Noninnocent Ligands for Efficient Dehydrogenation of Aqueous and Neat Formic Acid under Base-Free Conditions

Formic acid could play an important role in energy transition if robust catalysts for its efficient dehydrogenation are developed. Most importantly, additive-free protocols are sought to reduce the cost and simplify the dehydrogenation process. Ideally, the highest energy concentration requires the use of neat formic acid for which only a few catalysts, active under additive-free conditions, have been reported. We prepared several new ruthenium and iridium complexes incorporating dipyridylamine ligands with various electronic and steric properties. Among all these complexes, the air-stable Ir8 bearing a bis-dimethylamino-substituted dipyridylamine ligand displayed the best performances in the dehydrogenation of aqueous solutions of formic acid in the absence of any additives. The same catalyst could also dehydrogenate neat formic acid with a TOF of 11,373 h(-1) at 80 degrees C. High H-2/CO2 pressure, CO- free gas stream, and catalyst latency enabling storage and further use of FA/catalyst premix have been achieved. Experimental and theoretical studies have highlighted the roles of dipyridylamine and the SO42- ligand in the dehydrogenation process.