Isomerization olefin

Butene Isomerization and ti-Allyl Formation from Dienes and HNiL4 

With the addition of 1,3-butadiene, the initially yellow hydride solutions turn red with the formation of relatively stable l-Me-it-allyl-nickel complexes, and olefin isomerization activity stops. By measuring the rate of formation of the rc-allyl complexes in the presence of added P(OEt)3, it was possible to measure the rate constant for dissociation of L from HNiL4 and show that this is the rate-determining step (42). 

In a proton NMR experiment in which 1,4-pentadiene was added to a solution of HNi[P(OMe)3]4, it was possible to watch the isomerization of 1,4- to 1,3-pentadiene, followed by formation of l,3-dimethyl-7t-allyl complexes (53). The observation of 7t-allyl products in the reaction of the hydride with the conjugated diene, but not in the ff-alkyl intermediates involved in isomerization, illustrates the much greater stability of zr-allyl complexes of nickel compared to tr-alkyls, a feature which is also observed in the hydrocyanation reactions. 

The isomerization of the internal olefin 3PN to the terminal olefin 4PN is a critical step in the hydrocyanation of 3PN to ADN [Eqs. (9) and (10)]. Unfortunately, there is a loss in yield because the undesirable conjugated isomer 2PN is also produced. Observations discussed below have led us to the belief that cationic nickel-hydride complexes, HNiL4, may be important in the isomerization process. 

When 3PN solution containing Ni[P(0-p-tolyl)3]4 is treated with trifluoromethylsulfonic acid (1 eq/Ni) at 50°C, rapid isomerization occurs for less than 30 sec before catalyst degrades. During this short burst of isomerization, 4PN and 2PN are produced in a ratio of 70 1. Similar results are obtained at 40°C and 25°C (61). 

One other type of hydrocarbon isomerization should be mentioned— that of olefins. Processes for olefin isomerization were first developed in the mid 1930 s (17,19) after it was recognized that highly branched olefins have higher octane numbers than do their straight-chain isomers, and that the octane numbers of olefins increase as the double bond moves toward the middle of the molecule. 

In the manufacture of synthetic liquid fuels from natural gas by the Fischer-Tropsch process, this reaction can be used to increase the octane number of the product by as much as 20 units. Synthetic naphtha pro- 

ADMET polymerization is a versatile technique for the preparation of a wide variety of linear polymers (30,31). However, olefin isomerization side reactions may result in polymers with irregular repeating units (32). 

This method allows the quantification of the olefin isomerization that may occur in the course of ADMET polymerization using second generation ruthenium metathesis catalysts. 

Further, it was demonstrated that the addition of benzoquinone to the polymerization mixture prevents the olefin isomerization. Therefore, second generation ruthenium metathesis catalysts can be used for the preparation of well defined polymers via an ADMET technique causing little isomerization (32). 

5-Dimethyl-2,5-di-(tert-butylperoxy)hexane on inert filler (1)  

Mohanty, L.T. Drzal, B.R Rook, and M. Misra, Floor covering made from an environmentally friendly polylactide-based composite formulation, US Patent 7 354 656, assigned to Michigan State University, Board of Trustees (East Lansing, Ml), April 8, 2008. 

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Conducting the hydrogenation at high H2 pressures supresses olefin isomerization and often gives higher diastereoselectivity. 

Supression of olefin isomerization is critical for acyclic stereocontrol ... 

Olefin Isomerization- a variety of transition metal (RhCl3 H20) catalyst will isomerize doubles bonds to more thermodynamically favorable configurations (i.e. more substituted, trans, conjugated)... 

Olefin-CO coploymers Olefin p-complexes Olefin Fibers Olefin hydroformylation Olefin hydrogenation Olefimc alcohols Olefin isomerization Olefin metathesis Olefin oligomers Olefin oxides... 

Bisphosphites such as (7) combine excellent reactivity, straight-chain selectivity, and high resistance to the typical phosphite degradation reactions (29). Further, the corresponding 0x0 catalysts are excellent olefin isomerization catalysts so that high normal-to-branched isomer ratios are obtained even from internal olefins, enabling, in certain instances, the use of inexpensive mixed isomer olefin feedstocks. 

A number of smaller but nevertheless important apphcations in which activated alumina is used as the catalyst substrate include alcohol dehydration, olefin isomerization, hydrogenation, oxidation, and polymerization (43). 

Solvent for Base-Catalyzed Reactions. The abihty of hydroxide or alkoxide ions to remove protons is enhanced by DMSO instead of water or alcohols (91). The equiUbrium change is also accompanied by a rate increase of 10 or more (92). Thus, reactions in which proton removal is rate-determining are favorably accompHshed in DMSO. These include olefin isomerizations, elimination reactions to produce olefins, racemizations, and H—D exchange reactions. 

Olefin isomerization is often catalyzed by titanium. An example is the conversion of vinyl norhornene to the comonomer ethylidenenorhornene (141). The catalyst is a mixture of a sodium suspension, AlCl, and (RO)4Ti or Cp2TiCl2. Although isomerization is slow, the yield is high. The active reagent is doubdess a Ti(III) compound. 

Zirconium—ally complexes also have catalytic properties. Tetraally zirconium [12090-34-5] on a siUca substrate catalyzes ethylene polymerization (265). Supported on sihca, ZrR (R = allyl or neopentyl) catalyzes olefin isomerization (266). 

Olefin Isomerization. Some olefins can be isomerized in the presence of metal carbonyls. The carbonyl can act as a catalyst or a stoichiometric reagent in the reaction (137). 

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

Ethoxy-l,3-dioxolane, pyridinium tosylate (PPTS), benzene, heat, 8 h, 89% yield. In this case protection of an enone proceeds without olefin isomerization. 

The double bond migration in steroid hydrocarbons catalyzed by acids or noble metals (see, for example, ref. 185) will not be discussed here. A general review of nonsteroid olefin isomerization has recently been published. Iron carbonyl has been used to isomerize steroidal dienes. 

Simple diastereoselection in the reactions of 2-butenylboron compounds and aldehydes is critically dependent on the configurational stability of the reagentslb. As a general rule, most 2-bulenylorganometallics arc sensitive to sequential 1,3-metal shifts (1,3-metallotropic rearrangements) that result in E- to Z-olefin isomerization via the l-methyl-2-propenylmetal isomer. 

The formation of isomeric aldehydes is caused by cobalt organic intermediates, which are formed by the reaction of the olefin with the cobalt carbonyl catalyst. These cobalt organic compounds isomerize rapidly into a mixture of isomer position cobalt organic compounds. The primary cobalt organic compound, carrying a terminal fixed metal atom, is thermodynamically more stable than the isomeric internal secondary cobalt organic compounds. Due to the less steric hindrance of the terminal isomers their further reaction in the catalytic cycle is favored. Therefore in the hydroformylation of an olefin the unbranched aldehyde is the main reaction product, independent of the position of the double bond in the olefinic educt ( contrathermodynamic olefin isomerization) [49]. 

Olefin isomerization process Isomerization of internal olefins to a- 54... 

Recently, Grubbs138 demonstrated that olefin isomerization of allyl-lic ethers and alcohols is catalyzed by Ru(II)(H20)6(tos)2 (tos = p-toluenesulfonate) in aqueous medium. The olefin migration products, enols, and enol ethers thus generated are unstable and are hydrolyzed instantly to yield the corresponding carbonyl compounds (Eq. 3.34). 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

In contrast to the Johnson s D —> A-ring construction approach, Brown devised an A —> D-ring construction approach [22]. Starting from Wieland-Miescher ketone (30), a common source of the A, B-rings in the de novo synthesis of steroids, the C-ring was introduced via hydrazone allylation, ozonolysis, aldol condensation, and olefin isomerization (31 > 32). The D-ring was assembled by a reductive alkylation... 

The catalytic cycles that have been documented, namely alkyne eyelotrimerization and olefin isomerization, demonstrate that addition and elimination from dimetal centers can occur readily in the presence of metal-metal bonds and alkoxide 1igands. 

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). 

Tucci (54), studying mainly terminal olefins, cited two reasons for the high selectivity for linear products in the phosphine-modified cobalt catalysts (a) stereoselective addition of the hydride species to the olefinic double bond, and (b) inhibition of olefin isomerization. However, the results obtained with internal olefins as substrate tended to discount the likelihood of the second reason, and it is generally accepted that selective anti-Markovnikov addition arising from steric hindrance is the principal cause for linear products from nonfunctional olefins. 

Thus, the rule of Keulemans (49), that a-quaternary carbon formyl compounds are not formed, was followed. The olefin isomerized to allow formyl attachment to a primary carbon atom. Addition of phosphine, which decreases isomerization, resulted in no reaction. 

A convincing example of selectivity control in isomerization reactions is the formation of cis-2-butene from the isomerization of 1-butene using the catalyst [(C6H5)3P]2NiX2-P(CeH5)3-Zn-SnCl2 a ratio of c/i-2-bu-tene /ra .s-2-butene as high as 98 2 has been observed. Isomerization to the thermodynamically more stable /ra ns-olefin occurs only after conversion of all the 1-butene (98). Further examples of selective olefin isomerization will be discussed in Section IV,D. 

The rate also varies with butadiene concentration. However, the order of the rate dependence on butadiene concentration is temperature-de-pendent, i.e., a fractional order (0.34) at 30°C and first-order at 50°C (Tables II and III). Cramer s (4, 7) explanation for this temperature effect on the kinetics is that, at 50°C, the insertion reaction to form 4 from 3, although still slow, is no longer rate-determining. Rather, the rate-determining step is the conversion of the hexyl species in 4 into 1,4-hexadiene or the release of hexadiene from the catalyst complex. This interaction involves a hydride transfer from the hexyl ligand to a coordinated butadiene. This transfer should be fast, as indicated by some earlier studies of Rh-catalyzed olefin isomerization reactions (8). The slow release of the hexadiene is therefore attributed to the low concentration of butadiene. Thus, Scheme 2 can be expanded to include complex 6, as shown in Scheme 3. The rate of release of hexadiene depends on the concentra-... 

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