Mechanistic Study on Cu(II)-Catalyzed Oxidative Cross-Coupling Reaction between Arenes and Boronic Acids under Aerobic Conditions.
Mechanistic Study on Cu(II)-Catalyzed Oxidative Cross-Coupling Reaction between Arenes and Boronic Acids under Aerobic Conditions.
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DOI：
10.1021/jacs.8b01896
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发表时间：
2018-04
影响因子：
15
通讯作者：
Qian Zhang;Yang Liu;Ting Wang;Xinhao Zhang;Chao Long;Yundong Wu;Mei‐Xiang Wang
中科院分区：
文献类型：
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作者：
Qian Zhang;Yang Liu;Ting Wang;Xinhao Zhang;Chao Long;Yundong Wu;Mei‐Xiang Wang
近年来，由于与贵金属相比，铜盐天然丰富，价格便宜，毒性较小，因此现代有机铜化学受到了极大的关注。铜盐在催化和介导碳-碳和碳-杂原子成键反应方面也表现出多功能性。尽管铜盐在催化方面有广泛的应用，但其反应机理仍不清楚。本文以含芳烃的杜鹃花[1]芳烃[3]吡啶及其分离的结构明确的ArCu（II）和ArCu（III）化合物为分子工具，对Cu（II）催化的芳烃与硼酸在空气中氧化交叉偶联反应的机理进行了深入的实验和计算研究。有机铜化合物与对聚硼酸的化学计量反应验证了芳基铜（II）而不是芳基铜（III）是一种活性有机金属中间体。XPS、EPR、1H NMR、HRMS、UV-vis等光谱证据，结合对所有产物和铜形态的分离和定量，结合对瞬态中间体的电子结构和能量学的计算分析，提出了一个反应顺序：Cu（II）对芳烃的亲电金属化、芳基硼酸酯对ArCu（II）的金属化、ArCu（II）和ArCu（II）之间的氧化还原反应，分别形成ArCu(III)Ar'和ArCu(I)。最后还原消除ArCu(III)Ar′。在好氧催化条件下，所有由还原消除ArCu(III)Ar'释放的Cu(I)离子和由ArCu(I)水解释放的Cu(I)离子被氧氧化再生Cu(II), Cu（II）离子进入下一个催化循环。芳基铜（II）化合物的解旋反应性和催化循环将丰富我们对现代有机铜化学的认识，并为铜催化反应的设计提供有用的信息。
Substantial attention has been given to modern organocopper chemistry in recent years since copper salts are naturally abundant, cheap, and less toxic in comparison to precious metals. Copper salts also exhibit versatility in catalyzing and mediating carbon-carbon and carbon-heteroatom bond forming reactions. Despite the wide applications of copper salts in catalysis, reaction mechanisms have remained elusive. Using azacalix[1]arene[3]pyridine, an arene-embedded macrocycle, and its isolated and structurally well-defined ArCu(II) and ArCu(III) compounds as molecular tools, we now report an in-depth experimental and computational study on the mechanism of a Cu(II)-catalyzed oxidative cross-coupling reaction between arenes and boronic acids with air as the oxidant. Stoichiometric reaction of organocopper compounds with p-tolylboronic acid validated arylcopper(II) rather than arylcopper(III) as a reactive organometallic intermediate. XPS, EPR, 1H NMR, HRMS, and UV-vis spectroscopic evidence along with the isolation and quantification of all products and copper speciation, combined with computational analysis of the electronic structure and energetics of the transient intermediates, suggested a reaction sequence involving electrophilic metalation of arene by Cu(II), transmetalation of arylboronate to ArCu(II), the redox reaction between the resulting ArCu(II)Ar' and ArCu(II) to form respectively ArCu(III)Ar' and ArCu(I), and finally reductive elimination of ArCu(III)Ar'. Under aerobic catalytic conditions, all Cu(I) ions released from reductive elimination of ArCu(III)Ar' and from protolysis of ArCu(I) were oxidized by oxygen to regenerate Cu(II) species that enters into the next catalytic cycle. The unraveled reactivity of arylcopper(II) compounds and the catalytic cycle would enrich our knowledge of modern organocopper chemistry and provide useful information in the design of copper-catalyzed reactions.