<i>C</i><sub>3</sub>-Symmetric Chiral Organolanthanide Complexes: Synthesis, Characterization, and Stereospecific Polymerization of α-Olefins
作者:Lenka Lukešová、Benjamin D. Ward、Stéphane Bellemin-Laponnaz、Hubert Wadepohl、Lutz H. Gade
DOI:10.1021/om700504f
日期:2007.8.1
The trialkyl complexes [M(iPr-trisox)(CH2SiMe2R)(3)] (R = Me, M = Y, (1), R = Ph, M = Lu (2a), R = Me, M = Lu (2b), Tm (3), Er (4), Ho (5), and Dy (6)) were prepared from 1,1,1-tris[(S)-4-isopropyloxazolinyl]ethane (iPr-trisox) and the corresponding trialkyl precursors [M(CH2SiMe2R)(3)(THF)(n)]. Their molecular structures all display a highly distorted octahedral geometry, with the angles subtended at the metal center significantly deviating from the ideal 90 degrees, which is attributed to the steric demands imposed by the large CH2SiMe2R ligands, both with each other and with the isopropyl groups of the iPr-trisox ligand. Active catalysts for the polymerization of alpha-alkenes (n-hexene, n-heptene, and n-octene) were generated in situ by reaction of the trialkyl precatalyst with 2 equiv of trityl tetrakis(pentafluorophenyl)borate. In all cases polyolefins with M-w/M-n values of between 1.58 and 2.08 and isotacticities of 80-95% were obtained. The polymerization activity increases from lutetium to thulium and then subsequently decreases with increasing ionic radius of the metal due to a combination of activation with increasing ionic radius and decreasing catalyst stability.