Theoretical study on cycloaddition reaction of epoxides with CO2 catalyzed by metal-porphrin complexes: Reaction mechanisms and structure impacts on catalytic activity

摘要

The detailed reaction mechanisms for the coupling reaction of epoxides with CO2 catalyzed by metal-porphyrin complexes were investigated using density functional theory methods. A new concerted insertion process was proposed in this work and in comparison with the insertion step supported by the previous four-step mechanism. On the basis of the coupling reaction mechanisms, the potential relevance of structure and catalytic activity was also discussed. Our theoretical results show that the co-catalyst DMAP has significant effects on the free energy barriers of rate-determining steps by changing the electronic properties of metal centers, it suggested the co-catalyst could promote the catalytic activity as observed experimentally. As for the different metal centers (Co, Al, Mn), the rank of catalytic activity for metal-porphyrin catalysts was predicted to be Co > Al > Mn, which encouraged us to develop more catalytic systems with active metal center. Moreover, the electron-withdrawing substitutions in the meso-position also affect the energy barriers, the catalytic activity of metal-porphyrin catalysts were reduced along with more Br-substitutions in meso-position. (C) 2020 Elsevier B.V. All rights reserved.