An Operationally Unsaturated Iridium-Pincer Complex That C–H Activates Methane and Ethane in the Crystalline Solid-State

Gyton, Matthew R.; Sajjad, M Arif; Storm, Daniel J.; Altus, Kristof M; Goodall, Joe C.; Johnson, Chloe L; Page, Samuel J; Edwards, Alison J.; Piltz, Ross O.; Duckett, Simon B; Macgregor, Stuart A; Weller, Andrew S; Sajjad, M. Arif; Altus, Kristof M.; Johnson, Chloe L.; Page, Samuel J.; Duckett, Simon B.; Macgregor, Stuart A.; Weller, Andrew S.

Abstract

The known complex [Ir( t Bu-PONOP)MeH][BArF 4], 1[BAr F 4 ] [ t Bu-PONOP = κ3-2,6-( t Bu2PO)2C5H3N); ArF = 3,5-(CF3)2(C6H3); J. Am. Chem. Soc. 2009, 131, 8603], is a robust precursor for in crystallo single-crystal to single-crystal (SC-SC) C–H activation of methane and ethane at 80 °C. This contrasts with the reported solution (CD2Cl2) behavior, where 1[BAr F 4 ] decomposes by methane loss. Crystalline 1[BAr F 4 ] is accessed as a single polymorph on a gram scale. A single-crystal neutron diffraction study locates the hydride. 13C{1H} SSNMR experiments on 1[BAr F 4 ], and its isotopologue [Ir( t Bu-PONOP)(CD3)D][BArF 4], d 4 -1[BAr F 4 ], suggest a rapid and reversible endergonic reductive bond formation is occurring in crystallo to access an Ir(I) σ-methane complex. Heating 1[BAr F 4 ] to 80 °C under high vacuum results in loss of methane and intramolecular C–H activation to form cyclometalated [Ir(cyclo- t Bu-PONOP′)H][BArF 4], 2[BAr F 4 ], in a SC-SC reaction. This is reversible, and the addition of CH4 or CD4 to 2[BAr F 4 ] at 80 °C results in an equilibrium with 1[BAr F 4 ] or d 4 -1[BAr F 4 ], respectively. Complex 2[BAr F 4 ] is thus an operationally unsaturated source of 14-electron [Ir(tBu-PONOP)][BArF 4], III, that undergoes C–H activation with methane. Periodic DFT studies, alongside isotope labeling experiments, link 1[BAr F 4 ] and 2[BAr F 4 ]/CH4 via a reductive elimination/oxidative addition pathway. Heating 2[BAr F 4 ] to 80 °C under N2 forms [Ir( t Bu-PONOP)(κ1-N2)][BArF 4], in a SC-SC transformation. Reaction with CO forms [Ir( t Bu-PONOP)(CO)][BArF 4] at room temperature. Calculations suggest reaction with N2 occurs via an associative process or competitively through III, while with CO only an associative process operates. Heating 2[BAr F 4 ] to 80 °C under an ethane atmosphere results in alkane dehydrogenation, via a SC–SC reaction, forming a ∼1:1 mixture of [Ir( t Bu-PONOP)(η2-H2CCH2)][BArF 4], and [Ir( t Bu-PONOP)H2][BArF 4].

Citation

Gyton, M. R., Sajjad, M. A., Storm, D. J., Altus, K. M., Goodall, J. C., Johnson, C. L., Page, S. J., Edwards, A. J., Piltz, R. O., Duckett, S. B., Macgregor, S. A., Weller, A. S., Sajjad, M. A., Altus, K. M., Johnson, C. L., Page, S. J., Duckett, S. B., Macgregor, S. A., & Weller, A. S. (2025). An Operationally Unsaturated Iridium-Pincer Complex That C–H Activates Methane and Ethane in the Crystalline Solid-State. Journal of the American Chemical Society, 147(10), 8706-8719. https://doi.org/10.1021/jacs.4c18122

• Journal Article Type: Article
• Acceptance Date: Feb 6, 2025
• Online Publication Date: Feb 25, 2025
• Publication Date: Feb 25, 2025
• Deposit Date: Mar 19, 2025
• Publicly Available Date: Mar 19, 2025
• Journal: Journal of the American Chemical Society
• Print ISSN: 0002-7863
• Electronic ISSN: 1520-5126
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 147
• Issue: 10
• Pages: 8706-8719
• DOI: https://doi.org/10.1021/jacs.4c18122
• Public URL: https://durham-repository.worktribe.com/output/3709725