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Title: Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex

Abstract

The ability of cobalt-based transition metal complexes to catalyze electrochemical proton reduction to produce molecular hydrogen has resulted in a large number of mechanistic studies involving various cobalt complexes. In addition, while the basic mechanism of proton reduction promoted by cobalt species is well understood, the reactivity of certain reaction intermediates, such as CoI and CoIII–H, is still relatively unknown owing to their transient nature, especially in aqueous media. In this work we investigate the properties of intermediates produced during catalytic proton reduction in aqueous solutions promoted by the [(DPA-Bpy)Co(OH₂)]n+ (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6-methanamine) complex ([Co(L)(OH₂)]n+ where L is the pentadentate DPA-Bpy ligand or [Co(OH₂)]n+ as a shorthand). Experimental results based on transient pulse radiolysis and laser flash photolysis methods, together with electrochemical studies and supported by DFT calculations indicate that, while the water ligand is strongly coordinated to the metal center in the oxidation state 3+, one-electron reduction of the complex to form a CoII species results in weakening the Co–O bond. The further reduction to a CoI species leads to the loss of the aqua ligand and the formation of [CoI–VS)]⁺ (VS = vacant site). Interestingly, DFT calculations also predict the existence of a [CoI(κ⁴-L)(OH₂)]⁺ species at least transiently,more » and its formation is consistent with the experimental Pourbaix diagram. Both electrochemical and kinetics results indicate that the CoI species must undergo some structural change prior to accepting the proton, and this transformation represents the rate-determining step (RDS) in the overall formation of [CoIII–H]⁺. We propose that this RDS may originate from the slow removal of a solvent ligand in the intermediate [CoI(κ⁴-L)(OH₂)]⁺ in addition to the significant structural reorganization of the metal complex and surrounding solvent resulting in a high free energy of activation.« less

Authors:
 [1];  [2];  [2];  [3];  [3];  [3]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States); Adam Mickiewicz Univ., Poznan (Poland)
  2. Univ. of Memphis, Memphis, TN (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1213364
Report Number(s):
BNL-108199-2015-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: 9; 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

Citation Formats

Lewandowska-Andralojc, Anna, Baine, Teera, Zhao, Xuan, Muckerman, James T., Fujita, Etsuko, and Poyansky, Dmitry E. Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex. United States: N. p., 2015. Web. doi:10.1021/ic5031137.
Lewandowska-Andralojc, Anna, Baine, Teera, Zhao, Xuan, Muckerman, James T., Fujita, Etsuko, & Poyansky, Dmitry E. Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex. United States. doi:10.1021/ic5031137.
Lewandowska-Andralojc, Anna, Baine, Teera, Zhao, Xuan, Muckerman, James T., Fujita, Etsuko, and Poyansky, Dmitry E. Wed . "Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex". United States. doi:10.1021/ic5031137. https://www.osti.gov/servlets/purl/1213364.
@article{osti_1213364,
title = {Mechanistic studies of hydrogen evolution in aqueous solution catalyzed by a tertpyridine-amine cobalt complex},
author = {Lewandowska-Andralojc, Anna and Baine, Teera and Zhao, Xuan and Muckerman, James T. and Fujita, Etsuko and Poyansky, Dmitry E.},
abstractNote = {The ability of cobalt-based transition metal complexes to catalyze electrochemical proton reduction to produce molecular hydrogen has resulted in a large number of mechanistic studies involving various cobalt complexes. In addition, while the basic mechanism of proton reduction promoted by cobalt species is well understood, the reactivity of certain reaction intermediates, such as CoI and CoIII–H, is still relatively unknown owing to their transient nature, especially in aqueous media. In this work we investigate the properties of intermediates produced during catalytic proton reduction in aqueous solutions promoted by the [(DPA-Bpy)Co(OH₂)]n+ (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6-methanamine) complex ([Co(L)(OH₂)]n+ where L is the pentadentate DPA-Bpy ligand or [Co(OH₂)]n+ as a shorthand). Experimental results based on transient pulse radiolysis and laser flash photolysis methods, together with electrochemical studies and supported by DFT calculations indicate that, while the water ligand is strongly coordinated to the metal center in the oxidation state 3+, one-electron reduction of the complex to form a CoII species results in weakening the Co–O bond. The further reduction to a CoI species leads to the loss of the aqua ligand and the formation of [CoI–VS)]⁺ (VS = vacant site). Interestingly, DFT calculations also predict the existence of a [CoI(κ⁴-L)(OH₂)]⁺ species at least transiently, and its formation is consistent with the experimental Pourbaix diagram. Both electrochemical and kinetics results indicate that the CoI species must undergo some structural change prior to accepting the proton, and this transformation represents the rate-determining step (RDS) in the overall formation of [CoIII–H]⁺. We propose that this RDS may originate from the slow removal of a solvent ligand in the intermediate [CoI(κ⁴-L)(OH₂)]⁺ in addition to the significant structural reorganization of the metal complex and surrounding solvent resulting in a high free energy of activation.},
doi = {10.1021/ic5031137},
journal = {Inorganic Chemistry},
number = 9,
volume = 54,
place = {United States},
year = {2015},
month = {4}
}

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Works referencing / citing this record:

A Smorgasbord of 17 Cobalt Complexes Active for Photocatalytic Hydrogen Evolution
journal, June 2018

  • Hogue, Ross W.; Schott, Olivier; Hanan, Garry S.
  • Chemistry - A European Journal, Vol. 24, Issue 39
  • DOI: 10.1002/chem.201800396

μ-Pyridine-bridged copper complex with robust proton-reducing ability
journal, January 2017

  • Majee, Karunamay; Patel, Jully; Das, Babulal
  • Dalton Transactions, Vol. 46, Issue 43
  • DOI: 10.1039/c7dt03153j

Synthesis of a pentadentate, polypyrazine ligand and its application in cobalt-catalyzed hydrogen production
journal, January 2017

  • Chen, Lizhu; Khadivi, Amir; Singh, Manpreet
  • Inorganic Chemistry Frontiers, Vol. 4, Issue 10
  • DOI: 10.1039/c7qi00362e

Ligand dechelation effect on a [Co(tpy) 2 ] 2+ scaffold towards electro-catalytic proton and water reduction
journal, January 2019

  • Majee, Karunamay; Padhi, Sumanta Kumar
  • New Journal of Chemistry, Vol. 43, Issue 9
  • DOI: 10.1039/c8nj05712e

Cobalt-based molecular electrocatalysis of nitrile reduction: evolving sustainability beyond hydrogen
journal, January 2019

  • Child, Simon N.; Raychev, Radoslav; Moss, Nathan
  • Dalton Transactions, Vol. 48, Issue 26
  • DOI: 10.1039/c9dt00773c

A Smorgasbord of 17 Cobalt Complexes Active for Photocatalytic Hydrogen Evolution
journal, June 2018

  • Hogue, Ross W.; Schott, Olivier; Hanan, Garry S.
  • Chemistry - A European Journal, Vol. 24, Issue 39
  • DOI: 10.1002/chem.201800396

μ-Pyridine-bridged copper complex with robust proton-reducing ability
journal, January 2017

  • Majee, Karunamay; Patel, Jully; Das, Babulal
  • Dalton Transactions, Vol. 46, Issue 43
  • DOI: 10.1039/c7dt03153j

Synthesis of a pentadentate, polypyrazine ligand and its application in cobalt-catalyzed hydrogen production
journal, January 2017

  • Chen, Lizhu; Khadivi, Amir; Singh, Manpreet
  • Inorganic Chemistry Frontiers, Vol. 4, Issue 10
  • DOI: 10.1039/c7qi00362e

Ligand dechelation effect on a [Co(tpy) 2 ] 2+ scaffold towards electro-catalytic proton and water reduction
journal, January 2019

  • Majee, Karunamay; Padhi, Sumanta Kumar
  • New Journal of Chemistry, Vol. 43, Issue 9
  • DOI: 10.1039/c8nj05712e

Cobalt-based molecular electrocatalysis of nitrile reduction: evolving sustainability beyond hydrogen
journal, January 2019

  • Child, Simon N.; Raychev, Radoslav; Moss, Nathan
  • Dalton Transactions, Vol. 48, Issue 26
  • DOI: 10.1039/c9dt00773c