Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental-Theoretical Joint Study.

Telluronium salts [Ar2MeTe]X were synthesized and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. The structural X-ray diffraction analysis of 21 different salts revealed the electrophilicity of the Te centers in their interactions with anions. Telluroniums' propensity to form Lewis pairs was investigated with OPPh3. Diffusion-ordered NMR spectroscopy suggests that telluroniums may bind up to three OPPh3 molecules. Isotherm titration calorimetry showed that the related heats of association in 1,2-dichloroethane depend on the electronic properties of the substituents of the aryl moiety and on the nature of the counterion. The enthalpies of first association of OPPh3 span -0.5 to -5 kcal/mol. The study of the affinity of telluroniums for OPPh3 by state-of-the-art DFT and ab initio methods reveals the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar2MeTe]+ cations and OPPh3 are deemed insufficient to ensure alone the cohesion of [Ar2MeTe•Bn]+ complexes in solution (B= Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4 / MBD-vdW thermodynamics of formation of higher [Ar2MeTe•Bn]+ complexes reveals significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.

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