BIS(TRIMETHYLSILYL) BENZAMIDINATE ZIRCONIUM DICHLORIDES - ACTIVE CATALYSTS FOR ETHYLENE POLYMERIZATION

A study was made of the polymerization of ethylene involving the use o f a series of [eta(4)-4-RC(6)H(4)C(NSiMe(3))(2)]2ZrCl2 as precatalysts (R=H (1); CH3 (2)). The benzamidinate zirconium dichloride complexes were prepared from ZrCl4 and the corresponding 4-RC(6)H(4)C(NSiMe(3))( 2)Li . TMEDA ligand. The structure of complex 1 was determined by a lo w-temperature X-ray diffraction study. ''Cationic'' ethylene polymeriz ation catalysts were generated from 1 and 2 with methylalumoxane. The polymerization activity and the molecular weights of the polymers are strongly dependent on the catalyst and cocatalyst concentrations. The polymerization activity increases drastically with increase in pressur e and temperature and decreases when electron-releasing groups are att ached to the aromatic ring.