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.
N1 - Funding Information:
This work was supported by the NSF under the CCI Center for Enabling New Technologies through Catalysis (CENTC) Phase II Renewal (CHE-1205189). The authors thank Dr. Ashley M. Pennington for assistance in performing BET measurements and Rachel A. Yang for assistance in analyzing kinetic and spectroscopic data. The authors also thank Dr. Nagarajan Murali for assistance in collecting, processing, and interpreting solid-state MAS NMR spectra and Shinjae Hwang and Dr. Eric Garfunkel for collection and interpretation of XPS spectra.
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
AN - SCOPUS:85050088964
VL - 8
SP - 7828
EP - 7841
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 9
ER -