Platinum aquo complexes

Spectroscopic and crystallographic studies of platinum-base complexes give some insight into the reactivity of the platinum compounds and their possible binding sites on DNA. The reactions of the different nucleosides or nucleotides with the chloro and aquo derivatives of O Cs- and trans-DDP have been studied by UV spectroscopy (36), raman difference spectrophotometry (37) and high pressure liquid chromatography (38). For both chloro isomers, the rates of the reactions with various nucleic acid monomers show the following trend GMP > AMP > CMP and dG > dA > dC T, The dichloro and diaquo derivatives react slowly with thymidine and UMP (37) or not at all (38, 39). 

Such aquo complexes react with triphenylphosphine yielding the corresponding phosphino compound. It is noteworthy that while the dinuclear platinum complexes do not react with water to produce the hydroxo compound and the formation of this hydroxo compound requires the refluxing of the halide complexes with KOH or NBU4OH for 24 hours, the silver derivatives decompose in solution with NBU4OH and react with water under mild conditions to form the hydroxo complex. Similarly, while the dinuclear platinum complexes do not react, for instance, with tht to cleave the bridging Pt(y(i-X)Pt system, the aquo silver compound reacts with tetrahy-... 

Since "aquo-complexes" of platinum(ll), prepared by treating the chloro-complexes with aqueous silver nitrate solution, did interact with both thymine and uracil to give the platinum-pyrimidine blues (25), it was evident that the interaction of the chloro-complexes with DNA bases could be different from that... 

Thus we can understand that, while aquo-complexes of platinum(ll) exist in solution, it will be difficult to isolate them as solids unless a strong hydrogen-bonding species is used as a counter-ion. Further, monomeric hydroxo-species formed by the loss of a proton from the aquo-species will be thermodynamically unstable and will tend to oligomerize to hydroxo-bridged species. 

The kinetics of ring closure of the complex cw-[Co(en)2(OH2)-(NHaCHaCHaOH)] have been studied, and are consistent with the non-observance of this species in the aquation of cw-[Co(en)2(NH2CHaCH20H)X] + cations. An associative mechanism for the ring closure of the aquo-ethanol-amine complex is proposed. The kinetics and mechanisms of analogous ring-closure reactions of similar platinum(n) complexes are discussed in the appropriate section of Chapter 2 of this Part. Kinetic parameters for aquation of the isomeric cations cw-[Co(en)2LBr]2+ with L = 3- or 4-methylpyridine show the expected similarity. ... 

The Aquopalladium(II) Ion Compounds of Oxo Acids. Palladium, but not platinum, forms the aquo ion, and brown deliquescent salts such as [PdiH20)4] (C104)7 can be crystallizedTrom solutions of PdO in dilute non-complexing acids. In 3.94M HC104 the formal potential Pd/Pd2+ is -0.979 V at 25°.9... 

Fig. 2.3. Structures of principal second-generation platinum complexes (23) CBDCA diammine(l,l-cyclobutane-dicarboxylato)platinum(II) (24) CHIP [cis-difMoxo-trans-dihydroxy-cf>bis(isopropylamine)platinum(IV) (25) 4-carboxyphthalato(l,2-diaminocyclo-hexane)platinum(II) (26) TNO-6 (aquo)sulfato(l,l-bis-aminomethyl)cyclohexane)plati-num(II) (27) MALEN malonato(ethylenediamine)platinum(II).

One type of reaction where a palladium(n)-platinum(n) reactivity comparison is not possible is that of substitution at [Pd(OHa)4] +. Indeed substitution reactions of this cation provide a uniquely interesting case of complex formation from a square-planar aquo-cation. The rate law for the reaction of [Pd(OH2)4] + with chloride or bromide ion is... 

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