Alkenes hydrogenation/isomerization

Alkene isomerization Alkene hydrogenation Ketone hydrogenation Hydrogenation of cyanides Hydrogenation of nitro group Alkyne hydrogenation Aminomethylation Water gas shift reaction... 

Some reactions such as alkene isomerization, alkene hydrogenation, and H2 -I- D2 exchange can be used as sensitive chemical probes of the coordination environment of metal atoms associated with surface-bound metal clusters. Other catalytic reactions such as CO -I- H2 and alkane hydroge-nolysis, which are sensitive to metal ensemble sizes, are applied as a further structural probe. Several attempts have been made to stabilize cluster frameworks in such a way that catalytic activity is maintained. One of the more promising approaches involves the introduction of a capping group into the... 

Catalyst precursor Initial TO/min Aldehyde l b ratio Alkene isomerization (%) Alkene hydrogenation (%)... 

The reverse reaction (formation of metal alkyls by addition of alkenes to M-H) is the basis of several important catalytic reactions such as alkene hydrogenation, hydroformylation, hydroboration, and isomerization. A good example of decomposition by y3-elimination is the first-order intramolecular reaction ... 

The blue solutions have been found to catalyse alkene isomerization and hydrogenation and have very considerable synthetic utility (Figure 1.8). 

When hydrogenation os isomeric alkenes does not yield the same alkane, heats of... 

Fragments derived from photolysis of Fe(CO)s have been observed to catalyze olefin isomerization and hydrogenation (65-67). The key active species for the isomerization is iron tricarbonyl which can easily add alkene to give Fe(CO)3(alkene). 

We do not have the same strict stereochemical requirements as in the E2 mechanism, and isomeric alkenes may well be produced. If several hydrogens are available for elimination, then the preferred product formed is the more-substituted Saytzeff alkene. 

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)>... 

Of the technological modifications, Fischer-Tropsch synthesis in the liquid phase (slurry process) may be used to produce either gasoline or light alkenes under appropriate conditions249,251 in a very efficient and economical way.267 The slurry reactor conditions appear to establish appropriate redox (reduction-oxidation) conditions throughout the catalyst sample. The favorable surface composition of the catalyst (oxide and carbide phases) suppresses secondary transformations (alkene hydrogenation, isomerization), thus ensuring selective a-olefin formation.268... 

In the hydroformylation of optically active alkenes, all aldehydes were shown to be formed with predominant retention of configuration.53,54 This was interpreted to prove, in accordance with the transformation of deuterium labeled alkenes,55 56 that stereoselective hydrogen shifts of the coordinated olefins occur without dissociation of the isomeric alkenes.30... 

It would be helpful if there were more experimentally determined enthalpies of isomerization to provide an independent comparison with those derived from equation 11. The most recent ones are from References 30 and 31. However, as in the analysis of the enthalpies of hydrogenation, it is only because we can derive enthalpies of formation from enthalpies of combustion, isomerization and hydrogenation that we have a large enough database of compounds to confidently attempt an analysis. The same selected alkene enthalpies of formation are used for the analyses in this section as were used in the preceding section. 

Although the hydridorhodacarborane is formally a rhodium (III) derivative, it functions as a facile catalyst in alkenc isomerization, hydrogenation, hydroformylation, and hydrosilylation reactions 80). This catalyst system is extremely stable and may be recovered quantitatively from alkene isomerization and hydrogenation reactions. In addition to these reactions, the hydridorhodacarborane is very effective in the catalysis of deuterium exchange at terminal BH positions 59). These discoveries may soon lead to industrially useful metallocarborane catalysts. 

Part II of Figure 17.75 shows the side reactions that occur when the Pd-catalyzed hydrogenation is not completely cis-selective. The start is the formation of the -complex F from the hydropalladation product E. In a way, this reaction is the reverse of the reaction type that formed E from the -complex C (cf. part I of Figure 17.75). In an equilibrium reaction, the isomerized -complex F subsequently releases the alkene iso-B, which is a double bond isomer of the substrate alkene B—and represents a type of compound that could well be the side product of an alkene hydrogenation, too. 

Osmium carbonyls on MgO and on y-ALO, among other oxides, are catalysts (or catalyst precursors) for alkene isomerization and hydrogenation (Li et al., 1984). The activity depends on the metal oxide used as a support. The ligands present on the metal during catalysis have not yet been elucidated. 

The reaction occurs via the formation of the intermediate adduct 126 and a mixture of /Z-isomeric alkenes 127 (for R1 = R2 = R3 = R4 = H, the yield is 29 and 11%, respectively). The reaction product is formed by intramolecular cyclization of olefins initiated by bases (water, Na2C03, NaOH) in tetrahydrofuran (xylene). The authors did not give any interpretation of the reaction route. One can assume that the reaction proceeds by the following scheme. Under the action of bases, olefins undergo elimination of hydrogen fluoride and the formation of compound 128 containing a terminal double bond. 

---