Computational Exploration of Dinuclear MgCo Complex-Catalyzed Ring-Opening Copolymerization of Cyclohexene Oxide and CO2

Abstract

The mechanism of the heterodinuclear MgCo complex-catalyzed ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, which was developed by the Williams group, has been deeply investigated with density functional theory (DFT) calculations. Both of the two processes in the whole copolymerization reaction, chain initiation and chain propagation, involve two key steps, which are the ring-opening of Mg-binding CHO and the insertion of Co-binding CO2 to the Mg-alkoxide. The computational results suggest that the rate-determining step (RDS) is the second CO2 insertion step in the propagation process under 1 bar of CO2 pressure, and the RDS switches to the second CHO ring-opening step under 20 bar of CO2 pressure. The back-biting side reactions from the metal-alkoxide to generate trans-cyclic carbonate (trans-CC) or those from the metal carbonate to generate cis-cyclic carbonate (cis-CC) were computed to have relatively high barriers. The other homodinuclear/heterodinuclear catalytic systems including CoCo, MgZn, MgMg, and ZnZn systems were investigated for comparison with the MgCo system.