Redox Equilibration Observed for the Reduction of a Ruthenium(III) Complex by Ascorbate under Low‐Driving‐Force Conditions

Abstract

A detailed kinetic study of the reduction of trans‐[RuCl2(dipicOEt)2]–, where dipicOEt = dipicolinate mono ethyl ester anion, by l‐ascorbic acid that leads to the formation of the corresponding RuII complex, was carried out spectrophotometrically using the stopped‐flow technique. The reaction was studied as a function of [AscH2]T and pH. The observed kinetic traces could only be fitted by a three‐exponential function, characteristic of three parallel reaction paths. The complex was isolated as {[Na(H2O)2][trans‐RuCl2(dipicOEt)2]}n, of which a single‐crystal X‐ray diffraction structure was determined. Detailed spectroscopic studies on the complex in aqueous solution showed that, under the selected experimental conditions, only a single complex species is present in solution. The observed complication is suggested to arise from the low driving force of the reaction during which the reoxidation of RuII by the semioxidized l‐ascorbic acid, that is, ascorbyl radical Asc·–, accounts for the apparent three‐exponential behavior of the reaction. The results are in excellent agreement with those of a recent study on the same reaction for cis‐dichloridobispicolinatoruthenate(III) (Eur. J. Inorg. Chem. 2016, 5380–5386).