Acylcobalt tetracarbonyls carbonyl compounds

One final interesting isomerization achieved in the cobalt carbonyl system should be mentioned. Heck and Breslow (22b) found that acylcobalt tetracarbonyl compounds undergo alcoholysis with the formation of HCo(CO)4. With methanol, the reaction proceeds at 50° ... 

The one example where the simple insertion product is a stable product is the carbon monoxide insertion reaction. The addition of carbon monoxide to alkylcobalt tetracarbonyls to form acylcobalt tetracarbonyls has already been discussed above because of its basic importance in alkylcobalt and acylcobalt carbonyl chemistry. The mechanism of this insertion is thought to involve a 1 2 shift of the alkyl group from cobalt to carbon followed by reaction of the intermediate acylcobalt tricarbonyl with another external carbon monoxide. Although there is no conclusive evidence for or against this mechanism in the carbonylation of cobalt compounds, there is evidence for it in the related carbonylation of alkylmanganese pentacarbonyls (2, 24). 

Acetylene and monosubstituted acetylenes appear to give some of the 7T-(penteno-4-lactonyl)cobalt tricarbonyl complexes on reaction with alkylcobalt or acylcobalt tetracarbonyls also but other products are formed too. These other products have not been characterized but are thought to be linear, low molecular weight polymers of the acetylene or of the acetylene and carbon monoxide with an acyl group at one end of the polymer chain and a cobalt carbonyl group at the other. The formation of cyclic products from the more-substituted compounds and cyclic and linear ones from the less-substituted compounds is explainable because substitution is known to improve many cyclization reactions. 

Insertion reactions of alkylcobalt or acylcobalt tetracarbonyls with saturated aldehydes or ketones have not been observed. Carbonyl insertions do occur in some unsaturated carbonyl systems, however. The cyclization of the intermediate acylacrylylcobalt tricarbonyls, formed from acetylenes and alkylcobalt or acylcobalt tetracarbonyls, to butenolactone derivatives, as described above, is one example of the reaction. Another example is the addition of alkylcobalt or acylcobalt tetracarbonyls to a, -unsaturated aldehydes or ketones. In this reaction an acyl group from the cobalt compound is added to a carbonyl oxygen and the cobalt carbonyl group forms a iT-allyl system with the carbonyl carbon and the double bond 19). 

Acylcobalt carbonyl derivatives are cleaved by sodium methoxide to esters and sodium salts of the corresponding carbonyl anions. By means of this reaction, acetyl[bis(trimethylolpropane phosphite)]cobalt dicarbonyl has been converted into sodium [bis(trimethylolpropane phosphite)]cobalt dicarbonyl. The latter compound is readily alkylated by methyl iodide to form the methylcobalt derivative and this compound in turn reacts with another mole of the phosphite ester, in the same way that methylcobalt tetracarbonyl does, to form acetyl[tris(trimethylolpropane phosphite)]-cobalt carbonyl ... 

By the addition of a phosphine to an alkylcobalt tetracarbonyl, the phosphine-substituted acylcobalt carbonyl can be prepared (182,183). In the case of (methoxycarbonyl)methylcobalt tetracarbonyl as a model compound, some details of the reaction have been revealed. Adding a phosphine to this complex, the kinetically controlled formation of a phosphine-substituted acylcobalt carbonyl is observed that can be converted to the thermodynamically more stable phosphine -substituted derivative. 

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