Kinetics and Mechanism of Thermal Decomposition of Bis(Η3-Allyl)Nickel Complexes

Article abstract of DOI:10.1134/S0023158419020150

Abstract: The kinetics of thermal decomposition of bis(η³-allyl) nickel complexes in various media is studied. The specific features of the mechanism are determined, including the combination of the stages of trans-cis isomerization of Niall₂ and the bimolecular decomposition of the cis-isomer with diallyl formation. The effect of autocatalytic decomposition of complexes with metallic nickel is been detected. The qualitative dependences of the process rate on the nature of the solvent and the structure of the allyl ligand are determined. The activation parameters of individual steps, consistent with quantum chemical calculations, are found.

Full text of DOI:10.1134/S0023158419020150

ISSN 0023-1584, Kinetics and Catalysis, 2019, Vol. 60, No. 2, pp. 113–117. © Pleiades Publishing, Ltd., 2019.
Russian Text © V.R. Flid, V.V. Zamalyutin, R.S. Shamsiev, E.A. Katsman, 2019, published in Kinetika i Kataliz, 2019, Vol. 60, No. 2, pp. 141–146.
Dedicated to Academician of the Russian Academy
of Sciences Ilya Iosifovich Moiseev in connection with his jubilee
Kinetics and Mechanism of Thermal Decomposition
of Bis(η3-Allyl)Nickel Complexes
V. R. Flida, *, V. V. Zamalyutina, R. S. Shamsieva, and E. A. Katsmana
aMIREA–Russian Technological University (M.V. Lomonosov Institute of Fine Chemical Technologies),
Moscow, 119571 Russia
*e-mail: vitaly-flid@yandex.ru
Received January 13, 2019; revised January 13, 2019; accepted January 16, 2019
Abstract—The kinetics of thermal decomposition of bis(η3-allyl) nickel complexes in various media is stud-
ied. The specific features of the mechanism are determined, including the combination of the stages of trans-
cis isomerization of Niall2 and the bimolecular decomposition of the cis-isomer with diallyl formation. The
effect of autocatalytic decomposition of complexes with metallic nickel is been detected. The qualitative
dependences of the process rate on the nature of the solvent and the structure of the allyl ligand are deter-
mined. The activation parameters of individual steps, consistent with quantum chemical calculations, are
found.
Keywords: bis(η3-allyl)nickel complexes, kinetics, mechanism, autocatalytic effect, thermal decomposition,
allyl coupling
DOI: 10.1134/S0023158419020150
INTRODUCTION
nickel, which is an active center in many catalytic pro-
cesses. Initially, this decomposition was considered a
synchronous process occurring under the actions of
reagents capable of displacing allyl fragments from the
complex [6]. However, in 1970, Moiseev formulated
the idea of a complex multi-step mechanism involving
the stages of the η3–η1 isomerization of allyl ligands
coordinated to nickel [7].
Bis(η3-allyl)nickel complexes exist in the form
trans- and cis-isomers (Scheme 2). In crystals, their
ratio (possibly equilibrium) is 3 : 1 for Ni(C3H5)2 and
2.3 : 1 for Ni(2-CH3С3H4)2 [6, 8]. The relative activ-
ity of isomers can play an important role in the
implementation of regio- and stereoselective synthe-
sis, as well as at the stages of the formation of cata-
lytic centers.
The chemistry of η3-allyl complexes of transition
metals began to develop rapidly 60 years ago. This is
largely associated with an outstanding achievement of
I.I. Moiseev an co-workers, who synthesized and
characterized the first η3-allylic palladium complex,
η3-allylpalladium chloride [1]. Since then, this class of
compounds has filled an important place in organo-
metallic chemistry and catalysis. Nickel and palla-
dium complexes have found the greatest use among
them [2–5].
Bis(η3-allyl)nickel complexes are precursors of
many catalytic reactions [6]. They can exist only in
anaerobic conditions and are thermally unstable.
Their decomposition begins at the melting point and
leads to the formation of metallic nickel (Ni0) and
diallyl (Scheme 1):
Niall2 → all−all + Ni0
Ni
Ni
all = 1-CH3C3H4, C3H5, 2-CH3C3H4
Scheme 1. Decomposition of nickel bis(η3-allyl) com-
Scheme 2. Trans- and cis-isomers of bis(η3-allyl)nickel.
Nevertheless, the mechanisms of isomerization
plexes.
This reaction is important for organometallic and thermal decomposition of bis(η3-allyl)nickel are
chemistry, since it models the complete breaking of poorly studied. This information seems to be very use-
two allyl–metal bonds and the generation of atomic ful for the formation of catalytically active complexes.
113

114
FLID et al.
Nermag, France) with a CPS CP-Sil 5 CB capillary
column, electron impact mode, a scanning range of
m/z = 15–300, scanning rate of 1 scan for 300 ms, and
an ionization energy of 70 eV. In analyzing and inter-
preting mass spectra, we used data reported in [10, 11]
and standard databases.
A software package [12, 13] was used to process the
kinetic data, determine the rate constants to solve the
inverse kinetic problem, and perform identifiability
analysis.
trans-Ni(C3H5)2
0.10
0.05
C6H10
*
C6H10
cis-Ni(C3H5)2
RESULTS AND DISCUSSION
0
5
Time, h
During the reaction, the color of the solution
changed from light yellow to reddish, characteristic of
nickel olefin complexes. The solution loses its trans-
parency, and by the end of the reaction, a precipitate is
formed, which isolated and studied by us using ele-
mental analysis and electron microscopy. It was a
highly dispersed metallic nickel with a particle size of
0.1 to 10 μm.
Fig. 1. Kinetic dependences of the process of thermal
decomposition of Ni(С Н ) isomers in С Н at 40°С;
[Niall ] = 0.157 mol/L; * rotating ampoule.
3
5 2
6
6
2
The charge state of the central atom and the structure
of the η3-allyl ligand is likely to affect significantly its
reactivity.
The goal of this work was to study the kinetics and
mechanism of thermal decomposition of bis(η3-
allyl)nickel complexes, as well as the effect of their
structure and the nature of a solvent on this process.
The simplest scheme of the mechanism of thermal
decomposition of bis(η3-allyl)nickel complexes can be
described by the following equations:
(I)
(II)
trans-Niall2 ꢀ cis-Niall2,
trans-Niall2 → all–all + Ni0,
cis-Niall2 → all–all + Ni0.
EXPERIMENTAL
(III)
The thermal decomposition of bis(η3-allyl)nickel
However, it does not take into explain a number of
experimental observations: the process proceeds with
an induction period, which is confirmed by the
S-shaped form of the kinetic dependences of diallyl
accumulation and Ni(C3H5)2 isomer consumption
(Fig. 1).
One of the possible reasons for the observed phe-
nomenon is autocatalysis by the reaction products,
hexa-1,5-diene (HD) and metallic nickel. To deter-
mine the nature of this effect, a series of comparative
kinetic experiments have been carried out.
When hexa-1,5-diene is preliminarily introduced
into the reaction system (the HD/Ni(C3H5)2 molar
ratio ranging from 0.1 to 2.0), the nature of the process
does not change.
When Ni0 is added, the process is substantially
accelerated, and this indicates that autocatalysis is due
to metallic nickel.
complexes, Ni(C3H5)2 and Ni(2-CH3C3H4)2, was
studied in sealed NMR ampoules and in 0.3 cm3 vac-
uum batch reactors with a sampler. Experiments were
performed in vacuum or in an argon atmosphere,
thoroughly purified from oxygen impurities. The
experimental conditions were as follows: the concen-
tration of complex was 0.1–0.2 mol/L; the solvent was
С6D6, (C2D5)2O, СD3СN, THF-D8, DMFA-D7; the
temperature was 30–75°С.
The optimal method for analyzing all the compo-
nents of the reaction mixture in solution, including cis
and trans isomers of bis(η3-allyl)nickel, is H NMR
1
spectroscopy. The concentrations of bis(η3-
allyl)nickel isomers and the products of their recombi-
1
nation were determined from the intensities of Н
NMR signals [9]. Н and 13С NMR spectra were
1
recorded using an DPX 300 spectrometer (Bruker, Ger-
many), using a working frequency of 300.13 MHz for
nuclei 1H and 75.033 MHz for nuclei 13C.
Another series of experiments was carried out with
the rotation of the reaction ampoule in the resonator
of the NMR spectrometer. Under the action of cen-
trifugal force, metallic nickel formed during the
decomposition of Ni(C3H5)2 is deposited on the walls,
Independently, the reaction was monitored by
GLC using a Kristall PM-2000 chromatograph
(Khromatek, Russia) with a flame ionization detector,
an Agilent J&W HP-50+ capillary column (Agilent
Technologies, USA). The products of decomposition and its concentration in the reaction solution
were identified by gas chromatography/mass spec- decreases. At the same time, the induction period
trometry using an Automass-120 instrument (Delsi- increases significantly (Fig. 1, experiment *).
KINETICS AND CATALYSIS
Vol. 60
No. 2
2019

KINETICS AND MECHANISM
115
Table 1. Rate and equilibrium constants of individual steps of the thermal decomposition of bis(η3-allyl)nickel complexes
k1 × 105,
k2 × 105,
mol–1 L s–1 mol–1 L s–1 mol–1 L s–1
Ni(C3H5)2
k3 × 104,
k4 × 105,
ε25
K1 × 10
Solvent*
T, °С
s–1
Benzene
2.28
30
40
50
30
30
30
30
3.6 1.0
7.0 2.1
16 4.7
7.9 2.3
5.1 1.5
15 4.6
9.3 2.8
1.3 0.1
1.1 0.1
10.0 1.3
2.5 0.3
17.0 2.2
21 2.7
2.5 2.2
3.2 2.9
6.3 5.7
5.3 4.8
15.0 13.5
18 16
2.2 0.3
5.2 0.8
7.3 1.1
4.0 0.6
6.9 1.0
8.3 1.2
9.4 1.4
3.0 0.2
3.4 0.2
4.2 0.3
3.1 0.2
3.7 0.2
3.1 0.2
3.7 0.2
Diethyl ether
THF
Acetonitrile
DMFA
4.27
7.58
36.0
36.7
37 4.8
32 28
Ni(2-CH3С3Н4)2
Benzene
50
60
75
4.3 1.9
0.8 0.3
1.0 0.4
3.9 0.5
11 1.6
18 2.7
0.6 0.1
5.4 1.0
13 2.6
3.6 0.7
16 0.3
47 0.9
4.3 1.3
2.3 0.7
2.4 0.7
2.28
25
* In all experiments, a deuterated solvent was used. ε is the dielectric constant of the solvent at 25°С.
Based on the results obtained, the reaction mecha-
• the rate of initiation step has the second order in
nism was supplemented by the following steps of cata- the complex:
lytic decomposition of each of the Niall2 isomers:
W2 = k2(Ct2rans + CtransCcis + Cc2is );
• the rates of trans and cis isomer decomposition
are the second-order equations, the first order in each
reactant:
trans-Niall2 + Ni0 → all–all + 2Ni0,
cis-Niall2 + Ni0 → all–all + 2Ni0.
(IV)
(V)
W3 = k3CtransCN0 i = k3CtransCd,
W4 = k4CcisCN0 i = k4CcisCd,
These additional steps significantly improve the
description of the experimental data by the kinetic
model (the standard deviation is reduced to 4.8%).
However, this variant is also unacceptable because of
the systematic error observed at the initial stage of the
reaction. An adequate description is achieved for a
mechanism (Scheme 3), in which the initiation stage
is bimolecular, and the activity of the cis and trans iso-
mers in it is practically indistinguishable (deviation
4.5%). Metallic nickel catalyzes the decomposition of
both Niall2 isomers.
0
where Ctrans, C ,
Cd are the concentrations of
CNi,
trans and cis isocmis ers of Ni(С3Н5)2, metallic nickel and
diallyl, respectively.
The processing of kinetic data using the software
package [12] made it possible to calculate the values of
the rate constants and equilibria of all stages for differ-
ent temperatures (Table 1).
Step I trans-Niаll2 ꢀ cis-Niаll2 k1,K1.
Step II Niall2 + Niall2 → 2all–all + 2Ni0 k2
Step III trans-Niаll2 + Ni0 → all–all + 2Ni0 k3
The nature of a solvent has a significant effect on
the process. With an increase in its polarity, thermal
decomposition of bis(η3-allyl)nickel accelerates.
At a moderate temperature (30–50°С) in C6D6, the
values of the rate constants of steps I, II, and IV were
determined with a high accuracy (Table 1), which
points to the realization of a route related to trans → cis
isomerization and catalytic decomposition of cis-
Ni(C3H5)2 under this conditions. On the contrary, the
value of the rate constant k3 of the step of trans-
Ni(C3H5)2 decomposition is uncertain. It was deter-
mined with a high error (up to 90%) because of the low
contribution of this step to the overall rate of the pro-
cess. However, at a high temperature (60–75°С),
bimolecular decomposition (step II) begins to be
dominating over the catalytic one. This is evident from
Step IV cis-Niall2 + Ni0 → all–all + 2Ni0 k4,
ki is the rate constant step I
K1 is the equilibrium constant of step I
Scheme 3. Mechanism of thermal decomposition of
bis(η3-allyl)nickel.
According to Scheme 3, the kinetic description of
the process can be as follows:
• rate of trans–cis isomerization of the complex:
W1 = k1(Ctrans – Ccis K1);
KINETICS AND CATALYSIS Vol. 60 No. 2 2019

116
FLID et al.
decomposition is the most significant (Table 2). Anal-
75°С
ysis of the data obtained for these stages indicates the
complex nature of their occurrence.
60°С
One may assume that, in step I the η3 → η1 isom-
erization takes place with one of the allyl ligands (L is
the solvent) (Scheme 4):
0.10
0.05
50°С
L
L
cis-
Ni
Ni
Ni
trans-
-L
Scheme 4.
The reverse transition ηl → η3 leads to the forma-
tion of both trans- and cis-Ni(C3H5)2. The activation
energy of this step (~60 kJ/mol) is mostly related with
η3 → η1 isomerization of an allyl ligand. Its intramo-
lecular nature is confirmed by a low value of activation
entropy ΔS≠. It is likely that the polar solvent is favor-
able for η3 → η1 isomerization of an allyl ligand and
stabilizes the intermediate species formed.
0
5
Time, h
Fig. 2. Kinetic curves of accumulation of 2,5-dimethyl-
hexa-1,5-diene in the thermal decomposition of Ni(2-
CH C H ) . Solvent: С D .
3
3
4 2
6
6
The initiation step II is characterized by the sec-
ond-order rate equation with respect to Ni(С3Н5)2,
and isomers are not distinguishable in it. Step II is
likely to proceed through the formation of a binuclear
the disappearance of the induction period on the
kinetic curves (Fig. 2).
Based on the obtained values of the rate constants, intermediate 1, in which allyl ligands play the role of
we calculated the activation parameters for the stages, bridges between nickel atoms (Scheme 5). At this
whose contribution to the main route of thermal stage, the reaction is facilitated by the solvent.
L
Ni
2L
2C6H10 + 2Ni0
Ni
Ni
+
Ni
L
-2L
1
Scheme 5.
Certain analogies between steps I and II are con-
It is likely that the decomposition of the cis isomer
(step IV) also involves the consecutive η3 → η1 isom-
erization of allyl ligands and the coordination of the
double bond of one of them to a nickel atom, which
plays the role of a catalyst (Scheme 6).
firmed by the close values of the activation energies (Еа).
a
A somewhat lower value of
may be associated with
E2
the formation of dimeric complex 1. It has a fairly
ordered structure as evidenced by the small value of
the entropy of activation.
L
Ni
Ni
L
+ Ni0
Ni
L
cis-
Ni
Ni
L
-L
2
C6H10 + 2Ni0 + 2L
Ni
L
Ni
L
L
Ni
L
Ni
3
Scheme 6.
KINETICS AND CATALYSIS
Vol. 60
No. 2
2019

KINETICS AND MECHANISM
117
Table 2. Values of the activation parameters of the stages of
the thermal decomposition process of nickel bis-η3-allyl
complexes in С6D6
zation of the allyl ligand for С3Н5 and 2-CH3C3H4
allyls. These are in agreement with quantum chemical
calculations.
A mechanism of thermal decomposition was pro-
posed, which includes the trans–cis isomerization of
Niall2 and the catalytic decomposition of the cis iso-
mer. With increasing temperature, bimolecular
decomposition begins to prevail over catalytic.
Еа, kJ/mol ΔH≠, kJ/mol ΔS≠, J mol–1 K–1
Step
Ni(С3Н5)2
I
II
III
62 22
67 10
43 12
59 22
62 9.8
38 12
–136 51
–336 59
–390 46
Ni(2-СН3С3Н4)2
55
ACKNOWLEDGMENTS
II
70
9
9
–340 40
This work was supported by the Russian Founda-
tion for Basic Research (project 17-03-00463).
A further restructuring of complex 2 is related to
the participation of the second allyl ligand and migra-
tion of a double bond. The formation of the binuclear
center similar to 3 substantially decrease the activation
energy of this step. Taking into account the assump-
REFERENCES
1. Moiseev, I.I., Fedorovskaya, E.A., and Syrkin, Ya.K.,
Zh. Neorgh. Khim., 1959, vol. 4, p. 2641.
tion of the necessary and synchronous η3 → η1 isom-
2. Lautens, M. and Tam, W, In Advances in Metal-Organic
Chemistry, Liebeskind, L.S., Ed., JAI Press, 1996,
p. 125.
a
erization of two allyl ligands, we may expect that
E3
a
will two times higher than
However, its value is
E1 .
3. Tsuji, J., Palladium Reagents and Catalysis, New York:
three times lower than expected (≈40 kJ/mol).
Wiley, 1996.
The activation energy of the initiation step
increases when switching from the unsubstituted allyl
to 2-methyl-η3-allyl, which agrees with the results of
quantum chemical studies. The values of Mulliken
charges at the nickel atoms in Ni(C3H5)2 and Ni(2-
CH3C3H4)2, calculated by the DFT-PBE/TZ2P
method are +0.329 and +0.305, respectively. The
bond of 2-methyl-η3-allyl ligand with nickel has a less
ionic character. Therefore, its η3 → η1 isomerization is
more difficult compared to the unsubstituted η3-allyl.
The equilibrium constant of the trans-cis
Ni(C3H5)2 isomerization step is practically indepen-
dent of temperature in the studied range, which also
agrees with literature data [14]. The value of the Gibbs
energy calculated on the basis of the equilibrium con-
stant is approximately 3 kJ/mol.
4. Al-Wadhaf, H.A., Karpov, V.M., and Katsman, E.A.,
Catal. Commun., 2018, vol. 116, p. 67.
5. Flid, V.R., Gringolts, M.L., Shamsiev, R.S., and Fin-
kelshtein, E.Sh., Russ. Chem. Rev., 2018, vol. 87,
p. 1169.
6. Wilke, G., Bogdanović, B., Hardt, P., Heimbach, P.,
Keim, W., Kröner, M., Oberkirch, W., Tanaka, K.,
Steinrücke, E., Walter, D., and Zimmermann, H.,
Angew. Chem., 1966, vol. 5, p. 151.
7. Moiseev, I.I., π-Kompleksy v zhidkofaznom okislenii ole-
finov (π-Complexes in Liquid-Phase Oxidation of Ole-
phines), Moscow: Nauka, 1970.
8. Shamsiev, R.S. and Flid, V.R., Russ. Chem. Bull., 2013,
vol. 62, p. 2301.
9. Flid, V.R., Durakov, S.A., Morozova, T.A., Chesh-
kov, D.A., and Katsman, E.A., Izv. Akad. Nauk, Ser.
Khim., 2018, vol. 67, p. 1335.
CONCLUSIONS
10. Flid, V.R., Durakov, S.A., and Morozova, T.A., Russ.
Chem. Bull., 2016, vol. 65, p. 2639.
We studied the thermal decomposition of bis(η3-
allyl)nickel complexes in a solution at 30–75°С. The
reaction products are diallyl and metallic nickel. The
higher polarity of the solvent and the higher effective
positive charge on a nickel atom lead to the accelera-
tion of the process.
11. Durakov S.A., Shamsiev R.S., Flid V.R., and
Gekhman A.E., Russ. Chem. Bull., 2018, vol. 67,
p. 2234.
12. Gorskii, V.G., Katsman, E.A., Klebanova, F.D., and
Grigor’ev, A.A., Teor. Eksp. Khim., 1987, vol. 23, p. 181.
1Н NMR spectroscopy and GLC were used to
study the reaction kinetics. It was found that the
decomposition bis(η3-allyl)nickel complexes occurs
with autocatalysis. It was shown that the catalyst is
metallic nickel formed during the reaction. The values
of activation parameters of individual steps of thermal
decomposition of Niall2 were determined. The activa-
13. Silina, I.S., Katsman, E.A., Treger, Yu.A., Rozanov, V.N.,
Iskhakova, L.D., Ermakov, R.P., Koltashev, V.V., and
Bruk, L.G., Tonkie Khim. Tekhnol., 2017, vol. 12, no. 2,
p. 50.
14. Shamsiev, R.S., Drobyshev, A.V., and Flid, V.R., Russ.
Chem. Bull., 2013, vol. 62, p. 1549.
tion energies were estimated for the η3 → η1 isomeri-
Translated by Andrey Zeigarnik
KINETICS AND CATALYSIS Vol. 60 No. 2 2019