High tacticity control in organolanthanide polymerization catalysis: formation of isotactic poly(alpha-alkenes) with a chiral C-3-symmetric thulium complex

The thulium complexes [Tm(iPr-trisox)(CH2SiMe2R)3] (R = Me 1a, Ph 1b) were synthesized from the thulium trialkyl precursors [Tm(CH2SiMe2R)3(thf)2]; reaction of 1a with two equivalents of [Ph3C][B(C6F5)4] gave a cationic complex 1c, which was found to polymerize 1-hexene, 1-heptene and 1-octene to give the corresponding polyolefins with moderate to good activities and with minimum isotacticity of 90%, 83% and 95%, respectively

C-3-Symmetric chiral organolanthanide complexes: Synthesis, characterization, and stereospecific polymerization of alpha-olefins

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°, 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 α-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 Mw/Mn 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