New Oxygen Activation Reaction with Rationally Designed Metal Complexes

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The aim of this research is the elucidation of the reaction mechanism working in two enzymes, which play the interconversion between dioxygen and water, respectively. The detailed reaction mechanism for the four-electron reduction of cytochrome c oxidase has not clarified yet, but the role(s)of the each component around the active site is not fully understood. We obtained two major results on these account s with chemical models.1.The oxygenation of the reduced form of N_4Cu complex-tethered heme gave a stable peroxo complex. Its crystal structure was successfully disclosed to show that O_2 bound in a 'side-on' fashion to fom μ-η^2:η^1 structure. This gives a very substantial standpoint to discuss the chemistry of heterodinuclear complexes.2.We prepared CcO active site models, which have a tyrosine-cross linked imidazolate as the part of Cu_B ligand. The correponding peroxide complex showed the different decomposition pathway to give heme Fe(III)-OH/Cu(II). Thus, the phenolic hydroxyl group plays an important role in the reaction of the O_2 complex.Water oxidation is the key reaction to sustain life on the earth. We accomplished stoichiometric oxidation of Mn(III)porphyrin dimer, which has established to catalyze water oxidation under cathodic conditions. Upon oxidation with a peracid, the conesponding Mn(V)-O complex was generated in a good stability and was assigned its structure by spectroscopic methods. This is the first example of Mn(V)=O complex, which is well characterized. By the addition of an acid to the solution of Mn(V)=O spontaneously evolved O_2 in almost quantitative yield. Thus, we succeded to prove that [Mn(V)=O]_2 oxidizes water.