Chalcogen Bonding with Diaryl Ditellurides: Evidence from Solid State and Solution Studies

The chalcogen bonding (ChB) ability of Te is studied in symmetrical diaryl ditellurides ArTeTeAr. Among the two Te σ-holes, the one along the less polarized Te-Te bond was calculated as the more electropositive. This counter-intuitive situation is due to the hyperconjugation contribution from Te lone pair to the σ* of the adjacent Te which coincides with σ-hole along the more polarized Te-Ar bond. ArTeTeAr showed notable structural features in the solid state as a result of intermolecular Te⋅⋅⋅Te ChB, such as a Te₄ rectangle through dimer aggregation or a triangular Te₃ motif, where one Te interacts with both Te atoms of a neighboring molecule through both its σ-hole and lone pair, in a slightly frustrated geometry. Lewis acidity of ArTeTeAr was also evaluated by NMR with R₃ PO as σ-hole acceptors in different solvents. Thus, ¹²⁵ Te NMR allowed monitoring Te⋅⋅⋅O interaction and delivering association constants (K_a ) for 1 : 1 adducts. The highest value of K_a =90 M^-1 was measured for the adduct between ArTeTeAr bearing CF₃ groups and Et₃ PO in cyclohexane. Notably, by using nBu₃ PO, Te⋅⋅⋅O interaction was revealed by ¹⁹ F-¹ H HOESY showing spatial proximity between CF₃ and CH₃ of nBu₃ PO.