Ligand effects in catalysis by atomically precise gold nanoclusters

Atomically precise gold nanoclusters are ideal model catalysts with well-defined compositions and tunable structures. Determination of the ligand effect on catalysis requires the use of gold nanoclusters with protecting ligands as the only variable. Two isostructural Au₃₈ nanoclusters, [Au₃₈(L)₂₀(Ph₃P)₄]²⁺ (L = alkynyl or thiolate), have been synthesized by a direct reduction method, and they have an unprecedented face-centered cubic (fcc)-type Au₃₄ kernel surrounded by 4 AuL₂ staple motifs, 4 Ph₃P, and 12 bridging L ligands. The Au₃₄ kernel can be derived from the fusion of two fcc-type Au₂₀ via sharing a Au₆ face. Catalytic performance was studied with these two nanoclusters supported on TiO₂ (1/TiO₂ and 2/TiO₂) as catalysts. The alkynyl-protected Au₃₈ are very active (>97%) in the semihydrogenation of alkynes (including terminal and internal ones) to alkenes, whereas the thiolated Au₃₈ showed a very low conversion (<2%). This fact suggests that the protecting ligands play an important role in H₂ activation. This work presents a clear demonstration that catalytic performance of gold nanoclusters can be modulated by the controlled construction of ligand spheres.