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 concept of strong electron donating ability of the anionic N-atom have been developed for hydrogenation of CO2 and dehydrogenation of formic acid (FADH) in water. The effect in catalytic activities with the series of complexes differing in the position of the quinoline ring as well as electron donating methoxy (-OMe) and hydroxy (-OH) functional groups has been investigated in detail. The complex 9 bearing the ligand 4-hydroxy-N-(4-hydroxyphenyl) quinoline-2-carboxamide was found to be the most efficient in CO2 hydrogenation with a TOF of 2040 h-1 at 50 °C and 1 MPa H2/CO2 (1:1) pressurized conditions. The active catalyst 9 exhibited an initial TOF of 75 h-1for CO2 hydrogenation even under ambient temperature and pressure in basic aqueous solution. In FADH, the complex 2 bearing the ligand N-phenyl isoquinoline-1-carboxamide had the highest catalytic activity with the initial TOF > 26000 h-1 for 1 M formic acid (FA) solution (pH 1.7) at 60 °C and achieving initial TOF up to 115000 h1 for 8 M FA solution at 80 °C.