H-X (X = H, CH₃, CH₂F, CHF₂, CF₃, and SiH₃) Bond Activation by Criegee Intermediates: A Theoretical Perspective

Using theoretical calculations and Born-Oppenheimer molecular dynamics simulations, it is shown here that Criegee intermediate, which is principally produced in the olefin ozonolysis, can activate H-X (X = H, CH₃, CH₂F, CHF₂, CF₃, and SiH₃) under mild conditions, a reaction that has long been known for transition metals. The zwitterionic electronic structure of Criegee intermediate makes it an interesting metal-free system for activating enthalpically strong small molecules such as H₂, methane, silanes, and boranes. The calculated barriers for the H₂ or SiH₄ reactions of CH₂OO are significantly lower than those for the CH₄ or its fluorinated analogue reactions. The distortion-interaction energy model is found to be successful in explaining the differential reactivity of the Criegee intermediate toward activating the various H-X bonds. The canonical transition state theory calculations suggest that the CH₂OO-H₂ reaction is 9-11 orders of magnitude faster than the CH₂OO-CH₄ reaction over the 200-300 K temperature range. Considering that the laboratory synthesis of Criegee intermediate is now feasible, these findings may open up new vistas in the metal-free activation of small molecules.