Acetyliminopyridineiron(III) complexes immobilized in fluorotetrasilicic mica interlayer as efficient catalysts for oligomerization of ethylene

Article abstract of DOI:10.1246/cl.2012.461

As new heterogeneous catalysts, the 2-acetyl-6-{1-[(2,3,6-trisubstituted phenyl)imino]ethyl}pyridineiron(III) complexes immobilized in the fluorotetrasilicic mica interlayers were prepared by the reaction of acetyliminopyridine and Fe³⁺- exchan

Full text of DOI:10.1246/cl.2012.461

doi:10.1246/cl.2012.461
Published on the web April 5, 2012
461
Acetyliminopyridineiron(III) Complexes Immobilized in Fluorotetrasilicic Mica Interlayer
as Efficient Catalysts for Oligomerization of Ethylene
Takashi Kondo,1 Kazuhiro Yamamoto,2 Tsutomu Sakuragi,2 Hideki Kurokawa,*1 and Hiroshi Miura1
1Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570
2Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-8530
(Received December 19, 2011; CL-111209; E-mail: kuro@apc.saitama-u.ac.jp)
X
As new heterogeneous catalysts, the 2-acetyl-6-{1-[(2,3,6-
R
trisubstituted phenyl)imino]ethyl}pyridineiron(III) complexes
O
N
immobilized in the fluorotetrasilicic mica interlayers were
N
prepared by the reaction of acetyliminopyridine and Fe3+
-
exchanged fluorotetrasilicic mica. The catalysts showed a high
activity for the ethylene oligomerization with a high selectivity
to linear ¡-olefins in the presence of R¤3Al (R¤ = Et and i-Bu) as
an activator.
intercalation
Fe3+
O
AIP
R
X
N
R
X
The shell higher olefin process (SHOP) based on Ni(II)
complexes is the well-known process to produce ethylene
oligomers that are used as the raw materials of detergents,
lubricants, and various fine chemicals in addition to their use as
comonomers in ethylene polymerization.1 In 1998, two research
groups independently discovered that catalysts consisting of
a bis(imino)pyridineiron(II) complex and methylaluminoxane
(MAO) exhibited an extremely high activity for ethylene
oligomerization and a high selectivity for the formation of linear
¡-olefins.2 In recent decades, the design and synthesis of new
late-transition-metal complexes have attracted considerable atten-
tion by researchers.3 To use these catalysts in practical applica-
tions, immobilization of the metal complex on an inorganic carrier
is desirable, and we previously reported that the heterogeneous
catalysts prepared by the immobilization of bis(imino)pyri-
dineiron(III)4 and ¡-diiminenickel(II)5 complexes in the fluoro-
tetrasilicic mica interlayer showed a high activity for the ethylene
polymerization. In this study, we attempted to immobilize the
acetyliminopyridineiron(III) complexes in a fluorotetrasilicic
mica interlayer with the aim of developing useful heterogeneous
catalysts for ethylene oligomerization to produce ¡-olefins.
Detailed procedures for the synthesis of acetyliminopyr-
1
2
3
4
CH3
H
H
H
CH3
H
N
H
Cl
Figure 1. Outline of precatalysts.
The results of the ethylene oligomerization are listed in
Table 1. The precatalyst 1 consisting of AIP 1 having the 2,6-
dimethylphenyl group on an imino nitrogen atom produced
polyethylene (PE, Mn = 34700, PDI = 9.0) with a high catalytic
activity (Entry 1). On the contrary, the precatalyst 2 prepared by
the reaction of Fe3+-Mica and AIP 2 (2,5-dimethylphenyl group
on an imino nitrogen atom) exhibited an extremely high activity
for the ethylene oligomerization and afforded the linear ¡-
olefins along with a small amount of low-molecular-weight PE
(Mn < 1500, Entry 3). The steric bulk around the metal center in
the precatalyst 2 was lower than that in the precatalyst 1,
resulting in the chain-transfer reaction occurring more frequently
on the precatalyst 2 than on the precatalyst 1. Moreover, the
activity of the precatalyst 2 was higher than that of the
precatalyst 1, because of the high accessibility of ethylene to the
active center in the precatalyst 2. The base material Fe3+-Mica
(without ligand treatment) was completely inactive for the
ethylene polymerization/oligomerization under the same reac-
tion conditions in the presence of R¤3Al.
The activity based on the total amount of the ethylene
consumption increased with the increasing reaction temperature
up to 60 °C, indicating that the active species were stable at
60 °C (Entries 2 and 3). When the temperature was raised to
70 °C, the total amount of the ethylene consumption slightly
decreased (Entry 4) due to the faster deactivation of the active
species. The precatalyst 2 exhibited a high selectivity for linear
¡-olefins (>95%), and the oligomer distribution6 follows the
Schulz-Flory distribution, which can be characterized by the
constant ¡. The precatalysts that have a 2-methylphenyl group
(precatalyst 3) and a 2-methyl-5-chlorophenyl group (precatalyst
4) also showed an activity for the ethylene oligomerization, but
the activity obtained by precatalysts 3 and 4 were approximately
one-third of that obtained by precatalyst 2. Although the ¡ value
idines (AIP) 1-4 and Fe3+-changed fluorotetrasilicic mica (Fe3+
-
Mica, 482 ¯mol-Fe3+ per 1 g) are described in the Supporting
Information.6 The dried Fe3+-Mica was allowed to react with the
ligand (200 ¯mol for 1 g of Fe3+-Mica) in acetonitrile at 70 °C
for 120 h. The precatalyst was obtained by washing the solid part
with the solvent (CH3CN, toluene, and hexane) and subsequent-
ly drying at ambient temperature for 4 h under reduced pressure.
The prepared precatalysts are outlined in Figure 1.
Ethylene was oligomerized in heptane at 50-70 °C and
0.4 MPa ethylene pressure for 1-2 h using the precatalyst in
the presence of triethylaluminum (TEA), triisobutylaluminum
(TIBA), or MAO. The activity was determined by the total
amount of the consumed ethylene. The formed oligomers having
carbon numbers 4-20 (C4-C20) were analyzed by FID-GC (GC-
14A Shimadzu, DB-1 capillary column, 0.25 mm i.d. © 60 m).
The precatalysts were characterized by XRD analysis (Ultima-
RINT, Rigaku Corporation) and FT-IR measurement (Jasco FT/
IR 4100).
Chem. Lett. 2012, 41, 461-463
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

462
Table 1. Results of ethylene oligomerization using immobilized iron(III) complexesa
Selectivitye
/wt %
Product/wt %
Mass
balanced
f
Entry
Precatalyst
Tb/°C
Activator
Activityc
¡
C4-C20
Solid
1
2
3
4
5
1
2
2
2
2
2
3
4
60
50
60
70
60
60
60
60
60
60
60
TIBA
TIBA
TIBA
TIBA
TEA
MAO
TIBA
TIBA
TIBA
MAO
TIBA
450
3750
7800
6480
3750
7010
1970
2700
0
0
83.8
84.5
88.4
87.6
87.2
76.5
65.9
®
100
8.4
11.3
9.9
113
92.2
95.8
98.3
94.5
97.2
90.0
84.3
®
®
®
96.7
97.4
98.1
96.7
96.9
96.2
97.1
®
0.57
0.61
0.56
0.55
0.52
0.57
0.61
®
6.9
6
10.0
13.5
18.4
®
2.3
®
7g
8g
9h
10i
11i
Fe3+-Mica
2-FeCl3
2-FeCl3
7170j
0
93.1
®
95.4
®
98.9
®
0.51
®
aReaction conditions: precatalyst (1.0 mg, 200 ¯mol-ligand/g-Fe3+-Mica), activator (0.40 mmol), heptane (50 mL), time (1 h), ethylene
pressure (0.4 MPa, gauge). bReaction temperature. cTotal amount of ethylene consumption determined by a mass flow meter. Activity: g-
ethylene g-cat¹1 h¹1. dMass balance: 100 © (total amount of products)/(total amount of ethylene consumption). eSelectivity to linear ¡-
f
g
olefins calculated based on the C10-C16 products. Schulz-Flory constant ¡ (average of ¡8-¡14), ¡n = Cn+2 (mol)/Cn (mol). Reaction
time: 2 h. Fe3+-Mica (without ligand treatment) was used for the oligomerization as a precatalyst. Reaction conditions; 2-FeCl3:
0.2 ¯mol, Al/Fe = 2000, solvent: toluene (50 mL). Activity: kg-ethylene mol-Fe¹1 h
h
i
j
¹1
.
200
1.39 nm
1.41 nm
Entry 6
Entry 3
Entry 5
(d)
(c)
Entry 10
150
100
50
1.17 nm 2000 cps
(b)
0.99 nm
0
(a)
0
20
40
60
Reaction time /min
3
6
9
12
15
2θ /degree
Figure 2. Profiles of ethylene consumption using heteroge-
neous (precatalyst 2/R¤3Al) and homogeneous (2-FeCl3/MAO)
catalysts.
Figure 3. XRD profiles of (a) Fe3+-Mica (dried at 200 °C
under reduced pressure), (b) Fe3+-Mica (treated only with
CH3CN), (c) precatalyst 1, and (d) precatalyst 2. The profiles of
samples (b)-(d) were measured after drying at 110 °C under
reduced pressure.
obtained by precatalyst 4 was nearly equal to the values obtained
by the other precatalysts, a large amount of solid products was
formed. The solid products might be formed on a site different
from that of the oligomers formation. Nickel- and cobalt-based
acetyliminopyridine complexes were often used for the ethylene
oligomerization, but the report of the oligomerization using the
AIP iron complex was rare. An attractive example using the AIP
complex having a m-3-(trifluoromethyl)phenyl group on the
imino nitrogen atom was only reported by Bluhm et al., and the
¡ values obtained using that complex were 0.36-0.39.7
Figure 2 shows the profiles of the ethylene consumption
during the oligomerization using precatalyst 2 (Entries 3, 5, and
6) in addition to the profile obtained by the homogeneous
catalyst (Entry 10). When the 2-FeCl3/MAO catalyst was used
for the oligomerization, the activity was lower than those
obtained by the precatalyst 2. Moreover, the catalyst consisting
of 2-FeCl3/TIBA did not show any significant activity during
the oligomerization. When precatalyst 2 was used as the catalyst
in the presence of R¤3Al, the ethylene consumption gradually
increased, and the high rmax values were observed 20-30 min
after supplying the ethylene. These facts indicated that the active
species in our catalysts was effectively formed and have a long
lifetime, especially when TIBA was used as the activator. The
highest rmax was obtained using precatalyst 2 with MAO, but
remarkable deactivation was observed. The value of ¡ obtained
by the oligomerization with MAO was slightly lower than those
obtained by the oligomerization with R¤3Al.
The prepared precatalysts were characterized by XRD
analysis (Figure 3) and FT-IR spectra (Figure 4).
When Fe3+-Mica was treated with the ligand in CH3CN, the
basal spacing determined by the XRD measurement increased
Chem. Lett. 2012, 41, 461-463
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

463
ethylene consumption. The activity of the precatalyst 2/TIBA
was much higher than that of homogeneous 2-FeCl3/MAO
catalyst, because the TON value in Entry 10 (2-FeCl3/MAO
0.25
(e)
(d)
(c)
¹1
catalyst) was 71 s
.
In conclusion, the heterogeneous catalysts prepared by the
immobilizing acetyliminopyridineiron(III) complex in the fluo-
rotetrasilicic mica interlayer have characteristics, such as a
high catalytic activity, easy activation with conventional alkyl
aluminum, and a long lifetime of the active species, moreover,
the catalyst and products were readily separated by filtration.
0.50
This work was supported by a KAKENHI Grant-in-Aid for
Scientific Research (No. 23560927) from Japan Society for the
Promotion of Science.
(b)
(a)
1.0
References and Notes
1
2
M. Peuckert, W. Keim, Organometallics 1983, 2, 594.
a) B. L. Small, M. Brookhart, J. Am. Chem. Soc. 1998, 120,
7143. b) G. J. P. Britovsek, V. C. Gibson, S. J. McTavish,
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Britovsek, B. S. Kimberley, P. J. Maddox, Chem. Commun.
1998, 849.
1800
1600
1400
Wavenumber/cm-1
Figure 4. IR spectra of (a) Fe3+-Mica, (b) AIP 2, (c) 2-FeCl3
complex, (d) precatalyst 2 (560 ¯mol-2/g-Fe3+-Mica), and
(e) precatalyst 2 (200 ¯mol-2/g-Fe3+-Mica).
3
4
a) V. C. Gibson, C. Redshaw, G. A. Solan, Chem. Rev. 2007,
107, 1745. b) C. Bianchini, G. Giambastiani, L. Luconi, A.
Meli, Coord. Chem. Rev. 2010, 254, 431.
H. Kurokawa, M. Matsuda, K. Fujii, Y. Ishihama, T.
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1004.
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Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
from 0.99 to 1.41 nm for precatalyst 1 and 1.39 nm for
precatalyst 2, indicating that the interlayer space expanded with
the intercalation of the ligand.8 In the FT-IR measurement of
the precatalyst 2, the characteristic absorption band derived from
the coordinated C=N bond was observed at 1586 cm¹1, strongly
supporting the fact that the complex was effectively formed in
the interlayer space of the mica.
Finally, based on FT-IR measurements using standard
samples prepared with 2-FeCl3 and mica,6 the amount of the
formed complexes in the precatalyst 2 was determined as
111 ¯mol g-mica¹1, indicating that 55% of the used ligand
contributed to the formation of the complexes. The TON value
(7.0 © 102 s¹1) in Entry 3 (precatalyst 2) was calculated based
on the amount of the formed complex and the total amount of the
5
6
7
8
M. E. Bluhm, C. Folli, M. Döring, J. Mol. Catal. A: Chem.
2004, 212, 13.
The XRD profiles were measured with Cu K¡ radi-
ation (wavelength: 0.15406 nm) at the scan rate of 1.0
¹1
degree min
.
Chem. Lett. 2012, 41, 461-463
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/