Pt, Pd and Au nanoparticles supported on a DNA-MMT hybrid: Efficient catalysts for highly selective oxidation of primary alcohols to aldehydes, acids and esters

Article abstract of DOI:10.1039/c3cc41545g

Novel DNA-MMT hybrid supported metal nanoparticle catalysts, such as Pt/DNA-MMT, Pd/DNA-MMT, Au/DNA-MMT, were prepared for application in highly selective aerobic oxidation of primary alcohols to aldehydes, acids and esters, respectively. Taking advantage of the water-soluble reversibility of these catalysts, all the transformations could be performed smoothly in water and reuse of the catalysts has also been accomplished by a very simple phase separation process.

Full text of DOI:10.1039/c3cc41545g

ChemComm
View Article Online
View Journal
COMMUNICATION
Pt, Pd and Au nanoparticles supported on a DNA–MMT
hybrid: efficient catalysts for highly selective oxidation
of primary alcohols to aldehydes, acids and esters†
Cite this: DOI: 10.1039/c3cc41545g
Received 28th February 2013,
Accepted 11th April 2013
Lin Tang, Xuefeng Guo, Yunfeng Li, Shuai Zhang, Zhenggen Zha and
Zhiyong Wang*
DOI: 10.1039/c3cc41545g
www.rsc.org/chemcomm
Novel DNA–MMT hybrid supported metal nanoparticle catalysts, such
Recently organic–inorganic hybrids, maintaining mechanical
as Pt/DNA–MMT, Pd/DNA–MMT, Au/DNA–MMT, were prepared for properties of both organic and inorganic materials, have received
application in highly selective aerobic oxidation of primary alcohols to much attention.7 Montmorillonite (MMT), which is a type of
aldehydes, acids and esters, respectively. Taking advantage of the naturally occurring clay, has been used as a host material in the
water-soluble reversibility of these catalysts, all the transformations preparation of composites and has potential applications in
could be performed smoothly in water and reuse of the catalysts has catalysis, separation, and the optical and electrical fields.8 And
also been accomplished by a very simple phase separation process.
the natural DNA has been applied successfully as the template of
metal nanoparticles by our group for organic reactions.9 Taking
The selective oxidation of alcohols has been considered as one advantage of the easy availability and good water dispersibility of
of the most fundamental transformations in organic chemistry, MMT and DNA, we chose Na–MMT and fish sperm DNA as the
both for laboratory research and industrial manufacturing. starting materials to synthesize the hybrid. Herein, we describe
Traditionally, such transformation has been performed with the highly selective oxidation of primary alcohols to the corres-
stoichiometric inorganic oxidants and notably chromium ponding carbonyl compounds, such as aldehydes, acids and
reagents, accompanied with a large amount of waste.1 From esters under mild conditions in water, catalyzed by novel DNA
the viewpoints of atom economy and environmental concern, and MMT hybrid (DNA–MMT) supported metal nanoparticle
more and more attention has been directed toward the aerobic catalysts (metal/DNA–MMT).
oxidation of alcohols catalyzed by reusable heterogeneous
First of all, a hybrid of DNA–MMT was successfully prepared.
catalysts using molecular oxygen as the oxidant.2 Recently, After preparation of the hybrid, the different catalysts Pt/DNA–MMT,
heterogeneous catalysts for selective oxidation of secondary Pd/DNA–MMT, Au/DNA–MMT were synthesized according to the
alcohols to ketones have been widely developed.3 But selective method reported previously by our group (see experimental details
oxidation of primary alcohols to the corresponding aldehydes is in the ESI†). These metal/DNA–MMT catalysts exhibited stability
difficult because primary alcohols often suffer from overoxida- in air with good reversible solubility in water and ethanol. When
tion to generate acids. Esterification is also one of the most the catalysts were characterized (see the ESI† for the detailed
fundamentally important reactions in organic synthesis. The analyses), we employed them directly in selective aerobic oxida-
traditional esterification usually requires synthesis of carboxylic tion of benzyl alcohol (1a) in water at room temperature
acids or activated carboxylic acid derivatives such as acid with LiOHÁH2O as a base (Table 1, entries 1–3). To our delight,
anhydrides or acid chlorides.4 So the selective aerobic oxidation the Pd/DNA–MMT catalyst showed high catalytic activity for
of alcohols to esters is more attractive and challenging for oxidation of benzyl alcohol (1a) to benzoic acid (3a) with
organic synthesis and green chemistry. Although the direct an excellent yield of 99%. Although the catalytic activities of
transformation of alcohols to esters by dehydrogenation of Pt/DNA–MMT and Au–DNA–MMT were not very high under these
alcohols has been developed,5 the direct oxidative esterification conditions, Pt/DNA–MMT and Au/DNA–MMT could oxidize 1a to
from alcohols using molecular oxygen is rare.6
benzaldehyde (2a) and benzyl benzoate (4a), respectively, with
high selectivity. After simple optimization, when the temperature
was 60 1C and potassium phosphate was used as the base,
Pt/DNA–MMT could selectively oxidize 1a to 2a with a good
yield of 86% (Table 1, entry 6). The yield of 4a improved to 95%
when Au/DNA–MMT was employed as the catalyst under the
optimal conditions (Table 1, entry 9). Moreover, the comparison
of these metal/DNA–MMT catalysts with the reported metal/DNA
Hefei National Laboratory for Physical Sciences at Microscale, CAS Key Laboratory
of Soft Matter Chemistry and Department of Chemistry, University of Science and
Technology of China, Hefei, 230026, P. R. China. E-mail: zwang3@ustc.edu.cn;
Fax: +86 551-360-3185
† Electronic supplementary information (ESI) available: Experimental details,
characterization of catalysts and characterization of products. See DOI: 10.1039/
c3cc41545g
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun.

View Article Online
Communication
ChemComm
Table 1 Optimization of the reaction conditionsa
Table 3 Selective oxidation of alcohols to carboxylic acida
Entry
R1
Product
Yieldb (%)
Yieldb (%)
1
2
3
4
5
6
7
8
Ph
4-F-Ph
3-F-Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
98 (89c)
94
93
90
85
95
88
83
76
Entry
Catalyst
Base (equiv.)
2a
3a
4a
1c
2c
3c
4d
5d
6d
7e
8e
9e
Pt/DNA–MMT
Pt/DNA–MMT
Au/DNA–MMT
Pt/DNA–MMT
Pt/DNA–MMT
Pt/DNA–MMT
Au/DNA–MMT
Au/DNA–MMT
Au/DNA–MMT
LiOHÁH2O (1.5)
LiOHÁH2O (1.5)
LiOHÁH2O (1.5)
LiOHÁH2O (1.5)
K3PO4Á3H2O (1.5)
K3PO4Á3H2O (0.05)
LiOHÁH2O (1.5)
Cs2CO3 (1.5)
o1
33
15
60
70
86
20
11
3
99
12
5
38
26
7
n.d.
n.d.
38
n.d.
n.d.
n.d.
46
4-Cl-Ph
3-Cl-Ph
4-Me-Ph
3-Me-Ph
4-MeO-Ph
4-NO2-Ph
4-CF3-Ph
2-Thienyl
2-Furyl
9d
10e
11
12
30
3j
3k
3l
83
76
75
9
75
95
Cs2CO3 (0.75)
o1
a
Reaction conditions: 1a (0.50 mmol), metal/DNA–MMT (Pt: 1.5 mol%,
a
Reaction conditions: 1 (0.50 mmol) in 1 ml of H2O, Pd/DNA–MMT (Pd:
b
Pd: 1.7 mol%, Au: 2.9 mol%). Determined by GC-MS with an internal
standard. 25 1C. 60 1C. 50 1C.
b
1.7 mol%), LiOHÁH2O (1.5 equiv.), 25 1C, O2 balloon, 12 h. Isolated
c
d
e
c
d
e
yield. Reuse of the catalyst at the fifth round. 50 1C. 80 1C.
catalysts showed that metal/DNA–MMT catalysts had higher Table 4 Selective oxidation of alcohols to esters by self-esterificationa
catalytic activity (see Table S1, ESI†).
With the optimized conditions in hand, the selective oxidation
of various alcohols to the corresponding aldehydes was studied
(Table 2). Table 2 shows that substituents on the aromatic ring
hardly affected the reactivity and all the alcohols could afford the Entry
R1
Product
Yieldb (%)
products in good to excellent yields. And the retrieved catalysts
could be reused without a significant loss of their high catalytic
performance (Tables 2–4, entry 1).
Subsequently, the scope of the alcohols in the reaction catalyzed
by Pd/DNA–MMT was extended under the optimal conditions
(Table 3). The reactions with alcohols bearing electron-withdrawing
groups (entries 2–5) and electron-donating substituents (entries 6–8)
1
2
3
4
5
6
7
8
9
Ph
4-F-Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
94 (81c)
71
74
85
54
73
70
61
51
4-Cl-Ph
4-Br-Ph
2-Br-Ph
4-Me-Ph
3-Me-Ph
4-MeO-Ph
4-NO2-Ph
2-NO2-Ph
2-Naphthyl
proceeded smoothly to give the desired products in excellent 10
4j
4k
—
67
11d
yields. When strong electron-withdrawing groups were used,
the reaction temperature needed to be elevated (entries 9 and 10).
Moreover, heterobenzylic alcohol was also a good reaction substrate
(entries 11 and 12).
a
Reaction conditions: 1 (0.50 mmol) in 1 ml of H2O, Au/DNA–MMT (Au:
b
2.9 mol%), Cs2CO3 (0.75 equiv.), 50 1C, O2 balloon, 12 h. Isolated
yield. Reuse of the catalyst at the fifth round. 20 h.
c
d
As for Au/DNA–MMT, the direct catalytic transformation of
different alcohols to esters was also studied (Table 4). The
electronic effect of the aromatic substitution of the alcohols
had little influence on the reaction and a series of functional groups
including fluoro, chloro, bromo, methyl, methoxy and nitro were
well tolerated to give the desired products in moderate to good yields
(entries 2–4 and 6–9). However, the steric effect of the substituents
had a great influence on the reaction. The yield of 4-bromobenzyl
alcohol was apparently higher than that of 2-bromobenzyl alcohol
(entries 4 and 5) and 4j could not be obtained when the nitro group
was at the ortho-position of the benzene ring (entry 10). The reaction
of the large steric hindrance substrate also proceeded smoothly
upon increasing the reaction time (entry 11).
To get insight into the mechanism of the selective oxidation of
alcohols, some control experiments were performed (Scheme 1).
Firstly, the selective oxidation of alcohols to acids was studied.
Benzoic acid was not observed and only a small amount of
benzaldehyde was obtained in the absence of water. It was noted
that water was crucial for this oxidation of alcohols. Moreover,
cross-esterification was performed with o-nitrobenzyl alcohol and
various benzyl alcohols, affording the corresponding esters in
moderate to good yields. The reaction of o-nitrobenzyl alcohol
Table 2 Selective oxidation of alcohols to aldehydesa
Entry
R1
Product
Yieldb (%)
1
2
3
4
5
6
7
8
Ph
4-F-Ph
3-F-Ph
4-Cl-Ph
3-Cl-Ph
4-Me-Ph
3-MeO-Ph
4-MeO-Ph
2a
2b
2c
2d
2e
2f
86(80c)
78
75
96
87
74
90
98
2g
2h
a
Reaction conditions: 1 (0.50 mmol) in 1 mL of H2O, Pt/DNA–MMT
(Pt: 1.5 mol%), K3PO4Á3H2O (0.05 equiv.), 60 1C, O2 balloon, 12 h. b Deter-
mined by GC-MS using diphenyl as an internal standard. c Reuse of the
catalyst at the third round.
c
Chem. Commun.
This journal is The Royal Society of Chemistry 2013

View Article Online
ChemComm
Communication
transformations catalyzed by monometallic nanoparticles.
Taking advantage of the water-soluble reversibility of these
catalysts, all the transformations proceed well in water under
mild conditions and the catalysts can be recovered and reused
by a simple phase separation process. Detailed mechanistic
studies and other applications of these catalysts in organic
reactions are in progress.
We are grateful to National Nature Science Foundation of
China (20932002, 20972144, 90813008, 21172205, 20772188,
J1030412 and 973 program 2010CB912103).
Notes and references
1 (a) K. Bowden, I. M. Heilbron, E. R. H. Jones and B. C. L. Weeden,
J. Chem. Soc., 1946, 39; (b) G. Cainelli and G. Cardillo, Chromium
oxidation in organic chemistry, Springer, Berlin, 1984.
2 (a) G. ten Brink, I. W. C. E. Arends and R. A. Sheldon, Science, 2000,
287, 1636; (b) Y. Uozumi and R. Nakao, Angew. Chem., Int. Ed., 2003,
42, 194; (c) K. Mori, T. Hara, T. Mizugaki, K. Ebitani and K. Kaneda,
J. Am. Chem. Soc., 2004, 126, 10657; (d) T. Malat and A. Baiker, Chem.
Rev., 2004, 104, 3037; (e) H. Tsunoyama, H. Sakurai, Y. Negishi and
T. Tsukuda, J. Am. Chem. Soc., 2005, 127, 9374; ( f ) Y. H. Ng, S. Ikeda,
T. Harada, Y. Morita and M. Matsumura, Chem. Commun., 2008, 3181.
3 (a) H. Miyamura, R. Matsubara, Y. Miyazaki and S. Kobayashi, Angew.
Chem., Int. Ed., 2007, 46, 4151; (b) J. Zheng, S. Y. Lin, X. H. Zhu,
B. W. Jiang, Z. Yang and Z. Y. Pan, Chem. Commun., 2012, 48, 6235;
(c) D. Tsukakmoto, Y. Shiraishi, Y. Sugano, S. Lchikawa, S. Tanaka
and T. Hirai, J. Am. Chem. Soc., 2012, 134, 6309; (d) C. Shang and
Z.-P. Liu, J. Am. Chem. Soc., 2011, 133, 9938; (e) B. KaRimi and
F. K. Esfahani, Adv. Synth. Catal., 2012, 354, 1319; ( f ) A. Buonerba,
Scheme 1 Control experiments for the reaction mechanism.
Scheme 2 Plausible reaction mechanism.
´
C. Cuomo, S. O. Sanchez, P. Canton and A. Grassi, Chem.–Eur. J.,
with benzaldehyde can be carried out smoothly to obtain the ester
with a good yield (87%) whereas the reaction of o-nitrobenzyl
alcohol with benzoic acid did not work. These results indicated
that the aldehyde rather than the carboxylic acid should be the
intermediate of this transformation.
2012, 18, 709; (g) Z. S. Hou, N. Theyssen, A. Brinkmann and
W. Leitner, Angew. Chem., Int. Ed., 2005, 44, 1346.
4 (a) J. Iqbal and R. R. Srivastava, J. Org. Chem., 1992, 57, 2001;
(b) J. Otera, Chem. Rev., 1993, 93, 1449; (c) K. Ishihara, M. Kubota,
H. Kurihara and H. Yamatoto, J. Am. Chem. Soc., 1995, 117, 4413;
(d) G. W. Breton, J. Org. Chem., 1997, 62, 8952.
In terms of these experimental results and previous reports,5b,6,9b
the possible mechanism is depicted in Scheme 2. First of all,
the alcohol is oxidized to the aldehyde under the catalysis of
Pt/DNA–MMT, Pd/DNA–MMT or Au/DNA–MMT. Then the alde-
hyde is selectively converted to the diol (a) by hydration and a
was rapidly oxidized to the product of acid under the catalysis
of Pd/DNA–MMT, which is the first pathway. The other pathway
is that the alcohol attacks the aldehyde to generate the hemi-
acetal (b) and the product of ester is obtained by oxidation of b
in the presence of Au/DNA–MMT.
In conclusion, we have developed novel Pt, Pd and Au nano-
particle catalysts supported on a hybrid of natural DNA and MMT,
which show higher activity and selectivity for oxidation of primary
alcohols than DNA-templated nanoparticles. Depending on these
catalytic systems, highly efficient formation of the corresponding
aldehydes, carboxylic acids and esters is achieved. Both oxidative
self-esterification as well as cross-esterification of various alcohols
5 (a) J. Zhang, E. Balaraman, G. Leitus and D. Milstein, Organometallics,
2011, 30, 5716; (b) C. Gunanathan, L. J. W. Shimon and D. Milstein,
J. Am. Chem. Soc., 2009, 131, 3146; (c) S. Musa, L. Shaposhnikov,
S. Cohen and D. Gelman, Angew. Chem., Int. Ed., 2011, 50, 3533.
6 (a) F.-Z. Su, J. Ni, H. Sun, Y. Cao, H.-Y. He and K.-N. Fan, Chem.–Eur. J.,
2008, 14, 7131; (b) R. L. Oliveira, P. K. Kiyohara and L. M. Rossi, Green
Chem., 2009, 11, 1366; (c) T. Ishida, M. Nagaoka, T. Akita and M. Haruta,
Chem.–Eur. J., 2008, 14, 8456; (d) S. Gowrisankar, H. Neumann and
M. Beller, Angew. Chem., Int. Ed., 2011, 50, 5139; (e) K. Kaizuka,
H. Miyamura and S. Kabayashi, J. Am. Chem. Soc., 2010, 132, 15096;
( f ) S. Arita, T. Koike, Y. Kayaki and T. Ikariya, Chem.–Asian. J., 2008,
3, 1479.
7 (a) Y. S. Choi, K. H. Wang, M. Z. Xu and I. J. Chung, Chem. Mater.,
2002, 14, 2936; (b) A. Dolbecq, E. Dumas, C. R. Mayer and P. Mialane,
Chem. Rev., 2010, 110, 6009; (c) V. M. Agranovich, Yu. N. Gartstein
and M. Litinskaya, Chem. Rev., 2011, 111, 5179; (d) M. P. Shores,
B. M. Bartlett and D. G. Nocera, J. Am. Chem. Soc., 2005, 127, 17986.
8 (a) T. J. Pinnavaia, Science, 1983, 220, 365; (b) B. M. Choudary,
M. L. Kantam, K. V. S. Ranganath and K. K. Rao, Angew. Chem., Int.
´
´
´
Ed., 2005, 44, 322; (c) B. Veisz, Z. Kiraly, L. Toth and B. Pecz, Chem.
Mater., 2002, 14, 2882; (d) L. X. Shao and M. Shi, Adv. Synth. Catal.,
2003, 345, 963; (e) S. D. Miao, Z. M. Liu, B. X. Han, J. Huang, Z. Y. Sun,
J. L. Zhang and T. Jiang, Angew. Chem., Int. Ed., 2006, 45, 266.
can be performed smoothly. Although bimetallic nanoparticles as 9 (a) Y. Wang, G. H. Ouyang, J. T. Zhang and Z. Y. Wang, Chem.
Commun., 2010, 46, 7912; (b) Y. Wang, D. P. Zhu, L. Tang, S. J. Wang
and Z. Y. Wang, Angew. Chem., Int. Ed., 2011, 50, 1; (c) L. Tang,
H. Y. Sun, Y. F. Li, Z. G. Zha and Z. Y. Wang, Green chem., 2012,
efficient catalysts for selective oxidation of primary alcohols to the
aldehydes, carboxylic acids and esters have been reported,6e to
the best of our knowledge, this is the first example of these
14, 3423.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun.