Conversion of CO2 into Formate by Homogeneously Catalyzed Hydrogenation in Water: Tuning Catalytic Activity and Water Solubility through the Acid–Base Equilibrium of the Ligand

Abstract This Microreview focuses on the recently developed hydrogenation of CO 2 and hydrogen carbonate catalyzed by half‐sandwich complexes with 4,4′‐dihydroxy‐2,2′‐bipyridine (dhbp) and 4,7‐dihydroxy‐1,10‐phenanthroline (dhpt). An unprecedented high catalytic activity and reusability of the catalyst without waste generation were achieved by automatic tuning of the catalytic activity and water solubility of the catalyst through the acid–base equilibrium of the catalyst ligand. The oxyanion generated from the phenol hydroxy group played significant roles in the electronic effect and polarity. The catalyst design concept and the excellent properties of the ligands are expected to have significantly broader implications for the design of new homogeneous catalysts.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)