2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-aryliminoethyl] pyridyl cobalt dichlorides: Synthesis, characterization and ethylene polymerization behavior

Article abstract of DOI:10.1016/j.jorganchem.2012.05.020

A series of 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1- aryliminoethyl]pyridyl cobalt(II) dichloride complexes (Co1-Co5) were prepared and characterized by elemental and spectroscopic analysis. The molecular structures of the representative cobalt complexes Co1 and Co4 were determined by single-crystal X-ray diffraction, and revealed a pseudo-square-pyramidal geometry around each cobalt atom. Upon activation with either MMAO or MAO, all cobalt pre-catalysts exhibited high activities toward ethylene polymerization and produced polyethylene products with narrow molecular distributions (1.98-3.61) and molecular weights in the range 72.3-665 kg/mol; the latter is higher than any other molecular weight of polyethylenes obtained by previous cobalt pre-catalysts. Reaction parameters and the nature of the ligands were investigated for their influence on the resultant catalytic activities and properties of the polyethylene products obtained.

Full text of DOI:10.1016/j.jorganchem.2012.05.020

Journal of Organometallic Chemistry 713 (2012) 209e216
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-aryliminoethyl]pyridyl
cobalt dichlorides: Synthesis, characterization and ethylene polymerization
behavior
,
,
b
c
,
a,b,
Fan He a b, Weizhen Zhao b, Xiao-Ping Cao a , Tongling Liang , Carl Redshaw , Wen-Hua Sun
*
*
*
a State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
b Key Laboratory of Engineering Plastics, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
c Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-aryliminoethyl]pyridyl cobalt(II)
Received 15 April 2012
Received in revised form
15 May 2012
dichloride complexes (Co1eCo5) were prepared and characterized by elemental and spectroscopic analysis.
The molecular structures of the representative cobalt complexes Co1 and Co4 were determined by single-
crystal X-ray diffraction, and revealed a pseudo-square-pyramidal geometry around each cobalt atom. Upon
activation with either MMAO or MAO, all cobalt pre-catalysts exhibited high activities toward ethylene
polymerization and produced polyethylene products with narrow molecular distributions (1.98e3.61) and
molecular weights in the range 72.3e665 kg/mol; the latter is higher than any other molecular weight of
polyethylenes obtained by previous cobalt pre-catalysts. Reaction parameters and the nature of the ligands
were investigated for their influence on the resultant catalytic activities and properties of the polyethylene
products obtained.
Accepted 20 May 2012
Keywords:
Unsymmetrical bis(imino)pyridine
Cobalt pre-catalyst
Ethylene polymerization
Linear polyethylene
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
6-iminopyridines [43e45], 2-benzoxazolyl-6-iminopyridines [46,47],
2-quinoxalinyl-6-iminopyridines [48], N-((pyridin-2-yl)methy-
The discovery of bis(imino)pyridyl metal (Fe(II) and Co(II))
dichloride complexes as highly active pre-catalysts in ethylene
polymerization and oligomerization was pivotal in initiating the
resurrection of late-transition metal based polyolefin science
[1,2]. Subsequently, the variation of substituents on the bis(imino)
pyridine framework has been extensively explored with a view to
improving the catalytic performance of their metal complexes
[3e11]. Moreover, a number of studies have targeted the active
species and the mechanism of such Fe/Co-catalyzed
polymerization reactions [12e27]. Driven by the hypothesis that
N^N^N tridentate ligands would provide suitable iron(II) and
cobalt(II)-based pre-catalysts [28e35], numerous heterocyclic
compounds, which act as tridentate ligands, have been developed
in our group. These include 2-imino-1,10-phenanthrolines
[36e40], 2-(benzoxazolyl)-1,10-phenanthrolines [41], 2-(2-
benzimidazolyl)-1,10-phenanthrolines [42], 2-benzimidazolyl-
lene)-8-aminoquinolines [49], 8-(1H-benzimidazol-2-yl)quino-
lines [50], as well as the 2-methyl-2,4-bis(6-iminopyridin-2-yl)-
1H-1,5-benzodiazepines for bimetallic pre-catalysts [51,52]. In
addition, several types of iron and cobalt complexes bearing
bidentate ligands showed promise in ethylene polymerization or
oligomerization [53e55]. The analogous iron pre-catalysts
generally performed with higher activities and produced more
polyethylene than did their cobalt analogs. However, in the case
of pre-catalysts bearing 2-benzoxazolyl-6-iminopyridines, the
cobalt pre-catalysts were shown to exhibit an interesting
temperature-switch feature for ethylene reactivity, producing 1-
butene below 40 ꢀC and favoring ethylene polymerization at
elevated temperatures [46]; the iron analogs mainly gave olig-
omers and small amounts of waxes [47]. Moreover, this finding
was contrary to the common thinking that elevated reaction
temperatures result in lower activities and produce lower
molecular weight polyethylene products. As a consequence, the
room temperature inert system comprising the 2,8-bis(1-
aryliminoethyl)quinolylmetal halides was reinvestigated and
found to exhibit good activity for ethylene polymerization at
elevated reaction temperatures without observing any trace of
* Corresponding authors. Tel.: þ86 10 62557955; fax: þ86 10 62618239.
E-mail addresses: caoxplzu@163.com (X.-P. Cao), Carl.Redshaw@uea.ac.uk
(C. Redshaw), whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.020

210
F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
N
R1
N
R1
CoCl2
EtOH
N
N
N
N
DBCPh
DBCPh
Co
R1
R2
R1
R2
Cl Cl
L1 - L5
Ph NH2 Ph
Co1 - Co5
Ph
Ph
L1 L2 L3 L4 L5
Co1 Co2 Co3 Co4 Co5
Cl
R1
R2
2,6-dibenzhydryl-4-chloro
benzenamine(DBCPh-NH2)
Me Et i-Pr Me
Et
Me Me
H
H
H
Scheme 1. Synthesis of the complexes Co1eCo5.
oligomers [56]. Such catalytic behavior was also observed for
iron and cobalt complexes bearing 8-benzimidazolyl-quinolines,
with the cobalt pre-catalysts exhibiting ethylene oligomerization
at relatively low ethylene pressure and low reaction tempera-
ture, but ethylene polymerization at high reaction temperature
under 30 atm ethylene pressure [54]. Contrastingly, the iron
pre-catalysts showed good activity for ethylene polymerization
at elevated reaction temperatures only [53]. Inspired by these
results, we pondered again over the metal complexes bearing
dibenzhydryl-substituted bis(imino)pyridines, which were inert
for ethylene reactivity at ambient temperature. Surprisingly, the
iron(II) dichlorides complexes ligated by 2-[1-(2,6-dibenzhydryl-
Fig. 2. Molecular structure of Co4; thermal ellipsoids are shown at 30% probability.
Hydrogen atoms have been omitted for clarity.
polyethylenes. Indeed, there are no reports of polyethylene products
by cobalt pre-catalysts with molecular weight higher than a half
million. To explore the scope and potential application of cobalt pre-
catalysts in ethylene polymerization, more cobalt pre-catalysts need
to be designed and investigated for their catalytic behavior with
a view to obtaining polyethylenes with different molecular weights
and distributions. Following the extensive work on iron pre-catal-
ysts bearing 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-
[1-(arylimino)ethyl]pyridines, which showed the highest activity
within all reported iron pre-catalysts for ethylene polymerization [61],
the synthesis, characterization, and catalytic behavior of 2-[1-(2,6-
dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-(arylimino)ethyl]pyr-
idylcobalt(II) chloride complexes are investigated and reported herein.
4-methylphenylimino)ethyl]-6-[1-(arylimino)
ethyl]pyridines
[57] and 2-[1-(2,4-dibenzhydryl-6-methylphenylimino)ethyl]-6-
[1-(arylimino)ethyl]pyridines [58] showed high activities toward
ethylene polymerization at elevated temperatures, producing
polyethylene products with tunable polydispersity index (PDI).
Moreover, the cobalt pre-catalysts bearing the same ligands
were also highly active, producing polyethylenes at the elevated
temperature [59,60].
Besides exhibiting slightly lower catalytic activities than their iron
analogs, cobalt pre-catalysts often produced oligomers or low-Mw-
Table 1
Selected bond lengths (Å) and angles (ꢀ) for complexes Co1 and Co4.
Co1
Co4
2.217(4)
Bond lengths (Å)
Co1eN1
2.234(4)
Co1eN2
Co1eN3
Co1eCl1
Co1eCl2
N1eC2
N1eC10
N2eC3
N2eC7
2.067(4)
2.190(4)
2.3054(14)
2.2522(17)
1.248(7)
1.425(6)
1.359(6)
1.324(6)
1.266(7)
1.415(7)
2.065(4)
2.183(4)
2.3140(15)
2.2596(17)
1.274(7)
1.424(6)
1.335(7)
1.318(7)
1.284(7)
1.425(7)
N3eC8
N3eC42
Bond angles (ꢀ)
N2eCo1eN3
N2eCo1eN1
N3eCo1eN1
N2eCo1eCl2
N3eCo1eCl2
N1eCo1eCl2
N2eCo1eCl1
N3eCo1eCl1
N1eCo1eCl1
Cl2eCo1eCl1
73.97(17)
73.24(16)
141.50(16)
157.69(12)
106.33(13)
96.66(12)
92.46(12)
95.40(12)
105.60(11)
109.57(6)
74.25(18)
73.47(18)
141.53(16)
159.59(14)
107.00(13)
96.38(12)
91.31(13)
93.94(12)
107.14(11)
108.76(6)
Fig. 1. Molecular structure of Co1; thermal ellipsoids are shown at 30% probability.
Hydrogen atoms have been omitted for clarity.

F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
211
Table 2
Ethylene polymerization with Co4/MMAOa.
Activityb
Mw /
Mw/Mn
c
c
d
Tm /ꢀC
Run
T/ꢀC
t/min
Al/Co
Yield/g
104
g molꢁ1
1
2
3
4
5
6
7
8
20
20
20
20
30
40
50
30
30
30
30
30
30
30
30
30
30
30
30
5
10
20
45
60
500
1000
1500
2000
1500
1500
1500
1500
1500
1500
1500
1500
4.08
4.53
5.11
4.36
6.84
4.13
1.72
3.20
4.79
5.95
7.98
8.82
5.44
6.04
6.81
5.81
9.12
5.51
2.29
25.6
19.2
11.9
7.09
5.88
47.7
47.7
46.8
46.5
34.0
17.6
8.31
28.9
32.2
33.6
35.8
37.4
3.13
3.08
2.79
2.73
3.04
2.87
2.47
3.24
2.93
3.21
3.20
3.11
136.1
135.7
135.3
135.4
135.1
133.9
133.6
134.1
133.8
133.9
133.9
134.6
9
10
11
12
a
General conditions: 1.5 mmol of Co; 10 atm ethylene; 100 mL toluene.
b
c
106 g molꢁ1(Co) hꢁ1
Determined by GPC.
Determined by DSC.
.
d
2. Results and discussion
selected bond lengths and angles tabulated in Table 1. With Cl1
occupying the apical position and N1, N2, N3 and Cl2 forming the
square plane, both of the complexes are penta-coordinate with
a pseudo-square-pyramidal geometry at cobalt, which is similar to
that observed for their iron analogs [61] and numerous iron and
cobalt analog complexes bearing 2-[1-(2,6-dibenzhydryl-4-
methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines [57,59]
or 2-[1-(2,4-dibenzhydryl-6-methylphenylimino)ethyl]-6-[1-(ary-
limino)ethyl] pyridines [58,60]. The cobalt center is pushed out of
the chelate plane due to the associated sterics, namely 0.522 Å out
of the chelated plane (N1eN2eN3) in Co1 and 0.534 Å in Co4. For
both complexes, the Co1eN2 bond length is drastically shorter than
the lengths for Co1eN1 and Co1eN3, revealing the stronger
interaction between the Co atom and the pyridyl N atom than that
between the Co atom and the imino N atoms, consistent with the
double bond character of N1eC2 and N3eC8.
2.1. Preparation and characterization of the cobalt complexes
A
series of 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)
ethyl]-6-[1-(arylimino)ethyl]pyridines (L1eL5) were prepared
following the previously reported procedures [61]. As shown in
Scheme 1, the stoichiometric reaction of CoCl2 with L1eL5 in
ethanol at room temperature produced brown powders with the
general formula LCoCl2 (Co1eCo5) in good yields. Similar to their
iron analogs, all cobalt complexes were characterized by
elemental analysis and FT-IR spectra. Compared with the FT-IR
spectra of the free ligands (1636e1643 cmꢁ1), the stretching
vibrations for vC¼N in these cobalt complexes (1582e1586 cmꢁ1
)
shifted to lower wave-numbers and the intensities were
decreased due to coordination effects. The molecular structures of
the complexes Co1 and Co4 were confirmed by single-crystal X-
ray diffraction studies.
2.3. Catalytic behavior toward ethylene polymerization
2.2. X-ray crystallographic studies
Various alkylaluminum reagents were screened to find the most
suitable co-catalyst, and both modified methylaluminoxane
(MMAO) as well as methylaluminoxane (MAO) were found to be
Single-crystals of Co1 and Co4 were grown by diffusing n-
hexane into their respective dichloromethane solutions. The
molecular structures are shown in Figs. 1 and 2, respectively, with
Fig. 3. GPC curves of PEs obtained by Co4/MMAO with various Al/Co molar ratios
(Runs 1e4 in Table 2).
Fig. 4. GPC curves of PEs obtained by Co4/MMAO with various temperatures (Runs 3
and 5e7 in Table 2).

212
F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
temperature was investigated at the fixed molar ratio Al/Co of
1500 (Runs 3 and 5e7 in Table 2). The catalytic activity initially
increased to 9.12 ꢂ 106 g molꢁ1(Co) hꢁ1 at 30 ꢀC (Run 5 in Table 2)
and then decreased, probably the result of the deactivation of Co4/
MMAO and lower ethylene solubility in toluene at higher
temperature [65]. Furthermore, higher temperatures can also
accelerate chain transfer to aluminum, which led to the formation
of low-Mw-PEs [66].
As shown in Table 2 and Fig. 4, the molecular weights of the
polyethylenes reduced significantly from 468 kg/mol to 83.1 kg/
mol. The influence of the reaction time was studied by quenching
the catalytic system Co4/MMAO under optimum conditions over
different reaction periods (Runs 5, 8e12 in Table 2). On extending
the reaction time from 5 to 60 min, the catalytic activity decreased
from 2.56 ꢂ 107 g molꢁ1(Co) hꢁ1 to 5.88 ꢂ 106 g molꢁ1(Co) hꢁ1
,
indicative of little or no induction time during the catalytic process
[67]. The molecular weights of the polyethylenes increased from
289 to 374 kg/mol on extending the reaction time (Fig. 5) due to the
reduction of the available amount of MMAO, which in-turn resulted
in a deceleration of chain transfer to aluminum [3].
Fig. 5. GPC curves of PEs obtained by Co4/MMAO with various times (Runs 5 and 8e12
In order to investigate the influence of the nature of ligands on
the catalytic behavior, pre-catalysts with different aryl substitu-
ents (Co1eCo5) were employed for ethylene polymerization
under the optimum catalytic conditions found for Co4/MMAO
(10 atm ethylene, Al/Co ¼ 1500, 30 ꢀC); results are tabulated in
Table 3. The observed activity order for these pre-catalysts was
found to be Co1 > Co2 > Co3, which was governed by both the
electronic and steric influences of the ligands. The electronic
influence has been simulated by computational studies, which
indicated that the higher net charge of the metal center enhanced
the catalytic activity of the late-transition metal complex [68]. The
electron-donating properties of the ortho-alkyl substituents (R1)
of the arylimino followed the order Me (Co1) < Et (Co2) < i-Pr
(Co3), which is consistent with their performance in ethylene
polymerization. In addition, for the unsymmetrical ligands, the
presence of a bulky benzhydryl substituent on one side, further
increasing the steric hindrance (Me (Co1) < Et (Co2) < i-Pr (Co3)),
which is detrimental in terms of insertion of ethylene and thereby
catalytic activity [1e5]. The introduction of a methyl in the para-
position of the phenyl ring increased the catalytic activities
(Co4 > Co1 and Co5 > Co2), probably due to enhanced solubility
properties. Thus, the highest catalytic activity for these pre-
catalysts was obtained for the system Co4/MMAO (Run 4 in
Table 3), which is higher than that observed for the iron analog
(2.46 ꢂ 106 g molꢁ1(Fe) hꢁ1) [61].
in Table 2).
effective reagents for generating highly active cobalt complexes for
ethylene polymerization.
2.3.1. Ethylene polymerization with Co1eCo5/MMAO
The catalytic system Co4/MMAO was typically employed for
determining the optimum catalytic conditions by varying the
molar ratio of Al/Co, the reaction temperature and the reaction
time; results are tabulated in Table 2. By raising the molar
ratio of Al/Co from 500 to 2000 (Runs 1e4 in Table 2) under
10 atm pressure of ethylene, this catalytic system exhibited the
highest activity at an optimum ratio of 1500, namely,
6.81 ꢂ 106 g molꢁ1(Co) hꢁ1 (Run 3 in Table 2). Compared with the
polyethylene obtained using the analogous iron pre-catalysts, the
PDIs of the polyethylene herein were relatively narrow, with
values of about 3.00. The resultant PEs for the lower molar
ratios of Al/Co (less than 1500) exhibited bimodal features, whilst
those for higher molar ratios approached a more unimodal
distribution (Fig. 3). Meanwhile, the molecular weights of the
polyethylenes decreased slightly on enhancing the amounts of
MMAO used, indicative of chain transfer from cobalt to aluminum
as the primary termination process [62]. The precipitation of the
polyethylene disturbed the equilibrium between the cobalt and
aluminum species, and so the GPC curves at lower molar
ratios of Al/Co exhibited two distributions. Such phenomena
were observed for their iron analogs [61] as well as for
lanthanocene-based systems [63,64]. The influence of the reaction
Table 3
Ethylene polymerization with Co1eCo5/MMAO.a
Activityb
Mw /
Mw/Mn
c
c
d
Tm /ꢀC
Run
Cat.
Yield/g
104
g molꢁ1
1
2
3
4
5
Co1
Co2
Co3
Co4
Co5
5.62
5.31
4.93
6.84
5.96
7.47
7.08
6.57
9.12
7.95
17.0
22.5
66.5
34.0
27.2
2.90
2.30
2.09
3.04
2.15
134.4
135.3
135.8
135.1
135.4
a
General conditions: 1.5
mmol of Co; 10 atm ethylene; 100 mL toluene; Al/
Co ¼ 1500; 30 ꢀC; 30 min.
b
106 g molꢁ1(Co)$hꢁ1
Determined by GPC.
Determined by DSC.
.
c
d
Fig. 6. GPC curves of PEs obtained by Co1eCo5/MMAO (Runs 1e5 in Table 3).

F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
213
Fig. 7. 13C NMR spectrum of the polyethylene prepared with catalyst Co4/MMAO (Run 7 in Table 2).
As shown in Fig. 6, the order of molecular weights
(Co3 > Co2 > Co1) was reversed to that observed for the catalytic
activity, suggesting that an increase in the steric bulk at the ortho-
(Runs 1e4 in Table 4) and reaction temperatures (Runs 2, 5 and 6 in
Table 4). The highest activity was obtained at 20 ꢀC when a molar
ratio of Al/Co of 1000 (Run 2 in Table 4). Subsequently, all pre-
catalysts (Co1eCo5) were employed for ethylene polymerization
under these optimum conditions (Runs 2 and 7e10 in Table 4). The
variation of catalytic activities and molecular weights exhibited
similar trends to those observed when MMAO was employed as the
co-catalyst, but the molecular weight of the resultant polyethylene
was somewhat higher. Despite variations of the reaction condi-
tions, the PDI values of the polyethylenes were still relatively
narrow and were constant in the range between 1.98 and 3.61,
consistent with the presence of single-site species. On comparison
with the cobalt complexes bearing 2-[1-(2,4-dibenzhydryl-6-
position could result in a reduction of the rate of b-H transfer and
give polyethylene of higher molecular weight. We note that the
molecular weight of the polyethylene (eg. 665 kg/mol; Run 3 in
Table 3) is the highest obtained to-date using bis(imino)pyr-
idylcobalt(II) dichlorides pre-catalysts (Fig. 7) (Fig. 8).
2.3.2. Ethylene polymerization with Co1eCo5/MAO
Using MAO instead of MMAO as the co-catalyst, the title pre-
catalysts performed with relatively lower activities toward the
polymerization of ethylene; the results are given in Table 4. Using
a similar procedure to that for Co1eCo5/MMAO, the catalytic
system Co4/MAO was initially investigated to determine the
optimum catalytic conditions with various molar ratios of Al/Co
methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines
[60],
although the catalytic activities were lower, the two ortho-benz-
hydryls on the imino phenyl ring can further block the axial sites at
Fig. 8. 13C NMR spectrum of the polyethylene prepared with catalyst Co4/MAO (Run 6 in Table 4).

214
F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
Table 4
Ethylene polymerization with Co1eCo5/MAO.a
Activityb
Mwc/104 g molꢁ1
Mw/Mn
c
d
Tm /ꢀC
Run
Cat.
T/ꢀC
Al/Co
Yield/g
1
2
3
4
5
6
7
8
9
10
Co4
Co4
Co4
Co4
Co4
Co4
Co1
Co2
Co3
Co5
20
20
20
20
30
40
20
20
20
20
500
1000
1500
2000
1000
1000
1000
1000
1000
1000
4.67
5.98
5.30
5.06
4.98
3.85
5.40
5.08
4.49
5.47
6.23
7.97
7.07
6.75
6.64
5.13
7.20
6.78
5.99
7.29
52.3
47.9
47.2
44.5
26.5
7.23
35.7
39.5
64.4
58.8
2.27
2.54
2.66
3.04
3.61
2.90
2.21
1.98
2.13
2.41
135.3
135.6
134.7
134.7
134.6
134.4
134.9
134.9
134.6
135.1
a
General conditions: 1.5 mmol of Co; 10 atm ethylene; 100 mL toluene; 30 min.
b
c
106 g molꢁ1(Co) hꢁ1
Determined by GPC.
Determined by DSC.
.
d
the cobalt center and restrict the rate of
b
-H transfer, with the
characterized by 13C NMR spectroscopy at 110 ꢀC in deuterated 1,2-
dichlorobenzene and were shown to be highly linear in nature.
result that polyethylene with higher molecular weight was
obtained by using the title cobalt complexes [1e5]. On comparison
with the cobalt analog bearing 2-[1-(2,6-dibenzhydryl-4-
3. Conclusions
methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines
[59],
the current complex pre-catalysts showed similar catalytic activi-
ties, and the obtained polyethylenes had similar molecular weight
polydispersity. However, the polyethylenes obtained in the current
system showed much higher molecular weights than those in
reference [59], indicating the influence that the substituents of the
ligands present had on the produced polymer. Such phenomenon
highlights the importance of moderate fine tuning ligands and the
influence this can have on catalytic behavior.
A series of cobalt(II) complexes (Co1eCo5) bearing 2-[1-(2,6-
dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-(arylimino)ethyl]
pyridine ligands (L1eL5) were synthesized and fully characterized.
On treatment with MMAO or MAO as the co-catalyst, the pre-
catalysts (Co1eCo5) exhibited high activities and produced highly
linear polyethylene with high molecular weights (72.3e665 kg/
mol) and narrow PDIs (1.98e3.61). The molecular weights of
resultant polyethylenes could be controlled in the range
72.3e665 kg/mol by modifying the nature of ligands or by varying
reaction parameters (co-catalyst type, molar ratio of Al/Co, reaction
temperature and time).
In addition, representative polyethylene samples (Figure 7 for
Run 7 in Table 2 and Figure 8 for Run 6 in Table 4) were
4. Experimental
Table 5
Crystal data and structure refinement for Co1 and Co4.
4.1. General considerations
Co1
Co4
Empirical formula
Fw
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C49H42Cl3CoN3
838.14
173(2)
0.71073
Monoclinic
Cc
23.912(5)
14.466(3)
15.958(3)
90
125.27(3)
90
4506.9(16)
4
1.235
C50H44Cl3CoN3
852.16
173(2)
0.71073
Monoclinic
Cc
23.972(5)
14.687(3)
16.030(3)
90
126.67(3)
90
4526.9(16)
4
1.250
All manipulations of air and moisture-sensitive compounds
were performed under a nitrogen atmosphere using standard
Schlenk techniques. Toluene was refluxed over sodium-
benzophenone and distilled under nitrogen prior to use. Methyl-
aluminoxane (MAO, a 1.46 M solution in toluene) and modified
methylaluminoxane (MMAO, a 1.93 M solution in heptane, 3A)
were purchased from Akzo Nobel Corp. 2-[1-(2,6-dibenzhydryl-4-
b (Å)
c (Å)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
chlorophenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines
were
prepared following the previously reported procedures [61]. Other
reagents were purchased from Acros Chemicals or local suppliers.
1H and 13C NMR spectra of compounds were recorded on Bruker
DMX 400 MHz instrument at ambient temperature using TMS as an
internal standard. IR spectra were recorded on a PerkineElmer
System 2000 FT-IR spectrometer. Elemental analysis was carried
out using a Flash EA 1112 micro analyzer. Molecular weights and
polydispersity index of polyethylenes were determined by a PL-
GPC220 at 150 ꢀC, with 1,2,4-trichlorobenzene as the solvent. DSC
trace and melting points of polyethylenes were obtained from the
second scanning run on PerkineElmer DSC-7 at a heating rate of
10 ꢀC/min. 13C NMR spectra of PE samples were recorded on
a Bruker DMX-300 MHz instrument at 110 ꢀC in deuterated 1,2-
dichlorobenzene with TMS as an internal standard.
V (Å3)
Z
Dcalcd. (g cmꢁ3
)
m
(mmꢁ1
)
0.594
1740
0.592
1772
F(000)
Cryst size (mm)
range (ꢀ)
0.32 ꢂ 0.30 ꢂ 0.24
1.75e27.48
ꢁ21 ꢃ h ꢃ 31
ꢁ18 ꢃ k ꢃ 12
ꢁ20 ꢃ l ꢃ 20
10,376
6413 (0.0343)
99.1
None
0.37 ꢂ 0.16 ꢂ 0.11
1.74e27.48
ꢁ30 ꢃ h ꢃ 31
ꢁ18 ꢃ k ꢃ 19
ꢁ20 ꢃ l ꢃ 18
19,043
9307 (0.0469)
99.3
None
q
Limiting indices
No. of rflns collected
No. unique rflns [R(int)]
Completeness to
Abs corr.
q (%)
Data/restraints/parameters
6413/2/505
1.040
9307/2/514
1.031
Goodness of fit on F2
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 ¼ 0.0578
wR2 ¼ 0.1512
R1 ¼ 0.0619
wR2 ¼ 0.1549
0.609 and ꢁ0.404
R1 ¼ 0.0727
wR2 ¼ 0.1786
R1 ¼ 0.0783
wR2 ¼ 0.1844
0.564 and ꢁ0.447
4.2. Synthesis and characterization of cobalt complexes (Co1eCo5)
General procedure: to a solution of the ligand in ethanol
(10 mL), the equivalent CoCl2 was added and a brown suspension
Largest diff peak and hole (e Åꢁ3
)

F. He et al. / Journal of Organometallic Chemistry 713 (2012) 209e216
215
was observed. The reaction mixture was stirred at room tempera-
ture for 8 h. Then the precipitate was filtered and washed with
diethyl ether (3 ꢂ 5 mL). The pure complex was obtained as
collected by filtration, washed with ethanol and water, and dried in
a vacuum at 60 ꢀC until of constant weight.
a
brown powder after dried in-vacuo overnight. All of the
Acknowledgment
complexes were prepared in high yield following this procedure.
2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-(2,6-
dimethylphenylimino)ethyl]pyridylcobalt(II) dichloride (Co1) was
prepared in 86% yield. FT-IR (KBr, cmꢁ1): 3059, 2966, 2169, 2030,
1584 (nC¼N), 1495, 1431, 1261, 1192, 1078, 1027, 808, 772, 744, 698.
Anal. Calcd for C49H42Cl3CoN3 (838.17): C, 69.90; H, 5.40; N, 4.93.
Found: C, 70.22; H, 5.05; N, 5.01.
2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-(2,6-
diethylphenylimino)ethyl]pyridylcobalt(II) dichloride (Co2) was
prepared in 90% yield. FT-IR (KBr, cmꢁ1): 3061, 2965, 2166, 2032,
1582 (nC¼N), 1495, 1443, 1262, 1190, 1079, 1028, 809, 768, 741, 700.
Anal. Calcd for C51H46Cl3CoN3 (866.22): C, 70.48; H, 5.73; N, 4.72.
Found: C, 70.71; H, 5.35; N, 4.85.
This work is supported by MOST 863 program No.
2009AA034601. CR thanks the EPSRC for an Overseas Travel Grant.
Appendix A. Supplementary material
CCDC 855922 and 855923 contain the supplementary crystal-
lographic data for the complexes Co1 and Co4. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version.
2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-(2,6-
diisopropylphenylimino)ethyl]pyridylcobalt(II) dichloride (Co3)
was prepared in 80% yield. FT-IR (KBr, cmꢁ1): 3060, 2959, 2164,
2030, 1584 (nC¼N), 1494, 1439, 1263, 1194, 1110, 1027, 806, 767, 744,
699. Anal. Calcd for C53H50Cl3CoN3 (894.28): C, 70.87; H, 5.79; N,
4.49. Found: C, 71.18; H, 5.64; N, 4.70.
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