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.
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(III)(Me-TPEN)(eta(1)-OOH)](2+)(1) and the high-spin complex [Fe(III)(Me-TPEN)(eta(2)-O(2))](+)(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)= 1.81A) or side-on peroxo for 2 (r(Fe-O)= 1.99 A). 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(III)(N4Py)(eta(2)-O(2))](+)(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 [Fe(2)(III)(Me-TPEN)(2)(Cl)(2)(mu-O)](2+).
Koehntop
Kevin D
KD
Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA.
Rohde
Jan-Uwe
JU
Costas
Miquel
M
Que
Lawrence
L
D005029:Ethylenediamines / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D019159:Nonheme Iron Proteins / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D013057:Spectrum Analysis
D005029:Ethylenediamines; D008024:Ligands; D019159:Nonheme Iron Proteins; D010545:Peroxides; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine; D010100:Oxygen