Polyfluorinated carba-closo-dodecaboranes with amino and ammonio substituents bonded to boron

Abstract

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.