The synthesis of azaperylene-9,10-dicarboximides

Article abstract of DOI:10.1055/s-0030-1259060

The syntheses of two azaperylene 9,10-dicarboximides are presented. 1-Aza- and 1,6-diazaperylene 9,10-dicarboximides containing a 2,6-diisopropylphenyl substituent at the N-imide position were synthesized in two steps starting from naphthalene and isoquin

Full text of DOI:10.1055/s-0030-1259060

LETTER
3045
The Synthesis of Azaperylene-9,10-dicarboximides
Synthesis of
A
z
r
aperyle
n
i
e-9,10
s
-
dicarboxi
h
mide
s
a L. Andrew, Brett VanVeller, Timothy M. Swager*
Massachusetts Institute of Technology, Department of Chemistry, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Fax +1(617)2537929; E-mail: tswager@mit.edu
Received 4 October 2010
ing conjugated spacers between the metal center and PDI
p-system only yielded nonemissive complexes.7 Inspired
by the superior photophysical properties and high phos-
phorescence quantum yields of cyclometalated plati-
num(II), and ruthenium(II)–iridium(III) complexes,9 we
sought to synthesize PDI or PI analogues that contained a
2-phenylpyridine moiety that would eventually allow ac-
cess to cyclometalated perylene complexes.
Abstract: The syntheses of two azaperylene 9,10-dicarboximides
are presented. 1-Aza- and 1,6-diazaperylene 9,10-dicarboximides
containing a 2,6-diisopropylphenyl substituent at the N-imide posi-
tion were synthesized in two steps starting from naphthalene and
isoquinoline derivatives.
Key words: perylenes, isoquinolines, cross-coupling, cyclization,
oxidation
Along these lines, 1-azaperylene was previously synthe-
sized and reported to undergo directed C–H activation to
yield bay-functionalized 12-hydroxy-1-azaperylene,
which displayed excited state intramolecular proton trans-
fer (ESIPT).10 However, due to the lack of notable func-
tional groups in the perylene skeleton, a harsh anion-
radical cyclization of either 1- or 8-(a-naphthyl)isoquino-
line was necessary to generate the 1-azaperylene chro-
mophore. Moreover, we anticipated that the rigidity of 1-
azaperylene, combined with its lack of solubilizing
groups, would lead to complexes of poor solubility. In-
stead, we envisioned that (a) introduction of an electron-
withdrawing imide moiety to the azaperylene skeleton
would allow the use of a comparatively mild, base-pro-
moted cyclization procedure11,12 to synthesize the desired
azaperylene imides and that (b) introduction of bulky sub-
stituents at the N-imide position would greatly improve
the solubility of the chromophore. Additionally, the re-
sulting azaperylene imide chromophore would have ba-
thochromically shifted absorption and emission spectra
relative to the cyan-emitting 1-azaperylene.
Boasting brilliant colors, large extinction coefficients,
near-unity fluorescence quantum yields, and remarkable
photostability, perylene-based chromophores have found
unique prominence as dyes and pigments.1 Particularly,
perylene-3,4,9,10-tetracarboxdiimides (PDI, 1, Figure 1)
are suitable for demanding applications, such as photovol-
taic devices,2 dye lasers,3 light-emitting diodes,4 and
molecular switches.5 The related perylene-3,4-dicarbox-
imides (PI, 2) can be monofunctionalized more readily
than 1,6 which is interesting for certain applications, such
as fluorescence labeling and controlled conjugation to
other fluorophores.
R
O
N
O
R
N
O
O
O
N
O
N
O
N
N
O
N
Initially, a one-step synthesis of 1-azaperylene-9,10-di-
carboximide (3) by base-promoted heterocoupling of
naphthalene-1,8-dicarboximide and 1-chloroisoquinoline
was attempted, based on the previously reported one-pot
synthesis of terrylene diimides.12 However, only homo-
coupling between naphthalene-1,8-dicarboximide reac-
tants was observed and N,N¢-bis(2,6-diisopropylphenyl)
PDI was isolated in 80% yield. Therefore, a multistep ap-
proach to 3 and 4 was pursued. Precursors 7, 8, and 10
were synthesized by a one-pot Suzuki–Miyaura cross-
O
N
O
R
1
2
3
4
Figure 1 Structures of PDI, PI, and azaperylene imides
Although most of the aforementioned applications capi-
talize on the high fluorescence efficiencies of 1 and 2, ac-
cess to the PDI or PI triplet state represents a desirable
goal for some niche applications, such as solar energy
conversion,7 and as a method to generate deep red and/or
near IR phosphorescence. Previous attempts to directly at-
tach late transition metals to the perylene skeleton resulted
in minimal electronic interaction between the metal center
and PDI p-system.8 Moreover, it was found that introduc-
coupling between
a
4-bromonaphthalene-1,8-dicar-
boximide13 and either an isoquinoline derivative14 or a
2,7-naphthyridine derivative.15 The boronic ester deriva-
tive of bromide 5 was generated in situ by standard palla-
dium-catalyzed reaction with bis(pinacolato)diboron.
Subsequent addition of the corresponding isoquinoline or
2,7-naphthyridine coupling partner furnished precursors
7, 8, and 10 in good to high yield (Scheme 1). The use of
S-Phos was necessary in the cross-coupling reactions in-
volving 1-chloroisoquinoline and 1-chloro-2,7-naphthyri-
SYNLETT 2010, No. 20, pp 3045–3048
x
x
.x
x
.2
0
1
0
Advanced online publication: 24.11.2010
DOI: 10.1055/s-0030-1259060; Art ID: S06910ST
© Georg Thieme Verlag Stuttgart · New York

3046
T. L. Andrew et al.
LETTER
chromophores, which upon workup and oxidation formed
the desired products (Scheme 3). The individual reduced
forms of 3 and 4 generally displayed a greater resistance
to oxidation relative to their all-carbon perylene ana-
logues. For the base-promoted cyclization reactions of 7
and 10, stirring under air after a water workup yielded 3
and 4, respectively, after approximately one hour. In the
case of precursor 8, however, the yield of 3 was improved
if the workup procedure included hydrogen peroxide.
Based on this observation, we posit that leuco compound
14 is slightly more stable compared to leuco compound
13. Unfortunately, attempts to isolate and purify the vari-
ous reduced forms of 3 and 4 were unsuccessful, as the
OTf
N
O
N
O
N
6
Pd(dppf)Cl2,
B2pin2, KOAc
aq K2CO3
PhMe,
70 °C, 1 d
70 °C, 1 d
75% from 5
7
R
Cl
O
N
O
N
O
N
O
H
N
R
N
R
N
Pd2(dba)3,
S-Phos,
B2pin2, KOAc
O
O
O
O
O
N
O
aq K3PO4
base
11
80 °C, 1 d
88% from 5
1,4-dioxane,
70 °C, 12 h
H
H
H
Br
8
11
5
O
O
N
O
O
R
R
R
N
O
H
O
O
H
O
N
Cl
O
N
N
O
N
N
N
Pd2(dba)3,
S-Phos,
9
H2O, O2
base
B2pin2, KOAc
aq K3PO4
1,4-dioxane,
70 °C, 12 h
80 °C, 1 d
80% from 5
N
O
N
O
10
R
R
12
1
Scheme 1 Synthesis of precursors 7, 8, and 10
Ar
N
Ar
N
O
O
O
O
dine (9), as other phosphine ligands afforded low product
yields and resulted in extensive protodehalogenation.
In order to cyclize 7, 8, and 10, the base-promoted cy-
clization procedures described in the syntheses of extend-
ed rylene diimide chromophores were investigated.11,12 In
these examples, it is thought that nucleophilic attack of an
arylide anion initially generates the leuco form of the
chromophore 12, which subsequently oxidizes to form the
rylene skeleton (Scheme 2).16 Compounds 7 and 8, which
are both precursors to azaperylene imide 3, differ only in
the position at which the naphthalene imide and isoquino-
line rings are linked. We anticipated (a) that these isomer-
ic structures would display different amenabilities to the
initial arylide attack and (b) that the resulting isomeric
leuco forms of 3 would display varying stabilities to oxi-
dation.
i. base
ii. H2O
H
N
O
NH
7
13
Ar
Ar
N
O
O
H
N
O
i. base
ii. H2O
N
NH
Treatment of 7, 8, and 10 with K2CO3/ethanolamine and
subsequent heating initially resulted in the formation of
the reduced versions of the desired azaperylene imide
8
14
Scheme 2 Base-promoted cyclization of rylene imides
Synlett 2010, No. 20, 3045–3048 © Thieme Stuttgart · New York

LETTER
Synthesis of Azaperylene-9,10-dicarboximides
3047
i. K2CO3,
O
N
O
N
ethanolamine,
80 °C, 1 d
ii. H2O, O2
60%
7
O
N
O
N
i. K2CO3,
O
N
O
N
ethanolamine,
80 °C, 1 d
ii. 1% H2O2
3
77%
8
Figure 2 Absorption (grey) and emission (black) spectra of (A) 3
and (B) 4 in chloroform; the absorption and emission spectra of the
carbon analogue 2 (R = 2,6-diisopropylphenyl) is also superimposed
(dotted line)
O
N
N
O
N
O
N
N
O
i. K2CO3,
ethanolamine,
80 °C, 1 d
ii. H2O, O2
could be oxidized to yield 1-aza- and 1,6-diaza perylene-
9,10-dicarboximides. The azaperylene imides display
similar photophysical characteristics to their carbon ana-
logues. Studies into the cyclometalation of these chro-
mophores are currently under way.
80%
N
4
10
Scheme 3 Base-promoted cyclization to synthesize 3 and 4
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
azaperylene imides were inevitably obtained in most tri-
als.
Azaperylene imide 3 was very soluble in CH2Cl2, CHCl3,
MeOH, EtOH, and MeCN while 4 was very soluble in
MeOH and MeCN and only partially soluble in CHCl2
and CHCl3. The absorption and emission spectra of 3 and
4 are shown in Figure 2. Both azaperylene imides display
similar absorption and emission bands to the carbon ana-
logue 2 (R = 2,6-diisopropylphenyl). The fluorescence
quantum yield is 93% for both 3 and 4, compared to ca.
98% for 2. Additionally, the fluorescence lifetimes of all
three chromophores were also similar: 4.71 ns for 2, 4.82
ns for 3, and 4.94 ns for 4.
References and Notes
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were synthesized in two steps starting from naphthalene
imide and either an isoquinoline derivative or a 2,7-naph-
thyridine derivative. Base-promoted cyclization of bi-
naphthoid intermediates resulted in reduced versions of
the desired chromophores, which had a finite lifetime and
Synlett 2010, No. 20, 3045–3048 © Thieme Stuttgart · New York

3048
T. L. Andrew et al.
LETTER
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Synlett 2010, No. 20, 3045–3048 © Thieme Stuttgart · New York

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