Cerium-Based M4L4 tetrahedra as molecular flasks for selective reaction prompting and luminescent reaction tracing

Article abstract of DOI:10.1002/chem.201303560

The application of metal-organic polyhedra as "molecular flasks" has precipitated a surge of interest in the reactivity and property of molecules within well-defined spaces. Inspired by the structures of the natural enzymatic pockets, three metal-organic

Full text of DOI:10.1002/chem.201303560

DOI: 10.1002/chem.201303560
Full Paper
&
Luminescence
Cerium-Based M L Tetrahedra as Molecular Flasks for Selective
4
4
Reaction Prompting and Luminescent Reaction Tracing
Yang Jiao, Jian Wang, Pengyan Wu, Liang Zhao, Cheng He, Jing Zhang, and
[a]
Chunying Duan*
Abstract: The application of metal–organic polyhedra as
molecular flasks” has precipitated a surge of interest in the
excellent selectivity towards the substrates size. The amide
groups worked as trigger sites and catalytic driven forces to
achieve efficient guest interactions, enforcing the substrates
proximity within the cavity. Experiments on catalysts with
the different cavity radii and substrates with the different
molecular size demonstrated that the catalytic performance
exhibited enzymatical catalytic mechanism and occurred in
the molecular flask. These amides were also able to amplify
guest-bonding events into the measurable outputs for the
detection of concentration variations of the substrates, pro-
viding the possibility for metal–organic hosts to work as
smart molecular flasks for the luminescent tracing of catalyt-
ic reactions.
“
reactivity and property of molecules within well-defined
spaces. Inspired by the structures of the natural enzymatic
pockets, three metal–organic neutral molecular tetrahedral,
Ce-TTS, Ce-TNS and Ce-TBS (H TTS: N’,N’’,N’’’-nitrilo-
6
tris-4,4’,4’’-(2-hydroxybenzylidene)-benzohydrazide; H TNS:
6
N’,N’’,N’’’-nitrilotris-6,6’,6’’-(2-hydroxybenzylidene)-2-naphtho-
hydrazide; H TBS: 1,3,5- phenyltris -4,4’,4’’-(2-hydroxybenzyli-
6
dene)benzohydrazide), which exhibit different size of the
edges and cavities, were achieved through self-assembly by
incorporating robust amide-containing tridentate chelating
sites into the fragments of the ligands. They acted as molec-
ular flasks to prompt the cyanosilylation of aldehydes with
Introduction
for selective sensing special guests with luminescence respons-
[10,11]
es.
These synthetic strategies for the constructing of coor-
Recently, the application of metal–organic molecular hosts as
dination cages with various structures, metal-tunable optical
properties and new size- or shape-selective recognition proper-
ties have been inspired the development of an efficient molec-
[
1,2]
“
molecular flasks”
has precipitated a surge of interest in the
reactivity and property of molecules within well-defined
spaces. Driven by the ultimate goal of enzyme mimetics, the
investigations are rife with allusions and direct comparisons to
the natural enzymes, however, only few “artificial enzymes”
[12]
ular container. Furthermore, the possibility to amplify guest-
bonding events into measurable outputs and to detect the
concentration variations of substrates might allow the metal–
organic molecular hosts work as smart molecular flasks for the
luminescent tracing of catalytic reactions. In this case, an easy-
to-measure signal moiety and a suitable proper communica-
tion system must be included in the overall molecular design
to transduce the recognition information into a luminescence
[3,4]
achieved the magnificent catalysis of natural enzymes.
Most
metal–organic cages don’t constitute specific interactions ca-
pable of encapsulating guest molecules and catalyzing the re-
actions, due to the intrinsic difficulties on the producing guest-
[
5,6]
accessible sites inside the well-defined spaces.
In this case,
[13]
incorporating amide groups as guest-accessible sites within
the metal–organic cages is a powerful approach to achieve
functional flasks to prompt several important reactions, be-
cause amide groups are able to possess two types of hydro-
output.
Recently, we reported that by incorporating robust amide-
containing tridentate chelating sites into the three arms of a tri-
phenylamine fragment (the most common energy donor and
[
7,8]
[14]
gen-bonding sites
and act as base-type catalytic driving
blue emitter), a neutral tetrahedron Ce-TTS (H TTS: N’,N’’,N’’’-
6
[
9]
force.
nitrilotris-4,4’,4’’-(2-hydroxybenzylidene)-benzohydrazide;
Scheme 1) was functionalized as an enzyme-like pocket to en-
capsulate the spin-trapping agent molecule and prompt the
On the other hand, substantial developments have been
made in the creation of Werner-type capsules that can be used
[15]
spin-trapping reaction with NO in biological systems.
The
[
a] Y. Jiao, Dr. J. Wang, Dr. P. Wu, L. Zhao, Dr. C. He, J. Zhang, Prof. C. Duan
State Key Laboratory of Fine Chemicals
Dalian University of Technology
Linggong Road 2, Dalian,116024 (China)
E-mail: cyduan@dlut.edu.cn
possibility to amplify guest-bonding events into measurable
outputs and to detect the concentration variations of sub-
strates further allow the metal–organic molecular host to work
as smart molecular flasks for luminescent tracing of catalytic
reactions. Herein, we extended our clever self-assembly tech-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303560.
[16]
niques to create new Ce-based molecular tetrahedra Ce-TNS
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Scheme 1. Perspective views of the ligands and the Ce-based molecular tetrahedron showing the sizes and the volume of the cavities
and Ce-TBS (H TNS: N’,N’’,N’’’-nitrilotris-6,6’,6’’-(2-hydroxybenzy-
6
lidene)-2-naphthohydrazide; H TBS: 1,3,5- phenyltris -4,4’,4’’-(2-
6
hydroxybenzylidene)benzohydrazide), in which the triphenyl-
amine moiety was substituted by other three arms aromatic
rings to enlarge edge lengths as well as the cavity volumes
(Scheme 1). As the amide groups are introduced as trigger
sites to achieve efficient guest interactions, a powerful catalytic
driving force, and excellent signal responding communications,
we envisioned that these metal–organic polyhedra possibly
worked as efficient molecular flasks to prompt the cyanosilyla-
tion of aromatic aldehydes through recognizing the aldehydes
within their amide-containing cavities of the tetrahedra. Since
the molecular tetrahedra exhibited difference sizes and cavity
volumes, the potential mechanism of the enzymatically catalyt-
ic behavior corresponding to the cyanosilylation reactions
within the tetrahedron Ce-TTS was also investigated to discrim-
inate whether the catalytic performance occurred in a molecu-
lar flask or a normal homogeneous manner. In addition, the
potential of amide groups to amplify the guest-bonding
events into measurable outputs provided the opportunity for
Figure 1. Molecular structure of the Ce-based tetrahedron Ce-TTS showing
the cavity of the tetrahedron and the potential catalytic activity for the cya-
nosilylation reaction. The average CeÀOphenol, CeÀOamide, and CeÀN distances
of 2.24, 2.43, and 2.67 ꢁ, respectively. The average Ce···Ce separation is
14.90 ꢁ, the diameter of the pore is 9.21 ꢁ.
3À
2À
2
(H TTS)] and [Ce (HTTS) (H TTS) ] , respectively, suggesting
2
4
2
2
the formation of M L species in solution (Figure 1).
4
4
[15,16]
detecting the concentration variations of substrates.
It
By incorporating the triphenylamine blue emitter, Ce-TTS
(30 mm) exhibited bright emission at about 470 nm when excit-
ed at 320 nm in DMF. Upon addition of nitrobenzaldehydes, 1-
naphthaldehyde (NPA) or 4-hydroxy-1-naphthaldehyde (HNPA)
up to 0.6 mm, the luminescence of the solution decreased
gradually with the increasing concentration of the guests
seems that the metal–organic hosts were truly smart molecular
flasks for the luminescent tracing of the catalytic reactions.
Results and Discussion
(
Figure 2). A Hill-plot of the titration curves demonstrated a 1:1
[
15]
[17]
Ce-TTS was synthesized from the literature method. Magnet-
ic susceptibility revealed a diamagnetic behavior of the sample
from room temperature to 1.8 K, demonstrating the presence
stoichiometric host–guest behavior,
with the association
constant (log k ) ranging from 2.82 to 4.05. The ESI-MS spec-
ass
trum of the titration solution with HNPA exhibited a new peak
IV
of Ce ions of compound Ce-TTS in the solid state. ESI-MS
at m/z about 1213.13, assignable to [Ce (HTTS) (H TTS)ꢀ-
4
3
2
3À
spectrum of Ce-TTS in DMF/CH OH solution exhibited two in-
(HNPA)] , close to two peaks at m/z about 1155.78 and
3
3À
tense peaks at m/z=1155.75 and 1734.10, with the isotopic
distribution patterns separated by 0.33 and 0.50 Dalton.
Through the exact comparison of the experimental peaks with
the simulation results obtained on the basis of natural isotopic
abundances, the peaks were assigned to the [Ce (HTTS) -
1168.12 that were assigned to [Ce (HTTS) (H TTS)] and [Ce4-
4 3 2
3À
(HTTS) (H TTS)·2(H O)] , respectively. The result was consistent
3
2
2
with the 1:1 host/guest stoichiometry of the complexation.
Whereas, the addition of 2-(anthracen-9-yl)acetaldehyde
(ATDA) with a size larger than 7.5 ꢁ did not cause any obvious
4
3
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cavities of the tetrahedron, and there was no further
[
19]
space for other reaction substrates.
Detailed
1
H NMR spectroscopic experiments gave solid proof
to support the capture of HNPA within the cavity of
Ce-TTS (Figure 3). The upshift by Dd=À0.05 ppm for
the H-
signals upon addition of 1 molar equiv of
CHO
HNPA suggested the formation of hydrogen bonds
between the aldehyde and amino protons. NOESY
gave HÀH interactions between the H , H of the al-
1’
4’
dehyde and the phenyl protons of Ce-TTS, demon-
[20]
strating the potential p–p interactions
between
Figure 2. Right: Family of luminescence of Ce-TTS (30 mm) upon the addition of HNPA
up to 0.6 mm). Left: luminescence responses of Ce-TTS (30 mm) upon addition of alde-
hydes (1.2 mm); intensities were recorded at 470 nm and excited at 320 nm.
the naphthyl ring of HNPA and the phenyl rings of
the tetrahedron.
(
spectral change, it seems that only the molecules having a suit-
able size could enter into the cavities.
Our catalytic experiments focused on the cyanotrimethylsi-
lane reaction, an important reaction that provides a convenient
route to cyanohydrins, which are key derivatives in the synthe-
[
18]
sis of fine chemicals and pharmaceuticals.
As shown in
Table 1, the loading of 2 mol% Ce-TTS led to a more than 80%
Table 1. Results for the cyanosilylations of carbonyl substrates in the
[
a]
presence of Ce-TTS in a homogeneous manner.
Entry
Substrates
Conversion
%]
Association
constant
[
[log Kass]
1
2
3
4
5
6
4-nitrobenzaldehyde
3-nitrobenzaldehyde
2-nitrobenzaldehyde
1-naphthaldehyde
4-hydroxy-1-naphthaldehyde
2-(anthracen-9-yl)acetaldehyde
>99
93
86
68
25
3.35Æ0.08
2.93Æ0.09
2.82Æ0.15
4.05Æ0.22
5.71Æ0.12
–
Figure 3. Partial NOESY spectra of Ce-TTS (3.5 mm) and HNPA (3.5 mm) mix-
ture in [D ]DMSO, showing the interactions between the formyl group and
6
naphthyl ring of HNPA and the aromatic rings in the host.
20
Importantly, the preliminary results demonstrated that HNPA
could form the most stable host–guest complexation species
but exhibit the poorest catalytic activity. It seems that HNPA
was an ideal inhibitor for the new enzymatically catalytic sys-
tems. Furthermore, the addition of 0.08m of HNPA to the reac-
tion mixture containing (CH ) SiCN (0.20m), nitrobenzaldehyde
[
a] Reaction conditions: (CH
3
)
3
SiCN (0.20m), aldehyde (0.08m), Ce-TTS
for 1 hour in 2 mL DMF/CHCl (v/
(1.6 mm) at room temperature under N
2
3
v=1:99) solution.
conversion for nitrobenzaldehydes. Although there are lots of
factors influencing the conversion of the reactions, the same
sequence of the reactivity and the quenching efficiency partly
demonstrated that the recognition process seems to be an im-
portant step for these cyanosilylations. In the presence of
bulky aldehyde ATDA, whose size is larger than the pore size
of Ce-TTS as the aldehyde substrate, the cyanosilylation reac-
tion only gave 20% of product under the same reaction condi-
tions.
3
3
(0.08m), and Ce-TTS (1.6 mm) stopped the cyanosilylation di-
rectly. As the new competitive inhibition properties was one of
the intrinsic character for the enzymatic-like dynamics within
the cavity, these results demonstrated that Ce-TTS was the
[21]
actual molecular flask with excellent catalytic performance.
Furthermore, the product formation was pseudo-zero-order
À1
with the rate constant being 2.4mh (Figure 4a, top line), in
the case of the reaction of 3-NBA with a high concentration
(0.4m). When the concentration was decreased to 0.04m, the
dependence of the rate on substrate concentration tended to
the first order (Figure 4a, middle line), and the combined ki-
netic date followed the overall rate law: kinetic rate=
The size selectivity of the substrate suggested that the cya-
nosilylation reactions occurred mostly in the cavity of the cata-
lyst, not in a normal homogeneous manner. The only excep-
tion was that of 4-hydroxy-1-naphthaldehyde (HNPA); it exhib-
ited the largest quenching efficiency and associate constant,
but demonstrated relative lower conversion. These results are
partly due to that the size of HNPA itself fitted well with the
À1
k [guestꢁCe-TTS], with the k calculated as 3.6 h . The kinetic
2
2
rate of reaction depends on the concentration of host–guest
complexation species rather than the total concentration of
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centers and four deprotonated H TNS ligands. Each
2
cerium ion was chelated by three tridentate chelat-
ing groups from three different ligands to form ter-
nate coronary trigonal-prism coordination geometry
with pseudo-C symmetry. The four pseudo-C sym-
3
3
metric planar ligands positioned individually on the
four triangle faces of the tetrahedron defined by four
metal ions. Despite the fact that that the Ce···Ce sep-
aration (18.43 ꢁ) in the tetrahedron Ce-TNS is larger
than that in Ce-TTS (14.9 ꢁ), the inscribed globe of
Ce-TNS only has the radii of about 3.9 ꢁ, which is
not large enough to capture any aromatic molecules.
Weak CÀH···p interactions were found to attract
three naphthyl groups linked together by one metal
[25]
ion. The shortest distance between the centroid of
the naphthyl ring [defined by C(449), C(450), C(451),
C(452), C(453), C(454), C(455) C(456), C(457) and
C(458)] in one molecule and the interacting C atom
C(115) is 3.77 A with the H···centroid of 2.87 A, the
Figure 4. a) Time-dependence of integral area (IA) ratio variations of the reaction in
1
Table 1, entry 3 based on H NMR detection in DMF/CDCl
integral areas at d=5.61 and 10.14 ppm, respectively; b) Time-dependent luminescence-
variation (470 nm) of the reaction solution in DMF, in which F and F represent the fluo-
3 P R
. IA and IA represent the NMR
0
rescence intensities of the reaction mixture and Ce-TTS itself, respectively. The ratio of cy-
anotrimethylsilane/aldehyde/catalyst was maintained.
substrates suggested that the substrate and “enzyme” partici-
[22]
pated in a reversible equilibrium with an enzyme/complex.
Furthermore, the catalysis behavior is described in Michaelis–
Menten mechanism in which substrate binding is a first equi-
[
23]
librium prior to the rate-limiting step of the reaction.
Interestingly, the luminescent responses of Ce-TTS toward
the above mentioned aldehyde in Table 1 (entry 2) provided
the possibility to visualize the catalytic process. Under the di-
luted conditions (3-NBA of 0.04m), the emission of Ce-TTS was
quenched partially at the beginning of the cyanosilylation. The
weak luminescence recovered during the catalytic process, and
the kinetic behaviour was first order (Figure 4b, red line). With
the saturated conditions (3-NBA of 0.4m), the completely
quenched luminescence was hardly recovered during the cata-
lytic process. As a concequence, Ce-TTS seems to be a “smart”
molecular flask, which not only catalyzed the reaction through
an enzyme-like manner, but also monitored the reaction pro-
Figure 5. Molecular structure of the Ce-based tetrahedron Ce-TNS showing
the cavity of the tetrahedron and the potential catalytic activity for the cya-
[
15,24]
cess through an optical signal output.
nosilylation reaction. The average CeÀO
, CeÀO
, and CeÀN distances
phenol
amide
are 2.20, 2.45, and 2.64 ꢁ, respectively. The average Ce···Ce separation is
8.90 ꢁ, the diameter of the pore is 7.74 ꢁ.
To validate whether the catalytic performance occurred
within a molecular flask or a normal homogeneous catalytic
manner, a Ce-based analogue Ce-TNS, in which the triphenyl-
amine moiety was substituted by a trinaphthylamine moiety,
1
CÀH···centroid of 1638, and an inter-plane angle of 758, re-
spectively.
was constructed. Ligand H TNS was synthesized by the reac-
6
tion of 6, 6’, 6’’-nitrilo-trinaphthylhydrazide with salicylaldehyde
Similar to Ce-TTS, Ce-TNS (15 mm) also exhibited bright emis-
sion at about 485 nm when excited at 350 nm. Neither the ad-
dition of nitrobenzaldehyde in excess, nor the addition of 4-hy-
droxy-1-naphthaldehyde (HNPA) in excess caused any signifi-
cant luminescent spectroscopic variations Ce-TNS. The pres-
ence of Ce-TNS even at about 30% molar ratio relative to 4-ni-
trobenzaldehyde only gave 15% of product under the same
reaction conditions. Since the loading of 2% of Ce-TTS as the
catalyst gave more than 90% of the conversion within 1 h
under the same aerobic condition (Table 2), it is clear that no
4-nitrobenzaldehyde molecules were capsulated within the
cavity of the Ce-TNS tetrahedron. As both the two tetrahedra
have the same structural fashion just with different sizes of the
in methanol solution. Diffusing CH OH into a DMF solution of
3
H TNS and [Ce(NO ) ]·6H O generated the compound Ce-TNS,
6
3 3
2
in a yield of 45%. ESI-MS of Ce-TNS in DMF/CH OH solution ex-
3
hibited only an intense peak at m/z=1356.83, assignable to
3À
the species [Ce (H TNS) (H TNS)] . Elemental analyses along
4
2
3
3
with powder X-ray analysis indicated the pure phase of its
bulky sample.
X-ray single-crystal analysis confirmed the formation of a tet-
rahedron (Figure 5). Molecules of Ce-TNS exhibited the similar
tetrahedral structure with the coordination geometries and
structural distinctions of the cerium ions were the same as
those in Ce-TNS. The tetrahedron comprised four vertical metal
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hedral angles between pairs of phenyl rings of about 108, sug-
gesting the potential of p–p accumulation sites for recognizing
of organic molecule with polycyclic aromatic rings. The Ce···Ce
separations were about 1.7 nm and the inner radius of the tet-
rahedron was 5.1 ꢁ. These interacting sites had the potential
to encapsulate ATDA and prompt its chemical transformation
through the cooperative interactions.
Table 2. Conversions for the cyanosilylations of carbonyl substrates in
the presence of Ce-TNS and Ce-TBS in a homogeneous manner.
[
a]
Substrates
Ce-TTS
%]
Ce-TNS
[%]
Ce-TBS
[%]
[
4
3
2
1
4
2
-nitrobenzaldehyde
-nitrobenzaldehyde
-nitrobenzaldehyde
-naphthaldehyde
-hydroxy-1-naphthaldehyde
-(anthracen-9-yl)acetaldehyde
99
93
84
68
25
21
30
28
24
28
25
22
99
95
90
88
90
95
ESI-MS spectrum of Ce-TBS exhibited two intense peaks at
m/z=1237.18 and 1286.84 assigned to the [Ce (H TBS)-
4
2
3
À
3À
(
HTBS)3]
and [Ce (H TBS)(HTBS) (C H NO) ] species, respec-
4 2 3 3 7
2
tively, indicating the assembly and stability of the Ce L tetra-
4 4
hedron in solution. Upon the addition of ATDA, a new peak at
m/z about 1396.59 appeared. The new species was assigned to
[
a] Reaction conditions: (CH
3
)
3
SiCN (0.20m), aldehyde (0.08m), Ce-TNS
for 1 hour in 2 mL DMF/CHCl (v/
3
À
(1.6 mm) at room temperature under N
2
3
the complexation species [Ce (H TBS)(HTBS)(H O)ꢀ(ATDA) ] ,
4
2
2
2
v=1:99) solution.
by comparing the experimental peaks with the simulation re-
sults obtained on the basis of natural isotopic abundances.
The result demonstrated the formation of potential 1:2 com-
plexation species in solution. Whereas the addition of Ce-TBS
up to 0.5 molar ratio to the DMF solution of 2-(anthracen-9-
yl)acetaldehyde (0.1 mm) caused a quenching of the emission
at about 415 nm, confirming the formation of host–guest com-
plexation species. Because further addition of Ce-TBS did not
cause any significant emission quenching at the conditions,
the formation of a 1:2 stoichiometric complexation was also
suggested. Ce-TBS could be described as an efficient molecular
capsule for ATDA, which possibly catalyzed the relative chemi-
cal reactions.
opening and the cavity, it is concluded that the catalytic activi-
ty of Ce-TTS was realized within the inner cavity, and Ce-TTS
was the actual molecular flask with excellent catalytic perfor-
mance.
To further validate the enzymatically catalytic mechanism
and demonstrate that the catalytic performance occurs within
a molecular flask, especially for the largest aldehyde, 2-(anthra-
cen-9-yl)acetaldehyde (ATDA), another Ce-based analogue, Ce-
TBS, was constructed, in which the triphenylamine moiety was
substituted by a tetraphenyl aromatic fragment. Ligand H TBS
6
was synthesized by the reaction of 1,3,5-benzene-4,4’,4’’-triben-
zocarbo-hydrazide with salicylaldehyde in methanol solution.
Stirring the ligand H TBS and [Ce(NO ) ]·6H O in DMF solution
Ce-TBS exhibited an amide signal at d=13.80 ppm, in the
1
H NMR spectrum. Upon addition of 2-(anthracen-9-yl)acetalde-
hyde, the peak was significantly split and a new peak appeared
at d=13.4 ppm. This result might be one of the indicators of
the formation of encapsulation species through the amide-
containing hydrogen bonds. NOE spectra of solution contain-
ing Ce-TBS and 2-(anthracen-9-yl)acetaldehyde exhibited sever-
al HÀH interactions (Figure 7). These signals were assigned to
6
3 3
2
gave a black solid in 56% yield. Single-crystal X-ray structural
analysis revealed the formation of a tetrahedron in the solid
state. As shown in Figure 6, each neutral tetrahedral cage ex-
hibited a 2-fold axial symmetry with two cerium ions and two
ligands present in an unsymmetrical unit. The conjugate ben-
zene rings of each ligand fragment were almost planar with di-
the interactions between the CH=N proton and H2
of 2-(an-
,3,6,7
thracen-9-yl)acetaldehyde, and/or between the H10 of 2-(an-
Figure 6. Molecular structure of the Ce-based tetrahedron Ce-TBS showing
the cavity of the tetrahedron and the potential catalytic activity for the cya-
nosilylation reaction. The average CeÀOphenol, CeÀOamide, and CeÀN distances
are 2.20, 2.48, and 2.64 ꢁ, respectively. The average Ce···Ce separation is
6
Figure 7. NOE spectra of a [D ]DMSO solution containing Ce-TBS (1 mm) and
2-(anthracen-9-yl)acetaldehyde (ATDA; 1 mm), showing the potential inter-
16.90 ꢁ, the diameter of the pore is 10.24 ꢁ.
molecular NOE correlations between them.
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hibition of the cyanosilylation was displayed. In this
case, methyl anthracene-9-carboxylate was chosen as
the inhibitor, because it exhibited an anthracene ring
and an ester as hydrogen-bonding trigger, but did
not participate in cyanotrimethylsilane reactions.
Methyl anthracene-9-carboxylate exhibited anthra-
cene-based emission at 465 nm, addition of Ce-TBS
up to 0.5 molar ratio caused the efficient quenching
of this emission. Further addition of Ce-TBS did not
give additional quenching of the emission, demon-
strating the formation of the host–guest complexa-
tion species. The addition of two molar equiv of
methyl anthracene-9-carboxylate to the reaction mix-
ture directly shut down the cyanosilylation reaction.
These results give further evidence that Ce-TBS is an
interesting molecular flask, within which the ATDA
was activated.
1
Figure 8. The H NMR spectra (in DMF/CHCl
mixture of 2-(anthracen-9-yl)acetaldehyde (0.40m) and (CH
1.6 mm) (top) and the reaction mixture without Ce-TBS (bottom). The conversion of the
3
(v/v=1:99)) of the final product of reaction
3 3
) SiCN (2m) with Ce-TBS
(
reaction with 2-(anthracen-9-yl)acetaldehyde was fixed at 0.4, 0.08, and 0.04m: the ratio
of the cyanotrimethylsilane/aldehyde/catalyst was 2.5:1:0.004.
thracen-9-yl)acetaldehyde and the phenyl rings of Ce-TBS. Conclusion
These results provided preliminary evidence of the p–p inter-
actions between the tetrahedron and compound ATDA, further
supporting the inclusion of 2-(anthracen-9-yl)acetaldehyde
We have reported the achievement of neutral Ce-based molec-
ular tetrahedra Ce-TTS, Ce-TNS, and Ce-TBS, which exhibit dif-
ferent size of the edges and cavities, as efficient molecular
flasks to prompt the cyanosilylation of aromatic aldehydes.
These amide groups work as trigger sites and catalytically
driven forces to achieve efficient guest interactions, enforcing
the substrates proximity within the cavity, leading excellent
size-selectivity towards the substrate. The catalysts exhibit
a typically enzymatic catalytic mechanism and occur within
a molecular flask, not in a normal homogeneous manner.
These amides are also able to amplify the guest-bonding
events into the measurable outputs for the detection of con-
centration variations of the substrates, providing the possibility
of metal–organic hosts to work as smart molecular flasks for
the luminescent tracing of the catalytic reactions.
[
20]
ATDA within the cavity of the tetrahedron.
As shown in Figure 8, the cyanotrimethylsilane reaction was
carried out with (CH ) SiCN (1.0m), aldehyde (0.4m), Ce-TBS
3
3
(1.6 mm) at room temperature under N2 in DMF/CDCl3 (v/v,
1
:99) solution. A loading of 0.4% led to almost complete con-
version for 1 h for almost all these aldehydes (yield>90%). A
control experiment showed that the cyanosilylation reaction
could not take place in the absence of Ce-TBS (Figure 4b) or in
the presence of 10% acetic acid being added to the system as
the acid catalyst room temperature under N for 3 days. When
2
the concentration of 2-(anthracen-9-yl)acetaldehyde was 0.4m,
the product formation was pseudo-zero-order with the rate
À1
constant calculated as 1.74mh (Figure 4b) during the first 1.5
hours. As the apparent diassociation constant (K ) of the Ce-
d
TBSꢀATDA was calculated as 4.8 mm from the isothermal titra-
tion calorimetry between Ce-TBS and compound ATDA with
8
À1
7
À1 [8b]
DH=À1.36ꢂ10 calmol
and TDS=À1.14ꢂ10 calmol ,
Experimental Section
the ratio of [ATDA]/K was larger than 60, in which [ATDA] rep-
d
resents the concentration of ATDA. Such kinetics behaviors
suggested that the catalytic process was enzymatic-like. Fur-
thermore, the catalytic process possibly occurred in a saturation
regime in which the enzyme–substrate complexation species
was dominant. As mentioned above, the catalysis behavior is
analogous to Michaelis–Menten mechanism in which substrate
binding is a first equilibrium prior to the rate-limiting step of
the reaction and the kinetic rate of reaction depends on the
concentration of host–guest complexation species rather than
the total concentration of the substrate.
Materials and methods
All chemicals were of reagent grade quality obtained from com-
mercial sources and used without further purification. The elemen-
tal analyses of C, H, and N were performed on a Vario EL III ele-
1
mental analyzer. H NMR spectra was measured on a Varian INOVA
400m spectrometer. ESI mass spectra were carried out on a HPLC-
Q-TOF MS spectrometer using methanol as mobile phase. UV/Vis
spectra were measured on a HP 8453 spectrometer. The solution
fluorescent spectra were measured on JASCO FP-6500. Both excita-
tion and emission slit widths were 5 nm. Solutions of the tetrahe-
dra were prepared in DMF. The high concentration stock solutions
To investigate whether the cyanotrimethylsilane reaction
either occurred within the cavity of the tetrahedron Ce-TBS or
just displayed through normal homogeneous system, the in-
À2
of aldehyde (2.0ꢂ10 m) were prepared directly in DMF solvents.
For the time-dependent luminescence-variation experiment of the
cyanosilylation reaction solution, the luminescence was examined
Chem. Eur. J. 2014, 20, 2224 – 2231
www.chemeurj.org
2229
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
by diluting the corresponding reaction mixture into DMF solvent,
the intensity was recorded at 470 nm, excitation at 320 nm.
tate 6,6’,6’’-nitrilo-trinaphthylhydrazide was formed and used in
next step. Five drops of acetic acid were added to the mixture of
6
6
,6’,6’’-nitrilo-trinaphthylhydrazide and salicylaldehyde (0.80 g,
.6 mmol) in methanol solution. The mixture was heated at reflux
Crystallography
over 4 h and a yellow precipitate (0.56 g) was isolated by filtration.
Total yield (from methyl 6-amino-2-naphthoate): 32.5%. H NMR
1
The intensities of Ce-TNS and Ce-TBS were collected on a Bruker
SMART APEX CCD diffractometer with graphite monochromated
MoKa (l=0.71073 ꢁ) by using the SMART and SAINT programs.
The structures was solved by direct methods and refined on F2 by
([D ]DMSO): d=12.25 (s, 3HNH), 11.34 (s, 3HOH), 8.71 (s, 3CH=N),
6
[26]
8.57 (s, 3Hnaph
), 8.10 (d, J=8.8 Hz, 3Hnaph), 7.80–7.91 (m, 3Hnaph
,
3
1
3
7
Hnaph), 7.70 (s, 3Hnaph), 7.58 (d, J=7.2 Hz, 3Hnaph), 7.49 (d, J=
[27]
full-matrix least-squares methods with SHELXTL version 5.1. For
the refinement of data of Ce-TNS, four carbon atoms in three of
the phenyl rings of the salicylaldehyde moieties, and five carbon
atoms in another phenyl rings of the salicylaldehyde moieties were
all refined disordered, with the site occupancy factor of the two
parts being fixed in suitable value to make the thermal parameters
acceptable. Except for the solvent molecules, one of the bridged
naphthyl and the disordered atoms, the other skeleton non-hydro-
gen atoms were refined anisotropically. SQUEEZE was used with
the number being 14. Hydrogen atoms within the ligand back-
bones and the DMF molecules were fixed geometrically at calculat-
ed distances and allowed to ride on the parent non-hydrogen
atoms. To assist the stability of refinements, several restrains were
applied: 1) For all the disordered phenyl rings, the geometrical
constraints of idealized regular polygons were used, the CÀC bond
distance of the phenyl ring being 1.39 ꢁ and the diagonal CÀC dis-
tance of the phenyl ring being 2.78 ꢁ. 2) Several solvent DMF mol-
ecules were restrained as idealized geometry. 3) Thermal parame-
ters on adjacent atoms in several phenyl and naphthalene rings, as
well as several the solvent DMF molecules were restrained to be
similar. In the structural refinement of Ce-TBS, all the non-hydrogen
atoms were refined anisotropically. Except the solvent water and
methanol molecules, hydrogen atoms within were fixed geometri-
cally at calculated distances and allowed to ride on the parent
non-hydrogen atoms. For carbon atoms of one benzene ring, and
six carbon atoms of another benzene ring, both on the salicyalde-
hyde moieties, were disordered into two parts, with the s.o.f (site
occupancy factor) of each part being fixed with free value, respec-
tively. To assist the stability of refinements, several restrains were
applied: 1) For one benzene ring in the ligands and several solvent
DMF molecules, the geometrical constraints of idealized regular
polygons were used; 2) For several solvent DMF molecules, thermal
parameters on adjacent atoms in the solvent molecules were re-
strained to be similar.
0.4 Hz, 3Hsalicyl), 7.32 (m, 3Hsalicyl, 3Hnaph), 6.95 ppm (m, 3Hsalicyl,
Hsalicyl); elemental analysis calcd (%) for C H N O : H 4.46, C
54
39
7
6
3.54, N 11.12; found: H 4.52, C 73.51, N 11.21.
Ce-TNS: [Ce(NO ) ]·6H O (44.2 mg, 0.15 mmol) and H TNS (88.0 mg,
0
3
3
2
6
.10 mmol) were dissolved in DMF and diffused by CH OH. The
3
black crystals were isolated and dried under vacuum, yield 45%.
1
H NMR ([D ]DMSO): d=13.39 (s, 8H, -CONH-), 8.76 (s, 12H, -N=
6
CH-), 8.21 (m, 12H, ArH), 8.01 (m, 24H, ArH), 7.49 (m, 24H, ArH),
7
ArH); elemental analysis calcd (%) for Ce (C H N O ) : H 3.47, C
6
.27–7.23 (m, 12H, ArH), 6.75–6.60 (m, 24H, ArH), 5.54 ppm (s, 24H,
4
54 35
7
6 4
3.71, N 9.63; found: H 3.88, C 62.91, N 10.14.
[29]
H TBS: 1,3,5-Tris(4-carboxyphenyl acid)benzene (2 g),
thionyl
chloride (30 mL) and five drops of DMF were heated at reflux at
58C for 12 h. After evaporating the superfluous thionyl chloride,
6
9
dry hydrazine hydrate (30 mL) was added and stirred over 12 h;
a white precipitate 4,4’,4’’-triphenylcarbohydrazide was filtrated
and used in next step. 4,4’,4’’-triphenylcarbohydrazide (2.6 mmol,
1
.25 g) was added to a CH OH solution (60 mL) containing salicylal-
3
dehyde (8.58 mmol, 1.05 g) and five drops of acetic acid. The mix-
ture was refluxed at 858C for 8 h. During the reaction, a pale-
yellow precipitate was formed, which was collected by filtration.
Yield: 2.02 g, 86.9%. H NMR ([D ]DMSO): d=12.22(s, 1H-NH-),
1
6
1
7
1.33(s, 1H-CH-), 8.71(s, 1HOH), 8.15(m, 5Hbenzene), 7.58(d, 1Hsalicyl),
.33(m, 1Hsalicyl), 6.96 ppm (d, 2Hsalicyl); elemental analysis calcd (%)
for C H N O ·2H O: H 4.83, C 69.49, N 10.13; found: H 4.90, C
48
36
6
6
2
6
9.44, N 10.07.
Ce-TBS: A solution of [Ce(NO ) ]·6H O (0.15 g, 0.353 mmol), H TBS
3 3
2
6
(0.2 g, 0.253 mmol), and NaOH (30.36 mg, 0.759 mmol) in CH OH/
3
DMF (v/v=1:9, 10 mL) was stirred for 1 h. Then, the solution was
left for two weeks at room temperature to give X-ray-quality black
block crystals. Yield 56% (based on the crystal washed with metha-
nol and dried in vacuum). H NMR ([D ]DMSO): d=13.58(s, 1H-NH-),
8
7
1
6
.86(s, 1HOH), 8.11(m, 1H-CH-), 7.90(m, 4Hbenzene), 7.80(m, 1Hbenzene),
.52(m, 1Hsalicyl), 7.29(d, 1Hsalicyl), 6.66(d, 1Hsalicyl), 5.70 ppm
Crystal data for Ce-TBS: Ce4C235H258N O , M =4903.23, Monoclinic,
space group C2/c, a=38.234(3), b=16.101(1), c=43.828(3), b=
34
49
r
(d,1Hsalicyl).elemental analysis calcd (%) for Ce (C H N O ) : H 3.58,
4 48 33 6 6 4
3
À1
C 62.00, N 9.04; found: H 3.82, C 61.36, N 9.50.
1
6
04.67 (1), V=26127(3) ꢁ , m=12.99 mm , Z=4, T=200(2) K.
1689 reflections were collected of which 22696 reflections were
unique (Rint =0.1276). The final refinement gave R =0.0988 for
1
Acknowledgements
8
136 reflections with Iꢂ2s(I), and wR =0.1782 for all data.
2
Crystal data for Ce-TNS: C2
H Ce N O , M=4828.99, Monoclin-
216 4 36 40
42
We grateful thank the financial support from Program for
Changjiang Scholars and Innovative Research Team in Universi-
ty (IRT1213). The National Nature Science Funds for Distin-
guished Young Scholar of China (No. 21025102).
ic, space group P2 /c, a=18.867 (6), b=42.762 (14), c=34.263
1
3
À3
(
11) ꢁ, b=94.586 (4), V=27555 (2) ꢁ , Z=4, 1 =1.164 gcm ,
cald
T=180(2) K. 42467 unique reflections [Rint =0.1290]. Final R1
[
(
with I>2s(I)]=0.0973, wR2 (all data)=0.2696. CCDC-804648
Ce-TNS) and 929354 (Ce-TBS) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Keywords: aldehydes · amides · cerium · host–guest systems ·
luminescence
Syntheses
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: September 9, 2013
Published online on January 21, 2014
Chem. Eur. J. 2014, 20, 2224 – 2231
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2231
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim