title: Bis(oxazolinyl)phenyl-ligated rare-earth-metal complexes: highly regioselective catalysts for cis-1,4-polymerization of isoprene.
abstract: NCN-pincer (S,S)-2,6-bis(4'-isopropyl-2'-oxazolinyl)phenyl-ligated rare-earth-metal dichlorides [(S,S)-Phebox-(i)Pr]LnCl2(THF)2 (Ln = Sc (1); Y (2); Dy (3); Ho (4); Tm (5); Lu (6)) were synthesized via transmetalation between [(S,S)-Phebox-(i)Pr]Li and LnCl3 in THF solvent. Interestingly, treatment of LaCl3 by the same method generated tris(ligand) lanthanum complex [(S,S)-Phebox-(i)Pr]3La (7). Molecular structures of complexes 1, 2, 3, and 7 were established by single-crystal X-ray diffraction study. Pincer ligand (S,S)-Phebox-(i)Pr adopts a κC:κN:κN' tridentate coordination mode to the central metal ion. Upon activation with [PhNHMe2][B(C6F5)4] and Al(i)Bu3, complexes 2-5 exhibited highly catalytic activities and more than 98% cis-1,4-selectivity for isoprene polymerization while complexes 1 and 6 were inactive for this reaction. When use of the catalyst system consisted of complex 2, [PhNHMe2][B(C6F5)4], and Al(i)Bu3 for isoprene polymerization, the resultant polymer has a high cis-1,4-selectivity up to 99.5%. The reaction temperature had little effect on the regioselectivity, and high cis-1,4-selectivity almost remained even at 80 °C.
authors: State Key Laboratory of Fine Chemicals, College of Chemistry, Dalian University of Technology, Dalian 116024, China.
authors: Yu
authors: Y
authors: Pan
authors: Tieqi
authors: T
authors: Xu
authors: Guan-Wen
authors: GW
authors: Yang
authors: Kun
authors: K
authors: Jin
authors: Xiao-Bing
authors: XB
authors: Lu