Short metal–metal separations and in vitro anticancer studies of a new dinuclear silver(I)-N-heterocyclic carbene complex of para-xylyl-linked bis-benzimidazolium salt

A new benzyl-substituted bis-benzimidazolium derivative featuring a para-xylene spacer (1) has been prepared. Reaction of 1 with Ag2O in stoichiometric ratio followed by metathesis with KPF6 yielded a dinuclear silver-carbene complex 2. The benzimidazolium ligands in 2 are arranged in a head-to-head fashion (2:2), spanning a short Agsingle bondAg separation of 3.10(6) Å between two complex units with the other Ag center of each unit remaining uninteracted. Molecular structure of complex 2 is elucidated by single crystal X-ray diffraction method. Both, 1 and 2, were tested for their potential antiproliferative activity against human colorectal carcinoma (HCT 116) and human leukemia (HL 60) cell lines. Almost similar effects were found for both the cell lines; however, complex 2 displayed more specificity and nearly six fold higher anticancer activity compared to 1 toward both the cell lines.