Syntheses and ethylene polymerization behavior of supported salicylaldimine-based neutral nickel(II) catalysts

Article abstract of DOI:10.1021/om061061u

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr₂C₆H₃)N=CH(2-ArC₆H ₃O)]-Ni(PPh₃)Ph (6, Ar = 2-(OH)C₆H₄; 8, Ar = 2-OH-3-(2,6-iPr₂C₆H₃N=CH)C ₆H₃), have been synthesized, and their structures have also been confirmed by X-ray crystallography, elemental analysis, and ¹H and ¹³C NMR spectra. An important structural feature of the two complexes is the free hydroxyl group, which allows them to react with silica pretreated with trimethylaluminum under immobilization by the formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 × 10⁶ g PE/mol _Ni·h for ethylene polymerization, respectively, and yielded branched polymers. Requiring no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 × 105 g PE/mol _Ni·h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol and a moderate degree of branching (ca. 13-26 branches per 1000 carbon atoms).

Full text of DOI:10.1021/om061061u

Organometallics 2007, 26, 2609-2615
2609
Syntheses and Ethylene Polymerization Behavior of Supported
Salicylaldimine-Based Neutral Nickel(II) Catalysts
Tao Hu, Yan-Guo Li, Jing-Yu Liu, and Yue-Sheng Li*
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, People’s Republic of China
ReceiVed NoVember 20, 2006
Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr2C6H3)NdCH(2-ArC6H3O)]-
Ni(PPh3)Ph (6, Ar ) 2-(OH)C6H4; 8, Ar ) 2-OH-3-(2,6-iPr2C6H3NdCH)C6H3), have been synthesized,
1
and their structures have also been confirmed by X-ray crystallography, elemental analysis, and H and
13C NMR spectra. An important structural feature of the two complexes is the free hydroxyl group,
which allows them to react with silica pretreated with trimethylaluminum under immobilization by the
formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active
single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 ×
106 g PE/molNi·h for ethylene polymerization, respectively, and yielded branched polymers. Requiring
no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 × 105 g PE/
molNi·h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol
and a moderate degree of branching (ca. 13-26 branches per 1000 carbon atoms).
Chart 1
Introduction
In the past few years, more and more attention has been
concentrated on the late transition metal catalysts for olefin
polymerization.1-4 Due to their low electrophilicity and oxo-
philicity, the late transition metal catalysts can copolymerize
ethylene and certain polar comonomers5-12 and can even
catalyze some polymerizations in water.13-18 Remarkably,
Grubbs and his co-workers found that the salicylaldimine-based
neutral nickel(II) catalysts with bulky substituents ortho to a
phenoxy group such as 1a-d (Chart 1) not only showed high
catalytic activities for ethylene polymerization without cocata-
lysts and produced polyethylenes (PEs) with high molecular
weight but also could catalyze the copolymerization of ethylene
and some functionalized olefins.7-11,19-22 By avoiding hyper-
purification of the monomer feed and the use of cocatalysts these
readily available salicylaldimine-based neutral nickel(II) cata-
lysts have been attracting the attention of many researchers.23-33
As we all know, homogeneous catalysts have to be supported
on an innocuous carrier such as silica, alumina, or other
* To whom correspondence should be addressed. Fax: +86-431-
5262039. E-mail: ysli@ciac.jl.cn.
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10.1021/om061061u CCC: $37.00 © 2007 American Chemical Society
Publication on Web 04/05/2007

2610 Organometallics, Vol. 26, No. 10, 2007
Hu et al.
Scheme 1
Figure 1. ORTEP view of complex 6. Selected bond distances
(Å) and angles (deg): Ni-C(1) 1.894(3), Ni-O(1) 1.9157(17), Ni-
N(1) 1.947(2), Ni-P 2.1812(8), O(1)-C(21) 1.321(3), O(2)-C(27)
1.364(3), N-C(7) 1.456(3), N-C(19) 1.295(3), C(19)-C(20)
1.432(5), C(22)-C(26) 1.493(4), P-C(32) 1.825(3); N-Ni-P
170.89(7), C-Ni-P 84.90(8), C(1)-Ni-O(1) 174.45(10), C(1)-
Ni-N 93.41(10), O(1)-Ni-P 90.25(6), O(1)-Ni-N 91.80(8).
reported. This prompted us to explore the covalent supporting
of neutral nickel catalysts and their catalytic behavior for
ethylene polymerization so as to obtain PE with high molecular
weight.
For the covalent supporting of neutral catalysts, two factors
must be considered in the design of catalysts: one is introduction
of bulky substituents ortho to the phenoxy group in the backbone
of the salicylaldimine ligand, which favors obtaining high
catalytic activity and polyethylene with high molecular weight,
and the other is introduction of an active functional group such
as a hydroxyl or amino group in the salicylaldimine ligand,
which can react with a second functional group on the surface
of the support. Obviously, according to the conventional
synthetic methods, the preparation of such ligands will require
tedious multistep reactions with low yields.
Recently, we have developed a binuclear neutral Ni(II)
catalyst based on the bis(salicylaldimine) ligand, which was
derived from readily available 2,2′-biphenol, for the ethylene
polymerization.39 Here, we report the syntheses of two new
neutral nickel(II) catalysts with free hydroxyl groups and
attaching them covalently to silica as well as their catalytic
behavior as homogeneous catalysts and their supported coun-
terparts in ethylene polymerization.
Figure 2. ORTEP view of catalyst 8. Selected bond distances (Å)
and angles (deg): Ni-C(1) 1.891(7), Ni-O(1) 1.920(4), Ni-N(1)
1.922(5), Ni-P 2.178(2), O(1)-C(25) 1.266(6), O(2)-C(32) 1.316-
(7), N(1)-C(37) 1.297(7), N(1)-C(38) 1.474(7), N(2)-C(50)
1.239(7), N(2)-C(51) 1.416(8), P-C(19) 1.839(7); N(1)-Ni-P
165.56(17), C(1)-Ni-P 91.0(2), C(1)-Ni-O(1) 163.9(3), C(1)-
Ni-N(1) 92.7(3), O(1)-Ni-P 87.19(14), O(1)-Ni-N 93.0(2).
Results and Discussion
Syntheses and Characterizations of Catalysts with a Free
Hydroxyl Group. The general synthetic route for neutral nickel-
(II) complexes 6 and 8 with a free hydroxyl group is shown in
Scheme 1. Starting from 2,2′-biphenol, free ligands 5 and 7 were
readily synthesized in good yields via a four-step reaction. The
deprotonation of free ligands 5 and 7 with 1 equiv of sodium
hydride in anhydrous THF gave yellow sodium salts at room
temperature. Without further purification, the sodium salts were
directly reacted with 1 equiv of trans-NiCl(Ph)(PPh3)2 for 14 h
in benzene to afford the neutral nickel(II) complexes 6 and 8
inorganic or organic supports in order to be applied in industrial
gas-phase or slurry polymerization processes. Covalently at-
taching precatalysts to supports is a usual method that allows
the precatalysts whose ligands contain a functionality to react
with a second functional group on the surface of the support.
Recently, covalently supported cationic Ni, Fe, and Co catalysts
have been successfully used for ethylene polymerization;34-38
however, the supported neutral nickel catalysts were seldom
(36) Kim, I.; Han, B. H.; Ha, C. S.; Kim, J. K.; Suh, H. Macromolecules
2003, 36, 6689.
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G. E.; Lopez, R. M. Eur. Pat. Appl. 1 134 225, 2000; Chem. Abstr. 2001,
135, 242674.
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D.; Herrmann, W. A. Organometallics 2002, 21, 74.
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(38) Schrekker, H. S.; Kotov, V.; Preishuber-Pflugl, P.; White, P.;
Brookhart, M. Macromolecules 2006, 39, 6341.
(39) Hu, T.; Tang, L. M.; Li, X. F.; Li, Y. S.; Hu, N. H. Organometallics
2005, 24, 2628.

Salicylaldimine-Based Neutral Nickel(II) Catalysts
Organometallics, Vol. 26, No. 10, 2007 2611
Table 1. Crystal Data and Structure Refinement for Catalysts 6 and 8
catalyst 6
C49H46NNiO2P
catalyst 8
C62H63N2NiO2P
empirical formula
fw
770.55
957.82
temperature (K)
cryst syst
space group
a (Å)
187(2)
monoclicic
P21/n
18.0911(9)
293(2)
monoclicic
P21/n
10.109(3)
b (Å)
11.5610(6)
34.169(10)
c (Å)
18.9745(10)
3927.5(4)
15.642(4)
5383(3)
V (Å3)
R (deg)
â (deg)
γ (deg)
Z
90
90
94.89(2)
90
4
1.182
0.434
2032
98.2480(10)
90
4
1.303
0.576
1624
D
calc (Mg/m3)
abs coeff (mm-1
F(000)
)
cryst size (mm)
θ range (deg)
0.31 × 0.17 × 0.11
0.42 × 0.36 × 0.28
1.45 to 26.04
1.77 to 25.05
no. of indep rflns
7732 (Rint ) 0.0547)
semiempirical from equivalents
0.9383 and 0.8403
full-matrix least-squares on F2
R1 ) 0.0508, wR2 ) 0.1029
R1 ) 0.0781, wR2 ) 0.11152
0.451 and -0.241
Bruker SMART
graphite
8762 (Rint ) 0.0343)
psi-scan
abs corr
max. and min. transmn
refinement method
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole (e Å-3
type of diffractometer
monochromator
0.5989 and 0.5644
full-matrix least-squares on F2
R1 ) 0.0511, wR2 ) 0.0348
R1 ) 0.2615, wR2 ) 0.0510
0.435 and -0.275
Bruker SMART
graphite
)
with a free hydroxyl group. In order to protect 2′-OH from
deprotonation, the sequence of adding reactants is important in
the deprotonation of the ligands. The stoichiometric amount of
NaH should be added slowly to the ligands so that the ligands
are always in excess prior to the end of the reaction, and thus
the corresponding monosodium salts were obtained.
Complex 6 shows a strong intramolecular O-H‚‚‚O hydrogen
bonding between the free hydroxyl group and the oxygen atom
of the salicylideniminato ligand in the solid state. The O(2)H
hydrogen atom is located 1.82 Å from the oxygen atom O(1)
of the salicylideniminato ligand and 0.84 Å from the oxygen
atom O(2) of the free hydroxyl group, as shown in Figure 1.
The distance between the oxygen atom of the free hydroxyl
group and that of the salicylideniminato ligand is 2.62 Å, and
the O-H‚‚‚O bond angle is 158°. These values are very close
to those found for the intermolecular O-H‚‚‚O bond in the
phenoxo complex [NiMe(OPh)(HOPh)(PMe3)2] with free phe-
nol.40 However, as shown in Figure 2, the analogous hydrogen
bonding does not exist in catalyst 8 because the free hydroxyl
group is very far from the oxygen atom of the salicylideniminato
ligand, which results from the steric effect of the bulky (2,6-
diisopropylphenyl)iminomethylene ortho to the free hydroxyl
group.
The molecular structures of complexes 6 and 8 were
confirmed by single-crystal X-ray structure analyses. Crystals
suitable for X-ray diffraction analysis were obtained by slow
diffusion of pentane into a concentrated solution of catalysts 6
and 8 in benzene, respectively. The crystallographic data
including the collection and refinement parameters are sum-
marized in Table 1, and their ORTEP diagrams are shown in
Figures 1 and 2. In the solid state, the square-planar coordination
around nickel is only slightly distorted and the six-membered
Ni-N-C-C-C-O ring is nearly planar owing to electron
delocalization. The deviations of Ni atoms from the plane of
their ligands are approximately 0.0483 and 0.0023 Å for 6 and
8, respectively. The bulky 2,6-diisopropylbenzimine occupies
the position trans to the triphenylphosphine ligand with a nearly
linear P-Ni-N angle, and the phenyl group attached to the Ni
atom lies trans to the O atom, similar to the binuclear neutral
nickel(II) complex [((2,6-iPr2C6H3)NCH)C6H3ONi(PPh3)Ph]2
based on the 3,3′-bisalicylaldimine ligand reported previously.39
The dihedral angles between the plane defined by the atoms of
the salicylideniminato fragment and the planes of the phenyl
ring ortho to the phenoxy group of the salicylideniminato
fragment are 44.3° and 58.3° for 6 and 8, respectively, and that
for the corresponding binuclear complex is 53.6°. The Ni-O
bond lengths of complexes 6 (1.9157(17) Å) and 8 (1.920(4)
Å) are both longer than that (1.903(2) Å) found in the binuclear
complex reported previously. The other way round, the (Ni)O-C
bond lengths of complexes 6 (1.321(2) Å) and 8 (1.266(6) Å)
are both much shorter than that (1.903(2) Å) observed in the
binuclear complex. In addition, a great difference between the
Ni-N bond lengths of single-nuclear complexes 6 (1.947(2)
Å) and 8 (1.922(5) Å) and the corresponding binuclear complex
(1.932(3) Å) is also observed.
Preparations of Supported Catalysts SC-6 and SC-8. The
hydroxyl group on the surface of silica reacted with excess
AlMe3, which afforded the modified silica containing 4.26 wt
% Al. In order to covalently attach catalysts 6 and 8 to the silica,
their toluene solutions were combined with the modified silica
(Scheme 2). Via this procedure, only methane was generated
as a byproduct and the unreacted nickel(II) catalysts could be
easily washed off, while the pale yellow supported catalyst was
successfully obtained. During the immobilization process, no
obvious color changes occurred, and the supported catalyst was
stable both in the solid state and in the solvent; therefore we
presumed that the nickel(II) catalysts were not significantly
activated by the aluminum species on the surface of the silica.
In other words, the immobilization procedure does not change
the coordination structure of the Ni center. Accordingly, the
structures of SC-6 and SC-8 may be used to describe the
supported forms of catalysts 6 and 8. As shown in Figure 3,
FTIR spectra of the free neutral catalysts and the corresponding
(40) Kim, Y. J.; Osakada, K.; Takenaka, A.; Yamamoto, A. J. Am. Chem.
Soc. 1990, 112, 1096.

2612 Organometallics, Vol. 26, No. 10, 2007
Hu et al.
2. Catalysts 6 and 8 displayed high activities up to 1.47 × 106
g PE/molNi·h, which is comparable to that of neutral nickel(II)
catalyst 1c.20 Grubbs reported that catalyst 1b showed a catalytic
activity of only 1.0 × 105 g PE/molNi·h for ethylene polymer-
ization under similar conditions,20 which is 1 order of magnitude
lower than that of catalyst 6. This difference may result from
the intramolecular O-H‚‚‚O hydrogen bonding in catalyst 6.
As for catalyst 8, the more bulky (2,6-diisopropylphenyl)-
iminomethylene at the C-3′ position accelerates PPh3 dissocia-
tion. Therefore, catalyst 8 also exhibited much higher catalytic
activity than neutral nickel(II) catalyst 1b.
Scheme 2
Interestingly, the molecular weights of the PEs produced by
catalyst 6 are relatively low. The weight-average molecular
weight (Mw) usually achieves only 5-6 kg/mol, which is not
only lower than those of the PEs produced using catalyst 8, but
also much lower than those of the PEs reported by neutral
nickel(II) catalyst 1b. This indicates that the intramolecular
O-H‚‚‚O hydrogen bond in catalyst 6, which decreases the
electronic density at the Ni center, favors the â-hydride
elimination. Consequently, the ratio of chain transfer speed to
chain propagation speed increased during ethylene polymeri-
zation, and the low molecular weight PEs were obtained.
Braunstein and co-workers also found that the analogous
intramolecular hydrogen bonding in the SHOP-type catalysts
dramatically influenced the molecular weight distribution of the
ethylene oligomers and aided in obtaining products with low
molecular weights.41
It is noteworthy that the PEs produced by catalyst 6 exhibited
high branching degrees, which are higher than 80 branches per
1000 carbon atoms.42 Compared with catalyst 6, catalyst 8
produced PEs with lower branching degrees, which were usually
lower than 45 branches per 1000 carbon atoms.
In a series of ethylene polymerization experiments, temper-
ature and ethylene pressure were found to dramatically affect
catalytic activities and properties of the resultant polymers.
When the temperature was increased from 25 to 60 °C, at a
constant pressure of 21 atm, the activity of catalyst 6 increased,
and the highest value, 1.14 × 106 g PE/molNi·h, was observed
at 40 °C followed by a gradual decrease (Table 2, entries 1-4).
Meanwhile, Mw of the PE decreased from 11.5 to 2.7 kg/mol
and the degree of branching increased from 81 to 127 branches
per 1000 carbon atoms. On the basis of our experimental results
and the literature,20 we found that 40-50 °C was the most
suitable reaction temperature range for the two neutral nickel
catalyst for ethylene polymerization. As ethylene pressure was
increased from 7 to 21 atms, at 40 °C, the activity of catalyst
8 increased from 5.2 to 14.7 × 105 g PE/molNi·h (Table 2, entries
5-7). Simultaneously, Mw of the PEs increased from 36.3 to
72.6 kg/mol and the branching degrees of the polymers
decreased from 43 to 25 branches per 1000 carbon atoms.
Ethylene Polymerizations Using Supported Catalysts SC-6
and SC-8. Under 21 atm of ethylene pressure and at temper-
atures between 40 and 50 °C, supported catalysts SC-6 and SC-8
were used to catalyze ethylene polymerization without cocata-
lysts, and the typical experimental results are also summarized
in Table 2. The immobilized catalysts exhibited activities up to
4.0 × 105 g PE/molNi·h for ethylene polymerization. Compared
Figure 3. FTIR spectra of catalyst 6 and SC-6.
Figure 4. Molecular weight distributions of PEs synthesized by
catalyst 6 (entry 2) and SC-6 (entry 10).
supported ones indicate that the aluminum species on the surface
of the silica did not change the coordination structure of the Ni
center.
Polymerization of Ethylene Using Catalysts 6 and 8. In
the absence of cocatalysts, complexes 6 and 8 were used to
catalyze ethylene polymerization under ethylene pressures
between 7 and 21 atms and at temperatures between 25 and
60 °C. The typical experimental results are summarized in Table
(41) Braunstein, P.; Chauvin, Y.; Mercier, S.; Saussine, L.; Cian, A. D.;
Fischer, J. J. Chem. Soc., Chem. Commun. 1994, 2203.
(42) The branching numbers for polyethylene were determined by 1H
NMR spectroscopy using the ratio of the number of methyl groups to the
overall number of carbons (e.g., methyl + methylene + methine), and
reported as branches per one thousand carbon atoms. See the following
reference: Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.

Salicylaldimine-Based Neutral Nickel(II) Catalysts
Organometallics, Vol. 26, No. 10, 2007 2613
Table 2. Ethylene Polymerization Resultsa
PDI
c
react temp
(°C)
pressure
(atm)
react time
(min)
yield
(g)
activityb
Mw
(Mw/
Tm
branchese/
1000C
entry
cat.
wt % Ni
×10-5
×10-3
Mn)c
(°C)d
1
2
3
4
5
6
7
8
6
6
6
6
8
8
8
25
40
50
60
40
40
40
40
50
40
50
40
60
40
40
40
40
40
21
21
21
21
7
60
60
60
60
60
60
60
60
60
60
60
60
60
40
40
90
90
90
0.7
11.4
10.7
9.1
5.2
9.1
14.7
2.9
2.4
1.4
1.3
3.2
2.9
7.3
6.0
12.6
2.2
4.6
0.7
11.4
10.7
9.1
5.2
9.1
14.7
3.0
2.4
1.9
1.7
4.0
3.5
11.0
9.0
8.7
11.5
6.5
3.6
2.32
3.17
2.57
2.53
3.15
3.57
3.22
2.66
3.45
3.51
3.03
4.93
4.25
2.79
3.41
3.46
3.56
4.67
72
81
68
63
100
99
102
131
130
132
120
122
121
79
81
90
112
127
43
32
25
21
26
19
24
13
19
93
33
31
21
14
2.7
36.3
59.3
72.6
53.4
47.5
61.6
55.6
120.8
86.1
6.3
14
21
21
21
21
21
21
21
21
14
14
21
21
SC-6
SC-6
SC-6
SC-6
SC-8
SC-8
6
0.81
0.81
0.59
0.59
0.66
0.66
9
10
11
12
13
14
15
16
17
18
8
8
60.1
61.4
62.9
125.8
99
100
132
124
SC-6
SC-8
0.59
0.66
2.0
3.8
b
c
d
a Polymerizations run in 60 mL of toluene and 10 µmol of catalysts were used for entries 1-7. In units of g PE/molNi·h. Determined by GPC. Melting
e
1
temperature is determined by DSC. Determined by H NMR.
Figure 5. High-temperature 13C NMR spectra of the PEs by catalyst 6 (entry 2) and SC-6 (entry 8).
with catalysts 6 and 8, the activities of supported catalysts SC-6
and SC-8 decreased by more than half. The data of entries 8-13
of Table 2 indicate that supported catalyst SC-8 showed slightly
higher activity than supported catalyst SC-6, which is in
accordance with the scenario of the corresponding homogeneous
catalysts.
On the basis of Mandelkern’s protocol,43 all of the carbon
resonances can be unambiguously assigned. Furthermore, the
intensity of the peak corresponding to the methyl branch and
the nearby carbon at δ ) 20.35, 27.62, and 37.83 in the high-
temperature 13C NMR spectra indicates that methyl branches
predominate in the resulting PE chains. DSC analyses display
that the melting temperatures (Tm’s) of the PEs produced using
supported catalysts are 120-132 °C, which are much higher
than those (63-102 °C) of the PEs produced using catalysts 6
and 8. The reason is that the molecular weight of the resulting
PE significantly increased and the degree of branching dramati-
cally decreased after the immobilization of homogeneous
catalysts.
It is noteworthy that immobilized catalysts SC-6 and SC-8
produce PEs with much higher molecular weight and much
lower degree of branching under the same conditions, compared
with homogeneous catalysts 6 and 8. Especially for catalyst 6
and immobilized catalyst SC-6, the molecular weight of the PE
increased from 6.5 to 61.6 kg/mol, a magnitude enhancement
as shown in Figure 4, and the degree of branching decreased
from 90 to 19 branches per 1000 carbon atoms, a decrease of
about 75%. Without doubt, these differences result from the
changes in the structure of the ligands. Silica bound to catalyst
6 increased the steric bulk at the ortho position of the phenoxy
group in the salicylideniminato fragment, which aided in
inhibiting the chain migration and transfer to some extent, during
ethylene polymerization. Accordingly, catalyst SC-6 favors the
production of PE with high molecular weight and low branching
content.
Conclusions
Two new salicylideneiminato-based neutral Ni catalysts with
free hydroxyl groups have been synthesized, and the corre-
sponding supported neutral nickel catalysts have also been
prepared. Remarkably, both bulky substituent and active hy-
droxyl functional group were introduced into the ortho position
of the phenoxy group in the backbone of the salicylideniminato
As shown in Figure 5, high-temperature 13C NMR spectra
show that all the PEs obtained are mainly branched by methyl.
(43) Axelson, D. E.; Levy, G. C.; Mandelkern, L. Macromolecules 1979,
12, 41.

2614 Organometallics, Vol. 26, No. 10, 2007
Hu et al.
2H, CH2), 6.99 (m, 1H), 7.22 (m, 4H), 7.48 (d, 1H), 7.79 (d, 1H),
10.39 (s, 1H, CHO). FTIR (KBr, cm-1): 1153[ν(C-O-C)], 1602,
1584, 1496[ν(CdC)], 1689[ν(CdO)], 2849, 2828[ν(C-H, -CHO)],
2959[ν(C-H, -CH3)]. Anal. Calcd for C18H22O5: C, 67.91; H,
6.97. Found: C, 67.78; H, 6.93.
ligand at the same time, which avoided using complicated
multistep reactions in the process of respectively introducing
them on the ligand. By reaction of their free hydroxyl group
with activated silica, these two neutral Ni catalysts were
covalently bound to the support. Without cocatalyst, the two
immobilized catalysts can be used to polymerize ethylene with
high activity and produce PEs with high molecular weight. To
our best knowledge, they are the first covalently supported
neutral Ni catalysts that can produce PEs with high molecular
weight.
Synthesis of Compound 4. To a stirred solution of compound
3 (4.0 g, 13.2 mmol) in methane dichloride (10 mL) were added
ethanol (50 mL) and hydrochloric acid (6 M, 40 mL). Under
nitrogen, the mixture was refluxed at 60 °C for about 8 h. After
the mixture was cooled to room temperature, the organic phase
was separated and saturated NaHCO3 solution was added to the
aqueous layer up to pH ) 7-8. The aqueous phase was extracted
with methane dichloride (30 mL × 3), and the combined organic
phase was washed with water and then dried over Na2SO4.
Concentration with a rotary evaporator gave compound 4 as
colorless crystals in 99% yield. 1H NMR (CDCl3): δ 6.20 (s, 1H,
2′-OH), 7.00 (m, 2H), 7.11-7.21 (m, 3H), 7.61 (d, 2H), 9.92 (s,
1H, CHO), 12.05 (s, 1H, 2-OH). FTIR (KBr, cm-1): 1607, 1590,
1507[ν(CdC)], 1638[ν(CdO)], 2847, 2756[ν(C-H, -CHO)],
3324[ν(O-H)]. Anal. Calcd for C14H14O3: C, 73.03; H, 6.13.
Found: C, 67.92; H, 6.07.
Experimental Section
General Procedures and Materials. All manipulations of air-
and/or water-sensitive compounds were performed under a dry
nitrogen atmosphere using standard Schlenk techniques. Toluene,
benzene, n-pentane, diethyl ether, methane dichloride, and tetrahy-
drofuran were purified by a solvent purification system (SPS,
M.Braun Inertgas-Systeme GmbH). Commercial ethylene was
directly used for polymerization without further purification.
Trimethylaluminum was purchased from Akzo Nobel Chemical Inc.
Silica was purchased from Aldrich Chemicals (200 mesh, surface
area: 480 m2/g) and pretreated by heating under vacuum at 150
°C for 12 h to remove the water absorbed before use. 2,6-
Diisopropylaniline and NaH were purchased from Acros. trans-
[Ni(PPh3)2PhCl] was prepared according to the method reported.44
NMR spectra of the polyethylenes were recorded on a Varian
Unity 400 spectrometer at 400 MHz with o-dichlorobenzene as a
solvent at 120 °C. NMR data of the compounds and the complexes
were obtained on a Bruker Avance 300 spectrometer at 300 MHz
at ambient temperature. IR spectra were recorded on a Bio-Rad
FTS-135 spectrophotometer. DSC measurements were performed
on a Perkin-Elmer Pyris 1 differential scanning calorimeter. Melting
temperatures were recorded in the second heating run at a heating
rate of 10 °C/min. High-temperature GPC was performed in 1,2,4-
tirchlorobenzene at 140 °C using a PL-GPC 220 instrument
equipped with three PL gel 10 µm mixed-B LS columns. A
calibration curve was established with polystyrene standards.
Aluminum contents of silica pretreated with trimethyaluminum and
nickel contents of supported catalysts were determined by a TJA-
POEMS-I inductively coupled plasma optical emission spectrometer
(ICP-OES). Elemental analyses were performed on a Perkin-Elmer
Series II CHN/O 2400 analyzer.
Synthesis of Compound 5. To a stirred solution of compound
4 (1.61 g, 7.66 mmol) in ethanol (45 mL) were added 2,6-
diisopropylaniline (2.06 g, 10.72 mmol) and formic acid (0.05 mL)
as a catalyst. The mixture was refluxed under nitrogen for 24 h.
The resultant yellow solution was concentrated with a rotary
evaporator, and the excess 2,6-diisopropylaniline was evaporated
under reduced pressure. After recrystallizing the residue from
petroleum ether at -20 °C ligand 5 was isolated as orange crystals
1
3
in 76% yield. H NMR (CDCl3): δ 1.22 (d, J ) 6.6 Hz, 12H,
CH3), 3.02 (sept, 3J ) 6.6 Hz, 2H, CH), 7.09-7.17 (dd, 3H, Ar-
H), 7.24 (d, 3H, Ar-H), 7.35-7.47 (m, 3H, Ar-H), 7.53 (s, 1H,
2′-OH), 7.61 (dd, 1H, Ar-H), 8.40 (s, 1H, CHdN), 15.25 (s, 1H,
2-OH). 13C NMR (CDCl3): 24.03, 28.40, 116.43, 117.25, 118.93,
122.93, 123.64, 124.17, 125.65, 128.31, 129.07, 132.35, 135.83,
136.89, 139.30, 146.47, 158.28, 160.81, 167.11. FTIR (KBr, cm-1
)
ν: 3432 (OH), 1643 (CHdN), 1616, 1473, 1458 cm-1 (Ph). Anal.
Calcd for C26H31NO2: C, 80.17; H, 8.02; N, 3.60. Found: C, 80.03;
H, 8.07; N, 3.65.
Synthesis of Complex 6. To a solution of ligand 5 (0.47 g, 1.26
mmol) in anhydrous THF (10 mL) was added sodium hydride (30.2
mg, 1.26 mmol) in THF (10 mL). The resultant mixture was stirred
at room temperature for 4 h, then filtered and evaporated. The pale
yellow solid residue and trans-[Ni(PPh3)2PhCl] (0.88 g, 1.26 mmol)
were dissolved in benzene (35 mL) and stirred overnight at room
temperature. The resultant mixture was filtered, and the filtrate was
concentrated under vacuum to ca. 5 mL. Pentane (8 mL) was added
to the residue. The resultant yellow precipitate was recrystallized
with benzene/pentane to give 6 as a yellow powder in 72% yield.
1H NMR (300 MHz, C6D6): δ 1.17 (d, JHH ) 6.6 Hz, 6H, CH3),
1.33 (d, JHH ) 6.3 Hz, 6H, CH3), 4.32 (bs, 2H, CH), 6.25 (t, 2H,
Ar-H), 6.35 (t, 1H, Ar-H), 6.48 (dd, 1H, Ar-H), 6.71 (t, 1H,
Ar-H), 6.86-6.94 (m, 3H, Ar-H), 6.96-7.09 (m, 15H, Ar-H),
7.49 (dd, 2H, Ar-H), 7.69 (m, 5H, Ar-H), 8.01 (d, 1H, JHP ) 6.3
Hz, NdCH), 8.06 (s, 1H, 2′-OH). 13C NMR (C6D6): δ 23.0, 25.8,
29.3, 106.4, 116.8,118.8, 119.8, 121.7, 123.2, 123.5, 125.6, 126.6,
130.0, 130.7, 131.0, 131.6, 133.4, 134.2, 134.5, 137.4, 138.2, 140.8,
149.8, 156.5, 167.6. Anal. Calcd for C49H46NNiO2P: C, 76.38; H,
6.02; N, 1.82. Found: C, 76.53; H, 6.08; N, 1.91.
Synthesis of Compound 2. According to the reported method,45
compound 2 was prepared from 2,2-biphenol and was isolated as
a colorless, sticky liquid. 1H NMR (CDCl3): δ 3.25 (s, 6H, CH3),
4.98 (d, 4H, CH2O), 6.98 (m, 2H, Ar-H), 7.12-7.25 (m, 6H,
Ar-H).
Synthesis of Compound 3. Under nitrogen, n-BuLi (1.6 M in
hexane, 17.8 mL, 28.4 mmol) was added to a solution of compound
2 (7.63 g, 27.8 mmol) in ether (300 mL) at room temperature over
15 min. The mixture was stirred for 4 h and gave a meat-red
suspension. After the mixture was cooled to 0 °C, N,N-dimethyl-
formamide (2.37 mL, 30.5 mmol) was added dropwise over 10 min.
The reaction mixture was warmed to room temperature and stirred
overnight. Saturated NH4Cl (50 mL) was then added to the resulting
milk-white solution to quench the reaction. The organic phase was
separated, and the aqueous layer was extracted with ethyl acetate
(60 mL × 3). The combined organic phase was washed with water
and brine and then dried over Na2SO4. The solvent was evaporated
under reduced pressure, and the residue was purified by chroma-
tography on silica gel (petroleum ether/ethyl acetate, 10:1) to give
compound 3 as colorless crystals in 48% yield. 1H NMR (CDCl3):
δ 3.12 (s, 3H, CH3), 3.28 (s, 3H, CH3), 4.63 (s, 2H, CH2), 5.04 (s,
Synthesis of Compound 7. Compound 7 was prepared according
to the procedure reported previously.39 1H NMR (300 MHz,
CDCl3): δ 1.09 (d, 12H, CH3), 1.11 (d, 12H, CH3), 2.97 (sept,
4H, CH), 7.01 (t, 2H, Ar-H), 7.13 (s, 6H, Ar-H), 7.47 (d, 2H,
Ar-H), 7.53 (d, 2H, Ar), 8.33 (s, 2H, Ar-H). 13C NMR (300 MHz,
CDCl3): δ 24.04, 28.49, 118.92, 119.49, 123.65, 125.86, 132.49,
136.09, 139.30, 146.59, 159.20, 167.29. FTIR (KBr, cm-1): 1581,
1460[ν(CdC)], 1615[ν(CdN)], 2962[ν(C-H, -CH3)], 3408[ν(O-
(44) Hidai, M.; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet.
Chem. 1971, 30, 279.
(45) Zhang, H. C.; Huang, W. S.; Pu, L. J. Org. Chem. 2001, 66, 481.

Salicylaldimine-Based Neutral Nickel(II) Catalysts
Organometallics, Vol. 26, No. 10, 2007 2615
H)]. Anal. Calcd for C38H44N2O2: C, 81.39; H, 7.91; N, 5.00.
Found: C, 81.52; H, 7.86; N, 4.97.
suspension of supported catalyst (ca. 70 mg) in toluene (15 mL)
was added into the autoclave by a syringe. The reactor was sealed
and pressurized to the desired level, and the stirring motor was
engaged. Temperature control was maintained by internal cooling
water coils with temperature increases within 2 °C in every case.
After the prescribed reaction time, the stirring motor was stopped
and the reactor was vented, and the polymer was isolated via
precipitation from ethanol and dilute HCl (10%). The solid
polyethylene was filtered, washed with ethanol, and dried at 60 °C
for 15 h under vacuum.
Crystallographic Studies. The X-ray crystallographic analyses
were performed using crystal 6 with the size 0.31 × 0.17 × 0.11
mm and 8 with the size 0.42 × 0.36 × 0.28 mm, obtained by slow
diffusion of pentane into a concentrated solution of catalysts 6 and
8 in benzene, respectively. The intensity data were collected with
the ω scan mode (293 K) on a Bruker Smart APEX diffractometer
with CCD detector using Mo KR radiation (λ ) 0.71073 Å).
Lorentz, polarization factors were made for the intensity data, and
absorption corrections were performed using the SADABS program.
The crystal structures were solved using the SHELXTL program
and refined using full matrix least-squares. The positions of
hydrogen atoms were calculated theoretically and included in the
final cycles of refinement in a riding model along with attached
carbons.
Synthesis of Complex 8. Starting from compound 7, which was
prepared according to our previous method, complex 8 was isolated
as a brown powder in 59% yield following the procedure analogous
1
to the synthesis of catalyst 6. H NMR (300 MHz, C6D6): δ 1.09
(d, JHH ) 6.6 Hz, 12H, CH3), 1.30 (d, JHH ) 6.9 Hz, 6H, CH3),
1.39 (d, JHH ) 6.9 Hz, 6H, CH3), 3.06 (sept, 2H, CH), 4.27 (sept,
2H, CH), 6.33-7.91 (m, 32H, Ar-H), 8.02 (d, 1H, JHP ) 5.7 Hz,
NdCH), 8.21 (s, 1H, 2′-OH), 8.30 (s, 1H, NdCH). 13C NMR
(C6D6): δ 22.6, 25.3, 25.5, 28.8, 107.1, 115.8, 117.4, 117.8, 118.7,
120.7, 122.3, 122.6, 122.8, 123.2, 123.5, 125.1, 125.8, 126.1, 128.3,
128.7, 129.4, 130.3, 131.2, 132.7, 134.9, 137.3, 140.1, 141.3, 149.0,
166.3, 169.6. Anal. Calcd for C62H63N2NiO2P: C, 77.74; H, 6.63;
N, 2.92. Found: C, 78.02; H, 6.58; N, 2.81.
Pretreatment of the Silica. To a suspension of silica (3.2 g) in
toluene (40 mL) was added AlMe3 (0.92 mL, 9.6 mmol) over 5
min at room temperature. The mixture was stirred for 4 h and then
was filtered. The filter cake was washed with toluene (3 mL × 5)
and hexane (3 mL × 3) and then was dried to give the modified
silica as a white powder. Elemental analysis: 4.26 wt % Al.
Preparation of Supported Catalyst SC-6. To a solution of
complex 6 (34.8 mg, 45.2 mmol) in toluene (10 mL) was added a
suspension of the above modified silica (194 mg) in toluene
(10 mL) over 10 min at room temperature. The mixture was stirred
for 2 h and then was filtered. The filter cake was washed with
toluene (3 mL × 3) at 50 °C and then was dried to give the
supported catalyst SC-6 as a pale yellow powder.
Acknowledgment. The authors are grateful for a subsidy
provided by the National Natural Science Foundation of China
(Nos. 20334030 and 50525312) and by the Special Funds for
Major State Basis Research Projects (No. 2005CB623800) from
the Ministry of Science and Technology of China.
Preparation of Supported Catalyst SC-8. Supported catalyst
SC-8 was prepared following the method analogous to that for the
synthesis of supported catalyst SC-6.
General Procedure for Ethylene Polymerization. A 100 mL
autoclave was heated under vacuum to 140 °C for 10 h and then
was cooled to the desired reaction temperature in an oil bath with
constant temperature. The vessel was purged by ethylene three times
and then was charged with toluene (35 mL) under vacuum. A
solution of catalyst 6 or 8 (10 µmol) in toluene (15 mL) or a
Supporting Information Available: Figures and tables giving
crystallographic data and crystal cell diagrams of catalysts 6 and
8. These materials are available free of charge via the Internet at
http://pubs.acs.org.
OM061061U