Ruthenium Water Oxidation Catalysts based on Pentapyridyl Ligands

Marcos Gil-Sepulcre, Michael Böhler, Mauro Schilling, Fernando Bozoglian, Cyril Bachmann, Dominik Scherrer, Thomas Fox, Bernhard Spingler, Carolina Gimbert-Suriñach, Roger Alberto, Roger Bofill, Xavier Sala, Sandra Luber, Craig J. Richmond, Antoni Llobet

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18 Citations (Scopus)


© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 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 %.
Original languageEnglish
Pages (from-to)4517-4525
Issue number22
Publication statusPublished - 23 Nov 2017


  • kinetics
  • pentapyridyl ligand
  • ruthenium complexes
  • substitution reactions
  • water oxidation catalysis


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