Ethylene homopolymerization and ethylene/1-hexene copolymerization catalysed by mixed salicylaldiminato cyclopentadienyl zirconium complexes

Article abstract of DOI:10.1016/j.ica.2009.06.010

Three new mixed salicylaldiminato cyclopentadienyl zirconium complexes Cp′[2-Bu^t-6-(C₆H₁₁NCH)C₆H₃O]ZrCl₂ (Cp′ = ⁿBuC₅H₄ (3a), ^tBuC₅H

Full text of DOI:10.1016/j.ica.2009.06.010

Inorganica Chimica Acta 363 (2010) 2009–2015
Contents lists available at ScienceDirect
Inorganica Chimica Acta
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Ethylene homopolymerization and ethylene/1-hexene copolymerization
catalysed by mixed salicylaldiminato cyclopentadienyl zirconium complexes
*
*
Wenzhong Huang, Xueqin Sun, Haiyan Ma , Jiling Huang
Laboratory of Organometallic Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Three new mixed salicylaldiminato cyclopentadienyl zirconium complexes Cp0[2-But-6-(C6H11NCH)
C6H3O]ZrCl2 (Cp0 = nBuC5H4 (3a), tBuC5H4 (3b) and Me4C5H (3c)) were prepared and the structure of com-
plex 3c was confirmed by X-ray diffraction analysis. All of the three complexes showed high activities for
ethylene homopolymerization with the activation of methylaluminoxane, and 3a showed the highest
activity up to 1.15 ꢀ 106 g PE/mol Zr h for ethylene homopolymerization at 70 °C. The 13C NMR spectrum
showed that the obtained polymer is linear polyethylene. Complexes 3a–c also catalysed ethylene/1-hex-
ene copolymerization with high activities from 6.29 ꢀ 105 to 12.3 ꢀ 105 g Copolymer/mol Zr h and with
0.89–1.39% 1-hexene incorporation level. In addition, the influence of the substituted alkyl on Cp on the
catalytic behavior of corresponding zirconium complexes was discussed.
Article history:
Received 18 January 2009
Accepted 5 June 2009
Available online 11 June 2009
Keywords:
Zirconium
Salicylaldiminato
Cyclopentadienyl
Ethylene homopolymerization
Copolymerization
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Considering the different catalytic behavior of metallocenes and
salicylaldiminato complexes, several mixed salicylaldiminato
Since the discovery of the metallocene–methylaluminoxane
(MAO) catalytic system in the middle of 1970’s [1], the group 4
metallocene catalysts have attracted considerable attention due
to their high catalytic activities for olefin polymerizations [2,3].
Changes in the ligand skeleton of catalysts provided an access to
obtain more novel polymeric materials. It means that the micro-
structure and physical characters of polyolefins can be controlled
by modification of the ligand substituents of metallocene, so it is
possible to get tailor-made polymers [4].
With the rapid development of metallocene catalysts, a good
many of non-metallocene complexes [5,6] have been synthesized
to avoid the growing patent minefield in group 4 cyclopentadienyl
structures. Group 4 metal complexes with bidentate N,O [7,8], N,N
[9,10] chelate ligands behave as a versatile class of olefin polymer-
ization catalysts, capable of producing new polyolefin architec-
tures [11]. Since Grubbs synthesized the first salicylaldiminato
nickel complex [12], phenoxyimine ligand complexes including
bis(salicylaldiminato) complexes [13,14], momo(salicylaldiminato)
complexes [15,16] and binuclear salicylaldiminato complexes [17]
and so on have been widely investigated. Especially bis(salicylal-
diminato) complexes of group 4 metal have attracted more atten-
tion for efficient ethylene polymerization catalytic activities
[18,19], as well as their excellent copolymerization ability of ethyl-
cyclopentadienyl complexes of group 4 metal [24] were prepared
and expected to exhibit the characters of both cyclopentadienyl li-
gand and chelating salicylaldiminato ligand. Lancaster and his co-
workers concentrated on complexes with mixed cyclopentadienyl
and various salicylaldiminato ligands, which showed satisfactory
activities in ethylene polymerization. In order to investigate the
influence of the different bulky alkyl groups on cyclopentadienyl
on the catalytic behavior of resultant metal complexes, we synthe-
sized three new mixed alkyl-substituted cyclopentadienyl salicyl-
aldiminato zirconium complexes 3a–c (Scheme 1). Their catalytic
behavior for homopolymerization of ethylene and copolymeriza-
tion of ethylene/1-hexene was further investigated and compared
with that of the analogous zirconium complex with unsubstituted
cyclopentadienyl ligand, Cp[2-But-6-(C6H11NCH)C6H3O]ZrCl2 (3d)
[24].
2. Experimental
2.1. General procedures
All manipulations were carried out under a dry argon atmo-
sphere using standard Schlenk techniques unless otherwise indi-
cated. Toluene, diethyl ether (Et2O) and tetrahydrofuran (THF)
were refluxed over sodium benzophenone. Dichloromethane
(CH2Cl2) was refluxed over CaH2. Chloroform-d and 1-hexene were
dried over calcium hydride under argon and stored in the presence
of activated 4 Å molecular sieves. n-BuLi (2.5 M in n-hexane) were
ene with
a-olefin [20–23].
* Corresponding authors. Tel./fax: +86 21 64253519.
E-mail addresses: haiyanma@ecust.edu.cn (H. Ma), qianling@online.sh.cn (J.
Huang).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.06.010

2010
W. Huang et al. / Inorganica Chimica Acta 363 (2010) 2009–2015
NH2
R
.
nBuLi
Cp'ZrCl3 DME
OH
O
OH
N
O
N
Cl
Cl
2a: Cp' = nBuC5H4
2b: Cp' = tBuC5H4
2c: Cp' = Me4C5H
Zr
1
3a: R = nBu
3b: R = tBu
3c: R = Me4
Scheme 1. Synthetic route of complexes 3a–c.
purchased from Chemetall GmbH. The co-catalyst methylalumi-
noxane (MAO, 1.53 M in toluene) was purchased from Witco
GmbH. Polymer grade ethylene was directly used for polymeriza-
tion. Phenoxyimine 1 [24,25], Cp0SiMe3 (Cp0 = nBuC5H4, tBuC5H4
and Me4C5H) [26,27] were synthesized according to the published
procedures.
2.2.4. [nBuC5H4][2-But-6-(C6H11NCH)C6H3O]ZrCl2 (3a)
The lithium salt of 1 was prepared by the dropwise addition of
2.5 M butyllithium (1.10 mL, 2.75 mmol) to a solution of 1 (0.71 g,
2.74 mmol) in THF (50 mL) at ꢂ78 °C for 30 min. Then the solution
of 1Li was added to a mixture of (nBuC5H4)ZrCl3ꢃDME (1.12 g,
2.74 mmol) and THF (20 mL) at ꢂ78 °C. The yellow solution was al-
lowed to stir at this temperature and then at room temperature
overnight. After removing the solvent under reduced pressure,
the remainder was recrystallized with CH2Cl2 and light petroleum
at ꢂ10 °C. Complex 3a was obtained as a yellow crystal (0.54 g,
36.9% yield). 1H NMR (500 MHz, 298 K, CDCl3): d 8.46 (s, 1H,
HC@N), 7.54 (dd, 1H, J = 7.7, 1.6 Hz, Ar), 7.27 (dd, 1H, J = 7.7,
1.6 Hz, Ar), 6.94 (t, 1H, J = 7.7 Hz, Ar), 6.38–6.23 (br, 4H, C5H4),
4.38 (m, 1H, N–CH), 2.78 (m, 2H, CH2C5H4), 2.30–1.26 (br, 10H,
cyclohexyl CH2), 1.55 (m, 2H, –CH2CH2C5H4), 1.44 (s, 9H, tBu),
1.31 (m, 2H, CH3CH2), 0.89 (t, 3H, CH3CH2). Anal. Calc. for
C26H37Cl2NOZr: C, 57.65; H, 6.88; N, 2.59. Found: C, 57.03; H,
7.33; N, 2.05%.
1H NMR spectra were recorded on Bruker ADVANCE-500 spec-
trometers with CDCl3 as solvent. Chemical shifts for 1H NMR spec-
tra were referenced internally using the residual solvent
resonances and reported relative to tetramethylsilane (TMS). Ele-
mental analyses were carried out on an EA-1106 type analyzer.
13C NMR spectra of polymers were recorded on
a Bruker
ADVANCE-500 spectrometer with 1,2-dichlorobenzene-d at
100 °C. Intrinsic viscosity was determined in decahydronaphtha-
lene at 135 °C and viscosity average molecular weights of PEs were
calculated according to the equation [28]:
½
g
ꢁ ðdL=gÞ ¼ 6:77 ꢀ 10ꢂ4 M0g:67
The gel permeation chromatography (GPC) performed on a
2.2.5. [tBuC5H4][2-But-6-(C6H11NCH)C6H3O]ZrCl2 (3b)
Waters 150 ALC/GPC system in a 1,2-dichlorobenzene solution at
135 °C was used to determine the weight-average molecular
weights (Mw) and the molecular weight distribution (Mw/Mn) of
the polymer.
Following the procedure described for 3a, 1 (1.03 g, 3.97 mmol),
2.5 M butyllithium (1.59 mL, 3.98 mmol), and (tBuC5H4)ZrCl3ꢃDME
(1.63 g, 3.98 mmol) gave 3b as a brown crystal (1.10 g, 51.2% yield).
1H NMR (500 MHz, 298 K, CDCl3): d 8.49 (s, 1H, HC@N), 7.55 (dd,
1H, J = 7.7, 1.7 Hz, Ar), 7.28 (dd, 1H, J = 7.7, 1.7 Hz, Ar), 6.96 (t,
1H, J = 7.7 Hz, Ar), 6.82–5.88 (br, 4H, C5H4), 4.21 (m, 1H, N–CH),
2.2. Synthesis
t
2.28–1.23 (br, 10H, cyclohexyl CH2), 1.47 (s, 9H, BuC5H4), 1.44 (s,
2.2.1. (Me4C5H)ZrCl3ꢃDME (2c)
9H, tBuPh). Anal. Calc. for C26H37Cl2NOZr: C, 57.65; H, 6.88; N,
These complexes were prepared by the procedure according to
the method of CpZrCl3ꢃDME reported by Lund and Livinghouse
[29]. A typical route was given for 2c. To a suspension of ZrCl4
(1.84 g, 7.88 mmol) in 50 mL of CH2Cl2 was added Me2S (1.5 mL,
20.4 mmol) at 0 °C. Then the mixture was warmed to room temper-
ature and stirred for 2 h. Filtrating the solution of ZrCl4ꢃ2Me2S,
(Me4C5H)SiMe3 [26] (1.53 g, 7.88 mmol) was added dropwise to
the filtrate and the mixture was stirred overnight. DME (30 mL)
was added and stirred for 2 h, the solvent was then removed in va-
cuo. The resulted yellow solid was recrystallized with DME to afford
2c as a yellow crystal (1.97 g, 61.1% yield). 1H NMR (500 MHz, 298 K,
CDCl3): d 5.63 (s, 1H, Me4C5H), 4.02 (s, 4H, OCH2CH2O), 3.77 (s, 6H,
CH3O), 2.16 (s, 6H, (CH3)4Cp), 2.07 (s, 6H, (CH3)4Cp).
2.59. Found: C, 57.47; H, 6.87; N, 2.38%.
2.2.6. [Me4C5H][2-But-6-(C6H11NCH)C6H3O]ZrCl2 (3c)
Following the procedure described for 3a, 1 (1.15 g, 4.43 mmol),
2.5 M butyllithium (1.78 mL, 4.45 mmol), and (Me4C5H)ZrCl3ꢃDME
(1.82 g, 4.45 mmol) gave 3c as a yellow crystal (1.6 g, 66.7% yield).
1H NMR (500 MHz, 298 K, CDCl3): d 8.50 (s, 1H, HC@N), 7.53 (dd,
1H, J = 7.7, 1.7 Hz, Ar), 7.26 (dd, 1H, J = 7.7, 1.7 Hz, Ar), 6.93 (t,
1H, J = 7.7 Hz, Ar), 5.83 (s, 1H, Me4C5H), 4.01 (m, 1H, N–CH),
2.36–1.16 (br, 10H, cyclohexyl CH2), 2.33 (s, 3H, CH3C5H), 2.29 (s,
3H, CH3C5H), 2.22 (s, 3H, CH3C5H), 1.65 (s, 3H, CH3C5H), 1.45 (s,
t
9H, Bu). Anal. Calc. for C26H37Cl2NOZr: C, 57.65; H, 6.88; N, 2.59.
Found: C, 57.45; H, 6.71; N, 2.38%.
2.2.2. (nBuC5H4)ZrCl3ꢃDME (2a)
2.3. X-ray diffraction measurements
Following the above procedure, 2a was isolated as a colorless
crystal in 74.0% yield. 1H NMR (500 MHz, 298 K, CDCl3): d 6.51 (s,
2H, nBuC5H4), 6.42 (s, 2H, nBuC5H4), 4.11 (s, 4H, OCH2CH2O), 3.89
(s, 6H, CH3O), 2.84 (t, 2H, J = 7.7, CH2Cp), 1.60 (m, 2H, CH2CH2Cp),
1.37 (m, 2H, CH3CH2), 0.93 (t, 3H, J = 7.7, CH3CH2).
Single crystal of complex 3c suitable for X-ray diffraction mea-
surement was obtained by slowly cooling a saturated dichloro-
methane and light petroleum solution to ꢂ10 °C. The
crystallographic data for complex 3c was collected on a Bruker
2.2.3. (tBuC5H4)ZrCl3ꢃDME (2b)
AXSD8 diffractometer with graphite-monochromated Mo
(k = 0.71073 Å) radiation. All data were collected at 20 °C using
the -scan techniques. The structure of 3c was solved by direct
method and refined using Fourier techniques. An absorption cor-
rection based on SADABS was applied [30]. All non-hydrogen atoms
Ka
Following the above procedure, 2b was isolated as a colorless
crystal in 45.7% yield. 1H NMR (500 MHz, 298 K, CDCl3): d 6.56 (s,
x
t
t
2H, BuC5H4), 6.49 (s, 2H, BuC5H4), 3.97 (s, 4H, OCH2CH2O), 3.76
t
(s, 6H, CH3O), 1.41 (s, 9H, BuCp).

W. Huang et al. / Inorganica Chimica Acta 363 (2010) 2009–2015
2011
were refined by full-matrix least-squares on F2 using the SHELXTL
Table 2
Selected structural parameters for complex 3c.
program package [31]. Hydrogen atoms were located and refined
by the geometry method. The cell refinement, data collection,
and reduction were done by Bruker SAINT [32]. The structure deter-
mination and refinement were performed by SHELXS-97 [33] and
SHELXL-97 [34], respectively. The crystal and refinement data are
collected in Tables 1 and 2.
Distances (Å)
Zr–C(18)
Zr–C(19)
Zr–C(20)
Zr–C(21)
Zr–C(22)
Zr–N(1)
2.464(3)
2.553(3)
2.555(3)
2.507(3)
2.470(3)
2.348(2)
Zr–O(1)
1.9908
Zr–Cl(1)
Zr–Cl(2)
C(1)–N(1)
C(8)–N(1)
C(7)–O(1)
2.4332
2.4713
1.284(3)
1.499(3)
1.339(3)
Angles (°)
2.4. Polymerization procedure
O(1)–Zr–N(1)
Cl(1)–Zr–Cl(2)
O(1)–Zr–C(18)
C(7)–O(1)–Zr
76.84(7)
87.06(3)
112.06(9)
146.41(15)
N(1)–Zr–C(18)
Cl(1)–Zr–C(18)
Cl(2)–Zr–C(19)
C(8)–N(1)–Zr
75.86(9)
107.73(7)
112.97(8)
118.60(16)
2.4.1. Ethylene polymerization
A 100 mL autoclave, equipped with a magnetic stirrer, was
heated at 100 °C under vacuum for 30 min and then cooled to
the desired temperature by immerging it into a thermostatically
heated bath, then filled with ethylene. Proper amount of MAO solu-
tion and toluene were added to the autoclave and the mixture was
saturated with ethylene for 15 min at the desired temperature.
After that proper amount of toluene solution of zirconium complex
was injected to the autoclave and the reactor was pressurized with
ethylene to reach the required value to start the polymerization.
The ethylene pressure was kept constant during the polymeriza-
tion. The reaction mixture was stirred vigorously for a certain time
and the ethylene pressure in the autoclave was slowly vented.
Then the reaction was quenched with 3% HCl in ethanol (50 mL).
The contents of the reactor were transferred to a beaker and then
filtrated. The collected polymer was washed to neutral with etha-
nol and then dried overnight in a vacuum oven at 60 °C to constant
weight.
polymerization. The ethylene pressure was kept constant during
the polymerization. The reaction mixture was stirred vigorously
for a certain time and the ethylene pressure in the autoclave was
slowly vented. Then the reaction was quenched with 3% HCl in eth-
anol (50 mL). The collected polymer was washed to neutral with
ethanol and then dried overnight in a vacuum oven at 60 °C to con-
stant weight.
3. Results and discussion
3.1. Synthesis of the complexes 3a-c
Three new complexes 3a–c were prepared via the route de-
scribed in Scheme 1. Salicylaldehyde derivative [25] and substi-
tuted half-metallocenes (Cp0ZrCl3ꢃDME, 2a–c) [29] were prepared
according to established procedures. The salicylaldimine
1
2.4.2. Ethylene/1-hexene copolymerization
[24,25] was obtained as a yellow solid by the reaction of cyclohex-
ylamine with the salicylaldehyde derivative and recrystallized by
ethanol. The desired mono(salicylaldiminato) cyclopentadienyl zir-
conium complexes 3a–c were synthesized by the reaction of the
lithium salt of the salicylaldimine 1 with one equivalent of the cor-
responding Cp0ZrCl3ꢃDME in moderate yields (37–67%). All the new
complexes were characterized by 1H NMR spectroscopy and ele-
mental analysis.
A 100 mL autoclave, equipped with a magnetic stirrer, was
heated at 100 °C under vacuum for 30 min and then cooled to
the desired temperature by immerging into a thermostatically
heated bath, then filled with ethylene. Proper amount of MAO solu-
tion, 1-hexene and toluene were added to the autoclave and the
mixture was saturated with ethylene for 15 min at the desired
temperature. After that proper amount of toluene solution of zirco-
nium complex was injected to the autoclave and the reactor was
pressurized with ethylene to reach the required value to start the
Additionally, the complex Cp[2-But-6-(C6H11NCH)C6H3O]ZrCl2
(3d) was prepared to compare with complexes 3a–c.
In the 1H NMR spectra of 3a–c, the chemical shift of @N–CH
protons is observed at 4.01–4.24 ppm which is different from
3.23 ppm of ligand 1, denoting coordinative affect of N–Zr. The imi-
no protons of complexes 3a–c appearing at d 8.43–8.50 ppm while
the free imino proton at 8.37 ppm also indicates that the nitrogen
atom is coordinated to the metal center. The chemical shift of imi-
no protons have a tendency with 3a < 3b < 3c, suggesting strong
deshielding effect with increase of steric bulkiness of Cp0 group.
The chemical shifts of Cp protons of Cp0[2-But-6-
(C6H11NCH)C6H3O]ZrCl2 (3a–c) are also different from correspond-
ing half-metallocene complexes Cp0ZrCl3ꢃDME (2a–c). In complex
3a with less bulky Cp moiety, the chemical shifts of Cp protons
move from 6.51 to 6.42 ppm of 2a to upfield. The same tendency
is observed for the unsubstituted complex 3d. In contrast, the
chemical shift of Cp proton in complex 3c moves from 5.63 ppm
of 2c to downfield.
Table 1
Crystal data and structure refinement details for 3c.
3c
Empirical formula
Formula weight
T (K)
C26H37Cl2NOZr
541.69
293(2)
Wavelength (Å)
Crystal size (mm3)
Crystal system
Space group
a (Å)
0.71073
0.429 ꢀ 0.347 ꢀ 0.301
monoclinic
C2/c
25.305(4)
b (Å)
13.9834(19)
c (Å)
16.282(2)
a
(°)
90.00
b (°)
110.381(2)
c
(°)
90.00
5400.7(13)
Volume (Å3)
Z
8
Calculated density (Mg/m3)
Absorption coefficient (mmꢂ1
F (0 0 0)
1.332
0.662
2256
)
3.2. X-ray diffraction of complex 3c
h Range for data collection (°)
Limiting indices
Reflections collected/unique
1.74–27.00
ꢂ32 6 h 6 22, ꢂ15 6 k 6 17, ꢂ20 6 l 6 20
The structure of complex 3c has been confirmed by single crys-
tal X-ray diffraction (Fig. 1).
15 678/5887 [Rint = 0.0915]
Maximum and minimum transmission 1.00000 and 0.75145
The crystal data for complex 3c is collected in Table 1. Selected
structural parameters are given in Table 2. In 3c, the zirconium
atom is five-coordinate with the Cp ligand in the apical site of a
distorted square–pyramid. Similar to the titanium complex
[Cp{2-But-6-(2,4,6-Me3C6H2NCH)C6H3O}TiCl2] [24], the N,O – che-
Data/restrains/parameters
5887/0/287
0.934
R1 = 0.0403, wR2 = 0.0977
R1 = 0.0511, wR2 = 0.1009
1.190 and ꢂ0.642
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r(I)]
Largest difference in peak/hole (e Åꢂ3
)

2012
W. Huang et al. / Inorganica Chimica Acta 363 (2010) 2009–2015
Fig. 1. ORTEP diagram of the molecular structure of [Me4C5H][2-But-6-(C6H11NCH)C6H3O]ZrCl2 (3c). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity.
lating moiety which includes the –C@N group lies in the same
plane with the phenyl ring and two of the atoms of the tert-butyl
group (C(14) and C(16)), while the Cp ring is almost parallel with
the phenoxide ring. The two torsion angles of Zr–N(1)–C(8)–C(9)
and Zr–N(1)–C(8)–C(13) with values of ꢂ105.2(2) and 129.4(2),
denote that there is steric repulsion between the cyclohexyl group
and the Cp plane.
amount of metal catalyst. The polymerizations by Cp[2-But-6-
(C6H11NCH)C6H3O]ZrCl2 (3d) under identical conditions were ap-
plied for comparison. The polymerization results are listed in Table
3.
It was shown that the Al/Zr ratio from 200 to 2000 was effective
for the ethylene polymerization and a constant loading of 1000
equivalents MAO was employed for most of the polymerization
runs.
In order to investigate the influence of polymerization time on
catalytic activity, ethylene was polymerized for 5, 15 and 30 min
by using 3a as catalyst. Although the catalytic activities of bis[N-
(3-t-butylsalicylidene)-anilinato] zirconium(IV) dichloride [8]
slightly decreased from 15 to 30 min, the activities of complex 3a
slightly increase with the increase of polymerization time from
15 (Run 2) to 30 min (Run 3), and a 0.5 times increase of the viscos-
The Zr–O(1) length of 1.9908(18) which is shorter than the sin-
gle Zr–O bond (2.244 Å) [35] indicate a partial double bond charac-
ter due to oxygen
p-donation [36]. The Zr–N(1) bond distance
(2.348(2) Å) is slightly longer than that observed for (bis[N-(3-
tert-butylsalicylidene)] cyclohexylaminato zirconium(IV) dichlo-
ride (2.309(6) Å) [37], which indicates less donating ability of imi-
no nitrogen atom to the metal center. The Cl(1)–Zr–Cl(2) angle of
87.06(3)° is not only smaller than bis(phenoxyimine) zirconium
complex (99.8(2)°) [37] but also smaller than the analogous mixed
salicylaldiminato pentamethyl cyclopentadienyl zirconium com-
plex (88.04(4)°) [38], which may be due to a strong steric repulsion
between the Cl ligand and the salicyladimine.
ity average molecular weights (M ) can also be observed clearly.
g
These facts indicate that the active species of complex 3a can stea-
dy exist for relative long time at this temperature.
The effect of polymerization temperature on catalytic activity is
summarized in Fig. 2. It is clear that the catalytic activities increase
in the order of 3b < 3c < 3d < 3a within the temperature range of
70–90 °C. Only the complex 3a exhibits higher catalytic activity
than the unsubstituted Cp complex 3d. On the contrary, the com-
plexes 3b and 3c show lower activities. Generally electron-donat-
ing ligands weaken the bonds between the metal center and
other ligands, which induce a better catalytic reactivity of the com-
plex. Besides electronic factors, steric factors also play an impor-
3.3. Polymerization studies
3.3.1. Ethylene homopolymerizations
The zirconium complexes 3a–c are effective for the polymeriza-
tion of ethylene but not for propylene under different reaction con-
ditions upon activation with MAO. All polymerization runs of
ethylene were carried out in toluene and each with 2.5 lmol
Table 3
The polymerization of ethylene with 3a–d/MAO systems.a
b
g
c
c
Run
Cat.
Al/Zr
Time (min)
Yield (g)
Act. (Kg PE/mol Zr h)
M
(ꢀ103)
Mw (ꢀ103)
Mw/Mn
1
2
3
4
5
6
7
8
3a
3a
3a
3b
3c
3c
3c
3d
1000
1000
1000
1000
200
1000
2000
1000
5
0.163
0.379
0.784
0.410
0.223
0.608
0.504
0.399
782
606
627
656
357
973
806
638
246
436
684
690
612
503
447
458
15
30
15
15
15
15
15
287/3.7d
327
2.34/1.97
3.68
334
3.10
195
5.93
a
b
c
All polymerization runs were performed in toluene with total volume of 25 mL over 15 min at 50 °C, 10 bar ethylene pressure and 2.5 lmol catalyst.
Intrinsic viscosity was determined in decahydronaphthalene at 135 °C and viscosity average molecular weight was calculated using the relation: [
Mw and Mw/Mn were determined by GPC analysis.
g
] = 6.77 ꢀ 10ꢂ4 M0:67
.
g
d
The GPC trace has double distributions.

W. Huang et al. / Inorganica Chimica Acta 363 (2010) 2009–2015
2013
1200
1000
800
ceivable for these mixed-ligand complexes, and in comparison
with the complexes 3a–c the unsubstituted Cp complex 3d is obvi-
ously easier to get multiple catalytic active species though such by-
reactions due to its less steric hindrance.
3a
3b
3c
3d
Considering that the signal of unsaturated carbon is not found
in the 13C NMR spectra, it seems reasonable that the polymer
chains are terminated by chain migration to MAO, which is further
supported by the results that increasing Al/Zr molar ratio leads to
the fall of molecular weight (Table 3, Runs 5–7). According to 13C
NMR analyses, the polyethylene produced with complexes 3a–d
can be divided into two types. One is highly linear polyethylene
produced with unsubstituted Cp complex 3d and tert-butyl substi-
tuted Cp complex 3b, and the other type is also linear polyethylene
but with isopropyl end group produced with n-butyl substituted
Cp complex 3a and tetramethyl substituted Cp complex 3c.
Fig. 3 shows the 13C NMR spectrum of polyethylene obtained
with complex 3c, similar spectrum is obtained for complex 3a. In
Fig. 3, the chemical shifts at 14.06, 22.86, 32.16 ppm are assigned
as the terminated propyl group of linear polyethylene as suggested
by Wilhelm [41]. However, none of open-literatures gave explana-
tion on the chemical shifts at 23.03 and 36.97 ppm [42–45]. There-
by, we use the program of CALMOD reported by Cheng and Bennett
[46] to calculate the chemical shifts at 23.03, 29.30 and
36.97 ppm, which prove to more likely belong to the terminal
iso-butyl group (Table 4). Therefore, the 13C NMR spectroscopic
analyses indicate that these polymers are linear polyethylenes par-
tially end-capped with isopropyl group. The work on the possible
mechanism of forming isopropyl end is still in progress.
600
400
200
30
50
70
90
T
(oC)
p
Fig. 2. Influence of polymerization temperature on activity. (Polymerization
conditions: [Zr] = 1.0 ꢀ 10ꢂ4 mol/L, Al/Zr = 1000, 15 min, ethylene (10 bar), 25 mL
of toluene.)
tant role in final catalytic behavior. Therefore for complexes 3a–c,
the introduction of bulkier substituents decreases the reactivity,
obviously the bulky groups on Cp is not favor for the coordination
of C@C bond of the monomer to metal center.
At 70 °C, the complex 3a displays the highest catalytic activity
(1.15 ꢀ 106 g PE/mol Zr h) among the investigated complexes.
Comparably, complexes 3b and 3c show the maximal activities at
50 °C. These results indicate that suitable donor substituent such
as small steric bulky alkyl is benefit to increase the catalytic activ-
ity and stability of active species at higher temperature. These re-
sults are similar to other mixed salicylaldiminato cyclopentadienyl
complexes of group 4 metals [24], as Lancaster reported that zirco-
nium complex (C5H5)[3-But-2-(O)C6H3CH@N(C6F5)]ZrCl2 was sta-
ble at 60 °C. Furthermore, when compared with Liu’s report [39]
that bis(salicylaldiminato) zirconium complex, [3-But-2-
(O)C6H3CH@N(C6H11)]2ZrCl2, showed the highest activities at the
temperature of 30 °C, these mixed salicylaldiminato cyclopentadi-
enyl complexes exhibit more thermal stability.
The GPC data are obtained for different complexes (Table 3) and
the traces have broad distributions. It is found that the complexes
with alkyl substituent on Cp ring give higher molecular weight
polyethylenes with narrower distributions than the complex 3d
with unsubstituted Cp (Mw = 1.95 ꢀ 105 and Mw/Mn = 5.93, Run
8). The results are similar to other mono(salicylaldiminato) cata-
lysts, for example, complex [3-But-2-(O)C6H3CH@N(C6F5)]ZrCl3
(THF) [35] afforded polyethylenes with molecular distributions
Mw/Mn from 2.8 to 4.6 at ꢂ20 to 60 °C. Scott reported that bis(sal-
icylaldiminato) titanium catalysts may form different catalytically
active species through inter- or intra-molecular alkylization reac-
tion of the ligand imine moiety [40]. Similar by-reactions are con-
3.3.2. Ethylene/1-hexene copolymerizations
All of the complexes 3a–c can catalyze the copolymerization of
ethylene/1-hexene and the results are illustrated in Fig. 4. The cat-
alytic activities are closely dependant on the employed catalyst
and the 1-hexene feeds. The tetramethyl substituted Cp complex
3c showed the highest catalytic activity.
The introduction of the 1-hexene affects the catalytic activities
of complexes 3a–c in different ways. Although the 1-hexene pos-
sesses stronger electron-donating ability than ethylene which con-
duces to the coordination of 1-hexene to the active species and
stabilizes the cationic active species, the insertion rate of 1-hexene
is always slower than that of ethylene as the steric hindrance in-
creases [47]. The final results of the copolymerization are also re-
lated to the structure of the catalysts. Complexes 3a and 3c show
increased activities with the increase of 1-hexene feeds. On the
other hand, complex 3b displays decreased activity with the in-
crease of 1-hexene feeds, probably the steric factors play a more
important role when compared to the electronic factors caused
by 1-hexene insertion into the propagation chain. In comparison
with complexes 3a–c, complex 3d reaches the highest activity at
1-hexene feed of 1 mL and then a declined tendency is displayed,
Fig. 3. 13C NMR spectrum of the polyethylene obtained with 3c as catalyst (Run 6).

2014
W. Huang et al. / Inorganica Chimica Acta 363 (2010) 2009–2015
Table 4
13C NMR chemical shift assignments for the polyethylene end group.
Terminal of linear PE
C1
C2
C3
C4
C5
C6
C1AC2 (C) AC3AC4AC5AC6APE
calculated value
observed value
calculated value
observed value
22.90
23.03
14.05
14.06
28.36
29.30
22.55
22.86
39.62
36.97
32.05
32.16
27.03
30.34
30.32
29.94
30.04
30.00
29.99
30.00
C1–C2–C3–C4–C5–C6–PE
29.59
29.56
which however is a general phenomenon in the copolymerization
of ethylene and 1-hexene [47].
General speaking, the ansa-metallocene complexes [49] or
bis(salicylaldiminato) complexes [50] usually exhibit excellent
In Table 5, the copolymerization activities increase in the order
of 3b < 3d < 3a < 3c. The catalytic activities of n-butyl Cp complex
3a and tetramethyl Cp complex 3c are 27–38% higher than that
of the unsubstituent complex 3d with the 1-hexene feeds of
2 mL, which are all higher than the corresponding activities of eth-
ylene homopolymerization. The viscosity average molecular
efficiencies for ethylene/a-olefin copolymerizations, but the mixed
salicylaldiminato complexes show low 1-hexene incorporation le-
vel [24] in ethylene/1-hexene copolymerization. Lancaster
reported 1-hexene incorporation of 1.3–2.1% with monocyclopen-
tadienyl phenoxyimine zirconium complexes. The ethylene/1-hex-
ene copolymers obtained with the complexes 3a–c characterized
by 13C NMR spectroscopic method in high temperature have 1-
hexene incorporation contents of 0.89–1.39%, which are slightly
lower than that with complex 3d (1.44%). The low levels of 1-hex-
ene incorporation are probably due to the inherent steric bulkiness
of these complexes.
weights (M ) of copolymers are all lower than those of polymers
g
of ethylene homopolymerization. It is noticeable that the M of
g
copolymers obtained with complexes 3a–c lie on the similar level
with those of corresponding polyethylenes, but the molecular
weight of the copolymer obtained with complex 3d is seven times
lower than that of the corresponding homopolymer. The results
indicate that the introduction of alkyl on Cp can increase the cata-
lytic activity and inhibit to a certain degree the decrease of molec-
ular weight of copolymer.
4. Conclusion
Three new alkyl-substituted cyclopentadienyl salicylaldiminato
zirconium complexes were prepared and showed high activities for
ethylene homopolymerization. Within the temperature range of
70–90 °C, complex 3a with n-butyl substituted Cp exhibited higher
catalytic activities and the more bulky complexes 3b and 3c exhib-
ited lower catalytic activities than the unsubstituted Cp complex
3d, indicating that suitable alkyl substituent on Cp ring is benefit
to catalytic activity.
3a
1400
1200
1000
800
3b
3c
3d
The GPC and 13C NMR spectroscopic analyses indicate that com-
plexes 3a–c can catalyze ethylene polymerization to produce linear
polyethylene with broad distributions which is however narrower
than that obtained with unsubstituted complex 3d.
The complexes 3a–c can also catalyze the copolymerization of
ethylene/1-hexene but with low level of 1-hexene incorporation
in copolymer. The complexes 3a and 3c showed higher catalytic
activities in copolymerization than ethylene homopolymerization
and the tert-butyl cyclopentadienyl salicylaldiminato zirconium
complex 3b afforded ethylene/1-hexene copolymer of higher
molecular weight.
600
0
1
2
3
4
Feed of 1-hexene (mL)
Fig. 4. Influence of 1-hexene feed on the copolymerization of ethylene/1-hexene.
(Copolymerization conditions: [Zr] = 1.0 ꢀ 10ꢂ4 mol/L, Al/Zr = 1000, 50 °C, 15 min,
ethylene (10 bar), 25 mL of toluene.)
Acknowledgments
This work is subsidized by the National Basic Research Program
of China (2005CB623801), National Natural Science Foundation of
China (NNSFC, 20774027), the Program for New Century Excellent
Talents in University (for H. Ma, NCET-06-0413). All the financial
support is gratefully acknowledged.
Table 5
The copolymerization of ethylene/1-hexene with 3a–d/MAO systems.a
d
g
Run
Cat.b
Yield (g)
Act.c
M
(ꢀ103)
1-Hexene incorporatione (%)
9
3a
3b
3c
3d
0.708
0.393
0.768
0.603
1130
629
1230
890
322
334
264
68
1.39
0.89
1.14
1.44
Appendix A. Supplementary material
10
11
12
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2009.06.010.
a
All polymerization runs were performed in toluene with total volume of 25 mL
over 15 min at 50 °C, 10 bar ethylene pressure and 2.0 mL 1-hexene.
b
1.0 ꢀ 10ꢂ4 mol/L (2.5
l
mol) catalyst and 0.10 mol/L (2.5 mmol) MAO as co-
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