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 Ln2Na 8 (OCH2CF3)14(THF)6 (Ln = Sm 1, Y 2, Yb 3) have been synthesized by the reaction of anhydrous LnCl 3 with 7 equiv. ofNaOCH 2 CF 3 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 Ln 1 Na 2 O 4 open cubane capped by an additional Ln 1 O 2 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 (M w /M n = 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.