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The kinetics of the substitution reactions of [N′-(2-hydroxyethyl)ethylenediamine-N,N,N′-triacetato]-aquaruthenium(III), [Ru(hedtra)(H2O)], with X (Br−, CH3CN, SCN−, and pyridine) to give [RuX(hedtra)] were carried out at 25 °C and I=0.5 mol dm−3. The substitution reactions were found to be unusually rapid. The rate constants of the forward reaction (kf) and of the backward reaction (kb) were kf=0.13±0.01 mol−1 dm3 s−1 and kb=(1.9±0.2)×10−2 s−1 for the reaction with Br−, kf=0.48±0.02 mol−1 dm3 s−1 and kb=(3.0±0.2)×10−2 s−1 for the reaction with CH3CN, and kf=7.5±0.2 mol−1 dm3 s−1 and kb=(1.3±0.8)×10−2 s−1 for the reaction with SCN−, respectively. The kinetics of the reaction of [Ru(hedtra)(H2O)] with py was studied as a function of pH. The observed rate constants of the reaction were separated into two rate constants; the rate constant of the forward reaction of [Ru(hedtra)(H2O)] with py (18±2 mol−1 dm3 s−1) and that of [Ru(OH)(hedtra)]− with py (3.0±1.0 mol−1 dm3 s−1). The mechanisms of the reactions are discussed.

Kinetic studies confirm the nucleophilic assistence of the substitutions of the coordinated H2O molecule in (I) by the [Co(NH3)5]3 + moiety bound to one of the CHzCOO" groups of the EDTA4′ ligand.

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