Abstract
Pincer-ligated iridium complexes of the form [Ir(R4PCP)L] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr) are efficient homogeneous alkane dehydrogenation catalysts that have been reported to be highly active at temperatures of 240 °C or below. In this work, silica-supported [Ir(C2H4)(p-tBu2PO-tBu4POCOP)] (1/SiO2) was used to study a model continuous-flow gas-phase acceptorless alkane dehydrogenation system. This particular supported framework is thermally stable at temperatures up to 340 °C, 100 °C above the highest temperature at which analogous homogeneous complexes have been reported to show stable activity, with observed butane dehydrogenation rates of ca. 80 molbutenes molcat. -1 h-1. Solid-state 31P MAS NMR and ATR IR are used to demonstrate that the backbone pincer ligand remains intact and coordinated at 340 °C. The complex is fully converted to [Ir(CO)(p-tBu2PO-tBu4POCOP)] (3/SiO2) above 300 °C. 3/SiO2 is observed to be catalytically active at the higher temperatures tested, and reaction rates are comparable to those of 1/SiO2. 3/SiO2 and 1/SiO2 act as resting states for the active 14-electron fragment, through dissociation of the CO or olefin ligand, respectively. Given that 3/SiO2 is air resistant at ambient temperature and is structurally stable and catalytically active at elevated temperatures, it is a suitable candidate as a catalyst for the highly endothermic acceptorless dehydrogenation of alkanes.
| Original language | English |
|---|---|
| Pages (from-to) | 7828-7841 |
| Number of pages | 14 |
| Journal | ACS Catalysis |
| Volume | 8 |
| Issue number | 9 |
| DOIs | |
| Publication status | Published - Sep 7 2018 |
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ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
Cite this
Continuous-Flow Alkane Dehydrogenation by Supported Pincer-Ligated Iridium Catalysts at Elevated Temperatures. / Sheludko, Boris; Cunningham, Molly T.; Goldman, Alan S; Celik, Fuat E.
In: ACS Catalysis, Vol. 8, No. 9, 07.09.2018, p. 7828-7841.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Continuous-Flow Alkane Dehydrogenation by Supported Pincer-Ligated Iridium Catalysts at Elevated Temperatures
AU - Sheludko, Boris
AU - Cunningham, Molly T.
AU - Goldman, Alan S
AU - Celik, Fuat E.
PY - 2018/9/7
Y1 - 2018/9/7
N2 - Pincer-ligated iridium complexes of the form [Ir(R4PCP)L] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr) are efficient homogeneous alkane dehydrogenation catalysts that have been reported to be highly active at temperatures of 240 °C or below. In this work, silica-supported [Ir(C2H4)(p-tBu2PO-tBu4POCOP)] (1/SiO2) was used to study a model continuous-flow gas-phase acceptorless alkane dehydrogenation system. This particular supported framework is thermally stable at temperatures up to 340 °C, 100 °C above the highest temperature at which analogous homogeneous complexes have been reported to show stable activity, with observed butane dehydrogenation rates of ca. 80 molbutenes molcat. -1 h-1. Solid-state 31P MAS NMR and ATR IR are used to demonstrate that the backbone pincer ligand remains intact and coordinated at 340 °C. The complex is fully converted to [Ir(CO)(p-tBu2PO-tBu4POCOP)] (3/SiO2) above 300 °C. 3/SiO2 is observed to be catalytically active at the higher temperatures tested, and reaction rates are comparable to those of 1/SiO2. 3/SiO2 and 1/SiO2 act as resting states for the active 14-electron fragment, through dissociation of the CO or olefin ligand, respectively. Given that 3/SiO2 is air resistant at ambient temperature and is structurally stable and catalytically active at elevated temperatures, it is a suitable candidate as a catalyst for the highly endothermic acceptorless dehydrogenation of alkanes.
AB - Pincer-ligated iridium complexes of the form [Ir(R4PCP)L] (R4PCP = κ3-C6H3-2,6-(XPR2)2; X = CH2, O; R = tBu, iPr) are efficient homogeneous alkane dehydrogenation catalysts that have been reported to be highly active at temperatures of 240 °C or below. In this work, silica-supported [Ir(C2H4)(p-tBu2PO-tBu4POCOP)] (1/SiO2) was used to study a model continuous-flow gas-phase acceptorless alkane dehydrogenation system. This particular supported framework is thermally stable at temperatures up to 340 °C, 100 °C above the highest temperature at which analogous homogeneous complexes have been reported to show stable activity, with observed butane dehydrogenation rates of ca. 80 molbutenes molcat. -1 h-1. Solid-state 31P MAS NMR and ATR IR are used to demonstrate that the backbone pincer ligand remains intact and coordinated at 340 °C. The complex is fully converted to [Ir(CO)(p-tBu2PO-tBu4POCOP)] (3/SiO2) above 300 °C. 3/SiO2 is observed to be catalytically active at the higher temperatures tested, and reaction rates are comparable to those of 1/SiO2. 3/SiO2 and 1/SiO2 act as resting states for the active 14-electron fragment, through dissociation of the CO or olefin ligand, respectively. Given that 3/SiO2 is air resistant at ambient temperature and is structurally stable and catalytically active at elevated temperatures, it is a suitable candidate as a catalyst for the highly endothermic acceptorless dehydrogenation of alkanes.
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U2 - 10.1021/acscatal.8b01497
DO - 10.1021/acscatal.8b01497
M3 - Article
VL - 8
SP - 7828
EP - 7841
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 9
ER -