Syndiospecific Copolymerization of Styrene with para -Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes.

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl 3 with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH 2 PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH 2 SiMe 3 in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH 2 Py)Ln(CH 2 SiMe 3 ) 2 (THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y 3+ in the η 5 /κ 1 mode to form a constrained geometry configuration. In the presence of excess Al i Bu 3 , and on activation with 1 equiv of [Ph 3 C][B(C 6 F 5 ) 4 ] in toluene, complexes 1 and 2 became active for both styrene (St) and para -methoxystyrene ( p MOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/Al i Bu 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] was highly effective for the syndiospecific copolymerization of styrene with p MOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of p MOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the p MOS-to-St feed ratios.