Synthesis, characterization, and biological studies of multidentate gold(i) and gold(iii) NHC complexes

The synthesis and characterization of a novel macrocyclic Au(iii) N-heterocyclic carbene (NHC) imidazolyl complex, a novel macrocyclic tetra-NHC benzimidazole ligand, and the corresponding Ag(i) and Au(i) complexes are presented. Single-crystal X-ray diffraction analysis of the Au(i) benzimidazolyl complex 3 reveals an unusual structure, differing from the respective Au(i) imidazolyl complex 4. Both complexes have a Au₄L₂ composition; however, 3 has two C-Au(i)-C units acting as a connection between the two ligands with two Au(i) atoms being linearly coordinated inside the cavity of the macrocyclic ligand. In the case of complex 4, the structure shows a box-type coordination with all four Au(i) atoms being located between the two ligands. Stability studies in cell culture medium are performed for subsequent MTT assays and they show an unprecedented proton-to-deuterium exchange of the methylene bridge of the Au(iii) imidazolyl complex. In MTT assays, the tetranuclear acyclic Au(i) complex 5 displays the lowest IC₅₀ values in MCF-7, PC3, and A2780cisR cells with a selective cytotoxicity for MCF-7 and A2780cisR cells.