CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand

Naoya Onishi, Shaoan Xu, Yuichi Manaka, Yuki Suna, Wan Hui Wang, James T. Muckerman, Etsuko Fujita, Yuichiro Himeda

Research output: Contribution to journalArticle

74 Citations (Scopus)


The catalytic cycle for the production of formic acid by CO2 hydrogenation and the reverse reaction have received renewed attention because they are viewed as offering a viable scheme for hydrogen storage and release. In this Forum Article, CO2 hydrogenation catalyzed by iridium complexes bearing sophisticated N^N-bidentate ligands is reported. We describe how a ligand containing hydroxy groups as proton-responsive substituents enhances the catalytic performance by an electronic effect of the oxyanions and a pendent-base effect through secondary coordination sphere interactions. In particular, [(Cp∗IrCl)2(TH2BPM)]Cl2 (Cp∗ = pentamethylcyclopentadienyl; TH2BPM = 4,4′,6,6′-tetrahydroxy-2,2′-bipyrimidine) enormously promotes the catalytic hydrogenation of CO2 in basic water by these synergistic effects under atmospheric pressure and at room temperature. Additionally, newly designed complexes with azole-type ligands were applied to CO2 hydrogenation. The catalytic efficiencies of the azole-type complexes were much higher than that of the unsubstituted bipyridine complex [Cp∗Ir(bpy)(OH2)]SO4. Furthermore, the introduction of one or more hydroxy groups into ligands such as 2-pyrazolyl-6-hydroxypyridine, 2-pyrazolyl-4,6-dihydroxypyrimidine, and 4-pyrazolyl-2,6-dihydroxypyrimidine enhanced the catalytic activity. It is clear that the incorporation of additional electron-donating functionalities into proton-responsive azole-type ligands is effective for promoting further enhanced hydrogenation of CO2.

Original languageEnglish
Pages (from-to)5114-5123
Number of pages10
JournalInorganic Chemistry
Issue number11
Publication statusPublished - Jun 1 2015

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Fingerprint Dive into the research topics of 'CO<sub>2</sub> hydrogenation catalyzed by iridium complexes with a proton-responsive ligand'. Together they form a unique fingerprint.

  • Cite this