第一作者：中南大学 Juntao Tang
通讯作者：中南大学 喻桂朋
DOI：https://doi.org/10.1002/anie.202416879
酮的Baeyer-Villiger氧化生成相应的内酯/酯是化学工业中一个经典而重要的反应。然而，这种氧化过程尚未在氧气和异相光催化剂的辅助下在环境条件下实现。作者开发了一种基于共价三嗪/七嗪基框架（CTF-TB/CHF-TB）的有机光催化体系，通过级联反应途径在温和条件下实现B-V氧化反应。实验数据和理论计算表明，heptazine/triazine单元能够将原位生成的H2O2“螯合”并分解为羟基自由基（•OH）。与传统方法在高温（例如60℃）下主要涉及金属活化苯甲醛相比，我们研究中产生的•OH可以很容易地切割苯甲醛的C-H键，形成一个活性中间体，驱动后续的顺序过程：O2→H2O2→•OH→Ph-CO•→Ph-COOO•。采用该光催化工艺，室温下环己酮氧化制己内酯的收率达91%，选择性达99%以上。这一性能可与最先进的催化剂相媲美，而且我们的CHF-TB催化剂具有令人印象深刻的可重复使用性，在连续运行5次后仍保持高收率。本研究提出了一种直接的方法，利用有机催化剂通过Baeyer-Villiger氧化以温和的方式裂解C-H生成ε-己内酯。
Scheme 1. (a) Traditional approaches in Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone; (b) Schematic illustration of the photocatalytic tandem reaction system employed in this work.
Figure 1. (a) The design principle for the synthesis of CHF-TB/CTF-TB; (b) Fourier transform infrared (FT-IR) spectra; (c) C 1s XPS profiles; (d) N 1s XPS profiles; (e) Nitrogen sorption isotherms at 77k. Inset: pore size distribution plots.
Figure 2. (a) UV-Vis of CHF-TB and CTF-TB; (b) Mott-Schottky plots of CHF-TB and CTF-TB; (c) Band structure diagrams of CHF-TB and CTF-TB; (d) Transient photocurrent curves; (e) EIS plots of CHF-TB and CTF-TB; (f) Electron-hole distribution of typical fragments in CHF-TB (right) and CTF-TB (left) in the excited states.
Figure 3. (a) The yields of caprolactone with the addition of different scavengers; (b) The EPR spectra of Ph-CO•-PBN and Ph-COO•-PBN at different B-V Oxidation reaction times; (c) EPR spectra of DMPO-·OH; (d) Fluorescence peak of 7-hydroxycoumarin at different concentrations of benzaldehyde (BEA).
Figure 4. (a) H2O2 synthesis rate of CHF-TB and CTF-TB; (b) Photocatalytic H2O2 production experiments with the addition of different sacrificial agents (1 mM); (c) The adsorption mode of H2O2 by the duplicate structural units of CTF-TB (Left) and CHF-TB (Right); (d, e) Surface electrostatic potential distribution of the repeating unit of CTF-TB and CHF-TB; (f)Yields of cyclohexanone with different types of aldehydes; (g) Possible mechanisms of B-V oxidation over CHF-TB catalyst; (h) Summary of the B-V oxidation of cyclohexanone with O2 catalyzed by various catalysts.
Hydroxyl Radical Mediated Heterogeneous Photocatalytic Baeyer-Villiger Oxidation over Covalent Triazine/Heptazine- Based Frameworks
https://doi.org/10.1002/anie.202416879
