Synthesis of heterocyclic-fused cyclopentadienyl scandium complexes and the catalysis for copolymerization of ethylene and dicyclopentadiene

Article abstract of DOI:10.1021/om500992v

Heterocyclic-fused cyclopentadienyl scandium bis(alkyl) complexes L^1-4Sc(CH₂SiMe₃)₂THF ((5-Me-1-Ph-cyclopenta[b]pyrrol-4-yl)Sc(CH₂SiMe₃)₂THF (1), (2,5-Me₂-3-Ph-6H-cycl

Full text of DOI:10.1021/om500992v

Article
pubs.acs.org/Organometallics
Synthesis of Heterocyclic-Fused Cyclopentadienyl Scandium
Complexes and the Catalysis for Copolymerization of Ethylene and
Dicyclopentadiene
Runhai Chen,†,‡ Changguang Yao,†,∥ Meiyan Wang,§ Hongyan Xie,†,∥ Chunji Wu,*,† and Dongmei Cui*,†
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, People’s Republic of China
‡School of Chemical Engineering, Shandong University of Technology, Zibo 255049, People’s Republic of China
§Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun
130022, China
∥University of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, People’s Republic of China
S
* Supporting Information
ABSTRACT: Heterocyclic-fused cyclopentadienyl scandium bis(alkyl) complexes L1−4Sc(CH2SiMe3)2THF ((5-Me-1-Ph-
cyclopenta[b]pyrrol-4-yl)Sc(CH2SiMe3)2THF (1), (2,5-Me2-3-Ph-6H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF (2),
(2,4,5,6-Me4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF (3), (2,3,4,5,6-Me5-4H-cyclopenta[b]thiophenyl)Sc-
(CH2SiMe3)2THF) (4)) were facilely synthesized by alkane elimination reaction of Sc(CH2SiMe3)31(THF)2 with the
heterocyclic-fused cyclopentadienyl ligands HL1−4 in high yields. Complexes 1−4 were characterized by H and 13C NMR
spectroscopies and X-ray diffraction analyses as THF-solvated monomers, adopting a half-sandwich geometry. Upon activation of
[Ph3C][B(C6F5)4]/AliBu3, these half-sandwich scandium complexes displayed various activities toward the copolymerization of
ethylene (E) and dicyclopentadiene (DCPD). Complex 1, supported by the phenyl-substituted pyrrole-fused cyclopentadienyl
ligand, showed a slightly higher activity than the phenyl-substituted thiophene-fused cyclopentadienyl complex 2. Among the
thiophene-fused cyclopentadienyl complexes 2−4, 4, bearing pentamethyl substituents, showed the highest activity of 2.9 × 106
g/molSc·h·bar. The resultant copolymers had adjustable DCPD incorporation varying from 14.0 up to 46.1 mol %, of which the
alternating poly(E-alt-DCPD) had a high Tg of 166 °C. In addition, no cross-linking was observed in the copolymers, suggesting
that these catalytic systems were highly regioselective for the two active double bonds within DCPD.
glass transition temperature, excellent transparency, large
refractive index, and low birefringence.2 Among COCs,
poly(E-co-NB)s have been deeply investigated. High NB
incorporation leads to a high glass transition temperature
(Tg) but arouses the detrimental effect of increasing brittleness
of the material.3 Compared to poly(E-co-NB)s, poly(E-co-
DCPD)s are more promising and attractive; they possess
higher Tg’s at the same incorporation of the cyclic olefins
because of the bulkier DCPD, leading to improved mechanical
INTRODUCTION
■
Dicyclopentadiene (DCPD), generated from spontaneous
Diels−Alder reactions of cyclopentadiene, is a major con-
stituent in the C5 stream of naphtha cracking and commercially
available at a low price.1 However, for a long time, the C5
stream has not been used as a chemical source but is
incinerated as an energy source. Meanwhile, the copolymeriza-
tions of ethylene (E) with cyclic olefins such as norbornene
(NB) and DCPD afford typical polymer materials, the cyclic
olefin copolymers (COCs), which have found wide applications
because of their excellent properties such as high chemical
resistance, good UV resistance, low dielectric constant, high
Received: September 30, 2014
© XXXX American Chemical Society
A
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Chart 1. Molecular Structure of Thiophene and Pyrrole-Fused Cyclopentadienes and Scandium Complexes 1−4
performances and avoiding the brittleness problem. In addition,
poly(E-co-DCPD)s bearing reactive double bonds as the side
groups readily allow postpolymerization modification to
functional polymers. Therefore, polymerizations of DCPD
from the C5 stream to afford value-added polymer materials
have attracted the increasing interest of both industry and
academic fields.
sandwich scandium complexes bearing thiophene- and pyrrole-
fused cyclopentadienyl ligands and their catalysis toward the
copolymerization of ethylene and DCPD.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Sc Complexes.
Substituted thiophene- and pyrrole-fused cyclopentadiene
compounds (Chart 1) were synthesized according to previously
reported methods.14b,15b The alkane elimination reaction of
compounds HL1−HL4 with Sc(CH2SiMe3)3(THF)2 at 10 °C
for 1 day gave the bis(alkyl) scandium complexes L1−4Sc-
(CH2SiMe3)2(THF) ((5-Me-1-Ph-4H-cyclopenta[b]pyrrole)-
Sc(CH2SiMe3)2THF (1), (2,5-Me2-3-Ph-6H-cyclopenta[b]-
thiophenyl)Sc(CH2SiMe3)2THF (2), (2,4,5,6-Me4-4H-
cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF (3), (2,3,4,5,6-
Me5-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF (4)) in
high yields (75−95%). All these scandium complexes were fully
characterized by 1H NMR and 13C NMR analyses. The
disappearance of the Cp−CH (around 3.0−3.3 ppm) protons
of the ligands from the reaction mixture indicates the
completeness of the reaction. The methylene protons of the
remaining scandium alkyl moieties Sc−CH2SiMe3 in all
complexes 1−4 appear in the narrow region from −0.2 to
−0.4 ppm, while the silyl methyl Sc−CH2SiMe3 protons give
sharp singlet resonances at the downfield region from 0.2 to 0.3
ppm. It is interesting to note that substituents on cyclo-
pentadiene can significantly affect rotation of the η5(centroid)−
Sc axis. In complexes 1 and 2, rotation about the η5(centroid)−
Sc axis is so fast that the two CH2SiMe3 auxiliary ligands are
equivalent. However, the two methylene protons on a
CH2SiMe3 are diastereotopic and appear at −0.27/−0.37 and
−0.21/−0.26 ppm for 1 and 2, consequently exhibiting an AB
spin pattern, because of planar chirality of the attached η5-ring.
In complex 4, the rotation about the η5(centroid)−Sc axis is
restricted because of the presence of many methyl groups and
the two CH2SiMe3 are not equivalent. Therefore, two
methylene signals are separately observed at −0.25/−0.38
and −0.23 ppm, and one of these exhibits an AB spin pattern,
while the other is a singlet (Figures S5 and S6). In complex 3,
the rotation is slow, generating broad methylene signals
between the pattern observed for complex 2 and that observed
for complex 4. The 13C NMR spectra analyses further
confirmed the above 1H NMR analyses. The methylene
carbons of Sc−CH2SiMe3 in complexes 1−3 show one
resonance around 41 ppm, while complex 4 exhibits two
signals at 41.14 and 39.68 ppm, and all the signals of the SiMe3
fragments appear around 4 ppm.
The copolymerization of ethylene and DCPD was originally
achieved in 1999 by Shino with zirconocene catalysts such as
Cp2ZrCl2, rac-Et(Ind)2ZrCl2, Ph2C(Cp)(Flu)ZrCl2, and rac-
Et(Ind)2ZrCl2) under the activation of MAO, whereas the
incorporation of DCPD within the copolymer is low (13 mol
%), leading to low Tg (43.6 °C).4a Thereafter, research has been
focused on catalyst systems based on group 4 transition metal
precursors to improve the catalyst performances.4,5 The half-
sandwich Ti-based catalysts such as (t-BuNSiMe2CpMe4)TiCl2
were investigated, which unfortunately showed low selectivity
to the two double bonds of DCPD to give cross-linking
products.4c,d Breakthrough work was attributed by Hou et al.,
who used (C5Me4SiMe3)Sc(CH2SiMe3)2(THF)/[Ph3C][B-
(C6F5)4] to obtain the copolymer possessing a high Tg (125
°C) and high DCPD incorporation of up to 45 mol %.6
Recently, Li reported a similar copolymer with a 48 mol %
DCPD content prepared by using a non-cyclopentadienyl
bis(β-enaminoketonato) titanium complex combined with
MMAO.5a To date, (C5Me4SiMe3)Sc(CH2SiMe3)2(THF)/
[Ph3C][B(C6F5)4] is still the only rare-earth metal catalyst
system capable of catalyzing the copolymerization of ethylene
and DCPD. Hence, developing novel catalysts for copoly-
merization of ethylene and DCPC, in particular those based on
rare-earth elements, to access COCs with a higher Tg is a
challenging subject.7
Monocyclopentadienyl (Cp) half-sandwich rare-earth metal
complexes have attracted growing interest. Upon activation
with organoborate or AlR3, they generate cationic (or
pseudocationic) derivatives that have shown high activities for
the homo- and copolymerization of alkenes and styrene.8−11
The effects of substituents12a,c,f−h and the types of hetero-
atoms12b,d,e and the amino or ether functional side arms8a on
the stability of the active metal centers and their catalytic
performances have also been deeply investigated. The
heterocyclic-fused cyclopentadienyl ligands have not been
employed in constructing rare-earth metal catalysts as far as
we know, although heterocyclic-fused cyclopentadienyl ligated
Ti or Zr complexes have exhibited enhanced activity for alkene
polymerization due to the strong electron-donating nature of
the heteroatom-fused cyclopentadienyl rings.13,14 Herein, we
reported the synthesis and characterization of the first half-
B
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The molecular structures of complexes 1, 2, and 3 were
further confirmed by X-ray diffraction analyses. The crystallo-
graphic data are summarized in Table S1 (see Supporting
Information). The ORTEP drawings of their molecular
structures together with the data of the selected bond lengths
and angles are shown in Figures 1−3. All complexes exhibit the
Figure 3. Molecular structure of complex 3 with 35% probability
thermal ellipsoids; hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Sc(1)−O(1) 2.160(4), Sc(1)−
C(5) 2.219(6), Sc(1)−C(1) 2.225(6), O(1)−Sc(1)−C5 95.1(2),
O(1)−Sc(1)−C(1) 105.3(2), C(5)−Sc(1)−C(1) 105.9(3), Cpcent−Sc
2.202, Cpcent−Sc(1)−O(1) 112.89, Cpcent−Sc(1)−C(1) 114.94,
Cpcent−Sc(1)−C(5) 120.16.
Figure 1. Molecular structure of complex 1 with 35% probability
thermal ellipsoids; hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Sc(1)−O(1) 2.164(2), Sc(1)−
C(1) 2.211(4), Sc(1)−C(5) 2.223(4), O(1)−Sc(1)−C(1) 96.48(12),
O(1)−Sc(1)−C(5) 97.69(13), C(1)−Sc(1)−C(5) 109.32(15),
Cpcent−Sc(1) 2.204, Cpcent−Sc(1)−O(1) 115.45, Cpcent−Sc(1)−
C(5) 121.22, Cpcent−Sc(1)−C(1) 113.15.
2 are out of the Cp plane relative to those methyl groups, which
might arouse steric hindrance for the bulky DCPD monomer
coordination to the active metal center, resulting in reduced
DCPD incorporation in the copolymer (vide infra).
Copolymerization of Ethylene and Dicyclopenta-
diene. As expected, all catalytic systems based on Sc precursors
1−4 were low active for the homopolymerization of DCPD to
give trace amounts of products (Table 1, entry 1). Meanwhile
they could polymerize ethylene to produce low-molecular-
weight linear products with moderate activities (Tm = 130 °C)
(Table 1, entries 2−5).
To our delight, the copolymerizations of ethylene and DCPD
with these catalysts (Scheme 1) under the same polymerization
conditions showed much higher activities than both homo-
polymerizations, consistent with the previously reported
“comonomer effect” (entries 7, 10−12),17 which was partly
attributed to the coordination of the cyclic DCPD comonomer
to the polyethylene active species, reducing the transition-state
energy rather than that of the ethylene monomer.17e Molecular
weight distributions (Mw/Mn) of the obtained copolymers
appeared as monomodals in GPC traces ranging from 1.41 to
2.05, indicating the single-site nature of the active species and
that the polymerization products are true copolymers not
mixtures of the homopolymers.
The type of heterocyclic ring slightly affected the catalytic
activity. Complex 1, bearing the pyrrole-fused cyclopentadienyl
ligand (L1), exhibited a higher activity (2.8 × 106 g/molSc·h·
bar) than complex 2 (1.4 × 106 g/molSc·h·bar), supported by
the thiophene-fused cyclopentadienyl ligand (L2), which is
consistent with the energy levels of HOMOs (highest occupied
molecular orbitals) of −0.46 eV for L2 and −0.34 eV for L1
calculated by DFT (see Supporting Information). For the
thiophene-fused cyclopentadienyl complexes, an increasing
copolymerization activity from 1.4 × 106 g/molSc·h·bar for 2
and 2.2 × 106 g/molSc·h·bar for 3 to 2.9 × 106 g/molSc·h·bar for
Figure 2. Molecular structure of complex 2 with 35% probability
thermal ellipsoids; hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Sc(1)−O(1) 2.141(3), Sc(1)−
C(1) 2.210(4), Sc(1)−C(5) 2.222(4), O(1)−Sc(1)−C(1) 97.41(12),
O(1)−Sc(1)−C(5) 97.64(14), C(1)−Sc(1)−C(5) 110.01(17),
Cpcent−Sc(1) 2.210, Cpcent−Sc(1)−O(1) 112.71, Cpcent−Sc(1)−
C(5) 117.74, Cpcent−Sc(1)−C(1) 117.72.
same geometry model in which the central metal Sc3+ is
coordinated by one η5-Cp ring and two alkyl groups and a THF
molecule, adopting a pseudotetrahedral geometry in a typical
three-legged piano-stool configuration. The heterocyclic-fused
cyclopentadienyl ligands hardly influence the interaction
between Sc metal and Cp, and the distances from Sc3+ to the
Cp center in the three complexes are around 2.20 Å,
comparable to those in cyclopentadienyl ligated Sc complexes
(2.177−2.189 Å).16 However, the phenyl substituents in 1 and
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in copolymer is also affected by catalyst structure. Complexes 3
and 4 afforded the copolymers with higher comonomer
incorporation (38.0 mol % for 3 and 37.8 mol % for 4)
relative to 1 (27.7 mol %) and 2 (29.1 mol %) under the same
conditions. The enhancement of DCPD incorporation for
catalysts 3 and 4 may be caused by the methyl-substituted
heterocyclic Cp ligands that are planar and provide a more
opened coordination sphere as compared with the phenyl-
substituted heterocyclic Cp ligands, where the phenyl group
deviates from the Cp plane to create a more crowded
environment for the coordination and insertion of the bulky
DCPD monomer (vide supra). A similar observation has been
reported in copolymerization of ethylene and DCPD using
non-cyclopentadienyl titanium catalysts.5e
Besides the structural factors, polymerization conditions also
affected the catalytic performances. It seemed that increasing
the DCPD feed amount from 10 to 20 mmol would arouse
rapid polymerization for both complexes 1 and 4 (Table 1,
entries 6−9 vs entries 12−15), whereas the activity remained
unchanged with further loading of DCPD. In contrast, the
content of DCPD in the copolymer continuously increased
despite the ligand frameworks, which reached up to 34.2 mol %
and 46.1 mol % when 60 mmol of DCPD was added into 1 and
4 catalytic systems, respectively. At elevated temperatures, the
catalytic activity decreased while the incorporation of DCPD in
copolymer increased (entries 16, 17), which might be ascribed
to low ethylene solubility in the reaction media, while the
molecular weight of the copolymer dropped significantly as
chain transfer/termination reactions became active at high
temperature.
Table 1. Copolymerization of Ethylene and DCPD by
a
Complexes 1−4/[Ph3C][B(C6F5)4]/AliBu3
c
d
f DCPD
FDCPD
Mn
M /
wd
T /
g g
b
entry catalyst (mmol) activity (mol %) (kg/mol) Mn
Tm
1
1−4
1
10
0
trace
0.7
0.4
0.8
0.9
2.4
2.8
2.3
2.3
1.4
2.2
2.9
2.2
2.5
2.5
2.2
1.8
100
0
h
2
1.7
3.6
2.42
2.94
2.85
3.10
1.50
1.70
1.90
2.05
1.71
1.67
1.56
1.65
1.51
1.81
1.53
1.70
130
130
130
130
32
h
h
h
3
2
0
0
4
3
0
0
4.2
5
4
0
0
5.0
6
1
10
20
40
60
20
20
20
10
40
60
20
20
14.6
14.0
23.1
27.4
46.6
30.2
14.4
13.7
9.1
7
1
27.7
32.8
34.2
29.1
38.0
37.8
28.0
45.7
46.1
41.5
44.2
86
8
1
111
124
95
9
1
10
11
12
13
14
15
16
17
2
3
112
123
94
4
4
4
24.6
29.8
12.2
7.6
162
166
139
151
4
e
f
4
4
a
Polymerization conditions: 30 mL of toluene, 10 μmol of Sc, 10 μmol
of [Ph3C][B(C6F5)4], 100 μmol of AliBu3, 1 atm of ethylene, 40 °C,
b
c
polymerization time 5 min. In unit of 106 g/molSc·h·bar. Determined
d
1
by H NMR spectroscopy in CDCl3 at 25 °C. Measured by GPC in
THF at 40 °C using the polystyrene standard. Polymerization
temperature 60 °C. Polymerization temperature 80 °C. Determined
by DSC. Melting point for PE.
e
f
g
h
Scheme 1. Copolymerization of Ethylene and
Dicyclopentadiene with Sc Catalysts 1−4
It is found that the NMR spectra of the polymer samples
obtained from the four catalyst systems were similar. In the 1H
NMR spectrum, two double-bond resonances at δ 5.5−5.8 ppm
are clearly observed arising from the cyclopentene units (Figure
S7 in the Supporting Information), indicating that the vinyl-
polymerization reaction of DCPD occurred regioselectively. It
is seen virtually that no broad alkyl group signal at δ 0.6−3.4
ppm and deep valley around δ 1.75 ppm are observed,
suggesting that no continuous DCPD−DCPD units are present
in the copolymer chains.18 This is consistent with the fact that
the present catalyst systems are active for E-DCPD
copolymerization but show very low activity toward DCPD
4 is observed due to the increasing ligand electron-donating
ability of thiophene-fused cyclopentadienyl rings (see Support-
ing Information). Such an electronic effect has also been
observed in the previous reports that the electron-donating
ligands facilitate propylene insertion.14d DCPD incorporation
Figure 4. 13C NMR spectrum of poly(E-alt-DCPD) copolymer (entry 12).
D
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homopolymerization. The resonances at δ 130.7 and 132.7
ppm in the 13C NMR spectrum further prove the DCPD
incorporation into the ethylene chain with the endo-
configuration, as shown in Figure 4.19 In addition, the peak
methyl groups on the heterocyclic rings is crucial to establish an
effective catalyst system having high activity (2.9 × 106 g/molSc·
h·bar) and a high comonomer insertion ratio (45.7 mol %).
Therefore, the alternating poly(E-alt-DCPD) copolymer with a
high Tg of 166 °C can be achieved under high DCPD feeding.
We present here a strategy for designing new half-sandwich
rare-earth metal catalysts by modification of the Cp ring with
heterocyclic fusion, and the resultant catalytic precursors may
be used in a broad spectrum of applications in the catalytic
polymerizations.
1
at δ 1.3 ppm in the H NMR and a strong resonance at δ 30
ppm in the 13C NMR spectrum of the copolymer were assigned
to the continuous ethylene units.18 On the basis of the above
NMR spectroscopy analysis, it can be safely concluded that the
obtained poly(E-co-DCPD) comprises discrete DCPD units
separated by polyethylene units. Therefore, when the DCPD
content in the copolymer was close to 50 mol % (46.1 mol %),
the alternating microstructure was formed.
EXPERIMENTAL SECTION
■
All the copolymer products are amorphous without melting
temperature, and glass transition temperature (Tg) values fall in
the range 86−166 °C (Figure 5). The higher the incorporation
General Methods. All reactions were carried out under a dry and
oxygen-free argon atmosphere by using Schlenk techniques or under a
nitrogen atmosphere in an MBraun glovebox. All solvents were
purified with an MBraun SPS system. DCPD used for the
polymerization reaction was purchased from Aldrich and purified
over a Na/K alloy. AliBu3 (1.0 M in hexane) and LiCH2SiMe3 solution
(1.0 M in pentane) were purchased from Aldrich. Polymerization
grade ethylene was donated by the China Petroleum & Chemical
Corporation. Sc(CH2SiMe3)3(THF)2 was prepared according to the
literature.20 [Ph3C][B(C6F5)4] was synthesized following the literature
procedure.21 Organometallic samples for NMR spectroscopic measure-
ments were prepared in the glovebox by use of NMR tubes sealed by
1
paraffin film. H and 13C NMR spectra were recorded on a Bruker
AV400 (FT, 400 MHz for 1H; 100 MHz for 13C) spectrometer.
1
Variable-temperature H NMR spectra of complex 4 in C7D8 were
performed on a Bruker AV400 over a temperature range from −60 to
50 °C. Elemental analyses were performed at the National Analytical
Research Centre of Changchun Institute of Applied Chemistry
(CIAC). The molecular weight and molecular weight distribution of
the polymers were measured by a TOSOH HLC-8220 GPC.
Differential scanning calorimetry (DSC) analyses were carried out
on a Q 100 DSC from TA Instruments under a nitrogen atmosphere
at heating and cooling rates of 10 °C/min.
Figure 5. DSC curves of the poly(E-alt-DCPD)s with various DCPD
incorporations.
X-ray Crystallographic Studies. Crystals for X-ray analysis were
obtained by recrystallization in hexane at low temperature. The crystals
were manipulated in a glovebox. Data collections were performed at
−88.5 °C on a Bruker SMART APEX diffractometer with a CCD area
detector, using graphite-monochromated Mo Kα radiation (λ =
0.710 73 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. Refinement 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. The methyl carbon atoms (C2, C3, C4, C6, C7, and C8 in
2) of SiMe3 groups were disordered and were refined with 50%
occupancy anisotropically for all the atoms in complex 2.
of DCPD in the copolymers, the higher the Tg of the resulting
copolymer. The highest Tg of 166 °C was observed from the
sample with the 46.1 mol % DCPD content, which is
comparable to the value reported in a patent but much higher
than those found in the poly(E-alt-DCPD) isolated from the
catalyst system composed of the half-sandwich scandium
complex bearing a SiMe3-substituted cyclopentadienyl ligand
(125 °C).6 The high Tg value of the obtained poly(E-alt-
DCPD) could be mainly attributed to the stereostructures (the
high tacticity) of the copolymer; however, a quantitative
assignment of the tacticity of the copolymer is difficult. With
respect to the previous work on copolymerization of ethylene
and DCPD catalyzed by a silylmethyl-substituted Cp-supported
scandium system,6 we demonstrated in this work that by
designing new rare-earth metal catalysts bearing modified
heterocyclic-fused Cp rings, the competitive high catalytic
activity and DCPD incorporation in the copolymer could be
realized and, particularly, the more a stereoregular alternating
structure in the poly(E-co-DCPD) might be generated; thus the
poly(E-alt-DCPD) with higher Tg even at the same DCPD
incorporation can be obtained.
Synthesis of Complexes. Complex 1. Under a nitrogen
atmosphere, to a hexane solution (10 mL) of Sc(CH2SiMe3)3(THF)2
(0.90 g, 2.0 mmol) was added slowly at room temperature 1 equiv of
HL1 (0.39 g, 2.0 mmol). The mixture was stirred overnight to afford a
yellow solution. Removal of solvent gave the yellow solid, and the
analytically pure compound was obtained through recrystallization in
1
hexane at −30 °C in 95% (0.92 g) yield. H NMR (400 MHz, C6D6,
25 °C): δ 7.28 (d, J = 8.4 Hz, 2H, Ph-H), 7.14 (t, J = 8.8 Hz, 2H, Ph-
H), 6.92 (d, J = 3.2 Hz, 1H, pyrrole-H), 6.87 (t, J = 7.6 Hz, 1H, Ph-H),
6.20 (d, J = 3.2 Hz, 1H, pyrrole-H), 6.12 (s, 1H, Cp-H), 6.04 (s, 1H,
Cp-H), 3.47 (br s, 4H, THF), 2.44 (s, 3H, CH3), 1.11 (br s, 4H,
CONCLUSIONS
■
In summary, we have successfully synthesized and characterized
new half-sandwich scandium complexes 1−4 bearing pyrrole-
and thiophene-fused cyclopentadienyl rings to achieve the
controlled and regioselective copolymerization of ethylene and
dicyclopentadiene by giving linear products. Introduction of
2
THF), 0.30 (s, 18H, CH2SiMe3), −0.27 and −0.37 (AB, JH−H = 11.2
Hz, 4H, ScCH2SiMe3) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ
141.30, 131.69, 129.75, 126.06, 124.81, 123.38, 122.47, 117.80, 102.31,
95.21, 90.63, 71.31 (s, THF), 40.54 (1C, Sc-CH2SiMe3), 24.79 (s,
THF), 16.74, 4.15 (s, 3C, CH2SiMe3) ppm. Anal. Calcd for
E
DOI: 10.1021/om500992v
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
C26H41NOScSi2 (%): C, 64.42; H, 8.53; N, 2.89. Found: C, 64.68; H,
8.52; N, 3.04.
AUTHOR INFORMATION
■
Corresponding Authors
*(C. Wu) E-mail: wuchunji@ciac.ac.cn.
*(D. Cui) Fax: +86-431-85262774. E-mail: dmcui@ciac.ac.cn.
Complex 2. Under a nitrogen atmosphere, to a hexane solution (10
mL) of Sc(CH2SiMe3)3(THF)2 (0.90 g, 2.0 mmol) was added slowly
at room temperature 1 equiv of HL2 (0.45 g, 2.0 mmol). The mixture
was stirred 1 day to afford a light yellow solution. Removal of solvent
gave a light yellow solid, and analytically pure compound was obtained
through recrystallization in hexane at −30 °C (0.81 g, 78%). 1H NMR
(400 MHz, C6D6, 25 °C): δ 7.50 (dd, J = 8.0, 1.2 Hz, 2H, Ph-H), 7.26
(td, J = 8.0, 1.6 Hz, 2H, Ph-H), 7.11 (tt, J = 8.0, 1.6 Hz, 1H, Ph-H),
6.32 (d, J = 1.6 Hz, 1H, Cp-H), 6.24 (d, J = 1.6 Hz, 1H, Cp-H), 3.43
(br s, 4H, THF), 2.36 (s, 3H, CH3), 2.25 (s, 3H, CH3), 1.07 (br s, 4H,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by the National Natural
Science Foundation of China for Project Nos. 21104072,
51073148, 21361140371, 21374112, 21104074, and 21304088.
2
THF), 0.28 (s, 18H, CH2SiMe3), −0.21 and −0.26 (AB, JH−H = 12.0
Hz, 4H, ScCH2SiMe3) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ
136.50, 135.38, 135.08, 129.21, 129.06, 128.79, 127.06, 123.13, 101.15,
100.33, 71.64 (s, THF), 41.86 (1C, Sc-CH2SiMe3), 24.82 (s, THF),
16.51, 15.29, 4.04 (s, 3C, CH2SiMe3) ppm. Anal. Calcd for
C27H42OSScSi2 (%): C, 62.87; H, 8.21. Found: C, 62.68; H, 8.52.
Complex 3. The complex was synthesized using the same
conditions and procedure as for complex 2 using HL3. The product
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1
was obtained as a yellow solid in 78% yield. H NMR (400 MHz,
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Complex 4. The complex was synthesized using the same
conditions and procedure as for complex 3 using HL4. The product
was obtained as a pale yellow solid in 85% yield. 1H NMR (400 MHz,
C6D6, 25 °C): δ 3.59 (d, 2H, J = 8.0 Hz, THF), 3.50 (d, 2H, J = 8.0
Hz, THF), 2.41 (s, 3H, CH3), 2.19 (s, 3H, CH3), 2.15 (s, 3H, CH3),
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25 °C): δ 133.31, 130.43, 126.24, 124.77, 121.75, 110.13, 109.28,
71.53 (s, THF), 41.14 (s, CH2SiMe3), 39.68 (s, CH2SiMe3), 24.96 (s,
THF), 13.87, 13.30, 12.95, 12.68, 12.33, 4.34 (s, 3C, CH2SiMe3) ppm.
Anal. Calcd for C24H44OSScSi2 (%): C, 59.83; H, 9.21. Found: C,
60.14; H, 8.95.
Ethylene/DCPD Copolymerization Procedure. A detailed
polymerization procedure is described as a typical example (run 7 in
Table 1). In the glovebox, a Schlenk bottle containing a magnetic
stirring bar was charged with a toluene solution (30 mL) of DCPD
(2.64 g, 20 mmol) and AliBu3 (0.05 mL, 50 μmol, 1.0 M in hexane).
The reactor was equipped with an ampule bottle filled with 2 mL of a
toluene solution of complex 1 (4.9 mg, 10 μmol), AliBu3 (0.05 mL, 50
μmol, 1.0 M in hexane), and [Ph3C][B(C6F5)4] (9.2 mg, 10 μmol).
The reactor was taken out of the glovebox, connected to the Schlenk
line, and set in the thermostated oil bath (40 °C). The solution was
degassed and then saturated with ethylene (1 atm) three times under
vigorous stirring. The solution of the catalyst system was quickly
transferred to the polymerization bottle to initiate the polymerization.
The polymerization was quenched after 5 min by addition of acidified
ethanol (200 mL). The precipitated polymer was filtered and washed
with ethanol and then dried under vacuum at 40 °C for several hours.
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ASSOCIATED CONTENT
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S
* Supporting Information
CIF files, crystal data and structure refinement for Sc complexes
1
1−3, H NMR of Sc complexes 1−4, synthesis and character-
ization of ligands, NMR spectra of representative polymers, and
DFT calculation. This material is available free of charge via the
Internet at http://pubs.acs.org.
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DOI: 10.1021/om500992v
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DOI: 10.1021/om500992v
Organometallics XXXX, XXX, XXX−XXX