Electrochemical studies of a dinuclear copper complex with imidazole derivative ligand H 3bphenim

Abstract

A new polynucleating ligand 4,5-bis(phenylalanyl- N-methyl)-2-methylimidazole (H 3bphenim) has been synthesized and characterized. H 3bphenim produces the crystalline dinuclear copper compound, [(Cu 2bphenim)(H 2O) 4]NO 3 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 Cu II → Cu I peaks in the cyclic voltammogram (CV), corroborate the formation of the asymmetric Cu AbphenimCu B ( Cu A II LCu B II ) where each copper coordination sphere is identified by spectroelectrochemical procedures. The key role of the solvent was demonstrated when mixtures of variable CH 3CN:H 2O ratio were studied and the corresponding voltammograms compared. CV studies also confirm the formation of a copper(I) solvated species after Cu A(I) decoordination. Potential step procedures were applied to elucidate the mechanisms of two coupled homogeneous reactions: the decoordination and subsequent solvation of Cu A(I) and the reproportionation reaction between Cu A II LCu B II and Cu A I LCu B I 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.