A KINETIC-STUDY OF THE SUBSTITUTION BEHAVIOR OF AQUA AND CHLORO COMPLEXES OF ETHYLENEDIAMINEPALLADIUM(II) IN AQUEOUS-SOLUTION

Kinetic and thermodynamic data are reported for a series of substitution reactions of ethylenediamine (en) complexes of Pd(II), viz. Pd(en)(H2O)2(2+), Pd(en)(Cl)H2O+ and Pd(en)Cl2, with iodide as entering nucleophile. All reactions exhibit two consecutive steps, of which the first involves rapid anation by iodide followed by the replacement of chloride. The kinetic data for the second step suggest the participation of a common intermediate, Pd(en)(I)H2O+, which undergoes anation by iodide with a rate constant of 122 M-1 s-1 at 25-degrees-C. The temperature and pressure dependence of all reactions involved was studied and the corresponding activation parameters are reported. The data clearly reflect the role of steric hindrance during such substitution processes and are discussed in reference to related data reported for associative substitution reactions on square planar complexes in the literature.