DOUBLY [SIME2]-BRIDGED C-S-SYMMETRICAL AND C-2V-SYMMETRICAL ZIRCONOCENE CATALYSTS FOR PROPYLENE POLYMERIZATION - SYNTHESIS AND POLYMERIZATION CHARACTERISTICS

The C-s- and C-2v-symmetric doubly dimethylsilylene-bridged zirconocen e complexes (5)-C5H2-4-CHMe2}{eta(5)-C5H-3,5-(SiMe3)(2)}ZrCl2, 6a, and (Me2Si)(2){eta(5)-C5H-3,5-(CHMe2)(2)}(2)ZrCl2, 6b, have been synthesi zed by reaction of corresponding dilithio ligand salts with ZrCl4 in C H2Cl2. When activated with methyl aluminoxane, C-s-symmetric zirconoce ne 6a catalyzes the polymerization of propylene (liquid propylene, 0 d egrees C) to yield a syndiotactic polymer of Mw = 1,000,000 and rrrr% = 75.4. By contrast, C-2v-symmetric zirconocene 6b displays a low acti vity and affords an atactic polymer. (C) 1998 Elsevier Science B.V.