高分子氮化碳因其在可见光照射下的活性而引起了人们对多相光催化的极大兴趣。本文报道了利用氮化碳包覆核磁共振管进行光催化反应机理的原位研究。在第一步，作者利用氮化碳涂层小瓶作为批次光反应器，用于非活化C(sp3)-H键的可见光催化氟化，具有中等至优异的收率和多次循环的可重复使用性。最后，利用氮化碳包覆核磁共振管作为光反应器，直接在光谱仪内部与光纤辐照耦合。这使我们能够用原位核磁共振光谱跟踪反应，识别传统分析中难以捉摸的反应中间体。该方法为研究复杂反应的光催化机理提供了优势，并大大减少了描述反应中间体和转化途径的比较试验的需要。
Figure 1. (a) Schematic illustration of the pCN-coated NMR tube in combination with in-situ irradiation inside the NMR spectrometer. The entire NMR tube is uniformly coated with a highly homogeneous thin pCN film. (b) Photograph of the pCN thin film deposited on the NMR tube under ambient light. The polymeric structure of pCN is illustrated.
Figure 2. The first proof of principle for the excitation and catalytic activity of pCN thin films in combination with in-situ irradiation to monitor the oxidation of benzyl alcohol with NMR spectroscopy. (a) Reaction conditions for the heterogeneous photocatalyzed oxidation of benzyl alcohol. (b) 1H-NMR reaction monitoring of the photocatalyzed oxidation of benzyl alcohol with the pCNcoated NMR tube in combination with in-situ irradiation.
Figure 3. Comparison of the product yields using pCN films as photocatalyst with the reported yields. (a) Reaction conditions for the pCN photocatalyzed reaction. (b) Scope of the photocatalyzed C(sp3)-H fluorinations. NMR yields were determined by 19F NMR using trifluorotoluene as internal standard. Unless explicitly defined, yields correspond to a single monofluorinated regioisomer.Literature reported 19F NMR yields are given in parenthesis. a Yields corresponds to the combined mixture of regioisomers. b Yields in parenthesis correspond to the reported isolated yields. (c) Photograph of the pCN-coated crimp vials under UV light.
Figure 4. (a) The proposed mechanism for the direct C(sp3)-H fluorination using pCN as heterogeneous photocatalyst. (b) Detection of free fluoride (F‾) in the 19F{1H} spectra at –183.4 ppm during in-situ irradiation using a pCN-coated NMR tube.
In-situ Monitoring of Photocatalysis on Polymeric Carbon Nitride Thin Films
https://doi.org/10.1002/anie.202412972
