Migration of amide to imine group of lanthanide Schiff base complexes: effect of amido group

Abstract

The protonolysis of anionic lanthanide amide complexes (THF)LiLn(NPrⁱ₂)₄ with two equiv. of tridentate Schiff base HL (L = 3,5-Bu^t₂-2-O-C₆H₂CHN-C₅H₄N) afforded the unanticipated products LiL′₂Ln(THF) (L′ = 3,5-Bu^t₂-2-O-C₆H₂CH(NPrⁱ₂)-N-C₅H₄N; Ln = Y 1, Sm 2 and Yb 3) formed by intramolecular nucleophilic attack of the amide groups at the imine carbon atoms of the original ligand, L. The protonolysis is greatly affected by the amide group. When amine elimination was carried out with a mixture of Ln[N(TMS)₂]₃(μ-Cl)Li(THF)₃ (TMS = SiMe₃) and LiN(TMS)₂, the expected lanthanide amide complexes with two Schiff base ligands, L₂Ln[N(TMS)₂] (Ln = Sm 4 and Nd 5), were isolated and no migration of the N(TMS)₂ group was observed because of steric hindrance. Complexes 1–5 were well characterized including X-ray structural analyses.