Ruthenium carbonyl complexes with pyridylalkanol ligands: synthesis, characterization and catalytic properties for aerobic oxidation of secondary alcohols

Abstract

Reaction of Ru₃(CO)₁₂ with pyridylalkanol ligands PyC(CH₂)₄OH (L¹H), PyC(CH₂)₅OH (L²H) and PyCR¹R²OH (R¹ = R² = CH₃ (L³H); R¹ = CH₃, R² = C₆H₅ (L⁴H); R¹ = H, R² = C₆H₅ (L⁵H); R¹ = H, R² = 4-CH₃C₆H₄ (L⁶H); R¹ = H, R² = 4-OMeC₆H₄ (L⁷H); R¹ = H, R² = 4-ClC₆H₄ (L⁸H); R¹ = H, R² = 4-BrC₆H₄ (L⁹H); R¹ = H, R² = 4-CF₃C₆H₄ (L¹⁰H)) in refluxing xylene afforded the bis-chelate ruthenium carbonyl complexes [(Lⁿ)₂Ru₃(CO)₈] (n = 1 (1a); n = 2 (1b); n = 3 (1c); n = 4 (1d); n = 5 (1e); n = 6 (1f); n = 7 (1g); n = 8 (1h); n = 9 (1i); n = 10 (1j)), respectively. All the novel ruthenium complexes were fully characterized by NMR, elemental analyses and IR spectra and the molecular structures of 1a, 1c, 1e, 1g and 1i were further determined by single crystal X-ray diffraction analysis. In the presence of TEMPO (TEMPO = 2,2,6,6-tetramethyl-1-piperidinyloxyl), these trirhenium carbonyl clusters displayed high reactivity for aerobic oxidation of secondary alcohols to give the corresponding ketonic compounds in good to excellent yield using ambient air as the source of oxidant.