Syntheses, characterization, and ethylene (Co-)polymerization screening of amidate half-titanocene dichlorides

Article abstract of DOI:10.1021/om1000748

A series of amidate half-titanocene dichlorides, Cp′TiLCl₂ [Cp′ = Cp (as ⁵-C₅H₅) or Cp* (as ⁵-C₅Me₅), L = N-(2-methylquinolin-8-yl)-p-R- benzamides; C1: Cp′ = Cp, R = OMe; C2: Cp′ = Cp, R = Me; C3: Cp′ = Cp, R = H; C4: Cp′ = Cp, R = F; C5: Cp′ = Cp, R = Cl; C6: Cp′ = Cp*, R = OMe; C7: Cp′ = Cp*, R = Me], have been synthesized by the stoichiometric reaction of Cp′TiCl₃ with the corresponding potassium amidates. All complexes are fully characterized by elemental and NMR analyses. The molecular structures of complexes C2 and C4 are confirmed by single-crystal X-ray diffraction, and the amidate moieties coordinate the titanium center by imino and alkoxide groups. The systems C1-C7/MAO show much higher activities toward ethylene polymerization than CpTiCl₃/MAO or Cp*TiCl₃/MAO systems. The procatalysts (C6 and C7) bearing a Cp* ligand exhibit higher activities than their analogues (C1-C5) containing a Cp ligand, while the amidate ligands containing electron-donating groups positively affect the catalytic behavior. Both increasing the ratio of MAO to titanium and reducing reaction temperature enhance the productivities; however, the molecular weights of the resultant polymers decrease with higher activities. Moreover, the C6/MAO system performs with high activity in the copolymerization of ethylene and 1-hexene or 1-octene.

Full text of DOI:10.1021/om1000748

Organometallics 2010, 29, 2459–2464 2459
DOI: 10.1021/om1000748
Syntheses, Characterization, and Ethylene (Co-)Polymerization
Screening of Amidate Half-Titanocene Dichlorides
Shaofeng Liu,† Wen-Hua Sun,*,†,‡ Yanning Zeng,† Deligeer Wang,†,§
Wenjuan Zhang,† and Yan Li†
†Key Laboratory of Engineering Plastics and Beijing Natural Laboratory for Molecular Science,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China,
‡State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
§
Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China, and Department of Chemistry,
Inner Mongolia Normal University, Hohhot 010022, People’s Republic of China
Received January 28, 2010
A series of amidate half-titanocene dichlorides, Cp0TiLCl2 [Cp0 = Cp (as η5-C5H5) or Cp* (as
η5-C5Me5), L=N-(2-methylquinolin-8-yl)-p-R-benzamides; C1: Cp0 =Cp, R=OMe; C2: Cp0 =Cp,
R=Me; C3: Cp0 =Cp, R=H; C4: Cp0 =Cp, R=F; C5: Cp0 =Cp, R=Cl; C6: Cp0 =Cp*, R=OMe;
C7: Cp0 = Cp*, R = Me], have been synthesized by the stoichiometric reaction of Cp0TiCl3 with the
corresponding potassium amidates. All complexes are fully characterized by elemental and NMR
analyses. The molecular structures of complexes C2 and C4 are confirmed by single-crystal X-ray
diffraction, and the amidate moieties coordinate the titanium center by imino and alkoxide groups. The
systems C1-C7/MAO show much higher activities toward ethylene polymerization than CpTiCl3/MAO
or Cp*TiCl3/MAO systems. The procatalysts (C6 and C7) bearing a Cp* ligand exhibit higher activities
than their analogues (C1-C5) containing a Cp ligand, while the amidate ligands containing electron-
donating groups positively affect the catalytic behavior. Both increasing the ratio of MAO to titanium
and reducing reaction temperature enhance the productivities; however, the molecular weights of the
resultant polymers decrease with higher activities. Moreover, the C6/MAO system performs with high
activity in the copolymerization of ethylene and 1-hexene or 1-octene.
1. Introduction
such as controlled molecular weight, specific tacticity, and
narrow molecular weight distribution, as well as better
comonomer incorporation.4 Since the 1990s, inspired by fast
developments in coordination and organometallic chemis-
try, more and more transition metal procatalysts have been
designed and investigated for olefin polymerization.5 Exam-
ples of chelating ligands are amidinate,6 amide,7 and alkoxy,8
Polyolefins, the most popularly used synthetic polymer,
have been synthesized by employing commercial catalysts of
Ziegler-Natta,1 Phillip,2 and metallocene type.3 The con-
strained-geometry compounds (CGC) of half-metallocene
catalysts represent single-site catalysts that are particularly
considered due to the properties of the resultant polyolefins
(6) (a) Flores, J. C.; Chien, J. C. W.; Rausch, M. D. Organometallics
1995, 14, 2106. (b) Herskovicskorine, D.; Eisen, M. S. J. Organomet. Chem.
1995, 503, 307. (c) Volkis, V.; Shmulinson, M.; Averbuj, C.; Lisovskii, A.;
Edelmann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155.
*Corresponding author. Tel: þ86-10-62557955. Fax: þ86-10-62618239.
E-mail: whsun@iccas.ac.cn.
(1) (a) Ziegler, K.; Gellert, H. G.; Zosel, K.; Lehmkuhl, W.; Pfohl, W.
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r
2010 American Chemical Society
Published on Web 04/21/2010
pubs.acs.org/Organometallics

2460 Organometallics, Vol. 29, No. 11, 2010
Liu et al.
from which two significant procatalysts named as FI9 and
PI10 catalysts have drawn much attention due to their high
activities and their unique abilities to control polymer micro-
structures. The catalytic behavior of these procatalysts and
also the properties of the resultant polyolefin could be fine-
tuned by modifying the substituents of the complexes’
ligands.11 Attempts to combine the merits of the individual
systems have led to the successful development of a series
of nonbridged half-metallocene procatalysts, Cp0M(L)Xn
(M=Ti, Zr, Hf; L=anionic ligand; X=halogen or alkyl),12
which exhibited promising catalytic behavior and overcame
the synthetic problems associated with metallocene3 and/or
CGC procatalysts.4 Therefore, the half-titanocene Cp0M-
(L)Xn procatalysts containing a dianionic13 or monoanionic14
amidate ligands have been investigated in our group.
In view of the ease of synthesis and ligand variation, the
title amidate metal complexes15 have been synthesized
and characterized. Unexpectedly, N-(2-methylquinolin-8-yl)-
p-R-benzamidates act in the imine/alkoxide coordination of
the μ2-OCN mode of the amidate moiety; however, the
quinolinyl group does not coordinate to the titanium atom.
All title procatalysts (C1-C7) show high activities toward
ethylene polymerization, and the representative procatalyst
(C6) exhibits a high activity in the copolymerization of
ethylene with 1-hexene or 1-octene. Herein the syntheses and
characterizations of the title complexes are reported in detail
along with their catalytic behavior in olefin polymerization.
Figure 1. ORTEP view of the molecular structure of C2 (ellip-
soids enclose 50% electronic density; H atoms are omitted for
clarity). Selected bond lengths (A) and angles (deg): Ti1-O1=
2.0697(2), Ti1-C11=2.512(3), Ti1-N2=2.117(2), Ti1-C18=
2.332(3), Ti1-C19=2.341(3), Ti1-C20=2.348(3), Ti1-C21=
2.352(3), Ti1-C22=2.341(3), Ti1-Cl1=2.2944(1), Ti1-Cl2=
2.2906(9), C11-N2=1.309(3), C11-O1=1.296(3); N2-Ti1-
Cl1 = 86.16(7), N2-Ti1-Cl2 = 129.76(7), N2-Ti1-O1 =
62.26(8),Cl1-Ti1-O1=136.97(6), Cl2-Ti1-O1=86.63(6), Cl1-
Ti1-Cl2=93.42(4), N2-C11-O1=112.4(2).
˚
2. Results and Discussions
2.1. Synthesis and Characterization of Half-Titanocene Com-
plexes. All N-(2-methylquinolin-8-yl)benzamide derivatives
are prepared according to previously reported methods.13b,16
These compounds could be deprotonated with potassium
hydride in tetrahydrofuran (THF) at room temperature, and
the resultant potassium compounds react further with one
equivalent of Cp0TiCl3 (Cp0 =Cp or Cp*) in THF to afford
red solutions. Brown crystals of analytically pure amidate half-
titanocene complexes, Cp0TiLCl2 (C1-C7: Cp0 =Cp or Cp*;
L = N-(2-methylquinolin-8-yl)-p-R-benzamides) (Scheme 1),
are isolated in good yields (77.2-89.0%), and their molecular
structures are consistent with the 1H and 13C NMR spectra (see
Experimental Section). Regarding the proton resonances of
Scheme 1. Synthesis of Complexes C1-C7
of an electron-density decrease in the aromatic rings upon
coordination with titanium.
1
their H NMR spectra, the protons of the amidate ligand
Crystals of compounds C2 and C4 suitable for single-crystal
X-ray analysis were grown by slow diffusion of heptane into
toluene solutions of compounds C2 and C4. The molecular
structure of compound C2 is illustrated in Figure 1, with
selected bond lengths and angles, and the structure of its
analogue C4 is shown in the Supporting Information.
appear between 10.5 and 10.9 ppm, but disappear in the title
complexes due to the formation of Ti-N bonds. In all com-
plexes, the protons’ resonances are shifted to high-field because
(10) (a) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nakano, T.;
Tanaka, H.; Kashiwa, N.; Fujita, T. Organometallics 2001, 20, 4793.
(b) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nakano, T.; Tanaka, H.;
Kashiwa, N.; Fujita, T. Organometallics 2001, 20, 4793.
(11) Matsugi, T.; Fujita, T. Chem. Soc. Rev. 2008, 37, 1264.
(12) Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. J. Mol.
Catal. A: Chem. 2007, 267, 1.
(13) (a) Zuo, W.; Zhang, S.; Liu, S.; Liu, X.; Sun, W.-H. J. Polym.
Sci., Part A: Polym. Chem. 2008, 46, 3396. (b) Liu, S.; Yi, J.; Zuo, W.;
Wang, K.; Wang, D.; Sun, W.-H. J. Polym. Sci., Part A: Polym. Chem.
2009, 47, 3154. (c) Sun, W.-H.; Liu, S.; Zhang, W.; Zeng, Y.; Wang, D.;
Liang, T. Organometallics 2010, 29, 732.
Considering the centroid of Cp as a single coordination
site, the molecular structure of complex C2 (Figure 1) con-
sists of a distorted square-pyramid configuration, in which
the Cp group lies in the apical site and the amidate moiety
acts as a bidentate ligand together with the two chlorides in
the bottom plane. The sum of the metallocyclic bond angles
is 359.6°, indicating the coplanarity of titanium with all
atoms of the bidentate amidate group in a η2 fashion. The
bonding motif of the amidate ligand is a nonsymmetric one
bonded via the imine/alkoxide mode, which is in contrast to
the coordination manner of amidate found in tridentate tit-
(14) Zuo, W.; Zhang, M.; Sun, W.-H. J. Polym. Sci., Part A: Polym.
Chem. 2009, 47, 357.
(15) (a) Li, C.; Thomson, R. K.; Gillon, B.; Patrick, B. O.; Schafer,
L. L. Chem. Commun. 2003, 2462. (b) Zhang, Z.; Schafer, L. L. Org. Lett.
2003, 5, 4733. (c) Thomson, R. K.; Zahariev, F. E.; Zhang, Z.; Patrick, B. O.;
Wang, Y.; Schafer, L. L. Inorg. Chem. 2005, 44, 8680. (d) Zhang, Z.; Leitch,
D. C.; Lu, M.; Patrick, B. O.; Schafer, L. L. Chem.;Eur. J. 2007, 13, 2012.
(16) Wang, K.; Shen, M.; Sun, W.-H. Dalton Trans. 2009, 4085.
anium complexes.13,17 The C-O bond (C11-O1 1.296(3) A),
˚
(17) Liu, S.; Zuo, W.; Zhang, S.; Hao, P.; Wang, D.; Sun, W.-H.
J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3411.

Article
Organometallics, Vol. 29, No. 11, 2010 2461
Table 1. Ethylene Polymerization with C6/MAOa
c
activity
(kg mol-1(Ti) h-1
Mw
(kg mol-1
c
entry
Al/Ti
t (min)
T (°C)
PE (g)
)
Tmb (°C)
)
Mw/Mn
3
3
3
1
2
3
4
5
6
7
8
9
500
1000
1500
2000
1500
1500
1500
1500
1500
10
10
10
10
10
10
10
5
30
30
30
30
40
50
60
30
30
0.713
1.33
1.81
1.53
1.55
1.44
0.754
1.17
2.63
856
1600
2170
1840
1860
1730
905
128.1
127.7
125.3
126.8
125.6
125.3
125.0
125.2
125.8
54.7
42.2
30.5
25.3
5.81
5.55
4.80
22.3
40.8
17
15
13
12
1.7
1.8
1.6
7.1
17
2810
1050
30
a Conditions: 5 μmol of Ti; 10 atm of ethylene; toluene (total volume 100 mL). b Determined by DSC. c Determined by GPC.
somewhat shorter than a normal one, together with the C-N
˚
bond (C11-N2 1.309(3) A), suggests a delocalized bonding
motif within the amidate backbone where the negative
charge is mostly localized on the nitrogen atom. The Ti-N
˚
bond (Ti1-N2 2.117(2) A) and Ti-O bond (Ti1-O1
2.0697(2) A) are similar to previous amidate-based titanium
˚
complexes.15a,c,d The Cp ring is planar (maximum deviation
˚
from the plane of 0.003 A for C20) with a typical Ti-Cpcent
distance of 2.017 A. The dihedral angle of the planes defined
˚
by the Cp ring and the chelating ring is 23.7°, while the
dihedral angles between the chelating ring and the phenyl
group or quinoline ring are 35.9° or 61.1°, respectively. Two
chlorine atoms are located cis to each other, while the Ti-Cl
˚
bonds are almost identical (Ti1-Cl1 2.2944(1) A and
˚
Ti1-Cl2 2.2906(9) A) with an angle of 93.4°. The molecular
structures of complexes C2 and C4 (see Supporting Infor-
mation) are quite similar without distinct differences in
structural features.
Figure 2. GPC profiles of PEs obtained from entries 3 and 5-7
in Table 1.
2.2. Catalytic Behavior toward Ethylene Polymerization.
Influences of Al/Ti Molar Ratio, Reaction Temperature, and
Time on the Catalytic Behavior of C6. The reaction condi-
tions in ethylene polymerization have been optimized for
procatalyst C6. Good catalytic performances are observed in
the presence of MAO or MMAO as the cocatalyst, of which
MAO gives better results than MMAO. For example, for the
molar ratio of Al/Ti = 1500:1 under 10 atm of ethylene
pressure, the catalytic activity is 1560 kg mol-1(Ti) h-1 using
MMAO, while the system with MAO gives an activity of
2170 kg mol-1(Ti) h-1 (entry 3, Table 1). Therefore detailed
investigations have been carried out employing MAO through
varying the ratios of Al/Ti, reaction temperature, and time,
and the results are tabulated in Table 1.
According to observations at different Al/Ti ratios ran-
ging from 500 to 2000 (entries 1-4, Table 1), the maximum
activity is shown at an Al/Ti molar ratio of 1500 (entry 3,
Table 1). Such a phenomenon can be well clarified by the
influence of the Al concentration on the termination of
polymer chains.5f,18 In addition, the obtained polyethylene
exhibits lower Mw values when the ratio of Al:Ti is increa-
sed, because the chain transfer increases with high Al
concentration.18,19
Table 2. Ethylene Polymerization with C1-C7/MAOa
b
c
PE
activity
Tm
Mw
Mwc/
Mn
entry procat.
(g) (kg mol-1(Ti) h-1
)
(°C) (kg mol-1
)
3
3
3
1
2
3
4
5
6
7
8
C1
C2
C3
C4
C5
C6
C7
1.28
1.11
0.966
0.815
0.840
1.81
1540
1330
1160
978
1080
2170
2060
282
127.7
129.3
130.8
131.8
132.1
125.3
126.7
129.0
231
188
336
437
180
30.5
20.1
99.2
4.3
5.5
8.6
4.1
5.6
13
1.72
5.8
3.0
CpTiCl3 0.235
a Conditions: 5 μmol of Ti; 10 atm of ethylene; Al/Ti = 1500; 30 °C;
10 min; total volume, 100 mL. b Determined by DSC. c Determined by
GPC.
ligands is helpful in the thermal stability of half-titanocene
complexes and their active species. This observation that the
activity decreases at high temperature was also found in the
catalytic system of Cp2TiCl2 due to the bimolecular dispro-
portionation termination.20 In terms of the molecular weights
of the resultant polyethylenes (PEs), remarkable differences
have been found between reactions at 30 °C and those above
40 °C. At 30 °C, the C6/MAO system affords PEs with a
bimodal molecular weight distribution, while PEs with a mono-
modal distribution are obtained at 40 °C or above (Figure 2).
The influence of reaction temperatures or activators on the
molecular weight distribution is also observed in R-diimine
Regarding the thermal stability of complex C6, its acti-
vities significantly decrease with elevated reaction tempera-
ture from 30 to 60 °C (entries 3, 5-7, Table 1). In contrast to
the current system, half-titanocene chlorides bearing triden-
tate N-(2-benzimidazolylquinolin-8-yl)benzamidates exhibit
higher activities on elevating the temperature and possess
good thermal stability.13b The multidentate coordination of
(20) (a) Chien, J. C. W. J. Am. Chem. Soc. 1959, 81, 86. (b) Mallin,
D. T.; Rausch, M. D. J. Organomet. Chem. 1990, 381, 35. (c) Vanka, K.; Xu,
Z.; Ziegler, T. Organometallics 2005, 24, 419.
(18) Chen, E. Y. X.; Marks, T. J. Chem. Rev. 2000, 100, 1391.
(19) Koltzenburg, S. J. Mol. Catal. A: Chem. 1997, 116, 355.

2462 Organometallics, Vol. 29, No. 11, 2010
Table 3. Copolymerization of Ethylene with 1-Hexene or 1-Octene with C6/MAOa
Liu et al.
c
activity
(kg mol-1(Ti) h-1
Mw
(kg mol-1
c
entry
1-hexene (mol L-1
)
1-octene (mol L-1
)
polymer (g)
)
Tmb (°C)
)
Mw/Mn
3
3
3
1
2
3
4
5
6
7
8
9d
0.1
0.2
0.5
1.0
0
0
0
0
0.5
0
0
0
0
0.1
0.2
0.5
1.0
0
1.98
1.86
1.78
1.22
1.71
1.44
1.23
1.07
0.158
2380
2230
2140
1460
2050
1730
1480
1280
112.9
108.4
104.0
94.4
109.8
105.3
104.7
93.5
223
195
473
299
257
268
239
230
54.5
7.7
3.3
4.6
2.6
3.5
2.8
1.8
3.4
1.6
31.6
110.9
a Conditions: 5 μmol of catalysts; 10 atm of ethylene; 10 min; Al/Ti = 1500; 30 °C; toluene (total volume 100 mL). b Determined by DSC. c Determined
by GPC. d 1 atm of ethylene; 60 min; toluene (total volume 50 mL).
nickel or bis(imine)pyridine iron complexes.21 It is assumed
that the active species above 40 °C are uniform; however,
those active sites could not be prolonged in ethylene inser-
tions for high molecular weight PEs. Due to the highly exo-
thermal nature of the polymerization reaction, we had diffi-
culties controlling the reaction temperature below 30 °C. The
catalytic system produces highly active species for ethylene
polymerization at 30 °C; however, active species would
probably be changed into multiactive sites and PEs with a
bimodal distribution would be obtained because of reaction
temperature fluctuations during the exothermal polymeriza-
tion. Regarding the lifetime of the C6/MAO system (entries
3, 8, and 9, Table 1), the activities decreased with extending
the reaction time to 5, 10, or 30 min.
Ligands’ Environmental Effect on the Catalytic Behavior of
Procatalysts C1-C7. Using the optimized conditions from
above (10 atm of ethylene, 30 °C, and Al/Ti 1500), the procata-
Figure 3. 13C NMR spectrum of ethylene/1-hexene copolymer
lysts C1-C7 have been examined to understand the substituent
by the C6/MAO system (entry 3, Table 3).
effects of the ligands. For comparison, the polymerization
using CpTiCl3 was also conducted. The results are collected
in Table 2. In general, all procatalysts show high activities in the
range 978 to 2170 kg mol-1(Ti) h-1 (entries 1-7, Table 2),
sphere of titanium than chain transfer. Therefore bulky ligands
occupying more space around titanium disfavor chain pro-
pagation, but increase the chain transfer and result in PEs
with lower molecular weights.
2.3. Copolymerization of Ethylene/1-Hexene and Ethylene/
1-Octene. In addition to ethylene polymerization for PEs, the
copolymerization of ethylene with 1-hexene or 1-octene was
also investigated, using the representative example of proca-
talyst C6. The detailed copolymerization of ethylene/1-hexene
or octene by C6/MAO has been successfully carried out, and
the results are illustrated in Table 3.
3
3
while CpTiCl3 gave an activity of 282 kg mol-1(Ti) h-1
.
3
3
Their catalytic activities vary in the order C6 (R = OMe
and Cp0 =Cp*)>C7 (Me and Cp*)>C1 (OMe and Cp)>
C2 (Me and Cp) > C3 (H and Cp) > C5 (Cl and Cp) > C4
(F and Cp). In terms of steric influence, the bulky Cp* enhances
the activity of its procatalyst (C6 vs C1, and C7 vs C2)
because the active species are better protected in the polyme-
rization process.18 On the other hand, the electron-donating
substituents of the amidates and Cp* could increase the
electron density of titanium and stabilize the active species,
which are favorable for the alkyl-Ti bond and a cis-located
vacant coordination site for ethylene, therefore resulting in a
better activity.18,22 In addition, the molecular weights of the
resultant PEs are also catalyst-dependent; the Mw values of
In comparison with its ethylene polymerization activity
(2170 kg mol-1(Ti) h-1, entry 6, Table 2), the positive effect
3
3
of comonomer is observed at low concentration of 1-hexene
(entries 1 and 2, Table 3); however, the activities decreased
with a further increase of the concentration of 1-hexene
(entries 3 and 4, Table 3). This is similar to observations
for the imino-indolate half-titanocenes.14 DSC analysis shows
melting points of the obtained polymers in the range 103 to
94 °C, and the 13C NMR spectrum (Figure 3) of the resultant
poly(ethylene-co-1-hexene) (entry 3, Table 3) reveals a typi-
cal spectrum of linear low-density polyethylene (LLDPE)
with a 14.7 mol % 1-hexene incorporation. Comparing the
properties of the copolymers obtained by our previous half-
titanocene procatalysts,13b although reaction parameters are
not the same, reaction conditions for each catalytic system
were optimized, and the current system produced copoly-
mers with higher 1-hexene incorporation. Less crowding
around titanium in the systems employed herein is a plau-
sible cause for this. The 1-hexene incorporation ability herein
PEs by procatalysts C1-C5 (180-437 kg mol-1) are far
3
higher than that produced by CpTiCl3 (99.2 kg mol-1).
3
Concerning the same ancillary ligands, the procatalysts
bearing Cp* produced lower molecular weight PEs than
those ligated by Cp (C6 vs C1, and C7 vs C2). Less resistance
around the active species would be favorable for producing
polyolefins with higher molecular weights. It is supposed that
inthe titaniumcyclopentadienylamide catalytic systems, chain-
increasing processes occupy more space in the coordination
(21) (a) Zou, H.; Hu, S.; Huang, H.; Zhu, F.; Wu, Q. Eur. Polym. J.
2007, 43, 3882. (b) Wang, Q.; Li, L.; Fan, Z. Eur. Polym. J. 2004, 40,
1881.
(22) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255.

Article
Organometallics, Vol. 29, No. 11, 2010 2463
and washed with hexane before use to remove any mineral oil.
Tetrahydrofuran (THF), toluene, hexane, and heptane were ref-
luxed over sodium and benzophenone, distilled, and then stored
under a nitrogen atmosphere. Dichloromethane (CH2Cl2) was
distilled over calcium hydride and stored under a nitrogen atmos-
phere. Highly pure ethylene was purchased from Beijing Yansan
Petrochemical Co. and used as received. IR spectra were recor-
ded on a Perkin-Elmer FT-IR 2000 spectrometer using KBr
disks in the range 4000-400 cm-1. Elemental analysis was per-
1
formed on a Flash EA 1112 microanalyzer. H NMR and 13
C
NMR spectra were recorded on a Bruker DMX 400 MHz instru-
ment at ambient temperature using TMS as an internal standard.
DSC trace and melting points of polyethylenes were obtained
from the second scanning run on a Perkin-Elmer DSC-7 at a
heating rate of 10 °C/min. 1H NMR and 13C NMR spectra of the
polymers were recorded on a Bruker DMX-300 MHz instru-
ment at 110 °C in deuterated 1,2-dichlorobenzene with TMS as
an internal standard. Molecular weights and polydispersity indi-
ces (PDI) of (co)polyethylene were determined using a PL-GPC220
instrument at 135 °C in 1,2,4-trichlorobenzene with polystyrene
as the standard.
Figure 4. 13C NMR spectrum of ethylene/1-octene copolymer
by the C6/MAO system (entry 7, Table 3).
4.2. Synthesis of Complexes C1-C7. η5-Cyclopentadienyl-
[N-(2-methylquinolin-8-yl)-p-methoxybenzamide]titanium Dichlo-
rides (C1). To a stirred solution of 4-methoxy-N-(2-methylqui-
nolin-8-yl)benzamide (0.585 g, 2.00 mmol) in dried THF (30 mL)
at room temperature was added KH (0.080 g, 2.00 mmol). The
mixture was allowed to stir for 12 h, and a yellow suspension was
obtained. At -78 °C, 20 mL of a CpTiCl3 (0.438 g, 2.00 mmol)
solution in THF was added dropwise over a 30 min period. The
resultant mixture was allowed to warm to room temperature
and stirred for an additional 12 h. The residue, obtained by
removing the solvent under vacuum, was extracted with toluene
(3 ꢀ 20 mL). The combined filtrates were concentrated under
vacuum to reduce the volume to 5 mL and then filtered to give a
red solid (0.781 g, 1.64 mmol, yield 82.0%). 1H NMR (CDCl3,
400 MHz): δ 8.02 (d, J=8.4 Hz, 1H, quin), 7.65 (d, J=7.7 Hz,
2H, quin), 7.47 (dd, J1 = 7.7 Hz, J2 = 7.8 Hz, 1H, quin), 7.29 (d,
J = 8.4 Hz, 2H, aryl), 7.22 (d, J = 8.4 Hz, 1H, quin), 7.04 (s, 5H,
Cp), 6.57 (d, J=8.3 Hz, 2H, aryl), 3.69 (s, 3H, OCH3), 2.59 (s,
3H, CH3). 13C NMR (CDCl3, 100 MHz): δ 173.8, 162.8, 158.3,
142.6, 141.9, 136.4, 131.0, 127.6, 126.3, 126.0, 125.9, 123.5,
122.2, 121.5, 113.5, 55.4, 25.4. Anal. Calcd for C23H20Cl2N2O2-
Ti: C, 58.13; H, 4.24; N, 5.90. Found: C, 58.03; H, 4.28; N, 5.53.
η5-Cyclopentadienyl[N-(2-methylquinolin-8-yl)-p-methylben-
zamide]titanium Dichlorides (C2). Using the same procedure for
the synthesis of C1, C2 was obtained as a red solid in 80.5% yield
is also higher than those reported by others.23,24 At a fixed
1-hexene concentration, increasing ethylene pressure leads to
higher productivity and produces polymers with higher mole-
cular weight (entry 1 vs 9, Table 3).
Similarly, the ethylene/1-octene copolymerization was
also studied, and the results are summarized in Table 3. A
comparison of the ethylene/1-hexene copolymerization with
ethylene/1-octene copolymerization reveals slightly lower
activities (entry n vs entry n þ 4, n = 1-4, Table 3). DSC
analysis of the resultant copolymers shows melting points
from 93 to 110 °C. Figure 4 shows the 13C NMR spectrum of
ethylene/1-octene copolymer produced by the C6/MAO
system (entry 7, Table 3), and it indicates a 16.3 mol % in-
corporation of 1-octene.
3. Conclusions
The amidate half-titanocene dichlorides, Cp0Ti(L)Cl2 (Cp0 =
Cp or Cp*; L = amidate ligand, C1-C7), have been synthe-
sized and fully characterized, including single-crystal X-ray
diffraction for C2 and C4. All procatalysts show high activities
toward ethylene polymerization in the presence of MAO. The
procatalysts bearing substituted cyclopentadienyl groups give
higher activity, while the use of stronger electron-donating
groups of arylamidates enhances the catalytic activities of the
corresponding procatalysts. It is likely there is a single active
species above 40 °C, which produces PEs with narrow mole-
cular weights. Regarding the results with procatalyst C6, the
copolymerization of ethylene with 1-hexene or 1-octene pro-
duced copolymers incorporating branching of about 15%.
1
(0.739 g, 1.61 mmol). H NMR (CDCl3, 400 MHz): δ 8.01 (d,
J =8.3 Hz, 1H, quin), 7.64 (d, J=7.8 Hz, 2H, quin), 7.46 (dd,
J1 = 7.9 Hz, J2 = 7.6 Hz, 1H, quin), 7.27-7.16 (m, 3H, quin and
aryl), 7.05 (s, 5H, Cp), 6.89 (d, J=8.0 Hz, 2H, aryl), 2.58 (s, 3H,
CH3), 2.21 (s, 3H, CH3). 13C NMR (CDCl3, 100 MHz): δ 174.4,
158.3, 143.0, 142.4, 141.8, 136.4, 129.5, 128.8, 128.1, 127.5,
126.5, 125.9, 123.5, 122.1, 121.5, 25.3, 21.6. Anal. Calcd for
C23H20Cl2N2OTi: C, 60.16; H, 4.39; N, 6.10. Found: C, 60.13;
H, 4.66; N, 5.92.
η5-Cyclopentadienyl[N-(2-methylquinolin-8-yl)benzamide]titanium
Dichlorides (C3). Using the same procedure for the synthesis of
C1, C3 was obtained as a red solid in 77.2% yield (0.687 g, 1.54
mmol). 1H NMR (CDCl3, 400 MHz): δ 8.00 (d, J=8.4 Hz, 1H,
quin), 7.68 (d, J = 7.4 Hz, 1H, quin), 7.63 (d, J = 7.9 Hz, 1H,
quin), 7.46 (dd, J1 = 7.8 Hz, J2 = 7.8 Hz, 1H, quin), 7.33 (d, J=
7.6 Hz, 2H, aryl), 7.28-7.23 (m, 1H, quin), 7.19-7.16 (m, 1H,
aryl), 7.08 (d, J=7.7 Hz, 2H, aryl), 7.04 (s, 5H, Cp). 13C NMR
(CDCl3, 100 MHz): δ 174.7, 158.3, 142.1, 141.6, 136.4, 132.1,
130.0, 128.9, 128.3, 127.9, 127.5, 127.3, 126.2, 125.9, 125.3,
123.5, 122.1. Anal. Calcd for C22H18Cl2N2OTi: C, 59.36; H,
4.08; N, 6.29. Found: C, 59.10; H, 4.26; N, 6.29.
4. Experimental Section
4.1. General Considerations. All manipulations of air- and/or
moisture-sensitive compounds were performed under a nitrogen
atmosphere in a glovebox or using standard Schlenk techniques.
N-(2-Methylquinolin-8-yl)benzamide derivatives were prepared
as already reported.13b,16 Methylaluminoxane (MAO, 1.46 M in
toluene) was purchased from Albemarle. Potassium hydride
(KH) was bought from Beijing Chemical Regent Company
(23) Huang, J.; Lian, B.; Qian, Y.; Zhou, W.; Chen, W.; Zheng, G.
Macromolecules 2002, 35, 4871.
(24) Nomura, K.; Fujita, K.; Fujiki, M. J. Mol. Catal. A: Chem. 2004,
220, 133.
η5-Cyclopentadienyl[N-(2-methylquinolin-8-yl)-p-fluorobenz-
amide]titanium Dichlorides (C4). Using the same procedure for
the synthesis of C1, C4 was obtained as a red solid in 84.0% yield

2464 Organometallics, Vol. 29, No. 11, 2010
Liu et al.
(0.778 g, 1.68 mmol). 1H NMR (CDCl3, 400 MHz): δ 8.11-8.07
(m, 1H, quin), 8.02 (d, J=8.4 Hz, 1H, quin), 7.70 (d, J=7.4 Hz,
1H, quin), 7.66 (d, J = 8.1 Hz, 1H, quin), 7.52-7.47 (m, 1H,
quin), 7.37-7.33 (m, 1H, aryl), 7.25-7.23 (m, 1H, aryl) 7.03 (s,
Calcd for C28H30Cl2N2OTi: C, 63.53; H, 5.71; N, 5.29. Found:
C, 63.46; H, 5.75; N, 5.25.
4.3. Procedures for Ethylene Polymerization and Copolymeri-
zation of Ethylene with r-Olefin. A 250 mL autoclave stainless
steel reactor equipped with a mechanical stirrer and a tempera-
ture controller is heated under vacuum for at least 2 h at 80 °C. It
is allowed to cool to the required reaction temperature under
ethylene atmosphere and then charged with toluene (with co-
monomer), the desired amount of cocatalyst (MAO), and a tolu-
ene solution of the catalytic precursor. The total volume is 100 mL.
After reaching the reaction temperature, the reactor is sealed
and pressurized to 10 atm of ethylene pressure. The ethylene
pressure is kept constant during the reaction time by feeding the
reactor with ethylene. After the desired reaction time, the poly-
merization reaction is quenched by addition of a solution of
ethanol containing HCl. The precipitated polymer is washed
with ethanol several times and dried under vacuum.
5H, Cp), 6.77 (d, J = 8.2 Hz, 2H, aryl), 2.57 (s, 3H, CH3). 13
C
NMR (CDCl3, 100 MHz): δ 173.6, 158.4, 141.9, 141.4, 136.5,
131.1, 131.0, 129.1, 128.3, 127.6, 126.2, 126.1, 126.0, 125.4, 123.6,
122.3, 122.2, 25.3. Anal. Calcd for C22H17Cl2FN2OTi: C, 57.05;
H, 3.70; N, 6.05. Found: C, 57.03; H, 3.96; N, 5.99.
η5-Cyclopentadienyl[N-(2-methylquinolin-8-yl)-p-chlorobenz-
amide]titanium Dichlorides (C5). Using the same procedure for
the synthesis of C1, C5 was obtained as red solid in 79.5% yield
1
(0.763 g, 1.59 mmol). H NMR (CDCl3, 400 MHz): δ 8.02 (d,
J=8.0 Hz, 2H, quin), 7.70 (d, J=7.3 Hz, 1H, quin), 7.65 (d, J=
8.0 Hz, 1H, quin), 7.54-7.47 (m, 1H, quin), 7.28-7.26 (m, 2H,
aryl), 7.06 (d, J=7.9 Hz, 2H, aryl), 7.03 (s, 5H, Cp), 2.57 (s, 3H,
CH3). 13C NMR (CDCl3, 100 MHz): δ 173.8, 164.2, 158.4, 157.4,
141.8, 136.5, 129.9, 129.1, 129.0, 128.7, 128.3, 128.2, 123.6, 122.6,
122.2, 25.3. Anal. Calcd for C22H18Cl3N2OTi: C, 55.09; H, 3.57;
N, 5.84. Found: C, 54.93; H, 3.76; N, 5.88.
4.4. X-ray Structure Determination. Crystals of C2 and C4
suitable for single-crystal X-ray analysis are obtained by laying
heptane on their toluene solutions. Single-crystal X-ray diffrac-
tion for C2 and C4 are performed on a Rigaku RAXIS Rapid IP
diffractometer with graphite-monochromated Mo KR radiation
η5-Pentamethylcyclopentadienyl[N-(2-methylquinolin-8-yl)-
p-methoxybenzamide]titanium Dichlorides (C6). Using the same
procedure for the synthesis of C1, C6 was obtained as a red solid
in 89.0% yield (0.970 g, 1.78 mmol). 1H NMR (CDCl3, 400 MHz):
δ 7.93 (d, J=8.4 Hz, 1H, quin), 7.87 (d, J=7.4 Hz, 1H, quin),
7.56 (d, J=8.0 Hz, 1H, quin), 7.45 (dd, J1 = 8.4 Hz, J2 = 8.4 Hz,
quin), 7.30 (d, J = 8.5 Hz, 2H, aryl), 7.09 (d, J = 8.4 Hz, 1H,
quin), 6.53 (d, J = 8.5 Hz, 2H), 3.67 (s, 3H, CH3), 2.49 (s, 3H,
CH3), 2.34 (s, 15H, CH3). 13C NMR (CDCl3, 100 MHz): δ 174.8,
162.4, 157.1, 141.9, 136.5, 136.0, 134.1, 130.5, 129.1, 126.1, 122.4,
116.3, 114.0, 112.9, 55.5, 25.4, 13.8. Anal. Calcd for C28H30-
Cl2N2O2Ti: C, 61.67; H, 5.55; N, 5.14. Found: C, 61.55; H, 5.76;
N, 5.18.
˚
(λ = 0.71073 A) at 173(2) K. Cell parameters are obtained by
global refinement of the positions of all collected reflections.
Intensities are 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 anisotropically. Structure solution and refine-
ment are performed by using the SHELXL-97 package.25 Crys-
tal data collection and refinement details for all compounds are
available in the Supporting Information.
Acknowledgment. This work is supported by NSFC
Nos. 20874105 and 20904059.
η5-Pentamethylcyclopentadienyl[N-(2-methylquinolin-8-yl)-
p-methylbenzamide]titanium Dichlorides (C7). Using the same
procedure for the synthesis of C1, C7 was obtained as a red solid
Supporting Information Available: GPC diagrams of corre-
sponding polyolefins, the molecular structure of compound C4,
crystal data and processing parameters for complexes C2 and C4
and their CIF file giving X-ray crystal structural data. These
materials are available free of charge via the Internet at http://
pubs.acs.org.
1
in 85.2% yield (0.901 g, 1.70 mmol). H NMR (CDCl3, 400
MHz): δ 7.95 (d, J=8.3 Hz, 1H, quin), 7.82 (d, J=7.3 Hz, 1H,
quin), 7.50 (d, J=8.0 Hz, 1H, quin), 7.42 (dd, J1 = 8.3 Hz, J2 =
8.3 Hz, 1H, quin), 7.35 (d, J=8.5 Hz, 2H, aryl), 7.09 (d, J=8.3 Hz,
1H, quin), 6.76 (d, J = 8.5 Hz, 2H, aryl), 2.47 (s, 3H, CH3),
2.35(s, 15H, CH3), 2.21 (s, 3H, CH3). 13C NMR (CDCl3, 100
MHz): δ 174.2, 161.4, 155.1, 141.0, 137.5, 136.0, 134.7, 132.5,
129.8, 128.1, 123.4, 116.5, 114.1, 112.9, 25.4, 21.6, 13.8. Anal.
(25) Sheldrick, G. M. SHELXTL-97, Program for the Refinement of
€
€
Crystal Structures; University of Gottingen: Gottingen, Germany, 1997.