Direct Incorporation of a Ferric Ion in the Porphyrinogen Core: Tetrakis(cyclohexyl)iron Porphyrinogen Anion with Different Conformers and Its Reaction with Iodine

Et4N[L‘ ‘FeIII]·3DCM (1) is directly synthesized by adding ferric
chloride into a solution of a lithium salt of tetrakis(cyclohexyl)porphyrinogen (L‘ ‘). [L‘ ‘]4- is a good chelating ligand for both Fe(III) and Fe(II) ions. It is an avid proton scavenger but not a
reducing agent. 1 showed a magnetic moment (μeff) of 4.3 μB in
the solid, which changed to 6.0 μB in solution. This change in
spin state is common for all iron porphrinogens. 1 showed
polymorphism, and with pyridine in the lattice, it changed to Et4N[L‘ ‘FeIII]·DCM0.5Py1.5 (2), possessing two different conformers.
Calculation of these conformers at the density functional theory
level showed the relative energies of all d orbital changes in three
conformers, highlighting the influence of the disposition of a
peripheral ligand. Iodine oxidation of 1 yielded [L‘ ‘ΔΔFeIII][I3·I2+·I3-]
(3) with the introduction of two Cα−Cα bonds with concomitant
reduction of Fe(III) to Fe(II). Its μeff (5.4 μB) in the solid changed
to 4.8 μB in solution, suggesting a high spin state (S = 2) for
Fe(II).