Synthesis and characterization of titanium complexes bearing sulfoxide groups and their catalytic behaviors in ethylene homo- and copolymerization

Article abstract of DOI:10.1007/s11426-014-5137-4

Titanium complexes derived from 2,4-di-tert-butyl-6-((2-(arylsulfinyl) phenylimino)methyl)phenol are designed and synthesized. X-ray diffraction studies reveal that the complexes adopt distorted octahedral geometry with O(phenol), N(imine), and O(sulfoxide) coordinated with titanium. Combined with modified methylaluminoxane(MMAO), the complexes exhibit moderate to high activity to afford polyethylene even at 120 °C under 1 atm ethylene pressure. The complexes also show excellent capability in copolymerization of ethylene with either 1-hexene or norbornene. Results indicate that the introduction of sulfoxide groups could open the space around central metal and favors the insertion of bulky comonomers.

Full text of DOI:10.1007/s11426-014-5137-4

SCIENCE CHINA
Chemistry
August 2014 Vol.57 No.8: 1144–1149
doi: 10.1007/s11426-014-5137-4
• ARTICLES •
Synthesis and characterization of titanium complexes bearing
sulfoxide groups and their catalytic behaviors in ethylene
homo- and copolymerization
WANG Zheng, PENG Ai-Qing, SUN Xiu-Li & TANG Yong*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, China
Received February 28, 2014; accepted March 21, 2014; published online July 1, 2014
Titanium complexes derived from 2,4-di-tert-butyl-6-((2-(arylsulfinyl)phenylimino)methyl)phenol are designed and synthe-
sized. X-ray diffraction studies reveal that the complexes adopt distorted octahedral geometry with O(phenol), N(imine), and
O(sulfoxide) coordinated with titanium. Combined with modified methylaluminoxane(MMAO), the complexes exhibit moder-
ate to high activity to afford polyethylene even at 120 °C under 1 atm ethylene pressure. The complexes also show excellent
capability in copolymerization of ethylene with either 1-hexene or norbornene. Results indicate that the introduction of sulfox-
ide groups could open the space around central metal and favors the insertion of bulky comonomers.
sulfoxide, catalyst, synthesis, ethylene polymerization, copolymerization
eton [2534]. In this system, strong side-arm effects on cat-
alytic efficiency were observed. When the sidearm was SR,
SeR, or PPh2, high activity could be obtained whereas low
activity was always observed when OR was used as a
sidearm (Scheme 1). However, a less-hindered R group en-
hanced activity levels as well as -olefin incorporation [25,
26]. To understand the different effects of O-pendant and
S-pendant groups on activity, we developed single- crystal
titanium complexes 1a and 1b. As shown in Figure 1, the O
atom in the pendant group of complex 1a adopted sp2 hy-
bridization, whereas an sp3-hybridized S atom was observed
in compound 1b. The phenyl group in complex 1b deviated
from the [ONS] plane, but the phenyl group of complex 1a
was at the [ONO] plane (177.6(5)° for N–Ti–O–C(22)
compared to 107.51(13)° for N–Ti–S–C(22) in 1b). Due to
the hybridization pattern of the donor atom as well as the
bond lengths of TiS and TiO1, the space around the tita-
nium was much more open and favored the coordination
and insertion of ethylene by replacement of the side- arm
O-atom in compound 1a with S-atom in compound 1b.
1 Introduction
Many efforts have been made to develop well-defined or-
ganometallic species as homogeneous olefin polymerization
catalysts for the production of a variety of polymers that
have novel uses and properties [121]. Of the catalysts de-
veloped, ligand scaffolds have shown significant influence
in stabilizing polymerization-active metal centers and in
controlling their behaviors of olefin polymerization [2224].
For example, the introduction of bulky imine groups in -
diimine, salicylaldemine, and pyridine diimine backbones
allows the development of active late-transition metal cata-
lysts [1013]. In our previous study on olefin polymeriza-
tion catalysts, we developed a family of [ONX]titanium
complexes based on regulation of the electronic and steric
properties of the active species by introducing a ped-
ant-coordination group (side-arm) into a simple ligand skel-
Dedicated to Professor Qian Changtao on the occasion of his 80th birthday.
*Corresponding author (email: tangy@sioc.ac.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2014
chem.scichina.com link.springer.com

Wang Z, et al. Sci China Chem August (2014) Vol.57 No.8
1145
structures were solved by direct methods and refined on F2
by full-matrix least squares techniques with anisotropic
thermal parameters for non-hydrogen atoms. Hydrogen at-
oms were placed at the calculated positions and were in-
cluded in the structure calculation without further refine-
ment of the parameters. All calculations were carried out
using the SHELXS-97 program.
Scheme 1 Activity comparison between complexes bearing –OPh (1a)
and –SPh (1b) side-arm [26].
2.2 Synthesis of the ligands and complexes
(E)-2,4-di-tert-butyl-6-((2-(phenylsulfinyl)phenylimino)meth-
yl)phenol (7a)
A mixture of the aniline 6a (6.2 g, 28.5 mmol) and
3,5-di-tert-butylsalicylaldehyde (6.7 g, 28.5 mmol) in etha-
nol (50 mL) in the presence of a catalytic amount of acetic
acid (3 mL) was refluxed until the reaction was complete.
The mixture was cooled to room temperature and the col-
lected yellow solid was washed with cool ethanol to give
Figure 1 Molecular structures of complexes 1a and 1b.
1
pure product. Yield: 8.72 g (71%). H NMR (300 MHz,
CDCl3, ppm): δ 12.81 (s, 1 H), 8.45 (s, 1 H), 8.16–8.17 (m,
1H), 7.68–7.12 (m, 10 H), 1.50 (s, 9 H), 1.31 (s, 9 H). 13C
NMR (300 MHz, CDCl3): δ 165.1, 158.0, 145.7, 145.0,
140.9, 138.9, 137.2, 131.9, 131.1, 129.1, 129.1, 127.4,
127.4, 126.0, 124.5, 118.0, 117.8, 35.1, 34.1, 31.4, 29.3.
Anal. calcd. for C27H31NO2S: C 74.79, H 7.21, N 3.23.
Found: C 74.40, H 7.22, N 3.01.
In this work, we designed and synthesized ligand 7a- and
7b-bearing sulfoxide groups to further elaborate the influ-
ence of the electronic and steric properties of the pendant
group on the catalyst behaviors during ethylene polymeriza-
tion. The corresponding titanium complexes of 7b showed
good activity even at 120 °C upon activation with modified
methyl aluminominato (MMAO). 1-Hexene and norbornene
(NBE) could incorporate into polyethylene in more than 30
mol%.
(E)-2,4-di-tert-butyl-6-((2-(2,6-diisopropylphenylsulfinyl)ph-
enylimino)methyl)phenol (7b)
Using a similar procedure to 7a, pure 7b was obtained.
Yield: 2.82 g (67%). 1H NMR (300 MHz, CDCl3, δ ppm): δ
11.91 (s, 1 H), 7.96–7.98 (m, 2 H), 7.27–7.45 (m, 3 H),
7.00–7.09 (m, 2H), 6.85–6.91 (m, 2 H), 3.75–3.70 (m, 2 H),
1.42 (s, 9 H), 1.30 (s, 9 H), 0.96 (d, J = 6.6 Hz, 12 H). 13C
NMR (75 MHz, CDCl3): δ 166.7, 157.7, 150.7, 147.8, 140.6,
136.9, 137.0, 132.0, 131.1, 128.6, 127.3, 126.4, 125.7,
124.7, 120.6, 117.9, 35.0, 34.0, 31.3, 29.4, 28.6, 24.4, 23.2.
Anal. calcd. for C33H43NO2S: C 76.55, H 8.37, N 2.71.
Found: C 76.58, H 8.29, N 2.71.
2 Experimental
2.1 General information
All manipulations were carried out using standard Schlenk
technique or glove-box under nitrogen or argon. Toluene,
THF, hexane, and dichloromethane were purified by an MB
SPS-800 (MBRAUN Company, Germany) prior to use.
Modified methylaluminoxane (MMAO) was purchased
from Akzo Chemical (Holland) as heptane solution (1.88
M). Molecular weights (Mw and Mn) and molecular-weight
distributions (Mw/Mn) of polymers were determined using a
Waters Alliance GPC 2000 series (WATERS, USA) at
135 °C (using polystyrene calibration, 1,2,4-trichloroben-
zene as solvent at a flow rate of 0.92 mL/min). 1H NMR and
13C NMR spectra were recorded on a Varian XL-300 MHz
and Varian XL-400 MHz spectrometer (VARIAN, USA).
Elemental analysis was performed by the Analytical Labor-
atory of Shanghai Institute of Organic Chemistry (CAS).
13C NMR data for polymers were obtained using CDCl3 as
the solvent at 25 °C. X-ray crystallographic data were col-
lected at 20 °C on a Bruker SMART diffractometer with
graphite-monochromated Mo-Kα radiation ( = 0.71073 Å).
The SADABS absorption correction was applied. The
[(E)-2,4-di-tert-butyl-6-((2-(phenylsulfinyl)phenylimino)-
methyl) phenol] Ti(IV)Cl3 (8a)
To a solution of TiCl4 (0.56 mL, 5.0 mmol) in toluene (30 mL)
was added dropwise a solution of 7a (2.0 g, 4.6 mmol) in tolu-
ene (30 mL) over 10 min at 78 ºC. The resulting mixture was
allowed to warm to room temperature and stirred for 3 h. The
generated dark-red solids were collected and washed with tol-
uene (3 × 20 mL). Pure product was recrystallized in toluene at
1
30 ºC. Yield: 2.0 g (74%). H NMR (400 MHz, CDCl3, δ
ppm): 8.46 (s, 1 H), 7.99–7.24 (m, 10 H), 6.48–6.46 (m, 1H),
1.61 (s, 9 H), 1.36 (s, 9 H) ppm. 13C NMR (100 MHz, CDCl3,
δ ppm): δ 168.1, 161.1, 150.1, 146.4, 137.0, 135.4, 134.5,
133.2, 133.1, 131.9, 130.6, 129.6, 128.2, 127.3, 126.1, 125.0,
35.4, 34.7, 31.2, 31.1, 29.8. Anal. calcd. for C27H30Cl3NO2STi:

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Wang Z, et al. Sci China Chem August (2014) Vol.57 No.8
C 55.26, H 5.15, N 2.39. Found: C 55.87, H 5.39, N 2.11.
benzenethiol 3a and 3b, which were prepared according to
the procedures in literature [26]. Oxidation of 5 readily
generated 2-(phenylsulfinyl)aniline 6. Refluxing the mixture
of 6 and the aldehyde for several hours in ethanol resulted
in the formation of 7, which was recrystallized from cool
EtOH to give the pure product as yellow solid. Complexes
8a and 8b were obtained by treating ligand 7 with TiCl4 in
toluene as dark-red solid, which was purified from recrys-
tallization in toluene or CH2Cl2 at 30 ºC (Scheme 3).
[(E)-2,4-di-tert-butyl-6-((2-(2,6-diisopropylphenylsulfinyl)-
phenylimino)methyl)phenol] Ti(IV)Cl3 (8b)
By employing a similar procedure to that of 8a, 8b was ob-
tained as dark-red solid. Pure product was obtained from
recrystallization in CH2Cl2. Yield: 2.0 g (77%). 1H NMR
(300 MHz, CDCl3, δ ppm): δ 8.45 (s, 1 H), 7.26–7.77 (m, 8
H), 6.80–6.84 (m, 1H), 3.61–3.66 (m, 1 H), 3.48–3.52 (m, 1
H), 1.61 (s, 9 H), 1.42 (d, J = 3.9 Hz, 3 H), 1.40 ( d, J = 4.8
Hz, 3H), 1.35 (s, 9 H), 1.17 (d, J = 5.4 Hz, 3 H), 0.98 (d, J =
5.1 Hz, 3 H). 13C NMR (100 MHz, CDCl3, δ ppm): δ
167.9, 161.7, 155.2, 152.9, 150.4, 145.9, 136.8, 135.7,
134.3, 133.0, 130.5, 130.0, 128.7, 128.0, 127.0, 126.99,
125.5, 125.1, 124.1, 35.4, 34.6, 31.2, 31.0, 30.6, 29.8, 25.9,
25.2, 23.6, 22.6 ppm. Anal. calcd. for C33H42Cl3NO2STi: C
59.07, H 6.31, N 2.09. Found: C 59.30, H 6.28, N 1.82.
1
Complexes 8a and 8b were characterized by H and 13C
NMR and elemental analysis. Crystals of 8a and 8b were
developed from toluene/CH2Cl2 for X-ray structure deter-
mination. As shown in Figures 2 and 3, complexes 8a and
8b adopted a distorted octahedral coordination around the
titanium, similar to the parental complexes in 1 [26]. Three
chlorines appeared in a mer-position, which could facilitate
olefin insertion. Phenolate, imine, and sulfoxide fragment in
the ligands coordinated with titanium in both cases. The
TiO1 bond in complex 8a (2.013(4) Å) was significantly
shortened compared with the corresponding complex 1a
bearing ether appending group (2.249(5) Å) [26]. Bond
lengths of TiO2 and TiN1 in 8a were 1.793(4) and
2.236(5) Å, respectively. The bond angle of O1TiO2 in
8a was larger than in the corresponding complex 1a that
bore ether appending group (163.66(18) vs. 158.32(17)
[26]. In the molecular structure of 8b, similar bond lengths
and bond angles to those of 8a were observed.
2.3 General procedure of ethylene (co)polymerization
A flame-dried Schlenk flask was charged with ethylene and
placed in an oil bath at the polymerization temperature. The
desired amount of freshly distilled dry toluene was trans-
ferred into the flask and saturated with ethylene, followed
by a comonomer in the case of copolymerization. MMAO
was injected into the flask via a syringe and the mixture was
stirred for 5 min. Then the catalyst precursor in toluene was
added. After the polymerization was quenched with acidi-
fied ethanol, the mixture was poured into acidified ethanol
(300 mL, 10 vol% HCl in ethanol). The precipitated poly-
mer was collected, washed with ethanol, and dried at 50 ºC
under vacuum until it maintained a constant weight.
3.2 Ethylene homo-polymerization
Complex 8a was first used as a model to investigate the
ethylene polymerization in the presence of modified methyl
aluminoxane (MMAO) for optimizing the conditions. It is
worthwhile to note that 8a showed good thermostability. As
shown in Table 1, the highest activity of 5.3 × 105
g/mol[Ti] h atm was achieved at 60 ºC when 8a/MMAO
polymerized ethylene in toluene (entry 3). This activity was
influenced by the polymerization temperature. At 30 ºC, the
activity was 1.9 × 105 g/mol[Ti] h atm, which increased to 4.9
× 105 g/mol[Ti] h atm at 80 ºC (entry 6). Decalin was also a
3 Results and discussion
3.1 Synthesis and characterization of ligands and com-
plexes
The synthesis of ligands and complexes is summarized in
Scheme 2. Thioether 5a and 5b were readily available from
Scheme 2 Synthesis of ligand 7.

Wang Z, et al. Sci China Chem August (2014) Vol.57 No.8
1147
Table 1 Effect of reaction temperature on ethylene polymerization results
using catalyst 8a in toluene a)
T b)
(oC)
30
Time
(min)
10
d,e)
e)
Entry
Solvent
Activity c) Mw
Mw/Mn
1
2
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
decalin
decalin
decalin
1.9
4.6
5.3
2.7
4.8
4.9
3.2
3.2
2.4
8.0
5.0
2.2
20.2
9.5
2.0
1.6
1.7
2.9
1.5
1.7
1.7
1.8
2.0
2.7
1.9
1.7
50
60
10
10
10
10
10
20
30
60
10
10
10
3
4 f)
7.8
19.8
5.6
3.2
3.8
4.7
6.5
1.8
0.7
0.5
60
5
70
Scheme 3 Synthesis of titanium(IV) complexes 8.
6
80
7
60
8
60
9
60
10
11
12
80
100
120
a) Conditions: 8a (3 µmol) in 30 mL solvent; ethylene pressure, 0.1
MPa; reaction time, 10 min; cocatalyst, MMAO 3.2 mL (1.88 mmol/mL in
heptane). b) Temperature of the bath. c) 105 g/mol[Ti] h atm. d) 104 g/mol.
e) Determined by GPC. f) 8b (3 µmol) was used instead of 8a.
Figure 2 Molecular structure of 8a. Hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (o): Ti1O1, 2.013(4);
Ti1O2, 1.793(4); O1S1, 1.542(4); Ti1N1, 2.236(5); O2TiO11,
63.66(18); C13S1C14, 102.9(3).
Figure 4 The ethylene polymerization character of 8a/MMAO. Condi-
tions: 3 μmol of catalyst 8a in 30 mL solvent; ethylene pressure, 0.1 MPa;
cocatalyst, MMAO 3.2 mL (1.9 mmol/mL in heptane).
Figure 3 Molecular structure of 8b. Hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (o): Ti1O1, 2.004(3);
Ti1O2, 1.813(3); O1S1, 1.542(3); Ti1N1, 2.244(3); O2TiO1,
163.36(12); C6S1C12, 102.56(19).
10000, probably due to rapid chain transfer during
polymerization process at high temperature [35]. As shown
in Table 1, the molecular weight distribution was narrow,
similar to that of a single-site catalyst. Under the same
polymerization conditions, the activity of 8b was halved
relative to 8a and the molecular weight of the resulting
polymer from 8b/MMAO was almost doubled. These re-
sults could be ascribed to steric effects.
The cocatalyst/catalyst molar ratio (Al/Ti ratio) had little
effect on the polymerization activity (Table 2). For example,
reducing the Al/Ti ratio to 1000, the activity was nearly
maintained (5.3 × 105 vs. 4.5 × 105 g/mol[Ti] h atm, entries
2 and 4). The activity was 4.1×105 g/mol[Ti] h atm when
the ratio was further reduced to 500 (entry 1).
suitable solvent for the polymerization. For example, an
activity of 8.0 × 105 g/mol[Ti] h atm was achieved at 80 ºC
(entry 10) and was still very active even when the tempera-
ture was increased to 120 ºC (2.2 × 105 g/mol[Ti] h atm,
entry 12) under 1 atm of ethylene pressure (in spite of the
reduced solubility of ethylene at 120 ºC). The polymer yield
was increased when the polymerization time was prolonged
to 1 h, which indicated good catalyst thermostability (Figure
4).
The molecular weight of the polymer reduced sharply
when temperature was increased. For example, Mw in tolu-
ene decreased from 20.2 × 104 g/mol at 30 ºC to 3.2 × 104
g/mol at 80 ºC. When the polymerization proceeded in de-
calin at above 100 ºC, the molecular weights were below
We also examined 8a in the ethylene/1-hexene copoly-
merization (Table 3) and good activities were observed in
all cases. The 1-hexene incorporation proved to be influ-
enced by its initial concentration. For example, the copoly-
merization produced copolymer in an activity of 3.2 × 105

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Wang Z, et al. Sci China Chem August (2014) Vol.57 No.8
g/mol[Ti] h atm with 16.6 mol% incorporation in the case of
1.5 mL of 1-hexene. However, when 10 mL of 1-hexene
was added, the activity of 1.6 × 105 g/mol[Ti] h atm and
38.8 mol% incorporation was achieved (entries 3 vs. 4).
8b/MMAO was also active in the ethylene/1-hexene co-
polymerization but with low incorporation compared to 8a
(entry 5).
Complex 8a also proved to be suitable for ethylene/
norbornene (NBE) copolymerization although NBE was a
steric comonomer (Table 4). As summarized in Table 4,
moderate activity and high NBE incorporation (25–32
mol%) could be obtained under the optimized conditions
(entries 1–4). The copolymerization behaviors of the cata-
lysts and the chain structures of the copolymers were af-
fected by both the initial concentration of NBE and reaction
time. Higher initial NBE concentration favored the incor-
poration (entries 3 and 4). The incorporation of NBE had
little influence when the reaction time was prolonged from
10 to 60 min.
4 Conclusions
In summary, titanium complexes bearing sulfoxide as side-
arm were synthesized and fully characterized. In the pres-
ence of MMAO, the complexes exhibited good activity in
the polymerization of ethylene and copolymerization of
ethylene/1-hexene, ethylene/NBE, which was different than
the corresponding titanium complexes 1a bearing an ether
side-arm. Future study will focus on exploring the here-
oatom effects.
This work was supported by the National Natural Sciences Foundation of
China (21174159, 21121062), the Science and Technology Commission of
Shanghai Municipality, and the Chinese Academy of Sciences.
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208
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Mw
11.3
Mw/Mn
1.8
4
5
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1.6
267
5.3
1.7
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MPa; reaction time, 10 min; temperature of the bath, 60 ºC. b)Cocatalyst,
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Table 3 Results of ethylene/1-hexene copolymerization using catalyst 8a a)
1-Hexene
(mL)
t b)
Incorp.
e,f)
f)
Entry
Activity d) Mw
Mw/Mn
(min) (mol%) c)
1
2
1.5
1.5
1.5
10
60
30
10
10
10
11.0
13.1
16.6
38.8
0.6
1.0
1.3
3.2
1.6
2.2
7.9
10.1
2.0
1.8
3.7
3.3
3.8
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16.3
9.0
4
5 g)
1.5
14.3
a) Conditions: 8a (3 µmol) in 30 mL toluene; ethylene pressure, 0.1
MPa; temperature of the bath, 50 ºC; cocatalyst, MMAO 3.2 mL (1.88
mmol/mL in heptane); b) Reaction time. c) Determined by 13C NMR spec-
troscopy, mol%. d) 105 g/mol[Ti] h atm. e) 104 g/mol. f) Determined by
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Table 4 Results of ethylene/NBE copolymerization using catalyst 8a a)
NBE
(mmol)
10
Incorp.
(mol%) c)
22.2
e, f)
f)
Entry
t (min) b)
Activity d) Mw
Mw/Mn
1
2
3
4
60
30
10
10
3.6
3.6
6.0
8.0
3.3
5.4
3.0
3.8
3.0
4.2
10
10
20
23.4
20.7
30.4
7.7
5.4
a) Conditions: 8a (12 µmol) in 30 mL toluene; ethylene pressure, 0.1
MPa; temperature of the bath, 50 ºC; cocatalyst, MMAO 6.4 mL (1.88
mmol/mL in heptane); b) Reaction time. c) Determined by 13C NMR spec-
troscopy, mol%. d) 104 g/mol[Ti] h atm. e) 104 g/mol. f) Determined by
GPC.

Wang Z, et al. Sci China Chem August (2014) Vol.57 No.8
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35 No C=C double bond in the (co)polymers are observed by 13C NMR
1
and H NMR studies. The polymer chain may transfer to aluminum
27 Gao ML, Sun XL, Gu YF, Yao XL, Li CF, Bai JY, Wang C, Ma Z,
species as the Mw decreased when increasing the amount of MMAO.
TANG Yong received his Ph.D. degree in 1996 at Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, under the supervision of Prof. Yaozeng Huang and Prof. Lixin Dai. After
three years’ postdoctoral research in the USA, he joined Shanghai Institute of Organic Chemistry,
CAS, in 1999. He was promoted to a full Professor in 2000. His current research interests are the
development of new synthetic methodologies and the design and synthesis of olefin polymerization
catalysts.