Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.
Proc Natl Acad Sci U S A. 2012 Jul 24;109(30):11933-8. doi: 10.1073/pnas.1206457109. Epub 2012 Jul 11.
Oxoiron(V) species are postulated to be involved in the mechanisms of the arene cis-dihydroxylating Rieske dioxygenases and of bioinspired nonheme iron catalysts for alkane hydroxylation, olefin cis-dihydroxylation, and water oxidation. In an effort to obtain a synthetic oxoiron(V) complex, we report herein the one-electron oxidation of the S = 1 complex Fe(IV)(O)(TMC)(NCCH(3)) (1, where TMC is tetramethylcyclam) by treatment with tert -butyl hydroperoxide and strong base in acetonitrile to generate a metastable complex 2 at -44 °C, which has been characterized by UV-visible, resonance Raman, Mössbauer, and EPR methods. The defining spectroscopic characteristic of 2 is the unusual x/y anisotropy observed for the (57)Fe and (17)O A tensors associated with the high-valent Fe═O unit and for the (14)N A tensor of a ligand derived from acetonitrile. As shown by detailed density functional theory (DFT) calculations, the unusual x/y anisotropy observed can only arise from an iron center with substantially different spin populations in the d(xz) and d(yz) orbitals, which cannot correspond to an Fe(IV)═O unit but is fully consistent with an Fe(V) center, like that found for Fe(V)(O)(TAML) (where TAML is tetraamido macrocyclic ligand), the only well-characterized oxoiron(V) complex reported. Mass spectral analysis shows that the generation of 2 entails the addition of an oxygen atom to 1 and the loss of one positive charge. Taken together, the spectroscopic data and DFT calculations support the formulation of 2 as an iron(V) complex having axial oxo and acetylimido ligands, namely Fe(V)(O)(TMC)(NC(O)CH(3)).
氧代铁（V）物种被认为参与芳基顺式二羟基化 Rieske 双氧酶和生物启发的非血红素铁催化剂的反应机制，用于烷烃羟化、烯烃顺式二羟基化和水氧化。为了获得合成的氧代铁（V）配合物，我们在此报告通过用叔丁基过氧化氢和强碱在乙腈中处理 S = 1 配合物 [Fe（IV）（O）（TMC）（NCCH（3））]（2+）（1，其中 TMC 是四甲基环酰胺）来进行单电子氧化，在-44°C 下生成亚稳配合物 2，其通过 UV-可见、共振拉曼、穆斯堡尔和 EPR 方法进行了表征。2 的定义性光谱特征是与高价 Fe═O 单元相关的（57）Fe 和（17）O A 张量以及源自乙腈的配体的（14）N A 张量的不寻常的 x/y 各向异性，这是由详细的密度泛函理论（DFT）计算表明，观察到的不寻常的 x/y 各向异性只能来自于铁中心在 d（xz）和 d（yz）轨道中具有显着不同自旋密度的铁中心，这不能对应于 Fe（IV）═O 单元，但与 Fe（V）中心完全一致，就像在 [Fe（V）（O）（TAML）]-（其中 TAML 是四氨大环配体）中发现的那样，这是唯一报道的结构良好的氧代铁（V）配合物。质谱分析表明，2 的生成需要 1 中添加一个氧原子并失去一个正电荷。综合光谱数据和 DFT 计算支持 2 的化学式为具有轴向氧代和乙酰亚胺配体的铁（V）配合物，即 [Fe（V）（O）（TMC）（NC（O）CH（3））]（+）。
