Electrochemical studies of a dinuclear copper complex with imidazole derivative ligand H3bphenim

A new polynucleating ligand 4,5-bis(phenylalanyl-N-methyl)-2-methylimidazole (H3bphenim) has been synthesized and characterized. H3bphenim produces the crystalline dinuclear copper compound, [(Cu2bphenim)(H2O)4]NO3 the structure of which includes an imidazolato bridge between the two Cu(II) ions. Electrochemical and spectrophotometric evidence is produced for the cleavage of this imidazolato bridge when the complex is dissolved. The absence of the 375 nm band in the UV-Vis spectrum, known to be characteristic for such imidazolato-bridged Cu(II) compounds as well as the presence of two irreversible CuII → CuI peaks in the cyclic voltammogram (CV), corroborate the formation of the asymmetric CuAbphenimCuB(CuAIILCuBII) where each copper coordination sphere is identified by spectroelectrochemical procedures. The key role of the solvent was demonstrated when mixtures of variable CH3CN:H2O ratio were studied and the corresponding voltammograms compared. CV studies also confirm the formation of a copper(I) solvated species after CuA(I) decoordination. Potential step procedures were applied to elucidate the mechanisms of two coupled homogeneous reactions: the decoordination and subsequent solvation of CuA(I) and the reproportionation reaction between CuAIILCuBIIandCuAILCuBI formed during electrolysis. The mechanisms proposed from the electrochemical behavior are verified by the low catalytic activity shown by the complex in the 3,5-di-tert-butylcatechol oxidation, when it is compared with similar compounds having the imidazolato-bridged Cu(II) structure.