To broaden the scope of C-H bond activation, which is of remarkable importance, a method is introduced to activate C-H bonds in the gas phase by using fragmented closo-borate anions. Collision-activated dissociation (CAD) of gaseous icosahedral dianions [B12X12]2- (X = Cl, Br, or I) has been reported to result in the formation of [B12X11]- anions with one open binding site on one of the boron atoms. Although negatively charged, these fragment anions have been shown to be strongly electrophilic and bind spontaneously to adventitious water and nitrogen, and even to noble gases introduced into the vacuum system. In this study, reactions of [B12X11]- anions with several volatile hydrocarbons were explored by using a linear quadrupole ion trap (LQIT) mass spectrometer. The hydrocarbons include linear and branched, saturated and unsaturated compounds, cyclic compounds and aromatic compounds. Formation of a stable adduct between [B12X11]- and a hydrocarbon was observed for all hydrocarbons studied, in addition to adducts with H2O and N2. CAD of the adduct ions formed with saturated hydrocarbons required high collision energies and did not yield the separated reactants. Instead, formation of several other fragment ions was observed, such as [B12X11C2H4]-. These results suggest that the observed adduct is not a weakly-bound non-covalent complex. Two possible pathways for the formation of the strongly-bound adduct ions will be discussed: 1. Hydride abstraction from the hydrocarbon followed by Coulombic attraction of the resulting hydrocarbon carbocation to the resulting dianion [B12X11H]2-, and 2. B-C bond formation via C-H bond insertion reaction. Reactions of [B12X11]- with unsaturated hydrocarbons also yielded adduct ions as major products. These adduct ions underwent fragmentation via different pathways upon CAD, depending on the structure of the hydrocarbon. Dissociation into the reactants was observed exclusively if the hydrocarbon had no aliphatic hydrogens (like benzene). However, formation of the fragment ions [B12X11C2H4]- and [B12X11H]2-H+ was observed for unsaturated hydrocarbons with saturated aliphatic moieties, such as linear and branched alkenes. This finding suggests that the reactions of [B12X11]- may occur either via addition to a C=C double bond or via C-H activation as observed for saturated hydrocarbons.

closo-Borate anions activate C-H bonds in hydrocarbons in the gas phase

2019 Spring National Meeting

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