Telluronium Coordination of Crown Ethers and Polyethers via Chalcogen Bonding: Coulombically Driven Strong Association, Highly Selective Coordination, and Templated Cyclization

Abstract

The ability of telluronium [Ar3Te]+ to bind crown ethers and acyclic polyethers through chalcogen bonding is investigated in the solid state and in solution. X-ray diffraction of several 1:1 complexes revealed short Te···O interactions (dTe–O below the sum of van der Waals radii) and high linearity (Ar–Te–O angles in the range 163–178°). NMR and DOSY (diffusion-ordered NMR spectroscopy) experiments confirm that these interactions persist in solution. Isothermal titration calorimetry provides the thermodynamic parameters for the telluronium–crown ether and telluronium–polyether equilibria, with association constants reaching Ka ∼ 106 M–1 for the 5- to 7-membered crown ethers. Based on these results, selective coordination of certain crown ethers was efficiently achieved. Furthermore, the templating effect of the telluronium on acyclic polyethers is further demonstrated by its ability to promote the ring closure of a long polyether bearing both bromo and hydroxy termini. Theoretical analysis of the ligand-Te interaction points to a dominant Coulombic contribution, supported by dispersion forces, in stabilizing polyether binding to the Te center. Although the minor covalent contribution operates a crucial anchoring role, it is not sufficient to restrict the O atoms to exclusive σ-hole interactions, suggesting a fluxional dynamic behavior in solution in which all O atoms dynamically interact with the Te center.