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] (4a), [(p‐TolC5Me4)CpZrCl2] (4b), [(1‐p‐Tol‐3,4‐Me2C5H2)CpZrCl2] (4c), [(PhC5Me4)TiCl3] (5a), [(p‐TolC5Me4)TiCl3] (5b), and [(1‐p‐Tol‐3,4‐Me2C5H2)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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

A biphenylene-bridged dinuclear constrained geometry titanium complex for ethylene and ethylene/1-octene polymerizations

“…Exclusion of mutual steric effect between the active centers caused by the rigid and isolated ansa-nature in BPTi 2 may be supportive of the large involvement of electronic effect on molecular weight (vide infra). The similar increase of molecular weight of polyethylene, even though a less extent to the given system, was previously observed for the dinuclear zirconocenes linked by a biphenylene bridge [35,36]. 13 C NMR analyses of copolymers reveal high 1-octene incorporation in the copolymers obtained from BPTi 2 as comparable to those from PhTi 1 and MeTi 1 under identical 1-octene feeds.…”

“…In an effort to develop dinuclear catalytic systems, we disclosed that the dinuclear group 4 metal complexes linked by a rigid and/or a modulated biphenylene bridge between two cyclopentadienyl rings can exhibit the enhanced polymerization properties such as increase of molecular weight and catalytic activity in ethylene and styrene polymerizations [35,36]. These results prompted us to apply the biphenylene bridge to the synthesis of novel dinuclear CGC possessing two sterically isolated ansa-units.…”