Beyond Lindlar Catalyst: Highly-oxidized Pd Single Atoms as Promoter for Alkyne Semi-hydrogenation

Abstract

The semi-hydrogenation of alkynes is crucial for the synthesis of steroid hormone drugs, yet conventional approaches relying on Pd surfaces poisoning additives sacrifices activity and sustainability for selectivity. Herein, we present a “grafting-then-coordination” strategy to construct a Pd/C-NH2 catalyst featuring coexisting tetravalent Pd single atoms (PdIV SAs) and Pd nanoparticles (NPs), which achieves inhibitor-free, highly efficient hydrogenation of steroidal alkynes. The Pd/C-NH2 catalyst, functionalized with 3-aminopropyltriethoxysilane (APTES), exhibits 99% conversion with 97% selectivity in the selective hydrogenation of mifepristone under 0.1 MPa and 25 °C, with a remarkable turnover frequency (TOF) of 3675 h-1, representing a 17-fold enhancement over conventional Lindlar catalyst. Mechanistic studies reveal that the PdIV SAs are stabilized through Pd-N/O coordination by leveraging oxygen-containing groups of support and amino groups of the ligand. The electron-deficient PdIV SAs adsorb mifepristone, mitigating substrate self-poisoning on Pd NPs, while Pd NPs activate H2 and promote hydrogen spillover to PdIV SAs sites, enabling hydrogenation via a dual-site cooperative mechanism. The stable PdIV SAs transform conventional poisoning sites into productive active centers, offering valuable insights for the rational design of advanced selective hydrogenation catalysts.