Naked (C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>M Cations (M = Sc, Ti, and V) and Their Fluoroarene Complexes

The ionic metallocene complexes [Cp*<sub>2</sub>M][BPh<sub>4</sub>] (Cp* = C<sub>5</sub>Me<sub>5</sub>) of the trivalent 3d metals Sc, Ti, and V were synthesized and structurally characterized. For M = Sc, the anion interacts weakly with the metal center through one of the phenyl groups, but for M = Ti and V, the cations are naked. They each contain one strongly distorted Cp* ligand, with one (V) or two (Ti) agostic C−H···M interactions involving the Cp*Me groups. For Sc and Ti, these Lewis acidic species react with fluorobenzene and 1,2-difluorobenzene to yield [Cp*<sub>2</sub>M(κ<i>F</i>-FC<sub>6</sub>H<sub>5</sub>)<i><sub>n</sub></i>][BPh<sub>4</sub>] (M = Sc, <i>n</i> = 2; M = Ti, <i>n</i> = 1) and [Cp*<sub>2</sub>M(κ<sup>2</sup><i>F</i>-1,2-F<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)][BPh<sub>4</sub>], the first examples of κ<i>F</i>-fluorobenzene and κ<sup>2</sup><i>F</i>-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sup>-</sup>, both Sc and Ti form [Cp*<sub>2</sub>M(κ<sup>2</sup><i>F</i>-C<sub>6</sub>F<sub>5</sub>)B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>] contact ion pairs. The nature of the metal−fluoroarene interaction was studied by density functional theory (DFT) calculations and by comparison with the corresponding tetrahydrofuran (THF) adducts and was found to be predominantly electrostatic for all metals studied.