Cobalt-catalyzed carbonylations

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. 

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>. 

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... 

Aryl-4,5-dihydrooxazoles 380 undergo cobalt-catalyzed carbonylation to give 4,5-dihydro-l,3-oxazin-6-ones 381, generally in good yields (Scheme 177) <20030L1575>. 

The active species in the cobalt-catalyzed carbonylation of methanol to acetic acid are generally considered to be either the tetracarbonyl cobalt... 

Scheme 5. Proposed mechanism for the unpromoted cobalt-catalyzed carbonylation of methanol.

Scheme 6. Proposed mechanism of the iodide-promoted cobalt-catalyzed carbonylation of alcohols encompassing the effects discussed in Section IV,B.

Berty et ai. excluded methyl iodide as an intermediate, since it could not be homologated in anhydrous benzene, as was mentioned earlier [17), Based on data by Mizorokj et al. from the cobalt-catalyzed carbonylation of ntetbanol to acetic acid [64], Bahmiann et ai. proposed that the activating effect of iodine did not ensue via methyl iodide fomiation [5. Activation was correlated 10 the lahilization of the coordination sphere of cobalt carbonyls by iodine ligands and the sequence (21) (25) was suggested. 

A rather different approach to carbonylation of aliphatic halides involves the carbonyl anion [Co(CO)4] which, being a kinetically stable 18-electron species, attacks the halide by nucleophilic displacement rather than by undergoing oxidative addition. A probable catalytic cycle for cobalt-catalyzed carbonylation of benzyl chloride is shown in Scheme 6. ... 

An interesting reaction discovered by Wakamatsu involves the cobalt-catalyzed carbonylation of aldehydes in the presence of primary amides to give A-acylamino acids in high yield (equation 26). By combining this reaction with known catalytic routes to aldehydes, for example isomerization of allyl alcohols or hydroformylation of alkenes, it is possible to achieve the direct synthesis of A-acylamino acids from precursors other than aldehydes. ... 

Benzyl- and phenylacetyl derivatives of tetracarbonylcobalt(I) are believed to be important intermediates in the cobalt-catalyzed carbonylation of benzyl halides to phenylacetic acidi2twi and to phenylpyruvic acid ", carried out under phase transfer catalysis in the presence of catalytic amounts of a cobalt-carbonyl derivative. The carbonylation to phenylacetic acid proceeds as follows ... 

Light can often be used to promote SRN1 reactions [2]. Indeed, the photo-chemically induced, cobalt-catalyzed carbonylation of haloarenes, PhCl included, readily occurs under phase-transfer conditions. This interesting methodology was first developed by Brunet, Sidot, and Caubere [23,69] and subsequently used for the carbonylation of various chloroarenes in the presence of catalytic amounts of cobalt compounds (Sect. 3.3). 

Facile insertion of CO takes place, and the reaction offers a synthetic method of orf/to-substituted benzoic acid derivatives. The 2-aryl-3-indazolone 421 was obtained in high yield by carbonylation of 4-methylazobenzene complex 420 in alcohol or water [176]. Cobalt-catalyzed carbonylation of 421 and subsequent hydrolysis afforded aniline and 5-methylanthranilic acid (422). The results show that the cr-bond formation is an electrophilic substitution of PdCl2 on the benzene ring [176,177]. 

Iron-, Copper-, Nickel-, and Cobalt-Catalyzed Carbonylative Domino Reactions... 

Scheme 1.29 Cobalt-catalyzed carbonylative synthesis of malonic acid derivatives.

It is commonly assumed for cobalt catalyzed carbonylations that Co2(CO)g reacts with hydrogen or a nucleophile (NuH) with an acidic proton to form the catalyt-ically active species HCo(CO>4 [18]. After replacement of one CO ligand by the... 

In 1990 Alper and Lee reported on a cobalt-catalyzed carbonylation of aryl iodides and alkyl iodides [293, 294]. In the presence of cobalt chloride or acetate, potassium cyanide, base, and PEG-400, carboxylic acids were produced from the corresponding iodo compounds. Lewis acids, such as boron trifluoride etherate... 

The kinetic resolution of aziridines has also been reported. Alper showed that the car-bonylation of N-ferf-butyl- and N-adamantyl-2-arylaziridines in the presence of catalytic amounts of the combination of [Rh(COD)Cl]j and enantiopure menthol produced the corresponding N-alkyl-3-phenylazetidin-2-ones in up to 99.5% optical yield, although the isolated yields were modest. Consistent with the cobalt-catalyzed carbonylation of epoxides and related substrates, inversion of configuration occurs at the site of carbonyl insertion. 

In the cobalt catalyzed carbonylation, as well as in hydroformylation, an inhibition is observed with increase of the carbon monoxide pressure [365, 415-417]. An even larger inhibition effect is noted in nickel catalyzed reactions [411]. An explanation of these facts is given in the chapter on the reaction mechanism. 

---