Nickel(II) complexes bearing phosphinooxazoline ligands: Synthesis, structures and their ethylene oligomerization behaviors

Article abstract of DOI:10.1016/j.jorganchem.2005.05.026

A series of Ni(II) complexes 4a-f ligated by the unsymmetrical phosphino-oxazolines (PHOX) were synthesized and characterized by elemental analysis and IR spectroscopy, and the structures of complexes 4c-4e were confirmed by the X-ray crystallographic analysis. All derivatives showed distorted tetrahedron geometry by the nickel center and coordinative atoms. Upon activation with methylaluminoxane (MAO) or Et₂AlCl, these complexes exhibited considerable to high activity of ethylene oligomerization. The ligands environments and reaction conditions significantly affect their catalytic activities, while the highest oligomerization activity (up to 1.18 × 10⁶ g ? mol^-1(Ni) ? h^-1) was observed for 4d at 20 atm of ethylene. Incorporation of 2-4 equivalents of PPh ₃ as auxiliary ligands in the 4a-f/MAO catalytic systems led to higher activity and longer catalytic lifetime.

Full text of DOI:10.1016/j.jorganchem.2005.05.026

Journal of Organometallic Chemistry 690 (2005) 3918–3928
www.elsevier.com/locate/jorganchem
Nickel(II) complexes bearing phosphinooxazoline ligands:
Synthesis, structures and their ethylene oligomerization behaviors
a
a
a
a,
b
Xiubo Tang , Dongheng Zhang , Suyun Jie , Wen-Hua Sun *, Jiutong Chen
a
Key Laboratory of Engineering Plastics, 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
Received 26 January 2005; received in revised form 12 May 2005; accepted 24 May 2005
Available online 24 June 2005
Abstract
A series of Ni(II) complexes 4a–f ligated by the unsymmetrical phosphino-oxazolines (PHOX) were synthesized and character-
ized by elemental analysis and IR spectroscopy, and the structures of complexes 4c–4e were confirmed by the X-ray crystallographic
analysis. All derivatives showed distorted tetrahedron geometry by the nickel center and coordinative atoms. Upon activation with
methylaluminoxane (MAO) or Et2AlCl, these complexes exhibited considerable to high activity of ethylene oligomerization. The
ligands environments and reaction conditions significantly affect their catalytic activities, while the highest oligomerization activity
(up to 1.18 · 106 g Æ molÀ1(Ni) Æ hÀ1) was observed for 4d at 20 atm of ethylene. Incorporation of 2–4 equivalents of PPh3 as aux-
iliary ligands in the 4a–f/MAO catalytic systems led to higher activity and longer catalytic lifetime.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Phosphinooxazoline ligand; Nickel complex; Ethylene oligomerization
1. Introduction
resurrected the interest in designing new catalysts of late-
transition metal complexes with various ligands, such as,
diimine [4], unsymmetrical pyridylimine [5], salicylaldi-
mine [6] and phosphine-containing ligands [7]. These
numerous studies enrich the knowledge about the effects
of the ligand backbone on the catalysis behavior or mech-
anism aspect of the catalyzing process, although only a
few examples of the catalysts are comparable to Brook-
hartꢀs diimine–Ni(II) complexes in the catalytic activity
[8].
The ethylene oligomerization represents a major indus-
trial process for the production of linear a-olefins, which
are extensively used in the preparation of detergents,
plasticizers, fine chemicals as well as monomers for copo-
lymerization with ethylene in the production of the linear
low-density polyethylene (LLDPE). The linear a-olefins
were originally manufactured by the Ziegler (Alfen) pro-
cess [1], and current industrial catalysts include either
alkylaluminum compound or a combination of alkylalu-
minum compound with early transition metal compounds
or nickel (II) complexes containing bidentate monoan-
ionic [P,O] ligands (the SHOP process) [2]. The discovery
of the cationic (diimino NiCl2) complexes [3] as effective
catalysts for ethylene oligomerization and polymerization
O
PPh2 N
R
1
a R = Bn d R = t-Bu
b R = i-Pr e R = Me
c R = Ph
*
Corresponding author. Tel.: +86 1062557955; fax: +86 1062618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.026

X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
3919
The chiral phosphinooxazoline (PHOX) ligands 1,
R3 R4 R5
first developed independently in 1993 by Pfaltz, Helm-
chen, and Williams as highly effective non-C2-symmetric
ligands for asymmetric allylic alkylation, have been ap-
plied with great success in a diverse range of asymmetric
catalytic reactions [9]. Moreover, it would be interesting
to explore the scope of their coordination with late-tran-
sition metals and their further application in catalytic
systems. In our screening new nickel complexes ligated
by [P,N] ligands for ethylene oligomerization, a series
of various PHOX ligands could provide the information
of stereo- bulky and electronic effects around nickel cen-
ter and their relationship to the catalytic activities be-
cause the adaptation of substituents on oxazoline are
promising. Therefore we designed and synthesized a ser-
ies of Ni(II) complexes ligated by various PHOX and
investigated the catalytic behaviors of the nickel com-
plexes upon activation of methylaluminoxane (MAO)
or Et2AlCl as well as the presence of PPh3 as auxiliary
ligand. Herein we report the synthesis and characteriza-
tion of a series of (PHOX)NiBr2 complexes and their
catalytic behaviors in ethylene oligomerization.
R2
R1
COOH
X
R2
R1
COCl
X
SOCl2
H2N
OH
CH2Cl2
R3
R3
R4 R5
R4 R5
Cl
OH
R2
R1
CONH
R2
R1
CONH
SOCl2
Toluene
X
X
R5
R4
R3
O
R5
R4
R3
R2
R1
N
NaOH
O
CH3OH
R2
R1
X
2a-f
N
THF
PPh2
t-BuCl
THF
3a-f
MPPh2
CH2Cl2
M + PPh3
O
Br
Br
O
Ni
O
R5
R4
O
P
4a: R1=R2=R3=R4=H, R5=CH3;
4b: R1=R3=R3=R5=H, R4=C2H5;
4c: R1=R2=R5=H, R3=R4=CH3;
4d: R1=R3=R4=CH3, R2=R5=H;
4e: R1=R5=H, R2=OCH3, R3=R4=CH3;
4f : R1=R2=R3=R5=H, R4=Ph.
R3
R2
R1
N
Br
Ni
Br
Ph2
2. Results and discussion
4a-f
2.1. Synthesis of the PHOX ligands 3a–f
Scheme 1. Synthesis of the complexes 4a–4f. For 3a–e, X = Br,
M = Li; for 3f, X = F, M = K.
The 2-(2-bromophenyl)-oxazoline 2a–e and 2-(2-flu-
orophenyl)-oxazoline 2f were prepared in high yield
according to the methods cited in the literature [10].
1
O
2a–f were characterized by elemental analysis and H
O
Ph
Ph
NMR spectroscopy. The bromo-substituted precursors
2a–e can react with LiPPh2 in THF to furnish the
PHOX ligands 3a–e in acceptable yields (Scheme 1).
While for the synthesis of the ligand 3f, when the bro-
mo-substituted precursor was applied to react with
LiPPh2 or KPPh2, the homocoupling of bromo-substi-
tuted precursor to compound 5 was obtained as the
dominant product, along with a trace of ligand 3f. Syn-
thesis via the Grignard reagent procedure also furnished
the compound 5 as the main product (Scheme 2). There-
fore, we employed the 2-(2-fluorophenyl)-oxazoline 2f as
precursor to react with the phosphine reagent KPPh2 in
refluxing THF [11], and fortunately, the ligand 3f was
obtained in good yield, though the homo-coupling reac-
tion could not be completely avoided. The racemic li-
gands 3a and 3b were obtained from the racemic
starting materials, while the chiral ligand 3f was synthe-
sized using (S)-(+)-2-amino-2-phenylethanol and 2-flu-
orobenzoic acid as starting materials. These ligands
were isolated as colorless oil or white solid by flash col-
umn chromatography. Slow oxidation of the ligands oc-
curred when they are exposed to air. Ligands 3a–f were
characterized by elemental analysis, 1H NMR, 31P
NMR and IR spectroscopy. The 1H NMR spectrum
N
N
THF
+ Mg
+ PPh2Cl
Br
2f '
MgBr
O
N
MPPh2
THF
Ph
Ph
N
O
M = Li or K
5
Scheme 2. Synthesis of the compound 5.
of ligand 3a, in which the 5-position (neighboring the
oxygen atom) of the oxazoline ring is substituted by
one methyl group, contains one triplet and one quadru-
plet at 3.70 and 4.18 ppm, respectively, which are assign-
able for the CH2 protons in 4-position of the oxazoline
ring. The separation of chemical shifts for the two
protons attached to the same carbon is due to their
inequivalent chemical environment. One proton is in
cis-conformation to the methyl group in the vicinal

3920
X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
carbon, while another proton is in trans-conformation
to this substituent. Similar effect is also observed in
1
the H NMR spectra of 3b and 3f.
2.2. Synthesis of the complexes 4a–f
The Ni(II) complexes 4a–f were prepared by stirring
the corresponding ligands with 0.95 equiv of nickel(II)
bromide 2-methoxyethyl ether [(MEE)NiBr2] for 10 h
in dichloromethane at 25 ꢁC. After workup, the Ni (II)
complexes were isolated as air-stable orange or purple
powder in 67–90% yields.
These complexes were characterized by IR spectral
and elemental analysis. The elemental analysis reveals
that the components of these complexes are in accor-
dance with the formula MLBr2. In the IR spectra, the
stretching vibration of vC@N in complexes show red
shifts by 20–40 cmÀ1 with remarkable decrease in inten-
sity in comparison to the corresponding ligands, which
indicates the coordination of the nitrogen atom in the
oxazoline ring to the metal center. The paramagnetic
nature of these complexes hinders their NMR
characterization.
Fig. 2. Molecular structure of 4d. Hydrogen atoms are omitted for
clarity.
The single crystals of 4c–4e suitable for X-ray crystal-
lography were grown by layer-diffusion of hexane into
their dichloromethane solutions. The molecular struc-
tures of 4c–4e are depicted in Figs. 1–3, respectively.
Their selected bond lengths and angles are listed in
Table 1. The coordination geometry around the nickel
centers for complexes 4c–4e are similar and all adopt
distorted tetrahedron. Hence, only the crystal structure
of 4c was selected to describe in detail. The P, N bite an-
gle (P(1)–Ni(1)–N(1), 89.32(10)ꢁ) in 4c is comparable to
the recently reported P–Ni–N angle (83.52(9)ꢁ) of the
square planar [NiCl2(P, N)]-type complex [7e] and
remarkably deviates from the ideal tetrahedron. The
P(1)–Ni(1) and N(1)–Ni(1) bond lengths are also similar
to the previously reported values [7e,12]. The C(7)–N(1)
bond length in the oxazoline ring has distinctive double-
Fig. 3. Molecular structure of complex 4e. Hydrogen atoms are
omitted for clarity.
˚
bond character with the bond length of 1.299(5) A. The
N(1), Ni(1), P(1), C(1), C(6) and C(7) atoms in the che-
late ring are nearly coplanar and the mean deviation
˚
from the plane is 0.2673 A. In addition, the oxazoline
ring and the coordination ring are approximately copla-
nar with a dihedral angle of 15.4ꢁ, and therefore, the two
methyl groups attached to C(9) may provide some steric
hindrance on the axial sites. In addition, the geometry
around phosphine is also distorted tetrahedral with an-
gles in the range of 104.5(2)–117.95(14) and the three
phenyl rings attached to the phosphine atom are roughly
perpendicular to each other with the dihedral angles of
73.2ꢁ, 84.3ꢁ and 92.5ꢁ, respectively.
2.3. Catalytic oligomerization of ethylene
These nickel (II) complexes were investigated in the
oligomerization of ethylene using MAO or AlEt2Cl as
cocatalyst, and the results are listed in Table 2. In all
Fig. 1. Molecular structure of 4c. Hydrogen atoms and CH2Cl2 are
omitted for clarity.

X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
3921
Table 1
Selected bond lengths and bond angles for complex 4c–4e
4c
4d
4e
˚
Bond lengths (A)
Ni(1)–N(1)
Ni(1)–P(1)
Ni(1)–Br(1)
Ni(1)Br(2)
1.975(3)
2.2637(12)
2.3687(9)
2.3236(9)
1.816(4)
1.809(4)
1.816(4)
Ni–N
Ni–P
1.9900(19)
2.2731(6)
2.3595(5)
2.3303(4)
1.814(2)
Ni(1)–N(1)
Ni(1)–P(1)
Ni(1)–Br(1)
Ni(1)–Br(2)
P(1)C(1)
1.983(2)
2.2740(9)
2.3710(6)
2.3288(5)
1.814(3)
1.820(3)
1.821(3)
Ni–Br(1)
Ni–Br(2)
P–C(7)
P–C(1)
P–C(13)
P(1)–C(1)
P(1)–C(12)
P(1)–C(18)
1.817(2)
1.827(2)
P(1)–C(7)
P(1)–C(13)
Bond angles (ꢁ)
N(1)–Ni(1)–P(1)
N(1)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(2)
P(1)–Ni(1)–Br(1)
P(1)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
C(1)–P(1)–C(12)
C(1)–P(1)–C(18)
C(12)–P(1)–C(18)
C(1)–P(1)–Ni(1)
C(12)–P(1)–Ni(1)
C(18)–P(1)–Ni(1)
89.32(10)
101.63(10)
120.81(10)
104.30(5)
110.40(4)
124.05(3)
105.50(18)
105.72(19)
104.5(2)
N–Ni–P
88.49(6)
104.40(6)
118.62(6)
103.73(2)
114.67(2)
121.338(17)
106.84(10)
103.56(10)
106.90(10)
114.10(8)
119.46(8)
104.57(7)
N(1)–Ni(1)–P(1)
N(1)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(2)
P(1)–Ni(1)–Br(1)
P(1)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
C(1)–P(1)–C(7)
C(1)P(1)–C(13)
C(7)–P(1)–C(13)
C(1)P(1)–Ni(1)
88.09(7)
100.19(7)
119.27(7)
104.54(2)
113.67(3)
124.40(2)
105.39(13)
105.41(13)
106.22(13)
119.64(10)
115.11(10)
103.92(9)
N–Ni–Br(1)
N–Ni–Br(2)
P–Ni–Br(1)
P–Ni–Br(2)
Br(1)–Ni–Br(2)
C(1)–P–C(7)
C(1)–P–C(13)
C(7)–P–C(13)
C(1)–P–Ni
104.61(14)
117.32(13)
117.95(14)
C(7)–P–Ni
C(13)–P–Ni
C(7)–P(1)–Ni(1)
C(13)–P(1)–Ni(1)
Table 2
Ethylene oligomerization with 4a–f at 1 atm of ethyenea
Entry
Complex
Al/Ni (mol)
Temp (ꢁC)
Time (min)
Activityb 105 g Æ molÀ1
(Ni) Æ hÀ1
Oligomers distributionb (%)
C4/RC
C6/RC
CP8/RC
Linear a-olefin
1
2
4a
4b
4c
4d
4e
4f
1000
1000
1000
1000
1000
1000
500
25
25
25
25
25
25
25
25
0
30
30
30
30
30
30
30
30
30
30
60
90
30
30
30
2.29
0.71
1.78
3.73
3.95
1.34
1.46
1.10
1.08
0.54
0.98
0.60
0.60
6.66
2.72
89.62
99.38
85.50
75.72
84.13
82.40
88.93
95.45
98.20
98.48
81.77
81.88
98.54
74.21
80.71
10.38
0.62
–
11.0
52.6
33.1
19.5
25.41
21.29
22.7
22.9
32.2
52.2
23.6
15.8
9.63
8.5
–
3
11.59
21.94
14.79
14.47
6.62
2.91
2.34
1.09
3.13
4.45
–
4
5
6
7
4c
4c
4c
4c
4c
4c
4c
4c
4c
8
1500
1000
1000
1000
1000
20
4.55
1.80
9
–
10
11
12
13c
14c
15c
a
40
25
25
25
25
25
1.52
–
14.79
15.70
1.46
3.42
2.49
–
50
100
18.40
12.61
7.39
6.67
17.84
General conditions: 5 lmol precatalyst; 30 mL toluene as solvent; MAO as cocatalyst.
Determined by GC, RC means the total amounts of oligomers.
AlEt2Cl as cocatalyst.
b
c
the cases, ethylene dimers and trimers are the main olig-
5-position of the oxazoline ring shows the highest activ-
ity under identical reaction conditions. In comparison,
4b with an ethyl group in the 4-position of the oxazoline
shows the lowest activity (entry 1–3, Table 2). On com-
paring the structures of 4a and 4b, it can be observed
that the ethyl substituent in the 4-position of the oxazo-
line ring is closer to the nickel and will provide the steric
shielding around the metal center. In addition, substitu-
tion in the ortho position of the coordinated nitrogen
with electron-donating ethyl group will result in a lower
positive charge on nickel of the active catalytic species
omeric products. As analyzed by GC and GC-MS, the
selectivities for a-olefins in total olefins are relatively
lower.
2.3.1. The effect of ligand environment on the ethylene
oligomerization behaviors
It is observed that the size and position of the substit-
uents in the ligand backbone of the catalysts slightly af-
fect their ethylene oligomerization activity. Among
complexes 4a–4c, 4a with a methyl substituent in the

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X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
and, subsequently, weakens the metal–ethylene interac-
tion during the ethylene oligomerization. However,
methyl group in the 5-position of the oxazoline ring is
too far away from the metal center to affect its electronic
properties. Due to the steric and electronic consider-
ations, it is easily understood that complex 4b displays
lower ethylene oligomerization activity than its counter-
part 4a. However, their oligomerization activities in-
crease obviously when the ligand has a substituent on
the phenyl ring attached to the oxazoline, either methyl
(4d) or methoxyl (4e), compared to the analogue 4c. The
previous studies about the electronic effects on the ethyl-
ene polymerization activity gave the inconsistent results.
It is a general notion that decrease in the donor ability of
the substituents, (i.e. increase in the electrophilicity of
the metal center) should decrease the insertion barrier,
thus, resulting in higher activity [13]. While some of
the experimental [7a] and theoretical [14] results show
that in square-planar d [8] transition-metal complexes
containing unsymmetrical bidentate ligands and methyl
ethylene, increasing the donor strength trans to the
strong donor methyl group should lower the migration
barrier, while decreasing the donor strength should raise
the insertion barrier. In complex 4f, the bulky phenyl
ring was introduced to the 4-position of the oxazoline,
which will exert efficient steric hindrance to the metal
center. However, the electron-withdrawing property of
the phenyl ring will result in the formation of a more
electrophilic active catalytic metal center. Due to these
combined steric and electronic effects, the oligomeriza-
tion activity of 4f is higher than that of 4b and is lower
than that of 4a. In all the cases, the dimer and trimer of
ethylene are the major products. The selectivity for eth-
ylene dimer of 4b is especially high to 99.38%. Complex
4d shows the trend to produce oligomers with higher
carbon number. However, the lower oligomers (C4 and
C6) as major products will be not interested in industrial
consideration, moreover, the intern olefins are not pur-
sued in ethylene oligomerization. In general, the effects
of the ligand environment on the distribution of oligo-
mers are not as obvious as the catalytic activities for
the oligomers.
2.3.2. The effect of reaction parameters on the ethylene
catalytic activities
To probe the effect of reaction parameters on the eth-
ylene oligomerization behaviors, the precatalyst 4c was
typically investigated via changing the amounts of
MAO, the reaction temperature and the reaction time.
Variation of the Al/Ni molar ratio in the range of
500–1500 shows insignificant effect on oligomerization
activities and oligomer distributions, although the high-
est oligomerization activity was observed when the Al/
Ni molar ratio is 1000. The catalyst 4c shows higher
oligomerization activity at lower temperature, and ele-
vating the reaction temperature to 40 ꢁC leads to the
remarkable reduction in activity (entry 10, Table 2),
which may be ascribed to the decomposition of the ac-
tive catalytic sites and lower ethylene solubility at higher
temperature. The oligomerization activities progres-
sively decrease when reaction was prolonged from 30
to 60 min and finally to 90 min, which indicates that
the catalyst lifetime is relative short. Recently Braun-
ˆ
stein group reported that their NP coordinated nickel
complexes show high ethylene oligomerization activity
upon activation with only slightly excess of AlEtCl2
[7d,7e,7f], and we tested the ethylene oligomerization
with complex 4c using AlEt2Cl instead of MAO as
cocatalyst. It is observed that the complex 4c displays
high activity with only 50 equivalents of AlEt2Cl as
cocatalyst (entry 14, Table 2).
2.3.3. The effects of the ethylene pressure on the
oligomerization behavior
The complexes 4a–f were also tested for ethylene olig-
omerization at 20 atm of ethylene pressure and the results
are summarized in Table 3. The results show that increase
in the ethylene pressure lead to the remarkable increase in
ethylene activity. This observation of the increased
oligomerization activity at the elevated ethylene pressure
Table 3
Ethylene oligomerization with 4a–f/MAO at 20 atm of ethyenea
Entry
Complex
Activityb 105 g Æ molÀ1
Ni Æ hÀ1
Oligomers distributionb (%)
C4/RC
C6/RC
CP8/RC
Linear a-olefin
1
2
3c
4
5
6
a
4a
4b
4c
4d
4e
4f
5.74
5.42
6.27
11.80
7.37
7.99
78.90
45.47
79.06
85.34
82.07
90.21
7.84
7.24
7.63
9.31
6.63
4.36
13.26
47.29
13.31
5.35
13.8
28.6
30.4
23.1
17.4
16.8
11.30
5.43
General conditions: 20 lmol catalyst; 150 mL toluene; Al/Ni = 1000; 25 ꢁC; 30 min.
Determined by GC, RC means the total amounts of oligomers.
Determined by GC-MS.
b
c

X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
3923
Table 4
Ethylene oligomerization with 4a–f/MAO at 1 atm in the presence of PPh3
a
Entry
Complex
Al/Ni/PPh3 (mol)
Time (min)
Activityb 105 g Æ molÀ1 Ni Æ hÀ1
Oligomers distributionb (%)
C4/RC
C6/RC
CP8/R C
Linear a-olefin
1
2
4a
4b
4c
4d
4e
4f
1000:1:2
1000:1:2
1000:1:2
1000:1:2
1000:1:2
1000:1:2
200:1:2
500:1:2
500:1:4
500:1:10
500:1:2
500:1:2
30
30
30
30
30
30
30
30
30
30
60
90
5.27
2.71
2.62
3.62
4.40
11.20
1.73
3.76
4.05
1.40
3.33
2.44
88.90
91.00
78.70
91.13
77.12
79.32
90.67
77.87
82.80
89.73
71.60
76.70
10.79
5.91
0.3
6.2
12.1
4.7
3.09
1.25
1.57
1.52
1.67
–
3
20.05
7.30
4
7.9
6.3
5
21.36
19.01
9.33
6
8.30
12.4
4.4
7
4c
4c
4c
4c
4c
4c
8
21.70
16.95
10.27
25.62
22.33
0.43
0.25
–
9
9.0
10
11
12
a
11.7
2.3
2.78
0.97
5.5
General conditions: 5 lmol precatalyst; 30 mL toluene as solvent; 25 ꢁC.
Determined by GC, RC means the total amounts of oligomers.
b
is in accordance with the previously reported results for
the homogenous nickel catalyst [15]. At 20 atm of ethyl-
ene pressure, the effect of the ligand environments on
the oligomerization activity is similar to the results of
1 atm. In addition, the percentages of the higher carbon
number olefins in the oligomeric product are much higher
than the runs at 1 atm of ethylene pressure. No significant
improvement of the selectivity for a-olefin was observed
at the elevated ethylene pressure.
mers on the base of entries of 7, 11 and 12 in Table 2 be-
cause of further propagation of ethylene insertion.
The mechanism of the acceleration phenomena of
ethylene oligomerization induced by the addition of
the auxiliary ligand PPh3 is not well disclosed. We tenta-
tively attribute it to the temporary coordination of PPh3
with the vacant site formed by the activation of MAO,
and thus the active catalytic species are protected.
Remarkable induction period was observed during the
oligomerization reaction in the presence of PPh3, which
might reflect the coordination of PPh3 with the vacant
site. The PPh3 group may dissociate again upon ap-
proach and coordination of ethylene monomer. Further
studies to understand the effects of the auxiliary ligand
on the ethylene oligomerization are in progress.
2.3.4. The effect of auxiliary ligand (PPh3) on ethylene
oligomerization behaviors
For catalyst precursors 4a–f, oligomerization activi-
ties were remarkably enhanced when PPh3 was used as
the auxiliary ligand, and the results are listed in Table 4.
Similar effect of PPh3 was also observed in our recent
investigation on pyridine-monoimine Ni(II)/MAO cata-
lyst system [5d]. Contrarily, the decrease of ethylene
polymerization activity was also reported as due to the
addition of 5 equiv of PPh3 for the neutral nickel (II)
catalyst [16]. GC analysis indicates that the oligomer
distributions are not remarkably affected by the presence
of PPh3 in the reaction system and the selectivity for 1-
butene is still very low in the presence of PPh3 as auxil-
iary ligand. Results on the oligomerization reactivity
with various Ni/PPh3 molar ratio for 4c show that 2–4
equiv of PPh3 is optimal for accelerating the oligomeri-
zation reaction, and increase the PPh3 amount to 10
equiv leads to the reduction in oligomerization activity
(entries 7–9, Table 4). In addition, less amount of
MAO is sufficient for activation of the precatalyst to
reach the highest value. The turnover number (TON)
keeps increasing when the reaction time is increased
from 30 to 90 min (4700, 11,900 and 13,100 for 30, 60
and 90 min, respectively), which indicates that part of
the active catalytic species are still alive after 60 min.
The longer reaction time produced higher order oligo-
3. Conclusions
A series of bidentate Ni(II) complexes bearing the
phosphino-oxazoline ligands were synthesized and fully
characterized to reveal their distorted-tetrahedral
coordination geometry around the nickel center. Those
complexes were found to catalyze ethylene for oligomer-
ization with activities up to 1.18 · 106 g molÀ1 (Ni) hÀ1
(4d at 20 atm ethylene pressure), the dimers and trimers
being the major products. The ethylene oligomerization
activity was found to be affected by the substituents in
the ligands framework. Incorporation of steric bulky
and electron-donating groups on the carbon atom neigh-
boring the coordinating nitrogen of the oxazoline ring led
to the decrease in catalytic activity of ethylene oligomer-
ization, nevertheless, the ethylene oligomerization activ-
ity was enhanced with substitution of the groups on
phenyl ring attached to the oxazoline. In addition, the
oligomerization activity remarkably increased in the
presence of 2–4 equiv of PPh3 as auxiliary ligand.

3924
X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
4. Experimental
4.1. General considerations
solution of 2-bromo-N-(2-hydroxypropyl)benzamide
(2.26 g, 0.088 mol) in 30 mL of toluene at 0 ꢁC. The reac-
tion solution was kept at 80 ꢁC for 2 h, complete conver-
sion was reached to give the final product, 2.40 g of
2-bromo-N-(2-chlorohydroxypropyl)benzamide was ob-
tained in 99.0% yield. The 2-bromo-N-(2-chlorohydr-
oxypropyl)benzamide (2.40 g, 0.0087 mol) and NaOH
(0.52 g, 0.013 mol) in 40 mL of methanol was refluxed
for 5 h. After cooling to room temperature, the result-
ing solution was treated with brine and extracted
with diethyl ether. The organic layer was combined
and dried over anhydrous Na2SO4, then the solvent
was removed in vacuo, and its residue was purifies on
the column with silica gel to give the colorless oil,
2-(2-Bromophenyl)-4,5-dihydro-5-methyloxazole (2a)
(1.61 g, 77.2%). However, the yield of 2a based on 2-
Bromobenzoic acid is 67.2%. 1H NMR (300 MHz,
CDCl3): d 7.62–7.70(m, 2H, Ar–H); 7.24–7.37 (m, 2H,
Ar–H); 4.82–4.92 (m, 1H, –CH); 4.19 (q, 1H in
–CH2, J = 5.9 Hz); 3.67 (q, 1H in –CH2, J = 5.4 Hz);
1.45 (d, 3H, –CH3, J = 6.3 Hz). Anal. Calc. for
C10H10BrNO: C, 50.02; H, 4.20; N, 5.83. Found: C,
49.89; H, 4.11; N, 5.65%.
All manipulations of air- and/or moisture-sensitive
were performed under nitrogen atmosphere using stan-
dard Schlenk techniques. Solvents were dried by the liter-
ature methods. Methylaluminoxane (MAO) was
purchased from Albemarle as a 1.4 M solution in tolu-
ene. Other reagents were purchased from Aldrich or
Acros Chemicals. 1H and 13C NMR spectra were
recorded on Bruker DMX-300 or 400 MHz instrument
using TMS as internal standard. IR spectra were
recorded on a Perkin–Elmer system 2000 FT-IR
spectrometer. Elemental analysis was carried out using
HP-MOD 1106 microanalyzer. GC analysis was per-
formed with a Carlo Erba Strumentazione gas chro-
matograph equipped with a flame ionization detector
and a 30 m (0.25 mm i.d., 0.25 lm film thickness) DM-
1 silica capillary column. GC-MS analysis was per-
formed with HP 5890 SERIES II and HP 5971 SERIES
mass detector. The yield of oligomer was calculated by
referencing with the mass of the used solvent based on
the prerequisite that the mass of each fraction is approx-
imately proportional to its integrated areas in the
GC trace. Selectivity for linear a-olefin is defined the
percentage of a-olefin as (1-olefins/all fractions of
olefins) · 100%.
2b was obtained as colorless oil in 59.6% yield based
1
on 2-Bromobenzoic acid. H NMR (300 MHz, CDCl3):
d 7.62–7.69 (m, 2H, Ar–H); 7.27–7.32 (m, 2H, Ar–H);
4.50 (q, 1H in –CH2, J = 7.8 Hz); 4.27–4.33 (m, 1H,
–CH); 4.10 (t, 1H in –CH2, J = 7.8 Hz); 1.6–1.8 (m,
2H, –CH2 in ethyl); 1.03 (t, 3H, –CH3, J = 3.8 Hz).
Anal. Calc. for C11H12BrNO: C, 51.99; H, 4.76; N,
5.51. Found: C, 52.39; H, 4.78; N, 5.24%. 2c was ob-
tained as white solid in 71.3% yield based on 2-Bromo-
benzoic acid. M.p.: 37–39 ꢁC. 1H NMR (300 MHz,
CDCl3): d 7.60–7.65 (m, 2H, Ar–H); 7.27–7.33 (m, 2H,
Ar–H); 4.14 (s, 2H, –CH2); 1.42 (s, 6H, –CH3). Anal.
Calc. for C10H10BrNO: C, 51.99; H, 4.76; N, 5.51.
Found: C, 51.61; H, 4.83; N, 5.39%. 2d was obtained
as colorless oil in 52.7% yield on the base of 2-Bromo-
4.2. Synthesis of halogen-substituted oxazoline
compounds 2a–f
To synthesize the oxazoline compound, various liter-
ature methods were reported, including reaction of
benzonitrile and amino alcohol in chlorobenzene cata-
lyzed by zinc chloride or using benzoic acid and amino
alcohol as starting materials. In comparison, the latter
procedure is more controllable and can afford the oxaz-
oline compounds in high yields. Compounds, 2a–2d,
were prepared by the similar procedure, and the syn-
thesis of compound 2a is selectively as a representative
described in detail. 2-Bromobenzoic acid (2.01 g,
0.01 mol) was mixed with thionyl chloride (3.60 g,
0.03 mol), and the mixture was stirred at 40 ꢁC for
24 h. The excess thionyl chlordie was distilled, and
the remaining dark oil was further distilled to fur-
nish 2.02 g of the acyl chloride in 92.0% yield. The
obtained acyl chloride was dissolved in 20 mL of di-
chloromethane and dropwise added to a solution of
1-amino-2-propanol (1.38 g, 0.018 mol) in 20 mL of
dichloromethane at 0 ꢁC. Then the resulting mixture
was stirred at 25 ꢁC for 2 h, after being concentrated
and cooled, the white solid product was filtered and
washed with a little dichloromethane to give 2-bromo-N-
(2-hydroxypropyl)benzamide (2.26 g, 95.0%). Thionyl
chloride (3.12 g, 0.026 mol) was dropwise added to a
1
benzoic acid. H NMR (300 MHz, CDCl3): d 7.53 (d,
1H, Ar–H, J = 7.8 Hz); 7.44 (s, 1H, Ar–H); 7.12 (d,
1H, Ar–H, J = 7.9 Hz); 4.11 (s, 2H, –CH2); 2.34 (s,
3H, –CH3); 1.40 (s, 6H, –CH3). Anal. Calc. for
C11H14BrNO: C, 53.75; H, 5.26; N, 5.22. Found: C,
53.72; H, 5.43; N, 5.05%. 2e was obtained as white solid
in 68.4% yield on the base of 2-Bromobenzoic acid. M.
1
p.: 43–45 ꢁC. H NMR (300 MHz, CDCl3): d 7.48 (d,
1H, Ar–H, J = 8.9 Hz); 7.17 (d, 1H, Ar–H, J =
3.9 Hz); 6.84 (dd, 1H, Ar–H, J1 = 3.1 Hz, J2 = 8.9 Hz);
4.13 (s, 2H, –CH2); 3.81 (s, 3H, –OCH3); 1.41 (s, 6H,
–CH3). Anal. Calc. for C11H14BrNO2: C, 50.72; H,
4.97; N, 4.93. Found: C, 51.13; H, 5.14; N, 4.78%. 2f
was obtained as viscous colorless oil in 76.4% yield
based on 2-Bromobenzoic acid. 1H NMR (400 MHz,
CDCl3): d 7.15–7.98 (m, 9H, Ar–H); 5.43 (dd, 1H, –
CH, J = 9.0, 9.0); 4.80 (t, 1H in –CH2, J = 9.0); 4.28
(t, 1H in –CH2, J = 9.0). Anal. Calc. for C15H12FNO:

X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
3925
C, 74.67; H, 5.01; N, 5.81. Found: C, 74.50; H, 5.02; N,
5.76%.
4.3.4. 4,5-Dihydro-4,4-dimethyl-2-(4-methyl-2-(diphenyl-
phosphino)phenyl)oxazole (3d)
Using the same procedure as for the synthesis of 3a, 3d
was obtained as a white powder in 43.8% yield. M.p.: 76–
78 ꢁC. 1H NMR (300 MHz, CDCl3): d 7.75 (dd, 1H, Ar–
H, J1 = 4.1 Hz, J2 = 3.8 Hz,); 7.32–7.34 (m, 10H, Ar–H);
7.13 (d, 1H, –Ar–H, J = 7.5 Hz); 6.59 (d, 1H, Ar–H,
J = 4.8); 3.70 (s, 2H, –CH2); 2.18 (s, 3H, –CH3). 1.04 (s,
6H, –CH3). Anal. Calc. for C24H24NOP: C, 76.86; H,
6.17; N, 3.90. Found: C, 77.27; H, 6.14; N, 3.87%. 31P
NMR (CDCl3): d À3.59 (s). IR (KBr): 2967; 1649 (vC@N);
4.3. Synthesis of the PHOX ligands
4.3.1. 4,5-Dihydro-5-methyl-2-(2-(diphenylphosphino)-
phenyl) oxazole (3a)
To a solution of 2a (0.60 g, 2.5 mmol) in THF (10 mL)
was added freshly prepared LiPPh2 [17] (3.75 mmol, 1.5
equiv) in 10 mL THF solution dropwise at room temper-
ature. The resultant solution was gradually heated to ca.
50 ꢁC and stirred for additional 8 h. All volatiles were re-
moved in vacuo, and the residue was taken up in 30 mL
diethyl ether. This solution was washed with degassed
water (2 · 10 mL) and then the organic phase was dried
over anhydrous Na2SO4. Removal of solvent under re-
duced pressure produced yellow vicious oil. The crude
product was purified by flash column chromatography
under a nitrogen atmosphere with petroleum ether–ethyl
acetate (4:1) as eluent to afford 3a as white powder in
52.0% yield. M.p.: 92–94 ꢁC. 1H NMR (300 MHz,
CDCl3): d 7.84 (dd, 1H, Ar–H, J1 = 3.0 Hz, J2 =
6.0 Hz,); 7.31–7.33 (m, 12H, Ar–H); 6.87 (t, 1H, Ar–H,
J = 5.7); 4.52–4.55 (m, 1H, –CH); 3.87 (q, 1H in –CH2,
J = 7.9); 3.34 (q, 1H in –CH2, J = 7.2); 1.12 (d, 3H,
–CH3, J = 6.0). Anal. Calc. for C22H20NOP: C, 76.51;
H, 6.07; N, 4.01. Found: C, 76.51; H, 5.84; N, 4.06%.
31P NMR (CDCl3): d À4.58 (s). IR (KBr): 2969; 1661
1574; 1461; 1435, 1351, 1316 cmÀ1
.
4.3.5. 4,5-Dihydro-2-(5-methoxy-2-(diphenylphosphino)-
phenyl)-4,4-dimethyloxazole (3e)
Using the same procedure as for the synthesis of 3a
and 3e was obtained as light yellow viscous oil in
1
58.8% yield. H NMR (300 MHz, CDCl3): d 7.53 (d,
1H, Ar–H, J = 6.0 Hz); 7.49 (s, 1H, Ar–H); 7.28–
7.32(m, 9H, –Ar–H); 7.01 (dd, 1H, Ar–H, J1 = 3.0,
J2 = 3.0); 6.79 (dd, 1H, Ar–H, J1 = 3.0, J2 = 6.0); 4.10
(s, 2H, –CH2); 1.39 (s, 6H, –CH3); 1.09 (s, 3H, –CH3).
31P NMR (CDCl3): d–5.92 (s). IR (KBr): 2967; 1649
(vC@N); 1590; 1464; 1433, 1352, 1310 cmÀ1. Repeated
elemental analysis measurements for 3e did not give
acceptable results, which might be imputable to the pres-
ence of trace of homocoupling compound in 3e. How-
ever, the corresponding complex could be readily
purified by recrystallization.
(vC@N); 1472; 1433; 1366, 1329 cmÀ1
.
4.3.2. 4-Ethyl-4,5-dihydro-2-(2-(diphenylphosphino)-
phenyl)oxazole (3b)
4.3.6. (S)-4,5-Dihydro-4-phenyl-2-(2-(diphenyl-
phosphino)phenyl)oxazole (3f)
Using the same procedure as for the synthesis of 3a,
3b was obtained as a white powder in 41.0% yield.
M.p.: 68–70 ꢁC. H NMR (300 MHz, CDCl3): d 7.88
Using the similar procedure for synthesizing LiPPh2,
KPPh2 was prepared by the cleavage of PPh3 with
potassium. To the freshly prepared refluxing solution
of KPPh2 in THF, the fluoro-substituted oxazoline in
THF solution was added dropwise. After refluxing for
12 h, the reaction mixture was worked up as described
for 3a. Compound 3f was separated by flash column
chromatography under a nitrogen atmosphere with
petroleum ether–ethyl acetate (12:1) as a white solid in
44.5% yield. M.p.: 55–57 ꢁC. 1H NMR (400 MHz,
CDCl3): d 6.77–7.96 (m, 19H, Ar–H); 5.70 (t, 1H,
–CH, J = 9.4); 4.98 (dd, 1H in –CH2, J = 8.3, 8.3);
1
(dd, 1H, Ar–H, J1 = 3.4 and 5.8 Hz,); 7.30–7.3 (m,
12H, Ar–H); 6.86 (t, 1H, Ar–H, J = 3.8); 4.18 (q, 1H
in –CH2); 3.99 (m, 1H, –CH); 3.70 (t, 1H in –CH2,
J = 7.9); 1.23–1.38 (m, 2H, –CH2 in ethyl); 0.79 (t, 3H,
–CH3, J = 7.6 Hz). Anal. Calc. for C23H22NOP: C,
76.86; H, 6.17; N, 3.90. Found: C, 76.66; H, 6.48; N,
4.51%. 31P NMR (CDCl3): d À4.93 (s). IR (KBr):
2960; 1645 (vC@N); 1584; 1476; 1433, 1360, 1327 cmÀ1
.
4.3.3. 4,5-Dihydro-4,4-dimethyl-2-(2-(diphenyl-
phosphino)phenyl)oxazole (3c)
4.44 (t, H in –CH2, J = 8.5). Anal. Calc. for
C27H22NOP: C, 79.59; H, 5.44; N, 3.44. Found: C,
Using the same procedure as for the synthesis of 3a,
3c was obtained as a white powder in 52.1% yield.
M.p.: 78–80 ꢁC. H NMR (300 MHz, CDCl3): d 7.85
79.83; H, 5.39; N, 3.46%. IR (KBr): 3054; 1650 (vC@N);
1581; 1466; 1430, 1351, 1307 cmÀ1
.
1
(dd, 1H, Ar–H, J1 = 4.2 and 8.9 Hz,); 7.37–7.42 (m,
1H, Ar–H); 7.33 (s, 11H, –Ar–H); 6.79 (t, 1H, Ar–H,
J = 6.0); 3.73 (s, 2H, –CH2); 1.05 (s, 6H, –CH3). Anal.
Calc. for C23H22NOP: C, 76.86; H, 6.17; N, 3.90.
Found: C, 77.27; H, 6.14; N, 3.87%. 31P NMR (CDCl3):
d À3.92 (s). IR (KBr): 2968; 1646 (vC@N); 1585; 1460;
4.4. Synthesis of the nickel complexes (PHOX)NiBr2
Complexes 4a–f were prepared by the similar
methods and thus, only one representative procedure
is described. The ligand 3a (0.100 g, 0.29 mmol) and
(MEE)NiBr2 (0.079 g, 0.27 mmol) were added to a
Schlenk tube under nitrogen, followed by the addition
1438, 1351, 1311 cmÀ1
.

3926
X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
of freshly distilled dichloromethane (8 mL) with rapid
stirring at room temperature. The solution turned to
dark red immediately. The reaction mixture was stirred
for 5 h at room temperature, and then concentrated to
ca. 4 mL. Hexane (10 mL) was added to precipitate the
complex. After filtration and washing with hexane,
4a was obtained as purple powder in 67.3% yield.
IR (KBr): 2979; 1627 (vC@N); 1480; 1435, 1377,
1647 (vC@N); 1603; 1580; 1494, 1451, 1357, 1275, 1067,
1026, 974, 951, 760, 697, 540 cmÀ1
.
4.6. General procedure for ethylene oligomerization
4.6.1. Ethylene oligomerization at 1 atm pressure
Complex (5 lmol) was added to a Schlenk type flask
under nitrogen. The flask was back-filled three times
with N2 and twice with ethylene, and then charged with
toluene and cocatalyst solution in turn under ethylene
atmosphere. Under prescribed temperature, the reaction
solution was vigorously stirred under 1 atm ethylene for
the desired period of time. The oligomerization reaction
was quenched by the addition 60 mL 10% HCl solution.
About 1 mL of organic solution was dried by anhydrous
Na2SO4 for GC analysis. No polyethylene formation
was observed after pouring the remained solution into
100 mL of ethanol.
1345 cmÀ1
. Anal. Calc. for C22H20Br2NNiOP: C,
46.86; H, 3.58; N, 2.48. Found: C, 47.10; H, 3.70; N,
2.46%. 4b was obtained as orange powder in 84.2%
yield. IR (KBr): 2966; 1613 (vC@N); 1565; 1479; 1436,
1376, 1338 cmÀ1. Anal. Calc. for C23H22Br2NNiOP: C,
47.80; H, 3.84; N, 2.42. Found: C, 47.46; H, 4.40; N,
2.56%. 4c was obtained as purple powder in 72.5% yield.
IR (KBr): 2966; 1617 (vC@N); 1565; 1480; 1435, 1368,
1319 cmÀ1
.
Anal. Calc. for C23H22Br2NNiOP Æ C
H2Cl2: C, 43.49; H, 3.65; N, 2.11. Found: C, 42.89; H,
3.29; N, 2.03%. 4d was obtained as orange powder in
76.5% yield. IR (KBr): 2967; 1613 (vC@N); 1556; 1485;
1459, 1370, 1322 cmÀ1. Anal. Calc. for C24H24Br2-
NNiOP: C, 48.70; H, 4.09; N, 2.37. Found: C, 48.22;
H, 4.10; N, 2.31%. 4e was obtained as purple powder
in 69.4% yield. IR (KBr): 2972; 1624 (vC@N); 1588;
1490; 1438, 1368, 1328 cmÀ1. Anal. Calc. for C24H24-
Br2NNiO2P Æ CH2Cl2: C, 43.34; H, 3.78; N, 2.02. Found:
C, 43.74; H, 3.82; N, 2.31%. 4f was obtained as purple
powder in 90.5% yield. IR (KBr): 3055; 1621 (vC@N);
1532; 1435; 1391, 1269, 1120 cmÀ1. Anal. Calc. for
C27H22Br2NNiOP: C, 51.81; H, 3.54; N, 2.24. Found:
C, 51.65; H, 3.78; N, 2.06%.
4.6.2. Ethylene oligomerization at 20 atm pressure
High-pressure ethylene polymerization was per-
formed in a stainless steel autoclave (1 L capacity)
equipped with gas ballast through a solenoid clave for
continuous feeding of ethylene at constant pressure.
One hundred and thirty seven milliliters of toluene con-
taining the catalyst precursor was transferred to the fully
dried reactor under nitrogen atmosphere, and then
13 mL of MAO in toluene solution was then injected
into the reactor using a syringe. As the prescribed tem-
perature was reached, the reactor was pressurized to
the 20 atm. After stirring for 30 min, the reaction was
quenched and worked up using the same method as de-
scribed above for 1 atm reaction.
4.5. Synthesis of the compound 5
Method A: Reaction of 2-(2-bromophenyl)-oxazoline
2f (0.60 g, 2.5 mmol) with 1.5 equivalent (3.75 mmol) of
LiPPh2 or KPPh2 in THF solution, using the similar
procedure through coupling reaction for the synthesis
of 3a, gave the light yellow oil compound 5 in 39.5%
(LiPPh2) and 42.6% (KPPh2) yield, respectively, one
the base of 2f. Method B: The 2-(2-bromophenyl)-oxaz-
oline 2f (0.60 g, 2.5 mmol) reacted with magnesium in
10 mL THF by using the literature method [10a], to
the Grignard reagent was added diphenylphosphine
chloride (0.71 mL, 3.75 mmol). The mixture was re-
fluxed for 6 h, and the solution was worked up by the
similar method for 3a. Compound 5 was obtained in
4.7. X-ray crystallographic studies
The single-crystal X-ray diffraction for complex 4c
was carried out on a Rigaku RAXIS Rapid IP diffrac-
tometer with graphite monochromated Mo Ka radia-
˚
tion (k = 0.71073 A) at 173(2) K. Intensity data of
complex 4d and 4e were collected on a Bruker SMART
1000 CCD diffractometer with graphite monochro-
˚
mated Mo Ka radiation (k = 0.71073 A) at 293(2) K.
Cell parameters were obtained by global refinement
of the positions of all collected reflections. Intensities
were corrected for Lorentz and polarization effects
and empirical absorption. The structures were solved
by direct methods and refined by full-matrix least-
squares on F2. All non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were placed in a
calculated position. Structure solution and refinement
were performed by using the SHELXL-97 Package. Crys-
tal data and processing parameters for complexes 4c–4e
are summarized in Table 5. Crystallographic data of
complexes 4c–4e were deposited with the Cambridge
Crystallographic Data Centre, CCDC 268442, 268443
1
60.7% yield. H NMR (400 MHz, CDCl3): d 8.05 (dd,
4H, Ar–H, J1 = 1.0 Hz, J2 = 1.6 Hz); 7.29–7.51 (m,
16H, Ar–H); 5.40 (dd, 2H, –CH, J1 = 8.2 Hz,
J2 = 8.2 Hz); 4.80 (dd, 2H,, J1 = 8.4, J2 = 8.4); 4.28 (t,
2H, –CH2, J = 8.3). 13C NMR (100.61 MHz, CDCl3):
d 164.72; 142.35; 131.50; 128.72; 128.44; 128.34;
127.59; 127.54; 126.72; 74.85; 70.10. Anal. Calc. for
C30H24N2O2: C, 81.06; H, 5.44; N, 6.30. Found: C,
80.75; H, 5.97; N, 5.93%. IR (KBr): 3063; 3031, 1720,

X. Tang et al. / Journal of Organometallic Chemistry 690 (2005) 3918–3928
3927
Table 5
Crystallographic data and refinement for 4c Æ CH2Cl2, 4d and 4e
4c Æ CH2Cl2
4d
4e
Formula
Fw
C
23H22Br2NNiOP Æ CH2Cl2
C24H24Br2NNiOP
591.94
C24H24Br2NNiO2P
607.94
660.83
Monoclinic
P2(1)/c
9.0424(18)
15.728(3)
18.908(4)
90
Cryst syst.
Space group
Monoclinic
P2(1)/c
9.3188(11)
26.555(3)
9.8290(12)
90
Monoclinic
P2(1)/c
8.8285(13)
20.860(3)
14.168(2)
90
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
91.39(3)
90
95.831(2)
90
104.201(2)
90
3
˚
V (A )
2688.3(9)
4
1.633
2419.7(5)
4
1.625
2529.6(6)
4
1.596
Z
Dcalcd. (g Æ cmÀ3
)
Absorption coefficient, l, (mmÀ1
F(000)
)
3.969
1312
4.186
1184
4.009
1216
h range, (deg)
Number of data collected
2.59–27.45
11,159
6018
1.53–26.05
13,528
4766
1.78–26.03
14,119
4980
Number of unique data
R
0.0370
0.1119
0.623
0.0272
0.0360
1.029
0.0332
0.0496
1.032
Rw
Goodness-of-fit
(c) D.H. Camacho, E.V. Salo, J.W. Ziller, Z. Guan, Angew.
Chem., Int. Ed. Engl. 43 (2004) 1821.
and 268444, respectively. Copies of this information
may be obtained free of charge from CCDC, 12 Union
Road, Cambridge, CB2 1 EZ,UK (fax:+44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccd.cam.ac.uk).
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Acknowledgement
(d) X. Tang, W.-H. Sun, T. Gao, J. Hou, J. Chen, W. Chen, J.
Organomet. Chem. 690 (2005) 1570.
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The project supported by NSFC No.20272062 and
20473099. This work was partly completed in Polymer
Chemistry Laboratory, Chinese Academy of Sciences
and China Petro-Chemical Corporation.
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