Synthesis, crystal structures, and supramolecular assemblies of pyrrole-based anion receptors bearing modified pyrrole β-substituents

Article abstract of DOI:10.1021/jo2008687

Dipyrrolyldiketone BF₂ complexes acting as acyclic anion receptors form supramolecular assemblies with structures and properties that are dependent on the pyrrole β-substituents. In particular, although β-alkyl substituents interfered with the

Full text of DOI:10.1021/jo2008687

FEATURED ARTICLE
pubs.acs.org/joc
Synthesis, Crystal Structures, and Supramolecular
Assemblies of Pyrrole-Based Anion Receptors Bearing Modified
Pyrrole β-Substituents
Yohei Haketa,† Shohei Sakamoto,† Kengo Chigusa,† Takashi Nakanishi,‡ and Hiromitsu Maeda*,†
†College of Pharmaceutical Sciences, Institute of Science and Engineering, Ritsumeikan University, Kusatsu 525-8577, Japan
‡National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
S Supporting Information
b
ABSTRACT:
Dipyrrolyldiketone BF2 complexes acting as acyclic anion receptors form supramolecular assemblies with structures and properties
that are dependent on the pyrrole β-substituents. In particular, although β-alkyl substituents interfered with the formation of stable
gel states, the introduction of fluorine moieties induced a stable supramolecular gel when compared to that of β-unsubstituted
receptor.
’ INTRODUCTION
moieties such as 1c.5d On the other hand, pyrrole β-substituents such
as those bearing methyl (2a),5g ethyl (3a),5c and fluorine (4a)5b
moieties are also essential factors for controlling the anion-binding
and assembling properties of the anion receptors. In contrast to the
cases of 1a, 2a, and 4a, the β-ethyl groups in 3a interfere with the
construction of efficient stacking structures, as suggested by the solid-
state assembly.5a,b,g However, π-extension at pyrrole R-positions
provides solid-state stacking dimers, such as those found in R-phenyl
3b and related derivatives.4,5f
Focusing on the substituents, introduction of electron-with-
drawing fluorine moieties at pyrrole β-positions changes the proper-
ties of the corresponding oligopyrrole molecules compared to
those of alkyl moieties.6 For example, Sessler et al. reported the
β-fluorinated derivatives of calix[4]pyrrole and dipyrrolylquinoxa-
line, exhibiting enhanced binding constants for anions.6a,b As for π-
conjugated macrocycles, Osuka and Furuta et al. reported perfluori-
nated meso-aryl-substituted expanded porphyrins, which exhibited
extremely red-shifted absorption, for example, >1000 nm in the case
of [38]octaphyrin.6c The fluorine moiety does not significantly affect
the geometries of molecules because of its small size but can perturb
One of the strategies to form functional supramolecular
assemblies on the basis of noncovalent interactions is the introduc-
tion of appropriate substituents to the core π-conjugated platforms.
In particular, molecules possessing guest-binding ability are essential
building blocks of stimuli-responsive soft materials. For example,
appropriately programmed molecules afford soft materials such as
supramolecular gels, which comprise solvent molecules and dimen-
sionally controlled fibrous or sheetlike assemblies1 that can exhibit
dramatic changes in their states in response to various external
stimuli. Recently, supramolecular gels that are responsive to anions2
have attracted considerable attentions because they are soft materials
that can be tuned by the incorporation of various ionic components
including both bound anions and their counter cations.3 Such
charge-based soft materials would exhibit stimuli-responsive ferro-
electric properties based on polarized ion pairs and may show charge-
carrier behaviors if the charged components are appropriately
arranged. However, further detailed investigations of such soft
materials comprising charged species require the preparation and
examination of suitable π-conjugated molecules that efficiently bind
anions. As potential candidates, boron complexes of 1,3-dipyrrolyl-
1,3-propanediones (e.g., 1a,b, Figure 1a)4,5 form anion-responsive
supramolecular gels via the introduction of aliphatic chains to R-aryl
Received: May 2, 2011
Published: June 01, 2011
r
2011 American Chemical Society
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|

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FEATURED ARTICLE
and 0.89, respectively, suggesting that these molecules have
highly emissive properties in the solution state.
The single-crystal X-ray structure of the anion receptor affords
essential insights into the supramolecular stacking structures
(Figure 2). Similar to other derivatives 1b and 3b,5d,f the receptor
2b exhibits a fairly planar structure with terminal phenyl rings
tilted to the core plane consisting of 16 atoms at 22.7° and 29.3°,
which are intermediate values in average between 1b (20.0° and
28.6°)5d and 3b (24.3° and 31.9°).5f On the other hand, receptor
4b shows highly planar structure with a small tilted angle of 0.58°
between phenyl ring and core plane consisting of 16 atoms due to
the weak interaction between pyrrole β-fluorine moiety and
terminal phenyl o-CH. Further, β-methyl 2b and β-fluorinated
4b form infinite πꢀπ stacking structures similar to 1b, in sharp
contrast to the weakly stacked structures by β-ethyl 3b. In fact,
the distances between the stacking core planes, defined as the
average distance between the plane consisting of 16 core atoms
and each atom in the neighboring plane, in 3b were longer (3.73
and 4.19 Å) than those of 1b (3.19 Å), 2b (3.46 and 3.55 Å), and
4b (3.41 Å). This difference may have been due to interference
by β-ethyl substituents.
Figure 1. (a) BF2 complexes of dipyrrolyldiketones (β-unsubstituted
1aꢀc, β-alkyl-substituted 2aꢀc and 3aꢀc, and β-fluorine-substituted
4aꢀc) and (b) anion-binding mode of 1b. Synthesis of some derivatives
has already been reported in ref 5a for 1a, ref 5d for 1b,c, ref 5g for 2a, ref
5c for 3a, ref 5f for 3b, and ref 5b for 4a.
Anion-Binding Properties. The anion-binding behavior of
the β-substituted receptors was elucidated by 1H NMR upon the
addition of Clꢀ as a tetrabutylammonium (TBA) salt at ꢀ50 °C.
For example, the signals of pyrrole NH, bridging CH, and phenyl
o-CH of β-methyl 2b at 9.48, 7.55, and 6.45 ppm in CD2Cl2
disappeared, and new signals arose in the downfield region at
11.98 ppm (þ 2.50 ppm), 7.82 ppm (þ 0.27 ppm), and 8.53
ppm (þ 2.08 ppm), respectively. Similar NMR spectral changes
were also observed for β-ethyl 3b5f and β-fluorinated 4b. These
observations suggest the formation of pentacoordinated [1 þ 1]-
type receptor-anion complexes, which is supported by density
functional theory (DFT) calculations.7 In addition, similar to
the states of π-conjugated systems, resulting in the stabilization of
molecules as well as the modulation of electronic properties and
assembled structures. In this paper, on the basis of the initial findings
by our group,4,5 we show the modifications of the R-positions of the
β-substituted receptors to form functional assembled structures,
especially, anion-responsive supramolecular gels. In particular, in-
troduction of fluorine moieties at the pyrrole β-positions was found
to enable the formation of supramolecular gel at rt even in the
presence of Clꢀ as a tetraalkylammonium salt, suggesting that more
stable and useful soft materials consisting of charged species would
be prepared using β-fluorinated receptors if anions as salts of
appropriate countercation are incorporated.
1b Clꢀ,5d single-crystal X-ray analysis revealed the [1 þ 1]-type
3
anion complexes, 2b Clꢀ and 4b Clꢀ, as tetrapropylammonium
3
3
(TPA) and TBA salts, respectively (Figure 3). The binding mode
of 4b Clꢀ was in sharp contrast to that of 4a Clꢀ, with
’ RESULTS AND DISCUSSION
3
3
completely uninverted pyrrole rings to form a 1-D chain
Synthesis and Initial Characterization. Following the pro-
tocol reported for the preparation of 3b from 3a,5f R-phenyl-
substituted 2b and 4b were obtained in 46% and 20% yields,
respectively, by R-iodination using N-iodosuccinimide (NIS)
and subsequent Suzuki cross-coupling with phenylboronic acid
for 2a and 4a. Similar to the cases for 2b, 3b, and 4b, reactions
with 3,4,5-trihexadecyloxyphenyl-substituted boronic acid pina-
col ester afforded 2c, 3c, and 4c from the corresponding R-
unsubstituted derivatives (2a, 3a, and 4a) in 41%, 48%, and 20%
yields, respectively. Relatively low yields of β-fluorinated 4b,c
were due to the partial removal of BF2 units to provide the
corresponding R-aryl-substituted dipyrrolyldiketones, which
structure.5b In 2b Clꢀ, peripheral phenyl units are tilted in the
3
angle range of 30.99ꢀ47.68° due to the interference with β-
methyl units, whereas those of 4b Clꢀ are fairly coplanar with
3
the core unit with dihedral angles of 4.65° and 24.67°. Further,
both anion complexes 2b Clꢀ and 4b Clꢀ formed charge-by-
3
3
charge assemblies,5h consisting of negatively charged recep-
torꢀanion complexes and counter tetraalkylammonium cations,
in different stacking modes. In contrast to 2b Clꢀ, which is a
3
TPA salt showing alternate stacking of anionic and cationic
components, 4b Clꢀ is a TBA salt with columnar assemblies
3
comprising a pair of complexes and that of cations in a row.
Neighboring Clꢀ were closely located with a distance of 4.287 Å,
whereas the shortest distance between Clꢀ and TBA-N was
4.286 Å. Based on the 1:1 binding stoichiometry determined by
the Job plot, anion-binding affinities of 2b and 4b were also
estimated by UV/vis absorption spectral changes in CH2Cl2
upon the addition of TBA salts of anions (Table 1). In contrast
to the β-unsubstituted receptors, which showed enhanced Ka
values for halide anions via introduction of phenyl moieties at
R-positions, R-phenyl substitutions of β-alkyl-substituted recep-
tors were found to interfere with efficient anion binding. This
may have occurred due to there being less planar coordination by
β-substituents. Conversely, phenyl substitution of β-fluorinated
4a to 4b provided comparable Ka values for halide anions in both
were also converted to 4b,c by treatment with BF3 OEt2. The
3
chemical identifications of 2b,c, 3c, and 4b,c were performed by
1H NMR and MALDI-TOF-MS and ESI-TOF-MS. Electronic
properties of R-phenyl-substituted derivatives were also modu-
lated by β-substituents with the absorption maxima (λmax) and
fluorescence emission maxima (λem) of 2b, 3b, and 4b excited at
each λmax in CH2Cl2 at 499, 499, and 492 nm (λmax) and 534,
535, and 521 nm (λem), respectively. These values are compar-
able to those obtained from the analysis of 1b (500 and 529 nm).
The slight blue shifts of 4b were presumably due to the electron-
withdrawing β-fluorine moieties. Further, the corresponding
emission quantum yields of 2b, 3b, and 4b were 0.89, 0.94,
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FEATURED ARTICLE
Figure 2. Single-crystal X-ray structures (side view showing stacking structures) of (a) 1b,5d (b) 2b, (c) 3b,5f and (d) 4b. Solvent molecules are omitted
for clarity in (b) and (d). Atom color code: brown, pink, yellow, green, blue, and red refer to carbon, hydrogen, boron, fluorine, nitrogen, and oxygen,
respectively.
including deprotonation of pyrrole NH; this behavior is pre-
sumably because of the electron-withdrawing effect of β-fluorine
moiety and the stabilization by intramolecular CꢀH
N
3 3 3
hydrogen bonding using R-phenyl o-CH. Even though β-fluori-
nated 4a,b have electron-withdrawing substituents, they were
found to have Ka values similar to 1a,b, which was likely due to
the presence of less stable pyrrole-inverted preorganized con-
formations in 4a,b than in 1a,b.
Anion-Responsive Supramolecular Gels. The formation of
supramolecular gels of β-substituted receptors bearing aliphatic
chains was also examined. In contrast to 1c, which forms
supramolecular gels,5d β-alkyl 2c and 3c could not form gel
states at rt from octane (10 mg/mL). For example, the UV/vis
spectrum of 2c in octane (10 mg/mL) revealed a blue-shifted
absorption band with a λmax of 488 nm caused by the formation
of H-aggregates, whereas in diluted octane (10ꢀ5 M) a band was
produced at 490 nm, suggesting a dispersed monomer state.
Conversely, β-fluorinated 4c afforded octane gel (Figure 4a (i))
at a solꢀgel transition temperature at 38 °C, which is 10 °C
higher than that of 1c (27.5 °C), suggesting that the stability was
enhanced by β-fluorine moieties. Similar to the case of 1c,5d the
octane gel of 4c exhibited split broad absorption bands at 463,
523, and 555 nm, and a fluorescence maximum at 646 nm due to
the stacking receptor π-planes (Figure 4b (i), solid lines). It is
noteworthy that these absorption bands of 4c in the gel state
were in contrast to the sharp band at 518 nm in diluted CH2Cl2
derived from the dispersed monomeric state; this electronic
property was correlated with the fluorescence maximum of the
gel, which was red-shifted compared to that at 577 nm in diluted
CH2Cl2 (Figure 4b (i), broken lines). An assembled structure
such as that observed in the gel was also formed in diluted octane
(10ꢀ5 M).
In sharp contrast to the transition to solution of 1c that was
observed in response to the addition of TBACl (1 equiv),5d 4c
formed an another gelated material (Figure 4a) that had promis-
ing electronic and electrooptical properties such as a broad
absorption band around 565 nm reaching ca. 800 nm at the
edge (Figure 4b (ii), solid line)). The fluorescence maximum of
the gel of the Clꢀ complex was observed at 591 nm, which was
blue-shifted compared to the fluorescence maximum of anion-
free gel from 4c at 646 nm. The electronic and electrooptical
properties of the gel that contained Clꢀ as a TBA salt, which was
Figure 3. Single-crystal X-ray structures (top view showing single
molecules and side view showing charge-by-charge stacking structures)
of (a) 2b TPACl (one of the four independent complexes is re-
3
presented) and (b) 4b TBACl. Atom color code: yellow green repre-
3
sents chlorine.
Table 1. Binding Constants (Ka, Mꢀ1) of 1b,b 2b, 3b,c and 4b
with Various Anions as TBA Salts in CH2Cl2 at 20 °Ca
1b (1a)
2b (2a)
3b (3a)
4b (4a)
Clꢀ
30,000
(15,000)
2,800
2,500
(4,900)
320
2,700
(6,800)
300
30,000
(26,000)
1,600
Brꢀ
(2,100)
210,000
(930,000)
72,000
(680)
(1,200)
27,000
(210,000)
2,200
(1,700)
n.d.h
(960,000)
n.d.h
ꢀ
CH3CO2
35,000
(61,000)
2,700
ꢀ
H2PO4
(270,000)
(87,000)
(91,000)
(190,000)
a The values shown in parentheses are the Ka values of the corresponding
β-unsubstituted derivatives 1a,d 2a,e 3a,f and 4ag. The errors in Ka for
anions are within 10% as described in the Supporting Information. b Ref 5d.
c Ref 5f. d Ref 5e. e Ref 5g. f Ref 5c. g Ref 5b. h Not determined.
receptors due to the presence of less sterical hindrance of β-
fluorine moieties. Further, by addition of oxoanions, R-phenyl
and β-fluorinated 4b showed the complicated spectral changes
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Figure 4. (a) Photographs of supramolecular octane gels of 4c and (b) UV/vis absorption (black) and fluorescence emission (red) spectra of octane
gels (solid lines) and CH2Cl2 solution (1 ꢁ 10ꢀ5 M, broken lines) of 4c in the (i) absence and (ii) presence of TBACl (1 and 120 equiv for gel and
solution, respectively).
Figure 5. SEM images of xerogels from octane of (a) 4c and (b) 4c with TBACl (1 equiv).
completely different from the dispersed states in octane solutions
from 1c, 2c, and 3c with TBACl, suggested that the interactions
are required, introduction of an electron-withdrawing moiety
such as fluorine can induce the dipoles of the receptors and anion
complexes, resulting in the formation of stable stacking organized
structures. In addition, less bulky fluorine moieties do not inter-
fere with the stacking structures of both the anion-free receptor
and the Clꢀ complex. In contrast to ordinary hydrogen-bonding-
based supramolecular gels that show anion-responsive behav-
iors,3 the gelation behavior observed in 4c suggests that, since
hydrogen bonding is not a main driving force to construct supra-
molecular gel in the anion-free form, anion binding of the recep-
tors as gelating molecules can modulate the state of soft materials
but does not always interfere the formation of gelated state.
occurred between receptorꢀanion complexes 4c Clꢀ in the gel
3
state. The properties of the gel state of 4c containing TBACl were
also distinct from those of 4c Clꢀ in diluted CH2Cl2, which
3
exhibited sharp absorption and fluorescence bands with the
maxima at 513 and 559 nm, respectively, owing to the dispersed
state of 4c Clꢀ (Figure 4b (ii), broken lines).
3
Further information regarding the organized structures of
xerogels from 4c and the Clꢀ complex as a TBA salt, which
were prepared by freeze-drying procedures, was obtained by
scanning electron microscopy (SEM) (Figure 5). The samples
were fabricated on a silicon substrate. In the case of anion-free 4c
(Figure 5a), submicrometer-scale flakelike objects with flake
thickness of several tens of nanometers were assembled to form
more highly organized structures. These findings contrasted the
fairly unidentified objects observed in the octane gel of 1c.
Conversely, xerogel of 4c as a mixture with TBACl (Figure 5b)
revealed the assembly of rodlike objects with a length of ca. 1 μm.
Preliminary investigation of synchrotron X-ray diffractions of
xerogels of 1c and 4c suggested that there were similar stacking
structures with distances of ca. 4.5 Å along with interactions
between alkyl chains (ca. 4.2 Å). Although further investigations
’ SUMMARY
Modification of pyrrole β-positions was found to be essential
for the modulation of the supramolecular assemblies as well as the
electronic and electrooptical properties. While β-alkyl substituents
interfered with the formation of stable gel states, the introduction
of fluorine moieties induced a stable supramolecular gel when
compared to that of β-substituted receptor. Moreover, β-fluorine
groups enabled the receptor to form uncommon gelated materials,
even in the presence of Clꢀ as a TBA salt. Modification both at the
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pyrrole periphery on the basis of a sufficient pyrrole library and at a
boron moiety8 would provide various useful materials. Further
investigation of the formation of charge-by-charge assemblies
comprising alternately stacking positively and negatively charged
species5h,9 are currently underway.
29.7ꢀ29.4, 26.1, 24.8, 22.7, 14.1 (some of the signals for hexadecyl
chains were overlapped). MALDI-TOF-MS: m/z (% intensity) 924.8
(100), calcd for C60H113BO5 ([M]þ) 924.87. HRMS (ESI-TOF): m/z
(% intensity) 925.8765, calcd for C60H114BO5 ([M þ H]þ) 925.8764.
BF2 Complex of 1,3-Bis(3,4-dimethyl-5-(3,4,5-trihexade-
cyloxyphenyl)pyrrol-2-yl)-1,3-propanedione, 2c. A Schlenk
tube placed with 2a-I2 (64.7 mg, 0.116 mmol), 3,4,5-trihexadecyloxyphe-
nylboronic acid pinacol ester (266.7 mg, 0.267 mmol), tetrakis(triphenyl-
phosphine)palladium(0) (28.0 mg, 0.024 mmol), and Cs2CO3 (113.4 mg,
0.348 mmol) was flushed with nitrogen and charged with a mixture of
degassed DMF (3 mL), toluene (1.5 mL), and water (0.1 mL). The mixture
was heated at 95 °C for 21 h, cooled, and then partitioned between water and
CH2Cl2. The combined extracts were dried over anhydrous MgSO4 and
evaporated. The residue was then chromatographed over a silica gel flash
column (eluent: hexane/CH2Cl2 = 2: 1 and CH2Cl2) to give 2c (99.6 mg,
45%) as a reddish brown solid. Rf = 0.44 (CH2Cl2/hexane =2: 1). 1H NMR
(600 MHz, CDCl3, 20 °C): δ (ppm) 9.27 (s, 2H, NH), 6.66 (s, 1H, CH),
6.47 (s, 4H, Ar-H), 4.02 (m, 12H, OCH2), 2.04 (s, 6H, inner-CH3), 2.21 (s,
6H, outer-CH3), 1.84 (tt, J = 7.8 and 7.2 Hz, 8H, OCH2CH2), 1.77 (tt, J =
7.8 and 7.2 Hz, 4H, OCH2CH2), 1.50 (m, 12H, OC2H4CH2), 1.36ꢀ1.25
(m, 144H, OC3H6C12H24), 0.89ꢀ0.83 (m, 18H, OC15H30CH3). 13CNMR
(151 MHz, CDCl3, 20 °C): δ (ppm) 166.20, 153.5, 138.8, 138.0, 130.6,
126.2, 123.2, 120.5, 106.2, 92.1, 73.6, 69.4, 31.9, 30.4, 29.76, 29.74, 29.72,
29.68, 29.65, 29.62, 29.44, 29.41, 29.37, 26.1, 22.7, 14.1, 12.4, 10.3 (some of
the signals for hexadecyl chains were overlapped). UV/vis (CH2Cl2, λmax
(nm) (ε, 105 Mꢀ1 cmꢀ1)) 512.5 (1.2). Fluorescence (CH2Cl2, λem (nm)
(λex (nm))): 560.2 (512.0). MALDI-TOF-MS (% intensity): m/z 1899.6
(84), 1900.6 (100), calcd for C123H217N2O8BF2 ([M]ꢀ) 1899.67. HRMS
(ESI-TOF): m/z (% intensity) 1898.6628, calcd for C123H216N2O8BF2
([M ꢀ H]ꢀ) 1898.6628.
’ EXPERIMENTAL SECTION
General Procedures. Commercially available starting materials
were used without further purification unless otherwise stated. Assign-
ments of 1H NMR for 2b, 2c, and 3c were performed on the basis of 2D
NMR (COSY, NOESY, and ROESY).
BF2 Complex of 1,3-Bis(3,4-dimethyl-5-iodopyrrol-2-yl)-
1,3-propanedione, 2a-I2. To an acetone (100 mL) solution of 2a5g
(205.0 mg, 0.67 mmol) at room temperature was added N-iodosucci-
nimide (360.8 mg, 1.47 mmol). The mixture was stirred at room
temperature for 3 h. After consumption of the starting material was
confirmed by TLC analysis, the mixture was washed with water and
extracted with CH2Cl2, dried over anhydrous MgSO4, and evaporated to
dryness. The residue was then chromatographed over a silica gel flash
column (eluent: 3% MeOH/CH2Cl2) and recrystallized from CH2Cl2/
hexane to afford 2a-I2 (344.3 mg, 92%). Rf = 0.49 (CH2Cl2). 1H NMR
(600 MHz, CDCl3, 20 °C): δ (ppm) 9.40 (s, 2H), 6.28 (s, 1H), 2.36 (s,
6H), 2.06 (s, 6H). 13C NMR (151 MHz, CDCl3, 20 °C): δ (ppm) 167.6,
129.8, 127.7, 127.5, 90.6, 86.4, 12.6, 11.9. MALDI-TOF-MS: m/z (%
intensity) 556.9 (100), calcd for C15H14BF2I2N2O2 ([M ꢀ H]ꢀ)
556.92. HRMS (ESI-TOF): m/z (% intensity) 556.9213, calcd for
C15H14BF2I2N2O2 ([M ꢀ H]ꢀ) 556.9214.
BF2 Complex of 1,3-Bis(3,4-dimethyl-5-phenylpyrrol-2-
yl)-1,3-propanedione, 2b. A Schlenk tube placed with 2a-I2 (80.0
mg, 0.143 mmol), phenylboronic acid (52.45 mg, 0.430 mmol), tetrakis-
(triphenylphosphine)palladium(0) (34.67 mg, 0.03 mmol), and Cs2CO3
(140 mg, 0.43 mmol) was flushed with nitrogen and charged with a mixture
of degassed DMF (3 mL) and water (0.3 mL). The mixture was heated at
95 °C for 17 h, cooled, and then partitioned between water and CH2Cl2. The
combined extracts were dried over anhydrous MgSO4 and evaporated. The
residue was then chromatographed over a silica gel flash column (eluent:
0.5% MeOH/CH2Cl2) to give 2b (32.6 mg, 50%) as a pink solid. Rf = 0.52
(0.5% MeOH/CH2Cl2). 1H NMR (600 MHz, CDCl3, 20 °C): δ (ppm)
9.32 (s, 2H, NH), 7.53 (d, J = 7.2 Hz, 4H, Ar-o-CH), 7.49 (t, J = 7.2 Hz, 4H,
Ar-m-CH), 7.41 (t, J = 7.2 Hz, 4H, Ar-p-CH), 6.50 (s, 1H, CH), 2.42 (s, 6H,
inner-CH3), 2.22 (s, 6H, outer-CH3). 13C NMR (151 MHz, DMSO-d6,
20 °C): δ(ppm) 166.8, 137.8, 131.5, 130.8, 129.2, 128.7, 127.7, 123.7, 121.0,
92.3, 12.5, 10.4. UV/vis (CH2Cl2, λmax (nm) (ε, 105 Mꢀ1 cmꢀ1)): 499.0
(1.0). Fluorescence (CH2Cl2, λem (nm) (λex (nm))): 533.6 (499). MAL-
DI-TOF-MS: m/z (% intensity) 457.2 (100), calcd for C27H24BF2N2O2
([M ꢀ H]ꢀ) 457.19. HRMS (ESI-TOF): m/z (% intensity) 457.1909,
calcd for C27H24BF2N2O2 ([M ꢀ H]ꢀ) 457.1909.
BF2 Complex of 1,3-Bis(3,4-diethyl-5-(3,4,5-trihexadecy-
loxyphenyl)pyrrol-2-yl)-1,3-propanedione, 3c. A Schlenk tube
5f
placed with 3a-I2 (92.1 mg, 0.150 mmol), 3,4,5-trihexadecyloxyphe-
nylboronic acid pinacol ester (319.3 mg, 0.345 mmol), tetrakis-
(triphenylphosphine)palladium(0) (32.36 mg, 0.028 mmol), and
Cs2CO3 (146.6 mg, 0.45 mmol) was flushed with nitrogen and charged
with a mixture of degassed DMF (2 mL), toluene (1 mL), and water
(0.1 mL). The mixture was heated at 95 °C for 23 h, cooled, and then
partitioned between water and CH2Cl2. The combined extracts were
dried over anhydrous MgSO4 and evaporated. The residue was then
chromatographed over a silica gel flash column (eluent: 5% EtOAc/hexane
and 10% hexane/CHCl3) to give 3c (170.0 mg, 57%) as a reddish-brown
solid. Rf = 0.62 (20% hexane/CHCl3). 1HNMR(600MHz, CDCl3, 20°C):
δ (ppm) 9.25 (s, 2H, NH), 6.66 (s, 1H, CH), 6.53 (s, 4H, Ar-H), 4.02 (m,
12H, OCH2), 2.84 (q, J = 7.8 Hz, 4H, inner-CH2CH3), 2.61 (q, J = 7.8 Hz,
4H, outer-CH2CH3), 1.84 (tt, J = 7.8 and 7.2 Hz, 8H, OCH2CH2), 1.77 (tt,
J= 7.8 and 7.2 Hz, 4H, OCH2CH2), 1.50 (m, 12H, OC2H4CH2), 1.35(t, J=
7.8 Hz, 6H, inner-CH2CH3), 1.36ꢀ1.25 (m, 144H, OC3H4C12H24), 1.19
(t, J = 7.8 Hz, 6H, outer-CH2CH3), 0.89ꢀ0.83 (m, 18H, OC15H30CH3).
13C NMR (151 MHz, CDCl3, 20 °C): δ (ppm) 166.3, 153.5, 138.8, 138.0,
136.8, 126.5, 126.2, 122.5, 106.1, 90.7, 73.6, 69.3, 31.9, 30.4, 29.76, 29.74,
29.72, 29.68, 29.66, 29.62, 29.44, 29.40, 29.37, 26.1, 22.7, 19.2, 17.5, 16.2,
15.4, 14.1 (some of the signals for hexadecyl chains were overlapped).
UV/vis (CH2Cl2, λmax (nm) (ε, 105 Mꢀ1 cmꢀ1)): 512.0 (1.1). Fluores-
cence (CH2Cl2, λem (nm) (λex (nm))): 562.8 (512.0). MALDI-TOF-MS
(% intensity): m/z 1955.8 (76), 1956.7 (100), calcd for C127H225N2O8BF2
([M]ꢀ) 1955.73. HRMS (ESI-TOF): m/z (% intensity) 1954.7255, calcd
for C127H224N2O8BF2 ([M ꢀ H]ꢀ) 1954.7254.
3,4,5-Trihexadecyloxyphenylboronic Acid Pinacol Ester. A
Schlenk tube placed with 5-bromo-1,2,3-trihexadecyloxybenzene (878.3
mg, 1 mmol), dichlorobis(triphenylphosphine)palladium (23.16 mg,
0.033 mmol), bis(pinacolato)diboron (380.4 mg, 1.5 mmol), and
potassium acetate (294.2 mg, 3 mmol) was flushed with nitrogen and
charged with a mixture of degassed dioxane (13 mL). The mixture was
heated at 80 °C for 12 h, cooled, and then partitioned between water and
CH2Cl2. The combined extracts were dried over anhydrous MgSO4 and
evaporated. The residue was then chromatographed over a flash silica gel
column (eluent: 3% EtOAc/hexane) to give the desired product (613.3
mg, 66%) as a white solid. Rf = 0.25 (3% EtOAc/hexane). 1H NMR (600
MHz, CDCl3, 20 °C): δ (ppm) 6.99 (s, 2H), 4.00 (t, J = 6.6 Hz, 4H),
3.97 (t, J = 6.6 Hz, 2H), 1.81ꢀ1.77 (tt, J = 7.2 and 6.6 Hz, 4H),
1.75ꢀ1.70 (tt, J = 7.2 and 6.6 Hz, 2H), 1.48ꢀ1.43 (m, 6H), 1.33 (s,
12H), 1.30ꢀ1.25 (m, 72H), 0.88 (t, J = 6.6 Hz, 9H). 13C NMR (151
MHz, CDCl3, 20 °C): δ (ppm) 152.9, 141.1, 112.7, 73.3, 69.0, 31.9, 30.4,
BF2 Complex of 1,3-Bis(3,4-difluoro-5-iodopyrrol-2-yl)-
1,3-propanedione, 4a-I2. To a dioxane solution (10 mL) of
4a5b (46.5 mg, 0.144 mmol) was added N-iodosuccinimide (299 mg,
1.33 mmol) under dark, N2 gas, with stirring for 3 h at reflux temperature.
After removal of the solvent, the residue was chromatographed over a
silica gel column (eluent: 12% EtOAc/CH2Cl2), and recrystallization
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The Journal of Organic Chemistry
FEATURED ARTICLE
Table 2. Crystallographic Details for Anion Receptors and Anion Complexes
2b
4b
2b TPACl
4b TBACl
4bꢀ TBAþ
3
3
3
formula
C27H25BF2N2O2
C23H13BF2N2O2
2C4H8O
C
27H25BF2N2O2
C
23H13BF6N2O2
C23H12BF6N2O2
3
3
3
3
C12H28NCl
0.5dichloroethane
0.26watera
C16H36NCl
C16H36N
3
3
a
C6H14O
3
FW
458.30
618.37
731.75
752.07
817.79
crystal size, mm
crystal system
space group
a, Å
b, Å
c, Å
0.30 ꢁ 0.10 ꢁ 0.10
0.50 ꢁ 0.20 ꢁ 0.20
monoclinic
C2/c (no. 15)
24.8973(6)
11.4380(2)
9.8194(2)
90
92.5677(14)
90
2793.51(10)
1.470
0.50 ꢁ 0.30 ꢁ 0.20
monoclinic
P21 (no. 4)
16.897(3)
23.457(2)
21.571(2)
90
113.294(5)
90
7852.6(16)
1.238
0.70 ꢁ 0.40 ꢁ 0.35
triclinic
0.40 ꢁ 0.20 ꢁ 0.15
triclinic
triclinic
P1 (no. 2)
8.236(3)
16.744(6)
17.667(7)
109.518(12)
101.221(13)
95.073(12)
2221.4(13)
1.388
P1 (no. 2)
12.052(4)
12.904(6)
13.351(4)
79.952(16)
86.514(15)
66.794(15)
1878.9(12)
1.329
P1 (no. 2)
8.626(2)
9.917(4)
28.029(8)
96.182(13)
91.135(12)
112.602(13)
2195.6(12)
1.237
R, deg
β, deg
γ, deg
V, Å3
F
calcd, g cmꢀ3
Z
2
4
8
2
2
T, K
123(2)
0.098 (Mo KR)
21375
9822
621
93(2)
1.059 (Cu KR)
14125
2555
200
123(2)
0.213 (Mo KR)
117426
34687
1843
123(2)
0.17 (Mo KR)
18566
8532
473
123(2)
0.094 (Mo KR)
19315
9056
615
μ, mmꢀ1
no. of reflns
no. of unique reflns
variables
λR, Å
0.71075 (Mo KR)
0.0624
0.1527
1.54187 (Cu KR)
0.0389
0.0963
0.71075 (Mo KR)
0.0597
0.1451
0.71075 (Mo KR)
0.0363
0.1067
0.71075 (Mo KR)
0.0479
0.1508
R1 (I > 2σ(I))
wR2 (I > 2σ(I))
GOF
0.980
1.096
1.041
1.073
1.038
a Some of the cocrystallized solvents cannot locate their hydrogen atom appropriately, resulting in the description of them as the compound name.
from CH2Cl2/hexane afforded bisiodinated derivative 4a-I2 (46.1 mg, 57%)
as a brown solid. Rf = 0.60 (10% EtOAc/CH2Cl2). 1H NMR (600 MHz,
CDCl3, 20 °C): δ (ppm) 9.03 (s, 2H), 6.54 (s, 1H). 13C NMR (151 MHz,
DMSO-d6, 20 °C): δ(ppm) 166.8, 141.8 140.1, 113.0, 90.7, 71.0. 19F NMR
(564 MHz, CDCl3, 20 °C): δ (ppm) ꢀ142.13 (s, 2F), ꢀ155.42 (s, 2F),
ꢀ163.89 (s, 2F). MALDI-TOF-MS (% intensity): m/z 572.8 (100), calcd
for C11H2I2N2O2BF6 ([M ꢀ H]ꢀ) 572.82. HRMS (ESI-TOF): m/z (%
intensity): 572.8211, calcd for C11H2I2N2O2BF6 ([M ꢀ H]ꢀ) 572.8210.
BF2 Complex of 1,3-Bis(3,4-difluoro-5-phenylpyrrol-2-yl)-
1,3-propanedione, 4b. A two necked flask containing 4a-I2 (28.1 mg,
0.049 mmol), phenylboronic acid (15.0 mg, 0.12 mmol), tetrakis(triphenyl-
phosphine)palladium(0) (4.6 mg, 3.98 μmol), and Na2CO3 (42.6 mg, 0.40
mmol) was flushed with nitrogen and charged with a mixture of degassed
1,2-dimethoxyethane (0.9 mL) and water (0.09 mL). The mixture was
refluxed for 14 h, cooled, and then partitioned between water and CH2Cl2.
The combined extracts were dried over anhydrous MgSO4 and evaporated.
The residue was chromatographed over a silica gel column (eluent: 10%
EtOAc/CH2Cl2) to give 4b (4.6 mg, 20%) as a red solid. Rf = 0.46 (3%
and CH2Cl2. The combined extracts were dried over anhydrous MgSO4
and evaporated. The residue was then chromatographed over a silica gel
flash column (eluent: 5% EtOAc/hexane) to give 4c (78.4 mg, 20%) as a
red solid. Rf = 0.56 (CHCl3/hexane =3: 1). 1H NMR (600 MHz, CDCl3,
20 °C): δ(ppm) 8.72 (s, 2H), 6.82 (s, 1H), 6.69 (s, 4H), 4.04 (t, J =6.6 Hz,
12H), 4.01 (t, J = 6.6 Hz, 4H), 1.85 (tt, J = 7.2 and 6.6 Hz, 8H), 1.75 (tt, J =
7.2 and 6.6 Hz, 4H), 1.53ꢀ1.46 (m, 12H), 1.39ꢀ1.26 (m, 144H),
0.89ꢀ0.86 (m, 18H). 13C NMR (151 MHz, CDCl3, 20 °C): δ (ppm)
165.5, 153.7, 143.3, 139.7, 136.0, 124.4, 121.8, 107.9, 103.9, 92.8, 73.4, 69.3,
31.7, 30.1, 29.52, 29.46, 29.44, 29.39, 29.22, 29.16, 25.9, 22.5, 13.9 (some of
the signals for hexadecyl chains were overlapped). UV/vis (CH2Cl2, λmax
(nm) (ε, 105 Mꢀ1 cmꢀ1)): 518.0 (1.2). Fluorescence (CH2Cl2, λem (nm)
(λex (nm))): 577.4 (518). MALDI-TOF-MS (% intensity): m/z 1915.5
(80), 1916.6 (100), calcd for C119H205N2O8BF6 ([M]ꢀ) 1915.57. HRMS
(ESI-TOF): m/z (% intensity) 1914.5625, calcd for C119H204N2O8BF6
([M ꢀ H]ꢀ) 1914.5625.
Method for X-ray analysis. Crystallographic data are summarized
in Table 2. The data were collected at 123 K on a Rigaku RAXIS-RAPID
diffractometer with graphite-monochromated Mo KR radiation (λ =
0.71075 Å) for 2b, 2b TPACl, 4b TBACl, and 4bꢀ TBAþ and at 93 K
1
MeOH/CH2Cl2). H NMR (600 MHz, CDCl3, 20 °C): δ (ppm) 8.85
(s, 2H, NH), 7.69(d,J=7.8Hz, 4H, Ar-H), 7.53(t, J= 7.8 Hz, 4H), 7.46 (t, J
= 7.2 Hz, 2H), 6.73 (s, 1H). 13C NMR (151 MHz, DMSO-d6, 20 °C): δ
(ppm) 167.1, 141.6, 136.2, 129.7, 129.1, 127.4, 127.1, 125.0, 108.5, 92.4.
UV/vis(CH2Cl2, λmax (nm) (ε, 105 Mꢀ1cmꢀ1)): 492.0 (1.2). Fluorescence
(CH2Cl2, λem (nm) (λex (nm))): 520.6 (492.0). MALDI-TOF-MS (%
intensity): m/z 474.1 (100), calcd for C23H13N2O2BF6 ([M]ꢀ) 474.10.
HRMS (ESI-TOF): m/z (% intensity) 473.0908, calcd for C23H13N2O2BF6
([M ꢀ H]ꢀ) 473.0906.
3
3
3
on a Rigaku RAXIS-RAPID diffractometer with graphite-monochro-
mated Cu KR radiation (λ = 1.54187 Å) for 4b, and the structures were
solved by direct methods. A single crystal of 2b was obtained by vapor
diffusion of hexane into a CH2ClCH2Cl solution. The data crystal was a
red prism of approximate dimensions 0.30 mm ꢁ 0.10 mm ꢁ 0.10 mm. A
single crystal of 4b was obtained by vapor diffusion of heptane
into a THF/toluene solution. The data crystal was a red prism of
approximate dimensions 0.50 mm ꢁ 0.20 mm ꢁ 0.20 mm. A single
BF2 Complex of 1,3-Bis(3,4-difluoro-5-(3,4,5-trihexadecy-
loxyphenyl)pyrrol-2-yl)-1,3-propanedione, 4c. A two-necked
flask containing 4a-I2 (120.2 mg, 0.21 mmol), 3,4,5-trihexadecyloxy-
phenylboronic acid pinacol ester (537.2 mg, 0.58 mmol), tetrakis-
(triphenylphosphine)palladium(0) (58.2 mg, 0.050 mmol), and Na2CO3
(190.5 mg, 1.80 mmol) was flushed with nitrogen and charged with a
mixture of degassed 1,2-dimethoxyethane (3.6 mL) and water (0.36 mL).
The mixture was refluxed for 14 h, cooled, then partitioned between water
crystal of 2b TPACl was obtained by vapor diffusion of hexane into a
3
CH2ClCH2Cl solution of 2b with 1 equiv of TPA chloride. The data
crystal was an orange prism of approximate dimensions 0.50 mm ꢁ 0.30
mm ꢁ 0.20 mm. A single crystal of 4b TBACl was obtained by vapor
3
diffusion of octane into i-Pr2O and CD2Cl2 solutions of 4b and 1 equiv
of TBA chloride. The data crystal was an orange prism of approxi-
mate dimensions 0.70 mm ꢁ 0.40 mm ꢁ 0.35 mm. A single crystal of
5182
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The Journal of Organic Chemistry
FEATURED ARTICLE
4bꢀ TBAþ was obtained by vapor diffusion of i-Pr2O into a CH2Cl2
Dye Chemistry, Topics in Current Chemistry; W€urthner, F., Ed.; Springer-
Verlag: Berlin, 2005; Vol. 258, pp 119ꢀ160. (c) Molecular Gels; Weiss,
R. G., Terech, P., Eds.; Springer: Dordrecht, 2006.
3
solution of 4b and 1 equiv of TBA acetate. The data crystal was an orange
prism of approximate dimensions 0.40 mm ꢁ 0.20 mm ꢁ 0.15 mm. In
each case, the non-hydrogen atoms were refined anisotropically. The
calculations were performed using the Crystal Structure crystallographic
software package of Molecular Structure Corp.10 The CIF files (CCDC-
781979, 827559, and 781980ꢀ781982) can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
(2) Selected books for anion binding: (a) Supramolecular Chemistry
of Anions; Bianchi, A., Bowman-James, K., Gracía-Espa~na, E., Eds.;
Wiley-VCH: New York, 1997. (b) Fundamentals and Applications of
Anion Separations; Singh, R. P., Moyer, B. A., Eds.; Kluwer Academic/
Plenum Publishers: New York, 2004. (c) Anion Sensing; Stibor, I.,
Ed.; Topics in Current Chemistry; Springer-Verlag: Berlin, 2005; Vol.
255, p 238. (d) Sessler, J. L.; Gale, P. A.; Cho, W.-S. Anion Receptor
Chemistry; RSC: Cambridge, 2006. (e) Recognition of Anions; Vilar,
R., Ed.; Structure and Bonding; Springer-Verlag: Berlin, 2008; Vol. 129,
p 252.
(3) Reviews for anion-responsive supramolecular gels: (a) Maeda,
H. Chem.—Eur. J. 2008, 14, 11274–11282. (b) Lloyd, G. O.; Steed, J. W.
Nature Chem. 2009, 1, 437–442. (c) Piepenbrock, M.-O. M.; Lloyd,
G. O.; Clarke, N.; Steed, J. W. Chem. Rev. 2010, 110, 1960–2004. (d)
Steed, J. W. Chem. Soc. Rev. 2010, 39, 3689–3699. (e) Maeda, H. In
Supramolecular Soft Matter: Applications in Materials and Organic Elec-
tronics; Nakanishi, T., Ed.; Wiley: New York, 2011; Chapter 6, in press.
(4) (a) Maeda, H. In Handbook of Porphyrin Science; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; World Scientific: Hackensack, NJ, 2010;
Vol. 8, Chapter 38. (b) Maeda, H. In Anion Complexation by Heterocycle
Based Receptors, Topics in Heterocyclic Chemistry; Gale, P. A., Dehaen, W.,
Eds.; Springer-Verlag: Berlin, 2010; Vol. 24, pp 103ꢀ144.
Determination of Anion-Binding Constants. Anion-binding
constants (Ka) were estimated by fitting the 1:1 binding curves for the
changes of absorbance in UV/vis absorption spectra upon the addition
of CH2Cl2 solutions of anions as TBA salts to CH2Cl2 solutions of the
host molecules (1 ꢁ 10ꢀ5 M).
Supramolecular Gel Formation. Examination of formation of
supramolecular gels was conducted by addition of solvent (octane) to
examined molecules in the absence or presence of Clꢀ as a TBA salt,
heating to solution, and cooling for a while. Formation of gelated states
was checked by whether the gel could remain stable when the tube was
turned upside down.
Computational Methods. Ab initio calculations were carried out
by using the Gaussian 03 program.7 The structures were optimized, and
the total electronic energies were calculated at the B3LYP level using a
6-31G** basis set. Molecular orbitals were determined by single-point
calculations at the B3LYP level using a 6-31þG** basis set of the
optimized structures at the B3LYP level using a 6-31G** basis set.
Scanning Electron Microscopy (SEM). SEM images were
obtained with a HITACHI S-4800 scanning electron microscope at
acceleration voltages of 10 kV. Silicon (100) was used as substrate, and a
platinum coating was applied using a HITACHI E-1030 ion sputter.
(5) (a) Maeda, H.; Kusunose, Y. Chem.—Eur. J. 2005, 11,
5661–5666. (b) Maeda, H.; Ito, Y. Inorg. Chem. 2006, 45, 8205–8210.
(c) Maeda, H.; Kusunose, Y.; Mihashi, Y.; Mizoguchi, T. J. Org. Chem.
2007, 72, 2612–2616. (d) Maeda, H.; Haketa, Y.; Nakanishi, T. J. Am.
Chem. Soc. 2007, 129, 13661–13674. (e) Maeda, H.; Terasaki, M.;
Haketa, Y.; Mihashi, Y.; Kusunose, Y. Org. Biomol. Chem. 2008, 6,
433–436. (f) Maeda, H.; Haketa, Y. Org. Biomol. Chem. 2008, 6,
3091–3095. (g) Maeda, H.; Haketa, Y.; Bando, Y.; Sakamoto, S. Synth.
Met. 2009, 159, 792–796. (h) Haketa, Y.; Sasaki, S.; Ohta, N.; Masunaga,
H.; Ogawa, H.; Araoka, F.; Takezoe, H.; Maeda, H. Angew. Chem., Int. Ed.
2010, 49, 10079–10083.
(6) Some examples of β-fluorinated oligopyrrole systems: (a)
Anzenbacher, P., Jr.; Try, A. C.; Miyaji, H.; Jurseíkovꢀa, K.; Lynch,
V. M.; Marquez, M; Sessler, J. L. J. Am. Chem. Soc. 2000,
122, 10268–10272. (b) Sessler, J. L.; Cho, W.-S.; Gross, D. E.; Shriver,
J. A.; Lynch, V. M.; Marquez, M. J. Org. Chem. 2005, 70, 5982–5986.
(c) Shimizu, S.; Shin, J.-Y.; Furuta, H.; Ismael, R.; Osuka, A. Angew.
Chem., Int. Ed. 2003, 42, 78–82.
(7) All calculations were carried out using the Gaussian 03 program.
Gaussian 03, Revision C.01: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;
Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.;
Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.;
Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian, Inc., Wallingford, CT, 2004.
’ ASSOCIATED CONTENT
S
Supporting Information. Optimized structures, anion-
b
binding behavior, and X-ray structural analysis of 2b, 4b, 2b
3
TPACl, 4b TBACl, and 4bꢀ TBAþ (CIF). This material is
3
3
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: maedahir@ph.ritsumei.ac.jp.
’ ACKNOWLEDGMENT
This work was supported by PRESTO/JST (2007ꢀ2011),
Grants-in-Aid for Young Scientists (B) (No. 21750155) and (A)
(No. 23685032) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), and Ritsumeikan Global Innova-
tion Research Organization (R-GIRO) project (2008ꢀ2013). We
thank Prof. Atsuhiro Osuka, Mr. Eiji Tsurumaki, Mr. Taro Koide, and
Mr. Tomohiro Higashino, Kyoto University, for single-crystal X-ray
analyses, Dr. Naoki Aratani, Kyoto University, for ESI-TOF-MS, Dr.
Noboru Ohta, JASRI, for synchrotron X-ray diffractions at SPring-8
(BL40B2: 2010A1504 and 2010A1621), Ms. Mayumi Takayama for
optimization of coupling reaction conditions, and Prof. Hitoshi
Tamiaki, Ritsumeikan University, for various measurements. Y.H.
thanks JSPS for a Research Fellowship for Young Scientists.
(8) (a) Maeda, H.; Fujii, Y.; Mihashi, Y. Chem. Commun.
2008, 4285–4287. (b) Maeda, H.; Takayama, M.; Kobayashi, K.;
Shinmori, H. Org. Biomol. Chem. 2010, 8, 4308–4315. (c) Maeda, H.;
Bando, Y.; Shimomura, K.; Yamada, I.; Naito, M.; Nobusawa, K.;
Tsumatori, H.; Kawai, T. J. Am. Chem. Soc. 2011, 133, 9266–9269.
(9) Modified benzoate anions afford supramolecular structures
containing charge-by-charge assemblies by combination with the anion
’ REFERENCES
(1) Selected books for supramolecular gels: (a) Low Molecular Mass
Gelators, Topics in Current Chemistry; Fages, F., Ed.; Springer-Verlag:
Berlin, 2005; Vol. 256, p 283. (b) Ishi-i, T.; Shinkai, S. In Supramolecular
5183
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The Journal of Organic Chemistry
FEATURED ARTICLE
receptors 1a,b: Maeda, H.; Naritani, K.; Honsho, Y.; Seki, S. J. Am. Chem.
Soc. 2011, 133, 8896–8899.
(10) CrystalStructure (Ver. 3.8), Single Crystal Structure Analysis
Software, Rigaku/MSC and Rigaku Corp., 2006.
5184
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