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Enhanced CO2/Epoxide Cycloaddition Catalyzed by Pyridine-Substituted Triazole-Quaternary Ammonium Bromide

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide A series of ionic quaternary ammonium bromides featuring triazole moieties, QAS-trzBn 4, QAS-trzPic 4, and QAS-trzBn 2 Pic 2, were synthesized via Cu-catalyzed azide–alkyne cycloaddition (CuAAC) between propargyl-based ammonium bromide and benzyl- or 2-picolylazide. X-ray crystallographic analyses of QAS-trzBn 4 and QAS-trzBn 2 Pic 2 revealed strong interactions between Br – ions and both triazolyl H and methylene H atoms ( + NCH 2 ), as evidenced by short Br – ···H contacts ranging from 2.68 to 3.00 Å. The catalytic activities of these compounds as bifunctional, single-component catalysts for the CO 2 /epoxide cycloaddition were evaluated under both atmospheric and elevated CO 2 pressures. Notably, catalysts containing pyridyl-triazole groups exhibited superior catalytic performances compared with the benzyl-triazole-based catalyst, QAS-trzBn 4 . A substrate scope study using QAS-trzPic 4 under 20 atm of CO 2 at 100 °C revealed that electron-deficient epoxide substrates were more active, yielding good to excellent conversions (88–100%) to cyclic carbonates within 6 h. Computational studies identified key binding modes in pyridine-substituted systems that position both the epoxide and CO 2 in close proximity. In particular, the QAS-trzPic 4 -CO 2 -epoxide complex is more stabilized than its benzyl derivative, QAS-trzBn 4 -CO 2 -epoxide, due to favorable interactions of CO 2 with the pyridyl substituents.

Source: ACS Omega

DOI: 10.1021/acsomega.5c04751