Iron oxide catalyzed reduction of acid chlorides to aldehydes with hydrosilanes

Article abstract of DOI:10.1016/j.catcom.2014.02.018

Iron-catalyzed reduction of acid chlorides to the corresponding aldehydes with a hydrosilane as a reducing agent has been developed. A simple mixture of a commercially available iron oxide (FeO) and tris(2,4,6-trimethoxyphenyl) phosphine (TMPP) as a catalyst realized the reduction of acid chlorides to the corresponding aldehydes under mild reaction conditions.

Full text of DOI:10.1016/j.catcom.2014.02.018

Catalysis Communications 50 (2014) 25–28
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Iron oxide catalyzed reduction of acid chlorides to aldehydes
with hydrosilanes
Cong Cong, Tetsuaki Fujihara, Jun Terao, Yasushi Tsuji ⁎
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Iron-catalyzed reduction of acid chlorides to the corresponding aldehydes with a hydrosilane as a reducing agent has
been developed. A simple mixture of a commercially available iron oxide (FeO) and tris(2,4,6-trimethoxyphenyl)
phosphine (TMPP) as a catalyst realized the reduction of acid chlorides to the corresponding aldehydes under
mild reaction conditions.
Received 28 December 2013
Received in revised form 18 February 2014
Accepted 19 February 2014
Available online 27 February 2014
©
2014 Elsevier B.V. All rights reserved.
Keywords:
Acid chlorides
Aldehydes
Hydrosilanes
Iron oxide
Reduction
1
. Introduction
anhydride and hydrosilane [14]. Although these were good catalytic
reactions, complexes of precious metals such as ruthenium and palladium
must be used.
Acid chlorides are utilized as promising substrates in various organic
reactions with transition-metal catalysts [1–5] because the oxidative
addition of (acyl) carbon–chlorine bond to a low-valent metal center
smoothly occurs [6]. Recently, we have reported iridium-catalyzed
addition reaction of acid chlorides to terminal alkynes [7,8]. Importantly,
aliphatic acid chlorides as well as aroyl chlorides could be used in the
addition reaction with suppression of decarbonylation and β-hydrogen
elimination which have been two major intrinsic problems in
transition-metal-catalyzed reactions [8]. We also found the palladium-
catalyzed reactions of acid chlorides with hydrosilanes in the presence
of allenes, giving α,β-unsaturated ketones regio- and stereoselectively [9].
The reduction of acid chlorides to aldehydes is one of the important
methods to afford aldehydes. The transformation with molecular hydro-
Recently, much attention has been paid to iron catalysts since iron is
one of the most abundant metals on the earth. Efficient iron-catalyzed
transformations including carbon–carbon bond forming reactions
have been developed to date [15–19]. Regarding iron-catalyzed reduc-
tive transformations [20–31], iron complexes were found to be active
for reductions of carbonyl compounds such as aldehydes [20,21],
ketones [20,21], and amides [22]. However, some iron complexes must
be prepared before use and they might be unstable for further handling
[20,21]. Therefore, iron-catalyzed transformation by the use of simple
and commercially available catalyst precursors or in situ generated
system is highly desired.
In the present study, we report that acid chlorides can be reduced to
the corresponding aldehydes employing hydrosilane as a reducing
agent in the presence of a catalytic amount of iron oxide (FeO) (99.9%
4
gen over supported heterogeneous palladium catalysts (Pd/BaSO ) is
well-known as the Rosenmund reduction [10]. However, in the reac-
tion, the uptake of hydrogen must be monitored to avoid the over
reduction. Homogeneous transition-metal catalyzed reductions of acid
chlorides to the corresponding aldehydes have been also developed
employing palladium [11] or ruthenium [12] as catalysts. Recently, we
have reported a very efficient method of aldehydes synthesis from
acid chlorides employing palladium catalysis and hydrosilane, which
is stable, easy-to-handle and efficient reducing reagents [13]. Further-
more, we also developed the palladium-catalyzed reduction of carbox-
ylic acids to the corresponding aldehydes in the presence of pivalic
2 3
purity). Iron oxides such as FeO or Fe O are known as catalysts in
dehydrogenation reaction [32], Fenton reaction [33], or Fischer–Tropsch
reaction [34]. However, to the best of our knowledge, there has been
no precedent for the iron-catalyzed reduction of acid chlorides to
aldehydes.
2. Experimental
2.1. General procedure
All manipulations were performed under an argon atmosphere
using standard Schlenk-type glassware on a dual-manifold Schlenk
⁎
Corresponding author. Tel.: +81 75 383 2515; fax: +81 75 383 2514.
E-mail address: ytsuji@scl.kyoto-u.ac.jp (Y. Tsuji).
http://dx.doi.org/10.1016/j.catcom.2014.02.018
566-7367/© 2014 Elsevier B.V. All rights reserved.
1

26
C. Cong et al. / Catalysis Communications 50 (2014) 25–28
Table 1
a
Effect of iron precursors, ligands and hydrosilanes on the reduction of 3-phenylpropionyl chloride (1a).
Entry
Fe precursor
Ligand
Hydrosilane
Conv. of 1a (%)b
Yield of 2a (%)b
1
2
3
4
5
6
7
8
9
FeO
None
TMPP
TMPP
TMPP
TMPP
TMPP
TMPP
None
H
H
3
3
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
SiPh
93
31
83
26
33
53
39
11
32
34
91
13
62
24
34
42
46
89
57 (50)c
4
43
2
5
3
7
2
15
21
28
1
33
5
Fe
FeCl
FeF
2
O
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
2
2
Fe(acac)
FeO
FeO
FeO
FeO
FeO
FeO
FeO
FeO
FeO
FeO
FeO
FeO
2
PPh
P[2,6-(MeO)
P(o-MeOC
P(p-MeOC
P(Mes)
PCy
3
2
C
6
H ]
3 3
10
11
12
13
14
15
16
17
18
6 4 3
H )
H )
6 4 3
3
3
TMPP
TMPP
TMPP
TMPP
TMPP
HSiMePh
HSi(OEt)
2
3
2
H
H
2
SiMePh
SiPh
14
13
4
2
2
PMHS
a
Reaction conditions: Fe precursor(0.050 mmol, 20 mol%), ligand(0.013 mmol, 5.0 mol%) and hydrosilane(0.28 mmol) at 60 °C for 20 h, then, 1a (0.25 mmol) and toluene (0.50 mL) at
6
0 °C for 20 h.
b
c
Determined by GC analysis based on the internal standard technique.
Isolated yield of 2a.
line. Unless otherwise noted, materials obtained from commercial sup-
3. Results and discussion
pliers were used without further purification. THF and toluene were
1
dried and purified before use by usual methods [35]. H NMR spectra
To study activity of an iron catalyst system, we carried out reduc-
tion of 3-phenylpropionyl chloride (1a) as a model reaction.
When all these materials including FeO, ligand, hydrosilane and 1a
were mixed all at once, 2a was obtained only in moderate yields
with poor reproducibility. Thus, a mixture of FeO, tris(2,4,6-
1
were measured with a JEOL ECX-400P spectrometer. The H NMR chem-
ical shifts are reported relative to tetramethylsilane (TMS, 0.00 ppm). The
C NMR chemical shifts are reported relative to CDCl (77.0 ppm). GC
3
13
analysis was carried out using Shimadzu GC-17A equipped with an inte-
grator (C-R8A) with a capillary column (CBP-1, 0.25 mm i.d. × 25 m).
Matrix-assisted laser desorption/ionization time-of-flight (MALDI-
TOF) mass spectra were acquired on a SHIMADZU AXIMA-CFR Plus
or a Bruker Autoflex using α-cyano-4-hydroxycinnamic acid as a
matrix and NaTFA as a cationization reagent. Medium-pressure
column chromatography was performed with a Biotage IsoleraOne.
Column chromatography was carried out on silica gel (Kanto N60,
spherical, neutral, 63–210 μm). TLC analyses were performed on
commercial glass plates bearing a 0.25-mm layer of Merck Silica gel
3
trimethoxyphenyl)phosphine (TMPP), and H SiPh was stirred at
60 °C for 20 h. Then, toluene and 1a were added, and the resulting
mixture was further stirred at 60 °C for 20 h. Under the reaction con-
ditions, 3-phenylpropanal (2a) was obtained in 57% yield (entry 1).
In the reaction mixture, 3-phenylpropionic acid was detected and
its yield was determined as 32% by the GC internal standard method
after derivatization to the corresponding methyl ester. This observa-
tion was in contrast to the palladium catalyzed reductions of acid chlo-
rides [13], in which no carboxylic acids were formed. Without FeO, the
conversion of 1a was very low, and 2a was obtained in only 4% yield
(entry 2). Next, various iron precursors in place of FeO were employed.
6
0F254. Iron oxide (FeO, 99.9% purity) was purchased from Aldrich
and used without further purification.
The reaction with Fe
other soluble iron precursors such as FeCl
effective (entries 4–6). Without phosphine, the yield of 2a considerably
decreased (entry 7). Triphenylphosphine (PPh ) was not efficient at all
2
O
3
also afforded 2a in 43% yield (entry 3), while
2
, FeF and Fe(acac) were not
2
2
2
.2. Catalytic reaction
3
A typical procedure for the iron oxide catalyzed reduction of 3-
phenylpropionyl chloride (1a) with H SiPh (Table 1, entry 1): iron
3
oxide (3.6 mg, 0.050 mmol) and TMPP (6.7 mg, 0.013 mmol) were
added to a 10 mL Schlenk flask with a magnetic stir bar. The flask was
(entry 8). The reaction employing triarylphosphines with electron donat-
ing substituents afforded 2a in moderate yields (entries 9–11). Other
bulky phosphines such as tris(2,4,6-trimethylphenyl)phosphine and
tricyclohexylphosphine afforded the product in low yields (entries
12 and 13). Thus, the addition of a catalytic amount of a phosphine
evacuated and backfilled with argon three times. Then, H
3
SiPh (34 μL,
0
.28 mmol) was added to the flask and the reaction mixture was stirred
affects the activity considerably. As for a hydrosilane, HSiMePh
HSi(OEt) , H SiMePh, H SiPh , and PMHS (polymethylhydrosiloxane)
were less effective than H SiPh (entries 14–18 vs entry 1). As a solvent,
2
,
at 60 °C for 20 h under an argon atmosphere. Then, toluene (0.50 mL)
was added to the flask and the resultant solution was stirred at room
temperature for 5 min before 1a (37 μL, 0.25 mmol) was loaded. Further,
the reaction mixture was stirred at 60 °C for 20 h under an argon atmo-
sphere. After cooling to room temperature, the reaction mixture was
diluted with diethyl ether (5.0 mL) and tetradecane (50 μL, 0.19 mmol)
as an internal standard was added. The yield of 3-phenylpropanal (2a;
3
2
2
2
3
the reaction in THF under otherwise the same reaction conditions as
entry 1 afforded 2a in 40% yield. Regarding catalyst loadings, we carried
out the reactions in the presence of 10 mol%, 5 mol%, and 1 mol% of
FeO (the ratio of FeO:TMPP was kept in 4:1), and in these reactions 2a
was afforded in 49%, 19%, and 21% yields, respectively. In addition, the
ratio between FeO and TMPP (4:1) was changed to 2:1, 1:1, and 1:2. As
a result, the yield of 2a was reduced to 50%, 40%, and 17% yields,
respectively (Table S1, in the Supplementary data).
5
7%) was analyzed by gas chromatography. 2a was isolated by silica
gel column chromatography (hexane: EtOAc = 13: 1). Pale yellow oil
16.8 mg) was obtained in 50% yield.
(

C. Cong et al. / Catalysis Communications 50 (2014) 25–28
27
Various acid chlorides were reduced with H
3
SiPh in the presence
of FeO/TMPP catalyst system (Table 2). 3-Arylpropionyl chlorides
with different substituents (4-Me, 4-OMe, 4-Cl, 4-CF , and 3-F)
1b–f) afforded the corresponding aldehydes (2b–f) in moderate
3
(
yields (entries 1–5). Aliphatic acid chlorides such as 1g and 1h
were also converted to the corresponding product (entries 6 and 7).
Even sterically congested acyl chlorides such as 1i and 1j gave the prod-
ucts at higher reaction temperatures (entries 8 and 9). An acid chloride
with an alkenyl moiety (1k) also afforded the corresponding aldehyde
Scheme 1. Filtration test.
(
2k) in 40% yield (entry 10). Although we examined the substrates
including MALDI-TOF MASS and X-ray crystallographic analysis to char-
acterize active species were failed.
with other functional groups such as ester, cyano, and nitro groups,
the corresponding aldehydes were obtained only in trace yields. Un-
fortunately, aroyl chlorides (i.e., aromatic acid chlorides such as
benzoyl chloride) could not be employed as substrates due to their
low reactivities.
4. Conclusion
To gain some insight into catalytically active species, a reaction
mixture of FeO, TMPP and H SiPh was stirred at 60 °C for 20 h.
3
After adding toluene, the mixture was filtered through a 0.2 μm
membrane (13P, GL Science). Then, 1a was added to a resulting
pale yellow filtrate and the mixture was further stirred at 60 °C
In conclusion, we found that the iron-catalyzed reduction of acid
chlorides employing hydrosilane as a reducing agent has been developed.
A simple mixture of a commercially available and easy-to-handle iron
oxide (FeO) and 2,4,6-trimethoxyphenylphosphine (TMPP) was found
to be a good catalyst. Further application to reductive transformations
and elucidation of the reaction mechanisms is now in progress.
(
Scheme 1). As a result, 2a was obtained in 43% yield with 90% con-
version of 1a. Under the reaction conditions, carboxylic acid was de-
tected as a side product. In addition, the separated dark brown solid
was employed as the catalyst in the reaction of 1a. In the reaction, a
trace of 2a was obtained with the low conversion of 1a (18%). The result
may suggest that some soluble iron species would be responsible for the
present catalytic reaction. Unfortunately, various measurements
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.02.018.
Table 2
a
Iron oxide catalyzed reduction of acid chlorides.
Entry
1
Acid chlorides (1)
Temperature(°C)
60
Aldehydes (2)
Yield (%)b
45
(
64)
1
b
2b
2c
2
3
60
60
44
(
58)
1
c
44
(
56)
1
d
2d
2e
4
5
60
60
58
(
68)
1
e
53
(
68)
1f
2f
6
7
8
60
36
(40)
1
g
2g
80
(47)
(42)
1
h
2h
100
1
i
2i
9
120
60
(41)
1
j
2j
10
40
1k
2k
(52)
a
3
Reaction conditions: FeO (0.050 mmol, 20 mol%), TMPP (0.013 mmol, 5.0 mol%) and H SiPh (0.28 mmol) at 60 °C for 20 h, then, 1 (0.25 mmol) and toluene (0.50 mL) at 60–120 °C for
2
0 h.
b
Isolated yield of 2. Value in parenthesis showed GC yield based on the internal standard technique.

28
C. Cong et al. / Catalysis Communications 50 (2014) 25–28
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