Formation and Reactivity of the Terminal Vanadium Nitride Functionality


  • Dedicated to the memory of Professor Kurt Dehnicke

  • (1931–2011)


The transformation of vanadium(III) azides, [(nacnac)V(N3)(X)]n {nacnac = [ArNC(CH3)]2CH, Ar = 2,6-(CHMe2)2C6H3; X = Ntol2, where tol = 4-MeC6H4, n = 1; X = ArO, n = 2}, to their corresponding vanadium(V) nitrides, [(nacnac)V≡N(X)], was investigated through an isotopic labeling crossover experiment. The nuclearity of the azide species is dependent on the size of the supporting ligand, X, with X = ArO, thus featuring a V2N6 core with two μ2-1,3-N3 bridging ligands across the VIII centers. SQUID magnetization studies and multifrequency, high-field EPR (HFEPR) experiments reveal the mononuclear azide complex to be consistent with an S = 1 system, while the dimeric azide system is weakly antiferromagnetically coupled with a spin singlet ground state and thermally accessible triplet and quintet states. These combined results suggest that the transformation of a vanadium(III) azide to a vanadium(V) nitride most likely occurs by a bimetallic mechanism, where Lewis bases inhibit N2 extrusion. Room-temperature generation of the nitride products from their corresponding azides can also be accomplished stoichiometrically with a Lewis acid, such as B(C6F5)3, and catalytically, through an unsaturated vanadium(II) fragment, [(nacnac)V(Ntol2)].