Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, D-12489 Berlin, Germany.
J Am Chem Soc. 2012 Sep 12;134(36):14710-3. doi: 10.1021/ja306674h. Epub 2012 Aug 31.
High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu(III)-NR/Cu(II)N(•)R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at -90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu(II)N(•)Ts (Ts = tosyl group) and not Cu(III)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu(II)N(•)Ts cores as viable reactants in oxidation catalysis.
高价铜-亚氮中间体在铜催化的氮丙啶和酰胺化反应中一直被认为起作用。然而，这些中间体几十年来一直难以检测，这阻碍了对反应机理的明确分配。此外，文献中还对所提出的铜-亚氮中间体的电子结构进行了激烈的讨论。这些关于机理的问题和争议极大地激发了人们对 Cu(III)-NR/Cu(II)N(•)R 物种的可及性和反应性的探究。在本文中，我们报告了在该领域的一个突破，即在三氟甲磺酸镧的存在下，捕获瞬态铜-对甲苯磺酰亚氮物种 3-Sc。3-Sc 在-90°C 下具有足够的稳定性，使其可以通过光学、共振拉曼、NMR 和 X 射线吸收近边光谱学进行表征，这有助于确定其电子结构为 Cu(II)N(•)Ts（Ts = 对甲苯磺酰基）而不是 Cu(III)NTs。3-Sc 可以引发环己烷的对甲苯磺酰基化，从而表明 Cu(II)N(•)Ts 核作为氧化催化中的可行反应物。
