Crystal structure of a representative mixed adduct of trimethylaluminium and a lithium amide and a theoretical MO study on model systems

Reaction of the simple alane adduct [Me(3)Al . HN(CH(2)Ph)(2)] (2) with the lithium amide [(PhCH(2))(2)NLi] leads to the formation of the mixed adduct [Me(3)Al .(PhCH(2))(2)NLi . HN(CH(2)Ph)2] (1). The crystal structures of 1 and 2 are reported. Exhibiting a four-membered, mixed-metal, mixed-anion AlCLiN ring-core, the structure of 1 is unusual in containing a monomeric lithium dibenzylamide fragment. Such fragments generally convert to aza-allyl derivatives, so its existence here can be attributed to the stabilising effect of the attached Me(3)Al ligand. Crystalline 2 adopts the classical, distorted-tetrahedral arrangement of simple monomeric alane adducts. Ab initio MO calculations on model systems show that mixed adduct formation from Me(3)Al and Me(2)NLi is exothermic, while further reaction to give Me(2)AlNMe(2) and MeLi (i.e., complete transmetallation) is endothermic.