1,2-Bis(dimethylsilyl)phenylidene bridged zirconocene and hafnocene dichloride complexes as precatalysts for ethylene polymerization

Abstract

The synthesis and characterization of a new class of ansa bis(indenyl) complexes of zirconium and hafnium is described. Two indenyl moieties are linked at the 1-,1′-positions via a 1,2-bis(dimethylsilyl)benzene unit. The ligand precursor was prepared via three reaction steps including Grignard coupling of chlorodimethylsilane and 1,2-dibromobenzene, PdCl2-catalyzed chlorination, and the reaction with indenyllithium. The zirconium and hafnium complexes were obtained by deprotonation of the corresponding bis-(indenyl) compound with n-BuLi followed by metalation reactions of MCl4 (M = Zr, Hf) in tetrahydrofuran. The solid state molecular structures of both complexes were established by single crystal X-ray diffraction analyses. In ethylene polymerization reactions, both complexes exhibited high activities. The zirconocene catalyst 4 showed a higher activity (7610 kg PE/mol cat. h) compared to the hafnium catalyst 5 (3590 kg PE/mol cat. h).