A Two-Coordinate Iron(II) Imido Complex with NHC Ligation: Synthesis, Characterization, and Its Diversified Reactivity of Nitrene Transfer and C-H Bond Activation
A Two-Coordinate Iron(II) Imido Complex with NHC Ligation: Synthesis, Characterization, and Its Diversified Reactivity of Nitrene Transfer and C-H Bond Activation
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NHC 连接的双配位亚氨基铁配合物：合成、表征及其氮烯转移和 C-H 键活化的多样化反应活性
DOI：
10.1021/acs.inorgchem.9b01147
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发表时间：
2019-06-03
影响因子：
4.6
通讯作者：
Deng, Liang
中科院分区：
文献类型：
--
作者：
Cheng, Jun;Liu, Jian;Deng, Liang
铁末端亚氨基物质通常作为铁催化转化中的反应中间体。虽然大量工作致力于中价和高价铁亚胺基，但迄今为止，由于难以获取亚胺基铁（II），其化学性质在很大程度上仍未被探索。在此，我们研究了由铁（0）配合物与大叠氮化物反应制备的双配位铁（II）亚氨基配合物[（IPr）Fe（NArTrip）]（3；IPr = 1,3-双（2',6'-二异丙基苯基）咪唑-2-亚基；Ar-Trip = 2,6-双（2',4',6'-三异丙基苯基）苯基） (ArN3)-N-行程。光谱研究与 DFT 计算相结合，确定了 3 的高自旋 S = 2 基自旋态，与 X 射线衍射分析揭示的 1.715(2) 埃的长 Fe-N 多重键一致。与报道的铁亚氨基配合物相比，配合物3表现出异常的氮宾转移和C-H键活化活性。具体来说，3与CH2=CHArCF3（一种缺电子烯烃）和CO（一种强pi酸）的反应很容易分别产生氮宾转移产物（ArCH）-C-CF3=CHNHArTrip和（ArNCO）-N-Trip，但当3用富电子烯烃和PMe3处理时，没有发生类似的反应。此外，3对1,4-环己二烯、THF和甲苯中的弱C(sp(3))-H键呈惰性，而它可以裂解对三氟甲基苯乙炔中更强的C(sp)-H键，形成铁(II)酰胺基炔基络合物。有趣的是，通过将 (p-Tol)(2)CN2 添加到 3 中，观察到分子内 C(sp(3))-H 键功能化。3 的独特反应性归因于其低配位性质和亚氨基 N 原子上的高负电荷群，这使其铁亚氨基单元本质上具有亲核性。
Iron terminal imido species are typically implicated as reaction intermediates in iron-catalyzed transformations. While a large body of work has been devoted to mid- and high-valent iron imidos, to date the chemistry of iron(II) imidos has remained largely unexplored due to the difficulty in accessing them. Herein, we present a study on the two-coordinate iron(II) imido complex [(IPr)Fe(NArTrip)] (3; IPr = 1,3-bis(2',6'-diisopropylphenyl)imidazol-2-ylidene; Ar-Trip = 2,6-bis(2',4',6'-triisopropylphenyl)phenyl) prepared from the reaction of an iron(0) complex with the bulky azide (ArN3)-N-Trip. Spectroscopic investigations in combination with DFT calculations established a high-spin S = 2 ground spin state for 3, consistent with its long Fe-N multiple bond of 1.715(2) angstrom revealed by X-ray diffraction analysis. Complex 3 exhibits unusual activity of nitrene transfer and C-H bond activation in comparison to the reported iron imido complexes. Specifically, the reactions of 3 with CH2=CHArCF3, an electron-deficient alkene, and CO, a strong pi acid, readily afford nitrene transfer products, (ArCH)-C-CF3=CHNHArTrip and (ArNCO)-N-Trip, respectively, yet no similar reaction occurs when 3 is treated with electron rich alkenes and PMe3. Moreover, 3 is inert toward the weak C(sp(3))-H bonds in 1,4-cyclohexadiene, THF, and toluene, whereas it can cleave the stronger C(sp)-H bond in p-trifluoromethylphenylacetylene to form an iron(II) amido alkynyl complex. Interestingly, intramolecular C(sp(3))-H bond functionalization was observed by adding (p-Tol)(2)CN2 to 3. The unique reactivity of 3 is attributed to its low-coordinate nature and the high negative charge population on the imido N atom, which render its iron-imido unit nucleophilic in nature.