ACIDITY CONSTANTS, DIOXYGEN AFFINITY, UV-VISIBLE, ESR, AND ELECTROCHEMICAL STUDIES OF SOME COBALT(II) (N- OR C-MONOSUBSTITUTED) TETRAAZAMACROCYCLES COMPLEXES - DEVELOPMENT OF AN ELECTROCHEMICAL DIOXYGEN GENERATOR

摘要

The use of Cobalt(II)-(N- or C-monosubstituted)-tetraazamacrocycle complexes as potential dioxygen carriers is studied. The physicochemical properties (pK(a), half lifetime of the oxygenated complex, dioxygen affinity, redox potentials) depend on the macrocyclic cavity size and on the nature and place of the substituent in the macrocycle. A whole range of macrocycles substituted by a pendent arm bearing a terminal amine, o- or m-picolyl, or a terminal carboxylic function have been synthesized. Their studies connected the physicochemical properties of their cobalt complexes with the ring size and the substituent. The K-O2 determination, ESR spectra, and electrochemical studies afford particularly important insights into the nature of the dioxygen adduct that is obtained. In order to synthesize a ligand suitable for the development of an industrial electrochemical dioxygen generator, we have undertaken to understand the influence of the pendent arm for substituted macrocycles. Through UV-visible and electrochemical studies, it turns out that macrocycles substituted by functions bearing terminal carboxylic groups exhibit more efficient properties than their parent compounds bearing amine terminated substituents. The redox potential depends more on the size of the macrocycle than on the nature of the substituent, but this influence is reversed within the half lifetime. (C) 1996 Academic Press, Inc. [References: 46]