MOF-Incorporated Binuclear N-Heterocyclic Carbene-Cobalt Catalyst for Efficient Conversion of CO2 to Formamides

Environmental problem caused by carbon emission is of widespread concern. Involving CO2 as C-1 resource into chemical synthesis is one of the most attractive ways for carbon recycling. Herein, the first example of host-guest composites featuring metal-organic framework (MOF)-encapsulated binuclear N-heterocyclic carbene (NHC) complex, Co-2@MIL101, was developed with the molecularly dispersed [Co(IPr)Br](2)(mu-Br)(2) (Co-2) loading in the cage of MIL-101(Cr) via a "ligand-in-dimer-trap" strategy, which was comprehensively investigated through various techniques including synchrotron X-ray absorption, electron microscopy, X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and others. The noble-metal-free double-sites catalyst Co-2@MIL101 exhibited promising stability, activity, efficiency, reusability, and substrate adaptability for converting CO2 into various formamides with amines and hydrosilanes and achieved the best performance for one of the most useful formamides, N-methyl-N-phenylformamide (MFA), among the recyclable catalysts at ambient conditions, providing a reliable approach to successfully unify the advantages of both homo- and heterogeneous catalysts. Density functional theory calculations were applied to illustrate the superior activity of the binuclear NHC complex center as double-sites catalyst toward the activation of CO2.