Tuning the Geometric and Electronic Structure of Synthetic High-Valent Iron(IV)-Oxo Models in the Presence of a Lewis Acid and Various Axial Ligands,Journal of the American Chemical Society

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Tuning the Geometric and Electronic Structure of Synthetic High-Valent Iron(IV)-Oxo Models in the Presence of a Lewis Acid and Various Axial Ligands
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-03-12 , DOI: 10.1021/jacs.9b00795
Melanie A Ehudin ₁ , Leland B Gee ₂ , Sinan Sabuncu ₃ , Augustin Braun ₂ , Pierre Moënne-Loccoz ₃ , Britt Hedman ₄ , Keith O Hodgson _{2,

4} , Edward I Solomon _{2,

4} , Kenneth D Karlin ₁

Affiliation

High-valent ferryl species (e.g., (Por)FeIV═O, Cmpd-II) are observed or proposed key oxidizing intermediates in the catalytic cycles of heme-containing enzymes (P-450s, peroxidases, catalases, and cytochrome c oxidase) involved in biological respiration and oxidative metabolism. Herein, various axially ligated iron(IV)-oxo complexes were prepared to examine the influence of the identity of the base. These were generated by addition of various axial ligands (1,5-dicyclohexylimidazole (DCHIm), a tethered-imidazole system, and sodium derivatives of 3,5-dimethoxyphenolate and imidazolate). Characterization was carried out via UV-vis, electron paramagnetic resonance (EPR), 57Fe Mössbauer, Fe X-ray absorption (XAS), and 54/57Fe resonance Raman (rR) spectroscopies to confirm their formation and compare the axial ligand perturbation on the electronic and geometric structures of these heme iron(IV)-oxo species. Mössbauer studies confirmed that the axially ligated derivatives were iron(IV) and six-coordinate complexes. XAS and 54/57Fe rR data correlated with slight elongation of the iron-oxo bond with increasing donation from the axial ligands. The first reported synthetic H-bonded iron(IV)-oxo heme systems were made in the presence of the protic Lewis acid, 2,6-lutidinium triflate (LutH+), with (or without) DCHIm. Mössbauer, rR, and XAS spectroscopic data indicated the formation of molecular Lewis acid ferryl adducts (rather than full protonation). The reduction potentials of these novel Lewis acid adducts were bracketed through addition of outer-sphere reductants. The oxidizing capabilities of the ferryl species with or without Lewis acid vary drastically; addition of LutH+ to F8Cmpd-II (F8 = tetrakis(2,6-difluorophenyl)porphyrinate) increased its reduction potential by more than 890 mV, experimentally confirming that H-bonding interactions can increase the reactivity of ferryl species.

中文翻译：

在路易斯酸和各种轴向配体存在下调整合成高价铁 (IV)-Oxo 模型的几何和电子结构

在含血红素的酶（P-450s、过氧化物酶、过氧化氢酶和细胞色素 c 氧化酶）的催化循环中，观察到或提出了高价 Ferri1 物质（例如，(Por)FeIV=O、Cmpd-II）的关键氧化中间体。参与生物呼吸和氧化代谢。在此，制备了各种轴向连接的铁(IV)-氧配合物以检查碱基特性的影响。这些是通过添加各种轴向配体（1,5-二环己基咪唑（DCHIm）、束缚咪唑系统以及3,5-二甲氧基苯酚钠和咪唑钠衍生物）生成的。通过紫外-可见光、电子顺磁共振 (EPR)、57Fe 穆斯堡尔谱、Fe X 射线吸收 (XAS) 和 54/57Fe 共振拉曼 (rR) 光谱进行表征，以确认它们的形成并比较轴向配体扰动这些血红素铁(IV)-氧代物质的电子和几何结构。穆斯堡尔研究证实，轴向连接的衍生物是铁（IV）和六配位络合物。 XAS 和 54/57Fe rR 数据与铁-氧键的轻微伸长以及轴向配体贡献的增加相关。第一个报道的合成氢键铁(IV)-氧代血红素系统是在质子路易斯酸、2,6-三氟甲磺酸钚 (LutH+)、有（或没有）DCHIm 存在下制备的。穆斯堡尔、rR 和 XAS 光谱数据表明分子路易斯酸铁加合物的形成（而不是完全质子化）。这些新型路易斯酸加合物的还原电位通过添加外球还原剂而被括起来。在有或没有路易斯酸的情况下，弗瑞尔物质的氧化能力差别很大；将 LutH+ 添加到 F8Cmpd-II（F8 = 四（2,6-二氟苯基）卟啉酸盐）中，其还原电位增加了 890 mV 以上，实验证实氢键相互作用可以增加 Ferri1 物质的反应性。

更新日期：2019-03-12

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