Binuclear silver(I) complexes of p-xylyl/2,6-lutidinyl linked bis-N-heterocyclic carbene ligands: Synthesis, crystal structures and biological evaluation

Abstract

A series of p-xylyl/2,6-lutidinyl linked bis-(benz)imidazolium salts 1–4 and their binuclear Ag–NHC complexes 5–8 have been reported. Salts 1–4 were synthesized by the successive N-alkylation method, first reacting 1H-(benz)imidazole with α,α′-dichloro-p-xylene/2,6-dibromomethyl pyridine followed by the reaction of an appropriate alkyl bromide. Binuclear Ag complexes 5–8 having bis-NHC periphery with linear coordination modes have been prepared by the reaction of salts 1–4 with Ag2O at a mild reaction condition. Compounds 1–8 have been fully characterized by spectral and analytical techniques. Additionally, molecular structure of salt 4 and complex 6 has been unambiguously elucidated by single crystal XRD studies. The structure of complex 6 is a metallomacrocycle having two Ag centers supported by two bis-NHC ligands. Preliminary in vitro antibacterial studies against Escherichia coli and Staphylococcus aureus revealed the superior activity of Ag complexes compared to azolium salts with 12.4±1.5 to 27.5±2mm diameter of the zone of bacterial growth inhibition.