Chapter 14: Organometallic Compounds

Reactivity of Organometallics
As we have seen previously, the carbon attached to the metal is anionic in character, so it reacts as a carbanion, a nucleophilic carbon.

In principle there are 3 important groups of reactions where nucleophiles attack electrophilic C atoms.
For the organometallic reagents these types of reactions will result in the formation of new C-C bonds.
Limitations will be discussed below.
 

General Mechanism	Organometallic Application
1. Nucleophilic Substitution  Chapter 8
	R2CuLi with alkyl halides or tosylates to give alkanes
2. Nucleophilic Addition   Chapter 17
	RLi or RMgX with aldehydes or ketones to give 2o or 3o alcohols
3. Nucleophilic Acyl Substitution  Chapter 20
	RLi or RMgX with esters to give 3o alcohols

Study Tip : Note that the electrophilic C atoms can be recognised by realising that they are connected to electronegative atoms (esp. halides or oxygen).

Limitations:

• Organolithium, RLi, and organomagnesium, RMgX, reagents are typically too basic to be used in nucleophilic substitution reactions (1) with alkyl halides or tosylates where they tend to cause elimination reactions or other side reactions.
• Organocuprates, R₂CuLi, reagents are less reactive and do not react with aldehydes, ketones or esters but can be reacted with alkyl halides or tosylates to give alkanes without elimination.
• Nucleophilic acyl substitution (3) reactions of organolithium, RLi, and organomagnesium, RMgX, reagents are most commonly seen with esters.