Nature of the Entire Range of Rare Earth Metal-Based Cationic Catalysts for Highly Active and Syndioselective Styrene Polymerization

Article abstract of DOI:10.1021/acscatal.5b02334

Because of the steric bulkiness and the η⁵/κ¹-constrained-geometry-configuration (CGC) geometry, the entire range of pyridyl-methylene-fluorenyl-stabilized rare earth metal bisalkyl complexes, (Flu-CH₂-Py)Ln(CH₂SiMe₃)₂(THF)_x (Flu = fluorenyl; Py = pyridyl; for 1, Ln = Sc and x = 0; for 2-11, Ln = Lu, Tm, Er, Ho, Y, Dy, Tb, Gd, Nd, or Pr and x = 1), and monoalkyl complex, (Flu-CH₂-Py)₂La(CH₂SiMe₃) (THF) (12), has been successfully achieved for the first time via the sequential salt metathesis reactions. Activated by [Ph₃C][B(C₆F₅)₄] and AlⁱBu₃, complexes 1-9 showed high activity and perfect syndioselectivity for styrene polymerization, while the large Nd- and Pr-attached precursors 10 and 11 exhibited slightly decreased syndioselectivity but rather low activity; the monoalkyl La precursor 12 was completely inert. The activity increased with the decrease in the rare earth metal size, in striking contrast to the literature that has shown that a large metal facilitates a high activity, which was also not a result of an enthalpic effect (ΔH^≠) or an entropic effect (ΔS^≠) according to Eyring plots. The types of organoborates and the aluminum alkyls, the electron donors, and the polarity of the reaction medium, which affected the coordination of styrene to the active species, aroused significantly different catalytic activity, indicating that styrene coordination played the key role in the polymerization process. On the basis of this, the density functional theory calculation of the active species in the model of [(Flu-CH₂-Py)Ln-nC₁₇H₁₉]⁺ revealed whenever the orbitals of the pyridyl-methylene fluorenyl ligand overlapped with those of the rare earth metals, the LUMO energy of the active species was lowered and thus the catalytic activity was high. Therefore, the LUMO energy of the active species could be adopted as a potential criterion to estimate the activity of a catalytic system for styrene polymerization. This work reveals for the first time the power of the pyridyl-methylene fluorenyl ligand and the nature of the factors influencing the catalytic performance.

Full text of DOI:10.1021/acscatal.5b02334

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Article
Nature of the Entire Range of Rare-Earth Metal Based Cationic
Catalysts for Highly Active and Syndioselective Styrene Polymerization
Fei Lin, Xingbao Wang, Yupeng Pan, Meiyan Wang, Bo Liu, Yi Luo, and Dongmei Cui
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b02334 • Publication Date (Web): 23 Nov 2015
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Nature of the Entire Range of RareꢀEarth Metal Based Cationic Catalysts for Highly
Active and Syndioselective Styrene Polymerization
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Fei Lin1,2, Xingbao Wang3, Yupeng Pan1,2, Meiyan Wang4, Bo Liu,1* Yi Luo,3* and Dongmei Cui 1*
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1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, China
2University of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, China
3State Key Laboratory of Fine Chemicals, School of Pharmaceutical, Science and Technology, Dalian
University of Technology, Dalian 116024, China
4Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry,
Jilin University, Changchun 130022, China
*Corresponding authors: FAX +86 431 85262774; eꢀmail dmcui@ciac.ac.cn; liubo@ciac.ac.cn;
luoyi@dlut.edu.cn.
ABSTRACT
By
merit
of
the
steric
bulkiness
geometry,
and
the
the
η5/κ1ꢀconstrainedꢀgeometryꢀconfiguration
(CGC)
pyridylꢀmethyleneꢀfluorenyl stabilized entire range of rareꢀearth metal bis(alkyl)
complexes, (FluꢀCH2ꢀPy)Ln(CH2SiMe3)2(THF)x (Flu = fluorenyl; Py = pyridyl; 1: Ln
= Sc, x = 0; 2–11: Lu, Tm, Er, Ho, Y, Dy, Tb, Gd, Nd, Pr, x = 1) and mono(alkyl),
(FluꢀCH2ꢀPy)2La(CH2SiMe3)(THF) (12), have been successful achieved for the first
time via the sequential salt metathesis reactions. Activated by [Ph3C][B(C6F5)4] and
AliBu3, complexes 1–9 showed high activity and perfect syndioselectivity for styrene
polymerization, while the large Nd and Pr attached precursors 10 and 11 exhibited
slightly dropped syndioselectivity but rather low activity, and the monoalkyl La
precursor 12 was completely inert. The activity increased with the decrease of the
rareꢀearth metal size, in striking contrast to the literatures that a large sized metal
facilitates a high activity, which was also not a result of enthalpic effect (∆H‡) or
entropic effect (∆S‡) according to Eyring plots. The types of the organoborates and the
aluminum alkyls, the electronꢀdonors and the polarity of reaction medium, which
affected the coordination of styrene to the active species, aroused significantly
different catalytic activity, indicating that styrene coordination played the key role in
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the polymerization process. Based on this, the DFT calculation of the active species in
the model of [(FluꢀCH2ꢀPy)Ln−nC17H19)]+ revealed whenever the orbitals of the
pyridylꢀmethylene fluorenyl ligand overlapped with those of the rareꢀearth metals, the
LUMO energy of the active species was lowered and thus the catalytic activity was
high. Therefore the LUMO energy of the active species could be adopted as a
potential criterion to estimate the activity of a catalytic system for styrene
polymerization. This work reveals for the first time the power of the
pyridylꢀmethylene fluorenyl ligand and the nature of the factors influencing the
catalytic performances.
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INTRODUCTION
The cationic group 3 metal alkyl complexes have reached an upsurge of research
interests in the past two decades not only because they possess versatile catalytic
peroformances upon activation with MAO, or aluminum alkyls/organoborates for the
olefin (co)polymerizations, but also their potential of generating marvelous catalysis
when changing the electron donating or withdrawing substituents and the steric
bulkiness of the ligands, since no other metals have so variable electronics (d0−1−f0−14
)
and sterics (ionic radius: 0.89 − 1.17 Å).1 As the 4f electrons are believed not involve
in ligand or substrate bonding, the relative reactivity of these rareꢀearth metals based
catalytic precursors is expected to be determined mainly by the metal ionic radius.
However, to illustrate this has been a challenging project of the academic area, since
any one ligand is difficult to cover the entire range of rareꢀearth metals, in particular
the large ones for which the bisꢀ or trisꢀligands supported complexes are usually
isolated as the major products arising from ligand disproportionation. Okuda found
that the dicationic rareꢀearth metal (heavier than Tb) alkyl species without attaching to
any ligands displayed an increasing activity for ethylene polymerization with increase
of the ionic radius.2 Hessen discovered the amidinate ligand was fit for the full range
of cationic rareꢀearth metal monoalkyl species, of which the yttrium species exhibited
the highest activity.3 With regard to the polar monomer, Yasuda also found the
catalytic activity of Cp*2LnMe(THF) increased with the metal ion size towards the
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group transfer coordination polymerization (GTP) of MMA.4 It is the commonly
adopted explanation that the large sized active metal center facilitates the
polymerization owing to it providing a more opening coordination sphere, which,
however, usually lacks scrutinized investigation. Very recently, Rieger reported the
catalytic activity of Cp3Ln being accelerated by decreasing the metal radius for GTP
of vinylphosphonates, who elegantly explained and proved the origin being that the
steric demanding (small) active metal center changed slightly the ꢀS‡ of the transition
state while the less steric (large) active metal center dramatically decreased the ꢁS‡
but the ꢁH‡ remained constantly in both cases.5 The contradictive picture leaves the
investigation of the following questions open: What is the nature concerning the
relationship between the polymerization activity and the rareꢀearth catalyst? Does the
ligand play any role in it?
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Syndiotactic polystyrene (sPS) is a promising engineering plastics due to its high
melting point, rapid crystallization ability, high tensile modulus, low dielectric
constant and excellent resistance to heat and chemicals.6 The most efficient catalytic
systems towards syndiotactic styrene polymerization belong to the group 4 titanium
complexes.7 In contrast, the group 3 rareꢀearth metal complexes are always inert to
this polymerization until 2004 Carpentier reported the distinguished catalytic activity
(1710 Kg(sPS)·mol(Ln)–1·h–1) of the netural allyl ansaꢀneodymocene catalyst,
[FluꢀCMe2ꢀCp]Nd(C3H5)(THF), for the bulk styrene polymerization at 60 ºC.8 Almost
at the same time, Hou reported the first cationic halfꢀSandwich scandium alkyl
catalyst system, [(C5Me4SiMe3)Sc(CH2SiMe3)(THF)][B(C6F5)4], with the excellent
activity (13618 Kg(sPS)·mol(Ln)–1·h–1) and syndioselectivity (rrrr > 99 %).9 Thereafter,
many scandium precursors and only the scandium based precursors bearing
cyclopentadienyl Cp,10 linked Cp,11 heteroꢀCp,12 indenyl13 and fluorenyl14 ligands
unambiguously showed the similar distinguished performances, which seems to be
attributed to the nature of the scandium, electronically close to titanium. We reported
the pyridineꢀCp* ligated lutetium allyl complex, (C5Me4ꢀC5H4N)Lu(C3H5)2,15 which,
under the activation of [Ph3C][B(C6F5)4], can convert unprecedentedly 1000 equiv
styrene into sPS within 1 min but its yttrium analogue displayed a much lower activity.
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Therefore to explore the possibility of other lanthanide metals (much abundant and
cheaper) based complexes to catalyze this stereospecific polymerization and the
mechanism proceeded, is a great challenging but very attractive project from both
academic and industry points of view.
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Very recently, we found that the constrainꢀgeometryꢀconfiguration (CGC) pyridine
methylene fluorenyl (PyꢀCH2ꢀFlu) ligand stabilized rareꢀearth metal scandium,
yttrium and lutetium precursors all showed distinguished activity and
syndioselectivity.16 Herein we report this powerful PyꢀCH2ꢀFlu ligand, by the merit of
its steric bulkiness and the η5/κ1ꢀCGC structure, not only can stabilize almost the
entire range of rareꢀearth metal dialkyl species but also affect the catalytic activity of
the central metals to such a degree that most of the rareꢀearth metal precursors upon
activation show very high activity towards styrene polymerization except those of
large metals such as Nd and Pr. DFT calculation, thermaldynamics (Eyring plots), and
kinetics, as well as factors that may influence styrene coordination/insertion, were
investigated to scrutinize the nature of the catalytic activity of styrene polymerization
catalyzed by rareꢀearth metal complexes. Based this, a criterion to estimate the
catalytic activity is proposed.
RESURTS AND DISCUSSION
Synthesis and Characterization of Complexes 1–12. Since the preparation of
rareꢀearth metal alkyl complexes through deprotonating the ligand by the
corresponding rareꢀearth metal tris(alkyl)s16 was only available for metals of the sizes
smaller than Tb,2 complexes 1–12, [(η5ꢀFluꢀCH2ꢀPy)Ln(CH2SiMe3)2(THF)n, were
prepared via metathesis reaction between the lithium salt of pyridylꢀmethylene
functionalized fluorene (FluꢀCH2ꢀPy)Li and LnCl3 followed by the lithiation reaction
with 2 equiv Me3SiCH2Li (Ln = Sc (1), yield: 85%; for 2–9: Ln = Lu, Tm, Er, Ho, Y,
Dy, Tb, Gd in 70ꢀ80% yields). However, complexes 10 (Ln = Nd) and 11 (Ln = Pr)
were isolated at lower yields (10: 30 %; 11: 25%) since the strong Lewis acidity and
the large ionic radii of Pr and Nd metals led to unknown byproducts. The largest
lanthanum attached complex 12 was isolated as a mono(alkyl) (yielding 10%)
evidenced by the integral intensity ratio of 1:2 for the methylene protons from
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CH2SiMe3 (two doublets centered at –1.70 and –2.82 ppm) and the pyridylꢀmethylene
(doublet at 3.74 and 3.84 ppm) (Scheme 1). The scandium complex 1 is a solventꢀfree
monomer while 2–11 bear one solvated THF molecule. The auxiliary ligand
coordinates to the central metal ions in the η5/κ1ꢀCGC mode via the Cp carbons and
the dangling pyridyl nitrogen atom, combining two alkyl groups and a THF molecule
to generate a tetrahedral geometry around the metal center (Figure 1 for complex 11
and Figures S1−S3 from complexes 4, 9 and 10). These molecular structures are
consistent with those of yttrium and lutetium analogues reported previously.16 With
the ionic radius increasing, the Ln−Calkyl bond lengths increase (Table S1),
correspondingly, the Cpcent−Ln−N bite angles decrease (Lu: 92.23°, Er: 91.53°,Gd:
89.75°, Nd: 88.20°, Pr: 88.58°), all are smaller than 95.4(3)° of Cpcent1–Y(1)–N(1) in
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17
the complex NMe2ꢀC6H4ꢀCp*Y(C3H6)2 of an inert system to the styrene
polymerization, suggesting that this pyridylꢀmethyleneꢀCp* CGCꢀligand generates a
relatively opening sphere around the metal center irrespective of the ionic size.
Scheme 1. Synthesis of rare earth metal alkyl complexes 1–12.
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Figure 1. Xꢀray structure of complex 11 with thermal ellipsoids drawn at the 30%
probability level. Hydrogens are omitted for clarity.
Styrene polymerization
All these complexes 1−12 in combination with [Ph3C][B(C6F5)4] and AliBu3 were
employed to catalyze styrene polymerization. The scandium complex 1 showed the
highest activity to convert 10 000 equivalents styrene within 1 h to afford polystyrene
with high molecular weight (Mn = 82.3×104), narrow molecular weight distribution
(PDI = 1.73) and perfect syndiotacticity (Table 1, entry 1), comparable to the
literature.16 Surprisingly, complexes 2−9 based on the lanthanide elements varying
from Gd to Lu also displayed excellent performances with respect of the activity and
syndioselectivity (Table 1, entries 2−14). The polymerization performed in the
controlled manner that by using complex 5 as the catalyst changing the
monomerꢀtoꢀinitiator ratio from 500 to 5000, the molecular weight of the resultant
sPS almost increased proportionally, meanwhile the molecular weight distribution
kept constant (Table 1, entries 5−8). In addition, such distinguished catalytic
performances remained at elevated polymerization temperatures up to 80 ºC (Table 1,
entry 9). However, the large metal Nd and Pr precursors 10 and 11 showed much
lower activity albeit with the slightly dropped syndioselectivity while the lanthanum
mono(alkyl) complex 12 was completely inert (Table 1, entries 15−17). This
represented the rare example that most of the lanthanide elements based precursors
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displayed high activity towards syndioselective styrene polymerization, which might
be attributed to the power of the ligand that provided a more opening coordination
sphere by forming smaller bite angles with the rareꢀearth metals as compared to other
CGCꢀrareꢀearth metal analogues (vide supra).
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Table 1. Syndiospecific polymerization of styrene with rareꢀearth metal dialkyl
complexes 1−12 activated by AliBu3 and [Ph3C][B(C6F5)4] under various conditions.a
d
d
Entry Cat. [St]/Ln t(min)b Conv.(%) sPSc(%) Mn ×10ꢀ4 Mw/Mn
e
Tm (
℃)
1
2
3
4
5
6
7
8
Sc(1) 10000
Lu(2) 10000
Tm(3) 5000
60
120
30
30
5
5
10
30
30
120
120
90
90
90
36 h
72 h
72h
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
92
82.3
67.3
63.2
64.0
5.9
10.7
34.2
60.4
44.6
68.9
67.7
48.3
46.2
48.7
29.1
22.2
ꢀꢀ
1.73
1.60
1.48
1.48
1.11
1.15
1.31
1.52
1.44
1.62
1.81
1.61
1.60
1.56
1.84
2.00
ꢀꢀ
270
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
＞
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
270
270
270
270
270
270
270
270
270
270
270
270
270
256
252
ꢀꢀ
Er(4)
Ho(5)
5000
500
Ho(5) 1000
Ho(5) 2500
Ho(5) 5000
9f Ho(5) 5000
10 Ho(5) 10000
11 Y(6) 10000
12 Dy(7) 5000
13 Tb(8) 5000
14 Gd(9) 5000
15 Nd(10) 5000
16 Pr(11) 5000
17 La(12) 1000
90
ꢀꢀ
ꢀꢀ
a
Polymerization conditions: Ln (10
ꢁ
mol), [Cat]/AliBu3/[Ph3C][B(C6F5)4] = 1/10/1
(mol/mol/mol), when [St]/Ln
≤5000, toluene/monomer = 5/1 (v/v) ([St]/Ln = 10 000,
toluene/monomer = 2.5/1 (v/v)), Tp = 15 oC, unless otherwise noted. b The time hasn’t
been optimized. cMeasured by 1H NMR and 13C NMR spectroscopy in
o
tetrachloroethaneꢀd2 at 125 C. dDetermined by GPC in 1,2,4ꢀtrichlorobenzene at 150
f
oC against polystyrene standard. eDetermined by DSC.
Tp = 80 oC,
toluene/monomer = 15/1 (v/v).
Kinetics Experiments
The polymerization catalyzed by all complexes under low conversions indicated
the different polymerization rates of these complexes (Table S2), which could be
explicated in more details by the kinetics study at low monomer concentrations. The
linearship between ln{[St]0/[St]t} and time indicates the firstꢀorder dependence of
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polymerization rate on the styrene concentration catalyzed by complexes 1ꢀ11 (Figure
S5). The observed rate constant (kobs) for the catalyst based on Lu (2), Tm (3), Er (4),
Ho (5), Y (6), Dy (7), Tb (8) or Gd (9) was 6.0×10–2, 5.4×10–2, 5.2×10–2, 3.6×10–2,
3.3×10–2, 2.1×10–2, 2.1×10–2 and 1.7×10–2 minꢀ1 (Figure S4), respectively, which,
roughly, was one order of magnitude lower than the scandium complex 1 (12.9×10–2
minꢀ1) and one order of magnitude higher than the neodymium complex 10 (0.2×10–2
minꢀ1) and praseodymium complex 11 (0.1×10–2 minꢀ1). Apparently, the order of the
catalytic activity was well correlated with the effective ionic radius of the rareꢀearth
metal: the smaller the metal size, the higher the catalytic activity of the corresponding
complex (Figure 2). Noteworthy was that, the influence of the metal size on the
activity was opposite to the previous reports by Okuda and Hessen for ethylene
polymerization.2,3 Yasuda also found the GTP activity of MMA increased with the
increasing metal ion size although it was performed in different mechanism. These
results are understandable since it is commonly accepted that large metal center
usually provides opening coordination sphere to facilitate the polymerization,
although it lacks a direct proof.4 To date the only similar phenomena was reported by
Rieger that the catalytic activity of Cp3Ln was accelerated by decreasing the metal
radius for GTP of vinylphosphonates, which was attributed to the steric demanding of
the active metal center by changing the ∆S‡of the transition state.5 Hence, Eyring
analyses of styrene polymerization using scandium complex (1), lutetium complex (2),
holmium complex (5) and gadolinium complex (9) as catalytic precursors were
carried out.
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As shown in Table 2, the increase of metal ionic radius led to drop of the enthalpy
∆H‡ (Lu(2) 59.5 kJ molꢀ1 > Ho(5) 56.8 kJ molꢀ1> Gd(9) 55.8 kJ molꢀ1) but enhance of
ꢀT∆S‡ (Lu(2) 30.6 kJ molꢀ1 < Ho(5) 35.1 kJ molꢀ1 < Gd(9) 36.6 kJ molꢀ1). For the Sc (1)
precursor, a much lower ∆H‡ (40.6 kJ molꢀ1) was observed but was accompanied by a
much increased ꢀT∆S‡ (48.7 kJ molꢀ1). Therefore, it was hard to conclude that the
increase of polymerization activity with the decreasing metal ionic radius was a result
of enthalpic effects (∆H‡)18 or entropic effects (∆S‡)5. This was inconsistent with the
explanation drawn from the coordinationꢀanionic GTP of vinylphosphates where the
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smaller metal size accelerated the activity by dramatically increasing the ∆S‡ but
keeping ∆H‡ constant, because the crowded active metal center destabilized the
transition state.5
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0.12
0.10
0.08
0.06
0.04
0.02
0.00
Sc
Lu Tm
Er
Ho
Y
Dy
Tb
Gd Nd
Pr
Figure 2. The observed rate constants (kobs) of complexes 1−11 vs ionic radius (Ln
(10 ꢁmol), [Ln]/[AliBu3]/[Ph3C][B(C6F5)4]/[St]
=
1/5/1/2000 (in mole),
toluene/monomer = 30/1 (v/v), Tp = 15 °C)
Table 2. Activation enthalpy ∆H‡, ∆S‡ and kobs for the catalytic systems based on Sc
(1), Lu(2), Ho(5) and Gd(9) precursors.
Cat.
kobs×102 min
∆H‡(±2)(kJ·mol–1) ∆S‡(±2)( J
· ·
mol–1 K–1)a
Sc(1)
Lu(2)
Ho(5)
Gd(9)
12.9
6.0
3.6
40.6
59.5
56.8
55.8
–169.09
–106.09
–121.89
–126.96
1.7
a The polymerization temperature T = 288 K.
Origin of High Catalytic Activity
The binary catalytic system 1/[Ph3C][B(C6F5)4] was active towards styrene
polymerization but 6/[Ph3C][B(C6F5)4] was nearly inert under the same conditions
(Table 3, entries 1 and 2). The major difference between the two systems was 6
containing a solvated THF molecule. As reported previously, THF could be abstracted
easily by AliBu3 from the active metal center.19 Indeed, addition 1 equiv AliBu3 to
6/[Ph3C][B(C6F5)4] brought about an obvious increase of the activity (Table 3, entry
3). DFT calculation revealed that the barrier height for the styrene insertion process
between
the
systems
6/[Ph3C][B(C6F5)4]
(13.0
kcal/mol)
and
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6/[Ph3C][B(C6F5)4]/AliBu3 (11.4 kcal/mol) has no big difference as reported
previously,14 but the styrene coordination energy for the THF solvated former system
(16.4 kcal/mol) is 15.7 kcal/mol higher than the late system without THF (0.7
kcal/mol) (Figure 3), suggesting that abstracting THF to generate a vacancy for
monomer coordination is crucial to the polymerization.8 Hence, THF presence or not
is superficial phenomenon in structures, whether it impedes the coordination of
monomer to the active metal center is the reason behind it. This can explain why some
THF solvated systems are active to ethylene or styrene etc polymerizations.9,17
Replacing [Ph3C][B(C6F5)4] by [PhNMe2H][B(C6F5)4] to activate the scandium
complex 1 generated a low active system (Table 3 entries 4 and 5). The reaction was
monitored by 1H NMR spectroscope technique to show that the methylene protons of
3
4
5
6
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9
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2
2
ScCH2SiMe3 shift downfield (2.56: d, d, JH,H = 12 Hz; 1.94: d, JH,H = 15 Hz) as
compared to that in 1/[Ph3C][B(C6F5)4],20 meanwhile, the methyl protons of the
resultant PhNMe2 show at a higher field (2.85 ppm) than the free PhNMe2 (2.95 ppm)
because it coordinate to the Sc3+.21 Hence, Lewis base PhNMe2 reduces the catalytic
activity by occupying the active sites to obstruct styrene coordination.8,22 The lowest
activity of the system 1/[NEt3H][B(C6H6)4] might be ascribed to the interaction of the
–
counter anion B(C6H6)4 with the active metal center Sc3+ in a η2(m,p)ꢀmode (DFT
simulation result, Figure S9)23 thus blocking styrene coordination (Table 3, entry 6),
which was further proved by the 1H NMR spectrum analysis that the resonances of the
–
four phenyl rings from B(C6H6)4 are asymmetric and split into two sets.24 Moreover,
performing the polymerization in polar medium such as chlorobenzene (ε = 2.7), the
catalytic activity of 6/[Ph3C][B(C6F5)4]/AliBu3 was dramatically improved than those
in nonꢀpolar solvent such as hexane (ε = 0.06) (Table 3, entries 7−10), since the
interaction between the cation and anion was weakened in the polar medium, leaving
more space for styrene coordination.25 The above results demonstrated that any
factors influencing the coordination of styrene to the active metal center would arouse
obvious change of the activity, suggesting it being the rateꢀlimiting step.
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Figure 3. Free energy profiles calculated for coordination and insertion of styrene
with THF in the activated species.
Table 3. Syndiospecific polymerization of styrene with rareꢀearth metal bisalkyl
complexes 1 and 6 under various conditions.a
c
c
run
1
2
3
4
5
6
7
8
Cat./Borate/[Al]
1/[Ph3C][B(C6F5)4]/0
6/[Ph3C][B(C6F5)4]/0
6/[Ph3C][B(C6F5)4]/1.0
1/[Ph3C][B(C6F5)4]/0
Solvent
Toluene
Toluene
Time/min conv.b (%)
Mn (×10ꢀ4)
Mw/Mn
1.40
ꢀ
2
3
10
ꢀ
9.8
ꢀ
7.0
Toluene
3
8
1.15
1.45
1.54
1.74
4.60
1.97
1.19
1.26
Chlorobenzene
0.5
0.5
30
4
44
6
5
11.9
11.1
1.0
1/[PhNMe2H][B(C6F5)4]/0 Chlorobenzene
1/[NEt3H][B(C6H5)4]/0
6/[Ph3C][B(C6F5)4]/10.0
Chlorobenzene
Hexane
6
2.0
6.9
6/[Ph3C][B(C6F5)4]/10.0 Hexane/Toluened
4
4
4
21
49
71
9
10
6/[Ph3C][B(C6F5)4]/10.0
6/[Ph3C][B(C6F5)4]/10.0
Toluene
Chlorobenzene
16.4
23.8
a
Polymerization conditions: Ln = 10 ꢁmol, Tp = 15 °C, [Cat]/[St] = 1/2000 (entries
1ꢀ4) and 1/1000 (entries 5ꢀ10), solvent/monomer (v/v) = 20/1 (entries 1ꢀ4) and 10/1
(entries 5ꢀ1), according to the 13C NMR spectroscopy of the afforded polymer in
o
b
c
tetrachloroethaneꢀd2 at 125 C, rrrr > 99%; Calculated by weight; Determined by
d
GPC in 1,2,4ꢀtrichlorobenzene at 150 oC against polystyrene standard;
Hexane/toluene = 1:1 (v/v).
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6
As far as styrene coordination polymerization is concerned, the electron donation
−C=C bonding to the empty orbital of the active metal center is generally dominant.
π
7
8
9
Thus the energy gap (∆E) between the HOMO level of styrene (–0.22588 au) and the
LUMO level of the active species should refelect the catalytic activity on the basis of
the frontier molecular orbital theory. It is generally accepted that the cationic active
species of styrene polymerization is the metal center coordinated by the last inserted
styrene in η3ꢀallyl mode and the phenyl ring of penultimate inserted styrene.26 This
allowed us to establish the mode of the active species [(Flu−CH2−Py)Ln−(C17H19)]+
where the growing polystyrene chain is simplified as a methyl group and two
phenyls of styrene are distributed on both sides of the metal center (Figure 4).
10
11
12
13
14
15
16
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Figure
4.
The
simulation
structure
of
the
active
species
[(Flu−CH2−Py)Ln−(C17H19)]+.
Table 4. Energies of the LUMO of [(Flu−CH2−Py)Ln−(C17H19)]+ and energy gaps
(∆E) of HOMO of styrene and LUMO of [(Flu−CH2−Py)Ln−(C17H19)]+. a
Metal
Sc
Lu
Tm
Er
Ho
Y
Dy
Tb
Gd
Nd
Pr
La
ELUMO (au) ꢀ0.17312 ꢀ0.16752 ꢀ0.16703 ꢀ0.16670 ꢀ0.16645 ꢀ0.16607 ꢀ0.16607 ꢀ0.16584 ꢀ0.16561 ꢀ0.16445 ꢀ0.16403 ꢀ0.16328
∆Eb (au)
0.05276 0.05885 0.05918 0.05943 0.05962 0.05836 0.05981 0.06004 0.06027 0.06143 0.06185 0.06260
kobs×102 (min–1) 12.7
6.0
5.4
5.2
3.6
3.3
2.1
2.1
1.7
0.2
0.1
ꢀ
a The LUMO energy of [(Flu−CH2−Py)Ln−(C17H19)]+ was analyzed on the basis of its
b
optimized geometry afforded via using small core RECPs basic sets;
∆E =
ELUMO(active species) – EHOMO(Styrene) (EHOMO(Styrene) = –0.22588 au).
The LUMO energies of [(Flu−CH2−Py)Ln−(C17H19)]+ (Ln = Sc, Lu, Tm, Er, Ho, Y,
Dy, Tb, Gd, Nd, Pr, La) were analyzed on the basis of its optimized geometry
afforded via using small core RECPs basic sets. The results were summarized in
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Table 4. The cationic scandium species [(Flu−CH2−Py)Sc−(C17H19)]+ possesses the
lowest LUMO energy, leading to the smallest energy gap (∆E) (0.05276 au) between
it and the HOMO energy of styrene. While the LUMO energy of the other cationic
rareꢀearth metal species [(Flu−CH2−Py)Ln−(C17H19)]+ increased from –0.16752 to –
0.16328 corresponding to Ln = Lu, Tm, Er, Ho, Y, Dy, Tb, Gd, Nd, Pr and La,
respectively, in well consistence with the kinetics behavior of the precursors 1–11
(vide supra): the lower the LUMO energy is, the higher the activity is. As shown in
Figure 5, the LUMOs of the highly active species ([(Flu−CH2−Py)Ln−(C17H19)]+)
based on the rareꢀearth metals varying from Lu to Gd are formed by atomic orbitals
(AOs) from the metal, the ligand and the growing polystyrene chain, while those of
the low active La, Pr and Nd species have no contribution from the ligand,
suggesting that the participation of ligand orbital could reduce the energy of LUMO
and therefore make the LUMO energy closer to the HOMO of styrene.
3
4
5
6
7
8
9
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Sc
Y
La
Pr
Nd
Gd
Tb
Dy
Ho
Er
Tm
Lu
Figure 5. LUMOs of [(FluꢀCH2ꢀPy)Ln−(C17H19)]+ complexes. The isosurface value
of the MOs is set to be 0.03 au.
The LUMO energy of the active species could also be used to explain the activity
of other catalyst systems for the styrene polymerization. For instance, the LUMO
energy
of
the
cationic
halfꢀSandwich
rareꢀearth
metal
systems
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[(C5Me4SiMe3)Ln−(C17H19)]+ followed the order of Sc < Gd < Y < Lu, in well
agreement with the trend of the catalytic activity Sc > Gd > Y > Lu of the
experimental results9 (Figure S10). We synthesized the scandium and yttrium
precursors 13 and 14 (Chart 1) bearing the pyridylꢀmethylene dibenzo[a,i]fluorene
ligand, (FludibenzoꢀCH2ꢀPy)Ln(CH2SiMe3)2(THF)n (Ln = Sc (13), n =0; Y (14), n = 1),
the structurally analogues of 1 and 6. 13 showed an even higher activity (18 700
kg/(mol(Ln)•h) than 1 because of its low LUMO energy (ELUMO: –0.17425 au),
whilst its analogue 14 could only initiate the sluggish polymerization of styrene
similar to the Nd active species 10 but much lower than 6 (kobs: 0.4×10–2 minꢀ1 (14)
vs 0.2×10–2 minꢀ1 (10) vs 3.3×10–2 minꢀ1 (6)), in consistence with their LUMO
energies (ELUMO: –0.16477(14) vs –0.16445(10) vs –0.16607(6)).
3
4
5
6
7
8
9
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Chart 1. The structures of (FludibenzoꢀCH2ꢀPy)Sc(CH2SiMe3)2 (13) and
(FludibenzoꢀCH2ꢀPy)Y(CH2SiMe3)2(THF) (14).
CONCLUSION
Highly active and syndiotactic styrene polymerization catalyzed by the almost entire
period of rare earth metals based dialkyl complexes bearing the pyridylꢀmethylene
fluorene ligand except those attached to Nd and Pr elements, has been realized for the
first time, which is contributed mainly to the powerful ligand of steric bulkiness and
its CGC structure, which provides an opening coordination sphere for styrene
monomer. Apparently, the higher the catalytic activity is the smaller the metal size is,
in fact, the origin of which is that the orbitals of the ligand participates to form and
reduce the LUMO of the active species to facile the coordination of styrene to the
active metal species in the cases of small rareꢀearth metal center proved by the LUMO
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energy of the active species according to DFT simulation. Hence, the LUMO energy
of the active species could be considered as a potential criterion to estimate the
catalytic activity of rareꢀearth metal complexes toward styrene polymerization
whenever the styrene coordination being the key step in the polymerization process.
10
11
12
13
14
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EXPERIMENTAL SECTION
General Methods and Materials. All reactions were carried out under a dry and
oxygenꢀfree argon atmosphere by using Schlenk techniques or under a nitrogen
atmosphere in an MBraun glovebox. All solvents were purified from an MBraun SPS
system. Samples of organo rareꢀearth metal complexes for NMR spectroscopic
measurements were prepared in the glovebox by use of NMR tubes sealed by paraffin
film.1H and13C NMR spectra were recorded on a Bruker AV400 or 600 (FT, 400 or
1
13
1
600 MHz for H; 100 or 150 MHz for C) spectrometer. H, 13C NMR spectra of
1
polymer samples were recorded on a Bruker AV400 (FT, 400 MHz for H; 100MHz
for 13C) spectrometer in tetrachloroethaneꢀd2. The molecular weight and molecular
weight distribution of the polymers were measured by means of gel permeation
chromatography (GPC) on a PLꢀGPC 220 type highꢀtemperature chromatography
equipped with three PLꢀgel 10 ꢂm MixedꢀB LS type columns at 150 ° C. Tm of
polystyrene samples was measured through differential scanning calorimetry (DSC)
analyses, which were carried out on a Q 100 DSC from TA Instruments under
nitrogen atmosphere. Elemental analyses were performed at National Analytical
Research Centre of Changchun Institute of Applied Chemistry (CIAC). Styrene was
dried over CaH2 under stirring for 48 h and distilled under reduced pressure before
n
use. BuLi (2.5 M in hexane) was purchased from Aldrich. [Ph3C][B(C6F5)4] was
prepared following the literature procedures.27
DFT calculations. All the DFT calculations were performed with the Gaussian 09
program.28 The B3PW91 hybrid exchangeꢀcorrelation functional was utilized. In the
geometry optimizations and subsequent analytical frequency calculations, the 6ꢀ31G*
basis set was used for H, C, O, and N atoms, and the relativistic effective core
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potentials (RECPs) developed by the Stuttgart/Dresden group for Si and rareꢀearth
metal atoms were used. Geometries of all the species were fully optimized without
symmetry constrains. Population analyses were carried out to the natural bond orbital
(NBO) formalism. The TSs were characterized by a single imaginary frequency for
the correct mode. The stable species (minima) were verified to have all real
frequencies only.
10
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X-ray Crystallographic Studies. Crystals for Xꢀray analysis were obtained as
described in the preparations. The crystals were manipulated in a glovebox. Data
o
collections were performed at –88.5 C on a Bruker SMART APEX diffractometer
with a CCD area detector, using graphiteꢀmonochromated Mo Kα radiation (λ =
0.71073 Å). The determination of crystal class and unit cell parameters was carried
out by the SMART program package. The raw frame data were processed using
SAINT and SADABS to yield the reflection data file. The structures were solved by
using the SHELXTL program. Refinement was performed on F2 anisotropically for
all nonꢀhydrogen atoms by the fullꢀmatrix leastꢀsquares method. The hydrogen atoms
were placed at the calculated positions and were included in the structure calculation
without further refinement of the parameters.
Synthesis of dibenzo[a,i]FluCH2-Py.
For the preparation of di(naphthalenꢀ1ꢀyl)methanol, a modification of the procedure
reported by Koskinen29 was used. A solution of 41.4 g (200 mmol) of
1ꢀbromonaphthalene in 100 mL of THF was dropped within 20 min into a 5.1 g (210
mmol) of magnesium turnings in 100mL THF under vigorous stirring. The reaction
was stirred for 4h at 70 °C. Subsequently, a solution of 6.1 mL (100 mmol) of methyl
formate in 25 mL of THF was added to the reaction mixture within 20 min. After the
reaction mixture was stirred for 2h under 70 °C, volatile compounds were removed
under reduced pressure. The residue was dissolved in Et2O (500 mL) and the organic
layer was washed with 1 M HCl (500 mL), H2O (500 ml) and saturated NaCl (500
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mL). After the Et2O layer was dried over MgSO4, the volatile compounds were
removed under reduced pressure, then the residue was scattered by hexane (500 mL)
and stirred overnight, filtered and washed with cold hexane, then the filter cake was
dried under vacuum to give di(naphthalenꢀ1ꢀyl)methanol as a white powder with
satisfactory purity (27.0 g, 95%).
10
11
12
13
14
15
16
17
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19
20
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23
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Colorless suspension of di(naphthalenꢀ1ꢀyl)methanol (27.0 g, 95 mmol) in 150 ml of
PPA(polyphosphoric acid) was heated at 180 °C for 6 h. Subsequently, CHCl3 (1000
mL) and water (1000 mL) was added to the dark green reaction mixture, and organic
layer was separated, washed with a saturated Na2CO3 aqueous solution followed by a
saturated NaCl aqueous solution. The organic layer dried over MgSO4 and the
volatile compounds were removed under reduced pressure. Sublimation of the
resultant solid reside at 180 °C gave dibenzo[a,i]fluorene as a white or pale yellow
solid(10.6 g, 42%).1H NMR (400 MHz, CDCl3, 25
℃) δ 8.13 (d, J = 8.3 Hz, 2H,
ArꢀH), 7.99 (d, J = 8.4 Hz, 2H, ArꢀH), 7.92 (t, J = 8.0 Hz, 4H, ArꢀH), 7.55ꢀ7.59 (m,
2H, ArꢀH), 7.44ꢀ7.49 (m, 2H, ArꢀH), 4.49 (s, 2H, CH2).
Under a nitrogen atmosphere, dibenzo[a,i]fluorene (40 mmol, 10.6 g) dissolve in dry
n
Et2O (100 mL), BuLi (2.5 M in hexane) (42 mmol, 17 mL)was add dropwise to the
Et2O solution under ꢀ78 °C and stirred for 2 h under this temperature. The reaction
system was slowly heated to room temperature and stirred for another 2 h. At the
same time PyꢀCH2Cl was dissolved in dry Et2O (50 mL), and the Et2O solution of
dibenzo[a,i]FluꢀLi was added dropwise to PyꢀCH2Cl slowly under ꢀ30 °C. After the
reaction mixture was stirred for 12 h under ꢀ30 °C, the reaction mixture is poured into
200 mL of saturated NH4Cl, and the Et2O layer was washed with 200 ml water for
three times. After the organic layer was dried over MgSO4 overnight, volatile
compounds were removed under reduced pressure. After the residue was purified with
column chromatography (silica gel, Petroleum ether/ Ethyl acetate, 10:1, v/v),
dibenzo[a,i]FluCH2ꢀPy was gave as white or pale green powders.
1H NMR (400 MHz, CDCl3) δ 8.55 (d, J = 12.8 Hz, 1H, PyꢀH), 7.78ꢀ7.93 (m, 8H,
ArꢀH), 7.35ꢀ7.42 (m, 4H, ArꢀH), 7.22 (dt, J = 7.6, 1.8 Hz, 1H, PyꢀH), 7.02ꢀ7.11 (m,
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1H, PyꢀH), 6.42 (d, J = 7.7 Hz, 1H, PyꢀH), 5.43 (t, J = 5.9 Hz, 1H, CH), 3.52 (d, J =
5.9 Hz, 2H, CH2). 13C NMR (101 MHz, CDCl3) δ 159.30, 149.32, 144.69, 138.71,
135.76, 133.06, 130.13, 129.08, 128.28, 126.14, 124.91, 124.67, 124.25, 121.36,
118.56, 46.69, 43.72.
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General
Procedure
for
the
Preparation
of
Complexes
(Flu-CH2-Py)Ln(CH2SiMe3)2(THF)n. Under a nitrogen atmosphere, FluꢀCH2ꢀPy(1.0
n
equiv) reacted with 1.0 equiv of BuLi in the mixture solvent of toluene and THF
( Tol/THF = 10/1 ) to give a red [PyꢀCH2ꢀFlu]Li solution. And, to a suspension of
LnCl3 (1.0 equiv) in mixed solvents of toluene and THF ( Tol/THF = 10/1 ), 1 equiv
of [PyꢀCH2ꢀFlu]Li solution was slowly added at room temperature. The mixture was
stirred for 8 h to afford a yellow suspension, to which LiCH2SiMe3 (2.0 equiv) was
added and the resulting suspension was stirring overnight to afford a yellowishꢀbrown
solution (ꢀ30 °C). Removal of volatile compounds, extraction with toluene, and
recrystallization under ꢀ30 °C gave complex as crystalline solid and the crystal was
suitable for Xꢀray analysis.
Synthesis of Complex (FluCH2-Py)Tm(CH2SiMe3)2(THF)(3). According to the
general procedure mentioned above, TmCl3 (1 mmol, 0.28 g) was reacted with
[PyꢀCH2ꢀFlu]Li for 8h and then added LiCH2SiMe3(2 mmol, 0.19 g) to react over
night at room temperature to afford 4 as yellow powders(0.56 g, 83.1%). Anal. calcd
for C31H44NTmSi2O (%): C, 55.42; H, 6.60; N, 2.08. Found: C, 55.22; H, 6.51; N,
2.02.
Synthesis of Complex (FluCH2-Py)Er(CH2SiMe3)2(THF)(4). According to the
general procedure, ErCl3 (1 mmol, 0.27 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h
and then added LiCH2SiMe3(2 mmol, 0.19 g) to react over night at room temperature
to afford 5 as yellow powders (0.54 g, 80.2%). The identity of the product was
corroborated by single crystal Xꢀray diffraction. Anal. calcd for C31H44NErSi2O (%):
C, 55.56; H, 6.62; N, 2.09. Found: C, 55.12; H, 6.21; N, 2.01.
Synthesis of Complex (FluCH2-Py)Ho(CH2SiMe3)2(THF)(5). According to the
general procedure, HoCl3 (1 mmol, 0.27 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h
and then added LiCH2SiMe3(2 mmol, 0.19 g) to react over night at room temperature
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to afford 6 as yellow powders (0.54 g, 80.6%). Anal. calcd for C31H44NHoSi2O (%): C,
55.76; H, 6.64; N, 2.10. Found: C, 55.12; H, 6.41; N, 2.07.
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Synthesis of Complex (FluCH2-Py)Dy(CH2SiMe3)2(THF)(7). Following the above
procedure, DyCl3 (1 mmol, 0.27 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3(2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 7 as yellow
powders (0.52 g, 78.6%). Anal. calcd for C31H44NDySi2O (%): C, 55.96; H, 6.67; N,
2.11. Found: C, 55.27; H, 6.41; N, 2.09.
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Synthesis of Complex (FluCH2-Py)Tb(CH2SiMe3)2(THF)(8). Following the above
procedure, TbCl3 (1 mmol, 0.26 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3(2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 8 as yellow
powders (0.51 g, 76.4%). Anal. calcd for C31H44NTbSi2O (%): C, 56.26; H, 6.70; N,
2.12. Found: C, 55.87; H, 6.53; N, 2.09.
Synthesis of Complex (FluCH2-Py)Gd(CH2SiMe3)2(THF)(9). Following the above
procedure, GdCl3 (1 mmol, 0.26 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3 (2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 9 as yellow
powders (0.47 g, 72.1%).The identity of the product was corroborated by single
crystal Xꢀray diffraction. Anal. calcd for C31H44NGdSi2O (%): C, 55.56; H, 6.62; N,
2.09. Found: C, 55.12; H, 6.21; N, 2.01.
Synthesis of Complex (FluCH2-Py)Nd(CH2SiMe3)2(THF)(10). Following the above
procedure, NdCl3 (1 mmol, 0.25 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3 (2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 10 as
yellow powders (0.19 g, 30%).The identity of the product was corroborated by single
crystal Xꢀray diffraction. Anal. calcd for C31H44NNdSi2O (%): C, 57.54; H, 6.85; N,
2.16. Found: C, 57.04; H, 6.51; N, 2.11.
Synthesis of Complex (FluCH2-Py)Pr(CH2SiMe3)2(THF)(11). Following the above
procedure, PrCl3 (1 mmol, 0.25 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3 (2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 11 as
yellow powders (0.16 g, 50.2%). The identity of the product was corroborated by
single crystal Xꢀray diffraction. Anal. calcd for C31H44NPrSi2O (%): C, 57.84; H, 6.89;
N, 2.18. Found: C, 56.63; H, 6.43; N, 2.16.
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Synthesis of Complex (FluCH2-Py)2La(CH2SiMe3) (12). Following the above
procedure, LaCl3 (1 mmol, 0.24 g) was reacted with [PyꢀCH2ꢀFlu]Li for 8h and then
added LiCH2SiMe3 (2 mmol, 0.19 g) to react over night at ꢀ30 °C to afford 12 as
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yellow powders (0.08 g, 10%). H NMR (400 MHz, C6D6, 25 °C): δ –2.82 (d, 2JH,H
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= 9.3 Hz, 1 H, LaꢀCH2SiMe3), –1.70 (d, 2JH,H = 9.3 Hz, 1 H, LaꢀCH2SiMe3), –0.05 (s,
9 H, LaꢀCH2SiMe3), 1.38 (br s, 4H, THF), 3.58 (br s, 4H, THF), 3.76 (d, 2JH,H = 18.0
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Hz, 2 H, PyCH2), 3.76 (d, JH,H = 18.0 Hz, 2 H, PyCH2), 6.47 (t, 3JH,H = 7.5 Hz, 1H,
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6.73 (d, JH,H = 7.9 Hz, 1H, C5H4N), 6.94ꢀ7.15 (m, 2H, C5H4N 14H, C13H8), 7.23 (t,
3JH,H = 7.2 Hz, 1H, C13H8),7.40 (d, 3JH,H = 7.1 Hz, 1H, C13H8), 7.96 (d, 3JH,H = 8.0 Hz,
1H, C5H4N), 8.33 (d, 3JH,H = 5.0 Hz, 1H, C5H4N). Anal. calcd for C46H47N2LaSiO (%):
C, 68.14; H, 5.84; N, 3.45. Found: C, 68.12; H, 5.86; N, 3.44.
Synthesis of Complex (dibenzo[a,i]FluCH2-Py)Sc(CH2SiMe3)2 (13). Following the
above procedure, ScCl3(THF)3 (1 mmol, 0.37 g) was reacted with [dibenzo[a,i]Flu]Li
for 8h and then LiCH2SiMe3(2 mmol, 0.19 g) was added to react over night at ꢀ30 °C
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to afford the product as yellow powders of 13 (0.49 g, 85%). H NMR (400 MHz,
C6D6) δ 8.28 (d, J = 5.2 Hz, 1H, PyꢀH), 8.20 (d, J = 8.99 Hz, 2H, ArꢀH), 8.10ꢀ8.15 (m,
2H, ArꢀH), 7.80ꢀ7.82 (m, 2H, ArꢀH), 7.55 (d, J = 8.9 Hz, 2H, ArꢀH), 7.32ꢀ7.21 (m, 4H,
ArꢀH), 6.84 (td, J = 7.8, 1.6 Hz, 1H), 6.74 (d, J = 8.0 Hz, 1H), 6.27ꢀ6.20 (m, 1H), 5.18
(s, 2H), 2.11 (s, 1H), ꢀ0.13 (s, 18H), ꢀ0.96 (d, J = 3.1 Hz, 4H). 13C NMR (100 MHz,
C6D6) δ 169.16, 155.55, 138.13, 132.41, 135.68, 131.91, 126.06, 123.22, 122.90,
122.47, 122.02, 123.67, 121.69, 121.48, 120.31, 116.39, 100.07, 34.65, 25.96. Anal.
calcd for C39H48NYSi2O (%): C, 73.00; H, 7.00; N, 2.43. Found: C, 73.12; H, 7.03; N,
2.36.
Synthesis of Complex (dibenzo[a,i]FluCH2-Py)Y(CH2SiMe3)2(THF) (14).
Following the above procedure, YCl3 (1 mmol, 0.20 g) was reacted with
[dibenzo[a,i]Flu]Li for 8h and then added LiCH2SiMe3 (2 mmol, 0.19 g) to react over
night at ꢀ30 °C to afford the product 14 (0.47 g, 68%). Recrystallization from hexane
and toluene gave single crystals suitable for Xꢀray analysis. 1H NMR (400 MHz, C6D6)
δ 8.82 (d, J = 5.2 Hz, 1H, PyꢀH), 8.23 (dd, J = 8.6, 4.2 Hz, 2H, ArꢀH), 7.85ꢀ7.91 (m,
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4H, ArꢀH), 7.44 (d, J = 8.8 Hz, 2H, ArꢀH), 7.29ꢀ7.33(m, 4H, ArꢀH), 7.02 (dd, J = 7.3,
5.7 Hz, 1H, PyꢀH), 6.89ꢀ6.96 (m, 1H, PyꢀH), 6.64 (dd, J = 14.0, 7.1 Hz, 1H, PyꢀH),
5.36 (S, 2H, CH2), 3.50 (s, 4H, THF), 1.37 (s, 4H, THF), ꢀ0.18 (s, 18H, CH2SiMe3),
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ꢀ1.74 (d, J = 2.6 Hz, 4H, CH2SiMe3). C NMR (100 MHz, C6D6) δ 167.06, 150.55,
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138.73, 133.41, 130.68, 129.71, 128.06, 126.02, 124.90, 124.47, 124.02, 123.87,
121.89, 121.68, 120.35, 116.99, 103.07, 71.15, 39.49, 37.65, 25.16. Anal. calcd for
C39H48NYSi2O (%): C, 67.70; H, 7.99; N, 2.02. Found: C, 68.65; H, 7.63; N, 2.26.
Typical Procedure for Styrene Polymerization. A typical polymerization procedure
is as follow (Table 2, entry 1): In a glove box, 10.4 g (100 mmol) of styrene was
added into a toluene solution (50 ml) of AliBu (50
ꢁ
mol) in 100 mL flask. Then, a
mol), 1 equiv [Ph3C][B(C6F5)4] (9.2 mg, 10
ꢁmol) was added to the flask. After stirring for 60 min (the
3
toluene solution (7 mL) of 1 (5.4 mg, 10
mol) and AliBu3 (50
ꢁ
ꢁ
magnetic stirring was ceased within a few minutes), methanol was injected to
terminate the polymerization. The viscous mixture was poured into a large quantity of
methanol to precipitate the polymer product. The obtained white polymer was filtered
and then dried under vacuum at 40 °C to a constant weight.
Typical Procedure for Kinetic Experiment of Styrene Polymerization. A typical
kinetic experiment procedure is as follow: In a glove box, 2.08 g (20 mmol) of styrene
was added into a toluene solution (50 ml) of AliBu3 (25
a toluene solution (5 mL) of rareꢀearth metal complex (10
[Ph3C][B(C6F5)4] (9.2 mg, 10 mol) was added to the flask. The
mol) and AliBu3 (25
ꢁ
mol) in 100 mL flask. Then,
mol), 1 equiv
ꢁ
ꢁ
ꢁ
polymerization mixture was divided into six portions to six bottles, respectively. After
stirring for different times, methanol was injected to terminate the polymerization
systems. The viscous mixtures were poured into a large quantity of methanol to
precipitate the polymer products. The obtained white polymers were filtered and then
dried under vacuum at 40 °C to constant weights, The conversion was calculated by
weight.
ASSOCIATED CONTENT
Supporting Information
Xꢀray structures of complexes 4, 9 and 10; Plot of ln([St]0/[St]t) vs. time catalyzed by
complexes 1ꢀ11 under activation of [Ph3C][B(C6F5)4] and AliBu3; The molecular
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structure of the ion pair of (Flu−CH2−Py)Sc(CH2SiMe3)+[B(C6H6)4]ꢀ simulated by
DFT calculation; LUMOs of [(C5Me4SiMe3)Ln(C17H19)(THF)]+ complexes; Selected
bond distances (Å) and angles (deg) of complexes 2, 4, 9, 10 and 11; Representative
GPCꢀtraces, DSCꢀtraces, and NMR spectra of the polymers. These information are
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFOEMATION
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Corresponding Authors
* (D.C.) Eꢀmail: dmcui@ciac.ac.cn. Fax: (+86) 431 85262774. Telephone: +86 431
85262773.
* (B.L.) Eꢀmail: liubo@ciac.ac.cn.
* (Y.L.) Eꢀmail: luoyi@dlut.edu.cn.
Notes
The authors declare no competing financial interest.
ACHNOWLEDGMENTS
This work was supported by the NSF China for Projects Nos. 21374112 and
21174023, and MST for “973” project No. 2015CB654700. The authors are grateful
to Computing Center of Jilin Province for essential support.
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indicating that the formation of the ion pairs.
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ACS Catalysis
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Nature of the Entire Range of RareꢀEarth Metal Based Cationic Catalysts for Highly
Active and Syndioselective Styrene Polymerization
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Fei Lin1,2, Xingbao Wang3, Yupeng Pan1,2, Meiyan Wang4, Bo Liu,1* Yi Luo,3* and Dongmei Cui 1*
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1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China
2University of the Chinese Academy of Sciences, Changchun Branch, Changchun
130022, China
3State Key Laboratory of Fine Chemicals, School of Pharmaceutical, Science and
Technology, Dalian University of Technology, Dalian 116024, China
4Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and
Computational Chemistry, Jilin University, Changchun 130022, China
*Corresponding authors: FAX +86 431 85262774; eꢀmail dmcui@ciac.ac.cn;
liubo@ciac.ac.cn; luoyi@dlut.edu.cn
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