Anticancer Iron-Iridium Organometallic Conjugates

The diiron vinyliminium complexes [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C(3-C₅H₄N)CHCN(R)(Me)}]CF₃SO₃ (Cp = η⁵-C₅H₅; R = 2,6-C₆H₃Me₂ = Xyl, 2a, R = Me, 2b) reacted with [IrCp*(Phpy)Cl] (Ir^Cl; Cp* = η⁵-C₅Me₅, Phpy = κN,κC-2-phenylpyridine) and AgCF₃SO₃ to afford the bis-cationic iron-iridium conjugates [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C(3-C₅H₄NIrCp*Phpy)CHCN(Me)(R)}][CF₃SO₃]₂ (4a-b), in nearly quantitative yields. Similarly, the reaction of the ferracyclic compound [FeCp(CO){CN(Me)(Xyl)CHC(3-C₅H₄N)C(═O)}] (3a) with [IrCp*(Phpy)Cl]/AgNO₃ led to the monocationic species [FeCp(CO){CN(Me)(Xyl)CHC(3-C₅H₄NIrCp*Phpy)C((═O)}]NO₃ (5a, 70% yield). The new complexes 4a-b and 5a were characterized by mass spectrometry, IR and ¹H and ¹³C NMR spectroscopy. NMR and DFT analyses indicate that they exist as pairs of diastereoisomers due to the chirality centers in the iron and iridium scaffolds, and that the coordination strength of the pyridyl ligand to iridium is comparable to that observed in the iridium-pyridine adduct [IrCp*(py)(Phpy)] (Irpy). The cytotoxicity of 4a-b and 5a was evaluated on cancer (A2780, A549, U87) and noncancerous (MRC-5) cell lines, with 5a exhibiting superior activity compared to cisplatin and Irpy, along with a tendency toward selectivity. The activity of 4a-b and 5a, which is significantly higher compared to their iron precursors, is associated with enhanced iridium uptake in cancer cells (aligning with lipophilicity, determined as Log P_ow values), suppression of oxygen consumption rate and elevated ROS production.