One-pot Synthesis of 1,3-Butadiene and 1,6-Hexanediol Derivatives from Cyclopentadiene (CPD) via Tandem Olefin Metathesis Reactions

Article abstract of DOI:10.1002/cctc.201801088

A novel tandem reaction of cyclopentadiene leading to high value linear chemicals via ruthenium catalyzed ring opening cross metathesis (ROCM), followed by cross metathesis (CM) is reported. The ROCM of cyclopentadiene (CPD) with ethylene using commercially available 2^nd gen. Grubbs metathesis catalysts (1-G2) gives 1,3-butadiene (BD) and 1,4-pentadiene (2) (and 1,4-cyclohexadiene (3)) with reasonable yields (up to 24 % (BD) and 67 % (2+3) at 73 % CPD conversion) at 1–5 mol % catalyst loading in toluene solution (5 V% CPD, 10 bar, RT) in an equilibrium reaction. The ROCM of CPD with cis-butene diol diacetate (4) using 1.00 - 0.05 mol % of 3^rd gen. Grubbs (1-G3) or 2^nd gen. Hoveyda-Grubbs (1-HG2) catalysts loading gives hexa-2,4-diene-1,6-diyl diacetate (5), which is a precursor of 1,6-hexanediol (an intermediate in polyurethane, polyester and polyol synthesis) and hepta-2,5-diene-1,7-diyl diacetate (6) in good yield (up to 68 % or TON: 1180). Thus, convenient and selective synthetic procedures are revealed by ROCM of CPD with ethylene and 4 leading to BD and 1,6-hexanediol precursor, respectively, as key components of commercial intermediates of high-performance materials.

Full text of DOI:10.1002/cctc.201801088

Accepted Article
Title: One-pot Synthesis of 1,3-Butadiene and 1,6-Hexandiol
Derivatives from Cyclopentadiene (CPD) via Tandem Olefin
Metathesis Reactions
Authors: Gábor Turczel, Ervin Kovács, Eszter Csizmadia, Tibor Nagy,
Imre Tóth, and Robert Tuba
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To be cited as: ChemCatChem 10.1002/cctc.201801088
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10.1002/cctc.201801088
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One-pot Synthesis of 1,3-Butadiene and 1,6-Hexanediol
Derivatives from Cyclopentadiene (CPD) via Tandem Olefin
Metathesis Reactions
Gábor Turczel,[a] Dr. Ervin Kovács,[a] Eszter Csizmadia,[a] Dr. Tibor Nagy,[a] Dr. Imre Tóth,[a] Dr. Robert
Tuba[a]*
Abstract: A novel tandem reaction of cyclopentadiene (CPD) leading
to high value linear chemicals via ruthenium catalyzed ring opening
cross metathesis (ROCM) followed by cross metathesis (CM) is
reported. The ROCM of cyclopentadiene (CPD) with ethylene using
commercially available 2nd gen. Grubbs metathesis catalysts (1-G2)
gives 1,3-butadiene (BD) and 1,4-pentadiene (2) (and 1,4-
cyclohexadiene (3)) with reasonable yields (up to 24% (BD) and 67%
(2+3) at 73% CPD conversion) at 1-5 mol% catalyst loading in toluene
solution (5 V% CPD, 10 bar, RT) in an equilibrium reaction. The
ROCM of CPD with cis-butene diol diacetate (4) using 0.01 mol% of
3rd gen. Grubbs (1-G3) or 2nd gen. Hoveyda-Grubbs (1-HG2) catalysts
(CM) – of CPD leading to value added chemicals such as
butadiene (BD) or 1,6-hexanediol derivatives is reported.
The petrochemical industry continues to face enormous
challenges from product development and diversification, and
nowadays also from sustainability. For example, three decades
ago the plastic production was based on ethylene, propylene and
the aromatic BTX-fractions almost solely. Thus, refineries were
optimized for the production of these compounds.14 C4 and C5
olefin and diene streams or components were considered as low-
value intermediates and were typically recycled in steam-crackers
in order to increase the yields of the light olefins. Curiously, the
price of BD became attractively low enough to replace aromatics
with BD as major feedstock for nylon production until the mid or
late 90’s.
However, by the time the appropriate technologies and
plants were developed by the main nylon producers,15 the price of
BD had skyrocketed putting the butadiene-based nylon routes on
hold. The exploding demand for BD came from the development
of engineering plastic and high-performance materials. Thus, BD
has found major applications in styrene-butadiene rubbers (SBR),
polybutadiene rubber (PBR), acrylonitrile butadiene styrene
(ABS) resins, styrene-butadiene (SR) latex and others in
decreasing importance.16 Its market is expected to grow further,
higher than with the present 5% per year in the coming 5 years.
Most of the produced BD is obtained by extraction procedures of
the C4 streams of naphtha or oil steam-crackers, which contain
roughly 5% BD.16 BD can also be produced by already proven,
although not widely applied technologies via dehydrogenation of
butane and/or butenes.17–23
Another emerging area is the production of 1,6-hexanediol,
which can be used as intermediate in polyurethanes (PUR),
acrylates, polyesters (e. g. PET), polyols (for example, in reaction
with propylene oxide), coatings and plasticizers represent a large
slice of the present plastic slate of the world.24 The market of 1,6-
hexanediol is estimated at USD 730 million in 2016 and is
projected to grow over 1 billion USD by 2021.25 This intermediate
is an emerging material, which is not only a high-value building
block in the above mentioned commercial polymers, but it can
also be used as precursor for adipic acid production via aerobic
oxidation using heterogeneous Pt, Au and Pd based catalyst
systems.26
loading gives hexa-2,4-diene-1,6-diyl diacetate (5), which is
a
precursor of 1,6-hexanediol (an intermediate in polyurethane,
polyester and polyol synthesis) and hepta-2,5-diene-1,7-diyl diacetate
(6) in good yield (up to 68% or TON: 1180). Thus, a convenient and
selective synthetic procedure is revealed by ROCM of CPD with
ethylene and
4 leading to BD and 1,6-hexanediol precursor,
respectively, as key components of commercial intermediates of high-
performance materials.
Introduction
Cyclopentadiene (CPD) is a volatile, low strained and
reactive conjugated cyclic diolefin having minimal commercial
value. Nevertheless, it has unique chemical properties among the
cycloolefins as its hydrogen atoms undergo facile [1-5]-
sigmatropic shift.1,2 Moreover, CPD is an exceptionally acidic
hydrocarbon, which can be easily deprotonated giving an
aromatic cyclopentadienyl anion.3 The main reactions of CPD
includes cycloaddition,4–9 addition,10 substitution11 and oxidation12
reactions however its consecutive Diels-Alder reaction leading to
CPD polymers or oligomers are also reported.13
The unusual chemical properties and low commercial value
of CPD have prompted us to investigate its activity in olefin
metathesis reactions. In this paper a tandem reaction – ring
opening cross metathesis (ROCM) followed by cross metathesis
[a]
Gábor Turczel, Dr. Ervin Kovács, Eszter Csizmadia, Dr. Tibor Nagy,
Dr. Imre Tóth, Dr. Róbert Tuba
Institute of Materials and Environmental Chemistry
Research Centre for Natural Sciences, Hungarian Academy of
Sciences
Magyar tudósok körútja 2., 1519 Budapest, P.O. Box 286.
E-mail: tuba.robert@ttk.mta.hu
Despite the fact that many valuable materials and
intermediates (such as polyisoprene, butylrubber, styrene-
isoprene-butadiene
polymers,
unsaturated
polyesters,
norbornene, ethylidene norbornene, EPDM elastomers, other
dicyclopentadiene-based plastics etc.) are already made from the
C5 streams of naphtha or oil steam-crackers,27 most of these
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/cctc.201801088
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fractions are still underutilized and typically re-cracked.28 By using
high severity in present steam-cracker technologies, a 100 Mt/y
amount of ethylene production generates 4.1 Mt/y of
cyclopentadiene (CPD) using naphtha as feedstock.29–31 In
contrast, the global production of one of the most important C5
components, CPD, including dicyclopentadiene (DCPD) is only
680 kt/y.32,33
The commercial impact of organometallics to the
petrochemical downstream industry is enormous. Transition-
metal-catalyzed olefin metathesis (OM) was first invented for use
in the petrochemical industry more than 50 years ago by Phillips
Petroleum Co.34 By now, OM became an indispensable and
intrinsic part of the synthetic arsenal that initiated new
technological avenues leading to innovative materials,
petrochemicals and pharmaceuticals.35
However, the use of cross-coupling agents containing
electron withdrawing groups (i.e. like acrylonitrile)44–46 “shut down”
the secondary metathesis step of the cascade reactions via the
formation of an electron deficient, less nucleophile conjugated
intermediate.42
The ring opening metathesis polymerization (ROMP) or ring
opening cross-metathesis (ROCM) of cycloolefins is driven by the
release of ring strain energies.47 If the ring strain falls between 3
– 8 kcal/mol, then equilibrium polymerization is expected.48,49 It
has been reported that the ring strain energy of CPD is similar to
that of cyclopentene (CP),50 whose equilibrium ring opening
metathesis polymerization has recently been investigated in our
laboratories.51,52 Considering the similar ring strain energies of
CPD and CP it was assumed that these two compounds should
maintain similar thermodynamic properties in ROMP/ROCM
reactions (Table 1; ref. A53; ref. B50). As expected for an
equilibrium polymerization (e.g. ROMP of CP) using either
Grubbs or WCl6/Al(C2H5)Cl2 catalysts, the monomer equilibrium
concentration is not affected by the catalyst activity but the
Here we report on a very convenient and selective synthetic
procedure by using ROCM of CPD with ethylene and cis-
butenediol diacetate (4), leading to BD and hexa-2,4-diene-1,6-
diyl diacetate (5), as key components of commercial
intermediates for high-performance materials in enginering plastic. reaction temperature.54,55
The metathesis of DCPD with ruthenium metathesis catalysts is
well-known and has been investigated in detail.36 However, the
reported metathesis reactions of CPD and other compounds
containing conjugated double bonds are rare.37 This is not
surprising as CPD is relatively unstable, it can spontaneously
dimerize to DCPD via Diels-Alder (DA) reaction.38,39 In addition,
the conjugated electron system is expected to reduce activity in
metathesis reactions via the formation of less or non-reactive h4-
allylidene(vinylcarbene) species (Scheme 1).40–42
Moreover, ruthenium h4-allylidene systems disposing
distorted geometry have already been isolated from enyne
metathesis reaction mixtures.43 It was found that these complexes
show very limited catalytic activity. Nevertheless, systematic
experimental and theoretical studies of the “cascade” metathesis
of conjugated olefins have recently been carried out in our
laboratory indicating that the conjugation of the double bonds
itself has no significant impact on the overall catalyst performance.
Despite the relative instability of neat CPD at room
temperature, it was supposed that the DA reaction can be
hindered using low temperature and/or diluted solutions.29
Considering the mediocre ring strain, it was presumed that the
ring opening cross-metathesis (ROCM) of CPD should be feasible
in diluted solution (5 V%) using an excess of electron rich cross-
coupling agents (such as ethylene, cis-butenediol diacetate (4) or
cis-stilbene (7)) and highly active metathesis catalysts systems
(1) (Scheme 2). As mentioned above, the ring opening metathesis
reactions of CPD has not been investigated yet in detail, unlike
that of its cycloadduct, DCPD.37,56
Table 1. Ring strain energies of CP and CPD
(Estr).
compound
Estr
(kcal/mol)
CP
5.4740
5.9840
5.6937
5.0237
CPD
Scheme 1. General scheme of the mechanism of metathesis of conjugated
olefins, tentative formation of h2 and h4 - allylidene ruthenium complexes.
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10.1002/cctc.201801088
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Precipitation was also observed indicating some CPD
oligomerization reactions.
At extended reaction time however, significant amount of
1,4-cyclohexadiene (3) formation (up to 42%) was observed
(Figure S2). Hypothetically 3 may form via either the self-
metathesis of CPD oligomers or 9 (Scheme 3). This observation
indicates that the rate of the secondary metathesis step (k2)
should be relatively faster than that of the primary (k1).
Nevertheless, the rate of the formation of 3 (k1” or k1’”) is
supposedly slow (Scheme 3). Furthermore, according to
computational studies the secondary metathesis products (8 and
9) have higher thermodynamic stability compared to the primary
species (10), (Figure 3).
[Ru]
k1
R
+
R
R
R
Scheme 2. General scheme of ROCM of CP and assumed ROCM of CPD by
using commercially available ruthenium catalysts (1).
k-1
12, R = H
11
CPD
Ethylene
4, R = CH2OAc,
, R = H,
, R = CH2OAc,
10, R = Ph,
7
, R = Ph,
Results and Discussion
R
+
R
k2
k-2
k-1’ k1’
[Ru]
First the feasibility of the ROCM of CPD has been
investigated with cis-stilbene (7) at 25 °C. Compound 7 is an ideal
choice as a model compound for cross-metathesis (CM) reactions
because its reaction with catalysts 1 does not lead to the
formation of less active intermediate. Thus, the rate and
conversion of the ROCM reaction between CPD and 7 is
supposedly determined by CPD only.
The ROCM investigation of the reaction of CPD with eight-
fold excess of 7 (four-fold excess per CPD double bond) mixtures
in the absence and presence of 1-HG2 catalyst have been carried
out at 25 °C in toluene-d8 solution (5 V%) and monitored by in-situ
1H NMR spectroscopy (Figure 1). As expected, relatively fast (r =
7.8·10-5 1/s) ROCM reaction rate was observed meanwhile there
were no DA product formation revealed when the reaction was
repeated at the same conditions in the absence of catalyst (Figure
S1). The CPD conversion was almost 100% based on in-situ NMR
investigation (Figure 1, 2) and the formations of 1,4-diphenylbuta-
1,3-diene (8) and 1,5-diphenylpenta-1,4-diene (9) were observed
in high yields (8: 77%, 9: 80%). Based on the integral areas of the
crude, non-hydrogenated reaction mixture 20-80% Z-E
stereoisomer ratio could be estimated for each product.
R
R
R
R +
R
R
n
k-1”’
CPD oligomers may form
at low 4 and 7 excess
BD
, R = H
k1”’
5, R = CH2OAc,
+
R
- R
R
R
8
, R = Ph,
2
6
, R = H,
k-1” k1”
, R = CH2OAc,
9, R = Ph,
+
R
R
3
Scheme 3. Conversion of CPD via ROCM using commercially available Grubbs
catalyst systems (1).
The GC-MS investigations of the hydrogenated reaction
mixture have shown minor amount of hydrogenated homologs
(C6 and C8-C14) of 10, 8 and 9 with evenly declining integral
areas (Figure S4). The presence of homologs can be explained
by the inherent self-metathesis of the reaction products.
Hypothetically the formation of minor amount of CPD oligomers
may also be expected giving high molecular weight homologs,
which were not detected by the GC-MS.
Stochiometric experiments with 7 revealed the formation of
some primary product, (hepta-1,3,6-triene-1,7-diyl)dibenzene,
(10) however the secondary metathesis products 8, 9 and their
homologs (C6 and C8-C14) were also present in reasonable yield
(8: 10.6% and 9: 9.5%, based on GC-MS integral areas).
Figure 1. In-situ 1H NMR investigation of the ROCM of CPD with 7 as model
compound. (Toluene-d8, 5 V% (0.543 M), room temperatrure, 1-HG2 1 mol%, 7
(4.34 M, 8 equiv., four-fold excess per CPD double bond). (see full spectra in
suppl. mat. Figure S5). *Ethylbenzene, internal standard
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10.1002/cctc.201801088
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obtained (68% and 61%). Catalyst 1-G2 gave somewhat lower
conversion (84%) and 5 and 6 product yields (59% and 52%) than
the ones above. The GC-MS investigations of the hydrogenated
reaction mixture indicated the formation of minor amount of the
hydrogenated homologs of 5 and 6 (Figure S7).
Reproduction of the experiments at 0.05 mol% catalyst
loading high CPD conversions (up to 91%) and relatively high
turnover numbers (TONs) were observed (940 – 1180) (Table 2,
Entry 8 -10). The hydrogenation of the reaction mixture has been
carried out according to standard procedure giving 1,6-hexanediol
diacetate and 1,7-heptanediol diacetate in quantitative yields.57
When the reactions were carried out at 0.01 mol% catalyst loading,
low CPD conversions and only traces amount of the reaction
products were observed.
Carrying the reaction out in the presence of stoichiometric
amount of 4, beside 11 primary metathesis products, 5 and 6 were
formed in reasonable yield (6% and 20%), meanwhile the CPD
conversion was 77% (Table 2, Entry 1). Some precipitation –
supposedly oligomerization – was noticed. At extended reaction
time (24 h), the formation of a substantial amount of 3 (40%) and
a complete CPD conversion were detected. When the excess of
4 was gradually increased, higher yields of secondary metathesis
products (5 and 6) (up to 68%, Table 2, Entry 1 - 5) were observed
(at three hours reaction time), meanwhile only traces amount of 3
formed according to 1H NMR.
The ethenolysis58–60 of CPD (0.543 M) was carried out using
1 or 5 mol% of 1-G2 at room temperature and 10 bar of ethylene
pressure. Considering the solubility of the ethylene in toluene
under the applied reaction condition (10 bar and 25 ˚C), 2.6 mole
equivalent (1.55 M) ethylene could be calculated to one mole
CPD.61,62 As the ethylene could be used in this slight excess, only
a moderate CPD conversion and an equilibrium mixture of the
primary and secondary metathesis products were expected.
Indeed, beside some unreacted CPD the formation of BD, 1,4-
pentadiene (2) and 1,3,6-heptatriene (21) were observed in
reasonable yield (Table 3).
Figure 2. Conversion of CPD and the formation of secondary metathesis
reaction products 8 and 9 based on in-situ 1H NMR. (Toluene-d8, 5 V% (0.543
M), room temperature, 1-HG2 1 mol%, 7 (4.34 M, 8 equiv., four-fold excess per
CPD double bond)).
Following the investigations of ROCM of CPD with cis-
stilbene (7) our attention turned to synthesis of high value
chemicals such as hexa-2,4-diene-1,6-diyl diacetate (5) – a 1,6-
hexanediol precursor – and 1,3-butadiene (BD). Reactions have
been carried out at 25 °C using commercially available 1 catalyst
(0.05 and 1 mol%) systems in 5 V% CPD toluene solutions (0.543
M) using cis-butene diol diacetate (4) and ethylene (Table 2 and
3) as coupling agents.
Table 2. Conversion of CPD and yields of 5 and 6 at room temperature
using commercially available Grubbs catalyst systems. (Toluene solution,
5 V% CPD (0.543 M), 3 h, the yields were determined by 1H NMR)
Entry
1
1 (mol%)
4 equiv. CPD conv.
5 (%)
6
TON
[b]
Cat.
G3
(%)
(%) (of 5)
1[a]
2[a]
3
1
1
1
2
4
6
8
8
8
8
8
8
77
88
~6
~8
24
48
67
68
59
47
59
56
~20
~21
31
~6
~8
24
G3
G3
1
97
4
G3
1
>98
>98
>98
84
58
48
5
G3
1
68
67
6
HG2
G2
1
61
68
7
1
52
59
8
G2
0.05
0.05
0.05
74
44
940
9
G3
90
57 1180
57 1120
10
HG2
91
[a] Yields of 5 and 6 are estimated based on GC-MS (TIC).
[b] mol equiv. per CPD
Scheme 4. Conversion of 2 to 5 and 14.
Complete conversion of CPD and the formation of 5 and 6
were observed with reasonable yield (67% and 68%) within three
hours of reaction time (Table 2, Entry 5) using 1 mol% of 1-G3
catalyst loading and eightfold excess (four-fold excess per CPD
double bond) of 4. When the reaction was carried out using 1-
HG2 catalyst under the same conditions, similar yields were
Although, the conversion of CPD was moderate (50-73%),
the ROCM metathesis product formation was almost exclusive.
The extension of the reaction time from 3 to 12 hours resulted in
slightly higher CPD conversion (from 46 to 58%), however longer
than 12 hours of reaction time at 1 mol% catalyst loading had no
additional effect on the CPD conversion. It should be noted that
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beside the expected reaction products BD, 12 and 2, the
formation of 3 was also considerable due to self-metathesis of 2
or CPD oligomers (Scheme 3). Although 3 has low activity in
metathesis, it can be isomerized to 1,3-cyclohexadiene (13),63
which readily goes to metathesis reaction with 4 giving an
additional amount of 5 and tetradehydro-1,8-octanediol diacetate
(14) (Scheme 4).
Ethenolysis of CPD at relatively high (5 mol%) catalyst
loading and extended reaction time (120 h) gave higher CPD
conversion and higher yield of the secondary metathesis products
(BD and 2) than above. Considering that 3 is a low-strained
cycloolefin, one would expect that the corresponding equilibrium
should be fully shifted to the formation of 3. Thus, it could be
presumed that the overall reaction mixture should end up with
quantitative amount of 3. However, the quantitative formation of 3
was never observed in repeated ethenolysis tests (Table 3) even
at relatively high catalyst loadings and extended reaction time.
the chemical equilibrium is reached for the corresponding
metathesis steps after long enough reaction time – are aligned
with calculated relative high K2 = 2 and 220 equilibrium constants
(Figure 3). Nevertheless, when ethylene is used as cross-
coupling agent K2 is slightly lower than 1 (K2 = 0.37), which is
consistent with the observed significantly higher amount of
primary metathesis product considering a high, ~1.55 M solubility
of ethylene at 10 bar. (See details on solvation and chemical
equilibrium calculations in the S.I.) The equilibrium constant for
the formation of 1,3,5 hexatriene, 15 (1/2 mol) is K41/2=1.5, thus
also close to 1, which is qualitatively in line with its observed
formation. As it can be seen in Table 3, the overall yield of BD is
always lower than that of 2 and 3. This can be explained by the
self-metathesis of BD giving polyunsaturated compounds
including 15, which could be clearly observed in the GC-MS TIC
of the reaction mixture.77,78
Table 3. Ethenolysis of CPD. (1-G2 (1-5 mol%), room temperature, p = 10
bar of ethylene (1.55 M), in toluene as solvent, CPD 5 V%, 0.543 M) (L:
liquid, G: gas phase). (CPD conversion is determined by 1H NMR. The
yields of the reaction products were estimated based on GC integral areas
using FID and/or MS detectors)
CPD
conv.
(%)
BD
(G)
(%)
2.6±
1.0
1-G2
BD (L)
2 (L)
12 (L)
3 (L)
t (h)
(mol%)
(%)
(%)
(%)
(%)
20.0
3
1
46±6.0
11±1.5
13.0±6.9 1.2±0.47
±5.9
12
20
1
1
5
58
60
73
12.8
12.4
15.6
2.5
2.3
8.0
25.2
24.0
35.2
23.2
20.4
16.1
1.8
1.1
6.1
120
Theoretical calculations have been carried out to rationalize
the experimentally observed conversions in the ROCM of CPD
with 4, 7 and ethylene. Standard reaction free energy (with
reference state c0 = 1M) and equilibrium constant for all reaction
steps in Scheme 5 were calculated at DLPNO-CCSD(T)/cc-pVTZ
theory level64,65 (using M06-2X/cc-pVTZ geometry and
frequencies with scaling)63,64 and as a mean of the results of G3,
G4 and CBS-APNO (for the ethylene path) theories68–70 with
hindered rotor corrections71 and using an implicit toluene solvent
model.72,73 See details in the S.I. The free energy diagram of the
synthesis paths are shown in Fig. 3 for the favored all-trans
product isomers (e.g. 12E, 6EE, 11EEE).
Figure 3. Theoretically determined free energy diagram of the three synthesis
paths. Species indices, standard free energy changes and equilibrium constant
of reactions are shown in black, blue and red, resp. Species indices not
participating in a reaction step are printed in grey.
In accordance with the expectations, theoretical calculations
predict rather high, K3 = 1605 M value for the formation of 3 (1/2
mol) and ethylene from 2. Obviously, thermodynamic equilibrium
is not reached for this reaction, because k3 is supposedly slow
comparing to k2 and k1 and most probably the catalyst
decomposes before the full conversion of 2. Furthermore, it is
well-known that the ruthenium methylidene (R=CH2) intermediate
is quite unstable, which may affect the overall catalyst
performance.74–76 The same reasons can lie behind the observed
moderate conversions to 3 in the other two synthesis paths.
Considering the theoretical analysis of ROCM of CPD with
4 and 7 it can be concluded that the relatively high yield for the
secondary metathesis products (5, 6 and 8, 9) – assuming that
Scheme 5. Formation of 3 via the ethenolysis of CPD and the calculated K
values.
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10.1002/cctc.201801088
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mmol). The brown solution was transferred into a screw-capped NMR tube
under nitrogen and 1H NMR spectra were collected over six hours (t[min]=
14, 26, 40, 49,69, 102, 129, 192, 257, 308) at room temperature. 1H NMR
of the products 8 and 9 were in agreement with literature data (Figure 1).80-
83 After 24 hours, part of the reaction mixture (0.1 mL) was hydrogenated
over Pd/C in EtOH and the reaction mixture was analyzed by GC-MS
measurements.
Conclusions
A novel tandem reaction of CPD leading to value added
linear polyolefins has been demonstrated. It has been shown that
CPD can be readily converted to high value chemicals such as
1,6-hexanediol polyurethane monomer and 1,3-butadiene (BD) in
reasonable yields via ruthenium-catalyzed tandem ROCM and
CM reactions at low catalyst loading and ambient reaction
conditions (TON up to 1180). The reaction product composition
strongly depends on the applied reaction time and the excess of
the cross-coupling agents. When the tandem ROCM/CM of CPD
is carried out in the presence of stochiometric amount or slight
excess of cross coupling agents (Ethylene, 4 or 7) at extended
reaction time CPD oligomerization (giving a non-soluble solid),
some secondary metathesis products and 1,4-cyclohexadiene (3)
formation occur. When relatively short reaction time (3h) and high
excess of cross-coupling agents applied the target, secondary
metathesis products (e.g. 5 and 6) form in reasonable yield (up to
68%). The primary metathesis products (12, 11, or 10) could
always be detected, however the secondary metathesis products
are always the major components of the reaction mixture.
Theoretical calculations indicated that the relatively high yields for
the secondary metathesis products (5, 6 and 8, 9) are most
apparently due to the relative high K2 = 2 and 220 equilibrium
constants (Figure 3 and Scheme 5).
Representative example of the ROCM of CPD with cis-butene diol
diacetate (4). A screw-cap NMR tube under argon was charged with 4
(0.72 mL, 4.5 mmol), toluene-d8 (0.15 mL), EB (50 µL, 0.38 mmol) and
CPD (50 µL, 0.59 mmol). After the initial 1H NMR measurement of the
starting materials, the solution of the appropriate catalyst (5 mg 1-G2,
0.0059 mmol, 1 mol%) in toluene-d8 (0.1 mL) was added into the mixture.
After 3h in situ 1H NMR spectrum was taken (Table 2). An aliquot of the
reaction mixture (0.1 mL) was hydrogenated over Pd/C in EtOH and the
reaction mixture was analyzed by GC-MS measurements.
Representative example of the ethenolysis of CPD. A Schlenk tube was
charged with toluene (1.6 mL), EB (200 µL, 1.52 mmol) under argon. CPD
(200 µL, 2.3 mmol) was added under nitrogen. The mixture was transferred
to a Fischer-Porter bottle and the solution (toluene, 2.0 mL) of the catalyst
(20 mg 1-G2, 0.024 mmol) was added. The bottle was flushed four times
with ethylene before the final ethylene pressure was applied. After a period
of time, the gaseous products were collected in an airtight gas sampler bag
and analyzed by GC (FID). The mixture was quenched with ethyl vinyl
ether and the liquid phase was analyzed by GC-MS. Another part of the
liquid phase was diluted with CDCl3 and analyzed by 1H NMR (Table 3).
ROCM of 1,3-cyclohexadiene (13) with 4. A screw-capped NMR tube
was charged with 4 (1.1 mL, 6.7 mmol), toluene-d8 (0.3 mL), EB (50 µL,
0.38 mmol) and 13 (53 µL, 0.56 mmol) under argon. After the initial 1H
NMR measurement of the starting materials, the solution of the catalyst
(3.5 mg 1-HG2, 0.0057 mmol) in toluene-d8 (0.1 mL) was added to the
mixture. After 5 hours of reaction time, 1H NMR spectrum was taken of the
reaction mixture indicating 71% conversion of 13 and the formation of 5
(36%) and 14 (56%) (Figure S14). An aliquot of the sample (0.1 mL) was
hydrogenated over Pd/C in EtOH and analyzed by GC-MS.
Experimental Section
General information. All reactions were conducted under nitrogen
atmosphere using Schlenk-technique or under argon atmosphere in an
MBraun (Labmaster PRO) glovebox. 1-G2, 1-HG2 (Materia), palladium on
carbon, dicyclopentadiene, cis-stilbene (7), ethylbenzene (EB) and other
solvents (Aldrich), CDCl3, toluene-d8 (Eurisotop) were used as received.
1-G3 was synthetized according to literature procedure.79 CPD was freshly
cracked from DCPD at 210°C. Gaseous components were collected from
the Fischer-Porter Bottle to a Multi-Layer Foil Gas Sampling Bag (Restek).
The overall yield and conversion were determined for each reaction
product using 1H NMR with EB as internal standard. Routine 1H NMR
spectra were obtained on a Varian Unity INOVA spectrometer operating at
an equivalent 1H frequency of 500 MHz. GC-MS analyses were carried out
using a Shimadzu GC-MS-QP2010 instrument fitted with a Rxi-5Sil MS
column coupled with a quadrupole mass filter with pre-rods. The gaseous
reaction products were analyzed on-line by a Shimadzu GC-2010 gas
chromatograph (GC) equipped with a 50-m HP-PLOT-Fused Silica column
(Al2O3, KCl), flame ionization detector (FID). The GC column was
calibrated for 1,3-butadiene (BD).
Acknowledgements
We thank the Hungarian Academy of Sciences and National
Research, Development and Innovation Office (NKFIH) for
financial support under Grant Nos. OTKA NN 117986 and PD
120776 (T.N.), for János Bolyai Research Fellowship
BO/00279/16/7 (T.N.) and for the Hungarian NIIF HPC
infrastructure. We are grateful to Materia, Inc., for providing 1-G2
and 1-HG2.
In-situ 1H NMR investigation of the Diels Alder reaction of CPD with 7
in toluene. A Schlenk tube was charged with toluene- d8 (0.2 mL), EB (45
µL, 0.34 mmol), cis-stilbene (7) (0.77 mL, 4.32 mmol, 8 equiv. of CPD) and
CPD (45 µL, 0.54 mmol). The colorless solution was transferred into a
screw-capped NMR tube under nitrogen and 1H NMR spectra were
recorded over six hours (t[min]= 15, 30, 45, 90, 180, 240, 300) at room
temperature. Based on the 1H NMR spectra of the mixture, no reactions
were observed in six hours such as dimerization of CPD.
Keywords: Tandem reaction • ROCM • CM • ruthenium •
metathesis • cyclopentadiene • butadiene • 1,6-hexanediol
Representative example of the ROCM of CPD with cis-stilbene (7): A
Schlenk tube was charged with 1-G3 (4.8 mg, 1 mol%), toluene-d8 (0.2
mL), EB (45 µL, 0.34 mmol), 7 (0.77 mL, 4.32 mmol) and CPD (45 µL, 0.54
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Entry for the Table of Contents (Please choose one layout)
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Gábor Turczel, Dr. Ervin Kovács, Eszter
Csizmadia, Dr. Tibor Nagy, Dr. Imre
Tóth, Dr. Robert Tuba*
Page No. – Page No.
One-pot Synthesis of 1,3-Butadiene
and 1,6-Hexanediol Derivatives from
Cyclopentadiene (CPD) via Tandem
Olefin Metathesis Reactions
A novel cyclopentadiene (CPD) tandem Ring Opening Cross Metathesis (ROCM)
and Cross Metathesis (CM) reaction leading to linear polyolefins is presented. This
reaction opens new applications area of CPD leading to high value chemicals.
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