Iron chemistry of a pentadentate ligand that generates a metastable FeIII-OOH intermediate

Gerard Roelfes, Marcel Lubben, Kui Chen, Raymond Y.N. Ho, Auke Meetsma, Susan Genseberger, Roel M. Hermant, Ronald Hage, Sanjay K. Mandai, Victor G. Young, Yan Zang, Huub Kooijman, Anthony L. Spek, Lawrence Que, Ben L. Feringa

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181 Scopus citations


In an effort to gain more insight into the factors controlling the formation of low-spin non-heme FeIII-peroxo intermediates in oxidation catalysis, such as activated bleomycin, we have synthesized a series of iron complexes based on the pentadentate ligand N4Py (N4Py = N,N-(bis-2-pyridyImethyl)-N-(bis-2-pyridylmethyl)amine). The following complexes have been prepared: [(N4Py)FeII(CH3CN)](ClO4)2 (1), [(N4Py)FeIICl](ClO4) (2), [(N4Py)-FeIIIOMe](ClO4)2 (3), and [(N4Py)2Fe2O](ClO4)4 (4). Complexes 1 and 2 have low- and high-spin FeII centers, respectively, whereas 3 is an FeIII complex that undergoes a temperature-dependent spin transition. The iron centers in the oxo-bridged dimer 4 are antiferromagnetically coupled (J = -104 cm-1)- Comparison of the crystal structures of 1, 3, and 4 shows that the ligand is well suited to accommodate both FeII and FeIII in either spin state. For the high-spin FeIII complexes 3 and 4 the iron atoms are positioned somewhat outside of the cavity formed by the ligand, while in the case of the low-spin FeII complex 1 the iron atom is retained in the middle of the cavity with approximately equal bond lengths to all nitrogen atoms from the ligand. On the basis of UV/vis and EPR observations, it is shown that 1, 3, and 4 all react with H2O2 to generate the purple low-spin [(N4Py)-FeIIIOOH]2+ intermediate (6). In the case of 1, titration experiments with H2O2 monitored by UV/vis and 1H NMR reveal the formation of [(N4Py)FeIIIOH]2+ (5) and the oxo-bridged diiron(III) dimer (4) prior to the generation of the FeIII-OOH species (6). Raman spectra of 6 show distinctive Raman features, particularly a v(O-O) at 790 cm-1 that is the lowest observed for any iron-peroxo species. This observation may rationalize the reactivity of low-spin FeIII-OOH species such as "activated bleomycin".

Original languageEnglish (US)
Pages (from-to)1929-1936
Number of pages8
JournalInorganic chemistry
Issue number8
StatePublished - 1999


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