Controlled iso-specific polymerization of 2-vinylpyridine catalyzed by arylamide-ligated rare-earth metal aminobenzyl complexes

Abstract

Treatment of rare-earth tris(o-dimethylaminobenzyl) complexes Ln(CH₂C₆H₄NMe₂-o)₃ with one equivalent of the pyrrolyl-functionalized arylamide ligands 2,5-Me₂C₄H₂NCH₂CH₂NHC₆H₅ and 2,5-Me₂C₄H₂NSiMe₂NHC₆H₅ in toluene generated arylamide rare-earth metal bis(aminobenzyl) complexes (2,5-Me₂C₄H₂NCH₂CH₂NC₆H₅)Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Sc (1), La (2), Lu (3)) and (2,5-Me₂C₄H₂NSiMe₂NC₆H₅)Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Lu (5), Y (6)) in good isolated yields. Reaction of Y(CH₂C₆H₄NMe₂-o)₃ with 2,5-Me₂C₄H₂NCH₂CH₂NHC₆H₅ in 1 : 1 or 1 : 2 molar ratio specifically yielded bis(arylamide) yttrium mono(aminobenzyl) complex (2,5-Me₂C₄H₂NCH₂CH₂NC₆H₅)₂Y(CH₂C₆H₄NMe₂-o) (4). Complexes 1–6 were characterized by elemental analysis and NMR spectroscopy. Complexes 2, 4 and 5 were structurally validated by single crystal X-ray diffraction. These complexes were highly active for polymerization with 2-vinylpyridine to afford iso-tactic polymers with high molecular weight and narrow molecular weight distribution. Complex 4 promoted the polymerization in a controlled fashion, and the iso-selectivity of the polymerization reached up to a P_m value of 0.98. Analyses of the oligomer by NMR and MALDI-TOF showed that the polymerization proceeded via a group transfer polymerization mechanism.