Ruthenium carbonyl complexes supported by pyridine-alkoxide ligands: synthesis, structure and catalytic oxidation of secondary alcohols

Abstract

Five novel trinuclear ruthenium complexes [[PyCHC(RC₆H₄)O]₂Ru₃(CO)₈] [R = 4-OMe (6), 4-Br (7), 4-CF₃ (8)] and [[PyCH₂CH(RC₆H₄)O]₂Ru₃(CO)₈] [R = 2-Br (9), 2-CF₃ (10)], were synthesized by treating Ru₃(CO)₁₂ with two equivalents of the corresponding pyridine-alcohols PyCH₂CH(RC₆H₄)OH [1–5, R = 4-OMe, 4-Br, 4-CF₃, 2-Br and 2-CF₃] in refluxing toluene. The structures of 6–10 were fully characterized by IR and NMR spectroscopy, elemental analysis and single-crystal X-ray diffraction. They were found to be efficient catalysts for the oxidation of secondary alcohols by NMO, giving the corresponding ketones in good to excellent yields within 15 min, of which [PyCHC(4-OCH₃C₆H₄)O]₂Ru₃(CO)₈ (6) is the best.