Dehydrogenative amide synthesis from alcohols and amines utilizing N-heterocyclic carbene-based ruthenium complexes as efficient catalysts: The influence of catalyst loadings, ancillary and added ligands

The metal-catalyzed dehydrogenative coupling of alcohols and amines to access amides has been recognized as an atom-economic and environmental-friendly process. Apart from the formation of the amide products, three other kinds of compounds (esters, imines and amines) may also be produced. Therefore, it is of vital importance to investigate product distribution in this transformation. Herein, N-heterocyclic carbene-based Ru (NHC/Ru) complexes [Ru-1]-[Ru-5] with different ancillary ligands were prepared and characterized. Based on these complexes, we selected condition A (without an added NHC precursor) and condition B (with an added NHC precursor) to comprehensively explore the selectivity and yield of the desired amides. After careful evaluation of various parameters, the Ru loadings, added NHC precursors and the electronic/steric properties of ancillary NHC ligands were found to have considerable influence on this catalytic process. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the factors influencing product distribution in the metal-catalyzed dehydrogenative coupling of alcohols and amines to access amides using N-heterocyclic carbene-based Ru (NHC/Ru) complexes. The experimental results show that Ru loadings, added NHC precursors, and the electronic/steric properties of ancillary NHC ligands have a significant impact on the selectivity and yield of the catalytic process.