Experimental and Computational Investigations on Highly Syndioselective Styrene–Ethylene Copolymerization Catalyzed by Allyl ansa-Lanthanidocenes

Abstract

The syndioselective copolymerization of styrene with ethylene (in bulk or in aliphatic hydrocarbon solutions, (nBu)2Mg as scavenger, Tpolym = 60–140 °C) was achieved in the presence of a series of ansa-lanthanidocenes of the type {R2C(C5H4)(R′R′Flu)}Ln(1,3-C3H3(SiMe3)2)(THF)x (1-Nd-K-allyl, 2–7-Nd, and 2-Sc,La,Sm,Pr). While precursors based on small ionic radius metals (2-Sc) or bearing bulky substituents in 3,6-positions of the fluorenyl moieties (3-Nd and 5-Nd) were poorly or not active under standard polymerization conditions (60 °C), 2-La,Pr,Nd,Sm which bear 2,7-tBu2 substituents on the Flu ligand produced efficiently sPSE materials (productivity 300–400+ kg mol(Ln)−1 h–1, [r]5 = 71%; controlled amount of ethylene inserted in the range 1–15 mol %). Under harsher conditions (Tpolym = 100–140 °C, [St]0/[Nd]0 = 40 000–147 000 equiv), 2-Nd produced similar sPSE materials with a productivity increased by 1 order of magnitude (up to 5430 kg mol(Nd)−1 h–1). Theoretical DFT investigations including the solven...