Reversible Transformation Mechanism between Pd₄ and Pd₁₀ Clusters and Their Catalytic Hydrogenation Activities

The study of the mechanisms behind the structural transformation of clusters has consistently attracted much attention in recent years, as it contributes to the basic understanding of the growth mechanisms and structure-property relationships of clusters. In this study, two types of Pd nanoclusters with different core structures, [Pd₄(L)₄(CO)₂]²⁺ (Pd₄, L = ligand) and [Pd₁₀(L)₈(CO)₅X]³⁺ (Pd₁₀, X = OAc^- or Cl^-), are reported, whose reversible transformation mechanisms have been studied through UV-vis absorption spectroscopy (UV-vis), electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR), and single crystal X-ray diffraction (SC-XRD). The results reveal that zerovalent Pd₂⁰ and hydrogen bonds of the type AcOH···OAc^- play crucial roles in the cluster transformation process. Finally, due to structural differences, Pd₄ and Pd₁₀ clusters exhibit distinct differences in catalytic activity for olefin hydrogenation, with the Pd₁₀ cluster demonstrating high regioselective hydrogenation. Experimental and theoretical results indicate that the mobile OAc^- ligand on Pd₁₀ is crucial for creating the active site for the catalytic hydrogenation of olefins. This research provides insights into the mutual transformation and structure-property relationships of Pd nanoclusters.