[Ag]2[B12Cl12] as a Catalyst in Chlorination Reactions

[Ag]2[B12Cl12] as a Catalyst in Chlorination Reactions

Author: European Journal of Organic Chemistry

The chlorination of arenes via electrophilic aromatic substitution (SEAr) reactions is an important example of C–H functionalization. This strategy is particularly useful in drug design, because the introduction of a chlorine substituent to a medicinally active compound can be used to tune its pharmacokinetic properties. Iodobenzene dichloride (PhICl2) is an easy-to-handle solid that acts as a chlorinating agent. It could be a promising alternative to chlorine gas in SEAr reactions. However, it is a weaker oxidizing agent than Cl2.

Tiffany Poynder, Sevan Houston, and Jason Dutton, La Trobe University, Melbourne, Australia, have found that the activity of PhICl2 can be enhanced using readily accessible [Ag]2[B12Cl12] as a catalyst. This silver salt has a weakly coordinating carborane anion. The team chlorinated a variety of arenes at room temperature using PhICl2 as a chlorinating agent, [Ag]2[B12Cl12] as a catalyst, and CHCl3 as the solvent. The method was also extended to the dichlorination of alkenes and alkynes. The researchers propose a “iodonium”-type mechanism (pictured below), in which Ag+ abstracts a chloride ion from PhICl2, resulting in an active [PhICl]+ species, which might be stabilized by the weakly coordinating [B12Cl12]2– anion.


[Ag]2[B12Cl12] outperformed several commercially available Ag(I) salts. [Ag]2[B12Cl12] and related carborane reagents are typically only used by the inorganic chemistry community, but the researchers hope that this work encourages others to further investigate its application in organic synthesis.



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