Paramagnetic monocyclopentadienyl hydrocarbyl and borohydride compounds of vanadium(II) and vanadium(III): Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/om00154a015

Paramagnetic high-spin d² and d³ monocyclopentadienyl vanadium hydrocarbyl complexes CpV^IIIR₂-(PMe₃)₂ (R = Me, Ph) and CpV^IIR(dmpe) (R = Me, Pr, Ph) have been prepared from their corresponding halide precursors. From CpV(Me)Cl(PMe₃)₂, prepared by ligand exchange, the mixed hydrocarbyl complex CpV(η³-C₃H₅)Me(PMe₃) could be obtained. The V(II) borohydride complex CpV(η²-BH₄)dmpe is shown by EPR and solution magnetic measurements to have a low-spin (S = 1/2) d³ configuration. X-ray structures of CpVMe(dmpe) (P2₁2₁2₁, a = 12.526 (3) A?, b = 9.285 (2) A?, and c = 12.772 (3) A? at -158°C, Z = 4) and CpV(BH₄)dmpe (P2₁/m, a = 8.198 (2) A?, b = 13.435 (3) A?, c = 13.987 (4) A?, and β = 102.09 (1)° at -160 °C, Z = 4) have been determined. Several structural and electronic features are correlated to EHMO calculations. Both V(II) and V(III) alkyl compounds have been reacted with molecular hydrogen. Although catalytic activity in hydrogenation and isomerization of olefins has been observed, no stable V(III) hydrido species could be obtained, reductive elimination processes probably precluding their isolation. Reaction of CpVMe₂(PMe₃)₂ with H₂ generates active CpV fragments that can bind ligands like benzene and 2,3-dimethyl-1,3-butadiene.