Tuning the Halogen Bonding Strength of Cyclic Diaryliodonium Salts

Diaryliodonium(III) salts have recently received increasing interest as a new class of strong halogen bonding noncovalent organocatalysts. Even though this utilization of their Lewis acidity has only been investigated in few studies, their high potential in comparison to classical monovalent iodine based XB donors has become very apparent. So far, only acyclic and cyclic five-membered core structures have been used, and titration studies have shown the latter to be superior in terms of binding constants towards Lewis bases. Herein, we now compare the Lewis acidity and activity of these five-membered iodolium salts with those of six-membered iodininium derivatives. X-Ray structural analyses, ITC measurements and the reaction kinetics of a Ritter-type solvolysis reaction in wet acetonitrile (a typical halogen bond donor benchmark reaction) all demonstrate that iodolium salts are stronger halogen bond donors and catalysts than iodininium salts. Subsequently, we were able to improve the activity of both core structures significantly by introducing electron-withdrawing substituents.

Automated summary

Diaryliodonium(III) salts have been increasingly recognized as a new class of strong halogen bonding noncovalent organocatalysts. Comparisons between five-membered iodolium salts and six-membered iodininium derivatives have shown that the former are stronger halogen bond donors in terms of binding constants towards Lewis bases.