Highly trans-1,4 selective (co-)polymerization of butadiene and isoprene with quinolyl anilido rare earth metal bis(alkyl) precursors

Article abstract of DOI:10.1039/c1dt10100e

The N-R-quinolinyl-8-amino ligands HL^1-3 (R = 2,6- ⁱPr₂C₆H₃ (HL¹), 2,6-Et₂C₆H₃ (HL²), 2,6-Me ₂C₆H₃ (HL³)) have been prepared, which reacted readily with one equiv. of rare earth metal tris(alkyl)s to afford the corresponding bis(alkyl) complexes L¹Y(CH₂SiMe ₃)₂(THF) (1) and L^1-3Lu(CH₂SiMe ₃)₂(THF) (2-4) via alkane elimination. Contrastingly, treatment of the in situ generated neodymium tri(alkyl)s with HL¹ afforded a mono(alkyl) neodymium complex (5). Complexes 1, 2 and 5 in combination with aluminium alkyls and organoborates established homogenous ternary systems that exhibited versatile catalytic activities and trans-1,4 selectivities for the polymerization of butadiene, depending on the types of aluminium alkyl, organoborate and rare earth metal used. Furthermore, the trans-1,4 selective copolymerization of butadiene and isoprene was achieved by using the ternary system of 1/AlMe₃/[Ph₃C][B(C ₆F₅)₄]. Both the kinetics of copolymerization and the thermal behavior of the copolymers were investigated.

Full text of DOI:10.1039/c1dt10100e

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PAPER
Highly trans-1,4 selective (co-)polymerization of butadiene and isoprene with
quinolyl anilido rare earth metal bis(alkyl) precursors†
Dongtao Liua,b and Dongmei Cui*a
Received 18th January 2011, Accepted 1st March 2011
DOI: 10.1039/c1dt10100e
The N-R-quinolinyl-8-amino ligands HL1–3 (R = 2,6-iPr2C6H3 (HL1), 2,6-Et2C6H3 (HL2), 2,6-Me2C6H3
(HL3)) have been prepared, which reacted readily with one equiv. of rare earth metal tris(alkyl)s to
afford the corresponding bis(alkyl) complexes L1Y(CH2SiMe3)2(THF) (1)
and L1–3Lu(CH2SiMe3)2(THF) (2–4) via alkane elimination. Contrastingly, treatment of the in situ
generated neodymium tri(alkyl)s with HL1 afforded a mono(alkyl) neodymium complex (5). Complexes
1, 2 and 5 in combination with aluminium alkyls and organoborates established homogenous ternary
systems that exhibited versatile catalytic activities and trans-1,4 selectivities for the polymerization of
butadiene, depending on the types of aluminium alkyl, organoborate and rare earth metal used.
Furthermore, the trans-1,4 selective copolymerization of butadiene and isoprene was achieved by using
the ternary system of 1/AlMe3/[Ph3C][B(C6F5)4]. Both the kinetics of copolymerization and the
thermal behavior of the copolymers were investigated.
isoprene, such as Ziegler–Natta catalysts based on Ti5 and V6
Introduction
metals, and the recently reported [Cp*Ln(AlMe4)2]/B(C6F5)3,7
n
Y(allyl)2Cl(MgCl2)2/AlR3,2u [(C5Me4 Pr)Nd(BH4)2-(thf)2]/Mg-
(nBu)2,8 and [Me4C2(C5H4)2]Sm(allyl)2Li(dme).9 Comparatively,
the catalyst systems that can initiate the trans-1,4-selective poly-
merization of butadiene are explored less, which are mainly Fe,10
Ti,11 and V12 based precursors. To date, rare earth metal based
catalysts have been limited to the lanthanocene aluminates,2m,13
lanthanide bis(allyl)s,14 and neodymium alkoxides.15 Therefore,
to innovate new rare earth metal catalysts for trans-1,4 (co-
)polymerizations of 1,3-conjugated dienes is an obviously inter-
esting but very tough project.
During the past few decades, investigations into the stereospecific
polymerization of 1,3-conjugated dienes promoted by rare earth
metal complexes have gathered an upsurge in research interest
in both academic and industrial environments,1 among which
extraordinary attention has been devoted to the cis-1,4-selective
polymerization of 1,3-conjugated dienes because the given poly-
mers are the most important rubbers used for tires and other elastic
materials.2 Only recently, trans-1,4 regulated polydienes have at-
tracted renewed interest after the pioneering work of Natta,3 since
it became accepted that such polymers possess excellent dynamic
properties, including excellent anti-fatigue properties, low rolling
resistance, low heat buildup, good strength and low abrasion loss.
They are now an important component of long-life “green” tires.
Moreover, trans-1,4 polymerization may allow the incorporation
of an a-olefin into a polydiene chain to afford highly value added
copolymers.4 However, trans-selective catalytic systems are much
fewer in number than cis-selective ones, which might be because
Rare earth metal bis(alkyl) complexes supported by mono-
anionic ancillary ligands have been demonstrated to be highly
active single-component catalysts and excellent precursors for
the polymerization of conjugated dienes and olefins.1d–f We
recently reported the synthesis of quinolinyl anilido scandium
bis(alkyl) complexes, which are the first non-Cp ligated rare
earth metal precursors, providing high syndioselectivity for styrene
polymerization.16 Herein, we wish to report the isolation of quino-
linyl anilido yttrium, lutetium and neodymium complexes, which,
under the activation of organoborates and aluminium alkyls,
exhibited distinguished catalytic activity and trans-1,4 selectivity
for both butadiene and isoprene homo- and co-polymerizations.
4
4
the 1,3-conjugated dienes prefer h -cis to h -trans coordination
to the active metal center. Nevertheless, some catalyst systems
have been designed for the trans-1,4-selective polymerization of
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin
Street, Changchun, 130022, China. E-mail: dmcui@ciac.jl.cn; Fax: +86 431
85262774; Tel: +86 431 85262773
Results and Discussion
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
China
Synthesis and characterization of quinolinyl anilido rare-earth
metal complexes
† Electronic supplementary information (ESI) available: ORTEP drawing
of complex 3 and 13C NMR spectra of the selected polybutadiene sample
and polyisoprene sample. CCDC reference numbers 780668 (1), 780669
(2), 780670 (3) and 780671 (5). For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1dt10100e
The ligands N-R-quinolin-8-amines (HL1: R = diisopropy-
lphenyl; HL2: R = diethylphenyl; HL3: R = dimethylphenyl)
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7755–7761 | 7755
©

were prepared following the previously reported procedure.16
The acid–base reaction between the yttrium tris(alkyl) com-
plex, Y(CH2SiMe3)3(THF)2, and one equiv. of HL1 in hex-
ane at room temperature afforded the corresponding yttrium
bis(alkyl) complex 1 in a medium yield. Similarly, treatment of
Lu(CH2SiMe3)3(THF)2 with one equiv. of HL1–3 in hexane gave
the analogous lutetium bis(alkyl) complexes 2–4, respectively
(Scheme 1). The 1H NMR spectra of complexes 1–4 are displayed
in Fig. 1. The methylene protons of Y–CH2SiMe3 in 1 give a
doublet resonance at d = -0.10 due to coupling with the yttrium
ion (JY–C–H = 3.0 Hz). Meanwhile, the methylene protons of
the metal alkyl Lu–CH2SiMe3 in 2 exhibits an AB spin at d =
-0.35 and -0.27 (JH–H = 8.4 Hz), indicating that the methylene
protons are diastereotopic, whereas the methylene protons of Lu–
CH2SiMe3 in 3 and 4 show up as singlets at d = -0.33 and -0.34,
respectively, suggesting that the two alkyl ligands are equivalent.
As the neodymium tri(alkyl) complex is not stable, the synthesis
of the quinolinyl anilido neodymium alkyl complex did not follow
the alkane elimination method described above for the syntheses
of lutetium and yttrium alkyl complexes, but employed a one-
pot reaction: NdCl3(THF)2 was first treated with three equiv.
of LiCH2SiMe3 in THF and then to this one equiv. of ligand
HL1 was added in situ . However, repeated attempts to isolate the
neodymium bis(alkyl) complex from this reaction failed, as they
gave the mono(alkyl) complex 5 as the major product owing to the
ligand redistribution (Scheme 2).
Scheme 2 The synthesis of complex 5.
Fig. 2 An ORTEP drawing of complex 1 with a 35% probability of
thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ): Y(1)–N(1) = 2.445(4), Y(1)–N(2) =
2.314(4), Y(1)–O(1) = 2.336(3), Y(1)–C(22) = 2.400(6), Y(1)–C(23) =
2.380(5), N(1)–C(9) = 1.364(7), N(2)–C(8) = 1.374(7), N(2)–C(10) =
1.422(6), O(1)–Y(1)–N(1) = 161.72(13), C(23)–Y(1)–C(22) = 106.9(2),
N(2)–Y(1)–N(1) = 68.87(13).
coordinate isostructural monomers, adopting a distorted trigonal
bipyramidal geometry. The nitrogen atom in the quinolinyl ring
and the THF molecule are axial (N(1)–Y(1)–O(1) = 161.72◦ for
1; N(1)–Lu(1)–O(1) = 161.94◦ for 2) and the two alkyl carbon
atoms and the N(2) atom of the ligand occupy the equatorial
positions. While the six-coordinate complex 5 adopts a twisted
tetragonal bipyramidal geometry with the alkyl carbon and the
nitrogen atom N(1) axial and the THF oxygen and the other three
nitrogen atoms equatorial. It is noteable that in complexes 1, 2
Scheme 1 The synthesis of complexes 1–4.
˚
and 5 the bond length of N(1)–C(9) (average 1.365 A) is close to
˚
that of N(2)–C(8) (average. 1.371 A), suggesting that the electrons
delocalize within the N(1)–C(9)–C(8)–N(2) fragment. The NN
2
ligand chelates to the metal ion in a h -mode, leading to the N–
aryl ring and the quinolinyl ring perpendicular to each other. The
˚
˚
average bond length of Ln–C is 2.390 A for 1, 2.342 A for 2, and
˚
˚
2.528 A for 5, whilst, the Ln–N(2) bond lengths of 2.314(4) A for 1,
˚
˚
2.267(4) A for 2, and 2.381(3) A for 5, respectively. Both fall within
the normal values.17 The bond angles of C–Ln–C 106.9(2)◦ (1) to
107.22(18)◦ (2) are comparable to those found in other rare-earth
metal bis(alkyl) complexes.18
Polymerization of butadiene
Recently, we have been engaged in the stereospecific polymeriza-
tions of 1,3-conjugated dienes,19 which is a very important process
in the chemical industry to afford products that are among the
most significant and widely used rubbers. Therefore complexes
1, 2 and 5 were employed as precursors in the polymerization
of butadiene (BD) upon the activation of aluminium alkyls and
organoborates. The generated homogeneous catalysts showed
Fig. 1 1H NMR spectra of complexes 1–4. (*: impurity).
The solid-state structures of complexes 1, 2 and 5 were con-
firmed by X-ray diffraction (Fig. 2–4). Complexes 1 and 2 are five-
7756 | Dalton Trans., 2011, 40, 7755–7761
This journal is
The Royal Society of Chemistry 2011
©

The type of aluminium alkyl seemed to have no influ-
ence on the catalytic activity. All of the ternary systems
1/AlR3/[Ph3C][B(C6F5)4] exhibited similar high activities, reach-
ing complete conversion within 3 h, whichever aluminium alkyl
(AliBu3 or AlMe3 or AlEt3) was employed. In striking contrast,
the type of aluminium alkyl played a significant role in control
of the selectivity. The catalytic system 1/AlMe3/[Ph3C][B(C6F5)4]
was highly selective to providing polybutadiene (PBD) with up to
91% trans-1,4 regularity. When AlMe3 was replaced by AliBu3, the
resultant system afforded 78% cis-1,4 regulated PBD and when
complex 1 was activated by AlEt3, the resultant PBD had equal
cis-1,4 and trans-1,4 content (entries 1–3). The fluorinated borates
also significantly influenced the catalytic performances.
Fig. 3 An ORTEP drawing of complex 2 with a 35% probability of
thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ): Lu(1)–N(1) = 2.387(4), Lu(1)–N(2) =
2.267(4), Lu(1)–O(1) = 2.286(3), Lu(1)–C(22) = 2.338(5), Lu(1)–C(23) =
2.346(5), N(1)–C(9) = 1.365(7), N(2)–C(8) = 1.368(5), N(2)–C(10) =
1.428(5), O(1)–Lu(1)–N(1) = 161.94(12), C(22)–Lu(1)–C(23) = 107.22(18),
N(2)–Lu(1)–N(1) = 70.22(13).
When applying [PhNMe2H][B(C6F5)4] instead of [Ph3C]-
[B(C6F5)4] as the activator, the ternary system 1/AlMe3/
[PhNMe2H][B(C6F5)4] showed low activity and the borates had
a negligible effect on the selectivity (entry 6).
Besides the types of co-activators, the central metal also
exerted an obvious influence on the catalytic performances. Thus,
complexes based on various lanthanide elements bearing the
o-isopropyl substituent of the N-aryl ring of the ligand were
examined when combined with AlMe3 and [Ph3C][B(C6F5)4]. By
using the yttrium precursor, a complete conversion could be
achieved within 3 h and up to 91% trans-1,4 regulated PBD
was obtained. Comparatively, both the catalytic activity and the
trans-1,4 selectivity (68%) obviously dropped for the lutetium-
based systems (entry 4). Whilst the larger neodymium-based
mono(alkyl) precursor 5 displayed a lower activity and trans-1,4
selectivity (71%) compared to the yttrium system, which might be
attributed to the more sterically hindered environment around the
neodymium center bearing the two ligands (entry 5).
As the catalytic system based on yttrium precursor
1/AlMe3/[Ph3C][B(C6F5)4] displayed distinguished catalytic ac-
tivity and selectivity, it was used to further investigate the kinetics
of the polymerization at room temperature under a monomer-
to-Y ratio of 1000. The results demonstrated that the amount of
monomer conversion increased with polymerization time, which
displayed a nearly linear correlation with the molecular weight of
the obtained polymer (Fig. 5). Meanwhile, the molecular weight
distribution remained constant (PDI = 1.26–1.58). This meant that
the polymerization was pseudo-living and controllable. Intrigued
Fig. 4 An ORTEP drawing of complex 5 with a 35% probability of
thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
◦
˚
lengths (A) and angles ( ): Nd(1)–N(1) = 2.619(3), Nd(1)–N(2) = 2.381(3),
Nd(1)–N(3) = 2.559(3), Nd(1)–N(4) = 2.397(3),Nd(1)–O(1) = 2.603(3),
Nd(1)–C(43) = 2.528(4), N(3)–C(30) = 1.371(5), N(4)–C(29) = 1.376(4),
N(4)–C(31) = 1.436(5).
versatile catalytic performances depending on the type of alu-
minium alkyl, organoborate, and rare earth metal center. The
selected polymerization data are summarized in Table 1.
Table 1 Trans-1,4 polymerization of butadiene by complex/AlR3/boratea
microstructure(%)c
b
b
entry
cat.
AlR3
[BD]/[Ln]
time (h)
yield (%)
Mn (/10-4)
Mw/Mn
cis-1,4
trans-1,4
1,2-
1
2
3
4
5
6
7
8
9
1/A
1/A
1/A
2/A
5/A
1/B
1/A
1/A
1/A
1/A
AliBu3
AlEt3
1000
1000
1000
1000
1000
1000
500
2000
3000
5000
3
3
3
3
3
3
2
6
9
> 99
> 99
> 99
41
76
31
> 99
> 99
> 99
> 99
3.4
3.9
1.58
1.14
1.50
1.55
1.80
1.61
1.37
1.56
1.72
2.09
78
47
6
23
25
7
6
7
8
8
19
49
91
68
71
89
91
89
88
88
3
4
3
9
4
4
3
4
4
4
AlMe3
AlMe3
AlMe3
AlMe3
AlMe3
AlMe3
AlMe3
AlMe3
33.6
12.7
16.6
14.2
22.7
46.3
52.4
78.4
10
15
a General conditions: 10-5 mol of Ln complex; in toluene; monomer/solvent = 1 : 5 (v/v); Tp, 20 ◦C; [Al]/[Ln] = 10; [Ln]/[activator] = 1 : 1 (activator =
[Ph3C][B(C6F5)4] (A), [PhMe2NH][B(C6F5)4] (B)). b Determined by GPC in THF at 40 ◦C against a polystyrene standard. c Determined by 13C NMR and
1H NMR.
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7755–7761 | 7757
©

isoprene was explored under various monomer feed ratios. The
representative polymerization data are listed in Table 2. From
Table 2 it can be seen that all of the copolymerizations could reach
complete conversion, the resultant copolymers were random, the
composition of the copolymers was consistent with the monomer
feed ratio and the trans-1,4 regularity of both PBD and PIP
sequences dropped slightly compared with their homopolymers,
as shown by the 1H NMR spectroscopy analysis (Fig. 6). In
addition, the monomer competitive polymerization ratios were
calculated with the Fineman–Ross equation, based on data from
the copolymerization at low monomer conversions, to be r1 =
1.11 (BD) and r2 = 0.44 (IP) (Fig. 7).20 This result indicated that
butadiene was more active than isoprene.21 To our knowledge, this
represents the first rare earth metal based catalyst showing trans-
1,4 selectivity for the copolymerization of butadiene and isoprene.
Fig. 5 A plot of the number average molecular weight of PBD as a
function of the butadiene conversion. Conditions: [BD]/[Y] = 1000, [Y]0 =
1.15 mmol mL-1, [AlMe3]/[Y] = 10, toluene, 20 ◦C.
by this finding, we carried out polymerizations of butadiene under
monomer-to-initiator ratios varying from 500 to 5000, anticipating
that high molecular weight trans-1,4 PBD would be obtained. All
of the polymerizations went smoothly, indicating that the active
species was stable and its lifetime was long, although with the ratio
over 2000 a prolonged polymerization time was needed because
the catalyst concentrations became lower and the system turned
extremely viscous. The molecular weight of the resultant PBD
increased with the ratios, from 22.7 ¥ 104 g mol-1 up to 78.4 ¥
104 g mol-1, albeit with a slightly broadened molecular weight
distribution (from 1.37 to 2.09), which might be attributed to
the difficulty of monomer diffusion in a sticky system. Noteably,
the trans-1,4 tacticity of the resultant polymers did not change
obviously over the entire range of the monomer-to-Y ratios
(entries 7–10).
Fig. 6 1H NMR spectra (400 MHz) of the resulting polymers.
It is known that trans-1,4 PBD may exist in two different
forms. One form is stable at room temperature and is char-
acterized by a monoclinic unit cell. By heating the polymer,
an endothermic transition occurs leading to a second form,
characterized by a hexagonal mesophase.22 The thermal behavior
of the obtained butadiene–isoprene copolymers was examined
by DSC. We found that the copolymer composition strongly
influenced the monoclinic–hexagonal transition and the melting
temperature (Tt and Tm, respectively). Fig. 8 shows the DSC curves
of the butadiene homopolymer and of some selected butadiene–
isoprene copolymers. It can be observed that the values of Tt
and Tm in the copolymers (Fig. 8b) shift to lower temperatures
Copolymerization of isoprene and butadiene using complex
1/AlMe3/borate
The copolymerization of butadiene with isoprene is usually
adopted as an efficient way to reduce the crystallinity and lower
the melting temperature of trans-1,4 PBD, in order to improve
its processing and mechanical properties. However, a catalyst
that is active for butadiene polymerization is not guaranteed to
show the same performance in isoprene polymerization.10,12a To
our delight, the system 1/AlMe3/[Ph3C][B(C6F5)4] was able to
initiate isoprene polymerization with a similar activity in a trans-
1,4 selective manner. Thus, the copolymerization of butadiene and
Table 2 The copolymerization of isoprene (IP) and butadiene (BD) using complex 1/AlMe3/boratea
BD microstructure(%)c
Entry BD/IP (mmol/mmol) time [h] yield [%] Mn (/10-4) Mw/Mn BD content (mol%) cis-1,4
trans-1,4 1,2- cis-1,4
IP microstructure(%)c
trans-1,4 3,4-
b
b
11
12
13
14
15
16
0/50
5/45
15/35
25/25
35/15
45/5
15
15
15
15
15
15
> 99
> 99
> 99
> 99
> 99
> 99
68.9
63.3
64.2
63.5
71.1
71.6
1.71
1.86
1.83
1.89
1.84
2.04
0
10
30
50
70
90
—
17
15
14
14
12
—
78
81
82
82
84
—
5
4
4
4
5
11
12
15
17
18
87
79
79
76
74
73
8
10
9
9
9
4
9
a General conditions: 10-5 mol of the Y complex; in toluene (25 mL); Tp (20 ◦C); [Al] = AlMe3; [Al]/[Ln] = 10; [Ln]/[activator] = 1 : 1 (activator =
[Ph3C][B(C6F5)4] (A)). b Determined by GPC in THF at 40 ◦C against a polystyrene standard. c Determined by 13C NMR and 1H NMR.
7758 | Dalton Trans., 2011, 40, 7755–7761
This journal is
The Royal Society of Chemistry 2011
©

also exhibited similar activity and selectivity towards isoprene
polymerization. Thus, random copolymers with controlled com-
positions and both trans-1,4 regulated monomer sequences could
be achieved swiftly, owing to the comparable competitive polymer-
ization ratios of r1 = 1.11 and r2 = 0.44.
Experimental Section
General Considerations
All manipulations were performed under a dry and oxygen-
free argon atmosphere using standard high vacuum Schlenk
techniques or in a glove box. All solvents were purified via a
SPS system. Anilines, NaOtBu, bis[2-(diphenylphosphino)phenyl]
ether, 8-bromoquinoline, Pd(OAc)2, and aluminium alkyls were
purchased from Aldrich and used without further purification.
Butadiene (99%, Changchun Northern Special Gases Co., Ltd.)
was dried by passing it through a column filled with activated
Fig. 7 A Fineman–Ross plot for the copolymerization of butadiene and
isoprene with 1/AlMe3/[Ph3C][B(C6F5)4] at 20 ◦C (F = [BD]/[IP] in the
feed, f = [BD]/[IP] in the copolymer).
˚
molecular sieves (4 A). Isoprene (Aldrich) was purified by
distillation over calcium hydride under a nitrogen atmosphere.
[Ph3C][B(C6F5)4] and [PhNHMe2][B(C6F5)4] were prepared ac-
cording to the published procedures.23 All ligands were prepared
following the previously reported ◦procedure.16 All complexes were
stored at a low temperature (-30 C). 1H, 13C NMR spectra were
1
recorded on a Bruker AV400 (FT, 400 MHz for H; 100 MHz
for 13C) or AV300 (FT, 300 MHz for 1H; 75 MHz for 13C).
The molecular weight (Mn) was measured by TOSOH HLC-
8220 GPC at 40 ◦C using THF as the eluent (the flow rate was
0.35 mL min-1) against polystyrene standards. Elemental analyses
were performed at the National Analytical Research Centre of the
Changchun Institute of Applied Chemistry. Differential scanning
calorimetry (DSC) analyses were carried out on a Q100 DSC from
TA◦Instruments under a nitrogen atmosphere at a heating rate of
10 C min-1. The thermal history difference in the polymers was
eliminated by first heating the specimen to 150 ◦C, cooling at
10 ◦C min-1 to -60 ◦C, and then a second heating from -60◦C to
150 ◦C at 10 ◦C min-1 was performed.
Fig. 8 DSC curves of the resulting polymers. (a) Polybutadiene (Table 1,
entry 10, 100% butadiene); (b) butadiene–isoprene copolymer (Table 2,
run 16, 90% butadiene); (c) butadiene–isoprene copolymer (Table 2, run
15, 70% butadiene); (d) butadiene–isoprene copolymer (Table 2, run 14,
50% butadiene).
X-ray analysis was performed at -86.5 ◦C on a Bruker SMART
APEX diffractometer with a CCD area detector, using graphite
with respect to those of pure trans-1,4 polybutadiene (Fig. 8a).
Moreover, the temperature interval between the two endothermic
events is progressively reduced by increasing the isoprene content,
and for a certain copolymer composition (isoprene content 30%)
only one endothermic peak can be detected (Fig. 8c). A possible
explanation for such a behavior is that Tt and Tm become so close
with increasing isoprene content that it is no longer possible to
distinguish between them. Finally, no transition is observed for
the copolymers in which the isoprene content is 50% (Fig. 8d).
˚
monochromated Mo-Ka radiation (l = 0.71073 A). The determi-
nation of crystal class and the unit cell parameters was carried
out by the SMART program package. 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 reactivity ratios r1 and r2 were determined using the
Fineman–Ross method and the following linear relationship:
F(f - 1)/f = r1 - r2 (F2/f )
Conclusions
We have demonstrated that rare earth metal bis(alkyl)s complexes
bearing a non-Cp quinolinyl aniline ligand, upon the activation
by aluminium alkyls and organoborates, generated single-site,
homogeneous cationic systems for the (co-)polymerization of
1,3-conjugated dienes. The optimum catalytic system of yttrium
precursor/AlMe3/[Ph3C][B(C6F5)4] provided a high activity and
up to 91% trans-1,4 selectivity for butadiene polymerization. Such
good performances occurred for a broad range of monomer-
to-initiator ratios, therefore a high molecular weight, trans-1,4
regulated polybutadiene was obtained. Remarkably, the system
where F and f are the butadiene/isoprene molar ratios in the feed
and the polymer (by 1H NMR analysis), respectively.
Preparation of the complex L1Y(CH2SiMe3)2(THF) (1)
To a 3 mL hexane solution of Y(CH2SiMe3)3(THF)2 (0.20 g,
0.4 mmol), an equivalent of HL1 (0.12 g, 0.4 mmol in 4 mL
hexane) was added dropwise at room temperature. The resulting
red solution was stirred for 20 min at room temperature, and then
◦
concentrated to about 2 mL. The residue was cooled to -30 C
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7755–7761 | 7759
©

for 12 h to afford red crystalline solids that were washed carefully
with a small amount of cold hexane (0.5 mL) to remove impurities
and dried in vacuo to give red powders of complex 1 (0.16 g,
64%). Red cry◦stals for X-ray analysis grew from a solution of
4H, NC6H3Et2, quinoline), 7.67 (dd, 3JH–H = 8.4 Hz, 4JH–H = 1.5 Hz,
3 4
1H, quinoline), 8.29 (dd, JH–H = 4.8 Hz, JH–H = 1.5 Hz, 1H,
quinoline). 13C NMR (100 MHz, C6D6, 25 ◦C): d 4.78 (6C, SiMe3),
15.56 (2C, CH2CH3), 25.24 (2C, THF), 25.47 (2C, CH2CH3),
43.56 (2C, CH2SiMe3), 70.85 (2C, THF), 109.26, 110.85, 120.96
(3C, quinoline), 124.71 (1C, NC6H3Et2), 128.26 (2C, NC6H3Et2),
131.04, 131.55, 140.48 (3C, quinoline), 140.99 (2C, NC6H3Et2),
141.60 (1C, NC6H3Et2), 146.41, 148.24, 155.04 (3C, quinoline).
Anal. calcd for C31H49N2OSi2Lu(%): C, 53.43; H, 7.09; N, 4.02.
Found: C, 53.58; H, 6.96; N, 4.17.
1
hex◦ane at -30 C after several days. H NMR (300 MHz, C6D6,
2
25 C): d -0.10 (d, JY–C–H = 3.0 Hz, 4H, CH2SiMe3), 0.34 (s,
3
18H, SiMe3), 1.20 (br, 4H, THF), 1.21 (d, JH–H = 6.9 Hz, 6H,
2
CH(CH3)2), 1.31 (d, JH–H = 6.9 Hz, 6H, CH(CH3)2), 3.50 (br,
3
4H, THF), 3.56 (m, 2H, CH(CH3)2), 6.22 (dd, JH–H = 7.8 Hz,
3
4JH–H = 0.9 Hz, 1H, quinoline), 6.74 (d, JH–H = 7.2 Hz, 1H,
3
quinoline), 6.90 (q, JH–H = 4.5 Hz, 1H, quinoline), 7.20–7.32
i
(m, 4H, NC6H3 Pr2, quinoline), 7.68 (dd, 3JH–H = 8.4 Hz, 4JH–H
=
Preparation of the complex L3Lu(CH2SiMe3)2(THF) (4)
1.2 Hz, 1H, quinoline), 9.06 (dd, 3JH–H = 4.5 Hz, 4JH–H = 1.5 Hz, 1H,
quinoline).13C NMR (100 MHz, C6D6, 25 ◦C): d 4.74 (6C, SiMe3),
25.46 (4C, CH(CH3)2), 26.06 (2C, THF), 28.95 (2C, CH(CH3)2),
36.75 (d, 3JH–H = 53 Hz, 2C, CH2SiMe3), 70.90 (2C, THF), 110.05,
110.94, 120.94 (3C, quinoline), 124.93 (2C, NC6H3 Pr2), 125.44
(1C, NC6H3 Pr2), 130.57, 131.47, 140.49 (3C, quinoline), 141.68
(1C, NC6H3 Pr2), 146.36 (1C, NC6H3 Pr2), 145.35, 146.49, 155.68
(3C, quinoline). Anal. calcd for C33H53N2OSi2Y(%): C, 62.04; H,
8.36; N, 4.38. Found: C, 62.92; H, 8.09; N, 4.13.
Following a similar procedure to that described for the preparation
of 1, the reaction of Lu(CH2SiMe3)3(THF)2 (0.23 g, 0.4 mmol
in 3 mL hexane) with an equivalent of HL3 (0.10 g, 0.4 mmol
in 4 mL hexane) gave 4 (0.20 g, 74%). 1H NMR (400 MHz,
C6D6, 25 ◦C): d -0.34 (4H, CH2SiMe3), 0.30 (s, 18H, SiMe3),
1.11 (br, 4H, THF), 2.35 (s, 6H, o-NC6H3Me2), 3.54 (br, 4H,
i
i
i
i
3
3
THF), 6.19 (d, JH–H = 7.8 Hz, 1H, quinoline), 6.74 (d, JH–H
=
3
8.1 Hz, 1H, quinoline), 6.95 (q, JH–H = 4.5 Hz, 1H, quinoline),
7.04 (t, 1H, 3JH–H = 7.4 Hz, NC6H3Me2), 7.17 (d, 3JH–H = 7.5 Hz,
3
2H, NC6H3Me2), 7.23 (t, 1H, JH–H = 7.8 Hz, quinoline), 7.72
Preparation of the complex L1Lu(CH2SiMe3)2(THF) (2)
3
3
(d, JH–H = 8.1 Hz, 1H, quinoline), 8.94 (d, JH–H = 4.5 Hz,
1H, quinoline). 13C NMR (100 MHz, C6D6, 25 ◦C): d 4.84
(6C, SiMe3), 19.38 (2C, o-NC6H3Me2), 25.21 (2C, THF), 43.72
(2C, CH2SiMe3), 70.91 (2C, THF), 108.32, 110.96, 120.95 (3C,
quinoline), 124.24 (1C, NC6H3Me2), 129.31 (2C, NC6H3Me2),
131.29, 131.61 (2C, quinoline), 135.51 (2C, NC6H3Me2), 140.47
(1C, quinoline), 141.70 (1C, NC6H3Me2), 146.37, 149.40, 153.80
(3C, quinoline). Anal. calcd for C29H45N2OSi2Lu(%): C, 52.08; H,
6.78; N, 4.19. Found: C, 52.23; H, 6.57; N, 4.02.
Following a similar procedure to that described for the preparation
of 1, the reaction of Lu(CH2SiMe3)3(THF)2 (0.23 g, 0.4 mmol in
3 mL hexane) with an equivalent of HL1 (0.12 g, 0.4 mmol in
4 mL hexane) gave 2 (0.24 g, 81%). Red crystals for X-ray analysis
◦
1
grew from a solution of hexane at -30 C after several days. H
NMR (300 MHz, C6D6, 25 ◦C): d -0.35, -0.27 (AB, JH–H
=
2
8.4 Hz, 4H, CH2SiMe3), 0.32 (s, 18H, SiMe3), 1.19 (br, 4H,
THF), 1.21 (d, 6H, CH(CH3)2), 1.32 (d, 6H, CH(CH3)2), 3.55
(br, 4H, THF), 3.60 (m, 2H, CH(CH3)2), 6.22 (d, 3JH–H = 5.4 Hz,
Preparation of the complex L1 Nd(CH2SiMe3) (THF) (5)
3
2
1H, quinoline), 6.72 (d, JH–H = 6.0 Hz, 1H, quinoline), 6.92 (q,
3JH–H = 3.6 Hz, 1H, quinoline), 7.20–7.33 (m, 4H, NC6H3 Pr2,
i
Anhydrous NdCl3 (0.17 g, 0.68 mmol) was suspended in 10 mL
of THF and the suspension was stirred overnight. A solution of
LiCH2SiMe3 (0.19 g, 2.04 mmol in 10 mL of THF) was added to
the above suspension at ambient temperature, and a bright blue
solution formed in 10 min. The reaction mixture was stirred for
quinoline), 7.68 (dd, 3JH–H = 6.0 Hz, 4JH–H = 1.2 Hz, 1H, quinoline),
3
4
9.03 (dd, JH–H = 3.3 Hz, JH–H = 1.2 Hz, 1H, quinoline).13C
NMR (100 MHz, C6D6, 25 ◦C): d 4.81 (6C, SiMe3), 25.16 (2C,
CH(CH3)2), 26.22 (2C, CH(CH3)2), 25.46 (br, 2C, THF), 28.93
(2C, CH(CH3)2), 43.18 (2C, CH2SiMe3), 71.36 (br, 2C, THF),
◦
2 h and then cooled to 0 C. HL1 (0.21 g, 0.68 mmol) in 5 mL
i
110.99, 120.96 (2C, quinoline), 124.87 (2C, NC6H3 Pr2), 125.40
of THF ◦was then added. The reaction solution was stirred for
2 h at 0 C. The volatiles were removed under vacuum, and the
residue was extracted with 30 mL of hexane. Concentration of the
extract solution in vacuo to approximately 2 mL and cooling to
i
(1C, NC6H3 Pr2), 130.68, 131.51, 140.54 (3C, quinoline), 141.50
i
i
(1C, NC6H3 Pr2), 146.24 (1C, NC6H3 Pr2), 146.55, 146.71, 156.00
(3C, quinoline). Anal. calcd for C33H53N2OSi2Lu(%): C, 54.68; H,
7.37; N, 3.86. Found: C, 55.03; H, 7.51; N, 3.67.
◦
-10 C afforded 5 as red crystals (0.13 g, 42% yield). The NMR
spectrum of complex 5 was not available due to paramagnetism.
Anal. calcd for C50H65N4OSiNd(%): C, 65.96; H, 7.20; N, 6.15.
Found: C, 66.18; H, 7.04; N, 6.01.
Preparation of the complex L2Lu(CH2SiMe3)2(THF) (3)
Following a similar procedure to that described for the preparation
of 1, the reaction of Lu(CH2SiMe3)3(THF)2 (0.23 g, 0.4 mmol in
3 mL hexane) with an equivalent of HL2 (0.11 g, 0.4 mmol in
4 mL hexane) gave 3 (0.19 g, 83%). Red crystals for X-ray analysis
Polymerization of butadiene
A typical procedure for the polymerization was as follows (Table 1,
entry 3): in a glovebox, a toluene solution of 1 (2.0 mL, 10 mmol,
6.4 mg), 100 mmol AlMe3, a toluene solution of [PhC3][B(C6F5)4]
(1.0 mL, 10 mmol, 9.2 mg) and a toluene solution of butadiene
(2.0 mL, 10 mmol, 0.54 g) were added into a 25 mL reactor.
After a designated time, methanol was injected into the system to
quench the polymerization, and the reaction mixture was poured
into a large quantity of methanol containing a small amount of
◦
grew from a solution of hexane at -30 C after several days.1H
NMR (300 MHz, C6D6, 25 ◦C): d -0.33 (s, 4H, CH2SiMe3), 0.29
3
(s, 18H, SiMe3), 1.16 (br, 4H, THF), 1.19 (t, JH–H = 7.5 Hz,
6H, CH2CH3), 2.71 (m, 2H, CH2CH3), 2.91 (m, 2H,CH2CH3),
3
4
3.53 (br, 4H, THF), 6.19 (dd, JH–H = 8.1 Hz, JH–H = 1.2 Hz,
3
4
1H, quinoline), 6.70 (dd, JH–H = 7.8 Hz, JH–H = 0.9 Hz, 1H,
quinoline), 6.89 (q, 3JH–H = 4.8 Hz, 1H, quinoline), 7.14–7.24 (m,
7760 | Dalton Trans., 2011, 40, 7755–7761
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The Royal Society of Chemistry 2011
©

hydrochloric acid to precipitate the white solids. The precipitated
polymer was collected by filtration, washed with methanol and
dried under vacuum at 40 ◦C to a constant weight to afford 0.54 g
(100% yield) of polybutadiene.
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(Table 2, entry 14): in a glovebox, a toluene solution of 1
(12.5 mL, 10 mmol, 6.4 mg), 0.1 mmol AlMe3, a toluene solution
of [PhC3][B(C6F5)4] (5.0 mL, 10 mmol, 9.2 mg), a toluene solution
of butadiene (5.0 mL, 25 mmol, 1.35 g), and isoprene (2.5 mL,
25 mmol, 1.70 g) were added into a 50 mL reactor. After a
designated period of time, methanol was injected into the system to
quench the polymerization, and the reaction mixture was poured
into a large quantity of methanol containing a small amount of
hydrochloric acid to precipitate the white solids. The precipitated
polymer was collected by filtration, washed with methanol and
dried under vacuum at 40 ◦C to a constant weight to afford 3.05 g
(100% yield) of polybutadiene.
Acknowledgements
We are thankful for the financial support from The National
Natural Science Foundation of China for project Nos. 20674081;
20934006 and The Ministry of Science and Technology of China
for project Nos. 2005CB623802; 2009AA03Z501.
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This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7755–7761 | 7761
©