2-β-Benzothiazolyl-6-iminopyridylmetal dichlorides and the catalytic behavior towards ethylene oligomerization and polymerization

Article abstract of DOI:10.1016/j.ica.2011.06.037

A series of 2-(2-benzothiazolyl)-6-(1-(arylimino)ethyl)pyridines and their metal (Fe or Co) complexes were prepared. All organic compounds were fully characterized by NMR, FT-IR spectra and elemental analysis, and all metal complexes were identified by FT

Full text of DOI:10.1016/j.ica.2011.06.037

Inorganica Chimica Acta 376 (2011) 373–380
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Inorganica Chimica Acta
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2-b-Benzothiazolyl-6-iminopyridylmetal dichlorides and the catalytic behavior
towards ethylene oligomerization and polymerization
Shengju Song a, Rong Gao a, Min Zhang a, Yan Li a, Fosong Wang a, Wen-Hua Sun a,b,
⇑
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 2-(2-benzothiazolyl)-6-(1-(arylimino)ethyl)pyridines and their metal (Fe or Co) complexes
were prepared. All organic compounds were fully characterized by NMR, FT-IR spectra and elemental
analysis, and all metal complexes were identified by FT-IR spectroscopic and elemental analysis. The
molecular structures of representative metal complexes were confirmed by single-crystal X-ray diffrac-
tion and displayed the distorted trigonal bipyramid geometry. Upon activation with modified methylalu-
minoxane (MMAO), the iron pro-catalysts showed good catalytic activities up to the range of
107 g molÀ1(Fe) hÀ1 in ethylene reactivity with the high selectivity for the vinyl-type products of both
oligomers and polyethylene waxes; whereas the cobalt pro-catalysts showed moderate activities towards
ethylene oligomerization. The correlations between metal complexes and their catalytic activities and
products were investigated in detail under various reaction parameters and discussed.
Received 11 April 2011
Received in revised form 19 June 2011
Accepted 29 June 2011
Available online 5 July 2011
Keywords:
2-b-Benzothiazolyl-6-iminopyridine
Iron
Cobalt
Oligomerization
Polymerization
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
6-imino-pyridines [34,35]. Several review articles have highlighted
the progress of these research achievements [36–42].
Since the 2,6-diiminopyridylmetal (Fe or Co) complexes were
independently discovered as highly active pro-catalysts in ethyl-
ene polymerization by Bennett [1], Brookhart and co-workers [2]
and Gibson and co-workers [3] in 1998, the derivatives of 2,6-dii-
minopyridylmetal complexes have been extensively investigated
through fine-tuning substituents on 2,6-diiminopyridines [4–12].
Moreover, the metal (Fe or Co) complexes bearing non-symmetri-
cal 2,6-diiminopyridines, which were prepared by the reaction of
2,6-diacetylpyridine with two different anilines (including an
alkylamine sometime) instead of two identical anilines, were
investigated with a view to modify their catalytic behavior [13–
18]. In addition, new pro-catalysts performing interesting catalytic
behavior have been achieved with employing newly designed
ligands such as 2-ester-6-iminopyridines [19], 2-furan- or 2-thio-
phen-6-iminopyridines [20,21], 2-imino-1,10-phenan-throlines
[22–26], 2-oxazoline/benzoxazole-1,10-phenanthrolines [27], 2-
benzimidazolyl-1,10-phenanthrolines [28], N-(2-pyridylmethyl-
ene)-quinolin-8-amines [29], 2-quinoxalyl-6-iminopyridines [30],
2-benzimidazolyl-6-iminopyridines [31–33], and 2-benzoxazolyl-
Both pro-catalysts containing 2-benzimidazolyl- or 2-benzox-
azolyl-substituted 6-iminopyridines, A [31–33] and B [34,35] in
Scheme 1, were developed and showed competitive activities to-
wards ethylene. 2-Thiophen-6-iminopyridylcobalt pro-catalysts
had better activities than 2-furan-6-iminopyridylcobalt analogs
[20,21], and 2-(2-benzoxazolyl)-1,10-phenanthrolylchromium
pro-catalysts showed better activities than 2-(2-benzothiazolyl)-
1,10-phenanthrolylchromium analogs [43]. As a consequent work,
the pro-catalysts containing 2-b-benzothiazolyl-6-iminopyridines
(C in Scheme 1) are necessarily investigated with the comparison
of their analogs A and B. Herein the syntheses and characterization
of metal (Fe or Co) complexes bearing 2-(2-benzothiazolyl)-6-imi-
nopyridines are reported along with their catalytic behavior in eth-
ylene oligomerization and polymerization.
2. Experimental
2.1. General considerations
All manipulations of air- and moisture-sensitive compounds
were performed under a nitrogen atmosphere using standard
Schlenk techniques. 2-(2-Benzothiazole)-6-acetylpyridine was pre-
pared using a modified procedure according to the literature
[34,44]. Toluene was refluxed over sodium-benzophenone and dis-
tilled under argon prior to use. Methylaluminoxane (MAO, a 1.46 M
solution in toluene) and modified methylaluminoxane (MMAO,
⇑
Corresponding author at: Key Laboratory of Engineering Plastics and Beijing
National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China. Tel.: +86 10 62557955; fax: +86 10
62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.037

374
S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
1H, J = 7.3, Ar, H), 7.13 (d, 2H, J = 7.5, Ar, H), 7.05 (t, 1H, J = 6.7, Ar,
R
H), 2.46–2.33 (m, 4H, 2Â CH2), 2.31 (s, 3H, CH3), 1.15 (t, 6H,
J = 7.5, 2Â CH3). 13C NMR (400 MHz, CDCl3, TMS): d 169.6, 166.3,
156.1, 154.4, 150.3, 147.7, 137.5, 136.3, 131.1, 127.6, 126.3, 126.0,
125.7, 123.7, 123.5, 122.7, 122.0, 121.6, 118.3, 24.7, 24.3, 16.8,
13.8, 13.1. Anal. Calc. for C24H23N3S (385.52): C, 74.77; H, 6.01; N,
10.90. Found: C, 75.00; H, 5.85; N, 10.75%.
O
N
R1
N
R1
N
N
N
N
N
M
M
Cl
R1
Cl
Cl
R1
Cl
R2
R2
B
A
S
R1
N
2.2.3. 2,6-Diisopropyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine (L3)
N
N
M = Fe or Co
M
Cl
Cl
C (current work)
Using the same procedure as for the synthesis of L1, L3 was ob-
tained as a yellow powder in 63.6% yield. Mp: 196–197 °C. FT-IR
(KBr disk, cmÀ1): 1653 (s), 1568 (s), 1457 (s), 1366 (m), 1323 (s),
1237 (m), 1111 (s), 1001 (s), 826 (m), 785 (s). 1H NMR (400 MHz,
CDCl3, TMS): d 8.47 (q, 2H, J = 8.6, Py, Hm), 8.12 (d, 1H, J = 8.1, Py,
Hp), 7.99–7.94 (m, 2H, Ar, H), 7.52 (t, 1H, J = 7.3, Ar, H), 7.43 (t,
1H, J = 7.5, Ar, H), 7.18 (d, 2H, J = 7.2, Ar, H), 7.13–7.09 (m, 1H, Ar,
H), 2.80–2.73 (m, 2H, 2Â CH), 2.33 (s, 3H, CH3), 1.18–1.16 (m,
12H, 4Â CH3). 13C NMR (400 MHz, CDCl3, TMS): d 169.6, 166.3,
156.0, 154.4, 150.2, 146.3, 137.5, 136.2, 135.6, 126.2, 125.6.
123.7, 123.6, 123.0, 122.7, 122.6, 121.9, 121.4, 28.2, 23.2, 22.8,
17.0. Anal. Calc. for C26H27N3S (413.58): C, 75.51; H, 6.58; N,
10.16. Found: C, 75.87; H, 6.71; N, 10.04%.
R2
R1
Scheme 1. Systematic modification of model pro-catalysts.
1.93 M in heptane, 3A) were purchased from Akzo Nobel Corp. Diet-
hylaluminium chloride (Et2AlCl, 1.7 M in toluene) was purchased
from Acros Chemicals. 1H and 13C NMR spectra were recorded on
a Bruker DMX 400 MHz instrument at ambient temperature using
TMS as an internal standard. FT-IR spectra were recorded on a Per-
kin–Elmer System 2000 FT-IR spectrometer. Elemental analyses
were carried out using a Flash EA 1112 microanalyzer. GC analyses
were performed with
equipped with a flame ionization detector and a 30 m (0.2 mm
i.d., 0.25 m film thickness) CP-Sil 5 CB column. The yields of olig-
a Varian CP-3800 gas chromatograph
2.2.4. 2,4,6-Trimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine (L4)
l
omers were calculated by referencing with the mass of the solvent,
on the basis of the prerequisite that the mass of each fraction was
approximately proportional to its integrated areas in the GC trace.
Using the same procedure as for the synthesis of L1, L4 was ob-
tained as a yellow powder in 66.0% yield. Mp: 181–182 °C. FT-IR
(KBr disk, cmÀ1): 1648 (s), 1567 (w), 1450 (m), 1363 (m), 1321
(m), 1215 (m), 1111 (w), 1001 (m), 815 (w), 758 (s). 1H NMR
(400 MHz, CDCl3, TMS): d 8.46 (q, 2H, J = 7.8, Py, Hm), 8.11 (d, 1H,
J = 8.1, Py, Hp), 7.96 (t, 2H, J = 7.7, Ar, H), 7.52 (t, 1H, J = 7.2, Ar,
H), 7.43 (t, 1H, J = 7.1, Ar, H), 6.91 (s, 2H, Ar, H), 2.31 (s, 3H, CH3),
2.29 (s, 3H, CH3), 2.02 (s, 6H, 2 Â CH3). 13C NMR (400 MHz, CDCl3,
TMS): d 169.6, 166.7, 156.2, 154.4, 150.2, 146.1, 137.4, 136.2, 132.3,
128.6, 126.2, 125.6, 125.2, 123.6, 122.7, 121.9, 121.5, 20.7, 17.9,
16.3. Anal. Calc. for C23H21N3S (371.50): C, 74.36; H, 5.70; N,
11.31. Found: C, 74.24; H, 5.42; N, 11.38%.
Selectivity for the linear a-olefin was defined as (amount of linear
a
-olefin of all fractions)/(total amount of oligomer products) in per-
centage. 1H and 13C NMR spectra of the PE waxes were recorded on
a Bruker DMX 300 MHz instrument at 110 °C in 1,2-dichloroben-
zene-d4 using TMS as the internal standard.
2.2. Synthesis of 2-(benzothiazolyl)-6-iminopyridines
2.2.1. 2,6-Dimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine (L1)
A
solution of 2-(2-benzothiazole)-6-acetylpyridine (1.02 g,
2.2.5. 2,6-Diethyl-4-methyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-
yl)ethylidene)benzenamine (L5)
4 mmol), 2,6-dimethylaniline (0.67 g, 4.8 mmol), and a catalytic
amount of p-toluenesulfonic acid in toluene (50 mL) were refluxed
for 12 h. After solvent evaporation, the crude product was purified
with petroleum ether/ethyl acetate (v/v = 15/1) on an alumina col-
umn. The second part to elute was collected and concentrated to
give a yellow powder (0.65 g, 45.5 % yield). Mp: 131–132 °C. FT-
IR (KBr disk, cmÀ1): 1641 (m), 1568 (m), 1508 (w), 1436 (w),
1365 (m), 1323 (m), 1204 (m), 1112 (w), 1003 (w), 814 (m), 761
(m). 1H NMR (400 MHz, CDCl3, TMS): d 8.47 (q, 2H, J = 7.8, Py,
Hm), 8.11 (d, 1H, J = 8.1, Py, Hp), 7.96 (t, 2H, J = 7.7, Ar H), 7.52 (t,
1H, J = 7.3, Ar H), 7.42 (t, 1H, J = 7.5, Ar H), 7.09 (d, 2H, J = 7.5, Ar
H), 6.96 (t, 1H, J = 7.5, Ar H), 2.30 (s, 3H, CH3), 2.33 (s, 3H, CH3),
2.06 (s, 6H, 2Â CH3). 13C NMR (300 MHz, CDCl3, TMS): d 169.5,
166.5, 156.0, 154.4, 150.2, 148.6, 137.4, 136.2, 128.2, 127.9,
126.2, 125.6. 125.3, 123.6, 123.1, 122.6, 121.9, 121.5, 117.9, 17.9,
17.6, 16.3. Anal. Calc. for C22H19N3S (357.47): C, 73.92; H, 5.36;
N, 11.75. Found: C, 73.78; H, 5.46; N, 11.66%.
Using the same procedure as for the synthesis of L1, L5 was ob-
tained as a yellow powder in 60.8 % yield. Mp: 145–146 °C. FT-IR
(KBr disk, cmÀ1): 1638 (s), 1567 (w), 1461 (s), 1364 (m), 1321
(s), 1210 (m), 1112 (w), 1002 (s), 817 (m), 755 (s). 1H NMR
(400 MHz, CDCl3, TMS): d 8.46 (q, 2H, J = 7.9, Py), 8.11 (d, 1H, J =
8.1, Py), 7.95 (t, 2H, J = 6.7, Ar), 7.51 (t, 1H, J = 7.4, Ar), 7.41 (t,
1H, J = 7.6, Ar), 6.94 (s, 2H, Ar), 2.34 (m, 4H, CH2), 2.30 (s, 3H,
CH3), 1.14 (t, 6H, 2Â CH3). 13C NMR (400 MHz, CDCl3, TMS): d
169.8, 166.6, 156.4, 154.6, 150.4, 145.3, 137.7, 136.5, 132.8,
131.2, 126.9, 126.4, 125.8, 123.8, 122.8, 121.1, 121.6, 24.8, 21.2,
16.8, 14.0. Anal. Calc. for C25H25N3S (399.55): C, 75.15; H, 6.31; N,
10.52. Found: C, 75.27; H, 6.37; N, 10.36%.
2.3. Synthesis of 2-(2-benzothiazolyl)-6-iminopyridyliron dichlorides
2.3.1. 2,6-Dimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine FeCl2 (Fe1)
2.2.2. 2,6-Diethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine (L2)
A Shlenk tube was charged with solid 2,6-dimethyl-N-(1-(6-
(benzo[d]thiazol-2-yl)pyridin-2-yl)ethylidene)-benzenamine (0.1
1 g, 0.3 mmol) and FeCl2Á4H2O (0.06 g, 0.3 mmol) and purged three
times with argon, followed by the addition of 10 mL ethanol. The
reaction mixture was stirred at room temperature for 6 h. The
resulting precipitate was filtered off, washed twice with diethyl
ether and dried in vacuum to furnish the pure product as a blue
powder in 88.0% yield. FT-IR (KBr; cmÀ1): 1598 (w), 1491 (w),
Using the same procedure as for the synthesis of L1, L2 was ob-
tained as a yellow powder in 50.0% yield. Mp: 130–131 °C. FT-IR
(KBr disk, cmÀ1): 1633 (s), 1566 (m), 1454 (s), 1364 (m), 1321 (s),
1235 (m), 1106 (m), 1002 (s), 816 (s), 754 (s). 1H NMR (300 MHz,
CDCl3, TMS): d 8.46 (q, 2H, J = 7.8, Py, Hm), 8.11 (m, 1H, J = 8.1, Py,
Hp), 7.96 (t, 2H, J = 8.0, Ar, H), 7.52 (t, 1H, J = 7.3, Ar, H), 7.42 (t,

S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
375
1430 (w), 1372 (w), 1322 (w), 1256 (m), 1211 (s), 1098 (w), 1050
(w), 807 (m), 774 (s). Anal. Calc. for C22H19Cl2FeN3S (484.22): C,
54.57; H, 3.95; N, 8.68. Found: C, 54.57; H, 3.82; N, 8.97%. Com-
plexes Fe2–Fe5 were prepared by the same manner.
C26H27Cl2CoN3S (543.42): C, 57.47; H, 5.01; N, 7.73. Found: C,
57.28; H, 5.11; N, 7.66%.
2.4.4. 2,4,6-Trimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethy-
lidene)benzenamine CoCl2 (Co4)
Yield: 82.4%. FT-IR (KBr disk, cmÀ1): 1599 (m), 1568 (w), 1492
(s), 1459 (w), 1428 (w), 1372 (w), 1324 (w), 1251 (m), 1218 (m),
1187 (m), 1022 (w), 804 (w), 779 (m). Anal. Calc. for
2.3.2. 2,6-Diethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethylidene)-
benzenamine FeCl2 (Fe2)
Yield: 80.2%. FT-IR (KBr disk, cmÀ1): 1598 (m), 1585 (m), 1491
(w), 1458 (w), 1373 (w), 1320 (w), 1257 (m), 1201 (m), 1085
(w), 812 (m), 768 (s). Anal. Calc. for C24H23Cl2FeN3S (512.28): C,
56.27; H, 4.53; N, 8.20. Found: C, 56.00; H, 4.55; N, 8.01%.
C23H21Cl2CoN3S (501.34): C, 55.10; H, 4.22; N, 8.38. Found: C,
55.00; H, 4.30; N, 8.30%.
2.4.5. 2,6-Diethyl-4-methyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-
yl)ethylidene)benzenamine CoCl2 (Co5)
2.3.3. 2,6-Diisopropyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine FeCl2 (Fe3)
Yield: 82.0%. FT-IR (KBr disk, cmÀ1): 1597 (m), 1568 (w), 1487
(s), 1459 (s), 1425 (w), 1371 (m), 1321 (m), 1256 (s), 1213 (m),
1184 (w), 1023 (w), 813 (m), 774 (m). Anal. Calc. for
Yield: 88.0%. FT-IR (KBr disk, cmÀ1): 1598 (m), 1568 (w), 1493
(m), 1459 (w), 1427 (w), 1371 (m), 1319 (w), 1257 (m), 1199
(m), 1100 (w), 1018 (w), 816 (w), 761 (m). Anal. Calc. for
C25H25Cl2CoN3S (529.39): C, 56.72; H, 4.76; N, 7.94. Found: C,
C26H27Cl2FeN3S (540.33): C, 57.79; H, 5.04; N, 7.78. Found: C,
56.59; H, 4.79; N, 7.97%.
57.53; H, 5.15; N, 7.64%.
2.5. General procedure for ethylene reactivation
2.3.4. 2,4,6-Trimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine FeCl2 (Fe4)
Ethylene oligomerizations and polymerizations were performed
in a 500 mL stainless steel autoclave equipped with a mechanical
stirrer and a temperature controller. Toluene, the desired amount
of modified methylaluminoxane, and a toluene solution of the cat-
alyst precursor was added to the reactor in this order under an eth-
ylene atmosphere, the total volume was 100 mL. When the desired
reaction temperature was reached, ethylene at 10 atm pressures
was introduced to start the reaction, and the ethylene pressure
was maintained by a constant feed of ethylene during reaction per-
iod. After that, the reaction was stopped, and the autoclave was
cooled in an ice-water bath. Then the pressure was released and
a small amount of the reaction solution was collected, which was
then quenched with HCl-acidified ethanol (5%). The organic layer
was analyzed as quickly as possible by gas chromatography (GC)
to determine the composition and mass distribution according to
GC–Mass spectrum of oligomers. Then the remaining reaction mix-
ture was quenched with HCl-acidified ethanol (5%) in order to col-
lect polyethylene obtained with being additionally washed with
ethanol, and dried under vacuum at 60 °C to constant weight.
Yield: 76.7%. FT-IR (KBr disk, cmÀ1): 1599 (m), 1560 (w), 1492
(w), 1457 (w), 1428 (w), 1373 (w), 1324 (w), 1252 (m), 1218
(m), 1187 (w), 1086 (w), 1018 (w), 803 (w), 779 (m). Anal. Calc.
for C23H21Cl2FeN3S (498.25): C, 55.44; H, 4.25; N, 8.43. Found: C,
55.26; H, 4.37; N, 8.28%.
2.3.5. 2,6-Diethyl-4-methyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-
yl)ethylidene)benzenamine FeCl2 (Fe5)
Yield: 80.0%. FT-IR (KBr disk, cmÀ1): 1598 (m), 1560 (w), 1493
(s), 1459 (s), 1429 (m), 1372 (m), 1323 (m), 1258 (s), 1213 (s),
1188 (m), 1018 (w), 803 (w), 779 (m). Anal. Calc. for
C25H25Cl2FeN3S (526.30): C, 57.05; H, 4.79; N, 7.98. Found: C,
56.66; H, 4.82; N, 7.96%.
2.4. Synthesis of 2-(2-benzothiazolyl)-6-iminopyridylcobalt
dichlorides
2.4.1. 2,6-Dimethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-
yl)ethylidene)benzenamine CoCl2 (Co1)
2.6. X-ray crystallography
All the cobalt complexes were prepared in good yield with the
same synthetic procedure: An ethanol solution of equivalent
amount of CoCl2 was added to the ethanol solution of the corre-
sponding ligand, and the mixture was stirred for 6 h at room tem-
perature. The resultant precipitate was collected, washed with
diethyl ether and dried in vacuum. Co1 obtained as green powder
in 88.0% yield. FT-IR (KBr; cmÀ1): 1599 (m), 1570 (w), 1492 (m),
1468 (w), 1429 (w), 1372 (m), 1323 (w), 1254 (s), 1212 (s), 1097
(w), 1025 (w), 808 (w), 775 (s). Anal. Calc. for C22H19Cl2CoN3S
(487.31): C, 54.22; H, 3.93; N, 8.62. Found: C, 54.13; H, 4.18; N,
8.54%.
Single-crystals of Fe2, Fe3 and Co3 suitable for X-ray diffraction
were obtained by the slow diffusion of diethyl ether into the meth-
anol solution. Data were collected on a Rigaku RAXIS Rapid IP dif-
fractometer with graphite monochromated Mo
Ka radiation
(k = 0.71073 Å). Cell parameters were obtained by global refine-
ment of the positions of all collected reflections. Intensities were
corrected for Lorentz and polarization effects and empirical
absorption. The structures were solved by direct methods and re-
fined by full-matrix least squares on F2. All hydrogen atoms were
placed in calculated positions. Structure solution and refinement
were performed by using the SHELXL-97 package [45]. Crystal data
and processing parameters for Fe2, Fe3 and Co3 are summarized
in Table 1.
2.4.2. 2,6-Diethyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethylidene)-
benzenamine CoCl2 (Co2)
Yield: 80.2%. FT-IR (KBr disk, cmÀ1): 1599 (m), 1585 (s), 1491
(s), 1459 (w), 1373 (m), 1321 (w), 1256 (s), 1202 (s), 1024 (w),
814 (m), 767 (s). Anal. Calc. for C24H23Cl2CoN3S (515.36): C,
55.93; H, 4.50; N, 8.15. Found: C, 55.57; H, 4.54; N, 8.06%.
3. Results and discussion
3.1. 2-(2-Benzothiazolyl)-6-(1-(arylimino)ethyl)pyridines and their
iron and cobalt complexes
2.4.3. 2,6-Diisopropyl-N-(1-(6-(benzothiazol-2-yl)pyridin-2-yl)ethyli-
dene)benzenamine CoCl2 (Co3)
Yield: 76.0%. FT-IR (KBr disk, cmÀ1): 1599 (m), 1569 (w), 1493
(m), 1459 (w), 1426 (w), 1371 (m), 1317 (w), 1258 (m), 1199
(m), 1096 (w), 1024 (w), 817 (w), 770 (m). Anal. Calc. for
The 2-(2-benzothiazolyl)-6-acetylpyridine was prepared
according to our procedure [31–35], and then reacted with anilines
to form 2-(2-benzothiazolyl)-6-(1-aryliminoethyl)pyridines

376
S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
Table 1
Crystal data and structure refinement details for Fe2, Fe3 and Co3.
Fe2
Fe3
Co3
Empirical formula
Formula weight
T (K)
C
24H23Cl2FeN3S
C26H27Cl2FeN3S
540.32
173(2)
C26H27Cl2CoN3S
543.40
173(2)
512.26
293(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
monoclinic
P21/c
9.225 (1)
14.652(3)
18.154(4)
96.75(3)
2436.9(8)
4
0.71073
monoclinic
P21/c
9.374 (1)
14.918(3)
18.285(4)
93.20(3)
2553.0(9)
4
0.71073
monoclinic
P21/c
9.320 (1)
14.950(3)
18.323(4)
92.79(3)
2550.2(9)
4
b (°)
V (Å3)
Z
Dcalc (Mg mÀ3
)
1.396
0.940
1056
1.406
0.901
1120
1.415
0.984
1124
l
(mmÀ1
F (0 0 0)
)
Crystal size (mm)
h Range (°)
Limiting indices
0.39 Â 0.39 Â 0.34
2.62–25.00
À10 6 h 6 10
À17 6 k 6 17
À21 6 l 6 21
8205
0.13 Â 0.13 Â 0.12
1.76–25.00
À11 6 h 6 10
À17 6 k 6 17
À21 6 l 6 16
15 716
0.20 Â 0.20 Â 0.20
2.58–25.00
À11 6 h 6 10
À16 6 k 6 17
À21 6 l 6 21
16 923
Number of reflections collected
Number of unique reflections
Completeness to h (%)
Abs. Cor.
4274
4473
4474
99.7 (h = 25.00°)
multi-scan
290
99.7 (h = 25.00°)
multi-scan
298
99.8 (h = 25.00°)
multi-scan
298
Number of parameters
Goodness of fit on F2
1.197
1.152
1.162
Final R indices (I > 2
r
(I))
R1 = 0.0664
wR2 = 0.1264
R1 = 0.0923
wR2 = 0.1362
0.463, À0.298
R1 = 0.0505
wR2 = 0.1005
R1 = 0.0573
wR2 = 0.1040
0.531, À0.425
R1 = 0.0464
wR2 = 0.1103
R1 = 0.0514
wR2 = 0.1134
0.473, À0.401
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)
(L, Scheme 2). The blue iron(II) complexes Fe1–Fe5 were prepared
in good yields by stirring stoichiometric amounts of FeCl2 and the
corresponding ligand in ethanol for 6 h at room temperature
(Scheme 2). All ferrous complexes were characterized by FT-IR
spectra and elemental analyses, and agreed with the formula
LFeCl2. While the C@N stretching frequencies of the free ligands
appear in the range of 1633–1653 cmÀ1, the C@N stretching vibra-
tions were shifted to lower frequencies of 1598–1599 cmÀ1 in
complexes Fe1–Fe5. This shift and the reduced peaks’ intensities
indicate an effective coordination of iron by the imino nitrogen.
By the same procedure, the green cobalt complexes Co1–Co5 were
conveniently prepared in good yields (Scheme 2). These cobalt
complexes are stable in both solution and solid state. In addition,
the molecular structures of the complexes Fe2, Fe3 and Co3 were
determined by single crystal X-ray diffraction.
3.2. Crystal structures
Single crystals of Fe2, Fe3 and Co3 suitable for single-crystal X-
ray diffraction were grown from their methanol solutions layered
with diethyl ether. In complex Fe2 (Fig. 1), the coordination geom-
etry around iron is a distorted trigonal-bipyramidal, in which the
pyridine-nitrogen N(1) and two chlorine atoms approximately lie
in an equatorial plane with the deviation from the plane of
0.0598 Å for iron atom. The equatorial plane and the trans-nitrogen
atoms N(2) and N(3) form the angle of 88.9o. Similar to the iron
analogs bearing 2-(2-benzimidazolyl)-6-acetylpyridines [31–33],
the 2,6-dimethylphenyl is oriented nearly orthogonally (83.4°) to
the coordination plane (N(3)–N(1)–N(2)).
The similar coordination geometry also occurs within complex
Fe3 (Fig. 2). The fused-rings of Fe(1)–N(2)–C(6)–C(7)–N(1)–Fe(1)
and Fe(1)–N(1)–C(11)–C(12)–N(3)–Fe(1) are co-planar and nearly
perpendicular to the aryl ring linked through the imino-group
NH2
R1
R1
S
p-TsOH
N
O
N
Toluene
R2
R1
N
S
N
N
R2
R1
Ln (ligand)
FeCl2¡4¤H2O
or CoCl2
Ethanol
n
R1 R2 Fe Co
1
2
3
4
5
Me H Fe1 Co1
Et
iPr
H
H
Fe2 Co2
Fe3 Co3
S
R1
N
N
Cl
R1
N
M
Me Me Fe4 Co4
Et Me Fe5 Co5
Cl
R2
Fig. 1. Molecular structure of Fe2 with thermal ellipsoids at the 30% probability
Scheme 2. Synthesis of the iron and cobalt complexes.
level. Hydrogen atoms have been omitted for clarity.

S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
377
pressure, the investigation was performed at 10 atm C2H4
(Table 2). The highest activity was obtained with MMAO. The
performance with regard to both catalytic activity and
a-olefins’
selectivity is better than for its analog bearing 2-(benzimidazolyl)-
6-aminopyridines [31–33].
The influence of reaction parameters such as the molar ratio of
Al/Fe and reaction temperature was investigated in detail (Table 3).
Notably increasing the molar ratio from 300 to 750, the activities
were dramatically increased (entries 1–3 in Table 3), which might
be attributed to the scavenging of any impurities. A further in-
crease of the molar ratio to 1000 (entry 4 in Table 3) decreased
the activity. The distributions of oligomers semi-resembled the
Schulz–Flory rule [51,52], in which the probability of chain propa-
gation is given by K, where K = (rate of propagation)/((rate of prop-
agation) + (rate of chain transfer)) = (moles of C14)/(moles of C12).
The Al/Fe molar ratio had little influence on the oligomer distribu-
tion and K values. Employing the optimum Al/Fe ratio of 750, ele-
vating the reaction temperature from 30 °C to 60 °C resulted in a
great decrease in productivity (entries 3 and 5–7 in Table 3). This
probably caused with the thermally unstable active species and
lower ethylene absorption in solution at higher temperature
[5,53]. The oligomers’ distribution became narrower with more
shorter chain olefins, which attribute to faster b-hydrogen elimina-
tion at higher temperature.
Fig. 2. Molecular structure of Fe3 with thermal ellipsoids at the 30% probability
level. Hydrogen atoms have been omitted for clarity.
(84.1°), whereas the dihedral angle between the aryl plane linked
on imino-group and the pyridyl group is 82.8°. The Fe–N bond
lengths follow the order Fe(1)–N(3) > Fe(1)–N(2) > Fe(1)–N(1)
while the two Fe–Cl bond lengths are almost equal. This is a signif-
icant difference compared to the distorted square-pyramidal
coordination observed in the iron complexes ligated by 2-benzim-
idazolyl-6-iminopyridines [31–33] or 2-benzoxazolyl-6-imino-
pyridines [34,35]. The N(2)–C(6) bond distance is 1.312(4) Å
displaying clear C@N double bond character, shorter than C(6)–
O(1) by 1.722(3) Å.
The coordination geometry of complex Co3 (Fig. 3) is best de-
scribed as a distorted trigonal-bipyramidal with the equatorial
plane defined by the N(1), Cl(1) and Cl(2), and the position of the
cobalt atom deviates 0.0215 Å from the equatorial plane. Three
nitrogen atoms (N(1), N(2) and N(3)) occupy axial plane. The dihe-
dral angle between axial and equatorial planes with cobalt center
forms 148.3°. This is consistent with observations of its cobalt ana-
logs [31–33,35]. Due to the asymmetry of the molecule, the Co–N
bonds are significantly different, Co(1)–N(2) = 2.234(2) Å and
Co(1)–N(3) = 2.267(2) Å; while the C–Nimino bonds, (N(2)–
C(6) = 1.313(4) Å and N(3)–C(12) = 1.287(4) Å, are typical and
within the standard deviation [22–26,28–35,46–50].
In the Fe1/MMAO system, the ethylene reactivity was steadily
maintained over forty minutes (entries 1–4 in Table 4). Prolonging
the reaction time to one hour, however, resulted in decreased
activities for both ethylene oligomerization and polymerization
(entries 5 and 6 in Table 4). Regarding to polyethylene waxes ob-
tained, vinyl-nature of long-chain
a-olefin was confirmed by the
1H and 13C NMR spectra.
Subsequently, all iron pro-catalysts were investigated under the
optimum condition, and the results were tabulated in Table 5.
Regarding complexes Fe1ÀFe3 containing 2,6-dialkyl substituents
(entries 1–3 in Table 5), bulkier R1 groups cause lower activities in
both oligomerization and polymerization. We believe that the
bulkier substituents hinder the approach of ethylene to the active
species. Such tendency was similar with the observation by the
iron analogs bearing 2-(1-isopropyl-2-benzimidazolyl)-6-amino-
pyridines [32], but different to those by iron analogs having 2-
(1H-2-benzimidazolyl)-6-aminopyridines [33] and 2-(1-methyl-2-
benzimidazolyl)-6-minopyridines [31]. Regarding to the oligomer
distribution, the bulkier R1 substituents increase the content of
C4. In addition, the para-methyl of the aryl ring positively affected
the activity of iron pro-catalyst (entries 4 and 5 in Table 5) due to
better solubility caused. Such phenomenon was also observed by
iron pro-catalysts ligated by 2-quinoxalinyl-6-iminopyridines
[30] and 2-(1-isopropyl-2-benzimidazolyl)-6-iminopyridines [32].
The activities of the current iron pro-catalysts are comparable to
those of common bis(imino)pyridyliron pro-catalysts [2–4], but
3.3. Ethylene oligomerization and polymerization
3.3.1. Ethylene reactivity by iron complexes
Various alkylaluminiums such as methylaluminoxane (MAO),
modified methylaluminoxane (MMAO) and diethylaluminium
chloride (Et2AlCl) were used in evaluating the ethylene activation
by Fe1. Since low activity was observed at ambient ethylene
the current iron catalytic systems show higher selectivity of
fins in ethylene oligomerization.
a-ole-
3.3.2. Ethylene oligomerization by cobalt complexes
Using complex Co1 to select the co-catalyst (entries 1–3 in Ta-
ble 6), MMAO was found to be the most suitable one. Within molar
ratios of MMAO/Co from 200 to 1000 (entries 2 and 4–6 in Table 6),
the best activity of ethylene oligomerization was observed at 500.
At the MMAO/Co ratio of 500, further elevation of the reaction
temperature lowered activity (entries 5, 7 and 8 in Table 6). As
with their iron analogs [5,53], the cobalt active species are ther-
mally unstable, moreover, with a lower solubility of ethylene at
higher temperature. The cobalt complexes were investigated in de-
tail with the MMAO/Co molar ratio of 500 at room temperature
(Table 6).
Fig. 3. Molecular structure of Co3 with thermal ellipsoids at the 30% probability
level. Hydrogen atoms have been omitted for clarity.

378
S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
Table 2
Selection of a suitable cocatalyst based on Fe1.a
Entry
Cocat.
Al/Fe
Oligomer activityb
Oligomer distributionc
Polymer activityb
1
2
3
MAO
MMAO
Et2AlCl
1000
1000
200
14.4
59.3
4.2
C4–C28
C4–C28
C4–C8
3.43
6.06
trace
a
b
c
Conditions: 5 lmol Fe1; 10 atm ethylene; 30 min, 30 °C; 100 mL toluene.
105 g molÀ1(Fe) hÀ1
Determined by GC;
.
R
C denotes the total amount of oligomers.
Table 3
Ethylene oligomerization and polymerization by Fe1/MMAO.a
Entry
Al/Fe
T (°C)
K
a
-Ob (%)
Activityc
Oligomer
Oligomer distribn (%)d
Wax
C4/
R
C
C6/R
C
C8/R
C
R
CP10
/
R
C
1
2
3
4
5
6
7
300
500
750
1000
750
750
750
30
30
30
30
40
50
60
0.37
0.42
0.43
0.42
0.43
0.42
0.40
94.4
97.3
97.8
97.5
97.6
97.5
99.9
49.3
66.2
93.5
59.3
57.5
44.6
1.2
3.66
7.01
6.15
6.06
3.84
3.17
0.85
64.1
62.4
61.0
62.6
64.5
65.1
66.8
23.5
23.8
24.3
24.3
21.8
21.9
20.2
8.0
8.4
8.2
7.8
7.0
6.8
7.0
4.4
5.4
6.5
5.3
6.7
6.2
6.0
a
b
c
Conditions: 5 lmol Fe1; 10 atm ethylene; 30 min, 100 mL toluene.
a
-Olefin percentage determined by GC.
105 g molÀ1(Fe) hÀ1
Determined by GC;
.
d
R
C denotes the total amount of oligomers.
Table 4
Polymerization and oligomerization of ethylene with Fe1/MMAO.a
Entry
t (min)
K
a
-Ob (%)
Activityc
Oligomer distribution (%)d
Oligomer
Wax
C4/R
C
C6/R
C
C8/
R
C
R
CP10/RC
1
2
3
4
5
6
10
20
30
40
50
60
0.42
0.41
0.43
0.40
0.39
0.40
99.7
97.4
97.8
97.9
97.1
93.1
81.3
102
93.5
84.2
68.4
57.6
5.15
6.14
6.15
5.09
4.11
3.49
64.7
62.8
61.0
61.9
61.8
61.4
23.8
25.0
24.3
25.3
25.6
24.7
7.2
7.5
8.2
7.6
7.4
8.0
4.3
4.7
6.5
5.2
5.2
5.9
a
b
c
Conditions: 5 lmol Fe1; 10 atm ethylene; 750 equiv. MMAO; 30 °C; 100 mL toluene.
a
-Olefin percentage determined by GC.
105 g molÀ1(Fe) hÀ1
Determined by GC:
.
d
R
C denotes the total amount of oligomers.
Table 5
Polymerization and oligomerization of ethylene with Fe1–Fe5/MMAO.a
Entry
Cat.
a
-Ob (%)
Activityc
Oligomer
Oligomer distribution (%)d
Wax
C4/R
C
C6/R
C
C8/
R
C
R
CP10/RC
1
2
3
4
5
Fe1
Fe2
Fe3
Fe4
Fe5
97.8
97.5
99.2
96.6
97.4
93.5
77.9
49.3
110
6.15
1.25
0.28
4.91
1.12
61.0
72.4
87.9
63.0
68.3
24.3
20.5
10.0
24.8
20.3
8.2
5.2
2.0
7.7
6.0
6.5
1.9
0.1
4.5
5.4
81.8
a
b
c
Conditions: 5 lmol Fe; 750 equiv. MMAO; 10 atm ethylene; 30 °C; 30 min; 100 mL toluene.
a
-Olefin percentage determined by GC.
105 g molÀ1(Fe) hÀ1
Determined by GC;
.
d
R
C denotes the total amount of oligomers.
Their catalytic activities were significantly affected by the
and 2-benzoxazolyl-6-(1-(arylimino)ethyl)pyridine [34,35]. The
introducing one para-methyl resulted in higher activity (entries
11, 12 in Table 5) due to better solubility. In general, cobalt pro-
catalysts showed much lower activities than their iron analogs.
Such phenomena have commonly been observed within previous
pro-catalysts.
Compared with their analogs bearing 2-benzimidazole-6-(1-
aryliminoethyl)pyridines [31–33], 2-benzoxazolyl-6-(1-(arylimi-
no)ethyl)pyridine [35], and 2,6-bis(2-oxazolin-2-yl)pyridine [54],
ligands’ environment, and their activity varied in the order
Co3 > Co2 > Co1 and Co5 > Co4 > Co2 > Co1. The bulkier the sub-
stituents were, the higher activity cobalt pro-catalysts performed;
this is naturally different to their iron analogs. It was believed that
bulkier substituents might be helpful for both the solubility of
complexes and stability of active species due to less exposing to
impurity reactants. Such observation is different to their cobalt
analogs ligated by 2-benzimidazolyl-6-iminopyridines [31,32]

S. Song et al. / Inorganica Chimica Acta 376 (2011) 373–380
379
Table 6
Oligomerization of ethylene with cobalt pro-catalysts.a
Entry
Cat.
Cocat.
Al/Co
T (°C)
Activityb
Oligomer distribution (%)c
C4/R
C
C6/R
C
a
-C4
94.2
100
1
2
3
4
5
6
7
8
9
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co1
Co2
Co3
Co4
Co5
MAO
1000
1000
200
200
500
750
500
500
500
500
500
500
20
20
20
20
20
20
40
50
20
20
20
20
1.48
3.00
trace
4.01
7.94
3.54
4.50
0.90
8.85
15.80
9.90
9.98
100
98.6
–
0
1.4
–
MMAO
Et2AlCl
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
–
100
98.1
0
100
100
100
1.9
2.0
0.4
1.2
1.7
1.3
3.0
0
98.0
99.6
98.8
98.3
98.7
97.0
96.6
100
100
100
100
100
10
11
12
100
a
b
c
Conditions: 5 lmol Co; 10 atm ethylene; 30 min, 100 mL toluene.
105 g molÀ1(Co) hÀ1
Determined by GC;
.
R
C denotes the total amount of oligomers.
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D.J. Williams, J. Am. Chem. Soc. 121 (1999) 8728.
the current cobalt pro-catalysts showed higher production activity
towards ethylene oligomerization and polymerization. However,
the cobalt pro-catalysts did not perform ethylene polymerization
at the elevated reaction temperature, which were observed by 2-
benzoxazolyl-6-iminopyridylcobalt pro-catalysts [35]. These re-
sults by cobalt pro-catalysts resembled the simulation conclusion
on the correlation between the activity and net charge of late-tran-
sition metal complexes, in which the stronger the electron-donat-
ing ability of the ligand, the lower is the net charge on the metal,
resulted a lower activity [38,55].
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4. Conclusion
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[19] W.-H. Sun, X. Tang, T. Gao, B. Wu, W. Zhang, H. Ma, Organometallics 23 (2004)
5037.
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2545.
The iron and cobalt complexes bearing 2-(benzothiazolyl)-6-(1-
(arylimino)ethyl)pyridines provide accessible pro-catalysts for
ethylene oligomerization. Though the reaction at elevated
temperature would result in a deactivation and a lower selectivity
for
a
-olefins, the iron pro-catalysts show activities of up to 107 g
molÀ1(Fe) hÀ1 for oligomers and 7.01 Â 105 g molÀ1(Fe) hÀ1 for
waxes in the presence of MMAO. In most cases, the waxes obtained
have been confirmed to be vinyl-type olefins. The cobalt pro-cata-
lysts show moderate activity.
[21] C. Bianchini, G. Giambastiani, G. Mantovani, A. Meli, D. Mimeau, J. Organomet.
Chem. 689 (2004) 1356.
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Fröhlich, Organometallics 25 (2006) 666.
[23] S. Jie, S. Zhang, K. Wedeking, W. Zhang, H. Ma, X. Lu, Y. Deng, W.-H. Sun, C.R.
Chim. 9 (2006) 1500.
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Acknowledgments
This work is supported by NSFC No. 20874105 and MOST 863
program No. 2009AA033601. The authors are grateful to Rainer
Glaser (Department of Chemistry, University of Missouri-Colum-
bia, Columbia, MO) for proofreading the English language.
[25] S. Jie, S. Zhang, W.-H. Sun, Eur. J. Inorg. Chem. 35 (2007) 5584.
[26] M. Zhang, W. Zhang, T. Xiao, J.-F. Xiang, X. Hao, W.-H. Sun, J. Mol. Catal. A
Chem. 320 (2010) 92.
[27] M. Zhang, R. Gao, X. Hao, W.-H. Sun, J. Organomet. Chem. 693 (2008) 3867.
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483.
[29] K. Wang, K. Wedeking, W. Zuo, D. Zhang, W.-H. Sun, J. Organomet. Chem. 693
(2008) 1073.
Appendix A. Supplementary material
[30] W.-H. Sun, P. Hao, G. Li, S. Zhang, W. Wang, J. Yi, M. Asma, N. Tang, J.
Organomet. Chem. 692 (2007) 4506.
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2225.
CCDC 793698, 793699 and 793700 contain the supplementary
crystallographic data for complexes Fe2, Fe3 and Co3, respectively.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.2011.06.037.
[34] R. Gao, Y. Li, F. Wang, W.-H. Sun, M. Bochmann, Eur. J. Inorg. Chem. 27 (2009)
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