Scalable synthesis of quaterrylene: Solution-phase 1H NMR spectroscopy of its oxidative dication

Article abstract of DOI:10.1039/c3cc46270f

Quaterrylene is prepared in a single reaction and high yield by Scholl-type coupling of perylene, utilizing trifluoromethanesulfonic acid as catalyst and DDQ or molecular oxygen as oxidant. Dissolution in 1 M triflic acid/dichloroethane with sonication yields the aromatic quaterrylene oxidative dication, which is characterized by its ¹H NMR spectrum.

Full text of DOI:10.1039/c3cc46270f

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Scalable synthesis of quaterrylene: solution-phase
1H NMR spectroscopy of its oxidative dication†
Cite this: DOI: 10.1039/c3cc46270f
Rajesh Thamatam, Sarah L. Skraba and Richard P. Johnson*
Received 15th August 2013,
Accepted 28th August 2013
DOI: 10.1039/c3cc46270f
www.rsc.org/chemcomm
Quaterrylene is prepared in a single reaction and high yield by
Scholl-type coupling of perylene, utilizing trifluoromethanesulfonic
acid as catalyst and DDQ or molecular oxygen as oxidant. Dissolution
in 1 M triflic acid/dichloroethane with sonication yields the aromatic
quaterrylene oxidative dication, which is characterized by its 1H NMR
spectrum.
Fig. 1 Rylene structures.
As structural components of graphene nanoribbons,1–7 poly-
perinaphthalenes, commonly known as rylenes (Fig. 1), and their
derivatives are of intense current interest.8–19 Long-chain rylenes
absorb a broad spectrum of light20,21 and display electrical
conductivity.22 If rylenes are to find application as electronic
or photovoltaic components, the economical and large-scale
synthesis of pure substances is essential.23 It is surprising that
efficient and scalable synthetic routes to quaterrylene (4) have
not been described. This important hydrocarbon was first
described in 1948 by Clar24 and the tetra-t-butyl derivative
was reported by Mu¨llen in 1990,25 but the best current routes to
the parent hydrocarbon26 still follow classic Scholl conditions,27–30
which are suitable only for small scale reactions.
Our recent studies on superacid-catalyzed rearrangements of
arenes31 have led us to investigate optimal reaction conditions and
mechanisms for aryl–aryl coupling reactions. We report here that a
variation on Scholl reaction conditions using a superacid catalyst
in conjunction with either 2,3-dichloro-5,6-dicyanoquinone
(DDQ)32–36 or molecular oxygen as oxidant provides an efficient
and scalable route to quaterrylene. This structure is characterized
for the first time by the solution-phase NMR spectrum of its
oxidative dication.
initial formation of 1,1-binaphthyl, followed by intramolecular
cyclization. Further dimerization of perylene to quaterrylene was
later reported by Clar24 and recently reinvestigated by Cataldo, who
used a mixture of FeCl3 and AlCl3 as catalysts.26 Only milligram
quantities of 4 were prepared by these methods and we sought to
utilize its inherent insolubility to optimize a larger scale approach.
Building on our recent investigation of arene isomerizations,31 and
other recent studies on Scholl reactions,32–34,36 we have found that
reaction of 2 with 2 equivalents of trifluoromethanesulfonic acid
(TfOH) and 2 equivalents of DDQ in refluxing dichloromethane for
24 h gives a dark green solid product; this is the color previously
reported for quaterrylene (4).26 During reaction, the product
precipitates from solution. Neutralization of the cooled mixture
with diisopropylethylamine, followed by filtration and Soxhlet
extraction of the crude product with refluxing tetrahydrofuran
for 48 h afforded quaterrylene as a dark green solid (92% yield
from perylene). The presumed intermediate 1,10-biperylene (5) is
not observed in this reaction probably because of rapid cyclization
to 4. Further simplification came through conducting the reaction
under 1 atm of pure oxygen using chlorobenzene as solvent;
however, this yields product of somewhat lower purity and yield.
Following earlier precedent,26 isomer 6 is a likely by-product but
we could not obtain this in sufficient purity for characterization
(Scheme 1).
In 1910, Scholl reported that heating naphthalene (1) with
solid AlCl3 resulted in a low yield of perylene (2).37 Atmospheric
oxygen is assumed to be the oxidant in this reaction, while AlCl3
generates an acid catalyst. This is a two-step process, with
The MALDI mass spectrum of isolated quaterrylene is
exceptionally simple, showing a peak with m/z = 500 (C40H20).
The UV/VIS spectrum in N-methylpyrrolidone showed lmax at
665, 609 and 562 nm, in excellent agreement with reported
values.26
Our product was further characterized as quaterrylene by a
novel NMR technique. The well-known insolubility of high
melting crystalline substances such as 4 suggests that NMR
Department of Chemistry and Materials Science Program, University of New Hampshire,
Durham, NH 03824, USA. E-mail: Richard.johnson@unh.edu; Tel: +1-603-862-2302
† Electronic supplementary information (ESI) available: Experimental procedures,
spectra, Cartesian coordinates and energies for the dication. See DOI: 10.1039/
c3cc46270f
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Scheme 1 Synthesis of quaterrylene.
Fig. 3 Predicted and observed dication chemical shifts.
predicted to be aromatic48 because it retains a 34 p electron
periphery; our observed and calculated chemical shifts are
entirely consistent with this prediction.
While there is much precedent for oxidative or acid-catalyzed
arene coupling and polymerization,29,49,50 the high efficiency of the
present coupling and cyclization reaction appears to result from a
combination of superacid catalyst, stoichiometric equivalency of
DDQ or excess oxygen relative to the number of new sigma bonds,
and insolubility of the final product in the reaction medium.
Rylene 4 precipitates as formed in the reaction; this minimizes
the possibility of oligomerization. It is also essential that reactants
and intermediate structures are soluble in this medium so the
reaction can proceed to completion.
Our results provide a highly efficient route to quaterrylene (4).
We have carried out this reaction on a one gram scale; larger scale
reactions should be feasible. We are also exploring the possibility
that the ambient temperature NMR technique described here,
which does not require typical stable ion conditions,38,39 may be
applicable to other ‘‘insoluble’’ polyarenes.
Scheme 2 Synthesis of quaterrylene dication.
spectral characterization should be impossible; however, many
arenium ions and arene oxidative dications38,39 (neutral structure
minus two electrons) have been observed in solution40–47 and we
investigated whether protonation might increase solubility
and facilitate NMR analysis. Quaterrylene (4) is insoluble in
dichloroethane (DCE), but with the aid of mild sonication
(Scheme 2), we find that small amounts dissolve in 1 M triflic
acid-d/DCE-d4 with formation of a dark blue-green solution.
The 500 MHz 1H NMR spectrum of this sample (Fig. 2) showed
five principle resonances, with peak integration and spin multi-
plicity expected for a D2h symmetrical structure. The simplicity
of this spectrum clearly rules out an arenium ion.
Observed chemical shifts also do not support a neutral
structure but are in excellent agreement with GIAO B3LYP
predicted chemical shifts and expected spin multiplicities for
the oxidative dication. (C40H202+, Fig. 3) Minor resonances in
the spectrum have not yet been assigned. Dication 42+ has been
We are grateful for support from the National Science
Foundation (CHE-9616388) and to Professor Larry Scott for
helpful discussions. This work used the Extreme Science and
Engineering Discovery Environment (XSEDE), which is supported
by National Science Foundation grant number OCI-1053575.
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