Oxygen activation by metal complexes and alkyl hydroperoxides. Applications of mechanistic probes to explore the role of alkoxyl radicals in alkane functionalization

摘要: The mechanism of the oxidation cycloalkanes by tertiary alkyl hydroperoxides catalysed iron(III) dichlorotris(2-pyridylmethyl)amine [FeIIICl2(TPA)]+ and acetate bridged (µ-oxo) di-iron complex [Fe2III(TPA)2O(OAc)]3+ has been investigated. Product studies do not support via a high valent iron–oxo intermediate (formally FeVO), but are consistent with involving hydrogen atom abstraction from the alkane alkoxyl radicals derived from hydroperoxide. In the presence large excess tert-butyl hydroperoxide, the oxidation cyclohexane yields cyclohexanone, cyclohexanol and tert-butylcyclohexyl peroxide in more than stoichiometric amounts and, case mono-iron catalyst, one equivalent cyclohexyl chloride. Replacement Me3COOH hydroperoxides, which could yield tert-alkoxyl having much shorter lifetimes the tert-butoxyl radical prevents cycloalkane. The products obtained these hydroperoxide mechanistic probes are those derived fast unimolecular reactions (generally β-scissions) of corresponding radicals. inapplicability dimethyl sulfide as mechanistically diagnostic trap for putative FeVO value of di-tert-butyl hyponitrite non-iron-based source of tert-butoxyl discussed.