Syntheses of Rare-Earth Metal Alkyl Complexes Bearing a Dianionic α-Iminopyridyl Ligand and Their Catalytic Activities toward Polymerization of 2-Vinylpyridine
Xiuli Zhang, Shuangliu Zhou, Donghan Wang, Lijun Zhang, Yun Wei, Xiancui Zhu, Peng Cui, Gen Luo, Shaowu Wang
Abstract
The rare-earth metal alkyl complexes bearing a dianionic α-iminopyridyl ligand {μ-η2:σ1:κ1:κ1-2-[O(CH2CH2)2NCH2CH2NCH]C5H4N}2RE2(CH2SiMe3)2(THF)n (n = 2, RE = Gd(2a), Dy(2b), Y(2c); n = 0, RE = Lu(2e), Sc(2f)) and {μ-η2:σ1:κ1:κ1-2-[O(CH2CH2)2NCH2CH2NCH]C5H4N}{μ-η4:η2:κ1-2-[O(CH2CH2)2NCH2CH2NCH]C5H4N}Er2(CH2SiMe3)2(THF) (2d) were prepared through reactions of RE(CH2SiMe3)3(THF)2 with 2-aminomethylpyridine 2-[O(CH2CH2)2NCH2CH2NHCH2]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)2NCH2CH2NCH2]C5H4N}RE(CH2SiMe3)2 (3f) which would slowly transform into 2f at room temperature, indicating that the formation of dianionic α-iminopyridine went through the continual deprotonation reaction of the functionalized donor group 2-aminomethylpyridine. The α-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.