Kinetics of the reaction of Di-μ-acetatodi-μ-oxalatodiaquodiruthenium(II,III) anion with N-(2-hydroxyethyl)-ethylenediaminetriacetatoaquotitanium(III)

Abstract

Reduction of [Ru 2(CH 3COO) 2(C 2O 4) 2(H 2O) 2] − by N-(2-hydroxyethyl)-ethylenediaminetriacetatoaquotitanium(III) [Ti(HEDTA)] involves several distinct stages. The first stage has a half-time of less than 1 ms, and is interpreted as a substitution reaction leading to a multinuclear intermediate. The second stage has a second-order rate constant of 5 x 10 3M −1s −1 [25°C, μ = 0.1 m (LiCF 3SO 3)]. The rate-limiting process for the second stage is electron transfer within the assembled multinuclear complex. Subsequent slower stages correspond to breakup of the multinuclear Ru(II) 2-Ti(IV) complex formed by electron transfer. The overall rate of reduction of this oxidant by Ti(HEDTA) is less than the corresponding rate for the reaction in which Ti 3+ acts as reductant, mainly because the stability of the binuclear complex is reduced by the presence of the aminoacid ligand. The data are consistent with the conclusion that the ligand increases the rate of intramolecular ET, probably by reducing geometric change associated with oxidation of Ti(III) to Ti(IV).