Novel non-chelated cobalt(II) benzimidazole complex catalysts: Synthesis, crystal structures and cocatalyst effect in vinyl polymerization of norbornene

Article abstract of DOI:10.1016/j.jorganchem.2007.12.001

The novel non-chelated monodentate benzimidazole (BI) complexes CoCl₂(BI)₂ (1)-(3), where BI = 1-(2-methoxybenzyl)- 2-(2-methoxyphenyl)-1H-benzimidazole (1), BI = 2-(2,6-difluorophenyl)-1H-benzimidazole (2) and 2-methyl-1H-benzimidaz

Full text of DOI:10.1016/j.jorganchem.2007.12.001

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 729–736
www.elsevier.com/locate/jorganchem
Novel non-chelated cobalt(II) benzimidazole complex
catalysts: Synthesis, crystal structures and cocatalyst effect
in vinyl polymerization of norbornene
Naresh H. Tarte a, Seong Ihl Woo a,b,*, Liqiang Cui a, Young-Dae Gong c, Young Ho Hwang d
a Department of Chemical and Biomolecular Engineering (BK21 graduate program), Center for Ultramicrochemical Process System (CUPS),
Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea
b Department of Chemistry, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea
c Center for High Throughput Synthesis Technology, Korea Research Institute of Chemical Technology, Daejeon 305-600, Republic of Korea
d Daelim Daedeok R&D Center, Daejeon 305-345, Republic of Korea
Received 13 November 2007; received in revised form 27 November 2007; accepted 4 December 2007
Available online 8 December 2007
Abstract
The novel non-chelated monodentate benzimidazole (BI) complexes CoCl2(BI)2 (1)–(3), where BI = 1-(2-methoxybenzyl)- 2-(2-
methoxyphenyl)-1H-benzimidazole (1), BI = 2-(2,6-difluorophenyl)-1H-benzimidazole (2) and 2-methyl-1H-benzimidazole (3) were syn-
thesized and characterized by single X-ray crystallography. Unexpectedly, in solid state these complexes show similar coordination
behavior to their analogue nickel(II) benzimidazole complexes such as inter-molecular H-bonding pattern and presence of acetonitrile
solvent molecules per unit of complex molecule. Moreover, among these cobalt catalysts 1–3, similar trend to that of nickel catalysts
is observed for metal-to-nitrogen (M–X) coordination bond length and halogen–metal–halogen (X–M–X) bond angle. But unlike
nickel(II) benzimidazole complexes, these catalysts show very low activity for vinyl polymerization of norbornene (NB) upon activation
with methylaluminoxane (MAO); however, the activity abruptly increased in modified methylaluminoxane (MMAO). The presence of a
small amount of toluene strongly hampered the activity, and the use of dry methylaluminoxane (dMAO) as a cocatalyst did not result in
a high activity. The use of toluene-free solid modified methylaluminoxane (sMMAO) is found to be the best cocatalyst, where the highest
activity of value 3.9 Â 107 g of PNB molCoÀ1 hÀ1 was achieved for 3/sMMAO at 30 °C.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Non-chelated catalysts; Cobalt(II) catalysts; Norbornene polymerization; Cocatalyst effect; Benzimidazole ligand
1. Introduction
coating material of optical disks and as inter-level dielectrics
in the microelectronics industry [1]. The research on nor-
bornene polymerization with early transition metal single-
site catalysts has been directed to ring-opening metathesis
polymerization [2] rather than vinyl polymerization because
of their low activity for the latter.
Polynorbornene via vinyl addition possesses special
properties such as high thermal stability, high glass transi-
tion temperature (Tg), high transparency, and excellent
dielectric properties that make them a good candidate as a
After the discovery of nickel- and palladium-based cata-
lysts by Brookhart et al. [3] and iron- and cobalt-based cat-
alysts by Gibson et al. [4] for ethylene polymerization,
intense work has been carried out for the discovery of nickel
and cobalt based catalyst systems for a-olefin and cyclic ole-
fins such as norbornene addition polymerization. Particu-
larly, the nickel [5] and palladium [6] catalysts showed
*
Corresponding author. Address: Department of Chemical and Bio-
molecular Engineering (BK21 graduate program), Center for Ultramic-
rochemical Process System (CUPS), Korea Advanced Institute of Science
and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701,
Republic of Korea. Tel.: +82 42 869 3918; fax: +82 42 869 8890.
E-mail address: siwoo@kaist.ac.kr (S.I. Woo).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.001

730
N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
renewed interest due to high activity toward homopolymer-
ization of norbornene. Generally, the polymerization activ-
ity drop in group VIII metals show the trend Co > Ni >
Pd > Pt [7,5c], but the activity of cobalt-based catalyst for
norbornene polymerization showed a high drop [8] and
sometimes no activity compared to nickel at a given set of
experimental conditions. Alt et al. [9] proposed highly active
cobalt based catalysts for vinyl polymerization of norborn-
ene in chlorobenzene but the activity was strongly ham-
pered by the small amount of toluene present in
commercial MAO and hence highest activity was achieved
in MAO synthesized in chlorobenzene. This initiated us to
investigate the effect of structure of MAO on norbornene
polymerization using these cobalt catalysts.
Recently, we proposed [10] that nickel(II) monodentate
benzimidazole complex catalysts in combination with
MAO are the most active catalysts for vinyl polymerization
of norbornene. Interestingly, we found that the cobalt(II)
benzimidazole complexes show high structural analogy
toward nickel(II) benzimidazole complexes at molecular
level in solid state. Herein, we describe the structure of
these cobalt(II) benzimidazole complexes and the effect of
the cocatalyst on vinyl polymerization of norbornene by
these catalysts.
oration of solvent at room temperature yielded the fine crys-
tals within a month. These complexes were isolated in the
form of blue crystalline solid and are stable at room temper-
1
ature. Due to low solubility of the complexes 1–2, the H
NMR analyses was carried out in DMSO-d6. The 1H
NMR spectra’s are attributable to the protons of the respec-
tive derivative of benzimidazole ligand. Moreover, because
of the broad nature of the 1H NMR peaks, the methoxy pro-
ton peaks (O–CH3; d ꢀ 3.7 and d ꢀ 3.5) of 1 could be over-
lapped by the DMSO-d6 (d 4–3) peak and hence are not seen
in NMR spectra. Such broad NMR peak pattern suggests
that there is a significant interaction between the benzimid-
azole ligands and the cobalt atom. This has been confirmed
by the determination of their respective X-ray crystal struc-
tures which confirm the benzimidazole imine coordination
with the metal center.
2.2. Molecular structures of cobalt benzimidazole complexes
1–3
The X-ray crystal structures of complexes 1–3 are shown
in Figs. 1–3, respectively. The crystallographic data and
2. Results and discussion
2.1. Preparation of the ligands and complexes
The ligands 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-
1H-benzimidazole (MOBPBI) and 2-(2,6-difluorophenyl)-
1H-benzimidazole (DFPBI) have been synthesized
according to the reported procedure [10], whereas the ligand
2-methyl-1H-benzimidazole (MBI) is used as received from
the commercial sources. The neutral benzimidazole cobalt
derivatives [CoCl2(MOBPBI)2 (1)], [CoCl2(DFPBI)2 (2)]
and [CoCl2(MBI)2 (3)] were prepared by reaction of CoCl2
with the proper benzimidazole derivative in dichlorometh-
ane and purified by re-precipitation in diethyl ether. These
complexes were dissolved in acetonitrile and the slow evap-
Fig. 2. X-ray structure of complex 2 showing inter-molecular H-bonding
and acetonitrile solvent molecules.
Fig. 1. X-ray structure of complex 1.

N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
731
lists the relevant bond distances and angles of these cobalt
benzimidazole complexes.
Complex
2 shows three types of inter-molecular
H-bonding in solid state, one of which is between amide
hydrogen of one of benzimidazole from first complex mol-
ecule and chloride atom of neighboring second complex
molecule [N–H(8A)–Cl(1)]. Similarly, the chloride atom
of first complex molecule involved in H-bonding with the
amide hydrogen of third complex molecule [Cl(1)–N–
H(8A)] and the third H-bonding is between the second
benzimidazole amide hydrogen of first complex molecule
and the nitrogen of solvent acetonitrile molecule
[N–H(28A)–N(43)]. This indicate that each complex mole-
cule is connected to two neighboring complex molecules
and one acetonitrile molecule through inter-molecular H-
bonding giving high stability to the 3D complex structure
in solid state. Moreover, it also shows the presence of
one discrete acetonitrile solvent molecules per unit of com-
plex molecule in X-ray crystal. A similar pattern of H-
bonding and the presence of solvent molecules have been
seen in the analogue nickel complex [10].
Fig. 3. X-ray structure of complex 3 showing inter-molecular H-bonding.
refinement parameters of complexes 1–3 are summarized in
Table 1.
The coordination geometry around the cobalt is pseudo-
tetrahedral similar observed to that of analogous nickel
complexes [10]. The crystal structure of complex 2 consists
of two solvent molecules per unit of the complex. Table 2
Similar to analogue nickel complex, complex 3 (Fig. 3)
shows inter-molecular H-bonding only with the chloride
atom [N–H(8A)—Cl(1)]. The two Co–N bonds in complex
Table 1
Crystallographic data and structure refinement for complexes 1, 2 and 3
Parameter
[CoCl2(MOBPBI)2 (1)]
[CoCl2(DFPBI)2 (2)]
[CoCl2(MBI)2 (3)]
Empirical formula
Formula weight
Temperature (K)
C
818.63
296(2)
44H40Cl2Co N4O4
C30H22Cl2CoF4N6
672.37
296(2)
C16H16Cl2CoN4
394.16
296(2)
˚
Wavelength (A)
0.71073
Monoclinic
P2(1)/c
0.71073
Monoclinic
P2(1)/c
0.71073
Monoclinic
P2(1)/n
Crystal system
Space group
Unit cell dimensions
˚
a (A)
14.2536(10)
13.1213(9)
21.5173(15)
9.89690(10)
23.8815(3)
13.9141(2)
12.7017(3)
9.8602(2)
14.7287(3)
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
90
90
90
101.926(4)
90
3937.4(5)
110.069(10)
90
3088.95(7)
111.8680(10)
90
1711.91(6)
3
˚
V (A )
Z
4
4
4
Dcalc (Mg/m3)
1.381
0.620
1700
1.446
0.783
1364
1.529
1.317
804
Absorption coefficient (mmÀ1
F(000)
Crystal size (mm3)
h Range for data collection (°)
Index ranges
)
0.27 Â 0.20 Â 0.07
0.22 Â 0.20 Â 0.08
0.26 Â 0.23 Â 0.04
1.46–28.30
1.71–28.31
1.81–28.39
À18 6 h P 18, À13 6 k P 17,
À28 6 l P 26
40474
À13 6 h P 13, À31 6 k P 30,
À17 6 l P 18
32304
À16 6 h P 16, À13 6 k P 13,
À19 6 l P 19
17581
Reflections collected
Independent reflections [Rint
Completeness to theta = 28.30° (%)
Absorption correction
]
9762 [0.0430]
99.7
Multi-scan
7674 [0.0572]
99.8
Multi-scan
4270 [0.0255]
99.3
Multi-scan
Maximum and minimum transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
0.9579 and 0.8504
Full-matrix least-squares on F2
9762/0/454
0.9400 and 0.8466
Full-matrix least-squares on F2
7674/0/ 390
0.9492 and 0.7257
Full-matrix least-squares on F2
4270/0/208
1.081
0.997
1.028
Final R indices [I > 2r(I)]
R indices (all data)
Largest difference in peak and hole (e A
R1 = 0.0750, wR2 = 0.2136
R1 = 0.1306, wR2 = 0.2479
1.525 and À1.650
R1 = 0.0450, wR2 = 0.0872
R1 = 0.1263, wR2 = 0.1112
0.239 and À0.246
R1 = 0.0308, wR2 = 0.0826
R1 = 0.0455, wR2 = 0.0905
0.327 and À0.288
À3
˚
)

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N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
Table 2
˚
Comparison of selected bond lengths (A) and angles (°) for 1–3
[CoCl2(MOBPBI)2 (1)]
[CoCl2(DFPBI)2 (2)]
[CoCl2(MBI)2 (3)]
Co–N(39)–2.038(3)
Co–N(9)–2.063(3)
Co–Cl(2)–2.2409(13)
Co–Cl(1)–2.2551(15)
Co–N(21)–2.017(2)
Co–N(1)–2.017(2)
Co–Cl(2)–2.2458(8)
Co–Cl(1)–2.2501(8)
Co–N(1)–2.0352(15)
Co–N(11)–2.0357(16)
Co–Cl(2)–2.2443(6)
Co–Cl(1)–2.2636(6)
N(39)–Co–N(9)–110.84(13)
N(39)–Co–Cl(2)–113.73(11)
N(9)–Co–Cl(2)–102.86(10)
N(39)–Co–Cl(1)–106.53(11)
N(9)–Co–Cl(1)–105.35(11)
Cl(2)–Co–Cl(1)–117.17(6)
N(21)–Co–N(1)–112.91(9)
N(21)–Co–Cl(2)–105.99(6)
N(1)–Co–Cl(2)–104.93(6)
N(21)–Co–Cl(1)–105.91(7)
N(1)–Co–Cl(1)–114.03(7)
Cl(2)–Co–Cl(1)–112.92(3)
N(1)–Co–N(11)–104.15(6)
N(1)–Co–Cl(2)–117.11(5)
N(11)–Co–Cl(2)–105.77(5)
N(1)–Co–Cl(1)–105.15(5)
N(11)–Co–Cl(1)–114.73(5)
Cl(2)–Co–Cl(1)–110.14(3)
˚
˚
Table 3
1 [2.038(3) A and 2.063(3) A] are asymmetric, compared to
Cocatalyst dependence polymerization of norbornene by 1–3a
˚
˚
that of complex 2 [2.017(2) A and 2.017(2) A] and complex
Run Catalyst Cocatalyst
Time Yield Activityb Mw
Mw/
Mn
˚
˚
3 [2.0352(15) A and 2.0357(16) A]. Also the benzyl substi-
tution results in the increase of Cl(1)–Co–Cl(2) bond angle
in complex 1 [117.17°(6)] compared to the non-substituted
complex 2 [112.92°(3)]. In the case of complex 3, this angle
further decreased to 110.14°(3). The analogue nickel benz-
imidazole complexes also show a similar trend in Ni–N
(min) (g)
(Âl0À5
)
1
2
3
4
5c
6
7
8
1
1
1
1
1
2
2
2
2
3
3
3
3
3
3
MAO
30
30
1/2
1/2
5
0.02
0.008
0.27
ndf
5.2
7.1
4.5
dMAO
MMAO
sMMAO
dMAO
MAO
dMAO
MMAO
sMMAO
MAO
0.67
0.57
0.88
2.6
2.7
2.8
13.68
21.12
NAd
0.012
0.16
18.24
19.2
1.73
18.48
22.56
39.12
1.29
30
30
1/2
1/2
5
1/2
1/2
1/2
5
0.03
0.39
0.76
0.80
0.72
0.77
0.94
1.63
0.54
0.81
ndf
5.8
8.1
4.5
nsg
9.0
4.6
5.6
7.6
6.6
˚
˚
˚
˚
bonding [1: 1.993 A, 2.028 A; 2:1.993 A, 1.987 A; 3:2.000
2.6
3.4
2.9
˚
˚
A, 2.003 A] and similar trend in Br(1)–Ni–Br(2) bond angle
[1: (123.80°) > 2 (118.30°) > 3(112.73°)]. All this indicates
that the nucleation mechanism is common in both these
cobalt and nickel benzimidazole complexes.
9
10
11
12
13e
14
15
MMAO
sMMAO
sMMAO
dMAO
dMAO/
TMA
3.3
3.4
2.9
2.8
2.8
However, these bond angles are quite deviated from that
of monodentate pyrazole derivatives of palladium [11]
which is due to the geometric constraints as palladium
can form only square planar complexes whereas these
nickel and cobalt complexes show pseudo-tetrahedral
geometry. These complexes are found to be stable at high
temperature. The DSC–TGA analyses show that the first
onset decomposition temperature is 230, 245 and 265 °C
for complexes 1–3 which is in the similar range as reported
for different cobalt benzimidazole derivatives [12].
1
9.72
16
3
sMMAO/
TIBA
5
NAd
a
Conditions: Cobalt precatalyst: 5.0 lmol, Al/Co: 500, temp.: 30 °C,
Norbornene (Nb): 10.0 mmol, solvent: o-DCB, total volume: 15 mL.
b
Activity: 106 g PNB molÀ1 hÀ1
In 2:1 o-DCB/toluene.
NA: not active.
Nb: 25.0 mmol, Al/Co: 1000.
nd: not determined.
.
c
d
e
f
2.3. Polymerization of norbornene
g
ns: polymer not soluble in 1,2,4-trichlorobenzene.
The results of polymerization of norbornene using
cobalt complexes 1–3 with different kinds of methylalumi-
noxane are summarized in Table 3.
improved the activity for 1–2/dMAO (runs 2 and 7), but
in the case of 3/dMAO (runs 10 and 14) the activity
dropped compared to 3/MAO. However, the increased
activity in dMAO/Me3Al (run 15) indicates that free
Me3Al available in cages of dMAO was not sufficient for
the activation of complex 3. The alternative use of MMAO
(runs 3, 8 and 11) in toluene showed very high activity
compared to MAO and dMAO, which indicates that the
microstructure of the cocatalyst plays a major role in gen-
erating and stabilizing the highly mature active species
which is responsible for higher activity. However, the rela-
tively high activity for MAO and dMAO activation for 3
(runs 10 and 14) than 1 (runs 1–2) and 2 (runs 6–7) may
be due to the electronically poor ligand [10] which makes
the cobalt less cationic and hence fewer the aluminium to
We have reported [10] that the nickel benzimidazole cat-
alysts show very high activities for polymerization of nor-
bornene in combination with MAO. Similar attempts to
activate cobalt benzimidazoles using MAO were not suc-
cessful and showed smallest activity values (runs 1, 6, and
10) for vinyl polymerization of norbornene. The reason
can be attributed to the presence of toluene in commercial
MAO which has already been noted for its inhabitation
effect [9]. We have also reported for nickel benzimidazole
catalysts that the use of toluene as the solvent in polymer-
ization system dropped the activity drastically. Hence, to
improve the polymerization activity, we carried out the
polymerization in toluene-free environment by drying the
MAO and using its solution in o-DCB. The results

N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
733
Fig. 4a. 1H NMR spectra of polynorbornene produced by 1/MMAO.
cobalt interactions and less the possibility of bimetallic spe-
cies formation [13] which can be the reason for low activity
in 1/MAO (run 1) and 2/MAO (run 6).
In the case of MMAO, the drying process is not neces-
sary because iBu3Al cannot form the bimetallic species with
the active metal complex [13]. However, the presence of tol-
uene can hamper the activity and hence we prepared tolu-
ene-free MMAO, i.e., sMMAO and used in o-DCB. It is
observed that for all the catalysts, the highest activity
was achieved using sMMAO (runs 4, 9, and 12), whereas
3/sMMAO (run 13) represents the highest activity of value
3.9 Â 107 g of PNB molNiÀ1 hÀ1 within 30 s of polymeriza-
tion with norbornene to cobalt ratio of 5000. It is interest-
ing to note that the activity trend in cobalt benzimidazole
catalysts is different to that of nickel benzimidazole cata-
lysts, where in the earlier case 3/sMMAO and in the latter
case 1/MAO was found to be the most active catalyst.
However, among the cocatalysts used, the highest molecu-
lar weight was achieved using MMAO and a very high Mw
of value 9.0 Â 105 g molÀ1 was observed for PNB produced
by 3/MMAO (run 11). This data indicate that the sMMAO
is the best choice as cocatalyst for polymerization using this
class of cobalt catalysts.
Fig. 4b. 13C NMR spectra of polynorbornene produced by 1/MMAO.
of norbornene by Arndt et al. [14] and reports from Bearns
et al. [15], one would expect two peaks for C7 if the polynor-
bornene enchainment was divided between mm and mr
placements or between rr and mm. Two major peaks were
observed below 40 ppm for C1 and C4 for PNB produced
by 1/MMAO. According to Arndt et al. [14], only the mm
and mr triads of the hydrotrimers of norbornene exhibit
C1 and C4 resonances below 40 ppm. Additionally, C7 in
the mm norbornene triad resonates at 33.82 ppm, 34.30
ppm in the rr triad, and 34.12 ppm in the mr triad. Thus
one would expect a mixture of mm and mr or mm and rr
to be resolved sufficiently to yield two peaks.
2.4. Polymer microstructure
The 1H NMR spectrum of PNB produced by 1/MMAO
is presented in Fig. 4a.
The assignments of methylene and methine carbons were
carried out on the basis of 13C NMR analysis in combina-
tion with DEPT analysis (Figs. 4b and 4c) and based on pre-
vious reports [14]. The peaks between 53 and 37 ppm are
assigned as methine carbon peaks and from 37 to 28 ppm
are assigned as methylene carbons peaks. In PNB produced
by 1/MMAO, two peaks of non-equal intensity are observed
for C7. Again, on the basis of assignments for hydrotrimers
The resonance of C7 carbon (Figs. 4b and 4c) which is the
region between 37 and 34 ppm shows two peaks, the one at

734
N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
with its nickel counterpart but failed to produce similar
catalytic activity for vinyl polymerization of norbornene
in combination with MAO. The use of modified methyl-
aluminoxane (MMAO) abruptly increased the polymeriza-
tion activity, but a small amount of toluene present in the
polymerization system strongly hampers the catalyst per-
formance and hence toluene-free MMAO, i.e. sMMAO
is found to be the best cocatalyst for activation of these
cobalt benzimidazole catalysts. Moreover, the activity
trend among these cobalt catalysts also differs to the
nickel series, as in the case of cobalt series 3/sMMAO
showed highest activity values for vinyl polymerization
of norbornene.
4. Experimental
4.1. General procedures
All procedures were carried out by using standard
Schlenk techniques. 1,2-Dichlorobenzene (anhydrous
grade) and cobalt(II) chloride were purchased from
Aldrich and were used without any further purification.
Methylaluminoxane (MAO; Aldrich) was obtained as
10 wt% and MMAO (Akzo Nobel) as 7.25 wt% solutions
in toluene and were used without further treatment. The
dMAO was prepared under reduced pressure according
to the reported procedure [17] and a similar procedure
was followed to prepare sMMAO. 2-Methylbenzimidazole
was purchased from Fluka (98%). Norbornene (bicyclo-
[2.2.1]hept-2-ene; Aldrich) was purified by distillation over
potassium and was used as a solution in o-DCB just prior
to polymerization.
Fig. 4c. 13C DEPT NMR spectra of polynorbornene produced by 1/
MMAO.
34.3 ppm and the other at 36.9 ppm in which the intensity of
earlier peak is very strong to that of latter. Thus the micro-
structure of PNB produced by 1/MMAO can be best
described as a mixture of mm and mr triads in which mm
is highly populated. The presence of the shoulder peak near
39 ppm which is reported as the C1 and C4 peaks of the cen-
tral norbornene of the mm triad of hydronorbornene trimers
by Arndt et al. [14] supports the high population of mm tri-
ads in the polynorbornene. The polynorbornene produced
by 1/MMAO shows a typical WAXS pattern, and one addi-
tional broad and weak intense peak at 2h = 30.12° which
proves that the higher crystalline nature of PNB which
may be due to comparatively higher fraction of syndiotactic
microstructure. Such increased tacticity increases the per-
meability coefficient [16]. This polynorbornene shows high
glass transition temperature (Tg) of value 465 °C, which is
in consistence with the Tg reported for PNB produced by
these catalyst [10] upon activated with MAO. A similar high
value Tg are reported for PNB’s produced by neutral salicyl-
aldiminato Ni(II) complexes [5a].
4.2. Measurement
NMR spectra of ligands were recorded using CDCl3 and
complex using DMSO-d6 as solvents on a Bruker BMX-
500 MHz instrument with tetramethylsilane (TMS) as the
1
internal standard. The H NMR data of polynorbornene
were recorded at ambient temperature and the 13C NMR
data was recorded at 100 °C using 1,2-dichlorobenzene-d4
as solvent on a Bruker AMX-500 MHz spectrometer. The
FT-IR analyses of polynorbornene produced by 1–3 were
carried out using ATR-FTIR spectrometer (Sens IR).
The combine differential scanning calorimeter-thermo-
gravimetric analysis (DSC–TGA) was carried out under
nitrogen using Setsys 16/18 (SETRAM) instrument and
the DSC data were obtained under nitrogen up to 500 °C
with a heating rate of 10 °C/min using NETZSCH DSC-
204F1. Molecular weight and molecular weight distribu-
tion of polynorbornene were measured by gel permentation
chromatography (GPC) (PL-GPC 220) at 160 °C using
1,2,4-trichlorobenzene as solvent and calibrated using poly-
styrene standards. Elemental analysis was carried out by
Faison’s elemental analyzer-1110. The melting points of
ligands were measured by electrical apparatus with Mettler
Toledo FP90 Control Processor.
3. Conclusions
It is observed that the non-chelated cobalt(II) benz-
imidazole complexes show similar coordination behavior

N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
735
4.3. Syntheses
sky blue was observed yielding a dark sky blue precipitate
after stirring for 2 h at room temperature and filtered
through a glass filter. The filtrate was evaporated in vac-
uum; the solid was washed frequently with diethyl ether
to yield the title complex as sky blue solid. Crystallization
in acetonitrile yields the title compound with 92% (0.75 g)
yield. 1H NMR (500 MHz, DMSO-d6) d 8.73–8.17 (br,
1H); 7.99–7.34 (br, 9H); 7.34–6.98 (br, 12H); 6.98–6.66
(dd, 3H); 6.66–6.46 (d, 1H); 5.68–5.03 (br, 2H). Anal. Calc.
for C44H40Cl2CoN4O4: C, 64.55; H, 4.92; N, 6.84. Found:
C, 64.21; H, 4.63; N, 6.59%.
All ligands were synthesized according to the reported
procedures [10] and the complex syntheses were carried
out under nitrogen atmosphere.
4.3.1. Synthesis of 1-(2-methoxybenzyl)-2-(2-
methoxyphenyl)-1H-benzimidazole (MOBPBI)
The solution of 1,2-diaminobenzene (1.08 g, 10.0 mmol)
and stoichiometric amount of sodium acetate in glacial ace-
tic acid (30 mL), was added dropwise to the solution of o-
anisaldehyde (2.86 g, 21.0 mmol) in glacial acetic acid
(50 mL). After complete addition at room temperature,
the resultant mixture was set to reflux for 21 h. The reaction
mixture was cooled to room temperature, evaporated in
vacuum, and partitioned between dichloromethane and
water. The biphasic mixture was cooled in an ice bath,
and neutralized with solid potassium carbonate with vigor-
ous stirring. The phases were separated, and the extraction
was completed with additional portions of dichlorometh-
ane. The combined organic extracts were dried with
Na2SO4, and evaporated in vacuum. Purification by column
chromatography (silica gel, n-hexane/ethyl acetate, 10/1)
produced the title compound in 75% (2.58 g) yield. Melting
4.3.4. Synthesis of [CoCl2 (DFBPI)2 (2)]
A procedure similar to that for 1 produced dark blue
crystals in acetonitrile. Yield: 82% (0.48 g). 1H NMR
(500 MHz, DMSO-d6) d 13.33–12.62 (br, 2H), 7.87–7.50
(br, 6H), 7.50–7.14 (br, 8H). Anal. Calc. for C26H16Cl2Co-
F4N4 Á 2CH3CN: C, 53.59; H, 3.30; N, 12.50. Found: C,
53.45; H, 3.11; N, 12.81%.
4.3.5. Synthesis of [CoCl2(MBI)2 (3)]
A procedure similar to that for 1 produced a violet crys-
talline solid was obtained with 88% (0.35 g) yield. Anal.
Calc. for C16H16Cl2CoN4: C, 48.75, H, 4.09; N, 14.21.
Found: C, 49.20; H, 4.27; N, 14.35%.
1
point 151 °C. H NMR (500 MHz, CDCl3) d 7.84 (d, 1H);
7.53 (m, 1H); 7.51 (m, 1H); 7.25–7.17 (m, 4H); 7.03 (t,
1H); 6.93 (d, 1H); 6.81 (d, 1H); 6.75 (t, 1H); 6.69 (dd,
1H); 5.23 (s, 2H); 3.76 (s, 3H); 3.56 (s, 3H). 13C NMR
(500 MHz, CDCl3) d 157.6, 156.5, 143.3, 135.5, 132.4,
131.4, 128.4, 127.7, 124.5, 122.5, 121.9, 120.8, 120.4,
119.8, 119.8, 110.9, 110.6, 109.9, 55.1, 55.2, 55.1, 43.5 ppm.
4.4. X-ray structural determination
The X-ray structure analyses data were collected using a
Bruker SMART Apex II X-ray diffractometer, and the
structure, solution and refinement were performed by using
the SHELXS program [18].
4.3.2. Synthesis of 2-(2,6-difluorophenyl)-1H-benzimidazole
(DFPBI)
4.5. General procedure for the polymerization of norbornene
The 2,6-difluorobenzoyl chloride (1.94 g, 11.0 mmol)
was dissolved in dichloromethane (20 mL), and was added
dropwise over 1 h to a solution of 1,2-diaminobenzene
(1.08 g, 10.0 mmol) and triethylamine (1.9 mL, 13.5 mmol)
in dichloromethane (100 mL) at 0 °C. The reaction mixture
was stirred at 0 °C for 1 h, then the temperature was set to
room temperature while stirring continued over next 3 h,
the volatiles were removed in vacuum to produce a pale
yellow solid. The solid was dissolved in glacial acetic acid
(50 mL), sodium acetate (0.90 g, 11.0 mmol) was added,
and the mixture was refluxed for 21 h. Further treatment
similar to (MOBPBI) produced the title compound (1.9 g,
82%) as a white solid. Melting point 202 °C. 1H NMR
(500 MHz, CDCl3) d 10.16 (br, 1H), 7.90 (br, 2H), 7.50
(m, 1H), 7.39–7.31 (m, 2H), 7.06 (m, 2H). 13C NMR (500
MHz, DMSO-d6) d 109, 112, 118, 122, 132–134, 141–143,
159, 161 ppm.
The polymerization was carried out in a 100 mL glass
reactor using o-DCB as the solvent at 30 °C. In a typical
polymerization (run 3, Table 3), 5.0 lmol of precatalyst 1
was dissolved in o-DCB (10.0 mL) under nitrogen atmo-
sphere, and freshly prepared solution of norbornene
(1.5 mL, 10.0 mmol) in o-DCB was added. The polymeriza-
tion was initiated by adding a toluene solution of MMAO
(1.15 mL, 2.5 mmol). The highly viscous mass of polymer
was observed in a very short period after the MAO addi-
tion. Hence the polymerization was terminated within
30 s by adding acidified methanol (20 mL, 5 mol% HCl).
The polymer was isolated by filtration, washed with meth-
anol, and dried in vacuum at 100 °C for 24 h. Unless other-
wise stated, the total volume was 15 mL, which was
achieved by variation of amount of o-DCB when necessary.
All the polymers were characterized by IR and NMR and
were found to be vinyl-type polynorbornene exclusively.
4.3.3. Synthesis of [CoCl2 (MOBPBI)2 (1)]
Well-stirred solution of 0.76 g (2.2 mmol) of MOBPBI
in dichloromethane (10 mL) was added dropwise to a solu-
tion of cobalt(II) chloride (0.13 g, 1.0 mmol) in dichloro-
methane (20 mL). A color change from faint pink to a
Acknowledgements
This research was funded by the Center for Ultramicro-
chemical Process Systems (CUPS) sponsored by KOSEF

736
N.H. Tarte et al. / Journal of Organometallic Chemistry 693 (2008) 729–736
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(2006). We thank Dr. C.-H. Kim at Korea Research Insti-
tute of Chemical Technology, and Dr. J.-W. Shin at Korea
Advanced Institute of Science and Technology for their
technical assistance.
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