Platinum-oxalate complexes

The reaction of platinum(IV) complexes with ascorbate results in very slow reduction and for [PtCl2(OH)2(A ,A -dmen)], in the formation of the oxalate complex [Pt(C204)Cl(0H)(A , A-dmen)].508... 

We certainly do not intend these rules to restrict future research, but only to encompass a large amount of past experience with platinum(II) complexes. Obviously exceptions will, and have already, occurred. For example, the high activity of bidentate leaving groups such as oxalate and malo-nate (see structures of Fig. 4) first synthesized by M. Cleare and J. Hoe-schele in this laboratory are not encompassed nor is the effect of cyclic amines, developed by Tobe, which decrease the solubility of the complexes, but markedly enhance the antitumor activity. Here, studies of the rela-... 

Platinum dihydride complexes with small monodentate phosphines may also be prepared. Photolysis of the oxalate complexes [Pt(C204)(PR3)2] (R = Me, Et) generates the coordlnatively unsaturated bis(phosphine) species, to which H2 may add oxidatively ... 

Niobium solution, 1 mg of Nb in 1 ml. Heat 0.145 g of Nb205 in a platinum crucible with 5 ml of cone. HF until the oxide dissolves. Evaporate the solution to 1 ml, add 2 ml of H2SO4 (1 + 1), and heat to white fumes. Let cool, rinse the walls of the crucible with water, and heat until white fumes appear. Let cool, rinse the walls of the crucible with water and heat to fumes again. Repeat the operation once more to remove HF completely. Pour the niobium solution in cone. H2SO4 into 30 ml of 5% aqueous ammonium oxalate solution, dilute the clear solution of niobium oxalate complex to 100 ml, with water, and mix well. 

There has been considerable activity over the past few years in the area of oxygen exchange between chromium(m)-oxalate complexes and water. Now a consistent pattern appears to be emerging, as is shown by the discussion of recent work on oxygpn exchange with the [Cr(ox)(OH2)4]+ cation. In this, as in other chromium(m)- and platinum(n)-oxalate complexes, all the oxalate... 

In addition to the partially oxidized tetracyanoplatinates, bis(oxalato)platinate-(II) can be nonstoichiometrically oxidized by chemical oxidants13 to form highly lustrous needlelike crystals containing platinum in the 2.36 oxidation state. These complexes have not been characterized to the extent of the tetracyano-platinate complexes however, the oxalato complexes are reported to be highly conducting.13 The starting material is bis(oxalato)platinate(II), which can be prepared in 30% yields from hexachloroplatinate(lV) and potassium oxalate.9... 

Oxalo-niobates or niobo-oxalates correspond to the vanado-oxalates, and contain both oxalic acid and niobic add radicals in the complex anion. The only known series possesses the general formula 3R aO. Nb 205.6C203.a H20, where R stands for an alkali metal. The sodium, potassium and rubidium salts are prepared by fusing one molecular proportion of niobium pentoxide with three molecular proportions of the alkali carbonate in a platinum crucible. The aqueous extract of the melt jjs poured into hot oxalic add solution concentration and cooling, or addition of alcohol or acetone, then brings about precipitation of the complex salt. Comparison of the dectrical conductivity measurements of solutions of the alkali oxalo-niobates with those of the alkali hydrogen oxalates determined under the same conditions indicates that the oxalo-niobates are hydrolysed in aqueous solution, and that their anions contain a complex oxalo-niobic acid radical.6... 

Both the dry complex oxalate and its aqueous solution are unstable to direct light and deposit yellow ferrous oxalate. This property was formerly utilized in platinotypes—a photographic process by which the FeCaO produced by illumination reduces a platinic salt to a black platinum image. The oxalate is a mixture, which has been resolved into its mirror images. 

Os forms many complexes with nitnte. oxalate, carbon monoxide, amines, and thio ureas. The latter arc important analytically Osmium forms the interesting aromatic sandwich" compound, osmocene. A metallocene is described under Ruthenium. See also Chemical Elements and Platinum and Platinum Group. 

Photochemistry of Oxalate and Dithiooxalate Complexes of Nickel, Palladium, and Platinum... 

When dissolved in sulphuric acid, platinic sulphate is reduced by oxalic acid, yielding a complex sulphate of trivalent platinum, namely, Pt2(0H)6.(S03)4.(0H)2.8-5H20. This yields well-defined triclinic prisms which gradually lose water when dried over sulphuric acid under reduced pressure, yielding a stable complex, Pt203.(S03)3.H2S04.4H20. This acid is dibasic, and yields crystalline potassium, sodium, and barium salts.1... 

Whilst the platinum complex is not transformed either thermally or by addition of carbon monoxide into a Pt(0) species plus the oxalic ester, this transformation is quite easy for the corresponding palladium complex [23] ... 

Aqua ions are known but not very stable. Substitution of Pt in aqueous solution is sometimes zero-order in the added ligand, L, or can have both L-dependent and L-independent contributions to the rate, probably because intermediate formation of an unstable aqua complex is the rate-determining step for the L-independent pathway. A large number of O-donors, particularly anionic ones, give stable complexes, for example, carbonate, acetate, oxalate, acetylacetonate, and alkoxide. Tetrameric platinum(II) acetate is formed by formic acid reduction of Pt solutions in acetic acid. It does not appear to be a very useful synthetic precursor for Pt chemistry. The acetylacetonate [Pt(acac)2] is monomeric and square planar. 

The ion-pair approach to the design of photosensitizers for electron transfer processes has been followed also in the case of [Co" (sep)] -oxalate system. In a deoxygenated solution, the excitation in the IPCT band of [Co" (sep)] +-HC204 causes the reduction of [Co" (sep)] + to [Co"(sep)] " and the oxidation of oxalate to carbon dioxide. The [Co"(sep)] + complex is a sufficiently strong reductant to reduce H+ to H2 at moderately acidic pH values. Thus, when the photoreaction is carried out in the presence of colloidal platinum catalyst, such a reaction indeed occurs, and H2 evolves from the solution in addition to carbon dioxide. Under such conditions, the overall reaction is the oxidation of oxalate, which plays the role of sacrificial agent, combined with the reduction of water to yield carbon dioxide and dihydrogen, according to Eq. 8. 

The fluorescent complex [Ru(II)(3,4,7,8-tetramethylphen)3]Cl2 is readily taken up by P388 leukemia cells in culture and is visible on the cell surface, in the cytoplasm, and in the nucleus, but it does not exhibit antitumor activity in vivo (11). The platinum complexes [Pt(en)(oxalate)], [Pt(NH3)2(H20)2l (as the dinitrato complex), and [Pt(en)3] + also cause convulsions in animals (12) the latter two complexes are positively charged and relatively inert and the former is neutral and presumably undergoes an activation step before it binds to the neuromuscular junction. Curiously, the related malonato complex is not a neurotoxin. Care is taken in the clinic to administer cisplatin in saline solutions to avoid hydrolysis and minimize the production of neurotoxic aqua or hydroxobridged Pt(II) species. 

Trifluorophosphine complexes of nickel, palladium, and platinum have been obtained by direct reaction of PF3 with the metal at elevated temperatures and pressures (172). Similarly several fluorophosphine complexes of zero-valent nickel can be made under very mild conditions (60°C) using metallic nickel formed by decarboxylation of nickel oxalate... 

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