Main-Chain Organic Frameworks with Advanced Catalytic Functionalities

Over the past 10 years, there have been remarkable advances in the development of porous organic frameworks, which include covalent organic framework (COF), conjugated microporous polymer (CMP), porous aromatic framework (PAF), and covalent triazine framework (CTF). The emergence of organic frameworks brings about tremendous possibilities for heterogeneous catalyst development. In addition to well-controlled surface chemistry and porosity, these materials possess high physicochemical stability, high density or loading of functional groups with homogeneous distribution, and high surface area. These allow the organic framework catalysts to have potentially high activity and reusability. In particular, main-chain organic frameworks (MCOFs) represent a class of organic materials whereby the functionalities are directly embedded in the framework. They are generally synthesized through the bottom-up approach. In catalytic MCOFs, the functional moieties can have direct interactions with the main framework, leading to unique properties beyond the general advantages associated with porous polymer heterogeneous catalysts. Higher activity, selectivity, and stability can be attained with MCOF catalyst designs. This mini Review summarizes recent developments of MCOFs that have demonstrated superior catalytic properties as compared with their homogeneous analogs. The synthesis, structure and advanced functionalities of these MCOF catalysts are discussed, along with perspectives for future development.