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 beta-enamineimines [2-Pr-i-C6H4NCMeCHCMeNH-2-Pr-i-C6H4] and [2-MeO-C6H4NCMeCHCMeNH-2-MeO-C6H4], whereas TiCl4-mediated condensation was required to produce [2,6-Pr-2(i)-C6H3NHC(CF3)CHC(CF3)N-2,6-Pr-2(i)-C6H3], which was crystallographically characterized. All are conveniently metallated using (BuLi)-Li-n. The structures of monomer [2-Pr-i-C6H4NCMeCHCMeN-2-Pr-i-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-Pr-i-C6H4NCMeCHCMeN-2-Pr-i-C6H4.Li.], the lithium scorpionate[{(C10H14OLi)CH(CMeN-2-Pr-i-C6H4)(2)}(2)], is also reported. It undergoes retro-aldol dissociation upon dissolution in non-co-ordinating solvents. The efficient synthesis of alpha-C,C' dialkylated 'true' beta-diimines by repeat lithiation/alkylation of di- and mono-orthoisopropylanilino 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.