Polyfluorinated carba-closo-dodecaboranes with amino and ammonio substituents bonded to boron
The inner salts x-H3N-closo-1-CB11H11 (x = 12, 2) and 7-H3N-12-F-closo-1-CB11H11 were fluorinated with elemental fluorine in anhydrous hydrogen fluoride to give the B-perfluorinated ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2). Deprotonation of the ammonio group yielded the corresponding amino-functionalized anions [1-H-x-H2N-closo-1-CB11F10]− (x = 12, 7, 2) that were isolated as [Et4N]+ salts. Hydrolysis of the highly fluorinated inner salts 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) is very slow in acidic aqueous solutions. This stability of the ammonio derivatives is unprecedented because the related fluorinated anion [1-H2N-closo-1-CB11F11]− is immediately hydrolyzed to simple boron species in the presence of aqueous acids. The ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) are much more acidic compared to their non-fluorinated counterparts as assessed from potentiometric titrations and DFT calculations. The inner salts and the anions were characterized by NMR and vibrational sepectroscopy. Solid-sate structures of 1-H-12-H3N-closo-1-CB11F10·H2O, 1-H-7-H3N-closo-1-CB11F10·diglyme, 1-H-2-H3N-closo-1-CB11F10·0.5H2O, 7-H3N-12-F-closo-1-CB11H10·(CH3)2CO and [Et4N][1-H-12-H2N-closo-1-CB11F10] were determined by single-crystal X-ray diffraction.
- This article is part of the themed collection: Fluorine