Tilting a ground-state reactivity landscape by vibrational strong coupling

Shaking up reaction-site selectivity It seems intuitive that putting vibrational energy into a chemical bond ought to promote selective cleavage of that bond. In fact, the relation of vibrational excitation to reactivity has generally proven subtler and more complex. Thomas et al. studied how strong coupling of specific vibrational modes to an optical cavity might influence a molecule with two competing reactive sites. The molecule had two silicon centers that could react with fluoride by respective cleavage of a Si–C or Si–O bond. Exciting the vibrations at either center slowed down the overall reaction while favoring otherwise disfavored Si–O cleavage. Science, this issue p. 615 Strong coupling of vibrational modes to an optical cavity shifts site-selectivity in competing silyl substitution reactions. Many chemical methods have been developed to favor a particular product in transformations of compounds that have two or more reactive sites. We explored a different approach to site selectivity using vibrational strong coupling (VSC) between a reactant and the vacuum field of a microfluidic optical cavity. Specifically, we studied the reactivity of a compound bearing two possible silyl bond cleavage sites—Si–C and Si–O, respectively—as a function of VSC of three distinct vibrational modes in the dark. The results show that VSC can indeed tilt the reactivity landscape to favor one product over the other. Thermodynamic parameters reveal the presence of a large activation barrier and substantial changes to the activation entropy, confirming the modified chemical landscape under strong coupling.