Functionalization of saturated and unsaturated hydrocarbons with electrophilic anions [B12X11]– (X=Br, I) in the gas phase and at interfaces

Electrophilic dodecaborate fragment ions (X = halogen, CN) are among the most reactive anions and are capable of converting inert reagents into charged species through covalent bonding. In this study, we investigate the reactivity of [B12X11]– (X = Br, I) with a series of hydrocarbons in two environments: 1) In the gas phase, using ion–molecule reactions and collision-induced dissociation (CID), and 2) at interfaces, using fragment ion deposition onto surface layers of reagents. In the gas phase, n-alkyl groups are bound via the substitution of a proton by the electrophilic vacant boron atom. However, double and triple bonds are bound directly, resulting in strongly bound adducts with characteristic fragmentation behavior. Aromatic compounds can attach with their aryl groups to [B12X11]–. The adduct fragments upon CID by cleaving this bond again, forming back [B12X11]– ions. Contrary to the gas phase results, [B12X11]– reacts with all hydrocarbon units at layer interfaces via proton substitution, regardless of the degree of saturation. Computational investigations suggest that the binding mode in the gas phase correlates with calculated enthalpy minima of the formed collision complexes. However, in the condensed phase, low-lying transition states allow rearrangement into the proton substitution binding mode, which is favorable due to entropic effects (e.g., proton dissipation in the layer). These results emphasize the possible differences in the formation of products of reactive ions in the gas phase and at interfaces, contributing to the development of selectivity control in reactive ion deposition experiments and providing a foundation for the application of the 'universal binder' [B12X11]– in analytical and preparative mass spectrometry investigations for the charge tagging of non-polar organic molecules.