Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides.
Ru-Catalyzed C-H Arylation of Fluoroarenes with Aryl Halides.
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DOI：
10.1021/jacs.6b01615
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发表时间：
2016-03-16
影响因子：
15
通讯作者：
Larrosa I
中科院分区：
文献类型：
--
作者：
Simonetti M;Perry GJ;Cambeiro XC;Juliá-Hernández F;Arokianathar JN;Larrosa I
尽管带有定向基团的芳烃与卤代芳烃的卤代催化的C-H芳基化是众所周知的，但该方法从未在不存在定向基团的情况下实现。我们报告了这种方法的第一个例子，并表明，出乎意料的反应只发生在催化量的苯甲酸的存在下。此外，与其他过渡金属相反，芳基化位点的选择性受电子和空间因素的影响。化学计量学和NMR机理研究支持一个催化循环，涉及一个定义明确的η6-芳烃配体-自由Ru（II）催化剂。事实上，在初始新戊酸酯辅助的C-H活化后，所产生的芳基-Ru（II）中间体仅在苯甲酸酯添加剂存在下能够与芳基溴偶联配偶体反应。相比之下，含有导向基团的底物（例如2-苯基吡啶）不需要苯甲酸酯添加剂。氘标记和动力学同位素效应实验表明，C-H活化是可逆的和动力学显着。计算研究支持一个协调的金属化-去质子化（CMD）-型双烯化模式，并揭示了不寻常的芳基化区域选择性。
Although the ruthenium-catalyzed C–H arylation of arenes bearing directing groups with haloarenes is well-known, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η6-arene-ligand-free Ru(II) catalyst. Indeed, upon initial pivalate-assisted C–H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C–H activation is both reversible and kinetically significant. Computational studies support a concerted metalation–deprotonation (CMD)-type ruthenation mode and shed light on the unusual arylation regioselectivity.