CATALYSTS FOR THE REACTIONS OF EPOXIDES AND CARBON-DIOXIDE

Oxiranes and carbon dioxide are known to cycloadd and/or copolymerize in the presence of a variety of catalysts. Indeed, cyclic carbonates a re prepared on a technical scale by coupling epoxides and carbon dioxi de. The fact that cyclic carbonate formation represents one of the few examples of successful carbon dioxide utilization, coupled with the h igh reactivity of epoxides, has resulted in many papers which reveal a remarkable variety of active catalysts for the CO2/epoxide coupling p rocesses. Catalysts include simple alkali metal salts, ammonium salts, phosphines, main-group metal complexes, and both non-oxidative and ox idative transition-metal complexes. The purpose of this review is to c ompile the different catalysts into their general groups of similarity , with the hopes of shedding light on some of the important difference s in reaction pathways. There generally appears to be a lack of detail ed mechanistic studies; therefore, it is hoped that this review will e mphasize where mechanistic clarification is most importantly needed. F urthermore, we anticipate that this review will provide insight into c yclic carbonate vs. poIycarbonate production from the CO2/epoxide coup ling process.