Ir(III) complexes based on Quinoline Carboxamide ligands for CO2 hydrogenation and formic acid dehydrogenation in water

A series of new quinoline and isoquinoline carboxamide-based Ir(III) complexes based on the strong electron-donating ability of the anionic N atom have been developed for the hydrogenation of CO₂ and dehydrogenation of formic acid (FADH) in water. The effects of the position of the quinoline structure and the electron-donating methoxy (OMe) and hydroxy (OH) groups were investigated. In CO₂ hydrogenation, the complex with 4-hydroxy-N-(4-hydroxyphenyl)quinoline-2-carboxamide as a ligand was found to be the most efficient, with a turnover frequency (TOF) of 2040 h⁻¹ at 50 °C and 1 MPa H₂/CO₂ (1:1) pressurized conditions in a 1 M NaHCO₃ solution, and exhibited a high TOF of 75 h⁻¹ even under ambient temperature and atmospheric pressure. In formic acid (FA) dehydrogenation, on the other hand, the complex with N-phenylisoquinoline-1-carboxamide as a ligand had the highest catalytic activity with the initial TOF > 26,100 h⁻¹ for 1 M FA solution (pH 1.7) at 60 °C and achieving the initial TOF up to 114,000 h⁻¹ in 8 M FA solution at 80 °C.