Nucleophilic substitution reactions at planar four-co-ordinate monoanionic platinum(II) complexes

Abstract

The kinetics of displacement of chloride from complex anions of the type [Pt(4R-pydca)Cl]^–(pydca = pyridine-2,6-dicarboxylate; R = H, Cl or OMe) by a number of anionic and neutral nucleophiles have been studied in aqueous solution, at 25.0 °C, I= 0.50 mol dm^–3(LiClO₄). Apart from the reactions with OH^–, the reactivities of the substrates are not greatly sensitive to the nature of the substituent in the 4 position. Anionic nucleophiles can be as much as two orders of magnitude less reactive than neutral nucleophiles with similar n⁰_pt values. The rate law for the reaction with OH^– takes the form –dln[substrate]/dt=k_s+k₃[OH^–]², where k_s is the first-order rate constant for the solvolytic pathway observed in all the substitution reactions, and where k₃ is sensitive to the basicity of the nitrogen in the terdentate ligand.