A Dinuclear Oxoperoxomolybdenum(VI) Complex, [Mo2O6(OH)2(Pyridine Oxide Tetrazolate)2], Displaying the {MoO(O2)(μ-OH)2MoO(O2)}0 Core, and its Catalytic Performance in Olefin Epoxidation

Abstract

The dinuclear oxoperoxomolybdenum(VI) complex [Mo₂O₆(OH)₂(pto)₂] (1), containing a rare example of a hydroxo-bridged {MoO(O₂)(μ-OH)₂MoO(O₂)}⁰ core, has been synthesized via the reaction of MoO₃ with H₂O₂ and 5-(2-pyridyl-1-oxide)tetrazole (Hpto) and characterized by elemental analysis and ICP-OES, infrared and Raman spectroscopies, single crystal X-ray diffraction, nuclear magnetic resonance, and mass spectrometry. Compound 1 is an effective homogeneous catalyst for olefin epoxidation. The type of oxidant, namely tert-butyl hydroperoxide (TBHP) or H₂O₂, influences the catalytic performance. For cis-cyclooctene epoxidation, 1/TBHP led to 100% conversion after 4 h at 70 °C, and 1/H₂O₂ led to 80% conversion after 24 h at 70 °C. Catalyst recycling is feasible using an ionic liquid solvent with high affinity for the catalyst, and product separation via an extraction process. The catalytic potential of 1 was further explored for the chemical valorization of biomass-derived fatty acid methyl esters (FAMEs), namely C18-unsaturated methyl oleate and methyl linoleate derived from vegetable oils. The reaction of FAMEs/TBHP gave mainly epoxidized FAMEs (>97% selectivity at high conversions of 97–100%, at 70 °C). This catalyst is a rare example of a dinuclear organo-oxomolybdenum(VI) compound with the ability to epoxidize FAMEs.