Influence of catalyst nuclearity on copper-catalyzed aerobic alcohol oxidation

Abstract

Reactions of CuX with the bis(triazolyl) ligand Hbtm [bis(1-benzyl-1H-1,2,3-triazol-4-yl)phenylmethanol] in CH₂Cl₂ afforded trinuclear copper(II) complexes with a core structure (μ-X)Cu₃(μ-κ³-N,O,N-btm)₃(L)²⁺ [X = Cl, L = CH₃OH (1); X = Br, L = H₂O (2)], while a similar reaction of [Cu(CH₃CN)₄](PF₆) with the mono(triazolyl) ligand HPhtm [(1-benzyl-1H-1,2,3-triazol-4-yl)diphenylmethanol] resulted in the mononuclear complex [Cu(κ²-N,O-Phtm)(κ²-N,O-HPhtm)(κ¹-N-HPhtm)][PF₆] (3). The structural characterization of these complexes was made by single-crystal X-ray crystallography in combination with elemental and ESI mass analyses. Catalytic studies toward aerobic oxidation of benzyl alcohol to benzaldehyde revealed that the trinuclear 1 and 2 exhibited higher activities than the mononuclear 3 in both CH₃CN and EtOH/H₂O solvent systems.