Dinuclear metallocenes with a modulated biphenylene bridge for olefin polymerization

Abstract

Dinuclear group 4 metallocene catalysts linked by a biphenylene or 1,2-diphenylethylene bridge, namely [4,4'-(C5Me4)(2)(C6H4)(2)][CpZrCl2](2) (2a), [p-(C5Me4)C6H4CH2](2)[CpZrCl2](2) (2b), [p-(3,4-Me2C5H2)C6H4CH2](2)[CpZrCl2](2) (2c), [(C5Me4)(2)(C6H4)(2)][TiCl3](2) (3a), [p-(C5Me4)C6H4CH2](2)[TiCl3](2) (3b), and [p-(3,4-Me2C5H2)C6H4CH2](2)[TiCl3](2) (3c), have been prepared and the crystal structures of 2b and 3b determined by X-ray diffraction methods. The crystal structures reveal that these complexes consist of two equivalent metal units inverted with respect to the center of the bridge. All the complexes were tested for the polymerization of ethylene and styrene in the presence of methylaluminoxane (MAO), and direct comparisons of their catalytic properties with those of the corresponding mononuclear analogues [(PhC5Me4)-CpZrCl2](2) (4a), [(p-TolC(5)Me(4))CpZrCl2] (4b), [(1-p-Tol-3,4-Me2C5H2)CpZrCl2] (4c), [(PhC5Me4)TiCl3] (5a), [(p-TolC(5)Me(4))TiCl3] (5b), and [(1-p-Tol-3,4-Me2CH2)TiCl3] (5c) were performed. The dinuclear zirconocenes show a high activity in ethylene polymerization comparable with those of the corresponding mononuclear catalysts and give an increased molecular weight of polyethylene. The dinuclear half-sandwich titanocenes exhibit similar or slightly lower activity and molecular weight in styrene polymerization compared with their mononuclear analogues. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)