Octacarbonyl

Cobalt tetracarbonyl hydride cannot be preserved at room temperature except at pressures that would burst the usual glass sample tube. However, small quantities of the material as a yellow vapor will remain in equilibrium with hydrogen and the solid dicobalt octacarbonyl. 

Dicobalt octacarbonyl is a dark-brown microcrystalline solid. If it stands in a vacuum, it slowly sublimes, forming a few clear orange crystals on the walls. It has a vapor 

Above 51 dicobalt octacarbonyl decomposes into tetra-cobalt dodecacarbonyl [Co(CO) s]4, and carbon monoxide. This carbonyl is sparingly soluble in benzene and pentane and can be purified from these solvents to give pitch-black glistening crystals. Its molecular weight by the freezing-point method indicates the tetrameric formula.  

Submitted bt Abithtje A. Blanchaed and George W. Coleman Checked by C. M. MASONft and Robert L. BARNARof 

Iron pentacarbonyl is the starting material for this preparation. Althoi h iron pentacarbonyl can be prepared very readily on a commercial scale by a high-pressure technique, there is no convenient laboratory method available. However, iron pentacarbonyl is available conQmerciaUy admixed with 3 per cent of kerosene in lots as small as 1 lb. 

Submitted by Irving Wender, Heinz W. Sternberg, Sol Metlin, and Milton Orchin  

Dicobalt octacarbonyl has been prepared by the thermal decomposition of cobalt tetracarbonyl hydride1 and by the reaction of suspensions of cobalt(II) compounds such as the carbonate in inert organic liquids with carbon monoxide under superatmospheric pressure.2,3 The procedure described here may be regarded as a modification of the second approach. It is superior to the first in giving a higher yield. 

Caution. Some cobalt tetracarbonyl hydride results in this reaction. Because of its toxicity, previously outlined precautions1 must be observed. 

In a 500-ml. stainless-steel autoclave % are placed 150 ml. of petroleum ether (boiling range 32 to 63°) and 15 g. of cobalt(II) carbonate (0.126 mol). The autoclave is flushed three times with carbon monoxide and is then filled with an approximately equimolar mixture of carbon monoxide and hydrogen to a pressure of 3500 p.s.i. The autoclave is heated with agitation to 150 to 160° and maintained in this temperature range for 3 hours. A maximum 

X The commercial rocking autoclave available from the American Instrument Co., Superpressure Division, Silver Spring, Md., is satisfactory. Consistently high yields are obtained after the autoclave has been used several times. Addition of small portions of preformed carbonyl also increases the yield. 

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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. 

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). 

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... 

Ethanol can also be obtained by the reaction of methanol with synthesis gas at 185°C and under pressure (6.9—20.7 MPa or 68—204 atm) in the presence of a cobalt octacarbonyl catalyst (177). However, although ethanol was the primary product, methyl formate, methyl, propyl and butyl acetates, propyl and butyl alcohols, and methane were all present in the product. 

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]. 

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 dinuclear octacarbonyls are obtained by heating the metal (or in the case of iridium, IrCl3 -I- copper metal) under a high pressure of CO (200-300 atm). Co2(CO)s is by for the best known, the other two being poorly characterized it is an air-sensitive, orange-red solid melting at... 

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). 

Setzt man a-Brom-ketone mit aquivalenten Mengen Octacarbonyl-dikobalt bei Anwe-senheit von Benzyl-triathyl-ammoniumchlorid in Benzol und Natronlauge um, so erhalt man (trotz der Natronlauge in diesem Fall nicht iiber einen Hydrid-Komplex)2 in fast quantitativen Ausbeuten die reinen Ketone2 bei 20fachem OberschuB an Keton entste-hen zusatzlich 1,4-Diketone (s.S.533)2 ... 

Man isoliert z. B. beim Vcrhaltnis a-Brom-keton Octacarbonyl-dikobalt =1 1 4-Acetyl-biphenyl (98°/ d.Th.) sowie 2-Acetyl-naphthalin (97% d.Th.). 

Mit Octacarbonyl-dikobalt wird 2-Methyl-2,3-dimethoxycarbonyl-oxiran bei 23° in 95%iger Ausbeute zum Methyl-maleinsdure-dimethylester reduziert2 ... 

Thioketone werden unter Desulfurierung durch Dicyclopentadienyl-tetracarbonyl-dieisen4, Octacarbonyl-dikobalt4 und (Bis-[triphenylphosphino]-immonium)-tetracarbo-nyl-kobalt4 in Benzol, sowie durch Decacarbonyl-dimangan5 in Heptan zu Alkenen dimerisiert ... 

Bei Einsatz katalytischer Mengen Octacarbonyl-dikobalt fallen stets wechselnde Mengen des Enthalogenie-rungsprodukts mit an (s. S.527)1. 

Mit Octacarbonyl-dikobalt bzw. Cyclohexyl-nonacarbonyl-tetrakobalt in Benzol erhalt man aus Nitro-aromaten ebenfalls Azo-Verbindungen4. 

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. 

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

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... 

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... 

By analogy with hydroformylation, dicobalt octacarbonyl has been examined as a hydrosilylation catalyst. Various silanes and a-olefins react, often exothermically. Thermal deactivation occurs above 60° C hence, large exotherms and high temperatures must be avoided (56, 57,130). Isomerization is more pronounced than for the bridged olefin complexes of Pt(II) and Rh(I) (see below) it even occurs with trialkoxysilanes (57). Though isomerization is faster than hydrosilylation, little variation in the relative rates of these two processes with the nature of the silane is observed this is in marked contrast to the bridged systems (55). 

When dicobalt octacarbonyl is added to the silane prior to olefin addition, the activity of the system is drastically reduced 13, 14). 

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. 

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/. 

The synthesis of phthalimidines by dicobalt octacarbonyl-catalyzed carbonylation of Schiff bases was first described by Pritchard78 and the scope of the reaction was evaluated by Murahashi et a/.79 Later Rosenthal et al.80-83 subjected a variety of related compounds to carbonylation, and also achieved a phthalimidine synthesis directly from benzonitrile under the conditions of the oxo process.84 An example illustrating the formation of a phthalimidine is shown in Scheme 49 a comprehensive review of the scope and mechanism of reactions of this type is available.85... 

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... 

The indazoline products can also be made directly from the palladium complexes 78 by heating them with the isonitrile in toluene at 120CC.162 They are also formed in dicobalt octacarbonyl-catalyzed reactions of azo-arenes with isocyanides but in this case an alternative reaction pathway leading to indazolo[2,l- ]indazoles (79) is observed (Scheme 96).163 Products of the latter type are formed from sterically hindered isocyanides hence it is likely that in these cases a double metallation is favored over isocyanide insertion into a monometallated species (Scheme 97). 

A direct synthesis of triarylimidazoles and triarylimidazolines has been accomplished by the dicobalt octacarbonyl-catalyzed reaction of benzyla-mine derivatives with carbon tetrachloride. When the reaction temperature is 150°C a complex product is formed and yields of heterocyclic products are poor. By lowering the reaction temperature to 120°C or reducing the reaction time, or by using [Mo(CO)6] and [f)5-C5H5Mo(CO)3]2 as the... 

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... 

Pyrrolidone is the major product when allylamine is subjected to the conditions of the oxo process using dicobalt octacarbonyl as the catalyst.203 The by-products are pyridine derivatives 112 and 113 and these compounds become the major products when iron pentacarbonyl is used as the catalyst ... 

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