Synthesis and Characterization of the Series of d<SUP>0</SUP> Arene Complexes [Cp*MMe<INF>2</INF>(η<SUP>6</SUP>-arene)][MeB(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF>] (M = Ti, Zr, Hf)

Treatment of the neutral trimethyl compounds Cp*MMe<INF>3</INF> (M = Ti, Zr, Hf) with the highly electrophilic borane B(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF> 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<INF>2</INF>(η⁶-arene)][MeB(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF>] (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 ¹H 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<INF>2</INF>(η⁶-toluene)][MeB(C<INF>6</INF>F<INF>5</INF>)<INF>3</INF>] have been determined; as anticipated, there are no significant contacts between anion and cation, and the latter assumes a bent-metallocene type of structure.