Reaction of 7-{(N-2,6-R)iminomethyl)}lindole (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 = L-1: Ln = Lu. (1a), Sc (1b); L = L-2 : Ln = Lu (3a), Se (3b)] and mono(alkyl) complexes L-2 Lu-2(CH2SiMe3) (4a). Treatment of alkyl complexes 1a and 4a with N,N'-diisopropylcarbodiimide afforded the corresponding amidinates (LLu)-Lu-1{iPr(2)NC(CH2SiMe3) NiPr2}(2) (2a) and L-2 Lu-2{iPr(2)NC(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 (M-n = 2.65 x 10(5), M-w/M-n = 1.07, cis-1,4 98.2%, -60 degrees 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. (c) 2008 Wiley Periodicals, Inc.