Synthesis and molecular structure of new heterometal alkoxide
AbstractThe 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 e-caprolactone (e-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 e-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.
2008 Published by Elsevier Ltd.
Keywords: Heterometal cluster; Lanthanide; Alkali metal; Alkoxide; Polymerization; e-Caprolactone (e-CL); Trimethylene carbonate (TMC)
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