Bimetallic rare earth alkyl complexes bearing bridged amidinate ligands: Synthesis and activity for L-lactide polymerization

Article abstract of DOI:10.1002/cjoc.201090096

Four novel bridged-amidines H₂L {1,4-R¹[C(=NR²)(NHR²)]₂ [R¹=C₆H₄, R²=2,6-ⁱPr₂C₆H₃ (H₂L¹);

Full text of DOI:10.1002/cjoc.201090096

FULL PAPER
Bimetallic Rare Earth Alkyl Complexes Bearing Bridged
Amidinate Ligands: Synthesis and Activity for L-Lactide
Polymerization
Yang, Jianpinga(杨建平)
Xu, Pingb(徐萍)
Luo, Yunjie ,a,b,c(罗云杰)
*
a Department of Chemical Engineering, Ningbo University of Technology, Ningbo, Zhejiang 315211, China
b Organometallic Chemistry Laboratory, Ningbo Institute of Technology, Zhejiang University,
Ningbo, Zhejiang 315100, China
c State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun, Jilin 130022, China
Four novel bridged-amidines H2L {1,4-R1[C(＝NR2)(NHR2)]2 [R1＝C6H4, R2＝2,6-iPr2C6H3 (H2L1); R1＝C6H4,
R2＝2,6-Me2C6H3 (H2L2); R1＝C6H10, R2＝2,6-iPr2C6H3 (H2L3); R1＝C6H10, R2＝2,6-Me2C6H3 (H2L4)]} were syn-
thesized in 65%—78% isolated yields by the condensation reaction of dicarboxylic acid with four equimolar
amounts of amines in the presence of PPSE at 180 ℃. Alkane elimination reaction of Ln(CH2SiMe3)3(THF)2 (Ln＝
Y, Lu) with 0.5 equiv. of amidine in THF at room temperature afforded the corresponding bimetallic rare earth alkyl
complexes (THF)(Me3SiCH2)2LnL1Ln(CH2SiMe3)2(THF) [Ln ＝ Y (1), Lu (2)], (THF)(Me3SiCH2)2LnL2Ln-
(CH2SiMe3)2(THF) [Ln＝Y (3), Lu (4)], (THF)(Me3SiCH2)2YL3Y(CH2SiMe3)2(THF) (5), (THF)(Me3SiCH2)2YL4-
Y(CH2SiMe3)2(THF) (6) in 72%—80% isolated yields. These neutral complexes showed activity towards L-lactide
polymerization in toluene at 70 ℃ to give high molecular weight (M＞104) and narrow molecular weight distribu-
tion (Mw/Mn≤1.40) polymers.
Keywords rare earths, bridged amidinate ligand, synthesis, ring-opening polymerization
Introduction
centers.38,39 Although Marks and co-workers also de-
scribed that the bridged-Cp binuclear rare earth metal
amide complexes showed much more efficient catalytic
activity towards olefin intramolecular hydroamina-
tion/cyclization,40,41 in contrast, little is known about
multinuclear organo rare earth metal alkyl complexes to
date.42 Herein, we would like to report the preparation
of bimetallic rare earth alkyl complexes supported by
bridged-amidinates, as well as their performance as ini-
tiators for L-lactide polymerization.
Over the past decade organo rare earth metal
bis(alkyl) complexes with a general formula LLnR2(S)x
(L＝monoanionic ancillary ligand, Ln＝rare earth metal,
R＝alkyl, S＝coordinated solvent, x＝coordinated sol-
vent number) have attracted increasing interest and
made spectacular progress as catalyst precursors in or-
ganic transformation and polymerization.1-5 However,
such complexes are usually rather difficult to character-
ize and are often much less thermally stable compared
to rare earth metal mono(alkyl) complexes. Therefore,
most of rare earth metal bis(alkyl) complexes are
mononuclear, and should be stabilized by cyclopenta-
dienyl derivatives,6-19 or sterically bulky non-cyclopen-
tadienyl ancillary ligands such as β-diketiminates,20-25
amidinates,26-35 anilido-imine,36,37 etc. Very recently, it
was found that, in particular in the field of organo-
metallic chemistry of transition metals, multinuclear
metal complexes could possess unique or more efficient
homogeneous catalytic processes than mononuclear spe-
cies, benefiting from cooperative effects between
proximate functional groups or adjacent active metal
Results and discussion
Synthesis and characterization of the bridged amidi-
nes H2L1-4
According to procedures reported in the literature, in
some cases with little modification, we reported previ-
ously that carboxylic acids reacted with 2 equiv. of
amines in the presence of polyphosphoric acid
trimethylsilyl ester (PPSE) at 180 ℃ could afford a
variety of amidines in good isolated yields.35,43 In this
work, instead of monocarboxylic acids, dicarboxylic
acids were reacted with four equimolar amounts of
*
E-mail: lyj@nit.zju.edu.cn
Received September 14, 2009; revised October 25, 2009; accepted November 13, 2009.
Project supported by the National Natural Science Foundation of China (No. 20604023), Zhejiang Provincial Natural Science Foundation
(Y4090617), State Key Laboratory of Polymer Physics and Chemistry (No. 200902), and Ningbo Municipal Natural Science Foundation of China
(No. 2008A610056).
Chin. J. Chem. 2010, 28, 457— 462
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
457

Yang, Xu & Luo
FULL PAPER
amines in the presence of PPSE at 180 ℃ to give the
bridged amidines H2L1-4 as off-white/pale-green pow-
ders after extractive work-up and solvent evaporation
(Scheme 1). Recrystallization from hot toluene or THF
provided the pure bridged amidines as white/pale-green
solids or microcrystals, which were characterized by
NMR spectroscopy, HRMS, FT-IR spectroscopy, and
with 0.5 equiv. of the amidines H2L in THF at room
temperature, after workup, gave complexes 1—6 in
72%—80% yields (Scheme 2).
Complexes 1—6 are all air- and moisture-sensitive,
soluble in THF, toluene, and lightly soluble in aliphatic
solvents such as hexane and pentane. They were char-
acterized by elemental analysis, FT-IR, and NMR spec-
troscopy. Although some of these complexes could be
obtained in the form of single crystals, the attempts to
authenticate their single crystal structures were unsuc-
cessful due to their extremely fast desolvation.
1
elemental analysis. H NMR spectra of H2L1-4 indicate
that the N—H proton resonances appear as a broad
singlet between δ 5.2 and 5.7.
1
Scheme 1
Room-temperature H NMR spectra of 1, 3, 5 and 6
(yttrium complexes) in C6D6 show an AB spin for the
methylene resonances of Y-CH2SiMe3. The methylene
resonances for these complexes were found from δ
－0.2 to －0.4 (1H, d, JY-H＝2.7—3.0 Hz), which are
identical to the equivalent resonances in the related
mononuclear analogues.27,28,35 In 1, 3 and 5, 6, the main
difference is the linked-bridge at the carbon atom of
ligating NCN moiety (phenyl group for 1, 3 and cyclo-
hexyl group for 5, 6), however, all of the methylene
resonances of Y-CH2SiMe3 appear around δ 40 in 13C
NMR spectra, suggesting a similar electronic yttrium
environment. In the cases of lutetium complexes 2 and 4,
the methylene protons of Lu-CH2SiMe3 display sharp
1
singlet resonances at －0.40 and －0.43 in H NMR
spectra, respectively. Restricted rotation about the
N-Caryl bonds gives rise to two separate doublets for the
isopropyl methyl groups in the related complexes.
L-Lactide polymerization initiated by the bimetallic
rare earth alkyl complexes
Synthesis and characterization of the bimetallic rare
earth alkyl complexes
To investigate the reactivity of the bimetallic rare
earth alkyl complexes, these complexes were employed
as initiators for L-lactide polymerization. Some selected
mononuclear amidinate rare earth metal bis(alkyl) com-
plexes were also involved in this experiment to reveal
whether the bimetallic species could exhibit cooperative
effect. The preliminary polymerization results are sum-
marized in Table 1.
All these neutral bimetallic rare earth alkyl com-
plexes showed activity towards L-lactide polymerization,
and the conversions exceeded 76% at 70 ℃ for 30 min
in toluene in the case of [M]/[I]＝100 (molar ratio). The
bimetallic complexes showed very similar polymeriza-
To obtain neutral rare earth metal bis(alkyl) com-
plexes, it has proven that an appropriate metal/ligand
combination is rather critical and alkane elimination
reaction is a straightforward strategy. NMR monitoring
technique showed the reaction of Y(CH2SiMe3)3(THF)2
with 0.5 equiv. of H2L1 in benzene-d6 at room tempera-
ture occurred smoothly, affording (THF)x(Me3SiCH2)2-
YL1Y(CH2SiMe3)2(THF)x as a neat product in several
hours, with the elimination of tetramethylsilane. No
ligand redistribution was observed. On a preparative
scale, treatment of Ln(CH2SiMe3)3(THF)2 (Ln＝Y, Lu)
Scheme 2
458
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 457— 462

Bimetallic Rare Earth Alkyl Complexes Bearing Bridged Amidinate Ligands
Table 1 L-Lactide polymerization with rare earth alkyl amidinate complexesa
－
－
4
c
4
d
d
Run
1
Initiator
Yieldb/%
91
Mn,calcd ×10
Mn,obsd ×10
Mw/Mn
1.39
1.33
1.30
1.35
1.39
1.40
1.26
1.20
1
0.33
0.32
0.28
0.30
0.31
0.27
0.64
0.66
0.72
2.28
2.41
1.85
1.96
2.08
1.38
2.33
3.36
2
2
89
3
3
78
4
4
82
5
5
86
6
6
76
7
[PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)
[CyC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)
[CyC(N-2,6-iPr2C6H3)2]Lu(CH2SiMe3)2(THF)
89
8
91
9
100
4.71
1.25
－
Polymerization conditions: [L-LA]/[Ln]＝100, [L-LA]＝0.5 mol•L 1, in toluene, t＝30 min, 70 ℃; Isolated yields of PLA; Mn of
a
b
c
PLA calculated from Mn,calcd＝144×([LA]/4[Ln])×yield (LA), except for runs 7—9, in which Mn,calcd＝144×([LA]/2[Ln])×yield (LA);
d
Determined by GPC at 40 ℃ in THF relative to polystyrene standards; corrected by the Mark-Houwink equation [Mn,obsd＝0.58Mn
(GPC)].48
tion activity compared with the mononuclear complexes.
Although each bimetallic complex possesses two center
metals, GPC curves of the resulting polymers were all
unimodal with quite narrow molecular weight distribu-
tions (Mw/Mn≤1.40), indicative of single-site catalyst
behavior as observed in other rare earth metal bis(alkyl)
catalyst systems.21,35,44,45 However, the resulting mo-
lecular weight distributions (Mw/Mn ≤ 1.40) were
slightly broader than those from mononuclear com-
plexes (Mw/Mn ≤ 1.26).35 The observed molecular
weights of Mn are much greater than the calculated mo-
lecular weights, suggesting rather low initiation effi-
ciency with these initiators. Taking the activity and Mn
into consideration, each center metal in the bimetallic
complexes seems to be independent and has similar ini-
tiation capability. Cooperative effect has not been ob-
served in this polymerization system. Different to the
mononuclear amidinate rare earth metal bis(alkyl) com-
complexes bearing bridged-amidinate ligands were pre-
pared by alkane elimination reaction. These neutral bi-
metallic alkyl complexes were active for L-lactide po-
lymerization to give high molecular weight (Mn＞104)
and narrow molecular weight distribution (Mw/Mn≤
1.40) polymers. Cooperative effect was not observed
under current polymerization conditions.
Experimental
General considerations
All manipulations were performed under pure argon
with rigorous exclusion of air and moisture using stan-
dard Schlenk techniques and a glovebox. Solvents
(toluene, hexane, and THF) were distilled from sodium/
benzophenone ketyl, degassed by the freeze-pump-thaw
method, and dried over fresh Na chips in the glovebox.
Dichloromethane was dried by stirring with CaH2, and
distilled before use. Anhydrous LnCl3 were purchased
plexes, wit＋h which the effective ionic radii of center
＋
metals (Y3 ＝1.040 Å, Lu3 ＝1.001 Å)46 could affect
－1
from STREM. LiCH2SiMe3 (1 mol•L solution in pen-
the polymerization activity, the central metals in the
bimetallic amidinate complexes showed little influence
on the polymerization activity (runs 1 and 2, 3 and 4).
However, the polymerization activity is somewhat de-
pendent on the amidinate ligands. For example, em-
ploying the 1,4-phenylene group as a bridge, the initia-
tion activity of the resulting complexes increased with
the steric hindrance of the amidinates (runs 1 and 3).
However, the effect of the “bridge” in these amidinate
ligands on the polymerization is not so significant (runs
1 and 5).
tane) was obtained from Aldrich, dried under vacuum
before use. P2O5 was purchased from Sinopharm
Chemical Reagent Co. Ltd. Hexamethyldisiloxane,
2,6-diisopropylaniline, 2,6-dimethylaniline, terephthalic
acid, and 1,4-cyclohexanedicarboxylic acid were pur-
chased from Acros, and used as received. L-lactide was
purchased from TCI, and recrystallized from hot toluene.
Deuterated solvents (CDCl3, C6D6) were obtained from
CIL. Ln(CH2SiMe3)3(THF)2 (Ln＝Y, Lu),35,47 poly-
phosphoric acid trimethylsilyl ester (PPSE),42
[PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF),27,28 and
[CyC(N-2,6-iPr2C6H3)2]Ln(CH2SiMe3)2(THF) (Ln＝Y,
Lu)35 were prepared according to the literature.
Conclusion
Samples of organo rare earth metal complexes for
In summary, a series of bimetallic rare earth alkyl
Chin. J. Chem. 2010, 28, 457— 462
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
459

Yang, Xu & Luo
FULL PAPER
NMR spectroscopic measurements were prepared in the
glovebox using J. Young valve NMR tubes. NMR (1H,
13C) spectra were recorded on a Bruker AVANCE III
spectrometer at 25 ℃. Carbon, hydrogen, and nitrogen
analyses were performed by direct combustion on a
Carlo-Erba EA-1110 instrument, quoted data are the
average of at least two independent determinations.
Rare earth metal analyses were carried out by com-
plexometric titration. FT-IR spectra were recorded on a
Bruker TENSOR 27 spectrometer. TOF HRMS data
were obtained from a Micromass OR-TOF spectrometer.
Melting points were not calibrated. Molecular weight
and molecular weight distribution of the polymers were
measured by PL GPC 50 at 40 ℃ using THF as eluent
against polystyrene standards.
19.0 (CH3), 123.1, 126.7, 127.6, 128.0, 128.2, 128.6,
134.8, 136.3, 136.8, 145.7 (Ar—C), 153.4 (NCN);
FT-IR (KBr) v: 3375 (s), 2917 (m), 1630 (s), 1587 (m),
－1
1462 (m), 1348 (m), 1205 (m), 766 (m) cm . Anal.
calcd for C40H42N4: C 83.01, H 7.37, N 9.68; found C
83.18, H 7.65, N 9.16. HRMS calcd for [C40H42N4]＋
578.3409, found 578.3419.
Synthesis of p-cyclohexylene-bis[N,N'-bis(2,6-diiso-
propylphenyl)formamidine] 1,4-C6H10[C( ＝ N-2,6-
iPr2C6H3)(NH-2,6-iPr2C6H3)]2 (H2L3)
H2L3 was prepared by a procedure similar to that of
H2L1. Using 1,4-cyclohexanedicarboxylic acid (0.62 g,
3.75 mmol) and 2,6-diisopropylaniline (3.0 mL, 15.0
mmol), the title compound was produced as white pow-
der after recrystallization from toluene. Yield 2.16 g
1
Synthesis of p-phenylene-bis[N,N'-bis(2,6-diisopro-
pyl phenyl)formamidine] 1,4-C6H4[C(＝N-2,6-iPr2-
C6H3)(NH-2,6-iPr2C6H3)]2 (H2L1)
(71%), m.p. 271.6 ℃; H NMR (CDCl3, 400 MHz) δ:
0.97 [d, J＝6.8 Hz, 12H, CH(CH3)2], 1.12 [d, 12H,
CH(CH3)2], 1.25 [d, J＝6.8, 12H, Hz, CH(CH3)2], 1.26
[d, J＝6.8 Hz, 12H, CH(CH3)2], 1.66—1.70 (m, 4H,
CH2), 1.86 (d, J＝7.2 Hz, 4H, CH2), 2.15 (brs, 2H, CH),
3.04—3.08 [m, 4H, CH(CH3)2], 3.14—3.20 [m, 4H,
CH(CH3)2], 5.20 (s, 2H, NH), 6.98 (t, J＝7.6 Hz, 2H,
ArH), 7.10 (d, J＝8.0 Hz, 8H, ArH), 7.25 (t, J＝7.6 Hz,
2H, ArH); 13C NMR (CDCl3, 100 MHz) δ: 22.8, 23.0,
24.1, 25.5 [CH(CH3)2], 28.0, 28.1 [CH(CH3)2], 30.3
(Cy-CH2), 38.1 (Cy-CH), 122.9, 123.0, 123.8, 128.3,
132.6, 139.2, 143.7, 147.0 (Ar—C), 159.3 (NCN);
FT-IR (KBr) v: 3365 (m), 2961 (s), 2927 (m), 2867 (m),
1632 (s), 1586 (m), 1459 (m), 1432 (m), 1385 (m), 1346
In a Schlenk flask, P2O5 (9.0 g, 63.4 mmol), hexa-
methyldisiloxane (20 mL, 93.7 mmol), and dry dichlo-
romethane (20 mL) were refluxed for 30 min. Then the
volatiles were removed under vacuum to afford a vis-
cous syrup PPSE. Terephthalic acid (0.62 g, 3.75 mmol)
and 2,6-diisopropylaniline (3.0 mL, 15.08 mmol) were
added to this viscous syrup, and the mixture was reacted
at 180 ℃ for 8 h. The resulting mixture was poured
－1
into 1 mol•L NaOH solution (150 mL) to produce an
oily product, which was allowed to solidify overnight.
The solid was washed with water and recrystallized
from toluene to give the title compound as pale green
－1
(w), 763 (m) cm . Anal. calcd for C56H80N4: C 83.11,
1
powder. Yield 2.16 g (75%), m.p. 221.6 ℃; H NMR
H 9.96, N 6.92; found C 83.57, H 9.69, N 6.74. HRMS
(CDCl3, 400 MHz) δ: 0.85 [d, J ＝ 6.4 Hz, 12H,
CH(CH3)2], 0.94 [d, J＝6.4 Hz, 12H, CH(CH3)2], 1.16
[d, J＝6.4 Hz, 12H, CH(CH3)2], 1.32 [d, J＝6.4 Hz,
12H, CH(CH3)2], 3.10—3.15 [m, 8H, CH(CH3)2], 5.65
(s, 2H, NH), 6.95—7.23 (m, 16H, ArH); 13C NMR
(CDCl3, 100 MHz) δ: 22.4, 22.5, 24.2, 25.4 [CH(CH3)2],
24.4 [CH(CH3)2], 25.4 [CH(CH3)2], 28.3 [CH(CH3)2],
28.3, 28.6 [CH(CH3)2], 122.5, 123.2, 127.7, 127.9,
133.7, 136.0, 139.2, 143.5, 145.3 (ArC), 153.4 (NCN);
FT-IR (KBr) v: 3432 (s), 2962 (s), 2868 (m), 1618 (s),
1585 (m), 1465 (m), 1434 (m), 1384 (m), 1358 (m),
calcd for [C56H80N4]＋ 808.6383, found 808.6425.
Synthesis of p-cyclohexylene-bis[N,N'-bis(2,6-dime-
thylphenyl)formamidine] 1,4-C6H10[C(＝N-2,6-Me2-
C6H3)(NH-2,6-Me2C6H3)]2 (H2L4)
H2L4 was prepared by a procedure similar to that of
H2L1. Using 1,4-cyclohexanedicarboxylic acid (0.62 g,
3.75 mmol) and 2,6-dimethylaniline (1.85 mL, 15.0
mmol), the title compound was produced as white pow-
der after recrystallization from THF. Yield 1.4 g (65%),
m.p. 340.3 ℃; 1H NMR (CDCl3, 400 MHz) δ: 1.69 (m,
J＝9.5, 4H, CH2), 1.88—1.90 (m, J＝7.0 Hz, 4H, CH2),
2.07 (brs, 2H, CH), 2.18 (d, J＝4.8 Hz, 24H, CH3), 5.28
(s, 2H, NH), 6.85 (t, J＝7.4 Hz, 2H, ArH), 7.02—7.05
(m, 10H, ArH); 13C NMR (CDCl3, 100 MHz) δ: 17.8,
18.8 (CH3), 30.7 (Cy-CH2), 38.6 (Cy-CH), 122.5, 127.4,
128.2, 128.6, 128.9, 135.9, 136.4, 145.7 (Ar—C), 159.7
(NCN); FT-IR (KBr) v: 3442 (s), 2924 (m), 1641 (s),
1589 (m), 1473 (m), 1389 (w), 1222 (w), 1094 (w), 765
－1
1255 (w), 1188 (w), 760 (m) cm . Anal. calcd for
C56H74N4: C 83.74, H 9.29, N 6.98; found C 83.42, H
9.84, N 6.74. HRMS calcd for [C56H74N4]＋ 802.5913,
found 802.5938.
Synthesis of p-phenylene-bis[N,N'-bis(2,6-dimethyl-
phenyl)formamidine] 1,4-C6H4[C(＝N-2,6-Me2C6H3)-
(NH-2,6-Me2C6H3)]2 (H2L2)
－1
H2L2 was prepared by a procedure similar to that of
H2L1. Using terephthalic acid (0.62 g, 3.75 mmol) and
2,6-dimethylaniline (1.85 mL, 15.0 mmol), the title
compound was produced as pale green powder after
recrystallization from toluene. Yield 1.70 g (78%), m.p.
(m) cm . Anal. calcd for C40H48N4: C 82.15, H 8.27, N
9.58; found C 81.92, H 8.36, N 9.72. HRMS calcd for
[C40H48N4]＋ 584.3879, found 584.3853.
Synthesis of (THF)(Me3SiCH2)2YL1Y(CH2SiMe3)2-
(THF) (1)
1
277.6 ℃; H NMR (CDCl3, 400 MHz) δ: 2.07 (s, 12H,
To a 30 mL of THF solution of Y(CH2SiMe3)3-
(THF)2 (0.80 g, 1.62 mmol), was added H2L1 (0.65 g,
CH3), 2.31 (s, 12H, CH3), 5.68 (s, 2H, NH), 6.87—7.28
(m, 16H, ArH); 13C NMR (CDCl3, 100 MHz) δ: 17.9,
460
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 457— 462

Bimetallic Rare Earth Alkyl Complexes Bearing Bridged Amidinate Ligands
0.81 mmol) in 20 mL of THF slowly at room tempera-
ture. The mixture was stirred at room temperature for 4
h. Then the solution was concentrated under reduced
pressure and cooled at －30 ℃ to afford 1 as pale
green microcrystals in two crops. Yield 0.96 g (80.7%);
1H NMR (400 MHz, C6D6) δ: －0.20 (d, J＝2.9 Hz, 8H,
CH2SiMe3), 0.25 (s, 36H, SiMe3), 0.80 [d, J＝6.8 Hz,
24H, CH(CH3)2], 1.17 (brs, 8H, β-THF), 1.30 [d, J＝6.8
Hz, 24H, CH(CH3)2], 3.40—3.47 [m, 8H, CH(CH3)2],
3.60 (brs, 8H, α-THF), 6.80—6.92 (m, 16H, ArH); 13C
NMR (100 MHz, C6D6) δ: 4.3 (TMS), 23.7 [CH(CH3)2],
25.1 (β-THF), 26.4, 28.4 [CH(CH3)2], 40.0 (d, J＝41 Hz,
CH2TMS), 69.9 (α-THF), 123.9, 125.0, 133.3, 142.4,
142.5 (Ar—C), 175.0 (NCN); FT-IR (KBr) v: 2963 (s),
2871 (m), 1620 (s), 1466 (m), 1358 (m), 1250 (m), 856
126.9, 132.3, 134.9, 145.7 (Ar—C), 173.3 (NCN);
FT-IR (KBr) v: 2951 (s), 1627 (m), 1589 (m), 1467 (s),
1247 (m), 1200 (m), 1094 (m), 985 (m), 853 (s), 764 (s)
－1
cm . Anal. calcd for C64H100N4O2Si4Y2 (1247.86): C
61.60, H 8.09, N 4.49, Y 14.25; found C 61.32, H 8.01,
N 4.52, Y 13.88.
Synthesis of (THF)(Me3SiCH2)2LuL2Lu(CH2SiMe3)2-
(THF) (4)
Complex 4 was prepared by a procedure similar to
that of complex 3. Using H2L2 (0.43 g, 0.73 mmol) and
Lu(CH2SiMe3)3(THF)2 (0.847 g, 1.46 mmol), 4 was
afforded as pale yellow powder. Yield 0.77 g (74.4%);
1H NMR (400 MHz, C6D6) δ: －0.43 (s, 8H, CH2TMS),
0.25 (s, 36H, CH2TMS), 1.01 (brs, 8H, β-THF), 2.11 (s,
24H, Ph-Me), 3.54 (brs, 8H, α-THF), 6.55—6.83 (m,
16H, ArH); 13C NMR (100 MHz, C6D6) δ: 4.4 (TMS),
19.8 (Ph-Me), 24.9 (β-THF), 46.0 (CH2SiMe3), 69.9
(α-THF), 123.9, 126.9, 132.3, 134.9, 145.7 (Ar—C),
173.2 (NCN); FT-IR (KBr) v: 2951 (s), 1625 (s), 1589
(m), 1466 (s), 1392 (m), 1248 (s),－1200 (m), 1094 (m),
990 (m), 858 (s), 762 (s) cm 1. Anal. calcd for
C64H100Lu2N4O2Si4 (1419.98): C 54.13, H 7.11, N 3.95,
Lu 24.64; found C 54.32, H 7.01, N 3.86, Lu 24.56.
－1
(m), 764 (m) cm . Anal. calcd for C80H132N4O2Si4Y2
(1472.34): C 65.25, H 9.05, N 3.80, Y 12.08; found C
64.87, H 9.13, N 3.62, Y 11.76.
Synthesis of (THF)(Me3SiCH2)2LuL1Lu(CH2SiMe3)2-
(THF) (2)
Complex 2 was prepared by a procedure similar to
that of complex 1. Using H2L1 (0.65 g, 0.81 mmol) and
Lu(CH2SiMe3)3(THF)2 (0.94 g, 1.62 mmol), 2 was af-
forded as green powder. Yield 1.01 g (78.2%); 1H NMR
(400 MHz, C6D6) δ: －0.40 (s, 8H, CH2TMS), 0.26 (s,
36H, CH2TMS), 0.80 [d, J＝6.8 Hz, 24H, CH(CH3)2],
1.12 (brs, 8H, β-THF), 1.32 [d, J＝6.7 Hz, 24H,
CH(CH3)2], 3.42—3.49 [m, 8H, CH(CH3)2], 3.61 (brs,
8H, α-THF), 6.83—6.89 (m, 12H, ArH); 13C NMR (100
MHz, C6D6) δ: 5.7 (TMS), 25.2 [CH(CH3)2], 26.2
(β-THF), 27.7, 29.5 [CH(CH3)2], 47.6 (CH2TMS), 71.8
(α-THF), 125.2, 126.4, 134.9, 143.7, 144.0 (Ar—C),
175.7 (NCN); FT-IR (KBr) v: 2963 (s), 2871 (s), 1620
(s), 158－9 (s), 1458 (s), 1358 (s), 1250 (m), 856 (m), 764
Synthesis of (THF)(Me3SiCH2)2YL3Y(CH2SiMe3)2-
(THF) (5)
Complex 5 was prepared by a procedure similar to
that of complex 3. Using H2L3 (0.497 g, 0.62 mmol) and
Y(CH2SiMe3)3(THF)2 (0.614 g, 1.24 mmol), 5 was af-
forded as colorless needle crystals. Yield 0.71 g (77.9%);
1H NMR (400 MHz, C6D6) δ: －0.29 (d, J＝3.0 Hz, 8H,
CH2TMS), 0.24 (s, 36H, CH2TMS), 0.70—0.76 (m, 4H,
Cy-CH2), 1.07 (brs, 8H, β-THF), 1.11 [d, J＝6.8 Hz,
24H, CH(CH3)2], 1.29 [d, J＝6.8 Hz, CH(CH3)2], 1.53
(d, 4H, Cy-CH2), 2.08 (brs, 2H, Cy-CH), 3.34—3.41
[m , 8H, CH(CH3)2], 3.53 (brs, 8H, α-THF), 6.98—7.05
(m, 12H, Ar-H); FT-IR (KBr) v: 2963 (s), 2871 (s),
1636 (s), 1589 (m), 1458 (s), 1389 (s), 1358 (m), 1327
(m), 1250 (s), 1049 (m), 933 (m), 856 (m), 764 (m)
1
(m) cm . Anal. calcd for C80H132Lu2N4O2Si4 (1644.46):
C 58.42, H 8.10, N 3.40, Lu 21.28; found C 58.91, H
7.97, N 3.24, Lu 21.03.
Synthesis of (THF)(Me3SiCH2)2YL2Y(CH2SiMe3)2-
(THF) (3)
－1
cm . Anal. calcd for C80H138N4O2Si4Y2 (1478.40): C
To a 30 mL of THF solution of Y(CH2SiMe3)3-
(THF)2 (0.677 g, 1.36 mmol), was added H2L2 (0.40 g,
0.68 mmol) in 20 mL of THF slowly at room tempe-
rature. After the reaction mixture was stirred at room
temperature for 4 h, the solvent was removed under re-
duced pressure. The resulting pale yellow residue was
washed with hexane (5 mL×2), and the residue was
extracted by a mixture solution of THF and hexane in
1∶ 1 volume ratio. Then the extractant was filtrated,
and the filtrate was concentrated under reduced pressure
and cooled at －30 ℃ to afford 3 as pale green micro-
crystals. Yield 0.61 g (72%); 1H NMR (400 MHz, C6D6)
δ: －0.42 (d, J＝3.0 Hz, 8H, CH2TMS), 0.26 (s, 36H,
CH2TMS), 0.98 (brs, 8H, β-THF), 2.10 (s, 24H, Ph-Me),
3.52 (brs, 8H, α-THF), 6.55, 6.79—6.85 (m, 16H, ArH);
13C NMR (100 MHz, C6D6) δ: 4.4 (TMS), 19.8 (Ph-Me),
24.9 (β-THF), 40.1 (CH2SiMe3), 69.9 (α-THF), 123.9,
64.99, H 9.43, N 3.79, Y 12.03; found C 65.09, H 9.52,
N 3.73, Y 11.75.
Synthesis of (THF)(Me3SiCH2)2YL4Y(CH2SiMe3)2-
(THF) (6)
Complex 6 was prepared by a procedure similar to
that of complex 3. Using H2L4 (0.50 g, 0.86 mmol) and
Y(CH2SiMe3)3(THF)2 (0.85 g, 1.71 mmol), 6 was af-
forded as colorless needle crystals. Yield 0.60 g (76.3%);
1H NMR (400 MHz, C6D6) δ: －0.38 (d, J＝2.7 Hz, 8H,
CH2TMS), 0.23 (s, 36H, CH2TMS), 0.66—0.71 (m, 4H,
Cy-CH2), 1.05 (brs, 8H, β-THF), 1.55 (d, J＝7.6 Hz, 4H,
Cy-CH2), 1.79 (brs, 2H, Cy-CH), 2.18 (s, 24H, Ph-Me),
3.49 (brs, 8H, α-THF), 6.87 (s, 12H, ArH); 13C NMR
(100 MHz, C6D6) δ: 4.3 (TMS), 19.9 (Ph-Me), 24.8
(β-THF), 29.0 (Cy-CH2), 38.2, 38.6 (CH2TMS), 43.0
(Cy-CH), 69.8 (α-THF), 123.8, 132.1, 145.7 (Ar—C),
178.8 (NCN); FT-IR (KBr) v: 2950 (s), 1640 (s), 1590
Chin. J. Chem. 2010, 28, 457— 462
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
461

Yang, Xu & Luo
FULL PAPER
(s), 1473 (s), 1390 (m), 1375 (m),－1249 (s), 1035 (m),
988 (m), 856 (s), 764 (m) cm 1. Anal. calcd for
C64H106N4O2Si4Y2 (1253.92): C 61.30, H 8.54, N 4.47,
Y 14.18; found C 61.54, H 8.52, N 4.34, Y 14.32.
22 Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc.
2003, 125, 5622.
23 Henderson, L. D.; Maclnnis, G. L.; Piers, W. E.; Parvez, M.
Can. J. Chem. 2004, 82, 162.
24 Hayes, P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.;
Parvez, M.; Elsegood, M. R. J.; Clegg, W. Organometallics
2001, 20, 2533.
A typical procedure for L-lactide polymerization run
(1, Table 1)
In a 20 mL Schleck flask, complex 1 (19 mg, 13
µmol), L-lactide (368 mg, 2.6 mmol), and toluene (5.2
mL) were stirred at 70 ℃ for 30 min. The polymeriza-
tion was terminated by quenching with excess ethanol
containing 5% aq. HCl. The polymer was collected, and
dried under vacuum at 60 ℃ to constant weight (335
mg, 91%).
25 Lee, L. W. M.; Piers, W. E.; Elsegood, M. R. J.; Clegg, W.;
Parvez, M. Organometallics 1999, 18, 2947.
26 Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.;
Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics
2000, 19, 3197.
27 Bambirra, S.; Leusen, D. V.; Meetsma, A.; Hessen, B.; Teu-
ben, J. H. Chem. Commun. 2003, 522.
28 Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B.
J. Am. Chem. Soc. 2004, 126, 9182.
29 Bambirra, S.; Tsurugi, H.; Leusen, D. V.; Hessen, B. Dalton
Trans. 2006, 1157.
30 Bambirra, S.; Otten, E.; Leusen, D. V.; Meetsma, A.; Hessen,
B. Z. Anorg. Allg. Chem. 2006, 632, 1950.
31 Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics
2006, 25, 3454.
32 Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.;
Meetsma, A.; Hessen, B. Organometallics 2008, 27, 704.
33 Zhang, L. X.; Nishiura, M.; Yuki, M.; Luo, Y.; Hou, Z. M.
Angew. Chem., Int. Ed. 2008, 47, 2642.
34 Ge, S. Z.; Meetsma, A.; Hessen, B. Organometallics 2008,
27, 3131.
35 Luo, Y. J.; Wang, X. L.; Chen, J.; Luo, C. C.; Zhang, Y.; Yao,
Y. M. J. Organomet. Chem. 2009, 694, 1289.
36 Liu, B.; Liu, X. L.; Cui, D. M.; Liu, L. Organometallics
2009, 28, 1453.
37 Hayes, P. L.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.;
Piers, W. E.; Parvez, M. Organometallics 2003, 22, 1577.
38 Motta, A.; Fragala, I. L.; Marks, T. J. J. Am. Chem. Soc.
2009, 131, 3974.
39 Li, H. B.; Marks, T. J. PANS 2006, 103, 15295.
40 Yuen, H. F.; Marks, T. J. Organometallics 2008, 27, 155.
41 Yuen, H. F.; Marks, T. J. Organometallics 2009, 28, 2423.
42 Tardif, O.; Nishiura, M.; Hou, Z. M. Tetrahedron 2003, 59,
10525.
43 Ogata, S. I.; Mochizuki, A.; Kakimoto, M. A.; Imai, Y. Bull.
Chem. Soc. Jpn. 1986, 59, 2171.
44 Liu, X. L.; Shang, X. M.; Tang, T.; Hu, N. H.; Pei, F. K.;
Cui, D. M.; Chen, X. S.; Jing, X. B. Organometallics 2007,
26, 2747.
45 Liu, B.; Cui, D. M.; Ma, J.; Chen, X. S.; Jing, X. B. Chem.
Eur. J. 2007, 13, 834.
46 Shannon, R. D. Acta Cryst. 1976, A32, 751.
47 Lappert, M.; Pearce, R. Chem. Commun. 1973, 126.
48 Barakat, I.; Dubois, P.; Jerome, R.; Teyssie, P. J. Polym. Sci.,
Part A 1993, 31, 505.
References
1
Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem.
Rev. 2006, 106, 2404.
2
3
Arndt, S.; Okuda, J. Chem. Rev. 2002, 102, 1953.
Hou, Z. M.; Luo, Y. J.; Li, X. F. J. Organomet. Chem. 2006,
691, 3114.
4
Li, S. H.; Cui, D. M.; Li, D. F.; Hou, Z. M. Organometallics
2009, 28, 4814.
5
6
Gao, W.; Cui, D. M. J. Am. Chem. Soc. 2008, 130, 4984.
Li, X. F.; Nishiura, M.; Hu, L. H.; Mori, K.; Hou, Z. M. J.
Am. Chem. Soc. 2009, 131, 13870.
7
8
Xu, X.; Chen, Y. F.; Sun, J. Chem. Eur. J. 2009, 15, 846.
Yu, N.; Nishiura, M.; Li, X. F.; Xi, Z. F.; Hou, Z. M. Chem.
Asian J. 2008, 3, 1406.
9
Ravasio, A.; Zampa, C.; Boggioni, L.; Tritto, I.; Hitzbleck,
J.; Okuda, J. Macromolecules 2008, 41, 9565.
10 Zhang, H.; Luo, Y. J.; Hou, Z. M. Macromolecules 2008, 41,
1064.
11 Hitzbleck, J.; Okuda, J. Organometallics 2007, 26, 3227.
12 Li, X. F.; Nishiura, M.; Mori, K.; Mashiko, T.; Hou, Z. M.
Chem. Commun. 2007, 4137.
13 Hitzbleck, J.; Okuda, J. Z. Anorg. Allg. Chem. 2006, 632,
1947.
14 Hitzbleck, J.; Beckerle, K.; Okuda, J.; Halbach, T.; Mul-
haupt, R. Macromol. Symp. 2006, 236, 23.
15 Luo, Y. J.; Baldamus, J.; Hou, Z. M. J. Am. Chem. Soc.
2004, 126, 13910.
16 Arndt, S.; Spaniol, T. P.; Okuda, J. Organometallics 2003,
22, 775.
17 Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem. 2001,
621, 327.
18 Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int.
Ed. 1999, 38, 227.
19 Schaverien, C. J. Organometallics 1992, 11, 3476.
20 Kenward, A. L.; Piers, W. E.; Parvez, M. Organometallics
2009, 28, 3012.
21 Xu, X.; Xu, X. Y.; Chen, Y. F.; Sun, J. Organometallics
2008, 27, 758.
(E0909142 Cheng, F.; Fan, Y.)
462
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 457— 462