Nickel (II) complexes with β-enaminoketonato chelate ligands: Synthesis, solid-structure characterization and reactivity toward the addition polymerization of norbornene

Article abstract of DOI:10.1016/j.jorganchem.2005.12.001

Based on two β-enaminoketonato ligands [ArNC(CH₃)C(H) C(CF₃)OH] (L₁, Ar = 2,6-Me₂C₆H ₃; L₂, Ar = 2,6-i-Pr₂C₆H ₃), their mono(β-enaminoketonato)ni

Full text of DOI:10.1016/j.jorganchem.2005.12.001

Journal of Organometallic Chemistry 691 (2006) 1275–1281
www.elsevier.com/locate/jorganchem
Nickel (II) complexes with b-enaminoketonato chelate
ligands: Synthesis, solid-structure characterization and reactivity
toward the addition polymerization of norbornene
*
Hai-Yu Wang, Jun Zhang, Xia Meng, Guo-Xin Jin
Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200 433, China
Received 29 June 2005; received in revised form 28 November 2005; accepted 1 December 2005
Available online 5 January 2006
Abstract
Based on two b-enaminoketonato ligands [ArNC(CH3)C(H)C(CF3)OH] (L1, Ar = 2,6-Me2C6H3; L2, Ar = 2,6-i-Pr2C6H3), their
mono(b-enaminoketonato)nickel (II) complexes [(ArNC(CH3)C(H)C(CF3)O)Ni(Ph)(PPh3)] (1, Ar = 2,6-Me2C6H3; 3, Ar = 2,6-i-Pr2-
C6H3) and bis(b-enaminoketonato)nickel (II) complexes [(ArNC(CH3)C(H)C(CF3)O)2Ni] (2, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3)
have been synthesized and characterized. The molecular structures of complex 1, 2 and 4 have been confirmed by single-crystal X-ray
analyses. After being activated with methylaluminoxane (MAO) these catalytic precursors 1–4 could polymerize norbornene to afford
addition-type polynorbornene (PNB). Interestingly, catalytic activities and PNB productivity were greatly enhanced due to the introduc-
tion of strong electron-withdrawing group – trifluoro methyl into the ligands. Catalytic activities, polymer yield, Mw and Mw/Mn of PNB
have been investigated under various reaction conditions.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Nickel; Homogeneous catalysts; Polymerization; N,O ligands; Polynorbornene
1. Introduction
investigated their catalytic methyl methylacrylate polymer-
ization behaviors. Li et al. [6] also synthesized a series of
bis(b-enaminoketonato)nickel (II) and mono(b-enamino-
ketonato)nickel (II) complexes utilizing different nickel
sources, and studied their reactivities towards the polymer-
ization of norbornene and copolymerization of ethylene
with methyl methylacrylate, respectively. As we know that
a little variation of the ligand structure may lead to signif-
icant changes in the catalytic reactivity, our group have
designed and synthesized several series of nickel catalysts
supported by [N,O] monoanionic and bisanionic ligands
during the past few years [7]. Herein, we introduce strong
electron-withdrawing group into the b-enaminoketonato
chelate ligands and synthesize their nickel complexes.
Polynorbornene produced by the addition polymeriza-
tion possesses unique physical and chemical properties
[8]. After Deming and Novak introduced the first nickel
complex for the addition polymerization of norbornene
in 1993 [9], we [7d,10] other groups [11] have found that
Olefin addition polymerization is one of the most impor-
tant processes in industrial and academic chemistry.
Although this field typically has been the domain of
early-metal catalysts, in the past decade there has been
growing interest in late-transition-metal catalysts [1].
Among them, nickel-based catalysts especially neutral
nickel catalysts [2,3] play an important role and even are
considered to be very promising catalysts for the olefin
polymerization and copolymerization. Moreover, nickel-
based catalytic systems with ligands of the type O–Y
(where Y is N or S) are particularly interesting and have
been shown to be very effective catalysts in a-olefin and
polar olefin polymerization [4]. Recently, Wu et al. [5] have
prepared bis(b-enaminoketonato)nickel (II) complexes and
*
Corresponding author. Tel.: +86 21 65643776; fax: +86 21 65641740.
E-mail address: gxjin@fudan.edu.cn (G.-X. Jin).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.001

1276
H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
some other nickel complexes also show high catalytic activ-
ity toward this polymerization reaction.
ketonato)nickel (II) and bis(b-enaminoketonato)nickel
(II) complexes were synthesized, respectively, when the
ratio of trans-[Ni(PPh3)2(Ph)Cl] to ligands were ca. 1:1
and 1:2. In addition, experimental results showed that the
complexes 2 and 4 could be also formed from 1 and 3 upon
treatment with the lithium salts of ligand anions. All these
complexes were all purified by recrystallizing from toluene.
The syntheses of the nickel complexes as catalytic precur-
sors are shown in Scheme 2.
In this contribution we synthesized four nickel (II)
complexes with b-enaminoketonato chelate ligands and
investigated their polymerization behaviors towards nor-
bornene. Experimental results showed that these nickel
complexes displayed very high activities for the addition
polymerization of norbornene upon activation with meth-
ylaluminoxane (MAO) and catalytic activities were greatly
enhanced because of the introduction of strong electron-
withdrawing group (trifluoro methyl) into the ligands.
Especially, the highest polynorbornene productivity was
up to 92%, which was different from other reported
results [9,11]. Three typical molecular structures of nickel
catalysts were characterized by an X-ray crystallographic
study.
2.2. Structure analyses
Single crystals of complex 1, 2 and 4 suitable for X-ray
diffraction study were grown from a concentrated toluene
at À30 ꢁC. The collection data and refinement data of anal-
yses are summarized in Table 1. The ORTEP diagrams of
these three complexes are, respectively, shown in Figs.
1–3 with selected bond lengths and angles.
2. Results and discussion
Complex 1 contains a chelating b-enaminoketonato
ligand, a triphenylphosphane group (PPh3) and a phenyl
group. The bulky 2,6-dimethylbenzene moiety occupies
the position trans to PPh3 with a nearly linear P(1)–
Ni(1)–N(1) angle of 170.24(10)ꢁ, and the phenyl group
attached to Ni lies in a position trans to O(1) with a
C(14)–Ni(1)–O(1) angle of 165.98(14)ꢁ. The cis angles at
nickel center are in the range of 86.47–93.26ꢁ. Thus, the
nickel lies perfectly on the square plane defined by the four
donor atoms. In addition, the deviation of the metal ion
from the plane of [P(1), O(1), N(1) and C(14)] is approxi-
2.1. Syntheses of ligands and complexes
The syntheses of ligands are outlined in Scheme 1.
According to a modified method [12] on the condensation
reaction of Schiff-base, we did not obtain the desired
b-diketiminato ligands because of the strongly electron
withdrawing abilities of trifluoro methyl in 1,1,1-trifluoro-
2,4-pentanedione, whereas only got b-enaminoketonato
ligand L1 and L2 reported in this contribution. Herein, tita-
nium tetrachloride was employed to induce the reaction to
go along successfully in the process of the preparation of
ligands. Mechanistically, the titanium atom initially coor-
dinated with the carbonyl oxygen, thereby preparing the
carbonyl group for reaction with amines, and finally
induced the transfer of the carbonyl oxygen atom from car-
bon to titanium. Owing to the properties of electron with-
drawing of trifluoro methyl group the oxygen atom near to
the methyl group was replaced by 2,6-dimethylaniline.
The obtained organic ligands were treated with n-BuLi
in THF and then reacted with trans-chloro(phenyl)bis(tri-
phenylphosphane)nickel (II) to prepare complexes. After
lithium salts of ligands were obtained, mono (b-enamino-
˚
mately 0.022 A. As shown in Figs. 2 and 3, complex 2
has a crystal structure very similar to complex 4. The antic-
ipated formation of tetrahedral complex was not observed.
On the contrary they are both nearly ideal four-coordinate,
square-planar configurations in the solid state. In complex
2 the nickel atom deviates from the [N(1), C(1), C(2) C(3)
˚
and O(1)] plane about 0.0593 A. The bulky 2,6-dimethyl-
benzene rings substituted on the imine moieties are almost
perpendicular to the metallacycle plane [Ni, N(1), C(1),
C(2) C(3) and O(1)] (dihedral angle ca. 95.9ꢁ). The struc-
ture of complex 4 is nearly in consistent with reported
result [6b].
R
O
O
+
2
+
TiCl4
NH2
6
F3C
R
R
R
R
H
N
O
R
+ 4
+
TiO2
NH2·HCl
2
F3C
R= Me(L1) iso-Pr(L2)
Scheme 1. Synthesis of ligands.

H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
1277
R
Ph
Ph3P
O
R
H
Ni
N
O
N
1). n-BuLi,THF
R
R
2). trans-[Ni(PPh3)2(Ph)Cl]
F3C
in Toluene
F3C
R= Me(L1)
R= iso-Pr(L2)
R= Me(1)
R= iso-Pr(3)
CF3
R
R
O
H
N
O
R
N
R
O
Ni
1). n-BuLi,THF
R
N
2). 1/2 trans-[Ni(PPh3)2(Ph)Cl]
F3C
in Toluene
R
F3C
R= Me(L1)
R= iso-Pr(L2)
R= Me(2)
R= iso-Pr(4)
Scheme 2. Syntheses of nickel complexes.
Table 1
Crystal data and summary of data collection and refinement details for 1, 2 and 4
Formula
C
37H33F3NNiOP
C26H26F6N2NiO2
571.20
Triclinic
C34H42F6N2NiO2
683.40
Triclinic
Formula weight
Crystal system
Space group
654.32
Orthorhombic
Pna21
25.810(7)
13.568(4)
9.117(2)
90
ꢀ
ꢀ
P1
P1
˚
a (A)
7.687(13)
7.968(13)
11.085(18)
76.78(2)
79.04(2)
79.89(2)
642.7(18)
2
8.674(4)
8.878(4)
11.576(5)
77.559(5)
82.785(6)
81.712(6)
857.3(6)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
3
˚
V (A )
3192.6(14)
4
Z
Color
Red
Red-orange
0.25 · 0.20 · 0.15
1.476
Red-orange
0.15 · 0.10 · 0.08
1.324
Crystal size (mm)
0.20 · 0.10 · 0.08
1.361
0.706
1.58/26.01
Mo Ka (0.71073)
1360
Dcalc (g cmÀ3
)
l (mmÀ1
h Limits (ꢁ)
)
0.824
0.630
1.91/25.01
Mo Ka (0.71073)
294
1.81/25.01
Mo Ka (0.71073)
358
˚
Radiation (k/A)
F(000)
Number of observed reflections
Number of parameters refined
R1 [I > 2r(I)]
wR2 (all data)
Goodness-of-fit on F2
6043
400
0.0451
0.0975
1.065
2220
167
0.0562
0.1321
2987
210
0.0457
0.1258
1.039
1.104
2.3. Addition polymerization of norbornene
results are collected in Table 2. In general, the steric struc-
ture and bulky group in nickel complexes slightly influence
their catalytic activities. Complex 1, bearing 2,6-dimethyl-
benzene group, displays higher catalytic activities than
complex 3, with bulkier 2,6-diisopropylbenzene, at the
same polymerization conditions. Mechanistically [11f,
11h], the bulkier 2,6-diisopropylbenzene group of complex
3 makes the insertion of norbornene into Ni–C bond more
difficult than 2,6-dimethylbenzene of complex 1. Thus,
complex 3 displays lower catalytic activity than complex
For 1–4, preliminary catalytic studies revealed remark-
ably high activities in the presence of MAO for the addition
polymerization of norboenene. In no case has polynor-
bornene (PNB) been obtained using 1–4 in the absence of
aluminium cocatalyst, whilst the use of up to 5000 equiva-
lents of MAO in the absence of any nickel species, under
the polymerization conditions employed here, afforded
only negligible polymer. The norbornene polymerization

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H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
˚
Fig. 3. Molecular structure of complex 4. Selected bond lengths (A) and
angles (ꢁ): Ni(1)–O(1A) = 1.837(2), Ni(1)–O(1) = 1.837(2), Ni(1)–N(1A) =
1.932(2), Ni(1)–N(1) = 1.932(2), O(1A)–Ni(1)–O(1) = 180.00(17), O(1A)–
Ni(1)–N(1A) = 92.52(9), O(1)–Ni(1)–N(1A) = 87.48(9), O(1A)–Ni(1)–
˚
Fig. 1. Molecular structure of complex 1. Selected bond lengths (A) and
angles (ꢁ): Ni(1)–C(14) = 1.889(3), Ni(1)–O(1) = 1.915(2), Ni(1)–N(1) =
1.950(3), Ni(1)–P(1) = 2.1899(10), C(14)–Ni(1)–O(1) = 165.98(14), C(14)–
Ni(1)–N(1) = 92.89(13), O(1)–Ni(1)–N(1) = 93.26(11), C(14)–Ni(1)–P(1) =
86.47(10), O(1)–Ni(1)–P(1) = 89.56(7), N(1)–Ni(1)–P(1) = 170.24(10).
N(1) = 87.48(9),
180.00(13).
O(1)–Ni(1)–N(1) = 92.52(9),
N(1A)–Ni(1)–N(1) =
Table 2
Addition polymerization of norbornene with nickel complexes 1–4
activated by methylaluminoxane (MAO)a
Activityb
Mw
Mw/Mn
c
c
Entry
Complex
Polymer (g)
1
2
3
4
a
1
2
3
4
1.74
1.72
1.56
1.51
5.22
5.16
4.68
4.53
2.82
2.75
2.73
3.93
2.43
2.54
2.62
3.22
Polymerization conditions: solvent, chlorobenzene; total volume,
10 mL; nickel complex, 0.2 lmol; norbornene, 1.88 g [norbornene/
nickel(molar) = 100000]; 0.66 mL of MAO (1.51 M) [Al/Ni = 5000];
reaction time, 10 min; temperature, 30 ꢁC.
b
107 g PNB Æ molÀ1Ni Æ hÀ1
.
c
Mw (106 g molÀ1) and Mw/Mn values were determined by GPC.
˚
Fig. 2. Molecular structure of complex 2. Selected bond lengths (A) and
Table 3
angles (ꢁ): Ni(1)–O(1) = 1.826(4), Ni(1)–O(1A) = 1.826(4), Ni(1)–N(1A) =
1.922(4), Ni(1)–N(1) = 1.922(4), O(1)–Ni(1)–O(1A) = 180.00(17), O(1)–
Ni(1)–N(1A) = 87.48(16), O(1A)–Ni(1)–N(1A) = 92.52(16), O(1)–Ni(1)–
N(1) = 92.52(16), O(1A)–Ni(1)–N(1) = 87.48(16), N(1A)–Ni(1)–N(1) =
180.000(1).
Influence of the MAO amount on the activities of complex 1
Activitya
Mw
Mw/Mn
b
Entry
Amount of
MAO (equiv.)
Yield
(%)
1
2
3
4
5
6
7
a
2000
2500
3000
4000
5000
6000
10000
–
–
–
–
14.6
72.7
78.1
92.2
90.0
87.2
0.822
4.11
4.41
5.22
5.09
4.92
2.69
4.86
1.18
2.82
2.28
1.05
9.99
5.62
5.31
2.43
8.26
5.13
1. As seen from the polymerization data in Table 2, the
activities of complex 2 are very near to those of complex
1. Similarly, the activities of 4 are near to 3. These results
may be due to the similar polymerization mechanism in
the presence of excess MAO between mono(b-enaminoke-
tonato)nickel (II) and bis(b-enaminoketonato)nickel (II)
complexes at the same polymerization conditions.
To investigate the reaction parameters affecting addition
polymerization of norbornene, the catalytic precursor 1
was studied under different reaction conditions. Varying
the MAO:1 ratio (expressed here as Al:Ni ratio) had con-
siderable effects on catalytic activity and Mw, as shown in
Table 3. When Al:Ni is not more than 2000 (entry 1, Table
107 g PNB Æ molÀ1Ni Æ hÀ1
.
b
Mw (106 g molÀ1). Polymerization conditions: solvent, chlorobenzene;
total volume, 10 mL; nickel complex, 0.2 lmol; norbornene, 1.88 g [nor-
bornene/nickel(molar) = 100000]; temperature, 30 ꢁC; reaction time,
10 min.
3), the obtained polymer is negligible. The entry 2 in Table
3
showed that the activity is only up to 106 g
PNB Æ molÀ1Ni Æ hÀ1 when using up to 2500 equivalents

H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
1279
of MAO. However, the catalytic activity exceeds 107 g
PNB Æ molÀ1Ni Æ hÀ1 when Al:Ni > 3000. Moreover, the
activity is highest at Al:Ni = 5000 and at the same point
the highest PNB productivity (up to 92%) was also
observed.
Table 4 reveals the effects of reaction temperature on
catalytic activities and Mw. With increasing reaction tem-
perature, the catalytic activities first increase and then
decrease – the highest activity is at 30 ꢁC (5.22 · 107 g
PNB Æ molÀ1Ni Æ hÀ1). On the contrary, Mw always
decrease with increasing temperature.
Fig. 4 shows the X-ray diffraction (XRD) spectra of the
obtained PNB. The spectra display two broad halos at 2h
of ca. 11ꢁ and 18ꢁ that can be attributed to a short range
order, or pseudo-periodicity of the arrangement of the
bicycle units along the chain. This is almost in agreement
with the results reported by our and other groups [10,13].
No traces of Bragg refractions are revealed at crystalline
regions. Therefore, the PNB herein is amorphous.
The polymer obtained was characterized by IR, 1H
Fig. 5. 13C NMR spectra of PNB.
Our attempts to determine the glass transition temperature
(Tg) of PNB failed, and the differential scanning calorimet-
ric (DSC) studies did not give an endothermic signal upon
heating to the decomposition temperature (above 450 ꢁC).
1
NMR, 13C NMR and DSC analyses. All IR spectra, H
NMR spectra and 13C NMR spectra (see Fig. 5) were sim-
ilar and characteristic of addition-type PNB, and revealed
no traces of double bonds that are typical for ROMP
(ring-opening metathesis polymerization) PNB [14,11h].
3. Conclusion
We have synthesized mono(b-enaminoketonato)nickel
(II) and bis(b-enaminoketonato)-nickel (II) complexes 1–
4 and characterized three typical molecular structures of
complex 1, 2 and 4 by an X-ray crystallographic study.
The experimental results showed that all these complexes
displayed extremely high catalytic activities to the addition
polymerization of norbornene after being activated with
MAO. The catalytic activities of up to 5.22 · 107 g
PNB Æ molÀ1Ni Æ hÀ1 and Mw up to 4.86 · 106 g molÀ1 were
observed. Activities, polymer yield and Mw could be con-
trolled by the variation of reaction parameters. Interest-
ingly, catalytic activities and PNB productivity were
greatly enhanced because of the introduction of strong
electron-withdrawing group (trifluoro methyl) into the
ligands. The PNB obtained here are amorphous and solu-
ble in halogenated aromatic hydrocarbons. A study on syn-
theses and polymerization behaviors of mono(b-
diketiminato)nickel (II) complexes bearing trifluoro methyl
group is our current investigation.
Table 4
Influence of the reaction temperature (T) on the activities of complex 1
b
Entry
T (ꢁC)
Yield (%)
Activitya
Mw
Mw/Mn
1
2
3
4
0
30
60
90
62.3
92.2
71.6
31.3
3.52
5.22
4.04
1.77
2.92
2.82
2.69
2.61
1.73
2.43
1.82
2.22
Polymerization conditions: solvent, chlorobenzene; total volume, 10 mL;
nickel complex, 0.2 lmol; norbornene, 1.88 g [norbornene/nickel
(molar) = 100000]; Al/Ni = 5000; reaction time, 10 min.
a
107 g PNB Æ molÀ1Ni Æ hÀ1
Mw (106 g molÀ1).
.
b
4. Experimental
4.1. General considerations
All manipulations of air- and/or water-sensitive com-
pounds were carried out under dry nitrogen using standard
Schlenk and vacuum-line techniques. Solvents were dried
by refluxing with appropriate drying agents and distilled
under nitrogen prior to use. trans-[Ni(PPh3)2(Ph)Cl] were
prepared according to the literature procedures [15].
1,1,1-Trifluoro-2,4-pentanedione (98%) was purchased
from ACROS. Norbornene (bicyclo[2.2.1]hept-2-ene,
Acros) was purified by distillation over sodium and used
as a chlorobenzene solution. MAO was purchased from
Fig. 4. XRD diagram of PNB.

1280
H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
Aldrich as 10% weight of a toluene solution and used with-
out further purification. Other commercially available
reagents were purchased and used without purification.
1H NMR spectra were recorded with a Varian Unity-
400 spectrometer. Elemental analyses were performed on
an Elementar vario EL III Analyzer. FT-IR analyses were
detected with a Niclolet-FT-IR-50X spectrometer. NMR
data for PNB were obtained at ambient temperature on
Bruker AC 500 spectrometer instruments using o-chloro-
benzene-d4 as a solvent. Average molecular weight (Mw)
and molecular weight distribution (Mw/Mn) values of
PNB products were determined using a PL GPC-220 gel
permeation chromatograph at 150 ꢁC using a narrow stan-
dards calibration and equipped with three PL gel columns
(sets of PL gel 10 m MIXED-B LS). Trichlorobenzene was
employed as a solvent at a flow rate of 1.00 mL/min. DSC
measurements were performed with a Perkin–Elmer Pyris 1
DSC. The XRD diagram of the polymer powder was
obtained using a Bruker D4 Endeavor X-ray diffractometer
evaporation of THF under vacuum, the lithium salt of L1
was dissolved in 10 mL of toluene. Then the solution con-
taining the lithium salt of L1 was slowly channeled into a
50 mL flask with 0.668 g of trans-[Ni(PPh3)2(Ph)Cl]
(0.96 mmol) in 10 mL of toluene and continuously stirred
overnight at room temperature. The reaction mixture was
separated by centrifugation to remove LiCl. After the
upper clear dark red solution was concentrated to about
3 mL, 20 mL of hexane was added and complex 1 was
obtained as a red-orange solid. Yield: 0.446 g, 71%. Red
single crystals suitable for X-ray analysis were recrystal-
lized from toluene at À30 ꢁC. Anal. Calc. for
C37H33NOPF3Ni (654.32): C, 67.92; H, 5.08; N, 2.14.
1
Found: C, 68.18; H, 5.14; N, 1.97%. H NMR (CDCl3):
d = 7.41–7.00 (m, 23H, Ph–H), 5.36 (s, 1H, C–Hbackbone),
2.10 (s, 6H, Ph–CH3), 1.71 (s, 3H, –CH3).
4.2.4. ((2,6-Me2C6H3)NC(CH3)C(H)C(CF3)O)2Ni (2)
Complex 2 was prepared in a manner similar to that for
complex 1, but the ratio of trans-[Ni(PPh3)2(Ph)Cl] to L1
was ca. 1:2, instead of 1:1. Yield: 0.335 g, 61%. Red-orange
single crystals suitable for X-ray were recrystallized from
toluene at À30 ꢁC. Anal. Calc. for C26H26N2O2F6Ni
(571.20): C, 54.67; H, 4.59; N, 4.90. Found: C, 54.88; H,
˚
with monochromatic radiation at a wavelength of 1.54 A.
Scanning was performed with 2h ranging from 5ꢁ to 60ꢁ.
4.2. Ligand and complex synthesis
1
4.2.1. (2,6-Me2C6H3)NC(CH3)C(H)C(CF3)OH (L1)
1,1,1-Trifluoro-2,4-pentanedione (2.0 mL, 16.48 mmol)
was placed in a three neck flask with 52.19 mmol
(6.45 mL) of anhydrous 2,6-dimethylaniline dissolved in
20 mL of toluene at À10 ꢁC. Then 1.0 mL of TiCl4
(9.07 mmol) dissolved in ca. 8 mL of toluene was added
dropwise. The material turned dark brown. After permit-
ting the reaction mixture to warm to room temperature,
the material was heated at 90 ꢁC for 10–12 h, cooled,
allowed to stand overnight, filtered, and the salt cake
washed with more toluene. After removing solvent from
the combined filtrate and wash, the residue was passed
down a short alumina column eluting with hexane. Evapo-
rating the hexane, the product was isolated as yellow oil.
Yield: 2.76 g, 10.71 mmol, 65%. 1H NMR (CDCl3):
d = 12.10 (s, 1H, O–H), 7.14 (m, 3H, Ph–H), 5.56 (s, 1H,
C–Hbackbone), 2.16 (s, 6H, Ph–CH3), 1.79 (s, 3H, –CH3).
4.90; N, 5.11%. H NMR (CDCl3): d = 7.00–6.90 (m, 6H,
Ph–H), 5.14 (s, 2H, C–Hbackbone), 2.59 (s, 12H, Ph–CH3),
1.44 (s, 6H, –CH3).
4.2.5. ((2,6-i-Pr2C6H3)NC(CH3)C(H)C(CF3)O)Ni(Ph)-
(PPh3) (3)
Complex 3 was obtained as dark red powder in a yield
of 68%, 0.464 g. Anal. Calc. for C41H41NOPF3Ni
(710.44): C, 69.32; H, 5.82; N, 1.97. Found: C, 69.71; H,
5.54; N, 1.91%. 1H NMR (CDCl3): d = 7.67–6.45 (m,
23H, Ph-H), 5.77(s, 1H, C–Hbackbone), 3.72–3.69 (m, 2H,
i-Pr-CH), 1.60 (s, 3H, CN–CH3), 1.31–1.14 (dd, 12H,
i-Pr-CH3).
4.2.6. ((2,6-i-Pr2C6H3)NC(CH3)C(H)C(CF3)O)2Ni (4)
Complex 4 was obtained as dark red powder in a yield
of 57%, 0.374 g. Red-orange single crystals suitable for
X-ray were recrystallized from toluene at À30 ꢁC. Anal.
Calc. for C34H42N2O2F6Ni (683.40): C, 59.76; H, 6.19; N,
4.10. Found: C, 60.04; H, 6.08; N, 3.93%. 1H NMR
(CDCl3): d = 7.16–7.02 (m, 6H, Ph–H), 5.35 (s, 2H, C–
4.2.2. (2,6-i-Pr2C6H3)NC(CH3)C(H)C(CF3)OH (L2)
The synthesis of ligand L2 was carried out as described
1
for ligand L1. Yield: 3.56 g, 11.37 mmol, 69%. H NMR
(CDCl3): d = 12.20 (s, 1H, O–H), 7.36 (t, 1H, Ph–H),
7.22 (d, 2H, Ph–H), 5.56 (s, 1H, C–Hbackbone), 2.93 (m,
2H, i-Pr–CH), 1.81 (s, 3H, –CH3), 1.27–1.16 (dd, 12H,
i-Pr–CH3).
Hbackbone), 3.78 (m, 4H, i-Pr–CH), 1.54 (dd, 24H, i-Pr–
CH3), 1.21 (s, 6H, CN–CH3).
4.3. Structure solution and refinement for complex 1, 2, and 4
4.2.3. ((2,6-Me2C6H3)NC(CH3)C(H)C(CF3)O)Ni(Ph)-
(PPh3) (1)
For complexes 1, 2, and 4, a single crystal suitable for
X-ray analysis was sealed into a glass capillary, and the
intensity data of the single crystal were collected on the
CCD-Bruker Smart APEX system. All determinations of
the unit cell and intensity data were performed with graph-
A solution of ligand L1 (0.257 g, 1.0 mmol) in THF
(15 mL) was cooled to À78 ꢁC, and 1.1 equiv. of n-BuLi
was added dropwise (0.48 mL, 2.3 M, 1.1 mmol). The mix-
ture was warmed to room temperature by itself and stirred
for 2 h to afford the lithium salt of the ligand L1. After
˚
ite-monochromated Mo Ka radiation (k = 0.71073 A). All
data were collected at room temperature using the x scan

H.-Y. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 1275–1281
(b) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
1281
technique. These structures were solved by direct methods,
using Fourier techniques, and refined on F2 by a full-matrix
least-squares method. All the non-hydrogen atoms were
refined anisotropically, and all the hydrogen atoms were
included but not refined. Crystallographic data are summa-
rized in Table 1.
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4.4. Polymerization of norbornene
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In a typical procedure (entry 5, Table 3), 0.2 lmol of
nickel complex 1 in 1.0 mL of chlorobenzene, 1.88 g of nor-
bornene in 3.0 mL of chlorobenzene and another 3.0 mL
fresh chlorobenezene were added into a special polymeriza-
tion bottle (20 mL) with a strong stirrer under nitrogen
atmosphere. After the mixture was kept at 30 ꢁC for
10 min, 0.35 mL of MAO was charged into the polymeriza-
tion system via syringe and the reaction was initiated. Ten
minutes later, the acidic ethanol (Vethanol:Vconcd.HCl = 20:1)
was added to terminate the reaction. The PNB was isolated
by filtration, washed with ethanol and dried at 80 ꢁC for 48 h
under vacuum. For all polymerization procedures, the total
reaction volume was 10.0 mL, which can be achieved by the
variation of the amount of chlorobenzene when necessary.
IR (KBr): 2944, 2871, 1474, 1451, 1377, 1296, 1260, 1220,
(c) D. Zhang, G.-X. Jin, Organometallics 22 (2003) 2851;
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J. Polym. Sci. A 41 (2003) 2095;
1
1141, 1102, 1020, 940, 902, 864, 800 cmÀ1. H NMR: d
0.7–3.0 (m, maxima at 1.29 1.71 2.05 2.36 ppm).
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5. Supplementary material
(d) B. Berchtold, V. Lozan, P.G. Lassahn, C. Janiak, J. Polym. Sci.
A 40 (2002) 3604;
(e) W.-H. Sun, H. Yang, Z. Li, Y. Li, Organometallics 22 (2003)
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Kalamarides, S. Lenhard, L.H. Mclntosh III, K.T. Selvy, R.A. Shick,
L.F. Rhodes, Macromolecules 36 (2003) 2623;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Center, CCDC Nos. 276323–276325 for compound 1, 2
and 4. Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road, Cam-
bridge CB21EZ, UK (fax: +44 1223 336 033; e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(i) P.-G. Lassahn, V. Lozan, B. Wu, A.S. Weller, C. Jiniak, J. Chem.
Soc., Dalton. Trans. 23 (2003) 4437.
Acknowledgements
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¨
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Financial support by the National Science Foundation
of China for Distinguished Young Scholars (20421303,
20531020) and by the National Basic Research Program
of China (2005CB623800) is gratefully acknowledged.
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