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Using a method similar to that for L1Na. Yield: 3.03 g
1
(50%). H NMR (CDCl3, 200 MHz): δ 7.94 (1H, s, CHvN),
7.14–6.97, 6.47–6.40, (7H, m, ArH), 3.11, 2.54 (2H, br, CH
(CH3)2), 1.26, 0.88, 0.49 ppm (12H, br, CH(CH3)2)). 13C NMR
(CDCl3, 50 MHz): δ 171.29 (COH), 170.64 (CvN), 150.67,
139.14, 138.24, 134.47, 124.47, 123.69, 123.32, 122.10, 113.05
(Ar), 27.99 (CH(CH3)2), 25.89, 24.80, 23.30, 21.63 (CH
(CH3)2). Anal. Calcd (found) for C19H22NONa (303.41): C,
75.22 (75.65); H, 7.31 (6.90); N, 4.62 (4.03) %. Mp: 292 °C.
X-Ray crystallographic studies
Suitable crystals of complexes L5Li and L4Na were sealed in a
thin-walled glass capillary under dry nitrogen atmosphere and
mounted on a Bruker AXS SMART 1000 diffractometer. Inten-
sity data were collected in 1350 frames with increasing width of
0.3° per frame. The absorption correction was based on the sym-
metry-equivalent reflections using the SADABS program. The
space group determination was based on a check of the Laue
symmetry and systematic absences and confirmed by using the
structure solution. The structure was solved by a direct method
using an SHELXTL package. All non-H atoms were located
from successive Fourier maps, and hydrogen atoms were refined
using a riding model. Anisotropic thermal parameters were used
for all non-H atoms, and fixed isotropic parameters were used
for H atoms.
General procedures for the polymerization of L-lactides
A typical polymerization procedure was exemplified by the syn-
thesis of entry 21 (Table 1) using complex L4Na as a catalyst.
The polymerization conversion was analyzed by H NMR spec-
1
troscopic studies. Toluene (10.0 mL) was added to a mixture of
complex L4Na (0.0125 g, 0.0125 mmol) and L-lactide (0.72g,
5 mmol) at 25 °C. After the solution was stirred for 6.5 min, the
reaction was quenched by adding a drop of ethanol, and the
polymer was precipitated pouring into n-hexane (30.0 mL) to
give a white solid. The white solid was dissolved in CH2Cl2
(5.0 mL) and then n-hexane (70.0 mL) was added to give a
white crystalline solid. Yield: 0.68 g (94%).
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Acknowledgements
Financial support from the National Science Council of the
Republic of China is greatly appreciated. Thanks are due to
Prof. Chu-Chieh Lin (National Chung-Hsing University) for the
supply of chemical reagents and an important suggestion for the
experiments.
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