Ligand-Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution

Keita Koshiba, Kosei Yamauchi, Ken Sakai

研究成果: ジャーナルへの寄稿記事

抄録

Proton abstraction leading to the formation of a hydride species required to evolve H 2 largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square-planar Ni II (bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d z 2 orbital after formation of [Ni I (bpy −. )(dcbdt)] 2− via consecutive two one-electron reductions (bpy=2,2′-bipyridine; dcbdt=4,5-dicyanobenzene-1,2-dithiolate). The catalyst is likely to adopt the EECC′ mechanism in which the rate of the first protonation step is by far higher than that of the second step, even though an alternative path requiring another reduction (i. e., ECEC′) remains unexcluded. Our DFT calculations reveal that the first and second reductions are correlated with the electron injection into the metal-ligand anti-bonding and π*(bpy) orbitals, respectively, where the latter orbital shows non-negligible hybridization with the nickel d orbital. In addition, a homoleptic catalyst [Ni II (dcbdt) 2 ] 2− is shown to adopt the EC′EC mechanism with the rate-determing step being a hydride forming step, consistent with the largely delocalized nature of the injected electron over the two dcbdt ligands (π*(dcbdt) orbital). This work demonstrates the importance of raising the basicity of the metal d orbital, relevant to promote the proton-coupled electron transfer (PCET).

元の言語英語
ページ(範囲)2273-2281
ページ数9
ジャーナルChemElectroChem
6
発行部数8
DOI
出版物ステータス出版済み - 4 15 2019

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Electrocatalysts
Alkalinity
Protons
Hydrogen
1,2-benzenedicarbonitrile
Metals
Ligands
Hydrides
Catalysts
Electrons
Electron injection
Protonation
Nickel
Discrete Fourier transforms

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Electrochemistry

これを引用

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title = "Ligand-Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution",
abstract = "Proton abstraction leading to the formation of a hydride species required to evolve H 2 largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square-planar Ni II (bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d z 2 orbital after formation of [Ni I (bpy −. )(dcbdt)] 2− via consecutive two one-electron reductions (bpy=2,2′-bipyridine; dcbdt=4,5-dicyanobenzene-1,2-dithiolate). The catalyst is likely to adopt the EECC′ mechanism in which the rate of the first protonation step is by far higher than that of the second step, even though an alternative path requiring another reduction (i. e., ECEC′) remains unexcluded. Our DFT calculations reveal that the first and second reductions are correlated with the electron injection into the metal-ligand anti-bonding and π*(bpy) orbitals, respectively, where the latter orbital shows non-negligible hybridization with the nickel d orbital. In addition, a homoleptic catalyst [Ni II (dcbdt) 2 ] 2− is shown to adopt the EC′EC mechanism with the rate-determing step being a hydride forming step, consistent with the largely delocalized nature of the injected electron over the two dcbdt ligands (π*(dcbdt) orbital). This work demonstrates the importance of raising the basicity of the metal d orbital, relevant to promote the proton-coupled electron transfer (PCET).",
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T1 - Ligand-Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution

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AU - Yamauchi, Kosei

AU - Sakai, Ken

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N2 - Proton abstraction leading to the formation of a hydride species required to evolve H 2 largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square-planar Ni II (bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d z 2 orbital after formation of [Ni I (bpy −. )(dcbdt)] 2− via consecutive two one-electron reductions (bpy=2,2′-bipyridine; dcbdt=4,5-dicyanobenzene-1,2-dithiolate). The catalyst is likely to adopt the EECC′ mechanism in which the rate of the first protonation step is by far higher than that of the second step, even though an alternative path requiring another reduction (i. e., ECEC′) remains unexcluded. Our DFT calculations reveal that the first and second reductions are correlated with the electron injection into the metal-ligand anti-bonding and π*(bpy) orbitals, respectively, where the latter orbital shows non-negligible hybridization with the nickel d orbital. In addition, a homoleptic catalyst [Ni II (dcbdt) 2 ] 2− is shown to adopt the EC′EC mechanism with the rate-determing step being a hydride forming step, consistent with the largely delocalized nature of the injected electron over the two dcbdt ligands (π*(dcbdt) orbital). This work demonstrates the importance of raising the basicity of the metal d orbital, relevant to promote the proton-coupled electron transfer (PCET).

AB - Proton abstraction leading to the formation of a hydride species required to evolve H 2 largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square-planar Ni II (bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d z 2 orbital after formation of [Ni I (bpy −. )(dcbdt)] 2− via consecutive two one-electron reductions (bpy=2,2′-bipyridine; dcbdt=4,5-dicyanobenzene-1,2-dithiolate). The catalyst is likely to adopt the EECC′ mechanism in which the rate of the first protonation step is by far higher than that of the second step, even though an alternative path requiring another reduction (i. e., ECEC′) remains unexcluded. Our DFT calculations reveal that the first and second reductions are correlated with the electron injection into the metal-ligand anti-bonding and π*(bpy) orbitals, respectively, where the latter orbital shows non-negligible hybridization with the nickel d orbital. In addition, a homoleptic catalyst [Ni II (dcbdt) 2 ] 2− is shown to adopt the EC′EC mechanism with the rate-determing step being a hydride forming step, consistent with the largely delocalized nature of the injected electron over the two dcbdt ligands (π*(dcbdt) orbital). This work demonstrates the importance of raising the basicity of the metal d orbital, relevant to promote the proton-coupled electron transfer (PCET).

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