NHC catalyzed CO2 fixation with epoxides: Probable mechanisms reveal ter molecular pathway

Six different pathways for the NHC-mediated CO2 transformation reaction of epoxide to cyclic carbonate are investigated with DFT method at MPWB1K/6-311++G(3df,2p) level which confirms that the most favorable pathway is ter molecular in nature and passes through a regioselective SN2 anti-attack of NHC on the least substituted carbon of the epoxide-CO2 complex.