Halonium and chalconium salt-catalyzed Schiff condensation: kinetics and DFT insights into organocatalyst activity parameters†

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.