Cycloaddition of CO2 to Terminal Epoxides Catalyzed by NHC–ZnBr2 System under Mild Conditions
Shi et al. have reported NHC–ZnBr2 (N-Heterocyclic Carbene; NHC prepared from 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride) catalyzed cycloaddition reactions of CO2 (0.1 MPa) to terminal epoxides. The previously reported NHC–catalyzed systems needed high pressure and high temperature conditions, whereas this NHC–ZnBr2 system requires much milder conditions. They suggest a mechanism for the addition of the imidazolium carboxylate formed from CO2 with NHC to epoxides.