Direct incorporation of a ferric ion in the porphyrinogen core: Tetrakis(cyclohexyl)iron porphyrinogen anion with different conformers and its reaction with iodine

Abstract

Et₄N[L"Fe^III]·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 (μ eff) of 4.3 μ B in the solid, which changed to 6.0 μ B 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"Fe^III]·DCM_0.5Py_1.5 (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"Δ Δ ·Fe^III][I₃·I₂+·I₃¯ ] (3) with the introduction of two Cα -Cα bonds with concomitant reduction of Fe(III) to Fe(II). Its μ eff (5.4 μ B) in the solid changed to 4.8 μ B in solution, suggesting a high spin state (S = 2) for Fe(II).