Self-Assembly and Catalytic Reactivity of BINOL-Bridged Bis(phenanthroline) Metallocages

Article abstract of DOI:10.1021/acs.inorgchem.7b02540

Upon treatment with Zn^II ions, a series of BINOL-bridged bis(phenanthroline) ligands was self-assembled into [M₂L₃] metallocages, which were carefully characterized by NMR spectroscopy and ESI-MS spectrometry. Among them,

Full text of DOI:10.1021/acs.inorgchem.7b02540

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Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX
pubs.acs.org/IC
Self-Assembly and Catalytic Reactivity of BINOL-Bridged
Bis(phenanthroline) Metallocages
Kai-Yu Cheng, Shi-Cheng Wang, Yu-Sheng Chen, and Yi-Tsu Chan*
Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
*
S Supporting Information
II
ABSTRACT: Upon treatment with Zn ions, a series of BINOL-
bridged bis(phenanthroline) ligands was self-assembled into
[
M L ] metallocages, which were carefully characterized by
2 3
NMR spectroscopy and ESI-MS spectrometry. Among them, a
racemic mixture of the BINOL-bridged bis(phenanthrolines)
underwent chiral self-sorting to afford two homochiral metal-
locages. The narcissistic self-sorting process of the metallocages
was observed in the complexation reaction of the constitutionally
isomeric bis(phenanthrolines) with varying connection positions.
Moreover, the endo hydroxyl-functionalized metallocage
OH
[
Zn {(S)-L2 }3] exhibited catalytic activity and substrate
2
selectivity for the Knoevenagel condensation reactions of aromatic
tricarbaldehydes with malononitrile.
35,36
INTRODUCTION
lenes
have been assembled into a single diastereomer
■
upon coordination to suitable transition-metal ions. BINOL is
one of the chiral motifs ubiquitously utilized to create an
optically active environment, and its inward hydroxyl groups
could be easily converted to various derivatives used in diverse
catalytic modes, such as metal complexes, hydrogen bonding,
Brønsted acids, and ion pairing. Incorporation of catalytically
active sites into supramolecular frameworks is a straightforward
method to confer catalytic functions. For instance, the
In the field of supramolecular chemistry, chemists are often
inspired by precise self-assembly of biological subunits into
1
−5
well-defined and functional structures.
tion-driven approach
and proper bond strength allows chemists to efficiently prepare
highly ordered architectures, such as grids, helicates,
The metal-coordina-
6
−11
providing predictable directionality
12
13,14
37
1
5,16
8,10,11,17
knots,
and polygons and polyhedra.
In recent years,
the focus of supramolecular coordination chemistry has
gradually shifted from the creation of aesthetic structures
toward exploiting potential functions in catalysis,
delivery, molecular recognition, and others. In order to
increase functionalities and complexities, the precise control of
the arrangement of different ligands into a single discrete
assembly has drawn tremendous research interest.
Self-sorting is a common strategy to do so and can be
considered as a spontaneous process by which building blocks
in a complicated mixture undergo self- and/or nonself-
18−20
enantioselective addition of Et Zn to aldehydes could be
2
drug
2
1
22
23
catalyzed by a combination of the Pt-alkynyl BINOL-based
i
metallotriangle and Ti(O Pr) , demonstrating that the confined
4
38
active sites led to enhanced product selectivity.
Herein, we bridge two 1,10-phenanthroline (phen) ligands
with BINOL at the 3- and 5-positions, respectively, for self-
assembly of metallocages, because the BINOL unit provides not
only axial chirality but also a potential substrate binding site for
catalysis. The self-assembly and self-sorting behavior of the
BINOL-bridged bis(phenanthrolines) are investigated. Inspired
by the catalytic Knoevenagel condensation reactions using
24−26
recognition to produce well-defined assemblies.
To realize
high-fidelity self-sorting within a multicomponent system, a
delicate balance between intra-/intermolecular interactions is
needed. Molecular chirality is one of the most prominent
driving forces for successful self-sorting, especially for tris-
chelate metal complexes with octahedral coordination geom-
etry, whose configurations can be remotely controlled by
3
9
40
metal−organic frameworks (MOFs), organic cages, and
41−43
metallocages
under mild conditions, the newly prepared
metallocage [Zn {(S)-L2 }3] was subjected to condensation
OH
2
27−29
stereocenters elsewhere within the scaffold.
Over the past
tests and showed distinctive catalytic activity and selectivity for
tricarbaldehyde substrates.
decades, many stereoselectively self-assembled helicates and
metallocages have been achieved by using enantiopure organic
ligands capable of propagating their chiral information to the
metal centers. Along this trend, enantiomerically pure ligands
based on 1,1′-bi-2-naphthol (BINOL),
derivatives, 9,9′-spirobifluorene, and dissymmetric al-
2
9
Special Issue: Self-Assembled Cages and Macrocycles
Received: October 3, 2017
30−32
̈
Troger’s base
3
3
34
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02540
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Inorganic Chemistry
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a
Scheme 1. Ligand Synthesis
a
Reagents and conditions: (i) ethynylphenanthroline, CuI, Pd(PPh ) , DIPA/DMF, 70 °C, 1−4 days; (ii) concentrated HCl(aq), dioxane, reflux, 1
3
4
h.
Scheme 2. Cartoon Representations for Enantiopure Bis(phenanthroline) Ligands
RESULTS AND DISCUSSION
HMQC spectra (Figures S12 and S13 in the Supporting
■
Information). In comparison with uncoordinated (S)-L1, the
̈
Synthesis of Ligands. Lutzen and co-workers have
9
characteristic upfield shifts for phen-H (δ 8.89 ppm, Δδ =
developed an efficient synthetic route to prepare a number of
bis(bipyridyl) BINOL ligands through the Sonogashira cross-
coupling reactions of 5-ethynyl-2,2′-bipyridine with 3,3′-diiodo-
2
−
0.29 ppm) and phen-H (δ 7.69 ppm, Δδ = −1.54 ppm) were
1
observed after the complexation reaction. The simple H NMR
3
0,31
pattern indicated that the metal centers in [Zn {(S)-L1} ] have
2
3
BINOL derivatives.
According to this synthetic strategy,
the same configuration (Δ,Δ or Λ,Λ) instead of forming a
mesocate with Δ,Λ configuration, which was also supported by
the opposite Cotton effects of the two enantiomeric complexes
in the circular dichroism (CD) spectra (Figure 1e). Attempts to
grow single crystals suitable for X-ray diffraction analysis were
unsuccessful. Thus, the absolute configurations were assigned
by computational methods. Among the three possible energy-
similarly a variety of BINOL-based bis(phenanthroline) ligands
can be generated, and the ligand geometry is tunable by varying
the ethynyl position on the phenanthroline unit (Scheme 1). In
this work, L1 was prepared in good yield by the Pd-catalyzed
Sonogashira coupling reaction of 5-ethynylphenanthroline with
1. The further deprotection of L1 under acidic conditions
afforded a ligand with two hydroxyl groups, but it showed poor
solubility after complexation. In order to improve the ligand
solubility, two n-octyl groups were incorporated at the 6,6′-
positions of (S)-BINOL by a Kumada coupling reaction.
Ligands (S)-L2 and (S)-L3 (Scheme 2) were synthesized from
diiodo precursor (S)-2 and then deprotected to generate (S)-
minimized structures, (Δ,Δ)-[Zn {(S)-L1} ] showed the
2
3
lowest energy (Table S1 in the Supporting Information),
presumably because the suitable configurations of the
octahedral complexes could release the torsional strain derived
from the mismatched configurations. A similar stereoselective
self-assembly has been reported for bipyridine-based triple-
OH
OH
L2 and (S)-L3 , respectively.
30
stranded helicates.
Complexation Reactions. The BINOL-bridged ligand (S)-
In addition to (S)-L1 and (R)-L1, a racemic mixture, rac-L1,
was also employed to examine the chiral self-sorting behavior.
L1 was treated with Zn(OTf) (3/2 ratio) in a CHCl /MeOH
2
3
mixed solvent (1/1, v/v) to afford the complex. The high-
resolution electrospray ionization (ESI) mass spectrum of the
resultant complex revealed three intense signals corresponding
to the ions of [Zn {(S)-L1} ] with charge states ranging from
In principle, rac-L1 may produce four different isomers upon
II
coordination to Zn ions, including [Zn
{(R,R,R)-L1
}], and [Zn {(S,S,R)-
}]. When rac-L1 was mixed with Zn ions in a ratio of 3/
}],
2
3
[Zn
L1
2, the exact same H NMR signals as those for [Zn
{(S,S,S)-L1
}], [Zn
{(R,R,S)-L1
2
3
2
3
2
3
2
1
II
2
+ to 4+ (Figure S15 in the Supporting Information). The H
3
1
NMR spectrum of [Zn {(S)-L1} ] (Figure 1c) exhibited only
2
{(S)-L1} ]
3
2
3
one set of peaks for the phenanthroline units, and the DOSY
spectrum (Figure S14 in the Supporting Information)
were observed (Figure 1d), strongly supporting that the
reaction underwent completely chiral narcissistic self-sorting
to generate a racemic mixture of metallocages, [Zn {(R)-L1} ]
suggested the formation of a single species in a CDCl /
3
2
3
1
CD OD mixture (1/1, v/v). The complete H NMR
and [Zn {(S)-L1} ], which was also evident from its silent CD
3
2 3
assignments were further confirmed by COSY, NOESY, and
spectrum (Figure 1e).
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1
Figure 1. (a) Self-assembly of [Zn {(S)-L1} ] and the chiral self-sorting process. H NMR spectra of (b) (S)-L1 in CDCl and (c) [Zn {(S)-L1} ]
2
3
3
2
3
and (d) [Zn {(rac)-L1} ] in CDCl /CD OD (1/1, v/v). (e) CD spectra of [Zn {(S)-L1} ], [Zn {(R)-L1} ], and [Zn {(rac)-L1} ] in CHCl /
2
3
3
3
2
3
2
3
2
3
3
MeOH (1/1, v/v).
Upon complexation of (S)-L2 with ZnII ions, the
spontaneous formation of the desired [Zn {(S)-L2} ] was
found, as evidenced by the NMR experiments (Figure 2b and
Figures S16−S19 in the Supporting Information) and the
characteristic ESI-MS peaks as well as the explicit isotope
patterns (Figure S20 in the Supporting Information). On the
other hand, (S)-L3 is a constitutional isomer of (S)-L2, which
these two metallocages, ESI interfaced with traveling wave ion-
mobility mass spectrometry (TWIM-MS) was utilized to obtain
2
3
4
4−48
the corresponding collision cross sections (CCSs).
Although [Zn {(S)-L2} ] and [Zn {(S)-L3} ] have the same
2
3
2
3
molecular weight, the TWIM-MS analyses (Figure S36 in the
Supporting Information) showed that they exhibited distin-
guishable drift time distributions for the triply and quadruply
charged ions. In addition, the average experimental CCS of
has a connection at the phenanthrolinyl 3-position. Similarly,
II
2
(
S)-L3 was treated with Zn ions in a 3/2 ratio to afford
[Zn {(S)-L2} ] (616.3 ± 12.8 Å ) derived from the calibration
2
3
2
[
Zn {(S)-L3} ] in quantitative yield. COSY and NOESY
curve is larger than that of [Zn {(S)-L3} ] (492.8 ± 10.2 Å ),
2
3
2 3
experiments (Figures S22 and S23 in the Supporting
Information) were conducted to ensure the proper H NMR
assignments (Figure 2c). The computational energy-minimized
structures (Figure 3) suggested that the constitutional isomers
indicating that [Zn {(S)-L3} ] has a more compact geometry.
2 3
These results are in good agreement with the theoretical values.
To explore the self-sorting behavior of the isomeric ligands,
1
equimolar amounts of (S)-L2 and (S)-L3 in CHCl were
3
(S)-L2 and (S)-L3 led to self-assembled metallocages with
treated with a MeOH solution of Zn(OTf) , and the mixture
2
distinct shapes. Notably, the molecular geometry of [Zn {(S)-
was stirred at 25 °C for 30 min. After the resultant complexes
2
−
1
L3} ] is analogous to those of the reported triple-stranded
were counterion-exchanged with PF , the H NMR spectrum
3
6
3
0,35
helicates.
In order to gain more structural insights into
taken in CDCl /CD OD (5/1, v/v) displayed two distinct sets
3
3
C
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1
Figure 2. (a) Illustration of the narcissistic self-sorting process for complexation of (S)-L2 and (S)-L3. H NMR spectra of (b) [Zn {(S)-L2} ], (c)
2
3
[
Zn {(S)-L3} ], and (d) the self-sorted complexes. (e) ESI-TWIM-MS plots of the self-sorted complexes.
2 3
Figure 3. Energy-minimized structures of (a) [Zn {(S)-L2} ] and (b) [Zn {(S)-L3} ]. The n-octyl groups are omitted for clarity.
2
3
2
3
of signals assigned to [Zn {(S)-L2} ] and [Zn {(S)-L3} ],
respectively (Figure 2d), demonstrating a high-fidelity narcis-
sistic self-sorting process. The mixture generated from the self-
sorting experiment was analyzed with ESI-TWIM-MS to
2
3
2
3
D
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Figure 4. H NMR spectra of (a) (S)-L2 , (b) [Zn {(S)-L2OH}3], (c) (S)-L3OH, and (d) [Zn {(S)-L3 } ]. ESI-MS spectra of (e) [Zn {(S)-
1
OH
OH
2
2
3
2
OH
OH
L2 } ] and (f) [Zn {(S)-L3 }3].
3
2
differentiate the isomeric metallocages. It is worth noting that
(Figure 4d), and similarly the trimeric composition was
the TWIM-MS plot (Figure 2e) showed two separate drift time
supported by ESI-MS (Figure 4f).
3+
49
distributions for the triply charged species [[M L ]·(PF )] .
Catalytic Reactivity. The Knoevenagel condensation,
a
2
3
6
Two drift times at 9.70 and 13.45 ms corresponding to
modified aldol condensation reaction, is a nucleophilic addition
between a carbonyl group and an active hydrogen compound
followed by dehydration. Hence, it is challenging to perform
3
+
3+
[
Zn {(S)-L3} ] and [Zn {(S)-L2} ] , respectively, were
2 3 2 3
consistent with the previous observation for the individual
metallocage (Figure S36 in the Supporting Information).
the Knoevenagel condensation reactions under neutral and
OH
OH
OH
Deprotected ligands (S)-L2 and (S)-L3 were reacted
hydrous conditions. Since [Zn {(S)-L2 }3] is a triple-stranded
2
with Zn(OTf) to give the hydroxyl-functionalized metallocages
cage possessing three pairs of inward hydroxyl groups, it may
potentially interact with a trifunctional Knoevenagel con-
densation substrate, such as 1,3,5-benzenetricarbaldehyde (3),
to enhance the carbonyl electrophilicity. When 3 was treated
2
OH
OH
[
Zn {(S)-L2 } ] and [Zn {(S)-L3 } ] respectively, which
2 3 2 3
1
were fully characterized by NMR and ESI-MS. The H NMR
OH
spectrum of [Zn {(S)-L2 }3] (Figure 4b) exhibited a
2
significant upfield shift (δ 7.55 ppm, Δδ = −1.52 ppm) for
with 6 equiv of malononitrile and 10 mol % of [Zn {(S)-
2
2
OH
OH
phen-H in comparison to uncomplexed (S)-L2 , confirming
L2 } ] in CDCl /CD CN (5/2, v/v) at room temperature,
3
3
3
the formation of the octahedral complex [Zn(phen) ]. The
the Knoevenagel condensation product was obtained in 93%
yield after 2 days (Table 1, entry 3). In general, the
Knoevenagel condensation reactions are conducted under
3
[
M L ] composition was further verified by three major ESI-
2 3
MS peaks at m/z 1587.1195, 1008.4341, and 719.1054 derived
50
from the 2+ to 4+ ions, respectively (Figure 4e). Even though
basic conditions in anhydrous media to offer good yields.
OH
OH
the solubility of (S)-L3 in CHCl is poor, [Zn {(S)-L3 } ]
In contrast, in this test, the reaction took place under nonbasic
and hydrous conditions. Therefore, a series of control
experiments was conducted to confirm the catalytic activity of
3
2
3
has moderate solubility in a mixed solvent of CHCl and
3
1
MeCN (5/1, v/v). The H NMR spectrum of [Zn {(S)-
2
OH
OH
L3 } ] also showed a characteristic upfield shift (δ 7.92 ppm,
[Zn {(S)-L2 } ] (Table 1). In the absence of [Zn {(S)-
3
2
3
2
2
II
OH
Δδ = −1.28 ppm) for phen-H after coordination to Zn ions
L2 }3], entry 1 gave a yield of 4% under the same reaction
E
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Table 1. Catalyst Tests for Knoevenagel Condensation
Reactions
source of catalytic activity. Hence, it was envisioned that the
hydroxyl groups densely localized in the interior of the cage
allowed the substrate first to be included in the cavity through
hydrogen bonding to enhance the carbonyl electrophilicity and
then to be attacked by a nucleophile.
a
Additionally, the catalyst recycling experiments of [Zn {(S)-
2
OH
L2 }3] were carried out for the condensation reaction of 3
and malononitrile (Figure S39 in the Supporting Information).
After the reaction, the product was precipitated from the
solution, which could be easily removed by filtration. The
filtrate containing the catalyst was employed in the next cycle.
entry
catalyst
amt (mol %)
yield (%)
1
2
3
4
5
6
7
8
none
4
6
[Zn {(S)-L2} ](OTf)
10
10
10
30
30
20
20
OH
2
3
4
The results demonstrated that metallocage [Zn {(S)-L2 } ]
2
3
OH
[Zn {(S)-L2 }3](OTf)
93
<1
4
2
4
4
could be reused at least twice without dramatically losing its
catalytic reactivity.
The interaction of the metallocage with 3 was verified by
OH
[Zn {(S)-L3 }3](OTf)
2
BINOL
OH
(S)-L2
97
5
means of UV/vis spectroscopy in CHCl /MeCN (5/2, v/v).
3
Zn(OTf)2
Upon gradual addition of 3 into a solution of [Zn {(S)-
2
[Zn(phen) ](OTf)
7
OH
3
2
L2 } ], the intensity of the absorption band at 354 nm slightly
decreased as the molar ratio of [Zn {(S)-L2 }3]/3 was
3
a
OH
All reactions were perfomed in a CDCl /CD CN mixed solvent (5/2,
v/v) at room temperature. Reagent concentrations: 3 (0.04 M) and
3
3
2
changed from 1/0 to 1/22. On the basis of the UV/vis titration
experiment (Figure S40 in the Supporting Information), the
CH (CN) (0.24 M). The yields were determined after 2 days from
2
2
1
H NMR peak integration by using 1,2,4,5-tetramethylbenzene as an
internal standard.
association constant (K ) was determined to be (1.1 ± 0.2) ×
a
5
−1
1
0 M by using a 1/1 isotherm model and nonlinear least-
squares curve fitting (Figure S41 in the Supporting
5
1
Information). The titration experiment was also monitored
conditions. To confirm the function of the hydroxyl groups
within the metallocage, the reaction was performed with 10 mol
1
by H NMR. The signal for the hydroxyl groups gradually
disappeared with increasing concentration of 3, suggesting that
the proton was in a fast exchange with the substrate (Figure
S42 in the Supporting Information).
%
of [Zn {(S)-L2} ] bearing no hydroxyl groups. The resulting
2 3
yield of less than 6% (entry 2) was observed. On the basis of
OH
the results (Table 1, entries 1−3), only [Zn {(S)-L2 } ]
2
3
showed catalytic activity, suggesting that the hydroxyl groups
To investigate the substrate selectivity, a number of aromatic
tricarbaldehydes were chosen for the Knoevenagel condensa-
tion (Table 2). Intriguingly, the yield for methyl-substituted
substrate 4 was only 6% even after 5 days, indicating that the
methyl substituents might reduce the electrophilicity of the
formyl groups (Figure S48 in the Supporting Information)
and/or interrupt the interactions between the formyl groups
and the hydroxyl groups within the confined space (Figure S43
in the Supporting Information). Building on this observation,
were required for the condensation reaction. In entry 4, the
OH
more compact metallocage [Zn {(S)-L3 }3] composed of
2
three transoid-BINOL units did not show significant reactivity,
indicating that not only hydroxyl groups but also cisoid
conformations of BINOL (Figure S47 in the Supporting
Information) were essential for the reaction, and the cavity size
might also contribute to the reactivity. Moreover, control
experiments with the subunits of the metallocage were
OH
conducted, including BINOL, (S)-L2 , Zn(OTf) , and
an equimolar mixture of 3 and 4 was treated with malononitrile
in the presence of [Zn {(S)-L2 }3] to realize selective
catalysis. Indeed, only substrate 3 was reacted to afford a
2
OH
[
(
Zn(phen) ]. BINOL alone did not catalyze the reaction, but
3
2
OH
S)-L2
revealed reactivity due to the basic phen motifs
(
Table 1, entries 5 and 6; vide infra). The low yields in entries 7
95% yield of the condensation product. The control experiment
done by using phen or (S)-L2 as a base catalyst showed no
selectivity for 3 and 4, in which both substrates were converted
OH
and 8 excluded the assumption that the labile metal−ligand
coordinative interactions in the metallocage might be a possible
a
Table 2. Knoevenagel Condensation Reactions of Tricarbaldehydes
entry
substrate
yield (%)
1
2
3
4
3
4
5
6
95
6
<1
<1
a
All reactions were perfomed in a CDCl /CD CN mixed solvent (5/2, v/v) at room temperature for 5 days. Reagent concentrations: substrate (0.04
3
3
OH
1
M), [Zn {(S)-L2 } ] (4.1 mM), and CH (CN) (0.24 M). The yields were determined from H NMR peak integration by using 1,2,4,5-
2
3
2
2
tetramethylbenzene as an internal standard.
F
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to the condensation products (Figure S44). To examine size
selectivity in this catalytic system, tricarbaldehydes 5 and 6 with
larger molecular sizes were subjected to the same reaction
conditions. As expected, no reaction took place with these
tricarbaldehydes (Table 2, entries 3 and 4).
(d, J = 5.9 Hz, 2H), 5.03 (d, J = 5.9 Hz, 2H), 2.75 (t, J = 7.2, 4H), 2.61
(
s, 6H), 1.72−1.63 (m, 4H), 1.20−1.40 (20H), and 0.87 (t, J = 6.9 Hz,
6
1
1
9
1
H). 13C NMR (100 MHz, CDCl ): δ (ppm) 152.05, 150.83, 150.60,
3
46.03, 145.80, 140.48, 135.74, 134.81, 134.15, 132.49, 130.64, 130.48,
29.31, 128.16, 127.94, 126.37, 125.96, 125.79, 119.94, 116.56, 98.97,
2.56, 89.85, 56.24, 35.73, 31.74, 30.99, 29.35, 29.25, 29.14, 22.54, and
+
3.99. ESI-MS (m/z): 1003.5134 [M + H] (calcd m/z 1003.5162).
CONCLUSIONS
Synthesis of (S)-L3. By a protocol similar to that for (S)-L1, (S)-
■
L3 was obtained after 4 days in 25% yield (175.3 mg, 0.17 mmol) from
(S)-2 (598.0 mg, 0.7 mmol), 3-ethynylphenanthroline (365.3 mg, 1.8
mmol), Pd(PPh ) (92.4 mg, 80.0 μmol), CuI (30.4 mg, 0.2 mmol),
A series of BINOL-bridged bis(phenanthroline) ligands has
been successfully synthesized. The assembly of (S)-L1 with Zn
II
3
4
ions gave rise to the metallocage (Δ,Δ)-[Zn {(S)-L1} ] in
2
3
1
and DIPA/DMF (1/1, v/v, 20 mL). H NMR (400 MHz, CDCl ): δ
II
3
quantitative yield. When rac-L1 was mixed with Zn ions, the
ligands underwent chiral self-sorting to generate two
homochiral metallocages. On the other hand, the mixture of
(
ppm) 9.31 (d, J = 0.8 Hz, 2H), 9.21 (d, J = 4.4 Hz, 2H), 8.40 (d, J =
.8 Hz, 2H), 8.30−8.23 (m, 4H), 7.83 (d, J = 8.9 Hz, 2H), 7.78 (d, J =
.9 Hz, 2H), 7.68−7.60 (m, 4H), 7.19 (s, 4H), 5.18 (d, J = 6.1 Hz,
0
8
II
ligands (S)-L2 and (S)-L3 was complexed with Zn ions to
2H), 4.97 (d, J = 6.2 Hz, 2H), 2.73 (t, J = 7.6 Hz, 4H), 2.60 (s, 6H),
afford self-sorted isomeric metallocages [Zn {(S)-L2} ] and
1.79−1.65 (m, 4H), 1.40−1.21 (m, 20H), and 0.85 (t, J = 6.7 Hz, 6H).
2
3
13
[
Zn {(S)-L3} ], which could be easily identified by TWIM-MS
C NMR (100 MHz, CDCl ): δ (ppm) 152.62, 152.32, 150.69,
3
2
3
analysis. The improved ligand solubility through incorporating
145.84, 144.75, 140.70, 138.26, 136.64, 134.49, 132.82, 130.78, 129.64,
29.24, 128.08, 127.58, 126.75, 126.45, 126.30, 126.14, 123.63, 120.07,
1
n-octyl groups facilitated the formation of two hydroxyl-
OH
116.65, 99.38, 91.55, 90.61, 56.50, 36.07, 32.10, 31.34, 29.70, 29.60,
29.49, 22.90, and 14.35. ESI-MS (m/z): 1003.5653 [M + H] (calcd
functionalized metallocages [Zn {(S)-L2 } ] and [Zn {(S)-
2
3
2
+
OH
OH
L3 } ]. Interestingly, only [Zn {(S)-L2 }3] exhibited
3
2
m/z 1003.5162).
catalytic reactivity for the Knoevenagel condensation reactions
to a series of tricarbaldehyde substrates with malononitrile
under mild conditions, and the catalyst recycling was
demonstrated. On the basis of the control experiments, both
the cage structure and cisoid-hydroxyl conformation were
essential for catalyzing the Knoevenagel condensation.
Eventually, the substrate selectivity in the catalytic condensa-
tion was achieved by this unique metallocage. We believe our
findings may pave an avenue toward the rational design of
supramolecular catalysts.
Synthesis of (S)-L2OH. To a stirred solution of (S)-L2 (100.0 mg,
9.7 μmol) in dioxane (10 mL) was added HCl(aq) (0.2 mL)
9
dropwise at room temperature, and the reaction mixture was refluxed
for 1 h. After it was cooled to 25 °C, the reaction mixture was poured
into water to remove dioxane. The precipitates were collected and
then extracted by DCM and water. The organic layer was washed with
brine and 1% K CO (aq), dried over MgSO , and evaporated to
2
3
4
dryness under reduced pressure to give a yellow product in 99% yield
1
(
91.2 mg, 98.7 μmol). H NMR (400 MHz, CDCl ): δ (ppm) 9.07 (d,
3
J = 4.3, 2H), 8.89−8.84 (m, 4H), 8.19 (d, J = 8.2 Hz, 2H), 8.09 (s,
H), 7.61(s, 2H), 7.57−7.70 (m, 4H), 7.19 (d, J = 8.6 Hz, 2H), 7.13
d, J = 8.6 Hz, 2H), 2.72 (t, J = 7.6 Hz, 4H), 1.72−1.62 (m, 4H),
4
(
EXPERIMENTAL SECTION
13
■
1.39−1.21 (m, 20H), and 0.85 (t, J = 6.0 Hz, 6H). C NMR (100
MHz, CDCl ): δ (ppm) 152.95, 150.39, 150.32, 145.83, 145.62,
Synthesis of (S)-L1. In a flask containing (S)-1 (2.7 g, 4.5 mmol)
and 5-ethynylphenanthroline (2.0 g, 9.8 mmol) was placed DIPA/
DMF (1/1, v/v, 80 mL). After being degassed by freeze−pump−thaw
for three cycles, Pd(PPh ) (520.0 mg, 0.5 mmol) and CuI (171.4 mg,
3
139.08, 136.00, 135.61, 133.63, 132.69, 130.23, 129.90, 129.09, 128.73,
128.21, 126.71, 125.06, 123.56, 123.43, 120.52, 114.78, 113.52, 92.88,
90.59, 67.37, 36.04, 32.22, 31.65, 29.84, 29.62, 23.00, and 14.46. ESI-
3
4
+
0
.9 mmol) were added to the mixture, which was then stirred at 70 °C
MS (m/z): 937.4523 [M + Na] (calcd m/z 937.4522).
Synthesis of (S)-L3 . By the same protocol as that for (S)-L2OH,
OH
for 1 day under N . After it was cooled to 25 °C, the mixture was
poured into water for removal of amine and DMF. The precipitates
2
OH
(S)-L3 was obtained in 99% yield (36.5 mg, 39.5 μmol) from (S)-
1
were filtered and then extracted by DCM and NH Cl(aq). The
L3 (40.0 mg, 39.9 μmol), dioxane (5 mL), and HCl(aq) (0.1 mL). H
4
combined organic layer was washed with brine, dried over MgSO , and
NMR (400 MHz, DMSO-d ): 9.27 (s, 2H), 9.12 (d, J = 3.6, 2H), 9.04
6
4
then evaporated to dryness under reduced pressure to give the
product, which was subsequently purified by column chromatography
(s, 2H), 8.76 (s, 2H), 8.51 (s, J = 8.0, 2H), 8.70 (s, 2H), 8.07−7.98
(m, 4H), 7.79 (dd, J = 7.6, 4.0, 2H), 7.72 (s, 2H), 7.16 (d, J = 8.4, 2H),
6.88 (d, J = 8.4, 2H), 2.65 (t, J = 7.2, 4H), 1.66−1.53 (m, 4H), 1.36−
(
SiO , MeOH/DCM = 1/50−1/20, v/v) to afford (S)-L1 as a yellow
2
1
13
solid in 75% yield (2.6 g, 3.4 mmol). H NMR (400 MHz, CDCl ): δ
1.14 (m, 20H), and 0.8 (t, J = 6.8, 6H). C NMR (100 MHz, DMSO-
3
(
8
(
8
ppm) 9.23 (d, J = 4.4 Hz, 2H), 9.18 (d, J = 4.4 Hz, 2H), 8.97 (d, J =
.2 Hz, 2H), 8.40 (s, 2H), 8.23 (d, J = 8.1 Hz, 2H), 8.13 (s, 2H), 7.93
d, J = 8.1 Hz, 2H), 7.74 (dd, J = 8.2 Hz, 4.3 Hz, 2H), 7.66 (dd, J =
.0, 4.4 Hz, 2H), 7.49 (t, J = 8.0 Hz, 2H), 7.38 (t, J = 8.4, 2H), 7.30 (d,
d ): δ (ppm) 152.15, 151.44, 150.36, 145.12, 144.11, 138.29, 137.66,
6
136.53, 133.32, 132.81, 129.16, 129.02, 128.20, 127.78, 126.44, 126.38,
124.39, 123.77, 119.13, 115.70, 112.64, 91.20, 90.75, 35.04, 31.35,
30.98, 28.94, 28.84, 28.75, 22.14, and 14.01. ESI-MS (m/z): 937.4579
+
J = 8.5 Hz, 2H), 5.22 (d, J = 6.2 Hz, 2H), 5.05 (d, J = 5.8 Hz, 2H), and
[M + Na] (calcd m/z 937.4522).
2
1
1
9
.59 (s, 6H). 13C NMR (100 MHz, CDCl ): δ (ppm) 153.10, 151.26,
50.99, 146.42, 146.17, 136.09, 135.10, 135.06, 134.33, 131.11, 130.59,
28.70, 128.39, 128.03, 126.80, 126.18, 123.75, 120.14, 117.08, 99.35,
General Procedures for Complexation. (A) To a stirred
solution of metal salts in MeOH was added a solution of ligands in
3
CHCl
dried in vacuo. (B) To a stirred solution of metal salts in MeOH was
added a solution of ligands in CHCl . After the mixture was stirred at
directly. The mixture was stirred at 25 °C for 30 min and then
3
2.56, 90.45, 56.57, 24.51, 19.99, and 13.95. ESI-MS (m/z): 779.2760
+
[
M + H] (calcd m/z 779.2658).
3
Synthesis of (R)-L1 and rac-L1. (R)-L1 and rac-L1 were obtained
in 87% and 77% yields, respectively, by using the same protocol as that
for (S)-L1.
25 °C for 30 min, a slight excess of NH PF (>30 equiv with respect to
4 6
−
OTf ) was added to precipitate the counterion-exchanged complex
−
(PF ), which was filtered, washed with H O, and then dried in vacuo.
6
2
Synthesis of (S)-L2. By a protocol similar to that for (S)-L1, (S)-
Synthesis of [Zn {(S)-L1} ](OTf) . By general procedure A,
2 3 4
L2 was obtained after 4 days in 81% yield (1.9 g, 1.9 mmol) from (S)-
[Zn {(S)-L1} ](OTf) was obtained in 99% yield (39.0 mg, 12.8
2
3
4
2
(2.0 g, 2.4 mmol), 5-ethynylphenanthroline (1.1 g, 5.3 mmol),
μmol) from (S)-L1 (30.0 mg, 38.5 μmol), Zn(OTf) (9.3 mg, 25.6
2
1
Pd(PPh ) (288.9 mg, 0.3 mmol), CuI (95.2 mg, 0.5 mmol), and
DIPA/DMF (1/1, v/v, 80 mL). H NMR (400 MHz, CDCl ): δ
μmol), CHCl (5 mL), and MeOH (5 mL). H NMR (400 MHz,
3
4
3
1
CDCl /CD OD, 1/1, v/v): δ (ppm) 9.56 (d, J = 8.5 Hz, 6H), 8.89 (d,
3
3
3
(
8
8
ppm) 9.25 (d, J = 4.3 Hz, 2H), 9.20 (d, J = 4.3 Hz, 2H), 8.98 (d, J =
.2, 2H), 8.32 (s, 2H), 8.25 (d, J = 8.2, 2H), 8.14 (s, 2H), 7.77 (dd, J =
.2, 4.4 Hz, 2H), 7.69 (s, 2H), 7.68−7.64 (m, 2H), 7.22 (s, 4H), 5.18
J = 4.8, 6H), 8.80 (d, J = 8.4 Hz, 6H), 8.49 (s, 6H), 8.43 (s, 6H), 8.02
(dd, J = 8.0, 4.8 Hz, 6H), 7.97 (d, J = 8.4 Hz, 6H), 7.92 (dd, J = 8.0,
4.8 Hz, 6H)), 7.69 (d, J = 4.8 Hz, 6H), 7.32 (t, J = 8.4, 6H), 7.38 (t, J
G
DOI: 10.1021/acs.inorgchem.7b02540
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
=
8.6, 6H), 6.95 (d, J = 8.5 Hz, 6H), 4.83−4.76 (m, 12H), and 2.55 (s,
3
ASSOCIATED CONTENT
■
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02540.
8H). 1 C NMR (400 MHz, CDCl /CD OD, 1/1, v/v): δ (ppm)
1
1
1
1
4
8
3
3
S
52.7, 149.6, 149.5, 140.9, 140.3, 139.9, 139.6, 135.1, 134.3, 130.5,
29.9, 129.8, 128.3, 128.2, 127.4, 126.6, 126.2, 126.1, 125.3, 121.9,
90.0, 116.3, 99.2, 96.2, 88.8, and 56.5. ESI-MS (m/z): 616.8119 [M −
OTf]4 (calcd m/z 616.9082), 872.0793 [M − 3OTf] (calcd m/z
+
3+
2+
72.1949), and 1382.1121 [M − 2OTf] (calcd m/z 1382.2683).
Detailed experimental procedures and characterization
data for ligands and complexes and Schemes S1−S6,
Figures S1−S48, and Table S1 (PDF)
Synthesis of [Zn {(S)-L2} ](PF ) . By general procedure B, [Zn {(S)-
2
3
6 4
2
L2} ](PF ) was obtained in 90% yield (33.4 mg, 9.0 μmol) from (S)-
L2 (30 mg, 29.9 μmol), Zn(OTf) (7.2 mg, 19.9 μmol), CHCl (5
mL), MeOH (5 mL), and NH PF . H NMR (400 MHz, CDCl /
3
6 4
2
3
1
4
6
3
CD OD, 5/1, v/v): δ (ppm) 9.49 (d, J = 8.3 Hz, 6H), 8.89 (d, J = 4.5
Hz, 6H), 8.62 (d, J = 8.2 Hz, 6H), 8.35 (s, 6H), 8.27 (s, 6H), 8.0 (dd, J
AUTHOR INFORMATION
3
■
Corresponding Author
E-mail for Y.-T.C.: ytchan@ntu.edu.tw.
=
8.4, 3.6 Hz, 6H), 7.89 (m, dd, J = 8.4, 3.6 Hz, 6H), 7.70 (d, J = 4.1
*
Hz, 6H), 7.65 (s, 6H), 7.21−7.13 (m, 12H), 4.75−4.71 (m, 12H), 2.70
(
(
t, J = 7.2 Hz, 12H), 2.49 (s, 18H), 1.66−1.58 (m, 12H), 1.34−1.12
ORCID
13
m, 60H), and 0.78 (t, J = 6.8 Hz, 18H). C NMR (100 MHz,
Yi-Tsu Chan: 0000-0001-9658-2188
Notes
The authors declare no competing financial interest.
CDCl /CD OD, 5/1, v/v): δ (ppm) 152.13, 149.89, 149.63, 140.75,
3
3
1
1
8
40.23, 139.85, 139.58, 134.33, 132.65, 130.39, 129.82, 129.61, 129.45,
27.12, 126.86, 126.35, 126.14, 125.05, 121.81, 115.86, 98.96, 95.99,
8.59, 56.55, 35.52, 32.00, 30.83, 29.16, 29.09, 28.96, 22.36, and 13.72.
4+
ACKNOWLEDGMENTS
ESI-MS (m/z): 785.1364 [M − 4PF ] (calcd m/z 785.0968),
6
■
3+
1
−
095.1589 [M − 3PF ] (calcd m/z 1095.1138), and 1715.7120 [M
6
This research was supported by the Ministry of Science and
Technology of Taiwan (MOST105-2119-M-002-029 and
MOST106-2628-M-002-007-MY3).
2+
2PF ] (calcd m/z 1715.6578).
6
Synthesis of [Zn {(S)-L3} ](PF ) . By general procedure B, [Zn {(S)-
2
3
6 4
2
L3} ](PF ) was obtained in 90% yield (12 mg, 3.0 μmol) from L3
3
6 4
(
10 mg, 9.9 μmol), Zn(OTf) (2.4 mg, 6.6 μmol), CHCl (3 mL),
2
3
1
REFERENCES
MeOH (3 mL), and NH PF . H NMR (400 MHz, CDCl /CD OD,
5
■
4
6
3
3
/1, v/v): δ (ppm) 8.65−8.61 (m, 12H), 7.98−8.18 (m, 30H), 7.82
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(
(
(
(
dd, J = 8.2, 4.8 Hz, 6H), 7.56 (s, 6H), 7.09 (d, J = 8.8 Hz, 6H), 6.82
d, J = 8.7 Hz, 6H), 4.55−4.50 (m, 12H), 2.72−2.62 (m, 12H), 2.37
s, 18H), 1.66−1.56 (m, 12H), 1.12−1.34 (m, 60H), and 0.84−0.73
m, 18H). 13C NMR (100 MHz, CDCl /CD OD, 5/1, v/v): δ (ppm)
3
3
(
1
1
1
2
4
1
50.76, 149.65, 149.40, 142.18, 141.33, 141.21, 139.82, 138.83, 135.67,
32.98, 130.54, 130.48, 130.36, 129.54, 129.43, 127.43, 127.19, 126.47,
26.01, 125.67, 115.21, 98.34, 94.38, 88.11, 56.04, 35.88, 31.97, 31.21,
9.54, 29.36, 22.76, 22.68, and 14.14. ESI-MS (m/z): 784.9031 [M −
(
4
+
3+
PF ] (calcd m/z 785.0968), 1095.1956 [M − 3PF ] (calcd m/z
6
6
2+
095.1138), and 1715.2756 [M − 2PF ] (calcd m/z 1715.1578).
Synthesis of [Zn {(S)-L2 } ](OTf) . By general procedure A,
6
OH
2
3
4
OH
[
Zn {(S)-L2 } ](OTf) was obtained in 99% yield (126.1 mg, 36.4
2 3 4
OH
μmol) from (S)-L2 (100.0 mg, 109.3 μmol), Zn(OTf) (26.5 mg,
7
MHz, CDCl /CD CN, 5/1, v/v): δ (ppm) 9.53 (d, J = 8.5 Hz, 6H),
2
1
Cyclic Nanostructures Mediated by Transition Metals. Chem. Rev.
2.8 μmol), CHCl (10 mL), and MeOH (10 mL). H NMR (400
3
2
(
000, 100, 853−908.
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3
3
8
(
7
.94 (d, J = 4.7 Hz, 6H), 8.65 (d, J = 8.5 Hz, 6H), 8.30 (s, 6H), 8.22
s, 6H), 7.97 (dd, J = 8.3, 4.9 Hz, 6H), 7.72 (dd, J = 8.5, 4.8 Hz, 6H),
.62 (s, 6H), 7.55 (d, J = 3.5 Hz, 6H), 7.11 (d, J = 8.8 Hz, 6H), 6.91
d, J = 8.8 Hz, 6H), 6.54 (s, 6H), 2.69 (t, J = 6.8 Hz, 12H), 1.62−1.54
2
(
(
(
13
m, 12H), 1.35−1.12 (m, 60H), and 0.78 (t, J = 6.8 Hz, 18H).
C
NMR (100 MHz, CDCl /CD OD, 5/1, v/v): δ (ppm) 152.35, 150.18,
3
3
(
1
1
1
2
7
1
49.22, 140.45, 140.24, 140.10, 139.55, 134.50, 133.25, 130.32, 130.28,
29.91, 129.08, 129.03, 127.07, 126.84, 125.09, 122.70, 122.09, 118.91,
13.40, 112.42, 96.96, 89.40, 35.80, 31.96, 31.35, 29.56, 29.44, 29.35,
(
4+
2.74, and 14.10. ESI-MS (m/z): 719.1054 [M − 4OTf] (calcd m/z
3+
19.0565), 1008.4341 [M − 3OTf] (calcd m/z 1008.3928), and
2+
587.1195 [M − 2OTf] (calcd m/z 1587.0651).
(
OH
Synthesis of [Zn {(S)-L3 } ](OTf) . By general procedure A,
2
3
4
designs to fractal supramacromolecular constructs: understanding the
pathway to the Sierpin
3967.
OH
[
Zn {(S)-L3 } ](OTf) was obtained in 99% yield (12.6 mg, 3.6
2 3 4
́
ski gasket. Chem. Soc. Rev. 2015, 44, 3954−
OH
μmol) from (S)-L3 (10 mg, 10.9 μmol), Zn(OTf) (2.7 mg, 7.28
μmol), CHCl (5 mL), and MeOH (5 mL). H NMR (400 MHz,
CDCl /CD CN, 5/1, v/v): δ (ppm) 8.75−8.66 (m, 18H), 8.17 (d, J =
8
(
(
1
7
3
2
1
3
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3
3
.8 Hz, 6H), 9.09 (d, J = 9.0 Hz, 6H), 7.99 (s, 6H), 7.92 (s, 6H), 7.77
dd, J = 8.0, 3.4 Hz, 6H), 7.53 (s, 6H), 6.99 (d, J = 8.8 Hz, 6H), 6.90
d, J = 8.8 Hz, 6H), 6.73 (s, 6H), 2.65 (s, 12H), 1.60 (s, 12H), 1.36−
.16 (m, 60H), and 0.86 (t, J = 6.5 Hz, 18H). ESI-MS (m/z):
4+
19.1117 [M − 4OTf] (calcd m/z 719.1054), 1008.4708 [M −
OTf]3 (calcd m/z 1008.3928), and 1587.1896 [M − 2OTf] (calcd
+
2+
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H
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Inorg. Chem. XXXX, XXX, XXX−XXX