Task-Specific "Scorpion Ligand" for the Generation of Dihydrogen from Formic Acid

A new iridium catalyst for base-free dehydrogenation of formic acid was designed and synthesized. This air-stable "scorpion" catalyst enables the dehydrogenation of aqueous formic acid at temperatures as low as 60 °C and with a TOF of 109,460 h-1 at 100 °C. Notably, pure formic acid was dehydrogenated at 80 °C with a TOF of 14,844 h-1. No undesired CO could be detected in the gas flow. Mechanistic studies were conducted experimentally and theoretically, showcasing a metal-ligand cooperation that enables the formation of an iridium-hydride species requiring a very low activation energy of 10.0 kcal·mol-1, while the rate-determining step requires overcoming a low energy barrier of 15.3 kcal·mol-1.