Yu Han, Zhai Yongyan, Dai Guoyong, Ru Shi, Han Sheng, Wei Yongge
School of Chemical and Environmental Engineering, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai, 201418, P. R. China.
Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, P. R. China.
Chemistry. 2017 Oct 9;23(56):13883-13887. doi: 10.1002/chem.201703185. Epub 2017 Sep 12.
Most state-of-art transition-metal catalysts usually require organic ligands, which are essential for controlling the reactivity and selectivity of reactions catalyzed by transition metals. However, organic ligands often suffer from severe problems including cost, toxicity, air/moisture sensitivity, and being commercially unavailable. Herein, we show a simple, mild, and efficient aerobic oxidation procedure of amines using inorganic ligand-supported non-precious metal catalysts 1, (NH ) [MMo O (OH) ] (M=Cu ; Fe ; Co ; Ni ; Zn , n=3 or 4), synthesized by a simple one-step method in water at 100 °C, demonstrating that the catalytic activity and selectivity can be significantly improved by changing the central metal atom. In the presence of these catalysts, the catalytic oxidation of primary and secondary amines, as well as the coupling of alcohols and amines, can smoothly proceed to afford various imines with O (1 atm) as the sole oxidant. In particular, the catalysts 1 have transition-metal ion core, and the planar arrangement of the six Mo centers at their highest oxidation states around the central heterometal can greatly enhance the Lewis acidity of catalytically active sites, and also enable the electrons in the center to delocalize onto the six edge-sharing MO units, in the same way as ligands in traditional organometallic complexes. The versatility of this methodology maybe opens a path to catalytic oxidation through inorganic ligand-coordinated metal catalysis.
大多数最先进的过渡金属催化剂通常需要有机配体，这对于控制过渡金属催化反应的反应性和选择性至关重要。然而，有机配体常常存在严重问题，包括成本、毒性、对空气/水分敏感以及商业上无法获得。在此，我们展示了一种使用无机配体支撑的非贵金属催化剂1，即(NH₄)₃[MMo₆O₂₄(OH)₂]（M = Cu²⁺；Fe³⁺；Co²⁺；Ni²⁺；Zn²⁺，n = 3或4），在100℃的水中通过简单的一步法合成，对胺进行简单、温和且高效的有氧氧化过程，表明通过改变中心金属原子可以显著提高催化活性和选择性。在这些催化剂存在下，伯胺和仲胺的催化氧化以及醇与胺的偶联反应能够顺利进行，以O₂（1个大气压）作为唯一氧化剂生成各种亚胺。特别地，催化剂1具有过渡金属离子核心，六个处于最高氧化态的Mo中心围绕中心杂金属的平面排列能够极大地增强催化活性位点的路易斯酸性，并且还能使中心的电子离域到六个共边的MO单元上，这与传统有机金属配合物中的配体作用方式相同。这种方法的通用性可能为通过无机配体配位的金属催化实现催化氧化开辟一条道路。
