Noble-Metal-Free ZnII-Anchored Pyrene-Based Covalent Organic Framework (COF) for Photocatalytic Fixation of CO2 from Dilute Gas into Bioactive 2-Oxazolidinones.

Abstract

Photocatalytic conversion of CO2 into value-added chemicals offers a propitious alternative to traditional thermal methods, contributing to environmental remediation and energy sustainability. In this respect, covalent organic frameworks (COFs), are crystalline porous materials showcasing remarkable efficacy in CO2 fixation facilitated by visible light owing to their excellent photochemical properties. Herein, we employed Lewis acidic Zn(II) anchored pyrene-based COF (Zn(II)@Pybp-COF) to facilitate the photocatalytic CO2 utilization and transformation to 2-oxazolidinones. Notably, Zn-COF displayed absorption of visible light, with an optimal band gap of 1.8 eV, effectively catalyzing light-mediated functionalization of propargylic amines to 2-oxazolidinones under green conditions. Detailed experimental and theoretical mechanistic investigations demonstrated that light plays a crucial role in enhancing the efficacy of the photocatalyst, as it activates inert CO2 molecule to radical anion and thereby, lowers the energy barrier for its subsequent cyclization reaction with propargylic amine. Additionally, Zn-COF demonstrates promising catalytic performance utilizing dilute gas as the CO2 source. This is the first report regarding noble metal-free, Zn-COF exhibiting excellent photocatalytic carboxylative cyclization of CO2 with propargyl amines to prepare 2-oxazolidinones using dilute gas (13% CO2). This study offers a new direction for rationally constructing noble metal-free eco-friendly photocatalysts for achieving CO2 fixation reactions under eco-friendly conditions.