Synthesis, Characterization, and Application of Two Al(ORF)3 Lewis Superacids

• Published in: Chemistry : a European journal Vol. 18; no. 30; pp. 9371 - 9380
• Main Authors: Kraft, Anne, Trapp, Nils, Himmel, Daniel, Böhrer, Hannes, Schlüter, Peter, Scherer, Harald, Krossing, Ingo
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 23.07.2012; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: alanes; anions; Chemistry; Crystal structure; fluorinated ligands; Lewis acids; neutral adducts
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201200448

We report herein the synthesis and full characterization of the donor‐free Lewis superacids Al(ORF)3 with ORF=OC(CF3)3 (1) and OC(C5F10)C6F5 (2), the stabilization of 1 as adducts with the very weak Lewis bases PhF, 1,2‐F2C6H4, and SO2, as well as the internal CF activation pathway of 1 leading to Al2(F)(ORF)5 (4) and trimeric [FAl(ORF)2]3 (5, ORF=OC(CF3)3). Insights have been gained from NMR studies, single‐crystal structure determinations, and DFT calculations. The usefulness of these Lewis acids for halide ions has been demonstrated by reactions with trityl chloride (NMR; crystal structures). The trityl salts allow the introduction of new, heteroleptic weakly coordinating [Cl‐Al(ORF)3]− anions, for example, by hydride or alkyl ion reactions. A super method! The synthesis of the donor‐free Lewis superacids Al(ORF)3 with ORF=OC(CF3)3 (1) and OC(C5F10)C6F5 (2), as well as stabilization of 1 with the very weak Lewis bases PhF, 1,2‐F2C6H4, and SO2, is reported (see figure). Applications of 1 and 2 in bond heterolysis reactions with ClCPh3 giving the trityl cation and the respective weakly coordinating anion [ClAl(ORF)3]− are also described.