Catalytic Properties of Ionic Covalent Organic Frameworks (COFs) Materials in CO2 Cycloaddition
The cycloaddition of carbon dioxide (CO2) to epoxides (CCE) is a 100% atom-economical transformation yielding cyclic carbonates, which are valuable chemical products. This reaction valorizes CO2 as a carbon feedstock, mitigating the greenhouse effect and aligning with carbon neutrality goals. Conventional covalent organic framework (COF) catalysts often require co-catalysts to achieve high efficiency. To address this, we designed and prepared a series of ionic COFs, denoted EB-BT(nOH), that simultaneously incorporate acid (hydroxyl), base (nitrogen), and nucleophilic bromide (Br−) functionalities. These materials efficiently catalyze the CCE reaction without any co-catalyst. Among them, EB-BT(OH) exhibited the highest catalytic activity, achieving a 99% yield of the target product at 120 °C and 2.0 MPa CO2 pressure. By systematically varying the hydroxyl content in the COF backbone, we investigated the critical role of hydrogen bond donors (HBDs) in the CCE reaction. This work provides new design principles for COF-based catalysts for CCE, eliminating the need for co-catalysts and enhancing process sustainability.