U.S. Department of Energy Office of Scientific and Technical Information
Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and β-H Elimination Modes Induce Anomalous Selectivity
Journal Article·· Journal of the American Chemical Society
We report that the cationic iridium complex (iPrPCP)IrH+ catalyzes the transfer-dehydrogenation of alkanes to give alkenes and hydrogen isotope exchange (HIE) of alkanes and arenes. Contrary to established selectivity trends found for C–H activation by transition metal complexes, strained cycloalkanes, including cyclopentane, cycloheptane, and cyclooctane, undergo C–H addition much more readily than n-alkanes, which in turn are much more reactive than cyclohexane. Aromatic C–H bonds also undergo H/D exchange much less rapidly than those of the strained cycloalkanes, but much more favorably than cyclohexane. The order of reactivity toward dehydrogenation correlates qualitatively with the reaction thermodynamics, but the magnitude is much greater than can be explained by thermodynamics. Accordingly, the cycloalkenes corresponding to the strained cycloalkanes undergo hydrogenation much more readily than cyclohexene, despite the less favorable thermodynamics of such hydrogenations. Here, computational (DFT) studies allow rationalization of the origin of reactivity and the unusual selectivity. Specifically, the initial C–H addition is strongly assisted by β-agostic interactions, which are particularly favorable for the strained cycloalkanes. Subsequent to α-C–H addition, the H atom of the β-agostic C–H bond is transferred directly to the hydride ligand of (iPrPCP)IrH+ to give a dihydrogen ligand.
Parihar, Ashish, et al. "Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and <em>β</em>-H Elimination Modes Induce Anomalous Selectivity." Journal of the American Chemical Society, vol. 147, no. 12, Mar. 2025. https://doi.org/10.1021/jacs.4c16699
Parihar, Ashish, Emge, Thomas J., Hasanayn, Faraj, & Goldman, Alan S. (2025). Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and <em>β</em>-H Elimination Modes Induce Anomalous Selectivity. Journal of the American Chemical Society, 147(12). https://doi.org/10.1021/jacs.4c16699
Parihar, Ashish, Emge, Thomas J., Hasanayn, Faraj, et al., "Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and <em>β</em>-H Elimination Modes Induce Anomalous Selectivity," Journal of the American Chemical Society 147, no. 12 (2025), https://doi.org/10.1021/jacs.4c16699
@article{osti_2541612,
author = {Parihar, Ashish and Emge, Thomas J. and Hasanayn, Faraj and Goldman, Alan S.},
title = {Alkane Dehydrogenation and H/D Exchange by a Cationic Pincer-Ir(III) Hydride: Cooperative C–H Addition and <em>β</em>-H Elimination Modes Induce Anomalous Selectivity},
annote = {We report that the cationic iridium complex (iPrPCP)IrH+ catalyzes the transfer-dehydrogenation of alkanes to give alkenes and hydrogen isotope exchange (HIE) of alkanes and arenes. Contrary to established selectivity trends found for C–H activation by transition metal complexes, strained cycloalkanes, including cyclopentane, cycloheptane, and cyclooctane, undergo C–H addition much more readily than n-alkanes, which in turn are much more reactive than cyclohexane. Aromatic C–H bonds also undergo H/D exchange much less rapidly than those of the strained cycloalkanes, but much more favorably than cyclohexane. The order of reactivity toward dehydrogenation correlates qualitatively with the reaction thermodynamics, but the magnitude is much greater than can be explained by thermodynamics. Accordingly, the cycloalkenes corresponding to the strained cycloalkanes undergo hydrogenation much more readily than cyclohexene, despite the less favorable thermodynamics of such hydrogenations. Here, computational (DFT) studies allow rationalization of the origin of reactivity and the unusual selectivity. Specifically, the initial C–H addition is strongly assisted by β-agostic interactions, which are particularly favorable for the strained cycloalkanes. Subsequent to α-C–H addition, the H atom of the β-agostic C–H bond is transferred directly to the hydride ligand of (iPrPCP)IrH+ to give a dihydrogen ligand.},
doi = {10.1021/jacs.4c16699},
url = {https://www.osti.gov/biblio/2541612},
journal = {Journal of the American Chemical Society},
issn = {ISSN 0002-7863},
number = {12},
volume = {147},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2025},
month = {03}}