DFT calculations demonstrate that increasing the central atom size (Se/Te) and incorporating stronger electron-withdrawing substituents (-CF₃, -F, -NO₂) in cationic hypervalent ChB catalysts amplify the σ-hole, thereby strengthening ChB interactions. This polarization effect significantly lowers the bromine transfer barrier in the NBS bromolactonization reaction, enabling efficient and tunable organocatalysis.

Abstract

Chalcogen bond (ChB) catalysts have recently garnered considerable attention in the field of organocatalysis owing to their advantages of nontoxicity, environmental sustainability, extensive applicability, affordability, and remarkable reactivity. In this work, the Se- and Te-based cationic hypervalent ChB catalysis on the bromolactonization reaction of N-Bromosuccinimide (NBS) with 4-pentenoic acid is investigated by high-level density functional theory (DFT) calculations. The ChB-catalyzed bromolactonization reaction has an intricate process involving bromine transfer, cyclization, and proton transfer. Moreover, the bromine transfer process is identified as the rate-determining step with the highest Gibbs free energy barrier. The increase in the size of the central atom in the ChB catalysts and the enhancement of electron-withdrawing capabilities with greater dipole moments of substitutions on the catalysts provide larger σ-holes with stronger polarization effects, resulting in stronger ChB interactions with the reactant, thus lowering the reaction barrier. From a kinetic perspective, different electron-withdrawing groups on the catalyst can be used to regulate the reaction rate, leading to better experimental outcomes. These findings demonstrate the important roles of polarization effects in cationic hypervalent chalcogen bonds catalysis and provide a theoretical foundation for the development of novel environmentally friendly and efficient hypervalent ChB catalysts.