Metal–Ligand Cooperation in Cp*Ir-Pyridylpyrrole Complexes: Rational Design and Catalytic Activity in Formic Acid Dehydrogenation and CO<sub>2</sub> Hydrogenation under Ambient Conditions
Xiu‐Fang Mo, Chao Liu, Ze-Wen Chen, Fan Ma, Piao He, Xiao‐Yi Yi
Abstract
Interconversion between CO2 + H2 and FA/formate is the most promising strategy for the fixation of carbon dioxide and reversible hydrogen storage; however, FA dehydrogenation and CO2 hydrogenation are usually studied separately using different catalysts for each reaction. This report describes of the catalysis of [Cp*Ir(N∧N)(X)]n+ (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; X = Cl, n = 0; X = H2O, n = 1) bearing a proton-responsive N∧N pyridylpyrrole ligand for both reactions. Complex 2-H2O catalyzes FA dehydrogenation at 90 °C with a TOFmax of 45 900 h–1. Its catalysis is more active in aqueous solution than in neat solution under base-free conditions. These complexes also catalyze CO2 hydrogenation in the presence of base to formate under atmospheric pressure (CO2/H2 = 0.05 MPa/0.05 MPa) at 25 °C with a TOF value of 4.5 h–1 in aqueous solution and with a TOF value of 29 h–1 in a methanol/H2O mixture solvent. The possible mechanism is proposed by intermediate characterization and KIE experiments. The extraordinary activity of these complexes are mainly attributed to the metal–ligand cooperative effect of the the pyrrole group to accept a proton in the dehydrogenation of formic acid and assist cooperative heterolytic H–H bond cleavage in CO2 hydrogenation.