Tetracarboxy-Functionalized [8]-, [10]-, [12]-, and [14]Phenacenes

Article abstract of DOI:10.1002/ejoc.201700893

Mono- and diglyoxylation of chrysene and naphthalene leads to Perkin reactants that yield bismaleates, which efficiently photocyclize to elongated phenacenetetracarboxylic esters. Their band gaps remain significantly larger than the value postulated for p

Full text of DOI:10.1002/ejoc.201700893

A Journal of
Accepted Article
Title: Tetracarboxy-functionalized [8], [10], [12] and [14]Phenacenes
Authors: Thamires S. Moreira, Marli Ferreira, Alice Dall'armellina,
Rodrigo Cristiano, Hugo Gallardo, Elizabeth A. Hillard, Harald
Reinhart Bock, and Fabien Durola
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700893
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10.1002/ejoc.201700893
European Journal of Organic Chemistry
COMMUNICATION
Tetracarboxy-functionalized [8], [10], [12] and [14]Phenacenes
Thamires S. Moreira,[a, b] Marli Ferreira,[a] Alice Dall’armellina,[c] Rodrigo Cristiano,[b] Hugo Gallardo,[d]
Elizabeth A. Hillard,[a] Harald Bock*[a] and Fabien Durola*[a]
Abstract: Mono- and diglyoxylation of chrysene and naphthalene
leads to Perkin reactants that yield bismaleates which efficiently
photocyclize to elongated phenacene-tetracarboxylic esters. Their
band gaps remain significantly larger than the value postulated for
polyphenacene. Reaction with α-branched amines gives the
corresponding imides, which are significantly stronger electron
acceptors than the esters. The obtained [12] and [14]phenacenes
are the longest [n]phenacenes that have been synthesized to date.
bifunctional
phenacene
fragments
such
as
1,5-
naphthylenediglyoxylic acid 1 and 1,7-chrysenylenediglyoxylic
acid 2 as central building blocks (Scheme 2), should lead to long
phenacenes substituted with four solubilizing alkylester
substituents that allow modification of the chromophore by
transformation into the corresponding bis(alkylimides). As
terminal arylacetic acid building blocks, 1-naphtylacetic acid 3
and 1-chrysenylacetic acid
tetracarboxylic derivatives of [8], [10], [12] and [14]phenacene
(Scheme 3). [6]phenacene-tetracarboxdiimide has been
obtained recently in similar fashion from 1,5-naphthylenediacetic
acid and phenylglyoxylic acid,8 and similar elongated
dinaphtho[1,2-a;1’,2’-h]anthracene-tetracarboxylic
have been obtained previously by palladium-catalyzed double
dehydrobrominations.9
4 may be used, to lead to
A
The two conceptually simplest and thinnest hypothetical
graphene nanoribbons are polyacene and polyphenacene.
Whilst higher acenes longer than heptacene are too unstable to
be isolated due to their only minimal sextet stabilization and
derivatives
hypothetical polyacene is postulated to be
a
metal,1
polyphenacene (Scheme 1) is fully Fries-stabilized (i.e. it allows
a Kekulé formula where all hexagons are made of three double
and three single bonds),2 with a predicted band gap of about 2.5
eV.3 Phenacenes up to [6]phenacene (a.k.a. fulminene) have
been isolated from coal tar,4 and alkyl-substituted [7] and
[11]phenacenes have been synthesized by Mallory and co-
workers by Wittig condensations plus photocyclisations of alkyl-
substituted mono- and bifunctional phenanthrene precursors.5
We prepared 1, 2 and 4 from the corresponding bromoarenes.
1,5-dibromonaphthalene 5 is most conveniently obtained by
regioselective photobromination of 1-bromonaphthalene in
CCl4,10 whereas bromination of chrysene leads to 6,12- but not
1,7-dibromochrysene 6.11 We therefore synthesized 6 and 1-
bromochrysene 7 from 5-bromo-1-naphthaldehyde 812 or 1-
naphthaldehyde 9 and diethyl (2-bromobenzyl)phosphonate 10
by a Horner reaction followed by oxidative photocyclization of
the intermittent naphthylstyrenes 11 and 12 in ethyl acetate at
room temperature in the presence of iodine and air. These
photocyclizations proved to be surprisingly concentration-
independent, presumably because the rather voluminous
naphthyl and 2-bromophenyl moieties hinder intermolecular
side-photoreactions such as 2+2 cyclizations to tetraaryl-
.
cyclobutanes.13 The bromochrysenes
6 and 7 were thus
obtained on a 14-20 mM (4-7 g/L) scale in 78% and 75% yield
by simple filtration from the reaction medium, from which they
precipitate during the reaction. The photocyclization of 12 to 7
has previously been reported at high dilution – 1 mmol/L (0.3
g/L) – in similar (74%) yield.14 Treatment of 6 and 7 with n-BuLi
followed by diethyl oxalate yielded the glyoxylic esters 13 and 14.
Scheme 1. The two hypothetical polymers polyacene (top) and
polyphenacene (bottom).
The Perkin condensation of arylenediglyoxylic acids with
arylacetic acids followed by same-pot esterification smoothly
leads to arylenebis(arylmaleates),6 and such bismaleates may
Dibromonaphthalene
5 was transformed similarly into the
be
oxidatively
photocyclized
to
yield
extended
diglyoxylic ester 15, but t-BuLi had to be used in this case to
avoid butylation. Contrary to what has been observed with
bigger dibromoarenes, 5 cannot be substituted twice to 15 by
the usual action of n-BuLi and diethyl oxalate. The main
arenetetracarboxylic tetraesters.7 This approach, if pursued with
[a]
M. Ferreira, T. S. Moreira, E. A. Hillard, H. Bock, F. Durola
Centre de Recherche Paul Pascal, CNRS
115, av. Schweitzer, 33600 Pessac, France
E-mail: durola@crpp-bordeaux.cnrs.fr, bock@crpp-bordeaux.cnrs.fr
www.crpp-bordeaux.cnrs.fr
compound obtained by such
a
procedure is ethyl 5-
butylnaphthyl-1-glyoxylate, because naphthylene-1,5-dilithium
reacts once by nucleophilic substitution on bromobutane, which
is formed as a side product of the bromine-lithium exchange
reaction. To avoid this unwanted reaction, we used two
equivalents of t-BuLi per function, since the 2-bromo-2-
methylpropane formed by the bromine-lithium exchange reaction
immediately reacts with another t-BuLi molecule to give inert 2-
methylpropene and 2-methylpropane by β-elimination.
[b]
[c]
[d]
T. S. Moreira, R. Cristiano
Departamento de Química, Universidade Federal da Paraíba
CEP 58051-900, João Pessoa, Paraíba, Brazil
A. Dall’armellina
Centre de Recherche Paul Pascal, Université de Bordeaux
115, av. Schweitzer, 33600 Pessac, France
H. Gallardo
Diesters 13 and 15 were hydrolyzed to the corresponding
diglyoxylic acids 1 and 2, whereas monoester 14 was reduced
with concomitant hydrolysis to the monoacetic acid 4.
Departamento de Química, Universidade Federal de Santa Catarina
CEP 88040‐900, Florianópolis, Santa Catarina, Brazil
Supporting information for this article is given via a link at the end of
the document
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10.1002/ejoc.201700893
European Journal of Organic Chemistry
COMMUNICATION
Br
Br
a
much stronger aggregation tendency of the central unsubstituted
chrysene segments in 21 and 23 compared to the shorter and
thus sterically more shielded central unsubstituted naphthalene
segment in 22. The evolution of the melting temperature with
increasing molecular length confirms the relatively weak
aggregation tendency of 22: Albeit a linear increase of melting
temperature from 21 via 22 to 23 would be in line with the
growth of the arene system, 21 and 22 both melt at ca. 240ºC,
whereas no melting is observed with 23 up to 300ºC.
12
11
Br
9
8
Br
10
O
O
OEt
OEt
a
P
b
b
O
Br
O
Br
EtO2C
c
c
7
5
14
6
13
The four phenacene-tetracarboxylates were transformed directly
in 65-90% yield into the homologous swallow-tailed N,N’-
dialkylimides 24-27 by condensation with an appropriate
symmetrical (dialkylmethyl)amine in the presence of imidazole in
refluxing o-dichlorobenzene. The structures of the four
phenacene-diimides are unambiguously confirmed by their
highly symmetric and sufficiently deconvoluted aromatic regions
of their 1H NMR spectra that show only two aromatic triplets and
8, 10 or 12 doublets (in the notable absence of any singlets) for
25, 26 and 27, respectively, whilst for the shortest homologue 24
the two would-be triplets convolute, resulting in correspondingly
complex peaks for the two neighboring hydrogens, plus 4
doublets for the non-terminal aromatic hydrogens. This confirms
that neither the four-fold photocyclizations of the bismaleates to
the phenacene-tetracarboxylates 20-23 to nor the high-
temperature transformations of the latter to the final diimides 24-
27 are impeded by unexpected rearrangements.
Br
Br
EtO2C
CO2Et
e
Br
f
O
O
O
O
EtO2C
O
d
HO2C
15
Br
CO2Et
HO2C
O
3
e
2
4
HO2C
CO2H HO2C
CO2H
1
O
O
g
g
g
g
16
17
18
19
EtO2C
EtO2C
HxO2C
HxO2C
HxO2C
HxO2C
HxO2C
HxO2C
CO2Et
CO2Et
20
21
22
23
CO2Hx
CO2Hx
CO2Hx
CO2Hx
EtO2C
EtO2C
HxO2C
HxO2C
CO2Hx
CO2Hx
HxO2C
HxO2C
HxO2C
HxO2C
CO2Et
CO2Et
CO2Hx
CO2Hx
CO2Hx
CO2Hx
CO2Hx
CO2Hx
Scheme 2. Synthesis of naphthalene- and chrysene-based bismaleates 16-19
as precursors of phenacene-tetracarboxylic esters 20-23. (a) NaH, THF, 51-
73%; (b) h, I2, O2, EtOAc, 75-78%; (c) 1. THF, n-BuLi, 2. EtO2CCO2Et, 76-
84%; (d) 1. THF, t-BuLi, 2. EtO2CCO2Et, 85%; (e) NaHCO3, EtOH-H2O, 100%;
(f) 1. NaI, H3PO2, H2O, AcOH, 2. MeSO3H, 81%; (g) 1. NEt3, Ac2O, THF, 2.
ROH, RBr, DBU, 40-66%. Hx = n-hexyl.
O
Ud
N
Ud
O
O
Ud
N
Ud
O
O
Ud
Ud
N
The double Perkin condensations of either of the diglyoxylic
acids 1 and 2 with either of the acetic acids 3 and 4, followed by
in-situ esterification, led in 40-66% yield to the bismaleates 16-
19. Due to the low solubility and thus low reactivity of the initially
formed bismaleic dianhydride, the final esterification step leading
to the longest homologue 19 necessitated a prolonged reaction
time of five days. Photoreaction of the bismaleates in ethyl
acetate in the presence of iodine and oxygen under borosilicate-
filtered irradiation by a medium-pressure mercury immersion
lamp gave in 63-80% yield the targeted phenacene-
tetracarboxylates 20-23, which, with the exception of 22,
conveniently precipitated pure from the reaction medium. The
higher solubility of 22, with respect to its homologues 21 and 23
with identical solubilizing alkyl groups, may be imparted to the
O
Pn
N
O
O
O
N
O
Ud
N
Ud
Ud
Pn
O
Ud
O
O
O
Ud
N
Pn
N
Ud
O
Pn
O
27
26
25
24
Scheme 3. [8]-, [10]-, [12]- and [14]phenacene-tetracarboxylic esters 20-23
and -tetracarboxdiimides 24-27 obtained from bismaleates 16-19 by oxidative
photocyclization (h, I2, O2, EtOAc, 63-80%) and subsequent imidification
(R2CHNH3Cl, imidazole, o-C6H4Cl2, 65-90%). Pn = n-pentyl, Hx = n-hexyl, Ud
= n-undecyl.
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10.1002/ejoc.201700893
European Journal of Organic Chemistry
COMMUNICATION
The optical absorption spectra in dilute chloroform solution
(Figure 1) surprisingly show that both in the ester and in the
imide series, the long wavelength absorption edges of the two
shorter homologues are nearly identical (415 nm [corresponding
to an optical band gap of 2.99 eV] for for the esters 20 and 21,
505 nm [2.46 eV] for the imides 24 and 25), and occur at about
15nm shorter wavelength than the absorption edges of the two
longer homologues, which are also nearly identical (430 nm
[2.88 eV] for the esters 22 and 23, 520 nm [2.38 eV] for the
imides 26 and 27). This suggests that the positioning of the
substituents is of non-negligible influence on the optical band
gap, as we have observed previously in tetracarboxy-substituted
dinaphtho[1,2-a;1’,2’-h]anthracenes.9 In these dinaphtho-
anthracenes, the band gap was found to be smaller when the
substituents are closer to the middle of the arene system, i.e.
when they are more closely conjugated with each other. A
similar behavior is apparent in the phenacenes: The optical band
gap diminishes when the arene is lengthened at the ends (when
passing from peripheral naphthalenes to peripheral chrysenes,
i.e. from 21 to 22 or from 25 to 26), but remains constant if the
arene is lengthened by insertion in the center (when passing
from central naphthalene to central chrysene, i.e. from 20 to 21,
or 22 to 23, or 24 to 25, or 26 to 27). In the latter case, the
influence of the overall lengthening of the chromophore on the
optical band gap is thus compensated as the substituents are
simultaneously moved further apart.
oxidation and reduction potentials of these fully Fries-stabilized
systems. The reversibility of the reduction potentials of the
diimides is in agreement with the established electron acceptor
character of such imides. Due to the irreversible redox
transitions and to the limited solubility especially of the longer
imides in DCM, the obtained HOMO and LUMO values and the
resulting electrochemical band gaps are less precise than the
optical band gaps obtained from the absorption spectra. The
observed first oxidation and reduction potentials yield HOMO
and LUMO energies of ‒5.85±0.15 eV and ‒2.7±0.1 eV for the
four esters and of ‒5.9eV±0.15 eV and ‒3.2±0.1 eV for the four
imides (Table 1). Thus whilst both the HOMO and the LUMO
energies are only weakly dependent on length and the HOMO
energies are only weakly dependent on substitution, the
difference in LUMO energies between esters and imides is
striking, the latter thus being, as expected, considerably better
electron acceptors than the former. As the first oxidation
potentials (and HOMO energies) are quasi-independent of
substitution, whereas the first reduction potentials (and LUMO
energies) differ considerably between esters and imides, it may
be assumed that the positive charge injected on oxidation is
localized on the polycyclic aromatic core, whereas the negative
charge injected on reduction tends to be localized on the
carboxylic substituents. The observed differences between the
optical and electrochemical band gaps of 0.1-0.4 eV correspond
to the exciton binding energies and are similar to the values of
0.15-0.35 eV observed with the aforementioned dinaphtho-
anthracenes.9
At all four phenacene lengths, the absorption edge of the imide
is at 90 nm longer wavelength than that of the corresponding
ester, due to the appearance of a broad long wavelength
absorption peak in the imides, whose equivalent is discernible
only as a shoulder in the esters (Figure 1).
As the electrochemical band gaps of unsubstituted phenacenes
are expected to be larger than those of esters 20-23 (3.15±0.15
eV) and imides 24-27 (2.7±0.15 eV) with their conjugated
carboxylic substituents, the observation of band gaps in the
esters that are well above the value of 2.5 eV predicted for
unsubstituted polyphenacene3 indicates that unsubstituted
phenacenes might have to be considerably longer than the
phenacenes investigated here to be electronically quasi-identical
with polyphenacene.
Table 1. Observed first oxidation and reduction potentials, HOMO and LUMO
energies, electrochemical and optical band gaps, and exciton binding energies
Phen-
acene
1st ox.
(eV)[a]
1st red.
(eV) [a]
EHOMO
(eV) [b]
ELUMO
(eV) [b]
redox
gap
(eV)
opt.
gap
(nm)
opt.
gap
(eV)
20
21
+1.16
+0.96
‒2.09
‒2.13
‒5.96
‒5.76
‒2.71
‒2.67
3.25
3.09
415
415
2.99
2.99
Figure 1. Absorption spectra of [8]-, [10]-, [12]- and [14]phenacene-
tetracarboxylic esters 20-23 and -tetracarboxdiimides 24-27 (2.5 μmol L-1 in
chloroform).
22
23
24
25
26
27
+0.96
+0.92
+1.24
+1.08
+1.06
+0.96
‒2.07
‒2.17
‒1.61
‒1.66
‒1.57
‒1.62
‒5.76
‒5.72
‒6.04
‒5.88
‒5.86
‒5.76
‒2.73
‒2.63
‒3.19
‒3.14
‒3.23
‒3.18
3.03
3.09
2.85
2.74
2.63
2.58
430
430
505
505
520
520
2.88
2.88
2.46
2.46
2.38
2.38
To quantify the absolute donor/acceptor character of the esters
and imides, we also performed differential pulse and cyclic
voltammetry in DCM solution with ferrocene as internal standard.
In all cases, the first oxidation proved to be irreversible, and the
first reduction of the esters was found to be irreversible as well
under these conditions, only the first reduction of the imides
being quasi-reversible. This irreversibility is not surprising given
the characteristically large band gaps and thus rather outlying
[a] versus ferrocene (Fc) in DCM. [b] from Fc/Fc+ at 4.80eV below vacuum
In summary, following the elaboration of appropriate mono- and
difunctionalized chrysene and naphthalene precursors, the
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10.1002/ejoc.201700893
European Journal of Organic Chemistry
COMMUNICATION
[4]
[5]
K. F. Lang, Buffleb, J. Kalowy, Chem. Ber. 1964, 97, 494.
combination of Perkin condensations with oxidative
photocyclizations provided a simple and straightforward access
to phenacenes of unprecedented length. Whilst the respective
tetraesters and diimides differ considerably in band gap, the
evolution of the band gap with molecular length is only weakly
discernible. It remains to be seen whether even longer
phenacenes with similar substitution patterns will slowly
converge towards a significantly smaller gap than the [12] and
[14]phenacenes presented here.
a) F. B. Mallory, K. E. Butler, A. Bérubé, E. D. Luzik, C. W. Mallory, E. J.
Brondyke, R. Hiremath, P. Ngo, P. J. Carroll, Tetrahedron. 2001, 57,
3715; b) F. B. Mallory K. E. Butler, A. C. Evans, E. J. Brondyke, C. W.
Mallory, C. Yang, A. Ellenstein, J. Am. Chem. Soc. 1997, 119, 2119; c)
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2016, 22, 8043; b) M. Ferreira, G. Naulet, H. Gallardo, P.
Dechambenoit, H. Bock, F. Durola, Angew. Chem. Int. Ed. 2017, 56,
3379; c) M. G. Belarmino Cabral, D. M. Pereira de Oliveira Santos, R.
Cristiano, H. Gallardo, A. Bentaleb, E. A. Hillard, F. Durola, H. Bock,
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Acknowledgements
This research was financed partially by a Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior
- Comité
Français d’Evaluation de la Coopération Universitaire et
Scientifique avec le Brésil (CAPES-COFECUB, project Ph-C
803-14) grant, and by an Agence Nationale de la Recherche
(project 13-JS07-0009-01) grant.
[8]
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New J. Chem. 2016, 40, 113.
H. Bock, P. Carré, E. A. Hillard, F. Durola, Eur. J. Org. Chem. 2015,
1028.
[10] O. Cakmak, I. Demirtas, H. T. Balaydin, Tetrahedron 2002, 58, 5603.
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Org. Chem. 1999, 1191; b) H. Bock, S. Huet, P. Dechambenoit, E. A.
Hillard, F. Durola, Eur. J. Org. Chem. 2015, 1033.
Keywords: Arenes • Fused-ring systems • Cyclization •
Photooxidation • Chromophores
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[3]
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10.1002/ejoc.201700893
European Journal of Organic Chemistry
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
The longest known phenacenes so far
are constructed efficiently from
chrysene and naphthalene diglyoxylic
and monoacetic acids by Perkin
T. dos Santos Moreira, M. Ferreira, A.
Dall’armellina, R. Cristiano, H. Gallardo,
E. A. Hillard, H. Bock*, F. Durola*
RO2C
RO2C
Page No. – Page No.
condensations and photocyclizations.
4 steps
HO2C
O
1. Ac2O,
NEt3
Tetracarboxy-functionalized [8], [10],
[12] and [14]Phenacenes
EtO
EtO
P
O
O
2. Esterif.
3. h, I2
Br
O
HO2C
CO2R
CO2R
4 steps
CO2H
Br
O
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