Polar-Group Activated Isospecific Coordination Polymerization of ortho-Methoxystyrene: Effects of Central Metals and Ligands

Stereoselective polymerization of polar vinyl monomers has been a long-standing challenge because the employed transition-metal catalysts are easily poisoned by polar groups of monomers. In this contribution, a series of -diketiminato rare-earth metal complexes 1-5 (L(1-5)Ln(CH2SiMe3)(2)(THF)(n), Ln=Gd-Lu, Y, and Sc) were successfully synthesized. In combination with AliBu(3) and [Ph3C][B(C6F5)(4)], complexes 1c(Tb)-1g(Tm) exhibited high activities and excellent isoselectivities for the polymerization of ortho-methoxystyrene (oMOS), in which, the polar methoxy group of oMOS did not poison but activated the polymerization through sigma- chelation to the active species together with the vinyl group. Moreover, the large Gd-attached precursor 1b showed a higher activity, albeit with a slightly decreased isoselectivity. The small Sc-attached precursor 1i was completely inert. Meanwhile, the spatial steric arrangement and the coordination mode of the -diketiminato ligand could clearly affect and even block oMOS polymerization. This work sheds new light on the coordination polymerization of polar monomers.