Ion Chemistry of anti‐o , o ′‐Dibenzene

The ion chemistry of anti‐o , o ′‐dibenzene ( 1 ) was examined in the gaseous and the condensed phase. From a series of comparative ion cyclotron resonance (ICR) mass spectrometry experiments which involved the interaction of Cu + with 1 , benzene, or mixtures of both, it was demonstrated that 1 can be brought into the gas phase as an intact molecule under the experimental conditions employed. The molecular ions, formally 1 .+ and 1 .− , were investigated with a four‐sector mass spectrometer in metastable‐ion decay, collisional activation, charge reversal, and neutralization–reionization experiments. Surprisingly, the expected retrocyclization to yield two benzene molecules was not dominant for the long‐lived molecular ions; however, other fragmentations, such as methyl and hydrogen losses, prevailed. In contrast, matrix ionization of 1 in freon (77 K) by γ‐radiation or in argon (12 K) by X‐irradiation leads to quantitative retrocyclization to the cationic dimer of benzene, 2 .+ . Theoretical modeling of the potential‐energy surface for the retrocyclization shows that only a small, if any, activation barrier is to be expected for this process. In another series of experiments, metal complexes of 1 were investigated. 1 /Cr + was formed in the ion source and examined by metastable ion decay and collisional activation experiments, which revealed predominant losses of neutral benzene. Nevertheless, comparison with the bis‐ligated [(C 6 H 6 ) 2 Cr] + complex provided evidence for the existence of an intact 1 /Cr + under these experimental conditions. No evidence for the existence of 1 /Fe + was obtained, which suggests that iron mediates the rapid retrocyclization of 1 /Fe + into the bis‐ligated benzene complex [(C 6 H 6 ) 2 Fe] + .