Stereochemistry of Carbonylation and Decarbonylation

A stereochemical point of considerable interest concerns the position of entry of L with respect to the newly formed acyl moiety. This has been investigated for RMn(CO)5 and CpMo(CO)3R. 

Reactions of CpMo(CO)3R with L also yield products in which COR and L occupy closest possible positions. Thus, CpMo(CO)3CH2CH2CH2Br and PPh3 [Eq. (18)] afford the cis product (X) which then isomerizes to the 

Another aspect of stereochemistry of the CO insertion which has received attention concerns the actual process of formation of the acyl moiety from the coordinated CO and R. Three possible pathways may be envisaged. First, the alkyl moves from the metal onto an adjacent CO. This is known as the alkyl migration mechanism. Second, a coordinated CO moves to insert into the M—R bond—a CO insertion mechanism. Third, both CO and R move in a cooperative manner. These three pathways are represented schematically in Eq. (46). 

For the recently reported carbon monoxide insertion reaction (94) 

Complex (XV), which isomerizes to (XVI) in a subsequent, slower step, almost certainly is the kinetic product. Its stereoselective formation from 

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