A symmetrical tetra N-heterocyclic carbene binuclear silver(I) complex: synthesis, characterization and anticancer study

Abstract

The synthesis of dinuclear carbene complexes from tetrakis-N-heterocyclic (NHC) and silver(I) ions has been achieved through molecular self-assembly. The reaction between 1,2,4,5-tetra(bromomethyl)benzene with four equivalents of N-substituted alkyl benzimidazole resulted in formation of various tetra-benzimidazolium salts, [H4L]·4Br- (1–5). Further reaction of the respective salts with Ag2O yielded mono tetra-NHC dinuclear silver(I) complexes, [Ag2L1]·2PF6 (6–10). The salts and their silver(I) complexes were characterized by 1H and 13C NMR, FTIR, elemental analysis, molar conductivity, and UV–Visible spectroscopy. Structure elucidation from single crystal X-ray diffraction analyses data revealed that 10 is a dinuclear complex in a tweezer-like structure containing two silver(I) ions that are bridged by one tetra-carbene ligand with the cyclic aromatic backbone of the ligand perpendicular to the benzimidazolium moieties. Anticancer activities of the salts (1–5) and complexes (6–10) were studied, with Etoposide used as the positive control. Subsequently, 1 showed less activity at 24 h while all salts, 1–5, showed better activity at 48 h. The complexes (6–10) indicated moderate and better activity, which is higher compared to 1–5 and Etoposide, both within 24 and 48 h incubation periods.