Trans-cyclic Carbonates Research Articles

Computational Exploration of Dinuclear MgCo Complex-Catalyzed Ring-Opening Copolymerization of Cyclohexene Oxide and CO2

The mechanism of the heterodinuclear MgCo complex-catalyzed ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, which was developed by the Williams group, has been deeply investigated with density functional theory (DFT) calculations. Both of the two processes in the whole copolymerization reaction, chain initiation and chain propagation, involve two key steps, which are the ring-opening of Mg-binding CHO and the insertion of Co-binding CO2 to the Mg-alkoxide. The computational results suggest that the rate-determining step (RDS) is the second CO2 insertion step in the propagation process under 1 bar of CO2 pressure, and the RDS switches to the second CHO ring-opening step under 20 bar of CO2 pressure. The back-biting side reactions from the metal-alkoxide to generate trans-cyclic carbonate (trans-CC) or those from the metal carbonate to generate cis-cyclic carbonate (cis-CC) were computed to have relatively high barriers. The other homodinuclear/heterodinuclear catalytic systems including CoCo, MgZn, MgMg, and ZnZn systems were investigated for comparison with the MgCo system.

Highly Stereo-Controlled Synthesis of Fatty Acid-Derived Cyclic Carbonates by Using Iron(II) Complex and Nucleophilic Halide

A catalytic system comprising an iron(II) complex and a nucleophilic halide for the preparation of a series of stereo-bio-derived cyclic carbonates was developed. The protocol allows for the coupling of various cis-fatty acid-derived epoxides. For example, cis-epoxy substrates can be reacted with CO2 to selectively yield either the cis- or trans-cyclic carbonates by adjusting the nucleophilic halide. These reactions are highly stereoselective and have excellent yields even under mild reaction conditions. The stereochemical divergence in the fatty acid-derived products strongly depends on the leaving ability of the halide anion in the cocatalyst.

Dramatic Behavioral Differences of the Copolymerization Reactions of 1,4-Cyclohexadiene and 1,3-Cyclohexadiene Oxides with Carbon Dioxide

The copolymerization of 1,3-cyclohexadiene oxide (1,2-epoxy-3-cyclohexene) with CO2 in the presence of the binary catalyst (salen)CoX or (salen)CrX and onium salts was shown to selectively afford the completely alternating copolymer poly(1,3-cyclohexadiene carbonate) in good yield. In the process catalyzed by the cobalt(III) system, the reaction was 100% selective for copolymer, whereas employing the higher temperature chromium(III) catalyst, the reaction yielded in addition to copolymer a significant quantity of the cis-1,3-cyclohexadiene carbonate. Importantly, no corresponding trans-1,3-cyclohexadiene carbonate was produced. The reactivity of 1,3-cyclohexadiene oxide in coupling reactions with CO2 was strikingly greater than that of 1,4-cyclohexadiene oxide under either catalytic conditions. Authentic samples of the cis-cyclic carbonate and trans-cyclic carbonate were synthesized from epoxide and CO2 using ZnCl2/PPNI catalyzed and trans-diol/ethyl chloroformate routes, respectively. trans-1,3-Cyclohexa...

Copolymerization and Cycloaddition Products Derived from Coupling Reactions of 1,2-Epoxy-4-cyclohexene and Carbon Dioxide. Postpolymerization Functionalization via Thiol–Ene Click Reactions

The coupling reaction of 1,2-epoxy-4-cyclohexene with CO2 in the presence of a ZnCl2/nBu4NI catalyst system was shown to provide the naturally occurring cis-cyclohexadiene carbonate. An alternative synthesis of this compound, which was characterized by X-ray structural analysis, was carried out from the cis-diol and triphosgene. Upon utilizing binary or bifunctional (salen)CrX catalysts, this coupling process resulted in the selective formation of completely alternating copolymer of 1,2-epoxy-4-cyclohexene and carbon dioxide. In the case involving the binary chromium(III)/onium salt catalyst, small quantities of both the cis and trans cyclic carbonates were also produced. The (salen)CoDNP/PPNDNP (DNP = 2,4-dinitrophenolate) catalyst system was most effective at producing high molecular weight copolymer with 100% selectivity. The Tg of this polymer (Mn = 35.9 kDa) was determined to be 123 °C, which is higher than the Tg (116 °C) of the corresponding saturated copolymer. Depolymerization of poly(cyclohexadi...

Availability of Other Aliphatic Polycarbonates Derived from Geometric Isomers of Butene Oxide and Carbon Dioxide Coupling Reactions

In this study, we investigate the selectivity for copolymer versus cyclic carbonate production from the coupling of isomeric forms of butene oxide with carbon dioxide in the presence of binary and bifunctional cobalt(III) and chromium(III) salicylaldimine catalysts. Use of the less problematic 1-butene oxide has previously been reported to preferentially afford copolymer from its coupling with CO2. Of the epoxides, cis- and trans-2-butene oxide and isobutene oxide, only cis-2-butene oxide was shown to selectively provide polycarbonate, with both cobalt(III) catalysts being more effective than their chromium(III) analogues. The binary chromium catalyst system produced both cis- and trans-cyclic carbonates from the cycloaddition of CO2 and cis-2-butene oxide, whereas, the corresponding cobalt(III) catalyst selectively yielded 75.4% copolymer at 40 °C with the remaining product being trans-cyclic carbonate. In this instance, the trans-cyclic carbonate results from copolymer degradation, consistent with the observation that depolymerization of the copolymer derived from CO2 and cis-2-butene oxide affords trans-cyclic carbonate exclusively. By way of contrast, both bifunctional catalysts were efficient at producing copolymers with selectivities of 100% (40 °C) and 79% (70 °C) for the cobalt and chromium catalysts, respectively. The glass transition temperature (Tg) of poly(trans-2-butene carbonate) derived from the completely alternating copolymerization of CO2 and cis-2-butene oxide was found to be 68 °C, some 30 deg higher than poly(propylene carbonate). Furthermore, it was shown to have a significantly lower % elongation-to-break value than poly(propylene carbonate).

Enantioselective microbial hydrolysis of dissymmetrical cyclic carbonates with disubstitution

Enantioselective microbial hydrolysis of C 1 and C 2 dissymmetrical cyclic carbonates with disubstitution (methyl and another groups) has been developed. Pseudomonas diminuta (FU0090), a bacterium, efficiently catalyzes the hydrolysis of five-membered cyclic carbonates. While the trans-substrates are hydrolyzed with low enantioselectivities and/or reactivities, the microbe hydrolyzes the cis-substrates with very high enantioselectivities to afford the corresponding almost optically pure anti-(2 R,3 S)-diols. On the other hand, six-membered trans-cyclic carbonates are enantioselectively hydrolyzed to afford the corresponding optically active syn-(2 R,4 R)-diols, although the hydrolysis of the cis-substrates gives racemic compounds. In all cases, the enzyme prefers the ( R)-enantiomer for the carbon atom bearing a methyl group.

Palladium‐Catalyzed Carbon Dioxide Elimination—Fixation Reaction of 4‐Methoxycarbonyloxy‐2‐buten‐1‐ols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-catalyzed carbon dioxide elimination-fixation reaction of 4-methoxycarbonyloxy-2-buten-1-ols.

A new type of palladium-catalyzed CO(2) recycling reaction using allylic carbonates is described. Reaction of trans-4-methoxycarbonyloxy-2-buten-1-ols in the presence of a palladium catalyst produces cyclic carbonates having a vinyl group via a CO(2) elimination-fixation process. A variety of allylic carbonates participate in the reaction giving cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. An enantiospecific reaction proceeds to give chiral cyclic carbonate when a chiral methyl-substituted substrate is subjected to the reaction conditions.

A Novel Methodology for the Synthesis of Cyclic Carbonates Based on the Palladium-Catalyzed Cascade Reaction of 4-Methoxycarbonyloxy-2-butyn-1-ols with Phenols, Involving a Novel Carbon Dioxide Elimination-Fixation Process

A palladium-catalyzed CO(2)-recycling reaction has been developed. Reaction of 4-methoxycarbonyloxy-2-butyn-1-ols with phenols, carried out in the presence of a palladium catalyst, produces phenoxy-substituted cyclic carbonates by way of a pathway involving a CO(2) elimination-fixation. A variety of propargylic alcohols and phenols participate in these reactions which yield cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. Highly enantioselective reactions occur when (S)-BINAP is used as a ligand. Reaction of 4-phenoxycarbonyloxy-2-butyn-1-ol in the presence of the palladium catalyst yields the corresponding cyclic carbonates via a three-component decomposition-reconstruction process.

Mechanistic aspects of the copolymerization reaction of carbon dioxide and epoxides, using a chiral salen chromium chloride catalyst.

The air-stable, chiral (salen)Cr(III)Cl complex (3), where H(2)salen = N,N'-bis(3,5-di-tert-butyl-salicylidene)-1,2-cyclohexene diamine, has been shown to be an effective catalyst for the coupling of cyclohexene oxide and carbon dioxide to afford poly(cyclohexenylene carbonate), along with a small quantity of its trans-cyclic carbonate. The thus produced polycarbonate contained >99% carbonate linkages and had a M(n) value of 8900 g/mol with a polydispersity index of 1.2 as determined by gel permeation chromatography. The turnover number (TON) and turnover frequency (TOF) values of 683 g of polym/g of Cr and 28.5 g of polym/g of Cr/h, respectively for reactions carried out at 80 degrees C and 58.5 bar pressure increased by over 3-fold upon addition of 5 equiv of the Lewis base cocatalyst, N-methyl imidazole. Although this chiral catalyst is well documented for the asymmetric ring-opening (ARO) of epoxides, in this instance the copolymer produced was completely atactic as illustrated by (13)C NMR spectroscopy. Whereas the mechanism for the (salen)Cr(III)-catalyzed ARO of epoxides displays a squared dependence on [catalyst], which presumably is true for the initiation step of the copolymerization reaction, the rate of carbonate chain growth leading to copolymer or cyclic carbonate formation is linearly dependent on [catalyst]. This was demonstrated herein by way of in situ measurements at 80 degrees C and 58.5 bar pressure. Hence, an alternative mechanism for copolymer production is operative, which is suggested to involve a concerted attack of epoxide at the axial site of the chromium(III) complex where the growing polymer chain for epoxide ring-opening resides. Preliminary investigations of this (salen)Cr(III)-catalyzed system for the coupling of propylene oxide and carbon dioxide reveal that although cyclic carbonate is the main product provided at elevated temperatures, at ambient temperature polycarbonate formation is dominant. A common reaction pathway for alicyclic (cyclohexene oxide) and aliphatic (propylene oxide) carbon dioxide coupling is thought to be in effect, where in the latter instance cyclic carbonate production has a greater temperature dependence compared to copolymer formation.