School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.
University of Chinese Academy of Science, Shanghai 100049, China.
J Am Chem Soc. 2020 Apr 1;142(13):6216-6226. doi: 10.1021/jacs.0c00212. Epub 2020 Mar 23.
Modern photoredox catalysis has traditionally relied upon metal-to-ligand charge-transfer (MLCT) excitation of metal polypyridyl complexes for the utilization of light energy for the activation of organic substrates. Here, we demonstrate the catalytic application of ligand-to-metal charge-transfer (LMCT) excitation of cerium alkoxide complexes for the facile activation of alkanes utilizing abundant and inexpensive cerium trichloride as the catalyst. As demonstrated by cerium-catalyzed C-H amination and the alkylation of hydrocarbons, this reaction manifold has enabled the facile use of abundant alcohols as practical and selective hydrogen atom transfer (HAT) agents via the direct access of energetically challenging alkoxy radicals. Furthermore, the LMCT excitation event has been investigated through a series of spectroscopic experiments, revealing a rapid bond homolysis process and an effective production of alkoxy radicals, collectively ruling out the LMCT/homolysis event as the rate-determining step of this C-H functionalization.
现代光氧化还原催化传统上依赖于金属-配体电荷转移(MLCT)激发金属多吡啶配合物,以利用光能激活有机底物。在这里,我们展示了铈烷氧化物配合物的配体-金属电荷转移(LMCT)激发在利用丰富且廉价的三氯化铈作为催化剂轻松激活烷烃方面的催化应用。正如铈催化的 C-H 胺化和烃类的烷基化所证明的那样,这种反应机理使得丰富的醇可以作为实用且选择性的氢原子转移(HAT)试剂轻松使用,通过直接进入能量上具有挑战性的烷氧基自由基。此外,通过一系列光谱实验研究了 LMCT 激发事件,揭示了快速的键均裂过程和烷氧基自由基的有效生成,共同排除了 LMCT/均裂事件作为这种 C-H 官能化的速率决定步骤。
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