Cycloaddition of CO2 with epoxides by using an amino-acid-based Cu(II)–tryptophan MOF catalyst

Abstract

Metal organic frameworks (MOFs) constructed from natural/biological units (amino acids) are prospective candidates as catalysts in CO2 chemistry owing to their natural origin and high abundance of Lewis acid/base sites and functional groups. Herein, we report the catalytic efficiency of an amino-acid-based Cu-containing MOF, denoted as CuTrp (Trp = L-tryptophan). The CuTrp catalyst was synthesized by direct mixing at room temperature using methanol as a solvent—a synthetic route with notable energy efficiency. The catalyst was characterized using various physicochemical techniques, including XRD, FT-IR, TGA, XPS, ICP-OES, FE-SEM, and BET analysis. The catalytic activity of CuTrp was assessed in the synthesis of cyclic carbonates from epoxides and CO2. The CuTrp operated in synergy with the co-catalyst tetrabutylammonium bromide under solvent-free conditions. Several reaction parameters were studied to identify the optimal reaction conditions and a reaction mechanism was proposed based on experimental evidence and previous density functional theory studies. The CuTrp also exhibited satisfactory stability in water and could be reused more than three times without any significant loss of activity.