Synthesis and Application of Strong Br酶nsted Acids Generated from the Lewis Acid Al(ORF)3 and an Alcohol
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- 作者：Anne Kraft ; Jennifer Beck ; Gunther Steinfeld ; Harald Scherer ; Daniel Himmel ; Ingo Krossing
- 刊名：Organometallics
- 出版年：2012
- 出版时间：November 12, 2012
- 年：2012
- 卷：31
- 期：21
- 页码：7485-7491
- 全文大小：424K
- 年卷期：v.31,no.21(November 12, 2012)
- ISSN：1520-6041
文摘
The strong neutral Br酶nsted acids [(R)OH鈫扐l(OC(CF3)3)3] (R = 鈭扖(CF3)3 (1), 鈭扖6F5 (2), (鈭?-menthyl (3)) were synthesized by complexation of perfluoro tert-butyl alcohol, pentafluorophenol, and (鈭?-menthol with the Lewis superacid Al(OC(CF3)3)3. The 1:1 composition of the compounds was proven by NMR (except for compound 2), IR, and partially Raman spectroscopy and X-ray crystallography. Of the structures, 2 crystallized with a coordinated toluene molecule, which might be seen as a frozen intermediate or prestep to form the classical Wheland complex of protonated toluene. This interaction was calculated to be exothermic by 32 (no dispersion) or 88 kJ mol鈥? (Grimmes D3 dispersion correction included @ RI-BP86/SV(P)). 1 proved suitable to protonate mesitylene and Et2O, giving the acidic cationic Br酶nsted acids [H(C6H3(CH3)3)]+ (4b) and [H(OEt2)2]+ (5) with the respective weakly coordinating anion [Al(OC(CF3)3)4]鈭?/sup>. In dichloromethane solution 4b decomposes at room temperature, leaving the room-temperature-stable salt [H(C6H3(CH3)3)]+[((CF3)3CO)3Al鈥揊鈥揂l(OC(CF3)3)3]鈭?/sup> (4a; XRD). The acidities reached with 4 and 5 are discussed in terms of our recently introduced absolute Br酶nsted acidity scale. The absolute chemical potentials of a 0.001 M solution of protonated mesitylene and Et2O amount to 鈭?44 and 鈭?015 kJ mol鈥? or鈥攊n terms of absolute pHabs values鈥攖o 165 and 178 and thus are at the threshold of superacidity of 鈭?75 kJ mol鈥? or pHabs of 171.