Binding of saturated and unsaturated C 6 -hydrocarbons to the electrophilic anion [B 12 Br 11 ] - : a systematic mechanistic study.

The highly reactive gaseous ion [B 12 Br 11 ] - is a metal-free closed-shell anion which spontaneously forms covalent bonds with hydrocarbon molecules, including alkanes. Herein, we systematically investigate the reaction mechanism for binding of [B 12 Br 11 ] - to the five hexane isomers yielding [B 12 Br 11 (C 6 H 14 )] - , as well as to cyclohexane and several hexene isomers (yielding [B 12 Br 11 (C 6 H 12 )] - ) using collision-induced dissociation (CID), infrared photodissociation spectroscopy (IRPD) and computational methods. CID of the different [B 12 Br 11 (C 6 H 14 )] - ions results in distinct fragmentation patterns dependent on the structure of the hexane isomer. The observed fragmentation reactions provide insights into the addition mechanism of [B 12 Br 11 ] - to hexane. Based on the observed CID patterns, we identified that either B-C bond formation through heterolytic C-C or C-H bond cleavages or B-H bond formation through heterolytic C-H cleavage occur dependent on the structure of the hexane isomer. Meanwhile, we observe identical CID spectra of adducts originating from isomers of C 6 H 12 . Spectroscopic investigations of adducts of 1-hexene and cyclohexane indicate the same product structure with an open C 6 chain. Computational investigations evidenced that low lying transition states are present, which enable a ring opening reaction of cyclohexane when binding to [B 12 Br 11 ] - .