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The Unique Decomposition Behavior of the Dimeric Dialkylaluminum Hydrazide [(Me3C)2Al−N(H)−N(H)−Me]2−Butane versus Ammonia Elimination

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posted on 2009-01-19, 00:00 authored by Werner Uhl, Thomas Abel, Alexander Hepp, Tom Nilges, Friedhelm Rogel, Ernst-Ulrich Würthwein, Nugzar Ghavtadze
The hydrazine adducts (Me3C)3E←NH2−N(H)−Me [E = Al (1), Ga(2)] afforded the corresponding dimeric hydrazides [(Me3C)2E−N(H)−N(H)−Me]2 (3 and 4) upon heating to 95 and 300 °C, respectively, by the release of isobutane. The molecular structure of 3 in the solid state comprises a five-membered Al2N3 heterocycle (3b), while 4 possesses a four-membered Ga2N2 ring with two exocyclic hydrazine groups (4a). Quantum-chemical calculations revealed only small energetic differences between both isomers. The structures determined in the solid state correspond to the thermodynamically favored ones. In solution, equilibrium mixtures between both forms were detected. Further thermolysis of the aluminum compound 3 gave different products depending on the reaction conditions. Below its melting point, isobutane was released. A cage compound (5) was formed, which has four Al−CMe3 groups and four hydrazindiido ligands [N(H)−N(Me)]2− with all N−N bonds enclosed in the cage. Fast heating of 3 above the melting point (149 °C) yielded a singular product (6) by a remarkable rearrangement process and formal release of ammonia. The hydrazonido ligand [N(Me)−N(CH2)] resulted, which has a reformed N−N bond and an NC double bond and is in a bridging position between two aluminum atoms. An amido group (NH2) completes the five-membered Al2N3 heterocycle of 6.

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