Gold supported on a biopolymer (chitosan) catalyzes the regioselective hydroamination of alkynes

Article abstract of DOI:10.1016/j.jcat.2007.07.021

Gold nanoparticles on a polysaccharide-based support (chitosan) were found to catalyze with very high yields the regioselective hydroamination of alkynes without the need for acid promoters and inert atmosphere. The metal-support interactions were studied by Raman, IR, UV, and NMR spectroscopy. The interaction between gold and the NH and OH groups of chitosan allow good dispersion of the nanocrystals on the biopolymer. The chitosan-silica composite further stabilizes gold nanoparticles against agglomeration or leaching compared with other supports.

Full text of DOI:10.1016/j.jcat.2007.07.021

Journal of Catalysis 251 (2007) 39–47
www.elsevier.com/locate/jcat
Gold supported on a biopolymer (chitosan) catalyzes the regioselective
hydroamination of alkynes
Avelino Corma ∗, Patricia Concepción, Irene Domínguez, Vicente Fornés, María J. Sabater ∗
Instituto de Tecnología Química UPV-CSIC, Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, 46022 Valencia, Spain
Received 23 May 2007; revised 12 July 2007; accepted 12 July 2007
Available online 29 August 2007
Abstract
Gold nanoparticles on a polysaccharide-based support (chitosan) were found to catalyze with very high yields the regioselective hydroamination
of alkynes without the need for acid promoters and inert atmosphere. The metal–support interactions were studied by Raman, IR, UV, and NMR
spectroscopy. The interaction between gold and the NH and OH groups of chitosan allow good dispersion of the nanocrystals on the biopolymer.
The chitosan–silica composite further stabilizes gold nanoparticles against agglomeration or leaching compared with other supports.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Gold; Hydroamination; Catalysis; Heterogeneous; Biopolymer
1. Introduction
ported that Au(I) catalyzes the intermolecular hydroamination
of alkynes in the presence of acidic promoters and preferably
in absence of air [12]. The role of the acidic promoter is ex-
plained through protonolysis of the precatalyst (PPh3)AuCH3
to give Au(PPh)+3 , which is the active species involved in the
mechanism.
Catalytic hydroamination is a transformation of seemingly
fundamental simplicity that offers a straightforward route to nu-
merous organic nitrogen molecules, avoiding the formation of
byproducts [1–7]. At present, no general hydroamination pro-
cedure is known, due to the high activation barrier for this
reaction, especially when applied to alkenes. On the other
hand, hydroamination of alkynes is thermodynamically more
favorable and, accordingly, catalytic homogeneous hydroami-
nation of alkynes mediated by transition metals has progressed
slowly [8]. Over the past 5 years, gold complexes have been
applied as catalysts for various selective organic transforma-
tions, including the hydroamination of unactivated alkenes,
alkynes, allenes, and 1,3-dienes [9]. Even though intramolec-
ular hydroamination of 5-alkynylamines to form tetrahydropy-
ridine derivatives can be catalyzed by Au(III) [10,11], it is
generally recognized that the intermolecular hydroamination
process remains difficult to achieve and far less developed than
the intramolecular process, which is kinetically and thermo-
dynamically favored. In this respect, it has been recently re-
The heterogeneous version of both the intermolecular and in-
tramolecular hydroamination of alkynes has been accomplished
with different cationic metals (e.g., Ag1+, Cu2+, Zn2+, Pd2+
)
supported on acidic materials such as montmorillonite clay
K-10, phosphotungstic acid, and zeolite HBEA [13]. In the
latter case, it has been proposed that the high activity of the
ion-exchanged BEA zeolite could be a result of either struc-
tural properties or the particular environment of metal cations
in the pore system.
It is of much interest to design recyclable and stable solid
catalysts that can carry out the intermolecular hydroamination
of alkynes with high conversion and selectivity but without the
use of acid promoters or the need to perform the experiments
under inert atmosphere. We show here that gold nanoparticles
supported on a polysaccharide biopolymer (chitosan) achieve
the above requirements much better than other gold catalysts
used successfully in other reactions [14]. The interaction be-
tween Au and the nitrogen and oxygen functionalities present
in the biopolymer may positively contribute to these benefits
found in chitosan with respect to other supports [15].
*
Corresponding authors. Fax: +34 96 3877809.
E-mail addresses: acorma@itq.upv.es (A. Corma), mjsabate@itq.upv.es
(M.J. Sabater).
0021-9517/$ – see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2007.07.021

40
A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
Table 1
of the solids were recorded on a Shimadzu UV–vis scanning
Characterization data of materials
spectrophotometer. Elemental analysis of the samples was car-
ried out using a Fisons EA 1108-CHNS-O analyzer. For gold
size distribution, the samples were examined by electron mi-
croscopy in a Philips CM 300 FEG instrument operated at
100 kV. The BET surface area was determined in a Micromerit-
ics ASAP 2010 analyzer, with the samples previously treated at
373 K for 1 h. Thermogravimetric analysis was performed with
a Mettler Toledo TGA/SDTA 851e thermobalance.
a
Sample
BET
(m g
mmol
Au/g (%)
C
H
(%)
N
(%)
C/N
Metal
particle
size (nm)
2
−1
)
Chitosan
Ch(I)SiO
2.7
–
–
–
41.08 7.10 7.41 5.54
8.42 1.49 1.53 5.50
14.13 2.50 2.58 5.48
–
2
–
Ch(II)SiO
–
–
2
–
Au–Ch(I)SiO 152.5
0.243
0.254
0.117
0.088
0.228
0.076
4–6
2–4
3–4
3–4
2.4–4.6
2.3–5.3
X-ray photoelectron spectroscopy (XPS) studies of the gold-
chitosan-SiO2 samples were done with a Leybold–Hereus LHS-
10/20 spectrometer equipped with an EA 200 multichannel
analyzer using AlKα (1486.6 eV) irradiation. To avoid photore-
duction of the gold species due to the X-ray source, the spectra
were recorded at 77 K at low X-ray flux (anode operating at
12 kV and 10 mA). Binding energies (BEs) were determined
relative to Si(2p); BE = 103.6 eV.
2
Au–Ch(II)SiO 100.9
2
Au–CeO
170
540
42
2
Au–SiO
2
Au–Fe O
2
3
Au–TiO
39
2
a
C/N ratios are calculated from elemental analysis data (% C and % N) in-
cluded in the Table 1.
Raman spectra were obtained with an “in via” Renishaw
spectrometer, equipped with a Olympus microscope. The ex-
citing wavelength was 785 nm from a Renishaw HPNIR laser
with a power of ca. 15 mW on the sample.
2. Experimental
2.1. Materials and starting reagents
Low molecular weight chitosan was purchased from Aldrich
with a deacetylation degree of amino groups of 75–85%. Char-
acterization data for pure chitosan are given in Table 1. Au–
TiO2 and Au–Fe2O3 samples were supplied by the Gold World
Council (GWC) and their characteristics are given in Table 1.
Au–SiO2 and Au–CeO2 were synthesized in our laboratory as
reported previously [16,17] (Table 1). Au–Ch(I)–SiO2 and Au–
Ch(II)–SiO2 (Table 1) were prepared as follows:
2.3. Catalytic experiments
In a typical experiment, a mixture of alkyne (1 mmol), amine
(1 mmol), 30% mmol of dodecane (as internal standard), 1.1–
2.5% mmol of metal, and 1 ml of toluene was stirred at 373 K
for 22 h under air. Samples were obtained at regular time inter-
vals and analyzed by gas chromatography in a Hewlett–Packard
Series II 5890 apparatus equipped with a flame ionization de-
tector and an HP-5 column for product separation. Identifica-
tion of the final compounds was done by comparing them with
authentic samples prepared according to general experimental
procedures [19].
1. Ch(I)–SiO2 and Ch(II)–SiO2 composites were prepared ac-
cording to a reported procedure with modifications [18].
Two aqueous solutions of 6 g of chitosan in 350 ml of acetic
acid (1.5%) were stirred at room temperature for 24 h. Then
27 g and 15 g of SiO2 (Aerosil 200) was added to these
two acidic solutions. The resulting slurries were vigorously
stirred and brought to pH 13 with NaOH (4 N) to afford
the white solids Ch(I)–SiO2 and Ch(II)–SiO2, respectively.
Both materials were filtered and washed exhaustively with
deionized water until the filtrates were pH 8. The solids
were dried in an oven at 373 K for 12 h.
3. Results and discussion
3.1. Formation of Au nanoparticles on hybrid chitosan–SiO2
supports
Gold was supported on chitosan [20], a biopolymer formed
by linked β-(1,4)-2-amino-2-deoxy-D-glucan and 2-acetamid-
odeoxy-D-glucan units that has the ability to act as reduc-
ing/stabilizing agent in the formation of gold nanoparticles
from gold(III) salts with no additional reducer or stabilizer.
In this case, the existence of numerous hydroxyl and amino
groups in the biopolymer may enhance the surface-stabilizing
ability of the support for the formation of gold nanoclusters.
However, the need to improve the weak mechanical properties
and poor diffusion of chitosan led us to deposit this biopoly-
mer on silica to afford the composite material, Ch(I)–SiO2. The
preparation method was described in Section 2. Results from
Table 1 show that through this method, a composite material
with BET surface area of 152 m2 g−1 was obtained after gold
incorporation, whereas the surface area of pure chitosan was
<3 m2 g−1. Dispersing the chitosan in the silica did not change
2. To form the Au–Ch(I)–SiO2 and Au–Ch(II)–SiO2 samples,
100 mg of NaAuCl4·2H2O was added to two solutions of
10 ml of EtOH containing 1 g of Ch(I)–SiO2 and 1 g of
Ch(II)–SiO2, respectively. The mixtures were stirred at re-
flux temperature for 16 h. The solids were recovered by fil-
tration, washed with EtOH, and dried under vacuum to give
Au–Ch(I)–SiO2 and Au–Ch(II)–SiO2, respectively. Char-
acterization data for these materials are collected in Table 1.
2.2. Characterization methods
Fourier transform infrared (FTIR) spectra were recorded
within autoconsistent pellets in a Nicolet 710 FT spectropho-
tometer in the range of 4000–1300 cm−1. The samples were
treated at 323 K under vacuum for 1 h and the spectra recorded
at room temperature. Room temperature DR-UV–vis spectra

A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
41
Fig. 2. Evolution of the Raman spectra of the sample Au–Ch(I)–SiO during
2
the synthesis after (a) 2, (b) 8, and (c) 16 h of heating.
the Au–N or Au–O vibrations due to the replacement of chlo-
rine by oxygen or nitrogen atoms of the chitosan molecule [22].
Nonetheless, the exact assignment of this band to either Au–O
or Au–N interaction, is not possible on the basis of only the
Raman results; additional IR experiments are required, as dis-
cussed later. The Raman band at 265 cm−1 was assigned by Li
et al. [23] to an Au–Cl− vibration of adsorbed Cl−. The high
intensity of this band is due to the surface-enhanced Raman
scattering effect from the gold nanoparticles. If this is so, then
we would expect this type of metal–support interaction (Au–N
and Au–O) to help stabilize the gold nanoparticles, preventing
agglomeration and leaching.
IR spectroscopy also showed that this type of interaction be-
tween gold and chitosan occurred (Fig. 3). Indeed, a broad and
unstructured absorption at 3700–3000 cm−1 related to the su-
perposition of OH and NH stretching vibration bands appeared
in the FT-IR spectra of both the Ch(I)–SiO2 composite and the
gold supported material Au–Ch(I)–SiO2 (see Fig. 3A). Inter-
estingly, incorporation of the metal into the Ch(I)–SiO2 hybrid
led to significant changes in the 1800–1300 cm−1 region of
the spectrum. In fact, the intensity of the deformation vibra-
tion of NH group at 1597 cm−1 decreased slightly and a new
band at 1520 cm−1 appeared after incorporation of the metal
(Fig. 3). This new band has been assigned to the NH group vi-
bration of the amine group that shifts to lower wavenumbers
when interacting with the gold metal [24]. In addition to this,
slight shiftings and changes in the intensity of the bands in the
OH-bending region (1460–1300 cm−1) may account for the in-
teraction of Au0 with the OH groups of chitosan, although this
interaction appears less evident than in the case of the amine.
Characterization by UV–vis spectroscopy also pointed to the
same direction as previous spectroscopies, that is, the stabi-
lization of gold nanoparticles on Ch(I)–SiO2. Fig. 4 shows the
evolution of the UV–vis spectra of the solid with heating at
363 K for 16 h. It can be seen that a broad and characteristic ab-
sorption band associated with the formation of Au nanoparticles
appeared at 520 nm (the typical plasmon absorption resonance
band for gold nanoparticles) after 8 h [25]. The increased in-
tensity of the 520-nm absorption band with time, together with
13
Fig. 1. CP-MAS C-NMR spectra of (a) pure chitosan, (b) Ch(I)–SiO ,
2
(c) Au–Ch(I)–SiO (2 h of heating) and (d) Au-Ch(I)-SiO2 (16 h of heating).
2
the characteristics of the chitosan molecules significantly. In-
deed, comparison between the CP MAS 13C NMR spectra for
the Ch(I)–SiO2 composite and pure chitosan showed no signif-
icant differences (see Fig. 1) [21].
Both spectra exhibited two peaks, at 23.2 and 173.4 ppm,
which can be assigned to methyl and carbonyl groups, respec-
tively, of N-acetyl groups remaining in the polymer due to in-
complete deacetylation (see Section 2). The rest of the peaks in
the spectra can be assigned to methylenic groups in different en-
vironments (Fig. 1). When the 13C CP-MAS NMR spectrum of
the Au composite Au–Ch(I)–SiO2 was recorded and compared
with the spectrum for Ch(I)–SiO2, the only noticeable differ-
ence was the small (<2 ppm) upfield shifting of the glucosidic
carbon C1, together with an even smaller upfield shifting of C4.
These small shifts may indicate interaction of the gold with
the polysaccharide. However, interaction between gold and the
biopolymer is better shown by Raman and IR spectroscopy.
On addition of NaAuCl4 to the Ch(I)–SiO2 composite, a rel-
atively intense Raman band centered at 355 cm−1 appeared
(see Fig. 2a), which shifted to lower wavenumbers (332 cm−1
)
when the duration of heating at EtOH reflux temperature was
increased from 2 to 8 h (see Fig. 2b). Two new bands at 265
and 401 cm−1 also developed after 8 h (Fig. 2b). Because com-
mercial AuCl3 and AuCl showed similar bands at 375 and
340 cm−1, we have assigned the 355 and 332 cm−1 bands
in Fig. 2 to Au(III)–Cl and Au(I)–Cl vibrations, respectively.
After heating for 16 h, the Raman spectrum showed only the
relatively intense band at 265 cm−1 together with a shoulder
at 401 cm−1. The 401-cm−1 Raman band can be assigned to

42
A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
(a)
(b)
−1
Fig. 3. (A) FT-IR spectra of (a) Ch(I)–SiO and (b) Au–Ch(I)–SiO ; (B) FT-IR spectra in the 1800–1300 cm region of (a) Ch(I)–SiO and (b) Au–Ch(I)–SiO .
2
2
2
2
Fig. 4. Evolution of the UV–vis spectra during the synthesis of the metal hybrid Au–Ch(I)–SiO after (a) 2, (b) 8, and (c) 16 h of reaction time. At the right, digital
2
photographs of Au–Ch(I)–SiO during the synthesis showing the evolution of the color from (a) 2 h (yellowish), (b) 8 h (red-purple) to (c) 16 h (deep red-purple)
2
of reaction time.
the absence of the extended plasmon band (EPB) in the 600–
900 nm range typical of strong interparticle interactions among
aggregates, suggest that nucleation of gold nanoparticles occurs
without the apparent formation of aggregates [20,26]. Most im-
portantly, it suggests that a rather good dispersion of gold onto
this polysaccharide based hybrid should occur.
Determination of metal particle sizes by TEM of Au–Ch(I)–
SiO2 revealed the formation of very small gold nanoparticles af-
ter heating for 8 h, whereas the plasmon absorption band could
be observed by UV–vis spectroscopy. The particle size was dif-
ficult to measure due to the particles’ poorly defined shapes.
At longer heating times (16 h), the size of these small clusters
increased and their shape was well defined; the particle size dis-
tribution as measured by TEM is given in Fig. 5 and shows an
average particle size of 4–6 nm. These findings demonstrate that
the average size of gold nanoparticles decreased (average par-
ticle size, 2–4 nm) when chitosan/SiO2 ratio increased in the
Au–Ch(II)–SiO2 sample.
The XPS spectra in the Au4f region of Au–Ch(I)–SiO2 sam-
ple containing 0.243 mmol Au/g obtained after 16 h of heating
is shown in Fig. 6. Two peaks at 83.9 and 87.6 eV can be ob-
served due to the Au4f7/2 and Au4f5/2 transitions, respectively.
The position of the Au4f7/2 signal at 83.9 eV indicates the pres-
ence of metallic gold species [27]. Hole–electron excitations
near the Fermi level Ef (typical Donial-Sunjick shape charac-
teristic of XPS peaks in metals) could explain the slight asym-
metry of the band, although the presence of minor amounts of
the cationic species Au+ (85.5 eV) cannot be completely dis-
carded. In close connection to this, small amounts of Cl− ions
also were detected by XPS, in agreement with the existence of
remaining Au–Cl species (detected by Raman). Finally, Au3+
species were not detected by XPS on the Au–Ch(I)–SiO2 cata-
lysts.
We must remark that the commercial chitosan used in our
experiments does not contain glutaraldehyde as either a sta-
bilizer or a cross-linking agent. The absence of this aldehydic
reducing agent guarantees that the total or partial reduction to

A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
43
Fig. 5. TEM image of (a) Au–Ch(I)–SiO after 16 h of heating and histogram of particle size distribution; (b) TEM image of the composite Au–Ch(II)–SiO after
2
2
16 h of heating and the corresponding histogram of particle size distribution.
other metals) [28] through metal coordination with the amino
and or hydroxyl groups of chitosan followed by metal reduc-
tion.
3.2. Catalytic activity
The catalytic activity of gold nanoparticles on the chitosan–
silica hybrids for the hydroamination of 1-octyne by aniline
has been compared with gold supported on different carriers,
including CeO2 nanoparticles, TiO2, Fe2O3, and SiO2. The ini-
tial experiments were performed under air with an Au–CeO2
catalyst that has been successfully used together with Au–TiO2
as a catalyst for other reactions, such as regioselective hydro-
genations, oxidations, and hydrosilylation, and for C–C bond
formation [29,30]. The amine and alkyne conversion was al-
most completed after 22 h, and the yield of products ((N-2-
octylidene) aniline and 2-octanone) was also high (see entry 1
in Table 2).
Formation of these products is consistent with a reaction
scheme in where the initial step in the reaction is the regioselec-
tive formation of the Markovnikov enamine, followed by ther-
mal tautomerization to the more stable imine N-(2-octylidene)
aniline. Finally, the hydrolysis reaction would yield the ketone
(Scheme 1)
Gold nanoparticles supported on SiO2 (Au–SiO2), on com-
mercial inorganic oxides Fe2O3 (Au–Fe2O3) and on TiO2 (Au–
TiO2) afforded much lower yields of hydroamination products
compared with CeO2 (see entries 2–4 in Table 2). In striking
Fig. 6. XPS spectrum of Au4f core level line of the Au–Ch(I)–SiO catalyst.
2
metal Au0 is due to chitosan itself. Depolymerization of the
polysaccharide that may release aldehydic monomer units also
can account for the reducing ability of chitosan. However, this
possibility was discarded from the thermogravimetric analy-
sis, because the amount of organic material did not change
after six successive catalytic uses. Thus, the formation of dis-
persed gold nanoparticles by chitosan can be explained (as for

44
A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
Table 2
Table 3
Hydroamination of 1-octyne by aniline catalyzed by gold nanoparticles sup-
ported on different materials in toluene
Initial metal loading and metal particle size in the fresh prepared materials and
final metal loading and particle size of the supported gold nanoclusters after
being reused
a
b
c
Entry
Catalyst
C(%)
Y(%)
Imine:ketone
Catalyst
Initial metal
particle size
(nm)
Initial Final metal
mmol particle size
Au/g (nm)
Final
mmol
Au/g
Catalytic
uses
d
1
2
3
4
5
6
7
8
Au–CeO
96
68
92
89
63
57
64
99
92
96
91
40:60
93:3
64:36
88:12
55:45
94:6
2
Au–Fe O
2
3
Au–TiO
Au–SiO
2
e
Au–Ch(I)SiO
4–6
4–6
3–4
3–4
2.4–4.6
2.3–5.3
0.243 11–15
0.243 11–20
0.117 22–25
0.088 11–25
0.228 11–30
0.076 14–45
0.243
0.243
0.086
0.083
0.213
0.071
3
6
3
3
3
2
68
2
2
f
Au–Ch(I)–SiO (2 h)
Au–Ch(I)–SiO (2 h)
Au–Ch(I)–SiO
Au–Ch(II)–SiO
100
100
100
100
2
f,g
Au–CeO
2
2
Au–SiO
2
79:21
64:36
2
Au–Fe O
2
3
2
Au–TiO
2
a
Reaction conditions: 1.1% mmol Au, 1 mmol 1-octyne, 1 mmol aniline,
30% mmol dodecane, 1 ml toluene, 373 K, 22 h.
b
C(%) = percentage of conversion.
SiO2 (entry 5, Table 2). The curves show that almost complete
conversion with very high yield of the desired product was
achieved after 22 h of reaction.
c
Y(%) = percentage of yield.
d
2.2% mmol Au.
2.5% mmol Au.
e
f
The possibility that the catalyzed hydration reaction could
directly compete with hydroamination for the formation of the
ketone was discarded because control experiments with the
alkyne and the catalyst Au–Ch(I)–SiO2 (2 h) did not afford
2-octanone. We also confirmed that the ketone formation was
associated with the presence of water in the reaction media, be-
cause the yield of 2-octanone was strongly inhibited when the
reaction was carried out in the presence of activated molecular
sieves (zeolite 4A) to remove traces of moisture (see entry 6,
Table 2).
Sample obtained upon heating AuCl – and Ch(I)–SiO at ethanol reflux
4
2
temperature for 2 h.
g
1.1% mmol Au, 1 mmol 1-octyne, 1 mmol aniline, 30% mmol dodecane,
1 ml toluene, 373 K, 22 h and activated 4A zeolite.
Differences in activity can be associated with differences in
metal particle size of the starting material, as well as to dif-
ferences in metal agglomeration occurring during the reaction.
Results presented in Table 3 show that whereas the average par-
ticle size of gold on the starting catalyst was similar for all
samples, the particle size of the used catalysts differed, and
were different from that of their corresponding fresh samples
(see Table 3 and Fig. 8).
Scheme 1.
It is important to note that in general, gold nanoparticles sup-
ported on CeO2, SiO2, Fe2O3, and TiO2 have a broader particle
size distribution after being reused several times. Effectively,
these materials have a significant number of metal particles
with diameters >25 nm after two or three uses (see Table 3
and Fig. 8). Interestingly the gold clusters supported on the hy-
brid chitosan–SiO2 were smaller than 20 nm even after three
uses (see Table 3 and Fig. 8).
In other words, gold agglomerates during reaction with all
catalysts, with the agglomeration comparatively lower for the
Au–Ch(I)–SiO2 sample. Moreover, the chemical analysis of
gold on the different catalysts when fresh and after two or three
uses showed that slight leaching of gold from the different sup-
ports occurred, except for gold on the chitosan silica composite,
in which leaching was not observed after six uses (Table 3).
The effect of metal agglomeration and leaching occurring
on catalyst recycling should be responsible for the decreased
catalyst activity with increasing time of use (recycling) seen
in Fig. 9. This figure shows that Au–Ch(I)–SiO2 not only was
the most active but also retained higher activity after different
reuses. This resulted in an active and stable Au–Ch(I)–SiO2
catalyst for the hydroamination of alkynes, with a selectiv-
ity close to 100% and a total turnover number (TON) for the
Fig. 7. Reaction profile (conversion and yield with the time) of hydroamination
reaction of 1-octyne with aniline catalyzed by Au–Ch(I)–SiO (2 h) (see entry
2
5 in Table 2).
contrast, in all cases, gold nanoparticles on the chitosan-silica
hybrids afforded the highest yields of hydroamination products
(see entries 5, 7, and 8 in Table 2).
Fig. 7 shows the evolution of conversion and yield for the
hydroamination reaction of 1-octyne with aniline catalyzed by
gold nanoparticles on the chitosan–silica hybrid Au–Ch(I)–

A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
45
Fig. 8. Particle size distribution and TEM micrograph of the reused catalysts: (a) Au–Ch(I)–SiO -2 h after 3 uses; (b) Au–CeO after 3 uses; (c) Au–SiO after
2
2
2
3 uses and (d) Au-Fe O after 2 uses.
2
3
hydroamination of 1-octyne of 477, comparable to the TON
reported for hydroamination with Au(I) complexes in homo-
geneous phase [12].
Finally, hydroamination on Au–Ch(I)–SiO2 was carried out
with different substituted anilines and acetylenic compounds
(see Table 4). Only slight differences in the rate of hydroam-
ination of 1-octyne with various para-aryl-substituted anilines
(OCH3, Cl, H, CF3 groups) with differing electron-donating
or electron-withdrawing properties (see entries 3–7 in Table 4)
have been observed, suggesting that differently substituted ani-
lines might have similar basicities. Moreover, the electron-
donating or -withdrawing ability of the substituent did not influ-
ence the regioselectivity of the reaction; since the Markonikov
product remained the exclusive product in all cases.
Stronger bases, such as aliphatic amines, did not add to 1-
octyne under identical reaction conditions. This finding, which
had been previously observed for other Pd(II) metal com-
plexes, has been attributed to the increased tendency of aliphatic

46
A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
characterization techniques have demonstrated the interaction
of gold nanoparticles with the oxygen and nitrogen groups of
chitosan, suggesting that these interactions may be responsible
(at least in part) for the stabilization of gold on this support, and
thus for its higher activity and longer lifetime.
Acknowledgments
Financial support was provided by the Dirección General de
Investigación Científica y Técnica of Spain (project MAT2006-
14274-C02-01) and Generalidad Valenciana (project GV04B-
270). I.D. thanks the Consejo Superior de Investigaciones Cien-
tíficas for an I3-P fellowship. The authors thank Professor
Guillermo Munuera for his useful comments, the XPS Spec-
troscopy Service (Inst. Ciencia de Materiales Universidad de
Sevilla-CSIC) for the XPS measurements, and the Electronic
Microscopy Service (Universidad Politécnica de Valencia) for
the TEM measurements.
Fig. 9. Comparative yields of hydroamination products with different Au sup-
ported materials after successive reuses.
Table 4
References
Hydroamination of alkynes by amines catalyzed by Au–Ch(I)–SiO
(1.25% mmol Au) in toluene
2
d
a
[1] (a) T.G. Müller, M. Beller, Chem. Rev. 98 (1998) 675;
(b) M. Beller, A. Tillack, J. Seayad, Transition Metals for Organic Syn-
thesis, vol. 2, second ed., Wiley–VCH, Weinheim, 2004, pp. 403–414.
[2] (a) J. Barluenga, F. Aznar, Synthesis (1975) 704;
(b) J. Barluenga, F. Aznar, Synthesis (1977) 195;
(c) J. Barluenga, F. Aznar, R. Liz, R. Rodes, J. Chem. Soc. Perkin Trans. 1
(1980) 2732.
[3] (a) Y. Uchimaru, Chem. Commun. (1999) 1133;
(b) C.G. Hartung, A. Tillack, H. Trauthwein, M. Beller, J. Org. Chem. 66
(2001) 6339;
(c) M. Tokunaga, M. Eckert, Y. Wakatsuki, Angew. Chem. Int. Ed. 38
(1999) 3222.
[4] (a) I. Kadota, A. Shibuya, L.M. Lutete, Y. Yamamoto, J. Org. Chem. 64
(1999) 4570;
(b) T. Shimada, Y. Yamamoto, J. Am. Chem. Soc. 124 (2002) 12670.
[5] I. Bytschkov, S. Doye, J. Org. Chem. 6 (2003) 935.
[6] (a) T. Straub, A. Haskel, T.G. Neyroud, M. Kapon, M. Botoshansky, M.S.
Eisen, Organometallics 20 (2001) 5017;
b
c
Alkyne
Amine
C(%) Y(%) Imine: TON
ketone
1-Octyne
1-Phenylacetylene Aniline
1-Octyne
1-Octyne
Aniline
100
96
89
91
89
89
70
64:36 80
78:22 58
31:69 71
62:38 58
4-Bromoaniline
4-Trifluoromethyl-
aniline
4-Methylaniline
4-Methoxyaniline
3,5-(Ditrifluoromethyl)
aniline
72
1-Octyne
1-Octyne
1-Octyne
85
81
55
85
63
43
72:28 68
64:36 65
33:67 44
a
1.25% mmol Au, 1 mmol 1-alkyne, 1 mmol amine, 30% mmol dodecane,
toluene, 373 K, 22 h.
b
C(%) = percentage of conversion.
c
Y(%) = percentage of yield.
d
TON = mmol of converted substrate/mmol Au.
(b) A. Haskel, T. Straub, M.S. Eisen, Organometallics 15 (1996) 3773.
[7] (a) P.L. McGrane, T. Livinghouse, J. Am. Chem. Soc. 115 (1993) 11485;
(b) P.L. McGrane, T. Livinghouse, J. Org. Chem. 57 (1992) 1323.
[8] (a) Y. Li, T.J. Marks, Organometallics 15 (1996) 3770;
(b) Y. Li, T.J. Marks, J. Am. Chem. Soc. 120 (1998) 1757;
(c) P.J. Walsh, A.M. Baranger, R.G. Bergman, J. Am. Chem. Soc. 114
(1992) 1708;
amines to form stable complexes with electrophilic metal cen-
ters [1]. This experimental observation leads unavoidably to the
conclusion that when reacting amines, only weak nitrogen ba-
sic compounds will be able to react, because their competition
with the olefin for the metal should be avoided.
(d) Y. Shi, T. Ciszewski, A.L. Odom, Organometallics 20 (2001) 3967;
(e) F. Pohlki, S. Doye, Chem. Soc. Rev. 32 (2003) 104.
[9] (a) R.A. Widenhoefer, X. Han, Eur. J. Org. Chem. (2006) 4555;
(b) N. Nishima, Y. Yamamoto, Angew. Chem. Int. Ed. 45 (2006) 3314;
(c) E. Genin, P.-Y. Toullec, S. Antoniotti, C. Brancour, J.-P. Genet,
V. Michelte, J. Am. Chem. Soc. 128 (2006) 3112.
Aromatic terminal alkyne 1-phenylacetylene displays simi-
lar reactivity to that of aliphatic 1-octyne, (entry 2, Table 4). It
is important to note that the internal acetylenic bonds were not
reactive, presumably due to steric factors.
[10] (a) Y. Fukuda, K. Utimoto, H. Nozaki, Heterocycles 25 (1987) 297;
(b) T.E. Müller, Tetrahedron Lett. 39 (1998) 5961;
(c) M.R. Luzung, J.P. Markham, F.D. Toste, J. Am. Chem. Soc. 126 (2004)
10858;
4. Conclusion
We have demonstrated that solid gold catalysts are active and
regioselective for the hydroamination of alkynes. Interestingly,
these catalysts can work in the presence of air and do not require
the addition of acid into the reaction media. However, agglom-
eration of gold occurs during the reaction, causing a decrease in
activity on recycling. Gold on a composite formed by chitosan
and silica gives the highest activity and the lowest rate of ag-
glomeration, while experiencing no leaching. Different catalyst
(d) V. Mamane, T. Gress, H. Krause, A. Fürstner, J. Am. Chem. Soc. 126
(2004) 8654;
(e) O.N. Faza, C.S. Lopez, R. Alvarez, A.R. de Lera, J. Am. Chem.
Soc. 128 (2006) 2434;
(f) M.H. Suhre, M. Reif, S.F. Kirsch, Org. Lett. 7 (2005) 3925;
(g) L. Zhang, S. Wang, J. Am. Chem. Soc. 128 (2006) 1442;
(h) D. Kadzimirsz, D. Hildebrandt, K. Merz, G. Dyker, Chem. Commun.
(2006) 661.

A. Corma et al. / Journal of Catalysis 251 (2007) 39–47
47
[11] (a) For recent reviews see: A.S.K. Hashmi, Gold. Bull. 37 (2004) 51;
[21] O.A.C. Monteiro Jr., C. Airoldi, Int. J. Biol. Macromol. 26 (1999) 119.
(b) A. Höffmann-Roder, N. Krause, Org. Biomol. Chem. 3 (2005) 387;
(c) A. Arcadi, S. Di Giuseppe, F. Marinelli, E. Rossi, Curr. Org. Chem. 8
(2004) 795;
[22] (a) N. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordina-
tion Compounds, Wiley, New York, 1986;
(b) L. Delanoy, N. El Hassan, A. Musi, N.N. Le To, J.M. Krafft, C. Louis,
J. Phys. Chem. B 110 (2006) 22471;
(c) D.W. Freeman, F.G. Baglin, Inorg. Nucl. Chem. Lett. 17 (1981) 161;
(d) Y. Zhang, X. Gao, J. Weaver, J. Phys. Chem. 97 (1993) 8656.
[23] Z.L. Li, T.H. Wu, Z.J. Niu, W. Huang, H.D. Nie, Electrochem. Commun. 6
(2004) 44.
[24] (a) J. Brugnerotto, J. Lizardi, M.F. Goyevolea, W. Argüelles-Moral, J. De-
strieres, M. Rinaudo, Polymer 42 (2001) 3569;
(b) G.J. Domszy, A.F.G. Roberts, Makromol. Chem. 186 (1985) 1671.
[25] (a) U. Kreibig, M. Vomer, Optical Properties of Metal Clusters, Springer-
Verlag, Heidelberg, 1995;
(d) S. Ma, S. Yu, Z. Gu, Angew. Chem. Int. Ed. 45 (2006) 200.
[12] E. Mizushima, T. Hayashi, M. Tanaka, Org. Lett. 5 (2003) 3349.
[13] (a) N. Lingaiah, N. Seshu Babu, K. Mohan Reddy, P.S. Sai Prasad,
I. Suryanarayana, Chem. Commun. 3 (2007) 278;
(b) J. Penzien, C. Haeßner, A. Jentys, K. Köhler, T.E. Müller, C. Sievers,
J.A. Lercher, J. Catal. 221 (2004) 302;
(c) J. Penzien, T.E. Müller, J.A. Lercher, Chem. Commun. (2000) 1753;
(d) V. Ganapati, G.V. Shanbhag, S.M. Kumbar, T. Joseph, S.B. Halligudi,
Tetrahedron Lett. 47 (2006) 141;
(e) M.K. Richmond, S.L. Scout, H.J. Alper, J. Am. Chem. Soc. 123 (2001)
10521.
(b) G.P. Mitchell, C.A. Mirkin, R.L. Letsinger, J. Am. Chem. Soc. 121
(1999) 8122;
(c) Y. Voloktitin, J. Sinzing, L.J. Jong, G. Schmid, M.N. Vargaftik, I.I.
Moiseev, Nature 384 (1996) 621;
(d) G. Schmid, Chem. Rev. 92 (1992) 1709;
(e) M. Kanehara, E. Kodzuka, T. Tenarishi, J. Am. Chem. Soc. 128 (2006)
13084.
[14] (a) P. Landon, P.J. Collier, J. Papworth, J.C. Kiely, G.J. Hutchings, Chem.
Commun. (2002) 2058;
(b) D.I. Enache, J.K. Edwards, P. Landon, B. Solsona, A.F. Carley,
A.A. Herzing, M. Watanabe, C.J. Kiely, D.W. Knight, G.J. Hutchings,
Science 311 (2006) 362;
(c) A. Abad, P. Concepcion, A. Corma, H. García, Angew. Chem. Int.
Ed. 44 (2005) 4066;
[26] (a) A.N. Shipway, M. Lahav, R. Gabai, I. Willner, Langmuir 16 (2000)
8789;
(b) A.A. Lazarides, G.C. Schatz, J. Phys. Chem. B 104 (2000) 460.
[27] (a) C.D. Bain, H.A. Biebuyck, G.M. Whitesides, Langmuir 5 (1989) 723;
(b) Q. Fu, H. Saltsburg, M. Flitzani-Stephanopoulos, Science 301 (2003)
935.
[28] M. Adlim, M. Abu Bakar, K.Y. Liew, J. Ismail, J. Mol. Catal. A Chem.
212 (1–2) (2004) 141.
[29] (a) A. Corma, P. Serna, Science 313 (5785) (2006) 332;
(b) A. Abad, C. Almela, A. Corma, H. García, Tetrahedron 62 (28) (2006)
6666;
(d) B. Guzman, B.C. Gates, J. Am. Chem. Soc. 126 (2004) 2672.
[15] (a) K. Molvinger, F. Quignard, D. Brunel, M. Boissiere, J.-M. Devoisselle,
Chem. Mater. 16 (2004) 3367;
(b) V. Romain, K. Molvinger, F. Quignard, D. Brunel, New J. Chem. 27
(2003) 1690.
[16] S. Carretin, J. Guzman, A. Corma, J.M. Lopez Nieto, V. Puntes, Angew.
Chem. Int. Ed. 43 (2004) 2538.
[17] G. Budroni, A. Corma, Angew. Chem. Int. Ed. 45 (2006) 3328.
[18] M.-Y. Yin, G.-L. Yuan, Y.-Q. Wu, M.Y. Huang, Y.-Y. Jiang, J. Mol. Catal.
A Chem. 147 (1999) 93.
[19] B.S. Furniss, A.J. Hannaford, P.W.G. Smith, A.R. Tatchell, Vogel’s, Text-
book of Practical Organic Chemistry, fifth ed., pp. 782–783.
[20] (a) H.Z. Huang, X.R. Yang, Biomacromolecules 5 (2004) 2340;
(b) G.A.F. Roberts, in: G.A.F. Roberts (Ed.), Chitin Chemistry, Macmillan
Press Ltd., London, 1992;
(c) J. Guzman, S. Carrettin, J.-C. Fierro González, Y. Hao, B.C. Gates,
A. Corma, Angew. Chem. Int. Ed. 44 (2005) 4778;
(d) S. Carrettin, M.C. Blanco, A. Corma, A.S.K. Hashmi, Adv. Synth.
Catal. 348 (2006) 1283;
(e) H. Ito, T. Yajima, J. Tateiwa, A. Hosomi, Chem. Commun. 11 (2000)
981.
(c) P. Sorlier, A. Denuziere, C. Viton, A. Domard, Biomacromolecules 2
(2001) 765–772;
(d) I. Yamaguchi, S. Itoh, M. Suzuki, M. Sakane, A. Osaka, J. Tanaka,
Biomaterials 24 (2003) 2031–2036.
[30] C. Gonzalez-Arellano, A. Abad, A. Corma, H. García, M. Iglesias,
F. Sanchez, Angew. Chem. Int. Ed. 46 (2007) 1536.