Quantum Tunneling in Peroxide O–O Bond Breaking Reaction

Abstract

The importance of quantum-mechanical tunneling becomes increasingly recognized in chemical reactions involving hydrogen as well as heavier atoms. Here we report concerted heavy-atom tunneling in an oxygen–oxygen bond breaking reaction from cyclic beryllium peroxide to linear dioxide in cryogenic Ne matrix, as evidenced by subtle temperature-dependent reaction kinetics and unusually large kinetic isotope effects. Furthermore, we demonstrate that the tunneling rate can be tuned through noble gas atom coordination on the electrophilic beryllium center of Be(O2), as the half-life dramatically increased from 0.1 h for NeBe(O2) at 3 K to 12.8 h for ArBe(O2). Quantum chemistry and instanton theory calculations reveal that noble gas coordination notably stabilizes the reactants and transition states, increases the barrier heights and widths, and consequently reduces the reaction rate drastically. The calculated rates and in particular kinetic isotope effects are in good agreement with experiment.

Heavy‐Atom Tunneling in Bicyclo[4.1.0]hepta‐2,4,6‐trienes

“…This rearrangement is therefore another example of a rare heavy‐atom tunneling reaction. Such reactions have been reviewed by Borden, [34] Karney, [38] and more recently by us, [39] and additional examples have been reported over the last few years [40–47] . Quantum tunneling also explains why all attempts to isolate 3 a and related benzocyclopropenes failed: the narrower tunneling distance and lower barrier heights result in higher tunneling probabilities which diminish the lifetimes of the benzocyclopropenes.…”

Heavy‐Atom Tunneling in Bicyclo[4.1.0]hepta‐2,4,6‐trienes

“…Such reactions have been reviewed by Borden, [34] Karney, [38] and more recently by us, [39] and additional examples have been reported over the last few years. [40][41][42][43][44][45][46][47] Quantum tunneling also explains why all attempts to isolate 3 a and related benzocyclopropenes failed: the narrower tunneling distance and lower barrier heights result in higher tunneling probabilities which diminish the lifetimes of the benzocyclopropenes. While there are structural similarities between benzazirines 9 and benzocyclopropenes 3, the latter shows an even higher reactivity.…”

Norcaradiene–Cycloheptatriene Equilibrium: A Heavy-Atom Quantum Tunneling Case

“…Light atom tunneling has been detected in processes such as enzymatic catalysis, abstraction reactions, organometallic transformation, and reactions involving carbenes, among others. − QMT effects involving heavier atoms are termed heavy-atom tunneling. These processes, even if regarded as exotic and being nontrivial to be detected, play a crucial role in the isomerization of organic molecules, such as cycloaromatizations, pericyclic reactions, radical rearrangements, and π-bond-shifting. , While these rearrangements primarily involve carbon atoms, examples of heavy-atom tunneling with even heavier atoms have also been documented . In some instances, QMT prevents the detection of molecules due to its extremely rapid decay.…”

“… 40 , 41 While these rearrangements primarily involve carbon atoms, examples of heavy-atom tunneling with even heavier atoms have also been documented. 42 In some instances, QMT prevents the detection of molecules due to its extremely rapid decay. This phenomenon, known as “tunneling instability”, has recently been observed in systems distinct from those mentioned so far, such as hexazine, pentazine, and diazo compounds.…”