Structural Insights into Nonheme Alkylperoxoiron(III) and Oxoiron(IV) Intermediates by X-ray Absorption Spectroscopy

Transient mononuclear low-spin alkylperoxoiron(III) and oxoiron(IV) complexes that are relevant
to the activation of dioxygen by nonheme iron enzymes have been generated from synthetic iron(II)
complexes of neutral tetradentate (TPA) and pentadentate (N4Py, Bn-TPEN) ligands and structurally
characterized by means of Fe K-edge X-ray absorption spectroscopy (XAS). Notable features obtained
from fits of the EXAFS region are Fe−O bond lengths of 1.78 Å for the alkylperoxoiron(III) intermediates
and 1.65−1.68 Å for the oxoiron(IV) intermediates, reflecting different strengths in the Fe−O π interactions.
These differences are also observed in the intensities of the 1s-to-3d transitions in the XANES region,
which increase from 4 units for the nearly octahedral iron(II) precursor to 9−15 units for the alkylperoxoiron(III) intermediates to 25−29 units for the oxoiron(IV) species.

针对非血红素铁酶催化双氧水分解相关的瞬态单核低自旋烷基过氧铁(III)和氧化铁(IV)配合物，已从合成铁(II)的中性四齿配体（TPA）和五齿配体（N4Py，Bn-TPEN）配合物中生成，并通过Fe K边X射线吸收光谱（XAS）对其结构进行了表征。从EXAFS区域拟合中获得的显著特征包括烷基过氧铁(III)中间体的Fe−O键长为1.78 Å，氧化铁(IV)中间体的Fe−O键长为1.65−1.68 Å，这些差异反映了Fe−O π相互作用的强度不同。这些差异同样在XANES区域的1s至3d跃迁强度中得以体现，从近乎八面体的铁(II)前驱体的4单位增加至烷基过氧铁(III)中间体的9−15单位，再到氧化铁(IV)物种的25−29单位。