Catalytic Mechanism for the Ruthenium-Complex-CatalyzedSynthesis of Amides from Alcohols and Amines: A DFT Study.

Detailsof the reaction mechanism for the Ru–PNN pincer complex catalyzedamidation from an alcohol and an amine proposed by Milstein et al.was elucidated using M06 density functional theory calculations. Inaddition, the bifunctional double hydrogen transfer (BDHT) mechanismfor the dehydrogenative oxidation step was investigated for comparison.Finally, the BDHT mechanism was found to be preferred over the β-Helimination pathway that was proposed by Milstein et al. On the basisof the analysis of NBO charges and orbital interactions of intermediatesand transition states, we designed a new catalyst with the additionof an electron-donating substituent (−NEt2), whichprovided much reduced energy barriers and a lower potential energysurface along both mechanisms. [ABSTRACT FROM AUTHOR]