Atom-economic dehydrogenative amide synthesis via ruthenium catalysis

Abstract

Recently, a class of dehydrogenative transformations for amide bond formation have been developed. These transformations are atom-economic and environmentally-benign processes with their respective starting materials of alcohols and amines, aldehydes and amines, as well as symmetrical esters and amines, showing a promising prospect for applications. These unique protocols have been reported using various ruthenium-based catalytic systems. However, challenges still exist in this area. For example, existing catalytic systems usually suffer from low efficiency, high catalyst loading, and lack of structural diversity.

Synthesis, characterization, catalytic and biological application of half-sandwich ruthenium complexes bearing hemilabile (κ2-C,S)-thioether-functionalised NHC ligands

“…3 Ruthenium has been established as the metal of choice for this highly atom-economic and environmentally friendly transformation. 4 Consequently, a wide-array of Ru-based catalyst systems have been developed for the dehydrogenation of alcohol. 3a, 3b, 3d, 5 In this context, Rucomplexes bearing N-Heterocyclic carbenes (NHCs), as synthetically accessible and highly tuneable ligand, 6 either generated in situ 7 or well-defined, 8 are particularly interesting for this process.…”

Mechanism of atom economical conversion of alcohols and amines to amides using Fe(ii) pincer catalyst. An outer-sphere metal–ligand pathway or an inner-sphere elimination pathway?

“…5 Alternatively they can also be synthesized by using transition metal catalyzed dehydrogenation of alcohols with amines which is doubtlessly an efficient and atom economical method of synthesis. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] The rst transition metal catalyst (Ru-PNN pincer catalyst) for direct amide synthesis was proposed by Milstein which operates through metal-ligand cooperation by aromatization and dearomatization of the pyridine ring. 8 Since then a lot of attention has been paid to direct amide formation from alcohols and amines.…”

“…8 Since then a lot of attention has been paid to direct amide formation from alcohols and amines. 6,7,[9][10][11][12][13][14][15][16][17][18][19] The atom economic strategy of amide synthesis faces lot of challenges such as limited substrate scope, long reaction timings and harsh reaction temperatures needed for the reaction to carry out. To circumvent these problems some efforts are being made to develop the transition-metal catalysts for the dehydrogenative coupling of alcohols with amines to form amides.…”

Ruthenium-Based Catalytic Systems Incorporating a Labile Cyclooctadiene Ligand with N-Heterocyclic Carbene Precursors for the Atom-Economic Alcohol Amidation Using Amines

“…Recently, a methodology employing transition-metal-based catalytic systems for direct amide synthesis from alcohols and amines was proven to be far more atom-economic and environmentally friendly as the only byproduct is hydrogen [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Throughout this research, ruthenium (Ru) was most extensively studied [ 23 ]. Initially, the Murahashi [ 24 ] and Milstein [ 25 ] groups pioneered Ru-catalyzed amide synthesis in intramolecular and intermolecular manners, respectively.…”