The hydrogenation of CO2 to formic acid has attracted increasing attention as a hydrogen storage system. A number of groups have been devoted to improving the performance of CO2 hydrogenation catalysts. For homogeneous catalysis, the crucial factors are the metal ion and its immediate environment. In particular, the ligand dictates the complex's catalytic activity and solubility in the reaction medium. Thus, many kinds of excellent ligands with improved performance have been developed. Here we will discuss the design of catalysts for hydrogenation of CO2 in water on the basis of the concept of a proton-responsive ligand with pendant bases.We have developed a novel class of proton-responsive ligands (4,4'-dihydroxy-2,2'-bipyridine and 4,7-dihydroxy-1,10-phenanthroline), which is capable of losing two protons under basic conditions.[1] The strong electron-donating ability of the oxyanion generated by deprotonation of the hydroxyl groups can improve the catalytic activity of the complex. To further improve catalyst activity, we designed a 6,6'-dihydroxy-2,2'-bipyridine that has the combined effects of electronic activation and a pendent base in the secondary coordination sphere.[2] Finally, we have found that a dinuclear iridium complex with 4,4',6,6'-tetrahydroxy-2,2'-bipyrimidine hydrogenates CO2 under ambient temperature and pressure in water.[3] Y.H. acknowledge Japan-U.S. cooperation project for research and standardization of Clean Energy Technologies for financial support. The work at BNL was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences, & Biosciences, Office of Basic Energy Sciences. [1] Himeda, Y.; Onozawa-Komatsuzaki, N.; Sugihara, H.; Kasuga, K. Organometallics 2007 , 26, 702.[2] Wang, W.-H.; Hull, J. F.; Muckerman, J. T.; Fujita, E.; Himeda, Y. Energy Environ. Sci. 2012 , 5, 7923.[3] Hull, J. F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.; Periana, R.; Szalda, D. J.; Muckerman, J. T.; Fujita, E. Nat. Chem. 2012 , 4, 383.

Catalyst design for hydrogenation of CO<sub>2</sub> using proton-responsive ligand

246th National Meeting (2013)

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Catalyst design for hydrogenation of CO2 using proton-responsive ligand

Catalyst design for hydrogenation of CO₂ using proton-responsive ligand