Monomeric and Dimeric Iron(III) Complexes of 5‐Hydroxy‐10,15,20‐triphenylporphyrin: Formation of Cyano and Pyridine Complexes of (5‐Oxo‐10,15,20‐triphenylphlorin)iron

Abstract

The reaction of [(TrPP)FeII(py)2] (TrPP = dianion of 5,10,15‐triphenylporphyrin) with hydrogen peroxide results in oxygenation of the (porphyrin)iron and the formation of (10,15,20‐triphenyl‐5‐oxophlorin)iron [(5‐O‐TrPP)Fe(py)2]. Coupled oxidation of [(TrPP)FeIIICl] in the presence of ascorbic acid and potassium cyanide in methanol leads to oxidative hydroxylation of the porphyrin ring to form a cyclic dimer [(5‐O‐TrPP)FeIII]2. Three out of four pyrrole 1H NMR resonances of the dimeric complex present the characteristic displacement with respect to the typical position for the high‐spin (tetraphenylporphyrin)iron(III) complexes. The linewidths of the β‐H pyrrole resonances correlate with specific locations of the respective protons within the dimeric structure. Addition of HCl to [(5‐O‐TrPP)FeIII]2 results in cleavage of the dimer producing [(5‐OH‐TrPP)FeIIICl]. [(5‐O‐TrPP)FeIII]2 is also split with acetic anhydride to give (5‐acetoxy‐10,15,20‐triphenylporphyrin)iron(III). In the presence of [D5]pyridine or a large excess of cyanide ion, [(5‐O‐TrPP)FeIII]2 undergoes cleavage to form air‐sensitive [(5‐O‐TrPP)Fe(py)2] or [(5‐O‐TrPP)Fe(CN)2]2−. The pyrrole pattern observed for [(5‐O‐TrPP)Fe(py)2] is similar to that determined on the basis of an analysis carried out for four (oxophlorin)iron regioisomers obtained from hemes. For comparison, the characteristic 1H NMR features of the typical (5‐substituted‐10,15,20‐triphenylporphyrin)iron(III) complexes have been investigated for the series of high‐spin and low‐spin complexes. The spin‐density distribution in the (oxophlorin)iron skeleton is dominated by the radical‐like electronic structure. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Weak Interactions and Conformational Changes in Core-Protonated A2- and Ax-Type Porphyrin Dications

“…These compounds are listed in Table S1.2 , and generally exhibit less pronounced 5,15-stretching (anisotropy) to that observed for 5,15-diarylporphyrins. The crystal structure of the free base parent compound of this class, 5,10,15-triphenylporphyrin has been reported previously [ 51 ].…”

Nickel(II)meso‐Hydroxyporphyrin Complexes Revisited: Palladium‐Catalysed Synthesis, Electronic Structures of Derived Oxy Radicals, and Oxidative Coupling to a Dioxoporphodimethene Dyad

“…Despite these many studies of hydroxylated octaalkylporphyrinato species, reports of metal complexes of meso ‐hydroxyporphyrins derived from porphyrins that are unsubstituted at the eight peripheral β carbon atoms and have one or more free meso carbon atoms are rare. In 2002, Latos‐Grażyński and co‐workers reported the oxidation of an iron(II) complex of 5,10,15‐triphenylporphyrin (H 2 TriPP), namely [Fe(TriPP)(py) 2 ], to paramagnetic 5‐oxo‐10,15,20‐triphenylphlorinato iron(III) with coordinated [D 5 ]pyridine ligands . In 2014, Lucas and co‐workers reported the formation of a 5‐hydroxytriarylporphyrin nickel(II) complex by anodic nucleophilic substitution of a nickel(II) triarylporphyrin; they also noted the difficulty of obtaining a 1 H NMR signal due to the presence of the oxy radical .…”

Gold(III) Triggered Transformations of 22‐Methyl‐m‐benziporphyrin Involving an Effective Contraction of Benzene to Cyclopentadiene

“…The position of the tautomeric equilibrium in metal‐free meso ‐hydroxyporphyrin lies preferably on the keto (oxophlorin) side but acquires 5‐hydroxyporphyrin structure after protonation . Both tautomers have been identified after insertion of metal ions depending on the metal ion oxidation state and axial ligations …”