Cobalt complexes bearing pyridine-imino ligands with bulky aryl substituents: Synthesis, characterization, and 1,3-butadiene polymerization behaviors

Article abstract of DOI:10.1016/j.jorganchem.2015.05.004

A series of Co(II) complexes bearing pyridine-imino ligands [2-Ar₁-6-(CMe = NAr₂)C₅H₃N]CoCl₂ (Ar₁ = C₆H₅, Ar₂ = 2,6-i-Pr₂C₆H₃

Full text of DOI:10.1016/j.jorganchem.2015.05.004

Journal of Organometallic Chemistry xxx (2015) 1e8
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Journal of Organometallic Chemistry
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Cobalt complexes bearing pyridine-imino ligands with bulky aryl
substituents: Synthesis, characterization, and 1,3-butadiene
polymerization behaviors
,
, *
Jun Guo a b, Chunyu Zhang a, Jifu Bi a, Hexin Zhang a, Chenxi Bai a, Yanming Hu a
,
Xuequan Zhang a
,
*
a Key Laboratory of Synthetic Rubber, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China
b University of Chinese Academy of Sciences, 100049, PR 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 Co(II) complexes bearing pyridine-imino ligands [2-Ar1-6-(CMe
¼
NAr2)C5H3N]CoCl2
(Ar1 ¼ C6H5, Ar2 ¼ 2,6-i-Pr2C6H3 (3a); Ar1 ¼ 20-C10H7, Ar2 ¼ 2,6-i-Pr2C6H3 (3b); Ar1 ¼ 20-C10H7, Ar2 ¼ C6H5
(3c); Ar1 ¼ 20-C10H7, Ar2 ¼ 4-ClC6H4 (3d); Ar1 ¼ 40-C6H5eC6H4, Ar2 ¼ 2,6-i-Pr2C6H3 (3e); Ar1 ¼ 40-C6H5
eC6H4, Ar2 ¼ C6H5 (3f); Ar1 ¼ 40-C6H5eC6H4, Ar2 ¼ 4-ClC6H4 (3g)) with bulky aryl groups were syn-
thesized and characterized. Determined by single-crystal X-ray diffraction, 3a, 3b, and 3e adopted dis-
torted tetrahedron configurations. Activated by ethylaluminum sesquichloride (EASC), these complexes
exhibited high cis-1,4 selectivity for 1,3-butadiene polymerization. The steric and electronic properties of
substituent of the ligand remarkably influenced catalytic activity. The effects of polymerization param-
eters such as [Al]/[Co] ratio and temperature on the polymerization were also investigated in details.
© 2015 Elsevier B.V. All rights reserved.
Received 31 December 2014
Received in revised form
15 April 2015
Accepted 2 May 2015
Available online xxx
Keywords:
Pyridine-imino ligand
Cobalt complex
1,3-Butadiene polymerization
Introduction
Since pioneering studies by Brookhart and Gibson, various
imino-based ligands have been developed as supporting architec-
Polydienes are one of the most important synthetic polymers
for their wide application in tires and many other elastic materials
and produced in industrial capacity of billions of tons per year.
The stereoselective polymerization of 1,3-dienes, especially 1,3-
butadiene, has attracted both academic and industrial attention
[1e4]. Various catalytic systems based on transition metal such as
Ti [5e8], Fe [9e12], Ni [13e16], Co [14,17e21], etc., have been
developed for 1,3-butadiene polymerization. Among them,
cobalt-based catalysts are the most interest-grabbing for their
versatile nature. For instance, CoCl2 and Co(acac)2 produced high
cis-1,4 polybutadiene upon activation with methylaluminoxane
(MAO) [22e24]. CoCl2(PRPh2)2 activated by MAO was effective
catalyst to afford 1,2-polybutadiene [25,26]. In addition, (2-
PhC6H4O)3Al$Co(OAc)2/AlR3, Co(2-ethylhexanoate)2/AlEt(OPh)2/
AlEt3, and cobalt carboxylate$(dialkylphosphite)/AlR3/HOPh were
highly active for trans-1,4 selective polymerization of 1,3-
butadiene [27].
tures for olefin polymerization catalysts [28,29]. An intriguing
feature of bis(imino)pyridine-based precursors is facile tuning their
catalysis behaviors by modifying ancillary ligands [30]. Numerous
studies concerning the electronic and steric effects of imine ligand
have been published [30e34]. On the other hand, significant ad-
vances in development of highly efficient olefin polymerization
catalysts further spurred the exploitation of novel catalysts for 1,3-
butadiene polymerization [3,4]. For cobalt-based catalytic system,
(salen)cobalt(II)/MAO and bis(salicylaldiminate) cobalt(II)/EASC
were reported to be highly cis-1,4 selective in 1,3-butadiene poly-
merization [17,18]; bis(benzimidazolyl)-amine cobalt(II) dichloride/
MAO was an efficient system to afford polybutadiene with high cis-
1,4 content [35]; Co(II) complexes supported by 2-arylimino-6-
(alcohol) pyridine, 2-arylamino-6-(alcohol) pyridine, and 3-
aryliminomethyl-2-hydroxybenzaldehyde activated by MAO or
EASC exhibited both high activity and cis-1,4 stereospecificity for
1,3-butadiene polymerization [36,37]. We have recently reported
that cobalt complexes bearing bis(N-arylcarboximidoylchloride)
pyridine
and
2-(N-arylcarboximidoylchloride)quinoline
in
conjunction with MAO or EASC were effective systems for cis-1,4
polymerization of 1,3-butadiene [16,38], and cobalt complexes
* Corresponding authors.
E-mail addresses: ymhu@ciac.ac.cn (Y. Hu), xqzhang@ciac.ac.cn (X. Zhang).
http://dx.doi.org/10.1016/j.jorganchem.2015.05.004
0022-328X/© 2015 Elsevier B.V. All rights reserved.
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J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
bearing 2-pyrazolyl substituted 1,10-phenanthroline in combina-
tion with MAO gave high cis-1,4 polybutadienes in high yields [39].
In general, late-transition metal-based catalysts suffer from
deactivation at elevated temperature. Previous studies demon-
strated that incorporation of bulky substituent into the ligand
framework could shield the active center and thereby, improving its
thermal stability [16,39e41]. Li and coworkers reported a highly
active and long-life macrocycle trinuclear 2,6-bis(imino)pyridyl
Fe(II) precatalyst for ethylene polymerization [42]; Sun and co-
workers found that by incorporation bulky aniline into the ligand,
bis(imino)pyridine Fe(II) complex exhibited high activity (ca.
2.2 ꢀ 107 g PE molꢁ1 (Fe) hꢁ1) for ethylene polymerization at 80 ꢂC
Crystals of complexes 3a, 3b, and 3g suitable for X-ray diffrac-
tion were obtained by slow diffusion of pentane into their
concentrated CH2Cl2 solutions. Data collection, crystal and refine-
ment parameters are collected in Table 1. The molecular structures
of 3a, 3b, and 3g are shown in Figs. 1e3, respectively.
These three complexes have distorted tetrahedron geometry.
The distortion from a standard tetrahedron is remarkable in these
complexes, as exhibited by the bite angle (N1eCo1eN2), which is
much smaller than the regular tetrahedral angle. Regardless of
the substituent on the pyridine-imino ligand, the planes of the
imino-aryl rings are oriented essentially orthogonal to the plane
of the pyridine rings (88.11ꢂ for 3a, 84.95 for 3e, and 78.11ꢂ for
3b). The C]N bonds in these three complexes have a typical
double-bond character with bond lengths ranging from 1.280 (4)
to 1.285 (3) Å.
Because these three cobalt complexes had very similar geome-
tries and structural parameters, only complex 3e is described in
detail, and the selected bond lengths and angles of complexes 3a,
3b, and 3e are collected in Table 2. In the structure of complex 3e,
the dihedral angle formed by the planes Cl1Co1Cl2 and N1Co1N2 is
79.45ꢂ. The CoeN1 (Pyridine) distance is slightly longer than that of
CoeN2 (iminoaryl) (2.081(3) Å v.s. 2.042(3) Å). Compared with the
well-known bisimino-pyridyl Co complex, in which the CoeN
(imino) bond length is 2.211(3) Å, 3e has a shorter CoeN (imino)
bond. The N1eCoeCl1 angle are remarkably large, which reflected
the presence of a sterically demanding substituent at 6-position of
the pyridine ring. The atoms N1, C15, C13, and N1 are almost
coplanar, with the largest deviation of N1 at 0.183 Å, and the de-
viation of the cobalt atom from the plane is 0.252 Å.
[41]; Guan and coworkers reported that a-diimine Pd(II) and Ni(II)
complexes containing cyclophane groups produced high molecular
weight polyethylenes even at high polymerization temperatures
[43,44]. Therefore, it is considered that introduction of bulky rigid
groups into the ligand is of interest for the development of highly
thermal stable transition metal-based catalytic systems. Herein, we
reported the synthesis of cobalt complexes bearing pyridine-imino
ligands with bulky aryl groups and their 1,3-butadiene polymeri-
zation behaviors along with their counterpart without bulky sub-
stituent for comparison. Furthermore, the effects of ligand
environment and reaction conditions on the polymerization were
examined.
Results and discussion
Synthesis and characterization of complexes
Complexes 3aeh were synthesized by the reaction of CoCl2 with
1.0 equivalent of the corresponding ligand at room temperature
according to Scheme 1. These complexes were identified by FT-IR
and elemental analysis as well as single crystal X-ray analysis. In
the IR spectra, the stretching bands of C]N (arylimino) of free li-
gands appears at 1636e1649 cmꢁ1, which shift toward lower fre-
quencies by 6e25 cmꢁ1 in the complexes, indicating that the
nitrogen atom of imine coordinates to Co2þ ion.
1,3-Butadiene polymerization
Effect of ligand environment on 1,3-butadiene polymerization
The complexes activated by EASC for the polymerization of 1,3-
butadiene in toluene at 20 ꢂC were examined, and the results are
summarized in Table 3. The bulkiness of the substituent on ortho-
position of pyridine has a significant influence on catalytic activity.
Scheme 1. Synthesis of complexes 3aeh.
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J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
3
Table 1
Crystal data and data collection parameters for the cobalt complexes.
Complex
3a
3b
3e
Formula
C25H28Cl2CoN2
486.32
0.71073
Orthorhombic
Pbca
15.7812 (11)
16.2481 (11)
18.2296 (12)
90
C29H30Cl2CoN2
536.38
0.71073
Triclinic
P1
8.547 (2)
10.556 (3)
14.924 (4)
89.058 (4)
74.246 (4)
85.987 (4)
1292.8 (6)
2
C31H32Cl2CoN2
562.42
0.71073
Triclinic
P1
8.5186 (14)
10.3687 (17)
17.022 (3)
75.155 (3)
83.627 (3)
74.173 (3)
1396.8 (4)
2
Molecular weight
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
90
90
V (Å3)
4674.3 (5)
8
1.382
0.98
2024
Z
Dcalcd (Mg/m3)
1.378
0.89
558
1.337
0.83
586
Absorption coefficient (mmꢁ1
F (000)
)
Crystal size (mm)
q
No. of reflns collected
No. of indep. reflns
0.21 ꢀ 0.19 ꢀ 0.11
2.1e25.0
25,293
0.27 ꢀ 0.17 ꢀ 0.11
1.9e25.3
8925
0.21 ꢀ 0.11 ꢀ 0.09
2.1e26.1
7422
range (ꢂ)
4131
4538
5318
No. of data/restraints/params
4131/0/276
0.99
4538/0/307
1.04
5318/0/330
1.05
Goodness-of-fit on F2
ꢀ
R1 (1 > 2o (1))
0.033
0.046
0.061
wR2
0.088
0.124
0.168
Fig. 1. ORTEP drawing of complex 3a with thermal ellipsoids at the 30% probability level. Hydrogen atoms have been omitted for clarity.
The polymer yield decreased in the cases of Ar-substituted com-
plexes in the order of 3a > 3e > 3b. These results might be due to
steric reason as revealed by the dihedral angle between the planes
of the iminoaryl and pyridine rings, that is, a more open coordi-
nation sphere around the cobalt center allows more accessible to
the incoming monomer and therefore, resulting in higher activity
[38,45]. The steric bulkiness offered by ortho imino-aryl sub-
stituents also affected catalytic activity significantly; 2,6-isopropyl
substituted complexes 3b and 3e produced polybutadienes in
lower yields than their non-substituted analogs 3c and 3f. Notably,
introduction of electron-withdrawing groups enhanced catalytic
activity of the complex; chloro-substituted complexes 3d and 3g
afforded polymers in the yields of 74.4% and 84.4%, respectively,
which were higher than those of their chloro-free counterparts 3c
and 3f. Similar result was observed in our previous study, the high
activity might be ascribed to the enhanced electropositivity of the
central metal, which facilitates the coordination of monomer
[16,38,45].
The produced polymers possessed high molecular weights
(Mn ¼ 26.0e40.8 ꢀ 104) and relatively narrow molecular weight
distributions (Mw/Mn ~ 3.0). All the complexes exhibited high cis-
1,4 selectivity, and the cis-1,4 contents of the resultant polymers
ranging from 97.0% to 98.7%. As 3g gave polybutadiene with high
molecular weight and high cis-1,4 content in a high yield, it was
selected for further experiment.
Effects of cocatalyst on 1,3-butadiene polymerization
It has been reported that the catalytic performance of Co-based
catalysts was affected by cocatalyst. In this study, the effect of Al
compound on the polymerization was investigated (Table 4). EASC-
based catalyst gave the polymer with the highest molecular weight
(Mn ¼ 26.0 ꢀ 104) in the highest yield. Although MAO-based
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J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
Fig. 2. ORTEP drawing of complex 3b with thermal ellipsoids at the 30% probability level. Hydrogen atoms have been omitted for clarity.
Fig. 3. ORTEP drawing of complex 3e with thermal ellipsoids at the 30% probability level. Hydrogen atoms have been omitted for clarity.
Table 2
Table 3
Selected bond length (Å) and angles (ꢂ) for complexes 3a, 3b, and 3e.
Polymerization of 1,3-butadiene with 3aeg activated by EASC.a
Mn ꢀ 10ꢁ4c
Mw/Mn
Microstructureb (%)
c
Complex
3a
3b
3e
Entry
Cat.
Yield (%)
Bond lengths (Å)
Co(1)eN(1)
Co(1)eN(2)
Co(1)eCl(1)
Co(1)eCl(2)
Cis-1,4
Trans-1,4
1,2
2.0899 (16)
2.0495 (17)
2.2235 (7)
2.2151 (7)
2.062 (3)
2.081 (3)
1
2
3
4
5
6
7
3a
3b
3c
3d
3e
3f
54.5
11.4
60.5
74.4
42.9
58.1
84.4
27.5
40.8
32.5
33.7
37.8
31.3
26.0
3.4
2.4
2.9
3.3
2.8
2.9
3.1
97.2
98.5
97.8
97.4
98.7
97.4
97.0
1.7
0.7
1.1
1.6
0.8
1.6
2.0
1.1
0.8
1.1
1.0
0.5
1.0
1.0
2.068 (2)
2.2272 (10)
2.2175 (10)
2.042 (3)
2.2200 (13)
2.2279 (14)
Bond angles (ꢂ)
N(1)eCo(1)eN(2)
Cl(1)eCo(1)eCl(2)
N(1)eCo(1)eCl(1)
N(1)eCo(1)eCl(2)
N(2)eCo(1)eCl(1)
N(2)eCo(1)eCl(2)
81.02 (7)
114.06 (3)
105.92 (5)
129.34 (5)
115.08 (5)
107.19 (5)
80.37 (10)
111.96 (4)
106.29 (7)
127.34 (8)
121.58 (7)
107.14 (7)
80.74 (13)
111.12 (5)
127.35 (11)
107.49 (10)
110.60 (11)
116.88 (11)
3g
a
Polymerization in toluene at 20 ꢂC for 60 min, precatalyst: 18.5
m
mol, [BD]/
[Co] ¼ 2000, [Al]/[Co] ¼ 60.
b
Determined by 1H NMR and FT-IR.
Determined by GPC against polystyrene standards.
c
catalyst also afforded polymer in a high yield by prolonging the
polymerization time to 4 h, the molecular weight of the resultant
polymer was much lower than that with EASC-based system. On
the other hand, AlEt3 and Al(i-Bu)3-based systems only gave trace
polymers. Similar results were observed in the cases of other Co-
based catalysts [21,38].
Effects of [Al]/[Co] ratio and polymerization temperature on 1,3-
butadiene polymerization
3g/EASC was examined for the polymerization of 1,3-butadiene
by changing the [Al]/[Co] ratio and polymerization temperature
(Table 5). The polymerization remarkably accelerated with the
increase of polymerization temperature. The polymer yield was
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J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
5
Table 4
Experimental part
Effect of cocatalyst on 1,3-butadiene polymerization with 3g.a
Entry Cocat. Yield (%) Mn ꢀ 10ꢁ4c Mw/Mn
Microstructureb (%)
Cis-1,4 Trans-1,4 1,2
c
General consideration
All the manipulations were performed under an atmosphere of
dry argon or nitrogen by using standard Schlenk techniques or in a
glove box. Toluene, tetrahydrofuran (THF), and diethyl ether were
freshly obtained by distillation under nitrogen from sodium-
benzophenone ketyl. CH2Cl2 and pentane were refluxed over
CaH2 and distilled prior to use. 1,3-Butadiene was supplied by
Jinzhou Petrochemical Corporation and purified by passing through
four columns packed with molecule sieve 4 Å and KOH prior to use.
MAO (10 wt% solution in toluene) was purchased from AkzoNoble
and used as received. Ethylaluminum sesquichloride (EASC) was
purchased from SigmaeAldrich Co. and diluted into 1.0 mol/L so-
lution by toluene. Other chemicals were commercially available
and used as received. Compounds 1e4 were synthesized according
to the literatures [47e49].
8
9
10
11
EASC
84.4
26.0
7.4
e
3.1
3.0
e
97.0
95.8
e
2.0
2.4
e
1.0
1.8
e
MAOd 81.4
TEA
TIBA
Trace
Trace
e
e
e
e
e
a
Polymerization in toluene for 60 min, precatalyst: 18.5
m
mol, [BD]/[Co] ¼ 2000,
[Al]/[Co] ¼ 60.
b
c
Determined by 1H NMR and FT-IR.
Determined by GPC against polystyrene standards.
t ¼ 4 h.
d
Table 5
Effects of [Al]/[Co] ratio and temperature on 1,3-butadiene polymerization with 3g/
EASC and 3h/EASC catalyst.a
Entry [Al]/[Co] Temp. Yield (%) Mn ꢀ 10ꢁ4c Mw/Mn Microstructureb (%)
c
(ꢂC)
The molecular weights (Mn) and molecular weight distributions
(Mw/Mn) of polymers were measured at 30 ꢂC by gel permeation
chromatography (GPC) equipped with a Waters 515 HPLC pump,
four columns (HMW 7 THF, HMW 6E THF ꢀ 2, HMW 2 THF), and a
Waters 2414 refractive index detector. THF was used as eluent at a
flow rate of 1.0 mL/min. The molecular weight of polymer was
determined using the polystyrene calibration. 1H NMR (400 MHz)
and 13C NMR (100 MHz) were recorded on a Varian Unity spec-
trometer in CDCl3 at room temperature. IR spectra were recorded
on a BRUKE Vertex-70 FIR spectrophotometer. Elemental analysis
was performed on an elemental Vario EL spectrometer. The mi-
Cis-1,4 Trans-1,4 1,2
12
13
14
15
16
17
18
19
20
21
60
60
60
60
60
60
60
20
100
150
0
20
50
80
20
50
80
20
20
20
Trace
84.4 26.0
e
e
e
e
e
3.1
97.0
90.4
75.5
92.4
84.7
79.4
95.5
96.2
96.2
2.0
1.0
2.9
4.3
2.3
4.9
6.5
1.1
1.0
1.0
96.5
>99%
98.2
79.6
61.2
37.8 35.8
97.7 23.1
98.0 21.1
7.5
3.0
5.2
2.1
1.1
8.4
11.5
7.2
8.8
9.4
2.8
4.7
4.5
6.7
20.2
5.3
10.4
14.1
3.4
2.8
2.8
a
Polymerization in toluene for 60 min, precatalyst: 18.5
Determined by 1H NMR and FT-IR.
Determined by GPC against polystyrene standards.
m
mol, [BD]/[Co] ¼ 2000.
crostructures of polymers were determined by IR, 1H NMR, and 13
NMR spectra [50,51].
C
b
c
X-ray structure determinations
37.8% at 20 ꢂC, whereas the yield reached 99% at 80 ꢂC, indicating
the high thermal stability of the generated active species. This
result is in contrast to those with other late-transition metal-based
catalysts, which suffer from deactivation at high temperatures. For
instance, in the cases of 2,6-bis(benzimidazol-2-yl)-pyridine Co(II)
dichloride and 2-[1-(2,6-diisopropylphenylimino)ethyl]-6-(pyr-
azol-1-yl)-pyridine cobalt dichloride, the polymer yield decreased
from 80.1% at 50 ꢂC to 47.4% at 90 ꢂC and from 72% at 25 ꢂC to 11% at
80 ꢂC, respectively [19,46]. The high thermal stability of the pre-
sent catalytic system might be due to the presence of bulky aryl
substituent [12,16,39]. On the other hand, the polymer yield
increased with increasing [Al]/[Co] ratio from 20 to 100, and then
almost practically leveled off to 98%. 3h/EASC was also investi-
gated for 1,3-butadiene polymerization under the same condi-
tions. In contrast, although 3h afforded polymer in a high yield at
20 ꢂC, while the polymer yield decreased dramatically as the
polymerization temperature increased. For instance, the yield was
61.2% at 80 ꢂC which is much lower than that obtained with
3g/EASC.
Crystals for X-ray analysis were obtained as described in the
experimental section. Data collections were performed at ꢁ88.5 ꢂC
on a Bruker SMART APEX diffractometer with a CCD area detector,
using graphite monochromated Mo K radiation (
l
¼ 0.71073 Å). The
determination of crystal class and unit cell parameters was carried
out by the SMART program package. The raw frame data were
processed using SAINT and SADABS to yield the reflection data file.
The structures were solved using SHELXTL program. Refinement
was performed on F2 anisotropically for all non-hydrogen atoms by
the full-matrix least-squares method. The hydrogen atoms were
placed at the calculated positions and were included in the struc-
ture calculation without further refinement of the parameters.
Synthesis of the ligands
(2,6-Diisopropyl-phenyl)-[1-(6-phen-1-yl-pyridin-2-yl)-
ethylidene]-amine (2a)
To a solution of 6-phenyl-2-acetyl pyridine (0.60 g, 3.04 mmol)
in ethanol (10 mL), 2,6-diisopropylaniline (3.65 mmol, 0.77 mL) and
two drops of formic acid were added. After the reaction mixture
was refluxed for 24 h, the solvent was removed to gave a brown
solid, which was crystallized from ethanol to give a yellow solid,
yield 72.4%. 1H NMR (CDCl3, ppm): 8.33 (d, J ¼ 7.0 Hz, 1H), 8.13 (d,
J ¼ 7.2 Hz, 2H), 7.93e7.83 (m, 2H), 7.51 (t, J ¼ 7.4 Hz, 2H), 7.44 (t,
J ¼ 7.3 Hz, 1H), 7.18 (d, J ¼ 7.1 Hz, 2H), 7.15e7.08 (m, 1H), 2.86e2.72
(m, 2H), 2.33 (s, 3H), 1.16 (d, J ¼ 6.8 Hz, 12H). 13C NMR (CDCl3, ppm):
167.59, 156.17, 146.80, 139.31, 137.42, 136.05, 129.32, 128.99, 127.08,
123.74, 123.20, 121.33, 119.75, 28.48, 23.44, 23.12, 17.49. FT-IR (KBr,
cmꢁ1): 1654, 1576, 1449, 1361, 1314, 1240, 1118, 822, 792, 679, 625.
Anal. Calc. for C25H28N2: C, 84.23; H, 7.92; N, 7.86. Found: C, 84.36;
H, 8.02; N, 7.68.
The molecular weight of the resultant polymer tended to
decrease and the molecular weight distribution became broader
with increasing temperature and [Al]/[Co] ratio, which might be
due to the facilitated chain transfer reaction at high temperatures
and EASC levels. Regardless of the [Al]/[Co] ratio, the stereoreg-
ularity of the polymer was about same to one another, the cis-1,4
content stayed around 96%. On the other hand, the cis-1,4 content
of the polymer decreased with increasing polymerization tem-
perature. This tendency might be due to the isomerization of anti
and syn
h
3-butenyl forms of the propagating end, the later is
thermodynamically more stable and gives trans-1,4 structure
[1,2].
Please cite this article in press as: J. Guo, et al., Journal of Organometallic Chemistry (2015), http://dx.doi.org/10.1016/j.jorganchem.2015.05.004

6
J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
(2,6-Diisopropyl-phenyl)-[1-(6-naphthalen-2-yl-pyridin-2-yl)-
ethylidene]-amine (2b)
(4-Chloro-phenyl)-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-
ethylidene]-amine (2g)
This compound was prepared by the same method as for 2a.
Yellow powder, yield 87.4%. 1H NMR (CDCl3, ppm): 8.57 (s, 1H), 8.33
(dd, J ¼ 17.6, 8.0 Hz, 2H), 7.99 (dd, J ¼ 14.7, 8.0 Hz, 3H), 7.94e7.86 (m,
2H), 7.53 (s, 2H), 7.19 (d, J ¼ 7.4 Hz, 2H), 7.15e7.08 (m, 1H),
2.90e2.69 (m, 2H), 2.38 (s, 3H), 1.18 (s, 12H). 13C NMR (CDCl3, ppm):
167.57, 156.40, 156.07, 146.81, 137.46, 136.65, 136.05, 133.98, 133.73,
128.93,128.69,127.93,126.79,126.54,126.44,124.80,123.75,123.21,
121.62, 119.80, 28.50, 23.45, 23.14, 17.56. FT-IR (KBr, cmꢁ1): 1649,
1567, 1448, 1358, 1318, 1269, 1187, 1117, 1056, 821, 805, 780, 748,
739. Anal. Calc. for C29H30N2: C, 85.67; H, 7.44; N, 6.89. Found: C,
85.77; H, 7.59; N, 7.03.
This compound was prepared by the same method as for 2a.
Yellow powder, 44.3%. 1H NMR (CDCl3, ppm): 8.20 (d, J ¼ 7.7 Hz,
3H), 7.87 (d, J ¼ 6.2 Hz, 2H), 7.74 (d, J ¼ 8.0 Hz, 2H), 7.67 (d,
J ¼ 7.4 Hz, 2H), 7.48 (t, J ¼ 7.4 Hz, 2H), 7.39 (d, J ¼ 7.1 Hz, 1H), 7.35 (d,
J ¼ 8.3 Hz, 2H), 6.80 (d, J ¼ 8.2 Hz, 2H), 2.48 (s, 3H). 13C NMR (CDCl3,
ppm): 168.80, 156.44, 155.72, 150.09, 142.15, 140.77, 138.05, 137.44,
129.30, 129.07, 127.79, 127.71, 127.44, 127.30, 121.39, 120.95, 119.87,
16.87. FT-IR (KBr, cmꢁ1): 1636, 1567, 1483, 1446, 1359, 1322, 1215,
1159, 1007, 842, 810, 762, 723, 692. Anal. Calc. for C25H19ClN2: C,
78.42; H, 5.00; N, 7.32. Found: C, 78.34; H, 5.09; N, 7.50.
Phenyl-(pyridin-2-yl)-ethylidene]-amine (2h)
Phenyl-[1-(6-naphthalen-2-yl-pyridin-2-yl)-ethylidene]-amine (2c)
This compound was prepared by the same method as for 2a.
Yellow powder, yield 69.0%. 1H NMR (CDCl3, ppm): 8.56 (s, 1H), 8.26
(dd, J ¼ 22.2, 7.7 Hz, 2H), 7.97 (t, J ¼ 6.8 Hz, 3H), 7.89 (d, J ¼ 7.7 Hz,
2H), 7.53 (s, 2H), 7.39 (t, J ¼ 7.6 Hz, 2H), 7.13 (t, J ¼ 7.4 Hz, 1H), 6.87
(d, J ¼ 7.4 Hz, 2H), 2.51 (s, 3H). 13C NMR (CDCl3, ppm): 168.04,
156.79, 155.93, 151.64, 137.40, 136.60, 133.95, 133.69, 129.21, 128.91,
128.65, 127.90, 126.77, 126.52, 126.41, 124.76, 123.75, 121.58, 119.91,
119.49, 16.60. FT-IR (KBr, cmꢁ1): 1641, 1576, 1447, 1359, 1316, 1220,
1111, 809, 755, 735, 702. Anal. Calc. for C23H18N2: C, 85.68; H, 5.63;
N, 8.69. Found: C, 85.81; H, 5.69; N, 8.54.
This compound was prepared by the same method as for 2a.
Yellow powder, 65.7%. 1H NMR (CDCl3, ppm): 8.66 (d, J ¼ 4.6 Hz,
1H), 8.27 (d, J ¼ 8.0 Hz, 1H), 7.77 (td, J ¼ 7.8, 1.6 Hz, 1H), 7.40e7.33
(m, 3H), 7.11 (t, J ¼ 7.4 Hz, 1H), 6.83 (d, J ¼ 7.4 Hz, 2H), 2.35 (s, 3H).
13C NMR (CDCl3, ppm): 167.40, 156.88, 151.43, 148.66, 136.50,
129.12, 127.19, 124.89, 123.71, 121.53, 119.36, 16.49. FT-IR (KBr,
cmꢁ1): 1639, 1597, 1581, 1561, 1486, 1461, 1433, 1359, 1213, 1105,
903, 781, 740, 701. Anal. Calc. for C13H12N2: C, 79.56; H, 6.16; N,
14.27. Found: C, 79.69; H, 6.11; N, 14.37.
Synthesis of the complexes
(4-Chloro-phenyl)-[1-(6-naphthalen-2-yl-pyridin-2-yl)-
ethylidene]-amine (2d)
The general procedure for the synthesis of complexes is
described as follows: To the suspension of anhydrous CoCl2 in THF
(4 mL), 1.0 equivalent of ligand was added. The solution turned
green immediately, and then the reaction mixture was stirred at
room temperature for 6 h. After filtration, the precipitate was
washed with dry diethyl ether and dried under vacuum at 40 ꢂC for
24 h to give the desire product.
This compound was prepared by the same method as for 2a.
Yellow powder, yield 31.5%. 1H NMR (CDCl3, ppm): 8.56 (s, 1H), 8.28
(d, J ¼ 8.6 Hz,1H), 8.20 (d, J ¼ 7.7 Hz,1H), 7.98 (t, J ¼ 9.1 Hz, 3H), 7.90
(t, J ¼ 7.4 Hz, 2H), 7.53 (d, J ¼ 9.0 Hz, 2H), 7.36 (d, J ¼ 8.5 Hz, 2H),
6.81 (d, J ¼ 8.4 Hz, 2H), 2.51 (s, 3H). 13C NMR (CDCl3, ppm): 168.83,
156.51, 156.06, 150.11, 137.48, 136.52, 133.99, 133.70, 129.31, 129.10,
128.92, 128.70, 127.93, 126.84, 126.58, 126.46, 124.73, 121.77, 120.96,
119.92, 16.70. FT-IR (KBr, cmꢁ1): 1639, 1580, 1563, 1475, 1446, 1353,
1086, 1051, 857, 803, 734. Anal. Calc. for C23H17ClN2: C, 77.41; H,
4.80; N, 7.85. Found: C, 77.63; H, 4.99; N, 8.06.
(2,6-Diisopropyl-phenyl)-[1-(6-phen-1-yl-pyridin-2-yl)-
ethylidene]-amine cobalt(II) dichloride (3a)
Green powder, yield 80.5%. FT-IR (KBr, cmꢁ1): 1619, 1594, 1454,
1369, 1322, 1255, 1197, 814, 766, 701. Anal. Calc. for C25H28Cl2CoN2:
C, 61.74; H, 5.80; N, 5.76. Found: C, 61.97; H, 5.95; N, 5.63.
(2,6-Diisopropyl-phenyl)-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-
ethylidene]-amine (2e)
(2,6-Diisopropyl-phenyl)-[1-(6-naphthalen-2-yl-pyridin-2-yl)-
ethylidene]-amine cobalt(II) dichloride (3b)
This compound was prepared by the same method as for 2a.
Yellow powder, yield 79.0%. 1H NMR (CDCl3, ppm): 8.37e8.28
(m, 1H), 8.21 (d, J ¼ 8.2 Hz, 2H), 7.89 (d, J ¼ 3.7 Hz, 2H), 7.74
(d, J ¼ 8.2 Hz, 2H), 7.67 (d, J ¼ 7.5 Hz, 2H), 7.48 (t, J ¼ 7.5 Hz, 2H), 7.38
(t, J ¼ 7.3 Hz, 1H), 7.18 (d, J ¼ 7.4 Hz, 2H), 7.15e7.06 (m, 1H),
2.87e2.73 (m, 2H), 2.34 (s, 3H), 1.17 (d, J ¼ 6.8 Hz, 12H). 13C NMR
(CDCl3, ppm): 167.56, 156.39, 155.78, 146.81, 142.10, 140.83, 138.23,
137.44, 136.05, 129.07, 127.72, 127.49, 127.31, 123.74, 123.21, 121.25,
119.76, 28.49, 23.45, 23.13, 17.52. FT-IR (KBr, cmꢁ1): 1647, 1571,
1448, 1362, 1314, 1105, 855, 812, 764, 688. Anal. Calc. for C31H32N2:
C, 86.07; H, 7.46; N, 6.48. Found: C, 86.01; H, 7.67; N, 6.37.
Green powder, yield 77.8%. FT-IR (KBr, cmꢁ1): 1632, 1617, 1587,
1478, 1451, 1440, 1369, 1318, 1256, 1194, 1012, 815, 793, 757, 738.
Anal. Calc. for C29H30Cl2CoN2: C, 64.93; H, 5.64; N, 5.22. Found: C,
64.72; H, 5.71; N, 5.08.
Phenyl-[1-(6-naphthalen-2-yl-pyridin-2-yl)-ethylidene]-amine
cobalt(II) dichloride (3c)
Green powder, yield 79.3%. FT-IR (KBr, cmꢁ1): 1627, 1590, 1483,
1454, 1363, 1256, 1063, 1012, 914, 812, 759, 695. Anal. Calc. for
C23H18Cl2CoN2: C, 61.08; H, 4.01; N, 6.19. Found: C, 61.17; H, 3.96; N,
6.10.
Phenyl-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-ethylidene]-amine
(2f)
(4-Chloro-phenyl)-[1-(6-naphthalen-2-yl-pyridin-2-yl)-
ethylidene]-amine cobalt(II) dichloride (3d)
This compound was prepared by the same method as for 2a.
Yellow powder, yield 76.1%. 1H NMR (CDCl3, ppm): 8.20 (d, J ¼ 8.4
Hz, 3H), 7.91e7.83 (m, 2H), 7.73 (d, J ¼ 8.3 Hz, 2H), 7.67 (d, J ¼ 7.4 Hz,
2H), 7.47 (t, J ¼ 7.6 Hz, 2H), 7.38 (t, J ¼ 7.7 Hz, 3H), 7.12 (t, J ¼ 7.4 Hz,
1H), 6.86 (d, J ¼ 7.5 Hz, 2H), 2.48 (s, 3H). 13C NMR (CDCl3, ppm):
167.96, 156.87, 155.71, 151.74, 142.14, 140.89, 138.26, 137.35, 129.21,
129.06, 127.70, 127.48, 127.32, 123.75, 121.17, 119.91, 119.51, 16.50.
FT-IR (KBr, cmꢁ1): 1640, 1587, 1568, 1445, 1361, 1318, 1220, 1155,
896, 813, 764, 699. Anal. Calc. for C25H20N2: C, 86.17; H, 5.79; N,
8.04. Found: C, 86.30; H, 5.90; N, 8.17.
Green powder, yield 85.9%. FT-IR (KBr, cmꢁ1): 1628, 1599, 1564,
1485, 1445, 1258, 1090, 1011, 865, 804. Anal. Calc. for
C23H17Cl3CoN2: C, 56.76; H, 3.52; N, 5.76. Found: C, 56.91; H, 3.64;
N, 5.92.
(2,6-Diisopropyl-phenyl)-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-
ethylidene]-amine cobalt(II) dichloride (3e)
Green powder, yield 81.1%. FT-IR (KBr, cmꢁ1): 1626, 1609, 1457,
1385, 1371, 1254, 1199, 1004, 820, 798, 767, 692. Anal. Calc. for
Please cite this article in press as: J. Guo, et al., Journal of Organometallic Chemistry (2015), http://dx.doi.org/10.1016/j.jorganchem.2015.05.004

J. Guo et al. / Journal of Organometallic Chemistry xxx (2015) 1e8
7
C31H32Cl2CoN2: C, 66.20; H, 5.73; N, 4.98. Found: C, 66.32; H, 5.79;
Appendix A. Supplementary material
N, 4.77.
CCDC 1041157e1041159 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Phenyl-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-ethylidene]-amine
cobalt(II) dichloride (3f)
Green powder, yield 85.7%. FT-IR (KBr, cmꢁ1): 1628, 1593, 1491,
1458, 1255, 1180, 857, 815, 770, 694. Anal. Calc. for C25H20Cl2CoN2:
C, 62.78; H, 4.21; N, 5.86. Found: C, 62.49; H, 4.11; N, 6.07.
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(4-Chloro-phenyl)-[1-(6-([1,10-biphenyl]-4-yl)pyridin-2-yl)-
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The authors appreciate financial support from National
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