Bis[bis(oxazolinato)] complexes of yttrium and lanthanum:: Molecular structure and use in polymerization of DL-lactide and DL-β-butyrolactone

Bis[bis(oxazolinato)]lanthanide complexes of general type [BOX](2)Ln[N(SiHMe2)(2)] (Ln = Y, La; Box = deprotonated chiral and nonchiral 2,2'-methylene[bis(oxazoline)] ligands) have been prepared by amine elimination protocols. The complexes have been characterized by H-1 and C-13 NMR spectroscopy and elemental analysis. The solid-state structure of the first bis[bis(oxazolinato)]-lanthanide complex, i.e. {2,2'-(alpha-methylmethylene)bis(4,4-dimethyl-2-oxazolinato)}(2)Y[N(SiHMe2)(2)] (1), is reported. Complex 1 features a five-coordinate yttrium center in a distorted trigonal bipyramidal geometry, where the Box ligands adopts a conformation to minimize nonbonded interactions. The prepared complexes are among the most active initiators known in the ring-opening polymerization of DL-lactide and DL-beta-butyrolactone, with TOF up to 31200 h(-1) at room temperature, and are highly productive (TON up to 2400). The produced poly(lactide)s and poly (hydroxybutyrate) s have narrow polydispersities (M-w/M-n = 1.08-1.44) and controlled number-average molecular masses (M-n up to 182000 g mol(-1)). However, whether chiral or nonchiral Box ligands are used, the polymers show an atactic microstructure. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).