Bis(catecholato)telluranes: Probing Catecholato-Induced Hard Lewis Acidity via Redox-Coupled Halide Abstraction

This work explores the chemistry of neutral bis(catecholato)telluranes (BCTs), a class of chalcogen-based compounds that has remained relatively underexplored. The study focuses on the Lewis acidity, anion-binding, and redox behavior of unsubstituted (1a), perchloro- (1b), and perbromo- (1c) BCTs. Using experimental methods such as Gutmann-Beckett analysis and 125Te NMR, along with computational fluoride ion affinity (FIA) calculations, 1b and 1c were found to show similar Lewis acidic strength. Interestingly, 1b is found to defluorinate SbF6-, forming a tellurium-fluoride adduct, as verified by 19F NMR and HRMS. However, the calculated FIA values were lower than those of SbF5. This unexpected behavior prompted cyclic voltammetry (CV) studies, which revealed redox processes involving catecholato ligands. Based on CV data and HRMS detection of key intermediates, a fluoride-coupled electron transfer (FCET)-type mechanism is suggested as a possible pathway for SbF6- activation. Further studies on the BCTs reveal strong covalent interactions with fluoride and chloride ions, reinforcing their hard Lewis acidic nature.