Zirconium(IV) metallocavitands as blue-emitting materials

Article abstract of DOI:10.1021/ic402602d

A series of zirconium-carboxylate metallocavitands with the general formula [(CpZr)₃(μ-κ₂,O′,O″CR) ₃(μ₃-O)(μ₂-OH)₃]Cl (Cp = cyclopentadienyl; R = C₅H₄N (5), C₆

Full text of DOI:10.1021/ic402602d

Article
pubs.acs.org/IC
Zirconium(IV) Metallocavitands As Blue-Emitting Materials
Hassan Iden,†,‡,§ Wenhua Bi,† Jean-Francois Morin,*,†,‡ and Frederic-Georges Fontaine*,†,§
̧
́ ́
†Dep
́
artement de Chimie, Universite
́
Laval, 1045 Avenue de la Med
́
ecine, Queb
́
ec (Queb
́
ec), Canada, G1V 0A6
́ ́
ecine, Quebec (Quebec),
‡Centre de Recherche sur les Mater
́
iaux Avances
́
(CERMA), Universite
́
Laval, 1045 Avenue de la Med
́
Canada, G1V 0A6
§Centre de Catalyse et Chimie Verte (C3 V), Universite
́ ́ ́ ́
Laval, 1045 Avenue de la Medecine, Quebec (Quebec), Canada, G1V 0A6
S
* Supporting Information
ABSTRACT: A series of zirconium-carboxylate metallocavitands with the
general formula [(CpZr)3(μ-κ2,O′,O″CR)3(μ3-O)(μ2-OH)3]Cl (Cp = cyclo-
pentadienyl; R = C5H4N (5), C6H7N (6), C18H14N (7), and C18H12N (8))
were synthesized in moderate to high yields (40−83%) by reacting the
corresponding carboxylic acids 1−4 with Cp2ZrCl2 in a self-assembly
procedure at room temperature. The metallocavitands were characterized
1
using H and 13C NMR spectroscopy and by single-crystal X-ray diffraction.
Complexes 7 and 8 exhibit efficient photoluminescence properties in solution.
The photoluminescence peak of 7 was observed at 464 nm and that of 8 at 422
nm with respective quantum yields in solution of 87 and 65%.
complex structures with an unrestricted number of geometries,
allowing the synthesis of a wide variety of cavitands with
specific chemical functions.
INTRODUCTION
■
Host−guest systems are at the core of molecular recognition
and supramolecular catalysis.1 Most of the systems reported to
date are based on well-known and studied organic cavitands2
such as calixarenes,3 cucurbiturils,4 cyclotriveratrylenes,5 cyclo-
dextrins,6 resorci-n-arenes,7 and their derivatives. Their intrinsic
cavities have generated a lot of interest since they can
encapsulate small molecules through noncovalent interactions
and can be used as functional materials for separation,5a,8
catalysis,9 molecular sensing,10 and fullerene encapsulatio-
Recently, we reported a series of trinuclear tantalum
boronate half-sandwich metallocavitands where the center of
the cavity is composed of an aggregated trimetallic tantalum(V)
cluster stabilized by oxo and μ-O2BR bridges.13 These species
can be easily generated from arylboronic acids and Cp*TaMe4
(Scheme 1). The metallocavitands have been shown to interact
specifically with Lewis bases such as acetone and tetrahy-
drofuran by an interaction between the nucleophilic part of the
organic molecules and the electrophilic metallic core. Pursuing
our work on metallocavitands, we investigated the synthesis of
zirconium carboxylate species that would have a similar C3
symmetry, but without the electrophilic cavity, by the
replacement of the boron and tantalum atoms by carbon and
zirconium atoms, respectively. Indeed, we expected for these
species to show better stability since the B−R bond has been
shown to exhibit cleavage in some conditions.13b
Zirconium is one of the cheapest transition metals, and its
coordination chemistry is well established. While the self-
assembly of zirconium clusters in the presence of organic
ligands in water has attracted less attention from chemists,
probably due to the high reactivity and low stability of
zirconium precursors in the presence of moisture or oxygen,
some precedents exist demonstrating the ability of zirconium
species to generate polymetallic clusters that could lead to the
synthesis of metallocavitands.14 For instance, the hydrolysis of
n.5a,8 11
a,
Although tailoring of the cavitands for the desired
applications is possible, the synthetic procedures to do so can
be tedious and often require multistep syntheses. An interesting
alternative to the synthesis of organic cavitands is the self-
assembly between organic ligands and inorganic cores
generating metallocavitands, a subclass of cavitands.12 The
metallocavitands possess many advantages over their traditional
organic analogues. First, the size and the shape of their cavities
can be easily controlled by changing the nature of the metal
center and of the organic ligands. By adopting ligands having
specific geometries and symmetries, and by controlling the
coordination sites around the metal interacting with these
ligands, novel architectures can be achieved. Second, special
properties can be expected for the metallocavitands arising from
the presence of metal centers, which can offer potential
applications in various fields, such as in chemical sensing and
catalysis.12 Last but not least, a major advantage of metal-
locavitands lies in their synthetic simplicity because of the high
efficiency of the self-assembly process. Furthermore, the large
accessibility of organic ligands can lead to the generation of
Received: October 15, 2013
Published: February 26, 2014
© 2014 American Chemical Society
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Scheme 1. Typical Synthesis of Tantalum Boronate Metallocavitands (R = Aryl Group; the Hydroxyl Groups Were Omitted in
the Structure)
[(η5-C5Me5)ZrCl3] with a stoichiometric amount of water in
RESULTS AND DISCUSSION
■
toluene at 80 °C yields the trinuclear complex [{(η5-
Synthesis of Zirconium(IV) Metallocavitands. Follow-
C5Me5)ZrCl}3(μ-Cl)4(μ3-O)] (A) with Cs symmetry (Figure
ing the procedure depicted in Scheme 2, compounds 5−8 of
1A),15 and the hydrolysis of [Cp2ZrCH3(THF)]BPh4, “Jordan’s
general structure [(CpZr)3(κ2,O′,O″CR)3(μ3-O)(μ2-OH)3]·
cation,” in a mixture of dichloromethane/THF at −78 °C yields
similar trinuclear [(Cp2Zr)3(μ2-OH)3(μ3-O)]BPh4 complex
(B) with C3V symmetry (Figure 1B).16 As described above, in
order to get isoelectronic structures to the tantalum boronate
species, the ligands of choice for zirconium are the
arylcarboxylates. Some zirconium(IV) arylcarboxylate deriva-
tives have been prepared through the reaction of the
carboxylate salts with Cp2ZrCl2.17 Indeed, half-sandwich
metallocavitands such as [(CpZr)3(μ3-O)(μ2-OH)3(μ2-
O′,O″C-C6HF4)3]+·(C6HF4CO2−) (C; Figure 1C),18
[(CpZr)3(μ2-O′,O″C-C6H3Cl2)3(μ3-OH)(μ2-OH)3]-
HCl (where R = C5H4N (5), para-C6H4−NH2 (6), para-
C6H4−N(C6H5)2 (7), and para-C6H4−N(C12H8) (8)) were
prepared in moderate to good yields (40−83%) by reacting the
corresponding carboxylic acids 1−4 with a 1 M solution of
Cp2ZrCl2 in a 2:1 solution of dichloromethane in water at pH
7. Whereas the isonicotic acid and the 4-aminobenzoic acid
needed in order to generate species 5 and 6, respectively, are
commercially available, carboxylic acids 3 and 4 were prepared
using a cross-coupling methodology (Scheme 3). The key
intermediates to synthesize the former carboxylic acids, ethyl 4-
(diphenylamino)benzoate and ethyl 4-(9H-carbazol-9-yl) ben-
zoate, were prepared via an Ullman-type reaction where 4-iodo-
ethylbenzoate was coupled to diphenylamine and carbazole to
afford the esters in 87 and 75% yield, respectively. Hydrolysis of
the esters in a mixture of 9:1 EtOH/H2O at 60 °C afforded the
desired carboxylic acids 3 and 4 in 83 and 80% yield,
respectively.
The coordination of the carboxylate moiety on the zirconium
cluster was monitored using 1H NMR spectroscopy. The
cyclopentadienyl resonances appeared at δ = 6.72, 6.50, 6.81,
and 7.03 for complexes 5−8, respectively, which represented
significant downfield shifts in comparison to the resonance for
Cp2ZrCl2 (6.31 ppm). The μ3-OH was only observed for
complex 6 in polar aprotic solvents at 9.80 ppm; it was also
possible to observe the presence of the carboxylate ligands in all
complexes in a 1:1 ratio to the cyclopentadienyl rings.
Moreover, the 13C NMR spectra of all complexes did show a
significant downfield shift for all carbon resonances compared
to the free ligands, a consequence of the electronic transfer
from the ligand to the metal center.
−
(Cl2C6H3CO2 )2 (D; Figure 1D), and [(CpZr)3(μ2-O′,O″C-
C6H4Cl)3(μ3-OH)(μ2-OH)3]Cl2·CH2Cl2 (E; Figure 1E)19 have
been synthesized using a self-assembly approach in aqueous
media. To the best of our knowledge, two general synthetic
procedures were reported so far, either from a sodium ethoxide
mediated assembly of carboxylic acids with Cp2ZrCl2 (C) or by
the assembly of carboxylic acids and Cp2ZrCl2 in aqueous
dichloromethane (Figure 1D and E).
In order to further expand the properties of zirconium
metallocavitands as possible hosts for sensing applications, we
investigated the synthesis of zirconium analogues containing
extended cavities with nitrogen-containing carboxylate ligands.
It was our interest to determine if the presence of functional
groups on the organic moieties would impede the formation of
the expected metallocavitands, since all half-sandwich metal-
locavitands reported to date only have aryl groups containing
strong C−X bonds.15−19 Also, several nitrogen-containing
aromatic molecules, notably containing the carbazole and the
diphenylamine moieties, exhibit interesting photoluminescence
properties that could serve as spectroscopic probes for the
characterization of host−guest interactions.20 We herein report
the synthesis and characterization of four new half-sandwich
metallocavitands having amino, diphenylamino, carbazolyl, and
pyridyl moieties. It is possible to demonstrate that the presence
of the metallic core has a positive influence on the blue
luminescence of the conjugated carboxylate ligands.
Structural Study of the Metallocavitands. Colorless
crystals suitable for X-ray diffraction studies were obtained at
room temperature from a solution of methanol for 5, ether for
7, and acetone for 8. All the crystals are air-stable, and the
ORTEP representations are presented in Figures 2−4.
According to their X-ray structures, the central core of all
molecules is composed of a Zr3O10 cluster with pseudo-C3v
symmetry. These zirconium centers are in a slightly distorted
octahedral environment with the cyclopentadienyl ligand trans
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Figure 1. Solid state structures of [{(η5-C5Me5)ZrC1}3(μ-Cl)4(μ3-O)] (A),15 [(Cp2Zr)3(μ2-OH)3(μ3-O)+] (B),16 ([(CpZr)3(μ3-O)(μ2-
OH)3(C6HF4CO2)3]+·(C6HF4CO2 )) (C), [(CpZr)3(μ2-O′,O″C-C6H3Cl2)3(μ3-OH)(μ2-OH)3](Cl2C6H3COO)2 (D),19 and [(CpZr)3(μ2-
18
−
O′,O″C-C6H4Cl)3(μ3-OH)(μ2-OH)3]Cl2·CH2Cl2 (E).19 Carbon in gray; chlorine in green; oxygen in red; zirconium in cyan.
to the μ3-O and the bridging carboxylate cis to the μ2-hydroxyl
groups (see Figure 5 for a model of the metallic cluster). Due
to the steric bulk of the cyclopentadienyl ligand, the
octahedrons are heavily distorted, and the four equatorial O
atoms are greatly pushed toward the apex of μ3-O. The μ3-O
atom and the three μ2-OH’s form a slightly distorted
tetrahedron with three of the four triangular faces capped
with the Zr atoms. A model of the tetrahedron and of the
octahedrons is represented in Figure 6.
In the crystal structure of 5, the pyridinyl groups are
protonated as can be deduced by the presence of four chloride
anions that are linked by hydrogen bonds (see Figure S20, SI).
In the packing of compound 5, every two adjacent cationic
complexes are combined tightly by strong π−π interactions
between the cyclopentadienyl planes (distance of 3.560 Å) to
form molecular pairs, as shown in Figure 7. The neighboring
pairs are further linked together by hydrogen bonds between
the chlorides and the μ2-OH groups and the methanol molecule
present in the crystal lattice to form double-layered sheets in
the b−c plane (see Figure S19, SI). The sheets are packed
together along the a axis to form the final structure. Water
molecules are also present in the structure but are heavily
disordered.
The organic groups in 7 are much more flexible than those in
5 due to the presence of the phenyl rings on the nitrogen
atoms. The free rotation of the phenyl groups partially blocks
the cavity of the metallocavitand. Although two ether molecules
are present in the structure, none of them are located within the
cavity. The μ2-OH groups form strong hydrogen bonds with
the Cl− (O3−Cl1 = 3.017(3) Å, O3−H3O−Cl1 = 154.0(2)°)
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Scheme 2. Synthesis of Zirconium(IV) Metallocavitands by a Self-Assembly Process from Cp2ZrCl2
Scheme 3. Synthesis of the Carboxylic Acids 3 and 4 (NR2 = NPh2 and Carbazol-9-yl, Respectively)
Figure 3. The ORTEP plot of 7 with 50% probability. All hydrogen
atoms and solvent molecules are omitted for clarity.
heteroaromatic fragment can rotate easily along the N−C single
bond in the crystal structure of 8. One consequence of this
behavior is the presence of two crystallographic independent
[(CpZr)3(κ2,O′,O″CR)3(μ3-O)(μ2-OH)3]+ (R = carbazole)
cations in the asymmetric unit. Even if there is rotation
between the plane of the phenyl groups and of the carbazole
moiety, the cavity is wide enough to have one acetone molecule
captured in one of the independent molecules of 8, while there
is no guest molecule in the second cavity (see Figure S23, SI).
Five different solvent molecules are located in the structure,
two of them with occupancy factors of 0.8 and 0.5, respectively.
According to the differential Fourier map, more acetone
molecules can be assigned in the structure, but they are heavily
Figure 2. The ORTEP plot of 5 with 50% probability. All hydrogen
atoms and solvent molecules are omitted for clarity.
and with the oxygen atom of one of the ether molecules (O4−
O11 = 2.950(5) Å, O4−H4O−O11 = 144.30(2)°). The
complexes in the crystal structure of 5 are assembled together
to form single layers in the a−c plane, with the different layers
further packed together along the b axis to form a 3D structure.
One more ether molecule is located between the spacing of
adjacent cations, as illustrated in Figure S21 (see SI).
Although the carbazole ring is more rigid than the
diphenylamine moiety, it is possible to observe that the large
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Figure 6. Representation of the tetrahedron and of the three
octahedrons in the core of 5−8.
former layer in the a−b plane. Two kinds of layers are packed
together alternatively along the c axis to form the 3D structure
(see Figure S24, SI).
Contrarily to the neutral [(Cp*Ta)3(μ3-OH)(μ2-OH)(μ2-
O)2(μ2-O2BR)3] core observed for the tantalum species, the
zirconium analogues are observed as cationic [(CpZr)3(μ3-
O)(μ2-OH)3(μ2-O2CR)3]+ species where the charge is balanced
by the presence of a chloride in the structure. Therefore, the
position of the hydroxyl groups differs in the zirconium species
since in the latter complexes a μ3-O moiety is observed,
whereas μ3-OH is present in the tantalum analogues. As such,
species 5−8 have three bridging hydroxyl groups, as can be
deduced from the longer Zr−O and Zr−Zr distances compared
to the Ta−O and Ta−Ta distances. The difference between the
shortest and the longest Zr−O distances is very small (ΔM-(μ2-
O) and varies from 0.015 to 0.042 Å in complexes 5−8,
whereas the variation can be as important as 0.185 Å in the
tantalum metallocavitands, as represented for two characteristic
species in Table 1, as a consequence of the presence of two μ-O
and one μ-OH in the central core rather than three equidistant
μ2-OH’s. The average Zr−(μ3-O)−Zr bond angles at the
central oxygen atom in 5, 7, and 8 are nearly the same (108°)
Figure 4. The ORTEP plot of 8 with 50% probability. All hydrogen
atoms and solvent molecules are omitted for clarity.
disordered over different positions. Strong hydrogen bonds
between the μ2-OH group, the chlorides, and the O atoms of
the acetone molecules are found in the structure. Interestingly,
two of the first crystallographic independent
[Zr3O4H3Cp3(RCOO)3]+ cations are combined together in a
mouth-to-mouth mode to form a cage where two guest
molecules of acetone are sealed. The cages are tightly packed
together to form a layer in the a−b plane. As for the second
crystallographic independent [(CpZr)3(κ2,O′,O″CR)3(μ3-
O)(μ2-OH)3]+ species, the cations are interpenetrated into
each other in mouth-to-tail mode to form pairs without a guest
molecule. These pairs are arranged into layers parallel to the
Figure 5. Labeling scheme for the inorganic core in Ta3O4 and Zr3O4 complexes.
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Figure 7. Representation of the strong π−π interaction between Cp molecules in 5.
Table 1. Interatomic Distances in the Metallic Core of
Zirconium and Tantalum Metallocavitands
dM1−
dM2−
dM1−
av. M-(μ2-O) (ΔM-
complex
M2 (Å)
M3 (Å)
M3 (Å)
(μ2-O)) (Å)
a
Ta3-4OPh
3.322
3.337
3.346
3.295
3.341
3.361
3.477
3.407
3.341
2.02 (0.185)
2.06 (0.080)
2.12 (0.015)
a
Ta3-4PhEt
Zr3-4C5H5N
(5)
Zr3-4C18H15N
3.364
3.361
3.354
3.340
3.350
3.355
2.13 (0.042)
2.12 (0.026)
(7)
Zr3-4C18H13N
(8)
a
Values reported in ref 13a.
and are all comparable with those reported for [(C5H5Zr)3(μ3-
1 8
O)(μ2 -OH)3 (C6 HF4 CO2 )3 ]+ ·(C6 HF4 CO2
)
and
−
[(CpZr)3(μ2-O′,O″C−C6H3Cl2)3(μ3-OH)(μ2-OH)3]·
(Cl2C6H3COO)2.19 Moreover, the metal oxygen distances
(Zr−O) observed for all of the carboxylate ligands are longer
than those observed for the boronate (B−O) species in the
tantalum clusters. This difference can be attributed to the
difference in the bonding mode of the carboxylate ligand, which
is formally an LX (L = dative, X = covalent) type of bidentate
ligand, whereas the boronate is formally an X2 ligand. The bond
distances in the trimetallic cores of 5, 7, and 8 are unremarkable
compared to the ones in previously reported carboxylate
complexes with similar structures (Figure 1 C, D, and E), where
the Zr−Zr and Zr−O distances vary from 3.33 to 3.36 Å and
2.10 to 2.14 Å, respectively.18,19
As observed in the space-filling representations in Figure 8,
all species exhibit the expected C3 symmetry. In the case of 5,
the presence of the pyridinyl group does not alter significantly
the shape of the cavity compared to what was observed in the
presence of the phenylboranate tantalum clusters.13 However,
in the case of 7 and 8, the significant flexibility and the large
volume of the diphenylamine and carbazole moieties induce a
rotation along the Caryl−N bonds, which blocks in part the
cavity. As desired, the modification of the tantalum−boronate
core for a zirconium−carboxylate one reduces the electrophilic
character of the cavitands since they do not interact with Lewis
bases. Indeed, no interaction is observed in solution or in a
solid state between the inorganic core and THF or acetone. On
the contrary, the species get protonated readily and are
observed as [(CpZr)3(μ3-O)(μ2-OH)3(μ2-O2CR)3]+ cores.
Optical Properties of Metallocavitands. In the past few
years, many transition-metal-based organometallic compounds
Figure 8. Space-filling views of 5 (top), 7 (down left), and 8 (down
right), obtained from crystallographic data. Carbon atoms are in gray;
hydrogen atoms are in white; oxygen atoms are in red; zirconium
atoms are in navy blue, and nitrogen atoms are in purple.
have attracted attention for their fluorescence and phosphor-
escence properties in the solid state. When stable under
ambient conditions, these compounds become promising
candidates for light-emitting diodes.21 While the red and
green region of the visible spectrum can be reached quite easily
with organometallic compounds, stable blue emitters with high
solid-state quantum yield are much less common due to
decomposition22 or nonradiative deactivation processes.23 Also,
the preparation of blue organometallic emitters requires the use
of large π−π* energy gap ligands whose electronic properties
can be coupled to the metal center through various
mechanisms.
The absorption and photoluminescence properties of
metallocavitands 7 and 8 have been determined in solution,
with the typical spectra in Figure 9, and the results are
summarized in Table 2. Both metallocavitands absorb in the
UV region and exhibit blue photoluminescence under UV
excitation. Interestingly, the absorption and photoluminescence
spectra are red-shifted compared to the spectra of their ligands
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Figure 9. Photoluminescence (left) and absorption (right) spectra of compounds 3 (blue), 4 (black broken line), 7 (dark cyan), and 8 (red solid
line). The asterisk (∗) represents the excitation peaks.
CONCLUSION
Table 2. UV/Vis and Photoluminescence Data for Species
Containing the Conjugated Nitrogen Containing
Carboxylate Ligands
■
In the present study, the synthesis and characterization of new
trinuclear Zr(IV) metallocavitands based on nitrogen-contain-
ing carboxylic acids are reported and structurally compared to
previously reported Ta(V) boronate metallocavitands. As
expected, the inorganic core is more nucleophilic as observed
by the protonation of one of the bridging oxygens to generate
[(CpZr)3(κ2,O′,O″CR)3(μ3-O)(μ2-OH)3]Cl species rather
than neutral compounds as observed with tantalum. The
possibility of free rotation between the phenyl ring and the
diphenylamine and carbazolyl moieties in species 7 and 8,
respectively, induce the blockage of the cavities in the latter
complexes. As such, these species does not exhibit significant
interactions with the fullerenes.
a
b
compound λmax (absorption) (nm) λfluo (nm)
ΦF
ε (M−1 cm−1
)
3
4
7
8
326
327
333
342
415
400
464
422
0.73
0.66
0.87
0.65
8500
26 400
6500
20 700
a
All spectra were recorded in THF solutions at room temperature at c
= 1.4 × 10−6 to 7.2 × 10−6 M for absorption and photoluminescence.
b
Photoluminescence quantum yields were determined relative to 9,10-
diphenylanthracene in cyclohexane (ΦF = 0.9).
Nevertheless, these inorganic species are revealed to be
excellent blue-emitting materials. The inorganic carboxylate
materials are exhibiting a bathochromic shift compared to the
corresponding carboxylic acids. Interestingly, the quantum yield
of photoluminescence of the diphenylaminobenzoate moiety is
significantly enhanced when coordinated on zirconium.
in the carboxylic acid form (3 and 4, respectively), suggesting
that the effective conjugation length has been increased upon
attachment of the ligand to the zirconium center. More
experiments need to be performed to assess if these
bathochromic shifts are attributed to a donor−acceptor
interaction between a nitrogen-containing ligand and the
metal center or to the enhanced electro-withdrawing character
of the Zr−OOC moieties. The fact that this red-shift is
particularly marked in the photoluminescence spectrum of
metallocavitand 7, whose photoluminescence peak is shifted by
ca. 50 nm compared to that of ligand 3, supported this
hypothesis since triarylamine is known to be a stronger electron
donor than carbazole.24 Solvatochromism absorption experi-
ments were carried out, and the absorption maxima slightly
shift depending on the nature of the solvent. However, since in
most solvents, with the exception of THF, there is a presence of
partial precipitation and aggregation of the metallocavitands,
the interpretation of these data is unreliable.
The photoluminescence quantum yields (ΦF) of the ligands
and their metallocavitands have also been measured using 9,10-
diphenylanthracene as the reference. Surprisingly, the ΦF value
increased significantly when the triarylamine was attached to
the Zr center (ΦF = 0.73 and 0.87, for 3 and 7, respectively),
while the ΦF values are almost identical for 4 and 8. Moreover,
both metallocavitands 7 and 8 are highly fluorescent in the solid
state, although ΦF values could not be measured. These results
suggest that these new metallocavitands might be used as
efficient blue emitters in light-emitting diodes to enhance the
photoluminescence of already efficient carboxylate species.
EXPERIMENTAL SECTION
■
General Procedure. All solvents (ACS grade) were distilled and
put through a Vacuum Atmosphere Company (CA, USA) solvent
purification system. All of the reagents were purchased from Sigma-
Aldrich Co., TCI America, or Oakwood Products and used as received.
All reactions were carried out under an atmosphere of argon with
freshly distilled solvents, unless otherwise noted. Microwave heating
was performed in the single-mode microwave cavity of a Monowave
300 (Anton Paar Co.), and all microwave-irradiated reactions were
conducted in heavy-walled glass vials sealed with Teflon septa. Silica
gel (SiliaFlash P-60) was used for column chromatography. NMR
spectra were recorded on an Agilent Technologies NMR spectrometer
at 500 MHz (1H) and 125.758 MHz (13C) or a Varian Inova NMR
AS400 spectrometer, at 400.0 MHz (1H) and 100.580 MHz (13C). 1H
NMR and 13C NMR chemical shifts are referenced to residual protons
or carbons in deuterated solvent. Mass spectra were performed by the
Mass Spectrometry Facilities at Laval University with an Agilent 6210
Time-of-Flight (TOF) LC-MS apparatus equipped with an ESI or
APPI ion source (Agilent Technologies, Toronto, Canada). UV−vis
spectra were measured on a Varian Cary 500 Scan spectrophotometer.
The photoluminescence spectra were collected on a Varian Cary
Eclipse Spectrofluorometer with excitation and emission slits of 5 nm.
All samples were degassed by bubbling nitrogen or argon through the
solutions.
Synthesis. Ethyl 4-(Diphenylamino)benzoate. Diphenylamine
(0.66 g, 4.0 mmol), 4-iodoethyl benzoate (2.0 g, 7.2 mmol), copper
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powder (25 mg, 0.4 mmol), and potassium carbonate (1.66 g, 12
mmol) were mixed and stirred at 250 °C for 90 min using microwave
irradiation under a nitrogen atmosphere. After the reaction, the
reaction mixture was poured into brine, washed, and extracted using
dichloromethane. The organic extracts were dried over MgSO4 and
concentrated by rotary evaporation. The solid residue was purified by
column chromatography (DCM/n-hexane = 4:6) and gave the desired
product as an off-white solid (1.10 g, 3.5 mmol, 87%). 1H NMR (500
MHz, CDCl3): δ 7.86 (d, J = 7.3 Hz, 2H), 7.30 (t, J = 7.1 Hz, 4H),
7.12 (m, 6H), 6.99 (m, 2H), 4.37−4.30 (q, J = 7.0 Hz, 2H), 1.36 (t,
4.1 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ 166.4, 151.9,
146.7, 130.8, 129.5, 125.7, 124.3, 122.6, 120.1, 60.5, 14.4. HRMS
(ESI): m/z [M + H]+ calcd for C21H20NO2: 318.1485. Found:
318.1489.
Ethyl 4-(9H-Carbazol-9-yl)benzoate. Carbazole (0.66 g, 4.0
mmol), 4-iodoethyl benzoate (2 g, 7.2 mmol), copper powder (25
mg, 0.4 mmol), and potassium carbonate (1.656 g, 12 mmol) were
mixed and stirred at 250 °C for 90 min using microwave irradiation
under a nitrogen atmosphere. After the reaction was finished, the
reaction mixture was poured into brine, washed, and extracted using
dichloromethane. The organic extracts were dried over MgSO4 and
concentrated by rotary evaporation. The solid residue was purified by
column chromatography (DCM/n-hexane = 3:7) to give the expected
product as an off-white solid (0.95 g, 3.0 mmol, 75%). 1H NMR (500
MHz, CDCl3): δ 8.33−8.28 (m, 2H), 8.19−8.13 (m, 2H), 7.71−7.66
(m, 2H), 7.51−7.40 (m, 4H), 7.36−7.29 (m, 2H), 4.47 (q, J = 7.1 Hz,
2H), 1.47 (t, J = 7.1 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ
165.9, 141.2, 140.2, 131.3, 129.0, 126.4, 126.2, 123.7, 120.5, 120.4,
109.7, 61.2, 14.4. HRMS (ESI): m/z [M]*+ calcd for C21H17NO2:
315.1254. Found: 315.1249.
4-(Diphenylamino)benzoic acid (3). A solution of ethyl 4-
(diphenylamino)benzoate (0.16 g, 0.97 mmol) was dissolved in
ethanol (20 mL) and treated with a solution of KOH (20 mL, 4 M),
then heated to 60 °C for 12 h. After the completion of the reaction,
the solvent was removed in a vacuum and followed by the addition of
HCl (1 M solution in water) until it reached a pH ∼ 2. The aqueous
solution was extracted with EtOAc (3 × 10 mL), and the organic
layers were combined and dried over MgSO4. The solution was filtered
and concentrated under reduced pressure to afford the desired acid 3
as a white solid (0.61 g, 83%).1H NMR (500 MHz, CDCl3): δ 7.91 (d,
J = 7.9 Hz, 2H), 7.31 (t, J = 7.4 Hz, 4H), 7.14 (m, 6H), 6.98 (m, 2H).
13C{1H} NMR (125 MHz, CDCl3): δ 172.1, 152.7, 146.5, 131.6,
129.6, 126.0, 124.7 121.0, 119.5. HRMS (ESI): m/z [M + H]+ calcd
for C19H15NO2: 289.1097. Found: 289.1118.
were combined. The latter phase was dried over anhydrous MgSO4
and filtered, and the solvent was removed under reduced pressure. The
residue was further dried under vacuum conditions to give the crude
product, which was further purified by precipitation or crystallization.
[(CpZr)3(κ2,O′,O″C-C5H4N)3(μ3-O)(μ2-OH)3]·4HCl (5). Compound 5
was synthesized according to the general method described above and
1
crystallized from methanol (white solid, 80%). H NMR (500 MHz,
DMSO-d6): δ 8.73 (d, J = 5.7 Hz, 6H), 8.08 (d, J = 5.9 Hz, 6H), 6.72
(s, 15H). 13CNMR (125 MHz, CDCl3): δ 172.6, 149.0, 143.62, 126.1,
118.4. HRMS m/z [M + H]+ or [M]*+ not observed by ESI or TOF.
[(CpZr)3(κ2,O′,O″C-C6H7N)3(μ3-O)(μ2-OH)3]·HCl (6). Compound 6
was synthesized according to the general method described above and
1
purified by trituration from tetrahydrofuran (white solid, 40%). H
NMR (500 MHz, DMSO-d6): δ 9.80 (s, 3H), 7.57 (d, J = 8.7 Hz, 6H),
6.50 (s, 15H), 6.48 (d, J = 8.7 Hz, 6H). 13C NMR (125 MHz): 173.5,
154.4, 132.6, 117.5, 115.9, 113.0. HRMS (ESI): m/z [M]*+ calcd for
C36H36N3O10Zr3: 939.9536. Found: 940.9560.
[(CpZr)3(κ2,O′,O″C-C18H15N)3(μ3-O)(μ2-OH)3]·HCl (7). Compound 7
was synthesized according to the general method described above and
1
crystallized from acetone (white solid, 45%). H NMR (500 MHz,
CDCl3): δ 7.75−7.71 (m, 6H), 7.30−7.26 (m, 12H), 7.12−7.09 (m,
18H), 6.93−6.90 (m, 6H), 6.81 (s, 15H). 13C{1H} NMR (125 MHz,
CDCl3): δ 172.8, 152.0, 146.7, 131.5, 129.5, 125.7, 124.3, 120.1, 116.5.
HRMS (ESI): m/z [M]*+ calcd for C72H60O10N3Zr3: 1396.1414.
Found: 1396.1466.
[(CpZr)3(κ2,O′,O″C-C18H13N)3(μ3-O)(μ2-OH)3]·HCl (8). Compound 8
was synthesized according to the general method described above and
1
crystallized from acetone (white solid, 80%). H NMR (500 MHz,
CDCl3): δ 8.27 (d, J = 8.4 Hz, 6H), 8.10 (d, J = 7.6 Hz, 6H), 7.66 (d, J
= 8.4 Hz, 6H), 7.40 (d, J = 8.2 Hz, 6H), 7.34−7.29 (m, 6H), 7.28−
7.24 (m, 6H), 7.03 (s, 15H). 13C{1H} NMR (125 MHz, CDCl3): δ
172.5, 142.2, 140.1, 132.0, 130.7, 126.3, 126.2, 123.7, 120.5, 120.4,
117.0, 109.7. HRMS (ESI): m/z [M]*+ calcd for C72H54O10N3Zr3:
1390.0945. Found: 1390.0956.
Calculation of Photoluminescence Quantum Yield. Photo-
luminescence quantum yields were calculated using the standard
samples which have a fixed and known photoluminescence quantum
yield value, according to the following equation:
ΦF = Φ(I/Ir) × (OD /OD) × (η2/η 2)
r
r
r
Subscript r represents the standard samples, Φ represents the
photoluminescence quantum yield, η represents the refractive index
of the solvent, OD represents the calculated area from photo-
luminescence spectra in cm−1, and I represents the absorbance
intensity.
4-(9H-Carbazol-9-yl)benzoic Acid (4). A solution of ethyl 4-(9H-
carbazol-9-yl)benzoate (0.16 g, 0.97 mmol) was dissolved in ethanol
(20 mL) and treated with a solution of KOH (20 mL, 4 M), then
heated to 60 °C for 12 h. After the completion of the reaction, the
solvent was removed in a vacuum, followed by the addition of HCl (1
M solution in water) until it reached a pH ∼ 2. The aqueous solution
was extracted with EtOAc (3 × 10 mL), and the organic layers were
combined and dried over MgSO4. The solution was filtered and
concentrated under reduced pressure to afford the desired acid 4 (0.61
Procedure.
1. Prepare the sample of compounds 3, 4, 7, and 8 having
different absorbances between 0.01 and 0.1 at the excitation
wavelength of each compound.
2. Measure the photoluminescence spectrum for the entire
emission region with the prepared samples using the specific
excitation wavelength of the desired compound.
3. Calculate the area in cm−1 from the spectrum.
4. Calculate the photoluminescence quantum yield from the
equation mentioned above.
1
g, 85%) as a white solid. H NMR (500 MHz, CDCl3): δ 8.39 (d, J =
8.5 Hz, 2H), 8.16 (d, J = 7.7 Hz, 2H), 7.76 (d, J = 8.5 Hz, 2H), 7.55−
7.50 (m, 2H), 7.48−7.42 (m, 2H), 7.34 (m, 2H). 13C{1H} NMR (125
MHz, CDCl3): δ 171.1, 142.9, 140.1, 132.1, 127.6, 126.4, 126.2, 123.9,
120.7, 120.5, 109.8. HRMS (ESI): m/z [M]*+ calcd for C19H15NO2:
287.0941. Found: 287.0961.
Synthesis of Metallocavitands [(CpZr)3(κ2,O′,O″CR)3(μ3-
O)(μ2-OH)3]·HCl. All the cavitands were synthesized according to
the same general procedure. Benzoic acid (1.0 mmol) was dissolved in
water (5.0 mL), and sodium hydroxide NaOH (1.0 mmol) was then
added, and the solution was adjusted to pH 6−7 by addition of
hydrochloric acid, when a precipitate was formed. This suspension was
then added via pipet dropwise to a solution of zirconocene (Cp2ZrCl2,
1.0 mmol) in dichloromethane (15 mL) under vigorous stirring. The
reaction mixture was stirred for 15 more minutes at room temperature,
and the two-phase system was allowed to separate. The aqueous phase
was extracted with dichloromethane (10 mL), and the organic phases
Crystallographic Studies. Single crystals with suitable size of all
compounds were mounted on CryoLoops with Paratone-N and
optically aligned on a Bruker SMART APEX-II X-ray diffractometer
with a 1K CCD detector using a digital camera. Initial intensity
measurements were performed using a fine-focused sealed tube,
graphite-monochromated, X-ray source (Mo Kα, λ = 0.71073 Å) at 50
kV and 30 mA. The standard APEX-II25 software package was used for
determining the unit cells, generating the data collection strategy, and
controlling data collection. SAINT26 was used for data integration
including Lorentz and polarization corrections. Semiempirical
absorption corrections were applied using SCALE (SADABS).27 The
structures of all compounds were solved by direct methods and refined
by full-matrix least-squares methods with SHELX-9728 in the
SHELXTL6.14 package. As the solvent molecules in some compounds
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dx.doi.org/10.1021/ic402602d | Inorg. Chem. 2014, 53, 2883−2891

Inorganic Chemistry
Article
are highly disordered, the SQUEEZE subroutine of the PLATON29
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highly disordered guest molecules. The resulting new HKL files were
used to further refine the structures. All of the H atoms (on C atoms)
were generated geometrically and refined in riding mode. Crystallo-
graphic information for all obtained phases is summarized in Table S1.
Atomic coordinates and additional structural information are provided
in the cif files of the Supporting Information.
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ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectra of species 1−8 and additional crystallographic
figures are available. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystallographic data have
been deposited with CCDC (CCDC No. 966119 for 5, CCDC
No. 966120 for 7, and CCDC No. 966121 for 8). These data
can be obtained upon request from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK, e-mail: deposit@ccdc.cam.ac.uk, or via the Internet at
www.ccdc.cam.ac.uk.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: frederic.fontaine@chm.ulaval.ca.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
(16) Niehues, M.; Erker, G.; Meyer, O.; Frohlich, R. Organometallics
̈
We are grateful to FQRNT (Projet de recherche en eq
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uipe -
ec), and CQMF
́
ec) for financial support. We acknowledge the help of
2000, 19, 2813−2815.
Queb
(Queb
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Pierre Audet with the HR-MS experiments.
(19) Li, J.; Gao, Z.; Han, L.; Gao, L.; Zhang, C.; Tikkanen, W. J.
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