2,9-Disubstituted 1,10-phenanthroline nickel complexes: Syntheses, characterization, and their ethylene oligomerization

Article abstract of DOI:10.1134/S0023158407050114

Nickel complexes 1-4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis. The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with me

Full text of DOI:10.1134/S0023158407050114

ISSN 0023-1584, Kinetics and Catalysis, 2007, Vol. 48, No. 5, pp. 664–668. © MAIK “Nauka /Interperiodica” (Russia), 2007.
Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
2,9-Disubstituted 1,10-Phenanthroline Nickel Complexes:
Syntheses, Characterization, and Their Ethylene
Oligomerization1
Y. Songa, b, S. Zhangb, Y. Dengc, S. Jieb, L. Lia, X. Luc, and W.-H. Sunb
a College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China
b Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
c Department of Chemistry, Capital Normal University, Beijing 100037, China
e-mail: whsun@iccas.ac.cn
Abstract—Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and
characterized by FT-IR spectra and elemental analysis. The molecular structure of complex 2 was confirmed by
X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed mod-
erate activities for ethylene oligomerization.
DOI: 10.1134/S0023158407050114
1
INTRODUCTION
nickel model of 2,9-disubstituted 1,10-phenanthrolines
would be interesting. Therefore, the nickel complexes
bearing 2,9-dimethyl- and 2,9-diphenyl-1,10-phenan-
throline were synthesized. It was found that those
nickel complexes could be used as active catalysts for
ethylene oligomerization in the presence of MAO. The
various reaction conditions, such as different cocata-
lysts, the Al/Ni molar ratio, reaction temperature, and
ethylene pressure, were investigated for their effects on
the catalytic activity and the distribution of oligomers.
Ethylene oligomerization is an important industrial
process, in which products α-olefins are major indus-
trial reactants that are extensively used in the prepara-
tion of detergents, lubricants, plasticizers, and oil field
chemicals, as well as monomers for copolymerization.
The nickel complex was evidently proved as a good cat-
alyst for ethylene oligomerization in the SHOP process
[1]. Since the report of α-diimino nickel complexes for
ethylene polymerization by Brookhart in 1995 [2], late-
transition metal catalysts, especially nickel complexes
for ethylene oligomerization and polymerization, have
drawn great attention [3–5]. During the design of cata-
lysts, various ligands with different coordinative mod-
els play important roles. Nickel complexes bearing var-
ious organic ligands, such as pyridinylimino analogues
[6–8], iminophosphines [9, 10], and P,N-phosphinopy-
ridine [11], were demonstrated as active catalysts for
ethylene oligomerization or ethylene polymerization.
During the course of exploring new catalysts for ethyl-
ene oligomerization or polymerization in our group,
nickel complexes bearing 2,9-bis(imino)-1,10-phenan-
throline derivatives showed good catalytic activity for
ethylene oligomerization [12]. Furthermore, 1,10-
phenanthroline derivates have important meaning in
coordination chemistry and catalysis chemistry. The
nickel complexes with 2,9-dimethyl-1,10-phenanthro-
line had been synthesized by Sinn and Hodgson [13–
15]; however, there is no report of its application in acti-
vating ethylene. In our parallel research works related
to the frameworks of 1,10-phenanthroline derivatives
as ligands for new nickel catalysts [16], the bidentate
EXPERIMENTAL
General Considerations
All manipulations for air or moisture-sensitive com-
pounds were carried out under an atmosphere of nitro-
gen using standard Schlenk and Cannula techniques. IR
spectra were recorded on a Perkin-Elmer FT-IR 2000
spectrometer by using a KBr disc in the range of 4000–
400 cm–1. Elemental analysis was performed on a Flash
EA1112 microanalyzer. GC analysis was performed
with a Carlo Erba gas chromatograph equipped with a
flame ionization detector and a 30 m (0.25 mm i.d.,
0.24 µm film thickness) DM-1 silica capillary column.
Toluene and tetrahydrofuran were refluxed over
sodium-benzophenone and distilled under argon prior
to use. Methylaluminoxane (MAO, 1.46 M in toluene)
and modified-methylaluminoxane (MMAO, 1.93 M in
heptane) were purchased from Akzo Corp (United
States). Triethylaluminum (TEA, 2.0 M in hexane) and
ethylaluminum dichloride (EtAlCl2, 1.0 M in hexane)
were purchased from Acros Chemicals. 2,9-Dimethyl-
1,10-phenanthroline was purchased from Acros Chem-
icals, and 2,9-diphenyl-1,10-phenanthroline was syn-
1
This article was submitted by the authors in English.
664

2,9-DISUBSTITUTED 1,10-PHENANTHROLINE NICKEL COMPLEXES
665
thesized by the reaction of 1,10-phenanthroline with obtained commercially and used without further purifi-
phenyllithium in THF. All other chemicals were cation unless otherwise stated.
Synthesis of Complexes 1–4
1: R = Me, X = Cl
Troom
+ NiX2 · nH2O
2: R = Me, X = Br
3: R = Ph, X = Cl
4: R = Ph, X = Br
R
EtOH
N
N
N
N
X
R
R
Ni
R
X
(2,9-Dimethyl-1,10-phenanthroline)NiCl2 (1): A was dissolved with toluene in a Schlenk tube stirred
solution of NiCl2 · 6H2O (109 mg, 0.45 mmol) in EtOH with a magnetic stirrer under 1 atm of ethylene atmo-
(5 ml) was added dropwise to a solution of 2,9-dime- sphere, and the reaction temperature was controlled by
thyl-1,10-phenanthroline (87.4 mg, 0.42 mmol) in a water bath. The reaction was initiated by adding the
EtOH (10 ml). The mixed solution was stirred at room desired amount of cocatalyst. After the desired period
temperature for 9 h. The supernatant solution was of time, a small amount of the reaction solution was
removed, and the resultant precipitate was filtrated and collected with a syringe and terminated by the addition
washed with 3–5 mL of Et2O to give a pink powder of 5% aqueous hydrogen chloride; the analysis by gas
(105 mg) in 74% yield. FT-IR (KBr disc, cm–1): 3300, chromatography (GC) was carried out for determining
1620, 1595, 1571, 1507, 1427, 1368, 1220,1151, 862, the composition and distribution of oligomers.
785, 732, 681, 661. Anal. calc. for C14H12Cl2N2Ni: C,
Ethylene oligomerization at 10 atm of ethylene
49.77; H, 3.58; N, 8.29. Found: C, 49.26; H, 3.53; N,
pressure was carried out in a 250 ml autoclave stainless
8.04%.
steel reactor equipped with a mechanical stirrer and a
(2,9-Dimethyl-1,10-phenanthroline)NiBr2 (2): In a
similar manner as described for complex 1, complex 2
was obtained as a yellow powder in 84% yield through
the reaction of 2,9-dimethyl-1,10-phenanthroline and
NiBr2 · 4H2O. FT-IR (KBr disc, cm–1): 3298, 3170,
3056, 2362, 1700, 1595, 1506, 1428, 1369, 1150, 862,
731. Anal. calc. for C14H12Br2N2Ni · H2O: C, 37.81; H,
3.17; N, 6.30. Found: C, 37.54; H, 3.25; N, 6.28%.
(2,9-Diphenyl-1,10-phenanthroline)NiCl2 (3): In
a similar manner as described for complex 1, complex
3 was obtained as a pink powder in 50% yield through
the reaction of 2,9-diphenyl-1,10-phenanthroline and
NiCl2 · 6H2O. FT-IR (KBr disc, cm–1): 3047, 1621,
1586, 1552, 1508, 1487, 1447, 1422, 1361, 1275, 1243,
1156, 867, 774, 740, 703. Anal. calc. for
C24H16Cl2N2Ni: C, 62.39; H, 3.49; N, 6.06. Found:
C, 62.90; H, 3.58; N, 5.85%.
temperature controller. The solution of the catalyst pre-
cursor in 30 ml toluene, the desired amount of MAO,
and 120 ml of toluene were in turn added to the reactor
under ethylene atmosphere. At the desired reaction
temperature, ethylene with the desired pressure
(10 atm) was introduced to start the reaction. The pres-
sure in the autoclave was kept during the reaction by the
connection with an ethylene cylinder. After 0.5 h, the
pressure was released and a small amount of the reac-
tion solution was collected and terminated by the addi-
tion of 5% aqueous hydrogen chloride, which was then
analyzed by GC for the composition and distribution of
oligomers.
Date Collection, Structural Determination,
and Refinement
A purple single crystal with dimensions of 0.55 mm ×
0.20 mm × 0.10 mm was selected and mounted on a
Brucker Smart Apex II CCD diffractometer at 50 kV
and 20 mA by using a graphite-monochromatized
MoKα (λ = 0.71073 Å) radiation using the ω–2θ scan
mode, at 293(2) K. Unit cell dimensions were obtained
with least squares refinements. A total of 13154 reflec-
tions were collected, and 4659 reflections with I > 2σ(I)
were used in the structure determination and refine-
ment. The structures were solved by direct methods and
refined by full-matrix least squares on F2. Each hydro-
gen atom was placed in a calculated position and
(2,9-Diphenyl-1,10-phenanthroline)NiBr2 (4): In a
similar manner as described for complex 1, complex 4
was obtained as a purple powder in 86% yield through
the reaction of 2,9-diphenyl-1,10-phenanthroline and
NiBr2 · 4H2O. FT-IR (KBr disc, cm–1): 3060, 2361,
1700, 1651, 1621, 1588, 1554, 1511, 1487, 1446, 1421,
1360, 1152, 1120, 862, 762, 743. Anal. calc. for
C24H16Br2N2Ni: C, 52.32; H, 2.93; N, 5.09. Found:
C, 52.14; H, 2.93; N, 5.09%.
Ethylene Oligomerization
Ethylene oligomerization at 1 atm of ethylene pres- refined using a riding model. All non-hydrogen atoms
sure was carried out as follows: The catalyst precursor were refined anisotropically. Structure solution and
KINETICS AND CATALYSIS Vol. 48 No. 5 2007

666
SONG et al.
C13
C12
The molecular structure of complex 3 is shown in the
figure. The selected bond lengths and bond angles are
listed in Table 1. Complex 3 consists of discrete
monomelic molecules, and the coordination geometry
around the nickel atom can be described as a distorted
tetrahedron with two nitrogen atoms of the phenanthro-
line and two terminal chlorine atoms. The two Ni–N
bonds differ in length (Ni–N1, 2.0060(14) Å and Ni–
N2, 2.0252(14) Å). However, they are a little shorter
than those in dimeric complex 1 and 2 [13], which are
ascribed to the reduction of the coordination number
from 5 to 4. There is no large difference in the bond
length of the Ni–Cl linkage (Ni–Cl1, 2.2294(6) Å and
Ni–Cl2, 2.2219(6) Å). There is a little larger distortion
in bond angles of N1–Ni–N2 (84.28(6)°) and Cl1–Ni–
Cl2 (136.81(2)°). The two phenyl rings and the phenan-
throline plane are almost coplanar with the dihedral
angles of 4.5° (C1, C2 C3, C4, C5, C6) and 1.8° (C19,
C20, C21, C22, C23, C24), respectively.
C14
C10
C9
C16
C17
C8
C11
C15
C18
C19
N2
C7 N1
C24
C1
C6
Ni
C2
C20
Cl1
Cl2
C3
C2
C5
C21
C22
C4
Molecular structure of complex 3 with all the hydrogen
atoms omitted for clarity.
refinement were performed using SHELXL-97 pack-
age [17]. Its crystallographic data were deposited with
the Cambridge Crystallographic Data Centre, CCDC
285876.
Ethylene Oligomerization
On treatment with methylaluminoxane (MAO),
complexes 1–4 were active for ethylene oligomeriza-
tion and the results at 1 atm and 10 atm of ethylene
pressure were summarized in Table 2. At 1 atm of eth-
lylene pressure, complexes 1–4 showed moderate activ-
ity for ethylene oligomerization and butenes among the
oligomers obtained was the main product. The substit-
uents on the phenanthroline and the nature of halide
had no large influence on the catalytic activity, and
complex 2 displayed relatively higher activity under
the same conditions. However, complexes 3 and 4 with
phenyls on the phenanthroline could produce a little
larger amount of hexene (compare entry 3, 4 and 1, 2).
When ethylene pressure was enhanced to 10 atm, the
catalytic activity also increased. except for complex 2,
and complex 3 gave the highest catalytic activity
(1.71 × 106 g mol(Ni)–1 h–1). For the diphenyl-substituted
complexes 3 and 4, the mass content of hexene among
the oligomers exceeded 20 wt % (entries 7 and 8).
RESULTS AND DISCUSSION
Synthesis and Characterization
2,9-Dimethyl-1,10-phenanthroline was commer-
cially available and 2,9-diphenyl-1,10-phenanthroline
was prepared through the reaction of 1,10-phenanthro-
line and phenyl lithium according to the literature
method [18]. The 2,9-disubstituted-1,10-phenanthro-
lines reacted with NiCl2 · 6H2O or NiBr2 · 4H2O to form
the title complexes 1–4. The complexes were character-
ized by FT-IR spectra and elemental analysis as well as
X-ray single crystal diffraction analysis. The molecular
structures of complex 1 and 2 were confirmed as centro
symmetric dimmers with a chloro- or bromo-bridge,
which are the same as the results observed by Sinn [13],
while complex 3 exists as a monomer.
In order to find the optimum condition, complex 2,
which showed the highest activity at 1 atm ethylene
pressure, was investigated in detail by varying the reac-
tion conditions such as different cocatalysts, reaction
temperature, and the Al/Ni molar ratio at 1 atm of eth-
ylene pressure (Table 3). When 10 equiv. of ethylalumi-
num dichloride was used as a cocatalyst, complex 2
showed no activity for ethylene. When triethylalumi-
num and MMAO were employed, the catalytic activity
largely increased, while MAO was still the most effec-
tive cocatalyst, which is possibly due to the bulky MAO
molecular linking to the metal center after activation.
When the reaction temperature was enhanced from 0 to
80°ë, the catalytic activity of complex 2/åÄé
increased gradually, but the distribution of the produced
oligomers had no large difference. The dependence of
catalytic activity on theAl/Ni molar ratio was also stud-
ied in the range of 250 to 2000. As theAl/Ni molar ratio
Single crystals of complex 3 suitable for X-ray dif-
fraction analysis were obtained through the slow diffu-
sion of diethyl ether into its CH3OH–CH3CN solution.
Table 1. Selected bond lengths (Å) and bond angles (deg)
for complex 3
Bond Bond length, Å
Bond
Bond angle, deg
Ni–N1
2.0060(14)
2.0252(14)
2.2294(6)
2.2219(6)
N1–Ni–N2
N1–Ni–Cl2
N2–Ni–Cl2
N1–Ni–Cl1
N2–Ni–Cl1
Cl2–Ni–Cl1
84.28(6)
114.92(5)
100.01(5)
96.66(5)
Ni–N2
Ni–Cl1
Ni–Cl2
112.31(5)
136.81(2)
KINETICS AND CATALYSIS Vol. 48 No. 5 2007

2,9-DISUBSTITUTED 1,10-PHENANTHROLINE NICKEL COMPLEXES
Table 2. Ethylene oligomerization by complexes 1–4/MAOa
667
Distribution of oligomersd
Entry
Complex
Pb, atm
Toluene, ml
Activityc
C4
100
C6
1
2
3
4
5
6
7
8
a
1
2
3
4
1
2
3
4
1
1
30
30
1.98
2.16
1.88
1.59
6.27
1.19
17.10
7.24
0
98.2
87.3
86.7
98.7
98.6
75.5
76.1
1.8
1
30
12.7
13.3
1.3
1
30
10
10
10
10
150
150
150
150
1.4
23.7
23.9
b
c
Note: General conditions: complex: 5 µmol; Al/Ni = 500; reaction temperature: 20°C; reaction time: 30 min. Ethylene pressure; The
5
–1 –1 d
unit of activity: 10 g mol(Ni)
h . Determined by GC.
Table 3. Ethylene oligomerization by complex 2a
Distribution of oligomersd (%)
Entry
Cocat
Al/Ni
Tb, °C
Activityc
C4
–
C6
1
2
AlEtCl2
TEA
10
500
20
20
20
20
0
–
–
0.29
1.63
2.16
0.17
3.44
3.58
4.11
0.30
2.28
1.56
0.94
100
0
3
MMAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
500
98.7
98.2
95.2
97.8
95.1
95.9
93.7
98.0
98.0
96.5
1.3
1.8
4.8
2.2
4.9
4.1
6.3
2.0
2.0
3.5
4
500
5
500
6
500
40
60
80
20
20
20
20
7
500
8
500
9
250
10
11
12
a
1000
1500
2000
b
Note: General conditions: complex: 5 µmol; solvent: toluene (30 ml); reaction time: 30 min; ethylene pressure: 1 atm. Reaction tem-
c
5
–1 –1 d
perature. The unit of activity: 10 g mol(Ni)
h . Determined by GC.
increased, the catalytic activity first increased and then
decreased and the highest value was obtained at the
ratio of 1000. However, the Al/Ni molar ratio had little
influence on the distribution of oligomers.
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