Formation of Gilman Reagents
Formation of Gilman Reagents: A Gilman reagent is an organocopper compound with the general formula R₂CuLi. Step-by-step mechanism, reagents and practice.
What happens
A Gilman reagent is an organocopper compound with the general formula R₂CuLi. It is made from an alkyl halide in two main stages: first the alkyl halide is converted into an organolithium reagent (R–X → R–Li), then the organolithium reacts with CuI to form the Gilman reagent (2 R–Li + CuI → R₂CuLi). Gilman reagents are useful for making new carbon–carbon bonds: one of the R groups can be transferred to another carbon (R₂CuLi + R′–X → R–R′), so they let you join two carbon fragments.
Reaction summary
R–X → R–Li (with 2 Li), then 2 R–Li + CuI → Gilman reagent R₂CuLi
Reagents and conditions
- Starting material: Bromomethane (alkyl halide)
- Reagents: Lithium metal (2 Li); CuI (copper(I) iodide)
- Conditions: Dry conditions
- Products: Lithium dimethylcuprate (Me₂CuLi, a Gilman reagent)
Mechanism
- Lithium Reacts with the Alkyl Halide: Lithium reacts with the alkyl halide: the C–X bond is replaced by C–Li (R–X → R–Li).
- Two R–Li React with CuI: Two equivalents of the organolithium reagent react with CuI: 2 R–Li + CuI → R₂CuLi. The final product is the Gilman reagent.
- Product: The Gilman reagent, R₂CuLi: copper is attached to two carbon groups.
Common mistakes
- Notice the 2 in R₂CuLi: copper is attached to two carbon groups, which is why you need 2 R–Li + CuI → R₂CuLi. Also, like Grignard and organolithium reagents, these reactions need dry conditions because organolithium reagents are destroyed by water and other proton sources.
Memory trick
Lithium first → Copper second. R–X → R–Li → R₂CuLi. Or even shorter: Li → Cu → Gilman.