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
Koehntop, Kevin D.; Rohde, Jan-Uwe; Costas, Miquel; Que Jr., Lawrence; Koehntop Kevin D.; Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota; Rohde Jan-Uwe; Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota; Costas Miquel; Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota; Department of Chemistry, University of Girona; Que Jr. Lawrence; Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota
Журнал:
Dalton Transactions
Дата:
2004
Аннотация:
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 [Fe<sup>III</sup>(Me-TPEN)(η<sup>1</sup>-OOH)]<sup>2+</sup> (1) and the high-spin complex [Fe<sup>III</sup>(Me-TPEN)(η<sup>2</sup>-O2)]<sup>+</sup> (2) (the neutral pentadentate N-donor ligand Me-TPEN = N-methyl-N,Nâ ²,Nâ ²-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 (rFeâ O = 1.81 â «) or side-on peroxo for 2 (rFeâ O = 1.99 â «). 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 [Fe<sup>III</sup>(N4Py)(η<sup>2</sup>-O2)]<sup>+</sup> (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 [Fe2<sup>III</sup>(Me-TPEN)2(Cl)2(μ-O)]<sup>2+</sup>.
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