The Fe-Pypa Catalyzed Cycloaddition of Carbon Dioxide and Epoxides : Synthetic Optimization and Mechanistic Study

A serial of of pyridine-based chelates M-PYPA were synthesized via a facile and green strategy. The chelates served as highly efficient catalysts toward CO 2 cycloaddition. For Fe-PYPA, a conversion rate of 95.8% and a product selectivity of 98.6% to PO were achieved at 100 °C with 1.5 MPa CO 2 pressure. Moreover, the as-prepared catalyst showed excellent catalytic activity, good recyclability, remarkable termo-stability and desirable compatibility to a variety of epoxy substrates. Process understanding and mechnistic study play a vital role in the design and development of novel catalysts torward CO 2 conversion. In this work, in-situ ATR-IR spectroscopy was used as a powerful tool to gain insight into the reaction mechanism during CO 2 conversion for the first time. The process of PO’s ring opening, activation and insertion of CO 2 , closed-loop of carbonate intermediates and the formation of cyclic carbonate were illuminated explicitly and the possible mechanism was proposed. The present work paves a new way for theoretical and experimental explorations on novel catalyst design and process understanding for highly-efficient greenhouse gas re-utilization