Acid-base neutralization strategy for immobilization amino acid ionic liquid within sulfonic acid-based COF as a switch for selective conversion of epoxides

Covalent organic frameworks (COFs) and ionic liquids (ILs) as raw materials exhibit effective catalytic performance and adsorption capabilities in the reaction of epoxides and atmospheric CO₂, respectively. Nonetheless, bonding modes between ILs and COFs have restricted their utility, thereby constraining the in-depth study of synergistic catalytic mechanisms over these composite catalysts. Herein, a heterogeneous composite ([DBUH]₂Cys@COF-X) were successfully prepared by the facile acid-base neutralization method, incorporating varying amounts of amino acid ILs ([DBUH]₂Cys) into the pore channels of sulfonic acid-based COF (TpPa-SO₃H). [DBUH]₂Cys@COF-3 efficiently catalyzed epichlorohydrin with a yield of 96.38 % without any solvent or co-catalyst under atmospheric CO₂. Notably, larger sterically hindered epoxides were selectively blocked on the surface of [DBUH]₂Cys@COF-3, enabling [DBUH]₂Cys@COF-3 to act as a gatekeeper for selectively catalyzing small sterically hindered epoxides due to [DBUH]₂Cys was distributed within the pore channels of [DBUH]₂Cys@COF-3. Through DFT calculations, comprehensive understanding of the synergistic activation conferred of -COO^- and [DBUH]⁺ towards CO₂ and epoxides in [DBUH]₂Cys@COF-3 and the ring-opening mechanism was clarified. This work presents a fresh outlook on the catalyst design by the facile acid-base neutralization method for efficiently catalyzing small-hindered epoxides under atmospheric CO₂.