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 hex amethylphosphoric triamide (hmpa) produced a dimeric complex 2 in whic h oxygen bridges are retained. The crystal structures of both compound s were determined. Bond lengths indicate that an iminoenolate form of the ligand predominates, irrespective of aggregation state. The data a re used to rationalise the selectivity of dimetallations of enaminones .