Highly π electron-rich macro-aromatics: Bis(p-aminophenyl)-carbo- benzenes and their DBA acyclic references

Article abstract of DOI:10.1039/c2cc34176j

A series of stable quadrupolar bis(p-aminophenyl)-carbo-benzenes, featuring both donor-donor-donor π-frustration and central macro-aromaticity, is described and compared to the acyclic dibutatrienylacetylene (DBA) reference series.

Full text of DOI:10.1039/c2cc34176j

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Highly π electron-rich macro-aromatics.
Bis(p-aminophenyl)-carbo-benzenes and their DBA acyclic references#
Arnaud Rives,a,b Iaroslav Baglai,a,b,c Volodymyr Malytskyi,a,b,c Valérie Maraval,*a,b
Nathalie Saffon-Merceron,b Zoia Voitenkoc and Remi Chauvin*a,b
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
carbo-benzenes are aryl-subtituted (derivatives of 1a, Fig. 1),7
A
series of stable quadrupolar bis(p-aminophenyl)-carbo-
40 the aromaticity of the C18 ring has been long regarded as a key
stabilization factor.8 Recently, however, π-acyclic dibuta-
trienylacetylene (DBA) sub-motifs (carbo-mers of butadiene)
were also found to be quite stable.9 This allows the “macro-
aromaticity” of carbo-DATPs to be addressed by comparison
45 to their DBA-type components, here denoted as carbo-
DAPBs. “Macro-aromaticity” is indeed commonly invoked for
porphyrins,10 in which frontier electronic excitations exhibit
strong analogy with those of carbo-benzenes:11 this was
illustrated for the dianisyl derivative 1b, a moderately “π-
50 frustrated”2 parent of the di(aminophenyl) series disclosed
below, and consisting in two sub-series: the anilinyl type, and
the indolylphenyl type (Scheme 1).
benzenes, featuring both donor-donor-donor π-frustration and
10 central macro-aromaticity, is described and compared to the
acyclic dibutatrienylacetylene (DBA) reference series.
4,4’’-Diamino-p-terphenyl (DATP) is a valuable motif for the
design of electroluminescent devices.1 From the fundamental
viewpoint, the π-donating character of the two nitrogen atoms
15 flanking the π-electron-rich terphenyl rod makes it an a priori
“π-frustrated” motif,2 which ground state is stabilized by local
aromaticity of π-independent phenylene rings, while low lying
excited states may acquire global aromaticity in a coplanar
geometry.3 The invoked aromaticity can be quantified by
20 aromatic stabilization energies (ASEs) between the π-cyclic
structure and acyclic reference components (Fig. 1).4,5 While
many ASEs have been theoretically devised, their generality
vs the substitution pattern and their experimental realization
Ph Ph
MeO
OMe
R
2
O
O
1)
BrMg
Li
N
1)
BrMg
R = TMS, Me
2) H+
N
have been scarcely addressed in an explicit manner.5
A
R
or
MeO
OMe
25 chemically relevant simple definition for the range of
quadrupolar benzene derivatives relies on an eliminative [4+2]
retro-Diels-Alder process, where the C4 moiety preserves a π-
conjugation between electro-active ends. For DATPs, the C4
components are di(p-aminophenyl)butadienes (DAPBs), that
30 have long been used as key chromophoric units as well.6
Ph Ph
N
2) H+
Z
Z
Ph Ph
Ph Ph
N
R2N
MeO
OMe
OH
MeO
OMe
OH
HO
MeO
HO
MeO
OMe
OMe
N
NR2
Ph Ph
Z
Z = H, 4, 66 %; ZZ = -(CH=CH)2-, 5, 63 %
Ph Ph
acyclic reference components
¹ -cyclic structure
R = TMS, 3a; R = Me, 3b
Z
E
E
X
X
Ar
Ar = 4-NR2-C6H4: DATP
Ph Ph
Ar
1) SnCl2/HCl, DCM or Et2O, - 78 ¡C
2) 1 M NaOH
Ar
Ar
1) SnCl2/HCl, DCM, - 78 ¡C
2) 1 M NaOH
Ğ2 EX
eliminative [4+2] cycloaddition
Ar = 4-NR2-C6H4: DAPB
Ph
Ph
Ph
Ph
Ph
Ph
Z
E
E
Z
N
N
Z
R'2N
NR'2
dibutatrienyl-
acetylene
(DBA)
X
X
Z
carbo-benzene
core
Ar
Ar
Ar
Ar
Ğ2
E
X
core
Ph
Ph
ring-closing alkyne metathesis
Ph
Ph
Z = H, 8, 71 %; ZZ = -(CH=CH)2-, 9, 69 %
R = TMS, R' = H, 6, 26 %; R = R' = Me, 7, 6 %
Ph
Ph
Ph
Ph
Ar = C6H5: 1a
Scheme 1 Synthesis of carbo-DATPs.
Ar = 4-NR2-C6H4: carbo-DAPB
Ar = 4-MeO-C6H4: 1b
Ar = 4-NR2-C6H4: carbo-DATP
55 Macrocyclic carbo-DATPs were prepared from the known
[6]pericyclynedione 2,11,12 which was reacted with anilinyl
Grignard reagents (4-NR2-C6H4MgBr, R = TMS, Me) to give
the acid-sensitive [6]pericyclynediols 3a and 3b as crude
materials only. The more stable indolyl and carbazolyl
60 derivatives 4 and 5, respectively generated from Grignard and
lithium reagents, were purified as mixtures of stereoisomers.13
The [6]pericyclynediols 3-5 were then treated with SnCl2/HCl
Fig. 1 Simple carbo-meric ASE equations for the central ring of
quadrupolar terphenyl derivatives (DATPs) and carbo-mers thereof.
The relevance of ASE definitions is also submitted to the
35 condition that their absolute value should vanish, or at least
decrease, with the ring size.4 A ring-expanded version of
DATP is its central ring carbo-mer,7 i.e. bis(p-aminophenyl)-
carbo-benzene (carbo-DATP). Although most of the known
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in either DCM or Et2O,9b followed by aq. NaOH (Scheme 1).
Crude samples of 3a and 3b were thus converted to the acid-
sensitive carbo-DATPs 6 (after concommitant N-desilylation)
Absorption spectra of the carbo-DATPs 6-9 and carbo-
DAPBs 17-20 are shown in Fig. 3. The influence of the
aminophenyl substituents on the λmax value is similar in both
and 7, in 26 % and 6 % yield from 2, respectively, while pure 40 series, the higher bathochromic shift occuring for the
5
4 and 5 afforded the stable carbo-DATPs 8 and 9 in ca 70 %
yield. Both 7 and 9 proved poorly soluble, and full 13C NMR
analysis of 9 required CP-MAS techniques. All the carbo-
DATPs 6-9 are highly crystalline materials, but only crystals
dimethylaniline derivatives 7 and 18. The intrinsic aromaticity
of the indolyl substituents makes them more innocent toward
the central core (8-9 and 19-20 giving the same lowest λmax
values of 486.5 0.5 and 598 1 nm in each series), and the
of 6 were found suitable for X-ray diffraction (XRD) analysis 45 more donating the substituent, the stronger the bathochromic
10 (Fig. 2). In spite of a disorder between phenyl and anilinyl
substituents, quite accurate data were obtained in the classical
range for the C18 macrocycle.8a-b,11 In solution, the macro-
aromaticity of 6-9 was confirmed by the deshielding of the
ortho-1H nuclei of the aryl rings in the range 9.2-9.6 ppm.
shift. The range of variation of λmax is twice as wide in the
carbo-DAPB series (ꢀλmax = 72 nm for 18-20) as in the
carbo-DATP series (ꢀλmax = 35 nm for 7-8). The λmax values
are also higher for carbo-DAPBs than for carbo-DATPs (by at
50 least 113 nm, for 8 and 19). These observations are consistent
with the aromatic character of the carbo-benzene core, which
should thus be more “insulating” than the more substituent-
sensitive acyclic DBA core. Although no rationale is obvious,
the bathochomic effect of the donating character is found
55 prolounged beyond the aminophenyl series to the anisyl and
phenyl substituents (λmax(1b) = 482 nm > λmax(1a) = 472
nm).8a,11 As observed for other carbo-benzenes, the carbo-
DATPs also exhibit a secondary band at higher wavelength
(with relative intensity 7 > 6 > 8 ≈ 9), close to the λmax value
60 of their DBA homologue in the range 600-650 nm.
15
Fig. 2 Molecular views of the carbo-DATP 6 (left) and carbo-DAPB 17
(right. For 18, see Fig. S1 in the SI).
The carbo-DAPB acyclic counterparts of 6-9 (Fig. 1) were
targeted from the triynedial 10,12 via the pentaynediol 11 and
20 pentaynedione 12, which reacted with selected Grignard or
lithium reagents to give the diols 13-16 (Scheme 2). As in the
cyclic series, while the acid-sensitive anilinyl derivatives 13
and 14 could not be purified, the indolylphenyl counterparts
15 and 16 were isolated in good yields.
NR2
Fig. 3 UV-vis spectra (in CHCl3) of the carbo-DATPs 6-9 (left) and
corresponding carbo-DAPBs 17-20 (right).
O
Ph
MeO
Ph
H
H
TIPS
OMe
Ph
TIPS
Emission spectra of 8-9 and 19-20 were compared to those of
65 the respective diol precursors 4-5 and 15-16 serving as
standards of the π-isolated fluorophoric units (λEm ≈ 330 nm
for phenylindole,14 λEm ≈ 340, 360 nm for phenylcarbazole).15
For the carbo-DATPs 8-9, the wavelengths are similar in both
absorption (486.5 0.5 nm) and emission (596 1 nm), and
70 markedly different from those of 4-5, in accordance with the
increase of the conjugation extent and with previous results on
N-arylcarbazole conjugates.16 The fluorescence intensity of 8-
9 is also much lower than that of 4-5, as expected from the
reciprocal increase of the absorbance intensity. The same
75 trends were observed for the carbo-DAPBs 19-20 vs 15-16.
O
10
Ph
1) 2 Li
2) H+
TIPS
NR2 = NH2, 17, 53 % (DCM)
= NMe2, 18, 29 % (Et2O)
= indolyl, 19, 74 % (DCM)
= carbazolyl, 20, 52 % (Et2O)
NR2
H
HO
Ph
MeO
OH
TIPS
TIPS
OMe
Ph
H
1) SnCl2/HCl (DCM or Et2O)
2) 1 M NaOH
11, 82 %
M (= Li, MgBr)
MnO2
DCM
R2N
1)
O
OH
Ph
MeO
Ph
MeO
TIPS
NR2
TIPS
TIPS
TIPS
OMe
Ph
HO
Ph
2) H+
OMe
O
NR2
12, quantitative
NR2 = N(TMS)2, 13, non-isolatedNR2 = indolyl, 15, 85 %
= NMe2, 14, non-isolated = carbazolyl, 16, 82 %
25
Scheme 2 Four-step synthesis of the carbo-DAPBs 17-20.
Table 1 Absorption (λmaxAbs) and emission (λEm, vs λexc) wavelengths of p-
N-indolyl- and p-N-carbazolyl-phenyl-substituted chromophores.a,b
Treatment of 13-16 with SnCl2/HCl, followed by aq. NaOH,
was optimized from insights gained in the carbo-DATP series.
Reaction of crude 13 in DCM thus afforded the N-desilylated
30 carbo-DAPB 17 as a dark-blue material in 53 % yield from
12. Reduction of 14, 16 to 18, 20 was found more efficient in
Et2O (29-52 % yields), while reduction of 15 to 19 was
optimized to a 74 % yield in DCM over a short reaction time.
Whereas NMR spectroscopy indicated that 17-20 occured as
35 mixtures of isomers, XRD analysis of crystals of 17 (Fig. 2)
and 18 (Fig. S1 in the SI) showed the all-trans isomers only.
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a In CHCl3 solutions, in nm units. Secondary bands are given in brackets.
b
λ
Em values do not vary upon shifting the λexc values to the λmaxAbs values.
80 Noteworthy, the λEm values of 19-20 (500 1 nm) are lower
2
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45 a CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de
than the λmaxAbs values, with formal anti-Stokes shifts of –
98 2 nm, thus confirming that the fluorescence of 19-20
arises from electronic transitions corresponding to secondary
bands of the absorption spectra, vibronically independent
from the DBA core-centered allowed main transition.9c,11
Electrochemical properties were finally investigated by
square-wave (SWV) and cyclic (CV) voltammetry (Table 2).
Similar reduction behaviors were observed in both series, with
two reversible waves (except for 7 and, perhaps, 9), possibly
Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France. Fax: +33 (0)5
61 55 30 03; Tel: +33 (0)5 61 33 31 13; E-mail: vmaraval@lcc-
toulouse.fr, chauvin@lcc-toulouse.fr
b Université de Toulouse, UPS, ICT-FR2599, F-31077 Toulouse, France.
50 c Kiev National Taras Shevchenko University, 60 Volodymlyrska St,
01033 Kiev, Ukraine.
5
† Electronic Supplementary Information (ESI) available: experimental
procedures, characterization and crystallographic details. CCDC 886379
(6), 886380 (17), 886381 (18). See DOI: 10.1039/b000000x/
55 ‡ The first oxidation waves of 17 and 18 are very intense, suggesting an
overlap of two one-electron processes at the remote anilinyl motifs. This
could not be confirmed by electrolysis because of product decomposition.
#This article is part of the ChemComm 'Aromaticity' web themed issue.
1 See for example: (a) I. K. Spiliopoulos and J. A. Mikroyannidis,
Macromolecules, 1998, 31, 515; (b) M. Aonuma, T. Oyamada, H.
Sasabe, T. Miki and C. Adachi, Appl. Phys. Lett., 2007, 90, 183503;
(c) M. Treier, R. Fasel, N. R. Champness, S. Argent and N. V.
Richardson, Phys. Chem. Chem. Phys., 2009, 11, 1209.
10 accompanied with an irreversible one. The first potential
varies over a broader range in the carbo-DAPB series (from –
0.75 V for 20 to –0.95 V for 18) than in the carbo-DATP
series (from –0.71 V for 8 to –0.85 V for 7), thus confirming
that the DBA core is more sensitive to substituent effects than
15 the carbo-benzene core. The indole derivatives (8-9, 19-20)
are more readily reduced than the aniline analogues (6, 17),
and still more than the dimethylaniline derivatives (7, 18).
This is consistent with the relative π-donating character of the
substituents. While indolyl substituents appear slightly less
20 electron-donating than OMe substituents (E1/2(1b) = 0.77
V),11 the limit of reducibility (even at scan rate of 10 V.s-1) is
reached for the most π-frustrated carbo-DATP 7.
In the oxidation regime, the cations of the less π-frustrated
carbo-DATPs 6 (Ep = 0.576 V), 8 (Ep = 1.050 V) and 9 (Ep =
25 1.416 V), were found to deposit on the electrode, as observed
for 1b which value (Ep = 0.90 V) confirms the intermediate
donating character of anisyl substituents vs anilinyl and
indolylphenyl substituents.11 The dimethylanilinyl homologue
7 is the most π-frustrated carbo-benzene reported to date, and
30 undergoes a reversible oxidation at 0.512 V. Finally, the first
oxidation potentials of the carbo-DAPBs 17-18 and 20 are
reversible and close to those of their carbo-DATP parents.‡
2 Elementary molecular units for opto-electronics consist in two bridged
electroactive ends and a bridge between them: E1-B-E2. In the binary
typology based on the donating (D) or accepting (A) nature of E1 and
E2, D-D (push-push) and A-A (pull-pull) systems can be regarded as
“π-frustrated”. In a ternary typology involving the π-electronic
richness of the bridge as well, D-D-D or A-A-A systems are thus
more π-frustrated than D-A-D or A-D-A counterparts. Beyond the
established nucleophilic character of the benzene ring, the π-donating
character of the carbo-benzene ring has been evidenced in the study
of its nonlinear optical properties: J.-M. Ducere, C. Lepetit, P. G.
Lacroix, J.-L. Heully and R. Chauvin, Chem. Mater., 2002, 14, 3332.
3 (a) H. Shinohara and M. Kotani, Bull. Chem. Soc. Jpn., 1980, 53,
3171; (b) R. Katoh, K. Suzuki, A. Furube, M. Kotani and K.
Tokumaru, J. Phys. Chem. C, 2009, 113, 2961.
4 R. Chauvin, C. Lepetit, V. Maraval and L. Leroyer, Pure Appl. Chem.,
2010, 82,769, and references therein.
5 . M. K. Cyranski, Chem. Rev. 2005, 105, 3773.
6 See for example: (a) L. Katz, D. W. Hein, J. E. Pretka and R. S. Long,
US Patent 2,852,556, sept. 16, 1958; (b) M. Rumi, J. E. Ehrlich, A.
A. Heikal, J. W. Perry, S. Barlow, Z. Hu, D. McCord-Maughon, T. C.
Parker, H. Röckel, S. Thayumanavan, S. R. Marder, D. Beljonne and
J.-L. Brédas, J. Am. Chem. Soc., 2000, 122, 9500; (c) E. Beaumont,
J.-C. Lambry, C. Gautier, A.-C. Robin, S. Gmouh, V. Berka, A.-L.
Tsai, M. Blanchard-Desce and A. Slama-Schwok, J. Am. Chem. Soc.,
2007,129, 2178.
Table 2 CV and SWV data for carbo-DATPs and carbo-DAPBs.a
7 (a) R. Chauvin, Tetrahedron Lett., 1995, 36, 397; (b) V. Maraval and R.
Chauvin, Chem. Rev., 2006, 106, 5317.
8 (a) R. Suzuki, H. Tsukude, N. Watanabe, Y. Kuwatani and I. Ueda,
Tetrahedron, 1998, 54, 2477; (b) C. Saccavini, C. Sui-Seng, L.
Maurette, C. Lepetit, S. Soula, C. Zou, B. Donnadieu and R.
Chauvin, Chem. Eur. J., 2007, 13, 4914; (c) C. Zou, C. Duhayon, V.
Maraval and R. Chauvin, Angew. Chem. Int. Ed., 2007, 46, 4337.
9 (a) V. Maraval, L. Leroyer, A. Harano, C. Barthes, A. Saquet, C.
Duhayon, T. Shinmyozu, and R. Chauvin, Chem. Eur. J., 2011, 17,
5086; (b) L. Leroyer, V. Maraval and R. Chauvin, Chem. Rev., 2012,
112, 1310; (c) A. Rives, V. Maraval, N. Saffon-Merceron and R.
Chauvin, submitted for publication (under revision).
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10 See for example: S.-D. Jeong, A. Nowak-Krol, Y. Kim, S.-J. Kim, D.
T. Gryko and C.-H. Lee, Chem. Commun., 2010, 46, 8737.
11 L. Leroyer, C. Lepetit, A. Rives, V. Maraval, N. Saffon-Merceron, D.
Kandaskalov, D. Kieffer and R. Chauvin, Chem. Eur. J., 2012, 18,
3226.
a
Measurements at r.t. in DCM, 0.1 M [n-Bu4N][PF6]; electrodes: Pt
35 (working), SCE (reference); scan rate: 0.2 V.s-1 unless otherwise noted. b
0.1 V.s-1. Observed at 10 V.s-1. Undetermined reversibility due to the
poor solubility of 9. e The oxidation product deposited on the electrode.
c
d
12 L. Leroyer, C. Zou, V. Maraval and R. Chauvin, C. R. Chimie, 2009,
12, 412.
Two series of “π-frustrated” carbo-benzenes and DBA acyclic
references have been compared.2 The relative stability of the
40 latter illustrates a secondary effect of the macro-aromaticity of
the former. Beyond the fundamental aspects, the “carbo-mer
principle”7 now calls for the study of their electro-optical
properties by comparison to their DATP and DAPB parents.
13 C. Saccavini, C. Tedeschi, L. Maurette, C. Sui-Seng, C. Zou, M.
Soleilhavoup, L. Vendier and R. Chauvin, Chem. Eur. J. 2007, 13,
4895.
14 Q. Li, S. Yu, Z. Li and J. Qin, J. Phys. Org. Chem. 2009, 22, 241.
15 S. M. Bonesi and R. Erra-Balsells, J. Luminescence, 2001, 93, 51.
16 F. Liang, T. Kurata, H. Nishide and J. Kido, J. Polym. Sci. A 2005, 43,
5765.
Notes and references
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