Synthesis and characterization of heteroscorpionate rare-earth metal dialkyl complexes and catalysis on MMA polymerization

Article abstract of DOI:10.1002/ejic.201000108

A series of rare-earth metal alkyl complexes supported by a heteroscorpionate ligand were prepared and structurally characterized. X-ray diffraction analysis revealed that the heteroscorpionate ligand is face-capping on the rare-earth metal in k³

Full text of DOI:10.1002/ejic.201000108

FULL PAPER
DOI: 10.1002/ejic.201000108
Synthesis and Characterization of Heteroscorpionate Rare-Earth Metal
Dialkyl Complexes and Catalysis on MMA Polymerization
Zhichao Zhang,[a,b] Dongmei Cui,*[a] and Alexander A. Trifonov[c]
Keywords: Rare earths / Tridentate ligands / Polymerization
A series of rare-earth metal alkyl complexes supported by a
heteroscorpionate ligand were prepared and structurally
characterized. X-ray diffraction analysis revealed that the
heteroscorpionate ligand is face-capping on the rare-earth
metal in k3 mode, making the configuration of the afforded
dialkyl metal complexes similar to that of half-metallocenes.
These complexes are capable of polymerizing methyl meth-
acrylate, with the lutetium complex displaying the highest
activity even at low temperature. The poly(methyl methacryl-
ate) obtained is syndiotactically enriched with narrow mo-
lecular weight distribution.
are easily structurally modified either by varying the sub-
stituents of the heterocycle to change the spatial sterics or
by changing the functional groups to tune the electronic
properties, which is believed to be responsible for the cata-
lytic activity and stereoselectivity in catalytic reactions. Al-
though heteroscorpionates have been widely used in main
group and d-block metals,[8b,8c,9] their applications as an-
ionic ancillary ligands in rare-earth metals have been ex-
plored less in spite of the fact that highly efficient rare-earth
metal catalysts have been synthesized.[10] Herein we report
the synthesis and characterization of heteroscorpionate
rare-earth metal dialkyl complexes. Their application as a
catalyst for the polymerization of methyl methacrylate is
also included for the first time.
Introduction
Synthesis of organo rare-earth metal alkyl complexes is
of great importance because most are able to initiate poly-
merizations of monomers such as ethylene,[1] styrene,[2] con-
jugated dienes,[3] lactide,[4] and methyl methacrylate etc.[5]
However, as rare-earth metals have large ion radii and the
metal–carbon bond is highly active, in the formation of
such complexes, dimerization, ligand scrambling, formation
of ate complexes and C–H activation usually take place to
afford unexpected products, which significantly influence
their catalytic activity.[6] Thus, ancillary ligands with mul-
tiple coordinating sites and large steric bulkiness are fav-
oured to prevent these side reactions. Cyclopentadienyls,
which can provide a more steric environment around the
central metal in η5-mode via five carbon atoms, are among
the most commonly adopted ligands,[7] and have been
widely employed to stabilize rare-earth metal alkyl species.
However, structural modification is difficult in cyclopen-
tadienyl compounds, hampering improvement in the cata-
lytic performances of the attached (half) metallocenes. Het-
eroscorpionate compounds (Figure 1) derived from bis(pyr-
azolyl)methane are tridentate ligands and may face-cap on
the metal in κ3-fashion, representing a probable alternative
to the cyclopentadienyls.[8] In addition, heteroscorpionates
Figure 1. Structure of the heteroscorpionate ligand.
Results and Discussion
[a] State Key Laboratory of Polymer Physics and Chemistry,
Changchun Institute of Applied Chemistry, Chinese Academy
of Sciences,
The ligand precursor 2,2-[bis(3,5-dimethylpyrazolyl)]-
1,1-diphenylethanol was prepared according to reported
method with a minor modification.[11] Bis(3,5-dimethylpyr-
azolyl)methane was synthesized first by the reaction of 3,5-
dimethylpyrazole with excess dichloromethane under re-
fluxing for 1 d with the assistance of tetrabutylammonium
bromide, a kind of phase-transfer catalyst (Scheme 1). Li-
thiation in tetrahydrofuran (THF) resulted in an off-white
suspension, to which purified benzophenone was added.
The reaction mixture was warmed up to room temperature
Changchun, 130022, People’s Republic of China
Fax: +86-431-85262773
E-mail: dmcui@ciac.jl.cn
[b] Graduate School of Chinese Academy of Sciences,
Beijing, 100039, People’s Republic of China
[c] G. A. Razuvaev Institute of Organometallic Chemistry of the
Russian Academy of Sciences,
Tropinina 49, 603950 Nizhny Novgorod, GSP-445, Russian
Federation
Fax: +7-8312-661-497
E-mail: trif@imoc.sinn.ru
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Z. Zhang, D. Cui, A. A. Trifonov
FULL PAPER
and stirred for another 8 h (Scheme 1). The targeted ligand an umbrella, which limits the rotation of the pyrazole rings
precursor was obtained by recrystallization from a minimal (Figure 1). This observation further corroborated the re-
dichloromethane solution at low temperature.
sults of 1H NMR spectrum analysis that two types of
methyl groups were nonequivalent by giving two sets of res-
onances. The ligands generate a distorted octahedral geom-
etry around the central metal with the two oxygen atoms
occupying apices while the N1, N3, C25, C29 atoms form
the horizontal plane. Furthermore, Sc1, O1 and C24 define
a mirror plane bisecting the molecule. The bond lengths of
Sc–C and Sc–N [2.278(3) and 2.279(3) Å vs. 2.423(2) and
2.375(2)] are slightly longer than those reported by Anti-
onio Otero ([2.213(5) and 2.232(5) Å vs. 2.279(4) Å]
(Table 1).[12] 1H NMR spectra of complexes 2 and 3 were
similar to that of complex 1, indicating that 2 and 3 were
homologues of 1. Singlet resonance at δ = –0.22 ppm for 2
(δ = –0.37 ppm for 3) was ascribed to the methylene of the
alkyl bound to yttrium. Single crystals of complexes 2 and 3
were easily isolated from THF solution at low temperature
(–30 °C), which were further characterized by X-ray analy-
sis (Figures 3 and 4). The space group (C2/c) and symmetry
Scheme 1. Synthesis of heteroscorpionate ligand precursor.
Reaction of this heteroscorpionate ligand in THF with
an equimolar amount of trialkyl rare-earth metal
Ln[CH2Si(CH3)3]3(thf)2 in hexane at –30 °C for 10 h gave
the desired dialkyl rare-earth metal complexes (1: Ln = Sc,
2: Ln = Y, and 3: Ln = Lu) with the release of tetramethyl-
silane (Scheme 2). The formation of complex 1 was evi-
¯
(monoclinic) differ from that of 1 (P1, triclinic, Table 3). In
addition eight molecules of 2 (or 3) in each unit cell and
eight molecules of THF were detected. The Y–C bond
lengths of 2.443(4) and 2.452(4) Å and the Y–N bond
lengths of 2.540(3) and 2.578(3) Å in 2 fall within the nor-
1
denced by H NMR spectroscopic analysis. The resonance
of the hydroxy proton (originally at δ = 7.95 ppm) of the
ligand had disappeared. Meanwhile two sets of resonances
at δ = 2.20 and 1.64 ppm ascribed to the methyl groups on
the pyrazole ring were observed which were different to the
singlet in the ligand spectrum, suggesting that the two
methyl groups on one pyrazole ring were inequivalent. Two
broad peaks at δ = 3.77 and 1.39 ppm were assigned to
the THF molecule. The methylene protons of Sc–CH2SiMe3
gave a singlet resonance at δ = 0.16 ppm. The integrated
intensity of the resonances demonstrated there are two alkyl
groups and one heteroscorpionate ligand in complex 1. In
addition, one THF molecule coordinates to the scandium
through an oxygen atom to satisfy the high coordinating
number.
Figure 2. ORTEP drawing of complex 1 with thermal ellipsoids at
35% probability levels. The hydrogen atoms and the free THF mo-
lecule are omitted for clarity.
Scheme 2. Preparation of heteroscorpionate rare-earth metal di-
alkyl complexes 1, 2 and 3.
Table 1. Selected bond lengths [Å] and bond angles [°] for com-
plexes 1–3.
Ln = Sc
Ln = Y
Ln = Lu
The solid-state structure of 1 was further confirmed by
X-ray diffraction analysis. Each unit cell contains two mole-
cules of complex 1 (Figure 2). Four molecules of free THF
are trapped in a lattice. Complex 1 is a monomer of a THF
solvate, consistent with its solution-state structure. Each
scandium ion bonds to a THF molecule and two alkyl moi-
eties. Meanwhile, the heteroscorpionate ligand facially co-
ordinates to the scandium ion via the oxygen atom and the
two nitrogen atoms of the pyrazole rings in a κ3 mode, like
Ln–C(25)
Ln–C(29)
Ln–O(1)
Ln–O(2)
Ln–N(1)
Ln–N(3)
C(25)–Ln(1)–C(29)
O(1)–Ln(1)–O(2)
N(1)–Ln(1)–N(3)
2.279(3)
2.278(3)
1.9662(2)
2.2730(2)
2.423(2)
2.375(2)
97.80(1)
155.55(7)
75.85(7)
2.443(4)
2.452(4)
2.099(2)
2.401(3)
2.540(3)
2.578(3)
99.22(1)
151.79(9)
71.44(9)
2.388(4)
2.391(4)
2.067(3)
2.353(3)
2.472(4)
2.535(4)
99.23(2)
152.85(1)
72.60(1)
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Heteroscorpionate Rare-Earth Metal Dialkyl Complexes
mal range reported in the literature,[10] which are slightly its scandium and yttrium analogues 1 and 2 (runs 1–3).
longer than those of Lu–C [2.388(4) and 2.391(4) Å] and When the temperature decreased to 0 °C a higher conver-
Lu–N [2.472(4) and 2.535(4) Å] in 3, but are obviously sion of 92% could be achieved within 15 min. Meanwhile,
longer than those in 1, in good agreement with the ionic the molecular weight increased to 76600 from 31000 at
radii.
25 °C (run 4). However, with a further decrease of the tem-
perature to –20 °C, the catalytic activity clearly dropped,
but with enhanced syndiotacticity of the resultant PMMA
(run 5). Below a temperature of –40 °C, almost no poly-
merization occurred (runs 6, 7). Moreover, bimodal distri-
bution could be observed when the polymerization was car-
ried out at low temperature (runs 5, 7). Meanwhile, the po-
lymerization medium showed also an obvious influence on
the catalytic activity, although this seemed to have no effect
on the regularity of the resultant PMMA. When the poly-
merization was carried out in toluene it showed higher ac-
tivity as compared to that in THF. For instance with com-
plex 3, completeness could be achieved within 0.25 h at
–20 °C, and an up to 95% conversion could be reached even
at –40 °C in 0.25 h. Likewise, polymers with bimodal distri-
bution were obtained at low temperature.
Table 2. Polymerization of methyl methacrylate by complexes 1, 2
and 3.[a]
Figure 3. ORTEP drawing of complex 2 with thermal ellipsoids at
35% probability levels. The hydrogen atoms and the free THF mo-
lecule are omitted for clarity.
[c]
Run Cat Solvent Tp
[°C] [%]
Conv. Tacticity[b]
Mn
PDI[c]
mr
rr
(103)
1
1
2
3
3
3
3
3
3
3
3
thf
thf
thf
thf
thf
thf
thf
tol
tol
tol
25
25
25
0
18.3
49
37.0
43.9
37.2
34.2
31.8
63.0 22.4
56.1 19.6
62.8 31.0
65.8 76.6
1.4
1.3
1.3
1.2
2
3
4
74.5
92
–20 76
–40 no
–40 49
100
–20 100
–40 95
5[d]
6
68.2 299.8/42.3
1.4/1.2
7[d,e]
8
26.9
38
38.5
35.1
73.1 259.3/57.7
62.0 98.0
61.5 336.0/58.2
64.9 916.8/56.3
1.3/1.2
2.0
1.3/1.3
1.4/1.2
0
9[d]
10[d]
[a] Conditions: catalyst: 10 µmol, [MMA]0/[Ln]0 = 500, solvent:
1 mL, time = 15 min. [b] Determined by 1H NMR spectroscopy.
[c] Determined by GPC against polystyrene standards. [d] Bimodal
distribution. [e] Time: 17 h.
It seemed that the two alkyls behaved differently under
low temperature which was responsible for the generation
of bimodal peaks, which we have observed in our previous
report.[4b] Thus, we attempted to obtain a monoalkyl rare-
earth metal complex of the formula L2LnR (L is the hetero-
scorpionate ligand). However, both treating trialkyl yttrium
(or trialkyl lutetium) with 2 equiv. of ligand precursor di-
rectly at low temperature or a stepwise methodology from
complex 2 or 3 with 1 equiv. of ligand precursor proved
unsuccessful. We suggest that a highly spacious environ-
Figure 4. ORTEP drawing of complex 3 with thermal ellipsoids at
35% probability levels. The hydrogen atoms and the free THF mo-
lecule are omitted for clarity.
These dialkyl rare-earth complexes were evaluated as cat- ment is required if a sandwich complex is to form in which
alysts for the polymerization of methyl methacrylate the metal centre will be seven-coordinate or more. In com-
(MMA) and the results are collected in Table 2. All three plex 2 or 3 each metal centre is six-coordinate, which in-
complexes were able to polymerize MMA at room tempera- hibits the formation of a sandwich complex. This assump-
ture and the polymerization reaction was dependent on the tion might be partly supported by Otero’s report where only
metal centre. When polymerization was performed in THF one of the two pyrazole rings could coordinate to the scan-
complex 3 displayed the highest activity as compared with dium or yttrium centre.[12]
Eur. J. Inorg. Chem. 2010, 2861–2866
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Z. Zhang, D. Cui, A. A. Trifonov
FULL PAPER
hexane) was added dropwise to the stirred solution under nitrogen
to yield a white suspension. The mixture was stirred for another
1 h at this temperature, and benzophenone was added (3.64 g,
Conclusions
We have demonstrated the synthesis and characterization
of alkyl rare-earth metal complexes supported by a heteros- 20 mmol). The mixture was warmed up to room temperature and
stirred for an additional 8 h to generate a yellow suspension. White
solids were isolated by suction filtration and washed with a small
amount of THF. Then water and CH2Cl2 were added to form a
suspension. The organic layer was separated and the aqueous layer
was extracted with CH2Cl2 (3ϫ40 mL). The combined organic
solution was dried with anhydrous MgSO4 overnight. Crude prod-
ucts were isolate by suction filtration and removal of CH2Cl2. The
pure products (1.7 g, 44%) were obtained after crystallization from
hot CH2Cl2 solution. 1H NMR (CDCl3, 300 MHz, 25 °C): δ = 7.94
(s, 1 H, OH), 7.29 (m, 4 H, Ph-H), 7.24 (s, 2 H, Ph-H), 7.15 (m, 4
corpionate ligand. The ligand facially coordinated to the
rare-earth metal via O, N, N’ atoms in k3 mode, quite like
a cylopentadienyl ligand. These dialkyl complexes were all
effective catalysts for the polymerization of methyl meth-
acrylate albeit with low specific control on the resulting
polymers and a little higher PDI values compared to living
polymerization. This might be a consequence of the exis-
tence of two alkyl groups bound to the metal centre, both
of which are able to initiate polymerization of MMA. Fur-
ther work will be focused on the design and optimization H, Ph-H), 6.95 (s, 1 H, CH), 5.66 (s, 2 H, Pz-H), 2.01 (s, 12 H,
CH3) ppm.
of the heteroscorpionate ligand to produce PMMA with
high stereoregularity.
Complex 1: In a glovebox 1,1-diphenyl-2,2-bis(3,5-dimethylpyrazol-
yl)ethanol (0.1546 g, 0.4 mmol) in THF (8 mL) was slowly added
to the stirred solution of Sc(CH2SiMe3)3THF2 (0.18 g, 0.4 mmol)
in hexane (10 mL) at –30 °C. The reaction was slowly warmed to
room temperature and stirring was continued for a further 8 h to
form a white suspension. The product was isolated by suction fil-
tration followed by washing with cold THF in 63% yield. Single
crystals suitable for X-ray analysis were obtained by recrystalli-
zation from THF solution at –30 °C for several days. 1H NMR
(400 MHz, C6D6, 25 °C): δ = 7.83 (d, 4 H, o-H-Ar), 7.22 (br., 4 H,
m-H-Ar), 7.04 (t, 2 H, p-H-Ar), 6.59 (s, 1 H, CH), 5.33 (s, 2 H,
CH), 3.77 (s, 4 H, THF), 2.20 (s, 6 H, CH3), 1.64 (s, 6 H, CH3),
1.39 (s, 4 H, THF), 0.65 [s, 18 H, Si(CH3)3], 0.16 (s, 4 H, Si-
CH2) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ = 150.3, 147.2,
140.4 (C3,3Ј and C5,5Ј), 127.9, 127.6, 127.4 (Ph), 106.6 (C4,4Ј), 72.7
(THF), 69.4 (CH), 32.0 [ScCH2Si(CH3)3], 26.1 (THF), 15.1
(Me3,3Ј), 11.5 (Me5,5Ј), 5.4 [ScCH2Si(CH3)3] ppm.
Experimental Section
General: All reactions were carried out under a dry and oxygen-free
argon atmosphere using Schlenk techniques or under a nitrogen
atmosphere in a glovebox. Solvents such as n-hexane, toluene were
purified by an MBraun SPS system. THF was dried by distillation
over sodium potassium alloy with benzophenone as indicator un-
der a nitrogen atmosphere and was stored over freshly cut sodium
in a glovebox. 3,5-Dimethylpyrazole was purchased and purified
by recrystallization from hot cyclohexane prior to use. Benzophen-
one was purified by recrystallization from hot ethanol followed by
drying over anhydrous MgSO4 in CH2Cl2. CH2Cl2, anhydrous
K2CO3 and nBu4NBr were used as received. Bis(3,5-dimethylpyr-
azolyl)methane and 1,1-diphenyl-2,2-bis(3,5-dimethylpyrazolyl)-
ethanol were synthesized according to modified literature pro-
Complex 2: Following the same protocol as that for preparation of
complex 1, complex 2 was isolated as a white solid (0.228 g) in 72%
yield by treatment of Y(CH2SiMe3)3THF2 (0.2 g, 0.4 mmol)
with 1,1-diphenyl-2,2-bis(3,5-dimethylpyrazolyl)ethanol (0.1546 g,
0.4 mmol). Single crystals suitable for X-ray analysis were isolated
1
cedures and structurally characterized by the H NMR technique.
The synthesis of rare-earth metal tris(alkyl)s followed the estab-
lished method with a little modification.[13] The molecular weight
and molecular weight distribution of the polymers were measured
by the TOSOH HLC 8220 GPC at 40 °C using THF as eluent
against polystyrene standards. Organometallic samples for NMR
spectroscopic measurements were prepared in a glovebox by use of
NMR tubes and then sealed by paraffin film. 1H, 13C NMR spectra
1
from THF solution at –30 °C. H NMR (400 MHz, C6D6, 25 °C):
δ = 7.86 (d, 4 H, o-H-Ar), 7.23 (br., 4 H, m-H-Ar), 7.05 (t, 2 H, p-
H-Ar), 6.60 (s, 1 H, CH), 5.33 (s, 2 H, CH), 3.66 (br., 8 H, THF),
2.14 (s, 6 H, CH3), 1.61 (s, 6 H, CH3), 1.47 (br., 8 H, THF), 0.70
[s, 18 H, Si(CH3)3], –0.22 (s, 4 H, Si-CH2) ppm. 13C NMR
(100 MHz, C6D6, 25 °C): δ = 151.5, 141.2, 141.0 (C3,3Ј and C5,5Ј),
127.9, 127.5, 127.4, 126.1 (Ph), 106.7, 106.4 (C4,4Ј), 73.8 (THF),
73.2 (THF), 69.0 (CH), 28.3 [YCH2Si(CH3)3], 28.1 [YCH2Si-
(CH3)3], 27.9 (THF), 26.1 (THF), 14.8 (Me3,3Ј), 11.5 (Me5,5Ј), 5.6
[YCH2Si(CH3)3], 5.5 [YCH2Si(CH3)3] ppm.
1
were recorded with a Bruker AV400 (FT, 400 MHz for H NMR;
100 MHz for 13C NMR) spectrometer.
Bis(3,5-dimethylpyrazolyl)methane: 3,5-Dimethylpyrazole (6 g,
62 mmol), nBu4NBr (1.54 g, 4.8 mmol), KOH (5.4 g, 96 mmol), an-
hydrous K2CO3 (13.2 g, 95.5 mmol) and CH2Cl2 (150 mL) were
charged into a three-neck round-bottom flask filled with nitrogen
in advance. The reactants were stirred vigorously and heated at
reflux for 1 d. When the reaction mixture was cooled to room tem-
perature, a colourless dichloromethane solution was obtained by
suction filtration. The residue was extracted with CHCl3
(3ϫ50 mL) and the extractant was combined with the previous
dichloromethane solution. Then the organic solvents were removed
by rotary evaporation to afford white solids. The pure products
(2.87 g, 73% yield) were isolated as white solids by recrystallization
Complex 3: By using the same protocol complex 3 was synthesized
in 66% yield as a white solid from the reaction between 1,1-di-
phenyl-2,2-bis(3,5-dimethylpyrazolyl)ethanol (0.1546 g, 0.4 mmol)
and Lu(CH2SiMe3)3THF2 (0.232 g, 0.4 mmol). Single crystals suit-
able for X-ray analysis were isolated from mixed THF/hexane solu-
1
tion at –30 °C. H NMR (400 MHz, C6D6, 25 °C): δ = 7.88 (d, 4
H, o-H-Ar), 7.23 (br., 4 H, m-H-Ar), 7.07 (t, 2 H, p-H-Ar), 6.59 (s,
1 H, CH), 5.34 (s, 2 H, CH), 3.65 (br., 16 H, THF), 2.14 (s, 6 H,
CH3), 1.62 (s, 6 H, CH3), 1.48 (br., 16 H, THF), 0.70 [s, 18 H,
Si(CH3)3], –0.37 (s, 4 H, Si-CH2) ppm. 13C NMR (100 MHz, C6D6,
25 °C): δ = 150.0, 146.9, 140.4 (C3,3Ј and C5,5Ј), 127.8, 127.6, 127.5,
126.9 (Ph), 106.8 (C4,4Ј), 73.8 (THF), 67.8 (CH), 33.5 [LuCH2Si-
(CH3)3], 31.9 [LuCH2Si(CH3)3], 25.7 (THF), 23.0 (THF), 14.3
(Me3,3Ј), 11.0 (Me5,5Ј), 5.2 [LuCH2Si(CH3)3], 5.1 [LuCH2Si-
(CH3)3] ppm.
1
from hot n-hexane solution. H NMR (CDCl3, 300 MHz, 25 °C):
δ = 6.15 (s, 2 H, Pz-H), 5.80 (s, 2 H, CH2), 2.43 (s, 6 H, CH3), 2.19
(s, 6 H, CH3) ppm.
1,1-Diphenyl-2,2-bis(3,5-dimethylpyrazolyl)ethanol: Bis(3,5-dimeth-
ylpyrazolyl)methane (4.08 g, 20 mmol) was dissolved in dry THF
(100 mL) and then transferred to an ampoule (200 mL). When it
was cooled to –80 °C an equimolar amount of nBuLi (20 mmol, in
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Heteroscorpionate Rare-Earth Metal Dialkyl Complexes
Crystal Structure Determination (Table 3): Crystals for X-ray analy-
sis were obtained as described in the Exp. Section. Data collection
was performed at –86.5 °C with a Bruker SMART APEX dif-
fractometer with a CCD area detector, using graphite-monochro-
mated Mo-Kr radiation (λ = 0.71073 Å). The determination of
crystal class and 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 the SHELXTL program. Refine-
ment was performed on F2 anisotropically for all non-hydrogen
atoms by the full-matrix least-squares method. The hydrogen atoms
were placed at the calculated positions and were included in the
structure calculation without further refinement of the parameters.
Ministry of Science and Technology of China for project numbers
2005CB623802 and 2009AA03Z501.
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1·THF2
2·THF
3·THF
Formula
Fw
T [K]
C44H71N4O4Si2Sc C40H63N4O3Si2Y C40H63LuN4O3Si2
821.19
185(2)
0.71073
793.03
185(2)
0.71073
monoclinic
C2/c
39.924(5)
11.9231(1)
20.819(2)
90
119.058(2)
90
8663.0(2)
8
879.09
185(2)
0.71073
monoclinic
C2/c
39.9625(1)
11.8662(4)
20.7896(7)
90
119.1800(1)
90
8607.4(5)
8
Wavelength
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Crystal system triclinic
¯
Space group
a [Å]
b [Å]
c [Å]
α [°]
P1
9.2843(6)
13.4158(9)
19.9517(1)
99.8860(1)
97.6680(1)
101.4970(1)
2362.6(3)
2
β [°]
γ [°]
V [Å3]
Z
Dc [Mg/m3]
µ [mm–1]
F(000)
Reflections
collected
Rint
1.154
0.249
888
1.216
1.440
3376
1.357
2.388
3632
13400
9108 (0.0170)
52.08
23781
8520 (0.0580)
52.10
23531
8538 (0.0333)
52.22
2θmax [°]
GOF
R1
wR2
R1 (all data)
1.033
0.999
1.049
0.0564
0.1375
0.0707
0.0535
0.1188
0.0955
0.1365
0.0368
0.0892
0.0486
0.0970
wR2 (all data) 0.1488
CCDC-767818 (for 1), -767819 (for 2) and -767820 (for 3) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Typical Procedure for Polymerization of Methyl Methacrylate: Cat-
alyst 1 (6.8 mg, 10 µmol) was dissolved in THF (1 mL) in a
glovebox. Methyl methacrylate (0.5 g, 0.5 mmol) was added drop-
wise under vigorous agitation at room temperature. After a desig-
nated time the polymerization was quenched with alcohol contain-
ing 10% HCl. The afforded polymer was precipitated from a large
amount of alcohol and dried under vacuum to constant weight. Its
tacticity was determined by H NMR spectroscopy in CDCl3 and
the number-average molecular weight was determined by GPC
against polystyrene standards.
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1
Acknowledgments
We give thanks for financial support to The National Natural Sci-
ence Foundation of China for project no. 20934006 and to The
Eur. J. Inorg. Chem. 2010, 2861–2866
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2865

Z. Zhang, D. Cui, A. A. Trifonov
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Received: February 1, 2010
Published Online: April 13, 2010
2866
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Eur. J. Inorg. Chem. 2010, 2861–2866