Magnesium and Zinc Complexes Supported by N,O-Bidentate Pyridyl Functionalized Alkoxy Ligands: Synthesis and Immortal ROP of ε-CL andl-LA
writer：Yang Wang, Wei Zhao, Dongtao Liu, Shihui Li, Xinli Liu, Dongmei Cui and Xuesi Chen
keywords：ε-caprolactone ; l-lactide; zinc metal;immortal
source：期刊
specific source：http://pubs.acs.org/doi/pdf/10.1021/om300113p
Issue time：2012年
The N,O-bidentate
pyridyl functionalized alkoxy ligands
2-(6-methyl-2-pyridinyl)-1,1-dimethyl-1-ethanol (L1–H) and
2-(6-methyl-2-pyridinyl)-1,1-diphenyl-1-ethanol (L2–H) have
been prepared by treatment of acetone and benzophenone with monolithiated
2,6-lutidine. Deprotonolysis of the ligands L1–H and L2–H with
1 equiv of MgnBu2 and ZnEt2 in
toluene by releasing butane and ethane, respectively, gave the corresponding
dimeric metal-monoalkyl complexes [L1MgnBu]2(1),
[L2MgnBu]2 (2), [L1ZnEt]2 (3),
and [L2ZnEt]2 (4). Complexes 1–4 were
characterized by 1H and 13C NMR spectroscopy
analysis, and the molecular structures of 1, 3,
and 4 were further confirmed by X-ray diffraction analysis.
The investigation of the catalytic behavior of these complexes toward
ε-caprolactone (ε-CL) and l-lactide (l-LA) polymerizations showed that the
Mg-based complexes gave higher activity than those attached to zinc metal, probably
owing to the greater ionic character of the magnesium metal. Remarkably, the
magnesium complex 2exhibited a striking “immortal” nature in the
presence of primary alcohols where up to 500 PCL chains grew from each Mg
active center when benzyl alcohol was employed, while, in particular, in the
presence of triethanolamine, complex 2 also displayed an
immortal mode for the polymerization of l-LA.
