The reaction of pyrrolidine with a series of cationic diiron cyclopentadienyl complexes containing a bridging vinyliminium ligand gives access to piano stool monoiron complexes based on a five-membered metallacycle that includes a vinyl-aminoalkylidene moiety, in moderate to high yields. The resulting metallacyclic motif (aminoalkylidene-ferracyclopentenone) is unique in organometallic chemistry and is partially pre-constructed on the dinuclear frame. The monoiron products were fully characterized by elemental analysis, IR and multinuclear NMR spectroscopy, and in a number of cases by X-ray diffraction and cyclic voltammetry. They are robust in aqueous solutions and generally unreactive towards alkylating agents in organic solvents. However, a cationic derivative was prepared in high yield by methylation of a 2-pyridyl group. The cytotoxicity of both neutral and ionic complexes was assessed on cancerous (A2780 and A280cisR) and non-cancerous (HEK293) cell lines, revealing the influence of local structural modifications on the antiproliferative activity and the selectivity of the compounds.