Platinum complexes constants

The aquation rate is mainly determined by the trans effect of the ligand trans to Cl. The aquation rate constants of some platinum complexes are listed in Table I. For example, the rate of hydrolysis of CP trans to c-C6HnNH2 in complex 14, a metabolite of the oral drug 11 (42), is about twice as fast as trans to NH3 (43). 

Since these substitution reactions follow a two-term rate law, it is clear that solvent effects are very significant. Poorly coordinating solvents are benzene, carbon tetrachloride and sterically hindered alcohols and strongly coordinating solvents are water, lower alcohols, DMF, DMSO, acetonitrile and nitromethane. The first-order rate constants are greater in DMSO than in water. Since the majority of precursor platinum complexes used in synthetic and mechanistic studies are halo complexes, the replacement of halide ligands by solvent and the reversibility of this reaction are important features of platinum halide chemistry. 

Rate constants for chelate ring-opening in four-coordinated square-planar cf-platinum complexes [ 1,2-bis(phenylsulfinyl)ethane]dichloroplatinum(II) by a series of pyridines show from a negative deviation in a Bronsted plot (a = 0.53) an estimated rate decrease of steric origin of 200 for the 2-picoline (81IC71) (Scheme 33). 

Platinum and palladium complexes of thietane and 3,3-dimethylthietane have been prepared as illustrated for 90. The platinum complexes exist in cis and trans configurations, but no cis-trans isomerization of the palladium complexes in the solid state was observed. Stability constants of thietane with Mn(ll), Co(II), and Ni(II) chelates have been determined. Proton nmr studies show that the absorption of the a-methylene protons, which are syn to the metal, is shifted downfield (about 0.7 ppm) more than the absorption of the protons anti to the metal (about 0.4 ppm downfield). Energies of activation for pyramidal inversion were determined. Bis-ruthenium complexes of di-, tri- and tetraspirothietanes (e.g., 90a) show rapid electron transfer between the ruthenium ions long-range electron tunneling was proposed. ... 

Moreover, NMR studies have measured the coupling constant./,, of a number of trialkylphosphine platinum complexes. Trialkyl phosphines, as shown in Figures 7-la7 and b,s have a greater trans influence than Cl, and this is reflected in the higher coupling constant (/Pt P) and lower IR Pt-Cl stretching frequency... 

Chatt already had it in mind that physical measurements would be an important part of his work so there was a constant-temperature room which contained the dielectric constant machine and later a UV-visible spectrophotometer and a home-made calorimeter for measuring heats of ds/trans-isomerisation of complexes. L. A. Duncanson and his infrared spectrophotometer, with which the crucial spectra of the olefin-platinum complexes were measured, formed part of the Organic Chemistry Department in the next hut. As soon as he could, Chatt added an X-ray crystallography unit, run by his deputy, P. G. Owston, which was located in the old stables of the main house. 

Note the coupling constant decreases as the oxidation state for platinum complexes increases. 

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