Abstract
Iridium complexes bearing PCP-type pincer ligands are the most effective catalysts reported to date for the low-temperature (≤ca. 200 °C) dehydrogenation of alkanes. To investigate the activity of formally isoelectronic ruthenium complexes, we have synthesized the neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene ( iPr xanPSP) pincer ligand and several Ru complexes thereof. The ( iPr xanPSP)Ru complexes catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s -1 at 150 °C and 0.2 s -1 at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, is much less effective. A combination of experiment and DFT calculations allow us to explain why ( iPr xanPSP)Ru is more effective than ( iPr PCP)Ir for dehydrogenation of COA, while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin complexes, the ( iPr xanPSP)Ru fragment is calculated to be much more active than ( iPr PCP)Ir for dehydrogenation of both COA and n-alkanes. However, the resting state in the ( iPr xanPSP)Ru-catalyzed transfer dehydrogenation of n-alkane is a very stable linear-allyl hydride complex, whereas the corresponding cyclooctenyl hydride is much less stable.
| Original language | English |
|---|---|
| Pages (from-to) | 4072-4083 |
| Number of pages | 12 |
| Journal | ACS Catalysis |
| DOIs | |
| Publication status | Published - Jan 1 2019 |
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Keywords
- alkane dehydrogenation
- allyl complexes
- catalyst deactivation
- pincer ligand
- ruthenium
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
Cite this
Catalytic Alkane Transfer Dehydrogenation by PSP-Pincer-Ligated Ruthenium. Deactivation of an Extremely Reactive Fragment by Formation of Allyl Hydride Complexes. / Zhou, Xiaoguang; Malakar, Santanu; Zhou, Tian; Murugesan, Sathiyamoorthy; Huang, Carlos; Emge, Thomas J.; Krogh-Jespersen, Karsten; Goldman, Alan S.
In: ACS Catalysis, 01.01.2019, p. 4072-4083.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Catalytic Alkane Transfer Dehydrogenation by PSP-Pincer-Ligated Ruthenium. Deactivation of an Extremely Reactive Fragment by Formation of Allyl Hydride Complexes
AU - Zhou, Xiaoguang
AU - Malakar, Santanu
AU - Zhou, Tian
AU - Murugesan, Sathiyamoorthy
AU - Huang, Carlos
AU - Emge, Thomas J.
AU - Krogh-Jespersen, Karsten
AU - Goldman, Alan S
PY - 2019/1/1
Y1 - 2019/1/1
N2 - Iridium complexes bearing PCP-type pincer ligands are the most effective catalysts reported to date for the low-temperature (≤ca. 200 °C) dehydrogenation of alkanes. To investigate the activity of formally isoelectronic ruthenium complexes, we have synthesized the neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene ( iPr xanPSP) pincer ligand and several Ru complexes thereof. The ( iPr xanPSP)Ru complexes catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s -1 at 150 °C and 0.2 s -1 at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, is much less effective. A combination of experiment and DFT calculations allow us to explain why ( iPr xanPSP)Ru is more effective than ( iPr PCP)Ir for dehydrogenation of COA, while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin complexes, the ( iPr xanPSP)Ru fragment is calculated to be much more active than ( iPr PCP)Ir for dehydrogenation of both COA and n-alkanes. However, the resting state in the ( iPr xanPSP)Ru-catalyzed transfer dehydrogenation of n-alkane is a very stable linear-allyl hydride complex, whereas the corresponding cyclooctenyl hydride is much less stable.
AB - Iridium complexes bearing PCP-type pincer ligands are the most effective catalysts reported to date for the low-temperature (≤ca. 200 °C) dehydrogenation of alkanes. To investigate the activity of formally isoelectronic ruthenium complexes, we have synthesized the neutral 2,7-di-tert-butyl-4,5-bis(diisopropylphosphino)-9,9-dimethylthioxanthene ( iPr xanPSP) pincer ligand and several Ru complexes thereof. The ( iPr xanPSP)Ru complexes catalyze alkane transfer dehydrogenation of the benchmark cyclooctane/t-butylethylene (COA/TBE) couple with turnover frequencies up to ca. 1 s -1 at 150 °C and 0.2 s -1 at 120 °C, the highest rates for alkane dehydrogenation ever reported at such temperatures. Dehydrogenation of n-octane, however, is much less effective. A combination of experiment and DFT calculations allow us to explain why ( iPr xanPSP)Ru is more effective than ( iPr PCP)Ir for dehydrogenation of COA, while the reverse is true for dehydrogenation of n-alkanes. Considering only in-cycle species and simple olefin complexes, the ( iPr xanPSP)Ru fragment is calculated to be much more active than ( iPr PCP)Ir for dehydrogenation of both COA and n-alkanes. However, the resting state in the ( iPr xanPSP)Ru-catalyzed transfer dehydrogenation of n-alkane is a very stable linear-allyl hydride complex, whereas the corresponding cyclooctenyl hydride is much less stable.
KW - alkane dehydrogenation
KW - allyl complexes
KW - catalyst deactivation
KW - pincer ligand
KW - ruthenium
UR - http://www.scopus.com/inward/record.url?scp=85064826912&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85064826912&partnerID=8YFLogxK
U2 - 10.1021/acscatal.8b05172
DO - 10.1021/acscatal.8b05172
M3 - Article
SP - 4072
EP - 4083
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
ER -