Computational Study of Methane Activation at an Iridium Cyclometallated PONOP Complex in the Solid State

Metal complexes with supporting pincer ligands have been used extensively in the study of hydrocarbon C-H bond activation in solution.1 In 2009 the first example of a s-methane complex in solution was characterised spectroscopically at a neutral Rh-PONOP complex.2 An alternative approach to study s-alkane complexes is through Solid-state Molecular OrganoMetallic (SMOM) Chemistry.3 A recent example involves methane activation at the cyclometallated iridium PONOP complex, 1+ that has been characterised directly in the solid state.4 This poster describes the results of periodic density functional theory investigating this methane activation process. Pathway A involves rate-limiting C-H reductive coupling via TS(1+-2a+) to form 14e- [Ir(PONOP)]+ (2a+), followed by methane activation to obtain [Ir(PONOP)(H)Me]+ (3+). Alternative mechanisms all involve initial CH4 addition followed by C-H bond formation at the cyclometallated arm. The most accessible (Pathway B) involves an Ir(V) intermediate (2b+). Pathway A is computed to be the most stable with an overall barrier of 31.1 kcal/mol. This work will compare these different reaction mechanisms in both the solid-state and in the gas-phase. References 1. W. H. Bernskoetter, S. K. Hanson, S. K. Buzak, Z. Davis, P. S. White, R. Swartz, K. I. Goldberg and M. Brookhart, J. Am. Chem. Soc., 2009, 131, 8603–8613.2. W. H. Bernskoetter, C. K. Schauer, K. I. Goldberg and M. Brookhart, Science, 2009, 326, 553–556.3. F. M. Chadwick, T. Krämer, T. Gutmann, N. H. Rees, A. L. Thompson, A. J. Edwards, G. Buntkowsky, S. A. Macgregor and A. S. Weller, J. Am. Chem. Soc., 2016, 138, 13369-13378.4. M. R. Gyton, M. A. Sajjad, D. J. Storm, K. M. Altus, J. C. Goodall, C. L. Johnson, S. J. Page, A. J. Edwards, R. O. Piltz, S. B. Duckett, S. A. Macgregor and A. S. Weller, J. Am. Chem. Soc., 2025, 147, 10, 8706-8719