60 °C, an intense orange-red color in the solution was observed. Once the reaction finished, the stirring was stopped. A light solid white solid (NaCl) remained in the bottom of the flask, leaving the colored solution clear to perform the purification. The solution was separated from the solid by filtration via cannula. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst, and afterward, the solvent was removed under a vacuum to afford a slightly pale-yellow liquid, with a yield of 87% (1.64 g). The same procedure was conducted with 8.25 mg of 1a as a catalyst with a yield of 87% (1.64 g). ¹H NMR (CDCl₃,400 MHz): δ 7.37 (m, 8H). 7.32 (m, 2H), 4.86 (s, 2H), 4.67 (s, 4H). ¹³C{¹H} NMR (100 MHz, CDCl₃, 25 °C): δ 138.0, 128.5, 128.1, 127.8, 94.1, 69.7. IR (cm^─1): 3029 (ν C_Ar─H), 2879 (ν C_sp3–H), 1497 (ν C_Ar═C_Ar), 1102 (ν_as C─O─C), 1041 (ν_s C─O–C). Spectroscopic data is in accordance with data reported in literature. (37c)

Synthesis of CH₂(OMe)₂ from Methanol and Sodium Hydroxide

Sodium hydroxide (1.7 g, 44.5 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended on 25 mL of dried dichloromethane. Afterward, 1.19 g of methanol (37 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium methoxide. A solution of 37 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic layer was separated from the solid by filtration via cannula. The yellow mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst to afford a colorless solution of CH₂(OMe₂)₂ in dichloromethane with a yield of 89%. ¹H NMR (CDCl₃, 400 MHz): δ 4.52 (s, 2H), 3.30 (s, 6H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 97.7, 55.2. Spectroscopic data is in accordance with data reported in literature. (37a)

Synthesis of CH₂(OPh)₂ from Phenol and Sodium Hydroxide

Sodium hydroxide (0.37 g, 9.25 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. Afterward, 0.78 g of phenol (8.25 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium phenoxide. A solution of 8.25 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst. Afterward, the solvent was removed under a vacuum to afford a white powder in 89% yield (0.74 g). ¹H NMR (CDCl₃, 400 MHz): δ 7.32 (m, 4H). 7.13 (m, 4H), 7.05 (tt, J = 7.4 Hz, J = 1.1 Hz, 2H), 5.75 (s, 2H).¹³C{¹H} NMR (CDCl_3, 100 MHz): δ 157.2, 129.7, 122.6, 116.7, 91.4. IR (cm^–1): 3041 (ν C_Ar─H), 2973 (ν C_sp3─H), 1588 (ν C_Ar═C_Ar), 1490 (ν C_Ar═C_Ar), 1200 (ν_as C_Ar─O─C), 1012 (ν_s C_Ar─O─C). Spectroscopic data is in accordance with data reported in literature. (37b)

Synthesis of CH₂(OBn)₂ from Benzyl Alcohol and Sodium Hydroxide

Sodium hydroxide (0.37 g, 9.25 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. Afterward, 0.89 g of benzyl alcohol (8.25 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium benzyloxide. A solution of 8.25 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst. Afterward, the solvent was removed under a vacuum to afford a white powder in 89% yield (0.84 g). ¹H NMR (CDCl_3, 400 MHz): δ 7.37 (m, 8H), 7.32 (m, 2H), 4.86 (s, 2H), 4.67 (s, 4H). ¹³C{¹H} NMR (100 MHz, CDCl₃, 25 °C): δ 138.0, 128.5, 128.1, 127.8, 94.1, 69.7. IR (cm^─1): 3029 (ν C_Ar─H), 2879 (ν C_sp3–H), 1497 (ν C_Ar═C_Ar), 1102 (ν_as C─O─C), 1041 (ν_s C─O–C). Spectroscopic data is in accordance with data reported in literature. (37c)

Synthesis of CH₂(O-p-C₆H₄t-Bu)₂ from p-tert-Butylphenol and Sodium Hydroxide

Sodium hydroxide (0.37 g, 9.25 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. Afterward, 1.15 g of p-tert-butylphenol (7.66 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium p-tert-butylphenoxide. A solution of 15 mg of catalyst 2a (0.4 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. After a few minutes at 60 °C, an intense yellow-orange color in the solution. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst. Afterward, the solvent was removed under a vacuum to afford a white powder, in 85% yield (1.02 g). ¹H NMR (CDCl₃, 400 MHz): δ 7.31 (m, 4H), 7.04 (m, 4H), 5.69 (s, 2H, CH₂), 1.29 (s, 18H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 155.0,145.3,126.5, 116.1, 91.6, 34.3, 31.6. IR (cm^─1): 3041 (ν C_Ar─H), 2957 (ν C_sp3─H), 1509 (ν C_Ar═C_Ar), 1211 (ν_as C_Ar─O─C), 1016 (ν_s C_Ar─O─C). Anal. Calcd for C₂₁O₂₈O₂: C, 80.73%; H, 9.03%. Found: C, 81.16%; H, 8.87%.

Synthesis of CH₂(OCH₂CH═CH₂)₂ from Allyl Alcohol and Sodium Hydroxide

Sodium hydroxide (0.40 g, 9.25 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended in 15 mL of dried dichloromethane. Afterward, 0.48 g of allyl alcohol (8.25 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium allyloxide. A solution of 8.25 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. In order to remove the unreacted alcohol, 500 mg of sodium hydroxide was added to the solution, and it was stirred for 1 h. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst. Afterward, the solvent was removed by heating slightly to afford a pale-yellow liquid in 83% yield (0.44 g). ¹H NMR (CDCl₃, 400 MHz): δ 5.92 (ddt, J = 17.2 Hz, J = 10.4, J = 5.6 Hz), 5.29 (m, J = 17.2 Hz, J = 1.6 Hz, 2H), 5.18 (m, J = 10.4 Hz, J = 1.6 Hz, 2H), 4.72 (s, 2H), 4.08 (m, J = 5.6 Hz, J = 1.5 Hz, 4H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 134.5,117.2, 93.9, 68.5. IR (cm^─1): 3081 (ν C_sp2─H), 2881 (ν C_sp3─H), 1647 (ν C═C), 1105 (ν_as C─O─C), 1041 (ν_s C─O─C), 918 (δ C═CH₂). Spectroscopic data is in accordance with data reported in literature. (37c)

Synthesis of CH₂(O-i-Pr)₂ from 2-Propanol and Sodium Hydride

Sodium hydride (0.40 g, 9.25 mmol) was added to an ampule with an airtight PTFE valve and washed with hexane in order to remove the oil suspension. The dried solid was suspended in 15 mL of dichloromethane. Afterward, 0.50 g of 2-propanol (8.25 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium 2-propoxide. A solution of 8.25 mg of catalyst 2a (0.2 mol %) in 5 mL of dried dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. After a few minutes at 60 °C, an intense yellow-orange color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. In order to remove the unreacted alcohol, 500 mg of sodium hydroxide was added to the solution, and it was stirred for 1 h. The mixture was filtrated through a pad of silica gel in order to remove the traces of the catalyst. Afterward, the solvent was removed by heating slightly to afford a pale-yellow liquid in 67% yield (0.36 g). ¹H NMR (CDCl₃, 400 MHz): δ 4.72 (s, 2H), 3.90 (sep, J = 6.2, 2H), 1.17 (d, J = 6.2, 12H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 90.9,68.6, 22.6. IR (cm^–1): 2921 (ν C_sp3─H), 1033 (ν_s C─O─C). Spectroscopic data is in accordance with data reported in literature. (37e)

Synthesis of CH₂(SEt)₂ from Ethanethiol and Sodium Hydroxide

Sodium hydroxide (0.55 g, 13.75 mmol) was ground and added to an ampule with an airtight PTFE valve and suspended in 15 mL of dichloromethane. Afterward, 0.80 g of ethanethiol (12.9 mmol) was added to the mixture, which caused the appearance of a white sticky solid, sodium ethanethiolate. A solution of 25 mg of catalyst 2a (0.4 mol %) in 5 mL of dichloromethane was added with a syringe directly upon the suspension. The resulting colorless mixture was stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. The stirring was quite hindered at the beginning due to the formation of a water phase. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. No further purification was performed. Conversion >99% by NMR was found. ¹H NMR (CDCl₃, 400 MHz): δ 3.69 (s, 2H), 2.65 (q, J = 7.4 Hz, 4H), 1.26 (t, J = 7.4 Hz, 6H). Spectroscopic data is in accordance with data reported in literature. (37f)

Synthesis of CH₂Pz₂ from Pyrazole and Sodium Hydride

Sodium hydride (0.60 g, 24.9 mmol) was added to an ampule with an airtight PTFE valve and washed with hexane in order to remove the oil suspension. The dried solid was suspended in 15 mL of dichloromethane. Afterward, 1.13 g (16.6 mmol) of pyrazole was added to the suspension. The addition led to the formation of sodium pyrazolate and hydrogen. A solution of 16.5 mg of catalyst 2a (0.2 mol %) in 5 mL of dichloromethane was added with a syringe directly upon the suspension, and it is stirred at 60 °C for 24 h in an oil bath preset at the specified temperature. After a few minutes at 60 °C, a brownish white color in the solution was observed. Once the reaction finished, the stirring was stopped. The organic solution was separated from the solid by filtration via cannula. The solvent was removed under a vacuum to afford a pale-brown solid. The solid is purified by crystallization in heptane, where the product is soluble at high temperatures, and the impurities remain insoluble, to afford a white solid, in 72% yield (0.88 g). ¹H NMR (CDCl₃, 400 MHz): δ 7.65 (dd, J = 2.4 Hz, J = 0.6 Hz, 2H), 7.55 (dd, J = 1.9 Hz, J = 0.6 Hz, 2H), 6.31 (s, 2H), 6.29 (dd, J = 2.4 Hz, J = 1.9 Hz, 2H). ¹³C{¹H} NMR (CDCl₃, 100 MHz): δ 141.0, 129.8, 107.3, 65.5. IR (cm^─1): 3101 (ν C_Ar–H), 2924 (ν C_sp3─H), 1610 (ν C_Ar═N), 1514 (ν C_Ar═C_Ar), 1435 (ν C_Ar═C_Ar). Spectroscopic data is in accordance with data reported in literature. (37g)

Synthesis of [MeOCH₂·1a]⁺[Br^–] (3a)

To a 50 mL Schlenk flask was added 100 mg (0.22 mmol) of 1a. The yellow solid was dissolved in 10 mL of dried dichloromethane to afford a clear yellow solution. Then, 20 μL (0.22 mmol, 90%) of bromomethyl methyl ether was added, and the solution was stirred for 30 min while the color faded. Afterward, 10 mL of dried hexane was added to the solution, and the solvent was removed under a vacuum. The solid was washed with more hexane, to afford yellowish solid with a yield of 94% (0.12 g). ¹H NMR (CD₂Cl₂, 400 MHz): δ 8.30 (s, 2H), 7.15 (m, 2H), 7.04 (m, 4H), 6.43 (m, 2H), 5.25 (br s, 2H), 4.06 (m, 2H), 3.47 (s, 3H), 2.30 (s, 3H), 2.25 (s, 3H), 1.90 (m, 2H), 1.79 (m, 4H), 1.67 (m, 4H), 1.50 (m, 2H), 1.34 (m, 4H), 1.23 (m, 2H), 0.99 (m, 2H). ¹³C{¹H} NMR (CD₂Cl₂, 100 MHz): δ 143.3, 138.4, 136.1, 134.1, 130.8, 130.7, 124.7, 123.1, 121.0, 82.6, 60.4, 57.5, 33.5, 33.3, 25.9, 25.8, 24.7, 21.0, 20.9. Elemental analysis calcd for C₃₂H₄₃ON₄Br: C, 66.31; H, 7.48; N, 9.67. Found: C, 66.46; H, 7.22; N, 9.43. ESI-MS (1 μM in anhydrous THF): m/z 499.56 (MeOCH₂·1a⁺). HRMS (ESI) m/z: [M]⁺ calcd for C₃₂H₄₃N₄O, 499.3431; found, 499.3423.

Spectroscopic Data of 1b

In order to detect and characterize 1b, the general procedure of catalysis was applied to obtain methylal starting from NaOMe. Once the reaction showed an intense change of color to a deep orange-yellow, the mixture was filtered, and the liquid phase was dried under a vacuum. An oily deep red solid was obtained. No further purification was performed. ¹H NMR (CD₂Cl₂, 400 MHz): δ 6.98 (m, 2H). 6.93 (m, 2H), 6.90 (m, 2H), 6.65 (m, 2H), 4.69 (s, 2H), 3.75 (s, 3H), 3.30 (s, 3H), 2.24 (s, 3H), 2.20 (s, 3H). ¹³C{¹H} NMR (CD₂Cl₂, 100 MHz): δ 152.5, 145.2, 141.8, 134.3, 131.4, 129.5, 123.5, 121.9, 82.4, 55.7,55.7, 20.8, 20.8. ESI-MS (1 μM THF/wet methanol 1:100): m/z 299.30 (1b·H⁺, 100%); 321.30 (1b·Na⁺, 73%); 337.33 (1b·K⁺, 13%). HRMS (ESI) m/z: [M + H]⁺ calcd for C₁₈H₂₃N₂O₂, 299.1754; found, 299.1753. HRMS (ESI) m/z: [M + Na]⁺ calcd for C₁₈H₂₂N₂O₂Na, 321.1573; found, 321.1770.

Spectroscopic Data of 2b

In order to detect and characterize 2b, the general procedure of catalysis was applied to obtain methylal starting from NaOMe. Once the reaction showed an intense change of color to a deep orange-yellow, the mixture was filtered, and the liquid phase was dried under a vacuum. An oily, deep red solid was obtained. No further purification was performed. ¹H NMR (CD₂Cl₂, 400 MHz): δ 6.97 (m, 4H), 6.88 (m, 4H), 6.86 (m, 4H), 6.54 (m, 4H), 5.15 (s, 2H), 3.53 (s, 6H), 2.25 (s, 6H), 2.20 (s, 6H). ¹³C{¹H} NMR (CD₂Cl₂, 100 MHz): δ 152.5, 145.5, 141.1, 135.2, 131.2, 129.5, 129.4, 125.9, 122.2, 67.1, 55.9, 20.9, 20.8. ESI-MS (1 μM in THF/wet methanol 1:100): m/z 521.51 (2b·H⁺, 100%); 543.50 (2b·Na⁺, 19%); 559.45 (2b·K⁺, 7%). HRMS (ESI) m/z: [M + H]⁺ calcd for C₃₃H₃₇N₄O₂, 521.2911; found, 521.2902. HRMS (ESI) m/z: [M + Na]⁺ calcd for C₃₃H₃₆N₄O₂Na, 343.2730; found, 343.2719.

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Corresponding Authors
- Marta E. G. Mosquera - Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación en Química “Andrés M. del Río” (IQAR) Universidad de Alcalá, Campus Universitario, Alcala de Henares, Madrid 28871, Spain; https://orcid.org/0000-0003-2248-3050; Email: [email protected]
- Juan Cámpora - Instituto de Investigaciones Químicas, CSIC-Universidad de Sevilla, C/Américo Vespucio, 49, Sevilla 41092, Spain; https://orcid.org/0000-0001-7305-1296; Email: [email protected]
Author
- David Sánchez-Roa - Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación en Química “Andrés M. del Río” (IQAR) Universidad de Alcalá, Campus Universitario, Alcala de Henares, Madrid 28871, Spain
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Notes
The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the Spanish Research Agency (AEI), the European Union (Feder Funds), Junta de Andalucía, and the University of Alcalá through projects PGC2018-095768-B-100, RTI2018-094840-B-C31, UAH-AE-2017-2, and PY20_00104. D.S.R. thanks the Spanish Government for a Predoctoral Fellowship. We gratefully acknowledge Tomás G. Santiago, M. Sc. (IIQ), and Dr. Gloria Guitérrez Alcalá (Mass Spectrometry Service, IIQ) for their skillful assistance in sample preparation and recording ESI-MS spectra.

Abbreviations

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NHC	N-heterocyclic carbene
CDI	carbodiimide
DCM	dichloromethane
ICy	1,3-dicyclohexylimidazolylidene
PTBP	p-tert-butylphenol
AA	allyl alcohol
HPz	pyrazole
TON	turnover number
TOF	turnover frequency
NMR	nuclear magnetic resonance
DOSY	diffusion-ordered spectroscopy
HSQC	heteronuclear single quantum coherence spectroscopy
HMBC	heteronuclear multiple bond correlation

References

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This article references 38 other publications.

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It is well established that anthropogenic chlorine-contg. chems. contribute to ozone layer depletion. The successful implementation of the Montreal Protocol has led to redns. in the atm. concn. of many ozone-depleting gases, such as chlorofluorocarbons. As a consequence, stratospheric chlorine levels are declining and ozone is projected to return to levels obsd. pre-1980 later this century. However, recent observations show the atm. concn. of dichloromethane-an ozone-depleting gas not controlled by the Montreal Protocol-is increasing rapidly. Using atm. model simulations, we show that although currently modest, the impact of dichloromethane on ozone has increased markedly in recent years and if these increases continue into the future, the return of Antarctic ozone to pre-1980 levels could be substantially delayed. Sustained growth in dichloromethane would therefore offset some of the gains achieved by the Montreal Protocol, further delaying recovery of Earth's ozone layer.
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9a
Intensification of the temperature-swing adsorption process with a heat pump for the recovery of dichloromethane
Kane, Abdoulaye; Giraudet, Sylvain; Vilmain, Jean-Baptiste; Le Cloirec, Pierre
Journal of Environmental Chemical Engineering (2015), 3 (2), 734-743CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
The temp.-swing adsorption process (TSA) is a widely used process for solvent recovery. Steam or a heated gas is used for the desorption of org. pollutants from activated carbons. This study aims to show the efficiency of coupling the TSA process with a heat pump. Hence, the adsorption column was cooled down whereas the column under regeneration was warmed by the heat pump. An exptl. unit was designed and expts. were conducted with dichloromethane. The advantages of coupling the TSA process with a heat pump are twofold: the first benefit was for the adsorption step whose efficiency was increased. The decrease of temp. inside the fixed bed enabled a significant increase of breakthrough times (+30% on av.). The second benefit of using the heat pump during regeneration cycle is the warming of the activated carbon bed prior to steam desorption. Temps. up to 45 °C were measured during desorption when using the heat pump alone. Exptl., the results have shown an interesting recovery efficiency (up to 71%) during dichloromethane desorption if using only the heat pump. Numerical simulations, via the software ProSim DAC, predicted the expected process behaviors for dichloromethane on a larger scale: a TSA unit contg. 15 t of activated carbon. The results showed that the regeneration rate was not totally sufficient, 38.5%, and the use of a heat pump alone was not able to ensure the desorption of the VOC. Although the heap pump by itself was not sufficient to ensure the regeneration, the combination with the steam desorption shed light on new perspectives for the redn. of energy consumption.
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(b) Wu, X.-F. W.; Tlili, A.; Schranck, J.; Wu, X.-F. W. The Application of Dichloromethane and Chloroform as Reagents in Organic Synthesis. Solvents as Reagents in Organic Synthesis 2017, 125– 159, DOI: 10.1002/9783527805624.ch4
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10
(a) Lautenschütz, L.; Oestreich, D.; Seidenspinner, P.; Arnold, U.; Dinjus, E.; Sauer, J. Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers. Fuel 2016, 173, 129– 137, DOI: 10.1016/j.fuel.2016.01.060
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10a
Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers
Lautenschuetz, Ludger; Oestreich, Dorian; Seidenspinner, Philipp; Arnold, Ulrich; Dinjus, Eckhard; Sauer, Joerg
Fuel (2016), 173 (), 129-137CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
Oligomeric oxymethylene di-Me ethers (OMDMEs, CH3O-(CH2O)n-CH3) are promising diesel fuel additives, which can reduce soot formation as well as NOx emissions. Due to the poor availability of high purity OMDMEs a comprehensive characterization of diesel stds. was not feasible until now. Two types of oxymethylene dialkylethers (OMDMEs and oxymethylene di-Et ethers, OMDEEs) were synthesized, purified and characterized with respect to their physico-chem. and fuel properties. D., m.p., flash point, auto ignition point as well as lubricity, kinematic viscosity and surface tension of OMDMEs and OMDEEs were measured and compared to the corresponding n-alkanes. Fuel requirements such as b.ps., flash points and surface tensions can be fulfilled by OMDMEs and OMDEEs. Furthermore, OMDMEs (n = 3-5) and OMDEEs (n = 2-4) are, due to their high cetane nos. of 124-180 and 64-103, particularly promising since cetane nos. in this range can lead to improved motor efficiency and smoother fuel combustion. Addnl., the heat of combustion as well as the std. enthalpy of formation and reaction were detd. Apart from somewhat lower heating values, OMDMEs exhibit fuel properties similar to conventional diesel complying the required fuel stds. without the need of changing engines or fuel infrastructures.
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(b) Thenert, K.; Beydoun, K.; Wiesenthal, J.; Leitner, W.; Klankermayer, J. Ruthenium-Catalyzed Synthesis of Dialkoxymethane Ethers Utilizing Carbon Dioxide and Molecular Hydrogen. Angew. Chem., Int. Ed. 2016, 55, 12266– 12269, DOI: 10.1002/anie.201606427
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10b
Ruthenium-Catalyzed Synthesis of Dialkoxymethane Ethers Utilizing Carbon Dioxide and Molecular Hydrogen
Thenert, Katharina; Beydoun, Kassem; Wiesenthal, Jan; Leitner, Walter; Klankermayer, Juergen
Angewandte Chemie, International Edition (2016), 55 (40), 12266-12269CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The synthesis of dimethoxymethane (DMM) by a multistep reaction of methanol with carbon dioxide and mol. hydrogen is reported. Using the mol. catalyst [Ru(triphos)(tmm)] in combination with the Lewis acid Al(OTf)3 resulted in a versatile catalytic system for the synthesis of various dialkoxymethane ethers. This new catalytic reaction provides the first synthetic example for the selective conversion of carbon dioxide and hydrogen into a formaldehyde oxidn. level, thus opening access to new mol. structures using this important C1 source.
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(c) Schieweck, B. G.; Klankermayer, J. Tailor-made Molecular Cobalt Catalyst System for the Selective Transformation of Carbon Dioxide to Dialkoxymethane Ethers. Angew. Chem., Int. Ed. 2017, 56, 10854– 10857, DOI: 10.1002/anie.201702905
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10c
Tailor-made Molecular Cobalt Catalyst System for the Selective Transformation of Carbon Dioxide to Dialkoxymethane Ethers
Schieweck, Benjamin G.; Klankermayer, Juergen
Angewandte Chemie, International Edition (2017), 56 (36), 10854-10857CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Herein a non-precious transition-metal catalyst system for the selective synthesis of dialkoxymethane ethers from carbon dioxide and mol. hydrogen is presented. The development of a tailored catalyst system based on cobalt salts in combination with selected Triphos ligands and acidic co-catalysts enabled a synthetic pathway, avoiding the oxidn. of methanol to attain the formaldehyde level of the central CH2 unit. This unprecedented productivity based on the mol. cobalt catalyst is the first example of a non-precious transition-metal system for this transformation utilizing renewable carbon dioxide sources.
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11
(a) El-Brollosy, N. R.; Jørgensen, P. T.; Dahan, B.; Boel, A. M.; Pedersen, E. B.; Nielsen, C. Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants. J. Med. Chem. 2002, 45, 5721– 5726, DOI: 10.1021/jm020949r
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11a
Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants
El-Brollosy, Nasser R.; Jorgensen, Per T.; Dahan, Berit; Boel, Anne Marie; Pedersen, Erik B.; Nielsen, Claus
Journal of Medicinal Chemistry (2002), 45 (26), 5721-5726CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
This paper reports the synthesis and the antiviral activities of a series of 6-arylmethyl-1-(allyloxymethyl)-5-alkyluracil derivs., which can be viewed as analogs of the anti-HIV-1 drug emivirine (formerly MKC-442) from which they differ in the replacement of the ethoxymethyl group with variously allyloxymethyl moieties. The most active compds. N-1 allyloxymethyl- and N-1 3-methylbut-2-enyl substituted 5-ethyl-6-(3,5-dimethylbenzyl)uracils (12 and 13) showed activity against HIV-1 wild-type in the picomolar range with selective index of greater than 5 × 106 and activity in the submicromolar range against the clin. important Y181C and K103N mutant strains known to be resistant to emivirine. Structure-activity relationship studies established a correlation between the anti-HIV-1 activity and the substitution pattern of the N-1 allyloxymethyl group.
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(b) Wamberg, M.; Pedersen, E. B.; El-Brollosy, N. R.; Nielsen, C. Synthesis of 6-arylvinyl analogues of the HIV drugs SJ-3366 and Emivirine. Bioorg. Med. Chem. 2004, 12, 1141– 1149, DOI: 10.1016/j.bmc.2003.11.032
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11b
Synthesis of 6-arylvinyl analogues of the HIV drugs SJ-3366 and Emivirine
Wamberg, Michael; Pedersen, Erik B.; El-Brollosy, Nasser R.; Nielsen, Claus
Bioorganic & Medicinal Chemistry (2004), 12 (5), 1141-1149CODEN: BMECEP; ISSN:0968-0896. (Elsevier Ltd.)
This paper reports the synthesis and the antiviral activities of a series of 6-arylvinyl substituted analogs of SJ-3366, a highly potent agent against HIV. The objective was to investigate whether substitution of the 6-arylketone with a 6-arylvinyl group could leads to an improved antiviral activity against HIV-1. The most active compds., 1-ethoxymethyl, 1-(2-propynyloxymethyl), and 1-(2-methyl-3-phenylallyloxymethyl) substituted 6-[1-(3,5-dimethylphenyl)vinyl]-5-ethyl-1H-pyrimidine-2,4-dione showed activities against HIV-1 wild type in the range of Efavirenz, and moderate activities against Y181C and Y181C+K103N mutant strains were also obsd.
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(c) Loksha, Y. M.; Pedersen, E. B.; Loddo, R.; Sanna, G.; Collu, G.; Giliberti, G.; Colla, P. L. Synthesis of Novel Fluoro Analogues of MKC442 as Microbicides. J. Med. Chem. 2014, 57, 5169– 5178, DOI: 10.1021/jm500139a
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11c
Synthesis of Novel Fluoro Analogues of MKC442 as Microbicides
Loksha, Yasser M.; Pedersen, Erik B.; Loddo, Roberta; Sanna, Giuseppina; Collu, Gabriella; Giliberti, Gabriele; Colla, Paolo La
Journal of Medicinal Chemistry (2014), 57 (12), 5169-5178CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
Novel analogs of MKC442 [6-benzyl-1-(ethoxymethyl)-5-isopropylpyrimidine-2,4(1H,3H)-dione] were synthesized by reaction of 6-[(3,5-dimethylphenyl)fluoromethyl]-5-ethyluracil (I) with ethoxymethyl chloride and formaldehyde acetals. The Sonogashira reaction was carried out on the N1-[(p-iodobenzyl)oxy]methyl deriv. of compd. I using propargyl alc. to afford compd. II (YML220). The latter compd. was selected for further studies since it showed the most potent and selective activity in vitro against wild-type HIV-1 and non-nucleoside reverse transcriptase inhibitor-, nucleoside reverse transcriptase inhibitor-, and protease inhibitor-resistant mutants and a wide range of HIV-1 clin. isolates. II also showed microbicidal activity in long-term assays with heavily infected MT-4 cells.
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12
(a) Makosza, M.; Sypniewski, M. Reaction of sulfonium salts of formaldehyde dithioacetals with aromatic aldehydes and rearrangements of the produced thioalkyl oxiranes. Tetrahedron 1995, 51, 10593– 10600, DOI: 10.1016/0040-4020(95)00632-I
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12a
Reaction of sulfonium salts of formaldehyde dithioacetals with aromatic aldehydes and rearrangements of the produced thioalkyl oxiranes
Makosza, Mieczyslaw; Sypniewski, Michal
Tetrahedron (1995), 51 (38), 10593-600CODEN: TETRAB; ISSN:0040-4020. (Elsevier)
Arom. aldehydes react with sulfur ylides generated from sulfonium salts of formaldehyde dithioacetals to give corresponding 2-thioalkyl-3-aryloxiranes. Depending on substituents in arom. rings the oxiranes undergo rearrangements or are sufficiently stable to be isolated. To p-tolualdehyde and (4-chlorophenylthiomethyl)dimethylsulfonium iodide in DMF was added NaOH to give cis- and trans-2-(methylthio)-3-(4-methylphenyl)oxirane which did rearranged to 4'-methyl-2-hydroxyacetophenone.
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(b) Luh, T.-Y. Recent advances on the synthetic applications of the dithioacetal functionality. J. Organomet. Chem. 2002, 653, 209– 214, DOI: 10.1016/S0022-328X(02)01151-8
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12b
Recent advances in the synthetic applications of the dithioacetal functionality
Luh, Tien-Yau
Journal of Organometallic Chemistry (2002), 653 (1-2), 209-214CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science B.V.)
A review. The nickel-catalyzed silylolefination reaction has led to the synthesis of a range of silyl-substituted olefins for optoelectronic interests. The reactions of propargylic dithioacetals with organocopper or lithium reagents, followed by treatment with electrophiles, yield sulfur-substituted allenes. Further cross coupling with Grignard reagents in the presence of a nickel catalyst affords highly substituted allenes. Acid-catalyzed cyclization of the sulfur-substituted allenyl alcs. furnishes a useful route to oligoaryls having highly substituted furan or pyrrole moieties.
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13
(a) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez, A. Heteroscorpionate ligands based on bis(pyrazol-1-yl)methane: design and coordination chemistry. Dalton Trans. 2004, 10, 1499– 1510, DOI: 10.1039/B401425A
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(b) Krieck, S.; Koch, A.; Hinze, K.; Müller, C.; Lange, J.; Görls, H.; Westerhausen, M. s-Block Metal Complexes with Bis- and Tris(pyrazolyl)methane and -methanide Ligands. Eur. J. Inorg. Chem. 2016, 15, 2332– 2348, DOI: 10.1002/ejic.201501263
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14
(a) Csok, Z.; Vechorkin, O.; Harkins, S. B.; Scopelliti, R.; Hu, X. Nickel Complexes of a Pincer NN₂ Ligand: Multiple Carbon-Chloride Activation of CH₂Cl₂ and CHCl₃ Leads to Selective Carbon-Carbon Bond Formation. J. Am. Chem. Soc. 2008, 130, 8156– 8157, DOI: 10.1021/ja8025938
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14a
Nickel complexes of a pincer NN2 ligand: multiple carbon-chloride activation of CH2Cl2 and CHCl3 leads to selective carbon-carbon bond formation
Csok, Zsolt; Vechorkin, Oleg; Harkins, Seth B.; Scopelliti, Rosario; Hu, Xile
Journal of the American Chemical Society (2008), 130 (26), 8156-8157CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A new pincer-type bis(amido)amine (NN2) ligand and its lithium and nickel complexes, including Ni(II) Me, Et, and Ph complexes, were synthesized. The Ni(II) alkyl complexes react cleanly with alkyl halides including chlorides to form C-C coupled products and Ni(II) halides. More interestingly, the Ni(II) alkyls undergo unprecedented reactions with CH2Cl2 and CHCl3 to cleave all the C-Cl bonds and replace them with C-C bonds. The reactions are highly selective and lead to the first efficient catalytic coupling of CH2Cl2 with alkyl Grignards. A conversion of 82% and a turnover no. of 47 are achieved within minutes. Coupling of CD2Cl2 and 1,1-dichloro-3,3-dimethylbutane with nBuMgCl is also realized. Preliminary mechanistic study suggests a radical initiated process for these reactions.
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(b) Zhan, L.; Pan, R.; Xing, P.; Jiang, B. An efficient method for the preparation of dialkoxymethanes from dichloromethane with alcohols catalyzed by a Cu-NHC complex. Tetrahedron Lett. 2016, 57, 4036– 4038, DOI: 10.1016/j.tetlet.2016.07.056
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14b
An efficient method for the preparation of dialkoxymethanes from dichloromethane with alcohols catalyzed by a Cu-NHC complex
Zhan, Lewu; Pan, Renming; Xing, Ping; Jiang, Biao
Tetrahedron Letters (2016), 57 (36), 4036-4038CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
A facile, rapid and efficient method for the prepn. of dialkoxymethanes from dichloromethane with alcs. catalyzed by a Cu-NHC complex is reported. A variety of sym. dialkoxymethanes can be prepd. under mild condition in excellent yields (up to 98%). The unsym. ether is also obtained in 89% yield from the etherification of p-tolylmethanol and Bu chloride catalyzed by ICyCuCl complex at 80 °C. The reaction provides a new method for the prepn. of dialkoxymethanes under mild conditions in excellent yields.
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15
Lamb, J. R.; Brown, C. M.; Johnson, J. A. N-Heterocyclic carbene–carbodiimide (NHC–CDI) betaine adducts: synthesis, characterization, properties, and applications. Chem. Sci. 2021, 12, 2699– 2715, DOI: 10.1039/D0SC06465C
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15
N-Heterocyclic carbene-carbodiimide (NHC-CDI) betaine adducts: synthesis, characterization, properties, and applications
Lamb, Jessica R.; Brown, Christopher M.; Johnson, Jeremiah A.
Chemical Science (2021), 12 (8), 2699-2715CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
A review. An emerging class of betaine adducts made from the reaction of NHCs with carbodiimides (CDIs) form zwitterionic amidinate-like structures with tunable properties based on the highly modular NHC and CDI scaffolds. The adduct stability was controlled by the substituents on the CDI nitrogens, while the NHC substituents greatly affect the configuration of the adduct in the solid state. This Perspective was intended as a primer to these adducts, touching on their history, synthesis, characterization and general properties. Despite the infancy of the field, NHC-CDI adducts had been applied as amidinate-type ligands for transition metals and nanoparticles, as junctions in zwitterionic polymers, and to stabilize distonic radical cations, these applications and potential future directions were discussed.
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Baishya, A.; Kumar, L.; Barman, M. K.; Peddarao, T.; Nembenna, S. Air Stable N-Heterocyclic Carbene-Carbodiimide (“NHC-CDI”) Adducts: Zwitterionic Type Bulky Amidinates. ChemistrySelect 2016, 1, 498– 503, DOI: 10.1002/slct.201600019
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16
Air Stable N-Heterocyclic Carbene-Carbodiimide (''NHC-CDI'') Adducts: Zwitterionic Type Bulky Amidinates
Baishya, Ashim; Kumar, Lokesh; Barman, Milan Kr.; Peddarao, Thota; Nembenna, Sharanappa
ChemistrySelect (2016), 1 (3), 498-503CODEN: CHEMUD; ISSN:2365-6549. (Wiley-VCH Verlag GmbH & Co. KGaA)
A library of N-heterocyclic carbene-carbodiimide (''NHC-CDI'') adducts i. e., zwitterionic type amidinates from the reaction between N,N'-diaryl substituted sym. or unsym. carbodiimide and N-heterocyclic carbene at room temp. conditions were reported. Generally, normal amidinates are air and moisture sensitive; that can be achieved by the treatment of amidines with base under air and moisture free conditions. In contrast, these new zwitterionic type bulky amidinate compds. were neutral and air stable. All new 31 examples of ''NHC-CDI'' adducts were characterized by 1H, 13C{1H} and HRMS analyses. Further, six compds. were confirmed by single crystal X-ray structural anal.
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17
(a) Márquez, A.; Ávila, E.; Urbaneja, C.; Álvarez, E.; Palma, P.; Cámpora, J. Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands. Inorg. Chem. 2015, 54, 11007– 11017, DOI: 10.1021/acs.inorgchem.5b02141
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17a
Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands
Marquez, Astrid; Avila, Elena; Urbaneja, Carmen; Alvarez, Eleuterio; Palma, Pilar; Campora, Juan
Inorganic Chemistry (2015), 54 (22), 11007-11017CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
The 1st complexes contg. imidazolium-2-amidinates as ligands (betaine-type adducts of imidazolium-based carbenes and carbodiimides, NHC-CDI) are reported. Interaction of the sterically hindered betaines ICyCDIDiPP and IMeCDIDiPP [both bearing 2,6-diisopropylphenyl (DiPP) substituents on the terminal N atoms] with Cu(I) acetate affords mononuclear, electroneutral complexes (1a and 1b), which contain NHC-CDI and acetate ligands terminally bound to linear Cu(I) centers. In contrast, the less encumbered ligand ICyCDIp-Tol, with p-tolyl substituents on the N donor atoms, affords a dicationic trigonal paddlewheel complex, [Cu2(μ-ICyCDIp-Tol)3]2+[OAc-]2 (2-OAc). The NMR resonances of 2-OAc are broad and indicate that in soln. the acetate anion and the betaine ligands compete for binding the Cu atom. Replacing the external acetate with the less coordinating tetraphenylborate anion provides the corresponding deriv. 2-BPh4 that, in contrast with 2-OAc, gives rise to sharp and well-defined NMR spectra. The short Cu-Cu distance in the binuclear dication [Cu2(μ-ICyCDIp-Tol)3]2+ obsd. in the x-ray structures of 2-BPh4 and 2-OAc, ∼2.42 Å, points to a relatively strong cuprophilic interaction. Attempts to force the bridging coordination mode of IMeCDIDiPP displacing the acetate anion with BPh4- gave the cationic mononuclear deriv. [Cu(IMeCDIDiPP)2]+[BPh4]- (3b) that contains two terminally bound betaine ligands. Compd. 3b readily decomps. upon being heated, cleanly affording the bis-carbene complex [Cu(IMe)2]+[BPh4-] (4) and releasing the corresponding carbodiimide (C(=N-DiPP)2).
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(b) Baishya, A.; Kumar, L.; Barman, M. K.; Biswal, H. S.; Nembenna, S. N-Heterocyclic Carbene–Carbodiimide (“NHC–CDI”) Adduct or Zwitterionic-Type Neutral Amidinate-Supported Magnesium(II) and Zinc(II) Complexes. Inorg. Chem. 2017, 56, 9535– 9546, DOI: 10.1021/acs.inorgchem.7b00879
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17b
N-Heterocyclic Carbene-Carbodiimide ("NHC-CDI") Adduct or Zwitterionic-Type Neutral Amidinate-Supported Magnesium(II) and Zinc(II) Complexes
Baishya, Ashim; Kumar, Lokesh; Barman, Milan Kr.; Biswal, Himansu S.; Nembenna, Sharanappa
Inorganic Chemistry (2017), 56 (16), 9535-9546CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Structurally characterized Mg and Zn complexes L4-t-BuPh-M{N(SiMe3)2}2 [M = Mg (1) and Zn (2); L4-t-BuPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-t-butylphenyl)amidinate}], L4-iPrPh-M{N(SiMe3)2}2 [M = Mg (3) and Zn (4); L4-iPrPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-isopropylphenyl)amidinate}] and L4-iPrPh-ZnEt2 (5) bearing zwitterionic type neutral amidinate or N-heterocyclic carbene-carbodiimide (NHC-CDI) adduct and monoanionic amido or alkyl ligands are reported. The synthesis of compds. 1-5 was achieved by the direct addn. of NHC-CDI adduct to a corresponding metal bis(amide) or dialkyl reagent. All compds. 1-5 exist as monomers in the solid state. In all cases, the metal (Mg or Zn) centers adopt a distorted four-coordinate tetrahedral geometry bonded to one N,N'-chelated neutral zwitterionic ligand and two monoanionic amido or alkyl moieties. In contrast, sterically bulky zwitterionic amidinate LDipp [LDipp = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(2,6-diisopropylphenyl)amidinate}] upon treatment with Li bis-trimethylsilylamide, Li{N(SiMe3)2} affords the NHC-Li complex, MeIEt-[Li{N(SiMe3)2}]2 (6), in which one mol. of NHC (MeIEt = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) coordinates to one of the two Li centers. In a similar way, the reaction between LDipp and Mg{N(SiMe3)2}2 allowed to the formation of a NHC adduct of metal bis(amide), MeIEt-Mg{N(SiMe3)2}2 (7), instead of zwitterionic adduct of metal bis(amide). Alternatively, the synthesis of both compds. 6 and 7 was achieved by the direct addn. of one equiv. of NHC i.e. MeIEt to Li{N(SiMe3)2} (2.0 equiv) and Mg{N(SiMe3)2}2 (1.0 equiv) in benzene-d6, resp. All compds. (1-7) were characterized by multinuclear {1H, 13C, 29Si (for 1 , 2, 3, 4, 6 and 7) and 7Li (for compd. 6)} magnetic resonance spectroscopy, mass spectrometry, elemental anal. and single crystal x-ray structural anal. Preliminary reactivity studies of zwitterion supported metal complexes were carried out. The energetics of zwitterion supported Li and Mg complexes were obtained by d. functional theory (DFT) calcns.
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(a) Martínez-Prieto, L. M.; Cano, I.; Márquez, A.; Baquero, E. A.; Tricard, S.; Cusinato, L.; del Rosal, I.; Poteau, R.; Coppel, Y.; Philippot, K.; Chaudret, B.; Cámpora, J.; van Leeuwen, P. W. N. M. Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts. Chem. Sci. 2017, 8, 2931– 2941, DOI: 10.1039/C6SC05551F
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18a
Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts
Martinez-Prieto, L. M.; Cano, I.; Marquez, A.; Baquero, E. A.; Tricard, S.; Cusinato, L.; del Rosal, I.; Poteau, R.; Coppel, Y.; Philippot, K.; Chaudret, B.; Campora, J.; van Leeuwen, P. W. N. M.
Chemical Science (2017), 8 (4), 2931-2941CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
Ligand control of metal nanoparticles (MNPs) is rapidly gaining importance as ligands can stabilize the MNPs and regulate their catalytic properties. Herein we report the first example of Pt NPs ligated by imidazolium-amidinate ligands that bind strongly through the amidinate anion to the platinum surface atoms. The binding was established by 15N NMR spectroscopy, a precedent for nitrogen ligands on MNPs, and XPS. Both monodentate and bidentate coordination modes were found. DFT showed a high bonding energy of up to -48 kcal mol-1 for bidentate bonding to two adjacent metal atoms, which decreased to -28 ± 4 kcal mol-1 for monodentate bonding in the absence of impediments by other ligands. While the surface is densely covered with ligands, both IR and 13C MAS NMR spectra proved the adsorption of CO on the surface and thus the availability of sites for catalysis. A particle size dependent Knight shift was obsd. in the 13C MAS NMR spectra for the atoms that coordinate to the surface, but for small particles, ∼1.2 nm, it almost vanished, as theory for MNPs predicts; this had not been exptl. verified before. The Pt NPs were found to be catalysts for the hydrogenation of ketones and a notable ligand effect was obsd. in the hydrogenation of electron-poor carbonyl groups. The catalytic activity is influenced by remote electron donor/acceptor groups introduced in the aryl-N-substituents of the amidinates; p-anisyl groups on the ligand gave catalysts several times faster the ligand contg. p-chlorophenyl groups.
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(b) López-Vinasco, A. M.; Martínez-Prieto, L. M.; Asensio, J. M.; Lecante, P.; Chaudret, B.; Cámpora, J.; van Leeuwen, P. W. N. M. Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes. Catal. Sci. Technol. 2020, 10, 342– 350, DOI: 10.1039/C9CY02172H
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18b
Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes
Lopez-Vinasco, Angela M.; Martinez-Prieto, Luis M.; Asensio, Juan M.; Lecante, Pierre; Chaudret, Bruno; Campora, Juan; van Leeuwen, Piet W. N. M.
Catalysis Science & Technology (2020), 10 (2), 342-350CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-redn. to the corresponding alkane. In addn., the prepn. of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepd. Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temp., 3% mol Ni and 1 bar H2). The catalytic behavior of Ni NPs was influenced by the electron donor/acceptor groups (-Me, -OMe, -Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling expts. were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.
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Gallagher, N. M.; Zhukhovitskiy, A. V.; Nguyen, H. V. T.; Johnson, J. A. Main-Chain Zwitterionic Supramolecular Polymers Derived from N-Heterocyclic Carbene–Carbodiimide (NHC–CDI) Adducts. Macromolecules 2018, 51, 3006– 3016, DOI: 10.1021/acs.macromol.8b00579
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Main-Chain Zwitterionic Supramolecular Polymers Derived from N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Adducts
Gallagher, Nolan M.; Zhukhovitskiy, Aleksandr V.; Nguyen, Hung V.-T.; Johnson, Jeremiah A.
Macromolecules (Washington, DC, United States) (2018), 51 (8), 3006-3016CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Polyzwitterions have found extensive applications in biol. and materials sciences. Despite this success, most polyzwitterions have nondegradable polyolefin backbones with pendant zwitterionic groups. Transcension of this structural paradigm via the formation of main-chain zwitterionic supramol. polymers could lead to readily processable, as well as self-healing and/or degradable, polyzwitterions. Herein, we report the synthesis and characterization of poly(azolium amidinate)s (PAzAms), which are a new class of supramol. main-chain polyzwitterions assembled via the formation of N-heterocyclic carbene-carbodiimide (NHC-CDI) adducts. These polymers exhibit a wide range of tunable dynamic properties due to the highly structure-sensitive equil. between the NHC-CDI adduct and its constituent NHCs and CDIs: e.g., PAzAms derived from N-aryl-N'-alkyl CDIs are dynamic at lower temps. than those derived from N,N'-diaryl CDIs. We develop a versatile synthetic platform that provides access to PAzAms with control over the main-chain charge sequence and mol. wt. In addn., block copolymers incorporating PAzAm and poly(ethylene glycol) (PEG) blocks are water sol. (>30 mg mL-1) and self-assemble in aq. environments. This work defines structure-property relationships for a new class of degradable main-chain zwitterionic supramol. polymers, setting the stage for the development of these polymers in a range of applications.
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Gallagher, N. M.; Ye, H.-Z.; Feng, S.; Lopez, J.; Zhu, Y. G.; Van Voorhis, T.; Shao-Horn, Y.; Johnson, J. A. An N-Heterocyclic-Carbene-Derived Distonic Radical Cation. Angew. Chem., Int. Ed. 2020, 59, 3952– 3955, DOI: 10.1002/anie.201915534
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An N-Heterocyclic-Carbene-Derived Distonic Radical Cation
Gallagher, Nolan M.; Ye, Hong-Zhou; Feng, Shuting; Lopez, Jeffrey; Zhu, Yun Guang; Van Voorhis, Troy; Shao-Horn, Yang; Johnson, Jeremiah A.
Angewandte Chemie, International Edition (2020), 59 (10), 3952-3955CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
We present the discovery of a novel radical cation formed through one-electron oxidn. of an N-heterocyclic carbene-carbodiimide (NHC-CDI) zwitterionic adduct. This compd. possesses a distonic electronic structure (spatially sep. spin and charge regions) and displays persistence under ambient conditions. We demonstrate its application in a redox-flow battery exhibiting minimal voltage hysteresis, a flat voltage plateau, high Coulombic efficiency, and no performance decay for at least 100 cycles. The chem. tunability of NHCs and CDIs suggests that this approach could provide a general entry to redox-active NHC-CDI adducts and their persistent radical ions for various applications.
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Sánchez-Roa, D.; Santiago, T. G.; Fernández-Millán, M.; Cuenca, T.; Palma, P.; Cámpora, J.; Mosquera, M. E. G. Interaction of an imidazolium-2-amidinate (NHC-CDI) zwitterion with zinc dichloride in dichloromethane: role as ligands and C–Cl activation promoters. Chem. Commun. 2018, 54, 12586– 12589, DOI: 10.1039/C8CC07661H
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21
Interaction of an imidazolium-2-amidinate (NHC-CDI) zwitterion with zinc dichloride in dichloromethane: role as ligands and C-Cl activation promoters
Sanchez-Roa, David; Santiago, Tomas G.; Fernandez-Millan, Maria; Cuenca, Tomas; Palma, Pilar; Campora, Juan; Mosquera, Marta E. G.
Chemical Communications (Cambridge, United Kingdom) (2018), 54 (89), 12586-12589CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Adducts of imidazolium carbenes and carbodiimides (NHC-CDI) are emerging as a new class of thermally stable and modular zwitterions with many potential applications. Our study of the interaction of a representative NHC-CDI zwitterion with ZnCl2 in dichloromethane led to the serendipitous discovery of a highly selective, double activation of dichloromethane C-Cl bonds.
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22
(a) Rivlin, M.; Eliav, U.; Navon, G. NMR Studies of the Equilibria and Reaction Rates in Aqueous Solutions of Formaldehyde. J. Phys. Chem. B 2015, 119, 4479– 4487, DOI: 10.1021/jp513020y
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22a
NMR Studies of the Equilibria and Reaction Rates in Aqueous Solutions of Formaldehyde
Rivlin, Michal; Eliav, Uzi; Navon, Gil
Journal of Physical Chemistry B (2015), 119 (12), 4479-4487CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
Formaldehyde has an important role in the chem. industry and in biol. sciences. In dil. aq. solns. of formaldehyde only traces of the mol. formaldehyde are present and the predominant species are methylene glycol and in lower concns., dimethylene glycol. The chem. equil. and reaction rates of the hydration of formaldehyde in H2O and D2O solns. at low concns. were studied by 1H and 13C NMR at various conditions of pH (1.8-7.8) and temp. (278-333 K). These measurements became possible by direct detection of formaldehyde 13C and 1H peaks. The equil. and rate consts. of the dimerization reaction of methylene glycol were also measured. The rate consts. for both the hydration and the dimerization reactions were measured by a new version of the conventional selective inversion transfer method. This study, together with previous published work, completes the description of dynamics and equil. of all the processes occurring in dil. aq. formaldehyde solns.
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(b) Dankelman, W.; Daemen, J. M. H. Gas Chromatographic and Nuclear Magnetic Resonance Determination of Linear Formaldehyde Oligomers in Formaline. Anal. Chem. 1976, 48, 401– 404, DOI: 10.1021/ac60366a030
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22b
Gas chromatographic and nuclear magnetic resonance determination of linear formaldehyde oligomers in formalin
Dankelman, Wim; Daemen, Jacq. M. H.
Analytical Chemistry (1976), 48 (2), 401-4CODEN: ANCHAM; ISSN:0003-2700.
The oligomer distribution of polyoxymethylene glycols in formalin solns. can be detd. up to the heptamer [HO(CH2O)nH, n = 7] by direct silylation with BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide), followed by gas chromatog. anal. on a column filled with 10% OV-1 on Chromosorb W. The results were corroborated with a 220-MHz NMR anal. Only at 220 MHz is the water signal sufficiently sepd. from the methylene H absorptions. The exact amts. of the oligomers with n = 1 and n = 2 and the sum of n ≥3 can be detd. by NMR. The results are in accordance with the gas chromatog. anal. MeOH, added as a stabilizer to avoid pptn. of paraformaldehyde, breaks down high mol. oligomers of polymethylene glycols, thereby forming more sol. compds.
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(a) Li, M.; Long, Y.; Deng, Z.; Zhang, H.; Yang, X.; Wang, G. Ruthenium trichloride as a new catalyst for selective production of dimethoxymethane from liquid methanol with molecular oxygen as sole oxidant. Catal. Commun. 2015, 68, 46– 48, DOI: 10.1016/j.catcom.2015.04.031
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23a
Ruthenium trichloride as a new catalyst for selective production of dimethoxymethane from liquid methanol with molecular oxygen as sole oxidant
Li, Meilan; Long, Yan; Deng, Zhiyong; Zhang, Hua; Yang, Xiangui; Wang, Gongying
Catalysis Communications (2015), 68 (), 46-48CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
Dimethoxymethane was first synthesized from methanol with a liq. phase intermittent process which only used mol. oxygen as the sole oxidant. RuCl3 was proved to be an efficient catalyst as it showed ability of oxidizing methanol and Lewis acidic which promotes the oxidn. of methanol to formaldehyde and then methanol condensed with formaldehyde to form dimethoxymethane at Lewis acid site.
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(b) Thavornprasert, K.-a.; Capron, M.; Jalowiecki-Duhamel, L.; Dumeignil, F. One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts. Catal. Sci. Technol. 2016, 6, 958– 970, DOI: 10.1039/C5CY01858G
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23b
One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts
Thavornprasert, Kaew-arpha; Capron, Mickael; Jalowiecki-Duhamel, Louise; Dumeignil, Franck
Catalysis Science & Technology (2016), 6 (4), 958-970CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
Dimethoxymethane or DMM is a versatile chem. with applications in many industries such as paints, perfume, pharmacy, and fuel additives. DMM can be produced through the reaction of methanol and formaldehyde in the presence of acid catalysts or, directly, through the selective oxidn. of methanol over catalysts with redox and acid functionalities. In terms of sustainability, the so-called bio-methanol derived from syngas obtained via biomass gasification can be used in DMM synthesis. In this review article, we have condensed and classified the research outputs published over the past decade aimed at producing DMM from methanol over different types of catalysts. The majority of studies described the reaction of methanol to DMM in a promising way using heterogeneous catalysts in the gas phase for the ease of product and catalyst recovery as well as suitability for continuous processing. Likewise, the influence of parameters including catalyst component, feed compn., and temp. on the performance of catalysts utilized in DMM prodn. is analyzed and discussed. Further, some perspectives concerning the evolution of potential DMM market with respect to the characteristics of the best catalyst materials for high DMM productivity are expressed.
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(c) Chao, Y.; Lai, J.; Yang, Y.; Zhou, P.; Zhang, Y.; Mu, Z.; Li, S.; Zheng, J.; Zhu, Z.; Tan, Y. Visible light-driven methanol dehydrogenation and conversion into 1,1-dimethoxymethane over a non-noble metal photocatalyst under acidic conditions. Catal. Sci. Technol. 2018, 8, 3372– 3378, DOI: 10.1039/C8CY01030G
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23c
Visible light-driven methanol dehydrogenation and conversion into 1,1-dimethoxymethane over a non-noble metal photocatalyst under acidic conditions
Chao, Yuguang; Lai, Jianping; Yang, Yong; Zhou, Peng; Zhang, Yelong; Mu, Zijie; Li, Shiying; Zheng, Jianfeng; Zhu, Zhenping; Tan, Yisheng
Catalysis Science & Technology (2018), 8 (13), 3372-3378CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
The dehydrogenation and conversion of methanol into 1,1-dimethoxymethane (DMM) was achieved over noble metal-free photocatalyst CdS/Ni2P under visible light. This photocatalytic process for methanol-to-H2 and DMM conversion is efficient and atom economic, with an optimal rate and selectivity of DMM of 188.42 mmol g-1 h-1 and 82.93%, resp. This work supplies a new green approach for the direct efficient conversion of methanol into DMM and provides a promising avenue for sustainable bio-methanol applications.
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Łojewska, J.; Wasilewski, J.; Terelak, K.; Łojewski, T.; Kołodziej, A. Selective oxidation of methylal as a new catalytic route to concentrated formaldehyde: Reaction kinetic profile in gradientless flow reactor. Catal. Commun. 2008, 9, 1833– 1837, DOI: 10.1016/j.catcom.2008.02.014
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Selective oxidation of methylal as a new catalytic route to concentrated formaldehyde: Reaction kinetic profile in gradientless flow reactor
Lojewska, J.; Wasilewski, J.; Terelak, K.; Lojewski, T.; Kolodziej, A.
Catalysis Communications (2008), 9 (9), 1833-1837CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
Catalytic selective oxidn. of methylal (dimethoxy methane, DMM) was regarded as a new alternative for the prodn. of highly concd. formaldehyde. The aim of this work was to study the reaction kinetics in order to find optimum reaction conditions. The reaction was tested on iron-molybdenum mixed oxide catalysts in gradientless stirred jet reactor operating at atm. pressure. The activity and selectivity of the catalyst prepd. in our lab. has proved similar to the industrial catalyst. It has been demonstrated that the highest selectivity towards formaldehyde 90% is achieved at a fairly narrow parameter window: temp. in the range 230-260°, at a contact time around 1 s, in the reaction mixt. contg. O2:N2:(CH3)2CH2O2:H2O = 0.08:0.76:0.11:0.05.
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(a) Arnhold, M. Zur Kenntniss des dreibasischen Ameisensäureäthers und verschiedener Methylale. Justus Liebigs Ann. Chem. 1887, 240, 192– 208, DOI: 10.1002/jlac.18872400204
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(b) Löbering, J.; Fleischmann, A. Über Mono- und Dioxymethylen-dimethyläther. Ber. Dtsch. Chem. Ges. B 1937, 70, 1680– 1683, DOI: 10.1002/cber.19370700807
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25b
Mono- and dihydroxymethylene dimethyl ethers
Lobering, J.; Fleischmann, A.
Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen (1937), 70B (), 1680-3CODEN: BDCBAD; ISSN:0365-9488.
The methods of prepg. CH2(OMe)2 (I) and O(CH2OMe)2 (II) given in the literature are unsatisfactory, especially as regards homogeneity of the products. I prepd. according to Fischer and Giebe (Ber. 30, 3053(1897)) by refluxing MeOH, paraformaldehyde and HCl at 100° and distg. after 12 hrs. b760 42.3°. The end values for HCHO content obtained in decompn. measurements on this product (III) were only 81-4% of the calcd. values. That this was not due to the equil. in the reaction CH2(OMe)2 ↹ HCHO + 2MeOH not lying practically completely to the right was shown by the fact that no higher values were obtained when the HCHO was removed. This was demonstrated by treating III with a definite amt. of I, acidifying, making alk. from time to time (the liberated HCHO thereby being oxidized by the hypoiodite) and finally titrating the excess of I. It was suspected III might be an azeotropic mixt. of 2 mols. I and 1 mol. MeOH; a vapor density detn. (Victor Meyer method) gave 58.5-62.5 for the mol. wt. Breaking down the azeotropic mixt. indirectly through ternary mixts. with various "3rd substances" gave no definite results, but with p-O2NC6H4COCl it was found possible to remove the MeOH from the III; the filtrate now b. 39-40°. In order, however, to exclude the presence of MeOH from the very start, alc.-free NaOMe and CH2Cl2 were used for the synthesis of I; NaOMe mixed with pumice was placed in a tube 60 cm. long heated to 200° and CH2Cl2 was passed over it. I, MeOCH2Cl and unreacted CH2Cl2 distd. from the outlet end of the tube; the MeOCH2Cl, b. 61°, and CH2Cl2, b. 41°, were condensed in an upright condenser and again passed through the tube, while the I, passing through the condenser, was collected in a receiver cooled with CO2 snow. It boiled 33-5° and on decompn. gave 99.6-101.2% HCHO. It can be prepd. somewhat more simply by refluxing (cooling liquid, about 25-30°) an equimol. mixt. of MeOCH2Cl and alc.-free NaOMe. II was prepd. by Backes' method (C. A. 27, 4225), with some modifications; exactly equiv. amts. of paraformaldehyde and POCl3 were gently boiled some hrs. under a reflux, then distd., and the (ClCH2)2O fraction, b. 103°, was slowly dropped upon alc.-free NaOMe under a reflux. A violent reaction occurred, which necessitated cooling. The product was distd., the distillate (which contained much HCl, water and a trace of POCl3) was treated with cold KOH and again distd., yielding a II, b. 91-3°, which gave 101.4% of the calcd. amt. of HCHO. I and II when not quite pure polymerize rapidly, while the pure products are stable indefinitely. The dimers are considerably less sol. in water than the monomers.
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Direct separation of methylal from DCM is a technical problem that can be efficiently addressed by special distillation techniques. See, for example:Berg, L. Separation of methylene vhloride from methylal by extractive distillation. US Patent US5051153A. Sept. 24, 1991.
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Giacalone, F.; Gruttadauria, M.; Agrigento, P.; Noto, R. Low-loading asymmetric organocatalysis. Chem. Soc. Rev. 2012, 41, 2406– 2447, DOI: 10.1039/C1CS15206H
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Low-loading asymmetric organocatalysis
Giacalone, Francesco; Gruttadauria, Michelangelo; Agrigento, Paola; Noto, Renato
Chemical Society Reviews (2012), 41 (6), 2406-2447CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
This crit. review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Bronsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, and phase-transfer and N-heterocyclic carbene catalyzes.
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The TOF figure allows an estimation of the pseudo-first-order rate for the dichloromethane activation in the order k′ ≈ 10^–2 s^–1 (=45 h^–1/3600 s h^–1). We have shown before that the reaction of 1a with DCM is very slow at room temperature but completes within 24 h at 60 °C. Thus, taking the latter value as an indicative value for the half-life of 1a in DCM at 40 °C, the pseudo-first-order rate for this reaction should be in the order of 10^–5 s^–1 (k′ = Ln(2)/t_1/2).
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Catalysis in two-phase systems: phase transfer and related phenomena
Makosza, Mieczyslaw; Fedorynski, Michal
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Leading examples of phase transfer catalysis, as well as mechanistic questions pertaining to its specific features, are discussed in this review with 180 refs.
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Phase-transfer catalysis. A general green methodology in organic synthesis
Makosza, Mieczyslaw
Pure and Applied Chemistry (2000), 72 (7), 1399-1403CODEN: PACHAS; ISSN:0033-4545. (International Union of Pure and Applied Chemistry)
A review with 9 refs. Basic concept of phase-transfer catalysis (PTC), its field of applications and specific features as the most general, efficient, and environment-friendly green methodol. of org. synthesis, particularly for industrial processes, is discussed.
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(a) Liotta, C. L.; Berkner, J.; Wright, J.; Fair, B. Mechanisms and Applications of Solid─Liquid Phase-Transfer Catalysis. Phase-Transfer Catalysis 1997, 659, 29– 40, DOI: 10.1021/bk-1997-0659.ch003
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Díez-Barra, E.; Hoz, A.; Sánchez-Migallón, A.; Tejeda, J. Phase transfer catalysis without solvent: synthesis of bisazolylalkanes. Heterocycles 1992, 34, 1365– 1373, DOI: 10.3987/COM-92-6024
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Phase transfer catalysis without solvent. Synthesis of bisazolylalkanes
Diez-Barra, Enrique; De la Hoz, Antonio; Sanchez-Migallon, Ana; Tejeda, Juan
Heterocycles (1992), 34 (7), 1365-73CODEN: HTCYAM; ISSN:0385-5414.
The reaction of azoles and benzazoles with dihalomethanes and dihaloethanes was performed in the absence of solvent. This method provides a general procedure for the synthesis of bisazolylmethanes and ethanes. No solvent was used during the reaction and, when possible, during the work-up. Thus, pyrazole was stirred with KOH and Bu4N+ Br- for 1 h and then CH2Cl2 was added and the stirring continued to give 93% bispyrazol-1-ylmethane (I).
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Blümel, M.; Crocker, R. D.; Harper, J. B.; Enders, D.; Nguyen, T. V. N-Heterocyclic olefins as efficient phase-transfer catalysts for base-promoted alkylation reactions. Chem. Commun. 2016, 52, 7958– 7961, DOI: 10.1039/C6CC03771B
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N-Heterocyclic olefins as efficient phase-transfer catalysts for base-promoted alkylation reactions
Blumel, Marcus; Crocker, Reece D.; Harper, Jason B.; Enders, Dieter; Nguyen, Thanh V.
Chemical Communications (Cambridge, United Kingdom) (2016), 52 (51), 7958-7961CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
N-Heterocyclic olefins (NHOs), e.g., I have very recently emerged as efficient promoters for several chem. reactions due to their strong Bronsted/Lewis basicities. The novel application of NHOs as efficient phase-transfer organocatalysts for synthetically important alkylation reactions on a wide range of substrates, further demonstrates the great potential of NHOs in org. chem has been reported.
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(a) Wu, H.-S.; Jou, S.-H. Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis. J. Chem. Technol. Biotechnol. 1995, 64, 325– 330, DOI: 10.1002/jctb.280640403
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Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis
Wu, Ho-Shing; Jou, Sung-Hauh
Journal of Chemical Technology & Biotechnology (1995), 64 (4), 325-30CODEN: JCTBED; ISSN:0268-2575. (Wiley)
The reactions of phenol with dichloromethane using quaternary ammonium salts as a liq.-liq. phase-transfer catalyst in an org. solvent/alk. soln. were investigated. The technique of phase-transfer catalysis had a dramatic accelerating effect on the reaction and increased the yield of diphenoxymethane by more than 95%. The effects of catalysts, temp., and basic concn. on reaction rate were studied in order to find the optimum operating conditions for this reaction. Exptl. results indicated that a potassium hydroxide was preferred over sodium hydroxide in order to enhance the reactivity of the reaction. The reaction rate const. and the distribution coeff. of the intermediate product were obtained. During the reaction, the concn. of the intermediate product was also measured in order to study its behavior in the liq.-liq. system.
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(b) Cornélis, A.; Laszlo, P. Clay-Supported Reagents; II. Quaternary Ammonium-Exchanged Montmorillonite as Catalyst in the Phase-Transfer Preparation of Symmetrical Formaldehyde Acetals. Synthesis 1982, 1982, 162– 163, DOI: 10.1055/s-1982-29732
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Equilibrium and extraction of quaternary salt in an organic solvent/alkaline solution: effect of NaOH concentration
Wu, Ho-Shing; Fang, Tsung-Ran; Meng, Shang-Shin; Hu, Kwan-Hua
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This study measures the quaternary salt concn. in a dichloromethane (or chlorobenzene)/alk. soln. and dets. the thermodn. equil. data. The true extn. const., distribution coeff., dissocn. const. in the aq. phase and free energies of the true extn. const., distribution coeff. and dissocn. const. are obtained as well. The distribution coeff. increased and the real dissocn. const. decreased with increasing NaOH concn. The hydroxide ion concn. and the water content in the org. phase attain a max. value when the NaOH concn. is around 6 M.
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Practical synthesis of diaryloxymethanes
Liu, Wenming; Szewczyk, Joanna; Waykole, Liladhar; Repic, Oljan; Blacklock, Thomas J.
Synthetic Communications (2003), 33 (10), 1751-1754CODEN: SYNCAV; ISSN:0039-7911. (Marcel Dekker, Inc.)
Diaryloxymethanes were prepd. by treating phenols with sodium hydride and dichloromethane in N-methylpyrrolidinone (NMP) at 40°C. For example, PhOCH2OPh was prepd. in 97% yield from phenol and CH2Cl2.
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Liou, C.-C.; Brodbelt, J. S. Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method. J. Am. Soc. Mass Spectrom. 1992, 3, 543– 548, DOI: 10.1016/1044-0305(92)85031-E
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Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method
Liou, Chien Chung; Brodbelt, Jennifer S.
Journal of the American Society for Mass Spectrometry (1992), 3 (5), 543-8CODEN: JAMSEF; ISSN:1044-0305.
Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M1 + Cat + M2)+, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissocn. to (M1 + Cat)+ and (M2 + Cat)+ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li+, Na+, and K+ than the larger ions such as Cs+ and Rb+. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.
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Gobbi, A.; Landini, D.; Maia, A.; Secci, D. Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts. J. Org. Chem. 1995, 60, 5954– 5957, DOI: 10.1021/jo00123a036
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Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts
Gobbi, Alessandro; Landini, Dario; Maia, Angelamaria; Secci, Daniela
Journal of Organic Chemistry (1995), 60 (18), 5954-7CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Metal ion effects have been revealed on nucleophilic substitution reactions of n-octyl sulfonates,[n-C8H17OSO2R;R=Me (1), p-MeC6H4(2), p-O2NC6H4(3)] promoted by complexes of polyether ligands (PEGs, crown ethers, cryptands) with alkali metal salts MY (M = Li, Na, K; Y = I, Br) in low polarity solvents (chlorobenzene, o-dichlorobenzene, toluene) at 60 °. Rate consts. increase, in the order K+ < Na+ <Li+, with the complexes of crown ethers I and II and PEG 4 (III), whereas they are independent of the cation in the case of cryptates of IV. In the series of sulfonic esters 1-3 these effects progressively diminish with increasing nucleofugality of the leaving group. These results are interpreted on the basis of a transition state where the complexed cation (Lig∋M+) assists the departure of the leaving group (electrophilic catalysis).
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Archer, R. H.; Carpenter, J. R.; Hwang, S.-J.; Burton, A. W.; Chen, C.-Y.; Zones, S. I.; Davis, M. E. Physicochemical Properties and Catalytic Behavior of the Molecular Sieve SSZ-70. Chem. Mater. 2010, 22, 2563– 2572, DOI: 10.1021/cm9035677
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Physicochemical Properties and Catalytic Behavior of the Molecular Sieve SSZ-70
Archer, Raymond H.; Carpenter, John R.; Hwang, Son-Jong; Burton, Allen W.; Chen, Cong-Yan; Zones, Stacey I.; Davis, Mark E.
Chemistry of Materials (2010), 22 (8), 2563-2572CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
SSZ-70 is synthesized using 1,3-bis(isobutyl)imidazolium, 1,3-bis(cyclohexyl)imidazolium, and 1,3-bis(cycloheptyl)imidazolium structure directing agents (SDAs), and the solids obtained are characterized by powder X-ray diffraction (XRD), 29Si magic angle spinning NMR (MAS NMR), electron microscopy, nitrogen and hydrocarbon adsorption, and thermogravimetric analyses. The physicochem. properties of SSZ-70 show that it is a new mol. sieve that has similarities to MWW-type materials. The catalytic behavior of SSZ-70 is evaluated through the use of the constraint index (CI) test. Distinct differences in the reactivity between Al-SSZ-70 and SSZ-25 (MWW) are obsd. and are the consequences of the structural differences between these two mol. sieves.
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(a) https://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi.
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For diphenoxymethane, see:
(b) Salvador, T. K.; Arnett, C. H.; Kundu, S.; Sapiezynski, N. G.; Bertke, J. A.; Raghibi Boroujeni, M.; Warren, T. H. Copper Catalyzed sp3 C–H Etherification with Acyl Protected Phenols. J. Am. Chem. Soc. 2016, 138, 16580– 16583, DOI: 10.1021/jacs.6b09057
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Copper Catalyzed sp3 C-H Etherification with Acyl Protected Phenols
Salvador, Tolani K.; Arnett, Charles H.; Kundu, Subrata; Sapiezynski, Nicholas G.; Bertke, Jeffery A.; Raghibi Boroujeni, Mahdi; Warren, Timothy H.
Journal of the American Chemical Society (2016), 138 (51), 16580-16583CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A variety of acyl-protected phenols AcOAr participate in sp3 C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employing tBuOOtBu as oxidant with copper(I) β-diketiminato catalysts [CuI]. While 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [CuII]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [CuII]-OtBu intermediates generated upon reaction of [CuI] with tBuOOtBu.
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For dibenzyloxymethane, see:
(c) Cacciapaglia, R.; Di Stefano, S.; Mandolini, L. Metathesis Reaction of Formaldehyde Acetals: An Easy Entry into the Dynamic Covalent Chemistry of Cyclophane Formation. J. Am. Chem. Soc. 2005, 127, 13666– 13671, DOI: 10.1021/ja054362o
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Metathesis Reaction of Formaldehyde Acetals: An Easy Entry into the Dynamic Covalent Chemistry of Cyclophane Formation
Cacciapaglia, Roberta; Di Stefano, Stefano; Mandolini, Luigi
Journal of the American Chemical Society (2005), 127 (39), 13666-13671CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The acid-catalyzed transacetalation of formaldehyde acetals (formal metathesis) is a suitable reaction for the generation of well-behaved dynamic libraries of cyclophane formals. The compn. of the equilibrated mixts. solely depends on concn., and is totally independent of whether the feedstock is any of the pure cyclic oligomers, or a mixt. of oligomers/polymers. Effective Molarities related to the formation of the lower cyclic oligomers were directly measured as their equil. molar concns. above the crit. monomer concn. The finding that silver cation acts as a selective binder toward the cyclic dimer, coupled with the proof reading and editing capability of the quickly equilibrating system, translated into significant amplifications of the dimer when the equilibrated mixts. were exposed to the action of the silver template. These results highlight the potential of dynamic combinatorial chem. as a powerful tool for the prepn. in synthetically useful amts. of an otherwise elusive macrocyclic compd. The possibility of using a mixt. of high mol. wt. byproducts as feedstock adds considerably to the practical value of the procedure.
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For diallyloxymethane, see:
(d) El-Brollosy, N. R.; Jørgensen, P. T.; Dahan, B.; Boel, A. M.; Pedersen, E. B.; Nielsen, C. Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants. J. Med. Chem. 2002, 45, 5721– 5726, DOI: 10.1021/jm020949r
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38d
Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants
El-Brollosy, Nasser R.; Jorgensen, Per T.; Dahan, Berit; Boel, Anne Marie; Pedersen, Erik B.; Nielsen, Claus
Journal of Medicinal Chemistry (2002), 45 (26), 5721-5726CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
This paper reports the synthesis and the antiviral activities of a series of 6-arylmethyl-1-(allyloxymethyl)-5-alkyluracil derivs., which can be viewed as analogs of the anti-HIV-1 drug emivirine (formerly MKC-442) from which they differ in the replacement of the ethoxymethyl group with variously allyloxymethyl moieties. The most active compds. N-1 allyloxymethyl- and N-1 3-methylbut-2-enyl substituted 5-ethyl-6-(3,5-dimethylbenzyl)uracils (12 and 13) showed activity against HIV-1 wild-type in the picomolar range with selective index of greater than 5 × 106 and activity in the submicromolar range against the clin. important Y181C and K103N mutant strains known to be resistant to emivirine. Structure-activity relationship studies established a correlation between the anti-HIV-1 activity and the substitution pattern of the N-1 allyloxymethyl group.
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For diisopropoxymethane, see:
(e) Berkefeld, A.; Piers, W. E.; Parvez, M.; Castro, L.; Maron, L.; Eisenstein, O. Decamethylscandocinium-hydrido-(perfluorophenyl)borate: fixation and tandem tris(perfluorophenyl)borane catalysed deoxygenative hydrosilation of carbon dioxide. Chem. Sci. 2013, 4, 2152– 2162, DOI: 10.1039/c3sc50145k
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38e
Decamethylscandocinium-hydrido-(perfluorophenyl)borate: fixation and tandem tris(perfluorophenyl)borane catalyzed deoxygenative hydrosilation of carbon dioxide
Berkefeld, Andreas; Piers, Warren E.; Parvez, Masood; Castro, Ludovic; Maron, Laurent; Eisenstein, Odile
Chemical Science (2013), 4 (5), 2152-2162CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
This work was directed at studying the capability of structurally defined, strongly Lewis-acidic metal centers to effect catalytic reductive fixation of the small mol. substrate CO2. Exposing solns. or solid samples of the ion pair [Cp*2Sc][HB(C6F5)3] 1CIP, in which the highly electrophilic decamethyl-scandocene cation and [HB(C6F5)]- as a potentially reactive source of hydride equiv. are assocd., to CO2 selectively produces ion pair [Cp*2Sc][HCO2B(C6F5)3] 2CIP. The results of soln. and solid state structural anal. of 2CIP imply ionic assocn. of [Cp*2Sc]+ and [HCO2B(C6F5)3]- rather than B(C6F5)3-adduct formation to neutral Cp*2Sc-formate. In the presence of B(C6F5)3 co-catalyst and excess triethylsilane, the formation of 2CIP from 1CIP initiates the catalytic deoxygenative hydrosilation of CO2 to CH4. The roles of ion pairs 1 and 2, borane co-catalyst, and silane in the catalytic reaction were studied mechanistically by NMR spectroscopy. Intermediately formed 3,3,7,7-tetraethyl-3,7-disila-4,6-dioxanonane product was found to exert an accelerating effect on the overall reaction rate by promoting [HCO2B(C6F5)3]- dissocn. to give 2SIP through formation of sepd. ion pairs [Cp*2Sc(κ2-(Et3SiO)2CH2)][HCO2{B(C6F5)3}n], n = 1, 2. DFT calcns. show that the formation 2CIP from the reaction of 1CIP with CO2 is exoergic and without significant energy barriers. This work lays the basis for future studies of reactive ion pairs of this kind in the context of small mol. chem.
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For di(ethylthio)methane, see:
(f) Zaidi, J. H.; Naeem, F.; Khan, K. M.; Iqbal, R.; Zia-Ullah Synthesis of Dithioacetals and Oxathioacetals with Chiral Auxiliaries. Synth. Commun. 2004, 34, 2641– 2653, DOI: 10.1081/SCC-200025627
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Synthesis of Dithioacetals and Oxathioacetals with Chiral Auxiliaries
Zaidi, Javid H.; Naeem, Fazal; Khan, Khalid M.; Iqbal, Rashid; Zia-Ullah
Synthetic Communications (2004), 34 (14), 2641-2653CODEN: SYNCAV; ISSN:0039-7911. (Marcel Dekker, Inc.)
One-pot synthesis of dithioacetals as well as an efficient method for oxathioacetal is reported. Addnl., some chiral auxiliaries were used to synthesize enantiomerically pure dithioacetals and oxathioacetals.
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For bis(pyrazolyl)methane, see:
(g) Field, L. D.; Messerle, B. A.; Rehr, M.; Soler, L. P.; Hambley, T. W. Cationic Iridium(I) Complexes as Catalysts for the Alcoholysis of Silanes. Organometallics 2003, 22, 2387– 2395, DOI: 10.1021/om020938w
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Cationic Iridium(I) Complexes as Catalysts for the Alcoholysis of Silanes
Field, Leslie D.; Messerle, Barbara A.; Rehr, Manuela; Soler, Linnea P.; Hambley, Trevor W.
Organometallics (2003), 22 (12), 2387-2395CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Syntheses of five cationic iridium(I) complexes contg. bidentate ligands bis(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM), {[Ir(BPM)(COD)]+(BPh4)-} (1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(CO)2]+(BPh4)-} (3), {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4), and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5), are reported. In an example prepn., BPM reacted with {[Ir(COD)Cl]2} and NaBPh4 in a carbon monoxide atm. giving 3 in 90% yield. The complexes were characterized by NMR spectroscopy, and the solid-state structure of 3 was detd. by single-crystal X-ray crystallog. anal. Complexes 3 and 5 were effective catalysts for the alcoholysis of a range of alcs. and hydrosilanes, including secondary and tertiary hydrosilanes, under mild conditions. For example, Et3SiH reacted with EtOH in the presence of 3 giving Et3SiOEt in 93% yield.
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Liang, L. C.; Chien, P. S.; Lee, P. Y.; Lin, J. M.; Huang, Y. L. Terminal nickel(ii) amide, alkoxide, and thiolate complexes containing amido diphosphine ligands of the type [N(o-C₆H₄PR₂)₂]⁻ (R = Ph, ⁱPr, Cy). Dalton Trans. 2008, 25, 3320– 3327, DOI: 10.1039/b719894a
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Cite this: J. Org. Chem. 2021, 86, 23, 16725–16735

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https://doi.org/10.1021/acs.joc.1c01971

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Abstract
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Scheme 1
Scheme 1. Synthesis of 1a and 2a
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Scheme 2
Scheme 2. Synthesis of Methylal Using 2a as a Catalyst
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Figure 1
Figure 1. Yield vs time plot for the reaction of DCM with NaOMe catalyzed by 2a. Conditions: 40 °C, NaOMe, 2 g (31 mmol); DCM (neat) 40 mL (626 mmol); 2a, 37 mg (0.2 mol % with regard to NaOMe). The last check after 24 h was consistent with full NaOMe consumption.
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Scheme 3
Scheme 3. Catalytic Transformation of DCM into CH₂Z₂ Using Combinations of Weak Protic Acids and Suitable Bases (NaOH or NaH)
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Scheme 4
Scheme 4. Synthesis of the Catalyst Precursor 3a
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Figure 2
Figure 2. Solid–liquid phase-transfer catalysis.
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Scheme 5
Scheme 5. Transformation of 2a and 1a into 2b and 1b, Respectively, in Catalytic Media
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References
This article references 38 other publications.
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  (a) Lee, H. M.; Lu, C. Y.; Chen, C. Y.; Chen, W. L.; Lin, H. C.; Chiu, P. L.; Cheng, P. Y. Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C–C coupling reactions. Tetrahedron 2004, 60, 5807– 5825, DOI: 10.1016/j.tet.2004.04.070
  2a
  Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C-C coupling reactions
  Lee, Hon Man; Lu, Chi Ying; Chen, Chih Yuan; Chen, Wen Ling; Lin, Hung Ching; Chiu, Pei Ling; Cheng, Pi Yun
  Tetrahedron (2004), 60 (27), 5807-5825CODEN: TETRAB; ISSN:0040-4020. (Elsevier Science B.V.)
  A series of new ethylene-bridged bis(imidazolium) halides with various N-substitutions were synthesized. Complexation of these imidazolium halides with Pd(OAc)2 produced new Pd(II) ethylene-bridged bis(carbene) complexes. Crystallog. analyses of some of the new imidazolium salts and Pd(II) complexes were detd. Applications of these seven-member palladacycles in Suzuki and Heck coupling reactions produced comparable catalytic activities to those of six-member analogs.
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  N,N'-Disubstituted Methylenediimidazolium Salts: A Versatile Guest for Various Macrocycles
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  N,N'-Disubstituted methylenediimidazolium salts allow the formation of flexible inclusion complexes with β-cyclodextrin, cucurbit[7]uril, tetrapropoxycalix[4]arene, and dibenzo-24-crown-8 ether. Due to the salt nature of the imidazolium guest, the counterion largely dets. its soly. in a given solvent. Moreover, by the judicious choice of the imidazolium substituents, inclusion complexes of guest salts were obtained with a variety of macrocyclic hosts, and the binding parameters of the inclusion were detd. for each complex.
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  Rhodium-catalyzed double carbonylation of diiodomethane in the presence of triethylorthoformate
  Cheong, Minserk; Kim, Mi-Na; Shim, Ji Yeon
  Journal of Organometallic Chemistry (1996), 520 (1-2), 253-255CODEN: JORCAI; ISSN:0022-328X. (Elsevier)
  Catalytic double carbonylation of diiodomethane in triethylorthoformate in the presence of a homogeneous rhodium complex gives di-Et malonate in a fairly good yield.
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  (d) Zadykowicz, J.; Potvin, P. G. N-(2-tetrahydrofuranyl)azole nucleoside analogs by reactions of azoles with dihalomethanes in tetrahydrofuran. J. Heterocycl. Chem. 1999, 36, 623– 626, DOI: 10.1002/jhet.5570360308
  2d
  N-(2-Tetrahydrofuranyl)azole nucleoside analogs by reactions of azoles with dihalomethanes in tetrahydrofuran
  Zadykowicz, Jerzy; Potvin, Pierre G.
  Journal of Heterocyclic Chemistry (1999), 36 (3), 623-626CODEN: JHTCAD; ISSN:0022-152X. (HeteroCorporation)
  The reactions of the mono-N-substituted bispyrazolylpyridine 2-(1-methyl-4,5,6,7-tetrahydroindazol-3-yl)-6-(2H-4,5,6,7-tetrahydroin dazol-3-yl)pyridine, 3,5-dimethylpyrazole and benzimidazole with sodium hydride and diiodomethane or dibromomethane in THF produced the unexpected N-tetrahydrofuran-2-yl adducts as well as the expected diazolylmethanes. These side-reactions are thought to involve the 2-halo THF deriv. resulting from a free-radical halogenation by the dihalomethane.
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  (e) Zidan, A.; Garrec, J.; Cordier, M.; El-Naggar, A. M.; Abd El-Sattar, N. E. A.; Ali, A. K.; Hassan, M. A.; El Kaim, L. β-Lactam Synthesis through Diodomethane Addition to Amide Dianions. Angew. Chem., Int. Ed. 2017, 56, 12179– 12183, DOI: 10.1002/anie.201706315
  2e
  β-Lactam Synthesis through Diodomethane Addition to Amide Dianions
  Zidan, Alaa; Garrec, Julian; Cordier, Marie; El-Naggar, Abeer M.; Abd El-Sattar, Nour E. A.; Ali, Ali Khalil; Hassan, Mohamed Ali; El Kaim, Laurent
  Angewandte Chemie, International Edition (2017), 56 (40), 12179-12183CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  We present a novel route for the quick and easy synthesis of a broad range of β-lactams. The synthesis involves a [3+1] cyclization of amide dianions with diiodomethane. In contrast to the seminal work of Hirai et al. from 1979, the reaction proved to be a general and efficient approach towards azetidinones. The ease of the process was confirmed by DFT calcns. and its power demonstrated by a diversity-oriented synthesis of β-lactams with four points of diversity detd. by the choice of Ugi adducts as starting materials.
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3. 3
  (a) Durandetti, S.; Sibille, S.; Perichon, J. Electrochemical cyclopropanation of alkenes using dibromomethane and zinc in dichloromethane/DMF mixture. J. Org. Chem. 1991, 56, 3255– 3258, DOI: 10.1021/jo00010a015
  3a
  Electrochemical cyclopropanation of alkenes using dibromomethane and zinc in dichloromethane/DMF mixture
  Durandetti, Sylvie; Sibille, Soline; Perichon, Jacques
  Journal of Organic Chemistry (1991), 56 (10), 3255-8CODEN: JOCEAH; ISSN:0022-3263.
  An efficient electrosynthesis of cyclopropanes from gem-dibromoalkanes and alkenes is achieved in a one-compartment cell fitted with a sacrificial zinc anode. The part played by the anodically generated Zn(II) in the coupling reaction is pointed out, and evidence for the existence of an organozinc species as intermediate is presented.
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  (b) Hon, Y.-S.; Hsieh, C.-H.; Liu, Y.-W. Dibromomethane as one-carbon source in organic synthesis: total synthesis of (±)- and (−)-methylenolactocin. Tetrahedron 2005, 61, 2713– 2723, DOI: 10.1016/j.tet.2005.01.057
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  Dibromomethane as one-carbon source in organic synthesis: total synthesis of (±)- and (-)-methylenolactocin
  Hon, Yung-Son; Hsieh, Cheng-Han; Liu, Yu-Wei
  Tetrahedron (2005), 61 (10), 2713-2723CODEN: TETRAB; ISSN:0040-4020. (Elsevier B.V.)
  A general method was developed to construct monocyclic α-methylene-γ-butyrolactone moiety. The key step is to introduce the α-methylene group by the ozonolysis of mono-substituted alkenes followed by reacting with a preheated mixt. of CH2Br2-Et2NH. Application of this key step in the total synthesis of the (±)- and (-)-methylenolactocin was described. Thus, ozonolysis and methylenation of (-)-pentenyl ester I gave methylene aldehyde II which was converted to (-)-methylenolactocin.
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  (d) Raposo, C. D. C. B. G. Diiodomethane: A Versatile C1 Building Block. Synlett 2013, 24, 1737– 1738, DOI: 10.1055/s-0033-1338964
  3d
  Diiodomethane: a versatile C1 building block
  Raposo, Claudia Diana C. B. G.
  Synlett (2013), 24 (13), 1737-1738CODEN: SYNLES; ISSN:0936-5214. (Georg Thieme Verlag)
  A review. The prepn. and properties of diiodomethane is discussed.
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4. 4
  Though rather inert, DCM can undergo different reactions when used as a solvent, e.g., through free radical routes; see:
  (a) Levina, I. I.; Klimovich, O. N.; Vinogradov, D. S.; Podrugina, T. A.; Bormotov, D. S.; Kononikhin, A. S.; Dement’eva, O. V.; Senchikhin, I. N.; Nikolaev, E. N.; Kuzmin, V. A.; Nekipelova, T. D. Dichloromethane as solvent and reagent: a case study of photoinduced reactions in mixed phosphonium-iodonium ylide. J. Phys. Org. Chem. 2018, 31, e3844, DOI: 10.1002/poc.3844
  There is no corresponding record for this reference.
  and references cited therein
  In addition, DCM is known to react violently with some strong bases like potassium t-butoxide or some reactive metals (e.g., Li or Na/K alloy); see:
  (b) Lewis, R. J., Sr., Ed.; Sax’s Dangerous Properties of Industrial Materials, 11th ed.; Wiley-Interscience, Wiley & Sons, Inc: Hoboken, NJ, 2004; p 2436.
  There is no corresponding record for this reference.
  (c) Anhydrous DCM is not corrosive for most metals, but in the presence of water, it slowly hydrolyzes releasing small amounts of HCl, which can attack stainless steel, aluminum, or even copper pipes. See any dichlorometane Safety Data Sheet (MSDS, e.g., Fisher, ACC no. 14930).
  There is no corresponding record for this reference.
  Moreover, there are reports concerning dichloromethane C–Cl bond substitutions but are usually very slow processes, see:
  (d) Rudine, A. B.; Walter, M. G.; Wamser, C. C. Reaction of Dichloromethane with Pyridine Derivatives under Ambient Conditions. J. Org. Chem. 2010, 75, 4292– 4295, DOI: 10.1021/jo100276m
  4d
  Reaction of Dichloromethane with Pyridine Derivatives under Ambient Conditions
  Rudine, Alexander B.; Walter, Michael G.; Wamser, Carl C.
  Journal of Organic Chemistry (2010), 75 (12), 4292-4295CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Pyridine derivs. and dichloromethane (DCM) are commonly used together in a variety of different applications. However, DCM slowly reacts with pyridine and a variety of other representative pyridine derivs. to form methylenebispyridinium dichloride compds. under ambient conditions. The proposed mechanism (two consecutive SN2 reactions) was studied by evaluating the kinetics of the reaction between 4-(dimethylamino)pyridine and DCM. The second-order rate consts. for the first (k1) and second (k2) substitutions were found to be 2.56(±0.06) × 10-8 and 4.29(±0.01) × 10-4 M-1 s-1, resp. Because the second substitution is so much faster than the first, the monosubstitution product could not be isolated or detected during the reaction; it was synthesized independently in order to observe its kinetics.
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5. 5
  (a) Closs, G. L. Carbenes from Alkyl Halides and Organolithium Compounds. IV. Formation of Alkylcarbenes from Methylene Chloride and Alkyllithium Compounds. J. Am. Chem. Soc. 1962, 84, 809– 813, DOI: 10.1021/ja00864a026
  5a
  Carbenes from alkyl halides and organolithium compounds. IV. Formation of alkylcarbenes from methylene chloride and alkyllithium compounds
  Closs, Gerhard L.
  Journal of the American Chemical Society (1962), 84 (), 809-13CODEN: JACSAT; ISSN:0002-7863.
  cf. CA 55, 10350h. Alkyllithium compds. (I) and CH2Cl2 (II) yielded olefins and cyclopropanes. Formation and distribution of products could be interpreted by a carbene mechanism. It is postulated that chlorocarbene formed from I and II added to a second molecule of I to give alkylchloromethyllithium compds., which lost LiCl to form alkylcarbenes; these rearranged to stable products by hydrogen or alkyl migration, and by intramol. insertion. All reactions were carried out under dry argon. The products were sepd. by vapor phase chromatography; infrared spectroscopy was used for identification. II (0.06 mole) in 20 ml. Et2O added to a soln. of 0.1 mole BuLi in 75 ml. Et2O at -30° within 1 hr., and the mixt. warmed to room temp. gave 1-pentene, converted to 9.44 g. 1,2-dibromopentane for identification. II (0.3 mole) added to a stirred soln. of 0.5 mole AmLi (III) in 320 ml. Et2O at -30° within 1 hr. gave 96% mixt. (95:5) of 1-hexene (IV) + propylcyclopropane (V). If the reaction was run with 300 ml. pentane replacing the Et2O and within 65 min. at 30〈, a mixt. of IV + V (94:6) (41%) and 13.5% 1-chlorohexane was obtained. A cyclohexyllithium soln. (prepd. in 48% yield from 120 g. cyclohexyl chloride and 20 g. Li in 1 1. pentane) decanted from excess Li and LiCl and treated with 0.4 mole II over 1 hr. at 30 gave 37% C7-hydrocarbons [methylenecyclohexane and bicyclo [4.1.0] heptane (63:37)], and chlorocyclohexane, chloromethylcyclohexane, and cyclohexane. A sec-BuLi soln. (prepd. from 0.15 mole secBuCl and 3.5 g. Li in 100 ml. heptane at 35-8° in 57% yield) decanted from Li and salts, treated with 0.06 mole II at 25° within 90 min. (dry ice condenser to trap lowboiling compds.) gave 42% C5-compds., 2-methyl-1-butene, ethylcyclopropane, trans- and cis-dimethylcyclopropane (59:22:17:2). A tert-BuLi soln. (prepd. from 1 mole tert-BuCl and 20 g. Li in 500 ml. heptane at 35-40° in 47% yield) decanted from Li and salts, treated with 0.4 mole II at 30° within 1 hr. (dry. ice condenser to trap low-boiling compds.) gave 29% C5-compds., 2-methyl-1-butene, 2-methyl-2-butene, and 1,1-dimethylcyclopropane (18:13:69). Other hydrocarbons initially present in the solns. of I were frequently found with the products. The idea that alkylcarbenes are intermediates in these reactions is strongly supported by a comparison of the product distributions found in these reactions with those obtained from the carbenoid pyrolysis of tosylhydrazones of suitable aldehydes, p-Toluenesulfonylhydrazide (16.5 g.) in 40 ml. 60° MeOH added to 5 g. 2-methylbutanal in 20 ml. MeOH and the mixt. cooled at once gave 45% 2-methylbutanal p-toluenesulfonylhydrazone (VI), m. 73-4° (MeOH). NaOMe (2.7 g.) in 50 ml. diethylene glycol dimethyl ether (VII) heated to 160°, a soln. of 8 g. VI in 75 ml. VII added dropwise over 70 min., and heating of the mixt. regulated to permit the hydrocarbons and MeOH to distil into a flask at -70° gave 82% C5H10-hydrocarbons, 2-methyl-1-butene, ethylcyclopropane, trans- and cis-dimethylcyclopropane (63:20:12:5). Data from the literature on the decompn. of other hydrazones also supported the mechanism. The fact that the formation of pentene from BuLl and II in Et2O at -30° did not proceed via 1-chloropentane (VIII) was demonstrated by holding a mixt. of BuLl and VIII for 1 hr. at -30° without reaction.
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  (b) Böhm, A.; Bach, T. Radical Reactions Induced by Visible Light in Dichloromethane Solutions of Hünig’s Base: Synthetic Applications and Mechanistic Observations. Chem. - Eur. J. 2016, 22, 15921– 15928, DOI: 10.1002/chem.201603303
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  (c) Sturala, J.; Ambrosi, A.; Sofer, Z.; Pumera, M. Covalent Functionalization of Exfoliated Arsenic with Chlorocarbene. Angew. Chem., Int. Ed. 2018, 57, 14837– 14840, DOI: 10.1002/anie.201809341
  5c
  Covalent Functionalization of Exfoliated Arsenic with Chlorocarbene
  Sturala, Jiri; Ambrosi, Adriano; Sofer, Zdenek; Pumera, Martin
  Angewandte Chemie, International Edition (2018), 57 (45), 14837-14840CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Few-layer and monolayer arsenic (arsenene) materials have been attracting great attention mainly from a theor. perspective. Chem. modification of these materials would expand significantly the range of their applications. Here, we describe a chlorocarbene-mediated modification of exfoliated layered arsenic materials. Carbene-based species are highly reactive and offer further possibilities of functionalization. Our approach for modifying the arsenic surface by chlorocarbene generated from organolithium and dichloromethane resulted in a large surface coverage and a highly luminescent functionalized material, opening the door for its application in modern optoelectronic devices.
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6. 6
  Young, J. A. Dichloromethane. J. Chem. Educ. 2004, 81, 1415, DOI: 10.1021/ed081p1415
  6
  Dichloromethane
  Young, Jay A.
  Journal of Chemical Education (2004), 81 (10), 1415CODEN: JCEDA8; ISSN:0021-9584. (Journal of Chemical Education, Dept. of Chemistry)
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7. 7
  (a) Salthammer, T.; Mentese, S.; Marutzky, R. Formaldehyde in the Indoor Environment. Chem. Rev. 2010, 110, 2536– 2572, DOI: 10.1021/cr800399g
  7a
  Formaldehyde in the Indoor Environment
  Salthammer, Tunga; Mentese, Sibel; Marutzky, Rainer
  Chemical Reviews (Washington, DC, United States) (2010), 110 (4), 2536-2572CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review on the formaldehyde indoor air pollution, including sources, sampling and anal. of formaldehyde, indoor pollution and guidelines of formaldehyde, and exposure risk assessment.
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  (b) Li, W.; Wu, X.-F. The Applications of (Para)formaldehyde in Metal-Catalyzed Organic Synthesis. Adv. Synth. Catal. 2015, 357, 3393– 3418, DOI: 10.1002/adsc.201500753
  7b
  The Applications of (Para)formaldehyde in Metal-Catalyzed Organic Synthesis
  Li, Wanfang; Wu, Xiao-Feng
  Advanced Synthesis & Catalysis (2015), 357 (16-17), 3393-3418CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Paraformaldehyde (PFA), with the chem. formula CxHyOz, an infinite solid form of formaldehyde, is a very useful reagent in classical org. reactions. Numerous applications have been explored both in the chem. industry and org. chem. research labs. In this general review, the authors have summarized the main achievements in the use of paraformaldehyde in org. reactions with transition metals as the catalysts. In these methodologies, paraformaldehyde has been applied as methylene blocks, hydroxymethylation reagents, CO source, syngas surrogate, hydrogen donor or acceptor, formylation and methylation reagents. Addnl., in order to make this review systematic, recent reported organocatalyzed transformations of paraformaldehyde have been included as well.
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  (c) Pathak, D. D.; Gerald, J. J. An Efficient and Convenient Method for the Synthesis of Dialkoxymethanes Using Kaolinite as a Catalyst. Synth. Commun. 2003, 33, 1557– 1561, DOI: 10.1081/SCC-120018774
  7c
  An efficient and convenient method for the synthesis of dialkoxymethanes using kaolinite as a catalyst
  Pathak, Devendra D.; Gerald, J. Joe
  Synthetic Communications (2003), 33 (9), 1557-1561CODEN: SYNCAV; ISSN:0039-7911. (Marcel Dekker, Inc.)
  A one pot synthesis of dialkoxymethanes is described from the reaction of alcs. with paraformaldehyde under reflux in the presence of catalytic amt. of kaolinite.
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8. 8
  Hossaini, R.; Chipperfield, M. P.; Montzka, S. A.; Leeson, A. A.; Dhomse, S. S.; Pyle, J. A. The increasing threat to stratospheric ozone from dichloromethane. Nat. Commun. 2017, 8, 15962, DOI: 10.1038/ncomms15962
  8
  The increasing threat to stratospheric ozone from dichloromethane
  Hossaini, Ryan; Chipperfield, Martyn P.; Montzka, Stephen A.; Leeson, Amber A.; Dhomse, Sandip S.; Pyle, John A.
  Nature Communications (2017), 8 (), 15962CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  It is well established that anthropogenic chlorine-contg. chems. contribute to ozone layer depletion. The successful implementation of the Montreal Protocol has led to redns. in the atm. concn. of many ozone-depleting gases, such as chlorofluorocarbons. As a consequence, stratospheric chlorine levels are declining and ozone is projected to return to levels obsd. pre-1980 later this century. However, recent observations show the atm. concn. of dichloromethane-an ozone-depleting gas not controlled by the Montreal Protocol-is increasing rapidly. Using atm. model simulations, we show that although currently modest, the impact of dichloromethane on ozone has increased markedly in recent years and if these increases continue into the future, the return of Antarctic ozone to pre-1980 levels could be substantially delayed. Sustained growth in dichloromethane would therefore offset some of the gains achieved by the Montreal Protocol, further delaying recovery of Earth's ozone layer.
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9. 9
  (a) Kane, A.; Giraudet, S.; Vilmain, J.-B.; Le Cloirec, P. Intensification of the temperature-swing adsorption process with a heat pump for the recovery of dichloromethane. J. Environ. Chem. Eng. 2015, 3, 734– 743, DOI: 10.1016/j.jece.2015.02.021
  9a
  Intensification of the temperature-swing adsorption process with a heat pump for the recovery of dichloromethane
  Kane, Abdoulaye; Giraudet, Sylvain; Vilmain, Jean-Baptiste; Le Cloirec, Pierre
  Journal of Environmental Chemical Engineering (2015), 3 (2), 734-743CODEN: JECEBG; ISSN:2213-3437. (Elsevier Ltd.)
  The temp.-swing adsorption process (TSA) is a widely used process for solvent recovery. Steam or a heated gas is used for the desorption of org. pollutants from activated carbons. This study aims to show the efficiency of coupling the TSA process with a heat pump. Hence, the adsorption column was cooled down whereas the column under regeneration was warmed by the heat pump. An exptl. unit was designed and expts. were conducted with dichloromethane. The advantages of coupling the TSA process with a heat pump are twofold: the first benefit was for the adsorption step whose efficiency was increased. The decrease of temp. inside the fixed bed enabled a significant increase of breakthrough times (+30% on av.). The second benefit of using the heat pump during regeneration cycle is the warming of the activated carbon bed prior to steam desorption. Temps. up to 45 °C were measured during desorption when using the heat pump alone. Exptl., the results have shown an interesting recovery efficiency (up to 71%) during dichloromethane desorption if using only the heat pump. Numerical simulations, via the software ProSim DAC, predicted the expected process behaviors for dichloromethane on a larger scale: a TSA unit contg. 15 t of activated carbon. The results showed that the regeneration rate was not totally sufficient, 38.5%, and the use of a heat pump alone was not able to ensure the desorption of the VOC. Although the heap pump by itself was not sufficient to ensure the regeneration, the combination with the steam desorption shed light on new perspectives for the redn. of energy consumption.
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  (b) Wu, X.-F. W.; Tlili, A.; Schranck, J.; Wu, X.-F. W. The Application of Dichloromethane and Chloroform as Reagents in Organic Synthesis. Solvents as Reagents in Organic Synthesis 2017, 125– 159, DOI: 10.1002/9783527805624.ch4
  There is no corresponding record for this reference.
10. 10
  (a) Lautenschütz, L.; Oestreich, D.; Seidenspinner, P.; Arnold, U.; Dinjus, E.; Sauer, J. Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers. Fuel 2016, 173, 129– 137, DOI: 10.1016/j.fuel.2016.01.060
  10a
  Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers
  Lautenschuetz, Ludger; Oestreich, Dorian; Seidenspinner, Philipp; Arnold, Ulrich; Dinjus, Eckhard; Sauer, Joerg
  Fuel (2016), 173 (), 129-137CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
  Oligomeric oxymethylene di-Me ethers (OMDMEs, CH3O-(CH2O)n-CH3) are promising diesel fuel additives, which can reduce soot formation as well as NOx emissions. Due to the poor availability of high purity OMDMEs a comprehensive characterization of diesel stds. was not feasible until now. Two types of oxymethylene dialkylethers (OMDMEs and oxymethylene di-Et ethers, OMDEEs) were synthesized, purified and characterized with respect to their physico-chem. and fuel properties. D., m.p., flash point, auto ignition point as well as lubricity, kinematic viscosity and surface tension of OMDMEs and OMDEEs were measured and compared to the corresponding n-alkanes. Fuel requirements such as b.ps., flash points and surface tensions can be fulfilled by OMDMEs and OMDEEs. Furthermore, OMDMEs (n = 3-5) and OMDEEs (n = 2-4) are, due to their high cetane nos. of 124-180 and 64-103, particularly promising since cetane nos. in this range can lead to improved motor efficiency and smoother fuel combustion. Addnl., the heat of combustion as well as the std. enthalpy of formation and reaction were detd. Apart from somewhat lower heating values, OMDMEs exhibit fuel properties similar to conventional diesel complying the required fuel stds. without the need of changing engines or fuel infrastructures.
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  (b) Thenert, K.; Beydoun, K.; Wiesenthal, J.; Leitner, W.; Klankermayer, J. Ruthenium-Catalyzed Synthesis of Dialkoxymethane Ethers Utilizing Carbon Dioxide and Molecular Hydrogen. Angew. Chem., Int. Ed. 2016, 55, 12266– 12269, DOI: 10.1002/anie.201606427
  10b
  Ruthenium-Catalyzed Synthesis of Dialkoxymethane Ethers Utilizing Carbon Dioxide and Molecular Hydrogen
  Thenert, Katharina; Beydoun, Kassem; Wiesenthal, Jan; Leitner, Walter; Klankermayer, Juergen
  Angewandte Chemie, International Edition (2016), 55 (40), 12266-12269CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The synthesis of dimethoxymethane (DMM) by a multistep reaction of methanol with carbon dioxide and mol. hydrogen is reported. Using the mol. catalyst [Ru(triphos)(tmm)] in combination with the Lewis acid Al(OTf)3 resulted in a versatile catalytic system for the synthesis of various dialkoxymethane ethers. This new catalytic reaction provides the first synthetic example for the selective conversion of carbon dioxide and hydrogen into a formaldehyde oxidn. level, thus opening access to new mol. structures using this important C1 source.
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  (c) Schieweck, B. G.; Klankermayer, J. Tailor-made Molecular Cobalt Catalyst System for the Selective Transformation of Carbon Dioxide to Dialkoxymethane Ethers. Angew. Chem., Int. Ed. 2017, 56, 10854– 10857, DOI: 10.1002/anie.201702905
  10c
  Tailor-made Molecular Cobalt Catalyst System for the Selective Transformation of Carbon Dioxide to Dialkoxymethane Ethers
  Schieweck, Benjamin G.; Klankermayer, Juergen
  Angewandte Chemie, International Edition (2017), 56 (36), 10854-10857CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Herein a non-precious transition-metal catalyst system for the selective synthesis of dialkoxymethane ethers from carbon dioxide and mol. hydrogen is presented. The development of a tailored catalyst system based on cobalt salts in combination with selected Triphos ligands and acidic co-catalysts enabled a synthetic pathway, avoiding the oxidn. of methanol to attain the formaldehyde level of the central CH2 unit. This unprecedented productivity based on the mol. cobalt catalyst is the first example of a non-precious transition-metal system for this transformation utilizing renewable carbon dioxide sources.
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11. 11
  (a) El-Brollosy, N. R.; Jørgensen, P. T.; Dahan, B.; Boel, A. M.; Pedersen, E. B.; Nielsen, C. Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants. J. Med. Chem. 2002, 45, 5721– 5726, DOI: 10.1021/jm020949r
  11a
  Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants
  El-Brollosy, Nasser R.; Jorgensen, Per T.; Dahan, Berit; Boel, Anne Marie; Pedersen, Erik B.; Nielsen, Claus
  Journal of Medicinal Chemistry (2002), 45 (26), 5721-5726CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
  This paper reports the synthesis and the antiviral activities of a series of 6-arylmethyl-1-(allyloxymethyl)-5-alkyluracil derivs., which can be viewed as analogs of the anti-HIV-1 drug emivirine (formerly MKC-442) from which they differ in the replacement of the ethoxymethyl group with variously allyloxymethyl moieties. The most active compds. N-1 allyloxymethyl- and N-1 3-methylbut-2-enyl substituted 5-ethyl-6-(3,5-dimethylbenzyl)uracils (12 and 13) showed activity against HIV-1 wild-type in the picomolar range with selective index of greater than 5 × 106 and activity in the submicromolar range against the clin. important Y181C and K103N mutant strains known to be resistant to emivirine. Structure-activity relationship studies established a correlation between the anti-HIV-1 activity and the substitution pattern of the N-1 allyloxymethyl group.
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  (b) Wamberg, M.; Pedersen, E. B.; El-Brollosy, N. R.; Nielsen, C. Synthesis of 6-arylvinyl analogues of the HIV drugs SJ-3366 and Emivirine. Bioorg. Med. Chem. 2004, 12, 1141– 1149, DOI: 10.1016/j.bmc.2003.11.032
  11b
  Synthesis of 6-arylvinyl analogues of the HIV drugs SJ-3366 and Emivirine
  Wamberg, Michael; Pedersen, Erik B.; El-Brollosy, Nasser R.; Nielsen, Claus
  Bioorganic & Medicinal Chemistry (2004), 12 (5), 1141-1149CODEN: BMECEP; ISSN:0968-0896. (Elsevier Ltd.)
  This paper reports the synthesis and the antiviral activities of a series of 6-arylvinyl substituted analogs of SJ-3366, a highly potent agent against HIV. The objective was to investigate whether substitution of the 6-arylketone with a 6-arylvinyl group could leads to an improved antiviral activity against HIV-1. The most active compds., 1-ethoxymethyl, 1-(2-propynyloxymethyl), and 1-(2-methyl-3-phenylallyloxymethyl) substituted 6-[1-(3,5-dimethylphenyl)vinyl]-5-ethyl-1H-pyrimidine-2,4-dione showed activities against HIV-1 wild type in the range of Efavirenz, and moderate activities against Y181C and Y181C+K103N mutant strains were also obsd.
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  (c) Loksha, Y. M.; Pedersen, E. B.; Loddo, R.; Sanna, G.; Collu, G.; Giliberti, G.; Colla, P. L. Synthesis of Novel Fluoro Analogues of MKC442 as Microbicides. J. Med. Chem. 2014, 57, 5169– 5178, DOI: 10.1021/jm500139a
  11c
  Synthesis of Novel Fluoro Analogues of MKC442 as Microbicides
  Loksha, Yasser M.; Pedersen, Erik B.; Loddo, Roberta; Sanna, Giuseppina; Collu, Gabriella; Giliberti, Gabriele; Colla, Paolo La
  Journal of Medicinal Chemistry (2014), 57 (12), 5169-5178CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
  Novel analogs of MKC442 [6-benzyl-1-(ethoxymethyl)-5-isopropylpyrimidine-2,4(1H,3H)-dione] were synthesized by reaction of 6-[(3,5-dimethylphenyl)fluoromethyl]-5-ethyluracil (I) with ethoxymethyl chloride and formaldehyde acetals. The Sonogashira reaction was carried out on the N1-[(p-iodobenzyl)oxy]methyl deriv. of compd. I using propargyl alc. to afford compd. II (YML220). The latter compd. was selected for further studies since it showed the most potent and selective activity in vitro against wild-type HIV-1 and non-nucleoside reverse transcriptase inhibitor-, nucleoside reverse transcriptase inhibitor-, and protease inhibitor-resistant mutants and a wide range of HIV-1 clin. isolates. II also showed microbicidal activity in long-term assays with heavily infected MT-4 cells.
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12. 12
  (a) Makosza, M.; Sypniewski, M. Reaction of sulfonium salts of formaldehyde dithioacetals with aromatic aldehydes and rearrangements of the produced thioalkyl oxiranes. Tetrahedron 1995, 51, 10593– 10600, DOI: 10.1016/0040-4020(95)00632-I
  12a
  Reaction of sulfonium salts of formaldehyde dithioacetals with aromatic aldehydes and rearrangements of the produced thioalkyl oxiranes
  Makosza, Mieczyslaw; Sypniewski, Michal
  Tetrahedron (1995), 51 (38), 10593-600CODEN: TETRAB; ISSN:0040-4020. (Elsevier)
  Arom. aldehydes react with sulfur ylides generated from sulfonium salts of formaldehyde dithioacetals to give corresponding 2-thioalkyl-3-aryloxiranes. Depending on substituents in arom. rings the oxiranes undergo rearrangements or are sufficiently stable to be isolated. To p-tolualdehyde and (4-chlorophenylthiomethyl)dimethylsulfonium iodide in DMF was added NaOH to give cis- and trans-2-(methylthio)-3-(4-methylphenyl)oxirane which did rearranged to 4'-methyl-2-hydroxyacetophenone.
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  (b) Luh, T.-Y. Recent advances on the synthetic applications of the dithioacetal functionality. J. Organomet. Chem. 2002, 653, 209– 214, DOI: 10.1016/S0022-328X(02)01151-8
  12b
  Recent advances in the synthetic applications of the dithioacetal functionality
  Luh, Tien-Yau
  Journal of Organometallic Chemistry (2002), 653 (1-2), 209-214CODEN: JORCAI; ISSN:0022-328X. (Elsevier Science B.V.)
  A review. The nickel-catalyzed silylolefination reaction has led to the synthesis of a range of silyl-substituted olefins for optoelectronic interests. The reactions of propargylic dithioacetals with organocopper or lithium reagents, followed by treatment with electrophiles, yield sulfur-substituted allenes. Further cross coupling with Grignard reagents in the presence of a nickel catalyst affords highly substituted allenes. Acid-catalyzed cyclization of the sulfur-substituted allenyl alcs. furnishes a useful route to oligoaryls having highly substituted furan or pyrrole moieties.
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13. 13
  (a) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez, A. Heteroscorpionate ligands based on bis(pyrazol-1-yl)methane: design and coordination chemistry. Dalton Trans. 2004, 10, 1499– 1510, DOI: 10.1039/B401425A
  There is no corresponding record for this reference.
  (b) Krieck, S.; Koch, A.; Hinze, K.; Müller, C.; Lange, J.; Görls, H.; Westerhausen, M. s-Block Metal Complexes with Bis- and Tris(pyrazolyl)methane and -methanide Ligands. Eur. J. Inorg. Chem. 2016, 15, 2332– 2348, DOI: 10.1002/ejic.201501263
  There is no corresponding record for this reference.
14. 14
  (a) Csok, Z.; Vechorkin, O.; Harkins, S. B.; Scopelliti, R.; Hu, X. Nickel Complexes of a Pincer NN₂ Ligand: Multiple Carbon-Chloride Activation of CH₂Cl₂ and CHCl₃ Leads to Selective Carbon-Carbon Bond Formation. J. Am. Chem. Soc. 2008, 130, 8156– 8157, DOI: 10.1021/ja8025938
  14a
  Nickel complexes of a pincer NN2 ligand: multiple carbon-chloride activation of CH2Cl2 and CHCl3 leads to selective carbon-carbon bond formation
  Csok, Zsolt; Vechorkin, Oleg; Harkins, Seth B.; Scopelliti, Rosario; Hu, Xile
  Journal of the American Chemical Society (2008), 130 (26), 8156-8157CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A new pincer-type bis(amido)amine (NN2) ligand and its lithium and nickel complexes, including Ni(II) Me, Et, and Ph complexes, were synthesized. The Ni(II) alkyl complexes react cleanly with alkyl halides including chlorides to form C-C coupled products and Ni(II) halides. More interestingly, the Ni(II) alkyls undergo unprecedented reactions with CH2Cl2 and CHCl3 to cleave all the C-Cl bonds and replace them with C-C bonds. The reactions are highly selective and lead to the first efficient catalytic coupling of CH2Cl2 with alkyl Grignards. A conversion of 82% and a turnover no. of 47 are achieved within minutes. Coupling of CD2Cl2 and 1,1-dichloro-3,3-dimethylbutane with nBuMgCl is also realized. Preliminary mechanistic study suggests a radical initiated process for these reactions.
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  (b) Zhan, L.; Pan, R.; Xing, P.; Jiang, B. An efficient method for the preparation of dialkoxymethanes from dichloromethane with alcohols catalyzed by a Cu-NHC complex. Tetrahedron Lett. 2016, 57, 4036– 4038, DOI: 10.1016/j.tetlet.2016.07.056
  14b
  An efficient method for the preparation of dialkoxymethanes from dichloromethane with alcohols catalyzed by a Cu-NHC complex
  Zhan, Lewu; Pan, Renming; Xing, Ping; Jiang, Biao
  Tetrahedron Letters (2016), 57 (36), 4036-4038CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
  A facile, rapid and efficient method for the prepn. of dialkoxymethanes from dichloromethane with alcs. catalyzed by a Cu-NHC complex is reported. A variety of sym. dialkoxymethanes can be prepd. under mild condition in excellent yields (up to 98%). The unsym. ether is also obtained in 89% yield from the etherification of p-tolylmethanol and Bu chloride catalyzed by ICyCuCl complex at 80 °C. The reaction provides a new method for the prepn. of dialkoxymethanes under mild conditions in excellent yields.
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15. 15
  Lamb, J. R.; Brown, C. M.; Johnson, J. A. N-Heterocyclic carbene–carbodiimide (NHC–CDI) betaine adducts: synthesis, characterization, properties, and applications. Chem. Sci. 2021, 12, 2699– 2715, DOI: 10.1039/D0SC06465C
  15
  N-Heterocyclic carbene-carbodiimide (NHC-CDI) betaine adducts: synthesis, characterization, properties, and applications
  Lamb, Jessica R.; Brown, Christopher M.; Johnson, Jeremiah A.
  Chemical Science (2021), 12 (8), 2699-2715CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  A review. An emerging class of betaine adducts made from the reaction of NHCs with carbodiimides (CDIs) form zwitterionic amidinate-like structures with tunable properties based on the highly modular NHC and CDI scaffolds. The adduct stability was controlled by the substituents on the CDI nitrogens, while the NHC substituents greatly affect the configuration of the adduct in the solid state. This Perspective was intended as a primer to these adducts, touching on their history, synthesis, characterization and general properties. Despite the infancy of the field, NHC-CDI adducts had been applied as amidinate-type ligands for transition metals and nanoparticles, as junctions in zwitterionic polymers, and to stabilize distonic radical cations, these applications and potential future directions were discussed.
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16. 16
  Baishya, A.; Kumar, L.; Barman, M. K.; Peddarao, T.; Nembenna, S. Air Stable N-Heterocyclic Carbene-Carbodiimide (“NHC-CDI”) Adducts: Zwitterionic Type Bulky Amidinates. ChemistrySelect 2016, 1, 498– 503, DOI: 10.1002/slct.201600019
  16
  Air Stable N-Heterocyclic Carbene-Carbodiimide (''NHC-CDI'') Adducts: Zwitterionic Type Bulky Amidinates
  Baishya, Ashim; Kumar, Lokesh; Barman, Milan Kr.; Peddarao, Thota; Nembenna, Sharanappa
  ChemistrySelect (2016), 1 (3), 498-503CODEN: CHEMUD; ISSN:2365-6549. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A library of N-heterocyclic carbene-carbodiimide (''NHC-CDI'') adducts i. e., zwitterionic type amidinates from the reaction between N,N'-diaryl substituted sym. or unsym. carbodiimide and N-heterocyclic carbene at room temp. conditions were reported. Generally, normal amidinates are air and moisture sensitive; that can be achieved by the treatment of amidines with base under air and moisture free conditions. In contrast, these new zwitterionic type bulky amidinate compds. were neutral and air stable. All new 31 examples of ''NHC-CDI'' adducts were characterized by 1H, 13C{1H} and HRMS analyses. Further, six compds. were confirmed by single crystal X-ray structural anal.
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17. 17
  (a) Márquez, A.; Ávila, E.; Urbaneja, C.; Álvarez, E.; Palma, P.; Cámpora, J. Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands. Inorg. Chem. 2015, 54, 11007– 11017, DOI: 10.1021/acs.inorgchem.5b02141
  17a
  Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands
  Marquez, Astrid; Avila, Elena; Urbaneja, Carmen; Alvarez, Eleuterio; Palma, Pilar; Campora, Juan
  Inorganic Chemistry (2015), 54 (22), 11007-11017CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  The 1st complexes contg. imidazolium-2-amidinates as ligands (betaine-type adducts of imidazolium-based carbenes and carbodiimides, NHC-CDI) are reported. Interaction of the sterically hindered betaines ICyCDIDiPP and IMeCDIDiPP [both bearing 2,6-diisopropylphenyl (DiPP) substituents on the terminal N atoms] with Cu(I) acetate affords mononuclear, electroneutral complexes (1a and 1b), which contain NHC-CDI and acetate ligands terminally bound to linear Cu(I) centers. In contrast, the less encumbered ligand ICyCDIp-Tol, with p-tolyl substituents on the N donor atoms, affords a dicationic trigonal paddlewheel complex, [Cu2(μ-ICyCDIp-Tol)3]2+[OAc-]2 (2-OAc). The NMR resonances of 2-OAc are broad and indicate that in soln. the acetate anion and the betaine ligands compete for binding the Cu atom. Replacing the external acetate with the less coordinating tetraphenylborate anion provides the corresponding deriv. 2-BPh4 that, in contrast with 2-OAc, gives rise to sharp and well-defined NMR spectra. The short Cu-Cu distance in the binuclear dication [Cu2(μ-ICyCDIp-Tol)3]2+ obsd. in the x-ray structures of 2-BPh4 and 2-OAc, ∼2.42 Å, points to a relatively strong cuprophilic interaction. Attempts to force the bridging coordination mode of IMeCDIDiPP displacing the acetate anion with BPh4- gave the cationic mononuclear deriv. [Cu(IMeCDIDiPP)2]+[BPh4]- (3b) that contains two terminally bound betaine ligands. Compd. 3b readily decomps. upon being heated, cleanly affording the bis-carbene complex [Cu(IMe)2]+[BPh4-] (4) and releasing the corresponding carbodiimide (C(=N-DiPP)2).
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  (b) Baishya, A.; Kumar, L.; Barman, M. K.; Biswal, H. S.; Nembenna, S. N-Heterocyclic Carbene–Carbodiimide (“NHC–CDI”) Adduct or Zwitterionic-Type Neutral Amidinate-Supported Magnesium(II) and Zinc(II) Complexes. Inorg. Chem. 2017, 56, 9535– 9546, DOI: 10.1021/acs.inorgchem.7b00879
  17b
  N-Heterocyclic Carbene-Carbodiimide ("NHC-CDI") Adduct or Zwitterionic-Type Neutral Amidinate-Supported Magnesium(II) and Zinc(II) Complexes
  Baishya, Ashim; Kumar, Lokesh; Barman, Milan Kr.; Biswal, Himansu S.; Nembenna, Sharanappa
  Inorganic Chemistry (2017), 56 (16), 9535-9546CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Structurally characterized Mg and Zn complexes L4-t-BuPh-M{N(SiMe3)2}2 [M = Mg (1) and Zn (2); L4-t-BuPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-t-butylphenyl)amidinate}], L4-iPrPh-M{N(SiMe3)2}2 [M = Mg (3) and Zn (4); L4-iPrPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-isopropylphenyl)amidinate}] and L4-iPrPh-ZnEt2 (5) bearing zwitterionic type neutral amidinate or N-heterocyclic carbene-carbodiimide (NHC-CDI) adduct and monoanionic amido or alkyl ligands are reported. The synthesis of compds. 1-5 was achieved by the direct addn. of NHC-CDI adduct to a corresponding metal bis(amide) or dialkyl reagent. All compds. 1-5 exist as monomers in the solid state. In all cases, the metal (Mg or Zn) centers adopt a distorted four-coordinate tetrahedral geometry bonded to one N,N'-chelated neutral zwitterionic ligand and two monoanionic amido or alkyl moieties. In contrast, sterically bulky zwitterionic amidinate LDipp [LDipp = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(2,6-diisopropylphenyl)amidinate}] upon treatment with Li bis-trimethylsilylamide, Li{N(SiMe3)2} affords the NHC-Li complex, MeIEt-[Li{N(SiMe3)2}]2 (6), in which one mol. of NHC (MeIEt = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) coordinates to one of the two Li centers. In a similar way, the reaction between LDipp and Mg{N(SiMe3)2}2 allowed to the formation of a NHC adduct of metal bis(amide), MeIEt-Mg{N(SiMe3)2}2 (7), instead of zwitterionic adduct of metal bis(amide). Alternatively, the synthesis of both compds. 6 and 7 was achieved by the direct addn. of one equiv. of NHC i.e. MeIEt to Li{N(SiMe3)2} (2.0 equiv) and Mg{N(SiMe3)2}2 (1.0 equiv) in benzene-d6, resp. All compds. (1-7) were characterized by multinuclear {1H, 13C, 29Si (for 1 , 2, 3, 4, 6 and 7) and 7Li (for compd. 6)} magnetic resonance spectroscopy, mass spectrometry, elemental anal. and single crystal x-ray structural anal. Preliminary reactivity studies of zwitterion supported metal complexes were carried out. The energetics of zwitterion supported Li and Mg complexes were obtained by d. functional theory (DFT) calcns.
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18. 18
  (a) Martínez-Prieto, L. M.; Cano, I.; Márquez, A.; Baquero, E. A.; Tricard, S.; Cusinato, L.; del Rosal, I.; Poteau, R.; Coppel, Y.; Philippot, K.; Chaudret, B.; Cámpora, J.; van Leeuwen, P. W. N. M. Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts. Chem. Sci. 2017, 8, 2931– 2941, DOI: 10.1039/C6SC05551F
  18a
  Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts
  Martinez-Prieto, L. M.; Cano, I.; Marquez, A.; Baquero, E. A.; Tricard, S.; Cusinato, L.; del Rosal, I.; Poteau, R.; Coppel, Y.; Philippot, K.; Chaudret, B.; Campora, J.; van Leeuwen, P. W. N. M.
  Chemical Science (2017), 8 (4), 2931-2941CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  Ligand control of metal nanoparticles (MNPs) is rapidly gaining importance as ligands can stabilize the MNPs and regulate their catalytic properties. Herein we report the first example of Pt NPs ligated by imidazolium-amidinate ligands that bind strongly through the amidinate anion to the platinum surface atoms. The binding was established by 15N NMR spectroscopy, a precedent for nitrogen ligands on MNPs, and XPS. Both monodentate and bidentate coordination modes were found. DFT showed a high bonding energy of up to -48 kcal mol-1 for bidentate bonding to two adjacent metal atoms, which decreased to -28 ± 4 kcal mol-1 for monodentate bonding in the absence of impediments by other ligands. While the surface is densely covered with ligands, both IR and 13C MAS NMR spectra proved the adsorption of CO on the surface and thus the availability of sites for catalysis. A particle size dependent Knight shift was obsd. in the 13C MAS NMR spectra for the atoms that coordinate to the surface, but for small particles, ∼1.2 nm, it almost vanished, as theory for MNPs predicts; this had not been exptl. verified before. The Pt NPs were found to be catalysts for the hydrogenation of ketones and a notable ligand effect was obsd. in the hydrogenation of electron-poor carbonyl groups. The catalytic activity is influenced by remote electron donor/acceptor groups introduced in the aryl-N-substituents of the amidinates; p-anisyl groups on the ligand gave catalysts several times faster the ligand contg. p-chlorophenyl groups.
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  (b) López-Vinasco, A. M.; Martínez-Prieto, L. M.; Asensio, J. M.; Lecante, P.; Chaudret, B.; Cámpora, J.; van Leeuwen, P. W. N. M. Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes. Catal. Sci. Technol. 2020, 10, 342– 350, DOI: 10.1039/C9CY02172H
  18b
  Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes
  Lopez-Vinasco, Angela M.; Martinez-Prieto, Luis M.; Asensio, Juan M.; Lecante, Pierre; Chaudret, Bruno; Campora, Juan; van Leeuwen, Piet W. N. M.
  Catalysis Science & Technology (2020), 10 (2), 342-350CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-redn. to the corresponding alkane. In addn., the prepn. of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepd. Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temp., 3% mol Ni and 1 bar H2). The catalytic behavior of Ni NPs was influenced by the electron donor/acceptor groups (-Me, -OMe, -Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling expts. were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.
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19. 19
  Gallagher, N. M.; Zhukhovitskiy, A. V.; Nguyen, H. V. T.; Johnson, J. A. Main-Chain Zwitterionic Supramolecular Polymers Derived from N-Heterocyclic Carbene–Carbodiimide (NHC–CDI) Adducts. Macromolecules 2018, 51, 3006– 3016, DOI: 10.1021/acs.macromol.8b00579
  19
  Main-Chain Zwitterionic Supramolecular Polymers Derived from N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Adducts
  Gallagher, Nolan M.; Zhukhovitskiy, Aleksandr V.; Nguyen, Hung V.-T.; Johnson, Jeremiah A.
  Macromolecules (Washington, DC, United States) (2018), 51 (8), 3006-3016CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Polyzwitterions have found extensive applications in biol. and materials sciences. Despite this success, most polyzwitterions have nondegradable polyolefin backbones with pendant zwitterionic groups. Transcension of this structural paradigm via the formation of main-chain zwitterionic supramol. polymers could lead to readily processable, as well as self-healing and/or degradable, polyzwitterions. Herein, we report the synthesis and characterization of poly(azolium amidinate)s (PAzAms), which are a new class of supramol. main-chain polyzwitterions assembled via the formation of N-heterocyclic carbene-carbodiimide (NHC-CDI) adducts. These polymers exhibit a wide range of tunable dynamic properties due to the highly structure-sensitive equil. between the NHC-CDI adduct and its constituent NHCs and CDIs: e.g., PAzAms derived from N-aryl-N'-alkyl CDIs are dynamic at lower temps. than those derived from N,N'-diaryl CDIs. We develop a versatile synthetic platform that provides access to PAzAms with control over the main-chain charge sequence and mol. wt. In addn., block copolymers incorporating PAzAm and poly(ethylene glycol) (PEG) blocks are water sol. (>30 mg mL-1) and self-assemble in aq. environments. This work defines structure-property relationships for a new class of degradable main-chain zwitterionic supramol. polymers, setting the stage for the development of these polymers in a range of applications.
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20. 20
  Gallagher, N. M.; Ye, H.-Z.; Feng, S.; Lopez, J.; Zhu, Y. G.; Van Voorhis, T.; Shao-Horn, Y.; Johnson, J. A. An N-Heterocyclic-Carbene-Derived Distonic Radical Cation. Angew. Chem., Int. Ed. 2020, 59, 3952– 3955, DOI: 10.1002/anie.201915534
  20
  An N-Heterocyclic-Carbene-Derived Distonic Radical Cation
  Gallagher, Nolan M.; Ye, Hong-Zhou; Feng, Shuting; Lopez, Jeffrey; Zhu, Yun Guang; Van Voorhis, Troy; Shao-Horn, Yang; Johnson, Jeremiah A.
  Angewandte Chemie, International Edition (2020), 59 (10), 3952-3955CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  We present the discovery of a novel radical cation formed through one-electron oxidn. of an N-heterocyclic carbene-carbodiimide (NHC-CDI) zwitterionic adduct. This compd. possesses a distonic electronic structure (spatially sep. spin and charge regions) and displays persistence under ambient conditions. We demonstrate its application in a redox-flow battery exhibiting minimal voltage hysteresis, a flat voltage plateau, high Coulombic efficiency, and no performance decay for at least 100 cycles. The chem. tunability of NHCs and CDIs suggests that this approach could provide a general entry to redox-active NHC-CDI adducts and their persistent radical ions for various applications.
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21. 21
  Sánchez-Roa, D.; Santiago, T. G.; Fernández-Millán, M.; Cuenca, T.; Palma, P.; Cámpora, J.; Mosquera, M. E. G. Interaction of an imidazolium-2-amidinate (NHC-CDI) zwitterion with zinc dichloride in dichloromethane: role as ligands and C–Cl activation promoters. Chem. Commun. 2018, 54, 12586– 12589, DOI: 10.1039/C8CC07661H
  21
  Interaction of an imidazolium-2-amidinate (NHC-CDI) zwitterion with zinc dichloride in dichloromethane: role as ligands and C-Cl activation promoters
  Sanchez-Roa, David; Santiago, Tomas G.; Fernandez-Millan, Maria; Cuenca, Tomas; Palma, Pilar; Campora, Juan; Mosquera, Marta E. G.
  Chemical Communications (Cambridge, United Kingdom) (2018), 54 (89), 12586-12589CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Adducts of imidazolium carbenes and carbodiimides (NHC-CDI) are emerging as a new class of thermally stable and modular zwitterions with many potential applications. Our study of the interaction of a representative NHC-CDI zwitterion with ZnCl2 in dichloromethane led to the serendipitous discovery of a highly selective, double activation of dichloromethane C-Cl bonds.
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22. 22
  (a) Rivlin, M.; Eliav, U.; Navon, G. NMR Studies of the Equilibria and Reaction Rates in Aqueous Solutions of Formaldehyde. J. Phys. Chem. B 2015, 119, 4479– 4487, DOI: 10.1021/jp513020y
  22a
  NMR Studies of the Equilibria and Reaction Rates in Aqueous Solutions of Formaldehyde
  Rivlin, Michal; Eliav, Uzi; Navon, Gil
  Journal of Physical Chemistry B (2015), 119 (12), 4479-4487CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
  Formaldehyde has an important role in the chem. industry and in biol. sciences. In dil. aq. solns. of formaldehyde only traces of the mol. formaldehyde are present and the predominant species are methylene glycol and in lower concns., dimethylene glycol. The chem. equil. and reaction rates of the hydration of formaldehyde in H2O and D2O solns. at low concns. were studied by 1H and 13C NMR at various conditions of pH (1.8-7.8) and temp. (278-333 K). These measurements became possible by direct detection of formaldehyde 13C and 1H peaks. The equil. and rate consts. of the dimerization reaction of methylene glycol were also measured. The rate consts. for both the hydration and the dimerization reactions were measured by a new version of the conventional selective inversion transfer method. This study, together with previous published work, completes the description of dynamics and equil. of all the processes occurring in dil. aq. formaldehyde solns.
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  (b) Dankelman, W.; Daemen, J. M. H. Gas Chromatographic and Nuclear Magnetic Resonance Determination of Linear Formaldehyde Oligomers in Formaline. Anal. Chem. 1976, 48, 401– 404, DOI: 10.1021/ac60366a030
  22b
  Gas chromatographic and nuclear magnetic resonance determination of linear formaldehyde oligomers in formalin
  Dankelman, Wim; Daemen, Jacq. M. H.
  Analytical Chemistry (1976), 48 (2), 401-4CODEN: ANCHAM; ISSN:0003-2700.
  The oligomer distribution of polyoxymethylene glycols in formalin solns. can be detd. up to the heptamer [HO(CH2O)nH, n = 7] by direct silylation with BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide), followed by gas chromatog. anal. on a column filled with 10% OV-1 on Chromosorb W. The results were corroborated with a 220-MHz NMR anal. Only at 220 MHz is the water signal sufficiently sepd. from the methylene H absorptions. The exact amts. of the oligomers with n = 1 and n = 2 and the sum of n ≥3 can be detd. by NMR. The results are in accordance with the gas chromatog. anal. MeOH, added as a stabilizer to avoid pptn. of paraformaldehyde, breaks down high mol. oligomers of polymethylene glycols, thereby forming more sol. compds.
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23. 23
  (a) Li, M.; Long, Y.; Deng, Z.; Zhang, H.; Yang, X.; Wang, G. Ruthenium trichloride as a new catalyst for selective production of dimethoxymethane from liquid methanol with molecular oxygen as sole oxidant. Catal. Commun. 2015, 68, 46– 48, DOI: 10.1016/j.catcom.2015.04.031
  23a
  Ruthenium trichloride as a new catalyst for selective production of dimethoxymethane from liquid methanol with molecular oxygen as sole oxidant
  Li, Meilan; Long, Yan; Deng, Zhiyong; Zhang, Hua; Yang, Xiangui; Wang, Gongying
  Catalysis Communications (2015), 68 (), 46-48CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
  Dimethoxymethane was first synthesized from methanol with a liq. phase intermittent process which only used mol. oxygen as the sole oxidant. RuCl3 was proved to be an efficient catalyst as it showed ability of oxidizing methanol and Lewis acidic which promotes the oxidn. of methanol to formaldehyde and then methanol condensed with formaldehyde to form dimethoxymethane at Lewis acid site.
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  (b) Thavornprasert, K.-a.; Capron, M.; Jalowiecki-Duhamel, L.; Dumeignil, F. One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts. Catal. Sci. Technol. 2016, 6, 958– 970, DOI: 10.1039/C5CY01858G
  23b
  One-pot 1,1-dimethoxymethane synthesis from methanol: a promising pathway over bifunctional catalysts
  Thavornprasert, Kaew-arpha; Capron, Mickael; Jalowiecki-Duhamel, Louise; Dumeignil, Franck
  Catalysis Science & Technology (2016), 6 (4), 958-970CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  Dimethoxymethane or DMM is a versatile chem. with applications in many industries such as paints, perfume, pharmacy, and fuel additives. DMM can be produced through the reaction of methanol and formaldehyde in the presence of acid catalysts or, directly, through the selective oxidn. of methanol over catalysts with redox and acid functionalities. In terms of sustainability, the so-called bio-methanol derived from syngas obtained via biomass gasification can be used in DMM synthesis. In this review article, we have condensed and classified the research outputs published over the past decade aimed at producing DMM from methanol over different types of catalysts. The majority of studies described the reaction of methanol to DMM in a promising way using heterogeneous catalysts in the gas phase for the ease of product and catalyst recovery as well as suitability for continuous processing. Likewise, the influence of parameters including catalyst component, feed compn., and temp. on the performance of catalysts utilized in DMM prodn. is analyzed and discussed. Further, some perspectives concerning the evolution of potential DMM market with respect to the characteristics of the best catalyst materials for high DMM productivity are expressed.
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  (c) Chao, Y.; Lai, J.; Yang, Y.; Zhou, P.; Zhang, Y.; Mu, Z.; Li, S.; Zheng, J.; Zhu, Z.; Tan, Y. Visible light-driven methanol dehydrogenation and conversion into 1,1-dimethoxymethane over a non-noble metal photocatalyst under acidic conditions. Catal. Sci. Technol. 2018, 8, 3372– 3378, DOI: 10.1039/C8CY01030G
  23c
  Visible light-driven methanol dehydrogenation and conversion into 1,1-dimethoxymethane over a non-noble metal photocatalyst under acidic conditions
  Chao, Yuguang; Lai, Jianping; Yang, Yong; Zhou, Peng; Zhang, Yelong; Mu, Zijie; Li, Shiying; Zheng, Jianfeng; Zhu, Zhenping; Tan, Yisheng
  Catalysis Science & Technology (2018), 8 (13), 3372-3378CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  The dehydrogenation and conversion of methanol into 1,1-dimethoxymethane (DMM) was achieved over noble metal-free photocatalyst CdS/Ni2P under visible light. This photocatalytic process for methanol-to-H2 and DMM conversion is efficient and atom economic, with an optimal rate and selectivity of DMM of 188.42 mmol g-1 h-1 and 82.93%, resp. This work supplies a new green approach for the direct efficient conversion of methanol into DMM and provides a promising avenue for sustainable bio-methanol applications.
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24. 24
  Łojewska, J.; Wasilewski, J.; Terelak, K.; Łojewski, T.; Kołodziej, A. Selective oxidation of methylal as a new catalytic route to concentrated formaldehyde: Reaction kinetic profile in gradientless flow reactor. Catal. Commun. 2008, 9, 1833– 1837, DOI: 10.1016/j.catcom.2008.02.014
  24
  Selective oxidation of methylal as a new catalytic route to concentrated formaldehyde: Reaction kinetic profile in gradientless flow reactor
  Lojewska, J.; Wasilewski, J.; Terelak, K.; Lojewski, T.; Kolodziej, A.
  Catalysis Communications (2008), 9 (9), 1833-1837CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
  Catalytic selective oxidn. of methylal (dimethoxy methane, DMM) was regarded as a new alternative for the prodn. of highly concd. formaldehyde. The aim of this work was to study the reaction kinetics in order to find optimum reaction conditions. The reaction was tested on iron-molybdenum mixed oxide catalysts in gradientless stirred jet reactor operating at atm. pressure. The activity and selectivity of the catalyst prepd. in our lab. has proved similar to the industrial catalyst. It has been demonstrated that the highest selectivity towards formaldehyde 90% is achieved at a fairly narrow parameter window: temp. in the range 230-260°, at a contact time around 1 s, in the reaction mixt. contg. O2:N2:(CH3)2CH2O2:H2O = 0.08:0.76:0.11:0.05.
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25. 25
  (a) Arnhold, M. Zur Kenntniss des dreibasischen Ameisensäureäthers und verschiedener Methylale. Justus Liebigs Ann. Chem. 1887, 240, 192– 208, DOI: 10.1002/jlac.18872400204
  There is no corresponding record for this reference.
  (b) Löbering, J.; Fleischmann, A. Über Mono- und Dioxymethylen-dimethyläther. Ber. Dtsch. Chem. Ges. B 1937, 70, 1680– 1683, DOI: 10.1002/cber.19370700807
  25b
  Mono- and dihydroxymethylene dimethyl ethers
  Lobering, J.; Fleischmann, A.
  Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen (1937), 70B (), 1680-3CODEN: BDCBAD; ISSN:0365-9488.
  The methods of prepg. CH2(OMe)2 (I) and O(CH2OMe)2 (II) given in the literature are unsatisfactory, especially as regards homogeneity of the products. I prepd. according to Fischer and Giebe (Ber. 30, 3053(1897)) by refluxing MeOH, paraformaldehyde and HCl at 100° and distg. after 12 hrs. b760 42.3°. The end values for HCHO content obtained in decompn. measurements on this product (III) were only 81-4% of the calcd. values. That this was not due to the equil. in the reaction CH2(OMe)2 ↹ HCHO + 2MeOH not lying practically completely to the right was shown by the fact that no higher values were obtained when the HCHO was removed. This was demonstrated by treating III with a definite amt. of I, acidifying, making alk. from time to time (the liberated HCHO thereby being oxidized by the hypoiodite) and finally titrating the excess of I. It was suspected III might be an azeotropic mixt. of 2 mols. I and 1 mol. MeOH; a vapor density detn. (Victor Meyer method) gave 58.5-62.5 for the mol. wt. Breaking down the azeotropic mixt. indirectly through ternary mixts. with various "3rd substances" gave no definite results, but with p-O2NC6H4COCl it was found possible to remove the MeOH from the III; the filtrate now b. 39-40°. In order, however, to exclude the presence of MeOH from the very start, alc.-free NaOMe and CH2Cl2 were used for the synthesis of I; NaOMe mixed with pumice was placed in a tube 60 cm. long heated to 200° and CH2Cl2 was passed over it. I, MeOCH2Cl and unreacted CH2Cl2 distd. from the outlet end of the tube; the MeOCH2Cl, b. 61°, and CH2Cl2, b. 41°, were condensed in an upright condenser and again passed through the tube, while the I, passing through the condenser, was collected in a receiver cooled with CO2 snow. It boiled 33-5° and on decompn. gave 99.6-101.2% HCHO. It can be prepd. somewhat more simply by refluxing (cooling liquid, about 25-30°) an equimol. mixt. of MeOCH2Cl and alc.-free NaOMe. II was prepd. by Backes' method (C. A. 27, 4225), with some modifications; exactly equiv. amts. of paraformaldehyde and POCl3 were gently boiled some hrs. under a reflux, then distd., and the (ClCH2)2O fraction, b. 103°, was slowly dropped upon alc.-free NaOMe under a reflux. A violent reaction occurred, which necessitated cooling. The product was distd., the distillate (which contained much HCl, water and a trace of POCl3) was treated with cold KOH and again distd., yielding a II, b. 91-3°, which gave 101.4% of the calcd. amt. of HCHO. I and II when not quite pure polymerize rapidly, while the pure products are stable indefinitely. The dimers are considerably less sol. in water than the monomers.
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26. 26
  Direct separation of methylal from DCM is a technical problem that can be efficiently addressed by special distillation techniques. See, for example:Berg, L. Separation of methylene vhloride from methylal by extractive distillation. US Patent US5051153A. Sept. 24, 1991.
  There is no corresponding record for this reference.
27. 27
  Giacalone, F.; Gruttadauria, M.; Agrigento, P.; Noto, R. Low-loading asymmetric organocatalysis. Chem. Soc. Rev. 2012, 41, 2406– 2447, DOI: 10.1039/C1CS15206H
  27
  Low-loading asymmetric organocatalysis
  Giacalone, Francesco; Gruttadauria, Michelangelo; Agrigento, Paola; Noto, Renato
  Chemical Society Reviews (2012), 41 (6), 2406-2447CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  This crit. review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Bronsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, and phase-transfer and N-heterocyclic carbene catalyzes.
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28. 28
  The TOF figure allows an estimation of the pseudo-first-order rate for the dichloromethane activation in the order k′ ≈ 10^–2 s^–1 (=45 h^–1/3600 s h^–1). We have shown before that the reaction of 1a with DCM is very slow at room temperature but completes within 24 h at 60 °C. Thus, taking the latter value as an indicative value for the half-life of 1a in DCM at 40 °C, the pseudo-first-order rate for this reaction should be in the order of 10^–5 s^–1 (k′ = Ln(2)/t_1/2).
  There is no corresponding record for this reference.
29. 29
  (a) Dehmlow, E. V. Advances in Phase-Transfer Catalysis [New synthetic methods (20)]. Angew. Chem., Int. Ed. Engl. 1977, 16, 493– 505, DOI: 10.1002/anie.197704933
  There is no corresponding record for this reference.
  (b) Makosza, M.; Fedoryński, M.; Eley, D. D.; Pines, H.; Weisz, P. B. Catalysis in Two-Phase Systems: Phase Transfer and Related Phenomena. Adv. Catal. 1987, 35, 375– 422, DOI: 10.1016/S0360-0564(08)60097-8
  29b
  Catalysis in two-phase systems: phase transfer and related phenomena
  Makosza, Mieczyslaw; Fedorynski, Michal
  Advances in Catalysis (1987), 35 (), 375-422CODEN: ADCAAX; ISSN:0065-2342.
  Leading examples of phase transfer catalysis, as well as mechanistic questions pertaining to its specific features, are discussed in this review with 180 refs.
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30. 30
  (b) Makosza, M. Phase-transfer catalysis. A general green methodology in organic synthesis. Pure Appl. Chem. 2000, 72, 1399– 1403, DOI: 10.1351/pac200072071399
  30b
  Phase-transfer catalysis. A general green methodology in organic synthesis
  Makosza, Mieczyslaw
  Pure and Applied Chemistry (2000), 72 (7), 1399-1403CODEN: PACHAS; ISSN:0033-4545. (International Union of Pure and Applied Chemistry)
  A review with 9 refs. Basic concept of phase-transfer catalysis (PTC), its field of applications and specific features as the most general, efficient, and environment-friendly green methodol. of org. synthesis, particularly for industrial processes, is discussed.
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  (a) Liotta, C. L.; Berkner, J.; Wright, J.; Fair, B. Mechanisms and Applications of Solid─Liquid Phase-Transfer Catalysis. Phase-Transfer Catalysis 1997, 659, 29– 40, DOI: 10.1021/bk-1997-0659.ch003
  There is no corresponding record for this reference.
31. 31
  Díez-Barra, E.; Hoz, A.; Sánchez-Migallón, A.; Tejeda, J. Phase transfer catalysis without solvent: synthesis of bisazolylalkanes. Heterocycles 1992, 34, 1365– 1373, DOI: 10.3987/COM-92-6024
  31
  Phase transfer catalysis without solvent. Synthesis of bisazolylalkanes
  Diez-Barra, Enrique; De la Hoz, Antonio; Sanchez-Migallon, Ana; Tejeda, Juan
  Heterocycles (1992), 34 (7), 1365-73CODEN: HTCYAM; ISSN:0385-5414.
  The reaction of azoles and benzazoles with dihalomethanes and dihaloethanes was performed in the absence of solvent. This method provides a general procedure for the synthesis of bisazolylmethanes and ethanes. No solvent was used during the reaction and, when possible, during the work-up. Thus, pyrazole was stirred with KOH and Bu4N+ Br- for 1 h and then CH2Cl2 was added and the stirring continued to give 93% bispyrazol-1-ylmethane (I).
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32. 32
  Blümel, M.; Crocker, R. D.; Harper, J. B.; Enders, D.; Nguyen, T. V. N-Heterocyclic olefins as efficient phase-transfer catalysts for base-promoted alkylation reactions. Chem. Commun. 2016, 52, 7958– 7961, DOI: 10.1039/C6CC03771B
  32
  N-Heterocyclic olefins as efficient phase-transfer catalysts for base-promoted alkylation reactions
  Blumel, Marcus; Crocker, Reece D.; Harper, Jason B.; Enders, Dieter; Nguyen, Thanh V.
  Chemical Communications (Cambridge, United Kingdom) (2016), 52 (51), 7958-7961CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  N-Heterocyclic olefins (NHOs), e.g., I have very recently emerged as efficient promoters for several chem. reactions due to their strong Bronsted/Lewis basicities. The novel application of NHOs as efficient phase-transfer organocatalysts for synthetically important alkylation reactions on a wide range of substrates, further demonstrates the great potential of NHOs in org. chem has been reported.
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33. 33
  (a) Wu, H.-S.; Jou, S.-H. Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis. J. Chem. Technol. Biotechnol. 1995, 64, 325– 330, DOI: 10.1002/jctb.280640403
  33a
  Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis
  Wu, Ho-Shing; Jou, Sung-Hauh
  Journal of Chemical Technology & Biotechnology (1995), 64 (4), 325-30CODEN: JCTBED; ISSN:0268-2575. (Wiley)
  The reactions of phenol with dichloromethane using quaternary ammonium salts as a liq.-liq. phase-transfer catalyst in an org. solvent/alk. soln. were investigated. The technique of phase-transfer catalysis had a dramatic accelerating effect on the reaction and increased the yield of diphenoxymethane by more than 95%. The effects of catalysts, temp., and basic concn. on reaction rate were studied in order to find the optimum operating conditions for this reaction. Exptl. results indicated that a potassium hydroxide was preferred over sodium hydroxide in order to enhance the reactivity of the reaction. The reaction rate const. and the distribution coeff. of the intermediate product were obtained. During the reaction, the concn. of the intermediate product was also measured in order to study its behavior in the liq.-liq. system.
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  (b) Cornélis, A.; Laszlo, P. Clay-Supported Reagents; II. Quaternary Ammonium-Exchanged Montmorillonite as Catalyst in the Phase-Transfer Preparation of Symmetrical Formaldehyde Acetals. Synthesis 1982, 1982, 162– 163, DOI: 10.1055/s-1982-29732
  There is no corresponding record for this reference.
  (c) Wu, H.-S.; Fang, T.-R.; Meng, S.-S.; Hu, K.-H. Equilibrium and extraction of quaternary salt in an organic solvent/alkaline solution: effect of NaOH concentration. J. Mol. Catal. A: Chem. 1998, 136, 135– 146, DOI: 10.1016/S1381-1169(98)00054-5
  33c
  Equilibrium and extraction of quaternary salt in an organic solvent/alkaline solution: effect of NaOH concentration
  Wu, Ho-Shing; Fang, Tsung-Ran; Meng, Shang-Shin; Hu, Kwan-Hua
  Journal of Molecular Catalysis A: Chemical (1998), 136 (2), 135-146CODEN: JMCCF2; ISSN:1381-1169. (Elsevier Science B.V.)
  This study measures the quaternary salt concn. in a dichloromethane (or chlorobenzene)/alk. soln. and dets. the thermodn. equil. data. The true extn. const., distribution coeff., dissocn. const. in the aq. phase and free energies of the true extn. const., distribution coeff. and dissocn. const. are obtained as well. The distribution coeff. increased and the real dissocn. const. decreased with increasing NaOH concn. The hydroxide ion concn. and the water content in the org. phase attain a max. value when the NaOH concn. is around 6 M.
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  (d) Liu, W.; Szewczyk, J.; Waykole, L.; Repic, O.; Blacklock, T. J. Practical Synthesis of Diaryloxymethanes. Synth. Commun. 2003, 33, 1751– 1754, DOI: 10.1081/SCC-120018936
  33d
  Practical synthesis of diaryloxymethanes
  Liu, Wenming; Szewczyk, Joanna; Waykole, Liladhar; Repic, Oljan; Blacklock, Thomas J.
  Synthetic Communications (2003), 33 (10), 1751-1754CODEN: SYNCAV; ISSN:0039-7911. (Marcel Dekker, Inc.)
  Diaryloxymethanes were prepd. by treating phenols with sodium hydride and dichloromethane in N-methylpyrrolidinone (NMP) at 40°C. For example, PhOCH2OPh was prepd. in 97% yield from phenol and CH2Cl2.
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34. 34
  Liou, C.-C.; Brodbelt, J. S. Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method. J. Am. Soc. Mass Spectrom. 1992, 3, 543– 548, DOI: 10.1016/1044-0305(92)85031-E
  34
  Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method
  Liou, Chien Chung; Brodbelt, Jennifer S.
  Journal of the American Society for Mass Spectrometry (1992), 3 (5), 543-8CODEN: JAMSEF; ISSN:1044-0305.
  Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M1 + Cat + M2)+, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissocn. to (M1 + Cat)+ and (M2 + Cat)+ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li+, Na+, and K+ than the larger ions such as Cs+ and Rb+. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.
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35. 35
  Gobbi, A.; Landini, D.; Maia, A.; Secci, D. Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts. J. Org. Chem. 1995, 60, 5954– 5957, DOI: 10.1021/jo00123a036
  35
  Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts
  Gobbi, Alessandro; Landini, Dario; Maia, Angelamaria; Secci, Daniela
  Journal of Organic Chemistry (1995), 60 (18), 5954-7CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Metal ion effects have been revealed on nucleophilic substitution reactions of n-octyl sulfonates,[n-C8H17OSO2R;R=Me (1), p-MeC6H4(2), p-O2NC6H4(3)] promoted by complexes of polyether ligands (PEGs, crown ethers, cryptands) with alkali metal salts MY (M = Li, Na, K; Y = I, Br) in low polarity solvents (chlorobenzene, o-dichlorobenzene, toluene) at 60 °. Rate consts. increase, in the order K+ < Na+ <Li+, with the complexes of crown ethers I and II and PEG 4 (III), whereas they are independent of the cation in the case of cryptates of IV. In the series of sulfonic esters 1-3 these effects progressively diminish with increasing nucleofugality of the leaving group. These results are interpreted on the basis of a transition state where the complexed cation (Lig∋M+) assists the departure of the leaving group (electrophilic catalysis).
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36. 36
  Archer, R. H.; Carpenter, J. R.; Hwang, S.-J.; Burton, A. W.; Chen, C.-Y.; Zones, S. I.; Davis, M. E. Physicochemical Properties and Catalytic Behavior of the Molecular Sieve SSZ-70. Chem. Mater. 2010, 22, 2563– 2572, DOI: 10.1021/cm9035677
  36
  Physicochemical Properties and Catalytic Behavior of the Molecular Sieve SSZ-70
  Archer, Raymond H.; Carpenter, John R.; Hwang, Son-Jong; Burton, Allen W.; Chen, Cong-Yan; Zones, Stacey I.; Davis, Mark E.
  Chemistry of Materials (2010), 22 (8), 2563-2572CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  SSZ-70 is synthesized using 1,3-bis(isobutyl)imidazolium, 1,3-bis(cyclohexyl)imidazolium, and 1,3-bis(cycloheptyl)imidazolium structure directing agents (SDAs), and the solids obtained are characterized by powder X-ray diffraction (XRD), 29Si magic angle spinning NMR (MAS NMR), electron microscopy, nitrogen and hydrocarbon adsorption, and thermogravimetric analyses. The physicochem. properties of SSZ-70 show that it is a new mol. sieve that has similarities to MWW-type materials. The catalytic behavior of SSZ-70 is evaluated through the use of the constraint index (CI) test. Distinct differences in the reactivity between Al-SSZ-70 and SSZ-25 (MWW) are obsd. and are the consequences of the structural differences between these two mol. sieves.
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37. 37
  (a) https://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi.
  There is no corresponding record for this reference.
  For diphenoxymethane, see:
  (b) Salvador, T. K.; Arnett, C. H.; Kundu, S.; Sapiezynski, N. G.; Bertke, J. A.; Raghibi Boroujeni, M.; Warren, T. H. Copper Catalyzed sp3 C–H Etherification with Acyl Protected Phenols. J. Am. Chem. Soc. 2016, 138, 16580– 16583, DOI: 10.1021/jacs.6b09057
  38b
  Copper Catalyzed sp3 C-H Etherification with Acyl Protected Phenols
  Salvador, Tolani K.; Arnett, Charles H.; Kundu, Subrata; Sapiezynski, Nicholas G.; Bertke, Jeffery A.; Raghibi Boroujeni, Mahdi; Warren, Timothy H.
  Journal of the American Chemical Society (2016), 138 (51), 16580-16583CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A variety of acyl-protected phenols AcOAr participate in sp3 C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employing tBuOOtBu as oxidant with copper(I) β-diketiminato catalysts [CuI]. While 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [CuII]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [CuII]-OtBu intermediates generated upon reaction of [CuI] with tBuOOtBu.
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  For dibenzyloxymethane, see:
  (c) Cacciapaglia, R.; Di Stefano, S.; Mandolini, L. Metathesis Reaction of Formaldehyde Acetals: An Easy Entry into the Dynamic Covalent Chemistry of Cyclophane Formation. J. Am. Chem. Soc. 2005, 127, 13666– 13671, DOI: 10.1021/ja054362o
  38c
  Metathesis Reaction of Formaldehyde Acetals: An Easy Entry into the Dynamic Covalent Chemistry of Cyclophane Formation
  Cacciapaglia, Roberta; Di Stefano, Stefano; Mandolini, Luigi
  Journal of the American Chemical Society (2005), 127 (39), 13666-13671CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The acid-catalyzed transacetalation of formaldehyde acetals (formal metathesis) is a suitable reaction for the generation of well-behaved dynamic libraries of cyclophane formals. The compn. of the equilibrated mixts. solely depends on concn., and is totally independent of whether the feedstock is any of the pure cyclic oligomers, or a mixt. of oligomers/polymers. Effective Molarities related to the formation of the lower cyclic oligomers were directly measured as their equil. molar concns. above the crit. monomer concn. The finding that silver cation acts as a selective binder toward the cyclic dimer, coupled with the proof reading and editing capability of the quickly equilibrating system, translated into significant amplifications of the dimer when the equilibrated mixts. were exposed to the action of the silver template. These results highlight the potential of dynamic combinatorial chem. as a powerful tool for the prepn. in synthetically useful amts. of an otherwise elusive macrocyclic compd. The possibility of using a mixt. of high mol. wt. byproducts as feedstock adds considerably to the practical value of the procedure.
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  For diallyloxymethane, see:
  (d) El-Brollosy, N. R.; Jørgensen, P. T.; Dahan, B.; Boel, A. M.; Pedersen, E. B.; Nielsen, C. Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants. J. Med. Chem. 2002, 45, 5721– 5726, DOI: 10.1021/jm020949r
  38d
  Synthesis of Novel N-1 (Allyloxymethyl) Analogues of 6-Benzyl-1-(ethoxymethyl)-5-isopropyluracil (MKC-442, Emivirine) with Improved Activity Against HIV-1 and Its Mutants
  El-Brollosy, Nasser R.; Jorgensen, Per T.; Dahan, Berit; Boel, Anne Marie; Pedersen, Erik B.; Nielsen, Claus
  Journal of Medicinal Chemistry (2002), 45 (26), 5721-5726CODEN: JMCMAR; ISSN:0022-2623. (American Chemical Society)
  This paper reports the synthesis and the antiviral activities of a series of 6-arylmethyl-1-(allyloxymethyl)-5-alkyluracil derivs., which can be viewed as analogs of the anti-HIV-1 drug emivirine (formerly MKC-442) from which they differ in the replacement of the ethoxymethyl group with variously allyloxymethyl moieties. The most active compds. N-1 allyloxymethyl- and N-1 3-methylbut-2-enyl substituted 5-ethyl-6-(3,5-dimethylbenzyl)uracils (12 and 13) showed activity against HIV-1 wild-type in the picomolar range with selective index of greater than 5 × 106 and activity in the submicromolar range against the clin. important Y181C and K103N mutant strains known to be resistant to emivirine. Structure-activity relationship studies established a correlation between the anti-HIV-1 activity and the substitution pattern of the N-1 allyloxymethyl group.
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  For diisopropoxymethane, see:
  (e) Berkefeld, A.; Piers, W. E.; Parvez, M.; Castro, L.; Maron, L.; Eisenstein, O. Decamethylscandocinium-hydrido-(perfluorophenyl)borate: fixation and tandem tris(perfluorophenyl)borane catalysed deoxygenative hydrosilation of carbon dioxide. Chem. Sci. 2013, 4, 2152– 2162, DOI: 10.1039/c3sc50145k
  38e
  Decamethylscandocinium-hydrido-(perfluorophenyl)borate: fixation and tandem tris(perfluorophenyl)borane catalyzed deoxygenative hydrosilation of carbon dioxide
  Berkefeld, Andreas; Piers, Warren E.; Parvez, Masood; Castro, Ludovic; Maron, Laurent; Eisenstein, Odile
  Chemical Science (2013), 4 (5), 2152-2162CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  This work was directed at studying the capability of structurally defined, strongly Lewis-acidic metal centers to effect catalytic reductive fixation of the small mol. substrate CO2. Exposing solns. or solid samples of the ion pair [Cp*2Sc][HB(C6F5)3] 1CIP, in which the highly electrophilic decamethyl-scandocene cation and [HB(C6F5)]- as a potentially reactive source of hydride equiv. are assocd., to CO2 selectively produces ion pair [Cp*2Sc][HCO2B(C6F5)3] 2CIP. The results of soln. and solid state structural anal. of 2CIP imply ionic assocn. of [Cp*2Sc]+ and [HCO2B(C6F5)3]- rather than B(C6F5)3-adduct formation to neutral Cp*2Sc-formate. In the presence of B(C6F5)3 co-catalyst and excess triethylsilane, the formation of 2CIP from 1CIP initiates the catalytic deoxygenative hydrosilation of CO2 to CH4. The roles of ion pairs 1 and 2, borane co-catalyst, and silane in the catalytic reaction were studied mechanistically by NMR spectroscopy. Intermediately formed 3,3,7,7-tetraethyl-3,7-disila-4,6-dioxanonane product was found to exert an accelerating effect on the overall reaction rate by promoting [HCO2B(C6F5)3]- dissocn. to give 2SIP through formation of sepd. ion pairs [Cp*2Sc(κ2-(Et3SiO)2CH2)][HCO2{B(C6F5)3}n], n = 1, 2. DFT calcns. show that the formation 2CIP from the reaction of 1CIP with CO2 is exoergic and without significant energy barriers. This work lays the basis for future studies of reactive ion pairs of this kind in the context of small mol. chem.
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  For di(ethylthio)methane, see:
  (f) Zaidi, J. H.; Naeem, F.; Khan, K. M.; Iqbal, R.; Zia-Ullah Synthesis of Dithioacetals and Oxathioacetals with Chiral Auxiliaries. Synth. Commun. 2004, 34, 2641– 2653, DOI: 10.1081/SCC-200025627
  38f
  Synthesis of Dithioacetals and Oxathioacetals with Chiral Auxiliaries
  Zaidi, Javid H.; Naeem, Fazal; Khan, Khalid M.; Iqbal, Rashid; Zia-Ullah
  Synthetic Communications (2004), 34 (14), 2641-2653CODEN: SYNCAV; ISSN:0039-7911. (Marcel Dekker, Inc.)
  One-pot synthesis of dithioacetals as well as an efficient method for oxathioacetal is reported. Addnl., some chiral auxiliaries were used to synthesize enantiomerically pure dithioacetals and oxathioacetals.
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  For bis(pyrazolyl)methane, see:
  (g) Field, L. D.; Messerle, B. A.; Rehr, M.; Soler, L. P.; Hambley, T. W. Cationic Iridium(I) Complexes as Catalysts for the Alcoholysis of Silanes. Organometallics 2003, 22, 2387– 2395, DOI: 10.1021/om020938w
  38g
  Cationic Iridium(I) Complexes as Catalysts for the Alcoholysis of Silanes
  Field, Leslie D.; Messerle, Barbara A.; Rehr, Manuela; Soler, Linnea P.; Hambley, Trevor W.
  Organometallics (2003), 22 (12), 2387-2395CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Syntheses of five cationic iridium(I) complexes contg. bidentate ligands bis(1-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM), {[Ir(BPM)(COD)]+(BPh4)-} (1), {[Ir(dmBPM)(COD)]+(BPh4)-} (2), {[Ir(BPM)(CO)2]+(BPh4)-} (3), {[Ir(BPM)(COD)]+[Ir(COD)Cl2]-} (4), and {[Ir(dmBPM)(CO)2]+(BPh4)-} (5), are reported. In an example prepn., BPM reacted with {[Ir(COD)Cl]2} and NaBPh4 in a carbon monoxide atm. giving 3 in 90% yield. The complexes were characterized by NMR spectroscopy, and the solid-state structure of 3 was detd. by single-crystal X-ray crystallog. anal. Complexes 3 and 5 were effective catalysts for the alcoholysis of a range of alcs. and hydrosilanes, including secondary and tertiary hydrosilanes, under mild conditions. For example, Et3SiH reacted with EtOH in the presence of 3 giving Et3SiOEt in 93% yield.
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38. 38
  Liang, L. C.; Chien, P. S.; Lee, P. Y.; Lin, J. M.; Huang, Y. L. Terminal nickel(ii) amide, alkoxide, and thiolate complexes containing amido diphosphine ligands of the type [N(o-C₆H₄PR₂)₂]⁻ (R = Ph, ⁱPr, Cy). Dalton Trans. 2008, 25, 3320– 3327, DOI: 10.1039/b719894a
  There is no corresponding record for this reference.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.joc.1c01971.
- Additional experimental procedures and spectroscopic data (PDF)
- jo1c01971_si_001.pdf (1.65 MB)
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NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane ValorizationClick to copy article linkArticle link copied!

The Journal of Organic Chemistry

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Abstract

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Introduction

Scheme 1

Results and Discussion

Scheme 2

Figure 1

Scheme 3

Mechanistic Studies

Scheme 4

Figure 2

Scheme 5

Conclusions

Experimental Section

General Considerations

General Procedure

Preliminary Experiments

Optimization of the General Reaction Conditions for the Syntheses of Methylal from DCM and NaOMe with Catalyst 2a

Monitoring the Reaction of NaOMe with CH2Cl2

Comparative Assessment of Catalyst Efficiency in the Methylal Synthesis Using Different Catalysts and Alkali Metal Cations

Procedure for the Generation of Solid Sodium Benzyloxide and Sodium Phenoxide

Synthesis of CH2(OPh)2 from Sodium Phenoxide

Synthesis of CH2(OBn)2 from Sodium Benzyloxide

Synthesis of CH2(OMe)2 from Methanol and Sodium Hydroxide

Synthesis of CH2(OPh)2 from Phenol and Sodium Hydroxide

Synthesis of CH2(OBn)2 from Benzyl Alcohol and Sodium Hydroxide

Synthesis of CH2(O-p-C6H4t-Bu)2 from p-tert-Butylphenol and Sodium Hydroxide

Synthesis of CH2(OCH2CH═CH2)2 from Allyl Alcohol and Sodium Hydroxide

Synthesis of CH2(O-i-Pr)2 from 2-Propanol and Sodium Hydride

Synthesis of CH2(SEt)2 from Ethanethiol and Sodium Hydroxide

Synthesis of CH2Pz2 from Pyrazole and Sodium Hydride

Synthesis of [MeOCH2·1a]+[Br–] (3a)

Spectroscopic Data of 1b

Spectroscopic Data of 2b

Supporting Information

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Author Information

Acknowledgments

Abbreviations

References

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The Journal of Organic Chemistry

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Abstract

Scheme 1

Scheme 2

Figure 1

Scheme 3

Scheme 4

Figure 2

Scheme 5

References

Supporting Information

Supporting Information

Terms & Conditions

NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization
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Monitoring the Reaction of NaOMe with CH₂Cl₂

Synthesis of CH₂(OPh)₂ from Sodium Phenoxide

Synthesis of CH₂(OBn)₂ from Sodium Benzyloxide

Synthesis of CH₂(OMe)₂ from Methanol and Sodium Hydroxide

Synthesis of CH₂(OPh)₂ from Phenol and Sodium Hydroxide

Synthesis of CH₂(OBn)₂ from Benzyl Alcohol and Sodium Hydroxide

Synthesis of CH₂(O-p-C₆H₄t-Bu)₂ from p-tert-Butylphenol and Sodium Hydroxide

Synthesis of CH₂(OCH₂CH═CH₂)₂ from Allyl Alcohol and Sodium Hydroxide

Synthesis of CH₂(O-i-Pr)₂ from 2-Propanol and Sodium Hydride

Synthesis of CH₂(SEt)₂ from Ethanethiol and Sodium Hydroxide

Synthesis of CH₂Pz₂ from Pyrazole and Sodium Hydride

Synthesis of [MeOCH₂·1a]⁺[Br^–] (3a)