Half-Sandwich Scandium Complexes Bearing Heterocycle-Fused Ligands for the (Co)Polymerization of Styrene

Abstract Half-sandwich scandium complexes have been demonstrated to be efficient catalyst precursors for the (co)polymerization of styrene. In this study, we synthesized a series of half-sandwich scandium complexes bearing indole- and benzothiophene-fused cyclopentadienyl ligands with various substituents. With [Ph3C][B(C6F5)4] as a cocatalyst, all the scandium complexes exhibited considerable catalytic activity toward styrene polymerization. Notably, among the indole-fused ligand systems, catalytic activity increased as the steric bulk of the substituent decreased. This trend contrasts with previous reports, in which bulkier ligands generally afforded higher catalytic activities for half-sandwich scandium complexes. Furthermore, the scandium-based catalytic system bearing an indole-fused ligand also served as an efficient catalyst for the copolymerization of styrene with either ethylene or butadiene, producing high-molecular-weight copolymers containing highly syndiotactic styrene–styrene sequences (>99% rrrr). 1H and 13C NMR analyses reveal a random microstructure of ethylene-styrene copolymers and the block microstructure of butadiene-styrene copolymers with 1,4-enriched polybutadiene sequences (>90% 1,4-). The block microstructure of the butadiene–styrene copolymers was further confirmed by kinetic studies and atomic force microscopy (AFM), while tensile stress–strain measurements were performed to evaluate the mechanical properties of selected butadiene–styrene copolymers.