Ethylene oligomerization mediated by iron formazanates and organoaluminum compounds

Article abstract of DOI:10.1134/S0965544113020072

A number of iron(II) complexes have been synthesized on the basis of benzothiazolylformazans, and their structure and composition have been characterized by elemental analysis, mass spectrometry, and X-ray analysis. The catalytic behavior of Fe(II) formazanates in the reaction of ethylene oligomerization in the presence of various organoaluminum compounds has been studied. Methylaluminoxane facilitates the formation of α-olefins (butene-1, hexene-1) and the byproducts hexene isomers; ethylaluminum dichloride (AlC₂H₅Cl₂) increases the selectivity for alkyltoluenes.

Full text of DOI:10.1134/S0965544113020072

ISSN 0965ꢀ5441, Petroleum Chemistry, 2013, Vol. 53, No. 2, pp. 127–133. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © I.S. Pavlova, I.G. Pervova, G.P. Belov, I.I. Khasbiullin, P.A. Slepukhin, 2013, published in Neftekhimiya, 2013, Vol. 53, No. 2, pp. 144–150.
Ethylene Oligomerization Mediated by Iron Formazanates
and Organoaluminum Compounds
I. S. Pavlovaa, I. G. Pervovaa, G. P. Belovb, I. I. Khasbiullinb, c, and P. A. Slepukhind
a Ural State Forest Engineering University, Yekaterinburg, Russia
eꢀmail: biosphera@usfeu.ru
b Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia
eꢀmail: gbelov@cat.icp.ac.ru
c Kazan State Technological University, Kazan, Russia
eꢀmail: khailnaz@yandex.ru
d Institute of Organic Synthesis, Russian Academy of Sciences, Ural Division, Yekaterinburg, Russia
eꢀmail: slepukhin@ios.uran.ru
Received October 4, 2012
Abstract—A number of iron(II) complexes have been synthesized on the basis of benzothiazolylformazans,
and their structure and composition have been characterized by elemental analysis, mass spectrometry, and
Xꢀray analysis. The catalytic behavior of Fe(II) formazanates in the reaction of ethylene oligomerization in
the presence of various organoaluminum compounds has been studied. Methylaluminoxane facilitates the
formation of ꢀolefins (buteneꢀ1, hexeneꢀ1) and the byproducts hexene isomers; ethylaluminum dichloride
α
(AlC2H5Cl2) increases the selectivity for alkyltoluenes.
Keywords: oligomerization, ethylene, organoaluminum compounds, iron formazanates
DOI: 10.1134/S0965544113020072
The most common processes for preparing higher ates [8]. In continuation of the reported studies [9], we
olefins as a feedstock for manufacturing of polyethylꢀ synthesized in this work iron(II) formazanates and
ene and other useful products include cracking of first examined the effect of their composition and
hydrocarbon gases and oil fractions [1]. The use of structure on the kinetics and selectivity of the oligoꢀ
metal complex compounds for this purpose has greatly merization reaction of olefins using different orgaꢀ
improved the quality of the products and increased the noaluminum
compounds:
methylaluminoxane
efficiency of the cracking process.
(MAO), ethylaluminum dichloride (AlC2H5Cl2), triꢀ
ethylaluminum (Al(C2H5)3), and diethylaluminum
It is irrefutable that both the efficiency of a catalytic
process and the product composition of any catalytic
reaction directly depend on the nature of the metal
that enters into the composition of the organometallic
catalyst [2]. Thus, ironꢀcontaining catalyst systems are
characterized by high activity and selectivity in the
formation of higher linear oligomers of ethylene under
mild reaction conditions and, as such, hold promise
for sustainable use of raw materials in the industry. In
addition, an important role in catalysis is played by the
ligand nature and the type of substituents on the
ligand, which can affect the course of the oligomerizaꢀ
tion process. For example, the presence of chlorine
atoms in the coordination unit of a complex comꢀ
pound has an effect on the selectivity of the oligomerꢀ
ization process and activates the catalytic behavior of
the complex [3–7].
chloride (Al(C2H5)2Cl
.
EXPERIMENTAL
Highꢀpurity ethylene (99.9 wt %) was used to conꢀ
duct the catalytic process. The cocatalysts MAO (Aldꢀ
rich, 10 wt % solution in toluene), Al(C2H5)3,
Al(C2H5)2Cl (80 wt % solution in heptane), and
AlC2H5Cl2 (73 wt % solution in gasoline) were used
without further purification. The medium for preparꢀ
ing the required concentration of organoaluminum
compounds and for running the oligomerization of
ethylene was toluene, which had been purified accordꢀ
ing to a standard procedure and distilled over molecuꢀ
lar sieves 4–5Å.
Iron complexes with formazan ligands were synꢀ
thesized according to the procedure described in [8],
The catalytic properties of metal complexes based using the salts Fe(ClO4)3 Н2О and FeCl3 · 6Н2О for
⋅
on formazan ligands in the ethylene oligomerization the compounds 1.1Fe–1.5Fe and 1.6Fe or 1.7Fe,
reaction have been studied only for nickel formazanꢀ respectively.
127

128
PAVLOVA et al.
Elemental analysis and mass spectrometric data for Total 37 355 reflections were measured, of which 9321
the iron complexes and some physicochemical charꢀ were independent (Rint = 0.0435) and 4278 had
I >
acteristics are given in Table 1. The purity of the synꢀ
thesized iron complexes was monitoring by thin layer
chromatography (TLC) on Silufol UVꢀ254 fixed silica
gel layer.
2
σ
(
I
)
. The completeness of the experiment for an
angle of
θ
= 28.29о was 99.5%. A correction for
absorption was introduced analytically using the mulꢀ
tifaceted crystal model [11]. The structure was deterꢀ
mined by the direct statistical method and refined by
the fullꢀmatrix leastꢀsquares method on F2 in the
anisotropic approximation for all nonhydrogen atoms.
The hydrogen atoms were placed in geometrically calꢀ
culated positions and refined in the isotropic approxiꢀ
mation. All calculations were performed with the use
of the software suite SHELX 97 [12]. The final refineꢀ
ment results are R1 = 0.0436, wR2 = 0.1002 for reflecꢀ
Electronic absorption spectra in the visible and
nearꢀUV region were recorded on a Shimadzu UV–
1800 spectrophotometer. Elemental analysis was perꢀ
formed on a PE2400SII automated CHN analyzer
(Perkin Elmer Instruments, USA). The massꢀspectroꢀ
metric study of formazans and their complexes was
performed on a Shimadzu LCMSꢀ2010 liquid chroꢀ
matograph/mass spectrometer with atmosphericꢀ
pressure chemical ionization and electrospray ionizaꢀ
tion in both the positive and negative ion modes. Samꢀ
ples were introduced into the mass spectrometer by
direct injection into the ion source through the chroꢀ
matograph with an SPDꢀM10Avp diode array detecꢀ
tor.
tions with
reflections),
I
> 2σ(I), R1 = 0.1084, wR2 = 0.1108 (for all
S
= 1.017. The maximum and
minimum residual electron density peaks are 0.610
and –0.600
e
Å–3, respectively.
These XRD data have been deposited with the
Cambridge Crystallographic Data Centre (CCDC
910512) in the cif format and are freely available at
For Xꢀray diffraction analysis of the compound
with the empirical formula C35H32Cl2FeN10OS2, a
www.ccdc.cam.ac.uk/ data_request/cif on request.
0.28
tal was used. The crystal had a monoclinic unit cell,
space group Р21/ = 12.0969(7) = 20.5274(13)
= 111.301(7)°,
= 3777.5(5) Å3,
= 4, and
= 0.695 mm–1. The cell
× 0.15 × 0.03 mm piece of a black prismatic crysꢀ
The oligomerization of ethylene was conducted
according to the procedure described in [9].
n,
a
Å,
b
Å,
c
d
= 16.3277(14)
Å
,
Z
β
V
calcd 1.406 g/cm3,
μ
RESULTS AND DISCUSSION
parameters and a set of experimental reflections were
measured at 295(2) K on an Xcalibur 3 automatic
fourꢀcircle diffractometer with a CCD detector
(Oxford Diffraction) according to a standard proceꢀ
Based on the ligands (scheme), some of which had
been presented in [8, 9], we synthesized metal comꢀ
plexes of iron(II) with different steric positions of
functional groups (OCH3, Cl) in the aryl unit of the
ligand.
dure [10] by
МоK radiation in the angle range of 2.68 <
α
ω
ꢀ2
θ
scanning using monochromatized
< 28.29.
θ
Ligand no.
Composition
Iron complex no.
2R
2
1.1:
1.2:
1.3:
1.4:
1.5:
1.6:
1.7:
R1– C4H3S, R2–H, R3–H
R1– C4H3S, R2–OCH3, R3–H
R1– C4H3O, R2–Cl, R3–H
R1– C4H3S, R2–Cl, R3–H
R1– C2H5, R2–H, R3–Cl
R1– C4H3S, R2–H, R3–H
R1– C4H3S, R2–OCH3, R3–H
1.1Fe
1.2Fe
1.3Fe
1.4Fe
1.5Fe
1.6Fe
1.7Fe
N
S
NH
N
N
N
R3
R1
Ligand
Scheme.
Note that a portion of the ligand is oxidized to the mental analysis and mass spectrometry (Table 1). The
tetrazolium salt during the complexation reaction of general view of the molecule with labels according to
parent formazans with ferric ions, thereby facilitating the conventional atomic numbering scheme (hydroꢀ
the reduction of Fe3+ to Fe2+ and the formation of gen atoms are omitted for simplicity) is presented
divalent iron formazanates L2Fe; the composition and below. According to the Xꢀray diffraction (XRD) data
structure of the latter have been established by eleꢀ first obtained for the compounds 1.5Fe and the pubꢀ
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ETHYLENE OLIGOMERIZATION MEDIATED BY IRON FORMAZANATES
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130
PAVLOVA et al.
Table 2. Selected bond lengths of the compound
with acetone. The molecular packing is not specific,
there are no intermolecular contacts with a distance
less than the sum of van der Waals radii.
Bond
Å
Angle
Å
The catalytic properties of these iron(II) chelates
in the olefin oligomerization reaction were tested
under conditions that are optimal for nickel formazaꢀ
nates examined previously in this reaction [8, 9]:
Fe(1)
⎯
⎯
⎯
⎯
⎯
⎯
N(1)
1.934(2)
1.873(2)
1.993(2)
1.959(2)
2.004(2)
1.870(2)
1.313(3)
1.430(3)
1.370(4)
1.350(3)
1.324(3)
N(3)
⎯
⎯
⎯
⎯
⎯
⎯
⎯
⎯
⎯
N(4)
1.363(3)
1.342(3)
1.329(3)
1.390(3)
1.316(3)
1.424(3)
1.342(3)
1.330(3)
1.354(3)
Fe(1)
Fe(1)
Fe(1)
Fe(1)
Fe(1)
N(3)
N(5)
N(6)
N(7)
N(9)
N(4)
N(5)
N(5)
N(6)
N(6)
N(8)
N(9)
N(9)
C(10)
C(10)
C(11)
N(8)
Т
= 80oC;
Р
= 2.0 MPa, Сcat= 4
10–5 mol/L, diethꢀ
×
ylaluminum chloride (Al(C2H5)2Cl) as the cocatalyst.
The kinetics of the oligomerization catalyzed by
iron(II) formazanates in the presence of AlC2H5Cl2 as
a cocatalyst is similar to that in the case of nickel(II)
formazanates [8] in both the pattern of rate curves and
the composition of oligomeric products. However, the
catalyst onꢀstream time for the majority of iron formaꢀ
zanates 1.1Fe–1.3Fe (Fig. 2a) is much shorter in comꢀ
parison with the nickel catalysts [8]. The longest cataꢀ
lyst onꢀstream time with a catalyst activity of 19.04 kg
of product/(g Fe h) was observed for the complex
1.5Fe, which has a chlorine atom in the paraꢀposition
of the aryl moiety. In addition, most of the tested
Fe(II) formazanates exhibited a high selectivity
C(17)
C(23)
C(23)
N(10)
N(1)
N(1)
⎯
N(2)
C(1)
C(2)
⎯
C(1)
⎯
N(2)
N(3)
⎯
C(7)
C(7)
N(10)⎯C(26) 1.355(3)
⎯
lished data [13], all the synthesized complexes have (according to GLC) largely for alkyltoluenes (62–
the pseudoꢀoctahedral structure of the coordination 72 wt %) (Table 3) and quite a low selectivity for
α
ꢀ
unit FeN6 involving only the N1 and N4 nitrogen olefins (hexeneꢀ1, octeneꢀ1) in the reaction (Table 3)
atoms and the heterocyclic nitrogen of each of the two as in [8, 9]. However, we observed an interesting fact
formazan molecules (Fig. 1).
with the metal complex 1.7Fe, which contains the
thienyl group in the mesoꢀposition: there was a high
percentage (96 wt %) of tetramerization of ethylene
yielding octeneꢀ1 (bypassing the ethylene diꢀ and triꢀ
merization steps) with an amount of byproducts in the
form of monoꢀ and dialkyltoluenes of less than 1 wt %
(Table 3). The formation of alkyltoluenes in the presꢀ
ence of AlC2H5Cl2 is the result of the toluene alkylaꢀ
tion reaction with olefins.
Modification of homogeneous catalysts with comꢀ
pounds containing a labile chlorine atom or with other
oxidants in an amount comparable with that of the
catalyst promotes activation of the system. [2]. Orgaꢀ
noaluminum compounds are an example of such sysꢀ
tems used in the oligomerization reaction [2–7].
Thus, in this study we additionally examined the cataꢀ
lytic activity of the synthesized iron formazanates in
the presence of three types of organoaluminum comꢀ
pounds: methylaluminoxane (MAO), triethylalumiꢀ
num (Al(C2H5)3), and diethylaluminum chloride
The metal complex 1.5Fe crystallizes in the cenꢀ
trosymmetric monoclinic group. The structure is quite
typical: the two formazan ligands lie in perpendicular
planes forming a distorted octahedral environment of
the central iron ion. The Fe1–N3 and N9–Fe1 bonds
are somewhat shorter than the other metal–nitrogen
bonds (Table 2). The N–C and C–C bond lengths in
the formazan moiety are equal, indicating strong deloꢀ
calization of the electron density of the chelate rings
(Table 2). The compound crystallizes as a 1 : 1 solvate
Cl(1)
S(2)
C(3)
C(31)
C(30)
C(32)
C(4)
C(5)
C(2)
N(10)
C(25)
C(26)
C(24)
C(27)
C(28)
C(23)
C(29)
N(9)
C(1)
N(8)
N(7)
N(1)
C(6)
(
Al(C2H5)2Cl).
Fe(1)
N(2)
C(12)
C(13)
C(11)
C(14)
C(15)
C(16)
The use of a toluene solution of triethylaluminum
AlEt3) as a cocatalyst led to inhibition of the catalytic
N(6)
(
N(5)
N(3)
C(7)
C(22)
C(21)
C(20)
properties of formazanates 1.1Fe–1.7Fe down to
complete deactivation.
The catalytic activity of iron formazanates 1.1Fe–
1.7Fe in the presence of MAO is determined by the
nature of the chlorineꢀ and oxygenꢀcontaining ligands
C(17)
C(8) N(4)
C(10)
C(18)
C(19)
S(1)
C(9)
in the complex (Fig. 2b). Thus, in the case of оꢀchloꢀ
Cl(2)
rinated chelates 1.3Fe–1.5Fe, the product composiꢀ
tion of ethylene oligomerization is represented mainly
by ethylene trimers (hexeneꢀ1, 40–95 wt %), tetramꢀ
ers (octeneꢀ1, up to 10 wt %), and hexene isomers as
Fig. 1. Molecular structure of complex 1.5Fe.
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ETHYLENE OLIGOMERIZATION MEDIATED BY IRON FORMAZANATES
131
Ethylene consumption, L
(а)
Ethylene consumption, L
(b)
1.5Fe
1.7Fe
1.7Fe
1.3Fe
1.6
1.4Fe
1.5Fe
1.6Fe
2.0
1.5
1.0
0.5
1.6Fe
1.3Fe
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1.1Fe
1.2Fe
1.1Fe
1.2Fe
0
0
10
20
30
40
50
60
10
20
30
40
50
60
Time, min
Time, min
Ethylene consumption, L
(c)
2.0
1.5Fe
1.5
1.0
0.5
1.7Fe
1.2Fe
1.4Fe
1.3Fe
1.1Fe
1.6Fe
0
10
20
30
40
50
60
Time, min
Fig. 2. Ethylene consumption rate curves in the oligomerization reaction of in the presence of iron formazanates at
V
=
toluene
–5
60 mL,
T
= 80°C,
P
= 2 MPa, and
C
= 4 × 10 mol/L with cocatalysts: (a) AlC H Cl (AlC H Cl : Fe = 100 : 1 (by
ethylene
Fe 2 5 2 2 5 2
mole)), (b) MAO (MAO : Fe = 500 : 1 (by mole)), and (c) Al(C H ) Cl (Al(C H ) Cl : Fe = 20 : 1 (by mole)).
2
5 2
2 5 2
byproducts (Table 3). The highest catalytic activity of the parent ligand, it became possible to enhance the
13.42 kg/(g Fe h) was displayed by metal complexes selectivity of the metal complexes for
ꢀolefins; their
α
amounts in the reaction products were 71 and 29 wt %
for octeneꢀ1 and hexeneꢀ1, respectively, in the case of
1.4Fe or 50 wt % butaneꢀ1 and 50 wt % hexeneꢀ1 in
the case of 1.7Fe (Table 3).
1.3Fe and 1.7Fe. The application of the chelates 1.6Fe
and 1.7Fe, prepared with the use of FeCl3, leads to
the formation of
α
ꢀolefins (buteneꢀ1, hexeneꢀ1,
octeneꢀ1) alone and a small amount of byproducts,
with the highest selectivity for hexeneꢀ1 (yield 99 wt %)
being shown by the complex 1.7Fe (Table 3). Considꢀ
ering the kinetics of the oligomerization process in the
presence of methylaluminoxane as its cocatalyst, one
cannot fail to notice a gradual decrease in the ethylene
consumption with time (Fig. 2b). This phenomenon is
largely due to a decrease in the partial pressure of ethꢀ
ylene because of the accumulation of volatile products
Thus, the study of the catalytic properties of the
benzothiazolylformazanꢀbased iron complexes, synꢀ
thesized in this work, in the ethylene oligomerization
reaction has shown the possibility of controlling the
course of the reaction (catalytic activity and selectivꢀ
ity) by varying both the structure of the iron(II) formaꢀ
zanates used and the nature of the Al organic comꢀ
pound.
(
ꢀolefins) in the reaction zone as noted in [9], rather
α
than the decay of active sites.
ACKNOWLEDGEMENTS
It was found that the activity of the iron formazanꢀ
ates 1.1Fe–1.7Fe can be increased by using
Al(C2H5)2Cl as a coꢀcatalyst for the reaction (Fig. 2c).
This work was supported in part by the Russian
Academy of Sciences under Presidium program no. 3
Moreover, by varying the composition and structure of “Energy aspects of deep processing of fossil and
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ETHYLENE OLIGOMERIZATION MEDIATED BY IRON FORMAZANATES
133
6. W. Hang, Y. Weidong, J. Tao, et al., Chin. Sci. Bull. 47
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