A kinetic study on the reduction of CO2 by frustrated Lewis pairs: from understanding to rational design.

Carbon dioxide (CO2) is known as one of the major reasons for global warming. On the other hand, CO2 is considered as an abundant carbon source. Therefore, transformation of CO2 into target chemicals nowadays is of great interest. Recently, a concept of so-called "frustrated Lewis pairs" (FLPs) has been proposed. Such FLPs show unusual reactivity, such as hydrogen activation and the reduction of CO2. In this study, by means of density functional theory (DFT) and ab initio calculations, we conduct a kinetic survey on the reduction of CO2 by a series of FLPs. We investigate the relationship between the electronic structures and kinetic properties. The kinetic properties include: (1) reaction energy barriers, (2) the structural properties of the associated transition states (TSs), and (3) the natural charge population in these TSs. Our results indicate that there is a systematic relationship between the electronic structures and the kinetic properties, and, as a rule of thumb, similar activation barriers for both individual reactions are needed for best performance. The derived relationship can be used not only to rationalize the published experimental results, but also to assist the future design of more efficient Lewis acid-base pairs as metal-free catalysts for the reduction of CO2.