Rhenium(I)-tricarbonyl complexes with methimazole and its selenium analogue: Syntheses, characterization and cell toxicity.

This study explores the effect of a thione/selone ligand on the cell toxicity (in vitro) and light activity of diimine Re(CO) complexes. Six rhenium(I) complexes with general formula fac-[Re(CO)(N,N')X] were prepared, where X = 2-mercapto-1-methylimidazole (methimazole; MMI), and 1-methylimidazole-2-selone (MSeI); N,N' = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmphen). Their triflate salts were characterized using single-crystal X-ray diffraction, H, C and 2D NMR, UV-vis and vibrational spectroscopy. Their cytotoxic properties were tested, showing significant cytotoxicity (IC = 8.0-55 μM) towards the human breast cancer cell line MDA-MB-231. The half-inhibitory concentration (IC) for fac-[Re(CO)(dmphen)(MMI)], the most toxic complex in this series (8.0 ± 0.2 μM), was comparable to that of the corresponding aqua complex fac-[Re(CO)(dmphen)(HO)] with IC = 6.0 ± 0.1 μM. The fac-[Re(CO)(bpy)(MMI/MSeI)] complexes were somewhat less toxic towards the human embryonic kidney cell line HEK-293 T after 48 h of exposure. The stability of the complexes upon irradiation was monitored using UV-vis spectroscopy, with no CO released when exposed to UV-A light (λ = 365 nm).