The crystal structure of a high-spin oxoiron(IV) complex and characterization of its self-decay pathway.
The crystal structure of a high-spin oxoiron(IV) complex and characterization of its self-decay pathway.
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DOI：
10.1021/ja100366c
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发表时间：
2010-06-30
影响因子：
15
通讯作者：
Que, Lawrence, Jr.
中科院分区：
文献类型：
--
作者：
England, Jason;Guo, Yisong;Farquhar, Erik R.;Young, Victor G., Jr.;Muenck, Eckard;Que, Lawrence, Jr.
[FeIV(O)(TMG3tren)]2+ (1; TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-四甲基胍)]乙基}胺) 是可分离的合成 S = 2 氧代铁 (IV) 复合物的独特示例，可作为在非血红素铁酶中观察到的高价氧代铁 (IV) 中间体的模型。与预测更具反应性的 S = 2 氧铁 (IV) 中心的 DFT 计算一致，1 的寿命明显短于相关的 S = 1 氧铁 (IV) 配合物。 1 的自衰变表现出严格的一级动力学行为，并且不受溶剂氘化的影响，表明是分子内过程。这一假设得到了铁产品的 ESI-MS 分析的支持，并且使用全氘甲基 TMG3tren 同位素异构体 d36-1（25°C 时 KIE = 24）显着延缓了自衰变。 d36-1 大大增强的热稳定性允许衍射质量晶体的生长，从而获得高分辨率的晶体结构。该结构在预期的三角双锥几何形状中显示出 Fe=O 单元 (r = 1.661(2) Å)，由四齿三足 TMG3tren 配体的空间庞大的四甲基胍基供体强化。甲基取代基与氧代铁单元的紧密接近产生了三个对称定向的短C-D·O非键接触(2.38 – 2.49 Å)，这种排列通过决定速率的分子内氢原子提取和随后形成配体羟基化铁(III)产物来促进自衰变。各种铁产物的 EPR 和穆斯堡尔定量，参考 1 与 1,4-环己二烯反应获得的产物，可以制定自衰过程的详细机制。高自旋 (S = 2) 含氧铁 (IV) 中心的第一个晶体结构的解决方案代表了全面了解这些关键生物中间体的道路上迈出的基本一步。
[FeIV(O)(TMG3tren)]2+ (1; TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine) is a unique example of an isolable synthetic S = 2 oxoiron(IV) complex, which serves as a model for the high-valent oxoiron(IV) intermediates observed in nonheme iron enzymes. Congruent with DFT calculations predicting a more reactive S = 2 oxoiron(IV) center, 1 has a lifetime significantly shorter than related S = 1 oxoiron(IV) complexes. Self-decay of 1 exhibits strictly first-order kinetic behavior and is unaffected by solvent deuteration, suggesting an intramolecular process. This hypothesis was supported by ESI-MS analysis of the iron products and a significant retardation of self-decay upon use of a perdeuteromethyl TMG3tren isotopomer, d36-1 (KIE = 24 at 25°C). The greatly enhanced thermal stability of d36-1 allowed growth of diffraction quality crystals for which a high-resolution crystal structure was obtained. This structure showed an Fe=O unit (r = 1.661(2) Å) in the intended trigonal bipyramidal geometry enforced by the sterically bulky tetramethylguanidinyl donors of the tetradentate tripodal TMG3tren ligand. The close proximity of the methyl substituents to the oxoiron unit yielded three symmetrically oriented short C-D···O non-bonded contacts (2.38 – 2.49 Å), an arrangement that facilitated self-decay by rate-determining intramolecular hydrogen atom abstraction and subsequent formation of a ligand-hydroxylated iron(III) product. EPR and Mössbauer quantification of the various iron products, referenced against those obtained from reaction of 1 with 1,4-cyclohexadiene, allowed formulation of a detailed mechanism for the self-decay process. The solution of this first crystal structure of a high-spin (S = 2) oxoiron(IV) center represents a fundamental step on the path towards a full understanding of these pivotal biological intermediates.
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