XAS characterization of end-on and side-on peroxoiron(iii) complexes of the neutral pentadentate N-donor ligand N-methyl-N, N′, N′-tris(2-pyridylmethyl)ethane-1,2-diamine

Kevin D. Koehntop, Jan Uwe Rohde, Miquel Costas, Lawrence Que

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22 Scopus citations

Abstract

Peroxo intermediates are implicated in the catalytic cycles of iron enzymes involved in dioxygen metabolism. X-ray absorption spectroscopy has been used to gain insight into the iron coordination environments of the low-spin complex [FeIII(Me-TPEN)(η1-OOH)]2+(1) and the high-spin complex [FeIII(Me-TPEN)(η2-O2)]+(2) (the neutral pentadentate N-donor ligand Me-TPEN = N-methyl-N, N′, N′-tris(2-pyridylmethyl)ethane-1,2-diamine) and obtain metrical parameters unavailable from X-ray crystallography. The complexes exhibit relatively large pre-edge peak areas of approximately 15 units, indicative of iron centers with significant distortions from centrosymmetry. These distortions result from the binding of peroxide, either end-on hydroperoxo for 1 (r Fe–O= 1.81 Å) or side-on peroxo for 2 (r Fe–O= 1.99 Å). The XAS analyses of 1 strongly support a six-coordinate low-spin iron(iii) center coordinated to five nitrogen atoms from Me-TPEN and one oxygen atom from an end-on hydroperoxide ligand. However, the XAS analyses of 2 are not conclusive: Me-TPEN can act either as a pentadentate ligand to form a seven-coordinate peroxo complex, which has precedence in the DFT geometry optimization of [FeIII(N4Py)(η2-O2)]+(the neutral pentadentate N-donor ligand N4Py = N, N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), or as a tetradentate ligand with a dangling pyridylmethyl arm to form a six-coordinate peroxo complex, which is precedented by the crystal structure of [Fe2III(Me-TPEN)2(Cl)2(μ-O)]2+.

Original languageEnglish (US)
Pages (from-to)3191-3198
Number of pages8
JournalJournal of the Chemical Society. Dalton Transactions
Volume4
Issue number20
DOIs
StatePublished - Oct 14 2004

Keywords

  • Bioinorganic chemistry
  • Iron
  • X-ray absorption spectroscopy

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