Four iron(II) carbonyl complexes containing both pyridyl and halide ligands: Their synthesis, characterization, stability, and anticancer activity

Four iron(II) carbonyl complexes,fac-[Fe (CO)(3)X-2(py)] (X = I-,1and Br-,3),fac-[{Fe (CO)(3)X-2}(2)(bipy)] (X = I-,2and Br-,4), were facilely synthesized by reactingcis-[Fe (CO)(4)X-2] (X = I-, Br-) with pyridine (py) and 4,4 '-dipyridine (bipy) ligands, respectively, in good yields (70%similar to 85%). These complexes were fully characterized, and the structures of Complexes2and3were crystallographically analyzed. In dimethyl sulfoxide, they decomposed rapidly to release carbon monoxide (CO), and in methanol, they showed better stability which allowed kinetically analyzing their decomposing behaviors. The self-decomposing in methanol fitted first-order kinetics with a half-time ranging from several minutes to 1 h. Our results suggested that the ligand with great conjugation (bipy) and strong electron-donating capability (iodide) could stabilize the iron(II) carbonyl complexes. The decomposition of the iodo complexes (1and2) involved the production of iodine radicals. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assessments revealed that the efficacy against human bladder carcinoma cell line (RT112) is in the following trend:1>2>3>4. The relatively strong efficacy of Complexes1and2is mainly contributed to the in situ generated iodine radicals. The combination of the cytotoxicity of the in situ generated radicals with the anticancer activity of CO as reported in literatures may lead to developing novel anticancer drugs with enhanced efficacy.