Chemical fixation of CO2 with highly efficient ZnCl2/[BMIm]Br catalyst system

The chemical fixation of CO₂ with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl₂/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h⁻¹) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system.     

A novel and effective Ni complex catalyst system for the coupling reactions of carbon dioxide and epoxides

The coupling of carbon dioxide and mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under a Ni complex catalyst system without using additional organic solvents was achieved in excellent selectivity and TOF.     

溴化锌-离子液体复合催化体系高效催化合成环状碳酸酯

随着全球“温室效应”和能源危机的加剧,用CO2作为某些化学品的Cl起始原料,既经济、安全,又能降低CO2对环境的危害,由于CO2的性质极不活泼,在固定CO2的反应中最典型的一个催化过程就是利用CO2和环氧化合物通过环加成反应合成环状碳酸酯：     

Comparative kinetic studies of the copolymerization of cyclohexene oxide and propylene oxide with carbon dioxide in the presence of chromium salen derivatives. In situ FTIR measurements of copolymer vs cyclic carbonate production

The catalysis of the reaction of carbon dioxide with epoxides (cyclohexene oxide or propylene oxide) using the (salen)Cr(III)Cl complex as catalyst, where H(2)salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexenediimine (1), to provide copolymer and cyclic carbonate has been investigated by in situ infrared spectroscopy. As previously demonstrated for the cyclohexene oxide/CO(2) reaction in the presence of complex 1, coupling of propylene oxide and carbon dioxide was found to occur by way of a pathway first-order in catalyst concentration. Unlike the cyclohexene oxide/carbon dioxide reaction catalyzed by complex 1, which affords completely alternating copolymer and only small quantities of trans-cyclic cyclohexyl carbonate, under similar conditions propylene oxide/carbon dioxide produces mostly cyclic propylene carbonate. Comparative kinetic measurements were performed as a function of reaction temperature to assess the activation barrier for production of cyclic carbonates and polycarbonates for the two different classes of epoxides, i.e., alicyclic (cyclohexene oxide) and aliphatic (propylene oxide). As anticipated in both instances the unimolecular pathway for cyclic carbonate formation has a larger energy of activation than the bimolecular enchainment pathway. That is, the energies of activation determined for cyclic propylene carbonate and poly(propylene carbonate) formation were 100.5 and 67.6 kJ.mol(-1), respectively, compared to the corresponding values for cyclic cyclohexyl carbonate and poly(cyclohexylene carbonate) production of 133 and 46.9 kJ.mol(-1). The small energy difference in the two concurrent reactions for the propylene oxide/CO(2) process (33 kJ.mol(-1)) accounts for the large quantity of cyclic carbonate produced at elevated temperatures in this instance.     

Amino acids/superbases as eco-friendly catalyst system for the synthesis of cyclic carbonates under metal-free and halide-free conditions

An eco-friendly and efficient binary catalyst system of superbases and amino acids was developed for the synthesis of cyclic carbonates from epoxides and CO₂ under metal-free and halide-free conditions. Among the various amino acids and superbases systems tested, the L-histidine/1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) system achieved the highest conversion of propylene oxide and selectivity of propylene carbonate. The effect of various reaction parameters was evaluated. A possible catalyst mechanism for L-histidine synergized with DBU in the ring opening of epoxide and DBU introduced CO₂ activation. The process herein represents a green, simple, and cost-effective route for the chemical fixation of CO₂ into cyclic carbonates.     

溴化锌-卤化正四丁基铵高效催化合成苯乙烯环状碳酸酯

溴化锌-卤化正四丁基铵二元催化剂高效催化合成苯乙烯环状碳酸酯, 当n-Bu4NI/ZnBr2摩尔比为2时, 在短时间内(30 min)可将苯乙烯环氧化物几乎完全转化为环状碳酸酯, 无其它副产物的生成. 在ZnBr2/n-Bu4NX的催化体系中加入Au/SiO2 氧化催化剂时, 能将苯乙烯直接氧化, 然后碳酰化实现“一锅法”制备环状碳酸酯. 在此合成路线中担载的纳米金催化第一步苯乙烯环氧化反应; ZnBr2/n-Bu4NBr催化第二步CO2环加成反应. 在温和的反应条件下(80 ℃, 1 MPa, 4 h)将环状碳酸酯的产率提高到42%.     

Highly active, hexabutylguanidinium salt/zinc bromide binary catalyst for the coupling reaction of carbon dioxide and epoxides

An experimentally simple and inexpensive catalyst system based on hexabutylguanidinium/ZnBr₂ has been developed for the coupling of carbon dioxide and epoxides to form cyclic carbonates with significant catalytic activity under mild reaction conditions without using additional organic solvents (e.g. the turnover frequencies (TOF, h⁻¹) values as high as 6.6 × 10³ h⁻¹ for styrene oxide and 1.01 × 10⁴ h⁻¹ for epichlorohydrin). This catalyst system also offers the advantages of recyclability and reusability. Therefore, it is a very effective, environmentally benign, and simple catalytic process. The special steric and electrophilic characteristics of hexabutylguanidinium bromide ionic liquid result in the prominent performance of this novel catalyst system.     

双金属氰化络合物及其催化的聚合反应

本文综述了双金属氰化络合物及其催化的环氧化物参与的聚合反应研究。双金属氰化络合物是由其内界金属M^Ⅱ通过氰基与外界金属M^Ⅰ连接形成的含 M^Ⅱ-C≡N-M^Ⅰ 桥键的三维网络状无机高分子(M^Ⅰ一般为Zn²⁺、Fe²⁺、Co²⁺和Ni²⁺等二价金属离子,M^Ⅱ一般为Fe²⁺、Fe³⁺、Co²⁺、Co³⁺和Ni²⁺等过渡金属离子)。外界金属M^Ⅰ一般被认为是催化反应的活性中心金属。该类催化剂早期被用于催化环氧化物开环聚合,并逐步发展成为合成中高分子量、低不饱和度聚醚多元醇的极高效催化剂。近年来该类催化剂被用来催化环氧化物/环状酸酐共聚、环氧化物/CX₂(X≡O,S)共聚和环氧化物/环状酸酐/CO₂三元共聚反应合成聚酯、聚碳酸酯、聚(醚-碳酸酯)、聚硫代碳酸酯和聚(碳酸酯-酯)等具有生物降解性的聚合物。尤其对氧化环己烯(CHO)与CO₂(或酸酐)共聚,锌-钴双金属氰化络合物表现出了极高的催化活性和选择性。结合本研究组十多年的研究结果,本文讨论了双金属氰化络合物催化活性中心的可能结构和催化机理,提出了双金属氰化络合物催化聚合的共性难题和解决这些问题的方向。     

Carbon dioxide/epoxide coupling reactions utilizing Lewis base adducts of zinc halides as catalysts. Cyclic carbonate versus polycarbonate production

The reactions of zinc halides with 2,6-di-methoxypyridine or 3-trifluoromethylpyridine in dichloromethane have led to the formation of quite different complexes. Specifically, reactions involving pyridine containing electron donating methoxy substitutents have provided salts of the type [Zn(2,6-dimethoxypyridine)4][Zn2X6], as revealed by elemental analysis and X-ray crystallography. On the other hand, simple bis-pyridine adducts of zinc halides were isolated from the reactions involving the pyridine ligand with electron withdrawing substituents and characterized by X-ray crystallography, for example, Zn(3-trifluoromethylpyridine)2Br2. These zinc complexes were shown to be catalytically active for the coupling of carbon dioxide and epoxides to provide high molecular weight polycarbonates and cyclic carbonates, with the order of reactivity being Cl > or = Br > I, and 2,6-di-methoxypyridine > 3-trifluoromethylpyridine. Polycarbonate production from carbon dioxide and cyclohexene oxide was shown to be first-order in both metal precursor complex and cyclohexene oxide, as monitored by in situ infrared spectroscopy at 80 degrees C and 55 bar pressure. For reactions carried out in CO2 swollen epoxide solutions in the absence of added quantities of pyridine, the copolymer produced contained significant polyether linkages. Alternatively, reactions performed in the presence of excess pyridine or in hydrocarbon solvent, although slower in rate, afforded completely alternating copolymers. For comparative purposes, zinc chloride was a very effective homopolymerization catalyst for polyethers. Additionally, zinc chloride afforded copolymers with 60% carbonate linkages in the presence of high carbon dioxide pressures. In the case of cyclohexene oxide, the copolymer back-biting reaction led exclusively to the production of the trans cyclic carbonate as shown by infrared spectroscopy in v(C=O) region and X-ray crystallography. The unique feature of these catalyst systems is their simplicity.     

Triethanolamine/KI: A Multifunctional Catalyst for CO2 Activation and Conversion with Epoxides into Cyclic Carbonates

A catalytic system of triethanolamine/potassium iodide (KI) was proved to be efficient for the chemical fixation of CO₂ with epoxide. It was found that triethanolamine with dual function could activate both CO₂ and epoxides. Effects of parameters such as catalyst molar ratio and amount, reaction time, pressure, and temperature were studied systematically. As a result, 99% propylene oxide conversion as well as 99% propylene carbonate selectivity could be obtained under the optimal reaction condition. Furthermore, the catalyst was found to be applicable to a variety of terminal epoxides, providing the corresponding cyclic carbonates in good yields and selectivity. Moreover, the catalyst could be reused five times without loss of activity. This work presents an example of a cheap and efficient catalyst for the chemical fixation of CO₂ to high-value chemicals, which could help to improve the catalytic efficiency and decrease cost of products for larger applications.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Perfectly alternating copolymerization of CO2 and epichlorohydrin using cobalt(III)-based catalyst systems

Selective transformations of carbon dioxide and epoxides into biodegradable polycarbonates by the alternating copolymerization of the two monomers represent some of the most well-studied and innovative technologies for potential large-scale utilization of carbon dioxide in chemical synthesis. For the most part, previous studies of these processes have focused on the use of aliphatic terminal epoxides or cyclohexene oxide derivatives, with only rare reports concerning the synthesis of CO(2) copolymers from epoxides containing electron-withdrawing groups such as styrene oxide. Herein we report the production of the CO(2) copolymer with more than 99% carbonate linkages from the coupling of CO(2) with epichlorohydrin, employing binary and bifunctional (salen)cobalt(III)-based catalyst systems. Comparative kinetic studies were performed via in situ infrared measurements as a function of temperature to assess the activation barriers for the production of cyclic carbonate versus copolymer involving two electronically different epoxides: epichlorohydrin and propylene oxide. The relative small activation energy difference between copolymer versus cyclic carbonate formation for the epichlorohydrin/CO(2) process (45.4 kJ/mol) accounts in part for the selective synthesis of copolymer to be more difficult in comparison with the propylene oxide/CO(2) case (53.5 kJ/mol). Direct observation of the propagating polymer-chain species from the binary (salen)CoX/MTBD (X = 2,4-dinitrophenoxide and MTBD = 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) catalyst system by means of electrospray ionization mass spectrometry confirmed the perfectly alternating nature of the copolymerization process. This observation in combination with control experiments suggests possible intermediates involving MTBD in the CO(2)/epichlorohydrin copolymerization process.     

Biodegradable Polycarbonate Synthesis by Copolymerization of Carbon Dioxide with Epoxides Using a Heterogeneous Zinc Complex

As a means for the chemical fixation of carbon dioxide and the synthesis of biodegradable polycarbonates, copolymerizations of carbon dioxide with various epoxides such as cyclohexene oxide (CHO), cyclopetene oxide, 4-vinyl-1-cyclohexene-1,2epoxide, phenyl glycidyl ether, allyl glycidyl ether, propylene oxide, butene oxide, hexene oxide, octene oxide, and 1-chloro-2,3-epoxypropane were investigated in the presence of a double metal cyanide catalyst (DMC). The DMC catalyst was prepared by reacting K₃Co(CN)₆ with ZnCl₂, together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and was characterized by various spectroscopic methods. The DMC catalyst showed high activity (526.2 g-polymer/g-Zn atom) for CHO/CO₂ (P_CO2 = 140 psi) copolymerization at 80 °C, to yield biodegradable aliphatic polycarbonates of narrow polydispersity (M_w/M_n = 1.67) and moderate molecular weight (M_n = 8900). The DMC catalyst also showed high activities with different CO₂ reactivities for other epoxides to yield various aliphatic polycarbonates with narrow polydispersity.     

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.     

Mg(OH)Cl/KI as a Highly Active Heterogeneous Catalyst for the Synthesis of Cyclic Carbonates from CO2 and Epoxides under Solvent‐Free Conditions

The combination of magnesium hydroxyl chloride [Mg(OH)Cl] with KI could efficiently catalyze the coupling reaction of carbon dioxide with epoxides to give the corresponding cyclic carbonates in good to excellent yields (75.0% –98.3%) and high selectivity (99.6%) in the absence of organic solvents. The heterogeneous catalyst Mg(OH)Cl/KI could be reused at least six times almost without loss of the catalytic activity. The influence of some key factors (such as molar ratio of Mg(OH)Cl to KI, temperature, reaction time and CO₂ pressure) on the reaction was also discussed.     

超临界二氧化碳中组氨酸催化合成环状碳酸酯

研究了超临界二氧化碳中α-氨基酸催化二氧化碳与环氧化物环加成反应合成环状碳酸酯,发现组氨酸的催化活性最高.在二氧化碳压力为8MPa、反应温度130℃、反应时间48h、组氨酸加入量为0.8mol%的条件下,二氧化物可以顺利的与各种环氧化物反应,以高的选择性和产率生成相应的环状碳酸酯.     

溴化锌-季(鎓)三溴盐催化二氧化碳和环氧化合物偶联反应

研究了溴化锌-季鎓三溴盐催化二氧化碳和环氧化合物偶联反应,考察了反应温度、压力和不同金属盐对反应的影响以及催化剂的循环使用性能.结果表明,在413 K和1.0 MPa条件下,以溴化锌为催化剂,苯基三甲基三溴化铵为共催化剂,无需加入任何溶剂就可以使二氧化碳和环氧化合物发生偶联反应,并以很高的收率得到环碳酸酯.     

Experimental and theoretical studies on hydrogen bond-promoted fixation of carbon dioxide and epoxides in cyclic carbonates

The hydrogen bond donor-promoted fixation of CO(2) and epoxides into cyclic carbonates was investigated through experimental and density functional theory studies. A highly effective homogeneous system of 1,2-benzenediol-tetrabutyl ammonium bromide (TBAB) and heterogeneous poly-ionic liquids were developed for the fixation of CO(2) into cyclic carbonates via hydrogen bond activation, based on the understanding of the reaction mechanism and catalyst design. The work hence provides a molecular level understanding of the reaction process and forms the basis for the rational design of catalytic systems for the fixation of CO(2) into useful organic compounds.     

室温离子液体中二氧化碳与环氧化合物的电催化插入反应

在温和条件下，二氧化碳在室温离子液体中可以被电化学活化。同时，活化后 的二氧化碳在室温离子液体中与环氧化合物发生插入反应生成环状碳酸酯也得到了 较好的结果。[BMIm][BF4]离子液体为反应介质，环氧丙烷为反应底物时得到最佳 反应结果。电化学活化对反应的发生是必需的。     

新型Br?nsted酸性离子液体催化二氧化碳与环氧化合物偶联反应

设计合成了一系列由碳链长度可调节的Br?nsted酸中心阳离子及Lewis碱中心阴离子构成的酸性离子液体,,并应用于二氧化碳与环氧化合物的偶联反应合成环碳酸酯。考察了离子液体结构以及温度、压力和催化剂用量等参数的影响。结果表明,具有长碳链的离子液体表现出高催化活性及可重复使用性能。离子液体的酸性影响催化活性。     

Synthesis of Cyclic Carbonates from CO2 and Epoxides Catalyzed by Hexaalkylguanidinium Halides

Hexaalkylguanidinium halides exhibit an efficient catalytic activity in the synthesis of cyclic carbonates from epoxides and carbon dioxide. By this method cyclic carbonates can be obtained in a high yield and a high selectivity at a low temperature and atmospheric pressure. This procedure is easy for the product isolation and recycling of the catalyst.