Significant stabilization of palladium by gold in the bimetallic nanocatalyst leading to an enhanced activity in the hydrodechlorination of aryl chlorides

Article abstract of DOI:10.1039/c5cc04432d

The stabilization effect of Au towards Pd changed the reactivity of Pd in Au/Pd bimetallic nanoclusters, altering the reaction mechanism from homogeneous to heterogeneous in dechlorination reaction of aryl chlorides. This phenomenon was illustrated by the observed enhancement of the rate of reaction by in situ generated Au-rich bimetallic Au/Pd nanoclusters.

Full text of DOI:10.1039/c5cc04432d

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DOI: 10.1039/C5CC04432D.
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Significant Stabilization of Palladium by Gold in the Bimetallic
Nanocatalyst Leading to an Enhanced Activity in the
Hydrodechlorination of Aryl Chlorides
Received 00th January 20xx,
Accepted 00th January 20xx
a
b
b
a
c
DOI: 10.1039/x0xx00000x
Sangita Karanjit, Atchaleeya Jinasan, Ekasith Samsook, Raghu N. Dhital, Kenichi Motomiya,
c,d
c
a,e
Yoshinori Sato, Kazuyuki Tohji, Hidehiro Sakurai*
www.rsc.org/
The stabilization effect of Au towards Pd changed the reactivity of decades, researchers have been paying much effort on developing
Pd in Au/Pd bimetallic nanoclusters, altering the reaction new strategies for designing high performance heterogeneous
mechanism from homogeneous to heterogeneous in catalysts to prevent the usual homogenous coupling mechanism by
7
dechlorination reaction of aryl chlorides. This phenomenon was developing immobilizing protocols. Recent publications on
illustrated by observed enhancement of rate of reaction by in-situ coupling reactions utilizing catalysts such as Pd grafted on
7
a,b,f
7c
generated Au-rich bimetallic Au/Pd nanoclusters.
mesoporous material
or zeolites
and Pd on HAP
7
d,e
macroligand
assure to compete the usual homogenous
Catalysis by palladium nanoparticles (NPs) has aroused great
interest because of its widespread applications in organic synthesis,
including C–C bond-forming reactions. The nature of the active
mechanism. However, such strategies are limited and a new and
simple strategy to develop the efficient heterogeneous catalytic
system that can promise to prevent leaching, agglomeration and
deactivation of catalyst is essential.
1
catalytic species in such reactions as the Mizoroki–Heck and
2
Suzuki–Miyaura coupling reactions has been a mostly focused issue
Bimetallic nanoparticles have attracted attention because of their
enhanced catalytic activities, selectivities, and stabilities in
since the past several decades. Most of the C-C coupling reactions
are found to be catalyzed by soluble palladium complexes following
1
0
comparison to their single-metal counterparts. Especially, Au/Pd
bimetallic alloy has superior catalytic activities in various types of
3
,4d,5a,9
usual homogenous mechanism.
coupling reactions has already been well-established as
Leaching of Pd in the
1
1–17
reaction under mild conditions.
The activity and selectivity of Pd
9
a
demonstrated by various experimental approaches. It has been
reported that leaching of Pd species from the surface of a catalyst
through oxidative addition of aryl halides gives ArPdX species that
catalyst can be enhanced by alloying with Au due to the synergistic
16d–e
effects of bimetallic surfaces,
such as ensemble and the ligand
10b
effect. Furthermore, bimetallization can result in stabilization of
nanoparticles in cases where one metal acts as stabilizer for the
0
react homogenously, forming the desired product and Pd species
0
1
0b,16e,16f
(
scheme 1). The resulting Pd species can react further or they can
other, preventing aggregation.
In our previous report, we observed unique catalytic activity of
poly(N-vinylpyrrolidone) (PVP)-stabilized Au/Pd bimetallic
nanoparticles for C–Cl bonds activation in Ullmann coupling
4
-6
redeposit on the cluster surface. Alternatively, in the absence of a
strong ligand or stabilizer, they can be deactivated through the
4
1
7
formation of Pd black. It is a major limitation of Pd NPs chemistry
2
+
1
7a
in coupling reactions because once oxidative addition happens, Pd
reactions of chloroarenes and the unusual Suzuki-Miyaura-type
1
7b
will form and it will no longer stay on the surface. Stabilization of
such active palladium species either in solution or on
heterogeneous surface is a quite difficult task. From the last few
coupling reaction.
Through DFT calculation of the reaction
mechanism, we realized that spillover of Cl over gold is a crucial
step in the reaction, that drives the reaction through
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heterogeneous path preventing the homogeneous path (scheme
Journal Name
17a,18
1).
The best conditions for activation of C–Cl bonds for C–C
bond-formation reactions involved the use of N,N-
dimethylformamide (DMF) as solvent and hydrogen donor (Scheme
2, Conditions a; Table 1, entry 1). So, we expected that the use of
other reducing solvents, such as alcohols (Scheme 2; Conditions b),
would result in selective activation of the C–Cl bond towards
hydrodechlorination. Similar alteration of product selectivity of the
two competing process based on concentration of reductant has
identical conditions using physical mixtures of the two
monometallic catalysts in varying Au and Pd ratios (Figure S1, ESI).
Even a small amount of Pd in Au, or vice versa, enhanced the
catalytic activity to a value higher than that displayed by Au or Pd
alone.
8
been well discussed by Sasson and coworkers.
In the course of our study to elucidate the stabilizing effect of gold
toward palladium, we chose the hydrodechlorination reaction as
our model reaction because, for Pd, it is difficult to activate C-Cl
bond and once, it is activated, Pd may be released as Pd (II) ion in
solution due to oxidative addition process (scheme 2). To this
species, the second oxidative addition process is very difficult and it
is quite impossible to get the Ullmann coupling product due to low
Measurements of the kinetics of consumption of 1 (Figure 1)
showed differences in the catalytic activities of Au/Pd alloy, Pd, and
(
Au + Pd) nanoparticles. The reaction with bimetallic Au/Pd:PVP was
a very fast second-order reaction with a rate constant for
–1 –1
1
7a consumption of 1 of k = 5.6 × 10–1 Lmol h (Figure S2, ESI). The
nucleophilicity on Pd and strong electrophilicity of C-Cl bond.
reaction with monometallic Pd:PVP, on the other hand, was very
slow and showed first-order kinetics. The 1:1 physical mixture of
Au:PVP and Pd:PVP show a reactivity that was intermediate
between those of the two monometallic catalysts. At the beginning
of the reaction, the catalytic activity of Pd:PVP (2 atom%) was
higher, and the reaction rate was almost double than that observed
Instead, if we use the hydride source, it will possibly undergo
reduction, giving arene as the product even through usual
0
homogenous mechanism and release the Pd which can be
captured by Au as a stabilizing ligand. Au is the best choice among
other metals to capture Pd because of the similar lattice constant
1
6e-h
and low energy demand for bimetallization.
Besides, the
1
6i
with Au:PVP (1 atom%) + Pd:PVP (1 atom%) mixture. However, after
two hours, the activity of the Au + Pd mixture gradually increased in
comparison to that of Pd alone. The kinetic of consumption of 1 in
the presence of the Au + Pd mixture at 25 °C showed a linear fit to
the first-order plot of –ln[A] versus time, with an observed rate of
nucleation process of Pd is relatively slow. In this work, we
attempt to release Pd and trap it by Au during hydrodechlorination
reaction and tune the reaction mechanism from homogenous to
heterogeneous.
First, to identify optimal conditions for the dechlorination
dechlorination, the reaction of 1-chloro-4-methoxybenzene (1) was
carried out in the presence of Au/Pd:PVP as a catalyst and
potassium hydroxide as the base in dimethyl sulfoxide (DMSO), no
reaction occurred because of the nonreducing nature of the solvent
–2
–1
consumption of 1 (k ) = 3.7 × 10
h
for the initial 2 hours of
1a
reaction. However, the slope then increased significantly,
–2
–1
h
corresponding to an increase in the rate to 4.6 × 10
and a
(entry 2). However, the yield of dechlorination product
methoxybenzene (2) increased in alcohol solvents. Reactions in 1:1
mixtures of methanol, ethanol, or propan-2-ol with water gave 2 in
yields of 22%, 63%, and 70%, respectively (entries 3–5) and without
water in ethanol (78%) and propanol (>95%) (entries 6–7). The best
conditions involved the use of anhydrous propan-2-ol as the sole
solvent; under these conditions, the reaction was completed within
one hour at 45 °C and five hours at 25 °C giving >95% yield of 2
(entry 7-8). The optimized or slightly modified reaction conditions
were applied to the dechlorination of various substrates including
polychlorinated compounds and the results are summarized in
Table S1 (ESI).
The efficiency of various Au and Pd catalysts for the dechlorination
reaction was compared by performing the reaction of 1-chloro-4-
methoxybenzene (1) for 1 h (Table 1). The highest catalytic activity
was shown by Au/Pd bimetallic alloy nanoparticles, which gave 2
quantitatively (Table 1, entry 7). The dechlorination reaction of 1
did not proceed when Au:PVP was used as a catalyst (entry 9),
whereas Pd:PVP did give 2. When Pd:PVP was used as a catalyst
under the same conditions, the yield of 2 was only 24% (entry 10),
while the physical mixture of the two monometallic catalysts
Au:PVP and Pd:PVP (Au + Pd) gave 51% yield, which was higher than
that obtained with Pd:PVP alone (entry 11). To test the effect of Au
on the catalytic activity of Pd, we performed the reaction under
2
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however, the leached palladium species that are present in solution
are captured by Au to form bimetallic Au/Pd:PVP And both catalytic
cycles operating simultaneously in the case of physical mixtures of
Au:PVP and Pd:PVP.
To verify our hypothesis, we used transmission electron microscopy
(
TEM) to examine structural and morphological changes in the
metal nanoparticle as result of the reaction. The two
a
monometallic nanoparticles Au:PVP and Pd:PVP were mixed in a 1:1
ratio, and TEM images were recorded before and after the reaction
(
Figure S3 and S4, ESI). The images taken before reaction showed
the Au:PVP and Pd:PVP nanoparticles separately, with average sizes
of 1.6 ± 0.4 nm and 3.9 ± 0.6 nm, respectively. However, images
change in the order of the reaction (Figure 1c).
On the basis of the above results, we hypothesized that leaching
might occur from the surface during catalysis by monometallic Pd
due to oxidative addition of the C–Cl bond. This species must be
exclusively responsible for the initial catalytic activity through a
homogeneous mechanism because Au:PVP on its own shows no
activity in the reaction. In the presence of gold, in situ reduction of
Pd(II) under the reaction condition might lead to the Au/Pd
bimetallic catalyst with high dispersion of Pd on Au (Table 1, entry
1
1). We therefore propose the existence of two catalytic cycles for
the observed reactivities of monometallic and bimetallic
nanoparticles, respectively, (Scheme 3). The catalytic reaction
involving the bimetallic nanoparticles follows a heterogeneous
mechanism and occurs on the surface of the catalyst (cycle A)
because of the spillover of Cl over gold. The process is very fast,
with no aggregation or deactivation of the catalyst at any stage of
the reaction. In the case of monometallic Pd:PVP in the absence of
Au, the catalyst shows a homogeneous reaction mechanism (cycle
B) through leached Pd. This is a slow process and, as the reaction
0
proceeds, the Pd species becomes gradually deactivated through
aggregation, with the formation of Pd black. In the presence of Au,
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recorded after the reaction showed morphological changes, with a In summary, through the result of hydrodechlorination reaction
growth in the size of the nanoparticles. Detailed scanning reaction we could clearly conclude the leaching of Pd species; these
transmission electron microscopy (STEM) energy dispersive X-ray enhance the catalytic activity by interacting with the Au
spectroscopy (EDX) measurements showed that most of the nanoparticles in Au/Pd bimetallic nanoparticles generated in situ
particles are polymorphological with non-uniform lattice pattern. and the heteroatomic gold drives the reaction mechanism from
However, it revealed the existence of some of bimetallic homogeneous to heterogeneous. This phenomenon provides a
nanoparticles containing various amounts of Au and Pd (Table S2, good illustration of a bimetallic effect in which one metal dopes
Figure S5, ESI). These particles show uniform lattice pattern and another metal. We also found that Au plays two important roles.
single crystallinity but possessing two metals (Figure 2). This The first is to capture and stabilize Pd, and the second is to produce
supports our belief that the enhanced catalytic activity of Pd is due a bimetallic system that catalyzes the reaction by a different
to the dilution of surface Pd atoms by gold in forming these very mechanism.
few numbers of Au rich Au/Pd bimetallic nanoparticles in situ.
Trigueiro, A. Tolstogouzov, O. M. N. D. Teodoro, R. Zboril, R.
S. Varma, P. S. Branco, Green Chem., 2014, 16, 3494.
8
a) S. Mukhopadhyay, G. Rothenberg, D. Gitis, H. Wiener, Y.
Sasson, J. Chem. Soc. Perkin Trans. 2, 1999, 2481.
Notes and references
9
a) J. M. Richardson, C. W. Jones, Adv. Synth. Catal., 2006,
348, 1207; b) M. B. Thathagar, P. J. Kooyman, R. Boerleider,
E. Jansen, C. J. Elsevier, G. Rothenberg, Adv. Synth. Catal.,
2005, 347, 1965; C) S. S. Prockl, W. Kleist, M. A. Gruber, K.
Kohler, Angew. Chem. Int. Ed., 2004, 43, 1881.
1
a) R. F. Heck, J. P Nolley, J. Org. Chem., 1972, 37, 2320; b) K.
Mori, T. Mizoroki, A. Ozaki, Bull. Chem. Soc. Jpn., 1973, 46
505; d) R. F. Heck, Acc. Chem. Res., 1979, 12, 146.
a) N. Miyaura, A. Suzuki, Chem. Rev., 1995, 95, 2457; b) F.
,
1
2
Fernandez, B. Cordero, J. Durand, G. Muller, F. Malbosc, Y. 10 a) C. W. Yi, K. Luo, T. Wei, D. W. Goodman, J. Phys. Chem. B,
Kihn, E. Teumaa, M. Gomez, Dalton, 2007, 5572; c) D.
Sanhes, E. Raluy, S. Retory, N. Saffon, E. Teumaa, M. Gomez,
Dalton, 2010, 39, 9719.
a) N. T. S. Phan, M. Van Der Sluys, C. W. Jones, Adv. Synth.
Catal. 2006, 348, 609; b) R. L. Augustine, S. T. O’Leary, J. Mol.
Catal. A: Chem., 1995, 95, 277; c) R. L. Augustine, S. T.
O’Leary, J. Mol. Catal., 1992, 72, 229; d) S. Jansat, J. Durand,
I. Favier, F. Malbosc, C. Pradel, E. Teuma, M. Gomez,
2005, 109, 18535; b) F. Gao, D. W. Goodman, Chem. Soc.
Rev., 2012, 41, 8009.
11 a) J. Xu, T. White, P. Li, C. H. He, J. G. Yu, W. K. Yuan, Y. –F.
Han, J. Am. Chem. Soc., 2010, 132, 10398; b) T. Gracia, S.
Agouram, A. Dejoz, J. F. Sanchez-Royo, L. Torrente-Murciano,
3
4
B.
Solsona,
Catal.
Today,
2014,
doi:
10.1016/j.cattod.2014.03.039; c) M. O. Nutt, K. N. Heck, P.
Alvarez, M. S. Wong, Appl. Catal. B, 2006, 69, 115; d) A.
Sárkány, O. Geszti, G. Sáfrán, Appl. Catal. A, 2008, 350, 157;
e) N. E. Kolli, L. Delannoy, C. J. Louis, Catal., 2013, 297, 79; f)
T. Longfei, W. Xiaoli, C. Dong, L. Huiyu, M. Xianwei, T.
ChemCatChem, 2009,
P. Serp, M. Gomez, E. Teuma, ChemCatChem, 2011,
a) M. T. Reetz, E. Westermann, Angew. Chem. Int. Ed. 2000,
, 165; b) M. T. Reetz, G. Lohmer, R. Schwickardi, Angew.
Chem. Int. Ed. 1998, 37, 481; c) A. H. M. de Vries, J. M. C. A.
Mulders, J. H. M. Mommers, H. J. W. Hendrickx, J. G. de 12 a) X. Wei, X. F. Yang, A. Q. Wang, L. Li, X. Y. Liu; T. Zhang, J.
1, 244; e) L. Rodriguez-Perez, C. Pradel,
3, 749.
39
Fangqiong, J. Mater. Chem. A, 2013,
1, 10382; g) J. Long, H.
Liu, S. Wu, S. Liao, Y. Li, ACS Catal., 2013,
3, 647.
Vries, Org. Lett., 2003,
Elshof, G. Rothenberg, Angew. Chem. Int. Ed., 2006, 45
886; e) L. D. Pachon, G. Rothenberg, Appl. Organometal.
5
, 3285; d) M. B. Thathagar, J. E. ten
Phys. Chem., 2012, 116, 6222; b) S. Carrettin, P. McMorn, P.
Johnston, K. Griffin, C. J. Kielyc, G. J. Hutchings, Phys. Chem.
Chem. Phys., 2003, 5, 1329.
,
2
Chem., 2008, 22, 288; f) J. Durand, E. Teuma, M. Gómez, Eur. 13 N. Toshima, Macromol. Sci. Chem., 1990, 27, 1225.
J. Inorg. Chem., 2008, 3577; g) I. Favier, D. Madec, E. Teuma, 14 M. Chen, D. Kumar, C.-W. Yi, D. W. Goodman, Science, 2005,
M. Gomez, Curr. Org. Chem., 2011, 15, 3127.
a) A. V. Gaikwad, A. Holyuigre, M. B. Thathagar, J. E. ten 15 H. Zhang, T. Watanabe, M. Okumura, M. Haruta, N. Toshima,
Elshof, G. Rothenberg, Chem. Eur. J., 2007, 13, 6908; b) S.
Nat. Mater. 2012, 11, 49.
Mac-Quarrie, J. H. Horton, J. Barnes, K. McEleney, H. P. 16 a) N. K. Chaki, H. Tsunoyama, Y. Nigishi, H. Sakurai, T.
310, 291.
5
Loock, C. M. Crudden, Angew. Chem. Int. Ed., 2008, 47, 3279;
c) K. Kohler, R. G. Heidenreich, S. S. Soomro, S. S. Prockl, Adv.
Synth. Catal., 2008, 350, 2930; d) K. Q. Yu, W. Sommer, J. M.
Richardson, M. Weck, C. W. Jones, Adv. Synth. Catal., 2005,
Tsukuda, J. Phys. Chem. C, 2007, 111, 4885; b) S. S. Yudha, R.
N. Dhital, H. Sakurai, Tetrahedron Lett, 2011, 52, 2633; c) O.
Sophiphun, J. Wittayakun, R. N. Dhital, S. Haesuwannakij, A.
Murugadoss, H. Sakurai, Aust. J. Chem. 2012, 65, 1238; d) A.
Murugadoss, K. Okumura, H. Sakurai, J. Phys. Chem. C, 2012,
116, 26776; e) D. Wang, A. Villa, F. Porta, L. Prati, D. Su, J.
Phys. Chem. C, 2008, 112, 8617; f) C. Rossy, J. Majimel, E.
Fouquet, C. Delacôte, M. Boujtita, C. Labrugère, M. Tréguer-
Delapierre, F. X. Felpin, Chem. Eur. J., 2013, 19, 14024; g) H.
B. Liu, U. Pal, A. Medina, C. Maldonado, J. A. Ascencio, Phys.
Rev. B, 2005, 71, 075403; h) J. Cai, Y. Y. Ye, Phys. Rev. B,
1996, 54, 8398; i) M. L. Wu, D. H. Chen, T. C. Huang,
Langmuir, 2001, 17, 3877.
347, 161.
6
7
a) S. Higashibayashi, H. Sakurai, Chem. Lett., 2007, 36, 18; b)
A. F. G. Masud Reza, S. Higashibayashi, H. Sakurai, Chem.
Asian J., 2009, 4, 1329; c) S. Higashibayashi, A. F. G. Masud
Reza, H. Sakurai, J. Org. Chem. 2010, 75, 4626; d) M.
Yamanaka, M. Morishima, Y. Shibata, H. Higashibayashi, H.
Sakurai, Organometallics, 2014, 33, 3060.
a) N. Hoshiya, M. Shimoda, H. Yoshikawa, S. Shuto, M.
Arisawa, J. Am. Chem. Soc. 2010, 132, 7270; b) B. Yuan, Y.
Pan, Y. Li, B. Yin, H. Jiang, Angew. Chem. Int. Ed. 2010, 49
,
17 a) R. N. Dhital, C. Kamonsatikul, E. Somsook, K. Bobuatong,
M. Ehara, S. Karanjit, H. Sakurai, J. Am. Chem. Soc. 2012,
134, 20250. b) R. N. Dhital, H. Sakurai, Chem. Lett. 2012, 41,
4
5
054; c) L. Djakovitch, K. Koehler, J. Chem. Soc. 2001, 123,
990; d) K. Mori, K. Yamaguchi, T. Hara, T. Mizugaki, K.
Ebitani, K. Kaneda, J. Chem. Soc. 2002, 124, 11572; e) K.
630.
Mori, T. Hara, M. Oshiba, T. Mizugaki, K. Ebitani, K. Kaneda, 18 B. Boekfa, E. Pahl, N. Gaston, H. Sakurai, J. Limtrakul, M.
New J. Chem. 2005, 29, 1174; f) R. J. White, R. Luque, V. L.
Budarin, J. H. Clark, Chem. Soc. Rev., 2009, 38, 481; g) S. Sá,
M. B. Gawande, A. Velhinho, J. P. Veiga, N. Bundaleski, J.
Ehara, J. Phys. Chem. C, 2014, 118, 22188.
4
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Table of contents
The stabilization of Au by Pd in Au/Pd bimetallic
nanoclusters enhanced the reactivity of Pd and
changed the reaction mechanism.
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