Electron transfer. 141. Reactions of indium(I) with transition metal center oxidants

Aqueous solutions of the hypovalent state In(I) reduce a series of complexes of Fe(III) and selected derivatives of Ir(IV), Cr(V), Pt(IV), Ag(III), and Ni(IV). All reactions yield In(III). Ions derived from Fe(III) and Ir(IV) undergo net le- conversions, whereas the other oxidants change by two units. Reductions of Fe(III) are strongly promoted by increasing pH or by adding Cl-, Br-, NCS-, or N3-. Reaction appears to proceed through monoligated complexes, FeIII(Lig-)2+, and the kinetic response to alteration of added ligand indicates initiation mainly via a bridged transition state FeIII-Lig-InI. Oxidations by Fe(CN)6(3-) are exceptionally rapid, those by FeIII(EDTA) are unusually slow, and redox is blocked by addition of excess F-. Reduction of IrCl6(2-) proceeds somewhat more slowly than predicted by the marcus model for outer-sphere reactions. Conversions of the 2e- oxidants are rapid. For these, multistep routes initiated by le- changes are reasonable, but direct 2e-paths involving oxygen transfer (from CrVO) or Cl+ transfer (from PtCl6(2-)) cannot be ruled out. Whether inner-sphere 2e- transactions without transfer of atomic species can be competitive remains an open question.