Kinetics of oxidation of hydrogen peroxide by dioxo-bridged manganese(III,IV) complexes

The dioxo-bridged manganese(III, IV) complexes [L2MnIII(mu-O)(2)(MnL2)-L-IV](3+) [L = 2, 2'-bipyridine (bipy) 1 or 1, 10-phenanthroline (phen) 2] quantitatively oxidised H2O2 to O-2, and were themselves reduced to Mn-II. The bipy complex follows biphasic kinetics but the phen complex follows a single exponential profile. For 1, the mononuclear complex [Mn(bipy)(2)(H2O)(OH)](2+) is the intermediate, which is a solvolysis product of 1(+), generated by two-electron reduction of 1(3+) by hydrogen peroxide. The reaction rate increased with increasing [H+] and decreasing [L]. The aqua derivatives of 1 and 2 have greater kinetic activities than their respective parents. The reactions follow an inner-sphere mechanism though all other redox reactions studied so far for 1 and 2 proceed via an outer-sphere model.