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