DNA-supported palladium nanoparticles as a reusable catalyst for the copper- and ligand-free Sonogashira reaction

Article abstract of DOI:10.1039/c7cy00001d

DNA nanotechnology has recently emerged as a powerful discipline with diverse applications. However, studies focused on the combination of DNA and metal nanoparticles for catalyst design are scanty. We have prepared a catalyst composed of palladium nanoparticles supported on DNA which has been characterised by TEM, SEM, EDX, UV, FTIR and XPS. The catalyst, mainly composed of Pd(ii) and Pd(iv) species in the form of oxides, has been effectual in the copper- and ligand-free Sonogashira-Hagihara coupling of aryl iodides with terminal aromatic and aliphatic alkynes. The products are obtained in 54-86% isolated yields using low catalyst loading (0.5 mol%) under mild conditions (65 °C) in methanol without air exclusion. Moreover, the catalyst can be easily recovered and reused in five cycles and shows better performance than an array of commercial palladium catalysts. The mechanistic aspects of the reaction are also tackled in detail.

Full text of DOI:10.1039/c7cy00001d

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. S. Camacho, I.
Martín-García, C. A. Contreras-Celedón, L. Chacón-García and F. Alonso, Catal. Sci. Technol., 2017, DOI:
10.1039/C7CY00001D.
This is an Accepted Manuscript, which has been through the
Volume 6 Number 1 7 January 2016 Pages 1–308
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
Accepted Manuscripts are published online shortly after
www.rsc.org/catalysis
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
ISSN 2044-4753
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Please do not adjust margins
Page 1 of 12
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C7CY00001D
DNA-supported palladium nanoparticles as a reusable catalyst for
the copper- and ligand-free Sonogashira reaction
Received 00th January 20xx,
Accepted 00th January 20xx
Ana Silvia Camacho,a,† Iris Martín-García,a Claudia Contreras-Celedón,b Luis Chacón-Garcíab,* and
Francisco Alonsoa,*
DOI: 10.1039/x0xx00000x
DNA nanotechnology has recently emerged as a powerful discipline with diverse applications. However, studies focused on
the combination of DNA and metal nanoparticles for catalyst design are scanty. We have prepared a catalyst composed of
palladium nanoparticles supported on DNA which has been characterised by TEM, SEM, EDX, UV, FTIR and XPS. The
catalyst, mainly composed of Pd(II) and Pd(IV) species in the form of oxides, has been effectual in the copper- and ligand-
free Sonogashira-Hagihara coupling of aryl iodides with terminal aromatic and aliphatic alkynes. The products are obtained
in 54–86% isolated yields using low catalyst loading (0.5 mol%) under mild conditions (65 ºC) in methanol without air
exclusion. Moreover, the catalyst can be easily recovered and reused in five cycles and shows better performance than an
array of commercial palladium catalysts. The mechanistic aspects of the reaction are also tackled in detail.
www.rsc.org/
In recent decades, acetylene chemistry has experienced a
renaissance due not only to its exploitation in the chemical
Introduction
Nowadays, it is indisputable that the inertia that accompanies
discoveries in nanoscale sciences and technology is a car race
without brakes. In this context, nanoparticles (NPs)1 are
among the most attractive nanomaterials due to their
dependence on properties associated with its size,2 playing an
prominent role in pharmacology as an alternative to drug
delivery, in nanoelectronic systems as sensors and in chemistry
as a catalysts.3 On the other hand, enzymes, lipids and nucleic
acids are advantageous biomaterials because they are non-
toxic, environmentally friendly, readily available and
biodegradable; that is why the successful preparation of bio-
nanoparticles such as DNA-NPs has recently emerged.4
Leaving aside the relevance of the genetic information
inherent to DNA, nucleic acids have also become useful as
chemical and physical tools. Indeed, the combination of the
physical and chemical properties of DNA with nanotechnology
has given rise to DNA nanotechnology, a discipline covering
the design and study of synthetic structures based on DNA and
its manifold applications.5 The high affinity of DNA for
transition metals makes it suitable to act as a ligand for the
metallization of DNA, as a template for the synthesis of metal
nanomaterials and as a support for metal nanoparticles.6 In
spite of the soaring upsurge of interest in developing DNA-
metal nanoparticle hybrid materials, their application in
heterogeneous catalysis is still in its infancy.6 For instance, in
such a highly productive research area in catalysis as the
carbon-carbon coupling,7 to the best of our knowledge, there
are only three related reports, dealing with the application of
PdNPs-DNA to the Suzuki-Miyaura cross-coupling reaction.8
industry, biochemistry and materials science, but also because
of its versatility for the synthesis of natural products and
pharmaceuticals of interest.9 Alkyne chemistry has been
mainly driven by the progress of new synthetic methodologies
based on transition-metal catalysis, where palladium always
occupies a leading position. In this scenario, the Sonogashira-
Hagihara reaction is currently one of the most widely practiced
methods to prepare alkyl and aryl acetylenes as well as
conjugated enynes.10
The standard Sonogashira catalytic system involves
a
palladium source in the presence of copper(I) and an amine.
Depending on whether the catalyst is homogeneous or
heterogeneous, its nature (salt, complex, supported metal,
nanoparticles, etc.) and the presence or absence of copper
(and its oxidation state) and amine, other agents also come
into play; such is the case of ligands (e.g., PPh3) or
promoters/stabilisers (e.g., tetra-n-butylammonium halides).
However, both from the practical and environmental point of
view, simpler catalytic systems which function under mild
conditions in the absence of copper, amines and the aforesaid
additives are desirable. In this vein, the development of air-
stable and recyclable catalysts should be also a priority.
The solvent issue is another matter of concern, as most of the
common solvents deployed for this coupling reaction are not
recommended; they have been ranked according to a set of
safety, health and environment criteria as follows: toluene and
acetonitrile
dimethylformamide,
methylpyrrolidin-2-one (hazardous).11
(problematic),
1,4-dioxane,
N,N-
N-
N,N-dimethylacetamide
and
Therefore, despite the vast research devoted to the title
reaction, the design and implementation of new catalysts with
upgraded properties which operate under sustainable
conditions is welcome.
To the best of our knowledge, hybrid bio-metallic catalysts
based on Pd/DNA have not been applied to the Sonogashira-
Hagihara reaction hitherto. Due to our ongoing interest in
metal nanoparticles12 and transition-metal catalysed carbon-
carbon coupling reactions,13 we want to present herein our
effort to devise a catalyst composed of PdNPs on DNA for the
a.Instituto de Síntesis Orgánica (ISO) and Departamento de Química Orgánica,
Facultad de Ciencias, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain; E-
mail: falonso@ua.es
b.Laboratorio de Diseño Molecular, Instituto de Investigaciones Químico-Biológicas,
Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, 58066,
México; E-mail: lchacon@umich.mx
† Present address: Laboratorio de Diseño Molecular, Instituto de Investigaciones
Químico-Bilógicas, Universidad Michoacana de San Nicolás de Hidalgo, Morelia,
Michoacán, 58066, México.
Electronic Supplementary Information (ESI) available: [TEM and SEM images,
experimental procedures, compound characterisation and NMR spectra]. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 12
ARTICLE
Journal Name
efficient copper-, amine- and ligand-free Sonogashira-Hagihara
reaction of aryl iodides and terminal alkynes; we have also
made every endeavour to understand its mode of action.
View Article Online
DOI: 10.1039/C7CY00001D
70
60
50
40
30
20
10
0
Results and discussion
Catalyst preparation and characterisation
The catalyst was prepared following a simple procedure in the
absence of any stabilising or nucleation agent, i.e., by mixing
Li2PdCl4, NaOAc and salmon-sperm DNA in methanol at room
temperature with stirring for 48–72 hours (Figure 1).
0 - 2
2 - 4
4 - 6
6 - 8
8 - 10
10 - 12 12 - 14
The resulting brown solid was characterised by different
means. The palladium content in the catalyst, 6.4 wt%, was
determined by inductively coupled plasma optical emission
spectroscopy (ICP-OES). Analysis by Transmission Electron
Microscopy (TEM) (Figure 2, top) revealed the presence of
near spherical nanoparticles of ca. 7.1 ± 3.5 nm (Figure 3),
uniformly distributed on the DNA surface with no sign of
agglomeration. Scanning Electron Microscopy (SEM) brought
into view morphological and topological information of the
surface as visualised in Figure 2 (bottom), which corroborated
this regular particle dispersion.
diameter (nm)
Fig. 3 Particle size distribution of PdNPs/DNA. The sizes were determined for 138
nanoparticles selected at random.
Fig. 4 EDX spectrum of PdNPs/DNA run on a copper grid.
2,5
2
Fig. 1 Preparation sequence of PdNPs/DNA.
DNA
1,5
Pd salt
1
Pd/DNA
0,5
0
200
250
300
350
400
Wavelength (nm)
Fig. 5 UV spectrum of DNA, Li2PdCl4 and PdNPs/DNA in ethanol.
Energy-dispersive X-ray (EDX) analysis on various regions
confirmed the presence of palladium, with energy bands
around 3 eV corresponding to the Pd L lines,14 as well as that
of the elements present in DNA, with the following atomic
percentage: 73.6% carbon, 10.8% oxygen, 12.1% P, 0.35% Na
and 3.2% Pd (Figure 4). The nitrogen content in the catalyst, as
determined by elemental analysis, was found to be 15% (14%
for DNA). UV comparative absorption spectra of DNA (206
Li PdCl
2
nm),
(207 and 243 nm) and PdNPs/DNA (206 and 251
4
nm) in ethanol showed the composite character of the latter
(Figure 5). The fact that no resonant peak appeared above 300
nm was in agreement with the PdNPs mostly being <10 nm in
size.15 The most meaningful bands observed by IR
spectroscopic analysis of PdNPs/DNA come into view at 3000–
–
3500 cm–1 (N-H and O-H stretching), 1640, 1570 and 1540 cm
(C=O, C=N, C=C stretching and N-H bending of the
1
Fig. 2 TEM (top) and SEM (bottom) images of PdNPs/DNA.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 12
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C7CY00001D
Fig. 6 FT-IR spectrum of DNA (blue) and PdNPs/DNA (black).
Fig. 7 XPS spectrum of PdNPs/DNA at the Pd 3d5/2 and Pd 3d3/2 levels.
nucleobases), 1217 cm– (asymmetric PO2 stretching), 1062
1
–
and 965 cm– (symmetric PO2 and P–O–C backbone
stretching) (Figure 6).16 The IR spectra of DNA and PdNPs/DNA
look alike, with the only appreciable difference being that the
1
–
peak at 1062 cm– in PdNPs/DNA is resolved into two peaks
1
–
1
(1078 and 1051 cm ) in the parent DNA.
XPS analysis showed two deconvoluted Pd (3d5/2) peaks at
336.8 and 338.1 eV, and two deconvoluted Pd (3d3/2) peaks at
341.9 and 343.2 eV (Figure 7). In principle, the presence of
Pd(0) can be practically ruled out as the expected binding
energies (335.3 and 340.5 eV)17 are distinctly lower than those
displayed in Figure 7. The peaks at 336.8 and 341.9 eV could
be assigned to Pd(II) in the form of PdO,18 whereas those at
338.1 and 343.2 eV are very close to those in K2PdCl4.19
Although it may well be true that some Li2PdCl4 was present
on the support, it is important not to overlook the fact that
neither Cl nor Li were detected by EDX. On the other hand,
these binding energies are akin to those reported for Pd(IV) in
the form of PdO2.20 Therefore, it can be concluded that
PdNPs/DNA is primarily composed of Pd(II) and Pd(IV) species
in the form of the corresponding oxides (PdO and PdO2,
respectively). These results differ from those found for DNA-
modified graphene/PdNPs,8b oligonucleotide stabilised
PdNPs8c and DNA-templated Pd nanowires,16b were the use of
Fig. 8 XPS spectra of DNA [(a), (c)] and PdNPs/DNA [(b), (d)] at the P 2p and N 1s levels.
J. Name., 2013, 00, 1-3 | 3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 12
ARTICLE
Journal Name
a reductant (e.g., NaBH4) favoured the substantial formation of helix (Figure 9); the amino functionalities seem unaffected in
View Article Online
DOI: 10.1039/C7CY00001D
Pd (0).
this sense, taking part in the bases intermolecular hydrogen
XPS was found to be a useful tool also to analyse the N and P bonding.26
content as well as the interplay of these atoms with their
Optimisation of the reaction conditions
chemical environment. For instance, the relative atomic
percentage in surface allowed to estimate the N/P ratio, which The cross coupling of iodobenzene (1a) and phenylacetylene
did not practically vary from DNA (8.03) to PdNPs/DNA (8.77);
(2a) was chosen as a model reaction in order to optimise the
this ratio was notably higher than that published for the catalytic system and reaction conditions (Table 1); all reactions
commercial nucleotides (2.0‒4.0).21 XPS spectra at the P 2p were performed at 65 ºC (optimised temperature) in air. A first
and N 1s levels were carefully examined, with the following approach involving 0.5 mol% Pd, the standard co-catalysis by
results (Figure 8): (a) the DNA peaks at 132.8 (P 2p3/2) and CuI and Cs2CO3 as the base gave moderate conversions into
134.0 eV (P 2p1/2) are in agreement with the presence of 3aa only in dioxane and MeOH:H2O (1:1), together with
phosphate units (Figure 8a);22 (b) the area ratio between these considerable amounts of the diyne 4a derived from alkyne
two peaks remains unaltered from DNA to PdNPs/DNA (2.0 vs. homocoupling27 (Table 1, entries 1–6).
A remarkable
2.1, respectively) but they are shifted, to the same extent, to improvement was noticed in the absence of CuI, particularly,
higher binding energy in the latter case [133.5 (P 2p3/2) and when using polar protic organic solvents (Table 1, entries 7–
134.8 eV (P 2p1/2)] (Figure 8b); this shift points to the existence 12); MeOH was shown to be the best one, leading to a
of some phosphate-PdNPs interaction; (c) the DNA peaks at quantitative conversion into 3aa with no detectable diyne
399.0 and 399.8 eV (N 1s) can be correlated with the imino- (Table 1, entry 10).
(N=C) and amino-type (N-H) bonds of the nucleobases,
respectively (Figure 8c);23 (d) the N 1s area ratio in DNA is very
similar to that in PdNPs/DNA (2.2 and 2.0, respectively); (e) the
Table 1 The Sonogashira reaction of iodobenzene (1a) and phenylacetylene (2a).a
most important feature is, however, that the N 1s amino peak
in PdNPs/DNA maintains nearly the same binding energy
(399.6 eV) while the N 1s imino peak has been significantly
shifted to higher binding energy (401.1 eV) (Figure 8d).
The affinity of DNA for transition metals has been generally
Entry Pd/CuI (mol%)
Solvent
dioxane
DMSO
EtOH
Base Time (h) 3aa/4a (%)b
simplified to adsorption studies of the individual pyrimidine
and purine bases on zero-valent copper,24a-c silver and gold24d
surfaces. DFT calculations on a (C3TA2)3C3T DNA motif disclosed
that the preferential binding site for a Pd atom was the N3 of
the cytosines (i.e., the imino N).25 However, to the best of our
knowledge, the modes of interaction of DNA with (oxidised)
palladium nanoparticles have not been identified so far. The
results of our XPS study suggest that the PdNPs are stabilised
on DNA through a primary interaction with the imino N of the
nucleobases and a secondary interaction with the phosphate
units, both located in the periphery of the double-stranded
1
0.50/5
0.50/5
0.50/5
0.50/5
0.50/5
0.50/5
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.50/-
0.13/-
0.25/-
0.75/-
0.50/-
0.50/-
0.50/-
0.50/-
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
2
54/68
-/-
-/56
8/31
51/33
-/-
2
3
4
5
6
7
8
9
MeOH
MeOH:H2O (1:1) Cs2CO3
H2O
dioxane
DMSO
EtOH
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
3/-
-/-
71/15
>99/-
78/-
9/2
27/-
29/-
12/-
11/1
14/-
-/-
11/-
30/-
87/-
53/-
79/-
84/-
85/-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
MeOH
MeOH:H2O (1:1) Cs2CO3
H2O
Cs2CO3
Na2CO3
K2CO3
Et2NH
iPr2NH
Et3N
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
-
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
4
7
10
a Iodobenzene (1a, 0.24 mmol), phenylacetylene (2a, 0.24 mmol) and PdNPs/DNA
b
(2 mg), base (0.3 mmol), solvent (1 mL) at 65 ºC in air. Conversion determined
by GLC using n-decane as the internal standard referred to 1a.
Fig. 9 Model showing the estimated modes of interaction of PdNPs with DNA.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Please do not adjust margins
Page 5 of 12
Journal Name
ARTICLE
Table 2 The Sonogashira reaction of aryl iodides and aryl acetylenes catalysed by PdNPs/DNA.a
View Article Online
DOI: 10.1039/C7CY00001D
Aryl iodide
Aryl acetylene
Product
Conversion (%)b
Yield (%)c
a
b
Aryl iodide (1, 1.0 mmol), aryl acetylene (2, 1.0 mmol), PdNPs/DNA (8 mg, 0.5 mol%) and Cs2CO3 (1.4 mmol) in MeOH (2 mL) at 65 ºC in air, 24 h. Conversion
determined by GLC using n-decane as the internal standard referred to 1. c Isolated yield after column chromatography. d PdNPs/DNA (16 mg, 1.0 mol%). e Reaction at
80 ºC.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 12
Please do not adjust margins
Journal Name
ARTICLE
Bases other than Cs2CO3, either inorganic or organic, proved to
exert a detrimental effect on the conversion, being in all cases
below 30% (Table 1, entries 13–17). One control experiment in
the absence of the base failed and confirmed the necessity for
an external base in order to the reaction to occur (Table 1,
entry 18).
Table 3 The Sonogashira reaction of iodobenzene and aliphatic alkynes catalysed by
View Article Online
PdNPs/DNA.a
DOI: 10.1039/C7CY00001D
We next studied the effect of the palladium loading and the
reaction time. Either lower or higher Pd loadings than 0.5
mol% did not increase the conversion (Table 1, entries 19–21),
whereas prolonged stirring for 24 h is recommended to attain
the highest conversion (Table 1, compare entry 10 with entries
22–25). In view of the above results, the catalytic system of
choice consists of 0.5 mol% Pd/DNA and Cs2CO3 in MeOH at 65
ºC for 24 h in air (Table 1, entry 10).
Starting alkyne
Product
Conv. (%)b Yield (%)c
Substrate scope in the Sonogashira coupling reaction
The optimised catalytic system and reaction conditions were
applied to a series of aryl iodides and aryl acetylenes (Table 2).
Besides simple iodoaromatics, such as iodobenzene (1a) and 1-
iodonaphthalene (1b), those para-substituted with electron-
withdrawing groups (1c and 1d) also gave good conversions
and isolated yields of the Sonogashira products. Iodobenzenes
substituted with electron-donating substituents (1e and 1f) at
the para position reacted sluggishly under the standard
reaction conditions; this apparent limitation could be
overcome by either increasing the amount of catalyst (1.0
mol% Pd) or the reaction temperature (80 ºC). In contrast,
diiodobenzenes
(
1g and 1h
)
reacted nicely with
phenylacetylene (2a) to produce the conjugated triaryl diynes
3ga and 3ha in good conversions and moderate isolated yields.
Particularly interesting is the result of 3ha, which must
proceed through a more sterically encumbered 1-iodo-2-
(phenylethynyl)benzene intermediate. The reaction conditions
were compatible with the presence of an acidic hydrogen, such
as that in 1-(4-hydroxy-3-iodophenyl)ethanone (1i), which
furnished the trisubstituted phenol 3ia in moderate yield.
Not only aromatic but aliphatic alkynes could be coupled with
iodobenzene under the standard conditions to provide a range
of alkyl aryl acetylenes (Table 3). Linear-alkyl acetylene 2d
reacted quantitatively, in contrast with the cyclic alkyl
a Iodobenzene (1a, 1.0 mmol), alkyne (2, 1.0 mmol), PdNPs/DNA (8 mg, 0.5 mol%)
and Cs2CO3 (1.4 mmol) in MeOH at 65 ºC in air, 24 h. b Conversion determined by
c
counterpart 2e. The controlled mono-arylation of the terminal GLC using n-decane as the internal standard referred to 1a. Isolated yield after
diyne 2f leaves open the possibility for a second arylation
column chromatography.
reaction. Furthermore, the catalytic system was compatible
with the use of functionalised alkynes (2g-2i), even bearing
first four and some decrease in the fifth run.
The leaching issue was assessed by filtering a reaction after the
first run and analysing a sample of the filtrate by ICP-MS. The
palladium content in solution was determined to be 0.01 wt%
of the original amount. The hot filtration test was applied to a
33% (3aa) conversion reaction (2 h); further heating of the
filtrate at 65 ºC for 24 h gave 3aa in a lower percentage (11%)
due to by-product formation. Therefore, according to this
minor inactive leaching it can be concluded that the
interaction of DNA with the palladium nanoparticles leads to a
quite robust heterogeneous catalyst endowed of good
recycling properties.
acidic hydroxyl groups, to form the expected products in good
isolated yields.
Catalyst recycling
We next explored the recycling capability of PdNPs/DNA in the
coupling of iodobenzene (1a) with phenylacetylene (2a) to give
3aa. In order to check the performance after each cycle, the
catalyst was removed from the reaction medium by
centrifugation (Figure 10); the resulting precipitate was
washed, dried and used in subsequent cycles under the
standard conditions without any further treatment. As
depicted in Figure 11, the activity of the catalyst (only 8 mg)
could be extended over five cycles with no apparent loss in the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 6
Please do not adjust margins

Page 7 of 12
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C7CY00001D
Fig. 10 Pictures showing the reaction mixture before (left) and after (right)
centrifugation.
Fig. 12 TLC plate images under the UV lamp irradiation of 254 nm (left) and 365 nm
(right) corresponding to the crudes of the reactions shown in Table 4 (entries 1–4).
Certainly, commercial Pd(OAc)2 and PdCl2(PPh3)2 have been
successfully applied to the Sonogashira reaction in other
optimised copper-free catalytic systems.28 However, the use of
an inert atmosphere is mandatory in most cases and the
catalyst reutilisation is hampered because of their
homogeneous nature. Pd/C makes the possibility of
reutilisation plausible and, even though broadly used in
combination with CuI and PPh3,10d,29 some copper- and
phosphine-free procedures have been described in the
presence of an inert atmosphere.30
Mechanistic aspects
The mechanism of the copper-free palladium-catalysed
Sonogashira reaction has been a topic of continuous and
intense debate.10i,31 While most of these studies have been
focused on the homogeneous version of the reaction, the
heterogeneous counterpart has been disregarded and less
understood. In our case, we were intrigued about the role of
the different Pd species and DNA; various control experiments
were conducted with this purpose.
The ease of ionisation of the alkyne Csp–H bond can be
measured by H/D exchange and may give an idea about the
metal species participating in its activation. Two alkynes of
notable different pKa, phenylacetylene (2a) and 1-octyne (2d),
were subjected to the deuteration experiments in order to get
more reliable information (Table 5). As expected,
phenylacetylene (2a) got much easier ionised than 1-octyne
Fig. 11 Recycling of PdNPs/DNA in the synthesis of 3aa.
Comparison with commercial and other Pd catalysts
Ideally, any laboratory-made metal catalyst should manifest
distinguished catalytic activity when compared with the
commercial counterparts. This different behaviour could justify
the time and resources utilised in the preparation of the
former. With this hypothesis in mind, a variety of commercial
palladium catalysts, including three homogeneous and one
heterogeneous were tested in the coupling reaction of
iodobenzene (1a) and phenylacetylene (2a) (Table 4). The best
results were recorded with PdNPs/DNA as catalyst in both
terms of conversion and purity (Table 4, entry 1). As illustrated
in Figure 12, the commercial catalysts led to the formation of
abundant by-products under the standard conditions, whereas
the reaction with PdNPs/DNA was very clean.
(2d), with near quantitative deuteration of the former
irrespective of the presence of DNA, PdNPs/DNA or
commercial PdO·H2O (Table 5, entries 2‒4). It is noteworthy
Table 4 Comparison of PdNPs/DNA with commercial palladium catalysts.a
that DNA promoted the H/D exchange of phenylacetylene (2a
)
(Table 5, compare entries 1 and 2) but not at all that of 1-
octyne (2d) (Table 5, compare entries 2 and 6). On the
contrary, PdNPs/DNA and PdO·H2O were both effective on
phenylacetylene (2a) and 1-octyne (2d), though to a lesser
extent on the latter (Table 5, compare entries 3 and 4 with 7
and 8). These results suggest that the PdO contained in
PdNPs/DNA could enhance the acidity of the alkyne Csp–H
bond facilitating its deprotonation.32
We next paid attention to the evolution of the palladium
species in the reaction medium under the standard conditions
on the basis of XPS analysis. First, PdNPs/DNA in MeOH was
warmed at 65 ºC during 24 h; a substantial amount of Pd(0)
Entry
Catalyst
PdNPs/DNA
PdCl2
Pd(OAc)2
PdCl2(PPh3)2
Pd/C (10 wt%)
TLC label
Conversion (%)b
1
2
3
4
5
A
B
C
D
-
>99
48
51
49
42c
a
Iodobenzene (1a, 0.5 mmol), alkyne (2a, 0.5 mmol), catalyst (0.5 mol%) and
Cs2CO3 (0.7 mmol) in MeOH at 65 ºC in air, 24 h. b Conversion determined by GC-
MS. c Alkyne homocoupling product 4a was formed in 51%.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 8 of 12
ARTICLE
Journal Name
Table 5 Alkyne Csp–H ionisation.a
View Article Online
DOI: 10.1039/C7CY00001D
Entry
Alkyne
PhC≡CH (2a)
PhC≡CH (2a)
PhC≡CH (2a)
Catalystb
-
D1-2 (%)c
1
2
3
4
5
6
7
8
12
97
96
99
0
0
74
73
DNAd
PdNPs/DNA
PdO·H2O
-
DNAd
PdNPs/DNA
PdO·H2O
PhC≡CH (2a)
n-C6H13C≡CH (2d)
n-C6H13C≡CH (2d)
n-C6H13C≡CH (2d)
n-C6H13C≡CH (2d)
a Alkyne (2, 1.0 mmol) and catalyst in CD3OD at 65 ºC in air, 24 h. b 0.5 mol% Pd; c
Deuteration percentage determined by GC-MS. d 8 mg of DNA.
was generated at the expense of all the PdO and, might be, of
some PdO2 (Figure 13a). When commercial PdO·H2O was
submitted to the same essay, approximately, half of it was
transformed into Pd(0) (Figure 13b); this partial reduction
could be related to the bulk character of the PdO compared to
the nanosized PdO in PdNPs/DNA. We also analysed the
recovered PdNPs/DNA after a successful standard reaction of
iodobenzene (1a) and phenylacetylene (2a) (Figure 13c); Pd(0)
was the major species followed by PdO2, whereas the presence
of PdO was imperceptible by this technique and negligible in
any case. Opposite to this was the outcome for a failed
reaction of 4-iodoaniline (1f) and phenylacetylene (2a) under
the standard conditions, where a minute amount of Pd(0) was
formed (Figure 13d). Consequently, there is an evident trend
to accumulate Pd(0) from a working catalytic cycle which must
involve Pd(0)/Pd(II) rather than the Pd(II)/Pd(IV) system.
Considering the original PdO/PdO2 ratio in PdNPs/DNA (Figure
7) and the Pd(0)/PdO2 ratio in Figures 13a and 13c, it seems
reasonable to propose that part of the PdO2 is also converted
into Pd(0).
Given the complexity of DNA, we tried to additionally ascertain
the function of its different components within the catalytic
system. Thymine and guanine were selected as examples of
the pyrimidine and purine DNA bases, respectively, together
with diammonium hydrogenphosphate and ammonium
dihydrogenphosphate as the equivalent DNA phosphate units.
The influence of these additives in the reaction of iodobenzene
(1a) and phenylacetylene (2a) catalysed by PdNPs/DNA is
presented in Table 6. The addition of thymine markedly
depleted the catalytic activity but guanine inhibited the
reaction (Table 6, entries 2 and 3, respectively). This behaviour
could be understood as the bases in DNA having a stabilising
effect on the PdNPs; it is known that stabilisers can impede the
increase of the nanoparticle size but an excess of them can
make the catalyst less active or inactive.10i The stronger impact
of guanine could be connected with the presence of the imino
N atoms in its structure and the known affinity of the latter for
PdNPs,25 as also noted by XPS (see above). Conversely, the
phosphates did not essentially interfere in the reaction (Table
6, entries 4 and 5), reinforcing the major role of the bases in
the catalytic activity.
Fig. 13 XPS spectra of (a) PdNPs/DNA, MeOH, 65 ºC, 24 h; (b) PdO·H2O, MeOH, 65 ºC,
24 h; (c) recovered catalyst after a successful reaction of (1a) and (2a), (d) recovered
catalyst after a failed reaction of (1f) and (2a).
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 12
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
Table 6 The effect of different additives on the reaction of 1a and 2a.a
from PdO·H2O (Figure 13b), its catalytic activity was virtually nil
View Article Online
irrespective of the absence or presenceDoOfI:a1d0.d10it3iv9e/Cs7C(TYa0b0l0e016D,
entries 6–9). Seemingly, the nanosized nature of the DNA-
stabilised PdNPs makes all the difference when compared with
the bulk Pd of the commercial catalyst.
Three types of mechanisms are generally considered in C-C
coupling reactions catalysed by PdNPs:10i (a) PdNPs acting as
an authentic heterogeneous catalyst through its surface; (b)
leaching of Pd(0) atoms from the PdNPs which get into a
homogeneous catalytic cycle; (c) oxidative addition taking
place on the PdNPs surface with subsequent leaching of PdArX
species which start a homogeneous catalytic cycle.
The aforementioned negative filtration test lays aside the
mechanistic option (b). In this sense, further useful
information was obtained from two poisoning tests:33 the
addition of either mercury (10 equiv.) or CS2 (0.25 equiv.)
inhibited the standard reaction between iodobenzene (1a) and
phenylacetylene (2a), what highly evidences a heterogeneous
catalysis on the nanoparticle surface.
Entry
Catalystb
PdNPs/DNA
PdNPs/DNA
PdNPs/DNA
PdNPs/DNA
PdNPs/DNA
PdO·H2O
PdO·H2O
PdO·H2O
PdO·H2O
Additivec
-
thymine
guanine
(NH4)2HPO4
(NH4)H2PO4
-
DNA
thymine
guanine
3aa (%)d
1
2
3
4
5
6
7
8
9
>99
12
0
90
88
2
0
0
0
a
Iodobenzene (1, 1.0 mmol), phenylacetylene (2, 1.0 mmol), catalyst (0.5 mol%)
and Cs2CO3 (1.4 mmol) in MeOH (2 mL) at 65 ºC in air, 24 h. 0.5 mol% Pd; 10
mg. d Conversion determined by GLC.
b
c
Finally, the activity of commercial PdO·H2O was compared with
that of PdNPs/DNA. In spite of the fact that Pd(0) was formed
Fig. 14 Reaction mechanism proposed for the Sonogashira coupling of aryl iodides and alkynes catalysed by PdNPs/DNA.
Concluding this section, a reaction mechanism was put corresponding caesium acetylide;35 iodide displacement by the
forward on the basis of all the above experimentation (Figure latter from the oxidative addition species (ArPdI), with the
14). On one hand, the catalytically active Pd(0) species could concomitant formation of the arylpalladium acetylide,
be produced by the reduction of PdO (mainly)34 and PdO2 by followed by reductive elimination would afford the product
the action of MeOH which, in turn, would get oxidised to with regeneration of Pd(0).
formaldehyde. This becomes clear when one examines the XPS
of PdNPs/DNA after its preparation in MeOH at room
temperature [exempt from Pd(0), Figure 7] and the XPS of
Conclusions
PdNPs/DNA after warming in MeOH [presence of Pd(0), Figure
13a]. On the other hand, both PdO and PdO2 could participate
in the alkyne activation, surely, with a more important
contribution of the latter given the low levels of PdO noted
after the reaction (Figure 13c); it is normally accepted that
alkyne activation occurs by the coordination of RPdX species to
the C≡C bond but, from Table 5, it is obvious that other
components in the reaction medium can exert the same effect.
Alkyne deprotonation by the base would give the
We have demonstrated that DNA is a convenient support for
palladium nanoparticles, giving rise to a catalyst which is
applicable to the copper- and ligand-free Sonogashira-
Hagihara reaction.
A
series of aryl iodides bearing
electronically different functional groups, as well as diiodides,
have been successfully coupled with either aromatic or
aliphatic alkynes to give the expected products in moderate-
to-high isolated yields (51–86%). In our opinion, the following
advantages can be remarked on this catalytic system: (a)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 10 of 12
ARTICLE
Journal Name
simple preparation of the catalyst at ambient temperature
involving biodegradable support; (b) coupling under
Notes and references
View Article Online
DOI: 10.1039/C7CY00001D
a
1
(a) D. Vollath, Nanomaterials. An Introduction to Synthesis,
relatively mild conditions (65 ºC), what can prevent a
shrinkage of the catalytic activity by the Ostwald ripening
process; (c) the absence of copper salts and ligands; (d)
relatively low metal loading (0.5 mol% Pd) and low leaching,
(e) use of an easy-to-remove recommended solvent (MeOH),11
(f) all the experiments are carried out in air, (g) alkyne
homocoupling is minimised, (h) the catalyst can be easily
recovered and reused in five cycles (93–76% conversion) and
(i) it is superior to some commercial homogeneous and
heterogeneous palladium catalysts. A thorough mechanistic
survey comprising the major part played by the different
constituents of the catalyst has been provided, bolstering the
heterogeneous nature of the process.
Properties and Application, Wiley-VCH, Weinheim, 2008; (b)
Nanoparticles. From Theory to Application, ed. G. Schmid,
Wiley-VCH, Weinheim, 2nd edn., 2010; (c) Inorganic
Nanoparticles: Synthesis, Applications, and Perspectives, ed.
C. Altavilla and E. Ciliberto, CRC Press, London, 2011.
(a) Metal Nanoclusters in Catalysis and Materials Science.
The Issue of Size Control, ed. B. Corain, G. Schmid and N.
Toshima, Elsevier, Amsterdam, 2008; (b) review: K. An, S.
Alayoglu, T. Ewers and G. A. Somorjai, J. Colloid Interface Sci.,
2012, 373, 1–13.
Recent monographs: (a) Selective Nanocatalysts and
Nanoscience, ed. A. Zecchina, S. Bordiga and E. Groppo,
Wiley-VCH, Weinheim, 2011; (b) Nanocatalysis. Synthesis
and Applications, ed. V. Polshettiwar and T. Asefa, Wiley,
Hoboken (NJ), 2013; (c) Nanomaterials in Catalysis; ed. P.
Serp and K. Philippot, Wiley-VCH, Weinheim, 2013; (d) Metal
Nanoparticles for Catalysis: Advances and Applications, ed. F.
Tao, The Royal Society of Chemistry, Cambridge (UK), 2014.
Reviews: (a) H. Hosseinkhani, Int. J. Nanotechnol., 2006, 3,
416-461; (b) V. Vijayanathan, E. Agostinelli, T. Thomas and T.
2
3
Acknowledgements
4
5
This work was generously supported by the Spanish Ministerio
de Economía y Competitividad (MINECO; CTQ-2015 6624P),
the ISO and the Coordinación de la Investigación Científica of
the Universidad Michoacana de San Nicolás de Hidalgo (CIC-
UMSNH, México, grant no. 2.19). A. S. C. acknowledges the
Consejo Nacional de Ciencia y Tecnología (CONACYT, México)
for a mobility grant (no. 290842). I. M.-G. thanks the
J. Thomas, Amino Acids, 2014, 46
,
499–509; (c) Z. Yang, H. Liu
, e161.
and D. Liu, NPG Asia Mater., 2015,
7
Recent reviews: (a) L. Sun, L. Yu and W. Shen, J. Biomed.
Nanotechnol., 2014, 10, 2350–2370; (b) C. Liu and A. D.
Ellington, Nucleic Acids Mol. Biol., 2014, 29, 135–169; (c) for an
special issue on nucleic acid nanotechnology, see: Acc. Chem.
Res., 2014, 47, issue no. 6; (d) B. Zakeri, L. Bijan and K.
Timothy, Curr. Opin. Chem. Biol., 2015, 28, 9–14; (e) Y.-J. Chen,
B. Groves, R. A. Muscat and G. Seelig, Nat. Nanotechnol.,
2015, 10, 748–760; (f) C. Angell, S. Xie, L. Zhang and Y. Chen,
Small, 2016, 12, 1117–1132.
Vicerrectorado de Investigación
y
Transferencia del
Conocimiento of the Universidad de Alicante for a pre-doctoral
grant.
6
7
(a) A. Huzyk, R. Schreiber, Z. Fan, G. Pardatscher, E.-M.
Roller, A. Högele, F. C. Simmel, A. O. Govorov and T. Liedl,
Nature, 2012, 483, 311–314; (b) A. Kumar, J. H. Hwang, S.
Kumar and J. M. Nam, Chem. Commun., 2013, 49, 2597–
2609; (c) L. H. Tan, H. Xing and Y. Lu, Acc. Chem. Res., 2014,
47, 1881–1890; (d) J. Huang, L. Lin, D. Sun, H. Chen, D. Yang
and Q. Li, Chem. Soc. Rev., 2015, 44, 6330–6374.
For reviews on the application of PdNPs to C-C coupling
reactions, see: (a) J. Durand, E. Teuma and M. Gómez, Eur. J.
Inorg. Chem., 2008, 3577–3586; (b) D. Astruc, Tetrahedron:
Asymmetry, 2010, 21, 1041–1054; (c) D. Alonso and C. Najera,
Chem. Soc. Rev., 2010, 39, 2891–2902; (d) J. Guerra and M. A.
Experimental
Typical procedure for the preparation of PdNPs/DNA.
solution of Li2PdCl4 (0.50 M, 0.15 mL) in MeOH (1 mL) and
NaOAc (0.05 g) were added to 0.10 g of salmon-sperm DNA at
room temperature under argon. Stirring was continued for 2
days and, then, the mixture was diluted with H2O (2 mL). The
resulting precipitate was filtered and washed with H2O (3
mL) to produce a grey solid which was dried at room
temperature.
Typical procedure for the cross-coupling of aryl iodides with
alkynes catalysed by PdNPs/DNA. All reactions were
performed using tubes in a multi-reactor system under air.
Cs2CO3 (1.4 mmol, 456 mg) was slowly added to a solution of
A
–3

2
Herrero, Nanoscale, 2010,
2, 1390–1400; (e) A. Balanta, C.
Godard and C. Claver, Chem. Soc. Rev., 2011, 40, 4973–4985
;
(f) C. Deraedt and D. Astruc, Acc. Chem. Res., 2014, 47, 494–
503.
(a) H. Itoh, H. Maeda, S. Yamada and Y. Hori, ChemCatChem,
8
9
2012,
4, 1737–1740; (b) K. Qu, L. Wu, J. Ren and X. Qu, ACS
iodobenzene (1a, 1.0 mmol, 0.11 mL) and phenylacetylene (2a
,
Appl. Mater. Interfaces, 2012,
4
, 5001−5009; (c) W. Li, Y. Fu,
1.0 mmol, 0.10 mL) in MeOH (2 mL), followed by the addition
of PdNPs/DNA (8 mg, 0.5 mol%) and additional MeOH (2 mL).
The reaction mixture was subjected to constant stirring at 65
ºC for 24 h, time after which it became yellowish cloudy as a
result of the catalyst being converted into slurry. The solvent
was evaporated under vacuum, followed by the addition of
Y. Fu, X. Wang and J. Zhang, Catal. Lett., 2013, 143, 578–586.
Acetylene Chemistry: Chemistry, Biology and Material
Science, ed. F. Diederich, P. J. Stang and R. R. Tykwinski,
Wiley-VCH, Weinheim, 2005.
10 Reviews: (a) R. Chinchilla and C. Najera, Chem. Rev., 2007,
40, 874–922; (b) H. Doucet and J.-C. Hierso, Angew. Chem.
Int. Ed., 2007, 46, 834–871; (c) M. D. Heravi and S. Sadjadi,
Tetrahedron, 2009, 65, 7761–7775; (d) M. Pal, Synlett, 2009,
2896–2912; (e) R. Chinchilla and C. Najera, Chem. Soc. Rev.,
2011, 40, 5084–5121; (f) M. Bakherad, Appl. Organomet.
Chem., 2013, 27, 125–140; (g) A. M. Thomas, A. Sujatha and
EtOAc (3
 5 mL) and washing with water (3  5 mL). The
organic phase was dried with anhydrous Mg2SO4, filtered
through Celite and the filtrate was evaporated under reduced
pressure. The resulting brown amber reaction crude was
purified by column chromatography (hexane) to give white
crystals of 1,2-diphenylethyne (3aa) in 85% yield.
G. Anilkumar, RSC Adv., 2014,
4
, 21688–21698; (h) D. Wang
, 556–566; (i) M.
and S. Gao, Org. Chem. Front., 2014,
1
Karak, L. C. A. Barbosa and G. C. Hargaden, RSC Adv., 2014,
53442–53466.
4,
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 12
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
11 D. Prat, A. Wells, J. Hayler, H. Sneddon, C. R. McElroy, S.
Abou-Shehada and P. J. Dunn, Green Chem., 2016, 18, 288–
296.
12 Reviews: (a) F. Alonso, G. Radivoy and M. Yus, Russ. Chem.
Bull., 2003, 52, 2563-2576; (b) F. Alonso and M. Yus, Pure
Appl. Chem., 2008, 80, 1005–1012; (c) F. Alonso, Riente, P.
Green Chem., 2011, 13, 1238–1243; (b) E. Murugan, J. N.
DOI: 10.1039/C7CY00001D
222; (c) M. Bhardwaj, H. Sharma, S. Paul and J. H. Clark, New
J. Chem., 2016, 40, 4952—4961; (d) F. Zhang, S. Zheng, Q.
Xiao, Y. Zhong, W. Zhu, A. Linb and M. S. El-Shall, Green
Chem., 2016, 18, 2900–2908.
Jebaranjithama and A. Usha, Appl. Nanosci. 2012,
View Art2ic,le 2O1nl1in–e
and M. Yus, Acc. Chem. Res., 2011, 44, 379–391; (d) F. 27 For a perspective on alkyne homocoupling, see: F. Alonso
Alonso, in Metal Nanoparticles for Catalysis: Advances and and M. Yus, ACS Catal. 2012, 2, 1441–1451.
Applications, RSC Catalysis Series No. 17, ed. F. Tao, The 28 Pd(OAc)2: (a) S. Urgaonkar and J. G. Verkade, J. Org. Chem.,
Royal Society of Chemistry, Cambridge (UK), 2014, ch. 5, pp.
83–98; (e) F. Alonso, Y. Moglie and G. Radivoy, Acc. Chem.
Res., 2015, 48, 2516–2528; (f) see, also: P. Abdulkin, Y.
Moglie, B. R. Knappett, D. A. Jefferson, M. Yus, F. Alonso and
2004, 69, 5752–5755; (b) S. Shi and Y. Zhang, Synlett, 2007,
1843–1850; PdCl2(PPh3)2: (c) N. E. Leadbeater and B. J.
Tominack, Tetrahedron Lett., 2003, 44, 8653–8656; (d) Y.
Liang, Y.-X. Lie and J.-H. Li, J. Org. Chem., 2006, 71, 379–381;
(e) A. Komáromi, G. L. Tolnai and Z. Novák, Tetrahedron Lett.,
2008, 49, 7294–7298. (f) Z. Gu, Z. Li, Z. Liu, Y. Wang, C. Liu, J.
A. E. H. Wheatley, Nanoscale, 2013, 5, 342–350.
13 See, for instance: (a) Ni: F. Alonso, P. Riente and M. Yus,
Arkivoc, 2008, iv, 8–15; (b) Pd: C. A. Contreras-Celedón, D.
Xiang, Catal. Commun., 2008, 9, 2154–2157.
Mendoza-Rayo, J. A. Rincón-Medina and L. Chacón-García, 29 Review on Pd/C-catalysed coupling reactions: M. Seki,
Beilstein J. Org. Chem., 2014, 10, 2821–2826; (c) Pd: M. Synthesis, 2006, 2975–2992.
Planellas, Y. Moglie, F. Alonso, M. Yus, R. Pleixats and A. 30 (a) R. G. Heidenreich, K. Köhler, J. G. E. Krauter and J. Pietsch,
Shafir, Eur. J. Org. Chem., 2014, 3001–3008; (d) Cu: F. Alonso,
A. Arroyo, I. Martín-García and Y. Moglie, Adv. Synth. Catal.,
2015, 357, 3549–3561.
Synlett, 2002, 1118–1122; (b) M. B. Thathagar and G.
Rothenberg, Org. Biomol. Chem., 2006, 4, 111–115; (c) S.
Mori, T. Yanase, S. Aoyagi, Y. Monguchi, T. Maegawa and H.
Sajiki, Chem. Eur. J., 2008, 14, 6994–6999.
14 X. Yang, Q. Li, H. Wang, J. Huang, L. Lin, W. Wang, D. Sun, Y.
Su, J. B. Opiyo, L. Hong, Y. Wang, N. He and L. Jia, J. 31 (a) A. Tougerti, S. Negri and A. Jutand, Chem. Eur. J., 2007,
Nanoparticle Res., 2010, 12, 1589–1598.
13, 666–676; (b) M. García-Melchor, M. C. Pacheco, C.
15 Y. Xiong, J. Chen, B. Wiley, Y. Xia, Y. Yin, and Z.-Y. Li, Nano
Nájera, A. Lledós and G. Ujaque, ACS Catal., 2012, 2, 135–
Lett., 2005,
5
, 1237–1242.
144.
16 (a) H. Matsui, N. Toyota, M. Nagatori, H. Sakamoto and K. 32 The participation of PdO2 in the alkyne activation cannot be
Mizoguchi, Phys. Rev. B, 2009, 79, 235201; (b) M. N. Al-Hinai,
R. Hassaien, N. G. Wright, A. B. Horsfall, A. Houlton and B. R.
Horrocks, Faraday Discuss. 2013, 164, 71–91; (c) Y.-T. Huang,
D. J. Lowe, G. J. Churchman, L. A. Schipper, R. Cursons, H.
Zhang, T.-Y. Chen and A. Cooper, Appl. Clay Sci., 2016, 120
40–50.
dismissed; however, the synthesis of pure highly oxidised
Pd(IV)NPs without the presence of Pd(II)NPs is troublesome,
making difficult to prove this surmise: L. S. Kibis, A. I.
Stadnichenko, S. V. Koscheev, V. I. Zaikovskii and A. I.
,
Boronin, J. Phys. Chem. C, 2012, 116, 19342
33 Ref. 2a, ch. 31, 427–436.
–19348.
17 Z. Yinghuai, S. C. Peng, A. Emi, S. Zhenshun, Monalisa and R. 34 It has been recently demonstrated the superiority of
A. Kemp, Adv. Synth. Catal., 2007, 349, 1917–1922.
PdONPs/C in the Sonogashira reaction when compared with
Pd(0)NPs/C: C. Rossy, J. Majimel, M. Tréguer Delapierre, E.
18 (a) T. Tateishi, Y. Ito and Y. Okazaki, Mater. Trans., JIM, 1997,
38, 78–84; (b) J. Z. Shyu, K. Otto, W. L. H. Watkins, G. W.
Fouquet and F.-X. Felpin, Appl. Catal. A: Gen., 2014, 482
157–162.
,
Graham, R. K. Belitz and H. S. Gandhi, J. Catal., 1998, 114
,
23–33; (c) A. Gniewek, A. M. Trzeciak, J. J. Ziółkowski, L. 35 C. Spitz, J.-F. Lohier, V. Reboul and P. Metzner, Org. Lett.,
Kępiński, J. Wrzyszcz and W. Tylus, J. Catal., 2005, 229, 332–
343; (d) D. Tsvelikhovsky, I. Popov, V. Gutkin, A. Rozin, A.
Shvartsman and J. Blum, Eur. J. Org. Chem., 2009, 98–102.
19 G. Kumar, R. Blackburn, M. M. Jones, R. G. Albridge and W.E.
Moddeman, Inorg. Chem., 1972, 11, 296–300.
2009, 11, 2776–2779.
20 N. Semagina, A. Renken, D. Laub and L. Kiwi-Minsker, J.
Catal, 2007, 246, 308–314.
21 C. J. May, H. E. Canavan and D. G. Castner, Anal. Chem.,
2004, 76, 1114–1122.
22 (a) https://srdata.nist.gov/xps/; (b) P. Gong, G. J. Harbers
and D. W. Grainger, Anal. Chem., 2006, 78, 2342–2351.
23 (a) S. Ptasińska, A. Stypczyńska, T. Nixon, N. J. Mason, D. V.
Klyachko and L. Sanche, J. Chem. Phys., 2008, 129, 065102;
(b) J. Magulick, M. M. Beerbom and R. Schlaf, Thin Solid
Films, 2008, 516, 2396–2400.
24 (a) M. Furukawa, H. Fujisawa, S. Katano, H. Ogasawara, Y.
Kim, T. Komeda, A. Nilsson and M. Kawai, Surf. Sci., 2003,
532
M. Kawai, H. Ogasawara and A. Nilsson, Surf. Sci., 2007, 601
5433‒5440; (c) N. Tsud, S. Bercha, K. Ševčiková, R. G. Acres,
K. C. Prince and V. Matolín, J. Chem. Phys., 2015, 143
174704; (d) M. Pagliai, S. Caporali, M. Muniz-Miranda, G.
‒535, 261‒266; (b) M. Furukawa, T. Yamada, S. Katano,
,
,
Pratesi and V. Schettino, J. Phys. Chem. Lett., 2012,
242‒245.
3,
25 J. Zhang, X. Wang, Y. Fu, Y. Han, J. Cheng, Y. Zhang and W. Li,
Langmuir, 2013, 29, 14345‒14350.
26 For PdNPs stabilised by the amino group, see, for instance:
(a) F. Zhang, J. Jin, X. Zhong, S. Li, J. Niu, R. Li and J. Ma,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
Please do not adjust margins

Catalysis Science & Technology
Page 12 of 12
View Article Online
Graphical abstract
Palladium nanoparticles on DNA have been shown to be an effective andDOreI:u10s.1a0b3l9e/C7CY00001D
heterogeneous catalyst for the copper- and ligand-free Sonogashira coupling reaction of
aryl iodides under mild conditions in air.