The combination of experimental data and results of DFT calculations indicates that the catalytic activity of chalconium and halonium salts serving as sigma-hole donating organocatalysts cannot be clearly estimated via analysis of the electrostatic potential on the catalysts’ sigma-holes and values of the catalyst•••TS intermolecular interactions, such as polarization effects, charge transfer, or covalency of bonding. Moreover, the real catalytic effect might not correlate well with the values of Gibbs free energy of activation of the reactions, because solvation effects and other competitive binding processes play at least an equal or even more important role in the catalysis. It was shown in the present work that the solvation can either lead to the increase of equilibrium concentration of reactive catalyst•••electrophile associates, thus accelerating the reaction, or brings favorable generation of catalyst•••nucleophile species resulting in the suppression of the catalytic activity of the organocatalyst.
Synthesis of the sulfonium salt Cat1OTf; Synthesis of the sulfonium salt Cat2OTf; Synthesis of the sulfonium salt Cat3OTf; Spectra of Cat1OTf–Cat3OTf; Representative 1H NMR monitoring spectra; Derivation of equations for calculating the reaction rate constants; Table S1. Calculated total electronic energies (E, in Hartree), enthalpies (H, in Hartree), Gibbs free energies (G, in Hartree), and entropies (S, cal/mol•K) for optimized equilibrium model structures.
Optimized equilibrium structures of the model compounds