Carbon monoxide octacarbonyl

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Carbon Monoxide Process. This process involves the insertion of carbon monoxide [630-08-0] into a chloroacetate. According to the hterature (34) in the first step ethyl chloroacetate [105-39-5] reacts with carbon monoxide in ethanol [64-17-5] in the presence of dicobalt octacarbonyl [15226-74-1], Co2(CO)g, at typical temperature of 100°C under a pressure of 1800 kPa (18 bars) and at pH 5.7. Upon completion of the reaction the sodium chloride formed is separated along with the catalyst. The ethanol, as well as the low boiling point components, is distilled and the nonconverted ethyl chloroacetate recovered through distillation in a further column. The cmde diethyl malonate obtained is further purified by redistillation. This process also apphes for dimethyl malonate and diisopropyl malonate. 

Other processes described in the Hterature for the production of malonates but which have not gained industrial importance are the reaction of ketene [463-51-4] with carbon monoxide in the presence of alkyl nitrite and a palladium salt as a catalyst (35) and the reaction of dichioromethane [75-09-2] with carbon monoxide in the presence of an alcohol, dicobalt octacarbonyl, and an imida2ole (36). 

Dicobalt octacarbonyl [10210-68-1] M 341.9, m 51 . Orange-brown crystals by recrystn from n-hexane under a carbon monoxide atmosphere [Ojima et al. J Am Chem Soc 109 7714 1987 see also Hileman in Preparative Inorganic Reactions, Jolly Ed. Vol 1 101 1987]. 

Arylmetallic compounds have various, but not very widely used, applications in organic synthesis. Examples are acyl-de-metallation reactions using either dicobalt octacarbonyl in tetrahydrofuran (Seyferth and Spohn, 1969 Scheme 10-92), or carbon monoxide and a rhodium catalyst (Larock and Hershberger, 1980). 

MeaSiH) and carbon monoxide, catalyzed by dicobalt octacarbonyl See 10-92... 

When dicobalt octacarbonyl, [Co(CO)4]2, is the catalyst, the species that actually adds to the double bond is tricarbonylhydrocobalt, HCo(CO)3. Carbonylation, RCo(CO)3- -CO—>RCo(CO)4, takes place, followed by a rearrangement and a reduction of the C—Co bond, similar to steps 4 and 5 of the nickel carbonyl mechanism shown in 15-30. The reducing agent in the reduction step is tetra-carbonylhydrocobalt HCo(CO)4, ° or, under some conditions, H2. When HCo(CO)4 was the agent used to hydroformylate styrene, the observation of CIDNP indicated that the mechanism is different, and involves free radicals. Alcohols can be obtained by allowing the reduction to continue after all the carbon monoxide is... 

The dicobalt octacarbonyl-catalyzed transformation of azoarenes into 2-arylindazolin-3-ones by carbonylation has been known for many years157 high pressures of carbon monoxide are required and under more forcing conditions the products are quinazoline-2,4-diones (Scheme 92). Reactions... 

A somewhat related process, the cobalt-mediated synthesis of symmetrical benzo-phenones from aryl iodides and dicobalt octacarbonyl, is shown in Scheme 6.49 [100]. Here, dicobalt octacarbonyl is used as a combined Ar-I bond activator and carbon monoxide source. Employing acetonitrile as solvent, a variety of aryl iodides with different steric and electronic properties underwent the carbonylative coupling in excellent yields. Remarkably, in several cases, microwave irradiation for just 6 s was sufficient to achieve full conversion An inert atmosphere, a base or other additives were all unnecessary. No conversion occurred in the absence of heating, regardless of the reaction time. However, equally high yields could be achieved by heating the reaction mixture in an oil bath for 2 min. 

The [2+2+1] cycloaddition of an alkene, an alkyne, and carbon monoxide is known as the Pauson-Khand reaction and is often the method of choice for the preparation of complex cyclopentenones [155]. Groth and coworkers have demonstrated that Pauson-Khand reactions can be carried out very efficiently under microwave heating conditions (Scheme 6.75 a) [156]. Taking advantage of sealed-vessel technology, 20 mol% of dicobalt octacarbonyl was found to be sufficient to drive all of the studied Pauson-Khand reactions to completion, without the need for additional carbon monoxide. The carefully optimized reaction conditions utilized 1.2 equivalents of... 

Cyclopentanecarboxaldehyde has been prepared by the procedure described above 2 3 by the reaction of aqueous nitric acid and mercuric nitrate with cyclohexene 6 by the action of magnesium bromide etherate 6 or thoria 7 on cyclohexene oxide by the dehydration of frarei-l, 2-cyclohexanediol over alumina mixed with glass helices 8 by the dehydration of divinyl glycol over alumina followed by reduction 9 by the reaction of cyclopentene with a solution of [HFe(CO)4] under a carbon monoxide atmosphere 10 and by the reaction of cyclopentadiene with dicobalt octacarbonyl under a hydrogen and carbon monoxide atmosphere.11... 

F. Oldani, G. Bor. Fundamental Metal Carbonyl Equilibria. II. A Quantitative Study of the Equilibrium between Dirhodium Octacarbonyl and Tetrarhodium Dodecacar-bonyl under Carbon Monoxide Pressure. J. Organomet. Chem. 1983,246, 309-324 ibid. 1985,279, 459-460. 

A high carbon monoxide pressure ( 5 atmos.) favours the formation of the butane. Possible mechanisms for its formation include homolytic cleavage of the benzyl-cobalt tetracarbonyl complex and recombination of the radicals to generate 2,3-diphenylbutane and dicobalt octacarbonyl, or a base-catalysed decomposition of the benzylcobalt tetracarbonyl complex (Scheme 8.4). The ethylbenzene and styrene could arise from the phenylethyl radical, or from the n-styrene hydridocobalt tricarbonyl complex. 

Nitroarenes are reduced to anilines (>85%) under the influence of metal carbonyl complexes. In a two-phase system, the complex hydridoiron complex [HFe,(CO)u]2-is produced from tri-iron dodecacarbonyl at the interface between the organic phase and the basic aqueous phase [7], The generation of the active hydridoiron complex is catalysed by a range of quaternary ammonium salts and an analogous hydrido-manganese complex is obtained from dimanganese decacarbonyl under similar conditions [8], Virtually no reduction occurs in the absence of the quaternary ammonium salt, and the reduction is also suppressed by the presence of carbon monoxide [9], In contrast, dicobalt octacarbonyl reacts with quaternary ammonium fluorides to form complexes which do not reduce nitroarenes. 

Formal [2 + 2 +1] cycloaddition of an alkene, alkyne, and carbon monoxide mediated by octacarbonyl dicobalt. 

Cobalt octacarbonyl is used as a catalyst in the Oxo process (see Carbon Monoxide). It also is used as a catalyst for hydrogenation, isomerization, hydrosilation and polymerization reactions. The compound is also a source of producing pure cobalt metal and its purified salts. 

Cobalt octacarbonyl is prepared by the reaction of finely divided cobalt with carbon monoxide under pressure ... 

Metal derivatives of cobalt carbonyl hydride such as Tl[Co(CO)4], Zn[Co(CO)4]2, or Cd[Co(CO)4]2 are formed upon reaction of cobalt octacarbonyl with these metals in the presence of carbon monoxide under pressure. Reaction with halogens (X) produces cobalt carbonyl halides, Co(CO)X2. 

Additional support for the carbon monoxide-alkoxycobalt insertion reaction is found in the reaction of tert-butyl hypochlorite with sodium cobalt carbonyl. This reaction, if carried out at — 80°C. in ether solution under nitrogen or carbon monoxide, leads to about a 10% yield of /er/-butoxycarbonylcobalt tetracarbonyl which has been isolated as the monotriphenylphosphine derivative. The major product seems to be cobalt octacarbonyl, possibly formed by decomposition of an intermediate JerJ-butoxycobalt tetracarbonyl (34). This reaction appears to be a true insertion reaction although a direct attack of a coordinated carbonyl group upon oxygen cannot be ruled out. 

When dicobalt octacarbonyl is treated with acetylenes (ac) and carbon monoxide under pressure, stable crystalline complexes of the type [Co2(CO)s(ac)] are formed. They can also be prepared from [Co2(CO)6(ac)] and carbon monoxide (199) ... 

The dark red crystalline compound C ELCosOa formed by treating dicobalt octacarbonyl with acetylene, carbon monoxide, hydrogen, and isopropyl alcohol (57) may have a similar structure, i.e., (LXVIII R = allyl and one CO ligand replaced by the C=C bond of the allyl group). 

The reaction of dicobalt octacarbonyl with molecular hydrogen Eq. (17), can occur at room temperature and is similarly inhibited by carbon monoxide, again suggesting an unsaturated intermediate (158). Pino et al. (116) suggested that dicobalt octacarbonyl is in equilibrium with a more reactive lower carbonyl. Natta et al. have also shown that Co4(CO)12 and Co2(CO)8, in the absence of hydrogen, coexist at carbon monoxide pressures corresponding to the highest rates of hydroformylation (104, 158). 

Nickel carbonyl is the more widely known catalyst for the carboxylation reaction dicobalt octacarbonyl has the disadvantage of giving side reactions (15). Dicobalt octacarbonyl has been used in the presence of tributyl phosphine for the reaction of ethylene, carbon monoxide, water, and ethanol. Besides ethyl acetate, acetaldehyde and diethyl ketone were found (136). Hydrogen has been found to increase the rate of reaction (78), presumably by the formation of cobalt hydrocarbonyl. However, this can lead to the formation of aldehydes, as in the reaction of acetyl bromide when an 89.4% yield of aldehyde was obtained in spite of the presence of water (95). 

When nonconjugated dienes react with carbon monoxide and water in the presence of dicobalt octacarbonyl, saturated and unsaturated cyclic ketones are produced (55, 77). This appears to be due to the formation of unsaturated acylcobalt carbonyls followed by cyclization, as discussed in Section II, B,3. 

As noted above, the butyraldehyde was reduced to the alcohol in these experiments when no carbon monoxide was added and when 1000 psi was added, but not when 300 psi was added. When no carbon monoxide was present the reduction was catalyzed by the metallic cobalt. When the 1000 psi carbon monoxide was used, it was presumed that the reaction was homogeneous, soluble dicobalt octacarbonyl or cobalt hydrocarbonyl being the catalyst. It is known, however, that at 150° a carbon monoxide pressure of at least 600 psi is needed to keep [Co(CO)4U from decomposing to cobalt metal. When only 300 psi of carbon monoxide was present, therefore, the cobalt would remain as metal and be inactive because it was poisoned by the carbon monoxide. 

In another experiment butyraldehyde was treated with a benzene solution of dicobalt octacarbonyl at 158° with 2000 psi initial hydrogen pressure in the absence of carbon monoxide. No hydrogenation of the butyraldehyde occurred. The carbonyl was reduced to cobalt, which did not function as a catalyst because of carbon monoxide poisoning. 

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