A PEG/copper(i) halide cluster as an eco-friendly catalytic system for C-N bond formation

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 47; no. 22; pp. 7463 - 7470
• Main Authors: Li, Cheng-An, Ji, Wei, Qu, Jian, Jing, Su, Gao, Fei, Zhu, Dun-Ru
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 2018
• Subjects: Aromatic compounds; Catalysis; Clusters; Copper; Diethyl ether; Electron transfer; Electrons; Imidazole; Polyethylene glycol; Reaction time; Reagents; Recyclability
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt01310a

The catalytic activities of eight copper(i) halide clusters assembled from copper(i) halide and ferrocenyltelluroethers, 1-8, were investigated in C-N formation under various conditions. A catalytic procedure using poly(ethylene glycol) (PEG-400) as a greener alternative organic solvent has been developed. The PEG-400/5 system can achieve 99% targeted yield with a mild reaction temperature and short reaction time. After the isolation of the products by extraction with diethyl ether, this PEG-400/cluster system could be easily recycled. Spectroscopic studies elucidate a stepwise mechanism: firstly, proton-coupled electron transfer (PCET) involving the transfer of an electron from Cu+ and a proton from imidazole results in the formation of a labile penta-coordinated Cu2+ and aryl radical; the following effective electron transfer from the ferrocene unit reduces Cu2+ and forms the target product; finally, the ferrocenium unit is reduced by the I- anion. The merits of this eco-friendly synthesis are the efficient utilization of reagents and easy recyclability.