First rhodium-catalyzed hydroformylation of cyclopentadiene

Article abstract of DOI:10.1016/j.molcata.2015.06.003

This paper describes the first rhodium-catalyzed hydroformylation of cyclopentadiene (Cpd) using a homogeneous catalyst system consisting of [Rh(OAc)₂]₂ and the chelate ligand BISBI. At a reaction temperature of 100°C and a syngas pressure of 30 bar the cyclopentane carbaldehyde is formed in 68% yield while 20% of the respective dialdehyde species are obtained within 3 hours. An important side reaction in Cpd hydroformylation reaction can be the dimerization of Cpd to its dimer dicyclopentadiene (Dcpd). This unwanted side reaction could be overcome by the use of tertiary alkyl amines as additives. Furthermore, the possibility to steer the reaction via the influence of the bite angle of diphosphine ligands was found.

Full text of DOI:10.1016/j.molcata.2015.06.003

Journal of Molecular Catalysis A: Chemical 406 (2015) 114–117
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
First rhodium-catalyzed hydroformylation of cyclopentadiene
Arno Behr∗, Denys Levikov, Dennis Vogelsang
Technische Universität Dortmund, Lehrstuhl für Technische Chemie, Emil-Figge-Str. 66, 44227 Dortmund, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 April 2015
Received in revised form 1 June 2015
Accepted 2 June 2015
Available online 5 June 2015
This paper describes the first rhodium-catalyzed hydroformylation of cyclopentadiene (Cpd) using a
homogeneous catalyst system consisting of [Rh(OAc)2]2 and the chelate ligand BISBI. At a reaction tem-
perature of 100 ◦C and a syngas pressure of 30 bar the cyclopentane carbaldehyde is formed in 68% yield
while 20% of the respective dialdehyde species are obtained within 3 hours. An important side reaction
in Cpd hydroformylation reaction can be the dimerization of Cpd to its dimer dicyclopentadiene (Dcpd).
This unwanted side reaction could be overcome by the use of tertiary alkyl amines as additives. Further-
more, the possibility to steer the reaction via the influence of the bite angle of diphosphine ligands was
Keywords:
Cyclopentadiene
Rhodium
Homogeneous catalysis
Hydroformylation
Aldehydes
found.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
Dcpd can be hydroformylated to mono- or dialdehydes respec-
tively, which offer a broad range of applications. Through the
The transition metal catalyzed hydroformylation, discovered by
serendipity by Otto Roelen in 1938 [1], is a very important reaction
in industrial chemistry, which is carried out as a homogeneous reac-
tion with cobalt or rhodium-based catalysts [2,3]. The advantages
of the rhodium catalysts are the milder reaction conditions, the
higher linear/branched ratio of the products and the higher activ-
ity [4]. The year 2008 saw the production of nearly 10.4 million
tons of oxo chemicals [5], which impressively illustrates the great
importance of the “oxo-products”.
industrially processed hydrogenation of Dcpd-dialdehydes dioles
are obtained, which are used in polyesters or adhesives [16]. Fur-
thermore, esters of Dcpd-diols are used in hydraulic fluids [17].
In literature the rhodium-catalyzed hydroformylation of Cpd is
not described. So far, it was not possible to suppress the formation
of Dcpd in hydroformylation completely. Only aldehydes of Dcpd
can be obtained [14]. Therefore, the desired reaction, e.g. hydro-
formylation, has to be faster than the competitive dimerization
process.
Cyclopentadiene (Cpd) is one of the most important components
of the C5 fraction of the steamcracker with 25 weight% [6]. The
separation of Cpd from the C5 fraction is carried out by dimerization
of Cpd to dicyclopentadiene (Dcpd), which takes place at 30–100 ◦C
at normal pressure. Further, Dcpd can be catalytically cracked to
Cpd again, using copper or iron catalysts [7], by a retro-Diels-Alder
reaction [8]. Cpd is stable only over a short period at −80 ◦C.
Till now only a few technical applications for Cpd are known
[9]. For example it is used for the synthesis of polymers [10,11],
ethylidenenorbornene [8], and ferrocenes [12,13]. The mono- and
dialdehydes of Cpd can be used in different areas of the chemical
industry, e.g. as building blocks for polymers, as well as fragrances
[14,15].
To the best of our knowledge the first successful hydroformy-
lation of Cpd was investigated by Adkins at al. in 1952: hence,
cyclopentane carbaldehyde was obtained as a main product in
cobalt-catalyzed hydroformylation with 37% yield at 145–155 ◦C
and 255 bar synthesis gas [18].
The great challenge was to find a catalytic system and specific
reaction conditions to inhibit the dimerization and accelerate the
hydroformylation process. In our work, we investigated the first
rhodium-catalyzed hydroformylation of Cpd to the corresponding
saturated C6-aldehyde as main product.
2. Materials and methods
2.1. Laboratory experiments
All experiments were performed in an oxygen-free environment
using standard Schlenk techniques. All reactions were performed
in a 25 ml custom-made stainless steel autoclave [19]. In a typical
∗
Corresponding author. Fax: +49 0231 755 2311.
E-mail address: behr@bci.tu-dortmund.de (A. Behr).
http://dx.doi.org/10.1016/j.molcata.2015.06.003
1381-1169/© 2015 Elsevier B.V. All rights reserved.

A. Behr et al. / Journal of Molecular Catalysis A: Chemical 406 (2015) 114–117
115
Table 1
Hydroformylation of Cpd.
Run
Catalyst
Additives
Molar ratio Cpd:NEt3
Solvent
Conv.a(%)
Yield(%)
3
4
5
6
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
[Rh(cod)Cl]2
Rh(acac)CO2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
[Rh(OAc)2]2
–
–
–
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
–
–
–
2:1
3:1
1:1
1:2
2:1
2:1
2:1
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Cyclohexane
THF
46
38
55
90
76
77
44
46
42
12
9
5
6
5
18
6
13
4
-
12
-
21
12
18
8
14
15
7
12
11
6
1
2
4
2
5
2
1
-
11
26
56
32
38
26
6
14
3
5
-
DMF
Reaction conditions: 0.3 mol% precursor, 3 mol% BISBI, 5 mmol Cpd, 5 ml solvent, t = 3 h, T = 100 ◦C, 500 rpm, 30 bar CO.
a
Conversion of Cpd determined by GLC.
experiment, the rhodium precursor and phosphorus ligand were
first weighted out and then placed in an inerted Schlenk flask. Then
the reactant (Cpd), the additive triethylamine and the solvent were
added and placed in an ultrasonic bath until all solids were dis-
solved. The reaction mixture was transferred into the evacuated
autoclave and pressurized to the desired syngas pressure. Then the
autoclave was placed in a preheated oil bath at the chosen temper-
ature. The magnetic stirrer was accelerated to 500 rpm. After the
specified reaction time the reaction was stopped by rapidly cool-
ing to room temperature using an ice bath. The excess syngas was
expanded into the hood and the reaction mixture was taken out
Scheme 1. Product range of the hydroformylation of Cpd and Dcpd.
of the autoclave, weighted and then analysed by gas chromatogra-
phy using di-n-butylether as internal standard and isopropanol as
additional solvent if needed.
The experiments for the conversion time plot were conducted
equivalent to the screening experiments, but with sampling of the
reaction media at regular intervals. The reactor, a 300 ml steel auto-
clave (Parr instruments Company), was equipped with a sampling
unit consisting of a capillary in combination with a dosing valve.
This method allowed multiply sampling using the inner gas pres-
sure inside the reactor for the reaction media sampling.
Scheme 2. Possible reaction pathways in the hydroformylation of Cpd.
2.2. Chemicals
3. Results and discussion
All non-aqueous solvents used in this work were purchased
dryly from Acros Organics (Geel, Belgium) with a purity grade of
>99%. Other chemicals were purchased from commercial suppliers
and were of the highest purity available. They were used as received
without further purification. Selected rhodium catalysts were
purchased from Umicore AG & Co., KG (Hanau, Germany). The lig-
and BISBI ([2,2ꢀ-bis-((diphenylphosphino) methyl)-1,1ꢀ-biphenyl],
>99.0%) was purchased from Acros Organics. Argon gas (99.998%,
Messer Industriegase GmbH) and synthesis gas (99.9%, BASF) were
used as received.
3.1. Product range
Cpd was chosen as a cyclic 1,3-diene substrate for the studies on
the hydroformylation reaction. Scheme 1 shows the product range
of the hydroformylation of Cpd 1. First, saturated mono- and dialde-
hydes of Cpd (3 and 4) can be directly obtained through the oxo
synthesis. Dimerization of Cpd via Diels-Alder-reaction gives Dcpd
2, existing both in endo- and exo-isomers, which leads to formation
of respective monoaldehyde 5 and the dialdehyde 6.
The formation of 3 is a result of a tandem reaction, which
consists of selective hydrogenation of Cpd to cyclopentene
7
and subsequent hydroformylation to the respective satu-
2.3. Analytics
rated monoaldehyde (Scheme 2). Furthermore, cyclopentene was
observed in low amounts as a byproduct after the reaction was
performed.
Another way to obtain saturated monoaldehyde 3 would be first
hydroformylation to the unsaturated cyclopentene carbaldehyde 8
and subsequent hydrogenation to the saturated monoaldehyde of
Cpd. However, we did observe species 8 only in traces via GC/MS,
so the formation of 3 from 8 has have to be very quick. On the other
hand, cyclopentane dicarbaldehyde 4 was formed as a product in
moderate yield, which is an obvious indication for existing of 8 as
Standard gas chromatographic analyses were performed on a HP
6890 instrument (Hewlett–Packard GmbH, Waldbronn, Germany)
equipped with a flame ionization detector (FID) and a HP5 cap-
illary column (30 m, diameter 0.25 mm, film thickness 0.25 ␮m)
connected to an auto sampler. GC–MS analyses were carried out on
a Hewlett–Packard 5973 (70 eV). All pure components have been
calibrated to determine the conversion (X), yield (Y) and selectivity
(S) of the reaction.

116
A. Behr et al. / Journal of Molecular Catalysis A: Chemical 406 (2015) 114–117
Fig. 1. Kinetics of the hydroformylation of Cpd. Reaction conditions: 40 ml solvent (toluene), 500 rpm, 30 bar CO:H2 (1:1), T = 100 ◦C, 50 mmol Cpd, 25 mmol NEt3 0.25 mol%
[Rh(OAc)2]2, 2.5 mol% BISBI, t = 3 h.
an intermediate and simultaneously rapid running reactions to the
products 3 and 4.
possible coordination on them (run 1.7). Same effect was observed
by changing solvent from toluene to THF or DMF (runs 1.9–1.10).
Further, the use of non-polar solvents like cyclohexane (run 1.8) led
predominantly to dimerization of Cpd due to solubility problems
of the rhodium precursor.
3.2. Reaction parameter scope
We also tested further tertiary alkyl amines such as
the linear tri-n-hexyl-, tri-nonyl- and tri-decylamine, the
branched ethyldiisopropylamine or the more basic DABCO
(1,4-diazabicyclo[2.2.2]octane). As expected, tertiary alkyl amines
with long or branched carbon chain prevent the hydroformylation
reaction almost completely.
The starting reaction conditions were established as follows:
solvent toluene, a temperature of 100 ◦C, a syngas pressure (CO:H2
1:1) of 30 bar and a reaction time of 3 h. Moreover, different
rhodium precursors were screened in the presence of the chelate
ligand BISBI. This ligand was already patented by Eastman Kodak
[20] for Rh-catalyzed hydroformylation and subsequently used by
Casey and co-workers for mechanistic studies [21]. Best yields (Y)
of the cyclopentane carbaldehyde 3 were obtained in the presence
of the rhodium precursor [Rh(OAc)2]2 (Table 1).
Table 2
Influence of bite angle of ligands in the hydroformylation of Cpd.
As shown in Table 1 (runs 1.1–1.3), [Rh(OAc)2]2 showed the best
catalytic activity among the complexes investigated: in run 1.3 the
cyclopentane carbaldehyde 3 was obtained with 26% yield. Fur-
thermore, under given reaction conditions hydrogenation of Cpd
to cyclopentene cannot compete with the dimerization of Cpd to
the dimer, which gave 18% yield of respective aldehyde 5 of Dcpd.
To achieve possible prevention of the dimerization process, influ-
ence of tertiary amines as additives was studied: with an addition
of triethylamine (NEt3), a significantly increased yield of 3 to 56%
in contrast to 26% without NEt3 (runs 1.3–1.4) was observed. The
respective dialdehyde species of Cpd was obtained with 18% yield
(run 1.4). Amines have a high coordination ability to the metal
center [22] as well as to the C C double bond. As shown in runs
1.4–1.7, the yield of Cpd monoaldehyde 3 was greatly affected by
the molar ratio of the alkene to the NEt3. Cyclopentane carbalde-
hyde 3 was the main product with 56% yield when the molar ratio
of Cpd to NEt3 was 2 (run 1.4). As the molar ratio changed from
2:1 to 1:1 and 3:1 the formation of 3 was reduced (runs 1.5–1.6).
It shows that increasing the concentration of Cpd led to products
of Dcpd. Increasing the amount of amine in the substrate mixture
has also a negative influence on the hydroformylation reaction due
to the blocking both the alkene and the catalyst species through
Run
Ligand
Bite anglea(◦)
Conv.b(%)
Yield(%)
3
4
5
6
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
DPPM
DPPE
DPPP
BINAP
72
84
86
92
45
42
38
57
37
51
48
90
42
28
9
4
2
-
3
8
18
56
29
14
10
3
2
-
1
3
7
18
5
3
20
24
29
50
36
26
14
8
5
2
1
2
3
3
4
2
1
2
DPPB
94
DPEphos
Xantphos
BISBI
NORPHOS
DBFphos
102
112
122
123
131
6
5
Reaction conditions: 0.3 mol% [Rh(OAc)2]2, 3 mol% ligand, 5 mmol Cpd, 2.5 mmol
NEt3, 5 ml solvent (toluene), t = 3 h, T = 100 ◦C, 500 rpm, 30 bar CO.
Abbreviations:
DPPE = 1,2-Bis(diphenylphosphino)ethane,
Bis(diphenylphosphino)propane,
1,1’-binaphthyl,
DPEphos = Bis(2-(diphenylphosphino)phenyl)ether,
phos = 9,9-Dimethyl-4,6-bis(diphenylphosphino)xanthene,
NORPHOS = 2,3-Bis(diphenylphosphino)bicyclo-[2.2.1]hept-5-ene, DBFphos = 1,8-
Bis(diphenylphosphino)dibenzofuran.
DPPM = 1,1-Bis(diphenylphosphino)methane,
DPPP = 1,3-
BINAP = 2,2’-bis(diphenylphosphino)-
DPPB = 1,4-Bis(diphenylphosphino)butane,
Xant-
a
= [25]
b
Conversion of Cpd determined by GLC.

A. Behr et al. / Journal of Molecular Catalysis A: Chemical 406 (2015) 114–117
117
3.3. Investigation of ligands
mono- and dialdehydes in high yields. Investigations about addi-
tives showed that the NEt3 as co-substrate induced a significant
increase of the cyclopentane carbaldehyde yield. Furthermore, the
influence of the effect of bite angle of diphosphine ligands was
studied. It was possible to steer the reaction selectively producing
aldehydes of Cpd or Dcpd. A systematic screening led to [Rh(OAc)2]2
as the best catalyst with BISBI as ligand giving 68% of cyclopentane
carbaldehyde 3 and 20% of respective dialdehyde species within 3 h
under mild reaction conditions.
Very often the addition of phosphorus (III) ligands improves
the activity and selectivity of transition metal catalysts [23].
Diphosphine ligands possess different bite angles depending on
their structure. The bite angle effect can take a decisive influ-
ence on the coordination on the active site of the catalyst species
[24]. Accordingly, diphosphine ligands with a bite angle of 90◦
preferably occupy the axial-equatorial position while ligands
with a bite angle of 120◦ adopt a bis-equatorial binding mode
on the tetragonal bipyramidal rhodium complex, which takes a
crucial role in the reaction mechanism. We used BISBI (2,2ꢀ-bis-
((diphenylphosphino)-methyl)-1,1ꢀ-biphenyl) to achieve the best
results. We tested also other bidentate ligands with bite angles of
different ranges (Table 2).
According to the results in Table 2 a clear trend of the bite
angle effect of used ligands can be noticed. Diphosphine ligands
with bite angle near 90◦ led to products of Dcpd, involving higher
dimerization rate from Cpd to the dimer during the reaction (runs
2.1–2.5). With BINAP a very selective reaction leading to 50% yield
of monoaldehyde species of Dcpd 5 was observed (run 2.4). Going
to larger bite angle, BISBI gave the best result with 56% of cyclopen-
tane carbaldehyde 3 and 18% yield of respective dialdehyde species
of Cpd 4 (run 2.8). Other diphosphine ligands that have similar bite
angle, Xantphos, NORPHOS and DBFphos, showed strongly reduced
yields on desired products due to the steric bulkiness same as lower
rigidity of the ligand backbone.
Acknowledgments
This work was financially supported by the German Research
Foundation (Deutsche Forschungsgemeinschaft DFG). The authors
would like to thank Umicore AG & Co., KG for the donation of
rhodium catalysts.
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In summary, we have presented the first rhodium-catalyzed
hydroformylation of Cpd leading to the formation of respective