Second-coordination-sphere and electronic effects enhance iridium(iii)-catalyzed homogeneous hydrogenation of carbon dioxide in water near ambient temperature and pressure

Wan Hui Wang, Jonathan F. Hull, James Muckerman, Etsuko Fujita, Yuichiro Himeda

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133 Citations (Scopus)

Abstract

A new series of water soluble Ir(iii) catalysts has been designed and synthesized to determine the catalyst ligand's role in activating CO2 through electronic and second-coordination-sphere effects for the homogeneous catalytic hydrogenation of CO2. We report high catalytic hydrogenation activity of [Cp*Ir(6,6′-R2-bpy)(OH 2)]SO4 (bpy = 2,2′-bipyridine, R = OH) at ambient temperatures and pressures. Good correlation between the ligand substituents' Hammett parameters, which we varied by synthesizing ligands and catalysts substituted with R = H, Me, OMe and OH, and catalytic hydrogenation rates clearly illustrates the importance of electronic effects. Remarkably, additional rate enhancements are consistently observed when substituents are moved from 4,4′ positions to 6,6′ positions on 2,2′-bipyridine. Combined DFT calculations and NMR experiments suggest that the origin of these effects lies in the pendent base-aided heterolysis of H2, which significantly lowers the transition state energy. These studies are significant in elucidating new design principles for CO2 hydrogenation that lead to superior catalytic activity.

Original languageEnglish
Pages (from-to)7923-7926
Number of pages4
JournalEnergy and Environmental Science
Volume5
Issue number7
DOIs
Publication statusPublished - Jul 2012

Fingerprint

Iridium
iridium
Carbon Dioxide
ligand
Hydrogenation
Carbon dioxide
carbon dioxide
catalyst
Water
Ligands
Catalysts
temperature
water
Temperature
nuclear magnetic resonance
Electron transitions
Discrete Fourier transforms
Electron energy levels
Catalyst activity
Nuclear magnetic resonance

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Chemistry
  • Pollution
  • Nuclear Energy and Engineering

Cite this

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abstract = "A new series of water soluble Ir(iii) catalysts has been designed and synthesized to determine the catalyst ligand's role in activating CO2 through electronic and second-coordination-sphere effects for the homogeneous catalytic hydrogenation of CO2. We report high catalytic hydrogenation activity of [Cp*Ir(6,6′-R2-bpy)(OH 2)]SO4 (bpy = 2,2′-bipyridine, R = OH) at ambient temperatures and pressures. Good correlation between the ligand substituents' Hammett parameters, which we varied by synthesizing ligands and catalysts substituted with R = H, Me, OMe and OH, and catalytic hydrogenation rates clearly illustrates the importance of electronic effects. Remarkably, additional rate enhancements are consistently observed when substituents are moved from 4,4′ positions to 6,6′ positions on 2,2′-bipyridine. Combined DFT calculations and NMR experiments suggest that the origin of these effects lies in the pendent base-aided heterolysis of H2, which significantly lowers the transition state energy. These studies are significant in elucidating new design principles for CO2 hydrogenation that lead to superior catalytic activity.",
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AU - Wang, Wan Hui

AU - Hull, Jonathan F.

AU - Muckerman, James

AU - Fujita, Etsuko

AU - Himeda, Yuichiro

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N2 - A new series of water soluble Ir(iii) catalysts has been designed and synthesized to determine the catalyst ligand's role in activating CO2 through electronic and second-coordination-sphere effects for the homogeneous catalytic hydrogenation of CO2. We report high catalytic hydrogenation activity of [Cp*Ir(6,6′-R2-bpy)(OH 2)]SO4 (bpy = 2,2′-bipyridine, R = OH) at ambient temperatures and pressures. Good correlation between the ligand substituents' Hammett parameters, which we varied by synthesizing ligands and catalysts substituted with R = H, Me, OMe and OH, and catalytic hydrogenation rates clearly illustrates the importance of electronic effects. Remarkably, additional rate enhancements are consistently observed when substituents are moved from 4,4′ positions to 6,6′ positions on 2,2′-bipyridine. Combined DFT calculations and NMR experiments suggest that the origin of these effects lies in the pendent base-aided heterolysis of H2, which significantly lowers the transition state energy. These studies are significant in elucidating new design principles for CO2 hydrogenation that lead to superior catalytic activity.

AB - A new series of water soluble Ir(iii) catalysts has been designed and synthesized to determine the catalyst ligand's role in activating CO2 through electronic and second-coordination-sphere effects for the homogeneous catalytic hydrogenation of CO2. We report high catalytic hydrogenation activity of [Cp*Ir(6,6′-R2-bpy)(OH 2)]SO4 (bpy = 2,2′-bipyridine, R = OH) at ambient temperatures and pressures. Good correlation between the ligand substituents' Hammett parameters, which we varied by synthesizing ligands and catalysts substituted with R = H, Me, OMe and OH, and catalytic hydrogenation rates clearly illustrates the importance of electronic effects. Remarkably, additional rate enhancements are consistently observed when substituents are moved from 4,4′ positions to 6,6′ positions on 2,2′-bipyridine. Combined DFT calculations and NMR experiments suggest that the origin of these effects lies in the pendent base-aided heterolysis of H2, which significantly lowers the transition state energy. These studies are significant in elucidating new design principles for CO2 hydrogenation that lead to superior catalytic activity.

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