Combined Effects of Backbone and N-Substituents on Structure, Bonding, and Reactivity of Alkylated Iron(II)-NHCs.
Combined Effects of Backbone and N-Substituents on Structure, Bonding, and Reactivity of Alkylated Iron(II)-NHCs.
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DOI：
10.1021/acs.organomet.8b00466
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发表时间：
2018-09-24
期刊：
影响因子：
2.8
通讯作者：
Neidig ML
中科院分区：
文献类型：
--
作者：
Muñoz SB 3rd;Fleischauer VE;Brennessel WW;Neidig ML
铁和N-杂环卡宾（NHC）已被证明是一个成功的催化对，反应性和选择性高度依赖于NHC配体骨架饱和度和N-取代基的性质。四个（NHC）Fe（1，3-二氧六环-2-乙基）2配合物已被分离和光谱表征，从骨架饱和度和N-取代基的NHC的空间效应与它们的反应性相关。只有在NHC骨架和N-取代基的空间效应是最大的SIPr的极端情况下，有一个主要的结构扰动晶体学观察。仅添加两个氢原子就足以使1-碘-3-苯基丙烷与（2-（1，3-二氧杂环己烷-2-基）乙基）溴化镁偶联中的产物选择性发生剧烈变化，这是由于对预催化剂产生结构扰动。穆斯堡尔谱和磁性圆二色性使相关的共价性和空间体积在SIPr的情况下，其差的选择性烷基-烷基与铁的交叉偶联。密度泛函理论计算提供了深入了解的电子结构和分子轨道的影响，连接的变化，铁中心。最后，电荷捐赠分析和Mayer键级计算进一步证实了在SIPr配合物中更强的Fe-配体键合。总体而言，这些研究强调了考虑N-取代基和骨架空间对铁-NHC的结构、成键和反应性的贡献的重要性。
Iron and N-heterocyclic carbenes (NHCs) have proven to be a successful pair in catalysis, with reactivity and selectivity being highly dependent on the nature of the NHC ligand backbone saturation and N-substituents. Four (NHC)Fe(1,3-dioxan-2-ylethyl)2 complexes have been isolated and spectroscopically characterized to correlate their reactivity to steric effects of the NHC from both the backbone saturation and N-substituents. Only in the extreme case of SIPr where NHC backbone and N-substituent steric effects are the largest is there a major structural perturbation observed crystallographically. The addition of only two hydrogen atoms is sufficient for a drastic change in product selectivity in the coupling of 1-iodo-3-phenylpropane with (2-(1,3-dioxan-2-yl)ethyl)magnesium bromide due to resulting structural perturbations to the precatalyst. Mössbauer spectroscopy and magnetic circular dichroism enabled the correlation of covalency and steric bulk in the SIPr case to its poor selectivity in alkyl–alkyl cross-coupling with iron. Density functional theory calculations provided insight into the electronic structure and molecular orbital effects of ligation changes to the iron center. Finally, charge donation analysis and Mayer bond order calculations further confirmed the stronger Fe–ligand bonding in the SIPr complex. Overall, these studies highlight the importance of considering both N-substituent and backbone steric contributions to structure, bonding, and reactivity in iron-NHCs.
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影响因子：
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