Ligand effects on the reduction of iron(III) complexes by alkyl radicals. Formation of alkyl isocyanides and chlorides from cyanoiron(III) and chloroiron(III) species

Article abstract of DOI:10.1021/om00065a010

The reduction of the cyanoiron(III) complex (NC)₂Fe(phen)₂⁺ by various alkyl radicals occurs readily by addition to the cyanide ligand to form an alkyl isocyanide coordinated to iron(II). The infrared and electronic spectra of analogous cyanoiron(II) and (alkyl isocyanide)iron(II) complexes are compared in the series: (CH₃NC)₂Fe(phen)₂²⁺, (CH₃NC)(NC)Fe(phen)₂⁺, (NC)₂Fe(phen)₂. Electron-rich alkyl radicals such as tert-butyl also reduce (NC)₂Fe(phen)₂⁺ by an electron-transfer process which affords carbonium ion byproducts. For a particular alkyl radical, the competition between radical addition and electron transfer can be qualitatively related to its ionization potential. Various alkyl radicals also react readily with two series of chloroiron(III) complexes, tetrachloroferrate (III) and trichloroiron(III), to afford the reduced chloroiron(II) species and the corresponding alkyl chloride in essentially quantitative yield. The rates of chlorine atom transfer to alkyl radicals are measured by the competition method using BrCCl₃ as a bromine atom donor. The divergent trends in the reactivity pattern of alkyl radicals with tetrachloroferrate(III) and trichloroiron(III) are discussed in terms of FeCL₄^- and FeCl₂⁺, respectively, as the active chloroiron(III) species in acetonitrile solutions. The various pathways for the reduction of different iron(III) complexes by alkyl radicals are presented in the context of their reduction potentials.