Synthesis, structural studies and catalytic activity of dioxidomolybdenum(VI) complexes with aroylhydrazones of naphthol-derivative

Abstract

Reaction of the salicylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L1), anthranylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L2), benzoylhydrazone of 2-hydroxy-1-acetonaphthone (H2L3) and anthranylhydrazone of 2-hydroxy-1-acetonaphthone (H2L4; general abbreviation H2L) with [MoO2(acac)2] afforded a series of 5- and 6- coordinate Mo(VI) complexes of the type [MoO2L1–2(ROH)] [where R=C2H5 (1) and CH3 (2)], and [MoO2L3–4] (3 and 4). The substrate binding capacity of 1 has been demonstrated by the formation of one mononuclear mixed-ligand dioxidomolybdenum complex [MoO2L1(Q)] {where Q=γ-picoline (1a)}. Molecular structure of all the complexes (1, 1a, 2, 3 and 4) is determined by X-ray crystallography, demonstrating the dibasic tridentate behavior of ligands. All the complexes show two irreversible reductive responses within the potential window −0.73 to −1.08V, due to MoVI/MoV and MoV/MoIV processes. Catalytic potential of these complexes was tested for the oxidation of benzoin using 30% aqueous H2O2 as an oxidant in methanol. At least four reaction products, benzoic acid, benzaldehyde-dimethylacetal, methyl benzoate and benzil were obtained with the 95–99% conversion under optimized reaction conditions. Oxidative bromination of salicylaldehyde, a functional mimic of haloperoxidases, in aqueous H2O2/KBr in the presence of HClO4 at room temperature has also been carried out successfully.