Equilibrium studies of reactions of 4-chloro-1,2-diaminobenzene, 1-methyl-1,2-diaminobenzene, 4-methoxy-1,2-diaminobenzene and 4,5-dimethyl-1,2-diaminobenzene with dinuclear cobalt(II) 1,4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane

Potentiometric equilibrium studies and UV-Vis spectrophotometric measurements were carried out to determine the degree of binding of 4-chloro-1,2-diaminobenzene (ClDB), 4-methyl-1,2-diaminobenzene (MeDB), 4-methoxy-1,2-diaminobenzene (MeODB) and 4,5-dimethyl-1,2-diaminobenzene (diMeDB) with dicobalt(II)-OBISDIEN complexes (OBISDIEN is 1,4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane) in the absence and presence of dioxygen. Equilibrium constants for all major complexes formed are reported, and the results are presented in the form of distribution diagrams showing the concentrations of individual complexes as a function of p[H]. The log of oxygenation constants are: 2.37, 3.49, 3.51 and 3.71 for ClDB, MeDB, MeODB and diMeDB, respectively, and they increase with the protonation constants of these substrates. (C) 1999 Elsevier Science S.A. All rights reserved.