Divalent ansa-zirconocenes: stereoselective synthesis and high activity for propylene polymerization |
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Authors: | Chen Eugene Y-X Campbell Richard E Devore David D Green D Patrick Link Bernie Soto Jorge Wilson David R Abboud Khalil A |
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Institution: | The Dow Chemical Company, Midland, Michigan 48674, USA. eychen@lamar.colostate.edu |
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Abstract: | The reduction of ZrCl4(PR3)2 with Li powder, in the presence of a stoichiometric amount of trans-1,4-diphenyl-1,3-butadiene, affords the Zr(II) diene complexes (1) in 90-93% yields. This reaction consists of a rate-limiting step for the formation of the chloride-bridged Zr(III) dimer (2) and a fast diene-driven disproportionation of 2 to 1 and ZrCl4(PR3)2 that re-enters the reduction cycle. The reaction of 1 with Li2{Me2Si(2-Me-4-Ph-Ind)2} in toluene produces quantitatively the desired racemic, divalent ansa-zirconocene (3) that is a highly active isospecific propylene polymerization catalyst upon activation with common activators. |
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