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

Abstract

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.

Anticancer Potential of Diiron Vinyliminium Complexes

“…In general, the investigated complexes showed CV profiles in THF/[N n Bu 4 ]PF 6 or CH 2 Cl 2 /[N n Bu 4 ]PF 6 involving a chemically reversible oxidation and two reduction processes, complicated by subsequent chemical reactions (see Table and Figures S41–S43). These findings are in accordance with the previous studies on [Fe 2 Cp 2 (CO)(μ‐CO){μ‐η 1 :η 3 ‐C 3 (Et)C 2 HC 1 N(Me)(Xyl)}]CF 3 SO 3 , [ 20 ]CF 3 SO 3 …”

“…The 13 C NMR spectrum shows the resonance of the C 1 carbon at 265 ppm, which is in alignment with the aminoalkylidene character. The X‐ray structure of 21 c (Figure ) resembles that previously reported for 21 a , with the substituents around the partially double C 1 −N bond arranged in the E configuration …”

“… Synthesis of Fe II ‐vinyl‐aminoalkylidene complexes promoted by reduction of Fe II –Fe II vinyliminium precursors, by Fe 0 elimination. Red pathway: mechanism proposed for the conversion of [ 20 ] + to 21 a on the basis of NMR, electrochemical, magnetometric and DFT studies …”

Antiproliferative and bactericidal activity of diiron and monoiron cyclopentadienyl carbonyl complexes comprising a vinyl‐aminoalkylidene unit

“…Such X-ray structures share a 1-metalla-2-aminocyclopenta-1,3-dien-5-one five-membered ring core. [18,20,21] resonances, attributed to the E isomer with reference to the N-substituents, in analogy with what detected for the parent vinyliminium compounds and for 5a and 5h in the solid state (see X-ray diffraction studies), the only exception being 5g (E and Z isomers in 5:1 relative ratio). In the NMR spectra of 6a-c, the two methyl groups are nonequivalent, in agreement with the partial doublebond nature of C 1 -N, for instance they resonate at 51.8 and 44.0 ppm in the 13 C spectrum of 6c.…”

Mono-, Di- and Tetra-iron Complexes with Selenium or Sulphur Functionalized Vinyliminium Ligands: Synthesis, Structural Characterization and Antiproliferative Activity

“…Former findings indicate that the vinyliminium ligand in type 1 compounds displays a versatile and rich chemistry, offering much scope for derivatization [43][44][45]. Herein, we will describe the synthesis and the characterization of a series of S-and Se-functionalized derivatives [42][43][44][45][46][47]. Cytotoxicity data concerning both cancer and non-cancer cell lines and experiments aimed to clarify the mechanism of action of the compounds are described.…”