Mixed ligands supported yttrium alkyl complexes:. Synthesis, characterization and catalysis toward lactide polymerization

Article abstract of DOI:10.1016/j.jorganchem.2007.06.054

Treatment of yttrium tris(alkyl)s, Y(CH₂SiMe₃)₃(THF)₂, by equimolar H(C₅Me₄)SiMe₃(HCp′) and indene (Ind-H) afforded (η⁵-Cp′)Y(CH₂SiMe₃)₂

Full text of DOI:10.1016/j.jorganchem.2007.06.054

Journal of Organometallic Chemistry 692 (2007) 4828–4834
www.elsevier.com/locate/jorganchem
Mixed ligands supported yttrium alkyl complexes:
Synthesis, characterization and catalysis toward lactide polymerization
c
a,
c
Wei Miao a,b, Shihui Li a,b, Hongxia Zhang , Dongmei Cui *, Yurong Wang ,
a
Baotong Huang
a
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, China
b
Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
Chemical Engineering College, Dalian University of Technology, Dalian 116012, China
c
Received 30 March 2007; received in revised form 22 June 2007; accepted 22 June 2007
Available online 4 July 2007
Abstract
Treatment of yttrium tris(alkyl)s, Y(CH2SiMe3)3(THF)2, by equimolar H(C5Me4)SiMe3(HCp0) and indene (Ind-H) afforded
(g5-Cp0)Y(CH2SiMe3)2(THF) (1) and (g5-Ind)Y(CH2SiMe3)2(THF) (2) via alkane elimination, respectively. Complex 1 reacted with
methoxyamino phenols, 4,6-(CH3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-OH (HL1) and 4,6-(CMe3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-
OH (HL2) gave mixed ligands supported alkyl complexes [(g5-Cp0)(L)]Y(CH2SiMe3) (3: L = L1; 4: L = L2). Whilst, complex 2 was trea-
ted with HL2 to yield [(g5-Ind)(L2)]Y(CH2SiMe3) (5). The molecular structures of 3 and 5 were confirmed by X-ray diffraction to be
mono(alkyl)s of THF-free, adopting pyramidal and tetragonal-bipyramidal geometry, respectively. Complexes 3 and 5 were high active
initiators for the ring-opening polymerization of L-lactide to give isotactic polylactide with high molecular weight and narrow to mod-
erate polydispersity.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Yttrium; Alkyl complex; Lactide; Polymerization; Mixed ligands
1. Introduction
due to the merits of the combined ligands [12,13]. For
instance, mixed Cp*/bipyridine supported lutetium com-
plexes reported by Cameron et al. reacted with carbon
monoxide leading to interesting intramolecular C–H acti-
vation of the bipyridine ligand [12]. Lanthanide complexes
stabilized by mixed Cp*/bis(phosphinimino)-methanide
ligands could initiate controllable ring-opening polymeri-
zation of e-caprolactone [14]. Thus, further exploration of
rare earth metal complexes bearing one Cp moiety and a
non-Cp ligand is of obvious interest.
Indene (Ind-H) has been demonstrated to be a more ste-
rically demanding yet planar p ligand [15]. The differences
of the steric and electronic properties between indenyl and
cyclopentadienyl moieties would be reflected in the molec-
ular structure and reactivity of the corresponding com-
plexes. Therefore, we synthesized yttrium alkyl complexes
bearing mixed Cp/N,O-multidentate or mixed Ind/N,
Rare earth metal alkyl complexes stabilized by cyclopen-
tadienyl (Cp) ligands have been extensively developed in
the past decades, which exhibited tremendous catalytic
activities toward polymerizations of polar and non-polar
monomers [1–5]. Meanwhile, multidentate non-Cp ligands
have also attracted increasing attention, since these ligands
could provide proper steric and electronic environment for
compensating coordinative unsaturation of metal centers
[6–11]. Comparatively, rare earth metal complexes bearing
mixed Cp/non-Cp ligands have been less exploited, how-
ever, they have received considerable attention recently
*
Corresponding author. Tel.: +86 431 85262773; fax: +86 431
85263773.
E-mail address: dmcui@ciac.jl.cn (D. Cui).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.054

W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
4829
O-multidentate ligands. Herein, we report the preparation
and characterization of these novel complexes. The influ-
ence of ligand framework on molecular structure of these
complexes and their catalytic behavior toward the ring-
opening polymerization (ROP) of L-lactide will also be
discussed.
2. Results and discussion
2.1. Synthesis of ligands
Following the modified literature procedures [16],
ligands HL1 and HL2 were synthesized by Mannich con-
densations of the corresponding substituted phenols, para-
formaldehyde and bis(2-methyloxyethyl)amine in refluxing
1
methanol (Scheme 1). H NMR data were consistent with
the formation of the targeted products.
Scheme 2. Synthetic pathway for complex 3 and 4.
2.2. Synthesis and characterization of complexes 3 and 4
Reaction of HC5Me4SiMe3 (HCp0) with 1 equiv. of
yttrium tris(alkyl)s, Y(CH2SiMe3)3(THF)2, took place
immediately upon addition at room temperature. The
reaction mixture was remained for 1 h under stirring to
afford mono-cyclopentadienyl yttrium bis(alkyl) complex
(g5-Cp0)Y(CH2SiMe3)2(THF) (1) [17]. Further reaction
between 1 and HL1 at ꢀ35 ꢁC for 15 min gave mixed
ligands supported mono(alkyl) complex (g5-Cp0)(L1)-
Y(CH2SiMe3) (3) via alkane elimination (Scheme 2). The
1H NMR spectrum of 3 displays that the methylene pro-
tons of YCH2SiMe3 are diastereotopic to give an AB spin
around d ꢀ0.45 (JH–H = 8 Hz) and ꢀ0.99 ppm (JH–H
=
8 Hz). The AB lines split further into doublets due to cou-
pling with yttrium atom (JY–H = 4 Hz). This suggests that 3
is asymmetric in solution state.
The solid-state structure of complex 3 was figured out by
X-ray diffraction analysis as shown in Fig. 1. The complex
is seven-coordinate mono(alkyl) without solvated THF
molecule. The Cp0 moiety coordinates to yttrium atom in
a g5-mode, meanwhile the L1 fragment bonds to yttrium
atom in a tridentate O,N,O mode, generating distorted
pyramidal geometry around the metal center. The chelating
oxygen and nitrogen atoms combined with the alkyl carbon
Fig. 1. X-ray structure of 3 with 35% probability of thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
atom form the base, while the center of the Cp0 ring occu-
pies the apex. It is noteworthy that one pendent OCH3
group coordinates to yttrium ion while the other is hanging
away with respect to the steric environment and electron
saturation of central metal ion. This is consistent with the
1H NMR spectrum analysis. The coordinating OCH3
group gives a resonance at d = 2.88 ppm, shifting up field
compared to the free ligand (d = 3.23 ppm). In contrast,
the signal of the non-coordinating OCH3 appears at
d = 3.10 ppm, much close to that of free ligand. The similar
situation has been observed in a zinc alkyl complex
[4,6-tBu2-2-(Et2NCH2CH2)2NCH2-C6H2-O]Zn(CH2CH3),
where only one of the two diethylamino donor bonds to the
metal ion [18].
Scheme 1. Synthetic pathway for HL1 and HL2.

4830
W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
Table 1
coordination to the central metal. Whilst the other pendant
OCH3 group exhibits a signal at d = 3.21 ppm comparable
to the free ligand. The AB spin around d ꢀ0.76 and
ꢀ0.29 ppm is assignable to the methylene protons of
˚
Selected bond distances (A) and angles (ꢁ) for 3
Y–O(1)
Y–C(16)
Y–O(2)
Y–N
2.114(2)
2.406(3)
2.418(2)
2.566(2)
2.676(3)
Y–C(21)
Y–C(23)
Y–C(22)
Y–C(20)
Y–Cp0
2.691(3)
2.728(3)
2.731(3)
2.691(3)
2.410(3)
1
YCH2SiMe3. Thus, the H NMR spectrum is informative
enough to confirm complex 4 of a mono(alkyl) stabilized
Y–C(24)
ring centroid
by mixed ligands albeit without X-ray diffraction.
O(1)–Y–C(16)
O(1)–Y–O(2)
C(16)–Y–O(2)
O(1)–Y–N
99.70(11)
140.57(8)
89.11(10)
76.31(8)
O(2)–Y–N
66.09(7)
128.79(9)
92.68(11)
88.57(9)
137.02(9)
O(1)–Y–C(24)
C(16)–Y–C(24)
O(2)–Y–C(24)
N–Y–C(24)
2.3. Synthesis and characterization of complex 5
C(16)–Y–N
119.48(10)
Treatment of indene (Ind-H) with 1 equiv. of Y(CH2Si-
Me3)3(THF)2 at room temperature for 1 h gave an indenyl
yttrium bis(alkyl) complex (g5-Ind)Y(CH2SiMe3)2(THF)
(2) via alkane elimination. Reaction of 2 with equimolar
HL2 at ꢀ35 ꢁC for 15 min afforded (g5-Ind)(L2)Y(CH2-
SiMe3) (5) as yellow powders (Scheme 3). Single crystals
of 5 grew as yellow prisms from a mixture of toluene and
hexane (1:3 v/v) at ꢀ35 ꢁC within several days. The molec-
ular structure of complex 5 was confirmed by X-ray diffrac-
tion to be unsolvated mono(alkyl) of eight-coordinate
(Fig. 2). The indene moiety coordinates to yttrium ion in
g5-mode, whilst the phenoxide ligand chelates to yttrium
ion in O,N,O,O tetradentate mode, generating distorted
tetragonal-bipyramidal geometry core. The phenoxy oxy-
gen O(1), methoxy oxygen O(3), the alkyl carbon C(22)
and N atoms occupy the equatorial positions, while the
center of the five-member ring of the indenyl fragment
and the methoxy oxygen atom O(2) are axial. The bond
˚
The Y–O(2) bond length (2.418(2) A) is comparable to
˚
those observed for Y–Oether in a range of 2.45–2.50 A
[19] (Table 1), but longer than the distance between yttrium
atom and the phenoxy oxygen atom (Y–O(1): 2.114(2) A).
The bond lengths formed by yttrium and carbon atoms of
the Cp0 ring, Y-g -CCp , ranging from 2.676(3) to 2.731(3)
A, are comparable to those of Dy-g -CCp (2.638(2)–
2.704(3) A) in complex (C5Me4SiMe3)Dy(CH2SiMe3)2-
(THF) [20]. The distance between yttrium atom and the
centroid of Cp0 ring, Y–Cp cent (2.410 A), is comparable
to that (2.386(7) A) in complex [CH(PPh2NSiMe3)2Y(g -
C5Me5)Cl] if the difference of the ionic radii is considered
˚
5
0
5
˚
˚
0
˚
5
˚
˚
[14]. The Y–N bond length (2.566(2) A) and N–Y–O(2)
bond angle (66.09(7)ꢁ) are close to the corresponding those
˚
(Y–N: 2.507(3) A; N–Y–O(2): 67.25(8)ꢁ) found in complex
[4,6-tBu2-(MeOCH2CH2)2N-C6H2O-]Y(CH2SiMe3)2 [21].
The six-membered N,O-chelate ring YO(1)C3N with a bite
angle of 76.31(8)ꢁ has envelope conformation. The Y and
˚
˚
lengths of Y–N (2.549(4) A), Y–C(22) (2.433(5) A), Y–
˚
O(1) (2.123(3) A) are comparable to the corresponding
˚
data found in complex 3 (Y–N (2.566(2) A), Y–C(16)
˚
˚
N atoms sit about 0.5998 A and 1.1095 A, respectively,
out of the twisted OC3 plane.
˚
˚
(2.406(3) A), Y–O(1) (2.114(2) A)) and those in the dialkyl
yttrium complex [(CH3OCH2CH2)2NCH2-3,5-(CMe3)2-2-
Following the similar procedure, complex (g5-Cp0)(L2)-
Y(CH2SiMe3) (4) was obtained by treatment of 1 with
˚
C6H2O]Y(CH2-SiMe2Ph)2 (Y–N (2.5345(14) A, Y–C(22)
2.4453(19) A, Y–O(3) 2.1140(11) A) [6a]. The featuring
˚
˚
equimolar HL2 at ꢀ35 ꢁC (Scheme 2). The H NMR spec-
1
trum of 4 displays similar pattern to that of 3. One pendant
OCH3 group shows resonance at d = 2.93 ppm, indicating
Fig. 2. X-ray structure of 5 with 35% probability of thermal ellipsoids.
Scheme 3. Synthetic pathway for complex 5.
Hydrogen atoms are omitted for clarity.

W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
4831
bond angles of complex 5, N–Y–O(1) (77.70(12)ꢁ) and N–
100
90
80
70
60
50
40
30
20
Y–C(22) (144.32(16)ꢁ) are comparable to N–Y–O(1)
(76.31(8)ꢁ) and N–Y–C(16) (119.48(10)ꢁ) in 3 and the
corresponding those in the above mentioned dialkyl
yttrium complex (N–Y–O(3), 78.55(4)ꢁ); N–Y–C(22),
99.28(6)ꢁ) [6a]. It is noteworthy that both pendent methoxy
groups coordinate to yttrium ion and arrange in cis-posi-
tions. This is in contrast to the case of complex 3, where
only one methoxy group coordinates to yttrium ion. The
difference is mostly attributed to the crowded environment
caused by the indenyl moiety in 5. The Y–Oether bond
˚
˚
lengths (Y–O(2), 2.533(4) A and Y–O(3), 2.387(3) A) are
˚
longer than Y–Ophenoxy (Y–O(1), 2.123(3) A). The bond
0
20
40
60
80 100 120 140 160
angle formed by yttrium ion and methoxy oxygen atoms
(O(2)–Y–O(3)) is 78.59(11)ꢁ, much smaller than the
corresponding O(11)–Co–O(15) bond angle (121.31(4)ꢁ)
in a cobalt analogue [4,6-tBu2-2-(MeOCH2CH2)2NCH2-
C6H2O]Co(Cl2) [18] (see Table 2).
Time (min)
Fig. 3. Plot of L-lactide conversion against time using complex 5.
the metal center in 3. The 1H NMR spectrum of polylactide
displayed a symmetric quartet resonance assigned to the
methine proton at d = 5.15 ppm, indicating the configura-
tion of monomer was remained in PLA and the negligible
racemization.
2.4. Polymerization of L-lactide initiated by complexes 3 and
5
Yttrium alkyl complexes 3 and 5 were active initiators
for the ring-opening polymerization (ROP) of L-lactide
(L-LA) under mild conditions. The polymerization initiated
by complex 5 performed smoothly at room temperature in
THF, and complete conversion was achieved within 2.5 h
(Fig. 3). When the reaction time was prolonged over 5 h,
no obvious decrease in conversion was observed, indicating
the absence of degradation side-reaction. The influence of
monomer-to-initiator ratio was investigated. For both cat-
alytic systems, the molecular weight of the resultant poly-
lactide (PLA) increased with the increase of monomer-to-
initiator ratio, which was close to the theoretical value
(Table 3). However, slightly deviation was observed when
the ratio was raised over 800, which could be attributed
to difficulty of monomer diffusion caused by viscosity of
the system. We could also see from Table 3 that complex
5 was more efficient initiator than 3, which initiated ROP
of LA in more controllable manner to afford PLA with
much narrow molecular weight distribution. This might
be due to the more steric environment around the metal
center in 5 caused by the coordination of two methoxy
groups, whereas, only one methoxy group coordinates to
3. Conclusion
In summary, we have demonstrated the syntheses and
structures of several yttrium mono(alkyl) complexes stabi-
lized by mixed cyclopentadienyl (or indenyl) and N,O-mul-
tidentate methoxyamino phenoxide moieties. All
complexes are monomers of THF-free. The molecular
structures and the catalytic performance are strongly
dependent on the ligand framework. Complex 5 chelated
by bulky OONO-multidentate ligand initiates more con-
trollable ROP of L-LA than the less steric counterpart 3
coordinated by OON-tridentate moiety, affording PLA
with molecular weight closer to the theoretic value and
more narrow molecular weight distribution.
4. Experimental
4.1. General methods
All the syntheses and manipulations of air- and mois-
ture-sensitive materials were carried out under a dry and
oxygen-free argon atmosphere by using Schlenk techniques
or under a nitrogen atmosphere in an MBRAUN glove-
box. All solvents were purified from MBRAUN SPS sys-
tem. Organometallic samples for NMR spectroscopic
measurements were prepared in a glovebox by using
NMR tubes sealed with paraffin film.1H, 13C NMR spectra
were recorded on a Bruker AV400 (400 MHz for 1H,
100 MHz for 13C) spectrometer. NMR assignments were
Table 2
˚
Selected bond distances (A) and angles (ꢁ) for 5
Y–O(1)
Y–O(2)
Y–O(3)
Y–C(22)
Y–N
2.123(3)
2.533(4)
2.387(3)
2.433(5)
2.549(4)
Y–C(26)
Y–C(27)
Y–C(28)
Y–C(29)
Y–C(30)
2.926(5)
2.757(6)
2.711(5)
2.796(5)
2.973(5)
confirmed by the H–1H (COSY) and H–13C (HMQC)
experiments when necessary. IR spectra were recorded on
a VERTEX 70 FT-IR spectrometer. Gel permeation chro-
matography (GPC) analyses of polymer samples were car-
ried at 30 ꢁC using THF as eluent on a Waters-410
1
1
O(1)–Y–O(2)
O(1)–Y–O(3)
O(1)–Y–C(22)
O(1)–Y–N
82.21(11)
144.30(12)
114.09(15)
77.70(12)
78.59(11)
O(3)–Y–C(22)
O(3)–Y–N
C(22)–Y–O(2)
C(22)–Y–N
O(2)–Y–N
92.69(14)
67.05(12)
81.90(15)
144.32(16)
65.93(12)
O(3)–Y–O(2)

4832
W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
Table 3
Effect of monomer-to-initiator ratio on polymerization of L-LAa
Entry
Cat.
[LA]0/[Y]0
Conv.b (%)
Mccalc. · 10ꢀ4
Mdn · 10ꢀ4
Mw/Mdn
1
2
3
4
5
6
7
a
3
3
3
5
5
5
5
300
500
800
300
500
800
1000
89.0
87.3
85.5
100.0
99.2
98.6
3.84
6.28
9.85
4.32
7.20
3.71
6.77
10.31
4.80
8.13
10.57
13.69
1.87
2.02
1.69
1.54
1.48
1.47
1.57
11.52
14.40
98.90
Conditions: THF, [LA]0 = 1.0 mol/L, 20 ꢁC, 2.5 h.
b
c
Weight of polymer obtained/weight of monomer used.
Mcalc. = ([LA]0/[Y]0) · 144. 13 · X (X = conversion).
Measured by GPC calibrated with standard polystyrene samples.
d
Table 4
Summary of crystallographic data of complexes 3 and 5
instrument and calibrated using polystyrene standards.
Elemental analyses were performed at National Analytical
Research Centre of Changchun Institute of Applied Chem-
istry (CIAC). L-LA (Aldrich) was recrystallized from
CH3COOCH2CH3.
3
5
Formula
C
31H56NO3Si2Y
C41H59NO3SiY
Molecular weight
Crystal system
Space group
635.86
730.89
Orthorhombic
Pbca
Monoclinic
P2(1)/n
12.7001(17)
17.371(2)
16.060(2)
90.00
96.143(2)
90.00
3522.7(8)
4
˚
4.2. X-ray crystallographic studies
a (A)
8.9458(4)
25.8181(13)
34.9027(17)
90.00
90.00
90.00
˚
b (A)
˚
c (A)
Crystals for X-ray analysis were obtained as described in
the preparations. The crystals were manipulated in a glove-
box. Data collections were performed at ꢀ86.5 ꢁC on a
Bruker SMART APEX diffractometer with a CCD area
detector, using graphite monochromated Mo Ka radiation
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
8061.3(7)
8
Z
˚
Measurement temperature (ꢁC)
ꢀ86.5
ꢀ86.5
(k = 0.71073 A). The determination of crystal class and
Dcalc. (g cmꢀ3
)
1.199
1.204
unit cell parameters was carried out by the SMART program
package. The raw frame data were processed using SAINT
and SADABS to yield the reflection data file. The structures
were solved by using SHELXTL program. Refinement was
performed on F2 anisotropically for all non-hydrogen
atoms by the full-matrix least-squares method. The hydro-
gen atoms were placed at the calculated positions and were
included in the structure calculation without further
refinement of the parameters. The crystallographic data
and the refinement of complexes 3 and 5 are summarized
in Table 4.
˚
Radiation (k), A
2hmax (ꢁ)
Mo Ka (0.71073) Mo Ka (0.71073)
52.06
1.752
1360
52.10
1.512
3112
l (mmꢀ1
F(000)
)
Number of observed reflections 6900
7936
Number of parameters refined
357
201
Goodness-of-fit
R1
wR2
1.041
0.0453
0.0975
0.906
0.0682
0.1870
4.3.2. 4,6-(CMe3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-
OH (HL2)
4.3. Synthesis of ligands
Following the similar procedure, reaction of parafor-
maldehyde (1.32 g, 44.0 mmol) with bis(2-methyloxy-
ethyl)amine (5.0 mL, 33.86 mmol) and 2,4-di-tert-
butylphenol (7.01 g, 33.98 mmol) led to the isolation of
HL2 as golden-brown oil (11.3 g, 95% yield). 1H NMR
(300 MHz, CDCl3):d 1.19 (s, 9H, C(CH3)3), 1.34 (s, 9H,
C(CH3)3), 2.72 (t, 4H, J = 5 Hz, NCH2CH2O), 3.31 (s,
6H, OCH3), 3.43 (t, 4H, J = 5 Hz, NCH2CH2O), 3.75 (s,
2H, ArCH2N), 6.74 (s, 1H, ArH), 7.11 (s, 1H, ArH),
10.45 (s, 1H, ArOH).
4.3.1. 4,6-(CH3)2-2-[(MeOCH2CH2)2-NCH2]-C6H2-OH
(HL1)
Paraformaldehyde (1.59 g, 52.8 mmol) and bis(2-meth-
yloxyethyl)amine (6.0 mL, 40.63 mmol) were refluxed for
2 h.
A
solution of 2,4-di-methylphenol (4.93 mL,
40.78 mmol) in methanol (50 mL) was then added and
the mixture and remained refluxing for another 24 h.
Removal of the volatiles under reduced pressure afforded
yellow oil, which was purified at 100 ꢁC under vacuum
for 2 h to afford HL1 (10.31 g, 94% yield). 1H NMR
(300 MHz, CDCl3): d 2.20 (s, 6H, ArCH3), 2.79 (m, 4H,
NCH2CH2O), 3.33 (s, 6H, OCH3), 3.51 (m, 4H,
NCH2CH2O), 3.78 (s, 2H, ArCH2N), 6.61 (s, 1H, ArH),
6.84 (s, 1H, ArH), 10.20 (br s, 1H, Ar–OH).
4.4. Syntheses of complexes
4.4.1. [(g5-Cp0)L1]Y(CH2SiMe3) (3)
To a hexane solution (2.0 mL) of Y(CH2SiMe3)3(THF)2
(0.2 g, 0.4 mmol) was dropwise added equivalent HCp0

W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
4833
(0.0786 g, 0.4 mmol in 2.0 mL of hexane) at room temper-
ature. The mixture was then stirred for 1 h. To the above
mixture was added hexane solution (2.0 mL) of HL1
(0.108 g, 0.4 mmol) at ꢀ35 ꢁC. The reaction mixture was
maintained for 15 min, than concentrated to 3 mL and kept
at ꢀ35 ꢁC for 12 h to give white solids. The solids were
washed carefully with a small amount of cold hexane
(1 mL) and dried in vacuum to afford complex 3 in 83%
yields (0.211 g). Colorless single crystals for X-ray analysis
NCH2CH2OMe), 4.01 (d, 2H, J = 12 Hz, CH2N), 7.00 (s,
1H, ArH), 7.69 (s, 1H, ArH), 13C NMR (100 MHz,
C6D6, 25 ꢁC): d 3.75 (s, 3C, SiMe3), 5.62 (s, 3C,
CH2SiMe3), 12.515, 12.973, 15.458, 15.728 (s, 4C, CpMe4),
25.96 (d, 1C, J = 46.4 Hz, YCH2SiMe3), 31.04 (s, 3C,
ArCMe3), 32.63 (s, 3C, ArCMe3), 32.40 (s, 1C, Me4(C4–
C–)SiMe3), 34.64, 36.10 (s, 2C, CMe3); 43.20 (s, 1C,
CH2CH2OMe), 51.83 (s, 1C, CH2CH2O(Me)Y), 58.94 (s,
1C, CH2CH2O(Me)Y), 59.57 (s, 1C, CH2N), 62.61 (s, 1C,
CH2CH2OMe), 67.42 (s, 1C, CH2CH2O(Me)Y), 70.06
(s, 1C, CH2CH2OMe), 121.62, 122.95 (s, 4C, Me4(C4-C-)-
SiMe3), 125.23, 125.62 (s, 2C, aryls) 128.25–128.74 (s, 4C,
aryls); IR (KBr pellets): 622, 646, 683, 724, 745, 809, 839,
877, 910, 952, 985, 1024, 1090, 1166, 1202, 1247, 1308,
1361, 1389, 1415, 1443, 1478, 1548, 1604, 2954, 3425; Anal.
Calc. for C37H68NO3Si2Y: C, 61.72; H, 7.84; N, 1.95.
Found: C, 61.75; H, 7.85; N, 1.92%.
1
grew from a solution of hexane at ꢀ35 ꢁC within 24 h. H
NMR (400 MHz, C6D6, 25 ꢁC): d ꢀ0.99 (ABX, dd, 1H,
JH–H = 8 Hz, JY–H = 4 Hz, YCH2SiMe3), ꢀ0.45 (ABX,
dd, 1H, JH–H = 8 Hz, JY–H = 4 Hz, YCH2SiMe3), 0.40 (s,
9H, YCH2SiMe3), 0.59 (s, 9H, C5Me4SiMe3), 2.07 (s, 3H,
ArCH3), 2.11 (s, 3H, ArCH3), 2.34 (s, 3H, C5Me4SiMe3),
2.41 (s, 3H, C5Me4SiMe3), 2.45 (s, 3H, C5Me4SiMe3),
2.68 (s, 3H, C5Me4SiMe3), 2.56–2.61 (m, 4H,
NCH2CH2OMe, NCH2CH2O(Me)Y, NCH2CH2O(Me)Y),
2.74 (m, 1H, NCH2CH2O(Me)Y), 2.88 (s, 3H,
NCH2CH2O(Me)Y), 2.91 (s, 1H, NCH2CH2OMe), 3.10
(s, 3H, NCH2CH2OMe), 3.30 (br, 2H, CH2N,
NCH2CH2OMe), 3.58 (m, 1H, NCH2CH2OMe), 3.84 (s,
1H, CH2N), 6.72 (s, 1H, ArH), 7.15 (s, 1H, ArH), 13C
4.4.3. [(g5-Ind)L2]Y(CH2SiMe3) (5)
To
a
hexane solution (2.0 mL) of Y(CH2Si-
Me3)3(THF)2 (0.2 g, 0.4 mmol) was added dropwise equiv-
alent indene (0.047 g, 0.4 mmol in 2.0 mL of hexane)
under stirring. The mixture was then reacted for 1 h at
room temperature. To the resultant mixture was added
dropwise a solution of HL2 (0.141 g, 0.4 mmol in 2.0 mL
of toluene) at ꢀ35 ꢁC. After stirred for 15 min, the reac-
tion mixture was concentrated to 1 mL, and 2 mL hexane
was added. The mixture was kept at ꢀ35 ꢁC for 12 h to
give yellow solids. The solids were washed carefully by a
small amount of hexane (1 mL) and dried in vacuum to
afford complex 5 in 78% yields (0.22 g). Yellow single crys-
tals for X-ray analysis grew from a mixture of toluene and
hexane at ꢀ35 ꢁC (1:3 v/v) within 24 h. 1H NMR
(400 MHz, C6D6, 25 ꢁC): d ꢀ1.23 (s, 2H, YCH2SiMe3),
0.42 (s, 9H, YCH2SiMe3), 1.42 (s, 9H, ArCMe3), 1.81 (s,
9H, ArCMe3), 2.18 (s, 2H, NCH2CH2O(Me)Y), 2.40 (s,
2H, NCH2CH2O(Me)Y), 2.59 (s, 3H, NCH2CH2O(Me)Y),
2.76 (m, 2H, NCH2CH2O(Me)Y), 2.84 (s, 3H,
NCH2CH2O(Me)Y), 3.0 (s, 2H, NCH2CH2O(Me)Y),
3.58 (s, 2H, CH2N), 6.92, 7.59 (s, 2H, ArH), 6.30, 7.00,
7.02, 7.14(m, 4H, C9H4); 13C NMR (100 MHz, C6D6,
25 ꢁC): d 5.78 (s, 3C, CH2SiMe3), 26.26 (s, 1C, YCH2-
SiMe3), 32.40 (s, 3C, ArCMe3), 32.72 (s, 3C, ArCMe3),
34.73 (s, 2C, CMe3); 44.78 (s, 1C, CH2CH2O(Me)Y),
54.08 (s, 1C, CH2CH2O(Me)Y), 59.26 (s, 1C, CH2CH2O-
(Me)Y), 61.07 (s, 1C, CH2N), 63.91 (s, 1C, CH2CH2O-
(Me)Y), 68.34 (s, 1C, CH2CH2O(Me)Y), 70.19 (s, 1C,
CH2CH2O(Me)Y), 58.87, 120.81, 122.62, 123.23, 124.42,
132.91, 133.06, 144.34, 146.10 (9C, C9H4), 126.73,
127.42, 128.25–130.74 (6C, aryls); IR (KBr pellets): 645,
670, 699, 717, 745, 766, 793, 809, 848, 863, 910, 1010,
1022, 1034, 1055, 1083, 1136, 1168, 1203, 1218, 1237,
1279, 1302, 1322, 1330, 1361, 1383, 1415, 1445, 1476,
1561, 1603, 2863, 2897, 2950, 3039, 3684; Anal. Calc. for
C41H59NO3SiY: C, 67.38; H, 8.14; N, 1.92. Found: C,
67.41; H, 8.16; N, 1.91%.
NMR (100 MHz, C6D6, 25 ꢁC):
d
3.51 (s, 3C,
C5Me4SiMe3), 5.01 (s, 3C, CH2SiMe3), 12.44 (d, 2C,
J = 14.8 Hz, ArCH3), 14.98, 15.26, 18.18, 21.28 (s, 4C,
C5Me4), 25.70 (d, 1C, J = 48.5 Hz, YCH2SiMe3), 32.40
(s, 1C, Me4(C4–C–)SiMe3), 43.34 (s, 1C, NCH2CH2O-
(Me)Y), 52.25 (s, 1C, NCH2CH2O(Me)Y), 58.96 (br, 1C,
O(Me)Y), 58.96 (br, 1C, CH2N), 62.35 (s, 1C, OMe),
67.34 (s, 1C, NCH2CH2OMe), 70.01 (s, 1C, NCH2-
CH2OMe), 120.11, 122.31, 122.93, 123.73 (s, 4C, Me4(C4-
C-)SiMe3), 126.44, 127.38, 128.26–128.74, 133.27 (6C,
aryls); IR (KBr pellets): 623, 683, 752, 836, 850, 915, 953,
983, 1026, 1093, 1162, 1200, 1248, 1278, 1325, 1377,
1411, 1480, 1553, 1610, 2730, 2859, 2915, 3666; Anal. Calc.
for C31H56NO3Si2Y: C, 58.56; H, 8.88; N, 2.20. Found: C,
58.57; H, 8.90; N, 2.17%.
4.4.2. [(g5-Cp0)L2]Y(CH2SiMe3) (4)
Following a procedure similar to that described for the
preparation of 3, treatment of a hexane solution (2.0 mL)
of Y(CH2SiMe3)3(THF)2 (0.2 g, 0.4 mmol) with 1 equiv.
of Cp0 (0.0786 g, 0.4 mmol in 2.0 mL of hexane) followed
by addition of HL2 (0.141 g, 0.4 mmol in 2.0 mL of hexane)
at ꢀ35 ꢁC afforded complex 4 (0.19 g, 80%). 1H NMR
(400 MHz, C6D6, 25 ꢁC): d ꢀ0.76 (ABX, 1H, JH–H
=
12 Hz, YCH2SiMe3), ꢀ0.29 (ABX, 1H, JH–H = 12 Hz,
YCH2SiMe3), 0.31 (s, 9H, YCH2SiMe3), 0.56 (s, 9H,
SiMe3), 1.52 (s, 9H, ArCMe3), 1.90 (s, 9H, ArCMe3),
2.10 (s, 3H, C5Me4SiMe3), 2.14 (s, 3H, C5Me4SiMe3),
2.36 (s, 3H, C5Me4SiMe3), 2.41 (s, 3H, C5Me4SiMe3),
2.61–2.69 (m, 5H, NCH2CH2O(Me)Y, NCH2CH2O(Me)Y,
NCH2CH2OMe), 2.93 (m, 3H, NCH2CH2O(Me)Y), 2.93
(m, 1H, NCH2CH2O(Me)Y), 3.21 (br s, 3H, NCH2-
CH2OMe), 3.43 (s, 1H, NCH2CH2O(Me)Y), 3.59 (s, 1H,

4834
W. Miao et al. / Journal of Organometallic Chemistry 692 (2007) 4828–4834
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A typical procedure for polymerization of L-lactide was
performed in a 25 mL round-bottom flask in a glove-box.
To a stirred solution of L-lactide (0.5 g, 3.472 mmol) in
3.0 mL THF was added a THF solution (1.0 mL) of com-
plex 5 (5.04 mg, 6.94 lmol, [LA]0/[Y]0 = 500) (Table 3,
entry 5). The polymerization was proceeded for 2.5 h at
room temperature and then terminated by 1.0 mL of a mix-
ture of HCl/CH3OH/CHCl3 (1:100:600 v/v) to give white
solids. Filtered, washed with ethanol, and then dried at
40 ꢁC for 24 h in vacuo gave PLA (0.496 g, 99.2%). The
molecular weight and the molecular weight distribution
of the resulting polymer were determined by GPC. The
(b) D.J.H. Emslie, W.E. Piers, M. Parvez, R. McDonald, Organo-
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(c) L.W.M. Lee, W.E. Piers, M.R.J. Elsegood, W. Clegg, M. Parvez,
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1
microstructure was characterized by H NMR spectrum.
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Acknowledgements
We thank financial supports from Jilin Provincial Science
and Technology Bureau for Project No. 20050555; The Na-
tional Natural Science Foundation of China for Project
Nos. 20571072 and 20674081; The Ministry of Science
and Technology of China for Project No. 2005CB623802;
‘‘Hundred Talent Scientist Program’’ of CAS.
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Appendix A. Supplementary material
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2237.
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CCDC 637045 and 637131 contain the supplementary
crystallographic data for 3 and 5. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.jorganchem.2007.06.054.
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