Dicobalt octacarbonyl preparation

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]. 

Symmetrical ketones can be prepared in good yields by the reaction of organo-mercuric halides with dicobalt octacarbonyl in THF, or with nickel carbonyl in DMF or certain other solvents. The R group may be aryl or alkyl. However, when R is alkyl, rearrangements may intervene in the C02(CO)g reaction, though the Ni(CO)4 reaction seems to be free from such rearrangements. Divinylic ketones... 

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/. 

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... 

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. 

The dicobalt octacarbonyl-promoted Nicholas reaction has been used in the preparation of polycyclic ethers related to the marine polyethers ciguatoxin 32 and gambiertoxin <1999JOC37>. 

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 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. 

Dicobalt octacarbonyl, in Pauson—Khand reaction homogeneous catalysis, 11, 340 metal-coupled promoters, 11, 339 non-oxidative promoter-assisted, 11, 338 oxidative promoter-assisted, 11, 337 physical promoters, 11, 339 solid-supported promoters, 11, 339 Dicobalt triple-decker sandwiches, preparation, 3, 14 (+)-Dictamnol, via [5+2]-cycloadditions, 10, 613-614 Dicyclohexylborane, for alkene hydroboration, 9, 150... 

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. 

The radical-initiated addition of CBrCls or CBr4 to olefins followed by base-induced dehydrobromination of the adducts can be used to prepare a wide variety of RR C=C(Ii/,)CX3-type compounds whose reaction with dicobalt octacarbonyl will give the respective vinylic cluster derivatives. The reactions of the latter with appropriate reagents will extend further the number and types of organo-functional cluster complexes. Also, their... 

The 2-methylallylidynetricobalt nonacarbonyl used in Eq. (38) was prepared by the novel reaction of dimethylketene with dicobalt octacarbonyl.)... 

IV. Properties, Structure, and Preparation of Dicobalt Octacarbonyl and Cobalt... 

The first preparation of dicobalt octacarbonyl was made by reacting freshly reduced cobalt metal with 100 atm. of carbon monoxide at 200° (Mond, Hirtz, and Cowap, 25). No solvent was used in this preparation. Raney cobalt in an ether suspension has been recommended (Adkins and Kresk, 15). Treatment of the mixture with 200 atm. of carbon monoxide at 150° for 5 to 6 hours gave a dark red ether solution containing the dicobalt octacarbonyl. The simplest method of preparation consists of the treatment of a cobalt salt in benzene solution with synthesis gas. Cobalt acetate, carbonate, oleate, naphthoate, and octoate have been employed extensively. In a typical preparation (Wender, Greenfield, and Orchin, 18) a slurry of 15 g. cobalt(II)carbonate in 100 ml. of benzene is treated with synthesis gas at 250 atm. pressure in a 500 ml. autoclave at 130-160° for 1 hour. The clear dark benzene solution contains about 0.016 g. dicobalt octacarbonyl per milliliter. 

If the crystalline carbonyl is desired, low-boiling (30-60°) petroleum ether should be substituted for benzene in the above preparation. The petroleum-ether solution of the carbonyl is cooled overnight in the refrigerator, whereupon the crystalline dicobalt octacarbonyl separates. The solvent is decanted and the solid poured onto filter paper and then bottled. The carbonyl can be prepared directly in the crystalline form from metallic cobalt with carbon monoxide in the presence of 1 atm. of hydrogen sulfide. Some hydrocarbonyl is formed however. The crystalline carbonyl also can be prepared in a dry state from cobalt(II)-sulfide at 200° with carbon monoxide at 200 atm. if a metal like copper is present to combine with sulfur (Hieber, Schulten, and Marin, 42). 

To further expand the family of mannoside clusters obtainable from the alkyne derivatives, we also prepared cyclotrimerized hexamers using dicobalt octacarbonyl according to a known strategy (34). Thus dimer 37 and 30 were treated with Co2(CO)8 in refluxing dioxane to provide 48 and 50 in 61% and 42% yield, respectively (Scheme 9). 

The initial catalytic version of the PK reaction actually appeared in 1973, in the first paper detailing the preparation of cyclopentenones by Pauson and co-workers.3 By stirring a solution of dicobalt octacarbonyl (10 mol % with respect to the alkene) and norbornene (or norbornadiene), first under a pressure of acetylene and then under a pressure of mixed acetylene/CO (1 1), it was possible to obtain a good yield of the desired cyclopentenone products (42 and 8 - Scheme 16). It was possible to lower the loading of dicobalt octacarbonyl to 2.5 mol % and still obtain a 62% yield of the cyclopentenone. When norbornadiene was employed as the alkene, a lower yield of the desired cyclopentenone was obtained but this was due to the product reacting further under the conditions employed. 

When 3,4-di-O-acetyl-D-xylal (5), prepared by a modification of the procedure of Helferich and coworkers, was allowed to react with a mixture of carbon monoxide and hydrogen at a pressure of about 4000 Ib./in. and at a temperature of about 130° for about 90 minutes, in the presence of preformed dicobalt octacarbonyl in benzene as the catalyst, a mixture of two inseparable, partially acetylated hexitols was obtained in over 90% yield. Deacetylation of the latter with sodium methoxide in methanol yielded, in almost equimolar proportions, the chromatographically separable hexitols, l,5-anhydro-4-deoxy-L- yio-hexitol (6) and l,5-anhydro-4-deoxy-D-arahino-hexitol (7). Whenever the mixture of products was contaminated by the precursor aldehydo compounds, a prior reduction of these with sodium borohydride greatly facilitated the isolation of (6) and (7) in pure form. 

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