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:
[email protected] Received February 10, 2017
Abstract—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. 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 the most significant methods for the industrial production of linear α-olefins and has been actively studied in the years since the Ziegler’s pioneering works [1, 2]. A special place among the studies in this direction is held by the works devoted to nickel systems [3–6]. In addition, the nickel complex, namely, tris(ethylene) nickel(0), which was synthesized in 1973 for the first time [7], is considered as the first model compound for some α-olefin oligomerization stages. In more recent times, some other nickel complexes with N- or Р-donating ligands and alkenes were synthesized [3, 4, 6, 8] (in particular, the hydride complex [(o-CH3C6H4O)3P]2Ni(H)(О(CF3)С=О) [9]) and studied as model systems in the catalysis of ethylene and propylene oligomerization [9–11]. Nickel α-olefin oligomerization systems can be considered as the systems that have been best studied. They are most frequently classified depending on the oxidation 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 active in the oligo- or polymerization of α-olefins on systems of a similar kind are hydride and/or alkyl nickel complexes [9, 18, 29–31], and it has been shown that the principal quantitative characteristics (turnover frequency (TOF) and turnover number (TON)) of systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene nickel complexes in the for-
mal oxidation states of 0, +1, and +2 (the best-studied ones) barely depend on the oxidation state of nickel in a precursor and are governed, first of all, by the nature and concentration of the cocatalyst representing a Lewis acid [18, 31]. Moreover, it is known that Ziegler-type systems are characterized by a high level of sensitivity to different admixtures and, as a consequence, a low reproducibility of the results, in particular, in olefin oligo- and polymerization processes. However, it has been shown that Lewis acids can be converted into Brønsted acids in a solution under the action of different admixtures (e.g., traces of Н2О and/or О2, and peroxides) [32, 33]. The described increase in the TOF and TON of the catalyst [18] is produced by a growth in the concentration of Brønsted acids due to the irreversible BF3 · OEt2 reactions induced by the interaction with the trace water in a solvent. The quantitative characteristics of Zieglertype catalytic systems in α-olefin oligomerization reactions, such as TOF and TON described in the literature depending on the concentration of the water or other proton-donating compounds have a sketchy and, frequently, contradictory character [19, 34]. The analysis of the published data shows that a side process of the Friedel-Crafts alkylation of arenes used as a solvent is typical for some nickel Ziegler-type systems active in α-olefin oligomerization processes [27, 28, 35–37]. In the paper [37], this process is presented as resulting from the effect of the chemical nature of catalytic systems and the conditions of the process and called the tandem simultaneous alkylation/oligomeri-
749
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TITOVA, SHMIDT
Table 1. Oligomerization of ethylene on Ni(acac)2–DEAC catalytic system at different Al/Ni ratios* Al/Ni
TOF**, min–1
TON, molC 2H 4 mol Ni
12.50
80
1885
25.00
180
3421
31.25
240
3744
37.50
250
3872
50.00
246
3822
75.00
244
3797
* Reaction conditions: [Ni] = 2.5 × 10–3 mol/L, [Н2О] = 1.79 × 10–2 mol/L, toluene, 285 K. ** TOF corresponds to maximum values and was calculated from amount of ethylene adsorbed for 15 s.
zation process. No precise reasons of tandem alkylation/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 toluene 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 cocatalyst EtAlCl2. In this respect, the objective of this work is to study the role of Н2О in the formation of metal complex catalysts for the di- and/or oligomerization of α-olefins and the alkylation of arenes and, primarily, to obtain the quantitative characteristics (TOF and TON) of ethylene oligomerization and toluene alkylation, depending on the concentration of the water in the initial system. EXPERIMENTAL Materials Argon (at least 99.999%) was purified from humidity and oxygen by being sequentially passed through columns filled with P2O5, granular alkali, CaA molecular 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. Toluene was purified by the standard method [38]. For deeper drying, toluene was distilled over LiAlH4 in a distillation column and stored in an argon atmosphere in sealed ampoules over 4 Å molecular sieves. The water concentration measured in toluene by the Fischer method [39] was ~1.8 mmol/L.
The aluminum organic compounds (Et2AlCl and Et2AlCl · Cl2AlEt, Sigma-Aldrich) were purified by 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 synthesized by the methods described earlier [41]. The content of water in the nickel bis(acetylacetonate) samples was determined by simultaneous thermogravimetry–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. Toluene solutions with different water concentrations were prepared as follows. A calculated amount of toluene with an H2O concentration of ~1.8 mmol/L 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 temperature, 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 complete dissolution of the water. Formation of a Catalyst in the Presence of Ethylene and Oligomerization A “duck” type reaction vessel was placed on a shaker, connected with a volumetric flask, evacuated twice, and filled with ethylene. The reaction vessel was sequentially loaded with a nickel complex (0.75 × 10–5– 1 × 10–4 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 [cocatalyst]/[Ni] ratio was varied from 12 to 75. The overall volume of the reactionary system was 20 mL. Oligomerization was performed under ф continuous supply of the reactionary vessel with ethylene at a pressure of 1 atm and vigorous shaking. The ethylene flow rate was determined volumetrically from the change in the level of decane in the volumetric flask in millimeters (flask volume, 500 mL). The ethylene volume was further 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 systems were compared using the number of converted ethylene moles per mole of nickel (TON) for 2 h. Let us note that the adsorption of ethylene was completely stopped in about 2 h in most experiments. The TOF values given in Tables 1 and 2 correspond to the maximum levels and were calculated from the amount of ethylene adsorbed for 15 s. KINETICS AND CATALYSIS
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Table 2. Oligomerization of ethylene on Ni(acac)2–EASC and Ni(acac)2–DEAC catalytic systems* System Ni(acac)2–DEAC
Ni(acac)2—EASC
[Н2О], mol/L
[Ni], mol/L
TOF**, min–1
TON, mol C 2H 4 mol Ni
2.5 × 10–3
1.8 × 10–3
50
788
2.5 × 10–3
3.05 × 10–2
420
4280
7.5 × 10–4
1.8 × 10–3
279
5286
3.75 × 10–4
1.8 × 10–3
536
13811
2.5 × 10–3
1.8 × 10–3
402
3793
2.5 × 10–3
3.05 × 10–2
402
4035
7.5 × 10–4
1.8 × 10–3
682
13543
3.75 × 10–4
1.8 × 10–3
965
14213
* 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 Chromatech-Crystall 5000.2 chromatograph (Chromatech, Russia) equipped with a flame ionization detector using a capillary column (length, 30 m; diameter, 0.53 mm; SGE BPX5 phase) and on a Shimadzu GCMS-QP-2010 mass spectrometer (Japan). EPR spectra were recorded on a ESP 70-03 XD/2 spectrometer (the Experimental Design Office of Special Equipment of Belarus State University, Republic of Belarus) with a working frequency of 9.3 GHz. The spectrometer’s sweep ranges were calibrated using diphenylpicrylhydrazyl of the N,N-diphenyl-N'-picrylhydrazyl 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 electron and the hyperfine interaction in the first order of approximation. The concentration of the spins was calculated by comparison with the reference sample representing a Cu(acac)2 solution. The mathematical processing of the kinetic data and the calculation of the correlation coefficients were performed by linear or one of the nonlinear leastsquares techniques implemented in Excel 2016 [44]. RESULTS AND DISCUSSION The selected model systems were Ziegler catalysts based on Ni(acac)2 and chlorine-containing aluminum organic compounds (Et2AlCl and Et2AlCl · Cl2AlEt). Ni(acac)2 was selected, primarily, due to its stability in a solution of aromatic solvents under the conditions of the ethylene di- and oligomerization experiments. Et2AlCl (diethylaluminum chloride (DEAC)) and Et2AlCl · Cl2AlEt (ethylaluminum sesquichloride (EASC)) were used as cocatalysts, as, first, the catalytic systems formed based on these cocatalysts are KINETICS AND CATALYSIS
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highly active in the di- and oligomerization of olefins [13, 29] and, second, some results of similar experimental studies on the interaction of DEAC and EASC with H2O are available in the literature [45–47]. In a series of preliminary experiments, it has been established that DEAC, EASC, and Ni(acac)2 individually have no catalytic activity in ethylene di- and oligomerization, and this allows us to exclude their participation in the catalytic conversion of ethylene over the described Ziegler systems based on the Ni(acac)2 with DEAC or EASC described below. Table 1 contains the TOFs and TONs of the Ni(acac)2(subl)–DEAC system depending on the Al/Ni ratio in the process of ethylene oligomerization. Similar 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 concentration 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. When Ni(acac)2 ⋅ 0.5Н2О was used as the initial precursor under similar conditions, a slight increase in the TON was observed, while the TOF remained nearly the same. For this reason, all the further studies were performed using Ni(acac)2 ⋅ 0.5Н2О as a precursor. The activity and productivity of both Ni(acac)2– 50DEAC- and Ni(acac)2–50EASC-based catalytic systems also depend on the concentration of the initial compounds (Table 2). When the Ni(acac)2 concentration decreases by a factor of 6.67, the TOF increases by a factor of more than 10, and the productivity grows by
752
TITOVA, SHMIDT TON, mol C 2H 4 mol Ni
TOF, min–1 500 450 400 350 300 250 200 150 100 50
2 1
aTOF
0
10.3
20.5
30.8
41.0
4500 4000 3500 3000 2500 2000 1500 1000 aTON 500 0 51.3 61.5
–3
[H2O] × 10 , mol/L Fig. 1. Ethylene oligomerization TOF and TON versus Н2О concentration for Ni(acac)2–50DEAC system. [Ni] = 2.5 × 10–3 mol/L, toluene, 285 K. aTOF and aTON are TOF and TON in anhydrous system, respectively.
TON, mol C 2H 4 mol Ni
TOF, min–1
8000 670 620 570 520 470 420 370 320 270
7000 6000 5000 1
4000
aTOF
3000
2
2000 aTON
0
10.2
20.3
30.5
40.7
50.9
1000
0 61.0
[H2O] × 10–3, mol/L Fig. 2. Ethylene oligomerization TOF and TON versus Н2О concentration for Ni(acac)2–50EASC system. [Ni] = 2.5 × 10–3 mol/L, toluene, 285 K. aTOF and aTON are TOF and TON in anhydrous system, respectively.
a factor of more than 17 for the Ni(acac)2–50DEAC system. In the case of the Ni(acac)2–50EASC system, a decrease in the Ni(acac)2–50EASC concentration by a factor of 6.67 leads to an increase in the TOF and productivity by factors of 2.4 and 3.7, respectively. The dependences of the TOF and TON of the ethylene oligomerization on the concentration of the water in toluene for the Ni(acac)2–50DEAC system are shown in Fig. 1. An increase in the concentration of the water in the initial toluene by nearly 18 times
leads to the TOF and TON growing by nearly 9–10 and 5–6 times, respectively. The processing of the presented experimental data by the equation y = a + bx + cx2 – dx3, where х is the Н2О concentration (mol/L) and у is TOF (min–1) or TON ( mol C 2H4 mol Ni ), means that the coefficeint a corresponds to a TOF of 41 min–1 and TON of 91.5 mol C 2H4 mol Ni (see аTOF and аTON in Fig. 1). These values may be interpreted as the qualitative characteristics of an anhydrous system. Let us remark that the approximation validity coefficients for 2 this example will correspond to RTOF = 0.9746 and 2 RTON = 0.9271. 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 Ni(acac)2–50DEAC system, both dependences in Fig. 2 pass through a maximum, although the character of these curves is slightly different and described by higher values of parameters in comparison with the Ni(acac)2–50DEAC system (аTOF = 426 min–1, аTON = 1195 mol C 2H 4 mol Ni ). This may be due to the fact that EASC is a stronger Lewis acid than DEAC [49]. The interaction with the water contained in toluene leads to the formation of Brønsted acidic sites AlRxCl3 – x ⋅ H2O or H+[AlRxCl3 – xOH]– at the first stage and, further, much stronger Lewis acidic sites (in comparison with EASC and DEAC) representing alumooxane-like compounds at the second stage [33]. Both H+[AlRxCl3 – xOH]– and alumooxane-like compounds may act as both cocatalysts of ethylene oligomerization and stabilizers of Ni(II) cationic hydride complexes [18]. It is likely that the formation and efficient functioning of the Ni(II) hydride sites, which are catalytically active in ethylene oligomerization and formed on the basis of Ni(acac)2 and chlorine-containing 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. The products of the conversion of ethylene in the presence of a Ni(acac)2–50DEAC based catalytic system are generally presented by dimers, trimers, and a small number of oligomers. The dependence of the composition of the products formed in the process of ethylene oligomerization in the presence of a Ni(acac)2–50DEAC catalytic system on the concentration of the water in toluene used as a solvent are shown in Fig. 3. It can be seen that an increase in the concentration of the water in toluene has an effect on the composition of the products: The content of methylpentenes and linear hexenes increases, the content of butene-2 decreases, and the content of buteneKINETICS AND CATALYSIS
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1 remains nearly unchanged. This experimental fact is 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 coordination of the already formed butene-2 and ethylene with nickel. Another distinction of the studied catalytic systems consists in the absence of the dependence between the composition of the oligomerization products and the amount of water in toluene for the Ni(acac)2– 50EASC system (Fig. 4). Similarly to the Ni(acac)2– 50DEAC system, the products are generally presented by butenes (not more than 54–58%), methylpentenes (20–24%), linear hexenes (9.5–12.5%), and oligomers (6.5–9.7%), and the quantitative composition of the products formed at an Н2О concentration in toluene of 1.71 × 10–3 mol/L is nearly the same. An increase in the concentration of the water in toluene has an effect on the quantitative yield of the alkylation products (Figs. 3, 4): the higher the water concentration the more the toluene alkylation products on both catalytic systems. It is remarkable that the amount of alkylation products for the Ni(acac)2– 50EASC system is much greater than for the Ni(acac)2–50DEAC system and attains 2.0% of the total toluene amount used. 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 catalytic 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] performed 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. After the mixing of Ni(acac)2 with DEAC or EASC (Al/Ni = 50) in a toluene solution saturated with argon or ethylene at 285 K, the thriaxially anisotropic Ni(I) complex signal described by the g-factor parameters g1 = 2.003, g2 = 2.116, and g3 = 2.318, which are KINETICS AND CATALYSIS
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Oligomerization products, % 70
Alkylation products, % 0.6
60
0.5
50
0.4
40
0.3
30
0.2
20
0.1
10 0 1.7
753
11.6
21.5
31.4
41.3
51.2
0 61.1
[H2O] × 10–3, mol/L Butene-1 Methylpentenes Oligomers
Butene-2 Linear hexenes Alkylation products
Fig. 3. Composition of ethylene oligomerization and toluene alkylation products (toluene + alkylation products = 100%) on Ni(acac)2–50DEAC catalytic system versus water concentration in toluene. [Ni] = 2.5 × 10–3 mol/L, toluene, 285 K.
Oligomerization products, % 70
Alkylation products, % 2.5
60
2.0
50 40
1.5
30
1.0
20 0.5
10 0 1.7
11.6
21.5
31.4
41.3
51.1
0 61.0
[H2O] × 10–3, mol/L Butene-1 Methylpentenes Oligomers
Butene-2 Linear hexenes Alkylation products
Fig. 4. Composition of ethylene oligomerization and toluene alkylation products (toluene + alkylation products = 100%) on Ni(acac)2–50EASC catalytic system versus water concentration in toluene. [Ni] = 2.5 × 10–3 mol/L, toluene, 285 K.
caused by the presence of 58Ni and 35Cl 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 Ni(I) complex has a tetragonal structure [53]. Let us note that neither the shape of this signal nor its intensity depends on the atmosphere in which the catalytic system was formed (argon or ethylene). In other words, it is possible to exclude the incorporation
754
TITOVA, SHMIDT
[Ni(I)], % 35
Intensity
30
ΔV/Δt, mL/min 300
3
1
of a molecule (or molecules) of ethylene into the coordination 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 reactor, while the oligomerization of ethylene lasts longer for at least 1 h (Fig. 5).
250
4
25
200
20 150 15
280 300 320 340 Magnetic field, mT
10 5 0
This allows us to hypothesize that the Ni(I) complexes 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 catalytically active sites, but are not observed in the spectrum, may be formed during the functioning of a catalytically active system. The verification of this hypothesis requires additional studies.
100 50
2 5
10
15 t, min
20
25
0 30
Fig. 5. Time dependence of (1) ethylene oligomerization rate and (2) Ni(I) calculated concentration for Ni(acac)2–50DEAC system in ethylene conversion process. [Ni] = 2.5 × 10‒3 mol/L, [Н2О] = 6.76 × 10–3 mol/L, toluene, 285 K, Тrec = 77 K. Embedding: (3) EPR spectrum of toluene solution of Ni(acac)2–50DEAC catalyzate in ethylene conversion process, (4) model EPR spectrum of Ni(acac)2–50DEAC system. [Ni] = 2.5 × 10–3 mol/L, 285 K, Тrec = 77 K. For clarity, data are presented only for first 30 min of experiment.
The paper [31] proposes the scheme of the formation, functioning, deactivation, and regeneration of catalytically active nickel complexes in a chain mechanism 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,
AlR n X 3− n + H 2O AlR n X 3− n ⋅ H 2O, [45,46], (I)
AlR n X 3− n ⋅ H 2O H + [ AlR n X 3− nOH] , −
H+[AlRnX3 − nOH]−+ Lm −1Ni
CH2 CH2
H [Lm −1Ni]+[AlRnX3 − nOH]− + CH2=CH2 CH2 H2 C H
(II)
H [Lm −1Ni]+[AlRnX3 − nOH]−, CH2 H2 C
CH2 CH3 + [Lm − 1Ni] [AlRnX3 − nOH]− +
(III)
CH2=CH2
CH2 H2 C
[Lm −1Ni]+[AlRnX3 − nOH]− + CH2=CH CH2 CH3, CH2 H2 C
(IV)
H [Lm − 1Ni] [AlRnX3 − nOH]− + H+[AlRnX3 − nOH]− CH2 H2 C +
where L is a ligand (phosphine), R is a hydrocarbon moiety (–С2Н5), Х is chlorine, m = 1–2, and n = 1–2. In other words, a part of the cocatalyst representing a Lewis acid may be converted into a Brønsted acid
LmNiX2 + 2AlRnX(3 −n)− 1OH + H2 + C2H4,
(V)
AlRnCl3 – n ⋅ Н2О (reaction I) under the action of trace water in a catalytic system to be further converted into H+[AlRnX3 – nOH]– (reaction II). H+[AlRnX3 – nOH]– can react with the Ni(0) complex KINETICS AND CATALYSIS
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to form a hydride [LmNiH(C2H4)]+[AlRnCl(3 – n)OH]– (reaction III), which further participates in ethylene oligomerization (reaction IV). Moreover, [LmNiH(C2H4)]+[AlRnCl(3 ‒ n)OH]– is converted in the course of irreversible reactions into a Ni(II) complex (LmNiX2, reaction V), which transits into a catalytically active state under the action of AlRnCl3 – n (see the scheme).
755
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 complexes in the oligomerization reactions of the lower alkenes.
CH2−CH3 [Lm −1Ni]+[AlRnX3 −nOH]− CH2 H2 C
H2C=CH2
H2C=CH2
D
H
CH2=CH−CH2−CH3
[Lm −1Ni]+[AlRnX3 −nOH]− CH2 H2 C
H+[AlRnX3 −nOH]−
AlRnX3 −n . H2O
CH2 Lm −1Ni
H2 2AlRnX(3 −n) −1OH
CH2
AlRnX3 −n
H 2O 1/2[AlRnX(3 −n) −1]2 n = 1 and 2
AlRnX3 −n
H2O
n = 1 and 2
H2C=CH2
n = 1−3 LmNiX2 0≤m≤2
L
H2C=CH2
A Lm −1NiX
B(I)
AlRn −1X(3 −n) + 1
LmNiH(R)X AlRn −1X(3 −n) + 1 n = 1−3
1/2 [H2/RH]
AlRn −1X(3 −n) + 1
CH2 Lm −1Ni
CH2
AlRnX3 − n
B(II)
L
− [Lm −1NiH(R)]+AlRn −1X(3 − n) + 2
n = 1 and 2 CH2=CH−AlRnX(3 −n) −1
C
n = 1−3 AlRn −1X(3 −n) + 1
−
+
Lm −1Ni−CH2−CH2−AlRnX3 − n
H2C=CH2
CH2=CH−CH2−H2CH(R)
H(R) − + AlR X Lm −1Ni CH n −1 (3 −n) + 2 2 H2 C
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 Н2О).
ACKNOWLEDGMENTS This work was supported by the Government Assignment for Scientific Research from the Ministry of Education and Science of the Russian Federation (no. 4.5183.2017/8.9). KINETICS AND CATALYSIS
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Translated by E. Glushachenkova
