Photochemical hydrogen production based on the HCOOH/CO2 cycle promoted by a pentanuclear cobalt complex

The first catalytic cycle for hydrogen production based on the photochemical two-electron reduction of carbon dioxide (CO₂) and the dehydrogenation of formic acid at ambient temperature was demonstrated using a pentanuclear cobalt complex (Co5). A series of mechanistic studies were performed to elucidate the mechanism responsible for the promotion of the photocatalytic cycle by Co5.

Modulation of H+/H- exchange in iridium-hydride 2-hydroxypyridine complexes by remote Lewis acids

A series of iridium hydride complexes featuring dihydrogen bonding are presented and shown to undergo rapid H⁺/H^- exchange (1240 s^-1 at 25 °C). We demonstrate that the H⁺/H^- exchange rate can be modified by post-synthetic modification at a remote site using BH₃, Zn(C₆F₅)₂, and [Me₃O][BF₄]. This route provides a complementary strategy to traditional methods that rely on pre-metalation modifications to a metal's primary sphere.

Metal-Ligand Cooperation in Cp*Ir-Pyridylpyrrole Complexes: Rational Design and Catalytic Activity in Formic Acid Dehydrogenation and CO2 Hydrogenation under Ambient Conditions

Interconversion between CO₂ + H₂ and FA/formate is the most promising strategy for the fixation of carbon dioxide and reversible hydrogen storage; however, FA dehydrogenation and CO₂ hydrogenation are usually studied separately using different catalysts for each reaction. This report describes of the catalysis of [Cp*Ir(N∧N)(X)]ⁿ⁺ (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; X = Cl, n = 0; X = H₂O, n = 1) bearing a proton-responsive N∧N pyridylpyrrole ligand for both reactions. Complex 2-H₂O catalyzes FA dehydrogenation at 90 °C with a TOF_max of 45 900 h^-1. Its catalysis is more active in aqueous solution than in neat solution under base-free conditions. These complexes also catalyze CO₂ hydrogenation in the presence of base to formate under atmospheric pressure (CO₂/H₂ = 0.05 MPa/0.05 MPa) at 25 °C with a TOF value of 4.5 h^-1 in aqueous solution and with a TOF value of 29 h^-1 in a methanol/H₂O mixture solvent. The possible mechanism is proposed by intermediate characterization and KIE experiments. The extraordinary activity of these complexes are mainly attributed to the metal-ligand cooperative effect of the the pyrrole group to accept a proton in the dehydrogenation of formic acid and assist cooperative heterolytic H-H bond cleavage in CO₂ hydrogenation.

Catalytic hydrogenation of CO2 at a structurally rigidified cobalt center

Catalytic hydrogenation of CO₂ occurs at a cobalt center supported by a rigidified PNP ligand revealing higher catalytic performance.

Reductive C-C Coupling from α,β-Unsaturated Nitriles by Intercepting Keteniminates

We present an atom-economic strategy to catalytically generate and intercept nitrile anion equivalents using hydrogen transfer catalysis. Addition of α,β-unsaturated nitriles to a pincer-based Ru-H complex affords structurally characterized κ-N-coordinated keteniminates by selective 1,4-hydride transfer. When generated in situ under catalytic hydrogenation conditions, electrophilic addition to the keteniminate was achieved using anhydrides to provide α-cyanoacetates in high yields. This work represents a new application of hydrogen transfer catalysis using α,β-unsaturated nitriles for reductive C-C coupling reactions.