From a (Pseudo) Aluminum Sesquihalide Al2(Et)3(ORF)3 to Me3Si–Cl–Al(ORF)3 (RF = C(CF3)3)

Abstract

By reaction of AlEt3 with less than 3 equiv of HORF (RF = C(CF3)3) the ethylaluminum sesquialkoxide (Et)2Al(μ-ORF)2Al(Et)(ORF) (1a; NMR, XRD) can be obtained. As a univalent electronegative residue, the perfluorinated alkoxy moieties can be seen as pseudohalides. In this respect, 1a represents the closest approximation to the hitherto unknown crystal structure of the alkylaluminum sesquihalide Al2R3X3. By further reaction of 1a with HORF, the Lewis superacid Al(ORF)3 is formed, which reacts with Me3SiCl to give Me3Si–Cl–Al(ORF)3 (2a; NMR, XRD, IR, Raman). 2a can be used for further reactions as prepared but slowly decomposes at ca. 0 °C to give the known Me3Si–F–Al(ORF)3 (2b) and several byproducts. The observed decomposition products, combined with quantum chemical calculations, provide evidence for an even higher silylating potential of 2a over that of 2b.