Diiron Complexes with a Bridging Functionalized Allylidene Ligand: Synthesis, Structural Aspects, and Cytotoxicity

Regio- and stereoselective nucleophilic attack of cyanide (from NBu4CN) to cationic diiron vinyliminium compounds [Fe2Cp2(CO)­(μ-CO)­{μ-η1:η3-C­(R′)­C­(R″)­CNMe2}]­CF3SO3 ([1a–f]­CF3SO3) affords the nitrile-aminoallylidene derivatives 2a–f in good to excellent yield. The analogous reaction of [1g]­CF3SO3, comprising two different N substituents, gives 4 (63%) as a mixture of two stereoisomers. The new products [1g]­CF3SO3, 2a–f, and 4 were characterized by IR and NMR spectroscopy and in a number of cases by IR-spectroelectrochemistry and single-crystal X-ray diffraction. The allylidene complexes are air-stable and robust in aqueous solution; however, in general they undergo oxidation within a biologically relevant range of potentials. DFT calculations were carried out to rationalize the observed stereoselectivity of the synthesis reaction and other structural and thermodynamic aspects. The cytotoxicity of 2a–f was assessed on cisplatin-sensitive and -resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines and human embryonic kidney (HEK-293) cells. Experiments reveal that treatment with the compounds leads to ROS production, with an absence of direct interactions with double-stranded DNA (calf thymus) and bovine serum albumin.