Homo- and hetero-metallic rhenium oxomethoxide complexes with a M4(μ-O)2(μ-OMe)4 planar core—a new family of metal alkoxides displaying a peculiar structural disorder. Preparation and X-ray single crystal study

Abstract

The reaction of Re₂O₇ with MeOH at room temperature leads to a fine black powder. A product with the same crystal structure, according to X-ray powder data, was obtained in the form of single crystals on storage of solutions of Re₂O₃(OMe)₆, obtained by anodic oxidation of Re metal. It was identified as Re₄O₆(OMe)₁₂ (1) by an X-ray single crystal study. A mixed-valence complex of analogous composition and structure, Re₄O_6 − y(OMe)_12 + y (2), earlier erroneously described as Re₄O₂(OMe)₁₆, can be obtained via anodic dissolution of Re in MeOH using high current densities. The heterometallic members of this family, Re_4 − xM_xO_6 − y(OMe)_12 + y [M = Mo (3), W (4); x ≤ 0.55, y < 1.0], were obtained by interaction of Re₂O₇ with MO(OMe)₄ or M(OMe)₆ in toluene at reflux. Mo-poor samples of 3 (x ≤ 0.25) could also be obtained on storage of solutions prepared by anodic oxidation of Re in the presence of MoO(OMe)₄. The reaction of Re₂O₇ with Nb(OMe)₅ or Ta(OMe)₅ in refluxing toluene gave M₄(μ-O)₂(μ-OMe)₄(OMe)₁₄(ReO₄)₂ [M = Nb (5), Ta (6)] as the only crystalline products. The compounds 1–6 are insoluble in organic solvents and display a remarkable resistance to ambient atmosphere, making them attractive precursors for soft chemical preparation of rhenium metal and alloy powders.