Imidazolium zinc tetrahalide-catalyzed coupling reaction of CO2 and ethylene oxide or propylene oxide

Imidazolium zinc tetrahalides, (1-R-3-methylimidazolium)2ZnX2Y2 (R=CH3, C2H5, n-C4H9, CH2C6H5; X=Cl, Br; Y=Cl, Br), prepared by reacting ZnX2 with (1-R-3-methylimidazolium)Y, were found to have surprisingly high activities for the coupling reaction of CO2 and ethylene oxide or propylene oxide to produce corresponding cyclic carbonate. The catalytic activity of imidazolium zinc tetrahalide was greatly influenced by the nature of halide groups bonded to the zinc center. The catalytic activity was found in the order of [ZnBr4]2−>[ZnBr2Cl2]2−⪢[ZnCl4]2−. The turnover frequencies (TOF: h−1) increased with increasing temperature, but remained almost unchanged with the increase of pressure.