Researchers in Australia have studied how dichloroiodobenzene (PhICl2) interacts with pyridine ligands and their results contradict the previously proposed mechanism for the chlorination reaction with these reagents.
PhICl2, a common reagent for chlorinating a variety of substrates, is often used with pyridine as an additive to increase its reactivity. Examples include the chlorination of diazo compounds or hydrazones, electrophilic aromatic substitutions, and the oxidation of alcohols. Although pyridine plays an activating role in the chlorination reaction, it is unclear how it works. Classical textbooks of organic chemistry describe the pyridine-activating PhICl2by displacing one of the chlorides that form a cation ([PhI(Pyr)(Cl)] +), which in turn releases the chlorine to the substrate. But now Jason Dutton of La Trobe University, along with staff from the University of Queensland, have found out that this is not the case. During the crystallization of PhICl2 In pyridine, single crystal X-ray analysis showed that instead of displacing a chloride, pyridine forms a square planar complex through a halogen bond interaction with PhICl2.
In general, hypervalent iodine compounds are widely used in organic synthesis. Because their structure and reactivity are similar to transition metal derivatives, they are considered versatile and environmentally friendly reagents. When you learn more about how they work, chemists can develop more efficient synthetic methods.