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Ruthenium Water Oxidation Catalysts based on Pentapyridyl Ligands


Abstract

Ruthenium complexes containing the pentapyridyl ligand 6,6′′-(methoxy(pyridin-2-yl)methylene)di-2,2′-bipyridine (L-OMe) of general formula trans-[RuII(X)(L-OMe-κ-N5)]n+ (X=Cl, n=1, trans-1+; X=H2O, n=2, trans-22+) have been isolated and characterized in solution (by NMR and UV/Vis spectroscopy) and in the solid state by XRD. Both complexes undergo a series of substitution reactions at oxidation state RuII and RuIII when dissolved in aqueous triflic acid–trifluoroethanol solutions as monitored by UV/Vis spectroscopy, and the corresponding rate constants were determined. In particular, aqueous solutions of the RuIII-Cl complex trans-[RuIII(Cl)(L-OMe-κ-N5)]2+ (trans-12+) generates a family of Ru aquo complexes, namely trans-[RuIII(H2O)(L-OMe-κ-N5)]3+ (trans-23+), [RuIII(H2O)2(L-OMe-κ-N4)]3+ (trans-33+), and [RuIII(Cl)(H2O)(L-OMe-κ-N4)]2+ (trans-42+). Although complex trans-42+ is a powerful water oxidation catalyst, complex trans-23+ has only a moderate activity and trans-33+ shows no activity. A parallel study with related complexes containing the methyl-substituted ligand 6,6′′-(1-pyridin-2-yl)ethane-1,1-diyl)di-2,2′-bipyridine (L-Me) was carried out. The behavior of all of these catalysts has been rationalized based on substitution kinetics, oxygen evolution kinetics, electrochemical properties, and density functional theory calculations. The best catalyst, trans-42+, reaches turnover frequencies of 0.71 s−1 using CeIV as a sacrificial oxidant, with oxidative efficiencies above 95 %.

Abstract

Ruthenium complexes containing the pentapyridyl ligand 6,6′′-(methoxy(pyridin-2-yl)methylene)di-2,2′-bipyridine (L-OMe) of general formula trans-[RuII(X)(L-OMe-κ-N5)]n+ (X=Cl, n=1, trans-1+; X=H2O, n=2, trans-22+) have been isolated and characterized in solution (by NMR and UV/Vis spectroscopy) and in the solid state by XRD. Both complexes undergo a series of substitution reactions at oxidation state RuII and RuIII when dissolved in aqueous triflic acid–trifluoroethanol solutions as monitored by UV/Vis spectroscopy, and the corresponding rate constants were determined. In particular, aqueous solutions of the RuIII-Cl complex trans-[RuIII(Cl)(L-OMe-κ-N5)]2+ (trans-12+) generates a family of Ru aquo complexes, namely trans-[RuIII(H2O)(L-OMe-κ-N5)]3+ (trans-23+), [RuIII(H2O)2(L-OMe-κ-N4)]3+ (trans-33+), and [RuIII(Cl)(H2O)(L-OMe-κ-N4)]2+ (trans-42+). Although complex trans-42+ is a powerful water oxidation catalyst, complex trans-23+ has only a moderate activity and trans-33+ shows no activity. A parallel study with related complexes containing the methyl-substituted ligand 6,6′′-(1-pyridin-2-yl)ethane-1,1-diyl)di-2,2′-bipyridine (L-Me) was carried out. The behavior of all of these catalysts has been rationalized based on substitution kinetics, oxygen evolution kinetics, electrochemical properties, and density functional theory calculations. The best catalyst, trans-42+, reaches turnover frequencies of 0.71 s−1 using CeIV as a sacrificial oxidant, with oxidative efficiencies above 95 %.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:23 November 2017
Deposited On:28 Dec 2017 07:23
Last Modified:18 Apr 2018 11:49
Publisher:Wiley-VCH Verlag
ISSN:1864-5631
Funders:URPP LightChEC, Swiss National Science Foundation, Swiss National Supercomputing Center, AGAUR, FEDER, MINECO
OA Status:Closed
Publisher DOI:https://doi.org/10.1002/cssc.201701747
Project Information:
  • : Funder
  • : Grant ID
  • : Project TitleURPP LightChEC
  • : FunderSNSF
  • : Grant ID
  • : Project TitleSwiss National Science Foundation
  • : Funder
  • : Grant ID
  • : Project TitleSwiss National Supercomputing Center
  • : Funder
  • : Grant ID
  • : Project TitleAGAUR
  • : Funder
  • : Grant ID
  • : Project TitleFEDER
  • : Funder
  • : Grant ID
  • : Project TitleMINECO

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