Iron-Catalyzed Cross Coupling of Aryl Chlorides with Alkyl Grignard Reagents: Synthetic Scope and FeII/FeIV Mechanism Supported by X-ray Absorption Spectroscopy and Density Functional Theory Calculations
Iron-Catalyzed Cross Coupling of Aryl Chlorides with Alkyl Grignard Reagents: Synthetic Scope and FeII/FeIV Mechanism Supported by X-ray Absorption Spectroscopy and Density Functional Theory Calculations
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DOI：
10.1246/bcsj.20180333
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发表时间：
2019-02-01
影响因子：
4
通讯作者：
Nakamura, Masaharu
中科院分区：
文献类型：
--
作者：
Agata, Ryosuke;Takaya, Hikaru;Nakamura, Masaharu
氟化铁（III）和1,3-双（2,6-二异丙基苯基）咪唑啉-2-基（SIPr）的结合催化了富电子氯芳基与烷基格氏试剂的高收率交叉偶联，这是其他铁催化剂无法实现的。各种烷氧基或氨基取代的芳酰氯可以与各种烷基格氏试剂交叉偶联，而不管烷基中是否存在-氢。使用1-（丁-3-烯基）- 2-氯苯的自由基探针实验没有得到相应的环化产物，因此排除了自由基种的中间作用。借助密度泛函理论（DFT）计算，溶液相x射线吸收光谱（XAS）分析表明，在反应混合物中形成了高自旋（S = 2）异聚二氟有机铁酸盐（II）， [MgX][(FeF2)- f -II(SIPr)-(Me/alkyl)]。DFT计算还支持一种可行的反应途径，包括形成二氟有机铁酸盐（II）中间体，该中间体经过新的Lewis酸辅助氧化加成形成中性有机铁（IV）中间体，从而导致Fe-II/Fe-IV催化循环，其中氟配体和镁离子起关键作用。
A combination of iron(III) fluoride and 1,3-bis(2,6-diiso-propylphenyl) imidazolin-2-ylidene (SIPr) catalyzes the high-yielding cross coupling of an electron-rich aryl chloride with an alkyl Grignard reagent, which cannot be attained using other iron catalysts. A variety of alkoxy-or amino-substituted aryl chlorides can be cross-coupled with various alkyl Grignard reagents regardless of the presence or absence of beta-hydrogens in the alkyl group. A radical probe experiment using 1-(but-3-enyl)- 2-chlorobenzene does not afford the corresponding cyclization product, therefore excluding the intermediacy of radical species. Solution-phase X-ray absorption spectroscopy (XAS) analysis, with the help of density functional theory (DFT) calculations, indicates the formation of a high-spin (S = 2) heteroleptic difluorido organoferrate(II), [MgX][(FeF2)-F-II(SIPr)-(Me/alkyl)], in the reaction mixture. DFT calculations also support a feasible reaction pathway, including the formation of a difluorido organoferrate(II) intermediate which undergoes a novel Lewis acid-assisted oxidative addition to form a neutral organoiron(IV) intermediate, which leads to an Fe-II/Fe-IV catalytic cycle, where the fluorido ligand and the magnesium ion play key roles.