Reactivity of some square-planar palladium( II ) complexes in aqueous solution and in heptane–AOT–water microemulsions

The substitution reactions at square-planar palladium(II) complexes {[PdX(en)]2+, where X = 2,2′-bipyridine or 4,4′-dimethyl-2,2′-bipyridine, en = ethylenediamine} with ethylenediamine or N,N-dimethylethylenediamine have been studied at 25.0 °C in aqueous solution and in heptane–AOT–water microemulsions with various molar ratios, [H2O]/[AOT]=W, the AOT concentration being kept constant at 0.12 mol dm–3.The kinetic data, obtained by using both conventional and stopped-flow spectrophotometric methods, show that the reaction rates, either in bulk aqueous solution or in the microemulsions, decrease with increasing steric hindrance of both the entering nucleophile and the ligand coordinated to the metal. Moreover, the reaction rate in the microemulsions is accelerated compared with that in the bulk aqueous solution and exhibits a dependence on the molar ratio W. The microscopic AOT/water interface is suggested as the reaction site.