Anionic lanthanide complexes supported by a pyrrole-based tetradentate Schiff base ligand: Synthesis, structures and catalytic activity toward the polymerization of ε-caprolactone

Abstract

The synthesis of the anionic organolanthanide complexes supported by H2bppda (H2bppda=N,N′-bis(2-pyrrylmethylidene)-1,2-phenylenediamine) ligand via different synthetic strategies is reported. Treatment of 1:4 mixture of LnCl3(THF)3 and LiN(SiMe3)2 with 2 equivalents of H2bppda in THF gave complexes of the formula [Li(THF)4][Ln(bppda)2]·THF (Ln=Nd (1·THF), Sm (2·THF), Gd (3·THF), Dy (4·THF), Er (5·THF)) and [Li(THF)5][Yb(bppda)2] (6). Reaction of Nd(BH4)3(THF)3 with 2 equivalents of Na2bppda in THF generated [Na(THF)6][Nd(bppda)2] (7) in good yield. Treatment of 1·THF with 1 equivalent of CoCp2 in THF led to the isolation of [CoCp2][Nd(bppda)2] (8). All of the complexes have been characterized by single crystal X-ray diffraction and elemental analyses. Complexes 1·THF–5·THF are isomorphous and isostructural, and the geometry of the octa-coordinated Ln3+ ion in [Ln(bppda)2]− unit in these complexes is well described as either distorted dodecahedron or distorted bicapped trigonal prism. Lanthanide contraction was observed in 1·THF–5·THF and 6. The structures of complexes 1·THF, 7 and 8 are different from each other due to the variation of the cationic ions. The ring-opening polymerization reaction of ε-caprolactone initiated by 1·THF was conducted; it showed good activity.