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 language | English |
|---|---|
| Pages (from-to) | 15743-15757 |
| Number of pages | 15 |
| Journal | Journal of the American Chemical Society |
| Volume | 134 |
| Issue number | 38 |
| DOIs | |
| Publication status | Published - Sep 26 2012 |
Fingerprint
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 journal › Article
}
TY - JOUR
T1 - Thermodynamic and kinetic hydricity of ruthenium(II) hydride complexes
AU - Matsubara, Yasuo
AU - Fujita, Etsuko
AU - Doherty, Mark D.
AU - Muckerman, James
AU - Creutz, Carol
PY - 2012/9/26
Y1 - 2012/9/26
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84961979598&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84961979598&partnerID=8YFLogxK
U2 - 10.1021/ja302937q
DO - 10.1021/ja302937q
M3 - Article
VL - 134
SP - 15743
EP - 15757
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 38
ER -