Noninnocent Behavior of a (3-Imino)indol-2-yl Ligand in Metal Complexes

The
redox noninnocence of conjugated imino-alkenyl anions has been
disclosed in bis­((3-imino)­indol-2-yl)iron complexes. A charge-neutral
bis­((3-imino)­indol-2-yl)­iron­(II) complex, abbreviated as [Fe­(C-N)2], was synthesized from the salt elimination
reaction of FeCl2 with 2 equiv of 2-Li-1-(2′-(CH2)4NCH2CH2)-3-(2′,6′-Pri2C6H3NCH)­C8H5N). [Fe­(C-N)2] can further
react with 1 equiv of Li to form the one-electron-reduced complex
Li­[Fe­(C-N)2]. Single-crystal X-ray diffraction
studies, solution magnetic susceptibility measurements, EPR, and 57Fe Mössbauer spectroscopy, in combination with theoretical
studies, revealed that both complexes are high-spin iron­(II) complexes
and that [Fe­(C-N)2] features two closed-shell
monoanionic (3-imino)­indol-2-yl monoanion ligands, whereas Li­[Fe­(C-N)2] has one closed-shell monoanionic ligand
and one open-shell (3-imino)­indol-2-yl radical dianion ligand. An
attempt to prepare the dilithium salt of the ligand radical anion
by interacting 2-Li-1-(2′-(CH2)4NCH2CH2)-3-(2′,6′-Pri2C6H3NCH)­C8H5N) with Li led to the isolation of a ligand degradation
product.