Ligands Dominate Highly Syndioselective Polymerization of Styrene by Using Constrained-geometry-configuration Rare-earth Metal Precursors

A series of novel constrained-geometry-configuration (CGC) rare-earth metal complexes (RCH2-Py)Ln-(CH2SiMe3)(2)(THF)(n) (Py = pyridyl; Ln = Y, n = 1, R = C5Me4 (Cp') (1); Ln = Y, n = 1, R = C9H6 (Ind) (2); Ln = Y, n = 1, R = C13H8 (Flu) (3a); Ln = Lu, n = 1, R = C13H8 (Flu) (3b); Ln = Sc, n = 0, R = C13H8 (Flu) (3c)) have been synthesized by treating rare-earth metal trisalkyls with PyCH2-Cp', PyCH2-Ind, and PyCH2-Flu compounds, respectively, and fully characterized by NMR and X-ray diffraction analyses. Complexes 1, 2, and 3a-b are monomeric THF solvates while the scandium complex 3c is solvent-free, in which all the CGC ligands adopt a eta(5)/kappa(1) bonding mode via coordination of five carbon atoms from the cyclopentadienyl fragment and the pyridyl nitrogen atom with the central metals. Upon activation with (AlBu3)-Bu-i and [Ph3C][B(C6F5)(4)], these complexes showed different performances toward styrene polymerization. The Cp'CH2-Py and IndCH(2)-Py ligated yttrium complexes 1 and 2 showed very low activity to afford syndiotactic enriched polystyrene. Strikingly, the bulky FluCH(2)-Py supported complexes 3a-c displayed outstanding activities up to 1.56 x 10(7) g/(mol(Ln).h) and perfect syndioselectivity (rrrr > 99%), giving high molecular weight sPS; in particular, thus excellent performance was independent of the central metal type for the first time. In addition, the relationship of the ligand structure with the catalytic performances toward specific selective polymerization of styrene was reasonably revealed by comparison with the other Flu-based rare-earth metal catalysts reported previously by us. This might open a new pathway for designing catalysts for specifically selective polymerizations.