Chemistry of iron oxophlorins. 2. Oxidation of the iron(III) octaethyloxophlorin dimer and observation of stepwise, two-electron oxidation of the oxophlorin macrocycle

Oxophlorin and Metallooxophlorin Radicals—DFT Studies

“…)Fe III X (X Cl, Br, CF 3 COO) are consistent with an electronic structure where high-spin iron(III ) is strongly antiferromagnetically coupled to the unpaired electron of oxophlorin to give an S 2 ground electronic state. [12,13] Thus, two meso-resonances shifted remarkably downfield (345 and 245 ppm), and four a-CH 2 resonances shifted downfield and four upfield. Generally, the spectrum (presented schematically in trace C of Figure 7) can be considered as the mirror image of the previously described iron oxophlorin spectra (Figure 7, trace A).…”

“…)Fe III X. [12] The C(5)ÀO distances correspond to a carbonyl-like structure. [2,7] In contrast, the C(5)ÀO distance in [(5-OHÀP .…”

“…The figure is based on the experimental spectra measured at room temperature. [12,30,34] Only the most characteristic resonances are shown. Their labeling follows the numbering shown in Scheme 1.…”

“…)Fe III X (X Cl, Br). [12,13] 1 H NMR spectroscopy provides a uniquely useful probe for studying the structure of iron oxophlorin radicals in solution, as the hyperfine shift patterns are particularly sensitive to the spin, ligation, and oxidation state of the metal ion. [1, 17, 27, 29±35] Density functional theory (DFT) and ab initio calculations have been applied to porphyrins, porphyrin isomers, metalloporphyrins, and related systems.…”

NMR Studies of Paramagnetic Metallocarbaporphyrinoids

“…[21][22][23] Recently, octaethylporphyrin degradation (coupled oxidation) has been explored in order to establish the reactivity of iron complexes in various stages of heme degradation. [24][25][26][27][28][29][30][31][32][33][34][35] For instance, the paramagnetic shift patterns for the model iron octaethylbiliverdin-related radical complexes present several useful probes for detecting analogous species in hemoproteins by 1 H NMR spectroscopy. [35] Recent progress in the 1 H NMR spectroscopic characterization of paramagnetic hemoproteins is related to the search for suitable spectroscopic models that involve the synthesis of fine-tuned iron porphyrins.…”