Construction of optical active metallo-supramolecular polymers from enantiopure bis-pybox ligands

Article abstract of DOI:10.1016/j.tet.2019.04.023

Two types of optical active metallo-supramolecular polymers were successfully constructed from the complexation of two enantiopure bis-pyridine-dioxazole (bis-pybox) ligands and 3d transition metal ions such as Zn²⁺ and Fe²⁺ in organ

Full text of DOI:10.1016/j.tet.2019.04.023

Accepted Manuscript
Construction of optical active metallo-supramolecular polymers from enantiopure bis-
pybox ligands
Ya-Qi Wang, Yao Pan, Wan-Qing Gao, Yuan Wu, Chun-Hua Liu, Yuan-Yuan Zhu
PII:
S0040-4020(19)30425-9
https://doi.org/10.1016/j.tet.2019.04.023
TET 30268
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 23 January 2019
Revised Date: 5 April 2019
Accepted Date: 9 April 2019
Please cite this article as: Wang Y-Q, Pan Y, Gao W-Q, Wu Y, Liu C-H, Zhu Y-Y, Construction of optical
active metallo-supramolecular polymers from enantiopure bis-pybox ligands, Tetrahedron (2019), doi:
https://doi.org/10.1016/j.tet.2019.04.023.
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Graphical Abstract
Construction of optical active metallo-supramolecular polymers from enantiopure bis-pybox ligands
Ya-Qi Wang, Yao Pan, Wan-Qing Gao, Yuan Wu, Chun-Hua Liu,* and Yuan-Yuan Zhu*

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Construction of optical active metallo-supramolecular polymers from
enantiopure bis-pybox ligands
Ya-Qi Wanga, Yao Pana, Wan-Qing Gaoa, Yuan Wua, Chun-Hua Liua, and Yuan-Yuan Zhua,b,
aDepartment of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, and Anhui Key Laboratory
of Advanced Catalytic Materials and Reaction Engineering, Hefei 230009, China.
bState Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Two types of optical active metallo-supramolecular polymers were successfully constructed
from the complexation of two enantiopure bis-pyridine-dioxazole (bis-pybox) ligands and 3d
transition metal ions such as Zn2+ and Fe2+ in organic solution. The self-assembly process was
investigated via UV-vis and fluorescent titration. The chiral characteristic of polymers was
detected by circular dichroism. It was revealed that the phenyl-substituted polymers showed
higher stability than the benzyl-substituted ones. Temperature-dependent circular dichroism
spectra demonstrated the dynamic structure of this type polymer under the variation of
temperature. This work highlights the opportunity in designing and constructing of the optical
active metallo-supramolecular polymers from the organic privilege ligands in the field of
asymmetric catalysis.
Available online
Keywords:
metallo-supramolecular polymer
optical activity
pybox
self-assembly
2018 Elsevier Ltd. All rights reserved
.
metal-ligand charge transfer
———
Corresponding author. Y.-Y. Z. e-mail: yyzhu@hfut.edu.cn
Corresponding author. C.-H. L. e-mail: lchh88@hfut.edu.cn

2
Tetrahedron
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1. Introduction
from bis-terpyridines containing chiral tetra-ethylene glycol units
at the ortho-position of the peripheral pyridine rings.51 In these
polymers, the chiral information was successfully transferred
from the side chain of ligands to the coordination sphere of the
transition metal ions. It is well known that organic chemists have
developed lots of privilege ligands for asymmetric catalysis.
Among them, chiral pyridine-2,6-bis(oxazoline)s (pybox) belong
to a type of tridentate N ligands that display the excellent
performance in wide scope asymmetric syntheses52-55 and the
construction of enantiopure fluorescent complexes56,57. These
series of enantiopure ligands can be facilely synthesized from
chiral amino acid. In the previous work, we have demonstrated
the application of achiral ditopic pybox ligands to construct
fluorescent Zn(II) metallo-supramolecular polymers. These
polymers behaved structural stability in solution and solid state
and showed tuned fluorescent emission.58 As a continuation, we
proposed to design and synthesize optical active metallo-
supramolecular polymers by using chiral pybox moieties. In this
contribution, we report the synthesis of two enantiopure bis-
pybox ligands from chiral pybox moieties bearing phenyl (Ph)
and benzyl (Bn) chiral substituents. The self-assembly of bis-
pybox ligands and metal ions (Zn2+ and Fe2+) affords optical
active metallo-supramolecular polymers showing the chiral
transfer from pybox moiety to the coordination sphere of metal
ion.
Recently, there has been rapid development in the field of
metallo-supramolecular polymers due to their potential
applications as electrochromic materials, stimuli-responsive gels,
emissive materials, information storage devices, sensors,
photovoltaics, and self-healing materials.1-4 Different with the
traditional organic polymer in which the repeat units are
completely linked by covalent bond, metallo-supramolecular
polymers are formed by complexation of metal ions and multi-
topic organic ligands through coordination bond.5,6 So that this
new type of polymers combines common features of traditional
covalently bound polymers and the unique characteristics
provided by metal ions. In addition, unlike that of conventional
polymers, the degree of polymerization of metallo-
supramolecular polymers is not fixed in solution because of the
dynamic characteristic of coordination bond.7 Impressively, the
incorporation of metal ions endows this new type polymers with
quite a few interesting electronic, optical, and catalytic properties
and makes them as ideal candidates to access new functional and
stimuli-responsive materials.8-20 From 2003, Rowan and co-
workers pioneered constructing multi-stimuli and multi-
responsive metallo-supramolecular polymers based on ditopic
2,6-bis(N-methylbenzimidazolyl)pyridine (MeBip) ligands.21-23
Che,24 Tew,25,26 Hanabusa,27,28 Schubert29-31 and others32,33 used
terpyridine moiety as linker to construct a veriety of metal-
ligand-containing polymers. Higuchi, Kurth and co-workers
reported metallo-supramolecular polyelectrolytes self-assembled
bis-terpyridines ligands and metal ions towards the potential
applications in electrochromic materials.34-37 Recently, optical
active coordination polymers (CPs) and metal-organic
frameworks (MOFs) have proven to be an ideal platform for
asymmetric catalysis.38-40 So that the syntheses of enantiopure
CPs and MOFs have received intense interest and achieved rapid
development.41-45 Conversely, the examples of employing
multitopic chiral ligands to construct optical active metallo-
supramolecular polymers were still limited.46-50
2. Results and discussion
2.1. Preparation of bis-pybox ligands and metallo-
supramolecular polymers
In this work, two enantiopure bis-pybox ligands were facilely
synthesized. Firstly, bromined pybox substrates 3 (Ph) and 6 (Bn)
were obtained from commercially available amino acids
phenylglycinol and phenylalaninol, respectively. Then they
reacted with 1,4-phenylenediboronic acid via a palladium-
catalyzed Suzuki coupling reaction to afford L1 and L2. The
detailed synthetic route is depicted in scheme 1. The chiral
1
ligands and intermediates were well characterized by H NMR,
In 2009, Higuchi, Kurth and co-workers reported the
construction of optical active metallo-supramolecular polymers
13C NMR, HRMS, and optical rotation (see Figure S1−S19).
Scheme
1.
The
synthetic
routes
of
Chiral
bis-pybox
Ligands
L1S
and
L2S.
Metallo-supramolecular polymers P1–2 were prepared by 1:1
complexation of M(SO3CF3)2 or M(ClO4)2 (M = Zn2+ and Fe2+)
with L1-2 (see Scheme 2). After they reacted at 80 °C in
acetonitrile for 24 h, the polymers were purified by repeated
precipitations from acetonitrile in diethyl ether and characterized
by H NMR (see Figure S20−S23). The considerable broadness
1

3
of proton signals compared to their ligands indicates the
the the geometrical distortion in the Fe2+ coordination sphere
(see Figure S30(c, d)).
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polymeric characteristic after coordination. These polymers
exhibited moderate stability and solubility in organic solvents
such as dichloromethane, chloroform, THF, and acetonitrile but
decompose in polar solvents such as H2O, DMF, and DMSO (see
Figure S24). In general, the polymers with trifluorosulfonate as
counter anion show better solubility than the perchlorate ones.
The solid characteristic of these polymers was tested by powder-
XRD. They all show broad peaks which is typical characteristic
of amorphous structures (see Figure S25). Additionly, the
morphology of four polymers was investigated by scan electron
microscope (SEM). Nanofibers with an average width of 10 to 20
nm were observed (see Figure S26).
R
R
R
O
O
O
R
O
N
N
N
N
N
N
N
N
M(ClO4)2 or M(SO3CF )2
3
N
N
N
M2+
N
MeCN,80°C, 24 h
m = 1:R = Ph
m = 2:R = Bn
M = Zn2+ or Fe2+
O
Pm
R
R
O
O
O
R
R
n
Scheme 2. Synthesis of metallo-supramolecular polymers P1-2.
Figure 1. UV-vis spectra acquired upon titration of L1 (5 × 10-5 M) in
chloroform with Zn(ClO4)2 and Fe(ClO4)2. Shown are spectra at selected Zn2+
: L1 ratios ranging from 0 to 1 (a) and above 1 (b) and selected Fe2+ : L1 ratios
ranging from 0 to 1 (c) and above 1 (d).
2.2. UV-vis spectra
The self-assembly process in solution was investigated
through UV-vis spectra firstly. The chloroform solution of L1
(5.0 × 10-5 M) showed a strong absorption peak at 296 nm due to
the π−π* transition of the ligand. When it was titrated with the
acetonitrile solution of Zn(ClO4)2 up to 1 equiv, a notable change
in the π−π* transition was observed (see Figure 1(a)), the lowest-
energy absorption of L1 originally at 296 nm was incessantly red-
shifted to 334 nm because of the charge transfer between the
electron rich central phenyl component and the Zn2+-coordinated,
electron-deficient pybox moiety. Subsequent addition of
Zn(ClO4)2 above 1 equiv caused very slight blue-shift at 334 nm,
implying the partially decomposition of the coordination polymer
(see Figure 1(b)). A isobestic point at 312 nm displayed the
equilibrium and transition between free ligand L1 and the
coordination polymer in this titration process. The change of
absorption at 296 nm and 334 nm were showed in Figure S31(a)
as well. The increase at 334 nm and decrease at 296 nm in the
absorption intensity both obey a linear fashion, until a metal-to-
ligand ratio of 1:1 was reached, confirming the dynamic of
coordination polymer in the self-assembly process at metal-to-
ligand ratios below and above 1:1. This results demonstrated that,
in this linear polymer, each Zn2+ ion was complexed with two
ditopic ligands and the ligand was also complexed with two Zn2+
ions through two pybox moieties.
2.3. Single-crystal X-ray structures of the coordination moieties
In order to get the insight of coordination sphere of these
metallo-supramolecular polymers, the X-ray single crystal
structures of coordination moieties were compared. The structure
of [Fe((R)-LPh)][ClO4]2 (C1) (LPh = 2,6-bis((R)-4-phenyl-4,5-
dihydrooxazol-2-yl)pyridine) was obtained from the reported
literature by Halcrow and coworkers59 and [Fe((R)-LBn)][ClO4]2
(C2)
(LBn
=
2,6-bis((R)-4-benzyl-4,5-dihydrooxazol-2-
yl)pyridine) was synthesized from the reaction of Fe(ClO4)2 and
LBn in methanol. The crystals suited for X-ray diffraction were
obtained upon liquid-liquid diffusion method. Although Fe2+ ions
in two complexes are all octahedral, their distortion deviated
from ideal octahedron experience significant difference. Their
distortion can be quantitatively determined by some structural
parameters based on ideal octahedron such as Ʃ and S(Oh). Ʃ is
the sum of the deviations from 90° of 12 cis angles and S(Oh) is
the result of CShMs calculation denotes the deviation value of
ideal Oh symmetry. The values of Ʃ and S(Oh) in C1 are 105.56°
and 2.780, that are both smaller than that of 165.11° and 7.622 in
C2. According to the analysis of CPK model of two cationic
complexes, there are a pair of well paralleled and a pair of
slightly distorted π−π stacking between neighboring phenyl and
pyridine. These interactions can benifit to stabilize the complex.
However, the similar π−π stackings in C2 show more serious
distortion, implying the weaker coordination (see Figure S28).
The different strengths of their ligand field are also reflected in
the temperature dependent magnetic susceptibility data.
Halcrow’s work demonstrated that C1 is an SCO compound with
an approximate T1/2 of 350 K.59 Conversely, C2 showed the
complete high-spin characteristic at all temperatures because of
its weaker ligand field strength caused by the geometrical
distortion of the central Fe2+ ion (see Figure S29). These
investigations well explained why P1 series polymers show
stronger stability in solution than the P2 series. Strong π−π
stackings in the coordination moiety can suppress the dis-
assembly of polymer.
Compared with the UV-vis titration with Zn(ClO4)2, the
titration of L1 at the same condition with Fe(ClO4)2 not only
caused a significant change in the π−π* transition, but also
generated a new absorption peak around 600 nm. The new
absorption is originated from the metal-to-ligand charge transfer
(MLCT). Upon the addition of Fe(ClO4)2, the intensity of the
MLCT peak continuously increased in a linear fashion to the
metal-to-ligand ratio reached 1:1. After the ratio above 1:1, no
obvious change was observed (see Figure 1(c, d) and S31(b)).
Similarly, the UV-vis titration results of L2 gave the identical 1:1
self-assembly mode (see Figure S30 and S32). Impressively,
when the metal-to-ligand ratio was above 1:1, the blue-shift of
the lowest-energy absorption of L2 in the range of 300−360 nm is
larger than that in L1, implying the less stability of P2 than P1.
The relative intensity of the MLCT absorption peak in UV−vis
spectra of L2 is lower than that of L1, which may be caused by

4
Tetrahedron
for (R)-P1-Fe and a negative signal at 540 nm for (R)-P2-Fe. All
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enantiopure ligands and polymers show perfect mirror images.
Impessively, all polymers display the enhanced intensity of CD
signals. The results verify the tranfer of chiral information from
the ligand to the coordination sphere of the Fe2+ ion. Similarly,
the symmetric Cotton signals at 262 nm for P1-Zn and 263 nm
and 346 nm for P2-Zn were observed (see Figure S35). Like UV-
vis titration, CD titration experiments of (R)−L1,2 with Fe(ClO4)2
and Zn(ClO4)2 were carried out as well (see Figure S36). The
Cotton signals continuously increased to maximum when the
metal-to-ligand ratio reached 1:1 but decreased when excess
amount of ion salts was added, further confirming the
decomposition of the polymeric structure when metal-to-ligand
ratio is above 1:1. The solvent effect of their CD signals was also
investigated (see Figure S37), indicating the self-assembly of
these polymers was influenced by different solvents.
Figure 2. Molecular structures of [Fe((R)-LPh)][ClO4]2 (C1) and [Fe((R)-
LBn)][ClO4]2 (C2). The hydrogen atoms and counter anions are omitted for
clarity.
2.4. Emission spectra
Fluorescent titration experiments of the ligands L1,2 with
Zn(ClO4)2 were employed to prove the formation of coordination
polymers and also to give detailed insight of the emission
characteristics of ligands before and after metal-binding (see
Figure 3, S33, and S34). All emission spectra were recorded by
exciting the lowest-energy absorption maxima band. When the
chloroform solution of ligands L1,2 were titrated with Zn(ClO4)2,
the emission maxima (λem) were red-shifted significantly and
undergo a notable broadening. The red-shift and occurrence of
strong luminescence is originated from the intra-ligand charge
transfer (ILCT) between the metal site and the chromophore of
the ligands. It was found that the emission peak of the free
ligands disappeared completely when the metal-to-ligand ratio
reached 1:1. The blue-shift and decrease of the emission peak
occured when the metal-to-ligand ratio was above 1:1,
corresponding to the partial decomposition of the polymers. In
addition, the partial decomposition process of these polymers
were further investigated by dynamic light scattering (DLS)
measurement. At a metal-to-ligand ratio above 1:1, the average
particle size continuously decreased (see Figure S27). Similar to
the results by UV−vis titration, the larger blue-shift of L2 was
observed compared with that of L1, further supporting the weaker
coordination ability of L2.
Figure 4. CD and UV-vis spectra of (R or S)-L1 (a), (R or S)-P1-Fe (b), (R
or S)-L2 (c), and (R or S)-P2-Fe with the concentration of 5 × 10-5 M in
chloroform.
Finally, temperature-dependent CD spectra of (S)-P1-Fe were
measured to investigate the temperature influence on the chiral
conformation of these metallo-supramolecular polymers. This
temperature-dependent studies were performed at temperatures
from −13 to 50 °C in chloroform and the result was depicted in
Figure 5. It was found that the absorption intensity of MLCT
band around 532 and 611 nm gradually decreased with increasing
temperature. The changes of intensity against temperature obey
well defined linear fashion, implying the gradual decomposition
of polymers by the dis-assembly of metal coordination. In the
UV-vis spectra, the temperature-dependent intensities of the
MLCT band at 611 nm show identical trend (see Figure S38).
These investigations further support that these metallo-
supramolecular polymers are dynamic structure in solution.
Figure 3. Fluorescent titration spectra of L1 (5 × 10-5 M) (a) and L2 (5 × 10-5
M) in chloroform with gradual addition of Zn(ClO4)2.
2.5. Circular dichromism
The optical activity and enantiopure nature of the ligands L1,2
and their metallo-supramolecular polymers in chloroform
solutions were examined by circular dichroism spectra (see
Figure 4). The spectra of (R)−L1,2 both exhibit a negative Cotton
effect around 300 nm which are originated from the π−π*
transition. For the polymers, besides the signals from the π−π*
transition of ligands at short wavelength ragion, the Cotton effect
due to MLCT above 450 nm can also be observed clearly. There
are a positive signal at 532 nm and a negative signal at 611 nm

5
Figure 5. (a) CD spectra of (S)-P1-Fe in chloroform (c = 5 × 10-5 M, l = 1
cm) at different temperatures. (b) The linear fitting of CD intensity changes
of the MLCT band (λ = 532 and 611 nm) with increasing temperature.
at 0 °C for 3 h and then refluxed for 48 h. The mixture was
ACCEPTED MANUSCRIPT
washed with water (10 mL). The aqueous phase was extracted
with CH2Cl2 (10 mL × 3) and the combined organic solution over
anhydrous sodium sulfate. After evaporation, the crude product
was refluxed in ethanol for 2 h. After cooling to room
temperature, the reaction solution was filtered of pure 3 as a
white solid (3.17 g, 78%). 1H NMR (400 MHz, CDCl3): δ 8.53 (s,
2 H), 7.40−7.29 (m, 10 H), 5.46 (t, J = 9.6 Hz, 2 H), 4.94 (t, J =
9.6 Hz, 2 H), 4.44 (t, J =8.8 Hz, 2 H). [ꢀ]ꢂꢁꢃ −62.5 (c 4.1,
CH2Cl2) for (S)-3 and 67.2 (c 4.0, CH2Cl2) for (R)-3.
Synthesis of L1. A mixture of 3 (447 mg, 1 mmol), 1,4-
phenylenediboronic acid (66 mg, 0.4 mmol), Pd(dppf)Cl2 (33 mg,
0.04 mmol), and K2CO3 (442 mg, 3.2 mmol) was degassed and
backfilled with N2 three times, and then THF (8 mL) and
deionized water (2 mL) were added. The resulting mixture was
refluxed for 48 h. After cooling to room temperature, the reaction
solution was filtered of pure L1 as a white solid (230 mg, 71%).
1H NMR (600 MHz, CDCl3): δ 8.64 (s, 4 H), 7.90 (s, 4 H),
7.40−7.29 (m, 20 H), 5.50 (t, J = 9.3 Hz, 4 H), 4.97 (t, J = 9.3
Hz, 4 H), 4.47 (t, J = 8.7 Hz, 4 H). 13C NMR (150 MHz, CDCl3):
δ 163.6, 149.0, 147.5, 141.6, 137.8, 128.9, 128.1, 128.0, 126.9,
124.0, 75.7, 70.5. HRMS (MALDI−TOF) calcd for C52H41N6O4
[M + H]+ 813.3184, found 813.3213. [ꢀ]ꢁꢂꢃ −86.0 (c 5.0, CH2Cl2)
for (S)-L1 and 85.0 (c 4.9, CH2Cl2) for (R)-L1.
3. Conclusions
In summary, two types of optical active metallo-
supramolecular polymers named P1−2 were synthesized from the
complexation of two enantiopure bis-pybox ligands and Zn(II) or
Fe(II) ions in solution. Circular dichroism demonstrated that the
chiral information was successfully transferred from the ligands
to the coordination sphere of metal ions. Our research also
revealed that the stability of these metallo-supramolecular
polymers is sensitive to the structure of ligand and temperature.
This work shows the possibility of constructing optical active
metallo-supramolecular polymers from the organic privilege
ligands. Further applications of these metallo-supramolecular
polymers towards nonlinear optical materials and multi-stimuli
responsive polymers are underway.
4. Experimental Section
4.1. Instruments and materials
The NMR spectra were recorded on a Bruker 400 MHz or 600
MHz spectrometer and the 13C NMR spectra were recorded on
125 MHz or 100 MHz spectrometer. UV-vis spectra were
recorded on a Shimadzu UV-2550 spectrometer. Emission
spectra were recorded on a Hitachi F-4600 fluorescence
spectrophotometer. Mass spectrometric analyses were measured
on a Bruker BioTOF using positive-ion electrospray ionization
Powder X-ray diffraction (PXRD) patterns were measured in the
range of 5° < 2θ < 50° with Cu Kα radiation at ambient
temperature on a Rigaku Dmax 2000 diffractometer. Mass
Spectrometer. Circular dichroism spectra were recorded on a
JASCO J1500 spectropolarimeter. X-ray diffraction data was
collected on a Rigaku Saturn 724+ CCD diffractometer with Mo-
Kα radiation (λ =0.71073 Å). Least-squares refinements was
used for collecting unit cell dimensions. All crystal structures
were solved by shelXT and OLEX2-1.2 and the other
nonhydrogen atoms were synthesized by successive difference
Fourier. Anisotropic thermal parameters was used for refinement
of non-hydrogen atoms and the hydrogen atoms were placed at
calculated positions and riding on the concerned atoms.
Synthesis of 4. In a sealed tube, a mixture of 1 (2.74 g, 10
mmol) and (S)-phenylalaninol (3.78 g, 25 mmol) in methanol (10
mL) was stirred at 115 °C for 12 h. After cooling to ambient
temperature, the crude product was poured into crushed ice (100
g), stirred for 15 minutes, filtered, washed with water (20 mL ×
3) and the residues was dried under vacuum. The white product
was used for the next step without further purification (4.50 g,
88%). 1H NMR (400 MHz, CDCl3): δ 8.43 (s, 2 H), 7.94 (d, J = 8
Hz, 2 H), 7.32−7.21 (m, 10 H), 4.40−4.32 (m, 2 H), 3.83−3.74
(m, 4 H), 3.06−2.96 (m, 4 H), 2.59 (br, 2 H). 13C NMR (150
MHz, CDCl3): δ 162.6, 149.7, 137.5, 136.4, 129.4, 128.8, 128.5,
126.9, 63.6, 53.1, 37.0. HRMS (MALDI−TOF) calcd for
C25H27BrN3O4 [M + H]+ 512.1179, found 512.1186.
Synthesis of 5. In an ice bath, dichlorosulfoxide (10 mL) was
added into a solution of 4 (4.50 g, 8.8 mmol) in CH2Cl2 (10 mL)
dropwise. The solution was refluxed for 3 h. Then the solution
was cooled to ambient temperature, concentrated under reduced
pressure and the crude product was redissolved in CH2Cl2 (20
mL). The solution was washed with water (10 mL × 2), saturated
NaHCO3 (10 mL), and brine (10 mL) and dried over anhydrous
sodium sulfate. After the solvent was removed, the crude product
was purified by column chromatography (SiO2, CH2Cl2/CH3OH,
All solvents were purchased from Sinopharm. They were used
without further treatment and purification unless otherwise
indicated. Tetrahydrofuran (THF) was further dried over
Na/benzophenone ketyl and distilled under high vacuum prior to
use. All chemicals were purchased from Alfa Aesar, Aldrich,
Aladdin, and Sinopharm.
1
250:1) giving 5 as a white solid (4.52 g, 94%). H NMR (600
MHz, CDCl3): δ 8.49 (s, 2 H), 7.97 (d, J = 9.0 Hz, 2 H),
7.35−7.25 (m, 4 H), 4.70−4.65 (m, 2 H), 3.79−3.77 (m, 2 H),
3.68−3.66 (m, 2 H), 3.11−2.04 (m, 4 H). 13C NMR (100 MHz,
CDCl3): δ 161.6, 149.4, 136.6, 136.6, 129.3, 128.9, 128.7, 127.1,
50.9, 46.8, 37.6. HRMS (MALDI−TOF) calcd for
C25H25BrCl2N3O2 [M + H]+ 550.0481, found 550.0505.
4.2. Synthesis of the ligands and metallo-supramolecular
polymers
Synthesis of 2.60 In a sealed tube, a mixture of 161 (2.74 g, 10
mmol) and (R or S)-phenylglycinol (3.43 g, 25 mmol) in
methanol (10 mL) was stirred at 115 °C for 12 h. After cooling to
room temperature, the crude product was poured into ice water
(100 mL), stirred for 15 minutes, filtered, washed with water (20
mL × 3) and the residues was dried under vacuum. The white
product was used for the next step without further purification
(4.41 g, 91%). 1H NMR (400 MHz, CDCl3): δ 8.60 (d, J =7.6 Hz,
2 H), 8.45 (s, 2 H), 7.37−7.29 (m, 10 H), 5.26−5.22 (m, 2 H),
4.01 (d, J = 4.4 Hz, 4 H), 2.21 (br, 2 H).
Synthesis of 6. A solution of 5 (4.52 g, 7.9 mmol) in THF (10
mL) was added sodium hydride powder (1.6 g, 31.6 mmol, 60%
in mineral oil) in an ice bath under an N2 atmosphere. The
resulting mixture was stirred vigorously at ambient temperature
for 12 h. After THF was removed, CH2Cl2 (30 mL) was added.
The organic solution was washed with water (10 mL × 2),
saturated NaHCO3 (10 mL), and brine (10 mL) and dried over
anhydrous sodium sulfate. After the solvent was removed, the
crude product was purified by column chromatography (SiO2,
CH2Cl2/CH3OH, 200:1) giving 6 as a white solid (2.63 g, 70%).
1H NMR (400 MHz, CDCl3): δ 8.38 (s, 2 H), 7.33−7.21 (m, 10
Synthesis of 3.61 A mixture of 2 (4.41 g, 9.1 mmol), TsCl (4.3
g, 22.8 mmol) and Et3N (12.8 mL) in CH2Cl2 (30 mL) was stirred

6
Tetrahedron
ACCEPTED MANUSCRIPT
H), 4.69−4.61 (m, 2 H), 4.46 (t, J = 9.0 Hz, 2 H), 4.25 (t, J =
for about 10 minutes, the precipitate was filtered and dried under
8.2 Hz, 2 H), 3.27−2.23 (m, 2 H), 2.77−2.72 (m, 2 H). 13C NMR
(150 MHz, CDCl3): δ 161.8, 147.7, 137.5, 133.8, 129.2, 128.9,
128.7, 126.7, 72.8, 68.1, 41.6. HRMS (MALDI−TOF) calcd for
C25H25BrCl2N3O2 [M + H]+ 478.0948, found 478.0924. [ꢀ]ꢂꢁꢃ
−40.6 (c 0.97, CH2Cl2) for (S)-6 and 50.2 (c 0.99, CH2Cl2) for
(R)-6.
vacuum. The precipitate was dissolved in dichloromethane (4
mL) and added to the bottom of a clean glass tube. The solution
was layered carefully with blank dichloromethane/methanol
mixture solvent (4 mL, v/v 1:4) and blank methanol solvent (4
mL), sequentially. The tube was sealed and undisturbed at room
temperature for a week. Red block crystals were obtained in the
bottom of the tube. Yield: 70%. Anal. Calcd for
C51H50Cl2FeN6O13: C, 56.63; H, 4.66; N, 7.77. Found: C, 56.64;
H, 4.47; N, 7.95. IR (pure sample): ν = 3618 (w), 3536 (w), 3087
(w), 3062 (w), 3030 (w), 2926 (w), 2019 (w), 1644 (w), 1623
(w), 1603 (w), 1575 (m), 1496 (w), 1487 (w), 1455 (w), 1429
(w), 1401 (m), 1338 (w), 1305 (w), 1282 (w), 1265 (w), 1202
(w), 1158 (w), 1093 (s), 1028 (w), 1002 (w), 976 (w), 940 (w),
857 (w), 828 (w), 748 (w), 718 (w), 702 (w), 673 (w), 624 (m).
Synthesis of L2. Under an N2 atmosphere, a mixture of 4 (475
mg, 1 mmol), 1,4-phenylenediboronic acid (66 mg, 0.4 mmol),
Pd(dppf)Cl2 (33 mg, 0.04 mmol), and K3PO4·3H2O (710 mg, 2.7
mmol) in DMF (5 mL) was stirred at 95 °C for 48 h. After
cooling to ambient temperature, the crude product was poured
into crushed ice (100 g), stirred for 15 minutes, filtered and
washed with water (20 mL × 3) and then dissolved in CH2Cl2 (20
mL). The organic solution was washed with water (10 mL × 2),
saturated NaHCO3 (10 mL), and brine (10 mL) and dried over
anhydrous sodium sulfate. After the solvent was removed, the
crude product was purified by column chromatography (SiO2,
ethyl acetate) giving L2 as a white solid (125 mg, 36%). 1H NMR
(600 MHz, CDCl3): δ 8.52 (s, 4 H), 7.94 (s, 4 H), 7.34−7.24 (m,
20 H), 4.73−4.68 (m, 4 H), 4.50 (t, J = 9.0 Hz, 2 H), 4.31 (t, J =
8.1 Hz, 4 H), 3.34−3.30 (m, 4 H), 2.80−2.76 (m, 4 H). 13C NMR
(100 MHz, CDCl3): δ 162.9, 149.0, 147.5, 137.9, 137.6, 129.3,
128.7, 128.1, 126.7, 123.5, 72.7, 68.2, 41.7. HRMS
(MALDI−TOF) calcd for C52H41N6O4 [M + H]+ 869.3810, found
869.3943. [ꢀ]ꢂꢁꢃ −68.0 (c 0.97, CH2Cl2) for (S)-L2 and 71.0 (c
0.99, CH2Cl2) for (R)-L2.
Acknowledgments
This work is supported by the National Natural Science
Foundation of China (No. 21771049), and the State Key
Laboratory of Fine Chemicals at Dalian University of
Technology (KF 1607).
References and notes
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