Solvent Role on Cobalt(II) Dioxygen Carriers Based on Simple Polyamine Ligands

The kinetics and thermodynamics of O₂ 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 O₂ absorption measurements. A parallel investigation on the anaerobic formation of Co^II complexes with dmdien, as well as on their reactivity towards O₂, was carried out in aqueous 0.1M NaClO₄ solution. CoL]²⁺ and CoL₂]²⁺ were the common species formed under anaerobic conditions in both aqueous and DMSO solutions. Under aerobic conditions, O₂ 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.