Synthesis and characterization of trichlorotitanium 2-(2- pyridinyliminomethyl)phenolates and their ethylene (co-)polymerization behavior

Article abstract of DOI:10.1016/j.polymer.2011.06.036

The series of trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates, [4,6-tBu₂C₆H₂O-2-CHNC₅R ^1-4N]TiCl₃ (R^1-4 = H (1); R^1,3,4 = H, R² = Me (2); R^1,2,4

Full text of DOI:10.1016/j.polymer.2011.06.036

Polymer 52 (2011) 3732e3737
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and characterization of trichlorotitanium 2-(2-pyridinyliminomethyl)
phenolates and their ethylene (co-)polymerization behavior
,
a
a
b
,
a,
Youhong Wang a, Wenjuan Zhang a , Wei Huang , Lin Wang , Carl Redshaw
, Wen-Hua Sun
*
**
*
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
The series of trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates, [4,6-tBu2C6H2O-2eCH]NC5R1e4N]
TiCl3 (R1e4 ¼ H (1); R1,3,4 ¼ H, R2 ¼ Me (2); R1,2,4 ¼ H, R3 ¼ Me (3); R2,4 ¼ H, R1,3 ¼ Me (4); R1,3 ¼ H, R2 ¼ CF3,
R4 ¼ Cl (5)), were synthesized and characterized by elemental analysis and 1H/13C NMR spectroscopy. The
molecular structures of the representative complexes 2 and 4 were confirmed by single-crystal X-ray
diffraction, andrevealed distorted octahedralgeometryattitanium. In thepresence ofMAO, alltitaniumpro-
catalysts showed good activities for ethylene polymerization with good thermal stability at the optimum
temperature of 50 ꢀC. In comparison with the ethylene polymerization results, the activity observed for the
co-polymerization of ethylene/1-hexene was far lower, but the polymers produced were of high molecular
weight. For the co-polymerization of ethylene/1-octene, enhanced catalytic activity was observed, with 1-
octene incorporation of up to 3.83 mol%.
Article history:
Received 7 April 2011
Received in revised form
14 June 2011
Accepted 19 June 2011
Available online 25 June 2011
Keywords:
Trichlorotitanium
2-(2-pyridinyliminomethyl)phenolates
Ethylene polymerization
Co-polymerization
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
shown high productivities in ethylene polymerization, but were
synthesized via multi-step syntheses [18]. Beyond the modification
Bis(phenoxyimino)titanium dichlorides (titanium FI catalysts)
[1e3] and bis(pyrrolide-imino)titanium dichlorides (titanium PI
catalysts) [4] are easily synthesized pro-catalysts with high activi-
of FI catalysts [19e21], the (side-chain phenoxylimino)titanium
trichlorides were also explored and screening studies indicated
enhanced stability and higher activity (see I [22] and II [23] Scheme
1). Recently, it was reported that increased pyridine content in
latex-supported FI catalyst systems resulted in higher activity [24].
With this in mind, a series of 2-(pyridin-2-ylimino)methylphenols
were synthesized in order to have one pyridine in the ligand
backbone, and subsequently the trichlorotitanium 2-(pyridin-2-
ylimino)methyl phenolates (see III, Scheme 1) were prepared.
The new titanium complexes possess a 4-membered metal-
locyclic ring, in contrast to the more commonly encountered 5 and
6-membered metallocyclic rings in such species [22,23]. The title
titanium complexes, when activated with methylaluminoxane
(MAO), showed good catalytic activities and thermal stability in
ethylene (co)polymerization. Herein, the synthesis and character-
ization of these trichlorotitanium 2-(pyridin-2-ylimino)methyl-
phenolates are reported, and their catalytic performance toward
ethylene has been investigated.
ties in a-olefin polymerization. The FI catalysts sometime perform
olefin polymerization in a living manner and are capable of
producing functional polymers [1,5,6]. The activity of such FI
catalysts decreases sharply at elevated temperature [7,8], mean-
while with limited co-polymerization behavior. As a consequence,
the PI catalysts are developed with better stability and good co-
polymerization behavior due to the more open space at the metal
in the active species [9]. Subsequently, various modifications to the
FI catalysts have been carried out in order to achieve better co-
polymerization behavior [10e12]. More attractively, a novel poly-
merization process has been developed by using dual catalytic
systems including one FI catalyst with the assistance of Zn-shuttle
reagents [13]. We have also explored the use of titanium complexes
[14,15] and half-titanocenes [16,17] as pro-catalysts for ethylene
(co-)polymerization. Their ease of synthesis and better catalytic
performance suggests that such systems have high potential in
both academic and industrial studies. Interestingly, hybridized
(salicylaldiminato)(pyrrolylaldiminato)titanium dichlorides have
2. Experimental
2.1. General procedure
* Corresponding authors. Tel.: þ86 10 62557955; fax: þ86 10 62618239.
** Corresponding author. Tel.: þ44 (0) 1603 593137; fax: þ44 (0) 1603 592003.
E-mail addresses: zhangwj@iccas.ac.cn (W. Zhang), carl.redshaw@uea.ac.uk (C.
Redshaw), whsun@iccas.ac.cn (W.-H. Sun).
All manipulations of air and/or moisture-sensitive compounds
were carried out under nitrogen atmosphere in a glove-box or
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.06.036

Y. Wang et al. / Polymer 52 (2011) 3732e3737
3733
But
R3
R1
R4
R4
N
R1
N
R2
Cl
X
R2
R3
N
O
But
Ti
O
Cl
N
O
Ti
N
Cl
tBu
Ti
Cl
R1
Cl
Cl
Cl
Cl
Cl
I
X= O, S, Se
II
III
current work
Scheme 1. Model pro-catalysts of tridentate trichlorotitanium complexes.
using standard Schlenk techniques. Methylaluminoxane (MAO,
1.46 M in toluene) was purchased from Albemarle. Potassium
hydride (KH) was washed with n-hexane before use to remove
contained mineral oil. Toluene, n-hexane and n-heptane were
refluxed in the presence of sodium and benzophenone, then freshly
distilled under nitrogen atmosphere before to use, respectively.
Dichloromethane, 1-hexene and 1-octene were dried over calcium
hydride. Elemental analysis was performed on a Flash EA 1112
microanalyzer. 1H and 13C NMR spectra were recorded on a Bruker
DMX 400 MHz instrument at ambient temperature using TMS as an
internal standard at 25 ꢀC 13C NMR spectra of the polymers were
recorded on a Bruker DMX-300 MHz instrument at 110 ꢀC in
deuterated 1,2-dichlorobenzene with TMS as an internal standard.
DSC trace and melting points of polyethylene were obtained from
the second scanning run on a PerkineElmer DSC-7 at a heating rate
of 10 ꢀC/min. Molecular weights and polydispersity indices (PDI) of
(co-)polyethylenes were determined using a PL-GPC 220 instru-
ment at 135 ꢀC in 1, 2, 4-trichlorobenzene with polystyrene as the
standard.
155.7, 149.2, 140.7, 139.0, 136.9, 132.0, 128.6, 128.0, 119.8, 118.3, 35.2,
34.2, 31.5, 29.5, 18.1. Anal. Calcd. For C21H28N2O: C, 77.74; H, 8.70; N,
8.63%. Found: C, 77.87; H, 8.64; N, 8.54%.
2.2.3. 4,6-Di-tert-butyl-2-(4-methylpyridin-2-ylimino)
methylphenol (L3)
Obtained as yellow crystals in 74.5% yield (2.42 g). Mp: 125 ꢀC, IR
(KBr, cmꢁ1): 3049 (w), 2960 (s), 2908 (m), 2868 (m), 1607 (CH]N)
(s), 1584 (s), 1549 (s), 1456 (s), 1362 (m), 1251 (m), 1206 (m), 1157
(m), 1028 (w), 947 (w), 886 (w), 716 (w). 1H NMR: (CDCl3, 400 MHz,
ppm):
d 13.95 (s, 1H, OH), 9.44 (s, 1H, CH]N), 8.35 (d, 1H,
J ¼ 4.48 Hz, Py-H), 7.47 (t, 1H, Py-H), 7.34 (s, 1H, AreH), 7.17 (s, 1H,
AreH), 7.01 (d, 1H, J ¼ 4.73 Hz, Py-H), 2.39 (s, 3H, CH3), 1.48 (s, 9H, t-
Bu-H),1.32 (s, 9H, t-Bu-H). 13C NMR: (CDCl3,100 MHz, ppm):
d165.6,
159.3, 157.9, 149.9, 148.7, 140.7, 137.0, 128.8, 128.1, 123.4, 121.1, 118.3,
35.2, 34.3, 31.5, 29.5, 21.1. Anal. Calcd. For C21H28N2O: C, 77.74; H,
8.70; N, 8.63%. Found: C, 77.62; H, 8.76; N, 8.60%.
2.2.4. 4,6-Di-tert-butyl-2-(4,6-dimethylpyridin-2-ylimino)
methylphenol (L4)
Obtained as yellow crystals in 59.2% yield (2.01 g). Mp: 122 ꢀC, IR
(KBr, cmꢁ1): 3005 (w), 2960 (s), 2869 (m), 1609 (CH]N) (s), 1589
(s), 1549 (s), 1456 (s), 1362 (m), 1251 (m), 1207 (m), 1174 (m), 1153
(m), 1028 (w), 985 (w), 716 (w). 1H NMR: (CDCl3, 400 MHz, ppm):
2.2. Synthesis of ligands L1eL5
Synthesis of 2-(2-pyridinyliminomethyl)phenols (L1eL5)
As for our previous method [25],10 mmol equivalent amounts of
3,5-di-tert-butyl-2-hydroxybenzaldehyde and the corresponding
arylamine were mixed in an open flask and placed in the micro-
wave for 2 min on the “M-High” setting (616W). The products were
extracted with ethanol and recrystallized as yellow microcrystals.
d
14.07 (s, 1H, OH), 9.42 (s, 1H, CH]N), 7.45 (s, 1H, Py-H), 7.34 (s, 1H,
Py-H), 6.96 (s, 1H, AreH), 6.89 (s, 1H, AreH), 2.53 (s, 3H, CH3), 2.34
(s, 3H, CH3), 1.47 (s, 9H, t-Bu-H), 1.33 (s, 9H, t-Bu-H). 13C NMR:
(CDCl3, 100 MHz, ppm):
d 165.2, 159.3, 157.7, 157.3, 149.7, 140.5,
136.9, 128.5, 128.0, 122.9, 118.3, 118.0, 35.2, 34.3, 31.6, 29.5, 24.3,
20.9. Anal. Calcd. For C22H30N2O: C, 78.06; H, 8.93; N, 8.28%. Found:
C, 78.11; H, 8.99; N, 8.20%.
2.2.1. 4,6-Di-tert-butyl-2-(pyridin-2-ylimino)methylphenol (L1)
Obtained as a yellow solid in 81.2% yield (2.52 g). Mp: 116 ꢀC, IR
(KBr, cmꢁ1): 3000 (OeH) (w), 2960 (s), 2906 (m), 2867 (m), 1610
(CH]N) (m),1579 (s),1461 (s),1432 (s),1360 (m),1198 (m),1169 (s),
881 (m), 791 (m), 769 (m), 736 (m). 1H NMR: (CDCl3, 400 MHz,
2.2.5. 4,6-Di-tert-butyl-2-(3-chloro-5-(trifluoromethyl)pyridin-2-
ylimino)methylphenol (L5)
Obtained as yellow crystals in 30.3% yield (1.25 g). Mp: 130 ꢀC, IR
(KBr, cmꢁ1): 3001 (w), 2961 (s), 2916 (m), 2363 (s), 2343 (m), 1625
(CH]N) (m), 1564 (s), 1455 (s), 1319 (s), 1275 (m), 1253 (m), 1163
(s), 1122 (s), 1089 (m), 978 (w), 738 (w). 1H NMR: (CDCl3, 400 MHz,
ppm):
d 13.90 (s, 1H, OH), 9.47 (s, 1H, CH]N), 8,50 (d, 1H,
J ¼ 3.60 Hz, Py-H), 7.76 (t, 1H, J ¼ 7.56 Hz, Py-H), 7.49 (s, 1H, AreH),
7.35 (d, 1H, J ¼ 6.24 Hz, Py-H), 7.26 (s, 1H, AreH), 7.19 (t, 1H,
J ¼ 5.68 Hz, Py-H), 1.50 (s, 9H, t-Bu-H), 1.34 (s, 9H, t-Bu-H). 13C NMR:
ppm):
(s, 1H, Py-H), 7.57 (s, 1H, AreH), 7.37 (s, 1H, AreH), 1.50 (s, 9H, t-Bu-
H), 1.34 (s, 9H, t-Bu-H). 13C NMR: (CDCl3, 100 MHz, ppm):
168.5,
d 13.68 (s,1H, OH), 9.51 (s,1H, CH]N), 8.64 (s,1H, Py-H), 8.05
(CDCl3, 100 MHz, ppm):
d 165.8, 159.2, 157.9, 149.0, 140.8, 138.5,
137.0, 128.9, 128.2, 122.3, 120.4, 118.2, 35.2, 34.3, 31.5, 29.5. Anal.
Calcd. For C20H26N2O：C, 77.38; H, 8.44; N, 9.02%. Found: C, 77.26;
H, 8.50; N, 9.09%.
d
160.3, 157.2, 143.9, 141.3, 137.7, 135.9, 130.8, 128.7, 127.4, 125.7, 124.3,
118.1, 35.3, 34.3, 31.5, 29.5. Anal. Calcd. For C21H24ClF3N2O: C, 61.09;
H, 5.86; N, 6.78%. Found: C, 61.15; H, 5.89; N, 6.73%.
2.2.2. 4,6-Di-tert-butyl-2-(5-methylpyridin-2-ylimino)
methylphenol (L2)
Obtained as yellow crystals in 73.8% yield (2.39 g). Mp: 146 ꢀC. IR
(KBr, cmꢁ1): 2997 (w), 2958 (s), 2906 (m), 2868 (m), 1612 (CH]N)
(m), 1570 (s), 1462 (s), 1386 (m), 1358 (m), 1251 (m), 1169 (s), 1022
(m), 881 (m), 828 (m), 769 (w), 680 (w). 1H NMR: (CDCl3, 400 MHz,
2.3. Synthesis of trichlorotitanium 2-(2-pyridinyliminomethyl)
phenolates 1e5
To a stirred solution of 2-(pyridin-2-ylimino)methyl-phenol (L1)
(0.324 g, 1.00 mmol) in dried THF (30 mL), KH (0.040 g, 1.00 mmol)
was added at ꢁ25 ꢀC. The mixture was stirred for an additional 3 h,
then TiCl4(THF)2 (0.334 g, 1.00 mmol) was added to the solution
at ꢁ78 ꢀC, and the resultant mixture was allowed to warm to room
ppm): d 13.93 (s,1H, OH), 9.42 (s, 1H, CH]N), 8.31 (s, 1H, Py-H), 7.56
(d, 1H, J ¼ 7.88 Hz, Py-H), 7.46 (s, 1H, AreH), 7.34 (s, 1H, AreH), 7.23
(d, 2H, J ¼ 8.64 Hz, Py-H), 2.37 (s, 3H, CH3), 1.48 (s, 9H, t-Bu-H), 1.32
(s, 9H, t-Bu-H). 13C NMR: (CDCl3, 100 MHz, ppm):
d 164.8, 159.1,

3734
Y. Wang et al. / Polymer 52 (2011) 3732e3737
temperature and stirred for an additional 24 h. The residue,
obtained by removing the solvent under vacuum, was extracted
with CH2Cl2 (3 ꢂ 20 mL) and the combined filtrates were concen-
trated in vacuum to 20 mL. The complex 1 was recrystallized from
its dichloromethane solution at ꢁ20 ꢀC as brown powder. Yield:
0.25 g (49%). 1H NMR (CDCl3, 400 MHz): 8.96 (s, 1H, CH]N), 8.93 (s,
1H, Py-H), 8.12 (s, 1H, Py-H), 7.85 (s, 1H, Py-H), 7.69 (d,1H, J ¼ 7.8 Hz,
Py-H), 7.53 (s, 1H, AreH), 7.24 (s, 1H, AreH), 1.58 (s, 9H, t-Bu-H), 1.37
2.5. X-ray structure determination
Crystals of 2 and 4 suitable for single-crystal X-ray diffraction
were obtained by laying n-heptane onto dichloromethane solutions
of 2 and 4, respectively. Single-crystal X-ray diffraction for 2 and 4
was performed on a Rigaku RAXIS Rapid IP diffractometer with
graphite-monochromated Mo K
a
radiation (
l
¼ 0.71073 Å) at
173(2) K. Cell parameters are obtained by global refinement of the
positions of all collected reflections. Intensities were corrected for
Lorentz and polarization effects and empirical absorption. The
structures are solved by direct methods and refined by full-matrix
least-squares on F2. All non-hydrogen atoms are refined aniso-
tropically. Structure solution and refinement are performed by
using the SHELXL-97 package [26]. Details of crystal data collection
and refinements are given in (Table 1).
(s, 9H, t-Bu-H) 13C NMR: (CDCl3, 100 MHz, ppm):
d 162.2, 157.8,
154.9, 147.9, 146,7, 141.8, 134.5, 130.4, 127.2, 124.5, 111.8, 35.9, 31.3,
30.1, 29.8. Anal. Calcd. For C20H25Cl3N2OTi: C, 51.81; H, 5.43; N,
6.04%. Found: C, 51.87; H, 5.41; N, 6.09%.
Using the same procedure as for 1,2 (0.25 g) was formed as a red
solid in 52.3% yield. 1H NMR: (CDCl3, 400 MHz, ppm):
d 8.85 (s, 1H,
CH]N), 8.81 (s, 1H, Py-H), 7.93 (d, 1H, J ¼ 6.42, Py-H), 7.82 (s, 1H,
AreH), 7.54 (d, 1H, J ¼ 7.31 Hz, Py-H), 7.18 (s, 1H, AreH), 2.54 (s, 3H,
CH3), 1.58 (s, 9H, t-Bu-H), 1.37 (s, 9H, t-Bu-H). 13C NMR: (CDCl3,
3. Results and discussion
100 MHz, ppm): d 145.3,145.2,143.8,141.5,137.8,132.6,132.2,129.6,
122.8, 122.1, 114.1, 111.1, 31.9, 31.3, 29.6, 22.8, 14.2. Anal. Calcd. For
C21H27Cl3N2OTi: C, 52.80; H, 5.70; N, 5.86%. Found: C, 52.84; H,
5.75; N, 5.80%.
3.1. Synthesis and characterization
The
2-(pyridin-2-ylimino)methylphenols
(L1eL5)
were
Using the same procedure as for 1, 3 (0.41 g) was prepared by
synthesized according to the literature method [25]. To the solution
of the corresponding 2-(pyridin-2-ylimino)methylphenol with one
equivalent of KH in THF, one equivalent of TiCl4(THF)2 was added to
form the titanium complexes 1e5 in good yields (Scheme 2). The
titanium complexes thereby obtained were characterized and
confirmed as the formulas [4,6-tBu2C6H2O-2eCH]NC5R1e4N]TiCl3
(R1e4 ¼ H (1); R1,3,4 ¼ H, R2 ¼ Me (2); R1,2,4 ¼ H, R3 ¼ Me (3);
R2,4 ¼ H, R1,3 ¼ Me (4); R1,3 ¼ H, R2 ¼ CF3, R4 ¼ Cl (5)) by 1H/13C NMR
spectroscopy and elemental analysis. In the case of using 2 or 3
equivalents of potassium salts of L2 on reaction with TiCl4(THF)2,
a mixture of LTiCl3 and L2TiCl2 was detected by 1H NMR spectros-
copy, however the two titanium complexes could not be separated
and pure L2TiCl2 could not be obtained.
using L3 instead of L1 and isolated as red crystals in 86.5% yield. 1H
NMR: (CDCl3, 400 MHz, ppm):
d 8.86 (s, 1H, CH]N), 8.81 (d, 1H,
J ¼ 5.08 Hz, Py-H), 7.85 (s, 1H, Py-H), 7.52 (s, 1H, AreH), 7.47 (s, 1H,
AreH), 7.38 (d, 1H, J ¼ 5.02 Hz, Py-H), 2.51 (s, 3H, CH3), 1.58 (s, 9H, t-
Bu-H),1.37 (s, 9H, t-Bu-H). 13C NMR: (CDCl3,100 MHz, ppm):
d162.8,
158.6, 157.7,154.4, 154.2, 147.8, 145.9, 137.9, 134.4, 126.9, 112.0,100.1,
35.9, 31.3, 30.1, 22.3, 14.2. Anal. Calcd. For C21H27Cl3N2OTi: C, 52.80;
H, 5.70; N, 5.86%. Found: C, 52.82; H, 5.75; N, 5.82%.
Using the same procedure as for 1, 4 (0.403 g) was formed as
a red solid in 82.2% yield. 1H NMR (CDCl3, 400 MHz, ppm):
d 8.82 (s,
1H, CH]N), 7.82 (s, 1H, Py-H), 7.50 (s, 1H, Py-H), 7.24 (s, 1H, AreH),
7.17 (s, 1H, Py-H), 2.99 (s, 3H, CH3), 2.55 (s, 3H, CH3), 1.59 (s, 9H, t-
Bu), 1.37 (s, 9H, t-Bu). 13C NMR: (CDCl3, 100 MHz, ppm):
d 161.9,
The absorptions associated with the AreOH (14.1e13.6 ppm) of
the 2-(2-pyridinylimino)methylphenols disappeared in the 1H
NMR spectra of the titanium complexes, confirming the formation
of the TieO bond. The peak for CH]N (9.5e9.4 ppm) in the ligands
L1eL4 was shifted to higher field (8.82e8.96 ppm) in the titanium
complexes 1e4, but that of L5 (9.51 ppm) moved to lower field in 5
(9.74 ppm), due to the substituents bearing halogens; these NMR
157.2, 156.2, 154.4, 154.3, 147.7, 134.0, 130.0, 127.1, 125.4, 109.1, 35.9,
34.9, 31.3, 30.0, 22.7, 22.0. Anal. Calcd. For C22H29Cl3N2OTi: C, 53.74;
H, 5.94; N, 5.70%. Found: C, 53.71; H, 5.97; N, 5.73%.
Using the same procedure as for 1, 5 (0.11g, 0.529 mmol) was
formed as a red solid in 52.9% yield. 1H NMR: (CDCl3, 400 MHz,
ppm):
(s, 1H, AreH), 7.58 (s, 1H, AreH), 1.58 (s, 9H, t-Bu-H), 1.39 (s, 9H, t-
Bu-H). 13C NMR: (CDCl3, 100 MHz, ppm):
162.4, 160.5, 155.8, 154.8,
d 9.74 (s,1H, CH]N), 9.18 (s,1H, Py-H), 8.31 (s,1H, Py-H), 7.93
d
R2
R2
148.5, 142.2, 140.4, 136.4, 132.1, 127.8, 127.3, 127.0, 123.7, 35.8, 34.9,
31.1, 29.9. Anal. Calcd. For C21H23Cl4F3N2OTi: C, 44.56; H, 4.10; N,
4.95%. Found: C, 44.59; H, 4.13; N, 4.98%.
R1
R3
R4
R1
R3
R4
N
N
Cl
KH
TiCl4(THF)2
2.4. Procedures for ethylene polymerization and co-polymerization
N
Ti Cl
Cl
N
toluene
THF
A stainless steel autoclave (250 mL) equipped with a mechanical
stirrer and a temperature controller was heated in vacuum at 80 ꢀC
and recharged with ethylene three times, then cooled to room
temperature under ethylene atmosphere. A toluene solution of the
titanium pro-catalyst (with co-monomer) was transferred into the
reactor. After the desired reaction temperature was reached and the
required amount of co-catalyst (with total 100 mL volume main-
tained through adding toluene) was added, the autoclave was
immediately pressurized to 10 atm. The ethylene pressure was kept
constant during the reaction through feeding ethylene. After the
required time, the ethylene feed was stopped, and the autoclave
was placed in a water-ice bath for 1 h. The resultant mixture was
poured into 10% HCleethanol solution, and the solid polymer was
collected and washed with water and ethanol several times and
dried under vacuum to constant weight.
OH
O
t-Bu
t-Bu
t-Bu
t-Bu
L1-L5
1-5
Ln Complex R1 R2 R3 R4
L1
L2
L3
L4
L5
1
2
3
4
5
H
H
H
H
Me
H
H
H
H
H
H
Cl
H
Me
Me H Me
CF3
H
H
Scheme 2. Synthesis of titanium complexes (1e5).

Y. Wang et al. / Polymer 52 (2011) 3732e3737
3735
spectral changes indicated the effective coordination of the Nimine
to the Ti center.
The structures of the representative complexes 2 and 4 were
further confirmed by single-crystal X-ray diffraction, and the
molecular structures are shown in Figs. 1 and 2, respectively. As
shown in Fig. 1, the titanium is coordinated by Npy, Nimine, O and
three chlorides to give a distorted octahedral geometry, for which
the titanium is coplanar with the coordinated atoms of O1, N1, N2
and Cl1; the other two chlorines (Cl2 and Cl3) are located in trans-
positions with an angle Cl3eTi1eCl2 of 164.36(4)ꢀ. The phenyl and
pyridyl rings are almost coplanar. Moreover, a 4-membered met-
allocyclic ring comprising of Ti1, N1, C8 and N2 (the additional Npy
)
is formed; a few titanium complexes containing such 4-membered
rings have been reported in the literature [27e30]. The TieCl bond
lengths are consistent with those previously reported [22,23].
According to Fig. 2, the distorted octahedral geometry around
the Ti center in 2 is repeated in complex 4, though slight differences
are observed within the bond lengths TieO, Ti-Nimine [1.804(2),
2.130(3) Å] in 4 and in 2 [1.791(2), 2.128(2) Å], and shorter bond
length of Ti-Npy [2.202(3) Å] in 4 than that of 2 [2.255(3) Å], which
was caused by the stronger electron donation due to methyl
substituents in 4.
Fig. 2. ORTEP drawing of 4 with thermal ellipsoids drawn at the 30% probability level.
Hydrogen atoms are omitted for clarity. Selected bond length (ꢀ) and selected bond
angles (Å): Ti1eO1 1.804(2), Ti1eN1 2.130(3), Ti1eN2 2.202(3), Ti1eCl2 2.2647(11),
Ti1eCl1 2.3234(12), Ti1eCl3 2.3342(12), O1eC1 1.347(3), N2eC12 1.346(4), N2eC8
1.347(4), N1eC7 1.287(4), N1eC8 1.402(4). O1eTi1eN1 81.68(10), O1eTi1eN2
141.85(10), N1eTi1eN2 60.18(10), O1eTi1eCl2 108.09(8), N1eTi1eCl2 170.23(8),
N2eTi1eCl2 110.05(8), O1eTi1eCl1 95.17(8), N1eTi1eCl1 86.78(8), N2eTi1eCl1
84.24(7), Cl2eTi1eCl1 92.56(4), O1eTi1eCl3 94.44(8), N1eTi1eCl3 86.11(8),
N2eTi1eCl3 82.89(7), Cl2eTi1eCl3 92.63(5), Cl1eTi1eCl3 167.09(4), O1eTi1eC8
112.38(10), N1eTi1eC8 30.70(9), N2eTi1eC8 29.50(9), Cl2eTi1eC8 139.54(7),
Cl1eTi1eC8 83.88(7), Cl3eTi1eC8 84.51(7), C1eO1eTi1 141.7(2).
3.2. Catalytic behavior in polymerization
3.2.1. Ethylene polymerization
Various alkylaluminium reagents as co-catalysts were investi-
gated with pro-catalyst 4. The trialkylaluminium reagents AlEt3 or
AlMe3 afforded little or no activity, however, methylaluminoxane
(MAO) and modified methylaluminoxane (MMAO) showed
considerable catalytic activity for ethylene polymerization under
10 atm ethylene with 1000:1 M ratio of Al/Ti at 20 ꢀC over 30 min,
and the system with MAO performed with an activity of
2.3 ꢂ 104 g molꢁ1(Ti)$hꢁ1, which is several times higher that that
found with MMAO 0.60 ꢂ 104 g molꢁ1(Ti)$hꢁ1. As a consequence,
MAO was chosen as the co-catalyst for further investigation. The
reaction parameters of Al/Ti molar ratio (runs 1e6, Table 2) and
temperature (runs 3, 7e10, Table 2) were varied, and the optimum
conditions were found as a Al/Ti molar ratio 5000:1 at 50 ꢀC.
Checking the properties of the polyethylenes obtained, it was not
difficult to conclude that melting points decreased along with
elevating either the reaction temperature or the molar ratio of Al/Ti.
These results are consistent with enhanced termination at high
temperature or higher ratio of Al/Ti, which resulted in more chain
transfer from titanium to aluminum for the termination [31]. The
values of the melting points were also consistent with the molec-
ular weights and distributions of the polyethylenes, and decreased
with either higher temperatures or with higher Al concentration.
The optimum condition for ethylene polymerization was with a Al/
Ti molar ratio of 5000:1 at 50 ꢀC under 10 atm ethylene, indicating
the active species requiring the association with alkylaluminium
was efficiently activated at the elevated temperature. In most cases,
high Al concentration increased the chain transfer from the Ti-
species, and resulted in lower molecular weights and broader
molecular weight distributions, which agree with recent restults by
trichlorotitanium and half-titanocene pro-catalysts [32,33]. Given
this, ethylene polymerization using 1e5/MAO systems were carried
out with the Al/Ti ratio of 5000:1 at 50 ꢀC under 10 atm ethylene,
and the results are tabulated in Table 2.
The catalytic performances by the titanium pro-catalysts varied
due to the different ligand environments present (runs 8, 11e14,
Table 2). The 5/MAO (R2 ¼ CF3, R4 ¼ Cl) system exhibited the
highest activity (run 14, Table 2), whilst the 2/MAO (R2 ¼ Me)
system showed a higher activity (run 12, Table 2) than did the other
three pro-catalysts for which R2 ¼ H. These results indicated the
positive influence on activity caused by the meta-substituents of
the pyridyl framework. The catalytic system 1 showed better
activity than the pro-catalysts 3 and 4 (runs 8, 11, and 13, Table 2),
indicating a negative response from the para-methyl groups on the
pyridyl framework. For 4 with R1 ¼ Me, a slightly better activity
than that for 3 was observed.
Fig. 1. ORTEP drawing of 2 with thermal ellipsoids drawn at the 30% probability level.
Hydrogen atoms are omitted for clarity. Selected bond length (ꢀ) and selected bond
angles (Å): Ti1eO1 1.791(2), Ti1eN1 2.128(2), Ti1eN2 2.255(3), Ti1eCl1 2.2803(10),
Ti1eCl3 2.2979(10), Ti1eCl2 2.3282(11), N1eC7 1.286(4), N1eC8 1.390(4), O1eC1
1.347(3), N2eC12 1.337(4), N2eC8 1.342(4), O1eTi1eN1 81.28(9), O1eTi1eN2
140.67(9), N1eTi1eN2 59.55(9), O1eTi1eCl1 102.23(7), N1eTi1eCl1 174.93(7),
N2eTi1eCl1 117.08(7), O1eTi1eCl3 96.21(8), N1eTi1eCl3 91.13(7), N2eTi1eCl3
82.22(8), Cl1eTi1eCl3 92.10(4), O1eTi1eCl2 98.77(8), N1eTi1eCl2 86.75(7),
N2eTi1eCl2 83.36(7), Cl1eTi1eCl2 89.09(4), Cl3eTi1eCl2 164.36(4), C8eN2eTi1
95.14(18).

3736
Y. Wang et al. / Polymer 52 (2011) 3732e3737
Table 1
Table 3
Crystal refinement of 2 and 4.
Co-polymerization of Ethylene with 1-Hexene by 1e5/MAO.a
Actb
Mw
Mw/Mn
c,d
c
e
Tm (ꢀC)
2
4
Run
Cat.
1eC6H12
Poly (g)
(mol/L)
CCDC No.
807956
807957
Empirical formula
Formula weight
Crystal color
Temperature (K)
Wavelength (Å)
Crystal system
space group
a (Å)
C21H27Cl3N2OTi
477.70
Brown
173(2)
0.71073
Monoclinic
P2(1)/n
10.178(2)
14.711(3)
15.268(3)
90.00
93.95(3)
90.00
2280.7(8)
4
1.391
0.741
992
0.17 ꢂ 0.16 ꢂ 0.10
1.34e27.49
ꢁ13 ꢃ h ꢃ 11
20069
5161
0.0518
C22H29Cl3N2OTi
491.72
red
173(2)
0.71073
Monoclinic
P2(1)/n
10.106(2)
15.088(3)
17.570(4)
90.00
94.77(3)
90.00
2669.7(9)
4
1
2
3
4
5
6
7
5
5
5
1
2
3
4
0.1
0.3
1.0
0.3
0.3
0.3
0.3
0.144
0.642
0.222
0.334
0.717
0.275
0.186
0.58
2.59
0.89
1.34
2.87
1.10
0.75
32.0
48.3
ef
6.4
9.0
e
129.6
124.8
118.9
127.6
128.1
125.6
125.8
36.7
22.5
27.0
53.8
10.8
9.1
9.3
6.7
a
Conditions: 5
mmol Ti, MAO, Al/Ti ¼ 5000, 10 atm, toluene (total volume
b (Å)
100 mL), 1-hexene (mol/L), 30 min. 50 ꢀC.
c (Å)
b
Activity: 105 g molꢁ1 hꢁ1
Determined by GPC.
.
á (ꢀ)
c
d
e
f
b
ã (ꢀ)
(ꢀ)
104 g molꢁ1
.
Determined by DSC.
Polymer partly unsolvable.
Volume (Å3)
Z
Dcalc (Mg mꢁ3
)
1.223
0.635
1024
(mmꢁ1
)
The best performance was achieved with 0.3 mol/L 1-hexene, and
thus such conditions were employed in the further investigations of
the other pro-catalysts. Compared with the activity data for
ethylene polymerization, although lower, the activities for the co-
polymerization of ethylene and 1-hexene showed the same
trends due to the environmental influences exerted by the ligands,
thus the activities decreased in the order: 5 (CF3, Cl) > 2 (4-Me) > 1
(H) > 3 (3-Me) > 4 (2,4ediMe) (runs 2, 4e7, Table 3).
m
F (000)
Crystal size (mm)
range (ꢀ)
0.240 ꢂ 0.226 ꢂ 0.208
1.78e27.47
ꢁ13 ꢃ h ꢃ 12
23629
6029
0.0542
q
Limiting indices
No. of rflns collected
No. of unique rflns
Rint
Completeness to
q
(%)
98.8%
1.162
98.6%
1.174
Goodness-of-fit on F2
All the co-polymers obtained had higher molecular weights
(27.0e53.8 ꢂ 104 g molꢁ1) with broader distributions, which was
probably caused by the presence of several active species generated
during the catalytic process. On checking structural information in
the literature, it appears that four-membered metallocycles of
titanium with pyridyl and imino groups are not configurationally
stable in solution, and can thus generate different active sites
[35,36]. The polyethylenes obtained in the ethylene polymerization
were also found to possess broader molecular weight distributions.
Another plausible reason is the instability associated with the
imino (C]N) group [1,37e41]. The lower Tm values of co-polymers
(124e127 ꢀC) compared with those of the polyethylene
(131e133 ꢀC) suggested that some branched polymers resulted.
The co-polymerization of ethylene with 1-octene by the 1e5/
MAO systems was also conducted, and the results are collected in
Table 4. Interestingly, higher activities were achieved in the co-
polymerization of ethylene with 1-octene, suggesting here a posi-
tive “co-monomer effect”, which was significantly different to the
co-polymerization of ethylene with 1-hexene (Table 3). The envi-
ronmental influences of the ligands were similar to the above
copolymerzation of ethylene with 1-hexene.
Final R indices
[I > 2s (I)]
R indices (all data)
R1 ¼ 0.0608,
wR2 ¼ 0.1362
R1 ¼ 0.0668,
wR2 ¼ 0.1400
0.704, ꢁ0.341
R1 ¼ 0.0650,
wR2 ¼ 0.1654
R1 ¼ 0.0770,
wR2 ¼ 0.1759
0.565,ꢁ0.459
Largest diff peak,
hole (e Åꢁ3
)
3.2.2. Co-polymerization of ethylene with a-olefin
The trichlorotitanium complexes provide more space for the co-
monomer to coordinate. As the highest activity in ethylene poly-
merization was observed using pro-catalyst 5, this system was
employed in selecting the monomer concentration by using the
same optimum reaction conditions as for the ethylene polymeri-
zation runs. Surprisingly, lower activities were observed by the title
titanium pro-catalysts for the co-polymerization of ethylene with
1-hexene, and the results are collected in Table 3. The Tm values for
the resultant polymers (runs 1e3, Table 3) decreased along with
higher 1-hexene concentration. A 3.28% molar incorporation of 1-
hexene was achieved in the system with 1.0 mol/L 1-hexene [34].
Table 2
Resultant co-polymers had lower molecular weights
(16.8e28.5 ꢂ 104 g molꢁ1) and broader distributions than the co-
polymers obtained by the co-polymerization of ethylene with 1-
hexene. 13C NMR spectra of the poly(ethylene-co-1-octene)
(shown in Fig. 3) revealed a 3.83% molar incorporation of 1-octene.
Ethylene polymerization results by 1e5/MAO.a
Actb
Mw
Mw/Mn
Tm (ꢀC)
c,d
c
e
Run
Cat.
Al/Ti
T/(ꢀC)
PE (g)
1
2
3
4
5
6
7
8
4
4
4
4
4
4
4
4
4
4
1
2
3
5
3000
4000
5000
6000
7000
8000
5000
5000
5000
5000
5000
5000
5000
5000
20
20
20
20
20
20
40
50
70
80
50
50
50
50
0.122
0.293
0.355
0.263
0.172
0.128
0.376
0.513
0.490
0.469
0.630
0.795
0.498
1.328
4.86
91.4
80.5
73.9
40.2
28.3
25.1
77.3
46.0
32.4
20.3
18.7
37.7
62.1
11.9
4.1
4.1
3.4
4.5
9.5
13.3
5.4
5.6
6.8
8.1
8.1
6.1
7.0
3.3
134.3
133.8
132.7
131.1
130.8
128.2
132.8
132.5
132.1
131.8
131.8
132.6
133.0
133.1
11.7
14.2
10.5
6.89
5.10
15.1
20.5
19.6
18.8
25.2
31.8
19.9
53.1
Table 4
Co-polymerization of Ethylene with 1-octene by 1e5/MAO.a
c,d
c
e
Tm (ꢀC)
Run
Cat
Poly(g)
Actb
Mw
Mw/Mn
9
1
2
3
4
5
1
2
3
4
5
0.699
0.600
0.583
0.564
1.78
2.79
2.39
2.33
2.26
7.12
26.1
23.6
16.8
28.5
24.7
19.2
19.5
16.6
25.1
14.6
124.8
125.1
124.7
126.1
123.8
10
11
12
13
14
a
Conditions: 5
m
mol of cat, MAO, Al/Ti ¼ 5000, 10 atm, toluene, total volume
a
Condition: 5
m
mol Ti, 10 atm ethylene, toluene (total volume 100 mL), 30 min.
100 mL, 0.3 mol/L 1-octene, 30 min. 50 ꢀC.
b
c
b
Activity: 104 g molꢁ1(Ti) hꢁ1
Determined by GPC.
.
Activity:105 g molꢁ1 hꢁ1
Determined by GPC.
104 g molꢁ1
.
c
d
e
d
e
104 g molꢁ1
.
Determined by DSC.
Determined by DSC.

Y. Wang et al. / Polymer 52 (2011) 3732e3737
[3] Matsugi T, Fujita T. Chem Soc Rev 2008;37(6):1264e77.
3737
[4] Yoshida Y, Matsui S, Takagi Y, Mitani M, Nakano T, Tanaka H, et al. Organo-
metallics 2001;20(23):4793e9.
[5] Saito J, Mitani M, Mohri J, Yoshida Y, Mastui S, Ishii S, et al. Angew Chem Int Ed
2001;40(15):2918e20.
[6] Furuyama R, Mitani M, Mohri IJ, Mori R, Tanaka H, Fujita T. Macromolecules
2005;38(5):1546e52.
[7] Matsui S, Fujita T. Catal Today 2001;66(1):63e73.
[8] Matsukawa N, Matsui S, Mitani M, Saito J, Tsuru K, Kashiwa N, et al. Mol Catal
A Chem 2001;169(1e2):99e104.
[9] Yoshida Y, Matsui S, Fujita T. J Organomet Chem 2005;690(20):4382e97.
[10] Sobota P, Przybylak K, Utko J, Jerzykiewicz LB, Pombeiro AJL, Guedes da
Silva MFC, et al. Chem Eur J 2001;7(5):951e8.
[11] Motta O, Capacchione C, Proto A, Acierno D. Polymer 2002;43(22):5847e54.
[12] Long RJ, Gibson VC, White AJP. Organometallics 2008;27(2):235e45.
[13] Arriola DJ, Carnahan EM, Hustad PD, Kuhlman RL, Wenzel TT. Science 2006;
312(5774):714e9.
[14] Zuo W, Sun WH, Zhang S, Hao P, Shiga A. J Polym Sci Part A Polym Chem 2007;
45(5):3415e30.
[15] Liu S, Zuo W, Zhang S, Hao P, Wang D, Sun WeH. J Polym Sci A Polym Chem
2008;46(10):3411e23.
[16] Liu S, Sun WH, Zeng Y, Wang D, Zhang W, Li Y. Organometallics 2010;29(11):
2459e64.
[17] Sun WH, Liu S, Zhang W, Zeng Y, Wang D, Liang T. Organometallics 2010;
29(4):732e41.
Fig. 3. 13C NMR spectrum of the co-polymer of ethylene with 1-octene by 5/MAO (run
5, Table 4).
[18] Pennington DA, Coles SJ, Hursthouse MB, Bochmann M, Lancaster SJ. Chem
Commun 2005;25:3150e2.
[19] Clarkson GJ, Gibson VC, Goh PKY, Hammond ML, Knight PD, Scott P, et al.
Dalton Trans 2006;46:5484e91.
[20] Gendler S, Zelikoff AL, Kopilov J, Goldberg I, Kol M. J Am Chem Soc 2008;
130(7):2144e5.
4. Conclusion
[21] Oakes DCH, Kimberley BS, Gibson VC, White AJP, Williams DJ. Chem Commun
2004;19:2174e5.
[22] Wang C, Ma Z, Sun XL, Gao Y, Guo YH, Tang Y, et al. Organometallics 2006;
25(13):3259e66.
[23] Paolucci G, Zanella A, Sperni L, Bertolasi V, Mazzeo M, Pellecchia C. J Mol Catal
A 2006;258(1e2):275e83.
[24] Naundorf C, Saito J, Fujita T, Klapper M, Müllen KJ. Poly Sci Part A Polym Chem
2006;44(9):3103e13.
The trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates
1e5 were found to possess distorted octahedral geometry at Ti, and
included a 4-membered titanocyclic ring involving the imino and
pyridyl groups. In the presence of MAO, such titanium pro-catalysts
performed with high activities in ethylene (co) polymerization with
an optimum reaction temperature of 50 ꢀC. Good incorporation of
[25] Yang H, Sun WH, Li Z, Wang L. Synth Commun 2002;32(15):2395e402.
[26] Sheldrick GM. SHELXTL-97, Program for the refinement of crystal structures.
Göttingen, Germany: University of Göttingen; 1997.
[27] Volkis V, Nelkenbaum E, Lisovskii A, Hasson G, Semiat R, Kapon M, et al. J Am
Chem Soc 2003;125(8):2179e94.
[28] Talja M, Klinga M, Polamo M, Aitola E, Leskelä M. Inorg Chem Acta 2005;
358(4):1061e7.
[29] Fuhrmann H, Brenner S, Arndt P, Kempe R. Inorg Chem 1996;35(23):6742e5.
[30] Aragón PJ, Carrillo-Hermosilla F, Otero A, Antiñolo A, Rodríguez AM. Eur J
Inorg Chem 2006;5:965e71.
a
-olefins in co-polymerizations was achieved with more than
3 mol% for both 1-hexene and 1-octene; a negative “co-monomer
effect” was observed for 1-hexene, but a positive effect was seen for
1-octene. Regarding the environmental influence of ligands, pro-
catalysts with meta-substituents at the pyridyl group generally
showed higher activity, but negative influences were commonly
encountered by pro-catalysts bearing para-substituents at the
pyridyl group.
[31] Gibson VC, Redshaw C, Solan GA. Chem Rev 2007;107(5):1745e76.
[32] Huang W, Zhang W, Liu S, Liang T, Sun W-H. J Polym Sci A Polym Chem 2011;
49(8):1887e94.
Acknowledgments
[33] Huang W, Sun W.-H, Redshaw C. Dalton Trans doi 10.1039/CIDT0068H.
[34] Seger MR, Maciel GE. Anal Chem 2004;76(19):5734e47.
[35] Morton C, O’Shaughnessy P, Scott P. Chem Commun 2000;21:2099e100.
[36] Kempe R. Arndt P Inorg Chem 1996;35(9):2644e9.
[37] Tohi Y, Makio H, Matsui S, Onda M, Fujita T. Macromolecules 2003;36(3):
523e5.
This work was supported by National Natural Science Founda-
tion of China (No. 20904059 and 20874105). The EPSRC are thanked
for the award of a travel grant (to CR).
[38] Liu D, Wang S, Wang H, Chen W. J Mol Cata A 2006;246(1e2):53e8.
[39] Scott MJ, Lippard SJ. Organometallics 1997;16(26):5857e68.
[40] Makio H, Fujita T. Macromol Symp 2004;213:221e33.
[41] Knight PD, O’Shaughnessy PN, Munsolw IJ, Kimberley BS, Scott P. J Organomet
Chem 2003;683(1):103e13.
References
[1] Tian J, Hustad PD, Coates GW. J Am Chem Soc 2001;123(21):5134e5.
[2] Makio H, Fujita T. Acc Chem Res 2009;42(10):1532e44.