Ionic liquid boosting N-formylation of amines on polyoxometalate-stabilizing iridium single-atom catalysts

In this work, we have constructed a Ir single-atom substituted polyoxometalate (POM) salt K4[PW11O39Ir] (K-PWIr). The characterization by XRD, FT-IR, HAADF-STEM and XAFS confirmed that the single-atom Ir was anchored into the framework of the POM. The binary catalytic system K-PWIr and ionic liquid bis(1-butyl-3-methylimidazolium) malonate ([BMIM]2[Mal]) demonstrated outstanding catalytic activity for N-formylation of amines with CO2/H2, and TON values can reach as high as 448000. The [BMIM]2[Mal] played a crucial role in adsorption of CO2 and the isotopically labeled experiments confirmed that the ionic liquid aced as a shuttle to transport carbon dioxide from gas phase to catalytic Ir sites. Besides, the [BMIM]2[Mal] showed electron interaction with Ir sites, which can stabilize the catalytically active Ir+ sites. Detailed investigations confirmed the H2 underwent heterolytic dissociation on Ir-O sites and the reaction was proceeded via a formate intermediates.