Dioxo- and oxovanadium(V) complexes of biomimetic hydrazone ONO and NNS donor ligands: Synthesis, crystal structure and catalytic reactivity

Oxo- and dioxo-vanadium(V) complexes of hydrazone ONO donor ligands with the formula [(VO)-O-v(mu(2)-OCH3)(L-1)](2) (1) and [(VO2)-O-v(L-2)]center dot H2O (2) were synthesized by the reaction of [VO(acac)(2)] with proton-transfer complexes of benzenetricarboxylic acid/benzoylhydrazide and benzenetricarboxylic acid/isonicotinohydrazide, respectively (H2L1= monocondensation of benzoylhydrazide and acetylacetone, H2L2 = monoconclensation of isonicotinohydrazide and acetylacetone). Dioxo complex of V(V), [VO2(L-3)] (3), was synthesized by the reaction of equimolar amounts of VO(acac)(2), 2-acetylpyridine and thiosemicarbazide (H2L3 = hydrazone Schiff base of acetylpyridine and thiosemicarbazide and Hacac = acetylacetone). They were characterized by FT-IR, UV-Vis and NMR spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray analyses. The H-1 NMR spectrum of the complex 1 in CDCl3 solution indicated that this dimeric complex is converted appreciably into its respective monomeric form. The catalytic potential of the complexes has been tested for the oxidation of alkene, alkane and aromatic hydrocarbons using H2O2 as the terminal oxidant. Good to excellent conversions have been obtained for the oxidation of most of the hydrocarbons. (C) 2011 Elsevier Ltd. All rights reserved.