Synthesis of Benzoxazine Functionalized Amine‐Bridged Bis(phenolato) Rare Earth Complexes and Their Application in Ring‐Opening Polymerization of rac‐Lactide

Comprehensive Summary The reactivities of benzoxazine functionalized amine bridged bis(phenol)s L n H 2 ( n = 1—3) with rare earth metal complexes were explored, founding that both the aryl substituents of the ligand and the rare earth metals have profound influences on reaction outcomes. Reactions of L 1 H 2 (R = t Bu) with [N(SiMe 3 ) 2 ] 3 RE( μ ‐Cl)Li(THF) 3 (RE = La, Nd) afforded the expected rare earth amides L 1 RE[N(SiMe 3 ) 2 ](THF) (RE = La (1), Nd (2)). However, the similar reaction of L 2 H 2 (R = OMe) and L 3 H 2 (R = Me) with [N(SiMe 3 ) 2 ] 3 La( μ ‐Cl)Li(THF) 3 generated the unexpected amine bridged triphenolato lanthanum complexes L 2‐NR2 La(THF)( μ ‐Cl)Li(THF) 2 (3) and L 3‐NR2 La(THF)( μ ‐Cl)Li(THF) 2 (4), respectively, in which the benzoxazine ring is opened, and a plausible mechanism was proposed. Furthermore, the reactions of L 1 H 2 with [N(SiMe 3 ) 2 ] 3 RE( μ ‐Cl)Li(THF) 3 (RE = Y, Yb) produced the unexpected benzoxazine ring‐opened products L 1‐H RE(THF) (RE = Y (5), Yb (6)). Further study revealed that the reaction of L 1 H 2 with Cp 3 Y(THF) in a 1: 1 molar ration in THF gave the corresponding yttrium complex L 1 YCp·THF (7a), but the benzoxazine ring‐opened product L 1‐OCH2Ph Y(THF) (7b) was formed when 1 equivalent of benzoic alcohol was added. The benzoxazine functionalized amine bridged bis(phenolato) rare earth amides were efficient initiators for the ring‐opening polymerization of rac ‐lactide, giving heterotactic polylactide with P r value up to 0.93.