Direct Formation of C?C Triple-Bonded Structural Motifs by On-Surface Dehalogenative Homocouplings of Tribromomethyl-Substituted Arenes

Article abstract of DOI:10.1002/anie.201801056

On-surface synthesis shows significant potential in constructing novel nanostructures/nanomaterials, which has been intensely studied in recent years. The formation of acetylenic scaffolds provides an important route to the fabrication of emerging carbon nanostructures, including carbyne, graphyne, and graphdiyne, which feature chemically vulnerable sp-hybridized carbon atoms. Herein, we designed and synthesized a tribromomethyl-substituted compound. By using a combination of high-resolution scanning tunneling microscopy, non-contact atomic force microscopy, and density functional theory calculations, we demonstrated that it is feasible to convert these compounds directly into C?C triple-bonded structural motifs by on-surface dehalogenative homocoupling reactions. Concurrently, sp³-hybridized carbon atoms are converted into sp-hybridized ones, that is, an alkyl group is transformed into an alkynyl moiety. Moreover, we achieved the formation of dimer structures, one-dimensional molecular wires, and two-dimensional molecular networks on Au(111) surfaces, which should inspire further studies towards two-dimensional graphyne structures.

Full text of DOI:10.1002/anie.201801056

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Accepted Article
Title: Direct formation of C-C triple bonded structural motifs by
on-surface dehalogenative homocoupling of tribromomethyl
molecules
Authors: Qiang Sun, Xin Yu, Meiling Bao, Mengxi Liu, Jinliang Pan,
Zeqi Zha, Liangliang Cai, Honghong Ma, Chunxue Yuan,
Xiaohui Qiu, and Wei Xu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201801056
Angew. Chem. 10.1002/ange.201801056
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10.1002/anie.201801056
Angewandte Chemie International Edition
COMMUNICATION
Direct formation of C-C triple bonded structural motifs by on-surface
dehalogenative homocoupling of tribromomethyl molecules
Qiang Suna,, Xin Yu a,, Meiling Baoa, Mengxi Liub, Jinliang Panb,c, Zeqi Zhab,c, Liangliang Cai a,
Honghong Maa, Chunxue Yuana, Xiaohui Qiub,c* and Wei Xua,*
Abstract: On-surface synthesis shows significant potential in constructing
novel nanostructures/nanomaterials, which has been intensely studied over
the recent years. The formation of acetylenic scaffoldings provides an
important route to the fabrication of emerging carbon nanostructures
including carbyne, graphyne and graphdiyne, which involve the chemically
vulnerable sp-hybridized carbons. Herein, we designed and synthesized a
tribromomethyl group, by using the combination of high-resolution
scanning tunneling microscopy and non-contact atomic force microscopy
imaging and density functional theory calculations, we demonstrated that it
is feasibleto achievethe direct formation of C-C triple bonded structural
motifs via on-surface dehalogenative homocoupling reactions.
Correspondingly, we are able to convert the sp3 hybridized state to sp
hybridized state of carbon atoms, i.e., from an alkyl group to an alkynyl one.
Moreover, we successfully achieved the formation of dimer structures, one-
dimensionalmolecular wires and two-dimensional molecular networks
onAu(111) surface,which would inspire further studies towards the two-
dimensional graphyne structures.
and advanced recently.15-19 The demand for the formation of
acetylenic scaffoldings comes from the fabrication of emerging
carbon nanostructures/nanomaterials such as one-dimensional
linear
carbons
(i.e.,
carbyne)
and
two-dimensional
graphyne/graphdiyne structures, which involve sp-hybridized
carbons. However, scientific and technological advances made on
these interesting carbon nanomaterials are significantly impeded
due to the high chemical activity of sp-hybridized carbons. On-
surface C-X bond activations and following C-C couplings provide
a relatively efficient route to incorporating acetylenic linkages.
dehalogenative
homocoupling
TBP
1,2-diphenylethyne
dehalogenative
homocoupling
n
PAEs
On-surface synthesis has been a research area of intense
interest in recent years, and various chemical reactions have been
studied and achieved on different surfaces. Generally speaking,
most of the on-surface chemical reactions follow different reaction
pathways from their counterparts in solutions, due to the catalytic
effect of the surfaces.1-4 As a result, lots of unexpected reactions
have been surprisingly achieved on different surfaces.5-9 Thus, on-
surface synthesis demonstrates remarkable potential to fabricate
novel nanostructures/nanomaterials which still remain challenging
by traditional synthetic methods. For instance, carbon materials
including fullerenes, graphene, graphene nanoribbons, single-
chirality carbon nanotubes and metalated carbyne as well as
different hydrocarbons have been successfully fabricated by such
an on-surface synthesis strategy.10-14
bTBP
dehalogenative
homocoupling
tTBP
Figure 1.Schematic illustration of dehalogenative homocouplings of TBP, bTBP, and
tTBP molecules.
Remarkably, the formations of acetylenic scaffoldings (i.e.,
sp-hybridized carbon structures) have been attempted on surfaces
Through dehydrogenative or dehalogenativehomocouplings of
terminal alkynes and alkynyl bromides, various structures
involving diyne motifs are formed on surfaces.15-19 While, further
functionalizing the molecular precursors with more alkynyl groups
to form carbon allotropes (e.g., graphdiyne) is hampered due to the
increasing instability of the precursors (e.g.,hexaethynyl benzene).
Thus, it is of utmost importance to explore new strategies with the
aim of forming acetylenic linkages on surfaces.
So far, most of the halide precursors employed for
dehalogenative homocouplings have only one halogen attached to a
carbon atom. Very recently, we have introduced a new on-surface
reaction by dehalogenative homocouplings of alkenyl gem-
dibromides (i.e., generating two unpaired electrons), in which
cumulene motifs with newly formed C-C double bonds are
consequently constructed.20 In light of this previous work, we now
try to investigate on-surface dehalogenative homocouplings of
tribromomethyl groups (i.e., generating three unpaired electrons) to
[a]
[b]
[c]
Dr. Qiang Sun, Xin Yu, Meiling Bao,Liangliang Cai, Honghong Ma,
Dr. Chunxue Yuan, Prof. Dr. Wei Xu
Interdisciplinary Materials Research Center and College of Materials
Science and Engineering, Tongji University
Shanghai 201804, P. R. China
E-mail: xuwei@tongji.edu.cn
Dr. Mengxi Liu, Jinliang Pan, ZeqiZha, Prof. Dr. Xiaohui Qiu
CAS Key Laboratory of Standardization and Measurement for
Nanotechnology, CAS Center for Excellence in Nanoscience,
National Center for Nanoscience and Technology, Beijing 100190,
China
E-mail:xhqiu@nanoctr.cn
Jinliang Pan, Zeqi Zha,Prof. Dr. Xiaohui Qiu
University of Chinese Academy of Sciences, Beijing, 100049, China.
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201801056
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COMMUNICATION
explore the possibility of direct formation of C-C triple bonds from
sp3 hybridized carbons. As shown in Figure 1, we have designed
and synthesized a molecule functionalized with the tribromomethyl
group (named TBP, synthesis details are shown in SI). From the
interplay of high-resolution scanning tunneling microscopy (STM)
imaging, non-contact atomic force microscopy imaging (nc-AFM)
and density functional theory (DFT) calculations, we have
investigated dehalogenative homocouplings of TBP molecules on
the Au(111) surface. Interestingly, it is found that the formation of
1,2-diphenylethyne products (i.e., involving C-C triple bonds)
occurs at room temperature (RT) on the surface, which is verified
by the high-resolution STM and nc-AFM imaging. A step further,
we have functionalized the other molecular precursors with two
and three functional groups (named bTBP and tTBP, synthesis
details are shown in SI) with the aim of extending the strategy to
form one-dimensional molecular chains and two-dimensional
networks. By activating the dehalogenative homocoupling
reactions, we have successfully fabricated a linear graphyne wire,
which belongs to poly(aryleneethynylene)s (PAEs),21and also 2D
network structures on the Au(111) surface (cf. Figure 1). This
study exhibits the versatility of on-surface dehalogenative C−C
homocoupling reactions, and more importantly, it provides an
alternative strategy for the involvement of C-C triple bonds into
surface nanostructures.
(a)
(b)
5 Å
1 nm
(d)
(c)
(e)
(f)
After the deposition of TBP molecules on Au(111) at room
temperature (RT), we observed ordered molecular arrays as shown
in the STM image (Figure 2a). A closer examination of the image
revealed that the island was composed of dumbbell-shaped
molecular motifs and encircled bright spots.The dumbbell-shaped
motifs orientated along the [11-2] direction of the Au(111) surface.
According to the previous studies,22-24 the round bright spots can be
attributed to dissociated bromine atoms and stabilized the
molecules by forming weak hydrogen bonds on the surface. Close-
up STM image (Figure 2b) revealed that the length of the
dumbbell-shaped molecular motif is approximately 1.1 nm, which
agreed well with the length of the expected product of 1,2-
diphenylethyne from the TBP molecular precursors. To further
identify the atomic scale structure, we perform nc-AFM
experiments as shown in Figure 2c. The dumbbell-shaped
molecular motif is composed of two phenyls linked by
alinearbackbone. An enhanced contrast in the middle of the linear
bond can be assigned to the C-C triple bond.5,25 Moreover, we
perform extensive DFT calculations to identify the atomic-scale
structures on the surface as shown in the Figure 2d, where we
calculated the adsorption of the 1,2-diphenylethyne product on
Au(111). From a detailed comparison of the STM18,19 and nc-AFM
experimental morphologies and dimensions with the molecular
model, we identify that the dumbbell-like molecular motif should
be assigned to the 1,2-diphenylethyne product formed by
dehalogenative homocoupling of two TBP molecules on the
surface.
5 Å
5 Å
5 Å
5 Å
(g)
(i)
(h)
Figure 2. (a) Large-scale STM image of the 1,2-diphenylethyne product self-
assembled on the Au(111) surface (with overlaid molecular structures) (V = 500 mV, I
= 70pA). The blue balls denotethe detached Br atoms. White arrows represent the
close-packed lattice directions of the Au(111) surface. (b) Close-up STM image of the
1,2-diphenylethyne product (V = 500 mV, I = 30 pA) and (c)the corresponding nc-
AFM image recorded by CO-functionalized tip (f0≈ 40.7kHz, oscillation amplitude A
≈ 100 pm, quality factor Q ≈ 5.6×104). The black contour in (b) denotes the dimer
structure. (d) Top and side views of the DFT optimized model of the 1,2-
diphenylethyne product structure onAu(111). (e) High-resolution STM image and (f)
the corresponding STM simulation ofthe 1,2-diphenylethyne structure. (g) nc-AFM
image and (h) the corresponding AFM simulation of the 1,2-diphenylethynestructure.
(i) A series of STM images showing the lateral STM manipulation processes.
To further verify the formation of the C-C triple bonded
structural motif, we have also calculated the corresponding STM
image and the constant-height nc-AFM image of the 1,2-
diphenylethyne on Au(111) as shown in Figure 2f and 2h,26
respectively, which correspond well with the experimental data (cf.
Figure 2e and 2g). Moreover, lateral STM manipulations have been
performed to validate the robustness of the formed products as
presented in Figure 2i. After a series of STM manipulations, the
formed 1,2-diphenylethyne molecule always moved as a whole and
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10.1002/anie.201801056
Angewandte Chemie International Edition
COMMUNICATION
remained intact. Therefore, we concluded that the direct formation
of C-C triple bonded 1,2-diphenylethyne molecules has been
achieved by dehalogenative homocoupling of TBP molecular
precursors on the surface.
Au(111)
Cu(111)
(b)
(a)
(a)
(b)
2 nm
3 nm
Figure 4. Large-scale STM images showing the formation of the molecular network
after deposition of tTBP molecules on (a) Au(111) and (b) Cu(111) held at RT
followed by annealing to ~500 K and ~430 K, respectively. White arrows represent
the close-packed directions of the substrate.
7 Å
2 nm
A step further, to explore the generality of the formation of
acetylenic scaffoldings (i.e., C-C triple bonded motifs) in two-
dimensional network structures by such an on-surface synthesis
strategy, we have further functionalized the TBP molecule with
two additional tribromomethyl groups, named tTBP molecule (as
shown in Figure 4a), with the aim of forming two-dimensional
molecular networks. Similarly, after deposition of tTBP molecules
on Au(111) at RT followed by annealing to ~ 500K, we have also
observed some patches of network structures as shown in Figure 4a.
However, due to a large amount of detached Br atoms on the
surface, the network is hampered to grow into a more ordered and
larger structure. We have also carried out the tTBP experiment on
Cu(111). As shown in Figure 4b, similarly, we have mainly
observed some patches of network structures on Cu(111).Thus, we
demonstrate that it is possible to form the C-C triple bonded
network structure on surfaces as well, though more challenging
conditions (getting rid of the Br atoms from the surfaces) have yet
to be regulated towards fabrication of more and more ordered 2D
network structures. Note that the formation of the aimed molecular
wires and networks are not as efficient as that of the dimer
structure on the surface. So, post-annealing of the sample is needed
to achieve the formed structures with a higher quality. This is also
in line with our previous work on the formation of diyne wires and
networks on Au(111).19
In conclusion, from high-resolution UHV-STM and nc-AFM
imaging combined with DFT calculations, we have demonstrated
the feasibility of the direct formation of C-C triple bonded
structural motifs by dehalogenative homocoupling of
tribromomethyl molecules on surfaces. Notably, in this case, we
have converted the sp3 hybridized state to sp hybridized state of
carbon atoms, i.e., from an alkyl group to an alkynyl one. This
finding thus demonstrates the possibility of converting
hybridization states of carbon atoms by a multi-dehalogenation
process at one carbon site followed by the subsequent C-C
coupling. Thus, this strategy may shed light on the fabrication of
novel carbon nanostructures with acetylenic scaffoldings from pre-
designed molecular precursors. Practically, we have formed
graphyne-like molecular wires by such an on-surface synthesis
strategy, and inspired from this, design and synthesis of molecular
precursors towards the formation of two-dimensional graphyne
structures are underway.
(c)
3.05 Å
Figure 3.(a) Large-scale and (b) close-up STM images showing the formation of the
molecular chains (i.e.graphyne wires) after deposition of bTBP molecules on Au(111)
held at RT followed by annealing to ~430 K. The equally scaled DFT-relaxed model is
overlaid on the STM topography. (c) Top and side views of the DFT optimized model
of the molecular wire on Au(111). White arrows represent the close-packed directions
of the substrate.
In view of the successful formation of the C-C triple bond
from the sp3 hybridized carbon, we have further functionalized the
TBP molecule with an additional tribromomethyl group, named
bTBP molecule (as shown in Figure 3a), with the aim of forming
one-dimensional molecular chains incorporating C-C triple bonds.
As shown in Figure 3a, after deposition of bTBP molecules on
Au(111) held at RT and further anneal the sample to 430K,
expectedly, individual chain structures (surrounded by Br atoms)
are formed. From the close-up image shown in Figure 3b, we could
clearly resolve the chain structure with alternating acetylenic
linkages and phenyl groups. We then optimized the structural
model of the C−C coupled molecular chain on Au(111) as shown
in Figure 3c. The equally scaled structural model is overlaid on the
STM image (Figure 3b), where a good agreement in both
dimension and morphology is also achieved. It is worthy to note
that through the dehalogenative C-C couplings of the predesigned
molecular precursor bTBP, we have successfully formed a
graphyne wire (i.e., a kind of poly(aryleneethynylene) molecular
chain), which is in analogy to the previously reported graphdiyne
wire on the surface.18
Acknowledgements
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Mueller, M. Jansen, K. Amsharov, P. Ruffieux, R. Fasel. Nature,
2014, 512, 61-64.
[13] Q. Sun, L. Cai, S. Wang, R. Widmer, H. Ju, J. Zhu, L. Li, Y. He, P.
Ruffieux, R. Fasel, W. Xu, J. Am. Chem. Soc. 2016, 138, 1106.
[14] N. Pavliček, A. Mistry, Z. Majzik, N. Moll, G. Meyer, D. J. Fox, L.
Gross, Nat. Nanotechnol.2017, 12, 308-311.
[15] Y. Q. Zhang, N. Kepčija, M. Kleinschrodt, K. Diller, S. Fischer, A.
C. Papageorgiou, F. Allegretti,J. Björk, S. Klyatskaya, F.
Klappenberger, M. Ruben, J. V. Barth. Nat. Commun.2012, 3,
1286.
[16] J. Liu, Q. Chen, L. Xiao, J. Shang, X. Zhou, Y. Zhang, Y. Wang,
X. Shao, J. Li, W. Chen, G. Q. Xu, H. Tang, D. Zhao, K. Wu, ACS
Nano, 2015, 9, 6305-6314.
[17] H. Y. Gao, H. Wagner, D. Zhong, J. H. Franke, A. Studer, H.
Fuchs, Angew. Chem. Int. Ed.2013, 52, 4024-4028.
[18] B. Cirera, Y. Q. Zhang, J. Björk, S. Klyatskaya, Z. Chen, M.
Ruben, J. V. Barth, F. Klappenberger. Nano Lett.2014, 14, 1891-
1897.
[19] Q. Sun, L. Cai, H. Ma, C. Yuan, W. Xu, ACS Nano,2016, 10, 7023.
[20] Q. Sun, B. Tran, L. Cai, H. Ma, X. Yu, C. Yuan, M. Stohr, W. Xu,
Angew. Chem. Int. Ed.2017, 56, 12165.
[21] U. H. Bunz, Chemical Reviews,2000, 100, 1605-1644.
[22] W. Wang, X. Shi, S. Wang, M. A. Van Hove, N. Lin, J. Am. Chem.
Soc. 2011, 133, 13264.
The authors acknowledge the financial support from the National
Natural Science Foundation of China (21473123, 21622307,
21790351, 51403157, 21603045, 21425310, 91427301).
Keywords:Dehalogenativehomocoupling • scanning tunneling
microscopy• non-contact atomic force microscopy • acetylenic
scaffolding • surface chemistry
[1] G. Franc, A. Gourdon, Phys. Chem. Chem. Phys. 2011, 13,14283.
[2] Q. Fan, J. M. Gottfried, J. Zhu, Acc. Chem. Res.2015, 48, 2484.
[3] L. Dong, P. N. Liu, N. Lin, Acc. Chem. Res.2015, 48, 2765.
[4] P. A. Held, H. Fuchs, A. Studer, Chem. Euro. J.2017, 23, 5874–
5892
[5] D. G. de Oteyza, P. Gorman, Y. C. Chen, S. Wickenburg, A. Riss,
D. J. Mowbray, G. Etkin, Z. Pedramrazi, H. Tsai, A. Rubio, M. F.
Crommie, F. R. Fischer,Science,2013, 340, 1434.
[6] D. Zhong, J. Franke, S. K. Podiyanachari, T. Blçmker, H. Zhang,
G. Kehr, G. Erker, H. Fuchs, L. Chi, Science,2011, 334, 213.
[7] Q. Sun, C. Zhang, H. Kong, Q. Tan, W. Xu, Chem. Commun. 2014,
50, 11825.
[8] R. Zuzak, R. Dorel, M. Krawiec, B. Such, M. Kolmer, M.
Szymonski, A. M. Echavarren, S. Godlewski, ACS Nano, 2017, 11,
9321–9329.
[9] H. Y. Gao, P. A. Held, S. Amirjalayer, L. Liu, A. Timmer, B.
Schirmer, O. D. Arado, H. Monig, C. Muck-Lichtenfeld J.
Neugebauer, A. Studer, H. Fuchs, J. Am. Chem. Soc.2017, 139,
7012−7019
[10] G. Otero, G. Biddau, C. Sánchez-Sánchez, R. Caillard, M. F.
López, C. Rogero, F. J. Palomares, N. Cabello, M. A. Basanta, J.
Ortega, J. Méndez, A. M. Echavarren, R. Pérez, B. Gómez-Lor, J.
A. Martín-Gago, Nature, 2008, 454, 865-868.
[23] Q. Fan, C. Wang, Y. Han, J. Zhu, W. Hieringer, J. Kuttner, G. Hilt,
J. M. Gottfried, Angew. Chem., Int. Ed. 2013, 52, 4668.
[24] C. Zhang, Q. Sun, H. Chen, Q. Tan and W. Xu, Chem.
Commun.2015, 51, 495.
[25] A. Riss, A. P. Paz, S. Wickenburg, H. Z. Tsai, D. G. De Oteyza, A.
J. Bradley, M. M. Ugeda, P. Gorman, H. S. Jung, M. F. Crommie,
A. Rubio, F. R. Fischer,Nat. Chem.2016,8, 678.
[26] S. K. Hamalainen, N. van der Heijden, J. van der Lit, S. den
Hartog, P. Liljeroth, I. Swart, Phys. Rev. Lett.2014, 113, 186102.
[11] J. Cai, P. Ruffieux, R. Jaafar, M. Bieri, T. Braun, S. Blankenburg,
M. Muoth, A. P. Seitsonen, M. Saleh, X. Feng, K. Müllen, R.
Fasel, Nature, 2010, 466, 470-473.
[12] J. R. Sanchez-Valencia, T. Dienel, O. Gröning, I. Shorubalko, A.
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COMMUNICATION
dehalogenative
homocoupling
We have demonstrated the
feasibility of direct formation of
C-C triple bonded structural
motifs by dehalogenative
homocoupling of tribromomethyl
molecules on surfaces.
Qiang Sun, XinYu, MeilingBao,
Mengxi Liu, Jinliang Pan, ZeqiZha,
Liangliang Cai, Honghong Ma,
Chunxue Yuan, XiaohuiQiu,* Wei
Xu*
5 Å
5 Å
5 Å
5 Å
Page No. – Page No.
Direct formation of C-C triple
bonded structural motifs by on-
surface dehalogenative
homocoupling of
tribromomethyl molecules
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