Synthesis, characterization of homoleptic lanthanide amidinate complexes and their catalytic activity for the ring-opening polymerization of ε-caprolactone

Addition of [CyNC(R)NCy]Lithium (Cy=cyclohexyl, R=methyl, phenyl) to anhydrous lanthanide trichlorides in 3:1 molar ratio yielded a series of homoleptic amidinate lanthanide complexes with the general formula [CyNC(R)NCy]3Ln·nTHF (R=methyl, Ln=Nd (1), Gd (2), Yb (3), n=0; R=phenyl, Ln=Nd (4), Y (5), Yb (6), n=2). The X-ray crystal structural determination of 3 and 6 revealed that the ytterbium ions in both complexes are coordinated by three bidentate amidinate moieties with a trigonal planar geometry. These amidinate lanthanide complexes showed extremely high activity for the ring-opening polymerization of ε-caprolactone at room temperature.