Biphenyl-Bridged 6-(1-Aryliminoethyl)-2-iminopyridylcobalt complexes: Synthesis, characterization, and ethylene polymerization behavior

Article abstract of DOI:10.1021/om4010884

A series of biphenyl-bridged 6-(1-aryliminoethyl)-2-iminopyridine derivatives reacted with cobalt dichloride in dichloromethane/ethanol to afford the corresponding binuclear cobalt complexes. The cobalt complexes were characterized by FT-IR spectroscopy and elemental analysis, and the structure of a representative complex was confirmed by single-crystal X-ray diffraction. Upon activation with either MAO or MMAO, these cobalt complexes performed with high activities of up to 1.2 × 10⁷ g (mol of Co)^-1 h^-1 in ethylene polymerization, which represents one of the most active cobalt-based catalytic systems in ethylene reactivity. These biphenyl-bridged bis(imino)pyridylcobalt precatalysts exhibited higher activities than did their mononuclear bis(imino)pyridylcobalt precatalyst counterparts, and more importantly, the binuclear precatalysts revealed a better thermal stability and longer lifetimes. The polyethylenes obtained were characterized by GPC, DSC, and high-temperature NMR spectroscopy and mostly possessed unimodal and highly linear features.

Full text of DOI:10.1021/om4010884

Article
pubs.acs.org/Organometallics
Biphenyl-Bridged 6‑(1-Aryliminoethyl)-2-iminopyridylcobalt
Complexes: Synthesis, Characterization, and Ethylene Polymerization
Behavior
Qifeng Xing,† Tong Zhao,† Shizhen Du,† Wenhong Yang,† Tongling Liang,† Carl Redshaw,*,‡
and Wen-Hua Sun*,†
†Key Laboratory of Engineering Plastics, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, People’s Republic of China
‡Department of Chemistry, University of Hull, Hull HU6 7RX, U.K.
S
* Supporting Information
ABSTRACT: A series of biphenyl-bridged 6-(1-aryliminoeth-
yl)-2-iminopyridine derivatives reacted with cobalt dichloride in
dichloromethane/ethanol to afford the corresponding binuclear
cobalt complexes. The cobalt complexes were characterized by
FT-IR spectroscopy and elemental analysis, and the structure of
a representative complex was confirmed by single-crystal X-ray
diffraction. Upon activation with either MAO or MMAO, these
cobalt complexes performed with high activities of up to 1.2 ×
107 g (mol of Co)−1 h−1 in ethylene polymerization, which represents one of the most active cobalt-based catalytic systems in
ethylene reactivity. These biphenyl-bridged bis(imino)pyridylcobalt precatalysts exhibited higher activities than did their
mononuclear bis(imino)pyridylcobalt precatalyst counterparts, and more importantly, the binuclear precatalysts revealed a better
thermal stability and longer lifetimes. The polyethylenes obtained were characterized by GPC, DSC, and high-temperature NMR
spectroscopy and mostly possessed unimodal and highly linear features.
Scheme 1. Biphenyl-Bridged 2,6-Bis(imino)pyridylmetal
Complex Precatalysts (M = Fe,14 Co (This Work))
INTRODUCTION
■
2,6-Bis(imino)pyridylmetal (iron or cobalt) complexes were
found to act as highly active precatalysts in ethylene
polymerization in the 1990s.1 Subsequently, researchers from
both academia and industry have extensively explored various
ligand sets through modification of 2,6-bis(imino)pyridine
derivatives2 and designing new heterocyclic compounds,3
including examples of nonsymmetrical 2,6-bis(imino)-
pyridines,4 2-benzimidazolyl-6-iminopyridines,5 6-(quinoxalin-
3-yl)-2-iminopyridines,6 2-imino-1,10-phenanthrolines,7 2-(2-
benzimidazolyl)-1,10-phenanthrolines,7 2-(benzoxazolyl)-1,10-
phenanthrolines,8 N-((pyridin-2-yl)methylene)-8-aminoquino-
lines,9 and 2,8-bis (imino)quinolines.10 In addition, multi-
nuclear complex precatalysts are now attracting attention,11 and
progress in this area has been discussed in a recent review
article.12
Binuclear complexes and their catalytic behavior in ethylene
reactivity have also been an important topic in our research
group.13 Recently, the biphenyl-bridged 2,6-bis(imino)-
pyridyliron complexes were revisited and were shown to
exhibit high ethylene polymerization activity with enhanced
thermal stability (Scheme 1). However, all attempts to elucidate
their molecular structures were unsuccessful due to poor-
quality crystals. Now in subsequent work, the cobalt analogues
have been synthesized and single crystals suitable for X-ray
diffraction studies have been obtained. Moreover, the cobalt
analogues performed with high activity in ethylene polymer-
ization, and this is one of the most active cobalt precatalyst
systems reported. Herein, the synthesis and characterization of
the cobalt complexes are reported and the ethylene polymer-
ization behavior is discussed.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Organic
Compounds and Their Cobalt Complexes. Using the
method reported for our previous iron work,14 the N,N′-bis(1-
(6-(1-(arylimino)ethyl)pyridin-2-yl)ethylidene)benzidines
(L1−L11) were reacted with cobalt(II) dichloride in a
dichloromethane/ethanol mixture to afford the corresponding
binuclear cobalt complexes in good yield (Co1−Co11; Scheme
Received: November 11, 2013
Published: March 3, 2014
© 2014 American Chemical Society
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2). All cobalt complexes were consistent with their elemental
analyses, while effective coordination to cobalt was reflected in
bond C−N lengths of compound L5 are N(2)−C(20) =
1.432(5) Å and N(3)−C(10) = 1.427(6) Å, and the C−N
lengths of complex Co4 are N(2)−C(18) = 1.444(9) Å and
N(3)−C(10) = 1.448(9) Å. These indicate the effective
coordination with the cobalt center; meanwhile, the electron
donation to cobalt resulted in weak bonding between the
nitrogen and its nearby carbons and is illustrated by longer
bond lengths. In addition, there are significant differences in the
dihedral angles between nearby aryl planes: the coplanar nature
of the two benzene rings within the tetraalkylbenzidine motif in
organic L514 distorted into a dihedral angle of 33.39° within
complex Co4; the pyridyl plane is almost perpendicular to the
phenyl plane of the benzidine with a dihedral angle of ca.
88.77° in L5 versus an angle of ca. 72.50° within complex Co4,.
Meanwhile, the dihedral angle between the pyridyl and phenyl
groups of the aniline is observed at ca. 86.71° in L5 versus ca.
72.79° for complex Co4. Within complex Co4, there are no
direct bonding interactions between the two cobalt atoms, and
there is no conjugated interaction between the two phenyl
planes within the tetraalkylbenzidine motif.
Scheme 2. Synthetic Procedure for the Cobalt Complexes
Catalytic Behavior toward Ethylene Polymerization.
Cocatalysts such as methylaluminoxane (MAO) or modified
methylaluminoxane (MMAO) have been commonly employed
to activate cobalt complex precatalysts,5 and this was confirmed
to be true in the current work. The complex Co3 was used to
optimize catalytic parameters in the presence of MAO, and the
results are given in Table 2.
With the reaction temperature fixed at 40 °C, variation of the
molar ratio Al/Co was investigated (entries 1−4, Table 2), and
the best activity was obtained with Al/Co ratio of 1000/1
(entry 2, Table 2). The GPC data generally revealed a wider
polydispersity for the polyethylene formed (Figure 2);
moreover, the polyethylene obtained at the Al/Co ratio
1000/1 showed a higher molecular weight. The higher the
Al/Co ratios used (entries 2−4, Table 2), the lower the
molecular weight of the obtained polyethylene; this is ascribed
to more chain transfer occurring from the cobalt center onto
the aluminum center with more cocatalyst.3,15 In regard to the
mechanism of different terminations, commonly β elimination
at the metal species produces polyethylene with a terminal vinyl
group, while terminal alkyl (−Me) groups would be achieved
through termination after chain transfer from metal species
onto the aluminum center. Given this, NMR measurements
were employed for their characteristics.
the FT-IR spectra, where the CN stretching vibration bands
appeared in the range 1620−1632 cm−1 for cobalt complexes
versus 1639−1650 cm−1 for the free organic compounds. In
addition, the identities of the cobalt complexes were also
verified by MALDI-TOF measurements.
X-ray Crystallographic Studies. Single crystals of
complex Co4 were grown from a mixture of dichloromethane
and methanol (∼2/1 v/v). The molecular structure of Co4 was
confirmed by single-crystal X-ray diffraction, and the structure
is shown in Figure 1; selected bond lengths and angles are
collected in Table 1.
The polyethylene samples (entries 1 and 4, Table 2) were
tested (1H NMR) at 135 °C in C6D4Cl2, as shown in Figures 3
and 4. According to Figure 3 (quintet at 5.4 ppm and triplet at
4.6 ppm, which has intensity comparable to that of the singlet
at 1.0 ppm), the obtained polyethylenes (entry 1, Table 2) are
highly linear with a terminal vinylene (−CHCH2). However,
according to Figure 4, there are more terminal methyl groups
confirmed for the polyethylene obtained with weak signals for
the vinyl group and a strong signal for the methyl group,
indicating more chain transfer at high ratios of aluminum. In
general, most obtained polyethylenes with narrow polydisper-
sity showed highly linear character.
Figure 1. ORTEP drawing of Co4. Thermal ellipsoids are shown at
the 30% probability level. Hydrogen atoms have been omitted for
clarity.
With the Al/Co molar ratio fixed at 1000/1, the influence of
the reaction temperature was investigated over the range 40−
70 °C (entries 2 and 5−7, Table 2), which indicated an
optimum temperature of ca. 50 °C (entry 5, Table 2). The
higher the reaction temperature employed (entries 5−7, Table
2), the lower the molecular weights of the polyethylene
obtained (Figure 5). This is consistent with increased chain
In comparison to the previously determined structure of the
compound L5, which contains similar CN bond lengths such
as N(2)−C(6) = 1.267(5) Å and N(3)−C(8) = 1.268(6) Å,14
the corresponding CN lengths within the complex Co4
revealed one shorter bond N(2)−C(6) = 1.256(10) Å and one
longer bond N(3)−C(8) = 1.291(8) Å; meanwhile, the single-
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for Co4
Bond Lengths (Å)
N(2)−C(6)
N(2)−(18)
N(3)−C(8)
N(3)−C(10)
N(1)−C(1)
1.256(10)
1.444(9)
1.291(8)
1.448(9)
1.361(9)
N(1)−C(5)
Co(1)−N(1)
Co(1)−N(3)
Co(1)−N(2)
1.380(9)
2.038(6)
2.185(5)
2.188(6)
Bond Angles (deg)
C(1)−N(1)−C(5)
C(6)−N(2)−C(18)
C(8)−N(3)−C(10)
N(1)−Co(1)−Cl(1)
120.6(6)
121.4(7)
122.4(5)
155.12(16)
N(3)−Co(1)−Cl(2)
N(2)−Co(1)−Cl(2)
Cl(1)−Co(1)−Cl(2)
103.87(14)
98.81(16)
111.77(8)
a
Table 2. Ethylene Polymerization with Cobalt Complexes
b
c
c
d
entry
precat.
cocat.
Al/Co
T (°C)
t (min)
amt of PE (g)
activity
103Mw
Mw/Mn
Tm (°C)
1
2
Co3
Co3
Co3
Co3
Co3
Co3
Co3
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
MAO
MAO
500
40
40
40
40
50
60
70
50
50
50
50
50
50
30
40
50
60
70
50
50
50
30
30
30
30
30
30
30
15
30
45
60
30
30
30
30
30
30
30
30
30
30
7.5
9.3
7.6
6.6
10
5.0
6.2
5.1
4.4
6.7
4.3
2.8
12
26.2
46.8
28.0
19.9
120.6
32.8
10.0
1.60
1.80
2.00
1.90
1.30
1.70
1.40
1.10
1.70
1.80
2.00
2.30
1.80
1.60
20.2
23.3
18.3
15.3
27.3
10.2
4.20
2.10
2.20
2.50
2.60
2.80
2.40
2.00
2.50
2.60
2.60
2.90
3.00
2.60
125.7
130.8
128.8
126.0
131.4
129.6
128.6
120.9
124.4
121.6
122.1
104.6
122.6
117.0
116.5
115.8
115.1
112.9
121.1
114.6
115.5
1000
1500
2000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1500
1500
1500
1500
1500
500
3
MAO
4
MAO
5
MAO
6
MAO
6.5
4.2
9.0
11
7
MAO
8
MAO
9
MAO
7.3
5.9
4.7
0.3
4.1
3.8
4.5
3.6
2.0
0.9
1.1
6.0
3.1
10
11
MAO
13
MAO
14
e
12
MAO
0.5
6.6
5.7
6.7
5.4
3.0
1.4
1.6
9.0
4.6
f
13
MAO
14
15
16
17
18
19
20
21
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
1000
2000
2.30
a
b
c
General conditions: 1.5 μmol of Co; 100 mL of toluene; 10 atm of ethylene. In units of 106 g of PE (mol of Co)−1 h−1. Determined by GPC.
Determined by DSC. 1 atm of ethylene. 5 atm of ethylene.
d
e
f
Figure 2. GPC curves of polyethylenes obtained with different of Al/
Co ratios (entries 1−4, Table 2).
1
Figure 3. H NMR spectrum of the polyethylene obtained at the Al/
Co ratio 500/1 (entry 1 of Table 2).
transfer occurring at higher temperature.3,8,15 In comparison
with the result obtained at 50 °C (entry 5, Table 2), the lower
activities (entries 6 and 7, Table 2) at 60 and 70 °C were
probably caused by the partial decomposition of the active
species and lower concentration of ethylene in the solution at
higher temperature.16 A narrower polydispersity of the obtained
polyethylene was achieved at higher temperature, indicating
that single-site active species (entries 6 and 7, Table 2) were
operating. A common shortcoming of late-transition-metal
complex precatalysts is loss of activity at elevated reaction
temperatures;3 however, the current binuclear cobalt precata-
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production is promising, given the lack of byproducts such as
oligomers.17
In comparison with Co1/MAO, the Co1/MMAO system
generally exhibited relatively lower activities, although similar
molecular weights and polydispersity were observed for the
polyethylene produced. Therefore, all cobalt complex precata-
lysts were investigated with MAO at the Al/Co molar ratio
1000/1 at 50 °C for 30 min; the results are given in Table 3.
Table 3. Ethylene Polymerization with Complexes Con/
a
MAO
b
c
c
d
entry
precat.
yield (g) activity
103Mw
Mw/Mn
Tm (°C)
1
Figure 4. H NMR spectrum of the polyethylene obtained at the Al/
1
Co1
Co2
Co3
Co4
Co5
Co6
Co7
Co8
Co9
Co10
Co11
11.0
10.2
10.0
10.5
5.9
7.3
6.8
6.7
7.0
3.9
1.3
7.7
4.5
2.1
5.5
0.9
1.8
7.9
2.0
5.3
27.3
4.0
3.3
3.0
2.3
1.9
2.6
4.1
1.5
122.4
126.9
131.1
124.6
129.0
131.7
130.0
132.4
133.4
124.2
132.9
Co ratio 2000/1 (entry 4 of Table 2).
2
3
120.6
4.7
4
5
7.6
6
2.0
20.9
10.8
15.0
25.5
4.0
7
11.6
6.8
8
9
3.2
10
11
8.3
1.4
11.1
a
General conditions: 1.5 μmol of Co; 100 mL of toluene for 10 atm of
ethylene and MAO for the cocatalyst at 50 °C with an Al/Co ratio of
b
1000/1; time 30 min. In units of 106 g of PE (mol of Co)−1 h−1.
c
d
Determined by GPC. Determined by DSC.
Figure 5. GPC traces of polyethylenes produced by cobalt complexes
at different reaction temperatures.
According to Table 3, with the substituent R3 fixed, the
activities of the precatalysts decreased with a bulkier substituent
R1 within the Co1−Co9 family (entries 1−9, Table 3),
illustrating that a bulkier ortho substituent hindered coordina-
tion of ethylene to the active species.4 With regard to the
additional substituent R2, positive influences were achieved by
the precatalysts Co10 and Co11 in comparison with the
analogues Co1 and Co6 (entry 1 versus entry 10, entry 6 versus
entry 11, Table 3), which is ascribed to the better solubility of
the complexes bearing more alkyl substituents. In general, the
obtained polyethylenes have higher molecular weights for
complexes bearing bulkier substituents (entries 1−3, entries 4−
6, entries 7−9, Table 3), indicating that the active species were
protected by these bulkier substituents. In all cases, the
binuclear cobalt complexes exhibited higher activity and better
thermal stability than did the mononuclear analogues1,4b and
related binuclear analogues.17 In comparison to their iron
analogues,13 the cobalt complex precatalysts exhibited better
lifetimes and produced polyethylene of lower molecular weight
and narrower polydispersity. The melting points of the
resultant polyethylenes were generally higher than 122 °C,
consistent with their highly linear feature. To verify the
linearity, the 13C NMR spectrum of the polyethylene (entry 3,
Table 3) was recorded in dichlorobenzene and revealed a single
peak (Figure 6).
lysts exhibited better thermal stability and higher activities in
comparison to their mononuclear analogues1 and other
tridentate cobalt complex precatalysts.5,8,9
Employing the optimized parameters, namely an Al/Co
molar ratio of 1000/1 at 50 °C, the Co1/MAO system was
extensively investigated to understand its lifetime (entries 8−
11, Table 2). Within 15 min, the activity was as high as 107 g
(mol of Co)−1 h−1, which is one of the highest activities
observed for cobalt complex precatalysts. Prolonging the
reaction period to 15, 30, 45, and 60 min resulted in the
activities gradually falling, with the activity reaching 4.7 × 106 g
(mol of Co)−1 h−1 over 60 min. The binuclear system has a
shorter induction period, and the active species are maintained
over a long period. Another important parameter is ethylene
pressure, and it was found that the catalytic activity increased
with increasing ethylene pressure (entries 9, 12, and 13, Table
2). The higher the ethylene pressure used, the better the
activity observed with the catalytic reaction. Indeed, when the
ethylene pressure was increased to 10 atm, the activity observed
was more than twice that observed at 5 atm.
Using the cocatalyst methylaluminoxane (MMAO), the
catalytic behavior of complex Co1 was explored with various
parameters (entries 14−21, Table 2). Similar catalytic
tendencies were observed on variation of the reaction
temperature and the Al/Co molar ratio. Moreover, it is worth
emphasizing that there were no oligomers detected by GC from
the reaction solutions involving all such polymerization
procedures. Therefore, the current model precatalysts showed
higher activity and better thermal stability than did those of the
analogous systems, and the application for polyethylene
CONCLUSION
■
Binuclear biphenyl-bridged 6-(1-aryliminoethyl)-2-iminopyri-
dine cobalt chloride complexes were synthesized and fully
characterized, including by single-crystal X-ray diffraction for a
representative complex. Upon activation with MAO or MMAO,
all of the binuclear cobalt complex precatalysts exhibited high
activities toward ethylene polymerization; MAO was a better
initiator than MMAO. The current complex precatalysts
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(MAO, 1.46 M solution in toluene) and modified methylaluminoxane
(MMAO, 1.93 M in heptane) were purchased from Akzo Nobel Corp.
High-purity ethylene was purchased from Beijing Yansan Petrochem-
ical Co. and used as received. Other reagents were purchased from
Aldrich, Acros, or local suppliers. NMR spectra were recorded on a
Bruker DMX 400 MHz instrument at ambient temperature using TMS
as an internal standard; IR spectra were recorded on a Perkin-Elmer
System 2000 FT-IR spectrometer. Elemental analysis was carried out
using a Flash EA 1112 microanalyzer. Molecular weights and
molecular weight distribution (MWD) of polyethylene were
determined with a PL-GPC220 instrument at 150 °C, with 1,2,4-
trichlorobenzene as the solvent. The melting points of polyethylene
were measured from the second scanning run on a Perkin-Elmer TA-
Q2000 differential scanning calorimetry (DSC) analyzer under a
nitrogen atmosphere. In the procedure, a sample of about 4.0 mg was
heated to 150 °C at a rate of 20 °C/min and kept for 2 min at 150 °C
to remove the thermal history and then cooled at a rate of 20 °C/min
to −40 °C. 13C NMR spectra of the polyethylene were recorded on a
Bruker DMX 300 MHz instrument at 135 °C in deuterated 1,2-
dichlorobenzene with TMS as an internal standard. The biphenyl-
bridged 6-(1-aryliminoethyl)-2-iminopyridine derivatives were pre-
pared according to our previous procedure.13
Figure 6. 13C NMR spectrum of the polyethylene produced by Co3
(entry 3, Table 3).
performed with longer lifetimes and better thermal stability
than did their related monometallic complexes1 and other
binuclear analogues.16 The resultant polyethylene generally
revealed high linearity. Under optimized conditions, the
polyethylene obtained possessed narrow polydispersity, indicat-
ing the single-site feature of the active species. Further
explorations for higher activities and finely controlled poly-
ethylenes are still in progress in order to match industrial
requirements.
According to the procedure for synthesizing their iron analogues,13
the binuclear cobalt complexes were prepared. A typical procedure for
complex Co1 is illustrated as follows: N,N′-bis(1-(3-(1-(2,6-
dimethylphenylimino)ethyl)pyridin-2-yl)ethylidene)-
tetramethylbenzidine (L1; 0.074 g, 0.10 mmol) and CoCl2 (0.026 g,
0.20 mmol) were combined in CH2Cl2 (5 mL) and EtOH (5 mL) and
stirred for 8 h at room temperature. The precipitate was collected by
filtration, washed with diethyl ether (3 × 5 mL), and then dried under
vacuum to afford Co1 as a yellow solid (0.090 g, 72.0% yield). FT-IR
(cm−1): 2970 (w), 1626 (ν(CN), m), 1522 (w), 1457 (s), 1436 (s),
1403 (s), 1269 (m), 1248 (m), 1214 (w), 852 (m), 810 (m), 762 (m),
733 (w). Anal. Calcd for C50H52N6Co2Cl4 (996): N, 8.43; C, 60.25; H,
5.26. Found: N, 8.36; C, 59.92; H, 5.71. MS (MALDI-TOF, m/z):
996.16, found m/z 984.1 [M − CoCl4 + CCA]+, 735.8 [M −
Co2Cl4]+.
Co2. In a similar manner, the reaction of 0.10 mmol of L2 (0.079 g)
and CoCl2 (0.026 g, 0.20 mmol) afforded complex Co2 as a yellow
solid (0.10 g, 95.1% yield). FT-IR (cm−1): 2960 (m), 1630 (ν(CN),
m), 1587 (s), 1448 (m), 1368 (s), 1321 (w), 1263 (s), 1208 (s), 1097
(m), 870 (m), 818 (s), 791 (w), 742 (m), 695 (m). Anal. Calcd for
C56H60N6Co2Cl4 (1052): N, 7.98; C, 61.61; H, 5.74. Found: N, 8.06;
C, 61.64; H, 5.72. MS (MALDI-TOF, m/z): 1052.23, found m/z
1040.1 [M − CoCl4 + CCA]+, 852.0 [M − CoCl4]+.
Co3. Complex Co3 was collected as a yellow solid (0.120 g, 91.0%
yield) from the reaction of 0.10 mmol of L3 (0.084 g) and 0.20 mmol
of CoCl2. FT-IR (cm−1): 2958 (m), 2019 (w), 1636 (ν(CN), m),
1584 (s), 1465 (m), 1367 (s), 1322 (w), 1263 (s), 1211 (s), 1101 (m),
892 (w), 807 (s), 762 (m), 739 (m), 697 (w). Anal. Calcd for
C58H68N6Co2Cl4 (1108): N, 7.58; C, 62.82; H, 6.18. Found: N, 7.59;
C, 62.89; H, 6.10. MS (MALDI-TOF, m/z): 1108.29, found: m/z
1096.2 [M − CoCl4 + CCA]+, 943.1 [M − CoCl3]+, 908.1 [M −
CoCl4]+, 850.1 [M − Co2Cl4]+.
Co4. The reaction of 0.10 mmol of L4 (0.079 g) and 0.20 mmol of
CoCl2 gave complex Co4 as a yellow solid (0.091 g, 86.5% yield). FT-
IR (cm−1): 2968 (w), 1621 (ν(CN), m), 1584 (s), 1464 (m), 1369
(s), 1320 (w), 1259 (s), 1210 (s), 1099 (m), 1056 (w), 865 (m), 806
(s), 765 (m) Anal. Calcd for C54H60N6Co2Cl4 (1052): N, 7.58; C,
62.82; H, 6.18. Found: N, 7.46; C, 62.69; H, 6.45. MS (MALDI-TOF,
m/z): 1052.23, found m/z 1040.2 [M − CoCl4 + CCA]+, 887.0 [M −
CoCl3]+, 852.0 [M − CoCl4]+.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations involving air- and
moisture-sensitive compounds were performed using standard Schlenk
techniques under a nitrogen atmosphere. Toluene was refluxed over
sodium and distilled under nitrogen prior to use. Methylaluminoxane
Table 4. Crystal Data and Structure Refinement Details for
Co4
empirical formula
formula wt
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
C54H60N6Co2Cl4
1052.74
293(2)
0.71073
monoclinic
C2/c
38.653(8)
9.879(2)
16.927(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
110.59(3)
90
γ (deg)
V (Å3)
6051(2)
Z
4
Dcalcd (g cm−3
)
1.156
μ (mm−1
F(000)
)
0.761
2192
cryst size (mm)
θ range (°C)
limiting indices
0.35 × 0.18 × 0.06
1.13−25.00
−45 ≤ h ≤ 42
−11 ≤ k ≤ 11
−17 ≤ l ≤ 20
17644
no. of rflns collected
no. of unique rflns
R(int)
5284
0.1288
no. of params
335
Co5. The reaction of 0.10 mmol of L5 (0.084 g) and 2 equiv of
CoCl2 afforded complex Co5 as a yellow solid (0.076 g, 63.0% yield).
FT-IR (cm−1): 2963 (m), 2163 (w), 1623 (ν(CN), m), 1586 (s),
1447 (s), 1368 (s), 1260 (s), 1207 (m), 1105 (w), 1026 (w), 868 (m),
807 (m), 765 (m). Anal. Calcd for C58H68N6Co2Cl4 (1108): N, 7.58;
C, 62.82; H, 6.18. Found: N, 7.26; C, 63.20; H, 6.10. MS (MALDI-
TOF, m/z): 1108.29, found: m/z 1096.2 [M − CoCl4 + CCA]+, 908.2
[M − CoCl4]+.
completeness to θ
goodness of fit on F2
final R indices (I > 2∑(I))
99.1%
1.072
R1 = 0.1032
wR2 = 0.2742
R1 = 0.1424
wR2 = 0.3057
0.808 and −0.763
R indices (all data)
largest diff peak and hole (e Å−3
)
1386
dx.doi.org/10.1021/om4010884 | Organometallics 2014, 33, 1382−1388

Organometallics
Article
Co6. The stoichiometric reaction of 0.10 mmol of L6 with CoCl2
formed complex Co6 as a yellow solid (0.072 g, 62.0% yield). FT-IR
(cm−1): 2962 (m), 1621 (ν(CN), m), 1585 (s), 1449 (s), 1370 (s),
1322 (w), 1248 (s), 1208 (m), 1104 (w), 868 (m), 814 (m), 794 (s),
764 (m). Anal. Calcd for C62H76N6Co2Cl4 (1164): N, 7.21; C, 63.92;
H, 6.58. Found: N, 6.96; C, 64.29; H, 6.51. MS (MALDI-TOF, m/z):
1164.35, found m/z 1152.3 [M − CoCl4 + CCA]+, 999.2 [M −
CoCl3]+, 964.2 [M − CoCl4]+, 906.2 [M − Co2Cl4]+.
Co7. Complex Co7 was isolated as a yellow solid (0.070 g, 53.0%
yield) in the reaction of 0.10 mmol of L7 (0.084 g) and 0.20 mmol of
CoCl2. FT-IR (cm−1): 2958 (m), 1636 (ν(CN), m), 1569 (s), 1460
(s), 1362 (s), 1321 (w), 1244 (s), 1200 (m), 1117 (m), 868 (m), 822
(s), 760 (m). Anal. Calcd for C58H68N6Co2Cl4 (1108): N, 7.58; C,
62.82; H, 6.18. Found: N, 7.57; C, 62.98; H, 6.05. MS (MALDI-TOF,
m/z): 1108.29, found m/z 1096.3 [M − CoCl4 + CCA]+, 908.1 [M −
CoCl4]+.
Co8. A 0.065 g amount of complex Co8 as a yellow solid (56.5%
yield) was obtained from the reaction of 0.10 mmol of L8 (0.090 g)
and 0.20 mmol of CoCl2. FT-IR (cm−1): 2962 (s), 2019 (w), 1621
(ν(CN), m), 1585 (s), 1461 (s), 1368 (s), 1320 (m), 1262 (s),
1206 (m), 1104 (m), 870 (m), 806 (m). Anal. Calcd for
C62H76N6Co2Cl4 (1164): N, 7.21; C, 63.92; H, 6.58. Found: N,
6.99; C, 64.14; H, 6.60. MS (MALDI-TOF, m/z): 1164.35, found m/z
1152.3 [M − CoCl4 + CCA]+, 999.2 [M − CoCl3]+, 964.2 [M −
CoCl4]+, 906.2 [M − Co2Cl4]+.
Co9. Complex Co9 as a yellow solid (0.080 g, 55.0% yield) was
precipitated from the reaction of 0.10 mmol of L9 (0.096 g) and 0.20
mmol of CoCl2. FT-IR (cm−1): 2960 (s), 2160 (w), 2019 (w), 1621
(ν(CN), m), 1585 (s), 1462 (s), 1368 (s), 1321 (m), 1262 (s),
1207 (m), 1103 (w), 1024 (w), 940 (w), 869 (m), 802 (s). Anal.
Calcd for C66H84N6Co2Cl4 (1220): N, 6.88; C, 64.92; H, 6.93. Found:
N, 6.74; C, 65.26; H, 6.89. MS (MALDI-TOF, m/z): 1220.41, found
m/z 1208.4 [M − CoCl3 + CCA]+, 1055.2 [M − CoCl3]+, 1020.3 [M
− CoCl4]+, 962.2 [M − Co2Cl4]+.
the required amount of cocatalyst (MAO or MMAO), the residual
toluene were added by syringe successively. The reaction mixture was
rapidly stirred for the desired time under the corresponding pressure
of ethylene through the entire experiment. The reaction was
terminated and analyzed using the same procedure as above for
ethylene polymerization.
X-ray Crystallographic Studies. Complex Co4 (20 mg) was
dissolved in a ∼2/1 v/v mixture of dichloromethane and methanol (3
mL/1.5 mL), and the solution was kept in a test tube that was
wrapped with a PE membrane. On slow evaporation, brown needlelike
crystals suitable for single-crystal X-ray diffraction were obtained. The
X-ray diffraction study was conducted on a Rigaku RAXIS Rapid IP
diffractometer with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) at 293(2) K. Cell parameters were obtained by global
refinement of the positions of all collected reflections. Intensities were
corrected for Lorentz and polarization effects and empirical
absorption. The structure was solved by direct methods and refined
by full-matrix least-squares on F2. All hydrogen atoms were placed in
calculated positions. Using the SHELXL-97 package,18 structure
solution and refinement were performed. Details of the X-ray structure
determination and refinement are provided in Table 4.
ASSOCIATED CONTENT
* Supporting Information
A CIF file giving crystallographic data for Co4. This material is
■
S
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*C.R.: tel, +44 1482 465219; fax, +44 1482 466410; e-mail, c.
redshaw@hull.ac.uk.
■
*W.-H.S.: tel, +86-10-62557955; fax, +86-10-62618239; e-mail,
whsun@iccas.ac.cn.
Notes
Co10. Complex Co10 was formed (0.077 g, 75.2% yield) in the
reaction of 0.10 mmol of L10 (0.076 g) and 0.20 mmol of CoCl2. FT-
IR (cm−1): 2962 (m), 2030 (w), 1645 (ν(CN), w), 1579 (m), 1455
(m), 1366 (s), 1322 (w), 1256 (m), 1208 (s), 1121 (w), 857 (m), 815
(m), 740 (w), 698 (w). Anal. Calcd for C52H56N6Co2Cl4 (1024): N,
8.20; C, 60.95; H, 5.51. Found: N, 7.81; C, 61.26; H, 5.47. MS
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by NSFC Nos. 21374123 and
U1362204. The RSC is thanked for the awarded of a travel
grant (to C.R.).
(MALDI-TOF, m/z): 1024.20, found m/z 1012.3 [M − CoCl4
+
CCA]+, 859.1 [M − CoCl3]+, 824.1 [M − CoCl4]+, 766.1 [M −
Co2Cl4]+.
Co11. Compound L11 (0.092 g, 0.10 mmol) reacted stoichio-
metrically with CoCl2 to afford complex 0.097 g of Co11 as a yellow
solid (82.0% yield). FT-IR (cm−1): 2963 (s), 2017 (w), 1624 (ν(C
N), w), 1584 (m), 1451 (s), 1367 (s), 1323 (w), 1262 (s), 1205 (m),
1104 (w), 868 (m), 798 (m), 764 (m), 739 (w). Anal. Calcd for
C64H80N6Co2Cl4 (1192): N, 7.04; C, 64.43; H, 6.76. Found: N, 6.59;
C, 64.26; H, 6.86. MS (MALDI-TOF, m/z): 1192.38, found m/z
1180.6 [M − CoCl4 + CCA]+, 1027.4 [M − CoCl3]+, 992.4 [M −
CoCl4]+, 934.4 [M − Co2Cl4]+.
General Procedure for Ethylene Polymerization. Ethylene
Polymerization at Ambient Pressure. The precatalyst was dissolved in
toluene using standard Schlenk techniques, and the reaction solution
was stirred with a magnetic stir bar under an ethylene atmosphere (1
atm) with a steam bath for controlling the desired temperature.
Finally, the required amount of cocatalyst (MAO) was added by a
syringe. After the reaction was carried out for the required period, a
small amount of the reaction solution was collected and the reaction
was immediately terminated by the addition of 10% aqueous hydrogen
chloride. The organic layer was analyzed by gas chromatography (GC)
for monitoring the oligomers formed; the precipitated polymer was
collected, washed with water and ethanol, and finally dried.
Ethylene Polymerization at Elevated Pressure (10 atm). A 300 mL
stainless steel autoclave, equipped with a mechanical stirrer and a
temperature controller, was employed for the reaction. First, 50 mL of
toluene (freshly distilled) was injected into the clave, which was full of
ethylene. When the temperature required was reached, another 30 mL
of toluene which dissolved the complex (3.0 μmol of metal) before,
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