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

Abstract

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.

Telluronium‐Catalyzed Halogenation Reactions: Chalcogen‐Bond Activation of N‐Halosuccinimides and Catalysis

“…This result is in accordance with our recent analysis of the distribution of Bader charges in a telluronium-triphenylphosphine oxide (OPPh 3 ) adduct showing that a large part of the electron density is transferred from OPPh 3 to the ipso carbon of the telluronium. [12] In contrast, low Δδ were observed in both the 1 H and 13 C NMR spectra for the 2-and 4-positions of the aryl groups of telluronium 2.…”

“…[9] Being involved these last years in the study and application of ChB in solution, [10] we recently explored the catalytic properties of cationic telluronium salts, [11] where the trivalent tellurium(IV) exhibits three σ-holes and can establish three ChBs. [12] In particular, the methyldiaryltelluronium 1 (Scheme 1b) was able to catalyze the bromination of anisole and the intramolecular bromolactonization of some ω-unsaturated carboxylic acids in the presence of Nbromosuccinimide (NBS). [11a] N-halosuccinimides NXS (X=Cl, Br, I) are versatile and widely used sources of halogens in electrophilic halogenation reactions.…”

Distinction and Quantification of Noncovalent Dispersive and Hydrophobic Effects

“…With supramolecular complexes, typical values of T∆S = 5 to 9 kJ/mol are often observed [14,17,18], but values of 50 kJ/mol have been found [48]. Entropic contributions were also considered in theoretical analyses of noncovalent bound complexes [49,50], but were rarely compared to experimental data. The large and difficult to predict variations of thermodynamic parameters have been reviewed for complexation with, e.g., ionophores [51] or cyclodextrin [52]; typical examples are illustrated in Figures 2-5.…”

Chalcogen Bonding Catalysis: Tellurium, the Last Frontier?

“…[20][21][22] Furthermore, the σ-hole nature depends on the atom polarizability and on the electronic property of the substituent bonded to this atom, and thus can be tuned. [23] Interestingly, the divalent nature of chalcogen atoms induces the presence of two σ-holes, and even three for chalconium, [24] instead of one for halogen atom. More than one ChB can thus be established, and furthermore, the chalcogen atom can act both as Lewis acid through its σ-holes and as Lewis base due to its lone pairs (Figure 3).…”

“…Finally, the strongest ChBs were formed between Te(+ IV)-based telluroniums and different Lewis bases B, as demonstrated by NMR and Isothermal Titration Calorimetry (ITC) experiments (Figure 4F). [24,37] For instance, enthalpies of first association of triphenylphosphine oxide with telluronium salts could reach up to À 16 kJ/mol in 1,2-dichloroethane.…”