Cobaltocene Reduction of Cu and Ag Salts and Catalytic Behavior of the Nanoparticles Formed

Article abstract of DOI:10.1021/acscatal.8b02338

The modes of generation of nanoparticles (NPs) are of great interest for multiple applications in catalysis, optics, sensing, and nanomedicine. Here, fast reduction of CuSO₄·5H₂O and Ag salts by commercial cobaltocene yields small, stable, water-soluble Cu and Ag NPs with a narrow size distribution without any other ligand or support. The variation of the Ag salt counteranion (NO₃^-, F^-, BF₄^-) strongly influences both the plasmonic absorption of the AgNPs synthesized in this way and the high apparent rate constant of the AgNP-catalyzed reduction of 4-nitrophenol by NaBH₄, showing that the precursor counteranion binds to the AgNP surface. The CuNPs synthesized from CuSO₄ and cobaltocene are a recyclable catalyst for the Cu-catalyzed alkyne-azide cycloaddition reaction in water extended to various azides and alkynes, including functionalization of compounds of biomedical interest. Both CuNP and AgNP catalytic activities are also very promising signs for further extension to a variety of other truly efficient metal-NP-catalyzed reactions.

Full text of DOI:10.1021/acscatal.8b02338

Subscriber access provided by UNIV OF DURHAM
Article
Cobaltocene Reduction of Cu and Ag Salts and
Catalytic Behavior of the Nanoparticles Formed
Fangyu Fu, Roberto Ciganda, Qi Wang, Alexis Tabey, Changlong Wang, Ane Escobar, Angel M.
Martinez-Villacorta, Ricardo Hernandez, Sergio E. Moya, Eric Fouquet, Jaime Ruiz, and Didier Astruc
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b02338 • Publication Date (Web): 24 Jul 2018
Downloaded from http://pubs.acs.org on July 28, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 14
ACS Catalysis
1
2
3
4
5
Cobaltocene Reduction of Cu and Ag Salts and Catalytic Behavior of
the Nanoparticles Formed
6
7
8
9
Fangyu Fu,a Roberto Ciganda,a,b,* Qi Wang,a Alexis Tabey,a Changlong Wang,a Ane Escobar,c
Angel M. MartinezꢀVillacorta,c Ricardo Hernández,b Sergio Moya,c Eric Fouquet,a Jaime
Ruiz,a Didier Astruc a*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
a ISM, UMR CNRS Nº 5255, Univ. Bordeaux, 33405 Talence Cedex, France.
b Facultad de Quimica , Universidad del Pais Vasco, Apdo 1072, 20080 San Sebastian, Spain.
c Soft Matter Nanotechnology Lab, CIC biomaGUNE, Paseo Miramón 182. 20014. Donostiaꢀ
San Sebastián, Gipuzkoa, Spain.
Abstract
The modes of generation of nanoparticles (NPs) are of great interest for multiple applications
in catalysis, optics, sensing and nanomedicine. Here, fast reduction of CuSO4·5H2O and Ag
salts by commercial cobaltocene yields small stable waterꢀsoluble Cu and Ag nanoparticles
(NPs) with narrow size distribution without any other ligand or support. The variation of the
ꢀ
ꢀ
Ag salt counter anion (NO3 , Fꢀ, BF4 ) strongly influences both the plasmonic absorption of
the AgNPs synthesized in this way and the high apparent rate constant of the AgNPꢀcatalyzed
4ꢀnitrophenol reduction by NaBH4, showing that the precursor counter anion binds the AgNP
surface. The CuNPs synthesized from CuSO4 and cobaltocene are a recyclable catalyst for
CuAAC reactions in water that is extended to various azides and alkynes, including
functionalization of compounds of biomedical interest. Both CuNP and AgNP catalytic
activities are also very promising signs for further extension to a variety of other truly
efficient metal NPꢀcatalyzed reactions.
Keywords: copper nanoparticles; silver nanoparticles; nanocatalyst; click reaction; CuAAC;
nitrophenol; surface plasmon band; cobaltocene
1
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 14
1
2
3
4
5
6
Introduction
Transition metal nanoparticles (TMNPs) are an essential part of the nanoworld because of
their fundamental aspects and multiple applications in biomedicine, sensing, optoelectronics,1ꢀ
4
and particularly in catalysis.5ꢀ14 Although organometallic chemistry has provided efficient
7
transitionꢀmetal catalysts, they include expensive and sometimes toxic ligands.15 The
advantages of TMNP catalysts are the lack of such ligands and the simplicity of preparation
and fixation onto supports.16ꢀ19 It is necessary, however, that the synthesis be well controlled
and that for efficiency the TMNPs be small enough so that most atoms are located at the
periphery.20 Usually, the TMNPs are synthesized by reduction of TM salts using reducing
agents such as H2, NaBH4, (SiMe2)6, Mg, Li or Na in liquid NH3 and Li or Na naphthalenide
in the presence of a stabilizer.20ꢀ23 Key parameters in the TMNP synthesis are the control of
the reductant stoichiometry, its driving force and the nature of the stabilizer that define the
size, shape and protection type of the TMNPs. Very often the oxidized form of the reductant is
not removed and its combination with the TMNP is uncertain, so that it can partly inhibit the
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TMNP surface activity.
We propose the use of cobaltocene, CoCp2
24,25
(Cp = η5ꢀC5H5), because it presents many
advantages that solve the above problems. It is a commercially available electronꢀreservoir
compound,26ꢀ28 and its amount and reaction product, [CoCp2][X],24,25,29 are well controlled.
27,28
CoCp2 provides a strong driving force with a standard redox potential of ꢀ1.4 V vs. SCE
for the reduction of CuSO4·5H2O and Ag salts insuring the fast formation of very small
CuNPs and AgNPs respectively.
Following immediate reactions between CoCp2 and CuSO4·5H2O or Ag salts, the cationic
groups [CoCp2]+ obtained along with the metal NP form an encapsulating network around the
NP that is an excellent NP stereoelectronic and electrostatic stabilizer. This protecting network
does not bind the NP surface atoms that remain available for catalytic substrate binding and
activation. The activity of the NP surface will be investigated in order to know if it is
appropriate for excellent catalytic conditions. The AgNP plasmonic absorption and kinetics of
AgNPꢀcatalyzed 4ꢀnitrophenol reduction by NaBH4 are both therefore excellent tests. Overall
the major interest is the facile, fast and clean reduction under ambient conditions of standard
commercial salts to catalytically very efficient CuNPs for alkyne azide cycloaddition
(CuAAC) reaction.30
“Click” reactions were highlighted by Sharpless as a privileged way to couple two molecular
fragments for practical use in organic chemistry, biochemistry and nanomaterials science.30
The most currently used “click” reaction, Cu(I)ꢀcatalyzed alkyne azide cycloaddition
(CuAAC),31 was proposed with high amount of CuSO4 that is toxic for biomedical usage32 or
with sophisticated nitrogen ligands.33,34 CuNPs can also work as catalyst, although the
catalytic amounts are usually far higher than those of the reported molecular Cu(I) catalysts.34ꢀ
38
Here we have used CoCp2 to reduce and stabilize CuNPs with small particle size and narrow
histogram in water and tetrahydrofuran (THF). The CuNPs are characterized by UVꢀvis.
spectroscopy, Transmission Electron Microscopy (TEM) and Xꢀray photoelectron
spectroscopy (XPS). The CuNPs are examined for their catalytic activity in the CuAAC
reaction in neat water with low catalytic amounts, and their use is extended to various alkynes
and organic azides for CuAAC “click” reactions. Interestingly these CuNPs are in particular
2
ACS Paragon Plus Environment

Page 3 of 14
ACS Catalysis
1
2
3
successfully used to prepare functional biomedical substrates in neat water.
4
5
6
Results and discussion
Synthesis and Characterizations of the AgNPs. Quick addition of cobaltocene in THF to an
aqueous solution of the commercial salt AgNO3 at room temperature (rt) under N2 results in
instantaneous color change (vide infra) indicating the formation of AgNPs (Scheme 1, see
details in Experimental section). The cobaltocene stoichiometry matches that of the number of
electrons necessary to reduce the metal cation of the precursor salt to metal (0) atoms
precursors of nanoparticles. Thus no additional stabilizing agent is needed, and these AgNPs
are more stable than other nonꢀ or lessꢀprotected TMNPs synthesized by other means, which
shows the protecting role of the cobalticinium salt network.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
X
Co
Co
X
Co
X
Co
Co
Co
X
Co
X
X
X
X
rt, fast
X
X
Co
Co
Co
MXn
n
H2O/THF, N2
X
X
X
Co
Co
Co
Co
X
MX =
CuSO4 5H2O
n
Co
AgNO3, AgF, AgBF4
X
Co
Co
X
Scheme 1. Synthesis of CuNPs and AgNPs by reaction of CuSO4·5H2O or an Ag salt with
cobaltocene. For CuNPs, n = 2 and MXn = CuSO4. For AgNPs, n = 1, and MXn = AgX (X =
NO3, F or BF4).
Dependence of the AgNP surface plasmon band and 4-nitrophenol reduction rate
constants on the precursor counter anion
ꢀ
ꢀ
Various Ag salts (NO3 , Fꢀ and BF4 ) were probed for reduction by CoCp2 in order to
characterize the effects of the coordination of the anions on a plasmonic NP surface by
variations of the AgNP surface plasmon band (SPB).39 XPS analysis (Figure S1) and UVꢀvis.
spectroscopy show that the AgNPs are in the zero oxidation state, and the average size of the
AgNPs prepared by AgNO3, AgF and AgBF4 are 3.0, 3.1 and 3.2 nm respectively according to
the measurements made by TEM (Figures S5ꢀ7). The variations of color and SPB maximum
are dramatic upon anion variation. Reduction of the precursor salts AgNO3, AgF and AgBF4
respectively yield orange, darkꢀbrown and light brown AgNPs (Figure 1) with SPB maxima at
423, 439 and 410 nm respectively (Figures S2ꢀ4). These strong anion effects are best taken
into account as suggested above by the coordination of a good proportion of the anions onto
the AgNP surface that differently perturbs the electronic state of the surface.
3
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Photographs of the AgNPs obtained using cobaltocene for the reduction of AgX
precursor salts: (a) AgNO3; (b) AgF; (c) AgBF4
This coordination of the anion is corroborated by the variation of the effects of the nature of
anion coordination in the surface restructuring involved in surface catalysis as shown below.
The nature of this anion also influences the AgNPꢀcatalyzed 4ꢀnitrophenol reduction by
NaBH440 as anticipated from the influence of the anion coordination on the SPB (vide supra).
This reaction is a useful test to investigate the restructuration of the NP surface during a
catalytic reaction according to a LangmuirꢀHinshelwood model that involves adsorption of
the substrates on the NP surface as shown by Ballauff’s group.41 Indeed starting from AgBF4,
AgNO3 and AgF, the kapp values of the pseudoꢀfirst order rate constant of this reaction
measured by the disappearance of the nitrophenolate absorption band at 400 nm are
respectively 0.0010 sꢀ1, 0.0017 sꢀ1 and 0.0036 sꢀ1 without any retention time (Figures S8ꢀ10).
These rate constants are very different from an anion to another. Their comparison indicates
that the catalytic reaction with the small Fꢀ anion is more favorable than those involving other
larger anions. Also the reaction is fast with the three anions, even compared to the best
catalysts, i. e. the reported classic PdNPs and AuNPs, confirming the excellent catalytic
properties of the NPs synthesized using this method
Synthesis and Characterizations of the CuNPs
Reduction of CuSO4·5H2O by cobaltocene at rt under N2 results in instantaneous color change
from colorless to black indicating the formation of the CuNPs (Scheme 1, see details in
Experimental section). The stoichiometry is 2 equivalents of cobaltocene per Cu atom. The
CuNPs obtained by this method are stable as the AgNPs above and are characterized by TEM
pictures showing the very small NP core size and narrow histogram with a distribution around
1.7 nm (Figure 2). The very small CuNP size results from the strong driving force provided by
the reducing agent resulting in fast reduction of Cu(II) to Cu(0) followed by efficient
electrostatic and anion ligand stabilization by cobalticinium sulfate.
4
ACS Paragon Plus Environment

Page 5 of 14
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. TEM picture (left) and histogram (right) of the 1.7 nm CuNPs prepared by
reduction of CuSO4 by cobaltocene.
The XPS spectrum of the CuNPs essentially confirms their zero oxidation state in the core
and on the surface. The Cu 2p spectrum shows the Cu 2p3/2 and 2p1/2 peaks. The fitting of the
Cu 2p3/2 part of the spectrum reveals the presence of Cu(0) at around 932.5 eV, without
Cu(II) species (Figure 3).
Figure 3. XPS spectrum of the CuNPs prepared from CuSO4 and cobaltocene.
The absence of the absorption band in the UVꢀvis. spectra confirms that these CuNPs are
zeroꢀvalent Cu species, the CuNP plasmon band being only observable for large CuNPs,
contrary to those of AgNPs and AuNPs.4 On the other hand, the cobalticinium moiety is well
characterized by the broad absorption band at 397 nm in the UVꢀvis. spectrum (Figure 4).42
5
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. UVꢀvis. spectrum of the CuNPs obtained by reduction of CuSO4 by cobaltocene.
Some of the SO42ꢀ anions formed in these reactions are week “L2ꢀtype” (formally 4e) ligands25
for the zeroꢀvalent surface metal atoms in order to equilibrate the cobalticinium charges (vide
2ꢀ
infra). The number of SO4 ligands is limited by the number of surface metal atoms. Since
2ꢀ
2ꢀ
there are more SO4 species than surface metal atoms many SO4 anions remain only
2ꢀ
electrostatically bonded to cobalticinium groups without binding the CuNP surface. The SO4
anions weakly bonded to the surface electrostatically attract cobalticinium counter cations that
are close to the NP surface to form the stabilizing network. These considerations are
confirmed by the above experiments for AgNPs.
Efficient Cu(NP)-catalyzed alkyne azide cycloaddition in water. The CuNPs obtained by
reduction of CuSO4 by cobaltocene were probed for their catalytic activity in CuAAC
reaction between benzyl azide and phenylacetylene in neat water (eq 1 and Table 1). This
reaction produced 99% isolated yield with 0.1% catalytic amount for 24 h at 35°C and a TOF
of 250 with 50 ppm of CuNP catalyst. The scope of the application of this low level amount
of the waterꢀsoluble CuNP catalyst was explored with other CuAAC reactions between
various alkynes and organic azides in water. Good isolated yields were achieved in the
CuAAC reaction of a wide variety of alkynes with organic azides using 0.1% or 0.2%
catalysts (Table 2). Moreover, oneꢀpot threeꢀcomponents “click” reactions have been
conducted from benzyl bromide, sodium azide and phenylacetylene yielding 93% isolated
yield with 0.2% Cu of this CuNP nanocatalyst (Supporting Information). The waterꢀsoluble
CuNP catalyst was also easily recycled by simple filtration at least 4 times with only very
slight yield decrease, the click products being insoluble in water (Supporting Information).
6
ACS Paragon Plus Environment

Page 7 of 14
ACS Catalysis
1
2
3
4
5
6
7
8
Table 1. “CuAAC” reaction of eq 1catalyzed by the CuNPs a
9
Entry
Amount (%) b Yield (%) c
TON
6000
4800
1520
990
TOF (hꢀ1)
250
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
2
3
4
0.005
0.01
0.05
0.1
30
48
76
99
99
200
63.3
41.3
5
0.2
495
20.6
a
Reaction conditions: 0.5 mmol of benzyl azide, 0.505 mmol of phenylacetylene, and 2 mL
b
c
of H2O, 35°C, 24 h, under N2. Amount of catalysts used in the “CuAAC” reduction.
Isolated yield.
Table 2. “CuAAC” reactions between various azides and alkynes using the 0.1% or 0.2%
CuNP catalyst.a
a
Reaction conditions: 0.5 mmol of azide, 0.505 mmol of alkyne, 2 mL H2O, 35°C, 24 h,
under N2. b Solvent: 1 mL H2O and 1 mL tertꢀbutanol.
7
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 14
1
2
3
4
5
6
7
8
9
Functional substrates of biomedical interest were also successfully prepared using this CuNP
catalyst. In eq 2, pꢀbis (ferrocenylꢀ1,2,3ꢀtriazolylmethyl) benzene (2) was synthesized by the
click reaction between compound 1 and ethynylferrocene43 using 0.25% per branch at 35 °C
for 24 h with 92% isolated yield in water. This product 2 is of interest, because hostꢀguest
molecular interactions between βꢀCD and ferrocene derivatives44 are currently used to
synthesize nanocatalysts and AuNPs for photothermal therapy.45
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Coumarin derivatives are often used in the perfume industry. They also are fluorophores and
have been applied as fluorescent probes to visualize the metabolism of cysteine in living
cells.46 Thus the clickꢀtriazole functionalized 7ꢀ(propargyloxy)ꢀcoumarin 4 was synthesized
from 3 in H2O in 95% isolated yield upon using this CuNP catalyst (0.5% Cu) for 24 h at
35 °C.
Another key natural product, estradiol, is known as a medication and naturally
occurring steroid hormone. Estradiol is an estrogen that is mainly used in menopausal
hormone therapy and to treat low sex hormone levels in women. It has several biological
functions such as sexual development, reproduction, skeletal system, and nervous system.
Besides, the natural alkyne of estradiol also discloses various medicinal applications. Here,
the CuAAC click reaction between ethynyl estradiol (5) and benzyl azide using CuNP (0.5%)
in water at 35 °C for 24 h provides 6 in 96% isolated yield (eq 4).
8
ACS Paragon Plus Environment

Page 9 of 14
ACS Catalysis
1
2
3
4
Concluding remarks
The reduction of Cu and Ag salts to metal NPs by cobaltocene, a common commercial
product, provides a range of possibilities for further use of CuNPs and AgNPs that have large
catalytic applications. The reduction of these salts to NPs shows that cobaltocene should in
fact reduce a good number of transition metal salts to zeroꢀvalent metal NPs. Cobaltocene
being a neutral 19ꢀelectron complex is an electronꢀreservoir system that indeed provides a
large driving force leading to the formation of very small NPs ideal for catalysis. This stands
in contrast with isostructual ferrocene providing a weak driving force that produces large NPs
that have little catalytic activity.47,48 Another advantage of cobaltocene here is that its oxidized
cobalticinium form is perfectly defined and robust, contrary to the oxidized forms of most
other reductants.
The remarkable variation of the SPB wavelength and kinetics of the AgNPꢀcatalyzed 4ꢀ
nitrophenol reduction as a function of the nature of the counter anion of the precursor Ag(I)
salt shows the stabilization of the AgNPs by this counter anion acting as a weak ligand for the
AgNP surface. This means that the cobalticinium salts works as a nanoreactor around the NPs,
leaving the NP surface rather free for catalytic interactions with substrates at this NP surface.
This is corroborated by the high catalytic activity of the AgNP surface in 4ꢀnitrophenol
reduction by NaBH4.
Application of this principle to CuNPs synthesized by reduction of CuSO4 by cobaltocene
provides new possibilities in useful catalysis that have already been partly exploited in this
work. A variety of heterogeneous click CuAAC reactions have been shown to proceed very
efficiency with waterꢀinsoluble substrates using the waterꢀsoluble CuNP catalyst synthesized
in this way including click CuAAC synthesis of biologically relevant compounds.
Such CuNP catalysis is advantageous compared to that using sophisticated preꢀsynthesized
Cu(I) complexes. Yet the mechanism of CuAAC reactions is well known to proceed via Cu(I)
active species, whereas the CuNPs synthesized here have been shown by UVꢀvis. and XPS
spectroscopy to involve Cu(0) atoms on the CuNP surface as well as in the core. It is
probable, however, that terminal alkynes, whose coordination in complex Cu species has been
demonstrated earlier, react with the Cu(0)NP surface to form surface Cu(I)ꢀalkynyl
intermediate species.49ꢀ51 These principles of nanocatalyst design should be extended to
various other very efficient monoꢀ and polymetallic nanocatalysts in the close future.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section
Nanoparticle synthesis. CuSO4·5H2O (1 mg, 4×10ꢀ3 mmol) was dissolved in 19 mL milliꢀQ
water under nitrogen in a standard Schlenk flask and degassed for 10 min., then [CoCp2]52
(1.5 mg, 8×10ꢀ3 mmol) in dry THF (1 mL) was quickly injected under nitrogen into the
Schlenk flask. The color of the solution changed from colorless to black indicating the
formation of the CuNPs. This synthesis has also been scaled up 10 times. AgNPs were
synthesized similarly.
4-Nitrophenol reduction kinetics: 4ꢀNP (7 mg, 5×10ꢀ2 mmol) was mixed with NaBH4 (154
mg, 4.0 mmol) in water under nitrogen. The color of the solution changed from light yellow
to dark yellow due to the formation of the sodium 4ꢀnitrophenolate salt. Then a solution
containing 2 mol% Ag nanoparticles was added to the mixture under nitrogen. Then the
9
ACS Paragon Plus Environment

ACS Catalysis
Page 10 of 14
1
2
3
4
5
6
7
8
9
solution lost its dark yellow color with time, and the progress of the reaction kinetics was
monitored by UVꢀvis. spectroscopy (40 s for each run).
CuAAC reactions: A Schlenk flask equipped with a magnetic stir bar was charged with
benzyl azide (66.5 mg, 0.5 mmol) and phenylacetylene (51.5 mg, 0.505 mmol) under N2. The
catalyst was added into the Schlenk flask under N2, and degassed water was added in order to
obtain a 2 mL volume of aqueous solution. The reaction heterogeneous mixture was then
stirred for 24 h at 35 °C under N2, then the product was extracted with CH2Cl2 (3 x 15 mL).
The organic layer was dried over Na2SO4 and filtered, and the solvent was removed in vacuo
to give crude 1ꢀbenzylꢀ4ꢀphenylꢀ1Hꢀ[1,2,3]triazole. This product was then purified by silica
gel column chromatography using petroleum ether/ethyl acetate: 10/1 for elution to give a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
99% isolated yield (116 mg). H NMR (300 MHz, CDCl3): δ 7.89 – 7.77 (m, 2H), 7.68 (s,
1H), 7.49 – 7.37 (m, 5H), 7.38 – 7.30 (m, 3H), 5.60 (s, 2H) (SI). The other CuAAC reactions
were conducted analogously, the reaction being carried out on 0.5 mmol or 0.2 mmol scale.
The products were purified by silica gel column chromatography using petroleum ether/ethyl
acetate: 10/1 for elution or washed with pentane. The yields are given in tables 1 and 2, and
the data and spectra for all the products are provided in the SI.
AUTHOR INFORMATION
Corresponding Author
r.ciganda@hotmail.com
didier.astruc@uꢀbordeaux.fr
Notes
The authors declare no competing financial interest.
Supporting Information
The Supporting Information is available free of charge on the ACS Publications
website at DOI: xxx. General data, characterizations, catalytic procedures, kinetics
graphs, and spectra.
ACKNOWLEDGMENTS
Financial support from the China Scholarship Council of the Republic of China (PhD grants
to F. F. and Q. W.), Gobierno Vasco (R.C.), Universidad del País Vasco, the University of
Bordeaux, the CIC biomaGUNE and the Centre National de la Recherche Scientifique
(CNRS) is gratefully acknowledged.
References
(1) Schmid, G. Nanoparticles: From Theory to Application; WileyꢀVCH: Weinheim,
Germany, 2004.
(2) Xia, Y. N.; Xiong, Y. J.; Lim, B.; Skrabalak, S. E. Shapeꢀcontrolled Synthesis of Metal
Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem. Int. Ed. Engl. 2009,
48, 60–103.
(3) Brongersma, M. L.; Halas, N. J.; Nordlander, P. Plasmonꢀinduced Hot Carrier Science
and Technology. Nat. Nanotechnol. 2015, 10, 25–34.
10
ACS Paragon Plus Environment

Page 11 of 14
ACS Catalysis
1
2
3
4
5
(4) Daniel, M. –C.; Astruc, D. Gold Nanoparticles:ꢁ Assembly, Supramolecular Chemistry,
QuantumꢀSizeꢀRelated Properties, and Applications toward Biology, Catalysis, and
Nanotechnology. Chem. Rev. 2004, 104, 293–346.
6
7
8
9
(5) Basset, J. –M.; Psaro, R.; Roberto, D.; Ugo, R. Modern Surface Organometallic
Chemistry; WileyꢀVCH: Weinheim, 2009.
(6) Meyers, V. S.; Weier, M. G.; Carino, E. V.; Yancey, D. F.; Pande, S.; Crooks, R. M.
Dendrimerꢀencapsulated Nanoparticles: New Synthetic and Characterization Methods and
Catalytic Applications. Chem. Sci. 2011, 2, 1632–1646.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(7) Bronstein, L. M.; Shifrina, Z. B. Dendrimers as Encapsulating, Stabilizing, or Directing
Agents for Inorganic Nanoparticles. Chem. Rev. 2011, 111, 5301–5344.
(8) Ye, R.; Yuan, B.; Zhao, J.; Ralston, W. T.; Wu, C. Y.; Bari, E. U.; Toste, F. D.; Somorjai,
G. A. Metal Nanoparticles Catalyzed Selective Carbon–Carbon Bond Activation in the Liquid
Phase. J. Am. Chem. Soc. 2016, 138, 8533–8537.
(9) Reetz, M. T.; de Vries, J. G. Ligandꢀfree Heck Reactions Using Low Pdꢀloading. Chem.
Commun. 2004, 1559–1563.
(10) Haruta, M. Chance and Necessity: My Encounter with Gold Catalysts. Angew. Chem., Int.
Ed. 2014, 53, 52–56.
(11) Sankar, M.; Dimitratos, N.; Miedziak, P. J.; Wells, P. P.; Kiely, C. J.; Hutchings, G. J.
Designing Bimetallic Catalysts for a Green and Sustainable Future. Chem. Sci. 2012, 3, 20–44.
(12) Balanta, A.; Godard, C.; Claver, C. Pd Nanoparticles for C–C Coupling Reactions. Chem.
Soc. Rev. 2011, 40, 4973–4985.
(13) Polshettiwar, V.; Varma, R. S. Green Chemistry by Nanoꢀcatalysis. Green Chemistry
2010, 12, 743–754.
(14) Corma, A.; LeyvaꢀPerez, A.; Maria Sabater, J. GoldꢀCatalyzed Carbon−Heteroatom
BondꢀForming Reactions. Chem. Rev. 2011, 111, 1657–1712.
(15) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis with
Organometallic Compounds; WileyꢀVCH: Weinheim, 1996.
(16) Bell, A. T. The Impact of Nanoscience on Heterogeneous Catalysis. Science 2003, 299,
1688–1691.
(17) Cui, C. H.; Gan, L.; Heggen, M.; Rudi, S.; Strasser, P. Compositional Segregation in
Shaped Pt Alloy Nanoparticles and their Structural Behaviour During Electrocatalysis. Nat.
Mater. 2013, 12, 765–771.
(18) Prieto, G.; Zečević, J.; Friederich, H.; de Jong, K. P.; de Jongh, P. E. Towards Stable
Catalysts by Controlling Collective Properties of Supported Metal Nanoparticles. Nat. Mater.
2013, 12, 34–39.
(19) Na, K.; Choi, M.; Yaghi, O. M.; Somorjai, G. A. Metal Nanocrystals Embedded in
Single Nanocrystals of MOFs Give Unusual Selectivity as Heterogeneous Catalysts. Nano
Letters 2014, 14, 5979–5983.
(20) Astruc, D.; Lu, F.; Ruiz, J. Nanoparticles as Recyclable Catalysts: the Frontier between
Homogeneous and Heterogeneous Catalysis. Angew. Chem. Int Ed. Engl. 2005, 44, 7852–
7872.
(21) Yan, J. M.; Zhang, X. B.; Han, S.; Shioyama, H.; Xu, Q. Ironꢀnanoparticleꢀcatalyzed
Hydrolytic Dehydrogenation of Ammonia Borane for Chemical Hydrogen Storage. Angew.
Chem. Int. Ed. 2008, 47, 2287–2289.
11
ACS Paragon Plus Environment

ACS Catalysis
Page 12 of 14
1
2
3
4
5
(22) Schöttle, C.; Bockstaller, P.; Popescu, R.; Gerthsen, D.; Feldmann, C. Sodiumꢀ
NaphthalenideꢀDriven Synthesis of BaseꢀMetal Nanoparticles and Followꢀup Reactions.
Angew. Chem., Int Ed. 2015, 54, 9866–9870.
6
7
8
9
(23) Schöttle, C.; Doronkin, D. E.; Popescu, R.; Gerthsen, D.; Grünwald, J. D.; Feldmann, C.
Ti0 Nanoparticles via Lithiumꢀnaphthalenideꢀdriven Reduction. Chem. Commun. 2016, 52,
6316–6319.
(24) (a) Fischer, E. O.; Jira, R. Diꢀcyclopentadienylꢀkobalt(II). Z. Naturforsch. 1953, 8B, 327ꢀ
328; (b) Wilkinson, G. Bisꢀcyclopentadienyl Compounds of Nickel and Cobalt. J. Am. Chem.
Soc. 1954, 76, 1970ꢀ1974.
(25) Astruc, D. Organometallic Chemistry and Catalysis; Springer: Heidelberg, 2007.
(26) Astruc, D. Organoiron Electronꢀreservoir Complexes. Acc. Chem. Res. 1986, 19,
377−383.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(27) Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for Organometallic Chemistry.
Chem. Rev. 1996, 96, 877−910.
(28) Geiger, W. E. Electroreduction of Cobaltocene. Evidence for a Metallocene Anion. J. Am.
Chem. Soc. 1974, 96, 2632−2634.
(29) Sheats, J. E.; Rausch, M. D. Synthesis and Properties of Cobalticinium Salts. I. Synthesis
of Monosubstituted Cobalticinium Salts. J. Org. Chem. 1970, 35, 3245−3255.
(30) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function
from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004−2021.
(31) For selected reviews, see: (a) Meldal, M.; Tornøe, C. W. CuꢀCatalyzed Azide−Alkyne
Cycloaddition. Chem. Rev. 2008, 108, 2952−3015; (b) Hein, J. E.; Fokin, V. V. Copperꢀ
catalyzed Azideꢀalkyne Cycloaddition (CuAAC) and Beyond: New Reactivity of Copper(I)
Acetylides. Chem. Soc. Rev. 2010, 39, 1302−1315; (c) Haldón, E.; Nicasio, M. C.; Pérez, P.
Copperꢀcatalysed Azideꢀalkyne Cycloadditions (CuAAC): An Update. J. Org. Biomol. Chem.
2015, 13, 9528−9550; (d) Castro, V.; Rodríguez, H.; Albericio, F. CuAAC: An Efficient Click
Chemistry Reaction on Solid Phase. ACS Comb. Sci. 2016, 18, 1−14; (e) Wang, C.; Ikhlef, D.;
Kahlal, S.; Saillard, J.; Astruc, D. MetalꢀCatalyzed AzideꢀAlkyne “Click” Reactions:
Mechanistic Overview and Recent Trends. Coord. Chem. Rev. 2016, 316, 1−20; (f) Singh, M.
S.; Chowdhury, S.; Koley, S. Advances of Azideꢀalkyne Cycloadditionꢀclick Chemistry over
the Recent Decade. Tetrahedron 2016, 72, 5257−5283.
(32) Rostovtsev, V. V.; Geen, L. G.; Fokin, V. V.; Sharpless, K. B. A Stepwise Huisgen
Cycloaddition Process: Copper(I)ꢀcatalyzed Regioselective "Ligation" of Azides and
Terminal Alkynes. Angew. Chem., Int. Ed. 2002, 114, 2708−2711.
(33) Etayo, P.; Ayats, C.; Pericas, M. A. Synthesis and Catalytic Applications of C3ꢀsymmetric
Tris(triazolyl)methanol Ligands and Derivatives. Chem. Commun. 2016, 52, 1997−2010.
(34) Liu, X.; Gregurec, D.; Irigoyen, J.; Martinez, A.; Moya, S.; Ciganda, R.; Hermange, P.;
Ruiz, J.; Astruc, D. Precise Localization of Metal Nanoparticles in Dendrimer Nanosnakes
or Inner Periphery and Consequences in Catalysis. Nat. Commun. 2016, 7, 13152.
(35) Fu, F.; Martinez, A.; Wang, C.; Ciganda, R.; Yate, L.; Escobar, A.; Moya, S.;
Fouquet, E.; Ruiz, J.; Astruc, D. Exposure to Air Boosts CuAAC Reactions Catalyzed by
PEGꢀstabilized Cu Nanoparticles. Chem. Commun. 2017
(36) Alonso, F.; Moglie, Y.; Radivoy, G. Copper Nanoparticles in Click Chemistry. Acc.
Chem. Res. 2015 48, 2516−2528.
, 53, 5384−5387.
,
(37) Gawande, M. B.; Goswami, A.; Felpin, F. X.; Asefa, T.; Huang, X. X.; Silva, R.; Zou, X.
X.; Zboril, R.; Varma, R. S. Cu and CuꢀBased Nanoparticles: Synthesis and Applications in
Catalysis. Chem.Rev. 2016, 116, 3722−3811.
12
ACS Paragon Plus Environment

Page 13 of 14
ACS Catalysis
1
2
3
(38) Decan, M. R.; Impellizzeri, S.; Marin, M. L.; Scaiano, J. C. Copper Nanoparticle
4
Heterogeneous Catalytic
‘
Click’
Cycloaddition Confirmed by Singleꢀmolecule
5
6
7
8
Spectroscopy. Nat. Commun. 2014, 5, 4612.
(39) Rycenga, M.; Cobley, C. M.; Zeng, J.; Li, W. Y.; Moran, C. H.; Zhang, Q.; Qin, D.; Xia,
X. N. Controlling the Synthesis and Assembly of Silver Nanostructures for Plasmonic
Applications. Chem. Rev. 2011, 111, 3669−3712.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(40) (a) Sau, T. K.; Pal, A.; Pal, T. Size Regime Dependent Catalysis by Gold Nanoparticles
for the Reduction of Eosin. J. Phys. Chem. B 2001, 105, 9266–9272. (b) Hervés, P.; Pérezꢀ
Lorenzo, M.; LizꢀMarzan, L. M.; Dzubiella, J.; Lu, Y.; Ballauff, M. Catalysis by Metallic
Nanoparticles in Aqueous Solution: Model Reactions. Chem. Soc. Rev. 2012, 41, 5577–5587.
(c) Aditya, T.; Pal, A.; Pal, T. Nitroarene Reduction: A Trusted Model Reaction to Test
Nanoparticle Catalysts. Chem. Commun. 2015, 51, 9410–9431. (d) Zhao, P.; Feng, X.; Huang,
D.; Yang, G.; Astruc, D. Basic Concepts and Recent Advances in Nitrophenol Reduction by
Goldꢀ and Other Transition Metal Nanoparticles. Coord. Chem. Rev. 2015, 287, 114ꢀ136.
(41) (a) Wunder, S.; Lu, Y.; Albrecht, M.; Ballauff, M. Catalytic Activity of Faceted Gold
Nanoparticles Studied by a Model Reaction: Evidence for SubstrateꢀInduced Surface
Restructuring. ACS Catal. 2011, 1, 908−916; (b) Lu, Y.; Ballauff, M. Spherical
Polyelectrolyte Brushes as Nanoreactors for the Generation of Metallic and Oxidic
Nanoparticles: Synthesis and Application in Catalysis. Prog. Polym. Sci. 2016, 59, 86−104.
(42) Fu, F.; Wang, Q.; Ciganda, R.; MartinezꢀVillacorta, A. M.; Escobar, A.; Moya, S.;
Fouquet, E.; Ruiz, J.; Astruc, D. Electronꢀ and HydrideꢀReservoir Organometallics as
Precursors of Catalytically Efficient Transition Metal Nanoparticles in Water. Chem. Eur.
J. 2018
(43) Ornelas, C.; Ruiz, J.; Cloutet, E.; Alves, S.; Astruc, D. Click Assembly of 1,2,3
Triazole Linked Dendrimers, Including Ferrocenyl Dendrimers, Which Sense Both Oxo
Anions and Metal Cations. Angew. Chem. Int. Ed. 2007, 46, 872−877.
, 24, 6645−6653.
‐
‐
(44) Liu, J.; Mendoza, S.; Román, E.; Lynn, M. J.; Xu, R.; Kaifer, A. E. Cyclodextrinꢀ
Modified Gold Nanospheres. Host−Guest Interactions at Work to Control Colloidal Properties.
J. Am. Chem. Soc. 1999, 121, 4304−4305.
(45) Wang, Y.; Li, H.; Jin, Q.; Ji, J. Intracellular Host–guest Assembly of Gold Nanoparticles
Triggered by Glutathione. Chem. Commun. 2016, 52, 582−585.
(46) Yue, Y.; Huo, F.; Ning, P.; Zhang, Y.; Chao, J.; Meng, X.; Yin, C. DualꢀSite Fluorescent
Probe for Visualizing the Metabolism of Cys in Living Cells. J. Am. Chem. Soc. 2017, 139,
3181−3185.
(47) Ciganda, R.; Irigoyen, J.; Gregurec, D.; Hernández, R.; Moya, S.; Wang, C.; Ruiz, J.;
Astruc, D. Liquid–Liquid Interfacial Electron Transfer from Ferrocene to Gold(III): An
Ultrasimple and Ultrafast Gold Nanoparticle Synthesis in Water under Ambient Conditions.
Inorg. Chem. 2016, 55, 6361–6363.
(48) Astruc, D. Why is Ferrocene so Exceptional? Eur. J. Inorg. Chem. 2017, 6−29.
(49) Hu, P. G.; Chen, L. M.; Kang, X. W.; Chen, S. W. Surface Functionalization of Metal
Nanoparticles by Conjugated Metal−Ligand Interfacial Bonds: Impacts on Intraparticle
Charge Transfer. Acc. Chem. Res. 2016, 49, 2251−2260.
(50) Judai, K.; Numao, S.; Nishijo, J.; Nishi, N. In Situ Preparation and Catalytic Activation
of Copper Nanoparticles from Acetylide Molecules. J. Mol. Catal. A-Chemical 2011, 347,
28−33.
(51) Yam, W. W. W.; Lo, K. K. W.; Fung, W. K. M.; Wang, C. R. Design of Luminescent
Polynuclear Copper(I) and Silver(I) Complexes with Chalcogenides and Acetylides as the
Bridging Ligands. Coord. Chem. Rev. 2010, 171, 17−41.
13
ACS Paragon Plus Environment

ACS Catalysis
Page 14 of 14
1
2
3
4
(52) Cobaltocene, a purple black solid, is available at SigmaꢀAldrich or is readily best
synthesized by reaction between CoBr2 and NaCp in THF. See (a) Sheats, J. E. A
5
6
7
8
Comprehensive Review up to 1976 of Cobalt Sandwich Compounds. J. Organomet. Chem.
Library 1979, 7, 461ꢀ521; (b) Kemmitt, R. D. W.; Russell D. R. Comprehensive
Organometallic Chemistry, Wilkinson, J.; Stone, F. G. A.; Abel, E. W. Eds., Pergamon, New
York, 1982, Vol. 5, p. 244.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
TOC
N3
X
Co
Co
R
X
Co
X
Co
Co
Co
X
Co
R'
X
X
X
rt, fast
X
X
Co
Co
Co
2
H2O/THF, N2
CuSO4 5H2O
X
X
X
X
Co
Co
Co
Co
N
X
Co
N
R'
X
N
Co
Co
X
R
14
ACS Paragon Plus Environment