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](3)Ln(.)nTHF (R = methyl, Ln = Nd (1), Gd (2), Yb (3), n = 0; R = phenyl, Lit = 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 F-caprolactone at room temperature. (C) 2002 Published by Elsevier Science B.V.