Comparison of the catalytic activity of Ziegler-type catalysts based on Cp{sub 2}ZrCl{sub 2} and (Cp{sub 2}ZrCl){sub 2}O

The rates of ethylene polymerization catalyzed by Cp{sub 2}ZrCl{sub 2}-polymethylalumoxane and (Cp{sub 2}ZrCl){sub 2}O-polymethylalumoxane are equal. According to NMR and ESR spectral data, the same precatalyst, presumably Cp{sub 2}ZrMe{sub 2}, is formed in both systems by the action of AlMe{sub 3}. This accounts for the equal catalytic activity of the systems based on Cp{sub 2}ZrCl{sub 2} and AlMe{sub 3}. This accounts for the equal catalytic activity of the systems based on Cp{sub 2}ZrCl{sub 2} and (Cp{sub 2}ZrCl){sub 2}O. A scheme of reactions resulting in cleavage of the Zr-O-Zr bridge is proposed and confirmed by spectroscopic data.