Controlled Dissociation of Iron and Cyclopentadienyl from a Diiron Complex with a Bridging C 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 C ligand and was accompanied by the clean dissociation of one η-cyclopentadienyl ring and one iron as isolated units. Thus, the iron(II)-iron(II) μ-vinyliminium complex [FeCp(CO)(μ-CO){μ-η:η-C(Et)CHCN(Me)(Xyl)}][SOCF] ([1a]SOCF) reacted with cobaltocene in tetrahydrofuran (THF), affording the iron(II) vinylaminoalkylidene [FeCp(CO){CN(Me)(Xyl)CHC(Et)C(═O)}] (2a) in 77% yield relative to the C ligand. Analogously, [FeCp(CO){CN(Me)(Xyl)CHC(CHOH)C(═O)}] (2b) was obtained in 64% yield from the appropriate diiron precursor and CoCp. 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], 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 O and S by a radical intermediate along the reductive pathway of [1a]. The reaction of [FeCp(CO)(μ-CO){μ-η:η-C(SiMe)CHCN(Me)(Xyl)}][SOCF] ([1c]SOCF) with CoCp in THF afforded [FeCp(C≡CSiMe)(CO)(μ-CO){μ-CNMe(Xyl)}] (6) in 65% yield.