Synthesis and properties of alkaline metal complexes with new overcrowded β-diketiminato ligands

Enaminoimines TbtNHC(Me)CHC(Me)NAr (5, Tbt = 2,4,6-[CH(SiMe3)2]3C6H2) bearing a Tbt group were synthesized by the two steps condensation of acetylacetone with bulky amines. Enaminoimines 5 were treated with n-BuLi to give the corresponding lithium β-diketiminates, [Li{TbtNHC(Me)CHC(Me)NAr}] (1). The X-ray structural analysis of [Li{TbtNC(Me)CHC(Me)NMes}] (1c, Mes = mesityl) revealed that it is a monomeric, solvent-free lithium β-diketiminate. The equilibrium between free 1c plus THF and THF-coordinated (1c · thf) was investigated in detail by the determination of the association constant (Ka) in C6D6 at 293 K and the Job’s plot. The heavier alkali metal complexes, sodium and potassium β-diketiminates (6c–9c), were prepared by the two routes. THF-coordinated [M{TbtNC(Me)CHC(Me)NMes}(thf)] (6c: M = Na. 7c: M = K) were prepared by the reaction of 5c (Ar = Mes) with MH (M = Na, K). Solvent-free [M{TbtNC(Me)CHC(Me)NMes}] (8c: M = Na. 9c: M = K) were prepared by the reaction of 1c with t-BuOM (M = Na, K).

The monomeric, solvent-free lithium β-diketiminate bearing a Tbt group was synthesized, and the equilibrium between the free and THF-coordinated lithium β-diketiminates was examined by the 7Li NMR spectra. The transformation of lithium β-diketiminate into the sodium and potassium analogues is also achieved.Figure optionsDownload as PowerPoint slide