Electron Transfer Properties of Alkoxyl Radicals. A Time-Resolved Kinetic Study of the Reactions of the tert-Butoxyl, Cumuloxyl, and Benzyloxyl Radicals with Alkyl Ferrocenes

A time-resolved kinetic study on the reactions of the tert-butoxyl, cumyloxyl,and benzyloxyl radicals with alkylferrocenes has been carried out in MeCN solution. With all radicals, clear evidence for an electron transfer (ET) process has been obtained, and with the same ferrocene donor, the reactivity has been observed to increase in the order t-BuO.<CumO.<BnO., with the difference in reactivity approaching 3 orders o fmagnitude ongoing from t-BuO. to BnO. With BnO., an excellent fit to the Marcus equation has been obtained, from which a value of the reduction potential of BnO. (E=0.54V/SCE) has been derived. On the basis of computational evidence for the formation of a stacked prereaction complex in the reaction between BnO. and DcMFc, an alternative ET mechanism is proposed for the reactions of both CumO. and BnO. In these cases, the delocalized nature of the unpaired electron allows for the aromatic ring to act as an electron relay by mediating the ET from the ferrocene donor to the formal oxygen radical center.