Rivalling Self-Oxidation and Aldehyde Deformylation by a Dinuclear Copper(II)-Superoxide Complex

In this researchwe report the reactivity of dimeric Cu2L2 (HL = 2-{[[di(2-pyridyl)methyl](methyl)amino]-methyl}phenol) with KO2 in acetonitrile at -40 degrees C alone and in combination with 2-phenylpropionaldehyde (2-PPA) or cyclohexanecarboxaldehyde (CCA). The putative Cu2-superoxide intermediate undergoes self-oxidation at the ligand-sites in the absence of the aldehyde substrate. Instead, it acts as an efficient nucleophilic oxidative deformylation agent, via Baeyer-Villiger oxidation mechanism engaged by the aldehydes which behave as protective agents neutralizing parasitic ligand degradation by the superoxide. Electrospray ionization mass spectrometry analysis (ESI-MS) after warming up the solution to room temperature, confirmed the formation of Cu2L2-formate adducts along with acetophenone or cyclohexanone products. The cooperation between the two metal centres, one acting as binding site for the substrate and the other as active site for the superoxide activation was found to be fundamental for the aldehyde deformylation/oxidation mechanism and the overall complex stability.