Pore engineering of metal-organic frameworks with coordinating functionalities

Among porous materials, metal–organic frameworks (MOFs) take the lead in heterogeneous support catalysts because the structure of MOFs can be readily tuned by choice of metal and organic building blocks, and further be modified with diverse functional groups. In order to immobilize catalytically active metal sites on MOFs and efficiently utilize them, it would be essential to employ the coordinating functionalities to the pores and frameworks, which can anchor the metal sites with high stability and control the reactivity of the catalytic centres. However, in order not to obtain the unwanted structures by participation of additional coordinating groups in the framework construction of MOFs, the pore engineering with coordinating functionalities should be carefully implemented. In this review, we discuss various strategies of pore engineering to impart catalytic activities to the MOF architectures, classifying them into two approaches: pre-integrated ligand and sequential attachment. The former demonstrates the use of organic ligands that are already capable of possessing catalytic sites, and the ligands can directly integrate the metals before or after the production of the MOFs. The other approach is the post-synthetic attachment of coordinating functionalities through the sequential attachment process, in which immobilization of catalytically active metal sites also can be achieved by both pre- and post-metalation. Finally, this review will comprehensively discuss the representative catalytic reactions of MOF-based heterogeneous catalysts.