Synthesis and characterization of bimetallic lanthanide-alkali metal complexes stabilized by aminophenoxy ligands and their catalytic activity for the polymerization of 2,2-dimethyltrimethylene carbonate.

Electronic properties of the aminophenolate groups have obvious effect on the synthesis of aminophenolate lanthanide-lithium complexes. Amine elimination reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with lithium aminophenolates [ArNHCH2(3,5-(t)Bu2C6H2-2-O)Li(THF)]2 (Ar = p-ClC6H4, [ONH](Cl-p); p-BrC6H4, [ONH](Br-p)) in tetrahydrofuran (THF) in a 1 : 2 molar ratio gave the bimetallic lanthanide-lithium amido complexes [NO](Cl-p)2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (1), Yb (2)), and [NO](Br-p)2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (3), Yb (4)). When the Ar groups are p-MeOC6H4, ([ONH](MeO-p)) and o-MeOC6H4 ([ONH](MeO-o)), similar reactions generated the homoleptic lanthanide-lithium complexes [NO](MeO-p)3Ln[Li(THF)]3 (Ln = Y (5), Yb (6)) and [NO](MeO-o)2Ln[Li(THF)] (Ln = Y (7), Yb (8)) in high isolated yields, respectively. Whereas the bimetallic lanthanide-lithium amido complexes [NO](Cl-o)2Ln[N(SiMe3)2][Li(THF)]2 (Ln = Y (9), Yb (10)) can be obtained in good yields, when the Ar group is o-ClC6H4 ([ONH](Cl-o)). All of these complexes were well characterized. X-ray structure determination revealed that these complexes have solvated monomeric structures. In complexes 1-4, 9, and 10, the lanthanide atom is five-coordinated by two oxygen atoms and two nitrogen atoms from two aminophenoxy ligands and one nitrogen atom from N(SiMe3)2 group to form a distorted trigonal bipyramidal geometry, whereas in complexes 5-8, the central lanthanide atom is six-coordinated by oxygen atoms, and nitrogen atoms from the aminophenoxy ligands to form a distorted octahedron. It was found that complexes 1-10 are highly efficient initiators for the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC), affording the polymers with high molecular weights, and the homoleptic heterobimetallic lanthanide complexes showed apparently high activity.