Computational investigation of KICl2 iodination of thiophene and its electron-poor derivatives

Electrophilic iodination of thiophene and its electron-poor derivatives has been studied with KICl2 in dichloromethane and methanol using density function theory. KICl2 easily dissociates forming KCl and ICl, the latter being the iodinating agent. ICl forms an adduct with thiophene (pi-complex) followed by a nucleophilic attack of the ICl component by the aromatic component that forms the C-I bond. The nucleophilic attack is always the rate determining step with higher barriers that are in agreement the experimental conditions required for this reaction. The abstraction of a proton by the chloride anion on the last step is barrierless leading to the mono- and di-iodination of the thiophene derivatives. Side products derived from the nucleophilic addition of the chloride anion have been determined to be transient.