Aluminium Hydrazides: Reactions oftert-Butylaluminium Chlorides with Dilithium Bis(trimethylsilyl)hydrazide – Formation of Iminoalanes and their Hydrazido Adducts

Abstract

Di(tert-butyl)aluminium chloride reacted with dilithium bis(trimethylsilyl)hydrazide with the formation of a novel Al2Li2N4 cage compound 1. Its structure consists of a dimeric iminoalane RAl(μN–SiMe3)2AlR (R = CMe3), which is bridged by a dilithiumhydrazido ligand with an intact N–N bond. A heterocubane-type molecule is formed, in which two vertices are occupied by Al atoms, two by Li atoms and four by N atoms. One face of the cube is strongly distorted due to the short N–N distance of the hydrazido group. A similar compound, 3, was formed with bis(neopentyl)aluminium chloride but it was isolated in very poor yield. The reaction of Li2N2(SiMe3)2 with (Me3C)2AlCl in the presence of THF yielded an adduct 2, in which each Li atom of the cage is additionally coordinated via Li–Cl–Al bridges to the ligand (Me3Al)2Cl·THF. The reaction of dilithium bis(trimethylsilyl)hydrazide with tert-butylaluminium dichloride gave, by complete cleavage of the hydrazido groups, a dimeric iminoalane [Me3C(THF)AlNSiMe3]2 (4), in which each aluminium atom is coordinated to one THF molecule. Its uncoordinated, solvent-free form 5 was obtained by heating solid 4 to 150 °C in vacuo for several hours. It was identified as the tetrameric iminoalane (Me3CAlNSiMe3)4, which does not adopt the expected heterocubane-type structure, but consists of three anellated four-membered Al2N2 heterocycles in a kind of ladder structure. Remarkably, the cage compound 1 could not be obtained by the reaction of an excess of lithium hydrazide with the iminoalanes 4 and 5. All compounds 1–5 were characterized by crystal structure determinations.