Metathesis of renewable unsaturated fatty acid esters catalysed by a phoban-indenylidene ruthenium catalyst

Article abstract of DOI:10.1016/j.jorganchem.2006.06.021

The phoban-indenylidene complex is a robust catalyst for self-metathesis and ethenolysis reactions of methyl oleate. The phoban-indenylidene catalyst was characterized by X-ray analysis, NMR and microanalysis and was used in various self-metathesis and ethenolysis of methyl oleate, giving rise to significantly higher end of run conversions compared to Grubbs 1st generation catalyst. These complexes are more stable and active than commercial Grubbs 1st generation catalyst, can be accessed from simple precursors and should give rise to more economical metathesis processes.

Full text of DOI:10.1016/j.jorganchem.2006.06.021

Journal of Organometallic Chemistry 691 (2006) 5513–5516
www.elsevier.com/locate/jorganchem
Note
Metathesis of renewable unsaturated fatty acid esters catalysed by a
phoban-indenylidene ruthenium catalyst
a,
a
a
b
Grant S. Forman *, Ronan M. Bellabarba , Robert P. Tooze , Alexandra M.Z. Slawin ,
c
c
Ralf Karch , Roland Winde
a
Sasol Technology Research Laboratory, St Andrews, Sasol Technology (UK) Limited, Purdie Building, North Haugh, St Andrews, Fife,
KY16 9ST, Scotland, UK
b
School of Chemistry, University of St Andrews, Purdie Building, North Haugh, St Andrews, Fife, KY16 9ST, Scotland, UK
c
Umicore AG&Co. KG, Rodenbacher Chaussee 4, P.O. Box 1351, 63403 Hanau-Wolfgang, Germany
Received 5 May 2006; received in revised form 5 June 2006; accepted 6 June 2006
Available online 23 June 2006
Abstract
The phoban-indenylidene complex is a robust catalyst for self-metathesis and ethenolysis reactions of methyl oleate. The phoban-
indenylidene catalyst was characterized by X-ray analysis, NMR and microanalysis and was used in various self-metathesis and ethen-
olysis of methyl oleate, giving rise to significantly higher end of run conversions compared to Grubbs 1st generation catalyst. These
complexes are more stable and active than commercial Grubbs 1st generation catalyst, can be accessed from simple precursors and
should give rise to more economical metathesis processes.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Metathesis; Methyl oleate; Renewable; Green; Fatty acid ester; Grubbs; Carbene; Ethenolysis; Self-metathesis
Production of useful raw materials from natural
resources is becoming more relevant as the availability of
fossil fuel derived feedstocks slowly decreases [1]. In this
regard, the built-in functionality, relatively low price and
availability of natural seed oils render them feedstocks of
the future for the chemical industry [2]. Fatty acid monoes-
ters, such as methyl oleate, are usually derived from transe-
sterification of seed oils with a lower alcohol, such as
methanol, with concomitant production of glycerol as a
by-product [3]. These feedstocks have already found appli-
cation in several areas, including detergents, cosmetics and
coatings, and in the bulk of these applications only the car-
boxy group present within oleochemicals is utilized [4].
Ruthenium alkylidene complexes have attracted signifi-
cant attention in recent years as efficient functional group
tolerant catalysts for olefin metathesis [5]. Their relatively
high activity and ease of preparation has led to investiga-
tions of these catalysts towards metathesis of fatty acid
methyl esters [6]. In particular, reactions of unsaturated
fatty acid esters provide a convenient, efficient and environ-
mentally benign route to a variety of useful commercial
raw materials such as polar co-monomers [7]. Despite this,
the metathesis of fatty acid methyl esters places large
demands on Ru metathesis catalysts. The high carbon
number (C18+) of oleochemicals can give rise to a large
array of by-products if double-bond isomerisation and sub-
sequent secondary metathesis reactions occur. In addition,
the formation of equilibrium mixtures in oleochemical
metathesis reactions requires a robust and temperature-
stable catalyst that is capable of re-use and/or recycle [6].
We recently reported the preparation and catalytic
activity of phosphabicyclononane-containing ruthenium
carbene complexes [8]. These ruthenium based complexes
show excellent stability to air and moisture, can be recycled
by chromatography and are available from simple precur-
sors. Herein, we report the efficiency of various metathesis
*
Corresponding author. Tel.: +44 1334 460938; fax: +44 1334 460939.
E-mail address: grant.forman@uk.sasol.com (G.S. Forman).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.021

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G.S. Forman et al. / Journal of Organometallic Chemistry 691 (2006) 5513–5516
reactions of methyl oleate catalysed by phoban-indenylid-
ene catalyst 2 is significantly enhanced relative to Grubbs
1st generation catalyst 1, a consequence of which is more
economical processes.
PCy3
Cy
P
Ru
Cl
Cl
Ru
Ph
Cl
Cl
R
P
Cy
PCy3
1
2
We envisaged that combination of relatively inexpensive
phosphorus containing ligands such as cyclohexylphoban
with a Ru-indenylidene moiety could provide a non-
hazardous, economic and scaleable route to Ru-alkylidene
olefin metathesis catalysts [9]. The desired phoban-indeny-
lidene complex 2 was prepared by treatment of a ca. 3:1
mixture of cyclohexylphoban with indenylidene derivative
3, followed by precipitation from pentane (Scheme 1). For-
mation of 2 was monitored by 31P NMR spectroscopy as
the appearance of a very broad singlet at d = 22.0 ppm
[10]. The signal for the single proton on Cb of the indeny-
Fig. 1. Perspective drawing of [(PhobCy)2Cl2Ru=C15H10] (2).
lyst ratio for the self-metathesis reaction was increased to
200000:1 (Entry 3, Table 1), where 15 times more turnovers
were achieved using catalyst 2.
Interestingly, the self-metathesis of methyl oleate is only
one of the few examples of metathesis reactions where the
key propagating species is not a Ru methylidene species.
Because the double-bond present within methyl oleate is
internal, the propagating species becomes an alkylidene, a
consequence of which should be a longer lived catalyst
[15]. In addition, the absence of significant amounts of eth-
ylene being produced or consumed in the reaction should
reduce the amount of degenerate reactions of the active
metathesis catalyst that can lead to unproductive metathe-
sis [6]. Despite this, self-metathesis of methyl oleate cataly-
sed by Grubbs 1st generation catalyst 1 affords poor
conversions (Table 1). On the basis of the foregoing, it
seems reasonable to suggest that decomposition of catalyst
1 does not necessarily require methylidene intermediates
[16]. In addition, the results obtained above are consistent
with our previous observations that phoban-based metath-
esis catalysts are less temperature sensitive than Grubbs 1st
generation catalyst 1 [8].
1
lidene appears as a singlet at 8.25 ppm in the H NMR
spectrum of 2.
X-ray analysis [11] of 2 (Fig. 1) indicated a distorted
square-pyramidal geometry about the metal center in
which the carbene ligand occupies the apical position and
the phosphine ligands in the basal plane occupy a trans
position. The X-ray crystal structure of 2 confirmed that
the complex bears cyclohexylphoban ligands and an
indenylidene moiety.
The application of complex 2 towards the self-metathe-
sis [12] and ethenolysis [13] of methyl oleate [14] (Scheme 2)
was investigated and the results are depicted in Tables 1
and 2. For the self-metathesis of methyl oleate (Table 1)
reactions were performed at 50 ꢁC and were run neat.
Self-metathesis reactions catalyzed by 2 gave rise to signif-
icantly higher end of run conversions compared to Grubbs
1st generation catalyst 1. For example, with 0.0025 mol%
of catalyst 2, the self-metathesis of methyl oleate was
achieved in 49% conversion after 3 h, whereas only 6.2%
conversion was obtained using catalyst 1 (Entry 2, Table
1). A similar effect was observed when the substrate:cata-
Ethenolysis reactions of methyl oleate catalysed by pho-
ban-indenylidene catalyst 2 gave rise to higher end of run
conversions to 1-decene and methyl 9-decenoate compared
Cy
Cy
P
P
Cy
PPh3
P
Cy
+
P
Ru
Cl
Cl
Ph
+
Ru
Ph
Cl
Cl
(3:1)
P
Cy
PPh3
3
2
Scheme 1.

G.S. Forman et al. / Journal of Organometallic Chemistry 691 (2006) 5513–5516
5515
O
1-Decene
+
1 or 2
OMe
Ethylene
Methyl Oleate
O
Ethenolysis
OMe
Methyl 9-Decenoate
1 or 2 Self-Metathesis
9-Octadecene
+
O
O
MeO
OMe
Dimethyl 9-octadecene-1,18-dioate
Scheme 2.
Table 1
catalyst 2 (Entry 3, Table 2). Under the same conditions,
only 43% conversion was obtained using catalyst 1. It
should be noted that methyl oleate ethenolysis reactions
catalysed by the phoban-indenylidene catalyst 2 can also
be run at higher reaction temperatures. For example,
ethenolysis of neat methyl oleate at 65 ꢁC using 10 bar of
ethylene employing a substrate:catalyst ratio of 30000:1
afforded the desired products in 41% conversion using cat-
alyst 2. Under the same conditions, only 13% conversion
was obtained using catalyst 1.
In summary, the phoban-indenylidene complex 2 is a
robust catalyst for self-metathesis and ethenolysis reactions
of methyl oleate. These Ru-indenylidene complexes are
more stable and active than Grubbs 1st generation catalyst
1, can be accessed from simple precursors and should give
rise to more economical metathesis processes. Studies
aimed at further increasing the efficiency and applicability
of phoban metathesis catalysts are ongoing.
Self-metathesis reactions of methyl oleate to 9-octadecene and dimethyl
9-octadecene-1,18-dioate via Ru-alkylidene catalysts
Entrya Substrate: Catalystc Conv. Selectivity to
Productive
products (%)d TONf
catalyst
ratiob
(%)d,e
1
2
3
20000:1
40000:1
200000:1
1
2
1
2
1
2
10.5
49.6
6.2
49.0
2.5
94.5
97.8
92.1
97.3
93.7
96.5
1985
9702
2284
19071
4685
71603
37.1
a
b
c
d
e
f
Reactions were reproducible within 95% accuracy.
Purified by passing through alumina before use.
50 ꢁC, neat, 3 h.
Determined by GC.
Reaction reaches equilibrium at 50% conversion.
Productive TON = TON · selectivity to required product.
Table 2
Ethenolysis reactions of methyl oleate to 1-decene and methyl 9-decenoate
via Ru-alkylidene catalysts
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˚
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was fitted with a dry-ice reflux condenser, thermometer and septum.
A needle was inserted through the septum and connected to a gas
supply via a needle valve to ensure a slow and steady stream of argon
through the reaction solution. Methyl oleate (15.0 g, 51 mmol) was
added to the reaction vessel and the reaction was heated to 50 ꢁC.
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was weighed into an aluminum weighing tray and added to the
reaction mixture. Samples were taken at regular intervals via syringe
through the septum. Conversion and selectivity were measured by GC
with an MDN column. Calibrations of products and methyl oleate
were performed by preparing a range of known concentrations of
standard solutions to obtain a calibration curve and by using an
internal standard as reference. Reactions were reproducible within
95% accuracy.
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with dip-tube for sampling was charged with methyl oleate (12 g,
40.0 mmol), tetradecane (2.5 g, internal standard), and saturated with
ethylene. Catalyst 2 (8.1 mg, 0.010 mmol) was weighed and trans-
ferred into a Schlenk flask under argon, and dissolved in toluene
(5 mL, degassed). An aliquot (1 mL) of this stock solution was
transferred to the autoclave. The autoclave was pressurized (10 bar of
ethylene) and heated via computerized temperature controller to the
desired temperature. Samples were taken at regular intervals using a
dip-tube Samples were taken at regular intervals using a dip-tube
apparatus, and conversion and selectivity were measured by GC with
an MDN column using an internal standard as reference. Reactions
were reproducible within 95% accuracy.
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¨
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[10] Preparation of complex 2: A solution of cyclohexylphoban (ca. 3:1,
672 mg, 3 mmol) in CH2Cl2 (10 ml) was added to a solution of
complex 3 (1.0 g, 1.04 mmol) in CH2Cl2 (10 ml) under a nitrogen
atmosphere and stirred at room temperature for 24 h. After such time
the solvent was removed under vacuum and pentane (40 ml) was
added. The resulting brown solid was filtered and washed with
petroleum ether (40/60 fraction, 3 · 20 ml) to afford complex 2 as a
brown powder (598 g, 72% yield). 31P(1H) NMR (121 MHz, C6D6):
d = 22.0 (bs); 1H NMR (300 MHz, C6D6): d = 8.25 (s, 1H, C-1), 7.80–
6.75 (m, 9H), 2.80 (s, 4H, PCH of Phoban), 2.26–0.40 (m, 46H,
Phoban H); 13C (1H) NMR (75 MHz, CD2Cl2): d = 294.5 (m,
Ru = CH–), Anal. Calc., for C43H60Cl2P2Ru: C, 63.69; H, 7.46.
Found: C, 63.68; H, 7.55%.
[14] Methyl oleate (99%) was purchased from Aldrich and passed through
a short (2 cm) pad of alumina before use.
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Kirk, G.S. Forman, J. Am. Chem. Soc. 126 (2004) 14332.
[11] Red single crystals suitable for X-ray diffraction were obtained by
evaporation of an ether solution. Several different crystals were
examined and four different complete datasets were obtained. The
best data were obtained using a small crystal and copper radiation.
C
43H60Cl2P2Ru, Mr = 810.82, monoclinic, space group P2(1)/c,