Biomimetic Chemistry of Oxygen and Nitrogen Monoxide

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1.Field Control of Catalytic Activity of Model Oxygenase Complex. In biomimetic oxygenations of phenols, the reaction between a phenoxy radical intermediate and a superoxometal complex is promoted by model oxygenase complexes in the presence of a coordinative organic base. The model oxygenase complxes also catalyze the dehydrogenation of 2-aminophenols by oxygen leading to highly selective formation of 2-aminophenoxazin-3-ones, where a binary complex intermediate comprised of 2-iminoquinone and catalyst plays an important role as judged by ESR studies. It has also been found that the active species of the model oxygenase complexes catalyze carbon-carbon bond formation by Michael and aldol reactions, and highly regioselective solvoltic cleavage of epoxides controlled by the structure of the catalyst as well. These catalytic reactions are caused by field controlled super acid-base catalysis of the active species. These results provide interesting information in the biomimetic chemistry.2. Chemical Reactivity of Superoxocobalt (III) Complexes. It is found that coordinately unsaturated superoxocobalt (III) complexes catalyze the oxygenation of stirenes in the presence of sodium borohydride leading to the selective formation of 1-phenylethanols, whereas a coordinately saturated superoxocobalt (III) complex oxidizes nitrosobenzenes to nitrobenzenes selectively. ESR studies show that the oxidation of nitroso compounds involves radical addition of the superoxo species to the nitroso group.The chemistry of superoxocobalt (III) complexes with nitrogen monoxide and of mixed metal mu-peroxo complexes is currently investigated.