Kinetics of the displacement of chloroacetate ion from cis-bis(chloroacetato)bis(isopropylamine)platinum(II) and the (chloroacetato)(1,5-diamino-3-azapentane)platinum(II) cation

Abstract

The displacement of ClCH₂CO₂^– from cis-[Pt(PrⁱNH₂)₂(ClCH₂CO₂)₂] and [Pt(dien)(ClCH₂CO₂)]⁺(dien = 1,5-diamino-3-azapentane) by solvent, Cl^–, Br^–, and SCN^– has been studied in aqueous solution at 25.0 °C. The reactions are catalysed by acid by way of a pre-equilibrium protonation of the carboxylate ligand. In the absence of added acid the cationic monocarboxylato complex exhibits a normal nucleophilic discrimination power, comparable to that of the corresponding chloro complex and the nucleophile-independent pathway makes only a small contribution to the consumption of the substrate. In the uncatalysed reactions of the bis(carboxylato) complex, the nucleophile-independent pathway dominates the substitution by the weak nucleophile, Cl^–, and a relatively strong nucleophile, such as SCN^–, is required to make the direct substitution pathway important. The unusually large contribution from the nucleophile-independent pathway is discussed.