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

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 10−12 have been determined by X-ray crystallography, and a discussion of the crystallographic problems associated with the tert-amyl group is presented.