Synthesis, structure, and catalytic ethylene oligomerization of nickel complexes bearing 2-pyrazolyl substituted 1,10-phenanthroline ligands

Article abstract of DOI:10.1016/j.molcata.2008.08.015

A series of nickel(II) halide complexes [NiCl₂(L)] (1a-12a) and [NiBr₂(L)] (1b-12b) bearing 2-pyrazolyl substituted 1,10-phenanthroline derivatives (L¹-L¹²) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray diffraction analysis (for 1a′, 10b and 12b). Upon activation with methylaluminoxane (MAO), these complexes display good catalytic activities in ethylene oligomerization (up to 3.01 × 10⁵ g mol(Ni)^-1 h^-1 at 10 atm of ethylene for 12a with L¹² = 2-(3,5-diphenylpyrazol-1-yl)-9-mesityl-1,10-phenanthroline). Complexes with bulkier aryl groups in the 9-position of the phenanthroline ring and the 3- and 5-position of the pyrazolyl ring give higher activities. This is explained with the formation of a more directional environment, a reaction channel around the nickel center which enhances the probability of insertion over dissociation after ethylene coordination to Ni. Also, bulkier aryl substituents can suppress chain-transfer reactions (typically β-H elimination) and therefore increase the activity.

Full text of DOI:10.1016/j.molcata.2008.08.015

Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis, structure, and catalytic ethylene oligomerization of
nickel complexes bearing 2-pyrazolyl substituted 1,10-phenanthroline ligands
Yue Yanga,c, Peiju Yanga, Cui Zhanga,c, Gang Lia, Xiao-Juan Yanga, Biao Wua,∗, Christoph Janiakb,∗
a State Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
b Institut für Anorganische und Analytische Chemie, Universität Freiburg, Albertstr. 21, D-79104 Freiburg, Germany
c Graduate School of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2008
Received in revised form 22 August 2008
Accepted 22 August 2008
Available online 5 September 2008
A series of nickel(II) halide complexes [NiCl2(L)] (1a–12a) and [NiBr2(L)] (1b–12b) bearing 2-pyrazolyl sub-
stituted 1,10-phenanthroline derivatives (L1–L12 ) have been synthesized and characterized by elemental
analysis, IR spectroscopy and X-ray diffraction analysis (for 1aꢀ, 10b and 12b). Upon activation with methy-
laluminoxane (MAO), these complexes display good catalytic activities in ethylene oligomerization (up to
3.01 × 105 g mol(Ni)−1 h−1 at 10 atm of ethylene for 12a with L12 = 2-(3,5-diphenylpyrazol-1-yl)-9-mesityl-
1,10-phenanthroline). Complexes with bulkier aryl groups in the 9-position of the phenanthroline ring
and the 3- and 5-position of the pyrazolyl ring give higher activities. This is explained with the formation
of a more directional environment, a reaction channel around the nickel center which enhances the prob-
ability of insertion over dissociation after ethylene coordination to Ni. Also, bulkier aryl substituents can
suppress chain-transfer reactions (typically ␤-H elimination) and therefore increase the activity.
© 2008 Elsevier B.V. All rights reserved.
Keywords:
Nickel complexes
Ethylene oligomerization
Phenanthroline ligand
Nitrogen ligands
Methylalumoxane
1. Introduction
plexes because it is convenient to tailor their steric and electronic
structure by varying the substituents [16]. However, late transition
The oligomerization of ethylene is an important process that is
used to convert this basic feedstock into various useful products.
The development of new molecular catalysts for the oligomeriza-
tion and polymerization of ethylene is the key in this area [1,2]. Late
transition metal complexes have attracted intense attention in the
past decade because of their high activity for ethylene activation,
and various catalyst systems have been studied and reviewed [2,3].
Nickel complexes are of great interest in this respect due to their
activities in the SHOP process of ethylene oligomerization [4]. A
number of nickel complexes have been reported for olefin oligomer-
ization, including tetra-coordinated catalyst precursors containing
bidentate ligands such as PˆP [5], PˆO [6], PˆN [7], NˆN [8], and NˆO
[9], or penta-coordinated systems with tridentate ligands of NˆNˆO
[10], NˆOˆN [11], NˆNˆN [10-13], PˆNˆN [14] and NˆSˆN type [15].
Recently we have been interested in nickel complexes with
tridentate NˆNˆN ligands for ethylene oligomerization. For this
purpose a series of pyrazolyl-substituted 1,10-phenanthroline
compounds have been designed. 1,10-Phenanthroline and its
derivatives are widely used as ligands for late transition metal com-
metal complexes of 1,10-phenanthrolines have rarely been stud-
ied for catalytic ethylene oligomerization/polymerization [17]. We
have previously reported the catalytic behavior of some nickel and
cobalt complexes with bidentate 2,9-diaryl-1,10-phenanthrolines
(NˆN) [18]. Some nickel catalysts with tridentate 2-imino-1,10-
phenanthrolines have also been reported recently [19,20]. In the
present work, we have explored a series of tridentate (NˆNˆN) 1,10-
phenanthrolines bearing 2-pyrazolyl and 9-aryl substituents, and
present herein the synthesis and crystal structure of the nickel(II)
complexes as well as their catalytic activities for ethylene oligomer-
ization with the assistance of methylaluminoxane (MAO).
2. Results and discussion
2.1. Synthesis
The 2-(3-R2-5-R3-pyrazol-1-yl)-9-R1-1,10-phenanthroline lig-
ands (L1–L12) were synthesized using modified literature pro-
cedures, as reported for L1 [21] by the Knorr-type cyclization
from various diketones (acetylacetone, benzoylacetone or diben-
zoylmethane) and 2-hydrazine-9-aryl-1,10-phenanthrolines, as
depicted in Scheme 1. Notably, the reaction showed high regioselec-
tivity and only the 3-methyl-5-phenylpyrazolyl isomers have been
obtained in the condensation of the asymmetric benzoylacetone
∗
Corresponding authors. Fax: +86 931 4968286 (B. Wu); fax: +49 761 2036147
(C. Janiak).
E-mail addresses: wubiao@lzb.ac.cn (B. Wu), janiak@uni-freiburg.de (C. Janiak).
1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2008.08.015

10
Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
Scheme 1. Synthesis of the ligands (L1–L12 ) and the complexes [NiCl2(L)] (1a–12a) and [NiBr2(L)] (1b–12b). 1-Nap = 1-naphthyl, Mes = mesityl (–C6H2-2,4,6-Me3).
with 2-hydrazine-9-aryl-1,10-phenanthrolines (in the cases of lig-
ands L2, L5, L8, and L11 ), as confirmed by the 1H NMR spectra. The
nickel(II) complexes were obtained by treating the THF solution
of nickel chloride or bromide salts with the corresponding ligands
(L1–L12) at room temperature in high yields (89–97%, Scheme 1).
These complexes are air-stable in both solution and the solid state,
and were identified by FT-IR and elemental analysis.
2.2. X-ray crystallographic study
Crystals of the dibromide 10b and 12b and the dichloride 1aꢀ
suitable for single-crystal X-ray diffraction were obtained through
slow diffusion of diethyl ether into their dichloromethane (10b and
12b) or methanol (1aꢀ) solution. The molecular structures of the
complexes are shown in Figs. 1–3, and the selected bond lengths
and angles are given in Tables 1 and 2. In general, the complexes
[NiX2(L)] show a 1:1 metal-to-ligand ratio with the metal center
being five-coordinated by the tridentate ligand and the halide (X)
ligands. The structure of 1aꢀ [NiCl(L1)(H2O)2]Cl illustrates the effect
of excess water during crystallization. The association of aqua lig-
ands changes the nickel coordination polyhedron. In accordance
with the tridentate chelating pattern, the central Ni–N2 bond is
shorter than the terminal Ni–N1 and Ni–N4 bonds, while the two
Table 1
Selected bond lengths (Å) and angles (◦) for 10b and 12b
Fig. 1. The molecular structure of 10b (thermal ellipsoids at the 30% probability
level and hydrogen atoms are omitted for clarity).
10b
12b
Ni1–N1
Ni1–N2
Ni1–N4
Ni1–Br1
2.225(3)
1.981(3)
2.123(4)
2.4506(7)
2.3541(7)
78.8(1)
Ni1–N1
Ni1–N2
Ni1–N4
Ni1–Br1
2.183(3)
1.963(4)
2.199(4)
2.391(1)
2.3947(8)
79.5(1)
76.0(1)
155.4(1)
95.9(1)
109.0(1)
93.5(1)
146.17(3)
96.2(1)
104.2(1)
88.4(1)
Table 2
Selected bond lengths (Å) and angles (◦) for 1aꢀ
Ni1–N1
Ni1–N2
Ni1–N4
2.138(3)
1.996(2)
2.145(3)
79.0(1)
Ni1–Cl1
Ni1–O1
Ni1–O2
O1–Ni1–O2
N4–Ni1–Cl1
O1–Ni1–N1
O1–Ni1–N4
N1–Ni1–Cl1
O2–Ni1–N1
O2–Ni1–N4
2.368(1)
2.068(3)
2.074(2)
84.1(1)
93.45(8)
89.9(1)
Ni1–Br2
Ni1–Br2
N2–Ni1–N1
N2–Ni1–N4
N1–Ni1–N4
N1–Ni1–Br1
N2–Ni1–Br1
N4–Ni1–Br1
Br2–Ni1–Br1
N1–Ni1–Br2
N2–Ni1–Br2
N4–Ni1–Br2
N2–Ni1–N1
N2–Ni1–N4
N1–Ni1–N4
N1–Ni1–Br1
N2–Ni1–Br1
N4–Ni1–Br1
Br1–Ni1–Br2
N1–Ni1–Br2
N2–Ni1–Br2
N4–Ni1–Br2
76.2(1)
N2–Ni1–N1
N2–Ni1–N4
N1–Ni1–N4
N2–Ni1–Cl1
O2–Ni1–Cl1
N2–Ni1–O2
N2–Ni1–O1
O1–Ni1–Cl1
154.5(1)
95.21(8)
94.60(9)
92.2(1)
128.36(3)
99.54(9)
136.7(1)
94.86(9)
75.3(1)
154.3(1)
97.08(8)
90.99(8)
171.8(1)
87.8(1)
88.1(1)
90.67(9)
102.1(1)
103.2(1)
175.08(7)

Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
11
bite angles (N1–Ni–N2 and N2–Ni–N4) are comparable to each
other in the range 75.3–76.2◦.
Complex 10b displays a distorted square pyramidal geometry
around the nickel center (Fig. 1). The three nitrogen donors of the
ligand and one of the bromo atoms (Br2) define the basal plane,
while the other Br atom (Br1) occupies the apical coordination site.
The Ni(II) center is located slightly above the basal plane (0.54 Å).
Complex 12b is also five-coordinated by a ligand and two Br atoms
(Fig. 2) [22]. There is a molecule of CH2Cl2 in the crystal. While
the pyrazole ring is nearly coplanar with the phenanthroline plane
in 10b (dihedral angle 3.4◦), it is twisted away in 12b (17.0◦). This
could be attributed to the steric effect of the substituents on the
pyrazole ring (3,5-dimethyl in 10b vs 3,5-diphenyl in 12b). Mean-
while, the Br–Ni–Br angle in 12b (146.17(3)◦) is also significantly
widened compared to 10b (128.36(3)◦), and the mesityl group is
nearly perpendicular to the phenanthroline plane in 10b (dihedral
angle 88.6◦) and 12b (89.2◦) (Table 1).
Complex 1aꢀ [NiCl(L1)(H2O)2]Cl is obtained from water-
containing MeOH/Et2O. The presence of water changes the
coordination mode and sphere of the nickel atom, hence, 1aꢀ
exhibits a different solid-state structure from the above two com-
plexes. The Ni atom is six-coordinated by a tridentate L1, a Cl
atom and two aqua ligands with a distorted octahedral geome-
try (Fig. 3a, Table 2). A second chlorine atom is present as the
counter ion. The pyrazole ring is nearly coplanar with the phenan-
throline plane (dihedral angle 5.6◦), while the two aqua ligands are
cis-coordinated. The chloro ligand and the chloride anion accept
hydrogen bonds from the aqua ligands, leading to a 1D hydrogen-
bonded zigzag chain along the c-axis (Fig. 3b). It should be noted
that attempts to crystallize this compound in the [NiCl2(L)] form
have been unsuccessful. However, while the crystals were obtained
from methanol/ether, the powder samples used for the catalytic
investigation were prepared in THF and were carefully dried to
Fig. 3. (a) The molecular structure of the complex cation [NiCl(L1)(H2O)2]+ in 1aꢀ;
(b) hydrogen-bonded 1D zigzag chain in the crystal structure of 1aꢀ. Hydrogen
bonding parameters O· · ·Cl (Å), ∠O–H· · ·Cl (◦): O1 − H1C· · ·Cl2a: 3.075(3), 174(4);
O1−H1B· · ·Cl2b: 3.065(3), 175(4); O2−H2C· · ·Cl2a: 3.195(3), 163(4); O2−H2B· · ·Cl1c:
3.104(3), 165(4). Symmetry code: a x−1, y + 1, z; −x + 1, −y + 1, −z + 1; c −x, −y + 2,
b
−z + 2.
get the desired composition of [NiCl2(L1)] (1a), as confirmed by
elemental analysis and IR spectroscopy.
2.3. Ethylene oligomerization by the NˆNˆN-coordinated
nickel(II) complexes
The catalytic behavior of the complexes for ethylene oligomer-
ization was investigated using MAO as cocatalyst, and all
of the complexes displayed good catalytic activities (104 to
105 g mol−1 h−1). The catalytic activities are readily compared
to other nickel complexes incorporating tridentate ligands. For
instance, the NˆNˆO [10] and NˆOˆN [11] complexes show activities
of around 104 g mol−1 h−1 atm−1, while the PˆNˆN catalysts [14] can
reach 106 g mol−1 h−1 atm−1. The ethylene reactivity of the NˆNˆN
complexes [12,20] can be up to 105 g mol−1 h−1 atm−1, which is
similar to the nickel complexes presented in this work (the activity
of complex 12a is 14.7 × 104 g mol−1 h−1 atm−1). In a routine scan
of the effect of MAO, the optimum catalytic activity was observed
at an Al/Ni molar ratio of 1500 (vide infra). Therefore, the oligomer-
ization experiments were carried out with a fixed Al/Ni molar ratio
of 1500, and the resultant data are summarized in Table 3.
2.3.1. Effects of the coordination environment
The coordination environment and substituents of the com-
plexes showed different influences on their reactivity with ethy-
lene. The Ni dichloride complexes (1a–12a) and the corresponding
dibromide complexes (1b–12b) have similar oligomerization activ-
ities. As analyzed by GC and GC–MS, the major oligomeric products
are ethylene dimers (1-butene and trans-2-butene) with a small
Fig. 2. The molecular structure of 12b (thermal ellipsoids at the 30% probability
level and hydrogen atoms are omitted for clarity).

12
Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
Table 3
Ethylene oligomerization by complexes 1a–12a and 1b–12ba
Entry
Cat.
Yield (g)
Activity
␣-Olefin b (%)
Oligomer distributionb
(104 g mol−1 h−1
)
C4%
C6%
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
12a
1b
2b
3b
4b
5b
6b
7b
0.08
0.09
0.12
0.10
0.20
0.24
0.19
0.22
0.26
0.20
0.24
0.37
0.07
0.09
0.12
0.10
0.16
0.21
0.18
0.21
0.23
0.18
0.22
0.32
3.10
3.72
4.97
4.55
7.86
9.42
7.60
8.96
10.2
7.78
9.51
14.7
3.03
3.46
4.75
4.06
6.58
8.33
7.08
8.46
9.29
7.10
8.81
12.7
>67
>67
>59
>54
>56
>56
>52
>55
>56
>56
>53
>49
>67
>65
>66
>62
>50
>52
>56
>55
>53
>56
>57
>51
97.2
95.8
92.2
93.6
89.9
87.3
95.9
90.6
89.4
94.3
91.8
88.7
97.7
96.3
94.2
96.5
92.8
90.4
96.1
93.5
91.2
93.2
93.3
89.8
2.8
4.2
7.8
6.4
10.1
12.7
4.1
9.4
10.6
5.7
8.2
11.3
2.3
3.7
5.8
3.5
7.2
9.6
3.9
6.5
8.8
6.8
6.7
10.2
8b
9b
10b
11b
12b
a
Conditions: 5 ␮mol of catalyst, cocat MAO, Al/Ni = 1500, toluene 30 mL, 30 min, 1 atm, and 20 ◦C.
Determined by GC and GC–MS.
b
amount of trimers (up to 12.7%, entry 6 in Table 3) including mainly
1-hexene, 2-hexene and trace of 3-methyl-1-pentene.
With ␤-H elimination assumed as the only chain-transfer mech-
anism in an insertion polymerization the probability ˛ of chain
growth calculates to ˛ = kwcM/(kwcM + k␤-H) with kw = rate constant
activity could be attributed to the steric effects of the bulkier R sub-
stituents that can suppress chain-transfer reactions (typically ␤-H
elimination) and therefore increase the activity [25]. Complexes
with R1 = aryl, R2 = R3 = Ph (6, 9, and 12) indeed gave the highest C6
percentage in each NiCl2 (a) and NiBr2 (b) series. Still the C6 per-
centage of around 10% and its increase from about 5% cannot alone
account for the doubling or tripling of the yield and activity. We,
therefore, suggest that the steric bulk of the aryl groups creates
a reaction channel which makes the ethylene coordination to the
Ni atom more efficient in terms of increasing the probability for
insertion into the Ni–C or Ni–H bond and decreasing the probabil-
ity for a re-dissociation (Scheme 2). Such an activity increase with
increased steric bulk in a more directing environment has been
observed in olefin polymerization reactions with zirconocene/MAO
catalysts, elegantly exemplified in the so-called “advanced metal-
locenes” [26].
for propagation, cM = concentration of monomer, and k␤-H = rate
constant for ␤-H elimination. It could be shown that the growth
probability ˛ decreases with increasing chain length for the first
insertions, due to kw = f(P) and subsequently ˛ = f(P) with P = degree
of oligomerization. In order for a dimeric species (butene, P = 2) to
be the major product (80–90 mol%, cf. Table 3) in ethylene oligomer-
ization a very steep decrease of the insertion rate for the first (into
Ni–H) over the second and all subsequent insertions has to be
assumed together with the rate of the ␤-hydrogen elimination in
the range of kw. It was estimated that kw(P = 1)/kw(P ≥ 2) = 20 and
k␤-H/kw(P = 1) ≈ 5 for the predominant formation of a dimer [23].
The steric bulk of the ligands significantly affected the cat-
alytic activity of the complexes. As shown in Table 3 and Fig. 4,
increasing the size of the substituent R1 on the 9-position of 1,10-
phenanthroline and R2 and R3 on the pyrazolyl ring resulted in
better catalytic activities of the complexes. The activity of [NiCl2(L)]
(series a) and [NiBr2(L)] (series b) increased with larger R1 sub-
stituent (H → Ph → 1-naphthyl → mesityl) for a given R2 and R3
combination. For example, there is a nearly 3-fold increase of
activity for 12a (R1 = mesityl, Table 3, entry 12) compared to 3a
(R1 = H, entry 3). With the same R1 the activity also increased when
the R2 and R3 groups became bulkier from 1, 4, 7, and 10 (with
R2 = R3 = Me) over 2, 5, 8, and 11 (with R2 = Me and R3 = Ph) to 3, 6,
9, and 12 (with R2 = R3 = Ph). Hence, complexes 12a and 12b that
bear the bulkiest ligand, 2-(3,5-diphenylpyrazol-1-yl)-9-mesityl-
1,10-phenanthroline (L12), display the best catalytic activities (14.7
and 12.7 × 104 g mol(Ni)−1 h−1, respectively) among the two series
of complexes.
The aryl groups can exert a conjugating effect which can stabi-
lize the insertion transition state and thereby increase the activity,
as seen before in polymerization reactions [24]. The increase of the
Fig. 4. Effects of the ligands on the activity of the precatalysts (1a–12a, 1b–12b).

Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
13
Table 4
Ethylene oligomerization with 12a and 9a/MAO under different conditionsa
Entry
Al/Ni
T (◦C)
Time (min)
Yield (g)
Activity (104 g mol−1 h−1
)
␣-Olefinb (%)
Oligomer distributionb
C4%
C6%
12a/MAO
25
500
1000
2000
2500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
20
20
20
20
20
20
20
20
20
20
0
30
30
30
30
15
30
45
60
90
0.18
0.23
0.29
0.26
0.34
0.37
0.37
0.38
0.39
0.40
0.23
0.44
0.26
0.19
7.18
9.21
11.5
10.6
27.6
14.7
9.93
7.57
5.25
4.02
9.09
17.6
10.4
7.45
>55
>53
>59
>65
>48
>49
>47
>45
>43
>43
>56
>52
>51
>62
94.9
91.3
90.5
93.8
92.0
88.7
87.6
86.4
84.3
83.4
89.6
86.3
93.9
95.1
5.1
8.7
9.5
6.2
8.0
11.3
12.4
13.6
15.7
16.6
10.4
13.7
6.1
26
27
28
29a
30a
31a
32a
33a
34
35
36
37
38
120
30
30
30
30
40
60
80
4.9
9a/MAO
29b
30b
31b
32b
1500
1500
1500
1500
1500
20
20
20
20
20
15
30
45
60
90
0.24
0.26
0.26
0.27
0.28
19.5
10.2
6.92
5.31
3.73
>57
>56
>54
>52
>50
91.7
89.4
88.1
84.1
82.4
8.3
10.6
11.9
15.9
17.6
33b
a
Conditions: 5 ␮mol catalyst, cocat MAO, toluene 30 mL, 1 atm.
Determined by GC and GC-MS.
b
other hand, varying the MAO to nickel ratio has little influence on
the oligomer distribution.
2.3.3. Effects of oligomerization temperature and time
The catalytic lifetime of 12a was investigated by varying the
reaction time from 15 to 120 min (entries 29–33, Table 4). In the
presence of MAO, ethylene was consumed very quickly over the
first 15 min, and the highest activity of 2.76 × 105 g mol(Ni)−1 h−1
was obtained during 15 min (entry 29a). Between 15 and 30 min
the activity levelled off with only a low increase in yield from
15 to 120 min (entry 29a–34). With prolonged reaction time, the
oligomerization yield increased only very slightly but the yield of
C6 increased progressively, which could be attributed to the rein-
sertion of the 1-butene and 2-butene products to form cis-2-hexene
and 3-methyl-1-pentene [27]. Notably, at 120 min, the complexes
still showed some very low activity (small increase in yield from
entry 33a–34). Time experiments carried out with the less active
catalyst 9a/MAO showed the same trend with the activity level-
ling off after 15 min, a low increase in yield from 15 to 90 min but
progressive increase of C6 (entry 29b–33b).
Scheme 2. Representation of the reaction channel formed through the bulky aryl
groups (shaded areas) which renders the ethylene coordination more efficient
towards C–C bond formation (bold arrows) and decreases the back reaction of dis-
sociation (normal arrow).
2.3.2. Effects of Al/Ni molar ratio
The influence of MAO to metal molar ratio on ethylene activation
was investigated in detail with 12a in the range 500–2500 (entries
25–28 and 30a, Table 4). The catalytic activity first increased from
an Al/Ni ratio of 500 to 1500, at which point the highest catalytic
activity was attained (entry 12, Table 3). With further increasing the
Al/Ni ratio from 1500 to 2500, the activity decreased slightly. On the
The catalytic system of 12a with 1500 equiv of MAO was inves-
tigated at different reaction temperatures under 1 atm of ethylene
(entries 35–38 and 30a, Table 4). When the temperature was raised
by every 20 ◦C from 0 to 80 ◦C, the catalytic activity of 12a increased
gradually, reaching the optimum value at 40 ◦C (entry 36). Upon
Table 5
Ethylene oligomerization with 12a and 12b at different pressuresa
Entry
Cat.
P (atm)
Yield (g)
Activity (105 g mol−1 h−1
)
␣-Olefin b (%)
Oligomer distributionb
C4%
C6%
39
40
41
42
43
44
12a
12a
12a
12b
12b
12b
5.0
7.5
10
5.0
7.5
10
1.05
1.28
1.51
0.80
0.97
1.22
2.09
2.56
3.01
1.59
1.94
2.44
>28
>32
>32
>31
>28
>29
94.9
94.4
93.4
96.3
94.5
92.8
5.1
5.6
6.6
3.7
5.5
7.2
a
Conditions: 5 ␮mol catalyst, cocat MAO, Al/M = 1500, toluene 100 mL, 60 min, and 20 ◦C.
Determined by GC and GC–MS.
b

14
Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
further elevation of the temperature to 60 and 80 ◦C, the catalytic
activity began to decrease. This could be due to the thermal insta-
bility of the active species at higher temperature. However, part
of the activity decrease by ∼50% from 40 ◦C (entry 36, Table 4) to
80 ◦C (entry 38, Table 4) can also be ascribed to the decrease of ethy-
lene solubility, that is, monomer concentration in toluene which is
0.12 mol kg−1 bar−1 at 40 ◦C and 0.08 mol kg−1 bar−1 at 70 ◦C [28].
4.2. Synthesis of the ligands L1–L12
The compound 2-(3,5-dimethylpyrazol-1-yl)-1,10-phenan-
throline (ligand L1) is known [21]. The new analogs (L2–L12
)
were prepared using slightly modified procedures: a mixture
of 2-hydrazine-1,10-phenanthroline or 2-hydrazine-9-aryl-1,10-
phenanthroline (3.0 mmol) and the diketone (3.6 mmol), i.e.
acetylacetone (for L1, L4, L7, and L10), benzoylacetone (for L2,
L5, L8, and L11 ), or dibenzoylmethane (for L3, L6, L9, and L12),
was stirred in dry methanol (15 mL) containing a few drops of
acetic acid for 6–12 h. The solvent was removed and the residue
was recrystallized from chloroform/activated charcoal to give the
products.
2.3.4. Effects of ethylene pressure on the catalytic activity
Ethylene oligomerization experiments with the nickel dichloro-
(12a) and dibromo complexes (12b) were carried out under
different pressures of ethylene, as shown in Table 5. The catalytic
activities of the precatalysts 12a and 12b (entries 39–41 and 42–44)
are only slightly enhanced at higher pressure of ethylene, and the
nickel dichloride complexes are better than the dibromide analogs.
However, elevation of ethylene pressure significantly increased the
activities of the nickel complexes with bidentate (NˆN) 2,9-diaryl-
1,10-phenanthrolines [18]. The best catalytic activity at 10 atm of
ethylene was obtained with 12a (3.01 × 105 g mol(Ni)−1 h−1). The
results also indicate that the effects of the ligand environment on
the activity at 10 atm is similar to those observed at 1 atm of ethy-
lene.
4.2.1. 2-(3,5-Dimethylpyrazol-1-yl)-1,10-phenanthroline (L1)
White solid (79%). mp: 161 ◦C. ESI-MS: m/z 275.3 [M+H]+. 1H
NMR (400 MHz, CDCl3, ı/ppm): 9.16 (dd, J = 1.6, 4.4 Hz, 1H, H-9),
8.35–8.25 (m, 3H, H-8, H-4, H-7), 7.83–7.76 (m, 2H, H-5, H-6), 7.64
(dd, J = 8.0, 4.4 Hz, 1H, H-3), 6.09 (s, 1H, pyrazolyl-H), 3.02 (s, 3H,
CH3), and 2.35 (s, 3H, CH3). Anal. Calcd for C17 H14 N4: C 74.43, H
5.14, N 20.42; Found C 74.31, H 5.19, and N 20.48%.
4.2.2. 2-(3-Methyl-5-phenylpyrazol-1-yl)-1,10-phenanthroline
(L2)
3. Conclusions
Pale yellow solid (67%). mp: 174–175 ◦C. ESI-MS: m/z 337.3
[M+H]+. 1H NMR: 9.10 (dd, J = 1.6, 4.4 Hz, 1H, H-9), 8.23 (dd, J = 1.6,
8.0 Hz, 1H, H-7), 8.16 (d, J = 8.0 Hz, 1H, H-4), 7.80–7.75 (m, J = 9.2 Hz,
2H, H-5, H-6), 7.60 (dd, J = 4.4, 8.0 Hz, 1H, H-8), 7.42 (d, J = 8.0 Hz,
1H, H-3), 7.40 (m, 2H, Ph-o-H), 7.28 (m, 3H, Ph-H), 6.39 (s, 1H, H-
4ꢀ), and 2.46 (s, 3H, CH3). Anal. Calcd for C22H16 N4: C 78.55, H 4.79,
N 16.66; Found C 78.47, H 4.69, and N 16.82%.
A series of nickel complexes bearing 2-pyrazolyl substituted
1,10-phenanthroline derivatives have been synthesized and char-
acterized. These complexes exhibit good activities for ethylene
oligomerization in the presence of MAO as cocatalyst, and the main
products are ethylene dimers and trimers. In the tridentate NˆNˆN
catalytic system, complexes containing bulky aryl substituents have
higher ethylene activity. The ethylene oligomerization activities
are influenced by the Al/M molar ratio, reaction time, reaction
temperature and ethylene pressure, and complex 12a displays
the best catalytic activity among the series of complexes (up to
3.01 × 105 g mol(Ni)−1 h−1 at 10 atm). The increase of the activity
and the C6-percentage with the steric bulk of the ligand suggests
continuing along this route with the addition of even bulkier groups
in the 9-position of the phenanthroline ring and the 3- and 5-
position of the pyrazolyl ring to improve the catalytic behavior.
4.2.3. 2-(3,5-Diphenylpyrazol-1-yl)-1,10-phenanthroline (L3)
Pale yellow solid (63%). mp: 187–188 ◦C. ESI-MS: m/z 399.4
[M+H]+. 1H NMR: 9.08 (dd, J = 1.6, 4.4 Hz, 1H, H-9), 8.24 (dd, J = 8.8,
1.6 Hz, 2H, H-4, H-7), 8.03–8.01 (t, J = 1.2, 7.2 Hz, 2H, Ph-o-H), 7.79 (s,
2H, H-5, H-6), 7.73 (d, J = 8.4 Hz, 1H, H-8), 7.61 (dd, J = 4.4, 8.0 Hz, 1H,
H-3), 7.50–7.46 (m, 5H, Ph-H), 7.44–7.31 (m, 5H, Ph-H), and 6.92 (s,
1H, H-4ꢀ). Anal. Calcd for C27H18 N4: C 81.39, H 4.55, N 14.06; Found
C 81.37, H 4.32, and N 13.87%.
4. Experimental
4.1. General considerations
4.2.4. 2-(3,5-Dimethylpyrazol-1-yl)-9-phenyl-1,
10-phenanthroline (L4)
White solid (66%). mp: 154–155 ◦C. ESI-MS: m/z 351.2 [M+H]+.
1H NMR: 8.41–8.39 (m, 5H, Ph-o-H, H-4, H-7, H-8), 8.14 (d, J = 8.4 Hz,
1H, H-3), 7.81 (s, 2H, H-5, H-6), 7.58–7.49 (m, 3H, Ph-H), 6.13 (s,
1H, H-4ꢀ), 3.26 (s, 3H, CH3), and 2.37 (s, 3H, CH3). Anal. Calcd for
All air- and water-sensitive reactions were performed under
nitrogen using standard Schlenk techniques. THF and Et2O were
dried by sodium/benzophenone and distilled under nitrogen prior
to use. Toluene was dried by sodium. MAO solution (1.65 M in
toluene) was purchased from Albemarle Co. (USA). 1H and 13C NMR
spectra were obtained on a Mercury plus-400 spectrometer with
TMS as the internal standard. IR spectra were recorded as KBr pel-
lets with a Bruker IFS 120HR spectrometer. ESI-MS spectra were
measured on a Waters ZQ 4000 instrument. Element analyses were
performed with an Elementar VarioEL instrument.
1,10-Phenanthroline, bromobenzene, 1-bromonaphthalene,
acetylacetone, 2-bromomesitylene, and other common chem-
icals were commercially available and were used without
further purification. Benzoylacetone [29] and dibenzoylmethane
[30] were synthesized according to literature procedures. 2-
Phenyl-1,10-phenanthroline, 2-(1-naphthyl)-1,10-phenanthroline,
2-(2,4,6-trimethylphenyl)-1,10-phenanthroline [31], and 2-
hydrazine-1,10-phenanthroline [21] were prepared as described in
the literature.
C23H18 N4: C 78.83, H 5.18, N 15.99; Found C 78.84, H 5.06, and N
15.75%.
4.2.5. 2-(3-Methyl-5-phenylpyrazol-1-yl)-9-phenyl-1,10-
phenanthroline
(L5)
Pale yellow solid (61%). mp: 197–198 ◦C. ESI-MS: m/z 413.4
[M+H]+. 1H NMR: 8.35 (d, J = 8.8 Hz, 1H, H-4), 8.24 (d, J = 8.4 Hz,
1H, H-7), 8.09 (d, J = 8.0 Hz, 1H, H-8), 8.02 (d, J = 8.8 Hz, 1H, H-3),
7.92–7.90 (dd, J = 1.6, 6.8 Hz, 2H, Ph-o-H), 7.77 (s, 2H, H-5, H-6), 7.58
(d, J = 7.2 Hz, 2H, Ph-o-H), 7.49–7.44 (m, 3H, Ph-H), 7.34–7.27 (m,
3H, Ph-H), 6.43 (s, 1H, H-4ꢀ), and 2.44 (s, 3H, CH3). Anal. Calcd for
C28H20N4: C 81.53, H 4.89, N 13.58; Found: C 81.46, H 4.92, and N
13.47%.

Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
15
4.2.6. 2-(3,5-Diphenylpyrazol-1-yl)-9-phenyl-
H-5, H-6), 7.53–7.50 (m, 3H, Ph-H), 7.44 (t, J = 7.4 Hz, 2H), 7.35 (t,
J = 7.4 Hz, 1H, Ph-H), 7.09–7.07 (m, 3H, Ph-H, Mes-ArH), 6.97 (s, 1H,
Mes-ArH), 6.83 (s, 1H, H-4ꢀ), 2.38 (s, 3H, CH3), and 1.97 (s, 6H, CH3).
Anal. Calcd for C36H28N4: C 83.69, H 5.46, N 10.84; Found C, 83.45,
H 5.51, and N 10.95%.
1,10-phenanthroline (L6)
Pale yellow solid (56%). mp: 204–205 ◦C. ESI-MS: m/z 475.4
[M+H]+. 1H NMR: 8.35 (d, J = 8.4 Hz, 1H, H-4), 8.27–8.23 (t, J = 8.8 Hz,
2H, Ph-H), 8.04–7.98 (m, 3H, H-3, H-7, H-8), 7.93–7.91 (m, 2H, Ph-
o-H), 7.79 (s, 2H, H-5, H-6), 7.68 (dd, J = 7.2, 1.2 Hz, 2H, Ph-m-H),
7.51–7.45 (m, 5H, Ph-H), 7.39–7.27 (m, 5H, Ph-H), and 6.94 (s, 1H,
H-4ꢀ). Anal. Calcd for C33H22N4: C 83.52, H 4.67, N 11.81; Found C
83.43, H 4.43, and N 11.55%.
4.3. Synthesis of the nickel complexes
The nickel(II) complexes were synthesized by the following gen-
eral procedure: a solution of the ligand in THF was added to an
equimolar amount of NiCl2·6H2O or NiBr2·6H2O in THF. The reac-
tion mixture was stirred at room temperature for 12 h. The resultant
precipitate was collected, washed with THF and diethyl ether, and
dried in vacuum. All of the complexes were prepared in high yield
in this manner.
4.2.7. 2-(3,5-Dimethylpyrazol-1-yl)-9-(1-naphthyl)-
1,10-phenanthroline (L7)
Pale yellow solid (57%). mp: 178–179 ◦C. ESI-MS: m/z 401.3
[M+H]+. 1H NMR: 8.69 (d, J = 8.4 Hz, 1H, H-4), 8.40–8.30 (m, 3H,
Nap-H, H-7), 8.00-7.95 (m, 3H, Nap-H, H-8), 7.84 (d, J = 4.4 Hz, 3H,
H-5, H-6, H-3), 7.64–7.47 (m, 3H, Nap-H), 6.00 (s, 1H, H-4ꢀ), 2.93 (s,
3H, CH3), and 2.32 (s, 3H, CH3). Anal. Calcd for C27H20N4: C 80.97,
H 5.03, N 13.99; Found C 80.90, H 4.74, and N 13.76%.
[NiCl2(L1)] (1a). Light green powder (96.9%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3050, 2919, 1613, 1584, 1569, 1459, 1432, 1416, 1385,
1367, 1332, 1128, 1070, 985, 848, 757, 734, and 649. Anal. Calcd for
4.2.8. 2-(3-Methyl-5-phenylpyrazol-1-yl)]-9-
C17 H14 N4NiCl2 (403.92): C 50.55, H 3.49, N 13.87; Found: C 50.36,
H 3.28, and N 13.48%.
(1-naphthyl)-1,10-phenanthroline (L8)
Pale yellow solid (52%). mp: 181–182 ◦C. ESI-MS: m/z [M+H]+
463.4. 1H NMR: 8.29 (dd, J = 8.8, 8.0 Hz, 2H, Nap-H), 8.02 (d,
J = 8.4 Hz, H-4), 7.95 (t, J = 7.4 Hz, 3H, H-7, Nap-H), 7.88–7.80 (m, 3H,
H-5, H-6, H-8), 7.65–7.56 (m, 2H, H-3, Nap-H), 7.52–7.40 (m, 4H,
Nap-H, 2Ph-H), 7.06 (t, J = 7.6 Hz, 2H, Ph-H), 6.99 (t, J = 7.4 Hz, 1H, Ph-
H), 6.31 (s, 1H, H-4ꢀ), and 2.39 (s, 3H, CH3). Anal. Calcd for C32H22N4:
C 83.09, H 4.79, N 12.11; Found C 83.30, H 4.74, and N 11.94%.
[NiCl2(L2)] (2a). Light green powder (97.2%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3055, 2921, 1611, 1563, 1463, 1431, 1403, 1363, 1329,
1201, 1141, 1032, 978, 885, 854, 776, 764, 738, 702, and 649. Anal.
Calcd for C22H16 N4NiCl2 (465.99): C 56.70, H 3.46, N 12.02; Found:
C 56.92, H 3.54, and N 11.77%.
[NiCl2(L3)] (3a). Light green powder (94.0%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3053, 2920, 2871, 1613, 1588, 1558, 1497, 1462, 1433,
1404, 1332, 1152, 977, 851, 761, 733, 700, and 651. Anal. Calcd for
4.2.9. 2-(3,5-Diphenylpyrazol-1-yl)-9-(1-naphthyl)-
C27H18 N4NiCl2 (528.06): C 61.41, H 3.44, N 10.61; Found: C 61.02, H
3.25, and N 10.25%.
1,10-phenanthroline (L9)
Pale yellow solid (42%). mp: 189–190 ◦C. ESI-MS: m/z 525.7
[M+H]+. 1H NMR: 8.37 (d, J = 8.8 Hz, 2H, Nap-H), 8.29 (d, J = 8.0 Hz,
2H, Nap-H), 8.14 (d, J = 8.8 Hz, H-4), 8.07 (d, J = 8.0 Hz, H-7), 7.97
(t, J = 7.6 Hz, 4H, H-5, H-6, H-3, H-8), 7.88 (t, J = 7.6 Hz, 3H, Nap-
H), 7.65 (t, J = 7.8 Hz, 3H, Nap-H), 7.57–7.37 (m, 7H, Ph-H, Nap-H),
7.34 (t, J = 7.0 Hz, 1H, Ph-H), 7.09 (t, J = 7.6 Hz, 2H, Ph-H), 7.00
(t, J = 7.2 Hz, 1H, Ph-H), and 6.83 (s, 1H, H-4ꢀ). Anal. Calcd for
[NiCl2(L4)] (4a). Yellow powder (93.4%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3051, 2920, 1621, 1578, 1561, 1499, 1443, 1425, 1364, 1336,
1131, 984, 858, 778, 740, 704, and 655. Anal. Calcd for C23H18 N4NiCl2
(480.01): C 57.55, H 3.78, N 11.67; Found: C 57.21, H 3.90, and N
11.49%.
[NiCl2(L5)] (5a). Yellow powder (92.2%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3053, 2923, 2853, 1622, 1593, 1574, 1510, 1498, 1443,
1426, 1380, 1363, 1335, 1143, 1034, 978, 860, 760, 741, 701, and 654.
Anal. Calcd for C28H20N4NiCl2 (542.08): C 62.04, H 3.72, N 10.34;
Found: C 62.36, H 3.58, and N 10.03%.
C37H24N4: C 84.71, H 4.61, N 10.68; Found C 85.02, H 4.38,
and N 10.39%.
4.2.10. 2-(3,5-Dimethylpyrazol-1-yl)-9-mesityl-
[NiCl2(L6)] (6a). Yellow powder (93.0%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3055, 2922, 2852, 1622, 1611, 1593, 1571, 1497, 1457, 1426,
1363, 1337, 1154, 979,862, 771, 761, 740, 701, and 657. Anal. Calcd
for C33H22N4NiCl2 (604.15): C 65.60, H 3.67, N 9.27; Found: C 65.98,
H 3.82, and N 9.13%.
1,10-phenanthroline (L10
)
Pale yellow solid (52%). mp: 219–220 ◦C. ESI-MS: m/z 393.5
[M+H]+. 1H NMR: 8.28 (m, 3H, H-4, H-7, H-8), 7.81 (s, 2H, H-5, H-6),
7.59 (d, J = 8.0 Hz, 1H, H-3), 6.98 (s, 2H, Ph-m-H), 6.02 (s, 1H, H-4ꢀ),
2.91 (s, 3H, CH3), 2.36 (s, 3H, CH3), 2.32 (s, 3H, CH3), and 2.18 (s, 6H,
CH3). Anal. Calcd for C26H24N4: C 79.56, H 6.16, N 14.27; Found C
79.27, H 6.14, and N 13.81%.
[NiCl2(L7)] (7a). Light yellow powder (95.3%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3050, 2922, 2853, 1621, 1580, 1560, 1499, 1456,
1425, 1362, 1336, 983, 860, 781, 757, and 664. Anal. Calcd for
C27H20N4NiCl2 (530.07): C 61.18, H 3.80, N 10.57; Found: C 60.90,
4.2.11. 2-(3-Methyl-5-phenylpyrazol-1-yl)-9-mesityl-
H 3.62, and N 10.41%.
1,10-phenanthroline (L11
)
[NiCl2(L8)] (8a). Light yellow powder (93.0%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3054, 2924, 1623, 1591, 1577, 1499, 1442, 1426, 1360,
1336, 972, 900, 864, 782, 761, and 701. Anal. Calcd for C32H22N4NiCl2
(592.14): C 64.91, H 3.74, N 9.46; Found: C 64.97, H 4.02, and N 9.52%.
[NiCl2(L9)] (9a). Yellow powder (90.4%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3055, 2923, 2853, 1622, 1592, 1575, 1495, 1458,
1426, 1362, 1336, 973, 901, 863, 774, and 700. Anal. Calcd for
C37H24N4NiCl2 (654.21): C 67.93, H 3.70, N 8.56; Found: C 68.17,
H 3.49, and N 8.51%.
Pale yellow solid (48%). mp: 202–203 ◦C. ESI-MS: m/z 455.4
[M+H]+. 1H NMR: 8.27 (d, J = 8.8 Hz, H-4), 8.35 (d, J = 8.0 Hz, H-7),
7.81 (t, J = 4.8 Hz, 3H, H-5, H-6, H-8), 7.51 (d, J = 7.84 Hz, 1H, H-3),
7.42 (m, 2H, Ph-H), 7.08 (d, J = 2.8 Hz, 3H, Ph-o-H, Ph-p-H), 6.96 (s,
2H, Mes-ArH), 6.32 (s, 1H, H-4ꢀ), 2.39 (s, 3H, CH3), 2.37 (s, 3H, CH3),
2.25 (s, 3H, CH3), and 1.96 (s, 3H, CH3). Anal. Calcd for C31H26N4: C
81.90, H 5.70, N, 12.33; Found C 81.75, H 5.44, and N 12.55%.
4.2.12. 2-(3,5-Diphenylpyrazol-1-yl)-9-mesityl-
[NiCl2(L10)] (10a). Light yellow powder (92.8%). Mp: > 300 ◦C.
IR (KBr, ꢀ/cm−1): 3054, 2920, 2854, 1615, 1580, 1562, 1505, 1457,
1425, 1365, 1335, 987, 897, 858, 775, 751, and 701. Anal. Calcd for
C26H24N4NiCl2 (522.09): C 59.81, H 4.63, N 10.73; Found: C 59.51,
H 4.67, and N 10.36%.
1,10-phenanthroline (L12
)
Pale yellow solid (41%). mp: 192 ◦C. ESI-MS: m/z 517.4 +. 1H NMR:
8.35 (d, J = 8.8 Hz, 1H, H-4), 8.23 (d, J = 8.0 Hz, 1H, H-7), 8.06 (d,
J = 8.4 Hz, 1H, H-8), 7.96 (dd, J = 1.6, 6.8 Hz, 2H, H-3), 7.83 (s, 2H,

16
Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
[NiBr2(L12)] (12b). Pale blue powder (91.1%). Mp: > 300 ◦C. IR
[NiCl2(L11 )] (11a). Light yellow powder (91.9%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3056, 2919, 1612, 1592, 1573, 1493, 1457, 1430, 1359,
1337, 979, 892, 860, 766, and 701. Anal. Calcd for C36H28N4NiBr2
(735.14): C 58.82, H 3.84, N 7.62; Found: C 59.14, H 3.68, and N
7.59%.
(KBr, ꢀ/cm−1): 3050, 2921, 2855, 1615, 1577, 1497, 1451, 1427, 1364,
1336, 980, 895, 858, 758, and 701. Anal. Calcd for C31H26N4NiCl2
(584.16): C 63.74, H 4.49, N 9.59; Found: C 63.55, H 4.51, and N
9.34%.
[NiCl2(L12)] (12a). Yellow powder (92.0%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3054, 2921, 2858, 1612, 1573, 1493, 1457, 1427, 1361, 1336,
4.4. General procedure for ethylene oligomerization
979, 895, 864, 771, 759, and 703. Anal. Calcd for C36H28N4NiCl2
(646.23): C 66.91, H 4.37, N 8.67; Found: C 67.28, H 4.34, and N
8.90%.
4.4.1. Oligomerization at 1 atm
In a typical experiment, the complex (5 ␮mol) was added to a
glass reactor, which wasevacuatedandfilledthreetimes withnitro-
gen and once with ethylene. Then 30 mL of freshly distilled toluene
was introduced into the reactor with stirring. Methylaluminoxane
toluene solution of desired amount was injected into the suspen-
sion via a syringe and the color of the solution changed immediately
from colorless to yellow. After the reaction mixture was stirred
under 1 atm of ethylene for a given period using a water bath to
maintain the temperature, a small amount of the solution was taken
out with a syringe and quenched by ice-cooled 10% HCl solution
(ice-bath was used in order to prevent the loss of more volatile C4).
About 1 mL of the organic layer was dried with anhydrous MgSO4
for GC or GC–MS measurements. Then the reaction was terminated
by adding HCl/EtOH solution and no polymer was found.
[NiBr2(L1)] (1b). Pale blue powder (95.5%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3056, 2924, 1613, 1585, 1571, 1504, 1459, 1432, 1416, 1384,
1366, 1352, 1330, 1128, 1070, 984, 846, 786, 755, 733 680, and 650.
Anal. Calcd for C17 H14 N4NiBr2 (492.82): C 41.43, H 2.86, N 11.37;
Found: C 40.91, H 2.64, and N 11.20%.
[NiBr2(L2)] (2b). Pale blue powder (94.3%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3059, 2928, 1611, 1589, 1566, 1510, 1462, 1431, 1407, 1377,
1350, 1199, 1142, 1031, 976, 885, 853, 763, 736, 703, and 650. Anal.
Calcd for C22H16 N4NiBr2 (554.89): C 47.62, H 2.90, N 10.10; Found:
C 47.29, H 3.13, and N 9.89%.
[NiBr2(L3)] (3b). Pale blue powder (90.5%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3055, 2924, 1609, 1587, 1561, 1499, 1430, 1405, 1346,
1225, 1163, 1062, 1028, 975, 852, 764, 755, 735, 695, and 650. Anal.
Calcd for C27H18 N4NiBr2 (616.96): C 52.56, H 2.94, N 9.08; Found:
C 52.25, H 3.10, and N 8.70%.
4.4.2. High-pressure oligomerization
[NiBr2(L4)] (4b). Yellow powder (92.1%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3050, 2919, 1621, 1578, 1499, 1443, 1425, 1363, 1337,
1156, 1130, 983, 858, 777, 740, 707, 688, and 655. Anal. Calcd for
C23H18 N4NiBr2 (568.92): C 48.56, H 3.19, N 9.85; Found: C 48.02, H
2.80, and N 9.39%.
A 1L stainless-steel autoclave equipped with an electronically
controlled stirrer was evacuated and filled three times with nitro-
gen and twice with ethylene. Freshly distilled toluene (100 mL) was
added. After the temperature reached a certain point, MAO was
injected followed by a toluene (20 mL) solution of the catalyst. The
reactor pressure was kept constant throughout the oligomerization
process by manually controlled addition of ethylene. After 30 min
the reactor was cooled in an ice bath, the extra ethylene was vented
off and the run was quenched with a solution of 10% HCl. Quanti-
tative GC analysis of the product was performed immediately after
the termination of the reaction.
GC analysis was performed with an SP-2100 gas chromatogra-
phy spectrometer equipped with a flame ionization detector and an
SE-30 silica capillary column. The column temperature was started
at 50 ◦C (3 min), raised by 5 ◦C/min to 250 ◦C and kept at 250 ◦C for
10 min. GC–MS analysis was done using an Agilent 6890N/5973N
GC/MS spectrometer with an HP-1 capillary column. The column
temperature was started at 50 ◦C (2 min), raised by 15 ◦C/min to
280 ◦C and kept at 280 ◦C for 10 min. The yield of the oligomers was
calculated by referencing to the mass of the used solvent based
on the prerequisite that the mass of each fraction is approximately
proportional to its integrated areas in the GC trace.
[NiBr2(L5)] (5b). Dark yellow powder (90.4%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3056, 2923, 2852, 1622, 1613, 1593, 1576, 1510, 1499,
1443, 1426, 1381, 1364, 1337, 1201, 1143, 1034, 860, 761, 701, and
654. Anal. Calcd for C28H20N4NiBr2 (630.99): C 53.30, H 3.19, N 8.88;
Found: C 52.93, H 2.87, and N 9.03%.
[NiBr2(L6)] (6b). Dark yellow powder (89.6%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3054, 2923, 2852, 1621, 1610, 1591, 1571, 1496, 1459,
1425, 1363, 1337, 1151, 1068, 979, 859, 761, 739, 699, and 657. Anal.
Calcd for C33H22N4NiBr2 (693.06): C 57.19, H 3.20, N 8.08; Found:
C 57.51, H 3.10, and N 8.49%.
[NiBr2(L7)] (7b). Pale blue powder (94.7%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3050, 2922, 2851, 1623, 1580, 1560, 1501, 1425, 1363, 1337,
987, 860, 806, 781, 757, and 664. Anal. Calcd for C27H20N4NiBr2
(618.98): C 52.39, H 3.26, N 9.05; Found: C 52.68, H 3.39, and N
9.17%.
[NiBr2(L8)] (8b). Pale blue powder (93.0%). Mp: > 300 ◦C. IR (KBr,
ꢀ/cm−1): 3050, 2924, 1621, 1610, 1590, 1577, 1498, 1426, 1360, 1335,
972, 900, 866, 781, 761, and 701. Anal. Calcd for C32H22N4NiBr2
(681.05): C 56.43, H 3.26, N 8.23; Found: C 56.49, H 3.19, and N
8.13%.
4.5. X-ray crystal structure determination
[NiBr2(L9)] (9b). Dark yellow powder (90.2%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3054, 2923, 2852, 1617, 1592, 1575, 1496, 1458,
1428, 1362, 1336, 972, 901, 862, 773, and 699. Anal. Calcd for
Diffraction data for the complexes were collected on a Bruker
SMART APEX II diffractometer at room temperature (293 K) with
graphite-monochromated Mo K␣ radiation (ꢁ = 0.71073 Å). An
empirical absorption correction using SADABS [32] was applied
for all data. The structures were solved by direct methods using
the SHELXS program [33]. All non-hydrogen atoms were refined
anisotropically by full-matrix least-squares on F2 by the use of
the program SHELXL [33]. The hydrogen atoms bonded to car-
bon were included in idealized geometric positions with thermal
parameters equivalent to 1.2 times those of the atom to which
they were attached. Hydrogen atoms on water were located from
the difference Fourier map with O-H ≈0.85(1) Å and were refined
isotropically with U(H) = 0.08 Å2. Crystallographic data for the com-
plexes 1aꢀ, 10b and 12b are listed in Table 6.
C37H24N4NiBr2 (743.11): C 59.80, H 3.26, N 7.54; Found: C 59.69,
H 3.10, and N 7.35%.
[NiBr2(L10)] (10b). Pale blue powder (93.5%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3058, 2921, 2855, 1613, 1581, 1562, 1499, 1459,
1426, 1367, 1337, 987, 898, 863, 775, and 696. Anal. Calcd for
C26H24N4NiBr2 (611.00): C 51.11, H 3.96, N 9.17; Found: C 51.10, H
3.79, and N 8.94%.
[NiBr2(L11 )] (11b). Pale blue powder (92.8%). Mp: > 300 ◦C. IR
(KBr, ꢀ/cm−1): 3050, 2923, 2853, 1611, 1592, 1578, 1496, 1454,
1428, 1365, 1337, 980, 895, 858, 759, and 699. Anal. Calcd for
C31H26N4NiBr2 (673.07): C 55.32, H 3.89, N 8.32; Found: C 55.35, H
3.88, and N 8.11%.

Y. Yang et al. / Journal of Molecular Catalysis A: Chemical 296 (2008) 9–17
17
Table 6
Crystallographic data and structure refinement details
[7] (a) O. Daugulis, M. Brookhart, Organometallics 21 (2002) 5926–5934;
(b) F. Speiser, P. Braunstein, L. Saussine, R. Welter, Inorg. Chem. 43 (2004)
1649–1658.
[8] (a) C.M. Killian, L.K. Johnson, M. Brookhart, Organometallics 16 (1997)
2005–2007;
(b) E.V. Salo, Z. Guan, Organometallics 22 (2003) 5033–5046.
[9] (a) F. Speiser, P. Braunstein, L. Saussine, Inorg. Chem. 43 (2004) 4234–4240;
(b) T.R. Younkin, E.F. Connor, J.I. Henderson, S.K. Friedrich, R.H. Grubbs, D.A.
Bansleben, Science 287 (2000) 460–462.
[10] P. Hao, S. Zhang, W.H. Sun, Q. Shi, S. Adewuyi, X. Lu, P. Li, Organometallics 26
(2007) 2439–2446.
[11] N. Ajellal, M.C.A. Kuhn, A.D.G. Boff, M. Horner, C.M. Thomas, J.F. Carpentier, O.L.
Casagrande, Organometallics 25 (2006) 1213–1216.
[12] F.A. Kunrath, R.F.d. Souza, O.L. Casagrande, N.R. Brooks, V.G. Young,
Organometallics 22 (2003) 4739–4743.
[13] Y.D.M. Champouret, J.-D. Marechal, W.R.K. Chaggar, J. Fawcett, K. Singh, F.
Maserasc, G.A. Solan, New J. Chem. 31 (2007) 75–85.
[14] J. Hou, W.H. Sun, S. Zhang, H. Ma, Y. Deng, X. Lu, Organometallics 25 (2006)
236–244.
[15] L.L. de Oliveira, R.R. Campedelli, M.C.A. Kuhn, J.-F. Carpentier, O.L. Casagrande
Jr., J. Mol. Catal. A: Chem. 288 (2008) 58–62.
[16] J.P. Sauvage, Acc. Chem. Res. 23 (1990) 319–327.
[17] (a) H. Tanaka, Y. Kin, M. Nakano, A. Usuki, Patent No. JP 2000344815,
2000342000;
(b) M.D. Doherty, S. Trudeau, P.S. White, J.P. Morken, M. Brookhart,
Organometallics 26 (2007) 1261–1269.
[18] P. Yang, Y. Yang, C. Zhang, X.-J. Yang, H.-M. Hu, Y. Gao, B. Wu, Inorg. Chim. Acta
(2008), DOI: 10.1016/j.ica.2008.1003.1018.
[19] G.J.P. Britovsek, S.P.D. Baugh, O. Hoarau, V.C. Gibson, D.F. Wass, A.J.P. White, D.J.
Williams, Inorg. Chim. Acta 345 (2003) 279–291.
Complex
1aꢀ
10b
12b·CH2Cl2
Empirical formula
Fw
C17 H18 Cl2N4NiO2
439.96
C26H24Br2N4Ni
611.02
C37H30Br2Cl2N4Ni
820.08
yellow
rhombohedral
¯
R3
22.159(1)
22.159(1)
22.159(1)
116.196(1)
116.196(1)
116.196(1)
5367.4(5)
6
Crystal color
Crystal system
Space group
a (Å)
green
triclinic
¯
P1
violet
monoclinic
P21/c
10.0695(8)
13.960(1)
17.544(2)
90
98.341(4)
90
2440.0(3)
4
1.663
1224
4.09
8.424(1)
10.790(1)
11.486(1)
76.113(2)
77.981(2)
68.50(1)
934.6 (2)
2
1.563
452
1.34
0.33 × 0.19 × 0.12
1.84–25.10
4605
3249
1.317
b (Å)
c (Å)
˛ (◦)
ˇ (◦)
ꢂ (◦)
V (Å3)
Z
Dcalcd (g cm−3
F (0 0 0)
)
1.522
2472
2.957
ꢃ (mm−1
)
Crystal size (mm3)
0.26 × 0.24 × 0.23 0.36 × 0.30 × 0.26
ꢄ range (◦)
1.87–26.80
14196
1.67–28.34
33105
8550
0.971
0.0500, 0.1234
0.1380, 0.1551
Reflections collected
Unique reflections
Goodness of fit on F2
R1, wR2 (I > 2ꢅ(I))
R1, wR2 (all data)
5194
0.991
0.0437, 0.0891
0.0884, 0.1034
0.0425, 0.0998
0.0582, 0.1070
[20] (a) L. Wang, W.-H. Sun, L. Han, H. Yang, Y. Hu, X. Jin, J. Organomet. Chem. 658
(2002) 62–70;
(b) W.-H. Sun, S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen, K. Wedeking, R.
Frohlich, J. Organomet. Chem. 691 (2006) 4196–4203.
Acknowledgements
[21] A.M.S. Garas, R.S. Vagg, J. Heterocycl. Chem. 37 (2000) 151–158.
[22] The Addison ␶ parameter 0.30 for 10b and 0.15 for 12b with ␶ = 0.0 for an ideal
square pyramid and ␶ = 1.0 for an ideal trigonal bipyramid; see A.W. Addison,
T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc., Dalton Trans. (1984)
1349–1356.
This work was supported by the “Bairen Jihua” project of the
Chinese Academy of Sciences and by the University of Freiburg.
References
[23] C. Janiak, K.C.H. Lange, P. Marquardt, Macromol. Rapid Commun. 16 (1995)
643–650.
[24] F. Blank, C. Janiak, Coord. Chem. Rev. (2008), DOI: 10.1016/j.ccr.2008.1005.1010.
[25] G.J.P. Britovsek, S. Mastroianni, G.A. Solan, S.P.D. Baugh, C. Redshaw, V.C. Gibson,
A.J.P. White, D.J. Williams, M.R.J. Elsegood, Chem. Eur. J. 6 (2000) 2221–2231.
[26] (a) C. Janiak, K.C.H. Lange, P. Marquardt, J. Mol. Catal. A: Chem. 180 (2002)
43–58;
[1] (a) C. Janiak, F. Blank, Macromol. Symp. 236 (2006) 14–22;
(b) C. Janiak, Coord. Chem. Rev. 250 (2006) 66–94.
[2] (a) F. Speiser, P. Braunstein, L. Saussine, Acc. Chem. Res. 38 (2005)
784–793;
(b) C. Bianchini, G. Giambastiani, I.G. Rios, G. Mantovani, A. Meli, A.M. Segarra,
Coord. Chem. Rev. 250 (2006) 1391–1418.
[3] (a) L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc. 117 (1995)
6414–6415;
(b) C. Janiak, in: A. Togni, R.L. Halterman (Eds.), Metallocenes, vol. 2, Wiley/VCH,
Weinheim, 1998, p. 547, (Chapter 9);
(c) W. Kaminsky, R. Engehausen, K. Zoumis, W. Spaleck, J. Rohrmann, Makro-
mol. Chem. 193 (1992) 1643;
(d) U. Stehling, J. Diebold, R. Kirsten, W. Röll, H.H. Brintzinger, S. Jüngling, R.
Mülhaupt, F. Langhauser, Organometallics 13 (1994) 964;
(e) W. Spaleck, F. Küber, A. Winter, J. Rohrmann, B. Bachmann, M. Antberg, V.
Dolle, E.F. Paulus, Organometallics 13 (1994) 954;
(b) G.J.P. Britovsek, V.C. Gibson, S.J. McTavish, G.A. Solan, A.J.P. White,
D.J. Williams, B.S. Kimberley, P.J. Maddox, Chem. Commun. (1998)
849–850;
(c) B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc. 120 (1998)
4049–4050;
(f) N. Schneider, M.E. Huitenloch, U. Stehling, R. Kirsten, F. Schaper, H.H.
Brintzinger, Organometallics 16 (1997) 3414.
[27] Q.Z. Yang, A. Kermagoret, M. Agostinho, O. Siri, P. Braunstein, Organometallics
25 (2006) 5518–5527.
[28] A. Kruis, In: H. Hausen (Ed.), Technik, Part 4, Vol. c, Springer, Berlin, 1976, p. 121.
[29] D.S. Breslow, C.R. Hauser, J. Am. Chem. Soc. 62 (1940) 2385–2388.
[30] C.F.H. Allen, R.D. Abell, J.B. Normington, Org. Synth. Coll. 1 (1941) 205.
[31] F. Barigelletti, B. Ventura, J.-P. Collin, R. Kayhanian, P. Gavin˜a, J.-P. Sauvage, Eur.
J. Inorg. Chem. (2000) 113–119.
[32] G.M. Sheldrick, Program SADABS: Area-Detector Absorption Correction, Uni-
versity of Göttingen, Germany, 1996.
[33] G.M. Sheldrick, SHELXS-97, SHELXL-97, Programs for Crystal Structure Analysis,
University of Göttingen, Germany, 1997.
(d) V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007) 1745–1776.
[4] W. Keim, F.H. Kowalt, R. Goddard, C. Kruger, Angew. Chem. Int. Ed. 17 (1978)
466–467.
[5] (a) N.A. Cooley, S.M. Green, D.F. Wass, K. Heslop, A.G. Orpen, P.G. Pringle,
Organometallics 20 (2001) 4769–4771;
(b) J.N.L. Dennett, A.L. Gillon, K. Heslop, D.J. Hyett, J.S. Fleming, C.E. Lloyd-
Jones, A.G. Orpen, P.G. Pringle, D.F. Wass, J.N. Scutt, R.H. Weatherhead,
Organometallics 23 (2004) 6077–6079.
[6] (a) J. Heinicke, M.Z. He, A. Dal, H.F. Klein, O. Hetche, W. Keim, U. Florke, H.J.
Haupt, Eur. J. Inorg. Chem. (2000) 431–440;
(b) J.M. Malinoski, M. Brookhart, Organometallics 22 (2003) 5324–5335;
(c) P. Kuhn, D. Sémeril, D. Matt, M.J. Chetcuti, P. Lutz, Dalton Trans. (2007)
515–528.