Synthesis, characterization and ethylene oligomerization studies of nickel complexes bearing 2-imino-1,10-phenanthrolines

Article abstract of DOI:10.1016/j.jorganchem.2006.06.028

A series of nickel (II) complexes ligated by 2-imino-1,10-phenanthrolines were synthesized and characterized by elemental and spectroscopic analysis as well as by single-crystal X-ray crystallography. X-ray crystallographic analysis reveals complexes 3, 5, 7 and 11 as the five-coordinated distorted trigonal-bipyramidal geometry. Upon activation with Et₂AlCl, these complexes exhibited considerably high activity for ethylene oligomerization (up to 3.76 × 10⁷ g mol^-1(Ni) h^-1 for 12 with 10 equiv. of PPh₃). The ligand environment and reaction conditions significantly affect the catalytic activity of their nickel complexes.

Full text of DOI:10.1016/j.jorganchem.2006.06.028

Journal of Organometallic Chemistry 691 (2006) 4196–4203
www.elsevier.com/locate/jorganchem
Synthesis, characterization and ethylene oligomerization studies
of nickel complexes bearing 2-imino-1,10-phenanthrolines
a,
a
a
a
a
a
Wen-Hua Sun *, Shu Zhang , Suyun Jie , Wen Zhang , Yan Li , Hongwei Ma ,
b
a
c
Jiutong Chen , Katrin Wedeking , Roland Frohlich
¨
a
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
b
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou 350002, China
c
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstr. 40, 48149 Mu¨nster, Germany
Received 4 May 2006; received in revised form 14 June 2006; accepted 21 June 2006
Available online 30 June 2006
Abstract
A series of nickel (II) complexes ligated by 2-imino-1,10-phenanthrolines were synthesized and characterized by elemental and spec-
troscopic analysis as well as by single-crystal X-ray crystallography. X-ray crystallographic analysis reveals complexes 3, 5, 7 and 11 as
the five-coordinated distorted trigonal-bipyramidal geometry. Upon activation with Et2AlCl, these complexes exhibited considerably
high activity for ethylene oligomerization (up to 3.76 · 107 g molÀ1(Ni) hÀ1 for 12 with 10 equiv. of PPh3). The ligand environment
and reaction conditions significantly affect the catalytic activity of their nickel complexes.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 2-Imino-1,10-phenanthrolinyl ligands; Nickel complexes; Ethylene oligomerization
1. Introduction
diimino cationic nickel complexes [3] as effective catalysts
for ethylene oligomerization and polymerization resur-
rected the interest in designing new complexes for this pur-
pose. In the following, Brookhart and Gibson groups
individually reported 2,6-bis(imino)pyridyl metal (iron
and cobalt) complexes as highly active catalysts for ethyl-
ene polymerization and oligomerization in 1998 [4]. Focus-
ing on nickel complexes as catalysts for ethylene reactivity,
they are commonly four-coordinated nickel dihalides con-
taining bidentate ligands such as PꢁN [5], PꢁO [6], NꢁN
[7], or NꢁO [8]. Intensive researches have showed the mod-
erate to high catalytic activities for ethylene reactivity by
the five-coordinated nickel halides incorporated with tri-
dentate ligands of NꢁNꢁO [9], PꢁNꢁN [10], PꢁNꢁP [10]
and NꢁNꢁN [11]. The initial idea of designing 2,9-bis
(imino)-1,10-phenanthroline derivatives as NꢁNꢁN triden-
tate ligands for metal complexes [11] was to obtain the iron
complexes as highly active catalysts. However, the iron cat-
alysts showed very low activity for ethylene reactivity, in
The oligomerization of ethylene is one of the major
industrial processes for the production of linear a-olefins.
In the past decade, homogeneous complex catalytic sys-
tems for the ethylene polymerization and oligomerization
have attracted great attentions in both academic and indus-
trial research [1]. Late-transition metal complexes have
played an important role in searching the homogeneous
catalytic systems due to their advantage that by carefully
tuning of the ligands the corresponding catalytic products’
composition can vary from lower oligomers to polymer.
Among the studies of late-transition metal complexes,
nickel complexes attract much interest because a nickel
complex was evidentially proved as good catalyst for ethyl-
ene oligomerization in SHOP process [2]. The discovery of
*
Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.028

W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
4197
which the additional imino group was responsible for the
problem [12]. The NꢁNꢁN nickel complexes with high cat-
alytic activities encouraged further researches, however, the
new designed tridentate NꢁNꢁN complexes exhibited low
activity of ethylene dimerization (up to 15400 mol
molÀ1(Ni) hÀ1) [13]. On the base of considering highly
active iron catalyst, we endeavoured to prepare 2-imino-
1,10-phenanthroline derivatives and their iron complexes.
As expected, the desired iron complexes performed high
activities for ethylene reactivity [14]. Following that, the
arising interest is to synthesize their nickel analogues and
investigate the catalytic behavior of the nickel complexes.
The title complexes were routinely synthesized by the
reaction of 2-imino-1,10-phenanthroline derivatives with
nickel halides. After scanning various co-catalysts, diet-
hylaluminium chloride (Et2AlCl) was identified as the best
co-catalyst for current nickel catalysts. The nickel catalytic
system showed high catalytic activity up to 3.76 ·
107 g molÀ1(Ni) hÀ1 of ethylene oligomerization in the
presence of Ph3P. This is one kind of the highest catalytic
performance for nickel complexes in ethylene reactivity in
addition to diimino nickel catalysts [3,15]. Herein we
describe the synthesis and characterization of the title
nickel complexes as well as their catalytic behaviors in eth-
ylene oligomerization.
reaction of the corresponding ligand with (DME)NiBr2 in
dichloromethane under nitrogen atmosphere. All com-
plexes were fully characterized by IR spectra and elemental
analyses, nevertheless, the unambiguous molecular struc-
tures were confirmed through the single-crystal X-ray dif-
fraction studies of complexes 3, 5, 7 and 11.
2.2. Molecular structures
Crystals of complexes 3, 5, 7 and 11 suitable for single-
crystal X-ray diffraction were obtained by re-crystallization
through the slow diffusion of diethyl ether into their meth-
anol solution, respectively. Analysis of X-ray crystallogra-
phy reveals that all complexes display the distorted trigonal
bipyramidal geometry, in which the nickel core is coordi-
nated with the tridentate ligand and two halides. The nitro-
gen (N3) of the imino group and one nitrogen (N1) of the
phenanthrolinyl group with the nickel core form an axial
plane while the equatorial plane consists of one nitrogen
atom (N2) and two halide atoms. Their selected bond
lengths and bond angles are collected in Table 1, mean-
while their molecular structures are shown in Figs.
1,3,6,7, individually.
In complex 3, the data show the nickel atom deviates by
˚
0.0015 A from the equatorial plane. The two nitrogen
2. Results and discussion
Table 1
˚
Selected bond lengths (A) and bond angles (ꢂ) for 3, 5, 7 and 11
2.1. Synthetic aspects
3
5
7
11
The ligands were efficiently synthesized according to our
reported procedures [14]. Their nickel complexes were eas-
ily synthesized by reactions of NiCl2 Æ 6H2O with the corre-
sponding 2-imino-1,10-phenanthroline derivatives in
ethanol (Scheme 1). The mixture of NiCl2 Æ 6H2O with
the corresponding 2-imino-1,10-phenanthroline derivatives
was stirred at room temperature for 3 h, the resulting solu-
tion was concentrated and diethyl ether was then added to
precipitate the product. The resulting precipitate was col-
lected, washed with diethyl ether and dried in vacuum.
All of the complexes were prepared by this method in high
yields, except for complex 7 being synthesized through the
Bond lengths
Ni–N(1)
Ni–N(2)
Ni–N(3)
Ni–Cl(1)
Ni–Br(1)
Ni–Cl(2)
Ni–Br(2)
N(1)–C(1)
N(1)–C(11)
N(2)–C(10)
N(2)–C(12)
N(3)–C(13)
2.168(2)
2.157(3)
1.987(3)
2.194(3)
2.2522(1)
2.160(2)
1.988(2)
2.181(2)
2.156(2)
1.999(2)
2.225(2)
2.2552(8)
1.9938(2)
2.2436(2)
2.2307(7)
2.4005(4)
2.2784(8)
2.2863(1)
2.2707(8)
2.4321(4)
1.320(3)
1.371(3)
1.320(3)
1.338(3)
1.288(3)
1.327(4)
1.354(3)
1.329(3)
1.346(3)
1.272(3)
1.321(5)
1.364(4)
1.326(4)
1.348(4)
1.284(4)
1.323(4)
1.357(3)
1.334(3)
1.343(3)
1.294(3)
Bond angles
N(2)–Ni–N(1)
N(2)–Ni–N(3)
N(1)–Ni–N(3)
N(2)–Ni–Cl(1)
N(2)–Ni–Br(1)
N(1)–Ni–Cl(1)
N(1)–Ni–Br(2)
N(3)–Ni–Cl(1)
N(3)–Ni–Br(2)
N(2)–Ni–Cl(2)
N(2)–Ni–Br(2)
N(1)–Ni–Cl(2)
N(1)–Ni–Br(1)
N(3)–Ni–Cl(2)
N(3)–Ni–Br(1)
77.84(8)
75.11(7)
151.40(8)
146.23(6)
78.19(12)
75.03(12)
151.99(11)
153.12(8)
78.15(9)
75.58(8)
78.21(9)
74.88(9)
152.45(8)
142.02(7)
152.37(8)
153.17(6)
91.92(6)
99.37(5)
96.49(6)
97.76(6)
101.77(6)
110.210(2)
N
N
NiCl2. 6H2O or
DME. NiBr2
N
N
R
99.15(6)
98.15(5)
96.74(6)
92.89(6)
99.29(5)
97.69(9)
102.44(9)
96.18(8)
92.98(8)
97.86(8)
110.62(4)
97.64(6)
99.88(6)
104.31(6)
93.62(6)
98.57(6)
113.65(3)
+
R1
Ni
X
R
R1
EtOH
or CH2Cl2
X
N
N
R1
R1
1
2
3
4
5
6
7
8
9
10 11 12
R
R1
X
H
H
H
H
F
Me Me Me Me Me
Ph
Ph Ph
Me Et i-Pr
Cl Cl Cl
Me Et i-Pr
Cl Cl Cl
Me Et Et
Cl
F
i-Pr
Cl Cl
Cl Cl
Br
Cl(1)–Ni–Cl(2) 117.03(3)
Br(2)–Ni–Br(1)
Scheme 1. Synthesis of complexes 1–12.

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W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
atoms (N1 and N3) occupy the axial coordination sites
with the bond angle of 151.40(8)ꢂ for N(1)–Ni–N(3). The
equatorial plane and the axial plane form a dihedral angle
of 87.5ꢂ. Analysis of the packing diagram of complex 3
˚
(Fig. 2) shows the distance of H2AÁ Á ÁCl2 is 2.804 A and
˚
shorter than the anticipated van der Waals radii (3.0 A)
of H and Cl atoms indicating hydrogen bond is formed
between them in the solid state. The intermolecular hydro-
gen-chloride bonding links the molecules to form the zigzag
polymer chains (Fig. 2).
Similar to the structure of complex 3, the axial positions
are occupied by nickel with two nitrogen atoms N1 and N3
[N(1)–Ni–N(3) = 151.99(11)ꢂ] while the equatorial plane is
constructed with N2 and two chlorides in the structure of
complex 5 (see Fig. 3). The deviation of the nickel atom
Fig. 3. Crystal structure of complex 5. Hydrogen atoms were omitted for
clarity.
˚
from the equatorial plane is 0.0322 A. The dihedral angle
between its equatorial and axial planes is 89.4ꢂ. The C6 cen-
tral ring of phenanthroline of one nickel complex interacts
in a ‘‘face-to-face’’ fashion with another C6 central ring of
phenanthroline in the adjacent nickel moiety with the rele-
˚
vant plane-to-plane distance of 3.201 A, however, its cen-
˚
ter-to-center distance is 3.625 A (Fig. 4). In addition,
there exists a certain C–HÁ Á ÁCl hydrogen bond interactions
between two molecules with the bonding distance C(8)–
˚
H(8B)Á Á ÁCl(2) of 2.634 A. Two molecules form a dimmer,
bridged by hydrogen bonds, and the dimers extend to form
a parallel supramolecular architecture through p–p interac-
Fig. 4. p–p Stacking between the molecules.
tion, which link small metallo-supramolecular blocks into
infinite one-dimensional chain polymer (Fig. 5).
The molecular structure of complex 7 is shown in Fig. 6.
In the molecule, the equatorial plane contains N(2), Br(1),
Br(2) atoms while the other two atoms N(1) and N(3)
occupy the axial positions. The angle of N1–Ni–N3 is
˚
152.37(8)ꢂ and the nickel atom locates 0.0414 A above
the equatorial plane toward N3. The dihedral angle of
the equatorial and axial planes is 88.3ꢂ. The solid structure
of complex 7 showed similar structural feathers of intermo-
lecular hydrogen bond observed in complex 3, and of inter-
molecular ‘‘face-to-face’’ fashion p–p interaction of the
adjacent phenanthroline rings appeared in complex 5.
In complex 11, the axial positions are occupied by nickel
with two nitrogen atoms N1 and N3 [N(1)–Ni–
Fig. 1. Crystal structure of complex 3. Hydrogen atoms were omitted for
clarity.
˚
N(3) = 152.45(8)ꢂ], and the nickel atom locates 0.0172 A
above the equatorial plane toward N3. The dihedral of
the equatorial plane and the axial plane is 88.9ꢂ. Similar
weak interaction of hydrogen bonds is also observed in this
complex.
Compared with 2,9-diformyl-1,10-phenanthroline-bis
(2,6-diisopropylanil)nickel (II) complex [11], the title com-
plexes can also be described as a distorted trigonal bipyra-
Fig. 2. Part of the zigzag polymer chains present in the structure of 3.

W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
4199
˚
midal. The two axial Ni–N bond (2.168 and 2.244 A for
˚
complex 3, 2.157 and 2.194 A for complex 5, 2.160 and
˚
˚
2.181 A for complex 7, 2.156 and 2.225 A for complex
11) are longer than that of Ni–N(2) of the equatorial plane
˚
˚
˚
(1.994 A for complex 3, 1.987 A for complex 5, 1.988 A for
complex 7, 1.999 A for complex 11). In nickel complexes
˚
ligated by 2,9-diimino-1,10-phenanthroline ligands [11],
the ring atoms of the 1,10-phenanthroline ligand and
C(13), N(1), C(26), N(4) of the imino groups as well as
the Ni(1) atom form an almost perfect plane. However,
the co-plane phenomena were not observed in the title
complexes. The nickel atoms deviate from the phenanthro-
˚
line plane in a longer distance (0.2572 A for complex 3,
˚
˚
˚
0.2969 A for complex 5, 0.3346 A for complex 7,
0.2326 A for complex 11).
2.3. Ethylene oligomerization
The nickel (II) complexes 1–12 were systematically inves-
tigated for the ethylene oligomerization. Compared with
the nickel (II) complexes incorporating 2,9-diimino-1,10-
phenanthrolines [11], which showed good activity
(106 g molÀ1(Ni) hÀ1) with MAO as co-catalyst, the title
nickel complexes ligated by 2-imino-1,10-phenanthrolines
only reached low activity (about 104 g molÀ1(Ni) hÀ1) in
the presence of MAO even increasing ethylene pressure.
After various alkylaluminums (and their oxides) as co-cata-
lysts were scanned in activating the title nickel complexes
for ethylene reactivity at ambient pressure of ethylene, the
catalytic system using diethylaluminium chloride (Et2AlCl)
had better response with the observed catalytic activities in
the order of 104 g molÀ1(Ni) hÀ1. With elevated ethylene
pressure, the higher catalytic activity is obtained upon treat-
ment with Et2AlCl. Therefore all further investigation will
use Et2AlCl as the activator. In accordance with the oligo-
mers of C4 and C6 produced, the catalytic reaction mixture
was hydrolyzed with HCl acid in ice-water bath and ana-
lyzed by GC in order to prevent the loss of more volatile C4.
Fig. 5. Side view of polymer chains present in the structure of 5.
Fig. 6. Crystal structure of complex 7. Hydrogen atoms were omitted for
clarity.
2.3.1. Effects of reaction parameters on catalytic activity
As the ethylene reactivity considered, the reaction
parameters including reaction temperature, the ratio of
Et2AlCl to nickel complex and the pressure of ethylene
affect their catalytic activities. Due to the lower activity
at ambient pressure of ethylene, ethylene oligomerization
at elevated pressures was carried out and the results were
collected in Table 2.
The influence of the ethylene pressure and reaction tem-
perature on ethylene oligomerization were investigated in
detail with complex 8, which showed low activity
(2.8 · 104 g molÀ1(Ni) hÀ1) at 1 atm ethylene pressure. A
sharp increase in the activity was observed when the ethyl-
ene pressure was increased (entries 1–3 in Table 2). The ele-
vation of the reaction temperature resulted in a significant
decline in the activity (entries 3, 6 and 7 in Table 2), which
may be attributed to the decomposition of the catalysts and
lower ethylene solubility at higher temperature.
Fig. 7. Crystal structure of complex 11. Hydrogen atoms were omitted for
clarity.

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W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
Table 2
was carried out with changing the equivalent amount of
PPh3, the ethylene oligomerization activities were observed
as 2.8 · 104 (without PPh3), 1.4 · 105 (2 equiv. of PPh3),
4.7 · 105 (5 equiv. of PPh3), 5.8 · 105 (10 equiv. of PPh3),
6.4 · 105 (15 equiv. of PPh3) g molÀ1(Ni) hÀ1, which sug-
gests the increasing amount of PPh3 leads to an enhance-
ment of the ethylene oligomerization activity. Therefore
all catalytic precursors were fully studied in the presence
of 10 equiv. of PPh3, and their results were collected in
Table 3. In our previous work [8f,9], the potential catalytic
intermediates incorporating PPh3 were observed. The stoi-
chiometric amount of PPh3 to Ni did not make sense of
improving catalytic activity, however more equivalents of
PPh3 to Ni were necessary for their higher catalytic activity
of ethylene oligomerization, the plausible role of PPh3 will
be association and dissociation with nickel core to activate
and protect the active sites.
In the presence of 10 equiv. of PPh3, complex 8 showed
good activity in the Al/Ni molar ratio of 200–500 (entries 8,
13–15 in Table 3) at ambient pressure, and the optimum
data was observed at Al/Ni molar ratio of 300 with the
activity peaked at 8.36 · 105 g molÀ1(Ni) hÀ1. Accordingly
further investigations were carried out in the presence of
10 equiv. of PPh3 with the ratio 300 of Al/Ni. The result
showed no significant effect of the R and R1 groups for
the oligomerization activity. However, the steric and elec-
tronic effects of the aryl ring on the oligomer distribution
are remarkable. Increasing the bulk on the aryl ring of
the complex led to an enhancement of C6 (entries 1–3, 5–
6, 8 and 10–12 in Table 3). The complexes containing elec-
tron-withdrawing halogen groups show better selectivity
Ethylene oligomerization with 1–12/Et2AlCl
Entry Cat. Al/Ni Activity
(atm) (ꢂC) (g molÀ1(Ni) hÀ1
P
T
Oligomer
distribution
(%)
)
C4
C6
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
8
8
200
200
200
100
300
200
200
200
200
200
200
200
200
200
200
200
200
200
10
20
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
20
20
20
20
20
30
40
20
20
20
20
20
20
20
20
20
20
20
2.10 · 105
2.49 · 105
7.11 · 105
5.78 · 104
1.47 · 105
1.86 · 105
1.58 · 105
4.47 · 105
3.25 · 105
4.72 · 105
1.74 · 105
1.64 · 105
2.60 · 105
2.73 · 105
1.66 · 105
1.72 · 105
2.83 · 105
1.36 · 106
100
95.2
91.0
100
4.8
9.0
0
8
8
8
85.4 14.6
90.0 10.0
87.6 12.4
8
8
1
91.4
89.8 10.2
91.1 8.9
8.6
2
3
4
85.7 14.3
88.9 11.1
88.6 11.4
88.8 11.2
84.9 15.1
88.0 12.0
89.9 10.1
5
6
7
9
10
11
12
93.8
6.2
Conditions. 10 lmol Ni Cat.; 30 min; in 100 ml toluene.
The effect of Al/Ni molar ratio on ethylene oligomeriza-
tion were also investigated with complex 8. With Al/Ni
ratio of 200, the catalytic activity was peaked at
7.11 · 105 g molÀ1(Ni) hÀ1 (entries 3–5 in Table 2), how-
ever, the higher ratio of Al/Ni did not result in higher
activity.
Ethylene oligomerization with complexes 1–12 were
studied under 30 atm of ethylene pressure. The variation
of the
R substituent on the imino-C of ligands,
2-(ArN@CR)-1,10-phen, resulted in changes of the cata-
lytic performance. Comparing the complexes ligated by
the methyl-ketimine (R = Me), phenyl-ketimine (R = Ph)
with aldimine (R = H) containing the 2,6-diisopropylphe-
nyl group on the imino nitrogen, both 8 and 12 (entries 3
and 18 in Table 2) showed much better catalytic activity
than 3 (entry 10 in Table 2). Furthermore the R substituent
had different influences on methyl or phenyl-ketimine and
aldimine analogues. For methyl-ketimine and phenyl-keti-
mine complexes, it was observed that an increase in steric
hindrance of the R1 group led to an enhanced activity,
but no significant effect was noticed for aldimine com-
plexes. The electronic effect of the substitution pattern of
the phenyl ring connected with the imine nitrogen atom
is not significant. The halide anion linked to the nickel cen-
ter had no obvious influence on the catalytic activity (Table
2, entry 13 vs. entry 14).
Table 3
Ethylene oligomerization with 1–12/Et2AlCl and 10 equiv. of PPh3
Entry Cat. Al/Ni
P
T
Activity
Oligomer
distribution
(%)
(atm) (ꢂC) (g molÀ1(Ni) hÀ1
)
C4
C6
1a
2a
1
2
300
300
300
300
300
300
300
300
300
300
300
300
200
400
500
300
300
300
300
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
30
30
30
30
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
40
40
40
40
6.55 · 105
8.24 · 105
8.70 · 105
9.83 · 105
6.82 · 105
7.74 · 105
7.04 · 105
8.36 · 105
1.00 · 106
8.17 · 105
8.60 · 105
8.44 · 105
5.80 · 105
5.81 · 105
4.00 · 105
1.06 · 107
3.13 · 107
3.17 · 107
3.76 · 107
73.5 26.5
60.6 39.4
54.4 45.6
61.6 38.4
3a
3
4a
4
5a
5
94.0
6.0
6a
6
85.9 14.1
82.3 17.7
78.2 21.8
53.3 46.7
7a
7
8a
8
9a
9
10a
11a
12a
13a
14a
15a
16b
17b
18b
19b
a
10
11
12
8
93.1
6.9
71.3 28.7
70.1 29.9
79.9 20.1
75.2 24.8
8
8
100
0
2.3.2. Effects of PPh3 as the auxiliary ligand on catalyst
activity
Previous studies on nickel-based catalysts have demon-
strated that incorporating PPh3 into catalytic systems leads
to higher activity and longer catalyst lifetime [8b,8f,16].
Therefore, the oligomerization reaction with 8/Et2AlCl
5
86.8 13.2
87.8 12.2
83.0 17.0
83.1 16.9
8
9
12
5 lmol complex in 30 ml toluene within 30 min.
10 lmol complex in 100 ml toluene within 60 min.
b

W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
4201
for C6 (entries 4 and 9 in Table 3). In addition, some cat-
alyst precursors were investigated at 30 atm of ethylene
pressure, and their catalytic activities were sharply
increased up to a very high level with the order of
107 g molÀ1(Ni) hÀ1 (entries 16–19 in Table 3), which were
only observed within diimino nickel catalysts [3,15].
8.63. Found: C, 56.44; H, 4.60; N, 8.47%. FT-IR (KBr disc,
cmÀ1): 3062, 1609, 1511, 1408, 1185, 863, 778.
4.2.2. 2-Formyl-1,10-phenanthroline(2,6-diethylanil)NiCl2
(2)
Obtained as orange powder in 72% yield. Anal. Calc. for
C25H25Cl2NiN3 (469.03): C, 58.90; H, 4.51; N, 8.96.
Found: C, 58.55; H, 4.56; N, 8.72%. FT-IR (KBr disc,
cmÀ1): 2966, 1608, 1512, 1451, 1409, 866.
3. Conclusions
A series of nickel (II) complexes bearing 2-imino-1,10-
phenanthrolinyl ligands have been synthesized and fully
characterized. Upon treatment with Et2AlCl, these nickel
(II) complexes showed moderate activities up to 1.36 ·
106 g molÀ1(Ni) hÀ1 for ethylene oligomerization which is
higher than the reported NꢁNꢁN nickel complex [11]. Both
the R on the imino-C and the substituents on the N-aryl rings
had an obvious influence on the catalytic activity and distri-
bution of oligomers due to their different steric and electronic
properties. In addition, the ethylene oligomerization
activities increase up to 3.76 · 107 g molÀ1(Ni) hÀ1 when
additional PPh3 is employed as auxiliary ligand.
4.2.3. 2-Formyl-1,10-phenanthroline(2,6-
diisopropylanil)NiCl2 (3)
Obtained as orange powder in 83% yield. Anal. Calc. for
C25H25Cl2NiN3 (497.09): C, 60.41; H, 5.07; N, 8.45.
Found: C, 60.22; H, 5.16; N, 8.17%. FT-IR (KBr disc,
cmÀ1): 2965, 1605, 1514, 1465, 1411, 850, 766.
4.2.4. 2-Formyl-1,10-phenanthroline(2,6-difluoroanil)NiCl2
(4)
Obtained as orange powder in 42% yield. Anal. Calc. for
C19H11Cl2F2NiN3 (448.91): C, 50.84; H, 2.47; N, 9.36.
Found: C, 51.08; H, 2.76; N, 9.06%. FT-IR (KBr disc,
cmÀ1): 3018, 1612, 1513, 1471, 1409, 864, 789.
4. Experimental
4.2.5. 2-Acetyl-1,10-phenanthroline(2,6-dimethylanil)NiCl2
(5)
4.1. General
Obtained as orange powder in 81% yield. Anal. Calc. for
C22H19Cl2NiN3 (455.01): C, 58.07; H, 4.21; N, 9.24.
Found: C, 57.75; H, 4.22; N, 8.92%. FT-IR (KBr disc,
cmÀ1): 3050, 1612, 1511, 1408, 1288, 1212, 865, 772.
All moisture-sensitive manipulations were carried out
under an atmosphere of nitrogen using standard Schlenk
techniques. Solvents were refluxed over an appropriate dry-
ing agent and distilled. Elemental analyses were performed
on a Flash EA 1112 microanalyzer. The IR spectra were
obtained as KBr pellets on a Bruker DMX-300 spectrome-
ter. GC analysis were performed with a Carlo Erba Stru-
mentazione gas chromatograph equipped with a flame
ionization detector and a 30 m (0.2 mm i.d., 0.25 lm film
thickness) DM-1 silica capillary column. Et2AlCl
(1.90 mol lÀ1) solution in hexane was purchased from
Acros Chemicals. All other chemicals were used commer-
cially without further purification unless stated otherwise.
4.2.6. 2-Acetyl-1,10-phenanthroline(2,6-diethylanil)NiCl2
(6)
Obtained as orange powder in 65% yield. Anal. Calc. for
C24H23Cl2NiN3 (483.06): C, 59.67; H, 4.80; N, 8.70.
Found: C,59.64; H, 4.82; N, 8.53%. FT-IR (KBr disc,
cmÀ1): 2964, 1609, 1512, 1409, 1287, 874, 787.
4.2.7. 2-Acetyl-1,10-phenanthroline(2,6-diethylanil)NiBr2
(7)
Obtained as orange powder in 87% yield. Anal. Calc. for
C24H22Br2NiN3 (571.96): C, 50.40; H, 4.05; N, 7.35.
Found: C, 50.12; H, 4.17; N, 7.10%. FT-IR (KBr disc,
cmÀ1): 2976, 1608, 1416, 1286, 863, 787.
4.2. Synthesis of complexes 1–12
General procedure. A solution of NiCl2 Æ 6H2O in etha-
nol or (DME) NiBr2 in dichloromethane was added drop-
wise to
a solution of the ligand in ethanol (or
4.2.8. 2-Acetyl-1,10-phenanthroline(2,6-
diisopropylanil)NiCl2 (8)
Obtained as orange powder in 90% yield. Anal. Calc. for
C26H27Cl3NiN3 (511.11): C, 61.10; H, 5.32; N, 8.22.
Found: C, 60.91; H, 5.44; N, 7.88%. FT-IR (KBr disc,
cmÀ1): 2967, 1608, 1411, 1288, 850, 790.
dichloromethane). Immediately the color of the solution
changed and some precipitate formed. The reaction mix-
ture was stirred at room temperature for 3 h then diluted
with diethyl ether. The resulting precipitate was collected,
washed with diethyl ether and dried in vacuum. All of
the complexes were prepared in high yield in this manner.
4.2.9. 2-Acetyl-1,10-phenanthroline(2,6-difluoroanil)NiCl2
(9)
4.2.1. 2-Formyl-1,10-phenanthroline(2,6-dimethylanil)NiCl2
(1)
Obtained as orange powder in 83% yield. Anal. Calc. for
C20H13Cl2F2NiN3 (462.93): C, 51.89; H, 2.83; N, 9.08.
Obtained as orange powder in 77% yield. Anal. Calc. for
C21H17Cl2NiN3 Æ C2H6O (487.05): C, 56.72; H, 4.76; N,

4202
W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
Found: C, 51.88; H, 3.02; N, 9.01.%. FT-IR (KBr disc,
cmÀ1): 2967, 1612, 1472, 1281, 859, 778.
4.3. X-ray crystal structure determination of
3, 5, 7, and 11
4.2.10. 2-Benzoyl-1,10-phenanthroline(2,6-
dimethylanil)NiCl2 (10)
Obtained as orange powder in 62% yield. Anal. Calc. for
C27H21Cl2NiN3 (517.08): C, 62.72; H, 4.09; N, 8.13.
Found: C, 62.76; H, 3.75; N, 8.34%. FT-IR (KBr disc,
cmÀ1): 3067, 1604, 1511, 1440, 1409, 1288, 860, 768, 703.
Intensity data for complexes 3 and 7 were collected on
a Brucker SMART 1000 CCD diffractometer with graph-
˚
ite-monochromated Mo Ka radiation (k = 0.71073 A).
Single-crystal X-ray diffraction studies for complex 5
were carried out on a Rigaku RAXIS Rapid IP diffrac-
tometer with graphite-monochromated Mo Ka radiation
˚
(k = 0.71073 A). The data set for complex 11 was colle-
4.2.11. 2-Benzoyl-1,10-phenanthroline(2,6-diethylanil)NiCl2
(11)
Obtained as orange powder in 62% yield. Anal. Calc. for
C29H25Cl2NiN3 (545.13): C, 63.90; H, 4.62; N, 7.71.
Found: C, 63.89; H, 4.89; N, 7.31%. FT-IR (KBr disc,
cmÀ1): 2961, 1607, 1511, 1441, 1406, 867, 787, 701.
cted with a Nonius Kappa CCD diffractometer, equipped
with a Nonius FR591 rotating anode generator. 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 methods, and refined by full-matrix
least-square on F2. Each hydrogen atom was placed in
a calculated position, and refined using a riding model.
All non-hydrogen atoms were refined anisotropically.
Structure solution and refinement were performed using
SHELXL-97 package [17]. Crystal date and processing
parameters were summarized in Table 4.
4.2.12. 2-Benzoyl-1,10-phenanthroline(2,6-
diisopropylanil)NiCl2 (12)
Obtained as orange powder in 85% yield. Anal. Calc. for
C31H29Cl2NiN3 (573.18): C, 64.96; H, 5.10; N, 7.33.
Found: C, 65.13; H, 5.27; N, 7.01%. FT-IR (KBr disc,
cmÀ1): 2965, 1605, 1509, 1440, 1405, 998, 863, 782, 701.
Table 4
Crystal date and structure refinement for 3, 5, 7 and 11
3
5
7
11
Empirical formula
Formula weight
Crystal color
C
497.09
Red
25H25Cl2N3Ni
C22H19Cl2N3Ni
455.01
Red
C24H23Br2N3Ni
571.98
Red
C29H25Cl2N3Ni
545.13
Red
Temperature (K)
Wavelength (A)
Crystal system
Space group
293(2)
0.71073
Orthorhombic
Pbca
293(2)
0.71073
130(2)
0.71073
Monoclinic
P2(1)/c
8.1478(4)
19.7762(10)
13.5317(7)
90
99.358(2)
90
2151.38(19)
4
1.766
4.633
1144
198(2)
0.71073
Triclinic
˚
Monoclinic
P2(1)/c
7.9214(16)
18.777(2)
13.261(3)
90
102.77(3)
90
1923.7(6)
4
ꢀ
P1
˚
a (A)
14.7112(3)
15.98010(10)
19.7539(4)
90
90
90
4643.87(14)
8
1.422
1.083
2064
8.6570(10)
8.7780(10)
17.1590(10)
80.990(10)
89.200(10)
73.750(10)
1235.8(2)
˚
b (A)
˚
c (A)
a (ꢂ)
b (ꢂ)
c (ꢂ)
3
˚
Volume (A )
Z
2
Dcalc (Mg mÀ3
)
1.571
1.300
936
1.465
1.025
564
l (mmÀ1
F(000)
)
Crystal size (mm)
h range (ꢂ)
0.52 · 0.50 · 0.18
2.06–25.08
À17 6 h 6 17,
À15 6 k 6 18,
À23 6 l 6 22
17435
0.262 · 0.172 · 0.033
2.17–27.43
0 6 h 6 10,
0 6 k 6 24,
À17 6 l 6 16
4310
0.20 · 0.20 · 0.13
3.05–27.48
À10 6 h 6 10,
À25 6 k 6 22,
À14 6 l 6 17
16477
0.30 · 0.15 · 0.15
2.40–28.26
0 6 h 6 11,
À10 6 k 6 11,
À22 6 l 6 22
11766
Limiting indices
Reflections collected
Unique reflections
4067
4310
4923
6001
Completeness to h (%)
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
98.7 (h = 25.08)
Empirical
4067/0/280
1.055
R1 = 0.0330, wR2 = 0.0791
R1 = 0.0430, wR2 = 0.0862
0.318 and À0.372
98.4 (h = 27.43)
Empirical
4310/0/253
0.814
R1 = 0.0467, wR2 = 0.0751
R1 = 0.1100, wR2 = 0.0850
0.391 and À0.374
99.8 (h = 27.48)
Semi-empirical
4923/0/271
1.045
R1 = 0.0324, wR2 = 0.0688
R1 = 0.0415, wR2 = 0.0729
0.557 and À0.423
98.1 (h = 28.26)
Empirical
6001/0/318
1.014
R1 = 0.0463, wR2 = 0.1075
R1 = 0.0810, wR2 = 0.1240
0.868 and À0.632
Largest difference in
peak and hole (e A
À3
˚
)

W.-H. Sun et al. / Journal of Organometallic Chemistry 691 (2006) 4196–4203
4203
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Acknowledgements
The project supported by NSFC No. 20473099. We
thank Mr. Changxing Shao for English correction. K.W.
was supported by DAAD postdoctoral fellowship.
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Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.06.028.
(f) W.-H. Sun, W. Zhang, T. Gao, X. Tang, L. Chen, Y. Li, X. Jin,
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