Mono(amidinate) rare earth metal bis(alkyl) complexes: Synthesis, structure and their activity for l-lactide polymerization

Article abstract of DOI:10.1016/j.jorganchem.2008.12.014

Alkane elimination reaction between Ln(CH₂SiMe₃)₃(THF)₂ (Ln = Y, Lu) with one equivalent of the amidines with different steric demanding HL ([CyC(N-2,6-ⁱPr₂C₆H₃)₂

Full text of DOI:10.1016/j.jorganchem.2008.12.014

Journal of Organometallic Chemistry 694 (2009) 1289–1296
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mono(amidinate) rare earth metal bis(alkyl) complexes: Synthesis, structure
and their activity for L-lactide polymerization
a
a
a
b
b
Yunjie Luo a, , Xiulian Wang , Jue Chen , Chengcai Luo , Yong Zhang , Yingming Yao
*
a Organometallic Chemistry Laboratory, Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China
b School of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215123, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Alkane elimination reaction between Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with one equivalent of the ami-
dines with different steric demanding HL ([CyC(N-2,6-iPr2C6H3)2]H (HL1), [CyC(N-2,6-Me2C6H3)2]H
(HL2), [PhC(N-2,6-Me2C6H3)2]H (HL3)) in THF afforded a series of mono(amidinate) rare earth metal
bis(alkyl) complexes [CyC(N-2,6-iPr2C6H3)2]Ln(CH2SiMe3)2(THF) (Ln = Y (1), Lu (3)), [CyC(N-2,6-
Me2C6H3)2]Ln(CH2SiMe3)2(THF)2 (Ln = Y (4), Lu (6)), and [PhC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (7)
in 75–89% isolated yields. For the early lanthanide metal Nd, THF slurry of NdCl3 was stirred with three
equiv of LiCH2SiMe3 in THF, followed by addition of one equiv of the amidines HL1 or HL2 gave an ‘‘ate”
Received 23 September 2008
Received in revised form 1 December 2008
Accepted 4 December 2008
Available online 16 December 2008
Keywords:
Amidinate ligands
Organo rare earth metal bis(alkyl)
complexes
Synthesis
Crystal structure
complex [CyC(N-2,6-iPr2C6H3)2]Nd(CH2SiMe3)2(
l-Cl)Li(THF)3 (2) in 48% yield and a neutral [CyC(N-2,6-
Me2C6H3)2]Nd(CH2SiMe3)2(THF)2 (5) in 52% yield, respectively. They were characterized by elemental
analysis, FT-IR, NMR spectroscopy (except for 2 and 5 for their strong paramagnetic property). Complexes
2, 3, 4 and 5 were subjected to X-ray single crystal structure determination. These neutral mono(amidi-
L
-Lactide polymerization
nate) rare earth metal bis(alkyl) complexes showed activity towards
molecular weight and narrow molecular weight distribution polymers.
Ó 2008 Elsevier B.V. All rights reserved.
L-lactide polymerization to give high
1. Introduction
cationic catalysts with remarkable reactivity, can be achieved by
alkane elimination between tris(alkyl)/tris(benzyl) rare earth me-
tal complexes and the corresponding amidines [32–39]. Then, in
most cases, especially to gain a full range of such species, these
complexes are supported by the sterically bulky framework N,N0-
bis(2,6-diisopropylphenyl)benzamidinate [PhC(N-2,6-iPr2C6H3)2]ꢀ.
In addition, the application of mono(amidinate) rare earth metal
bis(alkyl) for the polymerization of polar monomers, such as lac-
tide, has not been reported to date. Herein, we would like to report
a series of mono(amidinate) rare earth metal bis(alkyl) complexes
bearing different amidinate ancillary ligands. Their reactivity
Organo rare earth metal complexes supported by ancillary li-
gands other than cyclopentadienyl and its derivatives have at-
tracted much attention and made spectacular progress in recent
years [1–4]. Among these non-metallocene rare earth metal com-
plexes, rare earth metal complexes bearing amidinate ligands, on
which the steric and electronic characters are easy to be tuned,
have found application in organic transformation and polymeriza-
tion [5–39]. Although a library of tris(amidinate) and bis(amidi-
nate) rare earth metal complexes have been prepared and their
reactivity has been explored [5–30], to our knowledge, mono(ami-
dinate) rare earth metal bis(alkyl) complexes are still quite limited
[31–39]. The significant difficulty to obtain rare earth metal bi-
s(alkyl) complexes is how to prevent the formation of ‘‘ate” com-
plexes and the ligand redistribution problem. Very recently,
however, pioneering and attractive works contributed indepen-
dently from Hessen’s group and Hou’s group demonstrated that
neutral mono(amidinate) rare earth metal bis(alkyl)/bis(benzyl)
complexes, which could be further employed as precursors for
towards L-lactide polymerization was also described.
2. Results and discussion
2.1. Synthesis and characterization of the amidinate ligands HL
([CyC(N-2,6-iPr2C6H3)2]H (HL1), [CyC(N-2,6-Me2C6H3)2]H (HL2),
and [PhC(N-2,6-Me2C6H3)2]H (HL3))
The amidines HL employed in this paper can be synthesized
according to the method developed by Kakimoto and co-workers
[40]. Carboxylic acids reacted with two equivalents of amines in
the presence of polyphosphoric acid trimethylsilyl ester (PPSE) at
180 °C for 8 h could afford the amidines HL1–HL3 in good isolated
yields (Scheme 1). These amidines were characterized by NMR
spectroscopy, HRMS, FT-IR spectroscopy, and elemental analysis.
* Corresponding author. Tel.: +86 574 88130085; fax: +86 574 88229516.
E-mail address: lyj@nit.zju.edu.cn (Y. Luo).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.12.014

1290
Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
R2
R2
R2
NH2
R2
N
N
PPSE
180 oC
R1
R2
+
+
R1COOH
2
2 H2O
H
R2
R1 =
R1 =
R2 = iPr(HL1), Me (HL2)
R2 = Me (HL3)
Scheme 1.
2.2. Synthesis and characterization of [CyC(N-2,6-iPr2C6H3)2]
bis(alkyl)/bis(benzyl) complexes [32–39]. However, these species
are supported mainly by steric demanding N,N0-bis(2,6-diisopro-
pylphenyl)benzamidinate [PhC(N-2,6-iPr2C6H3)2]ꢀ. Despite HL2
and HL3 are sterically less bulky than [PhC(N-2,6-iPr2C6H3)2]ꢀ,
our approach to amidinate rare earth metal bis(alkyl) complexes
with HL1–HL3 as ancillary ligands also involved alkane elimination.
Treatment of Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with one equivalent
of the amidines HL in THF at room temperature for several hours,
after workup, complexes 1, 3, 4, 6, and 7 could be successfully ob-
tained in 75–89% isolated yields (Scheme 2). For the early lantha-
Ln(CH2SiMe3)2(THF) (Ln = Y (1), Lu (3)), [CyC(N-2,6-iPr2C6H3)2]
Nd(CH2SiMe3)2(l-Cl)Li(THF)3 (2), [CyC(N-2,6-Me2C6H3)2]
Ln(CH2SiMe3)2(THF)2 (Ln = Y (4), Nd (5), Lu (6)), and
[PhC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (7)
It is well known that an appropriate metal/ligand combination
is rather critical to obtain neutral rare earth metal bis(alkyl) com-
plexes. Using the strategy of protonolysis, Hessen et al. and Hou
et al. prepared a series of mono(amindinate) rare earth metal
R2
R2
R1
H
R2
R2
N
THF, 4h, r.t
- TMS
Ln(CH2SiMe3)2(THF)n
R1
R2
+
N
Ln(CH2SiMe3)3(THF)2
N
N
R2
R2
R2
R1 = Cy, R2 = iPr, n = 1, Ln = Y (1), Lu (3)
R1 = Cy, R2 = Me, n = 2, Ln = Y (4), Lu (6)
R1 = Ph, R2 = Me, n = 2, Ln = Y (7)
N
N
H
N
Nd(CH2SiMe3)2(u-Cl)Li(THF)3
THF, 4 h, r.t
- TMS
N
3 LiCH2SiMe3
THF, r.t.
(2)
NdCl3
N
N
H
N
Nd(CH2SiMe3)2(THF)2
N
THF, 4 h, r.t
- TMS
(5)
Scheme 2.

Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
1291
nide metal Nd, because its quite difficult to obtain pure and isola-
ble Nd tris(alkyl) complex, one-pot synthetic route was adopted.
Thus, THF slurry of NdCl3 was stirred with three equiv of LiCH2-
SiMe3 in THF at room temperature for several hours, followed by
addition of one equiv of the amidinate ligands (HL1 and HL2), after
crystallization from hexane, complex 2 was isolated as an ‘‘ate”
complex in 48% yield and complex 5 as a neutral one in 52% yield
(Scheme 2). No ligand redistribution was observed in all these
cases.
Complexes 1–7 are all air- and moisture-sensitive, they are sol-
uble in THF and toluene. They were characterized by elemental
analysis, FT-IR spectroscopy, NMR spectroscopy (except for 2 and
5 for their strong paramagnetic property). Complexes 2–5 were
also subjected to X-ray single crystal structure determination.
Room-temperature 1H NMR spectra of 1, 4 and 7 in C6D6
show an AB spin for the methylene resonances of Y-CH2SiMe3.
The methylene resonances for 1 were found at d ꢀ0.23 ppm (1H, d,
JY-H = 3.4 Hz) and d 44.2 ppm (13C NMR), the latter is slightly up-
field-shifted relative to the equivalent resonance in the related
amidinate complex [PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)
(39.5 ppm) [32]. Restricted rotation about the N–Caryl bonds gives
rise to two separate doublets for the isopropyl methyl groups. In
4 and 7, the main difference is the substituents at the carbon atom
of ligating NCN moiety (cyclohexyl group for 4 and phenyl group
for 7), however, both methylene resonances of Y-CH2SiMe3 appear
around d 38 ppm in 13C NMR spectra, suggesting a similar elec-
tronic yttrium environment. In cases of lutetium complexes 3
and 6, the methylene protons of Lu-CH2SiMe3 display singlet reso-
nances at ꢀ0.47 and ꢀ0.48 ppm in 1H NMR spectra, respectively.
Single crystals of complexes 2, 3, 4, and 5 suitable for X-ray dif-
fraction were grown from hexane at ꢀ30 °C. Their molecular struc-
tures are shown in Figs. 1–4, and crystallographic data are
summarized in Table 1. With the same amidinate ligand Lꢀ1 , 3 is
a neutral bis(alkyl) complex, while 2 is an ‘‘ate” complex contain-
ing one equiv of LiCl(THF)3, which came from Nd tris(alkyl) com-
plex formed in situ between the reaction of NdCl3 and
LiCH2SiMe3 in THF. In 3, the bidentate amidinate ligand is bonded
to Lu through nitrogen atoms, the lutetium is five-coordinated by
two nitrogen atoms, two alkyls and one THF molecule to form an
Fig. 2. Molecular structure of [CyC(N-2,6-iPr2C6H3)2]Lu(CH2SiMe3)2(THF) (3).
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at
10% probability level. Selected bond lengths (Å) and angles (°): Lu(1)–N(1) =
2.317(3), Lu(1)–N(2) = 2.308(3), Lu(1)–O(1) = 2.315(3), Lu(1)–C(32) = 2.328(4),
Lu(1)–C(36) = 2.327(4), N(1)–C(1) = 1.341(5), N(2)–C(1) = 1.340(5), N(2)–Lu(1)–
N(1) = 57.98(11), C(36)–Lu(1)–C(32) = 110.98(17), N(1)–C(1)–N(2) = 113.5(3).
edge-bridged tetrahedral geometry [41]. The THF molecule occu-
pies a position roughly in the plane defined by the lutetium atom
and the NCN moiety of the amidinate ligand (dihedral angles of
NCNLu and the plane formed by N(2)Lu(1)O(1) is 178.67°). The
alkyl groups are oriented above and below the NCNLu plane to
minimize interaction with 2,6-iPr2C6H3 groups (dihedral angles of
NCNLu and the plane formed by C(32)Lu(1)C(36) is 89.65°). The
Fig. 1. Molecular structure of [CyC(N-2,6-iPr2C6H3)2]Nd(CH2SiMe3)2(
l-Cl)Li(THF)3
Fig. 3. Molecular structure of [CyC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (4).
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at
10% probability level. Selected bond lengths (Å) and angles (°): Y(1)–N(1) =
2.375(7), Y(1)–N(1A) = 2.375(7), Y(1)–C(11) = 2.429(11), Y(1)–C(11A) = 2.429(11),
Y(1)–O(1) = 2.463(8), Y(1)–O(1A) = 2.463(8), N(1)–C(1) = 1.320(9), C(1)–N(1A) =
1.320(9), C(11)–Y(1)–C(11A) = 140.9(5), N(1)–Y(1)–N(1A) = 55.8(3), N(1)–C(1)–
N(1A) = 114.8(10).
(2). Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at
10% probability level. Selected bond lengths (Å) and angles (°): Nd(1)–N(1) =
2.476(3), Nd(1)–N(2) = 2.498(3), Nd(1)–C(36) = 2.456(6), Nd(1)–C(32) = 2.476(5),
Nd(1)–Cl(1) = 2.7154(15), Nd(1)–C(1) = 2.941(4), Cl(1)–Li(1) = 2.321(10), N(1)–
C(1) = 1.319(5), N(2)–C(1) = 1.334(5), C(36)–Nd(1)–C(32) = 105.0(2), N(1)–Nd(1)–
N(2) = 53.08(11), N(1)–C(1)–N(2) = 113.8(4), Li(1)–Cl(1)–Nd(1) = 177.2(3).

1292
Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
tion reduces the steric repulsion between the amidinate Nd bis-
(alkyl) moiety and LiðTHFÞþ3 moiety. For 4 and 5, X-ray diffraction
revealed that they are isostructural, and both are neutral bis(alkyl)
bis(THF)-adduct complexes. Therefore, only the structure of 4 is
discussed here. As shown in Figs. 3, 4 is a C2 symmetric molecule.
The yttrium atom is six-coordinated by two nitrogen atoms, two
alkyl groups, and two THF molecules. The alkyl groups occupy axial
positions relative to the NCNY plane (dihedral angles of NCNY and
the plane formed by C(11)YC(11A) is 90.00°), while the THF mole-
cules lie exactly in the NCNY plane (dihedral angles of NCNY and
the plane formed by O(1)YO(1A) is 0°). In 4, both Y–CH2SiMe3 bond
distances are 2.437(14) Å, which are nearly identical to those in
[PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)2 (2.427 (2) and 2.433
(2) Å) [32]. The Y–N distances are 2.371(8) Å, which are slightly
shorter than those in [PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)2
(2.395 (1) and 2.397 (1) Å) [32], indicating the steric congestion
around the coordination sphere of the yttrium ion in 4 is reduced
with sterically less hindered amidinate ligand Lꢀ2 .
Fig. 4. Molecular structure of [CyC(N-2,6-Me2C6H3)2]Nd(CH2SiMe3)2(THF)2 (5).
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at 10%
probability level. Selected bond lengths (Å) and angles (°): Nd(1)–N(1) = 2.453(7),
Nd(1)–N(1A) = 2.453(7), Nd(1)–C(11) = 2.546(15), Nd(1)–C(11A) = 2.546(15), Nd(1)–
O(1) = 2.593(11), Nd(1)–O(1A) = 2.593(11), N(1)–C(1) = 1.322(10), C(1)–N(1A) =
1.322(10), C(11)–Nd(1)–C(11A) = 138.6(6), N(1)–Nd(1)–N(1A) = 53.6(4), C(1)–Nd(1)–
O(1) = 105.2(3), C(1)–Nd(1)–O(1A) = 105.2(3), N(1)–C(1)–N(1A) = 113.6(12).
2.3. Polymerization of L-lactide
Polylactides (PLAs) are the promising biodegradable and bio-
compatible synthetic macromolecules, and have been widely ap-
plied in medicine, pharmaceutics, as well as in tissue engineering
[43,44]. The most effective method to prepare PLAs is the ring-
opening polymerization (ROP) of lactides by metal-based cata-
lysts/initiators, and it has been proven that metal alkoxides usually
possess the highest efficiency [45–46]. Some rare earth metal com-
plexes also exhibited good performance for lactide polymerization
[47–53]. In order to understand the polymerization behavior of
mono(amidinate) rare earth metal bis(alkyl) complexes, the neu-
tral complexes 1, 3–7 were tested for the ring-opening polymeriza-
Lu–CH2SiMe3 distances are 2.328(4) and 2.327(4) Å, which are al-
most identical to the Y–CH2SiMe3 distances in [PhC(N-
2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF) (2.374(4) and 2.384(4) Å) [32],
if the ionic radius is considered [42]. The distances between lute-
tium and the ligating nitrogen atoms (Lu–N = 2.308(3) and
2.317(3) Å) are also consistent with those found in [PhC(N-
2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF) (2.339(3) and 2.369(2) Å) [32].
The bite angle of N(2)–Lu(1)–N(1) = 57.98(11)° is comparable with
that in [PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF) (N(1)–Y–
N(2) = 57.27(9)°). In 2, the central metal Nd is five-coordinated
by two alkyl groups, two nitrogen atoms and one chlorine to form
a distorted pyramid geometry. The amidinate Nd bis(alkyl) moiety
is linked with LiðTHFÞþ3 moiety by chlorine anion. The bond angle of
Nd(1)–Cl(1)–Li(1) (177.2(3)°) is close to straight angle, this deposi-
tion of
L
-lactide, [PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF) was
also employed in this experiment for comparison. The preliminary
polymerization results are listed in Table 2.
All of these neutral complexes are active for L-lactide polymer-
ization, and the conversions are all greater than 84% at 70 °C for
30 min in toluene in case of [M]/[I] = 100 (molar ratio). The influ-
ence of central metal on the polymerization activity is obvious.
For example, among these complexes, the lutetium complexes
Table 1
Details of the crystallographic date and refinements for 2–5.
2
3
4
5
Formula
FW
T (K)
Crystal system
Space group
a (Å)
C51H91ClLiN2NdO3Si2
1023.07
293(2)
Monoclinic
P21/n
14.9502(14)
18.7717(18)
21.408(2)
90.00
C43H75LuN2OSi2
867.20
293(2)
Monoclinic
P21/n
12.1257(11)
20.166(2)
18.9893(18)
90.00
C39H67N2O2Si2Y
741.04
213(2)
Orthorhombic
Cmcm
16.612(3)
19.550(4)
13.443(3)
90
C39H67N2NdO2Si2
796.37
293(2)
Orthorhombic
Cmcm
16.590(4)
19.922(5)
13.358(3)
90
b (Å)
c (Å)
a
(°)
b (°)
93.444(2)
90.00
5979.0(10)
4
1.133
0.986
92.505(2)
90.00
4639.0(8)
4
1.242
2.210
90
90
90
90
c
(°)
V (Å3)
4365.9(15)
4
1.127
4414.9(19)
4
1.198
Z
Dcalc (g cmꢀ3
)
l
(mmꢀ1
)
1.421
1.261
F (000)
2172
1816
1592
1676
Crystal size (mm)
hmax (°)
0.78 ꢁ 0.74 ꢁ 0.40
0.80 ꢁ 0.60 ꢁ 0.40
0.42 ꢁ 0.30 ꢁ 0.21
0.80 ꢁ 0.55 ꢁ 0.30
25.35
25.35
25.00
25.34
Reflections collected
Independent reflections
No. of variables
GOF on F2
57489
10962
550
1.147
43030
8456
442
1.107
19835
1983
127
20997
2184
116
1.156
1.198
R [I > 2
wR
r
(I)]
0.0576
0.1260
0.0369
0.0836
0.0995
0.2374
0.0803
0.2084

Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
1293
Table 2
L-lactide polymerization with mono(amidinate) rare earth bis(alkyl) complexesa
O
O
Initiator
O
O
n
O
O
n
O
O
L-Lactide
Run
Initiator
Yieldb (%)
Mn,calcd ꢁ 10ꢀ4
Mn,obsd ꢁ 10ꢀ4
Mw/Mn
Efficienye (%)
c
d
d
1
2
3
4
5
6
7
1
3
4
5
6
7
91
100
93
84
100
90
0.66
0.72
0.70
0.61
0.72
0.65
0.64
3.36
4.71
2.52
2.97
3.64
3.37
2.33
1.20
1.25
1.29
1.32
1.21
1.23
1.26
20
15
28
21
20
19
27
[PhC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)
89
a
b
c
Polymerization conditions: [L-LA]/[Ln] = 100, [L-LA] = 0.5 M, in toluene, t = 30 min, 70 °C.
Isolated yields of PLA.
Mn of PLA calculated from Mn,calcd = 144 ꢁ ([LA]/2[Ln]) ꢁ yield (LA).
d
e
Determined by GPC at 40 °C in THF relative to polystyrene standards; corrected by the Mark–Houwink equation [Mn,obsd = 0.58Mn (GPC)] [57].
Initiation efficiency = Mn,calcd/Mn,obsd
.
exhibited the highest activity (Table 2, runs 2 and 5), the activity
order is 6 > 4 > 5, which is strongly against the order of the effec-
tive ionic radii Nd3+ (1.123 Å) > Y3+ (1.040 Å) > Lu3+ (1.001 Å)
[42]. GPC curves of the resulting polymers were all unimodal with
quite narrow molecular weight distributions (Mw/Mn < 1.32), indic-
ative of single-catalyst behavior as observed in other rare earth
metal bis(alkyl) catalyst systems [51,54]. However, these amidi-
nate rare earth metal alkyl complexes showed rather low initiation
efficiency (15–28%). Under the present polymerization conditions,
the steric congestion around the central metal has little effect on
the polymerization activity (runs 1, 3, 6 and 7).
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 from STREM.
LiCH2SiMe3 (1 M solution in pentane) was obtained from Aldrich,
dried under vacuum before use. P2O5 was purchased from Sinop-
harm Chemical Reagent Co. Ltd. Hexamethyldisiloxane, 2,6-diiso-
propylaniline, 2,6-dimethylaniline, and cyclohexanecarboxylic
acid were purchased from Acros, and used as received. L-Lactide
was purchased from TCI, and was recrystallized from hot toluene.
Deuterated solvents (CDCl3 and C6D6) were obtained from CIL.
Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) [55,56] polyphosphoric acid tri-
methylsilyl ester (PPSE) [40], and [PhC(N-2,6-iPr2C6H3)2]Y(CH2Si-
Me3)2(THF) [32] were prepared according to the literature.
Samples of organo rare earth metal complexes for NMR spectro-
scopic measurements were prepared in the glovebox using
J. Young valve NMR tubes. NMR (1H and 13C) spectra were recorded
on a Bruker AVANCE III spectrometer at 25 °C. 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. X-ray structural determina-
tions were carried out on a Rigaku Mercury diffractometer. FT-IR
spectra were recorded on a Bruker TENSOR 27 spectrometer. TOF
HRMS spectra were obtained from a Micromass OR-TOF spectrom-
eter. Melting points were not calibrated. Molecular weight and
molecular weight distribution of the polymers were measured by
PL GPC 50 at 40 °C using THF as eluent against polystyrene
standards.
3. Conclusions
Alkane elimination reaction between Ln(CH2SiMe3)3(THF)2
(Ln = Y, Lu) with one equivalent of the amidines with different ste-
ric demanding HL ([CyC(N-2,6-iPr2C6H3)2]H (HL1), [CyC(N-2,6-
Me2C6H3)2]H (HL2), and [PhC(N-2,6-Me2C6H3)2]H (HL3)) in THF
afforded a series of mono(amidinate) rare earth metal bis(alkyl)
complexes [CyC(N-2,6-iPr2C6H3)2]Ln(CH2SiMe3)2(THF) (Ln = Y (1),
Lu (3)), [CyC(N-2,6-Me2C6H3)2]Ln(CH2SiMe3)2(THF)2 (Ln = Y (4),
Lu (6)), and [PhC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (7). Treat-
ment of Nd tris(alkyl) complexes, which was formed in situ from
the reaction of THF slurry of NdCl3 with LiCH2SiMe3, with 1 equiv.
of the amidines HL1 or HL2 gave an ‘‘ate” complex [CyC(N-
2,6-iPr2C6H3)2]Nd(CH2SiMe3)2(
l-Cl)Li(THF)3 (2) and a neutral
[CyC(N-2,6-Me2C6H3)2]Nd(CH2SiMe3)2(THF)2 (5), respectively. Li-
gand redistribution was not observed during the preparation of
these mono(amidinate) rare earth metal bis(alkyl) complexes, even
using sterically less demanding HL2 and HL3. These neutral
mono(amidinate) rare earth metal bis(alkyl) complexes showed
4.2. Synthesis of [CyC(N-2,6-iPr2C6H3)2]H (HL1)
activity towards L-lactide polymerization to give high molecular
In a Schlenk flask, P2O5 (9.0 g, 63.4 mmol), hexamethyldisilox-
ane (20 mL, 93.7 mmol), and dry dichloromethane (20 mL) were
refluxed for 30 min. Then the volatiles were removed under vac-
uum to afford a viscous syrup PPSE. Cyclohexanecarboxylic acid
(0.96 g, 7.50 mmol) and 2,6-diisopropylaniline (3.0 mL, 15.0 mmol)
were added to this viscous syrup, and the mixture was reacted at
180 °C for 8 h. The resulting mixture was poured into 1 M NaOH
solution (150 mL) to produce an oil that could solidify overnight.
The solid was washed with water and was recrystallized from ethyl
alcohol to give the title compound as colorless crystals (2.0 g, 60%).
1H NMR (400 MHz, CDCl3): d 0.97(d, J = 6.8 Hz, 6H, CH(CH3)2), 1.19
(d, J = 6.0 Hz, 6H, CH(CH3)2), 1.25 (d, 12H, CH(CH3)2), 1.61 (d, 1H,
weight and quite narrow molecular weight distribution polymers.
The polymerization activity is strongly dependent upon the central
metals with the activity order Lu > Y > Nd.
4. Experimental
4.1. Materials and procedures
All manipulations were performed under pure argon with rigor-
ous exclusion of air and moisture using standard Schlenk tech-
niques and glovebox. Solvents (toluene, hexane, and THF) were

1294
Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
CH2), 1.70, 1.73, 1.81, 2.10 (m, 11H, Cy-H), 3.13 (m, 2H, CH(CH3)2),
3.20 (m, 2H, CH(CH3)2), 5.20 (s, 1H, N–H), 7.02, 7.12 (m, 6H, Ar-H).
13C NMR (100 MHz, CDCl3): d 22.6, 23.0, 24.2, 25.6 (CH(CH3)2),
26.0, 26.3 (Cy-CH2), 28.2, 28.5 (CH(CH3)2), 31.1 (Cy-CH2), 39.3
(Cy-CH), 122.8, 123.1, 123.7, 128.1, 133.3, 139.2, 144.5, 147.3
(Ar-C), 159.1 (NCN). Anal. Calc. for C31H46N2: C, 83.35; H, 10.38;
N, 6.27. Found: C, 83.23; H, 10.41; N, 6.35%.
4.6. Synthesis of [CyC(N-2,6-iPr2C6H3)2]Nd(CH2SiMe3)2(
l-Cl)Li(THF)3
(2)
To a 20 mL of THF slurry of NdCl3 (0.376 g, 1.5 mmol), LiCH2-
SiMe3 (0.424 g, 4.50 mmol) in 20 mL of THF was added dropwisely
at room temperature. The resulting clear green solution was al-
lowed to stir at room temperature for half an hour. Then HL1
(0.670 g, 1.5 mmol) in 20 mL of THF was added slowly at room
temperature. The mixture was stirred at room temperature for
4 h. Then the solvent was removed under reduced pressure to af-
ford a green powder. The powder was extracted with hexane
(3 ꢁ 10 mL) and filtered. The filtrate was concentrated and cooled
at ꢀ30 °C overnight to give [CyC(N-2,6-iPr2C6H3)2]Nd(CH2Si-
4.3. Synthesis of [CyC(N-2,6-Me2C6H3)2]H (HL2)
Following the procedure as that for HL1. Using cyclohexanecar-
boxylic acid (0.96 g, 7.50 mmol) and 2,6-dimethylaniline (1.85 mL,
15.0 mmol) to produce the title compound as colorless crystals
after recrystallization from ethyl alcohol. Yield: 1.70 g (68%). 1H
NMR (400 MHz, CDCl3): d 1.05, 1.21, 1.60, 1.73, 1.91, 2.05 (m,
11H, Cy-H), 2.23 (d, 12H, CH3), 5.27 (br, 1H, N–H), 6.85, 7.04 (m,
6H, Ar-H). 13C NMR (100 MHz, CDCl3): d 17.9 (CH3), 18.9 (CH3),
25.8, 26.1, 31.2 (Cy-CH2), 39.7 (Cy-CH), 122.4 (Ar ipso-C), 127.1,
128.2, 128.4, 129.0, 136.2, 136.5, 146.0 (Ar-C), 159.8 (NCN). FT-IR
(KBr, cmꢀ1): 3422 (m), 3344 (m), 2927 (s), 2853 (m), 1641 (s),
1589 (m), 1472 (m), 1449 (m), 1390 (m), 1336 (m), 1275 (m),
782 (m), 760 (m). Anal. Calc. for C23H30N2: C, 82.59; H, 9.04; N,
8.37. Found: C, 82.63; H, 9.11; N, 8.27%. HRMS [C23H30N2]+: calcd
334.2409, found 334.2408. M.p. 132.4 °C.
Me3)2(l-Cl)Li(THF)3 as green crystals. Yield: (0.65 g, 48%). Anal.
Calc. for C51H91ClLiN2NdO3Si2: C, 59.87; H, 8.98; N, 2.74. Found:
C, 59.68; H, 8.75; N, 2.81%.
4.7. Synthesis of [CyC(N-2,6-iPr2C6H3)2]Lu(CH2SiMe3)2(THF) (3)
To a 20 mL of colorless THF solution of Lu(CH2SiMe3)3(THF)2
(0.58 g, 1.0 mmol), HL1 (0.447 g, 1.0 mmol) in 20 mL THF was
added dropwisely at room temperature. The mixture was stirred
at room temperature for 4 h. Then the solvent was removed under
reduced pressure to afford a off-white powder. The powder was ex-
tracted with 30 mL of hexane and filtered. The filtrate was concen-
trated and cooled at ꢀ30 °C overnight to give [CyC(N-
2,6-iPr2C6H3)2]Lu(CH2SiMe3)2(THF)2 as colorless crystals. Yield:
0.71 (76%). 1H NMR (500 MHz, C6D6) d: ꢀ0.47 (s, 4H, CH2SiMe3),
0.26 (s, 18H, SiMe3), 0.63 (m, 4H, Cy-CH2), 1.12 (m, 4H, b-THF),
1.18 (m, 4H, Cy-CH2), 1.32 (d, J = 6.5 Hz, 12H, CH(CH3)2), 1.38 (d,
J = 6.5 Hz, 12H, CH(CH3)2), 1.81 (d, 2H, Cy-CH2), 2.45 (m, 1H, Cy-
4.4. Synthesis of [PhC(N-2,6-Me2C6H3)2]H (HL3)
Following the procedure as that for HL1. Using benzonic acid
(0.92 g, 7.50 mmol) and 2,6-dimethylaniline (1.85 mL, 15.0 mmol)
to produce the title compound as off-white crystals after recrystal-
lization from ethyl alcohol. Yield: 2.12 g (86%). 1H NMR (400 MHz,
CDCl3): d 2.13 (s, 6H, CH3), 2.36 (s, 6H, CH3), 5.73 (s, 1H, N–H), 6.93,
7.11, 7.18, 7.29, 7.46 (m, 11H, Ar-H). 13C NMR (100 MHz, CDCl3): d
18.0 (CH3), 19.1 (CH3), 123.0, 126.6, 127.2, 127.8, 128.3, 128.5,
129.0, 129.5, 134.9, 135.3, 137.1, 145.9 (Ar-C), 153.9 (NCN). FT-IR
(KBr, cmꢀ1): 3441 (m), 2961 (s), 2867 (w), 1, 1644 (s), 1588 (w),
1464 (m), 1439 (w), 1376 (m), 1279 (m), 1226 (m), 1167 (s),
1100 (w), 779 (m), 768 (m). Anal. Calc. for C23H24N2: C, 84.11; H,
7.37; N, 8.53. Found: C, 83.75; H, 7.68; N, 8.58%. HRMS
[C23H24N2]+: calcd 328.1939, found 328.1939. M.p. 124.5 °C.
CH), 3.54 (m, 4H,
a-THF), 3.62 (m, 4H, CH(CH3)2), 7.06–7.16 (6H,
Ar-H). 13C NMR (125 MHz, C6D6) d: 4.2 (TMS), 23.7 (CH(CH3)2),
24.3 (b-THF), 25.7 (Cy-CH2), 26.1 (Cy-CH2), 26.4 (CH(CH3)2), 28.1
(Cy-CH2), 29.9 (CH(CH3)2), 44.2 (Cy-CH), 45.3 (CH2TMS), 70.5 (a-
THF), 123.7, 124.9, 142.7, 143.1 (Ar-CH), 180.2 (NCN). FT-IR (KBr,
cmꢀ1): 2961 (s), 2866 (s), 1634 (s), 1459 (s), 1384 (m), 1354 (m),
1315 (s), 1238 (s), 859 (s), 804 (m). Anal. Calc. for C44H77LuN2OSi2:
C, 59.97; H, 8.81; N, 3.18. Found: C, 59.94; H, 8.58; N, 3.32%.
4.8. Synthesis of [CyC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (4)
To a 20 mL of colorless THF solution of Y(CH2SiMe3)3(THF)2
(0.930 g, 1.88 mmol), HL2 (0.628 g, 1.88 mmol) in 20 mL THF was
added dropwisely at room temperature. The mixture was stirred
at room temperature for 4 h. Then the solvent was removed under
reduced pressure to afford an off-white powder. The powder was
washed with hexane and dried. Yield: 1.2 g (86%). 1H NMR
(400 MHz, C6D6) d: ꢀ0.30 (d, J = 2.8 Hz, 4H, CH2TMS), 0.31 (s,
18H, CH2TMS), 0.52–0.67 (m, 4H, Cy-CH2), 1.09 (d, 2H, Cy-CH2),
1.17 (br s, 8H, b-THF), 1.27 (d, 2H, Cy-CH2), 1.81 (d, 2H, Cy-CH2),
4.5. Synthesis of [CyC(N-2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF) (1)
To a 30 mL of colorless THF solution of Y(CH2SiMe3)3(THF)2
(0.990 g, 2.00 mmol), HL1 (0.893 g, 2.00 mmol) in 20 mL THF was
added dropwisely at room temperature. The mixture was stirred
at room temperature for 4 h. Then the solvent was removed under
reduced pressure to afford an off-white powder. The powder was
extracted with 30 mL of hexane and filtered. The filtrate was con-
centrated and cooled at ꢀ30 °C overnight to give [CyC(N-
2,6-iPr2C6H3)2]Y(CH2SiMe3)2(THF)2 as colorless crystals in two
crops. Yield: 1.4 g (89%). 1H NMR (500 MHz, C6D6) d: ꢀ0.23 (d,
J = 3.0 Hz, 4H, CH2SiMe3), 0.28 (s, 18H, SiMe3), 0.64 (m, 4H, Cy-
CH2), 1.10 (b, 4H, b-THF), 1.20 (m, 4H, Cy-CH2), 1.33 (d, J = 7.0 Hz,
12H, CH(CH3)2), 1.38 (d, J = 7.0 Hz, 12H, CH(CH3)2), 1.82 (d, 2H,
2.24 (m, 1H, Cy-CH), 2.40 (s, 12H, Ph-Me), 3.57 (br s, 8H,
a-THF),
6.91, 7.01 (6H, Ar-H). 13C NMR (100 HMz, C6D6) d: 4.5 (SiTMS),
20.2 (Ph-Me), 25.1 (b-THF), 25.9, 26.7, 29.3 (Cy-CH2), 36.9, 37.2
(CH2TMS), 44.1 (Cy-CH), 69.6 (a-THF), 123.8, 132.8, 146.5 (Ar-C),
179.8 (NCN). FT-IR (KBr, cmꢀ1): 2933 (s), 2853 (s), 1637 (s), 1589
(m), 1478 (s), 1375 (m), 1355 (m), 1309 (m), 1250 (m), 1035 (m),
959 (m), 861 (m), 763 (s). Anal. Calc. for C40H68N2O2Si2Y: C,
63.71; H, 9.09; N, 3.72. Found: C, 63.98; H, 8.86; N, 3.79%.
Cy-CH2), 2.47 (m, 1H, Cy-CH), 3.4 (b, 4H,
a-THF), 3.60 (m, 4H,
CH(CH3)2), 7.07–7.16 (6H, Ar-H). 13C NMR (100 MHz, C6D6) d: 4.3
(TMS), 23.7 (CH(CH3)2), 24.7 (Cy-CH2), 25.9 (b-THF), 26.4 (Cy-
CH2), 26.6 (CH(CH3)2), 28.5 (Cy-CH2), 30.2 (Cy-CH), 38.9, 39.3
4.9. Synthesis of [CyC(N-2,6-Me2C6H3)2]Nd(CH2SiMe3)2(THF)2 (5)
(CH(CH3)2), 44.2 (CH2TMS), 70.0 (a-THF), 123.9, 125.0, 143.1 (Ar-
C), 180.6 (NCN). FT-IR (KBr, cmꢀ1): 2959 (s), 2928(s), 2866 (m),
1636 (s), 1460 (s), 1434 (s), 1393 (m), 1323 (m), 1247 (m), 862
(m), 762 (m). Anal. Calcd for C44H77N2OSiY: C, 66.46; H, 9.76; N,
3.52. Found: C, 66.59; H, 9.88; N, 3.46%.
To a 20 mL of THF slurry of NdCl3 (0.376 g, 1.5 mmol), LiCH2-
SiMe3 (0.424 g, 4.50 mmol) in 20 mL of THF was added dropwisely
at room temperature. The resulting clear green solution was al-
lowed to stir at room temperature for half an hour. Then HL2

Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
1295
(0.424 g, 1.50 mmol) in 20 mL of THF was added slowly at room
temperature. The mixture was stirred at room temperature for
4 h. Then the solvent was removed under reduced pressure to af-
ford a green powder. Yield: 0.62 g (52%). FT-IR (KBr, cmꢀ1): 2930
(s), 2852 (s), 1638 (s), 1589 (m), 1471 (s), 1354 (m), 1308 (m),
1227 (s), 1094 (m), 862 (m), 763 (s). Anal. Calc. for C40H68N2NdO2-
Si2: C, 59.36; H, 8.47; N, 3.46. Found: C, 59.53; H, 8.42; N, 3.39%.
tures were solved by direct methods and refined by full-matrix
least-squares procedures based on |F|2. All the non-hydrogen
atoms were refined anisotropically. All the hydrogen atoms were
held stationary and included in the structure factor calculation in
the final stage of full-matrix least-squares refinement. The struc-
tures were solved and refined using SHELEXL-97 program.
5. Supplementary material
4.10. Synthesis of [CyC(N-2,6-Me2C6H3)2]Lu(CH2SiMe3)2(THF)2 (6)
CCDC 698451, 698452, 698453 and 698454 contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
To a 20 mL of colorless THF solution of Lu(CH2SiMe3)3(THF)2
(0.581 g, 1.00 mmol), HL2 (0.334 g, 1.00 mmol) in 20 mL THF was
added dropwisely at room temperature. The mixture was stirred
at room temperature for 4 h. Then the solvent was removed under
reduced pressure to afford an off-white powder. The powder was
washed with hexane and dried. Yield: 0.71 g (83.4%). 1H NMR
(500 MHz, C6D6) d: ꢀ0.48 (s, 4H, CH2SiMe3), 0.29 (s, 18H, SiMe3),
0.60 (m, 4H, CH2), 1.12 (m, 4H, CH2), 1.24 (m, 8H, b-THF), 1.81 (d,
2H, CH2), 2.25 (m, 1H, CH), 2.42 (s, 12H, Ph-Me), 6.91, 7.02 (6H,
Ar-H). 13C NMR (125 MHz, C6D6) d: 4.3 (TMS), 19.9 (Ph-Me), 20.5
(Cy-CH2), 25.1 (Ph-Me), 25.6 (b-THF), 26.4, 29.4 (Cy-CH2), 44.1
Acknowledgements
This work was partly financial supported by the National Natu-
ral Science Foundation of China (20604023), Zhejiang Provincial
Natural Science Foundation (Y406301), Ningbo Municipal Natural
Science Foundation (2008A610056), and Key Laboratory Founda-
tion of Ningbo (2007A22011).
(Cy-CH), 45.5 (CH2TMS), 68.7 (a-THF), 123.9, 132.7, 133.2, 145.8
(Ar-CH), 179.1 (NCN). FT-IR (KBr, cmꢀ1): 2938 (s), 2853 (s), 1638
(m), 1590 (w), 1472 (s), 1373 (m), 1355 (m), 1309 (m), 1236 (s),
1196 (w), 1044 (m), 858 (s), 763 (s). Anal. Calc. for C40H68LuN2O2-
Si2: C, 57.19; H, 8.16; N, 3.33. Found: C, 57.28; H, 8.15; N, 3.42%.
References
[1] F.T. Edelmann, D.M.M. Freckmann, H. Schumann, Chem. Rev. 102 (2002) 1851.
[2] S. Arndt, J. Okuda, Adv. Synth. Catal. 347 (2005) 339.
[3] P.M. Zeimentz, S. Arndt, B.R. Elvidge, J. Okuda, Chem. Rev. 106 (2006) 2404.
[4] Z.M. Hou, Y.J. Luo, X.F. Li, J. Organomet. Chem. 691 (2006) 3114.
[5] F.T. Edelmann, Coord. Chem. Rev. 137 (1994) 403.
[6] M. Wedler, M. Noltemeyer, U. Pieper, H.G. Schmidt, D. Stalke, F.T. Edelmann,
Angew. Chem., Int. Ed. 29 (1990) 894.
[7] A. Recknagel, F. Knosel, G. Gornitzka, M. Noltemeyer, F.T. Edelmann, J.
Organomet. Chem. 417 (1991) 363.
[8] M. Wedler, F. Knosel, U. Pieper, D. Stalke, F.T. Edelmann, H.D. Amberger, Chem.
Ber. 125 (1992) 2171.
[9] R. Duchateau, C.T.V. Wee, A. Meetsma, J.H. Teuben, J. Am. Chem. Soc. 115
(1993) 4931.
[10] J.R. Hagadorn, J. Arnold, Organometallics 15 (1996) 984.
[11] R. Duchateau, C.T.V. Wee, A. Meetsma, P.T.V. Duijnen, J.H. Teuben,
Organometallics 15 (1996) 2279.
[12] R. Duchateau, C.T.V. Wee, J.H. T euben, Organometallics 15 (1996) 2291.
[13] J.A.R. Schmidt, J. Arnold, Chem. Commun. (1999) 2149.
[14] K. Kincaid, C.P. Gerlach, G.R. Giesbrecht, J.R. Hagadorn, G.D. Whitener, A. Shafir,
J. Arnold, Organometallics 18 (1999) 5360.
[15] D. Barbier-Baudry, A. Bouazza, C.H. Brachais, A. Dormond, M. Visseaux,
Macromol. Rapid Commun. 21 (2000) 213.
4.11. Synthesis of [PhC(N-2,6-Me2C6H3)2]Y(CH2SiMe3)2(THF)2 (7)
To a 20 mL of colorless THF solution of Y(CH2SiMe3)3(THF)2
(0.754 g, 1.52 mmol), HL3 (0.50 g, 1.52 mmol) in 20 mL THF was
added dropwisely at room temperature. The mixture was stirred
at room temperature for 4 h. Then the solvent was removed under
reduced pressure to afford an off-white powder. The powder was
extracted with hexane (3 ꢁ 10 mL) and filtered. The filtrate was
concentrated and cooled at ꢀ30 °C overnight to give [PhC(N-2,6-
Me2C6H3)2]Y(CH2SiMe3)2(THF)2 as colorless crystals. Yield: 0.83 g
(75%). 1H NMR (400 MHz, C6D6) d: ꢀ0.18 (d, J = 2.9 Hz, 4H,
CH2TMS), 0.32 (s, 18H, CH2TMS), 1.20 (br s, 8H, b-THF), 2.37 (s,
12H, Ph-Me), 3.60 (br s, 8H,
Ph-H). 13C NMR (100 HMz, C6D6) d: 4.6 (SiTMS), 20.1 (Ph-Me),
25.1 (b-THF), 37.9, 38.3 (CH2TMS), 69.7 ( -THF), 123.3, 123.7,
a-THF), 6.62, 6.78, 6.85, 7.03 (11H,
a
126.9, 127.2, 128.5, 132.2, 132.5, 146.5, 147.2 (Ar-C), 174.7
(NCN). FT-IR (KBr, cmꢀ1): 3341 (m), 2955 (s), 1628 (s), 1589 (w),
1466 (s), 1435 (s), 1366 (s), 1250 (s), 1204 (m), 1034 (m), 987
(s), 833 (s), 764 (s), 694 (s). Anal. Calc. for C39H60N2O2Si2Y: C,
63.82; H, 8.24; N, 3.82. Found: C, 63.85; H, 8.13; N, 3.89%.
[16] D. Doyle, Y.K. Gun’ko, P.B. Hitchcock, M.F. Lappert, J. Chem. Soc., Dalton Trans.
(2004) 4093.
[17] S. Bambirra, A. Meetsma, B. Hessen, J.H. Teuben, Organometallics 20 (2001)
782.
[18] K.B. Aubrecht, K. Chang, M.A. Hillmyer, W.B. Tolman, J. Polym. Sci. A: Polym.
Chem. 39 (2001) 284.
[19] J. Zhang, R.Y. Ruan, Z.H. Shao, R.F. Cai, L.H. Weng, X.G. Zhou, Organometallics
21 (2002) 1420.
4.12. Polymerization of L-lactide
[20] Y.J. Luo, Y.M. Yao, Q. Shen, J. Sun, L.H. Weng, J. Organomet. Chem. 662 (2002)
44.
[21] J. Richter, J. Feiling, A.G. Schmidt, M. Noltemeyer, W. Bruser, F.T. Edelmann, Z.
Anorg. Allg. Chem. 630 (2004) 1269.
[22] C. Villiers, P. Thuery, M. Ephritikhine, Eur. J. Inorg. Chem. (2004) 4624.
[23] M.Y. Deng, Y.M. Yao, Y. Zhang, Q. Shen, Chem. Commun. (2004) 2742.
[24] J.F. Wang, Y.M. Yao, J.L. Cheng, X.A. Pang, Y. Zhang, Q. Shen, J. Mol. Struct. 743
(2005) 229.
[25] W.X. Zhang, M. Nishiura, Z.M. Hou, J. Am. Chem. Soc. 127 (2005) 16788.
[26] C. Li, Y.R. Wang, L.Y. Zhou, H.M. Sun, Q. Shen, J. Appl. Polym. Sci. 102 (2006) 22.
[27] W.P. Kretschmer, A. Meetsma, B. Hessen, N.M. Scott, S. Qayyum, R.Z. Kempe,
Anorg. Allg. Chem. 632 (2006) 1936.
[28] M.N. Bochkarev, T.V. Balashova, A.A. Maleev, A.A. Fagin, G.K. Fukin, E.V.
Baranov, Inorg. Chim. Acta 360 (2007) 2368.
A typical procedure for
(Table 2, run 1). In a 20 mL Schleck flask, complex 1 (20 mg,
26 mol), -lactide (368 mg, 2.6 mmol), and toluene (5.2 mL) were
stirred at 70 °C for 30 min. The resulting viscous solution was
quenched by an excess amount of ethanol, filtered, and then dried
at 60 °C in vacuo to constant weight (335 mg, 91%).
L-Lactide polymerization was described
l
L
4.13. X-ray crystallographic study
[29] J.F. Wang, T. Cai, Y.M. Yao, Y. Zhang, Q. Shen, Dalton Trans. (2007) 5275.
[30] G.B. Deacon, C.M. Forsyth, P.C. Junk, J. Wang, Inorg. Chem. 46 (2007) 10022.
[31] S. Bambirra, M.J.R. Brandsma, E.A.C. Brussee, A. vMeetsma, B. Hessen, J.H.
Teuben, Organometallics 19 (2000) 3197.
Suitable single crystals of complexes were sealed in a thin-
walled glass capillary for determining the single-crystal structure.
Intensity data were collected with a Rigaku Mercury CCD area
[32] S. Bambirra, D.V. Leusen, A. Meetsma, B. Hessen, J.H. Teuben, Chem. Commun.
(2003) 522.
[33] S. Bambirra, M.W. Bouwkamp, A. Meetsma, B. Hessen, J. Am. Chem. Soc. 126
(2004) 9182.
detector in
x scan mode using Mo Ka radiation (k = 0.71070 Å).
The diffracted intensities were corrected for Lorentz polarization
effects and empirical absorption corrections. Details of the inten-
sity data collection and crystal data are given in Table 1. The struc-
[34] S. Bambirra, H. Tsurugi, D.V. Leusen, B. Hessen, Dalton Trans. (2006) 1157.

1296
Y. Luo et al. / Journal of Organometallic Chemistry 694 (2009) 1289–1296
[35] S. Bambirra, E. Otten, D.V. Leusen, A. Meetsma, B. Hessen, Z. Anorg. Allg. Chem.
632 (2006) 1950.
[36] S. Bambirra, A. Meetsma, B. Hessen, Organometallics 25 (2006) 3454.
[37] S. Bambirra, F. Perazzolo, S.J. Boot, T.J.J. Sciarone, A. Meetsma, B. Hessen,
Organometallics 27 (2008) 704.
[47] N. Ajellal, D.M. Lyubov, M.A. Sinenkov, G.K. Flukin, A.V. Cherkasov, C.M.
Thomas, J.F. Carpentier, A.A. Trifonov, Chem. Eur. J. 14 (2008) 5440.
[48] P.L. Arnold, J.C. Buffet, R.P. Blaudeck, S. Sujecki, A.J. Blake, C. Wilson, Angew.
Chem., Int. Ed. 47 (2008) 6033.
[49] H.Y. Ma, T.P. Spaniol, J. Okuda, Inorg. Chem. 4 (2008) 3328.
[50] H.E. Dyer, S. Huijser, A.D. Schwarz, C. Wang, R. Duchateau, P. Mountford,
Dalton Trans. (2008) 32.
[38] L.X. Zhang, M. Nishiura, M. Yuki, Y. Luo, Z.M. Hou, Angew. Chem., Int. Ed. 47
(2008) 2642.
[39] S.Z. Ge, A. Meetsma, B. Hessen, Organometallics 27 (2008) 3131.
[40] S.I. Ogata, A. Mochizuki, M.A. Kakimoto, Y. Imai, Bull. Chem. Soc. Jpn. 59 (1986)
2171.
[41] T.R. Ward, H.B. Burgi, F. Gilardoni, J. Weber, J. Am. Chem. Soc. 119 (1997)
11974.
[51] X.L. Liu, X.M. Shang, T. Tang, N.H. Hu, F.K. Pei, D.M. Cui, X.S. Chen, X.B. Jing,
Organometallics 26 (2007) 2747.
[52] J.F. Wang, T. Cai, Y.M. Yao, Y. Zhang, Q. Shen, Dalton Trans. (2007) 5275.
[53] A. Amgoune, C.M. Thomas, T. Roisnel, J.F. Carpentier, Chem. Eur. J. 12 (2006)
169.
[42] R.D. Shannon, Acta. Crystallogr. A 32 (1976) 751.
[43] R.E. Drumright, P.R. Gruber, D.E. Henton, Adv. Mater. 12 (2000) 1841.
[44] E. Chiellini, R. Solaro, Adv. Mater. 8 (1996) 305.
[45] B.J. O’Keefe, M.A. Hillmyer, W.B. Tolman, Dalton Trans. (2001) 2215.
[46] O.D. Cabaret, B.M. Vaca, D. Bourissou, Chem. Rev. 104 (2004) 6147.
[54] B. Liu, D.M. Cui, J. Ma, X.S. Chen, X.B. Jing, Chem. Eur. J. 13 (2007) 834.
[55] M. Lappert, R. Pearce, Chem. Commun. (1973) 126.
[56] Y.J. Luo, J. Baldamus, Z.M. Hou, J. Am. Chem. Soc. 126 (2004) 13910.
[57] I. Barakat, P. Dubois, R. Jerome, P. Teyssie, J. Polym. Sci., Part A. 31 (1993)
505.