Pentamethylcyclopentadienyl Metalloradical Iron Complexes Containing Redox Noninnocent α‑Diimine-Type Ligands: Synthesis, Molecular, and Electronic Structures

The synthesis and characterization of pentamethylcyclopentadienyl iron complexes bearing the redox noninnocent α-diimine (N,N′-dimesitylbutane-2,3-diimine, MesDI) and α-iminopyridine (N-mesityl(pyridin-2-yl)ethanimine MesPI) ligands were explored. One-pot reduction and complexation of the cyclopentadienyl ring was accomplished by treatment of (κ2-N,N′)FeCl2 (N,N′= MesDI or MesPI) precursors with [C5Me5]Li. The resulting iron compounds were characterized by paramagnetic 1H NMR spectroscopy, magnetic susceptibility measurements, zero-field 57Fe Mössbauer spectroscopy, low-temperature electron paramagnetic resonance (EPR) spectroscopy, and cyclic voltammetry. The combined spectroscopic, structural, and density functional theory (DFT) computational data supported low-spin iron(III) compounds (SFe = 1/2) with π-acidic, formally doubly reduced chelating ligands.