Metal carbonyls dicobalt octacarbonyl

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). 

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 ... 

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... 

The binary metal carbonyls are named by giving the name of the metal followed by the name carbonyl, with the number of carbonyl groups indicated by the appropriate prefix. For example, Ni(CO)4 is nickel tetracarbonyl, whereas Cr(CO)6 is chromium hexacarbonyl. If more than one metal atom is present, the number is indicated by a prefix. Thus, Co2(CO)8 is dicobalt octacarbonyl, and Fe2(CO)9 has the name diiron nonacarbonyl. 

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. 

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... 

Dimerization reactions of 1-azirines with several transition metal complexes have been studied (76TL2589). Reaction of 2-arylazirines (289) with an equimolar amount of a Group VI metal carbonyl gives 2,5-diarylpyrazines (290) in good yield. On the other hand, these compounds are converted to 2-styrylindoles (291) with rhodium carbonyl compounds or with dicobalt octacarbonyl in benzene. 

The transition metal carboxylate mechanism (Scheme 10), illustrated with palladium, requires the generation of this type of complex in the initial steps. This can occur by the alcoholysis of dicobalt octacarbonyl (Scheme 6) or by, for example, the reaction of methanol with a palladium(II) carbonyl (equa-... 

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. 

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. 

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). 

It was thought that the formation of inactive cobalt clusters such as Co4(CO)i2, formed by dimerisation of the remaining cobalt carbonyl species after release of the cyclopentenone product, were responsible for the shutdown of the catalytic cycle when dicobalt octacarbonyl was employed.51 Krafft and co-workers were able to show that Co4(CO)12 can actually be exploited as a catalytic species in the PK reaction and were able to obtain excellent yields if cyclohexylamine was introduced as an additive alongside the metal cluster.57,58 The use of metal clusters as catalysts for the reaction has been extended to involve mixed metal clusters.59... 

One of the most important metal carbonyl anions, as far as catalytic processes are concerned, is the cobalt tetracarbonyl anion, Co(CO)4. Prior to attempting phase-transfer catalysis using Co(CO)4" as a catalyst, it was imperative to establish that the anion is actually formed under these conditions. Therefore, model experiments in the author s laboratory involved the initial use of dicobalt octacarbonyl in a stoichiometric role. 

Caution. All operations should be carried out in an efficient fume hood, since both escaping carbon monoxide and volatile metal carbonyls are toxic. Contact of the metal carbonyl solutions with skin and inhalation of their vapors should be avoided. Octacarbonyl dicobalt is oxidized readily by air and must be handled under an inert atmosphere. 

Silicon-hydrogen bonds also add to dinuclear complexes in reactions that are formally one-electron oxidative additions, or simply metal-metal bond cleavage reactions. The reaction of dicobalt octacarbonyl with an excess of silane leads to silylcobalt carbonyls (equation 13)2 3. Similar reactions involving Mn-Mn29, Re-Re30, Fe-Fe31, Ru-Ru32,... 

AstraZeneca published the use of an immobilized transition metal carbonyl complex as a catalyst in the Pauson-Khand reaction [67]. This reaction is known to produce useful products but it also suffers from a number of drawbacks dicobalt octacarbonyl and its analogs are volatile, toxic, and unstable due to loss of carbon monoxide and aerial oxidation. These drawbacks can be avoided by the use of an immobilized metal carbonyl complex (Scheme 13), which is safe and convenient to handle (see also [68]). It offers the additional advantages of being reusable after recovery from the reaction medium and the product becomes less contaminated with metal carbonyl remnants. The reaction was applicable to a wide range of substrates with the exception of tetra-substituted alkenes. A typical reaction of enine 32 to the bicyclic enone 33 is depicted in Scheme 13. 

A more detailed study into the mechanism of ruthenium bimetallic melt catalysis for alcohol/ester production has been undertaken for the ruthenium-cobalt combination. Specifically, for the triruthenium dodecacarbonyl-dicobalt octacarbonyl couple, dispersed in tetrabutyl-phosphonium bromide, we have defined the experimental limits of this catalysis, demonstrated multiple catalyst recycle (7) and most importantly, identified some of the relationships linking catalyst productivity, alcohol-ester carbon distributions, and certain key operating parameters with the catalytically active metal carbonyl species present in these reaction media. 

Solution Spectra. The typical crude product solutions from these triruthenium dodecacarbonyl-dicobalt octacarbonyl/tetrabutyl-phosphonium bromide catalyzed CO hydrogenations to Ci C alcohols and their acetate esters display three band sets in the metal carbonyl spectral region. The strong band at ca. 1888 cm is characteristic (57) of [Co(C0)4l. The group of bands at 1955, 1990, and 2017 cm is characteristic (32) of the hydridoruthenium carbonyl anion,... 

Diazonium salts also readily react with nickel carbonyl, yielding mainly carboxylic acids and ketones in the presence of water and hydrochloric add (26, 27). Iron pentacarbonyl and dicobalt octacarbonyl with diazonium salts behave similarly, but the hexacarbonyls of chromium and molybdenum are virtually ineffective. This reaction may be considered as a transition metal-catalyzed carbonylation of aryl radicals, and is closely related to the Meer-wein reaction (26). 

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