82149-93-7Relevant academic research and scientific papers
Dioxygen adducts of nickel(II) and cobalt(II) dioxopentaazamacrocyclic complexes: Kinetics, stabilities, and hydroxylation of the ligands in the nickel dioxygen complexes
Chen, Dian,Motekaitis, Ramunas J.,Martell, Arthur E.
, p. 1396 - 1402 (2008/10/08)
The macrocyclic ligands 1,4,7,10,13-pentaazacyclohexadecane-14.16-dione, 15-ethyl-1,4,7,10,13-pentaazacyclohexadecane-14,16-dione, and 15-benzyl-1,4,7,10,13-pentaazacyclohexadecane-14,16-dione have been prepared, and the stability constants of their Cu(II), Ni(II), and Co(II) complexes have been determined potentiometrically. The dioxygen affinities of the Ni(II) and Co(II) complexes have been measured as a function of partial pressure of dioxygen and temperature. The nickel(II) macrocycles form 1:1, superoxo-type dioxygen complexes, while the Co(II) complexes of the same ligands form 2:1 peroxo-bridged binuclear dioxygen adducts. Equilibrium constants (KO2), ΔH°, and ΔS° of dioxygenation are reported. All dioxygen complex formation reactions are strongly exothermic with strongly negative entropy changes. Both nickel and cobalt dioxygen complexes undergo facile degradation in aqueous solution but have significant lifetime for determination of oxygenation constants by dioxygen sorption measurements. The cobalt(II) complexes have higher dioxygen affinities than the nickel(II) complexes with the same ligands. The rates of dioxygen complex formation and degradation have been measured qualitatively and semiquantitatively by UV-visible absorbance studies. The result of this investigation confirms the previous discovery of the formation of dioxygen adducts from nickel(II) complexes, but they are found to undergo irreversible degradation too rapidly to be employed for dioxygen separation or transport. All three Ni(II) dioxygen complexes studied hydroxylate the macrocyclic ligand at the electron-rich 15-carbon position, thus providing new examples of oxygen insertion (monooxygenase-like activity) by the activation of coordinated dioxygen.
