Synthesis, structure and oxo-transfer properties of dioxotungsten(VI) complexes with pyridine-based NO- and NS-bidentate ligands

Abstract

Treatment of [WO₂Cl₂(DME)] with 2-pyridylalkoxo NO-bidentate ligands [HLⁿ (n  = 1–5)] in the presence of n-BuLi or 2-pyridylthiolato NS-bidentate ligands [LiLⁿ (n  = 6, 7)] gave the corresponding dioxotungsten(VI) complexes [WO₂(Lⁿ)₂] (n  = 1–7). The new compounds were spectroscopically characterised and the molecular structures of [WO₂(Lⁿ)₂] (n  = 3–5) were also determined by X-ray diffraction analysis. While the complexes [WO₂(Lⁿ)₂] (n  = 4, 5) adopt a normal distorted octahedral geometry with cis-dioxo ligands, the metal centre in [WO₂(L³)₂] exhibits an unusual bicapped tetrahedral coordination, which may arise from the strong σ-donating ability of the alkoxo ligands. These high-valent dioxo complexes, in particular [WO₂(L⁷)₂], which contains two sulfur-containing ligands, are active towards oxygen atom transfer reactions and can catalyse the oxidation of benzoin with DMSO.