Syntheses, characterization, and ethylene polymerization of titanium complexes with double-duty tridentate [ONN] ligands

Article abstract of DOI:10.1021/om300091e

A series of titanium complexes containing the tridentate [ONN] ligands La-Lf were synthesized and characterized. The ligands Lb (8-quinolinolato- CH₂NHAr; Ar = 2,6-diisopropylphenyl) has been prepared by the reduction of the corresponding imino

Full text of DOI:10.1021/om300091e

Article
pubs.acs.org/Organometallics
Syntheses, Characterization, and Ethylene Polymerization of
Titanium Complexes with Double-Duty Tridentate [ONN] Ligands
Ping Hu,† Ya-Lin Qiao,† Jian-Qiang Wang,‡ and Guo-Xin Jin*,†
†State Key Laboratory of Molecular Engineering of Polymers, Department of Chemistry, Fudan University, Shanghai 200433,
People's Republic of China
‡Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204,
People's Republic of China
S
* Supporting Information
ABSTRACT: A series of titanium complexes containing the
tridentate [ONN] ligands La−Lf were synthesized and
characterized. The ligands Lb (8-quinolinolato-CH2NHAr;
Ar = 2,6-diisopropylphenyl) has been prepared by the reduc-
tion of the corresponding imino-quinolinol compound La
(8-quinolinolato-CHNAr; Ar = 2,6-diisopropylphenyl) with
LiAlH4 in high yield. Ligands Lc−Lf were synthesized by a procedure similar to that used to prepare ligand Lb. Reaction of TiCl4
with imino-quinolinol ligand La affords the six-coordinate trichloride titanium complex 1. The selective synthesis of tri- and
dichlorotitanium complexes containing ligand Lb was achieved by changing the base for deprotonation. When it is deprotonated
by NaH, ligand Lb can be used as a tridentate monoanionic ligand to synthesize trichlorotitanium complex 2. While de-
n
protonated by BuLi, it can be used as a tridentate dianionic ligand to synthesize dichlorotitanium complex 3. Other
dichlorotitanium complexes 4−7 were synthesized by a procedure similar to that used to prepare complex 3. All complexes have
been characterized by 1H NMR spectra and elemental analysis. The molecular structures of ligand Lb and complex 1 have been
characterized by single-crystal X-ray diffraction analyses. XANES and EXAFS spectroscopy performed on the representative
complexes 2 and 3 reveals the different coordination geometries. When they are activated by excess methylaluminoxane (MAO),
all of the titanium complexes can be used as catalysts for ethylene polymerization and exhibit moderate to good activities. It was
found that the catalytic behaviors of the title complexes were highly affected by the coordination entironment of the metal center
and the effect of substituent groups on ligands.
as possible and from “non-toxic” starting materials.12 Recently,
we have reported half-sandwich zirconium complexes with
INTRODUCTION
The search for new olefin polymerization catalysts based on
■
tridentate imino-quinolinol ligands which exhibited high
transition-metal complexes is a field of major interest, involving
activities for ethylene polymerization.13 Herein, it is a natural
many academic and industrial research groups. Ever since the
discovery of Ziegler−Natta catalysis,1 non-metallocene cata-
extension of this type of imino-quinolinol ligand to synthesize a
lysts,2 which include early-,3 middle-,4 and late-transition-metal5
trichloride nonmetallocene titanium catalyst. Furthermore, the
and lanthanide6 species incorporating noncyclopentadiene-based
selective synthesis of tri- and dichlorotitanium species con-
taining tridentate [ONN] ligands, protonated from the imino-
ligands, have attracted great attention. Non-metallocene group
quinolinol ligand, was achieved by changing the base. These
IV metal complexes containing various types of ligands are
among the typical examples.7−10 Fujita et al.9 developed an FI
title complexes, activated with methylaluminoxane (MAO), show
moderate to high activities for ethylene polymerization. We report
catalyst family based on bis(salicylaldiminato) ligands. This type
the syntheses, characterization, and polymerization behavior of the
of catalyst can be used to produce polyethylene or syndiotactic
title complexes in detail.
polypropylene with high molecular weight and narrow molecular
weight distribution, and the catalytic behavior is highly affected
RESULTS AND DISCUSSION
Synthesis and Characterization. The synthesis of ligands
■
by the substituent on both the phenoxy and the imino groups.
Kol et al.10 reported [ONO] and [ONNO] ligand systems and
La and Lb is outlined in Scheme 1. The tridentate monoanionic
found that their [ONNO] zirconium complexes were highly
active in 1-hexene polymerization.
We noticed that most of the non-metallocene group IV pre-
catalysts described above were dihalide (or dialkyl or mono-
[O−NN] ligand La was prepared according to our previously
reported method.13 Ligand Lb was obtained easily in high yield
by reduction of ligand La with excess LiAlH4 in cool diethyl
ether.
halide monoalkyl) complexes. In comparison, only a few of the
trihalide (or trialkyl) nonmetallocene precursors were found to
be active for olefin polymerization.11 Commercially, it is of
Received: February 5, 2012
further interest if these catalysts can be procured in as few steps
Published: March 22, 2012
© 2012 American Chemical Society
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Article
Scheme 1. Synthetic Route to Ligands La and Lb
n
Ligands La and Lb were characterized by elemental analysis,
IR, and 1H NMR. The chemical shift of the CHN proton in
that deprotonation of ligand Lb using 2 equiv of BuLi instead
of NaH led to the five-coordinated dichlorotitanium complex 3
in toluene solution.
1
ligand La is 8.37 ppm. The signal disappeared in the H NMR
1
spectrum of compound Lb, while new signals appeared and
were identified as CH2 (4.4 ppm) protons, indicating that the
CHN (imine) has been transformed to CH2NH (amine).
In the IR spectrum of ligand Lb, a strong and sharp peak at
3351 cm−1 can be ascribed to the stretching vibration of N−H,
indicating the existence of secondary amine. The structure of
Lb was further confirmed by single-crystal X-ray diffraction
analysis (Figure 1). In Lb, the C(10)−N(2) bond length is
Complexes 1−7 were fully characterized by IR, H NMR,
and elemental analyses (see the Experimental Section). The
1
signal of the CHN proton in the H NMR spectrum of
complex 1 is downfield approximately 0.12 ppm from that of
the free ligand, indicating the obvious coordination of the imino
nitrogen atom to the metal center. In the IR spectrum of com-
plex 2, a strong and sharp peak at 3283 cm−1 can be ascribed to
the stretching vibration of N−H, indicating the existence of
secondary amine, but there are no stretching vibration signals of
N−H in the IR spectra of complexes 3−7. This phenomenon
indicated that the proton of the secondary amine cannot
n
be deprotonated by NaH. When using BuLi instead of NaH,
the proton of the secondary amine can be deprotonated.
Hence, we were pleased to find that ligand Lb is a double-duty
ligand. When it is deprotonated by NaH, ligand Lb can be
used as a tridentate monoanionic ligand. However, when it is
deprotonated by nBuLi, it can be used as a tridentate dianionic
ligand. The solid-state structure of complex 1 was further
determined by single-crystal X-ray diffraction. The crystal of
complex 1 was obtained by slow diffusion of hexane into its
CH2Cl2 solution. Selected structural parameters, along with
those for related titanium complex 1, are collected in the
Supporting Information.
The molecular structure of complex 1 is shown in Figure 2 as
a titanium trichloride complex with one imino-quinolinol
ligand. The geometry at the titanium center can be described as
a slightly distorted octahedral structure in which the five atoms
Ti(1), N(1), N(2), O(1), and Cl(2) are nearly coplanar. The
two atoms Cl(1) and Cl(3) are in a trans configuration
(Cl(1)−Ti(1)−Cl(3) = 168.44(4)°).
Figure 1. Molecular structure of Lb with thermal ellipsoids drawn at
the 30% level. Selected bond lengths (Å) and angles (deg): C(2)−
O(1), 1.354(3); C(10)−N(2), 1.471(3); C(1)−N(1), 1.370(3);
C(9)−N(1), 1.319(3); C(1)−C(2), 1.415(3); C(9)−C(10)−N(2),
114.6(2); C(10)−N(2)−C(11), 116.14(19).
1.471(3) Å, which is typical of a carbon−nitrogen single bond.
The three donor atoms ONN are not coplanar.
The synthesis of complexes 1−3 is outlined in Scheme 2.
Without any base ligand La could react with TiCl4 to give the
desired trichloride complex 1 in the presence of excess of TiCl4
(2 equiv) at −78 °C in toluene in high yield. We first attempted
to synthesized complex 2 by a procedure similar to that used to
prepare complex 1. The reaction of ligand Lb with excess TiCl4
without any base in toluene solution was carried out; however,
the reaction seemed to be more complicated than expected, and
the desired product was isolated in low yield. After continuous
screening of proper reaction conditions, we found a better way
to synthesize complex 2. On deprotonation of ligand Lb with
excess sodium hydride (NaH) in tetrahydrofuran (THF), the
resultant sodium compounds reacted further with 2 equiv of
TiCl4 in toluene. Red crystals of the pure trichloride titanium
complex 2 were isolated in good yield (83%). It is worth noting
X-ray absorption spectroscopy (XAS) was used to investigate
the local structure of Ti atoms in complexes 2 and 3. Figure 3
compares the XANES (X-ray absorption near edge structure)
of 2 and 3. There is no apparent difference, which proves that
the Ti atom has a similar coordination environment in the two
complexes. Further Fourier transforms of EXAFS (extended
X-ray absorption fine structure) data are compared in Figure 4.
The significant differences appear in the main peak at 1.9 Å,
which corresponds to the backscatter of Ti−Cl and Ti−N. In
order to explain the difference, the fitting of the Ti K-edge
EXAFS spectra (Table 1) of 2 and 3 was performed using a
three-shell model, which consists of Ti−O, Ti−N, and Ti−Cl.
With the help of EXAFS analysis, the solid-state structures of 2
and 3 were confirmed to be six-coordinate as [1O,2N,3Cl] and
five-coordinate as [1O,2N,2Cl], respectively.
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Scheme 2. Synthesis of Titanium Complexes 1−7
Figure 2. Molecular structure of complex 1 with thermal ellipsoids
drawn at the 30% level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ti(1)−N(1), 2.126(3);
Ti(1)−N(2), 2.305(2); Ti(1)−O(1), 1.862(2); Ti(1)−Cl(1),
2.2900(12); Ti(1)−Cl(2), 2.2510(11); Ti(1)−Cl(3), 2.3218(12);
C(10)−N(2), 1.281(4); Cl(1)−Ti(1)−Cl(2), 94.22(5); Cl(2)−
Ti(1)−Cl(3), 93.45(4); Cl(1)−Ti(1)−Cl(3), 168.44(4); Cl(2)−
Ti(1)−N(1), 177.09(8).
Figure 3. Ti K-edge XANES spectra of complexes 2 and 3.
was charged, indicating the active species had better solubility
in toluene. In the 1/MAO and 3/MAO systems, respectively,
according to observations at different Al/Ti ratios (entries 1−
3 and 15−17 in Table 2), the maximum activities were shown
at an Al/Ti molar ratio of 2000. However, the maximum
activity was shown at an Al/Ti molar ratio of 1000 in the
2/MAO system. Most worthy of note is the fact that the
activity of 2/MAO did not change very much when the
cocatalyst/catalyst ratio decreased from 2000 to 250 (entries
6−11, Table 2). Such a phenomenon suggested that its activity
could be maintained at a high level even at low Al/Ti ratios. In
addition, the obtained polyethylene exhibits lower Mv values
Ethylene Polymerization. Upon activation with methyl-
aluminoxane (MAO), complexes 1−7 were found to be active
for ethylene polymerization. The polymerization results are sum-
marized in Tables 2 and 3. The active catalysts were generated
in situ in toluene by addition of methylaluminoxane (MAO)
to the precursors in toluene. In the title catalytic systems, the
red mixture turned transparent yellow immediately as MAO
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Table 3. Results of Ethylene Polymerization Initiated by
a
Titanium Catalysts 3−7/MAO
b
c
entry
precat.
amt of PE (g)
activity
Mv × 10−4
1
2
3
4
5
3
4
5
6
7
3.17
1.08
1.81
2.40
0.29
9530
3240
5430
7210
870
52
21
38
44
23
a
Conditions: 2 μmol of catalyst, toluene (total volume 50 mL), 50 °C,
b
10 atm of ethylene, 10 min, Al/Ti ratio 2000. Activity in kg of PE
c
(mol of Ti)−1 h−1. Mv measured by the Ubbelohde calibrated
viscosimeter technique.
As presented in Table 2, the temperature tolerances of title
complexes 1−3 for performing ethylene polymerizations were
good. The 1/MAO system showed the highest activity around
80 °C, and the 2/MAO system showed the highest activity at
room temperature. The better thermal stability of complex 1
suggested that the ligand with imino-quinolinol backbone in the
catalyst plays an important role in stabilizing the active species
at high temperature. In addition, the 3/MAO system showed
the highest activity around 50 °C, which is similar to the case
for classical FI catalysts. The molecular weights of polyethylene
obtained decrease with elevating reaction temperature due to a
faster chain transfer and termination at higher temperature.
To determine the effect of reaction time on the activity and
molecular weight (Mv) of the resulting polymers, the ethylene
polymerization using the 2/MAO catalytic system was
conducted over different time periods, namely, 10, 30, and
60 min (entries 8, 13, and 14, Table 2); the highest activity
(4.11 × 106 g of PE (mol of Ti)−1 h−1) was obtained in a period
of 10 min. Complex 3 showed the highest activity (about
9.53 × 106 g of PE (mol of Ti)−1 h−1). Moreover, complex 1
was found to be less active by 1 order of magnitude than titanium
complexes 2 and 3, which contain a more flexible ligand.
Dichloride titanium complex 3 presented higher activity than
trichloride titanium complex 2. According to the literature,11d
one of the reasons is probably that the space of the central
metal in the trichloride complex is more open than in the
similar dichloride species because the chlorine atom is small,
influencing the chain-transfer process of polymerization. From
the electronic effect of an ancillary ligand, dianionic ligand Lb
coordinates more strongly to a titanium metal center than the
similar monoanion ligand Lb in a tridentate fashion. Therefore,
Lb, as a dianionic ligand, can stabilize TiIV species better. This is
probably one of the reasons complex 3 has better performance
than complex 2 in ethylene polymerizaiton.
Using the optimized conditions for the 3/MAO system
(10 atm of ethylene, 50 °C, and Al/Ti ratio 2000), the pre-
catalysts 3−7 have been examined to understand the substi-
tuent effects of the ligands. The results are collected in Table 3.
The activity data in Table 3 indicates that the R group on the
ligand has a significant effect on catalytic activity and Mv value
for resultant polymer. There are observable effects of the
ligands’ environment, and the activities of complexes de-
crease in the order 3 (R = iPr) > 6 (R = Et) > 5 (R = Me) > 4
(R = H) > 7 (R = Cl). In terms of steric influence, the bulky iPr
group enhances the activity of its precatalyst, because the active
species are better protected in the polymerization process.14b
The Cl-substituted derivatives showed the lowest activities
(entry 5 in Table 3). These results clearly demonstrate that the
Figure 4. Fourier transform of the k2 weighted EXAFS oscillations of
complexes 2 and 3.
Table 1. Fit Parameters of Ti EXAFS Spectra for Complexes
2 and 3
a
b
c
d
shell
N
R
σ2 (10−3 Å2)
ΔE0 (eV)
Complex 2
1.84 0.02
Ti−O
Ti−N
Ti−Cl
0.6 0.1
1.7 0.4
2.2 0.5
6.9 3.0
2.0 1.3
5.5 0.8
5.9 4.0
9.3 1.1
5.1 1.2
2.28 0.02
2.31 0.01
Complex 3
Ti−O
Ti−N
Ti−Cl
0.7 0.1
1.6 0.2
1.4 0.4
1.83 0.01
2.12 0.02
2.36 0.01
1.8 0.4
3.8 2.4
10.2 2.1
7.5 1.0
5.2 1.1
9.1 2.1
a
b
Coordination number. Distance between absorber and backscatter
c
d
atoms. Debye−Waller factor. Inner potential correction.
Table 2. Results of Ethylene Polymerization Initiated by
a
Titanium Catalysts 1−3/MAO
b
c
entry precat. t/min Al/Ti ratio temp/°C activity
Mv × 10−4
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
3
3
10
10
10
10
10
10
10
10
10
10
10
10
30
60
10
10
10
10
10
1000
2000
3000
2000
2000
2000
1500
1000
500
20
20
20
50
80
20
20
20
20
20
50
80
20
20
50
50
50
20
80
140
230
38
33
27
28
22
38
41
44
47
60
40
33
49
56
55
52
49
58
37
2
3
180
4
290
5
350
6
2300
3600
4110
3720
2700
3450
1530
3500
2010
6220
9530
4130
6680
4880
7
8
9
10
11
12
13
14
15
16
17
18
19
250
1000
1000
1000
1000
1000
2000
2500
2000
2000
a
Conditions: 2 μmol of catalyst, toluene (total volume 50 mL), 10 atm
b
c
of ethylene. Activity in kg of PE (mol of Ti)−1 h−1. Mv measured by
the Ubbelohde calibrated viscosimeter technique.
when the ratio of Al/Ti is increased, because the chain transfer
increases with high Al concentration.14
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1.28 (dd, 12H, iPr). IR (KBr): νN−H 3417 cm−1. Anal. Calcd for
C22H26N2O: C, 79.00; H, 7.84; N, 8.38. Found: C, 78.94; H, 7.83;
N, 8.36.
bulky and donating substituents on the ligands in the ortho
position seem to be important for high catalytic activity.
Ligand Lc. A procedure analogous to that used to prepare Lb
CONCLUSIONS
■
was used, but starting from an R-substituted imino-quinolinol ligand
1
New types of double-duty tridentate [ONN] ligands were easily
prepared in one step on the basis of the corresponding imino-
quinolinol ligands. On deprotonation by NaH, ligands Lb−Lf
can be used as tridentate monoanionic ligands to synthesize
trichlorotitanium complexes. However, when they are depro-
(R = H) (620 mg, 2.5 mmol). Yield: 82.5%. H NMR (400 MHz,
CDCl3, ppm): δ 8.42 (d, 1H, quin), 8.24 (d, 1H, quin), 8.19 (br, 1H,
OH), 7.48 (t, 1H, quin), 7.45 (d, 1H, quin), 7.23 (d, 1H, quin), 7.11−
7.07 (m, 4H, Ar H), 7.04 (d, 1H, Ar H), 4.32 (d, 2H, CH2NH). IR
(KBr): νN−H 3420 cm−1. Anal. Calcd for C16H14N2O: C, 76.78; H,
5.64; N, 11.19. Found: C, 78.76; H, 5.69; N, 11.15.
n
tonated by BuLi, they can be used as tridentate dianionic
Ligand Ld. A procedure analogous to that used to prepare Lb was
ligands to synthesize dichlorotitanium complexes. The mole-
cular structures of the double-duty tridentate [ONN] ligand Lb
and complex 1 have been characterized by single-crystal X-ray
diffraction analysis. The local atomic environments and charge
states of Ti in compounds 2 and 3 were investigated by X-ray
absorption spectroscopy. On activation by excess methylalu-
minoxane (MAO), titanium complexes 1−7 can be used as
catalysts for ethylene polymerization and exhibited different
catalytic behaviors. Titanium complexes 2 and 3, bearing the
secondary amine ligand Lb, are more active than titanium com-
plex 1, bearing imine ligand La. In addition, bulky and donating
substituents on analogous secondary amine ligands (Lb−Lf)
enhance the activity of their precatalysts.
used, but starting from an R-substituted imino-quinolinol ligand (R =
Me) (690 mg, 2.5 mmol). Yield: 85%. H NMR (400 MHz, CDCl3,
ppm): δ 8.42 (d, 1H, quin), 8.28 (d, 1H, quin), 8.18 (br, 1H, OH),
7.56 (t, 1H, quin), 7.41 (d, 1H, quin), 7.23 (d, 1H, quin), 7.11 (d, 2H,
Ar H), 7.02 (d, 1H, Ar H), 4.36 (d, 2H, CH2NH), 2.22 (s, 6H, 2CH3).
IR (KBr): νN−H 3427 cm−1. Anal. Calcd for C18H18N2O: C, 77.67; H,
6.52; N, 10.06. Found: C, 77.69; H, 6.50; N, 10.03.
1
Ligand Le. A procedure analogous to that used to prepare Lb was
used, but starting from an R-substituted imino-quinolinol ligand (R =
1
Et) (760 mg, 2.5 mmol). Yield: 88%. H NMR (400 MHz, CDCl3,
ppm): δ 8.44 (d, 1H, quin), 8.27 (d, 1H, quin), 8.14 (br, 1H, OH),
7.59 (t, 1H, quin), 7.48 (d, 1H, quin), 7.33 (d, 1H, quin), 7.21 (d, 2H,
Ar H), 7.08 (d, 1H, Ar H), 4.32 (d, 2H, CH2NH), 2.58 (m, 4H,
2CH2), 1.27 (t, 6H, 2CH3). IR (KBr): νN−H 3415 cm−1. Anal. Calcd
for C20H22N2O: C, 78.40; H, 7.24; N, 9.14. Found: C, 78.44; H, 7.23;
N, 9.14.
EXPERIMENTAL SECTION
■
Ligand Lf. A procedure analogous to that used to prepare Lb was
General Data. All manipulations of air- and/or water-sensitive
compounds were carried out under dry argon using standard Schlenk
techniques. Tetrahydrofuran (THF), hexane, and toluene were
distilled from sodium-benzophenone. Dichloromethane was distilled
from calcium hydride. Commercial reagents, namely TiCl4, methyl-
aluminoxane (MAO, 1.46 M in toluene), LiAlH4, NaH, nBuLi, 2-
methylquinolin-8-ol, SeO2, and 2,6-substituted benzenamine, were
purchased from Acros Co. 8-Hydroxyquinoline-2-carbaldehyde was
prepared according to the literature procedure.15
used, but starting from an R-substituted imino-quinolinol ligand (R =
1
Cl) (792 mg, 2.5 mmol). Yield: 64%. H NMR (400 MHz, CDCl3,
ppm): δ 8.44 (d, 1H, quin), 8.30 (d, 1H, quin), 8.17 (br, 1H, OH),
7.55 (t, 1H, quin), 7.41 (t, 3H, Ar H), 7.25 (d, 1H, quin), 7.06 (d, 1H,
quin), 4.45 (d, 2H, CH2NH). IR (KBr): νN−H 3434 cm−1. Anal. Calcd
for C16H12Cl2N2O: C, 60.21; H, 3.79; N, 8.78. Found: C, 60.19; H,
3.81; N, 8.73.
Preparation of Complexes. Complex 1. To a stirred solution
of La (83 mg, 0.25 mmol) in 20 mL of toluene was added TiCl4
(0.25 mL, 0.5 mmol) at −78 °C. The yellow solution imme-
diately changed to a red suspension, and HCl gas was evolved.
The mixture was warmed to room temperature by itself, and
stirring was maintained for 6 h at room temperature. The red
product 1 was obtained by filtration and washed twice with
IR spectra were measured on a Nicolet Avatar-360 spectropho-
tometer. NMR measurements were obtained on a Bruker AC 400
spectrometer in CDCl3 solution. The NMR spectra of all the com-
pounds and complexes were recorded at ambient temperature.
Elemental analyses for C, N, and H were carried out on an Elementar
III Vario EI analyzer.
1
10 mL of toluene and dried in vacuo (86% yield). H NMR
Preparation of Ligands. Ligand La. A mixture of 8-hydroxy-
quinoline-2-carbaldehyde (0.6 g, 3.5 mmol) and 30 mL of
ethanol was heated to 80 °C, and then a solution of (2,6-
diisopropylphenyl)amine (0.62 g, 3.5 mmol) in 30 mL of
ethanol was added dropwise. The reaction mixture was refluxed
for 6 h and cooled to room temperature. Purification by
column chromatography used 1/3 dichloromethane/petroleum
ether (1% triethylamine). The product was obtained as yellow
(400 MHz, CDCl3, ppm): δ 8.68 (d, 1H, quin), 8.49 (s, 1H,
HCN), 8.05 (d, 1H, quin), 7.91 (d, 1H, quin), 7.72 (d, 1H,
quin), 7.41 (d, 1H, quin), 7.35 (d, 2H, Ar H), 7.05 (d, 1H, Ar
H), 3.74 (sept, 2H, iPr), 2.35 (s, 12H, iPr). IR (KBr): νCN
1610 cm−1. Anal. Calcd for C22H23Cl3N2OTi: C, 54.41; H, 4.77;
N, 5.77. Found: C, 54.44; H, 4.79; N, 5.75.
Complex 2. To a slurry of NaH (24 mg, 1.0 mmol) in THF
(10 mL) was added a solution of ligand Lb (83.5 mg, 0.25 mmol) in
THF (10 mL) at 0 °C. The resulting yellow suspension was warmed to
room temperature and stirred for 1 h. After the solvent of the filtrate
was removed under vacuum, 30 mL of toluene was added to the resi-
due, followed by a toluene solution of TiCl4 (2 M, 0.25 mL, 0.5 mmol).
The yellow solution immediately changed to a red suspension. The
mixture was warmed to room temperature by itself, and stirring was
maintained for 6 h at room temperature. The red product 2 was
obtained by filtration and washed twice with 10 mL of toluene and
dried in vacuo (83% yield). 1H NMR (400 MHz, CDCl3, ppm): δ 8.70
(d, 1H, quin), 8.63 (s, 1H, NH), 8.08 (d, 1H, quin), 7.69−7.59 (m, 2H,
quin), 7.44 (d, 1H, quin), 7.37 (d, 1H, Ar H), 7.29 (d, 1H, Ar H), 7.19
(d, 1H, Ar H), 3.7 (d, 2H, CH2), 3.14 (sept, 1H, iPr), 2.97 (sept, 1H,
iPr), 1.35 (d, 6H, iPr), 1.22 (d, 6H, iPr). IR (KBr): νN−H 3283 cm−1.
Anal. Calcd for C22H25Cl3N2OTi: C, 54.18; H, 5.17; N, 5.74. Found: C,
54.22; H, 5.19; N, 5.72.
1
crystals in 72% yield. H NMR (400 MHz, CDCl3, ppm): δ
8.47 (d, 1H, quin), 8.40 (d, 1H, quin), 8.37 (s, 1H, NCH),
8.22 (br, 1H, OH), 7.77 (t, 1H, quin), 7.45 (d, 1H, quin), 7.23
(d, 1H, quin), 7.16 (d, 2H, Ar H), 7.08 (d, 1H, Ar H), 3.49
(sept, 2H, iPr), 1.21(d, 6H, iPr), 1.15 (d, 6H, iPr). IR (KBr):
νCN 1637 cm−1. Anal. Calcd for C22H24N2O: C, 79.48; H, 7.28;
N, 8.43. Found: C, 79.50; H, 7.31; N, 8.47.
Ligand Lb. To a suspension of LiAlH4 (0.38 g, 10.0 mmol) in ether
(20 mL) was slowly added a solution of ligand La (2.5 mmol) in ethyl
ether (30 mL). After the mixture was stirred for 2 h at room tem-
perature, water (6.5 mL) and aqueous HCl (20%; 10 mL) were added
sequentially at 0 °C. The organic phase was separated and washed with
water (15 mL × 3). The organic layers were dried with anhydrous
NaSO4. The solvent was removed under vacuum, and the pure
1
product Lb was obtained as a light yellow powder in 92% yield. H
NMR (400 MHz, CDCl3, ppm): δ 8.40 (d, 1H, quin), 8.14 (br, 1H,
OH), 7.46 (t, 1H, quin), 7.44 (d, 1H, quin), 7.20 (d, 1H, quin), 7.14
(d, 1H, quin), 7.12 (d, 2H, Ar H), 7.03 (d, 1H, Ar H), 6.80 (t, 1H, Ar
H), 4.40 (s, 2H, CH2NH), 3.40 (sept, 1H, iPr), 2.93 (sept, 1H, iPr),
Complex 3. nBuLi (1.6 M, 0.32 mL, 0.5 mmol) was added through a
syringe to a solution of Lb (83.5 mg, 0.25 mmol) in THF (20 mL)
cooled to 0 °C. The resulting dark red solution was stirred at room
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Article
temperature for 1 h. After the solvent was removed under vacuum,
30 mL of toluene was added to the residue, followed by a toluene
solution of TiCl4 (2 M, 0.25 mL, 0.5 mmol) at −78 °C. The solution
immediately changed to a red suspension. The mixture was warmed to
room temperature, and stirring was maintained for 6 h at room
temperature. The red product 3 was obtained by filtration and washed
twice with 10 mL of toluene and dried in vacuo (88% yield). 1H NMR
(400 MHz, CDCl3, ppm): δ 8.55 (d, 1H, quin), 7.61 (d, 1H, quin),
7.53 (d, 1H, quin), 7.36 (d, 1H, quin), 7.30 (d, 1H, quin), 7.22−7.15
(m, 2H, Ar H), 6.8 (d, 1H, Ar H), 3.63 (s, 2H, CH2), 3.07 (sept, 2H,
iPr), 1.28 (d, 6H, iPr), 1.16 (d, 6H, iPr). Anal. Calcd for
C22H24Cl2N2OTi: C, 58.56; H, 5.36; N, 6.21. Found: C, 58.60; H,
5.39; N, 6.19.
Complex 4. Using the same procedure for the synthesis of 3,
complex 4 was obtained as a red solid in 80% yield. 1H NMR
(400 MHz, CDCl3, ppm): δ 8.45 (d, 1H, quin) δ 7.82 (d, 1H, quin),
7.74 (t, 1H, quin), 7.40 (d, 1H, quin), 7.28 (d, 1H, quin), 7.22−7.16
(m, 4H, Ar H), 7.13 (d, 1H, Ar H), 3.81 (s, 2H, CH2). Anal. Calcd for
C16H12Cl2N2OTi: C, 52.36; H, 3.30; N, 7.63. Found: C, 52.31; H,
3.33; N, 7.58.
under argon. MAO (10 wt % in toluene) was added. A solution of the
precatalyst in toluene was added. After three exchanges of ethylene
gas, the ethylene pressure was raised to the specified value and main-
tained for a certain time. The polymerization was terminated by
addition of ethanol and dilute HCl (3%). The solid polyethylene was
filtered, washed with ethanol, and dried at 80 °C under vacuum.
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files, figures, and a table giving crystallographic data,
ORTEP diagrams, and details of the crystal structure deter-
minations of Lb and 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Tel: (+86)-21-65643776. Fax: (+86)-21-65641740. E-mail:
gxjin@fudan.edu.cn.
■
Complex 5. Using the same procedure for the synthesis of 3,
complex 5 was obtained as a red solid in 84% yield. H NMR (400
Notes
1
The authors declare no competing financial interest.
MHz, CDCl3, ppm): δ 8.54 (d, 1H, quin), 7.89 (d, 1H, quin), 7.67 (t,
1H, quin), 7.42 (d, 1H, quin), 7.25−7.17 (m, 3H, Ar H), 7.11 (d, 1H,
quin), 3.79 (s, 2H, CH2), 2.47 (s, 6H, 2CH3). Anal. Calcd for
C18H16Cl2N2OTi: C, 54.72; H, 4.08; N, 7.09. Found: C, 54.76; H,
4.08; N, 7.11.
ACKNOWLEDGMENTS
■
This work was supported by the Shanghai Science and Tech-
nology Committee (08DZ2270500), the Program for Changjiang
Scholars and Innovative Research Team in University (IRT1117),
the Shanghai Leading Academic Discipline Project (B108), and
the National Basic Research Program of China (2009CB825300
and 2010DFA41160).
Complex 6. Using the same procedure for the synthesis of 3,
1
complex 6 was obtained as a red solid in 79% yield. H NMR (400
MHz, CDCl3, ppm): δ 8.50 (d, 1H, quin), 7.84 (d, 1H, quin), 7.67 (t,
1H, quin), 7.46 (d, 1H, quin), 7.24−7.17 (m, 3H, Ar H), 7.05 (d, 1H,
quin), 3.68 (s, 2H, CH2), 3.25−3.10 (m, 2H, CH2), 3.05−3.00 (m,
2H, CH2), 1.59 (t, 3H, CH3), 1.12 (t, 3H, CH3). Anal. Calcd for
C20H20Cl2N2OTi: C, 56.77; H, 4.76; N, 6.62. Found: C, 56.71; H,
4.78; N, 6.62.
REFERENCES
■
(1) Sinn, H.; Kaminsky, W.; Vollmer, H. J.; Woldt, R. Angew. Chem.,
Int. Ed. 1980, 19, 390−392.
Complex 7. Using the same procedure for the synthesis of 3,
1
(2) (a) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283−
316. (b) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428−447.
(3) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169−1203. (b) Baumann, R.; Davis, W. M.; Schrock, R. R. J. Am.
Chem. Soc. 1997, 119, 3830−3831. (c) Tian, J.; Hustad, P. D.; Coates,
G. W. J. Am. Chem. Soc. 2001, 123, 5134−5135. (d) Lamberti, M.;
Pappalardo, D.; Zambelli, A.; Pellecchia, C. Macromolecules 2002, 35,
658−663. (e) Milano, G.; Cavallo, L.; Guerra, G. J. Am. Chem. Soc.
2002, 124, 13368−13369.
(4) (a) Kohn, R. D.; Haufe, M.; Kociok-Kohn, G.; Grimm, S.;
Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 4337−
4339. (b) Jones, D. J.; Gibson, V. C.; Green, S. M.; Maddox, P. J.
Chem. Commun. 2002, 1038−1039.
(5) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414−6415. (b) Small, B. L.; Brookhart, M.; Bennett, A. M.
A. J. Am. Chem. Soc. 1998, 120, 4049−4050. (c) Britovsek, G. J. P.;
Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.; McTavish, S. J.; Solan,
G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849−850.
(d) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460−462.
(6) (a) Bambirra, S.; Leusen, D. V.; Meetsma, A.; Hessen, B.;
Teuben, J. H. Chem. Commun. 2001, 637−638. (b) Li, D. F.; Li, S. H.;
Cui, D. M.; Zhang, X. Q.; Trifonov, A. A. Dalton Trans. 2011, 40,
2151−2153. (c) Jian, Z. B.; Cui, D. M. Dalton Trans. 2012, 41, 2367−
2373.
(7) (a) Chen, Y.; Chen, R.; Qian, C.; Dong, X.; Sun, J.
Organometallics 2003, 22, 4312−4321. (b) Sun, W. H.; Yang, H. J.;
Li, Z. L.; Li, Y. Organometallics 2003, 22, 3678−3683. (c) Zhang, D.;
Jin,
G.-X. Organometallics 2003, 22, 2851−2854. (d) Camacho, D. H.; Salo,
E. V.; Ziller, J. W.; Guan, Z. Angew. Chem Int. Ed. 2004, 43, 1821−1825.
(e) Oakes, D. C. H.; Kimberley, B. S.; Gibson, V. C.; Jones, D. J.;
White, A. J. P.; Williams, D. J. Chem. Commun. 2004, 19, 2174−2175.
complex 7 was obtained as a orange-red solid in 65% yield. H NMR
(400 MHz, CDCl3, ppm): δ 8.59 (d, 1H, quin), 8.44 (d, 1H, quin),
7.71 (t, 1H, quin), 7.63 (t, 3H, Ar H), 7.31 (d, 1H, quin), 7.16 (d, 1H,
quin), 3.40 (s, 2H, CH2). Anal. Calcd for C16H10Cl4N2OTi: C, 44.08;
H, 2.31; N, 6.43. Found: C, 44.01; H, 2.32; N, 6.41.
Single-Crystal X-ray Structure Determination of Ligand Lb
and Complex 1. Ligand Lb showed no signs of decomposition during
X-ray data collection, which was carried out at room temperature. For
complex 1, a single crystal suitable for X-ray analysis was sealed in a glass
capillary, and the intensity data of the single crystal were collected on a
CCD-Bruker Smart APEX system. All determinations of the unit cell
and intensity data were performed with graphite-monochromated Mo
Kα radiation (λ = 0.710 73 Å). All data were collected at room tem-
perature using the ω-scan technique. These structures were solved by
direct methods, using Fourier techniques, and refined on F2 by a full-
matrix least-squares method. All the calculations were carried out with
the SHELXTL program.16 All the non-hydrogen atoms were refined
anisotropically, and all the hydrogen atoms were included but not
refined. Crystallographic data are summarized in the Supporting
Information part.
XAFS Data Collection. The X-ray absorption data at the Ti
K-edge of the sample were measured in the fluorescence mode with a
Lytle fluorescence detector on beamline BL14W1 of the Shanghai
Synchrotron Radiation Facility (SSRF), Shanghai, People's Republic of
China. The station was operated with a double crystal monochro-
mator, Si(111), detuned to 40% intensity to minimize the presence of
higher harmonics. All measurements were done in transmission or
fluorescence mode using ion chambers filled with a mixture of He and
N2 to have an X-ray absorbance of 20% in the first and 80% in the
second chamber. Data processing and analysis were performed using
the program ATHENA.17 All fits to the EXAFS data were performed
using the program ARTEMIS.17
General Procedure for Ethylene Polymerization at High
Pressure. A 100 mL autoclave was charged with 50 mL of toluene
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(f) Li, W. D.; Zhang, X. C.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc.
2004, 126, 12246−12247. (g) Williams, B. S.; Leatherman, M. D.;
White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2005, 127, 5132−5146.
(h) Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Schmalz, T.;
Qayyum, S.; Kempe, R. Chem. Eur. J. 2006, 12, 8969−8978.
(i) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.; Meetsma, A.;
Hessen, B. Organometallics 2007, 26, 1014−1023.
(8) (a) Yu, S.-M.; Mecking, S. J. Am. Chem. Soc. 2008, 130, 13204−
13205. (b) Weng, Z. Q.; Teo, S. H.; Andy Hor, T. S. Dalton Trans.
2007, 32, 3493−3498. (c) Kermagoret, A.; Braunstein, P. Dalton
Trans. 2008, 12, 1564−1573. (d) Anselment, T. M. J.; Vagin, S. I.;
Rieger, B. Dalton Trans. 2008, 34, 4537−4548.
(9) (a) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.;
Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.;
Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847−
6856. (b) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru,
K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
3327−3336. (c) Mitani, M.; Furuyama, R.; Mohri, J.-I.; Saito, J.; Ishii,
S.; Terao, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
7888−7889. (d) Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2002,
124, 11578−11579. (e) Hustad, P. D.; Tian, J.; Coates, G. W. J. Am.
Chem. Soc. 2002, 124, 3614−3621. (f) Tian, J.; Coates, G. W. Angew.
Chem., Int. Ed. 2000, 39, 3626−3629.
(10) (a) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2000,
122, 10706−10707. (b) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Weitman,
H.; Goldschmidt, Z. Chem. Commun. 2000, 379−380.
(11) (a) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Carrillo-
Her-mosilla, F.; Tejeda, J.; Diez-Barra, E.; Lara-Sanchez, A.; Sanchez-
Barba, L.; Lopez-Solera, I.; Ribeiro, M. R.; Campos, J. M. Organometallics
2001, 20, 2428−2430. (b) Murtuza, S.; Casagrande, O. L. Jr.; Jordan,
R. F. Organometallics 2002, 21, 1882−1890. (c) Aaltonen, P.; Seppala,
J.; Matilainen, L.; Leskela, M. Macromolecules 1994, 27, 3136−3138.
(d) Hu, W.-Q.; Sun, X.-L.; Wang, C.; Gao, Y.; Tang, Y.; Shi, L. P.; Xia,
W.; Sun, J.; Dai, H.-L.; Li, X.-Q.; Yao, X.-L.; Wang, X.-R.
Organometallics 2004, 23, 1684−1688. (e) Yang, X. H.; Liu, C. R.;
Wang, C.; Sun, X. L.; Guo, Y. H.; Wang, X.-K.; Wang, Z.; Xie, Z. W.;
Tang, Y. Angew. Chem., Int. Ed. 2009, 48, 8099−8102.
(12) Keaton, R. J.; Jayaratne, K. C.; Henningsen, D. A.; Koterwas,
L. A.; Sita, L. R. J. Am. Chem. Soc. 2001, 123, 6197−6198.
(13) Hu, P.; Wang, F. S.; Jin, G.-X. Organometallics 2011, 30, 1008−
1012.
(14) (a) Gibson, V. C.; Redshaw, C.; Solan, G. A. Chem. Rev. 2007,
107, 1745−1746. (b) Chen, E. Y. X.; Marks, T. J. Chem. Rev. 2000,
100, 1391−1434.
(15) Chen, Q.; Zeng, M. H.; Zhou, Y. L.; Zou, H. H.; Kurmoo, M.
Chem. Mater. 2010, 22, 2114−2119.
(16) Sheldrick, G. M. SHELXL-97; Universitat Gottingen, Gottingen,
̈
̈
̈
Germany, 1997.
(17) Ravel, B.; Newville, M. J. Synchrotron Radiat. 2005, 12, 537−541.
3247
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