Platinum binuclear compounds

Among the less common oxidation states those of I and III have the most significance. Complexes of platinum(III) have been of interest for many years because of their intermediacy in substitution reactions of platinum(II) and (IV). More recently binuclear platinum(I) and (III) complexes have been isolated, and the chemistry of these new complexes will be of increasing interest in platinum chemistry. Platinum forms strong homometallic bonds giving rise to multimetallic chain compounds and cluster complexes. The increasing use of X-ray crystallography, and 31P and 19 PtNMR will allow systematic studies to be made on these multimetallic platinum complexes. 

Binuclear platinum complexes with the o -pyridinato ligand can be formed with the metals in a divalent oxidation state. Two such complexes are the head-to-tail dimer [Pt(QH4NO)(NH3)2]2+ and the head-to-head tetramer [Pt2(CsH4NO)2(NH3)4]2+. This tetrame-ric platinum(II)-(II) compound is prepared under experimental conditions where the pH is kept around neutrality to avoid the formation of the partially oxidized complex.1120 Platinum-195 NMR spectroscopy can be used to show that the head-to-head to head-to-tail isomerization of these complexes involves dissociation of one ligand arm followed by an intramolecular linkage isomerization. Finally bond formation occurs between the divalent platinum with the vacant coordination site and the uncoordinated end of the ligand.1121... 

A number of dppm complexes with hydride and methylene bridges have been referenced already in this chapter under the respective sections on hydrides and carbenes. These compounds will not be included again here. The binuclear platinum(I) chemistry of these complexes has also been developed. The complexes have a metal-metal bond between platinums, although this may be broken by formation of A-frame type molecules. This chemistry has been described in a series of papers, and the reaction types are outlined in Schemes 13 and 14, i28 .1438-1445 a similar chemistry will likely develop with the methylated ligand Me2PCH2PMe2.1450... 

Several blue tetra- and octanuclear Pt complexes, prepared upon reaction of cis-[Pt(NH3)2(H20)2]2+ with open and cyclic amides, as well as cyclic imides and a uracil nu-cleobase, and comprised of binuclear building blocks interacting through Pt-Pt bond formation, have been isolated and structurally characterized in recent years. Without exception, the average Pt oxidation state in these compounds is 2.25. Nevertheless, the structure and mode of action as antitumor agents of the Platinum Pyrimidine Blues , as prepared by Rosenberg in the early 70 s, remain elusive. This account represents a summary of our present knowledge on cationic Platinum Blues , with a focus on those blues obtained from cis-[Pt(NH3)2(H20)2]2+ and pyrimidine nucleobases, and presents speculations on reasonable alternative structures. 

In 1982, novel diplatinum(II) diphosphite complexes were reported162. These compounds were readily generated by oxidative addition to the binuclear platinum(II) tet-rakis(diphosphite) complex, [Pt2(pop)4]4 (pop = P205H2 ), with halogens or methyl... 

The checkers find that the pale green color is due to traces of oxidized binuclear platinum compounds. In order to obtain ultrahigh-purity crystalline material for solid state measurements, further purification by recrystallization is necessary. Alternatively, cations other than potassium can be used, since the nature of the counterion affects the solid state trace impurities that are occluded. 

In recent years, a number of low-valent group 10 complexes with anionic pincer ligands have been isolated and characterized. Milstein investigated the chemical reduction of palladium [81] and platinum [82] complexes with PCP Hgands with sodium (Scheme 2.8). The Pd-pincer framework of complex 2 does not resist reduction and collapses, giving rise to the unusual binuclear complex 29. In this compound, both PCP ligands are covalently bound to one of the Pd atoms, which... 

We bave previously prepared and described binuclear orthometallated complexes of palladium(II) which could be used as precursors to prepare potoitially mixed-valence compounds. Hie presence of unusual Pd-N amido bonds in these complexes adds further interest based cm the reactivity shown by amides of the platinum group metals. ... 

The demethylation of methylcobalamin by various platinum compounds requires the presence of species in the II and IV oxidation states. The initial step involves the platinum(II) complex, for example, [PtCU] , which gives a binuclear intermediate, equation (39), that in turn reacts with platinum(IV) to give methylplatinum(IV) species such as [CH3PtCl5f either directly or via a trinuclear intermediate, as in equations (40) and (42), respectively ... 

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