Kinetics of Organometallic Addition Reactions

The rates for the reaction of several aromatic ketones with alkyllithium reagents have been examined. The reaction of 2,4-dimethyl-4 -(methylthio)benzophenone with methyl lithium in ether exhibits the rate expression 

MO modeling (HF/3-21G) of the reaction of organolithium compounds with carbonyl groups has examined the interaction of formaldehyde with the dimer of methyllithium. The reaction is predicted to proceed by initial complexation of the carbonyl group at lithium, followed by a rate-determining formation of the new carbon-carbon bond. The cluster then reorganizes to incorporate the newly formed alkoxide ion. The TS is reached very early in the second step with only slight formation of the C—C bond. This feature is consistent with the fast and exothermic nature of the addition step. 

There is another possible mechanism for addition of organometallic reagents to carbonyl compounds, which involves a discrete electron transfer step.  

---