An old reaction in new media: kinetic study of a platinum(II) substitution reaction in ionic liquids

Abstract

We report the kinetic study of the substitution reaction of a cationic platinum(II) complex [Pt(dpma)Cl]⁺ (dpma ≡ di(2-picolyl)amine) with thioacetate in room temperature ionic liquids {[C₄C₁im][NTf₂], [C₄C₁py][NTf₂], [C₄C₁py][OTf] and [(C₃O)C₁im][NTf₂]} and molecular solvents (water, methanol and DMSO). The reaction was studied as a function of the nucleophile concentration and temperature, under pseudo-first order kinetics. The reaction follows an associative mechanism with a two-term rate law, both in the studied ionic liquids and molecular solvents. It was found that the reaction rate was higher in water, followed by the ionic liquids and DMSO and then methanol. The solvent effect on this reaction was examined using a linear solvation energy relationship based on the Kamlet–Taft solvent scale (α, β, and π*). The bimolecular reaction rate increases with increasing hydrogen bond donor ability (α) and dipolarity/polarizability (π*) of the solvent. The activation parameters ΔH^‡, and ΔS^‡ were estimated in each solvent and showed that the mechanism is the same in all solvents. No ‘ionic liquid effect’ was found for this reaction, since the reaction rates are found to be within the range observed in molecular solvents and described by the polarity parameters.