Platinum ammines trans

Platinum ammine complexes have been a fertile area for studying transinfluence. Table 3.21 lists data for a range of ammines showing how /(195Pt-15N) depends upon the trans-atom [153]. (A further selection of data can be found in R.V. Parish, NMR, NQR, EPR and Mossbauer Spectroscopy in Inorganic Chemistry, Ellis-Horwood, Chichester, 1991, pp. 76, 87.) Possibly the most detailed study (of complexes of tribenzylphosphine) examined over a hundred neutral and cationic complexes [154] (Table 3.22). 

The affinity of platinum(II) for N-donor ligands is well established. There are numerous examples in the literature of mono-, di-, and trinuclear platinum(II)-ammine and alkylamine complexes, most of which are structural analogues of the anticancer agent, mplatin (cis- PtCl2(NH3)2]), and the corresponding trans isomer. Selected novel complexes and synthetic methods are presented below. 

Osmium(IV) ammines have unusually low pXa values (see Table 5) and so persist only in strongly acidic media the complexes are more acid by an order of five to six than their platinum(IV) counterparts but only slightly more acidic than the corresponding iridium(IV) complexes. This has been correlated with the decreasing t2g electron occupancy in the series PtIV-Irlv-OsIV and attributed to charge transfer from ligands to the empty n orbitals on osmium(IV). The cis isomers are more acidic than the trans, and this can be correlated with differences between the osmium(III) and osmium(IV) complexes for the isomers.55... 

Oxalipladn was developed in an attempt to circumvent the problem of cispladn resistance noted in padents treated with cisplatin who subsequendy relapse and are retreated with cisplatin. This drug and the resistance to cisplatin are described in Chapter 15. Transplatin was included to demonstrate one of the primary structural requirements of the platinum complexes, that being that the stable ammines must be in the cis configuration. Ammines in the trans configuration, as in the case of transplatin, result in pladnum complexes that lack antitumor activity. 

The reactions of cw-[Pt(NH3)2Cl(OH2)] with L-methionine under an acidic condition and at pH ss 7 have been investigated by ID Pt and N NMR as well as 2D [ H, Nj HSQC NMR [74]. When the platinum complex is in excess in an acidic solution, the initial product, cw-[Pt(NH3)2Cl(Met-S)]+ undergoes slow ring closure to cw-[Pt(NH3)2(Met-N,S)f+. Slow ammine loss occurs to produce the isomer of c -[Pt(NH3)Cl(Met-N,S)]+ with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which tra 5 -[Pt(NH3)Cl(Met-S)2]+ isomerizes to the cis isomer, with subsequent ring closure reactions leading to the formation of cw-[Pt(Met-N,S)2] +. In contrast to methionine which is unreactive toward cw-[Pt(NH3)2Cl(OH)] at pH 7,... 

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