Phosphine-bound zinc halide complexes for the coupling reaction of ethylene oxide and carbon dioxide

Abstract

Phosphine adducts of zinc(II) halides, ZnX 2L 2 (X = Cl, Br, I; L = PMe 2Ph, PEt 3, PBu 3, PPh 3, PCy 3), prepared by the reaction of ZnX 2 with two equivalents of corresponding phosphines, showed high activities for the coupling reaction of CO 2 and ethylene oxide to produce ethylene carbonate. The catalytic activity of ZnX 2L 2 was hardly affected by the nucleophilicity of the phosphine ligands, with the exception of ZnX 2(PCy 3) 2, but depended strongly on the nature of halide ligands. An active species containing ethoxyphosphonium ligands, Zn 3Br 6[ μ-OCH 2CH 2-P(C 6H 5) 3] 3, was isolated and characterized by X-ray crystallography, elemental analysis, and NMR spectroscopy. The mechanistic pathway for the formation of active species and cyclic carbonates is discussed.