Formation of stable and metastable porphyrin- and corrole-iron(IV) complexes and isomerizations to iron(III) macrocycle radical cations

Abstract

Oxidations of three porphyrin-iron(III) complexes (1) with ferric perchlorate, Fe(ClO 4 ) 3 , in acetonitrile solutions at −40 °C gave metastable porphyrin-iron(IV) diperchlorate complexes (2) that isomerized to known iron(III) diperchlorate porphyrin radical cations (3) when the solutions were warmed to room temperature. The 5,10,15,5,10,15,and 2,3,7,8,12,13,17, systems were studied by UV-visible spectroscopy. Low temperature NMR spectroscopy and effective magnetic moment measurements were possible with the TPP and TMP iron(IV) complexes. Reactions of two corrole systems, 5,10,15-tris(pentafluorophenyl)corrole (TPFC) and 5,15-bis (pentafluorophenyl)-10-p-methoxyphenylcorrole (BPFMC), also were studied. The corrole-iron(IV) chlorides reacted with silver salts to give corrole-iron(IV) complexes. The corrole-iron(IV) nitrate complexes were stable at room temperature. (TPFC)-iron(IV) toslyate, (TPFC)-iron(IV) chlorate, and (BPFMC)-iron(IV) chlorate were metastable and rearranged to their electronic isomers iron(III) corrole radical cations at room temperature. (TPFC)-iron(III) perchlorate corrole radical cation was the only product observed from reaction of the corrole-iron(IV) chloride with silver perchlorate. For the metastable iron(IV) species, the rates of isomerizations to the iron(III) macrocycle radical cation electronic isomers in dilute acetonitrile solutions were relatively insensitive to electron demands of the macrocyclic ligand but reflected the binding strength of the ligand to iron. Kinetic studies at varying temperatures and concentrations indicated that the mechanisms of the isomerization reactions are complex, involving mixed order reactivity.

Binding of Catechols to Iron(III)–Octaethylporphyrin: An Experimental and DFT Investigation

“…Figure 11 shows the UV/Vis spectral change of Fe III (OEP)(4‐NO 2 ‐Hcat) upon oxidation at a constant potential of 1.28 V, in which the Soret band at 386 nm blueshifts to 357 nm with a decrease in intensity and generates a porphyrin dication, [Fe III (OEP)(L)] ++ , which is confirmed by DFT. These spectral changes are characteristic of the presence of a porphyrin π‐cation radical 23. Similar spectral features are also observed during the controlled oxidations of the other complexes reported here.…”

Spin–spin interactions in iron(III) porphyrin radical cations with ruffled and saddled structure

“…We not the pure (d xz , d yz ) 3 (d xy ) 1 (d z 2) 1 but the mixed (d xz , d yz ) 3 (d xy ) 1 (d z 2) 1 and (d xy ) 2 (d xz , d yz ) 2 (d z 2) 1 states [40]. We have also reported that [Fe(T i PrP)(PhCHO) 2 ](ClO 4 ) having the axial ligand with lowlying π* orbital adopts much purer (d xz , d yz ) 3 (d xy ) 1 (d z 2) 1 ground state on the basis of the 1 H NMR, 13 C NMR, and EPR spectroscopy although minor contribution from the (d xy ) 2 (d xz , d yz ) 2 (d z 2) 1 state is not negligibly small [41]. The stability of the (d xy ) 2 (d xz , d yz ) 2 (d z 2) 1 ground state in radical cationic Fe(T i PrP•)(ClO 4 ) 2 can be explained in terms of the weaker field-strength of pyrrole nitrogens as compared with those of parent Fe(T i PrP)(ClO 4 ).…”

“…To our knowledge, the bis-methoxo complex, [Fe IV (TMP)(OMe) 2 ], is the only example that is well characterized [8]. As for the iron(III) porphyrin radical cations, there are ample examples where the iron(III) ions adopt highspin (S = 5/2), low-spin (S = 1/2), or mixed high-and intermediatespin (S = 3/2, 5/2) states [9][10][11][12][13]. However, there is no example of the iron(III) radical cation where the iron(III) ion adopts a pure intermediate-spin state.…”

Grafting Copper and Gallium Corroles onto Zinc Oxide Nanoparticles

“…[1][2][3] These pyrrole-based macrocycles have demonstrated impressive synthetic versatility, allowing a fine tunability of their photophysical properties. [4][5][6][7][8][9] In order to improve the harvesting of solar energy in a broad spectral region, it is important to extend the corrole energy absorption across the visible spectrum as much as possible. As already documented, β-pyrrolic modification and extension of the porphyrin π system significantly broadens and redshifts the light absorption.…”

“…Over the last few years corroles have proved to be outstanding light‐harvesting materials, on surfaces or for solar cells . These pyrrole‐based macrocycles have demonstrated impressive synthetic versatility, allowing a fine tunability of their photophysical properties …”