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  Ch 8
	R2CuLi with alkyl halides or tosylates
2. Nucleophilic Addition   Ch 17
	RLi or RMgX with aldehydes or ketones
3. Nucleophilic Acyl Substitution  Ch 20
	RLi or RMgX with esters

Study Tip : Note that the electrophilic C atoms can be recognized by realizing 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 do not react with aldehydes, ketones or esters but can be reacted with alkyl halides or tosylates to give alkanes.
• Nucleophilic acyl substitution (3) reactions of organolithium, RLi, and organomagnesium, RMgX, reagents are most commonly seen with esters