Cycloaddition of carbon dioxide and epoxides over Fe-PYPA: Synthetic optimization and mechanistic study

A novel iron-pyridine-based chelate Fe-PYPA was synthesized via a facile and green strategy. The chelate served as a highly efficient catalyst toward CO2 cycloaddition. A 95.7% PO conversion and a 98.4% PC selectivity were achieved under moderate conditions. Even under solvent-free conditions, Fe-PYPA could achieve a 93.6% conversion and 98.2% selectivity, acting as a robust and efficient catalyst toward CO2 cycloaddition. Moreover, the as-prepared catalyst showed desirable catalytic activity, good recyclability, remarkable thermo-stability and ideal compatibility to a variety of epoxy substrates. In-situ ATR-IR spectroscopy was used as a powerful tool to gain process understanding for the whole conversion from CO2 to cyclic carbonate under atmospheric pressure in the presence of TBAI. The process of PO's ring opening, activation and insertion of CO2 and the formation of cyclic carbonate were illuminated explicitly through the change of characteristic absorption peaks, providing direct and visual evidence for the mechanism 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.