Synthesis, Characterization, and Catalytic Activity of Dinuclear Rare-Earth Metal Alkyl Complexes Bearing 2,6-Diisopropylphenylamidomethyl Functionalized Pyrrolyl Ligand

A series of structurally well-defined cationic rare-earth metal bridged sandwich pyrrolyl rare-earth metal dialkyl complexes with the general formula of (Me3SiCH2)2RE­(μ-L)2RE­(thf)2 (L = 2-(2,6-iPr2C6H3NCH2)­C4H3N; RE = Y (1a), Gd (2a), Dy (3a), Er (4a), Yb (5a), Lu (6a), thf = tetrahydrofuran) were synthesized by the reactions of rare-earth metal trialkyl complexes RE­(CH2SiMe3)3(thf)2 with 1 equiv of 2-(2,6-diisopropylphenyl­aminomethyl)­pyrrole (H2L) in toluene at room temperature. When the reaction temperature was raised to 45 °C, the centrosymmetric half-sandwich pyrrolyl rare-earth metal alkyl complexes (Me3SiCH2RELthf)2 (RE = Y (1b), Gd (2b), Yb (5b)) were obtained in good yields, unexpectedly. Further studies revealed that the sandwich pyrrolyl rare-earth metal dialkyl complexes can be transferred to the half-sandwich rare-earth metal isomers by heating the C6D6 solution to 60 °C. Single-crystal X-ray diffraction analyses revealed that the sandwich pyrrolyl rare-earth metal dialkyls were bridged by an octahedral cationic rare-earth metal coordinated by two N atoms of the pyrrolyl rings, two N atoms of the amido moieties, and two O atoms of the thf molecules; while in their isomers, the rare-earth metals were surrounded by a pyrrolyl ligand, an alkyl group, a molecule of thf, and an η5 type of pyrrolyl ring. All complexes were characterized by spectroscopic methods, elemental analyses, and single-crystal X-ray analyses. Moreover, the catalytic behaviors of these complexes were investigated, and the results showed that, in the presence of cocatalysts, the dinuclear rare-earth metal alkyl complexes exhibited high activities and high regio- and stereoselectivities for isoprene polymerization with cis-1,4-units up to 96.6%.