Platinum hydroxo

In 1979, the first isolation of the hydrido(hydroxo) complex by oxidative addition of water to an electron-rich platinum(O) complex was accomplished by Yoshida and Otsuka [22]. Highly coordinatively unsaturated bis(triisopropylphosphine)platinum (24b) can activate water very easily at room temperature to give the hydrido(hydroxo)... 

Hydrido(hydroxo) complexes derived from the oxidative addition of HjO to [Pt(PR3)3] (26) are stronger bases than aqueous alkali in organic media. Platinum(O)... 

A comprehensive study of aminolysis reactions involving dinuclear platinum(II)-hydroxo complexes has been described.176 Treatment of the di-/i-hydroxo complexes of the type [Pt2-(/i-OH)2(L2)2]2+ with an excess of aryl amine RNH2 (L = PPh3, R = Ph, p-tolyl, /)-Bu Cr,I I4,... 

The hydroxo-compoimd of the series, dihydroxo-diainmino-platinum, [Pt(NH3)2(QH)2], is formed by treating the sulphato-derivative with baryta water. A solution is obtained which is strongly alkaline, liberates ammonia from ammonium salts, absorbs carbon dioxide, and precipitates metallic salts. From the solution the hydroxide may be easily crystallised.1... 

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). 

The relative amounts of all these Pt species vary as a function of the pH and the chloride concentration. Only platinum species with a coordinated water molecule are regarded to be reactive, because, in contrast to coordinated chloride or hydroxide, this ligand can be easily substituted by other donor molecules. Hydroxo species are formed as indicated in Eqs. (3)-(7) (34, 35), with [ds-Pt(NH3)2(OH)2] as the stable end product in basic solution (36). It should be noted, however, that this species very easily dimerizes and trimerizes at higher concentrations, producing ions such as [cis-Pt(NH3)2]2(jU.-OH)2 and [cis-Pt(NH3)2]3(ju,-OH)3, as has been proved with, e.g., 195Pt NMR spectroscopy (36a, b). Very recently, accurate pAa values have been presented for the (de)hy-dronation equilibria (36b) the pKa values have been added to Eqs. (5)—(7). Miller and House (36c) have accurately determined the kinetic parameters for the several hydrolysis reactions. They concluded that acid hydrolysis of cis-Pt in vivo is unlikely to proceed beyond [cis-Pt(NH3)2Cl(H20)]+. 

W-(2-Aminoethyl)-l,2-diaminoethane (dien) yields complexes [PdX(dien)]X (X = Cl or I) 204,20s a range of solvated complexes may be obtained by reaction of [Pdl(dien)] with AgC104 in the appropriate solvent. As for the platinum analogue, the aqua complex [Pd(dien)(H20)](C104)2 reacts with tetraphenylborate to yield [PdPh(dien)](BPh4). Reaction of the hydroxo complex with carbon monoxide yields C02 and palladium metal is deposited.206... 

The [Hg3(OH)2]4+ cation has a zigzag structure 78 the [Hg(OH)]+ cation, in its chlorate and bromate salts, is an infinite chain analogue (17).79 A related cyclic /x-hydroxo trimer (18) is found in a platinum(II)-diaminocyclohexane complex.69... 

Platinum-alkylperoxo and -hydroperoxo complexes are much less effective ketonization reagents than their palladium analogs. The platinum-hydroperoxide complex generated by protonation of Pt(PPh3)202 as in equation (90) was found to be inactive,133 as well as Pt(CF3)(OOH)(depe) obtained from the reaction of H202 with the corresponding hydroxo complex.265... 

Mononuclear Hydroxo, Methoxo, and Hydrido Complexes of Platinum(ll)... 

Unexpectedly, the methoxo complex shows no tendency to decompose to a hydride by / -elimination, although it does react immediately with water to give the hydroxo complex. In contrast, cyclohexyne bis(triphenylphosphine)platinum(0) reacts with methanol to give a hydrido complex, presumably via an undetected intermediate methoxide (see Equation 3) ... 

A wide range of alkyl- and aryl-hydroxo-bis(tertiary phosphine) complexes of platinum(II) has been prepared now (17, 18, 19, 20, 21), generally by the route shown in Equation 4 or some variant of it... 

Hydrido-hydroxo complexes of platinum(II) are believed to be formed by reversible oxidative addition of water to bis(ligand) platinum(O) complexes containing bulky tertiary phosphines (22). Although the equilibrium favors the platinum(O) complex, trans-[PtH(OH)(P(iso-Pr)3)2] has been isolated and identified spectroscopically (see Equation 5) ... 

The hydroxo complexes behave as strong bases in aqueous organic solvents and react with weak acids, including carbon acids such as nitromethane, methyl ketones, acetylacetone, acetonitrile, phenylacetylene and cyclopentadiene this provides a useful synthesis under mild conditions of platinum(II)-carbon a-bonded complexes, as exemplified in Equation 6 (18) ... 

Preparing trans-hydrido-alkyls or -aryls of platinum(II) does not require prior isolation of a hydroxo complex. The main routes we have used are shown in Equations 9-11, and selected spectroscopic data, including some from the literature, are in Table IV. 

For the m-cornplcxcs, a dimerization reaction to q-hydroxo species can occur (Scheme 1). Such areaction becomes significant at high platinum concentrations [20], when the pH is in the 5-7 range [24] or when the aqua species remain in solution for long periods [17]. It can be also observed with triamineaqua complexes [16]. 

The synthesis of bridging hydroxo complexes of platinum has been reported by Fakley and Pidcock (64). Treatment of bridging chloro complexes (e.g., 58) with aqueous potassium hydroxide, benzene, and a... 

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