Synthesis and Characterization of Bulky Cationic Arylalkylaluminum Compounds

The cationic m -terphenyl-substituted organoaluminum compounds [Dipp*AlEt][CH 6 B 11 Cl 6 ] ( 3; Dipp* = 2,6-(2,6- i -Pr 2 C 6 H 3 ) 2 C 6 H 3 −), [DcpAlEt][CH 6 B 11 Cl 6 ] ( 4; Dcp = 2,6-(2,6-Cl 2 C 6 H 3 ) 2 C 6 H 3 −), [Dipp*AlEt][CH 6 B 11 I 6 ] ( 5 ), and [DcpAlEt][CH 6 B 11 I 6 ] ( 6 ) have been obtained by ethide elimination through trityl or preferably silylium salts from the precursors Dipp*AlEt 2 ( 1 ) and DcpAlEt 2 ( 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(NH 2 t -Bu) 2 ][CH 6 B 11 I 6 ] ( 8 ) upon exposure to t BuNH 2, and compounds 3 and 4 slowly catalyze the alkylation of benzene with 1-hexene. The compounds have been characterized by 1 H, 13 C, and 11 B NMR spectroscopy and by X-ray crystallography in the case of 1 − 5, 7, and 8 .