Cobalt sandwich complex-based covalent organic frameworks for chemical fixation of CO2

Carbon dioxide as a notorious greenhouse gas triggers severe global warming which is threatening the balance of ecosystem. In this respect, effectively capturing and transforming CO2 into value-added chemicals are essential but still challenging tasks. As a kind of emerging crystalline porous material, covalent organic frameworks (COFs) have been demonstrated to be able to adsorb gases and function as catalysts to facilitate chemical transformations. Herein, we report an imine-linked, cobalt sandwich complex-based COF (Co-BD-COF) with high crystallinity and large surface area. Co-BD-COF can efficiently catalyze the transformation of CO2 into cyclic carbonates due to abundant metal sites and high porosity. In addition, Co-BD-COF exhibits high catalytic selectivity toward small ethylene oxide derivatives in cycloaddition reaction due to the large steric hindrance around the cobalt complexes rendered by the peripheral phenyl moieties. This new metal sandwich-type building block provides a new strategy for improving catalytic selectivity of COFs.