Thermodynamic and kinetic hydricity of ruthenium(II) hydride complexes

Yasuo Matsubara, Etsuko Fujita, Mark D. Doherty, James Muckerman, Carol Creutz

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Abstract

Despite the fundamental importance of the hydricity of a transition metal hydride (δG° H-(MH) for the reaction M-H → M+ + H-) in a range of reactions important in catalysis and solar energy storage, ours (J. Am. Chem. Soc.2009, 131, 2794) are the only values reported for water solvent, and there has been no basis for comparison of these with the wider range already determined for acetonitrile solvent, in particular. Accordingly, we have used a variety of approaches to determine hydricity values in acetonitrile of Ru(II) hydride complexes previously studied in water. For [Ru(ν6-C6Me6)(bpy)H] + (bpy = 2,2′-bipyridine), we used a thermodynamic cycle based on evaluation of the acidity of [Ru(ν6-C6Me 6)(bpy)H]+ pKa = 22.5 ± 0.1 and the [Ru(ν6-C6Me6)(bpy)(NCCH3) 1/0]2+/0 electrochemical potential (-1.22 V vs Fc +/Fc). For [Ru(tpy)(bpy)H]+ (tpy = 2,2′:6′, 2″-terpyridine) we utilized organic hydride ion acceptors (A+) of characterized hydricity derived from imidazolium cations and pyridinium cations, and determined K for the hydride transfer reaction, S + MH+ + A+ → M(S)2+ + AH (S = CD3CN, MH + = [Ru(tpy)(bpy)H]+), by 1H NMR measurements. Equilibration of initially 7 mM solutions was slow-on the time scale of a day or more. When E°(H+/H-) is taken as 79.6 kcal/mol vs Fc+/Fc as a reference, the hydricities of [Ru(ν6-C 6Me6)(bpy)H]+ and [Ru(tpy)(bpy)H]+ were estimated as 54 ± 2 and 39 ± 3 kcal/mol, respectively, in acetonitrile to be compared with the values 31 and 22 kcal/mol, respectively, found for aqueous media. The pKa estimated for [Ru(tpy)(bpy)H] + in acetonitrile is 32 ± 3. UV-vis spectroscopic studies of [Ru(ν6-C6Me6)(bpy)]0 and [Ru(tpy)(bpy)]0 indicate that they contain reduced bpy and tpy ligands, respectively. These conclusions are supported by DFT electronic structure results. Comparison of the hydricity values for acetonitrile and water reveals a flattening or compression of the hydricity range upon transferring the hydride complexes to water.

Original languageEnglish
Pages (from-to)15743-15757
Number of pages15
JournalJournal of the American Chemical Society
Volume134
Issue number38
DOIs
Publication statusPublished - Sep 26 2012

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Ruthenium
Acetonitrile
Thermodynamics
Hydrides
Kinetics
Water
Cations
Positive ions
Solar Energy
Hydrogen
Catalysis
Acidity
Discrete Fourier transforms
Energy storage
Solar energy
Electronic structure
Transition metals
Metals
Ligands
Nuclear magnetic resonance

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Thermodynamic and kinetic hydricity of ruthenium(II) hydride complexes. / Matsubara, Yasuo; Fujita, Etsuko; Doherty, Mark D.; Muckerman, James; Creutz, Carol.

In: Journal of the American Chemical Society, Vol. 134, No. 38, 26.09.2012, p. 15743-15757.

Research output: Contribution to journalArticle

Matsubara, Yasuo ; Fujita, Etsuko ; Doherty, Mark D. ; Muckerman, James ; Creutz, Carol. / Thermodynamic and kinetic hydricity of ruthenium(II) hydride complexes. In: Journal of the American Chemical Society. 2012 ; Vol. 134, No. 38. pp. 15743-15757.
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