Role of Water in the Catalysis of Ethylene Di- and Oligomerization and Toluene Alkylation Reactions Based on Nickel Bis(Acetylacetonate) Systems

Article abstract of DOI:10.1134/S0023158417050214

It is established that the turnover frequency and number of Ni(acac)₂–50Et₂AlCl or Ni(acac)₂–50Et₂AlCl · EtAlCl₂-based systems in ethylene oligomerization processes depend on the concentration of the water in toluene. The possibility of the alkylation of toluene, used as a solvent under the considered reaction condition, is shown. The main reactions describing the role of water at the stage of the formation and functioning of catalytically active hydride nickel complexes are proposed.

Full text of DOI:10.1134/S0023158417050214

ISSN 0023-1584, Kinetics and Catalysis, 2017, Vol. 58, No. 6, pp. 749–757. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © Yu.Yu. Titova, F.K. Shmidt, 2017, published in Kinetika i Kataliz, 2017, Vol. 58, No. 6, pp. 735–742.
Role of Water in the Catalysis of Ethylene Di- and Oligomerization
and Toluene Alkylation Reactions Based on
Nickel Bis(acetylacetonate) Systems
Yu. Yu. Titova* and F. K. Shmidt
Irkutsk State University, Irkutsk, 664003 Russia
*
e-mail: ytitova60@gmail.com
Received February 10, 2017
Abstract—It is established that the turnover frequency and number of Ni(acac) –50Et AlCl or Ni(acac) –
2
2
2
5
0Et AlCl · EtAlCl -based systems in ethylene oligomerization processes depend on the concentration of the
2 2
water in toluene. The possibility of the alkylation of toluene, used as a solvent under the considered reaction
condition, is shown. The main reactions describing the role of water at the stage of the formation and func-
tioning of catalytically active hydride nickel complexes are proposed.
Keywords: water, ethylene oligomerization, toluene alkylation, nickel catalysts, nickel Bis(acetylacetonate),
electron paramagnetic resonance
DOI: 10.1134/S0023158417050214
The catalytic oligomerization of ethylene is one of mal oxidation states of 0, +1, and +2 (the best-studied
the most significant methods for the industrial pro- ones) barely depend on the oxidation state of nickel in
duction of linear α-olefins and has been actively stud- a precursor and are governed, first of all, by the nature
ied in the years since the Ziegler’s pioneering works [1, and concentration of the cocatalyst representing a
2
]. A special place among the studies in this direction Lewis acid [18, 31]. Moreover, it is known that
is held by the works devoted to nickel systems [3–6]. Ziegler-type systems are characterized by a high level
In addition, the nickel complex, namely, tris(ethylene) of sensitivity to different admixtures and, as a conse-
nickel(0), which was synthesized in 1973 for the first quence, a low reproducibility of the results, in partic-
time [7], is considered as the first model compound ular, in olefin oligo- and polymerization processes.
for some α-olefin oligomerization stages. In more However, it has been shown that Lewis acids can be
recent times, some other nickel complexes with N- or converted into Brønsted acids in a solution under the
Р-donating ligands and alkenes were synthesized [3, 4, action of different admixtures (e.g., traces of Н
8] (in particular, the hydride complex and/or О , and peroxides) [32, 33]. The described
О
2
6
,
2
[
(o-CH C H O) P] Ni(H)(О(CF )С=О) [9]) and increase in the TOF and TON of the catalyst [18] is
3
6
4
3
2
3
studied as model systems in the catalysis of ethylene produced by a growth in the concentration of Brønsted
and propylene oligomerization [9–11].
acids due to the irreversible BF · OEt reactions
3 2
induced by the interaction with the trace water in a
solvent. The quantitative characteristics of Ziegler-
type catalytic systems in α-olefin oligomerization
reactions, such as TOF and TON described in the lit-
erature depending on the concentration of the water or
other proton-donating compounds have a sketchy
and, frequently, contradictory character [19, 34].
Nickel α-olefin oligomerization systems can be con-
sidered as the systems that have been best studied. They
are most frequently classified depending on the oxida-
tion state of nickel in the initial precursor (Ni(0), Ni(I),
and Ni(II)) [4, 6, 12–18] and the structure of the
ligands in the initial nickel complex [4, 6, 12, 19–25], in
addition to the nature of the cocatalyst [26–28]. Most
researchers share the opinion that the complexes
The analysis of the published data shows that a side
active in the oligo- or polymerization of α-olefins on process of the Friedel-Crafts alkylation of arenes used
systems of a similar kind are hydride and/or alkyl as a solvent is typical for some nickel Ziegler-type sys-
nickel complexes [9, 18, 29–31], and it has been tems active in α-olefin oligomerization processes [27,
shown that the principal quantitative characteristics 28, 35–37]. In the paper [37], this process is presented
(
(
1
turnover frequency (TOF) and turnover number as resulting from the effect of the chemical nature of
TON)) of systems based on triphenylphosphine and catalytic systems and the conditions of the process and
,4-diazo-1,3-butadiene nickel complexes in the for- called the tandem simultaneous alkylation/oligomeri-
749

7
50
TITOVA, SHMIDT
Table 1. Oligomerization of ethylene on Ni(acac) –DEAC
The aluminum organic compounds (Et AlCl and
2
2
catalytic system at different Al/Ni ratios*
Et AlCl · Cl AlEt, Sigma-Aldrich) were purified by
2
2
standard techniques [31, 40]. Toluene solutions of
these aluminum organic compounds were stored in
sealed ampoules in an argon atmosphere.
Nickel bis(acetylacetonate) samples were synthe-
sized by the methods described earlier [41].
The content of water in the nickel bis(acetylaceto-
nate) samples was determined by simultaneous ther-
mogravimetry–differential scanning calorimetry on a
Netzsch Jupiter STA 449 F3 derivatograph (Germany)
at a nitrogen flow rate of 30 mL/min and a heating rate
of 5°C/min.
TOF**, min–1
Al/Ni
TON, molC2H4 molNi
1
2.50
5.00
1.25
7.50
80
180
240
250
246
244
1885
3421
3744
3872
3822
3797
2
3
3
5
0.00
5.00
7
–
3
Toluene solutions with different water concentra-
*
Reaction conditions: [Ni] = 2.5 × 10 mol/L, [Н О] = 1.79 ×
2
–2
tions were prepared as follows. A calculated amount of
1
*
0
mol/L, toluene, 285 K.
toluene with an H O concentration of ~1.8 mmol/L
* TOF corresponds to maximum values and was calculated from
2
amount of ethylene adsorbed for 15 s.
was placed into a preliminary dried argon-filled
ampoule with a magnetic stirrer in an argon flow (the
ampoule with a stirrer was evacuated thrice during
heating in a gas burner flame, cooled to room tem-
perature, and then filled with argon). Further, water
was introduced into the ampoule with a syringe, also
in an argon flow. The amount of water added was
determined from the difference between the mass of
the syringe before and after introduction. The
ampoule was sealed and left for stirring until the com-
plete dissolution of the water.
zation process. No precise reasons of tandem alkyla-
tion/oligomerization on nickel Ziegler-type systems
have been established yet; however, it has been
hypothesized in the paper [28] that the complexes
active in ethylene oligomerization processes are
decomposed in the course of a catalytic process and
transformed into a new Lewis acid, which acts as a tol-
uene alkylation catalyst. In the work [35], it has been
assumed that alkylation occurs due to the effect of the
HO functional group incorporated into one of the
ligands in the initial complex on the state of the cocat-
Formation of a Catalyst in the Presence
of Ethylene and Oligomerization
alyst EtAlCl .
2
In this respect, the objective of this work is to study
A “duck” type reaction vessel was placed on a
the role of Н О in the formation of metal complex cat- shaker, connected with a volumetric flask, evacuated
2
alysts for the di- and/or oligomerization of α-olefins twice, and filled with ethylene. The reaction vessel was
–5
and the alkylation of arenes and, primarily, to obtain sequentially loaded with a nickel complex (0.75 × 10 –
the quantitative characteristics (TOF and TON) of
ethylene oligomerization and toluene alkylation,
depending on the concentration of the water in the ini-
tial system.
–4
1
× 10 mol) and toluene (18–20 mL) as a solvent in
an ethylene flow. The reaction mixture was saturated
with ethylene by shaking the vessel; thereupon, a
cocatalyst solution in toluene was added. The [cocata-
lyst]/[Ni] ratio was varied from 12 to 75. The overall
volume of the reactionary system was 20 mL. Oligom-
erization was performed under ф continuous supply of
the reactionary vessel with ethylene at a pressure of
EXPERIMENTAL
Materials
1
atm and vigorous shaking. The ethylene flow rate
Argon (at least 99.999%) was purified from humid-
ity and oxygen by being sequentially passed through
columns filled with P O , granular alkali, CaA molec-
was determined volumetrically from the change in the
level of decane in the volumetric flask in millimeters
2
5
(
flask volume, 500 mL). The ethylene volume was fur-
ular sieves, and activated silica-gel-supported copper
heated to 200°C.
Ethylene (GOST (State Standard) 25070-87,
OAO Nizhnekamskneftekhim, at least 99.99%) was
used without pretreatment.
ther expressed in moles to calculate the TOF and
TON. Since the process of di- and oligomerization in
the presence of the studied catalytic systems has an
unsteady-state character, the properties of these sys-
tems were compared using the number of converted
Toluene was purified by the standard method [38]. ethylene moles per mole of nickel (TON) for 2 h. Let
For deeper drying, toluene was distilled over LiAlH in us note that the adsorption of ethylene was completely
4
a distillation column and stored in an argon atmo- stopped in about 2 h in most experiments. The TOF
sphere in sealed ampoules over 4 Å molecular sieves. values given in Tables 1 and 2 correspond to the max-
The water concentration measured in toluene by the imum levels and were calculated from the amount of
Fischer method [39] was ~1.8 mmol/L.
ethylene adsorbed for 15 s.
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ROLE OF WATER IN THE CATALYSIS OF ETHYLENE Di- AND OLIGOMERIZATION
751
Table 2. Oligomerization of ethylene on Ni(acac) –EASC and Ni(acac) –DEAC catalytic systems*
2
2
TOF**, min–1
System
[Ni], mol/L
2.5 × 10–3
[Н О], mol/L
TON, mol
mol
2
2
C H
Ni
4
Ni(acac) –DEAC
1.8 × 10–3
3.05 × 10–2
1.8 × 10–3
1.8 × 10–3
1.8 × 10–3
3.05 × 10–2
1.8 × 10–3
1.8 × 10–3
50
420
279
536
402
402
682
965
788
4280
5286
2
2
.5 × 10–3
.5 × 10–4
.75 × 10–4
2.5 × 10–3
.5 × 10–3
.5 × 10–4
.75 × 10–4
7
3
13811
3793
Ni(acac) —EASC
2
2
4035
7
13543
14213
3
*
Reaction conditions: Al/Ni = 50; solution volume, 20 mL; 285 K.
** TOF corresponds to maximum values and was calculated from amount of ethylene adsorbed for 15 s.
Ethylene conversion products were analyzed on a highly active in the di- and oligomerization of olefins
Chromatech-Crystall 5000.2 chromatograph (Chro- [13, 29] and, second, some results of similar experi-
matech, Russia) equipped with a flame ionization mental studies on the interaction of DEAC and EASC
detector using a capillary column (length, 30 m; diam- with H O are available in the literature [45–47].
2
eter, 0.53 mm; SGE BPX5 phase) and on a Shimadzu
In a series of preliminary experiments, it has been
GCMS-QP-2010 mass spectrometer (Japan).
established that DEAC, EASC, and Ni(acac) indi-
2
EPR spectra were recorded on a ESP 70-03 XD/2
vidually have no catalytic activity in ethylene di- and
spectrometer (the Experimental Design Office of Spe-
oligomerization, and this allows us to exclude their
cial Equipment of Belarus State University, Republic
participation in the catalytic conversion of ethylene
of Belarus) with a working frequency of 9.3 GHz. The
over the described Ziegler systems based on the
spectrometer’s sweep ranges were calibrated using
diphenylpicrylhydrazyl of the N,N-diphenyl-N'-pic-
Ni(acac) with DEAC or EASC described below.
2
Table 1 contains the TOFs and TONs of the
Ni(acac) –DEAC system depending on the Al/Ni
rylhydrazyl radical (DPPH). The model EPR spectra
were calculated on a GPU-Tesla computer cluster [42]
using the EasySpin module for the MatLab software
suite [43], taking into account only the Zeeman elec-
tron and the hyperfine interaction in the first order of
approximation. The concentration of the spins was
calculated by comparison with the reference sample
2(subl)
ratio in the process of ethylene oligomerization. Simi-
lar results were obtained for some other Ziegler nickel
catalytic systems in the earlier works [19, 48]. The
steady-state region depending on a Al/Ni ratio range
from 30 to 75 seems to be due to the fact that the con-
centration of the formed active nickel complexes at
these ratios remains nearly the same, while excess
DEAC (at least, in the region of 40 ≤ Al/Ni ≥ 75) does
not produce any effect on the catalytic activity of the
considered system in the oligomerization of ethylene.
The ratio Al/Ni = 50 was selected for the further
experiments.
representing a Cu(acac) solution.
2
The mathematical processing of the kinetic data
and the calculation of the correlation coefficients were
performed by linear or one of the nonlinear least-
squares techniques implemented in Excel 2016 [44].
RESULTS AND DISCUSSION
When Ni(acac) ⋅ 0.5Н О was used as the initial pre-
2
2
The selected model systems were Ziegler catalysts cursor under similar conditions, a slight increase in the
based on Ni(acac) and chlorine-containing aluminum TON was observed, while the TOF remained nearly the
2
same. For this reason, all the further studies were per-
organic compounds (Et AlCl and Et AlCl · Cl AlEt).
2
2
2
formed using Ni(acac) ⋅ 0.5Н О as a precursor.
Ni(acac) was selected, primarily, due to its stability in a
2
2
2
solution of aromatic solvents under the conditions of
The activity and productivity of both Ni(acac) –
2
the ethylene di- and oligomerization experiments.
5
0DEAC- and Ni(acac) –50EASC-based catalytic
2
Et AlCl (diethylaluminum chloride (DEAC)) and systems also depend on the concentration of the initial
2
Et AlCl · Cl AlEt (ethylaluminum sesquichloride compounds (Table 2). When the Ni(acac) concentra-
2
2
2
(
EASC)) were used as cocatalysts, as, first, the cata- tion decreases by a factor of 6.67, the TOF increases by
lytic systems formed based on these cocatalysts are a factor of more than 10, and the productivity grows by
KINETICS AND CATALYSIS Vol. 58 No. 6 2017

7
52
TITOVA, SHMIDT
TOF, min–1
leads to the TOF and TON growing by nearly 9–10
TON, molC H molNi
2
4
and 5–6 times, respectively. The processing of the pre-
sented experimental data by the equation
500
450
400
350
300
250
200
4500
4000
2
1
2
3
y = a + bx + cx – dx ,
where х is the Н О concentration (mol/L) and у is
3500
3000
2500
2000
2
–1
TOF (min ) or TON (mol
mol ), means that
the coefficeint a corresponds to a TOF of 41 min and
C2H4
Ni
–1
TON of 91.5 mol
mol (see аTOF and аTON in
2
C H
4
Ni
1500
Fig. 1). These values may be interpreted as the quali-
tative characteristics of an anhydrous system. Let us
remark that the approximation validity coefficients for
2
1
50
00
1000
1
aTOF
aTON
500
0
50
this example will correspond to R
= 0.9746 and
TOF
0
10.3 20.5 30.8 41.0 51.3 61.5
2
R
= 0.9271.
TON
–3
[
H O] × 10 , mol/L
2
The dependences of TON and TOF of the
Ni(acac)2—50EASC catalytic system in ethylene
oligomerization reactions on the concentration of the
water in toluene are shown in Fig. 2. Similarly to the
Fig. 1. Ethylene oligomerization TOF and TON versus
Н О concentration for Ni(acac) –50DEAC system.
2
2
–3
[
Ni] = 2.5 × 10 mol/L, toluene, 285 K. a
and a
TOF TON
Ni(acac) –50DEAC system, both dependences in
2
are TOF and TON in anhydrous system, respectively.
Fig. 2 pass through a maximum, although the charac-
ter of these curves is slightly different and described by
higher values of parameters in comparison with the
–1
TOF, min–1
Ni(acac) –50DEAC system (а = 426 min , а
=
TON,
mol
2
C H
molNi
2
TOF
TON
4
1
195 molC2H4 mol ). This may be due to the fact that
Ni
8000
7000
6000
5000
EASC is a stronger Lewis acid than DEAC [49]. The
670
620
570
520
interaction with the water contained in toluene leads
to the formation of Brønsted acidic sites AlR Cl
H O or H [AlR Cl OH] at the first stage and,
⋅
x
3 – x
+
–
2
x
3 – x
further, much stronger Lewis acidic sites (in compar-
ison with EASC and DEAC) representing alumoo-
xane-like compounds at the second stage [33]. Both
1
2
4000
4
4
3
70
20
70
aTOF
3000
000
+
OH]– and alumooxane-like com-
H [AlR Cl
x
3 – x
2
pounds may act as both cocatalysts of ethylene oligo-
merization and stabilizers of Ni(II) cationic hydride
complexes [18]. It is likely that the formation and effi-
cient functioning of the Ni(II) hydride sites, which are
catalytically active in ethylene oligomerization and
aTON
3
2
20
70
1000
0
0
10.2 20.3 30.5 40.7 50.9 61.0
–3
[
H O] × 10 , mol/L
2
formed on the basis of Ni(acac) and chlorine-con-
2
taining aluminum organic compounds, require a
cocatalyst of a certain acidity in a certain optimal
amount. With all the other conditions being equal, this
optimal amount is determined by the nature of the
cocatalyst itself.
Fig. 2. Ethylene oligomerization TOF and TON versus
Н О concentration for Ni(acac) –50EASC system.
[
2
2
Ni] = 2.5 × 10– mol/L, toluene, 285 K. aTOF and aTON
3
are TOF and TON in anhydrous system, respectively.
The products of the conversion of ethylene in the
presence of a Ni(acac) –50DEAC based catalytic sys-
2
a factor of more than 17 for the Ni(acac) –50DEAC tem are generally presented by dimers, trimers, and a
2
system. In the case of the Ni(acac) –50EASC system, small number of oligomers. The dependence of the
2
composition of the products formed in the process of
ethylene oligomerization in the presence of a
a decrease in the Ni(acac) –50EASC concentration
2
by a factor of 6.67 leads to an increase in the TOF and
productivity by factors of 2.4 and 3.7, respectively.
Ni(acac) –50DEAC catalytic system on the concen-
2
tration of the water in toluene used as a solvent are
The dependences of the TOF and TON of the eth- shown in Fig. 3. It can be seen that an increase in the
ylene oligomerization on the concentration of the concentration of the water in toluene has an effect on
water in toluene for the Ni(acac) –50DEAC system the composition of the products: The content of
2
are shown in Fig. 1. An increase in the concentration methylpentenes and linear hexenes increases, the con-
of the water in the initial toluene by nearly 18 times tent of butene-2 decreases, and the content of butene-
KINETICS AND CATALYSIS
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ROLE OF WATER IN THE CATALYSIS OF ETHYLENE Di- AND OLIGOMERIZATION
753
1
remains nearly unchanged. This experimental fact is
Oligomerization
products, %
70
Alkylation
likely to point to an increase in the contribution from
the codimerization of butene-2 with ethylene in the
formation of hexenes. It seems that the nature of the
anionic part of the nickel complex is changed with an
increase of the concentration of the water in toluene,
and this change increases the probability of the coor-
dination of the already formed butene-2 and ethylene
with nickel.
products, %
0.6
60
50
40
30
20
0
.5
.4
0
0.3
0
.2
.1
Another distinction of the studied catalytic systems
consists in the absence of the dependence between the
composition of the oligomerization products and the
0
10
0
0
amount of water in toluene for the Ni(acac) –
1.7
11.6 21.5 31.4 41.3 51.2
61.1
2
5
0EASC system (Fig. 4). Similarly to the Ni(acac) –
–3
2
[H O] × 10 , mol/L
2
5
0DEAC system, the products are generally presented
Butene-1
Methylpentenes
Oligomers
Butene-2
Linear hexenes
by butenes (not more than 54–58%), methylpentenes
(
20–24%), linear hexenes (9.5–12.5%), and oligo-
mers (6.5–9.7%), and the quantitative composition of
the products formed at an Н О concentration in tolu-
Alkylation products
2
Fig. 3. Composition of ethylene oligomerization and tolu-
ene alkylation products (toluene + alkylation products =
–3
ene of 1.71 × 10 mol/L is nearly the same.
1
00%) on Ni(acac) –50DEAC catalytic system versus
2
–3
An increase in the concentration of the water in tol-
uene has an effect on the quantitative yield of the
alkylation products (Figs. 3, 4): the higher the water
concentration the more the toluene alkylation prod-
ucts on both catalytic systems. It is remarkable that the
water concentration in toluene. [Ni] = 2.5 × 10 mol/L,
toluene, 285 K.
Oligomerization
products, %
Alkylation
products, %
amount of alkylation products for the Ni(acac) –
2
5
0EASC system is much greater than for the
7
0
0
0
2.5
Ni(acac) –50DEAC system and attains 2.0% of the
2
6
5
total toluene amount used.
2
.0
.5
.0
The role of Ni(I) complexes in the catalysis of the
α-olefin conversion is still ambiguously interpreted in
the literature [18, 20, 23, 31, 50–52]. In this respect,
we have applied the method of EPR spectroscopy in
combination with the kinetic studies. In the earlier
works [23, 50, 51], it has been concluded that the Ni(I)
complexes formed in situ during the interaction
between the initial compounds are catalytically active
in the considered processes. This point of view is based
on the EPR spectroscopy results and radically differs
from the common viewpoint, according to which cat-
alytic activity is inherent in Ni(II) hydride or alkyl
complexes [18, 30, 31]. In one of the recent paper [52],
it has been shown that Ni(I) complexes participate in
the formation of Ni(II) complexes, under the action of
which the dimerization of butene occurs. Despite the
fact that the work [52] is devoted to the heterogeneous
catalysis of the conversion of α-olefins, its results
should be taken into account. The authors [52] per-
formed spectroscopic studies using the operando
approach, which allow preventing a reaction system
from coming into contact with air and appreciably
increase the reproducibility of the obtained results.
1
40
3
0
0
1
2
0.5
10
0
0
1
.7
11.6 21.5 31.4 41.3
51.1
61.0
–3
[H O] × 10 , mol/L
2
Butene-1
Methylpentenes
Oligomers
Butene-2
Linear hexenes
Alkylation products
Fig. 4. Composition of ethylene oligomerization and tolu-
ene alkylation products (toluene + alkylation products =
1
00%) on Ni(acac) –50EASC catalytic system versus
2
–3
water concentration in toluene. [Ni] = 2.5 × 10 mol/L,
toluene, 285 K.
58
35
caused by the presence of Ni and Cl atoms in a
paramagnetic complex molecule, has been detected in
the EPR spectrum (Fig. 5, embedding). Moreover, as
g < g , it is possible to conclude that the described
┴
||
After the mixing of Ni(acac) with DEAC or EASC Ni(I) complex has a tetragonal structure [53].
2
(
Al/Ni = 50) in a toluene solution saturated with
Let us note that neither the shape of this signal nor
argon or ethylene at 285 K, the thriaxially anisotropic its intensity depends on the atmosphere in which the
Ni(I) complex signal described by the g-factor param- catalytic system was formed (argon or ethylene). In
eters g = 2.003, g = 2.116, and g = 2.318, which are other words, it is possible to exclude the incorporation
1
2
3
KINETICS AND CATALYSIS Vol. 58 No. 6 2017

7
54
TITOVA, SHMIDT
[
Ni(I)], %
ΔV/Δt, mL/min
of a molecule (or molecules) of ethylene into the coor-
Intensity
dination sphere of the Ni(I) complex. Note that the
described Ni(I) signal is observed only for 1–2 min
after mixing the initial compounds for both systems,
and the initial Ni(I) concentration does not exceed
30% of the total amount of nickel loaded into the reac-
tor, while the oligomerization of ethylene lasts longer
for at least 1 h (Fig. 5).
3
3
2
2
5
0
5
0
300
3
4
1
250
2
00
50
100
1
1
5
280 300 320 340
Magne tt ic field, mT
This allows us to hypothesize that the Ni(I) com-
plexes participate in the formation of catalytically
active sites but are not directly involved in the catalysis
of ethylene oligomerization. Let us note that Ni(I)–
Ni(I) dimeric compounds, which can also act as cata-
lytically active sites, but are not observed in the spec-
trum, may be formed during the functioning of a cat-
alytically active system. The verification of this
hypothesis requires additional studies.
1
0
50
5
2
0
0
5
10
15
t, min
20
25
30
Fig. 5. Time dependence of (1) ethylene oligomerization
rate and (2) Ni(I) calculated concentration for
Ni(acac) –50DEAC system in ethylene conversion process.
The paper [31] proposes the scheme of the forma-
tion, functioning, deactivation, and regeneration of
catalytically active nickel complexes in a chain mech-
anism where the hydride Ni(II) complexes are kinetic
chain carriers. Taking into account our data on the
effect of water on this scheme [31], it is necessary to
make some supplements, namely,
2
‒3
–3
[
Ni] = 2.5 × 10 mol/L, [Н О] = 6.76 × 10 mol/L, tolu-
2
ene, 285 K, Тrec = 77 K. Embedding: (3) EPR spectrum
of toluene solution of Ni(acac) –50DEAC catalyzate in
ethylene conversion process, (4) model EPR spectrum of
Ni(acac) –50DEAC system. [Ni] = 2.5 × 10 mol/L,
2
–
3
2
2
85 K, Тrec = 77 K. For clarity, data are presented only
for first 30 min of experiment.
AlR X + H O ꢀ AlR X ⋅H O, [45,46], (I)
n
3−n
2
n
3−n
2
+
−
AlR X ⋅ H O ꢀ H
[
AlR X3−nOH
]
,
(II)
n
3−n
2
n
H
+
CH2
+
−
−
H [AlR X OH] + Lm −1Ni
[Lm −1Ni] [AlRnX3 −nOH] ,
(III)
n
3 −n
CH2
CH2
H C
2
CH2 CH3
H
+
+
−
−
[Lm −1Ni] [AlR X OH] + CH =CH
n 3 − n 2 2
[
Lm −1Ni] [AlR X OH] + CH =CH
n
3 − n
2
2
CH2
CH2
H C
2
H C
2
H
+
−
[
Lm −1Ni] [AlR X OH] + CH =CH CH CH3,
n
3 − n
2
2
CH2
(IV)
(V)
H C
2
H
+
−
+
[
Lm − 1Ni] [AlR X OH] + H [AlR X OH]−
L NiX + 2AlR X
OH + H + C H ,
(3−n)− 1 2 2 4
n
3 − n
n
3 − n
m
2
n
CH2
H C
2
where L is a ligand (phosphine), R is a hydrocarbon AlR Cl
⋅ Н О (reaction I) under the action of
2
n
3 – n
moiety (–С Н ), Х is chlorine, m = 1–2, and n = 1–2. trace water in a catalytic system to be further con-
2
5
+
OH]– (reaction II).
In other words, a part of the cocatalyst representing a verted into H [AlR X
Lewis acid may be converted into a Brønsted acid H [AlR X OH] can react with the Ni(0) complex
n
3 – n
+
–
n
3 – n
KINETICS AND CATALYSIS
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No. 6
2017

ROLE OF WATER IN THE CATALYSIS OF ETHYLENE Di- AND OLIGOMERIZATION
755
+
–
to form a hydride [L NiH(C H )] [AlR Cl OH]
(3 – n)
Hence, Scheme 3 from the paper [31] can now be
presented as follows (see the scheme). This scheme
summarizes all the know reactions which describe the
mechanisms of the formation and functioning of
Ziegler-type catalytic systems based on nickel com-
plexes in the oligomerization reactions of the lower
alkenes.
m
2
4
n
(
reaction III), which further participates in ethylene
oligomerization (reaction IV). Moreover,
OH] is converted in
+
–
[
L NiH(C H )] [AlR Cl
m 2 4 n (3 ‒ n)
the course of irreversible reactions into a Ni(II) com-
plex (L NiX , reaction V), which transits into a cata-
m
2
lytically active state under the action of AlR Cl
n
3 – n
(
see the scheme).
CH −CH3
2
Lm −1Ni] [AlR X OH]−
+
[
n
3 −n
H2C=CH2
CH2
H C
2
H2C=CH2
CH2=CH−CH2−CH3
D
H
Lm −1Ni] [AlR X OH]−
+
[
n 3 −n
H [AlR X OH]−
+
CH2
n
3 −n
H C
2
.
AlR X
H O
2
n
3 −n
CH2
CH2
H2
Lm −1Ni
2
AlRnX(3 −n) −1OH
H2O
n = 1 and 2
H2C=CH2
AlR X
n 3 −n
H2O
n = 1−3
1
/2[AlRnX(3 −n) −1]2 n = 1 and 2
L
LmNiX2
≤ m ≤ 2
AlRn −1X(3 −n) + 1
0
AlRnX3 −n
H2C=CH2
A
LmNiH(R)X
Lm −1NiX1/2 [H2/RH]
B(I)
AlRn −1X(3 −n) + 1
n = 1−3
AlRn −1X(3 −n) + 1
L
H2C=CH2
CH2
−
B(II)
+
[
Lm −1NiH(R)] AlRn −1X
(3 −n) + 2
Lm −1Ni
CH2
n = 1 and 2
AlRnX3 −n
n = 1−3
CH2=CH−AlRnX(3 −n) −1
C
H(R)
AlRn −1X(3 −n) + 1
−
+
−
+
AlRn −1
X
(3 −n) + 2
Lm −1Ni−CH −CH −AlR X
Lm −1Ni
2
2
n
3 − n
CH2
CH2=CH−CH2−H2CH(R)
H C
2
H2C=CH2
Scheme 1. (A is the formation of active complexes, B(I) and B(II) are the regeneration of active complexes, C is the catalytic
ethylene dimerization cycle, and D is the catalytic ethylene dimerization cycle with allowance for the effect of Н О).
2
ACKNOWLEDGMENTS
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This work was supported by the Government
Assignment for Scientific Research from the Ministry
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Translated by E. Glushachenkova
KINETICS AND CATALYSIS Vol. 58 No. 6 2017