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tert-Amyl Compounds of Aluminum and Gallium:  Halides, Hydroxides, and Chalcogenides

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journal contribution
posted on 24.12.1996, 00:00 by C. Jeff Harlan, Edward G. Gillan, Simon G. Bott, Andrew R. Barron
The reaction of AlCl3 with 3 equiv of the tert-amyl Grignard reagent (Me2EtC)MgCl yields the monomeric trialkyl compound Al(CMe2Et)3 (1). Reaction of compound 1 with MeCN and [PPN]Cl yields the Lewis acid−base complexes Al(CMe2Et)3(MeCN) (2) and [PPN][AlCl(CMe2Et)3] (3), respectively. The hydrolysis of Al(CMe2Et)3 in hexane results in the formation of the trimeric hydroxide [(Me2EtC)2Al(μ-OH)]3 (4), which is converted to the dimer [(Me2EtC)2Al(μ-OH)]2 (5) upon heating. The reaction of Al(CMe2Et)3 with H2S at room temperature yields the cubane compound [(Me2EtC)Al(μ3-S)]4 (6). If the reaction is carried out at 0 °C, then the hexamer [(Me2EtC)Al(μ3-S)]6 (7) may be isolated along with compound 6. The selenide analog of 6, [(Me2EtC)Al(μ3-Se)]4 (8), is prepared directly from the reaction of compound 1 with H2Se, while the telluride analog, [(Me2EtC)Al(μ3-Te)]4 (9), is prepared by the direct reaction of compound 1 with tellurium metal. The gallium cubane compounds [(Me2EtC)Ga(μ3-E)]4, (E = S (10), Se (11), Te (12)) have been prepared from the reaction of Ga(CMe2Et)3 with the appropriate element. The tert-amyl compounds are compared to their tert-butyl analogs, and the isolation of compound 7 is used as a precedent to prepare [(tBu)Al(μ3-S)]6 (13). A structural analysis is made of the M4E4 cubane cores (M = Al, Ga, In; E = S, Se, Te), and a new topological method is proposed to predict the intracage bond angles in group 13 cage compounds, [(R)M(μ3-X)]n. The molecular structures of compounds 3, 6, 8, and 1012 have been determined by X-ray crystallography, and a discussion of the crystallographic problems associated with the tert-amyl group is presented.