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 C-3 ligand and was accompanied by the clean dissociation of one eta(5)-cyclopentadienyl ring and one iron as isolated units. Thus, the iron(II)-iron(II) mu-vinyliminium complex [Fe2Cp2(CO)(mu-CO){mu-eta(1):eta(3)-C-3(Et)(CHCN)-H-2-N-1(Me)(Xyl)}][SO3CF3] ([1a]SO3CF3) reacted with cobaltocene in tetrahydrofuran (THF), affording the iron(II) vinylaminoalkylidene [FeCp(CO){(CN)-N-1(Me)(Xyl)(CHC3)-H-2(Et)C(-O)}] (2a) in 77% yield relative to the C-3 ligand. Analogously, [FeCp(CO){(CN)-N-1(Me)(Xyl)(CHC3)-H-2(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 chromatographymass 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 O-2 and S-8 by a radical intermediate along the reductive pathway of [1a](+). The reaction of [Fe2Cp2(CO)(mu-CO){mu-eta(1):eta(3)-C(SiMe3)CHCN(Me)(Xyl)}][SO3CF3] ([1c]SO3CF3) with CoCp2 in THF afforded [Fe2Cp2(C equivalent to CSiMe3)(CO)(mu-CO){mu-CNMe(Xyl)}] (6) in 65% yield.