Kinetics of aquation of penta-amminechlororuthenium(III) dichloride and cis-dichlorobis(ethylenediamine)ruthenium(III) chloride hydrate in mixed water–organic solvents

Abstract

Kinetic data are reported for the spontaneous aquations of [Ru(NH₃)₅Cl]Cl₂ and cis-[Ru(en)₂Cl₂]Cl in a variety of mixed water–organic solvents. Plots of log k_H2O against Grunwald–Winstein Y values are linear with gradients ca. 0.25, suggesting essentially S_N1 mechanisms. The Hg²⁺-catalysed aquation of [Ru(NH₃)₅Cl]²⁺ has also been studied in both aqueous solution and in a variety of mixed water–organic solvents. Kinetic data in aqueous solution are consistent with pre-equilibnum formation of a chloro-bridged intermediate, [(NH₃)₅Ru–Cl–Hg]⁴⁺, followed by dissociation to release [HgCl]⁺ and the rapid pick up of water. Plots of log k_Hg²⁺ against Y values for the Hg²⁺-catalysed aquation in mixed solvents are markedly non-linear. This unusual behaviour is discussed in terms of the pre-equilibrium mechanism.