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Hydrogenation, catalytic, alkene catalysts

The choice of the metals is strictly related to the catalytic application. As we shall show later, the catal54ic reaction most commonly investigated with polymer supported M / CFP catalysts is hydrogenation (Table 3). The overwhelming majority of catalytic studies concerns the hydrogenation of alkenes and by far the most commonly employed metal is palladium, followed by platinum. Examples of rhodium and ruthenium hydrogenation catalysts supported on pol5uneric supports are very rare. [Pg.212]

One of the most famous catalysts, which operates through a mechanism involving formation of a mono-hydride (M—H), is [RuCl2(PPh3)3].38-40 In the catalytic hydrogenation of alkenes (Equations (1) and (2)) it shows very high selectivity for hydrogenation of terminal rather than internal C=C bonds. [Pg.77]

Another example of selective C=C bond hydrogenation has arisen from mechanistic studies on an iron m-hydride dihydrogen complex, [Fe(PP3)(FI)(H2)](BF4) [PP3 = P(CH2CH2PPh2)3], a catalyst inactive with alkene substrates. Scheme 6 shows that no decoordination of dihydrogen is required in any step of the cycle and that the vacant site is created by unfastening of one of the P-donor atoms (species (16)).50 Extensive studies on catalytic alkene hydrogenation by analogous tripodal (polyphosphine) Rh, Os, and Ir complexes have been carried by Bianchini and co-workers.51,52... [Pg.78]

Other catalytic hydrocarbon reactions indude decomposition of olefins over a powdered nickel catalyst [84], hydrogenation of alkenes, hydrocracking of cycloalk-enes, and water-gas shift reactions [64]. [Pg.361]

In hydrogenation, early transition-metal catalysts are mainly based on metallocene complexes, and particularly the Group IV metallocenes. Nonetheless, Group III, lanthanide and even actinide complexes as well as later metals (Groups V-VII) have also been used. The active species can be stabilized by other bulky ligands such as those derived from 2,6-disubstituted phenols (aryl-oxy) or silica (siloxy) (vide infra). Moreover, the catalytic activity of these systems is not limited to the hydrogenation of alkenes, but can be used for the hydrogenation of aromatics, alkynes and imines. These systems have also been developed very successfully into their enantioselective versions. [Pg.113]

This catalytic system was further studied by Strohmeier and Steigerwald, who performed reactions at 10 bar without solvent to achieve hydrogenation of a series of aldehydes (Table 15.1) [2]. Turnover numbers (TON) of up to 8000 were achieved in the case of the hydrogenation of benzaldehyde. The chemoselectivity of this catalyst towards carbonyl hydrogenation over alkene hydrogenation was... [Pg.414]

As recently recognized by the Nobel Chemistry award committee, the conceptualization, development, and commercial application of enantioselective, homogeneous hydrogenation of alkenes represents a landmark achievement in modem chemistry. Further elaboration of asymmetric hydrogenation catalysts by Noyori, Burk, and others has created a robust and technologically important set of catalytic asymmetric synthetic techniques. As frequently occurs in science, these new technologies have spawned new areas of fundamental research. Soon after the development of... [Pg.107]

The steric effects may be more pronounced in heterogeneous catalysts than in homogeneous reactions in solution. The rigid, solid surface restricts the approach of the reactants to the active centers and interaction between the reactants. The steric requirements are quite stringent when a two-point adsorption is necessary and when, in consequence, the internal motion of the adsorbed molecules is limited. In this way, the stereoselectivity of some heterogeneous catalytic reactions, for example, the hydrogenation of alkenes on metals (5) or the dehydration of alcohols on alumina and thoria (9), have been explained. [Pg.154]

Biphasic systems containing an ionic liquid and supercritical CO2 have been used effectively for catalytic hydrogenation of alkenes. The ionic liquid phase containing the catalyst could be reused (2/6). [Pg.207]

Only one paper has reported on catalytic asymmetric hydrogenation. In this study by Corma et al., the neutral dimeric duphos-gold(I)complex 332 was used to catalyze the asymmetric hydrogenation of alkenes and imines. The use of the gold complex increased the enantioselectivity achieved with other platinum or iridium catalysts and activity was very high in the reaction tested [195] (Figure 8.5). [Pg.475]

The structure of Os3(/r-H)2(CO)10 has been established by X-ray8 and neutron diffraction.9 The 46-electron complex displays a relatively high reactivity under mild conditions, associated with a stable triosmium framework and has been extensively studied as a model for the chemisorption of alkenes and alkynes on surfaces and in the catalytic isomerization and hydrogenation of alkenes.10 When supported onto alumina it is a catalyst for the methanation of CO and C02 slightly less efficient than NiOs3(/r-H)3(CO)9(,5-CsH5)>... [Pg.368]

The water-soluble Ru(II) complex [Ru(i76-C6H6)(CH3CN)3](BF4)2 catalyzed the biphasic hydrogenation of alkenes and ketones with retention of the catalyst in the aqueous phase (87). However, the ruthenium complex moved to the organic phase when benzaldehyde was hydrogenated. In a benzene-D20 system, H-D exchange was observed between H2 and D20. Both monohydridic pathway and a dihydridic pathway are possible for hydrogen activation, and these two different catalytic cycles influence the yield and product distribution. [Pg.489]

Alkanes are the most highly reduced of all organic compounds. As a consequence, virtually all preparations of alkanes are reductive. Alkenes and alkynes can both be reduced to alkanes by catalytic hydrogenation. While many catalysts can be employed, palladium on carbon is by far die most common. [Pg.207]


See other pages where Hydrogenation, catalytic, alkene catalysts is mentioned: [Pg.265]    [Pg.150]    [Pg.1522]    [Pg.115]    [Pg.223]    [Pg.44]    [Pg.45]    [Pg.256]    [Pg.74]    [Pg.75]    [Pg.441]    [Pg.10]    [Pg.25]    [Pg.36]    [Pg.69]    [Pg.89]    [Pg.234]    [Pg.365]    [Pg.379]    [Pg.379]    [Pg.1336]    [Pg.1338]    [Pg.1396]    [Pg.89]    [Pg.77]    [Pg.116]    [Pg.121]    [Pg.23]    [Pg.388]    [Pg.191]    [Pg.44]    [Pg.142]    [Pg.37]    [Pg.119]    [Pg.673]    [Pg.170]    [Pg.106]    [Pg.265]   
See also in sourсe #XX -- [ Pg.1057 ]




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