Synthesis, Fluorescence And Antibacterial Activity Study On Metal N-Heterocyclic Carbene Complexes

Since Arduengo and co-workers first isolated a stable and free N-heterocyclic carbene（NHC）, N-heterocyclic carbenes（NHCs） have been developed rapidly in organometallic chemistry. As the NHCs’ diversity of the structure and strong σ-donor, most of which can lead to stable metal-NHCs with fascinating properties. Recently, the applications of metal-NHCs in catalysis, fluorescent switch and biological activity have drawn scientist’s eyeballs.In this paper, the 9-imidazolyl acridine was prepared from 9-cl acridine, then the reaction of iodomethane, n-butane bromide, bromoethane, benzyl bromide and 9-（1-imidazolyl） acridine obtains the corresponding imidazolium salts, which can further react with NH₄PF₆ affording 1-acridinyl-3-methylimidazolium hexafluorophosphate salt（3a）, 1-acridinyl-3-butylimidazolium hexafluorophosphate salt（3b）, 1-acridinyl-3-ethylimidazolium hexafluorophosphate salt（3c） and 1-acridinyl-3-benzylimidazoliumhexafluoroposphate salt（3d）. Then, they were treated with silver oxide in CH3 CN or DMSO to afford silver-NHCs. All complexes were characterized by ¹H NMR, ¹³ C NMR spectroscopy, elemental analyses and X-ray diffraction. Two silver-NHCs formed mononuclear silver complexes which presented Ï€-Ï€ stacking interactions between acriding rings. Moreover, the other silver-NHCs formed one-dimensional coordination polymers through self-assembly of N1-Ag1-C16 and N1-Ag1-C14 bonds, respectively. In addition, the imidazolium salts and their corresponding silver complexes show a phenomenon of fluorescence quenching. Amazingly, silver-NHCs have been found to have efficient anti-bacterial activity against the Acinetobacter baumannii and Pseudomonas aeruginosa.In addition, N-heterocyclic carbene precursors based on 1, 5-dichloro anthraquinone and hydroquinone have been obtained, which further reacted with Ag₂ O in CH₃ CN affording the Ag-NHCs. All N-heterocyclic carbene precursors and Ag-NHCs were characterized by ¹H NMR and ¹³ C NMR spectroscopy. It’s a pity that the crystal structures of metal-NHCs are not obtained.