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

Abstract

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.