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

摘要

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H_2dhsm), have been synthesized. The complexes of the type cis-[MoO_2(dhsm)] (1a), cis-[MoO_2(dhsm)(D)] (1b-1d) [D = neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NAN)] (2a, 2b) [NAN = 2,2'-bipyridine (bipy) or 1,10- phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by 1H NMR, IR, UV-Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis- [MoO_2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H_2dhsm 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 H_2O_2 and t-BuOOH as co-oxidants under solvent free conditions is reported.