Anomalies in ligand exchange reactions for platinum(II) complexes

The coordination complexes of platinum(II) with their inherent inertness have provided a great variety of behaviour in their ligand substitution reactions. The present work, certainly not exhaustive of the subject, summarizes a number of results which were not to be expected in view of the coherent model of a simple nucleophilic attack which has been rather convincingly established and generally accepted. Studies of additional ligand exchange reactions employing either a stable or radio-active tracer will doubtlessly continue to provide significant information concerning these systems. It should be reemphasized that such techniques must be accompanied by thorough chemical characterization. Their utility may be seriously limited by the separation procedures; and without methods for separating al the major chemical components, a satisfactory characterization of the isotopic exchange may not result. The isotopic exchange studies so far have provided the means to fit the halides into a nucleophilicity scale for the “normal” substitution, especially in comparison to attack by solvent. By permitting the kinetics investigations to escape from the pseudo first order regions they have also made possible the demonstration of the “abnormal” processes which involve the dimer transition states. It seems that especially significant experiments will be possible investigations of the exchange catalysis for one complex by others. With the possibility of higher order reactions it also is important to investigate the dependence of the rates over the widest possible range of the concentration variables. It is hoped that the anomalies, which have been summarized, will provide a stimulus for additional experiments to ttest and tpossibly modify the models which have been discussed.