A binuclear lithium complex based on an <i>ansa</i> -bis(1-azaallyl) ligand: synthesis, structure and catalysis for ring-opening polymerization of ɛ-caprolactone

Deprotonation of the Schiff base 2,6-dimethyl-N-(1-phenylethylidene)aniline, C₁₆H₁₇N or [MeC(Ph)=N(2,6-Me₂C₆H₃)], 1, with one equivalent of lithium diisopropylamide (LDA) and subsequent reaction with half an equivalent of SiPh₂Cl₂ gave a new diimine, N-[2-({2-[(2,6-dimethylphenyl)imino]-2-phenylethyl}diphenylsilyl)-1-phenylethylidene]-2,6-dimethylaniline, C₄₄H₄₂N₂Si, 2. Further treatment of 2 with LDA in the presence of tetrahydrofuran (THF) yielded the target binuclear ansa-bis(1-azaallyl) lithium compound {μ-N-[2-({2-[(2,6-dimethylphenyl)azanidyl]-2-phenylethyl}diphenylsilyl)-1-phenylethylidene]-2,6-dimethylanilinido}bis[(tetrahydrofuran)lithium], [Li₂(C₄₄H₄₀N₂Si)(C₄H₈O)₂], 3. Both 2 and 3 were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis, and the structures of 1, 2 and 3 were confirmed by X-ray crystallography. Density functional theory (DFT) calculations were carried out for compounds 1-3. In addition, the catalytic properties of 3 towards the ring-opening polymerization of ϵ-caprolactone were investigated and the compound showed good catalytic activity.