Kinetics and mechanism of substitution on square-planar palladium(II) complexes in mixed aqueous solvents

Abstract

The kinetics of halide replacement in the complexes[Pd(iea)X]X and [Pd(ieda)X]X [iea = iminobis(ethyleneamine) and ieda = iminobis(ethylenediethylamine); X = Cl- or l-] have been measured in a variety of mixed aqueous organic solvents. The rate expression is Rate =k1+K2[X–]. Plots of log k1 and log k2 against the Grunwald–Winstein Y values are linear with gradients of between 0.33 and 0.63. The results are interpreted in terms of a similar associative mechanism for each reaction, involving appreciable Pd–X bond cleavage in the rate-determining transition state. The utility of log k against Y plots and other linear free-energy relations (such as rate–equilibrium correlations) in elucidating the intimate mechanisms of square-planar substitutions are discussed.