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CuI and I₂ Reagent

Catalytic systems for Coupling and Iodination reactions.

By chemca Team • Updated Jan 2026

Copper(I) Iodide ($CuI$) often works in tandem with Iodine ($I_2$) or as a standalone catalyst in various organic transformations. It is crucial for C-N, C-O, and C-C bond formation reactions, particularly in Ullmann-type couplings and synthesis of aryl halides.

1. Ullmann-Type Coupling Reactions

C-N and C-O Bond Formation

$CuI$ acts as a catalyst for coupling aryl halides with nucleophiles like amines, phenols, or amides.

A. Synthesis of Diaryl Ethers (Ullmann Ether Synthesis):

$$ Ar-X + Ar'-OH \xrightarrow{CuI, Base, \Delta} Ar-O-Ar' $$

B. N-Arylation of Amines/Amides: Also known as the Goldberg reaction when amides are used.

$$ Ar-I + R-NH_2 \xrightarrow{CuI, K_2CO_3} Ar-NH-R $$

Role of CuI: Copper acts as a Lewis acid to activate the aryl halide (via oxidative addition or $\pi$-complexation), facilitating nucleophilic attack.

2. Iodination Reactions ($CuI + I_2$)

Transformation of Aryl Bromides/Chlorides

The combination of $CuI$ and a ligand often facilitates the exchange of $Br/Cl$ with $I$ (Finkelstein-type aromatic substitution).

$$ Ar-Br + NaI \xrightarrow{CuI, \text{Ligand}, \Delta} Ar-I + NaBr $$

Direct Iodination: $I_2$ in the presence of copper salts can iodinate activated aromatic rings.

3. Sonogashira Coupling (Co-catalyst)

Alkyne-Aryl Coupling

$CuI$ is a standard co-catalyst used with Palladium ($Pd$) in the Sonogashira reaction to couple terminal alkynes with aryl or vinyl halides.

$$ Ar-X + H-C \equiv C-R \xrightarrow{Pd(PPh_3)_2Cl_2, CuI, Et_3N} Ar-C \equiv C-R $$

Function: CuI reacts with the terminal alkyne to form a Copper Acetylide ($Cu-C \equiv C-R$) intermediate, which then transmetallates to Palladium.

4. Synthesis from Carboxylic Acids

Hunsdiecker-Type Reaction

Reaction of silver carboxylates or carboxylic acids with $I_2$ often yields esters (Simonini Reaction) or alkyl iodides depending on stoichiometry, but $I_2$ is key.

$$ RCOOAg + I_2 \xrightarrow{CCl_4, \Delta} R-I + CO_2 + AgI $$

(Strictly Hunsdiecker uses $Br_2$, but $I_2$ follows similar radical path leading to esters or iodides).

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