Electron Transfer. 134. Reduction of Bound Ruthenium(III) by Indium(I)(1)

Aqueous solutions of the hypovalent state indium(I) react with oxidants of the type [(NH(3))(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 (NH(3))(5)Co(III) oxidants with V(2+)(aq), Cr(2+)(aq), Eu(2+)(aq), and U(3+)(aq), even though, for each comparison, no metal center is common to the two series chosen. This implies that changes in DeltaG()(redox) 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 (NH(3))(6)Ru(3+), 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 In(2+/+). This value lies well below the range characteristic of the most usual aqua-substituted cationic couples, suggesting a more severe H(2)O-metal bond contraction in going from the uni- to the dipositive cation.