Polymerization of conjugated dienes and olefins promoted by cobalt complexes supported by phosphine oxide ligands

Article abstract of DOI:10.1016/j.ica.2019.119046

Four cobalt complexes supported by phosphine oxide (P=O) donors (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine oxide) cobalt dichloride (Co1), (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine oxide) cobalt bromide (Co2), N, N'-(pyridine-

Full text of DOI:10.1016/j.ica.2019.119046

InorganicaChimicaActa496(2019)119046
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Research paper
Polymerization of conjugated dienes and olefins promoted by cobalt
complexes supported by phosphine oxide ligands
Dang Yanga, Qiao Gana, Huafeng Chena, Weilun Yinga, Junyi Zhaob,c, Xiaoyu Jiab,c
,
⁎
Dirong Gonga,b,c,
a Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, PR China
b Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, No. 1799, Jimei Road, Xiamen, Fujian 361021, PR
China
c Ningbo Urban Environment Observation and Research Station-NUEORS, Chinese Academy of Sciences, Ningbo, Zhejiang 315830, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Four cobalt complexes supported by phosphine oxide (P=O) donors (9,9-dimethyl-9H-xanthene-4,5-diyl)bis
(diphenylphosphine oxide) cobalt dichloride (Co1), (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine
oxide) cobalt bromide (Co2), N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide) cobalt dichloride
(Co3) and N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide) cobalt dichloride (Co4) were prepared
and characterized. Their catalyses performances in polymerization of isoprene, butadiene, myrcene as well as
MMA and styrene were examined. In combination with AlEt2Cl, Co1 and Co2 are able to convert isoprene to
polyisoprene, whereas the activities of Co3 and Co4 are much low. The resultant polyisoprene are mixture of cis-
1,4 and 3,4 isomers, whose ratio are not significantly affected by the type of catalysts and polymerization
conditions. Isoprene was found to be more active than myrcene, and butadiene in the case of Co1/AlEt2Cl,
suggestive of compromised sterical and electronic effect from the alkyl group at 2-positon of monomers. The
Co1/AlEt2Cl system is also moderately active in polymerizations of methyl methacrylate and styrene. Therefore,
the current catalysts provided dual polymerization reactivities towards conjugated dienes and olefins that are
rare in transition metals catalyzed coordinative polymerization.
Cobalt catalyst
Poly(conjugated diene)
Polyolefin
1. Introduction
catalysts, due to low cost, stability of catalyst components, ease in
catalyst preparation, and the high activity and high selectivity, parti-
The discovery and development of highly active and selective diene
and olefin polymerisation catalysts are the key driver for the exploita-
tion of high-quality rubber and polyolefin as well as for improving the
performances of existing materials. The regio- and/or stereoselective
polymerization of conjugated dienes play a significant role in the reg-
ularity, molecular weight, molecular weight distribution and chain end
group of the resultant polymers which are the key factors determining
the mechanical properties and the end use of the materials. In the past
century, the Ziegler–Natta catalysts have realized regio- and stereo-
specific polymerization of conjugated dienes to produce cis-1,4-, trans-
1,4- and 1,2 (3,4)-polydienes. Catalysts composed of Ti(OEt)4/AlEt3
[1], Nd(carboxylate)3/AlEt2Cl/AliBu3 [2,3], Co(acac)3/AliBu3/CS2
[4,5], Co(2-EHA)3/AlEt2Cl [6] or Ni(naphtha)2/AliBu3/BF3(OEt2) [7,8]
has been invented for industrial production of polybutadiene and
polyisoprene. Particular research attentions recently have been paid to
the late transition metals such as iron-, nickel- and cobalt-based
cularly the potential functional-group tolerance, rendering them com-
petitive in industrial application. Among the late transition metal cat-
alyst systems, versatile cobalt-based catalysts have been highlighted.
Over the past decade, efforts to expand variety of ligand families for
well-defined cobalt catalysts able to polymerize conjugated dienes have
resulted in cascade exploration of cis-1,4 and 1,2 selective systems.
Notably, tridentated ligands such as N-N-N [9–15], N-N-O [16–17], N-
N-P [18–21], N-O-X (X = S, O and P) [22,23] and N-S-N[24] have been
extensively explored, and the corresponding supported catalysts are
active and selective for cis-1,4 polymerization, moreover, the selectivity
can be switchable to 1,2 enchainment via external addition of PPh3 and
CS2 donors [10,13,19,24]. In the meanwhile, cobalt catalysts with
various N-N-N ligands, typically the bisiminopyridine has been in-
vented as versatile ligand for supporting iron, cobalt, chromium and
vanadium for ethylene, propylene, styrene, MMA as well as non-
conjugated dienes polymerizations [25–29]. Yet, the development of
⁎ Corresponding author.
E-mail address: gongdirong@nbu.edu.cn (D. Gong).
https://doi.org/10.1016/j.ica.2019.119046
Received 16 June 2019; Received in revised form 31 July 2019; Accepted 31 July 2019
Availableonline01August2019
0020-1693/©2019ElsevierB.V.Allrightsreserved.

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
cobalt catalysts has met limited monomer versatilities, for example,
catalysts efficient for olefin polymerizations are usually not active for
conjugated monomers, and vice versa [22]. On the other hand, it be-
comes more and more difficult, as well as costly, to synthesize new
catalysts with limited monomer availability.
In the previous study, our group has explored well-defined cobalt
catalysts supported by PN3 (phosphorus fused bipyridine, pyridinyl-
oxazole, pyridinyl-pyrazole) and the corresponding O = PN3 ligands for
highly active polymerizations of isoprene, where control of molecular
weight and selectivity have been realized [18–21]. Mechanism study
revealed that the P=O moiety is crucial to the elimination of the ir-
reversible chain transfer and chain termination. In ongoing efforts to-
ward cobalt catalyzed polymerizations and synthesis of poly(con-
jugated diene) as well as polyolefin materials, herein we will report the
synthesis and characterization of novel phosphine (P) or phosphine
oxide (P=O) ligands supported cobalt complexes, as well as the cata-
lytic application in polymerization of both conjugated dienes and ole-
fins, along with catalyst structure and polymerization parameters stu-
dies to provide insights into the factors important for both
polymerizations, which could advance to make further rational catalyst
predictions to monomer varieties.
Scheme 1. The synthetic route for cobalt complexes.
2. Experimental
2.1. Materials and methods
AlEt2Cl (2 mol L−1 in hexane), AlEt3 (1 mol L−1 in hexane), Al(iBu)3
(1.1 mol L−1 in toluene) and MAO (1.5 mol L−1 in toluene) were ob-
tained from Aldrich and used without any further purification. 4,5-Bis
(diphenylphosphino)-9,9-dimethylxanthene
(Energy
Chemical
Company, 98.0%), Hydrogen peroxide (H2O2, Sinopharm Chemical
Reagent Co., Ltd, 30%) were reagent grade and used as received.
Isoprene (IP, Aldrich, 99.9%), methyl methacrylate (MMA, Siam Fine
Chemical Co., Ltd, 99.5%), myrcene (Bailingwei Technology Co., Ltd,
70.0%), styrene (ST, Shanghai Aladdin Biochemical Technology Co.,
Ltd, 99.5%) were purified by the standard methods and stored over 4 Å
molecular sieves under a nitrogen atmosphere. 1,3-Butadiene was
supplied from Valley Gas Co., Ltd, purified by n-butyllithium and dis-
solved in toluene·THF and toluene were distilled under N2 from sodium
benzophenone and then stored molecular sieves under a dry nitrogen
atmosphere. Ligands L1–L3 were synthesized by oxidation of the cor-
responding ligand [18–21]. All operations were carried out under a dry
nitrogen atmosphere using a rigorous Schlenk technique or in glovebox.
Fig. 1. The mass spectral of complexes Co1, Co2 and Co3.
UV measurements were performed by using
a TU-1901 spectro-
photometer (PERSEE Corp, China). Mass analyses for cobalt compounds
in methanol or dichloromethane solution were performed on an LC-MS
Xevo G2-S QTOF instrument. Elemental analyses for cobalt were carried
out on Inductively Coupled Plasma Mass Spectrometry icap Q after
treatment with aqueous HNO3 or HCl. The microstructure of polymers
was determined by 1H (400 MHz), 13C (100 MHz) recorded on a Bruker
DMX-400 spectrometer in CDCl3 at room temperature and FT-IR spectra
measured with a Perkin Elmer FT-IR 2000 spectrometer. The number
average molecular weights (Mn) and molecular weight distributions
(PDI) of the polymer were measured with using gel permeation chro-
matography instrumentation (GPC) equipped with a Waters 515 HPLC
pump, four columns (HMW 7THF, HMW 6E THF × 2, and HMW 2THF),
and a Waters 2414 refractive index detector·THF was used as eluent at a
flow rate of 1.0 mL/min. The values of Mn and Mw/Mn were determined
using polystyrene calibration at 30 °C. The glass transition points of
polymers were analyzed by DSC from −100 to 50 °C.
Fig. 2. Drawing of complex Co1, hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (°): Co1-O1 1.9819(19), Co1-O2 1.983(2),
Co1-Cl2 2.2438(8), Co1-Cl1 2.2524(8), O1-Co1-O2 99.02(8), O1-Co1-Cl2
109.12(6), O2-Co1-Cl2 117.38(6), O1-Co1-Cl1 116.14(6), O2-Co1-Cl1
102.84(6), Cl2-Co1-Cl1 111.91(3), P1-O1-Co1 144.14(13), P2-O2-Co1
133.75(12).
monochromated Mo Kα radiation (λ = 0.71073 Å). The SMART pro-
gram package was used to determine the crystal class and unit cell
parameters. The reflection data file was produced from the raw frame
data by using SAINT and SADABS. The crystal structures were de-
termined by using SHELXTL program. Refinement was performed on F2
anisotropically for all nonhydrogen atoms by the full-matrix least-
squares method. The hydrogen atoms were added at the calculated
positions and were included in the structure calculation.
2.2. X-ray analyses of crystals
Crystals for X-ray analyses were collected as described in the result
and discussion part. Data were collected at −100 °C on a Bruker
SMART APEX diffractometer with a CCD area detector, using graphite
2

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
Table 1
The crystal parameters of complex Co1.
Identification code
Identification code
Empirical formula
Formula weight
Temperature
C39H32Cl2CoO3P2
740.42
293(2) K
Z, density (Calculated)
Absorption coefficient
F(0 0 0)
4, 1.428 mg/m3
0.784 mm−1
1524
Wavelength
Crystal system, space group
Unit cell dimensions
0.71073 Å
Crystal size
Theta range for data collection
Limiting indices
0.20 × 0.15 × 0.12 mm
1.74 to 25.05 deg.
−14 ≤ h ≤ 16, −20 ≤k ≤ 19, −20 ≤ l ≤ 20
Monoclinic, P2(1)/n
a = 14.2001(11) Å, α = 90 deg.
b = 16.8576(14) Å, β = 124.622(5) deg.
c = 17.4815(11) Å, γ = 90 deg.
3443.7(4) Å3
Volume
Reflections collected
17,114
Completeness to theta
(=25.05) 99.9%
Table 2
The isoprene polymerization results by cobalt catalysts under various polymerization conditions.
Run
Cat.
T/℃
Al
[M]/[Co]
[Al]/[Co]
Yield/%
Time/min
cis-1,4a/mol-%
3,4a/mol-%
Mn/10 kg
DPI
Tg (oC)
b
1
2
3
4
5
6
7
8
Co1
Co1
Co1
Co1
Co1
Co1
Co1
30
30
30
30
0
50
80
30
30
30
30
30
30
30
30
30
AlEt2Cl
AlEt3
2000
2000
2000
2000
2000
2000
2000
1000
4000
6000
8000
2000
2000
2000
2000
2000
300
300
300
300
300
300
300
300
300
300
300
100
500
300
300
300
99
0
0
30
30
30
30
30
30
30
30
30
30
30
30
30
30
240
1440
59.1
—
—
40.9
—
—
8.7
—
—
—
12.3
11.9
8.9
1.6
—
—
−38.6
—
—
—
—
—
—
—
—
—
—
—
—
−38.9
−40.4
−42.3
MAO
AliBu3
0
—
—
—
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
AlEt2Cl.
85
96
93
99
99
99
99
87
90
90
90
90
70.0
66.4
67.7
59.2
57.8
60.2
69.7
55.7
58.6
58.7
67.0
70.0
30.0
33.6
32.3
40.8
42.2
39.8
30.3
44.3
41.4
41.3
33.0
30.0
2.6
2.1
2.7
1.4
1.5
1.3
1.4
2.3
2.0
2.1
2.8
2.5
Co1c
Co1d
Co1e
Co1f
Co1
Co1
Co2
Co3
Co4
6.9
9
19.4
27.9
37.9
17.9
15.6
13.1
11.3
12.8
10
11
12
13
14
15
16
a
b
c
d
e
Polymerization conditions: Co = 0.10 mmol; toluene, 10 mL; Determined by 1H NMR and 13C NMR.
IP = 0.06 mol; IP = 0.08 mol; “—“ not detected.
IP = 0.02 mol; IP = 0.01 mol;
IP = 0.04 mol;
f
Table 3
The polymerizations of butadiene, myrcene, methyl methacrylate and styrene by Co1/AlEt2Cl.
Run
Mono.
[M]/[Co]
Yield/%
Time/min
Microstructures
Mn (kg/mol)
PDI
Tg (oC)
17
18
19
20
BD
2000
2000
2000
2000
10
24
26
65
240
240
240
240
Cis-1,4/1,2 = 98.4/1,4
13.1
25.3
34.5
21.4
2.1
1.5
1.9
1.7
−89
−45
68
Myrcene
MMA
St
Cis-1,4/3,4 = 67.2/22.8
mm/mr/rr = 0.8/32.5/66.7
mm/mr/rr = 23.1/43.2/33.7
79
a
Polymerization conditions: Co1 = 0.10 mmol; [AlEt2Cl]/[Co] = 300; monomer = 0.02 mol; toluene, 10 mL; T = 30 °C; Determined by 1H NMR and 13C NMR.
Fig. 3. The kinetic study for polymerization of isoprene by Co1 at different
temperature.
Fig. 4. The FT-IR of polyisoprenes obtained at run 1 (Co1), run 14 (Co2), run
15 (Co3) and run 16 (Co4) in Table 2.
3

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
Fig. 5. The 1H NMR of polyisoprene obtained at run 6 in Table 2.
Fig. 6. The 13C NMR of polyisoprene obtained at run 6 in Table 2.
2.3. Synthesis and characterization of ligands and complexes
1H NMR (400 MHz, CDCl3, ppm): 7.92–7.49 (m, 4H), 7.51–7.19 (m,
16H), 7.05 (d, 4H, J = 47.5 Hz,), 6.78 (d, 2H, J = 13.9 Hz), 1.70 (s,
6H). 31P NMR (162 MHz, CDCl3, ppm): 29.71 (s). IR (KBr, cm−1): 1437,
1101, 720 (υP–Ph), 1274 (υP=O), 1192 (υC-P);
(9,9-dimethyl-9H-xanthene-4,5-diyl)
bis(diphenylphosphine
oxide) L1: To a THF (25 mL) solution of the (9,9-dimethyl-9H-xan-
thene-4,5-diyl) bis(diphenylphosphane) (1.157 g, 2.00 mmol) was
slowly added three drops (～0.15 mL) of H2O2 and the formed solution
was stirred for 6 h. The solvent was removed under a reduced pressure
and the resultant raw product was dissolved in dichloromethane for
crystallization. Finally, a light yellow solid was collected by filtration,
washed with cold methanol and dried in vacuum (1.140 g, 93.4%
yield).
Ligands L2 (yield: 91.2%) and L3 (yield: 94.5%) were prepared by
the reported methods [18–21].
L2: IR (KBr, cm−1): 1437, 1105, 770 (υP–Ph); 1414 (υN-P); 1588,
1459, 1440 (υC=N); 1318 (υC-N); 1220 (υP=O).
L3: IR (KBr, cm−1): 1437, 1103, 732 (υP–Ph); 1451 (υN-P); 1633,
1604, 1475(υ C=N); 1320 (υC-N); 1177 (υP=O).
Synthesis of cobalt complexes: To an anhydrous CoCl2 (0.139 g,
4

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
Fig. 7. The 1H NMR of polymyrcene obtained in run 19, Table 3.
Fig. 8. The 13C NMR of polymyrcene obtained in run 19, Table 3.
1.07 mmol) in THF (15 mL) was added a THF (15 mL) solution of ligand
L1 (0.611 g, 1.00 mmol) under a nitrogen atmosphere. The color of the
solution was immediately changed to dark-blue and the solution was
stirred overnight at room temperature. The solvent was removed, and
the resultant residue was washed with diethyl ether and recrystallized
in methanol with a yield of 74.3% (0.640 g).
(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine
oxide) cobalt dichloride (Co1): Yield: 74.3%, IR (KBr, cm−1): 1435,
1097, 695 (υP–Ph), 1177 (υP=O), 1162 (υC-P); UV–vis: 304 nm; Anal.
Calcd for C39H32Cl2CoO3P2: C, 63.26; H, 4.36; Cl, 9.58; O, 6.48; P, 8.37;
Co, 7.96%; found: C, 63.31; H, 4.41; Cl, 9.63; O, 6.53; P, 8.42 Co,
7.71%.
1097, 695 (υP–Ph), 1190 (υP=O), 1280 (υC-P); UV–vis: 307 nm; Anal.
Calcd for C39H32Br2CoO3P2: C, 56.48; H, 3.89; Br, 19.27; O, 5.79; P,
7.47; Co, 7.11%; found: C, 56.53; H, 3.94; Br, 19.32; O, 5.84; P, 7.52;
Co, 6.86%; EI-MS: m/z 748.34, 750.36 (M-Br81, M-Br79 +
) .
N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide)
cobalt dichloride (Co3): Yield: 70.7%, IR (KBr, cm−1): 1437, 1105,
695 (υP–Ph); 1396 (υN-P); 1588, 1459, 1438 (υC=N); 1312 (υC-N); 1196
(υP=O); UV–vis: 305 nm; Anal. Calcd for C29H25Cl2CoN3O2P2: C, 54.48;
H, 3.94; Cl, 11.09; N, 6.57; O, 5.01; P, 9.69; Co, 9.22%; found: C, 54.53;
H, 3.99; Cl, 11.14; N, 6.62; O, 5.06; P, 9.74; Co, 8.92%; EI-MS: m/z
567.06 (M-HCl-Cl)+
.
N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide)
cobalt dichloride (Co4): Yield: 71.2%, IR (KBr, cm−1): 1437, 1103,
694 (υP–Ph); 1405 (υN-P); 1609, 1577, 1444(υ C=N); 1306 (υC-N); 1175
(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine
oxide) cobalt bromide (Co2): Yield: 76.2%, IR (KBr, cm−1): 1435,
5

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
Fig. 9. The 1H NMR of poly (methyl methacrylate) obtained in run 17, Table 3.
Fig. 10. The 13C NMR of poly (methyl methacrylate) obtained in run 17, Table 3.
(υP=O); UV–vis: 304 nm; Anal. Calcd for C21H41Cl2CoN3O2P2: C, 45.09;
H, 7.39; Cl, 12.68; N, 7.51; O, 5.72; P, 11.07; Co, 10.54%; found: C,
45.14; H, 7.44; Cl, 12.73; N, 7.56; O, 5.77; P, 11.12; Co, 10.24%; EI-MS:
acidified methanol (1.0%, 10 mL; 2,6-di-tert-butyl-4-methyl phenol,
1.0%). The coagulated polymer was filtered and collected, washed with
methanol (3 × 10 mL), dried in a vacuum at room temperature and
weighted for calculating the polymer yields. The polymer was re-dis-
solved in toluene, filtered and precipitated in methanol for character-
izations. Homopolymerizations of MMA, styrene, myrcene and buta-
diene were performed at the same procedures.
m/z 487.19 (M-HCl-Cl)+
.
2.4. Procedure for polymerization
The polymerization was carried out following a standard procedure.
In a 50 mL air and moisture free glass bottle equipped with a magnetic
stir bar was charged with a suspension of cobalt complex (0.10 mmol)
in toluene (10 mL), isoprene (2 mL, 20.00 mmol) and AlEt2Cl
(3.00 mmol). The obtained solution was brought to a desired tem-
perature stirring for a given time and then terminated with HCl
3. Results and discussions
3.1. Synthesis and characterization of ligands and complexes
The bis-phopshineoxide ligands L1-L3 were preapred via oxidation
6

D. Yang, et al.
InorganicaChimicaActa496(2019)119046
Co4 have the expected structures as depicted in Scheme 1.
The structural of Co1 was further confirmed by X-ray analyses. The
CCDC deposition number is 1922947. The geometry complex Co1 can
be described as a psuedo tetrahedron in which the cobalt center is sa-
turated by two netural oxygen donors and two cationic chlorines
(Fig. 2). Nevertheless, the O3 lies out of the coordinative atmosphere
indicated from the prolonged bonding of 3.815 Å. The Co-O co-
ordinative bondings are 1.9819(19) Å and 1.983(2) Å, comparable to
those found in PN3 ligand supported complexes, [20.21] but sig-
nificantly shorter than those of Co1-Cl2 2.2438(8) Å, Co1-Cl1 2.2524(8)
Å. The two planes formed by O(1)-Co(1)-O(2) and Cl(2)-Co(1)-Cl(1)
forms a dihedral angle of 88.34°. The bond angles of O1-Co1-O2, O1-
Co1-Cl2, O2-Co1-Cl2, O1-Co1-Cl1, O2-Co1-Cl1 and Cl2-Co1-Cl1 are
calculated to be 109.12(6)°, 117.38(6)°, 116.14(6)°, 102.84(6)°,
99.02(8)° and 111.91(3)°, respectively, all close to the standard value of
109.28°.
Fig. 11. The 1H NMR of polystyrene obtained in run 20, Table 3.
3.2. Polymerization of isoprene
of phosphines in the presence of H2O2. The complexes Co1-Co4 were
synthesized by refluxing cobalt salt with the corresponding ligands in
Scheme 1 and isolated as a green to brown solid with moderate to good
yields. The resultant complexes were characterized by FT-IR, elemantal
analyses and massspectral. The accomplishments of Co-O=P co-
ordination in the Co1 and Co2 were confirmed by the red shift and
reduced intensity of P=O vibration with respect to the corresponding
free ligands [21]. The absorption of C=N (pyridinyl) was red-shifted to
1438 cm−1 and 1444 cm−1 for Co3 and Co4 with respect to the pristine
ligands 1440 cm−1, and 1475 cm−1, respectively, and the intensities
were reduced accordingly. The absorption of P=O moiety at
1220 cm−1 and 1177 cm−1 (υP=O) were also reduced to the 1196 cm−1
and 1175 cm−1 confirmed the Co-O interaction occurred. The ele-
mental analyses of all complexes are in well accordance with the
theratical values. Additionally, mass spectrum results shown the Co2
The cobalt catalysts Co1-Co4 were examined in polymerization of
isoprene by varying the catalyst loading, type and feeding of catalyst as
well as the polymerization temperature. The polymerization parameters
and results were compiled at Table 1. AlEt2Cl was found to be most
efficient cocatalyst, and the formed catalyst converted 99% of monomer
to polyisoprene (run 1, Table 2). The resultant polymer typically has
59.1% of cis-1,4 and 40.9% of 3,4 units without any trace of trans-1,4
units, and the moderate cis-1,4 selectivity is common in cobalt cata-
lyzed polymerization [4,9,21,22]. AlEt3 (run 2, Table 2), MAO (run 3,
Table 2) or AliBu3 (run 4, Table 2) activated Co1 did not give any
polymeric product, which are quite inconsistent with most cobalt cat-
alyst where MAO or combination of alkyl aluminum and trace water are
known as the appropriate cocatalyst [31–37]. The formed of low oxi-
dation state bimetallic Co(I)L-Al active species are presumed to be fa-
cilitated and stabilized by stronger lewis acid alkyl aluminum chloride
[6]. Temperature variation at 0 °C (run 3, Table 2), 30 °C (run 1,
Table 2), 50 °C (run 6, Table 2), 80 °C (run 7, Table 2) did not sig-
nificantly change the activity and the selectivity, demonstrating the
generated active species are stable against temperature variation. Ki-
netic study shown higher temperature has prone to fast initiation and
also chain propagation, the polymerization was stagnant within
were ionized in the form of [M-Br]+ and Co3 and Co4 in [M-Cl-HCl]+
,
agreeing with the PN3 ligand supported cobalt complexes (see the mass
spectral in Fig. 1) [21]. Elimination of HCl for the Co3 and Co4 were
attempted in the presence of 1.0 equiv. of KOtBu in THF according to
our work [30], and the reaction was indicated from colour changing
from brow to yellow. The resultant complexes have the same mass
spectral as those of Co3 and Co4. These results indicate the Co3 and
Fig. 12. The 13C NMR of polystyrene obtained in run 20, Table 3.
7

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InorganicaChimicaActa496(2019)119046
18–20 min at 30, 50 and 80 °C (cal. 90% yield), but more time is needed
at 0 °C for the comparable polymer recovery (Fig. 3). The total
monomer conversion reached 99% and the moderate cis-1,4 selectivity
was maintained regardless the monomer feeding (run 1, 8, 9, 10 and 11,
Table 2). Of note is that the polymer was recovered at 99% of monomer
feeding even at [IP]/[Co] = 8000, thus the activity was calculated to be
1088 kg (polymer)/mol(Co)·h), which is the most active system ever
reported [4]. Varying the cocatalyst feeding from [Al]/[Co] = 100, 300
to 500 slightly changed the activity, and the comparable selectivity was
observed. For example, polymerization at [Al]/[Co] = 100 and 500 has
a slightly reduced activity than that of [Al]/[Co] = 300, this may be
related to the reduced number of active species in both cases of less or
more cocatalyst feeding [31]. The comparable activity and selectivity
were obtained in the case of Co2, virtually the same active species
generated. The effects of ligand structure on the polymerization per-
formances are significant. For example, polymerization time 240 mins
and 1440 mins are required for Co3 and Co4 for the same polymer
yield. These may be relevant to the coordinative saturated active specie
which makes monomer difficult to access. The polymers obtained from
the Co1-Co4 have the similar microstructure according to the FT-IR
(Fig. 4). The 1H NMR and 13C NMR of selected polymer from run 6 in
Table 2 were depicted in Figs. 5 and 6, respectively, where direct cis-
1,4-alt-3,4 linkage appearing from 36.67 ppm to 25.85 ppm in 13C NMR
[38–40]. The molecular weight distributions of polymers were calcu-
lated to be in the range of 1.6–2.5, a typical single site nature. And, the
glass transitional temperatures of selected polymers are from −38.6 °C
to −42.3 °C, between the values of each homopolymer. These results
verify the resultant polymer are true copolymer containing cis-1,4 and
3,4 units, instead of the mixtures of each homopolymer.
cobalt complex or AlEt2Cl alone did not give any polymeric products for
all monomers.
4. Conclusions
In combination with AlEt2Cl, the polymerization activities of Co1
and Co2 towards isoprene are remarkably higher than those of Co3 and
Co4. Whereas, cocatalyts AlEt3, Al(iBu)3 and MAO are unable to acti-
vate the complex to generate the active species. The formed catalyst
displayed cis-1,4 and 3,4 selectivities which are not significantly af-
fected by the type of catalysts and polymerization conditions. However,
myrcene and butadiene are far less active than isoprene under the same
polymerization conditions using Co1/AlEt2Cl. Moderately polymeriza-
tion activities towards methyl methacrylate and styrene were also
found. Thus, dual polymerization catalyses for conjugated dienes as
well as olefins have been realized by the current catalyst.
Acknowledgements
This work is supported by the National Natural Science Foundation
of China (Grant No. 21304050), and the open funding of Key
Laboratory of Urban Environment and Health, Institute of Urban
Environment, Chinese Academy of Sciences
(Grant No.
NUEORS201807). This work is also sponsored by K. C. Wong Magna
Fund in Ningbo University.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2019.119046.
3.3. Polymerization of conjugated dienes and olefins
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Cobalt catalysts are efficient for conjugated dienes polymerization,
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