An inverted and more oxidizing isomer of [Fe(IV)(O)(tmc)(NCCH3)]2+.
An inverted and more oxidizing isomer of [Fe(IV)(O)(tmc)(NCCH3)]2+.
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DOI：
10.1002/anie.200802219
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发表时间：
2008-10
影响因子：
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通讯作者：
Kallol Ray;Jason England;Adam T. Fiedler;M. Martinho;E. Münck;L. Que
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文献类型：
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作者：
Kallol Ray;Jason England;Adam T. Fiedler;M. Martinho;E. Münck;L. Que
在氧气激活单核非血红素铁酶的催化循环中，高价氧铁物种经常被引用为氧化剂。[1]到目前为止，这种铁(IV)中间体已经被表征为四种酶，为这一概念提供了强有力的支持。[2]在相同的时间框架内，含有氧合铁(IV)单元的合成非血红素络合物也被描述为此类反应中间体的模型。[3]这类合成氧化铁(IV)络合物的第一个结晶学表征和研究最广泛的成员是[FeIV(O)(Tmc)(NCCH3)](OTf)2(1-NCCH3)[4](Tmc=1，4，8，11-tetramethyl-1，4，8，11-tetraazacyclotetradecane).它的结构特征是具有一个短的Fe=O键(RFe=O=1.646 A)，其中一个乙腈反式连接到氧原子上。[4]大环TmC配体采用反式-I(R，S，R，S)构型，使得所有四个甲基相对于FeN_4平面定向，[5]，与氧原子相反。另一方面，单阴离子X配体配位于五配位的[FeII(TMC)(X)]+配合物的晶体结构中的甲基。[6]在这里，我们意外地制备了1-NCCH3的反式异构体，其中氧基与四个甲基的位置syn结合(方案1)。1-NCCH3转化为其反式异构体是在四氟硼酸根存在下用PHIO处理的结果，四氟硼酸根是一种惰性阴离子。氧基团结合位置的改变引起了氧合铁(IV)络合物光谱性质的变化，更重要的是，显著提高了氢原子提取和氧转移反应的反应性。
High-valent oxoiron species are often invoked as the oxidants in the catalytic cycles of dioxygen activating mononuclear nonheme iron enzymes.[1] To date, such iron(IV) intermediates have been characterized for four enzymes, lending strong support for this notion.[2] Within the same time frame, synthetic nonheme complexes containing oxoiron(IV) units have also been described that serve as models for such reactive intermediates.[3] The first crystallographically characterized and most extensively studied member of this family of synthetic oxoiron(IV) complexes is [FeIV(O)(TMC)(NCCH3)](OTf)2 (1-NCCH3)[4] (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Its structure features a short Fe=O bond (rFe=O = 1.646 A) with an acetonitrile bound trans to the oxo atom.[4] The macrocyclic TMC ligand adopts a trans-I (R,S,R,S) configuration, such that all four methyl groups are oriented in the same direction with respect to the FeN4 plane,[5] and anti to the oxo atom. On the other hand, monoanionic X ligands coordinate syn to the methyl groups in crystal structures of five-coordinate [FeII(TMC)(X)]+ complexes.[6] Herein, we report the unexpected preparation of an inverted isomer of 1-NCCH3 in which the oxo group binds to the site syn to the four methyl groups (Scheme 1). The conversion of 1-NCCH3 to its inverted isomer is effected by treatment with PhIO in the presence of tetrafluroborate, an otherwise inert anion. The switch in binding site of the oxo group engenders changes in the spectroscopic properties of the oxoiron(IV) complex and, more importantly, a significantly enhanced reactivity in hydrogen-atom abstraction and oxo-transfer reactions.