[Fe(NCN) 2 ]PF 6 (1·PF 6 ) [NCHN = 1,3-di(pyridin-2-yl)benzene] was readily obtained by a transmetalation reaction between [Fe 3 (CO) 12 ] and Hg(NCN)Cl followed by a metathesis reaction with KPF 6 . X-ray diffraction, electron paramagnetic resonance spectroscopy, and cyclic voltammetry studies confirmed
Bis-cyclometalated iron(II) complex [Fe(κC,Nphpy) 2 (CO) 2 ] (1) (phpyH = 2-phenylpyridine) has been prepared in good yield from [Fe(CO) 5 ] and [Hg(phpy) 2 ] in the presence of dibromine, which is unexpectedly a crucial component of the reaction mixture. It is needed for the generation of short-lived reactive intermediate [FeBr(CO) 5 ]Br, which is actually involved in the electrophilic substitution reaction with [Hg(phpy) 2 ]. When irradiated by visible light, compound 1 readily affords bis(2-(pyridine-2-yl)phenyl)methanone ( 2) and iron oxides through the insertion of CO in the Fe−C bond of the cyclometalated moiety. Structures of iron complex 1 and ketone 2 were confirmed by X-ray crystallography. Activation of [Fe(CO) 5 ] by Br 2 represents a new approach for generating an iron intermediate, which is active in transmetalation reactions. Cytotoxic activity of 1 was tested against three gastric cancer cell lines, KATO III, AGS, and NUGC3. The activity against KATO III and NUGC3 cells is moderate, while complex 1 displayed excellent cytotoxicity against AGS cells. The molecular mechanism investigation showed that the cytotoxic activity of 1 appears independent of caspase 3 and the TP53 tumor suppressor gene, suggesting an apoptotic-independent process.
In previous reports, it has been demonstrated that cyclometalated iron(II/III) complexes can be prepared by reacting iron(0) precursors and mercurated or brominated derivatives. However, in this report, the reaction between [Fe3(CO)12] and mercurated 6‐phenyl‐2,2′‐bipyridine or brominated 2,6‐diphenyl‐pyridine pincer derivatives led to compounds in which C(sp2)−C(sp2) bonds have been formed between two ligands. A 16‐electron iron(II) complex (1Cl) bearing a tetradentate ligand originating from the dimerization of 6‐phenyl‐2,2′‐bipyridine was isolated, while a protonated 14‐membered macrocycle with [FeBr4]− as counterion (2) was obtained from 2,6‐diphenyl‐pyridine. Studies by X‐ray diffraction crystallography, NMR, UV‐vis and cyclic voltammetry confirmed the structures. Additionally, the cytotoxicity of the new compounds toward gastric cancer cell lines was evaluated, and it was established that the presence of the iron(II) center was crucial for an elevated activity.
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