Synthesis and characterization of amine bridged bis(phenolate) lanthanide aryloxides and their application in the polymerization of lactide

A series of neutral lanthanide aryloxides supported by an amine bridged bis(phenolate) ligand were synthesized, and their catalytic behavior for the polymerization of L-lactide was explored. The reactions of (C(5)H(5))(3)Ln(THF) with amine bridged bis(phenol)LH(2) [L = Me(2)NCH(2)CH(2)N{CH(2)-(2-O-C(6)H(2)-Bu(t)(2)-3,5)}(2)] in a 1 : 1 molar ratio, and then with 1 equivalent of 2,6-diisopropylphenol, p-cresol or 4-methoxyphenol, respectively, in situ in THF gave the neutral lanthanide aryloxides LLn(OC(6)H(3)-2,6-Pr(i)(2))(THF) [Ln = Nd (1), Sm (2), Yb (3)], LLn(OC(6)H(4)-4-CH(3))(THF)(n) [Ln = Nd (4), Sm (5), n = 2; Ln = Y (6), n = 1] and LLn(OC(6)H(4)-4-OCH(3))(THF)(n) [Ln = Nd (7), Sm (8), n = 2; Ln = Yb (9), n = 1] in high isolated yields. These complexes were well characterized by elemental analyses, IR spectra and NMR spectroscopy in the case of complex 6. The definitive molecular structures of complexes 1-8 were determined by single-crystal X-ray analyses, which revealed that both the substituents of the aryloxo groups and the ionic radii of the lanthanide metals affect the solid-state structures of the bis(phenolate) lanthanide aryloxides. It was found that complexes 1-9 are efficient initiators for the ring-opening polymerization of l-lactide, and the structures of the aryloxo groups have no obvious effect on the catalytic activity and controllability. A further study revealed that complex 6 can initiate the highly heteroselective ring-opening polymerization of rac-lactide.