Synthesis and molecular structure of new heterometal alkoxide clusters Ln2Na8(OCH2CF3)14(THF)6 (Ln = Sm, Y, Yb): Highly active catalysts for polymerization of ε-caprolactone and trimethylene carbonate

The new polynuclear heterometal alkoxide clusters Ln2Na8(OCH2CF3)14(THF)6 (Ln = Sm 1, Y 2, Yb 3) have been synthesized by the reaction of anhydrous LnCl3 with 7 equiv. of NaOCH2CF3 in 68–75% yields. Crystal structural analysis revealed clusters 1–3 are isomorphous composed of two cubanes and a double open cubane, with one face of an Ln1Na2O4 open cubane capped by an additional Ln1O2 layer. Clusters 1–3 show extremely high activity for the polymerization of ε-caprolactone (ε-CL) and trimethylene carbonate (TMC). The reactivity is much higher than those found for the monometallic alkoxides lanthanide complexes previously reported. The dependence of catalytic activity on lanthanide metals is observed: Yb ≈ Y < Sm for ε-CL and Yb < Y < Sm for TMC. The polymers obtained with these clusters all show a unimodal molecular weight distribution with moderate molecular weight distributions (Mw/Mn = 1.4–1.7), indicating that clusters 1–3 can really be used as single-component catalysts. The bimetallic cooperation and the coordination–insertion mechanism were proposed.

Graphical abstractThe novel polynuclear heterometal alkoxide clusters Ln2Na8(OCH2CF3)14(THF)6 (Ln = Sm 1, Y 2, Yb 3) have been synthesized by the reaction of anhydrous LnCl3 with 7 equiv of NaOCH2CF3 in good yields. Clusters 1-3 show extremely high activity for the polymerization of ε-caprolactone (ε-CL) and trimethylene carbonate (TMC), and the reactivity is much higher than those found for the monometallic alkoxides lanthanide complexes previously reported.Figure optionsDownload full-size imageDownload as PowerPoint slide