2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl] pyridylcobalt(ii) dichlorides: Synthesis, characterization and ethylene polymerization behavior

Article abstract of DOI:10.1039/c1dt11062d

A series of unsymmetrical 2,6-bis(imino)pyridylcobalt(ii) complexes, {2-[2,6-(CH(C₆H₅)₂)₂-4-Me-C ₆H₂NC(CH₃)]-6-(2,6-R¹ ₂-4-R²-C₆H₂NCCH₃)-C ₅H₃NCoCl₂} where R¹ = Me, Et or ⁱPr, R² = H or Me, together with the new symmetrical complex 2,6-[2,6-(CH(C₆H₅)₂) ₂-4-Me-C₆H₂NC(CH₃)] ₂-C₅H₃NCoCl₂, were synthesized. All of the compounds were fully characterized by ¹H NMR and IR spectroscopy, as well as by elemental analysis. The molecular structures of Co1 (R¹ = Me, R² = H) and Co5 (R¹ = Et, R ² = Me) were further confirmed by single crystal X-ray diffraction, which indicated that the cobalt centres were penta-coordinate with a pseudo square-pyramidal geometry. Upon treatment with MAO or MMAO, these cobalt pre-catalysts exhibited higher activities than any previously reported cobalt pre-catalysts, with values as high as 4.64 × 10⁶ g PE mol ^-1(Co) h^-1 for ethylene polymerization at atmospheric pressure. The polyethylenes obtained were of high molecular weight and narrow molecular weight distribution. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt11062d

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PAPER
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]-
pyridylcobalt(II) dichlorides: Synthesis, characterization and ethylene
polymerization behavior†
Jiangang Yu,a Wei Huang,a Lin Wang,a Carl Redshaw*b and Wen-Hua Sun*a,c
Received 7th June 2011, Accepted 2nd August 2011
DOI: 10.1039/c1dt11062d
A series of unsymmetrical 2,6-bis(imino)pyridylcobalt(II) complexes, {2-[2,6-(CH(C6H5)2)2-4-Me–
C6H2N C(CH3)]-6-(2,6-R1 -4-R2–C6H2N CCH3)–C5H3NCoCl2} where R1 = Me, Et or iPr, R2 = H or
2
Me, together with the new symmetrical complex 2,6-[2,6-(CH(C6H5)2)2-4-Me–C6H2N C(CH3)]2–
C5H3NCoCl2, were synthesized. All of the compounds were fully characterized by 1H NMR and IR
spectroscopy, as well as by elemental analysis. The molecular structures of Co1 (R1 = Me, R2 = H) and
Co5 (R1 = Et, R2 = Me) were further confirmed by single crystal X-ray diffraction, which indicated that
the cobalt centres were penta-coordinate with a pseudo square-pyramidal geometry. Upon treatment
with MAO or MMAO, these cobalt pre-catalysts exhibited higher activities than any previously
reported cobalt pre-catalysts, with values as high as 4.64 ¥ 106 g PE mol-1(Co) h-1 for ethylene
polymerization at atmospheric pressure. The polyethylenes obtained were of high molecular weight and
narrow molecular weight distribution.
polymerization.2a,4e,6 Typically, the aryl substituents at the 2- and
6-positions have been functionalized to increase the steric demand
1. Introduction
The advent of bis(imino)pyridine metal (M = Fe2+ or Co2+) com-
plexes possessing high activity toward ethylene polymerization
was a milestone for late transition metal complexes as catalysts
for ethylene oligomerization and polymerization.1 Recent review
articles have indicated the growth in research papers based on
bis(imino)pyridylmetal (Fe2+ or Co2+) chlorides.2 The literature
highlights how the nature of the ligands used can significantly
affect the catalytic behavior of these complexes towards ethylene
oligomerization/polymerization.2,3 Facile modifications were
achieved through simply changing the substituents at the N-
bound aryl groups2e,4 or the substituents5 linked to the imino
groups of the bis(imino)pyridine framework. This allowed for
the control of the steric and electronic influences of the ligands,
thereby allowing for the manipulation of the catalytic activities of
such metal complexes and indeed the properties of the resulting
products formed during the ethylene oligomerization and/or
of the whole ligand set;6a,7 less bulky aryls tend to afford oligomeric
materials.4b,4e,f,8 One of the most successful modifications reported
by us is the 2-[1-(2,6-dibenzhydryl-4-methyl-phenylimino)ethyl]-6-
[1-(arylimino)ethyl]pyridyliron(II) chlorides,9 which showed high
catalytic activity of up to the value of 2.2 ¥ 107 g PE mol-1(Fe) h-1
for ethylene polymerization and possessed encouraging thermal
behavior with the optimum activity obtained at 80 ◦C in the
presence of MMAO, or at 60 ◦C in the presence of MAO.
However, the ever-present bimodal or multimodal features of the
polyethylenes, which are caused by the presence of multi-species of
active sites, led to relatively wide molecular weight distributions.
On the other hand, cobalt complexes can show differing catalytic
behavior during ethylene reactivity. For example, cobalt(II)
dichlorides bearing 2,8-bis(imino)quinolines produced higher
molecular weight polyethylene than their iron(II) counterparts did,
which had almost the same activity.10 2-(1H-2-Benzimidazolyl)-6-
(1-(arylimino)ethyl)pyridylcobalt(II) dichloride only gave butenes
and hexenes, while the iron counterparts afforded oligomers with
a wide molecular weight distribution.11 2-Oxazoline/benzoxazole-
1,10-phenanthrolinyl cobalt dichlorides were found to exhibit
lower activities, but with higher selectivity for a-olefins compared
to the iron complexes.12 Inspired by these ‘special’ properties
of cobaltous complexes, we embarked on the investigation of a
series of 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(arylimino)ethyl]pyridylcobalt(II) dichloride. Interestingly, these
newly synthesized cobalt complexes showed the highest activity
of all reported cobalt pre-catalysts for ethylene polymerization
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
bSchool of Chemistry, University of East Anglia, Norwich, UK, NR4 7TJ.
E-mail: carl.redshaw@uea.ac.uk
cState Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou,
730000, China
† CCDC reference numbers 828331 and 828332 for crystallographic data
of complexes Co1 and Co5. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1dt11062d
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Table 1 Selected bond lengths and angles for Co1 and Co5
Co1
without observing any oligomer in the products, with activities
similar to the iron-based pre-catalysts. However, the polyethylenes
obtained were of high-density with a narrow molecular weight
distribution. Herein, the synthesis and characterization of the 2-[1-
(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)-
ethyl]pyridyl cobalt(II) dichlorides are reported in detail, as well
as their catalytic behavior in the polymerization of ethylene.
Co5
˚
Bond lengths (A)
Co(1)–N(1)
2.179(3)
2.188(2)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–Cl(1)
Co(1)–Cl(2)
N(2)–C(40)
N(2)–C(36)
N(1)–C(35)
N(1)–C(19)
2.047(4)
2.165(4)
2.2334(14)
2.3228(13)
1.337(5)
1.340(6)
1.283(5)
1.446(5)
1.282(6)
1.448(6)
2.047(2)
2.163(2)
2.2451(10)
2.3004(9)
1.337(3)
1.331(3)
1.288(3)
1.436(3)
1.286(3)
1.436(3)
2. Results and discussion
2.1 Synthesis and characterization of the complexes Co1–Co6
N(3)–C(42)
N(3)–C(43)
All ligands of the type 2-[1-(2,6-dibenzhydryl-4-methylphenyl-
imino)ethyl]-6-[1-(arylimino)ethyl]pyridine, were prepared ac-
cording to the literature procedures.9 The stoichiometric reaction
of 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(aryl-
imino)ethyl]pyridine with CoCl2 in ethanol formed the
corresponding N,N,N-tridentate cobalt complexes, 2-[1-(2,6-
dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]-
pyridylcobalt(II) dichloride, in good yields (Scheme 1).
Bond angles (◦)
N(2)–Co(1)–N(3)
N(2)–Co(1)–N(1)
N(3)–Co(1)–N(1)
N(2)–Co(1)–Cl(1)
N(3)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(2)
N(3)–Co(1)–Cl(2)
N(1)–Co(1)–Cl(2)
Cl(1)–Co(1)–Cl(2)
74.87(14)
73.96(13)
140.68(14)
159.90(11)
101.60(10)
99.50(10)
88.00(11)
101.68(11)
100.57(10)
112.02(6)
74.17(9)
74.03(9)
140.31(8)
157.42(7)
101.07(7)
99.22(7)
91.44(7)
99.86(7)
104.05(7)
111.14(4)
Scheme 1 The synthetic procedure for 2-[1-(2,6-dibenzhydryl-4-methyl-
phenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(II) dichlorides.
Elemental analyses for all of the complexes were consistent with
the proposed formulae and, for their IR spectra, a strong band
in the range 1580–1590 cm-1 can be ascribed to the stretching
vibration of C N. The 1H NMR spectra of Co1–Co6 were
consistent with the paramagnetic nature of these compounds. The
molecular structures of Co1 and Co5 were further unambiguously
confirmed by the single X-ray diffraction.
Fig. 1 An ORTEP drawing of complex Co1. Thermal ellipsoids are shown
at 30% probability. Hydrogen atoms are omitted for clarity.
2.2 Molecular structures
Single crystals of Co1 and Co5 suitable for X-ray diffraction
analysis were obtained by layering n-pentane on dichloromethane
solution at room temperature. The molecular structures of com-
plexes Co1 and Co5 are shown in Figs 1 and 2 and the selected
bond lengths and angles are tabulated in Table 1.
Similar to the iron complexes, the coordinating environment
for the centre metal (for both Co1 and Co5) is a pseudo square-
pyramidal geometry, in which three nitrogen atoms, N(1), N(2),
N(3), and one chlorine atom, Cl(1), form the square plane. The
Fig. 2 An ORTEP drawing of one of two independent molecules in
complex Co5 (the other molecular is omitted; the C50a and C51a are
disordered atoms for C50 and C51). Thermal ellipsoids are shown at 30%
probability. Hydrogen atoms are omitted for clarity.
˚
cobalt atom lies 0.589 (ca.) A out of the chelated plane (N1–N2–
of Co–N(2) then Co–N(1) and Co–N(3). The two imino-phenyl
planes are nearly perpendicular to the chelated plane (N1–N2–
N3) and the four phenyl substituents of the two benzhydryl groups
almost block the axial sites at the metal centre, which is thought
to play a critical role in protecting the active site and maintaining
the high activity.
˚
N3) for Co1 and 0.597 (ca.) A out for Co5, indicating that the
central metal cobalt is not co-planar with the chelating ligand due
to the associated sterics. In the molecular structures of both Co1
and Co5, the interacting force of Co–N(2) is stronger than that of
Co–N(1) and Co–N(3), which is reflected by the shorter distance
10210 | Dalton Trans., 2011, 40, 10209–10214
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Table 2 Ethylene polymerization at atmospheric pressure by cobalt pre-catalystsa
c
d
T
t
Yield
g
Mw
Tm
c
Entry
Cat.
Co-cat
Al/Co
◦C
min
Activityb
kg mol-1
Mw/Mn
◦C
1
2
3
4
5
6
7
8
Co3
Co3
Co3
Co3
Co3
Co3
Co1
Co2
Co4
Co5
Co6
CoR
Co2
Co2
Co2
Co2
MAO
1000
1000
500
750
750
750
750
750
750
750
750
750
750
750
750
750
20
20
20
20
0
40
20
20
20
20
20
20
20
20
20
20
30
30
30
30
30
30
30
30
30
30
30
30
5
0.05
0.75
0.66
0.83
0.55
0.46
0.90
1.90
0.69
0.94
trace
0.09
0.58
1.13
1.79
2.00
0.7
10.0
8.8
11.1
7.3
122
142
157
153
249
108
130
157
102
264
—
1.9
2.1
2.6
2.3
2.4
2.2
2.1
2.8
1.9
4.1
—
133.9
133.7
134.0
133.8
134.3
133.5
133.2
134.3
133.1
134.1
—
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
6.1
12.0
25.3
9.2
12.5
trace
1.2
46.4
45.3
35.8
20.0
9
10
11
12
13
14
15
16
—
—
—
108
146
147
182
1.9
2.1
2.5
3.8
134.1
133.7
133.2
139.8
10
20
40
a Reaction conditions: 1.5 mmol of Co, 1 atm of ethylene and 30 mL of toluene. b Activity: 105 g PE mol-1(Co) h-1. c Determined by GPC. d Determined
by DSC.
2.3 Ethylene polymerization
nitrogen showed the highest activity amongst this family. Such
phenomena were also observed in the catalytic system utiliz-
ing 2-imino-1,10-phenanthrolinyliron complexes.14 Furthermore,
the cobalt complex 2,6-bis-[1-(2,6-diisopropylphenylimino)ethyl]-
pyridylcobalt(II) dichloride (CoR),1 which has the highest re-
ported activity of the bis(imino)pyridylcobalt dichloride family
for ethylene polymerization,2a,e was selected for evaluation as a
comparison. The activity of CoR (entry 12 in Table 1) was found
to be much lower than those of Co1–Co5 (entries 7–10 in Table 2).
To determine the lifetime of the active species, trials of
Co2/MMAO were carried out over different reaction times
(entries 8, 13–16 in Table 2) at 20 ◦C. After examination of the
data (and trends), it was evident that the active sites deactivated
rapidly in the first 30 min, possibly due to impurities present in
the catalytic system and the limitation of mass transfer caused
by some insoluble polyethylene formed, and after this period the
activity tended to a limiting value of about 2.0 ¥ 106 g PE mol-1(Co)
h-1. In addition, the Mw (107–182 kg mol-1) and Mw/Mn (1.9–3.8)
values of the obtained PEs were slightly increased upon extending
the reaction time and no induction time was observed during the
catalytic process.
2.3.1 Ethylene polymerization at atmospheric pressure. Ethy-
lene polymerization catalyzed by these cobalt complexes with
different co-catalysts was conducted at atmospheric pressure.
MAO and MMAO were initially used to activate complex Co3 for
ethylene polymerization at room temperature (Table 1). The type
of co-catalyst, molar ratio of Al/Co, reaction temperature, time
and nature of the complexes were shown to have an influence on
the activities, as well as the Mw and Mw/Mn values of the resultant
polyethylenes. The activity exhibited by Co3/MMAO (entry 2 in
Table 2) is one order of magnitude higher than that exhibited
by Co3/MAO (entry 1 in Table 2), though the polyethylene
produced had a similar molecular weight and molecular weight
distribution. Thus, the co-catalyst MMAO was selected for further
investigations.
The influence of the molar ratio of Al/Co was investigated
by increasing the Al/Co molar ratio from 500 to 1000 (entries
2–4 in Table 2). The activities peaked at an optimum ratio of
750 (entry 4 in Table 2). The molecular weight of the polymers
obtained decreased as the Al/Co molar ratio increased, which
was probably due to the enhanced chain transfer from cobalt to
aluminium, resulting in the short-chain polymers.13
2.3.2 Ethylene polymerization at elevated pressure. Based on
previous work, it is anticipated that increases in pressure will signif-
icantly increase the activities as well as the molecular weight of the
polyethylene obtained.6a,15 The ethylene polymerization with the
Co3/MMAO catalyst system was also conducted under different
pressures of ethylene (Table 3). Increasing the ethylene pressure,
the productivity was enhanced and the resultant PEs showed
higher molecular weights, which can probably be attributed to the
higher monomer concentration around the active species. Also,
similar variations of catalytic activities with regard to the co-
catalysts, the reaction temperature, time and Al/Co molar ratio,
as well as the nature of the ligand were observed on elevating the
ethylene pressure from 1 atm to 5 or 10 atm. The evaluation herein
was carried out at elevated ethylene pressures of 5 atm and 10 atm
(see Table 3). In general, the co-catalysts significantly impacted
With the molar ratio of Al/Co (750) fixed, the influence of
the reaction temperature was investigated (entries 4–6 in Table 2).
Similar to the observations for their iron counterparts,9 the highest
activity here was observed at 20 ◦C, however, the polymer obtained
was very different, as evidenced by the high molecular weight and
narrow molecular weight distribution.
The effects of the nature of the ligands on the catalytic
behavior were conducted via the catalytic experiments of ethylene
polymerization with cobalt pre-catalysts/MMAO (entries 4, 7–
11 in Table 2). In contrast to the catalytic system using the iron
complexes, the cobalt pre-catalysts, Co1 and Co2, provided slightly
higher catalytic activities than the pre-catalysts (Co4 and Co5),
which bear an additional para-methyl substituent, whilst Co2
possessing 2,6-diethyl groups on the phenyl ring of the imino
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Table 3 Ethylene polymerization at elevated pressure by the cobalt pre-catalystsa
c
d
T
P
Yield
g
Mw
Tm
c
Entry
Cat.
Co-cat
Al/Co
◦C
atm
Activityb
kg mol-1
Mw/Mn
◦C
1
2
3
4
5
6
7
8
Co3
Co3
Co3
Co3
Co3
Co3
Co1
Co2
Co4
Co5
Co6
CoR
Co3
Co3
Co3
Co3
Co3
Co3
Co1
Co2
Co4
Co5
Co6
CoR
MAO
1000
750
20
20
20
20
30
40
30
30
30
30
30
30
30
30
30
30
40
50
40
40
40
40
40
40
5
5
5
5
5
5
5
5
5
0.67
2.2
3.0
2.8
3.1
2.2
3.4
3.8
2.3
3.5
trace
0.22
0.9
4.4
5.2
4.3
5.8
5.0
6.4
7.4
5.7
6.7
trace
0.3
8.9
29.3
40.0
37.3
41.3
29.3
45.3
50.7
30.7
46.7
trace
2.9
12.0
58.7
69.3
57.3
77.3
66.7
85.3
98.7
76.0
89.3
trace
4.0
109
153
147
143
134
134
182
98
3.5
3.1
2.8
3.2
2.9
3.6
2.3
2.5
2.2
3.1
—
133.8
133.7
134.6
134.0
133.8
134.1
134.0
133.6
133.5
135.9
—
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
1000
1250
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1250
1500
1250
1250
1250
1250
1250
1250
1250
1250
9
156
179
—
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
5
5
5
—
—
—
10
10
10
10
10
10
10
10
10
10
10
10
240
186
136
124
169
133
107
324
216
101
—
3.7
2.8
2.9
2.2
3.0
2.5
2.1
3.0
4.0
2.2
—
133.8
134.3
134.0
133.6
133.9
134.1
133.3
133.4
133.0
133.2
—
—
—
—
a Reaction conditions: 1.5 mmol of Co; 30 min; 100 mL of toluene. b Activity, 105 g PE mol-1(Co) h-1. c Determined by GPC. d Determined by DSC.
on the activities both at 5 atm (entries 1 and 2 in Table 3) and 10
atm (entries 13 and 14 in Table 3). The activities exhibited in the
presence of MMAO (entries 2 and 14 in Table 3) are always far
higher than those in the presence of MAO (entries 1 and 13 in
Table 3).
characterized. Upon treatment with MMAO, the current family
of cobalt pre-catalysts was found to exhibit the highest activities
reported to date toward ethylene polymerization, with an observed
activity of up to 9.87 ¥ 106 g PE mol-1(Co) h-1, producing high-Mw
(100–330 kg mol-1) and narrow-Mw/Mn (1.9–4.0) polyethylene.
The molecular weights and the polydispersity indexes of the
resultant polyethylenes could be readily controlled by finely tuning
the nature of ligands through varying their substituents and
modifying the reaction parameters, such as the molar ratio of
Al/Co and reaction temperature.
As a consequence, MMAO was used as the activator for
further screening and the best performance was obtained with
Co3/MMAO at 30 ◦C with an Al/Co molar ratio of 1000 (entry 5,
Table 3) at 5 atm and at 40 ◦C with an Al/Co molar ratio of 1250
(entry 17, Table 3) for 10 atm, respectively, by varying the Al/Co
molar ratio and the reaction temperature (entries 2–6 and 14–18,
Table 3). Importantly, the molecular weight and the molecular
weight distribution of the polymers obtained remained virtually
unaffected, which should be of benefit for producing polymers
with a uniform molecular weight and narrow molecular weight
distribution. The alkyl substituents (R1 and R2) on the imino-aryl
ring proved to be influential to both the catalytic activity and the
molecular weight, as well as the molecular weight distribution of
the products. The activities decreased in the order Co2 > Co5 >
Co1 > Co3 > Co4 ꢀ Co6 at all ethylene pressures used (1, 5 and
10 atm) and the molecular weight of the polyethylenes varied from
97 to 179 kg mol-1 at 5 atm and from 107 to 323 kg mol-1 at 10 atm,
respectively (entries 5, 7–11, 17 and 19–23, Table 3). However,
the molecular weight distribution remained relatively narrow,
which is indicative of single-site catalysis. Most interestingly, the
catalytic activities observed for Co1–Co5 are much higher than
that observed for CoR (entries 12 and 24, Table 3).
4. Experimental section
4.1 General considerations
All manipulations of air- and/or moisture-sensitive compounds
were performed under a nitrogen atmosphere using stan-
dard Schlenk techniques. Toluene was refluxed over sodium–
benzophenone and distilled under nitrogen before use. Methylalu-
minoxane (MAO, 1.46 M solution in toluene) and modified methy-
laluminoxane (MMAO, 1.93 M in heptane, 3A) were purchased
from Akzo Nobel Corp. High-purity ethylene was purchased
from Beijing Yansan Petrochemical Co. and used as received.
Other reagents were purchased from Aldrich, Acros, or local
suppliers. NMR spectra (-40–140 ppm) were recorded on a Bruker
DMX 600 MHz instrument at ambient temperature using TMS
as an internal standard. IR spectra were recorded on a Perkin-
Elmer System 2000 FT-IR spectrometer in the range 4000–400
cm-1. Elemental analysis was carried out using a Flash EA 1112
microanalyzer. Molecular weights (Mw) and molecular weight
distribution (Mw/Mn) of the polyethylenes were determined by a
PL-GPC220 at 120 ◦C, with 1,2,4-trichlorobenzene as the solvent.
3. Conclusion
2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimi-
no)ethyl]pyridyl cobalt complexes were synthesized and fully
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A DSC trace and the melting points of the polyethylenes were
obtained from the second scanning run on Perkin-Elmer DSC-7
at a heating rate of 10 ◦C min-1.
Isolated as a yellow solid, yield: 130 mg (78.3%). 1H NMR
(600 MHz, CDCl3, TMS): d 112.30 (s, 1H, Py Hm); 111.07 (s, 1H,
Py Hm); 45.76 (s, 1H, Py Hp); 20.06 (s, 6H, 2 ¥ CH3); 9.26 (s, 2H,
Ar Hm); 8.54 (s, 2H, Ar Hm); 7.03 (s, 6H, aryl H); 5.54 (s, 2H, aryl
H); 4.44 (s, 2H, aryl H); 3.20 (s, 6H, aryl H); 2.48 (s, 2H, aryl
H); 1.28 (s, 2H, 2 ¥ CH); 0.994 (s, 2H, aryl H); -19.17 (s, 6H, 2
¥ CH3); -25.10 (s, 6H, 2 ¥ N CCH3). FT-IR (KBr, cm-1): 3025,
2917, 1617, 1585 (nC N), 1495, 1448, 1365, 1263, 1222, 1080, 1030,
858, 815, 769, 748, 701. Anal. calcd for C51H47Cl2CoN3 (831): C,
73.64; H, 5.70; N, 5.05%. Found: C, 73.44; H, 5.51; N, 5.34%.
4.2 Synthesis and characterization of complexes Co1–Co6
All of the cobalt complexes were prepared in the same manner
by the reaction of 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)-
ethyl]-6-[1-(arylimino)ethyl]pyridine with CoCl2 in ethanol. A
typical synthesis of complex Co1, 2-[1-(2,6-dibenzhydryl-4-
methylphenylimino)ethyl]-6-[1-(2,6-dimethylphenylimino)ethyl]-
pyridylcobalt(II) dichloride, is described as follows: a mixture
of 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(2,6-
dimethylphenylimino)ethyl]pyridine (138 mg, 0.20 mmol), CoCl2
(26 mg, 0.20 mmol) and ethanol (4 mL) was stirred at room
temperature for 3 h and 10 mL of diethyl ether was added to
precipitate the cobalt complex. Then, the precipitate was washed
with diethyl ether (3 ¥ 5 mL) and dried to give the pure product as
a yellow powder in 126 mg (76.9%). 1H NMR (600 MHz, CDCl3,
TMS): d 113.92 (s, 1H, Py Hm); 109.29 (s, 1H, Py Hm); 49.45
(s, 1H, Py Hp); 20.95 (s, 3H, CH3); 15.15 (s, 2H, Ar (represents
the phenyl core with 2,6-dibenzhydryl-4-methylphenylimino) Hm);
9.03 (s, 2H, Ar Hm); 4.96 (m, 10H, aryl (represents all phenyl
groups beyond the above assigned Ar group) H); 3.61 (s, 4H, aryl
H); 2.81 (s, 3H, aryl H); 2.04 (s, 3H, aryl H); 1.23 (s, 2H, 2 ¥ CH);
-2.11 (s, 3H, CH3); -19.09 (s, 3H, CH3); -7.59 (s, 1H, Ar Hp);
-23.50 (s, 6H, 2 ¥ N CCH3). FT-IR (KBr; cm-1): 3056, 3023,
2912, 1621, 1584 (nC N), 1495, 1446, 1373, 1260, 1217, 1028, 806,
773, 746, 703. Anal. calcd for C50H45Cl2CoN3 (818): C, 73.44; H,
5.55; N, 5.14%. Found: C, 73.32; H, 5.46; N, 5.51%.
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(2,6-
diethyl-4-methylphenylimino)ethyl]pyridylcobalt(II)
dichloride
(Co5). Isolated as a yellow solid, yield: 141 mg (82.1%). 1H
NMR (600 MHz, CDCl3, TMS): d 115.79 (s, 2H, Py Hm); 49.72
(s, 1H, Py Hp); 20.68 (s, 3H, CH3); 20.38 (s, 3H, CH3); 10.18 (s,
2H, Ar Hm); 8.78 (s, 2H, Ar Hm); 6.97 (s, 6H, aryl H); 5.39 (s, 2H,
aryl H); 4.70 (s, 2H, aryl H); 3.54 (s, 6H, aryl H); 3.11 (s, 2H, aryl
H); 1.76 (s, 2H, aryl H); 1.28 (s, 2H, 2 ¥ CH); -18.97 (s, 4H, 2 ¥
CH2); -19.59 (s, 6H, 2 ¥ CH3); -35.17 (s, 3H, N CCH3); -37.07
(s, 3H, N CCH3). FT-IR(KBr, cm-1): 3028, 2959, 2917, 2866,
1618, 1583 (nC N), 1495, 1446, 1371, 1264, 1217, 1080, 1030, 865,
830, 767, 746, 702. Anal. calcd for C53H51Cl2CoN3 (859): C, 74.03;
H, 5.98; N, 4.89%. Found: C, 73.99; H, 5.77; N, 4.94%.
2,6-Bis[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]pyridyl-
cobalt(II) dichloride (Co6). Isolated as a yellow solid, yield: 98.8
mg (43.5%). 1H NMR (600 MHz, CDCl3, TMS): d 115.79 (s, 2H,
Py Hm); 49.72 (s, 1H, Py Hp); 20.54 (s, 6H, 2 ¥ CH3); 7.73 (s, 4H,
Ar Hm); 3.53 (s, 30H, Ar H); 1.27 (s, 4H, 4 ¥ CH); 0.996 (s, 10H,
Ar H); -20.15 (s, 6H, 2 ¥ N CCH3). FT-IR (KBr,cm-1): 3026,
2920, 2166, 2029, 1978, 1583 (nC N), 1494, 1447, 1264, 1213, 1077,
1031, 916, 859, 809, 768, 747, 700. Anal. calcd for C75H63Cl2CoN3
(1136): C, 79.28; H, 5.59; N, 3.70%. Found: C, 78.89; H, 5.25; N,
4.05%.
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(2,6-
diethylphenylimino)ethyl]pyridinescobalt(II) dichloride (Co2).
Isolated as a yellow solid, yield: 130 mg (77.1%). 1H NMR
(600 MHz, CDCl3, TMS): d 113.53 (s, 1H, Py Hm); 112.54 (s, 1H,
Py Hm); 46.56 (s, 1H, Py Hp); 20.85 (s, 3H, CH3); 10.94 (s, 2H, Ar
Hm); 9.04 (s, 2H, Ar Hm); 7.20 (s, 6H, aryl H); 5.37 (s, 2H, aryl
H); 4.80 (s, 2H, aryl H); 3.59 (s, 6H, aryl H); 2.94 (s, 2H, aryl H);
2.40 (s, 2H, aryl H); 1.29 (s, 2H, 2 ¥ CH); -9.48 (s, 1H, Ar Hp);
-18.81 (s, 10H, aryl H); -35.30 (s, 3H, N CCH3); -39.06 (s, 3H,
4.3 X-ray crystallographic studies
Single crystals of Co1 and Co5 suitable for X-ray diffraction analy-
sis were obtained by layering n-pentane on their dichloromethane
solutions at room temperature. With graphite-monochromatic
N
CCH3). FT-IR (KBr, cm-1): 3057, 2969, 2918, 1620, 1587
(nC N), 1495, 1444, 1370, 1261, 1216, 1079, 1030, 866, 803, 768,
745, 700. Anal. calcd for C52H49Cl2FeN3 (846): C, 73.84; H, 5.84;
N, 4.97%. Found: C, 73.57; H, 5.77; N, 5.01%.
˚
Mo-Ka radiation (k = 0.71073 A) at 173(2) K, the 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 structures were solved by
direct methods and refined by full-matrix least squares on F2.
All hydrogen atoms were placed in calculated positions. Structure
solution and refinement were performed by using the SHELXL–
97 package.16 Details of the X-ray structure determinations and
refinements are provided in Table 4.
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(2,6-
diisopropylphenylimino)ethyl]pyridylcobalt(II) dichloride (Co3).
Isolated as a yellow solid, yield: 146 mg (83.3%). 1H NMR
(600 MHz, CDCl3, TMS): d 115.41 (s, 1H, Py Hm); 113.50 (s,
1H, Py Hm); 49.10 (s, 1H, Py Hp); 20.91 (s, 3H, CH3); 10.40 [s,
2H, Ar Hm]; 9.15 (s, 2H, Ar Hm); 7.48 (s, 6H, aryl H); 5.54 [s, 2H,
aryl H]; 4.87 (s, 2H, aryl H); 3.53 (s, 6H, aryl H); 2.63 (s, 2H, aryl
H); 2.02 (s, 2H, aryl H); 1.24 (s, 2H, 2 ¥ CH); -9.00 (s, 1H, Ar
Hp); -16.83 (s, 2H, 2 ¥ CH); -17.21 (s, 6H, 2 ¥ N CCH3); -17.94
(s, 12H, 4 ¥ CH3). FT-IR (KBr, cm-1): 2966, 2918, 1865, 1620,
1583 (nC N), 1494, 1448, 1374, 1263, 1029, 816, 794, 769, 745, 700.
Anal. calcd for C54H53Cl2FeN3 (874): C, 74.22; H, 6.11; N, 4.81%.
Found: C, 74.03; H, 5.87; N, 4.97%.
4.4 General procedure for ethylene polymerization
Ethylene polymerization under atmospheric ethylene. Firstly,
a 30 mL of toluene solution of the pre-catalyst was added to a
glass reactor using a syringe and then the required amount of co-
catalyst (MAO, MMAO) was added. The reaction progressed with
stirring under an ambient ethylene atmosphere. After the reaction
was carried out for the required period, the reaction solution was
quenched with 10% hydrochloric acid ethanol. The precipitated
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(2,4,6-
trimethylphenylimino)ethyl]pyridylecobalt(II) dichloride (Co4).
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10209–10214 | 10213
©

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Table 4 Crystal data and structure refinement for Co1 and Co5
Notes and references
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Williams, Chem. Commun., 1998, 849.
Co1
2Co5
Empirical formula
fw
C50H45Cl2CoN3
817.72
C106H102Cl4Co2N6
1719.60
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T/K
173(2)
173(2)
0.71073
˚
l/A
0.71073
monoclinic
P21/n
9.5984(19)
34.200(7)
13.446(3)
90
106.94(3)
90
4222.4(15)
4
Cryst. syst.
triclinic
¯
Space group
P1
˚
a/A
13.237(3)
16.590(3)
25.640(5)
89.00(3)
77.66(3)
88.11(3)
5497.2(19)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
˚
V (A3)
Z
Dcalcd. (gcm-3)
m/mm-1
1.286
0.571
1708
1.039
0.441
1804
F(000)
Cryst. size/mm
q range (◦)
Limiting indices
0.23 ¥ 0.20 ¥ 0.09 0.25 ¥ 0.21 ¥ 0.17
1.19–27.48
-12 £ h £ 12
-32 £ k £ 44
-12 £ l £ 17
34568
9681 (0.0746)
99.9%
none
9681/0/505
1.259
0.81–27.44
-17 £ h £ 17
-21 £ k £ 21
-33 £ l £ 33
68283
24934 (0.0461)
99.4%
none
24934/36/1082
1.037
R1 = 0.0634
wR2 = 0.1696
R1 = 0.0761
wR2 = 0.1795
No. of rflns collected
No. unique rflns [R(int)]
Completeness to q (%)
Abs corr
Data/restranints/params
Goodness of fit on F2
Final R indices [I > 2s(I)]
R1 = 0.0939
wR2 = 0.2220
R1 = 0.1132
wR2 = 0.2378
R indices (all data)
-3
˚
Largest diff. peak and hole/e A
0.461 and -0.545 1.388 and -0.480
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Do¨ring, J. Mol. Catal. A: Chem., 2004, 212, 13.
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29, 1168.
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G. R. Han, J. Cryst. Growth, 2009, 311, 4593.
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693, 3867.
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and D. J. Williams, J. Am. Chem. Soc., 2005, 127, 11037; (b) A. K.
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7033.
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Organometallics, 2006, 25, 666.
polymer was collected by filtration, washed with ethanol and
water and dried in a vacuum at 60 ◦C until it was of constant
weight.
Ethylene polymerization under 5/10 atm ethylene. 50 mL of
toluene was first injected into the autoclave, which is a 300 mL
stainless steel vessel equipped with a mechanical stirrer and
a temperature controller. When the temperature reached the
required value, another 30 mL toluene containing the dissolved
complex (1.5 mmol) and the required amount of co-catalyst
(MAO, MMAO), plus the residual toluene were successively added
using a syringe. The reaction mixture was aggressively stirred for
the desired time under the corresponding pressure of ethylene
throughout the entire experiment. The reaction was terminated
and the polymer was collected using the same method as above
for the ethylene polymerization at ambient pressure.
15 (a) M. Yang, B. Y. Liu, L. H. Wang, H. G. Ren, W. Y. Hu, L. F. Wen
and W. D. Yan, Catal. Commun., 2009, 10, 1427; (b) M. Mitani, R.
Furuyama, J. Mohri, J. Saito, S. Ishii, H. Terao, T. Nakano, H. Tanaka
and T. Fujita, J. Am. Chem. Soc., 2003, 125, 4293.
16 G. M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
Acknowledgements
This work is supported by MOST 863 program No.
2009AA034601. The EPSRC are thanked for the awarded travel
grant (to C. R.).
10214 | Dalton Trans., 2011, 40, 10209–10214
This journal is
The Royal Society of Chemistry 2011
©