Highly thermally stable eight-coordinate dichloride zirconium complexes supported by tridentate [ONN] ligands: Syntheses, characterization, and ethylene polymerization behavior

Article abstract of DOI:10.1021/om4009636

A series of novel eight-coordinate dichloride zirconium complexes with the general formula L₂ZrCl₂ supported by two tridentate [ONN] ligands have been synthesized by the reaction of ZrCl₄·2THF with 2 equiv of the correspon

Full text of DOI:10.1021/om4009636

Article
pubs.acs.org/Organometallics
Highly Thermally Stable Eight-Coordinate Dichloride Zirconium
Complexes Supported by Tridentate [ONN] Ligands: Syntheses,
Characterization, and Ethylene Polymerization Behavior
Aike Li, Haiyan Ma,* and Jiling Huang*
Laboratory of Organometallic Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237,
People’s Republic of China
S
* Supporting Information
ABSTRACT: A series of novel eight-coordinate dichloride zirconium complexes with the general formula L2ZrCl2 supported by
two tridentate [ONN] ligands have been synthesized by the reaction of ZrCl4·2THF with 2 equiv of the corresponding ligands
(tridentate phenoxy-imine ligands (L1H−L4H) or tridentate phenoxy-amine ligands (L5H and L6H)). These complexes were
characterized by NMR and elemental analyses. The molecular structures of representative zirconium complexes C2 and C6 were
confirmed by single-crystal X-ray diffraction and revealed that the metal center is eight-coordinated by two tridentate [ONN]
ligands and two chlorides in a distorted-square-antiprismatic geometry. When C1−C6 were activated by modified
methylaluminoxane (MMAO), the resultant catalysts displayed notable thermal stability and high activities toward ethylene
polymerization. The ligand substituents, the metal coordination environment, and the reaction conditions had a profound effect
on the polymerization. The catalytic activity increases consistently with increasing polymerization temperature, and the highest
activity of 1.04 × 106 g of PE (mol of Zr)−1 h−1 was achieved in o-xylene at 140 °C. A catalytic lifetime of nearly 5 h was observed
for the C5/MMAO catalyst system at 140 °C.
development of new catalysts that are stable and maintain
high activity at elevated temperatures is quite desirable. To
date, there are only a few examples of catalysts that are
thermally stable and active at temperatures close to or higher
than 100 °C among the many reports in the literature.6,31−41 In
2000, Yoshifuji and co-workers reported a dimethylpalladium
complex based on a phosphorus bidentate ligandl when it was
activated with H(OEt2)2BAr4, the generated active species
showed high thermal stability and moderate activity toward
ethylene polymerization (9.07 × 104 g of PE (mol of Pd)−1
h−1) at 100 °C.32 The author proposed that this remarkable
behavior may be attributed to the coordination of the
phosphorus-based ligand with the palladium center. In 2002,
Fujita and co-workers reported that bis(phenoxy-imine)
zirconium complexes possessing an electron-donating methoxy
group para to the phenolic oxygen (FI catalysts) exhibited very
high activities up to 1697 kg of PE (mmol of Zr)−1 h−1 for
ethylene polymerization at 90 °C.6,7 Pyridyl-amide hafnium
INTRODUCTION
■
In recent years, the nonmetallocene single-site catalysts have
drawn considerable attention in both academic and industrial
fields due to their high catalyst efficiencies and ability to
provide greater control of molecular weight distributions and
polymer microstructures.1−8 Among the most significant results
in this field are highly active catalysts based on Pd(II) and
Ni(II) α-diimine complexes,9−14 Fe(II) and Co(II) pyridine
diimine complexes,15−17 salicylaldiminato-based nickel cata-
lysts,18−20 bis(phenoxy-imine) group 4 complexes,6−8 and
tridentate and tetradentate metal complexes.21−30 Despite the
fact that these catalysts exhibit excellent catalytic properties,
their industrial utility is generally limited by their thermal
instability at elevated temperatures. Moreover, the mean
molecular weight of the polyethylene product generally
decreases as the reaction temperature increases.7,24
From the aspect of industrial applications, the thermal
stability of olefin polymerization catalysts is very important,
because performing a solution polymerization at high temper-
ature can reduce the viscosity of the reaction system, thus
leading to better mass transportation.31 Therefore, the
Received: September 30, 2013
© XXXX American Chemical Society
A
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Scheme 1. General Synthetic Route of the Ligands L1H−L6H
Scheme 2. Synthesis of Bis(ligand) Dichloride Zirconium Complexes C1, C2, C5, and C6
Scheme 3. Synthesis of Bis(ligand) Dichloride Zirconium Complexes C3 and C4
complexes, developed by the Dow Chemical Co., are well-
known to prepare olefin block copolymers and isotactic
polypropylene conducted in a solution polymerization process
at high temperatures (>100 °C).35−37 This catalyst system
typically generates productivities as high as 300 kg of polymer/
g of Hf, equivalent to nearly two million insertions during its
lifetime. Very recently, Tang developed a series of tridentate
trichloride titanium complexes bearing extra pendant S and P
donors on phenoxy-imine ligands,41 which exhibited good
thermal stability and high activities toward ethylene polymer-
ization. A high activity of 1.26 × 106 g of PE (mol of Ti)−1 h−1
was obtained at reaction temperatures up to 110 °C. However,
after 30 min beyond the period no increase in polymer yield
was observed.
we first report the syntheses and characterization of a series of
novel eight-coordinate dichloride zirconium complexes sup-
ported by two tridentate [ONN] ligands. When these
complexes were activated with modified methylaluminoxane
(MMAO), the resultant catalyst species showed notable
thermal stabilities and high activities for ethylene polymer-
ization at temperatures ranging from 110 to 140 °C. The C5/
MMAO catalyst system displayed the highest activity of 1.04 ×
106 g of PE (mol of Zr)−1 h−1 with a lifetime of at least 5 h at
140 °C. Modification of the ligand architecture has a strong
influence on the catalytic activity and the molecular weight of
the resultant polymers. The effects of the polymerization
conditions are discussed in detail.
RESULTS AND DISCUSSION
On the other hand, it is worth noting that the formation of
eight-coordinate geometry dichloride group 4 complexes
supported by tridentate ligands is rarely observed.40 Herein,
■
Synthesis and Characterization of Ligands L1H−L6H
and Complexes C1−C6. The general synthetic routes for
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Figure 1. ORTEP drawing of the molecular structure of C2. Thermal ellipsoids are at the 50% probability level. All hydrogen atoms and
uncoordinated toluene solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Zr1−O1 = 2.059(3), Zr1−O2 =
2.050(3), Zr1−N1 = 2.369(3), Zr1−N2 = 2.521(4), Zr1−N3 = 2.376(4), Zr1−N4 = 2.495(4), Zr1−Cl1 = 2.5427(13), Zr1−Cl2 = 2.5342(15), N1−
C7 = 1.265(6), N3−C37 = 1.280(5); O1−Zr1−N1 = 69.79(12), N1−Zr1−N2 = 65.80(12), N2−Zr1−Cl1 = 79.23(9), O1−Zr1−Cl1 = 145.18(9),
Cl1−Zr1−Cl2 = 91.83(5), O1−Zr1−O2 = 98.52(13), N1−Zr1−N3 = 129.54(13), N2−Zr1−N4 = 144.83(13), O1−Zr1−Cl2 = 95.10(10), N1−
Zr1−Cl2 = 75.64(10), N2−Zr1−Cl2 = 76.29(10), N1−Zr1−Cl1 = 144.66(9).
tridentate [ONN] ligands are shown in Scheme 1. Ligands
L1H−L4H were synthesized by the Schiff base condensation of
corresponding substituted o-aminophenol with pyridine-2-
aldehyde or quinoline-2-aldehyde using acetic acid as catalyst.
Ligands L5H and L6H were obtained easily in high yield by
reduction of the corresponding tridentate phenoxy-imine
derivatives L2H and L3H with excess NaBH4 in ethanol.
They have been well characterized by elemental analyses and
the signals observed for the protons ortho to the pyridine (C1−
C3) or quinoline group (C4) shifted dramatically downfield by
1.12−1.75 ppm relative to those of the free ligands. These
results indicate that the ligands are bound to the zirconium
center in a tridentate fashion by the phenolate and the imine
group and the nitrogen atom from the pyridine or quinoline
1
moiety. In addition, the H NMR spectra showed one set of
resonances for the ligands in C1−C4 in chloroform-d,
consistent with the formation of a single isomer with two
symmetry-related tridentate ligands. For example, the 1H NMR
spectra of C1 showed two singlets for the four tert-butyl groups
at 1.25 and 0.82 ppm and a singlet for the two imine CHN
groups at 8.75 ppm. The signals for the eight CH protons of the
two pyridyl groups were observed at 10.20, 8.00, 7.87, and 7.50
ppm.
1
1H and 13C NMR. H NMR analysis of ligands L5H and L6H
revealed no signals for imine CHN protons, whereas a new
resonance appeared for the CH2NH protons at 4.32 and 4.42
ppm for L5H and L6H, respectively. These results indicate that
CHN (imine) has been transformed into CH2NH (amine).
The bis(ligand) dichloride zirconium complexes C1, C2, C5,
and C6 were synthesized from ZrCl4·2THF and 2 equiv of the
corresponding ligands in the presence of triethylamine in good
yields (70.7−77.2%), as shown in Scheme 2. These compounds
were recrystallized from tetrahydrofuran (THF) or toluene
solution. Alternatively, the corresponding zirconium analogues,
C3 and C4, were prepared by the reaction of ZrCl4·2THF with
2 equiv of the corresponding lithium salt of L3H and L4H in
THF (Scheme 3). Purification of C3 and C4 was performed by
recrystallization from dichloromethane solution upon cooling
to −30 °C. It is worth noting that only the bis(ligand)
dichloride complexes were isolated, even when only 1 equiv of
ligand was used. Zirconium complexes C1−C6 were
characterized by elemental analyses and NMR spectroscopy;
the molecular structures of C2 and C6 were determined by
single-crystal X-ray diffraction analysis.
As observed for C1−C4, zirconium complex C6 also existed
as a single isomer with two symmetry-related tridentate
phenoxy-amine ligands. The two protons of the CH2NH
groups were observed as a triplet at 4.82 ppm. The chemically
inequivalent methylene protons of the CH2NH moiety
appeared as separate doublets of doublets centered at 4.28
and 3.39 ppm (J = 13.1, 4.1 Hz).
Interestingly, all regions of the 1H NMR spectra of tridentate
phenoxy-amine ligated zirconium complex C5 revealed the
presence of a minor amount of isomers at a level of about 9% in
chloroform-d solution. However, it was found that the chemical
shifts and the multiplicity are very similar between the two
1
isomers. In the H NMR spectra of C5, the four methylene
protons of CH2NH appeared as two separated doublets of
doublets at 4.17 and 3.41 ppm (J = 14.3, 4.0 Hz) for the major
isomer and at 4.07 and 3.35 ppm (J = 12.0, 3.5 Hz) for the
minor isomer, respectively. The CH2NH groups were detected
as a triplet at 4.72 ppm (J = 13.2 Hz) for the major isomer and
at 4.81 ppm (J = 12.8 Hz) for the minor isomer. These results
indicate that the minor isomer appears to be structurally similar
to the major isomer. In solution, FI catalysts often exist as a
1
In the H NMR spectra of the tridentate phenoxy-imine
ligated zirconium complexes C1−C4, the chemical shifts of the
phenoxy protons in the corresponding ligands (at 7.77, 7.45,
7.37, and 7.48 ppm for ligands L1H−L4H, respectively)
disappeared and the chemical shifts of the imine CHN
proton resonances were shifted upfield by 0.12−1.80 ppm
relative to those of the corresponding free ligand. Furthermore,
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Figure 2. ORTEP drawing of the molecular structure of C6. Thermal ellipsoids are at the 50% probability level. All hydrogen atoms (except those on
N1 and N3) and uncoordinated THF solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Zr1−O1 = 2.066(3),
Zr1−O2 = 2.063(3), Zr1−N1 = 2.403(3), Zr1−N2 = 2.521(4), Zr1−N3 = 2.417(3), Zr1−N4 = 2.498(3), Zr1−Cl1 = 2.5415(11), Zr1−Cl2 =
2.5406(11), N1−C7 = 1.470(5), N3−C42 = 1.473(6); O1−Zr1−N1 = 70.25(11), N1−Zr1−N2 = 65.61(11), N2−Zr1−Cl2 = 80.36(8), O1−Zr1−
Cl2 = 144.65(8), Cl1−Zr1−Cl2 = 99.90(4), O1−Zr1−N2 = 134.82(11), O1−Zr1−O2 = 102.04(11), N1−Zr1−N3 = 119.97(11), N2−Zr1−N4 =
139.27(11), O1−Zr1−Cl1= 89.52(8), N1−Zr1−Cl1 = 79.79(8), N2−Zr1−Cl1 = 74.00(8), N1−Zr1−Cl2 = 144.81(8).
mixture of configurational isomers that stem from different
coordination modes of the two phenoxy-imine ligands.7 In
addition, it should be noted that the trans-N/cis-O/cis-Cl
isomer is preferred in FI catalysts with more bulky substituents
on the imine nitrogen.7,47 Considering what is observed in FI
catalysts, we tentatively think that the isomers in complex C5
may also stem from the different coordination modes of the
two tridentate ligands.42−46 In contrast, complex C6, with a
more bulky triphenylmethyl group near the metal center, exists
as only one isomer in solution.
X-ray Crystallographic Studies. The molecular structures
of complexes C2 and C6 with selected bond distances and
angles are shown in Figures 1 and 2, respectively. As shown in
Figure 1, the X-ray structural analysis of complex C2 shows that
in the solid state the zirconium atom is bound to two tridentate
[ONN] ligands and two chlorides in a distorted-square-
antiprismatic geometry. The zirconium atom is located in the
plane defined by three donor atoms from the same tridentate
phenoxy-imine ligand and one chloride. The Zr1 atom slightly
deviates from the planes constructed by the coordinated atoms
(O1, N1, N2, Cl1 and O2, N3, N4, Cl2) by about 0.0373 and
0.0519 Å, respectively. The sum of the O1−Zr1−N1 =
69.79(12)°, N1−Zr1−N2 = 65.80(12)°, N2−Zr1−Cl1 =
79.23(9)°, and O1−Zr1−Cl1 = 145.18(9)° bond angles is
nearly 360°. Moreover, the mean planes of the two tridentate
phenoxy-imine ligands coordinated to the zirconium center are
nearly orthogonal with a dihedral angle of 95.3°. The Cl1−
Zr1−Cl2 angle is 91.83(5)°, indicating that the two chlorides
are located in positions cis to each other, which is favorable for
ethylene polymerization. The average Zr−ligand bond
distances (Zr−O = 2.054(5) Å, Zr−N(imine) = 2.372(5) Å,
Zr−N(pyridyl) = 2.508(4) Å, Zr−Cl = 2.5384(5) Å) are
comparable to those observed in six-coordinate zirconium
complexes which contain phenoxy-imine ligands or pyridyl
derivatives.21−24,48−54 In addition, in complex C2, the imine
CN bond has a distinctive double-bond character (N1−C7 =
1.265(6) Å, N3−C37 = 1.280(5) Å).
The molecular structure of C6, as shown in Figure 2, is
comparable to that of C2. The average Zr−ligand bond
distances (Zr−O = 2.064(5) Å, Zr−N(amine) = 2.410(3) Å,
Zr−N(pyridyl) = 2.509(5) Å, Zr−Cl = 2.5410(5) Å) of C6 are
slightly longer than those observed for C2. In addition, the
Cl1−Zr−Cl2 bond angle of 99.90(4)° is significantly larger
than that of 91.83(5)° in C2. The amine C−N bond distances
(N1−C7 = 1.470(5) Å, N3−C42 = 1.473(6) Å) are in the
range of carbon−nitrogen single-bond distances.
Ethylene Polymerization. The activation of C1−C6 with
MMAO afforded catalysts for promoting ethylene polymer-
ization in toluene. As shown in Table 1, these Zr-based catalysts
displayed notable thermal stability and high activities toward
ethylene polymerization at a high temperature of 110 °C and
afforded high-molecular-weight polyethylene.
The structures of the complexes have a pronounced influence
on the catalytic activity and the molecular weight (Mv) of the
obtained polyethylene (entries 1−6 in Table 1; see also Figure
3). The tridentate phenoxy-imine ligated zirconium complex
C1 bearing tert-butyl groups at the R1 and R2 positions of the
ligand gave high-molecular-weight polyethylene (Mv = 24.4 ×
104 g/mol) with a catalytic activity of 0.53 × 106 g of PE (mol
of Zr)−1 h−1. When the steric bulk of the substituents of the
ligand was increased, the zirconium analogue C2 (R1 = R2 =
CMe2Ph) exhibited relatively low catalytic activity but gave
higher molecular weight polyethylene (0.32 × 106 g of PE (mol
of Zr)−1 h−1, Mv = 31.9 × 104 g/mol). Moreover, complex C3
with a sterically bulky triphenylmethyl ortho to the phenoxy
oxygen (R1) showed the lowest catalytic activity (0.29 × 106 g
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sterically larger triphenylmethyl group at the R1 position (entry
5 vs 6). Generally, greater steric hindrance near the active metal
center is beneficial to increasing the molecular weight of
polyethylene.7,17 As investigated by Fujita and co-workers using
bis(phenoxy-imine) zirconium complexes, by increasing the
size of the ortho substituents on the aniline moiety, the
molecular weight of polyethylene increases in the following
order: H < Me < Pr < Bu. The increase in the Mv value may
reflect a concomitant decrease in the β-hydride elimination rate
by sterically impeding the chain transfer reactions.48
In comparison with complex C2, the analogue C4 bearing a
quinolinyl donor (R3 = R4 = benzo) displayed much higher
catalytic activity (0.57 × 106 g of PE (mol of Zr)−1 h−1) than
the corresponding catalyst with a pyridyl donor due to the
difference in the pendant donors (entry 2 vs 4). Complex C5
displayed the highest catalytic activity of 0.60 × 106 g of PE
(mol of Zr)−1 h−1 under the same conditions, due to the
difference in the phenoxy-amine and phenoxy-imine skeletons
(entry 2 vs 5). Similarly, a significant increase in catalytic
activity was also observed for complex C6 in comparison with
the case of complex C3 (entry 3 vs 6). This could be attributed
to the more electron-donating nature of the phenoxy-amine
ligand in comparison to that of the phenoxy-imine ligand. The
introduction of an electron-donating group is beneficial to
strengthen the bonds between the zirconium metal and the
ligand, thus improving the stability of the catalytically active
species and leading to higher activity.56−59
Table 1. Ethylene Polymerization Results Catalyzed by
Zirconium Complex C1−C6/MMAO Catalytic Systems in
a
Toluene
c
Al/Zr
(molar
ratio)
C2H4
Mv
temp pressure
yield
(mg) activity
(104 g/
mol)
b
entry catalyst
(°C)
(MPa)
1
C1
C2
C3
C4
C5
C6
C5
C5
C5
C5
C5
C5
C5
C5
C5
5000
5000
5000
5000
5000
5000
2500
7500
10000
5000
5000
5000
5000
5000
5000
110
110
110
110
110
110
110
110
110
70
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.2
0.4
0.6
0.8
1050
645
571
1141
1191
867
385
1364
1277
39
0.53
0.32
0.29
0.57
0.60
0.43
0.19
0.68
0.64
0.02
0.21
0.08
0.15
0.26
0.42
24.4
31.9
42.7
20.5
i
t
2
3
4
d
5
29.5
6
38.4
33.8
21.9
17.6
35.8
33.7
24.2
25.2
27.9
29.1
7
8
9
10
11
12
13
14
15
90
413
154
301
512
841
110
110
110
110
a
Polymerization conditions: 2 μmol of catalyst, 60 min, toluene (total
b
c
volume 25 mL). Activity in 106 g of PE (mol of Zr)−1 h−1. The
intrinsic viscosity was determined in decahydronaphthalene at 135 °C,
and molecular weight was calculated using the relatio: [η] = (6.77 ×
d
10−4)Mv0.67. Mw and Mw/Mn were determined by GPC. For entry 5,
Mw = 20.2 × 104 g/mol, Mw/Mn = 2.61.
To investigate the reaction parameters affecting the polymer-
ization of ethylene, the performance of precatalyst C5 was
investigated in detail by changing the reaction parameters such
as Al/Zr molar ratio, polymerization temperature, and ethylene
pressure (entries 5 and 7−15). The variation of the MMAO/Zr
molar ratio had a significant influence on the catalytic activity
and the molecular weight of the resultant polyethylene (entries
5 and 7−9). As the Al/Zr molar ratio increased from 2500 to
7500, the catalytic activity increased from 0.19 × 106 to 0.68 ×
106 g of PE (mol of Zr)−1 h−1. However, a further increase of
the Al/Zr molar ratio to 10000 resulted in a slightly reduced
catalytic activity (entry 9). In addition, the Mv value of the
resultant polyethylene was significantly decreased when the Al/
Zr molar ratio increased, which is possibly due to the enhanced
rate of chain transfer to aluminum for the termination.60
The catalytic activity was also influenced by reaction
temperature. The catalytic activity improved appreciably from
0.02 × 106 g of PE (mol of Zr)−1 h−1 at 70 °C to 0.60 × 106 g
of PE (mol of Zr)−1 h−1 at 110 °C (entries 5, 10, and 11). In
addition, the Mv value of resultant polyethylene slightly
decreased upon an increase in the temperature. This can be
attributed to a facilitated chain transfer reaction at elevated
temperatures.24 When the ethylene pressure was increased,
both the catalytic activity and the molecular weight increased
consistently (entries 5 and 12−15).
Figure 3. Catalytic activities of complexes C1−C6 at different
conditions. Polymerization conditions: (A) 110 °C, toluene as solvent
(entries 1−6 in Table 1); (B) 110 °C, o-xylene as solvent (entries 16−
21 in Table 2); (C) 140 °C, o-xylene as solvent (entries 22−27 in
Table 2).
of PE (mol of Zr)−1 h−1, Mv = 42.7 × 104 g/mol) for ethylene
polymerization under the same conditions. The catalytic
t
activity followed the order C3 (R1 = CPh3, R2 = Bu) < C2
t
(R1 = R2 = CMe2Ph) < C1 (R1 = R2 = Bu). These results
To further examine the thermal stability of these zirconium
complexes, a series of ethylene polmyerizations were carried
out using o-xylene as solvent at much higher temperatures
(110−140 °C). The results are summarized in Table 2 (see also
Figure 3). Under the same conditions, C1−C6 exhibited
somewhat lower activities but gave higher molecular weight
polyethylene in comparison to that obtained in toluene (entries
1−6 in Table 1 vs entries 16−21 in Table 2).
indicate that the catalytic activity decreases upon increasing the
steric size of the R1 group, which is presumably located near the
active metal center in the corresponding catalytic species
generated from its [ONN]2ZrCl2 precursor.7,48 A similar trend
was also observed for tridentate phenoxy-amine ligated
zirconium complexes C5 and C6. Complex C5, which features
a CMe2Ph group at the R1 position, was beneficial to the
catalytic activity (0.60 × 106 g of PE (mol of Zr)−1 h−1, Mv =
29.5 × 104 g/mol) in comparison with complex C6 (0.43 × 106
g of PE (mol of Zr)−1 h−1, Mv = 38.4 × 104 g/mol), which has a
The thermal stability of the C5/MMAO catalyst system was
further investigated by conducting ethylene polymerizations at
140 °C for varying polymerization times (Figure 4, entries 26
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time to 6 h resulted in a very slight increase of the polymers
(entry 38). This is presumably due to the limited ethylene
uptake in the reaction mixture, because the polymerization
mixture became more and more viscous after a long period of
polymerization. These results indicate that the catalyst has a
minimal lifetime of 5 h. In contrast, most of those reported six-
coordinate FI catalysts generally suffer from thermal instability
and their catalytic activities decayed rapidly at elevated
temperatures.6−8 These eight-coordinate zirconium complexes
with remarkable thermal stability may be attributable to the
good coordination ability of the two tridentate [ONN] ligands
which can stabilize the active catalytic species with higher
coordination numbers and sufficient steric protection better
than bidentate phenoxy-imine ligands.55,61
Table 2. Ethylene Polymerization Results Catalyzed by
Zirconium Complex C1−C6/MMAO Catalytic Systems in o-
a
Xylene
c
temp
(°C)
time
(min)
yield
(mg)
Mv (104 g/
b
entry catalyst
activity
mol)
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
C1
C2
C3
C4
C5
C6
C1
C2
C3
C4
C5
C6
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
C5
110
110
110
110
110
110
140
140
140
140
140
140
120
130
140
140
140
140
140
140
140
140
140
60
60
816
497
0.41
0.25
0.21
0.47
0.45
0.37
0.84
0.56
0.47
0.95
1.04
0.63
0.67
0.86
0.81
0.93
1.00
0.82
0.71
0.59
0.51
0.42
0.35
30.7
37.1
52.7
26.8
38.8
50.2
8.3
60
413
60
931
60
907
60
733
60
1675
1122
937
d
60
12.2
60
15.5
7.7
1H and 13C NMR analysis indicated that the resultant
polyethylene are highly linear with no detectable branches
(Figure S25, Supporting Information). According to the results
of differential scanning calorimetry (DSC), the polyethylene
product showed high melting points (Tm) in the range of 135−
142 °C, which also indicates that the polymer is a linear
polyethylene.62 In addition, the selected gel permeation
chromatography (GPC) analysis of the resultant polyethylene
revealed a narrow molecular weight distribution (Mw/Mn)
(sample of entry 5, 2.61; sample of entry 23, 2.29; sample of
entry 26, 2.46; sample of entry 27, 2.08), suggesting that the
polymer is produced by a single active species (Figures S27−
S30, Supporting Information).
60
1891
2070
1257
1339
1722
407
e
60
9.7
f
60
15.4
60
31.3
17.3
7.2
60
15
30
925
7.5
45
1505
2471
2822
3532
4042
4182
4213
8.6
90
10.3
10.9
11.2
11.3
11.3
11.5
120
180
240
300
360
a
CONCLUSIONS
Polymerization conditions: 2 μmol of catalyst, o-xylene (total volume
■
b
25 mL), Al/Zr molar ratio 5000, ethylene pressure 1.0 MPa. Activity
In summary, a series of eight-coordinate dichloride zirconium
complexes supported by two tridentate [ONN] ligands have
been synthesized and well characterized. The crystal structures
of complexes C2 and C6 were similar in that the zirconium
complexes adopt a eight-coordinate distorted-square-antipris-
matic geometry bearing two tridentate [ONN] ligands and two
chlorides. In the presence of MMAO, these zirconium
complexes showed notable thermal stability and high activities
toward ethylene polymerization at high temperature. The
highest catalytic activity of 1.04 × 106 g of PE (mol of Zr)−1 h−1
and a long lifetime of at least 5 h were observed on the basis of
the complex C5/MMAO catalyst system at 140 °C. This
remarkable thermal stability may be attributable to the good
coordination ability of the two tridentate [ONN] ligands that
possessed a pyridine or quinoline group as a pendant donor
which can stabilize the active catalytic species with higher
coordination numbers and sufficient steric protection. More-
over, the catalytic activity and the molecular weight of the
obtained polyethylene could be tuned by changing catalyst
structures and polymerization conditions. Therefore, the
zirconium complexes introduced in this paper have high
potential in developing efficient olefin polymerization catalysts
used in solution polymerization at high temperatures.
c
in 106 g of PE (mol of Zr)−1 h−1. The intrinsic viscosity was
determined in decahydronaphthalene at 135 °C, and the molecular
weight was calculated using the relation [η] = (6.77 × 10−4)Mv0.67
.
d
Mw and Mw/Mn were determined by GPC. For entry 23, Mw = 8.8 ×
e
104 g/mol, Mw/Mn = 2.29. For entry 26, Mw = 6.6 × 104 g/mol, Mw/
f
Mn = 2.46. For entry 27, Mw = 9.9 × 104 g/mol, Mw/Mn = 2.08.
●
Figure 4. Plots of polymerization time versus catalytic activity ( ) and
□
polymer yield ( ) of the resultant polyethylene obtained by C5/
EXPERIMENTAL SECTION
MMAO at 140 °C (entries 26 and 30−38 in Table 2).
■
General Considerations. All manipulations of air- and/or
moisture-sensitive compounds were performed under a dry argon
atmosphere using standard Schlenk techniques unless otherwise
indicated. Dichloromethane and chloroform-d were dried over calcium
hydride under argon prior to use. Toluene, o-xylene, petroleum ether,
and tetrahydrofuran (THF) were refluxed with sodium/benzophenone
ketyl and distilled under argon prior to use. Polymerization-grade
ethylene was directly used. ZrCl4 and modified methylaluminoxane
(MMAO) (2.5 M in toluene) were purchased from Sigma-Aldrich.
and 30−38 in Table 2). When the polymerization time was
prolonged, the catalytic activity increased in the early stage and
then decreased slowly. The highest activity of 1.04 × 106 g of
PE (mol of Zr)−1 h−1 was achieved in 1 h (entry 26). However,
the yield of the obtained polyethylene continuously increased
from 2070 to 4182 mg with polymerization time over the range
of 1−5 h, while further enhancement of the polymerization
F
dx.doi.org/10.1021/om4009636 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
nBuLi (2.4 M in n-hexane), NaBH4, SeO2, 2-methylquinoline,
pyridine-2-aldehyde, and substituted phenol were purchased from
J&K Chemical Ltd. Various o-aminophenols with different substituents
on the R1 and R2 positions were prepared by a procedure similar to
that in the literature.24 Quinoline-2-aldehyde and ZrCl4·2THF were
synthesized according to the published procedures.26,63 All other
chemicals were commercially available and used as received.
H), 1.20 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ 156.37,
154.55, 149.83, 149.36, 145.62, 141.67, 136.78, 134.01, 133.10, 131.24,
129.29, 127.32, 125.86, 125.25, 121.35, 111.58, 63.56, 34.73, 31.58.
Anal. Calcd for C35H32N2O: C, 84.64; H, 6.49; N, 5.64. Found: C,
84.63; H, 6.50; N, 5.59.
Synthesis of 2-[(Quinolin-2-yl)methyleneamino]-4,6-dicu-
mylphenol (L4H). To a stirred solution of 2-amino-4,6-dicumylphe-
nol (1.036 g, 3.0 mmol) in anhydrous ethanol (40 mL) were added
quinoline-2-aldehyde (0.495 g, 3.2 mmol) and a catalytic amount of
acetic acid. The mixture was refluxed and stirred for 6 h. When the
solution was cooled to ambient temperature, blue crystals were
Measurements. NMR spectra of ligands and complexes were
recorded on Bruker AVANCE-400 spectrometers with CDCl3 as the
1
solvent at ambient temperature. H and 13C NMR chemical shifts are
reported in ppm using the residual solvent resonances or reported
relative to tetramethylsilane. Elemental analyses (C, H, N) were
carried out on an EA-1106 type analyzer. IR spectra were recorded on
1
obtained in 81.7% yield (1.188 g). Mp: 154−156 °C. H NMR (400
MHz, CDCl3): δ 8.85 (s, 1H, CHN), 8.14−8.05 (m, 3H, quino-H),
7.78 (d, 1H, J = 8.0 Hz, quino-H), 7.70 (t, 1H, J = 7.7 Hz, quino-H),
7.53 (t, 1H, J = 7.4 Hz, quino-H), 7.48 (s, 1H, ArOH), 7.32−7.29 (m,
2H, Ar-H), 7.27−7.20 (m, 8H, Ar-H), 7.18−7.10 (m, 2H, Ar-H), 1.70
(s, 6H, CH3), 1.65 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3): δ
156.23, 154.70, 150.89, 150.69, 149.35, 148.12, 141.57, 136.81, 135.27,
133.79, 130.28, 129.70, 128.97, 128.27, 128.04, 127.97, 127.95, 126.89,
125.93, 125.89, 125.47, 118.19, 112.76, 43.11, 42.33, 31.24, 29.48.
Anal. Calcd for C34H32N2O: C, 84.26; H, 6.66; N, 5.78. Found: C,
84.13; H, 6.68; N, 5.72.
1
a Perkin-Elmer System 2000 FT-IR spectrometer. H and 13C NMR
spectra of the obtained polyethylene were recorded on a Bruker
ADVANCE-500 spectrometer using 1,2-dichlorobenzene-d4 as solvent
at 100 °C. Differential scanning calorimetry (DSC) traces and melting
points of polyethylene were obtained from the second scanning run on
a Universal V2.3C TA Instruments at a heating rate of 10 °C/min. The
intrinsic viscosities (η) of the obtained polyethylene were measured
with an Ubbelohde viscometer in decahydronaphthalene at 135 °C,
and viscosity average molecular weights (Mv) were calculated as
follows: [η] = (6.77 × 10−4)Mv0.67 64 Molecular weights (Mn and Mw)
.
Synthesis of 2-[(Pyridin-2-yl)methylamino]-4,6-dicumylphe-
nol (L5H). To a stirred solution of 2-[(pyridin-2-yl)methyleneamino]-
4,6-dicumylphenol (L2H) (1.738 g, 4.0 mmol) in anhydrous ethanol
(30 mL) was slowly added NaBH4 (1.362 g, 36.0 mmol). After the
mixture was stirred for 5 h at room temperature, acetone (5 mL) and
water (30 mL) were added sequentially at 0 °C. The mixture was
extracted with CH2Cl2 (3 × 60 mL), and the organic layer was dried
over Na2SO4. Then the volatiles were removed under vacuum, and the
crude product was recrystallized from a ethanol/petroleum ether
mixture. The product L5H was obtained as a pale red powder in 83.1%
and polydispersities (Mw/Mn) of the obtained polyethylene were
determined by high-temperature GPC using a PL-GPC 220 instru-
ment with 1,2,4-trichlorobenzene as the solvent at 150 °C, at a flow
rate of 1.0 mL/min. The calibration was made by polystyrene standard
samples.
Synthesis of 2-[(Pyridin-2-yl)methyleneamino]-4,6-di-tert-
butylphenol (L1H). To a stirred solution of 2-amino-4,6-di-tert-
butylphenol (1.107 g, 5.0 mmol) in anhydrous ethanol (40 mL) were
added pyridine-2-aldehyde (0.557 g, 5.2 mmol) and a catalytic amount
of acetic acid. The mixture was refluxed and stirred for 6 h. When the
solution was cooled to ambient temperature, a yellow solid was
obtained in 87.7% yield (1.361 g). L1H was characterized by
comparing its NMR spectra with those reported in the literature.65
1H NMR (400 MHz, CDCl3): δ 8.87 (s, 1H, CHN), 8.71 (d, 1H, J
1
yield (1.451 g). Mp: 128−129 °C. H NMR (400 MHz, CDCl3): δ
8.46 (d, 1H, J = 4.8 Hz, Py-H), 7.56 (td, 1H, J = 7.7, 1.7 Hz, Py-H),
7.39−7.30 (m, 4H, Ar-H and Py-H), 7.29−7.23 (m, 5H, Ar-H), 7.20
(d, 1H, J = 7.8 Hz, Py-H), 7.17−7.07 (m, 2H, Ar-H), 6.80 (d, 1H, J =
2.1 Hz, Ar-H), 6.42 (d, 1H, J = 1.9 Hz, Ar-H), 4.78 (t, 1H, J = 5.4 Hz,
CH2NH), 4.60 (s, 1H, ArOH), 4.32 (d, 2H, J = 5.4 Hz, CH2NH), 1.66
(s, 6H, CH3), 1.63 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3): δ
159.08, 151.45, 149.14, 149.10, 142.87, 139.60, 137.79, 136.63, 134.24,
129.26, 127.94, 126.89, 126.87, 126.24, 125.45, 121.99, 121.74, 113.81,
110.78, 50.29, 42.97, 42.09, 31.16, 29.77. Anal. Calcd for C30H32N2O:
C, 82.53; H, 7.39; N, 6.42. Found: C, 82.13; H, 7.38; N, 6.23.
Synthesis of 2-[(Pyridin-2-yl)methylamino]-4-tert-butyl-6-
(triphenylmethyl)phenol (L6H). Ligand L6H was prepared by a
procedure similar to that described above for L5H, using 2-[(pyridin-2-
yl)methyleneamino]-4-tert-butyl-6-triphenylmethylphenol (L3H; 1.192
g, 2.4 mmol) and NaBH4 (0.817 g, 21.6 mmol). L6H was obtained as a
= 4.4 Hz, Py-H), 8.23 (d, 1H, J = 7.9 Hz, Py-H), 7.82 (td, 1H, J = 7.7,
1.2 Hz, Py-H), 7.77 (s, 1H, ArOH), 7.38 (td, 1H, J = 7.4, 1.0 Hz, Py-
H), 7.33 (d, 1H, J = 2.1 Hz, Ar-H), 7.31 (d, 1H, J = 2.1 Hz, Ar-H),
1.46 (s, 9H, C(CH3)3), 1.33 (s, 9H, C(CH3)3). 13C NMR (100 MHz,
CDCl3): δ 156.17, 154.74, 149.90, 149.41, 141.86, 136.89, 135.74,
133.83, 125.26, 124.71, 121.36, 110.55, 35.18, 34.80, 31.78, 29.62.
Synthesis of 2-[(Pyridin-2-yl)methyleneamino]-4,6-dicumyl-
phenol (L2H). To a stirred solution of 2-amino-4,6-dicumylphenol
(3.455 g, 10.0 mmol) in anhydrous methanol (40 mL) were added
pyridine-2-aldehyde (1.125 g, 10.5 mmol) and a catalytic amount of
acetic acid. The mixture was refluxed and stirred for 6 h, and the
resulting mixture was cooled to −30 °C to afford a yellow crystals in
69.3% yield (3.012 g). Mp: 38−39 °C. 1H NMR (400 MHz, CDCl3):
δ 8.75 (s, 1H, CHN), 8.67 (d, 1H, J = 4.2 Hz, Py-H), 8.07 (d, 1H, J
= 8.0 Hz, Py-H), 7.73 (td, 1H, J = 7.6, 1.2 Hz, Py-H), 7.45 (s, 1H,
ArOH), 7.39−7.27 (m, 11H, Ar-H and Py-H), 7.24−7.17 (m, 2H, Ar-
H), 1.77 (s, 6H, CH3), 1.73 (s, 6H, CH3). 13C NMR (100 MHz,
CDCl3): δ 156.37, 154.56, 150.83, 150.67, 149.80, 149.06, 141.49,
136.75, 135.15, 133.90, 128.23, 128.00, 126.86, 126.44, 125.90, 125.87,
125.42, 125.20, 121.14, 112.74, 43.05, 42.29, 31.19, 29.45. Anal. Calcd
for C30H30N2O: C, 82.91; H, 6.96; N, 6.45. Found: C, 82.71; H, 6.99;
N, 6.39.
1
pale white powder in 75.8% yield (0.907 g). Mp: 185−187 °C. H
NMR (400 MHz, CDCl3): δ 8.41 (d, 1H, J = 4.6 Hz, Py-H), 7.56 (td,
1H, J = 7.7, 1.1 Hz, Py-H), 7.25−7.12 (m, 16H, Ar-H and Py-H), 7.08
(t, 1H, J = 5.6 Hz, Py-H), 6.62 (d, 1H, J = 1.9 Hz, Ar-H), 6.40 (d, 1H,
J = 1.9 Hz, Ar-H), 4.76 (br, 2H, CH2NH and ArOH), 4.42 (s, 2H,
CH2NH), 1.03 (s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ
159.30, 149.23, 144.96, 143.01, 140.06, 137.87, 136.79, 132.36, 131.26,
127.87, 126.67, 122.11, 121.83, 117.55, 109.48, 63.38, 50.70, 34.61,
31.63. Anal. Calcd for C35H34N2O: C, 84.30; H, 6.87; N, 5.62. Found:
C, 83.92; H, 6.68; N, 5.81.
Synthesis of (L1)2ZrCl2 (C1). To a stirred solution of ZrCl4·2THF
(0.453 g, 1.2 mmol) in dried THF (40 mL) was added slowly a
solution of 2-[(pyridin-2-yl)methyleneamino]-4,6-di-tert-butylphenol
(L1H; 0.745 g, 2.4 mmol) in THF (40 mL) at room temperature, and
then Et3N (0.50 mL, 0.364 g, 3.6 mmol) was added. The resulting
solution was stirred overnight at ambient temperature, and then the
mixture was filtered to remove the precipitated Et3N·HCl salt. The
final product was crystallized from THF by cooling at −30 °C, washed
with petroleum ether, and dried in vacuo. Complex C1 was obtained
as red crystals in 73.3% yield (0.687 g). Mp: >300 °C (C1 was
extremely stable and did not decompose at temperatures up to 300
°C). 1H NMR (400 MHz, CDCl3): δ 10.20 (d, 2H, J = 4.6 Hz, Py-H),
Synthesis of 2-[(Pyridin-2-yl)methyleneamino]-4-tert-butyl-
6-(triphenylmethyl)phenol (L3H). To a stirred solution of 2-amino-
4-tert-butyl-6-triphenylmethylphenol (2.445 g, 6.0 mmol) in anhy-
drous ethanol (40 mL) were added pyridine-2-aldehyde (0.675 g, 6.3
mmol) and a catalytic amount of acetic acid. The mixture was refluxed
and stirred for 6 h. When the solution was cooled to ambient
temperature, a yellow solid was obtained in 85.2% yield (2.539 g). Mp:
1
161−162 °C. H NMR (400 MHz, CDCl3): δ 8.85 (s, 1H, CHN),
8.66 (d, 1H, J = 4.8, Py-H), 8.05 (d, 1H, J = 7.9 Hz, Py-H), 7.72 (td,
1H, J = 7.6, 1.2 Hz, Py-H), 7.40 (d, 1H, J = 2.2 Hz, Ar-H), 7.37 (s, 1H,
ArOH), 7.32 (td, 1H, J = 7.6, 1.2 Hz, Py-H), 7.28−7.15 (m, 16H, Ar-
G
dx.doi.org/10.1021/om4009636 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
8.75 (s, 2H, CHN), 8.00 (td, 2H, J = 7.5, 1.5 Hz, Py-H), 7.87 (d,
2H, J = 7.5 Hz, Py-H), 7.50 (td, 2H, J = 7.5, 1.5 Hz, Py-H), 7.29 (d,
2H, J = 2.1 Hz, Ar-H), 7.11 (d, 2H, J = 2.1 Hz, Ar-H), 1.25 (s, 18H,
C(CH3)3), 0.82 (s, 18H, C(CH3)3). 13C NMR (100 MHz, CDCl3): δ
163.67, 153.77, 152.69, 146.38, 140.12, 138.60, 137.77, 134.90, 127.20,
126.94, 125.66, 109.95, 34.66, 34.28, 31.72, 28.89. Anal. Calcd for
C40H50Cl2N4O2Zr·0.5C4H8O: C, 61.74; H, 6.66; N, 6.86. Found: C,
61.91; H, 6.87; N, 6.47. The final product contains about 0.5 equiv of
THF, as verified by NMR spectroscopy.
major and minor isomers is ca. 10:1). H NMR (400 MHz, CDCl3):
major isomer (91%), δ 9.80 (d, 2H, J = 5.5 Hz, Py-H), 7.81 (t, 2H, J =
7.5 Hz, Py-H), 7.42−7.15 (m, 16H, Ar-H), 6.80−6.71 (m, 4H, Ar-H
and Py-H), 6.62 (s, 2H, Ar-H), 6.49 (m, 4H, Ar-H), 6.33 (t, 2H, J = 7.5
Hz, Py-H), 4.72 (t, 2H, J = 13.2, CH2NH), 4.17 (dd, 2H, J = 14.3, 4.0
Hz, CH2NH), 3.41 (dd, 2H, J = 14.3, 4.0 Hz, CH2NH), 1.76 (s, 6H,
CH3), 1.75 (s, 6H, CH3), 1.22 (s, 6H, CH3), 0.93 (s, 6H, CH3); minor
isomer (9%), δ 9.66 (d, 2H, J = 5.6 Hz, Py-H), 7.72 (t, 2H, J = 7.2 Hz,
Py-H), 7.21−7.17 (m, 4H, Ar-H), 7.09−7.04 (m, 6H, Ar-H), 6.98−
6.85 (m, 10H, Ar-H and Py-H), 6.65 (s, 2H, Ar-H), 6.59−6.53 (m, 4H,
Ar-H), 6.27 (t, 2H, J = 7.2 Hz, Py-H), 4.81 (t, 2H, J = 12.8, CH2NH),
4.07 (dd, 2H, J = 12.0, 3.5 Hz, CH2NH), 3.35 (dd, 2H, J = 12.0, 3.5
Hz, CH2NH), 1.73 (s, 6H, CH3), 1.71 (s, 6H, CH3), 1.16 (s, 6H,
CH3), 0.95 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3, only
resonances for the major isomer are reported): δ 158.41, 158.25,
152.57, 151.83, 151.40, 138.41, 137.77, 134.22, 128.21, 127.66, 126.94,
125.76, 125.48, 124.91, 124.55, 122.92, 122.31, 122.10, 119.96, 54.59,
42.78, 41.56, 32.71, 31.36, 31.30, 26.45. Anal. Calcd for
C60H62Cl2N4O2Zr·0.5C7H8: C, 70.66; H, 6.16; N, 5.19. Found: C,
70.44; H, 6.18; N, 4.91. The final product contains about 0.5 equiv of
toluene, as verified by NMR spectroscopy.
Synthesis of (L2)2ZrCl2 (C2). The procedure was similar to the
synthesis of C1 (except that it was recrystallized from toluene), using
ligand L2H (1.043 g, 2.4 mmol), ZrCl4·2THF (0.453 g, 1.2 mmol),
and Et3N (0.50 mL, 0.364 g, 3.6 mmol). Complex C2 was obtained as
red crystals (suitable for X-ray diffraction) in 76.1% yield (0.940 g).
1
Mp: 136−137 °C. H NMR (400 MHz, CDCl3): δ 10.00 (d, 2H, J =
4.7 Hz, Py-H), 7.92 (td, 2H, J = 7.6, 1.4 Hz, Py-H), 7.60 (s, 2H, CH
N), 7.58 (d, 2H, J = 7.6 Hz, Py-H), 7.40−7.14 (m, 12H, Ar-H and Py-
H), 7.07 (d, 2H, J = 1.8 Hz, Ar-H), 6.92 (d, 2H, J = 1.8 Hz, Ar-H),
6.88−6.82 (m, 4H, Ar-H), 6.74−6.66 (m, 6H, Ar-H), 1.76 (s, 6H,
CH3), 1.74 (s, 6H, CH3), 1.14 (s, 6H, CH3), 0.70 (s, 6H, CH3).
Because of its poor solubility, 13C NMR resonances were unavailable.
Anal. Calcd for C60H58Cl2N4O2Zr·C7H8: C, 71.76; H, 5.93; N, 5.00.
Found: C, 71.34; H, 6.12; N, 4.64. The final product contains about
1.0 equiv of toluene, as verified by NMR spectroscopy.
Synthesis of (L6)2ZrCl2 (C6). The procedure was similar to the
synthesis of C1, using ligand L6H (0.798 g, 1.6 mmol), ZrCl4·2THF
(0.302 g, 0.8 mmol), and Et3N (0.34 mL, 0.243 g, 2.4 mmol).
Complex C6 was obtained as orange crystals (suitable for X-ray
diffraction) in 70.7% yield (0.654 g). Mp: >300 °C (C6 was extremely
Synthesis of (L3)2ZrCl2 (C3). To a stirred solution of the ligand 2-
[(pyridin-2-yl)methyleneamino]-4-tert-butyl-6-triphenylmethylphenol
(L3H; 1.192 g, 2.4 mmol) in 50 mL of THF was added dropwise nBuLi
(2.4 M in n-hexane, 1.05 mL, 2.5 mmol) at −78 °C. The mixture was
stirred for an additional 3 h at ambient temperature, then ZrCl4·2THF
(0.453 g, 1.2 mmol) was added at −78 °C, and the reaction mixture
was slowly warmed to ambient temperature and stirred overnight.
Then the solvent was removed under reduced pressure and the residue
was extracted with dry CH2Cl2 (40 mL). The mixture was filtered, and
the volatiles were removed under reduced pressure. The final product
was crystallized from CH2Cl2 by cooling at −30 °C, washed with
petroleum ether, and dried in vacuo. Complex C3 was obtained as red
crystals in 25.5% yield (0.353 g). Mp: >300 °C (C3 was extremely
1
stable and did not decompose at temperatures up to 300 °C). H
NMR (400 MHz, CDCl3): δ 9.30 (d, 2H, J = 5.2 Hz, Py-H), 7.50 (td,
2H, J = 7.6, 1.2 Hz, Py-H), 7.20−7.07 (m, 20H, Ar-H), 7.02 (d, 2H, J =
2.0 Hz, Ar-H), 6.78−6.69 (m, 12H, Ar-H and Py-H), 6.67 (d, 2H, J =
7.6 Hz, Py-H), 6.64 (d, 2H, J = 2.0 Hz, Ar-H), 4.82 (t, 2H, J = 13.2,
CH2NH), 4.28 (dd, 2H, J = 13.1, 4.1 Hz, CH2NH), 3.39 (dd, 2H, J =
13.1, 4.1 Hz, CH2NH), 1.18 (s, 18H, (CH3)3). 13C NMR (100 MHz,
CDCl3): δ 159.71, 157.15, 151.54, 146.46, 138.60, 136.71, 133.92,
131.95, 131.05, 127.24, 126.81, 125.60, 122.51, 120.90, 119.27, 62.84,
56.07, 34.48, 31.89. Anal. Calcd for C70H66Cl2N4O2Zr·0.4C4H8O: C,
72.49; H, 5.88; N, 4.72. Found: C, 72.30; H, 5.80; N, 4.74. The final
product contains about 0.4 equiv of THF, as verified by NMR
spectroscopy.
X-ray Crystallographic Studies. Single-crystal X-ray diffraction
studies for complexes C2 and C6 were carried out on a Bruker AXS
D8 diffractometer with graphite-monochromated Mo Kα radiation (λ
= 0.71073 Å). All data were collected at 25 °C (for C2) or −133 °C
(for C6) using the ω-scan technique. Unit cell dimensions were
obtained with least-squares refinements. Intensities were corrected for
Lorentz and polarization effects and empirical absorption. The
structures were solved by direct methods66 and refined by full-matrix
least squares on F2.67 All calculations were carried out with the
SHELXTL program. All non-hydrogen atoms were refined anisotropi-
cally, and the hydrogen atoms were included in idealized positions.
The crystal data and structure refinement parameters are given in
Table S1 (Supporting Information).
Polymerization of Ethylene. Ethylene polymerization was carried
out in a 100 mL autoclave equipped with a magnetic stirrer. The
autoclave was heated at 100 °C under vacuum for 30 min and then
thermostatted to the desired temperature and filled with ethylene. The
proper amounts of modified methylaluminoxane (MMAO) solution
and toluene were added to the autoclave, which was then filled with
ethylene for 15 min at the reaction temperature. After the proper
amount of a toluene solution of the zirconium complex was injected
into the reactor, ethylene at the desired pressure was introduced to
start the polymerization. The reaction mixture was stirred vigorously
for a designated time, and the ethylene pressure in the autoclave was
slowly vented. Then 10 mL of ethanol was added to terminate the
polymerization. The resulting mixture was poured into 3% HCl in
ethanol (50 mL). The polymer was collected by filtration, washed with
ethanol (30 mL × 2), and then dried for 16 h in a vacuum oven at 60
°C to constant weight.
1
stable and did not decompose at temperatures up to 300 °C). H
NMR (400 MHz, CDCl3): δ 9.78 (d, 2H, J = 4.9 Hz, Py-H), 7.75 (s,
2H, CHN), 7.57 (t, 2H, J = 7.7 Hz, Py-H), 7.31 (d, 2H, J = 7.5 Hz,
Py-H), 7.21−6.76 (m, 34H, Ar-H and Py-H), 6.67−6.63 (m, 2H, Ar-
H), 1.19 (s, 18H, C(CH3)3). Because of its poor solubility, the 13C
NMR resonance was unavailable. Anal. Calcd for C70H62Cl2N4O2Zr·
1.5CH2Cl2: C, 67.05; H, 5.12; N, 4.37. Found: C, 67.04; H, 5.36; N,
4.27. The final product contains about 1.5 equiv of dichloromethane,
as verified by NMR spectroscopy.
Synthesis of (L4)2ZrCl2 (C4). The procedure was similar to the
n
synthesis of C3, using ligand L4H (1.163 g, 2.4 mmol), BuLi (2.4 M
in n-hexane, 1.05 mL, 2.5 mmol), and ZrCl4·2THF (0.453 g, 1.2
mmol). Complex C4 was obtained as a dark red solid in 29.2% yield
(0.330 g). Mp: >300 °C (C4 was extremely stable and did not
decompose at temperatures up to 300 °C). 1H NMR (400 MHz,
CDCl3): δ 9.87 (d, 2H, J = 9.3 Hz, quino-H), 8.36 (d, 2H, J = 8.3 Hz,
quino-H), 7.82−7.76 (m, 4H, quino-H), 7.59−7.50 (m, 4H, quino-H),
7.35−7.23 (m, 10H, Ar-H), 7.19−7.14 (m, 2H, Ar-H), 7.05 (s, 2H,
CHN), 7.01−6.96 (m, 4H, Ar-H), 6.94−6.80 (m, 8H, Ar-H), 1.71
(s, 6H, CH3), 1.70 (s, 6H, CH3), 1.17 (s, 6H, CH3), 0.67 (s, 6H, CH3).
13C NMR (100 MHz, CDCl3): δ 162.51, 152.88, 150.92, 150.46,
149.66, 147.81, 139.21, 138.70, 136.01, 134.77, 131.99, 129.94, 129.23,
128.83, 128.41, 128.28, 127.95, 127.15, 126.86, 126.33, 125.85, 124.90,
124.20, 114.11, 42.84, 42.19, 33.39, 31.40, 31.12, 26.28. Anal. Calcd for
C68H62Cl2N4O2Zr·0.2CH2Cl2: C, 71.45; H, 5.49; N, 4.89. Found: C,
71.28; H, 5.63; N, 4.84. The final product contains about 0.2 equiv of
dichloromethane, as verified by NMR spectroscopy.
Synthesis of (L5)2ZrCl2 (C5). The procedure was similar to the
synthesis of C1 (except that it was recrystallized from toluene), using
ligand L5H (0.873 g, 2.0 mmol), ZrCl4·2THF (0.377 g, 1.0 mmol),
and Et3N (0.42 mL, 0.303 g, 3.0 mmol). Complex C5 was obtained as
orange crystals in 77.2% yield (0.798 g). Mp: 216−218 °C. There are
two isomers found in chloroform-d solution (the ratio between the
H
dx.doi.org/10.1021/om4009636 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(18) Zwideveld, M. A.; Wehrmann, P.; Rohr, C.; Mecking, S. Angew.
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ASSOCIATED CONTENT
■
S
* Supporting Information
(19) Gottker-Schnetmann, I.; Korthals, B.; Mecking, S. J. Am. Chem.
̈
Figures, a table, and CIF files giving NMR spectra of ligands
L1H−L6H and zirconium complexes C1−C6, X-ray crystallo-
graphic data for zirconium complexes C2 and C6, 13C NMR
and IR spectra of polyethylene obtained by C5/MMAO (entry
26), and selected GPC plots regarding the data of entries 5, 23,
26, and 27. This material is available free of charge via the
Internet at http://pubs.acs.org. Crystallographic data for the
structures reported in this paper have also been deposited with
the Cambridge Crystallographic Data Centre under the
numbers CCDC 944109 (for C2) and 951475 (for C6).
Copies of the data can be obtained free of charge from the
Cambridge Crystallographic Data Centre (www.ccdc.cam.ac.
uk/data_request/cif).
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AUTHOR INFORMATION
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Corresponding Authors
(28) Long, R. J.; Jones, D. J.; Gibson, V. C.; White, A. J. P.
Organometallics 2008, 27, 5960−5967.
*H.M.: e-mail, haiyanma@ecust.edu.cn.
*J.H.: tel, +86-21-64253519; fax, +86-21-64253519; e-mail,
jlhuang@ecust.edu.cn.
(29) Cohen, A.; Kopilov, J.; Goldberg, I.; Kol, M. Organometallics
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(30) Mella, M.; Izzo, L.; Capacchione, C. ACS Catal. 2011, 1, 1460−
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Notes
The authors declare no competing financial interest.
(31) Liu, J.-Y.; Liu, S.-R.; Li, B.-X.; Li, Y.-G.; Li, Y.-S. Organometallics
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We are grateful for support from the National Natural Science
Foundation of China (No. 21274041 and 20774027) and the
key project of the Chinese Ministry of Education (No.
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