Novel Zinc and Magnesium Alkyl and Amido Cations for Ring-Opening Polymerization Reactions

Abstract

The reaction of [H(OEt2)2][B(C6F5)4] with Zn[N(SiMe3)2]2, MgBu2, and {Mg[N(SiMe3)2]2}2 in diethyl ether proceeds in very high yields to give the salts [(Et2O)3ZnN(SiMe3)2][B(C6F5)4] (2), [(Et2O)3MgnBu][B(C6F5)4] (3), and [(Et2O)3MgN(SiMe3)2][B(C6F5)4] (4), respectively. The structures of 2 and 4 were determined by X-ray crystallography; the compounds contain distorted-tetrahedral metal centers and are isostructural. [(Et2O)3ZnCH2CH3][B(C6F5)4] (1) as well as 2−4 catalyze the ring-opening polymerization of epoxides and e-caprolactone. Cyclohexene oxide is polymerized extremely rapidly to high molecular weight materials, while the polymerization of propene oxide gives low molecular weight materials via a cationic mechanism. The zinc species are more stable than their magnesium analogues and show higher productivities. e-Caprolactone is polymerized efficiently to high molecular weight polymers.