Nickel and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands: Drastic steric effect on coordinated geometry, and catalytic property toward olefin polymerization

Article abstract of DOI:10.1016/j.ica.2009.01.037

A series of new nickel complexes and palladium complexes bearing ortho-phenoxy modified anilido-imine ligands have been synthesized and characterized. X-ray diffraction analyses of the single crystal structures reveal that there are no direct metal-O inte

Full text of DOI:10.1016/j.ica.2009.01.037

Inorganica Chimica Acta 362 (2009) 3035–3042
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Nickel and palladium complexes bearing ortho-phenoxy modified anilido-imine
ligands: Drastic steric effect on coordinated geometry, and catalytic property
toward olefin polymerization
a
a
a
Jie-ming Long a, Hai-yang Gao a, , Feng-shou Liu , Ke-ming Song , Hao Hu ,
*
Ling Zhang a, Fang-ming Zhu a,b, Qing Wu a,b,
*
a Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-sen (Zhongshan) University, No. 135, Xingangxi Road, Guangzhou 510275, China
b PCFM Lab, OFCM Institute, Sun Yat-sen (Zhongshan) University, Guangzhou 510275, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new nickel complexes and palladium complexes bearing ortho-phenoxy modified anilido-
imine ligands have been synthesized and characterized. X-ray diffraction analyses of the single crystal
structures reveal that there are no direct metal–O interactions in all of the complexes. The steric hin-
drance of complexes has an importance influence on their coordinated geometries. The bulky complexes
with 2,6-diisopropylphenyl substituent exist as a dimers with bromine-bridged structure while those
with 2,6-dimethylphenyl or phenyl substituents adopt a distorted tetrahedral geometry with four nitro-
gen atoms of two anilido-imine ligands. The nickel complexes exhibited high activity up to 7.33 Â 106 g/
(mol of Ni Á h) and palladium complexes showed very high activity up to 2.63 Â 108 g/(mol of Pd Á h) for
norbornene polymerization with methylaluminoxane as cocatalyst. The nickel catalysts were attempted
to polymerize ethylene at atmosphere pressure, however, only oligomers were produced.
Ó 2009 Elsevier B.V. All rights reserved.
Received 9 September 2008
Received in revised form 13 January 2009
Accepted 28 January 2009
Available online 6 February 2009
Keywords:
Anilido-imine ligands
Nickel complexes
Palladium complexes
Norbornene polymerization
1. Introduction
good catalytic activity towards ring-opening polymerization of
L-lactide [5,6]. Because of strong electrophilic metal center, the
In transition metal olefin polymerization catalyst design, ortho-
alkoxy-aryl substituents approach is proven to be an efficient strat-
egy. A variety of transition metal complexes bearing ortho-alkoxy
modified ligands exhibit interesting properties in olefin catalysis.
Huang reported that zirconium complexes bearing mono-Cp and
tridentate Schiff base [ONOÀ] ligands exhibited high thermal sta-
bility and high catalytic activities for ethylene polymerization
[1,2]. Gibson showed that titanium complexes containing phen-
oxy-amide ligands modified by phenoxy group exhibited low activ-
ity for ethylene polymerization [3]. Tang synthesized titanium (IV)
complexes bearing monoanionic phenoxy modified salicylaldimi-
nate ligand, and found they exhibited high activity for ethylene
polymerization and excellent capability for copolymerization of
ethylene with 1-hexene in the presence of modified methylalumi-
noxane (MMAO) [4]. Rare earth metal (yttrium and lanthanide)
catalysts could also be stabilized by b-diiminato and anilido-imina-
to ligands modified by methoxy functional group, and showed
methoxy or phenoxy groups usually can coordinate to early
transition metal and rare earth metals. Besides, Wass reported that
chromium complexes of aminodiphosphine ligands containing
ortho-methoxyaryl groups (PNPOMe
) are active and selective
catalyst precursors for ethylene trimerization and tetramerization
[7–11] and for the cotrimerization of ethylene and styrenic como-
nomers [12].
During the last decade, late transition metal catalysts for nor-
bornene polymerization and ethylene oligomerization have been
extensively studied and reviewed [13–19]. Late transition metal
catalyst chelating a variety of ortho-alkoxy-aryl phosphine ligands
also exhibited interesting properties in catalysis. Because of weak
electrophilic metal center, the methoxy groups usually do not eas-
ily coordinate to late transition metal (Ni, Pd). Pd(II) catalysts con-
taining {bis(ortho-alkoxyaryl)phosphino}arene sulfonate ligands
(POÀ) could catalyze nonalternating ethylene/CO copolymerization
to ethylene-enriched polyketones [20,21], ethylene/alkyl acrylate
copolymerization to linear copolymers with in-chain acrylate
incorporation [22], and other unusual copolymerizations [23–27].
Consiglio reported that palladium catalysts containing ortho-meth-
oxysubstituted arylphosphine-oxazole ligands (PN) catalyze
regioirregular alternating styrene/CO copolymerization [28].
Additionally, in situ-generated Ni(II) complexes containing PNPOMe
ligands exhibit better performance in ethylene polymerization and
* Corresponding authors. Address: Institute of Polymer Science, School of
Chemistry and Chemical Engineering, Sun Yat-sen (Zhongshan) University, No.
135, Xingangxi Road, Guangzhou 510275, China. Tel.: +86 020 84113250; fax: +86
020 84112245 (Q. Wu).
E-mail addresses: gaohy@mail.sysu.edu.cn (H.-y. Gao), ceswuq@mail.sysu.edu.cn
(Q. Wu).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.01.037

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J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
oligomerization than their nonsubstituted analogues [29]. Jordan
reported the studies of synthesis, structures, dynamics, and ethyl-
ene reactivity of a series of nickel complexes containing a (PNPOMe
)
O
aminodiphosphine ligand [30]. In several cases, the enhancements
of catalytic activity and/or selectivity engendered by the ortho-
methoxy groups in aryl phosphine ligands have been proposed to
arise from steric effects [23], because similar enhancements were
observed for analogous ortho-alkyl-substituted aryldiphosphines
[25,28–31]. In other cases, it was proposed that the ortho-methoxy
groups act as hemilabile ligands and reversibly coordinate to the
metal center during catalysis [7,8].
Therefore, a understanding of the properties of ortho-alkoxy(or
phenoxy)-aryl is interesting and enable new opportunities in catal-
ysis. During the past few years, our groups have focused our atten-
tion on anilido-imino nickel complexes due to their easily modified
features. From the view points of ligand steric and electronic, we
previously synthesized a series of bulky anilido-imino nickel com-
plexes and investigated their catalytic behaviors toward olefin
polymerization [32–37]. Herein we reported the initial studies of
the synthesis and structure of a series of phenoxy-modified anilid-
o-imine nickel and palladium complexes, as well as their catalytic
properties toward norbornene polymerization and ethylene
oligomerization.
R
R
X
X
N
N
N
N
M
M
R
R
O
i
1 M=Ni, X=Br, R=Pr
4 M=Pd, X=Cl, R=Pr
i
O
R
R
NH
N
O
R
R
N
N
N
M
N
R
R
2 M=Ni, X=Br, R=Me
3 M=Ni, X=Br, R=H
5 M=Pd, X=Cl, R=Me
6 M=Pd, X=Cl, R=H
O
2. Results and discussion
Scheme 2. Synthesis of the complexes 1–6.
2.1. Ligand and complex synthesis
and palladium complexes with 2,6-diisopropylphenyl substituents
(1 and 4) are grass green, those with 2,6- dimethylphenyl substit-
uents (2 and 5) are brown, while those with phenyl substituent (3
and 6) is dark red. This indicated that steric hindrance of aryl sub-
stituents played an importance role in coordination geometries of
these complexes. Elemental analyses (EA) and mass spectrometry
(MS) proved the nickel and palladium complexes with 2,6-diiso-
propylphenyl substituents (1 and 4) are in the form of a dimers
Three phenoxy-modified anilido-imine ligands with various
sterically hindered substituents were synthesized. The general
synthetic route for the ligands was shown in Scheme 1. Condensa-
tion of 2-fluorobenzaldehyde with corresponding anilines afforded
the imines (1a–c) in high yields. The corresponding ligands HL can
be obtained via a nucleophilic aromatic displacement of fluorine in
the imines using 2-phenoxyaniline lithium salt (Ph–O–2-
C6H4NHLi). Pure products were obtained as yellow crystals by
recrystallization from ethanol in 43–57% yields. All of the ligands
had been confirmed by 1H NMR, 13C NMR and elemental analyses
(EA).
The general synthetic route for the complexes was shown in
Scheme 2. After the ligands HL were deprotonated by 1.0 equiv.
of n-butyllithium in toluene, certain amount of (1,2-dimethoxyeth-
ane) nickel(II) bromide ((DME)NiBr2) or (1,5-cyclooctadiene) chlo-
romethylpalladium ((COD)PdMeCl) was added to the solutions.
Nickel complexes 1–3 and palladium complexes 4–6 were ob-
tained in moderate yields. Surprisingly, the complexes with
different aryl substituents showed different colors. The nickel
and bromine-bridged structure (LM-lBr2-ML), while those with
2,6-dimethylphenyl or phenyl substituents are mononuclear che-
lating two ligands (L2M). 1H NMR spectra of palladium complexes
4–6 could be assigned accurately, but nickel complexes 1–3 were
hardly analyzed due to their paramagnetism.
2.2. Molecular structures
The single crystals of nickel complexes 2, 3 and palladium com-
plex 4 were grown in toluene/hexane solutions. The crystal data,
together with the data collection and structure refinement param-
eters are presented in Table 1, and the selected bond lengths and
R
NH2
F
N
F
1a R=iPr
1b R=Me
1c R=H
R
R
CHO
n-hexane
R
+
O
R
R
n-BuLi
O
1a-c
O
NH
º
LH1 R=iPr
LH2 R=Me
LH3 R=H
NH
N
º
NH2
Scheme 1. Synthesis of the ligands LH1–LH3.

J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
3037
Table 1
Crystallographic date and refinement for complexes 2, 3 and 4.
2
3
4
Empirical formula
Formula weight
T (K)
C54H46N4NiO2ÁC7H8
933.79
150(2)
C50H38N4NiO2
785.55
293(2)
C31H31Cl N2OPd
589.43
293(2)
k(Mo K
a
) (Å)
0.71073
0.71073
k(Cu K
a
) (Å)
1.54178
monoclinic
P21/n
21.2390(2)
9.71640(10)
23.5226(2)
90
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P21/n
ꢀ
9.5411(11)
10.3972(8)
20.5602(16)
93.349(6)
100.174(8)
105.906(8)
1918.3(3)
2
10.5659(3)
14.3227(3)
17.8926(4)
90
91.889(2)
90
2706.25(11))
4
1.447
a
(°)
b (°)
96.1280(10)
90
4826.54(8)
4
1.285
0.960
c
(°)
V (Å3)
Z
Dcalcd (Mg/cm3)
Absorption coefficient (mmÀ1
F(000)
1.360
0.554
820
)
0.811
1208
1968
Crystal size (mm)
h (°)
No. of reflections collected
0.30 Â 0.10 Â 0.10
0.38 Â 0.22 Â 0.19
0.48 Â 0.48 Â 0.36
2.69–26
12814
3.78–60
2.69–26
21055
11859
No. of independent reflections [R(int)
]
7062 [0.0259]
0.999
7174 [0.0659]
1.087
5248 [0.0290]
1.018
Goodness-of fit (GOF) on F2
Final R indexes [I > 2
r
(I)]
R1 = 0.0348
wR2 = 0.0830
R1 = 0.0496
wR2 = 0.0867
R1 = 0.1169
wR2 = 0.3563
R1 = 0.1598
wR2 = 0.3736
R1 = 0.0465
wR2 = 0.1355
R1 = 0.0702
wR2 = 0.1465
R indices (all data)
Table 2
Selected bond lengths and bond angles for complexes 2, 3 and 4.
2
3
4
Bond lengths (Å)
Ni(1)–N(4)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(1)
N(1)–C(9)
N(2)–C(15)
N(3)–C(36)
N(4)–C(42)
H(34ª)–Ni(1)
H(7B)–Ni(1)
C(34)–Ni(1)
C(7)–Ni(1)
O(1)–Ni(1)
O(2)–Ni(1)
1.9427(17)
1.9495(16)
1.9794(18)
1.9961(17)
1.305(3)
1.353(3)
1.308(3)
1.368(3)
2.7102(4)
3.2049(4)
3.4261(69)
3.7793(21)
4.2537(15)
4.3509(13)
Ni(1)–N(4)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(1)
N(1)–C(7)
1.925(7)
1.926(7)
1.968(7)
1.960(7)
Pd(1)–Cl(1)
2.246(2)
2.224(2)
1.975(3)
1.990(3)
3.7950(38)
Pd(1)–Cl(1A)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–O(1)
1.293(11)
1.365(11)
1.311(11)
1.401(12)
2.8272(15)
2.7867(11)
3.1792(96)
3.1816(15)
3.2573(78)
3.2310(73)
N(2)–C(9)
N(3)–C(32)
N(3)–C(26)
H(31A)–Ni(1)
H(6A)–Ni(1)
C(31)–Ni(1)
C(6)–Ni(1)
O(1)–Ni(1)
O(2)–Ni(1)
Bond angles (°)
N(4)–Ni(1)–N(3)
N(2)–Ni(1)–N(1)
N(4)–Ni(1)–N(2)
N(2)–Ni(1)–N(3)
N(4)–Ni(1)–N(1)
N(3)–Ni(1)–N(1)
93.38(7)
91.25(7)
107.65(7)
139.43(8)
118.42(8)
109.00(7)
N(4)–Ni(1)–N(3)
N(2)–Ni(1)–N(1)
N(4)–Ni(1)–N(2)
N(2)–Ni(1)–N(3)
N(4)–Ni(1)–N(1)
N(3)–Ni(1)–N(1)
94.9(3)
93.8(3)
115.6(3)
126.5(3)
131.7(3)
96.9(3)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1A)
N(2)–Pd(1)–Cl(1A)
Pd(1A)–Cl(1)–Pd(1)
Cl(1A)–Pd(1)–Cl(1)
91.15(14)
91.26(12)
173.83(13)
173.33(12)
92.90(12)
94.75(11)
85.25(11)
angles are summarized in Table 2. ORTEP diagrams are given in
Figs. 1–3, respectively.
slightly shorter than the sum of the Ni and H van der Waals radii
(2.73 Å). The Ni–H contact suggest the presence of either agostic
interaction or Ni–H–C hydrogen bond [31]. It was found that only
one ligand has the Ni–H weak interaction, and the Ni–H distances
in another ligand are longer than 3.20 Å. The Ni–C distances
(3.4261(69) Å) involved in the Ni–HC interaction (Ni(1)–C(34) are
Complex 2 (Fig. 1) crystallizes in the monoclinic space group
P21/n, and the nickel metal center exhibits a distorted tetrahedral
geometry with four nitrogen atoms of two anilido-imine ligands.
The O(1)–Ni(1) (4.2537(15) Å) and O(2)–Ni(1) (4.3509(13) Å) dis-
tances are much longer than the sum of the Ni and O van der Waals
radii (3.15 Å), therefore, there are no significant O–Ni interactions
in the complex. Close inspection of the structure of complex 2 re-
veals that the complex has a type of weak Ni–H interaction, which
has been found in other complexes [30,38]. A hydrogen atom
(H(34A)) in the ortho methyl of 2,6-dimethylphenyl points toward
the nickel center. The Ni–H distance (Ni(1)–H(34A) 2.7102(4) Å) is
longer than those observed for
2.30 Å) in a related system [39].
c-C–H agostic interactions (Ni–C,
Unlike the b-diketiminato complexes, the imino C@N bonds in
complex still retain double bond character (bond lengths
2
1.308(3) Å and 1.305(3) Å). Two 6-membered [N,N] chelate ring
planes (N1–C9–C10–C15–N2 and the N3–C36–C37–C42–N4) are
nearly perpendicular (bite angle 83.1°), and the metal atom lies

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J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
out of the two planes 0.1132 Å and 0.5343 Å, respectively. The
nitrogens bond to nickel with different bond lengths. The
N(amine)–Ni bond length is ca. 1.95 Å, while the N(imine)–Ni bond
length is ca. 1.99 Å.
Complex 3 also adopts a distorted tetrahedral geometry (Fig. 2),
ꢀ
but crystallizes in the triclinic space group P1. Because of the less
bulky of complex 3, the O(1)–Ni(1) (3.2573(78) Å) and O(2)–
Ni(1) (3.2310(73) Å) distances are much shorter than those of com-
plex 2, but slightly longer than the sum of the Ni and O van der
Waals radii (3.15 Å). Two ortho hydrogen atoms (H(31A) and
H(6A)) of complex 3 have close contacts to the metal center
(Ni(1)–H(31A) 2.8272(15) Å, H(6A)–Ni(1) 2.7867(11). The atoms
of N1–C7–C8–C9–N2–Ni are almost located in a plane (within
0.0222 Å) which is good coplanar with the benzene ring (bite angle
between the two plane, 3.3°). Another 6-number chelate plane has
the similar situation (within 0.0322 Å, 2.8°), and the bite angle of
these two chelate plane is 69.6°. The N(amine)–Ni bond lengths
(ca. 1.93 Å) and the N(imine)–Ni bond lengths(ca. 1.96 Å) of com-
plex 3 are also slightly shorter than those of complex 2, but longer
than nickel complex [(PhN@CHC6H4NPh)2Ni] reported by Jin group
previously [40].
Fig. 1. Molecular structure of complex 2. Most of the hydrogen atoms and toluene
Unlike complexes 2 and 3, complex 4 with 2,6-diisopropyl-
phenyl substituent (Fig. 3) exists as dimers in the solid state with
tetrahedral geometries about the palladium and a crystallographic
C2 axis of symmetry that makes the two units equivalent. Similar
structure was also reported in the literature [33,41]. The atoms
of N1–C13–C14–C19–N2 are almost located in a plane (within
0.0217 Å) which is good coplanar with the benzene ring (interpla-
nar angle = 3.2°). The palladium metal atom lays 0.2575 Å out of
the [N,N] chelate plane. In contrast to the nickel complexes, the
N(amine)–Pd bond lengths of the palladium complexes are slightly
longer than the N(imine)–Pd bond lengths. The plane (Pd–Cl–Pd–
Cl) slightly deviates from a rectangle. The bite angle of Cl–Pd–Cl
(85.25(11)°) is slightly less than 90°, and the bite angle of Pd–Cl–
Pd (94.75(11)°) is slightly more than 90°. The Pd–O distances are
close to 3.80 Å, suggesting that there is no direct Pd–O interaction.
molecule are omitted for clarity.
2.3. Norbornene polymerization
Norbornene polymerizations were investigated using 1–6/MAO
catalytic systems and the polymerization results are collected in
Table 3. In general, all of the complexes showed high catalytic
activities toward norbornene polymerization after activation with
MAO. The type of metal center had an important influence on cat-
alytic activity. Nickel catalysts showed catalytic activity up to ca.
6 Â 106 g/(mol of Ni Á h) while palladium catalyst showed very high
Fig. 2. Molecular structure of complex 3. Most of the hydrogen atoms are omitted
for clarity.
Table 3
Results of norbornene polymerization with 1–6/MAO.a
Activityb
Mw
Mw/Mn
c
Run
Complex
Tp (°C)
Al/Mt
Yield (%)
1
2
3
4
5
6
7
8
1
2
2
2
2
2
2
2
3
4
5
6
25
0
2000
2000
2000
2000
2000
1000
3000
4000
2000
4000
4000
4000
45.8
44.5
41.8
37.5
36.0
37.8
39.0
36.5
36.3
65.8
57.0
51.8
7.33
7.12
6.69
6.00
5.76
6.04
6.24
5.84
5.80
263
2.46
2.60
1.82
1.54
1.36
2.03
1.62
1.55
1.79
1.62
1.77
1.55
1.34
1.36
1.68
1.85
1.43
1.60
25
50
75
25
25
25
25
25
25
25
9
10d
11d
12d
228
207
a
Polymerization conditions: complex, 1 lmol; NB, 4 g; solvent, toluene; total
volume, 20 mL; reaction time t = 15 min.
b
(Â10À6 g PNB/(mol of cat Á h)).
c
(Â10À6 g/mol).
Fig. 3. Molecular structure of complex 4. The hydrogen atoms are omitted for
clarity.
d
Complex, 0.2 lmol; NB, 2 g; reaction time t = 1.5 min.

J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
3039
Table 4
Results of ethylene oligomerization with 1–3/MAO.a
Run
Complex
Tp (°C)
Al/Ni
Activityb
Oligomer distributionc (mol%)
P
P
P
P
C4/
C
C6/
C
C8/
C
Cn > 8/
C
1
2
3
4
5
6
7
8
1
2
2
2
2
2
3
4–6
25
0
200
200
200
200
300
400
200
200
6.90
3.07
5.75
4.60
6.13
6.51
4.98
Inactive
52.4
84.4
50.4
56.6
63.1
61.5
68.1
29.9
5.8
15.1
9.1
2.6
0.7
1.8
1.9
2.1
1.3
0.6
25
50
25
25
25
25
36.3
24.5
25.6
27.8
21.0
11.5
17.0
9.2
9.4
10.3
a
b
c
Polymerization conditions: complex, 20
(Â10À4 g/(mol of Ni Á h)).
lmol; solvent, toluene; total volume, 20 mL; reaction time = 1 h; ethylene pressure, 1 atm.
Determined by GC and GC–MS.
catalytic activity up to ca. 2 Â 108 g/(mol of Pd Á h). Moreover, the
nickel complexes bearing phenoxy modified anilido-imine ligands
also showed higher activity toward norbornene polymerization
than unmodified anilido-imino nickel complexes [(ArN@CHC6H4-
NAr)NiBr] (Ar = 2,6-diisopropylphenyl; Ar = 2,6-dimethylphenyl)
reported previously [32,33]. Obviously, the difference in their
activity is due to an effect of phenoxy group. A reasonable explana-
tion for the catalytic activity enhancement is that the presence of
phenoxy group would favor the norbornene monomer coordina-
tion and insertion in the growing chain.
Though complexes 1 and 4 exist as four-coordinate dimers in
the solid state, they would exist mainly as three-coordinate mono-
mers in the solution [32]. They differ from the dinuclear and poly-
nuclear complexes which show the higher polymerization activity
than mononuclear complexes for norbornene polymerization
[42,43]. Additionally, the steric hindrance of the complexes on aryl
substituent affects the catalytic activities and molecular weight of
polynorbornene. The complexes with bulky steric hindrance exhib-
ited higher catalytic activities and afforded higher molecular
weight polymers. These results can be ascribed to the stabilization
of the active center and suppression of the chain transfer by bulky
steric hindrance of the ligand.
For 2/MAO catalytic system, with an increase in reaction tem-
perature, the catalytic activity and the molecular weight of the ob-
tained polynorbornenes decreased gradually. The decrease of MW
values of the obtained polymers decreased with an increase of
reaction temperature suggests that the chain transfer or termina-
tion begins to accelerate at high temperature [33]. Preliminary
experiments indicated that these nickel or palladium complexes
were not able to catalyze norbornene polymerization without
cocatalysts. It is necessary to use an excessive amount of MAO
for high activities. With an increase in Al/Ni ratio from 1000 to
4000, the catalytic activity for norbornene polymerization was
essentially unchanged, while molecular weight of the obtained
polynorbornenes decreased uniformly. In a polymerization proce-
dure, cocatalyst MAO also is a chain transfer agent, therefore, high
MAO concentration would cause the molecular weight of obtained
polynorbornene to decrease [33,38].
curve was unsuccessful because Tg was close to decomposition
temperature [26,30]. The wide-angle X-ray diffraction analysis of
the obtained polynorbornene showed two major broad peaks
(2h = 9–11° and 17–19°), which indicates that the obtained poly-
mer is non-crystalline and has low stereoregularity [37].
2.4. Ethylene polymerization
The nickel and palladium complexes were attempted to cata-
lyze ethylene polymerization in the present of MAO. Unfortu-
nately, palladium complexes 4–6 were inactive for the reaction.
However, ethylene could be oligomerized with the nickel com-
plexes. The results of ethylene oligomerization with complexes
1–3 at atmospheric pressure are shown in Table 4. GC–MS analyses
confirmed that the oligomers mainly contained C4, C6, and C8, and
only traces of higher oligomers (Cn > 8) were detected.
As reported previously, the low electrophilic nature of the ani-
lido-imino nickel metal center and fast b-H elimination should
be responsible for the low activity ethylene oligomerization [25].
Because ortho-phenoxy groups did not act as hemilabile ligands,
the nickel complexes bearing ortho-phenoxyl modified anilido-
imine ligand still would produce low electrophilic nickel metal
centers in the present of MAO. Additionally, the steric structure
of the nickel complexes slightly influenced their catalytic activities.
The complex with bulky 2,6-diisopropylphenyl substituents exhib-
ited higher catalytic activity and produced higher content of high
olefin oligomers. For 2/MAO catalytic system, with an increase in
the reaction temperature, the catalytic activity for ethylene oligo-
meirization increased and reached the maximum value at 25 °C,
and then decreased. With an increase in Al/Ni ratio from 200 to
400, the catalytic activity of ethylene oligomerization was nearly
unchanged, but the content of C4 components increased slightly.
3. Conclusion
Nickel and palladium complexes base on phenoxy-modified
anilido-imine ligands have been synthesized and characterized.
These complexes have two coordination geometries with different
bulky substituents. The complexes with 2,6-diisopropylphenyl
substituents exist as dimers in the solid state, while the complexes
with 2,6-dimethylphenyl substituents or phenyl substituents are
demonstrate to be mononuclear chelating two ligands (L2M). The
X-ray diffraction studies reveal that these complexes feature dis-
torted tetrahedral coordination geometry of the central metal
and the complexes 2 and 3 have a type of Ni–H weak interaction.
In the presence of MAO, nickel complexes 1–3 showed moder-
ate activity for ethylene oligomerization, but palladium complexes
were inactive. All nickel and palladium complexes exhibited very
high activity (up to 7.33 Â 106 g/(mol of Ni Á h) for nickel com-
The polynorbornenes obtained by the nickel based catalysts are
soluble in common solvents such as chlorobenzene, 1,2-dichloro-
benzene, cyclohexane, while those obtained by the palladium
based catalysts are insoluble in common solvents. All of the ob-
tained polymers showed very similar IR spectra which prove the
absence of double bond at 1620–1680 cmÀ1 1H NMR spectra of
.
the polynorbornenes obtained with nickel based catalysts also
prove no any traces of double bond, ensuring all of the obtained
polymers catalyzed by 1–6/MAO are vinylic addition polynorborn-
enes. TGA curves of the obtained polynorbornenes showed that the
polymer samples were stable up to 450 °C. Attempts to measure
glass transition temperature (Tg) of polynorbornene from DSC

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J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
plexes and 2.63 Â 108 g/(mol of Pd Á h) for palladium complexes)
give 13.5 g large yellow crystals. The filtrate was condensed to
lower volume and cooled to À10 °C to give an additional 4.2 g of
pure crystal. Total yield: 17.7 g (66%). 1H NMR (300 MHz, CDCl3):
d (ppm) 8.53 (s, 1H, CH@NAr), 8.24 (dt, 1H, ph), 7.50 (q, 1H, ph),
for norbornene polymerization with MAO as cocatalyst.
4. Experimental
i
7.30 (t, 1H, ph), 7.24–7.09 (m, 4H, ph), 2.99 (sp, 2H, CH of Pr),
1.23 (d, 12H, CH3). 13C NMR (75 MHz, CDCl3): d (ppm) 164.3 (d,
C–F), 155.5 (d, CH@N), 149.2, 137.4, 132.9, 127.6, 124.5, 124.2,
123.7, 123.0, 116.0, 28.0, 23.6. Anal. Calc. for C19H22FN: C, 80.53;
H, 7.82; N, 4.94. Found: C, 80.54; H, 7.67; N, 4.73%.
4.1. General considerations
All manipulations of air- and moisture-sensitive compounds
were carried out under an atmosphere of nitrogen using standard
Schlenk and vacuum-line techniques. Polymerization-grade ethyl-
ene and extra-pure-grade nitrogen were further purified before
feeding into the reactor by passing them through a DC-IB gas puri-
fication instrument. Toluene, hexane, and THF were dried over so-
dium metal and distilled under nitrogen. Chloroform-d was dried
over CaH2. 2-Fluorobenzaldenyde (97%), 2,6-diisopropylaniline
(92%), 2,6-dimethylniline (95%), n-butyllithium solution in hexane
(2.86 M) and 2-phenoxyaniline (98%) were bought from Aldrich
Chemical Co. and used without further purification. Norbornene
(Acros) was purified by distillation and used as a solution (0.4 g/
ml) in toluene. (DME)NiBr2 [44] and (COD)PdMeCl [45] were syn-
thesized by the report in the literature. Methylaluminoxane
(MAO) was prepared by partial hydrolysis of trimethylaluminum
(TMA) in toluene at 0–60 °C with Al2(SO4)3 Á 18H2O as the water
source. The resulting mixture was stirred overnight and filtered.
The filtrate was concentrated under reduce pressure at 30 °C. After
the toluene was removed, the MAO solid was dried under reduce
pressure at 50 °C for another 2 h. The initial [H2O/Al] molar ratio
was 1.3. Other commercially available reagents were purchased
and used without purification.
6.2. 2-C6H4F(CH@NC6H3Me2-2,6) (1b)
A solution of 9.4 g of o-fluorobenzaldehyde (75.5 mmol) and
10.0 g of 2,6-diimethylaniline (82.5 mmol) in n-hexane (40 mL)
was stirred for 2 h before MgSO4 was added. The mixture was then
filtered, and the bright yellow solution was evaporated to dryness
in vacuo to give a yellow oil. The oil was distilled under reduced
pressure, and a light yellow distillate at 170 °C/5 mmHg was col-
lected. Yield: 13.4 g (78%). 1H NMR (300 MHz, CDCl3): d (ppm)
8.58 (s, 1H, CH@NAr), 8.29 (dt, 1H, ph), 7.50 (q, 1H, ph), 7.30 (t,
1H, ph), 7.24–7.06 (m, 3H, ph), 7.00 (t, 1H, ph), 2.12 (s, 6H, CH3).
13C NMR (75 MHz, CDCl3): d (ppm) 164.3 (d, C–F), 156.1 (d, CH@N),
151.0, 132.9, 127.9, 127.5, 126.9, 124.3, 123.8, 115.9, 18.4. Anal.
Calc. for C15H14FN: C, 79.22; H, 6.27; N, 6.16. Found: C, 79.37; H,
6.22; N, 6.13%.
6.3. 2-C6H4F(CH@NC6H5) (1c)
A solution of 9.4 g of 2-fluorobenzaldehyde (75.5 mmol) and
8.0 g of aniline (7.8 mL, 85.4 mmol) in n-hexane (40 mL) was stirred
for 2 h before MgSO4 was added. The mixture was then filtered, and
the bright yellow solution was evaporated to dryness in vacuo to
give a yellow oil. The oil was distilled under reduced pressure, and
a light yellow distillate at 120 °C/5 mmHg was collected. Yield:
11.5 g (77%). 1H NMR (300 MHz, CDCl3): d (ppm) 8.84 (s, 1H,
CH@NAr), 8.26 (dt, 1H, ph), 7.54–7.12 (m, 8H, ph), 13C NMR
(75 MHz, CDCl3): d (ppm) 164.3 (d, C–F), 153.2 (d, CH@N), 151.7,
132.8, 129.0, 127.7, 126.1, 120.8, 123.8, 115.8, Anal. Calc. for
C13H10FN: C,78.37; H,5.06; N,7.03. Found: C, 78.16; H, 5.15; N, 7.03%.
5. Measurement
Elemental analyses were performed on a Vario EL micro ana-
lyzer. Mass spectra were measured on a fast atom bombardment
mass spectrometry (FAB-MS) instrument. 1H NNR and 13C NMR
spectra were recorded on an INOVA 300 MHz instrument at room
temperature in CDCl3 solution for ligands and complexes with
TMS as internal standard and in o-dichlorobenzene solution for
polymers with the solvent as internal standard. IR spectra were re-
corded on a Nicolet NEXUS-670 spectrometer. Mn, Mw, and Mw/Mn
values of polymers were determined using a Waters Alliance GPC
2000 series at 135 °C and using polystyrene calibration and 1,2,4-
trichlorobenzene as the solvent at a flow rate of 1.0 mL/min. The
GC–MS data were recorded with a Finnigan Voyager GC-8000 TOP
series GC–MS system with DB-5MS GC column (30 m  0.25 mm Â
i
6.4. (2-C6H5OC6H4NH)-C6H4-2-CH@NC6H3 Pr2-2,6 (L1)
A solution of 2.86 M n-BuLi (9.30 mL, 26.6 mmol) in hexane was
dropped slowly to solution of 2-phenoxyaniline (4.92 g,
26.6 mmol) in THF (40 mL) at À78 °C, the reaction mixture was al-
lowed to warm to room temperature and stirred overnight. To this
0.25 lm). The column temperature was started at 40 °C (5 min),
pale suspension was added
a
solution of 1a (2-
i
raised by 8 °C/min to 110 °C and then raised by 15 °C/min from
110 °C to 250 °C, kept at 250 °C for 5 min. Differential scanning cal-
orimetry (DSC) analysis was conducted with a Perkin–Elmer DCS-7
system. The DSC curves were recorded at a heating rate of 10 °C/
min. The cooling rate was 10 °C/min. TGA data were collected with
a TG-290C thermal analysis system instrument under a nitrogen
atmosphere up to 600 °C at heating rate of 10 °C/min. Wide-angle
X-ray diffraction (WAXD) curves of the polymer powders were ob-
tained using a D/Max-IIIA powder X-ray diffractometer.
C6H4F(CH@NC6H3 Pr2-2,6)) (7.54 g, 26.6 mmol) in THF (20 mL) at
room temperature. After stirring for 24 h, the reaction was
quenched with H2O (20 mL) and extracted with n-hexane, the or-
ganic phase was evaporated to dryness in vacuo to give the crude
product as yellow oil. Pure product was obtained as yellow crystals
by recrystallization from ethanol. Yield (5.37 g, 45%). 1H NMR
(300 MHz, CDCl3): d (ppm) 11.03 (s, 1H, N–H); 8.20 (s, 1H, CH@N);
7.63 (d, 1H, Ar–H); 7.43 (d, 1H, Ar–H); 7.34–7.26 (m, 2H, Ar–H);
i
7.21–6.75 (m, 12H, Ar–H); 2.92 (sp, 2H, CH of Pr); 1.08, 1.06 (dd,
12H, CH3). 13C NMR(75 MHz, CDCl3): d (ppm) 165.0 (CH@N),
157.1, 148.6, 145.6, 136.0, 134.6, 132.9, 131.6, 129.3, 124.2,
123.8, 123.3, 122.7, 122.6, 122.1, 120.2, 118.7, 117.7, 117.2,
113.3, 28.0, 23.6. Anal. Calc. for C31H32N2O: C, 83.00; H, 7.19; N,
6.24. Found: C, 83.13; H, 7.27; N, 6.20%.
6. Syntheses of ligands and complexes
i
6.1. 2-C6H4F(CH@NC6H3 Pr2-2,6) (1a)
A solution of 11.7 g of 2-fluorobenzaldehyde (94.3 mmol) and
17.6 g of 2,6-diisopropylaniline (99.3 mmol) in n-hexane (40 mL)
was stirred for 2 h before MgSO4 was added. The mixture was then
filtered and washed with n-hexane. The bright yellow solution was
concentrated to ca. 30 mL and then cooled to À10 °C overnight to
6.5. (2-C6H5OC6H4NH)-C6H4-2-CH@NC6H3Me2-2,6 (L2)
The similar procedure as that for the preparation of L1 was
used. 2-phenoxyaniline (4.60 g, 24.8 mmol), 2.86 M n-BuLi

J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
3041
(8.71 mL, 24.9 mmol), 1b (5.64 g, 24.9 mmol) were used. Yield:
5.54 g (57%). 1H NMR (300 MHz, CDCl3): d (ppm) 11.12 (s, 1H, N–
H); 8.18 (s, 1H, CH@N); 7.67 (d, 1H, Ar–H); 7.46 (d, 1H, Ar–H);
7.35–7.25 (m, 2H, Ar–H); 7.20–6.73 (m, 12H, Ar–H); 2.01 (s, 6H,
CH3). 13C NMR(75 MHz CDCl3): d (ppm) 165.0 (CH@N), 157.4,
150.2, 147.6, 145.4, 134.5, 133.5, 131.6, 129.2, 127.8, 124.3,
123.7, 123.1, 122.2, 121.6, 121.2, 118.9, 117.2, 116.8, 113.2, 18.5.
Anal. Calc. for C27H24N2O: C, 82.62; H, 6.16; N, 7.14. Found: C,
82.53; H, 6.19; N, 7.24%.
overnight. (COD)PdMeCl (0.28 g) in 10 mL dichloromethane was
added at room temperature. The resulting mixture was stirred
overnight and filtered. The solid was washed with toluene
(10 mL Â 3). The combined organic filtrates were concentrated
under reduce pressure, and then 5 mL dry hexane was added.
The mixture was stirred for 30 min. The filtration of the
mixture gave complex 4 as green powder in 46% yield (0.28 g).
1H NMR (300 MHz, CDCl3): d (ppm) 7.42–6.51 (m, 28H, CH@N
and Ar–H); 6.30–6.16 (m, 4H, Ar–H); 3.50–3.00 (m, 4H, CH of
iPr); 1.62–0.64 (m, 24H, CH3). FAB-MS (m/z): 551, 552, 553, 554,
6.6. (2-C6H5OC6H4NH)-C6H4-2-CH@NC6H5. (L3)
555 (isotope, [L+Mt]+), 448 (Ligand+). Anal. Calc. for C62H62
-
Cl2N4O2Pd2: C, 63.16; H, 5.30; N, 4.75. Found: C, 63.36; H, 5.07;
N, 4.83%.
The similar procedure as that for the preparation of L1 was
used. 2-phenoxyaniline (5.70 g, 30.8 mmol), 2.86 M n-Buli
10.8 mL, 30.9 mmol), 1c (5.82 g, 30.8 mmol) were used. Yield:
4.8 g (43%). 1H NMR (300 MHz, CDCl3): d (ppm) 11.26 (s, 1H, N–
H); 8.45 (s, 1H, CH@N); 7.63 (d, 1H, Ar–H); 7.43 (d, 1H, Ar–H);
7.34 (d, 1H, Ar–H); 7.28–6.85 (m, 14H, Ar–H); 6.77 (t, 1H, Ar–H).
13C NMR (75 MHz, CDCl3): d (ppm) 161.7 (CH@N), 157.6, 150.5,
147.6, 145.1, 134.7, 133.5, 131.5, 129.4, 128.9, 125.6, 124.1,
122.8, 122.5, 120.9, 120.6, 119.4, 117.5, 117.4, 113.3. Anal. Calc.
for C25H20N2O: C, 82.39; H, 5.53; N, 7.69. Found: C, 82.16; H,
5.50; N, 7.56%.
6.11. Complex 5
The similar procedure as that for the preparation of complex 4
was used. L2 (0.52 g, 1.32 mmol), 2.86 M n-BuLi(0.46 mL,
1.32 mol), (DME)NiBr2 (0.19 g) were used. Yield: 0.35 g (45%). 1H
NMR (300 MHz, CDCl3): d (ppm) 7.87–7.79 (d, 2H, CH@N); 7.36–
6.41 (m, 25H, Ar–H); 6.39–6.31 (m, 4H, Ar–H); 6.08–6.00 (m, 3H,
Ar–H); 2.430–1.448 (m, 12H, CH3). FAB-MS (m/z): 887, 888, 889,
890, 891(isotope, [M]+), 495, 496, 497, 498, 499 (isotope,
[L+Mt]+), 392 (Ligand+). Anal. Calc. for C54H46N4O2Pd: C, 72.92; H,
5.21; N, 6.30. Found: C, 73.12; H, 5.34; N, 6.35%.
6.7. Complex 1
To a solution of L1 (0.57 g, 1.26 mmol) in dry toluene (30 mL) at
À78 °C was added a 2.86 M n-BuLi hexane solution (0.45 mL,
1.28 mmol) dropwise over 10 min period. The mixture was al-
lowed to warm to room temperature and stirred overnight. (DME)-
NiBr2 (0.40 g) was added at room temperature. The resulting
mixture was stirred overnight and filtered. The solid was washed
with toluene (10 mL Â 3). The combined organic filtrates were con-
centrated under reduce pressure, and then 5 mL dry hexane was
added. The mixture was stirred for 30 min, the filtration of the mix-
ture gave complex 1 as green powder in 46% yield (0.34 g). FAB-MS
(m/z): 521, 522, 523, 524, 525 (isotope, [MÀBr]+), 448 (Ligand+).
Anal. Calc. for C62H62Br2N4Ni2O2: C, 63.52; H, 5.33; N, 4.78. Found:
C, 63.29; H, 5.11; N, 5.87%.
6.12. Complex 6
The similar procedure as that for the preparation of complex 4
was used. L3 (0.47 g, 1.29 mmol), 2.86 M n-BuLi (0.45 mL,
1.29 mmol), (DME)NiBr2 (0.17 g) were used. Yield: 0.32 g (59%).
1H NMR (300 MHz, CDCl3): d (ppm) 7.95 (s, 1H, CH@N); 7.92 (s,
1H, CH@N); 7.33–6.32 (m, 33H, Ar–H); 6.08–6.01 (m, 3H, Ar–H).
FAB-MS (m/z): 832, 833, 834, 835 (isotope, [M]+), 467, 468, 469,
470, 471, 472, 473 (isotope, [L+Mt]+), 364 (Ligand+). Anal. Calc.
for C50H38N4O2Pd: C, 72.07; H, 4.62; N, 6.72. Found: C, 72.21; H,
4.54; N, 6.43%.
7. Norbornene polymerization
6.8. Complex 2
In a typical procedure, the appropriate MAO solid was added
into a 50 mL flask, and then freshly distilled toluene and norborn-
ene dissolved in toluene (0.4 g/mL) was added via syringe at the
desired polymerization temperature. The resulting mixture was
stirred for a further 10 min, and the catalyst precursor in toluene
was injected via a syringe. The polymerization was carried out
for the desired time and then quenched with concentrated HCl in
ethanol (150 mL, HCl/ethanol, 5:95, v/v). The precipitated polymer
was collected and washed with ethanol, and then dried overnight
in a vacuum at 50 °C.
The similar procedure as that for the preparation of complex 1
was used. L2 (0.74 g, 1.90 mmol), 2.86 M n-BuLi (0.67 mL,
1.91 mmol), (DME)NiBr2 (0.29 g) were used. Yield: 0.52 g (65%).
FAB-MS (m/z): 840, 841, 842, 843, 844 (isotope, [M]+), 448, 449,
450, 451, 452, 453 (isotope, [L+Mt]+), 392 (Ligand+). Anal. Calc.
for C54H46N4NiO2: C, 77.06; H, 5.51; N, 6.66. Found: C, 77.25; H,
5.33; N, 6.48%.
6.9. Complex 3
8. Ethylene oligomerization
The similar procedure as that for the preparation of complex 1
was used. L3 (0.60 g, 1.65 mmol), 2.86 M n-BuLi (0.58 mL,
1.66 mmol), (DME)NiBr2 (0.26 g) were used. Yield: 0.48 g (74%).
FAB-MS (m/z): 784, 785, 786, 787, 788, 789 (isotope, [M]+), 420,
421, 422, 423, 424 (isotope, [L+Mt]+), 364 (Ligand+). Anal. Calc.
for C50H38N4NiO2: C, 76.45; H, 4.88; N,7.13. Found: C, 76.29; H,
4.73; N, 7.05%.
The oligomerization under 1 atm of ethylene was carried out in
a typical procedure as follows. Appropriate MAO solid was added
into a 50 mL flask. The flask was back-filled twice with ethylene,
and then 20 mL freshly distilled toluene was added via syringe un-
der ethylene atmosphere at the desired polymerization tempera-
ture. The resulting mixture was stirred for a further 10 min, and
the catalyst precursor in toluene was injected via a syringe. The
reaction solution was vigorously stirred under 1 atm of ethylene
for the desired time. The flask was cooled to À10 °C and the
quenched with concentrated HCl in ethanol (10 mL, HCl/ethanol,
5:95, v/v). About 2 mL organic solution was dried by anhydrous
Na2SO4 for GC–MS analysis.
6.10. Complex 4
To a solution of compound L1 (0.46 g, 1.02 mmol) in dry toluene
(30 mL) at À78 °C was added a 2.86 M n-butyllithium hexane solu-
tion (0.36 mL, 1.03 mmol) dropwise over 10 min period. The mix-
ture was allowed to warm to room temperature and stirred

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J.-m. Long et al. / Inorganica Chimica Acta 362 (2009) 3035–3042
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Supports by the National Natural Science foundation of China
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