Synthesis of tetrathiafulvalene-containing zirconium(IV) pincers and metallocavitands for hosting fullerenes

Article abstract of DOI:10.1016/j.ica.2014.04.034

The synthesis and spectroscopic characterization of zirconium(IV) dicarboxylate 1 and metallocavitand 2 are described. Encapsulation studies of fullerenes C₆₀ and C₇₀ were performed using UV-Vis spectroscopy in chlorobenzene, toluene, benzene, carbon disulfide and in a mixture of toluene/dichloromethane. UV-Vis titrations have shown that the binding abilities of the hosts toward fullerene C₇₀ are considerably higher than those obtained for fullerene C₆₀.

Full text of DOI:10.1016/j.ica.2014.04.034

Accepted Manuscript
Synthesis of Tetrathiafulvalene-Containing Zirconium (IV) Pincers and Metal-
locavitands for Hosting Fullerenes
Hassan Iden, Jean-François Morin, Frédéric-Georges Fontaine
PII:
S0020-1693(14)00239-4
http://dx.doi.org/10.1016/j.ica.2014.04.034
ICA 15973
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 January 2014
22 April 2014
23 April 2014
Please cite this article as: H. Iden, J-F. Morin, r-G. Fontaine, Synthesis of Tetrathiafulvalene-Containing Zirconium
(IV) Pincers and Metallocavitands for Hosting Fullerenes, Inorganica Chimica Acta (2014), doi: http://dx.doi.org/
10.1016/j.ica.2014.04.034
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Synthesis of Tetrathiafulvalene-Containing Zirconium
(IV) Pincers and Metallocavitands for Hosting
Fullerenes
Hassan Iden,a,b,c Jean-François Morin* a,b and Frédéric-Georges Fontaine* a,c
a) Département de Chimie, Université Laval, 1045 Avenue de la Médecine, Québec (Québec),
Canada, G1V 0A6
b) Centre de Recherche sur les Matériaux Avancés (CERMA), Université Laval
c) Centre de Catalyse et Chimie Verte (C3V), Université Laval
email :
frederic.fontaine@chm.ulaval.ca
jean-francois.morin@chm.ulaval.ca
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if
required according to the journal that you are submitting your paper to)
Submitted to Inorganica Chimica Acta
1

Abstract
The synthesis and spectroscopic characterization of zirconium (IV) dicarboxylate 1 and
metallocavitand 2 are described. Encapsulation studies of fullerenes C60 and C70 were performed
using UV-vis spectroscopy in chlorobenzene, toluene, benzene, carbon disulfide and in a mixture
of toluene/dichloromethane. UV-vis titrations have shown that the binding abilities of the hosts
toward fullerene C70 are considerably higher than those obtained for fullerene C60.
Keywords
Metallocavitands, Zirconium, Fullerenes, Host-guest, Supramolecular
Highlights
- Tripodal zirconium metallocavitands having TTF-derivatized carboxylate ligands was made.
- The solubility of the carboxylate ligands has an influence on the structure of the complexes.
- The metallocavitands can host fullerenes C60 and C70.
2

Introduction
There has been a broad interest in the past few years in the chemistry of cavitands, notably for
recognition properties [1-6]. By modifying the structural parameters of the cavity, a large array
of guests with different size, shape and charge can be captured inside the void of the hosts. The
advantages that can result from these supramolecular assemblies include the possibility of
stabilizing reactive intermediates [2, 7], hosting unusual molecules within the cavity [8, 9], and
controlling reaction rates, regioselectivity and yields of catalytic processes [10-15]. Although
tailoring of the cavities of cavitands can be done by synthetic pathways in order to improve their
performance, the multi-step functionalization can be tedious and low yielding. An alternative is
the use of coordination chemistry to generate metallocavitands via self-assembly processes.
Using a large array of ligands and metal precursors, it is possible to obtain interesting nanoscale
architectures [16-21]. These structures may find use in a large array of applications as chemical
sensors, nanoscale reaction vessels [22, 23], containers for drug delivery [24, 25], molecular
switches [26-29] and memory storage devices [30]. Our research group has developed in the past
few years an aggregation approach to access trimetallic conical structures with tantalum [31-33].
We focused notably on the one-step synthesis of tantalum (V) boronate metallocavitands. These
metallocavitands can be prepared in good to excellent yield via the one-step reaction of
Cp*TaMe4 with aryl boronic acids [33].
3

Figure 1. Example of a tantalum metallocavitand obtained by X-ray crystallography [32].
These metallocavitands possess a conic cavity similar to calix[4]arenes with a pseudo-C3
symmetry (Figure 1). The cavity can be easily expanded to reach an upper rim area of 175 Å2 by
the introduction of spacers on the aryl boronate moiety [31]. The tantalum metallocavitands have
demonstrated hosting capabilities for Lewis bases such as acetone and tetrahydrofuran via
hydrogen bonding and electrostatic interactions [32]. Owing to their hosting properties, high
yielding synthesis and ease of manipulation, we wanted to expand this concept to the capture of
fullerenes, namely C60 and C70. The fullerenes are quite useful in modern electronics, but in order
to process this material covalent functionalization is needed to increase its solubility [34].
However, the covalent functionalization modifies the π system of the fullerene cages and
therefore reduces their electron accepting properties when compared to the pristine materials
[35]. In the hope of keeping the exceptional electronic properties of fullerenes, a supramolecular
approach is sought after to increase its solubility while keeping its electronic properties [34].
Nevertheless, since the fullerenes are known to be electron acceptors, we were concerned that the
electrophilic metallic core of the tantalum metallocavitands may alter the ability of the
supramolecules to host fullerenes. In order to reduce the electrophilicity of the core while
keeping the C3-conical structure, we decided to expand our study to zirconium (IV) carboxylate
complexes. By replacing the boron atoms of the boronate ligands with carbon atoms using
isoelectronic carboxylate ligands, we expected for the cavity to become less electrophilic and
more prone to interact with fullerenes while keeping similar structural parameters. Two
4

pathways have been used so far for the construction of zirconium (IV) carboxylates with the
desired architecture. The first method involves a sodium ethoxide mediated assembly of
carboxylic acids with Cp2ZrCl2 [36]. Also possible is the assembly of carboxylic acids with
Cp2ZrCl2 in aqueous dichloromethane [37].
-2e_
+2e_
Figure 2. Structures of the neutral (left) and oxidized (right) state of tetrathiafulvalene (TTF).
Non-covalent interactions such as π-π stacking and charge-transfer interactions are the main
driving forces in fullerene host-guest chemistry [38]. From this point of view, π-extended donor
systems such as the tetrathiafulvalene (TTF) are attractive molecules; they adopt a butterfly
shape at the neutral state, while the corresponding dications adopt a twisted conformation that
help the interaction with the spherical shape of the fullerene (Figure 2) [39]. This class of
molecules has been used in the construction of hosts for fullerenes using aromatic π–π-stacking
interactions between the surface of fullerenes and the extended tetrathiafulvalene (exTTF) [40-
47]. Therefore, the design and investigation of new recognition molecules based on zirconium
(IV) metallocavitands having TTF units will undoubtedly push forward the development of
metallocavitands as hosts for fullerenes. We report herein the synthesis and the structural
characterization of zirconium species containing extended cavities with exTTF carboxylate
ligands and demonstrate that these metallocavitands can host C60 and C70.
5

Results and Discussion
In order to generate the desired metallocavitands, the synthesis of the TTF-containing carboxylic
acids 8 and 12 were carried out. Compound 8 was synthesized in five steps as described in
Scheme 1. The synthesis starts by the protection of the hydroxyl group of 2-hydroxyquinone 3
using tert-butyldimethysilyl (TBS) in DMF [48]. The desired product 4 was isolated in 75%
yield after purification on silica gel. The reaction of TBS-protected 2-anthraquinone 4 with 2-
dimethoxyphosphinyl-1,3-dithiole using the Wittig–Horner reaction [49] in dry THF in the
presence of n-butyllithium at -78 oC gave product 5 in 60% yield. The subsequent removal of the
protecting group was accomplished by treatment of compound 5 with tetrabutylammonium
fluoride (TBAF) to obtain compound 6 in 84% yield [46]. The SN2 substitution reaction of the
phenol 6 with methyl 4-(bromomethyl)benzoate yielded corresponding ester 7 in 95% yield.
Hydrolysis of the latter product with lithium hydroxide followed by the acidification of the
aqueous phase and by filtration provided the desired acid 8 in 95% yield after purification by
precipitation.
Since most of the binding studies with fullerenes are done in organic solvents, the introduction of
an aliphatic chain was carried out at the 6 position to make the molecule more lipophilic which
should result in an enhanced solubility. The triethylene glycol (TEG) chain was used by ease of
preparation and high solubility in organic and aqueous systems [52]. It is also known that glycol
chains are helpful in the preparation of fullerene receptors, since they stabilize the complex
formed with fullerenes through n-π interaction [49-51]. Synthesis of TEG-TTF was
accomplished from anthraflavic acid in a four-step procedure as outlined in Scheme 2. The first
step of this synthesis was the TEGylation with triethylene glycol bromide; however, this product
was used as crude material due to the difficult separation from the bis TEGylated product and
unreactive glycol chains. Nucleophilic substitution of the crude material with methyl 4-
(bromomethyl)benzoate yielded the crude product 10 that was purified by precipitation in
methanol in 23% yield for the two-steps synthesis. The addition of 2-dimethoxyphosphinyl-1,3-
dithiole to compound 10 using the Wittig–Horner [49] reaction in dry THF in the presence of n-
o
butyllithium at -78 C yielded the corresponding ester 11 in 83% yield. Hydrolysis of the ester
with lithium hydroxide following by acidification with hydrochloric acid yielded the desired acid
12 in 92% yield (Scheme 3).
6

Scheme 1. Synthesis of monosubstituted TTF carboxylic acid 8.
7

Scheme 2. Synthesis of bissubstituted TTF carboxylic acid 12.
8

Scheme 3. Synthesis of host 1.
9

Scheme 4. Synthesis of TTF zirconium (IV) metallocavitand 2.
The synthesis of the zirconium carboxylate species 1 and 2 was accomplished according to a
published procedure by reacting carboxylic acids 8 and 12, respectively, with zirconocene
dichloride in aqueous media, as described in Schemes 3 and 4 [37]. It was possible to observe by
1H NMR spectroscopy of both solutions the disappearance of the acidic carboxylic protons,
suggesting that the coordination of the carboxylate moieties had taken place. The presence of
sharp singlets at δ = 6.31 and 6.33 for compounds 1 and 2, respectively, confirms the presence of
the cyclopentadienyl rings. The resonances for the aromatic protons were present in the ∼δ 8.10–
6.80 region. When looking at the integration values for the proton resonances of the carboxylate
ligands and of the cyclopentadienyl ligands, it is possible to observe that these two moieties are
present in a 1:1 ratio in both complexes 1 and 2. Although it was expected for compound 1 to
10

adopt a trimetallic structure reminiscent of analogous chemistry with arylcarboxylates [36,37],
including nitrogen-containing arylcarboxylates [54], the exact MS data does not agree with such
an assignment.
Indeed, a m/z of 1277.9918 was observed which correspond to a biscarboxylate
biscyclopentadienyl species as illustrated in Scheme 3. Similar biscarboxylate compounds had
already been described when carboxylic acids were added to zirconocene at lower pH [37]. It is
probable that the low solubility of carboxylic acid 8 or of complex 1 played a role in stopping the
reaction before the Cp ring could be extruded in order to generate the trimetallic species. The
mass spectrometry results of species 2 suggest that with more soluble TEG-TTF derivative a
metallocavitand was indeed obtained as expected from related chemistry. The formation of the
trimetallic species 2 is probably made possible by a better solubility of the carboxylic acid and of
the resulting complex, which allows the formation of larger molecular weight species.
Fullerenes Binding Studies
Interaction between a host and fullerenes in solution results in a decrease of the intensity of the
band of the host in UV-vis spectroscopy. Addition of a solution of the fullerenes into a solution
of the host 1 and of metallocavitand 2 allows measurement of the progressive decrease at the
absorption maximum (λmax) of the host and therefore allows the determination of the binding
constants. The association constants were obtained using the Hill equation [55] and are
summarized in Table 1. As mentioned above, the addition of fullerene C60 to a solution of host 2
results in a decrease and a small red shift in the absorbance band. Figure 3 illustrates an example
of titration of a 3 mL solution of host 2 at a concentration of 10-5 mol L-1 with a 7.2 10-3 mol L-1
stock solution of fullerene C60 in chlorobenzene. A clear isobestic point was observed at 445 nm
indicative of the formation of a 1:1 complex, as demonstrated by a Job plot (Figure S2). The
number of cooperative sites was calculated using Hill equation [55] which reveals the formation
of a 1:1 complex. Using the Hill equation, we estimate the binding constant (Ka) at 900 210
M-1, which is relatively low compare to the best TTF-based host reported to date [50].
11

ꢀ
n
n
ꢁ
ꢂ
K
ꢀ∆Abs
max
C
h
a
ꢅ
∆Absꢀ =
n
n
ꢀ
ꢃ
ꢁ
ꢂ ꢄ
C
1ꢀ + ꢀK
a
h
Ka is the association constant and n the Hill coefficient and [Ch] the concentration of host.
0,5
0 eq. C60
0,4
102 eq. C
0,06
60
0,04
0,3
Ka = 895 M-1
0,02
R2 = 0,996
0,2
0,00
0,1
0,0
0,5
[C ]x103
1,0
1,5
60
0,0
-0,1
450
500
[C ]x103
550
600
650
60
Figure 3. (a) UV-vis spectral changes of 2 (1.0. 10-5 M) upon addition of stock solution of C60
(7.3 10-3 M) in chlorobenzene at 298 K. Inset: Plot of the UV-vis changes at 431 nm.
Table 1 Binding constant Ka (M-1) and selectivity factor (Ka,C70/Ka,C60 ) for complexation of C60
and C70 with hosts 1 and 2 in four different solvents.
a
b
b
Host
Solvent
Ka C60 (M-1)
Ka C70 (M-1)
Ka,C70/Ka,C60
12

Chlorobenzene
Chlorobenzene
Toluene/DCM 2:1
CS2
640 150
900 210
2730 610
820 170
-
-
3.8
-
1
2
3380 1290
-
-
-
a DCM = dichloromethane. b UV-vis (298 °K). The Ka values were calculated using Hill
equation.
C60 is less soluble in toluene so we thought that decreasing fullerene solubility could increase the
binding interactions between the fullerene and the metallocavitand. However, toluene did not
improve the affinity, probably due to the low solubility of our guest in toluene and no association
constant was measured. Nevertheless, when a 2:1 mixture of toluene/DCM was used, a four fold
increase of the binding constant was observed compared to chlorobenzene. Correspondingly to
what was observed with chlorobenzene, the band at 440 nm for host 2 in toluene/DCM decreases
upon addition of C60 while a new band at (λmax) 490 nm appeared, forming a clear isobestic point
at 460 nm, which points to the formation of a 1:1 complex in this solvent. A binding constant of
2730 610 M-1 was estimated using Hill equation, with a Hill coefficient of 1, which is a clear
indication of the formation of a 1:1 complex (Figure S5). As a model for the binding between C60
and host 1, energy-minimized structure of 1-C60 was obtained (Figure 4). The model is consistent
with the data mentioned above which suggest the formation of 1:1 complex.
13

Figure 4. Energy-minimized structure of the self-assembled metallocavitand 2 with fullerene C60
obtained with amber field force using HyperChem (TEG chains were removed for clarity).
Figure 5. Energy-minimized structure of the self-assembled metallocavitand 2 with fullerene C70
obtained with amber field force using HyperChem (TEG chains were removed for clarity).
Not surprisingly, host 2 preferentially binds to C70 in comparison to C60 as the average selectivity
for C70 over C60 is 3.8. Such a stabilization of the C70⊂2 supramolecular complex can be
attributed to the presence of additional π-π interactions between the curved surface of C70, which
has a flatter surface than C60 (better π-contact), and the curved π-region of host. The slightly
lower solubility of C70 compare to C60 can also play a role. Surprisingly, host 2 formed a 2:1
complex with C70 (Figure 5) as determined with the Job’s plot (Figure S3), suggesting that host 2
is too tight to accommodate the bigger C70. To the best of our knowledge, this is one of the rare
cases in which such difference in the binding mode between C60 and C70 is observed. Similarly
to host 1, the energy-minimized structure of host 2 and C70 suggested the formation of 2:1
complex (Figure 5).
14

0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,00
0 eq. C
70
18 eq. C
70
0,08
0,06
0,04
0,02
0,00
Ka = 3376 M-1
R2 = 0,999
0,00
0,02
0,04
0,06
0,08
0,10
[C ]x103
70
450
500
[C ]x103
550
600
70
Figure 6. (a) UV-vis spectral changes of 2 (0.6.10-5 M) upon addition of stock solution of C70
(9.10-4 M) in chlorobenzene at 298 K. Inset: Plot of the UV-vis changes at 430 nm.
Finally, UV-vis spectrophotometric titrations were investigated using host 1. The titration of
fullerene C60 into a solution of host 1 results in a decrease and a red shift of the absorption at
λmax. A clear isobestic point can be observed at 447 nm. A binding constant of 642 M-1 was
measured in chlorobenzene using the Hill equation (Table 1). It is worth mentioning that the
values measured for host 1 are not accurate because of the presence of traces of impurities that
could not be removed.
Conclusions
In summary we have synthesized two new TTF containing zirconium complexes as hosts for
fullerene. In presence of the carboxylic acid 8, host 1, having two carboxylate ligands, was
formed rather than the expected metallocavitands, probably because of the lower solubility of the
15

precursors. The addition of a triethyleneglycol chain to the carboxylic acid increases
significantly the solubility and allows the formation of metallocavitand 2. The latter species has
shown low binding affinity toward C60 and the Job’s plot suggests the formation of a 1:1
complex between the fullerene C60 and host 2. A small improvement was observed toward C70
capture due to the ellipsoidal form, hence increasing the contact between host and guest.
Interestingly, in the latter case, a 2:1 complex was formed.
Experimental section
General Procedure
General: All solvents (ACS grade) were distilled and put through a Vacuum Atmosphere
Company (CA, USA) solvent purification system. All 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. NMR
spectra were recorded at 25 °C on Bruker 400 and 500 MHz instruments and calibrated with
tetramethylsilane (TMS) as an internal reference. Mass spectra were performed by the Mass
Spectrometry Facilities at Laval University. UV-vis spectra were measured on Varian Cary 500
Scan spectrophotometer.
Synthesis of Compounds
[(Cp2Zr(µ2-O′,O′′C-C6H4-4-CH2O-TTF)2] (1):
In a 100 mL round-bottom flask compound 8 (0.133 g, 0.25 mmol) was dissolved in water (1.5
mL) and sodium hydroxide NaOH (1 mmol) was then added. The pH of the solution was
adjusted to pH 6-7 by addition of hydrochloric acid, until a precipitate was formed. This
suspension was then added dropwise via pipette to a solution of zirconocene dichloride (0.073 g,
0.25 mmol) in dichloromethane (6 mL) under vigorous stirring. The reaction mixture was stirred
for 30 min at room temperature, and then the two-phase system was allowed to separate. The
16

aqueous phase was extracted with CH2Cl2 (10 ml), the organic layers were combined, dried over
anhydrous MgSO4, filtered, and the solvent was removed under reduced pressure. Compound 1
was purified by precipitation in acetone followed by trituration with acetone (yellow solid, 34%).
1H NMR (400 MHz, CDCl3) δ = ppm 8.08 (d, J = 7.3 Hz, 4H), 7.71-7.64 (m, 4H), 7.60 (d, J =
8.5 Hz, 2H), 7.55 (d, J = 8.0 Hz, 4H), 7.27 (m, 6H), 6.88 (m, 2H), 6.31 (s, 10H), 6.31 (d, J = 4.0
13
Hz, 8H), 5.20 (s, 4H). C{1H} NMR (100 MHz, CDCl3) δ = 156.4, 136.9, 136.2, 135.4, 135.2,
133.9, 130.1, 129.1, 127.0, 126.2, 125.9, 125.9, 125.0, 124.9, 121.9, 117.3, 117.2, 117.1, 117.0,
116.0, 114.8, 114.0, 112.5, 111.3, 76.7, 69.5. HRMS (ESI); m/z: [M]*+ calcd for C66H44O6S8Zr
1277.9945, found 1277.9918.
[(CpZr)3(µ2,O′,O′′C-C6H4-4-OCH2-(TTF-6-TEG))3(µ3-O)(µ2-OH)3]·HCl (2): In a 100 mL
round-bottom flask compound 12 (0.139 g, 0.25 mmol) was dissolved in water (1.5 mL) and
sodium hydroxide NaOH (1 mmol) was then added. The pH of the solution was adjusted to pH
6-7 by addition of hydrochloric acid, until a precipitate was formed. This suspension was added
dropwise via pipette to a solution of zirconocene dichloride (0.073 g, 0.25 mmol) in
dichloromethane (6 mL) under vigorous stirring. The reaction mixture was stirred for 30 min at
room temperature, and then the two-phase system was allowed to separate. The aqueous phase
was extracted with CH2Cl2 (10 ml), the organic layers were combined, dried over anhydrous
MgSO4, filtered, and the solvent was removed under reduced pressure. Compound 2 was purified
1
by precipitation in acetone followed by trituration with acetone (yellow solid, 43%). H NMR
(500 MHz, CDCl3) δ ppm 8.09 (m, 6H), 7.62-7.53 (m, 12H), 7.27-7.21 (m, 6H), 6.89 (m, 6H),
6.84 (m, 6H), 6.33 (s, 15H), 6.29 (m, 12H), 5.22 (s, 6H), 4.23-4.18 (m, 6H), 3.91-3.87 (m, 6H),
3.78-3.74 (m, 6H), 3.72-3.65 (m, 14H), 3.57-3.54 (m, 6H), 3.38 (s, 9H). 13C{1H} NMR (100
MHz, CDCl3): 156.8, 156.3, 137.1, 136.9, 134.2, 134.1, 130.1, 128.5, 126.9, 126.2, 126.0, 121.8,
121.7, 117.2, 117.1, 114.8, 114.3, 112.3, 112.2, 111.3, 111.0, 71.9, 70.9, 70.7, 70.6, 69.7, 67.7,
59.1. HRMS (ESI); m/z: [M]*+ calcd for C120H111O25S12 Zr3 2605.1199, found 2605.0969.
2-tert-butyldimethylsilyl-2-hydroxyanthraquinone
(4):
To
a
solution
of
2-
hydroxyanthraquinone (2.5 g, 11.2 mmol) in DMF (10 mL) was added tert-butyldimethylsilyl
chloride (2.51 g, 16.7 mmol) followed by imidazole (1.14 g, 16.7 mmol) and the reaction was
sonicated under nitrogen at 20 °C for 1 h. DMF was removed under reduced pressure, the residue
was dissolved in dichloromethane, washed with water, and dried over MgSO4. The solvent
17

removed under reduced pressure and the crude material was purified by column chromatography
on silica gel using hexanes/EtOAc (95: 5 v/v) afforded compound 4 (2.83 g, 75%) as a white
1
solid. H NMR (400 MHz, CDCl3) δ ppm 8.30-8.25 (m, 2H), 8.22 (d, J = 8.5 Hz, 1H), 7.79-7.75
(m, 2H), 7.66 (d, J = 2.6 Hz, 1H), 7.19 (dd, J = 8.5, 2.6 Hz, 1H), 1.01 (s, 9H), 0.29 (s, 6H).
13C{1H} NMR (100 MHz, CDCl3) δ = 183.2, 182.20, 161.3, 135.5, 134.1, 133.7, 129.9, 127.1,
127.1, 125.9, 117.4, 25.5, 18.6, -4.34. m/z [M+H]+ calcd for C20H23O3Si 339.1411, found
339.1431.
(9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracen-6-yloxy)(tert-butyl)dimethylsilane
(5): To a solution of dimethyl 1,3-dithiol-2-yl-2-phosphonate (3.18 g, 15 mmol) in dry THF (15
ml) at -78 °C under argon atmosphere, n-BuLi (1.6M, 15.0 mmol) was added over a period of 10
min. After 0.5 h at – 78 °C, the corresponding anthraquinone (1.97 g, 6.0 mmol), suspended in
dry THF (15 ml), was added dropwise into the solution of the phosphonate. The mixture was
stirred for an additional hour at -78 °C, then allowed to warm to 20 °C, and then left to stand
overnight at room temperature. The THF was evaporated under reduced pressure and water (75
ml) was added. The residue was extracted with CH2Cl2, (3 x 50 ml) and the combined organic
layers were dried over MgSO4, filtered and the solvent was removed under reduced pressure.
Chromatography of the crude reaction mixture was done on a short silica gel column using
1
hexanes/EtOAc (95:5 v/v) as eluent, to afford compound 5 (1.82 g, 60%) as a yellow solid. H
NMR (500 MHz, CDCl3) δ ppm 7.68 (m, 2H), 7.57-7.51 (m, 1H), 7.30-7.26 (m, 2H), 7.15 (d, J
= 2.4 Hz, 1H), 6.76 (dd, J = 8.4, 2.5 Hz, 1H), 6.31-6.26 (m, 2H), 6.27-6.25 (m, 2H), 1.02 (m,
13
9H), 0.27 (s, 6H). C{1H} NMR (125 MHz, CDCl3) δ = 153.7, 136.8, 135.6, 135.5, 135.3,
133.5, 129.0, 126.1, 125.9, 125.8, 124.9, 122.2, 117.4, 117.2, 117.1, 116.2, 25.7, 18.2, -4.29, -
4.20. m/z [M+H]+ calcd for C26H27OS4Si 511.0709, found 511.0731.
9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracen-2-ol (6): To a solution of compound 5
(1.75 g, 3.42 mmol) in dry THF, tetrabutylamonium fluoride (4.1 mmol, 4.1 ml) was added and
the reaction mixture was stirred at room temperature for 12 h. The solvent was removed in under
reduced pressure and methanol was added before the resulting solution was sonicated for 5 min.
The precipitate was filtered, washed with methanol and dried under high vacuum to yield the
1
desired product (1.14 g, 84%) as a yellow solid. H NMR (400 MHz, CDCl3) δ ppm 9.84 (s,
18

1H), 7.66-7.55 (m, 2H), 7.44 (d, J = 8.4 Hz, 1H), 7.32 (m, 2H), 7.06 (d, J = 2.4 Hz, 1H), 6.76-
6.69 (m, 3H), 6.67 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3) δ = 156.0, 136.6, 136.6, 135.3,
135.0, 133.6, 126.7, 126.5, 126.4, 126.4, 125.1, 125.0, 121.4, 121.3, 118.6, 118.4, 118.3, 118.2,
113.3, 111.9. m/z [M+H]+ calcd for C20H13OS4 396.9844, found 396.9865.
Methyl 4-((9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracen-6-yloxy)methyl)benzoate
(7): In a 25 mL round-bottom flask potassium hydroxide (0.76 g, 5.5 mol) was added to dry
DMF (9 ml) at room temperature. After stirring for 5 min, anthraquinone (0.73g, 1.83 mmol)
was added, followed by methyl 4-(bromomethyl)benzoate (460 mg, 2.0 mmol). The reaction
mixture was heated to 80 °C and the stirring was continued for 12 h, after which time the mixture
was poured into 50 mL of cold water. The precipitate was filtered, washed with water, methanol
and dried under reduced pressure to give the desired product (0.95 mg, 95%) as a yellow solid.
1H NMR (400 MHz, CDCl3) δ ppm 8.09-8.02 (m, 2H), 7.70-7.63 (m, 2H), 7.60 (d, J = 8.5 Hz,
1H), 7.53 (d, J = 8.5 Hz, 2H), 7.29-7.26 (m, 3H), 6.88 (dd, J = 8.5, 2.6 Hz, 1H), 6.29-6.22 (m,
4H), 5.19 (d, J = 3.5 Hz, 2H), 3.93 (d, J = 3.3 Hz, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ =
166.9, 156.4, 142.3, 136.9, 136.1, 135.4, 135.2, 133.8, 129.9, 129.6, 129.0, 126.9, 126.2, 125.9,
125.9, 124.9, 124.8, 121.9, 117.2, 117.1, 117.1, 117.0, 112.5, 111.2, 69.5, 52.2. m/z [M+H]+
calcd for C29H21O3S4 545.0368, found 545.0351.
4-((9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracen-6-yloxy)methyl)benzoic acid (8): A
solution of compound 7 (0.82 g, 1.5 mmol) was dissolved in THF (20 mL) and treated with a
solution of LiOH (2ml, 6.0 mmol), the reaction mixture was heated at 60 °C for 5 h (reaction was
monitored by TLC). After reaction completion, the reaction mixture was poured into 100 mL of
brine/water (1/1 v/v) mixture. The precipitate was filtered, washed with water, methanol, and
then dried under reduced pressure to afford the desired product (0.75 g, 95%) as a yellow solid.
1H NMR (500 MHz, CDCl3) δ ppm 7.93-7.90 (m, 2H), 7.64-7.60 (m, 2H), 7.55 (m, 1H), 7.47
(m, 2H), 7.35-7.31 (m, 2H), 7.21 (d, J = 2.6 Hz, 1H), 7.00 (dd, J = 8.6, 2.6 Hz, 1H), 6.75-6.67
(m, 4H), 5.22 (m, 2H). 13C{1H} NMR (125 MHz, CDCl3) δ = 168.7, 156.7, 140.4, 137.5, 136.6,
135.3, 135.0, 134.9, 129.8, 128.5, 127.4, 126.6, 126.6, 126.4, 125.12, 125.1, 121.0, 120.9, 118.6,
118.6, 118.4, 112.9, 111.6, 69.6. m/z [M+H]+ calcd for C28H19O3S4 531.0212, found 531.0240.
19

methyl 4-((2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-9,10-dihydro-9,10-dioxoanthracen-6-
yloxy)methyl)benzoate (10): In a 50 ml round-bottom flask compound 9 was dissolved in dry
DMF,methyl 4-(bromomethyl) benzoate (1.145g, 5 mmol) and potassium carbonate (1.38g, 10
mmol) were added. The reaction mixture was heated at 60 °C and stirred at the same temperature
for further 12 hours. The mixture was poured in 100 mL of water and extracted with
dichloromethane (3 x 50 ml). The organic layers were combined and washed with brine (3x100
ml), dried over MgSO4, and evaporated under reduced pressure. Addition of methanol to the
crude product produced a precipitate that was filtered-off and dried under reduced pressure to
yield compound 10 as off-white- solid. That was used directly in the next step of synthesis
1
without further purification (23% yield for the two steps of synthesis). H NMR (500 MHz,
CDCl3) δ ppm 8.20 (t, J = 8.7 Hz, 2H), 8.07 (d, J = 7.7 Hz, 2H), 7.72 (m, 2H), 7.53 (d, J = 7.8
Hz, 2H), 7.26 (m, 2H), 5.27 (s, 2H), 3.92 (s, 5H), 4.30 (s, 2H), 3.76 (m, 2H), 3.67 (m, 4H), 3.55
(m, 2H), 3.37 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): 181.9, 181.9, 166.6, 163.6, 163.1,
140.7, 135.7, 135.6, 130.0, 129.94, 129.7, 129.6, 127.4, 127.1, 127.0, 121.08, 121.03, 110.8,
110.9, 71.9, 70.6, 70.1, 69.35, 68.1, 59.0, 52.1. m/z [M+H]+ calcd for C30H31O9 535.1963 found
535.1986.
Methyl4-((2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-9,10-di(1,3-dithiol-2-ylidene)-9,10-
dihydroanthracen-6-yloxy)methyl)benzoate (11): To a solution of dimethyl 1,3-dithiol-2-yl-2-
phosphonate ( 5.2 mmol) in dry THF (15 ml) at - 78 °C and under argon atmosphere, n-BuLi (
1.6M, 5.44 mmol) was added. After 0.5 h. at – 78 °C, the corresponding quinine 10 (1.5 mmol)
suspended in dry THF (15 ml), was added dropwise into the phosphonate solution. The mixture
was stirred for 1 h at -78 °C, then allowed to warm at room temperature, and left to stand
overnight. The THF was evaporated under reduced pressure, water (75 ml) added, and the
residue extracted with CH2CI2, (3 x 50 ml). The combined organic layers were dried over
MgSO4, filtered and the solvent was removed under reduced pressure. Purification of the product
was achieved by column chromatography on silica gel with 20% EtOAc/DCM as eluent to yield
the desired product as a yellow solid (83%, 0.88 g). 1H NMR (500 MHz, CDCl3) δ ppm 8.07 (d,
J = 7.7 Hz, 2H), 7.58 (m, 2H), 7.53 (m, 2H), 7.24 (m, 2H), 6.85 (m, 2H), 6.30-6.21 (m, 4H),
5.24-5.15 (m, 2H), 4.20 (m, 2H), 3.93 (s, 3H), 3.89 (m, 2H), 3.76 (m, 2H), 3.72-3.65 (m, 4H),
3.56 (d, J = 3.45 Hz, 2H), 3.38 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): 166.8, 156.8, 156.3,
20

142.3, 137.0, 136.9, 134.2, 134.1, 129.9, 129.6, 128.9, 128.5, 126.9, 126.1, 126.0, 121.8, 121.7,
117.2, 112.3, 112.2, 71.9, 70.8, 70.6, 70.6, 69.7, 69.51, 67.6, 59.01, 52.1. m/z [M+H]+ calcd for
C36H35O7S4 707.126, found 707.1297.
4-((2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-9,10-di(1,3-dithiol-2-ylidene)-9,10-
dihydroanthracen-6-yloxy)methyl)benzoic acid (12): In a 50 mL round-bottom flask
compound 11 (0.707 g, 1 mmol) was dissolved in THF (20 mL) and treated with a solution of
LiOH (2ml, 3.0 mmol). The resulting mixture was heated at 60 °C for 12 h. After reaction
completion, the solvent was removed under reduced pressure, followed by addition of HCl (1 M
solution in water) until pH ~ 2. The aqueous layer was extracted with CH2Cl2 (3x10 ml) and the
organic layers were combined, dried over MgSO4, and filtered. The solvent was removed under
reduced pressure to afford the desired product 12 (0.64 g, 92%) as a yellow solid. 1H NMR (500
MHz, CDCl3) δ ppm 8.13 (d, J = 7.5 Hz, 2H), 7.61-7.52 (m, 4H), 7.22 (m, 2H), 6.85 (m, 2H),
6.25 (m, 4H), 5.20 (m, 2H), 4.19 (s, 2H), 3.92-3.87 (m, 2H), 3.77 (m, 2H), 3.73-3.66 (m, 4H),
3.57 (m, 2H), 3.39 (s, 3H). 13C{1H} NMR (125 MHz, CDCl3): 171.3, 156.7, 156.2, 143.2, 137.0,
136.8, 134.2, 129.0, 128.8, 128.5, 126.1, 126.0, 121.7, 121.6, 117.2, 117.1, 117.0, 112.3, 112.12,
111.1, 110.9, 71.9, 70.8, 70.6, 70.5, 69.7, 69.4, 67.6, 59.0. m/z [M+H]+ calcd for
C35H33O7S4 693.1104, found 693.1128.
General method for UV-vis titrations
UV-vis titrations were recorded on a Varian Carry 500 scan spectrophotometer. Analytical grade
solvents were used for all the titrations. UV-vis titration experiments were carried out with
solutions of cavitands (0.6 µM to 1.0 µM) in chlorobenzene, toluene, and carbon disulfide or in
toluene/DCM 2:1 (3 mL) in a quartz cuvette. 3 mL of solvent was added to the second cuvette
which was used as a reference solution. An aliquot of C60 or C70 from a stock solution of
fullerenes containing the host with the same concentration to the host in the cuvette was added
while another aliquot from solution of C60 or C70 with the same volume and concentration was
added to the reference cuvette. The absorption maximum (λmax) of the host was recorded after
each addition and a plot of ∆A versus the concentration of fullerene [fullerene] was ploted. The
binding constant (Ka) was evaluated by non-linear curve fitting with OriginPro 8.0 (OriginLab)
21

using the equation1. In all the solvent, the binding constant was estimated using Hill equation
(Eq. 1).
ꢀ
n
n
ꢁ
ꢂ
ꢀΔAbs
max
C
K
h
a
ꢅ
ΔAbsꢀ =
(1)
n
n
ꢀ
ꢃ
ꢁ
ꢂ ꢄ
C
1ꢀ + ꢀK
a
h
Where Ka is the association constant and n the Hill coefficient and [Ch] the concentration of host.
Supporting Information Available: NMR spectra of species and UV-titration experiments are
available.
Acknowledgment. We are grateful to FQRNT (Projet de recherche en équipe - Québec) and CFI
(Canada), CCVC (Québec), and CQMF (Québec) for financial support. We acknowledge the
help of Pierre Audet with the HR-MS experiments.
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24

Graphical abstract
Abstract
The synthesis and spectroscopic characterization of zirconium (IV) dicarboxylate 1 and
metallocavitand 2 are described. Encapsulation studies of fullerenes C60 and C70 were performed
using UV-vis spectroscopy in chlorobenzene, toluene, benzene, carbon disulfide and in a mixture
of toluene/dichloromethane. UV-vis titrations have shown that the binding abilities of the hosts
toward fullerene C70 are considerably higher than those obtained for fullerene C60.
25