Cationic Half-Sandwich Tetrahydrofluorenyl Rare-Earth Metal Complexes as Stable Single-Site Catalysts for...

As indenyl-derivates, the tetrahydrofluorenyl ligands had an expanded "wingspan" with considerable steric hindrance. In this text, the rare-earth metal complexes bearing tetrahydrofluorenyl ligands have been synthesized and fully characterized by NMR (¹H and ¹³C) and X-ray diffraction analyses. Upon the activation by [Ph₃C][B(C₆F₅)₄], all the scandium complexes exhibited excellent catalytic activity for highly syndioselective polymerization of styrene with a narrow molecular weight distribution (M_w/M_n < 2.0), suggesting the beneficial influence of tetrahydrofluorenyl ligands in stabilizing the single-site active species during the polymerization. Moreover, the scandium-based catalytic systems also promoted the 1,4-regular polymerization of butadiene and its copolymerization with styrene, affording diblock copolymers featuring a highly syndiotactic polystyrene block and a 1,4-specific PBD block. The kinetics investigation revealed the huge gap in TMS-Sc-catalyzed polymerization reactivity ratios (r_BD/r_St > 300) between butadiene and styrene, and this further proved the block structure of styrene-butadiene copolymers. The morphology and mechanical property of the selected diblock copolymer were, respectively, investigated by atomic force microscopy and stress-strain experiments.