The role of phosphine and 1,2-diimine complexes of nickel in the oxidation states 0, +1, and +2 in the catalyzed di-, oligo-, and polymerization of ethylene

Article abstract of DOI:10.1134/S0023158416010122

The turnover frequency and number have been determined for eighteen catalytic systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene complexes of nickel in the formal oxidation states 0, +1, and +2 in the oligoand polymerization of lower alkenes. The main catalytic characteristics are almost independent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are presented for nickel(I) 1,4-diazo-1,3-butadiene complexes and radical anions resulting from the reactions of the cocatalyst with nickel α-diimine complexes. Reactions describing the formation, functioning, decomposition, and regeneration of the catalytically active nickel hydride complexes are proposed.

Full text of DOI:10.1134/S0023158416010122

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2016, Vol. 57, No. 1, pp. 61–71. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © F.K. Shmidt, Yu.Yu. Titova, L.B. Belykh, 2016, published in Kinetika i Kataliz, 2016, Vol. 57, No. 1, pp. 63–73.
The Role of Phosphine and 1,2ꢀDiimine Complexes of Nickel
in the Oxidation States 0, +1, and +2 in the Catalyzed Diꢀ, Oligoꢀ,
and Polymerization of Ethylene
F. K. Shmidt, Yu. Yu. Titova*, and L. B. Belykh
Irkutsk State University, Irkutsk, 664003 Russia
*eꢀmail: ytitova60@gmail.com
Received April 16, 2015
Abstract—The turnover frequency and number have been determined for eighteen catalytic systems based on
triphenylphosphine and 1,4ꢀdiazoꢀ1,3ꢀbutadiene complexes of nickel in the formal oxidation states 0, +1,
and +2 in the oligoꢀ and polymerization of lower alkenes. The main catalytic characteristics are almost indeꢀ
pendent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the
cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are
presented for nickel(I) 1,4ꢀdiazoꢀ1,3ꢀbutadiene complexes and radical anions resulting from the reactions of
the cocatalyst with nickel ꢀdiimine complexes. Reactions describing the formation, functioning, decompoꢀ
α
sition, and regeneration of the catalytically active nickel hydride complexes are proposed.
Keywords: nickel catalysts; hydridonickel(II) complexes; phosphine complexes; 1,2ꢀdiimine complexes;
ESR of Ni(I); diꢀ, oligoꢀ and polymerization of ethylene; mechanism
DOI: 10.1134/S0023158416010122
INTRODUCTION
ride and weak Lewis bases, such as triphenylbismuth
or ꢀmethylpyrrole.
For the first three types of systems, there is rather
convincing experimental evidence that the nickel
hydrido complexes containing one phosphine moleꢀ
cule in the coordination sphere are active in the catalꢀ
ysis of the oligomerization of lower olefins. The
anionic ligand is weakly bound to the metal or located
in the second coordination sphere [4–10].
N
Catalysis by complexes of nickel in different oxidaꢀ
tion states (0, +1, and +2) combined with alkyl or
alkylꢀfree Lewis acids (most frequently, aluminumꢀ
and boronꢀcontaining compounds) has been investiꢀ
gated for more than half a century since Ziegler and
coauthors had discovered the catalytic effect of the
Ni(0) complexes in reactions of the aluminum alkyl
compounds with ethylene [1, 2].
The electrophilic reaction of the Lewis acid (BF3
)
The reaction
with the Ni(0) alkene complex followed by the formaꢀ
tion of the nickel(II) hydrido complex was shown [3]
to be the key step of the formation of active complexes.
The question about the nature of active complexes for
the systems of the fifth type is still disputable [11, 12].
CH =CH , Ni(0)
2
2
(C4H9)AlR2
C4H8ꢀ1 + (C2H5)AlR2
stimulated rapid investigation of the new class of cataꢀ
lysts for the polymerization of lower alkenes—Ziegler–
Natta catalysts.
The main specific feature of the catalytic systems
based on the nickel complexes is their multicompoꢀ
nent composition and, hence, numerous reactions
occurring at both the catalyst formation and functionꢀ
ing stage and the active complex decomposition stage,
the multiphase character of the systems, and sensitivity to
various impurities, first of all, protonꢀ and oxygenꢀconꢀ
taining compounds. In addition, such key characteristics
as turnover frequency (TOF), turnover number (TON),
and selectivity are affected in partticular catalytic proꢀ
cesses by the nature of the components used, their ratio
and order of introduction, process parameters (first of all,
temperature), and some other factors. This results in seriꢀ
ous difficulties in investigation.
It was proposed [3] that nickel systems for the diꢀ,
oligoꢀ, and polymerization of alkenes be classified by
such properties as the formal oxidation state of nickel
in the precursor and the cocatalyst nature. Five types
of nickel systems are distinguished according to this
classification: (1) nickel(II) complexes LnNiX2 (X is
the anionic ligand; L is the donor ligand, e.g., phosꢀ
phine, phosphite, or diimine with
n = 1 and 2) comꢀ
bined with aluminum alkyl halides; (2) organoꢀ or
hydridonickel(II) complexes activated by Lewis acids,
including aluminum alkyl halides; (3) Ni(0) comꢀ
plexes combined with a Brønsted acid; (4) Ni(0) or
Ni(I) complexes combined with a Lewis acid;
(5) Ni(II) complexes, for example, Ni(PPh3)2Cl2 in a
It was shown [9, 10] that a propylene dimerization
solution of ionic liquids consisting of aluminum chloꢀ catalyst can be prepared using complexes of nickel in
61

62
SHMIDT et al.
the oxidation states 0, +1, and +2 combined with the cocatalyst was added. The [cocatalyst]/[Ni] ratio
AlEtnCl3 –
(n = 1 or 2) as precursors, and the TON was varied from 2 to 50. The overall volume of the
and selectnivity of these systems are almost the same. reaction system was 16–20 mL. Oligomerization was
The question arises about the formation of catalytiꢀ carried out under the continuous supply of ethylene to
cally active complexes with the same composition and the reactor at a pressure of 1 atm under vigorous shakꢀ
structure in case the complexes of nickel in different ing of the reactor. Since the diꢀ and oligomerization
oxidation states (0, +1, and +2) are used as precursors. processes in the presence of the catalytic systems are
unsteadyꢀstate ones, the number of moles of ethylene
converted per mole of nickel (TON) throughout the
catalyst onꢀstream time was used to compare the propꢀ
erties of these systems. The value of TOF was deterꢀ
mined from the rate of ethylene dimerization at the
maximum catalytic activity point.
The products of ethylene conversion were analyzed
on a KhromatekꢀKristall 5000.2 chromatograph (Khroꢀ
matek, Russia) equipped with a flameꢀionization detecꢀ
tor using a capillary column (length of 30 m, diameter of
0.53 mm, SGE BPX5 phase) and on a GCMSꢀQPꢀ2010
mass spectrometer (Shimadzu, Japan).
Accordingly, the purpose of this work is to deterꢀ
mine the role of the nickel complexes in different oxiꢀ
dation states and that of the second component (Lewis
acid) in the formation of catalytically active species
and in their functioning in the diꢀ, oligoꢀ, and polyꢀ
merization of ethylene. The Ni(0), Ni(I), and Ni(II)
complexes with the phosphine and
were used as precursors.
α
ꢀdiimine ligands
EXPERIMENTAL
Materials
ESR spectra were recorded on an ESP 70ꢀ03 XD/2
spectrometer (Belarusian State University, Belarus
Republic) at a working frequency of 9.3 GHz. Dipheꢀ
Solvents (benzene, toluene, and octane) were puriꢀ
fied using standard procedures [13]. For deeper dryꢀ
ing, benzene and toluene were additionally distilled
from LiAlH4 using a distillation column and were
stored under argon in sealed tubes over molecular sieve
nylpicrylhydrazyl (or
N,NꢀdiphenylꢀN'ꢀpicrylhydraꢀ
zyl radical, DPPH) and 2,2,6,6ꢀtetramethylpiperiꢀ
dineꢀ1ꢀoxyl (TEMPO) were used in the calibration of
scan ranges of the spectrometer. Models of ESR specꢀ
tra were simulated on a GPUꢀTesla VK computing
cluster [21] using the EasySpin module for the Matlab
package [22] taking into account only the electron
Zeeman and hyperfine coupling interactions in the
first approximation. Spin concentrations were calcuꢀ
lated by comparing with a standard sample, namely, a
Cu(acac)2 solution for signals assigned to the nickel
complexes and TEMPO for the signals assigned to
radicals. NMR spectra were recorded on a VXRꢀ500S
pulse spectrometer (Varian, United States).
4
Å. The concentration of water in the solvents meaꢀ
sured by the Fischer method [14] was ~1 mmol/L.
The nickel phosphine complexes were synthesized
using standard procedures: Ni(PPh3)2(C2H4) [15],
Ni(PPh3)4, Ni(PPh3)2Cl2 [16], Ni(PPh3)3Cl [17], and
Ni(PPh3)2Cl [18]. The nickel
α
ꢀdiimine complexes
NiBr2(DAD–R) (R = CH3, C3H7) and Ni(DAD–
CH3)2, with (DAD(–CH3) = 1,4ꢀbis(2,6ꢀdimethylꢀ
phenyl)ꢀ2,3ꢀdimethylꢀ1,4ꢀdiazabutaꢀ1,3ꢀdiene and
DAD(–iꢀC3H7) = 1,4ꢀbis(2,6ꢀdiisopropylphenyl)ꢀ
2,3ꢀdimethylꢀ1,4ꢀdiazabutaꢀ1,3ꢀdiene), were syntheꢀ
sized according to a described procedure [19].
The organoaluminum compounds (AlEt3, AlEt2Cl
and AlEtCl2) [20] were distilled in vacuo: AlEt3 at 48–
49 C/1 Torr, AlEt2Cl at 78–79 C/4 Torr, and AlEtCl2 at
81–82 С/4 Torr. Solutions of the organoaluminum
compounds were stored in sealed tubes under argon.
Boron trifluoride etherate (BF3 OEt2) was distilled in
vacuo from calcium hydride (53 C/46 Torr) and were
,
RESULTS AND DISCUSSION
°
°
The quantitative characteristics of the catalytic sysꢀ
tems based on the nickel complexes in the oxidation
states 0, +1, and +2 with triphenylphosphine ligands
and AlEtCl2 (Al/Ni = 10) as a cocatalyst in ethylene
oligomerization are presented in Table 1. Additional
experiments showed that the Al/Ni molar ratio optiꢀ
mizing the activity of the nickel systems is 10. The
PPh3/Ni molar ratio in the first series of experiments
is 2, and that in the second series is 4.
As follows from the data presented in Table 1, the
values of TOF and TON and the composition of the
ethylene oligomerization products are almost indepenꢀ
dent of the oxidation state of nickel in the precursor.
°
·
°
stored in a Schlenk flask as a 0.5 M solution in degassed
toluene in an argon atmosphere or in sealed tubes.
Triphenylphosphine (Sigma–Aldrich) was addiꢀ
tionally recrystallized from ethanol. 31P NMR (solvent
C6H6): = –6 ppm.
δ
Formation of the Catalyst in the Presence
of Ethylene and Oligomerization
A duckꢀshaped shaker reactor was placed on a The TOF value is 229 30 min–1, and TON = 2867
rocking platform, connected to a volumetric flask, 350 (mol ethylene)/(mol Ni). Two main conclusions
evacuated two times, and filled with ethylene. A solꢀ can be drawn from these results. First, in these systems
vent (15–19 mL) and a nickel complex (
2.5
1
×
10–4 to the concentrations of the nickel complexes active in
×
10–4 mol) were successively placed in the reactor ethylene oligomerization almost coincide regardless of
in an ethylene flow. The reaction mixture was satuꢀ the nature of the initial nickel complexes (in particuꢀ
rated with ethylene under shaking, and a solution of lar, regardless of the oxidation state of nickel in the
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

THE ROLE OF PHOSPHINE AND 1,2ꢀDIIMINE COMPLEXES OF NICKEL
63
Table 1. Results of ethylene oligomerization in the presence of the catalytic systems based on the phosphine complexes of
nickel in different oxidation states and AlEtCl2
Product composition, %
System
no.
TOF
×
102,
TON
103,
×
Catalytic system
min–1
molC H /molNi
C4
C6
C8
2
4
1
NiP2Cl2* + AlEtCl2
NiP2Cl2 + AlEtCl2
1.2
1.4
1.2
1.1
1.3
2.3
2.0
2.0
1.9
2.8
3.5
3.4
3.8
3.8
2.9
2.7
2.8
3.4
64.8
60.9
69.4
68.3
73.6
60.6
57.4
54.2
60.4
32.0
36.3
25.7
22.8
18.9
34.4
38.5
39.0
27.6
3.2
2.8
4.9
8.9
7.5
5.0
4.1
6.8
4.0
2
3
NiP2Cl + AlEtCl2
4
NiP2(C2H4) + AlEtCl2
NiP2(C2H4) + AlEtCl2
NiP4 + AlEtCl2
5
6
7
NiP2Cl2 +2P + AlEtCl2
NiP3Cl +2P + AlEtCl2
NiP2(C2H4) + 2P + AlEtCl2
8
9
–4
Al/Ni = 10,
T
= 286 K, solution volume 20 mL, and
ν
= 1 × 10 mol.
Ni
* P = PPh .
3
Table 2. Results of ethylene oligomerization in the presence of the systems based on the Ni(0, I, and II)
α
ꢀdiimine comꢀ
Product
plexes combined with AlEtnCl3 –
(n = 1 and 2) or B(C6F5)3
n
TON,
TOF,
min–1
ν
×
10–4
,
System
no.
Ni
Catalytic system
molC H /molNi
composition, %
mol
2
4
1
2
3
4
5
6
7
8
9
NiBr2(DAD–CH3)–10 AlEtCl2
1
1
1
1
1
1
1
5
25
1
6.7
5.6
5.4
7.2
0.8
6.7
6.5
32
1.4
0.8
0.9
×
×
×
×
×
×
×
×
×
103
103
103
103
103
103
103
103
103
PM*
PM*
PM*
PM*
PM*
PM*
PM*
PM*
NiBr2(DAD–
i
ꢀC3H7)–10 AlEtCl2
NiBr(DAD–CH3)–10 AlEtCl2
Ni(DAD–CH3)2–10 AlEtCl2
NiBr2(DAD–CH3)**–10 AlEtCl2
NiBr2(DAD–CH3)***–10 AlEtCl2
Ni(DAD–CH3)2–40 AlEt2Cl
1.8
0.16
1.81
0.5
1.7
4.73
NiBr2(DAD–
NiBr2(DAD–
i
i
ꢀC3H7)–20 AlEt2Cl
ꢀC3H7)–200 AlEt2Cl
525
6.7
30.6
PM*
PM*, ****
PM*
10
11
Ni(DAD–CH3)2–3 B(C6F5)3
Ni(DAD–CH3)2–6 B(C6F5)3
= 15 mL.
45
120
1
T
= 280 K,
V
* PM (polymer) is branched polyethylene.
** The NiBr (DAD–CH )–AlEtCl system was formed in argon.
2
3
2
***
T
= 303 K.
**** PM/oligomer = 20/80; fractional oligomer composition (%): C , 46.6; C , 31.9; C , 21.5.
4
6
8
precursor). Second, processes leading to the formaꢀ
tion of the active nickel complexes of the same comꢀ
position and structure (notably, the Ni(II) hydride
complexes) occur in the catalytic systems
In addition to the nickel phosphine complexes, the
catalytic systems based on the ꢀdiimine complexes of
nickel in different oxidation states were studied in ethꢀ
ylene oligomerization. It turned out that both the
α
Ni(II) ꢀdiimine complexes described in numerous
α
+
CH2 CH2
works [23–25] and the Ni(0) and Ni(I) complexes
combined with the boronꢀ and aluminumꢀcontaining
Lewis acids can be used as precursors (Table 2). An
analysis of the experimental results shows that the
TOF and TON of the catalytic systems based on the
Ni(0) (Ni(DAD–CH3)2), Ni(I) (NiBr(DAD–CH3),
and Ni(II) (NiBr2(DAD–CH3) complexes in combiꢀ
H
Ni
AlR4 – nCln– .
PPh3
The formation of these complexes was proved [4–10]
(where is the vacant site for alkene coordination).
ᮀ
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

64
SHMIDT et al.
nation with AlEtnCl3 –
(n
= 1 and 2), as in the case of and boronꢀcontaining compounds (AlEt2Cl, AlEtCl2,
n
the nickel phosphine complexes, are almost indepenꢀ AlEt3, BF3 · OEt2, and B(C6F5)3) were studied by physꢀ
dent of the oxidation state of nickel in the precursor ical and chemical methods to substantiate the role of
(Table 2, systems 1–4). This fact allows us to advance the nickel complexes in different oxidation states in
an assumption about the identical natures and equal the formation of catalytically active species.
concentrations of the catalytically active nickel comꢀ
plexes formed in the systems based on the nickel
ꢀdiimine complexes in different oxidation states.
Reactions of the Ni(II) Phosphine and Diimine
Complexes with the Organoaluminum Compounds
α
The following factors should be mentioned among
those affecting the activity and productivity of the ethꢀ
ylene oligoꢀ and polymerization catalysts based on the
nickel ꢀdiimine complexes: [cocatalyst]/[Ni] molar
The reaction of Ni(PPh3)2Cl2 with AlEt3 or
AlEtCl2 was shown [26] to be accompanied by the forꢀ
mation of gaseous products, whose amount and comꢀ
position depended on the nature of the organoalumiꢀ
num compound, the molar ratio of the components,
and the solvent ratio. When using AlEt3, the gaseous
products are mainly presented by ethane (up to 96%)
and butenes, whereas the proportions of hydrogen and
butenes in the gaseous products increase in the presꢀ
ence of AlEtCl2 (Table 3). The fraction of butenes
decreases with an increasing AlEtCl2/Ni ratio. This is
due to the conversion of ethylene to higher oligomers,
because the activity of the systems in the process
increases sharply with an increase in the Al/Ni ratio
(Table 3). The formation of gaseous products is a result
of transmetallation between the nickel(II) phosphine
complex and organoaluminum compound leading to
unstable alkyl nickel complexes. The latter, in turn,
form the nickel(II) hydrido complexes and Ni(I) and
α
ratio (Table 2, systems 8–11), process temperature
(Table 2, nos. 1 and 6), and the gaseous atmosphere
used in catalyst formation. The NiBr2(DAD–CH3)–
AlEtCl2 system formed in an inert atmosphere (argon)
was characterized by TOF and TON values smaller by
one order of magnitude than those of a similar system
formed in the presence of ethylene (Table 2, systems 1
and 5). This result indicates an important role of the
substrate in the formation of the catalytically active
nickel complexes.
When both AlEt3 – nCln (n = 1 and 2) and B(C6F5)3
are used as cocatalysts, the major products of ethylene
conversion are branched polyethylene and trace
amounts of oligomers (butenes, hexenes, and octenes).
However, the oligomers form mainly at B/Ni
system 10).
≤
3 (Table 2,
The systems based on the Ni(II), Ni(I), and Ni(0) Ni(0) complexes in the course of further transformaꢀ
phosphine and diimine complexes and the aluminumꢀ tions (Scheme 1).
Reaction of Ni(II) phosphine complexes with organoaluminum compounds
P
P
H
X
AlR X
n
–HX
3 –
n
PmNi(0), 0
≤
m ≤ 4
Ni
–C H
2
4
P
P
R
•
–R
Ni
P2NiX2 + AlRnX3 –
+ AlRn – 1X(3 –
n
n) + 1
– AlRn – 2X5 –
n
X
P
P
X
Ni
AlRn−1X(3−n)
•
–R
X
Scheme 1.
The qualitative composition of the gaseous prodꢀ that Ni(II) is reduced to lower oxidation states. A simꢀ
ucts formed in the NiBr2(DAD– ꢀPr)–AlEt2Cl sysꢀ ilar situation was observed when Ni(acac)2 was used as
i
tem is the same as in the system based on the nickel a precursor [27].
complex Ni(PPh3)2Cl2, although the proportion of
Taking into account the possibility of the formation
ethane is somewhat larger and the proportions of ethꢀ
ylene and butene are smaller (Table 3). In particular, it
was found that the proportion of butenes also
increased with an increase in the Al/Ni ratio. The
composition of the gaseous products formed in the
NiL2X2–AlR3 – nCln systems (X = Cl and Br, L = PPh3
of the Ni(I) complexes in the reactions considered
[28, 29], we obtained an additional information by an
ESR spectroscopic study of the systems. The parameꢀ
ters of some Ni(I) complexes are given in Table 4.
The ESR spectrum of the Ni(PPh3)2Cl2–AlR3 – nCln
and DAD–R, AlR3 – nCln = AlEt3 and AlEtCl2) shows system (n = 0, 1) exhibits signal I (Table 4, system 1),
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

THE ROLE OF PHOSPHINE AND 1,2ꢀDIIMINE COMPLEXES OF NICKEL
65
Table 3. Quantitative composition of gaseous products evolved upon the reactions of Ni(PPh3)2Cl2 and NiBr2(DAD–
ꢀC3H7) with AlEt3 or AlEtCl2
i
Composition of products, %
System no.
Catalytic system
Al/Ni
ν
gas, mol/(mol of Ni)
H2
C2H6
C2H4
C4H8
1
2
3
4
2
4
6
8
1.41
4.40
8.05
7.05
1.05
0.80
0.67
0.65
93.70
94.88
96.03
94.50
1.07
0.27
0.20
0.30
4.41
4.15
3.00
4.55
Ni(PPh3)2Cl2–AlEt3
C
Ni = 2.5
10–2 mol/L
×
5
6
7
8
2
4
6
8
0.78
0.91
1.21
1.44
2.30
4.35
3.80
2.80
63.84
67.13
77.75
79.95
2.65
2.10
1.84
1.42
31.21
26.42
16.61
16.12
Ni(PPh3)2Cl2–AlEtCl2
Ni = 2.5
10–2 mol/L
C
×
9
10
11
2
4
7
1.50
1.50
3.60
Traces*
Traces
–
98.85
98.44
97.09
0.08
0.08
0.06
1.07
1.48
2.85
NiBr2(DAD–
iꢀPr)–AlEt3
C
Ni = 1.67
×
10–2 mol/L
12
13
5
3.20
5.70
–
–
96.76
94.33
0.09
0.09
3.15
5.58
NiBr2(DAD–
iꢀPr)–AlEt2Cl
C
Ni = 8.0
×
10–3 mol/L
18
T
= 286 K, solution volume 30 mL.
* Traces means trace amounts.
whose parameters are characteristic of the bridged ticular, the ESR spectrum of the NiBr2[DAD(–
iꢀPr)]–
Ni(I) complex [28]
AlR3 – nCln system (
n
= 0, 1) in the Al/Ni = 5–10 range
shows two signals conventionally designated as II and
III (Table 4, system 2). The ꢀfactor parameters of sigꢀ
PPh3
PPh3
g
Cl
Cl
.
nal II are characteristic of a Ni(I) complex with a tetꢀ
ragonal structure, one diimine ligand, and, probably,
two anions (–С2Н5 and halogen) in the first coordinaꢀ
tion sphere of nickel [30]. Signal III (Fig. 1a), whose
intensity increases in time, corresponds to the diimine
radical anion (Table 4, system 2). For Al/Ni = 3, the
Ni
AlEt2
An increase in the Al/Ni ratio leads to the disapꢀ
pearance of signal from the ESR spectrum and the
appearance of the ferromagnetic resonance signal with
= 2.2–2.4, which is characteristic of nickel nanoparꢀ
I
g
ESR spectra of the NiBr2[DAD(–
system contains a new, earlier unreported signal with
= 2.156 and = 2.388 along with signals II and III
iꢀPr)]–AlR3 – nCln
ticles [27]. This fact indicates the reduction and/or
disproportionation of the Ni(I) complexes to Ni(0)
and Ni(II) and the formation of nickel nanoparticles
responsible for the ferromagnetic resonance. If
AlEt2Cl is used instead of AlEtCl2, no signal from the
Ni(I) complexes is observed in the ESR spectrum in a
wide range of Al/Ni ratios, indicating that the Ni(I)
complexes are unstable in the presence of such a
g
g
(Fig. 1a). This signal corresponds to another Ni(I)
complex, whose identification requires further studies. In
the ESR spectra of the NiBr2[DAD(–
system ( = 0 and 1) recorded at room temperature,
signal III from the radical anion ( 2.004) has a
iꢀPr)]–AlR3 – nCln
n
g
≈
hyperfine structure (HFS) with 15 asymmetric wellꢀ
resolved lines (Fig. 1b). The HFS is due to the presꢀ
ence of two 14N nuclei and six 1H nuclei (Table 4, sysꢀ
tem 2). The signal broadening is associated with the
nickel site [31]. An analysis of the relationship between
the intensities of the ESR signals from the Ni(I) comꢀ
plexes and radical anion at different temperatures of
spectra recording and Al/Ni ratios assumes an equilibꢀ
strong Lewis acid as AlEtCl2
.
According to the ESR data, the reactions of the
nickel(II) diimine complexes (NiBr2(DAD–R)) with
the organoaluminum compounds (AlEt3 and AlEt2Cl
yield the Ni(I) complexes (Fig. 1), whose parameters
are presented in Table 4. Unlike the nickel complexes
with the phosphine ligands, the variation of the Al/Ni
molar ratio does not change the shape of the spectrum
)
but affects the intensity and stability of the signals. In parꢀ rium that can be presented by Scheme 2.
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

66
SHMIDT et al.
Reaction of nickel(II) diimine complexes with triethylaluminum
CH3
H3C
CH3
H3C
H3C
CH3
CH• CH
–
R
C
C
R
C
C
R
R
R
R
N
N
N
N
N
N
+
–1/2[C H , C H ]
2
6
2 4
Ni
Al
Ni
Ni
Br
Br
Et
Br
Et
Br
R
R
R
R
Br
Et
Br
Et
R
R
+
Al
AlEt3
CH3
CH
H3C
•
R
C
R
+ NiBr2
N
N
Al+
R = CH3 and iꢀPr
Et
Et
R
R
Scheme 2.
Reactions of the Ni(I) Complexes with the Aluminumꢀ
and Boronꢀcontaining Compounds
AlEt3 results in the reduction of nickel(I) to Ni(0)
nanoclusters.
It should be mentioned that the initial nickel(I)
complex decomposes in the reaction of Ni(PPh3)2Cl
The ESR spectrum of the Ni(PPh3)2Cl complex at
77 K shows an HFS characteristic of the interaction of an
unpaired electron with two equivalent phosphorus nuclei
(Fig. 2a; Table 4, signal IV). At 293 K, an isotropic signal
corresponds to the Ni(PPh3)2Cl complex [32].
with the alkylꢀfree Lewis acid
Ni(PPh3)2Cl2 a precipitate forma, according to IR specꢀ
troscopic data ( = 392 nm). It
= 740 L mol–1 cm–1 at
(BF3) and a
ε
λ
is reasonable to assume that the Ni(PPh3)2Cl complex
decomposes in the system via a disproportionation
reaction to form Ni(0) and Ni(PPh3)2Cl2, and the latꢀ
ter is poorly soluble in toluene [3].
The reactions of Ni(PPh3)2Cl with aluminum alkyl
halides (AlEt2Cl and AlEtCl2) at equimolar ratios of
the reactants yields a bridged Ni(I) complex with
AlEt3 – nCln (
[26]. As the Al/Ni ratio increases, signal
complex disappears from in the ESR spectrum of the
n
= 1, 2), to which signal
I
I
corresponds
of the Ni(I)
Reaction of the Ni(0) Complexes with the Aluminumꢀ
and Boronꢀcontaining Compounds
Ni(PPh3)2Cl–AlEt3 – nCln system (n = 1 and 2), indiꢀ
cating further transformations.
It was found [9, 10] that the reaction of Ni(PPh3)4
with AlEtCl2 (Al/Ni 2) resulted in the appearance of
≤
The reaction of Ni(PPh3)2Cl with AlEt3 affords the
nickel(I) phosphine complex Ni(PPh3)3Cl (Table 4,
signal V), but the ESR signal of this complex is charꢀ
acterized by a considerably lower intensity compared
to that of signal IV from the nickel precursor. An
increase in the number of triphenylphosphine ligands
in the coordination sphere of the Ni(I) complex
an ESR signal, whose parameters were identical to
those of signal IV of complex Ni(PPh3)2Cl. A similar
ESR signal was observed for the Ni(PPh3)2(C2H4)–
AlEtCl2 system (Al/Ni = 1), and the concentration of
the paramagnetic Ni(I) complex was close to that of
the initial Ni(0) complex. An increase in the Al/Ni
ratio leads to the subsequent appearance of ESR sigꢀ
nals corresponding to the bridged nickel(I) complex
(
Ni(PPh3)3Cl) and a decrease in the intensity of the
ESR signal IV indicate the reduction of a portion of
the Ni(PPh3)2Cl complex to Ni(0) and a redistribution
of the phosphine ligands [33].
(signal I) and Ni(0) nanoclusters.
As in experiments with the Ni(0) phosphine comꢀ
plexes, the reactions of the Ni(0) diimine complexes
According to ESR data, if the Ni(PPh3)3Cl comꢀ with the organoaluminum compounds provide their
plex is used as the nickel precursor, then its reaction oxidation to the Ni(I) complexes. In particular, two
with AlEtCl2 (Al/Ni = 1) yilds complex Ni(PPh3)2Cl
The transformation of complex Ni(PPh3)3Cl under the detected in the ESR spectra of the Ni[DAD(–CH3)]2–
action of AlEt2Cl(Al/Ni 2) results in the formation of AlEt3 – nCln system ( = 1 and 2): signal VI (Table 4,
a bridged nickel(I) complex, whereas the reaction with system 5) and the second (unidentified yet) signal
.
signals corresponding to the Ni(I) complexes were
≤
n
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

THE ROLE OF PHOSPHINE AND 1,2ꢀDIIMINE COMPLEXES OF NICKEL
67
(a)
2
2
1
1
(c)
(b)
III
II
2
1
2600
2800
3000
3200
3400
Magnetic field, G
(b)
2
1
(a)
2
1
2800 3000 3200 3400 3600 3800 4000 4200
Magnetic field, G
3250
3300
3350
3400
Magnetic field, G
Fig. 2. (1) Experimental and (2) simulated ESR spectra of
Fig. 1.
(
1
2
) Experimental and (
2) simulated ESR spectra of
(a) a toluene solution of Ni(PPh ) Cl in argon, (b) the
3 2
the NiBr [DAD(–
i
ꢀPr)]–3AlEt catalytic system at (a) 77
same solution saturated with ethylene, and (c) the
3
and (b) 293 K.
Ni(PPh ) Cl–5BF ⋅ OEt system at T = 77 K.
3 2 3 2
from the Ni(I) complex with
These signals are similar to those detected in the ESR
spectra of the NiBr2[DAD(– ꢀPr)]–AlEt3 – nCln system
= 0 and 1) (Table 4, system 2). The ESR spectrum
of the Ni[DAD(–CH3)]2–AlEt3 – nCln system ( = 0
and 1) also contains signal VII from the radical with
= 2.023 (Table 4, system 5). The ESR spectrum of
the Ni[DAD(–CH3)]2–AlEt3 – nCln system at 293 K is
similar to the spectrum of the NiBr2[DAD(– ꢀPr)]–
AlEt3 – nCln system. The difference is the number of particular, the formation of the Ni(I) cationic comꢀ
g
= 2.117 and
g
= 2.279. pounds in which aluminum formally existed in the
reduced form
i
2Ni[PPh3]4 + 2AlRCl2
(
n
n
2Ni[PPh3]2Cl + Cl(R)Al–Al(R)Cl.
–4 PPh
3
g
In addition to the organoaluminum compounds,
such compounds as BF3 OEt2 and B(C6F5)3 possess
oxidizing properties toward the Ni(0) complexes. In
·
i
plex [Ni(PPh3)3]BF4 (Table 4, signal VIII) was found
[34, 35] in the reaction of Ni(PPh3)4 with BF3 OEt2
(B/Ni ). A further increase in the B/Ni molar ratio
resolved lines of the radical anion. Possibly, this is due
to the aluminum atom incorporated into the radical
anion [30].
·
≤
3
(20, 40, and 60) results successively in a decrease in the
intensity of the ESR signal from the cationic paramagꢀ
netic Ni(I) complexes containing different numbers of
the phosphine ligands in the inner coordination
The experimental data on the reactions of the
Ni(0) complexes with the organoaluminum comꢀ
pounds show that AlEtCl2 is the oxidizer toward the
Ni(0) complexes with different types of ligands. We did
not consider the question about the mechanism of
Ni(0) oxidation by aluminum alkyl halides but earlier
showed for the Ni(0) phosphine complexes [10] that
sphere of nickel [Ni(PPh3)n]BF4 (n = 1, 2, 3) and in the
appearance of a signal from the nickel nanoclusters.
The scheme for the oxidation of the Ni(0) phosphine
complexes by boron trifluoride etherate can be preꢀ
the redox process yielded Ni(I) and dimeric comꢀ sented through the formation of ate complexes:
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

68
SHMIDT et al.
Table 4. ESR parameters for the Ni(I) complexes
Conventional
System
no.
g
designation
of signal
Signal assignment
g||
g
g
⊥
⊥
PPh3
PPh3
Cl
AlEt2
Cl
Ni
1
I
2.382
2.220
2.094
2.064
Et
Et
X
II
Ni(I) complex
Radical
Al
Ni(DAD−iꢀPr)
2.11*
2.022
2
X
III
X = C2H5 or halogen
g
= 2.004, A** = 9 G*
Ni(PPh3)2Cl
3
4
IV
V
2.343
2.06
2.23
2.126
2.396
2.068
2.117*
2.102
Ni(PPh3)3Cl
Et
Et
X
VI
Ni(I) complex
Radical
Al
Ni(DAD−CH3)
5
X
2.023
VII
X = C2H5 or halogen
g
= 2.007, A = 7.5 G*
Ni(PPh3)3BF4
6
7
VIII
IX
2.385
2.282
2.12
2.118
2.012
2.07
Ni(I) complex
Radical
2.063
–
[(DAD–i )
ꢀPr)Ni]+B(C6F5
4
X
8
Ni(PPh3)(C2H4)Cl
XI
2.449
2.181
1.997
T
= 77 K.
*
T
= 298 K.
** A is the hyperfine coupling constant.
NiP4
OEt2
P3Ni–F + P3NiBF2 + OEt2,
P3Ni–F + BF3 OEt2 P3Ni–F BF3 + OEt2,
OEt2 P3Ni–F BF3BF2 OEt2,
NiP3 + P,
[P3Ni–F]–+BF2OEt2
lar to that described in Scheme 2 can be proposed for
the systems based on Ni[DAD(–CH3)]2 in combinaꢀ
tion with the aluminumꢀ and boronꢀcontaining comꢀ
pounds.
NiP3 + BF3
⋅
+NiP
3
⋅
⋅
Interaction between the Components of the Systems
in the Catalytic Process
P3NiBF2 + BF3
⋅
+
⋅
where P = PPh3
.
Taking into account the oxidation properties of
BF3
As was mentioned above, the interaction of the
OEt2 and B(C6F5)3, we additionally studied the components of the Ni(PPh3)2Cl2–AlEt3 system
·
systems based on the Ni(0) diimine complexes and (Al/Ni = 1.5) in argon yields a bridged nickel(I) comꢀ
boronꢀcontaining compounds. The ESR spectra of plex. The ESR spectrum of the reaction solution of
the Ni[DAD(–CH3)]2–BX3 (BX3 = B(C6F5)3 and Ni(PPh3)2Cl2–AlEt3 changes substantially after the
BF3
·
OEt2) recorded at 77 K exhibited threeꢀaxially treatment with ethylene. The absence of the HFS from
, and signal two halogen atoms suggested that, under the action of
anisotropic signal IX, for which g||
>
g
X
⊥
from the radical anion (Table 4, system 7). Threeꢀaxiꢀ ethylene, the bridged nickel(I) complex transformed
ally anisotropic signal IX indicates the orthorhombic into the Ni(I) complex, whose coordination sphere
structure of the formed nickel(I) complex. The ESR contained one halogen atom; i.e., the action of ethylꢀ
spectra of this system at 293 K exhibit an isotropic sigꢀ ene broke one Al–Cl bond. The existence of the coorꢀ
nal from the nickel(I) complex and a signal from the dinately unsaturated Ni(I) complex in the system at
radical, but no additional HFS was observed in this 77 K is poorly probable and, hence, it is reasonable to
case. Therefore, the existence of an equilibrium simiꢀ assume that the first coordination sphere of Ni(I) also
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

THE ROLE OF PHOSPHINE AND 1,2ꢀDIIMINE COMPLEXES OF NICKEL
69
contains ethylene. Based on this, the Ni(I) complex alytically active nickel hydrido complexes in ethylene
(Table 4, signal XI) formed under the conditions close conversion.
to the catalytic ones can be presented as follows [33]:
Generalizing the available experimental and theoꢀ
retical data, we can suggest the main reactions that
occur during the formation, functioning, deactivaꢀ
tion, and regeneration of the catalytically active nickel
complexes in the framework of the earlier proposed
[33] chain process, in which the Ni(II) hydrido comꢀ
plexes are carriers of the kinetic chain.
CH2
CH2
Cl
.
Ni
Ph3P
Chain nucleation is the formation of catalytically
active nickel complexes and can be presented by three
main reactions:
The substitution of triphenylphosphine by ethylene
in the coordination sphere of Ni(I) is favored by the
formation of an adduct between the aluminumꢀ and
phosphorusꢀcontaining compounds.
(a) transmetalation,
The participation of the unsaturated substrates in the
formation of the catalytically active complexes was also
observed when the Ni(I) complexes were used as precurꢀ
sors. The ESR spectrum of complex Ni(PPh3)2Cl in tolꢀ
uene solution under an inert atmosphere is shown in
Fig. 2a. The parameters of the spectrum are given in
Table 4 (signal IV). The spectral pattern changed after
the solution of Ni(PPh3)2Cl was saturated with ethylꢀ
ene (Fig. 2b). The ESR signal corresponds to a superꢀ
position of signals from a mixture of complexes
P2NiX2 + AlRnX3 – n
(I)
P2Ni(R)X + AlRn – 1
X
,
(3 – n) + 1
P2Ni(R)X + AlRnX3 – n
(II)
+
–
[P2Ni(R)] (AlRnX(3 – n) + 1) ,
(b) interaction with the Brønsted acid,
Ni(PPh3)3Cl (signal
V) and Ni(PPh3)(C2H4)Cl (signal XI)
formed in the reaction
–
P2Ni(0) + H+[AlRnX4 – n
]
(III)
+
–
) ,
2Ni(PPh3)2Cl + C2H4
Ni(PPh3)3Cl + Ni(PPh3)(C2H4)Cl.
[P2Ni(H)] (AlRnX
(4 – n)
(c) process involving zwitterion formation via the
reaction of a Ni(0) alkene complex with a Lewis acid,
for example, with BF3 [3],
After the addition of BF3 · OEt2 (B/Ni = 1) or
AlEtCl2 (Al/Ni = 1) to the Ni(PPh3)2Cl solution satuꢀ
rated with ethylene, signal IV presented in Fig. 2b disꢀ
appeared and a signal from ferromagnetic Ni(0)
appeared (Fig. 2c). Similar transformations in the
ESR spectra are observed upon the introduction of
PnNi(C2H4)
3 PnNi–CH2–CH2–BF3
+
–
+BF
(IV)
CH2 CH2 BF2
PnNi
F
styrene into the catalytic system Ni(PPh3)2Cl–BF3
·
OEt2. The formation of the nickel nanoclusters can be
presented as a result of the disproportionation of comꢀ
plex Ni(PPh3)2Cl to Ni(PPh3)2Cl2 and Ni(0) under the
action of the Lewis acid. Complexes Ni(PPh3)n(С2Н4)
and NiCl2 can form in a similar way from complex
Ni(PPh3)(С2Н4)Cl [3].
+BF
3 [PnNi–CH2–CH2–BF2]BF4.
Similar transformations can occur in the presence
of AlRnX3 –
:
n
The concentration of the Ni(I) paramagnetic comꢀ
plexes decreases with an increase in the Al/Ni ratio,
and the TOF and TON of the nickel systems increase
in the same range. This suggests that the Ni(I) comꢀ
plexes are inactive in the catalysis of the considered
reaction but play an important role in the regeneraꢀ
tion of the catalytically active sites. At the same time,
a weak broadened signal with a chemical shift of
Pm – 1Ni(C2H4) + AlRnX3 – n
+
–
Pm – 1Ni–CH2–CH2AlRnX3 – n
–
(V)
–
+AlR
X
– 1 (3 –
n
n
) + 1
[Pm – 1AlH(R)]AlRn – 1X(3 – n) + 2
+
+ CH2=CH–AlRnX(3 – n) – 1
,
⎯
12.6 ppm corresponding to the nickel(II) hydride
1
complex was detected by H NMR spectroscopy in
the Ni(PPh3)2(С2Н4)–BF3 OEt2 systems even in the where the
absence of Brønsted acids. These results suggest that AlRnX(3 –
·
σ
ꢀvinyl aluminum compound СН2=СН–
(
n
= 1, 2) can form due to the
β
ꢀhydride
both the nickel precursor and cocatalyst and also the shift causend by the agostic interaction of
β
ꢀhydrogen with
) – 1
substrate itself are involved in the formation of the catꢀ the nickel atom (Scheme 3, cycle B(II)).
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

70
SHMIDT et al.
Formation and functioning of the catalytically active nickel complexes in the Ni(PPh3)2X2–AlRnX3 – n system:
A is the formation of the active complexes, B(I) and B(II) represent the regeneration
of the active complexes, and C is the catalytic cycle of ethylene dimerization
AlRnX3 –
n
n
= 1–3
n = 1 and 2
1/2[AlRnX(3 –
P
]
) – 1 2
Pm – 1NiX2
AlRn – 1X(3 –
n
n) + 1
0
≤
m
≤
2
AlRnX3 –
n
A
H2C=CH2
B(I)
PmNiH(R)X
AlRn – 1X(3 –
Pm – 1NiX
1/2[H2/RH]
AlRn – 1X(3 –
n) + 1
n
= 1–3
n
) + 1
B(II)
CH2
CH2
H2C=CH2
P
[Pm – 1NiH(R)]+AlRn – 1X(–3 –
Pm – 1Ni
n) + 2
n = 1 and 2
CH2=CH–AlRnX(3 –
AlRnX3 –
n
n
n) – 1
= 1–3
C
+
Pm – 1Ni–CH2–CH2–AlRnX3 –
–
H(R)
+
AlRn – 1X(3 –
n) + 1
n
AlRn – 1X–(3 –
CH2
Pm – 1Ni
H2C
n) + 2
CH2=CH–CH2–H2CH(R)
H2C=CH2
P = PPh3
Scheme 3.
Chain propagation is the catalytic conversion of providing high activity and productivity of these sysꢀ
lower alkenes (Scheme 3). Chain termination is the tems under mild conditions.
deactivation of the active nickel complex
The same scheme shows the main functions of the
aluminumꢀ and boronꢀcontaining cocatalysts in the
conversion of lower alkenes under the action of the
nickel complexes: the alkylation and reduction of the
transition metal to lower oxidation states; the oxidaꢀ
tion of the Ni(0) complexes to Ni(I), the elimination
–
2[P2Ni(H)]+(AlRnX4 –
)
n
(VI)
P2Ni(0) + P2NiX2 + 1/2H2 + AlRnX3 –
.
n
of the ligands (phosphines and
(
α
ꢀdiimines) and anion
The catalytically active nickel complexes are again
regenerated in the conversion of the Ni(II) and Ni(0)
complexes via reactions (I)–(III) (Scheme 3).
According to the above equations, the nickel(II)
hydride complexes are formed from the nickel comꢀ
pounds with an oxidation state of +2. Some Ni(II)
complexes are simultaneously reduced to the Ni(I)
complex, which undergoes disproportionation
Cl–) from the coordination sphere of the transition
metal, providing the formation of coordinatively
unsaturated nickel complexes and accelerating the
disproportionation of Ni(I) to Ni(II) and Ni(0); and
the stabilization of the catalytically active hydride
complexes by coordination with nickel through the
dichloride or hydrochloride bridge (in the case of
AlEt3 – nCln or AlEt3, respectively).
2PmNiX
PmNiX2 + PmNi(0),
(VII)
thus regenerating the Ni(II) complex. The resulting
Ni(0) is stabilized in the presence of alkene and is
reoxidized to Ni(I) under the action of aluminum
alkyl halides, returning to the regeneration cycle of the
active complexes (Scheme 3, B(II)). The catalytically
active nickel complexes are regenerated due to these
multiply repeated processes of alkylation, reduction,
disproportionation, and oxidation. The concentration
of the complexes is maintained at a fairly high level,
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, project no. 14ꢀ03ꢀ32037 mol_a.
REFERENCES
1. Ziegler, K., Gellert, H.G., Holzkamp, E., and Wilke, G.,
Brennst. Chem., 1954, vol. 35, p. 321.
KINETICS AND CATALYSIS Vol. 57
No. 1
2016

THE ROLE OF PHOSPHINE AND 1,2ꢀDIIMINE COMPLEXES OF NICKEL
71
2. Ziegler, K., Gellert, H.ꢀG., Holzkamp, E., Wilke, G., 20. Perrin, D.D. and Armarego, W.L.F., Purification of
Duck, E.W., and Kroll, W.ꢀR., Justus Liebigs Ann.
Chem., 1960, vol. 629, no. 1, p. 172.
Laboratory Chemicals, Oxford: Pergamon, 1988.
21. http://hpc.icc.ru
3. Titova, Yu.Yu., Belykh, L.B., Rokhin, A.V., Soroka, O.G.,
and Schmidt, F.K., Kinet. Catal., 2014, vol. 51, no. 1,
p. 35.
22. Stoll, S. and Schweiger, A., J. Magn. Reson., 2006,
vol. 178, no. 1, p. 42.
23. Gibson, V.C. and Spitzmesser, S.K., Chem. Rev., 2003,
4. Bogdanovich, B., Adv. Organomet. Chem., 1979, vol. 17,
vol. 103, no. 1, p. 283.
p. 105.
24. Ivanchev, S.S., Russ. Chem. Rev., 2007, vol. 76, no. 7,
5. Onsager, O.ꢀT., Wang, H., and Blindheim, U., Helv.
Chim. Acta, 1969, vol. 52, no. 1, p. 187.
6. Onsager, O.ꢀT., Wang, H., and Blindheim, U., Helv.
Chim. Acta, 1969, vol. 52, no. 1, p. 196.
p. 617.
25. Svejda, S.A. and Brookhart, M., Organometallics, 1999,
vol. 18, no. 1, p. 65.
26. Shmidt, F.K., Kataliz kompleksami metallov pervogo
perekhodnogo ryada reaktsii gidrirovaniya i dimerizatsii
(Catalysis of Hydrogenation and Dimerization Reacꢀ
tions by Complexes of FirstꢀRow Transition Metals),
Irkutsk: Irkutsk. Gos. Univ., 1986.
7. Onsager, O.ꢀT., Wang, H., and Blindheim, U., Helv.
Chim. Acta, 1969, vol. 52, no. 1, p. 215.
8. Onsager, O.ꢀT., Wang, H., and Blindheim, U., Helv.
Chim. Acta, 1969, vol. 52, no. 1, p. 224.
9. Shmidt, F.K., Mironova, L.V., Saraev, V.V., and
Tkatch, V.S., React. Kinet. Catal. Lett., 1976, vol. 4,
no. 1, p. 73.
27. Tkach, V.S., Shmidt, F.K., Saraev, B.V., and Kalaꢀ
bina, A.V., Kinet. Katal., 1974, vol. 15, no. 3, p. 617.
28. Saraev, V.V., Shmidt, F.K., Larin, G.M., Tkach, V.S.,
and Lipovich, V.G., Koord. Khim., 1975, vol. 1, no. 10,
p. 1352.
10. Shmidt, F.K., Mironova, L.V., Saraev, V.V., Gruznykh, V.A.,
Dmitrieva, T.V., and Ratovskii, G.V., Kinet. Katal.
1979, vol. 20, no. 3, p. 622.
,
11. Dotterl, M. and Alt, H.G., ChemCatChem, 2011, vol. 3, 29. Saraev, V.V. and Shmidt, F.K., ESR metallokompleꢀ
no. 11, p. 1799.
12. Dotterl, M. and Alt, H.G., ChemCatChem, 2012, vol. 4,
ksnykh katalizatorov (ESR spectroscopy Applied to
Metal Complex Catalysts), Irkutsk: Irkutsk. Gos.
Univ., 1985.
no. 3, p. 370.
30. Titova, Yu.Yu., Belykh, L.B., and Schmidt, F.K., Low
Temp. Phys., 2015, vol. 41, no. 1, p. 25.
13. Gordon, A.J. and Ford, R.A., A Handbook of Practical
Data, Techniques, and References, New York: Wiley,
1972.
31. Dong, Q., Yang, X.ꢀJ., Gong, S., Luo, Q., Li, Q.ꢀS.,
Su, J.ꢀH., Zhao, Y., and Wu, B., Chem. Eur. J., 2013,
vol. 19, no. 45, p. 15240.
14. Mitchell, J. and Smith, D.M., Aquametry, New York:
Wiley, 1972.
15. Wilke, J. and Herrmann, S., Angew. Chem., 1962,
32. Heimbach, P., Angew. Chem., 1964, vol. 76, no. 13,
vol. 74, no. 17, p. 693.
p. 586.
16. Dzhemilev, U.M., Popod’ko, N.R., and Kozlova, E.V.,
Metallokompleksnyi kataliz v organicheskom sinteze.
Alitsiklicheskie soedineniya (Catalysis by Metal Comꢀ
plexes in Organic Synthesis: Alicyclic Compounds),
Moscow: Khimiya, 1999.
33. Shmidt, F.K., Doctoral (Chem.) Dissertation, Moscow:
Inst. of Chemical Physics, 1978.
34. Tkach, V.A., Gruznykh, V.A., Murasheva, N.A.,
Zinchenko, S.V., and Shmidt, F.K., React. Kinet. Catal.
Lett., 1991, vol. 43, no. 2, p. 431.
17. Heimbach, P., Angew. Chem., Int. Ed. Engl., 1964,
35. Tkach, V.S., Gruznykh, V.A., Gomboogiin, M.,
Belykh, L.B., Saraev, V.V., and Shmidt, F.K., Koord.
Khim., 1994, vol. 20, no. 8, p. 618.
vol. 3, no. 9, p. 648.
18. D’Aniello, M.J. and Barefield, E.K., J. Am. Chem. Soc.
1978, vol. 100, no. 5, p. 1474.
,
19. Dieck, H.T., Svoboda, M., Greiser, T., Z. Naturforsch.,
B: Chem. Sci., 1981, vol. 36, p. 823.
Translated by E. Yablonskaya
KINETICS AND CATALYSIS Vol. 57
No. 1
2016