Hydrogenolysis complex

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

The first commercial production of fatty alcohol ia the 1930s employed the sodium reduction process usiug a methyl ester feedstock. The process was used ia plants constmcted up to about 1950, but it was expensive, hazardous, and complex. By about 1960 most of the sodium reduction plants had been replaced by those employing the catalytic hydrogenolysis process. Catalytic hydrogenation processes were investigated as early as the 1930s by a number of workers one of these is described ia reference 26. 

When camphene reacts with guaiacol (2-methoxyphenol), a mixture of terpenyl phenols is formed. Hydrogenation of the mixture results ia hydrogenolysis of the methoxy group and gives a complex mixture of terpenyl cyclohexanols (eg, 3-(2-isocamphyl) cyclohexanol [70955-71 (45)), which... 

Progress and prospects in hydrogenation, hydrogenolysis, and desulfurization of thiophenes with soluble metal complexes 98ACR109. 

The synthesis of a benzamide with a somewhat more complex side chain starts by condensation of acid 144 with racemic cis-aminopiperidine 152. Removal of the benzyl group of 153 by hydrogenolysis gives the secondary amine 154. Alkylation on nitrogen with the halide 155 gives finally the dopamine antagonist, cisapride (156) [38,39]. 

Hydrogenation of 2,5-diacetoxy-2,5-dimethyl-3-hexyne 10 over 0% palladium-on-carbon is exceptionally complex. Seven different products are formed together with acetic acid. All are hydrogenolysis products arising from the initially formed 2,5-diacetoxy-2,5-dimethyl-3-hexene 11. One of these, 2,5-dimethyl-2-acetoxy-4-hexene 12 forms in as much as 4S yield. 

The influence of reaction variables and catalyst is complex 19,62,83,84). It is difficult to formulate generalities from available data suffice it to note that much can be done to alter the extent of hydrogenolysis in compounds susceptible to this reaction. 

In saturation of ethyl p-tolyl ether in ethanol solvent, hydrogenolysis rose with metal in the order Pd < Ru Rh < Ir < Pi ( 7). The various complex factors contributing to this ordering are discussed at length in this reference. 

Hydrogenolysis of methylenediisoxazoles have been useful in preparing substituted resorcinols and aminophenols (7). The isoxazole annelation reaction (71,89,90,91,103) is well suited to the synthesis of steroids and other complex molecules. 

Other reactions that occur during hydrocracking are the fragmentation followed by hydrogenation (hydrogenolysis) of the complex asphaltenes and heterocyclic compounds normally present in the feeds. 

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

The values of the adsorption coefficient of hydrogen for both reactions were practically identical (1.9 and 2.1 atm-1). Here, the selectivity of the branched reactions depends on the partial pressure of methylcyclopentane. This difference may be accounted for by assuming that either the cleavage of the C—C bond of methylcyclopentane in the (3-position and in the 7-position with respect to the methyl group does not take place on the same sites of the surface of platinum (or on the sites of the same activity), or that the mechanism of hydrogenolysis is more complex than that ex-... 

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... 

Reaction of Organometallic Complexes with Particles of Transition Elements The Stepwise Hydrogenolysis... 

In the presence of H2, perhydrocarbyl surface complexes loose their ligands through the hydrogenolysis of their metal carbon bonds to generate putative hydride complexes, which further react with the neighbouring surface ligands, the adjacent siloxane bridges (Eqs. 8-9) [46,47]. 

The case of butane is noteworthy since the selectivity at low conversions indicates that there is no selectivity in the overall hydrogenolysis step between n- and sec-butyl zirconium surface intermediates, while earUer studies had shown that the -alkyl zirconium complexes were more stable than sec-alkyl derivatives (Table 3 and Scheme 23) [94]. 

The formation of a stable monobutyl species obtained at 50 °C is also further demonstrated by its hydrogenolysis at higher temperatures. Indeed, treatment under H2 of the grafted surface organometallic complex, Pts[SnBu]jy, at 300 °C for 4 h generates about one butane per Sn along with traces amounts of propane, ethane, and methane. 

From these data, some key information can be drawn in both cases, the couple methane/pentane as well as the couple ethane/butane have similar selectivities. This implies that each couple of products (ethane/butane and methane/pentane) is probably formed via a common intermediate, which is probably related to the hexyl surface intermediate D, which is formed as follows cyclohexane reacts first with the surface via C - H activation to produce a cyclohexyl intermediate A, which then undergoes a second C - H bond activation at the /-position to give the key 1,3-dimetallacyclopentane intermediate B. Concerted electron transfer (a 2+2 retrocychzation) leads to a non-cychc -alkenylidene metal surface complex, C, which under H2 can evolve towards a surface hexyl intermediate D. Then, the surface hexyl species D can lead to all the observed products via the following elementary steps (1) hydrogenolysis into hexane (2) /1-hydride elimination to form 1-hexene, followed by re-insertion to form various hexyl complexes (E and F) or (3) a second carbon-carbon bond cleavage, through a y-C - H bond activation to the metallacyclic intermediate G or H (Scheme 40). Under H2, intermediate G can lead either to pentane/methane or ethane/butane mixtures, while intermediate H would form ethane/butane or propane. 

Figure 13. Nanoparticle synthesis through hydrogenolysis of zerovalent metal complexes. (Reprinted from Ref [53], 2007, with permission from Wiley-VCH.)...

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