p?Nitrobenzyl-substituted N?heterocyclic carbene in Silver(I) and Gold(I) complexes and their antibacterial activities

The synthesis of the silver(I) N?heterocyclic carbene [Ag(NBMIM)Cl]2 (2) from the reaction of imidazolium salt {NBMIM}Cl (1a) (NBMIM = 1?methyl?3?(4?nitrobenzyl)?1H?imidazol?3?ium) and silver(I) oxide was achieved. Compound {NBMIM}PF6 (1b) was also obtained by a counteranion exchange reaction. Compound 2 was used as a transmetalation agent to form Au(I) monocarbene complex (3a) and biscarbene complex (3b), by using [AuCl(SMe2)]. All compounds were characterized in solution by infrared spectroscopy and by 1H and 13C{1H} NMR. The molecular structures of compounds {NBMIM}PF6 (1b), [Ag(NBMIM)Cl]2 (2), and [Au(NBMIM)Cl] (3a) were also determined by single crystal X?ray diffraction studies. The molecular structure of silver complex 2 showed a 1D?staircase structure with Ag?Ag and Ag?Cl intermolecular interactions. Compounds 2 and 3a were also characterized by elemental analysis, powder X?ray diffraction (PXRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) measurement. In preliminary in vitro antibacterial assays, compounds 2 and 3a were tested against four bacterial strains: two Gram positive (S. aureus and B. subtilis) and two Gram negative species (P. aeruginosa and E. coli) by Kirby?Bauer?s disk diffusion method. Compound 2 exhibited moderate antibacterial activity against both types of bacteria. Both silver(I) and gold(I) N?heterocyclic carbenes showed from good to high antibacterial activity against S. aureus and P. aeruginosa and moderate activity against B. subtilis and E. coli strains.