Acylcobalt tetracarbonyls oxidation

The formation of acylcobalt tetracarbonyls from alkylcobalt tetracarbonyls and carbon monoxide described above is an example of this type of reaction. The similar reactions with triarylphosphines and phosphite esters have been thoroughly studied because the equilibria are far on the side of the acyl compounds and the products are convenient derivatives to prepare from the alkylcobalt tetracarbonyls (7,10), The triarylphosphine and phosphite ester derivatives are much more thermally and oxidatively stable than the alkylcobalt tetracarbonyls themselves. 

Alkylcobalt and acylcobalt tetracarbonyls are generally rapidly oxidized by air but the products of this reaction have not been investigated. Presumably the products are carboxylic acids and cobalt oxide. 

Dissociation of carbon monoxide from an acylcobalt tetracarbonyl yield a 16-electron acylcobalt tricarbonyl complex which is the active intermediate in the decarbonylation, oxidative addition, and in various ligand substitution reactions. 

The proposed mechanism, which is based on the double carbonylation of styrene oxide, is shown in Scheme 6.2. The generation of an acylcobalt carbonyl complex from the reaction of cobalt tetracarbonyl anion with an alkyl halide is followed by reaction with a thiirane. This species can undergo carbonylation, the thioester function can undergo hydrolysis to reveal a sulfido nucleophile, and intramolecular cydization then produces thietan-2-one. The thietan-2-one can undergo ring cleavage and the mercapto acid results by protonahon. 

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