Gas Phase Ion Chemistry of Borazine, an Inorganic Analogue of Benzene.

The gas-phase reactivity of selected ionic species with borazine and of borazine-derived ions with selected neutrals has been studied by FT-ICR and ab initio computations and related to the corresponding ion chemistry of benzene. The most basic site of borazine is at nitrogen, and its conjugate acid, H3B3N3H4+, is similar in structure to the benzenium ion, as shown by ab initio calculations. H3B3N3H4+ ions undergo H/D exchange of up to four hydrogens with CD3OD and do not isomerize by stepwise 1,2-hydrogen shifts. Protonation at boron is calculated to be unfavored by 28 kcal/mol with respect to protonation at nitrogen. The H4B3N3H3+ ions show the features of a [B3N3H5-H2]+ complex, prone to dissociation at room temperature. The experimental gas-phase basicity of borazine is equal to 185.0 ( 1 kcal/mol. The Lewis basicity toward Me3Si+ places borazine into a linear correlation pertaining to model aromatic compounds. The experimental gas-phase acidity is 365.4 ( 1.5 kcal/mol. The reactions of neutral borazine with protonating, alkylating, and nitrating ions have been characterized and compared with the corresponding reactions of benzene. B3N3H5+ ions, retaining a cyclic structure, react similarly, in some respects, as phenylium ions, C6H5+.