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Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes

We report the solution‐phase electrochemistry of seven half‐sandwich iridium(III) complexes with varying pyridine‐alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of C...

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Detalles Bibliográficos
Autores principales: Sackville, Emma V., Marken, Frank, Hintermair, Ulrich
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470865/
https://www.ncbi.nlm.nih.gov/pubmed/31007774
http://dx.doi.org/10.1002/cctc.201800916
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author Sackville, Emma V.
Marken, Frank
Hintermair, Ulrich
author_facet Sackville, Emma V.
Marken, Frank
Hintermair, Ulrich
author_sort Sackville, Emma V.
collection PubMed
description We report the solution‐phase electrochemistry of seven half‐sandwich iridium(III) complexes with varying pyridine‐alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciation determines the electrochemical response: cationic complexes show over 1 V higher redox potentials that their neutral forms in a distinct demonstration of charge accumulation effects relevant to water oxidation. Building on previous work that analysed the activation behaviour of our pyalk‐ligated Cp*Ir complexes 1–7, we assess their catalytic oxygen evolution activity with sodium periodate (NaIO(4)) and ceric ammonium nitrate (CAN) in water and aqueous (t)BuOH solution. Mechanistic studies including H/D kinetic isotope effects and reaction progress kinetic analysis (RPKA) of oxygen evolution point to a dimer‐monomer equilibrium of the Ir(IV) resting state preceding a proton‐coupled electron transfer (PCET) in the turnover‐limiting step (TLS). Finally, true electrochemically driven water oxidation is demonstrated for all catalysts, revealing surprising trends in activity that do not correlate with those obtained using chemical oxidants.
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spelling pubmed-64708652019-04-19 Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes Sackville, Emma V. Marken, Frank Hintermair, Ulrich ChemCatChem Full Papers We report the solution‐phase electrochemistry of seven half‐sandwich iridium(III) complexes with varying pyridine‐alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciation determines the electrochemical response: cationic complexes show over 1 V higher redox potentials that their neutral forms in a distinct demonstration of charge accumulation effects relevant to water oxidation. Building on previous work that analysed the activation behaviour of our pyalk‐ligated Cp*Ir complexes 1–7, we assess their catalytic oxygen evolution activity with sodium periodate (NaIO(4)) and ceric ammonium nitrate (CAN) in water and aqueous (t)BuOH solution. Mechanistic studies including H/D kinetic isotope effects and reaction progress kinetic analysis (RPKA) of oxygen evolution point to a dimer‐monomer equilibrium of the Ir(IV) resting state preceding a proton‐coupled electron transfer (PCET) in the turnover‐limiting step (TLS). Finally, true electrochemically driven water oxidation is demonstrated for all catalysts, revealing surprising trends in activity that do not correlate with those obtained using chemical oxidants. John Wiley and Sons Inc. 2018-09-30 2018-10-09 /pmc/articles/PMC6470865/ /pubmed/31007774 http://dx.doi.org/10.1002/cctc.201800916 Text en © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Full Papers
Sackville, Emma V.
Marken, Frank
Hintermair, Ulrich
Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title_full Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title_fullStr Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title_full_unstemmed Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title_short Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes
title_sort electrochemical and kinetic insights into molecular water oxidation catalysts derived from cp*ir(pyridine‐alkoxide) complexes
topic Full Papers
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470865/
https://www.ncbi.nlm.nih.gov/pubmed/31007774
http://dx.doi.org/10.1002/cctc.201800916
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