Highly 3,4-selective living polymerization of isoprene and copolymerization with ε-Caprolactone by an Amidino N-heterocyclic carbene ligated lutetium bis(alkyl) complex

Article abstract of DOI:10.1021/om400925a

The amidino-modified N-heterocyclic carbene ligated lutetium bis(alkyl) complex 1, (Am-NHC)Lu(CH₂SiMe₃)₂, was synthesized by treatment of (AmH-NHC-H)Br ((2,6-ⁱPrC ₆H₃Ni - C(C₆H

Full text of DOI:10.1021/om400925a

Article
pubs.acs.org/Organometallics
Highly 3,4-Selective Living Polymerization of Isoprene and
Copolymerization with ε‑Caprolactone by an Amidino N‑Heterocyclic
Carbene Ligated Lutetium Bis(alkyl) Complex
Changguang Yao,†,‡ Dongtao Liu,† Ping Li,§ Chunji Wu,† Shihui Li,† Bo Liu,† 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
‡University of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, People’s Republic of China
§Jinzhou City Health School, Beijing Road 4-26, Jinzhou, Liaoning 121001, People’s Republic of China
S
* Supporting Information
ABSTRACT: The amidino-modified N-heterocyclic carbene ligated lutetium bis(alkyl) complex 1, (Am-NHC)Lu(CH2SiMe3)2,
was synthesized by treatment of (AmH-NHC-H)Br ((2,6-iPrC6H3NC(C6H5)NHCH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)-
Br) with ((trimethylsilyl)methyl)lithium (LiCH2SiMe3) and lutetium tris(alkyls) (Lu(CH2SiMe3)3(THF)2) via double-
deprotonation reactions and characterized by NMR spectroscopy and X-ray diffraction analysis. Under activation of an
organoborate, complex 1 exhibited distinguished catalytic performance for the polymerization of isoprene with respect to high
activity, 3,4-regioselectivity (99.3%), and livingness mode. In contrast to the systems reported to date, this system seemed not to
be affected obviously by the polymerization temperature (0−80 °C), solvents, monomer-to-initiator ratios (500−5000), and type
of organoborate. The resultant polymers have high glass-transition temperatures (38−48 °C) and moderate syndiotacticity
(racemic enchainment triad rr 45%, pentad rrrr 20%). In addition, the living lutetium−polyisoprene active species could further
initiate the ring-opening polymerization of ε-caprolactone to give selectively the poly(3,4-isoprene)-b-polycaprolactone block
copolymers with controllable molecular weight (from 4.9 × 104 to 10.2 × 104) and narrow polydispersity.
VCl3−AlR3,13 (C5Me5)Ln(AlMe4)2 (Ln = Y, La, Nd),14
INTRODUCTION
■
quinolyl anilido rare-earth-metal bis(alkyl) precursors and
It is well-known that 3,4-regulated polyisoprene (PIP) is a very
[N(PPh2NPh)2] Ln(CH2SiMe3)2 (Ln = Sc, Y, Lu),15 and
important component of high-performance rubbers because of
its excellent wet-skid resistance and low rolling resistance.1
Unlike its cis-1,4- and trans-1,4-regulated PIP analogues that
can be found in natural rubbers, 3,4-regulated PIP can only be
obtained by artificial synthesis. For the past half a century,
[(S,S)-BOPA]Ln(CH2SiMe3)2 ((S,S)-BOPA = (S,S)-bis-
(oxazolinylphenyl)amido; Ln = Sc, Lu)16 have been invented
to give trans-1,4-selectivity. Except for these achievements, the
number of 3,4-selective catalyst systems has remained very
small, as IP usually prefers to coordinate to a metal center in a
isoprene (IP) polymerizations have attracted extensive research
η4-cis-1,4-mode (two site) under generation of 1,4-config-
interest and made considerable progress. For instance, the
Ziegler−Natta catalyst systems,2,3 f- and d-block element
uration; thus, a 3,4-selectivity means IP coordination to a
sterically bulky active metal center in a η2 single site.17 Up to
now, efficient 3,4-selective systems have been the patented
organolithium and ferric acetylacetate and transition-metal
complexes such as AlEt3-Ti(OR)4, (dmpe)2CrCl2-MAO18
metallocenes,4−6 constrained-geometry-conformation rare-
earth-metal allyl complexes,7 non-Cp (Cp = cyclopentadienyl
and its derivatives) ligated lanthanide alkyl aluminates,8 β-
diketiminates,9 and pincer type10 rare-earth-metal complexes
have been thoroughly investigated to provide cis-1,4-selectivity.
In the meantime, catalyst systems of Ln(allyl)2Cl(MgCl2)2/
AlR3,11 Cp*Nd(BH4)2(THF)2/Mg(nBu)2,12 TiCl4−AlR3 and
Received: September 16, 2013
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of Amidino N-Heterocyclic Carbene Lutetium Bis(alkyl) Complex 1
(dmpe = 1,2-bis(dimethylphosphino)ethane), and ferric
complexes chelated by nitrogen ligands,19 among which few
cases exhibit 3,4-selectivity of over 90%. Only very recently has
significant progress been made in the 3,4-selective polymer-
ization of isoprene by using rare-earth-metal complexes bearing
half-sandwich ligands such as [{Me2Si(C5Me4)(PCy)}-
YCH2SiMe3]220 (Cy = cyclohexyl) and fluorenyl N-heterocyclic
carbene ligated rare-earth-metal precursors,21 and the rare-
earth-metal complexes attached to non-Cp ligands such as the
transesterification that occurs during the second polymerization
stage when ε-CL is present. In addition, the thus obtained
polydiene building blocks have low regiotacticity.30 Therefore,
the design of new catalysts for polymerizing dienes in a
specifically selective living coordination polymerization process
and further initiating the polymerization of polar monomers is
still urgently required and challenging.
Herein, we report that a lutetium bis(alkyl) complex attached
to an amidino-modified N-heterocyclic carbene ligand, upon
activation with organoborate, initiates the living polymerization
of isoprene with high activity, high 3,4-selectivity, and medium
syndioselectivity. The resultant cationic living metal−polydiene
species could further initiate the ring-opening polymerization
(ROP) of the polar monomer ε-CL to selectively provide the
first block copolymer of poly(3,4-IP)-b-poly(ε-CL).
i
NCN-yttrium complex [(PhC(NC6H4 Pr2-2,6)2)Y(o-
CH2C6H4-NMe2)2],22 NPN ligand stabilized rare-earth-metal
bis(alkyls),23 scandium aminopyridinates,24 and cationic rare-
earth-metal alkyl complexes bearing iminoamido ligands,25
some of which showed unprecedented high regio- and
stereoselectivities;20,22 however, few of these systems show
both high 3,4-selectivity and living characteristics.21,25
RESULTS AND DISCUSSION
On the other hand, a great variety of block copolymers have
been used as phase compatibilizers for blending incompatible
polymers.26 To obtain such block copolymers, the most
efficient method is via the copolymerization of polar and
nonpolar monomers; however, this has been retarded, as the
active metal centers facilitating the polymerization of nonpolar
monomers are extremely oxophilic and are easily poisoned by
polar monomers. The stalemate has been broken by the
invention of lanthanidocenes that initiate the block copoly-
merization of simple olefins such as ethylene with MMA (or
cyclic esters).27 Recently, transition-metal-based systems have
been demonstrated to possess high activities and high
incorporation rates of polar monomers.28 Nevertheless, the
copolymerization of conjugated dienes with polar monomers by
using coordination catalysts has been less explored.29 Diblock
copolymers comprising a poly(diene) block and a poly(polar
monomer) block such as poly(ε-caprolactone) (PCL) have
been known for a long time and are usually synthesized by a
standard method involving anionic living diene polymerization
by using alkyllithium in the first stage and sequentially adding
ε-CL in the second stage. However, this method has some
disadvantages, such as chain termination by alkyl cleavage and
■
Synthesis and Characterization of Complex 1. The
N H C - a m i n e h y d r o b r o m i d e c o m p o u n d
(NH2CH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)Br)·HBr was
synthesized from 1-mesitylimidazole and 2-bromoethylamine
hydrobromide according to a literature procedure.31 Sequential
treatment of the NHC-amine hydrobromide with NEt3 and
i
C6H5C(Cl)N(C6H3 Pr2-2,6) gave the amidino-modified imida-
zolium bromide (AmH-NHC-H)Br in high yield (79%)
1
(Scheme 1). The H NMR spectrum of (AmH-NHC-H)Br
exhibited a singlet at δ 10.38 ppm, typical for the ylidene
proton NHC-H. The two discrete triplet resonances at δ 5.13
and 4.28 ppm could be attributed to the ethylene protons.
(AmH-NHC-H)Br was treated with LiCH2SiMe3 to afford the
ethylene-bridged amidino N-heterocyclic carbene AmH-NHC.
AmH-NHC reacted with the lutetium tris(alkyl) (Lu-
(CH2SiMe3)3(THF)2) to give the rare-earth-metal bis(alkyl)
complex (Am-NHC)Lu(CH2SiMe3)2 (1) via alkane elimina-
1
tion. The H NMR spectrum of complex 1 reveals that the
characteristic resonance of the ylidene proton from the ligand
disappears. The methylene protons of LuCH2SiMe3 species are
diastereotopic, appearing as complicated resonances with two
B
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discrete AB spins in the upfield regions: δ −0.62/−0.65 and
−0.82/−0.85. The ylidene carbon gives a characteristic singlet
at δ 199.66 ppm, comparable to δ 199.18 ppm found in the
NHC-containing complex (Flu-NHC)Lu(CH2SiMe3)2,21 sug-
gesting the formation of a linkage between the lutetium ion and
the carbene carbon Lu−C. The molecular structure of complex
1 in the solution state illustrated by X-ray diffraction analysis
was consistent with that in the solid state, as shown in Figure 1.
The Lu3+ ion is bounded by the NNC-tridentate chelating
ligand and two alkyl CH2SiMe3 moieties, generating a twisted-
tetragonal geometry. Complex 1 is free of THF, in contrast to
the THF-solvated benzamidinate complex [PhC(NAr)2]Y-
32
i
(CH2SiMe3)2(THF) (Ar = C6H3 Pr2-2,6), owing to the
strong electron-donating effect of the ylidene carbon. The
Lu(1)−Ccarbene bond length is 2.516(4) Å, comparable to the
corresponding Lu−Ccarbene bond lengths of 2.443(3) and
33
2.431(3) Å in the complexes (Ind-NHC)Lu(CH2SiMe3)2
and (Flu-NHC)Lu(CH2SiMe3)2,21 respectively. The bond
lengths of Lu(1)−N(1) (2.352(3) Å) and Lu(1)−N(2)
(2.516(4) Å) fall in the normal range reported previously.32
Polymerization of Isoprene. Complex 1 alone was inert
to the polymerization of IP and upon activation with
[(Ph3C)][(B(C6F5)4)] showed a high activity to transfer 500
equiv of IP within 30 min at room temperature, which is among
the highest activities reported to date.22,25 The reaction
temperature had some influence on the activity of IP
polymerization. When the polymerization was performed at a
lower temperature (0 °C) while other conditions were kept
similar, the activity of polymerization decreased such that
monomer conversion was only 94% within 120 min. In
contrast, the catalytic activity increased at elevated temperatures
such that a complete conversion occurred in 20 min at 40 °C,
15 min at 60 °C, and 10 min at 80 °C (Table 1, entries 7−10).
In addition, this catalytic system was highly efficient, such that
by increasing stepwise the monomer to catalyst ratio from
500:1 to 5000:1, the polymerization performed readily, albeit
with prolonged polymerization times, and the molecular weight
of the obtained PIP increased correspondingly from 3.69 × 104
to 49.2 × 104 (Table 1, entries 1−6).
Furthermore, the system exhibited distinguished 3,4-
selectivity (98.7%) at room temperature, which improved
slightly to 99.3% at a lower polymerization temperature of 0 °C
and seemed not to be affected obviously at elevated
temperatures up to 80 °C (96.7%) (Table 1, entries 7−10).
Although the types of solvents affected the catalyst activity
significantly, such that a complete conversion of IP took 30 min
by using chlorobenzene as the polymerization media but 120
min in toluene and 240 min for a 90% conversion in 1-hexane,
which had almost no effect on the 3,4-selectivity. It was
Figure 1. Molecular structure of 1 (hydrogen atoms and solvent
molecule are omitted for clarity). Selected bond lengths (Å) and
angles (deg) for complex 1: Lu(1)−N(1) 2.352(3), Lu(1)−N(2)
2.260(4), Lu(1)−C(22) 2.516(4), Lu(1)−C(34) 2.337(5), Lu(1)−
C(38) 2.359(5); N(1)−Lu(1)−N(2) 57.55(12), N(1)−Lu(1)−C(22)
131.42(13), N(1)−Lu(1)−C(34) 100.62(14), N(1)−Lu(1)−C(38)
108.14(15), N(2)−Lu(1)−C(22) 74.25(14), N(2)−Lu(1)−C(34)
123.89(16), N(2)−Lu(1)−C(38) 122.15(16), C(22)−Lu(1)−C(34)
101.22(15), C(22)−Lu(1)−C(38) 101.84(16), C(34)−Lu(1)−C(38)
113.59(16), C(19)−N(1)−Lu(1) 92.3(2), C(19)−N(2)−Lu(1)
96.7(3).
a
Table 1. Polymerization of Isoprene using Lutetium Complex 1 under Various Conditions
b
c
d
d
e
entry
[IP]/[Lu]
temp (°C)
time (min)
yield (%)
3,4
Mn,calcd × 10−4
Mn,measd × 10−4
Mw/Mn
Tg (°C)
1
2
3
4
5
6
7
8
9
10
500
1000
2000
3000
4000
5000
500
25
25
25
25
25
25
0
30
60
>99
>99
>99
>99
>99
>99
94
98.7
98.7
98.2
98.2
98.1
98.1
99.3
97.9
97.7
96.7
98.7
98.7
98.7
98.7
3.41
6.81
13.6
20.4
27.2
34.1
3.21
3.41
3.41
3.41
3.41
3.01
3.41
3.41
3.69
9.63
24.1
35.4
42.7
49.2
3.95
3.85
4.02
3.74
3.79
4.63
4.73
5.76
1.03
1.04
1.07
1.07
1.08
1.09
1.03
1.03
1.03
1.06
1.04
1.06
1.09
1.04
45
45
46
43
47
42
48
43
40
38
39
39
39
39
120
180
240
300
120
20
500
40
60
80
25
25
25
25
>99
>99
>99
>99
90
500
15
500
10
f
11
500
120
240
30
g
12
500
h
13
500
>99
>99
i
14
500
30
a
b
1
Conditions: 1 10 μmol, [Ph3C][B(C6F5)4] 10 μmol, chlorobenzene 5 mL. Determined by H NMR and 13C NMR spectroscopy in CDCl3.
c
d
e
f
Calculated by ([IP]/[Ln]) × 68.12 × yield. Determined by GPC in THF at 40 °C against polystyrene standard. Measured by DSC. Toluene as
g
h
i
the solvent. Hexane as the solvent. [PhNHMe2][B(C6F5)4] as the activator. B(C6F5)3 as the activator.
C
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Figure 2. 13C NMR (CDCl3) spectrum of 3,4-polyisoprene (99.3%; Table 1, entry 7).
noteworthy was that no matter what kind of organoborate
([(Ph3C)(B(C6F5)4)], [(PhNHMe2)(B(C6F5)4)], or B(C6F5)3)
was used as the activator, the activity and selectivity of the IP
polymerization were always unchanged. The 13C NMR
spectrum revealed that the obtained PIP has medium 3,4-
stereotacticity by giving the syndiotactic triad rr (45%) from δ
146.0 to 146.7 ppm and pentad rrrr (20%) at δ 146.7 ppm,
respectively, while the signals between δ 147.0 and 148.3 ppm
arise from the atactic 3,4-IP sequences and the weak resonance
at δ 148.5 ppm is attributed to the isotactic triad mm (Figure
2). Such a microstructure endows the product high Tg (48 °C),
as evidenced by DSC analysis (Figure S13, Supporting
Information).
The kinetics study demonstrated that the conversion
Figure 3. Polymerization of IP with 1/[(Ph3C)(B(C6F5)4)]: molecular
weight vs conversion ([Lu]0 = 2.0 μmol/mL, [IP]/[Lu] = 500,
chlorobenzene, 25 °C).
increased with polymerization time, and the number-average
molecular weight (Mn) of the resulting polymer increased
linearly with the conversion while the molecular weight
distribution (Mw/Mn) remained almost unchanged (1.03−
1.07), indicating that this binary system 1/[(Ph3C)(B(C6F5)4)]
was among the few catalyst systems to date showing livingness
characteristics for 3,4-selective polymerization of IP (Figure
3).21,25
are attributed to the repeating units (−CO−(CH2)5−O−),
while the weak signals at δ 173.73, 34.27, 24.75, 25.37, 28.55,
and 62.56 ppm are derived from the terminal units (−CO−
(CH2)5−OH). A signal at δ 219.13 ppm is assignable to the
ketone carbonyl connecting with the PIP sequence, −CH2−
CH[C(CH3)CH2]−CO−(CH2)5−O−, the joint linkage of
the two blocks, indicating that the resultant polymers are
diblock copolymers (Figure S15, Supporting Information). The
molecular weights of the resultant PIP-b-PCL copolymers
increased proportionately with the monomer to Lu ratios, the
molecular weight distribution remained narrow and unimodal
(Figure 5), and the contents of the two blocks calculated by
their integral intensities in the 1H NMR spectrum were
consistent with their loadings, which meant that the catalytic
efficiency of the PIP-lutetium macroinitiators was very high and
the copolymers were clean with a negligible presence of
homopolymers. The thus medium syndiotactic 3,4-regulated
PIP-b-PCL copolymers are unprecedented and cannot be
accessed by the previously reported anionic living polymer-
ization manner. The incorporation of a polar PCL block into a
Block Copolymerization of Isoprene and ε-Caprolac-
tone. The binary system 1/[(Ph3C)(B(C6F5)4)] could initiate
the polymerization of ε-caprolactone (Table 2, entry 1). To our
delight, the living lutetium-PIP active species could catalyze
1
further ε-CL polymerization as the macroinitiator. In the H
NMR spectrum of the resultant PIP-b-PCL (Figure 4), the
signals at δ 1.11−1.27 (m, −CH2−), 1.53 (s, CH3), 1.96 (s,
CH), 4.57 (s, CH2), and 4.70 (s, CH2) arise from the PIP
block and the tripletd at δ 4.06 (3JH−H = 6.7 Hz) and δ 2.31
(3JH−H = 7.5 Hz) and the multiplets at δ 1.65 and 1.38 are
attributed to methylene protons of the PCL block. In order to
prove the resulting polymer has a block microstructure rather
than a mixture of the homopolymers, oligomeric PIP-b-PCL
was prepared.34 The 13C NMR spectrum of the oligomer gave
two sets of signals arising from the PCL block: the strong
signals at δ 173.53, 34.15, 24.61, 25.57, 28.39, and 64.16 ppm
D
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a
Table 2. Copolymerization of Isoprene and ε-Caprolactone with 1/[Ph3C][B(C6F5)4]
b
c
d
c
e
e
entry
feed ratio [IP]:[CL]:[Lu]
t1/t2 (min)
yield (%)
3,4
Mn, calcd × 10−4
found ratio IP:CL
Mn,measd × 10−4
Mw/Mn
1
2
3
0:100:1
60
98.0
96.5
>99
1.1
4.4
9.1
3.3
4.9
1.61
1.12
1.16
500:100:1
500:500:1
30/60
30/120
98.5
98.6
541:100
505:500
10.2
a
Conditions: Lu complex 10 μmol, [Ph3C][B(C6F5)4] 10 μmol, chlorobenzene/isoprene 10/1 (v/v), chlorobenzene/ε-caprolactone 10/1 (v/v).
b
c
d
1
Polymerization time. Determined by H NMR and 13C NMR spectroscopy in CDCl3. Calculated by [([IP]/[Ln]) × 68.12 + [ε-CL]/[Ln] ×
e
114.14] × yield. Determined by GPC in THF at 40 °C against polystyrene standard.
1
Figure 4. H NMR (CDCl3) spectrum of PIP-b-PCL (Table 2, entry 3).
PIP macromolecular chain indeed aroused the change in the
surface property such as the static water contact angle (WCA),
which was measured by using the sessile drop method. The
results showed that the WCA of the hydrophobic PIP (Table 1,
entry 1) was 105.4° and the WCA of the hydrophilic PCL
(Table 2, entry 1) was 82.9°, while a PIP-b-PCL block
copolymer with an IP:CL ratio of 5:1 (Table 2, entry 2) gave a
WCA of 98.6° between the two homopolymers (Figure S16,
Supporting Information).
CONCLUSION
■
We have demonstrated that an amidino N-heterocyclic carbene
ligand has been employed successfully to stabilize rare-earth-
metal bis(alkyl) species, which provides a spacially bulky
enough environment to the corresponding cationic active
species generated upon activation of an organoborate, resulting
in excellent activity and high 3,4-selectivity and livingness mode
toward isoprene polymerization. The 3,4-selectivity of this
system is nearly unaffected by the reaction temperature,
monomer to catalyst ratio, and types of solvents and
Figure 5. GPC traces of block copolymers of PIP-b-PCL (red) and the
homopolymer PIP (blue) (Table 2, entry 3).
E
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0.5 mL of pentane was added to a suspension of (AmH-NHC-H)Br
(0.287 g, 0.5 mmol) in 5 mL of toluene and the mixture stirred for 20
min. Then, the suspension was added to a solution of Lu-
(CH2SiMe3)3(THF)2 (0.290 g, 0.5 mmol) in 5 mL of toluene. The
reaction was maintained for another 2 h, and then the solution was
concentrated until it became cloudy. The LiBr precipitate was filtered
off. The filtrate was concentrated and then cooled to −30 °C.
Colorless crystalline complex 1 was isolated within 2 days (0.528 g,
organoborates, suggesting a highly thermostable active species.
In addition, the metal−3,4-polyisoprene active species could
further initiate the copolymerization of the polar monomer ε-
caprolactone to selectively afford unprecedented 3,4-PIP-b-PCL
diblock copolymers.
EXPERIMENTAL SECTION
■
1
62.9%). H NMR (400 MHz, C6D6, 25 °C): δ −0.85, −0.82 (AB,
General Considerations. All manipulations were performed
under a dry and oxygen-free nitrogen atmosphere using standard
high-vacuum Schlenk techniques or in a glovebox. All solvents were
purified from the MBRAUN SPS system. LiCH2SiMe3 solution (1.0 M
in pentane) was purchased from Aldrich. Glyoxal, mesitylamine, 2,6-
diisopropylphenylamine, 2-bromoethylamine hydrobromide, benzoyl
chloride, thionyl chloride, and formaldehyde were purchased from the
National Medicine Co. (People’s Republic of China) and were used
without further purification. Isoprene (99%, Acros) was dried over
CaH2 with stirring for 48 h and distilled before use. 1H and 13C NMR
spectra were recorded on a Bruker AV400 instrument (FT; 400 MHz
2JH−H = 11.2 Hz, 2H, Lu-CH2SiMe3), −0.65, −0.62 (AB, 2JH−H = 11.2
Hz, 2H, Lu-CH2SiMe3), 0.19 (s, 18H, Lu-CH2SiMe3), 1.13 (d, 3JH−H
=
3
6.8 Hz, 6H, CH(CH3)2), 1.50 (d, JH−H = 6.8 Hz, 6H, CH(CH3)2),
2.02 (s, 6H, C6H2Me3), 2.20 (s, 3H, C6H2Me3), 3.19−3.21 (m, 2H,
CH2CH2), 3.57−3.59 (m, 2H, CH2CH2), 3.71 (sept, 2H, CH(CH3)2),
3
3
5.95 (d, JH−H = 1.6 Hz, 1H, NCH), 6.01 (d, JH−H = 1.6 Hz, 1H,
NCH), 6.83−6.86 (m, 3H, 2,6−iPr2C6H3), 6.89−6.93 (m, 2H,
C6H2Me3), 6.95−7.06 (m, 5H, C6H5). 13C NMR (100 MHz, C6D6,
25 °C): δ 4.65 (s, 6C, Lu-CH2SiMe3), 18.15 (s, 2C, C6H2Me3), 21.07
(s, 1C, C6H2Me3), 24.13 (s, 2C, CH(CH3)2), 26.51 (s, 2C,
CH(CH3)2), 28.16 (s, 2C, CH(CH3)2), 46.72 (s, 2C, Lu-CH2SiMe3),
48.41 (s, 1C, CH2CH2), 54.55 (s, 1C, CH2CH2), 120.38 (s, 1C,
NCH), 121.67 (s, 1C, NCH), 123.66, 124.54, 127.94, 129.11, 129.32,
129.81, 133.02, 135.26, 136.56, 139.45, 142.87, 143.25 (m, ArC),
176.77 (s, 1C, NCN), 199.66 (s, 1C, Lu−Cylidene). Anal. Calcd for
C41H61LuN4Si2: C, 58.55; H, 7.32; N, 6.66. Found: C, 58.93; H, 7.52;
N, 6.47.
for H, 100 MHz for 13C). Elemental analysis was performed at the
1
National Analytical Research Centre of the Changchun Institute of
Applied Chemistry (CIAC). The number-average molecular weights
(Mn) and molecular weight distributions (Mw/Mn) of the polymer
samples were measured by means of gel permeation chromatography
(GPC) on a TOSOHHLC-8220GPC apparatus (column SuperHZM-
Hx3) at 40 °C using THF as the eluent (the flow rate was 0.35 mL/
min) against polystyrene standards. Differential scanning calorimetry
(DSC) analyses were carried out on a Q100 DSC from TA
Instruments under a nitrogen atmosphere. The instrument was
calibrated for temperature and enthalpy using pure indium (mp
156.6 °C) and sapphire before the experiments. Measurements during
the first heating from 25 to 180 °C and then the first cooling from 180
to 25 °C as well as the second heating from 25 to 180 °C at 10 °C/
min were performed. Crystallographic data were collected at −86.5 °C
on a Bruker SMART APEX diffractometer with a CCD area detector
(Mo K, λ = 0.71073 Å). The determination of crystal class and unit
cell parameters was carried out by the SMART program package. The
structures were solved by using the SHELXTL program. The static
contact angle of the film was assessed by sessile drop angle
measurement using a contact angle goniometer (DSA 100, Kruss
GmbH, Hamburg, Germany) at 20 °C. At least five measurements
were carried out for a single sample, and the values that were obtained
were averaged. The testing liquid used was deionized water.
Isoprene Polymerization. A typical polymerization procedure
(Table 1, entry 1) was as follows. Under a nitrogen atmosphere, a
chlorobenzene solution (2.5 mL) of [Ph3C][B(C6F5)4] (9.2 mg, 10
μmol) was added to a well-stirred chlorobenzene solution (2.5 mL) of
complex 1 (8.4 mg, 10 μmol) in a flask. The reaction apparatus was
placed in a bath at 25 °C. Then 0.5 mL of isoprene (0.34 g, 5 mmol)
was added to the above system to start the polymerization and stirring
was maintained for 30 min; the viscous reaction solution was poured
into ethanol (ca .30 mL) to terminate the polymerization. The PIP
product was precipitated, filtered, washed with ethanol, and dried
under vacuum at 40 °C to a constant weight (0.34 g, 100%). The
isolated PIP has a 98.7% 3,4-tacticity and a number-average molecular
weight of 3.69 × 104 with a molecular weight distribution of 1.03. The
glass transition temperature is 45 °C. 1H NMR (400 MHz, CDCl3, 25
°C): δ 1.11−1.27 (m, 2H, −CH2−), 1.53 (s, 3H, CH3), 1.96 (s, 1H,
CH), 4.57 (s, 1H, CH2), 4.70 (s, 1H, CH2). 13C NMR (100
MHz, CDCl3, 25 °C): δ 17.68−18.29 (m, 1C, CH3), 36.75−39.87 (m,
1C, −CH2−), 41.85−42.20 (m, 1C, −CH−), 111.42−112.63 (m, 1C,
CH2), 146.30−147.82 (m, 1C, C(CH3)CH2).
Synthesis of Amidino Imidazolium Bromide (AmH-NHC-
H)Br. At room temperature, triethylamine (2.23 g, 22 mmol) in 20 mL
of dichloromethane was added to
a suspension of
Copolymerization of Isoprene and ε-Caprolactone with 1/
[Ph3C][B(C6F5)4]. A typical polymerization procedure (Table 2, entry
3) was as follows. Under a nitrogen atmosphere, a chlorobenzene
solution (2.5 mL) of [Ph3C][B(C6F5)4] (9.2 mg, 10 μmol) was added
to a well-stirred chlorobenzene solution (2.5 mL) of complex 1 (8.4
mg, 10 μmol) in a flask. The reaction apparatus was placed in a bath at
25 °C. Then 0.5 mL of isoprene (0.34 g, 5 mmol) was added to the
above system to start the polymerization. After 30 min, a small amount
of polymer solution was taken to terminate the polymerization. Then a
chlorobenzene solution (5 mL) of ε-caprolactone (0.57 g, 5 mmol)
was added to the above system and the polymerization was continued
for another 120 min. The viscous reaction mixture was poured into a
large quantity (100 mL) of ethanol to give white solids of a copolymer
(NH2CH2CH2(NCHCHN(C6H2Me3-2,4,6)CH)Br)·HBr (3.91 g, 10
mmol) in 50 mL of dichloromethane and the mixture stirred 30 min.
i
Then, C6H5C(Cl)N(C6H3 Pr2-2,6) (3.00 g, 10 mmol) in 50 mL of
dichloromethane was added dropwise to the solution and refluxed for
12 h. Removal of the volatiles under reduced pressure gave an off-
white residue that was washed three times with 500 mL of deionized
water and then three times with 100 mL of ether and dried in vacuo to
1
afford a white solid (4.5 g, 79%). H NMR (400 MHz, CDCl3, 7.26
ppm, 25 °C): δ 10.38 (s, 1H, imidazolium-H), 7.68 (s, 1H, NCH),
7.25−7.17 (m, 5H, C6H5), 7.00 (s, 2H, C6H2Me3), 6.97−6.89 (m, 3H,
3
2,6-iPr2C6H3), 6.39 (s, 1H, NCH), 5.13 (t, JH−H = 5.6 Hz, 2H,
CH2CH2), 4.27 (s, 2H, CH2CH2), 2.89 (sept, 2H, CH(CH3)2), 2.35
3
(s, 3H, C6H2Me3), 2.03 (s, 6H, C6H2Me3), 1.28 (d, JH−H = 6.8 Hz,
1
6H, CH(CH3)2), 0.85 (d, 3JH−H = 6.8 Hz, 6H, CH(CH3)2). 13C NMR
(100 MHz, C6D6, 25 °C): δ 17.40 (s, 2C, C6H2Me3), 20.94 (s, 1C,
C6H2Me3), 22.05 (s, 2C, CH(CH3)2), 24.04 (s, 2C, CH(CH3)2), 28.07
(s, 2C, CH(CH3)2), 41.60 (s, 1C, CH2CH2), 48.58 (s, 1C, CH2CH2),
130.49 (s, 1C, NCH), 128.25 (s, 1C, NCH), 138.33 (s, 1C,
imidazolium-CH), 121.65, 122.04, 122.68, 127.28, 127.89, 128.84,
129.68, 133.12, 134.05, 137.58, 141.14, 145.24 (m, ArC), 157.58 (s,
1C, NCN). Anal. Calcd for C33H41N4Br: C, 69.10; H, 7.20; N, 9.77.
Found: C, 69.49; H, 7.35; N, 9.52.
that were dried to a constant weight (0.81 g, 100%). H NMR (400
MHz, CDCl3, 25 °C): δ 1.11−1.27 (m, 2H, −CHCH2−), 1.38 (m,
2H, −(CH2)2CH2(CH2)2−), 1.53 (s, 3H, −CH (CH3CH2), 1.65
(m, 4H, −CH2CH2CH2CH2CH2−), 1.96 (s, 1H, −CHCH2−), 2.31 (t,
3
3JH−H = 7.5 Hz, 2H, −COCH2−), 4.06 (t, JH−H = 6.7 Hz, 2H,
−CH2O−), 4.57 (s, 1H, −CHCH2), 4.70 (s, 1H, −CHCH2). 13
C
NMR (100 MHz, CDCl3, 25 °C): δ 17.68−18.29 (m, 1C,
−CH(CH3)), 24.66 (s, 1C, −COCH2CH2−), 25.61 (s, 1C,
−(CH2)2CH2(CH2)2−), 28.43 (s, 1C, −CH2CH2O−), 34.20 (s, 1C,
−COCH2−), 36.75−39.87 (m, 1C, −CHCH2−), 41.85−42.20 (m,
1C, −CHCH2−), 64.21 (s, 1C, −OCH2−), 111.42−112.63 (m,
Synthesis of the Complex (Am-NHC)Lu(CH2SiMe3)2 (1).
Under a nitrogen atmosphere, LiCH2SiMe3 (0.047 g, 0.5 mmol) in
F
dx.doi.org/10.1021/om400925a | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1C,−CH CH2), 146.30−147.82 (m, 1C, −C(CH3)CH2). 173.59
(s, 1C, −CO−).
A.; Perdih, F.; Herdtweck, E.; Anwander, R. Organometallics 2006, 25,
1626−1642. (d) Meermann, C.; Tornroos, K.; Nerdal, W.; Anwander,
̈
R. Angew. Chem., Int. Ed. 2007, 46, 6508−6513. (e) Dietrich, H.;
Zapilko, C.; Herdtweck, E.; Anwander, R. Organometallics 2005, 24,
5767−5771.
ASSOCIATED CONTENT
* Supporting Information
■
S
(9) Li, D.; Li, S.; Cui, D.; Zhang, X. Organometallics 2010, 29, 2186−
2193.
Figures, a table, and a CIF file giving characterization data for 1
and the polymers, contact angles of the polymers PIP, PCL and
PIP-b-PCL, and crystallographic data for 1. This material is
available free of charge via the Internet at http://pubs.acs.org.
(10) (a) Gao, W.; Cui, D. J. Am. Chem. Soc. 2008, 130, 4984−4991.
(b) Lv, K.; Cui, D. Organometallics 2010, 29, 2987−2993.
(11) Ajellal, N.; Furlan, L.; Thomas, C.; Casagrande, O., Jr.;
Carpentier, J. Macromol. Rapid Commun. 2006, 27, 338−343.
(12) (a) Bonnet, F.; Visseaux, M.; Pereira, A.; Barbier-Baudry, D.
Macromolecules 2005, 38, 3162−3169. (b) Bonnet, F.; Visseaux, M.;
Pereira, A.; Bouyer, F.; Barbier-Baudry, D. Macromol. Rapid Commun.
2004, 25, 873−877.
AUTHOR INFORMATION
Corresponding Author
*D.C.: fax, +86-431-85262774; e-mail, dmcui@ciac.ac.cn.
■
Notes
(13) (a) Natta, G.; Porri, L.; Carbonaro, A. Makromol. Chem. 1964,
77, 126−128. (b) Natta, G.; Porri, L.; Corradini, P.; Morero, D. Chim.
Ind. 1958, 40, 362−368.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(14) Zimmermann, M.; Tornroos, K.; Anwander, R. Angew. Chem.,
̈
■
Int. Ed. 2008, 47, 775−778.
This work was partially supported by The National Natural
Science Foundation of China for Project Nos. 51073148,
21104074, 2136114037, 21374112, 21304088, and 21104072
and The Ministry of Science and Technology of China for
Project No. 2011DFR50650.
(15) (a) Liu, D.; Cui, D. Dalton Trans. 2011, 40, 7755−7761.
(b) Rong, W.; Liu, D.; Zuo, H.; Pan, Y.; Jian, Z.; Li, S.; Cui, D.
Organometallics 2013, 32, 1166−1175.
(16) Liu, H.; He, J.; Liu, Z.; Lin, Z.; Du, G.; Zhang, S.; Li, X.
Macromolecules 2013, 46, 3257−3265.
(17) Zhang, L.; Suzuki, T.; Luo, Y.; Nishiura, M.; Hou, Z. Angew.
Chem., Int. Ed. 2007, 46, 1909−1913.
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(34) 1H NMR (400 MHz, CDCl3, 25 °C) of the oligomer of
homopolyisoprenes: δ 4.70 (1H, CH2C, 3,4-PIP), 4.57 (1H, CH2
C, 3,4-PIP), 1.96 (1H, CH, 3,4-PIP), 1.53 (3H, CH3, 3,4-PIP), 1.19
(2H, CH2, 3,4-PIP), 0.36 (0.05H, CH2Si(CH3)3), −0.04 (0.24H,
1
CH2Si(CH3)3). The molecular weight (Mn) is 2700. H NMR (400
MHz, CDCl3, 25 °C) of the oligomer of the copolymers PIP-b-PCL: δ
4.70 (1H, CH2C, 3,4-PIP), 4.57 (1H, CH2C, 3,4-PIP), 4.06
(1.8H, CH2, PCL), 3.64 (0.06H, −CH2OH), 2.31 (1.8H, CH2, PCL),
1.96 (1H, CH, 3,4-PIP), 1.65 (3.7H, CH2, PCL), 1.53 (3H, CH3, 3,4-
PIP), 1.38 (1.8H, CH2, PCL), 1.19 (2H, CH2, 3,4-PIP), 0.36 (0.05H,
CH2Si(CH3)3), −0.04 (0.24H, CH2Si(CH3)3). The molecular weight
(Mn) is 5800. For the 13C NMR spectrum of oligomeric copolymers
PIP-b-PCL, see Figure S15 in the Supporting Information.
H
dx.doi.org/10.1021/om400925a | Organometallics XXXX, XXX, XXX−XXX