The development of a simple and highly efficient catalytic system for the selective oxidation of alcohols in open air is an extremely important but challenging task in the fields of organic chemistry and catalysis. In this study, three novel bifunctional ligands, named L1-L3, were designed by combining a N-alkyl substituted ethylenediamine skeleton with a TEMPO moiety varying the length of the linker between the two components. When paired with CuBr, ligand L2, which contains six methylene groups in the linker, demonstrated excellent catalytic activity in the aerobic oxidation of benzyl alcohol, achieving a quantitative yield under ambient conditions. Moreover, the developed CuBr/L2 catalytic system exhibited a broad substrate scope, including primary benzylic, heterocyclic, allylic, aliphatic alcohols, and secondary benzylic alcohols. Mechanistic insights were gained using cyclic voltammetry (CV), ultraviolet–visible (UV–vis) spectroscopy, and electron spray ionization mass (ESI-MS) spectrometry, enabling stepwise monitoring of the reaction. These studies revealed that the mono-copper species is a key intermediate, with its oxidation state cycling between Cu(I) and Cu(II), playing a pivotal role in the aerobic oxidation of alcohols. Additionally, the moderate linker length in ligand L2 facilitated internal interaction between the TEMPO moiety and the copper center, thereby enhancing catalytic activity with a high turnover frequency (TOF) of 33 h−1.

中文翻译：

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通过合理设计具有 N-烷基取代的乙二胺骨架和 TEMPO 部分的双功能配体，增强基于 CuBr 的催化剂，用于有氧醇氧化


在有机化学和催化领域，开发一种简单而高效的催化系统，用于在空气中对醇进行选择性氧化，是一项极其重要但具有挑战性的任务。在这项研究中，通过将 N-烷基取代的乙二胺骨架与改变两种组分之间接头长度的 TEMPO 部分相结合，设计了三种名为 L1-L3 的新型双功能配体。当与 CuBr 配对时，接头中包含六个亚甲基的配体 L2 在苯甲醇的有氧氧化中表现出优异的催化活性，在环境条件下实现了定量产率。此外，开发的 CuBr/L2 催化体系表现出广泛的底物范围，包括伯苄酸、杂环、烯丙基、脂肪醇和仲苯甲醇。使用循环伏安法 （CV）、紫外-可见光 （UV-Vis） 光谱和电子喷雾电离质量 （ESI-MS） 光谱法获得了机理信息，从而能够逐步监测反应。这些研究表明，单铜是一种关键的中间体，其在 Cu（I） 和 Cu（II） 之间的氧化态循环，在醇的有氧氧化中起着关键作用。此外，配体 L2 中适度的接头长度促进了 TEMPO 部分和铜中心之间的内部相互作用，从而增强了催化活性，具有 33 h-1 的高周转频率 （TOF）。