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Title: CO 2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand

Abstract

In this study, the catalytic cycle for the production of formic acid by CO₂ hydrogenation and the reverse reaction has 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 N^N-bidentate ligands is reported. We describe how a ligand containing hydroxyl groups as proton-responsive substituents enhances catalytic performance by an electronic effect of the oxyanions and a pendent-base effect through secondary coordination sphere interaction. In particular, [(Cp*IrCl)₂(TH2BPM)]Cl₂ (Cp* = pentamethyl cyclopentadienyl, TH2BPM = 4,4',6,6'-tetrahydroxy-2,2'-bipyrimidine) promotes enormously the catalytic hydrogenation of CO₂ by these synergistic effects under atmospheric pressure and at room temperature. Additionally, newly designed complexes with azole-type ligands are applied to CO₂ hydrogenation. The catalytic efficiencies of the azole-type complexes are much higher than that of the unsubstituted bipyridine complex [Cp*Ir(bpy)(OH₂)]SO₄. Furthermore, the introduction of one or more hydroxyl groups into ligands such as 2-pyrazolyl-6-hydroxypyridine, 2-pyrazolyl-4,6-dihydroxyl pyrimidine, and 4-pyrazolyl-2,6-dihydroxyl pyrimidine enhanced catalytic activity. It is clear that the incorporation of electron-donating hydroxyl groups into proton-responsive ligands is effective for promoting the hydrogenation of CO₂.

Authors:
 [1];  [1];  [2];  [2];  [2];  [3];  [3];  [1]
  1. National Institute of Advanced Industrial Science and Technology, Ibaraki (Japan); Japan Science and Technology Agency, Saitama (Japan)
  2. National Institute of Advanced Industrial Science and Technology, Ibaraki (Japan)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1182536
Report Number(s):
BNL-107637-2015-JA
Journal ID: ISSN 0020-1669; R&D Project: CO026; KC0304030
Grant/Contract Number:  
SC00112704
Resource Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 54; Journal Issue: 11; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; proton-responsive ligand; iridium complexes; CO₂ hydrogenation

Citation Formats

Onishi, Naoya, Xu, Shaoan, Manaka, Yuichi, Suna, Yuki, Wang, Wan -Hui, Muckerman, James T., Fujita, Etsuko, and Himeda, Yuichiro. CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand. United States: N. p., 2015. Web. doi:10.1021/ic502904q.
Onishi, Naoya, Xu, Shaoan, Manaka, Yuichi, Suna, Yuki, Wang, Wan -Hui, Muckerman, James T., Fujita, Etsuko, & Himeda, Yuichiro. CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand. United States. doi:10.1021/ic502904q.
Onishi, Naoya, Xu, Shaoan, Manaka, Yuichi, Suna, Yuki, Wang, Wan -Hui, Muckerman, James T., Fujita, Etsuko, and Himeda, Yuichiro. Wed . "CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand". United States. doi:10.1021/ic502904q. https://www.osti.gov/servlets/purl/1182536.
@article{osti_1182536,
title = {CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand},
author = {Onishi, Naoya and Xu, Shaoan and Manaka, Yuichi and Suna, Yuki and Wang, Wan -Hui and Muckerman, James T. and Fujita, Etsuko and Himeda, Yuichiro},
abstractNote = {In this study, the catalytic cycle for the production of formic acid by CO₂ hydrogenation and the reverse reaction has 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 N^N-bidentate ligands is reported. We describe how a ligand containing hydroxyl groups as proton-responsive substituents enhances catalytic performance by an electronic effect of the oxyanions and a pendent-base effect through secondary coordination sphere interaction. In particular, [(Cp*IrCl)₂(TH2BPM)]Cl₂ (Cp* = pentamethyl cyclopentadienyl, TH2BPM = 4,4',6,6'-tetrahydroxy-2,2'-bipyrimidine) promotes enormously the catalytic hydrogenation of CO₂ by these synergistic effects under atmospheric pressure and at room temperature. Additionally, newly designed complexes with azole-type ligands are applied to CO₂ hydrogenation. The catalytic efficiencies of the azole-type complexes are much higher than that of the unsubstituted bipyridine complex [Cp*Ir(bpy)(OH₂)]SO₄. Furthermore, the introduction of one or more hydroxyl groups into ligands such as 2-pyrazolyl-6-hydroxypyridine, 2-pyrazolyl-4,6-dihydroxyl pyrimidine, and 4-pyrazolyl-2,6-dihydroxyl pyrimidine enhanced catalytic activity. It is clear that the incorporation of electron-donating hydroxyl groups into proton-responsive ligands is effective for promoting the hydrogenation of CO₂.},
doi = {10.1021/ic502904q},
journal = {Inorganic Chemistry},
number = 11,
volume = 54,
place = {United States},
year = {2015},
month = {2}
}

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