Syntheses of iron, cobalt, chromium, copper and zinc complexes with bulky bis(imino)pyridyl ligands and their catalytic behaviors in ethylene polymerization and vinyl polymerization of norbornene

Article abstract of DOI:10.1016/j.molcata.2006.06.016

The syntheses, characterization, and ethylene and norbornene polymerization behaviors of iron, cobalt, chromium, copper and zinc complexes (3-7b) bearing chelating bulky 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine ligand (1) or 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl]pyridine ligand (2) are reported. X-ray diffraction study of the cobalt complex (4) shows the geometry of the cobalt center to be distorted trigonal bipyramid. Treatment of the iron, cobalt 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl pyridine complexes (3 and 4) with methylaluminoxane (MAO) lead to a highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE), while the corresponding chromium complex (5) is disclosed as moderate catalytic activity for the polymerization of ethylene. The specific catalytic activities were evaluated at different temperature and Al/M (M = Fe, Co and Cr) ratio. In addition, the complexes 3-5 and corresponding compounds of FeCl₂, CoCl₂(THF)_1.5 and CrCl₃(THF)₃ can also catalyze vinyl polymerization of norbornene activated with MAO and show good activities. However, the copper and zinc complexes (6a-7b) showed no active in ethylene and norbornene polymerization in the presence of MAO.

Full text of DOI:10.1016/j.molcata.2006.06.016

Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
Syntheses of iron, cobalt, chromium, copper and zinc complexes with bulky
bis(imino)pyridyl ligands and their catalytic behaviors in ethylene
polymerization and vinyl polymerization of norbornene
Jianxin Chen∗, Yuanbiao Huang, Zhongshui Li, Zhichun Zhang,
Chunxia Wei, Tingyan Lan, Wenjie Zhang
College of Chemistry and Materials Science, Fujian Normal University, Fuzhou, Fujian 350007, PR China
Received 18 February 2006; received in revised form 4 May 2006; accepted 7 June 2006
Available online 24 July 2006
Abstract
The syntheses, characterization, and ethylene and norbornene polymerization behaviors of iron, cobalt, chromium, copper and zinc
complexes (3–7b) bearing chelating bulky 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine ligand (1) or 2,6-bis[1-(2,5-ditertbutyl-
phenylimino)ethyl]pyridine ligand (2) are reported. X-ray diffraction study of the cobalt complex (4) shows the geometry of the cobalt center
to be distorted trigonal bipyramid. Treatment of the iron, cobalt 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl pyridine complexes (3 and 4) with
methylaluminoxane (MAO) lead to a highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE), while
the corresponding chromium complex (5) is disclosed as moderate catalytic activity for the polymerization of ethylene. The specific catalytic activ-
ities were evaluated at different temperature and Al/M (M = Fe, Co and Cr) ratio. In addition, the complexes 3–5 and corresponding compounds
of FeCl2, CoCl2(THF)1.5 and CrCl3(THF)3 can also catalyze vinyl polymerization of norbornene activated with MAO and show good activities.
However, the copper and zinc complexes (6a–7b) showed no active in ethylene and norbornene polymerization in the presence of MAO.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Ethylene and norbornene polymerization; Bis(imino)pyridyl ligands; Iron; Cobalt; Chromium; Copper; Zinc
1. Introduction
cursor were described [6], as were bis(imino)pyridine com-
plexes containing dendritic wedges [7] and metallodendrimer
[8].
Non-metallocene complexes have been shown to be impor-
tant catalysts in the polymerization of olefins [1]. One of the
most effective catalyst are Fe(II), Co(II) and Cr(II or III) N,N,N-
bis(imino)pyridyl-type complexes [2]. Treatment of these com-
plexes LMXn (M = Fe, Co, Cr) with methylaluminoxane (MAO)
leads to highly active ethylene polymerization catalysts convert-
ing ethylene to highly linear polyethylene (PE) or oligomer-
ization. Several modifications of the bis(imino)pyridine back-
bone, which have already been described in the literature
[1b,3–5], mostly lead to a decrease in catalytic activity. Recently,
simultaneous polymerization and Schulz–Flory oligomeriza-
tion of ethylene made possible by activation with MAO of a
C1-symmetric [2,6-bis(arylimino)pyridyl]iron dichloride pre-
The NBE (norbornene) addition polymer displays a charac-
teristic rigid random coil conformation, which shows restricted
rotation about the main chain and exhibits strong thermal
stability (Tg > 350 ◦C). In addition, it has excellent dielectric
properties, optical transparency and unusual transport proper-
ties. Therefore, it has been attracted many chemists to study the
NBE vinyl polymerization. In recent years, the vinyl-type poly-
norbornene (PNB) can be prepared by nickel-based complexes
and other metal complexes [9–15]. Yasuda et al. [16] reported
several cobalt complexes bearing substituted terpyridine
´ ´
ligands for vinyl norbornene polymerization. Frederic et al.
[17] reported polymerization of NBE with CoCl2 and pyridine
bisimine cobalt(II) complexes activated with MAO. Janiak and
co-workers [18] reported dihalogeno(diphosphane)metal(II)
complexes (metal = Co, Ni, Pd) as pre-catalysts for the
vinyl/addition polymerization of norbornene-elucidation of
∗
Corresponding author. Tel.: +86 591 83448669.
E-mail address: jxchen 1964@163.com (J. Chen).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.06.016

134
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
merization of ethylene nor vinyl norbornene polymerization in
the presence of MAO.
2. Experimental
All manipulations of air and/or moisture-sensitive com-
pounds were performed under an atmosphere of nitrogen using
standard Schlenk techniques. Solvents were dried prior to use
by refluxing over and distillation from sodium (THF, toluene,
hydrocarbons)orcalciumhydride(dichloromethane, chloroben-
zene). Norbornene (Across) was purified by distillation over
sodium and used as a solution in chlorobenzene. IR spectra
were recorded using a Nicolet AV-360 spectrometer. Elemental
analyses were Perkin-Elmer 2400 elemental analyzer for C, H,
N. 2,6-Diacetylpyridine, 2,5-ditertbutylaniline were purchased
from Aldrich; MAO (10% solution in toluene) was obtained
from Witco. CoCl2(THF)1.5 and CrCl3(THF)3 was prepared
according to a published procedure [22]. Anhydrous CuCl2
and ZnCl2 were obtained from the corresponding aqueous salts
which heated up under vacuum condition.
Fig. 1. Iron, cobalt and chromium bis(imino)pyridyl precatalysts for the poly-
merization of ethylene.
the activation process with B(C6F5)3/AlEt3 or Ag[closo-1-
CB11H12]. Janiak and co-workers [19] also reported novel
polynuclear cage complexes as precatalysts in the vinyl or
addition polymerization of norbornene activated with MAO
as well as with B(C6F5)3, in combination with or without
AlEt3 and correlated with the results of the known mononu-
clear precatalysts M(acac)x (M = NiII, CoIII, CrIII and FeIII,
acac = acetylacetonate, x = 2 or 3).
The nature of the metal center has a large influence on catalyst
productivity. In general, Fe catalysts are more active than the
corresponding Co analogues. It is well known that the position
and steric bulk of the substituents on the imino nitrogen donors
of the bis(imino)pyridyl catalysts (Fig. 1) play a pivotal role in
determining the selectivity of the catalyst. The ortho substituents
(R1 and R2) have been identified as being particularly important.
If only one of the ortho substituents R1 or R2 on each ring is
an alkyl group and the other is a hydrogen or halogen [4], then
the catalyst is selective for the oligomerization of ethylene to
linear 1-alkenes with a Schultz–Flory chain length distribution.
If both the ortho substituents R1 and R2 groups are bulky alkyl
substituents such as iso-propyl groups, then the catalysts are
selective for the production of high molecular weight polymers
from ethene.
2.1. Synthesis of 2,6-bis[1-(2,6-diisopropylphenylimino)
ethyl]pyridine (1)
2,6-Bis[1-(2,6-diisopropylphenylimino)ethylpyridine was
synthesized according to the public literature [2c]. IR (KBr):
3063.2, 2960.6, 2926.7, 2867.4, 1643.2 (vs, C N), 1577.56,
1457.55, 1383.5, 1364.6, 1322.5, 1240.1, 1192.4, 1118.3,
1077.6, 935.9, 875.7, 825.6, 767.5 and 689.2. Anal. Calcd for
C33H43N3: C, 82.20; H, 8.93; N, 8.72. Found: C, 82.45; H,
9.01; N, 8.45.
2.2. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridine (2)
To date, reports on olefin polymerization catalysts based on
copper are scarce [1b]. The ␣-diimine CuII complex produces
very high-molecular-weight PE with moderate activity [20].
Although there have been no reports of single-site olefin poly-
merization catalysts based on Group 12 metals, it has recently
been shown that transition metal catalysts can catalyze PE chain
growth on zinc centers, affording linear alkanes or ␣-olefins
with a Poisson distribution [21]. The effect of substituents in
the meta-position has been less studied [4,5d]. Here we report
the syntheses, structures and ethylene and norbornene additional
polymerization behaviors of iron, cobalt, chromium, copper and
zinc complexes bearing bulky bis(imino)pyridyl ligands with
2,6-diisopropylphenyl or 2,5-ditertbutylphenyl substituents. We
also report the effects observed on variation of the reaction
conditions, such as the concentration of methylaluminoxane
(MAO) and the temperature of ethylene polymerization. The
results show that iron and cobalt bis(imino)pyridine complexes
are highly active in the polymerization of ethylene by activa-
tion with MAO, while the corresponding chromium complex is
disclosed as moderate active for the polymerization of ethylene.
The iron and cobalt and chromium complexes show good active
for the vinyl norbornene polymerization. However, the copper
and zinc complexes almost show no active neither for the poly-
To a solution of 2,6-diacetylpyridine (0.50 g, 3.07 mmol) in
absolute ethanol (20 ml) was added 2,5-ditertbutylphenyaniline
(1.258 g, 6.14 mmol). After the addition of a few drops of glacial
acetic acid, the solution was refluxed overnight. Upon cooling
to room temperature, the product crystallized from ethanol. The
yellow solid formed was then filtered and washed with cold
ethanol and dried under vacuum; the yield was 86%. IR (KBr):
2958.8, 2866.8, 1635.6 (νC N), 1566, 1491, 1457.7, 1385.5,
1363.6, 1297.6, 1248.9, 1205, 1119.5, 1072, 974, 927, 886, 820,
722 and 652 cm−1. Anal. Calcd for C37H51N3: C, 82.68; H, 9.49;
N, 7.82. Found: C, 82.75; H, 9.52; N, 7.71.
2.3. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridineiron(II) chloride (3)
Ligand 2 (107 mg, 0.2 mmol) was added to a suspension
of FeCl2 (25 mg, 0.2 mmol) in CH2Cl2 (15 ml) at room tem-
perature with rapid stirring. The solution turned deep blue
immediately. After it was stirred at room temperature for 12 h,
the excess FeCl2 was removed. The reaction volume was con-
centrated, and n-hexane (30 ml) was added to precipitate the
product as a blue powder, which was subsequently washed

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
135
with n-hexane (3 × 10 ml), filtered, and dried to afford 105 mg
2.8. Synthesis of 2,6-bis[1-(2,6-diisopropylphenylimino)
ethyl]pyridinezinc(II) chloride (7a)
(79%) of 3. IR (KBr): 2960, 2868.5, 1633 (νC N), 1491, 1467.5,
1366.8, 1265.9, 1206, 1134.6, 1070, 1035, 928, 891, 820 and
733.5 cm−1. Anal. Calcd for C37H51N3FeCl2: C, 67.89; H, 7.80;
N, 6.42. Found: C, 67.93; H, 7.86; N, 6.38.
A solution of ligand 1 (50 mg) and anhydrous ZnCl2 (50 mg)
in THF (10 ml) was stirred at room temperature for 24 h. The
reaction volume was concentrated, and n-hexane was added to
afford a light yellow solid, which was washed three with n-
hexane and dried in vacuum. IR (KBr): 2965.2, 2926.3, 2867.6,
1634.4, 1587.0, 1463.0, 1329.2, 1253.8, 1203.4, 1100.1, 1056.6,
1024.7, 937.6, 820.6, 798.4 and 776.8 cm−1. Anal. Calcd for
C33H43N3ZnCl2: C, 64.06; H, 6.96; N, 6.79. Found: C, 64.01;
H, 6.99; N, 6.59.
2.4. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridinecobalt(II) chloride (4)
A suspension of 2 (107 mg, 0.2 mmol) in n-butanol was added
to a solution of CoCl2 (25 mg; 0.2 mmol) in n-butanol (20 ml) at
80 ◦C to yield a grass green solution. After being stirred at 80 ◦C
for 30 min, the reaction was allowed to cool to room temperature.
The reaction volume was concentrated, and n-hexane (30 ml)
was added to precipitate the product as a grass green powder,
which was subsequently washed with n-hexane (3 × 10 ml), fil-
tered, and dried to afford 116 mg (85%) of 3. Grass green crystals
of the product 3 formed in THF/n-hexane solution at 0 ◦C for
several days. IR (KBr): 2959.7, 2868, 1630 (νC N), 1590, 1497,
1464, 1367.6, 1264.5, 1210, 1135, 1068, 1027, 927, 891 and
823 cm−1. Anal. Calcd for C37H51N3CoCl2·H2O: C, 64.82; H,
7.74; N, 6.13. Found: C, 64.76; H, 7.68; N, 6.24.
2.9. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridinezinc(II) chloride (7b)
The procedure as above in (2.8) using 2 and ZnCl2 gave
complex 7b as a light yellow solid. IR (KBr): 2956.9, 2903.5,
2866.2, 1642.3, 1600.6, 1568.2, 1491.4, 1448.1, 1387.3, 1363.6,
1296.6, 1249.5, 1208.1, 1118.5, 1073.8, 977.6, 925.7, 885.8,
819.9, 741.1 and 720.9 cm−1. Anal. Calcd for C37H51N3ZnCl2:
C, 65.89; H, 7.57; N, 6.23. Found: C, 65.91; H, 7.62; N,
6.15.
2.5. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridinechromium(III) chloride (5)
2.10. X-ray structure determination
Data collection for complex 4 were performed at 293 K
on a Rigaku R-AXIS RAPID Weissenberg IP diffractometer
equipped with a graphite-monochromatized Mo K␣ radiation
A solution of CrCl3(THF)3 (75 mg, 0.2 mmol) and 2 (107 mg,
0.2 mmol)inacetone(10 ml)wasrefluxedovernight, givingatan
suspension. The reaction volume was concentrated, and diethyl
ether was added to afford a jade-green solid, which was washed
repeatedly with diethyl ether and dried in vacuum. Yield: 128 mg
(92%). IR (KBr): 2963, 1631, 1501, 1471, 1368.6, 1269.2, 1081,
1044 and 816 cm−1. Anal. Calcd for C37H51N3CrCl3: C, 63.76;
H, 7.32; N, 6.03. Found: C, 64.36; H, 7.41; N, 5.91.
˚
(λ = 0.71073 A). Lorentz-Polarization corrections and empiri-
cal absorption correction were applied to the data. The struc-
tures was solved by direct methods with SHELXS-97 [23] and
refined on F2 using full-matrix least-squares calculations with
SHELXL-97 [24]. All non-hydrogen atoms were refined with
anisotropic thermal parameters, and all the hydrogen atoms were
placed at the idealized positions with Uiso(H) = 1.2Ueq(C) and
Uiso(H) = 1.5Ueq(C) for aromatic and methyl H atoms, respec-
tively. Crystal data and processing parameters for complex 4
are summarized in Table 1. The crystallographic data for com-
plex 4 has been deposited at the Cambridge Crystallographic
DataCentreandallocatedthedepositionnumberCCDC290535.
Copies of the data can be obtained free from the Director, CCDC,
12 Union Road, Cambridge CB2 1EZ (fax: C44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
2.6. Synthesis of 2,6-bis[1-(2,6-diisopropylphenylimino)
ethyl]pyridinecopper(II) chloride (6a)
A solution of ligand 1 (50 mg) and anhydrous CuCl2 (14 mg)
in THF (10 ml) was stirred at room temperature for 24 h, The
reaction volume was concentrated, and diethyl ether was added
to afford a brown solid, which was washed three with diethyl
ether and dried in vacuum. IR (KBr): 2962.6, 2918.4, 2863.2,
1630.4, 1582.2, 1463.8, 1383.3, 1260.3, 1205.9, 1054.3, 800.6
and 561.5 cm−1. Anal. Calcd for C33H43N3CuCl2: C, 64.21; H,
6.97; N, 6.81. Found: C, 64.38; H, 7.01; N, 6.74.
2.11. Ethylene polymerization
2.7. Synthesis of 2,6-bis[1-(2,5-ditertbutylphenylimino)
ethyl]pyridinecopper(II) chloride (6b)
The precatalyst was dissolved in toluene and MAO (10 wt%
in toluene) added to the solution. The flamedried Schlenk flask
was placed in a water bath and purged with ethylene, and the
contents were magnetically stirred and maintained under ethy-
lene (1 atm) for 1 h. The polymerization was terminated by the
addition of 10% (by mass) acidified ethano1. The solid PE was
recovered by filtration, washed with ethanol and dried under
vacuum at 70 ◦C overnight.
The procedure as above in (2.6) using 2 and CuCl2 gave com-
plex 6b as a brown solid. IR (KBr): 2961.4, 2871.1, 1626.5,
1586.1, 1467.2, 1427.7, 1384.1, 1267.6, 1067.6, 822.3 and
556.7 cm−1. Anal. CalcdforC37H51N3CuCl2:C, 65.99;H, 7.58;
N, 6.24. Found: C, 66.03; H, 7.61; N, 6.18.

136
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
2.12. Vinyl polymerization of norbornene
Table 1
Crystallographic data and structure refinement for complex 4
In a typical procedure, the precatalyst (3.07 ␮mol) was
added in a Schlenk tube in 11.12 ml chlorobenzene and 2.88 ml
chlorobenzenesolutionofnorbornene(1 g/ml, 2.88 g)wasadded
via syringe. The polymerization was initiated by adding 1 ml
toluene solution of MAO (10%) at 30 ◦C. After 12 h, the poly-
merization was terminated by injecting 50 ml 10% acidic ethanol
into the reactor. The PNB was isolated by filtration, washed with
ethanol, dried in vacuum at 100 ◦C for 48 h.
Formula
C37H53ON3CoCl2
685.65
Formula weight
Crystal system
Space group
Monoclinic
P2(1)/c
11.6063(4)
26.2498(10)
16.0347(5)
90
108.8538(11)
90
4623.1(3)
4
˚
a (A)
˚
b (A)
˚
c (A)
α (◦)
β (◦)
γ (◦)
3
˚
V (A )
2.13. Polymer characterization
Z
Dcalc (Mg m−3
)
0.985
The intrinsic viscosity [η] of polymer solution in decalin was
determined using a modified Ubbelohde viscosimeter at 135 ◦C
and the one-point intrinsic viscosity method [25]. SEM study on
polymermorphologywascarriedoutonaKYKY-1000Bfacility.
The viscosity–average molar masses (Mv) of the polyethylene
were calculated using the Mark–Houwink equation [26]:
Crystal size (mm)
0.72 × 0.63 × 0.54
μ (mm−1
F(0 0 0)
)
0.512
1460
27.48, 1.55
θmax, θmin (◦)
Index range
h
k
l
0 → 15
0 → 34
[η] = 6.77 × 10−2Mv0.67
.
−20 → 19
Rint
0.0548
10081
5917
396
0.0658
0.1696
0.982
The thermal characteristics of the polymers were examined
using a DSC-822 instrument (Mettler toledo) with a heating rate
of 10 ◦C/min, in the range from 50 to 200 ◦C. The crystallinity
of the polyethylene was calculated using the following equation
[27]:
No. of independent reflections
No. of observed reflections
No. of variables
R
wR
GOF
a
−3
ꢀH
˚
Largest difference peak (hole) (e A
Δ/σ
)
0.577 (−0.369)
χc (%) =
× 100%
0.000, 0.000
ꢀHo
ꢀ
ꢀ
ꢀ
ꢀ
R = ||Fo| − |Fc||/ |Fo|; wR = { [w(Fo2 − Fc2)2]/[ w(Fo2)2]}1/2
.
(ꢀHo = 287.3 J/g for completed crystal polyethylene).
a
Largest peak (hole) in difference Fourier map.
The viscosity–average molar masses (Mv) of the PNB
were obtained using the Mark–Houwink coefficients [28,29]:
α = 0.56, K = 7.78 × 10−4 dl/g.
Scheme 1. Synthesized iron, cobalt, chromium, copper and zinc bis(imino)pyridyl complexes; reagents and conditions: (i) EtOH, H+ and (ii) 3, FeCl2,
R1 = R3 = tertbutyl, R2 = H, CH2Cl2; 4, CoCl2, R1 = R3 = tertbutyl, R2 = H, n-BuOH, Δ; 5, CrCl3(THF)3, R1 = R3 = tertbutyl, R2 = H, acetone, Δ; 6a, CuCl2,
R1 = R2 = isopropyl, R3 = H, THF; 6b, CuCl2, R1 = R3 = tertbutyl, R2 = H, THF, Δ; 7a, ZnCl2, R1 = R2 = isopropyl, R3 = H, THF; Δ; 7b, ZnCl2, R1 = R3 = tertbutyl,
R2 = H, THF, Δ.

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
137
Fig. 2. Molecular structure of the cobalt complex 4 (One H2O molecule in the
lattice is not included).
3. Results and discussion
3.1. Syntheses and structures of complexes
Fig. 3. Side-on view, perpendicular to the plane of the three ligand nitrogen
atoms of the complex 4, showing the pronounced differences in coordination
geometry and the deviation of the metal centers from the ligand plane.
The ligands 1 and 2 were prepared in high yield from the
condensation of two equivalents of appropriate aniline with one
equivalent of 2,6-diacetylpyridine (Scheme 1). Ligands 1 and
2 was characterized by elemental analyses, IR spectroscopy
(see Section 2). The complexes 3–7b were synthesized in good
yield by treating MCln (M = Fe, Co, Cr, Cu and Zn; n = 2, 3)
with the ligands 1 or 2 in different solvent (Scheme 1). All
the complexes, 3–7b, were characterized by elemental analyses,
IR spectroscopy (see Section 2). The elemental analysis results
revealed that the components of all complexes were in accord
with the formula MLCln (n = 2, 3), and one molecule of H2O
in 4. The IR spectra of the ligands 1 and 2 show that the C N
stretching frequency appear at 1643 and 1635.6 cm−1, respec-
tively. In complexes 3–7b, the C N stretching vibrations shift
toward lower frequencies and were greatly reduced in intensity,
which indicated the coordination interaction between the imino
nitrogen atoms and the metal ions. In addition, the cobalt com-
plex 4 was subject to single-crystal X-ray diffraction study. The
molecular structure of the cobalt complex 4 is shown in Fig. 2,
and selected bond lengths and angles are presented in Table 2.
The complex 4 displays an approximate C2 symmetry about
a plane containing the cobalt atom, the two chloro atoms, and
the pyridyl nitrogen atom. The Co N (pyridyl) bond (2.033
Co analogues [2b,2c,2g]. In addition, in the complex 4, the
two imino C N bonds have distinctive double-bond charac-
˚
ter, with C N distances in the range 1.273(4) and 1.276(3) A.
Although the substitutes on the bis(imino)pyridine ligand back-
bone is bulky 2,5-ditertbutylphenyl, the planes of the phenyl
rings are oriented essentially orthogonal to the plane of the
backbone (ranging between 83.29(14)◦ and 87.77(11)◦) which
˚
is coplanar to within 0.0029–0.0067 A. The cobalt atom devi-
˚
ates by 0.0882(28) A from the plane formed by three coordinated
nitrogen atoms. The Cl(1)–Co–Cl(2) angle is 116.20(4)◦. Two
N(1)–Co–Cl angles are unsymmetrical: one is 113.43(8)◦, while
the other is 130.31(8)◦. The “axial” Co N bonds subtend an
angle of 149.83(8)◦, which is near to that of 2,6-dimethylphenyl
substituted Co complex (150.42(17)◦) [2g], but wider than that
of 2,6-diisopropylphenyl [2c] and 2-terbutyl [2b] substituted
Co complexes (141.3(7)◦, 142.1(4)◦). Inspection of the space-
filling model reveals a bulky steric interactions created by the
2,5-tertbutyl of the phenyl within the cobalt center (Fig. 4). The
coordination geometry of the central cobalt can be best described
as distorted trigonal bipyramidal, with the pyridyl nitrogen atom
and the two chloro atoms forming the equatorial plane (Fig. 3),
which is similar to that of 2,6-dimethylphenyl substituted Co
complex [2g]. However, the 2,6-diisopropylphenyl [2c] and 2-
terbutyl substituted Co complexes [2b] can be regarded as dis-
torted square pyramidal grometry.
˚
(2) A) is significantly shorter than the Co N (imino) bonds
˚
(2.250(2) and 2.294(2) A), but the bond lengths Co N (pyridyl)
and Co N (imino) are very similar to that of three related
Table 2
◦
˚
Selected bond lengths (A) and angles ( ) for complex 4
Co–N(1)
Co–N(3)
Co–Cl(2)
N(3)–C(8)
N(1)–Co–N(2)
N(3)–Co–N(2)
Cl(1)–Co–Cl(2)
Cl(1)–Co–N(2)
Cl(2)–Co–N(2)
2.033(2)
2.250(2)
2.260(10)
1.273(4)
74.81(9)
149.83(8)
116.20(4)
98.02(7)
95.59(7)
Co–N(2)
Co–Cl(1)
N(2)–C(6)
2.294(2)
2.233(10)
1.276(3)
3.2. Ethylene polymerization experiments
All the complexes (3–7b) are generated in situ in toluene by
the addition of methylaluminoxane as activator in the presence
of ethylene. The chromium complex 5 was previously dissolved
and preactivated in a methylaluminoxane/toluene solution for
60 min, which helps to solubilize the poorly soluble complex and
performs the actual catalytic species [2e]. The activity results
N(1)–Co–N(3)
Cl(1)–Co–N(3)
N(1)–Co–Cl(2)
N(3)–Co–Cl(2)
N(1)–Co–Cl(1)
75.19(9)
98.82(7)
113.43(8)
99.16(7)
130.31(8)

138
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
Fig. 4. Space-filling model of the complex 4.
Fig. 6. Effect of the [Al]/[M] (M = Fe, Co) ratio on the viscosity average molecu-
lar weight using complexes 3 and 4. General conditions: 3.0 ␮mol of M (M = Fe,
Co), 100 ml of toluene, 1 atm, 35 ◦C, 60 min.
and molecular weights with diverse sets of conditions are given
in Figs. 5–8 and Table 3.
In order to investigate detailed polymerization behavior of
the complexes (3–5), polymerizations were carried out at var-
ious MAO concentrations. The [Al]/[M] ratios in complexes 3
and 4 can have a significant effect on the activity and molec-
ular weights (Figs. 5 and 6). When [Al]/[Fe] = 1500, the cat-
alytic activity of the complex 3 achieved the maximum value
(2.33 × 106 g PE/mol Fe h) (see Fig. 5). As the [Al]/[Fe] still
rising, the activity and the molecular weights possess decrease
trend. Similarly, the Co complex 4 obtained the maximum activ-
ityvalue1.15 × 106 g PE/mol Co h(see Fig. 5)asthe[Al]/[Co]is
2000. First, increasing the MAO concentration results in higher
activity may be due to an increase in the number of active sites.
However, excess MAO concentrations will block the contact of
the ethylene and the active sites. On the other hand, the trimethy-
laluminum (TMA) of the MAO will reduce the active sites. The
MAO concentrations affect unconspicuous on the activity and
molecular weights of the chromium complex 5. The poorly solu-
Fig. 7. Dependence of the activity and the viscosity average molecular weight on
temperatureforcomplex3. Generalconditions:3.0 ␮molofFe, [Al]/[Fe] = 1500,
100 ml of toluene, 1 atm, 60 min.
Fig. 8. Dependence of the activity and the viscosity average molecular
weight on temperature for complex 4. General conditions: 3.0 ␮mol of Co,
[Al]/[Co] = 2000, 100 ml of toluene, 1 atm, 60 min.
Fig. 5. Influence of the [Al]/[M] (M = Fe, Co) ratio on the activity of complexes
3 and 4. General conditions: 3.0 ␮mol of M, 100 ml of toluene, 1 atm, 35 ◦C,
60 min.

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
139
Table 3
The results of ethylene polymerization by complex 5 in the presence of MAOa
Entry
Catalyst (␮mol)
[Al]/[Cr]
T (◦C)
PE (g)
Activityb
Mv (×104 g/mol)
1
2
3
4
5c
6
7
8
9
10
2.87
2.58
2.87
3.70
2.87
2.87
2.29
2.87
1.58
1.43
200
500
30
30
30
30
30
30
30
0
0.090
0.085
0.123
0.207
0.256
0.344
0.154
0.048
0.015
0.091
3.10 × 104
3.29 × 104
4.31 × 104
5.60 × 104
8.91 × 104
11.9 × 104
6.75 × 104
1.67 × 104
0.95 × 104
6.34 × 104
18.2
13.4
25.6
10.8
9.8
11.1
6.2
12.3
9.0
1000
1500
2000
2000
2500
2000
2000
2000
50
75
5.6
a
Polymerization conditions: run time = 60 min, 50 ml of toluene, Tp = 30 ◦C, PC H4 = 1.0 atm.
2
b
c
g/mol Cr h.
Using 50 ml of CH2Cl2 instead of toluene.
Table 4
The PE results of DSC
ble chromium complex may be responsible for the result. When
using CH2Cl2 instead of toluene as solvent in entry 5 (Table 3),
the activity increases to 11.9 × 104 g/mol Cr h.
Complex
χc (%)
Tm (◦C)
Tc (◦C)
Figs. 7 and 8; Table 3 show the results of polymerizations
performed at various temperatures between 0 and 80 ◦C employ-
ing the three complexes. For the three complexes, a significant
reduction in the activity and the molecular weights as the temper-
aturerising. However, theactivityofthecomplex3firstincreases
and reaches max at about 35 ◦C then decline, while chromium
complex 5 increases again when the temperature at 75 ◦C. Ele-
vated temperatures will result in higher chain propagation and
chain-transfer rates, which would be expected to afford higher
activity and lower molecular weight product. The other hand a
decrease in ethylene solubility at higher temperatures will lead
to reduced productivity and result in higher rates of catalyst
deactivation. It is a combination of these effects that is likely to
account for the observed temperature dependence [2c]. The sol-
ubility of the complex 5 increases when at higher temperature
may be explain the activity increase at 75 ◦C.
3a
4b
5c
79.70
71.02
49.26
136.76
145.42
128.75
106.91
120.45
100.01
a
Conditions: 3.0 ␮mol of Fe, [Al]/[Fe] = 1500, 100 ml of toluene, 1 atm,
60 min, Tp = 0 ◦C.
b
Conditions: 3.0 ␮mol of Co, [Al]/[Co] = 2000, 100 ml of toluene, 1 atm,
60 min, Tp = 0 ◦C.
c
Conditions: 2.87 ␮mol of Cr, [Al]/[Cr] = 2000, 50 ml of toluene, 60 min,
1.0 atm, Tp = 30 ◦C.
complexes (6a–7b) showed almost no active for ethylene poly-
merization in the presence of MAO. The metal center also
influencesmolecular weight. Feprecatalystyield Mv intherange
of 2.1 × 104–32.6 × 104 (see Figs. 6 and 7). The Co-based com-
plex polymer’s Mv are in the range of 1.8 × 104–18.5 × 104
(see Figs. 6 and 8), which is lower than complex 3. Sim-
ilarly, the chromium complex 5 yield Mv in the range of
5.6 × 104–25.6 × 104 (see Table 3). According to the results
of the differential scanning calorimetry (DSC) (Table 4), the
polymer samples obtained by the 3 and 4 complexes showed
sharp single melting peaks and very high crystallinities, demon-
strating they are highly linear chains, which is different from
The nature of the metal center has a significant effect on
catalyst activity. The Fe complex 3 (2.33 × 106 g/mol Fe h)
is more active than the corresponding Co complex 4
(1.52 × 106 g/mol Co h) (see Fig. 8), while the chromium com-
plex 5 is only 1.19 × 105 g/mol Cr h, which is in accordance
with the previously reported results [2]. The copper and zinc
Fig. 9. The SEM of the PE obtained from (a) complex 3, 3.0 ␮mol of Fe, [Al]/[Fe] = 1500, 100 ml of toluene, 1 atm, 60 min, Tp = 0 ◦C and (b) complex 4, 3.0 ␮mol
of Co, [Al]/[Co] = 2000, 100 ml of toluene, 1 atm, 60 min, Tp = 0 ◦C.

140
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 259 (2006) 133–141
Table 5
the branching polymer obtained by the Ni(II) and Pd(II) diimine
catalysts [30], whereas the PE obtained from the complex 5 pos-
sesses moderate linear chain. The SEM study shows the PE with
the different morphology obtained from the complexes 3 and 4
(Fig. 9).
The results of PNB with the precatalysts in the presence of MAOa
Precatalyst
Activity (×103 g PNB/(mol M h))
Mv (×104 g/mol)
Complex 3
Complex 4
Complex 5
FeCl2
CoCl2(THF)1.5
CrCl3(THF)3
9.25
11.4
0.35
0.65
0.60
0.73
1.9
1.2
41.7
1.7
4.6
8.4
The reason for the different performance of the iron, cobalt
and chromium complexes, 3–5, bearing 2,5-ditertbutylphenyl
may be the differences of the electronic environments [2,31]
and chain-transfer mechanisms [2]. The Fe(II) complex pos-
sessesfourunpairedelectronswhiletheCo(II)complexhasthree
unpaired electrons. The chain-transfer in Fe complex involves
a combination of ␤-H transfer and chain transfer to aluminum.
In contrast, the Co complex is characteristic of chain transfer
exclusively by ␤-H transfer. The Cr complex may occur several
chain transfer fasion: ␤-H transfer to the monomer and chain
transfer to MAO. The near full d-orbit for copper center and
full d-orbit zinc center may be responsible for the complexes
(6a–7b) showing almost no active for ethylene polymerization.
The complexes, 3–5, with 2,5-ditertbutyl in each aryl
ring are compared to that with 2-tert-butyl in the litera-
tures [2b,2e] under the similar conditions. The results show
that the iron and cobalt complexes with 2,5-di-tert-butyl sub-
stitutes have a slight decrease activity than the complexes
with 2-tert-butyl {Fe (25 ◦C): 2.65 × 106 g/mol Fe h; Co (0 ◦C):
1.63 × 106 g/mol Co h} [2b], while the chromium complex 5
shows a high activity relative to the 2-tert-butyl complex [2d].
The relationship between the different activity and the presence
of an additional tert-butyl group in the 5-position of the aryl rings
may be that the additional tert-butyl group increases the steric
bulky hindrance in another face of the pyrindyl ring. The other
reason may be the additional tert-butyl group in the 5-position
of the aryl rings which increases the net charge in the lower
charge area and reduce the net charge in the higher area [29].
The increase of the bond length of Co–N(2), Co–N(3) indicates
that the density of electron cloud of the metallic center decrease
[5a].
Reaction time, 12 h; chlorobenzene; total volume, 15 ml; norbornene/
M = 10000:1.
a
Polymerization condition: 3.07 ␮mol of precatalyst; [Al:M] = 500:1;
Tp = 30 ◦C.
[9b–15,18,19]. In the same condition, similar to the ethylene
polymerization behavior, the copper and zinc complexes show
almost no active for NBE additional polymerization. All the
polymers obtained have been characterized by IR spectra. The
IR spectra prove the absence of a double bond, as no peaks
appeared between 1620 and 1680 cm−1. This further ensures the
occurrence of vinyl-type polymerization. The polymers molec-
ular mass Mv are between 1.2 × 104 and 8.4 × 104 g/mol except
the polymer (41.7 × 104) which obtained from complex 5.
4. Conclusions
In summary, the syntheses and characterization of three
new iron-, cobalt- and chromium-based precatalysts (3–5)
with bulky 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl] pyri-
dine ligand (1) and copper and zinc complexes (6a–7b) bear-
ing bulky 2,6-bis[1-(2,6-diisopropylphenylimino)ethylpyridine
or 2,6-bis[1-(2,5-ditertbutylphenylimino)-ethyl]pyridine ligand
(2) have been described. Activation with MAO the complexes
3 and 4 produce highly active catalysts converting ethylene
to highly linear polyethylene (PE), while the corresponding
chromium complex 5 is disclosed as moderate active for the
polymerization of ethylene. And their catalytic activity were
evaluated at different temperature and Al/M (M = Fe, Co and
Cr) ratio. The complexes 3–5 and FeCl2, CoCl2(THF)1.5 and
CrCl3(THF)3 can catalyse vinyl polymerization of norbornene
activated with MAO and show good activity. However, the cop-
per and zinc complexes show almost no active for ethylene and
NBE polymerization.
3.3. Norbornene polymerization
The iron, cobalt and chromium complexes showed high
activity for ethylene polymerization, there will be active for
norbornene polymerization [17]. The catalysis of the com-
plexes 3–7b and the corresponding salts or the complex of
tetrahydrofuran for the polymerization of norbornene were
also investigated in the presence of MAO as a cocatalyst
(Table 5). Without a cocatalyst, these complexes showed no
catalytic activity. The complexes (3–5) showed good activi-
ties, in particular, the cobalt complex 4 showed the highest
activity 11.4 × 103 g PNB/(mol Co h). In addition, to our best
knowledge, it is the first time that FeCl2, CoCl2(THF)1.5 and
CrCl3(THF)3 are shown to be active catalysts for the addi-
tion polymerization of norbornene. Interestingly, the activity of
CrCl3(THF)3 is higher than the complex 5, and the activity of
FeCl2 is higher than the CoCl2(THF)1.5 [17]. These complexes
are as active as the recently described nickel- and palladium-
based complexes activated with MAO [32,33], but less active
than some others exhibiting activities up to 5 × 107 g/mol h
Acknowledgements
Project supported by the Natural Science Foundation of
Fujian Province (E0310016) and the Education Committee
Foundation of Fujian Province (JB05309).
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