2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization

Abstract

ansa metallocene complexes of Ti, Zr and Hf were synthesized, characterized and tested as catalysts for homogeneous ethylene polymerization. The ligand system comprises two indenyl moieties tethered at the 1,1′-positions via a 2,2′-dimethyl biphenylene bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH4), followed by the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. After activation with methylaluminoxane (MAO), the zirconium and hafnium complexes proved as highly active catalysts for ethylene polymerization. The zirconium complex 6 showed the best performance with 12,460 kg PE/mol cat. h. The titanium complex 5 showed no catalytic activity obviously because of decomposition reactions.