Synthesis and Structural Characterization of β-Diketiminate−Lanthanide Amides and Their Catalytic Activity for the Polymerization of Methyl Methacrylate and ε-Caprolactone

Abstract

The synthesis and catalytic activity of lanthanide monoamido complexes supported by a beta-diketiminate ligand are described. Donor solvents, such as DME, can cleave the chloro bridges of the dinuclear beta-diketiminate ytterbium dichloride {[(DIPPh)2nacnac]YbCl(mu-Cl)3Yb[(DIPPh)2nacnac](THF)} (1) [(DIPPh)2nacnac = N,N-diisopropylphenyl-2,4-pentanediimine anion] to produce the monomeric complex [(DIPPh)2nacnac]YbCl2(DME) (2) in high isolated yield. Complex 2 is a useful precursor for the synthesis of beta-diketiminate-ytterbium monoamido derivatives. Reaction of complex 2 with 1 equiv of LiNPri2 in THF at room temperature, after crystallization in THF/toluene mixed solvent, gave the anionic beta-diketiminate-ytterbium amido complex [(DIPPh)2nacnac]Yb(NPri2)(mu-Cl)2Li(THF)2 (3), while similar reaction of complex 2 with LiNPh2 produced the neutral complex [(DIPPh)2nacnac]Yb(NPh2)Cl(THF) (4). Recrystallization of complex 3 from toluene solution at elevated temperature led to the neutral beta-diketiminate-lanthanide amido complex [{(DIPPh)2nacnac}Yb(NPri2)(mu-Cl)]2 (5). The reaction medium has a significant effect on the outcome of the reaction. Complex 2 reacted with 1 equiv of LiNPri2 and LiNC5H10 in toluene to produce directly the neutral beta-diketiminate-lanthanide amido complexes 5 and [{(DIPPh)2nacnac}Yb(NC5H10)(THF)(mu-Cl)]2 (6), respectively. These complexes were well characterized, and their crystal structures were determined. Complexes 4-6 exhibited good catalytic activity for the polymerization of methyl methacrylate and epsilon-caprolactone.