Quasi-living trans-1,4-polymerization of isoprene by cationic rare earth metal alkyl species bearing a chiral (s, s)-bis(oxazolinylphenyl)amido ligand

A series of chiral mononuclear dialkyl complexes [(S,S)-BOPA]Ln(CH ₂SiMe₃)₂ (1, 2) (BOPA = (S,S)- bis(oxazolinylphenyl)amido; Ln = Sc (1); Ln = Lu (2)) and binuclear alkyl complexes [o-(S)-OPA-C₆H₄-(CH₂SiMe ₃)C=N-CH(ⁱPr)CH₂-O]Ln(CH₂SiMe ₃)}₂ (3,4) (OPA = (oxazolinylphenyl)amine; Ln = Y (3); Ln = Tm (4)) have been synthesized in moderate yields via one-pot acid-base reactions by use of the tris(trimethylsilylmethyl) rare earth metal complexes with the chiral tridentate (S,S)-bis(oxazolinylphenyl)amine ligand. In the presence of activator with or without a small amount of AlⁱBu ₃, the dialkyl complexes 1 and 2 exhibit very high activities (up to 6.8 × 10⁵ g mol_Ln^-1 h^-1) and trans-1,4-selectivity (up to 100%) in the quasi-living polymerization of isoprene, yielding the trans-1,4-PIPs with moderate molecular weights (M _n = (0.2-1.0) × 10⁵ g/mol) and narrow molecular weight distributions (M_w/M_n = 1.02-2.66).