Iron olefin hydrogenation

Table 1 Olefin hydrogenation reactions catalyzed by iron complexes...

Commercial 7-aluminas containing traces of iron can, after treatment with aqueous alkali, bring about the dissociation of H2 and catalyse olefin hydrogenation at and above room temperature.217 Trapped hydrogen atoms were found to be produced when HI-[2H,4]3-methylpentane was photolysed (254 nm) at less than 50 K.218... 

Iron, cobalt, and nickel are highly selective for olefin formation because the olefins are least strongly bound and hence most easily displaced from their surfaces, and because these metals exhibit lower inherent activities for olefin hydrogenation than do the noble metals. 

The lower selectivities afforded by ruthenium and rhodium reflect the higher activity of these metals for olefin hydrogenation, compared to iron and cobalt. 

Iron-catalysed cross-coupling and olefin hydrofunctionalisation reactions have emerged that operate well in the absence of the more commonly required noble metals. Similarly, operationally simple and practical iron-catalysed carbonyl and olefin hydrogenation procedures are now available, providing inexpensive routes for molecule construction. 

Olefin Hydrogenation Using a Homogeneous Iron Catalyst... 

Despite their availability and practical utility, examples of iron-catalysed olefin reductions using borohydride reagents are quite limited. Both Ashby and Boger reported the use of either stoichiometric or superstoichiometric quantities of iron in combination with borohydride reagents for olefin hydrogenation (see Section 12.6.2). ... 

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

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. 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Shale oil contains large quantities of olefinic hydrocarbons (see Table 8), which cause gumming and constitute an increased hydrogen requirement for upgrading. Properties for cmde shale oil are compared with petroleum cmde in Table 10. High pour points prevent pipeline transportation of the cmde shale oil (see Pipelines). Arsenic and iron can cause catalyst poisoning. 

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). 

Hydrogenation of olefins has been known and practiced for almost a century (1). In some early reports (2-4) careful reading reveals that the tranx-isomer was less reactive than the other isomers. In this paper we will confirm that irons-isomers do react more slowly and that they can have a negative effect on the hydrogenation of other, notionally more strongly bound, molecules. 

The question as to the existence of 17 versus 16 electron intermediates was also raised in the example of the photocatalytic hydrogenation of olefins using iron pentacarbonyl as the catalyst precursor (Equation 35). Schroeder and Wrighton studied this reaction at normal pressure, and they suggested H2Fe(C0)4 and H2Fe(CO)3> respectively, as the active catalysts /36/. 

---