Divalent ansa-zirconocenes: stereoselective synthesis and high activity for propylene polymerization.
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.
Chen
Eugene Y-X
EY
The Dow Chemical Company, Midland, Michigan 48674, USA. eychen@lamar.colostate.edu
Campbell
Richard E
RE
Devore
David D
DD
Green
D Patrick
DP
Link
Bernie
B
Soto
Jorge
J
Wilson
David R
DR
Abboud
Khalil A
KA