INNER-SPHERE ELECTRON-TRANSFER IN SOME RUTHENIUM(III)-TITANIUM(III) REACTIONS

The kinetics of oxidation of Ti3+ by Ru(NH3)5OOCCH32+, Ru(NH3)5C2O4+, and Ru(NH3)4C2O4+ have been measured in aqueous media (μ = 1 M, 25 °C). For the first-named cation, LiCF3SO3-HCF3SO3 media were used; for the others, LiCl-HCl media. All reactions follow second-order kinetics with rate constant dependent on acidity according to the rate law kb = kK/(K + [H+]). Values of k (M-1 s-1) are 7 × 102, 2.5 × 104, and 3.6 × 104. Values of K (M) are 0,2,, 0,23, and 0.13. The reduction potentials (mV vs. NHE) of the complexes are +44, -109, and -88. The values of k are too large to be consistent with an outer-sphere mechanism and indicate that the redox reaction proceeds via electron transfer in a deprotonated binuclear intermediate. The rate-limiting process is substitution on Ti(III), and k may be identified as the rate constant for that process. Comparison of the values of k for these oxidants with corresponding values for Co(III) oxidants indicates a significant degree of cross-bridge electronic interaction prior to the transition state for the Ru(III)-Ti(III) reactions. © 1979, American Chemical Society. All rights reserved.