A Gilman reagent is a lithium and copper (diorganocopper) reagent compound, R2CuLi, where R is an organic radical. These are useful because they react with organic chlorides, bromides, and iodides to replace the halide group with an R group. This is extremely useful in creating larger molecules from smaller ones.[1]
These reagents were discovered by Henry Gilman.[2] Lithium dimethylcopper (CH3)2CuLi can be prepared by adding copper(I) iodide to methyllithium in tetrahydrofuran at −78 °C. In the reaction depicted below,[3] the Gilman reagent is a methylating reagent reacting with an alkyne in a conjugate addition, and the negative charge is trapped in a nucleophilic acyl substitution with the ester group forming a cyclic enone.
Gilman reagents have complicated structures in crystalline form and in solution. Lithium dimethylcuprate is a dimer in diethyl ether forming an 8-membered ring with two lithium atoms coordinating between two methyl groups. Similarly, lithium diphenylcuprate forms a dimeric etherate, [{Li(OEt2)}(CuPh2)]2, in the solid state.[4]
If the Li+ ions are rendered inert by complexation with the crown ether 12-crown-4, the isolated diorganylcuprate anions that remain adopt a linear coordination geometry at copper.[5]
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