Preparation and characterization of lithium imidoalanate complexes Li-2[(RN)(4)(AlH2)(6)] (R = me or Bu-t): First examples of aluminum-rich imidoalanes with an adamantoid structure

Whereas methylammonium chloride, [MeNH3]Cl, reacts with LiGaH4 in an ether solution to give, according to the conditions, either the adduct MeH2N center dot GaH3 or the cationic derivative [(MeH2N)(2)GaH2]Cl-+(-), the corresponding reaction of [MeNH3]Cl or [(BuNH3)-Bu-t]Cl with LiAlH4 proceeds mainly, with H-2 elimination, to the imidoalane Li-2[(RN)(4)(AlH2)(6)] (R = Me, 1, or Bu-t, 2). The crystal structure of 1 center dot 2Et(2)O reveals, for the first time, anionic units with an adamantane-like Al6N4 skeleton. The Li cations exist at two distinct sites, each linked via Li(mu-H)Al bridges to two [(MeN)(4)(AlH2)(6)](2-) cages. Despite disordering of the Bu-t groups, the crystal structure of 2 evidently includes analogous anionic units. By contrast, the main product of the reaction between [(PrNH3)-Pr-i]Cl and LiAlH4 under similar conditions is the known neutral, hexameric imidoalane [(PrNAlH)-Pr-i](6), 3, the crystal structure of which has been redetermined.