Abstract
A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(PCy 2Nt-Bu 2)2](BF4)2 (PCy 2Nt-Bu 2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl- 1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the NiII complex gives three isomers of the doubly protonated Ni0 complex [Ni(PCy 2Nt-Bu 2H)2](BF4) 2. Using the pKa values and NiII/I and Ni I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(PCy 2Nt-Bu 2)2]2+ was determined to be -7.9 kcal mol -1. The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s-1 is observed at 23 C.
| Original language | English |
|---|---|
| Pages (from-to) | 9700-9712 |
| Number of pages | 13 |
| Journal | Journal of the American Chemical Society |
| Volume | 135 |
| Issue number | 26 |
| DOIs | |
| Publication status | Published - Jul 3 2013 |
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ASJC Scopus subject areas
- Chemistry(all)
- Catalysis
- Biochemistry
- Colloid and Surface Chemistry
Cite this
Two pathways for electrocatalytic oxidation of hydrogen by a nickel bis(diphosphine) complex with pendant amines in the second coordination sphere. / Yang, Jenny Y.; Smith, Stuart E.; Liu, Tianbiao; Dougherty, William G.; Hoffert, Wesley A.; Kassel, W. Scott; Dubois, M. Rakowski; DuBois, Daniel L; Bullock, R Morris.
In: Journal of the American Chemical Society, Vol. 135, No. 26, 03.07.2013, p. 9700-9712.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Two pathways for electrocatalytic oxidation of hydrogen by a nickel bis(diphosphine) complex with pendant amines in the second coordination sphere
AU - Yang, Jenny Y.
AU - Smith, Stuart E.
AU - Liu, Tianbiao
AU - Dougherty, William G.
AU - Hoffert, Wesley A.
AU - Kassel, W. Scott
AU - Dubois, M. Rakowski
AU - DuBois, Daniel L
AU - Bullock, R Morris
PY - 2013/7/3
Y1 - 2013/7/3
N2 - A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(PCy 2Nt-Bu 2)2](BF4)2 (PCy 2Nt-Bu 2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl- 1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the NiII complex gives three isomers of the doubly protonated Ni0 complex [Ni(PCy 2Nt-Bu 2H)2](BF4) 2. Using the pKa values and NiII/I and Ni I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(PCy 2Nt-Bu 2)2]2+ was determined to be -7.9 kcal mol -1. The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s-1 is observed at 23 C.
AB - A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(PCy 2Nt-Bu 2)2](BF4)2 (PCy 2Nt-Bu 2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl- 1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the NiII complex gives three isomers of the doubly protonated Ni0 complex [Ni(PCy 2Nt-Bu 2H)2](BF4) 2. Using the pKa values and NiII/I and Ni I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(PCy 2Nt-Bu 2)2]2+ was determined to be -7.9 kcal mol -1. The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s-1 is observed at 23 C.
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U2 - 10.1021/ja400705a
DO - 10.1021/ja400705a
M3 - Article
C2 - 23631473
AN - SCOPUS:84879756609
VL - 135
SP - 9700
EP - 9712
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 26
ER -