Aluminium hydrazides: Reactions of tert-butylaluminium chlorides with dilithium bis(trimethylsilyl)hydrazide - Formation of iminoalanes and their hydrazido adducts

Di(tert-butyl)aluminium chloride reacted with dilithium bis(trimethylsilyl) hydrazide with the formation of a novel Al2Li2N4 cage compound 1. Its struc ture consists of a dimeric iminoalane RAl(mu N-SiMe3)(2)AlR (R = CMe3), whi ch is bridged by a dilithiumhydrazido ligand with an intact N-N bond. A het erocubane-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 strong ly distorted due to the short N-N distance of the hydrazido group. A simila r 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)(2) AlCl in the presence of THF yielded an adduct 2, in which each Li atom of t he cage is additionally coordinated via Li-Cl-Al bridges to the Ligand (Me3 Al)(2)Cl . THF. The reaction of dilithium bis(trimethyl-silyl)hydrazide wit h tert-butylaluminium dichloride gave, by complete cleavage of the hydrazid o groups, a dimeric iminoalane [Me3C(THF)AlNSiMe3](2) (4), in which each al uminium atom is coordinated to one THF molecule. Its uncoordinated, solvent -free form 5 was obtained by heating solid 4 to 150 degrees C in vacuo for several hours. It was identified as the tetrameric iminoalane (Me(3)CAlNSiM e3)4, which does not adopt the expected heterocubane-type structure, but co nsists of three anellated four-membered Al2N2 heterocycles in a kind of lad der 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. A ll compounds 1-5 were characterized by crystal structure determinations.