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

Telluronium salts [Ar₂ MeTe]X were synthesized, and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. 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 suggested that telluroniums can 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^-1 . Study of the affinity of telluroniums for OPPh₃ by state-of-the-art DFT and ab-initio methods revealed the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar₂ MeTe]⁺ cations and OPPh₃ are deemed insufficient on their own to ensure the cohesion of [Ar₂ MeTe ⋅ B_n ]⁺ complexes in solution (B=Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4/MBD-vdW thermodynamics of formation of higher [Ar₂ MeTe ⋅ B_n ]⁺ complexes revealed significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.