Selective Encapsulation and Separation of Dihalobenzene Isomers with Discrete Heterometallic Macrocages

Article abstract of DOI:10.1002/chem.201805383

A series of metallosupramolecular architectures have been prepared, including rectangles, prisms and cages, that feature half-sandwich rhodium(III) fragments at the vertices. Remarkably, a stable cage-like heteropolymetallic complex possessing eight rhodi

Full text of DOI:10.1002/chem.201805383

A Journal of
Accepted Article
Title: Selective encapsulation and separation of dihalobenzene
isomers with discrete heterometallic macrocages
Authors: Guo-Xin Jin, Hai-Ning Zhang, Ye Lu, Wen-Xi Gao, and Yue-
Jian Lin
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Selective encapsulation and separation of dihalobenzene isomers
with discrete heterometallic macrocages
Hai-Ning Zhang, Ye Lu, Wen-Xi Gao, Yue-Jian Lin and Guo-Xin Jin*[a,b]
Abstract: A series of metallosupramolecular architectures have been
prepared including rectangles, prisms and cages, and featuring half-
sandwich rhodium(III) fragments at the vertices. Remarkably, a stable
cage-like heteropolymetallic complex possessing eight rhodium(III)
and two silver(I) metal ions (3) has been obtained following a multistep
recognition.[4] Due to their remarkable solubility in a wide variety
of solvents, self-assembled metallamacrocycles and
metallacages have found application in several research areas,
[
5,6]
including catalysis, biosciences, separation processes and the
development of advanced sensors.[
7,8]
III
I
procedure. The Rh /Ag mixed macrocage enables the separation of
dihalogenated benzene derivatives with high selectivity. Furthermore,
Haloarenes are valuable starting materials for cross-coupling
reactions, a key step in the synthesis of drugs and conjugated
organic compounds.[9,10] Due to their similar chemical and
a
detailed X-ray crystallographic study confirmed that the
discriminative encapsulation of para-dihalobenzene (dichlorobenzene, physical properties, traditional methods either have great
dibromobenzene and diiodobenzene) is favored by Ag-π interactions
difficulties in separating of haloarene isomers or effect the
separation with high cost. Therefore, purification of these
chemical compounds demands particular attention, both at
research laboratory and large-scale industrial levels.[ Previously
reported procedures to separate haloaromatic constitutional
isomers are mainly based on the different molecular radii of these
and steric effects.
11]
Introduction
compounds and use porous materials with different pore sizes
Molecular recognition, the concept was initially proposed by
chemists and biologists to explore chemical problems in biological
systems in the molecular level and well utilized to describe
effective and selective biological function, which can also be
regarded as the process forming the crucial part of self-assembly
in the essence.[1,2] Together with most advancements in
Supramolecular Chemistry, molecular recognition has been
widely used to depict the process in which the host (receptor)
selectively binds to the guest (substrate) and both of them
together produces a particular function. As the most significant
field in Supramolecular Chemistry, molecular recognition has
raised more and more attentions from supramolecular chemists
and further inspires them to design and synthesize molecular
machines with intricate structures and various kinds of
functions.[3]
[11]
and shapes
(zeolites, activated carbon, carbon molecular
sieves, aluminophosphates, inorganic or polymeric resins, metal-
organic frameworks and composite materials).[12,13] However, due
to unique peculiarities of these materials, most of these studies
relied on computational models to explain the principles of
separation rather than experimental evidence. For discrete half-
sandwich iridium-, rhodium- and ruthenium-based organometallic
architectures, the existence of Cp* (pentamethylcyclopentadienyl)
or Cy (para-cymene) fragments not only improves the solubility of
metallosupramolecular compounds but also facilitates their
crystallization, allowing the facile determination of crystal
structures of encapsulation compounds.[5,6] These structures
provide reliable evidence for the driving force of encapsulation
and push forward the exploration of separation on a single-
molecule level.
Understanding the coordination-driven self-assembly of
discrete metallosupramolecular architectures can shed light on
significant behavioral aspects of complicated recognition process,
thus allowing major breakthroughs in supramolecular
Herein, we report the rational and straightforward preparation
of Cp*Rh-based metallosupramolecular architectures featuring
stable heterarylrhodium(III) complexes via metal-directed self-
assembly of heterocyclic boronic acids and rhodium precursors
under mild conditions. Moreover, in order to realize the
construction of heterometallic macrocages, the spatial regulating
strategy[4e] was adopted and three types of proligands were
selected in this work (Scheme 1). According to the results, we
found the halogen atoms not only play a crucial role in forming
heterometallic macrocages, but also affect the properties of the
macrocages in the separation of isomers of guest molecules and
stability of encapsulation compounds. On this basis, a separation
method is presented for a series of constitutional isomers of ortho-,
meta- and para-dihalogenated benzene derivatives at ambient
temperature. Thereby, the existence of bridging silver(I) ions in
the cages enables reversible encapsulation and release of guest
molecules by taking advantage of the well-known reduction of
[
a]
H.-N. Zhang, Dr. Y. Lu, W.-X. Gao, Dr. Y.-J. Lin, Prof. G.-X. Jin
State Key Laboratory of Molecular Engineering of Polymers
Collaborative Innovation Center of Chemistry for Energy Materials
Department of Chemistry, Fudan University
Shanghai 200433 (P.R. China)
[
b]
Prof. G.-X. Jin
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
Shanghai 200032 (P. R. China)
E-mail: gxjin@fudan.edu.cn
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/chem.XXXXXX.
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silver(I) ions under sunlight, or the reaction of silver(I) and chloride
ions under mild conditions.
different singlets for the carbon nuclei of the methyl groups. These
1
1
features, in addition to the H, H-COSY NMR spectrum,
confirmed the existence of an isomeric mixture (see the
Supporting Information). Furthermore, the HR-ESI mass
3
spectrum of 1 in CH OH showed strong peaks at m/z 1848.74
–
+
(
2
assigned to [1 − OTf ] ) and m/z 849.89 (assigned to [1 −
–
2+
OTf ] ), indicating that complexes 1a and 1b exhibit remarkable
stability in solution.
Scheme 1. Selected proligands with distinct coordination modes and two N-
heterocyclic boronic acids.
Results and Discussion
The proligand 2,5-dibromo-3,6-dihydroxycyclohexa-2,5-diene-
1
,4-dione (H
2
-L
1
) and 2,5-difluoro-3,6-dihydroxycyclohexa-2,5-
-L ) were synthesized according to the
diene-1,4-dione (H
2
4
literature method.[
boronic acid, B(OH)
,5-dihydroxycyclohexa-2,5-diene-1,4-dione
purchased from commercial sources and used without purification.
The ligand Na -L was synthesized via the reaction of proligand
-L (1.0 equiv.) with sodium methoxide (2.0 equiv.) in methanol
at ambient temperature. Analogously, the ligands Na -L and Na
were also prepared by replacing proligand H -L with proligand
-L and -L in the reaction with sodium methoxide,
respectively.
15a,15c]
The ligands (B(OH)
: pyrimidine-5-boronic acid) and proligand
(H -L were
2
2
-L : pyridine-4-
2
-L
3
2
2
5
)
Scheme 3. Synthesis of metallarectangle 2 and heterometallic macrocage 3.
2
1
H
2
1
2
4
2
-
L
H
5
2
1
2
4
H
2
5
Scheme 2. Synthesis of metallarectangles 1.
Figure 1. a) Side and b) top view of the cationic part of metallarectangle 1a. c)
Side and d) top view of metallarectangle 2a. All triflate anions, solvent molecules,
and hydrogen atoms are omitted for clarity. Color code: N, blue; O, orange; C,
black; Br, brown; Rh, red.
Synthesis of tetranuclear rhodium metallarectangles. A
methanolic solution of [Cp*RhCl
AgOTf (OTf SO CF with exclusion of light for
Subsequently, ligand Na (1.0 equiv.), ligand Na -L (1.0 equiv.)
2
]
2
was treated with 4.0 equiv. of
=
3
3
)
-L
6
h.
The facile formation of metallarectangles 1a and 1b prompted
2
1
2
2
and deionized water were added to the reaction mixture. Isomeric
us to investigate the related reaction involving pyrimidine-5-
complexes 1a and 1b were obtained after 24 h in a yield of 90%
boronic acid (B(OH)
be easily activated by rhodium(III), as was previously observed
for B(OH) -L , the heterocyclic boronic acid B(OH) -L has three
2 2
3 3
-L ). Since the C–B bond of B(OH) -L can
(
Scheme 2).
Formation of 1a and 1b as isomeric mixture was
2
2
2
3
unambiguously confirmed by NMR spectroscopy and single-
crystal X-ray diffraction analysis. While the 1H NMR spectrum
exhibited two sets of mutually coupled signals in the aromatic
region at δ 7.64-6.59 ppm, the 13C{ H} NMR spectrum showed
potential coordination sites. The pair of boat-shaped isomers 2a
and 2b was obtained with a yield of 87% following a procedure
similar to that introduced previously for the synthesis of 1a and 1b
(Scheme 3). The mixture of tetra-RhIII complexes 2a and 2b was
1
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1
studied by H NMR spectroscopy, elemental analysis and mass
spectra of the complex mixture 2a/2b and 3 are different, the
variations of the δ values can be attributed to the N-coordination
of the metalloligands 2a and 2b to silver(I).
spectrometry. Multiple resonances were observed for the protons
of the Cp* groups in the 1H NMR spectrum, suggesting the
existence of isomers in solution and that the Cp* groups are not
chemically equivalent. Furthermore, the HR-ESI mass spectrum
of 2 in CH
3
+
OH showed strong peaks at m/z 1850.73 (assigned to
–
– 2+
[
2 – OTf ] ) and m/z 850.89 (assigned to [2 − 2OTf ] ), which
indicates that complexes 2a and 2b exhibit remarkable stability in
solution.
In addition, single-crystals suitable for X-ray diffraction analysis
were grown by slow vapor diffusion of diethyl ether into a
saturated methanolic solution of the mixture of tetranuclear
rhodium metallarectangles 2a and 2b with a meta-C,N-bridging
coordination mode. A remarkable feature of the structure of 2a is
that one nitrogen atom from each pyrimidinyl moiety is “bare”, as
demonstrated by its solid-state structure (Figure 1).
Synthesis of decanuclear heterometallic macrocages and
hexanuclear prisms. In order to utilize the “bare” nitrogen atoms
in complex 2, potential coordination sites for further metal ions,
silver(I) was selected to bridge two metallarectangles 2 to form a
heterometallic macrocage. AgOTf (1.0 equiv.) was added with
exclusion of light to a solution of 2 (1.0 equiv.) in methanol. The
obtained mixture was stirred at ambient temperature to afford
complex 3. Red crystals of complex 3 were obtained in 92% yield
by slow diffusion of diethyl ether into a saturated solution of 3 in
methanol with exclusion of light (Scheme 3).
Figure 3. a) Chemical structure of hetermetallic macrocage 4; b) side view of
the cationic part of heterometallic macrocage 4. All triflate anions, solvent
molecules, and hydrogen atoms are omitted for clarity. Color code: N, blue; O,
orange; C, black; F, light green; Rh, red; Ag, violet.
Scheme 4. Construction of hexanuclear prisms 5 and 6.
Figure 2. a) Side and b) top view of the cationic part of heterometallic
macrocage 3. All triflate anions, solvent molecules, and hydrogen atoms are
omitted for clarity. Color code: N, blue; O, orange; C, black; Br, brown; Rh, red;
Ag, violet.and hydrogen atoms are omitted for clarity. Color code: N, blue; O,
orange; C, black; Br, brown; Rh, red.
Furthermore, with the aim of exploring the steric effects of the
ligands upon forming the heterometallic macrocages, ligands Na
and Na -L were introduced into this system under conditions
similar to those used for the previous frameworks. As shown in
Scheme S1, the related heterometallic macrocage was
-L
2
-
L
4
2
5
4
subsequently prepared based on ligand Na
2
-L
3
and ligand Na
2
4
Single-crystal X-ray crystallographic analysis of these crystals
confirmed the formation of a cage-shaped heterometallic complex
featuring RhIII and Ag ions (Figure 2). The molecular structure of
1
in a yield of 90% and was fully characterized by H NMR
spectroscopy, elemental analysis and X-ray diffraction analysis.
As shown in Figure 3, the crystallographically-derived molecular
structure of macrocage 4 is very similar to that of 3, as revealed
by crystallographic means. The size of metallacage 4 is ca.
I
III
the cationic part of 3 shows the eight Rh metal centers to occupy
the vertices of the metallacage. Whereas the rhodium(III) centers
adopt the classical piano-stool geometry typical for half-sandwich
rhodium complexes, the geometry around the silver(I) ions is best
1
0.0×6.0×8.0 Å (Rh···Rh separations) and the measured Ag···Ag
distance is ca. 8.7 Å.
Notably, a hexanuclear rhodium prism (5) was subsequently
prepared via synthetic route in the Scheme 4 in a yield of 93%
I
described as linear. The Ag metal centers are each bound to
nitrogen atoms of two pyrimidine-5-boronic acid-derived ligands.
In addition, the Cp*Rh fragments are coordinated to both ligands
based on ligands Na
2
-L
3
and Na
2
-L
5
with less steric hindrance.
2
-
-. The size of metallacage 3 is ca. 10.4×6.1×8.0 Å
L
1
and L
3
1
Prism 5 was fully characterized by H NMR spectroscopy,
elemental analysis and X-ray diffraction analysis. Due to the poor
quality of single crystals of prism 5, its structure was roughly
determined from an initially reduced structure through
(
Rh···Rh separations), while the Ag···Ag distance is ca. 7.7 Å.
1
The heteropolymetallic complex 3 was also characterized by H
NMR spectroscopy and elemental analysis. Since the 1H NMR
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crystallographic means (see the Supporting Information).
Although many efforts were made to follow the synthetic methods
used to prepare cages 3 and 4, the synthesis of a macrocage
new signals belonging to free PDBB and an encapsulated form
(PDBB⊂3). The H NMR spectrum showed two singlets at δ 7.44
1
and 6.55 ppm, which can be attributed to the protons of PDBB. A
1
based on ligand Na
2
-L
5
was unsuccessful, which may be
comparison with the H NMR spectrum of pure PDBB established
explained by the steric differences between the proton and
fluoride or bromide groups and its effect on the structure of
product. In addition, the formation of prism 5 prompted us to focus
on the effect of the length of the building blocks on the structure
of the resulting compounds, and an experiment based on the
shorter bridging ligand μ-Cl was performed following the synthetic
method used to prepare prism 5 (Scheme 4). Thereby, the
smaller prism 6 was obtained in a yield of 95% and was fully
that the singlet at δ 7.44 ppm belongs to free PDBB and the signal
at δ 6.55 ppm belongs to PDBB inside the metallacage (guest
state). Integration of the signals suggests that the host:guest ratio
is 1:1. The encapsulation of one molecule of PDBB by complex 3
1
was subsequently confirmed with a H DOSY NMR experiment
involving the host-guest system PDBB⊂3. The diffusion
-6
2
-1
coefficient of both the host and guest was D = 2.67 × 10 m s .
In addition, 2D EXSY experiments of a 2:1 sample of PDBB and
empty macrocage 3 allowed determination of the exchange rate
1
characterized by H NMR spectroscopy, elemental analysis and
X-ray diffraction analysis. It was subsequently found that prism 6
can also serve as a precursor to prism 5, in a yield of 96%.
−
1
of the guests (k ≈ 2.36 s ).
Figure 4. Space-filling representations of two prisms and two capsules. Cp*
rings, all triflate anions, solvent molecules, and hydrogen atoms are omitted for
clarity. Color code: N, blue; O, orange; C, black; F, bright green; Cl, green; Br,
brown; I, olive green; Ag, violet; Rh, red.
Scheme 5. Reversible encapsulation and release of dihaloaromatic compounds
with heterometallic assembly 3.
From these results in this work, it becomes clear that the
substituents on aromatic ligands play a crucial role in determining
the supramolecular structures of the products; i.e. fluoride,
bromide and chloride groups lead to heterometallic macrocages
while hydrogens lead to the formation of hexanuclear prism. This
can be attributed to the steric effects of the substituents and
further be regarded as a controllable method to prepare
compounds with targeted structures (Figure 4).
Table 1. Selected distances (Å) of heterometallic macrocages 3 and 4 and
host-guest complexes PDCB⊂3, PDBB⊂3 and PDIB⊂3.
Xa
Ag
1
···Ag
X···π
2
1
Ag ···π
Selective encapsulation of dihalobenzene derivatives.
Given the size of the cavity inside macrocages 3 and 4, we sought
to explore their host-guest properties. Therefore, we expected
that varying the aromatic substituents could enable the formation
of more capsules, in order to reveal their exact structures by X-
ray single-crystal analysis and to effect separation of para-
dihalobenzene derivatives. These two potential advances would
help gain a better understanding the driving force of encapsulation
as well as expanding the application of these heterometallic
capsules in the domain of separation.
Cage 4
Cage 3
-
-
8.66
7.72
7.50
7.50
7.58
-
-
-
-
PDCB⊂3
PDBB⊂3
PDIB⊂3
Cl
Br
I
3.37
3.37
3.33
3.76
3.67
3.52
[
a] X stands for the halogen atoms which belong to guest molecules (PDCB,
PDBB and PDIB), respectively.
Initially, an excess of para-dibromobenzene (PDBB) was
Single crystals suitable for X-ray diffraction were obtained by
slow vapor diffusion of diethyl ether into a methanol solution of
PDBB⊂3. Analysis of these crystals confirmed the presence of
one molecule of PDBB inside the heterometallic macrocage 3
3
added to a saturated solution of complex 3 in CD OD in an NMR
tube. The mixture obtained was stirred with exclusion of light at
room temperature for 10 min (Scheme 5). A subsequent NMR
spectroscopic analysis of the mixture revealed the appearance of
(
Figure 5). Comparison of the metric parameters for the complex
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3
and host-guest system PDBB⊂3 reveals variations in bond
lengths due to the encapsulation of guest PDBB. As shown in the
Table 1, the distance between the Ag and Ag atoms shortens
shortening of the distance between the two silver atoms (induced
by the Ag-π interaction between host and guest), as shown in
Table 1. Additionally, halogen-π interactions between host and
guest were observed in these two encapsulation compounds: the
Cl-π distance is ca. 3.76 Å and I-π distance is ca. 3.52 Å (the
distances are between halogen atoms and the centroid of
aromatic rings), which are within the range normally found in the
literature for this type of intermolecular interaction.[ A detailed
study of the chemical properties of PDBB⊂3 and PDIB⊂3 was
carried out, which suggested the high stability of the host-guest
system over time in solution and also in the solid state (in the
absence of ambient light).
1
2
from 7.72 Å to 7.50 Å, which may be respectively induced by the
Ag-π interaction between two silver atoms and one PDBB
molecule, and the apparent Br-π interaction[14] between the
bromine atoms of PDBB and the plane of nearby ligand L
1
(Table
14]
1). Most notably, the plane of guest molecule PDBB is not totally
parallel to the plane containing pyrimidine and a silver(I) ion; the
guest molecule exists in the host with a certain torsion angle
I
(
(
Figure 5). Interestingly, the N–Ag –N angle of PDBB⊂3 is 177.0°
173.0° for complex 3) which may be an effect of interactions
between silver ions and the PDBB molecule. Given that 3
appeared to be of suitable size to host PDBB and allow formation
of significant interactions between host and guest (Ag-π
interaction and Br-π interaction ), a detailed study of the
chemical properties of PDBB⊂3 was carried out, thereby
indicating the high stability of the host-guest system over time in
solution as well as the solid state (in the absence of ambient light).
The macrocage 4 was also treated with potential guest
molecules PDCB, PDBB and PDIB; however, no obvious change
was observed in the H NMR spectrum of the reaction mixture,
probably due to the inappropriate Ag···Ag distance (8.66 Å).
Moreover, as the distance between the two proximal fluorine
4 5
atoms (F and F atoms) becomes longer, the cavity becomes
1
1
4
less able to form a stable encapsulated structure.
I
In addition, the existence of two Ag metal ions in 3 prompted
us to study the light-induced degradation and subsequent
regeneration of the cage-shaped complex. A flask containing a 10
mL solution of host-guest system PDBB⊂3 in MeOH was
exposed to sunlight for 8 h and this reaction mixture was filtered.
The solvent amount was reduced to 1 mL under vacuum and
diethyl ether was added to precipitate a red solid, which was
filtered, washed with diethyl ether and dried to gain a red
1
crystalline solid. The H NMR spectrum of this red solid showed
signals corresponding to the tetranuclear rhodium(III)
metallarectangle 2. AgOTf (1.0 equiv. based on 2) and PDBB (0.5
equiv. based on 2) were then added with exclusion of light to the
NMR tube and the obtained mixture was stirred for 10 min,
resulting in the regeneration of the host-guest system PDBB⊂3.
Identical conclusions were also drawn from related experiments
involving PDCB or PDIB as guest molecules. Furthermore, the
addition of NaCl to an NMR tube containing a saturated solution
of PDBB⊂3 led to the formation of a white precipitate (AgCl),
which also led to release of the guest molecules. The addition of
AgOTf (1.0 equiv. based on 2) can then form the corresponding
encapsulated structures both in the solution and solid state, as
Figure 5. Side view of the cationic part of host-guest system PDBB⊂3: Ball-
and-stick representation of macrocage 3 and space-filling representation of
guest PDBB. All triflate anions, solvent molecules, and hydrogen atoms are
omitted for clarity. Color code: N, blue; O, orange; C, black; Br, brown; Ag, violet;
Rh, red.
Due to the successful formation of the host-guest complex
PDBB⊂3, we subsequently attempted to encapsulate other
dihalobenzene derivatives with metallacage 3. Para-
dichlorobenzene (PDCB) and para-diiodobenzene (PDIB) were
also found to be suitable guest molecules for 3, as confirmed by
1H and 1H DOSY NMR spectroscopy and X-ray diffraction
analysis. The resonances corresponding to PDCB and PDIB are
1
confirmed by H NMR spectroscopy and X-ray crystallography. In
the studies of the host-guest properties of macrocage 3 and 4
described above, we were delighted to find that the interactions
between guest molecules and macrocage 3 can induce structural
changes, which consequently affects the selectivity for these
dihaloaromatic benzene derivatives as guest molecules, as
illustrated in Table 1. Considering the considerable stability of
encapsulation compounds based on macrocage 3, we selected 3
as the template for separation of para-dihalobenzene from
mixtures of dihalobenzene isomers.
Selective encapsulation of dihalobenzene derivatives.
Taking advantage of the intriguing host-guest properties of
macrocage 3, a series of constitutional isomers containing ortho-,
meta- and para-dihalogenated benzene derivatives, such as
ortho-dichlorobenzene (ODCB), ortho-dibromobenzene (ODBB),
ortho-diiodobenzene (ODIB), meta-dichlorobenzene (MDCB),
meta-dibromobenzene (MDBB), meta-diiodobenzene (MDIB),
1
shifted downfield in the H NMR spectra upon encapsulation of
the compounds by macrocage 3, as has been previously
observed for PDBB. Furthermore, 2D EXSY experiments of a 2:1
sample of PDCB or PDIB and empty macrocage3 allowed
−
1
determination of the exchange rate of the guests (k ≈ 1.05 s for
PDCB⊂3 and k ≈ 1.88 s−1 for PDIB⊂3).
Slow vapor diffusion of diethyl ether into a methanol solution of
PDCB⊂3 and PDIB⊂3 yielded single crystals suitable for X-ray
diffraction analysis, confirming their guest-encapsulated
structures in the solid state (Figure S48). When comparing with
the structure of guest-free capsule 3, some structural changes of
these two encapsulation compounds were noted, including the
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para-dichlorobenzene (PDCB), para-dibromobenzene (PDBB)
and para-diiodobenzene (PDIB), were selected to separate para-
dihalogenated benzene derivatives from the remaining isomers
under mild conditions.
addition of AgOTf (1.0 equiv., based on complex 2) to the
methanol solution of 2, to realize the reversible encapsulation.
The structures of complex 2, macrocage 3 and PDBB⊂3 from this
separation process were furthermore confirmed by single-crystal
X-ray analysis after crystallization by comparison of their cell
parameters. Subsequently, PDCB and PDIB can be respectively
separated from the mixture of dichlorobenzene and
diiodobenzene derivatives by adopting similar methods under
ambient temperatures (Figure 6). Details of the experiments can
be found in Experimental Section.
Initially, reaction mixtures of experiments aimed at the selective
encapsulation of dihalobenzene derivatives were monitored via
NMR spectroscopy. After obtaining the desired result, we then
immediately carried out an experiment under the larger scale in
the lab. As shown in Figure 6, taking dibromobenzene derivatives
as an example, a mixture of ODBB, MDBB and PDBB in n-
hexane was added to a methanol solution of an excess of
heterometallic macrocage 3, and tetrahydrofuran (THF) was used
to further precipitate PDBB⊂3 after 10 min, leaving ODBB and
MDBB in the filtrate (liquid I). Then, PDBB can be extracted into
a new filtrate (liquid II) by leaving the methanol solution of
precitipate PDBB⊂3 under sunlight or adding NaCl (2.0 equiv.,
based on encapsulation compounds) and precipitating complex 2
Furthermore, application of the above-mentioned method
(Figure 6) allowed isolation of PDCB from a mixture of PDCB,
TRCB
(1,3,5-trichlorobenzene)
and
TECB
(1,2,4,5-
tetrachlorobenzene) under mild conditions. PDBB and PDIB can
also be respectively separated from a mixture of PDBB, TRBB
(1,3,5-tribromobenzene) and TEBB (1,2,4,5-tetrabromobenzene),
and PDIB and TRIB (1,3,5-triiodobenzene) derivatives using a
similar method.
with THF and Et
Moreover, heterometallic macrocage 3 can be regenerated by
2
O, as confirmed by 1H NMR spectroscopy.
Figure 6. Method for separation of para-dihalogenated benzene derivatives from their isomers.
Conclusions
We have reported the construction of a series of discrete Cp*Rh- Experimental Section
based metallosupramolecular architectures featuring stable
heteroarylrhodium(III) units, ranging from metallarectangles to
heterometallic macrocages and hexanuclear prisms, prepared by
heterocyclic boronic acids and rhodium precursors under mild
conditions. We then utilized the excellent host-guest abilities of
these macrocages, to enable selective, reversible encapsulation
of para-dihaloaromatic benzene derivatives and their separation
from their constitutional isomers under mild conditions. We hope
that these findings will promote further research into the
applications of discrete heterometallic macrocages in the
separation of complex mixtures, which could be useful in the
separation of high-value halogenated compounds, such as
isotopically labeled or radioactive derivatives.
General Procedures. All mentioned reagents and solvents were
purchased from commercial sources and used as supplied directly unless
otherwise mentioned. The starting materials [Cp*RhCl and 2,5-dibromo-
,6-dihydroxycyclohexa-2,5-diene-1,4-dione were synthesized according
2 2
]
3
to literature methods.[ 2,5-dibromo-3,6-dihydroxycyclohexa-2,5-diene-
,4-dione (H -L ), 2,5-difluoro-3,6-dihydroxycyclohexa-2,5-diene-1,4-
dione (H -L ) and 2,5-dihydroxycyclohexa-2,5-diene-1,4-dione (H -L
were treated with sodium methoxide in methanol to obtain ligands Na -L
Na -L and Na -L , respectively. NMR spectra were recorded on a Bruker
15]
1
2
1
2
4
2
5
)
2
1
,
2
4
2
5
AVANCE I 400 spectrometer. NMR spectra were recorded at room
temperature and referenced to the residual protonated solvent. Proton
chemical shifts are reported relative to the solvent residual peak (δ H =
3
3.31 for CD OD). Coupling constants are expressed in Hertz. Elemental
analyses were performed on an Elemental Vario EL III analyzer. ESI-MS
spectra were recorded on a Micro TOF II mass spectrometer. Adequate
1
3C NMR spectra of these compounds could not be obtained even after 24
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Chemistry - A European Journal
10.1002/chem.201805383
FULL PAPER
h due to their limited solubility in CD
3
OD.
stirred. The solvent was evaporated under vacuum and then 5 mL
methanol was added. Diethyl ether was then added to precipitate the red
solid, which was filtered, washed with diethyl ether and dried to obtain a
red crystalline solid. Yield: 80.5 mg, 93%. Anal. calcd for
Preparation of complex 1. A 30 mL methanol solution of [Cp*RhCl
1.0 equiv., 61.8 mg, 0.1 mmol) was treated with AgOTf (OTf = SO CF
.0 equiv., 102.3 mg, 0.4 mmol) in the dark for 6 h, followed by the addition
of ligand Na -L (1.0 equiv., 34.0 mg, 0.1 mmol), ligand B(OH) -L (1.0
2 2
]
(
4
3
3
,
C
90
H
102
F
12
N
4
O
24Rh
6
S
4
: C, 41.62; H, 3.96; N, 2.16. Found: C, 41.60; H,
OD, ppm): δ 8.33-8.28 (m, 6H,
-H), 1.76-1.73 (m, 90H, Cp*).
Preparation of complex 6. A 30 mL methanol solution of [Cp*RhCl
(1.0 equiv., 61.8 mg, 0.1 mmol) was treated with AgOTf (2.0 equiv., 51.2
mg, 0.2 mmol) in the dark for 6 h, followed by ligand B(OH) -L (1.0 equiv.,
2
1
2
2
1
3.98; N, 2.13. H NMR (400 MHz, CD
3
equiv., 12.3 mg, 0.1 mmol) and deionized water (2 mL), and this reaction
mixture was stirred in the dark for 24 h. The solvent was evaporated under
vacuum and then 5 mL methanol was added. Diethyl ether was added to
precipitate the red solid, which was then filtered, washed with diethyl ether
and dried to obtain a red crystalline solid. Yield: 89.9 mg, 90%. Anal. calcd
Pyrim-H), 5.57-5.48 (m, 6H, ligand L
5
2 2
]
2
3
for C64
H
68Br
4
F
6
N
2
O
14Rh
4
S
2
: C, 38.46; H, 3.43; N, 1.40. Found: C, 38.50;
OD, ppm): δ 7.65-7.63 (m, 4H,
12.4 mg, 0.1 mmol) and deionized water (2 mL), and this reaction mixture
was stirred. The solvent was evaporated under vacuum and then 5 mL
methanol was added. Diethyl ether was then added to precipitate the red
solid, which was filtered, washed with diethyl ether and dried to obtain a
red crystalline solid. Yield: 75.9 mg, 95%. Anal. calcd for
1
H, 3.40; N, 1.39. H NMR (400 MHz, CD
Py-H), 7.44-7.41 (m, 4H, Py-H), 1.65-1.60 (m, 60H, Cp*). ESI-TOF-MS:
m/z 849.89 (calcd for [M – 2OTf–]2+ 849.89), 1848.74 (calcd for [M – OTf–]+
3
1848.74).
C
72
H
96Cl
6
F
12
N
4
O
12Rh
6
S
4
: C, 36.09; H, 4.04; N, 2.34. Found: C, 36.11; H,
Preparation of complex 2. A synthetic procedure similar to that for
complex 1 was used to afford red crystalline solid complex 2, using AgOTf
1
4.01; N, 2.35. H NMR (400 MHz, CD
3
OD, ppm): δ 8.61-8.28 (m, 4H,
Pyrim-H), 8.55 (s, 2H, Pyrim-H), 1.69-1.64 (m, 90H, Cp*).
(
(
102.3 mg, 0.4 mmol), [Cp*RhCl
34.0 mg, 0.1 mmol) and ligand B(OH)
2
]
2
(61.8 mg, 0.1 mmol), ligand Na
-L (12.4 mg, 0.1 mmol). Yield: 87.0
: C, 37.22; H, 3.33; N,
.80. Found: C, 37.20; H, 3.36; N, 2.83. H NMR (400 MHz, CD OD, ppm):
δ 8.47 (br, 4H, Pyrim-H), 8.16 (s, 2H, Pyrim-H), 1.72-1.68 (m, 60H, Cp*).
2
-L
1
2
3
Reversible encapsulation and release of para-dihaloaromatic
compounds with macrocage 3.
mg, 87%. Anal. calcd for C62
H66Br
4
F
6
N
4
O
14Rh
4
S
2
1
2
3
General encapsulation process: in the dark, an excess of the guest
dihaloaromatic compound was added to a solution of macrocage 3 in
methanol and this mixture was stirred at ambient temperature. After 24 h
the resulting solution was concentrated to 1 mL under vacuum and diethyl
ether was added to precipitate the red solid, which was filtered, washed
with diethyl ether and dried to obtain a red crystalline solid (dihaloaromatic
compound⊂3).
–
2+
ESI-TOF-MS: m/z 850.89 (calcd for [M – 2OTf ] 850.89), 1850.73 (calcd
–
+
for [M – OTf ] 1850.73).
Preparation of complex 3. The heterometallic macrocage 3 can be
prepared by two different methods:
1) AgOTf (1.0 equiv., 12.8 mg, 0.05 mmol) was added to a methanol
solution of complex 2 (1.0 equiv., 100.0 mg, 0.05 mmol) and the mixture
was stirred in the dark for several hours. The solvent was evaporated
under vacuum and then 1 mL methanol was added. Diethyl ether was then
added to precipitate the red solid, which was filtered, washed with diethyl
ether and dried to obtain a red crystalline solid. Yield: 103.8 mg, 92%.
General release process: exposure of encapsulation compounds in 30
mL methanol solution under sunlight for 8 h, or addition of 2.0 equiv. NaCl
or NH Cl (based on encapsulation compounds) into the methanol solution
4
for 10 min, led to formation of mixtures containing tetranuclear
metallarectangle 2 and the guest molecules. The resulting solution was
then concentrated to 5 mL under vacuum and diethyl ether was added to
precipitate the red solid, which was filtered, washed with diethyl ether and
dried to obtain a red crystalline solid (metallarectangle 2).
2
) A 30 mL methanol solution of [Cp*RhCl
mmol) was treated with AgOTf (4.0 equiv., 102.3 mg, 0.4 mmol) in the dark
for 6 h, followed by the addition of ligand Na -L (1.0 equiv., 34.0 mg, 0.1
mmol), ligand B(OH) -L (1.0 equiv., 12.4 mg, 0.1 mmol), AgOTf (0.5
2 2
] (1.0 equiv., 61.8 mg, 0.1
2
1
2
3
General reversible process: an excess of the guest molecule (2.0
equiv. based on complex 2) and AgOTf (1.0 equiv. based on complex 2)
was added to a methanol solution of complex 2 prepared in the previous
step and the mixture was stirred in the dark about for 10 min. The resulting
solution was then concentrated to 1 mL under vacuum and diethyl ether
was added to precipitate the reddish solid, which was filtered, washed with
diethyl ether and dried to obtain a red crystalline solid (dihaloaromatic
compound⊂3).
equiv., 12.8 mg, 0.05 mmol) and deionized water (2 mL), and this reaction
mixture was stirred in the dark for 24 h. The solvent was evaporated under
vacuum and then 5 mL methanol was added. Diethyl ether was then added
to precipitate the red solid, which was filtered, washed with diethyl ether
and dried to obtain a red crystalline solid. Yield: 100.5 mg, 89%. Anal.
calcd for C126
C, 33.49; H, 2.96; N, 2.50. H NMR (400 MHz, CD
H
132Ag
2
Br
8
F
18
N
8
O
34Rh
8
S
6
: C, 33.52; H, 2.95; N, 2.48. Found:
1
3
OD, ppm): δ 8.72 (br,
8
H, Pyrim-H), 8.26 (s, 4H, Pyrim-H), 1.77-1.72 (m, 120H, Cp*).
Preparation of complex 4. The 30 mL methanol solution of [Cp*RhCl
1.0 equiv., 61.8 mg, 0.1 mmol) was treated with AgOTf (4.0 equiv., 102.3
mg, 0.4 mmol) in the dark for 6 h, followed by the addition of ligand Na -L
1.0 equiv., 22.0 mg, 0.1 mmol), ligand B(OH) -L (1.0 equiv., 12.4 mg, 0.1
Characterization details for PDCB⊂3 (7) follow. Yield: 91.8 mg, 98.5%.
2
]
2
Anal. calcd for C132
Found: C, 34.03; H, 3.97; N, 2.38. H NMR (400 MHz, CD
H
136Ag
2
Cl
2
Br
8
F
18
N
8
O
34Rh
8
S
6
: C, 34.00; H, 2.94; N, 2.40.
1
(
3
OD, ppm): δ
2
4
8.73-8.52 (m, 8H, Pyrim-H), 8.45 (s, 4H, Pyrim-H), 6.75 (s, 4H, PDCBinside-
H), 1.77-1.74 (m, 120H, Cp*).
(
2
3
mmol), AgOTf (0.5 equiv., 12.8 mg, 0.05 mmol) and deionized water (2
mL), and this reaction mixture was stirred in the dark for 24 h. The solvent
was evaporated under vacuum and then 5 mL methanol was added.
Diethyl ether was then added to precipitate the red solid, which was filtered,
washed with diethyl ether and dried to obtain a red crystalline solid. Yield:
Characterization details for PDBB⊂3 (8) follow. Yield: 91.2 mg, 96%.
Anal. calcd for C132
Found: C, 33.35; H, 2.90; N, 2.37. H NMR (400 MHz, CD
.74-8.53 (m, 8H, Pyrim-H), 8.46 (s, 4H, Pyrim-H), 6.87 (s, 4H, PDBB inside
H136Ag
2
Br10
F
18
N
8
O
34Rh
8 6
S
: C, 33.37; H, 2.89; N, 2.36.
1
3
OD, ppm): δ
8
-
H), 1.78-1.73 (m, 120H, Cp*).
9
0.6 mg, 90%. Anal. calcd for C126
H
132Ag
2
F
26
N
8
O
34Rh
8 6
S : C, 37.57; H,
1
Characterization details for PDIB⊂3 (9) follow. Yield: 94.0 mg, 97%.
3.30; N, 2.78. Found: C, 37.55; H, 3.28; N, 2.79. H NMR (400 MHz,
Anal. calcd for C132
Found: C, 32.73; H, 2.85; N, 2.30. H NMR (400 MHz, CD
.74-8.53 (m, 8H, Pyrim-H), 8.49 (s, 4H, Pyrim-H), 6.96 (s, 4H, PDIB inside
H), 1.77-1.74 (m, 120H, Cp*).
2
H136Ag Br
8
I
2 18
F
N
8
O
34Rh
8 6
S
: C, 32.72; H, 2.83; N, 2.31.
CD
(
3
OD, ppm): δ 8.66 (br, 8H, Pyrim-H), 8.19 (s, 4H, Pyrim-H), 1.75-1.70
m, 120H, Cp*).
Preparation of complex 5. A 30 mL methanol solution of [Cp*RhCl
1.0 equiv., 61.8 mg, 0.1 mmol) was treated with AgOTf (4.0 equiv., 102.3
-L
(0.67 equiv., 8.33 mg,
.067 mmol), and deionized water (2 mL), and this reaction mixture was
1
3
OD, ppm): δ
8
-
2 2
]
(
Separation of para-dihalobenzene derivatives from their isomers with
capsule 3.
mg, 0.4 mmol) in the dark for 6 h, followed by the addition of ligand Na
2
5
2
(1.0 equiv., 18.4 mg, 0.1 mmol), ligand B(OH) -L
3
0
General process: in the dark, a solution (20 mL) of capsule 3 (0.01
3
mmol/mL) in CH OH was added to mixture I, which consisted of ortho-
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Chemistry - A European Journal
10.1002/chem.201805383
FULL PAPER
dihalobenzene (0.2 mmol), meta-dihalobenzene (0.2 mmol), and para-
dihalobenzene (0.2 mmol) in 3 mL n-hexane. After being stirred at room
temperature for 10 min, the solution was allowed to stand and separate
into layers; the upper layer was colorless and the lower layer was deep
red. The lower layer was separated by a separating funnel, and then 100
mL of THF was added to produce a deep-red precipitate, which was
collected by filtration and dried. The filtrate, liquid I, contained ortho-
dihalobenzene and meta-dihalobenzene. A deep-red solid was obtained in
a yield of 95.1% (886.7 mg for PDCB⊂3), 96.3% (915.0 mg for PDBB⊂3)
and 94.3% (916 mg for PDIB⊂3).
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Leaving a 10 mL methanol solution of above-mentioned encapsulation
compounds under sunlight for ca. 12 h, or addition of NaCl (0.38 mmol for
PDCB⊂3, 0.39 mmol for PDBB⊂3 and 0.38 mmol for PDIB⊂3) to the
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[
[
4]
5]
THF and Et
red precipitate, which was collected by filtration and provided liquid II,
containing para-dihalobenzene. deep-red solid (complex 2) was
2 2
O (Volume, THF/Et O = 1:1) was added to achieve a deep-
A
obtained in a yield of 91.4% (696 mg for PDCB⊂3), 93.7% (722 mg for
PDBB⊂3) and 92.3% (703 mg for PDIB⊂3), which was based on the
product in the previous step. Subsequently, AgOTf (0.35 mmol for
PDCB⊂3, 0.39 mmol for PDBB⊂3 and 0.35 mmol for PDIB⊂3) was added
to the solution of complex 2 in the dark to form capsule 3, which can be
used in the next separation.
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X-ray crystal structure analysis
Single crystals of 1, 2, 3, 4, 6, 7, 8 and 9 suitable for X-ray diffraction study
were obtained at room temperature. X-ray intensity data of 1, 2, 4, 7, 8 and
9
were collected at 203 K on a CCD-Bruker SMART APEX system,
respectively, data of 3 and 6 was collected at 173 K on a Bruker D8
VENTURE system. In these data, the disordered solvent molecules that
could not be restrained properly were removed using the SQUEEZE route.
The single-crystal X-ray diffraction data of 1, 2, 3, 4, 6, 7, 8 and 9 have
been deposited in the Cambridge Crystallographic Data Centre under
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Acknowledgements
This work was supported by the National Science Foundation of China
(21531002, 21720102004) and the Shanghai Science Technology
2017, 23, 5193.
Committee (13JC1400600); G.-X. Jin thanks the Alexander von Humboldt
Foundation for a Humboldt Research Award.
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The authors declare no conflict of interest.
Keywords: Ag-π interaction • dihalobenzene isomers • halogen-
π interaction • heterometallic macrocages • selective
encapsulation • separation
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Chemistry - A European Journal
10.1002/chem.201805383
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Ag-π interactions and steric effects:
H.-N. Zhang, Y. Lu, W.-X. Gao, Y.-J. Lin,
G.-X. Jin*
III
I
two stable Rh /Ag mixed macrocages
have been obtained following a
multistep procedure and the
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exploration of cage in the separation
of dihalogenated benzene derivatives
with high selectivity.
Selective encapsulation and
separation of dihalobenzene isomers
with discrete heterometallic
macrocages
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