dissymmetric dinuclear transition metal complexes as dual site catalysts for the polymerization of ethylene

a series of dissymmetric dinuclear complexes were synthesized, as dual site catalysts in ethylene polymerization,by coupling the allylated a-diimine complexes of the metals ti, zr, v, ni and pd with the ansa-zirconocenecomplex [c5h4-sih(me)-c5h4]zrcl2 possessing a hydride silane moiety. the different stages of syntheses includedthe formation of bis(cyclopentadienide)methyl silane which was utilized to prepare the silyl-bridged zirconocenecomplexes. the dinuclear complexes were prepared by mixing the latter complexes with allylated alpha-diiminevia a hydrosilylation reaction using the karstedt catalyst, platinum (0)1,3 divinyl-1,1,3,3,-tetramethyldisiloxane toreact at room temperature for 40 h. these dinuclear complexes were activated with methylaluminoxane (mao)and tested for the polymerization of ethylene. the dinuclear catalysts showed various activities depending on thenature of the metals and produced polyethylenes with broad or bimodal molecular weight distributions. the trendin polymerization activities was: ni>pd>v>zr>ti. the ethylene polymerization activities of the dinuclear catalystswere almost double the activities of their analogous alpha-diimine precursors.