Formation of Gilman reagents (organocuprates) from alkyl halides
Description: Alkyl halides will react with lithium metal (Li) to make organolithium reagents. When two equivalents of organolithium are combined with a copper halide, this will form organocuprates (Gilman reagents)
Notes: X here is a halide (Cl, Br, I). Two equivalents of lithium metal are required for every equivalent of alkyl halide. Sometimes “ether” is written during this step – it’s just the solvent. Two equivalents of the organolithium reagent combine with one equivalent of copper salt to form the organocuprate.
Notes: Again, ether here is just the solvent. Sometimes you see it, sometimes you don’t. The byproduct of these reactions is LiX (a lithium halide salt).
Mechanism: Lithium easily gives up its single valence electron, in this case to Br (Step 1, arrow A) to form the radical anion. Fragmentation of the radical anion (Step 2, arrow B) leads to brief formation of a free radical, which gains an additional electron from a second equivalent of Li (Step 3, arrow C). Upon addition of a copper salt, the organolithium displaces the halide (Step 3, arrows D and E) and then undergoes a second addition of organolithium to give the organocuprate (Step 4, arrow F).