Angewandte
Communications
Chemie
On-Surface Reactions Very Important Paper
Steering On-Surface Reactions by a Self-Assembly Approach
Qiwei Chen, Jacob R. Cramer, Jing Liu, Xin Jin, Peilin Liao,* Xiang Shao,* Kurt V. Gothelf,*
and Kai Wu*
Abstract:
4,4’-Bis(2,6-difluoropyridin-4-yl)-1,1’:4’,1’’-ter-
Typically, substrate-induced confinement effect could
result in the formation of ordered low dimensional surface
nanostructures.[23] Furthermore, the substrate constraint
might also help realize unexpected large-barrier reactions
on the surface.[25] Similarly, we propose that the space
confinement resulting from the molecules, that is, the
formation of self-assembled structures, would also affect the
reactivity and selectivity of on-surface reactions. Molecular
self-assemblies may mediate preorganization of the molecules
for on-surface reactions, but little[26] has been reported in
literature, possibly because the interactions between the
assembling molecules and the substrate are too weak to hold
the molecules at reaction temperatures.
phenyl (BDFPTP) molecules underwent dehydrocyclization
and covalent coupling reactions on Au(111) according to
scanning tunneling microscopy (STM) measurements and
density functional theory (DFT) calculations. Self-assembly
of the reactants in well-defined molecular domains prior to
reaction could greatly enhance the regioselectivity of the
dehydrocyclization reaction and suppress defluorinated cou-
pling, demonstrating that self-assembly can efficiently steer on-
surface reactions. Such a strategy could be of great importance
in surface chemistry and widely applied to control on-surface
reactions.
O
n-surface synthesis has drawn great attention in the past
decade due to its application as the bottom-up approach to
fabricating functional nanostructures at surfaces.[1–4]
In this study, self-assembly-mediated reactions of 4,4’-
bis(2,6-difluoropyridin-4-yl)-1,1’:4’,1’’-terphenyl (BDFPTP)
on Au(111) were studied by combined scanning tunneling
microscopy (STM), scanning tunneling spectroscopy (STS),
and density functional theory (DFT) calculations. The
experimental results and theoretical simulations revealed
unexpected dehydrocyclization (DHC) and coupling reac-
tions of BDFPTP at elevated temperatures (Scheme 1). More
A
number of homogeneous reactions including Ullmann cou-
pling,[5–8] Glaser coupling,[9–11] imine formation,[12,13] Bergman
cyclization[14] and the like have been explored at metal
surfaces. However, their mechanisms are largely elusive
except for well-studied Ullmann[15–18] and Glaser[10,11,19–21]
coupling reactions. Different from the intrinsic reactivity of
homogeneous synthesis in wet chemistry, on-surface synthesis
can be seriously influenced by various surface effects, such as
catalytically active adatoms,[22] reconstruction and step
edges,[23] poison adatoms,[15] surface mobility,[16] space con-
finement,[24] and lattice guiding[10] as well.
[*] Dr. Q. Chen, Dr. J. Liu, Dr. X. Jin, Prof. K. Wu
BNLMS, College of Chemistry and Molecular Engineering
Peking University
Beijing 100871 (China)
E-mail: kaiwu@pku.edu.cn
Dr. J. R. Cramer, Prof. K. V. Gothelf
Danish-Chinese Centre for Self-Assembly and Function of Molecular
Nanostructures on Surfaces at iNANO and Department of Chemistry
Aarhus University
Aarhus C 8000 (Denmark)
E-mail: kvg@chem.au.dk
Scheme 1. Possible dehydrocyclization and coupling reaction pathways
of BDFPTP on Au(111). D1–D4 potential reaction positions for DHC.
C potential reaction positions for coupling.
Prof. P. Liao
importantly, formation of a well-ordered self-assembled
structure prior to the reactions could effectively narrow
down the product distribution of the DHC reaction and
completely suppress the coupling reaction. These findings
showed that the intermolecular confinement in the self-
assembly could play a crucial role in mediating the on-surface
reaction of the individual molecules therein.
Scheme 1 shows the DHC and coupling reaction pathways
of BDFPTP. The reactions proceed via the ends and/or sides
of BDFPTP. For the DHC reaction, four potential reaction
positions (RPs) are marked in blue from D1 through D4.
School of Materials Engineering
Purdue University
West Lafayette, IN 47907 (USA)
E-mail: peilin.lpl@gmail.com
Prof. X. Shao
Department of Chemical Physics, School of Chemistry and Materials
Science
University of Science and Technology of China
Hefei 230026 (China)
E-mail: shaox@ustc.edu.cn
Supporting information for this article can be found under:
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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