A Zn()-functionalized COF as a recyclable catalyst for the sustainable synthesis of cyclic carbonates and cyclic carbamates from atmospheric CO

• Published in: Organic & biomolecular chemistry 2022-02, Vol.2 (8), p.177-1722
• Main Authors: Sarkar, Somnath, Ghosh, Swarbhanu, Islam, Sk. Manirul
• Format: Article
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/d1ob01938d

A simple covalent organic framework (COF) bearing β-ketoenamine units as a potential heterogeneous ligand for Zn II -catalyzed fixation and transformation of CO 2 into value-added chemicals is reported. Catalytic investigations convincingly demonstrated that the Zn II -functionalized covalent organic framework (Zn@TpTta) exhibits perfect catalytic activity in the fixation of CO 2 for diverse epoxides with various substituents under sustainable conditions. A variety of terminal epoxides and slightly more complicated disubstituted epoxides were transformed into the corresponding cyclic carbonates with satisfactory to excellent yields ( i.e. , 69 to 99% yield) upon exposure to CO 2 (1 atm) under solvent-free conditions (sustainable approach). On the other hand, this Zn II -loaded covalent organic framework also displayed excellent performance in facilitating atmospheric cyclizative CO 2 capture, which led to the formation of diverse cyclic carbamates ( i.e. , 61 to 94% yield) from unsaturated amine systems using N -iodosuccinimide (NIS) as an iodinating agent and PEG-400 as a biodegradable and green polymeric solvent under base-free conditions (sustainable approach). The newly synthesized COF-based catalyst, namely, Zn@TpTta, has been completely characterized by SEM (scanning electron microscopy), EDX (energy dispersive X-ray analysis), HRTEM (high-resolution transmission electron microscopy), BET (Brunauer-Emmett-Teller), PXRD (powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), ICP (inductively coupled plasma), etc . More intriguingly, the catalytic system could be recycled over five times without a noticeable loss of catalytic performance for both reactions. This study opens an avenue for the Zn( ii ) embedded COF as a promising platform for regulating regioselectivity. This study emphasizes the utility of a Zn( ii )-functionalized COF in developing a heterogeneous recyclable catalytic system for the generation of cyclic carbonates (up to 99% yield) and cyclic carbamates (up to 94% yield) under sustainable conditions.