The Reaction of Cobalt Hydrocarbonyl with Vinylacetate, Crotonate, Styrene, and Acrylates

Abstract

Ethyl vinylacetate and ethyl crotonate reacted with cobalt hydrocarbonyl at 25°C to give three isomeric acylcobalt carbonyls, α- and γ-carbethoxy-butyrylcobalt carbonyls and β-carbethoxy-iso-butyrylcobalt carbonyl. The distribution of these complexes depends greatly on the reaction time (0.5–20 hr). In both cases the β-isomer predominates at shorter reaction times (0.5–1.5 hr), while the γ-isomer predominates at longer reaction times. This shows that isomerization occurs among the complexes and that the equilibrium is very favorable to the γ-isomer. Acrylates and styrene react with cobalt hydrocarbonyl to give two isomeric acylcobalt carbonyls. The isomerization of the acylcobalt complex with a branched structure to that with a straight-chain structure is much promoted by the phenyl and ester groups. The promoting effect of the ester groups is the highest in benzyl, followed by allyl, and ethyl, isopropyl, butyl, and cyclohexyl. Such a promoting effect can reasonably be attributed to the −I effect of these groups.