Synthesis, Reactivity, and Characterization of Sodium and Rare-Earth Metal Complexes Bearing a Dianionic N-Aryloxo-Functionalized β-Ketoiminate Ligand

Abstract

The synthesis and reactivity of a series of sodium and rare-earth metal complexes stabilized by a dianionic N-aryloxo-functionalized beta-ketoiminate ligand were presented. The reaction of acetylacetone with 1 equiv of 2-amino-4-methylphenol in absolute ethanol gave the compound 4-(2-hydroxy-5-methylphenyl)imino-2-pentanone (LH2, 1) in high yield. Compound 1 reacted with excess NaH to afford the novel sodium cluster [LNa2(THF)2]4 (2) in good isolated yield. Structure determination revealed that complex 2 has the 22-vertex cage structure. Reactions of complex 2 with anhydrous LnCl3 in a 1:4 molar ratio, after workup, gave the desired lanthanide chlorides [LLnCl(DME)]2 [Ln = Y (3), Yb (4), Tb (5)] as dimers. A further study revealed that complexes 3-5 are inert for chlorine substitution reactions. (ArO)3Ln(THF) (ArO = 2,6-Bu(t)2-4-MeC6H2O) reacted with compound 1 in a 1:1 molar ratio in tetrahydrofuran (THF), after workup, to give the desired rare-earth metal aryloxides as dimers [LLn(OAr)(THF)]2 [Ln = Nd (6), Sm (7), Yb (8), Y (9)] in high isolated yields. All of these complexes are well characterized, and the definitive molecular structures of complexes 2 and 4-6 were determined. It was found that complexes 6-9 can be used as efficient initiators for L-lactide polymerization, and the ionic radii of the central metals have a significant effect on the catalytic activity.