Novel Michael Addition Products of Bis(amino acidato)metal(II) Complexes: Synthesis, Characterization, Dye Degradation, and Oxidation Properties

Michael addition reactions of bis(amino acidato)metal(II) complexes (metal = copper, nickel, zinc; amino acid = glycine, dl-alanine, l-alanine) with acrylonitrile have been carried out under various experimental conditions in the absence of a base, resulting in mono- and disubstituted products in high yield, including partially hydrolyzed products. A reaction mechanism for the Michael addition on the nitrogen atom of the coordinated amino acid moiety, replacing the amino hydrogen atom(s), is proposed. All of the products have been characterized by Fourier transform infrared spectroscopy, electron paramagnetic resonance spectra, and elemental and electrochemical analyses. The single-crystal structures of bis(N-cyanoethylglycinato)copper(II) monohydrate (1a), diaquabis(N-cyanoethylglycinato)nickel(II), aquabis(N,N-dicyanoethylglycinato)copper(II) (2a), and bis[(N-propionamido-N-cyanoethyl)glycinato]copper(II) dihydrate (4a) have been confirmed by X-ray diffraction techniques. The products 1a, 2a, 4a, and bis(N-propionamidoglycinato)copper(II) monohydrate (3a) have been used as catalysts for the degradation of a phenol red dye and mild oxidation of various organic substrates in the presence of hydrogen peroxide. The monosubstituted complexes have been found to catalyze the reactions to a greater extent than the disubstituted complexes.