Multifunctional Zn-N4 Catalysts for the Coupling of CO<sub>2</sub> with Epoxides into Cyclic Carbonates
Bingyang Wang, Lixian Wang, Jin Lin, Chungu Xia, Wei Sun
Abstract
The catalytic conversion of greenhouse gas CO 2 into valuable chemicals is a vital goal toward carbon balance and sustainability. In recent decades, the chemical fixation of CO 2 into cyclic carbonates has gained much attention. In this work, a series of zinc complexes bearing tetradentate aminopyridine (N4) ligands have been synthesized and characterized. These zinc complexes were applied to the coupling of CO 2 with epoxides in excellent yields and with a broad substrate scope under cocatalyst- and solvent-free conditions. Moreover, the zinc catalysts could be readily recovered and reused five times without an obvious loss in catalytic activity. Based on spectroscopic characterizations and experimental results, catalyst Zn-3 (DAP-ZnBr 2, DAP = 1,4-bis(2-pyridymethyl)-1,4-diazepane) has been found to be a multifunctional catalyst because of the presence of a Lewis acidic zinc center and a nuclephilic halide anion, and one pyridine is released for the activation of CO 2 during the reaction.