Table 4 Crystallographic data
t
La[CyNC(N(SiMe3)2)NCy](N(SiMe3)2)2 1
La[CyNC(N(SiMe3)2)NCy](OC6H3 Bu2-2,6)2 3
Formula
M
C31H76LaN5Si6
826.39
C47H82LaN3O2Si2
916.26
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/n
a/Å
b/Å
c/Å
9.5129(2)
24.1821(1)
20.3228(3)
91.340(1)
4673.82(9)
4
10.3424(5)
19.440(1)
25.212(1)
93.241(1)
5060.9(4)
4
β/Њ
V/Å3
Z
Total reflections
22292
8409
10.88
24671
9340
11.55
Independent reflections
µ(Mo-Kα)/cmϪ1
Rint
R
Rw
0.039
0.030
0.040
0.039
0.036
0.032
T/ЊC
Ϫ83
Ϫ112
Preparations
a pre-determined period, after which time the reaction was
quenched by the addition of 5 drops of 1 M HCl solution. The
reaction mixture was then poured into cold heptane to precipi-
tate the polymer, which was collected and dried under vacuum
La[CyNC(N(SiMe3)2)NCy](N(SiMe3)2)2 1. 1,3-Dicyclohexyl-
carbodiimide (3.80 g, 18.4 mmol) and La[N(SiMe3)2]3 (11.4 g,
18.4 mmol) were combined in a large Schlenk tube and toluene
(200 mL) was added. The yellow solution was heated to reflux
for 2 d, after which time the solvent was removed under
vacuum. The resultant solid was extracted into the minimum
amount of pentane, and the solution cooled to Ϫ30 ЊC. The
product was isolated as large yellow plates (9.12 g, 60% yield).
The less soluble bis-ligand complex La[CyNC(N(SiMe3)2)-
NCy]2(N(SiMe3)2) 2 was isolated by fractional crystallization
(2.85 g, 15% yield). For 1: mp 210–213 ЊC (Found: C, 45.44; H,
9.16; N, 8.03%. C31H76LaN5Si6 requires C, 45.06; H, 9.27; N,
8.47%); νmax/cmϪ1 1612w, 1302m, 1243s, 1182m, 1135m, 1014s,
964w, 939w, 861s, 827s, 753s and 662m (Nujol); δH(C6D6) 3.37
(mult, 2H, unique Cy H), 1.95–1.15 (mult, 20H, C6H10), 0.38 (s,
18H, ligand SiMe3) and 0.22 (s, 36H, amide SiMe3); δC(C6D6)
166.7 (NCN), 55.5, 39.2, 26.7 and 26.6 (C6H11), 4.7 and 3.1
(SiMe3). For 2: mp 213–215 ЊC (Found: C, 50.97; H, 9.38; N,
9.10%. C44H98LaN7Si6 requires C, 51.17; H, 9.56; N, 9.49%);
νmax/cmϪ1 1610w, 1345m, 1300w, 1252s, 1173m, 1132m, 1070w,
1015s, 961m, 943s, 862m, 839s, 764w, 665w and 640w (Nujol);
δH(C6D6) 3.45 (mult, 4H, unique Cy H), 2.00–1.20 (mult, 40H,
C6H10), 0.50 (s, 18H, amide SiMe3) and 0.29 (s, 36H, ligand
SiMe3); δC(C6D6) 167.3 (NCN), 55.7, 38.9, 26.8 and 26.7
(C6H11), 5.3 and 3.4 (SiMe3).
1
for 24 h. H and 13C-{1H} NMR spectra of polylactide were
recorded in CDCl3.
General procedures for X-ray crystallography
Pertinent details for the individual compounds can be found in
Table 4. The data were corrected for Lorentz and polarization
effects, but no correction for crystal decay was applied. All
non-hydrogen atoms were refined anisotropically, unless stated
otherwise. Hydrogen atoms were assigned idealized positions
and included in structure factor calculations, but not refined,
unless stated otherwise.
CCDC reference number 186/2333.
Acknowledgements
We thank Dr Nikolai Vladimirov for obtaining the GPC
spectra and for helpful discussions, the NSF for the award of a
predoctoral fellowship to G. D. W. and the DOE for support of
this work.
References
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La[CyNC(N(SiMe3)2)NCy](OC6H3tBu2-2,6)2 3. To a pentane
solution (100 mL) of complex 1 (3.50 g, 4.06 mmol) cooled to
Ϫ78 ЊC was added a pentane solution (50 mL) of 2,6-di-tert-
butylphenol via cannula. The pale yellow solution was left to
stir overnight and warm to room temperature. The volume was
then reduced, and the contents of the flask were cooled to
Ϫ30 ЊC. The product was isolated as yellow rods (3.47 g, 93%
yield). mp 251–253 ЊC (Found: C, 61.79; H, 8.86; N, 4.71%.
C47H82LaN3O2Si2 requires C, 61.61; H, 9.02; N, 4.59%); νmax
/
cmϪ1 1582w, 1404s, 1348s, 1304m, 1253s, 1188s, 1136m, 1098m,
1070w, 1002m, 964m, 939s, 863s, 834s, 820s, 745s, 652s and 642s
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Macromolecules, 1996, 29, 3332.
3
(Nujol); δH(C6D6) 7.28 (d, 4H, m-H, JH-H = 7.7), 6.83 (t, 2H,
3
p-H, JH-H = 7.7 Hz), 3.40 (mult, 2H, unique Cy H), 1.95–1.05
(mult, 20H, C6H10), 1.59 (s, 36H, CMe3) and 0.21 (s, 18H,
SiMe3); δC(C6D6) 168.0 (NCN), 163.4, 137.3, 125.4, 117.5 (di-
tert-butyl phenyl), 55.7, 38.7, 35.0 and 26.6 (C6H11), 32.5
(CMe3), 26.4 (CMe3) and 2.4 (SiMe3).
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Lactide polymerization
Compound 3 (15 mg, 0.016 mmol) and 50–1000 equivalents of
lactide (≈0.1–2.3 g) were combined in a Schlenk tube and 10 mL
of CH2Cl2 added. The contents of the flask were then stirred for
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W. B. Tolman, Macromolecules, 2000, 33, 3970.
926
J. Chem. Soc., Dalton Trans., 2001, 923–927