Rare-earth metal bis(alkyl)s that bear a 2-pyridinemethanamine ligand: Dual catalysis of the polymerizations of both isoprene and ethylene

Article abstract of DOI:10.1039/c1dt11890k

New pyridinemethanamido-ligated rare-earth metal bis(alkyl) complexes [C₅H₄N-CH(Me)-NC₆H₃( ⁱPr)₂]Ln(CH₂SiMe₃)₂(THF) (Ln = Sc (1), Y (2), Lu (3)) have been prepared at 0°C via a protonolysis reaction between rare-earth metal tris(alkyl)s and the corresponding 2-pyridinemethanamine ligand and fully characterized by NMR and X-ray diffraction analysis. Bis(alkyl) complexes 1-3 are analogous monomers of THF solvate, where the ligand bonds to the metal center in a κN:κN- bidentate mode. Complexes 1-3, in combination with [Ph₃C][B(C ₆F₅)₄], showed a good activity towards isoprene polymerization to give polyisoprene with a main 3,4-selectivity (60%-66%); in particular the yttrium catalyst system, 2/[Ph₃C][B(C ₆F₅)₄], displayed a living mode. By contrast, only the precatalyst 2 exhibited activity for isoprene polymerization in the presence of [PhNMe₂H][B(C₆F₅)₄]. The influence of alkylaluminium (AlR₃, R = Me, Et, ⁱBu) and the metal center on the polymerization of isoprene was also studied, and it was found that addition of AlMe₃ to the catalyst systems could lead to a dramatic change in the microstructure of the polymer from 3,4-specific to 1,4-selective (89%-95%), but the ionic radius of the central metal had little influence on the selectivity. In addition, by using the 1(Sc)/[Ph ₃C][B(C₆F₅)₄]/10 Al ⁱBu₃, the polymerization of ethylene was also achieved with moderate activity (up to 3.2× 10⁵ g (PE) mol _Sc^-1 h^-1 bar^-1) and narrow polydispersity (M_w/M_n = 1.19-1.28); while the effect of temperature on the activity was discussed. Such dual catalysis for the polymerizations of both isoprene and ethylene is rare. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c1dt11890k

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PAPER
Rare-earth metal bis(alkyl)s that bear a 2-pyridinemethanamine ligand: Dual
catalysis of the polymerizations of both isoprene and ethylene†
Zhongbao Jiana,b and Dongmei Cui*a
Received 6th October 2011, Accepted 14th November 2011
DOI: 10.1039/c1dt11890k
New pyridinemethanamido-ligated rare-earth metal bis(alkyl) complexes [C5H4N-CH(Me)-
NC6H3(iPr)2]Ln(CH2SiMe3)2(THF) (Ln = Sc (1), Y (2), Lu (3)) have been prepared at 0 ◦C via a
protonolysis reaction between rare-earth metal tris(alkyl)s and the corresponding 2-pyridin-
emethanamine ligand and fully characterized by NMR and X-ray diffraction analysis. Bis(alkyl)
complexes 1–3 are analogous monomers of THF solvate, where the ligand bonds to the metal center in
a kN:kN-bidentate mode. Complexes 1–3, in combination with [Ph3C][B(C6F5)4], showed a good
activity towards isoprene polymerization to give polyisoprene with a main 3,4-selectivity (60%–66%); in
particular the yttrium catalyst system, 2/[Ph3C][B(C6F5)4], displayed a living mode. By contrast, only
the precatalyst 2 exhibited activity for isoprene polymerization in the presence of [PhNMe2H]-
[B(C6F5)4]. The influence of alkylaluminium (AlR3, R = Me, Et, iBu) and the metal center on the
polymerization of isoprene was also studied, and it was found that addition of AlMe3 to the catalyst
systems could lead to a dramatic change in the microstructure of the polymer from 3,4-specific to
1,4-selective (89%–95%), but the ionic radius of the central metal had little influence on the selectivity.
In addition, by using the 1(Sc)/[Ph3C][B(C6F5)4]/10 AliBu3, the polymerization of ethylene was also
achieved with moderate activity (up to 3.2¥ 105 g (PE) molSc h-1 bar-1) and narrow polydispersity
-1
(Mw/Mn = 1.19–1.28); while the effect of temperature on the activity was discussed. Such dual catalysis
for the polymerizations of both isoprene and ethylene is rare.
systems or cationic rare-earth metal catalytic systems;3 while
Introduction
trans-1,4-PIP, which is produced naturally as gutta-percha
One of the ongoing topics in macromolecular chemistry is to
and has been applied in the fabrication of golf ball and
insulating materials,4 can be synthesized by using some rare-earth
catalyst systems, such as [(C5Me5)Ln(AlMe4)2]/organoborate,
Cp*Ln(BH4)2(THF)n/Mg(nBu)2, and Ln(allyl)2Cl(MgCl2)2/
AlR3.5 Compared with the extensive number of reports on the
1,4-polymerization of isoprene, 3,4-selective polymerization of
isoprene by rare-earth catalysts is less well explored,6 especially in
a living fashion,6b,c,g although 3,4-regulated PIP is an important
component of high-performance rubbers such as those with
wet-skid resistance or low-rolling resistance tread.7
On the other hand, polyethylene (PE), which is the largest
volume synthetic polymer applied in every aspect of our daily lives,
such as packaging materials, pipes, textiles, etc, has been exten-
sively studied in both academic and industrial fields. Nevertheless,
in contrast to the rare-earth catalyst systems for the polymerization
of isoprene, catalyst systems for ethylene polymerization are
mostly focused on transition metals or late-transition metals,8
those based on rare-earth metals are less well explored.9 So far,
some Cp-based (or its derivatives) rare-earth metal complexes have
exhibited excellent activities for the polymerization of ethylene;10
while these non-Cp ligated rare-earth metal complexes, especially
the N-type amino and imino ligand stabilized complexes, have
also been reported to initiate the polymerization of ethylene with
prepare polymers with designated properties through precisely
controlling the microstructures of polymer chains. Thus, the
polymerization of isoprene (a simple and cheap C5 monomer)
has been one of the most important processes, which can
generate cis-1,4, trans-1,4 or 3,4 regulated polyisoprene (PIP)
to meet various applications.1 To date a variety of catalyst
systems have been reported for the polymerization of isoprene,
among which those catalysts based on rare-earth metals
have attracted special attention because of their high activity
and selectivity.2 For instance, cis-1,4-PIP, which is a major
component of natural rubber and can act as one of the most
important elastomers used for tires and other elastic materials,
has been extensively reported by using Ziegler–Natta catalyst
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
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
China
† Electronic supplementary information (ESI) available: 1H and 13C
NMR of complexes 1–3. CCDC reference number 837822. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt11890k
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medium to high activities (104–106 g (PE) mol-1 h-1 bar-1).11
However, despite the development of those rare-earth catalysts
for the polymerization of either isoprene or ethylene, one catalyst,
which is able to concurrently promote the polymerization of both
isoprene and ethylene, still remains scarce and challenging,10d,e,11j,k
because these two monomers show completely different reactivity
for a given catalyst, and in some cases conjugated dienes can act
as poisons for the catalysts designed for ethylene polymerization.12
Carpentier10d and Maron11k reported an allyl ansa-neodymocene
catalyst and a borohydrido half-lanthanidocene complex for
the both polymerizations of trans-1,4 selective isoprene and
ethylene, respectively; while Hou10e also presented Cp-based
scandium bis(alkyl)s for the polymerizations of both living 3,4-
selective isoprene and ethylene. In contrast, only one non-Cp
aminopyridinate-stabilized lanthanide complex was described by
Kempe for the polymerizations of both non-living 3,4-selective
isoprene and ethylene.11j However, one non-Cp lanthanide catalyst
for the polymerizations of both living 3,4-selective isoprene and
ethylene has been not reported to date.
In the past two decades, there has been tremendous research
progress in non-Cp lanthanide chemistry.13 Within this develop-
ment, we are always interested in the N-type donor ligands, among
which the pyridinemethanamino-type N,N-bidentate ligands are
important. Since the first pyridinemethanamido-ligated hafnium
catalyst was explored for the chain shuttling polymerization of
olefins,14 the pyridinemethanamido-type ligands have received a
lot of attention and have been developed for Ti, Zr, Hf, Pd and
Ni based catalysts for olefin polymerizations due to their rich
variation and potential for the control of olefin catalysis, which
clearly emphasizes the general applicability of the ligand class
(Chart 1).15 However, it is well known that, in the
pyridinemethanamido-ligated metal alkyl or hydrido complexes,
when the 6-position of pyridine has a substituent R3 group (such
as R3 = phenyl, 1-naphthyl), a C–H activation reaction always
takes place on the R3 group via alkane elimination. For example,
a family of yttrium mono(alkyl) complexes has been synthesized
via C–H activation.16
C–H activation was avoided. Under the activation of different
cocatalysts, all these rare-earth metal bis(alkyl) complexes dis-
played varied catalytic performances towards the polymerization
of isoprene, while the scandium bis(alkyl)s also showed moderate
activity for the polymerization of ethylene. In addition, the factors
that influence the catalytic activity and the specific regularity of
the resultant polymers will also be discussed.
Results and discussion
Synthesis and characterization of rare-earth metal bis(alkyl)
complexes 1–3
It is well known that the preparation of rare-earth metal bis(alkyl)
complexes usually encounters problems of salt addition, dimeriza-
tion, ligand scrambling, and unpredictable C–H activation, due
to the highly active character of the metal–carbon bonds and
relatively less crowded steric environment of the molecules.17 Treat-
ing 1 equiv. of 2-pyridinemethanamine ligand C5H4N-CH(Me)-
NHC6H3(iPr)2 with rare-earth tris(alkyl)s Ln(CH2SiMe3)3(THF)2
at room temperature, only a mixture of both the bis(alkyl)
complex and the mono(alkyl) complex was isolated. Fortu-
nately, the acid–base reaction between Ln(CH2SiMe3)3(THF)2
and 1 equiv. [(C5H4N-CH(Me)-NHC6H3(iPr)2] in hexane at
lower temperature, 0 ◦C, selectively afforded the correspond-
ing pyridinemethanamido-ligated rare-earth bis(alkyl) complexes
[C5H4N-CH(Me)-NC6H3(iPr)2]Ln(CH2SiMe3)2(THF) (Ln = Sc
(1), Y (2), Lu (3)) in 54%–62% yields (Scheme 1). The 1H
NMR spectra of 1–3 clearly confirmed the absence of the N-H
proton and the presence of two alkyls; while interestingly the two
methylene protons arising from the CH2SiMe3 alkyl groups gave
completely different signals. For example, the scandium complex
1 exhibits four broad singlets at -0.30, -0.13, 0.03, 0.12 ppm
for the CH2SiMe3 groups; in contrast, the yttrium complex 2
displays four doublets at -0.54, -0.43, -0.27, -0.21 ppm with
2
the same coupling constant JY–H = 12.0 Hz; while the AB spin
systems at -0.73, -0.63, -0.48, -0.37 ppm (2JH–H = 11.4 Hz) are
observed for the diastereotopic methylene protons in the lutetium
complex 3. The existence of two alkyls was also reflected by 13C
NMR spectra, in which the complexes 1 and 3 give two singlets
at 33.63, 35.93 ppm and at 37.36, 40.10 ppm, respectively; but
the yttrium complex 2 exhibits two doublets at 31.32, 33.23 ppm
(JY–C = 37.5 Hz). Furthermore, the doublet signals of the H proton
on the 6-position of the pyridine ring are also found at 9.08,
9.02, 8.98 ppm, respectively, which confirm the absence of a C–
H activation reaction. X-ray diffraction analysis further revealed
that complexes 1–3 were analogous monomers with a coordinating
THF molecule (Fig. 1).18 The 2-pyridinemethanamido ligand in
Chart 1 Related complexes based on pyridinemethanamido-type ligands.
In this contribution, on the basis of a strategy of preparing
new rare-earth bis(alkyl) catalysts for the polymerizations of both
isoprene and ethylene, we selected the simple and available com-
pound 2,6-diisopropyl-N-(1-(pyridin-2-yl)ethyl)aniline, C5H4N-
CH(Me)-NHC6H3(iPr)2, as a suitable pyridinemethanamido-type
ligand. Treatment of the ligand with Ln(CH2SiMe3)3(THF)2
successfully yielded the desired 2-pyridinemethanamido rare-earth
metal bis(alkyl) complexes via alkane elimination, where the
Scheme 1 Synthesis of rare-earth metal bis(alkyl) complexes 1–3.
2368 | Dalton Trans., 2012, 41, 2367–2373
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1 bonds to the scandium center in a kN:kN-bidentate binding
mode with reasonable Sc–N distances (Sc(1)–N(1) 2.292(2) A
molecular weight (Table 1, run 9). To the best of our knowledge, the
3,4-selective living polymerization of isoprene remains scarce to
date.6b,c,g By contrast, in combination with [PhNMe2H][B(C6F5)4],
only the ytttrium complex 2 showed activity towards isoprene
polymerization to give a main 3,4-selective PIP (Table 1, run 10).
The possible mechanism for the formation of 3,4-PIP has been
described by Hou and coworkers.3g,10e
˚
˚
and Sc(1)–N(2) 2.085(2) A); while the five-membered ring (Sc1,
N1, C5, C6, N2) almost constitutes a perfect planar geometry.
The two alkyl ligands are located in the two sides of the plane.
The bond angle of C(20)–Sc(1)–C(24) (108.44(12)◦) also falls
within the normal range observed in other lanthanide bis(alkyl)
complexes.19
It has been reported that the alkylaluminium (AlR3) could
influence the catalytic performances and the microstructures
of the isolated polymers in the polymerization of conjugated
dienes.3g–i,11j Herein, AlR3 was also added to the catalyst system
to see whether the alkylaluminium compounds have any influence
on the polymerization of isoprene. Under the activation of
[Ph3C][B(C6F5)4], the addition of AlEt3 or AliBu3 had little effect
on the microstructures of the obtained PIP (Table 1, runs 2, 12,
13, 20, and 21). In the presence of [PhNMe2H][B(C6F5)4], however,
upon the addition of 10 equiv. AlEt3 or AliBu3, complexes 1
and 3 exhibited a complete change for the polymerization of
isoprene from inertness (Table 1, runs 4 and 18) to high activity
(Table 1, runs 5, 23, and 24). All obtained PIP had main 3,4-
selectivity (61%–63%), as well. To our surprise, in the presence
of either [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4], addition of
10 equiv. AlMe3 to the catalyst systems of complexes 2 and 3
changed the selectivity of the polymerization dramatically from
main 3,4-specific (64%–66%) to 1,4-selective (89%–95%) (Table 1,
runs 11, 14, 19 and 22), although the polymerization activity
decreased. This unusual effect of AlMe3 on the polymerization
of isoprene was also observed in the amidinate-ligated and
aminopyridinate-stabilized rare-earth catalyst systems,3g,11j while a
possible mechanism has also been proposed by Hou and coworkers
to explain the dramatic switch of the regioselectivity.3g
We further focused on the influence of the central metal on
the selectivity. Under the same polymerization conditions, with
increasing ionic radius of the central metal (Sc < Lu < Y),
we observed that the 3,4-selectivity of PIP almost remained
unchanged, suggesting that the microstructure of the polymer
does not depend on the metal size, which is a significant
contrast to those results reported previously.3g,6d On the basis of
this fact, because the 1(Sc)/[Ph3C][B(C6F5)4]/10AliBu3 catalyst
system showed the highest activity for isoprene polymerization
(Table 1, run 2), the polymerization was further carried out at low
temperature (-20 ◦C); a higher 3,4-selectivity (80%) was expectedly
achieved with a good activity (Table 1, run 3).
Fig.
1
X-ray structures of complex 1 with 35% probability of
thermal ellipsoids. Hydrogen atoms and solvents are omitted for
clarity. Selected bond distances (A) and angles (deg): Sc(1)–N(1)
2.292(2), Sc(1)–N(2) 2.085(2), Sc(1)–C(20) 2.259(3), Sc(1)–C(24) 2.242(3),
Sc(1)–O(1) 2.2100(19); N(1)–Sc(1)–N(2) 73.65(8), C(20)–Sc(1)–C(24)
108.44(12), C(20)–Sc(1)–N(2) 130.43(11), C(24)–Sc(1)–N(2) 119.54(11).
˚
Catalysis of the polymerization of isoprene
We first explored the isoprene polymerization catalyzed by 1–3
precursors in toluene under different conditions, these results are
summarized in Table 1. Upon activation with [Ph3C][B(C6F5)4]
only, complexes 1–3 showed a medium to high activity towards
isoprene polymerization to give PIP with a main 3,4-selectivity
(60%–66%) (Table 1, runs 1 and 6–9 and 17). It is noteworthy that
the performance of 2/[Ph3C][B(C6F5)4] in isoprene polymerization
was studied in detail, which converted 500 equiv. of isoprene into
PIP in 30 min (Table 1, run 6). The resultant PIP had moderate
3,4-regularity (66%) and narrow molecular weight distribution
(Mw/Mn = 1.04). When the monomer loading was doubled and
quadrupled, the molecular weight of the obtained PIP was almost
doubled and quadrupled and the narrow molecular weight distri-
bution remained unchanged (Mw/Mn = 1.03–1.04), indicating a
living fashion (Table 1, runs 7 and 8). The living mode could be
further confirmed by adding another 500 equiv. of isoprene to a
completely converted isoprene (500 equiv.) polymerization system,
a total of 100% conversion was achieved to give PIP with doubled
Catalysis of the polymerization of ethylene
It has recently been demonstrated that the pyridinemethanamido-
ligated Hf or Ni catalysts showed an excellent polymerization
behavior for ethylene. Therefore these 2-pyridinemethanamido
rare-earth metal bis(alkyl) complexes 1–3 were anticipated to
polymerize the ethylene with a good activity, although rare-earth
metal catalysts usually showed no or low activity for the ethylene
polymerization. Upon activation with an equimolar amount of
[Ph3C][B(C6F5)4] and 10 equiv. AliBu3, the yttrium and lutetium
bis(alkyl) complexes 2–3, unfortunately, displayed no activity
towards the polymerization of ethylene. In contrast, under the
conditions of 1 bar ethylene atmosphere and room temperature
(20 ◦C), the scandium complex 1 showed a moderate activity (1.4¥
105 g (PE) molSc-1 h-1 bar-1) to afford PE with low molecular weight
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Table 1 Isoprene polymerization using 1–3 as precursors under various conditionsa
c
c
Run
Cat.
Borateb
AlR3
t/min
Conv. (%)
Mn ¥ 10-4
Mw/Mn
1,4d (%)
3,4d (%)
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
A
A
A
B
B
A
A
A
A
B
A
A
A
B
B
B
A
B
A
A
A
B
B
B
—
5
2
100
100
87
5.5
8.9
40.1
—
1.56
1.10
1.63
—
40
37
20
—
38
34
35
35
34
36
95
50
36
89
35
37
36
—
93
40
36
90
39
37
60
63
80
—
62
66
65
65
66
64
5
50
64
11
65
63
64
—
7
2
AliBu3
AliBu3
—
3e
10
20
20
30
60
90
60
60
180
90
60
180
180
60
60
60
90
90
60
180
180
60
4
trace
100
100
100
100
100
100
100
100
100
24
100
100
92
trace
49
5
AliBu3
—
—
—
—
8.5
2.9
6.6
13.5
6.7
2.2
15.7
3.8
4.7
10.6
4.7
2.3
9.7
—
15.8
5.7
5.3
6.6
5.4
2.7
1.50
1.04
1.03
1.04
1.05
1.56
2.20
1.54
1.32
1.82
1.26
1.56
1.36
—
1.97
1.40
1.71
1.59
1.29
1.78
6f
7
8g
9h
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
—
AlMe3
AlEt3
AliBu3
AlMe3
AlEt3
AliBu3
—
—
AlMe3
AlEt3
AliBu3
AlMe3
AlEt3
AliBu3
100
100
18
100
100
60
64
10
61
63
a Polymerization conditions: 20 ◦C; toluene (5.0 ml); Ln (10 mmol); Borate (10 mmol); [AlR3]/[Ln] = 10; [IP]/[Ln] = 1000. b A = [Ph3C][B(C6F5)4]; B =
[PhNMe2H][B(C6F5)4]. c Measured by GPC in THF at 40 ◦C calibrated with standard polystyrene samples. d Determined by 1H NMR spectroscopy in
CDCl3. e Tp = -20 ◦C. f [IP]/[Ln] = 500. g [IP]/[Ln] = 2000. h After polymerization of 5 mmol of isoprene for 30 min, another 5 mmol of isoprene were
added and the reaction mixture was stirred for another 30 min.
a
Table 2 Ethylene polymerization with 1(Sc)/[Ph3C][B(C6F5)4]/AliBu3
activity towards isoprene polymerization to give PIP with a main
3,4-microstructure, especially the yttrium catalyst system which
◦
Run Tp (◦C) Yield (g) Activityb Mn ¥ 10-3 Mw/Mn
Tm ( C)
c
c
d
exhibits a living fashion. Addition of alkylaluminium has various
effects on the isoprene polymerization depending on the nature
of alkylaluminium. In particular, the incorporation of AlMe3 can
dramatically change the microstructure of the polymer from 3,4-
specific to 1,4-selective. By contrast, the ionic radius of the central
metal has little influence on the selectivity. Moreover, the scandium
precursor, in combination with [Ph3C][B(C6F5)4] and AliBu3, also
shows a moderate activity for the polymerization of ethylene, and
the polymerization activity increases with increasing temperature.
Such a dual catalyst for the polymerizations of both isoprene and
ethylene is rare. Study on the copolymerization of isoprene and
ethylene is in progress.
1
2
3
20
40
60
0.12
0.17
0.27
1.4
2.0
3.2
1.2
1.7
2.6
1.28
1.25
1.19
107
112
119
a Polymerization conditions: toluene (40.0 mL), Sc (10 mmol),
[Ph3C][B(C6F5)4] (10 mmol), [AliBu3]/[Sc] = 10, ethylene pressure (1.0
bar), 5 min. b Given in 105 g of PE molSc h-1 bar-1. c Determined by
-1
GPC in 1,2,4-trichlorobenzene at 150 ◦C against a polystyrene standard.
d Determined by DSC.
(Mn = 1200) and narrow molecular weight distribution (Mw/Mn =
1.28) (Table 2, run 1). Furthermore, we studied the influence of
temperature on the activity. With the increase of temperature from
◦
◦
20 C to 60 C, the polymerization activity increased from 1.4¥
105 g (PE) molSc h-1 bar-1 to 3.2¥ 105 g (PE) molSc h-1 bar-1;
while the molecular weight also increased from Mn = 1200 to Mn =
2600, but the molecular weight distribution still remained narrow
(Mw/Mn = 1.19–1.28) (Table 2, runs 2 and 3). In the DSC curve,
we also found that all three PEs exhibited a melting point (Tm)
peak at 107 ◦C, 112 ◦C, and 119 ◦C, respectively.
-1
-1
Experimental
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 a MBraun glovebox. All solvents were purified
with a MBraun SPS system. Organometallic samples for NMR
spectroscopic measurements were prepared in the glovebox by
Conclusions
1
use of NMR tubes sealed by paraffin film. H and 13C NMR
We have demonstrated that by introduction of
a
sim-
spectra were recorded on a Bruker AV600 (FT, 600 MHz for
1H; 150 MHz for 13C) spectrometer. NMR assignments were
confirmed by 1H–1H COSY and 1H–13C HMQC experiments
when necessary. Elemental analyses were performed at the Na-
tional Analytical Research Centre of Changchun Institute of
Applied Chemistry (CIAC). Isoprene was dried over CaH2 under
ple N,N-bidentate ligand, C5H4N-CH(Me)-NHC6H3(iPr)2, new
pyridinemethanamido-ligated rare-earth metal bis(alkyl) com-
plexes have been successfully synthesized and fully character-
ized, in which the C–H activation reaction is avoided. Upon
activation with [Ph3C][B(C6F5)4], all complexes show a good
2370 | Dalton Trans., 2012, 41, 2367–2373
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stirring for 48 h and distilled under vacuum before use. The
2-pyridinemethanamine ligand 2,6-diisopropyl-N-(1-(pyridin-2-
yl)ethyl)aniline, C5H4N-CH(Me)-NHC6H3(iPr)2, was prepared
13C NMR (150 MHz, C6D6, 25 ◦C): d 4.58 (s, 6C, CH2SiMe3), 25.40
(s, 2C, THF), 24.58, 25.76, 25.94, 26.11, 27.20 (s, 5C, CH(CH3)2
and NCHCH3), 27.57, 27.98 (s, 2C, CH(CH3)2), 33.63, 35.93 (br
s, 2C, ScCH2SiMe3), 66.86 (s, 1C, NCHCH3), 71.52 (s, 2C, THF),
121.76, 122.93, 124.32, 124.43, 124.95 (s, 5C, Ar-C and Pyridyl-
C), 138.25 (s, 1C, Pyridyl-C), 146.62, 147.56 (s, 2C, Ar-C), 148.31
(s, 1C, Pyridyl-C), 149.80 (s, 1C, Ar-C), 170.03 (s, 1C, Pyridyl-C).
Anal. Calcd for C31H55ON2Si2Sc (%): C, 64.99; H, 9.68; N, 4.89.
Found: C, 65.23; H, 9.51; N, 4.75.
by following the known procedure.15g Ln(CH2SiMe3)3(THF)2
20
was prepared according to the literature. [Ph3C][B(C6F5)4] and
[PhNMe2H][B(C6F5)4] were synthesized following the literature
procedures.21 The microstructure (1,4- and 3,4-) of polyisoprene
was determined by 1H NMR spectra. The molecular weights (Mn)
and molecular weight distributions (Mw/Mn) of polyisoprene were
measured by a TOSOH HLC-8220 GPC. The molecular weights
(Mn) and molecular weight distributions (Mw/Mn) of polyethylene
were measured by means of gel permeation chromatography
(GPC) on a PL-GPC 220 type high-temperature chromatograph
equipped with three PL-gel 10 mm Mixed-B LS type columns at
150 ◦C. 1,2,4-trichlorobenzene (TCB), containing 0.05 w/v % 2,6-
di-tert-butyl-p-cresol (BHT) was employed as the solvent at a flow
rate of 1.0 mL min-1. The calibration was made by polystyrene
standard Easi Cal PS-1 (PL Ltd). Tm of polyethylene was measured
through DSC analyses, which were carried out on a Q 100 DSC
from TA Instruments under a nitrogen atmosphere at heating and
cooling rates of 10 ◦C min-1 (temperature range: 25~300 ◦C).
Synthesis of complex [(C5H4N-CH(Me)-
NC6H3(iPr)2]Y(CH2SiMe3)2(THF) (2)
Following a similar procedure described for the preparation
of 1, complex 2 was isolated from the acid–base reaction of
Y(CH2SiMe3)3(THF)2 (0.495 g, 1.0 mmol) with 1 equiv. of ligand
(0.282 g, 1.0 mmol) in a 54.3% yield (0.335 g). 1H NMR (600 MHz,
C6D6, 25 ◦C): d -0.54 (d, 2JY–H = 12.0 Hz, 1H, YCH2SiMe3), -0.43
(d, 2JY–H = 12.0 Hz, 1H, YCH2SiMe3), -0.27 (d, 2JY–H = 12.0 Hz,
2
1H, YCH2SiMe3), -0.21 (d, JY–H = 12.0 Hz, 1H, YCH2SiMe3),
0.31 (s, 9H, CH2SiMe3), 0.41 (s, 9H, CH2SiMe3), 1.22 (br s, 4H,
THF), 1.33–1.42 (m, 15H, NCHCH3 and CH(CH3)2), 3.48 (br
3
s, 4H, THF), 3.58–3.65 (sept, JH–H = 6.6 Hz, 1H, CH(CH3)2),
X-ray crystallographic studies
4.25–4.32 (sept, 3JH–H = 6.6 Hz, 1H, CH(CH3)2), 4.90–4.94 (quart,
3
Crystals for X-ray analysis were obtained as described in the
preparations. 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-
3JH–H = 6.6 Hz, 1H, NCHCH3), 6.74 (t, JH–H = 12.0 Hz, 1H,
pyridyl-H), 6.87 (d, 3JH–H = 6.0 Hz, 1H, pyridyl-H), 7.04 (t, 3JH–H
=
3
12.0 Hz, 1H, pyridyl-H), 7.17 (t, JH–H = 18.0 Hz, 1H, ArH),
3
3
7.22 (d, JH–H = 6.0 Hz, 1H, ArH), 7.27 (d, JH–H = 6.0 Hz, 1H,
ArH), 9.02 ppm (d, JH–H = 6.0 Hz, 1H, pyridyl-H). 13C NMR
(150 MHz, C6D6, 25 C): d 4.93 (s, 3C, CH2SiMe3), 5.02 (s, 3C,
3
˚
monochromated Mo-Ka radiation (l = 0.71073 A). The deter-
◦
mination 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.
CH2SiMe3), 25.35 (s, 2C, THF), 25.21, 25.69, 26.44, 26.80, 26.87
(s, 5C, CH(CH3)2 and NCHCH3), 27.56, 28.05 (s, 2C, CH(CH3)2),
31.32 (d, JY–C = 37.5 Hz, 1C, YCH2SiMe3), 33.23 (d, JY–C = 37.5
Hz, 1C, YCH2SiMe3), 67.55 (s, 1C, NCHCH3), 70.52 (s, 2C, THF),
121.79, 123.19, 123.91, 124.33, 125.02 (s, 5C, Ar-C and Pyridyl-
C), 138.29 (s, 1C, Pyridyl-C), 148.13, 143.19 (s, 2C, Ar-C), 148.37
(s, 1C, Pyridyl-C), 148.59 (s, 1C, Ar-C), 171.35 (s, 1C, Pyridyl-C).
Anal. Calcd for C31H55ON2Si2Y (%): C, 60.36; H, 8.99; N, 4.54.
Found: C, 60.64; H, 9.01; N, 4.45.
Synthesis of complex [(C5H4N-CH(Me)-
NC6H3(iPr)2]Sc(CH2SiMe3)2(THF) (1)
Synthesis of complex [(C5H4N-CH(Me)-
NC6H3(iPr)2]Lu(CH2SiMe3)2(THF) (3)
Under a nitrogen atmosphere, to a hexane solution (10 mL) of
Sc(CH2SiMe3)3(THF)2 (0.451 g, 1.0 mmol), 1 equiv. of ligand
(0.282 g, 1.0 mmol) was added slowly at 0 C. The mixture was
Following a similar procedure described for the preparation
of 1, complex 3 was isolated from the acid–base reaction of
Lu(CH2SiMe3)3(THF)2 (0.581 g, 1.0 mmol) with 1 equiv. of
◦
stirred for 1 h to afford a clear yellow solution. Evaporation of
the solvent left complex 1 as a yellow crystalline solid (0.357 g,
62.3%). Recrystallization from hexane gave single crystals suitable
ligand (0.282 g, 1.0 mmol) in a 60.1% yield (0.423 g). 1H
NMR (600 MHz, C6D6, 25 ◦C): d -0.73, -0.63 (AB, JH–H
=
2
for X-ray analysis. H NMR (600 MHz, C6D6, 25 ◦C): d -0.30
11.4 Hz, 2H, LuCH2SiMe3), -0.48, -0.37 (AB, JH–H = 11.4
Hz, 2H, LuCH2SiMe3), 0.29 (s, 9H, CH2SiMe3), 0.39 (s, 9H,
CH2SiMe3), 1.20 (br s, 4H, THF), 1.34–1.43 (m, 15H, NCHCH3
and CH(CH3)2), 3.32 (br s, 2H, THF), 3.57 (br s, 2H, THF),
3.59–3.66 (sept, 3JH–H = 6.6 Hz, 1H, CH(CH3)2), 4.26–4.33 (sept,
3JH–H = 6.6 Hz, 1H, CH(CH3)2), 4.96–4.99 (quart, 3JH–H = 6.6 Hz,
1
2
(br s, 1H, ScCH2SiMe3), -0.13 (br s, 1H, ScCH2SiMe3), -0.03 (br
s, 1H, ScCH2SiMe3), 0.12 (br s, 1H, ScCH2SiMe3), 0.25 (s, 9H,
CH2SiMe3), 0.30 (s, 9H, CH2SiMe3), 1.24 (br s, 4H, THF), 1.32–
1.41 (m, 15H, NCHCH3 and CH(CH3)2), 3.46 (br s, 2H, THF),
3
3.53–3.60 (sept, JH–H = 6.6 Hz, 1H, CH(CH3)2), 3.78 (br s, 2H,
THF), 4.15–4.21 (sept, 3JH–H = 6.6 Hz, 1H, CH(CH3)2), 4.88–4.92
1H, NCHCH3), 6.74 (t, JH–H = 12.0 Hz, 1H, Pyridyl-H), 6.86
3
3
3
3
3
(quart, JH–H = 6.6 Hz, 1H, NCHCH3), 6.78 (t, JH–H = 12.8 Hz,
(d, JH–H = 6.0 Hz, 1H, Pyridyl-H), 7.04 (t, JH–H = 18.0 Hz, 1H,
3 3
3
1H, pyridyl-H), 6.86 (d, JH–H = 8.0 Hz, 1H, pyridyl-H), 7.07 (t,
Pyridyl-H), 7.18 (t, JH–H = 12.0 Hz, 1H, ArH), 7.23 (d, JH–H =
3
3JH–H = 15.4 Hz, 1H, pyridyl-H), 7.20–7.21 (m, 2H, ArH), 7.28–
7.29 (m, 1H, ArH), 9.08 ppm (d, 3JH–H = 5.4 Hz, 1H, pyridyl-H).
6.0 Hz, 1H, ArH), 7.29 (d, JH–H = 6.0 Hz, 1H, ArH), 8.98 ppm
3
(d, JH–H = 6.0 Hz, 1H, Pyridyl-H). 13C NMR (150 MHz, C6D6,
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2367–2373 | 2371
©

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◦
25 C): d 5.01 (s, 3C, CH2SiMe3), 5.14 (s, 3C, CH2SiMe3), 25.37
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(br s, 2C, THF), 25.50, 25.83, 26.22, 26.60, 26.99 (s, 5C, CH(CH3)2
and NCHCH3), 27.51, 27.98 (s, 2C, CH(CH3)2), 37.36, 40.10 (s,
2C, LuCH2SiMe3), 67.67 (s, 1C, NCHCH3), 70.76 (s, 2C, THF),
121.86, 123.31, 123.82, 124.31, 124.96 (s, 5C, Ar-C and Pyridyl-
C), 138.29 (s, 1C, Pyridyl-C), 147.70, 147.97 (s, 2C, Ar-C), 148.17
(s, 1C, Pyridyl-C), 150.22 (s, 1C, Ar-C), 171.32 (s, 1C, Pyridyl-C).
Anal. Calcd for C31H55ON2Si2Lu (%): C, 52.97; H, 7.89; N, 3.99.
Found: C, 53.31; H, 7.71; N, 4.05.
Isoprene polymerization
A detailed polymerization procedure is described as follows (run
2, Table 1). Under a nitrogen atmosphere and room temperature,
a toluene solution (2 mL) of [Ph3C][B(C6F5)4] (9.2 mg, 10 mmol)
was added to a toluene solution (3 mL) of complex 1 (5.7 mg,
10 mmol) in a 25 mL flask. Then 10 equiv. of AliBu3 (0.1 mL,
100 mmol, 1.0 M in toluene) were added under stirring after a
few minutes. Upon the addition of 1000 equiv. of isoprene (1 mL,
0.01 mol), polymerization was initiated and carried out for 2 min.
The reaction mixture was poured into a large quantity of methanol
and then dried under vacuum at ambient temperature to a constant
weight (0.68 g, 100%).
Ethylene polymerization
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160.
A detailed polymerization procedure is described as a typical
example (run 3, Table 2). In a glovebox, a toluene solution (40 mL)
of complex 1 (5.7 mg, 10 mmol) was charged into a two-necked
flask with a magnetic stir bar. The flask was taken outside of the
glove box and set in a water bath, and connected to a well-purged
Schlenk ethylene line with a mercury-sealed stopper by use of a
three-way cock. Ethylene (1.0 bar) was introduced into the system
and was saturated in the solution at 60 ◦C by stirring for 5 min. The
toluene solution of [Ph3C][B(C6F5)4] (9.2 mg, 10 mmol) and AliBu3
(0.1 mL, 100 mmol, 1.0 M in toluene) was then added through
a syringe under vigorous stirring. The mixture was stirred under
constant ethylene pressure (1.0 bar) for 5 min. After that, methanol
(2 mL) was added to terminate the reaction, and the reaction
mixture was added to acidified methanol (20 mL concentrated
HCl in 500 mL of ethanol). Polyethylene was obtained by filtration,
washed with methanol, and dried at 40 ◦C for 24 h in vacuum.
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Acknowledgements
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references therein.
This work was partly supported by The National Natural Science
Foundation of China for project Nos. 20934006, 51073148, and
51021003. The Ministry of Science and Technology of China for
projects Nos. 2009AA03Z501 and 2011DF50650.
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˚
group P21/c; a = 16.5704(11),◦b = 11.4058(7), c = 19.3785(12) A; a =
◦
◦
3
˚
90 , b = 107.0320(10) , g = 90 ; V = 3501.9(4) A ; Z = 4; Dc = 1.087 g
cm-3; m(MoKa) = 3.02 cm-1; 2qmax = 50.10◦; F(000) = 1248; no. of obsd
reflns = 6177; no. of params refnd = 351; GOF = 1.053; R1 = 0.0530;
wR2 = 0.1407 (all data).
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This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2367–2373 | 2373
©