Ferrous and cobaltous chlorides bearing 2,8-bis(imino)quinolines: Highly active catalysts for ethylene polymerization at high temperature

Article abstract of DOI:10.1021/om9010142

A series of 2,8-bis(l-aryliminoethyl)quinolines [2,8-(2,6-R ¹₂-4-R²C₆H₂N=CCH ₃)₂C₉H₅N (L), R¹ = Me, Et, or i-Pr, R²=H or Me] is synthesized and used in the reaction with ferrous or cobaltous chlorides. The corresponding complexes LMCl₂ are limitedly formed with ligands containing ortho-methyl groups of the imino phenyl rings (R=H, M = Fe (Fel), M=Co (Col); R=Me, M = Fe (Fe2), M=Co (Co2). The X-ray diffraction study reveals a distorted pyramidal geometry of Col around the cobalt atom. These complexes, activated with methylaluminoxane (MAO), show unique properties toward ethylene polymerization: no activity observed at low temperature, but high activity achieved at temperatures higher than 80 °C (up to 7.61 x 10⁶ g·mol^-1 ·h^-1 at 100 °C). Moreover, the polyethylenes obtained are high molecular weight with narrow molecular distribution. This is the first example of iron and cobalt procatalysts with high activity for ethylene polymerization at high temperature.

Full text of DOI:10.1021/om9010142

1168 Organometallics 2010, 29, 1168–1173
DOI: 10.1021/om9010142
Ferrous and Cobaltous Chlorides Bearing 2,8-Bis(imino)quinolines:
Highly Active Catalysts for Ethylene Polymerization
at High Temperature
Shu Zhang,† Wen-Hua Sun,*,†,‡ Tianpengfei Xiao,† and Xiang Hao†
†Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China and ‡State Key Laboratory
for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, China
Received November 23, 2009
A series of 2,8-bis(1-aryliminoethyl)quinolines [2,8-(2,6-R1 -4-R2C6H2NdCCH3)2C9H5N (L), R1=
2
Me, Et, or i-Pr, R2=H or Me] is synthesized and used in the reaction with ferrous or cobaltous chlorides.
The corresponding complexes LMCl2 are limitedly formed with ligands containing ortho-methyl groups
oftheiminophenylrings(R=H,M=Fe(Fe1), M=Co(Co1);R=Me, M=Fe(Fe2), M=Co(Co2). The
X-ray diffraction study reveals a distorted pyramidal geometry of Co1 around the cobalt atom. These
complexes, activated with methylaluminoxane (MAO), show unique properties toward ethylene
polymerization: no activity observed at low temperature, but high activity achieved at temperatures
higher than 80 °C (up to 7.61 ꢀ 106 g mol-1 h-1 at 100 °C). Moreover, the polyethylenes obtained are
3
3
high molecular weight with narrow molecular distribution. This is the first example of iron and cobalt
procatalysts with high activity for ethylene polymerization at high temperature.
1. Introduction
addition to their high productivity, the ferrous and cobaltous
catalysts commonly produce R-olefins and/or long-chain
R-olefin waxes.3,5,6 Recognizing the advantages of the high
productivity and linear R-olefins, many scientists have
modified the ligands of complex catalysts through changing
substituents of aryl groups7 or direct substituents8 linked to
imino groups of bis(imino)pyridines. These modifications
modify the steric and electronic influences of ligands in order
to control the catalytic activities and products of complex
catalysts in ethylene oligomerization and/or polymeriza-
tion.4,7,8 In addition, there are extensive modifications with,
The advent of the bis(imino)pyridine ferrous and cobal-
tous complexes is a milestone of late transition metal com-
plexes as highly active catalysts for ethylene reactivity.1-4 In
*Corresponding author. Tel: þ86 10 62557955. Fax: þ86 10
62618239. E-mail: whsun@iccas.ac.cn.
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r
pubs.acs.org/Organometallics
Published on Web 02/04/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 5, 2010 1169
Scheme 1. Synthesis of L1-L4
instead of the pyridine or the imino groups, heteroatomic
cycles.6,9-11 The ferrous and cobaltous complexes with
modified ligands are obtained with high activities. Although
some catalytic systems had high activities in ethylene poly-
merization, the reaction conditions are limited at relatively
low temperature. While most reported late transition metal
catalysts with ethylene polymerization activity produce
more oligomers or low molecular polyolefins when the
reaction temperature was elevated, thermostable nickel and
palladium procatalysts bearing modified bidentate ligands
were reported for ethylene polymerization.12 Regarding
oligomers and/or polyethylene with low molecular weights,
considering the highly exothermic reaction of ethylene poly-
merization, the late transition catalysts reported are hardly
considerable for the potential application in industrial poly-
merization of commercial common operating temperatures
about 80 °C. Beyond the academic interest in late transition
metal complexes as catalysts for olefin polymerization, the
critical problem must be solved of finding novel complex
catalysts with high polymerization activity at commercial
operating temperatures. In such catalytic systems, there is no
appreciable byproduct of oligomers and/or polyolefin waxes
observed.
Scheme 2. Synthesis of Iron and Cobalt Complexes
Cobaltous complexes bearing 2-(2-benzoxazolyl)-6-
(1-(arylimino)ethyl)pyridines as catalysts are promising; they
perform ethylene oligomerization at room temperature but
ethylene polymerization at higher than 40 °C.13 Encouraged
with this achievement, numerous N∧N∧N tridentate ligands
are designed and used for their late transition metal com-
plexes, which are expected to be highly active catalysts for
ethylene polymerization at commercial operating tempera-
tures. A series of 2,8-bis(1-aryliminoethyl)quinolines was
synthesized; however, there are only limited ferrous and
cobaltous complexes formed containing ligands having
methyl groups at the ortho-positions of the imino phenyl
rings. The title complexes, activated with methylalumino-
xane (MAO), show uncommon catalytic behaviors of ethy-
lene polymerization: no activity at ambient temperature and
high activity at elevated temperature. These ferrous and
cobaltous complexes have high activities toward ethylene
polymerization at high reaction temperature, producing
polyethylenes with narrow molecular weight distribution.
This is the first example of an iron complex catalyst and the
second case for a cobalt complex catalyst. Herein the syn-
theses and characterization of 2,8-bis(imino)quinolines and
the title complexes are reported, along with the ethylene
polymerization results of the title complexes.
(Scheme 1). All compounds are well characterized by ele-
mental, 1H and 13C NMR, and IR spectrometric analyses. In
addition, compound L4 is confirmed by X-ray diffraction
analysis.
2.2. Synthesis of Iron and Cobalt Complexes. All newly
synthesized 2,8-bis(1-aryliminoethyl)quinolines (L1-L4) are
explored for their coordination with iron(II) and cobalt(II)
chlorides. The coordination reaction is limited to the
ligands (L1, L2) having methyl groups at ortho-positions of
the imino phenyl rings; however, no identifiable complex
formed with the ligands L3 and L4 though different solvents
have been tried for the reactions at various reaction tem-
peratures. The iron(II) complexes Fe1 and Fe2 are routinely
prepared by mixing the corresponding ligand (L1 or L2) and 1
equiv of FeCl2 4H2O in THF at room temperature under
3
nitrogen, and the cobalt(II) complexes Co1 and Co2 by
mixing the corresponding ligand (L1 or L2) and 1 equiv of
CoCl2 in ethanol at room temperature (Scheme 2). All metal
complexes are characterized by FT-IR spectra and elemental
analyses; they are stable in air and decomposed above 280 °C
without clear melting points. According to their IR spectra,
the stretching vibrations of CdN in these complexes
(1615-1623 cm-1) apparently shift to lower wavenumber
and their peak intensities are greatly reduced, as compared to
the corresponding ligands (1641-1647 cm-1), indicating the
effective coordination interaction between the imino-nitrogen
and the cationic metal. It is a rare case that the substituents at
ortho-position of the imino phenyl rings of ligands L3 and L4
cause problems in forming tridentate coordination complexes,
which is contrary to the coordination behavior of their analo-
gues L1 and L2. The molecular structure of complex Co1 is
confirmed by the X-ray diffraction analysis, which gives an
additional explanation for the difficulty of forming tridentate
metal complexes containing ligands L3 and L4.
2. Results and Discussion
2.1. Preparation of 2,8-Bis(1-aryliminoethyl)quinolines
(L1-L4). According to the procedure of transforming car-
boxylate groups into acetyl groups,14 2,8-diacetylquinoline is
prepared in an appropriate yield. The 2,8-bis(1-arylimino-
ethyl)quinolines are formed through the condensation re-
action of 2,8-diacetylquinoline and the corresponding ani-
lines using a catalytic amount of p-toluenesulfonic acid
(12) (a) Popeney, C. S.; Rheingold, A. L.; Guan, Z. Organometallics
2009, 28, 4452–4463. (b) Liu, F.-S.; Hu, H.-B.; Xu, Y.; Guo, L.-H.; Zai, S.-B.;
Song, K.-M.; Gao, H.-Y.; Zhang, L.; Zhu, F.-M.; Wu, Q. Macromolecules
2009, 42, 7789–7796.
(13) Gao, R.; Wang, K.; Li, Y.; Wang, F.; Sun, W.-H.; Redshaw, C.;
Bochmann, M. J. Mol. Catal. A: Chem. 2009, 309, 166–171.
(14) Asma, M.; Adewuyi, S.; Kuang, X.; Badshah, A.; Sun, W.-H.
Lett. Org. Chem. 2008, 5, 296–299.
2.3. X-ray Crystallographic Studies. Crystals of L4 suita-
ble for X-ray structural determination are obtained by the
slow evaporation of its ethyl acetate solutions. The mole-
cular structure of L4 is shown in Figure S1 along with
its selected bond lengths and angles in the Supporting
Information.

1170 Organometallics, Vol. 29, No. 5, 2010
Zhang et al.
optimum catalytic conditions. With various alkylaluminums
as cocatalyst, there was no activity observed at ambient
temperature, under both ambient pressure and elevated
pressure. Inspired by the success of a cobalt catalyst per-
forming ethylene polymerization at elevated temperature,
further investigation was carried out with increasing reaction
temperature at 10 atm of ethylene pressure. Good activity
was observed with temperatures higher than 60 °C by
employing MAO as the most effective cocatalyst.
Detail results are shown in Table 1 with varying reaction
conditions such as the molar ratio of Al/Fe and reaction
temperature. As reflected with the data (entries 1-4,
Table 1), there was a trace amount of polyethylene produced
at 40 °C; more amounts of polyethylenes were obtained with
increasing the reaction temperature up to 100 °C. Elevated
reaction temperature increase chain transfer and hinder
chain propagation, resulting in products (polyethylene
waxes or oligomers) with lower molecular weights. In the
current system, all polyethylenes obtained have high molec-
ular weights with relatively narrow molecular distributions.
The active species are formed and are stable at higher
reaction temperature. To the best of our knowledge, this is
the first example of an iron catalyst maintaining good
activity for ethylene polymerization without oligomerization
at a commercial operating temperature (about 80 °C for
the Ziegler-Natta catalytic system), although a few iron
complexes ligated by modified bis(imino)pyridines were
still highly active for ethylene oligomerization along with
polymerization.15
Figure 1. Molecular structure of complex Co1 with thermal
ellipsoids at 30% probability. Hydrogen atoms have been omit-
˚
ted for clarity. Selected bond lengths (A) and angles (deg):
Co-N1 = 2.133(7), Co-N2 = 2.151(8), Co-N3 = 2.088(8),
Co-Cl1 = 2.309(3), Co-Cl2 = 2.280(3), N1-C2 = 1.298(1),
N3-C12 = 1.278(1), N1-Co-N2 = 74.1(3), N2-Co-N3 =
82.6(3), N1-Co-N3 = 131.6(3), N1-Co-Cl1 = 113.1(2), N1-
Co-Cl2 = 94.8(2), N2-Co-Cl1 = 86.2(2), N2-Co-Cl2 =
167.9(2), N3-Co-Cl1 = 106.8(2), N3-Co-Cl2 = 102.2(2),
Cl1-Co-Cl2 = 102.79(1).
Single crystals of complex Co1 suitable for X-ray structur-
al determinations were grown by the slow diffusion of diethyl
ether into its methanol solution; its molecular structure is
shown in Figure 1 along with selected bond lengths and
angles. In the solid-state structure, the cobalt of Co1 adopts a
distorted square-based pyramidal coordination environment
with Cl1 in the apical position and the cobalt lying about
Higher activities were observed with increasing the Al/Fe
molar ratio from 1500 to 3000 (entries 4-7, Table 1). At the
Al/Fe molar ratio 3000, its catalytic activity reached 4.14 ꢀ
105 g mol-1(Fe) h-1 under 10 atm of ethylene (entry 4,
3
3
Table 1). Further increasing the Al/Fe molar ratio to 3500
produced a slight decrease of activity (entry 8, Table 2). In
addition, the molecular weights and distributions both in-
creased gradually with an increase in Al/Fe molar ratios of
the catalytic system. It is assumed that the higher Al/Fe ratio
is required to maintain active species, which are not formed
at the same time to start ethylene polymerization.
˚
0.47 A out of the Cl2-N1-N2-N3 basal plane. The quinoline
and N3 planes are slightly inclined (about 9.9°). The cobalt
center is coordinated with the nitrogen atom from the ligand,
forming one five-membered cobaltacyclic ring and one six-
membered cobaltacyclic ring with acute N-Co-N angles of
74.1(3)° and 82.6(3)°. The two rings of chelate cobaltacycles
are nonplanar, with a dihedral angle of 15.57°. The cobalt
atom deviates from the coordination plane (based on
The ethylene polymerization with Fe1/MAO catalysts was
also conducted under different pressures of ethylene (entries
4, 9, 10, Table 1). The catalytic activities were greatly
improved with an increase in ethylene pressure (as shown
in Figure 2), attributable to the higher monomer concentra-
tion around the active iron centers at higher pressure. Under
30 atm of ethylene, the highest activity reached to 7.61 ꢀ 106
g mol-1(Fe) h-1; however, its molecular weight and PDI
˚
N1-N2-N3) by a large distance (0.860 A) due to the
bulkiness of the ligand. The Co-N3 bond length (2.088(8)
˚
A) is slightly shorter than the other Co-N bonds because of
the formation of the six-membered cobaltacyclic ring. The
Co-Cl bonds are noticeably asymmetric, with that to the
apical chloride being 2.309(3) A and that to its basal chloride
3
3
˚
value were slightly lower than the data of polyethylene
obtained under 10 atm (entry 4 vs 10, Table 1). In general,
the resultant polyethylenes possessed high molecular weights
with unimodal molecular weight distribution, suggesting
uniform active species in the catalytic system.
˚
being 2.280(3) A. Both imino bonds clearly display double-
bond character. Compared with the analogue of its ligand,
˚
the N1-C2 (1.298(1) A) imino bond at the ortho-position of
quinoline becomes longer after coordination; however, no
significant difference of the imino bond at the 8-position is
observed. Predictably, the phenyl groups linked to the imino
groups are oriented to the basal coordination plane
N1-N2-N3, with dihedral angles of 106.3° and 107.2°.
2.4. Ethylene Polymerization. The title complexes were
investigated for their catalytic behaviors in ethylene reacti-
vity. In the presence of methylaluminoxane, however, the
synthesized complexes showed high activities toward ethy-
lene polymerization at higher reaction temperatures.
Using optimum conditions, complex Fe2 also showed high
activity toward ethylene polymerization (entry 11, Table 1),
producing polymer with high molecular weight and narrow
molecular distribution. In our trial of NMR spectra of
(15) (a) Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Fones, B. B.;
Fish, B. M.; Schiffhauer, M. F.; Soper, P. D.; Waterland, R. L.; Spence,
R. E.; Xie, T. Y. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 585–611.
(b) Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Fones, B. B.; Fish, B. M.;
Schiffhauer, M. F. Organometallics 2008, 27, 1902–1911. (c) Ionkin, A. S.;
Marshall, W. J.; Adelman, D. J.; Fones, B. B.; Fish, B. M.; Schiffhauer, M. F.
Organometallics 2008, 27, 1147–1156.
2.4.1. Ethylene Polymerization by Iron Complexes. The
system of Fe1/MAO was typically investigated for the

Article
Organometallics, Vol. 29, No. 5, 2010 1171
Table 1. Ethylene Polymerization by Iron Procatalysts/MAOa
b
entry
complex
Al/Fe
P/atm
T/°C
activity/105 g mol-1 h-1
Mwb/ꢀ 10-4
nd
24.1
22.1
11.3
8.0
Mw/Mn
3
3
1
2
3
4
5
6
7
8
Fe1
Fe1
Fe1
Fe1
Fe1
Fe1
Fe1
Fe1
Fe1
Fe1
Fe2
3000
3000
3000
3000
1500
2000
2500
3500
3000
3000
3000
10
10
10
10
10
10
10
10
20
30
30
40
60
80
trace
1.35
2.00
4.14
0.386
2.49
3.80
3.76
26.3
76.1
65.1
nd
4.3
3.2
2.9
2.3
2.4
2.5
3.1
2.3
2.8
3.3
100
100
100
100
100
100
100
100
9.6
10.9
15.7
10.2
9.9
9c
10c
11c
12.5
a General condition: 5 μmol of Fe; 30 min; toluene (100 mL). b Determined by GPC. c 2 μmol of Fe; 30 min; toluene (40 mL).
Table 2. Ethylene Polymerization of Cobalt Procatalysts/MAOa
b
entry
complex
Al/Fe
P/atm
T/°C
activity/105 g mol-1 h-1
Mwb/ꢀ 10-4
nd
Mw/Mn
3
3
1
2
3
4
5
6
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co2
3000
3000
3000
2000
2500
3500
3000
3000
3000
10
10
10
10
10
10
20
30
30
60
80
trace
0.509
3.41
1.22
1.74
2.40
38.2
69.3
63.1
nd
29.8
23.4
20.1
21.2
31.8
16.7
14.6
16.9
3.5
5.2
4.0
4.6
6.1
3.7
3.6
3.1
100
100
100
100
100
100
100
7c
8c
9c
a General conditions: 5 μmol of Co; 30 min; toluene (100 mL). b Determined by GPC. c 2 μmol of Co; 30 min; toluene (40 mL).
lower the molecular weight and the narrower the molecular
distribution of polyethylenes obtained. Its analogue Co2,
activated with MAO, also showed high activity toward
ethylene polymerization (entry 9, Table 2).
3. Conclusion
Iron(II) and cobal(II) complexes ligated by 2,8-bis-
(1-aryliminoethyl)quinolines have been proved as good
procatalysts in ethylene polymerization at higher reaction
temperatures (80-100 °C). On increasing the Al/M (M=Fe
or Co) molar ratio, the polyethylene obtained has a higher
molecular weight and wider molecular distribution. The
higher the ethylene pressures used, the higher the catalytic
activities observed and the lower the molecular weight and
the narrower the molecular distribution of polyethylenes
obtained. Compared with other iron and cobalt complexes,
these complexes showed better thermostability; there-
fore such procatalysts could have considerable industrial
application.
Figure 2. Effect of ethylene pressure on catalytic activity by Fe1.
resultant polyethylenes at 110 °C in 1,2-dichlorobenzene-d4,
only one carbon peak confirmed its high molecular weight
and high linearity of obtained polyethylenes.
4. Experimental Section
4.1. General Considerations. All manipulations of air- and
moisture-sensitive compounds were performed in a nitrogen
atmosphere using standard Schlenk techniques. Toluene was
refluxed over sodium-benzophenone and distilled under nitro-
gen prior to use. Methylaluminoxane (a 1.46 M solution in
toluene) was purchased from Akzo Nobel Corp. Other reagents
2.4.2. Ethylene Polymerization by Cobalt Complexes. To
compare with the catalytic behavior of iron complexes, the
catalytic system of Co1/MAO was again investigated in
detail, and the results are collected in Table 2. The similar
tendency of catalytic activities and polyethylenes obtained
depends on the molar ratio of Al/Co, reaction temperature,
and ethylene pressure. The cobalt complex could be fully
activated at higher reaction temperature (entries 1-3,
Table 2), and the catalytic activity reached its optimum value
at a ratio of 3000 (entries 3-6, Table 2). On increasing the
Al/Co molar ratio, the polyethylene obtained has a higher
molecular weight and wider molecular distribution. The
higher the ethylene pressures used (entries 3, 7, and 8,
Table 2), the higher the catalytic activities observed and the
were purchased from Aldrich or Acros Chemicals. 1H and 13
C
NMR spectra were recorded on a Bruker DMX 300 MHz or a
Bruker DMX 400 MHz instrument at ambient temperature
using TMS as an internal standard. IR spectra were recorded
on a Perkin-Elmer System 2000 FT-IR spectrometer. MALDI-
TOF mass spectra were obtained with a Bruker Autoflex III
matrix-assisted laser desorption/ionization time of-flight mass
spectrometer, with DHB as the matrix. 1H NMR spectra of the
iron and cobalt complexes were recorded with a Bruker DMX
600 MHz instrument at 20 °C with the use of TMS as the internal

1172 Organometallics, Vol. 29, No. 5, 2010
Zhang et al.
standard. Elemental analysis was carried out using an HPMOD
1106 microanalyzer. 1H and 13C NMR spectra of the PE samples
were recorded on a Bruker DMX 300 MHz instrument at 110 °C
in 1,2-dichlorobenzene-d4 using TMS as the internal standard.
Molecular weights and polydispersity indices (PDI) of PE were
determined by a PL-GPC220 instrument at 150 °C with 1,2,
4-trichlorobenzene as the eluant.
Mp: 214-216 °C. IR (KBr; cm-1): 3062 (w), 2962 (s), 1645 (s),
1591 (m), 1565 (m), 1461 (m), 1435 (m), 1363 (m), 1277 (m), 1185
(m), 1095 (m), 856 (m), 765(s). 1H NMR (300 MHz, CDCl3): δ
8.56 (d, J=8.6 Hz, 1H); 8.31 (d, J=8.9 Hz, 1H); 8.02 (d, J=6.9
Hz, 1H); 7.96 (d, J = 7.9 Hz, 1H); 7.70 (t, J = 7.5 Hz, 1H);
7.21-7.09 (m, 6H); 3.17 (q, J=6.9 Hz, 2H); 2.79 (q, J=6.9 Hz,
2H); 2.44 (s, 3H); 2.33 (s, 3H); 1.28-1.16 (m, 24H). 13C NMR
(75 MHz, CDCl3): δ 171.2,167.4, 155.8, 146.6, 146.1, 145.2,
142.2, 136.7, 136.6, 135.8, 129.1, 129.0, 127.6, 123.9, 123.8,
123.2, 119.0, 28.5, 28.3, 23.6, 23.4, 23.3, 23.0, 17.4. Anal. Calcd
for C37H45N3 (531.36): C, 83.57; H, 8.53; N, 7.90. Found: C,
83.18; H, 8.58; N, 7.75.
Synthesis of 2,8-Bis[1-(2,4,6-trimethylphenylimino)ethyl]quino-
line (L4). Using the same procedure as for the synthesis
of L1, L4 was obtained as a yellow powder in 57% yield. Mp:
196-197 °C. IR (KBr; cm-1): 2982 (w), 2913 (w), 1641 (s), 1568
(m), 1477 (s), 1361 (m), 1276 (m), 1215 (m), 1147 (m), 1097 (m),
858 (s), 771 (m). 1H NMR (300 MHz, CDCl3): δ 8.56 (d, J=8.6
Hz, 1H); 8.28 (d, J=8.6 Hz, 1H); 8.00 (d, J=7.2 Hz, 1H); 7.93 (d,
J=8.2 Hz, 1H); 7.66 (dd, J1=7.2Hz, J2=8.0 Hz, 1H); 6.91 (s, 4H),
2.35 (s, 3H); 2.31(s, 3H); 2.30 (s, 3H); 2.24 (s, 3H); 2.20 (s, 6H);
2.02 (s, 6H). 13C NMR (75 MHz, CDCl3): δ 171.5, 167.6, 155.8,
146.3, 146.2, 145.2, 142.2, 136.5, 132.5, 132.2, 128.9, 127.5, 125.8,
125.2, 118.9, 22.9, 20.9, 18.0, 16.7. Anal. Calcd for C31H33N3
(447.27): C, 83.18; H, 7.43; N, 9.39. Found: C, 82.94; H, 7.67;
N, 9.21.
4.2. Preparation of the Ligands. Synthesis of 2,8-Diacetyl-
quinoline. A solution of diethyl quinoline-2,8-dicarboxylate
(4.10 g, 15 mmol) in 50 mL of freshly distilled ethyl acetate
was added dropwise to 8.7 equiv of dried C2H5ONa (8.84 g,
130 mmol) with stirring to afford a yellow mixture, which was
refluxed for 9 h and allowed to stand overnight. Concentrated
HCl (45 mL) was added dropwise with stirring, and the mixture
was refluxed for another 6 h to complete the reaction. With
addition of 50 mL of water, the aqueous phase was then
extracted with CH2Cl2 (4 ꢀ 30 mL), and the combined extracts
were washed with 5% aqueous Na2CO3. The organic phase was
dried over anhydrous Na2SO4 and filtered before the solvent
was evaporated at reduced pressure. The desired compound,
2,8-diacetylquinoline, was obtained as a white solid (2.03 g, 9.53
mmol) in 63.5% yield after purification by column chromato-
graphy (silica gel, 5:1 (v/v) petroleum ether/ethyl acetate). Mp:
81-82 °C. IR (KBr; cm-1): 3001 (w), 1695 (s), 1668 (s), 1593 (s),
1557 (s), 1428 (m), 1361 (m), 1279 (s), 1259 (s), 1207 (s), 1095 (s),
856 (s), 775 (s), 615 (s). 1H NMR (300 MHz, CDCl3): δ 8.34 (d,
J=8.5 Hz, 1H); 8.20 (d, J=8.5 Hz, 1H); 8.07 (d, J=7.1 Hz, 1H);
8.02 (d, J=8.2 Hz, 1H); 7.81 (t, J=7.7 Hz, 1H); 3.04 (s, 3H); 2.86
(s, 3H). 13C NMR (75 MHz, CDCl3): δ 202.8, 200.0, 152.9,
144.5, 140.0, 137.7, 131.4, 130.7, 129.6, 128.3, 118.3, 32.9, 26.1.
Anal. Calcd for C13H11NO4 (213.23): C, 73.23; H, 5.20; N, 6.57.
Found: C, 73.01; H, 5.20; N, 6.57.
4.3. Synthesis of Iron Complexes Fe1 and Fe2. Ligand and 1.0
equiv of FeCl2 4H2O were added together in a Schlenk, which
3
was purged three times with nitrogen and then charged with
freshly distilled THF. The reaction mixture was stirred at room
temperature for 6 h, and absolute diethyl ether was added to
precipitate the complex. The resulting precipitate was filtered,
washed with diethyl ether, and dried under vacuum to furnish
the product Fe1 as a green powder in 87% yield. IR (KBr; cm-1):
3010 (w), 1621 (m), 1586 (s), 1560 (m), 1469 (s), 1371 (m), 1284
(m), 1208 (m), 782 (m), 767 (s). Anal. Calcd for C29H29Cl2FeN3
(546.31): C, 63.76; H, 5.35; N, 7.69. Found: C, 63.47; H, 5.00; N,
7.49. 1H NMR (600 MHz, CD3OD): δ 8.5 (br, 2H, quino-H), 8.1
(d, 2H, quino-H), 7.7 (br, 1H, quino-H), 7.0 (d, 4H, Ar-Hm), 6.9
(d, 2H, Ar-Hp), 2.2 (br, 12H, Ar-CH3), 1.9 (br, 6H, NdCCH3).
MALDI-TOF: calcd for C29H29Cl2FeN3 m/z 545, found m/z
510 (M - Cl)þ.
Synthesis of 2,8-Bis[1-(2,6-dimethylphenylimino)ethyl]quinoline
(L1). A mixture of 2,6-dimethylaniline (0.917 g, 7.6 mmol), 2,8-
diacetylquinoline (0.426 g, 2.0 mmol), and a catalytic amount
of p-toluenesulfonic acid in toluene (40 mL) was refluxed for
24 h. After solvent evaporation, the crude product was purified
by an alumina-based column with petroleum ether/ethyl acet-
ate (10:1 v/v) as an eluant to afford the product as a yellow
powder (0.652 g, 1.55 mmol) in 78% yield. Mp: 132-134 °C. IR
(KBr; cm-1): 2940 (w), 1647 (s), 1593 (m), 1467 (s), 1441 (m),
1
1360 (m), 1205 (m), 1091 (m), 763 (s). H NMR (300 MHz,
Fe2 was prepared in 79% yield by using a similar procedure to
that for Fe1. IR (KBr; cm-1): 3050 (w), 2912 (m), 1615 (m), 1585
(s), 1479 (s), 1452 (m), 1432 (m), 1370 (m), 1277 (m), 1215 (s),
1150 (m), 853 (s). Anal. Calcd for C31H33Cl2FeN3 (574.36): C,
CDCl3): δ 8.57 (d, J=8.7 Hz, 1H); 8.30 (d, J=8.7 Hz, 1H); 8.03
(d, J=7.0 Hz, 1H); 7.95 (d, J=8.2 Hz, 1H); 7.68 (dd, J1=7.2
Hz, J2=8.0 Hz, 1H); 7.09 (d, J=7.5 Hz, 4H), 6.95 (m, 2H); 2.36
(s, 3H); 2.26 (s, 3H); 2.24 (s, 3H); 2.17 (s, 3H); 2.06 (s, 6H). 13
C
1
64.82; H, 5.79; N, 7.32. Found: C, 64.68; H, 5.69; N, 7.17. H
NMR (75 MHz, CDCl3): δ 171.1, 167.2, 155.4, 148.6, 148.4,
144.9, 141.8, 136.4, 128.7, 128.7, 128.6 127.8, 127.3, 125.7,
125.1, 123.0, 122.8, 118.6, 22.7, 17.8, 16.5. Anal. Calcd for
C29H29N3 (419.56): C, 83.02; H, 6.97; N, 10.02. Found: C,
83.22; H, 6.97; N, 9.88.
NMR (600 MHz, CD3OD): δ 8.4 (br, 2H, quino-H), 8.0 (br, 1H,
quino-H), 7.9 (br, 1H, quino-H), 7.7 (br, 1H, quino-H), 6.8 (d,
4H, Ar-Hm), 2.2 (3H, Ar-CH3), 2.2 (6H, Ar-CH3), 2.1 (3H, Ar-
CH3), 2.1 (6H, Ar-CH3), 1.9 (br, 6H, NdCCH3). MALDI-TOF:
calcd for C31H33Cl2FeN3 m/z 573, found m/z 538 (M - Cl)þ.
4.4. Synthesis of Cobalt Complexes Co1 and Co2. To a
mixture of L1 and CoCl2 was added freshly distilled ethanol at
room temperature. The reaction mixture was stirred for 6 h, and
the precipitate was collected by filtration and washed with
diethyl ether, followed by drying under vacuum. The desired
complex Co1 was obtained as a brown powder in 83% yield. IR
(KBr; cm-1): 3050 (w), 1623 (m), 1589 (s), 1562 (m), 1468 (s),
1372 (m), 1283 (m), 1208 (m), 782 (m), 767 (s). Anal. Calcs for
C29H29Cl2CoN3 (549.4): C, 63.40; H, 5.32; N, 7.65. Found: C,
63.49; H, 5.44; N, 7.26. 1H NMR (600 MHz, CD3OD): δ 8.5 (br,
2H, quino-H), 8.1 (br, 1H, quino-H), 8.0 (br, 1H, quino-H), 7.7
(br, 1H, quino-H), 7.1 (br, 4H, Ar-Hm), 6.9 (br, 2H, Ar-Hp), 2.3
(s, 3H, Ar-CH3), 2.2 (s, 9H, Ar-CH3), 2.0 (s, 6H, NdCCH3).
MALDI-TOF: calcd for C29H29Cl2CoN3 m/z 548, found m/z
513 (M - Cl)þ.
Synthesis of 2,8-Bis[1-(2,6-diethylphenylimino)ethyl]quinoline
(L2). Using the same procedure as for the synthesis of L1, L2
was obtained as a yellow powder in 67% yield. Mp: 130-131 °C.
IR (KBr; cm-1): 3056 (m), 2926 (m), 1636 (s), 1589 (m), 1566
(m), 1453 (s), 1362 (s), 1280 (m), 1257 (m), 1198 (m), 1187 (m),
1095 (s), 876 (m), 856 (m), 767 (s). 1H NMR (300 MHz, CDCl3):
δ 8.55 (d, J=8.6 Hz, 1H); 8.30 (d, J=8.6 Hz, 1H);7.99 (d, J=6.9
Hz, 1H); 7.94 (d, J=8.2 Hz, 1H); 7.68 (dd, J1=7.9 Hz, J2=7.2
Hz, 1H); 7.13 (d, J=7.2 Hz, 4H); 7.07-7.01 (m, 2H), 2.68 (q, J=
8.4 Hz, 2H); 2.59 (q, J=8.4 Hz, 2H); 2.45-2.32 (m, 7H); 2.27 (s,
3H); 1.23 (t, J=7.5 Hz, 6H); 1.15 (t, J=7.2 Hz, 6H). 13C NMR
(75 MHz, CDCl3): δ 170.7, 166.8, 155.3, 147.4, 147.2, 144.7,
141.8, 136.2, 131.4, 130.7, 128.5, 128.4, 127.1, 125.7, 125.6,
123.1, 123.0, 24.3, 24.1, 22.8, 16.6, 13.6, 13.4. Anal. Calcd for
C33H37N3 (475.67): C, 83.33; H, 7.84; N, 8.83. Found: C, 82.90;
H, 7.99; N, 8.67.
Synthesis of 2,8-Bis[1-(2,6-diisopropylphenylimino)ethyl]-
quinoline (L3). Using the same procedure as for the synthesis
of L1, L3 was obtained as a yellow powder in 41% yield.
Co2 was prepared in 89% yield by using a similar method to
that for Co1. IR (KBr; cm-1): 3050 (w), 2912 (w), 1621 (s), 1588
(s), 1560 (s), 1479 (s), 1460 (m), 1436 (m), 1372 (m), 1312 (m),

Article
Organometallics, Vol. 29, No. 5, 2010 1173
1282 (m), 1217 (s), 1154 (m), 853 (s), 785 (m). Anal. Calcs for
C31H33Cl2CoN3 (577.45): C, 64.48; H, 5.76; N, 7.28. Found: C,
64.77; H, 5.71; N, 6.97. 1H NMR (600 MHz, CD3OD): δ 8.4 (br,
2H, quino-H), 8.1 (br, 1H, quino-H), 7.9 (br, 1H, quino-H), 7.7
(br, 1H, quino-H), 6.9 (s, 4H, Ar-Hm), 2.3 (3H, Ar-CH3), 2.2
(9H, Ar-CH3), 2.2 (6H, Ar-CH3), 2.0 (br, 6H, NdCCH3).
MALDI-TOF: calcd for C31H33Cl2CoN3 m/z 576, found m/z
541 (M - Cl)þ.
4.5. Procedure for Ethylene Polymerization. Ethylene poly-
merization at 10 atm of ethylene pressure was performed in a
stainless steel autoclave (250 mL capacity) equipped with a gas
ballast through a solenoid clave for continuous feeding of
ethylene at constant pressure. A 100 mL amount of toluene
containing the catalyst precursor was transferred to the fully
dried reactor under a nitrogen atmosphere. The required
amount of cocatalyst was then injected into the reactor via a
syringe. At the reaction temperature, the reactor was sealed and
pressurized to high ethylene pressure, and the ethylene pressure
was maintained by feeding of ethylene. After the reaction
mixture was stirred for the desired period, the pressure was
released and a small amount of the reaction solution was
collected, which was then analyzed by gas chromatography
(GC) for determining the composition and mass distribution
of oligomers obtained. Then the residual reaction solution was
quenched with 30% hydrochloric acid ethanol. The precipitated
polymer was collected by filtration, washed with ethanol and
water, and dried in a vacuum until constant weight.
temperature, the reaction apparatus was then immediately
pressurized to 30 atm. The mixture was magnetically stirred
for 30 min, the ethylene remaining was purged after the reaction,
and the mixture was cooled to room temperature. Then the
residual reaction solution was quenched with 30% hydrochloric
acid ethanol. The precipitated polymer was collected by filtra-
tion, thoroughly washed with ethanol and water, and then dried
in a vacuum until constant weight.
4.6. X-ray Crystallographic Studies. Single-crystal X-ray dif-
fraction studies for L4 and Co1 were carried out on a Rigaku
RAXIS Rapid IP diffractometer with graphite-monochromated
˚
Mo KR radiation (λ = 0.71073 A). Cell parameters were
obtained by global refinement of the positions of all collected
reflections. Intensities were corrected for Lorentz and polariza-
tion effects and empirical absorption. The structures were solved
by direct methods and refined by full-matrix least-squares on F2.
All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were placed in calculated positions. Structure
solution and refinement were performed by using the SHELXL-
97 package.16 Crystal data and processing parameters for
L4 and Co1 are summarized in Table S1 of the Supporting
Information.
Acknowledgment. This work was supported by NSFC
No. 20674089.
Supporting Information Available: 1H NMR spectra of the
iron and cobalt complexes, crystal data, and structure refine-
ment for L4 and Co1 with their cif data. This material is
available free of charge via the Internet at http://pubs.acs.org.
Ethylene polymerization at 30 atm was performed in a
stainless steel autoclave (100 mL scale). A typical reaction
procedure was as follows. Catalyst (2 μmol), toluene (40 mL),
and the required amount of MAO (1.4 mol/L solution in
toluene) were added into the autoclave in a drybox. The reactor
was sealed and moved out of the drybox. At the reaction
(16) Sheldrick, G. M. SHELXTL-97, Program for the Refinement of
Crystal Structures; University of Gottingen: Germany, 1997.