Catalytic Preparation of Cyclic Carbonates from CO2 and Epoxides by Metal–Porphyrin and −Corrole Complexes: Insight into Effects of Cocatalyst and meso-Substitution

Extensive DFT calculations have been performed to elucidate the plausible mechanisms and effects of the cocatalyst and meso -substitution of the macro ring on the coupling reaction of CO 2 with epoxide catalyzed by metal prophyrin and corrole complexes. Here the catalytic generation of cyclic carbonate from CO 2 and epoxide by the Al–, Mg–, and Zn–porphyrin catalysts is predicted to follow a similar multistep mechanism, in which the ring-opening and -closure steps experience relatively high free energy barriers, while the CO 2 insertion is facile. The computational results lend support to the remarkable catalytic role of a quaternary ammonium salt cocatalyst in the order PPNCl > PPNBr > PPNI. Introduction of the aryl and chlorinated aryl substituents on the porphyrin ligand reduces the electrophilicity of an aluminum center to some extent but remarkably enhances binding interactions among catalyst, cocatalyst, and reactant, which may facilitate the initial reaction. The ring-closure step is less influenced by the meso -substitution. The corrole-based complexes have similar catalytic behaviors, and they are also promising catalysts for the cycloaddition of CO 2 to epoxides.