Heavy-Atom Tunneling\nin Ring-Closure Reactions of\nBeryllium Ozonide Complexes

Quantum mechanical tunneling (QMT) has long been recognized\nas\ncrucial for understanding chemical reaction mechanisms, particularly\nin reactions involving light atoms like hydrogen. However, recent\nfindings have expanded this understanding to include heavy-atom tunneling\nreactions. In this report, we present the observation of two heavy-atom\ntunneling reactions involving the spontaneous conversions from end-on\nbonded beryllium ozonide complexes, OBeOOO (<b>A</b>) and BeOBeOOO\n(<b>C</b>), to their corresponding side-on bonded ozonide isomers,\nOBe­(η<sup>2</sup>-O<sub>3</sub>) (<b>B</b>) and BeOBe­(η<sup>2</sup>-O<sub>3</sub>) (<b>D</b>), respectively, in a cryogenic\nneon matrix. This discovery is supported by the weak temperature dependence\nof the rate constants and unusually large <sup>16</sup>O/<sup>18</sup>O kinetic isotope effects. Quantum chemistry calculations reveal\nextremely low barriers (<1 kcal/mol) for both ring-closure reactions.\nAdditionally, instanton theory calculations on both reactions unveil\nthat the tunneling processes involve the concerted motion of all four\noxygen atoms.