Redox-Active Heteroacene Chromophores Derived from a Nonlinear Aromatic Diimide

Article abstract of DOI:10.1021/acs.joc.9b01502

This work describes a three-step chromatography-free protocol for the synthesis of a novel organic materials building block, dichlorinated mellophanic diimide (MDI), that is shown to undergo nucleophilic substitution with a variety of ortho disubstituted

Full text of DOI:10.1021/acs.joc.9b01502

Article
pubs.acs.org/joc
Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX
Redox-Active Heteroacene Chromophores Derived from a Nonlinear
Aromatic Diimide
Stella M. Luo, Kellie A. Stellmach, Stella M. Ikuzwe, and Dennis D. Cao*
Chemistry Department, Macalester College, 1600 Grand Avenue, Saint Paul, Minnesota 55105, United States
S
* Supporting Information
ABSTRACT: This work describes a three-step chromatog-
raphy-free protocol for the synthesis of a novel organic
materials building block, dichlorinated mellophanic diimide
(MDI), that is shown to undergo nucleophilic substitution
with a variety of ortho disubstituted benzenes to yield a series
of chromophores. Furthermore, 1,2,4,5-tetrasubstituted ben-
zenes can be used to synthesize tetraimide heteropentacene
derivatives endcapped by MDI motifs. The fine-tuning effects
of heteroatom identity were investigated by UV−vis and
fluorescence spectroscopy, cyclic and differential pulse
voltammetries, and density functional theory calculations. Oxidation of diamino MDI derivatives yields di- and tetraimide
functionalized azaacenes with significantly lowered LUMO levels (down to −4.49 eV), narrowed band gaps (down to 1.81 eV),
and high molar absorptivities (up to 84,000 M−1 cm−1).
linear PMDI, the angled MDI core positions are ortho to each
other and thus should be able to access a wider selection of
nucleophilic substitution and annulation reactivity. This
geometrical arrangement also sets the stage for directional
construction of extended aromatic π systems that are edge-
functionalized with diimides, which is compelling because it
has been shown recently that heteroacenes24−26 can be
stabilized by end-capping27,28 with benzo rings as an alternative
to modifying the central positions.29,30 With these attributes in
mind, we therefore targeted the preparation of halogenated
MDI derivatives that could serve as valuable building blocks for
novel organic materials.
The mellophanic diimide scaffold has been investigated
sparingly to date, with the literature focusing on its
incorporation into polyimides in place of pyromellitic
diimide.23,31,32 In these reports, the key precursor mellophanic
dianhydride (3-H) is derived from oxidation of either 1,2,3,4-
tetramethylbenzene33 or cyclohexene derivatives.32 A central
challenge of MDI synthesis is that incorrect cyclizations during
the reaction between amines and 3-H lead to phthalimide
derivatives instead of MDI ones. Fang et al.23 reported that a
two-step procedure involving ambient temperature amic acid
formation followed by acetic anhydride-activated imidization
avoided phthalimide formation completely (Scheme 1, route
B). It was argued that under the reaction conditions,
mellophanic dianhydride reacted regioselectively to afford the
desired MDIs. More recently, Yang et al.34 reported the elegant
Cu-catalyzed cycloaddition of 2 equiv of maleimide with
oximes to generate the MDI core. This method and other
INTRODUCTION
■
Linear aromatic diimides such as perylene, naphthalene, and
pyromellitic diimides are important building blocks in the
development of intense chromophores, n-type semiconductors,
and robust polymers.1−8 Research on these compounds has
focused on derivatization at both the imide and aromatic core
positions, with the latter being a more recent development.9−12
Some attention has also been paid to the preparation of other
aromatic diimides. The 1,2,5,6 structural isomer of NDI is
known,13 and recent synthetic developments have also enabled
the preparation of anthracene,14 pyrene,15 coronene,16 and
hexacene diimides,17,18 in addition to larger nanographene
polyimide systems.19,20
Over the course of our investigations into core-functional-
ization chemistry of pyromellitic diimide (PMDI),21 we
became interested in the other benzene diimide structural
isomer, which has been termed mellophanic diimide (MDI) in
the literature (Figure 1).22,23 We found this angled benzene
diimide isomer to be an interesting target because unlike the
Figure 1. Structures of naphthalene diimide (NDI), pyromellitic
diimide (PMDI), and mellophanic diimide (MDI).
Received: June 6, 2019
Published: July 18, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.9b01502
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the formation of nucleophilic aromatic substitution byproducts
in addition to incorrectly cyclized phthalimide derivatives. We
believe that the increased nucleophilicity of alkylamines
relative to arylamines together with the increase in electro-
philicity of the halogenated dianhydride leads to reduced
regioselectivity during amic acid formation. Attempting to use
higher reaction temperatures to drive the incorrectly cyclized
imides toward the diimide thermodynamic product23 was
unsuccessful because of undesired aryl halide substitution.
Next, we attempted solid-state dehydration of ammonium
carboxylate salts (Scheme 1, route A), which is an approach
that has been employed successfully in the synthesis of
benzene triimide.37 Heating (2-Cl)(RNH2)2 in a glass drying
oven at 110 °C for 2.5 days led to the desired transformation in
37% yield for R = Ph and 50% yield for R = Hex. Furthermore,
we found that Cl2-MDI-Hex was relatively insoluble in MeOH,
allowing us to simply triturate the crude reaction mixture to
remove undesired byproducts. With these optimized proce-
dures in hand, we were able to produce gram-scale quantities
of Cl2-MDI-Hex and begin an exploration of MDI substitution
chemistry.
We started by targeting both alkyl and aryl monodentate N-,
O-, and S-nucleophiles. Unlike halogenated NDIs and PDIs for
which alkoxide and thiolate nucleophiles react exclusively at
the aryl halide positions,4,12,38 the Cl2-MDI-Hex scaffold
proved to be unamenable to reaction with monodentate
nucleophiles because of the competitive ring-opening attack at
the cyclic imides. This reactivity difference can be attributed in
part to an increase in SNAr activation energy as a consequence
of the reduced size of the aromatic system in MDI. From one
of our attempts to react phenol and Cl2-MDI-Hex at high
temperatures in the presence of 1,8-diazabicyclo[5.4.0]undec-
7-ene (DBU), we unexpectedly isolated the product of
annulation between DBU and MDI (DBU-MDI, Scheme 2).
A literature search revealed that this mode of reactivity has
been observed for other electron-poor ortho dihaloarenes39 and
for both NDI40 and PDIs.41 This result encouraged us to focus
our efforts on bidentate nucleophiles instead.
In contrast to the monodentate nucleophiles, we found that
1,2-disubstituted benzenes (4-YZ, Y and Z = N, O, or S)
preferentially attacked the ortho aryl dichloride positions of
Cl2-MDI-Hex to yield the six possible disubstituted YZs in 50
to 91% yields. For bidentate nucleophiles with acidic protons,
reactivity was achieved between 20 and 60 °C in the presence
of DBU as the base. Formation of DBU-MDI was not detected
at these temperatures. To synthesize NN, it was most effective
to perform the reaction at 130 °C with an extra equivalent of
4-NN acting as the base. With these successes in hand, we then
reacted Cl2-MDI-Hex with two tetradentate nucleophiles
4,6-diaminoresorcinol (5) and 2,5-diaminobenzene-1,4-dithiol
(6)to yield the heteroatom-embedded pentacene derivatives
NONO and NSSN in 78 and 88% yields, respectively. For the
dihydro compounds NN and NSSN, oxidation by MnO2 in
CHCl3 produced the azaacene derivatives oxNN and oxNSSN,
respectively. All these MDI derivatives are soluble in common
organic solvents, with the tetraimides being more difficult to
solubilize (∼1 mg/mL in CH2Cl2) because of their increased π
surface areas.
Scheme 1. Development of New Synthetic Route toward X2-
MDI-R (X = H and Cl)
cycloaddition approaches,35,36 however, are limited in substrate
scope and are not suitable for producing halogenated MDIs.
RESULTS AND DISCUSSION
■
Synthesis. We set out to develop a viable synthetic
protocol for the preparation of dichlorinated MDIs (Cl2-MDI-
R). We initially assessed the literature preparation of H2-MDI-
Ph33 that entailed exhaustive oxidation of 1,2,3,4-tetramethyl-
benzene (1-H) with KMnO4 in pyridine to form tetracarbox-
ylic acid 2-H. This oxidation was followed by acetic anhydride
driven dehydration to form dianhydride 3-H and lastly
imidization to afford H2-MDI-R (Scheme 1, route A). While
the literature procedure for oxidation of 1,2,3,4-tetramethyl-
benzene was reproducible, it was a tedious reaction to perform
because it required small batchwise addition of a large excess of
KMnO4 to reduce the risk of uncontrolled exotherm. Through
reaction optimization, we found that the use of tert-butanol
instead of pyridine as the solvent allowed for the addition of
fewer total equivalents of KMnO4 and did not lead to any
significant exotherms even with large additions of the oxidant
to the reaction. To obtain the analogous dichlorinated
dianhydride 3-Cl, we first synthesized 1-Cl by chlorination
of 1,2,3,4-tetramethylbenzene with N,N′-dichlorohydantoin in
acetic acid before proceeding with the same oxidation and
dehydration protocol developed for 3-H.
In our hands, the literature method23 (Scheme 1, route B)
for the synthesis of H2-MDI-Ph from 3-H proceeded in 58%
yield. With the aim of producing MDIs with superior solubility
characteristics, we then targeted the synthesis of H2-MDI-Hex
by using hexylamine in place of aniline. To our surprise, this
subtle change reduced the imidization yield to only 5% (Table
1). We also applied this two-step method to 3-Cl and again
observed reduced yields, with Cl2-MDI-Ph and Cl2-MDI-Hex
being produced in only 10 and 3% yields, respectively (Table
1). In these lower yielding reactions with 3-Cl, we observed
Table 1. Synthetic Optimization toward X2-MDI-R
route
X
R
2-X to X2-MDI-R yield
route A
route A
route B
route B
route B
route B
Cl
Cl
H
Cl
H
Ph
Hex
Ph
Ph
Hex
Hex
37%
50%
58%
9%
3%
2%
Optical Properties. These MDI derivatives all exhibit
intense colors that reflect fine-tuning of absorption and
emission features in response to changes in heteroatom
substitution of the MDI core. Absorption spectra were
collected on dilute solutions of compounds in CH2Cl2 (Figure
Cl
B
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Article
Scheme 2. Synthesis of Substituted MDI Derivatives
neighboring imide CO. The absorption profiles of SO and
SS are very similar to each other, with λmax = 437 and 441 nm,
respectively. The molar absorptivity of SS, however, is higher
(εSS = 5,500 M−1 cm−1and εSO = 3,200 M−1 cm−1). Except for
the very weakly fluorescent NN, the emission profiles of YZs
are mirror images of the absorption profiles. A heavy atom
effect is also observed in which the S-containing derivatives
exhibit larger Stokes shifts compared to non-S-containing
MDIs.
The extension of π conjugation in NSSN (purple solid) and
NONO (red solid) leads to further red-shifting of absorption
features in comparison to NS and NO (λmaxNS = 500 to
λmaxNSSN = 549 nm and λmaxNO = 454 to λmaxNONO = 511 nm)
and an increase in molar absorptivity (εNS = 12,200 to εNSSN
=
18,400 M−1 cm−1 and εNO = 9,800 to εNONO = 13,400 M−1
cm−1).
The UV−vis spectra of the oxidized compounds oxNN and
oxNSSN exhibit significant changes compared to those of their
dihydro analogues (Figure 2c,d). Both compounds have molar
absorptivities higher than their dihydro analogs (εoxNN= 23,400
and εoxNSSN= 84,000 M−1cm−1). oxNN exhibits a significantly
blue-shifted absorption profile (λmaxoxNN = 404 vs λmaxNN = 538
nm), while the absorption of oxNSSN is red-shifted (λmaxoxNSSN
= 633 vs λmaxNSSN = 549 nm). Density functional theory
calculations (see below, Figure 4) predict that differences in
extent of HOMO stabilization are responsible for the opposing
shifts in absorption maxima.
Figure 2. (a) UV−vis absorption (solid thick lines) and (b) emission
(dashed lines) profiles of MDI derivatives in CH2Cl2. Changes in
absorption profile upon oxidation from (c) NN to oxNN and (d)
NSSN to oxNSSN in CH2Cl2 and the normalized emission profile of
oxNSSN in CH2Cl2 are also shown (dashed line).
Electrochemistry. Aromatic diimides are well-known to
undergo reversible one-electron reduction processes to reach
radical anionic and dianionic states. There have been no
previous investigations on electrochemical features of MDI, so
we sought to investigate them here using cyclic (CV) (Figure
3) and differential pulse (DPV) voltammetries (Figure S1).
Electrochemical experiments were conducted on about 1 mM
compound solutions in CH2Cl2 solutions with 0.1 M Bu4NPF6
supporting electrolyte and referenced to the ferrocene/
ferrocenium couple (Fc/Fc+) (Table 2). H2-MDI-Hex under-
2 and Table 2). YZs containing more electron-donating or
polarizable heteroatoms (NH > S > O) generally have more
red-shifted absorption features. OO is a pale yellow solid with
an electronic transition centered at λmax = 395 nm, while NN is
a red solid with a longest wavelength absorbance centered at
λmax = 538 nm. The absorption band of NN also features a
pronounced vibronic structure, perhaps due to increased
rigidity introduced by hydrogen bonding between the NH and
C
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Table 2. Summary of Optical and Electronic Properties
a
E / (V vs Fc/Fc+)
1
2
c
d
e
f
E1ox
E2ox
λmax
ε
λem
Eg
LUMO
(eV)
HOMO
b
compounds
E2r (V) E1r (V)
(V)
(V)
color
white
white
(nm)
(103 M−1 cm−1
)
(nm)
(eV)
(eV)
H2-MDI-Hex
Cl2-MDI-Hex
OO
SO
SS
NS
NO
NN
NSSN
NONO
oxNN
oxNSSN
−1.56
−1.34
−1.54
−3.33
−3.56
−3.38
−3.50
−3.46
−3.34
−3.26
−3.14
−3.41
−3.24
−4.21
−4.49
pale yellow
yellow
orange
red
395
437
441
500
454
538
549
511
404
633
8.9
3.2
5.5
12.2
9.8
7.4
18.4
13.4
23.4
84.0
487
522
567
614
560
641
2.70
2.40
2.23
2.02
2.22
1.97
1.83
2.04
2.56
1.81
−5.60
−5.90
−6.16
−5.35
−5.49
−5.10
−5.24
−5.28
−6.76
−6.30
−1.96
−2.01
−2.15
−2.15
−2.27
−2.15
−2.18
−1.30
−0.79
−1.45
−1.51
−1.60
−1.68
−1.80
−1.60
−1.72
−0.76
−0.53
1.14
1.26
0.76
0.89
0.46
0.52
0.60
orange
red
purple
red
orange
blue
g
0.78
0.86
h
h
g
663
a
b
c
About 1 mM analyte in CH2Cl2, 0.1 M Bu4NPF6. Values from DPV. Color in the solid state. Longest wavelength absorption maxima of analyte
in CH2Cl2 solution. Optical band gap estimated from the absorption onset. LUMO estimated from the reduction onset. HOMO = LUMO − Eg.
d
e
f
g
h
Irreversible. Two-electron process.
The derivatized MDI compounds retain redox activity. All
the YZs exhibit at least one reversible one-electron reduction
1
process. The E / of the first reduction process is shifted toward
2
more negative potentials by N atom incorporation, with NN
1
being the most difficult to reduce at E / = −1.80 V. Although
2
the difference is small, YZs containing S atoms undergo
reductions at slightly more positive potentials than the O-
containing analogues. The second one-electron reduction of
YZs is observed by DPV in all cases other than OO (Table 2)
at approximately −0.5 V more negative potential than the first
reduction. Because of the incorporation of electron-donating
atoms, oxidation processes are also observed for all YZs other
than OO. The CV of NN displays a reversible one-electron
1
oxidation (E / = 0.46 V) followed by a second irreversible
2
oxidation process. The remaining YZs only exhibit a single
reversible one-electron oxidation process, with SS being the
1
most difficult to oxidize (E / = 1.26 V).
2
The tetraimides undergo electrochemical behavior analo-
gous to their diimide analogues. NONO undergoes a one-
1
electron reduction at E / = −1.72 V and a one-electron
2
1
oxidation at E / = 0.60 V. Both the reduction and oxidation are
2
shifted to less positive potentials compared to those of NO,
which reflects the increased number of electron-donating
atoms on the central benzene ring. In contrast, NSSN exhibits
a reversible two-electron reduction process, while on oxidation,
Figure 3. Cyclic voltammograms of MDI derivatives collected on
about 1 mM solutions of analyte in CH2Cl2 with 0.1 M Bu4NPF6
electrolyte.
1
both a reversible one-electron (E / = 0.52 V) and an
2
irreversible one-electron oxidation process are observed.
Drastically shifted first reduction potentials are observed for
both azaacenes. The first reduction of oxNN takes place +1.04
V more easily than it does in NN. In addition, the second one-
electron reduction expected for MDIs is reversible for NN
1
goes a reversible one-electron reduction (E / = −1.56 V) that
2
occurs at significantly more negative potentials than the
analogous N,N′-dialkyl PMDI (E / = −1.35 V),42 NDI (E /
=
1
1
1
under CV conditions (E / = −1.30 V), unlike the analogous
2
2
2
−1.09 V),43 or PDI (E / = −0.98 V).3 In CH2Cl2 solution, the
1
process in X2-MDI-Hex and YZs. For oxNSSN, three
reversible reduction processes are observed, with the first
2
second reduction of H2-MDI-Hex takes place at the edge of
the electrochemical window of the solvent and is difficult to
observe reproducibly by CV. The inclusion of electronegative
Cl atoms in Cl2-MDI-Hex leads to a +220 mV shift of the first
reduction process, and additional irreversible reduction
processes are observed.
1
reduction (E / = −0.53 V) being a two-electron process, much
2
like the first reduction process in the dihydro analogue. No
oxidation processes were observed for these heteroacenes.
Computational Section. We also probed the electronic
structure of PMDI, MDI, and MDI derivatives using the
D
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density functional theory (DFT) on N-methylated analogues
of the compounds studied experimentally. The trends in DFT-
predicted band gaps of these compounds agree with the
EXPERIMENTAL SECTION
■
General Information. Reagents were purchased from TCI
Chemicals or Sigma-Aldrich and used as supplied. Anhydrous THF
was obtained from a Vacuum Atmospheres 103991 Solvent
Purification System. Reactions were heated using aluminum bead
baths in stainless steel bowls on a hot plate. Column chromatography
was performed using a Teledyne Isco Combiflash Rf+ and Silicycle
1
SiliaSep flash cartridges (normal phase, 40−63 μm, 60 Å). H NMR
and 13C NMR spectra were collected on a Bruker Avance III 400
MHz and referenced to residual solvent as the internal standard
1
(CDCl3: H - 7.26 ppm and 13C - 77.16 ppm, acetone-d6: 1H - 2.05
ppm and 13C - 29.84 ppm). High-resolution ESI-MS data were
collected on a Bruker BioTOF II ESI/TOF-MS (University of
Minnesota) or Agilent 6210A LCTOF high- resolution time-of-flight
mass spectrometer connected to an Agilent 1200 series HPLC
(Northwestern University).
Figure 4. Frontier molecular orbitals for N,N′-dimethyl PMDI, MDI,
and selected MDI derivatives (B3LYP/6-311+G(2d,p), isovalue =
0.03).
UV−vis data were collected with an Evolution 300 UV−vis
spectrophotometer. Fluorescence data were collected with a Cary
Eclipse fluorescence spectrophotometer. Cyclic and differential pulse
voltammetry experiments were performed using a Pine Research
WaveNow potentiostat equipped with a Pt working electrode (1.6
mm diameter disk, PCTFE shroud), Pt coil counter electrode
(PCTFE shroud), and nonaqueous reference electrode (Ag wire, 0.01
M AgNO3, 0.1 M Bu4NPF6, MeCN). Electrochemical samples (ca. 1.0
mM analyte, 0.1 M Bu4NPF6, CH2Cl2) were thoroughly deoxygenated
by bubbling Ar through the solutions. Ferrocene (Fc) was used as an
internal standard, and each sample was evaluated both with and
without Fc to ascertain that there were no significant interactions
between Fc and the analyte. Graphs were plotted with Veusz.
Computational calculations were performed using the Gaussian 09
software package, employing the B3LYP functional at the 6-
311+G(2d,p) level of theory. Structures and orbital isosurfaces
(isovalue = 0.03) were visualized with ChemCraft.
experimental data. The reduction in symmetry in going from
PMDI to MDI has significant consequences on the frontier
molecular orbitals (FMOs). The HOMO of MDI and its
dichlorinated derivative were found to be a σ-type MO (Figure
4 and Figure S2), whereas all the other MDI derivatives and
PMDI present typical π-type HOMOs. The LUMO of MDI is
higher in energy than the LUMO of PMDI, a finding that is in
agreement with the difference in experimentally determined
first reduction potentials. The distribution of the LUMO in
MDI is altered from the one in PMDI to include the entire
benzene core in addition to the imide N atoms.
The YZ compounds generally have similar FMO features,
with the LUMO largely located on the MDI portion of the
molecules, while the HOMO is distributed across all three six-
membered rings. In the asymmetric NO and NS, the LUMO is
distorted such that one of the imide carbonyls does not
participate in the conjugation (Figure S2). In SO, however,
this effect is reduced. These general trends extend to the
tetraimides NONO and NSSN, with the central ring of the
molecules being the biggest contributor to the HOMO, while
the LUMO occupies the MDI core. In oxNN and oxNSSN, the
extension of conjugation upon oxidation is evident since both
the HOMO and LUMO are distributed across the entire
heteroacene framework. While the LUMO levels of oxNN and
oxNSSN are stabilized by a similar amount relative to NN and
NSSN, respectively, oxNN has a significantly more stabilized
HOMO (E = −7.07 eV) than oxNSSN (E = −6.36 eV), thus
leading to the opposing direction of absorption shifts observed
by UV−vis spectroscopy.
Synthesis of 1-Cl44 (1,2-Dichloro-3,4,5,6-tetramethylben-
zene). Setup: A 250 mL round-bottom flask equipped with a
magnetic stir bar was charged with AcOH (100 mL), 1,2,3,4-
tetramethylbenzene (10.00 g, 11.11 mL, 74.50 mmol, 1 equiv), and
1,3-dichloro-5,5-dimethylhydantoin (18.35 g, 93.13 mmol, 1.25
equiv). The flask was then equipped with an air condenser left
open to the air. The reaction mixture was stirred at 90 °C for 2.5 h at
which point GC−MS indicated the complete consumption of 1,2,3,4-
tetramethylbenzene and monochlorinated intermediates. Workup:
Upon cooling to room temperature, the solids that formed were
collected by vacuum filtration and rinsed with AcOH until the filtrate
was colorless. The white solid was found to be 1-Cl (4.93 g, 24.28
mmol, 33% yield). Additional crops of material were precipitated from
the filtrate. However, these crops were contaminated substantially by
overchlorinated side products. Characterization: 1H NMR (400 MHz,
CDCl3-d): δ 2.39 (s, 3H), 2.23 (s, 3H). 13C{1H} NMR (101 MHz,
CDCl3): δ 134.7, 133.4, 130.3, 18.5, 17.4.
Synthesis of 2-Cl (5,6-Dichlorobenzene-1,2,3,4-tetracarbox-
ylic Acid). Setup: A 500 mL three-neck flask equipped with a
magnetic stir bar, and a water-cooled condenser was charged with 1-
Cl (5.34 g, 26.27 mmol, 1 equiv), tBuOH (60 mL), and H2O (60
mL). Subsequently, KMnO4 (20.77 g, 131.35 mmol, 5 equiv) was
added in one batch to the reaction mixture. The open necks were
sealed with glass stoppers, the condenser was left open, and the
reaction mixture was then refluxed gently with vigorous stirring until
the purple color of the solution faded, indicating complete
consumption of KMnO4. The reaction flask was removed from the
heating bath, and then more KMnO4 (20.77 g, 140.28 mmol, 5 equiv)
was added. The reaction mixture was refluxed gently with vigorous
stirring for 16 h at which point it was observed that the solution was
still purple in color. Workup: Before cooling to room temperature,
EtOH (10 mL) was added to quench the remaining KMnO4. Once
the purple color of KMnO4 disappeared, the reaction mixture was hot
filtered to remove the MnO2 byproduct. The solvents were distilled
off by rotary evaporation. The residue was then carefully redissolved
in concentrated HCl to obtain a solution with pH < 2. The excess
CONCLUSIONS
■
We have developed an efficient and convenient synthesis of
dichlorinated mellophanic diimide Cl2-MDI-Hex. This val-
uable building block was reacted with bi- and tetradentate aryl
N-, O-, and S-nucleophiles to construct colorful and redox-
active aromatic di- and tetraimides. The oxidation of the
dihydro compounds leads to heteroacenes with significantly
lowered LUMO levels and altered band gaps, which suggests
the potential of this class of compounds in n-type semi-
conductor applications. Further work on the synthesis of
extended MDI-containing azaacenes and investigations into
their solid-state characteristics are ongoing currently in our
laboratory.
E
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concentrated HCl and H2O were removed by rotary evaporation to
yield a white solid, consisting of what we presume to be a mixture of
product and KCl. Acetone (100 mL) was added to the residue, and
the mixture was stirred vigorously to break up the solid aggregates and
extract the product. The insoluble inorganic material was removed by
vacuum filtration, and the filtrate was evaporated to yield a white solid
that was found to be analytically pure 2-Cl (6.03 g, 18.66 mmol, 71%
yield). Characterization: 13C{1H} NMR (101 MHz, acetone-d6): δ
166.0, 165.4, 137.1, 132.9, 132.1. HRMS (ESI/QTOF) m/z: [M −
H]− calcd for C10H4Cl2O8, 320.9210; found, 320.9211.
Additional Notes: (1) Although pure 1-Cl was employed for the
protocol described here, our other experiments indicate that the
overchlorinated byproducts of the previous reaction step are oxidized
cleanly by this procedure to 2-Cl. (2) The change in the solution
color during oxidation was checked by dipping a glass rod into the
reaction mixture then dabbing it on paper. (3) Although we never
observed any significant exotherm when performing the second
addition of KMnO4 at or below the scale described here, caution
should be exercised whenever adding an oxidant to a hot reaction
mixture. (4) Performing this reaction on a 2.00 g scale of 1-Cl yielded
2.315 g of the product (73% yield).
complete dissolution of 2-Cl was achieved, 1-hexylamine (2.43 mL,
37.5 mmol, 2 equiv) was added, and the mixture was stirred for 15
min at which time a precipitate was observed. At this point, the stir
bar was removed from the flask, and the MeOH was distilled away by
rotary evaporation. The reaction flask was then placed in a glass
drying oven set at 110 °C for 66 h (one weekend). Over this time, the
solids in the flask changed from white to yellow in color. Workup:
Upon cooling to room temperature, MeOH (150 mL) was added to
the reaction mixture, and the solids were dispersed by sonication. A
white solid was collected by vacuum filtration and rinsed with MeOH
until the filtrate was no longer yellow in color. The solids were dried
in a 60 °C oven and found to be Cl2-MDI (4.20 g, 9.30 mmol, 50%
yield).
Route B. Setup: A 25 mL two-neck flask was equipped with a
magnetic stir bar and an Ar inlet. Under flowing Ar, the flask was
charged with 3-Cl (100 mg, 348 μmol, 1 equiv), anhydrous THF (3
mL), and 1-hexylamine (73 μL, 732 μmol, 2.1 equiv). The open neck
was sealed with a glass stopper, and the reaction mixture was stirred at
room temperature for 6 h. At this point, Ac2O (493 μL, 5.22 mmol,
15 equiv) and Et3N (243 μL, 1.74 mmol, 5 equiv) were added to the
reaction mixture, which was then stirred for a further 16 h at room
temperature under Ar. Workup: DI water (10 mL) was added to the
reaction mixture, and the suspension was then extracted with CH2Cl2
(10 mL × 3). The combined organic layers were dried over MgSO4,
and the volatiles were evaporated under reduced pressure.
Purification: The residue was purified by column chromatography
on SiO2 (eluent: CH2Cl2) to yield Cl2-MDI-Hex as a yellow solid (5
mg, 11 μmol, 3% yield).
Synthesis of 3-Cl (4,5-Dichlorobenzo[1,2-c:3,4-c′]difuran-
1,3,6,8-tetraone). Setup: A 100 mL round-bottom flask equipped
with a magnetic stir bar was charged with 2-Cl (400 mg, 1.24 mmol, 1
equiv) and Ac2O (3 mL, 31.70 mmol, 25.6 equiv). The reaction
mixture was stirred at 115 °C for 2 h. Complete dissolution of the
suspension was observed when the heating bath reached 60 °C.
Workup: Upon cooling to room temperature, the volatiles were
distilled off by rotary evaporation to yield a yellow solid that was
found to be 3-Cl (309 mg, 1.08 mmol, 87% yield). Characterization:
13C{1H} NMR (101 MHz, acetone-d6): δ 159.4, 157.5, 139.4, 136.8,
1
Characterization: H NMR (400 MHz, CDCl3): δ 3.75 (t, J = 7.3
Hz, 4H), 1.69 (p, J = 7.7 Hz, 4H), 1.40−1.23 (m, 13H), 0.94−0.81
(m, 5H). 13C{1H} NMR (100 MHz, CDCl3): δ 164.0, 162.4, 137.0,
133.6, 127.6, 39.3, 31.4, 28.3, 26.6, 22.6, 14.2. HRMS (ESI/QTOF)
m/z: [M + Na]+ calcd for C22H26Cl2N2O4Na, 475.1162; found,
475.1155.
128.7. HRMS (ESI/QTOF) m/z: [M + H]+ calcd for C10HCl2O6,
286.9145; found, 286.9154.
Synthesis of Cl2-MDI-Ph (4,5-Dichloro-2,7-diphenylpyrrolo-
[3,4-e]isoindole-1,3,6,8(2H,7H)-tetraone). Route A. Setup: A 50
mL round-bottom flask equipped with a magnetic stir bar was charged
with 2-Cl (50 mg, 155 μmol, 1 equiv) and MeOH (20 mL). Once
complete dissolution of 2-Cl was achieved, (28 μL, 310 μmol, 2
equiv) aniline was added, and the mixture was stirred for 15 min. The
stir bar was then removed from the flask, and the MeOH was distilled
away by rotary evaporation. The reaction flask was then placed in a
glass drying oven set at 110 °C for 48 h. Purification: Upon cooling to
room temperature, the residue was purified by column chromatog-
raphy on SiO2 (eluent: CH2Cl2) to yield Cl2-MDI-Ph as a yellow
solid (25 mg, 57 μmol, 37% yield).
Synthesis of H2-MDI-Ph23 (2,7-Diphenylpyrrolo[3,4-e]-
isoindole-1,3,6,8(2H,7H)-tetraone). Setup: A 25 mL two-neck
flask was equipped with a magnetic stir bar and an Ar inlet. Under
flowing Ar, the flask was charged with 3-H (100 mg, 459 μmol, 1
equiv), anhydrous DMAc (3 mL), and aniline (84 μL, 917 μmol, 2
equiv). The open neck was sealed with a glass stopper, and the
reaction mixture was stirred at room temperature for 6 h. At this
point, Ac2O (650 μL, 6.88 mmol, 15 equiv) and Et3N (320 μL, 2.29
mmol, 5 equiv) were added to the reaction mixture, which was then
stirred for a further 16 h at room temperature under Ar. Workup: DI
water (30 mL) was added to the reaction mixture to precipitate a
brown solid, which was collected by vacuum filtration. Purification:
This residue was purified by column chromatography on SiO2
(eluent: CH2Cl2) to yield Ph-MDI-Hex as a white solid (113 mg,
308 μmol, 67% yield). Characterization: 1H NMR (400 MHz,
CDCl3): δ 8.39 (s, 2H), 7.57−7.51 (m, 4H), 7.51−7.43 (m, 6H).
13C{1H} NMR (101 MHz, CDCl3): δ 165.5, 163.0, 137.7, 131.2,
Route B. Setup: A 25 mL two-neck flask was equipped with a
magnetic stir bar and an Ar inlet. Under flowing Ar, the flask was
charged with 3-Cl (100 mg, 348 μmol, 1 equiv), anhydrous THF (3
mL), and aniline (67 μL, 732 μmol, 2.1 equiv). The open neck was
sealed with a glass stopper, and the reaction mixture was stirred at
room temperature for 6 h. At this point, Ac2O (493 μL, 5.22 mmol,
15 equiv) and Et3N (243 μL, 1.74 mmol, 5 equiv) were added to the
reaction mixture, which was then stirred for a further 16 h at room
temperature under Ar. Workup: DI water (10 mL) was added to the
reaction mixture, and the suspension was then extracted with CH2Cl2
(10 mL × 3). The combined organic layers were dried over MgSO4,
and the volatiles were evaporated under reduced pressure.
Purification: The residue was purified by column chromatography
on SiO2 (eluent: CH2Cl2) to yield Cl2-MDI-Ph as a yellow solid (15
mg, 34 μmol, 10% yield).
129.4, 129.3, 128.9, 128.6, 126.6.
Synthesis of H2-MDI-Hex (2,7-Dihexylpyrrolo[3,4-e]-
isoindole-1,3,6,8(2H,7H)-tetraone). Setup: A 25 mL two-neck
flask was equipped with a magnetic stir bar and an Ar inlet. Under
flowing Ar, the flask was charged with 3-H (100 mg, 459 μmol, 1
equiv), anhydrous DMAc (3 mL), and 1-hexylamine (121 μL, 917
μmol, 2 equiv). The open neck was sealed with a glass stopper, and
the reaction mixture was stirred at room temperature for 6 h. At this
point, Ac2O (650 μL, 6.88 mmol, 15 equiv) and Et3N (320 μL, 2.29
mmol, 5 equiv) were added to the reaction mixture, which was then
stirred for a further 16 h at room temperature under Ar. Workup: DI
water (30 mL) was added to the reaction mixture, and the suspension
was then extracted with CH2Cl2 (10 mL × 3). The combined organic
layers were dried over MgSO4, and the volatiles were evaporated
under reduced pressure. Purification: The residue was purified by
column chromatography on SiO2 (eluent: CH2Cl2) to yield H2-MDI-
Hex as a white solid (8 mg, 23 μmol, 5% yield). Characterization: 1H
NMR (400 MHz, CDCl3): δ 8.17 (s, 2H), 3.74 (t, J = 7.3 Hz, 4H),
1
Characterization: H NMR (400 MHz, CDCl3): δ 7.57−7.50 (m,
4H), 7.49−7.42 (m, 6H). 13C{1H} NMR (101 MHz, CDCl3): δ
162.9, 161.1, 138.1, 133.6, 130.8, 129.5, 129.1, 127.5. HRMS (ESI/
QTOF) m/z: [M + Na]+ calcd for C22H10Cl2N2O4Na, 458.9910;
found, 458.9907.
Synthesis of Cl2-MDI-Hex (4,5-Dichloro-2,7-dihexylpyrrolo-
[3,4-e]isoindole-1,3,6,8(2H,7H)-tetraone). Route A. Setup: A 250
mL round-bottom flask equipped with a magnetic stir bar was charged
with 2-Cl (6.05 g, 18.8 mmol, 1 equiv) and MeOH (150 mL). Once
F
DOI: 10.1021/acs.joc.9b01502
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
1.69 (p, J = 7.9 Hz, 4H), 1.39−1.24 (m, 6H), 0.87 (t, J = 7.1 Hz, 3H).
13C{1H} NMR (101 MHz, CDCl3): δ 166.7, 164.3, 137.6, 128.6,
128.2, 38.9, 31.4, 28.4, 26.61, 22.60, 14.1. HRMS (ESI/QTOF) m/z:
[M + Na]+ calcd for C22H28N2O4Na, 407.1941; found, 407.1944.
Synthesis of OO (2,5-Dihexylbenzo[5,6][1,4]dioxino[2,3-
e]pyrrolo[3,4-g]isoindole-1,3,4,6(2H,5H)-tetraone). Setup: A 5
mL round-bottom flask equipped with a magnetic stir bar was charged
with Cl2-MDI-Hex (20 mg, 44 μmol, 1 equiv), catechol (5 mg, 49
μmol, 1.1 equiv), DMF (1 mL), and DBU (15 μL, 97 μmol, 2.2
equiv). A precipitate was formed immediately. The reaction mixture
was stirred at 60 °C for 20 h. Workup: Upon cooling to room
temperature, DI water (20 mL) was added to the reaction mixture.
The yellow precipitate was collected by vacuum filtration and dried
under air. Purification: The solid was purified by column
chromatography on SiO2 (eluent: CH2Cl2) to yield OO as a pale
yellow solid (15 mg, 30 μmol, 69% yield). Characterization: 1H NMR
(400 MHz, CDCl3): δ 7.15−7.05 (m, 4H), 3.69 (t, J = 7.2 Hz, 4H),
1.66 (p, J = 7.2 Hz, 1H), 1.37−1.25 (m, 3H), 0.87 (t, J = 6.8 Hz, 1H).
13C{1H} NMR (101 MHz, CDCl3): δ 166.2, 164.5, 163.4, 163.2,
and the suspension was extracted with CH2Cl2 (10 mL). The organic
layer was dried over MgSO4, and the volatiles were evaporated under
reduced pressure. Purification: The residue was purified by column
chromatography on SiO2 (eluent: CH2Cl2) to yield SS as an orange
1
solid (35 mg, 66 μmol, 61% yield). Characterization: H NMR (400
MHz, CDCl3): δ 7.45 (AA′BB′, JAB = 7.35 Hz, JAB′ = 1.65 Hz, 2H),
7.31 (AA′BB′, JAB = 7.35 Hz, JAB′ = 1.65 Hz, 2H), 3.73 (t, J = 7.3 Hz,
4H), 1.68 (p, J = 8 Hz, 4H), 1.37−1.24 (m, 12H), 0.88 (t, J = 7.0 Hz,
6H). 13C{1H} NMR (101 MHz, CDCl3): δ 166.1, 163.6, 141.7, 130.9,
130.1, 129.3, 129.3, 126.6, 39.0, 31.5, 28.4, 26.62, 22.59, 14.2. HRMS
(ESI/QTOF) m/z: [M + Na]+ calcd for C28H30N2O4S2Na, 545.1539;
found, 545.1597.
Synthesis of NS (2,5-Dihexyl-1H-dipyrrolo[3,4-a:3′,4′-c]-
phenothiazine-1,3,4,6(2H,5H,12H)-tetraone). Setup: A 20 mL
glass vial equipped with a magnetic stir bar was charged with Cl2-
MDI-Hex (50 mg, 110 μmol, 1 equiv), 2-aminobenzenethiol (17 mg,
14 μL, 132 μmol, 1.2 equiv), DMF (2 mL), and DBU (41 μL, 276
μmol, 2.5 equiv). The reaction mixture was stirred at room
temperature for 20 h. Workup: DI water (20 mL) was added to the
reaction mixture. The red precipitate was collected by vacuum
filtration and dried under air. Purification: The solid was purified by
column chromatography on SiO2 (eluent: CH2Cl2) to yield NS as an
orange solid (26 mg, 51 μmol, 50% yield). Characterization: 1H NMR
(400 MHz, CDCl3): δ 8.61 (s, 1H), 6.95 (td, J = 7.5, 2.0 Hz, 1H),
6.86−6.75 (m, 2H), 6.46 (d, J = 7.9 Hz, 1H), 3.61 (t, J = 7.3 Hz, 2H),
3.60 (t, J = 7.3 Hz, 2H), 1.62 (p, J = 7.3 Hz, 4H), 1.29 (m, 12H), 0.87
(t, J = 6.4 Hz, 3H), 0.86 (t, J = 6.6 Hz, 3H). 13C{1H} NMR (101
MHz, CDCl3): δ 169.5, 166.3, 163.6, 163.4, 141.8, 133.8, 128.8,
128.4, 127.7, 126.9, 126.3, 125.0, 119.6, 116.5, 115.1, 110.5, 38.6,
38.1, 31.5, 28.4, 28.3, 26.6, 22.59, 22.58, 14.1. HRMS (ESI/QTOF)
m/z: [M + Na]+ calcd for C28H31N3O4SNa, 528.1927; found,
528.1925.
151.0, 148.0, 130.4, 129.4, 127.8, 127.4, 127.1, 126.5, 123.2, 120.1,
118.8, 114.1, 38.9, 38.8, 31.5, 31.4, 28.4, 28.3, 26.62, 26.59, 22.6, 14.2.
HRMS (ESI/QTOF) m/z: [M + Na]+ calcd for C28H30N2O6Na,
513.1996; found, 513.1975.
Synthesis of NO (2,5-Dihexyl-1H-dipyrrolo[3,4-a:3′,4′-c]-
phenoxazine-1,3,4,6(2H,5H,12H)-tetraone). Setup: A 20 mL
glass vial equipped with a magnetic stir bar was charged with Cl2-
MDI-Hex (50 mg, 110 μmol, 1 equiv), 2-aminophenol (14 mg, 132
μmol, 1.2 equiv), DMF (2 mL), and DBU (41 μL, 276 μmol, 2.5
equiv). The vial was capped, and the reaction mixture was stirred at
room temperature for 20 h. Workup: DI water (20 mL) and 1 M HCl
(2 mL) were added to the reaction mixture, and the suspension was
extracted with CH2Cl2 (10 mL). The organic layer was dried over
MgSO4, and the volatiles were evaporated under reduced pressure.
Purification: The residue was purified by column chromatography on
SiO2 (eluent: CH2Cl2) to yield NO as an orange solid (40 mg, 82
Synthesis of NN (2,5-Dihexyl-7,12-dihydrodipyrrolo[3,4-
a:3′,4′-c]phenazine-1,3,4,6(2H,5H)-tetraone). Setup: A 50 mL
three-neck flask was equipped with a magnetic stir bar and an Ar inlet.
Under flowing Ar, the flask was charged with Cl2-MDI-Hex (150 mg,
330 μmol, 1 equiv), 1,2-phenylenediamine (72 mg, 663 μmol, 2
equiv), and deoxygenated anhydrous DMF (10 mL). The open necks
were sealed with glass stoppers, and the reaction mixture was stirred at
130 °C for 6 h. Workup: Upon cooling to room temperature, DI
water (30 mL) was added to the reaction mixture. The red precipitate
was collected by vacuum filtration and dried under air. Purification:
The solid was purified by column chromatography on SiO2 (eluent:
CH2Cl2) to yield NN as an orange solid (93 mg, 191 μmol, 58%
1
μmol, 75% yield). Characterization: H NMR (400 MHz, CDCl3): δ
7.87 (s, 1H), 7.04−6.77 (m, 3H), 6.57 (d, J = 7.8 Hz, 1H), 3.61 (q, J
= 7.0 Hz, 4H), 1.76−1.42 (m, 4H), 1.28 (d, J = 4.4 Hz, 12H), 0.86 (t,
J = 5.4 Hz, 3H), 0.85 (t, J = 5.4 Hz, 3H). 13C{1H} NMR (101 MHz,
CDCl3): δ 168.4, 164.5, 163.40, 163.36, 145.5, 142.2, 135.4, 126.3,
126.0, 124.6, 123.1, 120.4, 118.2, 117.3, 115.2, 112.5, 38.5, 38.4, 31.5,
31.4, 28.4, 28.3, 26.58, 26.56, 22.6, 14.1. HRMS (ESI/QTOF) m/z:
[M + Na]+ calcd for C28H31N3O5Na, 512.2156; found, 512.2181.
Synthesis of SO (2,5-Dihexylbenzo[5,6][1,4]oxathiino[2,3-
e]pyrrolo[3,4-g]isoindole-1,3,4,6(2H,5H)-tetraone). Setup: A 20
1
yield). Characterization: H NMR (400 MHz, CDCl3): δ 7.86 (s,
2H), 6.71 (AA′BB′, JAB = 7.5 Hz, JAB′ = 1.6 Hz, 2H), 6.39 (AA′BB′,
mL glass vial equipped with a magnetic stir bar was charged with Cl2-
MDI-Hex (50 mg, 110 μmol, 1 equiv), 2-hydroxybenzenethiol (17
mg, 14 μL, 132 μmol, 1.2 equiv), DMF (2 mL), and DBU (41 μL,
276 μmol, 2.5 equiv). A precipitate was formed immediately. The
reaction mixture was stirred at room temperature for 20 h. Workup:
DI water (20 mL) was added to the reaction mixture. The yellow
precipitate was collected by vacuum filtration and dried under air.
Purification: The solid was purified by column chromatography on
SiO2 (eluent: CH2Cl2) to yield SO as a yellow solid (51 mg, 100
J
AB = 7.5 Hz, JAB′ = 1.6 Hz, 2H), 3.59 (t, J = 7.2 Hz, 4H), 1.62 (p, J =
7.2 Hz, 4H), 1.33−1.24 (m, 6H), 0.87 (t, J = 6.5 Hz, 6H). 13C{1H}
NMR (101 MHz, CDCl3): δ 168.8, 163.7, 137.6, 128.5, 124.7, 120.2,
115.1, 108.6, 38.3, 31.5, 28.5, 26.62, 22.62, 14.2. HRMS (ESI/
QTOF) m/z: [M + Na]+ calcd for C28H32N4O4Na, 511.2316; found,
511.2315.
Synthesis of NSSN (2,5,11,14-Tetrahexyl-9,18-
dihydrodipyrrolo[3,4-a:3′,4′-c]pyrrolo[3″,4″:6′,7′]isoindolo-
[4′,5′:5,6][1,4]thiazino[3,2-i]phenothiazin-1,3,4,6,10,12,13,15-
(2H,5H,11H,14H)-octaone). Setup: A 50 mL three-neck flask was
1
μmol, 91% yield). Characterization: H NMR (400 MHz, CDCl3): δ
7.21−7.15 (m, 1H), 7.13−7.02 (m, 3H), 3.68 (t, J = 7.3 Hz, 4H),
1.67 (p, J = 7.2 Hz, 4H), 1.39−1.22 (m, 12H), 0.87 (t, J = 6.9 Hz,
4H). 13C{1H} NMR (101 MHz, CDCl3): δ 166.2, 164.5, 163.4, 163.2,
151.0, 148.0, 130.4, 129.4, 127.8, 127.4, 127.1, 126.5, 123.2, 120.1,
118.8, 114.1, 38.9, 38.8, 31.5, 31.4, 28.4, 28.3, 26.62, 26.59, 22.6, 14.2.
HRMS (ESI/QTOF) m/z: [M + Na]+ calcd for C28H30N2O5SNa,
529.1768; found, 529.1801.
equipped with a magnetic stir bar and an Ar inlet. Under flowing Ar,
the flask was charged with Cl2-MDI-Hex (150 mg, 330 μmol, 2.1
equiv), 2,5-diaminobenzene-1,4-dithiol dihydrochloride (40 mg, 158
μmol, 1 equiv), deoxygenated anhydrous DMF (5 mL), and DBU
(117 μL, 789 μmol, 5 equiv). The open necks were sealed with glass
stoppers, and the reaction mixture was stirred at 60 °C for 5 h.
Workup: Upon cooling to room temperature, MeOH (20 mL) was
added to the reaction mixture. The purple precipitate was collected by
vacuum filtration and dried in a 110 °C oven to remove trace DMF.
This purple solid was found to be NSSN (114 mg, 139 μmol, 88%
Synthesis of SS (2,5-Dihexylbenzo[5,6][1,4]dithiino[2,3-e]-
pyrrolo[3,4-g]isoindole-1,3,4,6(2H,5H)-tetraone). Setup: A 20
mL glass vial equipped with a magnetic stir bar was charged with Cl2-
MDI-Hex (50 mg, 110 μmol, 1 equiv), 1,2-benzenedithiol (19 mg, 15
μL, 132 μmol, 1.2 equiv), DMF (2 mL), and DBU (41 μL, 276 μmol,
2.5 equiv). The reaction mixture was stirred at room temperature for
20 h. Workup: DI water (20 mL) was added to the reaction mixture,
1
yield). Characterization: H NMR (400 MHz, CDCl3): δ 8.60 (s,
2H), 6.09 (s, 2H), 3.72−3.52 (m, 8H), 1.64 (d, J = 8.2 Hz, 8H), 1.29
(t, J = 4.3 Hz, 24H), 0.87 (t, J = 3.5 Hz, 12H). 13C{1H} NMR (101
MHz, CDCl3): δ 163.5, 163.3, 140.9, 130.8, 129.0, 119.8, 115.8,
G
DOI: 10.1021/acs.joc.9b01502
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The Journal of Organic Chemistry
Article
114.1, 111.1, 103.0, 77.5, 38.7, 38.6, 31.5, 28.4, 26.62, 26.60, 22.61,
14.2. HRMS (ESI/QTOF) m/z: [M
C50H56N6O8S2Na, 955.3493; found, 955.3494.
Synthesis of NONO (2,5,11,14-Tetrahexyl-16,18-
dihydrodipyrrolo[3,4-a:3′,4′-c]pyrrolo[3″,4″:6′,7′]isoindolo-
[4′,5′:5,6][1,4]oxazino[2,3-i]phenoxazin-1,3,4,6,10,12,13,15-
(2H,5H,11H,14H)-octaone). Setup: A 50 mL three-neck flask was
Characterization: 1H NMR (400 MHz, CDCl3): δ 4.77 (t, J = 6.0 Hz,
2H), 3.66 (t, J = 7.4 Hz, 2H), 3.66 (t, J = 7.3 Hz, 2H), 3.53−3.48 (m,
2H), 3.48−3.44 (m, 2H), 3.41 (t, J = 5.7 Hz, 2H), 2.22 (p, J = 5.7 Hz,
2H), 1.99 (p, J = 5.8 Hz, 2H), 1.92 (p, J = 5.8 Hz, 1H), 1.67 (dt, J =
14.8, 7.2 Hz, 4H), 1.40−1.22 (m, 12H), 0.91−0.82 (m, 6H). 13C{1H}
NMR (101 MHz, CDCl3): δ 169.1, 167.7, 166.3, 165.6, 153.6, 133.7,
132.0, 122.6, 119.8, 115.4, 114.9, 98.8, 54.2, 49.1, 45.5, 38.4, 38.2,
31.6, 31.6, 28.8, 28.7, 28.6, 26.8, 26.7, 26.0, 24.4, 22.7, 22.6, 14.2.
HRMS (ESI/QTOF) m/z: [M + Na]+ calcd for C31H36N4O6Na,
583.2527; found, 583.3801.
+
Na]+ calcd for
equipped with a magnetic stir bar and an Ar inlet. Under flowing Ar,
the flask was charged with Cl2-MDI-Hex (104 mg, 220 μmol, 2.1
equiv), 4,6-diaminoresorcinol dihydrochloride (22 mg, 105 μmol, 1
equiv), deoxygenated anhydrous DMF (3 mL), and DBU (78 μL, 526
μmol, 5 equiv). The open necks were sealed with glass stoppers, and
the reaction mixture was stirred at 60 °C for 16 h. Workup: Upon
cooling to room temperature, MeOH (10 mL) was added to the
reaction mixture. The red precipitate was collected by vacuum
filtration and dried in a 110 °C oven to remove trace DMF. This red
solid was found to be NONO (74 mg, 82 μmol, 74% yield).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.9b01502.
■
S
Differential pulse voltammograms, computational re-
sults, and copies of 1H and 13C NMR spectra reported in
the experimental section (PDF)
1
Characterization: H NMR (400 MHz, CDCl3): δ 7.84 (s, 2H), 6.70
(s, 1H), 5.96 (s, 1H), 3.65 (t, J = 7.2 Hz, 8H), 1.76−1.60 (m, 8H),
1.38−1.22 (m, 24H), 0.90 (t, J = 6.6 Hz, 6H), 0.91 (t, J = 6.6 Hz,
6H). 13C{1H} NMR (101 MHz, CDCl3): δ 168.4, 164.2, 163.3, 144.6,
137.9, 134.5, 123.9, 123.3, 121.1, 118.7, 113.1, 76.8, 38.7, 31.51,
31.47, 28.44, 28.35, 26.62, 26.60, 22.62, 22.62, 14.2. HRMS (ESI/
QTOF) m/z: [M + Na]+ calcd for C50H56N6O10Na, 923.3959; found,
923.3959.
Synthesis of oxNSSN (2,5,11,14-Tetrahexyldipyrrolo[3,4-
a:3′,4′-c]pyrrolo[3″,4″:6′,7′]isoindolo[4′,5′:5,6][1,4]thiazino-
[3,2-i]phenothiazin-1,3,4,6,10,12,13,15(2H,5H,11H,14H)-oc-
taone). Setup: A 25 mL round-bottom flask equipped with a
AUTHOR INFORMATION
Corresponding Author
*E-mail: dcao@macalester.edu.
■
ORCID
Dennis D. Cao: 0000-0002-0315-1619
Notes
This publication first appeared as a preprint on ChemRxiv.45
The authors declare no competing financial interest.
magnetic stir bar was charged with NSSN (21 mg, 23 μmol, 1 equiv),
CHCl3 (10 mL), and MnO2 (24 mg, 276 μL, 12 equiv). The reaction
mixture was stirred at room temperature for 2 h. A color change was
observed within 5 min of MnO2 addition. Workup: The reaction
mixture was filtered to remove MnO2, and the filtrate was evaporated
to yield a blue/purple solid that was found to be oxNSSN (18 mg, 20
ACKNOWLEDGMENTS
■
This work was made by possible by a Precollege and
Undergraduate Science Education Program Award from the
Howard Hughes Medical Institute, the Violet Olson Beltmann
Fund, and Collaborative Summer Research Funds from
Macalester College. Acknowledgment is made to the Donors
of the American Chemical Society Petroleum Research Fund
for the support of this research. Computational resources were
provided by an NSF-MRI award #CHE-1039925 through the
Midwest Undergraduate Computational Chemistry Consorti-
um (MU3C). This work made use of the IMSERC at
Northwestern University, which has received support from the
Soft and Hybrid Nanotechnology Experimental (SHyNE)
Resource (NSF ECCS-1542205), the State of Illinois, and the
International Institute for Nanotechnology (IIN).
1
μmol, 85% yield). Characterization: H NMR (400 MHz, CDCl3): δ
7.38 (s, 2H), 3.74 (t, J = 7.3 Hz, 4H), 3.73 (t, J = 7.3 Hz, 4H), 1.69
(q, J = 7.2 Hz, 8H), 1.42−1.20 (m, 24H), 0.89 (t, J = 6.9 Hz, 6H),
0.88 (t, J = 7.0 Hz, 6H). 13C{1H} NMR (101 MHz, CDCl3): δ 166.3,
165.0, 163.4, 163.1, 152.1, 142.3, 141.8, 131.7, 126.2, 77.5, 77.2, 76.8,
39.1, 31.50, 31.45, 28.4, 26.6, 22.6, 14.2. HRMS (ESI/QTOF) m/z:
[M + Na]+ calcd for C50H54N6O8S2Na, 953.3312; found, 953.3328.
Synthesis of oxNN (2,5-Dihexyldipyrrolo[3,4-a:3′,4′-c]-
phenazine-1,3,4,6(2H,5H)-tetraone). Setup: A 25 mL round-
bottom flask equipped with a magnetic stir bar was charged with NN
(32 mg, 66 μmol, 1 equiv), CHCl3 (10 mL), and MnO2 (30 mg, 345
μL, 5 equiv). The reaction mixture was stirred at room temperature
for 2 h. A color change was observed within 5 min of MnO2 addition.
Workup: The reaction mixture was filtered to remove MnO2, and the
filtrate was evaporated to yield an orange solid that was found to be
oxNN (30 mg, 62 μmol, 94% yield). Characterization: 1H NMR (400
MHz, CDCl3): δ 8.50 (AA′BB′, JAB = 8.5 Hz, JAB′ = 1.7 Hz, 2H), 8.06
(AA′BB′, JAB = 8.5 Hz, JAB′ = 1.7 Hz, 2H), 3.86 (t, J = 7.2 Hz, 4H),
1.79 (p, J = 7.4 Hz, 4H), 1.46−1.21 (m, 12H), 0.87 (t, J = 6.5 Hz,
6H). 13C{1H} NMR (101 MHz, CDCl3): δ 165.8, 164.5, 146.0, 140.1,
134.4, 134.3, 131.2, 129.7, 39.0, 31.5, 28.5, 26.7, 22.6, 14.2. HRMS
(ESI/QTOF) m/z: [M + Na]+ calcd for C28H30N4O4Na, 509.2159;
found, 509.2126.
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