Oxidations by the “hydrogen peroxide–manganese(IV) complex–carboxylic acid” system. Part 4. Efficient acid-base switching between catalase and oxygenase activities of a dinuclear manganese(IV) complex in the reaction with H2O2 and an alkane

Abstract

Whereas the dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (1a, L = 1,4,7-trimethyl-1,4,7-triazacyclononane) does not react with H₂O₂ in acetonitrile solution containing cyclohexane, acetic acid added to this mixture in small amounts induces the catalytic decomposition of hydrogen peroxide to O₂ and H₂O (catalase activity) and the transformation of cyclohexane to cyclohexyl hydroperoxide (oxygenase activity). Addition to the acetic acid containing solution only 2 equivalents (relative to the Mn catalyst) of a base enhances the catalase activity and suppresses the oxygenase activity. The proposed mechanism includes the formation of dinuclear dihydroperoxy derivatives of manganese, which can be transformed under the action of acetic acid to OMn(V)–Mn(IV)–OOH species. The latter can abstract a hydrogen atom from an alkane. The interaction of the so-formed R˙ radical with Mn(IV)–OOH can give the alkyl hydroperoxide, ROOH, which is the main primary product of the oxidation process.