Cobalt Octacarbonyl-dicobalt

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 ... 

The cobalt catalyst can be introduced into the reactor in any convenient form, such as the hydrocarbon-soluble cobalt naphthenate [61789-51 -3] as it is converted in the reaction to dicobalt octacarbonyl [15226-74-17, Co2(CO)g, the precursor to cobalt hydrocarbonyl [16842-03-8] HCo(CO)4, the active catalyst species. Some of the methods used to recover cobalt values for reuse are (11) conversion to an inorganic salt soluble ia water conversion to an organic salt soluble ia water or an organic solvent treatment with aqueous acid or alkah to recover part or all of the HCo(CO)4 ia the aqueous phase and conversion to metallic cobalt by thermal or chemical means. 

Unmodified Cobalt Process. Typical sources of the soluble cobalt catalyst include cobalt alkanoates, cobalt soaps, and cobalt hydroxide [1307-86 ] (see Cobalt compounds). These are converted in situ into the active catalyst, HCo(CO)4, which is in equihbrium with dicobalt octacarbonyl... 

In addition to rhodium(III) oxide, cobalt(II) acetylacetonate or dicobalt octacarbonyl has been used by the submitters as catalyst precursors for the hydroformylation of cyclohexene. The results are given in Table I. 

The reaction of dicobalt octacarbonyl with [NP(OPh) (OCgH P-Pl O 3)n gives three different phosphine bound cobalt carbonyls. The initial hydroformylation activity of the heterogeneous catalyst... 

A combination of Co-mediated amino-carbonylation and a Pauson-Khand reaction was described by Pericas and colleagues [286], with the formation of five new bonds in a single operation. Reaction of l-chloro-2-phenylacetylene 6/4-34 and dicobalt octacarbonyl gave the two cobalt complexes 6/4-36 and 6/4-37 via 6/4-35, which were treated with an amine 6/4-38. The final products of this domino process are azadi- and azatriquinanes 6/4-40 with 6/4-39 as an intermediate, which can also be isolated and separately transformed into 6/4-40 (Scheme 6/4.11). 

A typical example of this is the dicobalt octacarbonyl catalyzed hydroformylation of olefins to yield aldehydes. According to the classical mechanism proposed by Heck and Breslow /29/ (Equations 28-31), the cobalt carbonyl reacts with hydrogen to form hydrido cobalt tetracarbonyl, which is in equilibrium with the coordinatively unsaturated HCo(C0)2. The tricarbonyl coordinates the olefin, and rearranges to form the alkyl cobalt carbonyl. 

The hypothesis that the cobalt carbonyl radicals are the carriers of catalytic activity was disproved by a high pressure photochemistry experiment /32/, in which the Co(CO), radical was prepared under hydroformylation conditions by photolysis of dicobalt octacarbonyl in hydrocarbon solvents. The catalytic reaction was not enhanced by the irradiation, as would be expected if the radicals were the active catalyst. On the contrary, the Co(C0)4 radicals were found to inhibit the hydroformylation. They initiate the decomposition of the real active catalyst, HCo(C0)4, in a radical chain process /32, 33/. 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

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. 

Cobalamin, 25 803 folic acid and, 25 802 Cobalt (Co), 7 207-228. See also Co-base superalloys 60Co isotope 60Co nucleus Fe-Ni-Co alloys Dicobalt octacarbonyl Tetracobalt dodecacarbonyl analysis, 7 215-216 in ceramic-matrix composites, 5 554t coke formation on, 5 266 colloidal suspensions, 7 275 economic aspects, 7 214-215 effect on copper resistivity, 7 676t environmental concerns, 7 216 health and safety factors, 7 216-218 in M-type ferrites, 11 66, 69 occurrence, 7 208... 

A second interfacial exchange reaction of the o-acylcobalt complex with hydroxide ion leads to the production of the alkanecarboxylate anion, which migrates into the aqueous phase, leaving the cobalt tetracarbonyl anion in the organic phase for subsequent reaction (Scheme 8.2). Optimum yields of the carboxylic acids are obtained with ca. 40 1 ratio of the alkyl halide to dicobalt octacarbonyl. Co(Ph,P)2Cl2 can also be used and has the advantage that the cobalt can be recycled easily [5]. 

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. 

Acetylation occurs at the 2-position of allene systems (Scheme 8.14). The intermediate 7t-allyl complex breaks down via the nucleophilic displacement of the cobalt carbonyl group by the hydroxide ion to produce the hydroxyketone (7) [ 11 ]. An alternative oxygen-initiated radical decomposition of the complex cannot, however, be totally precluded. The formation of a second major product, the divinyl ketone (8), probably arises from direct interaction of the dicobalt octacarbonyl with the allene and does not require the basic conditions. 

Desulphurization of thiols has been accomplished in high yield under phase-transfer conditions using tri-iron dodecacarbonyl (or dicobalt octacarbonyl). The mechanism proposed for the formation of the alkanes and the dialkyl sulphide byproducts involves a one electron transfer to the thiol from the initially formed quaternary ammonium hydridoiron polycarbonyl ion pair [14], Similar one electron transfers have been postulated for the key step in the cobalt carbonyl promoted reactions, which tend to give slightly higher yields of the alkanes (Table 11.18). 

Catalytic hydrogenation of thiophene poses a problem since noble metal catalysts are poisoned, and Raney nickel causes desulfurization. Best catalysts proved to be cobalt polysulfide [425], dicobalt octacarbonyl [426], rhenium heptasulfide [5i] and rhenium heptaselenide [54]. The last two require high temperatures (230-260°, 250°) and high pressures (140, 322 atm) and give 70% and 100% of tetrahydrothiophene (thiophane, thiolene), respectively. 

Cobalt(II) acetate is prepared hy dissolving cohalt(II) carbonate or hydroxide in dilute acetic acid, followed by crystaUization. Also, it may be prepared by oxidation of dicobalt octacarbonyl in the presence of acetic acid. 

Synonyms dicobalt octacarbonyl cobalt carbonyl cobalt tetracarbonyl dimer... 

The alkyne-cobalt carbonyl complex 3 formed from the alkyne 1 and dicobalt octacarbonyl 2 should lose at least one of the GOs on the metal to provide the vacancy for the incoming olefins. Subsequently, an olefin-bound complex 5 rearranged oxidatively to yield a metallacyclic intermediate 6. Migratory insertion of GO of 6 would provide the homologated ring intermediate 7, and the following two successive reductive eliminations afford the cyclopentenone... 

Jeong and co-workers devised the method by using a phosphite-modified cobalt catalyst, which was obtained m situ by mixing of dicobalt octacarbonyl (3 mol%) and triphenylphosphite (10mol%) prior to the addition of reactants. Best results were obtained under mild pressure of GO (3 atm). ... 

Dicobalt Octacarbonyl. The chemistry of this interesting and versatile catalyst has been the subject of several recent reviews (Orchin, 38 Wender, Sternberg, and Orchin, 39). Dicobalt octacarbonyl reacts readily with molecular hydrogen in solution to form cobalt hydrocarbonyl ... 

The cobalt(O) complex shown in Entry 2 (Table 3.49) could be prepared either by heating a mixture of an alkyne cobalt carbonyl complex with polystyrene-bound tri-phenylphosphine, or by pretreating resin-bound triphenylphosphine with dicobalt octacarbonyl and then treating the resulting support with the alkyne. 

Step 4 Decobaltation of the Reaction Product. The product of the hydroformylation reactor containing the catalyst as a mixture of cobalt carbonyl hydride and dicobalt octacarbonyl is fed to the decobaiting section. Mixing the product at 120 °C and 10 atm with a dilute formic acid/ cobalt formate solution in the presence of air decomposes the catalyst (Reaction 9) (12). 

The metal carboxylate insertion mechanism has also been demonstrated in the dicobaltoctacarbonyl-catalyzed carbomethoxylation of butadiene to methyl 3-pentenoate.66,72 The reaction of independently synthesized cobalt-carboxylate complex (19) with butadiene (Scheme 8) produced ii3-cobalt complex (20) via the insertion reaction. Reaction of (20) with cobalt hydride gives the product. The pyridine-CO catalyst promotes the reaction of methanol with dicobalt octacarbonyl to give (19) and HCo(CO)4. 

In the present review we shall describe recent developments in the catalysis of reactions by dicobalt octacarbonyl. Although many of the reactions to be described do not necessarily involve dicobalt octacarbonyl directly in the catalytic cycle, but some derivative, there are several reasons for choosing this compound as a starting point. The most important reason being that dicobalt octacarbonyl is a reasonably stable, commercially available, fairly well characterized compound which easily gives active catalytic intermediates. Although by no means unique in their catalytic properties, the cobalt carbonyls do provide a particularly active and versatile example of metal carbonyl catalysis. Their catalytic reactions are also by far the most investigated and best understood. 

Most of the growth in our understanding of reactions catalyzed by dicobalt octacarbonyl has resulted from a study of the individual reactions of catalytic intermediates such as cobalt hydrocarbonyl. At much lower temperatures and pressures than are used in the corresponding catalytic processes, cobalt hydrocarbonyl has been found to give rise to similar reactions, but stoichiometrically. The study of these noncatalytic reactions has enhanced our understanding of the corresponding catalytic reactions to the point where we can focus on the reasons for the smaller differences rather than the larger similarities. Because of their importance, a discussion of the... 

A reaction closely related to hydrogenation which is catalyzed by dicobalt octacarbonyl or cobalt hydrocarbonyl under very mild conditions (0°C,... 

It has been observed that rapid isomerization accompanies the cobalt carbonyl-catalyzed hydrosilation of olefins (18). The reaction of equimolar amounts of a trisubstituted silane and dicobalt octacarbonyl has been shown to result in the formation of cobalt hydrocarbonyl (cf. Section IV). A very effective isomerization catalyst may be prepared by treatment of a solution of Co2(CO)8 in olefin ( 0.01 M) with a silicon hydride in sufficient quantity to slightly exceed the cobalt carbonyl concentration. 

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). 

Heck (59) has suggested that the first step in the carboxylation reaction is the formation of cobalt hydrocarbonyl, which can be formed from dicobalt octacarbonyl and solvent (55). Alkylation and carbonylation then produce an acylcobalt carbonyl. Reaction of the acylcobalt carbonyl with the compound containing active hydrogen then regenerates cobalt hydrocarbonyl, e.g.,... 

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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