Supramolecular assemblies derived from Formyl-Substituted π-Conjugated acyclic anion receptors

Article abstract of DOI:10.1002/ejoc.200901346

We report on the synthesis and properties of formyl-substituted dipyrrolyl diketone-BF₂ complexes (anion receptors) and their extended derivatives. The formyl-substituted receptors exhibited efficient anion-binding behavior and complicated soli

Full text of DOI:10.1002/ejoc.200901346

FULL PAPER
DOI: 10.1002/ejoc.200901346
Supramolecular Assemblies Derived from Formyl-Substituted π-Conjugated
Acyclic Anion Receptors
Hiromitsu Maeda,*[a,b] Rika Fujii,[a] and Yohei Haketa[a]
Keywords: Anions / Boron / Formyl units / Pyrrole derivatives / Receptors / Supramolecular chemistry
We report on the synthesis and properties of formyl-substi-
tuted dipyrrolyl diketone–BF2 complexes (anion receptors)
prepared by the formation of Schiff bases and their subse-
quent reduction, behaved as building subunits to provide
and their extended derivatives. The formyl-substituted re- gel-like materials in spite of the existence of β-ethyl substitu-
ceptors exhibited efficient anion-binding behavior and com-
plicated solid-state hydrogen-bonding assembly patterns,
due to the formyl group’s electron-withdrawing and hydro-
gen-bond-accepting properties. The extended derivatives,
ents. Fairly unspecific spherical particle morphologies were
observed for these gel-like materials by optical microscopy
and AFM. The anion-responsive behavior of the supramolec-
ular assemblies (gelated materials) was also examined.
become all the more fascinating as a result of their potential
as stimuli-responsive functional soft materials.[8,9]
Introduction
Soft matter has been attracting increasing attention as
a “transformable” functional material due to its moderate
mobility and flexibility, which readily enable it to change its
bulk shape and properties depending on the conditions.[1]
Supramolecular gels are dimensionally controlled assem-
blies made up of low-molecular-weight (LMW) molecules
held together by noncovalent interactions such as hydrogen
bonding, metal coordination, van der Waals interaction,
and π–π stacking. Gels derived from molecular assemblies,
in which the components can be readily replaced with alter-
natives, may provide promising material systems for drug
delivery and tissue engineering.[2,3] Supramolecular gels
made up of molecules sensitive to external physical stimuli
can be modulated and controlled by the conditions.[4] In
contrast to physical stimuli, chemical stimuli such as the
incorporation of a specific species can afford versatile sup-
ramolecular gels that change their states as a result of the
interactions between the additives and the gelator molec-
ules.[5] Of the various available chemical stimuli available,
inorganic and biotic anions, such as halides, acetates, and
phosphates, which are ubiquitous in biology, are essential,
as can be seen in the activity of enzymes, transport of hor-
mones, protein synthesis, and DNA regulation.[6,7] Recently,
Supramolecular gels based on metal complexes also ex-
hibit transformation by anions.[9a–9c] Lee et al., for example,
prepared a dendrimer-like oxyethylene-substituted bis(pyr-
idine) derivative that forms coordination polymers or oligo-
mers, such as dispersed helical structures and discrete cyclic
conformations, through Ag+ complexation; the mor-
phologies of the organized structures depend on the counter
–
–
–
anions present, such as NO3 , BF4 , and CF3SO3 , without
specific interactions with the gelators.[9a,9b] Aida et al. re-
ported the synthesis of an alkyl-substituted pyrazole–Au+
trinuclear complex that forms a red-emissive supramolec-
ular hexane gel with states and emission behavior controlled
by the anion-driven “liberation” of metal ions.[9c] Further,
some of the amide- and urea-based supramolecular gels are
anion-responsive because of the affinities of the polarized
NH sites for anions, which disrupt the hydrogen-bond-as-
sembled structures.[9d–9k] Under suitable conditions, the
chemical stimuli not only act as inhibitors of the formation
of supramolecular assemblies but also function as tuneable
components that are included in the organized structures.
As efficient receptors for anions, we have reported acyclic
planar π-conjugated systems in the form of BF2 complexes
of 1,3-dipyrrolylpropane-1,3-diones (e.g., 1a–c, 2a–d, Fig-
ure 1a),[10–12] which can bind anions through the action of
two pyrrole NH moieties and the bridging CH system, with
the inversion of the pyrrole rings (Figure 1b). In fact, α-
aryl-substituted receptors containing long aliphatic chains
(e.g., 1b) form anion-responsive supramolecular organogels
on gelation from octane solutions and exhibit transitions to
the solution state on addition of appropriate anions,[8,12a]
whereas amphiphilic receptors possessing hydrophilic
chains (e.g., 1c) form solvent-assisted assemblies, such as
vesicular structures, in aqueous solution.[12d]
the chemistry of anion-responsive supramolecular gels has
[a] College of Pharmaceutical Sciences, Institute of Science and
Engineering, Ritsumeikan University
Kusatsu 525-8577, Japan
Fax: +81-77-561-2659
E-mail: maedahir@ph.ritsumei.ac.jp
[b] 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/ejoc.200901346.
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Figure 1. (a) BF2 complexes of dipyrrolyl diketones 1a–c, 2a–d, and formyl-substituted derivatives (3m1, 3m2, 3p1, and 3p2). (b) Anion-
binding mode of 1a.
Unlike the β-unsubstituted compounds 1a–c, which are (formylphenyl)boronic acid derivatives. The synthesis pro-
obtained from α-arylpyrroles as starting materials, the β-
alkyl-substituted receptor 2a, as an essential key starting ma-
terial,[11e] can be converted into various π-extended receptors
such as α-phenyl- (2b, 2c) and α-pyrrolyl-substituted (2d) de-
rivatives via α-iodinated intermediates.[12b,12c] Accordingly,
the introduction of appropriate moieties that are readily
transformable into other units would afford various anion-
receptor derivatives. Of the potentially transformable groups,
we chose the formyl (CHO) group, which is reactive for re-
duction to alcohols, oxidation to carboxylic acids, coupling
to alkenes, condensation with amines to Schiff bases, etc.[13]
In this paper we discuss formyl-substituted derivatives of the
acyclic anion receptors (3m1 and 3m2, or 3p1 and 3p2),
which were converted into various derivatives that behaved
as building blocks for supramolecular assemblies with/with-
out anions in hydrocarbon solvents to afford gel-like materi-
als. Effects of the sp3-linkages between the core π-plane and
the side aryl moieties are also discussed.
cedure with iodo-substituted receptors afforded better
yields than those obtained with α-borylated dipyrrolyl dike-
tones.[12d] The synthetic route starting from α-form-
ylphenyl-substituted pyrrole and malonyl chloride, as in
the case of 1a–c,[12a] did not work well, possibly due to po-
lymerization during the reactions to yield unidentified com-
pounds. Chemical identification of 3m1, 3m2, 3p1, and 3p2
1
was carried out by H NMR and MALDI-TOF MS. The
UV/Vis absorption bands of 3m1, 3m2, 3p1, and 3p2 in
CH2Cl2 were observed at 474, 495, 482, and 510 nm, respec-
tively, suggesting that the formyl substitution at the para
position extended the π-conjugation, whereas that at the
meta position disrupted the π-conjugation to some extent,
comparable to the situation with α-unsubstituted 2a
(451 nm),[11e] mono-α-phenylsubstituted 2b (476 nm), and
bis(α-phenyl)-substituted 2c (499 nm).[12b] The order of
these λmax values was correlated to the order of the
HOMO–LUMO gaps (3m1: 3.300 eV; 3m2: 3.191 eV; 3p1:
2.844 eV; 3p2: 3.163 eV) as estimated by DFT calculations
(Figures S3 and S4 in the Supporting Information).[14] Fur-
ther, fluorescence emissions (and quantum yields ΦF) ex-
cited at each absorption maximum in CH2Cl2 were ob-
served at 504 (0.92) (3m1), 532 (0.98) (3m2), 511 (0.95)
(3p1), and 547 nm (0.97) (3p2), suggesting that the formyl-
substituted derivatives, like 2b (ΦF = 0.70) and 2c (0.94),
were also highly emissive fluorophores.
Results and Discussion
Synthesis and Characterization of BF2 Complexes of
Formyl-Substituted Dipyrrolyl Diketones
Mono- and diformyl substituents were introduced into
acyclic anion receptors to yield the meta-monoformyl com-
pound 3m1, the meta-diformyl compound 3m2, the para-
The solid-state structures of 3m1, 3m2, 3p1, and 3p2 were
monoformyl compound 3p1, and the para-diformyl com- determined by single-crystal X-ray analyses (Figure 2). All
pound 3p2, in 40, 44, 29, and 15% yields, respectively, the receptor molecules formed hydrogen-bonding assembl-
through cross-coupling reactions with mono- and bis(α- ies through their CHO moieties, along with the pyrrole NH
iodo)-substituted BF2 complexes[12b] and the corresponding and BF units. Here we have labeled the distances (C=)O···
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Supramolecular Assemblies from Formyl-Substituted Anion Receptors
(H–)N, (C=)O···(H–)o-C, F···(H–)C(=O), F···(H–)o-C, and
F···(H–)N as a, b, c, d, and e, respectively. The monoformyl
compound 3m1 formed hydrogen-bonding dimers with
(C=)O···(H–)N and (C=)O···(H–)o-C distances of 2.963 (a)/
3.418 (aЈ) and 3.080 (b)/3.331 (bЈ) Å, respectively. The B–
F···H–C(=O) interaction [F···(H–)C(=O): 3.486 (c)/3.301
(cЈ) Å] also supported the assembled dimer structure (Fig-
ure 3a). On the other hand, the receptors 3m2, 3p1, and
3p2 exhibited the formation of 1-D hydrogen-bonding chain
structures.
In the case of 3m2, the (C=)O···(H–)N, (C=)O···(H–)o-
C, and F···(H–)C(=O) distances in the chain structures were
3.075 (a)/3.029 (aЈ), 3.121 (b)/3.163 (bЈ), and 3.400 (c)/3.436
(cЈ) Å, respectively. The two formyl units in the receptor
displayed inequivalent interaction, as observed in the hy-
drogen bond lengths (Figure 3b). The derivative 3m1
formed fairly planar supramolecular assemblies, which were
efficient stacking structures. Interestingly, the monoformyl
compound 3p1 produced 1-D chains through C=O···H–N
interactions, which further constructed “knit”-like assem-
blies through B–F···H–N and B–F···H–o-C hydrogen bond-
ing. The (C=)O···(H–)N, F···(H–)o-C, and F···(H–)N dis-
tances were 2.888 (a), 3.300 (d), and 3.235 (e) Å, respec-
tively. A dihedral angle of 117.9° was observed between the
two neighboring units (core π-planes) in the 1-D chains
formed by C=O···H–N interactions (Figure 3c). The “cen-
ter” molecules in this figure formed hydrogen-bonding as-
semblies through F···(H–)o-C and F···(H–)N with another
C=O···H–N-based 1-D chain. Furthermore, the (C=)O···
(H–)N, (C=)O···(H–)o-C, and F···(H–)C(=O) distances in
3p2 were 2.826 (a)/2.856 (aЈ), 3.248 (b)/3.113 (bЈ), and 3.426
(c)/3.301 (cЈ) Å, respectively. “Disordered” molecules
formed 1-D chain structures through CHO units [Fig-
ure 3d(i)], whereas one of the CHO units of a molecule
without a disordered structure [right in Figure 3d(ii)] served
to associate with the hydrogen-bonding sites of the disor-
dered molecule [left in Figure 3d(ii)]. The remaining hydro-
gen-bonding sites were partially associated with water mo-
lecules.
These formyl-substituted receptors had slightly distorted
side aryl rings: the dihedral angles (minimum and maxi-
mum values) between the aryl rings and the dipyrrolyl core
plane comprising 16 atoms were 27.5° and 30.7° for 3m1
(two independent structures), 29.2°/31.5° for 3m2, 29.2° for
3p1, and 33.1°/44.0° and 32.4°/44.1° for 3p2 (two indepen-
dent structures). These values were comparable to or
slightly larger than those in 2c (24.3°/31.9°). The larger val- Figure 2. Single-crystal X-ray structures (top and side view) of: (a)
3m1 (one of the two independent structures), (b) 3m2, (c) 3p1, and
ues were due to the intermolecular hydrogen bonding. The
deviations in the mean plane consisting of 16 atoms were
0.26/0.35 Å (3m1), 0.20 Å (3m2), 0.37 Å (3p1), and 0.12/
(d) 3p2 (one of the two independent structures including a disor-
dered pair). Atom color code: brown, pink, yellow, green, blue, and
red refer to carbon, hydrogen, boron, fluorine, nitrogen, and oxy-
0.21 Å (3p2); these values are comparable to the value in 2c
(0.30 Å). Furthermore, as in other β-ethyl-substituted re-
ceptors,[11h,12b,12c] π–π stacking dimer structures were ob-
served in the cases of 3m2 and 3p1 (Figure S2 in the Sup-
gen, respectively. See also Figure S1 in the Supporting Information.
porting Information), which had short distances of 3.774 ing up the receptors. On the other hand, 3m1 gave infinite
(3m2) and 3.695 (3p1) Å. The longer distances of 4.085 stacking assemblies, in which the parallel stacking distances
(3m2) and 4.389 (3p1) Å between the stacking dimers sug- were 3.600 and 3.994 Å and the nonparallel one was ca.
gested the influence of van der Waals interactions in stack- 3.40 Å (estimated from the averaged distances from the 16
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H. Maeda, R. Fujii, Y. Haketa
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structure comprising more than two units due to supporting
van der Waals interactions between ethyl moieties and be-
tween ethyl units and the π-plane.
Anion-Binding Behavior of Formyl-Substituted Receptors
The values of the anion-binding constants (Ka) of 3m1,
3m2, 3p1, and 3p2 (Table 1) were determined from the UV/
Vis absorption spectral changes induced by the addition of
appropriate anions, as their tetrabutylammonium (TBA)
salts, in CH2Cl2 (Figures S6–S9 in the Supporting Infor-
mation). The α-unsubstituted 2a and the α-phenyl-substi-
tuted receptors 2b and 2c exhibited Ka values that decreased
with increasing number of phenyl substituents, due to the
steric hindrance between the α-phenyl and β-ethyl moie-
ties.[12b] In contrast, the diformyl-substituted receptor 3m2
exhibited higher Ka values than the corresponding mono-
formyl compound 3m1, whereas 3p2 showed larger Ka val-
–
ues than 3p1 for halide and CH3CO2 anions but slightly
–
–
smaller Ka values for H2PO4 and HSO4 . This tendency in
the formylphenyl-substituted receptors, in contrast with the
phenyl-substituted receptors (2b, 2c), was a result of the in-
creased affinities of the o-CH sites in 3m1, 3m2, 3p1, and
3p2 arising from the substitution with the electron-with-
1
drawing formyl moiety.[16] The H NMR spectral changes
in 3m2 for anions such as Cl– in CD2Cl2 suggested that the
anions were bound to multiple binding sites of o-CH. Upon
the addition of, for example, Cl– (1.5 equiv.) to a CD2Cl2
solution of 3m2 (1ϫ10–3 ) at –50 °C, the signals of the
pyrrole NH, o-CH (two kinds), and bridging CH groups
were shifted from δ = 9.60, 8.02/7.81, and 6.55 ppm to δ =
12.09 (chemical shift gap ∆δ = 2.49 ppm), 8.35/8.13 (∆δ =
0.33/0.32), and 8.56 (∆δ = 2.01 ppm) ppm, respectively, sug-
gesting that Cl– was associated with the five hydrogen-
bonding donor sites, as observed in 1a and 2a.[12a,12b] As
well as the [1 (receptor) + 1 (anion)] complex, the [2 + 1]
complex – with chemical shifts of NH (δ =10.87 ppm, ∆δ =
1.27 ppm), CHO (δ =9.67 ppm, ∆δ = –0.38 ppm from free
receptor of δ = 10.05 ppm), o-CH (7.88/7.62 ppm, ∆δ =
–0.14/–0.19 ppm), and bridging CH (δ =7.48 ppm, ∆δ =
0.93 ppm) – was also identified (Figure S12 in the Support-
ing Information).[17]
Substituted Aminomethyl Moieties from Formyl Groups to
Enable the Receptors to Form Supramolecular Assemblies
The formyl group is well known to be transformable into
imine (Schiff base) moieties by treatment with primary
amines. The condensation of 3m1, 3m2, 3p1, and 3p2 with
hexadecylamine by general procedures was examined, and
the formation of Schiff base products was detectable by
MALDI-TOF MS. Isolation of the products was not easy,
however, due to regeneration of starting materials by hy-
drolysis during silica gel column chromatography. Re-
Figure 3. Hydrogen-bonding assemblies of (a) 3m1, (b) 3m2, (c)
3p1, and (d) 3p2 in the solid state.
atoms of the receptor unit to the mean plane of the other duction of the Schiff base units with NaBH(OAc)3 in the
unit). Relative to 3m2, 3p1, and other β-ethyl-substituted same pot as used for the condensation was therefore tried,
derivatives,[12b,12c,15] 3m1 exhibited a more tightly stacked and the formation of C–N single bonds worked well to sta-
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Supramolecular Assemblies from Formyl-Substituted Anion Receptors
Table 1. Binding constants (Ka [–1]) of 2a–c (references), 3m1, 3m2, 3p1, and 3p2 with various anions as TBA salts in CH2Cl2.[a]
Ka(2a)[b]
Ka(2b)[c]
Ka(2c)[c]
Ka(3m1)
Ka(3m2)
Ka(3p1)
Ka(3p2)
Cl–
6800
1200
210000
91000
1200
4200 (0.61)
600 (0.50)
98000 (0.47)
36000 (0.40)
n.d.[d]
2700 (0.40)
300 (0.25)
27000 (0.13)
2200 (0.024)
25 (0.021)
13000 (1.91)
2000 (1.67)
120000 (0.57)
9700 (0.11)
400 (0.33)
27000 (4.0)
2700 (2.3)
200000 (0.95)
71000 (0.78)
870 (0.73)
20000 (2.9)
2200 (1.83)
250000 (1.19)
74000 (0.81)
420 (0.35)
65000 (9.6)
3900 (3.3)
320000 (1.5)
37000 (0.41)
320 (0.27)
Br–
–
CH3CO2
H2PO4
HSO4
–
–
[a] The values in parentheses are the ratios of the Ka values to the Ka value of 2a. [b] Ref.[11e] [c] Ref.[12b] [d] Not determined.
bilize the products 4m1, 4m2, 4p1, and 4p2 as aminomethyl- (and quantum yields ΦF) of 5m1, 5m2, 5p1, and 5p2 in
substituted derivatives (Figure 4). The alkyl-substituted
4m1, 4m2, 4p1, and 4p2 did not exhibit good solubility in
hydrocarbon solvents such as octane.
CH2Cl2 were 510 (0.011), 536 (0.003), 515 (0.012), and 546
(0.007) nm, respectively. The low quantum yields were poss-
ibly the result of photoinduced electron transfer of amine
lone pair(s). In contrast with their behavior in CH2Cl2,
5m1, 5m2, 5p1, and 5p2 were “soluble” in octane at
1ϫ10–5 , possibly as stacking dimers and/or monomers,
as suggested by fairly blueshifted UV/Vis absorption bands
at 455, 484, 463, and 473 nm, respectively, wavelengths
shorter by 23, 19, 17, and 32 nm than those seen in CH2Cl2.
The fluorescence emissions (and quantum yields ΦF) of
5m1, 5m2, 5p1, and 5p2 in octane were observed at 488
(0.072), 519 (0.003), 492 (0.338), and 517 (0.114) nm,
respectively (Figures S13 and S14 in the Supporting Infor-
mation). The lower octane solubilities of the monosubsti-
tuted 5m1 and 5p1 at higher concentrations (ca. 10–3 )
were not appropriate for the formation of gel-like materials
but afforded precipitates, and so in further studies we fo-
cused on the disubstituted 5m2 and 5p2.[19]
The aliphatic derivative 1b, which formed an octane gel
below 27.5 °C (10 mgmL–1),[12a] could be considered to be
the “analogue” lacking the β-ethyl substituents and flexible
aminomethyl-substituted phenyl moieties of 5m2 and 5p2.
Here we used octane as a solvent to construct supramolec-
ular assemblies composed of 5m2 and 5p2, as was at-
tempted for 1b. Unlike 1b, 5m2 and 5p2 in octane
(10 mgmL–1) appeared to have fairly dispersed states, not
gel-like ones, at room temp. When the solutions of 5m2 and
5p2 were cooled, they became opaque below ca. 1 and ca.
–10 °C, respectively, and formed gel-like materials below ca.
–10 and ca. –30 °C, respectively (Figure 5a).[20] Like the dis-
Figure 4. Extended derivatives 4m1, 4m2, 4p1, 4p2, 5m1, 5m2, 5p1,
and 5p2 from formyl-substituted 3m1, 3m2, 3p1, and 3p2.
As observed in the derivatives 4m1, 4m2, 4p1, and 4p2,
imine formation and subsequent reduction reaction ap-
peared to be useful for introduction of various substituents
on either one or two sides of the acyclic anion receptors,
and so we focused on derivatives that would be “soluble”
in nonpolar solvents. The connection of aryl rings with ali-
phatic chains, for example, afforded building blocks for sup-
ramolecular assemblies based on π–π interaction at the core
plane, along with van der Waals interactions of the side persed states in dilute octane solution, the gelated materials
chains. In fact, the presence of bulky β-ethyl moieties often formed from 5m2 and 5p2 were less emissive but showed
inhibited the formation of infinite π–π stacking structures weak fluorescence (at around 595 and 517 nm for 5m2 and
but yielded “dimers,” as suggested by the single-crystal X- 5p2, respectively) at room temp. The absorption maxima of
ray analysis of 2a. However, supporting van der Waals in- 5m2 and 5p2 (10 mgmL–1) at room temp. were observed at
teractions between β-ethyl units (and π-planes), as observed 485 and 470 nm, which were almost the same as the values
in 3m1, 3m2, and 3p1, were able to produce columnar struc- in octane solutions at 1ϫ10–5 , in the dispersed states as
tures under appropriate conditions. In view of the above stacking dimers and/or monomers. The variable-tempera-
observations, 3m1, 3m2, 3p1, and 3p2 were transformed ture (VT) UV/Vis spectral changes in 5m2 at 1 ϫ10–3  be-
into 5m1, 5m2, 5p1, and 5p2 (Figure 4) in yields of 54, 73, tween 60 and –50 °C exhibited the formation of stacking
64, and 64%, respectively, by treatment with 3,4,5-tris(hex- structures at lower temperatures: the absorption maxima
adecyloxy)aniline[18] and subsequent NaBH(OAc)3 re- were shifted from 482 (60 °C) to 487 nm (–40 °C), along
duction. The UV/Vis absorption bands of 5m1, 5m2, 5p1, with the augmentation of the shoulder at around 540 nm.
and 5p2 in CH2Cl2 (1ϫ10–5 ) were observed at 478, 503, Compound 5p2, on the other hand, showed slightly compli-
480, and 505 nm, respectively, suggesting that only α-aryl cated, two-step transitions: the band at 476 nm (60 °C) was
substitution extended the π-conjugation observed in both shifted to 471 nm (0 °C) with a slightly augmented ab-
m- and p-substituted receptors. The fluorescence emissions sorbance and, further, to 475 nm (–50 °C) as a broader and
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H. Maeda, R. Fujii, Y. Haketa
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weaker absorption. At this concentration (1ϫ10–3 ), the through the assembly and folding of relatively weak, thin
absorbance at around 600–700 nm increased below –20 °C stacking wires during the removal of the solvents. The frag-
for 5m2 and 5p2, suggesting that increases in absorbance at ile gel-like states were also suggested by the absence of any
around 600–700 nm below –20 °C (Figure S15 in the Sup- distinctions between the assembled features of 5m2 and 5p2.
porting Information) may be attributable to light scattering The interconnection of three π-conjugated moieties, a core
by larger objects, as observed in opaque solutions. The ab- π-plane and two side aryl units, by an sp3 methylene bridge
sorption spectra of solid-state compounds 5m2 and 5p2, (or bridges) provided supramolecular assemblies that were
prepared from octane solutions (1ϫ10–3 ) by air drying, not very rigid but yielded soft materials through fairly or-
with use of optical waveguides exhibited the assembled fea- dered organization under appropriate conditions (Fig-
tures of broad absorption bands with λmax values of 452 ure 5b).
and 441 nm, respectively, with shoulders at around 550 nm
in both cases.
VT 1H NMR measurements of 5m2 and 5p2 (1ϫ10–3 )
in [D18]octane from 60 °C to –20 °C revealed the formation
of aggregates at low temperatures (Figure 6). Both 5m2 and
5p2 showed broad but simple dispersed signals at 60 °C: in
the case of 5p2, for example, at δ = 9.60 (pyrrole-NH), 7.44
(core-aryl-CH), 6.37 (bridging CH), and 6.02 (terminal-
aryl-CH) ppm. These observations suggested that the
monomers were stable as major components at this tem-
perature. At lower temperatures (0–40 °C for 5m2 and 0–
20 °C for 5p2), complicated features possibly derived from
the formation of stacking dimers and/or other smaller as-
semblies were observed. At –20 °C, no signals ascribable to
the formation of larger aggregates that were the basis of
gelated materials at higher concentrations were observed.
Figure 5. (a) Photographs of the gel-like materials formed from
5m2 (left) and 5p2 (right) in octane (10 mgmL–1). (b) One of the
possible assembling modes of 5m2 and 5p2.
The morphologies of the organized structures of 5m2
and 5p2 were elucidated by optical microscopy (OM) and
atomic force microscopy (AFM) measurements. Analytical
samples of 5m2 and 5p2 (10 mgmL–1) were prepared by
drying gelated materials at –50 °C.[21] AFM measurements
of the samples with use of glass and silicon substrates ex-
hibited unspecific spherical morphologies with sizes of ca.
0.1–0.5 µm both for 5m2 and for 5p2 (see Figures S23a,b
and 24a,b in the Supporting Information). Because gelated
materials not derived from fibrous structures are rare,[4e,22]
1
Figure 6. VT H NMR spectral changes of (a) 5m2 and (b) 5p2 in
[D18]octane (1ϫ10–3 ) from 60 °C to –20 °C. * Signals derived
the spherical objects could possibly have been formed from solvents and solvent-related impurities.
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Supramolecular Assemblies from Formyl-Substituted Anion Receptors
The assembled behavior of 5m2 and 5p2 in dilute octane ure S16 in the Supporting Information). In the case of
solutions (1ϫ10–5  and 1ϫ10–4 ) was also examined by 1ϫ10–5 , a redshift from 482 to 491 nm was observed in
means of VT UV/Vis absorption spectral changes and com- 5m2 on cooling from 60 to –50 °C, and furthermore, in-
pared to the behavior at 1ϫ10–3  (Figure 7 and Fig- creases in the absorbance at around 600–700 nm below
–20 °C may also be attributable to the formation of larger
objects. On heating from –50 to 60 °C, a reversible process
was observed, although time-dependent absorption spectral
changes at lower temperatures were also seen. Compound
5p2, on the other hand, showed a blueshift from 484 to
477 nm on cooling from 60 to –50 °C, during which a de-
crease in absorbance due to the formation of assemblies was
observed. At this concentration, the absorbance at around
600–700 nm increased below –20 °C for 5m2 and 5p2. Simi-
larly, measurements at 1ϫ10–4  showed spectral changes
that indicated increased absorbance under –20 °C due to
the formation of aggregates, along with some time-depend-
ent behavior. There were no significant differences observed
under these two sets of conditions. Furthermore, heating
from room temp. to 60 °C at any concentration resulted in
absorption changes, possibly due either to a transition from
a stacking dimer to monomer or to changes in the stacking
structures. From these results, which were basically similar
to the features at 1ϫ10–3 , we identified the formation of
organized structures resulting from the introduction of an
aliphatic alkyl chain, as well as the effects of the substitu-
tion positions, even in dilute solutions.
Dynamic light scattering (DLS) measurements of 5m2 at
1ϫ10–3  exhibited mainly two diameter distributions at
each temperature: 4 and 600 nm at 2 °C, 4 and 350 nm at
10 °C, 4 and 230 nm at 20 °C, 4 and 540 nm at 40 °C, and
3 and 100 nm at 80 °C. The smaller objects around 4 nm
were presumably derived from the stacking of dimers and/
or monomers,[23] whereas the larger ones may be small
amounts of the higher aggregates. On the other hand, mea-
surements at 1ϫ10–4  showed fairly random distributions
at 2 and 10 °C and no DLS peaks at higher temperatures
over 10 °C. Similarly, 5p2 showed only fairly random distri-
butions or no peaks either at 1ϫ10–3  or at 1ϫ10–4

(Figure S20 in the Supporting Information).[24]
Anion-Responsive Behavior of Supramolecular Assemblies
Supramolecular assemblies made up of anion receptors
(5m2 and 5p2) could be responsive and tuneable, because
of the existence of anions. In fact, the addition of Cl–
(1 equiv.) as its TBA salt was capable of modulating the
assembled structures, along with their optical and electronic
properties; Cl– complexes of both 5m2 and 5p2 in octane
(10 mgmL–1) were opaque solutions below ca. 5 °C and
formed gel-like materials below ca. –10 °C (Figure 8), sug-
gesting that the introduction of an anion also produced ri-
gid organized structures, possibly due to the formation of
assemblies consisting of alternately stacked positively and
negatively charged species, as observed in the solid state
with the Cl– complexes of 1a and 2d.[12a,12c] Examination of
the assembled structures containing TBACl was performed
with the aid of AFM measurements on samples prepared
Figure 7. VT UV/Vis absorption spectral changes of (a) 5m2 and
(b) 5p2 in octane (1ϫ10–5 ) from 60 °C to –50 °C (top) and from
–50 °C to 60 °C (bottom). Insets: Photographs at 60 and –50 °C.
Eur. J. Org. Chem. 2010, 1469–1482
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1475

H. Maeda, R. Fujii, Y. Haketa
FULL PAPER
by drying at –50 °C on glass and silicon substrates, which monomeric states, whereas those at lower temperatures
revealed spherical morphologies with sizes of ca. 0.1– were due to the assembled structures. The absorbance at
0.5 µm for the Cl– complexes of 5m2 and 5p2 (Figures 23c,d around 600–700 nm increased below –20 °C with the forma-
and 24c,d in the Supporting Information).[21] The features tion of larger organized structures.
of the Cl– complexes were quite similar to those of anion-
free 5m2 and 5p2, presumably due to the fragilities of the
assembled structures in the cases both of the receptors and
of the anion complexes. The morphologies of the organized
structures depended on the substitution positions of the ter-
minal aryl rings, regardless of the presence of the TBA salt.
Figure 8. Photographs of the gel-like materials formed from 5m2
(left) and 5p2 (right) with Cl– (1 equiv.) as a TBA salt in octane
(10 mgmL–1).
1
As under anion-free conditions, VT H NMR measure-
ments of the Cl– complexes of 5m2 and 5p2 (1ϫ10–3 ) in
Figure 9. VT 1H NMR spectral changes of (a) 5m2 and (b) 5p2
with Cl– (1 equiv.) as its TBA salt in [D18]octane (1ϫ10–3 ) from
60 °C to –20 °C. * Signals derived from solvents and solvent-related
impurities. The 1H NMR anion-binding behavior is consistent with
the UV/Vis absorption spectra of these materials (10 mgmL–1) at
room temp. (Figures S18h and S19h in the Supporting Infor-
mation).
[D18]octane also revealed the formation of aggregates at
lower temperatures (Figure 9). The samples were prepared
by addition of [D18]octane to mixtures of the receptors and
TBACl (1 equiv.), initially complexed in CH2Cl2, and the
solvents were evaporated to dryness. The Cl– complex of
5m2 exhibited fairly sharp signals as a monomeric complex
at 60–20 °C: at 40 °C, 5m2·Cl– showed signals at δ = 12.18
(pyrrole-NH), 8.75 (bridging CH), and 8.66 (core-aryl-o-
Complexation with an anion (Cl–) afforded fairly sharp
CH) ppm (Figure 9b). On the other hand, 5p2·Cl– showed DLS peaks, presumably due to the formation of rigid as-
broad and dispersed signals at 60–20 °C: at δ = 12.29 (pyr- semblies consisting of charged species rather than those
role-NH), 8.94 (bridging CH), and 8.04 (core-aryl-o-CH) from anion-free receptors. Upon the addition of Cl–
ppm at 40 °C, for example (Figure 9b). In neither case were (1 equiv.) as a TBA salt to an octane solution of 5m2
signals observed at lower temperatures (0 to –20 °C), which (1ϫ10–3 ), a single distribution at 2000 nm was observed
is ascribable to the formation of larger aggregates, suggest- at 2 °C, whereas at 10–80 °C smaller assemblies at 2–5 nm,
ing that such aggregates were produced directly from mono- which were smaller at higher temperatures, and larger and
meric anion complexes. On the other hand, the VT UV/Vis fairly dispersed ones at 100–1000 nm were formed. The
absorption spectral changes in the Cl– complexes of 5m2 peak at 2–5 nm was from the result of the stacking of di-
and 5p2 (1ϫ10–5 ) exhibited redshifts from 498 to 513 nm mers and/or monomer, whereas the peaks at 2000 nm and
(5m2) and from 485 to 515 nm (5p2) on cooling from 60 to around 100–1000 nm were due to the higher assembled
–50 °C (Figure 10 and Figures S17–S19 in the Supporting structures. Compound 5p2 (1ϫ10–3 ), on the other hand,
Information). Compounds 5m2 and 5p2 formed Cl– com- which showed only random peaks in the absence of Cl–,
plexes at all the temperatures used for measurements, as exhibited a larger but dispersed feature at 2 °C in the pres-
suggested by the relatively augmented and sharp bands at ence of Cl– (1 equiv.), whereas at 10–80 °C temperature-de-
around 250–400 nm. The absorption spectra of 5m2 and pendent smaller peaks at 3–6 nm and larger ones at around
5p2 at above room temp. possibly originated from dispersed 100–1000 nm were observed (Figure S21 in the Supporting
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Supramolecular Assemblies from Formyl-Substituted Anion Receptors
the presence of Cl– (1 equiv.) showed distributions at 4 and
250 nm at 2 °C, 5 and 240 nm at 10 °C, and 4 and 400 nm
at 20 °C. At over 40 °C, the peaks at around 4 nm were
disordered and new ones representing larger assemblies ap-
peared (Figure S22 in the Supporting Information).[24]
Conclusions
We have reported the synthesis and properties of formyl-
substituted dipyrrolyl diketone–BF2 complexes (anion re-
ceptors) and their extended derivatives. Formyl-substituted
receptors exhibited efficient anion-binding behavior and
complicated solid-state hydrogen-bonding assembly, due to
the presence of additional hydrogen-bonding formyl moie-
ties. The extended derivatives, which were prepared through
the formation of Schiff bases and subsequent reduction, be-
haved as building subunits to provide gel-like materials re-
sponsive to anions. The synthesis of the other derivatives
with the aid of formyl transformation and examination of
their properties are now in progress.[25,26]
Experimental Section
General: Starting materials were purchased from Wako Chemical
Co., Nacalai Chemical Co., and Aldrich Chemical Co. and were
used without further purification unless otherwise stated. UV/Vis
spectra were recorded with a Hitachi U-3500 spectrometer for the
solution state and a System Instruments SIS-50 surface and inter-
face spectrometer for the solid state. Variable-temperature UV/Vis
spectra were measured with the aid of a Unisoku USP-203A cryo-
stat for spectrophotometers. Fluorescence spectra and quantum
yields were recorded with a Hitachi F-4500 fluorescence spectrome-
ter for ordinary solutions and a Hamamatsu C9920-02 quantum
yields measurements system for organic LED materials. NMR
spectra used in the characterization of products were recorded with
a JEOL ECA-600 600 MHz spectrometer. All NMR spectra were
referenced to solvent. Matrix-assisted laser desorption ionization
time-of-flight (MALDI-TOF) mass spectra were recorded with a
Shimadzu Axima-CFRplus instrument in negative mode. Electro-
spray ionization mass spectrometry (ESI MS) studies were recorded
with a Bruker microTOF instrument with use of a negative mode
ESI-TOF method. TLC analyses were carried out on aluminium
sheets coated with silica gel 60 (Merck 5554). Column chromatog-
raphy was performed on Sumitomo alumina KCG-1525, Wakogel
C-200, C-300, and Merck silica gel 60 and 60H.
BF2 Complex of 1-[3,4-Diethyl-5-(3-formylphenyl)pyrrol-2-yl]-3-
(3,4-diethylpyrrol-2-yl)propane-1,3-dione (3m1): A Schlenk tube
containing the 5-iodo-substituted derivative of the bis(diethylpyr-
rolyl) diketone–BF2 complex[12b] (49.1 mg, 0.10 mmol), m-formyl-
phenylboronic acid (19.8 mg, 0.13 mmol), tetrakis(triphenylphos-
phane)palladium(0) (12.8 mg, 0.011 mmol), and Na2CO3 (42.2 mg,
0.40 mmol) was flushed with nitrogen and charged with a mixture
of degassed DME (2 mL) and water (0.2 mL). The mixture was
heated at 80 °C for 24 h, allowed to cool, and partitioned between
water and CH2Cl2. The combined extracts were dried with anhy-
drous Na2SO4, and the solvents were evaporated to dryness. The
residue was then chromatographed by silica gel flash column
chromatography (MeOH/CH2Cl2, 1%), and crystallization from
CH2Cl2/hexane afforded 3m1 (18.5 mg, 40%) as an orange solid.
Figure 10. VT UV/Vis absorption spectral changes of (a) 5m2 and
(b) 5p2 with Cl– (1 equiv.) as its TBA salt in octane (1ϫ10–5 )
from 60 °C to –50 °C (top) and from –50 °C to 60 °C (bottom).
Insets: Photographs at 60 and –50 °C.
Information). At a lower concentration (1ϫ10–4 ), 5m2 in
the presence of Cl– (1 equiv.) showed two distributions at
around 4 and 400 nm at 10 °C, whereas 5p2 (1ϫ10–4 ) in Rf = 0.48 (MeOH/CH2Cl2, 2%). 1H NMR (600 MHz, CDCl3,
Eur. J. Org. Chem. 2010, 1469–1482
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1477

H. Maeda, R. Fujii, Y. Haketa
20 °C): δ = 10.10 (s, 1 H, CHO), 9.42 (br., 1 H, NH), 9.34 (br., 1 dium(0) (115.9 mg, 0.10 mmol), Na2CO3 (424.2 mg, 4.00 mmol),
FULL PAPER
H, NH), 8.02 (s, 1 H, ArH), 7.92 (d, J = 7.8 Hz, 1 H, ArH), 7.78
(d, J = 7.8 Hz, 1 H, ArH), 7.67 (t, J = 7.8 Hz, 1 H, ArH), 6.97 (d,
and water (1.5 mL) was heated at reflux under N2 for 25 h, allowed
to cool, and partitioned between water and CH2Cl2. The combined
J = 3.0 Hz, 1 H, pyrrole-H), 6.53 (s, 1 H, CH), 2.85 (q, J = 7.8 Hz, extracts were dried with anhydrous Na2SO4, and the solvents were
2 H, CH2), 2.81 (q, J = 7.8 Hz, 2 H, CH2), 2.63 (q, J = 7.8 Hz, 2
H, CH2), 2.49 (q, J = 7.8 Hz, 2 H, CH2), 1.34 (t, J = 7.8 Hz, 3 H,
CH3), 1.28 (t, J = 7.8 Hz, 3 H, CH3), 1.23 (t, J = 7.8 Hz, 3 H,
evaporated to dryness. The residue was then chromatographed by
silica gel flash column chromatography (MeOH/CHCl3, 1%), and
crystallization from CH2Cl2/hexane afforded 3p2 (93.3 mg, 15%)
CH3), 1.21 (t, J = 7.8 Hz, 3 H, CH3) ppm. UV/Vis (CH2Cl2): λmax as a red solid. Rf = 0.43 (MeOH/CH2Cl2, 5%). 1H NMR
(εϫ105) = 474 nm (1.15 –1 cm–1). MALDI-TOF MS: m/z (%) =
465.4 (100) [M – H]–, 466.2 (76). ESI-TOF MS (HR): calcd. for
C26H28BF2N2O3 [M – H]– 465.2171; found 465.2171.
(600 MHz, CDCl3, 20 °C): δ = 10.08 (s, 2 H, CHO), 9.44 (br., 2 H,
NH), 8.01 (d, J = 7.8 Hz, 2 H, ArH), 7.70 (d, J = 7.8 Hz, 2 H,
ArH), 6.63 (s, 1 H, CH), 2.88 (q, J = 7.2 Hz, 4 H, CH2), 2.67 (q,
J = 7.2 Hz, 4 H, CH2), 1.36 (t, J = 7.2 Hz, 6 H, CH3), 1.23 (t, J =
7.2 Hz, 6 H, CH3) ppm. UV/Vis (CH2Cl2): λmax (εϫ105) = 510 nm
(1.06 –1 cm–1). MALDI-TOF MS: m/z (%) = 569.3 (100) [M –
H]–, 570.3 (98). ESI-TOF MS (HR): calcd. for C33H32BF2N2O4
[M – H]– 569.2434; found 569.2435.
BF2 Complex of 1,3-Bis[3,4-diethyl-5-(3-formylphenyl)pyrrol-2-yl]-
propane-1,3-dione (3m2): A degassed DME solution (15 mL) of the
diiodo-substituted derivative of the bis(diethylpyrrolyl) diketone–
BF2 complex[12b] (601.7 mg, 0.98 mmol), m-formylphenylboronic
acid (367.3 mg, 2.45 mmol), tetrakis(triphenylphosphane)palla-
dium(0) (114.0 mg, 0.099 mmol), Na2CO3 (416.1 mg, 3.93 mmol),
and water (1.5 mL) was heated at reflux under N2 for 25 h, allowed
to cool, and partitioned between water and CH2Cl2. The combined
extracts were dried with anhydrous Na2SO4, and the solvents were
evaporated to dryness. The residue was then chromatographed by
silica gel flash column chromatography (MeOH/CHCl3, 2%), and
crystallization from CH2Cl2/hexane afforded 3m2 (159.9 mg, 44%)
as a red solid. Rf = 0.43 (MeOH/CH2Cl2, 2%). 1H NMR
(600 MHz, CDCl3, 20 °C): δ = 10.11 (s, 2 H, CHO), 9.45 (br., 2 H,
NH), 8.04 (s, 2 H, ArH), 7.93 (d, J = 7.8 Hz, 2 H, ArH), 7.79 (d,
J = 7.8 Hz, 2 H, ArH), 7.68 (t, J = 7.8 Hz, 2 H, ArH), 6.61 (s, 1
H, CH), 2.88 (q, J = 7.8 Hz, 4 H, CH2), 2.65 (q, J = 7.8 Hz, 4 H,
CH2), 1.36 (t, J = 7.8 Hz, 6 H, CH3), 1.22 (t, J = 7.8 Hz, 6 H, CH3)
ppm. UV/Vis (CH2Cl2): λmax (εϫ105) = 495.5 nm (1.19 –1 cm–1).
MALDI-TOF MS: m/z (%) = 569.4 (100) [M – H]–, 570.4 (86).
ESI-TOF MS (HR): calcd. for C33H32BF2N2O4 [M – H]– 569.2434;
found 569.2434.
BF2 Complex of 1-{3,4-Diethyl-5-[3-(hexadecylaminomethyl)phen-
yl]pyrrol-2-yl}-3-(3,4-diethylpyrrol-2-yl)propane-1,3-dione
(4m1):
Compound 3m1 (9.4 mg, 0.02 mmol) and hexadecylamine
(24.3 mg, 0.1 mmol) were mixed in 1,2-dichloroethane (0.8 mL) at
room temperature under nitrogen for 1 h. Sodium triacetox-
yborohydride (16.9 mg, 0.08 mmol) and AcOH (1 µL, 0.02 mmol)
were added, and the mixture was stirred at room temperature for
4 h. The reaction mixture was quenched with aqueous saturated
NaHCO3 solution and partitioned between water and CH2Cl2. The
combined extracts were dried with anhydrous Na2SO4, and the sol-
vents were evaporated to dryness. The residue was then chromato-
graphed by silica gel column chromatography (MeOH/CH2Cl2,
3%), and crystallization from CH2Cl2/hexane afforded 4m1
(3.2 mg, 23%) as an orange solid. Rf = 0.20 (MeOH/CH2Cl2, 2%).
1H NMR (600 MHz, CDCl3, 50 °C): δ = 10.19 (br., 2 H, NH), 7.78
(s, 1 H, ArH), 7.42 (d, J = 6.6 Hz, 1 H, ArH), 7.22 (s, 2 H, ArH),
6.94 (s, 1 H, CH), 6.83 (s, 1 H, pyrrole-H), 3.96 (s, 2 H, CH2),
2.92–2.88 (m, 6 H, CH2, NHCH2), 2.63 (q, J = 7.2 Hz, 2 H, CH2),
2.49 (q, J = 7.2 Hz, 2 H, CH2), 1.77 (br., 2 H, NHCH2CH2), 1.33–
1.16 [m, 38 H, (CH2)13, CH3], 0.89 (t, J = 7.2 Hz, 3 H, CH3) ppm
(amino-NH signal is missing, possibly due to its broadening char-
BF2 Complex of 1-[3,4-Diethyl-5-(4-formylphenyl)pyrrol-2-yl]-3-
(3,4-diethylpyrrol-2-yl)propane-1,3-dione (3p1): A degassed DME
solution (10 mL) of the 5-iodo-substituted derivative of the bis(die-
thylpyrrolyl) diketone–BF2 complex[12b] (224.9 mg, 0.46 mmol), m-
formylphenylboronic acid (104.1 mg, 0.69 mmol), tetrakis(triphen-
ylphosphane)palladium(0) (53.6 mg, 0.046 mmol), Na2CO3
(166.1 mg, 1.57 mmol), and water (1 mL) was heated at reflux un-
der N2 for 30 h, allowed to cool, and partitioned between water
and CH2Cl2. The combined extracts were dried with anhydrous
Na2SO4, and the solvents were evaporated to dryness. The residue
was then chromatographed by silica gel flash column chromatog-
raphy (MeOH/CH2Cl2, 1%), and crystallization from CH2Cl2/hex-
ane afforded 3p1 (61.6 mg, 29%) as an orange solid. Rf = 0.52
(MeOH/CH2Cl2, 5%). 1H NMR (600 MHz, CDCl3, 20 °C): δ =
10.07 (s, 1 H, CHO), 9.40 (br., 1 H, NH), 9.34 (br., 1 H, NH), 7.99
(d, J = 7.8 Hz, 1 H, ArH), 7.69 (d, J = 7.8 Hz, 1 H, ArH), 6.99 (d,
J = 3.0 Hz, 1 H, pyrrole-H), 6.56 (s, 1 H, CH), 2.85 (q, J = 7.2 Hz,
2 H, CH2), 2.81 (q, J = 7.2 Hz, 2 H, CH2), 2.66 (q, J = 7.2 Hz, 2
H, CH2), 2.50 (q, J = 7.2 Hz, 2 H, CH2), 1.33 (t, J = 7.2 Hz, 3 H,
CH3), 1.28 (t, J = 7.2 Hz, 3 H, CH3), 1.23 (t, J = 7.2 Hz, 3 H,
CH3), 1.22 (t, J = 7.2 Hz, 3 H, CH3) ppm. UV/Vis (CH2Cl2): λmax
(εϫ105) = 482.5 nm (1.04 –1 cm–1). MALDI-TOF MS: m/z (%) =
465.2 (100) [M – H]–, 466.2 (90). ESI-TOF MS (HR): calcd. for
C26H28BF2N2O3 [M – H]– 465.2171; found 465.2171.
acteristics). UV/Vis (CH2Cl2): λmax (εϫ105)
=
474.5 nm
(0.71 –1 cm–1). MALDI-TOF MS: m/z (%) = 691.7 (100) [M]–.
ESI-TOF MS (HR): calcd. for C42H63BF2N3O2 [M – H]– 690.4994;
found 690.4994.
BF2 Complex of 1,3-Bis{3,4-diethyl-5-[3-(hexadecylaminomethyl)-
phenyl]pyrrol-2-yl}propane-1,3-dione (4m2): Compound 3m2
(11.5 mg, 0.02 mmol) and hexadecylamine (48.1 mg, 0.2 mmol)
were mixed in 1,2-dichloroethane (0.8 mL) at room temperature
under nitrogen for 3 h. Sodium triacetoxyborohydride (25.8 mg,
0.12 mmol) and AcOH (2 µL, 0.04 mmol) were added, and the mix-
ture was stirred at room temperature for 8 h. The reaction mixture
was quenched with aqueous saturated NaHCO3 solution and parti-
tioned between water and CH2Cl2. The combined extracts were
dried with anhydrous Na2SO4, and the solvents were evaporated to
dryness. The residue was then chromatographed by silica gel col-
umn chromatography (MeOH/CH2Cl2, 5%), and crystallization
from CH2Cl2/hexane afforded 4m2 (12.4 mg, 61%) as a red solid.
Rf = 0.32 (MeOH/CH2Cl2, 5%). 1H NMR (600 MHz, CDCl3,
50 °C): δ = 9.94 (br., 2 H, NH), 8.35 (s, 2 H, ArH), 7.69 (d, J =
6.6 Hz, 2 H, ArH), 7.45 (t, J = 7.2 Hz, 2 H, ArH), 7.23 (d, J =
7.2 Hz, 2 H, ArH), 7.14 (s, 1 H, CH), 4.23 (s, 4 H, CH2), 2.97 (q,
BF2 Complex of 1,3-Bis[3,4-diethyl-5-(4-formylphenyl)pyrrol-2-yl]- J = 7.2 Hz, 4 H, CH2), 2.84 (t, 4 H, NHCH2), 2.72 (q, J = 7.2 Hz,
propane-1,3-dione (3p2): A degassed DME solution (15 mL) of the
diiodo-substituted derivative of the bis(diethylpyrrolyl) diketone–
BF2 complex[12b] (616.7 mg, 1.08 mmol), m-formylphenylboronic
acid (374.9 mg, 2.50 mmol), tetrakis(triphenylphosphane)palla-
2 H, CH2), 1.81 (br., 4 H, NHCH2CH2), 1.30–1.17 [m, 64 H,
(CH2)13, CH3], 0.88 (t, J = 7.2 Hz, 6 H, CH3) ppm (amino-NH
signal is missing possibly due to its broadening characteristics).
UV/Vis (CH2Cl2): λmax (εϫ105)
=
499.5 nm (0.60 –1 cm–1).
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Supramolecular Assemblies from Formyl-Substituted Anion Receptors
MALDI-TOF MS: m/z (%) = 1020.6 (100) [M]–. ESI-TOF MS
(HR): calcd. for C65H102BF2N4O2 [M – H]– 1019.8080; found
1019.8080.
silica gel column chromatography (MeOH/CH2Cl2, 2%), and
crystallization from CH2Cl2/MeOH afforded 5m1 (6.8 mg, 54%) as
an orange solid. Rf = 0.57 (MeOH/CH2Cl2, 1%). 1H NMR
(600 MHz, CDCl3, 20 °C): δ = 9.34 (br., 1 H, NH), 9.29 (br., 1 H,
NH), 7.51 (s, 1 H, ArH), 7.45–7.40 (m, 3 H, ArH), 6.94 (d, J =
3.6 Hz, 1 H, pyrrole-H), 6.51 (s, 1 H, CH), 5.87 (s, 2 H, ArH), 4.36
(s, 2 H, CH2), 3.93 (s, 1 H, NH), 3.88 (t, J = 6.6 Hz, 4 H, m-
OCH2), 3.83 (t, J = 6.0 Hz, 2 H, p-OCH2), 2.83 (q, J = 7.8 Hz, 2
H, CH2), 2.79 (q, J = 7.8 Hz, 2 H, CH2), 2.55 (q, J = 7.8 Hz, 2 H,
CH2), 2.49 (q, J = 7.8 Hz, 2 H, CH2), 1.75–1.69 (m, 6 H,
OCH2CH2), 1.44–1.39 (m, 6 H, OCH2CH2CH2), 1.33–1.10 [m, 84
H, (CH2)12, CH3], 0.87 (t, J = 7.8 Hz, 9 H, CH3) ppm. UV/Vis
(CH2Cl2): λmax (εϫ105) = 478 nm (0.99 –1 cm–1). MALDI-TOF
MS: m/z (%) = 1263.5 (100) [M – H]–, 1264.4 (82). ESI-TOF MS
(HR): calcd. for C80H131BF2N3O5 [M – H]– 1263.0168; found
1263.0166.
BF2 Complex of 1-{3,4-Diethyl-5-[4-(hexadecylaminomethyl)phen-
yl]pyrrol-2-yl}-3-(3,4-diethylpyrrol-2-yl)propane-1,3-dione
(4p1):
Compound 3p1 (13.9 mg, 0.03 mmol) and hexadecylamine
(37.1 mg, 0.15 mmol) were mixed in 1,2-dichloroethane (1.6 mL) at
room temperature under nitrogen for 1 h. Sodium triacetoxy-
borohydride (31.8 mg, 0.15 mmol) and AcOH (2 µL, 0.04 mmol)
were added, and the mixture was stirred at room temperature for
8 h. The reaction mixture was quenched with aqueous saturated
NaHCO3 solution and partitioned between water and CH2Cl2. The
combined extracts were dried with anhydrous Na2SO4, and the sol-
vents were evaporated to dryness. The residue was then chromato-
graphed by silica gel column chromatography (MeOH/CH2Cl2,
4%) to afford 4p1 (15.6 mg, 77%) as an orange solid. Rf = 0.16
(MeOH/CH2Cl2, 2%). 1H NMR (600 MHz, CDCl3, 50 °C): δ =
9.31 (br., 2 H, NH), 7.47 (s, 4 H, ArH), 6.93 (d, J = 2.4 Hz, 1 H,
pyrrole-H), 6.53 (s, 1 H, CH), 3.87 (s, 2 H, CH2), 2.85 (q, J =
7.2 Hz, 2 H, CH2), 2.81 (q, J = 7.2 Hz, 2 H, CH2), 2.69 (t, J =
7.8 Hz, 2 H, NHCH2), 2.62 (q, J = 7.2 Hz, 2 H, CH2), 2.50 (q, J
= 7.2 Hz, 2 H, CH2), 1.58 (br., 2 H, NHCH2CH2), 1.33–1.16 [m,
38 H, (CH2)13, CH3], 0.89 (t, J = 7.2 Hz, 3 H, CH3) ppm (amino-
NH signal is missing, possibly due to its broadening characteris-
tics). UV/Vis (CH2Cl2): λmax (εϫ105) = 479 nm (1.07 –1 cm–1).
MALDI-TOF MS: m/z (%) = 689.1 (40) [M – H]–, 690.1 (100).
ESI-TOF MS (HR): calcd. for C42H63BF2N3O2 [M – H]– 690.4994;
found 690.4994.
BF2 Complex of 1,3-Bis{3,4-diethyl-5-[3-(3,4,5-trihexadecyloxy-
phenylaminomethyl)phenyl]pyrrol-2-yl}propane-1,3-dione
(5m2):
Compound 3m2 (22.8 mg, 0.04 mmol) and 3,4,5-trihexadecyloxy-
aniline (97.7 mg, 0.12 mmol) were mixed in 1,2-dichloroethane
(2 mL) at room temperature under nitrogen for 3 h. Sodium tri-
acetoxyborohydride (51.7 mg, 0.24 mmol) and AcOH (5 µL,
0.09 mmol) were added, and the mixture was stirred at room tem-
perature for 20 h. The reaction mixture was quenched with aqueous
saturated NaHCO3 solution, and the product was extracted with
CH2Cl2. The combined extracts were dried with anhydrous
Na2SO4, and the solvents were evaporated to dryness. The residue
was then chromatographed by silica gel column chromatography
(MeOH/CH2Cl2, 2%), and crystallization from CH2Cl2/MeOH af-
forded 5m2 (63.0 mg, 73%) as a red solid. Rf = 0.68 (MeOH/
BF2 Complex of 1,3-Bis{3,4-diethyl-5-[4-(hexadecylaminomethyl)-
1
phenyl]pyrrol-2-yl}propane-1,3-dione (4p2): Compound
3p2
CH2Cl2, 1%). H NMR (600 MHz, CDCl3, 20 °C): δ = 9.35 (s, 2
(11.4 mg, 0.02 mmol) and hexadecylamine (48.4 mg, 0.2 mmol)
were mixed in 1,2-dichloroethane (0.8 mL) at room temperature
under nitrogen for 3 h. Sodium triacetoxyborohydride (34.2 mg,
0.16 mmol) and AcOH (2 µL, 0.04 mmol) were added, and the mix-
ture was stirred at room temperature for 21 h. The reaction mixture
was quenched with aqueous saturated NaHCO3 solution and parti-
tioned between water and CH2Cl2. The combined extracts were
dried with anhydrous Na2SO4, and the solvents were evaporated to
dryness. The residue was then chromatographed by silica gel col-
umn chromatography (MeOH/CH2Cl2, 10%) to afford 4p2
(12.0 mg, 59%) as a red solid. Rf = 0.51 (MeOH/CH2Cl2, 10%).
1H NMR (600 MHz, CDCl3, 20 °C): δ = 9.40 (s, 2 H, NH), 7.47
(s, 8 H, ArH), 6.51 (s, 1 H, CH), 3.84 (s, 4 H, CH2), 2.84 (br., 4 H,
CH2), 2.68 (br., 4 H, NHCH2), 2.60 (br., 4 H, CH2), 1.58 (br., 4
H, NHCH2CH2), 1.32–1.16 [m, 64 H, (CH2)13, CH3], 0.87 (t, J =
7.2 Hz, 6 H, CH3) ppm (amino-NH signal is missing, possibly due
H, NH), 7.45–7.40 (m, 8 H, ArH), 6.55 (s, 1 H, CH), 5.88 (s, 4 H,
ArH), 4.36 (s, 4 H, CH2), 3.93 (s, 2 H, NH), 3.89 (t, J = 6.6 Hz, 8
H, m-OCH2), 3.84 (t, J = 6.0 Hz, 4 H, p-OCH2), 2.84 (q, J =
7.8 Hz, 4 H, CH2), 2.56 (q, J = 7.8 Hz, 4 H, CH2), 1.76–1.70 (m,
12 H, OCH2CH2), 1.44–1.39 (m, 12 H, OCH2CH2CH2), 1.34–1.11
[m, 156 H, (CH2)12, CH3], 0.88–0.86 (m, 18 H, CH3) ppm. UV/Vis
(CH2Cl2): λmax (εϫ105) = 503 nm (1.03 –1 cm–1). MALDI-TOF
MS: m/z (%) = 2164.4 (70) [M – H]–, 2165.5 (100). ESI-TOF MS
(HR): calcd. for C141H238BF2N4O8 [M – H]– 2165.8451; found
2165.8416.
BF2 Complex of 1-{3,4-Diethyl-5-[4-(3,4,5-trihexadecyloxyphenyl-
aminomethyl)phenyl]pyrrol-2-yl}-3-(3,4-diethylpyrrol-2-yl)propane-
1,3-dione (5p1): Compound 3p1 (9.4 mg, 0.02 mmol) and 3,4,5-tri-
hexadecyloxyaniline (24.4 mg, 0.03 mmol) were mixed in 1,2-
dichloroethane (0.8 mL) at room temperature under nitrogen for
4 h. Sodium triacetoxyborohydride (17.5 mg, 0.08 mmol) and
AcOH (1 µL, 0.02 mmol) were added, and the mixture was stirred
at room temperature for 41 h. The reaction mixture was quenched
with aqueous saturated NaHCO3 solution, and the product was
extracted with CH2Cl2. The combined extracts were dried with an-
to its broadening characteristics). UV/Vis (CH2Cl2): λmax
=
505 nm. MALDI-TOF MS: m/z (%) = 1018.9 (80) [M – H]–, 1020.0
(100). ESI-TOF MS (HR): calcd. for C65H102BF2N4O2 [M – H]–
1019.8080; found 1019.8080.
BF2 Complex of 1-{3,4-Diethyl-5-[3-(3,4,5-trihexadecyloxyphenyl- hydrous Na2SO4, and the solvents were evaporated to dryness. The
aminomethyl)phenyl]pyrrol-2-yl}-3-(3,4-diethylpyrrol-2-yl)propane- residue was then chromatographed by silica gel column chromatog-
1,3-dione (5m1): Compound 3m1 (4.6 mg, 0.01 mmol) and 3,4,5-
trihexadecyloxyaniline (12.2 mg, 0.015 mmol) were mixed in 1,2-
dichloroethane (0.4 mL) at room temperature under nitrogen for
2 h. Sodium triacetoxyborohydride (8.8 mg, 0.04 mmol) and AcOH
(0.5 µL, 0.01 mmol) in 1,2-dichloroethane (0.1 mL) were added,
and the mixture was stirred at room temperature for 20 h. The reac-
tion mixture was quenched with aqueous saturated NaHCO3 solu-
tion, and the product was extracted with CH2Cl2. The combined
extracts were dried with anhydrous Na2SO4, and the solvents were
evaporated to dryness. The residue was then chromatographed by
raphy (MeOH/CH2Cl2, 2%), and crystallization from CH2Cl2/
MeOH afforded 5p1 (16.1 mg, 64%) as an orange solid. Rf = 0.48
(MeOH/CH2Cl2, 1%). 1H NMR (600 MHz, CDCl3, 20 °C): δ =
9.32 (br., 1 H, NH), 9.29 (br., 1 H, NH), 7.48 (s, 4 H, ArH), 6.95
(d, J = 2.4 Hz, 1 H, CH), 6.52 (s, 1 H, CH), 5.89 (s, 2 H, ArH),
4.33 (s, 2 H, CH2), 3.90 (t, J = 6.6 Hz, 4 H, m-OCH2; this peak
overlaps the NH peak), 3.84 (t, J = 6.0 Hz, 2 H, p-OCH2), 2.84 (q,
J = 7.2 Hz, 2 H, CH2), 2.80 (q, J = 7.8 Hz, 2 H, CH2), 2.61 (q, J
= 7.2 Hz, 2 H, CH2), 2.49 (q, J = 7.8 Hz, 2 H, CH2), 1.77–1.70 (m,
6 H, OCH2CH2), 1.44–1.43 (m, 6 H, OCH2CH2CH2), 1.34–1.17
Eur. J. Org. Chem. 2010, 1469–1482
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1479

H. Maeda, R. Fujii, Y. Haketa
FULL PAPER
[m, 84 H, (CH2)12, CH3], 0.87 (t, J = 7.2 Hz, 9 H, CH3) ppm. UV/
Vis (CH2Cl2): λmax (εϫ105) = 480 nm (1.10 –1 cm–1). MALDI-
TOF MS: m/z (%) = 1263.2 (100) [M – H]–, 1264.2 (83). ESI-TOF
methods. A single crystal of 3m2 was obtained by vapor diffusion
of hexane into a CHCl3 solution of 3m2. The data crystal was a
yellow prism. Data were collected with a Rigaku RAXIS-RAPID
MS (HR): calcd. for C80H131BF2N3O5 [M – H]– 1263.0168; found diffractometer and with use of graphite-monochromated Mo-Kα
1263.0167.
radiation; the structure was solved by direct methods. A single crys-
tal of 3p1 was obtained by vapor diffusion of hexane into a CHCl3
solution of 3p1. The data crystal was a yellow prism. Data were
collected with a Rigaku RAXIS-RAPID diffractometer and with
use of graphite-monochromated Mo-Kα radiation; the structure
was solved by direct methods. A single crystal of 3p2 was obtained
by vapor diffusion of hexane into a CHCl3 solution of 3p2. The
data crystal was a yellow prism. Data were collected with a Rigaku
RAXIS-RAPID diffractometer and with use of graphite-mono-
chromated Mo-Kα radiation; the structure was solved by direct
methods. In each case, the non-hydrogen atoms were refined aniso-
tropically. The calculations were performed with the aid of the
Crystal Structure crystallographic software package from the Mo-
lecular Structure Corporation. CCDC-723260 (for 3m1), -723261
(for 3m2), -723262 (for 3p1), and -723263 (for 3p2) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
BF2 Complex of 1,3-Bis{3,4-diethyl-5-[4-(3,4,5-trihexadecyloxy-
phenylaminomethyl)phenyl]pyrrol-2-yl}propane-1,3-dione
(5p2):
Compound 3p2 (22.7 mg, 0.04 mmol) and 3,4,5-trihexadecyloxyan-
iline (48.9 mg, 0.06 mmol) were mixed in 1,2-dichloroethane
(0.8 mL) at room temperature under nitrogen for 21 h. Sodium tri-
acetoxyborohydride (51.4 mg, 0.24 mmol) and AcOH (4.5 µL,
0.08 mmol) were added, and the mixture was stirred at room tem-
perature for 24 h. The reaction mixture was quenched with aqueous
saturated NaHCO3 solution, and the product was extracted with
CH2Cl2. The combined extracts were dried with anhydrous
Na2SO4, and the solvents were evaporated to dryness. The residue
was then chromatographed by silica gel column chromatography
(MeOH/CH2Cl2, 2%), and crystallization from CH2Cl2/MeOH af-
forded 5p2 (55.2 mg, 64%) as a red solid. Rf = 0.68 (MeOH/
1
CH2Cl2, 1%). H NMR (600 MHz, CDCl3, 20 °C): δ = 9.33 (s, 2
H, NH), 7.49 (s, 8 H, ArH), 6.56 (s, 1 H, CH), 5.89 (s, 4 H, ArH),
4.34 (s, 4 H, CH2), 3.86 (t, J = 6.0 Hz, 8 H, m-OCH2), 3.89 (s, 2
H, NH), 3.85 (t, J = 6.6 Hz, 4 H, p-OCH2), 2.86 (q, J = 7.8 Hz, 4
H, CH2), 2.62 (q, J = 7.8 Hz, 4 H, CH2), 1.78–1.69 (m, 12 H,
OCH2CH2), 1.45–1.41 (m, 12 H, OCH2CH2CH2), 1.36–1.17 [m,
156 H, (CH2)12, CH3], 0.88–0.86 (m, 18 H, CH3) ppm. UV/Vis
Atomic Force Microscopy (AFM): AFM measurements were car-
ried out with an Olympus LEXT OLS3500 in dynamic force mode
(tapping mode).
Methods for DLS: DLS measurements were determined by dy-
(CH2Cl2): λmax (εϫ105) = 506 nm (1.23 –1 cm–1). MALDI-TOF namic light scattering with a Malvern Zetasizer Nano-ZS instru-
MS: m/z (%) = 2164.5 (80) [M – H]–, 2165.5 (100). ESI-TOF MS
(HR): calcd. for C141H238BF2N4O8 [M – H]– 2165.8451; found
2165.8404.
ment.
DFT Calculations: Ab initio calculations for 3m1, 3m2, 3p1, and
3p2 and AM1 calculations for 5m2 and 5p2 were carried out with
the aid of the Gaussian 03 program[14] and an HP Compaq dc5100
SFF computer. The structures for 3m1, 3m2, 3p1, and 3p2 were
optimized, and the total electronic energies were calculated at the
B3LYP level by use of a 6-31G** basis set.
Single-Crystal X-ray Analysis: Crystallographic data for 3m1, 3m2,
3p1, and 3p2 are summarized in Table 2. A single crystal of 3m1
was obtained by vapor diffusion of hexane into a CH2Cl2 solution
of 3m1. The data crystal was a yellow prism. Data were collected
with a Bruker CCD diffractometer and with use of graphite-mono-
chromated Mo-Kα radiation; the structure was solved by direct
Supporting Information (see footnote on the first page of this arti-
cle): X-ray crystallographic data (3m1, 3m2, 3p1, and 3p2), opti-
Table 2. Crystallographic details for compounds 3m1, 3m2, 3p1, and 3p2.
3m1
3m2
3p1
3p2
Empirical formula
Molecular mass
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C26H29BF2N2O3
466.32
C33H33BF2N2O4·CHCl3
689.79
C26H29BF2N2O3
466.32
C33H33BF2N2O4·0.66H2O
581.05
0.45ϫ0.20ϫ0.05
triclinic
0.50ϫ0.30ϫ0.20
triclinic
0.50ϫ0.30ϫ0.10
monoclinic
C2/c (no. 15)
17.711(6)
9.322(3)
28.431(10)
90
101.648(15)
90
4598(3)
1.347
0.80ϫ0.40ϫ0.20
monoclinic
C2/c (no. 15)
41.419(13)
11.164(4)
27.785(7)
90
113.364(12)
90
11794(6)
1.309
¯
¯
P1 (no. 2)
P1 (no. 2)
12.525(2)
14.885(3)
15.601(3)
113.977(3)
113.436(3)
94.245(3)
2340.1(7)
1.324
10.321(4)
10.625(4)
15.474(8)
74.619(17)
82.100(18)
83.994(14)
1616.5(12)
1.417
γ [°]
V [Å3]
ρcalcd [gcm–3]
Z
4
2
8
16
T [K]
90(2)
0.096
11779
123(2)
0.337
15525
123(2)
0.098
21222
123(2)
0.095
55377
µ(Mo-Kα) [mm–1]
No. of reflections
No. of unique reflections 8059
7028
416
5240
315
13476
810
Variables
621
λMo-Kα [Å]
R1 [IϾ2σ(I)]
wR2 [I Ͼ 2σ (I)]
GOF
0.71073
0.0917
0.2143
1.103
0.71075
0.0560
0.1737
1.284
0.71075
0.0498
0.1269
0.71075
0.0814
0.2159
1.046
1.023
1480
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 1469–1482

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Acknowledgments
This work was supported by Grants-in-Aid for Young Scientists
(B) (No. 21750155) and for Scientific Research in a Priority Area
“Super-Hierarchical Structures” (No. 18039038, 19022036) from
the Ministry of Education, Culture, Sports, Science and Technol-
ogy (MEXT) and the Ritsumeikan Global Innovation Research
Organization (R-GIRO) project 2008-2013. The authors thank
Prof. Atsuhiro Osuka, Dr. Shigeki Mori (currently at Ehime Uni-
versity), Mr. Shohei Saito, and Mr. Sumito Tokuji, Kyoto Univer-
sity, for X-ray analyses, Prof. Hiroshi Shinokubo and Dr. Satoru
Hiroto, Nagoya University, for ESI MS measurements, and Prof.
Hitoshi Tamiaki, Ritsumeikan University, for various measure-
ments. Y. H. thanks the Japan Society for the Promotion of Science
(JSPS) for a Research Fellowship for Young Scientists.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1481

H. Maeda, R. Fujii, Y. Haketa
FULL PAPER
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
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unspecific objects, such as spheres, were observed in the dried
samples of the gelated materials. Further, spin-coating of the
solution at room temp. on glass substrate afforded fibers in the
case of free receptors and no morphologies in anion complexes.
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Theoretical studies at the AM1 level for 5m2 and 5p2 suggested
that the lengths of these receptors in one of the stable confor-
mations were 6.3 and 6.7 nm, respectively (Figure S5 in the
Supporting Information).
DLS peak intensities are not always proportional to the
amounts of the corresponding aggregates in the solution state.
Larger objects often provide fairly intense light scattering in
relation to smaller ones, so it is not easy to discuss the quanti-
tative aspects only on the basis of DLS measurements, which
may show less strong correlations with UV/Vis absorption
spectra.
[22]
[23]
[24]
[15] The distances between π-planes in the β-ethyl-substituted de-
rivatives in the solid state were 3.729 and 4.191 Å for α-phenyl
compound 2c, 3.378 and 5.011 Å for α-pyrrolyl compound 2d,
and 3.386 and 5.087 Å for the α-thienyl compound (not
shown). On the other hand, α-H (2a) and α-furyl (not shown)
formed only the stacking dimers without infinite columnar
structures.
[16] The relative energies of the preorganized conformations with
the inversion of two pyrrole rings, as appropriate for anion
binding, were +3.59 (3m1), +2.69 (3m2), +5.21 (3p1), and
+4.38 (3p2) kcalmol–1, as calculated by DFT studies. These
values showed almost no correlations with the binding affin-
ities (Ka) for anions.
[25] Extended derivatives based on formyl substituents – dipyrrin-
pendant acyclic anion receptors, for example – were prepared
from 3m1 and 3m2 through subsequent treatment with α-meth-
ylpyrrole in the presence of an acid catalyst and DDQ oxi-
dation. Here, in order to exclude axial coordination at ZnII as
a bridging metal cation, methyl groups were introduced at the
α-positions of the pyrrole rings. Mono- and bis(dipyrrin)-pen-
dant acyclic anion receptors afforded the anion receptors with
bis(dipyrrin)ZnII complexes and ZnII-bridged coordination
polymers (below), respectively, by treatment with Zn(OAc)2.
Such metal-coordination dimers and polymers exhibited anion-
responsive behavior in their UV/Vis absorption spectral
changes in CH2Cl2 upon addition of anions (Figure S11 in the
Supporting Information). See also ref.[26]
[17] The existence of the [2 + 1] complexes has already been con-
firmed in a previous report. See ref.[12a]
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[19] The binding constants (Ka values) of 5p2 in CH2Cl2 were 6100
–
–
(Cl–), 560 (Br–), 42000 (CH3CO2 ), 7000 (H2PO4 ), and 20 –1
–
(HSO4 ) (Figure S10 in the Supporting Information), which
were similar to the values of 2c. Therefore, the effect of the
aminomethyl substituents did not seem very significant.
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[21] The morphologies were significantly dependent on the prepara-
tion conditions (temperatures on drying, etc.); at least, only
Received: November 23, 2009
Published Online: January 29, 2010
1482
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Eur. J. Org. Chem. 2010, 1469–1482