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

Abstract

Alkyl zirconocenes [Zr(η-C₅H₄R)₂X₂] (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(η-C₅H₅)(η-C₅H₄CH₂Ph)Cl₂] 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(η-C₅H₄CH₂Ph)₂Me}₂(µ-Me)]⁺[B(C₆F₅)₄]^–. The related compound [{Zr(C₅H₄CH₂Ph)₂Me}₂(µ-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(η-C₅H₄CH₂Ph)₂Zr(µ-Me)B(C₆F₅)₃] 6a and the ion pair [Zr(η-C₅H₄CH₂Ph)₂Me][MeB(C₆F₅)₃] 6b which are in equilibrium with each other. A similar observation was made when 2b was used instead of 1b. The sterically more demanding 4b does not show this behaviour. The role of the ligands in ethylene polymerisation was investigated.