A mechanistic and synthetic study on Ziegler-Natta polymerization catalysts based on vanadium complexes.

A series of V(III) catalysts with different substituted 1,3-dionates $\rm(V(acac)\sb3$ 2.1, V(Cy-$\rm acac)\sb3$ 2.2, V(t-Bu-$\rm acac)\sb3$ 2.3 and V(F-$\rm acac)\sb3$ 2.4 were prepared and characterized and their activities towards olefin polymerization were systematically compared. V(Cy-$\rm acac)\sb3$ 2.2 shows a slightly higher activity than the traditional catalyst $\rm V(acac)\sb3$ 2.1. The catalytically active species is relatively insensitive to modification of both the electronic and steric features of the acac ligand. The preparation of V(II) and V(IV) 1,3-dionate complexes was designed to study the role of the oxidation state of vanadium in terms of polymerization activity. Two unprecedented V(II) complexes (R-$acac)\sb2\rm V(TMEDA)$ (R = H(2.7), t-Bu (2.7c)) have been prepared and reacted with halocarbons to model the reactivation process. The isolation of (t-Bu-$acac)\sb2\rm V(TMEDA)\rbrack\lbrack X\rbrack\ \lbrack X = ZnCl\sb4\sp-$ 2.8, $\rm CuCl\sb2\sp-$ 2.9) indicates that the primary role of reactivating substances, commonly employed in the industrial processes, is to reoxidize V(II) to the trivalent state. Reaction of $\rm VCl\sb3(THF)\sb3$ with two equivalent of $\rm R\sp1(R\sp2)NLi{\cdot}Et\sb2O\ (R\sp1 = Ph,$ Bz; $\rm R\sp2 = Bz)$ gave the paramagnetic and monomeric $\rm\lbrack R\sp1(R\sp2)N\rbrack\sb4V$ (3.1) and (3.2). Reactions of $\rm VCl\sb3(THF)\sb3$ with one equivalent of $\rm R\sp1(R\sp2)NLi\ (R\sp1 = Bz;\ R\sp2 = Ph)$ and $\rm R\sb2NLi$ (R = Bz) formed the paramagnetic, monomeric $\rm\lbrack R\sp1(R\sp2)N\rbrack\sb3VCl$ (3.3) and $\rm\lbrack R\sb2N\rbrack\sb3VCl$ (3.4). Reaction of $\rm VCl\sb3(THF)\sb3$ with an excess of $\rm NaBH\sb4$ gave the paramagnetic and monomeric $\rm V(BH\sb4)\sb2(THF)\sb3$ (4.1), $\rm V(BH\sb4)\sb2(TMEDA)\sb2$ (4.2), and $\rm V(BH\sb4)\sb2(py)\sb4$ (4.3). (Abstract shortened by UMI.