Solvent-modulated Binding Selectivity of Reaction Substrates to Onium-based Sigma-Hole Donors

Combination of experimental data and results of DFT calculations indicates that the catalytic activity of chalconium and halonium salts served 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 energies of activation of the reactions, because solvation effects and other competitive binding processes play at least the same or even more important role in the catalysis. It was showed in present work, that the solvation either can 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 suppression of the catalytic activity of the organocatalyst.