Kinetics of α-olefin metathesis over the heterogeneous catalytic system (MoOCL4/SiO2)-SnMe4

Article abstract of DOI:10.1134/S0023158412030056

The kinetics of 1-hexene and 1-octene metathesis over the (MoOCl4/SiO ₂)-SnMe₄ catalytic sys- tem at 27 and 50°C has been investigated. The rate constants of the forward and reverse reactions and the cat- alyst deactivation constants have been measured. The number of active sites has been determined to be 10- 13 mol % of the total number of molybdenum atoms. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0023158412030056

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2012, Vol. 53, No. 3, pp. 353–356. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.I. Bykov, B.A. Belyaev, T.A. Butenko, E.Sh. Finkelshtein, 2012, published in Kinetika i Kataliz, 2012, Vol. 53, No. 3, pp. 368–371.
Kinetics of
α
ꢀOlefin Metathesis over the Heterogeneous Catalytic
System (MoOCl4/SiO2)–SnMe4
V. I. Bykov, B. A. Belyaev, T. A. Butenko, and E. Sh. Finkelshtein
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
eꢀmail: bykov@ips.ac.ru
Received October 13, 2011
Abstract—The kinetics of 1ꢀhexene and 1ꢀoctene metathesis over the (MoOCl4/SiO2)–SnMe4 catalytic sysꢀ
tem at 27 and 50 C has been investigated. The rate constants of the forward and reverse reactions and the catꢀ
°
alyst deactivation constants have been measured. The number of active sites has been determined to be 10–
13 mol % of the total number of molybdenum atoms.
DOI: 10.1134/S0023158412030056
Olefin metathesis is finding increasingly wide stirrer, a dropping funnel, a backflow condenser, and a
application in organic synthesis. However, individual gas burette for measuring the volume of ethylene
Schrock and Grubbs metallacarbene complexes used released during the reaction. A weighed sample of the
as metathesis catalysts [1] are very expensive and have catalyst prepared as described in our earlier publicaꢀ
drawbacks inherent in homogeneous catalysts: they tion [10] was placed in the reactor, and certain
are difficult to separate from the catalysate, undergo amounts of
α
ꢀolefin and cocatalyst (Me4Sn) were
bimolecular deactivation, and so on.
charged into the dropping funnel. All operations were
performed in flowing predried argon (specialꢀpurity
grade). Kinetic data were acquired by a volumetric
method and were verified by chromatographic deterꢀ
mination of the concentration of the symmetric olefin
in the catalysate.
Researchers of the Topchiev Institute of Petroꢀ
chemical Synthesis, Russian Academy of Sciences,
suggested a new, flexible, fewꢀstep strategy for the synꢀ
thesis of a wide variety of pheromones and other natuꢀ
ral compounds. This strategy is based on the cometꢀ
athesis of a petrochemical feedstock (
cycloolefins, cyclooctadiene, ethylene) [2–6] over
efficient heterogeneous catalytic systems developed by
α
ꢀolefins,
On the completion of the reaction, gas evolution
practically ceased. The catalysate was removed, and a
new, equal portion of the ꢀolefin was added to the
α
us [7–9]. As compared to individual metallacarbene catalyst partially deactivated during the reaction. This
complexes, classical catalytic systems usually have a procedure was repeated 5–8 times. Specialꢀpurpose
small number of active sites and are more fastidious experiments demonstrated that the kinetics is indeꢀ
about the nature of their functional groups. It is, thereꢀ pendent of whether the cocatalyst is added to each
fore, a challenging problem to find efficient and inexꢀ new portion of the
α
ꢀolefin or it is introduced only
pensive heterogeneous catalysts with a large number of together with the first portion of the olefin. For this
active sites.
We have demonstrated in a recent work [10] that
reason, in subsequent experiments tetramethyltin was
added only with the first portion of the reactant.
The purity of the initial and resulting compounds
was determined and the reaction was monitored by
GLC on an LKhMꢀ8MD chromatograph (flameꢀionꢀ
use of МоOСl4 in place of MoCl5 affords more active
metathesis catalysts and that the activity and stability
of the latter increases with an increasing silica gel calꢀ
ization detector, 50 m
× 0.2 mm i.d. quartz capillary
cination temperature (Tcalcin) and with a decreasing
column, SCTFP or SEꢀ30 stationary phase, Н2 as the
carrier gas). Analyses were performed in the linear
temperatureꢀprogrammed mode by heating the colꢀ
catalyst immobilization temperature (
we report kinetic data for 1ꢀhexene and 1ꢀoctene metꢀ
athesis in the presence of the most active and most staꢀ
T
immob). Here,
umn from 35
°
С
to the temperature 100 С below the
°
ble (MoОCl4/SiO2)–SnMe4 catalyst (Tcalcin
Timmob 25 ).
=
460°С,
boiling point of the symmetric olefin at a rate of
12 deg/min.
1H and 13C NMR spectra were recorded in СDСl3
on a Bruker MSLꢀ300 spectrometer, with chemical
=
°
С
EXPERIMENTAL
α
ꢀOlefin metathesis was carried out in a temperaꢀ shifts measured relative to Ме4Si. IR spectra were
tureꢀcontrolled glass reactor fitted with a magnetic obtained from thin films on a Specord IRꢀ75 spectroꢀ
353

354
BYKOV et al.
photometer. Mass spectra were recorded on a Finigan
MAT 95 XL 70 system (accelerating voltage of 70 eV).
RESULTS AND DISCUSSION
We have recently demonstrated that, depending on
the immobilization conditions and silica gel calcinaꢀ
tion temperature, MoOCl4 can react with surface OH
groups to release one or two equivalents of HCl (reacꢀ
tions (I) and (II), respectively). The latter reaction
yields the catalytically inactive precursor of the metꢀ
athesis catalyst, while МоСl5, unlike MoOCl4, forms
the active precursor [8].
All reactions and pretreatment of the initial comꢀ
pounds (reagentꢀgrade
α
ꢀolefins from the
Novocherkassk Plant of Synthetic Products) were
performed in a specialꢀpurity argon atmosphere, using
LiAlH4 or Na as the drier. According to GLC data, the
purity of the initial olefins was over 99.9%.
O
O
H
H
O
O
MoOCl3
H
(I)
SiO2
+ MoOCl4
SiO2
SiO2
+ HCl,
O
H
H
O
(II)
MoOCl2 + 2HCl,
Cl
SiO2
+ MoOCl4
O
O
Cl
+2SnMe4
SiO2
SiO2
SiO2
O
MoCl3
O
(III)
O
Mo(CH3)2
O
O
Mo = CH2 + CH4.
O
–2SnMe3Cl
−kdntot
The metathesis of the
stoichiometric equation (IV), according to which two
ꢀolefin molecules yield an ethylene molecule and a
symmetric olefin molecule:
2(RꢀCH=CH2) = RꢀCH=CHꢀR + CH2=CH2, (IV)
α
ꢀolefins is described by the
(1)
r = (k1C − k Cs)e
,
α
−1
where
r
is the metathesis rate in (mol symmetyric oleꢀ
α
fin) L–1 s–1 (mol Mo)–1 units, Сs is the concentration
of the symmetric olefin (mol/L),
С
is the ꢀolefin
α
α
concentration (mol/L), k1 and k–1 are the rate constants
of the forward and reverse reactions (s–1 (mol Mo)–1), kd
is the catalyst deactivation constant (dimensionless
where R = C4H9 or C6H13
The figure illustrates the kinetics of 1ꢀhexene metꢀ
athesis at 27 . The 1ꢀhexene conversion in all runs
was below 100%. A plausible explanation of this fact is
that the symmetric olefin– ꢀolefin equilibrium is
.
°
С
quantity), and
is the total number of moles of the
ñtot
substances resulting from the metathesis of the symꢀ
metric olefin per mole of molybdenum atoms (in (mol
symmetric olefin)/(mol Mo) units).
The processing of kinetic data for 1ꢀoctene and
1ꢀhexene metathesis using the procedure described in
our earlier publications [8, 9] enabled us to determine
α
established after a certain concentration of the symꢀ
metric olefin is reached and this equilibrium involves
secondary and primary metallacarbene active sites:
[Mo] = CHR
+
[Mo]
| |
CHR
| |
the numerical values of constants k1, k–1, and kd
+
.
(V)
(Tables 1, 2). It is clear from these data that the cataꢀ
lytic system based on molybdenum tetrachloride oxide
is more active and more stable than the system based
on molybdenum pentachloride.
H2C = CHR
CH2
CHR
The kinetic data presented below were obtained for
the most active and longest storable sample of the
МоОСl4/SiO2 catalyst [10].
The number of active sites was determined in the
It was established earlier [8, 9] that the rate of reacꢀ same way as in our earlier work [8] under the assumpꢀ
tion (IV) fits satisfactorily to the following differential tion that the interaction of a primary metallacarbene
rate equation:
site with excess 7ꢀtetradecene yields 1ꢀoctene:
LnMo = CH2
+
LnMo
| |
CH2
| |
(VI)
+
.
CH3(CH2)5CH = CH(CH2)5CH3 CH3(CH2)5CH
CH(CH2)5CH3
The latter can readily be quantified using
as the internal standard.
nꢀoctane
According to GLC data, the proportion of these
sites relative to the total number of molybdenum
KINETICS AND CATALYSIS Vol. 53
No. 3
2012

KINETICS OF
α
ꢀOLEFIN METATHESIS OVER THE HETEROGENEOUS CATALYTIC
355
1ꢀHexene
concentration, mol/L
5ꢀDecene
concentration, mol/L
1
2.5
60
50
40
30
20
10
2
3
4
5
2.0
1.5
1.0
0.5
0
0
100
200
300
400
500
Time, s
1ꢀHexene metathesis kinetics observed upon successive addition of equal portions of 1ꢀhexene to the catalytic systems (curves
1–5).
The points represent experimental data, and the curves represent the data calculated using Eq. (1).
molar ratio of 1 : 4 : 400.
T= 27°C, МоОСl : SnMe : 1ꢀhexene
4
4
atoms in MoOCl4 is (10.4 0.3)% at 27
°
С
and (13.1
listed in Table 1, expressed in terms of moles of Mo
0.3)% at 50 . In the case of MoCl5, this proportion is divided by the total number of moles of symmetric
°
С
5–6%. The fact that the MoOCl4ꢀbased catalyst has olefin, allow the true deactivation constants to be
more active sites than the MoCl5ꢀbased catalyst can determined as the number of moles of active sites per
likely be explained as follows: in the case of МoOCl4
ꢀelimination yielding a molybdenum–carbene site and active sites is known. The inverse of kd is the total numꢀ
methane proceeds more intensively than reductive elimꢀ ber of product (symmetric olefin) molecules forming
,
mole of symmetric olefin, provided that the number of
α
ination yielding ethane and inactive tetravalent Mo,
on one active site before its decay. The true deactivaꢀ
tion constants and their inverse values are listed in
Table 3.
The slight increase in the deactivation constant
observed on passing from 1ꢀhexene to 1ꢀoctene is
likely due to the fact that the probability of the asynꢀ
chronous decomposition of metallacyclobutane
CH3
O
SiO2
Mo=O
O
CH3
(VII)
O
increases with an increasing
α
ꢀolefin chain length.
SiO2
MoO + CH3–CH3.
The longer the carbon chain, the larger the number of
its vibrational degrees of freedom and, accordingly, the
stronger its destabilizing effect on the cyclic transition
state. The same effect is exerted by an increasing temꢀ
perature. Similar regularities were observed earlier for
MoCl5ꢀbased catalytic systems [8].
O
The formation of methane and ethane was proved
by the GCꢀMS method.
The deactivation constant, which characterizes the
operating stability of the catalyst, is a measure of active
Knowing the rate constants of the reaction at difꢀ
site decay probability. The deactivation constants ferent temperatures, we estimated the activation enerꢀ
Table 1. 1ꢀHexene and 1ꢀoctene metathesis rate constants per mole of molybdenum at 27
°C and catalyst deactivation conꢀ
stants for these reactions
1ꢀHexene metathesis
MoOCl4/SiO2 MoCl5/SiO2
1ꢀOctene metathesis
MoOCl4/SiO2 MoCl5/SiO2
10
Constant
32
30
4
4
14
13
2
2
26
24
3
3
1
k
1, s–1 (mol Mo)–1
–1, s–1 (mol Mo)–1
kd ×
103
k
9.6 1.2
2.5 0.3
1.3 0.2
2.0 0.3
1.6 0.2
KINETICS AND CATALYSIS Vol. 53
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2012

356
BYKOV et al.
Table 2. 1ꢀHexene and 1ꢀoctene metathesis rate constants per mole of molybdenum at 50
°C and catalyst deactivation conꢀ
stants for these reactions
1ꢀHexene metathesis
MoOCl4/SiO2 MoCl5/SiO2
1ꢀOctene metathesis
MoOCl4/SiO2 MoCl5/SiO2
Constant
k
k
1, s–1 (mol Mo)–1
–1, s–1 (mol Mo)–1
170 18
100 11
2.1 0.3
50
33
6
4
160 17
90 10
39
26
4
3
kd
×
103
3.2 0.4
2.6 0.4
4.1 0.5
Table 3. True deactivation constants for the NoOCl4/SiO2 catalytic system at 27°C and their inverse values
Parameter
kd
104
1/kd
1ꢀHexene metathesis
1ꢀOctene metathesis
×
1.4 0.2
7400 700
1.7 0.2
5900 600
Table 4. Activation energies of 1ꢀhexene and 1ꢀoctene metathesis
Activation energy, kJ/mol
Direction of the reaction
1ꢀhexene metathesis
1ꢀoctene metathesis
Forward
Reverse
44.0 5.3
32.3 4.0
47.1 5.5
34.5 4.2
5. Bykov, V.I. and Finkelshtein, E.Sh., J. Mol. Catal. A:
Chem., 1998, vol. 133, p. 17.
gies for the forward and reverse metathesis reactions
(Table 4).
6. Bykov, V.I., Butenko, T.A., Petrova, E.B., and
Finkelshtein, E.Sh., Tetrahedron, 1999, vol. 55,
p. 8249.
Thus, we have investigated the kinetics of olefin
metathesis over the most active and most stable
MoOCl4ꢀbased catalyst.
7. Bykov, V.I., Butenko, T.A., and Finkel’shtein, E.Sh.,
USSR Inventor’s Certificate no. 1666177, Byull. Izoꢀ
bret., 1991, no. 28.
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KINETICS AND CATALYSIS Vol. 53
No. 3
2012