Dual Lewis Acidic/Basic Pd0.5Ru0.5-Poly(N-vinyl-2-pyrrolidone) Alloyed Nanoparticle: Outstanding Catalytic Activity and Selectivity in Suzuki-Miyaura Cross-Coupling Reaction

Article abstract of DOI:10.1002/cctc.201500758

This article anticipates the development of dual Lewis acidic/basic alloyed nanoparticle (NP) of poly(N-vinyl-2-pyrrolidone)-stabilized Pd_0.5Ru_0.5 solid solution, revealing equivalent Pd^δ+ and Ru^δ- on the NP surface. This unsupported NP disclosed excellent catalytic efficiency with high turnover frequency, 15 000 h^-1 in Suzuki-Miyaura cross-coupling under notable drop of both Pd loading (0.08 mol %) and time (5 min) in air, attributed for its bifunctional acidic/basic modes. The bifunctional modes exposed the most interesting new reaction mechanism ascribed by the inductive effects of p-substituents in arylboronic acid, accelerated reactivity by electron-withdrawing group, revealing an opposite reactivity trend relative to other Pd-based catalysts. Besides, the significant drops of Pd loading and reaction time impeded the metal leaching associated with no changes in NP surface composition/structure after the 3rd cycle (>99 % efficiency), revealing a line-up for this NP in the environmental sustainability. Opposing charges, working together: Bifunctional Lewis acidic/basic Pd^δ+Ru^δ-(1:1) solid-solution nanoparticles disclose a remarkable catalytic efficiency in the Suzuki-Miyaura reaction at very low Pd loading and short reaction time in air. It reveals enhanced reactivity by the electron-withdrawing groups on arylboronic acids, resulting negatively charged aromatic ring in the transition state, which is a clear controversy to the conventional Pd catalysis.

Full text of DOI:10.1002/cctc.201500758

DOI: 10.1002/cctc.201500758
Full Papers
Dual Lewis Acidic/Basic Pd0.5Ru0.5–Poly(N-vinyl-2-
pyrrolidone) Alloyed Nanoparticle: Outstanding Catalytic
Activity and Selectivity in Suzuki–Miyaura Cross-Coupling
Reaction
Md. Shahajahan Kutubi,*[a, b] Katsutoshi Sato,[a, c] Kenji Wada,[d] Tomokazu Yamamoto,[b, e]
Syo Matsumura,[b, e] Kohei Kusada,[b, f] Hirokazu Kobayashi,[b, f] Hiroshi Kitagawa,*[b, f, g, h] and
Katsutoshi Nagaoka*[a, b]
This article anticipates the development of dual Lewis acidic/
basic alloyed nanoparticle (NP) of poly(N-vinyl-2-pyrrolidone)-
stabilized Pd0.5Ru0.5 solid solution, revealing equivalent Pdd+
and RudÀ on the NP surface. This unsupported NP disclosed ex-
cellent catalytic efficiency with high turnover frequency,
15000 hÀ1 in Suzuki–Miyaura cross-coupling under notable
drop of both Pd loading (0.08 mol%) and time (5 min) in air,
attributed for its bifunctional acidic/basic modes. The bifunc-
tional modes exposed the most interesting new reaction
mechanism ascribed by the inductive effects of p-substituents
in arylboronic acid, accelerated reactivity by electron-withdraw-
ing group, revealing an opposite reactivity trend relative to
other Pd-based catalysts. Besides, the significant drops of Pd
loading and reaction time impeded the metal leaching associ-
ated with no changes in NP surface composition/structure
after the 3rd cycle (>99% efficiency), revealing a line-up for
this NP in the environmental sustainability.
Introduction
Noble-metal nanostructures have engrossed enormous interest
because of their novel properties and corresponding applica-
tions in broad-range areas, such as catalysis, sensing, surface-
enhanced spectroscopy, biological imaging, optoelectronics
etc.,[1] and catalysis has been signified as the most important
chemical application of metal nanoparticles (NPs) from recent
years.[1b] Among the nanostructures, bimetallic NPs have been
fascinating a significant scientific and technological perspective
by their distinctly different superior catalytic activity in chemi-
cal transformations over that of the corresponding component
metal,[1b,2–5] and in addition, a noteworthy synergistic effect,
observed in the investigative studies on these distinctly differ-
ent properties, attributes the considerable changes in both
geometrical and electronic structures in bimetallic NPs.[6,7]
However, the bimetallic alloyed structure among bimetallic
NPs structures, such as core–shell, heterostructure etc., was
found to be the most important nanocatalyst (NC) structure in
numerous catalytic reactions (oxidation; reduction, hydrogena-
tion, dehydrogenation, cross-coupling, etc.),[7,8] because of the
uniformity in the homogeneous composition of both compo-
nent metals and equal infirmity in charge (charge density)
transfer,[9] revealing a well-defined catalytic active site for catal-
[a] Dr. M. S. Kutubi, Prof. K. Sato, Prof. K. Nagaoka
Department of Applied Chemistry
Oita University
[e] T. Yamamoto, Prof. S. Matsumura
Department of Applied Quantum Physics and Nuclear Engineering
Kyushu University
700 Dannoharu, Oita, Oita 870-1192 (Japan)
E-mail: nagaoka@oita-u.ac.jp
Motooka 744, Nishi-ku, Fukuoka 819–0395 (Japan)
[f] Prof. K. Kusada, Prof. H. Kobayashi, Prof. H. Kitagawa
Division of Chemistry, Graduate School of Science
Kyoto University
kutoubimohamado@oita-u.ac.jp
[b] Dr. M. S. Kutubi, T. Yamamoto, Prof. S. Matsumura, Prof. K. Kusada,
Prof. H. Kobayashi, Prof. H. Kitagawa, Prof. K. Nagaoka
CREST
Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606–8502 (Japan)
E-mail: kitagawa@kuchem.kyoto-u.ac.jp
Japan Science and Technology (JST)
4–1–8 Honcho, Kawaguchi, Saitama 332–0012 (Japan)
[g] Prof. H. Kitagawa
Institute for Integrated Cell-Material Sciences (iCeMS)
Kyoto University
[c] Prof. K. Sato
Elements Strategy Initiative for Catalysts and Batteries
Kyoto University
1–30 Goryo-Ohara, Nishikyo-ku, Kyoto 615–8245 (Japan)
Yoshida, Sakyo-ku, Kyoto 606–8501 (Japan)
[h] Prof. H. Kitagawa
INAMORI Frontier Research Center
Kyushu University
[d] Prof. K. Wada
Department of Chemistry for Medicine, Faculty of Medicine
Kagawa University
1750–1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761–0793 (Japan)
Motooka 744, Nishi-ku, Fukuoka 819–0395 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500758.
ChemCatChem 2015, 7, 3887 – 3894
3887
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
ysis.[10] Thus, bimetallic alloyed NCs are now a hot research
topic from both scientific and technological viewpoints,[11] be-
cause the development of highly active and selective, and du-
rable noble NCs is vitally important for atomically utilizing the
catalysts and the reactants with the maximum product output
at low cost and low environment impact in the chemical trans-
formation.[12] However, it is still difficult to synthesize bimetallic
alloyed solid-solution NPs of uniformly homogeneous compo-
sition with predetermined shape and composition by wet
chemical synthesis because of the variations in the standard re-
duction potential of individual alloyed metallic component, as-
sociated different atomic sizes, and reduction rates.[8,13] For ex-
ample, a miscible solid solution in binary form, e.g., RuÀRh,
RhÀPd, and RuÀPd, is very difficult to synthesize,[14] although
Ru, Rh, and Pd are neighboring 4d-series noble metals in the
periodic table. Recently Kitagawa and co-workers have success-
fully synthesized a bimetallic Ag0.5Rh0.5 alloyed NPs in uniform
and homogeneous composition of both Ag and Rh.[15a] Very re-
cently our group Kusada et al. successfully synthesized uniform
and homogeneous alloyed NPs of PVP (PVP: poly(N-vinyl-2-pyr-
rolidone))-stabilized PdxRu1Àx (PdxRu1Àx–PVP) solid solution
through a chemical reduction of metal cations by overcoming
scientifically and technologically challenging barriers of differ-
ent redox potentials of Pd and Ru,[15b,16] and then observed
a higher catalytic activity of Pd0.5Ru0.5–PVP NPs in CO oxidation
than with a usual catalyst.[15b] In addition, Wu et al. and Huang
et al. reported Pd0.6Ru0.4/C NPs for formic acid electrooxidation
and PdRu/MSN (MSN: mesoporous silica nanoparticles) for
phenol hydrogenation separately.[16,17] However, only few of
numerous Pd-based bimetallic NPs were applied to cross-cou-
pling reactions so far[7a,4b,12,18] although Pd-based catalysts
have become a hot topic because of excellent catalytic per-
formance in CÀC cross-couplings, for example, Suzuki–Miyaura,
Heck, Sonogashira etc. reactions in organic synthesis.[7,19] To
the best of our knowledge, unsupported bimetallic alloyed
NCs[12,18a] are very limited, although several supported bimetal-
lic NCs were reported on cross-coupling.[7,4b,20] However, sup-
porting materials clearly impede the evaluation of the basic
and essential properties of the NP surface without the effect of
metal–support interaction and therefore more uniform particle
sizes cannot be obtained.[1b] In addition, the supporting materi-
al can change the original surface criteria of NPs, and different
catalytic activities of the same NP supported on different mate-
rials were observed in the Suzuki–Miyaura cross-coupling
(SMC) reaction by Choi and co-workers,[4b,20] for example, cata-
lytic efficiency decreases in the order: PdÀAg/ZnO>PdÀCu/
ZnO[20b] and PdÀCu/C>PdÀAg/C.[4b] However, PdRu NPs have
yet not been applied for cross-coupling reaction. Herein, we
further applied unsupported Pd0.5Ru0.5–PVP NPs to cross-cou-
pling reactions to evaluate the catalytic proficiency in organic
synthesis and SMC reaction was tested as a model reaction. As
the catalytic performance of the NPs catalyst is largely depen-
dent on the nanostructures, processing technologies, and the
intrinsic physical and chemical properties of the constitutive
components in the nanostructures,[7b] and the more important
possible synergetic catalytic effect in nanocomposite catalysts
is prevailed in many nanocomposites mostly synthesized by
chemical processes,[7b,19d,21] we first synthesized Pd0.5Ru0.5–PVP
NPs in chemical reduction process[15b] and then characterized
the NP surface. After that, NP was tested in SMC reaction with
the aim of achieving considerable reduction of both Pd load-
ing and reaction time to overcome the current metal-leaching
issue[12,22] toward the development of environmentally benign
bifunctional catalysts regarding greener perception, and subse-
quently its catalytic mechanism for CÀC cross coupling reac-
tion, as bimetallic nanoparticles are expected to reduce the
cost of catalysts and improve their resistance to poisoning.[19a]
In this article, we, for the first time, focus on the new devel-
opment of a robust dual Lewis acid/base characteristic NC of
unsupported PVP-stabilized Pd0.5Ru0.5 solid-solution NPs, which
revealed uniformity and homogeneity in composition of both
Pd and Ru at the atomic level and equally opposite charges
(both d+ and dÀ) on its surface, and showed its bifunctional
catalytic activity revealing high catalytic efficiency and selectivi-
ty with recycle ability in SMC reaction under mild conditions in
air without structural change and metal leaching.
Results and Discussion
Characterization of Pd0.5Ru0.5–PVP NPs
At first, our synthesized Pd0.5Ru0.5-PVP NPs were characterized
by high-resolution transmission electron microscopy (HRTEM),
high-angle annular dark-field (HAADF) scanning transmission
electron microscopy (STEM), and energy dispersive X-ray spec-
troscopy (EDS) mapping and linescan analysis, X-ray photoelec-
tron spectroscopy (XPS) and X-ray diffraction (XRD) spectrosco-
py, and in addition, after the 3rd cycle of SMC reaction, this
used catalyst was characterized to investigate broadly its cata-
lytic mode in SMC reaction. The experimental results of
HRTEM, HAADF–STEM, EDS mapping, and linescan analysis for
fresh Pd0.5Ru0.5–PVP shown in Figure S1 in the Supporting Infor-
mation revealed Pd0.5Ru0.5–PVP alloyed solid solution with ho-
mogeneous composition of both Pd and Ru at the atomic
level throughout the whole crystalline Pd0.5Ru0.5–PVP NPs corre-
lated to the previous results reported by our group.[15b]
As the XPS method is recognized as informative enough for
understanding the catalytic properties of bimetallic NPs, which
are dominated mainly by the metal composition and structure
of the nanoparticle surface,[1b] Pd0.5Ru0.5–PVP NP surface was
also characterized by XPS. The XPS results of fresh Pd0.5Ru0.5–
PVP NP are shown in Figures S2(a) and S2(b) and Table 1.
Table 1. Core-level XPS data of Pd 3d and Ru 3p for fresh nanoparticles
of Pd–PVP, Pd0.5Ru0.5–PVP and Ru–PVP.
Sample[a]
Pd 3d5/2 [eV]
(top peak)
Ru 3p3/2 [eV]
(top peak)
dPd or dRu [eV]
(assigned)
Pd–PVP
Pd0.5Ru0.5-PVP
Ru-PVP
334.30
334.55
0.0 (Pd0)
+0.25 (Pdd+
)
461.4
460.6
0.0 (Ru0)
À0.80 (RudÀ
Pd0.5Ru0.5–PVP
)
[a] PVP in all cases was 13.5Æ0.5 wt%.
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3888
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
These results revealed the binding energy shift positively in Pd
3d5/2 and negatively in Ru 3p3/2 relative to those in individual
monometal Pd–PVP and Ru–PVP. These results predicted the
surface electronic structure of fresh Pd0.5Ru0.5–PVP NPs clearly
correlated to the results in earlier article.[15b] The binding
energy shifts, which were positively in Pd 3d and negative in
Ru 3p, addressed somewhat oxidation on Pd by +0.25 eV, as-
suming the developing of partial positive charge (d+), and
somewhat reduction in Ru by À0.8 eV, growing partial nega-
tive charge (dÀ) in Pd0.5Ru0.5–PVP NP surface for electron-densi-
ty transfer from the fully occupied 4d orbital of Pd (Pd(46)=
[Kr]4d10) toward the partially filled 4d orbital of Ru (Ru(44)=
[Kr]4d75s1).[23,24]
3 mmolK2CO3 in 6 mL DMA/H2O (1:1) system at 1008C for
5 min stirring in air, affording product 3a in 98% (isolated)
with >99% selectivity (entry 1 in Table 3).
To investigate the surface criteria of PdxRu1-x–PVP (x = 0.0 –
1.0) NPs with different composition in Pd and Ru, PdxRu1-x–PVP
NPs and Pd salts (PdCl2 and Pd(CH3CO2)2) were screened for
the reaction in Scheme 1 under optimized conditions (except
for the catalyst), and the corresponding results are listed in
Table 2. Here Pd0.5Ru0.5–PVP NPs afforded the highest efficiency,
yielding>99% 3a (entry 6), whereas, monometallic Ru0–PVP
NPs did not show any catalytic performance, even at a higher
amount (3 times the amount in entry 6) of catalyst loading (en-
tries 1, 2), although only Na et al. found efficient catalysis of
5 mol% Ru–PVP NP supported on Al2O3 at 908C for 12 h reac-
tion time.[28] Here we reduced both time (from 12 h to 5 min),
and catalyst amount (Ru from 5 mol% to 0.08 mol%) relative
to their developed method. However, 0.16 mol% Pd0–PVP NPs
gave 39% yield of 3a (entry 3), and a physical mixture of
0.16 mol% Pd0–PVP and 0.16 mol% Ru0–PVP gave 52% yield
(and 55% yield for 0.32 mol% Ru0–PVP) of 3a (entries 4 and 5).
Such results assign the synergistic effects in bimetallic alloyed
solid solution and cooperative participation of both metallic
components. In addition, 0.16 mol% of each of Pd0.1Ru0.9–,
Pd0.3Ru0.7–, and Pd0.7Ru0.3–PVP yielded 52%, 75%, and 70% of
3a, respectively (entries 7–9), and 0.16 mol% of PdCl2 and
Pd(CH3CO2)2 in homogeneous catalysis gave 29% and 65%
yield of 3a with Pd-black formation (entries 10 and 11). This
study focused on the best catalytic activity of Pd05Ru0.5–PVP rel-
ative to other compositions in PdxRu1Àx-PVP (x¼ 0.5). Such out-
standing catalytic activity of Pd0.5Ru0.5–PVP NC was ascribed to
In addition, these results of XPS experiments also support
the d-band theory (recently developed), which reveals a signifi-
cant role of electronic and geometric properties of NCs with
their catalytic performance[25] exploring the generation of
a new electronic state during bimetallic alloy formation by hy-
bridization of valence shell orbitals of component metals and,
consequently, a flow of charge density (d electrons and d
holes (d-band center)) towards the metal of partially unoccu-
pied valence orbitals from the metal of fully occupied valence
orbitals (valence bands).[26,27] Therefore, the uniform distribu-
tion of both d+ on Pd and dÀ on Ru are attributed to the
Pd0.5Ru0.5–PVP NPs surface assigning Pdd+RudÀ(1:1)–PVP NPs.
For simplicity, Pd0.5Ru0.5–PVP stands for Pdd+RudÀ(1:1)–PVP
throughout this article.
Pd0.5Ru0.5–PVP NPs-catalyzed SMC Reaction
uniform coexistence of both opposite charges (Pdd+ and RudÀ
)
Evaluation of the catalytic efficiency of the Pd0.5Ru0.5–PVP NPs
catalyst was first performed by optimizing the condition of the
SMC reaction between bromobenzene (1a) and 4-methylphe-
nylboronic acid (2a) in Scheme 1 under the screening of differ-
ent amounts of both substrates (1a and 2a) and catalyst
(Pd0.5Ru0.5–PVP NPs), different bases (Na2CO3, K2CO3, Rb2CO3,
Cs2CO3, NaOAc, KSCN, (NH4)2HPO4, and Na2HPO4), different sol-
vents (toluene, CH3CN, ethanol, 1,4-dioxane, DMA (N,N-dime-
thylacetamide), DMF (N,N-dimethylformamide), 1,2-dimethoxy-
ethane, and water) in either single or binary system with H2O)
by stirring at a different temperature for a different time in air,
regarding very high efficiency and selectivity with a significant
reduction in both metal loading and reaction time in greener
perception. The experimental results were tabulated in the Ta-
bles S1–S3 in the Supporting Information. This study summar-
ized the optimized conditions of 1.0 mmol 1a with 1.2 mmol
2a in the presence of 0.16 mol% Pd0.5Ru0.5–PVP NPs and
on its surface in bifunctional modes, serving acceptor and
donor properties[24] as well as dual Lewis acid/base properties
at a time. The charge transfer rises somewhat of the Pd charac-
teristics on Ru by the synergetic effect.[24] These bifunctional
modes cooperatively participate in the catalysis through rapid
cleavage of both the polar Cd+ÀXdÀ bond of ArÀX (Ar=aryl),
and the polar CdÀÀBd+ bond of ArÀB(OH)2. But, in another
composition, for example, either Pd>Ru or Ru>Pd in
Table 2. Screening of catalysts in SMC reaction (Scheme 1) under
optimized conditions.
Entry
Catalyst/PVP[a]
[mol%]
Size
[nm]
Yield (3a)
[%][b]
1
2
3
4
5
6
7
8
Ru (0.16)
Ru (0.5)
Pd (0.16)
Pd, Ru (0.16, 0.16)
Pd, Ru (0.16, 0.32)
Pd0.5Ru0.5 (0.16)
Pd0.1Ru0.9 (0.16)
Pd0.3Ru0.7 (0.16)
Pd0.7Ru0.3 (0.16)
PdCl2 (0.16)
6.4Æ1.7
6.4Æ1.7
9.8Æ2.6
mixture
mixture
10.0Æ1.2
9.4Æ1.7
10.4Æ1.9
8.2Æ1.6
bulk
0
0
39
52
55
>99
52
75
70
29
9
10
11
Pd(CH3CO2)2 (0.16)
bulk
65
Scheme 1. Pd0.5Ru0.5–PVP NPs-catalyzed SMC reaction between bromoben-
zene (1a) and 4-methylphenylboronic acid (2a) for the optimization of the
reaction conditions.
[a] PVP: 13.5Æ0.5 wt%. [b] 1H NMR yield based on internal standard
1,3,5-trimethoxybenzene.
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3889
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
PdxRu1ÀxPVP (x¼ 1Àx), opposite charges on the NP surface are
not uniform and equal to each other. Therefore, the Pd0.5Ru0.5–
PVP surface in 1:1 composition of Pd/Ru shows outstanding
catalytic efficiency in SMC reaction relative to other composi-
tions.
ents and lower reactivity by EDG substituents (entries 5, 9, and
10) were observed in the reactivity trend: H>CH3 >OCH3, and
this reactivity trend is the same as that observed in either Pd-
catalyzed[29,30] or bimetallic NPs-catalyzed[12,19a] SMC reactions.
Here, this is caused by inductive effects governed by the in-
crease of electron density for EDG (or decrease for EWG) sub-
stituents in the CÀX bond, making it stronger, resulting in
lower reactivity (or weaker by EWG, revealing higher reactivity).
However, p-substituted arylboronic acids, p-R1ÀC6H4B(OH)2 (2),
showed higher reactivity by EWG substituents and lower reac-
tivity by EDG substituents, affording >99% 3a for R1 =H (2b)
in entry 3 and 70% 3c for R1 =OCH3 (2c) in entry 5 with the
same p-MeÀC6H4ÀBr (1c). This reactivity trend observed for 2 is
absolutely opposite to that in Pd-catalyzed SMC reactions.[31,30b]
Therefore, inspired by such new reactivity trend for 2, a kinetic
study for 2 regarding a variety of p-substituents, R1: OCH3 (2c),
CH3 (2a), H (2b), and Cl (2d) with 1a was investigated in
Scheme S1 (Section 2.4 in the Supporting Information) to clear-
ly elucidate the inductive effects for EWG and EDG in 2 and
then kinetic results was used to sketch the familiar Hammett
plots[30a,b] shown in Figure 1. The Hammett plot explored
a linear correlation by higher catalytic activity for EWG and
vice versa for EDG in the reactivity trend: R1 =Cl>H>CH3 >
OCH3 in 2, and revealed negative charge built up on aromatic
ring of 2 in the transition state (see the mechanism in
Scheme 4), which is stabilized by EWG (and destabilized by
EDG) on 2, and subsequently the reaction rate accelerated by
EWG, but slowed down by EDG.
Encouraged by this outstanding catalytic efficiency with the
particular attention to uniform Pdd+ and RudÀ components on
Pd0.5Ru0.5–PVP NP surface, this catalyst was also tested to inves-
tigate the role of the inductive effect by electron-donating-
group (EDG) and electron-withdrawing-group (EWG) substitu-
ents, on both p-substituted aryl halides (1) and p-substituted
arylboronic acids (2) in Scheme 2 under optimized conditions.
The corresponding results are summarized in Table 3.
The results in Table 3 show that most of the SMC reactions
afforded 97%–>99% yield with >99% selectivity except for
entries 5, 9, and 10. The reactions of EDG (CH3 or OCH3)-substi-
tuted phenyl bromides (1c, 1d) with EDG (OCH3)-substituted
phenylboronic acid (2c) afforded relatively low yields in 70%
3c, 78% 3d, and 65% 3e (entries 5, 9, and 10). Here, for p-sub-
stituted phenyl bromides, higher reactivity by EWG substitu-
Besides, although supported nanoparticles usually show re-
cycle ability,[32] the recycling assessment of the unsupported
Pd0.5Ru0.5–PVP NPs in the successive three cycles[12] (by addition
of substrates base and solvents[29]) revealed >99% efficiency
(>99% product 3j in each cycle) without any loss of the cata-
lytic activity in SMC reaction between phenyl iodide (1b) and
4-chlorophenylboronic acid (2d) under optimized conditions in
Scheme 2. Pd0.5Ru0.5-PVP NPs-catalyzed SMC reactions of aryl halide (1) with
arylboronic acid (2) under optimized conditions.
Table 3. Results of substrates (1 and 2) screening in Scheme 2.[a]
Entry R, X (1); R1 (2)
Product (3)
Yield[b] [%]
1
2
3
H, Br (1a); CH3 (2a)
H, I (1b); CH3 (2a)
CH3, Br (1c); H (2b)
98
>99
>99
4
CH3, Br (1c); CH3 (2a)
>99
5
6
CH3, Br (1c); OCH3 (2c)
OCH3, Br (1d); CH3 (2a)
70
97
7
8
9
OCH3, Br (1d); H (2b)
H, I (1b); OCH3 (2c)
H, Br (1a); OCH3 (2c)
OCH3, Br (1d);
99
>99
78
10
11
65
OCH3 (2c)
CH3CO, Br (1e); H (2b)
>99
CH3CO, Br (1e);
CH3 (2a)
12
13
>99
>99
CH3CO, Br (1e);
OCH3 (2c)
14
15
H, I (1b); H (2b)
H, Br (1a); H (2b)
>99
98
16
H, I (1b); Cl (2d)
>99
Figure 1. Hammett plot for Pd0.5Ru0.5–PVP NPs-catalyzed SMC reactions
(Scheme S1).
[a] Under optimized conditions. [b] Isolated yield.
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3890
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
air (see details in the Supporting Information Section 2.5 and
Table S4) at the significant reduction of both Pd loading
(0.08 mol%) and reaction time (5 min) focusing on very high
average turnover frequency (TOF: the mole of product pro-
duced per mole Pd (total) per hour) 15000 hÀ1 relative average
TOF: ꢀ3600 hÀ1 (ꢀ1.0 sÀ1 for three cycles, calculated as the
product formed per surface Pd atom per second for PdÀRh
NPs[12]), as average TOF values giving the rate of product for-
mation measured in each cycle are valid and meaningful
data.[19c,e] As consistently high conversions or yields in a few re-
peated runs are taken as evidence to prove the high potential
of the catalyst,[19c] and change in bimetallic composition and
geometrical structure during SMC reaction,[12] this used catalyst
after the 3rd cycle, without farther recycle experiment, was
tested for the STEM–EDS mappings and linescan analysis, and
XRD spectroscopy experiments to find out any change in NP
surface during SMC reactions. However, some reports focused
on 5–10 times recyclability, but there longer reaction times
were required, resulting in very low average TOF, for example,
Hoshiya et al. reported 10 recycles with 0.007 mol% Pd for
supported Pd-Au NPs, each for 12 h at 808C in argon, revealing
average TOF 113 hÀ1[22a] (ꢀ1/133 of that observed in
Pd0.5Ru0.5–PVP NPs).
Here, the experimental results of STEM–EDS mappings and
linescan analyses, and XRD spectroscopy for used Pd0.5Ru0.5–
PVP NC after 3rd cycle shown in Figures 2, and S3 separately
revealed the existence of a uniform homogeneous solid solu-
tion of both Pd and Ru without any changes in both i) uniform
bimetallic composition of Pd and Ru in solid solution alloyed
NPs and ii) geometrical structure in Pd0.5Ru0.5–PVP NPs after
3rd cycle of SMC reaction, compared with those of fresh
Pd0.5Ru0.5–PVP NPs (Figures S1 and S3). Such result of unchang-
ing in the bimetallic composition and structural geometry ex-
plored no displacement of compositional metals (Pd and Ru)
in the alloyed Pd0.5Ru0.5–PVP NPs during the SMC reaction and
therefore, no metal leaching occurred, whereas recently Wang
and co-workers reported the changes in shape and surface
structure of bimetallic Pd–Rh nanocrystal associated with
metal leaching (5–15%of original amount of catalyst found by
inductively coupled plasma atomic emission spectroscopy
(ICP–AES) in SMC reaction.[12]
Figure 2. HAADF–STEM image of Pd0.5Ru0.5–PVP NPs after the third cycle in
the SMC reaction and TEM–EDS analyses of the region marked by a red box.
a) HAADF–STEM image; b–d) EDS maps for Pd, Ru, and overlay of both Pd
(green) and Ru (red), respectively; e) compositional linescan profile along
the arrow in (a) (Pd: green and Ru: red).
leached metal detected. Thus both experimental results ob-
served in STEM–EDS mappings and linescan analyses
(Figure 2), and XRD pattern (Figure S3) correlated with the re-
sults of the leaching test. Therefore, we concluded that no
metal (Pd and/or Ru) leaching was caused for the cooperative
catalysis by Pdd+–RudÀ NPs, which possess a stronger polar co-
valent bond impeding the metal leaching in very short time re-
action than monometallic or nonalloyed core–shell bimetallic
NCs, in which only one metal participates in activating the
CÀX and CÀB bonds for cleavage, resulting longer reaction
time.[19d,22,32]
Moreover, to clarify the metal leaching in Pd0.5Ru0.5–PVP NPs
catalysis, at first, the SMC reaction between 1a and 2a
Scheme 1 (see also Supporting Information Section 2.6), per-
formed under optimized conditions (or in 6 mL EtOH/H2O (1:1)
at 308C for 10 min in air) for the three catalysts Pd0.5Ru0.5–PVP
NPs, Pd–PVP NPs and homogeneous Pd(CH3CO2)2, separately
for the original catalytic activity test and then leached metal
activity test for each catalyst, was performed for additional 3 h
described in detail in the Supporting Information Section 2.6.
The results are shown in Tables S5 and S6. The leached metal
activity test revealed additional yields of 3a of 0% for
Pd0.5Ru0.5–PVP at both 1008C and 308C, respectively, and 5%
and 35% for Pd–PVP NPs and homogeneous Pd(CH3CO2)2 at
1008C, respectively, (but 0% and 79% yield of 3a, respectively,
at 308C). Besides, ICP–AES analysis of the residual water part
collected after separation of the organic part confirmed no
On the other hand, any homocoupling products of either
aryl halide or arylboronic acid were not observed under opti-
mized conditions. Besides, experiments with only single sub-
strates of either 2a or 1a did not show any corresponding ho-
mocoupling product under optimized conditions. Therefore, it
was concluded that the very low amount of catalyst and the
very short reaction time were the actual reason for no homo-
coupling, although several studies reported somewhat homo-
coupling product formation during SMC reaction at low Pd
loadings with long reaction time (0.09 mol% Pd, 24 h)[29] and
high Pd loading with long reaction time (0.5 mol% Pd, 6 h).[33]
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3891
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
showed somewhat high catalytic activity at either
low Pd loading with longer reaction time or high Pd
loading with short reaction time, associating metal
leaching.
Table 4. Comparative catalytic efficiency in terms of TOF between Pd0.5Ru0.5–PVP NPs
and other catalysts developed very recently for SMC Reaction.
Catalyst [mol% of Pd]
R (1)
t [min]
TOF
[hÀ1
]
In addition, the Pd0.5Ru0.5–PVP-catalyzed SMC reac-
tion showed the same efficiency with the same TOF
of 15000 hÀ1 under 3 or 5 times of both substrates (3
or 5 mmol) and catalyst loading (0.6 or 1.0 mg) com-
pared with optimized conditions (1 mmol substrate
and 0.2 mg catalyst) and after two years in air. This
reveals a high stability of this catalyst in normal at-
mosphere without any loss of its catalytic activity.
As a number of researchers insisted that the Suzuki
and Heck reactions would proceed at the surface of
Pd-based NPs in truly heterogeneous reactions,[7b] all
our results, that is, Pdd+RudÀ on the NP surface, no
change in NP composition and structural geometry,
Pd0.5Ru0.5–PVP NPs (0.08)[a]
Pd0.5Ru0.5–PVP NPs(0.08)[a]
Poly(imidazole–Pd) (0.004)[b]
Graphene–Ni/Pd NPs (0.91)[c]
PdxRh1Àx nanocrystal (0.002)[d]
Pd–PVP NPs (0.006)[e]
CH3 (1c)
OCH3 (1d)
OCH3 (1d)
H (1a)
CH3 (1c)
H (1a)
5
5
180
30
20
24 h
15000
14850
8166[34a]
171[32c]
max.ꢀ2880[12]
688[34b]
[a] Conditions (this work): 1 mmol 1c (or 1d), 1.2 mmol 2b, 3 mmolK2CO3, 6 mL DMA/
H2O(1:1), 1008C. [b] Conditions:[34a] 0.5 mmol 1c (or 1d), 0.6 mmol 2b, 2 mmolK2CO3,
1 mol TBAF (additive), 1.5 mL H2O, 1008C; [c] Conditions:[32c] 2.0 mmol 1a, 0.82 mmol
2b, 2 equiv K2CO3, 10 mL DMF/H2O(7:3), 110 8C. [d] Conditions:[12] 0.3 mmol 1c,
0.6 mmol 2b, 1 mmolK2CO3, 4 mL EtOH, 858C. [e] Conditions:[34b] 0.5 mmol 1a,
0.75 mmol 2b, 1.5 mmolK3PO4, 4 mL EtOH/H2O (1:3), 908C.
As SMC reaction is one of the most industrially applicable or-
ganic synthesis reactions, numerous catalytic systems (both
homogeneous and heterogeneous) were developed, and this
is still of interest to researchers because of the universal issue
of metal leaching in both homogeneous and heterogeneous
catalysis, including the global industrial voice of “faster, better,
and cheaper.” In Table 4, comparative catalytic efficiencies are
presented in terms of TOF (based on total Pd) between
Pd0.5Ru0.5–PVP NPs catalyst and other catalysts: poly(imida-
zole)–Pd,[34a] graphene–Ni/Pd NPs,[32c] PdÀRh nanocrystal,[12] and
PVP-stabilized Pd NPs[34b] developed by Yamada et al., 2012,[34a]
Metin et al., 2012,[32c] Wang et al., 2014,[12] and Uberman et al.,
2012[34b], individually reported earlier (for SMC reaction in
Scheme 3).
and no metal leaching for Pd0.5Ru0.5–PVP NP catalysis in SMC
reactions, attributed to truly heterogeneous catalytic
mode.[7b,12,32a] Therefore, we ascribed the following reaction
mechanism (shown in Scheme 4) for the SMC reaction in
Scheme 2.
a
In Scheme 4, step 1 involves the interaction between 1 and
catalyst surface by chemisorption, affording species A (p-RÀ
C6H4Àcat.ÀX) through the rapid cleavage of Cd+ÀXdÀ bond by
cooperative participation of both Pdd+ and RudÀ. In the pres-
ence of water, KOH (K2CO3 +H2OQKOH+KHCO3) is usually
formed because the SMC reaction did not proceed at all in the
absence of base. Therefore, in step 2, reactant 2 interacts with
species A by Pdd+ with CdÀ and RudÀ with Bd+ through a transi-
tion state developing negative charge on the aromatic ring of
2 (supported by the Hammett plot, Figure 1), promoted by
OHÀ for rapid cleavage of the CdÀÀBd+ bond, and B(OH)3
leaves, and finally species B is formed. This species B at step 3
rapidly undergoes associative chemisorption between the
Lewis acid characteristics of the aryl part of 1 having a positive
charge and the Lewis basic characteristics of the aryl part of 2
The results in Table 4 reveal very high efficiency and selectiv-
ity of the Pd0.5Ru0.5 catalyst in the SMC reaction with higher
TOF of 15000 hÀ1 compared with those of other catalysts, poly-
(imidazole)–Pd: 8166 hÀ1, graphene–Ni/Pd NP: 171 hÀ1, PdÀRh
nanocrystal: 2880 hÀ1, and PVP-stabilized Pd NP: 688 hÀ1, for
the same SMC reactions involving the same substrates 1 and
2b. In the case of poly(imidazole)–Pd, large amounts (2 equiv.)
of expensive nBu4NF (tetra-n-butylammonium fluoride) as an
additive along with 2 equivalents of K2CO3 seemed to be es-
sential to activate the catalyst for high TOF of 8166 hÀ1,[34a] but
Pd0.5Ru0.5–PVP NPs revealed very high TOF without such addi-
tive. Therefore, compared to Pd-based catalysts, Pd0.5Ru0.5–PVP
NC revealed very high catalytic activity at the reduction of
both Pd loading and reaction time, resulting in the prevention
of metal leaching accompanied with no changes in bimetallic
composition and geometrical structure, although other reports
Scheme 3. SMC reaction for comparing the catalytic efficiencies of different
Scheme 4. Plausible mechanism for Pd0.5Ru0.5–PVP NPs-catalyzed SMC
catalysts.
reaction.
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3892
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
chromatograph mass spectrometer of GCMS–QP2010 Ultra SHI-
MADZU. Thin-layer chromatography analysis was performed on
silica gel 60 F254 (Merck KGaA, Germany). Column chromatography
was performed on silica gel 60 of either 0.040–0.063 mm or 0.063–
0.2 mm (Merck KGaA, Germany). In addition, ICP–AES was per-
formed on a Shimadzu ICPS-8100 instrument by the chemical anal-
ysis team at RIKEN (Saitama 351–0198, Japan) for the metal leach-
ing test.
having a negative charge in the manner of Lewis acid–base in-
teraction, and subsequently biaryl product 3 is afforded fol-
lowed by leaving Pd0.5Ru0.5–PVP NP for the next catalytic cycle.
Here step 2 was assumed to play a significant role over the
whole catalytic cycle, associating the significant transition state
with negatively charged aromatic ring, correlated by the kinet-
ic study of the Hammett plot. Therefore, step 2 was ascribed
as the rate-determining step (RDS) here, conversely to the oxi-
dative addition step as RDS[7b,35] under strongly basic support
materials or ligands that lead to higher electron density on the
Pd-based catalyst surface and accelerate the oxidative addi-
tion[7b] because electron-deficient Pdd+ impedes oxidative ad-
dition in Pd0.5Ru0.5–PVP NPs catalysis.
Synthesis of PdxRu1Àx–PVP nanoparticles
At first the Pd0.5Ru0.5–PVP NPs were synthesized by a typical
method of wet chemical reduction of metal ions under very slow
addition of an aqueous solution (40 mL) of K2[PdCl4] (0.1634 g,
0.5 mmol) and RuCl3·nH2O (n=3, 0.1311 g, 0.5 mmol) to a hot solu-
tion of PVP (molecular weight, MWꢀ40000; 0.444 g) in triethylene
glycol (100 mL) under constant stirring at 2008C in air; the temper-
ature of approximately 2008C was constantly maintained during
the addition. After completing the addition, the whole solution
Conclusions
We have demonstrated anomalous behavior of bimetallic
Pd0.5Ru0.5–PVP (poly(N-vinyl-2-pyrrolidone)-stabilized Pd0.5Ru0.5)
solid solution nanocatalyst in the Suzuki–Miyaura cross-cou-
pling (SMC) reaction, revealing very high efficiency with excel-
lent recyclability under the significant reduction of both Pd
loading and reaction time without inert atmosphere. The most
important findings are that this alloyed nanoparticle surface
contains uniformly Pdd+ and RudÀ, which attributes bifunction-
al catalytic activity in dual Lewis acidic/basic modes, and the
reaction mechanism likely is completely different from that of
the conventional Pd-based catalyzed SMC reaction, which is
usually described in terms a single Pd metal associating the ox-
idative addition as rate-determining step, whereas here the
transmetallation-type step is ascribed as rate-determining step
regarding the transition state with negatively charged aromatic
ring. The fruitful impeding of metal leaching attributed to no
changes in NP surface composition/geometrical structure and
a significant drop in Pd loading and reaction time would make
this catalyst as a footprint in the environmental sustainability
regarding a novel strategy of interelemental fusion to create
highly efficient functional materials for the material conver-
sions in organic synthesis. We believe that this development
with the arguments presented hopefully makes Pd0.5Ru0.5–PVP
an attractive nanocatalyst to open new possibilities for large-
scale application in other cross-coupling reactions as well as
chemical transformation.
was cooled to RT under constant stirring and then the Pd0.5Ru0.5
–
PVP NPs were isolated by centrifuging followed by vacuum drying
overnight.[15b]
Catalyst characterization
The synthesized Pd0.5Ru0.5–PVP alloyed NPs were characterized
before (fresh) and after the SMC reaction (3rd cycle) by the analysis
of (a) HRTEM, HAADF–STEM, and EDS, (b) XPS, and (c) XRD pat-
terns. HRTEM, HAADF–STEM, and EDS analysis were performed
firstly by sample preparation by dropwise placing thoroughly dis-
persed Pd0.5Ru0.5–PVP in ethanol onto a C-coated grid followed by
drying through exposure under ambient conditions for 24 h, and
then finally recording the HRTEM, HAADF-STEM, and EDS mapping
data on a JEOL JEM–ARM 200F instrument operated at 120 kV. XPS
experiments were performed on a Shimadzu ESCA-850 under the
binding energy calibration with a reference of C1s orbital at
284.6 eV[23a] by placing the sample (sampling on a metal grid) into
the chamber. XRD patterns were recorded on a MiniFlex 600 X-ray
diffractometer (Rigaku, Japan) with CuKa radiation.
Typical procedure for the SMC reaction of aryl halide (1)
with arylboronic acid (2)
A 10 mL glass vial was charged with aryl halide (1, 1 mmol) , aryl-
boronic acid (2, 1.2 mmol ), Pd0.5Ru0.5–PVP (0.2 mg, 0.0016 mmol;
0.0008 mmol Pd loaded, that is, 0.08 mol% Pd), K2CO3 (3 mmol),
and mixed solvent (6 mL) of DMA (3 mL) and H2O (3 mL) followed
by constant stirring at 1008C for 5 min in air. The reaction was
then stopped immediately by dipping the bottom part of the reac-
tion vial into ice cold water (08C). The organic part was extracted
with diethyl ether (or ethyl acetate) (5 mL”4) followed by centri-
fuging to collect the solid catalyst. Next, the combined organic
part was dried over anhydrous Na2SO4, and concentrated under re-
duced pressure. The crude product was purified by silica gel flash
column chromatography (hexane/ethyl acetate 19:1) to obtain the
cross-coupling product, 3 and then isolated products were charac-
terized by 1H NMR, 13C NMR, and GC–MS spectroscopies. The
1H NMR yield was quantified by using the internal standard of
1,3,5-trimethoxybenzene.
Experimental Section
General
All manipulations were performed under normal atmospheric con-
ditions unless otherwise noted. Reagents and solvents were pur-
chased from commercial suppliers (Wako Pure Chemical Industries,
Ltd., Japan; Tokyo Chemical Industry, TCI, Japan and Sigma Aldrich,
Japan) and used without further purification. Water was deionized
1
with a Millipore system as a Milli-Q grade. H NMR (400 MHz) and
13C NMR (100 MHz) spectra were recorded on a Bruker-400 NMR-
spectrometer. Chemical shifts (d) in H and 13C NMR spectroscopy
1
were reported relative to that of tetramethylsilane (TMS, d=
0.00 ppm) in NMR solvents (Cambridge Isotope Laboratories Inc.,
USA). GC–MS of individual pure product was performed on a gas
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3893
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
K. Sato, K. Nagaoka, H. Kitagawa, J. Am. Chem. Soc. 2014, 136, 1864–
1871.
Acknowledgements
[16] D. Wu, M. Cao, M. Shen, R. Cao, ChemCatChem 2014, 6, 1731–1736.
[17] C. Huang, X. Yang, H. Yang, P. Huang, H. Song, S. Liao, Appl. Surf. Sci.
2014, 315, 138–143.
[18] a) R. N. Dhital, H. Sakurai, Chem. Lett. 2012, 41, 630–632; b) J. Xiang, P.
Li, H. Chong, L. Feng, F. Fu, Z. Wang, S. Zhang, M. Zhu, Nano Res. 2014,
7, 1337–1343; c) S. U. Son, Y. Jang, J. Park, H. B. Na, H. M. Park, H. J. Yun,
J. Lee, T. Hyeon, J. Am. Chem. Soc. 2004, 126, 5026–5027.
[19] a) M. Chen, Z. Zhang, L. Li, Y. Liu, W. Wang, J. Cao, RSC Adv. 2014, 4,
30914–30922; b) G. M. Scheuermann, L. Rumi, P. Steurer, W. Bannwarth,
R. Mülhaupt, J. Am. Chem. Soc. 2009, 131, 8262–8270; c) . Molnµr,
Chem. Rev. 2011, 111, 2251–2320; d) N. Miyaura, A. Suzuki, Chem. Rev.
1995, 95, 2457–2483; e) J. A. Gladysz, Pure Appl. Chem. 2001, 73, 1391–
1324.
This work was financially supported for “Core Research for Evolu-
tional Science and Technology (CREST)” by Japan Science and
Technology Agency (JST), Japan.
Keywords: alloys · CÀC coupling · nanoparticles · palladium ·
reaction mechanisms
[1] a) Y. Hu, Y. Liu, Z. Li, Y. Sun, Adv. Funct. Mater. 2014, 24, 2828–2836;
b) N. Toshima, T. Yonezawa, New J. Chem. 1998, 22, 1179–1201.
[2] a) J. I. He, I. Ichinose, T. Kunitake, A. Nako, Y. Shirashi, N. Toshima, J. Am.
Chem. Soc. 2003, 125, 11034–11040; b) J. M. Thomas, B. F. G. Johnson,
R. Raja, G. Sankar, P. A. Midgley, Acc. Chem. Res. 2003, 36, 20–30.
[3] a) P. V. Kamat, J. Phys. Chem. B 2002, 106, 7729–7744; b) S. Sun, C. B.
Murray, D. Weller, L. Folks, A. Moser, Science 2000, 287, 1989–1992;
c) J. A. Christodoulides, Y. Huang, Y. Zhang, G. C. Hadjipanayis, I. Pana-
giotopoulos, D. Niarchos, J. Appl. Phys. 2000, 87, 6938–6940; d) J.-I.
Park, M. G. Kim, Y.-W. Jun, J. S. Lee, W.-R. Lee, J. Cheon, J. Am. Chem.
Soc. 2004, 126, 9072–9078; e) S. R. Nicewarner-PeÇa, R. G. Freemann,
B. D. Reiss, L. He, D. J. PeÇa, I. D. Walton, R. Cromer, C. D. Keating, M. J.
Natan, Science 2001, 294, 137–141.
[4] a) Z. Zheng, H. Li, T. Liu, R. Cao, J. Catal. 2010, 270, 268–274; b) S.-J.
Kim, S.-D. Oh, S. Lee, S.-H. Choi, J. Ind. Eng. Chem. 2008, 14, 449–456;
c) S. Koh, P. Strasser, J. Am. Chem. Soc. 2007, 129, 12624–12625; d) K.
Sasaki, H. Naohara, Y. Cai, Y. M. Choi, P. Liu, M. B. Vukmirovic, J. X. Wang,
R. R. Adzic, Angew. Chem. Int. Ed. 2010, 49, 8602–8607; Angew. Chem.
2010, 122, 8784–8789; e) V. R. Stamenkovic, B. Fowler, B. S. Mun, G.
Wang, P. N. Ross, C. A. Lucas, N. M. Markovic, Science 2007, 315, 493–
497.
[20] a) R. Narayanan, Molecules 2010, 15, 2124–2138; b) M.-R. Kim, S.-H.
Choi, J. Nanomater. 2009, 2009, 302919.
[21] a) C. Boissiere, D. Grosso, A. Chaumonnot, L. Nicole, C. Sanchez, Adv.
Mater. 2011, 23, 599–623; b) D. P. Debecker, P. H. Mutin, Chem. Soc. Rev.
2012, 41, 3624–3650; c) G. A. Somorjai, J. Y. Park, Angew. Chem. Int. Ed.
2008, 47, 9212–9228; Angew. Chem. 2008, 120, 9352–9368.
[22] a) N. Hoshiya, M. Shimoda, H. Yoshikawa, Y. Yamashita, S. Shuto, M. Ari-
sawa, J. Am. Chem. Soc. 2010, 132, 7270–7272; b) L. D. Pachón, G. Roth-
enberg, Appl. Organomet. Chem. 2008, 22, 288–299; c) M. B. Thathagar,
J. E. ten Elshof, G. Rothenberg, Angew. Chem. Int. Ed. 2006, 45, 2886–
2890; Angew. Chem. 2006, 118, 2952–2956; d) A. V. Gaikwad, A. Holui-
gue, M. B. Thathagar, J. E. ten Elshof, G. Rothenberg, Chem. Eur. J. 2007,
13, 6908–6913.
[23] a) C. D. Wanger, W. M. Riggs, L. E. Davis, J. Moulder, in Handbook of X-
ray photoelectron Spectroscopy-A Reference Book of Standard Data for
Use in X-ray Photoelectron Spectroscopy, PerkinElmer Corporation, Physi-
cal Electronic Division, Minnesota, 1979, pp. 8–11 and pp. 110–111;
b) J. M. Tura, P. Regull, L. Victori, M. D. de Castellar, Surf. Interface Anal.
1988, 11, 447–449; c) M. M. Coulter, J. A. Dinglasan, J. B. Goh, S. Nair,
D. J. Anderson, V. M. Dong, Chem. Sci. 2010, 1, 772–775; d) J. Y. Shen, A.
Adnot, S. Kaliaguine, Appl. Surf. Sci. 1991, 51, 47–60.
[5] a) Y. Lu, W. Chen, ACS Catal. 2012, 2, 84–90; b) E.-Y. Ko, E. D. Park, H. C.
Lee, D. Lee, S. Kim, Angew. Chem. Int. Ed. 2007, 46, 734–737; Angew.
Chem. 2007, 119, 748–751.
[6] a) L. Prati, A. Villa, F. Porta, D. Wang, D. Su, Catal. Today 2007, 122, 386–
390 and references 2, 8–11 therein; b) D. I. Enache, J. K. Edwards, P.
Landon, B. Solsona-Espriu, A. F. Carley, A. A. Herzing, M. Watanabe, C. J.
Kiely, D. W. Knight, G. J. Hutchings, Science 2006, 311, 362–365; c) J. K.
Edwards, B. E. Solsona, P. Landon, A. F. Carley, A. Herzing, C. J. Kiely, G. J.
Hutchings, J. Catal. 2005, 236, 69–79.
[24] J. A. Rodriguez, D. W. Goodman, Science 1992, 257, 897–903.
[25] a) P. J. Feibelman, D. R. Hamann, Phys. Rev. Lett. 1984, 52, 61; b) L. M. Fa-
licov, G. A. Somorjai, Proc. Natl. Acad. Sci. USA 1985, 82, 2207–2211;
´
c) M. H. Cohen, M. V. Ganduglia-Pirovano, J. Kudrnovsky, Phys. Rev. Lett.
1994, 72, 3222; d) J. Harris, S. Andersson, Phys. Rev. Lett. 1985, 55, 1583.
[26] C. Q. Sun, Y. Wang, Y. G. Nei, B. R. Mehta, M. Khanuja, S. M. Shivaprasad,
Y. Sun, J. S. Pan, L. K. Pan, Z. Sun, Phys. Chem. Chem. Phys. 2010, 12,
3131–3135.
[7] a) A. K. Singh, Q. Xu, ChemCatChem 2013, 5, 652–676; b) J. Shi, Chem.
Rev. 2013, 113, 2139–2181.
[8] a) H.-L. Jiang, Q. Xu, J. Mater. Chem. 2011, 21, 13705–13725; b) D. A.
Hansgen, D. G. Vlachos, J. G. Chen, Nat. Chem. 2010, 2, 484–489; c) H.
Kobayashi, M. Yamauchi, H. Kitagawa, Y. Kubota, K. Kato, M. Takata, J.
Am. Chem. Soc. 2010, 132, 5576–5577; d) F. Studt, F. Abild-Pedersen, T.
Bligaard, R. Z. Sørensen, C. H. Christensen, J. K. Nørskov, Science 2008,
320, 1320–1322.
[9] S. Nishimura, Y. Yakita, M. Katayama, K. Higashimine, K. Ebitani, Catal.
Sci. Technol. 2013, 3, 351–359.
[10] I. Notar Francesco, F. Fontaine-Vive, S. Antoniotti, ChemCatChem 2014,
6, 2784–2791.
[11] a) J. Zhang, L. Zhang, Y. Jia, G. Chen, X. Wang, Q. Kuang, Z. Xie, L.
Zheng, Nano Res. 2012, 5, 618–629; b) M. Chen, D. Kumar, C.-W. Yi,
D. W. Goodman, Science 2005, 310, 291–293; c) J. Xu, T. White, P. Li, C.
He, J. Yu, W. Yuan, Y.-F. Han, J. Am. Chem. Soc. 2010, 132, 10398–10406.
[12] S.-B. Wang, W. Zhu, J. Ke, M. Lin, Y.-W. Zhang, ACS Catal. 2014, 4, 2298–
2306.
[13] a) D. Wang, Y. Li, J. Am. Chem. Soc. 2010, 132, 6280–6281; b) S. Maksi-
muk, S. Yang, Z. Peng, H. Yang, J. Am. Chem. Soc. 2007, 129, 8684–
8685; c) Z. Peng, H. Yang, Nano Today 2009, 4, 143–164; d) L. Zhang, J.
Zhang, Q. Kuang, S. Xie, Z. Jiang, Z. Xie, L. Zheng, J. Am. Chem. Soc.
2011, 133, 17114–17117.
[27] E. Nikolla, J. Schwank, S. Linic, J. Am. Chem. Soc. 2009, 131, 2747–2754.
[28] Y. Na, S. Park, S. B. Han, H. Han, S. Ko, S. Chang, J. Am. Chem. Soc. 2004,
126, 250–258.
[29] S. Proch, Y. Mei, J. M. R. Villanueva, Y. Lu, A. Karpov, M. Ballauff, R.
Kempe, Adv. Synth. Catal. 2008, 350, 493–500.
[30] a) S. Saito, S. Oh-tani, N. Miyaura, J. Org. Chem. 1997, 62, 8024–8030;
b) C. M. Nunes, A. L. Monterio, J. Braz. Chem. Soc. 2007, 18, 1443–1447.
[31] P. K. Mandali, D. K. Chand, Catal. Commun. 2013, 31, 16–20.
[32] a) P. J. Ellis, I. J. S. Fairlamb, S. F. J. Hackett, K. Wilson, A. F. Lee, Angew.
Chem. Int. Ed. 2010, 49, 1820–1824; Angew. Chem. 2010, 122, 1864–
1868; b) Z. Niu, Q. Peng, Z. Zhuang, W. He, Y. Li, Chem. Eur. J. 2012, 18,
9813–9817; c) Ö. Metin, S. F. Ho, C. Alp, H. Can, M. N. Mankin, M. S. Gül-
tekin, M. Chi, S. Sun, Nano Res. 2013, 6, 10–18; d) Y. Wu, D. Wang, P.
Zhao, Z. Niu, Q. Peng, Y. Li, Inorg. Chem. 2011, 50, 2046–2048.
[33] F. Gonzàlez de Rivera, I. Angurell, M. D. Rossell, R. Erni, J. Llorca, N. J.
Divins, G. Muller, M. Seco, O. Rossell, Chem. Eur. J. 2013, 19, 11963–
11974.
[34] a) Y. M. A. Yamada, S. M. Sarkar, Y. Uozumi, J. Am. Chem. Soc. 2012, 134,
3190–3198; b) P. M. Uberman, L. A. PØrez, G. I. Lacconi, S. E. Martin, J.
Mol. Catal. A 2012, 363–364, 245–253.
[35] J. P. Corbet, G. Mignani, Chem. Rev. 2006, 106, 2651–2710.
[14] a) S. N. Tripathi, S. R. Bharadwaj, M. S. Chandransekh-araiah, J. Phase
Equilib. 1996, 17, 362–365; b) S. N. Tripathi, S. R. Bharadwaj, S. R. Dhar-
wadkar, J. Phase Equilib. 1993, 14, 638–642.
Received: July 7, 2015
[15] a) K. Kusada, M. Yamauchi, H. Kobayashi, H. Kitagawa, Y. Kubota, J. Am.
Chem. Soc. 2010, 132, 15896–15898; b) K. Kusada, H. Kobayashi, R.
Ikeda, Y. Kubota, M. Takata, S. Toh, T. Yamamoto, S. Matsumura, N. Sumi,
Revised: August 7, 2015
Published online on October 5, 2015
ChemCatChem 2015, 7, 3887 – 3894
www.chemcatchem.org
3894
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim