Synergy of Ru single atoms and nanoparticles on Br-tethered covalent organic framework boosting reductive amination

Maximizing the atom efficiency of noble metal species is crucial for their application, but directly reducing the size down to single atoms (SAs) is limited when facing complex situations requiring the simultaneous adsorption and activation of multiple reactants. Herein, Schiff base condensation of 1,3,5-tris(4-aminophenyl)benzene and 2,5-dibromoterephthalaldehyde offered a Br-tethered covalent organic framework (COF) TAPB-DBDH for the co-loading of ruthenium (Ru) SAs and nanoparticles (NPs). We demonstrated a triadic synergism of Ru SAs (Ru–C₃N₁), Ru NPs, and the TAPB-DBDH framework in reductive aminations of carbonyl compounds with ammonia and hydrogen to primary amines, showing the high yield, large turnover number, and turnover frequency, stable recycling, and broad substrate compatibility. A systematic theoretic and experimental study revealed that the cooperation of Ru SAs and the TAPB-DBDH framework provided a strong affinity toward the carbonyl compound and imine intermediate to promote their conversion, while the co-existed Ru NPs lowered the energy barrier of H₂ cleavage.