Unsaturated fatty acid esters metathesis catalyzed by silica supported WMe5

Article abstract of DOI:10.1016/j.molcata.2015.11.003

Metathesis of unsaturated fatty acid esters (FAEs) by silica supported multifunctional W-based catalyst is disclosed. This transformation represents a novel route towards unsaturated di-esters. Especially, the self-metathesis of ethyl undecylenate results almost exclusively on the homo-coupling product whereas with such catalyst, 1-decene gives ISOMET (olefinisomerization and metathesis) products. The olefin metathesis in the presence of esters is very selective without any secondary cross-metathesis products demonstrating that a high selective olefin metathesis could operate at 150 °C. Additionally, a cross-metathesis of unsaturated FAEs and α-olefins allowed the synthesis of the corresponding ester with longer hydrocarbon skeleton without isomerisation.

Full text of DOI:10.1016/j.molcata.2015.11.003

Journal of Molecular Catalysis A: Chemical 411 (2016) 344–348
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Unsaturated fatty acid esters metathesis catalyzed by silica supported
WMe5
∗
∗
Nassima Riache, Emmanuel Callens , Karima Talbi, Jean-Marie Basset
KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 June 2015
Received in revised form 29 October 2015
Accepted 9 November 2015
Available online 14 November 2015
Metathesis of unsaturated fatty acid esters (FAEs) by silica supported multifunctional W-based catalyst
is disclosed. This transformation represents a novel route towards unsaturated di-esters. Especially, the
self-metathesis of ethyl undecylenate results almost exclusively on the homo-coupling product whereas
with such catalyst, 1-decene gives ISOMET (olefinisomerization and metathesis) products. The olefin
metathesis in the presence of esters is very selective without any secondary cross-metathesis products
demonstrating that a high selective olefin metathesis could operate at 150 C. Additionally, a cross-
metathesis of unsaturated FAEs and ␣-olefins allowed the synthesis of the corresponding ester with
longer hydrocarbon skeleton without isomerisation.
◦
Keywords:
Unsaturated fatty esters
Silica supported WMe5 catalyst
Metathesis
©
2015 Elsevier B.V. All rights reserved.
Surface organometallic chemistry
1
. Introduction
[11] and linear alkanes are converted into higher and lower lin-
ear alkanes [12]. As during this alkane metathesis process olefins
are formed in minute amount [13], we also examined the reactiv-
ity of terminal olefins with W-based catalysts supported on silica
[12]. For instance, 1-decene is transformed into a distribution of
linear terminal and internal olefins (up to C30 olefins) through
successive reactions of isomerization and metathesis (ISOMET)
[12]. Thus, we envisaged employing solely this multifunctional full
supported methylated catalyst for the metathesis of unsaturated
FAEs. Herein, we report the unprecedented catalytic activity of
[( 8801;Si O)WMe5] (1) towards readily available monounsatu-
rated FAEs.
With the decrease of fossil organic feedstock, renewable
resources in particular unsaturated fatty acid esters (FAEs) have
been widely studied as starting materials in the chemical industry
[
1,2]. These chemicals are interesting building blocks possessing
two modifiable functional groups, the ester and the olefin. The
reactivity of the alkene moiety has been illustrated in particu-
lar via the metathesis of unsaturated FAEs towards the synthesis
of unsaturated diesters of fatty acids. In fact, metathesis reac-
tions of unsaturated FAEs are a convenient approach to long
chain diesters, useful intermediates towards macromolecules and
polyesters synthesis [3]. Pioneer in this field, Boelhouwer and
co-workers discovered that homogeneous WCl /Me Sn system
6
4
catalyzed the metathesis of methyl oleate [4–6]. This provides an
approach towards the preparation of mono- and diesters of fatty
acids and their corresponding fatty acid esters. Following this work,
numerous homogeneous and heterogeneous catalysts using tran-
sition metals, W, Mo, Re have been reported [7–9,1]. In particular,
Ru Grubbs catalysts with an alkylidene moiety were found to be the
most effective catalysts. Recently, we reported the synthesis of the
homoleptic WMe6 grafted on silica, [( Si O)WMe5] (1) [10]. This
precursor catalyzes the metathesis of alkanes into lower and higher
homologues: cyclooctane is transformed into macrocyclic alkanes
2. Results and discussion
2.1. Ethyl undecylenate metathesis catalyzed by silica supported
W-based catalyst [( Si O)WMe ] (1)
5
In the present work, we evaluate the catalytic activity of (1) in
ethyl undecylenate (C11) metathesis in a sealed glass tube. At the
end of the catalytic run, an aliquot of the reaction mixture was
analyzed by gas chromatography and GC–MS spectroscopies. At
room temperature, only traces of the diesters products from self-
metathesis were detected. However when conducting the catalytic
◦
run at 150 C for 3 h, we exclusively observed the expected diesters,
corresponding to non-degenerative metathesis process associated
with the concomitant release of ethylene (Scheme 1) (see also Fig.
S2). The regiochemistry of the diester alkene consists of a mixture
∗ Corresponding authors.
E-mail addresses: emmanuel.callens@kaust.edu.sa (E. Callens),
jeanmarie.basset@kaust.edu.sa (J.-M. Basset).
http://dx.doi.org/10.1016/j.molcata.2015.11.003
1
381-1169/© 2015 Elsevier B.V. All rights reserved.

N. Riache et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 344–348
345
Scheme 1. Self-metathesis (SM) of ethyl undecylenate catalyzed by silica supported W-based catalyst.
of E/Z internal olefins with the formation of trans ester thermody-
namically favored (molar ratio, 7:3).
olefin followed by ␤-elimination of the possible metal alkyls).
These elementary steps are important to account for the ISOMET
reaction. Moreover, a dual Ru/W catalysts has been recently in
which the Ru catalyst serves only as the isomerization catalyst
in the ISOMET reaction [16]. As silica supported tungsten species
(1) acts as a multifunctional catalyst, we initially thought that (1)
would be ideal to produce a distribution of unsaturated diesters
of fatty acids with variable chain length from a functionalized
olefin (monounsaturated FAEs in our case), together with a distri-
bution of resulting olefins and monoesters. Indeed, it is known that
unsaturated fatty acid methyl esters (FAMEs) in presence of both
isomerizing and metathesis catalysts represent an elegant access
to a mixture of unsaturated diesters of fatty acids. France et al. dis-
closed one of the first tandem isomerization/metathesis processes
of unsaturated FAMEs by employing a dual catalytic Ir/Ag system
[17]. Later on, Ohlmann et al. employed a Pd/Ru system for this
transformation [18]. Starting from an unsaturated FAME, with an
internal double bond, they observed the formation of a distribu-
tion of olefins, unsaturated diesters and unsaturated monoesters
(resulting from both primary and secondary self-metathesis and
isomerization/cross metathesis reactions) (Scheme 2).
The conversion of ethyl undecylenate versus time was carried
◦
out at 150 C. The plots of TONs and conversion versus time are given
in Fig. 1. A final conversion of 12% is reached with 26 TONs. A plateau
is observed after 3 h which would correspond to a thermodynamic
equilibrium. The reaction is very fast reaching 8% conversion and 17
TONs at t = 15 min. The observable equilibrium must result from the
degenerative metathesis process and the accumulation of ethylene
in this closed system. The reaction conversion could further be opti-
mized by varying the concentration of the precatalyst. The study on
the concentration of the substrate is illustrated in Fig. S3. Varying
the W/substrate ratio (from 2.3% to 9.3%) gave a higher conversion
of 19% with TONs of 33 (see Fig. S3).
Despite the need of heating, the level of temperature of the
reaction was found to have a minor impact on the efficiency of
◦
◦
the catalyst. Indeed, for a given period of 18 h at 80 C, 150 C or
◦
2
00 C, the maximum unsaturated FAE conversion based on diester
◦
products reached respectively 14%, 12% and 11%. At 200 C, traces
amount of isomerized ethyl undecylenate were detected by GC–MS.
Employing Ru based catalyst, Grubbs first generation complex,
under similar reaction conditions, afforded self-metathesis prod-
ucts and two newly formed isomers of ethyl undecylenate with 28%
conversion towards expected diesters after 24 h reaction time (see
Fig. S4). Yet, our turnovers are comparable with the ones obtained
with the supported catalytic system WCl /Me Sn [6]. This suggests
With silica supported [( Si O)WMe5] (1) such diesters distri-
bution could not be observed. Interestingly, we also found that the
reaction of saturated FAE (as the ethyl undecylate) with 1 did not
◦
produce alkane metathesis products at 150 C for 3 days period.
This result can be rationalized by considering the possible coordi-
nation of a W-methylidene hydride, propagative species in alkane
metathesis [12], into the functional ester group. And, this would
prevent two crucial steps in the alkane metathesis: the C H alkane
activation required for the olefin intermediate and the release of
catalytic amount of hydrogen. These observations are consistent
with the absence of isomerization using unsaturated FAEs as sub-
strates, pointing out a detrimental effect from the ester group by
preventing the isomerization step in the olefin metathesis process.
6
4
that with the latter system, the in situ alkylation of WCl6 should
initially occur to form the desired propagative W carbene species.
To account for the low activity for this silica supported W sys-
tem, we assume that the geometry of the W metallocyclobutanes
plays an important role. Indeed, extensive DFT studies on metal-
lacyclobutanes with 5-coordinated W metal center have shown
that a square pyramidal (SP) geometry is likely to be responsible
for the deactivation of the catalyst [14,15]. While in the case for
the Grubbs Ru catalyst, calculations have shown that the trigonal
bipyramidal metallacyclobutane, (required for the cycloreversion
metathesis step) is generally much more stable than SP metalla-
cyclobutanes. Following the same catalytic procedure described
for ethyl undecylenate, we found that (1) catalyzes also FAEs with
internal double bond. For instance, ethyl oleate was converted to
the corresponding primary metathesis products: the symmetri-
cal unsaturated diesters and 9-octadecene (mixture of substituted
2.2. Cross metathesis study between ˛-olefin and an unsaturated
fatty acid ester
As species (1) is active in ␣-olefins ISOMET reaction but led
only to the self-metathesis products with unsaturated FAEs, we
investigated the reactivity of (1) in presence of both unsaturated
FAE and ␣-olefins. We examined the cross reaction of 1-decene
and ethyl undecylenate. The cross-metathesis involving a func-
tionalized and an unfunctionalized olefin gave only three types of
primary products: (i) self-metathesis product of 1-decene metathe-
sis, (ii) self-metathesis product of ethyl undecylenate metathesis
and (iii) cross metathesis products (with ethylene formation in
each metathesis reaction) as shown in Scheme 3. The reaction of
◦
symmetrical olefins, ratio of Z/E, 34:66) at 150 C for 3 h (see Fig.
S5).
Surprisingly, this reaction catalyzed by silica-supported pre-
cursor (1) is highly selective leading only to the primary
self-metathesis products of ethyl undecylenate or ethyl oleate
without apparent isomerization of the starting unsaturated FAE.
These observations strongly suggest that the ester group plays a
role in the inhibition of the isomerization process. In fact as men-
tioned earlier under the same reaction conditions, using solely
1
-decene (C10) with ethyl undecylenate (C11) (molar ratio of 1:1)
catalyzed by (1) produced the internal olefins, 9-octadecene (C18),
the higher molecular weight FAE (C19) and the symmetrical diester
of fatty acid (C20). By comparison with the linear ␣-olefins metathe-
sis, the conversions observed for the unsaturated FAE metathesis
or for the metathesis with a 1:1 molar ratio of ␣-olefin/unsaturated
FAE metathesis were found to be low. Metathesis of 1-decene and
ethyl undecylenate was also studied at different molar ratios of
ethyl undecylenate/1-decene; the results are depicted in Fig. 2 (see
1
-decene as a substrate gave a distribution of terminal and internal
olefins corresponding to the self-metathesis and secondary cross-
metathesis products (ISOMET) (see Fig. S6).
We previously proposed a mechanism involving in the metathe-
sis of ␣-olefins by 1, in which the isomerization steps take place
through the in situ formation of a W–H species (insertion of the

3
46
N. Riache et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 344–348
Fig. 1. Ethyl undecylenate metathesis catalytic performance.
Scheme 2. Primary and secondary metathesis of unsaturated fatty acid ester catalyzed by Ir/Ag or Pd/Ru catalytic systems.
Scheme 3. Metathesis of a mixture of 1-decene and ethyl undecylenate catalyzed by (1) leading to the self-metathesis (SM) of 1-decene, SM of ethyl undecylenate and cross
metathesis of both substrates.

N. Riache et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 344–348
347
Fig. 2. Ethyl undecylenate and 1-decene cross metathesis catalyzed by (1 at variable
molar ratio 1:1; 3:2 and 5:1 (ethyl undecylenate/1-decene). Self-metathesis product
of 1-decene, in blue, cross metathesis products, in purple and self-metathesis prod-
ucts of ethyl undecylenate, in green. Reaction conditions: batch reactor, 1 (50 mg,
◦
9
.3 ␮mol, W loading: 3.44%wt), 500 rpm, 150 C. For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this article.
Fig. S7 for chromatogram, and Fig. S8 for molar fraction selectiv-
ity). Regardless the molar unsaturated FAE/olefin ratio, only the
expected primary products of self-metathesis and cross-metathesis
were observed. Besides, varying the molar ratio did not affect the
conversion toward self-metathesis of ethyl undecylenate under
these reaction conditions. A selective formation of longer chain
unsaturated fatty acid monoester was constantly obtained. Inter-
estingly, for all these catalytic runs, no secondary metathesis
products from ISOMET reaction were observed suggesting that no
isomerization occurred in neither for 1-decene nor ethyl unde-
cylenate substrates. These results corroborate with our previous
observations in regards to the inhibition of the double bound iso-
merization in the presence of functionalized ester olefins. Even if
1
-decene is introduced in large excess compared to ethyl unde-
cylenate (molar ratio 4:1), secondary metathesis products are not
observed despite traces of detectable 1-decene isomers. This func-
tional group appears also to be unfavorable regarding the efficiency
of the metathesis reaction. Indeed, the conversion based on prod-
ucts reaches only 5% for the internal olefin, 6% for the fatty acid
monoester and 9% for the diester of fatty acid. Similar results have
been obtained while substituting 1-decene by 1-hexene or 1-octene
(
see Fig. S9).
Finally, we also studied if the ISOMET transformation could
occur in the presence of terminal alkyne with a ratio of sub-
Fig. 3. Reaction conditions: batch reactor, precursor (1) (50 mg, 5.92 ␮mol, W
loading: 2.19%wt): (a) 1-decene (0.5 mL, 2.64 mmol), (b) mixture of 1-decene and
strate per catalyst of 446–469 under similar reaction conditions
◦
1-decyne (0.25 mL, 1.32 mmol and 0.25 mL, 1.39 mmol) and (c) 1-decyne (0.5 mL,
(
150 C, 3 h). In principle, the alkyne group should also react with
◦
2
.78 mmol), 150 C, 500 rpm, 3 h.
the supported W–H intermediate. We recently discovered that
1) converts terminal alkynes into substituted benzene derivatives
via cyclotrimerization mechanism under solvent free conditions
(
[
19]. Following the same line of thought, 1 being active for olefins
methylation of WCl /Me Sn. Additionally, the cross-metathesis of
6 4
(
ISOMET) (Fig. 3a) and alkynes (cyclotrimerization) (Fig. 3c), cat-
olefins with unsaturated fatty esters was also possible represent-
ing a powerful tool towards the formation of mono and diesters
of fatty acids with variable chain length. Although in our previous
work, (1) was found to act as a multifunctional pre-catalyst promot-
ing ISOMET reaction of ␣-olefins and alkane metathesis reaction,
in the presence of unsaturated FAEs, the W catalytic intermediate
is only participating to the olefin metathesis transformation. We
believe that these results will enable us to have a better understand-
ing on the metathesis of the challenging functionalized saturated
alkanes.
alytic experiments with a molar mixture of 1-decene/1-decyne
were carried out (Fig. 3b). Fig. 3c displays the GC chromatogram
corresponding to the total conversion of 1-decyne, showing
only cycloctrimerization products [19]. No secondary metathe-
sis products from ISOMET reactions were observed and no enyne
metathesis products were detected. These results strongly suggest
that alkyne functions are playing apparently the same role of the
ester function by preventing the olefin isomerization process to
occur.
3
. Conclusion
Acknowledgment
Within this study, we have demonstrated that silica-supported
precatalyst [( Si O)WMe5] (1) catalyzes the metathesis transfor-
mation of monounsaturated FAE highlighting the importance of the
This work was supported by the King Abdullah University of
Science and Technology.

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N. Riache et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 344–348
[9] M.V. Kovalenko, C. Copéret, Dalton Trans. 42 (2013) 12520.
Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molcata.2015.11.
003.
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