Description
Ph. Wernet on behalf of the collaborations in references 4-7.
Conceptually attractive but practically very hard, bond activation in small inert molecules for functionalization and transformation into valuable chemicals is notoriously difficult because the bonds in inert molecules are so stable. Understanding bond activation also poses seemingly insurmountable challenges to experiment and theory. How can we selectively pick, for observation in both space and time, the one functional group that gets activated? How can we accurately describe what it is that activates the bond down to what matters, which is the level of orbital interactions? And what is the role of solvent fluctuations in mediating and ultimately enabling bond activation?
The aim of this talk is to demonstrate how ultrafast X-ray spectroscopy [1-3] can help. On the example of photochemical C–H bond activation in alkanes with transition-metal complexes, we will show how the selectivity of X-ray spectroscopy to the reactive metal helps in looking at the one alkane C–H bond that gets activated [4-7]. With an optical pulse we trigger the activation reaction and by measuring in a time-resolved mode, we pick the essential reaction intermediates in their reactive electronic ground state. We follow how the C–H bond transforms as it is modulated at the metal site and how a proton then transfers from the alkane to the metal. The sensitivity to specific orbitals and comparison to calculated spectra enables us to quantify the chemical interactions that facilitate bond activation. Understanding the dynamics of bond activation in a fluctuating solvent environment and at the level of orbital interactions, we hope, helps in the design of new catalysts for C–H activation reactions.
[1] Ph. Wernet, Phil. Trans. R. Soc. A 377, 20170464 (2019), http://dx.doi.org/10.1098/rsta.2017.0464
[2] U. Bergmann, J. Kern, R. W. Schoenlein, Ph. Wernet, V. K. Yachandra, J. Yano, Nature Reviews Physics 3, 264 (2021), https://doi.org/10.1038/s42254-021-00289-3
[3] R. M. Jay, K. Kunnus, Ph. Wernet, K. J. Gaffney, Annu. Rev. Phys. Chem. 73, 187 (2022), https://doi.org/10.1146/annurev-physchem-082820-020236
[4] R. M. Jay, A. Banerjee, T. Leitner, R.-P. Wang, J. Harich, R. Stefanuik, H. Wikmark, M. R. Coates, E. V. Beale, V. Kabanova, A. Kahraman, A. Wach, D. Ozerov, C. Arrell, P. J. M. Johnson, C. N. Borca, C. Cirelli, C. Bacellar, C. Milne, N. Huse, G. Smolentsev, T. Huthwelker, M. Odelius, Ph. Wernet, Science 380, 955 (2023), https://doi.org/10.1126/science.adf8042
[5] A. Banerjee, R. M. Jay, T. Leitner, R.-P. Wang, J. Harich, R. Stefanuik, M. R. Coates, E. V. Beale, V. Kabanova, A. Kahraman, A. Wach, D. Ozerov, C. Arrell, C. Milne, P. J. M. Johnson, C. Cirelli, C. Bacellar, N. Huse, M. Odelius, Ph. Wernet, Chemical Science 15, 2398 (2024), https://doi.org/10.1039/d3sc04388f
[6] R. M. Jay, M. R. Coates, H. Zhao, M.-O. Winghart, P. Han, R.-P. Wang, J. Harich, A. Banerjee, H. Wikmark, M. Fondell, E. T. J. Nibbering, M. Odelius, N. Huse, Ph. Wernet, J. Am. Chem. Soc. 146, 14000-14011 (2024), https://doi.org/10.1021/jacs.4c02077
[7] T. Dederichs, A. Banerjee, V. Kabanova, R. Stefanuik, A. Freibert, E. V. Beale, F. Dworkowski, R. G. Castillo, P. J. M. Johnson, C. Cirelli, N. Huse, C. Bacellar, R. M. Jay, Ph. Wernet, J. Am. Chem. Soc., accepted (2026)
