Partial Oxidation of Methane Enabled by Decatungstate Photocatalysis Coupled to Free Radical Chemistry
Partial Oxidation of Methane Enabled by Decatungstate Photocatalysis Coupled to Free Radical Chemistry
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DOI：
10.1021/acscatal.3c00750
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发表时间：
2023-04
期刊：
影响因子：
12.9
通讯作者：
C. Musgrave;Kaeleigh Olsen;Nichole S. Liebov;J. Groves;W. Goddard;T. Gunnoe
中科院分区：
文献类型：
--
作者：
C. Musgrave;Kaeleigh Olsen;Nichole S. Liebov;J. Groves;W. Goddard;T. Gunnoe
十聚钨酸盐阴离子[W10 O32]4-或DT是一种有用的光催化剂，用于涉及C-H官能化的有机转化。在此，我们利用DT独特的光氧化还原性质，从氯离子产生氯自由基，用于甲烷的光化学部分氧化。在优化的条件下，DT-氯化物-碘系综实现了甲烷到三氟乙酸甲酯的转化，基于三氟乙酸溶剂中的甲烷，具有>350个光催化剂周转，产率为约60%。三氟乙酸甲酯在反应条件下表现出优异的稳定性，在41小时后检测到最小量的降解（<6%）。基于密度泛函理论计算，我们提出了一种机制，涉及DT，氯化物和碘物质之间的协同关系，具有以下关键特征：（1）DT与Cl-发生光氧化还原电子转移反应生成Cl·，（2）DT与甲烷发生光激发反应，通过净夺取氢原子生成甲基自由基，（3）基于Cl/I自由基的途径，其中甲烷转化为MeTFA，以及（4）还原DT物质被分子氧再氧化。该机制利用DT独特的氧化还原电位和DT介导电子转移和氢原子转移反应的能力，最终产生好氧甲烷部分氧化的有效途径。
The decatungstate anion, [W10O32]4–or DT, is a useful photocatalyst for organic transformations involving C–H functionalization. Herein, we leverage the unique photoredox properties of DT to generate a chlorine radical from chloride ion for the photochemical partial oxidation of methane. Under optimized conditions, the DT–chloride–iodine ensemble achieves methane to methyl trifluoroacetate conversion with >350 photocatalyst turnovers at ∼60% yield based on methane in trifluoroacetic acid solvent. Methyl trifluoroacetate exhibits excellent stability under reaction conditions with minimal amounts of degradation (<6%) detected after 41 h. Based on density functional theory calculations, we propose a mechanism that involves synergistic relationships among the DT, chloride, and iodine species with the following key features: (1) photoredox electron transfer reaction of DT with Cl–to generate Cl•, (2) reaction of photoexcited DT with methane to generate methyl radicals via net hydrogen atom abstraction, (3) a Cl/I radical-based pathway in which methane is converted to MeTFA, and (4) reoxidation of reduced DT species by dioxygen. This mechanism takes advantage of the unique redox potential of DT and the ability of DT to mediate both electron transfer and hydrogen atom transfer reactions, ultimately generating an efficient pathway for aerobic methane partial oxidation.