Synthesis, characterization and olefin polymerization of the nickel catalysts supported by [N,S] ligands

Article abstract of DOI:10.1016/j.jorganchem.2008.10.009

The novel nickel (II) complexes (2a, 2b) bearing 1-pyridyl-(3-substituedimidazole-2-thione) ligands were synthesized by the reaction of the corresponding ligands with NiBr₂(DME). 2a and 2b have been characterized by IR, NMR and elemental analys

Full text of DOI:10.1016/j.jorganchem.2008.10.009

Journal of Organometallic Chemistry 694 (2009) 86–90
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and olefin polymerization of the nickel catalysts
supported by [N,S] ligands
*
Yuan-Biao Huang, Wei-Guo Jia, Guo-Xin Jin
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200433, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel nickel (II) complexes (2a, 2b) bearing 1-pyridyl-(3-substituedimidazole-2-thione) ligands were
synthesized by the reaction of the corresponding ligands with NiBr2(DME). 2a and 2b have been charac-
terized by IR, NMR and elemental analysis. The nickel complexes show high catalytic activities for nor-
bornene polymerization in the presence of MAO (methylaluminoxane), although low activities for
ethylene polymerization.
Received 28 August 2008
Received in revised form 27 September
2008
Accepted 7 October 2008
Available online 14 October 2008
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Nickel complex
Pyridyl-imidazole-2-thione ligands
Polymerization
Norbornene
Ethylene
1. Introduction
now, there was no report of the nickel catalyst bearing [NS] ligands
for olefin polymerization [2–6]. Herein, we report the synthesis
Since Brookhart discovered the
a
-diimine nickel and palladium
and characterization of the nickel complexes with new hard–soft
nitrogen–sulfur donor ligands 1-pyridyl-(3-tbutylimidazole-2-thi-
one) (1a) and 1-pyridyl-(3-(2,6-diisopropylphenylimidazole)-2-
thione) (1b) and the test of the complexes for the polymerization
of ethylene and norbornene.
catalysts which can produce high molecular weight polyethylene
in 1995 [1], olefin polymerization of late transition metal catalysts
has attracted considerable attention in academic and industrial
fields over the past decade [2–6]. After activation with MAO, the
pyridyl-imine based NiII catalyst can produce mainly oligomer
and methyl branched PE with good to moderate activity [7–11].
The NB (norbornene) addition polymerization product (PNB)
displays a characteristic rigid random coil conformation, which
shows restricted rotation about the main chain and exhibits high
thermal stability (Tg > 350 °C). In addition, it has excellent dielec-
tric properties, optical transparency and unusual transport proper-
ties [2–3]. Therefore, it has been attracted many chemists to study
the NB addition–polymerization. Up to now, catalytic systems
based on titanium [12], zirconium [13], cobalt [14–17], chromium
[14,18–19], nickel [20–33], palladium [33–35] and copper [31–
32,36–37] have been mainly reported for the addition–polymeriza-
tion of NB. Especially, the nickel complexes bearing [N,O] and [N,N]
ligands using for norbornene polymerization exhibited high activ-
ity [21–22,25–27,29–32]. Recently, our group found that nickel
complexes bearing soft atom donor ligands N-substituents imidaz-
ole-2-thione and imidazole-2-selone activated with MAO exhib-
ited very high activity for norbornene polymerization [38]. Up to
2. Results and discussion
2.1. synthesis and characterization of the ligands and complexes
The bidentate ligands with N-substituents imidazole-2-thione
and imidazole-2-selone can be easily prepared with moderate
yields by the reaction of methylene and ethylene bridged N-substi-
tutedimidazolium dibromide with sulfur or selenium powder and
K2CO3 under reflux condition in MeOH solution [38–40]. The new
hard–soft nitrogen–sulfur donor ligands 1-pyridyl-(3-tbutylimid-
azole-2-thione) (1a) and 1-pyridyl-(3-(2,6-diisopropylphenylimi-
dazole)-2-thione) (1b) were readily prepared by deprotonation of
corresponding imidazolium salt with potassium tert-butoxide
(Scheme 1) in THF solution, followed by adding the sulfur at room
temperature. All the ligands were stable in the air and moisture,
and were soluble in common organic solvents such as CH2Cl2,
CHCl3 and THF. The ligands 1a and 1b were characterized by 1H
NMR, 13C NMR, IR spectroscopy and elemental analysis. The forma-
tion of 1a is conformed by the appearance of the 1H signals at 1.87,
6.98 and 7.36 ppm, which can be assigned to the methyl, two
* 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 Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.10.009

Y.-B. Huang et al. / Journal of Organometallic Chemistry 694 (2009) 86–90
87
Scheme 1. Synthesis of ligands 1a and 1b and complexes 2a and 2b.
olefinic H protons of the imidazole, respectively, and the IR spectra
exhibit intense C@S stretching at about 1158 cmꢀ1. Similarly, the
structure of 1b was conformed by the resonances at 1.13, 1.28,
6.77, 7.85 ppm in the 1H NMR spectra. And the formation of C@S
bond was further confirmed by 13C NMR spectra which show sin-
glet at about d 164.6 ppm and d 164.4 ppm for 1a and 1b,
respectively.
The green complexes 2a and 2b were obtained by the reaction
of 1a and 1b with NiBr2(DME) in dichloromethane in good yields.
In the IR spectra of complexes 2a–2b, the C@S stretching vibrations
shift toward lower frequencies (2a: from 1158 to 1156; 2b: from
1178 to 1154) and were greatly reduced in intensity, which indi-
cated the coordination interaction between the S atoms and the
metal nickel ions. Elemental analysis is in all cases consistent with
the stoichiometry (ligand)NiBr2. 1H NMR spectroscopy of com-
plexes 2a and 2b exhibited paramagnetic properties indicating that
mononuclear structure configuration, which not like the pyridyli-
mine nickel complexes that crystallize as centrosymmetric dimers
with two ligand nitrogen atoms, one terminal bromine and two
bridging bromine atoms forming the coordination sphere around
each five-coordinate nickel center [7–11]. The nickel center of
complex 2b adopted a distorted tetrahedral geometry, which
further confirmed the paramagnetic results of the NMR measure-
ments. A bulky steric interactions was created by the 2,6-diisopro-
pyl of the phenyl within the nickel center (Fig. 1), which could be
prevent the b-H transfer. The bond length of Ni–N (2.008(8) Å) was
shorter than that of the pyridylimine nickel complexes (2.023(5)–
2.086(3) Å) (Ni–N(pyridine)) [8] and pyridine functionalized
chelate N-heterocyclic carbene nickel complexes (2.032(5)–
2.103(5) Å) [41]. And the Ni–S (2.282(3) Å) bond distance was also
shorter than that the nickel complexes bearing different N-substit-
uents imidazole-2-thione (2.2837(15)–2.3155(18) Å) [38]. The
dihedral angel of the pyridine ring and the imidazole plane was
36.2°, and do not possess in the same plane. The phenyl ring of
the N-substituent was oriented essentially orthogonal to the imid-
azole plane (89.1°). And the dihedral angle of the phenyl ring and
the pyridine ring is 60.6°.
the complexes possess a tetrahedral geometry as seen for (
ne)NiBr2 complexes [1].
a-diimi-
Green single crystals of 2b bearing N-2,6-diisopropylphenyl
substituted ligand were grown in CH3CN/ether (1:10) at room tem-
perature and the corresponding X-ray crystallographic data were
given in Table 1. As depicted in Fig. 1, the complex 2b forms a
2.2. Olefin polymerization
Table 1
The
a-diimine Ni and Pd complexes with bulky aryl substitu-
ents ligands, which can prevent b-H transfer, can produce high
Crystallographic data of the complex 2b.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C20H23N3SNiBr2
556.00
Triclinic
ꢀ
P1
8.041(7)
8.796(7)
16.330(14)
77.158(12)
85.275(10)
80.194(10)
1108.4(16)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalcd. (mg mꢀ3
)
1.666
Crystal size (mm3)
0.12 ꢁ 0.10 ꢁ 0.08
l
(mmꢀ1
F(000)
)
4.584
556
hmax, hmin (°)
27.41, 2.40
Index range
h
k
l
ꢀ10 ? 9
ꢀ11 ? 8
ꢀ19 ? 20
[R(int)
]
0.0469
No. of independent reflections
No. of observed reflections
No. of variables
4546
3071
160
Fig. 1. Crystal structure of 2b. For clarity, the hydrogen atoms are omitted. The
ellipsoids are drawn at 30% probability level. Selected bond length (Å) and angles
(°): Ni(1)–N(1), 2.008(8); Ni(1)–S(1), 2.282(3); Ni(1)–Br(1), 2.337(2); Ni(1)–Br(2),
2.342(3); S(1)–C(6) 1.690(9); N(1)–Ni(1)–S(1), 94.0(2); Br(1)–Ni(1)–Br(2),
133.80(8); N(1)–Ni(1)–Br(1), 107.0(2); S(1)–Ni(1)–Br(1), 103.51(9); N(1)–Ni(1)–Br(2),
103.1(2); S(1)–Ni(1)–Br(2), 108.47(9); C(5)–N(1)–Ni(1), 122.8(7); C(6)–S(1)–Ni(1),
94.1(4); C(6)–N(2)–C(5), 126.2(8); C(10)–C(9)–N(3), 118.6(9); C(14)–C(9)–N(3),
118.8(10).
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0842, wR2 = 0.2497
R1 = 0.1084, wR2 = 0.2589
1.078
Goodness-of-fit (GOF)
Largest difference peak*(hole) (e Åꢀ3
)
1.786 (ꢀ0.881)
D/r
0.000, 0.000
P
P
P
P
2
2
1=2
R = ||Fo| ꢀ |Fc||/ |Fo|, RW ¼ f ½wðF2o ꢀ Fc2Þ ꢂ=½ wðFo2Þ ꢂg
.
*
Largest peak(hole) in difference Fourier map.

88
Y.-B. Huang et al. / Journal of Organometallic Chemistry 694 (2009) 86–90
molecular weight polyethylene [1]. The nickel complexes 2a and
2b bearing bulkyl N-substituents possess potentially reactive sites
susceptible to ethylene polymerization. However, unfortunately,
after activation with MAO, the bulkier steric hindrance nickel com-
plex 2b with N-2,6-diisopropylphenyl substituent catalyzed ethyl-
ene to a few wax with low activity at atmosphere pressure, even
under 7 bar of ethylene press only obtained a few high molecular
weight PE, while the complex 2a bearing N-tbutyl substituent ob-
tained a few wax under the same condition. The catalyst activity
for ethylene transform to high molecular weight PE was lower than
7
4
3
5
1
that of the pyridylimine nickel complexes [7] and a-diimine nickel
catalysts [1]. The reasons may be that only one bulky arm side
6
2
Chart 1.
(imidazole N-substituent) resulted in the chain propagation was
quite slow than chain transfer which different from the a-diimine
nickel catalysts (two bulky arm sides) [1]. And also the pyridine
ring and the imidazole ring were not positioned in a square, which
caused the introduction of the steric bulk deviates the axial sites,
may be responsible for the low activity for ethylene transform to
high molecular weight PE [2].
glass transition temperature (Tg) of PNB failed, and the DSC studies
did not give an endothermic signal upon heating to the decompo-
sition temperature (above 450 °C).
The complex 2a (3.56 ꢁ 107 gPNBmolꢀ1 Nihꢀ1) bearing N-tbutyl
substituent exhibited higher activity than that of 2b (3.14 ꢁ
107 gPNBmolꢀ1Nihꢀ1) containing N-2,6-diisopropylphenyl substi-
tuent under the same conditions (Entry 1 and 2, Table 2). The rea-
son may be that norbornene is a sterically encumbered monomer,
and it need more sterically open nature [38,48]. Although these Ni
complexes 2a–2b exhibited a little lower activity than the nickel
complexes bearing N-substituents imidazole-2-thione ligands
(1.36 ꢁ 108 gPNBmolꢀ1Nihꢀ1) [38], they are as highly active as
nickel complexes bearing [N,O] and [N,N] ligands [21–22,25–
27,29–32] and show a very higher activity polymerization than
other transition metal catalysts [12–20,23–24,28,33–37]. The
amount of the co-catalyst MAO affects obviously the activity and
molecular weight of the PNB obtained by the complex 2a (Entry
3–5, Table 2). When MAO/Ni = 500, there is almost no polymer.
The catalytic activity sharply increases from 2.12 ꢁ 107 to
3.56 ꢁ 107 gPNBmolꢀ1Nihꢀ1 when MAO/Ni increases from 1000/1
to 2000/1. In contrast, the viscosity-average molecular weight
(Mv) of the polymer decreases from 6.76 ꢁ 105 to 5.91 ꢁ 105
gmolꢀ1 with the increase in the molar ratio of MAO to 2a due to
the chain transfer to MAO [44]. When the amount of the MAO con-
tinues increase, the activity increases a little (Entry 5, Table 2). The
temperature also influences the catalytic activity of 2a and the
molecular weights of the PNB. As shown in Table 2, with the in-
crease the polymerization temperature from 0 °C to 50 °C, the
After activation with MAO, the Ni complexes 2a–2b exhibit high
catalytic activity for norbornene polymerization. The norbornene
polymerization results of the nickel complexes 2a and 2b are sum-
marized in Table 2. The norbornene polymerization was typical
addition-vinyl type through the FT-IR spectra and 1H NMR and
13C NMR spectra of the obtained PNB. In the FT-IR spectra (IR,
KBr, cmꢀ1): 2947, 2869, 1474, 1453, 1375, 1294, 1258, 1222,
1190, 1148, 1107, 1039, 942, 893, 805), there are no absorptions
at 1680–1620 cmꢀ1, especially around 960 and 735 cmꢀ1, assigned
to the trans and cis form of double bonds, respectively, which are
characteristic of the ROMP (ring-opening metathesis polymeriza-
tion) structure of PNB [23]. 1H NMR and 13C NMR spectra
confirmed the above conclusions. 1H NMR spectra (1H NMR: d
0.9–2.7 ppm (m, maxima at 0.96, 1.36, 2.11, 2.50) show signals in
the 0.9–3.0 ppm range, where no resonances are displayed at about
5.1 and 5.3 ppm in the 1H NMR spectrum of the PNB, assigned to
the cis and trans form of the double bonds, which generally indi-
cates the presence of the ROMP structure [23]. The 13C NMR spec-
trum shows the main four broad groups of resonances (13C NMR
(o-dichlorobenzene-d4): d = 28–52 ppm (m, maxima at 48.7, 39.4,
35.6, 31.8)), attributed to carbons 2 and 3, carbons 1 and 4, carbon
7, and carbons 5 and 6, respectively (Chart 1). These data indicate
that the obtained PNB was an addition-type (2,3-linked) product,
which was not 2-exo, 70-syn linked norbornene polymer [42–43].
Their 13C NMR spectra show that the PNB are exo enchained; the
spectra do not exhibit resonances in the 20–24 ppm region [23].
Unfortunately, the broad, unresolved nature of the spectra (PNB
is more stiff with hindered rotation than the ethene-norbornene
copolymer) made it difficult to assign exact stereochemistry to
the enchainment of norbornene in the polymers with absolute cer-
tainty [23–24,44–46]. All of the obtained PNB are soluble in chlo-
robenzene, o-dichlorobenzene and cyclohexane solvents, which
indicate low stereoregularity [47]. Attempted to determine the
activity increase from 0.98 ꢁ 107 to 3.72 ꢁ 107 gPNBmolꢀ1Nihꢀ1
.
However, when the temperature increases to 80 °C, the nickel
complex displayed no activation which may be the complex
decomposes at high temperature [38].
3. Conclusions
In conclusion, the nickel complexes bearing hard–soft nitrogen–
sulfur donor ligands 1-pyridyl-(3-substituedimidazole-2-thione)
Table 2
Results of norbornene polymerizationa initiated by nickel catalyst 2a and 2b.
Entry
Catalyst
MAO/Ni
T (°C)
Yield (g)
Activity (107 gPNBmolꢀ1Nihꢀ1
)
Mv (105 gmolꢀ1
)
1
2
3
4
5
6
7
8
2a
2b
2a
2a
2a
2a
2a
2a
2000
2000
500
1000
3000
2000
2000
2000
27
27
27
27
27
0
1.78
1.57
Trace
1.06
1.81
0.49
1.86
Trace
3.56
3.14
–
2.12
3.62
0.98
3.72
–
5.91
4.82
–
6.76
4.35
6.52
3.17
–
50
80
a
Polymerization conditions: [Ni] = 0.2 lmol, [NB] = 3.76 g; time = 15 min; Vtotal = 15 mL; solvent: chlorobenzene.

Y.-B. Huang et al. / Journal of Organometallic Chemistry 694 (2009) 86–90
89
exhibit high activities for norbornene addition polymerization,
although show poor activity for ethylene polymerization to pro-
duce high molecular weight PE.
2a was obtained by filtration and washed twice with 10 mL of Et2O
and dried in vacuo. (0.35 g, 78% yield), Anal. Calc. for
C12H15N3SNiBr2: C, 31.90; H, 3.35; N, 9.30. Found: C, 31.88; H,
3.34; N, 9.32%. IR (KBr cmꢀ1): 1156 (C@S).
4. Experimental
4.3.2. (1-Pyridyl-((3-(2,6-diisopropylphenylimidazole))-2-thione))
NiBr2 (2b)
4.1. General
The complex 2b was prepared by similar procedures of complex
2a using 1-pyridyl-(3-(2,6-diisopropylphenylimidazole))-2-thione.
(0.42 g, 76% yield), Anal. Calc. For C20H23N3SNiBr2: C, 43.21; H,
4.17; N, 7.56. Found: C, 43.24; H, 4.19; N, 7.54%. IR (KBr cmꢀ1):
1154 (C@S).
All experiments and manipulations were carried out under ar-
gon using standard Schlenk techniques. All solvents were purified
by standard procedures. NB was purchased from Alfa Aesar and
purified by distillation over sodium. Methylaluminoxane (MAO)
was purchased from Aldrich as 10% weight of a toluene solution
and used without further purification. Other chemicals were ana-
lytical grade and used as received. IR spectra were recorded on a
Niclolet AVATAR-360IR spectrometer. Element analyses were per-
formed on an Elementar III vario EI Analyzer. 1H NMR spectra were
obtained using Bruker DMX-400 spectrophotometer in CDCl3,
CD3CN for complexes and o-dichlorobenzene-d4 solution for PNB
using TMS as an internal standard. N-tbutyl-N0-2-pyridylimidazoli-
um bromide and N-2,6-diisopropylphenyl-N0-2-pyridylimidazoli-
um bromide were synthesized according to the public literature
4.4. Ethylene polymerization
The precatalyst was dissolved in toluene and MAO (10 wt% in
toluene) added to the solution. The flamedried Schlenk flask (or
stainless steel polymerization autoclave) was placed in a water
bath and purged with ethylene, and the contents were magneti-
cally stirred and maintained under 1 bar ethylene (or 7 bar ethyl-
ene press) for 1 h. The polymerization was terminated by the
addition of 10% (by mass) acidified ethano1. The solid PE was
recovered by filtration, washed with ethanol and dried under vac-
uum at 70 °C overnight.
[49]. The intrinsic viscosity [g] was measured in chlorobenzene
at 25 °C using an Ubbelohde viscometer. Viscosity average molec-
ular weight (Mv) values of polymer were calculated by the follow-
4.5. Norbornene polymerization
ing equation [50]: ½
g
ꢂ ¼ 5:97 ꢁ 10ꢀ4 M0v:56
.
In a typical procedure for norbornene polymerization, precata-
lyst nickel complex in chlorobenzene was added into a polymeriza-
tion bottle (50 mL) with a stirrer under nitrogen atmosphere. Then
MAO was charged into the polymerization system via syringe. At
last the norbornene in chlorobenzene was added the polymeriza-
tion system the reaction was started. After designated time, the
acidic ethanol (Vethanol:Vconcd.HCl = 10:1) was added to terminated
the reaction. The PNB was isolated by filtration, washed with eth-
anol and dried at 80 °C for 48 h under vacuum. For all polymeriza-
tion procedures, the total reaction volume was 15.0 mL, which can
be achieved by the variation of the amount of chlorobenzene when
necessary. Spectra of the obtained polynorbornenes: IR (KBr pellet,
4.2. Synthesis of ligands (1a–1b)
4.2.1. 1-Pyridyl-(3-tbutylimidazole-2-thione) (1a)
To a solution of N-tbutyl-N0-2-pyridylimidazolium bromide
(2.62 mmol) in THF (50 ml) and potassium tert-butoxide
(3.0 mmol) was added at r.t. The mixture was stirred for 10 min
and then sulphur (3.0 mmol) was added. After 12 h the solution
was filtered and the solvent was removed to give a pure product
1a which was flash chromatography (CH2Cl2). (0.46 g, 75% yield).
Anal. Calc. for C12H15N3S: C, 61.77; H, 6.48; N, 18.01. Found: C,
61.75; H, 6.47; N, 18.04%. 1H NMR (400 MHz, CDCl3, ppm): d 1.87
(s, CH3, 9H), 6.98 (d, J = 2.92, 1H, H4-Im), 7.36 (d, J = 2.92, 1H,
H5-Im), 7.28 (m, 1H, H5-Py), 7.86 (t, 1H, H3-Py), 8.51 (m, 1H,
H4-Py), 8.68 (d, J = 8.32, 1 H, H6-Py). 13C NMR (CDCl3, ppm): 28.2
(CH3), 59.8 (tC), 115.3 (C5-Im), 115.8 (C3-Py), 120.6 (C4-Im),
122.7 (C5-Py), 137.4 (C4-Py), 147.2 (C2-Py), 148.5 (C6-Py), 164.6
(C2-Im). IR (KBr cmꢀ1): 1158 (C@S).
m
(cmꢀ1)): 2947, 2869, 1474, 1453, 1375, 1294, 1258, 1222, 1190,
1148, 1107, 1039, 942, 893, 805. 1H NMR (o-dichlorobenzene-
d4): d = 0.9–2.7 ppm (m, maxima at 0.96, 1.36, 2.11, 2.50). 13C
NMR (o-dichlorobenzene-d4): d = 28–52 ppm (m, maxima at 31.8,
35.6, 39.4, 48.7).
4.6. X-ray crystallography
4.2.2. 1-Pyridyl-(3-(2,6-diisopropylphenylimidazole)-2-thione) (1b)
The ligand 1b was prepared by similar procedures of ligand 1a
using N-2,6-diisopropylphenyl-N0-2-pyridylimidazolium bromide.
(0.65 g, 74% yield). Anal. Calc. for C20H23N3S: C, 71.18; H, 6.87; N,
12.45. Found: C, 71.15; H, 6.89; N, 12.46%. 1H NMR (400 MHz,
CDCl3, ppm): d 1.13 (d, J = 6.88, 6H, CH3), 1.28 (d, J = 6.88, 6H,
CH3), 2.65(m, 2H, CH), 6.77 (d, J = 2.72, 1H, H4-Im), 7.29–7.31 (m,
3H, Ph), 7.47 (t, 1H, H5-Py), 7.85 (d, J = 2.72, 1H, H5-Im), 7.89 (m,
1H, H2-Py), 8.53 (m, 1H, H4-Py), 9.21 (d, J = 8.28, 1H, H6-Py). 13C
NMR (CDCl3, ppm): 23.5 (CH3), 28.8 (CH), 116.5 (C5-Im), 118.2
(C3-Py), 119.2 (C4-Im), 122.5 (C5-Py), 124.4 (C3-Ph), 130.3 (C4-
Ph), 133.3 (C1-Ph), 138.0 (C4-Py), 146.6 (C2-Ph), 148.3 (C2-Py),
150.5 (C6-Py), 164.4 (C2-Im). IR (KBr cmꢀ1): 1178 (C@S).
Diffraction data of complexes 2b were collected at room tem-
perature on a Bruker Smart APEX CCD diffractometer with graph-
ite-monochromated Mo
structure was solved by direct methods and subsequently refined
on F2 by using full-matrix least-squares techniques (SHELXL) [51],
absorption corrections were applied to the data. The non-hydrogen
atoms were refined anisotropically, and hydrogen atoms were lo-
cated at calculated positions.
Ka
radiation (k = 0.71073 Å). The
Supplementary material
CCDC 699351 contains the supplementary crystallographic data
for 2b. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif.
4.3. Synthesis of complexes (2a–2b)
4.3.1. (1-Pyridyl-(3-tbutylimidazole-2-thione))NiBr2 (2a)
Acknowledgments
Ligand 1a (1.0 mmol) was dissolved in CH2Cl2 (10 ml) and
NiBr2(DME) (1.0 mmol) was added the colorless solution. The reac-
tion mixture was stirred at room temperature for 24 h which
resulting in the formation of a green suspension. The green product
Financial support by the National Science Foundation of China
(20531020, 20721063, 20771028), by Shanghai Leading Academic

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