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

The diiron compounds [Fe₂Cp₂(CO)₂(μ-CO)­(μ-CSEt)]­CF₃SO₃, [1]­CF₃SO₃, K­[Fe₂Cp₂(CO)₃(CNCH₂CO₂)], K­[2], [Fe₂Cp₂(CO)₂(μ-CO)­(μ-CNMe₂)]­NO₃, [3]­NO₃, [Fe₂Cp₂(CO)₂(PTA)­{μ-CNMe­(Xyl)}]­CF₃SO₃, [4]­CF₃SO₃, and [Fe₂Cp₂(CO)­(μ-CO)­{μ–η:¹η³-C­(4-C₆H₄CO₂H)­CHCNMe₂}]­CF₃SO₃, [5]­CF₃SO₃, containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K­[2], [3]­NO₃, and [4]­CF₃SO₃ were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]­CF₃SO₃ were elucidated by ¹H 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]­NO₃, 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.