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 Au(38) nanoclusters, [Au(38)(L)(20)(Ph(3)P)(4)](2+) (L = alkynyl or thiolate), have been synthesized by a direct reduction method, and they have an unprecedented face-centered cubic (fcc)–type Au(34) kernel surrounded by 4 AuL(2) staple motifs, 4 Ph(3)P, and 12 bridging L ligands. The Au(34) kernel can be derived from the fusion of two fcc-type Au(20) via sharing a Au(6) face. Catalytic performance was studied with these two nanoclusters supported on TiO(2) (1/TiO(2) and 2/TiO(2)) as catalysts. The alkynyl-protected Au(38) are very active (>97%) in the semihydrogenation of alkynes (including terminal and internal ones) to alkenes, whereas the thiolated Au(38) showed a very low conversion (<2%). This fact suggests that the protecting ligands play an important role in H(2) activation. This work presents a clear demonstration that catalytic performance of gold nanoclusters can be modulated by the controlled construction of ligand spheres.