Mechanistic Investigation of Oxygen Rebound in a Mononuclear Nonheme Iron Complex

An iron(III) methoxide complex reacts with para-substituted triarylmethyl radicals to give iron(II) and meth-oxyether products. Second-order rate constants for the radical derivatives were obtained. Hammett and Marcus plots suggest the radical transfer reactions proceed via a concerted process. Calculations support the concerted nature of these reactions involving a single transition state with no initial charge-transfer. These findings have implications for the radical “re-bound” step invoked in nonheme iron oxygenases, halogenases, and related synthetic catalysts.