Synthesis and characterization of the series of d(0) arene complexes [Cp*MMe(2)(eta(6)-arene)] [MeB(C6F5)(3)] (M=Ti, Zr, Hf)

Treatment of the neutral trimethyl compounds Cp*MMe(3) (M = Ti, Zr, Hf) with the highly electrophilic borane B(C6F5)(3) in methylene chloride in the presence of various arenes results in methyl carbanion abstraction and coordination of the arene to form complexes of the type [Cp*MMe(2)(eta(6)-arene)][MeB(C6F5)(3)] (M = Ti, Zr, Hf; arene = benzene, toluene, m- and p-xylene, anisole, styrene, mesitylene). Indications of relative metal-arene affinities have been gleaned from a variety of low-temperature H-1 NMR experiments, and it seems that both steric and electronic factors play significant roles in determining stabilities. The crystal and molecular structures of [Cp*HfMe(2)(eta(6)-toluene)][MeB(C6F5)(3)] have been determined; as anticipated, there are no significant contacts between anion and cation, and the latter assumes a bent-metallocene type of structure.