Effects of added alkali-metal and alkylammonium bromides on the kinetics of reaction between the [PdCl{Et2N(CH2)2NH(CH2)2NEt2}]+ cation and bromide ion in aqueous solutions

Abstract

Rate constants are reported for the reaction between bromide ions and the complex ion [PdCl(tedien)]⁺(tedien =NNN″N″-tetraethyldiethylenetriamine) in aqueous solution containing various concentrations of bromide salts. The first-order rate constant for the unimolecular substitution reaction decreases with increase in salt concentration, the effect being more marked through the series NBuⁿ₄⁺ > NPr₄⁺ > NEt₄⁺ > NMe₄⁺ > K⁺≃ Na⁺. Comparison of rate data and solubilities of the complex chloride salt in 1.0 mol dm ^–3 KCl, [NEt₄]Cl, and [NBu₄]Cl indicates that the dominant salt effect operates on the transition state, where hydration and ion-size effects lead to a marked destabilisation.