A suitable model for computational study giving reliable estimation of the catalytic effect of σ-hole donating organocatalysts is suggested.

The Schiff condensation between 4-methylbenzaldehyde and 2-aminopyridine, catalyzed by chloronium, bromonium, and iodonium triflates, as well as sulfonium, selenonium, and telluronium triflates, was investigated. ¹H NMR monitoring revealed that the catalytic activity increased significantly with heavier σ-hole-bearing heteroatoms. DFT calculations showed that the maximum electrostatic potential at the σ-hole was a more reliable predictor of the catalytic activity of these organoelement species. In contrast, the equilibrium concentrations of the activated form of the electrophile and the electrophile-to-onium cation charge transfer values did not accurately reflect the catalytic activity of the onium salts.

The base-catalyzed reaction might proceed not via the previously suggested radical route, but via the nucleophilic attack on the meta-position to the iodine(iii) center, which rise another view on the reactivity of aryliodolium salts.