No 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.

The reaction of di(tert-butyl)aluminum hydride with a mixture of 1,1-and 1,2-bis(trimethylsilyl)hydrazine afforded colorless crystals of the title compound Me 3 CAl[N(SiMe 3 )N(H)SiMe 3 ] 2 (1) in 60% yield. 1 is a monomer in the solid state. Its aluminum atom has a coordination number of 5 and is side-on coordinated by both hydrazido ligands. Different Al-N distances of 1.814(2) and 2.072(2) Å are observed according to the different coordination by amido or amino nitrogen atoms, respectively.

Treatment of the hydrazine adduct (Me3C)2AlCl·NH2NHSiMe3 (2) with n‐butyllithium afforded the colorless dialkylaluminium hydrazide (Me3C)2AlN(SiMe3)NH2 (3) by the release of butane and the precipitation of LiCl. Hydrazide 3 gave a dimer in solution and in the solid state. As shown by a crystal structure determination, a six‐membered Al2N4 heterocycle with two intact endocyclic N−N bonds was formed by a head‐to‐tail dimerization. Upon sublimation of 3 in vacuum, a rearrangement was observed which gave an isomeric compound 4 after the migration of a hydrogen atom of a hydrazido ligand. The molecular core of 4 comprises a five‐membered Al2N3 heterocycle, in which the Al atoms are bridged by one hydrazido ligand similar to 3. The second ligand, however, has only one nitrogen atom in a bridging position with an exocyclic N−N bond. A similar compound (5) was obtained by the reaction of bis(tert‐butyl)aluminium chloride with phenylhydrazine and n‐butyllithium.

Bis(trimethylsilyl)hydrazin reagiert mit Dialkylaluminiumchloriden R2AlCl [R = CH2CMe3, CMe3 und CH(SiMe3)2] nicht unter Bildung von Trimethylchlorsilan, sondern unter Dismutierung zu Tris(trimethylsilyl)hydrazin und Trimethylsilylhydrazin. Das sterisch weniger hoch abgeschirmte NH2NHSiMe3, das in freier Form unbeständig ist, wird durch die koordinativ ungesättigten Aluminiumverbindungen unter Komplexierung stabilisiert. Dabei entstehen die Addukte R2AlCl · NH2NHSiMe3, die für R = CMe3 und CH(SiMe3)2 kristallstrukturanalytisch charakterisiert wurden und in denen das Hydrazinderivat immer über das basischere NH2‐Stickstoffatom an Aluminium koordiniert. Im Rahmen dieser Untersuchungen wurde in Spuren das Addukt Me3CAlCl2 · NH2N(SiMe3)2 isoliert, das ebenfalls kristallstrukturanalytisch charakterisiert wurde und das intakte 1,1‐Bis(trimethylsilyl)hydrazin enthält.