Self-metathesis of methyl oleate on silica-supported Hoveyda-Grubbs catalysts

Article abstract of DOI:10.1016/j.catcom.2013.08.007

The self-metathesis of methyl oleate (MO) to yield 9-octadecene and 9-octadecene-1,18-dioate (9-OD) was studied in liquid-phase on silica-supported Hoveyda-Grubbs complex catalysts (HG/SiO₂) containing 0.43-6.0 wt.% HG. The reaction was carried out in a batch reactor at 303-343 K and 101.3 kPa, using cyclohexane as solvent. HG/SiO₂ catalysts were active and highly selective for the MO metathesis reaction; equilibrium values of MO conversion and 9-OD yield were reached in 80 min. No catalyst leaching took place in cyclohexane. Catalysts containing HG > 0.87 wt.% showed no significant deactivation after two consecutive catalytic tests.

Full text of DOI:10.1016/j.catcom.2013.08.007

Catalysis Communications 42 (2013) 84–88
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Self-metathesis of methyl oleate on silica-supported
Hoveyda–Grubbs catalysts
⁎
Juan Zelin, Andrés F. Trasarti, Carlos R. Apesteguía
Catalysis Science and Engineering Research Group (GICIC), INCAPE, UNL-CONICET, Santiago del Estero 2654, 3000 Santa Fe, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2013
Received in revised form 10 August 2013
Accepted 13 August 2013
Available online 22 August 2013
The self-metathesis of methyl oleate (MO) to yield 9-octadecene and 9-octadecene-1,18-dioate (9-OD) was stud-
ied in liquid-phase on silica-supported Hoveyda–Grubbs complex catalysts (HG/SiO2) containing 0.43–6.0 wt.%
HG. The reaction was carried out in a batch reactor at 303–343 K and 101.3 kPa, using cyclohexane as solvent.
HG/SiO2 catalysts were active and highly selective for the MO metathesis reaction; equilibrium values of MO con-
version and 9-OD yield were reached in 80 min. No catalyst leaching took place in cyclohexane. Catalysts contain-
ing HG N0.87 wt.% showed no significant deactivation after two consecutive catalytic tests.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Methyl oleate
9-Octadecene-1,18-dioate
Metathesis reactions
Hoveyda–Grubbs catalysis
Oleochemistry
1. Introduction
suitable solid catalysts for the metathesis of functionalized olefins
should tolerate the presence of polar functional groups.
Fatty acid methyl esters (FAME) are usually obtained from the
transesterification of natural oils and fats with a lower alcohol. Most of
oleochemical reactions of FAME are carried out in the carboxy functions,
but the synthesis of products formed by reactions of the C C bonds such
as epoxidation, metathesis, ozonolisis and hydrogenation is becoming
increasingly important at industrial level [1,2]. Olefin metathesis is a
very powerful tool for the efficient catalytic formation of carbon–carbon
double bonds allowing the synthesis of various useful intermediates and
compounds for fine chemistry and for the synthesis of polymers. FAME
metathesis has been studied in homogeneous catalysis using mainly
Grubbs' Ru complexes [3] as recyclable catalysts. In particular, second
generation ruthenium Hoveyda–Grubbs (H-G) catalysts (Fig. 1) present
high activity and selectivity, and also exhibit remarkable stability to the
presence of moisture and oxygen [4,5]. Nevertheless, only a limited
number of industrial processes use homogeneous olefin metathesis
because of the high cost of Ru complexes, the difficulties associated
with removing ruthenium from the reaction media and the expensive
separation/recovery steps required to obtain high-purity products.
This situation turns clearly attractive the development of active and
stable immobilized supported complexes that would allow straightfor-
ward catalyst separation. However, very few papers deal with the use
of supported HG catalysts for the metathesis of functionalized sub-
strates. Other than the requirements of high activity and selectivity,
Several methods for immobilization of HG-type complexes have
been studied [6–8], but frequently the resulting catalysts suffer from
leaching or losses of activity as a result of immobilization. Recently,
it has been reported that commercially available Ru–alkylidene
complexes immobilized on SiO2, MCM-41 and SBA supports can be
employed without leaching in some solvents or significant activity
loss for olefin metathesis reactions (ROMP, RCM, CM) [9–11]. Here, we
study the self-metathesis of methyl oleate (MO) on Hoveyda–Grubbs
complexes supported on commercial silica to yield 9-octadecene-1,18-
dioate (9-OD) and 9-octadecene (Fig. 2). The synthesis of diesters
such as 9-OD from the self- and cross-metathesis of FAME was one of
the first reactions studied in oleochemistry [12] because unsaturated
diesters are valuable intermediates for the production of polymers
and fine chemicals [13,14]. The reaction of Fig. 2 has been studied
on methyltrioxorhenium (CH3ReO3) and Re2O7/SiO2–Al2O3 promoted
with SnBu4 [15,16] but not on HG complex supported on solid supports.
Our results in the present study show that silica-supported HG com-
plexes are stable, highly active and selective catalysts for the metathesis
of methyl oleate.
2. Experimental
Five HG/SiO2 samples containing 0.43, 0.87, 1.21, 1.67 and 6.0 wt.%
HG (Sigma-Aldrich, 97%) were prepared by impregnating at 298 K a
commercial silica (Sigma-Aldrich G62, 230 m2/g, 200 mesh) previously
calcined 2 h at 773 K with a solution of HG in cyclohexane.
The crystalline structure of the samples was determined by X-ray dif-
fraction (XRD) using a Shimadzu XD-D1 diffractometer and Ni-filtered
⁎
Corresponding author at: INCAPE, Santiago del Estero 2654, 3000 Santa Fe, Argentina.
Tel.: +54 342 4555279; fax: +54 342 4531068.
E-mail address: capesteg@fiq.unl.edu.ar (C.R. Apesteguía).
URL: http://www.fiq.unl.edu.ar/gicic/ (C.R. Apesteguía).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.08.007

J. Zelin et al. / Catalysis Communications 42 (2013) 84–88
85
CH3
H3C
MO at reaction time t. Yields (ηj, mol of product j/mol of MO fed) were
calculated as ηj = CjνMO/CM0 Oνj, where vMO and vj are the stoichiometric
coefficients of MO and product j, respectively. Selectivities (Sj, mol of
N
N
product j/mol of MO reacted) were calculated as Sj = ηj/XBN
.
Cl
H3C
CH3
Ru
O
CH3
3. Results and discussion
H3C
Cl
3.1. Catalyst characterization
The XRD diffractograms of HG complex [17], silica support and
HG(0.87%)/SiO2 sample are shown in Fig. 3. The diffractogram of
HG(0.87%)/SiO2 presented only the amorphous halo of SiO2 support.
No diffraction peaks attributable to the HG crystalline structure were
detected, probably reflecting both the low HG loading and a high disper-
sion of the HG complex on the support as it has been observed by other
authors [9].
The thermal stability of HG complex was studied by DRIFT spectros-
copy and the results are presented in Fig. 4. The IR spectrum of HG com-
plex dried at 303 K was similar to those reported by other authors [18].
Several absorption bands appeared in the 1200–1700 cm−1 region. The
bands at 1651 cm−1, 1454 cm−1, and 1298 cm−1 correspond to v(C C)
styrene, v(C C) aromatic and δ(CH2), respectively [18]. Typically, the in-
tensity of the styrene vibration v(C C) at 1651 cm−1 is relatively weak in
the HG spectrum due to coordination to Ru. In the 2800–3200 cm−1
region the absorption bands at 2945 cm−1 and 2976 cm−1 are attribut-
able to v(CH3, CH2) asymmetric and v(CH3, CH2) symmetric stretches.
Essentially the same HG DRIFT spectrum was obtained after heating
the HG complex at 373 K but further treatment at 423 K caused the dis-
appearance of several absorption bands, probably reflecting the partial
decomposition of the HG complex. The HG(6.0%)/SiO2 sample dried at
303 K presented the main IR bands characteristics of pure HG complex,
thereby indicating that the HG structure was preserved after its deposi-
tion on silica.
Fig. 1. Second generation ruthenium Hoveyda–Grubbs catalyst.
Cu Kα radiation. The Ru content in HG/SiO2 samples was determined by
measuring by UV–vis spectroscopy (Perkin-Elmer Lambda 20 spectro-
photometer) the colorimetric difference of the HG impregnating solu-
tion, before and after impregnation.
The thermal stability of HG complex was studied by diffuse reflec-
tance infrared Fourier transform spectroscopy (DRIFTS) using
Shimadzu IRPrestige-21 spectrophotometer, equipped with an in-situ
high-temperature/high pressure SpectraTech cell and liquid
a
a
nitrogen-cooled MCT detector. The sample holder, a ceramic crucible
containing a heating resistor and a thermocouple, was placed inside a
dome with CaF2 windows. The spectral resolution was 4 cm−1 and
140 scans were added. The DRIFT spectra were collected in Ar (60 ml/
min). The HG(6%)/SiO2 sample was also characterized by DRIFTS at
303 K. The spectrum of silica support was previously collected. The IR
spectrum given herein for HG(6%)/SiO2 is the difference spectrum
where the SiO2 spectrum served as the reference.
The self-metathesis of methyl oleate (Sigma-Aldrich, 99%) was
carried out in a glass batch reactor under Ar atmosphere, at 101.3 kPa
and temperatures between 303 and 343 K. Cyclohexane (Sigma-
Aldrich, anhydrous 99.5%) previously dehydrated in a reflux distillation
column was used as solvent. Variable amounts of MO and the catalyst
together with cyclohexane (10 ml) and n-dodecane (internal standard)
were added to the reactor and agitated with a magnetic stirrer; then the
reaction mixture was heated to the reaction temperature in a thermo-
static bath. Product concentrations were followed during the reaction
by ex-situ gas chromatography using a Agilent 6850 GC chromatograph
equipped with flame ionization detector, temperature programmer and
a 50 m HP-1 capillary column (50 m × 0.32 mm ID, 1.05 μm film).
Product identification was carried out using gas chromatography
coupled with mass spectrometry (Varian Saturn 2000) both equipped
with a VF5-HT capillary column. Data were collected every 10–20 min
for 160–250 min. The only products detected were 9-octadecene and
9-octadecene-1,18-dioate (9-OD).
3.2. Self-metathesis of methyl oleate on HG/SiO2 samples
Taking into account the results in Fig. 4 on the thermal stability of HG
complex, we performed all the catalytic tests for the self-metathesis of
methyl oleate at temperatures lower than 373 K. Fig. 5 shows the MO
MO conversion was calculated as XMO = (C0MO − CMO)/CM0 O, where
C0MO is the initial concentration of MO and CMO is the concentration of
(a)
(c)
(b)
10
20
30
40
50
2θ
Fig. 2. Self-metathesis of methyl oleate.
Fig. 3. XRD diffractograms of: (a) HG complex (from 17); (b) SiO2; (c) HG(0.87%)/SiO2.

86
J. Zelin et al. / Catalysis Communications 42 (2013) 84–88
0,6
0,4
0,2
HG-303 K
HG(6%)/SiO2-303 K
HG-373 K
HG-423 K
0,0
0
50
100
150
tWcat /n0MO (h gcat /mol)
3500
3000
1500
1000
Frequency (cm-1)
Fig. 6. Self-metathesis of methyl oleate on HG/SiO2: Effect of %HG. 1.67 %HG (■); 1.21 %HG
(○); 0.87 %HG (▲); 0.43 %HG (◊) [T = 303 K, solvent: cyclohexane, C0MO = 0.059 M;
Wcat = 30 mg].
Fig. 4. DRIFT spectra of HG complex treated at increasing temperatures and of HG(6%)/
SiO2.
conversion (XMO) and yields (ηi) as a function of time obtained at
323 K on HG(0.87%)/SiO2 and typically illustrates the catalyst behavior
during the reaction. The only products detected were 9-octadecene
and 9-octadecene-1,18-dioate (9-OD) that reached yields of about 50%
for XMO = 0.5 after 90 min of reaction. The fact that XMO remained con-
stant after reaching a value of 0.5 is in agreement with previous work
reporting that the MO equilibrium conversion for the self-metathesis
of MO at 323 K is 50% [16]. In order to verify that our results in Fig. 5
reflect the approach to equilibrium we introduced to the reactor an
additional amount of 30 mg of HG(0.87%)/SiO2 after 130 min of reac-
tion and we effectively observed that XMO was not modified by the
addition of catalyst (Fig. 5).
In Fig. 6 we have represented XMO as a function of parameter tW/
n0MO for all the catalysts used in this work, where t is the reaction
time, W is the catalyst weight, and n0MO are the initial moles of MO.
The local slope of each curve in Fig. 6 gives the MO conversion rate
at a specific value of MO conversion and reaction time. Thus, we
determined the initial MO conversion rates (r0MO, mol/h gcat) by
calculating the initial slopes of the curves in Fig. 6. Results
are given in Table 1 (entries 1 to 4) and as expected we observed
that r0MO increased with the HG loading on the catalyst. We also
determined the initial MO conversion turnover rates (TOF, mol
MO/mol HG min) obtaining a value of TOF ≅ 13.8 mol MO/mol HG
min for all the catalysts of Fig. 6. This result showed that the HG
complex deposited on silica in the 0.43%–1.67% range was in all the
cases entirely accessible and active for carrying out the catalytic re-
action. It is significant noting that the HG monolayer on our silica
support is about 11.6%. We determined this value by successively
adding small amounts of the HG complex to 100 mg of SiO2 placed
in 3 ml of cyclohexane into a beaker. We analyzed the supernatant
solution following every HG addition until detecting the presence
of the HG complex. On the other hand, theoretical calculations
using an effective diameter of 1.76 nm for the HG molecule on the
support predict a monolayer value of 11.9% HG.
At the end of catalytic runs in Fig. 6, XMO, η9-OD, and η9-octadecene
reached their equilibrium values on HG(1.67%)/SiO2 and HG(1.21%)/
SiO2 and were slightly lower on HG(0.87%)/SiO2 (the η9-octadecene values
are not included in Table 1 because they were practically the same than
those of η9-OD). In contrast, XMO on HG(0.43%)/SiO2 reached 15% after
50 min reaction and remained constant until the end of the catalytic
run. This result strongly suggests that HG/SiO2 catalysts are deactivated
during the MO self-metathesis when containing low HG loadings. The
HG loading on HG(0.43%)/SiO2 sample is only about 3.7% of the HG
monolayer value, which would favor a high dispersion of the active spe-
cies on the support surface. Probably, the isolation of HG molecules on
the silica support may facilitate the HG active site deactivation by inter-
mediate species or products formed during the progress of the reaction.
Table 1 also includes data allowing comparison between homoge-
neous and heterogeneous catalysis for promoting the self-metathesis
of MO (entries 5 and 6). Specifically, the initial activity of HG(0.87%)/
SiO2 and dissolved HG complex were determined at 523 K; similar HG
amounts were loaded to the reactor in both catalytic runs. The initial
MO conversion turnover rate on HG(0.87%)/SiO2 (29.7 mol MO/mol
HG min) was about three times lower as compared to that obtained
via homogeneous catalysis (80.5 mol MO/mol HG min).
1,0
Catalyst addition
0,6
0,8
0,6
0,4
0,4
0,2
0,2
0,0
0,0
250
0
50
100
150
200
Time (min)
Finally, it has be noted that the carbon balance for all the samples in
Table 1 was higher than 95% showing that HG/SiO2 catalysts are highly
selective for producing 9-octadecene and 9-OD via the self-metathesis
of MO.
Fig. 5. Catalytic results: MO conversion (XMO) and yields on HG(0.87)/SiO2. ▽ 9-
octadecene, ● 9-OD [T = 323 K, CM0 O = 0.059 molar; Wcat = 30 mg, solvent: cyclohex-
ane (10 ml)].

J. Zelin et al. / Catalysis Communications 42 (2013) 84–88
87
Table 1
Catalytic results for the self-metathesis of methyl oleate on HG/SiO2 catalysts.
Entry
Catalyst
Temperature
(K)
Initial reaction rates
MO conversión a
Yielda
9-OD (%)
Carbon balance a
r0MO (mmol/h gcat
)
TOF (mol MO/mol HG min)
XMO (%)
η
(%)
1
2
3
4
5
6
HG(0.43%)/SiO2
HG(0.87%)/SiO2
HG(1.21%)/SiO2
HG(1.67%)/SiO2
HG (dissolved) b
HG(0.87%)/SiO2
303
303
303
303
323
323
3.9
11.6
16.0
22.2
–
13.7
13.9
13.8
13.9
80.5
29.7
15
44
50
50
50
50
14
43
49
50
50
50
96
96
98
98
99
100
24.7
C0MO = 0.059 molar; Wcat = 30 mg, solvent: cyclohexane (10 ml).
a
At the end of catalytic runs.
WHG = 0.3 mg.
b
Taking into account the results in Table 1 (entries 5 and 6) showing
that the intrinsic activity of the HG complex for MO conversion was
higher when dissolved in the reaction media (homogeneous catalysis),
we performed additional tests in order to verify if our results in Table 1
really reflect the activity of the HG complex immobilized on silica; i.e. to
exclude the existence of catalyst leaching during the reaction. In this
regard, we carried out a standard catalytic test using HG(0.87%)/SiO2
sample, and after 32% MO conversion, 2 ml (20% vol.) of supernatant so-
lution was transferred into another reactor (Fig. 7). Then, the metathesis
reaction continued in both reactors under identical operating condi-
tions. Fig. 7 shows that while XMO continued to increase up to equilib-
rium in the standard reaction, it remained constant in the reactor
containing the removed supernatant solution. Similar qualitative results
were obtained using HG(1.21%)/SiO2 and HG(1.67%)/SiO2 samples.
These results clearly demonstrated that data in Table 1 effectively reflect
the activity of immobilized HG complex; in other words, there is not cat-
alyst leaching in cyclohexane.
Finally, we studied the in-situ deactivation of HG(0.87%)/SiO2 sam-
ple by performing two consecutive catalytic tests without stopping the
run. The procedure was as follows: after XMO and η9-OD reached their
equilibrium values (50%) in a standard run at 323 K, we introduced to
the reactor the amount of MO required for reaching again the initial
MO concentration, C0MO, and performed a second consecutive run.
Fig. 9 shows the evolution of MO concentration during the two consec-
utive runs. It is observed that in the second run CMO rapidly decreased
eq
from C0MO to the equilibrium concentration, C , thereby suggesting
MO
that the in situ deactivation of HG(0.87%)/SiO2 during the first catalytic
run was not significant.
4. Conclusions
Second generation Ru Hoveyda–Grubbs complexes supported on
silica efficiently promote the self-metathesis of methyl oleate towards
9-octadecene and 9-octadecene-1,18-dioate (9-OD). At 303 K, the
methyl oleate equilibrium conversion and the 9-OD and 9-octadene
equilibrium yields are rapidly reached on HG/SiO2 catalysts containing
%wt HG higher than 0.87%, being the C balance near 100%. The HG
leaching is negligible during the progress of the reaction in cyclohexane
reflecting the effective immobilization of the HG complex on the silica
surface. The initial MO conversion turnover rate (TOF, mol MO/mol
HG min) was almost the same on HG/SiO2 catalysts containing up to
1.67%HG, thereby suggesting that the HG complex was entirely
The effect of temperature on catalyst activity was studied on sample
HG(0.87%)/SiO2. Fig. 8 shows the evolution of XMO as a function of time
obtained at 303, 313 and 323 K. From the slopes of the curves in Fig. 8
we determined the initial MO conversion rates for the three tempera-
tures and then we plotted the ln r0MO values as a function of 1/T for cal-
culating the apparent activation energy (Ea) of MO metathesis via an
Arrhenius-type function. From the slope of the resulting linear plot,
we obtained Ea = 10
1 kcal mol−1
.
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0,6
0,4
323 K
313 K
303 K
0,2
0,0
0
40
80
120
160
200
0
50
100
150
Time (min)
tWcat /n0MO (h gcat /mol)
Fig. 7. Split-test for investigating catalyst leaching. Standard catalytic run using
HG(0.87%)/SiO2 (■); removed supernatant (○) [solvent: cyclohexane (10 ml), Wcat
=
Fig. 8. Effect of temperature on catalyst activity [catalyst: HG(0.87%)/SiO2, solvent:
cyclohexane, C0MO = 0.059 M; Wcat = 30 mg].
30 mg, T = 323 K, ROM/H-G: 1460, C0MO = 0.059 M].

88
J. Zelin et al. / Catalysis Communications 42 (2013) 84–88
0.06
0.05
0.04
0.03
0.02
Acknowledgements
Authors thank the Universidad Nacional del Litoral (UNL), Consejo
Second run
Nacional de Investigaciones Científicas y Técnicas (CONICET), and
Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT),
Argentina, for the financial support of this work.
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accessible and active for carrying out the catalytic reaction. Low-loading
HG/SiO2 samples (HG b0.87 wt.%) rapidly deactivate during the reac-
tion but samples containing higher HG loadings maintain their catalytic
activity after two consecutive catalytic tests.