A Bifunctional Cationic Covalent Organic Polymer for Cooperative Conversion of CO2 to Cyclic Carbonate without Co-catalyst

A cationic covalent organic polymer with bifunctional active site was synthesized, which was treated by N, N'-bis(5-bromomethylsalicylaldehyde)ethylenediamine (salen ligand) and tris(1H-imidazol-1-yl) triazine (TIT) in the presence of aluminum ethoxide. The bifunctional cationic covalent organic polymer was investigated by various characterization technologies including PXRD, FT-IR, XPS, TG, SEM, EDS, N2-adsorption and CO2-adsorption. In this polymer, aluminum acts as lewis acid site and bromine ion acts as nucleophile, cooperatively catalyzing the cycloaddition reaction of CO2 and epoxides. Due to its cooperative effect, a higher catalytic activity was found to exhibit 98.1% conversion of epichlorohydrin under optimized conditions (Initial pressure 1.0 MPa, 0.57 mol% catalyst of COP-Al, 90 °C, reaction time 18 h, in the absence of a co-catalyst). Notably, the heterogeneous catalyst still showed good activity and stability after five cycles. A salen-based cationic covalent organic polymers (COP-Al) was used as a bifunctional catalyst for the cycloaddition reaction of CO2 and epoxides with high activity under solvent-free and co-catalyst-free conditions.