Cobalt(II) dioxygen carriers based on dinucleating ligands -: Part 2.: Kinetics of dioxygen binding

We consider here the kinetics of the reaction of formation of dioxygenated Co(II) complexes with the binucleating ligands 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (Me(2)Octaen), 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane ([27]aneN(9)), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane ([30]aneN(10)), and 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane ([33]aneN(11)). The most important result is that the Co(II) complexes with these polyamines in aqueous solution and at room temperature are very flexible in binding dioxygen: by changing the value of the ligand to cobalt concentration ratio (R = C-L(0)/C-Co(0)) and the pH of the solution, it is possible to modulate the dioxygen uptake obtaining two-to-one or one-to-one, Co/O-2 superoxo complexes. As to the kinetics of the formation of these complexes, we find that the rate-determining step is the transformation of a cobalt-ligand precursor complex, inert towards dioxygen, to yield an active form, whereas the reaction of dioxygen uptake is fast in all the investigated systems. (C) 2000 Elsevier Science B.V. All rights reserved.