A novel gold-catalyzed chemoselective reduction of α,β- unsaturated aldehydes using CO and H2O as the hydrogen source

Article abstract of DOI:10.1039/b922662a

Chemoselective reduction of α,β-unsaturated aldehydes in the presence of CO and H₂O proceeds effectively over a ceria-supported gold catalyst system, providing a novel, efficient and clean approach to produce useful primary allyl alcohols with excellent activity and selectivity. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b922662a

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
A novel gold-catalyzed chemoselective reduction of a,b-unsaturated
aldehydes using CO and H O as the hydrogen sourcew
2
Lin He,z Feng-Jiao Yu,z Xia-Bing Lou, Yong Cao,* He-Yong He and Kang-Nian Fan
Received (in Cambridge, UK) 29th October 2009, Accepted 15th January 2010
First published as an Advance Article on the web 28th January 2010
DOI: 10.1039/b922662a
Chemoselective reduction of a,b-unsaturated aldehydes in the
presence of CO and H O proceeds effectively over a ceria-
2
high purity H for a number of technological applications, it is
2
conceivable that a combination of the direct hydrogenation
and WGS reaction over supported gold may provide an
attractive alternative for more efficient green reductions. Very
recently, we have described a highly effective gold-catalyzed,
CO/H O-mediated reduction that bypasses inconvenient H
supported gold catalyst system, providing a novel, efficient and
clean approach to produce useful primary allyl alcohols with
excellent activity and selectivity.
2
2
Recent state-of-the-art research in organic chemistry requires
the design of ultraselective catalytic systems for the production
1
of fine chemical and pharmaceutical intermediates. In this
activation to enable the rapid, efficient, and chemoselective
reduction of a wide range of organic nitro compounds under
10
very mild conditions. Herein, we demonstrate for the first
context, the chemoselective reduction of a,b-unsaturated
aldehydes to the corresponding unsaturated alcohols, an
important step in the industrial synthesis of fine chemicals, is
a long-standing scientific and technological challenge in
time that gold supported on ceria can catalyze the reduction of
a,b-unsaturated aldehydes to the corresponding unsaturated
alcohols in high yields in the presence of CO and H
Compared with those conventional catalytic hydrogenation
processes, the present Au-catalyzed CO/H O-mediated reduction
2
O.
2
heterogeneous catalysis. It is well known that classical
hydrogenation metal catalysts (Pt, Pd, Ru, Rh etc.) show no
2
system has the following significant advantages: (i) unprece-
dented high chemoselectivity and high yields in the reduction
of a,b-unsaturated aldehydes; (ii) mild conditions; and
(iii) without the direct use of molecular hydrogen.
or low selectivity towards the specific hydrogenation of the
3
CQO bond. Therefore, great efforts have been made to
overcome this problem over the past decades, including
introducing special additives (promoters or inhibitors),
modifying the active metal with a second metal component,
Initially, crotonaldehyde (CAL) was chosen as a model
substrate to study the catalytic activity of the various catalysts
under 5 atmospheres of CO in water. The most salient feature
in Table 1 is the high chemoselectivity attained using
supported gold nanoparticles as catalysts for the production
of crotyl alcohol (CROL) (Table 1, entries 1–3), conditions
under which the Pt, Pd, and Ru catalysts, previously known
3b,4
or tuning the particle sizes of the catalysts.
Although these
modified systems are effective, catalyst preparation often
remains critical, and the amount of the modifying agent
4
must be precisely controlled. Alternative economical and
eco-friendly heterogeneous reduction protocols that would
ensure the preferred hydrogenation of the CQO group versus
CQC is highly desirable.
1
1
for their high hydrogenation activity, were totally ineffective
(Table 1, entries 5–7). In all cases, the main by-products
(butanal (BAL) and butanol (BOL)) did not exceed 15% with
no detectable amount of other side products. Among the
Supported gold nanoparticles have recently emerged as
active and selective catalysts for a broad array of organic
5
transformations including chemoselective reduction of un-
catalysts examined, Au deposited on CeO
Au/CeO , see details in the ESIw) showed the highest activity
and selectivity (Table 1, entry 1). Thus, using CO and H O as
the reductant, complete reduction of CAL occurred in 5 h over
Au/CeO . Remarkably, an excellent yield up to ca. 82% can be
2
(denoted as
6
saturated carbonyl compounds by molecular hydrogen. The
2
2c,7
8
and Claus et al. have
pioneering works by Hutchings et al.
2
shown that supported gold nanoparticles are highly selective
for the hydrogenation of the conjugated CQO bond, reaching
in some cases exceptionally high values of selectivity towards
the unsaturated alcohol. One critical limitation associated with
the current Au-catalyzed hydrogenation process, however, is the
unfavorably low hydrogen-delivery capacity compared to
2
achieved for CROL production, in stark contrast to the poor
selectivity (o30%) as reported for catalytic liquid phase CAL
1
2
hydrogenation (10 atm H
) by gold supported on CeO
.
Of
2
2
particular note is that the reaction can proceed efficiently even
at atmospheric pressure (Table 1, entry 8), which permits the
use of common glass reactors thus eliminating the need for a
specialized apparatus. No conversion was found in the absence
5
e,6a
the conventional hydrogenation metals.
In view of the
excellent performance of supported gold for low temperature
9
2 2 2
water–gas shift (WGS) reaction (CO + H OQCO + H ,
generally in the temperature range of 150–250 1C) to produce
2
of catalysts or in the presence of Au-free CeO catalyst under
identical conditions (entry 4), illustrating that the presence of
gold was indispensable for high catalytic activity of the titled
reaction.
Shanghai Key Laboratory of Molecular Catalysis and Innovative
Materials, Department of Chemistry, Fudan University,
Shanghai 200433, P. R. China. E-mail: yongcao@fudan.edu.cn;
Fax: (+86-21)65643774
w Electronic supplementary information (ESI) available: Experimental
section, TEM and XPS data. See DOI: 10.1039/b922662a
z These authors contributed equally to this work.
2
The Au/CeO catalyst was stable and can be easily reused in
the CO-induced reduction of CAL. After the first CAL
reduction under the conditions in entry 1 of Table 1, the
catalyst was separated from the reaction mixture by filtration,
This journal is ꢀc The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 1553–1555 | 1553

View Article Online
Table 1 Catalytic performance of various catalysts for the reduction
Table 2 Reduction of a,b-unsaturated aldehydes to unsaturated
a
a
of crotonaldehyde by CO/H
2
O
alcohols by CO/H
2
O
b,e
Sel. (%)
b
c
t/h Con. (%) Sel. (%)
Entry Substrates
e
Entry Catalyst
P
CO (atm) t/h Conv. (%) CROL BAL BOL
1
2
CH
3
3
CHQCHCHO
0.5 50
.5 96
88
85 (84)
4
1
2
3
4
5
6
7
8
9
Au/CeO
Au/TiO
Au/Fe
CeO
2
5
5
5
5
5
5
5
1
5
4.5 96
4.5 67
85
87
88
—
—
—
—
84
85
4
5
11
8
2
—
—
—
—
13
10
c
c
2
CH
CH
CHQC(CH
)CHO 0.5 28
.5 95
91
84
2
3
2
O
3
4.5
9
10
—
—
—
—
3
7
2
4.5 n.r.
4.5 n.r.
4.5 n.r.
4.5 n.r.
11 94
c
c
c
2
Ru/Al O
3
b
b
b
0.5 36
96
94
90
Pd/C
Pt/CeO
3
4
5
6
2
Au/CeO
Au/CeO
2
d
2
4.5 91
5
0.5 31
7 90
90
84
a
Reaction conditions: 1 mmol substrate, 2.8 mol% metal, 20 mL
b
H O, 96 1C. CROL: crotyl alcohol, BAL: butanal, BOL: butanol.
2
c
Au/TiO , Au/Fe
2
2
O
3
provided by the World Gold Council. Pt/CeO
2
,
0.5 42
94
95
93 (92)
prepared by wet impregnation. Pd/C, Ru/Al
d
Aesar. Results for the third run. Conversion and selectivity were
determined by GC and GC-MS. n.r. = no reaction.
2 3
O
provided by Alfa
5
e
a
Reaction conditions: 1 mmol substrate, Au/CeO
b
2
(Au: 2.8 mol%),
2
2 2
0 mL H O, 96 1C, 5 atm CO. 1 mmol substrate, Au/CeO
13
(
Au: 2.8 mol%), 10 mL H
2
O, 10 mL EtOH, 96 1C, 5 atm CO.
Conversion and selectivity were determined by GC and GC-MS.
Numbers in parenthesis refer to selectivity of isolated products.
c
thoroughly washed with acetone then water, and reused for
the next run under the same conditions. The catalytic results
indicate that there is no appreciatable loss in either activity or
selectivity between the first and third runs (Table 1, entries 1
and 9). This was also consistent with the characterization
results for this catalyst. TEM and XPS results (Fig. S1, S2
and S3 in ESIw) showed essentially no changes, after three
successive runs in the mean diameters of the Au nanoparticles
or metallic state of Au, respectively. Moreover, it was
confirmed by ICP that the Au content of the reused
9
a,14
often the catalyst of choice for the latter process.
it is worth noting that a stoichiometric amount of CO (1 mol
However,
2
of CO uptake per mole of substrate conversion) without
accompanying H2 was formed at the end of the reduction.
In addition, control experiments in the absence of aldehydes
indicated that the independent low temperature WGS could
not be ignited under the experimental conditions as employed
in this work. Moreover, when molecular hydrogen was applied
instead of CO, a significantly decreased reduction rate and
selectivity were identified for CAL reduction with Au/CeO2
(see Fig. 1). Therefore, the seemingly simple and straight-
forward reduction of the aldehyde via hydrogen gas in situ
2
Au/CeO catalyst remains unchanged and that no Au was in
the filtrate.
2
To examine the scope of the present system with Au/CeO in
2
the presence of CO/H O, we extended our studies to a range of
a,b-unsaturated aldehydes. As depicted in Table 2, various
structurally diverse a,b-unsaturated aldehydes, including
aliphatic, aromatic ones could be transformed into the
corresponding unsaturated alcohols in high to excellent yields.
Notably, selectivity up to >85% was achieved in the initial
stage (0.5 h) for all cases and decreased only slightly at high
conversion. As far as we know, few simple heterogeneous
reduction systems are available that enable such high chemo-
selectivity. Table 2 also points to a marked substrate structure
effect on the chemoselective reduction of various a,b-unsatu-
rated aldehydes. For example, CAL displayed a significantly
higher activity than 2-methyl-2-pentene aldehyde (Table 2,
entries 1, 2), revealing that the activity is largely influenced by
the presence of a b-bulky group due to steric hindrance. In
addition, cinnamaldehyde with electron-withdrawing groups
on the benzene ring reacted smoothly (entry 5), while the
substitution of electron-donating groups decreased the
reactivity (entry 4). Moreover, in the transformations of
chloro-cinnamaldehyde, high selectivity could also be attained
with no observation of dehalogenation or ring reduction
(
entry 5).
It may be assumed that the present gold-catalyzed reaction
Fig. 1 Reduction of crotonaldehyde by CO/H
conversion of crotonaldehyde, SCROL: selectivity to crotyl alcohol,
BAL: selectivity to butanal, SBOL: selectivity to butanol). Reaction
conditions: 1 mmol substrate, Au/CeO (Au: 2.8 mol%), 20 mL H O,
2 2
O or H (CCAL:
proceeds through the reduction of a,b-unsaturated aldehyde
with hydrogen gas in situ generated from the low-temperature
S
2
2
WGS reaction, particularly on considering that Au/CeO is
2
96 1C, 5 atm CO or H
2
, 4.5 h.
1
554 | Chem. Commun., 2010, 46, 1553–1555
This journal is ꢀc The Royal Society of Chemistry 2010

View Article Online
generated from the WGS reaction is thought to be unlikely in
the present reaction system.
121, 69; (c) P. Gallezot and D. Richard, Catal. Rev. Sci. Eng.,
1998, 40, 81.
(a) E. Janin, J. Catal., 2003, 215, 245; (b) G. M. R. van Druten,
L. Aksu and V. Ponec, Appl. Catal., A, 1997, 149, 181;
4
While further work is needed to fully understand the
mechanism of the present gold-catalyzed reaction under
CO/H O conditions, we believe that the transient
(
c) T. B. L. W. Marinelli, S. Nabuurs and V. Ponec, J. Catal.,
1995, 151, 431; (d) G. J. Hutchings, F. King, I. P. Okoye,
M. B. Padley and C. H. Rochester, J. Catal., 1994, 148, 464;
2
0
15
Au -H species formed by the CO-induced reduction of
O is indispensable for the genesis of catalytically active
(e) P. Concepcion, A. Corma, J. Silvestre-Albero, V. Franco and
J. Y. Chane-Ching, J. Am. Chem. Soc., 2004, 126, 5523.
H
2
sites for aldehyde reduction. Although the Au-catalyzed WGS
reaction needed a much higher temperature, it is reasonable
that ceria supported small Au nanoparticles with superior
5 (a) C. Della Pina, E. Falletta, L. Prati and M. Rossi, Chem. Soc.
Rev., 2008, 37, 2077; (b) F. Z. Su, Y. M. Liu, L. C. Wang, Y. Cao,
H. Y. He and K. N. Fan, Angew. Chem., Int. Ed., 2008, 47, 334;
(
c) H. Tsunoyama, H. Sakurai, Y. Negishi and T. Tsukuda, J. Am.
0
16
redox reactivity can readily form Au -H in this procedure.
Chem. Soc., 2005, 127, 9374; (d) F. Z. Su, L. He, J. Ni, Y. Cao,
H. Y. He and K. N. Fan, Chem. Commun., 2008, 3531; (e) A. Corma
and P. Serna, Science, 2006, 313, 332; (f) A. Corma, P. Serna and
H. Garcia, J. Am. Chem. Soc., 2007, 129, 6358.
0
Once being formed, the Au -H species should be
rapidly consumed together with a final formation of the
a,b-unsaturated alcohol product without liberation of
molecular hydrogen, which may account for the enhanced
6
7
(a) C. Milone, R. Ingaglia, M. L. Tropeano, G. Neri and
S. Galvagno, Chem. Commun., 2003, 868; (b) P. Claus, Appl.
Catal., A, 2005, 291, 222.
efficiency in the CO/H O-mediated reduction of a,b-unsaturated
2
(a) J. E. Bailie and G. J. Hutchings, Chem. Commun., 1999, 2151;
(
aldehydes.
b) J. E. Bailie, H. A. Abdullah, J. A. Anderson, C. H. Rochester,
In summary, we have developed an efficient gold-catalyzed
approach for the chemoselective reduction of a range of a,b-
unsaturated aldehydes using cheap and easily accessible CO
N. V. Richardson, N. Hodge, J. G. Zhang, A. Burrows, C. J. Kiely
and G. J. Hutchings, Phys. Chem. Chem. Phys., 2001, 3, 4113.
(a) P. Claus, A. Brueckner, C. Mohr and H. Hofmeister, J. Am.
Chem. Soc., 2000, 122, 11430; (b) C. Mohr, H. Hofmeister,
J. Radnik and P. Claus, J. Am. Chem. Soc., 2003, 125, 1905.
8
2
and H O as the hydrogen source. The present clean synthesis
of primary allyl alcohols may be viewed as an appealing and
economical alternative for existing protocols.
Financial support by the NSF of China (20633030,
9 (a) Q. Fu, H. Saltsburg and M. Flytzani-Stephanopolous, Science,
2003, 301, 935; (b) F. Boccuzzi, A. Chiorino, M. Manzoli,
A. Andreeva and T. Tabakova, J. Catal., 1999, 188, 176;
(
c) D. Andreeva, V. Idakiev, T. Tabakova, L. Ilieva, P. Falaras,
2
0721063 and 20873026), the State Key Basic Research
A. Bourlinos and A. Travlos, Catal. Today, 2002, 72, 51.
10 L. He, L. C. Wang, H. Sun, J. Ni, Y. Cao, H. Y. He and K. N. Fan,
Angew. Chem., Int. Ed., 2009, 48, 9538.
Program of PRC (2009CB623506) and Science & Technology
Commission of Shanghai Municipality (08DZ2270500) is
kindly acknowledged.
1
1 P. N. Rylander, Hydrogenation Methods, Academic Press, London,
985, p. 66.
2 (a) B. Campo, C. Petit and M. Volpe, J. Catal., 2008, 254, 71;
b) B. Campo, G. Santori, C. Petit and M. Volpe, Appl. Catal., A,
009, 359, 79.
13 To rule out the possibility that the hydrogen atoms are supplied by
the alcoholic solvent, the reaction was carried out under N at
1
1
(
2
Notes and references
1
(a) S. Patai, The Chemistry of Double-bonded Functional Groups,
Wiley, Chichester, 1997, p. 844; (b) R. C. Larock, Organic
Transformations, VCH, New York, 1989, p. 411; (c) S. C. Tsang,
N. Cailuo, W. Oduro, A. T. S. Kong, L. Clifton, K. M. K. Yu,
B. Theibaut, J. Cookson and P. Bishop, ACS Nano, 2008, 2, 2547.
(a) S. Nishimura, Handbook of Heterogeneous Catalytic
Hydrogenation for Organic Synthesis, Wiley, Chichester, 2001,
p. 178; (b) C. Mohr, H. Hofmeister, M. Lucas and P. Claus, Chem.
Eng. Technol., 2000, 23, 324.
2
96 1C. Under these conditions, no conversion of cinnamaldehyde
was observed up to 6 h of contact time.
14 A. Karpenko, R. Leppelt, V. Plzak, J. Cai, A. Chuvilin,
B. Schumacher, U. Kaiser and R. J. Behm, Top. Catal., 2007, 44,
183.
15 (a) M. Conte, H. Miyamura, S. Kobayashi and V. Chechik, J. Am.
Chem. Soc., 2009, 131, 7189; (b) A. Abad, C. Almela, A. Corma
and H. Garcia, Chem. Commun., 2006, 3178.
16 L. He, J. Ni, L. C. Wang, F. J. Yu, Y. Cao, H. Y. He and
K. N. Fan, Chem.–Eur. J., 2009, 15, 11833.
2
3
(a) M. A. Aramendıa, V. Borau, C. Jimenez, J. M. Marinas, A. Porras
´ ´
and F. J. Urbano, J. Catal., 1997, 172, 46; (b) M. Englisch,
V. S. Ranade and J. A. Lercher, J. Mol. Catal. A: Chem., 1997,
This journal is ꢀc The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 1553–1555 | 1555