Imidazolyl Phosphine as Versatile Hemilabile Ligand: Synthesis and Characterization of a New Tetracationic Au₂₀ Nanocluster

As the new type of molecular catalysts, hemilabile ligand-protected Au nanoclusters hold greater promise in realizing a better trade-off between catalytic activity and structural stability. Despite the large amount of Au nanoclusters (co-)protected by organic nitrogen ligands, little has been known about those containing dynamically labile Au─N bonds, where the hemilabile ligands are solely limited to pyridyl-phosphine. In this study, we chose imidazolyl-phosphine (dpim) as the main protecting ligand and synthesized a new tetracationic cluster [Au₂₀(dpim)₆(dppe)₂Cl₂]⁴⁺ (Au₂₀-S, dppe = Ph₂P(CH₂)₂PPh₂), which was structurally characterized crystallographically, spectroscopically, and computationally. Albeit the similar electronic structure of the Au₂₀ core, Au₂₀-S possesses different ligand arrangements and positive charges from those of its two reported structural analogues, and thus they may serve as an ideal cluster triad for comparatively studying the ligand/charge effect on their catalytic activities. This work proved the potential of imidazolyl phosphine as a versatile hemilabile ligand in the syntheses of Au NCs with labile Au─N bonds. The imidazolyl-phosphines are more amenable to derivatizations, which provides a new opportunity for further enriching the library of hemilabile ligand-protected Au NCs with potentially better catalytic performance.