Chemistry of Coordinatively Unsaturated Transition Metal-Dioxygen Complex

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Electronically and sterically designed four coordinate cobalt (II) Schiff base complexes and their dioxygen adducts formed at low temperature were prepared. Chemical behavior of these coordinatively unsaturated superoxocobalt (III) complexes [CoIII(SB)(O2)] were investigated to find the following results.(1) CoIII (SB) (O2) as an oxidizing agent was found to be very low : normally oxidizable phenolic compounds as wsell as triphenylphosphin were not oxidized with any coordinatively unsaturated CoII (SB) (O2). However, in the presence of an acid or acyl chloride, triphenylphosophin was oxidized to triphenylphosphin oxide, where hydrogen peroxide or diacylperoxide formed in situ was the oxidizing agent.(2) CoIII (SB) (O2) was found ito reduce o-quinons to igve semiquinonatocobalt (III) complex quantitatively. On the other hand, no reaction took place with p-quinons. These results suggest that the electron density of the coordinated superoxo species in coordinatively unsaturated complex is poor compaired to that in coordinatively sturated one.(3) Radical reactivity of CoIII (SB) (O2) : no reaction with phenoxy radicals were found contrary to the case with coordinatively saturated superoxocobalt (III) complex, which can couple with phenoxy radicals at lower temperature. The less radical reactivity of CoIII (SB) (O2) may be attributed to its electronic stae having metal characteristics.(4) Anionic nature of CoIII (SB) (O2) was found in the reaction wiht benzoyl chloride to give dibenzoyl peroxide, of which formation is considered to recombination of two molecules of benzoylperoxy radical.