Highly Isospecific Styrene Polymerization Catalyzed by Single-Component Bridged Bis(indenyl) Allyl Yttrium and Neodymium Complexes

摘要

Polystyrene is a commodity polymer that can be obtained by many different mechanisms, that is, radical, cationic, anionic, and coordinative-insertive catalysis, with the latter technique being the best one for achieving precise control of the microstructure. Thus, syndiotactic polystyrene (sPS) has been effectively prepared with homogeneous cationic half-titanocene catalysts,[1] as well as Group 3 metal catalysts such as Hou's cationic half-scandocene[2] and neutral discrete [(CpCMe2Flu)Ln(allyl)(thf)] complexes (Cp=cyclopentadienyl; Flu=9-fluorenyl; Ln=Nd, Y; allyl=C3H5) that we recently introduced.[3] On the other hand, isotactic polystyrene (iPS) is still best produced by heterogeneous catalysis[4] or anionic polymerization.[5] Although a range of homogeneous catalysts have been reported to give isotactic-enriched polystyrene and oligomers,[6] there are very few examples of true single-site catalysts that form polystyrene isospecifically. Among those is the binary titanium-based system supported by a 1,4-dithiabutane-bridged bis(phenolato) (OSSO) ligand recently described by Okuda et al.[7], [8] Herein, we report the synthesis of new ansa-bridged bis(indenyl) allyl yttrium and neodymium complexes [(IndCMe2Ind)Ln(allyl)(ether)n] (Ind=2-indenyl; ether=Et2O) as the first single-component catalysts for purely isospecific styrene homopolymerization.