Carbonyl Hypoiodites as Extremely Strong Halogen Bond Donors

Abstract

Neutral halogen-bonded O−I−N complexes were prepared from in situ formed carbonyl hypoiodites and aromatic organic bases. The carbonyl hypoiodites have a strongly polarized iodine atom with larger σ-holes than any known uncharged halogen bond donor. Modulating the Lewis basicity of the selected pyridine derivatives and carboxylates leads to halogen-bonded complexes where the classical O−I⋅⋅⋅N halogen bond transforms more into a halogen-bonded COO−⋅⋅⋅I−N+ ion-pair (salt) with an asymmetric O−I−N moiety. X-ray analyses, NMR studies, and calculations reveal the halogen bonding geometries of the carbonyl hypoiodite-based O−I−N complexes, confirming that in the solid-state the iodine atom is much closer to the N-atom of the pyridine derivatives than its original position at the carboxylate O-atom.