Synthesis, structure and catalytic activity of alkali metal-free bent-sandwiched lanthanide amido complexes with calix[4]-pyrrolyl ligands

Abstract

Simple silylamine elimination reactions of calix[4]-pyrrole [R₂C(C₄H₂NH)]₄ (R = Me (1), {–(CH₂)₅–}_0.5 (2)) with 2 equiv. of [(Me₃Si)₂N]₃Ln(μ-Cl)Li(THF)₃ (Ln = Nd, Sm, Dy) in reflux toluene, afforded the novel dinuclear alkali metal-free trivalent lanthanide amido complexes (η⁵:η¹:η⁵:η¹-R₈–calix[4]-pyrrolyl){LnN(SiMe₃)₂}₂ (R = Me, Ln = Nd (3), Sm (4), Dy (5); R = {–(CH₂)₅–}_0.5, Ln = Nd (6), Sm(7)). The complexes were fully characterized by elemental analyses, spectroscopic analyses and single-crystal X-ray analyses. X-ray diffraction studies showed that each lanthanide metal was supported by bispyrrolyl anions in an η⁵ fashion and along with three nitrogen atoms from N(SiMe₃)₂ and two other pyrroyl rings in η¹ modes formed the novel bent-sandwiched lanthanide amido bridged trivalent lanthanide amido complexes, similar to ansa-cyclopentadienyl ligand-supported lanthanide amides with respect to each metal center. The catalytic activities of these organolanthanide complexes as single component L-lactide polymerization catalysts were studied.