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.

The cyclopentadienylaluminum aryloxide derivatives bis(cyclopentadienyl)(2,6-di-tert-butyl-4-methylphenoxy)aluminum (1) and (eta(5)-cyclopentadienyl)bis(2,6-di-tert-butyl-4-methylphenoxy)aluminum (2) have been prepared via the alcoholysis of tricyclopentadienylaluminum with 2,6-di-tert-butyl-4-methylphenol. The X-ray crystal structure of 2 was determined. The molecule crystallizes in the monoclinic space group C2/c with a = 15.4870(6) Å, b = 11.5404(5) Å, c = 18.3294(7) Å, beta = 103.0990(10) degrees, Z = 4, and V = 3190.7(2) Å(3) (R[I > 2sigma(I)] = 0.0755, R(w) = 0.1489). In the solid state, the cyclopentadienyl ring is bound eta(5) to the aluminum atom. Ab initio calculations on model compounds indicate that the pentahapto geometry of the cyclopentadienyl ring is due to the electron-withdrawing nature of the aryloxide ligands which allows greater pi-interaction between the aluminum center and the cyclopentadienyl ligand.