Efficient conversion of CO2 into cyclic carbonates at room temperature catalyzed by Al-salen and imidazolium hydrogen carbonate ionic liquids

Abstract

A novel process for the efficient synthesis of cyclic carbonates from CO₂ and epoxides at room temperature in the absence of a solvent has been achieved by using Al-salen complexes as catalysts and imidazolium hydrogen carbonate ionic liquids ([C_nC_mIm][HCO₃]) as cocatalysts. As a halide ion-free cocatalyst, [C_nC_mIm][HCO₃] showed higher catalytic reactivity compared to traditional halogen-containing quaternary ammonium salts (such as (nBu)₄NBr) and organic bases. The catalytic system can be used for the cycloaddition of a series of substrates with good to excellent yields at room temperature in the absence of a solvent. Besides, the catalytic system can be easily recycled at least four times without significant loss of catalytic activity. A possible mechanism was proposed, in which Al-salen and carbene activate the epoxides and CO₂ respectively.