Selective hydroformylation-hydrogenation tandem reaction of isoprene to 3-methylpentanal

Article abstract of DOI:10.1039/c1dt11292a

The hydroformylation of isoprene catalysed by rhodium phosphine complexes usually yields a broad mixture of the monoaldehydes, the isomeric methylpentenals, as well as the dialdehyde 3-methyl-1,6-hexandial. Under usual reaction conditions the products of a consecutive hydrogenation are only formed as minor by-products. Surprisingly we discovered now a selective auto-tandem reaction consisting of a hydroformylation and a hydrogenation step if a rhodium complex with the chelate ligand bis(diphenylphosphino)ethane is used as catalyst. If branched aromatic solvents like cumene are applied the conversion of isoprene is nearly quantitatively and the yield of the tandem product 3-methylpentanal amounts to 85%. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt11292a

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PAPER
Selective hydroformylation-hydrogenation tandem reaction of isoprene to
3-methylpentanal
Arno Behr,* Sebastian Reyer and Nils Tenhumberg
Received 7th July 2011, Accepted 24th August 2011
DOI: 10.1039/c1dt11292a
The hydroformylation of isoprene catalysed by rhodium phosphine complexes usually yields a broad
mixture of the monoaldehydes, the isomeric methylpentenals, as well as the dialdehyde
3-methyl-1,6-hexandial. Under usual reaction conditions the products of a consecutive hydrogenation
are only formed as minor by-products. Surprisingly we discovered now a selective auto-tandem reaction
consisting of a hydroformylation and a hydrogenation step if a rhodium complex with the chelate ligand
bis(diphenylphosphino)ethane is used as catalyst. If branched aromatic solvents like cumene are
applied the conversion of isoprene is nearly quantitatively and the yield of the tandem product
3-methylpentanal amounts to 85%.
prene were used as conjugated dienes, but the reaction often results
1
Introduction
in a complex mixture of unsaturated and saturated, linear and
branched monoaldehydes and dialdehydes. Possible side reactions
are the hydrogenation of the dienes and the unsaturated aldehydes
and the isomerisation of the unsaturated aldehydes. Fell et al.12
showed that for the rhodium catalyzed hydroformylation an excess
(Rh : L = 1 : 30) of a tertiary phosphine is necessary to inhibit the
hydrogenation of the diene and the isomerisation of unsaturated
aldehydes and to enhance the yield of dialdehydes. In 2007, dos
Santos et al.19,20 reported the hydroformylation of isoprene yielding
four unsaturated aldehydes.
Also the asymmetric hydroformylation of conjugated dienes
with (R,S)-BINAPHOS as chiral ligand was reported by Horiuchi
et al.21,22 and with (-)-DIOP by Botteghi et al.23
Isoprene is a very interesting starting compound, because it
is an easily accessible petrochemical, which is obtained as a by-
product in the steamcracking of naphtha to short-chained alkenes.
Today most of the isoprene is used for the production of the
different type’s polyisoprene. Besides, isoprene could be a cheap
base chemical for the production of functional low molecular
compounds.
One interesting low molecular target molecule is the 3-
methylpentanal which is so far produced in industry by hydro-
formylation of methylbutenes thus yielding complex mixtures of
methylpentanals which have to be separated with great technical
effort.24–26 3-Methylpentanal is an odorous substance with an
intensive green and fresh smell.27 It serves, too, as a starting
material for a number of intermediates, e.g. in the synthesis of
tranquilizers.24
In the present contribution, we report the selective
hydroformylation-hydrogenation tandem reaction of isoprene to
3-methylpentanal with special emphasis on the evaluation of the
phosphine ligands, the solvents and the global kinetics.
Hydroformylation of alkenes leads to aldehydes which are im-
portant intermediates in organic synthesis because of their high
reactivity and versatile reactions. Aldehydes are used for the
production of alcohols, carboxylic acids and amines, for the
synthesis of plasticizers, pharmaceuticals, agrochemicals and as
flavors.1 The worldwide production of aldehydes is currently more
than 8.0 ¥ 106 t/a.2
In comparison to the hydroformylation of alkenes the hy-
droformylation of dienes is fundamentally much more difficult.
Depending on the reaction conditions a broad mixture of saturated
and unsaturated monoaldehydes as well as of dialdehydes is
observed.
Especially the hydroformylation of 1,3-dienes is of high interest.
For example a multistage process for the production of adipic
dialdehyde via hydroformylation of 1,3-butadiene has been re-
3
ported by Packet.3 Conjugated dienes, however, form stable h -
allyl-complexes with the catalyst metal, which may inhibit the
reaction. Thus hydroformylation of conjugated dienes usually
occurs much slower than the reaction of alkenes.4 Most notable is
the considerable effect of the substrate on the regioselectivity of
the reaction: The hydroformylation of conjugated dienes occurs
mostly via a formal 1,4-addition and only in a minor part via
1,2-addition. The 1,4-addition was verified by Bertozzi et al.5 via
isotope experiments. Also a density functional study by Beller et
al.6 showed that the 1,4-addition is favored to the 1,2-addition.
Several publications report the hydroformylation of conjugated
dienes proceeding under severe reaction conditions (100–175 ◦C,
200–300 bar).5,7–18 Mainly 1,3-butadiene, 1,3-pentadiene and iso-
Lehrstuhl fu¨r Technische Chemie A, Technische Universita¨t Dortmund,
Emil-Figge Str. 66, Germany. E-mail: behr@bci.tu-dortmund.de; Fax: +49
0231/755-2311; Tel: +49 231/755-2310
11742 | Dalton Trans., 2011, 40, 11742–11747
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Fig. 1 Products of the hydroformylation of isoprene followed by hydrogenation steps.
Reaction control via ligands and solvents
Results and discussion
In the hydroformylation of isoprene the influence of ligands
was investigated especially in view of the regioselectivity of the
reaction. A new reactor concept with a small volume (20 ml)
and small amounts of catalyst and substrate was used to perform
a fast and cost-effective ligand screening.28 High conversions of
isoprene (X > 86%) were observed when using arylphosphines as
ligands (Table 1). If toluene was used as the solvent the yield
of the saturated aldehyde 6 could not be determined because
of peak overlapping in GC. Therefore in later reactions 1,2,4-
trimethylbenzene (TMB) or cumene were used as solvents.
As expected no conversion of isoprene was observed when
the reaction was carried out without any ligand (entry 1). With
triphenylphosphine (entry 3) as the ligand and trimethylbenzene
as the solvent a high conversion (99%) was achieved as already
described by dos Santos et al.19 In our first investigations (entries
2–6) the major products proved to be the E- and the Z-3-methyl-3-
pentenals 2a and 2b, whereas the formation of the a,b unsaturated
aldehydes 3a and 3b was only observed in low yields.
Products and reaction mechanism
The products of the hydroformylation of isoprene 1 are shown
in Fig. 1. The major products are the E- and Z-3-methyl-3-
pentenals 2a and 2b, formed via a formal 1,4-hydroformylation.
The conjugated E- and Z-3-methyl-2-pentenals 3a and 3b are
formed only in lower yields. These unsaturated aldehydes 2 and 3
can be further hydroformylated to a dialdehyde or hydrogenated
to 3-methylpentanal 6. The 1,2-addition product of the hydro-
formylation of isoprene, the 4-methyl-4-pentenal 4, is formed as
well which is partially further hydroformylated to 3-methyl-1,6-
hexandial 5. Further side products in very low yields are the 3-
methylpentanol 7 and the 4-methylpentanal 8 which are formed
by the hydrogenation of the aldehydes 6 and 4, respectively.
2-Methyl-1-butene, 2-methyl-2-butene and 2-methylbutane are
formed only in traces by direct hydrogenation of the isoprene
molecule.
The reaction mechanism of the hydroformylation of isoprene
was proposed by dos Santos et al.19 (Fig. 2). The rhodium catalyst
reacts mainly with the less substituted C–C double bond of
isoprene. n-Alkyl-(D) and iso-alkyl-(A) complexes are formed by
addition of rhodium hydride to isoprene 1. h /h -rearrangement
of A leads to complex C and to a formal 1,4-addition of the
metal hydride to isoprene (Route II). Reaction of C with CO
and H2 forms the b,g-unsaturated aldehydes 2a and 2b and the
a,b-unsaturated aldehydes 3a and 3b. Alternatively, 4-methyl-4-
pentenal 4 is formed by n-hydroformylation via intermediate D
(Route I).
The selectivity to product 4 increased by using diphosphines
with a high bite angle (bn). The best n-selectivity’s to 4 (entries
4–6) were observed when using Xantphos (bn = 111◦), DPEphos
(bn = 102◦) and diphenylphosphinobutane (DPPB) (bn = 98◦) as
ligands (Fig. 3).
1
3
Surprisingly
in
contrast
to
all
other
ligands
bis(diphenylphosphino)ethane (DPPE) formed 3-methylpentanal
6 as a major product with high yield (entry 7, 69%). DPPE
obviously favours the hydrogenation of the unsaturated aldehydes
2 and 3 to the saturated aldehyde 6. Furthermore the small bite
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Fig. 2 Reaction mechanism of isoprene hydroformylation.19
Table 1 Variation of ligands and solvents in isoprene hydroformylationa
Yield [%]
Entry Ligand
bn
Solvent
X [%]
2a
2b
3a
3b
4
5
6
1
2
3
4
5
6
7
8
9
Without ligand
PPh3
PPh3
DPPB
—
—
—
98
102
111
84
84
84
TMB
Toluene
TMB
Toluene
TMB
TMB
TMB
TMB
Cumene
0
0
0
0
2
1
5
0
5
4
2
6
0
1
1
6
0
1
14
9
5
0
8
6
28
31
29
6
4
0
0
9
14
2
3
10
0
0
0
n.d.
5
n.d.
1
7
69
75
85
88
99
83
86
91
93
91
97
24
26
14
17
14
0
40
42
26
29
24
1
DPEphos
Xantphos
DPPE
DPPEb
DPPEb
0
0
0
0
0
a Reaction conditions: isoprene (2.0 mmol); Rh(acac)(CO)2 (0.008 mmol); Rh : P = 1 : 30; toluene or TMB (6 ml); 20 bar (CO : H2 = 1 : 1); 100 ◦C; 24 h;
TMB = 1,2,4-trimethylbenzene; structures of the ligands: see Fig. 3; results in%; n.d. = not determined. b isoprene (30 mmol); Rh(acac)(CO)2 (0.12 mmol);
Rh : P = 1 : 30; TMB (30 ml) or cumene (60 ml); 50 bar (CO : H2 = 1 : 1); 100 ◦C; 24 h.
angle of DPPE (bn = 84◦) favours the formation of the formal
1,4-hydroformylation products.
Performing the reaction with DPPE as ligand in a 300 ml
stainless steel reactor with a higher pressure of 50 bar of CO/H2
instead of 20 bar the yield of aldehyde 6 could be increased to 75%
(entry 8), with cumene as the solvent the yield of aldehyde 6 could
even be increased up to 85% (entry 9).
samples could be drawn during the reaction time of 400 min.
For comparison the kinetic plot of the hydroformylation with the
unselective catalyst rhodium/PPh3 in the solvent trimethylbenzene
(TMB) is shown in Fig. 4.
At the beginning of the reaction the conversion of isoprene and
the yield of aldehydes 2 and 4 rise up quickly. A nearly quantitative
conversion of isoprene is achieved after a reaction time of only 120
min, when the aldehydes 2 and 4 reach an optimum yield.
The three aldehydes 2a, 2b and 4 are the primary products
in this hydroformylation reaction, whereas the a,b-unsaturated
aldehydes 3a, 3b are only formed in negligible amounts and
are therefore not shown in the kinetic plot. After isoprene has
almost completely reacted the formation of derivative products
starts. The yield of the monoaldehyde 4 decreases with continuous
reaction time due to the transformation of the aldehyde 4 into the
dialdehyde 5, thus increasing the yield of dialdehyde 5 up to 18%.
Kinetic investigations
To understand why in the hydroformylation of isoprene with a
rhodium/DPPE catalyst the 3-methylpentanal 6 is formed in high
yields, and why this catalyst is totally different in contrast to
others, the reaction scope of the hydroformylation of isoprene
was investigated in detail with the help of conversion-time-
plots. Reactions were carried out in a pressure reactor where
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Fig. 5 Kinetic plot of the isoprene hydroformylation with the cata-
lyst system rhodium/DPPE. Reaction conditions: isoprene (90 mmol),
Rh(acac)(CO)2 (0.37 mmol), DPPE (5.54 mmol), TMB (90 ml), 50 bar
(CO : H2 = 1 : 1), 100 ◦C.
Fig. 3 Structures of Xantphos, DPEphos, DPPB and DPPE.
We assume that a rapid isomerization of the C–C double bond
takes place on the rhodium/DPPE catalyst because there is no
formation of the b,g-unsaturated aldehyde 2 when using DPPE
as ligand (Fig. 5). The mechanistic proposal for the isomerization
to the conjugated unsaturated aldehyde 3 with DPPE as ligand
is shown in Fig. 6. As already described in Fig. 2 the reaction of
3
the rhodium catalyst I with isoprene leads to the h -complex II.
3
1
h /h -arrangement of II leads to III and to a formal 1,4-addition
of the metal hydride to isoprene. The rhodium complex IV is
formed by subsequent insertion of CO. With PPh3 as ligand the
reaction of IV with H2 forms the b,g-unsaturated aldehyde 2. In
1
3
contrast with DPPE as ligand a h /h -rearrangement of IV occurs
instead of oxidative addition of H2. The complex VI is formed
Fig. 4 Kinetic plot of isoprene hydroformylation with the catalyst system
rhodium/PPh3. Reaction conditions: isoprene (90 mmol), Rh(acac)(CO)2
(0.369 mmol), PPh3 (11.07 mmol), TMB (90 ml), 50 bar (CO : H2 = 1 : 1),
100 ◦C.
The unsaturated aldehydes 2a and 2b are partially hydrogenated
to small amounts of 3-methylpentanal 6.
This kinetic investigation proves that the unsaturated aldehydes
as well as the saturated aldehydes and the dialdehyde are formed
in a consecutive reaction and not simultaneously.
In contrast, totally different results were obtained in the
hydroformylation with the catalyst system rhodium/DPPE, which
is shown in the kinetic plot of Fig. 5.
After a reaction time of 400 min a nearly quantitative conversion
of isoprene is achieved. The major difference in the results with
DPPE and PPh3 is the formation of the saturated aldehyde
6 as major product. The formation of the aldehydes 3a and
3b instead of the aldehydes 2a and 2b is a further essential
difference. Aldehyde 4 is only obtained in low yields, and the
dialdehyde 5 cannot be observed. Thus DPPE favours clearly the
1,4-hydroformylation of isoprene. The formation of the saturated
aldehyde 6 starts already after a short reaction time (30 min), while
using PPh3 as ligand the formation of 6 is only obtained after
long reaction times (180 min). The yield of the a,b-unsaturated
aldehydes 3a and 3b decreases with longer reaction times due to
the hydrogenation to the saturated aldehyde 6.
Fig. 6 Reaction mechanism proposal for the hydroformylation of iso-
prene via isomerizing allyl intermediates.
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Table 2 Starting compounds and typical reaction conditions for the
hydroformylation-hydrogenation tandem reaction of isoprene using the
catalyst system rhodium/DPPE
via the allyl-acyl-complex V. Addition of H2 to VI leads to the
a,b-unsaturated aldehydes 3, which were fast hydrogenated to the
saturated aldehyde 6.
To our knowledge this selective hydroformylation-
hydrogenation tandem reaction of isoprene to 3-methylpentanal 6
with the catalytic system rhodium/DPPE has not been described
before. Our catalytic study and kinetic investigations clearly show
that the saturated 3-methylpentanal 6 is formed in high yields
up to 85% with rhodium/DPPE as catalyst via the conjugated
unsaturated aldehydes 3a and 3b.
Amount/ Mass/
Compounds
mmol
g
Reaction conditions
Temperature
Syngas (CO : H2) = 1 : 1 50 bar
Reaction time
Isoprene
Cumene
30.00
215.16
Rh(acac)(CO)2 0.12
DPPE 3.60
2.43
25.86
0.03
100 ◦
C
400 min
60 ml
0.245
Volume of liquid
Using the standard Schlenk-technique oxidation of the sub-
strates was prevented. This involved glass vessels and the reactor
being evacuated and purged with argon. For description of the
“multiplex reactor” see ref. 28.
In a typical reaction the following quantities of the starting
compounds and the reaction conditions are shown in Table 2. All
results were reproduced several times
Conclusions
The hydroformylation of isoprene with different catalyst systems
was investigated in detail. A study of the influence of the
ligand in different solvents showed that hydroformylation with
the classic catalytic system rhodium/PPh3 yields preferentially
the monoaldehydes 2 and 4 which convert at longer reaction
times to the dialdehyde 5 and only in small amounts to the
hydrogenated product 6. The catalytic system rhodium/DPPE,
however, achieved surprisingly high yields of the target aldehyde
6 up to 85%, which could be explained by a different mechanistic
pathway.
To sum up an efficient hydroformylation of isoprene under mild
reactions conditions and with a nearly quantitative conversion
could be performed. The cheap starting compound isoprene
proved to be a very promising starting compound for the one-
step synthesis of 3-methylpentanal 6.
Analytics
The product samples were analyzed by GC-FID (HP 6890 with a
HP-5 column 30 m ¥ 0.25 mm ¥ 0.25 mm) using a flame ionization
detector. As internal standard di-n-butyl ether was used. The
preparative GC was performed with the same instrument.
GC-MS analyses were carried out on a Hewlett-Packard 5973
(HP-5 column, 30 m ¥ 0.25 mm ¥ 0.25 mm) with an ionization
energy of 70 eV.
3-Methylpentanal 6 was isolated by preparative GC and identi-
fied by NMR and MS: 1H-NMR (400 MHz, CDCl3) d = 0.89 (t,
3H, CH2-CH3), 0.95 (t, 3H, CH-CH3), 1.26 (hex., 1H, CH2-CH3),
1.37 (hex., 1H, CH2-CH3), 1.88 (hex., 1H, CH-CH3), 2.11–2.16
(dd, 1H, CH2-C(O)H), 2.32–2.37 (dd, 1H, CH2-C(O)H), 9.75 (t,
1H, C(O)H); 13C-NMR (100 MHz, CDCl3): d = 11.9; 19.9; 29.9;
32.4; 41.9; 180.5; m/z 100 (M+, >0.5%), 82 (2), 71 (15), 67 (4), 56
(100), 53 (6), 51 (3), 43 (45), 41 (78), 39 (36).
Experimental
Chemicals
Acetylacetonatodicarbonylrhodium(I) was donated by Umicore
AG & Co. KG. Isoprene (purity 99+%), triphenylphosphine (pu-
rity 99%), 1,2-bis(diphenylphosphino)ethane (purity 98+%), 1,2-
bis(diphenylphosphino)butane (purity 98%), Xantphos (purity
98%), DPEphos (purity 99%), toluene (purity 99+%) cumene (pu-
rity 99%) and 1,2,4-trimethylbenzene (purity 98%) were purchased
from Acros. Syngas (CO : H2 = 1 : 1; purity 1.8 : 3.0) was acquired
from BASF.
4-Methylpent-4-enal 4 was isolated as a mixture with 3-
methylpent-3-enal by preparative GC and identified by 1H-NMR
and MS: 1H-NMR (400 MHz, CDCl3): d = 1.62 (s, 3H, C-CH3),
2.28–2.30 (m, 2H, C(O)H-CH2), 2.54 (t, 2H, C-CH2), 9.54 (dt,
1H, C(O)H); m/z 98 (M+, 3%), 83 (18), 79 (9), 77 (2), 70 (54), 69
(35), 67 (7), 55 (68), 53 (24), 41 (100), 39 (81).
(E)/(Z)-3-Methylpent-3-enal 2a,b was isolated as a mixture
with 4-methylpent-4-enal by preparative GC and identified by
Instrumental
1
The kinetic investigations were performed in a 300 ml pressure
vessel, model 4561 (Parr instrument). The reactor consists of a
steel bomb and a steel cover, which includes the armatures for
filling and regulation. The reactor is certified for temperatures up
to a maximum of 350 ◦C and pressures up to 207 bar, whereby
exceeding of the maximum pressure is prevented by a breaker
plate. The system pressure can be read off a manometer attached
to the reactor cover. The heating of the reactor up to the desired
reaction temperature takes place using an electrical steam jacket.
The temperature was measured by a thermocouple, which is
attached to a PID automatic controller (Parr type 4842). Stirring
was performed using a standard turbine impeller. The samples
for the kinetic investigation were drawn with a closable capillary,
which was attached on the reactor cover. Small samples (0.5–1 ml
of the reaction solution) could be drawn during the reaction time
of 400 min. The samples were cooled and then analyzed by GC.
1H-NMR and MS: H-NMR (400 MHz, CDCl3): d = 1.56 (t,
3H, CH-CH3), 1.70 (t, 3H, C-CH3), 3.60 (m, 2H, C-CH2-C(O)H),
9.72 (m, 1H, C(O)H); m/z 98 (M+, 16%), 83 (16), 80 (5), 70 (14),
69 (33), 67 (7), 55 (40), 53 (20), 51 (10), 41 (100), 39 (52).
(E)-3-Methylpent-2-enal 3a was isolated by column chromatog-
raphy (silica, ethyl acetate–cyclohexene = 3 : 1) as a mixture with
1
1
Z-3-methylpent-2-enal and identified by H-NMR and MS: H-
NMR (500 MHz, CDCl3): d = 1.13 (t, 3H, CH2-CH3), 1.92 (s, 3H,
C-CH3), 2.56 (q, 2H, CH2-CH3), 5.80 (d, 1H, CH-C(O)H), 9.93
(d, 1H, C(O)H); m/z 98 (M+, 82%), 83 (11), 79 (6), 69 (37), 67
(12), 65 (5), 63 (4), 57 (13), 55 (70), 53 (22), 51 (15), 50 (11), 41
(100), 39 (62).
(Z)-3-Methylpent-2-enal 3b was isolated by column chromatog-
raphy (silica, ethyl acetate–cyclohexene = 3 : 1) as a mixture with
1
1
E-3-methylpent-2-enal and identified by H-NMR and MS: H-
NMR (500 MHz, CDCl3): d = 1.07 (t, 3H, CH2-CH3), 1.71 (s, 3H,
11746 | Dalton Trans., 2011, 40, 11742–11747
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C-CH3), 2.20 (q, 2H, CH2-CH3), 5.85 (d, 1H, CH-C(O)H), 9.97
(d, 1H, C(O)H); m/z 98 (M+, 82%), 83 (11), 79 (6), 69 (37), 67
(12), 65 (5), 63 (4), 57 (13), 55 (70), 53 (22), 51 (15), 50 (11), 41
(100), 39 (62).
6 M. Beller, Y. W. Li, C. F. Huo and H. Jiao, Organometallics, 2005, 24,
3634–3643.
7 Eur. Pat., EP 0033554 A2, 1981.
8 P. W. N. M. van Leeuwen and C. F. Roobeck, J. Mol. Catal., 1985, 31,
345–353.
9 Y. Ohgomori, N. Suzuki and N. Sumitani, J. Mol. Catal. A: Chem.,
3-Methylhexan-1,6-dial 5 was identified by comparison of the
retention time in the gas chromatogram with a synthesized sample.
It was synthesized from 4-methylcyclohexene, which was first
converted with potassium permanganate to the 1,2-diol followed
by the cleavage with sodium periodate.29,30 1H-NMR (500 MHz,
CDCl3): d = 1.65 (m, 2H, CH2-CH2-C(O)H), 2.32 (m, 2H, -CH-
CH2-C(O)H), 2.44 (t, 2H, CH2-CH2-C(O)H), 9.58 (t, 1H, C(O)H),
9.73 (t, 1H, C(O)H); 13C-NMR (100 MHz, CDCl3): d = 13.2; 19.3;
26.6; 43.6; 46.0; 201.9; 204.5; m/z: 128 (M+, >0.5%), 110 (2), 96
(2), 84 (24), 82 (16), 81 (19), 70 (50), 67 (28), 58 (55), 57 (100), 53
(18), 51 (7), 43 (70), 41 (99), 39 (80), 31 (8).
1998, 133, 289–291.
10 B. Fell and H. Bahrmann, J. Mol. Catal., 1977, 2, 211–218.
11 B. Fell and H. Bahrmann, J. Mol. Catal., 1980, 8, 329–337.
12 B. Fell and W. Boll, Chemiker-Zeitung, 1975, 99, 452–458.
13 B. Fell, W. Boll and J. Hagen, Chemiker-Zeitung, 1975, 99, 485–
492.
14 B. Fell and B. Falk, J. Mol. Catal., 1983, 18, 127–134.
15 B. Fell, J. Hagen and W. Rupilius, Chemiker-Zeitung, 1976, 100, 308–
312.
16 B. Fell and W. Hermanns, J. Prakt. Chem., 1998, 340, 459–467.
17 B. Fell and W. Meltzow, J. Mol. Catal., 1985, 31, 93–106.
18 B. Fell and W. Rupilius, Tetrahedron Lett., 1969, 10, 2721–2723.
19 H. J. V. Barros, E. N. dos Santos, C. C. Guimaraes and E. V. Gusevskaya,
Organometallics, 2007, 26, 2211–2218.
20 H. J. V. Barros, C. C. Guimaraes, E. N. dos Santos and E. V. Gusevskaya,
Catal. Commun., 2007, 8, 747–750.
21 T. Horiuchi, T. Ohta, K. Nozaki, H. Takaya and E. Shirakawa,
Tetrahedron, 1997, 53, 7795–7804.
22 T. Horiuchi, T. Ohta, H. Takaya and K. Nozaki, Chem. Commun.,
1996, 155–156.
Acknowledgements
The authors would like to thank Umicore AG & Co. KG,
especially Dr. Ralf Karch, for providing the rhodium catalyst,
Rh(acac)(CO)2.
23 C. Botteghi, M. Branca and A. Saba, J. Organomet. Chem., 1980, 184,
17–19.
24 German Pat., DE 2933919, 1979.
Notes and references
25 United States Pat., US 4317945, 1982.
26 Eur. Pat., EP 0335221 A2, 1989.
1 C. W. Kohlpainter, M. Schulte, J. Falbe, P. Lappe and J. Weber, in Ull-
mann’s Encyclopedia of Industrial Chemistry, Wiley–VCH, Weinheim,
7 edn, 2005.
2 A. Behr, Angewandte homogene Katalyse, Wiley–VCH, Weinheim,
2008.
27 D. Bartschat and A. Mosandl, Z. Lebensm.–Unters.–Forsch., 1998, 206,
4.
28 A. Behr, G. Henze, L. Johnen and S. Reyer, J. Mol. Catal. A: Chem.,
2008, 287, 95–101.
29 P. M. Hardy, A. C. Nicholls and H. N. Rydon, J. Chem. Soc., Perkin
Trans. 2, 1972, 2270.
30 W. P. Weber and J. P. Shepherd, Tetrahedron Lett., 1972, 13, 4907–
4908.
3 Eur. Pat., EP 0577042 A1, 1994.
4 G. Liu and M. Garland, J. Organomet. Chem., 2000, 608, 76–85.
5 S. Bertozzi, N. Campigli, G. Vitulli, R. Lazzaroni and P. Salvadori, J.
Organomet. Chem., 1995, 487, 41–45.
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