Linked cyclopentadienyl-amido complexes of zirconium; ligand dependence of cation-anion interactions and ethene polymerisation activity Sinnema, P.J; Liekelema, K.; Staal, O.K.B.; Hessen, B.; Teuben, J.H

Polymerization of propene with dimethylsilylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl2{η5-1-(t-BuSiMe2N-κN)-2,3,4-Me3-5-R-C5}], where R = Me (1), H (2), Ph (3), 4-fluorophenyl (4), but-2-en-2-yl (5), and butyl (6), combined with excess methylaluminoxane revealed a moderate effect of the substituent R on the catalyst activity and the molecular weight of polypropene. The asymmetric substitution in the position adjacent to the bridging carbon atom resulted in polymer yields decreasing in the order 1 > 6 > 3 ≈ 5 > 4 > 2 while polymers with the molecular weights (Mw) close to 2.5 × 105 for 1, 3, and 4, 1.5 × 105 for 5 and 6, and 7.5 × 104 for 2 were obtained. The 13C NMR analysis of the polymers has shown that atactic polypropene is slightly enriched with syndiotactic triads for all the catalysts. Investigation of the crystal structure of 5 by X-ray crystallography revealed that the double bond in but-3-en-2-yl had shifted to an internal position to give the isomeric, but-2-en-2-yl-substituted complex. Likewise, the spectroscopic data for complex 7 prepared from the ligand containing but-3-en-1-yl substituent, indicate the absence of terminal double bond.