Syntheses of Rare-Earth Metal Alkyl Complexes Bearing a Dianionic alpha-Iminopyridyl Ligand and Their Catalytic Activities toward Polymerization of 2-Vinylpyridine

The rare-earth metal alkyl complexes bearing a dianionic alpha-iminopyridyl ligand {mu-eta(2): sigma(1): kappa(1): kappa(1)- 2-[O(CH2CH2)(2)NCH2CH2NCH]-C5H4N} 2RE2(CH2SiMe3)(2)(THF)(n) (n = 2, RE = Gd(2a), Dy(2b), Y(2c); n = 0, RE = Lu(2e), Sc(2f)) and {mu-eta(2): sigma(1): kappa(1): kappa(1)-2-[O(CH2CH2)(2)NCH2CH2NCH] C5H4N}{mu-eta(4) :. eta(2) : kappa(1) - 2-[O(CH2CH2)(2)NCH2CH2NCH] C5H4N}Er-2(CH2SiMe3)(2)(THF) (2d) were prepared through reactions of RE(CH2SiMe3)(3)(THF)(2) with 2-amino-methylpyridine 2-[O (CH2CH2)(2)NCH2CH2NHCH2]C5H4N (1). In the process, the reactions underwent double deprotonation of the functionalized donor group 2-aminomethylpyridine. Reaction of Sc(CH2SiMe3)(3)(THF)(2) with compound 1 in a shortened reaction time afforded the scandium dialkyl complex {2-[O(CH2CH2)(2)NCH2CH2NCH2]C5H4N}RE(CH2SiMe3)(2) (3f) which would slowly transform into 2f at room temperature, indicating that the formation of dianionic alpha-iminopyridine went through the continual deprotonation reaction of the functionalized donor group 2-aminomethylpyridine. The alpha-iminopyridyl rare-earth metal alkyl complexes exhibited high catalytic activities toward polymerization of 2-vinylpyridine with high iso-selectivity. The polymerization mechanism and the origins of stereoselectivity was deduced by DFT calculations.