Naked (C5Me5)2M cations (M = Sc, Ti, and V) and their fluoroarene complexes.

The ionic metallocene complexes [Cp*(2)M][BPh(4)] (Cp* = C(5)Me(5)) 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*(2)M(kappaF-FC(6)H(5))(n)][BPh(4)] (M = Sc, n = 2; M = Ti, n = 1) and [Cp*(2)M(kappa(2)F-1,2-F(2)C(6)H(4))][BPh(4)], the first examples of kappaF-fluorobenzene and kappa(2)F-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C(6)F(5))(4)](-), both Sc and Ti form [Cp*(2)M(kappa(2)F-C(6)F(5))B(C(6)F(5))(3)] 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.