Bifunctional Iodoazolium Salts: Searching for Cooperation Between Halogen Bonding and Hydrogen Bonding

Non-covalent interactions play an important role in all sub-fields of chemistry, including catalysis, where interactions of different natures can work together to improve reactivitiy and selectivity. Several families of molecules that incorporate both hydrogen bond (HB) and halogen bonding (XB) donors have already been studied. However, there is a lack of data on how grafting HB donors to iodoazolium salts could impact their association and reactivity properties. Herein, we disclose the synthesis of a library of iodoazolium salts bearing varied HB donors, along with a study of their physico-chemical properties using different techniques (X-ray diffraction, 31P NMR, ITC) and their behavior in catalysis. Even though no clear-cut evidence of cooperation between XB and HB could be obtained through physico-chemical evaluations, a iodoazolium salt bearing a urea function displayed better conversion and product selectivity in a Ritter reaction than all other activators lacking one or the other function. An efficient synthetic route was designed to prepare bifunctional iodoazolium-based halogen bond (XB) donors bearing varied hydrogen bond (HB) donors. Even though physico-chemical studies did not show clear evidence for a cooperation between the two non-covalent interactions, the bifunctional ureido iodoazolium salt proved to be the best activating agent in a Ritter-type reaction. image