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 (C5H5)(3)Ln(THF) with amine bridged bis(phenol)LH2 [L = Me2NCH2CH2N{CH2-(2-O-C6H2-Bu-2(t)-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(OC6H3-2,6-Pr-2(i))(THF) [Ln = Nd (1), Sm (2), Yb (3)], LLn(OC6H4-4-CH3)(THF)(n) [ Ln = Nd (4), Sm (5), n = 2; Ln = Y (6), n = 1] and LLn(OC6H4-4-OCH3)(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.