Structures and reactions of monomeric and dimeric lithium diazapentadienyl complexes with electrophiles: synthesis of α-C,C′-dialkyl-β-diimines, and dissolution-reversible synthesis of an α-alkoxylithium-β-diimine

Direct acid-catalysed condensation of substituted anilines with acetylacetone was found to give convenient access to β-enamineimines [2-Pri-C6H4NCMeCHCMeNH-2-Pri-C6H4] and [2-MeO-C6H4NCMeCHCMeNH-2-MeO-C6H4], whereas TiCl4-mediated condensation was required to produce [2,6-Pri2-C6H3NHC(CF3)CHC(CF3)N-2,6-Pri2-C6H3], which was crystallographically characterized. All are conveniently metallated using BunLi. The structures of monomer [2-Pri-C6H4NCMeCHCMeN-2-Pri-C6H4·Li(thf)2], and dimer [{ 2-MeO-C6H4NCMeCHCMeN-2-MeO-C6H4·Li}2] are reported. The structure of the dimeric product of aldol addition of adamantan-2-one to [2-Pri-C6H4NCMeCHCMeN-2-Pri-C6H4·Li.], the lithium scorpionate [{(C10H14OLi)CH(CMeN-2-Pri-C6H4)2}2], is also reported. It undergoes retro-aldol dissociation upon dissolution in non-co-ordinating solvents. The efficient synthesis of α-C,C′ dialkylated ‘true’ β-diimines by repeat lithiation/alkylation of di- and mono-ortho-isopropylanilino diketiminates is also reported. The differing reactivity of the monomers and dimer with electrophiles, and its relation to the structures of the intermediates, are discussed.