Evidence for and evaluation of fluorine-tellurium chalcogen bonding

In the field of noncovalent interactions, chalcogen bonding (ChB) involving the tellurium atom is currently attracting much attention in supramolecular chemistry and in catalysis. However, as a prerequisite for its application, the ChB should be studied in solution to assess its formation and, if possible, to evaluate its strength. In this context, new tellurium derivatives bearing CH₂F and CF₃ groups were designed to exhibit Te⋯F ChB and were synthesized in good to high yields. In both types of compounds, Te⋯F interactions were characterized in solution by combining ¹⁹F, ¹²⁵Te and HOESY NMR techniques. These Te⋯F ChBs were shown to contribute to the overall J_Te-F coupling constants (94-170 Hz) measured in the CH₂F- and CF₃-based tellurium derivatives. Finally, a variable temperature NMR study allowed us to approximate the energy of the Te⋯F ChB, from 3 kJ mol^-1 for the compounds with weak Te σ-holes to 11 kJ mol^-1 for Te σ-holes activated by the presence of strong electron withdrawing substituents.