Synthesis, structure, and anticancer activity of four silver(I)-N-heterocyclic carbene complexes and one polymer containing quinolin-8-yl groups

Abstract

Four Ag(I)-N-heterocyclic carbene (NHC) complexes containing quinolin-8-yl groups, viz. Ag(L1)2PF6 (L1 = 1-(quinolin-8-yl)-3-methyl-1H-imidazol-2-ylidene) (7), Ag(L2)2PF6 (L2 = 1-(quinolin-8-yl)-3-benzyl-1H-imidazol-2-ylidene) (8), Ag(L3)2PF6 (L3 = 1-(quinolin-8-yl)-4-methyl-1H-1, 2, 4-triazoline-5-ylidene) (9), and Ag(L4)PF6 (L4 =1-(quinolin-8-yl)-3-methyl-1H-benzimidazolin-2-ylidene) (12), were synthesized from Ag oxide and the corresponding ligand precursors (4, 5, 6, and 11). They were characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy, carbon-13 NMR (13C NMR) spectroscopy, electrospray ionization–mass spectrometry (ESI–MS), elemental analysis (EA), and single-crystal X-ray diffraction (XRD) analysis. X-ray crystallography revealed that complexes 7, 8, and 9 adopted a mononuclear Ag carbene geometry with a linear carbene C–Ag–C bond, whereas 12 exhibited a one-dimensional (1D) linear polymer with carbene C–Ag–C and quinoline N–Ag–N bonds. The structural assignments for 7 and 8 were further supported by density functional theory (DFT) calculations. Complex 9 has a distinct broad absorption at 421 nm, which could be attributed to the conjunctive effect increasing within the substituted quinoline and triazolium rings, and the strong π–π interaction between the intermolecular quinoline and triazolium rings. Study on the in vitro cytotoxic activity of 8, 9, and 12 against breast cancer MCF-7 cells indicated that complex 12 displayed the best anticancer activity in MCF-7 cells at a concentration of 5 × 10−6 mol/L. Additionally, the three Ag-NHC complexes 8, 9, and 12 had significant inhibitory effects on breast cancer cell growth at a concentration of 5 × 10−5 mol/L.