The kinetics and thermodynamics of O-2 addition to Co-II complexes containing the simple triamine ligand (L) diethylenetriamine (= N-(2-aminoethyl)ethane-1,2-diamine; dien) or N,N''-dimethyldiethylenetriamine (= N-methyl-N'-[2-(methylamino)ethyl]ethane-1,2-diamine; dmdien) in the aprotic solvent dimethyl sulfoxide (DMSO) were studied by UV/VIS spectrophotometry, potentiometry, and O-2 absorption measurements. A parallel investigation on the anaerobic formation of Coll complexes with dmdien, as well as on their reactivity towards O-2, was carried out in aqueous 0.1M NaCIO4 solution. [CoL](2+) and [CoL2](2+) were the common species formed under anaerobic conditions in both aqueous and DMSO solutions. Under aerobic conditions, O-2 adducts of different stoichiometry were formed: a superoxo complex [CoL2O2](2+) in DMSO and dimeric species in H2O. The role of the reaction medium as well as effects of N-alkylation of the triamine ligand in the formation and reactivity of the [Co-II(triamine)] complexes are discussed.
