Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: synthesis, characterization, and olefin polymerization behavior

Novel zirconocene complexes (1-Biph-3,4-Me₂Cp)₂ZrCl₂ (3), (C₅Me₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (4), and (C₅H₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (5) containing a 1-biphenyl-3,4-dimethylcyclopentadienyl ligand (2) have been prepared and their solid state structures were characterized by X-ray diffraction method. The crystal structure of 3 revealed a racemic, C₂-symmetric nature in the solid state. In ethylene polymerization, they all afforded high-density polyethylene with very high activity. Especially, the catalytic properties of 3 were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed good activity on the polymerization of propylene, but afforded nearly atactic, amorphous polypropylenes with a little higher mmmm] methyl pentad values by 3 and 4 than that by the most active 5 under the given reaction conditions.