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-Cl(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 center dot center dot center dot anion contacts are preferred to intramolecular Al center dot center dot center dot Cl interactions in the Dcp species 4. Compound 4 forms the bisamine adduct [DcpAlEt(NH(2)t-Bu)(2)] [CH(6)B(11)I(6)] (8) upon exposure to tBuNH(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 crystallogrzphy in the case of 1-5, 7, and 8.