Angewandte
Communications
Chemie
Graphene Functionalization Hot Paper
Mono- and Ditopic Bisfunctionalization of Graphene
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Kathrin C. Knirsch , Ricarda A. Schäfer , Frank Hauke, and Andreas Hirsch*
Abstract: For the first time, the bisfunctionalization of
graphene by employing two successive reduction and covalent
bond forming steps is reported. Bulk functionalization in
dispersion and functionalization of individual sheets deposited
on surfaces have both been carried out. Whereas in the former
case attacks from both sides of the basal plane are possible and
can lead to strain-free architectures, in the latter case,
retrofunctionalizations can become important when the corre-
sponding anion of the addend is a sufficiently good leaving
group.
arylated, and hydrogenated graphenes with high degrees of
addition on both sides of the basal plane can be prepared in
[16–18]
this way.
In the case of related reductive functionaliza-
[
19]
[20]
tions of carbon nanotubes and fullerenes, we and others
have demonstrated that such reactions can be reversible. It
has not yet been shown, but it is reasonable to assume that
related reversible processes such as that depicted in Scheme
1b can also play a role in graphene chemistry. It is important
to keep in mind that: a) covalent addition reactions on
fullerenes and carbon nanotubes are monotopic (only exohe-
dral addend binding can take place), whereas addend binding
on graphene can be both monotopic (when the sheets are
supported on a surface) or ditopic (in dispersion); b) exhaus-
tive homotopic additions will eventually lead to an increase in
strain energy (eclipsing addend interactions, deviation from
normal bond angles); c) ditopic addition can lead to more
stable and less strained geometries, including complete strain-
free graphane with an all-chair configuration of the six-
M
ultiple covalent functionalization of synthetic carbon
allotropes, such as fullerenes, carbon nanotubes, and gra-
phene, with different addends represents an attractive con-
cept for the design and combination of specific chemical,
physical, and materials properties. As a consequence, prom-
ising practical applications of nanocarbons such as in sen-
[
1]
[2]
[3]
sors, nanocomposites, and biomedical products can be
targeted. The construction of molecular architectures con-
sisting of a carbon allotrope core and two or more different
covalently attached functionalities has so far been realized
[18,21,22]
membered carbon rings.
It is to be expected that the
degree of retrofunctionalization (Scheme 1b) represents an
interplay between the strain energy of the graphene adduct
[
4–10]
[11–15]
À
with fullerenes
and carbon nanotubes,
whereas
itself and the stability of the leaving group R . We now
examples for mixed graphene derivatives are still elusive.
One of the most efficient methods for the functionalization of
graphene is the reduction/exfoliation of graphite with alkaline
metals in suitable solvents followed by quenching of
the intermediately formed graphenides with electrophiles
present for the first time a) a reaction sequence that allows
the successful bisfunctionalization of graphene and b) an
investigation of the topicity and leaving group dependence of
the retrofunctionalization.
As subsequent addition reactions we chose the treatment
[16]
[17]
(
Scheme 1a). We have recently shown that alkylated,
of graphenides with diazonium salts and alkyl iodides. To
investigate the influence of graphene topicity, we carried out
the addition to graphenides in dispersion (double-sided bulk
functionalization) and to CVD graphenide supported on a
Si/SiO surface (single-sided functionalization). For the bulk
2
functionalization, pristine natural graphite G was exfoliated
P
by wet chemical reduction using Na/K alloy in 1,2-dimethoxy-
ethane (DME). After this activation, the negatively charged
graphenide sheets were treated with the first electrophile.
After work-up, a second activation with Na/K alloy was
initiated followed by the addition of the second electrophile.
For the synthesis of 4-methoxyphenyl-hexyl-graphene
GAB we used 4-methoxyphenyldiazonium tetrafluoroborate
A as the first and n-hexyl iodide B as the second electrophile
Scheme 1. a) Reductive functionalization and b) reductive retrofunc-
tionalization of graphene.
(Scheme 2).
Thermogravimetric analysis coupled with mass spectrom-
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[
*] K. C. Knirsch, R. A. Schäfer, Dr. F. Hauke, Prof. Dr. A. Hirsch
Department of Chemistry and Pharmacy & Joint Institute of
Advanced Materials and Processes (ZMP)
etry (TGA-MS; Figure 1) revealed a mass loss of À20.6%
(
black curve) in the G relative to the starting material (gray
AB
curve). The large mass loss correlates with the characteristic
fragments of the 4-methoxyphenyl as well as hexyl units
detected by mass spectrometry. Signals for m/z 39, 77, 78, 107,
and 108 (see Scheme S1) are observed at about 5108C (see
Figure S1, top and center). These mass fragments can be
assigned to allyl (m/z 39), phenyl (m/z 77, 78), and methoxy-
phenyl units (m/z 107, 108), which clearly demonstrates the
Friedrich-Alexander University of Erlangen-Nürnberg
Henkestrasse 42, 91054 Erlangen (Germany)
E-mail: andreas.hirsch@fau.de
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[
] These authors contributed equally to this work.
Angew. Chem. Int. Ed. 2016, 55, 5861 –5864
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5861