One-Pot Synthesis of Au11(PPh2Py)7Br3 for the Highly Chemoselective Hydrogenation of Nitrobenzaldehyde

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• 作者：Chao Liu ; Hadi Abroshan ; Chunyang Yan ; Gao Li ; Masatake Haruta
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：January 4, 2016
• 年：2016
• 卷：6
• 期：1
• 页码：92-99
• 全文大小：407K
• ISSN：2155-5435

文摘

In this study, the gold clusters Au₁₁(PPh₃)₇Cl₃ and Au₁₁(PPh₂Py)₇Br₃ (PPh₂Py = diphenyl-2-pyridylphosphine) are synthesized via a one-pot procedure based on the wet chemical reduction method. The Au₁₁(PPh₃)₇Cl₃ cluster is found to be active in the chemoselective hydrogenation of 4-nitrobenzaldehyde in the presence of hydrogen (H₂) and a base (e.g., pyridine). Interestingly, the cluster with the functional ligand PPh₂Py shows similar activity without losing catalytic efficiency in the absence of the base. The structure of the gold clusters and reaction pathway of the catalytic hydrogenation are investigated at the atomic/molecular level via UV–vis spectroscopy, electrospray ionization (ESI) mass spectrometry, and density functional theory (DFT) calculations. It is found that one ligand (PPh₃ or PPh₂Py) removal is the first step to expose the core of the gold clusters to reactants, providing an active site for the catalytic reaction. Then, the H–H bond of the H₂ molecule becomes activated with the aid of either free amine (base) or ligand PPh₂Py which is attached to the gold clusters. This work demonstrates the promise of the functional ligand PPh₂Py in the catalytic hydrogenation to reduce the amount of materials (free base: e.g., pyridine) that ultimately enter the waste stream, thereby providing a more environmentally friendly reaction medium.