New Development of the Coordination Chemistry of Transition Metal-Oxygen Complexes

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In order to clarify functions and structure of the active sites of oxygenation catalysts and metalloproteins relevant to oxygen transport and oxygenation reactions, systematic synthetic study of transition metal-dioxygen complexes with hydrotrispyrazolylborates, which can easily modify the coordination electronic and steric environment by appropriate substituents, has been carried out. Key findings are as follows1. Chemistry of high valent bis(μ-oxo) speciesDinuclear μ-η2:η2-dioxygen complexes of nickel and cobalt are converted via O-O cleavage to high valent bis(μ-oxo) species, which are capable of oxygenation of hydrocarbons. The compounds attract much attention due to their relevance to the active species of methane monooxygenase.2. Oxygen activation on a mononuclear speciesThe function of metalloproteins containing mononuclear active center such as catechol dioxygenase, which oxidizes aromatics, has been successfully reproduced.3. Synthesis of dioxygen complexes of second row metals and early transition metalsThe target of the synthetic study has been extended to metals which are not involved in metalloproteins, and such study reveals the characteristic aspects of first row metal species found in the proteins.4. Regioselective oxidative polymerization of phenolsThe dicopper-dioxygen complexes prepared by us are found to be active for oxidative polymerization of phenols to give poly(p-phenylene oxide) in a regioselective manner. The result of a bioinorganic study has been applied to an industrial process.Other aspects such as mononuclear copper-oxygen complexes relevant to copper enzymes and oxidation of aromatics in the absence of dioxygen are also studied.