Controlled Dissociation of Iron and Cyclopentadienyl from a Diiron Complex with a Bridging C₃ Ligand Triggered by One-Electron Reduction

The one-electron reduction of a diiron cationic complex revealed unique features: cleavage of the diiron structure occurred despite a multidentate bridging C3 ligand and was accompanied by the clean dissociation of one η5-cyclopentadienyl ring and one iron as isolated units. Thus, the iron­(II)–iron­(II) μ-vinyliminium complex [Fe2Cp2(CO)­(μ-CO)­{μ-η1:η3-C3(Et)­C2HC1N­(Me)­(Xyl)}]­[SO3CF3] ([1a]­SO3CF3) reacted with cobaltocene in tetrahydrofuran (THF), affording the iron­(II) vinylaminoalkylidene [FeCp­(CO)­{C1N­(Me)­(Xyl)­C2HC3(Et)­C­(O)}] (2a) in 77% yield relative to the C3 ligand. Analogously, [FeCp­(CO)­{C1N­(Me)­(Xyl)­C2HC3(CH2OH)­C­(O)}] (2b) was obtained in 64% yield from the appropriate diiron precursor and CoCp2. The formation of 2a is initiated by the one-electron reduction of [1a]+, followed by a reversible intramolecular rearrangement terminating with the irreversible release of CpH (NMR and gas chromatography–mass spectrometry) and Fe [electron paramagnetic resonance (EPR) and magnetometry]. The key intermediate iron­(I) ferraferrocene (3) was detected by EPR and IR spectroelectrochemistry, while the related species 3-H-3 was isolated after the addition of a hydrogen source and then identified by X-ray diffraction. A plausible mechanism for the route from [1a]+ to 3 was ascertained by density functional theory calculations. The dication [1a]2+, displaying both carbonyl ligands in terminal positions, and the anion [3]− were electrochemically generated. The functionalized diiron compounds 4 (52% yield) and 5 (62%) were afforded through the activation of O2 and S8 by a radical intermediate along the reductive pathway of [1a]+. The reaction of [Fe2Cp2(CO)­(μ-CO)­{μ-η1:η3-C­(SiMe3)­CHCN­(Me)­(Xyl)}]­[SO3CF3] ([1c]­SO3CF3) with CoCp2 in THF afforded [Fe2Cp2(CCSiMe3)­(CO)­(μ-CO)­{μ-CNMe­(Xyl)}] (6) in 65% yield