Rhodium isomerization catalyst

G-19 Dicarboxylic Acids. The C-19 dicarboxyhc acids are generally mixtures of isomers formed by the reaction of carbon monoxide on oleic acid. Since the reaction produces a mixture of isomers, no single chemical name can be used to describe them. Names that have been used include 2-nonyldecanedioic acid, 2-octylundecanedioic acid, l,8-(9)-heptadecanedicarboxyhc acid, and 9-(10)-carboxystearic acid. The name 9-(10)-carboxystearic acid can be used correctiy if the product is made with no double bond isomerization (rhodium triphenylphosphine catalyst system). 

Asymmetric hydrogenolysis of epoxides has received relatively little attention despite the utility such processes might hold for the preparation of chiral secondary alcohol products. Chan et al. showed that epoxysuccinate disodium salt was reduced by use of a rhodium norbornadiene catalyst in methanol/water at room temperature to give the corresponding secondary alcohol in 62% ee (Scheme 7.31) [58]. Reduction with D2 afforded a labeled product consistent with direct epoxide C-O bond cleavage and no isomerization to the ketone or enol before reduction. 

The ester is prepared by catalytic hydrogenation of 4-tert-butylphenol followed by acetylation of the resulting 4-tert-butylcyclohexanol [132]. If Raney nickel is used as the catalyst, a high percentage of the trans isomer is obtained. A rhodium-carbon catalyst yields a high percentage of the cis isomer. The trans alcohol can be isomerized by alkaline catalysts the lower-boiling cis alcohol is then removed continuously from the mixture by distillation [133]. 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

III,C, isomerization often accompanies hydroformylation. It has, however, been found that [(PhCN)2PdCl2] absorbed onto silica gel is 100 times more active for the isomerization of a-olefins, such as 1-heptene, than is the same complex alone (116). This implies some specific role for the silica gel. Attempts to use rhodium(III) chloride absorbed onto silica gel, alumina, activated charcoal, and diatomaceous earth as a-olefin isomerization catalysts showed that all these catalysts were unstable even at room temperature (100). 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

In the case of rhodium as a catalyst metal for the hydroformylation of methyl oleate, lower pressure and lower temperature have to be compared to cobalt catalysis [20, 21], The use of rhodium is also advantageous because of the lower isomerization. Frankel showed that with a rhodium triphenylphosphine catalyst, hydroformylation occurs only on the ninth and tenth carbon atoms of the methyl oleate [22]. 

A convenient catalyst precursor is RhH(CO)(PPh3)3. Under ambient conditions this will slowly convert 1-alkenes into the expected aldehydes, while internal alkenes hardly react. At higher temperatures pressures of 10 bar or more are required. Unless a large excess of ligand is present the catalyst will also have some isomerization activity for 1-alkenes. The internal alkenes thus formed, however, will not be hydroformylated. Accordingly, the 2-alkene concentration will increase while the 1-alkene concentration will decrease this will slow down the rate of hydroformylation. This makes the rhodium triphenylphosphine catalyst... 

SHOP [Shell Higher Olefins Process] A process for producing a-olehns by oligomerizing ethylene, using a proprietary rhodium-phosphine catalyst. The a-olehns can then be isomerized to internal olefins as required. Invented by W. Keim in the Institut fur Technische Chemie und Petrolchemie, Aachen, West Germany, in the 1970s. The first plant was built in Geismar, LA, in 1979 the second in Stanlow, Cheshire, UK, in 1982. Licensed worldwide by a consortium of Union Carbide, Davy-McKee, and Johnson Matthey. 

One additional favourable feature of the use of rhodium-BINAP catalysts is that they are stereospecific the ( )-enamine gives the (i )-amine and the Z)-enamine gives the (5)-amine with catalysts containing (5)-BINAP. Obviously, the use of (i )-BINAP catalysts affords the opposite enantiomers of the amine (Figure 21). Thus to obtain a high enantiomeric purity, it is essential to start from isomerically pure amine. Almost perfect enantioselectivity (> 96% ee) and quantitative yields were obtained by all routes. Initially, [Rh(BINAP)(-COD)]" (COD = 1,5-cyclooctadiene) was used as catalyst precursor, and TON up to 8000 were achieved. Further improvements in TON were achieved with... 

Unlike cobalt, the rhodium catalyst exhibits little or no aldehyde hydrogenation activity, but it is 10 -10 limes more active than the cobalt analog. The rhodium system is also a highly active isomerization catalysts but gives rise to a low n iso ratio (about I compared to 4 of Co2(CO) ). 

A better example for the possible intervention of a distinct intermediate was recently disclosed in a study of the valence isomerization of cubane (79) to syw-tricyclooctadiene 20) using various rhodium (I) catalysts. 

Because the possibility of olefinic isomerization still loomed important in considering product distributions, we decided to add the powerful olefin isomerization catalyst (17), rhodium trichloride, to the system. No change in product distribution from that of palladium chloride alone was found with either hexene or 2-hexene when a 1 1 molar ratio of rhodium trichloride/palladium chloride was used (Table VII). This is further evidence that the relative rate of vinylation is greater than that of isomerization. When rhodium chloride was used with hexene without any added palladium chloride at 115°C., only slight reaction occurred, and the product contained 85.7% 2-acetate, 10.2% 1-acetate, and 4.1% 3-acetate. Apparently, vinylation had occurred with rhodium trichloride in a manner analogous to oxymercuration and the low-temperature palladium vinylation reaction. 

Structure 4 is an intermediate for manufaeturing vitamin A (Scheme 2). The annual demand for vitamin A is about 3000 tons. Major producers are BASF, Hoffmann-La Roche and Rhone-Poulenc Animal Nutrition [55]. At an early stage in the synthesis BASF and Hoffmann-La Roche are using a hydroformylation step to synthesize 4 starting from l,2-diacetoxy-3-butene (5) and 1,4-di-aeetoxy-2-butene (6), respectively [56, 57]. The selectivity toward the branched product in the BASF process is achieved by using an unmodified rhodium carbonyl catalyst at a high reaction temperature. The symmetry of 6 in La Roche s process does not lead to regioselectivity problems. Elimination of acetic acid and isomerization of the exo double bond (La Roche) yields the final product 4 in both processes. 

Comparison of this sequence with Fig. 33 shows clearly that the metals that are most active for olefin isomerization, rhodium (> 80°) and nickel, yield the least 1-butene in 1,3-butadiene hydrogenation the reverse is also true in that copper and iridium, being poor isomerization catalysts, give the most 1-butene. Platinum, ruthenium, and osmium occupy intermediate positions in the expected order. Furthermore, the activity of all metal catalysts for isomerization increases with increasing temperature and the yield of 1-butene from 1,3-butadiene decreases as the temperature is raised this agrees with expectation and helps to confirm the proposed mechanism. 

Although the unmodified rhodium carbonyl catalyst HRh(CO) shows high activity, it gives a low regioselectivity and tends to hydrogenate or isomerize olefins, i.e., this catalyst is not practically useful. 

Catalysts for hydrogenation and hydroformylation reactions also catalyze isomerization of olefins. In the case of rhodium(I) catalysts for hydroformylation, the rate of isomerization decreases, depending upon the ligands, as follows CO > NR3 > S > PR3. 

The more highly phosphine substituted rhodium species RhH(CO) (PlCeHslsls is an even more active catalyst, 1 atm pressure and 25°C being sufficient, and it is even more selective for the n product (21). Rh4(CO)i2 is also very active but has very poor selectivity, so once again, the presence of phosphine improves the selectivity. The mechanism is broadly similar to the Co-catalyzed process. In practice, excess PlCeHsls is added to the reaction mixture to prevent the formation of the less selective HRh(CO)4 and HRhL(CO)3 species by phosphine dissociation. The system is also an active isomerization catalyst, because much of the same mixture of aldehydes is formed from any of the possible isomers of the starting alkene. This is a very useful property of the catalyst, because internal isomers of an alkene are easier to obtain than the terminal one. The commercially valuable terminal aldehydes can still be obtained from these internal alkenes. The catalyst first converts the internal alkene, for example, 2-butene, to a mixture of isomers including the terminal one. The latter is hydroformy-lated much more rapidly than the internal ones, accounting for the predominant n aldehyde product. As the terminal alkene can only ever be a minor constituent of the alkene mixture (because it is thermodynamically less stable than the other isomers), this reaction provides another example of a catalytic process in which the major product is formed from a minor intermediate (eq. 21). 

The intramolecular Buchner reaction of aryl diazoketones has been carried out using both copper(I) and rhodium(II) catalysts. For example, 1-diazo-4-phenylbutan-2-one 27a cyclizes in bromobenzene with copper(I) chloride catalysis, furnishing 3,4-dihydroazulen-l(2//)-one 30 in 50% yield after purification by chromatography over alumina. Trienone 30 is not the primary cyclization product, and the less conjugated isomeric trienone 29a is first produced, but contact with alumina causes isomerization to 30. The yield of this cyclization is further improved when rhodium(II) acetate is used as the catalyst instead of copper(I) chloride. Thus a catalytic amount of rhodium(II) acetate brings about the nearly quantitative conversion of 27a to 29a within minutes in hot dichloromethane. Compound 29a isomerizes to 30 on treatment with triethylamine, and rearranges to 2-tetralone 31a when exposed to silica gel or acid. 

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