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.

中文翻译：

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有氧条件下Cu(II)催化芳烃与硼酸氧化交叉偶联反应的机理研究

近年来，现代有机铜化学受到了极大的关注，因为与贵金属相比，铜盐天然丰富、价格低廉且毒性较小。铜盐还表现出催化和介导碳-碳和碳-杂原子键形成反应的多功能性。尽管铜盐在催化中有着广泛的应用，但反应机制仍然难以捉摸。使用氮杂杯[1]芳烃[3]吡啶，一种嵌入芳烃的大环，及其分离且结构明确的ArCu(II)和ArCu(III)化合物作为分子工具，我们现在报告了一项深入的实验和计算研究以空气为氧化剂，Cu(II) 催化芳烃和硼酸之间的氧化交叉偶联反应的机理。有机铜化合物与对甲苯基硼酸的化学计量反应验证了芳基铜 (II) 而不是芳基铜 (III) 作为反应性有机金属中间体。XPS、EPR、1H NMR、HRMS 和紫外-可见光谱证据以及所有产物和铜形态的分离和量化，结合对瞬态中间体的电子结构和能量学的计算分析，提出了涉及亲电子金属化的反应序列芳烃通过 Cu(II)，芳基硼酸盐金属转移为 ArCu(II)，所得的 ArCu(II)Ar' 和 ArCu(II) 之间的氧化还原反应分别形成 ArCu(III)Ar' 和 ArCu(I)，和最后还原消除 ArCu(III)Ar'。在有氧催化条件下，ArCu(III)Ar' 还原消除释放的所有 Cu(I) 离子 并且从 ArCu(I) 的质子分解中被氧气氧化以再生 Cu(II) 物种，进入下一个催化循环。芳基铜（II）化合物的未解开的反应性和催化循环将丰富我们对现代有机铜化学的了解，并为铜催化反应的设计提供有用的信息。