η6-(2-phenoxyethanol) ruthenium(II)-complexes of 2,2′-bipyridine and its derivatives: Solution speciation and kinetic behaviour

Guilherme Nogueira, Orsolya Dömötör, Adhan Pilon, M. Paula Robalo, Fernando Avecilla, M. Helena Garcia, Éva A. Enyedy, Andreia Valente

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Abstract

A novel family of RuII-arene compounds with the general formula of [RuII6-(2-phenoxyethanol))(L)Cl]+(L: 2,2′-bipyridine (bpy) (3), 4,4′-dimethyl-2,2′-bipyridine (4) and 4,4′-diyldimethanol-2,2′-bipyridine (5)) was synthesized and characterized by standard spectroscopic and analytical methods. Complex 3 was further studied by single-crystal X-ray diffraction analysis, showing a pseudo octahedral geometry and strong π-π lateral stacking interactions in the crystal packing. Effect of the substituents on the electrochemical properties and on the aqueous solution stability was monitored by cyclic voltammetry, UV–Vis and1H NMR spectroscopy. Complexes 3–5 presented multiple irreversible redox processes according to their cyclic voltammograms recorded in acetonitrile, and their RuII → RuIIIoxidation peaks were found at ca. +1.6 V. Hydrolysis of the binuclear [RuII6-(2-phenoxyethanol))(μ2-Cl)Cl]2precursor (1) resulted in binuclear hydroxido bridged species [(RuII6-(2-phenoxyethanol)))2(μ-OH)3]+and [(RuII6-(2-phenoxyethanol)))2(μ-OH)2Z2] (Z = H2O/Cl) in the presence of chloride ions in water. The hydrolytic behaviour of this RuIIprecursor is similar to that of the analogous species [RuII6-p-cymene)(μ2-Cl)Cl]2regarding the hydrolysis products and their stability constants. Formation of complexes 3–5 by reaction of the RuIIprecursor with the (N,N) bidentate ligands was found to be relatively slow in aqueous solution. The complexation is complete already at pH 1 due to the formation of [RuII6-(2-phenoxyethanol))(L)Z] complexes of significantly high stability in all cases, which are predominant species up to pH 6. However, besides the formation of the mixed hydroxido species [RuII6-(2-phenoxyethanol))(L)(OH)]+at neutral and basic pH values, the slow oxidation of the RuIIcentre takes place as well leading to the partial loss of the arene moiety. The rate of these processes depends on the pH and its maximum was found at pH 8–9. Additionally the chlorido/aqua co-ligand exchange processes of the [RuII6-(2-phenoxyethanol))(L)Cl]+species were also monitored and only ∼5% of the chlorido ligand was found to be replaced by water in 0.1 M chloride ion containing aqueous solutions at pH 5.

Original languageEnglish
Pages (from-to)20-29
Number of pages10
JournalJournal of Organometallic Chemistry
Volume820
DOIs
Publication statusPublished - Jan 1 2016

Keywords

  • Equilibria
  • Ruthenium(II)-arene
  • Stability constants
  • η-(2-phenoxyethanol)

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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