Pyridine-oxazoline and quinoline-oxazoline ligated cobalt complexes: Synthesis, characterization, and 1,3-butadiene polymerization behaviors

Article abstract of DOI:10.1016/j.ica.2015.07.013

A series of cobalt complexes supported by pyridine-oxazoline (Pyox) and quinoline-oxazoline (Quox) were synthesized. Determined by single crystal X-ray crystallography, complexes 6a and 7c adopted distorted octahedron and trigonal bipyramid geometries, re

Full text of DOI:10.1016/j.ica.2015.07.013

Accepted Manuscript
Pyridine-oxazoline and Quinoline-oxazoline Ligated Cobalt Complexes: Syn-
thesis, Characterization, and 1,3-Butadiene Polymerization Behaviors
Jun Guo, Heng Liu, Jifu Bi, Chunyu Zhang, Hexin Zhang, Chenxi Bai, Yanming
Hu, Xuequan Zhang
PII:
S0020-1693(15)00347-3
http://dx.doi.org/10.1016/j.ica.2015.07.013
ICA 16606
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
24 May 2015
5 July 2015
7 July 2015
Please cite this article as: J. Guo, H. Liu, J. Bi, C. Zhang, H. Zhang, C. Bai, Y. Hu, X. Zhang, Pyridine-oxazoline
and Quinoline-oxazoline Ligated Cobalt Complexes: Synthesis, Characterization, and 1,3-Butadiene
Polymerization Behaviors, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.07.013
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Pyridine-oxazoline and Quinoline-oxazoline Ligated Cobalt
Complexes: Synthesis, Characterization, and 1,3-Butadiene
Polymerization Behaviors
1,2
1,2
1
1
1
1
Jun Guo, Heng Liu, Jifu Bi, Chunyu Zhang, Hexin Zhang, Chenxi Bai,
1
*
1*
Yanming Hu, Xuequan Zhang
1
Key Laboratory of Synthetic Rubber, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, China
2
University of Chinese Academy of Sciences, 100049, China
*Correspondence to: Prof. Xuequan Zhang (E-mail: xqzhang@ciac.ac.cn), Tel & Fax:
+
86-4318526-2303; Prof. Yanming Hu (E-mail: ymhu@ciac.ac.cn), Tel & Fax:
86-4318526-2305.
+
1

Abstract
A series of cobalt complexes supported by pyridine-oxazoline (Pyox) and
quinoline-oxazoline (Quox) were synthesized. Determined by single crystal X-ray
crystallography, complexes 6a and 7c adopted distorted octahedron and trigonal
bipyramid geometries, respectively, while complex 6b existed as an ion pair
2
+
2-
comprised of [CoL
2
]
4
and [CoCl ] , in which the cationic and anionic moieties
displayed distorted octahedron and tetrahedral geometries, respectively. Upon
activation with ethylaluminum sesquichloride (EASC), these cobalt complexes
exhibited high catalytic activity and cis-1,4-selectivity towards 1,3-butadiene
polymerization. The selectivity of the catalytic system could be switched from cis-1,4
3
to 1,2-fashion via the addition of PPh . The effects of ligand environment,
polymerization temperature, and [Al]/[Co] ratio on the polymerization were
investigated in detail.
Keywords: Pyridine; Oxazoline; Quinoline; Cobalt complex; 1,3-Butadiene
polymerization
2

1
. Introduction
The development of new catalysts for the chemo- and stereo-selective
polymerization of conjugated dienes has attracted considerable attention in the past
decades[1-5]. Numerous catalyst systems based on transition metals (Ti, Ni, Co, etc.)
and rare earth metal have been developed so far[6-8]. Among them, cobalt-based
catalyst systems are of particular interest because they can produce polybutadienes
with versatile microstructures including cis-1,4, trans-1,4, and syndiotactic-1,2
isomers depending on the catalyst formulation[9-11]. Additionally, the catalytic
activity and selectivity of catalysts mainly depend on the steric and electronic nature
of the active site. In recent years, research interest has been focused on the design and
synthesis of well-defined single-site catalysts in order to gain precise control of the
catalysis behavior and polymer composition [12-15]. Since the discovery of
bis(arylimino)pyridine ligated Co(II) and iron(II) complexes as effective catalysts for
ethylene polymerization/oligomerization [16,17], a variety of transition metal
complexes bearing α-diimine, pyridinediimine, and their derivatives have been
synthesized and exploited as catalyst precursors for olefin polymerization [18-24].
Tremendous progress has also been made in the aspect of conjugated diene
polymerization. For example, (salen)cobalt(II) [25] and bis(salicylaldiminate)
cobalt(II) [26] were reported to be highly active for cis-1,4 polymerization of
1
,3-butadiene. Cobalt dichloride complexes bearing various tridentate ligands such as
,6-bis(imino)pyridine [6,27], 2,6-bis(pyrazol)pyridine [28],
[29], 2-arylimino-6-(alcohol)
2
bis(N-arylcarboximidoylchloride)pyridine
3

pyridine/2-arylamino-6-(alcohol)
-aryliminomethyl-2-hydroxybenzaldehyde [31] afforded cis-1,4 polybutadienes in
high yields.
pyridine
[30],
and
3
Pyridine bisoxazoline (Pybox) is an important class of ligands in scientific
research owing to its facile preparation and easy modification of the parent framework
[
32,33]. Various Pybox/metal complexes have been synthesized and found
applications in asymmetrical catalysis. However, its potential as coordination
polymerization catalyst is quite limited. Iron(II) [34] and ruthenium(II) [35]
complexes bearing 2,6-bis[4'-(S)-isopropyloxazolin-2'-yl]pyridine were reported as
catalytic precursors for ethylene polymerization but exhibited low activities. To our
knowledge, there is only one paper that reported the polymerization of 1,3-butadiene
with 2,6-bis[4'-(S)-isopropyloxazolin-2'-yl]pyridine chromium trichloride/MMAO
catalyst [36]. On the other hand, many studies have disclosed that the ligand
environment of the complex affected catalytic behaviors significantly. In the present
study, a series of pyridine-oxazoline and quinoline-oxazoline ligated Co(II)
complexes were synthesized and characterized. Furthermore, the effects of the ligand
and polymerization parameter on the activity and selectivity towards 1,3-butadiene
polymerization was investigated in detail.
2
. Experimental Part
2.1. General consideration
n
The molecular weights (M ) and molecular weight distributions (MWD) of
°
polymers were measured at 30 C by gel permeation chromatography (GPC) equipped
4

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
1
13
the polystyrene calibration. H-NMR (400 MHz) and C-NMR (100 MHz) were
recorded on a Varian Unity spectrometer in CDCl or DMSO-d at room temperature.
3
6
IR spectra were recorded on a BRUKER Vertex-70 FT-IR spectrophotometer.
Elemental analysis was performed on an elemental Vario EL spectrometer. The
proportion of 1,2, cis-1,4, and trans-1,4 units of polymer were determined by IR,
1
13
H-NMR, and C-NMR spectra [37,38].
All the manipulations were performed under an atmosphere of dry argon 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. CHCl
3
and triethylamine were refluxed over CaH
2
and
distilled prior to use. N,N-dimethylformamide (DMF) was dried over CaH
2
and then
distilled under reduced pressure before use. 1,3-Butadiene was supplied by Jinzhou
Petrochemical Corporation and purified by passing through four columns packed with
4
Å molecule sieve and KOH prior to use. MAO (10 wt%) was purchased from Akzo
Noble and used as received. Ethylaluminum sesquichloride (EASC) was purchased
from Sigma-Aldrich Co. and diluted to 1.0 mol/L solution by toluene. Other
chemicals were commercially available and used as received unless otherwise
mentioned. The ligands were synthesized referring to the modified literature methods
(
Scheme 1) [32, 39-41].
5

Scheme 1. Synthesis of complexes 6a-e and 7a-e.
.2. Synthesis and characterization of ligands 3a-e and 5a-e
.2.1. Synthesis of 2-(oxazolin-2'-yl) pyridine, Pyox (3a).
2
2
Pyridine-2-carboxylic acid (1.23 g, 10.0 mmol) was treated with SOCl (15.0 mL)
2
at reflux temperature under a nitrogen atmosphere. Excess SOCl was then removed
2
under reduced pressure to give the acid chloride as a white solid (100%). The
chloroform solution of crude 2-pyridine carbonyl chloride was slowly added to an
aqueous solution of chloroethylamine hydrochloride (2.55 g, 22.0 mmol) and KOH
°
(
1.69 g, 30.0 mmol) at 0 C. After 1 h, the aqueous layer was discarded, the organic
layer filtered and washed with water. After the solvent was removed under reduced
pressure, the crude carboxamide was yielded as a light yellow solid. This solid was
dissolved in THF and then added to a suspension of NaH (0.60 g, 60% in mineral oil)
°
in THF at 0 C. The reaction mixture was stirred at room temperature for 24 h, and
then quenched with 10% HCl aq. The THF was removed under reduced pressure, and
the residue was dissolved in dichloromethane. The resulting organic layer was dried
over anhydrous MgSO
4
. After evaporating the solvent, the product was obtained as a
1
white powder in 60% yield (0.89 g). H NMR (CDCl
3
, ppm): 8.71 (d, J = 4.5 Hz, 1H),
8.05 (d, J = 7.9 Hz, 1H), 7.79 (td, J = 7.8, 1.4 Hz, 1H), 7.46 – 7.35 (m, 1H), 4.53 (t, J
1
3
=
3
9.6 Hz, 2H), 4.14 (t, J = 9.7 Hz, 2H). C NMR (CDCl , ppm): 163.93, 149.73,
6

−
1
1
1
5
2
46.95, 136.60, 125.49, 123.85, 68.23, 55.19. FT-IR (KBr; cm ): 1661, 1584, 1471,
366, 1266, 1100, 940, 800, 748, 672. Anal. Calc. for C
.44; N, 18.91. Found: C, 64.72; H, 5.59; N, 19.20.
8 8 2
H N O (148.16): C, 64.85; H,
.2.2. Synthesis of 2-[4'-(S)- methyloxazolin-2'-yl]pyridine, Me-Pyox (3b).
Crude 2-pyridine carbonyl chloride was prepared by the same method as for 3a.
The obtained crude carbonyl chloride reacted with (S)-2-Amino-1-propanol with
triethylamine as a deacid reagent, then excess SOCl was added, and the solution was
2
reflux for 2h. The resultant mixture was poured into ice water.
The organic layer was collected, washed with brine (20 mL × 3) and aqueous
2 3 4
K CO aq. (0.1 mol/L, 30 mL), and dried over anhydrous MgSO . After evaporating
the solvent, the crude product was purified by silica gel column chromatography to
give 2b (1.59 g, ca. 8.0 mmol) as a light yellow solid. The solid (3.20 g) was treated
with a THF suspension of NaH (0.60 g) at room temperature for 24 h. The THF was
removed under reduced pressure, and the residue was dissolved in dichloromethane.
The organic layer was dried over Na
2
SO
4
. After evaporation the solvent, the product
1
was obtained as a colorless liquid (1.04g, 64% yield). H NMR (CDCl
3
, ppm): 8.71 (d,
J = 4.4 Hz, 1H), 8.04 (d, J = 7.9 Hz, 1H), 7.77 (td, J = 7.8, 1.3 Hz, 1H), 7.44–7.33 (m,
H), 4.69–4.57 (m, 1H), 4.53–4.38 (m, 1H), 4.05 (t, J = 8.1 Hz, 1H), 1.40 (d, J = 6.6
1
1
3
3
Hz, 3H). C NMR (CDCl , ppm): 162.47, 149.61, 146.86, 136.42, 125.31, 123.70,
−1
7
4.52, 62.22, 21.18. FT-IR (KBr; cm ): 1661, 1588, 1529, 1472, 1361, 1123, 1084,
1
045, 960, 751, 622. Anal. Calc. for C O (162.19): C, 66.65; H, 6.21; N, 17.27.
9
10 2
H N
Found: C, 66.86; H, 6.29; N, 17.34.
2.2.3. Synthesis of 2-[4'-(S)- ethyloxazolin-2'-yl]pyridine, Et-Pyox (3c).
This compound was prepared by the same method as for 3b. Yield, 1.04 g (59%).
1
H NMR (CDCl
3
, ppm): 8.71 (d, J = 4.3 Hz, 1H), 8.05 (d, J = 7.9 Hz, 1H), 7.84–7.71
7

(
m, 1H), 7.45–7.35 (m, 1H), 4.58 (t, J = 8.9 Hz, 1H), 4.39–4.26 (m, 1H), 4.14 (t, J =
.1 Hz, 1H), 1.83 (td, J = 13.7, 7.2 Hz, 1H), 1.72–1.58 (m, 1H), 1.03 (t, J = 7.4 Hz,
8
3
5
9
1
3
H). C NMR (CDCl
3.70, 24.42, 10.64. FT-IR (KBr; cm ):1660, 1525, 1464, 1432, 1291, 1245, 1090,
97, 750, 616. Anal. Calc. for C10 O (176.22): C, 68.16; H, 6.86; N, 15.90.
3
, ppm): 165.04, 149.95, 148.16, 137.44, 126.24, 122.38, 65.11,
−1
H
12
N
2
Found: C, 67.95; H, 6.95; N, 15.73.
2.2.4. Synthesis of 2-[4'-(S)-isopropyloxazolin-2'-yl]pyridine, i-Pr-Pyox (3d).
This compound was prepared by the same method as for 3b. Yield, 0.95 g (50%).
1
3
H NMR (CDCl , ppm): 8.71 (d, J = 4.3 Hz, 1H), 8.06 (d, J = 7.9 Hz, 1H), 7.77 (td, J
=
7.8, 1.3 Hz, 1H), 7.45–7.33 (m, 1H), 4.51 (t, J = 8.4 Hz, 1H), 4.27–4.12 (m, 2H),
13
1
.91 (dh, J = 13.2, 6.6 Hz, 1H), 1.06 (d, J = 6.7 Hz, 3H), 0.95 (d, J = 6.7 Hz, 3H). C
NMR (CDCl , ppm): 162.73, 149.87, 147.24, 136.64, 125.51, 124.07, 73.19, 70.91,
3
−1
3
2.92, 19.14, 18.36. FT-IR (KBr; cm ): 1663, 1584, 1466, 1357, 1099, 1044, 963,
7
47, 674, 622. Anal. Calc. for C11 O (190.24): C, 69.45; H, 7.42; N, 14.73.
H
14
N
2
Found: C, 69.13; H, 7.28; N, 14.90.
2.2.5. Synthesis of 2-[4'-(R)-phenyloxazolin-2'-yl]pyridine, Ph-Pyox (3e).
This compound was prepared by the same method as for 3b. Yield, 1.12 g (60%).
1
3
H NMR (CDCl , ppm): 8.75 (d, J = 4.1 Hz, 1H), 8.18 (d, J = 7.8 Hz, 1H), 7.82 (dd, J
=
10.9, 4.4 Hz, 1H), 7.47–7.41 (m, 1H), 7.41–7.28 (m, 5H), 5.60–5.37 (m, 1H),
1
3
5
.01–4.82 (m, 1H), 4.40 (t, J = 8.5 Hz, 1H). C NMR (CDCl
3
, ppm): 164.81, 149.79,
148.27, 139.27, 137.49, 128.94, 127.91, 127.00, 126.42, 122.51, 66.60, 56.24. FT-IR
−1
(
KBr; cm ):1666, 1521, 1464, 1433, 1291, 1071, 1040, 748, 700, 614. Anal. Calc. for
14 12 2
C H N
O (224.26): C, 74.98; H, 5.39; N, 12.49. Found: C, 74.83; H, 5.51; N, 12.37.
2.2.6. Synthesis of 2-[oxazolin-2'-yl]quinoline, Quox (5a).
8

This compound was prepared by the same method as for 3a. Yield, 1.23 g
1
(
62%). H NMR (CDCl
3
, ppm): 8.48–8.09 (m, 3H), 7.86 (d, J = 8.1 Hz, 1H), 7.76 (t, J
=
7.3 Hz, 1H), 7.61 (t, J = 7.4 Hz, 1H), 4.61 (t, J = 9.6 Hz, 2H), 4.20 (t, J = 9.6 Hz,
1
3
2
1
1
5
2
H). C NMR (CDCl
3
, ppm): 164.33, 147.79, 146.99, 136.82, 130.56, 130.15, 128.88,
−1
28.03, 127.64, 120.81, 101.13, 68.58, 55.37. FT-IR (KBr; cm ): 1649, 1590, 1459,
371, 1120, 1081, 839, 766, 624. Anal. Calc. for C12
.08; N, 14.13. Found: C, 72.64; H, 5.26; N, 14.17.
H
10
2
N O (198.22): C, 72.71; H,
.2.7. Synthesis of 2-[4'-(S)- methyloxazolin-2'-yl]quinoline, Me-Quox (5b).
This compound was prepared by the same method as for 3b. Yield, 1.21 g (57%).
1
3
H NMR (CDCl , ppm): 8.35–8.10 (m, 3H), 7.86 (d, J = 8.1 Hz, 1H), 7.76 (t, J = 7.6
Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 4.70 (t, J = 8.8 Hz, 1H), 4.59–4.45 (m, 1H), 4.15 (t,
13
J = 8.0 Hz, 1H), 1.44 (d, J = 6.6 Hz, 3H). C NMR (CDCl
3
, ppm): 170.31, 164.94,
1
1
49.68, 146.48, 137.50, 130.14, 129.72, 129.31, 127.97, 127.76, 118.87, 66.83, 48.15,
−1
7.24. FT-IR (KBr; cm ): 1658, 1530, 1498, 1426, 1052, 847, 775, 623. Anal. Calc.
O (212.25): C, 73.56; H, 5.70; N, 13.20. Found: C, 73.44; H, 5.92; N,
for C13
H
12
N
2
13.31.
2.2.8. Synthesis of 2-[4'-(S)- ethyloxazolin-2'-yl]quinoline, Et-Quox (5c).
This compound was prepared by the same method as for 3b. Yield, 1.22 g (54%).
1
3
H NMR (CDCl , ppm): 8.46–8.18 (m, 3H), 8.11 (d, J = 8.5 Hz, 1H), 7.86 (d, J = 8.1
Hz, 1H), 7.75 (t, J = 7.6 Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 4.17–4.04 (m, 1H), 3.87
dd, J = 11.1, 3.5 Hz, 1H), 3.78 (dd, J = 11.1, 6.0 Hz, 1H), 1.88–1.66 (m, 2H), 1.06 (t,
(
1
3
J = 7.4 Hz, 3H). C NMR (CDCl
3
, ppm): 164.92, 149.54, 146.25, 137.26, 129.92,
129.53, 129.06, 127.75, 127.53, 118.70, 64.57, 53.53, 24.49, 10.57. FT-IR (KBr;
−1
cm ): 1662, 1530, 1501, 1426, 1168, 843, 773, 626. Anal. Calc. for C14
H
14
2
N O
(
226.27): C, 74.31; H, 6.24; N, 12.38. Found: C, 74.10; H, 6.65; N, 12.10.
9

2.2.9. Synthesis of 2-[4'-(S)-isopropyloxazolin-2'-yl]quinoline, i-Pr-Quox (5d).
This compound was prepared by the same method as for 3b. Yield, 1.32 g (55%).
1
3
H NMR (CDCl , ppm): 8.34–8.20 (m, 3H), 7.86 (d, J = 8.1 Hz, 1H), 7.76 (t, J = 7.6
Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 4.61 (t, J = 9.0 Hz, 1H), 4.32 (t, J = 8.3 Hz, 1H),
.29 – 4.20 (m, 1H), 1.96 (dq, J = 13.3, 6.6 Hz, 1H), 1.09 (d, J = 6.7 Hz, 3H), 0.98 (d,
4
1
3
J = 6.7 Hz, 3H). C NMR (CDCl
3
, ppm): 163.02, 147.77, 147.18, 136.79, 130.56,
130.14, 128.91, 128.02, 127.67, 121.06, 73.18, 71.18, 32.99, 19.22, 18.38. FT-IR
−1
(
KBr; cm ): 1647, 1462, 1367, 1267, 1121, 1085, 968, 840, 762, 622. Anal. Calc. for
O (240.30): C, 74.97; H, 6.71; N, 11.66. Found: C, 74.73; H, 6.74; N, 11.85.
15 16 2
C H N
2
.2.10. Synthesis of 2-[4'-(R)-phenyloxazolin-2'-yl]quinoline, Ph-Quox (5e).
This compound was prepared by the same method as for 3b. Yield, 1.34 g (49%).
1
3
H NMR (CDCl , ppm): 8.28 (m, 3H), 7.88 (d, J = 8.1 Hz, 1H), 7.78 (t, J = 7.5 Hz,
1
1
1
7
6
7
2
H), 7.63 (t, J = 7.4 Hz, 1H), 7.44–7.28 (m, 5H), 5.60–5.47 (m, 1H), 5.05–4.93 (m,
1
3
H), 4.48 (d, J = 17.1 Hz, 1H). C NMR (CDCl
3
, ppm): 164.29, 147.78, 146.87,
41.89, 136.92, 130.53, 130.25, 128.99, 128.19, 127.96, 127.71, 127.01, 121.17,
−1
5.73, 70.61. FT-IR (KBr; cm ): 1645, 1560, 1451, 1365, 1126, 1088, 970, 838, 759,
97, 643. Anal. Calc. for C18
8.60; H, 5.25; N, 10.03.
14 2
H N O (274.32): C, 78.81; H, 5.14; N, 10.21. Found: C,
.3. Synthesis and characterization of Cobalt complexes 6a-e and 7a-e
Complex 6a was obtained by mixing CoCl
2
with 2.0 equivalents of ligand in THF
with 1.0 equivalent of ligand in
and other complexes were prepared by mixing CoCl
2
THF. The solution turned green immediately, and a green suspension was obtained
after several minutes. The mixture was stirred at room temperature overnight. The
precipitate was filtered, washed with dry diethyl ether, and then dried under vacuum
10

°
at 40 C for 24 h.
2
+
2-
2
.3.1. Synthesis of [Co (2,6-bis[oxazolin-2'-yl] pyridine)
2
] [Cl
Yield, 0.15 g (69%). FT-IR (KBr; cm ):1647, 1590, 1398, 1276, 1146, 1014, 929,
71. Anal. Calc. for C16 CoN (426.16): C, 45.09; H, 3.78; N, 13.15. Found: C,
5.25; H, 4.07; N, 13.04.
.3.2. Synthesis of [Co(2-[4'-(S)- methyloxazolin-2'-yl]pyridine)
2
] (6a).
−1
6
4
2
H
16Cl
2
4
O
2
2
+
2-
2
] [CoCl
Yield, 0.25 g (65%). FT-IR (KBr; cm ):1653, 1593, 1400, 1256, 1161, 1014, 946,
53, 679. Anal. Calc. for C18 Co (584.06): C, 37.02; H, 3.45; N, 9.59.
4
] (6b).
−1
7
H
20Cl
4
2
N
4
O
2
Found: C, 37.19; H, 3.75; N, 9.24.
2
+
2-
2
.3.3. Synthesis of [Co (2-[4'-(S)- ethyloxazolin-2'-yl]pyridine)
2
] [CoCl
Yield, 0.21 g (71%). FT-IR (KBr; cm ): 1633, 1596, 1560, 1261, 1053, 1018,
77, 754. Anal. Calc. for C20 Co (612.11): C, 39.24; H, 3.95; N, 9.15.
4
] (6c).
−1
8
H
24Cl
4
2 4 2
N O
Found: C, 39.15; H, 4.16; N, 9.07.
2
+
2-
2
.3.4. Synthesis of [Co (2-[4'-(S)-isopropyloxazolin-2'-yl]pyridine)
2
] [CoCl
Yield, 0.25 g (70%). FT-IR (KBr; cm ): 1648, 1593, 1403, 1257, 1159, 1016,
35, 805, 757, 674. Anal. Calc. for C22 Co (640.16): C, 41.28; H, 4.41; N,
.75. Found: C, 41.23; H, 4.56; N, 8.55.
.3.5. Synthesis of [Co (2-[4'-(R)-phenyloxazolin-2'-yl]pyridine)
4
] (6d).
−1
9
8
2
H
28Cl
4
2 4 2
N O
2
+
2-
2
] [CoCl
Yield, 0.20 g (78%). FT-IR (KBr; cm ): 1631, 1595, 1558, 1474, 1171, 1022,
54, 702. Anal. Calc. for C28 Co (708.19): C, 47.49; H, 3.42; N, 7.91.
4
] (6e).
−1
7
H
24Cl
4
2 4 2
N O
Found: C, 47.17; H, 3.59; N, 7.65.
.3.6. Synthesis of 2-[oxazolin-2'-yl]quinoline Cobalt(II) chloride (7a).
2
11

−1
Yield, 0.18 g (77%). FT-IR (KBr; cm ): 1635, 1592, 1483, 1409, 1381, 1253,
1
171, 1118, 838, 764, 629. Anal. Calc. for C12 CoN O (328.06): C, 43.93; H,
H
10Cl
2
2
3.07; N, 8.54. Found: C, 44.04; H, 3.28; N, 8.45.
2.3.7. Synthesis of 2-[4'-(S)- methyloxazolin-2'-yl]quinoline Cobalt(II) chloride (7b).
−1
Yield, 0.30 g (75%). FT-IR (KBr; cm ): 1637, 1565, 1507, 1477, 1402, 1380,
1
8
2
173, 958, 836, 766. Anal. Calc. for C13 CoN O (342.09): C, 45.64; H, 3.54; N,
H
12Cl
2
2
.19. Found: C, 45.42; H, 3.27; N, 8.24.
.3.8. Synthesis of 2-[4'-(S)- ethyloxazolin-2'-yl]quinoline Cobalt(II) chloride (7c).
−1
Yield, 0.26 g (71%). FT-IR (KBr; cm ): 1639, 1616, 1564, 1512, 1481, 1406,
379, 1174, 920, 837, 768. Anal. Calc. for C14 CoN O (356.11): C, 47.22; H,
.96; N, 7.87. Found: C, 47.08; H, 4.31; N, 7.96.
.3.9. Synthesis of 2-[4'-(S)-isopropyloxazolin-2'-yl]quinoline Cobalt(II) chloride
1
3
2
H
14Cl
2
2
(
7d).
Yield, 0.24 g (70%). FT-IR (KBr; cm ): 1635, 1617, 1591, 1476, 1405, 1384,
220, 1175, 1121, 933, 839, 769. Anal. Calc. for C15 CoN O (370.14): C, 48.67;
−1
1
H
16Cl
2
2
H, 4.36; N, 7.57. Found: C, 48.70; H, 4.41; N, 7.35.
.3.10. Synthesis of 2-[4'-(R)-phenyloxazolin-2'-yl]quinoline Cobalt(II) chloride (7e).
2
−1
Yield, 0.18 g (82%). FT-IR (KBr; cm ): 1636, 1588, 1479, 1408, 1381, 1260,
1172, 929, 764. Anal. Calc. for C18
H
14Cl
2
CoN O (404.16): C, 53.49; H, 3.49; N, 6.93.
2
Found: C, 53.40; H, 3.78; N, 6.75.
2.4. X-ray structure determinations
Crystals for X-ray analysis were obtained as described in the result and
discussion section. Data collections were performed at -88.5 °C on a Bruker SMART
APEX diffractometer with a CCD area detector, using graphite monochromated Mo K
12

radiation (λ = 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
2
solved by using SHELXTL program. Refinement was performed on F 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 structure
calculation without further refinement of the parameters. CCDC 1013806 to 1013808.
2.5. Polymerization procedures
A typical procedure for the polymerization by 6b is as follows: a toluene solution
-2
(
10 mL) of 1,3-butadiene (1 g, 1.85 × 10 mol) was added to a oxygen- and
-6
moisture-free ampoule preloaded with complex 6b (2.7 mg, 9.26 × 10 mol). Then,
-3
EASC (1.0 × 10 mol/mL, 0.185 mL) was injected to initiate the polymerization at
°
2
0 C. After 15 min, acidified ethanol containing 2,6-di-tert-butyl-4-methylphenol
(
1.0 wt%) as a stabilizer was added to the system to quench the polymerization. The
°
polymer was washed with ethanol repeatedly, and then dried under vacuum at 40 C
to constant weight. The polymer yield was determined by gravimetry.
13

3
. Results and Discussion
3.1. Synthesis and characterization of complexes
2
Complexes 6a-e and 7a-e were synthesized by the reaction of CoCl with the
corresponding ligand at room temperature in good yields. The ligands and complexes
were identified by FT-IR, NMR, and elemental analysis. In the IR spectra, the
absorption bands of the arylimino C=N moieties of the complexes appeared at
−1
1
631−1653 cm , which are obviously red-shifted compared to those of the
−1
corresponding ligands (1645−1666 cm ), indicating that the nitrogen atom of
arylimino coordinates to the central metal. The structures of 6a, 6b, and 7c were
further analyzed by single crystal X-ray crystallography. Data collection and crystal
and refinement parameters are listed in Table S1. The molecular structures of 6a, 6b,
and 7c are shown in Fig. 1-3.
Single crystals of 6a, 6b, and 7c suitable for X-ray diffraction analysis were
obtained by slow diffusion of Et O into their saturated solutions of DMF. Quite
2
surprisingly, the three kinds of crystals displayed different geometries. Anchored by
two ligands, complex 6a can be best described as a distorted octahedron formed by
the four coordinated nitrogen atoms of the two ligands and the two chlorine atoms.
Due to the highly symmetric nature of complex 6a, the cobalt atom is precisely on the
plane defined by the four coordinated nitrogen atoms. The four imino C=N bonds in
6a have typical double bond character with C=N bond lengths of 1.264(4) Å and
1.344(4) Å. 6b crystallizes with two independent ion-pairs per asymmetric unit. Due
to the fact that the bond distances and angles are similar in the two independent
14

molecules (e.g Co(1)−N(1), 2.159(4); Co(3)−N(5), 2.154(5);Co(1)−N(2), 2.108(4);
Co(3)−N(6), 2.105(4); Co(1)−N(3), 2.177(4); Co(3)−N(7), 2.158(5); Co(1)−N(4),
2
.090(5); Co(3)−N(8), 2.104(5); N(1)−Co(1)−N(2), 77.63(16); N(5)−Co(3)−N(6),
7.23 (17); N(3)−Co(1)−N(4), 77.68 (18); N(7)−Co(3)−N(8), 77.9 (2)), reference can
7
be made to the molecule identified by Co(1).
The analysis of X-ray crystallography revealed that 6b is ion-paired complexed
2
+
2−
[
[
(
L
2
Co] [CoCl
4
]
(Fig. 2). The cobalt center in the cationic moieties of
2
+
2−
Co(Me-Pyox)2] [CoCl
4
] is six-coordinate and chelated by two ligands with Co-N
imino nitrogen and pyridine nitrogen) bonds ranging from 2.090(5) Å to 2.177(4) Å,
O molecule, and a chloride atom, 6b can be best described as a distorted
a H
2
octahedron. The oxygen atom (O1W) lies 0.014 Å out of one pyox plane (defined by
N1, N2, O1) and the chloride atom (Cl1) lies 0.555 Å out of the other one (defined by
2
N3, N4, O2). The incorporation of H O and chloride atom demonstrated the highly
unsaturated nature of the cobalt core. The bond length of Co1-N1 (pyridine) (2.159(4)
Å) is shorter than that of Co1-N2 (oxazoline) (2.108(4) Å), and Co1-N3 (pyridine)
(
2.177(4) Å) is shorter than Co1-N4 (oxazoline) (2.090(5) Å). The dihedral angles
between the pyridine planes (defined by C5, N1, C3 and C10, N3, C14) and their
°
corresponding oxazoline planes (defined by N2, C6, O1 and N4, C15, O2) is 2.66
°
and 2.88 , respectively, indicating the coplanar structure of this rigid ligand
framework. The cobalt atom (Co1) slightly lies 0.138 Å out of one pyox plane
(
defined by N1, N2, O1W) and 0.0138 Å for the other one (defined by N3, N4, Cl1)..
2
−
The [CoCl
4
]
anion displays as a slightly distorted tetrahedral geometry with
15

nearly uniform Co-Cl bond lengths of 2.2699–2.3080 Å and Cl-Co-Cl angles ranging
°
°
from 106.61(6) to 114.61(6) . The two C=N bonds, N(1)=C(5) and N(2)=C(6), have
a typical double bond character with bond length of 1.352 Å and 1.273 Å,
respectively.
Fig. 1. ORTEP drawing of complex 6a with thermal ellipsoids at the 30% probability
2
level. Hydrogen atoms have been omitted for clarity (One H O molecule in the lattice
is not included). Selected bond lengths (Å) and angles (deg): Co(1)−N(1), 2.123(2);
Co(1)−N(2), 2.163(2); Co(1)−Cl(1), 2.4727(7); N(1)−C(3), 1.264(4); N(2)−C(4),
1.344(4); N(1)−Co(1)−N(2), 77.21(9); N(1)−Co(1)−Cl(1), 88.29(7) ; N(2)−Co(1)−Cl
(
1), 89.39(7).
16

Fig. 2. ORTEP drawing of complex 6b·H O with thermal ellipsoids at the 30%
2
probability level. Hydrogen atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Co(1)−N(1), 2.159(4); Co(1)−N(2), 2.108(4);
Co(1)−N(3), 2.177(4); Co(1)−N(4), 2.090(5); Co(1)−Cl(1), 2.5336(16); Co(2)−Cl(1),
2
.3080(14); Co(2)−Cl(2), 2.2895(16); Co(2)−Cl(3), 2.2700(16); Co(2)−Cl(4),
.2699(15); N(1)−Co(1)−N(2), 77.63(16); N(3)−Co(1)−N(4), 77.68 (18);
2
Cl(1)−Co(2)−Cl(2), 108.68(6); Cl(1)−Co(2)−Cl(3), 108.98(6); Cl(1)−Co(2)−Cl(4),
06.99(6); Cl(2)−Co(2)−Cl(3), 106.61(6); Cl(2)−Co(2)−Cl(4), 110.84(6);
Cl(3)−Co(2)−Cl(4), 114.61(6).
1
Fig. 3. ORTEP drawing of complex 7c·DMF with thermal ellipsoids at the 30%
probability level. Hydrogen atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Co(1)−N(1), 2.259(2); Co(1)−N(2), 2.055(2);
N(1)−C(9), 1.328(3); N(2)−C(10), 1.271(3); Co(1)−Cl(1), 2.2815(8); Co(1)−Cl(2),
2
.2836(7); Co(1)−O(1), 2.1134(15); N(1)−Co(1)−N(2), 76.71(8); Cl(1)−Co(2)−Cl(2),
20.03(3).
1
As depicted in Fig. 3, with coordination of one DMF molecule to the cobalt atom,
7
c adopted a penta-coordinate structure and the geometry around the metal centre can
17

be best described as a distorted trigonal bipyramid in which the nitrogen atom of
oxazoline and the two chloride atoms form the equatorial plane, the oxygen atom of
DMF and the quinolyl nitrogen atom posit at the apical points. The deviations of the
metal ion from the equatorial plane and the plane formed by the coordinated nitrogen
atoms and oxygen atom are only 0.139 Å and 0.049 Å, respectively. The quinoline
ring is approximately orthogonal to the equatorial plane, and the dihedral angle is
83.11°. The quinoline planes (defined by C1, N1, C9) and the oxazoline planes
(
defined by N2, C10, O2) are nearly coplanar with a dihedral angle of 4.63°.
3.2. 1,3-Butadiene polymerization
3
.2.1. Effect of the ligand on 1,3-butadiene polymerization
The complexes activated by EASC for the polymerization of 1,3-butadiene were
examined, and the results are summarized in Table 1. For 6a-e (Entry 1-5), when the
bulkiness of the substituent at 4-position of oxazoline ring increased, namely from
hydrogen (6a), methyl (6b), ethyl (6c), and isopropyl (6d) to phenyl (6e), a decrease
in catalytic activity was observed (from 91.2% to 36.1%). These results indicate that
the spacial steric of the lignad significantly affects the activity of the catalytic
precursor. All the complexes gave cis-1,4-rich polybutadienes (86.8%~97.2%), and
the cis-1,4 content increased with the increasing bulkiness of the attached substituent
on the oxazoline ring. On the other hand, the complex with bulkier substituent
produced polymer having higher M and narrower MWD. Similar tendency was
n
observed in the case of quinoline-oxazoline-based 7a-e. Probably due to the more
open nature revealed by the single crystal structure analysis, complex 6a exhibited
18

higher activity than 6b. Complex 7c afforded polybutadienes with the highest
molecular weight, which might be ascribed to the steric and highly rigid skeleton of
2
quinoline. In contrast, CoCl -based system under the identical conditions or EASC
alone could not initiate 1,3-butadiene polymerization. Since 6b and 7b exhibited high
activity and high cis-1,4 selectivity, they were selected for further experiments.
a
Table 1. Polymerization of 1,3-butadiene with 6a-e and 7a-e activated by EASC.
b
Microstructure (%)
-4c
c
Entry Cat.
Yield (%)
91.2
83.1
79.2
58.3
36.1
95.2
87.5
86.5
72.2
35.5
trace
−
M
n
× 10
M
w
/M
n
Cis-1,4 Trans-1,4
1,2
4.7
3.0
1.8
1.5
1.3
5.3
1.8
1.7
1.4
1.0
−
1
2
3
4
5
6
7
8
9
1
6a
6b
6c
4.3
7.0
8.7
4.3
4.0
4.0
3.1
2.3
3.6
3.3
3.0
2.8
2.2
−
86.8
92.2
95.4
97.0
97.2
92.3
95.1
95.5
97.2
98.0
−
8.5
4.8
2.8
1.6
1.5
2.3
3.1
2.7
1.4
1.0
−
6d
6e
14.7
21.4
6.7
7a
7b
7c
11.5
11.6
16.0
21.0
−
7d
7e
0
11
CoCl
2
12
−
−
−
−
−
−
a
o
Polymerization in toluene at 20 C for 15 min, precatalyst: 9.26 µmol, [BD]/[Co] =
2000, [Al]/[Co] = 20.
b
1
Determined by H NMR and FT-IR.
c
Determined by GPC against polystyrene standards.
3.2.2. Effects of [Al]/[Co] ratio and polymerization temperature on 1,3-butadiene
polymerization
19

The effects of [Al]/[Co] ratio and polymerization temperature on catalytic
behaviors were investigated (Table 2 and Table 3). For 6b, upon activation with
EASC, as increasing [Al]/[Co] ratio from 20 to 150, the polymer yield increased
slightly, while the cis-1,4 content, the M , and MWD of the resultant polymers
n
remained almost the same. Similar results were observed in previously reported
Co-based catalyst systems, in which [Al]/[Co] ratio did not have large influence on
the M
n
and MWD of the polymers [41,42]. On the other hand, polymerization
temperature significantly affected the catalytic behaviors of the complex. The polymer
°
°
yield sharply increased from 2.7% at 0 C to 81.1% at 20 C, and then almost
practically leveled off to 80% at 40 °C and above, indicating high thermal stability of
4
4
n
the active species. Meanwhile, the M decreased from 11.5 × 10 to 2.6 × 10 , and the
MWD increased from 1.7 to 6.6. This result is attributable to the facilitated chain
transfer reaction at the elevated temperature. When the polymerization temperature
°
°
increased from 0 C to 80 C, the cis-1,4 content of the polymer decreased from 97.9%
to 79.3%, while the trans-1,4- and 1,2-contents increased gradually. As shown in
Table 3, a similar tendency was observed in 7b. It is noteworthy that the thermal
stability of the active species generated by 7b was even higher than 6b; the polymer
°
yield was still up to 87% even at a high temperature of 80 C. This result is in contrast
to most late transition metal-based catalysts which suffered from the decay of
catalytic activity as polymerization temperature increased. For instance, in the cases
of
2,6-bis(benzimidazol-2-yl)-pyridine
Co(II)
dichloride
and
2
-[1-(2,6-diisopropylphenylimino)ethyl]-6-(pyrazol-1-yl)-pyridine cobalt dichloride,
20

the polymer yield decreased from 80.1% at 50 °C to 47.4% at 90 °C and from 72% at
5 °C to 11% at 80 °C, respectively [43,44]. The high thermal stability might be due
2
to the rigid structure backbone which protected the active centre [45,46].
Table 2. Effects of [Al]/[Co] ratio and temperature on 1,3-butadiene polymerization
a
with 6b/EASC catalyst.
b
Microstructure (%)
Temp.
Yield
(%)
M
n
×
c
Entry [Al]/[Co]
M
w
/M
n
Cis-1,4 Trans-1,4 1,2
o
-4c
(
C)
10
1
1
1
1
1
1
1
3
4
5
6
7
8
9
0
20
20
20
20
20
0
83.1
88.6
93.3
93.3
2.7
7.0
7.3
7.4
7.1
11.5
3.0
2.8
2.6
4.0
3.7
3.3
3.4
1.7
7.3
6.5
6.6
92.2
92.4
92.3
93.6
97.9
84.4
80.8
79.3
4.8
3.0
2.8
2.2
2.1
0.6
6.4
8.0
8.3
60
4.8
100
150
20
5.5
4.4
1.6
20
40
60
80
83.8
81.7
79.6
9.3
20
11.2
12.4
2
20
a
Polymerization in toluene for 15 min, precatalyst: 9.26 µmol, [BD]/[Co] = 2000.
b
c
1
Determined by H NMR and FT-IR.
Determined by GPC against polystyrene standards.
21

Table 3. Effects of [Al]/[Co] ratio and temperature on 1,3-butadiene polymerization
a
with 7b/EASC catalyst.
b
Microstructure (%)
Temp.
Yield
(%)
M
n
×
c
n
Entry [Al]/[Co]
M
w
/M
Cis-1,4 Trans-1,4 1,2
o
-4c
(
C)
10
2
2
2
2
2
2
2
1
2
3
4
5
6
7
8
20
20
20
20
20
0
87.5
89.2
91.3
88.4
4.5
11.5
10.1
10.1
10.2
14.1
7.7
3.3
3.0
2.9
3.0
1.6
4.0
5.5
7.0
95.1
95.3
95.9
95.1
98.9
88.2
85.0
82.5
3.2
3.2
2.8
3.4
0.5
7.2
9.7
11.5
1.7
1.6
1.3
1.6
0.6
4.7
5.2
6.0
60
100
150
20
20
40
60
80
90.7
88.2
87.4
20
6.6
2
20
5.7
a
Polymerization in toluene for 15 min, precatalyst: 9.26 µmol, [BD]/[Co] = 2000.
b
c
1
Determined by H NMR and FT-IR.
Determined by GPC against polystyrene standards.
.2.3. Effect of cocatalyst on 1,3-butadiene polymerization
3
The effect of cocatalyst type on 1,3-butadiene polymerization were examined
(
Table 4). The polymerization with EASC-based catalyst gave polybutadiene in high
yield within 15 min, while alkylaluminum (AlEt
3
and Al(i-Bu) )-based systems could
3
not polymerize 1,3-butadiuene. In the case of MAO-based system, it is worth noting
that 1,3-butadiene polymerization proceeded even at a low MAO level ([Al]/[Co] =
5
0) to afford polymer in 73.9% yield. When the [Al]/[Co] ratio further increased to
00, the polymer yield reached 88.6%. This catalytic system is more active than
1
22

2
CoCl /MAO; the latter gave polybutadiene in a low yield of 29% at [Al]/[Co]=100
[
40].
Table 4. Effect of cocatalysts on polymerization behaviors with 6b and 7b catalyst
a
system.
b
Microstructure (%)
-4c
c
Entry Cat. Cocat. Al/Co Yield(%) M
n
×10
7.0
−
M
w
/M
n
Cis-1,4 Trans-1,4 1,2
2
3
3
3
3
3
3
3
3
3
3
4
9
0
1
2
3
4
5
6
7
8
9
0
6b EASC
6b
TEA
6b TIBA
20
40
83.1
−
4.0
−
92.2
−
4.8
−
3.0
−
40
−
−
−
−
−
−
d
6b MAO
6b MAO
6b MAO
30
31.7
84.4
98.7
87.5
−
1.6
2.9
3.0
3.5
3.5
3.2
3.3
−
91.5
95.0
94.2
95.1
−
3.9
2.7
2.5
3.1
−
4.6
2.3
3.4
1.8
−
d
d
50
100
20
7b EASC
7b
TEA
7b TIBA
11.5
−
40
40
−
−
−
−
−
−
d
7b MAO
7b MAO
7b MAO
30
5.2
73.9
88.6
2.1
2.2
5.2
2.3
3.7
3.6
96.4
95.9
95.6
1.8
2.3
2.4
1.8
1.8
2.0
d
d
50
100
a
Polymerization conditions: precatalyst: 9.26 µmol, [BD]/[Co] = 2000, in toluene,
°
2
0 C, 15min. TEA: triethylaluminium; TIBA: triisobutylaluminium; MAO: methyl
aluminoxane.
b
1
Determined by H NMR and FT-IR.
Determined by GPC against polystyrene standards.
Polymerization time: 3h.
c
d
3
3.2.4. Effects of PPh on 1,3-butadiene polymerization
23

It is known that the addition of Lewis base influences both the activity and
specificity of Co-based catalyst systems [10,47,48]. As reflected in Table 5, at
[
3
Al]/[Co] = 20, the addition of PPh to the EASC-based system resulted in a decrease
of polymer yield and a slight increase of 1,2-content of the resultant polymer, whereas
the yield and cis-1,4 content did not affected at a high EASC level ([Al]/[Co] = 40).
These results are presumably due to the reaction between EASC and PPh
in the case of MAO-based system, the addition of PPh not only increased the
catalytic activity but also switched the selectivity from cis-1,4 to 1,2 manner. For
instance, the addition of 1.0 equivalent of PPh resulted in a increase of polymer yield
3
. In contrast,
3
3
from 84.5 to 97.9% for 6b and from 87.6% to 97.8% for 7b, respectively, and the 1,2
selectivity was remarkably enhanced from 2.3% and 1.8% to 81.3% and 87.8%.
1
3
Based on C NMR and DSC analyses (see Fig. S1 and S2), the 1,2- and cis-1,4 units
in the resulting polymers were randomly distributed along the polymer chain, as
observed in other cobalt/phosphine systems [44]. The mechanism of transition metal
catalyzed 1,3-butadiene polymerization has been extensively studied [3,49]. It is
2
known that 1,3-butadiene coordinates to the cobalt center either via one (η ) or both
4
(
η ) double bonds, resulting in an allyl ligand. In the absence of PPh
3
, 1,3-butadiene
4
coordinates to the cobalt centre predominantly with η manner, followed by the
1
3
C -insertion into the terminal π-η allylic polymer chain, giving rise to cis-1,4
structure. In the presence of PPh , the change of selectivity may be attributable to that
3
external electron donor occupies the coordination site and consequently, the
2
coordination mode of 1,3-butadiene becomes η -fashion, then 1,2-enchainment is
24

favorable [3, 10, 49-51]. Moreover, the effect of amine on the polymerization was
also investigated (Table 6.). Fixing the MAO/Co ratio at 50, the addition of an
equimolar amount of amine resulted in a slight decrease of catalytic activity, whereas
the selectivity did not change.
a
Table 5. Effect of PPh
3
on polymerization behaviors with 6b and 7b catalyst system.
b
Microstructure (%)
c
M
n
c
Entry Cat. Cocat. PPh
3
/Co Yield(%)
M /M
w n
Cis-1,4 Trans-1,4
1,2
-
4
×10
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
6b EASC
6b EASC
6b EASC
−
1
83.1
74.0
42.4
92.1
94.4
84.4
84.5
91.4
94.3
97.9
98.1
87.5
55.0
18.8
87.2
93.7
73.9
87.6
90.9
7.0
6.5
1.4
3.1
4.2
2.9
3.7
4.7
4.9
5.1
5.7
4.0
3.3
2.0
4.9
5.0
3.5
3.0
3.0
2.7
2.6
2.3
3.3
2.3
1.8
3.9
4.5
3.7
3.8
3.2
92.2
93.6
81.5
91.6
94.2
95.0
36.7
25.4
20.0
19.4
18.6
95.1
95.7
83.5
93.3
94.1
95.9
25.7
18.6
4.8
2.9
4.2
4.4
3.1
2.7
1.1
1.1
1.4
0.8
0.1
3.1
2.5
4.0
3.3
2.9
2.3
0.7
0.4
3.0
3.5
3
14.3
4.0
d
6b EASC
3
e
6b EASC
3
2.7
f
6b MAO
6b MAO
6b MAO
6b MAO
6b MAO
6b MAO
−
2.3
f
0.1
0.2
0.5
1.0
3
62.2
73.5
78.6
79.8
81.3
1.8
f
f
f
f
7b EASC
7b EASC
7b EASC
−
11.5
16.4
2.1
5.1
5.4
2.2
6.4
6.8
1
1.8
3
12.5
3.4
d
7b EASC
7b EASC
3
e
3
3.0
f
7b MAO
7b MAO
7b MAO
−
1.8
f
0.1
0.2
73.6
81.1
f
25

f
f
f
60
61
62
7b MAO
7b MAO
7b MAO
0.5
1
93.1
97.8
97.7
6.9
6.9
7.3
2.7
2.6
2.2
16.8
11.8
11.1
0.3
0.4
0.3
83.0
87.8
88.6
3
a
Polymerization conditions: precatalyst: 9.26 µmol, [BD]/[Co] = 2000, [Al]/[Co] =
°
2
0, MAO/Co = 50, in toluene, 20 C, 15 min.
b
1
Determined by H NMR and FT-IR.
c
d
e
Determined by GPC against polystyrene standards.
[
Al]/[Co] = 40.
[
Al]/[Co] = 60.
f
Polymerization time: 3h.
Table 6. Effect of amines on polymerization behaviors with 6b and 7b catalyst
a
system.
b
Microstructure (%)
c
M
n
c
Entry Cat.
Amine
aniline
Yield(%)
M
w
/M
n
Cis-1,4 Trans-1,4 1,2
-
4
×
10
63
64
65
66
6b
80.9
78.4
72.8
71.9
2.1
3.2
9.1
7.0
3.2
94.0
94.5
95.5
96.1
3.2
2.8
2.4
1.9
2.8
2.8
2.1
2.0
6b triethylamine
7b
aniline
7b triethylamine
3.5
2.7
3.6
a
Polymerization conditions: precatalyst: 9.26 µmol, [BD]/[Co] = 2000, MAO/Co =
°
5
0, [Amine]/[Co] = 1, in toluene, 20 C, 3h.
b
1
Determined by H NMR and FT-IR.
c
Determined by GPC against polystyrene standards.
4
. Conclusion
In summary, several cobalt complexes bearing pyridine-oxazoline and
quinoline-oxazoline ligands were synthesized and characterized. Single crystal X-ray
26

analysis revealed that 6a and 7c adopted distorted octahedron and trigonal
bipyramidal, respectively, and 6b existed as an ion pair of [CoL ][CoCl ], in which
the cobalt center was surrounded by the two [NN] ligands in the cationic moiety and
2
4
2
−
adopted distorted octahedronal geometry, and the tetrahedral [CoCl
4
]
anion existed
as the counterion. Activated by EASC or MAO, these complexes exhibited high
activity for 1,3-butadiene polymerization. The resulting polymers had high molecular
4
weights (M
n
> 4.3 × 10 ) and high cis-1,4 contents. In particular, 6b and 7b afforded
polymers in high yields (79.6% and 87.4%, respectively) even at a relatively high
°
polymerization temperature of 80 C, indicating the high thermal stability. In the case
of MAO-based system, the addition of PPh
3
could enhance catalytic activity and
switch the selectivity from cis-1,4 to 1,2-enchainment.
27

Acknowledgments
The authors appreciate financial support from National Basic Research Program of
China, Grant No. 2015CB654700(2015CB674702), The CAS Hundred Talents
Program (Y220011001), the Funds for National Natural Scientific Foundation of
China (No. 51473156 and 51203147) and Jilin Provincial Research Fund for Basic
Research, China (No. 20130102007JC).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at
http://dx.doi.org/xx.xxxx/ xxxx.xx.xxx.
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