title: Bimetallic lanthanide amido complexes as highly active initiators for the ring-opening polymerization of lactides.
abstract: A series of neutral bimetallic lanthanide amido complexes supported by rigid phenylene bridged bis(β-diketiminate) ligands were synthesized, and their catalytic behavior for the polymerization of L-lactide and rac-lactide was explored. The amine elimination reaction of Ln[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) with PARA-H(2), [PARA-H(2) = 2[2,6-(i)Pr(2)C(6)H(3)NHC(Me)C(H)C(Me)N]-(para-phenylene)] in a 2:1 molar ratio in THF at 25 °C afforded the corresponding bimetallic lanthanide amido complexes PARA-{Ln[N(SiMe(3))(2)](2)}(2) [Ln = Nd(1), Sm(2), Y(3)] in high isolated yields. Similar reaction of Nd[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) with META-H(2), [META-H(2) = 2[2,6-(i)Pr(2)C(6)H(3)NHC(Me)C(H)C(Me)N]-(meta-phenylene)] at 90 °C in toluene for about 48 h gave META-{Nd[N(SiMe(3))(2)](2)}(2) (4). Complexes 1-4 were well characterized by elemental analysis, IR spectroscopy, and their definitive structures were confirmed by an X-ray crystal structure analysis. The coordination environment and coordination geometry around the metal atoms are similar in these complexes. Each of the metal atoms is four-coordinated with two nitrogen atoms from the N,N-chelating β-diketiminate unit, and two nitrogen atoms from two (Me(3)Si)(2)N- groups to form a distorted tetrahedron. These complexes can serve as highly active initiators for L-lactide polymerization in toluene. In addition, they also showed high activity towards rac-lactide polymerization in THF at room temperature, giving heterotactic-enriched polymers (P(r) ≈ 0.70), and complex 4 displays obviously higher activity in comparison with complex 1.
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: Song
authors.initials: S
authors.lastname: Sun
authors.forename: Kun
authors.initials: K
authors.lastname: Nie
authors.forename: Yufang
authors.initials: Y
authors.lastname: Tan
authors.forename: Bei
authors.initials: B
authors.lastname: Zhao
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen
authors.forename: Yingming
authors.initials: Y
authors.lastname: Yao
mesh_terms: D000577:Amides / Q000737:chemistry*; D004146:Dioxanes / Q000138:chemical synthesis* / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization
chemical_list: D000577:Amides; D004146:Dioxanes; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; C091880:dilactide