Abstract
Four derivatives of a hydrogen oxidation catalyst, [Ni(P Cy 2N Bn-R 2) 2] 2+ (Cy = cyclohexyl, Bn = benzyl, R = OMe, COOMe, CO-alanine-methyl ester, CO-phenylalanine-methyl ester), have been prepared to investigate steric and electronic effects on catalysis. Each complex was characterized spectroscopically and electrochemically, and thermodynamic data were determined. Crystal structures are also reported for the -OMe and -COOMe derivatives. All four catalysts were found to be active for H 2 oxidation. The methyl ester (R = COOMe) and amino acid ester containing complexes (R = CO-alanine-methyl ester or CO-phenylalanine-methyl ester) had rates slower (4 s -1) than that of the parent complex (10 s -1), in which R = H, which is consistent with the lower amine pK a's and less favorable ΔG H 2's found for these electron-withdrawing substituents. Dynamic processes for the amino acid ester containing complexes were also investigated and found not to hinder catalysis. The electron-donating methyl ether derivative (R = OMe) was prepared to compare electronic effects and has a catalytic rate similar to that of the parent complex. In the course of these studies, it was found that water could act as a weak base for H 2 oxidation, although catalytic turnover requires a higher potential and utilizes a different sequence of catalytic steps than when using a base with a higher pK a. Importantly, these catalysts provide a foundation upon which larger peptides can be attached to [Ni(P Cy 2N Bn 2) 2] 2+ hydrogen oxidation catalysts in order to more fully investigate and implement the effects of the outer coordination sphere.
| Original language | English |
|---|---|
| Pages (from-to) | 6719-6731 |
| Number of pages | 13 |
| Journal | Organometallics |
| Volume | 31 |
| Issue number | 19 |
| DOIs | |
| Publication status | Published - Oct 8 2012 |
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ASJC Scopus subject areas
- Organic Chemistry
- Physical and Theoretical Chemistry
- Inorganic Chemistry
Cite this
Incorporating amino acid esters into catalysts for hydrogen oxidation : Steric and electronic effects and the role of water as a base. / Lense, Sheri; Ho, Ming Hsun; Chen, Shentan; Jain, Avijita; Raugei, Simone; Linehan, John; Roberts, John; Appel, Aaron; Shaw, Wendy.
In: Organometallics, Vol. 31, No. 19, 08.10.2012, p. 6719-6731.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Incorporating amino acid esters into catalysts for hydrogen oxidation
T2 - Steric and electronic effects and the role of water as a base
AU - Lense, Sheri
AU - Ho, Ming Hsun
AU - Chen, Shentan
AU - Jain, Avijita
AU - Raugei, Simone
AU - Linehan, John
AU - Roberts, John
AU - Appel, Aaron
AU - Shaw, Wendy
PY - 2012/10/8
Y1 - 2012/10/8
N2 - Four derivatives of a hydrogen oxidation catalyst, [Ni(P Cy 2N Bn-R 2) 2] 2+ (Cy = cyclohexyl, Bn = benzyl, R = OMe, COOMe, CO-alanine-methyl ester, CO-phenylalanine-methyl ester), have been prepared to investigate steric and electronic effects on catalysis. Each complex was characterized spectroscopically and electrochemically, and thermodynamic data were determined. Crystal structures are also reported for the -OMe and -COOMe derivatives. All four catalysts were found to be active for H 2 oxidation. The methyl ester (R = COOMe) and amino acid ester containing complexes (R = CO-alanine-methyl ester or CO-phenylalanine-methyl ester) had rates slower (4 s -1) than that of the parent complex (10 s -1), in which R = H, which is consistent with the lower amine pK a's and less favorable ΔG H 2's found for these electron-withdrawing substituents. Dynamic processes for the amino acid ester containing complexes were also investigated and found not to hinder catalysis. The electron-donating methyl ether derivative (R = OMe) was prepared to compare electronic effects and has a catalytic rate similar to that of the parent complex. In the course of these studies, it was found that water could act as a weak base for H 2 oxidation, although catalytic turnover requires a higher potential and utilizes a different sequence of catalytic steps than when using a base with a higher pK a. Importantly, these catalysts provide a foundation upon which larger peptides can be attached to [Ni(P Cy 2N Bn 2) 2] 2+ hydrogen oxidation catalysts in order to more fully investigate and implement the effects of the outer coordination sphere.
AB - Four derivatives of a hydrogen oxidation catalyst, [Ni(P Cy 2N Bn-R 2) 2] 2+ (Cy = cyclohexyl, Bn = benzyl, R = OMe, COOMe, CO-alanine-methyl ester, CO-phenylalanine-methyl ester), have been prepared to investigate steric and electronic effects on catalysis. Each complex was characterized spectroscopically and electrochemically, and thermodynamic data were determined. Crystal structures are also reported for the -OMe and -COOMe derivatives. All four catalysts were found to be active for H 2 oxidation. The methyl ester (R = COOMe) and amino acid ester containing complexes (R = CO-alanine-methyl ester or CO-phenylalanine-methyl ester) had rates slower (4 s -1) than that of the parent complex (10 s -1), in which R = H, which is consistent with the lower amine pK a's and less favorable ΔG H 2's found for these electron-withdrawing substituents. Dynamic processes for the amino acid ester containing complexes were also investigated and found not to hinder catalysis. The electron-donating methyl ether derivative (R = OMe) was prepared to compare electronic effects and has a catalytic rate similar to that of the parent complex. In the course of these studies, it was found that water could act as a weak base for H 2 oxidation, although catalytic turnover requires a higher potential and utilizes a different sequence of catalytic steps than when using a base with a higher pK a. Importantly, these catalysts provide a foundation upon which larger peptides can be attached to [Ni(P Cy 2N Bn 2) 2] 2+ hydrogen oxidation catalysts in order to more fully investigate and implement the effects of the outer coordination sphere.
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U2 - 10.1021/om300409y
DO - 10.1021/om300409y
M3 - Article
VL - 31
SP - 6719
EP - 6731
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 19
ER -