Dehydrogenation of Aqueous Formic Acid by Iridium and Ruthenium Complexes with Nitrogen-rich Diamino-bis(1H-1,2,4-triazole)

The development of efficient catalysts for the dehydrogenation of formic acid (FA) through molecular level control and precise regulation remains challenging. Herein, we report the newly developed complexes of iridium and ruthenium with nitrogen-rich ligand for aqueous FA dehydrogenation. The Cp*Ir complex 1 (Cp*=cyclopentadienyl) and Ru(p-cym) complex 2 (p-cym=p-Cymene) were synthesized and fully characterized. The single crystal structures of these complexes have a typical piano-stool structure. A turnover frequency of 12468 h(-1) was achieved for FA dehydrogenation at 90 degrees C by using complex 1 bearing 3,3'-diamino-5,5'-bis(1H-1,2,4-triazole) (DABT). The effects of pH, temperature, concentration of formic acid and amount of catalyst on the reaction kinetics were studied in detail. Kinetic isotope effect (KIE) experiments and H-1 NMR detection of reaction revealed that a plausible mechanism involves the decarboxylation of formate and the formation of H-2. More importantly, the influence of H2O and H+ was involved in the rate-determining step. This study demonstrated the effectiveness of nitrogen-rich ligand for FA dehydrogenation, which would contribute to the development of new and effective hydrogen release systems.