Ligand- and metal-centered oxidative degradations in binuclear dioxygen complexes

Abstract

Synthesis and potentiometric equilibrium studies of the stabilities of the complexes of 1, 3-bis (2', 5;, 8', 11'-tetraaza-undecyl) benzene (MATRIEN) with Cu(II), Co (II), Ni(II), and Zn(II) are reported. Equilibrium constants are determined for the formation of mononuclear and dinuclear chelates of these metal ions, as well as several protonated and hydroxo chelates. Dioxygen combines with the cobalt (II) complex to form a stable dibridged (μ-hydroxo)( μ-peroxo) dinuclear cobalt dioxygen complex. The autoxidation of the cobaltous complex through the formation of the dioxygen complex results in a metal-centered oxidation to form the dicobalt (III) chelate and hydrogen peroxide. The first step to the autoxidation reaction is first order with respect to the concentration of both the dioxygen complex and hydroxide ion. Protonation as well as metal binding constants with Cu(II), Co(II), Ni(II), and Zn(II) are determined at 25.0² C and 0.100 M ionic strength for the hexaaza macrocycle L=3, 12, 20, 29, 35, 36, hexaaza- 6, 9,23, 26-tetraoxyatricyclo [29.3.1.1 ¹⁴ ¹⁸] hexatriaconta- 1(34), 14, 15, 17, 31, 32-hexaene (O2-BISBAMP). Mononuclear and dinuclear chelates of these metal ions are identified in all systems investigated. Mono, disprotonated and monohydroxy mononuclear complexes of O2-BISBAMP are formed with all metal ions studied..