Co(ii)-embedded covalent organic framework for catalyzing CO2 fixation to highly valuable N-formamides and 2-oxazolidinones under mild conditions

Abstract

Turning carbon dioxide (CO₂) into useful substances, such as fuel and chemicals, offers a clear way to lower the amount of this greenhouse gas in the environment. In the present scenario, COFs (covalent organic frameworks) provide tremendous potential for CO₂ fixation. Accordingly, a hydroxyl-rich EtDh-COF was constructed through Schiff-base condensation using 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetraaniline (Et-NH₂) with 2,5 dihydroxyterephthalaldehyde (Dh-CHO). The prepared EtDh-COF possesses an abundant number of imine and hydroxyl groups, facilitating the easy grafting of non-noble Co(II) ions to acquire a Co-COF, which was subsequently applied to formylate various amines to valuable N-formamides utilizing CO₂ as a C-1 feedstock with phenylsilane as the reductant. Moreover, the effective conversion of propargylic amines into 2-oxazolidinones, valuable bioactive commodity chemicals, has also been accomplished by consuming carbon dioxide. Notably, the Co-COF displayed excellent catalytic activity for producing formamides and 2-oxazolidinones, which serve as crucial precursors of pharmaceuticals, agrochemicals, and other bioactive substances. Moreover, the Co-COF can be easily recycled for multiple runs without losing scaffold stability and catalytic activity. Thus, this work demonstrates the sensible design of a Co-COF for the efficient use of CO₂ to produce two useful products, N-formamides and 2-oxazolidinones, under mild conditions.