Synthesis, characterization and ethylene oligomerization behavior of neutral nickel complexes bearing N-fluorinated phenyl salicylaldiminato chelate ligands

Article abstract of DOI:10.1002/cjoc.201100463

A series of neutral nickel complexes featuring N-fluorinated phenyl salicylaldiminato chelate ligands was synthesized, and the novel molecular structure of complex C14 was further confirmed by X-ray crystallographic analysis. The neutral nickel complexes showed high activity up to 9.96×10⁵ g oligomers/(mol NiA·h) and high selectivity of C₆ in catalyzing ethylene oligomerization using methylaluminoxane (MAO) as cocatalyst. It was observed that the strong electron-withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalytic activity for oligomerization of ethylene. In addition, the influence of reaction parameters such as Al/Ni molar ratio, reaction temperature, a variety of cocatalyst and ethylene pressure on catalytic activity was investigated.

Full text of DOI:10.1002/cjoc.201100463

FULL PAPER
DOI: 10.1002/cjoc. 201100463
Synthesis, Characterization and Ethylene Oligomerization Be-
havior of Neutral Nickel Complexes Bearing N-Fluorinated
Phenyl Salicylaldiminato Chelate Ligands
Song, Lipinga,b(宋力平)
Song, Shaodia(宋绍迪)
Huang, Jiling*,a(黄吉玲)
a Laboratory of Organometallic Chemistry, East China University of Science and Technology,
Shanghai 200237, China
b Department of Chemistry, School of Science, Shanghai University, Shanghai 200444, China
A series of neutral nickel complexes featuring N-fluorinated phenyl salicylaldiminato chelate ligands was syn-
thesized, and the novel molecular structure of complex C14 was further confirmed by X-ray crystallographic analy-
sis. The neutral nickel complexes showed high activity up to 9.96×105 g oligomers/(mol Ni•h) and high selectivity
of C6 in catalyzing ethylene oligomerization using methylaluminoxane (MAO) as cocatalyst. It was observed that
the strong electron-withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase
the catalytic activity for oligomerization of ethylene. In addition, the influence of reaction parameters such as Al/Ni
molar ratio, reaction temperature, a variety of cocatalyst and ethylene pressure on catalytic activity was investi-
gated.
Keywords neutral nickel complex, N-fluorinated phenyl salicylaldiminato ligand, crystal structure, ethylene oli-
gomerization
Introduction
gated with a vast array of metals.[8] More recently, a
series of novel nickel complexes as catalyst for olefins
oligomerization or polymerization was reported.[9]
Herein, we wish to report the synthesis of a series of
arylnickel phosphine complexes featuring salicylaldi-
minato ligands with fluoro-substituents in different po-
sitions on the imine aryl and their reactivity and selec-
tivity in ethylene oligomerization.
During the past decades, considerable advances have
been achieved in the design and application of late tran-
sition metal complexes for oligomerization and polym-
erization of olefins.[1] Compared with early transition
metal complexes, late transition metals are generally
more tolerant of polar media because of their less oxo-
phillic nature. Therefore, it is possible to catalyze not
only olefin polymerization, polar-functionalized
α-olefins polymerization, but also copolymerization of
ethylene and α-olefins.[2] The commercially practiced
Shell High Olefin Process (SHOP) based on the pio-
neering research of Keim produced olefins in the range
of C4—C30 at the rate of more than one million tons
every year.[3] Recently, cationic nickel α-diimine cata-
lyst was reported by Brookhart’s group,[4] following the
report, iron and cobalt complexes with mono-alkyl sub-
stituted bis(imino)pyridyl ligands were reported by
Brookhart[5] and Gibson.[6] These iron and cobalt com-
plexes exhibited high activity in ethylene oligomeriza-
tion, and the oligomers consisted of ＞95% linear
α-olefins. A series of neutral nickel complexes based on
salicylaldiminato ligands with bulky imino substitnents
was reported by Grubbs[7] and showed interesting prop-
erties for ethylene polymerization. Meanwhile, fluori-
nated ligands and their complexes have been investi-
Results and Discussion
Synthesis and characterization of the ligands and
complexes
Based on our modification of a procedure reported
by Fujita et al.[8a,8b] and Nomura et al.,[8c] all ligands
were prepared by condensation of fluorinated anilines
with corresponding salicyaldehydes at 100 ℃ for 8 h
without solvents. Pure ligands were then obtained in
excellent yields by either re-crystallization in proper
solvents or column chromatography on silica gel. All
1
the ligands were characterized by H NMR and 19F
NMR. A series of novel nickel complexes C6, C7 and
C9—C14 were synthesized in good yields (Scheme 1)
according to the previously reported procedues.[10] Un-
fortunately, the designed complex C8 was not obtained
under the same reaction conditions, although we tried
*
E-mail: Jlhuang@ecust.edu.cn; Tel.: ＋86-21-54282375
Received October 7, 2011; accepted November 29, 2011; published online March 7, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201100463 or from the author.
Chin. J. Chem. 2012, 30, 1119—1126
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Song, Song & Huang
FULL PAPER
several methods to improve the reaction conditions, but
the result was fail.
diffraction result further confirmed the structure of C14
(Figure 1).[13]
Scheme 1 Synthesis of ligands and complexes
NH2
CHO
N
OH
R
i
(F)n
+
OH
L1−L5, L7−L14
(F)n
R
Ar
N
Ph3P
Ni
(F)n
O
ii
R
H
C1−C7, C9−C14
F
NH2
F
F
,
,
=
2
(F)n
Cl
1
C14
F
F
F
F
F
F
F
Figure 1 Molecular structure of complex C14 [2-((N-C6F5)-
CHN)-η-6-t-Bu-C6H3O]Ni(Ph)(PPh3).
,
,
Cl
F
F
3
F
5
4
Because of the obvious structural similarity, com-
plex C14 had a molecular structure (Figure 1) similar to
complex C4.[10b] The four-coordinate atoms [C(18),
N(1), O(1) and P(1)] and the central Ni atom were also
in the same planar. Due to the repulsion between bulkier
tert-butyl substituent attached on salicylaldiminato
ligand and PPh3 ligand, the O(1)-Ni-P(1) angle
[93.56(5)°] for complex C14 was larger than that of the
corresponding angle of the complex C4 [88.34(7)°],
whereas the C(18)-Ni-P(1) angle [85.43(8)°] for com-
plex C14 was smaller than that of the corresponding
angle of the complex C4 [89.17(10)°]. In addition, the
bond length of Ni—O [1.9224(16) Å] for complex C14
was much longer than that of the corresponding length
[1.898(2) Å] for complex C4; and the bond length of
Ni—N [1.925(2) Å] for complex C14 was much shorter
than that of the corresponding length of complex C4
[1.935(2) Å], suggesting that in the solid state there was
an obvious steric interaction between the tert-butyl sub-
stituent and the triphenylphosphine ligand compared
with the unsubstituted analogues.
Reagents and conditions: (i) solvent-free, 100 ℃, 8 h; (ii) THF, NaH,
trans-Ni(Ar)(Cl)(PPh3)2
Ligand
L1
L7 L8 L9 L10 L11 L12 L13 L14
R＝
H
CH3 CH3 CH3 CH3 t-Bu t-Bu t-Bu t-Bu
Arf＝
Ar＝
1
1
2
3
5
1
2
3
5
p-MePh Ph
C6 C7
—
—
Ph Ph Ph Ph Ph Ph
Complex
C9 C10 C11 C12 C13 C14
Usually, the C＝N stretching vibration of ligands in
IR spectra was distributed in the range from 1630 to
1640 cm , approximately, while in the corresponding
complexes the C＝N stretching vibration was distrib-
uted in the range from 1603 to 1613 cm ; these shifts
were attributed to the formation of N—Ni complex
－
1
－
1
bonds. The strong absorption bands at about 1435 (νP
)
—
and 693 (νNi P) cm－ could confirm the existence of
C
1
—
PPh3.[11] The weak absorption bands of complexes in
572—576 and 460—464 cm－ might be attributed to
1
νNi
and νNi O, respectively.[12] The signals for the
—
—
N
Ethylene oligomerization
triphenylphosphine ligand in the 31P NMR spectra of
complexes C7, C9—C14 are observed between δ 27.6
and 42.5. Compared with the corresponding
N-fluorinated phenyl salicylaldiminato chelate ligands,
the signals for the fluorine atoms in 19F NMR spectra of
complexes C1—C7, C9—C14 showed the similar pat-
terns.
The catalyst precursors C1—C7 and C9—C14
could be activated for ethylene oligomerization with
methylaluminoxane (MAO). Firstly, the complexes
C1—C6 were chosen to investigate the catalytic activi-
ties. The results with 12 atm of ethylene were summa-
rized in Table 1. As shown in Table 1, the complexes
C1—C6 showed good catalytic activities and high
catalytic selectivity for ethylene oligomerization, the
major oligomers were C6 component (containing
Crystal structures
1
In addition to the H NMR, the single crystal X-ray
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Chin. J. Chem. 2012, 30, 1119—1126

Synthesis, Characterization and Ethylene Oligomerization Behavior of Neutral Nickel Complexes
1-hexene, 2-methyl-pentene-2, 2-hexene, 3-hexene, re-
spectively), along with the minor oligomers C4 compo-
nent (containing 1-butene exclusively), and no ethylene
polymers were detected. In the cases of precatalysts C4
and C5, no remarkable increase in catalytic activity
could be seen by further increasing the amount of fluo-
rine atoms in salicylaldiminato ligands. (for C4, 5.30×
105 g/(mol Ni•h), for C5, 5.08×105 g/(mol Ni•h) (En-
tries 4 and 5, Table 1). Compared with the complex C1,
the complex C6 bearing methyl substituent on para po-
sition of phenyl group attached to nickel hardly affected
the catalytic activity and selectivity for ethylene oli-
gomerization because the methyl substituent was irrele-
vant in the catalytic active species (Ni-alkyl species) in
terms of oligomers distribution (Entries 6 and 7, Table
1).
ene oligomerization with complex C1 (Scheme 2). After
ethylene insertion and chain propagation occurred
(Scheme 2, Path A), if chain transfer (β-H elimination)
took place, α-olefins could be formed. On the contrary,
if chain isomerization took place, the formation of in-
ternal olefins was inevitable (Scheme 2, Path B).
The data in Table 1 demonstrated the electrophillic
characteristic of center nickel atom was one of the most
important factors determining the rate of chain propaga-
tion. The more electrophillic the nickel center, the
higher the rate of ethylene oligomerization. This was
because the introduction of fluorine atom(s) into the
salicylaldimine ligand could weaken the electron re-
leasing ability of the ligands and enhanced the electro-
phillic characteristic of the center nickel atom, benefit-
ing chain propagation.
Svejda and Brookhart proposed the mechanism of
chain isomerization and chain transfer with diimine
nickel complexes in ethylene oligomeriztion.[14] Analo-
gously, we supposed the possible mechanism of ethyl-
Owing to the fact that complex C4 showed the high-
est activity under the same conditions among these com-
plexes, C4 was selected as the precatalyst and was
Table 1 Ethylene oligomerization using C1-C6/MAO system and their oligomers distributiona
b
Reaction condition
Oligomers distribtion/%
Distribution of C6 /%
Activity/
Distribution of C4/%
Entry
[105 g/(mol Ni•h)]
Cat Cocat Al∶Ni
C6
1-Hex 2MP 2-Hex 3-Hex
C4
1-Butene
100
1
2
3
4
5
6
7
C1 MAO
C2 MAO
C3 MAO
C4 MAO
C5 MAO
C6 MAO
C1 MAO
2000
2000
2000
2000
2000
1000
1000
16.6
15.4
14.6
13.6
14.0
8.8
83.4
84.6
85.4
86.4
86.0
91.2
94.4
21.4 25.5 19.0 34.1
20.4 30.5 26.2 22.9
19.2 23.9 26.1 30.8
21.8 26.2 18.3 33.7
19.1 34.5 18.1 28.3
24.8 19.2 25.9 30.1
25.9 18.1 24.8 31.2
2.53
4.52
3.77
5.30
5.08
1.18
1.25
100
100
100
100
100
5.6
100
a Conditions: cat.: 1.5 μmol, solvent: toluene, total volume: 30.0 mL, ethylene pressure: 12.0 atm, temperature: 30 ℃, reaction time: 0.5 h.
b 1-Hex: 1-hexene; 2MP: 2-methyl-pentene-2; 2-Hex: 2-hexene; 3-Hex: 3-hexene.
Scheme 2 Proposed mechanism of ethylene oligomerization
nickel-alkyl species
R1
O
N
O
N
R1
Path B
Ni
Ni
H
H
Path A
Path C
Path C
R2
O
Ni
N
internal olefins
and
branched olefins
1-Olefins
Path C
H
Path D
nickel-hydride
species
R1
Path C
Path A
R2
O
O
N
R2
Ni
Ni
N
H
Path B
H
nickel-alkyl species
Path A: ethylene in sertion and chain propagation, Path B: chain isomerization, Path C: chain transfer (β-H elimination), Path D: the reinsertion
of previously formed olefins
Chin. J. Chem. 2012, 30, 1119—1126
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Song, Song & Huang
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carefully investigated its catalytic activity through
varying reaction conditions, such as the molar ratio of
cocatalyst (MAO) to nickel complex (Al/Ni), reaction
temperature, and the pressure of ethylene, for the opti-
mum.
When the Al/Ni molar ratio was increased, the catalytic
activity efficiently increased. The best Al/Ni molar ratio
for this catalytic system was 2000. Further increasing
the Al/Ni molar ratio up to 2500, the catalytic activity
was slightly decreased. However, the distribution of
resultant oligomers was almost the same. The fact that a
large excess of MAO did not significantly increase the
activity suggested that catalytic active species (Ni-alkyl
species) could be possibly deactivated by the reaction
with excess MAO, or the enveloping of excess MAO on
the surface of active species.[16]
Effects of ethylene pressure on the catalytic activity
For the complex C4/MAO, it was very clear that,
with the fixed molar ratio of Al/Ni, the ethylene pres-
sure largely affected the catalytic performance (Table 2).
The oligomerization activity increased significantly
along with the increase of ethylene pressure. Further-
more, the reaction gave C4 component as the major oli-
gomer (55.8%) at 3.0 atm of ethylene pressure (Entry 1,
Table 2), by comparison of the reaction performed at
higher ethylene pressure (Entries 2—4, Table 2). Higher
ethylene pressure meant the enhancement of ethylene
concentration in toluene. As explained above, Scheme 2
illustrated that ethylene concentration affected not only
the steps of ethylene insertion and chain propagation
(Path A), but also the step of chain transfer (Path C).[15]
Therefore, in principle, higher ethylene pressure im-
proved the catalytic activities and the content of C6 frac-
tion. However, as shown in Path B, ethylene pressure
should have less influence on the step of chain isomeri-
zation. As a result, the distribution of both C6 olefins
and C4 olefin did not change.
Effects of oligomerization temperature
With the fixed Al/Ni molar ratio of 1000∶1, the re-
action temperature significantly affected the catalytic
activity. And the good oligomerization activity was ob-
tained at 30 ℃ (Entry 1, Table 4). Along with elevat-
ing reaction temperature in the range of 30 to 90 ℃, the
oligomerization activity significantly declined. In addi-
tion, the ratio of C4 component of the resultant oli-
gomers increased obviously at higher reaction tempera-
ture. However, temperature had no effect on the distri-
bution of trimer. This result was consistent with the
above explanation, in which the solubility of ethylene in
toluene decreased dramatically while increasing the
temperature.[17]
Effects of co-catalyst
Effects of Al/Ni molar ratio
Combined with the complex C5, a variety of co-
catalyst affecting the catalytic activity was also explored.
As shown in Table 5, when 2 equiv. of Ni(COD)2 was
used as the cocatalyst, the catalytic activity was slightly
decreased to 2.76×105 g/(mol Ni•h), and the reaction
The variation of Al/Ni molar ratio in catalytic sys-
tem of C4/MAO was explored at 30 ℃. As shown in
Table 3, at Al/Ni molar ratio of 500∶1, the catalytic
activity was relatively low [2.84×105 g/(mol Ni•h)].
Table 2 Influence of ethylene pressure on C4/MAO catalytic system and their oligomers distributiona
b
Reaction condition
Oligomers distribution/%
Distribution of C4/%
1-Butene
Distribution of C6 /%
Activity/
[105 g/(mol Ni•h)]
Entry
Cat.
p
ethylene/atm
C4
C6
1-Hex 2MP 2-Hex 3-Hex
1
2
3
C4
C4
C4
C4
3
6
55.8
19.6
16.7
16.4
44.2
80.4
83.3
83.6
100
100
100
100
17.2 32.3 29.3 21.2
19.0 30.0 27.6 23.4
20.2 28.6 22.6 28.6
18.9 32.3 19.9 28.9
0.52
1.43
2.09
4.22
9
4
12
a
Conditions: cat.: 1.5 μmol, Al∶Ni＝1000, reaction temperature: 30 ℃, solvent: toluene, total volume: 30.0 mL, reaction time: 0.5 h.
b 1-Hex: 1-hexene; 2MP: 2-methyl-pentene-2; 2-Hex: 2-hexene; 3-Hex: 3-hexene.
Table 3 Influence of Al/Ni molar ratio on C4/MAO catalytic system and their oligomers distributiona
b
Reaction condition Oligomers distribution/%
Distribution of C6 /%
Distribution of C4/%
1-Butene
Entry
Activity/[105 g/(mol Ni•h)]
Cat.
C4
C6
1-Hex 2MP 2-Hex 3-Hex
Al∶Ni
500
1
2
3
4
5
C4
C4
C4
C4
C4
15.1
16.4
15.5
13.6
13.3
84.9
83.6
84.5
86.4
86.7
100
100
100
100
100
17.8 38.1 21.6 22.5
18.9 32.3 19.9 28.9
19.6 29.7 21.6 29.1
21.8 26.2 18.3 33.7
19.7 29.5 22.8 27.9
2.84
4.22
4.71
5.30
4.98
1000
1500
2000
2500
a Conditions: cat.: 1.5 μmol, pethylene＝12.0 atm., reaction temperature: 30 ℃, solvent: toluene, total volume: 30.0 mL, reaction time: 0.5 h.
b 1-Hex: 1-Hexene; 2MP: 2-methyl-pentene-2; 2-hex: 2-hexene; 3-hex: 3-hexene.
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Synthesis, Characterization and Ethylene Oligomerization Behavior of Neutral Nickel Complexes
gave the C8 component predominately, without forma-
tion of the longer carbon chain oligomers. It should be
indicated that, in the absence of the co-catalyst such as
MAO or Ni(COD)2, no ethylene oligomerization or po-
lymerization product was detected by GC analysis. It
was well known that phosphine scavengers, such as
Ni(COD)2, played an important role in the removal of
PPh3 in the course of olefin oligomerization and polym-
erization.[7,18] In combining with Ni(COD)2, SHOP-type
oligomerization catalysts could also convert ethylene to
polyethylene with molecular weights over 1000000.
Interestingly, when phosphine scavenger was applied to
the neutral fluorinated salicylaldiminato-nickel catalytic
system, the molecular weights of oligomers only
slightly increased, and no polymer could be obtained.
Although C5/Ni(COD)2 showed moderate activity to
produce olefin oligomers, as a non-organoaluminium
activator, Ni(COD)2 played a crucial role in the stabili-
zation of the catalytic active site.
ronment of corresponding ligand, and the bulkier the
substituents, the higher the catalytic activity.
With this aim of view, to verify the role of the R
substituent attached to the salicylaldiminato ligands in
the catalytic performance, the complexes C7, C9—C14
bearing the methyl or tert-butyl attached on the salicy-
laldiminato moieties were also studied for ethylene oli-
gomerization. As shown in Table 8, under the optimal
conditions, the complexes C7, C9—C14 displayed the
higher oligomerization activities than that of
un-substituted analogs C1—C5. Furthermore, a re-
markable increase in catalytic activity could be ob-
served by introduction of the bulky substituent in sali-
cylaldiminato ligands [for C5, 5.30×105 g/mol•Ni•h],
for C10, 6.50×105 g/(mol Ni•h), for C14, 9.96×105
g/(mol Ni•h)]. It was very clear that the bulkier group
was recognized to increase the catalytic activity of
late-transition metal complexes, the highest activity up
to 9.96×105 g oligomers/(mol Ni•h) could be obtained
by C14/MAO catalytic system. This result was consis-
tent with the previous work in which bulky substituents
on the phenolic ring might decrease the rate of catalyst
deactivation.[7] It should be noted that the steric effects
Effects of the coordination environment
It was well known that the catalytic activity of the
nickel complex was greatly affected by arched envi-
Table 4 Influence of temperature on C4/MAO catalytic system and their oligomers distributiona
Reaction condition
Oligomers distribution/%
Distribution of C4/%
Distribution of C6/%
1-Hex 2MP 2-Hex 3-Hex
18.9 32.3 19.9 28.9
21.2 21.2 23.4 34.2
22.5 29.5 26.4 21.4
Activity/
[105 g/(mol Ni•h)]
4.22
Entry
Cat.
C4
C6
1-Butene
100
T/℃
1
2
3
30
60
90
16.4
39.4
52.8
83.6
60.6
47.2
C4
C4
C4
100
2.08
100
2.29
b
a Conditions: Cat.: 1.5 μmol, Al∶Ni＝1000, pethylene＝12.0 atm, solvent: toluene, total volume: 30.0 mL, reaction time: 0.5 h. 1-Hex:
1-hexene; 2MP: 2-methyl-pentene-2; 2-Hex: 2-hexene; 3-Hex: 3-hexene.
Table 5 Influence of co-catalyst on C5 complex and their oligomers distributiona
Reaction Conditiona
Oligomers distribution/%
Entry
Activity/[105 g/(mol Ni•h)]
Cat.
C5
C5
C5
Cocat.
MAO
Cocat.∶Cat.
C4
C6
91.3
15.6
—
C8
1
2
3
1000
2
8.7
10.1
—
—
74.3
—
3.90
2.76
—
Ni(COD)2
—
—
a Conditions: cat.: 1.5 μmol, solvent: toluene, total volume: 30.0 mL, ethylene pressure: 12.0 atm, temperature: 30 ℃, reaction time: 0.5
h.
Table 6 Ethylene oligomerization using C7, C9—C14/MAO catalytic system and their oligomers distributiona
Reaction condition
Oligomers distribution/%
Activity/[105 g/(mol Ni•h)]
Entry
Cat.
Cocat.
Cocat.∶Cat.
C4
C6
1
2
3
4
5
6
7
C7
C9
MAO
MAO
MAO
MAO
MAO
MAO
MAO
2000
2000
2000
2000
2000
2000
2000
9.9
8.6
90.1
91.4
87.7
92.3
94.2
84.3
92.7
6.35
5.93
6.50
7.35
9.67
7.19
9.96
C10
C11
C12
C13
C14
12.3
7.7
5.8
15.7
7.3
a Conditions: Cat.: 1.5 μmol, solvent: toluene, total volume: 30.0 mL, ethylene pressure: 12.0 atm, temperature: 30 ℃, reaction time: 0.5
h.
Chin. J. Chem. 2012, 30, 1119—1126
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Song, Song & Huang
FULL PAPER
of the bulkier R substituents had little influence on the
oligomer distribution, and the main oligomer was C6
component.
1
122 ℃; H NMR (300 MHz, CDCl3) δ: 12.51 (s, 1H,
OH), 8.83 (s, 1H, CH＝N), 7.34 (d, J＝7.5 Hz, 1H,
aromatic-H), 7.26 (d, J＝7.5 Hz, 1H, aromatic-H), 6.91
(t, J＝7.5 Hz, 1H, aromatic-H), 2.34 (s, 3H, CH3); 19F
NMR (282 MHz, CDCl3) δ: －152.33 (dd, J＝22.56,
5.64 Hz, 2F, 2-F, 6-F), －158.67 (t, J＝22.56 Hz, 1F,
4-F), －162.57—－162.74 (m, 2F, 3-F, 5-F).
Experimental
General
N-2-Fluorophenyl-3-tert-butyl-salicylaldimine
(L11)[8b] Yellow solid, yield 89%; m.p. 55—56 ℃;
1H NMR (300 MHz, CDCl3) δ: 13.71 (s, 1H, OH), 8.70
(s, 1H, CH＝N), 7.42—6.85 (m, 7H, aromatic-H), 1.47
(s, 9H, t-Bu); 19F NMR (282 MHz, CDCl3) δ: －125.97
(m, 1F, 2-F).
All manipulations involving air- and/or moisture-
sensitive compounds were carried out under an atmos-
phere of argon using standard Schlenk techniques. Sol-
vents were refluxed over the appropriate drying reagents
and distilled under argon prior to use. Melting points
(m.p.) were determined with a digital electrothermal
apparatus without calibration. IR spectra were recorded
on a Nicolet AV-360 spectrophotometer using KBr pel-
N-2,4-Difluorophenyl-3-tert-butyl-salicylaldimine
1
(L12)[8c] Yellow sticky oil, yield 89%; H NMR (300
1
let. H and 19F NMR spectra were recorded on Bruker
MHz, CDCl3) δ: 13.60 (s, 1H, OH), 8.69 (s, 1H, CH＝
N), 7.45—6.88 (m, 6H, aromatic-H), 1.49 (s, 9H, t-Bu);
19F NMR (282 MHz, CDCl3) δ: －112.30 (m, 1F, 2-F),
－121.07 (m, 1F, 4-F).
AM-300 or AM-500 instruments with Me4Si and CFCl3
(with upfield negative) as the internal and external
standards, respectively. The 31P NMR spectra were re-
corded on a Bruker AM-300 instrument with H3PO4
(85%) as the external standard. Mass spectra were de-
termined with a Finnigan GC-MS 4021 instrument us-
ing the electron impact ionization technique (70 eV).
The elemental analyses were performed on a Flash EA
1112 microanalyzer. Distribution of oligomers obtained
was measured on a Varian VISTA 6000 GC spectrome-
ter (SE-30 capillary column, 30 m×0.25 mm) and an
HP 5971A GC-MS detector. trans-Ni(Ar)(Cl)(PPh3)2
and Ni(COD)2 were prepared according to the litera-
tures.[10,19]
N-3-Chloro-4-fluorophenyl-3-tert-butyl-salicylal-
dimine (L13) Yellow solid, yield 93%; m.p. 58—59
1
℃; H NMR (300 MHz, CDCl3) δ: 13.49 (s, 1H, OH),
8.58 (s, 1H, CH＝N), 7.45—6.88 (m, 6H, aromatic-H),
1.48 (s, 9H, t-Bu); 19F NMR (282 MHz, CDCl3) δ:
－118.47 (d, J＝8.18 Hz, 1F, 4-F).
N-2,3,4,5,6-Pentafluorophenyl-3-tert-butyl-salicyl-
aldimine (L14)[8a] Yellow solid, yield 93%; m.p.
1
70—71 ℃; H NMR (300 MHz, CDCl3) δ: 12.87 (s,
1H, OH), 8.80 (s, 1H, CH＝N), 7.46 (d, J＝7.5 Hz, 1H,
aromatic-H), 7.23 (d, J＝7.5 Hz, 1H, aromatic-H), 6.89
(t, J＝7.5 Hz, 1H, aromatic-H), 1.45 (s, 9H, t-Bu); 19F
NMR (282 MHz, CDCl3) δ: －152.33 (dd, J＝21.15,
6.20 Hz, 2F, 2-F, 6-F), －158.80 (t, J＝21.43 Hz, 1F,
4-F), －162.61—－162.79 (m, 2F, 3-F, 5-F)
General procedure for preparation of ligands
In a 10 mL round bottle flask was placed 5.0 mmol
of salicylaldehyde and 5.5 mmol of fluorinated aniline.
The mixture was stirred at 100 ℃ for 8 h. After cool-
ing to room temperature, the resultant crude product
was purified by recrystallization with ethyl acetate/
petroleum (V/V＝1/9).
General procedure for preparation of complexes
A solution of the Schiff base (1.5 mmol) in THF
(20.0 mL) was added to 80% sodium hydride (70.0 mg,
2.5 mmol). The resulting mixture was stirred for 1 h at
ambient temperature. After filtered, the filtrate was re-
duced in vacuum. The solid residue was washed with
n-hexane (10.0 mL) and dried in vacuum. The salt was
immediately used in next step without further purifica-
tion. The sodium salt of ligand and trans-
NiCl(Ar)(PPh3)2 (1.44 mmol) dissolved in toluene (30.0
mL) were in a Schlenk flask and stirred for 8 h at room
temperature. After this time, the reaction mixture was
filtered by cannula filtration, and the filtrate was con-
centrated to ca. 5.0 mL. n-Hexane (30.0 mL) was added
to the reaction. A brown-yellow needle crystal was iso-
lated by cannula filtration to give the complexes.
N-2-Fluorophenyl-3-methyl-salicylaldimine (L7)
1
Yellow solid, yield 82%; m.p. 60—62 ℃; H NMR
(300 MHz, CDCl3) δ: 13.41 (s, 1H, OH), 8.72 (s, 1H,
CH＝N), 7.33—6.86 (m, 7H, aromatic-H), 2.34 (s, 3H,
CH3); 19F NMR (282 MHz, CDCl3) δ: －125.88 (m, 1F,
2-F).
N-2,4-Difluorophenyl-3-methyl-salicylaldimine
1
(L8) Yellow solid, yield 83%; m.p. 76—78 ℃; H
NMR (300 MHz, CDCl3) δ: 13.23 (s, 1H, OH), 8.68 (s,
1H, CH＝N), 7.430—6.85 (m, 6H, aromatic-H), 2.33 (s,
3H, CH3); 19F NMR (282 MHz, CDCl3) δ: －112.17 (m,
1F, 2-F), －121.04 (m, 1F, 4-F).
N-3-Chloro-4-fluorophenyl-3-methyl-salicylaldi-
mine (L9) Yellow solid, yield 85%; m.p. 98—99 ℃;
1H NMR (300 MHz, CDCl3) δ: 13.05 (s, 1H, OH), 8.56
(s, 1H, CH＝N), 7.35—6.84 (m, 6H, aromatic-H), 2.31
(s, 3H, CH3); 19F NMR (282 MHz, CDCl3) δ: －118.38
(d, J＝8.18 Hz, 1F, 4-F).
{2-[(N-2-F-C6H4)-CHN]-η-C6H4O}Ni(p-MePh)-
(PPh3) (C6) Brown solid, yield 71%; m.p. 120 ℃
1
(decomposed); H NMR (300 MHz, C6D6) δ: 7.85 (d,
JH P＝8.4 Hz, 1H, N＝CH), 7.71—7.65 (m, 6H), 7.11
—
—7.08 (m, 3H, ArH), 7.03—6.91 (m, 9H, ArH), 6.88—
6.85 (m, 1H, ArH), 6.57—6.33 (m, 7H, ArH), 6.20 (d,
J＝7.5 Hz, 1H, ArH), 1.97 (s, 3H, CH3); 19F NMR (282
N-2,3,4,5,6-Pentafluorophenyl-3-methyl-salicylal-
dimine (L10)[8a] Yellow solid, yield 89%; m.p. 121—
1124
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 1119—1126

Synthesis, Characterization and Ethylene Oligomerization Behavior of Neutral Nickel Complexes
MHz, d6-C6D6) δ: －122.0 (s, 1F, ArF); IR (KBr pellet)
ν: 3048 (w), 2915 (w), 1613 (vs), 1581 (vs), 1530 (s),
1498 (s), 1451 (s), 1444 (s), 1434 (s), 1337 (m), 1178
(m), 1146 (m), 1095 (m), 750 (vs), 693 (vs), 529 (vs),
508 (vs) cm . Anal. calcd for C38H31FNNiOP: C 72.88,
H 4.95, N 2.24; found C 72.65, H 4.89, N 2.21.
NMR (282 MHz, C6D6) δ: －122.9 (s, 1F, ArF); 31P
NMR (121 MHz, C6D6) δ: 27.7 (m, Ph3P); IR (KBr
pellet) ν: 3047 (w), 2947 (m), 2905 (w), 1591 (vs), 1564
(m), 1533 (s), 1493 (s), 1436 (s), 1416 (s), 1228 (m),
1176 (m), 1146 (m), 1096 (m), 754 (s), 741 (s), 730 (s),
－
1
－
1
693 (vs), 529 (s), 511, 496 (s) cm . Anal. calcd for
C41H37FNNiOP: C 73.69, H 5.54, N 2.10; found C
73.78, H 5.58, N 1.89.
{2-[(N-2-F-C6H4)-CHN]-η-6-CH3-C6H3O}Ni(Ph)-
(PPh3) (C7) Brown solid, yield 85%; m.p. 114
1
－116 ℃, H NMR (300 MHz, C6D6) δ: 7.92 (d,
{2-[(N-2,4-F2C6H3)-CHN]-η-6-t-Bu-C6H3O}Ni(Ph)-
(PPh3) (C12) Brown solid, yield 66%; m.p. 138—140
JH P＝8.7 Hz, 1H, N＝CH), 7.73—7.67 (m, 6H, m,
—
1
ArH), 7.22 (d, J＝8.1 Hz, 2H, ArH), 7.11—6.81 (m,
11H, ArH), 6.57—6.29 (m, 8H, ArH), 1.40 (s, 3H, CH3);
19F NMR (282 MHz, C6D6) δ: －122.2 (m, 1F, ArF);
31P NMR (121 MHz, C6D6) δ: 42.0 (m, Ph3P); IR (KBr
pellet) ν: 3047 (w), 1605 (vs), 1562 (s), 1544 (m), 1495
(m), 1434 (m), 1382 (m), 1335 (m), 1224 (m), 1179 (m),
1079 (m), 1084 (m), 864 (s), 803 (s), 757 (vs), 742 (vs),
℃; H NMR (300 MHz, C6D6) δ: 7.85—7.79 (m, 6H,
ArH), 7.40 (d, JH P＝7.2 Hz, 1H, N＝CH), 7.05 (d, J＝
—
9.6 Hz, 2H, ArH), 6.95—6.92 (m, 10H, ArH), 6.57 (t, J
＝7.5 Hz, 1H, ArH), 6.32—6.144 (m, 7H, ArH), 0.87 [s,
9H, C(CH3)3]; 19F NMR (282 MHz, C6D6) δ: －115.2
(m, 1F, ArF), －118.0 (m, 1F, ArF); 31P NMR (121
MHz, C6D6) δ: 27.6 (m, Ph3P); IR (KBr pellet) ν: 3048
(w), 2952 (w), 2865 (w), 1602 (vs), 1536 (s), 1500 (s),
1435 (m), 1418 (m), 1174 (s), 1137 (s), 1097 (s), 963 (s),
849 (s), 745 (vs), 731 (vs), 691 (vs), 528 (vs), 511 (vs)
－
1
730 (vs), 693 (vs), 532 (s), 510 (s) cm . Anal. calcd for
C38H31FNNiOP: C 72.88, H, 4.95, N 2.24; found C
73.51, H 5.21, N, 1.92.
－
1
{2-[(N-3-Cl-4-F-C6H3)-CHN]-η-6-CH3-C6H3O}Ni-
cm . Anal. calcd for C41H36F2NNiOP: C 71.75, H 5.25,
N 2.04; found C 71.67, H 5.36, N 1.95.
(Ph)(PPh3) (C9) Brown solid, yield 56%; m.p. 118—
1
120 ℃; H NMR (300 MHz, C6D6) δ: 7.78 (d, JH
＝
P
{2-[(N-3-Cl-4-FC6H3)-CHN]-η-6-t-Bu-C6H3O}Ni-
(Ph)(PPh3) (C13) Brown solid, yield 99%; m.p.
123—125 ℃; 1H NMR (300 MHz, C6D6) δ: 7.81—7.75
—
8.4 Hz, 1H, N＝CH), 7.67—7.62 (m, 6H, ArH), 7.12 (d,
J＝7.8 Hz, 1H, ArH), 7.00—6.91 (m, 12H, ArH),
6.58—6.50 (m, 2H, ArH), 6.40—6.28 (m, 4H, ArH),
6.20—6.22 (m, 1H, ArH), 1.42 (s, 3H, CH3); 19F NMR
(282 MHz, C6D6) δ: －121.7 (m, 1F, ArF); 31P NMR
(121 MHz, C6D6): 40.6 (m, Ph3P); IR (KBr pellet) ν:
3047 (w), 2966 (w), 1609 (vs), 1584 (s), 1541 (m), 1490
(m), 1448 (m), 1433 (m), 1377 (m), 1334 (m), 1259 (m),
1186 (m), 1096 (m), 869 (m), 753 (vs), 730 (vs), 692
(m, 6H, ArH), 7.40 (d, JH P＝6.9 Hz, 1H, N＝CH),
—
6.95—6.90 (m, 13H, ArH), 6.63—6.56 (m, 2H, ArH),
6.32—6.18 (m, 5H, ArH), 0.89 [s, 9H, C(CH3)3]; 19F
NMR (282 MHz, C6D6) δ: －121.7 (m, 1F, ArF); 31P
NMR (121 MHz, C6D6) δ: 40.6 (m, Ph3P); IR (KBr
pellet) ν: 3046 (w), 2960 (w), 2906 (w), 2867 (w), 1604
(vs), 1586 (s), 1536 (s), 1490 (s), 1420 (m), 1181 (s),
－
－
1
1
(vs), 532 (vs), 519 (vs), 509 (vs), 439 (m) cm . Anal.
calcd for C38H30ClFNNiOP: C 69.07, H 4.54, N 2.12;
found C 69.73, H 4.59, N 2.10.
1094 (s), 726 (s), 692 (vs), 529 (s), 514 (s) cm . Anal.
calcd for C41H36ClFNNiOP: C 70.07, H 5.13, N 1.99;
found C 70.25, H 5.22, N 1.83.
{2-[(N-C6F5)-CHN]-η-6-CH3-C6H3O}Ni(Ph)(PPh3)
{2-[(N-C6F5)-CHN]-η-6-t-Bu-C6H3O}Ni(Ph)(PPh3)
(C14) Brown solid, yield 58%; m.p. 168—170 ℃; 1H
NMR (300 MHz, C6D6) δ: 7.76—7.72 (m, 6H, ArH),
(C10) Brown solid. yield 79%; m.p. 178—180 ℃; 1H
NMR (300 MHz, C6D6) δ: 7.73 (d, JH P＝8.1 Hz, 1H,
—
N＝CH), 7.62—7.58 (m, 6H, ArH), 7.21 (d, J＝6.9 Hz,
2H, ArH), 7.09 (d, J＝6.7 Hz, 1H, ArH) , 6.96—6.90,
(m, 4H, ArH), 6.86—6.82 (m, 6H, ArH), 6.47 (t, J＝7.5
Hz, 1H, ArH), 6.33—6.27 (m, 3H, ArH), 1.31 (s, 3H,
CH3); 19F NMR (282 MHz C6D6) δ: －147.4 (dd, J＝
24.0, 6.0 Hz, 2F, ArF), －161.3 (t, J＝24.0 Hz, 1F,
ArF), －164.2 (td, J＝24.0, 6.0 Hz, 2F, ArF); 31P NMR
(121 MHz, C6D6): 42.5 (m, Ph3P); IR (KBr pellet) ν:
3044 (w), 3016 (w), 2973 (w), 1609 (vs), 1583 (vs),
1543 (s), 1515 (vs), 1435 (s), 1375 (m), 1227 (s), 1097
(s), 1000 (vs), 967 (s), 869 (m), 753 (s), 733 (s), 693
7.40 (d, JH P＝6.9 Hz, 1H, N＝CH), 7.19—7.17 (m, 2H,
—
ArH), 6.95—6.91, (m, 4H, ArH), 6.87—6.84 (m, 7H,
ArH), 6.56 (t, J＝7.5 Hz, 1H, ArH), 6.33—6.27 (m, 3H,
ArH), 0.79 [s, 9H, C(CH3)3]; 19F NMR (282 MHz, C6D6)
δ: －147.5 (dd, J＝22.5, 5.4 Hz, 2F, ArF), －161.6 (t,
J＝25.5 Hz, 1F, ArF), －165.0 (t, J＝25.5 Hz, 2F, ArF);
31P NMR (121 MHz, C6D6): 41.4 (m, Ph3P); IR (KBr
pellet) ν: 3051 (w), 2942 (w), 2865 (w), 1604 (vs), 1593
(vs), 1535 (s), 1509 (vs), 1415 (s), 1347 (m), 1148 (m),
1099, 995 (vs), 751 (s), 732 (s), 696 (vs), 534 (s), 509 (s)
－
1
cm . Anal. calcd for C41H33F5NNiOP: C 66.51, H 4.46,
－
1
(vs), 533 (vs), 508 (s) cm . Anal. calcd for C38H27F5N-
NiOP: C 65.36, H 3.87, N 2.00; found C 65.16, H 3.85,
N 1.95.
N 1.89; found C 66.37, H 4.60, N 1.90.
Oligomerization procedure
A 100 mL autoclave, equipped with a magnetic stir
bar, was preheated at 100 ℃ under vacuum for 30 min
and then cooled to the required temperature. Toluene
was injected into the reactor and pressured with ethyl-
ene to 1 atm. After equilibrating for 20 min, the appro-
priate volume of catalysts solution and cocatalysts were
{2-[(N-2-F-C6H4)-CHN]-η-6-t-Bu-C6H3O}Ni(Ph)-
(PPh3) (C11) Brown solid, yield 65%; m.p. 140—142
℃ (decomposed); 1H NMR (300 MHz, C6D6) δ: 7.83—
7.74 (m, 6H, ArH), 7.36 (d, JH P＝7.5 Hz, 1H, N＝CH),
—
6.98—6.86 (m, 13H, ArH), 6.58—6.40 (m, 5H, ArH),
6.25—6.15 (m, 3H, ArH), 0.86 [s, 9H, C(CH3)3]; 19F
Chin. J. Chem. 2012, 30, 1119—1126
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
1125

Song, Song & Huang
FULL PAPER
[4] (a) Killiam, C. M.; Johnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005; (b) Svejde, S. A.; Brookhart, M. Organometallics
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[6] Britovesk, G. J. P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.;
Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; Else-
good, M. R. J. Chem. Eur. J. 2000, 6, 2221.
injected to start the reaction. The ethylene pressure was
kept constant during the reaction. After the desired run
time, the reactor was vented and the reaction mixture
was terminated by ethanol. n-Heptane was added to the
mixture as internal standard for GC analysis. An upper-
layer clear solution was separated from the reaction
mixture to analyze and quantify the soluble components
by GC and GC-MS.
[7] Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.;
Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
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Nakano, T.; Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125,
4293; (b) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.;
Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh,
S.; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
3327; (c) Iwasa, N.; Katao, S.; Liu, J.; Fujiki, M.; Furukawa, Y.;
Nomura, K. Organometallics 2009, 28, 2179; (d) Chen, Y.; Qian, C.;
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C. J. Organometallics 2009, 28, 3264; (b) Flapper, J.; Kooijman, H.;
Lutz, M.; Spek, A. L.; van Leeuwen, P. W. N. M.; Elsevier, C. J.;
Kamer, P. C. J. Organometallics 2009, 28, 3272; (c) Caris, R.;
Peoples, B. C.; Valderrama, M.; Wu, G.; Rojas, R. J. Organomet.
Chem. 2009, 694, 1795; (d) Liu, F. S.; Gao, H. Y.; Song, K. M.;
Zhang, L.; Zhu, F. M.; Wu, Q. Polyhedron 2009, 28, 1386; (e)
Huang, Y. B.; Jia, W. G.; Jin, G. X. J. Organomet. Chem. 2009, 694,
86; (f) Shen, M.; Hao, P.; Sun, W. H. J. Organomet. Chem. 2008,
693, 1683; (g) Chen, Y. J.; Hao, P.; Zuo, W. W; Gao, K.; Sun, W. H.
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693, 3858; (i) Hu, T.; Li, Y. G.; Liu, J. Y.; Li, Y. S. Organometallics
2007, 26, 2609; (j) Song, D. P.; Li, Y. G.; Lu, R.; Hu, N. H.; Li, Y. S.
Appl. Organomet. Chem. 2008, 22, 333; (k) Zhao, W.; Qian, Y. L.;
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Qian, M. X.; Wang, M.; Zhang, Y. L.; He, R. Chin. J. Chem. 2002,
20, 676.
X-ray crystallography measurements
Single crystal X-ray diffraction studies for complex
C14 was carried out on a Bruker P4 diffractometer with
graphite-monochromated Mo Kα radiation (k＝0.71073)
at 293(2) K. Cell parameters were obtained by global
refinement of the positions of all collected reflections.
Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix
least-squares on F2. All non-hydrogen atoms were re-
fined anisotropically. All hydrogen atoms were placed
in calculated positions. Structure solution and refine-
ment were performed by using the SHELXL-97 Pack-
age.
Conclusions
In summary, neutral arylnickel phosphine complexes
C1—C7, C9—C14 bearing N-fluorinated phenyl sali-
cylaldimine chelate ligand showed considerable activi-
ties and high selectivies in oligomerization of ethylene.
The complexes with more fluoro-substituents on the
ligands exhibited higher activity than those with less
fluoro-substituents. The catalytic activity and selectivity
of the nickel complex were greatly affected by arched
environment of corresponding ligand, the variation of
Al/Ni molar ratio, the variety of cocatalyst, the reaction
temperature and the pressure of ethylene.
[10] (a) Hidai, M.; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet.
Chem. 1971, 30, 279; (b) Song, L. P.; Zhao, W.; Huang, J. L.; Zhu,
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[12] Donia, A. M.; EL-Saied, F. A. Polyhedron 1988, 7, 2149.
[13] CCDC 752856 and 752857 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@
ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: ＋44
(1223)336033.
[14] Svejda, S. A.; Brookhart, M. Orgamometallics 1998, 18, 65.
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[17] Fogg, P. G. T.; Gerrard, W. Solubility of Dases in Liquids, Wiley,
West Sussex, England, 1991.
Acknowledgement
The authors gratefully acknowledge the financial
support subsidized by the National Basic Research Pro-
gram of China (No. 2005CB623800), the National
Natural Science Foundation of China (NNSFC) (No.
21072128).
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1126
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 1119—1126