Functional Development and Reaction Mechanism of Model Oxygenase Complexes

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The following results are obtained in catalytic oxidation processe using cobalt schiff base complexes [Co(SB)] as model oxidoreductases.1. Co^<111>(salpr)(OH), a coordinately saturated hydroxocobalt (III) Schiff base complex, has been found to promote the oxygenation of o-hydroxydibenzoylmethane to flavones and retro-Claisen reaction products (chromanones) in methanol. The results are rationalized by assuming base catalysis of Co(SB)(OH) and provide complexes a new route to the synthesis of chromanones and flavones.2. Coordinately unsaturated Co^<111>(SB)(OH) complexes catalyze the oxygenation of 4-substituted phenylacetylenes in alcohol resulting in highly selective incorporation of dioxygen into the triple bond to give the corresponding acetophenones, mandelic and phenylglyoxylic esters.3. Co(SB) catalyzed oxidation of secondary aromatic amines with t-butyl hydroperoxide results selectively in dehydrogenation to give the corresponding imines. Under the reaction conditions, amines including tertiary amines which are not susceptible to the O_2/Co(SB) oxidation system undergo the oxidation to gives the products similar to those obtained in the P450 system. Proposed mechanism involves electron transfer from the nitrogen atom in the substrate to t-butyloxyl or t-butylperoxyl radical produced in situ from a t-butylperoxocobalt (III) complex intermediate.4. Co(SB) are found to catalyze the oxidation of alkenes with NaOCI to give mainly epoxides together with 1,2-dichloro and chlorohydrin compounds as the primary products. The reaction rate depends on the nature of the cobalt catalyst as well as the structure of the alkene substrate. Proposed mechanism involves rate determining formation of Co^<111>(SB)(OCI)^-, a water soluble green complex followed by homolytic cleavage of the Co-O bond giving rise to C10, which reacts with the substrate to gives the products.