Assisted carbonyl insertion reactions bonding

The use of CO containing 3% H2 in the hydroesteriflcation reaction is standard, suggesting that a cobalt hydrocarbonyl is the active catalyst species. The reaction sequence involves olefin insertion into the Co—H bond, (carbonyl insertion) to give an acyl complex and cleavage with alcohol assisted by the pyridine promoter ... 

However, iron complexes may also display a beneficial effect. Thus, a promoting effect on hydroformylation was observed with Si02-supported Rh-Fe " bimetallic carbonyl clusters (Scheme 1.61) [12]. Based on Mossbauer spectroscopy, it was proposed that iron assists during the insertion reaction of CO into the Rh-C bond. Likewise, the hydrogenation of the intermediary alkoxy rhodium species to produce the alcohols may benefit from this bi-site interaction. 

When octahedral alkylpentacarbonyl derivatives of manganese(I) undergo carbon monoxide insertion assisted by a nucleophile L different from carbon monoxide (L = tertiary phosphines, amines, CO, etc.), the cis product is initially formed this observation, however, is not sufficient to permit one to distinguish between the alkyl migration mechanism [reaction (a)] and the insertion of a precoordinated carbonyl group into the manganese-carbon bond [reaction (e)]. In both cases mutually cis positions are involved. 

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