Iron Chemistry of a Pentadentate Ligand That Generates a Metastable Fe(III)-OOH Intermediate

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

doi:10.1021/ic980983p

Iron Chemistry of a Pentadentate Ligand That Generates a Metastable Fe(III)-OOH Intermediate

Inorg Chem. 1999 Apr 19;38(8):1929-1936. doi: 10.1021/ic980983p.

Authors

Gerard Roelfes¹, Marcel Lubben, Kui Chen, Raymond Y. N. Ho, Auke Meetsma, Susan Genseberger, Roel M. Hermant, Ronald Hage, Sanjay K. Mandal, Victor G. Young Jr, Yan Zang, Huub Kooijman, Anthony L. Spek, Lawrence Que Jr, Ben L. Feringa

Affiliation

¹ Department of Organic and Molecular Inorganic Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, Unilever Research Laboratory, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands, and Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands.

PMID: 11670967
DOI: 10.1021/ic980983p

Abstract

In an effort to gain more insight into the factors controlling the formation of low-spin non-heme Fe(III)-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-pyridylmethyl)-N-(bis-2-pyridylmethyl)amine). The following complexes have been prepared: [(N4Py)Fe(II)(CH(3)CN)](ClO(4))(2) (1), [(N4Py)Fe(II)Cl](ClO(4)) (2), [(N4Py)Fe(III)OMe](ClO(4))(2) (3), and [(N4Py)(2)Fe(2)O](ClO(4))(4) (4). Complexes 1 and 2 have low- and high-spin Fe(II) centers, respectively, whereas 3 is an Fe(III) 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 Fe(II) and Fe(III) in either spin state. For the high-spin Fe(III) 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 Fe(II) 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 H(2)O(2) to generate the purple low-spin [(N4Py)Fe(III)OOH](2+) intermediate (6). In the case of 1, titration experiments with H(2)O(2) monitored by UV/vis and (1)H NMR reveal the formation of [(N4Py)Fe(III)OH](2+) (5) and the oxo-bridged diiron(III) dimer (4) prior to the generation of the Fe(III)-OOH species (6). Raman spectra of 6 show distinctive Raman features, particularly a nu(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 Fe(III)-OOH species such as "activated bleomycin".