Platinum IV , compounds

Platin-oxyd, n. platinum oxide, specif, platinic oxide, platinum(IV) oxide. -oxydul, n. platinous oxide, platinum(II) oxide, -oxy-dulverbindung, /. platinous compoimd, platinum (II) compound, -oxydverbindung, /. platinic compound, specif, platinum (IV) compound. 

The most important of the tertiary phosphine complexes of platinum(IV) are Pt(QR3)2X4, generally prepared by halogen oxidation [174] of cis- or trans-Pt(QR3)2X2 (Q = P, As, R = alkyl Q = Sb, R = Me), since direct reaction of the platinum(IV) halides with the ligands leads to reduction. Once made, the platinum(IV) compounds are stable to reduction ... 

Compared with the plethora of platinum(IV) compounds, the palladium(IV) complexes are as yet relatively few in number [10, 11]. When isolable, they tend to resemble the corresponding platinum compounds. 

The use of this phosphine facilitates assignment of configuration as virtual coupling is observed when the phosphines are trans (section 2.9.5).) Syntheses follow established routes using methyllithium as an alkylating agent the platinum(iV) complexes can be made by direct alkylation of platinum(IV) compounds or by oxidative addition to platinum(II) species. 

The platinum(IV) compound that has shown most promise is carboplatin (paraplatin), which received FDA approval in 1990. Features to note in its structure are the use of hydroxy and carboxylate groups to improve water solubility. As noted above, the ammine ligand has been found to need at least one hydrogen, possibly for hydrogen-bonding to phosphate groups in the DNA (Figure 3.116). 

Figure 3.117 (a) JM-216, a platinum(IV) compound under clinical tests as an orally administered anti-tumour agent (b) the platinum(II) product of in vivo reduction, likely to be the active... 

The active Pt(IV) compounds are octahedrally coordinated and possess axial bound chloride or—to improve the solubility—hydroxo ligands, i.e., two Y ligands in the trans orientation. These compounds are far more inert than the corresponding Pt(II) compounds that lack these axial ligands. Most likely the Pt(IV) compexes are reduced in vivo to the corresponding Pt(II) complexes, which are in fact the active species (17-19). They can therefore be considered as a type of prodrug that requires in vivo activation (substitution and reduction) to the square-planar Pt(II) compounds to exhibit antineoplastic activity. This hypothesis is supported by the observation that platinum(IV) compounds are unable to react with DNA under ambient conditions (19), and that appreciable amounts of Pt(II) derivatives can be detected in the urine of Pt(IV)-treated patients(fS). 

Platinum(ll) hydroxide is made by adding KOH to a solution of platinum 11) chloride. 1 he unstable black powder is easily oxidized by air and must therefore be handled in an inert atmosphere. In hoi alkali or HC1, it disproportionates into the platinum(IV) compound and the metal. Very careful dehydration results in tire formation of a gray pov/dcr that approaches the composition of platinum(II) oxide. Platinum(II) oxide can also be made by combining the elements at 420 440 C at an 0> pressure of 8 atm. 

In the recent time, a great interest was aroused for platinum IV compounds. The scientists-organochemists of the Institute of Theoretical Problems of Chemical Physics synthesized complexes of platinum IV with aminonitroxyl radicals. These compoimds were tested on the experimental model of P-388 leukemia. In the experiments, the complexes exhibited a strong effect on mice-leukemia-carriers sometimes to complete recovery the toxicity reduced two- to four-fold [70]. 

The product is a useful starting material for the preparation of several platinum(IV) compounds such as dichlorodihydroxo(ethylenediamine)platinum(IV), [Pt-(en)(OH)2Clj], and tetrachloro(ethylenediamine)platinum-(IV), [Pt(en)Cl4]. - ... 

Werner studied cobalt(III), chromium(III), platinum(II), and platinum(IV) compounds because they are inert and can be more readily characterized than labile compounds. This tendency has continued, and much of the discussion in this chapter is based on inert compounds because they can be more easily crystallized from solution and their structures determined. Labile compounds have also been studied extensively, but their study requires techniques capable of dealing with very short times (stopped flow or relaxation methods, for example, temperature or pressure jump, nuclear magnetic resonance). 

Palladium(IV) and platinum(IV) compounds are accessible by oxidative addition of organic halides to the corresponding divalent species. In general, the Pt(IV) derivatives are more stable, but a number of organopalladium(IV) compounds have been isolated. 

The compound is a dark red-purple dichroic cystalline material. In time, the crystals develop a thin coating of sulfur. The rhodium(III) complex, which appears to be structurally similar to the platinum(IV) compound, shows much greater reactivity in that sulfur is readily lost on dissolving in water, dimethyl-formamide, or pyridine. From water, a product may be precipitated which appears to contain the [RhSi0] anion. Reaction with cyanide ultimately produces the thiocyanato complex. 

The availability of equipment to measure molar conductivity of solutions was turned to good use. It is interesting to note that coordination chemists still make use of physical methods heavily in their quest to assign structures - it s just that the extent and sophistication of instrumentation has grown enormously in a century. What conductivity could tell the early coordination chemist was some further information about the apparently ionic species inferred to exist through the silver ion precipitation reactions. This is best illustrated for a series of platinum(IV) complexes with various amounts of chloride ion and ammonia present (Figure 3.1). From comparison of measured molar conductivity with conductivities of known compounds, the number of ions present in each of the complexes could be determined. We now understand these results in terms of modern formulation of the complexes as octahedral platinum(IV) compounds with coordinated ammonia, where coordinated chloride ions make up any shortfall in the fixed coordination number of six. This leaves in most cases some free ionic chloride ions to balance the charge on the complex cation. 

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