Dimerisation of cyclooctene using Grubbs' catalysts

Article abstract of DOI:10.1016/j.apcata.2011.09.005

The dimerisation of cyclooctene (COE) to 1,9-cyclohexadecadiene, a molecule of interest to the fragrance industry, has been achieved using ruthenium catalysts in organic solvents with significantly better selectivities (47-74%) and yields (39-60%) than previously reported (34% and 30%, respectively). Grubbs' first and second generation catalysts, the Hoveyda-Grubbs' catalyst and a phosphonium alkylidene catalyst were tested in a range of organic solvents and ionic liquids (ILs), including 1:1 IL/dichloromethane mixtures and biphasic IL + pentane systems. The best results (74% selectivity, 60% yield) were obtained using Grubbs' first generation catalyst in 1,2-dichloroethane. The formation of trimer, tetramer and other higher molecular mass products were found to be favoured at low catalyst loadings (<8.5 mol%) and high concentration of cyclooctene (>0.77 mM). Studies of metathesis reactions using 1,9-cyclohexadecadiene as substrate indicated that the monomer-dimer and monomer-trimer reactions are faster than the dimer-dimer reaction. The use of IL media allowed for the recyclability of the catalyst, although a drop in the yield of dimer generally occurred after the first run. Heterogeneized catalysts, where the IL-catalyst system was immobilised onto silica, resulted in fast reactions leading to poor yields of dimer.

Full text of DOI:10.1016/j.apcata.2011.09.005

Applied Catalysis A: General 408 (2011) 54–62
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Dimerisation of cyclooctene using Grubbs’ catalysts
Sandra M. Rountreea, M. Cristina Lagunasa,∗, Christopher Hardacrea,∗∗, Paul N. Daveyb
a QUILL Research Centre, School of Chemistry and Chemical Engineering, Queen’s University, Belfast BT9 5AG, Northern Ireland, UK
b Givaudan Schweiz AG, Ueberlandstrasse 138, CH-8600 Duebendorf, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 June 2011
Received in revised form 28 August 2011
Accepted 8 September 2011
Available online 16 September 2011
The dimerisation of cyclooctene (COE) to 1,9-cyclohexadecadiene, a molecule of interest to the fragrance
industry, has been achieved using ruthenium catalysts in organic solvents with significantly better selec-
tivities (47–74%) and yields (39–60%) than previously reported (34% and 30%, respectively). Grubbs’ first
and second generation catalysts, the Hoveyda–Grubbs’ catalyst and a phosphonium alkylidene cata-
lyst were tested in a range of organic solvents and ionic liquids (ILs), including 1:1 IL/dichloromethane
mixtures and biphasic IL + pentane systems. The best results (74% selectivity, 60% yield) were obtained
using Grubbs’ first generation catalyst in 1,2-dichloroethane. The formation of trimer, tetramer and other
higher molecular mass products were found to be favoured at low catalyst loadings (<8.5 mol%) and high
concentration of cyclooctene (>0.77 mM). Studies of metathesis reactions using 1,9-cyclohexadecadiene
as substrate indicated that the monomer–dimer and monomer–trimer reactions are faster than the
dimer–dimer reaction. The use of IL media allowed for the recyclability of the catalyst, although a drop in
the yield of dimer generally occurred after the first run. Heterogeneized catalysts, where the IL-catalyst
system was immobilised onto silica, resulted in fast reactions leading to poor yields of dimer.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Metathesis
Cyclooctene
Grubbs’ catalysts
Ionic liquids
Dimerisation
1. Introduction
catalysts of general formula [M( CHR)( NAr)(ORꢀ)2] (M = Mo or
W), developed by Schrock and co-workers showed high activity
Olefin metathesis is a popular and useful reaction which occurs
when two olefins exchange alkylidene fragments in the presence
of certain transition-metal compounds [1]. This can result in
several different outcomes [2]; cross-metathesis (CM) involving
the straight swapping of groups between two acyclic olefins;
ring-closing metathesis (RCM) the closure of large rings; ring-
opening metathesis (ROM), formation of dienes from cyclic and
acyclic olefins; ring-opening metathesis polymerisation (ROMP),
the polymerisation of cyclic olefins, and acyclic diene metathe-
sis polymerisation (ADMET), the polymerisation of acyclic dienes.
The metathesis reaction is reversible and forms both the cis and
trans isomers. It allows the synthesis of well-defined, functionalised
polymers and complex architectures, including medium sized and
large ring structures [3].
over a diverse range of olefins [5]. However, the development
of the Grubbs’ 1st generation catalyst in 1995, 1 (Scheme 1), is
mainly credited with putting olefin metathesis at the forefront of
organic synthesis [6]. Subsequently, the more stable second gen-
eration Grubbs’ catalysts were reported [7], such as 2 (Scheme 1),
containing a NHC ligand with bulky side groups. However, these
catalysts are homogeneous and subsequently have two major
disadvantages; namely their poor recyclability and difficulty in
removing ruthenium waste from the final products. Following
this, Hoveyda and co-workers developed the Hoveyda–Grubbs’
third generation catalysts (e.g., catalyst 3, Scheme 1) [8]. These
catalysts are based on a release and return olefin metathe-
sis mechanism and are commonly referred to as ‘boomerang
catalysts’, as the styrenyl ligand can readily detach from the
metal centre, allowing metathesis to take place, then reattach
to the metal after the reaction. Since the development of these
catalysts, there have been significant improvements in catalyst
design, based on Grubbs’ catalysts, for metathesis reactions [9]. In
particular, of interest to the present research, are the ionic phos-
phonium catalysts [{Ru CH(PCy3)}(H2IMes)Cl2][X] (H2IMes = 1,3-
bis(mesityl)-2-imidazolidinylidene; X = B(C6F5)4, BF4, BPh4, OTf (4,
Scheme 1)) which have been found to have superior activity
to Grubbs’ catalysts in some instances. Specifically, the RCM of
5,5-dicarbethoxy-2-methyl-l,7-octadiene using these ionic cata-
lysts gave approximately 90% conversion, compared with only 5%
Until the 1980s, metathesis reactions were carried out using
catalysts based on transition metal salts such as WCl6/Bu4Sn,
MoO3/SiO2 and Re2O7/Al2O3 [4]. Although limited due to their
sensitivity to many functional groups, these catalysts have
been commercially employed widely. A family of well-defined
∗
Corresponding author. Tel.: +44 028 90974436; fax: +44 028 90976524.
Corresponding author. Tel.: +44 028 90974592; fax: +44 028 90976524.
E-mail addresses: c.lagunas@qub.ac.uk (M.C. Lagunas), c.hardacre@qub.ac.uk
∗∗
(C. Hardacre).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.09.005

S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
55
Scheme 1. Grubbs’ first (1) and second (2) generation catalysts, Hoveyda–Grubbs’ catalyst (3) and phosphonium alkylidene catalyst (4).
conversion using catalyst 2 [10]. Recently, the utilisation of ionic
catalysts has been combined with ionic liquids to provide an effec-
tive recyclable catalytic system. The charged state of the catalyst
enhances the ability of the ionic liquid to retain the catalyst on
recycle and reduces the leaching into the organic phase [11]. In
addition, ionic liquids have been found to be suitable media for
metathesis reactions using conventional Grubbs’ catalysts [12]. For
example, the dimerisation of 1-octene to form 7-tetradecene using
the Hoveyda–Grubbs’ catalyst has been reported to give improved
yields and selectivities when ionic liquids are used, in comparison
to conventional solvents or in solventless conditions [12b,c].
In this paper, the use of Grubbs’ catalysts is investigated for
the dimerisation of cyclooctene (COE) to 1,9-cyclohexadecadiene
(Scheme 2) in both organic solvents and ILs. 1,9-Cyclohexa-
decadiene has potential as an intermediate for macrocyclic musk
compounds [13]. Muscone for example is the principal odour con-
stituent of musk pod; however, due to its rare occurrence in
nature, many synthetic routes have been developed [14]. In addi-
tion, 1,9-cyclohexadecadiene can also be used in the production
of Animusk® [13a]. Therein, COE is ultimately obtained from buta-
diene and then used to produce 1,9-cyclohexadecadiene through
a self-metathesis reaction. Finally, after selective epoxidation of
one of the double bonds, followed by its rearrangement, Animusk®
is produced (Scheme 2). Selectivity in the dimerisation process
is problematic with trimer, tetramer and higher molecular mass
polymers being formed readily. Previous research focusing on the
dimerisation of cycloolefins has been limited due to the fast poly-
merisation and low selectivities. The formation of cyclic derivatives
vs. linear polymers is generally favoured at higher temperatures
and lower reactant concentrations, but also depends on a vari-
ety of factors such as solvent, reaction time and catalyst [15].
Dimerisation of C7–C10 cycloolefins was reported by Warwel et al.
[16] using Soxhlet extraction and a heterogeneous (rhenium hep-
toxide/aluminium oxide/tetramethyltin) catalyst in n-hexane at
35–50 ◦C. With the exception of the C8 (COE) ring, all ring sizes
were found to produce reasonable selectivities and yields of the
corresponding dimers (59–80% selectivity, 58–68% yield). How-
ever, in the case of COE, a significantly reduced selectivity (34%)
and yield (30%) of the dimer was obtained. Dimerisation of COE
has also been carried out using cyclic olefins and open-chain
olefins together [17], using WOCl4/Al(C2H5)2Cl (8.6% yield after
24 h) or WOCl4/Sn(C4H9)4 (3.4% yield after 14 min) as catalyst. It
was found that WOCl4/Sn(C4H9)4 leads to more selective reac-
tions, whereas WOCl4/Al(C2H5)2Cl had a higher thermal stability.
However, products of higher molecular weight were dominant and
due to the low concentration of the dimer, it was impossible to
separate the products. More recently, tandem Ir/Mo catalyst sys-
tems have been used for the dehydrogenation and subsequent
oligomerisation of cyclooctene, with 0.7–15% of dimer found in
the mixtures of cycloalkenes obtained [18]. Despite the increas-
ing popularity of Grubbs’ ruthenium catalysts for olefin metathesis,
currently there are no reports of their use on the dimerisation of
cycloolefins.
2. Experimental
2.1. General
Cyclooctene, decane and solvents (dichloromethane, 1,2-
dichloroethane, ethyl acetate, 2-propanol, benzene and pentane)
were obtained from Aldrich, distilled and/or dried over activated
molecular sieves, degassed with nitrogen for 1–2 h and stored
under a nitrogen atmosphere. Methanol and tetrahydrofuran were
collected from a MBRAUN manual solvent purification system,
under nitrogen and dried over activated molecular sieves (85 ◦C).
All other reagents were obtained from Aldrich and used as received.
NMR spectra were performed on either a Bruker Avance DRX
(300 MHz) or DPX (500 MHz) spectrometer. GC-FID samples were
analysed using a Hewlett Packard 6890 GC fitted with an RTX-5
column (30 m, 0.25 ␮m diameter). GC–MS (Perkin Elmer Turbo
Mass) was performed using a PE5MS column (length, 30 m;
Scheme 2. Dimerisation of COE to 1,9-cyclohexadecadiene, which is used in the
production of Animusk®
.

56
S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
4:[H2IMesH][OTf] ratio is 2:1]: 18.43 (s, 1H, Ru = CH)4, 7.06 (s, 4H,
Mes-mH)4, 7.00 (s, 4H, Mes-mH)*, 4.52 (s, 4H, (CH2)2 bridge in
H2IMesH)*, 4.11 (s, 4H, (CH2)2 bridge in H2IMes)4, 2.41 (s, 12H,
Mes-oCH3)4, 2.39 (s, 6H, Mes-pCH3)4, 2.37 (s, 12H, Mes-oCH3)*,
2.32 (s, 6H, Mes-pCH3)*, 1.94 (broad m, P(C6H11)3)4+other, 1.77
thickness, 0.25 ␮m; IDO, 0.32 mm). Decane was used as internal
standard for GC analysis.
2.2. Ionic liquids
(broad m, P(C6H11)3)4+other, 1.36 (broad m, P(C6H11)3)4+other
.
The ionic liquids [A][NTf2] (A = 1-butyl-3-methylimidazolium
(C4mim), 1-butyl-1-methyl-pyrrolidinium (C4Pyr), 1-butyl-
2,3-dimethylimidazolium (C4dmim); NTf2
= N(CF3SO2)2) and
2.4. ICP analyses
[C4mim][X] (X = PF6, CF3SO3 (OTf)) were prepared in-house
from the corresponding bromide salts and LiNTf2 or NaX
(X = PF6, OTf) following methods similar to those previously
described [19]. Analogous procedures were also used to prepare
[A][NTf2] (A = methyl(trioctyl)ammonium (N8,8,8,1), tetrade-
cyl(trihexyl)phosphonium (P6,6,6,14)), using the chloride salts
[N8,8,8,1]Cl and [P6,6,6,14]Cl, which were obtained from Aldrich
and Cytec, respectively. The ILs were dried for 24–48 h under
high vacuum at 60–70 ◦C prior to use, the resulting ILs typically
containing a residual water content of <0.02 wt% as determined by
Karl Fischer titration. They were stored and handled in a glove box
or under nitrogen atmosphere. The results of the catalytic reactions
were reproducible when different batches of IL were used, and no
attempts were made to determine the residual content of halide
or 1-methylimidazole in the ILs. The presence of such impurities,
however, have been shown to have an effect in the self-metathesis
of 1-octene in ILs [12c].
ICP analyses were performed at the ASEP unit in Queen’s Univer-
sity, Belfast. Samples to determine the amount of catalyst dissolved
in various solvents were prepared by adding 5.4 mg (0.007 mmol)
of 1 and 10 mL of solvent (dichloromethane, methanol, hex-
ane, benzene, ethyl acetate, tetrahydrofuran, 2-propanol or
1,2-dichloroethane) into a Schlenk flask, under nitrogen. The mix-
tures were stirred for 10 min and then passed through a sintered
glass funnel. Any undissolved catalyst remaining on the funnel
was washed with dichloromethane (5 mL) into a crucible. The
dichloromethane was allowed to evaporate and the remaining
residue in the crucible was submitted for ICP-MS analysis. A
sample was also analysed where the catalyst was dissolved in
dichloromethane and no filtration was undertaken, giving a value
of 268 ppm. Compared to this standard the % of undissolved Ru in
each solvent was: dichloromethane (4%), 1,2-dichloroethane (13%),
ethyl acetate (15%), methanol (18%), benzene (27%), tetrahydro-
furan (48%), 2-propanol (49%) and pentane (84%). ICP analyses
to determine the loss of Ru in reactions using catalyst 3 or
4 in IL/dichloromethane or IL/pentane were carried out on the
IL/catalyst phase after three recycles, and the results compared to
the standard. Prior to analysis, the organic solvent was removed, as
described in Section 2.8, and the samples dried under high vacuum
for ca. 24 h.
2.3. Catalysts
Catalysts 1, 2 and 3 were obtained from Aldrich, stored and
handled in a glove box, and used without further purification. Cata-
lyst 4 and its precursor [(Ru C)(PCy3)(H2IMes)Cl2] were prepared
following literature procedures [10], as summarised below. Feist’s
Ester was also synthesised as previously reported [20].
[(Ru C)(PCy3)(H2IMes)Cl2]: Grubbs’ 2nd generation catalyst [2]
(1.0 g, 1.178 mmol) was weighed in a glove box and dissolved in dry
dichloromethane (10 cm3). To this, a solution of Feist’s Ester (0.2 g,
1.178 m mol) in dichloromethane (5 cm3) was added. The resulting
solution was stirred under nitrogen for 15 h, after which the solvent
was removed under vacuum. The resulting brown residue was dis-
solved in pentane (15 cm3) and sonicated for 10 min. The solid was
then filtered and repeatedly washed with cold pentane, forming a
2.5. Dimerisation of COE in organic solvents
To 0.066 mmol of catalyst [1 (54 mg), 2 (56 mg), 3 (41 mg) or
4 (60 mg)] into a Schlenk flask, under nitrogen, 100 mL of sol-
vent (dichloromethane, methanol, hexane, benzene, ethyl acetate,
tetrahydrofuran, 2-propanol or 1,2-dichloroethane) were added,
followed by degassed cyclooctene (0.1 mL, 0.77 mmol) and decane
(0.1 mL, 0.51 mmol). The reaction mixtures were stirred at r.t., for
24 h, under nitrogen. Samples (1 mL) for GC analysis were taken
every 10 min for the first hour and subsequently every hour for 8 h.
Finally, a 24 h sample was taken. Each sample was quenched with
tert-butylhydroperoxide (TBHP, 2 drops), diluted with diethyl ether
(1 mL) and filtered through a silica plug prior to being submitted
for GC analysis.
light brown solid which was dried under vacuum (0.69 g, 75%). 1
H
NMR (300 MHz, CDCl3, ı): 6.96 (s, 2H, Mes-mH), 6.89 (s, 2H, Mes-
mH), 4.07 (m, 4H, (CH2)2 bridge in H2IMes), 2.54 (s, 6H, Mes-oCH3),
2.49 (s, 6H, Mes-oCH3), 2.29 (s, 3H, Mes-pCH3), 2.24 (s, 3H, Mes-
pCH3), 1.88 (m, P(C6H11)3), 1.65 (m, P(C6H11)3), 1.17 (m, P(C6H11)3).
31P NMR (300 MHz, CDCl3, ı): 35.4 (s).
[{Ru CH(PCy3)}(H2IMes)Cl2][OTf] (4): A solution of triflic acid
(0.039 g, 0.259 mmol) in dichloromethane (5 cm3) was added to
a solution of [(Ru C)(PCy3)(H2IMes)Cl2] (0.2 g, 0.259 mmol) in
dichloromethane (5 cm3), and the mixture stirred for 30 min.
The solvent was removed under vacuum, and the resulting solid
suspended in pentane (15 cm3) and stirred for 10 min. The pentane
was then decanted, leaving a brown solid which was dried under
vacuum (0.18 g, 90%). The product obtained was used without
further purification. However, fast degradation of 4 was observed
in CDCl3 by 1H NMR, most likely producing [H2IMesH][OTf] [21]
and other unidentified product(s). Attempts to obtain a better 1H
NMR spectrum and/or study the degradation of 4 in solution in
detail were not made. The major product in the 1H NMR spectrum
after dissolution of the catalyst in CDCl3 corresponded well with
the spectroscopic data previously reported for 4 [10]. After 72 h
in solution, the signals for 4 had disappeared leaving only those
attributed to [H2IMesH][OTf] [21] plus other PCy3-containing
impurities. 1H NMR (300 MHz, CDCl3, ı): [fresh solution; signals
attributed to [H2IMesH][OTf] are indicated with *; the approximate
For experiments at different catalyst loadings, the reactions
were carried out as above, in dichloromethane, using 14, 27, 54 and
108 mg (2.2, 4.3, 8.5 and 17.1 mol%, respectively) of catalyst 1. The
same procedure was also used for reactions at different substrate
concentrations, using 0.01, 0.05, 0.1, 0.2 and 1 mL (0.077, 0.35, 0.77,
1.54 and 7.7 mmol, respectively) of COE and 0.01, 0.05, 0.1, 0.2 and
1 mL, respectively, of decane.
2.6. Reactions involving 1,9-cyclohexadecadiene
For the reaction of COE and 1,9-cyclohexadecadiene, Grubbs’
1st generation catalyst 1 (54 mg, 0.066 mmol) was weighed into a
Schlenk flask, under nitrogen. Distilled dichloromethane (100 mL)
was added, followed by degassed cyclooctene (0.1 mL, 0.77 mmol),
1,9-cyclohexadecadiene (0.2 mL, 0.77 mmol) and decane (0.1 mL,
0.51 mmol). The reaction mixture was stirred, at r.t., for 24 h, under
nitrogen. Samples for GC analysis were obtained as described
above for the dimerisation of COE. The reaction using only

S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
57
1,9-cyclohexadecadiene was carried out in the same way but with-
out adding COE.
2.7. Dimerisation of COE in ILs or IL/dichloromethane
Catalyst 1 (5.4 mg, 0.007 mmol), 3 (4.1 mg, 0.007 mmol) or 4
(6.0 mg, 0.007 mmol) was weighed into a Schlenk flask, under nitro-
gen. To this was added the corresponding IL (10 mL), followed by
degassed COE (10 ␮L, 0.077 mmol) and decane (10 ␮L, 0.051 mmol).
The reaction mixture was stirred, at r.t., for 24 h, under nitrogen.
Samples (1 mL) for GC analysis were taken every 10 min for the first
hour and subsequently every hour for 8 h. Finally, a 24 h sample was
taken. Each sample was quenched with TBHP (2 drops), diluted with
diethyl ether (1 mL) and filtered through a silica plug prior to being
submitted for GC analysis. For reactions in 1:1 IL/dichloromethane,
the same procedure was followed but using 5 mL of IL and 5 mL of
degassed dichloromethane instead of 10 mL of IL.
Scheme 3. Proposed routes for formation of dimer (D), trimer (Tri) and tetramer
(Tet) starting from COE (M = monomer).
was increased from 2.2 mol% to 17.1 mol%, the yield of dimer
increased from 49% to 69%. However, only a limited increase in
dimer yield (3%) was obtained on doubling the catalyst loading
from 8.5 mol% to 17.1 mol%. Therefore, 8.5 mol% was used in fur-
ther experiments as it provided the best balance between activity
and yield. These observations are as expected, with a higher
catalyst loading there is a lower amount of monomer available to
polymerise into products of higher molecular mass.
As previously stated, dilute conditions are used to favour the
low molecular weight products and to prevent the formation of
polymer. The selectivity/yield to dimer was therefore investigated
as a function of the COE concentration from 0.07 to 7.70 mM at a
constant catalyst concentration of 6.6 × 10−4 M (8.5 mol%). All reac-
tions were found to result in >98% COE conversion with an average
initial rate of 0.023 (mols COE)(mols cat)−1 s−1 (see ESI). A small
increase in dimer production was observed on increasing the COE
concentration from 0.39 to 0.77 mM from 51 to 60% yield; however,
thereafter, the yield significantly reduces up to a COE concentration
of 7.70 mM forming only 28% yield of dimer. These observations
are expected as there will be a critical amount of COE present such
that COE dimerisation is favoured due to the slower dimer + COE
and dimer + dimer reactions (Scheme 3). However, at high concen-
trations of COE, the dimer concentration will also be significant
which will favour further oligomerisation and thus a reduction in
the dimer yield.
In summary, under optimised conditions with catalyst 1 in
dichloromethane (8.5 mol% of catalyst, 0.77 mM of COE, at r.t.
for 8 h; Table 1, entry 1a), 99% conversion of COE and a 60%
yield of 1,9-cyclohexadecadiene was achieved with the ratio of
dimer:trimer:tetramer being 63:30:7, respectively. In compari-
son with previous reports using Re2O7/Al2O3 catalyst activated by
SnMe4 where the dimer was obtained with 34% selectivity at 90%
conversion [16], a significant improvement is found. In order to gain
an understanding of the processes involved in the formation of the
trimer and tetramer compared with dimer and their relative rates,
the dimer was used as a substrate both in the presence and absence
of COE. Scheme 3 shows four proposed routes for the formation of
the dimer, trimer and tetramer whereby:
2.8. Recycling of catalyst 3 or 4 in IL/dichloromethane or
IL/pentane
Catalyst 3 (4.1 mg, 0.007 mmol) or 4 (6.0 mg, 0.007 mmol) was
weighed into a Schlenk flask, under nitrogen. To this was added
ionic liquid ([C4Pyr][NTf2] or [C4mim][NTf2], 5.0 mL) and the
corresponding organic solvent (degassed dichloromethane or pen-
tane, 5 mL), followed by degassed COE (10 ␮L, 0.077 mmol) and
decane (10 ␮L, 0.051 mmol). The reaction mixture was stirred, at
r.t., for 6 h, under nitrogen. The organic solvent was removed under
vacuum (dichloromethane) or via a syringe (pentane). The IL layer
was then extracted with pentane (3 × 10 mL). The combined pen-
tane washes were reduced under vacuum and submitted for GC
analysis. To begin a new reaction fresh dichloromethane or pentane
and substrates were added to the IL. This process was repeated up
to three times for each catalyst.
2.9. Preparation of supported catalyst 3
Catalyst 3 (41 mg, 0.066 mmol) was weighed into a Schlenk
flask, under nitrogen. To this was added dichloromethane (5 mL),
[C4mim][NTf2] (0.1 mL) and pre-dried Davicat sp 550-10654
silica, pH 4 (0.2 g). This was stirred for 10–15 min and the
dichloromethane removed under vacuum. Further drying under
vacuum (4–5 h) produced the supported catalyst as a green powder.
2.10. Dimerisation of COE with supported catalyst 3 and
recycling of the catalyst
Catalyst 3 was immobilised onto silica as described above and
used directly. To this was added pentane (20 mL), COE (10 ␮L,
0.077 mmol) and decane (10 ␮L, 0.051 mmol). The reaction mixture
was stirred, at r.t., for 6 h, under nitrogen. After 6 h the pentane
layer was removed, via a syringe and the supported catalyst was
washed with pentane (3 × 20 mL). The combined pentane washes
were reduced under vacuum and submitted for GC analysis. To
begin a new reaction fresh pentane and substrates were added to
the silica. This was repeated twice for a total of 3 reactions.
(a) two monomers of COE react to form dimer;
(b) a monomer of COE reacts with the dimer forming trimer;
(c) a monomer of COE reacts with the trimer producing the
tetramer; or
3. Results and discussion
(d) two dimers react to produce tetramer.
3.1. Dimerisation of COE in dichloromethane with catalyst 1
Fig. 1a shows the time course from the reaction of COE and
1,9-cyclohexadecadiene. As the COE and dimer react, both trimer
and tetramer products are formed with the trimer being the
dominant product. Fig. 1b shows the result from the self-metathesis
of 1,9-cyclohexadecadiene. After a short induction period, the
dimer reacts to again form both trimer and tetramer. In addition, a
The dimerisation of COE was studied using dichloromethane as
solvent and Grubbs’ 1st generation catalyst 1 in the first instance.
The reaction was initially screened as a function of catalyst loading
and was carried out using 0.77 mM of COE at r.t., for 8 h (see ESI). It
was observed that as the loading of catalyst 1 in dichloromethane

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S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
Table 1
Summary of the results for the self-metathesis reaction of COE (entry 1a), the reaction between COE and 1,9-cyclohexadecadiene (dimer, entry 1b) and the self-metathesis
reaction of the dimer (entry 1c).a
Entry
Initial rateb
COE
Conversion of COE (%)
Yield of dimer (%)
Ratio of COE, dimer, trimer and tetramer
Dimer
COE
Dimer
Trimer
Tetramer
1a
1b
1c
0.021
0.022
–
–
99
94
–
60
–
–
–
–
9
63
47
48
30
36
32
7
17
11
0.009
0.003
a
All reactions carried out using 0.77 mM of substrate, 8.5 mol% of catalyst 1, at r.t., for 8 h in dichloromethane. All data obtained by GC analysis.
b
(mols COE)(mols cat)−1 s−1
.
small amount of COE is also produced via the dissociation of the
dimer. Although only dimer is present at the start of the reac-
tion, more trimer than tetramer is formed, indicating that dimer
decomposition and subsequent reaction of the monomer with
dimer is faster than dimer–dimer reaction (route (d), Scheme 3). It
is, therefore, likely that the tetramer formed is also due to the reac-
tion of the monomer with trimer (route (c), Scheme 3) and there is
little reaction via the direct reaction of two dimer molecules. This
may be due to steric hindrance as the monomer should be able
to bind to the Ru centre more easily than the dimer and thus this
reaction dictates the pathway observed. In addition, the presence of
trans olefins in the dimer makes this molecule less reactive towards
the Ru centre than the monomer, with a highly reactive cis-olefin
[9j]. This is exemplified by comparing the initial rates of reaction
(Table 1). It is clear that the reactivity of the dimer both with
itself and with the monomer is significantly slower than that of the
monomer with itself; and that the monomer rate is not significantly
altered by the presence of the dimer.
produced and polymeric products were observed. 2-Propanol also
had a low overall conversion of COE (30%) and an extremely slow
initial rate; however, some dimer (58% selectivity) albeit with a
poor yield (15%) was obtained. In this case, trimer and tetramer
were also present and the reaction was dominated by polymeric
products. In contrast, the use of pentane resulted in good conver-
sion of COE (55%) and good selectivity to dimer was found (63%)
but the overall dimer yield was only 30%. Four solvents resulted
in COE conversions of >90% namely ethyl acetate, benzene, 1,2-
dichloroethane and dichloromethane; of which ethyl acetate has
the lowest initial rate, 0.013 (mols COE)(mols cat)−1 s−1. Further-
more, ethyl acetate also resulted in the lowest COE conversion (92%)
after 8 h and it produced the smallest dimer yield (45%) of this group
of solvents. Dichloromethane and benzene produce similar results
with initial rates of 0.021 and 0.019 (mols COE)(mols cat)−1 s−1
,
respectively. Both solvents also led to almost quantitative conver-
sion of COE with a similar ratio of dimer:trimer:tetramer (63:30:7)
and dimer yield (60%). 1,2-Dichloroethane also showed a high ini-
tial rate, 0.021 (mols COE)(mols cat)−1 s−1, and resulted in 100%
conversion of COE with a high selectivity and yield of dimer (74%
selectivity, 60% yield) and only a small trimer selectivity (16%).
Of the solvents studied, 1,2-dichloroethane was found to give the
highest selectivity and yield of the desired dimer product.
During the course of these reactions the dimer, 1,9-cyclohexa-
decadiene, can be observed in three isomeric forms, namely cis–cis,
trans–trans and cis–trans. As found in previously reported studies,
the isomeric ratio of the cis–cis:cis–trans:trans–trans isomers was
found to be 0.2:0.6:0.2 [16].
One reason why the reaction does not proceed well in some
solvents may be due to catalyst solubility and/or stability (i.e.,
colour changes can be observed throughout the reactions). In
dichloromethane, the catalyst 1 dissolved rapidly in the solvent
forming a purple solution which slowly turned brown during
the course of the reaction. Whereas a similar colour change is
often attributed to catalyst reaction, it the present case may be
indicative of catalyst decomposition/poisoning as, thereafter, no
significant reaction was observed. Analogous colour changes were
also observed in the other solvents used, but tetrahydrofuran
showed the fastest rate, with solutions turning brown only after
a few minutes, possibly due to the high coordinating ability of
tetrahydrofuran. In addition, in some solvents the catalyst was
only found to be partially soluble and this contributed to the low
3.2. Solvent studies
Solvents are known to have a significant effect on both rates of
reaction and the reaction selectivity [1a,22]. In order to examine
the effect of catalyst solubility and stability in a variety of sol-
vents as well as the effect of polarity and protic/aprotic nature of
the solvent, the dimerisation of COE was performed using catalyst
1 in 1,2-dichloroethane, benzene, ethyl acetate, pentane, tetrahy-
drofuran, 2-propanol and methanol. The results of this study are
summarised in Table 2 (entries 2a, 2e, 2h, 2k, 2n–2q). Moderate
to good activity was observed in all solvents, with the excep-
tion of methanol, where no reaction occurred. Tetrahydrofuran
resulted in a low conversion of COE (35%); however, no dimer was
Fig. 1. Distribution of products (as determined by GC) during (a) the reaction of COE and 1,9-cyclohexadecadiene (0.77 mM each) and (b) the self-metathesis reaction of
1,9-cyclohexadecadiene (0.77 mM). Both reactions carried out in dichloromethane using catalyst 1 (8.5 mol%) at r.t. (ꢀ COE, ᭹ dimer, ꢁ trimer, ꢂ tetramer).

S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
59
Table 2
Kinetic data for the dimerisation of cyclooctene.a
Entry
Solvent
Catalyst
Initial rateb
Conversion of COE (%)
Yield of dimer (%)
Ratio of dimer, trimer and tetramer
Dimer
Trimer
Tetramer
2a
2b
2c
2d
Diclhoro-methane
Diclhoro-methane
Diclhoro-methane
Diclhoro-methane
1
2
3
4
0.021
0.032
0.010
0.031
99
100
98
60
50
47
43
63
55
48
68
30
32
37
25
7
14
15
7
97
2e
2f
2g
1,2-Dichloro-ethane
1,2-Dichloro-ethane
1,2-Dichloro-ethane
1
2
3
0.021
0.033
0.027
100
100
100
60
43
58
74
64
64
16
29
32
10
7
4
2h
2i
2j
Benzene
Benzene
Benzene
1
2
3
0.019
0.032
0.032
98
100
100
60
45
39
63
50
47
30
33
37
7
17
16
2k
2l
2m
Pentane
Pentane
Pentane
1c
2
0.010
0.031
0.029
55
94
95
30
49
48
63
54
54
25
33
34
13
14
12
3c,d
2n
2o
2p
2q
Ethyl acetate
Tetrahydrofuran
2-Propanol
1
0.013
0.009
0.001
0.000
92
35
30
0
45
–
15
0
65
–
58
–
30
–
37
–
5
–
5
–
1
1c
1c
Methanol
a
All reactions performed using 0.77 mM of COE and 8.5 mol% catalyst, at r.t. for 8 h. All data obtained by GC analysis.
(mols COE)(mols cat)−1 s−1
b
c
.
The catalyst did not fully dissolve.
d
Estimated concentration of catalyst 3 in solution is 4.6 × 10−5 M.
activity found. ICP studies following catalyst dissolution showed
that only 42 ppm of Ru dissolved in pentane; 136 ppm and 139 ppm
were found in 2-propanol and tetrahydrofuran, respectively. Better
solubility was found in benzene (196 ppm), methanol (220 ppm),
ethyl acetate (229 ppm) and 1,2-dichloroethane (231 ppm); with
dichloromethane giving the best solubility (257 ppm).
is not possible to control the oligomerisation. A comparison of the
catalysts 1, 2 and 3 in 1,2-dichloroethane, dichloromethane, ben-
zene and pentane is shown in Table 2 (entries 2a–2c and 2e–2m).
With the exception of catalyst 1 in pentane, all catalysts resulted in
≥94% conversion of COE; however, a significant variation in dimer
selectivity and yield was observed. In all cases, the dimer was found
to be the dominant product and significant selectivity was observed
compared with the trimer and tetramer. However, in only one case,
that of catalyst 1 in 1,2-dichloroethane, was a sufficiently high yield
(82%) and selectivity (74%) towards the dimer obtained.
The activity results herein are comparable with those reported
previously for Grubbs’ catalysts over a range of metathesis reactions
[7,25]. In most cases, as well as for COE dimerisation, catalysts 2 and
3 were found to be more active than 1, with the exception of the
reaction in dichloromethane (entry 2c, Table 2). However, due to
this high activity, increased polymerisation of COE is observed and
consequently less yield dimer is obtained. Therefore, although cata-
lysts 2 and 3 have been found to have better activity for numerous
reactions they are too active, compared with 1, for the selective
dimerisation of COE. Catalyst 1 provides a balance in being able
to activate the monomer but not have too high an activity to over
oligomerise the monomer or further react the dimer.
Solubility alone cannot explain the variation in the solvent
effect. It is clear that protic solvents do not favour the reaction
as both primary and secondary alcohols are found to result in the
lowest activity. Degradation of Grubbs’ catalysts in the presence
of protic functionalities has previously been reported, in particu-
lar, ruthenium hydrido carbonyl species have been isolated upon
reaction with primary alcohols [23]. Regarding polarity, both non-
polar and polar solvents can result in high conversion and similar
selectivity, for example dichloromethane and benzene. Therefore,
the polarity per se is not the important factor. However, the ini-
tial rate in benzene is slightly slower than in 1,2-dichloroethane
or dichloromethane, in agreement with previous observations that
more polar solvents lead to higher initiation rates [22b]. The coor-
dinating ability of each solvent to the metal centre of the catalyst is
a contributing factor. 1,2-Dichloroethane, dichloromethane, ben-
zene and pentane will only weakly coordinate to the ruthenium
centre whereas the oxophilic centre will coordinate strongly to the
oxygen lone pairs in tetrahydrofuran, 2-propanol, methanol and
ethyl acetate. This may hinder the olefin binding to the metal centre
to form the metallacyclobutane intermediate which is critical for
the metathesis reaction [1]. These effects are consistent with those
reported previously for the metathesis of 1-octene, where low con-
versions have been found in tetrahydrofuran or alcohols compared
to less coordinating solvents such as toluene [12c,22a,24]. Herein,
the combination of low coordinating ability and high solubility indi-
cates why 1,2-dichloroethane shows the highest activity for the
COE conversion.
3.4. Dimerisation of COE in ILs
In order to examine the possibility of recycling the catalyst,
a range of ionic liquids were also examined for the dimerisa-
tion of COE using catalysts 1 and 3 as a function of the anion
with a common cation ([C4mim]anion; anion = [NTf2]−, [PF6]−,
[OTf]−) and of the cation with a common anion (Cation[NTf2];
+
cation = [C4Pyr]+, [C4dmim]+, [N8,8,8,1
]
and [P6,6,6,14]+). The reac-
tions were performed in either pure IL or in a equivolume
IL/dichloromethane homogeneous mixture. The dichloromethane
was required in the case of catalyst 1 which had a low solubil-
ity in the ILs. In contrast, catalyst 3 was, in general, soluble in
the ILs and the addition of dichloromethane did not make a sub-
stantial difference to the results. Although reaction was observed
in all ionic liquids, significant polymerisation was found with the
exception of those ILs based on [NTf2]−. Overall, the best results
were obtained with catalyst 3 in [C4mim][NTf2]/dichloromethane
3.3. Catalyst studies
Of clear importance is the overall activity of the catalyst. In order
to maximise the yield of dimer, a balance in the activity of the cata-
lyst must be obtained between too little COE conversion with high
selectivity to the dimer and too high a COE conversion such that it

60
S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
Table 3
Recycle experiments for the dimerisation of cyclooctene in IL/dichloromethane and IL/pentane 1:1 mixtures.a
Entry
Solvent
Catalyst
Run
Initial rateb
Conversion of COE (%)
Yield of dimer (%)
Ratioofdimer, trimerandtetramer
Dimer
Trimer
Tetramer
3a
3b
3c
[C4Pyr][NTf2]/diclhoromethane
[C4Pyr][NTf2]/diclhoromethane
[C4Pyr][NTf2]/diclhoromethane
3
3
3
1
2
3
0.032
0.032
0.032
100
99
99
32
23
17
46
44
44
37
37
38
17
18
19
3d
3e
3f
[C4Pyr][NTf2]/pentane
[C4Pyr][NTf2]/pentane
[C4Pyr][NTf2]/pentane
3
3
3
1
2
3
0.032
0.032
0.032
100
100
99
19
15
14
47
46
43
36
37
38
8
17
17
3g
3h
3i
[C4Pyr][NTf2]/diclhoromethane
[C4Pyr][NTf2]/diclhoromethane
[C4Pyr][NTf2]/diclhoromethane
4
4
4
1
2
3
0.032
0.032
0.029
99
98
87
61
59
50
70
60
56
32
31
23
11
9
7
3j
3k
3l
[C4Pyr][NTf2]/pentane
[C4Pyr][NTf2]/pentane
[C4Pyr][NTf2]/pentane
4
4
4
1
2
3
0.024
0.020
0.019
69
58
54
41
0
0
87
0
0
11
0
0
2
0
0
3m
3n
3o
[C4mim][NTf2]/diclhoromethane
[C4mim][NTf2]/diclhoromethane
[C4mim][NTf2]/diclhoromethane
3
3
3
1
2
3
0.032
0.032
0.032
100
99
99
22
21
17
46
45
44
36
37
37
17
18
19
3p
3q
3r
[C4mim][NTf2]/pentane
[C4mim][NTf2]/pentane
[C4mim][NTf2]/pentane
3
3
3
1
2
3
0.032
0.032
0.032
100
100
100
15
15
12
48
44
40
36
37
37
16
18
18
a
All reactions performed using 0.77 mM of COE and 8.5 mol% catalyst, at r.t. for 6 h. All data obtained by GC analysis.
(mols COE)(mols cat)−1 s−1
.
b
and [C4Pyr][NTf2]/dichloromethane, which yielded 22% and 32%
of dimer, respectively, at 100% conversion of COE after 6 h.
carbides with acids containing weakly coordinating anions such
as [B(C6F5)]4 or [OTf]− [26]. Although the degradation of 4
−
Similar initial rates (0.032 (mols COE))(mols cat)−1 s−1
)
and
in solution has not been studied in detail, herein, it is possi-
ble that the protonated carbide [(Ru CH)(PCy3)(H2IMes)Cl2]+ also
forms in the process. For example, it has been shown that the
osmium analogue [(Os CH)(PCy3)2Cl2][OTf] is obtained by reac-
tion of [(Os C)(PCy3)2Cl2] and HOTf [27].
dimer:trimer:tetramer selectivities (46:37:17, respectively) were
found in both cases.
Recycle experiments were performed using IL/dichloromethane
solutions and biphasic reactions IL + pentane with [C4Pyr][NTf2]
or [C4mim][NTf2], using catalyst 3. In the biphasic reactions the
catalyst was observed to reside in the lower IL phase while the
pentane remained as a separate upper layer. After each run,
the organic solvent was removed from the mixture under vac-
uum (dichloromethane) or via decantation (pentane). The IL layer
was then extracted with pentane before fresh organic solvent
was added. Table 3 summarises the results obtained. For the
IL/dichloromethane systems (entries 3a–3c and 3m–3o), a good ini-
tial rate, 0.032 (mols COE)(mols cat)−1 s−1 was observed for all runs
with ∼99% conversion of COE found in 6 h. As indicated above, cata-
lyst degradation was observed after this reaction time, which partly
explain the sharp decrease in the yield of dimer found in subse-
quent runs (i.e., from 32 to 17% and from 22 to 17% in [C4Pyr][NTf2]/
dichloromethane and [C4mim][NTf2]/dichloromethane, respec-
tively). In comparison, similar initial rates and conversions of
COE were obtained using pentane (entries 3d–3f and 3p–3r) and
although less dimer was produced in the first run, a less pro-
nounced decrease in the yield of dimer in the 2nd and 3rd runs
was observed (19–14% and 15–12% yield in [C4Pyr][NTf2]/pentane
and [C4mim][NTf2]/pentane, respectively). Although less dimer is
formed using [C4mim][NTf2], the activity of the catalyst over the
three runs shows less deactivation in the case of the imidazolium
based ionic liquid. This is consistent with the ICP results (Table 4).
These indicated that, on recycle, there was an average loss in Ru in
the [C4Pyr][NTf2] systems of ca. 26%, but this was less significant in
the case of [C4mim][NTf2] (13% and 3% in IL/dichloromethane and
IL/pentane, respectively). In order to limit the loss of catalyst, the
ionic catalyst 4 was also examined using [C4Pyr][NTf2].
The dimerisation of COE was performed using catalyst 4 and
[C4Pyr][NTf2] and dichloromethane or pentane, Table 3, entries
3g–3l. For comparison, the reaction in pure dichloromethane was
also carried out (Table 2, entry 2d). As in the case of catalyst 3,
in the presence of [C4Pyr][NTf2]/dichloromethane, entries 3g–3i, a
good initial rate of ∼0.031 (mols COE)(mols cat)−1 s−1 was found
in all reactions; however, a drop in the conversion of COE was
observed on the 3rd run from 99% to 87%. Reasonable yields of
dimer were found for all runs although a drop was noted on recy-
cle from 61% to 50%. Interestingly, the ionic liquid was found to
increase the dimer yield over that of the pure dichloromethane
(Table 2, entry 2d) possibly reflecting the increased viscosity and
lowering of the diffusion coefficient which limits the activity of
the catalyst. In contrast, in the biphasic reaction (Table 3, entries
3j–3l), although reaction did occur, significantly reduced initial
rates and COE conversions were observed (∼0.021 (mols COE)(mols
cat)−1 s−1, ∼60% conversion after 6 h). In this case, recycle of the
catalyst/IL led to some reaction but a drop in dimer yield from
41% to 0% from the first to second reactions, with only polymeric
material and some cracking products formed after the first run.
Disappointingly, ICP analysis has shown there to be an average
loss of ruthenium of 40% in the reactions using ionic catalyst 4
(Table 4). This change in the concentration of the catalyst has been
shown herein to have a significant effect on the dimer formed.
The results of all the recycle experiments reported in Table 3 are
consistent with the observation that a reduction in the catalyst
loading decreases the dimer in favour of higher molecular weight
products.
Catalyst 4 was prepared following published methods [10]
and used without further purification, but fast degradation
was noted in CDCl3 by 1H NMR (see Section 2). Whereas
3.5. Heterogeneized catalysts
4
has been reported to be relatively stable, formation of
In an attempt to further improve the catalyst recyclability, the
IL-catalyst 3 system was supported on silica using the ‘supported
[H2IMesH]+ has been observed during the reaction of analogous Ru

S.M. Rountree et al. / Applied Catalysis A: General 408 (2011) 54–62
61
Table 4
Leaching of Ru (%) after three recycles, using catalyst 3 or 4 in IL/diclhoromethane and IL/pentane mixtures. Data obtained by ICP analysis.a
Solvent
Catalyst
Ru content (ppm)
Before
Difference
Ru loss (%)
After
[C4Pyr][NTf2]/diclhoromethane
[C4mim][NTf2]/diclhoromethane
[C4Pyr][NTf2]/pentane
[C4mim][NTf2]/pentane
[C4Pyr][NTf2]/diclhoromethane
[C4Pyr][NTf2]/pentane
3
3
3
3
4
4
51
39
57
17
9
43
33
52
17
4
8
6
5
22
13
30
3
44
38
∼0.08
5
5
8
3
a
ICP studies were carried out on the IL/catalyst phase after three recycles, with each reaction performed in a 1:1 mixture of IL/diclhoromethane or IL/pentane, using
0.77 mM of COE and 8.5 mol% catalyst, at r.t. for 6 h. The organic solvent was removed under vaccum (dichloromethane) or via a syringe (pentane), and the samples dried
under vacuum for 24 h, prior to analysis.
ionic liquid phase’ (SILP) concept. This method has been exten-
sively researched in recent years for many different catalysts in
a variety of reactions [28]. Catalyst 3 (8.5 mol%) was supported
using [C4mim][NTf2] and Davicat sp 550-10654 silica, pH 4. The
recycling of the supported catalyst was then examined for the
dimerisation of COE (0.77 mM of COE at r.t, 6 h per run), using
pentane as the solvent. In all cases, high COE conversions were
found; however, extremely low yields of dimer were observed (run
1 (5.4%), run 2 (0.6%) and no dimer was observed by the 3rd run)
with polymeric material formed during reaction. The use of the
IL–silica system without catalyst produced little reaction showing
that the presence of the catalyst is indeed needed for the reac-
tion, and also indicating that accessibility to the catalyst may be
the issue in this case (i.e., the effective catalyst concentration is
reduced, favouring polymerisation over dimerisation). The reac-
tion in biphasic [C4mim][NTf2]/pentane (Table 3, entries 3p–3r)
also shows good conversion of COE and recyclability, but gives
better yields of dimer (15–12%) than the heterogeneous systems,
again indicating that accessibility to the catalyst may be hindered
when supported on the silica. Compared with the reaction in pen-
tane using catalyst 3 (Table 2, entry 2m), the reactions using the
supported catalyst were faster, with ca. 100% conversion of COE in
the first two runs observed after only 10 min. This indicates that
there is little leaching of the ruthenium catalyst into the organic
phase.
the catalysts remained active after three recycles, a drop in the
yield of dimer was observed after the first run due to loss of
catalyst between cycles. The IL-assisted immobilisation of cata-
lyst 3 onto silica resulted in fast reactions leading to poor yields
of dimer.
Acknowledgements
The authors acknowledge support from QUILL. S.M.R. acknowl-
edges support from the Department of Education and Learning in
Northern Ireland and Givaudan SA.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2011.09.005.
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