Controlled Synthesis of Thiol-Protected Pd Nanoclusters via an Organophosphine Pre-Protection Strategy

Thiol-modified Pd nanoparticles exhibit excellent performance in heterogeneous catalysis. However, as an ideal catalytic model, thiol-protected Pd nanoclusters have faced limited research due to the lack of effective synthetic strategies. In this work, we develop one simple and efficient strategy for synthesizing thiol-protected Pd nanoclusters using organophosphines as pre-protection ligands. Via this approach, four structurally well-defined Pd clusters were obtained: [Pd₃(S-Adm)₃(PPh₂Py)₃]⁺ (1), [Pd₆(S-Adm)₇(PPh₂Py)₂]⁺ (2), [Pd₄(S-Adm)₂(dppm)₃]²⁺ (3), and [Pd₉(S-Adm)₆(dppm)₃Cl₂]²⁺ (4) (S-Adm = 1-adamantanethiol, PPh₂Py = diphenyl-2-pyridylphosphine, dppm = bis(diphenylphosphino)methane). The precise chemical composition and structure of these clusters were confirmed using single-crystal X-ray diffraction, electrospray ionization mass spectrometry, and ultraviolet-visible absorption spectroscopy. Furthermore, mechanistic investigation into the cluster conversion revealed that the formation of clusters follows a dissociation-reassembly mechanism. Moreover, thermal stability testing revealed that clusters 1-4 are stable below 373 K. Hydrogen activation experiments revealed that all clusters exhibit varying hydrogen dissociation capabilities, enabling efficient H/D exchange in D₂/MeOH systems. This work provides an effective strategy for the controlled synthesis of thiol-protected Pd clusters and establishes the potential for further application in the field of catalysis.