Structural studies of lithiated enaminones: the 1-oxa-5-azapenta-dienyllithium fluxional heterocubane [(Pr-i;NCMeCHCMeOLi)(4)] and its dimeric hexamethylphosphoric triamide complex [{Pr-i;NCMeCHCMeOLi.OP(NMe2)(3)}(2)]

Lithiation of 4-isopropylaminopent-3-en-2-one in hexane gave a 1-oxa-5-azapentadienyl compound [((PrCMeCHMeOLi)-C-i)(4)] 1, which comprises a tetrameric aggregate of Li-4 and O-4 interpenetrating tetrahedra in which chelating terminal nitrogens undergo a fluxional process around each face of the Li-4 tetrahedron in toluene solution. Addition of hexamethylphosphoric triamide (hmpa) produced a dimeric complex 2 in which oxygen bridges are retained. The crystal structures of both compounds were determined. Bond lengths indicate that an iminoenolate form of the ligand predominates, irrespective of aggregation state. The data are used to rationalise the selectivity of dimetallations of enaminones.