Cationic zirconocene complexes with benzyl and Si(SiMe3)3 substituted cyclopentadienyl ligands

Alkyl zirconocenes [Zr(eta-C5H4R)(2)X-2] (where R = CH2Ph, X = Cl 1a or Me 1b; R = CHPh2, X = Cl 2a or Me 2b R = Si(SiMe3)(3), X = Cl 4a or Me 4b) and for comparison [Zr(eta-C5H5)(eta-C5H4CH2Ph)Cl-2] 3a were prepared and characterised. The reactions of these compounds with the methide abstracting reagents B(C6F5)(3), B(o-C6F5C6F4)(3) and [Ph3C](+)[B(C6F5)(4)](-) were investigated by low temperature NMR spectroscopy. Compound 1b reacts with [Ph3C](+)[B(C6F5)(4)](-) to form the homodinuclear complex [{Zr(eta-C5H4CH2Ph)(2)Me}(2)(mu-Me)](+)[B(C6F5)(4)](-). The related compound [{Zr(C5H4CH2Ph)(2)Me}(2)(mu-Me)](+)[MeB(C6F5)(3)](-) 5a was formed from the reaction of 1b with 0.5 equivalent of B(C6F5)(3). Reaction between 1b and 1 equivalent B(C6F5)(3) gave [Me(eta-C5H4CH2Ph)(2)Zr(mu-Me)B(C6F5)(3)] 6a and the ion pair [Zr(eta-C5H4CH2Ph)(2)Me][MeB(C6F5)(3)] 6b which are in equilibrium with each other. A similar observation was made when 2b was used instead of Ib. The sterically more demanding 4b does not show this behaviour. The role of the ligands in ethylene polymerisation was investigated.