Facile Synthesis of (Imido)vanadium(V)-Alkyl, Alkylidene Complexes Containing an N-Heterocyclic Carbene Ligand from Their Trialkyl Analogues

(Imido)vanadium(V)-alkyl, alkylidene complexes containing an N-heterocyclic carbene (NHC) ligand, V(CHSiMe3)(NR)(CH2SiMe3)(NHC) [R = 1-adamantyl (Ad) or 2,6-Me2C6H3 (Ar), NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], have been prepared from the trialkyl analogues, V(NR)(CH2SiMe3)(3), by alpha-hydrogen elimination in C6D6 in the presence of NHC. The V-C(NHC) bond distance [2.172(2) angstrom] in V(CHSiMe3)(NAd)(CH2SiMe3)(NHC) is much longer than the V-C(alkylidene) [1.829 angstrom] and the V-C(alkyl) [2.069 angstrom] distances, indicating that NHC plays an important role in the stabilization of the high-oxidation-state vanadium(V)alkylidene as a neutral carbene ligand.