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 CO 2 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 CO 2 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 CO 2 to cyclic carbonate under atomspheric pressure in the presence of TBAI. The process of PO’s ring opening, activation and insertion of CO 2 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. A pyridine-based chelate Fe-PYPA served as a highly efficient catalyst to convert CO 2 into cyclic carbonates even under solvent-free condition. In-situ ATR-IR spectroscopy was used as a powerful tool to achieve process and mechanism understanding during CO 2 coupling reaction. • A new kind of pyridine-based chelate Fe-PYPA was synthesized via a facile and green strategy. • The chelate served as a highly efficient catalyst to convert CO 2 and a variety of epoxides into cyclic carbonates in milder conditions and even under solvent-free condition. • Highly catalytic activity, good recyclability, desirable thermo-stability and substrate compatibility of Fe-PYPA are achieved. • In-situ ATR-IR spectroscopy was used as a powerful tool to achieve process and mechanism understanding during cycloaddition reaction between CO 2 and epoxides.