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.