Catalytic mechanism for the ruthenium-complex-catalyzed synthesis of amides from alcohols and amines: A DFT Study

Details of the reaction mechanism for the Ru-PNN pincer complex catalyzed amidation from an alcohol and an amine proposed by Milstein et al. was elucidated using M06 density functional theory calculations. In addition, the bifunctional double hydrogen transfer (BDHT) mechanism for the dehydrogenative oxidation step was investigated for comparison. Finally, the BDHT mechanism was found to be preferred over the β-H elimination pathway that was proposed by Milstein et al. On the basis of the analysis of NBO charges and orbital interactions of intermediates and transition states, we designed a new catalyst with the addition of an electron-donating substituent (-NEt₂), which provided much reduced energy barriers and a lower potential energy surface along both mechanisms.