Synthesis, Structural Analysis and Antibacterial Studies of Bis- and Open Chain Tetra-N-Heterocyclic Carbene Dinuclear Silver(I) Complexes

Abstract

Abstract The synthesis, characterization and antibacterial studies of two bisbenzimidazolium salts (1 and 2), eight open chain tetrabenzimidazolium salts (3-10) and their respective silver(I)-NHC complexes (Ag1-Ag10) (where NHC\u202f=\u202fN-heterocyclic carbene) were reported. Salts 3-10 were synthesized through the reaction of 3-(2-bromoethyl)-1-alkylbenzimidazole bromide (alkyl\u202f=\u202fethyl, propyl, butyl, benzyl), i-iv with either 1,4-butylbisbenzimidazole or 1,3-bis(methylbenzimidazole)benzene. The bisbenzimidazolium bromide salt 1 and 2 were obtained either as a the minor product from the reaction that resulting i and ii, or through the simple addition reaction between n-alkylbenzimidazole (where alkyl=ethyl, propyl) with 1,2-dibromoethane. Futhermore, silver(I)-NHC complexes Ag1-Ag10 were synthesized via in-situ deprotonation of the respective salts with Ag2O. The formation of all compounds were proved by elemental analyses, FTIR, 1H and 13C NMR spectroscopy. The structure elucidation of i and Ag9 were conducted using single crystal X-ray diffraction data. From this study, complex Ag9 present as a tetra-NHC dinuclear complexes with the general formula of [Ag2(NHC)]∙2PF6. From the spectra studies, other tetra-NHC silver(I) complexes are suggested to have the similar connectivity as in Ag9. All silver(I)-NHC Ag1-Ag10 show medium to higher activities against E.coli (ATCC 25922) and S. aureus (ATCC 12600) compared to the standard antibiotic drug, Ampicillin and reported mononuclear silver(I)-NHC complexes.