Dynamic properties of molecular tweezers with a bis(2-hydroxyphenyl) pyrimidine backbone

Article abstract of DOI:10.1002/chem.201304380

4,6-Bis(2-hydroxyphenyl)-2-alkylpyrimidines with two anthryl or 9-ethylnylanthryl substituents at the positions para to the OH groups prefer a U-shaped conformation supported by two intramolecular OH...N hydrogen bonds in the solid state and in CDCl₃

Full text of DOI:10.1002/chem.201304380

DOI: 10.1002/chem.201304380
Full Paper
&
Molecular Tweezers
Dynamic Properties of Molecular Tweezers with a
Bis(2-hydroxyphenyl)pyrimidine Backbone
Yoshitaka Tsuchido,[a] Yuji Suzaki,[a] Tomohito Ide,[a, b] and Kohtaro Osakada*[a]
Abstract: 4,6-Bis(2-hydroxyphenyl)-2-alkylpyrimidines with
two anthryl or 9-ethylnylanthryl substituents at the positions
para to the OH groups prefer a U-shaped conformation sup-
ported by two intramolecular OH···N hydrogen bonds in the
solid state and in CDCl3 solution. The compound with
a hexyl substituent on the pyrimidine group and two 9-ethy-
nylanthryl arms at the hydroxyphenyl groups forms a 1:1
complex with 2,4,7-trinitrofluorenone. Its association con-
stant Ka was estimated to be 2100mÀ1 at 298 K, which is
larger than those of other molecular tweezers (Ka <
1000mÀ1). DFT calculations suggested that the complex
adopts a stable conformation supported by intramolecular
hydrogen bonds among the OH groups and the pyrimidine
ring as well as by intermolecular p–p interaction between
the anthryl groups and 2,4,7-trinitrofluorenone. Addition of
nBu4NF to a solution of the molecular tweezers or their com-
plexes causes the cleavage of one or two OH···N hydrogen
bonds, formation of new O···HF hydrogen bonds, and
changes in the molecular conformation. The resulting struc-
ture of the molecular tweezers contains nonparallel anthryl
groups, which do not bind the guest molecule. Photochemi-
cal measurements on 4,6-bis(2-hydroxyphenyl)-2-methylpyri-
midine with two anthryl substituents showed negligible lu-
minescence (quantum yield f<0.01), owing to photoin-
duced electron transfer of the molecule with a U-shaped
structure. However, the O-hexylated compound exhibits
emission from the anthryl groups with f=0.39.
gated parts,[5] planar transition metal complexes,[6] fullerenes,[7]
carbon nanotubes,[8] and crown ether and dialkyl ammonium
pseudorotaxanes.[9] Host molecules whose stable conformation
does not have a cavity that allows for complexation were also
reported to bind guest molecules on their structural change.
Klꢀrner et al. prepared a host compound in which anthracene
groups are arranged in a nonparallel orientation because of
the spacer structure; the conformation becomes parallel on
forming a complex with an aromatic guest.[10] Similar induced-
fit conformational changes are observed for various host–
guest combinations.[11] A compulsory structural change of bi-
functional compounds is induced in a molecular motor.[12]
Lehn designed unsymmetrical host compounds and demon-
strated complexation of a guest molecule induced by outer
stimulation.[13] The addition of transition metal ions to terpyri-
dine with two anthracene groups in the meta positions
changes its open conformation to a U-shaped one by the che-
lation of the terpyridine group to the metal centers.[14] Two
parallel terminal anthryl groups bind planar aromatic guest
molecules. This system enables reversible catching and release
of organic guests by repeated cycles of coordination and de-
coordination of the transition metals. Jang et al. reported allo-
steric molecular tweezers whose binding of an organic guest is
highly influenced by the chloride anion.[15] Saint-Aman, Bucher
et al. designed redox-responsive porphyrin-based molecular
tweezers.[16] Petitjean, Leroux et al. employed 2,6-diarylpyridine
as the spacer for the naphthalene moieties of their molecular
tweezers and showed its pH-dependent behavior based on
their conformational change.[17] As shown in Scheme 1a, the
Introduction
The history of host–guest chemistry dates back to the discov-
ery of cyclic host molecules that bind guest molecules effi-
ciently.[1] In 1978, Whitlock et al. reported a complex of aromat-
ic carboxylic acids with an acyclic host composed of two caf-
feine groups connected by a polymethylene spacer.[2] The in-
teraction between the guest molecule and the aromatic func-
tional groups of the host stabilizes the complex, and a more
directional interaction than that of complexes of cyclic hosts is
required for stoichiometric aggregation. Acyclic host com-
pounds of this type were proposed as molecular tweezers.[3]
Zimmerman et al. designed such host compounds containing
two anthracene groups separated by a rigid spacer and report-
ed their complexation of many aromatic guests and applica-
tions, such as the selective recognition of nucleobases and the
separation of polyaromatic hydrocarbons.[4] Guests in such
complexes include planar organic molecules or their p-conju-
[a] Y. Tsuchido, Dr. Y. Suzaki, Dr. T. Ide, Prof. Dr. K. Osakada
Chemical Resources Laboratory, Tokyo Institute of Technology
4259 R2-3, Nagastuta, Midori-ku, Yokohama 226-8503 (Japan)
Fax: (+81)45-924-5224
E-mail: kosakada@res.titech.ac.jp
[b] Dr. T. Ide
Present address: Corporate Research and Development Center
Toshiba Corporation
1, Komukai-Toshiba-cho, Saiwai-ku, Kawasaki 212-8582 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304380.
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Figure 2. Crystal structures of molecular tweezers (ball-and-stick representa-
tion). a) 2-OH and b) 3-OH·2CHCl3.[18] The OH hydrogen atoms of 2-OH were
calculated by assuming OH···N hydrogen bonds. Dashed lines indicate
OH···N hydrogen bonds.
without an alkynyl group was prepared in accordance with
a previous report.[18]
The structure of 2-OH determined by X-ray crystallography
is compared with that of 3-OH[18] in Figure 2. Molecules of 2-
OH and 3-OH·2CHCl3 have small dihedral angles between the
pyrimidyl (Pyr) and arene (Ar) rings (]Ar–Pyr=5.3 and 1.48, re-
spectively). The difference Fourier synthesis of 3-OH·2CHCl3 re-
vealed the position of the OH hydrogen atoms with H···N dis-
tances of 1.75 ꢂ, whereas the crystallographic study on 2-OH
did not provide information on the position of OH hydrogen
atoms. The coplanarity of the three aromatic rings and the
close contact of the O and N atoms (2.54 and 2.56 ꢂ) of 2-OH,
however, suggest hydrogen bonds. The IR spectra of 2-OH and
3-OH·2CHCl3 (KBr disk) show broad n(OH) peaks at 2550 and
2710 cmÀ1, which also indicate OH···N hydrogen bonds. The
anthracene planes of 2-OH are tilted by 72.08 (Figure 2a). A
CÀH···p interaction[20] exists between the anthryl proton and
the p surface. However, 3-OH·2CHCl3 has two CHCl3 molecules
of solvation, which are intercalated between the two parallel
anthracene planes (Figure 2b). The CÀH···p interaction of
CHCl3 with anthryl groups serves to maintain the conformation
with parallel anthracene planes. Yam et al. designed OH-free
bis-aryl pyridine-type molecular tweezers with two square-
planar Pt complexes at the end of the two arms to maintain its
conformation.[21]
Scheme 1. Conformational change of backbone structures by addition of
acid or base. a) 2,6-Diarylpyridine[17] and b) bis(2-hydroxyphenyl)pyrimi-
dine.[18]
molecule adopts an open conformation under non-acidic con-
ditions, and the addition of protic acid gives it a pinched struc-
ture. Recently, we reported bis(hydroxyphenyl)pyrimidine de-
rivatives and their different conformations depending on their
substituents.[18] Bis(hydroxyphenyl)pyrimidine has a U-shaped
structure stabilized by OH···N hydrogen bonds (Scheme 1b).
The addition of a proton to a pyrimidine nitrogen atom forms
a molecule with an S-shaped conformation (Scheme 1bi),
whereas protonation of both nitrogen atoms yields a W-
shaped molecule (Scheme 1bii). The use of FÀ instead of H+
was expected to cause a clear structural change, because Dai
and Zhao have recently reported cleavage of the OH···N hydro-
gen bond of polyaromatic compounds caused by the addition
of FÀ.[19] Herein, we present the preparation, structure, and
stimulation-dependent properties of 4,6-pyrimidine-based mo-
lecular tweezers.
Results and Discussion
We compared the structures of the above molecular tweez-
ers with those of O-alkylated derivatives. Hexylation of the OH
groups of 2-OH and 3-OH produced compounds 2-OHex and
3-OHex (Scheme 2).[18] X-ray structure determination revealed
Preparation and structure of molecular tweezers
Figure 1 shows the host molecules used in this study. Com-
pounds 1-OH and 2-OH with two anthrylalkynyl groups
bonded to 4,6-bis(2-hydroxyaryl)pyrimidine were prepared by
a combination of cross-coupling reactions involving organo-
magnesium and organoboron compounds. Compound 3-OH
Figure 1. Structures of molecular tweezers with bis(2-hydroxylphenyl)pyrimi-
dine backbone. a) 1-OH and 2-OH. b) 3-OH.
Scheme 2. Synthesis of O-alkylated bis(2-hydroxyphenyl)pyrimidines 2-OHex
and 3-OHex.
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W-shaped conformations with dihedral angles between the ar-
ylene (Ar) and pyrimidine (Pyr) rings of 26.48 (2-OHex) and
40.0, 30.68 (3-OHex). CH···O interactions (2.32 ꢂ in 2-OHex;
2.40 and 2.32 ꢂ in 3-OHex) between oxygen and pyrimidinyl
hydrogen atoms were noted.
1
The H NMR spectra of 3-OH and 3-OHex are compared in
1
Figure 3. The H NMR spectrum of 3-OH shows a broad signal
for an OH hydrogen atom (Hj) at a much lower field (dH =
Scheme 3. Complexation of molecular tweezers 1-OH with TNF to form
1
1-OHꢀTNF. Inset: Job plot of 1-OH and TNF determined by H NMR titration
(CDCl3, [1-OH]+[TNF]=1.0 mmolLÀ1, 298 K).
Figure 3. 1H NMR spectra of i) 3-OH and ii) 3-OHex (CDCl3, 400 MHz, 298 K).
See Scheme 2 for assignments of the signals.
14.01) than typical OH groups due to the intramolecular
OH···N hydrogen bonds between hydroxyl hydrogen and pyri-
midinyl nitrogen atoms. This signal suggests that 3-OH main-
tains its U-shaped conformation in CDCl3 solution, as well as in
the solid state (Figure 2b). Stueber et al. reported similar intra-
molecular OH···N hydrogen bonds in 2,4-bis(2’-hydroxyaryl)-
1
1,3,5-triazine (dH(OH)=13.2).[22] The H NMR signal of the pyri-
Figure 4. UV/Vis monitoring of the titration of a solution of 1-OH (CHCl3,
[1-OH]=0.050 mmolLÀ1, 298 K) with TNF. The inset shows the isosbestic
point at 453 nm.
midinyl hydrogen atom of 3-OHex (Hi, dH =8.51 ppm) was ob-
served at a lower field than that of 3-OH (dH =7.85 ppm),
which is attributed to the CH···O interaction of the former
compound with a W-shaped conformation in CDCl3. The above
results are consistent with the notion that the conformations
of 3-OH and 3-OHex are stabilized by OH···N and CH···O hydro-
gen bonds in both CDCl3 solution and the solid state.
(Figure 4). Observation of an isosbestic point at 453 nm indi-
cated formation of a single complex from 1-OH and TNF.
The addition of TNF to a solution of 1-OH in CDCl3 ([1-OH]=
1
1.0 mmolLÀ1) also changed the H NMR spectrum. An upfield
shift of anthryl protons (Ha, Hb, Hc, Hd, He), phenyl protons (Hf,
Hg), and a hydroxyl proton (Hj), as well as a downfield shift of
the pyrimidine proton (Hi) and TNF protons were noted. The
peak of Ha was shifted from dH =8.41 ppm ([1-OH]=
1.0 mmolLÀ1, [TNF]=0.0 mmolLÀ1) to 7.79 ppm ([TNF]=
20.0 mmolLÀ1). These shifts are explained by the charge-trans-
fer (CT) interaction between the anthryl groups of 1-OH and
electron-deficient TNF. The CT should cause upfield shifts of
electron-rich anthryl protons and downfield shifts of the elec-
tron-deficient TNF protons. A Job plot for 1-OH and TNF, ob-
Host–guest complexation of molecular tweezers and guest
molecules
Complexation of molecular tweezers 1-OH and 3-OH with
guest molecules 2,4,7-trinitrofluorenone (TNF), 1,2,4,5-tetracya-
nobenzene (TCB), and tetracyanoquinodimethane (TCNQ) was
1
investigated by UV/Vis spectroscopy, H NMR titration, and DFT
calculations.
In CDCl3, 1-OH and TNF formed inclusion complex
1
1-OHꢀTNF, as shown in Scheme 3. The addition of
a
tained by H NMR titration in CDCl3 at 298 K ([1-OH]+[TNF]=
colorless solution of TNF to a yellow solution of 1-OH
(1.0 mmolL-1 CHCl3) resulted in a brown solution, suggesting
interaction between the anthryl groups of 1-OH and TNF. De-
creased absorbance of 1-OH (0.050 mmolLÀ1) at 430 nm, as-
signed to the p–p* transition of anthryl groups, was accompa-
nied by the growth of a new broad peak at 460–550 nm
1.0 mmolLÀ1), showed a peak maximum at a mole fraction of
0.5 (Scheme 3, inset), which indicates formation of 1:1 inclusion
complex 1-OHꢀTNF between 1-OH and TNF.
The association constant Ka of complex formation was esti-
mated to be 2100mÀ1 (CDCl3, 298 K) from a Scatchard plot ob-
tained on the basis of the shift of an anthryl proton (Ha). It is
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larger than that of molecular tweezers with a rigid dibenzo-
[c,h]acridine backbone unit (Ka =1000mÀ1, CHCl3, 298 K) report-
ed by Zimmerman et al.[4] The high affinity of 1-OH for TNF is
due to the two following reasons. The OH···N hydrogen bonds
between the pyrimidinyl nitrogen and hydroxyl hydrogen
atoms allow for adjustment of the conformation of the bis-an-
thryl pyrimidine backbone, so that the anthryl groups are situ-
ated in a position optimal for squeezing the guest molecule.
Ethynylene spacers between the backbone and the anthryl
groups form a cavity suitable for large guest molecules. The
thermodynamic parameters of this reaction were calculated to
be DG8=À19.0 kJmolÀ1, DH8=À29.4 kJmolÀ1
,
and DSo =
À35 JmolÀ1 KÀ1. The large negative DH and DS imply intermo-
lecular complex formation driven by the attractive interaction
between 1-OH and TNF.
The association constants Ka of the complexation of 1-OH
and 3-OH with TNF, TCB, and TCNQ are listed in Table 1. Molec-
ular tweezers 1-OH showed association constants of 2100mÀ1
Figure 5. Optimized conformations Conf1 (a) and Conf2 (b) of inclusion com-
plex 1-OHꢀTNF determined by DFT calculations (B97-D/TZVP).
Table 1. Association constants of complex formation.
1-OH, whereas in Conf2 the TNF guest is stabilized by interac-
tion of an NO2 group of TNF with the pyrimidine CH group
and in the opposite direction to that in Conf1. Both structures
were optimized by DFT calculation (B97-D/TZVP). The calculat-
ed relative free energies suggested higher stability of Conf1
than Conf2 by DG=À6.3 kJmolÀ1. The interaction between the
carbonyl oxygen atom of TNF and the acidic hydrogen atom is
effective for the stabilization of Conf1. The downfield shift of
Molecular
tweezers
Guest
Association constant
Ka [mÀ1
[a]
]
1-OH
TNF
TCB
TCNQ
TNF
TCB
2100
550
93
300
<1
<1
3-OH
TCNQ
1
the H NMR peak of the pyrimidyl proton (Hi) is explained by
[a] Determined by 1H NMR titration (Scatchard plot), CDCl3, [molecular
tweezers]=1.0 mmolLÀ1, 298 K.
the interaction with the carbonyl oxygen atom of TNF with the
conformation Conf1, as shown in Figure 5a. The molecular or-
bitals of Conf1 were also obtained by DFT calculation. The
HOMO and its degenerate orbital HOMOÀ1 are extended over
the anthracene rings and phenyl groups of 1-OH, whereas the
LUMO is localized on TNF. The Mꢃlliken charges of 1-OH and
TNF were calculated to be positive (+0.096) and negative
(À0.096), respectively, and thus indicate CT between the elec-
tron-rich anthracene units and the electron-deficient TNF
guest.
for TNF, 530mÀ1 for TCB, and 93mÀ1 for TCNQ. 3-OH has a low
affinity to TNF (Ka =300mÀ1) and undergoes negligible com-
plex formation with TCB and TCNQ. The difference in affinity
between 1-OH and 3-OH to the electron-deficient guests can
be attributed to the size of the cavity for guest binding. The
anthracene units of 3-OH are bonded directly to aromatic
rings, which are perpendicular to the anthracene plane. As
shown in Figure 2b, the CÀH groups of the aromatic rings
narrow the cavity for the guest molecules. In contrast, 1-OH
has a large cavity for guest binding and allows for a strong in-
teraction between the anthracene units and the guest mole-
cule. The negatively charged p surface of TNF due to electron-
withdrawing nitro groups causes a strong CT interaction with
two anthracene units of the molecular tweezers. The Ka values
of the O-alkylated compounds 2-OHex and 3-OHex with the
guest molecules (TNF, TCNQ, and TNF) are negligible (Ka <
40mÀ1, CDCl3, 298 K) owing to their unfavorable conformations
for guest binding.
We attempted to perform ROESY (rotating Overhauser en-
hancement and exchange spectroscopy) measurements to in-
vestigate the actual structure of the inclusion complex, but the
poor solubility of TNF prevented this. Therefore, we synthe-
sized a derivative of a TNF isomer with an alkoxycarbonyl sub-
stituent at the 2-position of fluorenone (TNF-C16). The Ka value
of 1-OH and TNF-C16 was estimated to be 180mÀ1, which is
lower than that of TNF (Ka =2100mÀ1). The high solubility of
TNF-C16 and the inclusion complex in CDCl3 enabled ROESY
1
measurements. The H NMR and 1D ROESY spectra are shown
in Figure 6 ([1-OH]=5.0 mmolLÀ1, [TNF-C16]=100 mmolLÀ1).
Selective irradiation of Hh (dH =8.61 ppm) in the backbone re-
sulted in a positive peak at dH =8.75 ppm. This suggests an in-
termolecular correlation between Hh (1-OH) and HB (TNF-C16),
which indicates intercalation of TNF-C16 between the two an-
thryl groups of molecular tweezers 1-OH. A negative peak at
8.69 ppm can be attributed to the intramolecular correlation
(TOCSY) between Hh and Hi of 1-OH.
The interactions of 1-OH and TNF were studied in detail by
DFT calculations. Figure 5a and b show two plausible confor-
mations of the inclusion complex 1-OHꢀTNF (i.e., Conf1 and
Conf2, respectively), which differ in the orientation of the TNF
molecule in the cavity of 1-OH. In Conf1, the carbonyl oxygen
atom of TNF is hydrogen-bonded to the pyrimidine ring of
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Scheme 4. Deprotonation of molecular tweezers 1-OH by addition of
nBu4NF (TBAF) to form a mixture of 1:1 ([1-OH+F]À) and 1:2 ([1-OH+2F]2À
)
complexes (CDCl3, 298 K). Inset: Job plot of 1-OH and TBAF determined by
1H NMR titration (CDCl3, [1-OH]+[TBAF]=2.0 mmolLÀ1, 298 K). R=-C6H13.
Figure 6. a) 1H NMR and b) 1D ROESY (selective excitation of Hh) spectra of
inclusion complex 1-OHꢀTNF-C16 (CDCl3, [1-OH]=5.0 mmolLÀ1
,
[TNF-C16]=100 mmolLÀ1, 298 K, mixing time=200 ms).
the aromatic rings. Scheme 4 depicts a plausible structural
change of the molecule caused by addition of FÀ. Addition of
fluoride to 1-OH cleaves an OH···N hydrogen bond. Facile rota-
tion about the CÀC bond between pyrimidine and phenol
rings changes the conformation of the molecule, so that the
bulky anthryl rings are orientated in less sterically crowded di-
rections in an S-type structure (Scheme 4, [1-OH+F]À). The ad-
dition of two fluoride ions cleaves both of the OH···N hydrogen
bonds of 1-OH. The resulting dianionic species prefers to form
a W-shaped structure by rotation about the two CÀC bonds,
similar to the O-alkylated molecular tweezers.[18]
Deprotonation of the host molecule and complex
Figure 7 shows the results of 1H NMR titration of molecular
tweezers 1-OH with tetra-n-butylammonium fluoride (TBAF) in
CDCl3 at 298 K ([1-OH]=1.0 mmolLÀ1
,
[TBAF]=0.05–
10.0 mmolLÀ1). The addition of TBAF to a solution of 1-OH in
CDCl3 caused a significant shift and broadening of aromatic hy-
drogen peaks (Hf, Hg, Hh, Hi) of the backbone. Comparison of
Figure 7i and x suggests that the peak due to Hh is shifted by
0.20 ppm to lower field on complexation of FÀ. The peaks of
Hf and Hg also show large shifts (0.18 and 0.20 ppm, respec-
tively), suggesting significant change of the electronic state of
1
The Job plot of 1-OH and TBAF, monitored by H NMR titra-
tion in CDCl3 at 298 K ([1-OH]+[TBAF]=2.0 mmolLÀ1), shows
a maximum at X=0.40 (Scheme 4 inset). The result is ascribed
to formation of both 1:1 (X=0.50) and 1:2 (X=0.33) complexes
of 1-OH and TBAF, accompanied by cleavage of one and two
OH···N hydrogen bonds of 1-OH, respectively.[23] The Ka value
for fluoride addition was estimated to be 820mÀ1 by means of
a Scatchard plot in CDCl3 at 298 K.
Addition of TBAF to inclusion complex 1-OHꢀTNF also
caused cleavage of the OH···N hydrogen bonds and release of
TNF owing to a change in molecular conformation of 1-OH.
The results of the 1H NMR titration (CDCl3, [1-OH]=
1.0 mmolLÀ1, [TNF]=1.0 mmolLÀ1, [TBAF]=0–10 mmolLÀ1,
298 K) are shown in Figure 8. Increasing the amount of added
TBAF changed the peak positions of TNF and anthryl groups.
The peaks due to phenoxyl groups (Hf and Hg) showed similar
changes on titration of 1-OH with TBAF (Figure 7), although
the shift of Hh is much less significant. The spectrum after addi-
tion of 20.0 equivalents of TBAF to the CDCl3 solution (Fig-
ure 8vii) contains signals at similar positions to the deprotonat-
ed molecular tweezers (Figure 7x). These results indicate that
addition of TBAF to inclusion complex 1-OHꢀTNF causes de-
complexation of the inclusion complex to form the deproton-
ated molecular tweezers and free TNF (Scheme 5). Addition of
an excess of Lewis acid (BF3·OEt2, ca. 100 mmolLÀ1) regenerates
Figure 7. 1H NMR titration of 1-OH with TBAF (400 MHz, CDCl3, 298 K,
[1-OH]=1.0 mmolLÀ1). i) [TBAF]=0.0, ii) 0.05, iii) 0.10, iv) 0.50, v) 1.0, vi) 2.0,
vii) 3.0, viii) 5.0, ix) 8.0, and x) 10.0 mmolLÀ1. The dotted lines indicate shifts
of the signals of the backbone protons of molecular tweezers (1-OH).
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Figure 9. Free-energy change DG for deprotonation of model compound
7-OH from DFT calculations [PCM-B97-1/DZV+(d,p)]. nBu4N+ was ignored in
the calculation because of FÀ of TBAF is regarded as a naked anion in CHCl3.
bond between the pyrimidine and bulky substituent. Concur-
rent of addition of two fluoride ions to 1-OH is ascribed to the
large energy difference between the intramolecular OH···N hy-
drogen bonds and intermolecular O···HF hydrogen bonds.
Photochemical properties
UV/Vis and fluorescence spectra of molecular tweezers 2-OH
and 3-OH, their O-alkylated derivatives 2-OHex and 3-OHex,
and model compound 9-(4-hydroxyphenyl)anthracene (8-OH)
are shown in Figure 10. The absorption and fluorescence data
are summarized in Table 2.
Figure 8. 1H NMR titration of 1-OHꢀTNF with TBAF (400 MHz, CDCl3, 298 K,
[1-OH]=1.0 mmolLÀ1, [TNF]=1.0 mmolLÀ1). i) [TBAF]=0.0, ii) 1.0, iii) 2.0,
iv) 3.0, v) 5.0, vi) 8.0, vii) 10.0 mmolLÀ1, viii)+BF3·OEt2 (excess). The dotted
lines indicate shifts of the signals of molecular tweezers 1-OH. The asterisks
denote signals of TNF.
These compounds show typical absorption bands due to
the p–p* transition of the anthryl group at similar positions
(lmax =368–405 nm) and at longer wavelength than anthracene
Scheme 5. Decomplexation of the inclusion complex 1-OHꢀTNF by addition
of TBAF (CDCl3, 298 K). R=-C6H13.
1-OH (Figure 8viii). The signals due to 1-OH (Ha–Hg) of the mix-
ture are observed at lower field than in the original spectrum
(Figure 8i), but much closer than in the mixture before addi-
tion of BF3 (Figure 8vii). The peaks of TNF included in the com-
plex are also clearly observed at dH =8.88, 8.42, 8.28, 8.23, and
8.04 ppm, at positions close to those in Figure 8i.
Deprotonation of a model compound of 1-OH, namely, 4-(2-
hydroxyphenyl)-2-methylpyrimidine (7-OH), by FÀ was investi-
gated by DFT calculations [PCM-B97-1/DZV+(d,p)] in CHCl3.
The free energy of formation of [7-OH+F]À from 7-OH and FÀ
Figure 10. a) UV/Vis (CHCl3, [compound]=0.010 mmolLÀ1, RT) and b) fluores-
cence spectra (CHCl3, [compound]=0.0010 mmolLÀ1, RT) of i) 2-OH,
ii) 3-OH, iii) 2-OHex, iv) 3-OHex, v) 8-OH, and vi) 8-OH+pyridine ([pyridi-
ne]=100 mmolLÀ1). The asterisks in b) indicate the excitation light. The
insets show the fluorescence of ii) 3-OH and iv) 3-OHex in CHCl3 under UV ir-
radiation (365 nm).
was calculated to have
a large negative value (DG=
À18.3 kJmolÀ1; Figure 9). The formation of the stable OH···F
hydrogen bond may compensate for rotation about the CÀC
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Conclusion
Table 2. Absorption and fluorescence data.
Absorption
Compound
Fluorescence[c]
We have synthesized molecular tweezers with anthrylethynyl
arms and a 4,6-bis(2-hydroxyaryl)pyrimidine backbone spacer.
Their U-shaped conformation is stabilized by intramolecular
OH···N hydrogen bonds between the pyrimidinyl nitrogen
atoms and the OH groups. Formation of host–guest complexes
[a]
lmax [nm]
e [mÀ1 cmÀ1
]
lmax [nm]
f
2-OH
3-OH
2-OHex
3-OHex
8-OH
405
368
404
368
368
359
30000
24500
38300
25700
9700
–
–
439
<0.01
<0.01
0.40
1
410, 428
412, 429
405
0.39
was confirmed by H NMR and UV/Vis spectroscopy as well as
0.33 (0.36[b]
0.09[b]
)
by theoretical studies. 1-OH and TNF formed a 1:1 host–guest
complex in CDCl3, the association constant Ka of which was es-
timated to be 2100mÀ1, which is larger than those of known
molecular tweezers (Ka <1000mÀ1). This is ascribed to the intra-
molecular hydrogen bonds formed by the backbone unit. The
U-shaped conformation of 1-OH can be switched to W- and S-
shaped structures by the addition of FÀ with cleavage of the
OH···N hydrogen bonds. Thus, we demonstrated decomplexa-
tion of host–guest complex 1-OHꢀTNF by fluoride-induced
transformation of 1-OH into an unfavorable conformation for
guest binding.
anthracene
7200
[a] Standard sample: quinine (in 0.5 mmolLÀ1 H2SO4 aq., f=0.546).
[b] Determined at 0.0020 mmolLÀ1 in CHCl3. [c] lex =lmax(abs).
(lmax =359 nm). The absorption bands of 3-OH trail up to
about 440 nm, and its CHCl3 solutions show a yellow color,
whereas solutions of 3-OHex are colorless, which is attributed
to a intramolecular CT excitation between electron-rich anthryl
groups and the electron-deficient backbone unit. Three aro-
matic rings of the backbone structure of 3-OH are aligned in
a planar fashion owing to the intramolecular OH···N hydrogen
bonds and form an electron-poor p surface, which induces
a decrease in the LUMO level, so that 3-OH can absorb longer
wavelengths than 3-OHex due to the intramolecular CT excita-
tion.
Experimental Section
The synthesis of molecular tweezers 1-OH, 2-OH, and 2-OHex is
summarized in Scheme 6. 9-Ethynylanthracene,[25] 4,6-diiodo-2-
chloropyrimidine,[26] and 4,5,7-trinitro-9-fluorenone-2-carboxylic
acid[27] were prepared by literature methods. Syntheses of 6-OH,
6-OMe, 3-OH, 3-OHex, 8-OH were previously reported.[18] Anhy-
drous solvents were purchased and used without further purifica-
tion. Other materials were commercially available and used with-
Excitation of 2-OHex and 3-OHex at 404, 368 nm (in CHCl3)
induces a strong fluorescence at 439, 410 nm, which corre-
sponds to p–p* transition of the anthryl groups. The quantum
yields of 2-OHex (f=0.40) and 3-OHex (f=0.39) are higher
than that of anthracene (f=0.09). The fluorescence of 2-OH
and 3-OH under the same conditions is almost negligible (f<
0.01) despite the presence of anthracene rings. Model com-
pound 8-OH can be regarded as a partial structure of molecu-
lar tweezers 3-OH, but 8-OH showed strong fluorescence (f=
0.33). The addition of an excess of pyridine to a solution of
1
out further purification. H and 13C{1H} NMR spectra were acquired
on a Bruker AV-400M spectrometer (400 MHz). The chemical sifts
were referenced to TMS (d=0.00) for 1H and CDCl3 (d=77.16),
C2D2Cl4 (d=74.20) for 13C as internal standards. Fast atom bom-
bardment mass spectra (FAB MS) were measured on a JEOL JMS-
700 (3-nitrobenzyl alcohol (NBA) matrix). High-resolution ESI MS
spectra were measured with a Bruker micrOTOF II (eluent: ace-
tone+1%CF3COONa). Elemental analyses were obtained from
a Yanaco MT-5 CHN autorecorder. IR absorption spectra were mea-
sured on Shimadzu FTIR-8100 and a JASCO FTIR-4100 spectrome-
ters. UV/Vis absorption spectra were measured on a JASCO V-530
spectrometer. Emission spectra were measured on a JASCO FP-
6300 spectrometer. X-ray crystal structure analyses were performed
at a Rigaku AFC-10R Saturn CCD diffractometer or a Bruker APEXII
ULTRA/CCD diffractometer with graphite-monochromated MoKa ra-
diation.
8-OH in CHCl3 ([8-OH]=0.0010 mmolLÀ1
,
[pyridine]=
100 mmolLÀ1) decreased the fluorescence intensity to f=0.05.
The efficient quenching of fluorescence of 8-OH in the pres-
ence of pyridine is ascribed to an intermolecular photoinduced
electron-transfer (PET) process.[24] The electron-rich phenoxyl
group undergoes partial deprotonation with pyridine and
transfers an electron to an excited state of the anthryl group
(Figure 11a). Much weaker fluorescence of molecular tweezers
2-OH and 3-OH compared to O-alkylated compounds 2-OHex
and 3-OHex is also explained by the PET process. The phenox-
yl groups are formed by OH···N hydrogen bonds with the
neighboring pyrimidinyl groups (Figure 11b).
4,6-Bis(5-bromo-2-methoxyphenyl)-2-chloropyrimidine (4-
OMe)
A mixture of 4,6-diiodo-2-chloropyrimidine (1.83 g, 5.0 mmol), 5-
bromo-2-methoxyphenylboronic acid (2.31 g, 10 mmol), K2CO3
(2.76 g, 20 mmol), and [Pd(PPh3)4] (353 mg, 0.31 mmol) was dis-
solved in 1,4-dioxane (75 mL)/H2O (25 mL) under argon atmos-
phere. After stirring for 24 h at 808C, the mixture was allowed to
cool to room temperature. The solid that separated from the solu-
tion was removed by filtration, and the filtrate was evaporated to
dryness. The obtained yellow oil was dissolved in CH2Cl2 (300 mL)
and the solution was washed with water (2ꢄ100 mL). The separat-
ed organic phase was dried over MgSO4, filtered, and evaporated
to give the crude product as a yellow oil, which was purified by
column chromatography on silica gel (eluent: CH2Cl2/hexane 10/3)
Figure 11. Plausible quenching mechanism of a) 8-OH+pyridine and
b) 3-OH by PET processes.
Chem. Eur. J. 2014, 20, 4762 – 4771
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Scheme 6. Synthesis of molecular tweezers. a) 1-OH, b) 2-OH, and c) 2-OHex. i) 5-Bromo-2-methoxyphenylboronic acid, [Pd(PPh3)4], K2CO3, 1,4-dioxane, H2O,
808C, 18–24 h; ii) C6H13MgBr, Fe(acac)3, THF, N-methylpyrrolidone, RT, 1 h; iii) BBr3, CH2Cl2, RT to reflux, 17–22 h; iv) 9-Ethynylanthracene, Pd(OAc)2, PPh3, CuI,
iPr2NH, THF, 708C, 24 h; v) C6H13I, K2CO3, CH3COC2H5, 808C, 19 h.
to yield 4-OMe (1.83 g, 3.8 mmol, 76%) as a white solid. 1H NMR
(400 MHz, CDCl3, RT): d=8.48 (s, 1H, C4N2H), 8.17 (d, 2H, C6H3, J=
2.8 Hz), 7.56 (dd, 2H, C6H3, J=2.4, 8.8 Hz), 6.92 (d, 2H, C6H3, J=
8.8 Hz), 3.91 ppm (s, 6H, Me); 13C NMR (100 MHz, CDCl3, RT): d=
164.1, 160.9, 157.3, 134.9, 134.2, 127.0, 120.6, 113.8, 113.6,
56.1 ppm; FAB MS (NBA matrix) calcd for C18H13Br2ClN2O2: 484;
found: m/z 485 [M+H+]; elemental analysis calcd (%) for
C18H13Br2ClN2O2: C 44.62, H 2.70, N 5.78; found: C 44.55, H 2.67, N
5.77.
and the reaction was quenched by addition of cold water (100 mL)
and CH2Cl2 (200 mL). The separated organic phase was washed
with water (100 mL), dried over MgSO4, and evaporated to yield
a yellow solid. The crude product was purified by reprecipitation
from CH2Cl2 (30 mL)/methanol (150 mL) to yield 5-OH (784 mg,
1
1.5 mmol, 78%) as a yellow solid. H NMR (400 MHz, CDCl3, RT): d=
13.78 (s, 2H, OH), 8.03 (d, 2H, C6H3, J=2.4 Hz), 7.96 (s, 1H, C4N2H),
7.51 (dd, 2H, C6H3, J=2.4, 8.8 Hz), 6.97 (d, 2H, C6H3, J=8.8 Hz),
3.06 (t, 2H, CH2, J=7.6 Hz), 1.91 (tt, 2H, CH2, J=7.2, 14.8 Hz), 1.44–
1.32 (m, 6H, CH2), 0.90 ppm (t, 3H, CH3, J=7.2 Hz); 13C{1H} NMR
(100 MHz, CDCl3, RT): d=167.6, 164.3, 160.5, 136.8, 129.5, 121.3,
118.5, 111.4, 106.2, 38.7, 31.6, 29.0, 27.8, 22.6, 14.2 ppm; FAB MS
(NBA matrix) calcd for C22H22Br2N2O2: 506; found: m/z 507 [M+H+];
elemental analysis calcd (%) for C22H22Br2N2O2: C 52.20, H 4.38, N
5.53; found: C 52.10, H 4.15, N 5.50.
4,6-Bis(5-bromo-2-methoxyphenyl)-2-hexylpyrimidine
(5-OMe)
A mixture of 4-OMe (1.70 g, 3.5 mmol) and Fe(acac)3 (37 mg,
0.11 mmol) was dissolved in dry THF (30 mL) and N-methylpyrroli-
done (3.0 mL). C6H13MgBr (3.9 mmol, 3.9 mL of a 1.0m solution in
THF) was added dropwise to the solution under argon at 08C. The
mixture was stirred at room temperature for 1 h. The reaction mix-
ture was quenched by addition of water (1 mL) followed by evapo-
ration of the solvent. The obtained brown oil was dissolved in
CH2Cl2 (300 mL) and washed with water (100 mL) and brine
(100 mL). The separated organic phase was dried over MgSO4, fil-
tered, and evaporated to give a crude product, which was purified
by column chromatography on silica gel (eluent: CH2Cl2/hexane
10/3) to obtain 5-OMe (969 mg, 1.8 mmol, 52%) as a white solid.
1H NMR (400 MHz, CDCl3, RT): d=8.17 (s, 1H, C4N2H), 8.09 (d, 2H,
C6H3, J=2.4 Hz), 7.51 (dd, 2H, C6H3, J=2.8, 8.8 Hz), 6.90 (d, 2H,
C6H3, J=8.8 Hz), 3.88 (s, 6H, OCH3), 3.05 (t, 2H, CH2, J=7.6 Hz),
1.92 (m, 2H, CH2), 1.49–1.34 (m, 6H, CH2), 0.93 ppm (t, 3H, CH3, J=
6.9 Hz); 13C NMR (100 MHz, CDCl3, RT): d=171.5, 161.3, 157.0,
133.9, 133.8, 129.3, 119.5, 113.8, 113.5, 56.1, 40.0, 31.9, 29.4, 29.1,
22.8, 14.3 ppm; FAB MS (NBA matrix) calcd for C24H26Br2N2O2: 534;
found: m/z 535 [M+H+].
4,6-Bis[5-(anthracen-9-ylethynyl)-2-hydroxyphenyl]-2-hexyl-
pyrimidine (1-OH)
A
mixture of 5-OH (244 mg, 0.48 mmol), PPh3 (15.6 mg,
0.059 mmol), Pd(OAc)2 (4.5 mg, 0.020 mmol), CuI (4.2 mg,
0.022 mmol), and 9-ethynylanthracene (403 mg, 1.99 mmol) was
dissolved in iPr2NH (10 mL)/THF (10 mL) under argon. After the
mixture was stirred at 708C for 24 h, the solids that separated from
the solution were removed by filtration followed by evaporation of
the filtrate. The obtained yellow oil was dissolved in CH2Cl2
(200 mL) and the solution was washed with 10% HCl aq. (50 mL)
and water (2ꢄ50 mL). The separated organic phase was dried over
MgSO4, filtered, and evaporated to form a crude product, which
was purified by column chromatography on silica gel (eluent:
CH2Cl2/hexane 10/3) and reprecipitation (CH2Cl2/CH3CN 10/100 mL)
to yield 1-OH (302 mg, 0.40 mmol, 84%) as an orange solid.
1H NMR (400 MHz, CDCl3, RT): d=14.19 (br, 2H, OH), 8.62 (d, 4H,
C14H9, J=8.6 Hz), 8.38 (s, 2H, C14H9), 8.33 (d, 2H, C6H3, J=2.0 Hz),
8.22 (s, 1H, C4N2H), 7.95 (d, 4H, C14H9, J=8.4 Hz), 7.80 (dd, 2H,
C6H3, J=1.9, 8.5 Hz), 7.40 (ddd, 4H, C14H9, J=1.1, 6.6, 7.8 Hz), 7.31
(ddd, 4H, C14H9, J=0.8, 6.6, 7.7 Hz), 7.14 (d, 2H, C6H3, J=8.5 Hz),
3.08 (t, 2H, CH2, J=7.7 Hz), 1.96 (tt, 2H, CH2, J=7.8, 15.0 Hz), 1.50
(tt, 2H, CH2, J=7.8, 14.6 Hz), 1.39 (m, 4H, CH2), 0.93 ppm (t, 3H,
CH3, J=7.1 Hz); 13C{1H} NMR (100 MHz, CDCl3, RT): d=166.9, 164.3,
4,6-Bis(5-bromo-2-hydroxyphenyl)-2-hexylpyrimidine (5-OH)
BBr3 (20 mmol, 20 mL of a 1.0m solution in CH2Cl2) was slowly
added to a solution of 4-OMe (1.05 g, 2.0 mmol) in CH2Cl2 (60 mL)
at 08C. The mixture was stirred at room temperature for 4 h then
heated at reflux for 16 h. The resulting mixture was cooled to 08C
Chem. Eur. J. 2014, 20, 4762 – 4771
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161.8, 137.1, 132.6, 131.2, 130.7, 128.7, 127.6, 126.8, 126.7, 125.8,
119.7, 117.3, 117.1, 114.8, 106.0, 100.2 (CꢁC), 85.4 (CꢁC), 38.5, 31.7,
29.1, 27.6, 22.7, 14.2 ppm; IR (KBr disk, RT): n˜ =3050, 2952, 2925,
2854, 2592 (OÀH···N), 2197 (CꢁC), 1608, 1574, 1537, 1482, 1467,
1418, 1406, 1291, 879, 855, 839, 826, 784, 734, 678, 663, 614, 551,
512 cmÀ1; FAB MS (NBA matrix) calcd for C54H40N2O2: 748, found:
m/z 749 [M+H+]; elemental analysis calcd (%) for C54H40N2O2 86.60,
H 5.38, N 3.74; found: C 86.40, H 4.97, N 3.62.
tal analysis calcd (%) for C61H54N2O2 +H2O: C 84.69, H 6.52, N 3.24;
found: C 84.96, H 6.40, N 3.10. (Scheme 6)
4,5,7-Trinitro-9-fluorenone-2-carboxylic acid[27]
9-Fluorenone-2-carboxylic acid (2.26 g, 10 mmol) was slowly added
a solution of fuming HNO3 (40 mL) and conc. H2SO4 (40 mL) at 08C
and the mixture was heated to reflux for 3 h. After cooling to RT,
the yellow solution was poured into 400 mL of crushed ice. The re-
sulting yellow precipitate was collected by suction filtration. The
crude product was purified by reprecipitation from CH3NO2/CH2Cl2
to yield 4,5,7-trinitro-9-fluorenone-2-carboxylic acid (2.87 g,
4,6-Bis[5-(anthracen-9-ylethynyl)-2-hydroxyphenyl]-2-meth-
ylpyrimidine (2-OH)
1
A mixture of 6-OH (87 mg, 0.20 mmol), PPh3 (32 mg, 0.12 mmol),
Pd(OAc)2 (9.0 mg, 0.040 mmol), CuI (7.6 mg, 0.040 mmol), and 9-
ethynylanthracene (121 mg, 0.60 mmol) was dissolved in iPr2NH
(3 mL)/THF (1 mL) under argon. After the mixture was stirred at
708C for 24 h, the undissolved solids were removed by filtration
followed by evaporation of the filtrate. The obtained orange solid
was dissolved in CH2Cl2 (150 mL) and the solution was washed
with 10% HCl aq. (50 mL) and water (2ꢄ50 mL). The separated or-
ganic phase was dried over MgSO4, filtered, and evaporated to
give a crude product, which was purified by column chromatogra-
phy on silica gel (eluent: CHCl3) to yield 2-OH (52 mg, 0.076 mmol,
38%) as an orange solid. 1H NMR (400 MHz, CDCl3, RT): d=13.80
(br, 2H, OH), 8.63 (d, 4H, C14H9, J=8.8 Hz), 8.41 (s, 2H, C14H9), 8.38
(d, 2H, C6H3, J=2.0 Hz), 8.32 (s, 1H, C4N2H), 7.97 (d, 4H, C14H9, J=
8.4 Hz), 7.83 (dd, 2H, C6H3, J=2.0, 8.4 Hz), 7.40 (ddd, 4H, C14H9, J=
1.2, 6.5, 7.8 Hz), 7.32 (ddd, 4H, C14H9, J=1.0, 6.6, 7.8 Hz), 7.16 (d,
2H, C6H3, J=8.4 Hz), 2.87 ppm (s, 3H, CH3); 13C{1H} NMR (100 MHz,
C2D2Cl4, RT): d=164.7, 163.9, 161.8, 137.5, 132.7, 131.3, 130.9,
128.9, 128.0, 127.2, 126.8, 126.1, 120.0, 117.3, 117.2, 115.0, 106.5,
100.4 (CꢁC), 85.7 (CꢁC), 25.7 ppm; IR (KBr disk, RT): n˜ =3050, 3020,
2550 (OÀH···N), 2251 (CꢁC), 1577, 1537, 1438, 1418, 1288, 1263,
8.0 mmol, 79%) as a pale yellow solid. H NMR is matched with the
reported literature.[27]
Hexadecyl 4,5,7-trinitro-9-fluorenone-2-carboxylate (TNF-C16)
A
mixture of 4,5,7-trinitro-9-fluorene-2-carboxylic acid (1.06 g,
2.9 mmol), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydro-
chloride (0.675 g, 3.5 mmol), 4-dimethylaminopyridine (0.042 g,
0.34 mmol), and cetyl alcohol (0.741 g, 3.1 mmol) was dissolved in
CH2Cl2 (100 mL) under argon. After the mixture was stirred at RT
for 14 h, the solution was washed with 10% HCl aq. (100 mL),
water (100 mL) and brine (100 mL). The separated organic phase
was dried over MgSO4, filtered, and evaporated to give a crude
product, which was purified by column chromatography on silica
gel (eluent: CH2Cl2/hexane 2/1) to yield TNF-C16 (1.09 g, 1.9 mmol,
63%) as a pale yellow solid. 1H NMR (CDCl3, RT): d=8.99 (d, 1H,
C13H4O, J=2.0 Hz), 8.85 (d, 1H, C13H4O, J=2.1 Hz), 8.81 (d, 1H,
C13H4O, J=1.5 Hz), 8.72 (d, 1H, C13H4O, J=1.5 Hz), 4.44 (t, 2H,
OCH2, J=6.8 Hz), 1.83 (tt, 2H, CH2, J=7.0, 13.8 Hz), 1.94–1.20 (m,
26H, CH2), 0.88 ppm (t, 3H, CH3, J=6.6 Hz); 13C{1H} NMR (CDCl3,
RT): d=185.1, 162.8, 149.7, 146.9, 146.6, 138.6, 138.5, 137.8, 136.2,
136.1, 131.7, 129.3, 125.5, 122.7, 67.2, 32.0, 29.8, 29.8–29.7, 29.6
29.5, 29.4, 28.7, 26.0, 22.8, 14.2 ppm; ESI TOF MS (eluent: acetone+
1% CF3COONa) calcd for C30H37N3O9 +Na+: 606.2422; found: m/z
606.2431 [M+Na]+.
1221, 1185, 1131, 882, 852, 824, 749, 732, 660, 614, 549, 510 cmÀ1
;
FAB MS (NBA matrix) calcd for C49H30N2O2: 678; found: m/z 679
[M+H+]; elemental analysis calcd (%) for C49H30N2O2 +1.2CHCl3: C
73.35, H 3.83, N 3.41; found: C 73.05, H 3.92, N 3.48.
4,6-Bis{5-(anthracen-9-ylethynyl)-2-(hexyloxy)phenyl}-2-
methylpyrimidine (2-OHex)
Computational methods
The relative free energies of Conf1 and Conf2 were obtained by
using the empirical dispersion-corrected B97-D density functional
and TZVP basis set with density fitting approximations and TZVPFit
auxiliary basis set. The calculations were performed with the Gaus-
sian 09 program package.[28] The free-energy change of the reac-
tion between 7-OH and fluoride anion was calculated with the
B97-1 density functional and DZV+(d,p) basis set. The effect of sol-
vation was considered by using the conductor-like polarizable con-
tinuum model (PCM) with the parameters of CHCl3. The calculation
was performed with GAMESS 2013 (R1).[29] These free energies
were obtained as a total electronic energies and an unscaled Gibbs
free-energy correction. All structures were optimized and verified
to be local minima by Hessian calculation.
2-OH (203 mg, 0.30 mmol), K2CO3 (248 mg, 1.8 mmol), and C6H13I
(180 mL, 1.2 mmol) were dissolved in CH3COC2H5 (15 mL). After the
mixture was stirred at 808C for 19 h, the solids were removed by
filtration followed by evaporation of the filtrate. The obtained solid
was dissolved in CH2Cl2 (50 mL) and the solution was washed with
water (2ꢄ20 mL). The separated organic phase was dried over
MgSO4, filtered, and evaporated to give a crude product, which
was purified by column chromatography on silica gel (eluent:
CH2Cl2) to yield 2-OHex (114 mg, 0.13 mmol, 45%) as yellow
powder. 1H NMR (400 MHz, CDCl3, RT): d=8.69 (d, 4H, C14H9, J=
8.7 Hz), 8.41 (s, 2H, C14H9), 8.34 (d, 2H, C6H3, J=2.1 Hz), 8.33 (s, 1H,
C4N2H), 8.02 (d, 4H, C14H9, J=8.4 Hz), 7.81 (dd, 2H, C6H3, J=2.2,
8.4 Hz), 7.60 (ddd, 4H, C14H9, J=1.1, 6.5, 7.8 Hz), 7.51 (ddd, 4H,
C14H9, J=0.9, 6.6, 8.1 Hz), 7.07 (d, 2H, C6H3, J=8.6 Hz), 4.10 (t, 4H,
OCH2, J=6.3 Hz), 2.96 (s, 3H, CH3), 1.76 (m, 4H, CH2), 1.38 (m, 4H,
CH2), 1.23–1.09 (m, 8H, CH2), 0.77 ppm (t, 6H, J=7.0 Hz); 13C{1H}
NMR (100 MHz, CDCl3, RT): d=168.1, 162.3, 157.6, 136.4, 134.5,
132.7, 131.4, 128.8, 128.1, 127.5, 127.1, 126.6, 125.8, 119.9, 117.8,
116.5, 112.9, 100.7 (CꢁC), 85.6 (CꢁC), 69.1, 31.7, 29.3, 26.7, 26.1,
22.6, 14.1 ppm; IR (KBr disk, RT): n˜ =3046, 2925, 2855, 2204 (CꢁC),
1605, 1574, 1530, 1496, 1465, 1439, 1389, 1334, 1263, 1251, 1146,
1044, 877, 842, 813, 783, 729, 615, 550, 408 cmÀ1; FAB MS (NBA
matrix) calcd for C61H54N2O2: 846; found: m/z 847 [M+H+]; elemen-
X-ray diffraction
Single crystals suitable for X-ray diffraction studies were obtained
by recrystallization from CHCl3 (2-OH) and CH2Cl2/hexane (2-OHex).
Crystallographic data and detailed results of refinement are sum-
marized in Table S1 of the Supporting Information. CCDC 937957
(2-OH), 937958 (2-Ohex), 822408 (3-OH·2CHCl3) and 822409
(3-OHex) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
Chem. Eur. J. 2014, 20, 4762 – 4771
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Acknowledgements
This research was supported by Global COE program and KA-
KENHI from the Japan Society for the Program of Science
(JSPS). Y.T. thanks JSPS Research fellowship for Young Scientists.
This work was supported by a Grant-in-Aid for Scientific Re-
search on Innovative Areas “The Coordination Programming
(24108711)”. We thank our colleagues in the Center for Ad-
vanced Materials Analysis, Technical Department, Tokyo Insti-
tute of Technology for NMR and X-ray analysis as well as MS
measurement.
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Keywords: host–guest systems · hydrogen bonds · molecular
tweezers · pi interactions · supramolecular chemistry
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Received: November 10, 2013
Published online on March 6, 2014
Chem. Eur. J. 2014, 20, 4762 – 4771
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