Iodonium and Telluronium Triflates Serving as Noncovalent Organocatalysts Provide Catalytic Effect in the Schiff Condensation Due to Different Reasons

Sulfonium, selenonium, telluronium triflates, as well as chloronium, bromonium, and iodonium triflates have been examined in the model Schiff condensation as chalcogen- and halogen bond donating organocatalysts, respectively. The kinetic data indicated that the catalytic effect of the telluronium salt is provided via the decrease of enthalpy of activation of the reaction, whereas the catalytic effect of the iodonium salt – unexpectedly – is caused by the decrease of the value of the entropy of activation. In addition, it was experimentally shown that the catalytic activity of sulfonium and selenonium salts is significantly lower than that of chloronium and bromonium salts, but the latter pair of species is significantly less stable under the reaction conditions than the former pair.