The mechanisms for N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO2 and propargylic alcohols.

The mechanistic details of N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO2 and propargylic alcohols were investigated by DFT calculations. Six mechanisms, four for the formation of five-membered cyclic carbonate (M-A, M-B, M-B' and M-C), and two for six-membered cyclic carbonate (M-D and M-E), were fully investigated. The energy profiles in dichloromethane showed that M-B is the predominant reaction with the lowest barrier of 31.99 kcal mol(-1), while M-C and M-D may be kinetically competitive to M-B. The very high activation energy of 45.37 kcal mol(-1), 57.07 kcal mol(-1) and 59.61 kcal mol(-1) for M-A, M-B' and M-E, respectively, suggest that they are of lesser importance in the overall mechanism.