環境調和型環状カーボネート合成を志向した触媒反応系の構築

抄録

Carbon dioxide (CO₂) is recognized as an unfavorable industrial waste due to its greenhouse effect, and the reduction of CO₂ emissions has become integral to the creation of a sustainable society. From a different point of view, however, CO₂ is also recognized as an ideal C1 source for chemical synthesis because it is inexpensive, abundant, and nontoxic. In this context, the development of chemical transformations to useful compounds via the use of CO₂ as a reactant has become a hot topic in the field of green sustainable chemistry. Among these transformations, the synthesis of cyclic carbonates from epoxides and CO₂ has been the most extensively studied due to their high utility in industrial processes. Although a wide variety of metal catalysts and organocatalysts such as quaternary onium salts have been developed to promote this reaction, high temperature (>100 °C) and pressure (>10 atm) are often required to produce the products in satisfactory yields. Therefore, the development of catalysts that can be effective for this reaction under mild conditions continues to be highly desired. Herein, we summarize our catalytic approaches for the CO₂ fixation under mild reaction conditions. Design concepts of our catalytic systems were discussed based on experimental results. Our catalytic system could also be applied to cyclic thiocarbonate synthesis by the use of carbon disulfide (CS₂). The mechanisms for these two reactions are discussed based on the stereochemistry of cyclic carbonate and thiocarbonate products. Although these two reactions are similar, the reaction mechanisms are totally different.