MOF-Incorporated Binuclear N-Heterocyclic Carbene-Cobalt Catalyst for Efficient Conversion of CO 2 to Formamides.

Environmental problem caused by carbon emission is of widespread concern. Involving CO 2 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 (μ-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 CO 2 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 CO 2 .