Dicobalt octacarbonyl Compounds

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... 

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). 

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... 

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 ... 

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 dark red crystalline compound C ELCosOa formed by treating dicobalt octacarbonyl with acetylene, carbon monoxide, hydrogen, and isopropyl alcohol (57) may have a similar structure, i.e., (LXVIII R = allyl and one CO ligand replaced by the C=C bond of the allyl group). 

Si(CH=CH2)4 with dicobalt octacarbonyl yielded the cluster compound H2C=CH—SiCo3(CO)9 (87). 

The reaction was also used for the synthesis of compounds containing SiMe2SiMe3 and CH2SiMe3 groups in the cyclopentadienyl ring (7). In a similar manner, triorganotin groups are eliminated in reactions with dicobalt octacarbonyl, with formation of -complexes (7) ... 

The syntheses of many Co3(CO)9X compounds from dicobalt octacarbonyl and XCCI3 have been optimized 347), and further reactions starting from 0(60)4 and XCCI3 360), or RCF —Co(CO)4 46) have been investigated in order to determine the mechanism of formation of the clusters. Methinyltricobalt enneacarbonyls are also formed from Co2(CO)g and such apical carbon precursors as acetylenes 140), dimethyl ketene 408), or carbyne chromium complexes (7 73). In several cases (7 72,... 

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. 

Dicobalt octacarbonyl was one of the earliest known compounds believed to be capable of activating molecular hydrogen in homogeneous solution (48). The hydrogenation of organic substrates in the presence of this catalyst has been described in several earlier reviews (140a, 158). Reduction of olefins and aldehydes will be considered here. 

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.,... 

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... 

Pure compound studies demonstrated (Adkins and Kresk, 7) that certain olefinic compounds reacted exclusively by hydrogenation rather than by hydroformylation, Treatment of crotonaldehyde with synthesis gas and dicobalt octacarbonyl at 125° gave butyraldehyde in about 50% yield. The addition of small amounts of diphenylsulfide to the dicobalt octacarbonyl did not interfere with the hydrogenation. Later it was shown (Wender, Levine, and Orchin, 9) that if the temperature was raised from 125° to 170-185°, crotonaldehyde was reduced to butanol ... 

The unique hydrogenating ability of a mixture of synthesis gas and a cobalt catalyst is intimately associated with the chemistry of the cobalt compounds formed under these conditions, namely dicobalt octacarbonyl and cobalt hydrocarbonyl. Before any mechanism for the hydrogenation reaction is discussed it is imperative to consider, if even briefly, the chemistry of the cobalt carbonyls. 

Recent work (Wender, Sternberg, and Orchin, 36) suggests a revision of the view (Hieber, Muhlbauer, and Ehmann, 37) that the reaction between dicobalt octacarbonyl and compounds like methanol, ethanol pyridine, and o-phenanthroline involves only the displacement of one or more carbon monoxide groups of the carbonyl by the base according to Equation (1), using pyridine as an example. 

Equation (2) is representative of a group of reactions between dicobalt octacarbonyl and a compound having an available unshared pair of electrons, i.e., a base in the Lewis sense. It is apparent from the above equations that there has been an internal exchange of electrons and... 

The species shown in the system 8.13 are those present under reaction conditions. At lower temperatures and pressures, a wealth of different complexes are present, including dicobalt octacarbonyl and cationic complexes of cobalt that differ depending on what cobalt compound was initially charged [17,23-25]. 

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. 

---