Monoalkylaluminum(III) compounds of the type RAlX2 {R=Cp* (C5Me5), X=Cl, Br, I (1–3); (BisAlCl2)2 (Bis=(Me3Si)2CH) (5); TrisSi [(Me3Si)3Si], X=Cl, Br, I (6–8); CycTris [(CycMe2Si)(Me3Si)2C], X=Me, F, Cl, Br, I (11–15)} were prepared and characterized by NMR-, IR-, and mass spectroscopy as well as elemental analysis. The single-crystal X-ray structures of Cp*AlBr2, TrisSiAlX2·THF (X=Cl, Br, I), CycTrisAlX2·THF (X=Me, Cl, Br, I), and [CycTrisAl(μ-O(CH2)3CH2)]2 are reported. The monoalkylaluminum(I) compound (Cp*Al)4 (4) was isolated after the reduction of Cp*AlX2 (X=Cl, Br, I) using a Na/K alloy. The yield of (Cp*Al)4 has been improved compared to the previously reported method. However, completely different products were obtained when the THF adducts of TrisSiAlI2·THF and CycTrisAlI2·THF were used for the reduction with Na/K alloy. In the former case, the cleavage of the Si–Al bond was observed with the formation of elemental aluminum and (TrisSi)2, while in the latter the THF ring opening reaction occurred. CycTrisAlF2·THF was prepared by reacting CycTrisAlMe2·THF with Me3SnF.