Synthesis, structural characterization, and antibacterial studies of N-heterocyclic Ag(I) carbenes derived from dicationic imidazolium salts

This work describes synthetic routes to dicationic imidazolium chlorides bearing allylic substituents and the p-xylyl and o-xylyl spacers, and their reactivity studies aimed to synthesize silver(I) N-heterocyclic monocarbene derivatives. The synthesis of the chlorides {pXiAlImo}Cl2 (1), {pXiMeAlImo}Cl2 (2), [oXiAlImo]Cl2 (3) and [oXiMeAlImo]Cl2 (4) was carried out using a two-step methodology, in which the reaction times, solvents, temperature, and base used were evaluated. The synthesized salts 1 to 4 were used to produce NHC-Ag(I) carbenes via the silver oxide route, which allowed the formation of the silver(I) metallic compounds [Ag2Cl2{pXiAlImil}] (1a), [Ag2Cl2{pXiMeAlImil}] (2a) [Ag2Cl2{oXiAlImil}] (3a) and [Ag2Cl2{oXiMeAlImil}] (4a) with moderate yields. Single-crystal X-ray Diffraction analysis confirmed the solid-state structure of salts 1 and 2. NMR, IR, and HR-MS spectra were used to characterize all compounds to verify the proposed structures. The antibacterial activity of the synthesized silver(I) NHC carbenes was evaluated by determining the minimum inhibitory concentration (MIC) and the inhibition halo by the Kirby-Bauer method against two Gram-positive bacteria (B. subtilis and S. aureus), and two Gram-negative bacteria (P. aeruginosa and E. coli).