Lanthanocene Diolate Complexes: Synthesis, Structures and Catalytic Property for ε-Caprolactone Polymerization

Reaction of LnCl₃ first with three equivalent of C₅H₅Na in THF, then with one equivalent of N-phenyldiethanolamine in THF-DME afforded complexes of {[(C₅H₅)Ln((-OCH₂CH₂)₂N(C₆H₅)]₄((₄-Cl)}[Na(DME)₄] (Ln=Sm (1), Yb (2)), being characterized by infrared spectra, elemental analyses and X-ray crystallography. They are ionic pair compounds. The anionic part is a cluster, which can be viewed as a cyclic tetramer with four (C₅H₅)Ln units bridged by four pairs of OR groups, forming a pinwheel structure. Both the complexes can catalyze the ring-opening polymerization of ε-caprolactone under mild conditions, and complex 1 is more active than complex 2. The polymerization accords with one order reaction kinetics for monomer concentration. The molecular weight increases with the yield increasing, and the molecular weight distribution is rather narrow (1.19<PDI<1.29).