Switching of molecular insertion in a cyclic molecule via photo- and thermal isomerization

Article abstract of DOI:10.1021/ic200145h

Two new cyclic ligands were synthesized: a ligand with two trans-azobenzene moieties and one bipyridine moiety, trans₂-oAB-O13, and a ligand with two trans-azobenzene moieties and two bipyridine moieties, trans ₂-oAB-bpy. Both ligands underwent reversible trans-cis isomerization at the azobenzene moieties. The mole ratios of the trans₂ form:trans-cis form:cis₂ form, evaluated by ¹HNMR spectroscopy of the photostationary states prepared by 1 h illumination, were 0.13:0.27:0.60 (365 nm irradiation) and 0.41:0.47:0.12 (436 nm irradiation) for oAB-O13, and 0.18:0.12:0.70 (365 nm irradiation) and 0.36:0.43:0.21 (436 nm irradiation) for oAB-bpy. When trans₂-oAB-O13 was mixed with Cu(I), both the bipyridine units and the polyether chains coordinated to the copper center. Addition of a noncyclic bipyridine ligand, trans₂-oAB-2OH, afforded a bis(bipyridine)copper(I) complex, [Cu(trans₂- oAB-O13)(trans₂-oAB-2OH)]BF₄. The bis(bipyridine) ligand, trans₂-oAB-bpy, formed a 1:1 complex with Cu(I), [Cu(trans ₂-oABbpy)] BF₄. [Cu(cis2-oAB-bpy)]BF₄ did not undergo the ligand substitution reaction with a noncyclic ligand with two azobenzene moieties and one bipyridine moiety, oAB, whereas its thermal isomerization in the presence of oAB caused the formation of [Cu(trans ₂-oAB-bpy)(trans₂-oAB)]BF₄, indicating that the isomerization and ligand exchange reactions synchronized via a conformational change of the cyclic ligand.

Full text of DOI:10.1021/ic200145h

ARTICLE
pubs.acs.org/IC
Switching of Molecular Insertion in a Cyclic Molecule via
Photo- and Thermal Isomerization
Satoshi Umeki, Shoko Kume, and Hiroshi Nishihara*
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku 113-0033, Japan
S Supporting Information
b
ABSTRACT:
Two new cyclic ligands were synthesized: a ligand with two trans-azobenzene moieties and one bipyridine moiety, trans2-oAB-O13,
and a ligand with two trans-azobenzene moieties and two bipyridine moieties, trans2-oAB-bpy. Both ligands underwent reversible
trans-cis isomerization at the azobenzene moieties. The mole ratios of the trans2 form:trans-cis form:cis2 form, evaluated by 1H NMR
spectroscopy of the photostationary states prepared by 1 h illumination, were 0.13:0.27:0.60 (365 nm irradiation) and
0.41:0.47:0.12 (436 nm irradiation) for oAB-O13, and 0.18:0.12:0.70 (365 nm irradiation) and 0.36:0.43:0.21 (436 nm irradiation)
for oAB-bpy. When trans2-oAB-O13 was mixed with Cu(I), both the bipyridine units and the polyether chains coordinated to the
copper center. Addition of a noncyclic bipyridine ligand, trans2-oAB-2OH, afforded a bis(bipyridine)copper(I) complex, [Cu(trans2-
oAB-O13)(trans2-oAB-2OH)]BF4. The bis(bipyridine) ligand, trans2-oAB-bpy, formed a 1:1 complex with Cu(I), [Cu(trans2-oAB-
bpy)]BF4. [Cu(cis2-oAB-bpy)]BF4 did not undergo the ligand substitution reaction with a noncyclic ligand with two azobenzene
moieties and one bipyridine moiety, oAB, whereas its thermal isomerization in the presence of oAB caused the formation of
[Cu(trans2-oAB-bpy)(trans2-oAB)]BF4, indicating that the isomerization and ligand exchange reactions synchronized via a
conformational change of the cyclic ligand.
’ INTRODUCTION
We also achieved acidꢀbase-responsive photoisomerization
of a copper complex containing OHꢀ groups attached to
azobenzene-appended bipyridine ligands, oAB-2OH.6 In the
present study, we synthesized new cyclic ligands based on the
oAB structure, one ligand with a polyether chain, oAB-O13, and
the other ligand with a polyether chain linked by an additional
bpy moiety, oAB-bpy (Figure 2). In these cyclic structures, the
ability to coordinate Cu(I) was controlled by changing the cycle’s
structure by photoisomerization of the azobenzene moieties. In
this study, we examined the relationship between isomerization
and coordination of oAB-O13 and oAB-bpy to Cu(I) and found
that isomerization of the oAB-bpy complex created a binary
structure in which one moiety was either inserted or removed
from the coordination sphere formed by the cycle (Scheme 1).
We describe the synthesis and characterization of the cyclic
Molecular machines have attracted much attention in nanoscale
research, and their development has been accompanied by the
introduction of new technologies for handling and assembling
functional molecules.1 The construction of molecular machines via
combination and synchronization of molecular modules with well-
characterized responses constitutes an efficient design strategy.2 One
of the examples of the molecular modules is azobenzene. The large
conformational change through the reversible photoisomerization of
azobenzenes can be used as a mechanical motion of molecular
machines.3 We have studied photochromic metal complexes, in
which photochromic organic ligands are coordinated to transition
metals. These complexes show unique physical and chemical
properties.4 We developed a photoelectric conversion system based
on the ligand exchange reaction between a copper complex contain-
ing azobenzene-appended bipyridine ligands (oABs) and free bipyr-
idines (bpys). Ligand exchange was modulated by the reversible
photoisomerization of the azobenzene moieties (Figure 1).5
Received: January 21, 2011
Published: May 05, 2011
r
2011 American Chemical Society
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Figure 1. Photoelectric conversion system composed of [Cu(oAB)2]BF4.
Figure 2. oAB-O13 and oAB-bpy.
ligands, their isomerization behavior, and their coordination to a
Cu(I) center.
from an alcohol to an ether. The peak corresponding to Hd was
shifted dramatically upfield from 8.90 ppm to 8.21 ppm, suggesting
that the bipyridine moieties underwent a conformational change via
cyclization. Normal bipyridine derivatives, including oAB-2OH, are
in the trans conformation because of steric hindrance at Hd.
’ RESULTS AND DISCUSSION
t
However, steric hindrance between the Bu groups and the poly-
Synthesis. The synthesis of the cyclic compound, oAB-O13,
was carried out under dilute conditions (see Scheme 2 and the
Experimental Section) to prevent polymerization. The reaction
produced oAB-O13 by the reaction of oAB-2OH and O13-Ts in a
ratio of 1:1, in addition to various byproducts from the reaction
of oAB-2OH and O13-Ts in a ratio of 2:2, 3:3, and so forth. The
products could be separated by gel permeation chromatography
(GPC). oAB-bpy was synthesized by the same procedure (see
Scheme 3 and the Experimental Section).
ether chains was even stronger in the trans conformation of the
bipyridine moiety of oAB-O13 (Figure 3), making the cis con-
formation thermodynamically more favorable. The conformations
of isomers in Figure 3 were estimated with minimized steric energy
using the MM2 force-field method. The arrow in Figure 3 represents
that the polyether chain cannot rotate around the oAB moiety
t
because of the steric hindrance between the Bu group and the
polyether chain. This conformational change of the bipyridine
moiety shifted the Hd signal upfield because of steric repulsion. A
similar upfield shift was observed in oAB-bpy, in which the
bipyridine moieties were even more strongly constrained to the
cis conformation (Supporting Information, Table S2).
1
Comparison between the H NMR spectra of oAB-2OH and
oAB-O13 in CDCl3 (see Supporting Information, Table S1)
indicated that the peak corresponding to Hi was shifted downfield
after cyclization from 6.97 ppm to 7.09 ppm, upon transformation
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Scheme 1. Schematic Presentation of the Coordination of oAB-O13 (a) and oAB-bpy (b) to Cu(I)
Scheme 2. Synthesis of oAB-O13
Isomerization of oAB-O13. The photoisomerization beha-
vior of oAB-O13 in CD2Cl2 was monitored by 1H NMR
measurements (Figure 4). Before irradiation, oAB-O13 was
present in the trans2 form. New signals were observed upon
365 nm light irradiation, indicating a trans-to-cis isomerization.
Both the cis2 form and the cis-trans form were observed, and
isomerization occurred through the cis-trans form. The ratios of
the trans2 form, the cis-trans form, and cis2 form were
0.13:0.27:0.60. Isomerization in the reverse direction was
achieved upon 436 nm irradiation. The solution reached a
reversible dynamic photostationary state upon irradiation with
365 or 436 nm light for 1 h. The ratios of the trans2 form, the cis-
trans form, and the cis2 form after irradiation with 436 nm light
were 0.41:0.47:0.12. The original state (100% trans2 form) was
recovered upon heating the solution at 40 °C in the dark for 12 h.
Comparison between the 1H NMR spectra of trans2-oAB-O13
and cis2-oAB-O13 in CD2Cl2 (see Supporting Information, Table
S3) indicated that the signal of Hd was shifted downfield from
8.54 ppm to 8.87 ppm because of the trans-to-cis isomerization,
which altered the conformation of the bipyridine moiety. The
bipyridine moiety of trans2-oAB-O13 was in the cis conforma-
tion, as noted above. In contrast, because the tension in the ring
was relieved through the trans-to-cis isomerization of the azo-
benzene moieties, the bipyridine moiety of cis2-oAB-O13 was in
the trans conformation, which had less steric hindrance. This
conformational adjustment shifted the Hd signal downfield. The
bipyridine moiety of cis-trans-oAB-O13 was also in the trans
conformation, and its Hd signal was near to that of cis2-oAB-O13
(see Figure 3). On the other hand, trans-to-cis isomerization
shifted all signals upfield, except for the signal of Hd. The upfield
shift resulted from the shielding effects of the proximal aromatic
rings, brought together by the trans-to-cis isomerization. The
fact that the Hg (from 8.11 ppm to 7.04 ppm) and Hh (from
7.99 ppm to 6.99 ppm) shifts, which were nearest the azo moiety,
showed large upfield shifts of more than 1 ppm, supports this
conclusion.
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Scheme 3. Synthesis of oAB-bpy
Figure 3. Molecular models of the isomers of oAB-O13 estimated with minimized steric energy using the MM2 force-field method (ChemBio3D 11.0).
The thermal cis-to-trans isomerization at 25 °C in the dark was
monitored by 1H NMR analysis, from which the ratio of each isomer
was obtained (Supporting Information, Figure S1). Isomerization
from the cis form to the trans form proceeded with the passage of
time. The rate constant associated with isomerization from cis2-oAB-
O13 to cis-trans-oAB-O13, k1, and the rate constant associated with
isomerization from cis-trans-oAB-O13 to trans2-oAB-O13, k2, were
estimated to be 8.0 ꢁ 10ꢀ5 sꢀ1 and 1.3 ꢁ 10ꢀ5 sꢀ1, respectively
(see the Supporting Information). k1 was found to be larger than k2.
That is, isomerization from cis2-oAB-O13 to cis-trans-oAB-O13 was
faster than isomerization from cis-trans-oAB-O13 to trans2-oAB-
O13. Most likely, the trans2-oAB-O13 conformation was thermally
unstable to the extent that the bipyridine moiety was in the cis
conformation and steric repulsion was significant (vide supra).
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Figure 4. 1H NMR spectral changes of oAB-O13 (1.5 ꢁ 10ꢀ3 M) in CD2Cl2 (a) initially, (b) after irradiation at 365 nm for 1 h, and (c) after further
irradiation at 436 nm for 1 h.
Figure 5. 1H NMR spectral changes of oAB-O13 (1.0 ꢁ 10ꢀ3 M) and
[Cu(CH3CN)4]BF4 (1.0 ꢁ 10ꢀ3 M) in CD2Cl2 (a) initially and (b)
after addition of oAB-2OH.
Figure 6. MALDI-TOF-MS spectrum of a solution containing oAB-
O13, oAB-2OH, and [Cu(CH3CN)4]BF4.
Analysis of the absorption spectral changes of oAB-O13 (1.0 ꢁ
10ꢀ5 M) in CH2Cl2 upon thermal cis-to-trans isomerization at
298 K in the dark also indicated that k1 was larger than k2 (see
Supporting Information, Figures S2 and S3).
Coordination Behavior of oAB-O13 to Copper. The co-
ordination of oAB-O13 to Cu(I) was examined using 1H NMR
and UVꢀvis spectroscopy. When trans2-oAB-O13 and
[Cu(CH3CN)4]BF4 were mixed in CD2Cl2, the 1H NMR peaks
broadened (Figure 5a), indicating that the copper was coordi-
nated by not only the bipyridine unit but also loosely by the
polyether chain. When a noncyclic ligand, trans2-oAB-2OH, was
added to the mixture, the signals became sharp and the tBu peak
shifted upfield (Figure 5b). The tBu upfield shift was attributed to
shielding caused by interligand πꢀπ stacking, which stabilized
the structure of [Cu(trans2-oAB-O13)(trans2-oAB-2OH)]BF4
1
and bound stably to the copper ion, sharpening the H NMR
peaks. The formation of [Cu(oAB-O13)(oAB-2OH)]BF4 was
confirmed by the MALDI-TOF-MS spectrum of this sample
(Figure 6). These results indicated that the oAB-O13 ring was so
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Figure 7. (A) UVꢀvis spectra of (a) oAB-O13 (1.3 ꢁ 10ꢀ5 M) in CH2Cl2, (b) after addition of 1 equiv of [Cu(CH3CN)4]BF4, (c) oAB-O13 (8.7 ꢁ
10ꢀ6 M) after irradiation at 365 nm for 5 min, and (d) after addition of [Cu(CH3CN)4]BF4. (B) UVꢀvis spectra of (a) oAB-bpy (1.3 ꢁ 10ꢀ5 M) in
CH2Cl2, (b) after addition of 1 equiv of [Cu(CH3CN)4]BF4, (c) oAB-bpy (1.4 ꢁ 10ꢀ5 M) after irradiation at 365 nm for 5 min, and (d) after addition of
[Cu(CH3CN)4]BF4.
Figure 8. 1H NMR spectral changes of oAB-bpy (5.5 ꢁ 10ꢀ3 M) in CD2Cl2 (a) initially, (b) after irradiation at 365 nm for 1 h, and (c) after further
irradiation at 436 nm for 1 h.
large and soft that oAB-2OH could insert it and, thus, could
coordinate to Cu(I).
trans-to-cis isomerization of azobenzene moieties. During the
addition of Cu(I) ion, the πꢀπ* transition band increased
because the cis-to-trans isomerization took place a little, and
the absorbance in the visible region from 400 to 550 nm,
attributed to the d-π* transition (MLCT) band, increased
through the formation of the complex (Figure 7d).
Isomerization of oAB-bpy. The photoisomerization behavior
of trans2-oAB-bpy in CD2Cl2 was monitored by NMR (Figure 8).
New signals were observed after 365 nm light irradiation,
indicating that trans-to-cis isomerization had taken place. Evi-
dence for both the cis2 form and the cis-trans form was observed,
suggesting that isomerization proceeded stepwise via the cis-trans
form. The ratios of the trans2 form, the cis-trans form, and the cis2
form were 0.18:0.12:0.70. Isomerization in the reverse direction
was observed upon 436 nm light irradiation. Irradiation with
365 or 436 nm light for 1 h produced a photostationary state
solution in which the ratios of the trans2 form, the cis-trans form,
The UVꢀvis absorption spectrum of oAB-O13 in CH2Cl2
showed an intense band at 365 nm (Figure 7a), ascribed to the
πꢀπ* transition of the azobenzene moiety. The nꢀπ* transition
band was observed in the visible region from 400 to 550 nm.
After addition of 1 equiv of [Cu(CH3CN)4]BF4, the πꢀπ*
transition band decreases a little (Figure 7b). This decrease
showed the interaction between oAB-O13 and Cu(I) ion. The
absorbance in the visible region from 400 to 550 nm increased.
This increase was attributed to the d-π* transition (MLCT)
band,7 generated through the formation of the complex. The
absorption spectrum of the cis complex was gained by two steps;
first, oAB-O13 was transferred to the cis form under 365-nm light
irradiation, then, [Cu(CH3CN)4]BF4 was added. The πꢀπ*
transition band decreased and the nꢀπ* transition band in-
creased under the UV irradiation (Figure 7c), indicating the
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Figure 9. 1H NMR spectral changes of oAB-bpy (4.6 ꢁ 10ꢀ3 M), oAB (4.6 ꢁ 10ꢀ3 M), and [Cu(CH3CN)4]BF4 (4.6 ꢁ 10ꢀ3 M) in CD2Cl2 (a) before
addition of [Cu(CH3CN)4]BF4, (b) after addition of [Cu(CH3CN)4]BF4 in the cis form, and (c) after addition of [Cu(CH3CN)4]BF4 in the
trans form.
1
and the cis2 form were 0.36:0.43:0.21. The azobenzene moieties
thermally isomerized from the cis to the trans forms, and the
original state (or oAB-O13) was recovered upon heating the
solution at 40 °C in the dark for 12 h.
to this solution, the H NMR signals of oAB were unchanged.
However, the peaks corresponding to oAB-bpy disappeared and
new peaks appeared (Figure 9b). The new peaks in the aromatic
ring region were upfield relative to the peaks from oAB-bpy,
indicating coordination of oAB-bpy to the copper ion. ESI-MS
data also indicated formation of [Cu(oAB-bpy)]BF4 (Supporting
Information, Figure S4a). Next, [Cu(oAB-bpy)]BF4 and oAB
were converted to the trans2 form by heating the solution at
40 °C in the dark for 15 h. 1H NMR peaks for the free trans2-oAB
were observed, although signals of the free trans2-oAB-bpy were
not observed (Figure 9c). Instead, the peaks attributed to
[Cu(trans2-oAB-bpy)]BF4 appeared (red line in Figure 9c).
The green spectrum in Figure 9c showed that the tBu peak was
shifted upfield, indicating the presence of interligand πꢀπ
stacking. These peaks were different from those of [Cu(trans2-
oAB)2]BF4 and thus were attributable to [Cu(trans2-oAB)-
(trans2-oAB-bpy)]BF4. This attribution was supported by the
observation of peaks due to [Cu(oAB)(oAB-bpy)]þ in the ESI-
MS spectrum (Supporting Information, Figure S4b). The ratios
of [Cu(trans2-oAB)(trans2-oAB-bpy)]BF4:[Cu(trans2-oAB-
The 1H NMR spectra of trans2-oAB-bpy and cis2-oAB-bpy in
CD2Cl2 were compared in Supporting Information, Table S4.
The Hd peak shifted downfield and the Hg and Hh peaks shifted
upfield through the trans-to-cis isomerization. These shifts
were the same as those of oAB-O13, indicating the same
conformational changes of the bipyridine moiety attached to
the azobenzene units.
Synchronization of Isomerization and Ligand Exchange in
[Cu(oAB-bpy)]þ. The UVꢀvis spectral change of oAB-bpy
through trans-to-cis isomerization by 365 nm light irradiation,
followed by coordination to Cu(I) by adding 1 equiv of
[Cu(CH3CN)4]BF4 was similar with that of oAB-O13
(compare Figure 7 A and B). The isomerization and ligand
exchange reactions in the oAB-bpy complex of copper were
synchronized as follows. First, trans2-oAB-bpy and trans2-oAB in
CD2Cl2 were converted to the cis2 and cis-trans forms under
365 nm light irradiation for 1 h. The cis form of azobenzene was
1
bpy)]BF4:trans2-oAB, calculated from the H NMR spectrum,
were 0.21:1.0:1.0. According to the formation of [Cu(trans2-
oAB)(trans2-oAB-bpy)]BF4, the ratio of trans2-oAB became
1
present at 83% in oAB-bpy and 76% in oAB, based on the H
NMR results (Figure 9a). When [Cu(CH3CN)4]BF4 was added
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smaller. The fact that the ratio of [Cu(trans2-oAB-bpy)]BF4:
trans2-oAB was 1:1 also indicated the formation of [Cu(trans2-
oAB)(trans2-oAB-bpy)]BF4. This implied that the conversion
from the cis form to the trans form of the azobenzene moieties
caused the penetration of oAB into oAB-bpy. In other words, the
isomerization and ligand exchange reactions were synchronized.
bpy-Ts. A mixture of 4,40-(2,20-bipyridine-5,50-diyl)dibutan-1-ol
(1.33 g, 4.43 mmol) and NaH (1.00 g, 41.7 mmol) in dry tetrahydrofur-
an (THF, 35 mL) was stirred for 1 h under N2. To the pale brown
solution was added pentaethylene glycol ditosylate (7.06 g, 12.9 mmol)
in dry THF (35 mL). After refluxing for 18 h, water was added to destroy
residual NaH, and the solvent was removed in vacuo. The dark brown
residue was dissolved in water (100 mL) and extracted with chloroform
(5 ꢁ 50 mL). The organic layer was collected, dried over Na2SO4, and
the solvent was removed in vacuo. The residue was subjected to column
chromatography (silica gel, CHCl3:MeOH = 19:1) and bpy-Ts was
obtained as a pale brown liquid (1.12 g, 24.1%).
’ CONCLUSIONS
Novel cyclic ligands with azobenzene moieties and bipyridine
moieties, oAB-O13 and oAB-bpy, were synthesized, and their
photochemical and coordination properties were investigated. Both
oAB-O13 and oAB-bpy underwent reversible photoisomerization.
1HNMR and MS measurements showed that mixing of [Cu(trans2-
oAB-O13)]BF4 with oAB-2OH yielded [Cu(trans2-oAB-2OH)-
(trans2-oAB-O13)]BF4. This product indicated that the ring size
of trans2-oAB-O13 was sufficiently large and soft that oAB-2OH
could penetrate it and coordinate to the copper ion. When
[Cu(CH3CN)4]BF4 was added to a solution of cis2-oAB-bpy and
cis2-oAB in CD2Cl2, [Cu(cis2-oAB-bpy)]BF4 and cis2-oAB formed.
Upon conversion of these compounds to their trans2 forms, oAB
penetrated into oAB-bpy. This result implied that the isomerization
and ligand exchange reactions were synchronized.
1H NMR(400 MHz, CDCl3, TMS): δ 8.48 (s, 2H, py), 8.25 (d, 2H, J =
8.0 Hz, py), 7.80 (d, 4H, J = 8.2 Hz, Ph), 7.62 (d, 2H, J = 8.0 Hz, py), 7.34
(d, 4H, J = 8.2 Hz, Ph), 4.15 (t, 4H, J = 4.6 Hz, TsOCH2), 3.69ꢀ3.57 (m,
36H, OCH2CH2O), 3.49 (t, 4H, J= 6.4 Hz, OCH2), 2.68 (t, 4H, J= 7.6 Hz,
pyCH2), 2.44 (s, 6H, CH3), 1.75ꢀ1.65 (m, 8H, CH2CH2).
MALDI-TOF-MS (m/z): [MþH]þ calcd for C52H77N2O16S2,
1049.47; found, 1049.40.
oAB-bpy. A mixture of oAB-2OH (106 mg, 0.130 mmol) and bpy-
Ts (145 mg, 0.138 mmol) in dry DMF (50 mL) was added dropwise
over 5 h under N2 to a suspension of Cs2CO3 (211 mg, 0.648 mmol) in
dry DMF (50 mL) maintained at 50 °C. After the addition, the solution
was stirred and heated for 8 days. The solvent was removed in vacuo.
Water (100 mL) was added to the red residue, and the solution was
extracted with chloroform (3 ꢁ 40 mL). The organic layer was collected,
dried over Na2SO4, and the solvent was removed in vacuo. The residue
was subjected to HPLC, and oAB-bpy was obtained as an orange powder
(14 mg, 7.1%).
’ EXPERIMENTAL SECTION
oAB-2OH,6 pentaethylene glycol ditosylate,8 dodecaethylene glycol
ditosylate (O13-Ts),8 4,40-(2,20-bipyridine-5,50-diyl)dibutan-1-ol,9 and
tetrakis(acetonitrile)copper(I) tetrafluoroborate10 were prepared according
to procedures reported in the literature. All reagents were purchased from
Tokyo Kasei, except for acetic acid (from Kanto Chemicals) and cesium
carbonate (from Wako Chemicals), and were used as received.
NMR spectra were recorded using JEOL AL-400 or ECX-400
spectrometers. MALDI-TOF MS spectra were recorded using a KRA-
TOS AXIMA-CFR. ESI-TOF MS spectra were recorded using a
Micromass-LCT spectrometer. UVꢀvis spectra were recorded using a
Hewlett-Packard 8453 spectrometer. Photoirradiation experiments
were performed using a super high-pressure mercury lamp (USHIO-
500D) as a light source, and each emission line was separated with a
monochromator (Jasco CT-10T, Δλ = ( 30 nm).
1H NMR (400 MHz, CD2Cl2): δ 8.76 (s, 2H, py), 8.41 (d, 4H, J = 8.7
Hz, Ph), 8.15 (s, 2H, py), 8.10 (s, 2H, py), 8.04 (d, 4H, J = 8.7 Hz, Ph),
7.99 (d, 4H, J = 8.7 Hz, Ph), 7.94 (d, 2H, J = 7.9 Hz, py), 7.82 (d, 4H, J =
8.7 Hz, Ph), 7.61 (d, 4H, J = 8.7 Hz, Ph), 7.26 (d, 2H, J = 7.9 Hz, py), 7.13
(d, 4H, J = 8.7 Hz, Ph), 4.30 (t, 4H, J = 4.4 Hz, CH2), 3.87 (t, 4H, J = 4.4
Hz, CH2), 3.70ꢀ3.36 (m, 32H, OCH2CH2O), 3.26 (t, 4H, J = 6.6 Hz,
CH2), 2.39 (t, 4H, J = 7.6 Hz, CH2), 1.46 (m, 8H, CH2CH2), 1.42 (s,
18H, tBu).
13C NMR (100 MHz, CDCl3, TMS): δ 161.38 (Ph), 156.51 (py),
156.06 (py), 155.42 (py), 153.00 (Ph), 152.36 (Ph), 150.19 (py), 148.61
(py), 147.20 (Ph), 141.23 (Ph), 136.47 (Ph), 133.75 (py), 129.81 (py),
127.80 (Ph), 127.04 (Ph), 126.13 (Ph), 124.84 (Ph), 123.04 (Ph),
120.77 (py), 118.80 (py), 118.24 (py), 114.86 (Ph), 71.32ꢀ67.72
(OCH2CH2O), 34.79 (tBu), 31.35 (tBu).
oAB-O13. A solution of oAB-2OH (190 mg, 0.234 mmol) and O13-Ts
(200 mg, 0.234 mmol) in dry DMF (80 mL) was added dropwise over 6 h
under N2 to a suspension of Cs2CO3 (200 mg, 0.614 mmol) in dry
dimethylformamide (DMF, 40 mL) maintained at 50 °C. After the addition,
the solution was stirred and heated for 7 days. The solvent was removed in
vacuo. Water (100 mL) was added to the red residue and was extracted with
chloroform (3 ꢁ 50 mL). The organic layer was collected, dried over
Na2SO4, and the solvent was removed in vacuo. The residue was subjected
to HPLC, and oAB-O13 was obtained as an orange powder (21 mg, 6.9%).
1H NMR (400 MHz, CDCl3, TMS): δ 8.47 (d, 4H, J = 8.8 Hz, Ph), 8.21
(s, 2H, py), 8.12 (s, 2H, py), 8.07(d, 4H, J= 8.8 Hz, Ph), 7.96 (d, 4H, J=9.2
Hz, Ph), 7.78 (d, 4H, J = 8.4 Hz, Ph), 7.60 (d, 4H, J = 8.4 Hz, Ph), 7.09 (d,
4H, J = 9.2 Hz, Ph), 4.29 (t, 4H, J = 4.8 Hz, CH2), 3.90 (t, 4H, J = 4.8 Hz,
CH2), 3.80ꢀ3.43 (m, 44H, OCH2CH2O), 1.42 (s, 18H, tBu).
MALDI-TOF-MS (m/z): [MþH]þ calcd for C92H109N8O12,
1517.82; found, 1517.48.
Anal. Calcd for C92H114N8O15 3H2O: C, 70.29; H, 7.31; N, 7.13.
3
Found: C, 70.28; H, 7.15; N, 6.82.
’ ASSOCIATED CONTENT
S
Supporting Information. Further details are given in
b
Tables S1ꢀS4 and Figures S1ꢀS4. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
13C NMR (100 MHz, CDCl3, TMS): δ 161.40 (Ph), 157.44 (py),
157.08 (py), 153.03 (Ph), 152.51 (Ph), 150.24 (py), 147.18 (Ph),
141.07 (Ph), 135.67 (Ph), 127.99 (Ph), 126.91 (Ph), 126.14 (Ph),
124.75 (Ph), 123.00 (Ph), 119.15 (py), 118.26 (py), 115.12 (Ph),
70.94ꢀ67.81 (OCH2CH2O), 34.79 (tBu), 31.31 (tBu).
Corresponding Author
*Phone: 81-3-5841-4346. Fax: 81-3-5841-4489. E-mail: nisihara@
chem.s.u-tokyo.ac.jp.
MALDI-TOF-MS (m/z): [MþH]þ calcd for C78H95N6O13,
1323.67; found, 1323.67.
’ ACKNOWLEDGMENT
This work was supported by Grants-in-Aid for Scientific
Research from MEXT, Japan (Nos. 20245013 and 21108002,
Anal. Calcd for C78H94N6O13 2H2O: C, 68.90; H, 7.26; N, 6.18.
Found: C, 68.99; H, 7.22; N, 5.75.
3
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Inorganic Chemistry
ARTICLE
area 2107), and the Global COE Program for Chemistry
Innovation.
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