Synthesis and Characterization of Bulky Cationic Arylalkylaluminum Compounds

Abstract

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(NH2 t-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.

Cationic organoaluminum compounds as intramolecular hydroamination catalysts

“…Whereas trialkylalanes readily react with primary and secondary amines under ethane elimination to give dialkylaluminum amides [25], the analogous reaction is more difficult for cationic organoaluminum compounds [17]. We suggest that under the reaction conditions only one of the ethyl groups is displaced and that species such as [EtAlN(H)R{NH 2 R} n ] þ may be present in the reaction mixture.…”

“…The activity of four cationic organoaluminum compounds as intramolecular hydroamination catalysts was determined using four aminopentene substrates ( [17]. The aminopentenes differ in the substitution pattern of the double bond as well as the central quaternary carbon (Scheme 1).…”

“…Neutral complexes of the latter metals are isoelectronic with cationic group 13 species. As we have been working with cationic organoaluminum compounds [16,17], we were interested in their potential as hydroamination catalysts. Furthermore, there were only two reports regarding aluminum based hydroamination catalysts: one featured a four-coordinate aluminum amide featuring a bidentate phenylene-diamine ligand [18], the other a five-coordinate aluminum complex with a tridentate OCO-pincer ligand [19].…”

Cationic Complexes of Boron and Aluminum: An Early 21st Century Viewpoint

“…Wehmschulte and co-workersa lso described as eries of hetero-substituted diorganyl aluminum cations that bear one terphenyl-ando ne ethyl group and are paired with polyhalocarboranatec ounteranions ([Terph(Et)Al][CH 6 B 11 X 6 ], 80 a,b[CH 6 B 11 X 6 ]; X= Cl, I; Terph = see Figure 23). [97] In summary, their structurals tudies revealed aluminum centers in distorted trigonal pyramidal coordinatione nvironments in all instances. In addition to one carbon atom of each organyl group, the aluminum atom coordinates to two halogen functionalities of the anion.…”

Synthesis and structure of diethylaluminum malonate: An unusual hexanuclear aluminum complex with malonate trianion ligands

“…The central Al 2 O 2 ring in the molecule of 1 is typical for monoalkoxide aluminum compounds. However, in comparison with AleO bond lengths in dimethylaluminum 2,6-diphenylphenolate [1.879(1) Å] [12] and di-tert-butyl tert-butoxide aluminum [1.880(1) and 1.878(1) Å] [13], the Al(1)eO(1) distances [1.901(1) and 1.891(1) Å] are slightly longer. This is probably caused by an electronwithdrawing effect of carboxylate groups.…”