Novel heteroligated titanium complexes with fluorinated salicylaldiminato and β-enaminoketonato ligands: Synthesis, characterization and catalytic behavior in vinyl addition polymerization of norbornene

Article abstract of DOI:10.1039/c0dt01225d

A series of heteroligated (salicylaldiminato)(β-enaminoketonato) titanium complexes of the general formula [3-Bu^t-2-OC ₆H₃CHN(C₆F₅)][PhNC(CF ₃)CHC(R)O]TiCl₂ (3a: RPh, 3b: RC₆H ₄Ph(p), 3c: RC₆H₄Ph(o), 3d: R = 1-naphthyl, 3e: R = C₆H₄F₂(2,6), 3f: R = C₆H ₄Cl₂(2,5), 3g: RC₆F₄(2,3,5,6)OMe(4)) were synthesized. The structure of complexes 3d, 3f-g were determined by single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicated these complexes adopted a distorted octahedral geometry around the titanium center. Upon activation with modified methylaluminoxane, complexes 3a-g exhibited moderate to good catalytic activity for norbornene (NB) vinyl addition polymerization, producing moderate molecular weight polynorbornenes under mild conditions. The introduction of electron-withdrawing groups can greatly enhance the catalytic activity. Significantly, the heteroligated titanium complexes displayed greatly improved activity for vinyl addition polymerization of NB compared to homoligated counterparts, which may stem from the suitable combinations of electronic and steric effects.

Full text of DOI:10.1039/c0dt01225d

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PAPER
Novel heteroligated titanium complexes with fluorinated salicylaldiminato and
b-enaminoketonato ligands: synthesis, characterization and catalytic behavior
in vinyl addition polymerization of norbornene†
Ying-Yun Long,a,b Wei-Ping Ye,a Ping Taoa,b and Yue-Sheng Li*a
Received 14th September 2010, Accepted 14th November 2010
DOI: 10.1039/c0dt01225d
A series of heteroligated (salicylaldiminato)(b-enaminoketonato)titanium complexes of the general
formula [3-But-2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(R)O]TiCl2 (3a: R Ph, 3b:
R
R
C6H4Ph(p), 3c: R C6H4Ph(o), 3d: R = 1-naphthyl, 3e: R = C6H4F2(2,6), 3f: R = C6H4Cl2(2,5), 3g:
C6F4(2,3,5,6)OMe(4)) were synthesized. The structure of complexes 3d, 3f–g were determined by
single crystal X-ray diffraction analysis. The X-ray crystallographic analysis indicated these complexes
adopted a distorted octahedral geometry around the titanium center. Upon activation with modified
methylaluminoxane, complexes 3a–g exhibited moderate to good catalytic activity for norbornene (NB)
vinyl addition polymerization, producing moderate molecular weight polynorbornenes under mild
conditions. The introduction of electron-withdrawing groups can greatly enhance the catalytic activity.
Significantly, the heteroligated titanium complexes displayed greatly improved activity for vinyl
addition polymerization of NB compared to homoligated counterparts, which may stem from the
suitable combinations of electronic and steric effects.
palladium is very expensive. Research in our group and other
Introduction
groups indicated well-defined neutral nickel(II) complexes were
efficient catalysts for vinyl polymerization of NB in the presence
of methylaluminoxane (MAO) or modified methylaluminoxane
(MMAO), producing high molecular weight and amorphous
poly(NB)s.11–12 However, early transition metal complexes at-
tracted little attention for NB vinyl addition polymerization
despite the fact that they have been tested as active catalyst
precursors for ethylene/NB copolymerization and ring-opening
metathesis polymerization.13–15
Recently, some group IV single-site catalyst systems were
reported for the vinyl addition polymerization of NB.16–17 To the
best of our knowledge, there have been only a few successful
titanium complexes reported dealing with the vinyl addition
homo-polymerization of NB. The half sandwich titanocene pre-
catalyst (tBuN-Me2Si-Flu)TiMe216d–e showed good activities in the
region of 106 g PNB /molTi h at 20 and 40 ◦C activated with
MMAO. Complex (2-Me4Cp-4,6-tBu2-PhO)TiCl2 also displayed
catalytic activity up to 106 g PNB/molTi h in the presence of iBu3Al
and Ph3CB(C6F5)4.17a However, from the structural point of view,
all these titanium complexes were constrained geometry catalysts
(CGCs)17a and low activities of about 103 g PNB/molTi h were
observed in non-CGC systems.16a–b Hence, it would be interesting
to know whether the constrained geometry of the titanium com-
plexes was necessary for the achievement of high activity for vinyl
addition polymerization of NB. Accordingly, we were prompted
to synthesize some new non-bridged titanium complexes for NB
polymerization based on the ligand-oriented catalyst design.
Polycycloolefins, via vinyl addition, have been widely used as high
performance materials in the microelectronics industry because
of their special properties (e.g. good heat resistivity and excellent
dielectric properties), which led to increasing interest in the field
of polyolefin research.1 Of these cycloolefins with strained rings,
norbornene (NB) is one of the most representative and industrially
available examples. Vinyl addition polymerization of NB was first
studied with TiCl4/R3Al in the early 1960s, but these systems and
subsequent zirconocenes showed very low activities.2 Thereafter,
late transition-metal catalysts became the focus of attention
because they displayed high activity for vinyl addition polymer-
ization of NB.3 A large number of complexes based on nickel,4–5
palladium6–7 chromium,8 cobalt8b,9 and copper10 were subsequently
reported for efficient NB vinyl addition polymerization. Palladium
and nickel complexes were two typical and important types for NB
vinyl polymerization. For example, cationic palladium complexes,
such as [Pd(CH3CN)4]-[BF4]2, exhibited high catalytic activity and
produced high molecular weight polymers that were soluble in
organic solvents and possessed high Tg’s > 350 ◦C. However,
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun,
130022, China. E-mail: ysli@ciac.jl.cn; Fax: +86-431-85262039
bGraduate School of the Chinese Academy of Sciences, Changchun Branch,
Changchun 130022, China
† CCDC reference numbers 791299–791301. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01225d
1610 | Dalton Trans., 2011, 40, 1610–1618
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Scheme 1 General synthetic route of the heteroligated titanium complexes.
The complexes of group 4 transition metals bearing two
phenoxy-imine chelate ligands (FI catalysts)18–19 and bis(b-
enaminoketonato) chelate ligands20 are successful single site
catalysts for ethylene/NB copolymerization, some of which dis-
played living catalytic nature and produced copolymers with NB
incorporation up to 50 mol%. However, pentafluorinated complex
{3-But-(O)C6H3CHN(C6F5)}2TiCl2 1 showed almost no activity
for NB polymerization due to its bulky hindrance.21 The bis(b-
enaminoketonato)titanium catalysts 2 exhibited very low activity
for NB polymerization because of the less positive charge on the
metal which would mitigate the coordination of NB to the metal
center.21 We reasoned an alternative approach to synthesizing com-
plexes for high NB polymerization would be producing hybrids
with a combination of two different ligands from 1 and 2, affording
catalysts with strong electron-withdrawing groups and an inher-
ently open structure. We previously reported a family of heteroli-
gated (salicylaldiminato)(b-enaminoketonato)titanium complexes
which displayed high activities for ethylene/NB copolymerization
with high NB incorporation,22a suggesting such catalysts might
possess potential for NB homo-polymerization. Considering the
fact that the variation of the ligand structure may lead to profound
changes in the catalytic activity and the property of polymer, we
were prompted to design and synthesize complexes 3a–g with
different electronic property and steric hindrance for comparison,
investigating their NB vinyl addition polymerization behavior.
As expected, the introduction of strong electron-withdrawing
groups to b-enaminoketonato ligand of the complexes led to good
catalytic activity (about 3.8 ¥ 105 gpolymer/molTi h) for NB vinyl
addition polymerization. The results discussed here would provide
a new strategy to design catalysts for special olefin polymerization.
used to synthesize the new b-enaminoketones in moderate to high
yields (55–82%). Salicylaldiminato ligand was synthesized in high
yield (80%) by the Schiff base condensation of the corresponding
fluorine-containing aniline with 3-But-(O)C6H3CHO using an
acid as a catalyst. The systematic synthesis of heteroligated
complexes required a stepwise approach through a mono(ligand)
intermediate. First, treatment of TiCl4 in toluene with the
trimethylsilyl ether derivatives of an iminophenol provided a
facile route to complex {3-But-(O)C6H3CHN (C6F5)}TiCl2(THF).
Then, deprotonation of the b-enaminoketonates with KH in
dichloromethane solution afforded the corresponding potas-
sium salts. Subsequently, 3a–g were prepared through overnight
reactions between mono(salicylaldiminato)titanium complex
and (b-enaminoketonato) potassium salts at -78 ◦C, giving
dark red solids. Finally, purification by precipitation from
dichloromethane/hexane at room temperature formed the desired
complexes as dark red needles or solids in good yields (3a, 55%;
3b, 65%; 3c, 63%; 3d, 58%; 3e, 68%; 3f, 55%; 3g, 72%).
All the heteroligated titanium complexes were well soluble
in toluene, dichoromethane, tetrahydrofuran and other organic
solvents. Complexes 3a–g were well identified by 1H and 13C NMR
in CDCl3 solution at 25 ◦C as well as elemental analyses. The 1H
NMR spectra showed a single set of resonances for titanium-
bonded salicylaldiminato and b-enaminoketonato ligands in a
1 : 1 ratio. The peaks at 8.26 and 6.60 ppm can be assigned
to the typical methine protons of CH N on salicylaldiminato
and b-enaminoketonato ligands, respectively, while the peaks in
the range of 7.7–6.7 ppm can be ascribed to the 10 hydrogen
atoms on the phenyl ring as shown by Fig. 1. Besides, no spectral
changes were observed in d1-choroform solutions of 3a–g stored
in an inert atmosphere at room temperature over 24 h, indicating
the complexes were stable and resistant to ligand redistribution
reactions.
Results and discussion
It is well-known that there are a number of possible geometric
isomers for octahedral complexes with two bidentate monoanionic
ligands. In addition, the geometry calculated to be most stable
for these systems is that in which the two anionic functions are
trans and the two chlorides cis to one another, respectively.18d
Both complexes 1 and 2 featured such geometric isomers. To
further confirm the structures of these new complexes, crystals
of 3d and 3f–g suitable for X-ray diffraction were grown in
CH2Cl2/hexane solution. The crystallographic data together
Synthesis and characterization of the titanium complexes
A general synthetic route for the heteroligated titanium complexes
used in this study22 is shown in Scheme 1. b-Enaminoketone lig-
ands were prepared following our reported method23 while salicy-
laldiminato ligand was synthesized according to the procedures re-
ported previously.18b A tandem sequence of Claisen condensation
between methyl ketones and ethyl trifluoroacetate and the conden-
sation of the resulting b-diketone with aniline in acidic toluene was
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Table 1 Crystal data and structure refinements for complex 3d and 3f–g
Complex
3d
3f
3g
Formula
C38H28Cl4F8N2O2Ti·1/2CH2Cl2
C33H22Cl4F8N2O2Ti
820.23
Monoclinic
P21/n
13.5344(5)
12.2293(4)
20.8540(8)
90
99.9460(10)
90
3399.8(2)
4
1.602
0.645
1648
0.34 ¥ 0.23 ¥ 0.11
1.94 to 26.07
18614
6720(Rint = 0.0338)
6720/0/454
1.026
C68H44Cl4F24N4O6Ti2
1706.68
Monoclinic
P21/c
21.5519(8)
11.7525(5)
27.6927(11)
90
96.1620(10)
90
6973.7(5)
4
1.626
0.502
3424
0.32 ¥ 0.21 ¥ 0.11
0.95 to 26.08
38066
13799(Rint = 0.0276)
13799/0/969
1.032
Formula weight
Crystal system
Space group
858.91
Monoclinic
P21/n
14.6015(7)
15.5255(7)
17.1760(8)
90
97.235(1)
90
3862.7(3)
4
1.524
0.574
1792.0
0.23 ¥ 0.11 ¥ 0.09
1.77 to 26.24
21431
7736 (Rint = 0.0276)
7736/0/499
1.051
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
Dc/Mg m-3
Absorption coefficient (mm-1)
F(000)
Crystal size/mm
q range (◦)
Reflections collected
Independent reflections
Data/restraints/parameters
GOF on F2
R1
0.0513
0.1496
1.099 and -0.914
0.0354
0.0774
0.296 and -0.355
0.0463
0.1159
1.703 and -1.531
wR2
-3
˚
Largest diff. peak and hole/e A
Fig. 2 Thermal ellipsoid plot of complex 3d (30% probability displace-
ment ellipsoids).
Fig. 1 1H NMR spectrum of compound 3a.
with the collection and refinement parameters were summarized
in Table 1. The molecular structures and the ORTEP diagrams
for 3d and 3f–g were shown in Fig. 2–4, while selected bond
lengths and angles were given in Table 2. X-Ray crystallographic
analysis displayed they featured a distorted octahedral geometry
in which the titanium was bound to two cis-coordinated [N,N]
chelating ligands (trans-O,O) and the two chlorine atoms
(cis-Cl,Cl) in the solid state, just as those reported previously.22
In the unit cell of 3d, there is a CH2Cl2 solvent molecule per
Ti(IV) complex, while in the unit cell of complex 3g there are
two crystallographically independent molecules with only minor
differences from each other (e.g., bond angles O(1)-Ti(1)-O(2),
N(1)-Ti(1)-N(2), O(4)-Ti(2)-O(5) and N(3)-Ti(2)-N(4) are 167.01,
165.62, 83.70 and 82.75◦, respectively). Although the Ti–O, Ti–N,
Ti–Cl bond distances for complexes 3d and 3f–g are similar to
Fig. 3 Thermal ellipsoid plot of complex 3f (30% probability displace-
ment ellipsoids).
1612 | Dalton Trans., 2011, 40, 1610–1618
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◦
˚
Table 2 Selected bond lengths [A] and angles[ ]
modified methyl aluminoxanes (MMAO), complexes 3a–g showed
moderate to high activity for NB polymerization to produce high
molecular weight polymers (entries 1–7) while catalyst 1 displayed
almost no activity due to its highest steric hindrance among them
(entries 8). It is well known that the activity greatly depends on
the structure of complexes. Complexes 3e–g with strong electron-
withdrawing groups in the phenoxy benzene ring showed much
higher activities than 3a for NB polymerization at 40 ◦C (entries
5–7), whereas 3b–d with electron-donating substituents on the
phenolate group displayed lower catalytic activity (entries 1–
4), suggesting electronic effect plays a significant role in NB
polymerization. On the other hand, the catalytic activity order
of 3a > 3d > 3b > 3c indicated the bulkiness of the ligand
would hinder the access of NB to coordinate to the active center
and thus decreased the activity. Accordingly, the poly(NB)s with
higher molecular weight (MW) were achieved by the complexes
displaying higher activities.
In order to determine suitable NB polymerization conditions,
we focused on 3g due to its higher activity to further investi-
gate the effect of the reaction time, temperature and monomer
concentration. There was obvious reduction in catalytic activity
of 3g for NB polymerization with the increase of reaction time
(entries 9–11). The MW of the resultant polymer enhanced, while
the molecular weight distributions (MWDs) broadened. These
results might derive from the deactivation of the titanium center
caused by the polymer precipitation during the polymerization
process due to the low solubility of the poly(NB)s in toluene. As
can be seen by Fig. 5, the catalytic activity and the MW of the
resultant polymer increased with enhancement in polymerization
temperature from 0–40 ◦C (entries 11–13) and began to decrease
with further increasing the polymerization temperature (entries
14–15). In addition, the increase of NB concentration also resulted
in the enhancement of the catalytic activity and MW of the
resultant polymer as expected.
Complex
3d
3f
3g
1
Bond distances
Ti–Cl(1/3)
2.2955(9) 2.2797(7)
2.2702(9) 2.2612(7)
2.2834(8)
2.2846(9)
2.2639(8)
2.2544(9)
2.2876(7)
2.2578(8)
1.841(1)
1.845(1)
2.234(2)
2.217(2)
Ti–Cl(2/4)
Ti–O(1/4)
Ti–O(2/5)
Ti–N(1/3)
Ti–N(2/4)
Bond angles
1.814(2)
1.931(2)
2.206(2)
2.164(2)
1.8164(14) 1.8209(18)
1.8282(19)
1.9218(14) 1.9500(19)
1.9459(19)
2.2439(17) 2.226(2)
2.245(2)
2.2219(18) 2.213(2)
2.209(2)
Cl(1/3)-Ti-Cl(2/4) 95.92(4)
97.11(3)
163.67(9) 163.53(6)
86.45(9) 83.16(6)
99.78(3)
99.51(4)
167.01(8)
165.62(9)
83.70(8)
82.75(8)
96.42(3)
163.61(6)
86.94(7)
O(1/4)-Ti-O(2/5)
N(1/3)-Ti-N(2/4)
Fig. 4 Thermal ellipsoid plot of complex 3g (30% probability displace-
ment ellipsoids).
those for complex 1,18d the bond angles between the ligands
(O–Ti–O, N–Ti–N and Cl–Ti–Cl) are rather different. Complex
3d has the narrower Cl–Ti–Cl angles while complexes 3f–g
have wider Cl–Ti–Cl and narrower N–Ti–N angles relative to
those for their analogue complex 1, which may be caused by
the different electron withdrawing group R. It was noted that
complex 3g possessed the widest Cl–Ti–Cl and O–Ti–O angles
and the narrowest N–Ti–N angles among these catalysts, which
probably originated from the four fluorine atoms in the phenoxy
benzene ring of the b-enaminoketonato ligand. For most of these
complexes, stronger electron-withdrawing groups in the phenoxy
benzene ring of the b-enaminoketonato would result in wider
Cl–Ti–Cl and O–Ti–O bond angles and a narrower N–Ti–N angle
as indicated by the corresponding data of complex 3g in Table 2.
Besides, wider Cl–Ti–Cl and O–Ti–O bond angles demonstrated
an inherently more open nature of the catalyst, which would
provide a larger aperture of the coordination sphere favoring easy
access of norbornene to propagate.
Fig. 5 Plots of reaction temperature versus catalytic activity and the
molecular weight of poly(NB)s obtained by 3g/MMAO system.
The polymerizations activated with different cocatalysts were
also investigated under the same monomer concentration at
40 ◦C. The obtained results were listed in Table 3. The activity
of the dried MAO system was similar to that of MMAO system
(entries 7 and 17). On the other hand, though no activity was
Norbornene polymerization results
The results of the NB polymerization using complexes
3a–g in the presence of various cocatalysts at different reaction
temperatures were summarized in Table 3. Upon activation with
i
observed in the absence of Bu3Al (entry 19), the borate/iBu3Al
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Table 3 Norbornene polymerization results catalyzed by complexes 3a–g
Temp .(◦C)
Polymer (mg)
Activityb
Mwc(kg mol-1)
Mw/Mn
c
Entry
Cat.
Cocatalyst.
Al/Ti
Time (min)
1a
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
dry MAO
Ph3CB(C6F5)4/(iBu)3Al
Ph3CB(C6F5)4
B(C6F5)3/Me3Al
B(C6F5)3/Et3Al
AlMe3
AlEt3
MMAO/Me3Al
MMAO/Et3Al
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
40
5
5
5
5
5
5
5
5
15
30
60
5
5
5
5
5
5
5
40
40
40
40
40
40
40
40
40
40
40
0
20
60
80
40
40
40
40
40
40
40
40
40
40
36
22
16
26
112
152
190
trace
415
520
888
26
43.2
26.4
19.2
31.2
134.4
182.4
228.0
—
166.0
152.0
88.8
31.2
110.4
222.0
114.0
252.0
206.4
242.4
—
34.0
24.7
20.3
28.8
44.7
48.3
51.9
—
58.8
60.4
64.2
20.6
40.8
54.8
36.2
56.9
52.1
53.7
—
1.60
1.96
1.89
1.62
1.88
1.90
1.97
—
1.99
2.18
2.29
1.81
1.90
2.04
2.38
1.98
1.80
1.72
—
3g
1
9
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
3g
10
11
12
13
14
15
16d
17e
18f
19
20g
21g
22
23
24h
25i
92
185
95
210
172
202
trace
trace
trace
n.o.
n.o.
52
0
10
10
500
500
500/10
500/10
5
5
5
5
5
5
5
—
—
—
—
62.4
26.4
—
—
—
—
10.3
8.2
—
—
—
—
2.66
2.88
22
a Polymerization conditions: Ti = 10 mmol, [NB] = 1.0 mol L-1, solvent = toluene, total volume = 30 mL, cocatalyst = MMAO unless specially noted.
b kg PE/molTi h bar. c Determined by GPC data in 1,2,4-trichlorobenzene versus polystyrene standard. d [NB] = 4.0 mol L-1. e Cocatalyst = 232 mg
dry MAO. f Cocatalyst = Ph3CB(C6F5)4 + (iBu)3Al, B/Ti = 2, (iBu)3Al = 400 mmol. g B/Ti = 9, Me3Al = 100 mmol. h MMAO/Me3Al/Ti = 500/10/1.
i MMAO/Et3Al/Ti = 500/10/1.
system showed the same activity as that of MMAO system (entry
18) because of the better separation of the ion pair. In the case
of 3g/B(C6F5)3/R3Al (R = Me, Et), no or low activity were
observed (entries 20–23). The addition of R3Al (R = Me, Et) to the
3g/MMAO catalyst system decreased both the catalytic activity
and the MW of the resultant poly(NB)s (entries 24–25), which
indicated the chain transfer reactions caused by R3Al.
As is well-known, in the vinyl addition polymerization of
NB, chain termination via b-hydrogen elimination is prohibited
because the b-hydrogen of the propagation chain end is at the
endo position of the NB unit.16e,24 Besides, the chain transfer
to monomer should also be impossible because of the sterically
hindered propagation chain end and NB monomer.16e,24 Thus,
we proposed the major chain transfer reaction might transfer
to aluminium. To further confirm our speculation, we increased
the MMAO and dry MMAO dosage and investigated their
polymerization behavior. As can be seen by Fig. 6, the catalytic
activity of both systems increased. Though the MW of the
resultant poly(NB)s increased with enhancement of dry MMAO
Fig. 6 Plots of Al/Ti molar ratio versus the catalytic activity and
molecular weight of the resultant polymer obtained by 3g (10 mmol
catalyst, polymerization time 5 min, reaction temperature 40 ◦C). The
solid line(—) and dashed line(- - -) display the MMAO and dry MMAO
systems, respectively.
dosage, the MW of the polymer obtained by 3g/MMAO system
reduced, indicating chain transfer to aluminium occurred in
signals from 28 to 55 ppm and absence of peaks at 20–24 ppm
3g/MMAO system, which is consistent with our speculation.
indicated the poly(NB)s were exo enchained.27 The signals at
The 13C NMR spectra of all the poly(NB)s obtained were
29–33.5 ppm and 35–38.5 ppm can be assigned to C5/C6 and
similar and indicative of the vinyl addition of NB irrespective
C7, while the peaks at 38.5–44 ppm and 47.5–55 ppm can be
of the activator employed.16d–e Fig. 7(a) showed the 13C NMR
ascribed to C1/C4 and C2/C3, respectively. The distribution of
the stereotriad sequences of the poly(NB)s is determined from
spectrum of polymer obtained by 3g/MMAO system. Though
the signals of the saturated carbons were split into several peaks
the C1 and C4 regions (C1/C4 at 38.8 ppm in the mm triad,
due to the different stereoisomers of the NB unit, reference
at 40.3 ppm in the mr triad and at 41.3 ppm in the rr triad).16a
to polynorbornenes,25 and norbornene hydrotrimers26 allowed
The high intensity peak at 40.4 ppm of C1/C4 suggested that
assignments of the 13C signals reported in Fig. 7. The presence of
the inserted NB units of poly(NB)s obtained by 3g/MMAO
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is consistent with their 13C NMR analyses. In addition, the
poly(NB)s catalysed by 3g were much more stable than those by
(tBuN-Me2Si-Flu)TiMe2.16d–e DSC experiment was also performed
but no melting transition heating to 400 ◦C was observed under a
nitrogen atmosphere. In addition, it is very difficult to determine
the glass transition temperature (Tg) of the poly(NB)s because Tg
should be very close to their decomposition temperature.
Conclusions
We have synthesized and characterized a series of new heteroli-
gated titanium complexes which were used as efficient catalysts for
NB polymerization. The catalytic activities were greatly enhanced
with increase of the electron-withdrawing groups and decrease of
the steric bulkiness of groups attached to the b-enaminoketonato
ligand. In addition, the cocatalyst type also played an important
role in the catalytic activity. The poly(NB)s obtained were
predominantly heterotactic and stable up to 450 ◦C, which showed
moderate solubility in halogenated aromatic hydrocarbons for the
determination of MW. The 13C NMR analyses of the polymer
suggested that the catalytic polymerization occurred via vinyl
addition mechanism.
Significantly, the heteroligated titanium complexes effectively
combined the more open nature required for NB incorporation
and displayed greatly improved activity for vinyl addition polymer-
ization of NB compared to homoligated counterparts. Though it
was not clear why such a ligand combination was needed for good
activity of NB polymerization in detail, we supposed the ligand
differences might result in faster rates for NB insertion and slower
rates for chain transfer to aluminium. The nature of the metal,
the steric and electronic properties of the ligand play important
roles in determining the olefin insertion at octahedral catalysts,
while the suitable combinations of these effects may result in an
improved olefin polymerization behavior. Thus, we believe this
may help to design catalysts for special olefin polymerization.
Moreover, from the structural point of view, these catalysts were
the first titanium complexes which displayed good catalytic activity
for NB polymerization with unsymmetrical and non-constrained
geometry.
Fig.
7
(a) 13C NMR spectrum of poly(NB)s obtained with
3g/MMAO(entry 7 of Table 3).(b) 13C NMR spectrum of poly(NB)s
obtained with neutral nickel complexes bearing salicylaldiminato ligands
reported previously.
can be predominantly heterotactic with very small amount of
isotactic units, while our previously reported poly(NB)s achieved
by neutral nickel complexes bearing salicylaldiminato ligands
displayed typical atactic units as shown by Fig. 7(b).11a In addition,
only one peak of C7 assigned indicated an overlapping of rr
and mr triad sequences, because a mixture of rr and mr would
probably resolve and overlap. These results were similar to those
of poly(NB)s produced with Ni(dpm)2,25 but different from those
obtained by (tBuN-Me2Si-Flu)TiMe2
and [(h -crotyl)Ni(1,4-
16d–e
3
COD)]PF6 with three and two peaks assigned to C7, respectively.
The thermal property of poly(NB)s with Mw about 52 kg mol-1
obtained by 3g/MMAO and neutral nickel(II) salicylaldiminato
complex previously reported,11a for comparison, were studied by
thermogravimetric analysis (TGA). Both samples were stable up to
400 ◦C under a nitrogen atmosphere. Only about 3.3% weight loss
◦
was recorded at 449 C for the sample catalysed by 3g (Fig. 8a),
but about 10% weight loss was detected at 442 ◦C for poly(NB)s
by neutral nickel(II) salicylaldiminato complex (Fig. 8b), which
Experimental section
General procedure and materials
All manipulation of air- and/or moisture-sensitive compounds
were carried out under a dry argon atmosphere by using standard
Schlenk techniques or under a dry argon atmosphere in an
MBraun glovebox unless otherwise noted. All solvents were
purified from MBraun solvent purification system (SPS). The
NMR data of the ligands and complexes used were obtained on
1
a Bruker 300 MHz spectrometer (300 MHz for H, 75 MHz for
13C) at ambient temperature, with CDCl3 as the solvent (dried by
˚
MS 4 A). The NMR data of the copolymers ◦were obtained on a
Varian Unity-400 MHz spectrometer at 135 C, with o-C6D4Cl2
as a solvent. Elemental analyses were recorded on an elemental
Vario EL spectrometer. The weight-average molecular weight
(Mw) and the polydispersity index (PDI) of polymer samples were
determined at 135 ◦C by a PL-GPC 220 type high-temperature
chromatograph equipped with three Plgel 10 mm Mixed-B LS
Fig. 8 TGA thermograms of poly(NB)s with Mw about 52 kg mol-1
obtained from the complex 3g (a) and neutral nickel(II) salicylaldminato
complex (b).
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type columns. 1,2,4-Trichlorobenzene (TCB) was employed as the
solvent at a flow rate of 1.0 mL min-1. The calibration was made
by polystyrene standard EasiCal PS-1 (PL Ltd).
Calc. for C37H26Cl2F8N2O2Ti: C 55.45, H 3.27, N 3.50. Found: C
55.41, H 3.30, N 3.45.
[3-But-2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(p-PhPh)O]-
TiCl2 (3c). Catalyst 3c was prepared via a procedure similar to
that for 3a as dark red needles in 63% yield. 1H NMR (300 MHZ,
CDCl3, 20 ◦C): d 8.41 (s, 1H, CH N), 8.25 (s, 1H, Ar) 7.89–7.97
(d, 1H, Ar), 7.82–7.86 (d, 2H, Ar), 7.75–7.79 (d, 1H, Ar),
7.56–7.61 (q, 5H, Ar), 7.13–7.18 (m, 3H, Ar), 6.98–7.03 (t, 1H,
Ar), 6.88–6.91(t, 1H, Ar), 6.75–6.81 (t, 1H, Ar), 6.69 (s,1H, CH),
6.59–6.62 (d, 1H, Ar), 1.30 (s, 9H, t-Bu). 13C NMR (75.5 MHZ,
TiCl4 and Me3SiCl were purchased from Aldrich. KH (40% min-
eral oil suspension) was purchased from Aldrich and washed with
light petroleum. Modified methylaluminoxane (MMAO, 7% alu-
minium in heptane solution), R3Al, B(C6F5)3 and Ph3CB(C6F5)4
were purchased from Akzo Nobel Chemical Inc. Norbornene
was purchased from Aldrich and purified by sublimation under
reduced pressure before use. The stock solution of NB was
prepared in toluene (6.07 M). The other reagents and solvents
were commercially available.
◦
CDCl3, 20 C): d 176.6, 172.6, 160.8, 157.5, 147.3, 139.7, 138.9,
136.5, 134.0, 132.1, 129.0, 128.4, 128.3, 128.1, 127.6, 127.2, 127.1,
126.5, 126.3, 125.4, 123.1, 122.3, 121.1, 117.3, 96.0, 35.2, 30.0.
Anal. Calc. for C39H28Cl2F8N2O2Ti: C 56.61, H 3.41, N 3.39.
Found: C 56.59, H 3.39, N 3.35.
Synthesis of titanium catalysts
[3-But-2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(Ph)O]TiCl2
(3a). To a solution of compound 3-But-2-OC6H3CH N(C6F5)
(0.69 g, 2 mmol) in dried tetrahydrofuran (20 mL) at -78 ◦C
was added a 2.5 M n-butyllithium hexane solution (0.8 mL,
2 mmol) dropwise over 5 min. The mixture was allowed to warm
to room temperature and stirred for 4 h, affording a yellow
[3-But-2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(o-PhPh)O]-
TiCl2 (3d). Catalyst 3d was prepared via a procedure similar to
that for 3a as dark red needles in 58% yield. 1H NMR (300 MHZ,
CDCl3, 20 ◦C): d 8.13 (s, 1H, CH N), 7.77–7.79 (d, 1H,
Ar),7.47–7.55 (q, 2H, Ar), 7.25–7.48 (m, 6H, Ar), 7.14–7.18 (t,
2H, Ar), 7.08–7.11(q, 1H, Ar), 6.91–6.99 (m, 2H, Ar), 6.70–6.80
(m, 2H, Ar), 6.56–6.58 (d, 1H, Ar), 5.79 (s, 1H, CH), 1.39 (s,
◦
solution. Then, at 0 C (CH3)3SiCl (4 mmol, 0.5 mL) was added
dropwise over 3 min and stirred for 18 h, the formed colorless
solution was concentrated and added dried toluene 15 mL, then
filtered. The colorless filtrate was added dropwise to a toluene
solution of TiCl4 (2 mmol) at 0 ◦C, and allowed to warm to
room temperature, then evaporated under reduced pressure after
stirred for 12 h to afford a solid residue, which was needed to
recrystallized with dichloromethane and hexane to form dark red
solid [3-But-2-OC6H3CH N(C6F5)]TiCl3(THF). Thereupon, a
solution of [3-Bu-2-OC6H3CH N (C6F5)]TiCl3(THF) (0.78 g,
1.4 mmol) in dichlorometane (10 mL) at -78 ◦C was treated with
[PhN C(CF3)CHC(Ph)]OK (0.46 g, 1.4 mmol). The reaction
mixtures was allowed to warm slowly to room temperature and
stirred for 20 h, affording a dark red solution. The solution was
filtered to remove KCl and the isolated product was concentrated.
Purification by precipitation from dichloromethane/hexane at
room temperature gives the desired complex a dark red power in
◦
9H, t-Bu).13C NMR (75.5 MHZ, CDCl3, 20 C): d 176.6, 172.6,
160.8, 158.5, 148.3, 139.9, 138.4, 136.2, 134.3, 132.0, 129.2, 128.3,
128.2, 128.1, 127.6, 127.2, 127.1, 126.5, 126.3, 125.4, 123.1, 122.3,
121.1, 117.3, 96.0, 35.2, 30.0. Anal. Calc. for C39H28Cl2F8N2O2Ti:
C 56.61, H 3.41, N 3.39. Found: C 56.55, H 3.37, N 3.36.
[3-But -2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(2,6-F2Ph)-
O]TiCl2 (3e). Catalyst 3e was prepared via a procedure similar
to that for 3a as dark red needles in 68% yield. 1H NMR (CDCl3,
◦
20 C): d 8.18 (s, 1H, CH N), 7.53–7.58 (t, 1H, Ar), 7.30–7.44
(m, 1H, Ar), 7.13–7.16 (d, 2H, Ar), 7.00–7.07 (t, 1H, Ar), 6.95–
6.99 (m, 3H, Ar), 6.76–6.89 (m, 2H, Ar), 6.64–6.67 (d, 1H, Ar),
6.36 (s,1H, CH), 1.35 (s, 9H, t-Bu).13C NMR (75.5 MHZ, CDCl3,
20 ◦C): d 161.3, 155.0, 147.1, 139.0, 137.2, 135.9, 134.6, 133.9,
132.7, 131.3, 128.9, 127.6, 127.0, 126.5, 123.8, 122.3, 102.2, 77.9,
77.4, 76.9, 35.6, 30.4. Anal. Calc. for C33H22F2Cl2F8N2O2Ti: C
50.34, H 2.82, N 3.56. Found: C 50.36, H 2.84, N 3.52.
55% yield. H NMR (300 MHZ, CDCl3, 20 ◦C): d 8.24 (s, 1H,
1
CH N), 7.83–7.86 (q, 2H, Ar), 7.54–7.59 (m, 2H, Ar), 7.43–7.48
(t, 2H, Ar), 7.23 (t,1H, Ar), 7.10–7.16 (t, 2H, Ar), 6.99–7.04 (t,
1H, Ar), 6.87–6.92 (t, 1H, Ar), 6.74–6.78 (t, 2H, Ar), 6.62–6.64 (t,
1H, Ar), 6.57 (s, 1H, CH), 1.24 (s, 9H, t-Bu). 13C NMR (20 ◦C): d
177.3, 172.9, 147.6, 139.4, 136.8, 134.4, 133.7, 129.4, 128.7, 127.9,
126.9, 126.6, 125.8, 123.5, 122.7, 96.3, 35.6, 30.4. Anal. Calc. for
C33H24Cl2F8N2O2Ti: C 52.75, H 3.22, N 3.73. Found: C 52.71, H
3.27, N 3.68.
[3-But-2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(2,5-Cl2Ph)-
O]TiCl2 (3f). Catalyst 3f was prepared via a procedure similar
to that for 3a as dark red needles in 55% yield. 1H NMR (CDCl3,
20 ◦C): d 8.19 (s, 1H, CH N), 7.63 (s,1H, Ar), 7.54–7.57 (d, 1H,
Ar), 7.35–7.36 (q, 2H, Ar), 7.15–7.17 (d, 2H, Ar), 6.96–7.07 (m,
2H, Ar), 6.77–6.88 (m, 2H, Ar), 6.73 (s, 1H, Ar), 6.63–6.65 (d,
1H, Ar), 1.36 (s, 9H, t-Bu). 13C NMR (75.5 MHZ, CDCl3, 20 ◦C):
d 161.0, 154.9, 146.9, 139.1, 137.0, 135.8, 134.5, 133.8, 132.5,
131.2, 128.9, 127.5, 126.9, 126.4, 123.6, 122.1, 102.1, 77.8, 77.4,
76.9, 35.6, 30.4. Anal. Calc. for C33H22Cl4F8N2O2Ti: C 48.32, H
2.70, N 3.42. Found: C 48.34, H 2.65, N 3.40.
[3-But -2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(1-C10H7)-
O]TiCl2 (3b). Catalyst 3b was prepared via a procedure similar to
that for 3a as a dark red power in 65% yield. 1H NMR (300 MHZ,
CDCl3, 20 ◦C): d 8.28 (s, 1H, CH N), 7.92–7.95 (d, 2H, Ar),
7.68–7.71 (m, 4H, Ar), 7.65–7.67 (d, 1H, Ar), 7.56–7.58 (t, 2H,
Ar), 7.48–7.50 (t, 1H, Ar), 7.15–7.20 (t, 1H, Ar), 6.92–7.01 (t, 1H,
Ar), 6.89–6.91 (t, 1H, Ar), 6.70–6.75 (t, 1H, Ar), 6.60–6.65 (d, 1H,
Ar), 6.59 (s◦, 1H, CH), 1.30 (s, 9H, t-Bu). 13C NMR (75.5 MHZ,
CDCl3, 20 C): d 177.0, 172.5, 160.9, 139.0, 136.5, 135.5, 133.9,
132.8, 130.7, 129.7, 129.4, 129.0, 128.9, 128.8, 128.3, 128.2, 127.8,
127.0, 126.5, 126.3, 125.4, 123.0, 122.8, 96.5, 53.4, 35.2, 30.0. Anal.
[3-But -2-OC6H3CH N(C6F5)][PhN C(CF3)CHC(2,3,4,6-
F4,4-OMePh)O]TiCl2 (3g). Catalyst 3g was prepared via a
procedure similar to that for 3a as dark red needles in 72% yield. 1H
NMR (CDCl3, 20 ◦C): d 8.11 (s, 1H, CH N), 7.48–7.51 (d, 1H,
Ar), 7.16–7.19 (d, 1H, Ar), 7.07–7.10 (d, 1H, Ar), 6.90–7.01 (m,
2H, Ar), 6.75–6.82 (m, 2H, Ar), 6.58–6.60 (d, 1H, Ar), 6.27 (s, 1H,
CH), 4.10 (s, 3H, OMe), 1.32 (s, 9H, t-Bu).13C NMR (75.5 MHZ,
1616 | Dalton Trans., 2011, 40, 1610–1618
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◦
CDCl3, 20 C): d 173.6, 168.7, 161.1, 157.6, 147.2, 146.7, 143.4,
3 F. Blank and C. Janiak, Coord. Chem. Rev., 2009, 253, 827–861 See the
references in this review.
140.0, 139.0, 137.0, 134.5, 128.9, 127.6, 126.9, 126.4, 125.9, 123.6,
122.1, 121.1, 103.4, 77.4, 62.4, 35.7, 31.9, 30.5. Anal. Calc. for
C34H22Cl2F12N2O2Ti: C 48.77, H 2.65, N 3.35. Found: C 48.78, H
2.67, N 3.32.
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Crystallography studies
Single crystals of complexes 3d and 3f–g suitable for X-ray struc-
ture determination were grown from a dichlorometane/hexane
solution at room temperature in a glovebox, thus maintaining
a dry, O2 free environment. X-ray densities of these complexes
were collected with the w scan mode (185 K) on a Bruker
Smart APEX diffractometer with CCD detector using Mo-Ka
˚
radiation (l = 0.71073 A). Empirical absorption corrections
were applied to the data using SADABS program. The crystal
structures were solved using the SHELXTL program and refined
using full matrix least squares. All the non-hydrogen atoms were
refined anisotropically. The crystallographic data together with the
collection and refinement parameters are summarized in Table 1.
Procedure for norbornene polymerization
Polymerizations were performed in a 100 mL glass reactor
equipped with a seal septum and a magnetic stirrer. At first, the
reactor was charged with a stock solution of norbornene in toluene
and a prescribed amount of MMAO solution (2.5 M) was added.
Additional toluene was added to make up the total volume to
25 mL and the reactor was kept in an ice or oil bath for 30 min
to reach reaction temperature. Five mL of the aliquot of catalyst
solution in toluene was added to start the polymerization. Tem-
perature was kept constant during polymerization. Polymerization
was terminated with acidic methanol. The polymer obtained was
adequately washed with methanol and dried under vacuum at
60 ◦C for 10 h. If the polymerization was activated with dry
MAO, the reactor was first charged with a prescribed amount
of dry MAO and the NB solution. If the activators are R3Al
and/or perfluorinated boranes, the polymerization procedure is
performed as follows: a prescribed amount of NB in toluene and
R3Al in toluene was first added into the reactor and the solution
was heated to 40 ◦C in an oil bath. The polymerization was
started by addition of perfluorinated boranes in toluene into the
above solution soon after the addition of a precatalyst in toluene.
The following procedure is the same as those of polymerizations
activated with MMAO.
Acknowledgements
The authors are grateful for subsidy provided by the National Nat-
ural Science Foundation of China (Nos. 20734002 and 20923003).
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1618 | Dalton Trans., 2011, 40, 1610–1618
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