Coordination-assembly for quantitative construction of bis-branched molecular shuttles

Article abstract of DOI:10.1039/c0ob01124j

The development and utilization of a new way to build molecular devices is of importance. To build a novel topology of interlocked molecular systems with a controllable mechanical motion, an axle-like compound comprising azobenzene and alkoxy isophthalate

Full text of DOI:10.1039/c0ob01124j

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Organic &
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PAPER
Coordination-assembly for quantitative construction of bis-branched
molecular shuttles†
Liangliang Zhu, Meiqun Lu, Dahui Qu, Qiaochun Wang and He Tian*
Received 6th December 2010, Accepted 24th March 2011
DOI: 10.1039/c0ob01124j
The development and utilization of a new way to build molecular devices is of importance. To build a
novel topology of interlocked molecular systems with a controllable mechanical motion, an axle-like
compound comprising azobenzene and alkoxy isophthalate moieties was synthesized first. It would
form a switchable hemi-rotaxane structure with a-cyclodextrin (a-CD) ring encapsulated in aqueous
solution. Next, the hemi-rotaxane was reacted with ethylene diamine palladium nitrate (Pd(en)(NO3)2)
and ethylene diamine platinum nitrate (Pt(en)(NO3)2), respectively, to quantitatively form two
bis-branched molecular shuttles in situ. The bis-coordinated Pd(II) complex was formed quickly at
room temperature, whereas the bis-coordinated Pt(II) one was effectively treated at 333 K but more
stable than the former. In this case, transformation of ring shuttling direction could take place in the
stable bis-branched Pt(II) complex. The steric effect of the co-stopper, namely the Pt(II) metal center,
made the a-CD ring dynamically shuttle inwards to the alkoxy isophthalate station with the
azobenzene’s photoisomerization, rather than dethreading from the axle.
Coordination-assembly is a well-established methodology in
Introduction
supramolecular chemistry, because it allows for the spontaneous,
selective formation of highly stable and specific supramolecular
frameworks for materials and biological applications.5 Thus
far, coordination-driven or -assembly has been utilized for
construction of supramolecular ensembles capable of control-
lable transformations.6 However, the report about employing
coordination-assembly to establish switchable molecular shuttles
is still rare.7 Furthermore, there is also a need to realize the
modulation or change of the components’ shuttling motion with
coordination-assembly as a cooperatively controlled manner.
We have focused on designing and preparing light-powered
interlocked molecular shuttles for years, as photochemical re-
sponse has the advantage of remote operations without generating
any chemical waste.8 Azobenzene is an essential skeleton in
building cyclodextrin-based light-driven9 molecular devices. To
create a novel topology with light-controllable shuttling motion
via coordination-assembly, an axle-like ligand ([L][NO3]3) was
synthesized in this work (shown in Scheme 1). It comprises
a light-active azobenzene unit as a strong binding station for
a-cyclodextrin (a-CD), and this moiety can be encircled by
one a-CD ring to form a stable hemi-rotaxane structure ([L(a-
CD)][NO3]3). An alkoxy isophthalate unit was also introduced as a
potential second binding station for the host. The two stations were
harnessed to be covalently linked by a hydrophilic viologen unit,
and only the pyridine nitrogen of the end group in the axle can
participate in the coordination-assembly.
The design and construction of novel supramolecular devices
can be categorized in one of the currently interesting fields of
modern chemistry.1 As a primary prototype of synthetic molec-
ular machines, rotaxane analogue based interlocked molecular
systems have been unfolding a developing course from simple
to complicated, and from single-mode to multi-mode in the last
two decades.2 An intriguing challenge for developing this kind of
system next is to enlarge their mechanical motion-mode, such as
the controllable shuttling of the subcomponents,3 to achieve an
integral device function. One practical approach is to incorporate
switchable monomers to advanced topological systems for loading
the functional performances. Recently, a class of Janus-type archi-
tectures bearing a two-component [c2]daisy chain topology4 was
prepared. It was more advanced than a conventional molecular
shuttle, and could mimic artificial muscle-like materials. Inspired
by such innovative chemical systems that bring in reformative
conceptions, chemists are developing more topologies with high
yield for building advanced molecular machinery systems.
Key Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science & Technology, Shanghai, 200237, P.R.
China. E-mail: tianhe@ecust.edu.cn; Fax: (+86) 21-64252288; Tel: (+86)
21-64252756
† Electronic supplementary information (ESI) available: ESI-MS spec-
tra of [Pt-2L][NO3]8 and [Pt-2L(a-CD)2][NO3]8; Absorption spectra of
[L(a-CD)][NO3]3, [Pt-2L(a-CD)2][NO3]8 and their photostationary states;
Fundamental characteristics (1H NMR, 13C NMR, and MS spectra) of
the precursors, the ligand and the bis-coordinated complexes. See DOI:
10.1039/c0ob01124j
Herein, we choose ethylene diamine palladium nitrate and
ethylene diamine platinum nitrate as the metal center, because
both of the metals are prone to have a strong and quantitative
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Scheme 1 Illustration of the construction of the bis-branched molecular
shuttles.
chelation with two eq. of the ligandsvia the pyridine nitrogen atom,
to form stable bis-branched complexes with high yield in situ. A
natural angle10 settled by the two ligands linked with Pd(II) or Pt(II)
could form a co-stopper to well avoid the ring over-encircling.11
Moreover, it is supposed that the strong steric effect generated
by a high-stable coordination could effectively prevent the ring
departing from the axle even under the photo-irradiation, thus
resulting in the ring dynamically moving to the alkoxy isophthalate
station across the viologen barrier.12 In this way, transformation
of ring shuttling direction would be realized via coordination-
assembly as a cooperative control. This type of the bis-branched
molecular shuttles could be regarded as a new topology with two of
the switchable hemi-rotaxanes linked together by a metal center as
the spacer ([M-2L(a-CD)2][NO3]8, M = Pd or Pt) (Scheme 1). The
demonstration of constructing such interlocked molecular system
via coordination-assembly might be an important step towards the
ultimate goal of building nano-machinery combination system.
Fig. 1 Parts of the 1H NMR spectra (400 MHz in D2O at 298 K) of A)
[L][NO3]3, B) [L][NO3]3 + 0.1 eq. of Pd(en)(NO3)2, C) [L][NO3]3 + 0.3 eq.
of Pd(en)(NO3)2, D) [Pd-2L][NO3]8 ([L][NO3]3 + 0.5 eq. of Pd(en)(NO3)2),
E) [Pt-2L][NO3]8 ([L][NO3]3 + 0.5 eq. of Pt(en)(NO3)2). The black triangle
marks the methylene protons of the coordinated ethylene diamine group.
efficiency in situ, as almost no peaks of [L][NO3]3 remained in
1
the H NMR spectrum in Fig. 1D. Ha and Hb protons display
great downfield shifts (from d = 8.65 to 8.89 for Ha, and from
d = 7.78 to 7.89 for Hb), because of the coordination of the Pd(II)
with two ligands via the pyridine nitrogen atoms. The shift of
the methylene protons in ethylene diamine group to the value of
2.84 ppm appears to be gradual in Fig. 1. This would indicate slow
Metal–Ligand exchange on the NMR timescale (Fig. 1A to 1D).
Keeping the mixture of [L][NO3]3 and Pt(en)(NO3)2 in a 2 : 1
ratio in D2O at 333 K for 12 h resulted in the formation of
[Pt-2L][NO3]8 (Scheme 1). The bis-coordinated Pt(II) complex
revealed similar chemical shifts in 1H NMR spectrum in Fig. 1E
as that of the Pd(II) complex in Fig. 1D, but Ha and Hb protons
display greater downfield shifts to d = 8.95 and 7.93, respectively
(Fig. 1E). The signals of the methylene protons also behave
differently between the Pd(II) and Pt(II) systems where Metal–
Ligand exchange rates would differ dramatically (see Fig. 1D
and 1E). ESI mass spectrometry provides further evidence for
the formation of this more stable bis-coordinated ensemble. In
the mass spectrum of [Pd-2L][NO3]8, peak at m/z = 1036.9,
corresponding to [M–4NO3]2+, is observed (Figure S1A, ESI†).
Thus the reference compounds of the bis-branched molecular
shuttles were obtained with high yield.
The hemi-rotaxane ligand [L(a-CD)][NO3]3 was prepared from
[L][NO3]3 by co-grind14 of the axle with 1 equiv. solid a-
cyclodextrin for ca. 15 min. The uniformity of the well mixed
sample can help enhance the inclusion rate of the host–guest
structure in the aqueous solution. The NOEs pattern confirms
that the a-CD ring dominantly stays at the azobenzene station
in the initial state (see Fig. 4A).15 As cyclodextrin cavity has
the primary and secondary site, some proton signals appearing
in two different positions (e.g. two separate resonances for Hs,
Ht in Fig. 2A) proves that two threading direction of a-CD are
both involved in this supramolecular system. [L(a-CD)][NO3]3 was
Results and Discussion
Coordination-assembly for quantitative construction of
bis-branched molecular shuttles
The synthetic details of the precursors and the ligand [L][NO3]3 are
arranged in Experimental Section. All the anions were exchanged
-
to NO3 because the nitrate ion is hydrophilic and can hardly
compete with the pyridine ligand for the coordinations. [L][NO3]3
was fully characterized by 1H NMR, 13C NMR, MS and elemental
analysis. [L][NO3]3 can be quickly reacted with Pd(en)(NO3)2 at
room temperature. Fig. 1 shows the 1H-NMR spectra of mixtures
of Pd(en)(NO3)2 and [L][NO3]3 in D2O at different molar ratios.
We found the yield of the bis-branched complex was chiefly ratio-
dependent. When the ratio reached 2 : 1 (0.5 eq. of Pd(en)(NO3)2
addition), almost all of the [L][NO3]3 was converted to the
complex.13
The assignment of the proton signals in this system is to some
1
extent assisted by the NOEs in 2D H NOESY spectroscopy. As
shown in Fig. 1D, it clearly reveals well-assigned proton signals of
the coordinated Pd(II) complex structure ([Pd-2L][NO3]8), which
is totally different from that of [L][NO3]3 (Fig. 1A). It is suggested
that such coordination brings in extremely high complexation
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365 nm led to a cluster of new signals with the azobenzenyl
group turning to cis-form, and the azobenzenyl protons are shifted
dramatically towards upfield, for Hf¢ to Hi¢ appearing at d = 7.42 ~
6.95.16 Meanwhile, the a-CD ring displayed a shuttling motion
along with the azobenzene’s photoisomerization. However, it
exhibits significant differences on the ring shuttling direction
among the hemi-rotaxane ligand and the bis-branched complexes.
The proton H1 of a-cyclodextrin will be shifted towards upfield
to d = 4.82 when azobenzene moiety is located in the cavity,
whereas the one of a small amount of free a-cyclodextrin appears
at d = 4.95 in [L(a-CD)][NO3]3 (Fig. 2A). The peak at d = 4.82
dropped with the photoisomerization, but the one at d = 4.95
grew (see Fig. 3B). Comparing the proton signals in Fig. 3B
with those in Fig. 3A, the cluster of new proton signals (He¢ to
Hj¢, and Hs¢, Ht¢) of [L(a-CD)][NO3]3 has appeared at the same
positions as the corresponding protons of the photostationary
state of [L][NO3]3. These results indicate that the a-CD host in
[L(a-CD)][NO3]3 indeed took place a dethreading behavior with
the photoisomerization, leaving a guest component with a-CD
departed (Scheme 2). This phenomenon should be caused by the
barrier effect of the electropositive viologen which blocks the ring
shuttling inward. Similar to the case in [L(a-CD)][NO3]3, the a-
CD rings also reveal a dethreading behavior in bis-branched Pd(II)
Fig. 2 Parts of the1H NMR spectra (400 MHz in D2O at 298 K) of
A) [L(a-CD)][NO3]3, B) [L(a-CD)][NO3]3 + 0.1 eq. of Pd(en)(NO3)2, C)
[L(a-CD)][NO3]3 + 0.3 eq. of Pd(en)(NO3)2, D) [Pd-2L(a-CD)2][NO3]8
([L(a-CD)][NO3]3 + 0.5 eq. of Pd(en)(NO3)2), E) [Pt-2L(a-CD)2][NO3]8
([L(a-CD)][NO3]3 + 0.5 eq. of Pt(en)(NO3)2). The denotation “1” stands
for protons on the 1-position of a-CD.
also reacted with a half equiv. of Pd(en)(NO3)2 or Pt(en)(NO3)2
to generate [M-2L(a-CD)2][NO3]8 (M = Pd or Pt) in situ at the
same condition as the formation of [M-2L][NO3]8 (M = Pd or Pt)
(Scheme 1). Still, NMR spectra for Ha and Hb protons reveal great
downfield shifts (from d = 8.70 to 8.92 for Ha and from d = 7.82
to 7.97 for Hb) because of the Pd(II) coordination (see Fig. 2A
and 2D). The Pt(II) coordination brought in a greater downfield
shifts of Ha and Hb to d = 8.98 and 7.99, respectively (Fig. 2E).
Also, because the Pt(II) coordinated complex is more stable than
the corresponding Pd(II) coordinated complex, the formation of
[Pt-2L(a-CD)2][NO3]8 can be well evidenced by ESI-MS shown in
Figure S1B.† The peak at 1886.4 is assigned to [M–8NO3]2+. In
this way, we have constructed a co-stopper with one metal center
linked to two of the hemi-rotaxane ligands at a natural angle, thus
leading to a new topology of closed multi-component molecular
systems. The bis-branched complexes [M-2L][NO3]8 and [M-2L(a-
CD)2][NO3]8 (M = Pd or Pt) could be also prepared and isolated
(see the details in Experimental Section). Once these samples are
studied in solution, however, similar results are obtained to those
studied in situ because of the slow exchange phenomena and the
presence of minor equilibrium components.
Transformation of ring shuttling direction in bis-branched Pt(II)
complex
Fig. 3 Parts of the1H NMR spectra (400 MHz in D2O at 298 K)
of the photostationary states of A) [L][NO3]3; B) [L(a-CD)][NO3]3;
C) [Pd-2L][NO3]8; D) [Pd-2L(a-CD)2][NO3]8; E) [Pt-2L][NO3]8 and F)
[Pt-2L(a-CD)2][NO3]8. The denotation “1” stands for protons on the
1-position of a-CD.
Irradiation by 365 nm light caused the trans-to-cis photoisomer-
ization of the azobenzene unit on the ligand [L(a-CD)][NO3]3 and
the complex [M-2L(a-CD)2][NO3]8, M = Pd or Pt, which generates
their corresponding photostationary states. The irradiation by
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Scheme 2 Interconversions of the bis-branched molecular shuttles with
photoisomerization.15
complex (Scheme 2) because of the labile nature of the Pd(II)-Py
bond even in room temperature.17 Such linkage is insufficient to
help the ring overcome the barrier under the photoirradiation.
This process is also confirmed by a similar comparison of the new
emerged proton signals in Fig. 3D and 3C.
The case on the more stable bis-branched Pt(II) complex is
totally different. Here we found that this co-stopper, formed by
high-stable chelation of Pt(II) center, could originate a strong steric
effect to transform the ring shuttling direction. The irradiation on
[Pt-2L(a-CD)2][NO3]8 by 365 nm led to the emergence of a new
peak at d = 5.01 shown in Fig. 3F, which should be assigned
to the H1¢ of a-cyclodextrin encapsulating a deshielding moiety
(the alkoxy isophthalate station) of the axle. In addition, the new
proton signals (He¢ to Hj¢, and Hs¢, Ht¢) of the photostationary
state of [Pt-2L(a-CD)2][NO3]8 appeared at the different positions
(Fig. 3F), while compared with the corresponding protons of
the photostationary state of [Pt-2L][NO3]8 (Fig. 3E). Hg¢, h¢, and
Hi¢, f¢ are overlapped but Hj¢ becomes split in Fig. 3F, showing
another conformational structure is affecting the resonances of
these protons while the a-CD ring has moved along the axle away
from the azobenzene. Also, Hs¢ and Ht¢ in the photostationary state
of [Pt-2L(a-CD)2][NO3]8 are shifted towards upfield to d = 7.26
and 7.23, respectively, compared with those in the photostationary
state of [Pt-2L][NO3]8. It is demonstrated that the ring should
shuttle to the alkoxy isophthalate side with a major shielding effect
on Hs¢ and Ht¢.
A further investigation of the transformation of ring shuttling
direction was carried out by 2D 1H NOESY spectroscopy, which
gave out precise information of the interconvert geometries in these
a-CD based complexes. NOEs are observed from the azobenzenyl
protons Hg, h, to the internal protons H3, H5 of a-CD (Fig. 4A
and 5A). These sets of NOEs show that the azobenzene stations
are well encapsulated by a-CD in both of the initial states ([L(a-
CD)][NO3]3 and [Pt-2L(a-CD)2][NO3]8). Irradiation by 365 nm
on [L(a-CD)][NO3]3 caused the generation of its photostationary
state. No NOE is found from the new emerged protons to
the internal protons of a-CD (Fig. 4B), which can further
Fig. 4 The two-dimensional 1H NOESY NMR spectra (500 MHz in D2O
at 298 K) of (A) [L(a-CD)][NO3]3; B) irradiation on [L(a-CD)][NO3]3 by
365 nm for 2 h.
demonstrate that the structure is consistent with the geometry of
the photostationary state of [L(a-CD)][NO3]3 shown in Scheme 2,
where the a-CD ring is departed from the axle component. A
completely different pattern of NOEs is observed in the bis-
coordinated Pt(II) ensemble system. When [Pt-2L(a-CD)2][NO3]8
is photoisomerized to its photostationary state, new NOEs are
found from the protons Hs¢, t¢, to the internal protons H5 of a-
CD (Fig. 5B). The experimental results suggest that cis-formed
azobenzene station has pushed the a-CD shuttling away, and the
NOEs are consistent with the geometry of the photostationary
state of [Pt-2L(a-CD)2][NO3]8 shown in Scheme 2, where the a-CD
ring stays at the alkoxy isophthalate unit (the second station) on the
axle.18 The ring can be reset to encapsulate the azobenzenyl group
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Fig. 6 ICD signals in water at 298 K of [L(a-CD)][NO3]3 a) in the initial
state, b) after irradiation at 365 nm for 30 min and of [Pt-2L(a-CD)2][NO3]8
c) in the initial state, d) after irradiation at 365 nm for 30 min.
[L(a-CD)][NO3]3 and [Pt-2L(a-CD)2][NO3]8 were maintained at the same
concentration of 1.25 ¥ 10-4 M. Inset: changes in the ICD signal at 325 nm
of [Pt-2L(a-CD)2][NO3]8 for several cycles. In one cycle, 365-nm UV light
and visible light irradiation was used to isomerize the azobenzene unit.
of the ring that shuttles back and forth between the two stations
could be repeated for several cycles because of the reversibility of
the photochemical operations (the inset of Fig. 6).
Conclusions
In summary, two novel bis-branched molecular shuttles have
been prepared via quantitative coordination between one equiv.
Pd(en)(NO3)2 and Pt(en)(NO3)2, respectively with two equiv.
of hemi-rotaxane ligands. It is a highly efficient approach to
prepare a coordinated host–guest architecture, which can be easily
conducted in situ. In particular, transformation of ring shuttling
direction was observed in the bis-branched Pt(II) complex. The
a-CD ring in the hemi-rotaxane and in the bis-branched Pd(II)
complex took place a dethreading behavior to depart from the
axles, but the ring behaved an inward shuttling motion along the
axles in the bis-branched Pt(II) ensemble. Therefore, it is a new
approach for cooperatively modulating the components’ relative
motion by coordination-assembly. The bis-branched molecular
shuttle can be repetitively operated. It provides a methodology
for the design and construction of a new-type nano-machinery
combination system, which may find application in fields of
advanced molecular switches or digital information processings.23
Fig. 5 The two-dimensional 1H NOESY NMR spectra (500 MHz
in D2O at 298 K) of (A) [Pt-2L(a-CD)2][NO3]8; B) irradiation on
[Pt-2L(a-CD)2][NO3]8 by 365 nm for 2 h.
again for the full reversibility of the photochemical operations
(Figure S3, ESI†).
Induced circular dichroism signal expression for the bis-branched
molecular shuttle
Optical spectra could be channels of fast and convenient signal
readout for this bis-branched molecular shuttle. Cyclodextrin-
based host–guest structures are typical species which are sensitive
to induced circular dichroism (ICD) signals.19 The encapsulation
of a-CD to the azobenzene stations produces a positive cotton
effect of ICD at about 330 nm, and a negative one at around 450 nm
both in [L(a-CD)][NO3]3 and [Pt-2L(a-CD)2][NO3]8 (Fig. 6, curve
a and c).20 Both of the positive and the negative bands of
[Pt-2L(a-CD)2][NO3]8 have reached almost double altitude than
those of [L(a-CD)][NO3]3 at the same concentration, because
two of the hemi-rotaxane moieties are comprised in the bis-
branched complex. This result shows an output signal amplifi-
cation through the improvement of the chemical structure.21 As
[Pt-2L(a-CD)2][NO3]8 is converted to its photostationary state,
the intensity of the positive band at around 330 nm is drastically
decreased from 9.6 to 4.5 mdeg, and the negative signal at around
450 nm is also weakened from -3.4 to -2.5 mdeg (Fig. 6, curve
d). Such signal reduction is caused by the a-CD ring that has
significantly shuttled far away from the azobenzene.22 The motion
Experimental Section
Synthesis of compound A1: This compound was prepared as in
our previous report.24
Compound A2: Compound A1 (4.2 g, 20 mmol) was added with
magnetic stirring to a solution of 1, 4-dibromobutane (43.2 g, 0.2
mol) in acetone (ca. 150 mL). The mixture was then added upon
K2CO3 (6.3 g, 45.6 mmol) and 18-Crown-6 (288 mg, 1.1 mmol).
The solution was stirred refluxing for 14 h under Ar protection.
The mixture was filtered. After the filtrate was concentrated in
vacuo, the residue was applied to silica gel chromatography twice
(petroleum ether as the eluent) to afford white compound A2
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◦
1
(5.66 g, 82.3%). M.p. 46 ~ 48 C. H NMR (400 MHz, CDCl3,
298 K, TMS): d = 8.27 (s, 1H), 7.74 (s, 2H), 4.09 (t, J = 5.6 Hz,
2H), 3.93 (s, 6H), 3.50 (t, J = 6.4 Hz, 2H), 2.09 (m, 2H), 1.99
(m, 2H). 13C NMR (400 MHz, CDCl3, 298 K, TMS): d = 160.88,
153.68, 126.52, 117.76, 114.50, 62.23, 47.19, 28.03, 24.09, 22.46.
HRMS (EI): m/z: 344.0259 (79Br), 346.0239 (81Br).
123.07, 123.00, 122.58, 121.75, 119.26. 67.46, 62.73, 60.46, 52.59,
33.50, 27.58, 25.06. HRMS (ESI): m/z: 708.1957 (79Br), 710.1953
(81Br). [A4-2Br]+.
Target Ligand [L][NO3]3: 4, 4¢-b◦ipyridine (1.1 g, 6.9 mmol) was
dissolved in DMF (85 mL) at 70 C. A4 (0.6 g, 0.69 mmol) was
added into the solution and the mixture was stirred at 90 ◦C for 5 h.
After cooling to room temperature, the mixture was filtered. And
then the solid was washed with acetonitrile and gave an orange
compound (L∑3Br-) ca. 0.20 g. M.p. > 250 ◦C. 1H NMR (400 MHz,
DMSO-d6, 298 K, TMS): d = 9.59 (d, J = 6.4 Hz, 2H), 9.44 (d, J =
6.4 Hz, 2H), 9.41 (d, J = 6.8 Hz, 2H), 8.87 (d, J = 6.4 Hz, 2H), 8.83
(d, J = 6.8 Hz, 2H), 8.80 (d, J = 6.8 Hz, 2H), 8.69 (d, J = 6.8 Hz,
2H), 8.07 (s, 1H), 8.04 (d, J = 6.0 Hz, 2H), 7.97 (d, J = 8.0 Hz,
2H), 7.95 (d, J = 8.0 Hz, 2H), 7.85 (d, J = 8.4 Hz, 2H), 7.81 (d,
J = 8.4 Hz, 2H), 7.69 (s, 2H), 6.10 (s, 2H), 6.03 (s, 2H), 4.80 (t, J =
7.2 Hz, 2H), 4.19 (t, J = 6.0 Hz, 2H), 3.89 (s, 6H), 2.19 (m, 2H),
1.83 (m, 2H). AgNO3 (89 mg, 0.52 mmol) was added to an aqueous
solution (20 mL) containing [L][Br]3 (180 mg, 0.17 mmol) and the
mixture was stirred for 1 h at 65 ◦C in the dark. AgBr formed
and was removed by filtration while it was hot. Evaporation of the
filtrate and washing with a little water yielded L as an orange solid
(125 mg, 74%). M.p. 161~162 ◦C. The chemical shift of its protons
Compound A3: A solution of A2 (1.0 g, 2.9 mmol) and 4, 4¢-
bipyridine (3.2 g, 20.3 mmol) in acetonitrile (30 mL) was stirred
for 2 days at 80 ◦C. The solvent was removed in vacuo, and
the residue was dissolved in acetonitrile to applied to silica gel
chromatography (dichloromethane:methanol = 50 : 3) to afford
white compound A3 (1.21 g, 83.4%). M.p. 203 ~ 204 ◦C. 1H NMR
(400 MHz, DMSO-d6, 298 K, TMS): d = 9.27 (d, J = 6.8 Hz,
2H), 8.88 (d, J = 6.0 Hz, 2H), 8.64 (d, J = 6.8 Hz, 2H), 8.07 (s,
1H), 8.03 (d, J = 6.4 Hz, 2H), 7.68 (s, 2H), 4.73 (t, J = 7.2 Hz,
2H), 4.17 (t, J = 6.0 Hz, 2H), 3.88 (s, 6H), 2.16 (m, 2H), 1.82 (m,
2H). 13C NMR (400 MHz, DMSO-d6, 298 K, TMS): d = 165.15,
158.71, 152.23, 150.96, 145.36, 140.79, 131.46, 125.38, 121.87,
121.73, 119.24, 67.44, 59.94, 52.57, 27.48, 25.04. HRMS (ESI):
m/z: 421.1755 [A3 – Br]+.
Bis-(4-methyl-phenyl)-diazene (Compound B1): Cuprous chlo-
ride (30 g) was added slowly into anhydrous pyridine (200 mL),
and the mixture was kept stirring at room temperature for 10 min.
Then the solid was removed by filtration. p-toluidine (42.8 g, 0.44
mol) was added slowly into the above-mentioned filtrate, and the
solution was kept stirring at room temperature for 12 h with air
blowing. The pyridine solution was poured into 1300 mL water,
and extracted with dichloromethane (180 mL ¥3). The combined
organic layer was washed with water (200 mL ¥3), dried with
anhydrous MgSO4, and concentrated in vacuo. The residue was
washed with 70 mL toluene to give out orange compound B1
1
in H NMR is almost the same as that of [L][Br]3. 13C NMR
(400 MHz, DMSO-d6, 298 K, TMS): d = 165.17, 158.74, 152.91,
152.14, 152.06, 151.00, 149.32, 148.61, 145.95, 145.82, 145.51,
140.83, 137.63, 137.37, 131.50, 130.21, 130.06, 127.14, 126.71,
125.92, 123.31, 122.00, 121.75, 119.26, 113.40, 67.45, 62.91, 62.40,
60.56, 52.58, 27.57, 25.07. MS (ESI): m/z = 423.1 [L-2NO3 ]2+.
-
Elemental analysis calcd. for L (C48H45N9O14) (H2O)8: C 51.61, H
5.47, N 11.29; found: C 51.13, H 5.34, N 11.41.
Ethylene diamine palladium nitrate (Pd(en)(NO3)2): Ethylene
diamine palladium chloride (73.6 mg, 0.31 mmol) was suspended
in 20 mL water at room temperature. AgNO3 (105.3 mg,
0.62 mmol) was added to the suspension and the mixture stirred
for 0.5 h. A white solid of AgCl formed and was filtered off.
The filtrate was evaporated in vacuo and the pale-yellow solid was
directly used for the next step.
Ethylene diamine platinum nitrate (Pt(en)(NO3)2): Ethylene
diamine platinum chloride (60 mg, 0.18 mmol) was suspended
in 20 mL water at 50 ◦C. AgNO3 (64 mg, 0.38 mmol) was added
to the suspension and the mixture stirred for 2 h. A white solid of
AgCl formed and was filtered off. The filtrate was evaporated in
vacuo and the white solid was directly used for the next step.
[Pd-2L][NO3]8: An aqueous solution (10 mL) containing
Pd(en)(NO3)2 (8.7 mg, 0.03 mmol) and [L][NO3]3 (60 mg,
0.0617 mmol) was stirred in the dark for 1 h at room temperature
and a very small amount of precipitate was removed away by
filtration. The filtrate was concentrated in vacuo. The residue was
washed by deionized water (0.5 mL) and was dried to give the
product (50.9 mg, 76%).
◦
1
(14 g, 33.3%). M.p. 131 ~ 133 C. H NMR (400 MHz, CDCl3,
298 K, TMS): d = 7.83 (d, J = 8.0 Hz, 4H), 7.32 (d, J = 8.0 Hz,
4H), 2.45 (s, 6H).
Bis-(4-bromomethyl-phenyl)-diazene (Compound B2): A mix-
ture of B1 (8.0 g, 38.04 mmol), NBS (16.3 g, 91.0 mmol), BPO
(0.18 g, 0.74 mmol) and CCl4 (360 mL) was refluxed for 20 h
under an atmosphere of Ar gas. The resulting solution was filtered
while it was hot. The filter cake was washed with water (350 mL),
dried in vacuo, and then gave out orange compound B2 (8.6 g,
61.4%). M.p. 178 ~ 180 ◦C. 1H NMR (400 MHz, CDCl3, 298 K,
TMS): d = 7.90 (d, J = 8.4 Hz, 4H), 7.54 (d, J = 8.0 Hz, 4H), 4.54
(s, 4H).
Compound A4: B2 (4.0 g, 10.9 mmol) was dissolved in DMF
(75 mL) at 90 ◦C. The solution was then added upon A3 (0.78 g,
1.56 mmol) and stirred for 7 h at that temperature. It was filtered
while it was hot. The filtrate was poured into toluene (300 mL)
to precipitate some orange solid. The mixture was kept overnight
and then filtered. The filter cake was washed with hot chloroform
(30 mL), dried in vacuo, and then gave out pure orange compound
A4 (1.07 g, 78.7%). M.p. > 250 ◦C. 1H NMR (400 MHz, DMSO-
d6, 298 K, TMS): d = 9.59 (d, J = 6.8 Hz, 2H), 9.44 (d, J = 6.8 Hz,
2H), 8.83 (d, J = 6.8 Hz, 2H), 8.80 (d, J = 6.4 Hz, 2H), 8.07 (s,
1H), 7.98 (d, J = 8.4 Hz, 2H), 7.89 (d, J = 8.4 Hz, 2H), 7.85 (d, J =
8.4 Hz, 2H), 7.69 (s, 2H), 7.68 (d, J = 8.4 Hz, 2H), 6.10 (s, 2H), 4.82
(s, 2H), 4.80 (t, J = 7.6 Hz, 2H), 4.19 (t, J = 6.0 Hz, 2H), 3.89 (s,
6H), 2.19 (m, 2H), 1.83 (m, 2H). 13C NMR (400 MHz, DMSO-d6,
298 K, TMS): d = 165.17, 158.74, 145.92, 145.81, 141.95, 137.20,
131.50, 130.52, 130.30, 130.24, 130.20, 127.15, 126.73, 123.22,
[Pt-2L][NO3]8: An aqueous solution (10 mL) containing
Pt(en)(NO3)2 (11.4 mg, 0.03 mmol) and [L][NO3]3 (60 mg,
0.0617 mmol) was stirred in the dark for 18 h at 60 ◦C and a
very small amount of precipitate was removed away by filtration.
The filtrate was concentrated in vacuo. The residue was washed by
deionized water (1 mL) and was dried to give the product (45.3 mg,
65%).
[Pd-2L(a-CD)2][NO3]8: An aqueous solution (5 mL) containing
Pd(en)(NO3)2 (8.7 mg, 0.03 mmol) and [L(a-CD)][NO3]3 (120 mg,
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0.0617 mmol) was stirred in the dark for 1 h at room temperature.
The solution was concentrated in vacuo and washed with a very
small amount of deionized water to give the product (48.9 mg,
39%).
[Pt-2L(a-CD)2][NO3]8: An aqueous solution (5 mL) containing
Pt(en)(NO3)2 (11.4 mg, 0.03 mmol) and [L(a-CD)][NO3]3 (120 mg,
0.0617 mmol) was stirred in the dark for 18 h at 60 ◦C. The solution
was concentrated in vacuo and washed with a very small amount
of deionized water to give the product (32.0 mg, 25%).
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Acknowledgements
This work is financially supported by National Basic Research
973 Program, NSFC/China (20972053, 20902024). The authors
are grateful for assistance from Dr D. Zhang, Dr X. Ma, Mr.
Q. W. Zhang, Mr. C. Gao.
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16 The photoisomerization efficiencies of the light-activity systems here
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photostationary states of the bis-coordinated ensembles.
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also confirmed by the finding of similar NOEs in NMR spectra of A3-
CD, i.e., NOEs are found from the protons Hs¢, t¢, in the isophthalate
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21 It could be also illustrated by a comparison of the absorption spectra
shown in Figure S4, ESI.
22 The ring that shuttles inward or depart from the azobenzene will both
weaken the ICD signals (Fig. 6, Curve b and d).
20 The positive ICD signal should be attributed to the electronic transition
p–p* of the azobenzenyl moiety, which located in the cavity of CD ring
and aligned parallel to the axis of the chiral host, whereas the negative
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