Two step activation of Ru-PN³P pincer catalysts for CO₂ hydrogenation

Abstract

Activation of homogeneous catalysts is an important step in ensuring efficient operation of any catalytic system as a whole. For the majority of pincer catalysts, the activation step leans heavily on the metal ligand cooperative chemistry that allows these complexes to react with small molecule substrates and engage in catalytic transformations. While the majority of such catalysts require a single activation event to become cooperative, herein we report an exception to this trend. Specifically, we demonstrate that a Ru-PN³P aminopyridine pincer catalyst, which lacks conventional reactivity with hydrogen upon typical one-fold activation, can exhibit this reactivity when a sequential two-step activation is performed. The resulting anionic complexes readily activate molecular hydrogen and react further with CO₂ showing the previously unknown reactivity that is critical for CO₂ hydrogenation catalysts. While active in CO₂ hydrogenation, Ru-PN³Ps are significantly more efficient in hydrogenation of bicarbonates - a likely consequence of the chemistry of these pincers requiring formation of anionic complexes for hydrogen activation.