Formation of Gilman reagents

Formation of Gilman reagents Definition:


Alkyl halide will react with lithium metal to make organolithium reagents. When two equivalents of organolithium are combined with a copper halide, this will form organocuprates (Gilman reagents).



Formation of Gilman reagents Explained:


Gilman reagent is another one organometallic compound often used in organic synthesis. Their general formula is R2CuLi, where R is alkyl, aryl, allyl or benzyl group. These species are also called organocuprate reagents, or just organocuprates.

Gilman reagents are obtained from an alkyl halide, lithium and copper halide, CuX (X=Cl, Br, I) in two steps.

In the first step, lithium (two equivalents) will be 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-bromide 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 second lithium ion, producing lithium bromide.



In the second step, two equivalents of organolithium reagent react with copper iodide. Both alkyl groups will be attached to a copper. Copper bears a negative charge and one of these two lithiums remains with copper. The other lithium pair up with iodide. The final product contains two copper-carbon bonds and positive counter-ion lithium.



Gilman reagents have a less polar carbon-metal bond in contrast to the other organometallic compounds and are therefore less reactive. They do participate in substitution and conjugate addition reactions, in which Grignard reagents and organolithium reagents typically do not do. 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.