Autocatalytic Activation of a Ruthenium-PNN-Pincer Hydrogenation Catalyst

In this article, we describe a detailed experimental and computational study of the activation mechanism for a highly active pincer ruthenium(0) precatalyst for the hydrogenation of polar organic compounds. The precatalyst activates by reaction with 2 equiv of hydrogen, resulting in a net oxidative addition to ruthenium and hydrogenation of an imine functional group on the supporting ligand. The kinetics of precatalyst hydrogenation were measured by UV-visible spectroscopy under catalytically relevant conditions (10-39 bar hydrogen, 298 K). The kinetic data, in combination with density functional theory calculations, support an intriguing autocatalytic mechanism, where the product ruthenium(II) complex catalyzes the hydrogenation of the ruthenium(0) precatalyst.