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

Permethylated cyclopentadienyl dinuclear constrained geometry titanium catalyst, [μ-(C₆H₄)₂-2,2′]{(η⁵-C₅Me₃)[1-Me₂Si(η¹-N-^tBu)](TiCl₂)}₂ (BPTi₂) linked by a biphenylene bridge was synthesized and tested in ethylene and ethylene/1-octene polymerizations upon activation by TIBA (triisobutylaluminum)/[Ph₃C][B(C₆F₅)₄]. When compared with the corresponding highly active, mononuclear analogs, Me₂Si(η⁵-2-PhC₅Me₃)(η¹-N-^tBu)TiCl₂ (PhTi₁) and Me₂Si(η⁵-C₅Me₄)(η¹-N-^tBu)TiCl₂ (MeTi₁), BPTi₂ exhibits significantly increased molecular weight of polymer (>two-fold), as well as high level of activity and 1-octene incorporations in ethylene and ethylene/1-octene polymerizations. Although the lower activity was observed at high 1-octene feeds, the combined effects of rigidity and electronic conjugation induced by the biphenylene bridge might be responsible for the observed polymerization properties of BPTi₂.