Vinyl addition polymerization of norbornene catalyzed by β-iminoamine Ni(II) complexes/methylaluminoxane systems

Article abstract of DOI:10.1016/j.jorganchem.2011.08.017

Two nickel(II) complexes (A and B) bearing β-iminoamine ligands, [2-(ArNCH)-C₆H₄-NMe₂] (La, Ar = 2,6-i-Pr ₂C₆H₃; Lb, Ar = 2,6-Me₂C ₆H₃), were synthesized an

Full text of DOI:10.1016/j.jorganchem.2011.08.017

Journal of Organometallic Chemistry 696 (2011) 3697e3702
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Vinyl addition polymerization of norbornene catalyzed by
Ni(II) complexes/methylaluminoxane systems
b-iminoamine
*
Jun-Kai Zhang , Peng-Chao Wang, Xiao-Wei Wang, Liang Wang, Jun-Cai Chen, Zhi-Wu Zheng,
**
Yong-Ping Niu
School of Chemical Engineering and Pharmaceutics, Henan University of Science and Technology, Luoyang 471003, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two nickel(II) complexes (A and B) bearing
b-iminoamine ligands, [2-(ArN]CH)-C6H4-NMe2] (La,
Received 12 May 2011
Received in revised form
14 August 2011
Ar ¼ 2,6-i-Pr2C6H3; Lb, Ar ¼ 2,6-Me2C6H3), were synthesized and characterized by elemental analyses
and 1H NMR. X-ray crystal structure of complex B reveals that the six-membered chelate ring adopts
a envelope conformation, with nickel(II) atom deviating from the plane of backbone aromatic ring by
1.164 Å. In the presence of methylaluminoxane (MAO), both complexes showed moderate activities of
Accepted 18 August 2011
105 g molNꢀi1 hꢀ1 for norbornene polymerization.
b-iminoamine Ni(II)/MAO catalysts gave unimodal
Keywords:
Norbornene
polymers (Mw, 3.16e8.02 ꢁ 105 g/mol) with a relatively narrow MWD (Mw/Mn, 1.59e2.14), indicative of
single-site catalyst behavior. The obtained polymers are vinyl-type polynorbornenes (PNBs), which are
soluble in common solvents such as toluene, cyclohexane and dichlorobenzene.
Ó 2011 Elsevier B.V. All rights reserved.
b
-Iminoamine Ni(II) complex
Vinyl addition polymerization
Methylaluminoxane
Six-membered chelate ring
Cationic Ni(II) catalyst system
1. Introduction
diimine catalysts by Brookhart [11] have aroused general interest in
LTM catalyst systems [12e14] (Fig. 2).
Norbornenes represent a wide range of monomers derived from
dicyclopentadiene (DCPD) by DielseAlder reaction. Norbornenes
can be polymerized via ring opening metathesis polymerization
(ROMP), cationic or radical polymerization and vinyl addition
polymerization [1e3]. Through the choice of catalyst, each route
leads to its own polymers with different chain structure (Fig. 1) [2].
The vinyl-type polynorbornenes (PNBs) obtained with early tran-
sition metal catalysts are usually crystalline and insoluble polymers
[4], which are brittle and unsuitable for applications. In the 1990s,
cycloolefin copolymers (COCs) had been successfully prepared by
using metallocene catalysts [5e7]. These saturated copolymers
have excellent properties such as high transparency, high temper-
ature capability and good processability. In early 1990s, Risse and
coworkers [8e10] reported that norbornene could be polymerized
to soluble amorphous polymers, by using a series of late transition
metal (LTM) catalysts ([Pd(RCN)4][BF4]2). Since then, the research
interests of vinylic polymerization of norbornene were turned to
It was generally accepted that the catalyst nature (cationic or
neutral), the size of steric hindrance and the size of chelate ring play
important roles in ethylene polymerization [15]. The cationic Ni(II)-
and Pd(II)-based
a-diimine catalysts are very active for ethylene
polymerization [11,16]. In contrast, they were reported to be inac-
tive or less active catalysts for norbornene homopolymerization
[17e19]. The neutral anilinotropone-based Ni(II) systems are
relatively less active in ethylene polymerization than the cationic
Ni(II)-
a
-diimine systems [20,21]. Comparing with the cationic
-diimine systems, cationic Ni(II)- -diimine systems are
Ni(II)-
a
b
much less active in ethylene polymerization [22,23]. However,
these cationic six-membered ring systems were found to be
considerably active in norbornene homopolymerization [24]. The
neutral Ni(II)-b-diketiminato systems are moderately active cata-
lysts for both norbornene polymerization and ethylene polymeri-
zation [23,24]. The neutral Ni(II)-salicylaldimine systems were
reported to be very active catalysts for norbornene polymerization
[25e27]. The neutral Ni(II)-salicylaldimine systems bearing bulky R0
substituent (Fig. 2) also exhibited high activity for ethylene poly-
merization [28,29]. That said there is still a lack of understanding on
the nature of the active species to understand the activity trends [2].
LTM catalysts [1]. In 1995, the discoveries of Ni(II)- and Pd(II)-a-
* Corresponding author. Tel.: þ86 0379 64231914; fax: þ86 0379 64232193.
** Corresponding author.
The discussed
b-iminoamine Ni(II) complexes are six-
membered chelates with steric hindrance on one side (Fig. 2).
E-mail addresses: zhjunkai@gmail.com (J.-K. Zhang), ypniu@163.com (Y.-P. Niu).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.017

3698
J.-K. Zhang et al. / Journal of Organometallic Chemistry 696 (2011) 3697e3702
Scheme 1. Synthesis of b-amino-imine ligands and corresponding Ni(II) complexes.
benzaldehyde with the aromatic amines were carried out in
toluene at 80 ꢂC, with formic acid as catalyst. The coordination of
ligands to nickel(II) ions was preformed in dichloromethane (DCM)
at room temperature. Filtration of the reaction mixture gave clear
dark-purple filtrate. Crystals of complexes were obtained by
precipitating the concentrated filtrate with n-hexane. Both
complexes are slightly sensitive to moisture and soluble in chlo-
roform. Complex A is more soluble in toluene than complex B.
Exposure of these blue-purple crystals to vacuum or to dry nitrogen
resulted in opaque purple compounds, due to lose of solvent from
the crystals. Thus, it should be noted that, for both complexes,
elemental analysis gave results that are consistently low, which are
close to the calculated values of the unsolvated complexes because
the lose of the solvated dichloromethane in storage and in opera-
tion. Single crystals suitable for X-ray diffraction studies were ob-
tained by layering a DCM solution of complex B with n-hexane, as
a mono-dichloromethane solvate.
Fig. 1. The three different types of norbornene polymerization through the choice of
catalyst [2].
Upon activation with MAO, these Ni(II) precursors would generate
cationic Ni(II) active species [11,30], which should possess a steri-
cally open nature. In this paper, norbornene polymerization
behavior of these six-membered chelates was reported. Influences
of temperature, Al/Ni ratios and precursor structure on polymeri-
zation behavior were examined.
2. Results and discussion
2.1. Synthesisofligands(LaandLb)andnickel(II)complexes(A and B)
The synthetic routes of ligands and complexes were shown in
Scheme 1. 2-(Dimethylamino)benzaldehyde was prepared in a one-
pot procedure [31]. The ratio of n-butyllithium/N,N,N0,N0-tetrame-
thylethane-1,2-diamine (TMEDA) should be less than 1:1 in the o-
metallization step [32]. The condensations of 2-(dimethylamino)
2.2. Crystal structure of nickel complex B
The ORTEP diagrams of complex B, the selected bond distances
and angles are shown in Fig. 3. The ratio of complex molecules
with mutual mirror conformation is 1:1 in a packing diagram. The
Fig. 3. ORTEP view of complex B is drawn with thermal ellipsoids at the 30% proba-
bility level. Hydrogen atoms and the cocrystallized methylene dichloride molecule are
omitted for clarity. Selected bond distances (Å) and angles (deg): NieBr1 2.3507(9), Ni-
Br2 2.3524(8), NieN1 2.028(4), NieN2 1.974(4), N1eC2 1.472(6), N1eC7 1.489(6),
N1eC8 1.489(7), N2eC9 1.280(6), N2eC10 1.455(6), C1eC9 1.450(6), C1eC2 1.398(6);
N1eNieN2 92.27(15), Br1eNieBr2 120.26(3), N1eNieBr1 103.42(12), N1eNieBr2
109.34(12), N2eNieBr1 110.03(11), N2eNieBr2 116.85(11), C2eN1eNi 111.5(3),
C9eN2eNi 120.8(3), C1eC2eN1 118.6(4), C1eC9eN2 126.0(4), C2eC1eC9 126.6(4).
Fig. 2. Ligand series of related catalyst precursors (auxiliary ligands on metal were
omitted).

J.-K. Zhang et al. / Journal of Organometallic Chemistry 696 (2011) 3697e3702
3699
crystal structure of complex B reveals that Ni(II) atom is coordi-
nated in a tetrahedral geometry. The N1eNieN2 bite angle in
the contribution of the later is often small in orthorhombic system
[37]. The splitting singals of Pr groups, of which the two methyl
i
complex B is 92.27(15)ꢂ, which is smaller than that observed in
b-
groups would stay above and below the aniline plane, respectively
[38], suggest that the NieH distance would play a more important
role than the orientation in space (Fig. 3). The ranges of the NieH
distance, measured in crystal of complex B, are 2.812e3.754 Å for
N-methyl groups and 3.287e4.805 Å for Ar-methyl groups,
respectively. Thus, the rotation of methyl groups would also lead to
a broad signal. That said, the existence of the paramagnetic core
made it difficult to distinguish the chelate-ring conversion from the
overlap of signals. Moreover, the chelate-ring conversion, in low or
high frequency, should be a quick procedure. The chelate ring in
solution would like to adopt a time-averaged conformation, which
should be similar to those in crystal.
diimine Ni(II) complex (93.7(2)ꢂ) [22] and larger than that
observed in
a
-diimine Ni(II) complex (82.6(2)ꢂ) [33]. The six-
membered chelate ring adopts an envelope conformation with
a C2eC1eC9eN2 torsion angle of 18.05ꢂ, which is larger than that
found in anilido-imino nickel complexes (10.42ꢂ) [34]. The
distance from Ni(II) atom to the plane of backbone aromatic ring is
1.164 Å, which is larger than that observed in anilido-imino nickel
complexes (0.366 Å) [34].
2.3. 1H NMR spectra of paramagnetic complexes A and B
1H NMR spectra of paramagnetic complexes in CDCl3 are shown
in Fig. 4. Most of the resonance peaks can be assigned to appropriate
protons as marked in Fig. 4. A clean spectrum of complex B made it
possible to discriminate the signal of a (1.77 ppm) from the signal of
impurities (from free ligand, *), by comparing their integral values
with that of the other peaks. In the spectrum of complex A, the
signal of a (1.68 ppm) was overlapped by the signals of impurities
(from n-hexane, 0.88, 1.29e1.31 ppm). The i&i0 signal of complex A
was considered to be the broaden peak centered at 7.66 ppm. In
a static structure (Fig. 3), the methyl groups should give a different
chemical shift because they would be in a different orientation in
space. It might be reasonable to ascribed the coincidence of the
methyl signals, e&e0 and i&i0, to the “boat-to-boat” conversion of the
2.4. Norbornene polymerization
In the presence of MAO, norbornene polymerization experi-
ments were carried out in toluene by using complexes A and B as
catalyst precursors (Table 1). At a constant temperature of 65 ꢂC,
the catalyst activities were observed to increase continuously with
increasing Al/Ni ratios (entries 1e4, 10, 14, 15; 17, 20, 21). For the
selected conditions, the significant increases in activities were,
respectively, observed at Al/Ni ratio of 800 for a precatalyst loading
of 4 umol (entry 4) and at Al/Ni ratio of 400 for a precatalyst loading
of 10 ummol (entry 6). Low Al/Ni ratio would decrease the molec-
ular weight (Mw) and broaden the molecular weight distribution
(MWD) (entry 4 vs. 10, entry 6 vs. 8). Excess MAO would gives rise
to easy chain transfer because of the influence of AlMe3 [24,39,40],
which decreases the molecular weight and give a slightly broaden
MWD (entry 15). Higher conversion rates of norbornene can be
achieved by adding more catalyst precursors (entry 5e8) as well as
by extending the reaction time (entry 13).
six-membered chelate ring [35]. The observed chemical shift (dobs
)
in paramagnetic compounds can be divided into three parts, the
diamagnetic shifts (ddia), the Fermi contact (dcon) and the dipolar
contribution (ddip, which can be very small compared with dcon
)
[36,37]. The contribution of ddia and dcon to dobs should be equal to
the protons in the paired methyl groups. The dipolar contribution
(
ddip) is strongly dependent on the distance between the para-
The influence of temperatures on polymerization was carried
out at a constant Al/Ni ratio of 1000 (entries 9e12, 16e19). The
magnetic center and the nucleus and the orientation in space, and
Fig. 4. 1H NMR spectra of Ni(II) complexes A and B in CDCl3 at 25 ꢂC. Ni and Br atoms were omitted for clarity of labeling. “*” Free ligand impurities.

3700
J.-K. Zhang et al. / Journal of Organometallic Chemistry 696 (2011) 3697e3702
Table 1
Table 2
Influence of temperatures and Al/Ni ratios on norbornene polymerizationsa.
Crystal data and structure refinement for complex B.
c
c
Entry Cat.
m
mol Al/Ni Tp (ꢂC) Yield (%) Activityb Mw
Mw/Mn
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal size (mm3)
Crystal system
Space group
a (Å)
C18H22Br2Cl2N2Ni
555.81
296(2)
0.71073
1
2
3
4
A
A
A
A
4
4
4
4
200 65
400 65
600 65
800 65
3.7
5.9
12.4
21.3
0.69
1.11
2.34
4.01
0.3 ꢁ 0.23 ꢁ 0.17
4.48
1.90
Orthorhombic
5
6
7
8
A
A
A
A
10
10
10
10
200 65
400 65
600 65
800 65
8.2
53.7
57.7
59.5
0.62
4.04
4.34
4.48
Pbca
12.6137(10)
14.4154(12)
24.364(2)
90
90
90
4430.1(6)
3.16
4.79
2.14
1.67
b (Å)
c (Å)
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
9
A
A
A
A
A
A
A
4
4
4
4
4
4
4
1000 55
1000 65
1000 75
1000 85
1000 65
1500 65
2000 65
17.8
24.9
22.1
20.0
32.3
26.0
29.3
3.35
4.68
4.16
3.77
1.01
4.89
5.51
8.02
6.55
4.34
3.56
6.56
1.68
1.64
1.64
1.61
1.88
10
11
12
13
14
15
Volume (Å3)
Z
8
Calculated density (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.667
4.729
2208
2.30e25.50
)
5.45
1.70
q
range for data collection (ꢂ)
16
17
18
19
20
21
B
B
B
B
B
B
4
4
4
4
4
4
1000 55
1000 65
1000 75
1000 85
1500 75
2000 75
13.3
18.0
20.7
17.1
23.7
28.8
2.51
3.38
3.90
3.22
4.46
5.42
7.13
5.37
4.36
3.54
1.65
1.71
1.59
1.65
Limiting indices
ꢀ15 ꢃ h ꢃ 14
ꢀ17 ꢃ k ꢃ 16
ꢀ29 ꢃ l ꢃ 29
Reflections collected/unique
24,520/4122 [R(int) ¼ 0.0512]
Completeness to
q
¼ 25.50
100.0%
Absorption correction
Max. and min. transmission
Refinement method
None
a
Polymerization conditions: solvent, toluene; total volume, 20 ml; norbornene,
0.04 mol(3.77 g); reaction time, 30 min (except entry 13, 3 h).
0.5003 and 0.3130
Full-matrix least-squares on F2
4122/0/230
b
In units of 10ꢀ5 g PNB/(molNih).
Data/restraints/parameters
Mw (in units of 10ꢀ5 g/mol) and Mw/Mn were determined by GPC with standard
polystyrene as the reference and with 1,2,4-trichlorobenzene (TCB) as the eluent at
c
Goodness-of-fit on F2
1.051
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0412, wR2 ¼ 0.0995
R1 ¼ 0.0794, wR2 ¼ 0.1181
0.754 and ꢀ0.633
150 ꢂC.
R indices (all data)
Largest diff. peak and hole (e Åꢀ3
)
catalyst activities increased firstly then decreased gradually with
increasing temperature. The result should be ascribed to the
opposing effects of the increased temperature on the polymeriza-
tion rate and catalyst decomposition [41]. At the same temperature,
the bulky A/MAO catalyst presented slightly higher activities than
the less bulky B/MAO catalyst. This activity sequence agrees with
which are related to ROMP polymers, suggests a vinyl addition
polymerization pathway of norbornene [17,42]. An unknown peak
is present at 5.42 ppm, which is close to the chemical shift of vinyl
proton observed in 2-methylnorbornene (5.47 ppm) [43]. It is
reasonable to think that the NieC bonds of the propagating active
species have tendency to be cleaved. However, the intensity of this
signal does not increase with increasing temperature. Therefore,
the presence of vinyl-type chain end in polymer products needs
further confirmation. The obtained norbornene polymers are
soluble in common solvents such as toluene, xylene, cyclohexane
and chlorobenzene.
that observed in b-diimine Ni(II)/MAO and b-diketiminato Ni(II)/
MAO systems [24]. Upon increased temperature, molecular weight
(Mw) of polymer products decreased with a minor change of MWD
(1.59e1.71). The obtained GPC curves of the polymers were all
unimodal with narrow molecular weight distributions (1.59e2.14)
(Table 1), indicative of single-site catalyst behavior. Compared with
the other six-member chelated Ni(II) systems [24e29], the low
activity of b-iminoamine Ni(II)/MAO systems should be aroused by
the nature of their cationic active species, which possessed a less
planar chelate ring.
3. Conclusion
1H NMR spectra of norbornene polymers, obtained with A/MAO
at 65 ꢂC and 85 ꢂC (Table 1, entries 10 and 12), are shown in Fig. 5.
The absence of proton resonances at 5.15(cis) and 5.31(trans) ppm,
b
-iminoamine ligands and corresponding Ni(II) complexes were
synthesized and characterized. X-ray crystal structure of complex B
displays that the six-membered chelate ring adopts a envelope
conformation, with nickel(II) atom deviating from the plane of
backbone aromatic ring by 1.164 Å. In the presence of MAO,
b-
iminoamine Ni(II) complexes were used as catalyst precursors for
norbornene polymerization. The results showed the b-iminoamine
Ni(II)/MAO catalysts exhibited an activity level of 105 molNꢀi1 hꢀ1
and gave vinyl-type polynorbornenes with unimodal and narrow
molecular weight distribution (1.59e2.14), indicative of single-site
catalyst behavior. The low activity of
b-iminoamine Ni(II)/MAO
systems should be aroused by the nature of their cationic active
species, which possessed a less planar chelate ring.
4. Experimental
4.1. General remarks
1
Fig. 5. H NMR spectra of norbornene polymers obtained with A/MAO at 65 ꢂC and
Allnecessarymanipulations involvingair-andmoisture-sensitive
compounds were performed by standard Schlenk techniques under
85 ꢂC (Table 1, entry 10, 12), in 1,2-dichlorobenzene-d4 at 50 ꢂC.

J.-K. Zhang et al. / Journal of Organometallic Chemistry 696 (2011) 3697e3702
3701
nitrogen atmosphere in vacuum-line. 2,6-Diisopropylaniline, 2,6-
dimethylaniline and n-butyllithium were purchased from Aldrich.
N,N-dimethylformamide (DMF) was dried on ahydrous MgSO4 and
distilled before use. (DME)NiBr2 was prepared according to literature
procedures [44]. 2-(Dimethylamino)benzaldehyde, golden yellow
liquid (bp: 120e122 ꢂC w12 mmHg), was prepared according to the
reported literature [31]. MAO solid was prepared by the controlled
hydrolyzation of TMA in toluene at 0e60 ꢂC with grinding
Al2(SO4)3$$18H2O powders as water source (H2O/Al ¼ 1.3). Hexane
and toluene were thoroughly dried over phosphorus pentoxide and
sodium, respectively. Norbornene was purchased from Acros, puri-
fied by drying over sodium and distillation, used as toluene solution
(4.0 mol/L). Other commercially available reagents were purchased
and used as received.
backbone, overlapped peak), ꢀ6.69 (1H, 4-Ar-backbone), ꢀ8.56
(1H, 5-Ar-backbone), ꢀ13.51 (1H, p-Ar-aniline).
4.2.4. ((2,6-dimethyl)Phenyl-N]CH-C6H4-o-N(Me)2)NiBr2 (B)
By using the similar procedure described for complex A, complex
B was obtained as purple solid in 87% yield. Found: C, 43.43; H, 4.32;
N, 6.08. Anal. Calc. (C17H20Br2N2Ni): C, 43.36; H, 4.28; N, 5.95; 1H
NMR (CDCl3) (ppm): 175.29 (6H, N-(CH3)2), 28.61 (1H, eCH]Ne),
26.24 (6H, CH3eAr-aniline), 21.44 (2H, m-Ar-aniline), 16.95 (1H, 3-
Ar-backbone), 1.76 (1H, 6-Ar-backbone), ꢀ6.86 (1H, 4-Ar-
backbone), ꢀ9.06 (1H, 5-Ar-backbone), ꢀ14.92 (1H, p-Ar-aniline).
4.3. X-ray diffraction measurements
1H NMR spectra were recorded on a Bruker Avance III 400 MHz
NMR spectrometer. Elemental Analysis was determined with
Thermo Scientific Flash 2000 Organic Elemental Analyzer. Gel
permeation chromatography (GPC) analyses of the molecular
weight and molecular weight distribution (MWD) of the polymers
were performed on a PL-GPC 220 instrument with standard poly-
styrene as the reference and with 1,2,4-trichlorobenzene (TCB) as
the eluent at 150 ꢂC.
The crystal data for complex B were collected on a Bruker SMART
APEX II CCD diffractometer with graphite-monochromatized MoK
a
radiation (
l
¼ 0.71073 Å) at 296(2) K. Crystal structure was solved
by direct methods with SHELXS-97 [45]. A full-matrix least-squares
refinement on F2 was carried out using SHELXL-97 [46]. The final
agreement factor values are R1 ¼0.0412, wR2 ¼ 0.0995. Crystal data
and structure refinement details for complex B are summarized in
Table 2.
4.2. Synthesis of ligands and complexes
4.4. Norbornene polymerization
4.2.1. 2-(((2,6-Diisopropylphenyl)imino)methyl)-N,N-dimethylaniline
(La)
A typical polymerization procedure was carried out in a 50 ml
round-bottom glass flask, which was equipped with a magnetic
stirring bar and thoroughly dried by heating under vacuum. The
desired amounts of methylaluminoxane (dissolved in 9 ml toluene)
and norbornene solution (10 ml, 4.0 mol/L) were added into the
flask via syringe. The system was allowed to equilibrate at the
selected temperature for 20 min with stirring. Then, the desired
amount of precursor (dissolved 1 ml toluene) was added into the
flask to start the polymerization. The reaction mixture was
continuously stirred at the selected temperature for 30 min. Then,
polymerization was terminated by adding acidic ethanol (20 ml,
ethanol/HCl: 95/5). The white precipitate was filtered, washed
repeatedly with ethanol and dried under vacuum at 60 ꢂC to
a constant weight.
La was synthesized by the direct condensation of 2-(dimethy-
lamino)benzaldehyde (0.9 g, 6 mmol) with 2,6-diisopropylaniline
(1.1 g, 6 mmol) in 50 ml toluene at 80 ꢂC, with formic acid as
catalyst. After hours of heating, the reaction mixture was allowed to
cool to room temperature and dried by ahydrous MgSO4. After
filtration, toluene was distilled off under vacuum. The remaining
yellow oil was chromatographed on a column of neutral alumina or
silica gel with n-hexane as eluent. Ligand La was finally obtained as
light yellow crystals after concentration of the eluent and recrys-
tallization from n-hexane (yield: 1.2 g, 65%). m.p.: 65e66 ꢂC;
Found: C, 81.73; H, 9.18; N, 9.05. Anal. Calc.: C, 81.77; H, 9.15; N,
9.08; 1H NMR (400 MHz, CDCl3)
1H), 7.44 (t, J ¼ 7.7 Hz, 1H), 7.10 (ddd, J ¼ 26.5, 12.9, 6.8 Hz, 5H),
3.23e2.95 (m, 2H), 2.77 (s, 6H), 1.18 (d, J ¼ 6.9 Hz, 12H).
d
8.58 (s, 1H), 8.17 (d, J ¼ 7.9 Hz,
Acknowledgment
4.2.2. 2-(((2,6-Dimethylphenyl)imino)methyl)-N,N-dimethylaniline
(Lb)
The authors would like to acknowledge the Doctor Fund (project
no. 09001304) and School Fund (project no. 13090074) from Henan
University of Science and Technology.
By using the similar procedure described for ligand La, ligand Lb
was obtained as yellow crystals in 72% yield. m.p.: 93e94 ꢂC;
Found: C, 80.85; H, 8.03; N, 11.06. Anal. Calc.: C, 80.91; H, 7.99; N,
Appendix ASupplementary material
11.10; 1H NMR (400 MHz, CDCl3)
d
8.56 (s, 1H), 8.16 (d, J ¼ 7.1 Hz,
1H), 7.43 (t, J ¼ 7.0 Hz, 1H), 7.11 (dd, J ¼ 19.6, 11.5 Hz, 3H), 6.97 (dd,
The supplementary data associated with this article can be
found in the online version at doi:10.1016/j.jorganchem.2011.08.
017. CCDC 824799 contains the supplementary crystallographic
data for complex B. This data can be obtained free of charge from
The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.
uk/data_request/cif.
J ¼ 29.6, 22.3 Hz, 2H), 2.78 (s, 6H), 2.15 (s, 6H).
4.2.3. ((2,6-diisopropyl)Phenyl-N]CH-C6H4-o-N(Me)2)NiBr2 (A)
To a stirred solution of La (0.77 g, 2.5 mmol) in dry methylene
chloride (30 mL), NiBr2(DME) (2.5 mmol, 0.77 g) was added, and
the reaction mixture was stirred at ambient temperature for 24 h.
The resultant dark-purple solution was filtrated to get rid of the
possible insoluble impurities, and then the filtrate was concen-
trated to a volume of 1e20 ml under vacuum. n-Hexane was added
to precipitate the product. The blue-purple precipitate was filtered,
washed repeatedly with n-hexane and dried under vacuum (yield:
1.11 g, 84%). Found: C, 47.94; H, 5.38; N, 5.47. Anal. Calc.
(C21H28Br2N2Ni): C, 47.86; H, 5.36; N, 5.32; 1H NMR (CDCl3)
(ppm): 176.99 (6H, Ne(CH3)2), 28.55 (1H,eCH]Ne), 21.39 (2H, m-
Ar-aniline), 16.39 (1H, 3-Ar-backbone), 7.72 (eCH(isopropyl), bro-
den peak), 3.93 and 2.82 (6H and 6H, eCH3(isopropyl)), 1.68 (6-Ar-
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