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 (η5-C5H4R)TiCl3 (1a, R=CMe2Ph; 2a, R=CMe2CH2Ph; 4a, R=SiMe2Ph; 5a, R=CHPh2) 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 (η5-C5H4CHPh2)Ti(CH2Ph)3 (5b) has been determined. Treatment of (η5-C5H4R)MMe3 with [Ph3C]+[B(C6F5)4]− in dichloromethane at low temperatures generates cationic [(η5-C5H4R)MMe2]+ complexes; the complexes are stabilised by π-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.