A Bidentate Iodine(III)-Based Halogen-Bond Donor as a Powerful Organocatalyst

In contrast to iodine(I)-based halogen bond donors, iodine(III)-derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro-Michael addition reaction as well as in a Diels-Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)-based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF3.

Automated summary

This study presents the first application of a bidentate bis(iodolium) salt as an organocatalyst in various reactions, surpassing the performance of iodine(I)-based organocatalysts and approaching that of strong Lewis acids like BF3. Coordination of the bidentate XB donor to the substrate was confirmed through structural analysis and DFT calculations of the transition states.