Half-sandwich complexes of titanium and zirconium with pendant phenyl substituents.: The influence of ansa-aryl coordination on the polymerisation activity of half-sandwich catalysts

Benzyl-substituted Group 4 half-sandwich complexes (eta(5)-C5H4R)TiCl3 (1a, R = CMe2Ph; 2a, R=CMe2CH2Ph; 4a, R = SiMe2Ph; 5a, R = CHPb2) are readily accessible from C5H4(R)SiMe3 and TiCl4, while the reaction of C5H4(CMe2CH2Ph)SiMe3 with ZrCl4(SMe2)(2) affords (C5H4CMe2CH2Ph)ZrCl3.dme (3a). The structures of 1a, 4a and 5a have been determined by X-ray diffraction; the compounds are monomeric in the solid state, Alkylation readily affords the corresponding trimethyl and tribenzyl derivatives: the crystal structure of (eta(5)-C5H4CHPh2)Ti(CH2Ph)(3) (5b) has been determined. Treatment of (eta(5)-C5H4R)MMe3 with [Ph3C](+)[B(C6F5)(4)](-) in dichloromethane at low temperatures generates cationic [(eta(5)-C5H4R)MMe2](+) complexes; the complexes are stabilised by pi-coordination to the phenyl ring to give ansa-arene complexes with one- and two-carbon linkages. The complexes catalyse the polymerisation of propene. Compared to the system Cp*TiMe3/B(C6F5)(3) the ansa complexes show reduced catalytic activity and enhanced chain termination. (C) 1999 Elsevier Science S.A. All rights reserved.