Synthesis and Characterization of Bulky Cationic Arylalkylaluminum Compounds

The cationic m-terphenyl-substituted organoaluminum compounds [Dipp*AlEt][CH6B11Cl6] (3; Dipp* = 2,6-(2,6-i-Pr2C6H3)2C6H3−), [DcpAlEt][CH6B11Cl6] (4; Dcp = 2,6-(2,6-Cl2C6H3)2C6H3−), [Dipp*AlEt][CH6B11I6] (5), and [DcpAlEt][CH6B11I6] (6) have been obtained by ethide elimination through trityl or preferably silylium salts from the precursors Dipp*AlEt2 (1) and DcpAlEt2 (2). The crystal structures of compounds 3−5 reveal the presence of cation−anion adducts involving two halides of the carborane anions, and the NMR spectroscopic data and solubility properties indicate such an interaction for 6. The interactions of the hexaiodocarborane anion with the [Dipp*AlEt]+ cation are stronger than those of the hexachlorocarborane anion. Interestingly, cation···anion contacts are preferred to intramolecular Al···Cl interactions in the Dcp species 4. Compound 4 forms the bis-amine adduct [DcpAlEt(NH2t-Bu)2][CH6B11I6] (8) upon exposure to tBuNH2, and compounds 3 and 4 slowly catalyze the alkylation of benzene with 1-hexene. The compounds have been characterized by 1H, 13C, and 11B NMR spectroscopy and by X-ray crystallography in the case of 1−5, 7, and 8.