C3-symmetric zinc complexes as sustainable catalysts for transforming carbon dioxide into mono- and multi-cyclic carbonates

In this study, we report a single-step preparation method for the synthesis of a series of C-3-symmetric zinc complexes containing both a Lewis acidic zinc center and a nucleophilic halide counter ion for coupling CO2 with epoxides. The Zn-complexes were shown to be effective one-component bifunctional catalysts and displayed high catalytic activity and selectivity for the transformation of CO2 into cyclic carbonates under mild conditions. This strategy is simple, efficient, environmentally benign, and does not require an additional cocatalyst or solvent, and the catalyst can be easily recovered and reused several times without significant loss in catalytic activity. The CO2 coupling reaction proceeded on broad range of substrates and exhibited good tolerance to functional groups, and the cyclic carbonate products were isolated in high yields. On the basis of the experimental results, a plausible reaction mechanism was proposed, and the high catalytic activity was explained.