Olefin also alkene hydrogenation

The various modes of bonding that have been observed for alkenes to the trinuclear osmium clusters are shown in Fig. 7 [see (88)]. The simple 77-bonded structure (a) is relatively unstable and readily converts to (c) the vinyl intermediate (b) is obtained by interaction of alkene with H2Os3(CO)10 and also readily converts to (c) on warming. Direct reaction of ethylene with Os3(CO)12 produces (c), which is considered to be formed via the sequence (a) — (b) — (c) and (d). Both isomers (c) and (d) are observed and involve metal-hydrogen and metal-carbon bond formation at the expense of carbon-hydrogen bonds. In the reaction of Os3(CO)12 with C2H4, the complex 112088(00)902112, (c), is formed in preference to (d). Acyclic internal olefins also react with the carbonyl, with isomerization, to yield a structure related to (c). Structure (c) is... 

The extent of double bond isomerization also varies with the nature of the catalyst. The degree of isomerization over metal catalysts usually decreases in the order Pd > Ni > Rh > Ru > Os =Ir =Pt.5.6 The extensive double bond isomerization observed with palladium and, to some extent, with nickel catalysts can be attributed to the formation of the adsorbed 7t-allyl species with these catalysts. While double bond isomerization may not be important in a routine alkene hydrogenation, it may influence a selective hydrogenation because the isomerized olefin can have different adsorption characteristics from those of the... 

The selective hydrogenation of one alkene in the presence of another is an example of Type I selectivity (Chapter 5). The olefin that is hydrogenated faster will be favored for saturation. However, with this type of selectivity the faster reaction is more influenced by diffusion limitations, so it is best to use a relatively unreactive catalyst. It is particularly important that the migration of the organic substrates to the catalyst is beyond mass transport limitations so the catalyst will have equal access to both alkenes. As the reaction proceeds, the amount of the more readily adsorbed species decreases so reaction selectivity may also decrease. 

Olefins — A group of unsaturated hydrocarbon compounds that contain less hydrogen atoms than the maximum possible. Olefins have at least one double carbon-to-carbon bond that displaces two hydrogen atoms. Significant amounts of olefins are found only in refined products. (See also Alkenes.)... 

Shapiro reaction. (2, 418-419 6, 598-600). Several laboratories have used EDA instead of an alkyllithium for decomposition of tosylhydrazones of ketones to olefins. Trisubstituted alkenes can be prepared by this modification in moderate yields from tosylhydrazones that contain only tertiary a-hydrogens. This modification also favors formation of the (Z)-disubstituted olefin. ... 

Complexes [RhI(CO)(mPTA)2]l2 (33) and [Rhl(C0)(mPTA)3]l34H20 (34) found applications as catalysts for olefin hydroformylation (see Sect. 7.3) and alkene hydrogenation under biphasic or aqueous phase conditions [37]. The hydrogenation of C=C double bond in unsaturated carboxyhc acids such as maleic and fumaric acid was also tested successfully, see Table 7.5. Acetalyzation products were also formed in the case of aldehyde hydrogenations. When terminal... 

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

Thermal decomposition of LiR eliminates a /6-hydrogen atom to give an olefin and LiH, a process of industrial importance for long-chain terminal alkenes. Alkenes can also be produced by treatment of ethers, the organometallic reacting here as a very strong base (proton acceptor) ... 

In addition, also nonheme iron catalysts containing BPMEN 1 and TPA 2 as ligands are known to activate hydrogen peroxide for the epoxidation of olefins (Scheme 1) [20-26]. More recently, especially Que and coworkers were able to improve the catalyst productivity to nearly quantitative conversion of the alkene by using an acetonitrile/acetic acid solution [27-29]. The carboxylic acid is required to increase the efficiency of the reaction and the epoxide/diol product ratio. The competitive dihydroxylation reaction suggested the participation of different active species in these oxidations (Scheme 2). 

---