A computational analysis of substituent effects in pnictogen-, chalcogen-, and halogen-bond donors

The interaction enthalpies of differently substituted cationic pnictogen-, chalcogen-, and halogen-bond donors with the fluoride anion have been analyzed computationally. In general, electron-withdrawing substituents increase the binding strength of the Lewis acid, but the precise location of a given substituent (e.g., within the benzimidazolium group or within the aryl group) has only little influence on the reaction enthalpies. While no single parameter could be identified that describes all Lewis acids across the periodic table, both electrostatic (V_s,max) and charge-transfer approaches (LUMO energies) can be used to predict the binding enthalpies for structurally related compounds. The computational analysis eventually led to the synthesis of a new selenium-based catalyst with an improved catalytic activity in a transfer hydrogenation of imines.