Platinum methylation-metalation

A large number of papers has been devoted to the influence of substituents upon the reactivity of benzene nucleus. Extensive studies concerning various benzene derivatives and catalysts from the platinum group metals have been published by H. A. Smith and his co-workers (for a summary see 36). The most consistent sets of data on alkylbenzenes are available from him and other groups of authors. Table VI summarizes the influence of the structure of a single alkyl group Table VII (94, 95, 97-103) summarizes the influence of the number and position of the methyl groups. Both series show very similar behavior on all metal catalysts, a decrease in rate with the size... 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

Methyl-metal bond cleavage also occurred in the reactions of gold(I), gold(III), and platinum(II) compounds with thiols and selenols (207-209). The reactions of gold(I) and platinum(II) complexes were much faster than those of gold(III), due to the operation of a radical chain mechanism in the former cases. For the reactions with diphenylphosphine, however, the following order of reactivity was found (209) ... 

Kambara and Nishimura studied the hydrogenation of the methyl esters of o-, m-, and p-methoxybenzoic acid over platinum group metals in f-butyl alcohol at 60°C and atmospheric hydrogen pressure.197 As seen from the results shown in Table 11.15, hydrogenolysis occurred most extensively over platinum and iridium and much less extensively over rhodium and ruthenium, especially with the meta and para isomers. It is noted that the ortho isomer was hydrogenolyzed as extensively as the meta isomer over platinum and iridium, and much more extensively than the meta and para isomers over rhodium and ruthenium. Over Pd-C the most extensively hydrogenolyzed was the meta isomer. One of the reasons for the extensive hydrogenolysis in the case of the ortho isomer can be attributed to the direct formation of methyl benzoate, which amounted to 17.1% over rhodium, 20.7% over ruthenium, and 16.6% over platinum,... 

The marked dependence of 7( P—M— P) on stereochemistry for complexes of the platinum group metals has been used in NMR spectroscopy for several years 109,115). For methyl or tert-h xty tertiary phosphines, when the two phosphines are mutually trans then a triplet pattern results, but if the two phosphines are mutually cis, then a doublet pattern results as a consequence of the spectrum being of the AA X X type and the dependence of V( P—M— P) on stereochemistry. Exactly the same behavior is found in NMR spectroscopy with the advantage that the technique is far more versatile and is not normally troubled by resolution problems. Thus for cr-[RhCl3(CO)(PBu"2Ph)2] triplet patterns have been observed for six of the eight different carbon atoms in the tertiary phosphine ligand 164). When —M—is... 

Prior to 1982, Crabtree s report of the reaction of cyclopentane with a solvated IrH2(PPh3)2+ species to give a cyclopentadienyl-iridium product stood as the only well characterized example of a reaction of an alkane with a homogeneous transition metal, in contrast to the widespread reactivity of arenes [2]. Based upon the instability of the platinum methyl hydride complex Pt(PPh3)2(CH3)H, it was believed that alkane oxidative addition might not be a thermodynamically feasible process, and consequently few attempts were made to attempt such a reaction [3]. It was not until the discovery of the formation of stable alkane oxidative addition products in 1982 that it was realized that reactions of hydrocarbons were in fact feasible. 

L. Mond and his co-workers discovered it in 1888. The platinum methyls, prepared in 1907 by W. J. Pope, were amongst the first-known transition metal alkyls, and the discovery by W. Reppe in 1940 that Ni complexes catalyse the cyclic oligomerization of acetylenes produced a surge of interest which was reinforced by the discovery in I960 of the jr-allylic complexes of which those of Pd arc by far the most numerous. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Cyan-kalium, n. potassium cyanide, -kalium-losung, /. potassium cyanide solution, -ko-balt, m. cobalt cyanide, -kohlensaure, / cyanocarbonic acid. -kupfer, n. copper cyanide, -laugerei, -laugung, /. cyaniding. cyanidation. -losung, / cyanide solution, -metall, n. metallic methyl cyanide, -natrium, n. sodium cyanide. -platin, n. platinum cyanide. 

Another example is the hydrogenation of the homoallylic eompound 4-methyl-3-cyclohexenyl ethyl ether to a mixture of 4-methylcyclohexyl ethyl ether and methylcyclohexane. The extent of hydrogenolysis depends on both the isomerizing and the hydrogenolyzing tendencies of the catalysts. With unsupported metals in ethanol, the percent hydrogenolysis decreased in the order palladium (62.6%), rhodium (23 6%), platinum (7.1%), iridium (3.9%), ruthenium (3.0%) (S3). 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

Methanol is a major bulk chemical, and its global annual production exceeds 37 million tons. It is mainly used for the production of formaldehyde and methyl 6butyl ether (MTBE). Especially, formaldehyde is dominantly used for producing resins. At present, methanol and its decomposed derivatives can be oxidized to CO2 and H2O by the proper selection of supported noble metal catalysts such as palladium, platinum, and gold. 

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