Zn(II)-Embedded Nanoporous Covalent Organic Frameworks for Catalytic Conversion of CO₂ under Solvent-Free Conditions

Covalent organic frameworks (COFs) have been gaining substantial attention over the past decade due to their developing crystalline porous polymeric nature linked by strong covalent bonds and widespread applications in various fields. Currently, three-dimensional COFs (3D COFs) are engaging the spotlight due to their distinctive porous features, greater surface area, and exceptional performances in comparison with formerly published two-dimensional (2D) frameworks with the AA-stacking layered mode. In this paper, we present, for the first time, a nanoporous 3D-COF-based zinc(II) catalyst (Zn@RIO-1), which shows an efficient pathway for the chemical conversion of carbon dioxide to produce α-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols. The microporous material with a high surface area (312.61 m2/g) facilitates both types of catalytic reactions under atmospheric CO2 pressure. More importantly, easily recyclable and reusable catalysts produced moderate to high yields of desired carbonates as well as oxazolidinone products under solvent-free conditions. This study emphasizes the capability of nanoporous 3D-COF-based material in the catalysis field, more specifically in the field of CO2 capture and chemical fixation to fine chemicals. These results pave a spectacular pathway for the chemical fixation of CO2 into α-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols using 3D-COF as a potential heterogeneous ligand under sustainable conditions (i.e., solvent-free).