Axial ligation of iron(III) porphyrin with a series of aliphatic bases: Piperazine, Piperidine and Pyrrolidine

The binding of a series of nitrogen donor ligands (Piperazine (Pipz), Piperidine (Pip) and Pyrrolidine (Pyr)) to iron porphyrin, OEPFeClO₄, where OEP is octaethylporphyrin, has been characterized by electronic spectroscopy in CH₂Cl₂. In nonaqueous media, in the presence of a neutral ligand, the equilibria observed are: OEPFeClO₄ + 2L ⇆ OEPFeL₂]⁺ ClO₄⁻ (β₂) where the product is an ion pair and in some cases: OEPFeClO₄ + L ⇆ OEPFeLClO₄ (K ₁), where the product may either be the six-coordinate or the five-coordinate OEPFeL]⁺ ClO₄⁻ ion pair, that L denotes neutral N-donor ligands. This behavior for the nitrogen donor ligands (L = Pipz, Pip, Pyr) is confirmed by spectrophotometric titrations data and the binding constants for the substitution reaction have been reported.