Kinetics of the Ligand Substitution Reactions of a Labilized Ruthenium(III) Complex, [Ru{N′-(2-hydroxyethyl)ethylenediamine-N,N,N′-triacetate}(H2O)]

Abstract

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.

RuIII Complexes of Edta and Dtpa Polyaminocarboxylate Analogues and Their Use as Nitric Oxide Scavengers

“…[28] Alternatively, it has been proposed that the activation for associative attack of the incoming nucleophile is a result of the transient coordination of the pendant carboxylate group. [53,54] Modification of the coordination sphere can drastically change the rate of substitution. For instance, k is reduced at least one order of magnitude when a N 2 O 4 coordination environment in AMD6245 is changed to a N 2 pyO 3 coordination environment as in 14.…”

A Personal Account on Inorganic Reaction Mechanisms

“…During the late nineteen seventies to the late‐nineties, the [Ru III (edta)(H 2 O] − complex was subjected to kinetic and mechanistic studies pertaining to aqua‐substitution reaction with various substituting molecules (L) [76,79–87] . Binding to edta labilizes both the Ru(III) and Ru(II) metal centers towards aqua‐substitution reactions, with the extent of the labilization being much greater for Ru(III).…”

“…During the late nineteen seventies to the late-nineties, the [Ru III (edta)(H 2 O] À complex was subjected to kinetic and mechanistic studies pertaining to aqua-substitution reaction with various substituting molecules (L). [76,[79][80][81][82][83][84][85][86][87] Binding to edta labilizes both the Ru(III) and Ru(II) metal centers towards aqua-substitution reactions, with the extent of the labilization being much greater for Ru(III). The rate of aqua-substitution reactions of Ru III (edta) complexes outlined in (Eqs 1-3) is highly pH dependent because of the substitution lability of various [Ru III (Hedta)(H 2 O)], [Ru III (edta)(H 2 O)] À and [Ru III -(edta)(OH)] 2À species in equilibria (Scheme 5).…”