Rates and Mechanisms of Reduction of Tris(phenanthroline)iron(III) by Various Radicals. Effect of Solvent

Article abstract of DOI:10.1021/j100266a044

Tris(phenthroline)iron(III) (Fe^III(phen)3) is reduced to Fe^II complex by a wide variety of radicals in aqueous solutions.Reduction by α-hydroxyalkyl radicals takes place with nearly diffusion-controlled rate constants (3-5*1E9 M^-1 s^-1) and involves an outer-sphere electron transfer.Reduction by other substituted alkyl radicals, as well as methyl and ethyl, is less rapid to varying degrees (k ca. 1E6-1E9 M^-1 s^-1) and may involve an inner-sphere mechanism, whereby the radical attaches to the iron center in an intermediate stage.Addition of alkyl radicals to a phenanthroline carbon, which occurs in acetonitrile solutions, becomes less likely in water, because it is slow relative to the other processes.In the case of the OH radical reaction, however, addition to carbon followed by an intramolecular electron transfer may be the only operative mechanism for reduction of Fe^III(phen)3).