Cobalt-catalyzed carbonylation

Remarkably few examples of this type of ring construction are available. The cobalt carbonyl hydride catalyzed hydroformylation of A/,A/ -diallylcarbamates has provided 3-pyrrolidinones (Scheme 61a) (81JOC4433). The pyrrole synthesis shown in Scheme 61b depends on Michael addition of ethyl a-lithioisocyanoacetate to ethyl a-isocyanocrotonate (77LA1174). 

Ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [PBuJBr was reported by Knifton as early as in 1987 [2]. The author described a stabilization of the active ruthenium-carbonyl complex by the ionic medium. An increased catalyst lifetime at low synthesis gas pressures and higher temperatures was observed. 

The Co2(CO)g/pyridine system can catalyze carbomethoxylation of butadiene to methyl 3-pentenoate (Eq. 6.44) [80]. The reaction mechanism of the cobalt-catalyzed carbalkoxylation of olefins was investigated and the formation of a methoxycar-bonylcobalt species, MeOC(0)Co from a cobalt carbonyl complex with methanol as an intermediate is claimed [81, 82]. 

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

Stoichiometric, nucleophilic addition of alkylcobalt compounds to carbonyl compounds were reviewed in 1996.374 This chapter focuses on recent progress in the reactions of cobalt enolates with carbonyls and cobalt-catalyzed coupling reactions. 

Although a cobalt-catalyzed intermolecular reductive aldol reaction (generation of cobalt enolates by hydrometal-lation of acrylic acid derivatives and subsequent reactions with carbonyl compounds) was first described in 1989, low diastereoselectivity has been problematic.3 6 However, the intramolecular version of this process was found to show high diastereoselectivity (Equation (37)).377,377a 378 A Co(i)-Co(m) catalytic cycle is suggested on the basis of deuterium-labeling studies and the chemistry of Co(ll) complexes (Scheme 81). Cobalt(m) hydride 182, which is... 

One process that capitalizes on butadiene, synthesis gas, and methanol as raw materials is BASF s two-step hydrocarbonylation route to adipic acid(3-7). The butadiene in the C4 cut from an olefin plant steam cracker is transformed by a two-stage carbonylation with carbon monoxide and methanol into adipic acid dimethyl ester. Hydrolysis converts the diester into adipic acid. BASF is now engineering a 130 million pound per year commercial plant based on this technology(8,9). Technology drawbacks include a requirement for severe pressure (>4500 psig) in the first cobalt catalyzed carbonylation step and dimethyl adipate separation from branched diester isomers formed in the second carbonylation step. 

Acetic acid has been generated directly from synthesis gas (CO/H2) in up to 95 wt % selectivity and 97% carbon efficiency using a Ru-Co-I/Bu4PBr "melt" catalyst combination. The critical roles of each of the ruthenium, cobalt and iodide catalyst components in achieving maximum selectivity to HOAc have been identified. Ci Oxygenate formation is observed only in the presence of ruthenium carbonyls [Ru(C0)3l3] is here the dominant species. Controlled quantities of iodide ensure that initially formed MeOH is rapidly converted to the more reactive methyl iodide. Subsequent cobalt-catalyzed carbonylation to acetic acid may be preparatively attractive (>80% selectivity) relative to competing syntheses where the [00(00)4] concentration is optimized that is, where the Co/Ru ratio is >1, the syngas feedstock is rich in 00 and the initial iodide/cobalt ratios are close to unity. 

Hydrogenation of acetic anhydride to acetaldehyde (equation 23) has been demonstrated utilizing cobalt carbonyl under one atmosphere of hydrogen. However, the cobalt complex is short lived. A more efficient cobalt catalyzed reaction with substantial catalyst longevity was realized at a temperature of 190 and 3000 psi pressure CO and hydrogen. The main products were equal amounts of EDA and acetic acid. Upon investigation, this reaction was found exceptionally efficient at a more reasonable 1500 psi pressure provided that the temperature was maintained... 

Aryl-4,5-dihydrooxazoles 556 underwent cobalt-catalyzed carbonylation to give 4,5-dihydro-l,3-oxazin-6-ones 557, usually in good yields, but an exception was the ring enlargement of 556 containing a 5-methyl (R = Me) or a sterically bulky 2-(o-tolyl) substituent (Equation 67) <20030L1575>. 

Since Wakamatsu serendipitously discovered amidocarbonylation while performing the cobalt-catalyzed hydroformyla-tion of olefins in 1971, this unique carbonylation reaction, affording a-amino acids directly from aldehydes, has been extensively studied.More recently, palladium-catalyzed processes have been developed to expand the scope of this reaction.The Pd-catalyzed amidocarbonylation has been applied to aldehydes,aryl halides, and imines. As a related reaction, lactamization " of aryl halides catalyzed by a rhodium complex has also been developed. 

Formate esters of the various alcohols formed are observed as major products in these cobalt-catalyzed reactions, and the mole ratio of formates to alcohols remains constant throughout a reaction. This observation would be consistent with the occurrence of a rapid carbonylation equilibrium process,... 

Y. Kamiya illustrates the influence on catalytic activity of the form of the catalyst. Thus, in the cobalt-catalyzed oxidation of hydrocarbons in acetic acid solution, introduction of bromide ions increases the activity of the catalyst, especially when the metal ion concentration is fairly high. The presence of bromides also results in a marked increase in the proportion of carbonyl compounds among the products and it is believed that these are formed as a result of a propagation step in which bromine-containing cobaltous ions react with alkylperoxy radicals. 

Metal-catalyzed reactions of CO with organic molecules have been under investigation since the late 1930s and early 1940s, when Roelen (/) discovered the hydroformylation reaction and Reppe (2) the acrylic acid synthesis and other related carbonylation reactions. These early studies of the carbonyla-tions of unsaturated hydrocarbons led to extremely useful syntheses of a variety of oxygenated products. Some of the reactions, however, suffered from the serious problem that they produced isomeric mixtures of products. For example, the cobalt-catalyzed hydroformylation of propylene gave mixtures of n-butyraldehyde and isobutyraldehyde. 

The carbonylation of methanol is an important route to acetic acid and is the basis for two industrial processes (cobalt- and rhodium-catalyzed). The cobalt-catalyzed route uses [Co2(CO)s] as catalyst with an iodide promoter, and lies outside the scope of this work. The companion volumes Comprehensive Organometallic Chemistry should be consulted. 

Recently, it has been discovered that catalysis by rhodium compounds is more effective than by the older cobalt catalyst when tris(triphenylphosphine)rhodium chloride is treated with carbon monoxide, the catalyst bis(triphenylphosphine)rhodium carbonyl chloride is formed. This catalyst is very effective under very mild conditions (49-51). It is believed that the tr-ir rearrangement is also important with this catalyst and operates in a manner analogous to that in the cobalt-catalyzed process, since stablization of the cr complex has been shown to lead to olefin isomerization and lower linear selectivity (52). 

Aminocarbonylation can also be carried out by use of CO and a silyl amide. Watanabe et al. reported the cobalt-catalyzed aminocarbonylation of epoxides [55]. Some silyl amides such as PhCH2NHSiMe3 and Et2NSiMe3 were applicable to the reaction to give the /Asiloxyamidc in good yields, whereas high reaction temperature was required. The use of 4-(trimethylsilyl) morpholine was found to be crucial for a milder and more efficient carboami-nation here, the reaction proceeded at ambient temperature under 0.1 MPa of CO. However, N-(2-hydroxyalkyl)morpholines, a product without carbonylation, were yielded as by-products (Scheme 18) [56]. 

Fig. 72 Cobalt-catalyzed ring expansion reactions of carbonyl compounds...

Further results on asymmetric hydrogenations of activated carbonyl compounds catalyzed by bis(dimethylglyoximato) cobalt (Il)-chiral amine complexes have been reported (55,56). Some chiral reductive dimerizations were observed (55). 

Mukhopadhyay M, Bhatia B, Iqbal J, Cobalt catalyzed multiple component condensation route to /1-acetamido carbonyl compound libraries, Tetrahedron Lett., 38 1083-1086, 1997. 

The rate of cobalt-catalyzed carbonylation is strongly dependent on both the pressure of carbon monoxide and methanol concentration. Complex 4.7, unlike 4.1, is an 18-electron nucleophile. This makes the attack on CH3I by 4.7 a comparatively slow reaction. High temperatures are required to achieve acceptable rates with the cobalt catalyst. This in turn necessitates high pressures of CO to stabilize 4.7 at high temperatures. 

FISCHER-TROPSCH REACTION AND COBALT-CATALYZED CARBONYLATION... 

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