Oxygen-containing mononuclear iron species—iron(iii)–peroxo, iron(iii)–hydroperoxo and iron(iv)–oxo—are key intermediates in the catalytic activation of dioxygen by iron-containing metalloenzymes1,2,3,4,5,6,7. It has been difficult to generate synthetic analogues of these three active iron–oxygen species in identical host complexes, which is necessary to elucidate changes to the structure of the iron centre during catalysis and the factors that control their chemical reactivities with substrates. Here we report the high-resolution crystal structure of a mononuclear non-haem side-on iron(iii)–peroxo complex, [Fe(iii)(TMC)(OO)]+. We also report a series of chemical reactions in which this iron(iii)–peroxo complex is cleanly converted to the iron(iii)–hydroperoxo complex, [Fe(iii)(TMC)(OOH)]2+, via a short-lived intermediate on protonation. This iron(iii)–hydroperoxo complex then cleanly converts to the ferryl complex, [Fe(iv)(TMC)(O)]2+, via homolytic O–O bond cleavage of the iron(iii)–hydroperoxo species. All three of these iron species—the three most biologically relevant iron–oxygen intermediates—have been spectroscopically characterized; we note that they have been obtained using a simple macrocyclic ligand. We have performed relative reactivity studies on these three iron species which reveal that the iron(iii)–hydroperoxo complex is the most reactive of the three in the deformylation of aldehydes and that it has a similar reactivity to the iron(iv)–oxo complex in C–H bond activation of alkylaromatics. These reactivity results demonstrate that iron(iii)–hydroperoxo species are viable oxidants in both nucleophilic and electrophilic reactions by iron-containing enzymes.
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The crystallographic data for 1 have been deposited with the Cambridge Crystallographic Data Center under accession number CCDC 804038.
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The work was supported by NRF/MEST of Korea through the CRI (W.N.), the GRL (2010-00353; W.N.), the WCU (R31-2008-000-10010-0; W.N. and J.S.V.) and the 2011 KRICT OASIS Project (W.N.), by NIH grants GM 40392 (E.I.S.) and RR-001209 (K.O.H.), and by NSF grant MCB 0919027 (E.I.S.). J.J.B. acknowledges a Fellowship from NSF EAPSI (OISE-1014685) and the Warner Linfield Award from the University of Michigan. SSRL operations are funded by the Department of Energy (DOE) Office of Science and operated by Stanford University. The SSRL Structural Molecular Biology programme is supported by the DOE, Office of Biological and Environmental Research, and by the NIH, National Center for Research Resources (grant 5P41RR001209), Biomedical Technology Program.
The authors declare no competing financial interests.
This file contains a Supplementary Experimental Section, Supplementary Results and Discussion, Supplementary Acknowledgements, Supplementary References, Supplementary Tables 1-8 and Supplementary Figures 1-23 with legends (see Contents for full details). (PDF 2931 kb)
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Cho, J., Jeon, S., Wilson, S. et al. Structure and reactivity of a mononuclear non-haem iron(III)–peroxo complex. Nature 478, 502–505 (2011). https://doi.org/10.1038/nature10535
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