Ligand substitution reactions platinum

Square planar complexes of palladium(II) and platinum(II) readily undergo ligand substitution reactions. Those of palladium have been studied less but appear to behave similarly to platinum complexes, though around five orders of magnitude faster (ascribable to the relative weakness of the bonds to palladium). 

As already mentioned, complexes of chromium(iii), cobalt(iii), rhodium(iii) and iridium(iii) are particularly inert, with substitution reactions often taking many hours or days under relatively forcing conditions. The majority of kinetic studies on the reactions of transition-metal complexes have been performed on complexes of these metal ions. This is for two reasons. Firstly, the rates of reactions are comparable to those in organic chemistry, and the techniques which have been developed for the investigation of such reactions are readily available and appropriate. The time scales of minutes to days are compatible with relatively slow spectroscopic techniques. The second reason is associated with the kinetic inertness of the products. If the products are non-labile, valuable stereochemical information about the course of the substitution reaction may be obtained. Much is known about the stereochemistry of ligand substitution reactions of cobalt(iii) complexes, from which certain inferences about the nature of the intermediates or transition states involved may be drawn. This is also the case for substitution reactions of square-planar complexes of platinum(ii), where study has led to the development of rules to predict the stereochemical course of reactions at this centre. 

The kinetics and mechanism of ligand substitution reactions of square-planar platinum(II) dimethyl sulfoxide complexes have been exhaustively studied (173), and these workers conclude that the cis and trans influences and the trans effects of Me2SO and ethylene are similar in magnitude whereas the cis effect of Me2SO is about 100 times as large as that of ethylene. The results for reaction (5), where the stability constants, Kt, are reported to be 1.5 x 108 (L = S-Me2SO) and 4.5 x 108 (L = ethylene) corroborate this analogy (213). 

Nonsymmetrical ligand substitution reactions also play an important role in a number of biological processes. One of these concerns the antitumor activity of platinum metal complexes, for which substitution processes involving DNA moieties are generally accepted to... 

A solution of the isolated platinum blue compound usually contains several chemical species described in the previous section. Such complicated behaviors had long been unexplored, but were gradually unveiled as a result of the detailed equilibrium and kinetic studies in recent years. The basic reactions can be classified into four categories (l)HH-HT isomerization (2) redox disproportionation reactions (3) ligand substitution reactions, especially at the axial coordination sites of both Pt(3.0+)2 and Pt(2.5+)4 and (4) redox reactions with coexisting solvents and atmosphere, such as water and 02. In this chapter, reactions 1-4 are summarized. 

Ligand substitution reactions of planar platinum(II) complexes occur with retention of configuration such that cis reactants give cis products, and treats reactants give treats products. Substitution reactions of X- for Y in PtXL3 (equation 548) follow a two-term rate law ... 

They are prepared by ligand substitution reactions,95 sometimes using a heterogeneous catalyst such as CoCl2, activated carbon, or metallic platinum on an oxide support as in... 

Relatively high stability in ligand substitution reactions is associated with the rather high ability of platinum to form retrodative bonds. Thus the acetylene is a 77-acceptor and should therefore facilitate the trans-ligand A-type substitution 1). This has been confirmed by the data of Allen and Theophanides 18) on the hydrolysis of K[(acetylene)PtCl3],... 

A multitude of reactions of platinum compounds continues to receive attention. In particular ligand substitution reactions have been widely studied as some of these reactions have biological and pharmacological relevancei Examples of reactions in which pressure has been shown to be a valuable experimental variable, are now presented. The first is the latest... 

Kinetics and Mechanisms of Ligand Substitution Reactions of Platinum(II) Complexes... 

As stated by Chatt and co-workers, their early speculation on the role of trans-n bonding groups in ligand substitution of platinum(ii) complexes was based on the assumption that the reactions proceed by an 8 2 mechanism. However, at the time (1955) most of the observations reported on such reactions were qualitative and little had been done to use detailed kinetic studies in attempts to elucidate the mechanism of ligand substitution. Since the valence bond theory in use then assigned dsp hybridisation to the square-planar plati-num(ii) complexes, coordination chemists believed an entering nucleophile would readily attack the low energy vacant p orbital on the metal and substitution would take place by an 8 2 mechanism. Furthermore, a coordination... 

It was clear in the 1950s that there was a need for detailed kinetic studies of ligand substitution reactions of platinum(ii) complexes, and our laboratory was prepared to do this because it was engaged in such studies of octahedral substitution. However, only a brief account of our studies is given in this article. At about this time Martin and his students initiated their investigations of aquation reactions of chloroammineplatinum(ii) complexes. 

Figure 1 General Sf 2 mechanisms of ligand substitution reactions of square-planar metal complexes, such as platinum n) compounds, where S is solvent and Y is entering nucleophile...

The examples in Tables 5.7 and 5.8 illustrate the magnitude of the trans effect and cis effect on the ligand substitution reaction of typical platinum(II) coordination and... 

---