TEMPO-mediated homocoupling of aryl Grignard reagents: mechanistic studies.
TEMPO-mediated homocoupling of aryl Grignard reagents: mechanistic studies.
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DOI：
10.1039/c4ob02689f
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发表时间：
2015-02
影响因子：
3.2
通讯作者：
Sandip Murarka;Juri Möbus;G. Erker;Christian Mück‐Lichtenfeld;A. Studer
中科院分区：
文献类型：
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作者：
Sandip Murarka;Juri Möbus;G. Erker;Christian Mück‐Lichtenfeld;A. Studer
通过实验和计算研究详细研究了 TEMPO 介导的芳基格氏试剂氧化自偶联的机制。实验数据表明，硝基氧介导的芳基格氏试剂的自偶联反应不是通过自由基发生的。提供了联芳自由基阴离子作为偶联反应中间体存在的证据。还表明，在 TEMPO 存在的无溴化物条件下，PhMgPh 不会发生自偶联。然而，添加 MgBr2 后，C-C 键形成顺利进行，证明了溴阴离子在氧化自偶联中的重要作用。 DFT 计算表明，分子内电子转移至 Mg 络合的 TEMPO 配体，随后在二聚络合物中形成联芳基是可行的，并且与实验反应条件一致。
The mechanism of the TEMPO mediated oxidative homo-coupling of aryl Grignard reagents is investigated in detail by experimental and computational studies. Experimental data reveal that the nitroxide-mediated homocoupling reaction of aryl Grignard reagents does not occur via free aryl radicals. Evidence for the presence of biaryl radical anions as intermediates in the coupling reaction is provided. It is also shown that PhMgPh under bromide free conditions in the presence of TEMPO does not undergo homocoupling. However, upon addition of MgBr2, C-C bond formation smoothly proceeds documenting the important role of the bromide anions in the oxidative homocoupling. DFT calculations show that an intramolecular electron transfer to a Mg-complexed TEMPO ligand with subsequent biaryl formation in a dimeric complex is viable and in agreement with experimental reaction conditions.