Catalytic hydrogenation of olefins

Scheme 6 Proposed mechanism for catalytic hydrogenation of olefin with 5...

Khan, M. M., Ph.D. dissertation, Effects of Solvent and Surface Structure on Catalytic Hydrogenation of Olefins, Southern Illinois University at Carbondale, 1982, pp. 30-31. 

RuCl(PPh3 )3(alkyl) (90). Because of the fact that the orthometallated complex reacts with H2 to re-form HRuCl(PPh3)2, catalytic hydrogenation of olefins can result via such pathways, although product formation via reaction (11) is kinetically preferred (88). 

Table 9.12 Catalytic hydrogenation of olefins with Pd nanoparticles in a water-in-hexane microemulsion. (Reprinted with the permission of the American Chemical Society [79])...

Infrared measurements have also provided information about the catalytic hydrogenation of olefins (Eischens, 105). Thus, the spectrum of ethylene (Fig. 15) chemisorbed on a nickel surface (on which some hydrogen... 

When an oxidation or a reduction could be considered in a previous chapter, this was done. For example, the catalytic hydrogenation of olefins is a reduction, but it is also an addition to the C==C bond and was treated in Chapter IS. In this chapter are discussed only those reactions that do not fit into the nine categories of Chapters 10 to 18. An exception to this rule was made for reactions that involve elimination of hydrogen (9-1 to 9-6) which were not treated in Chapter 17 because the mechanisms generally differ from those in that chapter. 

Asymmetric synthesis (i) has gained new momentum with the potential k use of homogeneous catalysts. The use of a transition metal complex with chiral ligands to catalyze a synthesis asymmetrically from a prochiral substrate is beneficial in that resolution of a normally obtained racemate product may be avoided. In certain catalytic hydrogenations of olefinic bonds, optical purities approaching 100% have been attained (2,3,4,5) hydrogenations of ketones (6,... 

Mechanism. A consideration of the NMR data and the kinetic data leads us to propose the following mechanism for the catalytic hydrogenation of olefins by RhCl(ttp) and excess AlEt2Cl. 

Wilkinson s (I) discovery that the soluble rhodium(I) phosphine complex, [Rh(PPh3)3Cl], was capable of homogeneous catalytic hydrogenation of olefins immediately set off efforts at modifying the system for asymmetric synthesis. This was made possible by the parallel development of synthetic methods for obtaining chiral tertiary phosphines by Horner (2) and Mislow (3,4, 5). Almost simultaneously, Knowles (6) and Horner (7) published their results on the reduction of atropic acid (6), itaconic acid (6), a-ethylstyrene (7) and a-methoxystyrene (7). Both used chiral methylphenyl-n-propyl-phosphine coordinated to rhodium(I) as the catalyst. The optical yields were modest, ranging from 3 to 15%. 

The use of NHCs has also found application in the catalytic hydrogenation of olefins. By the simple ligand exchange reaction of [Ir(COD)2(py)2]PF6 with SIMes in toluene, Nolan and coworkers have prepared the SIMes analog (27) of Crabtree s catalyst (26) [67]. The reactivity of this complex was tested for catalytic activity in the hydrogenation of several olefins. While the complex did show activity, it was less efficient than Crabtree s catalyst at ambient temperature and atmospheric H2 pressure. However, the SIMes complex did display greater activity at 60 psi of H2 pressure and 50 °C. 

Saturation of a carbohydrate double bond is almost always carried out by catalytic hydrogenation over a noble metal. The reaction takes place at the surface of the metal catalyst that absorbs both hydrogen and the organic molecule. The metal is often deposited onto a support, typically charcoal. Palladium is by far the most commonly used metal for catalytic hydrogenation of olefins. In special cases, more active (and more expensive) platinum and rhodium catalysts can also be used [154]. All these noble metal catalysts are deactivated by sulfur, except when sulfur is in the highest oxidation state (sulfuric and sulfonic acids/esters). The lower oxidation state sulfur compounds are almost always catalytic poisons for the metal catalyst and even minute traces may inhibit the hydrogenation very strongly [154]. Sometimes Raney nickel can... 

Summary From catalytic hydrogenation of olefinic silicon-functionalized compounds (chloro-Si, alkoxy-Si, alkyl-Si, and aryl-Si) the saturated products are available in good yield. In general, the chloro- and alkoxy substituents are unaffected and for silaheterocyclic compounds the cyclic or the bicyclic moieties, respectively, remain intact. Thus, the silanorbomenes 1, 2, and 3, compounds containing cyclopentenyl groups 13 and 15, and various carbon vinyl substituted silacyclobutanes 7, 8, and 11 were hydrogenated in a simple apparatus. The reactions were performed in ether and THF as solvents the hydrogenation catalyst Pd/C can be used several times. 

One of the most fundamental examples of a surface-mediated reaction is the heterogeneous catalytic hydrogenation of olefins and acetylenes on charcoal-supported transition metals like Pd, Pt, Ni,... 

Finke s group has synthesized [(C0D)Ir-P2Wi5Nb3062] (89) in which the iridium is bound, in addition to the COD, to three oxygens from the polyoxoanion see Polyoxometalate. NMR evidence (from 0 NMR) indicates that the iridium is bound to the polyoxoanion at the NbOs portion. Under hydrogen, this material converts into a complex that is active for the catalytic hydrogenation of olefins. While the nature of the actual catalyst is not known, evidence suggest that the iridium must still be attached to the polyoxoanion. ... 

Catalytic Hydrogenation of Olefins in Supercritical Carbon Dioxide Using Rhodium Catalysts Supported on Fluoroacrylate Copolymers... 

The catalytic hydrogenation of olefins provides an example of ignition at relativity low temperatures. Figure 5.13 shows rate data for hydrogenation of ethylene with 0.14-in. spheres of Ni/Al203 [24]. For temperatures of 34°C to 73°C, the reaction rate nearly doubled for each 12°C increase in temperature and then increased ninefold for an 8°C increase in temperature. Analysis shows that the external temperature difference was about... 

In addition to transfer hydrogenation reactions, arene ruthenium complexes also display excellent activity in the catalytic hydrogenation of olefins and alkynes including asymmetric reduction [40]. Remarkably, this process occurs under milder conditions, than required for catalysis with the dissociation of arene-metal bond. Lately, arene iridium complexes have also been found to be effective hydrogenation catalysts [41 ]. It is noteworthy that iridium can also promotes addition to the carbon-nitrogen double bond. 

Scheme 1.24B shows the other possibility of catalytic hydrogenation of olefin driven by a transition metal monohydride. The monohydride can be sometimes obtained by cleavage of dinuclear transition metal complexes such as Co2(CO)g on treatment with dihydrogen or it can be generated by protonation of an electron rich metal complex [71]. Insertion of an olefin into the M-H bond to form an alkyl may proceed similarly to Scheme 1.24A. 

Following the development of successful catalytic hydrogenation of olefins, recent attention is directed to catalytic hydrogenation and transfer hydrogenation of ketones and imines [77]. Because of requirement of production of various pharmaceutical compounds of importance, further development is expected in asymmetric catalytic hydrogenation. 

Kaifer et al. were particularly interested in the catalytic properties of Pd nanoparticles derivatized with surface-attached perthiolated cyclodextrins and their use in various catalytic reactions such as Suzuki reactions [57] or the hydrogenation of alkenes [58] or allylamine [59]. The modified cyclodextrins play the role of a ligand, leading to a steric stabilization. To our knowledge, only one report describes the catalytic hydrogenation of olefins using colloidal Rh dispersions embedded by nahve cyclodextrins [60], generating steric stabilization via hydrophobic interactions. 

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