Highly active electrophile–nucleophile catalyst system for the cycloaddition of CO2 to epoxides at ambient temperature

The cycloaddition of CO2 to epoxides proceeds effectively under extremely mild temperatures and pressures by using a bifunctional catalyst system of tetradentate Schiff-base aluminum complexes (SalenAlX) as electrophile in conjunction with polyether–KY complexes as nucleophile. The steric factor of the substituent groups on the aromatic rings of SalenAlX and the nucleophilicity and leaving ability of the anion Y−1 of polyether–KY complexes all have great effects on the activity of the bifunctional catalyst system. The reaction of CO2 with (S)-propylene oxide in the presence of the SalenAlEt/18-crown-6–KI catalyst system gives (S)-propylene carbonate in image ee with retention of stereochemistry.