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 %.
In order to rationally design water oxidation catalysts (WOCs), an in-depth understanding of the reaction mechanism is essential. In this study we showcase the complexity of catalytic water oxidation, by elucidating how modifications of the pentapyridyl (Py5) ligand-framework influence the thermodynamics and kinetics of the process. In the reaction mechanism the pyridine-water exchange was identified as a key reaction which appears to determine the reactivity of the Py5-WOCs. Exploring the capabilities of in silico design we show which modifications of the ligand framework appear promising when attempting to improve the catalytic performance of WOCs derived from Py5.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.