An Organometallic Cu20 Nanocluster: Synthesis, Characterization, Immobilization on Silica, and "click" Chemistry

Article abstract of DOI:10.1021/jacs.7b10960

The development of atomically precise nanoclusters (APNCs) protected by organometallic ligands, such as acetylides and hydrides, is an emerging area of nanoscience. In principle, these organometallic APNCs should not require harsh pretreatment for activat

Full text of DOI:10.1021/jacs.7b10960

Subscriber access provided by READING UNIV
Article
An Organometallic Cu20 Nanocluster: Synthesis,
Characterization, Immobilization on Silica, and “Click” Chemistry
Andrew W. Cook, Zachary R. Jones, Guang Wu, Susannah L Scott, and Trevor W. Hayton
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b10960 • Publication Date (Web): 06 Dec 2017
Downloaded from http://pubs.acs.org on December 6, 2017
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 free 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 accessible to all
readers and 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.
Journal of the American Chemical Society 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 8
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
An Organometallic Cu20 Nanocluster: Synthesis, Characterization,
Immobilization on Silica, and “Click” Chemistry
Andrew W. Cook†, Zachary R. Jones‡, Guang Wu†, Susannah L. Scott‡*, and Trevor W. Hayton†*
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
†Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
‡Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
Supporting Information Placeholder
ABSTRACT: The development of atomicallyꢀprecise nanoclusters (APNCs) protected by organometallic ligands, such as acetyꢀ
lides and hydrides, is an emerging area of nanoscience. In principle, these organometallic APNCs should not require harsh preꢀ
treatment for activation towards catalysis, such as calcination, which can lead to sintering. Herein, we report the synthesis of the
mixedꢀvalent organometallic copper APNC, [Cu20(CCPh)12(OAc)6)] (1), via reduction of Cu(OAc) with Ph2SiH2 in the presence of
phenylacetylene. This cluster is a rare example of a twoꢀelectron copper superatom, and the first to feature a tetrahedral [Cu4]2+
core, which is a unique “kernel” for a Cuꢀonly superatom. Complex 1 can be readily immobilized on dry, partiallyꢀdehydroxylated
silica, a process that cleanly results in release of 1 equiv of phenylacetylene per Cu20 cluster. Cu Kꢀedge EXAFS confirms that the
immobilized cluster 2 is structurally similar to 1. In addition, both 1 and 2 are effective catalysts for [3+2] cycloaddition reactions
between alkynes and azides (i.e., “Click” reactions) at room temperature. Significantly, neither cluster requires any preꢀtreatment
for activation toward catalysis. Moreover, EXAFS analysis of 2 after catalysis demonstrates that the cluster undergoes no major
structural or nuclearity changes during the reaction, consistent with our observation that supported cluster 2 is more stable than
unsupported cluster 1 under “Click” reaction conditions.
workers reported that preꢀtreatment of Au25(SR)18/CeO2 (R =
INTRODUCTION
C2H4Ph) with O2 at 150 °C was required to activate the mateꢀ
rial for catalytic CO oxidation.19 Similarly, preꢀtreatment of
Atomicallyꢀprecise nanoclusters (APNCs) have been the subꢀ
ject of intense interest over the past decade for their use in a
Au25(SR)18/TiO2 at 300 °C was required to activate this mateꢀ
variety of emerging technological applications, including caꢀ
rial for the catalytic semiꢀhydrogenation of internal alkynes.20
talysis.1ꢀ7 Significantly, their perfectly monoꢀdisperse and
The need for harsh conditions is significant because they can
atomicallyꢀprecise nature permits their complete structural
cause irreversible changes in the structure and/or nuclearity of
characterization, facilitating the development of detailed strucꢀ
the APNCs, which dramatically diminishes our ability to exꢀ
ture/activity relationships (SARs).8ꢀ11 Yet, while the study of
tract robust SARs using APNC catalysts. Notably, in both of
APNCs could uncover new insights in catalysis, many APNCs
the examples described above, the catalyst structure during
are actually not wellꢀsuited for this purpose. For example, the
and/or after activation was not determined.
vast majority of the known nanoclusters have been synthesized
with a passivating shell of thiolate capping ligands.12 While
To address this challenge, several research groups are develꢀ
oping APNCs which are not passivated by thiolate ligands,
such ligands impart significant thermal and chemical stability
and which, in principle, should not require harsh preꢀtreatment
to APNCs, and are often required to render the APNCs isolaꢀ
for activation.21 These organometallic APNCs are most comꢀ
ble, they block active sites, and must be partially removed
monly stabilized with hydrides (i.e., Hꢀ) as capping ligands,22ꢀ
before catalysis can occur.13ꢀ15 At the same time, the strength
of the metalꢀsulfur bond often makes it difficult to remove the
thiolate ligands efficiently.16ꢀ18 For example, Jin and coꢀ
27
and more recently, acetylides (i.e., RC≡Cꢀ).28ꢀ40 For examꢀ
ple, we reported the syntheses of [Cu25H22(PPh3)12]Cl and
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 8
1
2
(a)
(b)
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
Ph
(c)
O
O
Cu
Cu
Cu
Cu
Ph
4x
4x
Cu
Cu
Cu
Ph
Cu
O
Ph
Cu
Cu
O
O
Ph
Cu
O
Ph
2+
Figure 1. Ball and stick diagrams showing (a) complex 1·C4H8O; (b) the tetrahedral Cu4 core (blue), shown with faceꢀcapping copper
atoms (green); and (c) illustrations of the ligand binding modes present in 1·C4H8O. Hydrogen atoms, four THF solvate molecules and one
coordinated THF molecule omitted for clarity. Color legend: Cu = blue, green; C = grey; O = red.
[Cu29Cl4H22(Ph2phen)12]Cl (Ph2phen
=
4,7ꢀdiphenylꢀ1,10ꢀ
that organometallic APNCs can maintain their structural integꢀ
rity during catalysis, permitting the development of SARs for
these unique nanomaterials.
phenanthroline), both of which are ligated by a mix of hydride
and neutral Lewis base ligands.25, Similarly, Liu and coꢀ
27
workers recently synthesized the copper acetylide nanocluster
[Cu13{S2CNnBu2}6(CCR)4][PF6] (R = C(O)OMe, C6H4F),
Zhang and coꢀworkers generated the silver acetylide cluster
Ag74(CCPh)44, and Wang and coꢀworkers prepared the gold
acetylide APNC [Au19(CCPh)9(Hdppa)3](SbF6)2 (Hdppa =
N,Nꢀbis(diphenylphosphino)amine).28, 33, 39
RESULTS AND DISCUSSION
Synthesis of a Cu20 nanocluster. Addition of 0.6 equiv of pheꢀ
nylacetylene (HCCPh) to a slurry of Cu(OAc) (1 equiv) in
THF results in a rapid color change from pale green to bright
yellow, characteristic of the known Cu(I) coordination polyꢀ
mer, [Cu(CCPh)]n,42 concomitant with the generation of
HOAc.42ꢀ43 Addition of 0.36 equiv of diphenylsilane (Ph2SiH2)
to this slurry results in a gradual color change to dark redꢀ
brown, accompanied by the appearance of a dark brown powꢀ
der. Workꢀup of the solution after stirring at room temperature
for 15 h resulted in the isolation of the mixedꢀvalent copper
acetylide nanocluster, [Cu20(CCPh)12(OAc)6] (1), as a redꢀ
orange, crystalline solid in 49% yield (Scheme 1a). Copper
metal is also formed during the reaction, and was isolated in
42% yield (based on Cu(OAc)) by filtration of the reaction
mixture through a 0.2 µm PTFE filter. The presence of the byꢀ
product Ph2Si(OAc)2 was confirmed by 1H NMR spectroscopy
of the supernatant (see Figure S3). For comparison, the only
Preliminary results suggest that organometallic APNCs are
more reactive than their thiolateꢀcapped cousins. For example,
[Au24Ag20(SPy)4(CCPh)20Cl2] (SPy = 2ꢀpyridylthiolate) was
observed to release its phenylacetylide capping ligands at relaꢀ
tively low temperatures (~100 °C), although the cluster was
not screened for any catalytic reactivity.31 Also of note, Zheng
and coꢀworkers claimed that [Au34Ag28(CCPh)34] supported on
XCꢀ72 carbon was active for catalytic hydrolysis of triꢀ
ethylsilane without any preꢀtreatment.41 One drawback of the
aboveꢀmentioned study, however, is that the structure of the
supported cluster was not interrogated. Therefore, it is still an
open question whether organometallic APNCs maintain their
structural integrity upon deposition onto a support. This conꢀ
cern is especially relevant for organometallic APNCs, given
their higher thermal, oxygen, and water sensitivity, relative to
thiolateꢀcapped APNCs.12, 41
other
Cu
acetylide
nanocluster,
[Cu13{S2CNnBu2}6(CCR)4][PF6] (R = C(O)OMe, C6H4F), was
formed during semihydrogenation of an alkyne by the Cu(I)
hydride nanocluster [Cu28H15{S2CNnBu2}12][PF6].33
Herein, we report the synthesis and characterization of an unꢀ
Scheme 1. Syntheses of complex 1
precedented
organometallic
copperꢀbased
APNC,
[Cu20(CCPh)12(OAc)6], and explore its ability to catalyze
Huisgen [3+2] cycloadditions. Significantly, we find that the
silicaꢀimmobilized cluster is a highly effective catalyst for this
transformation. More importantly, the supported cluster is
more stable under the “Click” reaction conditions than is the
unsupported cluster. We have also confirmed that the supportꢀ
ed cluster, both preꢀ and postꢀcatalysis, has not undergone any
major structural and/or nuclearity changes relative to the unꢀ
supported cluster. This study demonstrates for the first time
ACS Paragon Plus Environment

Page 3 of 8
Journal of the American Chemical Society
tegrating for 18 protons, assigned to the six magnetically
1
2
3
4
5
6
7
8
equivalent acetate ligands. In addition, resonances at 7.41,
7.15, and 6.95 ppm, integrating for 24, 12, and 24 protons,
respectively, are assigned to the oꢀPh, pꢀPh, and mꢀPh enviꢀ
ronments of 12 magnetically equivalent phenylacetylide ligꢀ
ands. The 13C{1H} NMR spectrum of 1 features a resonance at
23.31 ppm, which is assigned to the methyl groups of the aceꢀ
tate coꢀligands, while a resonance at 135.31 ppm is assigned to
the Cuꢀbound acetylide carbons. Electrospray ionization mass
spectroscopy (ESIꢀMS) of isolated complex 1 in THF, acꢀ
quired in positive ion mode, is consistent with our proposed
formulation (Figure S17). The major features, at m/z
2778.1309 and 2902.0662, correspond to [M ꢀ OAc]+ (calcd
m/z 2778.1221) and [M + Cu]+ (calcd m/z 2902.0608) ions,
respectively.
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
Complex 1 crystallizes as the THF adduct, 1·C4H8O, as red
blocks in the triclinic space group P1 (Figure 1). Four addiꢀ
ꢀ
tional THF molecules are incorporated into the crystal lattice
as solvates. In the solid state, 1·C4H8O contains a tetrahedral
[Cu4]2+ core (Figure 1b). Encapsulating the tetrahedral core is
a [Cu16(CCPh)12(OAc)6]2ꢀ shell. The CuꢀCu distances within
the cluster span a large range (2.463(3) – 2.934(3) Å), similar
to other structurally characterized copper nanoclusters.25, 27, 33,
We also briefly examined the chemical properties of 1. It is
soluble in benzene, toluene, THF, and CH2Cl2, but insoluble in
MeCN, Et2O, and nonpolar solvents. It is stable in CD2Cl2 for
at least 48 h, and stable to air and water (as a CD2Cl2 solution)
for up to 24 h. As a solid, complex 1 shows no signs of deꢀ
composition after 2 months of exposure to air and water on the
bench top. We also explored the electrochemical properties of
complex 1 in CH2Cl2 at 25 °C. The cyclic voltammogram of 1
features two irreversible oxidation events at E = 0.20 and 0.55
V (vs. Fc/Fc+) (Figure S24). These features remain irreversiꢀ
ble, even at scan rates of up to 2000 mV sꢀ1. We hypothesize
that electrons are being removed from the a1 symmetric bondꢀ
ing orbital, disrupting the CuꢀCu bonding network, and resultꢀ
ing in rapid decomposition of the cluster.52 For comparison,
the related Cu13 cluster, [Cu13{S2CNnBu2}6(CCR)4][PF6] (R =
C(O)OMe), exhibits two comparable quasiꢀreversible oxidaꢀ
tion features (ꢀ0.05 and 0.34 V, vs. Fc/Fc+), which the authors
also ascribe to removal of CuꢀCu bonding electrons.33 The
cyclic voltammogram of 1 also features an irreversible reducꢀ
tion event at –1.02 V, which only appears after sampling the
two irreversible oxidations. These observations are suggestive
of an ECEꢀtype process, but the identity of the species responꢀ
sible for reduction feature is not known at this time.
44ꢀ45
The twelve acetylide ligands incorporated into the
[Cu16(CCPh)12(OAc)6]2ꢀ shell are arranged in four [cycloꢀ
Cu(CCPh)]3 units, which are situated at the vertices of a tetraꢀ
hedron (Figure 1c). One acetylide ligand features
a
µ4:η1,η1,η2,η2 binding mode, four of the acetylide ligands feaꢀ
ture a µ3:η1,η1,η2 binding mode, and seven feature a
µ4:η1,η1,η1,η2 binding mode. The six acetate ligands are bound
in κ2 fashion, are located on the edges of the tetrahedron, and
feature an average CuꢀO distance of 1.96(2) Å (Figure 1c). To
the best of our knowledge, complex 1 is the first group 11
nanocluster to incorporate acetate coꢀligands.12 Additionally, a
THF molecule is coordinated to Cu18, with a Cu–O bond disꢀ
tance of 2.47(1) Å. Consequently, complex 1·C4H8O exhibits
no symmetry in the solid state. However, NMR spectroscopic
characterization in CD2Cl2 demonstrates that complex 1 exhibꢀ
its idealized Td symmetry in solution (vide infra), suggesting
that this THF molecule is only weakly bound to the cluster.
This observation also suggests that the acetylide ligands interꢀ
convert between the three observed binding modes.
Mechanistic Considerations. The first step in the formation of
complex 1 appears to be the generation of the wellꢀknown
yellow Cu(I) coordination polymer [Cu(CCPh)]n, along with
HOAc.42ꢀ43 Ph2SiH2 then reacts with HOAc to make H2 and
Ph2Si(OAc)2. In parallel, we surmise that Ph2SiH2 also reacts
with unconsumed Cu(OAc) to give Cu(0), which is captured
by [Cu(CCPh)]n to generate the final nanocluster product. This
mechanism is consistent with the formation of the yellow solid
we observe in the reaction mixture at short reaction times. It is
also consistent with the observation of bulk Cu metal in the
reaction mixture, which is likely formed when some of the
Cu(0) source is not captured by [Cu(CCPh)]n during the reacꢀ
tion, and eventually precipitates as bulk copper metal.
Interestingly, because there are only 18 anionic ligands (12
acetylides and six acetates), two of the 20 Cu atoms in 1 must
have a formal oxidation state of 0 to maintain charge balance.
Accordingly, complex 1 can be viewed as a superatom with a
magic number N* = 2 and an [M4]2+ core.1, 25, 27, 33ꢀ34, 40, 46ꢀ48
This is a relatively uncommon magic number, and a rare core
structure, for group 11 superatoms.39, 41, 44ꢀ45, 49ꢀ51 Almost all
structurally characterized superatoms, such as the related copꢀ
per acetylide superatom, [Cu13{S2CNnBu2}6(CCR)4][PF6],33
contain metalꢀcentered icosahedral, cuboctahedral, or antiꢀ
cuboctahedral cores.12, 25, 27, 40, 45ꢀ51 In complex 1, no such cenꢀ
tral metal atom is present, therefore the two “extra” electrons
most likely occupy the a1 symmetric bonding molecular orbital
formed from the linear combination of the four Cu 4s orbitals
within the tetrahedral [Cu4]2+ core. The three t2 symmetric
orbitals remain unoccupied.52 The unique core structure and
incorporation of acetate ligands in 1 expands the structural
diversity of copper superatoms, and raises the possibility that
many more copper superatoms, with a wide variety of ligand
types, should be isolable.
To test this hypothesis, we attempted the synthesis of 1 using a
mixture of Cu(OAc) (8 equiv) and independentlyꢀsynthesized
[Cu(CCPh)]n (12 equiv) as Cu sources (Scheme 1b). Reaction
of this combination with Ph2SiH2 (1 equiv) in THF for 30 h
resulted in the formation of a redꢀorange THF solution and a
greenꢀbrown solid. Workꢀup of the THFꢀsoluble fraction reꢀ
sulted in the isolation of 1 in 26% yield. While its yield is low,
the formation of 1 under these conditions is consistent with
our proposed mechanism. Additionally, the reaction of
Ph2SiH2 with 95% HOAc in CD3CN, in the presence of 10
mol% of Cu(OAc), resulted in rapid formation of H2,
Both the 1H and 13C{1H} NMR spectra of 1 in CD2Cl2 are conꢀ
sistent with a Tdꢀsymmetric structure in solution. For example,
1
the H NMR spectrum of 1 features a singlet at 2.01 ppm, inꢀ
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 8
1
Ph2SiH(OAc) and Ph2Si(OAc)2, according to H NMR specꢀ
Comparable yields of triazoles ethylꢀ1ꢀbenzylꢀ1Hꢀ1,2,3ꢀ
triazoleꢀ4ꢀcarboxylate (4) and 1ꢀbenzylꢀ4ꢀtertꢀbutylꢀ1Hꢀ1,2,3ꢀ
triazole (5) were observed upon substitution of HCCPh with
either HCC(CO2Et) or HCCtBu, respectively (entries 3 and 4,
Table 1). Notably, however, in these two cases we also obꢀ
serve the formation of 3 in the reaction mixture (see Figures
S14 and S15), indicating that the phenylacetylide ligands preꢀ
sent in 1 play a role in the catalytic cycle and can be incorpoꢀ
rated into the product. To rationalize this observation, we proꢀ
pose that the first step of the catalytic cycle involves reaction
of benzyl azide with a bound phenylacetylide ligand, resulting
in formation of a copperꢀbound triazolate fragment.56 This
fragment undergoes subsequent protonolysis by incoming
alkyne to generate 3 and a new copperꢀbound acetylide ligand.
1
2
3
4
5
6
7
8
troscopy (Figure S5), confirming our hypothesis regarding the
mechanism of formation of Ph2Si(OAc)2. Interestingly, no
reaction between Ph2SiH2 and HOAc was observed in the abꢀ
sence of Cu(OAc).
We also attempted the synthesis of 1 in the presence of excess
Ph2SiH2 (10 equiv total). Under these conditions, we observed
almost exclusive formation of Cu0. Thus, it appears that when
1 is formed in the presence of unreacted silane, the cluster
rapidly decomposes. Consistent with this observation, reaction
of 1 with 3 equiv of Ph2SiH2 in CD2Cl2 resulted in decomposiꢀ
tion of 1 and formation of Cu metal as the only identifiable
Cuꢀcontaining material (Figure S4).
Several groups,12 including ours,25 have demonstrated that the
metal:ligand ratio employed during nanocluster syntheses can
affect the final cluster size. In the system described here, howꢀ
ever, increasing the Cu(OAc):alkyne ratio to 20:6 (from 20:12
used in Scheme 1a), in an attempt to isolate a larger nanoclusꢀ
ter, resulted only in formation of copious amounts of Cu metal
(and no tractable Cu acetylide clusters). Decreasing the
Cu(OAc):alkyne ratio to 20:20 still resulted in the formation
of complex 1, but in a lower isolated yield.
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
Interestingly, as the homogeneous catalytic reaction proceeds,
the redꢀorange color of 1 slowly disappears and a bright yelꢀ
low solid resembling [Cu(CCPh)]n begins to precipitate from
the reaction mixture.42 This phenomenon was observed for all
1
three alkyne substrates. Additionally, the H NMR signals
attributed to complex 1 lose > 95% of their intensity (relative
to the internal standard) over the course of the reaction. These
data suggest that 1 has somewhat limited stability under the
reaction conditions, and likely dissociates into smaller clusters
and/or discrete Cu+ ions, either of which may also be catalytiꢀ
cally active.57 Accordingly, we cannot definitively conclude
that complex 1 is the active catalyst in this system, and it may
simply function as a preꢀcatalyst. Similar behavior has been
observed in other Cu nanoparticle systems.58ꢀ59
Grafting of 1 onto Silica. We also explored the reaction of 1
with dehydrated and partiallyꢀdehydroxylated silica (Sylopol
952, pretreated in vacuum at 200 °C). Reaction of a red C6D6
solution of 1 with 36.0 mg silica (to give a solid containing ca.
3 wt% Cu) results in gradual transfer of 1 from solution to the
silica (1 h total reaction time), to provide an orange solid and a
1
We also examined the ability of heterogeneous 2 to catalyze
the [3+2] cycloaddition of phenylacetylene and benzyl azide,
under conditions identical to those employed in the homogeꢀ
neous reaction. Thus, addition of 2 (0.5 mol% Cu20 cluster) to
a CD2Cl2 solution of benzyl azide (1.1 equiv) and HCCPh (1
equiv) generated 3 in comparable yields to those observed
using intact 1 (entry 5, Table 1). The recycled silicaꢀsupported
catalyst also generated 3 in comparable yield (entry 6, Table
1). Notably, we see no evidence for leaching of complex 1
from the SiO2 support into CD2Cl2 over 7 h by 1H NMR specꢀ
troscopy, either in the absence or presence of the alkyne and
azide substrates (Figures S16 and S9). Supported cluster 2 is
also an effective catalyst for the [3+2] cycloaddition reaction
at 40 °C (entry 7, Table 1). However, at these elevated temꢀ
peratures, the catalyst undergoes a gradual color change from
redꢀorange to pale yellow over the course of the reaction, sugꢀ
gesting that it may undergo a structural change upon heating.
colorless solution. A solutionꢀstate H NMR spectrum of the
reaction supernatant after 1 h revealed a complete absence of
peaks assignable to 1, as well as formation of 1 equiv of
PhCCH (Scheme 2 and Figure S6). We see no evidence for
formation of HOAc in solution, consistent with the relative
basicities of [OAc]ꢀ and [PhCC]ꢀ. To explain these observaꢀ
tions, we suggest that reaction of 1 with a surface hydroxyl
group (≡SiOH) results in protonation of one acetylide ligand
of 1 and formation of immobilized cluster 2 via a new CuꢀOꢀ
Si bond.
Scheme 2. Reaction of 1 with Silica
HOSi
[Cu20(CCPh)11(OAc)6(OSi )]
[Cu20(CCPh)12(OAc)6]
C6D6
1
2
+ Ph
H
“Click” Chemistry with 1 and 2. Copperꢀcatalyzed [3+2]
Huisgen cycloadditions of terminal alkynes and organic azides
(CuAAC) have been the cornerstone of “Click” chemistry
since the seminal reports of Meldal and Sharpless in 2002.53ꢀ54
Recently, Straub and coꢀworkers reported that a small Cu(I)
acetylide cluster was a competent catalyst for the “Click” reacꢀ
tion.55 Intriguingly, that cluster features acetylide ligands with
µ4:η1,η1,η1,η2 and µ3:η1,η1,η2 binding modes, which are nearly
identical to those observed in complex 1.55 Thus, we hypotheꢀ
sized that 1 would also be a competent catalyst for the same
transformation. Accordingly, we examined the ability of 1 to
catalyze the [3+2] cycloaddition of several alkynes (HCCR, R
It is well known that solvated Cu+ ions can effectively catalyze
the Click reaction.43, 57 As a result, it has been a challenge to
establish if Cu nanomaterials themselves are the actual cataꢀ
lysts or if leached Cu+ ions are responsible for the observed
reactivity.60 To probe the stability of 2, we separated the supꢀ
ported catalyst from the supernatant of a reaction between
benzyl azide and HCCPh by filtration, then exposed the superꢀ
natant to fresh substrate (Figure S11). Under these conditions,
we observed no conversion of alkyne and benzyl azide to the
triazole after 7 h, suggesting that Cu+ ions were not leached
from the supported catalyst into solution over the course of the
initial reaction. Overall, this result suggests that 2 is more staꢀ
ble than 1 under “Click” reaction conditions.
t
= Ph, CO2Et, and Bu) with benzyl azide. Addition of 1 (0.5
mol% Cu20 cluster) to a CD2Cl2 solution of benzyl azide (1.1
equiv) and HCCPh (1 equiv), at room temperature, generated
1ꢀbenzylꢀ4ꢀphenylꢀ1Hꢀ1,2,3ꢀtriazole (3) in good yield (entry 1,
Table 1). Complex 1 is also effective at a much lower catalyst
loading (0.05 mol% Cu20 cluster, entry 2, Table 1).
Table 1. [3+2] cycloadditions between benzyl azide and
various terminal alkynes catalyzed by 1 and 2. a
ACS Paragon Plus Environment

Page 5 of 8
Journal of the American Chemical Society
N
N
N
cat. Cu20
1
2
3
Ph
+
R
Ph
N3
CD2Cl2, 25 ºC
R
loading
yield
(%)c
4
5
6
7
8
9
Entry
R
time (h)
TON
190
(mol %)b
1
2
3
4
5
6
7f
Ph
Ph
5
7
5
5
7
7
2
0.5
95
85
86
92
95
94
>99
0.05
0.5
1700
172
184
190
188
198
CO2Et
tBu
Ph
0.5
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
0.5d
0.5e
0.5
Ph
Ph
aFor experimental details, see Supporting Information. Cataꢀ
lyst loading defined as mol% Cu20 cluster. Yield of triazole
determined by integration of H NMR spectra acquired with a
60 s pulse delay, using hexamethyldisiloxane as internal
b
c
1
d
standard. Catalyst immobilized on SiO2 (see SI for experiꢀ
Figure 2. Comparison of Cu K-edge EXAFS (displayed as FT
magnitude, points, with curvefits, lines) for
[Cu20(CCPh)12(OAc)6] (1, blue), freshly-prepared Cu20/SiO2
(2, green), and post-catalysis Cu20/SiO2 (2post, red).
mental details). eRecovered catalyst, still immobilized on SiO2
f
(see SI for experimental details). Reaction performed at 40
°C.
For comparison, several groups have shown that supported
copper nanomaterials can catalyze CuAAC chemistry.58, 61ꢀ68
Broadly speaking, these materials exhibit activities and recyꢀ
clabilities similar to those observed for 2. However, many of
these nanomaterials feature large polydispersities,69ꢀ71 or suffer
from illꢀdefined surface chemistries.61, 63 As such, it is a chalꢀ
lenge to reliably and predictably deposit these material on a
support. Additionally, this polydispersity makes it a significant
challenge to extract SARs in an effort to develop better cataꢀ
lyst systems.
The curvefit of the EXAFS of 1 (Figure S30) includes a Cu–O
path and a Cu–C path, whose distances were fixed at the most
commonly observed values in the Xꢀray crystal structure
(1.951 and 2.061 Å, respectively, the latter being the distance
corresponding to the CuꢀC πꢀbonds). The fit returned N(Cu–
O) and N(Cu–C) values of 0.6(3) and 1.2(4), respectively (Taꢀ
ble 2). The number of CuꢀO paths agrees with the average
number of bidentate acetate ligands per Cu (0.3), while the
value for the Cu–C path exceeds the average number of acetyꢀ
lide ligands per Cu (0.6), as expected due to the presence of
both ꢀ and πꢀinteractions involving these ligands. The CuꢀCu
paths, which range from 2.471 to 3.085 Å in the crystal strucꢀ
ture, were represented in the curvefit by two paths whose disꢀ
tances were fixed at the most frequent CuꢀCu bond lengths.
The resulting fit returned a combined N(CuꢀCu) of 2.3(5),
similar to the crystallographicallyꢀdetermined value of 2.7.
Characterization of 1 and 2 by X-ray Absorption Spectrosco-
py. Previous studies25,
on Cuꢀbased APNCs revealed reꢀ
27
markable XAS sensitivity to both ligand sets and Cu nucleariꢀ
ty. Therefore, Cu Kꢀedge XAFS was undertaken to compare
structural features of complex 1 with its silicaꢀsupported anaꢀ
log, 2, as well as the recovered postꢀcatalysis material, 2post
.
The absence of significant differences in the XANES profiles
of 1 and 2 suggests that the nanocluster structure is preserved
upon grafting onto SiO2 (Figure S27). In the EXAFS, two
prominent features appear at 1.6 and 2.3 Å in the FT magniꢀ
tude of the EXAFS of 1 (Figure 2). The first peak represents
light atoms directly coordinated to Cu, i.e., the donor atoms of
the bidentate acetate and sideꢀon bound acetylide ligands. The
second peak represents the contributions of the CuꢀCu paths.
The EXAFS of silicaꢀsupported 2 features two similar peaks,
at 1.6 and 2.2 Å, with slightly different relative intensities
compared to those observed for 1 (Figure 2). The distances for
the CuꢀO and CuꢀC paths were again fixed using the most
common values found in the molecular cluster 1, while both
coordination numbers were refined. Minor changes in the fitꢀ
ted values of N(Cu–O) and N(Cu–C), to 1.0(1) and 0.6(4),
respectively, are consistent with a reaction of 1 with silica,
which results in one acetylide ligand being replaced by a surꢀ
face silyloxide (likely in a bridging configuration), among
other possible interactions (see Figure S31 and Table 2). Altꢀ
hough the intensity of the peak in the FT magnitude correꢀ
sponding to the CuꢀCu paths decreased slightly upon deposiꢀ
tion onto silica, curvefitting returned a similar total value for
N(Cu–Cu), 2.3(3). We hypothesize that the CuꢀCu distribution
becomes less uniform upon deposition, and the number of
longer paths increases at the expense of the shorter paths. The
resulting destructive interference results in an overall decrease
in FT magnitude, without any cluster fragmentation. Thus,
our EXAFS analysis suggests that immobilization of 1 results
in little or no change to the cluster nuclearity, and only minor
changes to the cluster structure.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Table 2. Curvefit parameters for the Cu K-edge EXAFSa
Page 6 of 8
deposition on a solid support, and after use in a catalytic reacꢀ
1
tion.
2
3
4
5
6
7
8
9
Path
EXAFS curvefit
Material
1b
CONCLUSION
103 σ2(Åꢀ1)
N
R(Å)
In summary, we have synthesized and characterized the novel
organometallic nanocluster [Cu20(CCPh)12(OAc)6] (1). Comꢀ
plex 1 is a rare example a 2ꢀelectron copper superatom, and
the first copper superatom to feature a [Cu4]2+ core. Complex 1
can be readily immobilized on dry, partiallyꢀdehydroxylated
silica, a process that results in release of 1 equiv of phenylaꢀ
cetylene per Cu20 cluster. According to qualitative and quantiꢀ
tative EXAFS analysis, the immobilized cluster 2 is structuralꢀ
ly similar to 1. In addition, both 1 and 2 are effective catalysts
for [3+2] cycloaddition of alkynes and azide at room temperaꢀ
ture. Intriguingly, supported cluster 2 appears to be substanꢀ
tially more stable than 1 under the reaction conditions. More
importantly, however, neither 1 nor 2 require harsh preꢀ
treatment for activation, demonstrating the innate promise of
organometallic APNCs for development of SARs in the field
of supported catalysis.
CuꢀO
CuꢀC
0.6(3)
1.2(4)
2.1(5)
0.2(1)
1.0(1)
0.6(4)
1.7(2)
0.6(2)
1.7(3)
0.7(3)
1.2(3)
0.5(3)
1.951c
2.061c
2.563c
2.671c
1.951c
2.061c
2.505(6)
2.62(2)
1.951c
2.061c
2.53(4)
2.66(1)
5(3)d
5(3)d
6(2)e
6(2)e
7(2)d
7(2)d
7(2)e
7(2)e
7(1)d
7(1)d
6(1)e
6(1)e
CuꢀCu1
CuꢀCu2
CuꢀO
2f
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
CuꢀC
CuꢀCu1
CuꢀCu2
CuꢀO
g
2post
CuꢀC
CuꢀCu1
CuꢀCu2
a Uncertainties in the last significant figure are shown in parentheꢀ
ses. Values without uncertainties were fixed at values determined
ASSOCIATED CONTENT
Supporting Information
by Xꢀray crystallography. bGlobal fit parameters: So = 0.8(1);
2
c
∆Eo = 5(1) eV. Fixed at values determined by single crystal Xꢀ
d
The Supporting Information is available free of charge on the
ACS Publications website.
ray diffraction (this work). Constrained to have the same meanꢀ
squared displacement. eConstrained to have the same meanꢀ
f
2
squared displacement. Global fit parameters: So = 0.8(2); ∆Eo =
8(2) eV. gGlobal fit parameters: So2 = 0.8(1); ∆Eo = 9(1) eV.
Xꢀray data for compound 1·5C4H8O (CIF)
The supported cluster material was recovered after use as a
catalyst for the cycloaddition of benzyl azide and HCCPh. The
EXAFS of the recovered postꢀcatalysis material, 2post, is again
similar to that of the immobilized cluster 2 (Figure 2). The
curvefit reveals an increase in N(CuꢀO), to 1.7(3), while the
value for N(CuꢀC) remains essentially unchanged at 0.7(3)
(Figure S32 and Table 2). The peak arising from the CuꢀCu
paths broadened, while the total value of N(CuꢀCu) decreased
to 1.7(5). Although these values are slightly different than
those found for 2, qualitative inspection of the spectrum for
2post suggests that the supported cluster’s ligand complement is
largely preserved, i.e., there has been minimal rearrangement
of the CuꢀCu skeleton. More importantly, these changes are
not consistent with extensive cluster fragmentation or aggregaꢀ
tion. The qualitative similarities in the EXAFS are also conꢀ
sistent with the XANES profiles of 2 and 2post, which show
nearly indistinguishable, superimposable edges and absorbꢀ
ance maxima (Figure S27 and Table S3).
Experimental procedures, crystallographic details, and specꢀ
tral data (PDF)
AUTHOR INFORMATION
Corresponding Author
*hayton@chem.ucsb.edu
*sscott@engineering.ucsb.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
T.W.H. and A.W.C. thank the National Science Foundation (CHE
1361654) for financial support. Z. J. and S. L. S. thank the U.S.
Department of Energy, Office of Science, Office of Basic Energy
Sciences, under the Catalysis Science Initiative (DEꢀFGꢀ02ꢀ
03ER15467), and the NSF PIRE program (OISEꢀ0968399), for
financial support. NMR spectra were collected on an instrument
supported by an NIH Shared Instrumentation Grant (SIG,
1S10OD012077ꢀ01A1). ESI mass spectra were acquired at the
MRL Shared Experimental Facilities, supported by the MRSEC
Program of the NSF under Award No. DMR 1121053 and a
member of the NSFꢀfunded Materials Research Facilities Netꢀ
work. Xꢀray absorption spectra were acquired at the Stanford
Synchrotron Radiation Lightsource, a Directorate of SLAC Naꢀ
tional Accelerator Laboratory and an Office of Science User Faꢀ
cility operated for the U.S. Department of Energy Office of Sciꢀ
ence by Stanford University. A. W. C. thanks the Mellichamp
Academic Initiative in Sustainability at UCSB for a summer felꢀ
lowship.
There are only a handful of prior reports describing the characꢀ
terization of APNCs before and after deposition onto a solid
support. For example, Spivey and coꢀworkers demonstrated by
EXAFS that deposition of a thiolateꢀcapped Au38 cluster on
TiO2 resulted in aggregation.72 In contrast, Wu and coꢀworkers
concluded that deposition of a Au22 nanocluster onto TiO2
resulted in no agglomeration, on the basis of HAADF–STEM
imaging.73 While this cluster was competent for CO oxidation,
the postꢀcatalysis cluster was not characterized, so its nucleariꢀ
ty is unknown. Similarly, Scott and coꢀworkers demonstrated
that thiolateꢀprotected Au25(11ꢀMUA)18 (11ꢀMUA = merꢀ
captoundecanoic acid) maintained its structure after deposition
onto SiO2, but agglomerated upon calcination at 250 °C.18
Thus, the nanocluster series 1, 2, and 2post represents an excepꢀ
tionally rare example of retention of cluster structure after
REFERENCES
1.
2.
Hakkinen, H., Chem. Soc. Rev. 2008, 37, 1847ꢀ1859.
Schmid, G., Chem. Soc. Rev. 2008, 37, 1909ꢀ1930.
ACS Paragon Plus Environment

Page 7 of 8
Journal of the American Chemical Society
3.
4.
Li, G.; Jin, R., Acc. Chem. Res. 2013, 46, 1749ꢀ1758.
Yamazoe, S.; Koyasu, K.; Tsukuda, T., Acc. Chem. Res.
36.
Wan, X.ꢀK.; Cheng, X.ꢀL.; Tang, Q.; Han, Y.ꢀZ.; Hu, G.;
Jiang, D.ꢀe.; Wang, Q.ꢀM., J. Am. Chem. Soc. 2017, 139, 9451ꢀ9454.
1
2
3
4
2014, 47, 816ꢀ824.
5.
6.
37.
C. W., Inorg. Chem. 2017, 56, 10412ꢀ10417.
38. Wan, X. K.; Guan, Z. J.; Wang, Q. M., Angew. Chem. Int.
Ed. 2017, 56, 11494–11497.
Jin, J.ꢀL.; Xie, Y.ꢀP.; Cui, H.; Duan, G.ꢀX.; Lu, X.; Mak, T.
Daniel, M.ꢀC.; Astruc, D., Chem. Rev. 2004, 104, 293ꢀ346.
Parker, J. F.; FieldsꢀZinna, C. A.; Murray, R. W., Acc.
Chem. Res. 2010, 43, 1289ꢀ1296.
7.
Harkness, K. M.; Tang, Y.; Dass, A.; Pan, J.; Kothalawala,
39.
Qu, M.; Li, H.; Xie, L.ꢀH.; Yan, S.ꢀT.; Li, J.ꢀR.; Wang, J.ꢀ
5
6
7
8
N.; Reddy, V. J.; Cliffel, D. E.; Demeler, B.; Stellacci, F.; Bakr, O.
M.; McLean, J. A., Nanoscale 2012, 4, 4269ꢀ4274.
8.
13294ꢀ13304.
9.
Ed. 2010, 49, 1295ꢀ1298.
H.; Wei, C.ꢀY.; Wu, Y.ꢀW.; Zhang, X.ꢀM., J. Am. Chem. Soc. 2017,
139, 14346ꢀ12349.
40.
Jiang, D.ꢀe.; Wang, Q.ꢀM., Nanoscale 2017, 9, 11405ꢀ11409.
41. Wang, Y.; Wan, X.ꢀK.; Ren, L.; Su, H.; Li, G.; Malola, S.;
Yan, N.; Yuan, Y.; Dyson, P. J., Dalton Trans. 2013, 42,
Yuan, S.ꢀF.; Li, P.; Tang, Q.; Wan, X.ꢀK.; Nan, Z.ꢀA.;
9
Zhu, Y.; Qian, H.; Drake, B. A.; Jin, R., Angew. Chem. Int.
Lin, S.; Tang, Z.; Häkkinen, H.; Teo, B. K.; Wang, Q.ꢀM.; Zheng, N.,
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
10.
11462.
11.
6799.
12.
116, 10346ꢀ10413.
Zhu, Y.; Qian, H.; Jin, R., Chem. Eur. J. 2010, 16, 11455ꢀ
J. Am. Chem. Soc. 2016, 138, 3278ꢀ3281.
42.
Chui, S. S. Y.; Ng, M. F. Y.; Che, C.ꢀM., Chem. Eur. J.
Zhu, Y.; Qian, H.; Jin, R., J. Mater. Chem. 2011, 21, 6793ꢀ
Jin, R.; Zeng, C.; Zhou, M.; Chen, Y., Chem. Rev. 2016,
2005, 11, 1739ꢀ1749.
43.
Shao, C.; Cheng, G.; Su, D.; Xu, J.; Wang, X.; Hu, Y., Adv.
Synth. Catal. 2010, 352, 1587ꢀ1592.
44.
Freitag, K.; Banh, H.; Gemel, C.; Seidel, R. W.; Kahlal, S.;
13.
Das, S.; Goswami, A.; Hesari, M.; AlꢀSharab, J. F.;
Saillard, J.ꢀY.; Fischer, R. A., Chem. Commun. 2014, 50, 8681ꢀ8684.
Mikmeková, E.; Maran, F.; Asefa, T., Small 2014, 10, 1473ꢀ1478.
14.
2015, 9, 3050ꢀ3059.
15.
45.
Ganesamoorthy, C.; Weßing, J.; Kroll, C.; Seidel, R. W.;
Elliott, E. W.; Glover, R. D.; Hutchison, J. E., ACS Nano
Gemel, C.; Fischer, R. A., Angew. Chem. Int. Ed. 2014, 53, 7943ꢀ
7947.
Wang, L.; Tang, Z.; Yan, W.; Yang, H.; Wang, Q.; Chen,
46.
Yang, H.; Lei, J.; Wu, B.; Wang, Y.; Zhou, M.; Xia, A.;
S., ACS Appl. Mater. Interfaces 2016, 8, 20635ꢀ20641.
Zheng, L.; Zheng, N., Chem. Commun. 2013, 49, 300ꢀ302.
16.
Fan, J.; Dai, S., Chem. Commun. 2012, 48, 11413ꢀ11415.
17. Fang, J.; Li, J.; Zhang, B.; Yuan, X.; Asakura, H.; Tanaka,
T.; Teramura, K.; Xie, J.; Yan, N., Nanoscale 2015, 7, 6325ꢀ6333.
18. Sudheeshkumar, V.; Shivhare, A.; Scott, R. W. J., Catal.
Sci. Tech. 2017, 7, 272ꢀ280.
Ma, G.; Binder, A.; Chi, M.; Liu, C.; Jin, R.; Jiang, D.ꢀe.;
47.
Yang, H.; Wang, Y.; Zheng, N., Nanoscale 2013, 5, 2674ꢀ
2677.
48.
Kang, X.; Wang, S.; Song, Y.; Jin, S.; Sun, G.; Yu, H.;
Zhu, M., Angew. Chem. Int. Ed. 2016, 55, 3611ꢀ3614.
49. van der Velden, J. W. A.; Bour, J. J.; Vollenbroek, F. A.;
Beurskens, P. T.; Smits, J. M. M., J. Chem. Soc., Chem. Commun.
1979, 1162ꢀ1163.
19.
Nie, X.; Qian, H.; Ge, Q.; Xu, H.; Jin, R., ACS Nano 2012,
6, 6014ꢀ6022.
20.
21.
2017, 139, 2122ꢀ2131.
22.
Chiang, M.ꢀH.; Piltz, R. O.; Kahlal, S.; Saillard, J.ꢀY.; Liu, C. W.,
Angew. Chem. Int. Ed. 2014, 53, 7214ꢀ7218.
23.
Chiang, M.ꢀH.; van Zyl, W. E.; Saillard, J.ꢀY.; Liu, C. W., Chem. Eur.
J. 2015, 21, 8369ꢀ8374.
24.
G.; Peters, B.; Hayton, T. W., Chem. Eur. J. 2015, 21, 5341ꢀ5344.
25. Nguyen, T.ꢀA. D.; Jones, Z. R.; Goldsmith, B. R.; Buratto,
W. R.; Wu, G.; Scott, S. L.; Hayton, T. W., J. Am. Chem. Soc. 2015,
137, 13319ꢀ13324.
26.
2016, 49, 86ꢀ95.
27.
S. L.; Hayton, T. W., Chem. Mater. 2016, 28, 8385ꢀ8390.
28.
M., J. Am. Chem. Soc. 2015, 137, 652ꢀ655.
29. Wan, X.ꢀK.; Yuan, S.ꢀF.; Tang, Q.; Jiang, D.ꢀe.; Wang, Q.ꢀ
M., Angew. Chem. Int. Ed. 2015, 54, 5977ꢀ5980.
30. Wan, X.ꢀK.; Xu, W. W.; Yuan, S.ꢀF.; Gao, Y.; Zeng, X.ꢀC.;
Wang, Q.ꢀM., Angew. Chem. Int. Ed. 2015, 54, 9683ꢀ9686.
31. Wang, Y.; Su, H.; Xu, C.; Li, G.; Gell, L.; Lin, S.; Tang,
Z.; Häkkinen, H.; Zheng, N., J. Am. Chem. Soc. 2015, 137, 4324ꢀ
4327.
32.
Cryst. Growth Des. 2015, 15, 2505ꢀ2513.
33.
Chiang, M.ꢀH.; Saillard, J.ꢀY.; Liu, C. W., Angew. Chem. Int. Ed.
2016, 55, 14704ꢀ14708.
34.
50.
Sansoni, M., J. Chem. Soc., Chem. Commun. 1981, 222ꢀ223.
51. Zeller, E.; Beruda, H.; Schmidbaur, H., Inorg. Chem. 1993,
32, 3203ꢀ3204.
Demartin, F.; Manassero, M.; Naldini, L.; Ruggeri, R.;
Li, G.; Jin, R., J. Am. Chem. Soc. 2014, 136, 11347ꢀ11354.
Liu, P.; Qin, R.; Fu, G.; Zheng, N., J. Am. Chem. Soc.
Edwards, A. J.; Dhayal, R. S.; Liao, P.ꢀK.; Liao, J.ꢀH.;
52.
Saillard, J.ꢀY.; Halet, J.ꢀF., Structure and Bonding Patterns
in Large Molecular Ligated Metal Clusters. In The Chemical Bond I:
100 Years Old and Getting Stronger, Mingos, D. M. P., Ed. Springer
International Publishing: Cham, 2016; pp 157ꢀ179.
Dhayal, R. S.; Liao, J.ꢀH.; Kahlal, S.; Wang, X.; Liu, Y.ꢀC.;
53.
Tornøe, C. W.; Christensen, C.; Meldal, M., J. Org. Chem.
2002, 67, 3057ꢀ3064.
Nguyen, T.ꢀA. D.; Goldsmith, B. R.; Zaman, H. T.; Wu,
54.
Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless,
K. B., Angew. Chem. Int. Ed. 2002, 41, 2596ꢀ2599.
55.
Angew. Chem. Int. Ed. 2015, 54, 7431ꢀ7435.
56. Jin, L.; Tolentino, D. R.; Melaimi, M.; Bertrand, G., Sci.
Adv. 2015, 1, e1500304.
Makarem, A.; Berg, R.; Rominger, F.; Straub, B. F.,
Dhayal, R. S.; van Zyl, W. E.; Liu, C. W., Acc. Chem. Res.
57.
Meldal, M.; Tornøe, C. W., Chem. Rev. 2008, 108, 2952ꢀ
Nguyen, T.ꢀA. D.; Jones, Z. R.; Leto, D. F.; Wu, G.; Scott,
3015.
58.
Alonso, F.; Moglie, Y.; Radivoy, G., Acc. Chem. Res.
Wan, X.ꢀK.; Tang, Q.; Yuan, S.ꢀF.; Jiang, D.ꢀe.; Wang, Q.ꢀ
2015, 48, 2516ꢀ2528.
59.
Lee, B.ꢀH.; Wu, C.ꢀC.; Fang, X.; Liu, C. W.; Zhu, J.ꢀL.,
Catal. Lett. 2013, 143, 572ꢀ577.
60.
Decan, M. R.; Impellizzeri, S.; Marin, M. L.; Scaiano, J.
C., Nat. Commun. 2014, 5, 4612.
61.
Lipshutz, B. H.; Taft, B. R., Angew. Chem. Int. Ed. 2006,
45, 8235ꢀ8238.
62.
Sharghi, H.; Khalifeh, R.; Doroodmand, M. M., Adv. Synth.
Catal. 2009, 351, 207ꢀ218.
Zhang, R.; Hao, X.; Li, X.; Zhou, Z.; Sun, J.; Cao, R.,
63.
Alonso, F.; Moglie, Y.; Radivoy, G.; Yus, M., Adv. Synth.
Catal. 2010, 352, 3208ꢀ3214.
Chakrahari, K. K.; Liao, J.ꢀH.; Kahlal, S.; Liu, Y.ꢀC.;
64.
Lee, B. S.; Yi, M.; Chu, S. Y.; Lee, J. Y.; Kwon, H. R.;
Lee, K. R.; Kang, D.; Kim, W. S.; Lim, H. B.; Lee, J.; Youn, H.ꢀJ.;
Chi, D. Y.; Hur, N. H., Chem. Commun. 2010, 46, 3935ꢀ3937.
Wang, Y.; Su, H.; Ren, L.; Malola, S.; Lin, S.; Teo, B. K.;
65.
Alonso, F.; Moglie, Y.; Radivoy, G.; Yus, M., Org.
Häkkinen, H.; Zheng, N., Angew. Chem. Int. Ed. 2016, 55, 15152ꢀ
15156.
35.
Biomol. Chem. 2011, 9, 6385ꢀ6395.
66.
Nador, F.; Volpe, M. a. A.; Alonso, F.; Feldhoff, A.;
Lei, Z.; Wan, X.ꢀK.; Yuan, S.ꢀF.; Wang, J.ꢀQ.; Wang, Q.ꢀ
Kirschning, A.; Radivoy, G., Appl. Catal., A 2013, 455, 39–45.
M., Dalton Trans. 2017, 46, 3427ꢀ3434.
67.
Rance, G. A.; Solomonsz, W. A.; Khlobystov, A. N.,
Chem. Commun. 2013, 49, 1067ꢀ1069.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 8
68.
Sarmah, B.; Satpati, B.; Srivastava, R., RSC Adv. 2016, 6,
72.
Gaur, S.; Miller, J. T.; Stellwagen, D.; Sanampudi, A.;
87066ꢀ87081.
Kumar, C. S. S. R.; Spivey, J. J., Phys. Chem. Chem. Phys. 2012, 14,
1627ꢀ1634.
1
2
3
4
69.
Molteni, G.; Bianchi, C. L.; Marinoni, G.; Santo, N.; Ponti,
A., New J. Chem. 2006, 30, 1137ꢀ1139.
73.
Wu, Z.; Hu, G.; Jiang, D.ꢀe.; Mullins, D. R.; Zhang, Q.ꢀF.;
70.
Abdulkin, P.; Moglie, Y.; Knappett, B. R.; Jefferson, D. A.;
Allard, L. F.; Wang, L.ꢀS.; Overbury, S. H., Nano Lett. 2016, 16,
6560ꢀ6567.
Yus, M.; Alonso, F.; Wheatley, A. E. H., Nanoscale 2013, 5, 342ꢀ350.
71.
Fu, F.; Martinez, A.; Wang, C.; Ciganda, R.; Yate, L.;
5
6
7
Escobar, A.; Moya, S.; Fouquet, E.; Ruiz, J.; Astruc, D., Chem.
Commun. 2017, 53, 5384ꢀ5387.
8
9
TOC Graphic
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
After Deposition
On Silica
Before Deposition
[Cu20(CCPh)12(OAc)6
ACS Paragon Plus Environment