title: Syntheses and structures of lanthanide borohydrides supported by a bridged bis(amidinate) ligand and their high activity for controlled polymerization of ε-caprolactone, L-lactide and rac-lactide.
abstract: Metathesis reaction of LLnCl(THF)(2) [L = (Me(3)SiNC(C(6)H(5))N)(2)(CH(2))(3)] with NaBH(4) in a 1 : 1.5 molar ratio in THF (THF = tetrahydrofuran) at 60 °C afforded the monoborohydride LLn(BH(4))(DME) [Ln = Y (1), Nd (2), Sm(3) and Yb(4)] crystallized from DME solution (DME = dimethoxyethane). Crystal structure analyses revealed 1-4 are monomers, in which each metal is ligated by one L ligand, one η(3)-BH(4) group and one DME molecule in a trigonal bipyramid geometry. Complexes 1-4 were found to be very active single-site initiators for the controlled ring opening polymerization of ε-caprolactone (ε-CL) and L-lactide (L-LA) as judged by relatively narrow molecular weight distributions (M(w)/M(n): 1.34-1.50) and experimental values M(n)(exp) were in good agreement with theoretic values M(n)(theo). The highest activity and the best control over the molecular weight for both monomers were found for the system with 2. These monoborohydride complexes can also initiate the ring opening polymerization of rac-LA to gave heterotactically enriched polyLA with Pr (heterotactic enrichment) values in a range of 0.69-0.85 depending on the lanthanide metals and the most effective heterotactic enrichment (Pr) was found for 1 (Pr = 0.85). Moreover, complex 1 initiated the polymerization of rac-LA in a living fashion.
authors.affiliation: Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
authors.forename: Wenbo
authors.initials: W
authors.lastname: Li
authors.forename: Mingqiang
authors.initials: M
authors.lastname: Xue
authors.forename: Jing
authors.initials: J
authors.lastname: Tu
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen
mesh_terms: D001894:Borohydrides / Q000138:chemical synthesis* / Q000737:chemistry*; D002208:Caproates / Q000737:chemistry*; D002384:Catalysis; D060326:Chemistry Techniques, Synthetic; D004146:Dioxanes / Q000737:chemistry*; D005663:Furans / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D058105:Polymerization; D013237:Stereoisomerism
chemical_list: D001894:Borohydrides; D002208:Caproates; D004146:Dioxanes; D005663:Furans; D007783:Lactones; D028581:Lanthanoid Series Elements; D008024:Ligands; C469777:bisamidine; C121056:caprolactone; C091880:dilactide