Control of Symmetry in Active Cationic Ansa-Zirconocene Species: Catalyst Preparation, Characterization and Ethylene–norbornene Copolymerization

New bis-hydrocarbyl complexes of methylene bridged ansa-metallocenes [H2C(C5Me2H2)(2)]ZrR2 {R = Me (1), CH2Ph (2), CH2SiMe3 (3), Ph (4)} have been prepared. They form catalytically active intermediates with borane or borate depending on solvent and Zr-R group. Specifically, [H2C(Me2C5H2)(2)]Zr(CH2Ph)(2) (2) produced an ion pair upon treatment with B(C6F5)(3) whereas [H,C(Me2C5H2)(2)]Zr(CH2SiMe3)(2) (3) produced a zwitterionic species, identified by H-1, C-13, and F-19 NMR spectroscopy. Copolymerization of ethylene and norbornene for the metallocene dichloride/MAO and bis-hydrocarbyl complex/borate systems was compared. (C) 2004 Elsevier B.V. All rights reserved.