Reaction of B(C6F5)3 with zirconium and hafnium benzyl diene complexes. The crystal and molecular structures of Cp″Zr(C6F5){η4-CH2CMeCHCHB(C6F5)2} and [Cp″Hf(2,3-Me2C4H4)(OEt2)][PhCH2B(C6F5)3] [Cp″ = 1,3-(SiMe3)2C5H3]

Abstract

The zirconium and hafnium diene complexes Cp″MCl(η⁴-CH₂CMeCR¹CH₂) react with benzylmagnesium chloride to give the benzyl complexes Cp″M(η⁴-CH₂CMeCR¹CH₂)(CH₂Ph) (M = Zr, R¹ = Me or H; M = Hf, R¹ = Me) which react with B(C₆F₅)₃ selectively under benzyl abstraction to give the zwitterionic products Cp″M(η⁴-diene){ηⁿ-PhCH₂B(C₆F₅)₃}. The zirconium derivative exists as a mixture of two isomers which interchange via ring-flipping of the diene ligand, whereas the Hf compound is rigid. The isoprene analogue Cp″Zr(CH₂CMeCHCH₂){PhCH₂B(C₆F₅)₃} decomposes at room temperature under C–H activation and C₆F₅ migration from boron to zirconium to give toluene and the structurally characterised boryldiene complex Cp″Zr(C₆F₅){CH₂CMeCHCHB(C₆F₅)₂}. In the hafnium (but not zirconium) complexes, the [PhCH₂B(C₆F₅)₃]^– anion is displaced by CH₂Cl₂. The addition of diethyl ether leads to the ionic compound [Cp″Hf(2,3-Me₂C₄H₄)(OEt₂)]⁺[PhCH₂B(C₆F₅)₃] which was characterised by X-ray diffraction.