End-on and side-on peroxo derivatives of non-heme iron complexes with pentadentate ligands:: Models for putative intermediates in biological iron/dioxygen chemistry
End-on and side-on peroxo derivatives of non-heme iron complexes with pentadentate ligands:: Models for putative intermediates in biological iron/dioxygen chemistry
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DOI：
10.1021/ic034065p
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发表时间：
2003-04-21
影响因子：
4.6
通讯作者：
Que, L
中科院分区：
文献类型：
--
作者：
Roelfes, G;Vrajmasu, V;Que, L
在抗肿瘤药物博莱霉素和多种酶（如细胞色素 P450 和 Rieske 双加氧酶）的催化循环中，已提出或鉴定出具有端接和侧接过氧化物的单核铁 (III) 物质。直到最近，才在低温下生成并表征了此类反应物质的仿生类似物。我们报道了一系列具有五齿 N5 配体的铁 (II) 配合物的合成和表征，这些配合物与 H2O2 反应生成瞬时低自旋 Fe-III-OOH 中间体。这些中间体具有低自旋铁 (III) 中心，在 500-600 nm 区域表现出氢过氧到铁 (III) 的电荷转移带。它们的共振拉曼频率 nu(O-O) 在 800 cm(-1) 附近，明显低于高自旋对应物观察到的共振拉曼频率。随着 N5 配体的电子供给能力增强，氢过氧到铁 (III) 的电荷转移跃迁发生蓝移，并且 Fe-OOH 单元的 nu(O-O) 减少。因此，增加低自旋 Fe(III) 中心的电子密度会削弱 O-O 键，根据已发表的 DFT 计算得出的结论，该系列中的母体 [(N4Py)Fe-III(eta(1)-OOH)](2+) (1a) 离子 (N4Py = NN-双(2-吡啶基甲基)-N-双(2-吡啶基)甲胺）可以转化为其共轭碱，这被证明是具有侧过氧配体的高自旋铁 (III) 配合物 [(N4Py)Fe-III(eta(2)-O-2)](+) (1b)。通过 EPR 和穆斯堡尔光谱对 1a 和 1b 进行详细分析，深入了解它们的电子特性。观察到的 1 a 的 Fe-57 A 张量的方向可以用常用的格里菲斯模型来解释，前提是配体场的菱形分量（由氢过氧配体的配置决定）相对于八面体场旋转 45 度。 la 和 1b 的 EXAFS 研究揭示了该络合物家族中铁过氧单元的第一个计量细节：[(N4Py)Fe-III(eta(1)-OOH)](2+) 具有 1.76 埃的 Fe-O 键，而 [(N4Py)Fe-III(eta(2)-O-2)]- 具有两个 1.93 埃的 Fe-O 键，值在与 DFT 计算得到的结果非常吻合。
Mononuclear iron(III) species with end-on and side-on peroxide have been proposed or identified in the catalytic cycles of the antitumor drug bleomycin and a variety of enzymes, such as cytochrome P450 and Rieske dioxygenases, Only recently have biomimetic analogues of such reactive species been, generated and characterized at low temperatures. We report the synthesis and characterization of a series of iron(II) complexes with pentadentate N5 ligands that react with H2O2 to generate transient low-spin Fe-III-OOH intermediates. These intermediates have low-spin iron(III) centers exhibiting hydroperoxo-to-iron(III) charge-transfer bands in the 500-600-nm region. Their resonance Raman frequencies, nu(O-O), near 800 cm(-1) are significantly lower than those observed for high-spin counterparts. The hydroperoxo-to-iron(III) charge-transfer transition blue-shifts and the nu(O-O) of the Fe-OOH unit decreases as the N5 ligand becomes more electron donating. Thus, increasing electron density at the low-spin Fe(III) center weakens the O-O bond, in accord with conclusions drawn from published DFT calculations, The parent [(N4Py)Fe-III(eta(1)-OOH)](2+) (1a) ion in this series (N4Py = NN-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) can be converted to its conjugate base, which is demonstrated to be a high-spin iron(III) complex with a side-on peroxo ligand, [(N4Py)Fe-III(eta(2)-O-2)](+) (1b). A detailed analysis of 1a and 1b by EPR and Mossbauer spectroscopy provides insights into their electronic properties. The orientation of the observed Fe-57 A-tensor of 1 a can be explained with the frequently employed Griffith model provided the rhombic component of the ligand field, determined by the disposition of the hydroperoxo ligand, is 45degrees rotated relative to the octahedral field. EXAFS studies of la and 1b reveal the first metrical details of the iron-peroxo units in this family Of complexes: [(N4Py)Fe-III(eta(1)-OOH)](2+) has an Fe-O bond of 1.76 Angstrom, while [(N4Py)Fe-III(eta(2)-O-2)]- has two Fe-O bonds of 1.93 Angstrom, values which are in very good agreement with results obtained from DFT calculations.