Ligand Engineering toward the Trade‐Off between Stability and Activity in Cluster Catalysis

Abstract

We report the structures, stability and catalysis properties of two Ag21 nanoclusters, namely [Ag21(H2BTCA)3(O2PPh2)6]SbF6 (1) and [Ag21(C≡CC6H3‐3,5‐R2)6(O2PPh2)10]SbF6 (2) (H4BTCA=p‐tert‐butylthiacalix[4]arene, R=OMe). Both Ag21 structures possess an identical icosahedral kernel that is surrounded by eight peripheral Ag atoms. Single‐crystal structural analysis and ESI‐MS revealed that 1 is an 8‐electron cluster and 2 has four free electrons. Theoretical results show that the P‐symmetry orbitals are found as HOMO‐1 and HOMO states in 1, and the frontier unoccupied molecular orbitals (LUMO, LUMO+1 and LUMO+2) show D‐character, indicating 1 is a superatomic cluster with an electronically closed shell 1S21P6, while 2 has an incomplete shell configuration 1S21P2. These two Ag21 clusters show superior stability under ambient conditions, and 1 is robust even at 90 °C in toluene and under oxidative conditions (30 % H2O2). Significantly, 2 exhibits much higher activity than 1 as catalyst in the reduction of 4‐nitrophenol. This work demonstrates that ligands can influence the electronic structures of silver clusters, and further affect their stability and catalytic performance.

Hydride-doped coinage metal superatoms and their catalytic applications

“…The reduction of 4-nitrophenol (4-NP) has emerged as one of the most extensively used model reactions for evaluating the catalytic and photocatalytic characteristics of nanoscale and nanostructured materials. 91–95 Sodium borohydride (NaBH 4 ) as a reducing agent (H 2 source) in combination with supported metal catalysts, such as Au, Pd, Pt, Ag, and Cu, 96,97 ranks among the numerous 4-NP reduction reactions that have drawn the most interest because of its simple and environmentally benign reduction process. Real-time monitoring with high accuracy is achieved by detecting the gradual decrease in the absorbance of 4-nitrophenol at 400 nm and the gradual increase at 300 nm, corresponding to the formation of the reaction product, 4-aminophenol (4-AP).…”