Electron transfer .134. Reduction of bound ruthenium(III) by indium(I)

Aqueous solutions of the hypovalent state indium(I) react with oxidants of the type [(NH3)(5)Ru-III(Lig)](3+), in which the sixth ligand, ''Lig'', is devoid of groups allowing inner-sphere bridging. Reaction stoichiometry conforms to the relationship In-I + 2Ru(III) --> In-III + 2Ru(II). Kinetic profiles are consistent with a two-step sequence initiated by the formation of metastable In-II, which then reacts rapidly with Ru-III. Rate constants for the rate-determining steps in this series (k(Ru,In) values) are proportional to those for reductions of the corresponding (NH3)(5)Co-III oxidants with V2+(aq), Cr2+(aq), Eu2+(aq), and U3+(aq), even though, for each comparison, no metal center is common to the two series chosen. This implies that changes in Delta G(redox)(double dagger) arising from substitution of one N-donor ligand for another are nearly independent of the metal centers involved in the net transfer. The rate for the reduction of (NH3)(6)Ru3+, considered in the framework of the Marcus model, leads to an estimated rate constant of 10(-9) M-1 s(-1) for electron self-exchange in the system In2+/+. This value lies well below the range characteristic of the mast usual aqua-substituted cationic couples, suggesting a more severe H2O-metal bond contraction in going from the uni- to the dipositive cation.