Question

Which among the following is known as Gilman reagent?
A. \[{R_2}CuLi\]
B. LiI
C. CuI
D. Li

Answer 1

Hint: Gilman reagent is also known as organocopper compounds which is used for carbon-carbon bond formation in organic synthesis. Compounds of this type were first described in the 1930s by the American chemist Henry Gilman, for whom they are named.

Complete step by step solution:
- A Gilman reagent is a lithium (Li) and copper (Cu) (diorganocopper) reagent compound, \[{R_2}CuLi\], where R is an alkyl or aryl.
- The most widely used organocopper compounds are the lithium organocuprates, which are prepared by the reaction between organolithium reagents (RLi) and copper(I) halides (CuX); for example, ArLi gives \[A{r_2}CuLi\].
- Gilman reagents are obtained from an alkyl halide, lithium and copper halide, CuX (Where, X = Cl, Br, I) in two steps. In the first step, lithium is added to alkyl halide, forming an organolithium. Lithium is in the first column of the periodic table and it has one valence electron. From both lithiums, both electrons will be added to carbon and break the carbon-bromine bond.
- Now, carbon has a partial negative charge and it will take one lithium ion which has a partial positive charge. The bromide ion (negative charge) will pair up with a second lithium ion, producing lithium bromide. In the second step, two equivalents of organolithium reagent react with copper iodide. Both alkyl groups are attached to a copper. Copper bears a negative charge and one of these two lithiums remains with copper. The other lithium pair up with the iodide. The final product contains two copper-carbon bonds and positive counter-ion lithium.

Therefore, the correct answer is option (A).

Note: Gilman reagents have a less polar carbon-metal bond in contrast to the other organometallic compounds and thus it is the reason why they are less reactive. They do participate in substitution and conjugate addition reactions, unlike the Grignard reagents and organolithium reagents which typically do not participate. Generally, organometallic reagents are useful synthetically because they react as if they were free carbanions. Carbon bears a partial negative charge, so the reagents react as bases and nucleophiles.