Half-zirconocene anilide complexes: Synthesis, characterization and catalytic properties for ethylene polymerization and copolymerization with 1-hexene

Article abstract of DOI:10.1039/c0dt01789b

A number of half-zirconocene anilide complexes of the type Cp*ZrCl₂[N(2,6-R¹₂C₆H ₃)R²] [R¹ = ⁱPr (1, 3), Me (2); R² = Me (1, 2), Bn (3)] and Cp*ZrCl[N(2,6-M

Full text of DOI:10.1039/c0dt01789b

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PAPER
Half-zirconocene anilide complexes: synthesis, characterization and catalytic
properties for ethylene polymerization and copolymerization with 1-hexene†
Kefeng Liu, Qiaolin Wu, Wei Gao and Ying Mu*
Received 17th December 2010, Accepted 16th February 2011
DOI: 10.1039/c0dt01789b
A number of half-zirconocene anilide complexes of the type Cp*ZrCl2[N(2,6-R1 C6H3)R2]
2
i
[R1 = Pr (1, 3), Me (2); R2 = Me (1, 2), Bn (3)] and Cp*ZrCl[N(2,6-Me2C6H3)Me]2 (4) (Cp* =
pentamethylcyclopentadienyl) were synthesized from the reactions of Cp*ZrCl3 with the lithium salts of
the corresponding anilide in diethyl ether at room temperature. All new zirconium complexes were
characterized by 1H and 13C NMR and elemental analysis. Molecular structures of complexes 1, 2 and 4
were determined by single crystal X-ray diffraction analysis. Upon activation with AliBu3 and
Ph3CB(C6F5)4, complexes 1–4 exhibit good catalytic activity for ethylene polymerization, and produce
polyethylene with a moderate molecular weight. Among these zirconium complexes, complex 1 shows
the highest catalytic activity while complex 4 shows the lowest catalytic activity for ethylene
polymerization. Complexes 1–3 also exhibit moderate catalytic activity for copolymerization of
ethylene with 1-hexene, and produce copolymers with relatively high molecular weight and reasonable
1-hexene incorporation. In addition, the activation procedure of these catalyst systems were studied by
1H NMR spectroscopy.
synthesized and tested as catalysts for ethylene polymerization
Introduction
and copolymerization with a-olefins. So far, only a few number
Since Sinn and Kaminsky discovered that metallocene complexes
of zirconium complexes of this type with an amide ligand have
been reported,24 and none of them have been studied as catalysts
for ethylene–a-olefin copolymerization. We have recently found
that non-bridged monocyclopentadienyl titanium complexes with
an anilide ligand show good catalytic properties for ethylene–1-
hexene copolymerization.25 It is therefore of interest to develop the
analogous zirconium complexes of this type and investigate their
catalytic performance for ethylene polymerization and ethylene–
a-olefin copolymerization. In this contribution, we report the
show high catalytic activity for ethylene polymerization when
activated with methylaluminoxane (MAO),1 group 4 metallocene
complexes have attracted great interest both in academic and
industrial institutes due to their excellent performance as cat-
alysts in the production of polyolefin materials with tailored
structures and properties.2–7 To develop new metallocene catalysts
with good catalytic performance, a large number of group 4
metallocene complexes have been synthesized.2,8–10 As one of
the most efficient catalyst types for olefin polymerization, zir-
conocene complexes have been widely studied for ethylene11 and
propylene1,5,12 polymerization and copolymerization with higher
a-olefins.13 Some non-bridged and bridged zirconocene complexes
have been found to exhibit unique catalytic characteristics for the
stereospecific polymerization of propylene.14–18 Since constrained
geometry and non-bridged monocyclopentadienyl titanium com-
plexes have been known to be good catalysts for ethylene
copolymerization with a-olefins,19 some non-bridged monocy-
clopentadienyl zirconium complexes bearing a benzamidinate,20
aryloxy,21 salicylaldiminato22 or b-diketiminate23 ligand were also
synthesis and characterization of several half-zirconocene anilide
i
complexes of the type Cp*ZrCl2[N(2,6-R1 C6H3)R2] [R1 = Pr(1, 3),
2
Me(2); R2 = Me(1, 2), Bn(3)] and Cp*TiCl[N(2,6-Me2C6H3)Me]2
(4) (Cp* = pentamethylcyclopentadienyl), and their catalytic per-
formance for ethylene homopolymerization and copolymerization
with 1-hexene.
Results and discussion
Synthesis and characterization of new compounds
i
The aniline free ligands HN(2,6-R1 C6H3)R2 [R1 = Pr (HLa, HLc),
2
Me (HLb), R2 = Me (HLa, HLb), Bn (HLc)] were synthesized
according to previously reported procedures.25,26 The free ligands
HLa and HLb were synthesized in high yields (>85%) from
State Key Laboratory for Supramolecular Structure and Materials, School
of Chemistry, Jilin University, 2699 Qianjin Street, Changchun, 130012,
People’s Republic of China. E-mail: ymu@jlu.edu.cn; Fax: (+86)-431-
85193421; Tel: (+86)-431-85168376
† Electronic supplementary information (ESI) available. CCDC reference
numbers 804798–804800. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01789b
the reaction of CH3I with a corresponding lithium 2,6-R1 -
2
anilide obtained by treating the corresponding 2,6-R1 -aniline with
2
nBuLi. The free ligand HLc was synthesized in a high yield of
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˚
Table 1 Selected bond lengths (A) and angles (deg) for complexes 1, 2
and 4
about 80% by a two step procedure: a condensation reaction of
benzaldehyde with 2,6-diisopropylaniline, followed by reduction
of the formed Schiff base compound with LiAlH4. Complexes 1–3
were synthesized in high yields (65–80%) according to a published
Complexes
1
2
4
procedure24,27 by reactions of Cp*ZrCl3 in diethyl ether with 1
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–Cl(1)
Zr(1)–Cl(2)
2.0141(15)
—
2.4147(5)
2.4141(5)
2.197
106.51(2)
104.74(5)
—
1.998(3)
—
2.3890(15)
2.4171(15)
2.214
106.36(6)
103.52(10)
—
2.032(4)
2.051(4)
2.4398(12)
—
2.258
—
103.02(11)
99.06(11)
105.99(14)
—
106.3(3)
142.5(3)
115.9(3)
132.2(3)
109.0
i
equiv of the corresponding LiN(2,6-R1 C6H3)R2 [R1 = Pr (LiLa,
2
LiLc), Me (LiLb); R2 = Me (LiLa, LiLb), Bn (LiLc)], respectively
(Scheme 1). The bisanilide zirconium complex 4 was obtained from
the reaction of Cp*ZrCl3 with 2 equiv of LiN(2,6-Me2C6H3)Me
in a yield of 75%. Complexes 1–4 are quite soluble in methylene
chloride, toluene, benzene, and diethyl ether, but less soluble in n-
pentane and n-hexane. These complexes were all characterized by
1H and 13C NMR spectroscopy along with elemental analysis. The
1H NMR spectra of complexes 1 and 3 show two set of doublets
for the methyl protons of the CH(CH3)2 group (1.14 and 1.33 ppm
for 1; 0.59 and 1.22 ppm for 3), and the 13C NMR spectra of
both complexes show two signals for the two methyl groups (27.0
and 27.2 ppm for 1; 25.0 and 25.9 ppm for 3) of the iPr group in
these complexes, indicating that the rotation of the 2,6-iPr2C6H3
Zr(1)–Cp*(cent)
Cl(1)–Zr(1)–Cl(2)
N(1)–Zr(1)–Cl(1)
N(2)–Zr(1)–Cl(1)
N(1)–Zr(1)–N(2)
N(1)–Zr(1)–Cl(2)
Zr(1)–N(1)–C(11)
Zr(1)–N(1)–C(12)
Zr(1)–N(2)–C(20)
Zr(1)–N(2)–C(21)
Cp*(cent)–Zr(1)–Cl(1)
Cp*(cent)–Zr(1)–Cl(2)
Cp*(cent)–Zr(1)–N(1)
Cp*(cent)–Zr(1)–N(2)
—
—
104.30(5)
100.44(12)
146.35(13)
—
103.42(10)
104.2(2)
144.2(3)
—
—
113.3
113.8
117.3
—
—
112.2
111.5
116.8
—
114.3
122.8
—
1
group about the N–C (Ar group) bond is restricted.25,28 The H
approximately parallel to the Cp* ring, with an angle of 11.7◦,
while the aryl ring in another anilide ligand is nearly perpendicular
to the Cp* ring, with an angle of 84.7◦. The Zr–N distances
in complexes 1 and 2 are somewhat shorter than the ones in
complex 4 and those previously reported in the complex [(2,6-
NMR signal for the N–Me protons in the two anilide ligands of
complex 4 shifts about 0.6 ppm toward higher field compared to
the corresponding signal in complex 2 with one anilide ligand.
i
24b
˚
Pr2C6H3)(SiMe3)N]2ZrCl2 (2.029, 2.030 A). The average Zr–
˚
˚
Cl distances in complexes 1 (2.4144 A), 2 (2.4030 A) and 4 are
3
20
˚
in line with the one in CpZrCl2[h -CPh(NSiMe3)2] (2.422 A),
i
˚
but longer than that in [(2,6- Pr2C6H3)(SiMe3)N]2ZrCl2 (2.380 A).
The Cp*(cent)–Zr distances in complexes 1 and 2 are shorter
than that in the more crowded complex 4. The Cl–Zr–Cl an-
gles in complexes 1 and 2 are la◦rger than those reported for
CpZrCl2[h -CPh(NSiMe3)2] (90.95 )20 a◦nd a hafnium analogue
3
Cp*HfCl2[N(2,6-iPr2C6H3)SiMe3] (101.9 ).24b The Cp*(cent)–Zr–
Cl angles in complexes 1 and 2 are slightly larger than that in
complex 4. The two Cp*(cent)–Zr–N angles in complex 4 are
quite different with one being smaller, but the other being larger
than those in complexes 1 and 2. The Zr–N–C(phenyl) angles in
complexes 1 and 2 are larger than those in complex 4, probably
due to the larger repulsion between the two anilide ligands in the
latter complex.
Scheme 1 Synthetic procedure of complexes 1–4.
Crystal structures of complexes 1, 2 and 4
Molecular structures of complexes 1, 2 and 4 were determined by
single crystal X-ray diffraction analysis. The ORTEP drawings of
their molecular structures are shown in Fig. 1, 2 and 3, respectively.
The selected bond lengths and angles are summarized in Table 1.
The molecular structural analysis reveals that all the complexes
1, 2 and 4 have a pseudo-octahedral coordination environment in
their solid state and adopt a three-legged piano stool geometry
with the anilide N and Cl atoms being the three legs and the
Cp* ring being the seat. The aryl ring in the anilide ligand in
complexes 1 and 2 is almost parallel to the Cp* ring with the
N–CH3 group directed away from the cyclopentadienyl ring. In
the case of complex 4, the aryl ring in one anilide ligand is
Fig. 1 Perspective view of 1 with thermal ellipsoids drawn at the 30%
probability level. Hydrogens are omitted for clarity.
4716 | Dalton Trans., 2011, 40, 4715–4721
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known that electron-donating substituents on the ligands can
stabilize the catalytically active cationic species and improve
the catalytic activity.29 On the other hand, moderately bulky
ligands will weaken the interaction between the cationic catalyst
and the anionic cocatalyst species, and therefore enhance the
catalytic activity too.13,30 The complex 4 with two anilide ligands
exhibits obviously lower catalytic activity than complex 2 with
one anilide ligand under the same conditions. On the basis of
current understanding on the reaction mechanism of group 4
metallocene catalyst systems,21,31 the catalytically active cationic
species in the two catalyst systems might be the same. However,
the bulky bisanilide complex 4 should be more difficult to activate
than complex 2. The catalytic activity of these catalyst systems
is sensitive to the polymerization temperature and Al : Zr molar
ratio. The maximal catalytic activity for all four catalyst systems
was observed around 60 ◦C with a Al : Zr molar ratio about 300.
The polyethylenes obtained with complexes 1–4 possess moderate
molecular weight (Mw = 10–26 ¥ 104 g mol-1) with a relatively
narrow molecular weight distribution, and the molecular weight
values of the resultant polyethylenes are remarkably dependent
on the structure of the catalyst. The polyethylenes obtained with
complex 3 show the highest molecular weight while those produced
with complex 2 have the lowest molecular weight under similar
conditions, indicating that the substituents on the anilide ligand
play an important role in controlling the length of the growing
polymer chain. Based on the present results, it seems that catalysts
with a bulkier anilide ligand produce polyethylenes with higher
molecular weight. In addition, as reported previously for other
catalyst systems, the molecular weight values of the resultant
polyethylenes decrease with the increase in the polymerization
temperature and Al : Zr molar ratio. The m◦elting points of the
resultant polyethylenes range from 138–142 C, which is typical
for linear polyethylene. 13C NMR analysis on the polymer samples
proves that the polyethylenes produced by these catalysts are
indeed linear with no signals for branches.
Fig. 2 Perspective view of 2 with thermal ellipsoids drawn at the 30%
probability level. Hydrogens are omitted for clarity.
Fig. 3 Perspective view of 4 with thermal ellipsoids drawn at the 30%
probability level. Hydrogens are omitted for clarity.
Ethylene polymerization
Ethylene polymerization reactions using complexes 1–4 as pre-
catalysts under different conditions were studied, and the results
are summarized in Table 2. Upon activation with AliBu3 and
Ph3CB(C6F5)4, complexes 1–4 all exhibit good catalytic activity for
ethylene polymerization. Under similar conditions, the catalytic
activity decreases in the order of 1 > 3 > 2 > 4, indicating
that the catalytic activity of these complexes is influenced by
the nature of the substituents on the anilide ligands. It is well
Copolymerization of ethylene with 1-hexene
Copolymerization reactions of ethylene with 1-hexene using
complexes 1–4 as precatalysts under different conditions were
also explored, and the copolymerization results are summarized
in Table 3. As observed in the ethylene homopolymerization,
the catalytic activity of these catalysts for the ethylene–1-hexene
copolymerization under similar conditions also changes in the
Table 2 Summary of ethylene polymerization catalyzed by 1–4–AliBu3–Ph3CB(C6F5)4 systemsa
◦
Temp (◦C)
Al : Zr molar ratio
Yield (g)
Activityb
Mwc ¥ 10-4
Mw/Mnc
Tm ( C)
d
Run
Catalyst
1
2
3
4
5
6
7
8
1
1
1
1
1
2
3
4
40
60
60
60
80
60
60
60
300
200
300
400
300
300
300
300
0.418
0.381
0.732
0.705
0.508
0.360
0.485
0.258
334
305
586
564
406
288
388
206
19.1
18.1
17.2
10.4
12.2
15.3
25.7
20.1
3.17
3.16
2.30
2.26
2.72
2.41
2.35
2.64
141.6
140.1
140.9
139.6
138.3
139.2
139.4
139.5
a Polymerization conditions: toluene 70 mL, catalyst 1 ¥ 10-6 mol, B : Zr molar ratio 1.5, time 15 min, ethylene pressure 5 bar. b Activity in g PE (mmol
Zr)-1 h-1 bar-1. c Determined by GPC in o-dichlorobenzene vs. polystyrene standard. d Determined by DSC at a heating rate of 10 ◦C min-1; the data from
the second scan are used.
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Table 3 Summary of ethylene–1-hexene copolymerization catalyzed by 1–4–AliBu3–Ph3CB(C6F5)4 systemsa
◦
e
Run
Catalyst
1-hexene (mol L-1)
Yield (g)
Activityb
1-hexene contentc (mol%)
Mwd ¥ 10-4
Mw/Mnd
Tm ( C)
1
2
3
4
5
6
7
8
1
1
1
1
1
2
2
2
3
3
3
4
0.4
0.6
0.8
1.0
1.2
0.4
0.8
1.2
0.4
0.8
1.2
0.8
0.192
0.250
0.323
0.350
0.532
0.194
0.239
0.265
0.186
0.332
0.500
trace
768
0.64
1.11
2.02
3.75
5.12
trace
040
0.84
trace
0.46
0.90
—
15.1
14.3
12.3
10.4
7.97
14.7
12.8
10.5
18.2
15.6
13.7
—
3.29
3.33
3.52
3.22
3.43
2.94
2.53
2.60
2.20
2.87
3.14
—
131.5
130.8
130.2
129.4
125.5
135.6
133.2
129.5
134.3
131.2
130.2
—
1000
1292
1400
2128
776
956
1060
744
9
10
11
12
1328
2000
—
a Polymerization conditions: toluene + 1-hexene total 70 mL, catalyst 1 ¥10-6 mol, Al : Zr molar ratio 300, B : Zr molar ratio 1.5, time 15 min, temperature
60 ◦C, ethylene pressure 5 bar. b Activity in g polymer (mmol Zr)-1 h-1. c Calculated based on 13C NMR spectra. d Determined by GPC in o-dichlorobenzene
vs. polystyrene standard. e Determined by DSC at a heating rate of 10 ◦C min-1; the data from the second scan are used.
order of 1 > 3 > 2 > 4. The 4–AliBu3–Ph3CB(C6F5)4 catalyst
system shows very low catalytic activity for the copolymerization
reaction and only a trace amount of polymer was obtained. As
discussed above for the ethylene homopolymerization, the low
catalytic activity of the 4–AliBu3–Ph3CB(C6F5)4 catalyst system
may be caused mainly by the difficult activation process of complex
4. The catalytic activity of complexes 1–3 for the copolymerization
reaction was found to increase with an increase of the feed
concentration of 1-hexene from 0.40 mol L-1 to 1.20 mol L-1.
A similar comonomer effect has previously been observed in the
ethylene–1-hexene copolymerization with other zirconium catalyst
systems.32,33
The ethylene–1-hexene copolymers were analyzed by 13C NMR
spectroscopy. The 13C NMR spectrum of a typical copolymer
sample is shown in Fig. 4. No resonance ranging from 40–
42 ppm for the a,a-carbon in the HH dyad sequence34 was
observed in the 13C NMR spectra, indicating that 1-hexene units
are essentially isolated by ethylene units in the polymer chains.
The comonomer content of the ethylene–1-hexene copolymers
were calculated based on 13C NMR analysis,34 and the results
are given in Table 3. It can be seen from these results that
the comonomer incorporation ability of these catalyst systems
is evidently dependent on the structure of the catalyst. The
comonomer content of the copolymers obtained with complex
1 are obviously higher than those of the copolymers produced
by complexes 2 and 3 under similar conditions. The comonomer
incorporation ability of a catalyst system can be affected by several
factors.35 In the present work, the steric bulk of the anilide ligand
seems to be a major factor. An adequate steric hindrance from the
ligands would weaken the interaction between the cationic catalyst
and the anionic cocatalyst species, which would favor coordination
of the comonomer to the metal center of the catalyst. However,
an excessively bulky coordination environment would block the
coordination of the comonomer.36 GPC analysis reveals that the
obtained ethylene–1-hexene copolymers possess relatively high
molecular weight values (Mw = 8–16 ¥ 104 g mol-1). The molecular
weight distribution (MWD) of the copolymers is relatively narrow,
which is characteristic of LLDPE produced using a metallocene
catalyst.37 The molecular weight values of the obtained copolymers
are dependent on the structure of the catalyst and the comonomer
content. In addition, DSC analysis indicates that the melting
temperatures of the resultant copolymers decrease with an increase
in the comonomer content, which is similar to the previous
observations for ethylene–a-olefin copolymers with other single
site catalyst systems.38
Studies on catalyst activation procedure
To understand the activation procedure of these catalyst systems,
reactions of complexes 2 and 4 with AliBu3 and Ph3CB(C6F5)4
were studied by 1H NMR spectroscopy, and the results are shown
in Fig. S1 and S2 in the supporting information.† When complex
2 was treated with about 5 equiv of AliBu3 in C7D8, almost only
signals for complex 2 and AliBu3 can be observed (see A–C in
Fig. S1†) even after the reaction mixture was heated to 60 ◦C for
an hour, indicating that no reaction has taken place. However,
upon addition of Ph3CB(C6F5)4 to the mixture of 2 and AliBu3,
reactions take place immediately with the formation of Ph3CH
(singlet, 5.37 ppm) and CH2 CMe2 (septet, 4.71 ppm and triplet,
1.60 ppm) as seen in Fig. S1D.† Similar results were obtained from
the reaction of 4 with AliBu3 and Ph3CB(C6F5)4 except that this
reaction is relatively slow, as shown in Fig. S2.† The formation of
Ph3CH and CH2 CMe2 was also observed from the reaction of
Fig. 4 13C NMR spectrum for poly(ethylene-co-1-hexene) obtained with
1–AliBu3–Ph3CB(C6F5)4 (run 5 in Table 3).
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AliBu3 and Ph3CB(C6F5)4 as reported previously.39 These observa-
tions imply that the activation of these catalyst systems begins with
the abstraction of a b-H of the AliBu3 by the Ph3C+ cation to form
a iBu2Al+ cation, Ph3CH and CH2 CMe2 as shown in Scheme 2.
The iBu2Al+ cation can react either with AliBu3 to form iBu2AlH,
Experimental
General comments
All manipulations involving air- and/or moisture-sensitive com-
pounds were carried out under a nitrogen atmosphere (ultra-high
purity) using either standard Schlenk techniques or glove box
techniques. Toluene, diethyl ether, and n-hexane were distilled
under nitrogen in the presence of sodium and benzophenone. 1-
i
CH2 CMe2 and a new Bu2Al+ cation, or with the precatalyst
to produce Cp*ZrCl[N(2,6-R1 C6H3)R2]+ and iBu2AlCl. The pro-
2
duced Cp*ZrCl[N(2,6-R1 C6H3)R2]+ further reacts with AliBu3,
2
iBu2AlH or iBu2AlCl to form the final catalytically active species
Cp*ZriBu[N(2,6-R1 C6H3)R2]+ or Cp*ZrH[N(2,6-R1 C6H3)R2]+.
Hexene were purified by distilling over calcium hydride before use.
2
2
Cp*ZrCl3,40 HN(2,6-R1 C6H3)R2 [R1 = Pr, R2 = Me (HLa); R1 =
i
2
The 1H NMR spectra of the 2–AliBu3–Ph3CB(C6F5)4 and 4–
AliBu3–Ph3CB(C6F5)4 mixtures show some broad signals, which
seems to demonstrate that the formed catalytically active species
of half-sandwich zirconium in these systems are either unstable
Me, R2 = Me (HLb); R1 = Pr, R2 = Bn (HLc)]25 and Ph3CB(C6F5)4
i
41
were prepared according to literature procedures. Polymerization
grade ethylene was further purified by passage through columns
i
˚
of 5 A molecular sieves and MnO. Al Bu3, n-BuLi, and ZrCl4
i
or exist in different forms by combining with AliBu3, Bu2AlH,
were purchased from Aldrich or Acros. 1H and 13C NMR spectra
were measured using a Varian Mercury-300 NMR spectrometer.
13C NMR spectra of the copolymers were recorded on a Varian
Unity-400 NMR spectrometer at 125 ◦C with o-C6D4Cl2 as the
solvent. The molecular weight and molecular weight distribution
of the polymer samples were measured on a PL-GPC 220 at 140 ◦C
with 1,2,4-trichlorobenzene as the solvent. The melting points of
the polymer were measured by differential scanning calorimetry
(DSC) on a NETZSCH DSC 204 at a heating/cooling rate of
iBu2AlCl, iBuAlCl2 and B(C6F5)4 . Similar results have been
-
reported in literature.39
◦
10 C min-1 from 35 to 180 ◦C and the data from the second
heating scan were used.
Synthesis of LiN(2,6-R1 C6H3)R2. The lithium salts of the
2
anilide ligands, LiN(2,6-R1 C6H3)R2, were prepared according to
2
the following typical procedure. A solution of n-BuLi (1.60 M in
n-hexane, 14.2 mL, 22.7 mmol) was slowly added to a solution
of HN(2,6-iPr2C6H3)Me (4.34 g, 22.7 mmol) in n-hexane (15 mL)
at -20 ◦C. A large amount of white precipitate formed during
the addition. The reaction mixture was allowed to warm to room
temperature and stirred for 4 h. The resultant precipitate was
collected on a frit, washed with cold n-hexane (2 ¥ 10 mL) and
dried under vacuum to give the pure product (3.09 g, 15.7 mmol,
69%).
Scheme 2 A possible mechanism for the catalyst activation procedure.
Conclusions
A
number of half-zirconocene anilide complexes of the
type and Cp*ZrCl[N(2,6-
Cp*ZrCl2[N(2,6-R1 C6H3)R2]
2
Me2C6H3)Me]2 have been synthesized in good yields from
the reactions of Cp*ZrCl3 with the corresponding lithium anilide.
These new zirconium complexes were all characterized by 1H
and 13C NMR spectroscopy, as well as elemental analysis. Single
crystal X-ray diffraction analysis on complexes 1, 2 and 4 reveals
that these complexes have a pseudo-octahedral coordination
environment in their solid state and adopt a three-legged piano
stool geometry with the anilide N and Cl atoms being the three
legs and the Cp* ring being the seat. Upon activation with AliBu3–
Ph3CB(C6F5)4, complexes 1–4 exhibit good catalytic activity for
ethylene polymerization, producing moderate molecular weight
polyethylene. Complexes 1–3 also show good catalytic activity
for ethylene–1-hexene copolymerization in the presence of
AliBu3–Ph3CB(C6F5)4, producing poly(ethylene-co-1-hexene)s
with relatively high molecular weight. The catalytic activity of
complexes 1–4 for both ethylene polymerization and ethylene–1-
hexene copolymerization changes in the order of 1 > 3 > 2 > 4.
The comonomer incorporation ability of complexes 1–3 under
similar conditions decreases in the order of 1 > 3 > 2. 1H NMR
studies on the reactions of complexes 2 and 4 with AliBu3 and
Ph3CB(C6F5)4 indicate that these zirconium complexes do not
react directly with AliBu3 in the absence of Ph3CB(C6F5)4.
Synthesis of Cp*ZrCl2[N(2,6-iPr2C6H3)CH3] (1). LiN(2,6-
iPr2C6H3)CH3 (0.540 g, 2.74 mmol) was added to a suspension
of Cp*ZrCl3 (0.910 g, 2.74 mmol) in 40 mL diethyl ether at 0 ◦C.
The reaction mixture was allowed to warm to room temperature
and stirred overnight. The solvent was removed under reduced
pressure, and the residue was extracted with 50 mL of hexane.
After fi◦ltration, the filtrate was concentrated to 15 mL and stored
at -25 C several days. Pure 1 was obtained as colorless crystals
(0.865 g, 1.78 mmol, 65%) (Found: C, 57.1; H, 7.20; N 2.83.
C23H35Cl2NZr requires C, 56.7; H, 7.23; N, 2.87%). Mp: 252–
254 ◦C. 1H NMR (CDCl3, 300 MHz, 298 K): d 7.06–7.22 (m, 3H,
ArH), 3.50 (s, 3H, NCH3), 3.00 (sept, 2H, CHMe2, 3JH–H = 6.9 Hz),
1.98 (s, 15H, CpMe5), 1.33 (d, 6H, CHMe2, 3JH–H = 6.9 Hz), 1.14
(d, 6H, CHMe2, 3JH–H = 6.9 Hz). 13C NMR (CDCl3, 75 MHz, 298
K): d 144.3, 126.1, 125.0, 123.8, 122.1, 38.7, 27.2, 27.0, 23.9, 11.8.
Synthesis of Cp*ZrCl2[N(2,6-Me2C6H3)CH3] (2). Complex 2
was synthesized using a procedure identical to that for complex 1
with LiN(2,6-Me2C6H3)CH3 (0.424 g, 3.00 mmol) and Cp*ZrCl3
(1.00 g, 3.00 mmol) as starting materials. Pure 2 was obtained as
colorless crystals (0.921 g, 2.13 mmol, 71%) (Found: C, 52.6; H,
6.38; N, 3.23. C19H27Cl2NZr requires C, 52.9; H, 6.31; N, 3.25%).
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Table 4 Crystallographic parameters, data collections, and structure refinements for complexes 1, 2 and 4
Complexes
1
2
4
Formula
Fw
C23H35Cl2NZr
487.64
C19H27Cl2NZr
431.54
C28H39ClN2Zr
530.28
Wavelength (A)
Crystal system
Space group
0.71073
0.71073
Monoclinic
P2(1)/n
8.189(5)
27.869(19)
9.933(7)
90
114.34
90
2066(2)
4
888
1.388
0.790
0.23 ¥ 0.18 ¥ 0.15
1.46–26.61
12197
4169
0.0497
0.71073 A
Triclinic
P-1
Orthorhombic
P2(1)2(1)2(1)
9.2297(3)
12.1798(4)
21.4452(8)
90
˚
a (A)
8.4521(8)
11.6652(11)
14.8715(14)
85.017(2)
75.515(2)
73.171(2)
1358.7(2)
2
556
1.296
0.520
0.21 ¥ 0.17 ¥ 0.12
1.41–25.04
6859
4699
0.0391
˚
b (A)
˚
c (A)
a (deg)
b (deg)
90
90
g (deg)
3
˚
V (A )
2410.78(14)
4
1016
1.344
0.686
0.23 ¥ 0.16 ¥ 0.12
1.90–26.02
13134
4729
0.0168
Z
F(000)
Dc (g cm-3)
Abs. coeff. (mm-1)
Crystal size (mm)
q range (deg)
No. of reflns
No. of indep. reflns
R(int)
Data/restraints/parameters
GOF
4729/0/254
1.048
0.0208, 0.0525
0.0217, 0.0530
0.293, -0.245
4169/90/302
1.029
0.0438, 0.0989
0.0701, 0.1079
0.472, -0.364
4699/0/300
0.977
0.0523, 0.1055
0.0820, 0.1183
0.548, -0.469
R1, Rw [I > 2s(I)]
R1, Rw (all data)
-3
˚
Max(min) diff. peak (e A )
◦
1
Mp: 129–132 C. H NMR (CDCl3, 300 MHz, 298 K): d 6.97–
7.12 (m, 3H, ArH), 3.41 (s, 3H, NCH3), 2.13 (s, 6H, ArCH3), 1.92
(s,15H, CpMe5). 13C NMR (CDCl3, 75 MHz, 298 K): d 133.2,
128.3 125.3, 124.8, 124.3. 36.0, 17.5, 11.4.
structures were solved by direct method42 and refined by full-
matrix least-squares on F2. The non-hydrogen atoms were refined
anisotropically and hydrogen atoms were included in idealized
position. All calculations were performed using the SHELXTL
crystallographic software packages.43 Details of the crystallo-
graphic parameters, data collections, and structure refinements
are summarized in Table 4.
Synthesis of Cp*ZrCl2[N(2,6-iPr2C6H3)Bn] (3). Compound 3
was synthesized using a procedure identical to that for 1 with
Cp*ZrCl3 (1.00 g, 3.00 mmol) and LiN(2,6-iPr2C6H3)Bn (0.821 g,
3.00 mmol) as starting materials. Pure 3 was obtained as colorless
crystals (1.35 g, 2.39 mmol, 80%) (Found: C, 61.6; H, 6.98; N,
2.46. C29H39Cl2NZr requires C, 61.8; H, 6.97; N, 2.48%). Mp: 222–
225 ◦C. 1H NMR (CDCl3, 300 MHz, 298 K): d 6.94–7.22 (m, 8H,
ArH), 4.85 (s, 2H, NCH2), 2.98 (sept, 2H, CHMe2, 3JH–H = 6.6 Hz),
2.10 (s, 15H, CpMe5), 1.22 (d, 6H, CHMe2, 3JH–H = 6.6 Hz), 0.59
(d, 6H, CHMe2, 3JH–H = 6.6 Hz). 13C NMR (CDCl3, 75 MHz, 298
K): d 145.4, 137.7, 130.4, 128.1, 127.6, 126.3, 125.5, 124.1, 54.3,
27.4, 25.9, 25.0, 12.1.
Polymerization reactions
The ethylene polymerization experiments were carried out as
follows: A dry 250 mL steel autoclave with a magnetic stirrer
was charged with 60 mL of toluene, thermostated at the de-
sired temperature and saturated with ethylene (1.0 atm). The
polymerization reaction was started by addition of a mixture
of the catalyst and AliBu3 in toluene (5 mL) and a solution of
Ph3CB(C6F5)4 in toluene (5 mL) at the same time. The vessel
was pressurized to 5 atm with ethylene immediately and the
pressure was maintained by continuous feeding of ethylene. The
reaction mixture was stirred at the desired temperature for 15 min.
The polymerization was then quenched by injecting acidified
ethanol containing HCl (3 M). The polymer was collected by
filtration, washed with water and ethanol, and dried to a constant
weight under vacuum. For the ethylene–1-hexene copolymeriza-
tion experiments, appropriate amounts of 1-hexene were added in
toluene.
Synthesis of Cp*ZrCl[N(2,6-Me2C6H3)CH3]2 (4). Complex 4
was synthesized using a procedure identical to that for complex 1
with LiN(2,6-Me2C6H3)CH3 (0.423 g, 3.00 mmol) and Cp*ZrCl3
(0.500 g, 1.50 mmol) as starting materials. Pure 3 was obtained as
colorless crystals (0.599 g, 1.13 mmol, 75%) (Found: C, 63.6; H,
7.48; N, 5.26. C28H39ClN2Zr requires C, 63.4; H, 7.41; N, 5.28%).
◦
1
Mp: 120–123 C. H NMR (CDCl3, 300 MHz, 298 K): d 6.99
(d, 4H, ArH, 3JH–H = 7.5 Hz), 6.87 (t, 2H, ArH, 3JH–H = 7.5 Hz),
2.85 (s, 6H, NCH3), 2.17 (s, 12H, ArCH3), 1.91 (s, 15H, CpMe5).
13C NMR (CDCl3, 75 MHz, 298 K): d 151.9, 128.3, 128.1, 124.2,
121.9, 37.6, 31.2, 11.2.
Acknowledgements
X-Ray structural analysis of complexes 1, 2 and 4
All measurements were made on a Rigaku RAXIS-RAPID
This work was supported by the National Natural Science
Foundation of China (Nos. 21074043 and 20772044).
˚
diffractometer with Mo-Ka (l = 0.71073 A) radiation. The
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©