Efficient Cp∗Ir Catalysts with Imidazoline Ligands for CO2 Hydrogenation

Shaoan Xu, Naoya Onishi, Akihiro Tsurusaki, Yuichi Manaka, Wan Hui Wang, James Muckerman, Etsuko Fujita, Yuichiro Himeda

Research output: Contribution to journalArticle

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Abstract

We report newly developed iridium catalysts with electron-donating imidazoline moieties as ligands for the hydrogenation of CO2 to formate in aqueous solution. Interestingly, these new complexes promote CO2 hydrogenation much more effectively than their imidazole analogues and exhibit a turnover frequency (TOF) of 1290 h-1 for the bisimidazoline complex compared to that of 20 h-1 for the bisimidazole complex at 1 MPa and 50 C. In addition, the hydrogenation proceeds smoothly even under atmospheric pressure at room temperature. The TOF of 43 h-1 for the bisimidazoline complex is comparable to that of a dinuclear complex (70 h-1, highest TOF reported) [Nat. Chem. 2012, 4, 383], which incorporates proton-responsive ligands with pendent-OH groups in the second coordination sphere. The catalytic activity of the complex with an N-methylated imidazoline moiety is much the same as that of the corresponding pyridylimidazoline analogue. This result and the UV/Vis titrations of the imidazoline complexes indicate that the high activity is not attributable to the deprotonation of NH on the imidazoline under the reaction conditions. A novel complex having imidazoline ligands shows much higher catalytic activity for CO2 hydrogenation than the conventional complex having imidazole ligands. The change from a double bond in imidazole to a single bond in imidazoline leads to a 60-fold increase in the catalytic activity.

Original languageEnglish
Pages (from-to)5591-5594
Number of pages4
JournalEuropean Journal of Inorganic Chemistry
Volume2015
Issue number34
DOIs
Publication statusPublished - Dec 1 2015

Fingerprint

Imidazolines
Hydrogenation
Ligands
Catalysts
Catalyst activity
formic acid
Iridium
Deprotonation
Titration
Atmospheric pressure
Protons
Electrons
imidazole

Keywords

  • CO hydrogenation
  • Homogeneous catalysis
  • Iridium

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Efficient Cp∗Ir Catalysts with Imidazoline Ligands for CO2 Hydrogenation. / Xu, Shaoan; Onishi, Naoya; Tsurusaki, Akihiro; Manaka, Yuichi; Wang, Wan Hui; Muckerman, James; Fujita, Etsuko; Himeda, Yuichiro.

In: European Journal of Inorganic Chemistry, Vol. 2015, No. 34, 01.12.2015, p. 5591-5594.

Research output: Contribution to journalArticle

Xu, Shaoan ; Onishi, Naoya ; Tsurusaki, Akihiro ; Manaka, Yuichi ; Wang, Wan Hui ; Muckerman, James ; Fujita, Etsuko ; Himeda, Yuichiro. / Efficient Cp∗Ir Catalysts with Imidazoline Ligands for CO2 Hydrogenation. In: European Journal of Inorganic Chemistry. 2015 ; Vol. 2015, No. 34. pp. 5591-5594.
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AB - We report newly developed iridium catalysts with electron-donating imidazoline moieties as ligands for the hydrogenation of CO2 to formate in aqueous solution. Interestingly, these new complexes promote CO2 hydrogenation much more effectively than their imidazole analogues and exhibit a turnover frequency (TOF) of 1290 h-1 for the bisimidazoline complex compared to that of 20 h-1 for the bisimidazole complex at 1 MPa and 50 C. In addition, the hydrogenation proceeds smoothly even under atmospheric pressure at room temperature. The TOF of 43 h-1 for the bisimidazoline complex is comparable to that of a dinuclear complex (70 h-1, highest TOF reported) [Nat. Chem. 2012, 4, 383], which incorporates proton-responsive ligands with pendent-OH groups in the second coordination sphere. The catalytic activity of the complex with an N-methylated imidazoline moiety is much the same as that of the corresponding pyridylimidazoline analogue. This result and the UV/Vis titrations of the imidazoline complexes indicate that the high activity is not attributable to the deprotonation of NH on the imidazoline under the reaction conditions. A novel complex having imidazoline ligands shows much higher catalytic activity for CO2 hydrogenation than the conventional complex having imidazole ligands. The change from a double bond in imidazole to a single bond in imidazoline leads to a 60-fold increase in the catalytic activity.

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