Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

[Image: see text] The diiron compounds [Fe(2)Cp(2)(CO)(2)(μ-CO)(μ-CSEt)]CF(3)SO(3), [1]CF(3)SO(3), K[Fe(2)Cp(2)(CO)(3)(CNCH(2)CO(2))], K[2], [Fe(2)Cp(2)(CO)(2)(μ-CO)(μ-CNMe(2))]NO(3), [3]NO(3), [Fe(2)Cp(2)(CO)(2)(PTA){μ-CNMe(Xyl)}]CF(3)SO(3), [4]CF(3)SO(3), and [Fe(2)Cp(2)(CO)(μ-CO){μ–η:(1)η(3)-C(4-C(6)H(4)CO(2)H)CHCNMe(2)}]CF(3)SO(3), [5]CF(3)SO(3), containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K[2], [3]NO(3), and [4]CF(3)SO(3) were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]CF(3)SO(3) were elucidated by (1)H NOESY NMR and single-crystal X-ray diffraction. Cell proliferation studies on human skin cancer (A431) and nontumoral embryonic kidney (HEK293) cells, with and without a 10-min exposure to low-power UV light (350 nm), highlighted the performance of the aminocarbyne [3]NO(3), nicknamed NIRAC (Nitrate-Iron-Aminocarbyne), which is substantially nontoxic in the dark but shows a marked photoinduced cytotoxicity. Spectroscopic (IR, UV–vis, NMR) measurements and the myoglobin assay indicated that the release of one carbon monoxide ligand represents the first step of the photoactivation process of NIRAC, followed by an extensive disassembly of the organometallic scaffold.