Kao Shih-Chieh, Bian Kang-Jie, Chen Xiao-Wei, Chen Ying, Martí Angel A, West Julian G
Department of Chemistry, Rice University, Houston, TX, USA.
Department of Materials Science and Nanoengineering, Rice University, Houston, TX, USA.
Chem Catal. 2023 Jun 15;3(6). doi: 10.1016/j.checat.2023.100603. Epub 2023 Apr 12.
Ligand-to-metal charge transfer (LMCT) using stoichiometric copper salts has recently been shown to permit decarboxylative C-N bond formation via an LMCT/radical polar crossover (RPC) mechanism; however, this method is unable to function catalytically and cannot successfully engage unactivated alkyl carboxylic acids, presenting challenges to the general applicability of this approach. Leveraging the concepts of ligand-to-metal charge transfer (LMCT) and radical-ligand-transfer (RLT), we herein report the first photochemical, iron-catalyzed direct decarboxylative azidation. Simply irradiating an inexpensive iron nitrate catalyst in the presence of azidotrimethylsilane allows for a diverse array of carboxylic acids to be converted to corresponding organic azides directly with broad functional group tolerance and mild conditions. Intriguingly, no additional external oxidant is required for this reaction to proceed, simplifying the reaction protocol. Finally, mechanistic studies are consistent with a radical mechanism and suggest that the nitrate counteranion serves as an internal oxidant for turnover of the iron catalyst.
最近研究表明，使用化学计量的铜盐进行配体到金属的电荷转移（LMCT）能够通过LMCT/自由基极性交叉（RPC）机制实现脱羧C-N键的形成；然而，该方法无法进行催化反应，且不能成功应用于未活化的烷基羧酸，这给该方法的广泛适用性带来了挑战。利用配体到金属的电荷转移（LMCT）和自由基配体转移（RLT）的概念，我们在此报告了首例光化学铁催化的直接脱羧叠氮化反应。在叠氮基三甲基硅烷存在下，简单地照射一种廉价的硝酸铁催化剂，就能使多种羧酸直接转化为相应的有机叠氮化物，具有广泛的官能团耐受性和温和的反应条件。有趣的是，该反应无需额外的外部氧化剂即可进行，简化了反应流程。最后，机理研究与自由基机理一致，表明硝酸根抗衡阴离子作为铁催化剂周转的内部氧化剂。
