Xu Binyu, Senthilkumar Samuthirarajan, Zhong Wei, Shen Zhongquan, Lu Chunxin, Liu Xiaoming
School of Chemistry, Nanchang University Nanchang Jiangxi China
College of Biological, Chemical Sciences and Engineering, Jiaxing University Jiaxing Zhejiang China
RSC Adv. 2020 Jul 10;10(44):26142-26150. doi: 10.1039/d0ra04064a. eCollection 2020 Jul 9.
In this work, core-shell FeO@CuO and FeO@CuO-Cu nanomaterials for aerobic oxidation of benzylic alcohols are reported with 2,2,6,6-tetramethylpiperidine--oxyl (TEMPO) and -methylimidazole (NMI) as the co-catalysts. To anchor CuO nanoparticles around the magnetic particles under solvothermal conditions, the magnetic material FeO was modified by grafting a layer of l-lysine (l-Lys) to introduce -NH groups at the surface of the magnetic particles. With amine groups as the anchor, Cu(NO) was used to co-precipitate the desired CuO by using ethylene glycol as the reducing agent. Prolonging the reaction time would lead to over-reduced forms of the magnetic materials in the presence of copper, FeO@CuO-Cu. The nanomaterials and its precursors were fully characterized by a variety of spectroscopic techniques. In combination with both TEMPO and NMI, these materials showed excellent catalytic activities in aerobic oxidation of benzylic alcohols under ambient conditions. For most of the benzylic alcohols, the conversion into aldehydes was nearly quantitative with aldehydes as the sole product. The materials were recyclable and robust. Up to 7 repeat runs, its activity dropped less than 10%. The over-reduced materials, FeO@CuO-Cu, exhibited slightly better performance in durability. The magnetic properties allowed easy separation after reaction by simply applying an external magnet.
在本工作中，报道了以2,2,6,6 - 四甲基哌啶 - 氧基（TEMPO）和N - 甲基咪唑（NMI）作为共催化剂用于苄醇有氧氧化的核壳结构FeO@CuO和FeO@CuO - Cu纳米材料。为了在溶剂热条件下将CuO纳米颗粒锚定在磁性颗粒周围，通过接枝一层L - 赖氨酸（L - Lys）对磁性材料FeO进行改性，以在磁性颗粒表面引入 - NH基团。以胺基为锚定基团，使用Cu(NO₃)₂，以乙二醇作为还原剂共沉淀所需的CuO。延长反应时间会导致在有铜存在的情况下磁性材料过度还原，形成FeO@CuO - Cu。通过多种光谱技术对纳米材料及其前驱体进行了全面表征。结合TEMPO和NMI，这些材料在环境条件下对苄醇的有氧氧化表现出优异的催化活性。对于大多数苄醇，转化为醛的反应几乎是定量的，且醛是唯一产物。这些材料可回收且稳定。重复运行多达7次，其活性下降不到10%。过度还原的材料FeO@CuO - Cu在耐久性方面表现略好。磁性特性使得在反应后通过简单施加外部磁场即可轻松分离。
