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Title: Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

 [1];  [1];  [1]
  1. Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Catalytic Hydrocarbon Functionalization (CCHF)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 137; Journal Issue: 8; Related Information: CCHF partners with University of Virginia (lead); Brigham Young University; California Institute of Technology; Colorado School of Mines; University of Maryland; University of North Carolina, Chapel Hill; University of North Texas; Princeton University; The Scripps Research Institute; Yale University
Country of Publication:
United States
catalysis (homogeneous), catalysis (heterogeneous), bio-inspired, hydrogen and fuel cells, materials and chemistry by design, synthesis (novel materials)

Citation Formats

Boaz, Nicholas C., Bell, Seth R., and Groves, John T. Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer. United States: N. p., 2015. Web. doi:10.1021/ja508759t.
Boaz, Nicholas C., Bell, Seth R., & Groves, John T. Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer. United States. doi:10.1021/ja508759t.
Boaz, Nicholas C., Bell, Seth R., and Groves, John T. 2015. "Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer". United States. doi:10.1021/ja508759t.
title = {Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer},
author = {Boaz, Nicholas C. and Bell, Seth R. and Groves, John T.},
abstractNote = {},
doi = {10.1021/ja508759t},
journal = {Journal of the American Chemical Society},
number = 8,
volume = 137,
place = {United States},
year = 2015,
month = 2
  • Ferryl porphyrins, P–Fe IVmore » $=$O, are central reactive intermediates in the catalytic cycles of numerous heme proteins and a variety of model systems. There has been considerable interest in elucidating factors, such as terminal oxo basicity, that may control ferryl reactivity. Here in this study, the sulfonated, water-soluble ferryl porphyrin complexes tetramesitylporphyrin, oxoFe IVTMPS (FeTMPS-II), its 2,6-dichlorophenyl analogue, oxoFe IVTDClPS (FeTDClPS-II), and two other analogues are shown to be protonated under turnover conditions to produce the corresponding bis-aqua-iron(III) porphyrin cation radicals. The results reveal a novel internal electromeric equilibrium, P–Fe IV$=$O $$\leftrightarrows$$ P +–Fe III(OH 2) 2. Reversible pKa values in the range of 4–6.3 have been measured for this process by pH-jump, UV–vis spectroscopy. Ferryl protonation has important ramifications for C–H bond cleavage reactions mediated by oxoiron(IV) porphyrin cation radicals in protic media. Both solvent O–H and substrate C–H deuterium kinetic isotope effects are observed for these reactions, indicating that hydrocarbon oxidation by these oxoiron(IV) porphyrin cation radicals occurs via a solvent proton-coupled hydrogen atom transfer from the substrate that has not been previously described. The effective FeO–H bond dissociation energies for FeTMPS-II and FeTDClPS-II were estimated from similar kinetic reactivities of the corresponding oxoFe IVTMPS + and oxoFe IVTDClPS + species to be ~92–94 kcal/mol. Similar values were calculated from the two-proton P +–Fe III(OH 2) 2 pK a obs and the porphyrin oxidation potentials, despite a 230 mV range for the iron porphyrins examined. Thus, the iron porphyrin with the lower ring oxidation potential has a compensating higher basicity of the ferryl oxygen. The solvent-derived proton adds significantly to the driving force for C–H bond scission.« less
  • Successive protonation by trifluoroacetic acid of meso-tetraphenylporphyrin derivatives bearing one, two, or four p-dimethylamino groups gives rise to new types of spectra. With one free amino group, the spectrum of the centrally protonated porphyrin shows a strong far-red band, a broad, flat absorption in the visible, and a less intense Soret band. With two or more free amino groups, the Soret band of the centrally protonated porphyrin is further split into two components. Complete protonation, including the peripheral amino groups, in all cases restores the spectral structure of the unsubstituted tetraphenylporphyrin dication. The spectra of the dianions of tetraanilino- andmore » tetraphenylporphyrins are also similar. These results, and the related behavior of p-oxyphenylporphyrins and protonated Schiff base porphyrins, lead to a general interpretation of hyperporphyrin spectra in terms of charge-transfer excited states, involving charge movement either into or out of the porphyrin ring. 26 refs., 4 figs., 2 tabs.« less
  • The association of pentaammineruthenium(II) with the reducible ligand 4,4[prime]-azopyridine leads to a pH-induced redox reaction in which ruthenium is oxidized to the III state, while 4,4[prime]-azopyridine is reduced to hydrazopyridine. In this process, the conjugated ligand is transformed in a nonconjugated one, with loss of its intramolecular electron-transfer properties. In order to exploit this control of an intramolecular electron transfer by a protonation process, the authors have prepared shish kebab oligomers by first inserting a ruthenium chloro carbonyl complex in tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin. The resulting Ru(CO)(porphyrin) complex is photochemically decarbonylated in the presence of bridging ligands (4,4[prime]-azopyridine or pyrazine). Oligomers are thusmore » obtained, which can be oxidized by iodine, giving rise to intervalence transitions between ruthenium(II) and -(III) in the near-infrared. This provides a convenient way to monitor electron transfer along the oligomer chain. In the case of 4,4[prime]-azopyridine, the pH-induced redox reaction is again observed. Starting from a homovalent ruthenium(II) chain, this gives the possibility to switch on or off the intervalence transition by a protonation/deprotonation reaction. 17 refs., 8 figs. 2 tabs.« less
  • PFe{sup II} and PFe{sup III}OH (P is a porphyrin dianion) catalyze the decomposition of tert-butyl hydroperoxide in toluene solution without appreciable attack on the porphyrin ligand. {sup 1}H NMR spectroscopic studies at low temperature ({minus}70{degree}C) give evidence for the formation of a high-spin, five-coordinate intermediate, PFe{sup III}OOC(CH{sub 3}){sub 3}. Organic products formed from this reaction are tert-butyl alcohol, di-tert-butyl peroxide, benzaldehyde, acetone, and benzyl-tert-butyl peroxide, which arise largely from a radical chain process initiated by the iron porphyrin but continuing without its intervention.