A computational study on hydrogenation of CO2, catalyzed by a bridged B/N frustrated Lewis pair

Abstract

A DFT-based computational study has been performed on the hydrogenation of CO2, catalyzed by a bridged FLP. Formic acid might be formed in two possible pathways as revealed by this study. In one way, the Lewis basic center of the FLP activates H2, and the Lewis acidic center activates CO2 simultaneously in the first step of the reaction. Alternatively, the Lewis basic center of the FLP activates CO2, and the Lewis acidic center activates H2. The simultaneous activation of CO2 and H2 through single TS is confirmed by NBO analysis. Free energy profiles are also generated for both the possible pathways in solvent phase. It appears from these profiles that the first step, i.e., simultaneous activation of CO2 and H2, is the rate determining for both the reaction pathways. A significant amount of barrier height is reduced in comparison to that in the corresponding uncatalyzed reaction as observed in these profiles. The nature of donor-acceptor interactions present in the transition state geometries is further analyzed by energy decomposition analysis (EDA) methods. The EDA analysis shows that the HOMO of the FLP donates electron density to the LUMO of H2, the HOMO of H2 donates electron density to the LUMO of CO2, and several occupied MOs of CO2 donate electron density to the LUMO of FLP at the TS geometry.