Platinum complexes, substitution reactions

Entering group effect platinum complexes substitution reactions, 494 EXAFS spectroscopy cadmium complexes, 929 copper(II) complexes, 720 zinc complexes, 929... 

Lanthanide shift reagents silver complexes, 806 Leaving group effect platinum complexes substitution reactions, 494 Leucine aminopeptidase zinc, 1005 Ligases zinc, 1002... 

In conclusion, nucleophilic substitution by H20, Cl, low- and high-molecular-weight thiols, and other nucleophiles plays a major role in the metabolism of platinum complexes. These reactions direct the activation, deactivation, toxification, detoxification, distribution, and excretion of platinum anticancer drugs. Given the large differences in reactivity, and the multiplicity... 

In many other cases, detailed examination of platinum(IV) substitution reactions has shown that the mechanisms involve oxidation-reduction steps. These redox reactions can be collected into two classes according to whether a bielectronic or a monoelectronic redox species reacts with the platinum complex (i.e. complementary and non-complementary redox reactions, respectively). 

Another unusual behavior of NHC TM complex was recently reported by Nolan et al. and involves the insertion of an NHC into a platinum-olefin bond. In the course of preparation of new NHC-containing platinum complexes by reaction of equimolar amounts of [(l,5-hexadiene)PtCl2] and free NHC, the substitution product (286) in which one coordinated double bond was substituted by an NHC was isolated in good yield (Scheme 48). A by-product was also... 

Platinum(Tv) Complexes. Substitution reactions at this centre are generally ligand replacements, but with the added feature of marked catalysis by platinum(n) compounds. Indeed, this area is as much one of inner-sphere redox reactions as of substitution. Recent kinetic studies include those of substitution at /ra/ij-[PtCl2L4] +, where L = NHj, amine,... 

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). 

Application of the principle of microscopic reversibility can be used to eliminate a mechanism suggested at one time for the nucleophilic substitution reactions of square-planar platinum(II) complexes. For the sake of specificity, we take PtCl - as a typical... 

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. 

Because most complexes of platinum are quite stable, substitution reactions are generally slow. For the reaction... 

Ring opening reactions are the main feature of a brief review (though with 69 references) of kinetics and mechanisms of hydrolysis and substitution reactions of platinum(II) complexes (219). 

Two examples of aquation/anation studies of chloro-platinum(II) complexes of possible medical relevance appeared in subsection 1 above 202,207). Aquation of cisplatin is slower in the presence of DNA but not in the presence of phosphate 220). DNA also inhibits substitution in [Pt(terpy)(py)]2+ and related complexes. For reaction of these charged complexes with iodide ion inhibition is attributable to electrostatic interactions - the complex is concentrated on the double helix and thus separated from the iodide, which distances itself from the helix. Intercalation of these complexes within the helix also serves to make nucleophilic approach by neutral reagents such as thiourea more difficult 221). 

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... 

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