Synthesis, Characterization and Catalytic Activity of Two Novel cis-Dioxovanadium(V) Complexes: [VO2(L)] and [VO2(HLox)]

Two novel complexes, [VO2(L)] (1) and [VO2(HLox)] (2), were synthesized and characterized by IV, UV-Vis and NMR spectroscopy, cyclic voltammetry, elemental analysis and X-ray diffraction. The synthesis of a new ligand, H(2)Lox, is also described. Complexes 1 and 2 were obtained by the reaction of [VO(acac)(2)] with the ligands HL and H(2)Lox, respectively. Alternatively, 2 was also obtained by the reaction of HL with [VO(acac)(2)] in the presence of hydroxylamine, and by the reaction of 1 with hydroxylamine. Crystallographic data show that complexes 1 and 2 have similar molecular structures, in which the cis-dioxovanadium(V) center is coordinated to L- or HLox(-), respectively, in a distorted octahedral environment. The catalytic activity of these compounds towards cyclohexane oxidation was evaluated using H2O2 and t-BuOOH as oxidants. Both complexes presented > 70% selectivity for cyclohexylhydroperoxide formation. B3LYP/6-31G(d) calculations were used to confirm the geometry and to help assign the electronic spectra.