Single-Atom Ru on N-Heterocyclic Carbene-Functionalized Hypercrosslinked Polymers for N-Formylation of Amines with CO2 and H2.

Catalytic transformation of carbon dioxide (CO2) into high-value-added chemicals represents a promising approach for CO2 emission reduction and utilization. Herein, single-atom ruthenium (Ru) supported on N-heterocyclic carbene (NHC)-functionalized hypercrosslinked polymers were fabricated and applied as recyclable catalysts for the N-formylation of amines using CO2 and H2 as feedstocks. Catalytic evaluations demonstrated that the chemical structure of the NHC ligand had a significant influence on catalytic activity. Specifically, P(PhPy-TPB)-Ru, functionalized with a single pyridine moiety on the NHC ligand, exhibited the optimal catalytic performance, even slightly outperforming its homogeneous counterpart. Furthermore, mechanistic studies indicated that both the base and solvent played pivotal roles in modulating the reaction activity. In particular, the use of methanol as the solvent in the presence of a base significantly enhanced reaction efficiency, which was attributed to the in situ generation of methyl formate as a key intermediate. Notably, the developed catalytic system possessed excellent catalytic efficiency, a broad substrate scope, superior stability, and easy recyclability, allowing the catalyst to be reused for up to eight consecutive cycles without significant loss of catalytic activity.