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(2,3Me2C4H4)(OEt2)][PhCH2B(C6F5)3] [Cp"=1,3-(SiMe3)2C5H3]

The zirconium and hafnium diene complexes Cp " MCl(eta(4)-(CH2CMeCRCH2)-C-1)react with benzylmagnesium chloride to gi ve the benzyl complexes Cp " M(eta(4)-(CH2CMeCRCH2)-C-1)(CH2Ph) (M = Zr, R-1 = Me or H; M = Hf, R-1 = Me) which react with B(C6F5)(3) selectively under benzyl abstraction to give the zwitterionic products Cp " M(eta(4)-diene)-{eta(n-)PhCH(2)B(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 CH2CI2. The addition of diethyl ether leads to the ionic compound [Cp " Hf(2,3-Me2C4H4)(OEt2)(+)[PhCH2B(C6F5) which was characterised by X-ray diffraction.