Sodium-potassium alloy for the reduction of monoalkyl aluminum(III) compounds

Monoalkylaluminum(III) compounds of the type RAIX(2) {R = Cp* (C5Me5), X = Cl, Br, I (1-3); (BisAlCl(2)), (Bis = (Me3Si)(2)CH) (5); TrisSi [(Me3Si)(3)Si], X = Cl, Br, I (6-8); CycTris [(CycMe(2)Si) (Me2Si)(2)C], 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, TrisSiALX(2) . THF (X = Cl, Br, I), CycTrisAlX(2) .THF (X=Me, Cl, Br, I), and [CycTrisAl(mu-O(CH2)(3)CH2)], 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 TrisSiAlI(2) . THF and CycTrisAlI(2) .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. CycTrisAlF(2) . THF was prepared by reacting CycTrisAlMe(2) . THF with Me3SnF. (C) 2001 Elsevier Science.