Cobalt hydrocarbonyl, reactions epoxides

Equation (44) is reminiscent of the reaction of cobalt hydrocarbonyl with epoxides which therefore suggests the preceding step... 

A third method for preparing alkylcobalt tetracarbonyls is the reaction of cobalt hydrocarbonyl with epoxides. The products are 2-hydroxyalkyl-cobalt tetracarbonyl derivatives (9). Ethylene oxide produces 2-hydroxy-ethylcobalt tetracarbonyl. 

The mechanism most consistent with all the data is an ionic acid opening of the epoxide —apparently where the hydrocarbonyl is used as an acid to attack the epoxide— which is more sensitive to steric effects than to electronic factors. This conclusion may at first appear to be inconsistent with our previous finding that isobutylene reacted with cobalt hydrocarbonyl to give exclusively addition of the cobalt to the tertiary position. The inhibitory effect of carbon monoxide on that reaction, however, indicated that it was probably cobalt hydrotricarbonyl that was actually adding to the olefin and steric effects would be expected to be much less important with the tricarbonyl than with the tetracarbonyl (7) Apparently he feels now that the former reactions really involve the tricarbonyl, loss of CO being important to get the reaction running whereas epoxide attack perhaps involves a tetracarbonyl, steric factors are more important here. 

The acyl cobalt carbonyls are very probably then hydrogenated to aldehydes and cobalt hydrocarbonyl, in analogy to the described mechanism for the olefins. As Yokokawa, et al. [298] found, the yield depends strongly on the reaction temperature. At higher temperatures (see table 23), isomerization of the epoxides to the corresponding ketones and aldehydes frequently occurs first. Further reaction gives a large number of polymeric products. 

From the work of Takegami et aL, and Heck, it must foUow that cobalt hydrocarbonyl reacts with epoxides in the acid form. The reaction of epoxide compounds should be accelerated by addition of small amounts of alcohols, ketones, ethers and esters [303], as well as copper oxide or halide, silver oxide and aluminium chloride [304]. 

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