The Insertion Reactions of Olefins into Metal-Ethyl Bonds in the Vanadium Compounds-Ethyl Aluminum Ziegler Catalyst System. A Proposed Mechanism for the Syndiotactic Polymerization of α-Olefin

In order to clarify the mechanism of the syndiotactic polymerization of olefin, the insertion reaction of several olefins into metal-ethyl bonds in VCl4-AlEtnCl3−n, VOCl3-AlEtnCl3−n, and V(AA)3-AlEtnCl3−n systems were studied. Cyclohexene was easily inserted into metal-ethyl bonds in these catalysts to give a metal-ethylcyclohexyl bond at −70°C. Pentene-1 and 4-methylpentene-1 gave (Remark: Graphics omitted.) (I) and (Remark: Graphics omitted.) (II). At −70°C with VCl4-AlEt2Cl, where the syndiotactic polymerization of propylene proceeds, four times as much (II) as (I) was obtained. However, at 0°C or in the VCl4-AlEt3 catalyst system, the amount of (I) exceeded the amount of (II). With the VOCl3-AlEtnCl3−n or the V(AA)3-AlEt3Cl3−n system, the selectivity for the formation of metal-alkyl (II) was decreased. The above results lead to the conclusion that, in the course of syndiotactic polymerization, the secondary metal-alkyl bond (II) was an intermediate of the polymerization. By means of this mechanism every experimental result reported can be explained without difficulty.