Thiazolium Salts as Chalcogen Bond Donors

The nitrogen atom is commonly considered to be the positive site in thiazolium cations. Counterintuitively, the shortest cation center dot center dot center dot anion contacts in thiazolium salts and their benzoderivatives involve the sulfur atom. The geometric features of these contacts allow for their rationalization as charge assisted chalcogen bonds (ChBs). Analyses of the Cambridge Structural Database and calculation of the surface electrostatic potential of benzo[d]thiazolium cations support this rationalization. The relevance and impact of the general tendency of thiazolium derivatives to function as ChB donors are exemplified by the ChBs as short as 87% of the sum of van der Waals radii of involved atoms in thiamine monophosphate, a key compound in human metabolism, and in two commonly used thiazolium organo-catalysts.