Highly Robust Diamino-Substituted Phenanthroline-Based Iridium Catalysts for Dehydrogenation of Formic Acid in Water with Mechanistic Insights

High Resolution Image Download MS PowerPoint Slide Highly robust Ir complexes were developed for the additive-free dehydrogenation of formic acid (FA) in water under harsh reaction conditions. Phenanthroline as the core unit of the ligand with amino groups as substituents enhanced both catalytic activity and durability with a negligible amount of CO formed as a contaminant (below 0.5 ppm). Notably, when a 20 M FA solution was continuously supplied to the Ir phenanthroline complex with two pyrrolidino-substituents (0.2 μmol) in 8 M FA (100 mL) under reflux conditions, a maximum turnover frequency of 245,000 h –1 was maintained for 14 h, and a turnover number of up to 14 million was achieved. Additionally, the iridium-bound formato intermediate was characterized in situ using 1 H and 13 C NMR, as well as electrospray ionization-mass spectrometry.