Synthesis and characterization of anionic rare-earth metal amides stabilized by phenoxy-amido ligands and their catalytic behavior for the polymerization of lactide

Abstract

A dianionic phenoxyamido ligand was the first to be used to stabilize organo-rare-earth metal amido complexes. Amine elimination reaction of Nd[N(TMS)₂]₃(μ-Cl)Li(THF)₃ (TMS = SiMe₃) with aminophenol [HNOH] {[HNOH] = N-p-methylphenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine} in a 1 : 1 molar-ratio gave the anionic phenoxyamido neodymium amide [NO]₂Nd[N(TMS)₂][Li(THF)]₂ (2) in a low isolated yield. A further study revealed that the stoichiometric reactions of Ln[N(TMS)₂]₃(μ-Cl)Li(THF)₃ with the lithium aminophenoxy [HNOLi(THF)]₂ (1) in tetrahydrofuran (THF) gave the anionic rare-earth metal amido complexes [NO]₂Ln[N(TMS)₂][Li(THF)]₂ [Ln = Nd (2), Sm (3), Yb (4), Y (5)] in high isolated yields. All of these complexes are fully characterized. X-Ray structure determination revealed that complex 1 has a solvated dimeric structure, and complexes 2–5 are isostructural, and have solvated monomeric structures. Each of the rare-earth metal ions is coordinated by two oxygen atoms and two nitrogen atoms from two phenoxyamido ligands and one nitrogen atom from the N(TMS)₂ group to form a distorted trigonal bipyramidal geometry. Each of the lithium atoms in complexes 2–5 is coordinated with one oxygen atom and one nitrogen atom from two different phenoxyamido groups, and one oxygen atom from one THF molecule to form a trigonal planar geometry. Furthermore, the catalytic behavior of complexes 2–5 for the ring-opening polymerization of L-lactide was explored.