The Synthesis, Bonding, and Transformation of a Ligand-Protected Gold Nanohydride Cluster

Gold does not react with H₂ to form bulk hydrides. Here we report the synthesis and characterization of a gold nanohydride protected by diphosphine ligands, [Au₂₂ H₄ (dppo)₆ ]²⁺ [dppo=1,8-bis(diphenylphosphino)octane]. The Au₂₂ core consists of two Au₁₁ units bonded by eight Au atoms not coordinated by the diphosphine ligands. The four H atoms are found to bridge the eight uncoordinated Au atoms at the interface. Each Au₁₁ unit can be viewed as a tetravalent superatom forming four delocalized Au-H-Au bonds, similar to the quadruple bond first discovered in the [Re₂ Cl₈ ]^2- inorganic cluster. The [Au₂₂ H₄ (dppo)₆ ]²⁺ nanohydride is found to lose H atoms over an extended time via H evolution (H₂ ), proton (H⁺ ) and hydride (H^- ) releases. This complete repertoire of H-related transformations suggests that the [Au₂₂ H₄ (dppo)₆ ]²⁺ nanohydride is a versatile model catalyst for understanding the mechanisms of chemical reactions involving hydrogen on the surface of gold nanoparticles.