Ion chemistry of anti-o,o '-dibenzene

The ion chemistry of anti-o,o'-dibenzene (1) was examined in the gaseous an d the condensed phase. From a series of comparative ion cyclotron resonance (ICR) mass spectrometry experiments which involved the interaction of Cuwith 1, benzene, or mixtures of both, it was demonstrated that 1 can be bro ught into the gas phase as an intact molecule under the experimental condit ions employed. The molecular ions, formally 1(.+) and 1(.-), were investiga ted with a four-sector mass spectrometer in metastable-ion decay, collision al 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 fragmen tations, such as methyl and hydrogen losses, prevailed. In contrast, matrix ionization of 1 in freon (77 K) by gamma -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 i s 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 ex amined by metastable ion decay and collisional activation experiments, whic h revealed predominant losses of neutral benzene. Nevertheless, comparison with the bis-ligated [(C6H6)(2)Cr](+) complex provided evidence for the exi stence 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 [( C6H6)(2)Fe](+).