Nucleophilic square-planar substitutions. Part III. The application of the generalisation of group mobility factors to substitutions of halogenodiethylenetriamineplatinum(II) complexes in aqueous solutions

Abstract

The kinetics for the direct replacement of halogens in halogenodiethylenetriamineplatinum(II) cations by pyridine have been determined over a range of temperatures. The relative mobilities of the outgoing groups are compared with the corresponding data for organic compounds. These reactions are mechanistically more similar to aromatic than to aliphatic substitutions. The kinetic results are discussed and an attempt is made to interpret them in terms of the electronegativity of the halogens, which facilitates bond formation with the incoming nucleophile in an associative mechanism. By analogy with aromatic substitutions, the rate order is expected to depend entirely on activation energy, and in this way, square-planar substitutions differ from octahedral substitutions where the entropy of activation exerts a significant influence on rate.