In situ Generated Ruthenium Catalyst Systems Bearing Diverse N‐Heterocyclic Carbene Precursors for Atom‐Economic Amide Synthesis from Alcohols and Amines |
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Authors: | Dr Hua Cheng Mao‐Qian Xiong Chuan‐Xiang Cheng Hua‐Jing Wang Qiang Lu Hong‐Fu Liu Fu‐Bin Yao Dr Cheng Chen Prof?Dr Francis Verpoort |
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Institution: | 1. Department of Chemical Engineering and Food Science, Hubei University of Arts and Science, Xiangyang, P.?R. China;2. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, P.?R. China;3. School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan, P.?R. China;4. National Research Tomsk Polytechnic University, Tomsk, Russian Federation |
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Abstract: | The transition‐metal‐catalyzed direct synthesis of amides from alcohols and amines is herein demonstrated as a highly environmentally benign and atom‐economic process. Among various catalyst systems, in situ generated N‐heterocyclic carbene (NHC)‐based ruthenium (Ru) halide catalyst systems have been proven to be active for this transformation. However, these existing catalyst systems usually require an additional ligand to achieve satisfactory results. In this work, through extensive screening of a diverse variety of NHC precursors, we discovered an active in situ catalyst system for efficient amide synthesis without any additional ligand. Notably, this catalyst system was found to be insensitive to the electronic effects of the substrates, and various electron‐deficient substrates, which were not highly reactive with our previous catalyst systems, could be employed to afford the corresponding amides efficiently. Furthermore, mechanistic investigations were performed to provide a rationale for the high activity of the optimized catalyst system. NMR‐scale reactions indicated that the rapid formation of a Ru hydride intermediate (signal at δ=?7.8 ppm in the 1H NMR spectrum) after the addition of the alcohol substrate should be pivotal in establishing the high catalyst activity. Besides, HRMS analysis provided possible structures of the in situ generated catalyst system. |
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Keywords: | amides atom economy carbenes reaction mechanisms ruthenium |
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