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In situ Generated Ruthenium Catalyst Systems Bearing Diverse N‐Heterocyclic Carbene Precursors for Atom‐Economic Amide Synthesis from Alcohols and Amines
Author(s) -
Cheng Hua,
Xiong MaoQian,
Cheng ChuanXiang,
Wang HuaJing,
Lu Qiang,
Liu HongFu,
Yao FuBin,
Chen Cheng,
Verpoort Francis
Publication year - 2018
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201701734
Subject(s) - catalysis , carbene , ruthenium , chemistry , combinatorial chemistry , amide , ligand (biochemistry) , atom economy , organic synthesis , organic chemistry , photochemistry , biochemistry , receptor
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 1 H 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.