Platinum complexes cyanides

Procedure. One drop of a saturated mercuric cyanide solution, followed by a drop of the test solution, and a further drop of mercuric cyanide solution, are placed on filter paper. The palladium is precipitated as palladous cyanide in the middle of the fleck, whereas the gold and platinum complex cyanides diffuse outwards, and can be completely washed away with several drops of water. Stannous chloride is then placed on the middle of the fleck. A dark orange to yellow-gold color appears if palladium is present. 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

PLATINUM COMPLEXES OF GROUP IVA LIGANDS 52.4.1 Monomeric Platinum(II) Cyanide Complexes... 

Complexes of platinum having cyanide and non-stoichiometric quantities of halide ligand have been prepared. A review by Miller gives a broad coverage of this subject,285 and a book series Extended Linear Chain Compounds has a number of articles which are of direct interest and relevance to workers in this field.286 This section will only briefly cover the topic, and will emphasize the more recent work. 

Platinum complexes incorporating an optically active amine have been employed for resolution of racemic mixtures of optically active olefins by reaction of the olefin with dichloro-platinum(II). The differing solubility of the diastereoisomers permits separation by fractional crystallization and the olefin can be recovered by reaction of the complex with aqueous alkali cyanide. Using either (-f)-l-phenyl-2-aminopropane (Dexedrine) or (-f)- or (—)-a-phenyl-ethylamine. Cope and co-workers have resolved the optical isomers of trans double bond coordinated and, with (—)-phenylethyl-amine)dichloroplatinum(II), a bridged complex with each double bond coordinated to a different platinum atom. 

The zerovalent cyanometallates are compounds with strong reducing properties, and they are known to reduce water. The stability of these complex cyanides decreases with increasing atomic number. The nickel compound is stable in vacuo) up to 160° C. the palladium compound decomposes slowly in vacuo) at ordinary temperatures, while the platinum derivative could not be isolated at all. 

Use for resolution of cycloalkenes. W s-Cycloalkenes of intermediate size (Cg-Cjo) should be capable of existing in enantiomeric forms because of the inability of the trans double bond to rotate with respect to the remainder of the molecule. But in the absence of salt-forming groups, resolution cannot be accomplished by the usual methods of forming derivatives. However, Cope et al.s found that the strong tendency of an alkene to complex with a platinum compound provides an effective method of resolution. The complex of ethylene with platinous chloride and (+) or (-)-a-methylbenzylamine exists in only one form since ethylene is symmetrical. But addition of the base to a solution of the platinum complex of trans-cyclooctene opens the way for formation of the diastereoisomeric complexes derived from the R- and S-forms of the base. Fractional crystallization at —20° (liquid at 25°) effected separation. Liberation of the (—)-hydrocarbon from the complex with potassium cyanide gave a product of aD — 411°. 

Discovered more than 70 years ago, hydroformylation is nowadays one of the most important reactions in the chemical industry because aldehydes can be transformed to many other products. In the enantioselective version, rhodium/ diphosphorus ligand complexes are the most important catalytic precursors, although cobalt and platinum complexes have also been widely used. For these systems, the active species are pentacoordinated trigonal-bipyramidal rhodium hydride complexes, [HRh(P-P)(CO)2]. In those complexes, the coordination mode of the bidentate ligand (equatorial-equatorial or equatorial-apical) is an important parameter to explain the outcome of the process. The most common substrates of enantioselective hydroformylation are styrenes followed by vinyl acetate and allyl cyanide. With these substrates, mixtures of the branched (b, chiral) and linear (1, not chiral) aldehydes are usually obtained. In addition, some hydrogenation of the double bond is often observed. Therefore, chemo- and regioselectivity are prerequisites to enan-tioselectivity and all of them must be controlled. An additional eomplieation is that chiral aldehydes are prone to racemise in the presenee of rhodium spe-... 

Of great interest is the use of intermetallic compounds of platinum with rare-earth metals such as cerium and praseodymium for anodic methanol oxidation, known from the work of Lux and Cairns (2006). This combination is attractive inasmuch as it involves two metals that differ strongly in their own electrode potentials Pt with = -1-1.2 V and Pr with = —2.3 V(SHE), and thus in their electronic structure. However, for the same reason, traditional methods of preparing joint disperse deposits of these metals by chemical or electrochemical reduction in a solution of the corresponding salts fail in such a situation. Lux and Cairns developed a new technology for preparing disperse powders of such compounds by thermal decomposition of complex cyanide salts of these metals. The catalyst obtained had some activity in ethanol oxidation (although somewhat... 

Substitution of nickel, palladium, and platinum complexes forms part of a recent review on the kinetics of reactions of these compounds. A review up to 1971 on the chemistry of Co cyanides contains references relevant to Sections 2 [Mixed-ligand Carbonyls displacement of CO], 3, and 4 of this chapter. ... 

By the use of masking agents, some of the cations in a mixture can often be masked so that they can no longer react with EDTA or with the indicator. An effective masking agent is the cyanide ion this forms stable cyanide complexes with the cations of Cd, Zn, Hg(II), Cu, Co, Ni, Ag, and the platinum metals, but not with the alkaline earths, manganese, and lead ... 

C and weighed. The precipitate is almost insoluble in hot water, but dissolves readily in ammonia and cyanide solutions. Gold is reduced to the metal by the reagent, and platinum (if present in appreciable quantity) is partially precipitated either as a greenish complex compound or as the metal, upon boiling the solution. The precipitation of palladium is not complete in the presence of nitrates. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Hydrogen cyanide reactions catalysts, 6,296 Hydrogen ligands, 2, 689-711 Hydrogenolysis platinum hydride complexes synthesis, 5, 359 Hydrogen peroxide catalytic oxidation, 6, 332, 334 hydrocarbon oxidation iron catalysts, 6, 379 reduction... 

---