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 PNN-pincer ruthenium(0) pre-catalyst for the hydrogenation of polar organic compounds. The pre-catalyst activates by reaction with two equivalents of hydrogen, resulting in a net oxidative addition to ruthenium and hydrogenation of an imine functional group on the supporting ligand. The kinetics of pre-catalyst 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) pre-catalyst.