Platinum palladium compounds

Nitro groups are readily reduced to primary amines by a variety of methods Cat alytic hydrogenation over platinum palladium or nickel is often used as is reduction by iron or tin m hydrochloric acid The ease with which nitro groups are reduced is especially useful m the preparation of arylamines where the sequence ArH ArN02 ArNH2 IS the standard route to these compounds... 

Selenium occurs in the slimes as intermetallic compounds such as copper silver selenide [12040-91 -4], CuAgSe disilver selenide [1302-09-6], Ag2Se and Cu2 Se [20405-64-5], where x < 1. The primary purpose of slimes treatment is the recovery of the precious metals gold, silver, platinum, palladium, and rhodium. The recovery of selenium is a secondary concern. Because of the complexity and variabiUty of slimes composition throughout the world, a number of processes have been developed to recover both the precious metals and selenium. More recently, the emphasis has switched to the development of processes which result in early recovery of the higher value precious metals. Selenium and tellurium are released in the later stages. Processes in use at the primary copper refineries are described in detail elsewhere (25—44). 

Platinum, palladium, and rhodium will function well under milder conditions and are especially useful when other reducible functions are present. Freifelder (23) considers rhodium-ammonia the system of choice when reducing -amino nitriles and certain )5-cyano ethers, compounds that undergo extensive hydrogenolysis under conditions necessary for base-metal catalysis. 

Despite the fact that PtL3X2 and PtXs- species have an 18-electron configuration, 5-coordinate palladium(II) and platinum(II) compounds are rare. One of the first examples to be established was Pt(SnCl3)5-... 

Compared with the plethora of platinum(IV) compounds, the palladium(IV) complexes are as yet relatively few in number [10, 11]. When isolable, they tend to resemble the corresponding platinum compounds. 

A review27 has 554 references, on palladium and platinum coordination compounds. 

For preparing organotin trichlorides by this route, the slowest step is the reaction of R2SnCl2 with SnCLr, and it has been shown that this reaction (and that of ILtSn) is catalyzed by platinum and palladium compounds, for example, Equation (127).329... 

The reaction of alcohols with CO can also be catalysed by palladium iodides, and various ligands or solvents. Acetic acid is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a palladium compound, an ionic iodide compound, a sulfone solvent at conditions similar to those of the rhodium system (180 °C, 60 bar), and, in some cases, traces of a nickel-bipyridine compound were added. Sulfones or phosphine oxides play a stabilising role in preventing metal precipitation [26], Palladium(II) salts catalyse the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective [27],... 

Although all of the above elements catalyze hydrogenation, only platinum, palladium, rhodium, ruthenium and nickel are currently used. In addition some other elements and compounds were found useful for catalytic hydrogenation copper (to a very limited extent), oxides of copper and zinc combined with chromium oxide, rhenium heptoxide, heptasulfide and heptaselen-ide, and sulfides of cobalt, molybdenum and tungsten. 

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

Before 1970 there was very little unleaded gasoline on the market, but by 1974 all gas stations were offering it. In 1974, unleaded fuel had become a necessity for most new cars because of their catalytic converters placed in the exhaust system. These contain platinum or palladium compounds that act as a surface catalyst to bum the hydrocarbons more completely. But lead coats the platinum and palladium and deactivates the converters, so unleaded gas must be used. Up to 4 g/gal of lead could be used in the 1970s, but this was decreased to 0.1 g by 1986. Since 1995 no leaded gas could be used in the U.S. Fig. 7.6 shows the dramatic shift from leaded to unleaded gas between 1975 and 1992. 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

The compounds discussed in this section are restricted to nickel, as the existence of palladium (I) or platinum (I) compounds has not been established. Since nickel(I) contains nine d-electrons, analogies with copper(II) might be expected, but these do not arise there are, however, certain similarities with cobalt(O), particularly in the tendency to dimerization. 

Platinum(II) compounds are to be found only towards the bottom of this scheme, palladium(II) reaches further up, its fluoride belonging to the tetragonal, paramagnetic class. Nickel(II) complexes cover the whole range of behavior, and may in addition be tetrahedral. 

Bivalent halides.—These halides include those of beryllium, mangesium, zinc, cadmium, mercury, copper, lead, tin, platinum, palladium, etc. They could be subdivided into at least two classes typified (i) by KCl.MgCl2 and (ii) by 2KCl.MgCl2 2NH4Cl.CuCl2.2HoO etc. P. Pfeiffer represents known and unknown compounds by the scheme ... 

Although complexes with these ligands are common in palladium(II) chemistry, their occurrence is more scarce in platinum(II) compounds. Nevertheless these complexes can be prepared, examples being platinum(II) complexes of the optically active quadridentate Schiff base of salicylaldehyde and (R)-l, 2-diamines.1212 An alternative synthesis involves formation of the Schiff base by reaction of a complexed amino ligand on platinum(II) with amide acetates (equation 372).1213... 

P NMR spectroscopy.53 Steric factors account for the different coordination modes, while the influence of electronic factors is evidenced by the difference in structure between analogous palladium(II) and platinum(II) compounds, for example, the thiocyanates are N- and S-bonded in [Pd(NCS)(SCN)(diars)], but only S-bonded in [Pt(SCN)2(diars)].54 These and other diphosphine or diarsine complexes of palladium(II) with thio- or seleno-cyanate ligands are further discussed in Section 51.8.2.6. 

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