Addition Reactions of Organometallic Compounds

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

The nucleophilic displacement reactions of organolithium compounds with alkyl halides are second order insofar as the rates have been measured, but there are unexplained examples of autocatalysis and non-reproducable rate constants. The product of the reaction in the case of the methylallyl chlorides is the same mixture regardless of 

Even the Cannizzaro reaction might have a similar transition state. Although the coordinating tendency of alkali metals is less than that of aluminum or magnesium, it is not negligible. An alternative structure is possible in this case in which a proton occupies the bridging position. 

The reactions of alkyl lithium compounds, although closely related to those of the Grignard reagents, are somewhat easier to study because of the greater simplicity of the organometallic reagent. They are very fast reactions but some rates have been successfully measured by resort to the flow method. The reaction is second order and a transition state like LXXII has been suggested.891 

Given a sufficiently electronegative carbon atom, no carbonyl or conjugated carbonyl group is heeded for addition to take place. For example, a carbon atom that is part of the cyclopentadiene system is able to stabilize the negative charge quite well. The cyclopentadienyl anion is comparatively stable.8 8 

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Neither the mechanism for all addition reactions of hydride donors to the carbonyl carbon nor the mechanism for all addition reactions of organometallic compounds to the carbonyl carbon is known in detail. It is even doubtful whether only ionic intermediates occur. For instance, for some LiAlH4 additions an electron transfer mecha-... 

Lewis Acid Promoted Addition Reactions of Organometallic Compounds... 

Lewis Acid Promoted Addition Reactions of Organometallic Compounds Nucleophilic Addition to Imines and Imine Derivatives Nucleophilic Addition to Carboxylic Acid Derivatives... 

Gihnan H, Kirby RH (1941) Addition Reactions of Organometallic Compounds with Conjugated Systems. J Am Chem Soc 63 2046-2048... 

The carbonyl group of acid derivatives reacts with the nucleophilic carbanion available from organo-metallic reagents. However, the reactions of the individual classes of compounds are not as straightforward as the addition reactions of organometallic compounds with aldehydes and ketones. Addition of a carbanion to the acyl carbon atom generates a tetrahedral intermediate that can decompose to give a ketone that will react further with another equivalent of the carbanion. 

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