CO2 Cycloaddition under Ambient Conditions over Cu-Fe Bimetallic Metal-Organic Frameworks

Carbon dioxide cycloaddition into fine chemicals is prospectivetechnology to solve energy crisis and environmental issues. However,high temperature and pressure are usually required in the conventionalcycloaddition reactions of CO2 with epoxides. Moreover,metal active sites play a vital role in the CO2 cycloaddition,but it is still unclear. Herein, we select the isostructural MOF-919-Cu-Feand MOF-919-Cu-Al as models to promote the performance and clarifythe effects of metal type on the CO2 cycloaddition. TheMOF-919-Cu-Fe with exposed Fe and Cu Lewis acid sites reaches theCO(2) cycloaddition with over 99.9% conversion and over 99.9%selectivity at room temperature and a 1 bar CO2 atmosphere,3.0- and 52.6-fold higher than those of the MOF-919-Cu-Al with Aland Cu sites (33.8%) and the 1H-pyrazole-4-carboxylic acid, Fe, andCu mixed system (1.9%), respectively. The proposed mechanism demonstratedthat the exposed Fe3+ sites facilitate the ring openingof epoxide and CO2 activation to boost the CO2 cycloaddition reaction. This work provides a new insight to tunethe catalytic sites of MOFs to achieve high performance for CO2 fixation. TheMOF-919-Cu-Fe acts as a heterogeneous catalyst for theCO(2) cycloaddition with epoxides to give cyclic carbonateproducts under mild conditions, which affords high conversion andselectivity.