Theoretical Studies on the Fixation of CO2 with Propylene Oxide Catalyzed by Squaramide/TEAB

摘要

The chemical fixation of carbon dioxide (CO2) with propylene oxide catalyzed by a binary squaramide/TEAB catalyst, leading to a five-membered cyclic propylene carbonate, has been fully investigated by density functional theory (DFT). Our results reveal that the overall reaction involves three elementary steps: the epoxide ring opening, CO2 electrophilic attack, and intramolecular cyclization. The rate-determining step of the catalytic reaction is found to be the ring-opening step with an energy barrier of 28.4 kcal/mol in mesitylene solvent, which is kineti-cally more favourable than that of non-catalytic CO2 fixation with a relatively higher barrier of 68.8 kcal/mol. The remarkable catalytic activity originates from the stabilization effect of squaramide on the oxyanionic transition states with multiple hydrogen bonding.