N-Iodopyridinium Cations: Kinetic Trapping as Sulfonate Complexes

Abstract The pursuit of N-iodopyridinium cation isolation and characterization remains a challenge. Here, we report seven N-iodopyridinium sulfonate complexes that were prepared and isolated at low temperatures and characterized by X-ray diffraction analysis. These inherently instable N-iodopyridinium cations are stabilized by an oxygen of sulfonate anions via I···O halogen bond. In these complexes, the large positive charge on iodine of the (pyridine)N + –I cation act as an electron acceptor and the sulfonate oxygen as the electron donor. These complexes are stable enough in the crystalline state, yet decompose rapidly under ambient conditions, also being unstable in solution. The (pyridine)N + –I bond lengths [2.140(3) - 2.197(2) Å] and the I···O halogen bonds [2.345(6) - 2.227(3) Å] are analogous to (imide)N–I···ˉO–N + (N-oxide) uncharged halogen-bonded complexes formed from N-haloimides and pyridine N-oxides, thus confirming the existence of elusive N-iodopyridinium cation.