Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV) with a tridentate ONS donor ligand: synthesis, spectroscopic properties, X-ray crystal structure and catalytic activity.

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H2dhsm), have been synthesized. The complexes of the type cis-[MoO2(dhsm)] (1a), cis-[MoO2(dhsm)(D)] (1b-1d) [D=neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NN)] (2a, 2b) [NN=2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by (1)H NMR, IR, UV-Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-[MoO2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H2dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh3. The reactivity of the complexes toward catalytic oxidation of alcohols in the presence of H2O2 and t-BuOOH as co-oxidants under solvent free conditions is reported.
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