Imidazolium zinc tetrahalide-catalyzed coupling reaction of CO 2 and ethylene oxide or propylene oxide

Abstract

Imidazolium zinc tetrahalides, (1-R-3-methylimidazolium) 2ZnX 2Y 2 ( R=CH 3, C 2H 5, n-C 4H 9, CH 2C 6H 5; X=Cl, Br; Y=Cl, Br), prepared by reacting ZnX 2 with (1-R-3-methylimidazolium)Y, were found to have surprisingly high activities for the coupling reaction of CO 2 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 [ZnBr 4] 2−>[ZnBr 2Cl 2] 2−⪢[ZnCl 4] 2−. The turnover frequencies (TOF: h −1) increased with increasing temperature, but remained almost unchanged with the increase of pressure.