Metal-free imidazolium hydrogen carbonate ionic liquids as bifunctional catalysts for the one-pot synthesis of cyclic carbonates from olefins and CO2

A direct route for the synthesis of cyclic carbonates from olefins and CO2 has been achieved by using imidazolium hydrogen carbonate ionic liquids ([CnCmIm][HCO3]) as bifunctional catalysts in the absence of a solvent. [CnCmIm][HCO3] can convert into a carbene–CO2 adduct spontaneously. The HCO3− anion and carbene–CO2 can serve as catalysts for olefin epoxidation and CO2 cycloaddition, respectively, which obviously simplifies the synthesis of cyclic carbonates. The reaction proceeds quite well under mild conditions. This cheap and simple method can be applied to various olefins with good to excellent yields of cyclic carbonates. The catalyst can be easily recycled at least four times without significantly losing its catalytic activity.