Synthesis, electrochemistry, and oxygen-atom transfer reactions of dioxotungsten(VI) and -molybdenum(VI) complexes with N2O2 and N2S2 tetradentate ligands

A series of N2O2 tetradentate Ligands with a range of substituents attached to the nitrogen atoms have been prepared (H2Ln) (n = 1-9). Treatment of th ese Ligands and the N2S2 tetradentate Ligand H2L10 with [WO2Cl2(DME)] (DME = 1,2-dimethoxyethane) in the presence of triethylamine leads to the format ion of cis-dioxotungsten(VI) complexes [WO2(L-n)] (n = 1-10). Reaction of t he N2O2 tetradentate ligands H2Ln (n = 1, 3-7) with ammonium molybdate tetr ahydrate and dilute hydrochloric acid gives the corresponding molybdenum(VI ) analogs [MoO2(L-n)] (n = 1, 3-7). These compounds have been spectroscopic ally characterized and the molecular structures of [WO2(L-n)] (n = 1, 2, 9) and [MoO2(L-5)] have been established by X-ray diffraction analysis. These high-valent compounds participate in oxygen-atom transfer reactions and ca n catalyze the oxidation of benzoin with dimethyl sulfoxide. The complex [W O2(L-10)], which contains an S-donor ligand, has lower reduction potential and higher reactivity toward ore-transfer reactions than analogous tungsten complexes having N2O2 ligands. The kinetics of these catalytic processes a long with the structure and electrochemistry of these dioxotungsten and -mo lybdenum complexes are described and compared.