Novel zinc and magnesium alkyl and amido cations for ring-opening polymerization reactions

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)(3)ZnN(SiMe3)21 [B(C6F5)41 (2), [(Et2O)(3) MgnBul [B(C6F5)(4)] (3), and [(Et2O)(3)MgN(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)(3)ZnCH2CH3] [B(C6F5)(4)] (1) as well as 2-4 catalyze the ring-opening polymerization of epoxides and 6-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. is an element of-Caprolactone is polymerized efficiently to high molecular weight polymers.