Co 4 2 Dicobalt octacarbonyl

Co(CO)4K Cobalt tetracarbonyl hydride, potassium salt, 2 238 [Co(CO)4]2 Dicobalt octacarbonyl, 2 238, 242 6 190, 194 [Co(CO)4]2[Co(C6H5N)6] Cobalt tetracarbonyl hydride, hexa-pyridinecobalt(II) salt, 5 192 [Co(CO)4]2[Ni(C,2H8N2)3] Cobalt tetracarbonyl hydride, tris-(1,10-phenanthroline)nickel-(II) salt, 5 193n., 195 [Co (C204) 3JK3 Potassium trioxa-latocobaltate(III), 1 37 [Co(C5H5N)a][Co(CO)4]2 Cobalt tetracarbonyl hydride, hexa-pyridinecobalt(II) salt, 5 192 Co(C5H702)3 Cobalt(III) acetyl-acetonate, 6 188... 

Ni(CO)4 Nickel tetracarbonyl [Co(CO)4]2 Dicobalt octacarbonyl CoNO(CO)3 Cobalt nitrosyl tricarbonyl H2Fe(CO)4 Iron tetracarbonyl dihydride... 

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... 

In the carbonyls, each molecule of carbon monoxide donates two electrons to the central atom. Cobalt has 27 extra nuclear electrons, and if two electrons are contributed by each of four carbon monoxide molecules, the cobalt would have an E.A.N. of 35. One more electron is needed to attain the rare gas structure of krypton and this is secured by the sharing of one electron pair between two cobalt monomers. The existence of a metal to metal bond in dicobalt octacarbonyl has been postulated by Ewens (34) and cryoscopic measurements have established without doubt the dimeric structure [Co(CO)4]2 for dicobalt octacarbonyl. 

The salt is insoluble in water and in solvents such as hexane or toluene and may, therefore, be separated from dicobalt octacarbonyl which is readily soluble in hydrocarbon solvents. Thus, two analyses and the requisite simple calculations permit the estimation of both [Co(CO)4]2 and Co(CO)4-. A convenient apparatus for the determination has been described (Orchin and Wender, 41). Alternately, the concentration of dicobalt octacarbonyl may be measured by adding pyridine to the solution containing the carbonyls. All the dimer is converted to the anion with the evolution of carbon monoxide according to Equation (2). After gas evolution has ceased, a solution of iodine in pyridine may be added. This reagent is similar to aqueous iodine and liberates all the carbon monoxide in the anion originally present as well as that formed from the dimer by reaction with pyridine. 

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... 

The palladium-catalyzed annulation of arynes, derived from 2-(trimethylsilyl)phenyl triflate, by 2-halobenzaldehydes provides variably substituted fluoren-9-ones in good yields (eq 4). Catalytic dicobalt octacarbonyl under CO pressure furnishes anthraquinones in the presence of the ar5me derived from 2-(trimethylsilyl)phenyl triflate. ... 

Reaction of dicobalt octacarbonyl with Lewis bases. A very common type of reaction, discussed in detail earlier in this chapter, is the reaction of dicobalt octacarbonyl with a great variety of Lewis bases (23, 24, 54) to give the derivatives [Co(base)g][Co(CO)4]2... 

An intermediate in the reduction with sodium amalgam appears to be the mercury derivative Hg[Co(CO)4]2- This method of preparation of [Co (00)4]- possesses the advantage, at least theoretically, that all of the cobalt of dicobalt octacarbonyl may be converted to the [Co(CO)4] anion. 

A variety of cobalt carbonyl derivatives have been obtained in which the cobalt atom is o-bonded to an element other than carbon. These have been obtained both by wet methods involving metathesis of a solution of [Co(CO)4] with an appropriate derivative of the element to be bonded to cobalt and by dry methods involving high-pressure reactions of carbon monoxide with a mixture of cobalt metal or one of its compounds and an appropriate derivative of the other element. Thus, treatment of aqueous solutions of [Co(CO)4] with silver nitrate or mercury(II) cyanide gave the derivatives AgCo(CO)4 or Hg[Co(CO)4], respectively (220). The mercury derivative can also be prepared by the dry method, involving treatment of a mixture of mercury(II) bromide and cobalt metal with 200 atm of carbon monoxide at 150° C (247). The silver derivative AgCo(CO)4 could not be prepared by the dry method (247). The yellow zinc and cadmium derivatives M[Co(CO)4]2 (M = Zn or Cd) can be obtained by treatment of cobalt(II) bromide, cobalt metal, or dicobalt octacarbonyl with zinc or cadmium metal in the presence of carbon monoxide under pressure (247). 

This reaction, preceded by the formation of Hg[Co(CO)4]2 from sodium amalgam and dicobalt octacarbonyl in a hydrocarbon solvent, is the basis of a recently proposed method for the purification of mercury 37). However, the cost of dicobalt octacarbonyl makes the widespread application of this mercury purification method unlikely. Treatment of Hg[Co(CO)4]2 with trimethylphosphite also liberates mercury, producing the nonionic derivative [Co(CO)3P(OCH3)3]2 rather than a salt 26)... 

Seyferth, D., Spohn, R. J., Churchill, M. R., Gold, K. Scholer, F, R. (1970) Co8(CO)24C6, a bis(tricobaltnonacarbonyl)/dico-balt hexacarbonyl derivative of 2,4-hexadiyne from the reaction of dicobalt octacarbonyl with hexachlorocyclopropane, J. Or-ganomet. Chem. 23, 237-255. 

Jacobsen (1999) has carried out carbomethoxylation of asymmetric epoxides. Thus, the carbomethoxylation of (R)-propylene oxide with CO and methanol yields 92% of (3R)-hydroxybutanoic acid in greater than 99% ee. Similarly, the reaction of (/ )-epichlorohydrin gives 96% of 4-chloro-(3R)-hydroxybutanoic acid in greater than 99% ee. The catalyst consists of dicobalt octacarbonyl and 3-hydroxy pyridine. A continuous process for making enantiomeric 1-chloro-2-propanol has been suggested. With a suitable catalyst propylene reacts with O2, water, cupric and lithium chloride to give 78% of (S)-l-chloro-2-propanol in 94% ee. 

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). 

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... 

The stoichiometry of Eq. (2) requires the absorption of 1 mole of CO per 2 moles of HCo(CO)4. However, Heck and Breslow (17) showed that, when olefin is used as the solvent, the absorption of CO approaches 1 mole per mole of HCo(CO)4, and they further showed that the 1 1 1 HCo(CO)4 CO olefin complex suggested as a possible intermediate by Kirch and Orchin (16) was in fact an isolable intermediate, namely, an acylcobalt tetracarbonyl, RCOCo(CO)4. Accordingly, the formation of aldehyde and dicobalt octacarbonyl proceeds ... 

The hydroformylation (or 0x0 ) reaction was discovered in 1938 by Roelen who was working on the formation of oxygenates as by-products of the Fischer-Tropsch reaction over cobalt catalysts. It soon became clear that the aldehydes and alcohols found were the products of secondary reactions undergone by the 1-alkenes (which are the primary products of the Fischer-Tropsch reaction, Section 4.7.2) with syngas. Further work showed that Roelen had discovered a new reaction, in which the elements of H and CHO were added to an olefin (hence hydroformylation), and which was catalyzed by cobalt. It was later found that the true precatalyst was not cobalt metal but derivatives of dicobalt octacarbonyl, such as the hydride, CoH(CO)4. 

The passage of allene into a benzene solution of dicobalt octacarbonyl at room temperature produces air-sensitive yellow crystals of composition [(C3H4)Co(CO)3]2 (428). The spectral data indicate a 77-allyl complex in which a CO grouping has been transferred to the 2-position of each allylic moiety. Although Co2(CO)g does not form a 77 complex with tetraphenylallene, cyclopentadienyldicarbonylcobalt does react under reflux in isooctane to yield the product [C3(C(,H5)4]Co(CO)(C5H6) in which the olefin appears to be a monodentate ligand (434). 

The 0X0 reaction, which involves heating an olefin with hydrogen and carbon monoxide under pressure in the presence of dicobalt octacarbonyl, with the introduction of a formyl or (hydroxymethyl) group at one carbon atom, is believed to proceed by the addition of the hydride HCo(CO)4 across the double bond, followed by insertion of CO into the newly formed carbon-cobalt bond. It would be anticipated that the cobalt ion would be nucleophilic and would therefore mainly attack glycals at C-1. In accordance with this view, the products of the reaction with the model glycal 2,3-dihydro-4Ff-pyran have been found to contain 78% of 2-(hy-... 

The Pauson-Khand reaction provides another new approach to the metal-catalyzed synthesis of heterocycles. This reaction involves the interaction of the multiple bonds of an alkyne with an alkene and carbon monoxide in the presence of dicobalt octacarbonyl (Co2(CO)g), or with just this reagent as a source of CO. The overall process has been described as a [2 -h 2 -h 1] cycloaddition. Only a few applications to heterocyclic synthesis have been reported so far. A 2008 paper that is illustrative of the process describes the use of this reaction for the construction of a heterocyclic ring that is part of an azabicy-clo[3.3.1]nonane derivative. This ring system is present in the alkaloid (-)-alstonerine (4.37), which prompted this study. 

The alkali salt of cobalt tetracarbonyl hydride can best be prepared by the absorption of carbon monoxide in an alkaline cobalt(II) cyanide suspension. Treatment of this solution with nitric oxide yields the volatile cobalt nitrosyl tricarbonyl/ while treatment with acid yields the volatile cobalt tetracarbonyl hydride. At room temperature, the latter compound decomposes into hydrogen and the nonvolatile dicobalt octacarbonyl, [Co(CX))4]2. 

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