Mechanistic Study on the Addition of CO₂ to Epoxides Catalyzed by Ammonium and Phosphonium Salts: A Combined Spectroscopic and Kinetic Approach

Abstract

Herein we report the evaluation of the frequently employed tetrabutyl ammonium and phosphonium halides as well as their bifunctional analogs as catalysts in cyclic carbonate synthesis under benchmarked conditions. The kinetic data of all catalysts were evaluated and the rate constants determined. Moreover, a systematic infrared spectroscopic study of the interactions between cation and anion of the catalysts as well as the interactions between the catalysts and the substrate were conducted. These experimental results were additionally supported by DFT calculations. The observed trends in the interaction between the onium cation and the anion are correlated to their catalytic activity. Moreover, these investigations revealed the mode of the substrate activation for the monofunctional and the bifunctional catalysts. Furthermore, the kinetic studies and in situ infrared experiments revealed a product inhibition of the bifunctional catalysts via the unexpected formation of catalyst−carbonate adducts. The interaction between the catalysts and the product was further studied by infrared spectroscopy. Finally, the rate and the equilibrium constants for the binfunctional catalysts were determined by a Michaelis− Menten model considering a reversible product inhibition.

(Thio)urea containing quaternary ammonium salts for the CO2-fixation with epoxides

“…To obtain a better mechanistic understanding of this CO 2 -fixation reaction (for three illustrative mechanistic studies of these reactions by others please see Ref. [39][40][41]), we carried out detailed computational studies of different possible mechanistic scenarios using DFT calculations (Fig. 4).…”

Metal‐Free Cycloaddition of Epoxides and Carbon Dioxide Catalyzed by Triazole‐Bridged Bisphenol

“…Werner et al . developed bifunctional ammonium and phosphonium salts to simultaneously activate the epoxide by a HBD and a nucleophile under mild conditions. Very recently, North et al .…”

Plasma‐Assisted Immobilization of a Phosphonium Salt and Its Use as a Catalyst in the Valorization of CO2

“…Lately, highly active systems based on OH‐functionalized organocatalysts were reported for the synthesis of cyclic carbonates . The superior activity of these catalysts is attributed to epoxide activation and stabilization of intermediates by hydrogen bonding . We are interested in the development of bifunctional onium salt catalysts for synthesis of cyclic carbonates as well as their recovery and reuse .…”

“…[17] Thes uperior activity of these catalysts is attributed to epoxide activation ands tabilization of intermediates by hydrogen bonding. [18] We are interested in the development of bifunctional onium salt catalysts for synthesis of cyclic carbonates as well as their recovery and reuse. [17a, b, 19] In this respect, one strategy is the immobilization of the onium salt catalyst on organic or inorganic supports.…”