Elucidating the Binding Mode of Sulfur- and Selenium-Based Cationic Chalcogen-Bond Donors.

For a comparison of the interaction modes of various chalcogen-bond donors, 2-chalcogeno-imidazolium salts have been designed, synthesized, and studied by single crystal X-ray diffraction, solution NMR and DFT as well as for their ability to act as activators in an SN1-type substitution reaction. Their interaction modes in solution were elucidated based on NMR diffusion and chemical shift perturbation experiments, which were supported by DFT-calculations. Our finding is that going from lighter to the heavier chalcogens, hydrogen bonding plays a less, while chalcogen bonding an increasingly important role for the coordination of anions. Anion-π interactions also show importance, especially for the sulfur and selenium derivatives.