Oxygenation patterns for iron(II) porphyrins. Peroxo and ferryl (FeIVO) intermediates detected by proton nuclear magnetic resonance spectroscopy during the oxygenation of (tetramesitylporphyrin)iron(II)

Abstract

7779such as 2 are expected to be the most sensitive of aromatics to ring current effects, for normal biphenyl-type aromatics interaction between the rings will be more readily observed through UV spectra than nuclear magnetic resonance data. Experimental Section'H NMR spectra were determined in CDCI, on a Perkin-Elmer R32 (90 MHz) spectrometer and are reported in parts per million downfield from tetramethylsilane as internal standard. UV spectra were determined in cyclohexane on a Cary 17 spectrophotometer. Mass spectra were determined on a Hitachi Perkin-Elmer RMU-7 (high-resolution) or Finnigan 3300 (low-resolution) mass spectrometer at 70 eV. Microanalyses were performed by this department and by Canadian Microanalytical services Ltd. All evaporations were carried out under reduced pressure on a rotary evaporator at ca. 40 OC. Extracts were dried with anhydrous sodium sulfate.Bi(2,Z'-tmns -lob, 10c-dimethyl-lob, l0c-dihydropyrenyl) (2). A solution of n-butyllithium (0.2 mmol in hexane, 0.1 mL) was added under N, to a stirred solution of 2-bromo-~rans-10b,10c-dimethyl-1Ob,10c-dihydropyrene (5)e (50 mg, 0.16 mmol) in dry ether (2 mL) in a flamed flask. After 5 min this solution was added under N2 to a slurry of TlBr (0.08 g, 0.3 mmol) in benzene (2 mL) and ether (2 mL). The mixture was then heated under reflux with stirring for 4 h. It was then cooled, poured into water, and extracted with dichloromethane. The extract was washed, dried, and evaporated and the residue was chromatographed over silica gel. Pentane eluted first the green dimethyldihydropyrene 4, ca. 10 mg, and then the purple bipyrene 2, 13 mg (35% yield), as very dark greenish black crystals from methanol that formed purple solutions; mp ca. 195-199 OC dec; 'H NMR 8 9.46 (s, 4 H, H-1,3), 8.8-8.5 (m, 14 H, other ArH), -3.68 and -3.77 (s, 6 H each, CH,); MS, Mt. at m / e 462 402 (M -4CH3, 55) plus many doubly charged ions; UV A,, (log e,,,) 577 nm (4.20), 544 (sh, 4.13), 480 (sh, 3.80) 436 (3.83), 400 (4.12), 368 (4.72), 345 (4.42), 332 (sh, 4.35). Anal. Calcd for C,,H,,,: C, 93.46; H, 6.54; mol wt., 462.23. Found: C, 92.91; H, 6.06; mol wt, 462.24 (MS). When anhydrous CoC1, (0.8 g) was used as oxidant (reflux, 4 h) from bromide 5 (800 mg), there was obtained bipyrene 2 (1 50 mg, 25% yield), identical with the above sample. trans-10b,10c-Dimethyl-2-phenyl-lOb,lOc-dihydropyrene (3). A solution of phenyllithium (3.2 mmol in hexane 1.8 mL) was added to a (24%), 447 (M -CH,, 38), 432(M -2CH3, 26), 417 (M -3CH3 IOO),stirred slurry of CuBr (0.23 g 1.6 mmol) in dry ether (5 mL) at 0 OC under N,. After 30 min the solution was allowed to warm to ca. 20 OC and a solution of the bromodihydropyrene 58 (100 mg, 3.2 mmol) in dry ether (5 mL) was added. The mixture was kept at ca. 20 OC for 8 days. Nitrobenzene (0.2 mL) was then added and stirring maintained for ca. 15 min, after which the mixture was poured into water and extracted with dichloromethane. The extract was washed, dried, and evaporated, and the residue was chromatographed over silica gel using pentane...

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

“…This is most certainly due to the increased stability ofhigh-valent metals when bound to highly basic oxo ligands. The reactivity of the iron(IV)-oxo species generated electrochemically is very similar to that reported for the iron(IV)-oxo species produced chemically (25)(26)(27)(28). The decomposition of the iron(IV)-oxo porphyrin at temperatures above -50'C shows that it is more chemically reactive than the iron(III) porphyrin ir-cation radical, even though the redox potential of the latter is more positive.…”

Pulsed EPR and NMR Spectroscopy of Paramagnetic Iron Porphyrinates and Related Iron Macrocycles: How To Understand Patterns of Spin Delocalization and Recognize Macrocycle Radicals

“…It should be noted that the pyrrole-H chemical shift (-63 ppm at -60°C, Table 1) 66 of this complex is much more negative than that for the bis(methoxide) complex discussed in the previous paragraph, suggesting a different electron configuration for the phenyl complex, i.e., ( 69 A similar pattern is observed for the N-methylimidazole adduct of this species (Table 1). 69 This pattern of small upfield shifts for both types of protons is unlike that predicted for any distribution of metal d electrons, and it likely results from most of the spin density being delocalized to the oxo group, rather than the porphyrin ring. In fact, theoretical calculations of some 20 years ago indicated that the small upfield nature of both pyrrole-H and meso-H isotropic shifts is consistent with most of the spin density being on the oxo group.…”

“…71,72 Hence, in terms of observed chemical shifts, the 1 H NMR spectra of oxoiron-(IV) porphyrinates behave more like diamagnetic d 6 Fe(II) bound to a six-electron (two unpaired) oxygen atom, rather than paramagnetic d 4 Fe(IV) centers. [67][68][69][70][71][72] …”

Durene-capped porphyrins: synthesis and characterization

“…Second, coordination of oxygen to the five coordinate species at room temperature leads rapidly and irreversibly to the formation of bridged 0x0-iron(II1) species (2,3). Autoxidation of the iron centre proceeds via the initial formation of a monomeric iron-dioxygen adduct, followed by the reaction with a second iron(I1) porphyrin unit (4).…”