Isoprene polymerization with indolide‐imine supported rare‐earth metal alkyl and amidinate complexes

Abstract

AbstractReaction of 7‐{(N‐2,6‐R)iminomethyl)}indole (HL1, R = dimethylphenyl; HL2, R = diisopropylphenyl) and rare‐earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, generated new rare‐earth metal bis(alkyl) complexes LLn(CH2SiMe3)2(THF) [L = L1: Ln = Lu (1a), Sc (1b); L = L2: Ln = Lu (3a), Sc (3b)] and mono(alkyl) complexes L22Lu(CH2SiMe3) (4a). Treatment of alkyl complexes 1a and 4a with N,N′‐diisopropylcarbodiimide afforded the corresponding amidinates L1Lu{iPr2NC(CH2SiMe3)NiPr2}2 (2a) and L22Lu{iPr2NC(CH2SiMe3)NiPr2} (5a), respectively. These new rare‐earth metal alkyls and amidinates except 4a in combination with aluminum alkyls and borate generated efficient homogeneous catalysts for the polymerization of isoprene, providing high cis‐1,4 selectivity and high molar mass polyisoprene with narrow molar mass distribution (Mn = 2.65 × 105, Mw/Mn = 1.07, cis‐1,4 98.2%, −60 °C). The environmental hindrance around central metals arising from the bulkiness of the ligands, the Lewis‐acidity of rare‐earth metal ions, the types of aluminum tris(alkyl)s and borate, and polymerization temperature influenced significantly on both the catalytic activity and the regioselectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5251–5262, 2008