Non-innocent PNN ligand is important for CO oxidation by NO catalyzed by a (PNN)Ru-H pincer complex: insights from DFT calculations.

Milstein et al. developed an efficient and mild method for CO oxidation by NO to give CO and N catalyzed by a (PNN)Ru-H pincer complex. To gain mechanistic information on this catalytic transformation, the reaction mechanism has been studied using density functional theory (DFT) calculations. It was found that the catalytic cycle for CO oxidation by NO proceeds in three stages: NO activation to form a (PNN)Ru-OH intermediate, CO insertion into the Ru-OH bond to form a (PNN)Ru-COOH intermediate and CO release from (PNN)Ru-COOH. In the CO release stage, CO is not released via a β-H elimination mechanism as proposed in experiments, instead it is released via a deprotonation mechanism. The calculations demonstrated that the Ru-H bond of the catalyst plays an important role in facilitating the activation of NO, which is the rate-determining step for the whole catalytic cycle, and the non-innocent PNN ligand is very important for CO oxidation by NO. Our theoretical results are consistent with the experimental observations and could help design highly efficient catalysts for NO activation.