Lanthanide bis(borohydride) complexes coordinated by tetradentate phenoxide ligand: Synthesis, structure, and catalytic activity in ring-opening polymerization of rac-lactide and epsilon-caprolactone

摘要

New lanthanide bis(borohydride) complexes coordinated by monoanionic tetradentate phenoxide ligand [(C5H4NCH2)(2)NCH2(3,5-tBu(2)C(6)H(2)O)]Ln(BH4)(2) [Ln = Y (1), Nd (2), Sm (3)] were synthesized by the reactions of Ln(BH4)(3)(THF)(3) with an equimolar amount of the lithium phenoxide [(C5H4NCH2)(2) NCH2(3,5-tBu(2)C(6)H(2)O)Li] in THE at 60 degrees C. The complexes were isolated after recrystallization from toluene in 75, 64, and 69% yields, respectively. X-ray analysis revealed that in 1 the phenoxide ligand is tetradentate, while two borohydride groups are coordinated to the Y3+ ion in a K-3-fashion. Compounds 1-3 initiate ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and racemic lactide (rac-LA) in toluene at 25 degrees C. The obtained polylactides are characterized by atactic structures P-r= 0.54-0.58, and rather narrow polydispersities (M-w/M-n= 1.1-1.5). For epsilon-caprolactone polymerization, the resulting polymers have moderate polydispersities (M-w/M-n = 1.4-2.4) and molecular weights (6.2-54.1.10(3)).