Mit N-Methylpiperidin stabilisierte Halogenalane

Alanes of the formula HxAlX3–x(x = 0, 1, 2, 3; X = Cl, Br, I) and the mixed halogen species HAlClBr were synthesized asN-methyl-piperidin (nmp) adducts HxAlX3–x·znmp (z = 1, 2) and HAlClBr·2nmp by different routes. The crystal and molecular structures of (H3Al·nmp)2, H2AlBr·2nmp, H2AlI·2nmp, the isotypic and isomorphous HAlBr2·2nmp, HAlI2·2nmp, as well as ACl3·nmp, ABr3·nmp, AI3·nmp, and HAlClBr·2nmp are described. The aluminum atoms in these molecular structures either form a pentagonal bipyramid as coordination sphere with the amine bases in apical positions or are in the center of a distorted tetrahedron (AlCl3·nmp, ABr3·nmp, AI3·nmp). In the nmp adduct of alane, a central Al2H2ring is formed by dimerisation of AlH3, each aluminum atom displaying a further nmp ligand together with two terminal hydrogen atoms. The influence of the halogen atoms on the hydrogen bonds in the iso-structural compounds were studied by IR spectroscopy, showing in both series H2AlX·2nmp and HAlX2·2nmp (X= Cl, Br, I) a dependence of ν(Al–H) on the substitution pattern: 1770.2–1775.2–(not measured) cm–1(H2AlX) and 1785.0–1788.0–1791.0 cm–1(HAlX2). The δ values of the27Al-NMR spectra in solution show dependences on the halide numbers bonded to aluminum and display a regular growth with heavier element in the H2AlX·2nmp series δ (27Al): 121.2 (Cl), 126.0 (Br), 131.5 (I)], whereas they have an unsteady evolution in the HAlX2·2nmp series [δ (27Al): 118.0 (Cl), 122.0 (Br), 108.0 (I)] and the AlX3·nmp series [δ (27Al): 102.1 (Cl), 104.8 (Br), 61.9 (I)].