Cu and Au nanocomposites in catalytic olefination reaction

Article abstract of DOI:10.1016/j.mencom.2010.06.005

Metal-vapor synthesis-prepared Cu, Ag, Au and bimetallic Au-Cu (optimal) nanocomposites catalyse olefination of hydrazones with polyhalomethanes.

Full text of DOI:10.1016/j.mencom.2010.06.005

Mendeleev
Communications
Mendeleev Commun., 2010, 20, 200–202
Cu and Au nanocomposites in catalytic olefination reaction
Valentine G. Nenajdenko,*a Alexander Yu. Vasil’kov,a Aleksey A. Goldberg,a Vasiliy M. Muzalevskiy,a
Alexander V. Naumkin,b Vladislav L. Podshibikhin,b Aleksey V. Shastinc and Elizabeth S. Balenkovaa
a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 932 8846; e-mail: nen@acylium.chem.msu.ru
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation
c Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka,
Moscow Region, Russian Federation. E-mail: shastin@icp.ac.ru
DOI: 10.1016/j.mencom.2010.06.005
Metal-vapor synthesis-prepared Cu, Ag, Au and bimetallic Au–Cu (optimal) nanocomposites catalyse olefination of hydrazones
with polyhalomethanes.
Transformation of carbonyl compounds to olefins is one of
the most common approaches to the construction of new C=C
bonds.1 A new catalytic olefination reaction (COR), developed
in our group, consists in interaction of hydrazones of carbonyl
compounds with polyhaloalkanes in the presence of copper salts
(0.1–10 mol%). High applicability of COR gave rise to a great
variety of alkenes starting from available and cheap reagents
by a simple experimental technique.2 An attractive challenge
for further development of COR is the use of heterogeneous
catalysts, which is advantageous of easy separation from reac-
tion products and multiple re-use of catalytic material. All of
that makes the reaction environmentally more friendly.
High activity of Cu, Cu–Au and Cu–Ag heterogeneous sys-
tems have been demonstrated previously.3 Hence, one can expect
that mono- and bimetallic copper-containing heterogeneous
catalysts can be also good in COR. In addition, it is very
interesting to study the influence of another valence state of
copper on the reaction outcome. Such states are realized in the
particles of Au–Cu bimetallic nanosystems deposited on Al2O3
and SiO2 supports by metal-vapor synthesis (MVS). Mono- and
bimetallic nanoparticles prepared by MVS demonstrated effective
magnetic,4 antibacterial5 and catalytic properties.6 Moreover,
nanoparticles of Au and Cu obtained by MVS are intensively
studied in various catalytic processes.7 Here, we would like to
present the synthesis and study of the catalytic activity of MVS
obtained mono- and bimetallic Cu and Au–Cu/X (X = Al2O3,
SiO2) systems in COR.†
of monometallic copper system 2, bimetallic Cu–Au system 7
demonstrates the synergetic effect giving higher yields. We also
found that the manner of catalyst synthesis is not crucial for its
activity. Thus, successive deposition of metals in the case of 5
gave yields of alkenes compared to those for simultaneous
deposition used in 6. Other polyhaloalkanes were also involved
into the reaction using most active catalysts 6, 7 and 8 (Table 2).
A series of experiments with varying of the amount of catalyst
clarified that it is optimal to use 150 mg of catalyst 6, 7 or 8 for
5 mmol of hydrazone.
Three catalytic cycles were carried out for each polyhalo-
methane with separation and re-use of the catalyst (Table 2).
In case of the most active CHBr3, CCl3Br and CBr3F repeated
reactions were possible, but with noticeable decrease in the reac-
tion yield. Nevertheless, non-zero yields were detected even after
the third reaction cycle. This fact clearly indicated, that hetero-
geneous catalysts provided results comparable with those for
i, N2H4 · H2O
ii, NH2CH2CH2NH2
catalyst, EtOH,
CXYHal2
X
O
Y
Cl
Cl
CCl4, X = Y = Cl
CBrCl3, X = Y = Cl
CFBr3, X = F, Y = Br
CHBr3, X = H, Y = Br
Scheme 1
Since hydrazones are the true reactants in COR, it should be
expected that this process will be very sensitive to the catalyst
due to the active copper leaching by complexation with hydrazine
derivatives. Thus, we have observed in preliminary experiments
that heterogeneous catalysts, based on copper complexed with
immobilized amine, become completely inactive after the first
cycle of reaction.
Table 1 Catalyst for catalytic olefination reaction: active metal components
and content.
Yield of alkene (%)
Mmol
of active
metal (%)
Metal/
Content of
metal (%)
Catalyst
Support
from
CCl3Br
from
CCl4
We tested eight mono- Au, Ag, Cu and bimetallic Au–Cu
nanosystems deposited on Al2O3 and SiO2 (Scheme 1, Table 1).
Hydrazone of 4-chlorobenzaldehyde, CCl3Br and CCl4 were
chosen for model reactions to search for optimal catalyst. Reac-
tion was carried out during 24 h in ethanol using ethylene-
diamine as a base. Cu and Au catalysts 6, 7 and 8 provided the
best results. The yields of alkene for CCl4 and CCl3Br were
comparable with those obtained using homogeneous catalysis.
In contrast, Ag- and Au-containing catalysts 1, 3 and 4 appeared
to be considerably less effective. Obtained by the modification
1
2
3
4
5
Au/Al2O3 0.09
Cu/Al2O3 0.23
Ag/SiO2 0.16
Ag/Al2O3 0.45
0.015
0.12
0.047
0.133
Cu, 0.016
Au, 0.0024
Cu, 0.048
Au, 0.0037
Cu, 0.012
Au, 0.0032
0.23
41
58
65
67
75
2
45
4
6
42
Cu–Au/
Al2O3
Cu, Au/
Al2O3
Cu, Au/
Al2O3
Cu/SiO2
Cu, 0.033
Au, 0.015
Cu, 0.096
Au, 0.023
Cu, 0.023
Au, 0.02
0.46
6
7
8
73
81
81
59
65
70
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© 2010 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2010, 20, 200–202
Table 2 The yields of alkenes depending on catalyst (%).a
(a)
6
7
8
300
200
100
0
Polyhalo-
methane
I
II
III
I
II
III
I
II
III
CCl3Br
CCl4
CBr3F
CHBr3
73
59
73
66
46
8
11
9
35
5
8
81
65
71
63
62
33
52
29
40
16
17
11
81
70
70
64
39
23
24
25
35
8
10
11
3
3
2
1
aThe reaction is accompanied by the formation of the corresponding azine
as a major by-product.
homogeneous catalysts. The decline of catalytic activity is
probably due to leaching of copper nanoparticles from catalysts
as well as simple mechanical destruction of catalyst granules in
the course of the reaction. It should be noted that bimetallic
Cu–Au system 7 showed higher yields for the second and third
cycles comparing to those for monometallic Cu system 8. One can
attribute that to the stabilizing effect of Au, which prevents
leaching of Cu from the catalyst. Additional explanation can be
regarded to the synergism between Cu and Au.
Au–Cu nanocomposites were studied by X-ray photoelectron
spectroscopy as well as transmission electron microscopy (TEM)
to have insight into catalyst structure and size distribution. Quanti-
tative analysis using relative sensitivity factors developed for
Kratos XSAM-800 gave composition C0.28O0.25Cu0.13Al0.34Au0.001
for the Au–Cu/Al2O3 system. Intensity ratio of the main and
satellite peaks in the spectrum of Cu 2p indicates that the spectrum
contains at least two states of copper atoms, Cu2+ and Cu+
or Cu0. The Cu 2p3/2 peak occupied an intermediate position
between those of Cu2+ and Cu+ and/or Cu0 states (Figure 1).
The Cu 2p photoelectron spectra of the Au–Cu/Al2O3 nano-
composite are practically independent of bias voltage applied
to the sample holder. In contrast, positive biasing the sample
(Figure 1) leads to noticeable broadening of the Au 4f and total
Al 2p + Cu 3p peaks. Analysis of the Cu 3p peak is difficult owing
to superposition of the Al 2p and Cu 3p peaks. Binding energy
position of the Au 4f7/2 peak at 84.3 eV indicates a metallic
state of gold and a manifestation of the size effect. The O 1s
spectrum is also depends on the bias voltage. The dependence
970
960
950
940
930
Binding energy, Eb/eV
150
100
50
(b)
Al 2p
Cu 3p
Au 4f
4
3
2
1
0
90
85
80
75
70
Binding energy, Eb/eV
Figure 1 (a) Cu 2p photoelectron spectra of Au–Cu/Al2O3 nanocomposite
measured at Ub: (1) 0, (2) –7 and (3) +7 V. (b) Photoelectron spectra of
(1) Al2O3 support and Au–Cu/Al2O3 nanocomposite measured at Ub: (2) 0,
(3) –7 and (4) +7 V.
reflects the heterogeneity of the sample and the presence of
copper in the oxidized state. The difference in the O 1s spectra
of the support and the nanocomposite in the low energy region
is also associated with the presence of oxidized copper.
Typical TEM micrograph of the Cu/SiO2 nanocomposites is
presented in Figure 2. For sample 8, some differences in the
average size of stabilized metal particles, measured before and
after the catalytic tests were observed. The initial sample consists
of particles with an average size of 12.2 nm, which is about
twice higher than that measured after olefination (6.2 nm). This
result can be explained considering that TEM image of the
original sample shows that copper nanoparticles contain small
fragments with sizes of 4.7 nm, which are grouped into clusters
and can be washed out from the support during the catalytic
experiments. For system 1, gold particles with an average size
of 3.6 nm and aggregates 6.5–8.6 nm consisting of smaller entities
were observed. As can be seen in the photos the chain length of
particles is 30–84 nm and a transverse size is 2.5–3.0 nm.
†
Catalysts were obtained by the MVS method for the preparation of
mono- and bimetallic systems using earlier reported technique.4 Copper
(shavings, 99%), gold (foil, 99.99%), toluene (99%, Aldrich), triethyl-
amine (99%, Aldrich), SiO2 (Kieselgel, 70–270 mesh, 60 Å, Aldrich),
γ-Al2O3 (IKT-02-6 M from JSC ‘Katalizator’, Novosibirsk, S = 138 m2 g–1)
have been used. In typical experiments, 0.1–0.3 g of metal were evaporated
from tantalum boats with 100–150 ml of solvent; 3–5 cm3 of the supports
were modified by the obtained metal organosols in a vacuum. The supports
were previously activated by calcinations at 300 °C in a vacuum. The XPS
measurements were performed at room temperature on an XSAM-800
spectrometer (Kratos Analytical, UK) with non-monochromatic MgKα
radiation. Data were acquired at 15 kV and 6 mA under the vacuum of
~5×10–8 Pa. Spectra were recorded in the fixed retarding ratio mode.
Photoelectron spectra were recorded with a step of 0.1 eV. After sub-
traction of a linear background, a Gaussian function was used to decon-
volve the measured spectra. The energy scale of the spectrometer was
calibrated against the following peaks: the Au 4f7/2 (84.0 eV), the Ag 3d5/2
(368.3 eV) and the Cu 2p3/2 (932.7 eV). The atomic concentration has
been determined from C 1s, O 1s, Al 2p, Cu 2p and Au 4f XPS peak
areas using linear background subtraction and atomic sensitivity factors
provided by the spectrometer manufacturer. The samples were secured
to a titanium holder in air using two-sided conductive adhesive tape. To
compensate for X-ray induced surface charging all the binding energies
were referred to the C–C,H peak at 285.0 eV in the fitted C 1s spectrum
(support) and to the Al 2p (75.0 eV) (nanocomposite). Micrographs were
obtained using a LEO 912 AB OMEGA, Zeiss (Germany) microscope.
COR with heterogeneous catalysts was carried out using previously
reported standard procedure for the homogeneous ones.2 1H NMR data
of alkenes were identical to literature data.2
20 μm
Figure 2 TEM photograph of 8. Inset: image of electronogram.
100 nm
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Mendeleev Commun., 2010, 20, 200–202
2003, 302; (g) V. N. Korotchenko, A. V. Shastin, V. G. Nenajdenko and
In summary, the use of heterogeneous catalysts in the catalytic
olefination reaction gave comparable to homogeneous catalysis
results. Synergetic effect of bimetallic catalysts in Cu–Au nano-
particles in comparison with monometallic particles of copper
was found. The promising direction of further investigations is
a search of heterogeneous catalysts resistant to leaching.
E. S. Balenkova, Tetrahedron, 2001, 57, 7519; (h) V. G. Nenajdenko,
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Volkov and V. L. Podshibikhin, Mendeleev Commun., 2007, 17, 268;
(b) A. Yu. Vasil’kov, B. A. Zachernyuk, Z. N. Karpikov, I. O. Volkov,
Y. V. Zubavichus, A. A. Veligzhanin, A. A. Chernyshov, M. I. Buzin and
L. N. Nikitin, Zh. Prikl. Khim., 2007, 80, 2058 (Russ. J. Appl. Chem.,
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This work was supported by the Russian Foundation for
Basic Research (grant nos. 08-03-00389, 08-03-00736-a and
10-03-00897-a) and Federal Special Program (grant no. P622-13/5).
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Received: 15th February 2010; Com. 10/3468
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