Highly Robust but Surface-Active: An N-Heterocyclic Carbene-Stabilized Au25 Nanocluster

Article abstract of DOI:10.1002/anie.201908983

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without

Full text of DOI:10.1002/anie.201908983

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Accepted Article
Title: Highly Robust but Surface-Active: N-Heterocyclic Carbene-
Stabilized Au25 Nanocluster
Authors: Hui Shen, Guocheng Deng, Sami Kaappa, Tongde Tan, Ying-
Zi Han, Sami Malola, Shui-Chao Lin, Boon K. Teo, Hannu
Häkkinen, and Nanfeng Zheng
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201908983
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10.1002/anie.201908983
Angewandte Chemie International Edition
RESEARCH ARTICLE
Highly Robust but Surface-Active: N-Heterocyclic Carbene-
Stabilized Au25 Nanocluster
Hui Shen,+ Guocheng Deng,+ Sami Kaappa, Tongde Tan, Yingzi Han, Sami Malola, Shuichao Lin,
Boon K. Teo, Hannu Häkkinen* and Nanfeng Zheng*
[6]
Abstract: Surface organic ligands play a critical role in stabilizing
atomically precise metal nanoclusters in solutions. However, it is still
challenging to prepare highly robust ligated metal nanoclusters that
are surface-active for liquid-phase catalysis without any pre-
phosphines,[5] thiols,
and alkynyls, [7], quite limited success
has been achieved to demonstrate the direct use of the ligated
atomically precise Au NCs as a truly homogeneous catalyst in
liquid-phase reactions without being loaded on supports. [8]
Recently, N-heterocyclic carbenes (NHCs) have been shown
excellent attributes in stabilizing surfaces, nanoparticles or
clusters of coinage metals.[9] Several groups have demonstrated
that NHCs readily form robust self-assembled monolayer on
coinage metal surface and function as a performance-enhancing
modifier.[10] NHCs stabilized Au nanoparticles with excellent
water-solubility, thermal stability, and chemical resistance to thiol
exchange have also been reported.[11] Several coinage metal
treatment. Herein, we report
a novel N-heterocyclic carbene-
stabilized Au25 nanocluster with high thermal and air stabilities as a
homogenous catalyst for cycloisomerization of alkynyl amines to
indoles. The nanocluster, characterized as [Au25(iPr2-bimy)10Br7]2+
(iPr2-bimy=
1,3-diisopropylbenzimidazolin-2-ylidene) (1), was
synthesized by direct reduction of AuSMe2Cl and iPr2-bimyAuBr with
NaBH4 in one pot. X-ray crystallization analysis revealed that the
cluster comprises two centered Au13 icosahedra sharing a vertex.
Cluster 1 is highly stable and can survive in solution at 80 oC for 12 h, clusters stabilized by NHCs have been prepared as well.[12]
which is superior to Au25 nanoclusters passivated with phosphines or
thiols. DFT computations reveal the origins of both electronic and
thermal stability of 1 and point to the probable catalytic sites. This
work provides new insights into the bonding capability of N-
heterocyclic carbene to Au in a cluster, and offers an opportunity to
probe the catalytic mechanism at the atomic level.
Theoretical work also suggested that NHCs may function as new
ligands for Au surface modification and NCs protection.[13] Very
recently, Crudden et al. reported a pioneer work on imparting
NHCs on Au clusters via ligand-substituent strategy, yielding the
first single-crystal structure of Au nanoclusters with N-
heterocyclic carbene (NHC) as surface ligands.[14] The reported
[Au11(PPh3)7(iPr-bimy)Cl2]+ cluster contains both phosphine and
NHC ligands on its surface.
Introduction
Herein, we report the direct synthesis, structure, optical
property, stability investigation, and catalytic performance of an
NHC-stabilized Au25 nanocluster, [Au25(iPr2-bimy)10Br7]2+(1),
where iPr-bimy is 1,3-diisopropylbenzimidazolin-2-ylidene.
Unlike the reported [Au11(PPh3)7(iPr-bimy)Cl2]+ cluster, NHCs are
the only organic ligands on its cluster. Cluster 1 shows ultra-high
thermal and air stability in solution, far better than that of
thiolated Au25 clusters. More impressively, the cluster also
Gold catalysis has attracted increasing research interest over in
the past three decades because of the unexpected activity of Au
and especially its high selectivity in organic reactions.[1] The
catalytic properties of Au nanoparticles (NPs) depend on many
parameters, including size, shape, and surface structure. [2] Due
to their truly monodispersity having well-defined composition and
structure, atomically precise Au nanoclusters (NCs) are
exhibits
high
catalytic
activities
as
modeled
by
expected to provide an ideal model system for investigating the
cycloisomerization of alkynyl amine to indoles. DFT analysis
gives a clear view of the electronic structure and optical
absorption characteristics of 1, and points to the probable
catalytic sites.
[3]
complicated surface chemistry of Au NPs.
For this purpose,
the structurally well-defined NCs should be soluble and stable
enough in reaction media while having open surface metal sites
accessible by reactants.[4] Although a large number of ligated
atomically precise Au NCs have been successfully attained in
recent decades by employing organic ligands including
Results and Discussion
Synthesis and atomic structure. In a typical synthesis of
cluster 1, 0.05 mmol (14.8 mg) AuSMe2Cl was first dissolved in
ethanol, and after ultrasonication, equimolar Pr2-bimyAuBr was
[a]
H. Shen, G. C. Deng, T. D. Tan, Y. Z. Han, Dr. S. C. Lin, Prof. Z. C.
Tang, Prof. B. K. Teo, Prof. N. F. Zheng
i
State Key Laboratory for Physical Chemistry of Solid Surfaces,
Collaborative Innovation Center of Chemistry for Energy Materials,
and National & Local Joint Engineering Research Center for
Preparation Technology of Nanomaterials, College of Chemistry and
Chemical Engineering, Xiamen University
added. After stirring for 15 min, freshly-prepared NaBH4 in
ethanol was added dropwise. The suspension gradually
dissolved and the solution turns from pale brown to finally dark
o
brown in 2 min. The reaction continued for 20 h at 20 C in the
Xiamen 361005, China
E-mail: nfzheng@xmu.edu.cn
Dr. S. Kaappa, Dr. S. Malola, Prof. H. Häkkinen
Departments of Physics and Chemistry, Nanoscience Center,
University of Jyväskylä
FI-40014 Jyväskylä, Finland
E-mail: hannu.j.hakkinen@jyu.fi
These authors contributed equally to this work.
dark. After that, excess NaNO3 was added to the reaction
mixture. After stirring for 30 min, it was centrifuged to afford a
black precipitate. 6 mL of mixed solvent of tetrahydrofuran and
dichloromethane (1:1) was used to dissolve the precipitate and
the mixture was centrifuged at 14000 rpm for 4 min. The UV-Vis
and electrospray ionization mass (ESI-MS) spectra of the as-
obtained supernatant are given in Figure S1, suggesting that the
clusters were of high purity in terms of cluster in the crude
mixture which should also contained free ligands. Moreover,
[b]
[+]
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201908983
Angewandte Chemie International Edition
RESEARCH ARTICLE
typical transmission electron microscopy (TEM) images on the
insoluble precipitate is provided in Figure S2. Finally, the
supernatant was subjected to the diffusion of toluene. Rod-like
brown crystals were obtained after 3 weeks (yield: 16.6% based
on Au, Figure S3).
binding modes with tertiary phosphines. The similar observation
has also been revealed in organometallic complexes. Cluster 1
is also closely related to the series of vertex-sharing
biicosahedral bimetallic (Au-Ag) and trimetallic (Au-Ag-M where
M = Ni, Pd, Pt) clusters stabilized by phosphine and halide
ligands reported by Teo and coworkers as early as the 1980s.
X-ray crystallographic analysis revealed that 1 crystallized
in the P-1 space group (Table S1 and Figure S4). Each unit cell
[18]
contains two independent clusters (Figure S5). Cluster
1
i
consists of 25 Au atoms, 10 Pr2-bimy ligands, and 7 Br atoms,
formulated as [Au25(iPr2-bimy)10Br7]2+. The unit cell contains
-
counter anions like NO3 and Cl-, based on which the +2 charge
of 1 was determined. The structure of 1 (Figure 1) can be
described as two centered Au13 icosahedra sharing a vertex,
giving rise to a prolate shape with an 1a:5b:1c:5d:1e:5d:1c:5b:1a
arrangement of Au atoms (the subscripts designate the positions
on the fivefold axis). The four Au5 pentagons are arranged in a
staggered-eclipse-staggered configuration. As such, the cluster
conforms to idealized D5h symmetry. The ten N-heterocyclic
carbene ligands coordinate to the two outer Au (5b) pentagons.
Of the seven bromides, five are doubly bridging the two inner Au
(5d) pentagons while the remaining two terminally coordinated to
the two outermost Au (1a) atoms. The rod-like metal core
measures about 1.1 nm along the fivefold axis (Figure S6). The
Au-Au bond lengths, averaged in accord with D5h symmetry, are:
Aua-Aub, 2.935 (13) Å, Aub-Auc, 2.723 (12) Å, Auc-Aud, 2.778 (12)
Å, Aub-Aud, 2.898 (13) Å, Aud-Aue, 2.857 (12) Å, Aua-Auc, 2.736
(11) Å, Auc-Aue, 2.811 (11) Å. It can be seen that intra-
icosahedral Au-Au bonds are significantly shorter than those on
the surface as well as those between the two icosahedra (Figure
S7).
Figure 2. a) ESI-MS spectrum of 1 crystals dissolved in CH2Cl2. Inset: the
experimental (black trace) and simulated (red trace) isotopic patterns of
[Au25(iPr2-bimy)10Br7]2+. b) UV-Vis spectrum of crystals of 1 dissolved in CH2Cl2.
The composition of 1 was confirmed by ESI-MS under
positive ion mode in CH2Cl2. As shown in Figure 2a, the ESI-MS
spectrum revealed only
a
single peak at 3756 m/z,
corresponding to [Au25(iPr2-bimy)10Br7]2+. Perfect agreement was
observed between the experimental spectrum and simulated
isotopic distribution pattern. Proton nuclear magnetic resonance
spectroscopy (1H NMR) of 1 was shifted slightly to lower field as
i
compared to that of Pr2-bimyHBr (Figure S8). The absence of
other peaks demonstrates the high purity of the sample.
Electronic structure and optical properties. DFT calculations
were employed to investigate the ground-state electronic
structure of 1 (see Supporting Information for technical details).
The calculated HOMO-LUMO energy gap (Figure S9) is
significant, 1.52 eV, which implies a good electronic stability of
the cluster. However, the chemical composition of 1 implies 16
metallic free electrons, [19] which is not an expected shell-closing
electron number of metal clusters. This prompted us to look
further to the reasons of the electronic stability. According to
Figure S9a, six highest occupied orbitals of the system have
clear P-type symmetries when the symmetry analysis is done in
one of the icosahedral half-cores of the cluster. Visualization of
the orbitals (Figure 3) reveals that these six orbitals (with overall
 and  symmetries) are arranged in two groups having a clear
bonding and antibonding characters with respect to the plane
bisecting the core. This implies a strong interaction of the
superatom P-type orbitals between the icosahedral half-cores,
indicating that the free-electron count of 16 of the whole cluster
can be understood as a strongly interacting dimer of two 8-
electron systems.
Figure 1. Crystal structure of [Au25(iPr2-bimy)10Br7]2+. (a) Overall structure and
(b) Au25 metal core showing the binding modes between Au atoms and the
ligands (one of each is highlighted). Color legend: orange, Au; cyan, Br; blue,
N; gray, C. H atoms are omitted for clarity.
The average Au-Br bond distance of the doubly-bridging
bromides is 2.563 (3) Å which somewhat longer than that of
2.442 (3) Å of the terminal bromides. The ten NHC ligands
coordinate to the ten Aub atoms forming Au-C bonds. The
average Au-C distance is 2.069 (2) Å, suggesting strong
bonding interaction. For comparison, this value is slightly larger
i
[15]
than that in Pr2-bimyAuBr (1.978 (8) Å),
but somewhat less
than that in [Au11(PPh3)7(iPr-bimy)Cl2]Cl (2.09 (2) Å).[14]
Interestingly, structure of 1 quite resembles that of Au25, [16]or
[17]
Pt2Ag23 protected by tertiary phosphines,
indicating that in
shaping structure of nanoclusters, NHCs can adopt similar
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10.1002/anie.201908983
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RESEARCH ARTICLE
shown in Figure 4a and S12, the UV-vis profile of 1 was
practically unchanged upon heating in 1,2-dichloroethane at 80
C for 12 h, indicating ultrahigh thermal stability. The intensity of
the peak at 650 nm was plotted as a function of heating time in
Figure 4d (black curve). The relative intensity showed almost no
degradation in the thermal measurement, suggesting that there
is no decomposition. Note that 1 is also highly stable in other
solvents such as tetrahydrofuran (Figure S13). For comparison,
the stability of thiol and phosphine stabilized Au25 NCs were also
investigated under the same conditions. As shown in Figure 4b,
UV-vis spectra of 2, Au25(PPh3)10(SC2H4Ph)5Cl2, deteriorates
progressively in the 12 h heating period, and the relative
absorbance intensity of the peak at 650 nm decreases
significantly (Figure 4d, red curve). Furthermore, thiol-protected
Au25(SC2H4Ph)18 (3) also exhibits much worse stability than that
[6b]
of 1 (Figure 4c and pink curve in Figure 4d).
calculations on
Earlier DFT
a
mixed-ligand [Au11(PPh3)7(NHCi-Pr)Cl2]Cl
cluster have shown, that the Au-carbene bond can be stronger
than Au-phosphine bond by up to 0.9 eV. This explains also the
observed superior thermal stability of 1 over 2 in this work.[14]
Figure 3. Visualization of the  and  symmetries of the six highest occupied
molecular orbitals HOMO-5 to HOMO (with 12 electrons), marked in Figure
S6a. HOMO-5 to HOMO-3 (bottom) have clear bonding characters with
respect to the horizontal plane bisecting the Au25 metal core, while HOMO-2 to
HOMO (top) have antibonding characters. The center graph shows the
schematic energy splitting of the bonding/anti-bonding orbitals formed as
combination of P-type orbitals in each icosahedral half-core.
1 exhibits a distinct optical absorption spectrum in the UV-
Vis region (Figure 2b) with seven features: five shoulders at 333,
362, 406, 508 and 727 nm as well as two peaks at 469 and 650
nm. The absorption spectrum of 1 is very similar to that of
phosphine and thiolate co-protected Au25(PPh3)10(SC2H4Ph)5Cl2
(2) (Figure 4b), suggesting that discrete electronic states of Au25
with similar metal framework are most likely dictated by the
vertex-sharing biicoshedral metal architecture.
Figure 4. Comparison stabilities of Au25 nanoclusters stabilized by different
organic ligands: a-c) UV-vis spectra of 1, 2 and 3 clusters dissolved in 1,2-
dichloroethane upon heating at 80C. d) Relative absorbance intensity of
peaks marked with arrow (for 1, 650 nm; for 2, 675 nm; for 3, 520 nm).
Time-dependent DFT was employed to compute and
analyze the optical absorption spectrum (see Supporting
Information for technical details). Figure S10 shows the
comparison of the calculated and measured spectra. We were
able to identify the same five features in the computed spectrum
as in the measured data, although the two lowest-energy peaks
are somewhat red-shifted in the calculations. Analysis of these
five features in terms of transition contribution maps (TCMs)
(Figure S11) decomposing the state symmetries in the D5h point
group (Figure S9b) shows that the two lowest-energy peaks are
mostly single-state transitions between symmetries A2’’ to A1’
(650 nm in the exp. data) and E1’’ to E1’ (469 nm) while the
higher-energy transitions have multi-state features with
contributions from ligands as well.
Surface reactivity and catalytic performance. While 1 was
highly stable in solution, the presence of halides on the cluster
motivated us to explore its surface reactivity. To our surprise,
when mixing phenylacetylene (PA) and 1 together, both Fourier
transform infrared spectroscopy (FTIR) and 13C NMR showed
that the chemical environment of PA changed significantly
(Figure S14 and S15), indicating that PA can easily bind to the
surface of 1. We thus proposed that 1 would be a nice candidate
catalyst for reactions involving the activation of alkynes. Here we
chose the cycloisomerization of alkynyl amines to form indoles
Stability of 1 in solution. The stability of 1 was investigated by
tracking its UV-vis spectrum under thermal treatments. As
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10.1002/anie.201908983
Angewandte Chemie International Edition
RESEARCH ARTICLE
as a model reaction. Indoles are important heterocycles which
are broadly used in material science and biology. [20]
Conclusion
In conclusion, a novel Au25 nanocluster protected by pure N-
heterocyclic carbene ligands was synthesized for the first time
via a one-pot reaction protocol. X-ray crystallographic analysis
revealed that the cluster consists of two icosahedra sharing a
vertex. DFT analysis revealed that the electronic sub-systems of
the two icosahedra can be understood as 8-electron
configurations that are strongly interacting giving a stable 16-
electron system with a large HOMO-LUMO energy gap. The
cluster displays ultra high thermal and air stabilities in solution,
superior to all other reported Au25 nanoclusters. In addition, 1
exhibits high catalytic activity and stability in the
The catalytic reaction was conducted by adding 1.5 %
mmol (based on Au) of 1 to a solution of alkynyl amine in
organic solvents. As envisioned, 1.5 % mmol catalyst (calculated
based on Au atom) succeeded in accelerating the
cycloisomerization
reaction
of
N-(2-ethylnylphenyl)-4-
methylbenzenesulfonamide to 1-tosyl-1H-indole at 25 oC in 10 h
(Table S2, entry 1). The catalytic conditions were optimized by
exploring the effects of solvent, time and temperature. The
optimal conditions were identified at 50 oC in 1,2-dichloroethane,
providing the desired product with over 99% yield. Of note, the
reaction generally worked well in aprotic solvents (Table S2,
entry 2-5). As illustrated in Table 1, the cluster displayed an
extremely high activity in cycloisomerization of alkynyl amines at
50 oC as its conversion close to 100% after 10 h. Moreover, the
catalyst is stable during the catalytic process, as practically no
apparent changes in the UV-vis and ESI-MS spectra were
observed before and after the catalytic reaction (Figure S16 and
S17). Given the optimal reaction conditions (Table S2, entry 6),
the catalytic performance of the other two types of Au25 (2 and 3)
were also compared. As shown in Table 1, 1 showed a much
higher yield of over 99% than that by 2, 3 (entry 1, 2 and 3).
Furthermore, the catalytic performance of Au(I) carbene
precursors, iPr-bimyAuBr and iPr-bimyAuNTf2, was also
evaluated under the same condition. While iPr-bimyAuBr shows
o
cycloisomerization of alkynyl amines to indoles at 50 C. This
work paves ways to use heterocyclic carbene stabilized metal
nanoclusters in homogenous catalysis. Finally, it is hoped that,
[18]
in analogy to its phosphine stabilized kins,
the biicosahedral
framework can be extended to polyicosahedral architecture
which, given their superior thermal and air stabilities, may find
other applications in nanotechnology that are difficult to fill with
other metal cluster systems.
Acknowledgements
We thank the National Key R&D Program of China
(2017YFA0207304) and the NSF of China (21890752,
21731005, 21420102001, 21721001) for financial support. The
computational work in the University of Jyväskylä was supported
by the Academy of Finland through HH’s Academy
Professorship. HH acknowledges support from China’s National
Innovation and Intelligence Introduction Base visitor program.
SK thanks the Väisälä Foundation for a personal PhD study
grant. The computations were made at the CSC supercomputing
center in Finland.
i
no activity for the reaction (entry 4), Pr-bimyAuNTf2 exhibits
slightly lower activity than 1 (entry 5). Based on these catalysis
results, we attribute the observed excellent catalysis of 1 to its
good stability and also sterically open halide sites, which are, on
the basis of DFT local charge analysis, gaining significant
negative charge as donated by the carbene ligands through Au
(Table S3). To further facilitate separation and reuse of the
catalyst, commercial activated carbon (XC-72) was used as a
solid support material. The model reaction was conducted 5
times with XC-72 supported 1 and nearly quantitative yields
were obtained in all runs (Figure S18). The NMR spectra of
various compounds used in the catalysis are given as Figure
S19-S22.
Keywords: Carbene ligands • gold nanocluster • homogeneous
catalysis • gold catalysis • Au25
[1] a) A. Corma, A. Leyva-Perez, M. J. Sabater, Chem. Rev. 2011, 111,
1657-1712; b) A. Corma, H. Garcia, Chem. Soc. Rev. 2008, 37, 2096-
2126; c) M. Rudolph, A. S. K. Hashmi, Chem. Soc. Rev. 2012, 41, 2448-
2462; d) S. P. Nolan, Acc. Chem. Res. 2011, 44, 91-100; e) A. S. K.
Hashmi, G. J. Hutchings, Angew. Chem. Int. Ed. 2006, 45, 7896-7936; f)
R. Dorel, A. M. Echavarren, Chem. Rev. 2015, 115, 9028-9072.
[2] a) G. J. Hutchings, J. Cat. 1985, 96, 292-295; b) T. Hayashi, K. Tanaka,
M. Haruta, J. Cat. 1998, 178, 566-575; c) M. Haruta, N. Yamada, T.
Kobayashi, S. Iijima, J. Cat. 1989, 115, 301-309; d) S. Carrettin, M. C.
Blanco, A. Corma, A. S. K. Hashmi, Adv. Synth. Cat. 2006, 348, 1283-
1288; e) J. O. Meseguer, J. R. C. Antonino, I. Domínguez, A. L. Pérez, A.
Corma, Science 2012, 338, 1452-1455.
Table 1. A comparison of catalytic activities of different catalysts.†
Entry
Catalyst
Time (h)
10
Yield§ (%)
＞99
1
2
3
4
5
1
2
10
trace
trace
trace
84
3
10
iPr2-bimyAuBr
iPr2-bimyAuNTf2
10
[3] a) P. X. Liu, R. X. Qin, G. Fu, N. F. Zheng, J. Am. Chem. Soc. 2017, 139,
2122-2131; b) G. Li, R. C. Jin, Acc. Chem. Res. 2013, 46, 1749-1758; c)
S. Yamazoe, K. Koyasu, T. Tsukuda, Acc. Chem. Res. 2014, 47, 816-
824.
10
[†] Reaction conditions: 50oC, 1,2-dichloroethane as solvent, 1.5% mmol
catalyst. [§] Determined by 1H NMR.
[4] a) F. Y. Fu, J. Xiang, H. Cheng, L. J. Cheng, H. B. Chong, S. X. Wang, P.
Li, S. Q. Wei, M. Z. Zhu, Y. D. Li, ACS Cat. 2017, 7, 1860-1867; b) C. L.
This article is protected by copyright. All rights reserved.

10.1002/anie.201908983
Angewandte Chemie International Edition
RESEARCH ARTICLE
Lv, H. Cheng, W. He, M. I. A. Shah, C. Q. Xu, X. J. Meng, L. Jiao, S. Q.
Wei, J. Li, L. Liu, Y. D. Li, Nano Res. 2016, 9, 2544-2550; c) Y. Wang, X.
K. Wan, L. T. Ren, H. F. Su, G. Li, S. Malola, S. C. Lin, Z. C. Tang, H.
Häkkinen, B. K. Teo, Q. M. Wang, N. F. Zheng, J. Am. Chem. Soc. 2016,
138, 3278-3281; d) J. Z. Yan, J. Zhang, X. M. Chen, S. Malola, B. Zhou,
E. Selenius, X. M. Zhang, P. Yuan, G. C. Deng, K. L. Liu, H. F. Su, B. K.
Teo, H. Häkkinen, L. S. Zheng, N. F. Zheng, Natl. Sci. Rev. 2018, 5, 694-
702.
[17] M. Bootharaju, S. Kozlov, Z. Cao, M. Harb, N. Maity, A. Shkurenko, M.
Parida, M. Hedhili, M. Eddaoudi, O. Mohammed, O. Bakr, L. Cavallo, J.
Basset, J. Am. Chem. Soc. 2017, 139, 1053-1056.
[18] a) B. K. Teo, H. Zhang, Proc. Nat. Acad. Sci. 1991, 88, 5067-5071; b) B.
K. Teo, H. Zhang, Coord. Chem. Rev. 1995, 143, 611-636.
[19] M. Walter, J. Akola, O. L. Acevedo, P. D. Jadzinsky, G. Calero, C. J.
Ackerson, R. L. Whetten, H. Gronbeck, H. Häkkinen, Proc. Natl. Acad.
Sci. 2008, 105, 9157–9162.
[5] a) P. Bellon, M. Manassero, M. Sansoni, J. Chem. Soc., Dalton Trans.
1972, 1481-1487; b) G. Schmid, R. Pfeil, R. Boese, F. Bandermann, S.
Meyer, G. C. Velden, Chem. Ber. 1981, 114, 3634- 3642; c) D. M.
Mingos, Dalton. Trans. 2015, 44, 6680-6695.
[20] T. V. Sravanthi, S. L. Manju, Eur. J. Pharm. Sci. 2016, 91, 1-10.
[6] a) P. Jadzinsky, G. Calero, C. Ackerson, D. Bushnell, R. Kornberg,
Science 2007, 318, 430-433; b) M. Z. Zhu, C. Aikens, F. Hollander, G.
Schatz, R. C. Jin, J. Am. Chem. Soc. 2008, 130, 5883–5885; c) N. Yan,
N. Xia, L. Liao, M. Zhu, F. Jin, R. Jin, Z. Wu, Sci. Adv. 2018, 4, eaat7259.
[7] a) P. Maity, H. Tsunoyama, M. Yamauchi, S. Xie, T. Tsukuda, J. Am.
Chem. Soc. 2011, 133, 20123-20125; b) X. K. Wan, Q. Tang, S. F. Yuan,
D. E. Jiang, Q. M. Wang, J. Am. Chem. Soc. 2015, 137, 652-655; c) Z.
Lei, J. J. Li, X. K. Wan, W. H. Zhang, Q. M. Wang, Angew. Chem. Int. Ed.
2018, 57, 8639-8643.
[8] Y. Zhu, H. Qian, B. A. Drake, R. C. Jin, Angew. Chem. Int. Ed. 2010, 49,
1295-1298.
[9] a) A. V. Zhukhovitskiy, M. J. MacLeod, J. A. Johnson, Chem. Rev. 2015,
115, 11503-11532; b) S. Engel, E. C. Fritz, B. J. Ravoo, Chem. Soc. Rev.
2017, 46, 2057-2075; c) Christene A. Smith, Mina R. Narouz, Paul A.
Lummis, Ishwar Singh, Ali Nazemi, Chien-Hung Li, C. M. Crudden,
Chem. Rev. 2019, 119, 4986-5056.
[10] a) A. V. Zhukhovitskiy, M. G. Mavros, T. Van Voorhis, J. A. Johnson, J.
Am. Chem. Soc. 2013, 135, 7418-7421; b) M. J. MacLeod, A. J.
Goodman, H. Z. Ye, H. V. Nguyen, T. Van Voorhis, J. A. Johnson, Nat.
Chem. 2019, 11, 57-63; c) G. Wang, A. Ruhling, S. Amirjalayer, M. Knor,
J. B. Ernst, C. Richter, H. J. Gao, A. Timmer, H. Y. Gao, N. L. Doltsinis,
F. Glorius, H. Fuchs, Nat. Chem. 2017, 9, 152-156; d) C. M. Crudden, J.
H. Horton, Ebralidze, II, O. V. Zenkina, A. B. McLean, B. Drevniok, Z.
She, H. B. Kraatz, N. J. Mosey, T. Seki, E. C. Keske, J. D. Leake, A.
Rousina-Webb, G. Wu, Nat. Chem. 2014, 6, 409-414.
[11] a) R. W. Y. Man, C. H. Li, M. W. A. MacLean, O. V. Zenkina, M. T.
Zamora, L. N. Saunders, A. Rousina-Webb, M. Nambo, C. M. Crudden, J.
Am. Chem. Soc. 2018, 140, 1576-1579; b) K. Salorinne, R. W. Y. Man, C.
H. Li, M. Taki, M. Nambo, C. M. Crudden, Angew. Chem. Int. Ed. 2017,
56, 6198-6202.
[12] a) A. M. Polgar, F. Weigend, A. Zhang, M. J. Stillman, J. F. Corrigan, J.
Am. Chem. Soc. 2017, 139, 14045-14048; b) N. B. Khalili, J. F. Corrigan,
Chem. Commun. 2015, 51, 665-667; c) T. J. Robilotto, J. Bacsa, T. G.
Gray, J. P. Sadighi, Angew. Chem. Int. Ed. 2012, 51, 12077-12080.
[13] Q. Tang, D. E. Jiang, Chem. Mater. 2017, 29, 6908-6915.
[14] M. R. Narouz, K. M. Osten, P. J. Unsworth, R. W. Y. Man, K. Salorinne,
S. Takano, R. Tomihara, S. Kaappa, S. Malola, C. T. Dinh, J. D. Padmos,
K. Ayoo, P. J. Garrett, M. Nambo, J. H. Horton, E. H. Sargent, H.
Häkkinen, T. Tsukuda, C. M. Crudden, Nat. Chem. 2019, 11, 419-425.
[15] H. V. Huynh, S. i. Guo, W. Q. Wu, Organometallics 2013, 32, 4591-4600.
[16] Y. Shichibu, Y. Negishi, T. Watanabe, N. Chaki, H. Kawaguchi, T. T., J.
Phys. Chem. C 2007, 111, 7845-7847.
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10.1002/anie.201908983
Angewandte Chemie International Edition
RESEARCH ARTICLE
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RESEARCH ARTICLE
An atomically precise N-heterocyclic
carbene-stabilized Au25 nanocluster is
successfully synthesized in one-pot,
which exhibits much higher thermal
stability in the solution form as
Hui Shen, Guocheng Deng, Sami
Kaappa, Tongde Tan, Yinzi Han, Sami
Malola, Shuichao Lin, Boon K. Teo,
Hannu Häkkinen* and Nanfeng Zheng]
Page No. – Page No.
compared to Au25 protected by thiol or
phosphine ligands. The cluster
displays excellent catalytic activity in
cycloisomerization of alkynyl amine as
a homogeneous catalyst.
Highly Robust but Surface-Active: N-
Heterocyclic Carbene-Stabilized Au25
Nanocluster
This article is protected by copyright. All rights reserved.