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 CHF and CF 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 F, Te and HOESY NMR techniques. These Te⋯F ChBs were shown to contribute to the overall coupling constants (94-170 Hz) measured in the CHF- and CF-based tellurium derivatives. Finally, a variable temperature NMR study allowed us to approximate the energy of the Te⋯F ChB, from 3 kJ mol for the compounds with weak Te σ-holes to 11 kJ mol for Te σ-holes activated by the presence of strong electron withdrawing substituents.