Homogeneous hydrogenation of saturated bicarbonate slurry to formates using multiphase catalysis

Formic acid and formate salts are key intermediates along the pathways for CO2 utilization and hydrogen storage. Herein we report a highly efficient multiphase catalytic system utilizing ruthenium PNP pincer catalyst for converting supersaturated bicarbonate solutions and slurries to aqueous formate solutions up to 12M in molarity. The biphasic catalytic system delivers turnover frequencies up to 73 000 h-1 and remains stable for up to 474’000 turnovers once reaction conditions are optimized.</jats:p

Homogeneous hydrogenation of saturated bicarbonate slurry to formates using multiphase catalysis

Formic acid and formate salts are key intermediates along the pathways for CO2 utilization and hydrogen storage. Herein we report a highly efficient multiphase catalytic system utilizing ruthenium PNP pincer catalyst for converting supersaturated bicarbonate solutions and slurries to aqueous formate solutions up to 12M in molarity. The biphasic catalytic system delivers turnover frequencies up to 73 000 h-1 and remains stable for up to 474’000 turnovers once reaction conditions are optimized

Porphyrin Cobalt(III) “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH)

In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier

Porphyrin Cobalt(III) “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH)

In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier

Homogeneous hydrogenation of saturated bicarbonate slurry to formates using multiphase catalysis

A highly efficient bicarbonate hydrogenation catalyst system based on ppm concentrations of a Ru-PNP pincer complex is presented. It allows converting supersaturated bicarbonate slurries to aqueous formate solutions up to 12 M in molarity.</jats:p

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

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