From helix to macrocycle: Anion-driven conformation control of π-conjugated acyclic oligopyrroles

Article abstract of DOI:10.1002/chem.201002748

Anion-responsive pyrrole-based linear receptor oligomers were newly synthesized and their anion-driven dynamic conformation changes were investigated. Phenylene-bridged dimers and a tetramer of dipyrrolyldiketone boron complexes as π-conjugated acyclic an

Full text of DOI:10.1002/chem.201002748

FULL PAPER
DOI: 10.1002/chem.201002748
From Helix to Macrocycle: Anion-Driven Conformation Control of
p-Conjugated Acyclic Oligopyrroles
Yohei Haketa[a] and Hiromitsu Maeda*[a, b]
Abstract: Anion-responsive pyrrole-
based linear receptor oligomers were
newly synthesized and their anion-
driven dynamic conformation changes
were investigated. Phenylene-bridged
dimers and a tetramer of dipyrrolyldi-
ketone boron complexes as p-conjugat-
ed acyclic anion receptors formed
anion-driven helical structures in the
solid and solution states. In fact, single-
crystal X-ray analyses of the receptor-
anion complexes exhibited various heli-
cal structures, such as [1+1]- and
[1+2]-type single helices and a [2+2]-
type double helix according to the
lengths of oligomers and the existence
of terminal aryl substituents. Anion-
binding modes and behaviors of the
oligomers in solution state were also
examined by 1H NMR and UV/Vis
spectra along with ESI-TOF MS. Dif-
ferences in the binding modes were ob-
served in the solid and solution states.
The oligomers showed augmented
anion-binding constants and anion-tun-
able electronic and optical properties
in comparison with the monomer re-
ceptor. A negative cooperative effect
in the tetramer was observed in the
second anion binding of the [1+2]-type
single helix due to electrostatic repul-
sion between two anions captured in
the helix. Further, an anion-template
coupling reaction from the linear dimer
provided a receptor macrocycle, which
was obtained as a ClÀ complex with
distinct electronic and optical proper-
ties. The macrocycle exhibited ex-
tremely high anion-binding constants
(>1010 mÀ1 in CH2Cl2) through multiple
hydrogen bonding.
Keywords: anions · heterocycles ·
host–guest systems
· receptors ·
supramolecular chemistry
Introduction
bonding and van der Waals forces.[2] In particular, p-conju-
gated oligomers with guest-binding abilities are fascinating
components of such helical structures and are attractive be-
cause of their potential to show characteristic and tunable
electronic states and form assemblies. Among the various
“glues” available for folding helical structures together, pos-
itively charged species such as metal cations have been
widely used thus far.[2a,3] Anions also play essential roles in
the formation of complexes with organic receptor molecules
through electrostatic hydrogen bonding, thereby yielding
various assembled structures.[4] However, only a few anion-
driven helical structures have been reported[5,6] because only
few suitable motifs can form anion-responsive oligomer sys-
tems. Therefore, to fabricate such folding structures, it is
necessary to design and synthesize appropriate anion-recep-
tor molecules that exhibit high affinities for anions and can
be transformed into oligomers.
The geometry of molecules, such as cyclic and linear struc-
tures, is an essential factor that determines their electronic
and optical properties and preferred folding and assembling
modes. In contrast to the fairly rigid cyclic geometries ob-
served in hemes and cyclodextrins, linear oligomer and poly-
mer structures in biotic systems can afford various spirals
such as protein a-helices and DNA double helices.[1] Similar
to biological systems, the guest-responsive regulation of heli-
cal structures that comprise synthetic molecules can be
ACHTUNGTRENNUNGachieved by using noncovalent interactions such as hydrogen
[a] Y. Haketa, Prof. Dr. H. Maeda
College of Pharmaceutical Sciences
Institute of Science and Engineering, Ritsumeikan University
Kusatsu 525–8577 (Japan)
Fax : (+81)77-561-2659
As candidates for the building subunits, BF2 complexes of
1,3-dipyrrolyl-1,3-propanediones (e.g., 1a) exhibit anion-
driven dynamic conformational changes such as the inver-
sion of pyrrole rings (Scheme 1a).[7,8] Anion receptors, which
allow absorption and emission in the visible region, can
behave as sensors for anions and, thus, are potential elec-
E-mail: maedahir@ph.ritsumei.ac.jp
[b] Prof. Dr. H. Maeda
PRESTO (Japan) Science and Technology Agency (JST)
Kawaguchi 332-0012 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002748.
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a-aryl-substituted 2b and 2c in 48 and 18% yields, respec-
tively. The same protocols can also be applied to the synthe-
sis of higher oligomers such as tetramer 3a from mono-iodo
2a-I1 and 1,3-benzenediboronic acid bisACTHNUTRGNEUNG(pinacol)ester in an
8% yield. UV/Vis absorption maxima (lmax) of the oligo-
mers in CH2Cl2 are 489 nm for 2a,[8c] 514 nm for 2b, and
478 nm for 3a, thus suggesting no significant p extension rel-
ative to monomer 1a (499 nm)[8c] due to the cross-conjugat-
ed meta-phenylene spacer(s) along with the distortion of
planarity. In particular, the broad absorption band of 3a
with a shoulder at 515 nm suggests the formation of partially
folding structures. From the UV/Vis spectra, which show
almost no or weak exciton couplings of the receptor units,
the oligomers basically prefer linear conformations in the
absence of anions. Further, fluorescence emissions of 2a,b
and 3a were observed at 511, 545, and 564 nm with quantum
yields (FF) of 0.89, 0.91, and 0.73, respectively.
Solid-state anion-binding behaviors of linear oligomers: The
formation of anion-driven helical structures was initially elu-
cidated by the single-crystal X-ray analysis of anion com-
plexes of receptor oligomers prepared by treatment with a
tetrapropylammonium (TPA) salt of ClÀ (Figure 1). In the
solid state, driven by ClÀ complexation, 2a and 3a form
single helices, whereas 2b forms a double helical structure.
All the crystals are racemic states containing equimolar M
and P helices. In 2a·ClÀ, which forms a [1+1]-type helix,
pyrrole rings are completely inverted to bind ClÀ through
multiple hydrogen bonding. In this case, the terminal a-CH
moieties with distances of 3.510(9) and 3.629(8) ꢁ are slight-
ly overlapped to construct a single helix. Two of either M or
P strands of 2a are stacked at distances of 3.4–3.5 ꢁ to form
Scheme 1. a) Anion-binding mode and b) oligomeric derivatives of p-con-
jugated acyclic anion receptors.
tronic and optical materials. Thus, covalently linked oligo-
mers (e.g., 2a,[8c] Scheme 1b) exhibit folding behavior and
resulting drastic changes in electronic and optical properties
because of multiple hydrogen bonding with anions. Here we
report the formation and properties of anion-responsive
linear oligomers with various helical structures, along with a
macrocycle as an extremely efficient anion-binding agent. In
particular, linear oligomers are required to arrange their
conformations by multiple inversions of p-conjugated moiet-
ies such as pyrrole rings. Stable orientations of pyrrole rings,
the NH site of which faces
toward oxygen in the absence
of anions, induce anion-driven
conformation changes. Fairly
slow folding processes due to
pyrrole inversions enable us to
evaluate time-resolved spectral
changes according to anion
binding and to find that esti-
mated kinetic parameters were
correlated with the lengths of
oligomers. To the best of our
knowledge, this is the first
report that discusses the kinet-
ics of the formation of artificial
helical structures.
Results and Discussion
Synthesis of anion receptor
oligomers: The Suzuki coupling
Figure 1. Single-crystal X-ray structures in i) side and ii) top view) as M helices of a) 2a·ClÀ (one of the two in-
reaction of the bis-iodo-substi-
dependent structures), b) 3a·ClÀ (one of the two independent structures), and c) 2b2·ClÀ2. Solvents and TPA
2
[8c]
tuted dimer 2a-I2
with phe-
cations are omitted for clarity. Atom color code: brown, pink, yellow, green, blue, and red refer to carbon, hy-
nylboronic acid gave terminal- drogen, boron, fluorine, nitrogen, and oxygen, respectively.
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p-Conjugated Acyclic Oligopyrroles
FULL PAPER
dimers and their piled-up structures with TPA cations. In
range of 3.4–3.5 ꢁ. Layers that comprise double helices with
the same chirality are alternatively stacked with other layers
that have counter chirality.
contrast, for 3a·ClÀ , intramolecular p–p stacking of the
2
tetramer assisted by two ClÀ is crucial for the formation of
the [1+2]-type single helix. The distance between two ClÀ is
4.638(2)/4.632(2) ꢁ, and each ClÀ is bound by half of the
tetramer. Single helices of 3a are also piled up to form the
columnar structures that consist of either enantiomer. In
sharp contrast to 2a and 3a, which form single helices, a-
phenyl-substituted dimer 2b exhibits the formation of
[2+2]-type assemblies, in which two strands bind two ClÀ by
six hydrogen bonds for each anion: hydrogen-bonding dis-
Anion-binding behaviors of linear oligomers in solution
state: Formation of [1+1]-type single helices of 2a,b in the
solution state, which were also supported by other methods
discussed later, was initially examined by means of NMR
spectral changes. For example, upon the addition of
1.0 equiv of ClÀ as a tetrabutylammonium (TBA) salt to a
solution of 2b in CD2Cl2 at 208C, 1H NMR spectroscopic
signals at d=9.49 (NHa), 9.43 (NHb), 7.69 (CHd), and
6.60 ppm (CHc) decreased in intensity with the concurrent
appearance of new signals (and shifted values) at d=11.32
(+1.83), 10.32 (+0.89), 8.65 (+0.96), and 7.75 ppm (+1.15),
respectively (Figure 2a, i), thereby suggesting the formation
of a ClÀ complex. In particular, the difference between NHa
and NHb (d=1.00 ppm) indicates the existence of [1+1]-
type helices, not [2+2]-type, in the solution state because of
the weak interaction by NHb due to the existence of the
tances to ClÀ in 2b2·ClÀ are 3.551(2) and 3.552(2) ꢁ by
2
outer NH, 3.279(2) and 3.270(2) ꢁ by inner NH, and
3.410(2) and 3.424(2) ꢁ by bridging CH for each anion.[9]
Two ClÀ are located with the distance of 5.802(14) ꢁ inside
the channel structure, which is capped by TPA cations. Al-
though o-CH sites of the terminal phenyl rings and center
phenylene–CH show no significant interactions with anions,
p–p stacking between two strands stabilizes the double heli-
ces; the distance between two helical planes of 2b is in the
Figure 2. a) Schematic representations of ClÀ complexes (left) and 1H NMR spectral changes in CD2Cl2 upon the addition of TBACl (1 and 2 equiv, re-
spectively; right) of i) 2b and ii) 3a (ROE correlations are indicated). b) DFT-optimized structures of i) 2b and 2b·ClÀ (side and top view) and ii) 3a and
3a·ClÀ2 (side and top view).
Chem. Eur. J. 2011, 17, 1485 – 1492
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1487

H. Maeda and Y. Haketa
neighboring terminal phenyl moiety. In addition, there are
no driving forces to assemble two [1+1]-type single helices
to double helices in the solution state. At À508C, the
1H NMR spectroscopic signal of b-ethyl-CH2 units (e.g., He)
of 2b·ClÀ splits into two complicated signals through diaste-
reotopic coupling due to the formation of helical structures.
Similarly, the 19F NMR spectroscopic signal for the BF2
moiety of 2b at À508C exhibited a singlet peak at d=
À142.2 ppm and split into two doublet signals at d=À142.1
and À143.6 ppm with 19F,19F coupling constants of 82 Hz
upon the addition of 1.0 equiv of ClÀ. At 208C, only broad
and coalesced signals were observed, which may be due to
the faster interconversion between helical enantiomers. On
the other hand, 2a·ClÀ showed weak diastereotopic coupling
1
in H and 19F NMR spectra even at À908C because of the
absence of terminal aryl rings, and the [1+1]-type ClÀ com-
plex of 2c exhibited split 19F NMR spectroscopic signals
even at RT due to slower interconversion. Dimers 2a–c,
even with an excess amount of ClÀ (10 equiv), showed [1+1]
binding to be the most stable mode.[10]
In the presence of 2 equiv of TBACl in CD2Cl2 at À508C,
tetramer 3a, which is less soluble without TBA salts of
1
anions in this solvent, showed downfield H NMR spectro-
Figure 3. UV/Vis (solid line) and fluorescence (broken line, excited at
a) 478 and b) 458 nm) spectra: a) 2b (green), 2b·ClÀ (blue), and photo-
graphs of 2b and 2b·ClÀ (inset) in CH2Cl2 (5 mm); b) 3a (green), 3a·ClÀ
(blue), and 3a·ClÀ (purple), and photographs of 3a and 3a·ClÀ (inset)
scopic signals at d=11.30 (NHa), 10.75 (NHb), 10.28 (NHc,d),
9.09 (CHe), 8.02 (CHf), 7.21 (CHi), and 7.01 ppm (CHj) that
were ascribable to the interaction sites of 3a·ClÀ . Due to
2
2
2
in CH2Cl2 (2.5 mm).
the low solubility of 3a, the details of the [1+1]-type com-
plex could not be examined at the millimolar-order concen-
tration in CD2Cl2. The helical structure of 3a·ClÀ as ob-
This resulted in a shift of the absorption at 476 nm in
CH2Cl2 to those at 452 and 453 nm that corresponded to
2
served in the solid state was suggested by the downfield
shift of CHe interacting with both ClÀ; this was also support-
ed by COSY and ROESY, particularly the correlations be-
tween CHn and NHa and between CHn and CHk (Figure 2a,
ii). Terminal a-CHn was observed at d=5.49 ppm, which is
upfield shifted at d=0.71 ppm compared to the correspond-
ing CH of 2a·ClÀ; this is presumably due to the shielding
effect of the stacking pyrrole unit. Four sets of signals in the
19F NMR spectra also suggested a helical structure. Other
possible binding modes, including an unfolded [1+4] com-
plex, were not observed in the presence of an excess
amount (10 equiv) of TBACl under these conditions. Anion-
3a·ClÀ and 3a·ClÀ , respectively, by the addition of 2 and
2
2000 equiv of ClÀ (Figure 3b). On the other hand, under the
same conditions, fluorescence emissions of 2a,b and 3a
changed to those observed at 520, 550, and 562/556 nm with
quantum yields (FF) of 0.72, 0.76, and 0.50/0.48, respectively.
The anion-binding modes were supported by Job plots (2b),
stepwise spectral changes (3a), and ESI-TOF MS of ClÀ
complexes of the oligomers: [1+1]-type complexes for 2a,b
and a [1+2]-type complex for 3a in the solution state. In the
case of 2b, the binding mode in solution is different from
that in the solid state, which may induce further aggregation
of the [1+1] complex to afford a [2+2]-type double helix. To
binding single helices of 2a·ClÀ, 2b·ClÀ, and 3a·ClÀ in the
2
solution state are also supported by the theoretically opti-
mized structures (Figure 2b, right),[11,12] which are complete-
ly different conformations of the optimized conformations
of the anion-free oligomers (Figure 2b, left).
the best of our knowledge, 3a·ClÀ is the first example of a
2
single helix that contains two anions,[13] the electrostatic re-
pulsion of which may be subdued by other factors, such as
the formation of stable folding structure. Further, 2a–c and
3a exhibited significantly augmented binding constants Ka
for halide anions in CH2Cl2, determined by UV/Vis absorp-
tion spectral changes upon the addition of TBA salts
(Table 1). For example, Ka values in the [1+1] complexation
with ClÀ are 5.9ꢂ107, 1.2ꢂ107, and 1.2ꢂ108 mÀ1, respectively,
which are much higher than that of 1a (2700mÀ1). The Ka
values for BrÀ and IÀ in CH2Cl2 were 4.8ꢂ106 and 5.8ꢂ
104 mÀ1 for 2a, 2.4ꢂ104 and 6.8ꢂ103 mÀ1 for 2b, 2.3ꢂ107 and
8.8ꢂ104 mÀ1 for 3a, and 300 and 14mÀ1 for 1a, respectively.
These oligomers show the selectivity for halide anions as
ClÀ >BrÀ >IÀ according to their basicities and ion sizes. Fur-
Characteristic points of the pyrrole-based oligomers 2a–c
and 3a are electronic and optical properties that can be
tuned by anion binding and the resulting molecular folding.
The oligomers showed dramatic anion-driven changes in the
UV/Vis absorption and fluorescence spectra. Upon the addi-
tion of ClÀ as a TBA salt, the absorption bands of 2a–c at
489, 514, and 521 nm in CH2Cl2 decreased with new bands
at 444, 474, and 484 nm, respectively, presumably due to the
exciton coupling of the monomeric chromophore units (Fig-
ure 3a). Tetramer 3a exhibited the stepwise spectral changes
for [1+1]- and [1+2]-type binding under diluted conditions.
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p-Conjugated Acyclic Oligopyrroles
FULL PAPER
Table 1. Binding constants (Ka, mÀ1) of 1a (reference), 2a–c, and 3a with
by stopped-flow measurements has been correlated with the
conformation changes, which require the inversions of pyr-
role rings. Furthermore, fairly flexible behaviors in the heli-
cal ClÀ complexes of the oligomers were also suggested by
variable-temperature absorption spectra.
various halide anions in CH2Cl2.[a]
1a[b]
2a
2b
2c
3a
ClÀ
BrÀ
IÀ
2700
59000000
12000000
850000
K1:
K2:
K1:
K2:
K1:
K2:
120000000
3200
23000000
1600
300
17
4800000
58000
24000
6800
38000
130
Synthesis and properties of the macrocycle that exhibits ex-
tremely high anion affinity: The crystal and optimized struc-
tures of 2a·ClÀ inspired us to connect the proximal terminal
pyrrole a-positions of 2a to obtain cyclic structures. The Pd-
catalyzed intramolecular coupling[15] of 2a-I2 provided mac-
rocycle 4a in a 31% yield with the existence of ClÀ
(TBACl) as a template. To our surprise, 4a was isolated as a
TBA salt of a stable ClÀ complex (4a·ClÀ; Figure 5a, i) even
after purification by several executions of silica gel column
88000
33
[a] The errors in Ka for anions are within 10% as observed in the Sup-
porting Information. [b] Ref. [8c].
ther, K2 values of 3a for ClÀ, BrÀ, and IÀ are 3200, 1600, and
33mÀ1, respectively, which are smaller than those of [1+1]-
type binding.[14] This result suggests the significant negative
cooperativity of 3a for second anion binding presumably
due to electronic repulsions between two anions captured in
the helices.
UV/Vis absorption spectral changes of 2a–c and 3a as de-
tected by stopped-flow measurements (Figure 4) exhibited
the time-resolved anion-driven dynamic conformation
changes and kinetic parameters k of 2a–c and 3a as 1.2ꢂ
107, 4.8ꢂ106, 1.6ꢂ106, and 1.2ꢂ106 mÀ1 sÀ1, respectively, for
[1+1] complexation with ClÀ. This result suggests a slower
folding process by longer oligomers even when possessing
higher anion affinities. The examination here is the first ex-
ample of the time-resolved detection of the formation of or-
dered synthetic helical structures. The timescale detectable
1
chromatography. The H NMR spectra of 4a·ClÀ in CD2Cl2
at 208C showed signals at d=11.74 (NHa), 10.83 (NHb), 8.72
(CHc), and 8.39 ppm (CHd) (Figure 5a, ii), which shifted
downfield relative to the corresponding protons of 2a. At
À508C, new signals corresponding to twisted sandwichlike
dimer 4a2·ClÀ appear at 10.13, 9.34, 9.27, and 8.86 ppm for
NH, and d=7.75, 7.50, 7.45, 7.30, 7.04, 6.81, and 6.58 ppm
for other protons. The dimerization constant Kdim, defined
as ([4a2·ClÀ][ClÀ])/[4a·ClÀ]2, is estimated to be 2.5ꢂ10À3 at
ACTHNUTRGENNUG CAHTUNGTRENNUGN
À508C. By the addition of another 1 equiv of TBACl, the
stacking dimer cannot be observed.[16] In addition, the re-
moval of ClÀ in 4a·ClÀ was attempted by treatment with var-
ious Ag+ salts; it resulted in the formation of a complicated
mixture including decomposed species. On the basis of these
observations, ClÀ was found to be tightly bound by 4a and
to stabilize this cyclic structure; competitive titration of 2a
with 4a·ClÀ suggested an extremely high Ka value of 4a for
ClÀ (ca. 2ꢂ1010 mÀ1) in CH2Cl2. This value is much higher
than that of the triazole-based macrocycle, 1.1ꢂ107 mÀ1 in
CH2Cl2.[5e,17] Further, relative to acyclic 2a and 2a·ClÀ, cyclic
4a·ClÀ in CH2Cl2 exhibited unique electronic properties in a
fairly sharp absorption band at 450 nm along with a broad
band around 605 nm (Figure 5b, i). Interestingly, in contrast
to 2a and 2a·ClÀ, the macrocycle 4a·ClÀ showed a redshift-
ed emission at 660 nm (lex =450 nm) with FF of 0.31 in
CH2Cl2 (Figure 5b, ii).
Conclusion
The linear and cyclic structures reported here are fascinating
molecular architectures and potential building blocks of
stimuli-responsive utility materials. Compared to anion-as-
sisted helical structures reported thus far, the electronic and
optical properties of the oligopyrrole systems reported here
can be controlled by anions, because the flexibility, stability,
and p conjugation of these oligomers are suitable for visible
light excitation and direct electronic perturbation in pyrrole
NH by anion binding. Significant changes in conformations
by anions are due to the requirement of inversions of pyr-
role rings that result in the formation of helical structures.
Time-resolved observations of the changes in the electronic
Figure 4. a) Time-resolved UV/Vis absorption spectral changes and
b) time-dependent changes at 489 nm detected by stopped-flow measure-
ment of 2a (5 mm) upon the addition of ClÀ (1 and 10 equiv for i and ii,
respectively) as a TBA salt in CH2Cl2. Different time scales in i and ii
depend on the amounts of added anion: detailed time-resolved examina-
tion in ii requires an excess amount of anion due to the analysis through
pseudo-first-order kinetic parameters.
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1489

H. Maeda and Y. Haketa
Figure 5. a) i) Schematic and DFT-optimized structure of 4a·ClÀ and ii) selected 1H NMR spectrum of 4a·ClÀ as a TBA salt in CD2Cl2 (1 mm) at RT;
b) i) UV/Vis and ii) fluorescence spectra (excited at 453 nm for 2a and 2a·ClÀ and 450 nm (lmax) for 4a·ClÀ) of 2a (green), 2a plus 1 equiv of ClÀ (blue),
and 4a·ClÀ (red) in CH2Cl2 (5 mm for 2a and 2a·ClÀ, 10 mm for 4a·ClÀ) and their photographs (inset).
(17.3 mg, 48%) as a red solid. Rf =0.30 (1% MeOH/CH2Cl2); 1H NMR
(600 MHz, CDCl3, 208C): d=9.38 (s, 2H; NH), 9.35 (s, 2H; NH), 7.65 (s,
1H; phenylene-CH), 7.62–7.60 (m, 1H; phenylene-CH), 7.55–7.54 (m,
states by anion binding revealed the effects of lengths of the
oligomers for folding behaviors. Further higher organization
of helical and cyclic structures assisted by peripheral modifi-
cation, along with chiral amplification in helices induced by
appropriate chiral auxiliaries, would help in the realization
of utility devices such as circular polarized light emitters in
the near future.
2H; phenylene-CH), 7.53–7.52 (m, 4H; phenyl-o-CH), 7.50–7.47 (m, 4H;
phenyl-m-CH), 7.43–7.40 (m, 2H; phenyl-p-CH), 6.59 (s, 2H; bridged-
CH), 2.88 (m, 8H; CH2CH3), 2.65 (m, 8H; CH2CH3), 1.38–1.35 (m, 12H;
CH2CH3), 1.23–1.19 ppm (m, 12H; CH2CH3); UV/Vis (CH2Cl2): lmax
(e)=514.0 nm (2.4ꢂ105 mÀ1 cmÀ1); fluorescence (CH2Cl2): lem (lex)=
546.0 nm (514.0 nm); ESI-TOF MS: m/z: (%): 949.46 (100), 950.47 (56);
calcd for C56H59B2F4N4O4: 949.47 [MÀH]À. This compound as a ClÀ com-
plex was further characterized by X-ray diffraction analysis.
Bis(3,4,5-trihexadecyloxyphenyl)-substituted phenylene-bridged dimer
(2c): A Schlenk tube filled with 2a-I2 (80.0 mg, 0.076 mmol), 3,4,5-tri-
[8c]
Experimental Section
hexadecyloxyphenylboronic acid pinacol ester[8g] (176.2 mg, 0.19 mmol),
tetrakis(triphenylphosphine)palladium(0) (21.96 mg, 0.019 mmol), and
cesium carbonate (185.7 mg, 0.57 mmol) was flushed with nitrogen and
charged with a mixture of degassed DMF (2.5 mL), toluene (2.5 mL),
and water (0.2 mL). The mixture was heated at 908C for 20 h, cooled,
then partitioned between water and CH2Cl2. The combined extracts were
dried over anhydrous MgSO4 and evaporated. The residue was then chro-
matographed over silica gel flash column (eluent: 0.5% MeOH/CH2Cl2)
and recrystallized from CH2Cl2/MeOH to give 2c (33.3 mg, 18%) as a
red solid. Rf =0.30 (1% MeOH/CH2Cl2); 1H NMR (600 MHz, CDCl3,
208C): d=9.37 (s, 2H; NH), 9.28 (s, 2H; NH), 7.64 (s, 1H; phenylene-
CH), 7.62–7.59 (m, 1H; phenylene-CH), 7.55–7.53 (m, 2H; phenylene-
CH), 6.66 (s, 4H; phenyl-o-CH), 6.57 (s, 2H; bridged-CH), 4.02–4.00 (m,
12H; OCH2), 2.88–2.84 (m, 8H; CH2CH3), 2.66 (q, J=7.8 Hz, 4H;
CH2CH3), 2.62 (q, J=7.8 Hz, 4H; CH2CH3), 1,83 (tt, J=7.2 and 6.6 Hz,
8H; OCH2CH2), 1.77 (tt, J=7.2 and 6.6 Hz, 4H; OCH2CH2), 1.52–1.47
(m, 12H; OC2H4CH2), 1.37–1.34 (m, 12H; CH2CH3), 1.34–1.25 (m,
144H; OC3H6C12H24), 1.22–1.19 (m, 12H; CH2CH3), 0.88–0.86 ppm (m,
18H; OC15H30CH3); UV/Vis (CH2Cl2): lmax (e)=521.5 nm (2.2ꢂ
105 mÀ1 cmÀ1); fluorescence (CH2Cl2): lem (lex)=557.0 (521.0 nm); ESI-
TOF MS: m/z (%): 2390.94 (100), 2391.95 (73); calcd for
General procedures: Starting materials were purchased from Wako Pure
Chemical Industries Ltd., Nacalai Tesque Inc, and Sigma–Aldrich Co.
and used without further purification unless otherwise stated. UV-visible
spectra were recorded using a Hitachi U-3500 spectrometer. Fluores-
cence spectra were recorded using a Hitachi F-4500 fluorescence spec-
trometer for ordinary solutions and a Hamamatsu Quantum Yields Meas-
urements System for Organic LED Materials C9920-02 for measurement
of quantum yields. NMR spectra used in the characterization of products
were recorded using a JEOL ECA-600 600 MHz spectrometer. All NMR
spectra were referenced to solvent. Matrix-assisted laser desorption ioni-
zation time-of-flight mass spectrometries (MALDI-TOF MS) were re-
corded using a Shimadzu Axima-CFRplus in negative mode. Electrospray
ionization mass spectrometric studies (ESI-MS) were recorded using a
Bruker microTOF with the negative mode ESI-TOF method. TLC analy-
ses were carried out on aluminum sheets coated with silica gel 60 (Merck
5554). Column chromatography was performed using Sumitomo alumina
KCG-1525, Wakogel C-200, C-300, and Merck silica gel 60 and 60H.
Diphenyl-substituted phenylene-bridged dimer (2b):
A
Schlenk tube
filled with 2a-I2 (62.1 mg, 0.059 mmol), phenylboronic acid (15.83 mg,
0.129 mmol), tetrakis(triphenylphosphine)palladium(0) (11.56 mg,
[8c]
C152H251B2F4N4O10: 2390.94 [MÀH]À.
0.01 mmol), and cesium carbonate (67.67 mg, 0.18 mmol) was flushed
with nitrogen and charged with a mixture of degassed DMF (3 mL), tolu-
ene (3 mL), and water (0.1 mL). The mixture was heated at 908C for
20 h, cooled, then partitioned between water and CH2Cl2. The combined
extracts were dried over anhydrous MgSO4 and evaporated. The residue
was then chromatographed over silica gel flash column (eluent: 1%
MeOH/CH2Cl2) and recrystallized from CH2Cl2/hexane to give 2b
[8c]
Tetramer (3a):
A
Schlenk tube filled with 2a-I1
(230.0 mg,
0.249 mmol), benzene-1,3-diboronic acid pinacol ester (41.09 mg,
0.124 mmol), tetrakis-(triphenylphosphine)palladium(0) (28.89 mg,
0.025 mmol), and cesium carbonate (121.21 mg, 0.372 mmol) was flushed
with nitrogen and charged with a mixture of degassed DMF (4 mL), tolu-
ene (4 mL), and water (0.1 mL). The mixture was heated at 908C for
1490
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Chem. Eur. J. 2011, 17, 1485 – 1492

p-Conjugated Acyclic Oligopyrroles
FULL PAPER
20 h, cooled, then partitioned between water and CH2Cl2. The combined
extracts were dried over anhydrous MgSO4 and evaporated. The residue
was then chromatographed over silica gel flash column (eluent: 1%
MeOH/CHCl3) to give 3a (12.4 mg, 6%) as a red solid. Rf =0.44 (3%
MeOH/CHCl3); 1H NMR (600 MHz, [D8]THF, 208C: [D8]THF was used
due to the low solubility of 3a in CDCl3 in the absence of anions as TBA
salts): d=11.42 (s, 2H; NH), 11.34 (s, 6H; NH), 7.78 (s, 3H; phenylene-
CH), 7.60 (m, 6H; phenylene-CH), 7.57 (m, 3H; phenylene-CH), 7.02 (s,
2H; pyrrole-CH), 6.63 (s, 2H; bridged-CH), 6.54 (s, 2H; bridged-CH),
2.94 (m, 12H; CH2CH3), 2.85 (m, 4H; CH2CH3), 2.67 (m, 12H;
CH2CH3), 2.51 (m, 4H; CH2CH3), 1.36 (m, 18H; CH2CH3), 1.28 (m, 6H;
CH2CH3), 1.22 (m, 6H; CH2CH3), 1.18 ppm (m, 18H; CH2CH3); UV/Vis
(CH2Cl2): lmax (e)=478.0 nm (2.8ꢂ105 mÀ1 cmÀ1); The e value in CH2Cl2
was estimated by means of a soluble THF stock solution, the concentra-
tion of which was determined by integrals of 1H NMR spectroscopy in
[D8]THF in comparison with a reference additive (EtOAc in this case);
fluorescence (CH2Cl2): lem (lex)=564.0 nm (478.0 nm); ESI-TOF MS:
m/z (%): 1669.82 (100); calcd for C94H105B4F8N8O8: 1669.84 [MÀH]À.
This compound as a ClÀ complex was further characterized by X-ray dif-
fraction analysis.
Table 2. Crystallographic details for anion complexes.
2a·TPACl
2b ·
C56H60B2F4N2O4· C94H106B4F8N8O8·
(TPACl)2
(TPACl)2
3a·ACTHNGUTRENU(NG TPACl)2
formula
C44H52B2F4N4O4·
TPACl·1.75CH2ClCH2Cl TPACl·0.5CH2Cl2 CAHTUNGTRENNNUG
Mr
1193.49
1214.97
2114.72
0.30ꢂ0.30ꢂ0.10
crystal
size [mm]
crystal
system
space
group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
0.50ꢂ0.20ꢂ0.10
0.40ꢂ0.30ꢂ0.20
monoclinic
monoclinic
triclinic
¯
P21/c (no. 14)
P2/c (no. 13)
P1 (no. 2)
17.3673(12)
23.9699(16)
36.2984(19)
90
15.683(4)
17.188(3)
28.437(4)
90
19.305(3)
24.644(3)
29.522(5)
88.52(5)
81.42(6)
89.69(5)
13883(4)
1.012
b [8]
118.387(3)
90
13293.8(15)
1.193
119.134(8)
90
6696(9)
1.205
g [8]
V [ꢁ3]
1calcd
[gcmÀ3
Z
]
Macrocycle as a TBACl complex (4a·TBACl): A Schlenk tube filled with
4
2
4
[8c]
2a-I2
(170.0 mg, 0.162 mmol), hydroquinone (93.67 mg, 0.85 mmol),
T [K]
90(2)
0.255
123(2)
0.158
123(2)
0.107
cesium carbonate (554.2 mg, 1.70 mmol), and tetrabutylammonium chlo-
ride (907.14 mg, 3.26 mmol) was degassed and flushed with nitrogen, and
charged with degassed DMA (68 mL). Then the solution of palladium
mACHTUGNETRN(UNNG MoKa)
[mmÀ1
reflns
]
71657
24718
57080
13719
86346
38845
acetate (19.04 mg, 0.085 mmol) and triACTHNUGTRNEUNG(o-tolyl)phosphine (25.84 mg,
unique
reflns
0.085 mmol) in degassed DMA (5 mL) was added. The mixture was
heated at 958C for 2 d, cooled, then partitioned between water and
CH2Cl2. The combined extracts were dried over anhydrous MgSO4 and
evaporated. The residue was then chromatographed over silica gel flash
column (eluent: 3% MeOH/CH2Cl2 and 40% EtOAc/hexane) and re-
crystallized from CH2Cl2/hexane to give 4a·TBACl (53.6 mg, 31%) as a
dark green solid. 1H NMR (600 MHz, CDCl3, 208C): d=11.63 (s, 2H;
NH), 10.73 (s, 2H; NH), 8.70 (s, 1H; phenylene-CH), 8.36 (s, 2H;
bridged-CH), 7.43 (m, 3H; phenylene-CH), 2.94 (t, J=8.4 Hz, 8H;
NCH2), 2.88 (m, 8H; CH2CH3), 2.68 (m, 4H; CH2CH3), 2.59 (q, J=
7.2 Hz, 4H; CH2CH3), 1.41 (m, 8H; NCH2CH2), 1.24 (m, 18H; CH2CH3),
1.14 (m, 6H; CH2CH3), 1.14 (m, 8H; NC2H4CH2), 0.81 ppm (t, J=
7.2 Hz, 12H; NC3H6CH3); UV/Vis (CH2Cl2): lmax (e)=450.0 nm (1.0ꢂ
105 mÀ1 cmÀ1); fluorescence (CH2Cl2): lem (lex)=660.0 nm (450.0 nm);
ESI-TOF-MS: m/z (%): 831.34 (100); calcd for C44H50B2F4N4O4Cl: 831.37
[M+Cl]À.
variables 1448
796
2748
0.71075
0.1112
lMo [ꢁ] 0.71073
0.71069
0.0634
Ka
R1
0.1078
0.3071
1.025
(I>2s(I))
wR2
0.1574
1.037
0.2689
0.914
(I>2s(I))
GOF
data can be obtained free of charge from The Cambridge Crystallograph-
ic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Stopped-flow measurements: Stopped-flow measurements were carried
out using a Unisoku RSP-1000 stopped-flow rapid-scan spectroscopy
system.
DFT calculations: Ab initio and semiempirical calculations of linear and
cyclic oligomers and their ClÀ-binding complexes were carried out by
using the Gaussian 03 program[11] and an HP Compaq DC5100 SFF com-
puter. The structures were optimized, and the total electronic energies
Single-crystal X-ray analysis: Crystallographic data for ClÀ complexes of
receptor oligomers are summarized in Table 2.
A single crystal of
2a·TPACl was obtained by vapor diffusion of hexane into a 1,2-dichloro-
ethane (10% toluene) solution. The data crystal was a yellow prism of
approximate dimensions 0.50 mmꢂ0.20 mmꢂ0.10 mm. Data were col-
lected at 90 K using a Bruker SMART CCDC diffractometer with graph-
ite-monochromated MoKa radiation (l=0.71075 ꢁ), and the structure
were calculated at the B3LYP level by using the 6-31G
ACHTUNGTREN(NGNU d,p) and 6-31+G-
AHCTUNGTRENNUNG
was solved by direct methods. A single crystal of 2b2·ACTHNUGTRNE(UNG TPACl)2 was ob-
tained by vapor diffusion of hexane into a 1,2-dichloroethane solution.
The data crystal was a red prism of approximate dimensions 0.40 mmꢂ
Acknowledgements
0.30 mmꢂ0.20 mm. Data were collected at 123 K using
a Rigaku
RAXIS-RAPID diffractometer with graphite-monochromated MoKa ra-
diation (l=0.71075 ꢁ), and the structure was solved by direct methods.
A single crystal of 3a·ACHTNUGTRNEU(NG TPACl)2 was obtained by vapor diffusion of
This work was supported by a grant-in-aid for Young Scientists (B) (no.
21750155) and for Scientific Research in Priority Area “Super-Hierarchi-
cal Structures” (no. 19022036) from the MEXT and Ritsumeikan R-
GIRO project (2008–2013). The authors thank Prof. Atsuhiro Osuka, Dr.
Naoki Aratani, Dr. Yasuhide Inokuma, Mr. Eiji Tsurumaki, and Mr.
Taro Koide, Kyoto University, for the X-ray analyses; Prof. Hiroshi Shi-
nokubo and Dr. Satoru Hiroto, Nagoya University, for ESI-TOF MS
measurements; and Prof. Hitoshi Tamiaki, Ritsumeikan University, for
various measurements. Y.H. thanks JSPS for a Research Fellowship for
Young Scientists.
octane into a 1,2-dichloroethane solution. The data crystal was an orange
prism of approximate dimensions 0.40 mmꢂ0.30 mmꢂ0.20 mm. Data
were collected at 123 K using a Rigaku RAXIS-RAPID diffractometer
with graphite-monochromated MoKa radiation (l=0.71075 ꢁ), and the
structure was solved by direct methods. In each compound, the non-hy-
drogen atoms were refined anisotropically. The calculations were per-
formed using the Crystal Structure crystallographic software package by
the Molecular Structure Corporation.[18] The scattering that arose from
the presence of disordered solvents in the crystals was removed by use of
the utility SQUEEZE in the PLATON software package.[19,20] CCDC-
[1] D. Voet, J. G. Voet, Biochemistry, 3rd ed., Wiley, New York, 2004.
[2] Selected book and reviews for artificial helical structures: a) Fol-
damers: Structures, Properties, and Applications (Eds.: S. Hecht, I.
778926 (2a·TPACl), 778927 (2b2·ACHTUNGTRENG(NU TPACl)2), and 778928 (3a·ACHTUNGTNER(NUGN TPACl)2)
contain the supplementary crystallographic data for this paper. These
Chem. Eur. J. 2011, 17, 1485 – 1492
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1491

H. Maeda and Y. Haketa
Huc), Wiley-VCH, Weinheim, 2007; b) D. J. Hill, M. J. Mio, R. B.
Prince, T. S. Hughes, J. S. Moore, Chem. Rev. 2001, 101, 3893–4011;
c) E. Yashima, K. Maeda, Y. Furusho, Acc. Chem. Res. 2008, 41,
1166–1180; d) D. Haldar, C. Schmuck, Chem. Soc. Rev. 2009, 38,
363–371; e) H. Juwarker, J.-m. Suk, K.-S. Jeong, Chem. Soc. Rev.
2009, 38, 3316–3325.
[9] Details for 2a·ClÀ and 3a·ClÀ are summarized in the Supporting In-
2
formation.
[10] Bridging aryl units are essential for controlling anion-binding
modes, as suggested by the observation that thiophene-bridged
dimer exhibits [1+1]- and [1+2]-type complexes in the presence of
an excess amount of ClÀ in CD2Cl2.
[3] Selected reviews for metal-assisted helical structures: a) C. Piguet,
G. Bernardinelli, G. Hopfgartner, Chem. Rev. 1997, 97, 2005–2062;
b) M. Albrecht, Chem. Rev. 2001, 101, 3457–3497; c) J. R. Nitschke,
Acc. Chem. Res. 2007, 40, 103–112; d) R. W. Saalfrank, H. Maid, A.
Scheurer, Angew. Chem. 2008, 120, 8924–8956; Angew. Chem. Int.
Ed. 2008, 47, 8794–8824.
[4] Selected books for anion binding: a) Supramolecular Chemistry of
Anions (Eds.: A. Bianchi, K. Bowman-James, E. Garcꢃa-EspaÇa),
Wiley-VCH, New York, 1997; b) Fundamentals and Applications of
Anion Separations (Eds.: R. P. Singh, B. A. Moyer), Kluwer Aca-
demic/Plenum Publishers, New York, 2004; c) Anion Sensing, Topics
in Current Chemistry, Vol. 255 (Ed. I. Stibor), Springer, Berlin 2005;
d) J. L. Sessler, P. A. Gale, W.-S. Cho, Anion Receptor Chemistry,
RSC, Cambridge, 2006; e) Structure and Bonding, Recognition of
Anions, Vol. 129 (Ed.: R. Vilar), Springer, Berlin, 2008.
[5] Selected examples of anion-assisted single helices: a) K.-J. Chang,
B.-N. Kang, M.-H. Lee, K.-S. Jeong, J. Am. Chem. Soc. 2005, 127,
12214–12215; b) J.-m. Suk, S.-K. Jeong, J. Am. Chem. Soc. 2008,
130, 11868–11869; c) V. R. Naidu, M. C. Kim, J.-m. Suk, H.-J. Kim,
M. Lee, E. Sim, K.-S. Jeong, Org. Lett. 2008, 10, 5373–5376; d) U.-I.
Kim, J.-m. Suk, V. R. Naidu, K.-S. Jeong, Chem. Eur. J. 2008, 14,
11406–11414; e) H. Juwarker, J. M. Lendhardt, D. M. Pham, S. L.
Craig, Angew. Chem. 2008, 120, 3800–3803; Angew. Chem. Int. Ed.
2008, 47, 3740–3743; f) Y. Li, A. H. Flood, J. Am. Chem. Soc. 2008,
130, 12111–12122; g) J.-i. Kim, H. Juwarker, X. Liu, M. S. Lah, K.-S.
Jeong, Chem. Commun. 2010, 46, 764–766; h) Y. Hua, A. H. Flood,
J. Am. Chem. Soc. 2010, 132, 12838–12840.
[6] There have been few examples of anion-assisted double helices: a) J.
Sꢄnchez-Quesada, C. Seel, P. Prados, J. de Mendoza, J. Am. Chem.
Soc. 1996, 118, 277–278; b) S. J. Coles, J. G. Frey, P. A. Gale, M. B.
Hursthouse, M. E. Light, K. Navakhun, G. L. Thomas, Chem.
Commun. 2003, 568–569; c) S. J. Brooks, L. S. Evans, P. A. Gale,
M. B. Hursthouse, M. E. Light, Chem. Commun. 2005, 734–736.
[7] a) H. Maeda in Handbook of Porphyrin Science, Vol. 8 (Eds.: K. M.
Kadish, K. M. Smith, R. Guilard), World Scientific, New Jersey,
2010, Chapter 38; b) H. Maeda in Anion Complexation in Supra-
molecular Chemistry, Topics in Heterocyclic Chemistry, Vol. 24
(Eds.: P. A. Gale, W. Dehaen), Springer, Berlin, 2010, pp. 103–144;
c) H. Maeda in Supramolecular Soft Matter: Applications in Materi-
als and Organic Electronics (Ed.: T. Nakanishi), Wiley, submitted;
d) H. Maeda, Y. Haketa, Pure Appl. Chem., DOI: 10.1351/PAC-
CON-10-09-34.
[11] Gaussian 03 (Revision C.01), M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O.
Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Fores-
man, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Na-
nayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wallingford
CT, 2004.
[12] DOSY of 2b, 2b·ClÀ, and 3a·ClÀ in CD2Cl2 show no distinct diffu-
2
sion coefficients (D) as ÀlogD of 9.37, 9.48, and 9.48, respectively,
thereby suggesting no significant differences in their sizes even
though the oligomers form folded structures as TBA complexes.
[13] Cyclic double helix that contains two anions: D. Meshcheryakov, V.
Bçhmer, M. Bolte, V. Hubscher-Bruder, F. Arnaud-Neu, H. Hersch-
bach, A. van Dorsselaer, I. Thondorf, W. Mçgelin, Angew. Chem.
2006, 118, 1679–1682; Angew. Chem. Int. Ed. 2006, 45, 1648–1652.
[14] The K1 and K2 values of 3a were estimated by SPANA v. 2.03: Spec-
tral Analyses Program (developed by Prof. Yasuhisa Kuroda, Kyoto
Institute of Technology).
[15] D. D. Hennings, T. Iwama, V. H. Rawal, Org. Lett. 1999, 1, 1205–
1208.
[16] Similar anion-binding sandwichlike dimers in solution state have al-
ready been reported: a) S. Kubik, R. Goddard, R. Kirchner, D. Nolt-
ing, J. Seidel, Angew. Chem. 2001, 113, 2722–2725; Angew. Chem.
Int. Ed. 2001, 40, 2648–2651; b) K. H. Choi, A. D. Hamilton, J. Am.
Chem. Soc. 2001, 123, 2456–2457; c) K. H. Choi, A. D. Hamilton, J.
Am. Chem. Soc. 2003, 125, 10241–10249; d) Z. Rodriguez-Docam-
po, S. I. Pascu, S. Kubik, S. Otto, J. Am. Chem. Soc. 2006, 128,
11206–11210; e) Y. Li, M. Pink, J. A. Karty, A. H. Flood, J. Am.
Chem. Soc. 2008, 130, 17293–17295.
[17] Recent examples of macrocycles that exhibit high anion-binding
constants, which were estimated in different solvents and cannot be
compared with that of 4a: a) K-J. Chang, D. Moon, M. S. Lah, K-S.
Jeong, Angew. Chem. 2005, 117, 8140–8143; Angew. Chem. Int. Ed.
2005, 44, 7926–7929; b) J. L. Sessler, D. An, W-S. Cho, V. Lynch, M.
Marquez, Chem. Commun. 2005, 540–542.
[8] a) H. Maeda, Y. Kusunose, Chem. Eur. J. 2005, 11, 5661–5666; b) H.
Maeda, Y. Haketa, T. Nakanishi, J. Am. Chem. Soc. 2007, 129,
13661–13674; c) H. Maeda, Y. Haketa, Org. Biomol. Chem. 2008, 6,
3091–3095; d) H. Maeda, Y. Ito, Y. Haketa, N. Eifuku, E. Lee, M.
Lee, T. Hashishin, K. Kaneko, Chem. Eur. J. 2009, 15, 3706–3719;
e) H. Maeda, Y. Bando, Y. Haketa, Y. Honsho, S. Seki, H. Nakaji-
ma, N. Tohnai, Chem. Eur. J. 2010, 16, 10994–11002; f) Y. Haketa,
S. Sasaki, N. Ohta, H. Masunaga, H. Ogawa, N. Mizuro, F. Araoka,
H. Takezoe, H. Maeda, Angew. Chem. 2011, DOI: 10.1002/
ange.201006356; Angew. Chem. Int. Ed. 2011, DOI: 10.1002/
anie.201006356; g) Y. Haketa, S. Sakamoto, T. Nakanishi, H. Maeda,
unpublished results.
[18] CrystalStructure (Ver. 3.8), Single Crystal Structure Analysis Soft-
ware, Rigaku/MSC and Rigaku Corporation, The Woodlands, 2006.
[19] A. L. Spek, PLATON,
A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, 2005.
[20] P. van der Sluis, A. L. Spek, Acta Crystallogr. Sect. A 1990, 46, 194–
201.
Received: September 24, 2010
Published online: December 16, 2010
1492
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 1485 – 1492