Synthesis, Characterization, and Selected Properties of 7- and 12-Ammoniocarba-closo-dodecaboranes



The inner salts 12-H3N-closo-1-CB11H11 (H1) and 7-H3N-12-Hal-closo-1-CB11H10 [Hal = F (H3), Cl (H4)] were synthesized by a microwave-assisted Buchwald–Hartwig amination starting from the corresponding monoiodinated {closo-1-CB11} clusters and LiN(SiMe3)2. H1 was methylated to result in the zwitterion 12-Me3N-closo-1-CB11H11 (2). All new compounds were characterized by multinuclear NMR spectroscopy, elemental analysis, and mass spectrometry. The crystal structures of HMe2CO and 2 were determined. The pKa value of H1 in aqueous solution was estimated by potentiometric titration and by 11B{1H} NMR spectroscopic studies. The stepwise deprotonation of H1 with nBuLi in [D8]THF was studied by multinuclear NMR spectroscopy. In a first step, the amine 1 is obtained and then the amide [12-HN-closo-1-CB11H11]2– and finally the trianion [12-HN-closo-1-CB11H10]3– or more probably lithiated species thereof are formed. The experimental spectroscopic and structural data, as well as the pKa value of H1 are compared to values derived from DFT and ab initio calculations.