RESUMEN
Bulk protonated mesitylene, toluene, and benzene bromoaluminate salts were stabilized and characterized in the superacidic system HBr/n AlBr3 with NMR spectroscopy and X-ray analysis of [HC6 H3 (CH3 )3 ](+) [AlBr4 ](-) (1), [HC6 H5 (CH3 )](+) [AlBr4 ](-) (2), and [C6 H7 ](+) [Al2 Br7 ](-) â C6 H6 (3). Protonation attempts in bromoaluminate ILs led to a complete protonation of mesitylene, and a protonation degree of up to 15 % for toluene in the IL BMP(+) [Al2 Br7 ](-) . Benzene could only be protonated in the more acidic IL BMP(+) [Al3 Br10 ](-) , with a degree of 25 %. Protonation attempts on aromatics provide evidence that the bromoaluminate ILs tolerate superacidic environments. On the basis of the absolute Brønsted acidity scale, quantum chemical calculations confirmed the superacidic properties, and rank the acidities in ILs down to a pHabs value of 164 with an error of less than one pH unit compared with experimental findings. The neat AlBr3 /HBr system even may reach acidities down to pHabs 163.
RESUMEN
Crystalline and properly ordered protonated benzene as the [C6 H7 ](+) [Al2 Br7 ](-) â (C6 H6 ) salt 1 are obtained by the combination of solid AlBr3 , benzene, and HBr gas. Compound 1 was characterized and verified by NMR, Raman and X-Ray spectroscopy. This unexpected simple and straight forward access shows that HBr/AlBr3 is an underestimated superacid that should be used more frequently.
RESUMEN
Weakly coordinating anions (WCAs) facilitate the stabilization and isolation of highly reactive and almost "naked" cations. Alkoxyaluminate-based WCAs such as [Al(OC(CF3)3)4]- ([pf]-) are widely used due to their synthetic accessibility and their high stability. However, small cations are still able to coordinate the oxygen atoms of the [pf]- anion or even to abstract an alkoxy ligand. The novel WCA [Al(OC10F15)4]- ([pfAd]-; OC10F15 = perfluoro-1-adamantoxy) is characterized by a very rigid core framework, thus indicating a higher stability towards fluoride-ion abstraction (DFT calculations) and providing hope to generate less disordered crystal structures. The [pfAd]- anion was generated by the reaction of the highly acidic alcohol perfluoro-1-adamantanol C10F15OH with LiAlH4 in o-DFB. Li[pfAd] could not be synthesized free of impurities (and still contains unreacted alcohol). Yet, starting from contaminated Li[pfAd], the very useful pure salts Ag[pfAd], [Ph3C][pfAd] and [H(OEt2)2][pfAd] could be synthesized. The salts were characterized by NMR spectroscopy, single-crystal X-ray diffraction and IR spectroscopy. Additionally, [NO][pfAd] could be synthesized containing alcohol impurities but nonetheless enabled the synthesis of the salt P9+[pfAd]-. The synthesis of Tl[pfAd] in a mixture of H2O/acetone/o-DFB demonstrated the water stability of the [pfAd]- anion.