Platinum, ligands

The suggested mechanism involves breaking of a platinum-ligand bond, again forming a platinum(IV) hydride that can then eliminate the alkane. 

A structural investif tion of the anion in Zeise s salt has shown that the ethylene occupies the fourth coordination site of the square planar complex wth the C—C axis perpendicular to the platinum-ligand plane (Fig. 15.22).75 Relative to free ethylene, the C—C bond is lengthened slightly (from 133.7 pm to 137.5 pm), and the hydregens are slightly tilled back from a planar arrangement. 

We can now identify the major factors which play a role in the DNA-platination and chelation steps i) The nature and charge of the actual platinum species, ii) the bases to be platinated and their neighboring sequences, and iii) the nature of the nonleaving platinum ligands and their eventual interaction with the nucleic acid. To get a deeper insight into these parameters, in order to achieve selective DNA-platination, the study of oligonucleotide models is an appropriate approach. 

More work is needed to clearly establish the role of outer-sphere association in DNA-platination. We can infer its influence on the rate of platination according to the relation kp = kK0 [N]/(l + K0 [N]) (with N = nucleotide-binding sites of Pt, i.e., N G, [N] [Pt]) (Scheme 3). It could also influence the selectivity of platination via selective association between the cationic species and the sites of higher negative electrostatic potential. To test this hypothesis one will have to analyze the influence of various sequences, of different types of platinum ligands, and of the ionic status of the DNA medium. 

A series of complexes with bipyridine ligands has also been described <2003EJI2749, 2004EJI4484, 20060M2074>.The reaction between 6,6 -diphenyl-2,2 -bipyridine 124 and [Pt(Me)2(DMSO)2] was carried out with a platinum/ligand ratio of 2 1 in toluene at 80 °C (Equation 44). The reaction was slow and led to the isolation of a yellow product that was insoluble in the reaction medium, was stable in air, and had high thermal stability <2006OM2253>. 

Platinum-ligand and palladium-ligand bond energies. C. T. Mortimer, Rev. Inorg. Chem., 1984, 6, 233 (50). 

Platinum ligand Thiocthcr Amide Azo Hydrazonc Ester... 

After ligands are classified with respect to their /ra s-directing ability, the information can be used to synthesize specific desired compounds. The three isomers of [Pt(N02)Cl(CH3NH2)NH3] can be prepared by the reactions outlined in Figure 4.1. The success of these syntheses depends on the trans effect order NO2 > Cr > NH3 CH3NH2. However, this information on the trans effect will not of itself permit one to propose such a reaction sequence. Another consideration is the stability of the various platinum-ligand bonds. The trans effect will explain the synthetic results in steps (a), (c), and (/) but the relative ease of replacement of chloride coordinated to platinum(n) accounts for steps (b), (d), and (e). 

After the components are mixed and heated, the catalyst initiates the cross-linking reaction by addition of the Si—H group to the double bond (eq. 37). Latent cure catalysts have been developed that allow the formulation of one-component products (499). These systems work by incorporation of platinum ligands that deactivate the platinum hydrosilylation catalysts at room temperature. When heated to temperatures above 100°C, these catalysts become active (see also Silicone Network Formation). 

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