Highly active Cr(iii) catalysts for the reaction of CO2 with epoxides

Abstract

This paper describes the synthesis and characterization of [Cr(babhq)OAc^F(EtOH)] (OAc^F− = CF₃CO₂⁻) as well as the application of the complex as the catalyst in the reaction of CO₂ with epoxides. While cyclic propylene-carbonate was obtained as the sole product when propylene oxide was used as epoxide, alternating polycarbonate was obtained with cyclohexene oxide. Following the course of the reaction with in situ IR spectroscopy revealed that a direct pathway to the formation of cyclic carbonate prevails in the case of propylene oxide whereas the polycarbonate obtained from cyclohexene oxide is prone to degradation to cyclic carbonate. The differences in chemoselectivity are rationalised on the basis of the propensity of the ligand to adopt a podand-like structural motif allowing for an inner-sphere mechanism.