Synthesis of 21,23-selenium- and tellurium-substituted 5-porphomethenes, 5,10-porphodimethenes, 5,15-porphodimethenes, and porphotrimethenes and their interactions with mercury

Article abstract of DOI:10.1021/acs.joc.5b00007

The 3+1 condensation of symmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/tellurophene-2,5-diols in the presence of BF₃-etheratre or BF₃-methanol followed by oxidation with DDQ gave 5,10-porphodimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave 5-porphomethenes. In addition, the reaction of unsymmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave the corresponding porphotrimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave the 5,15-porphodimethenes. The structures of different products were characterized by IR, ¹H and ¹³C NMR, ¹H-¹H COSY, CHN analysis, and mass spectrometry. The binding of mercury with the calix[4]phyrins mentioned above had been observed in the decreasing order of porphodimethenes > porphomethenes > porphotrimethenes by UV-vis and ¹H NMR spectroscopy.

Full text of DOI:10.1021/acs.joc.5b00007

Article
pubs.acs.org/joc
Synthesis of 21,23-Selenium- and Tellurium-Substituted
5‑Porphomethenes, 5,10-Porphodimethenes, 5,15-
Porphodimethenes, and Porphotrimethenes and Their Interactions
with Mercury
Sohail Ahmad, Kumar Karitkey Yadav, Soumee Bhattacharya, Prashant Chauhan, and S. M. S. Chauhan*
Bioorganic Research Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India
S
* Supporting Information
ABSTRACT: The 3+1 condensation of symmetrical 16-
Selena/telluratripyrranes with symmetrical selenophene-2,5-
diols/tellurophene-2,5-diols in the presence of BF3-etheratre
or BF3-methanol followed by oxidation with DDQ gave 5,10-
porphodimethenes, whereas the process with unsymmetrical
selenophene-2,5-diols/tellurophene-2,5-diols gave 5-porpho-
methenes. In addition, the reaction of unsymmetrical 16-
Selena/telluratripyrranes with symmetrical selenophene-2,5-
diols/tellurophene-2,5-diols gave the corresponding porpho-
trimethenes, whereas the process with unsymmetrical
selenophene-2,5-diols/tellurophene-2,5-diols gave the 5,15-
porphodimethenes. The structures of different products were
characterized by IR, 1H and 13C NMR, 1H−1H COSY, CHN analysis, and mass spectrometry. The binding of mercury with the
calix[4]phyrins mentioned above had been observed in the decreasing order of porphodimethenes > porphomethenes >
1
porphotrimethenes by UV−vis and H NMR spectroscopy.
reductive alkylation of porphyrins,11 dealkylation of calix[4]-
INTRODUCTION
■
pyrroles,12 oxidation of porphyrinogens,13 and reduction of
Porphomethenes, porphodimethenes, and porphotrimethenes
porphyrins.14 The methods described above require expansive
are the classes of calixphyrins in which porphomethene
reagents, multistep synthesis, and vigorous reaction conditions.
[calix(4)phyrin-(1.1.1.1)] contains one sp2-hybridized meso-
Recently, calix[4]phyrins have been synthesized by reaction
of 5,5-disubstituted dipyrromethane and aldehyde or by
reaction of 5-substituted dipyrromethane and ketone under
carbon atom and three sp3-hybridized meso-carbon atoms,
porphodimethene [calix(4)phyrin-(1.1.1.1 and 1.1.1.1)] con-
tains two sp2-hybridized and two sp3-hybridized meso-carbon
acidic conditions followed by oxidation with DDQ, chloranil, or
atoms, and porphotrimethene [calix(4)phyrin-(1.1.1.1)] con-
FeCl3 under mild conditions.15 The introduction of different
tains three sp2-hybridized meso-carbon atoms and one sp3-
substituents at the sp2- or sp3-hybridized meso position15
hybridized meso-carbon atom (Figure 1).1 The presence of sp3-
impacts calixphyrin’s stability, structure, and spectroscopic,
hybridized meso-carbon centers disrupts the π-conjugation and
allows the macrocycle to adapt a nonplanar conformation;2
electrostatic, and anion and cation binding properties.
Modification of the calix[4]phyrin core by replacement of
because of the presence of the sp3-hybridized unit, these
one or two nitrogen atoms with donor atoms15 (O, S, and P)
compounds display an intriguing multielectron redox chem-
leads to the synthesis of core-modified calix[4]phyrins.16 The
porphodimethenes are stable, and their properties have been
extensively studied; on the other hand, core-modified
porphomethenes and porphotrimethenes (Figure 1) have
remained unexplored because of the instability and complexity
of the synthesis.17 Therefore, a similar development is
anticipated for the calixphyrins with heavier chalcogen donor
atoms such as selenium and tellurium, because of their
“softness” and better σ-donor capacity compared to that of
the lighter group 16 congeners. Selenium and tellurium
istry.3 Calix[4]phyrins consist of the intermediate structure of
porphyrin and calix[4]pyrrole; thus, they have properties
analogous to those of both porphyrins and calix[4]pyrroles
and play diverse roles as metal ion receptors4 and anion-
complexing agents5 and reveal a rich coordination chemistry.6
However, the lack of π-conjugation compromises the
spectroscopic properties of these macrocycles in comparison
to those of the porphyrins.7 Naturally, calix[4]phyrins have
been proposed as intermediates in the synthesis of chlorophyll
a,1b,c heme P460,8 chlorins,9 and porphyrins.9b Calix[4]phyrin
was recently identified as a potential chemical inhibitor of
uroporphyrinogen decarboxylase and reduced the viability of
cancer cells.10 Calix[4]phyrins have been synthesized by
Received: January 21, 2015
Published: March 24, 2015
© 2015 American Chemical Society
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Figure 1. Structures of porphyrinoids.
Scheme 1. Synthesis of Selenophene and Tellurophene Diols (3a−h), Tripyrranes (4a and 4b), 5,10-Porphodimethenes (5a−d),
and Porphomethenes (6a and 6b)
1
porphyrinoids and their derivatives keep attracting the attention
of several research groups18 beginning from the seminal
contributions of Ulman and Manassen.19 The absence of a
suitable synthetic procedure, starting precursors, and instability
toward air and light limit the chemistry of Se/Te calixphyrins.
Recently, we had reported the first synthesis of Se/Te core-
modified porphyrinogens and their coordination ability for the
selective detection of Hg2+ by UV−vis, fluorescence, and H
NMR spectroscopy.20
In this paper, we report the synthesis of novel 21,23-Se/Te-
substituted porphomethenes, porphodimethenes, and porpho-
trimethenes via acid-catalyzed 3+1 condensation of 16-
selenophene/tellurophene tripyrranes with corresponding
selenophene-2,5-diols/tellurophene-2,5-diols. The interactions
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of meso-substituted calixphyrins with Hg2+ ion have been
examined by UV−vis, fluorescence, and 1H NMR spectroscopy.
In some cases, the HRMS analysis of the reaction mixture
revealed the formation of desired porphyrinogen intermediates
(7e−h), which disappeared without providing corresponding
porphodimethene products upon oxidation with DDQ or p-
chloranil. To understand the detailed mechanism of reaction,
the intermediate porphyrinogens (7e−h) were isolated and
characterized. These porphyrinogens (7e−h) were further
oxidized under neutral conditions. Porphodimethenes (5e−h)
were obtained by condensation of 1 equiv of tripyrranes (4a
and 4b) with 1 equiv of the corresponding diol (3e−h) in the
presence of BF3-methanol using dichloromethane as a solvent
(3.2 mM) at 0 °C for 1 h, and then the reaction mixture was
stirred at room temperature for 45 min (method B). The crude
porphyrinogens were purified by silica gel column chromatog-
raphy to afford white solids in 10−14% yield. The methyl-
substituted porphyrinogens (7e and 7f) were oxidized with
chloranil, and meso-unsubstituted porphyrinogens (7g and 7h)
were oxidized with 0.1% aqueous FeCl3 in CHCl3 at room
temperature to obtain 16π-conjugated systems 5e in 6%, 5f in
7%, 5g in 5%, and 5h in 4% yields (Scheme 2).
RESULTS AND DISCUSSION
■
Acetylenic coupling is an important tool for the synthesis of
natural products, pharmaceuticals, polymers, and nanomater-
ials.21a The two-step homocoupling of terminal alkynes using a
stoichiometric amount of CuCl and NH4OH in an oxygen
atmosphere was reported by Glaser in 1869.21b,c The one-step
homocoupling using CuCl and TMEDA was reported in
1962.21d The CuI, NiCl2·6H2O system had been used for the
homocoupling of 2-methylbut-3-yn-2-ol (1a) to give diynediol
(2a).22 Diynediol (2a) reacts with Na2Se in the presence of
silver acetate to give 2,5-bis[hydroxy(dimethyl)methyl]-
selenophene (3a). The structure of 3a was fully confirmed by
1H NMR and comparison of other spectroscopic data from the
literature.20 Similarly, other selenophene and tellurophene diols
(3b−h) were synthesized and characterized. Selenophene diol
3a reacts with an excess of pyrrole to give 16-selenatripyrrane
(4a) in 75% yield. Similarly, 16-telluratripyrrane (4b) was
synthesized and characterized by various spectroscopic
techniques in 78% yield (Scheme 1).
Scheme 2. Synthesis of Porphyrinogens (7e−h) and 5,10-
Porphodimethenes (5e−h)
The 3+1 condensation is an important method for the
synthesis of selected porphyrins15c and core-modified porphyr-
ins.15,20,23 The 3+1 condensation of 1 equiv of tripyrranes (4a)
with 1 equiv of corresponding diols (3c) in the presence of
BF3-etherate in dichloromethane (3.2 mM) at room temper-
ature in 30 min, followed by treatment with 2.2 equiv of 2,3-
dichloro-5,6-dicyanobenzoquinone (DDQ), gave the new
selenium core-modified 5,5,10,10-tetramethyl-15,20-bisphenyl-
21,23-diselenaporphodimethene [5a (Scheme 1, method A)].
From the reaction, a mixture of two calixphyrins, 5a and 8a, was
obtained. On the basis of the oxidation state of the π-
conjugated moiety, 8a is classified as a 2e−-oxidized product
(14π) and 5a as a 4e−-oxidized product (16π).15b In the high-
resolution mass spectra, peaks corresponding to 8a along with
5a were observed (see the Supporting Information), and TLC
analysis of the crude reaction mixture indicated that product 5a
was a predominant product of this condensation. However, all
attempts to isolate 8a from the reaction mixture resulted in its
decomposition, and only 16π-conjugated system 5a was
isolated by column chromatography in 10% yield. Even with
a decrease in the amount of oxidant from 2 to 0.5 equiv, no
significant improvements were observed in the yield of 8a. The
greater selectivity of the 16π-conjugated system (4e−-oxidized)
and the instability of the 14π-conjugated system (2e−-oxidized)
may be explained on the basis of weak hydrogen bonding
interaction of the lone pair (Se) with the pyrrolic NH proton
(X···H−N, where X = Se or Te) or its absence in 8a; therefore,
stabilization of the 14π system is not possible. Sulfur and
oxygen core-modified calixphyrins showed greater stability of
the 14π-conjugated system in comparison to that of 16π, which
may arise from the repulsive or attractive electrostatic
interactions between the core heteroatoms and the pyrrole
NH groups.15b,c Similarly, the other porphodimethenes (5b−d)
were synthesized and characterized by various spectroscopic
techniques.
The structures of all the products were characterized by IR,
1H NMR, 13C NMR, CHN analysis, and mass spectrometry
(see the Supporting Information). The H NMR spectra of
1
tellurium-embedded porphodimethenes 5b, 5d, 5f, and 5h were
recorded in CDCl3 at room temperature. In general, the sp3-
hybridized 5,10-meso-tetramethyl protons (CH3) resonate as a
doublet at δ 1.78−1.75, while conjugated tellurophene protons
are more deshielded and appeared as a sharp singlet at δ 7.60−
7.62 compared to the nonconjugated tellurophene protons (δ
1
7.59−7.47). On the other hand, in the H NMR spectra of
On the other hand, sp2-hybridized meso-methyl-substituted
porphodimethene (5e and 5f) and sp2-hybridized meso-
unsubstituted porphodimethene (5g and 5h) could not be
synthesized by method A described above, and it led to the
formation of a complex mixture. No corresponding porphodi-
methenes were detected by HRMS or in the UV−vis spectrum.
selenium-embedded porphodimethenes 5a, 5c, 5e, and 5g,
5,10-meso tetramethyl proton (CH3) resonate as a sharp singlet
at δ 1.77 while conjugated and nonconjugated selenophene
protons appeared at δ 7.07 and 6.91, respectively. The sp2 meso-
CH protons of 5g and 5h resonate as a sharp singlet in the
range of δ 6.73−6.71. The difference in sp3-hybridized 5,10-
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Scheme 3. Synthesis of 5,15-Porphodimethenes (12a and 12b) and Porphotrimethenes (11a and 11b)
meso tetramethyl chemical shifts and the splitting pattern
between Te and Se calixphyrins reflects the difference in the
degree of distortion in their conformation; this may be ascribed
to the difference in sizes of Se/Te incorporated in their π-
conjugated N-X-N subunits. The UV−vis absorption spectra of
Se hybrids 5a, 5c, 5e and 5g showed the transitions at lower
wavelengths at around 343 and 520 nm. For Te hybrids 5b, 5d,
5f, and 5h in CH2Cl2, broad absorptions due to π−π*
transitions were observed around 561−559 nm along with an
intense band around 360−358 nm (Supporting Information).
Unsubstituted 15,20-meso-carbon porphodimethenes (5g and
5h) are highly unstable and very difficult to handle and become
dark at room temperature in comparison to 15,20-meso-
substituted porphodimethene.
The reaction of unsymmetrical 16-selenatripyrrane (10a) and
symmetrical selenophene diols (3c) in dichloromethane, in the
presence of a catalytic amount of trifluoroacetic acid at room
temperature, followed by oxidation with DDQ gave the
porphotrimethene (11a) in 9% yield. The presence of a strong
M+ ion peak in the mass spectra and correct elemental analysis
confirmed the synthesis of phlorin (11a). Similarly, the other
porphotrimethene 11b was synthesized in 11% yield and
characterized by IR, NMR, and UV−vis spectroscopy. Phlorins
11a and 11b are quite stable under nitrogen and isolable
(Scheme 3).
1
The H NMR data of 11b are typical for a nonaromatic
conjugated system with four sets of signals of four β-pyrrole
protons in the range of δ 6.3−7.1 as compared to the 21,23-
ditelluraporphyrins.18c,d The four β-tellurophene protons
appeared as two sets of signals: a doublet at δ 7.5 and a
multiplet at δ 7.6. The inner NH proton showed two broad
signals at δ 11.2 and 12.2 that were attributed tentatively to the
The cross coupling of haloalkyne with a terminal alkyne
catalyzed by Cu(I) is the most important method for the
synthesis of unsymmetrical diynes (Scheme 3).24 Although the
nickel-catalyzed oxidative coupling reaction of two different
terminal alkynes using O2 as the oxidant at room temperature
has been reported for the facile synthesis of unsymmetrical
diynes,21 the symmetrical diynes are also formed and separated
from the reaction mixture. The reaction of 1 equiv of
unsymmetrical diols (9a) with 1 equiv of corresponding 16-
selenatripyrranes (4a) in dichloromethane (method A) gave
porphomethenes 6a in 9% yield (Scheme 1). Similarly,
ditelluraporphomethene (6b) was obtained in 7% yield. The
absorption spectra of ditelluraporphomethene (564 and 360
nm) and diselenaporphomethene (440 and 328 nm) were quite
similar to the absorption spectra of ditellura/diselenaporpho-
1
presence of tautomers in solution. However, when the H
NMR spectrum was recorded using deuterated pyridine
(C5D5N) as a solvent, only one broad signal at δ 10.2 was
observed, which disappeared upon addition of a drop of D2O
(exchange of the NH proton with a deuterium atom),
confirming the NH signal. The tautomeric effect of the inner
NH proton has been previously reported with 21,23-
dithiaphlorins.17
i
Generally, the electronic absorption spectra of phlorins
displayed absorption at a wavelength longer than that of
porphyrins.17,18c,d The electronic absorption spectra of
diselenaphlorin 11a showed absorption bands at 679 and 438
nm, whereas ditelluraphlorin (11b) showed a pattern different
from that of 21,23-dithia/diselenaphlorins and appeared as a
broad Q-band at 583 nm and a Soret band at 362 nm. The
change in conformation due to the presence of tellurium had
been previously reported with 21,23-ditelluraporphyrin;18b
1
dimethene. In the H NMR spectra of selenaporphomethene
(6a), the four β-pyrrole protons appeared as two sets of
multiplets in the range of δ 6.0−6.3, and two different β-
selenophene protons appeared as a multiplet and a singlet at δ
6.9 and 7.1, respectively (Supporting Information).
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21,23-ditelluraporphyrin has been shown to adapt a nonplanar
macrocyclic conformation, and its chromophore is found to be
different from regular heteroporphyrins.18b
The reaction of unsymmetrical 16-selenatripyrrane (10a)
with unsymmetrical selenophene diols (9a) in dichloro-
methane, in the presence of trifluoroacetic acid (1.5h), followed
by DDQ oxidation gave the newer 5,15-porphodimethene
(12a). The newer 5,15-porphodimethene (12a) was charac-
1
terized by UV−vis, H NMR, and correct elemental analysis.
1
The H NMR spectra of both the compounds are in good
agreement for the given structure. Similarly, the other 5,15-
porphodimethene (12b) was synthesized (Scheme 3). The
electronic absorption spectrum of 5,15-diselenaporphodime-
thene 12a is quite different from that of 5,10-diselenaporpho-
dimethene 5a. The UV−vis spectrum of 5a showed two sharp
peaks at 343 and 520 nm, whereas in the UV−vis spectrum of
12a, a broad peak at 426 nm along with a shoulder at 525 nm
was observed. It is quite understandable due to the presence of
conjugated double bonds in diselenaporphodimethene 5a.
1
Figure 2. UV−vis titration profile of 5a (5.1 × 10−8 M) with the
gradual addition of Hg2+ in an acetonitrile/water solution [6:4 (v/v)].
The inset shows the Benesis−Hildebrand plot of 5a, assuming a 1:1
stoichiometry for association between 5a and Hg2+.
Compared to those of 5,10-porphodimethene (5a), the H
NMR spectra of 5,15-porphodimethene (12a) showed a
different pattern. The selenophene protons appeared as two
sets of doublets at 7.52 and 7.35 ppm, whereas the β-pyrrolic
proton appeared at 6.83 and 6.22 ppm as doublets. Similarly,
porphodimethene (12b) showed a broad absorption spectrum
at 443 and 536 nm. Porphodimethene (12b) readily undergoes
decomposition in air.
temperature. Compound 5a showed characteristic emission
peaks at 404 and 430 nm upon excitation at 350 nm. The
fluorescence was gradually quenched upon the stepwise
addition of Hg2+ (from 0.5 to 5.0 μm) to a solution of 5a (2
μm) (Figure 3). The fluorescence quenching upon addition of
Hg2+ was attributed to the formation of a complex between 5a
and Hg2+.27 The fluorescence response of 5a was also examined
in the presence of 1−100 equiv of various metal ions such as
K+, Ag+, Mn2+, Cu2+, Pb2+, Cr2+, Zn2+, and Cd2+ in an
acetonitrile/water solution [6:4 (v/v)] (Figure S16 of the
Supporting Information). No significant changes in fluores-
cence intensity were observed with these metal ions, whereas
the significant quenching of fluorescence intensity was observed
with 1 equiv of Hg2+. Hence, selective chelation of Hg2+ with 5a
was observed.
The electronic absorption spectroscopic titration of 5b with
Hg2+ was also performed, and their respective preliminary peaks
were shifted by 18−20 nm. The binding constant was
calculated to be 3 × 106 M−1 (Figure 4). The detection limits
of 5a and 5b were calculated for Hg2+ ions, and we found that
5a (1.1 × 10−7 M) showed a detection limit higher than that of
5b (3.2 × 10−6 M) (Figures S19 and S20 of the Supporting
Information). Similar studies were conducted with 5,15-
porphodimethenes 12a and 12b, but no significant changes
were observed (Figures S20 and S21 of the Supporting
Information).
The problematic role of mercury for the environment has
necessitated the investigation of the detection of mercury with
suitable chemosensors.25 The chalcogenophilicity of mercury
led to the development of various sensors from compounds
containing chalcogen atoms. Chalcogen−mercury binding is
stronger than chalcogen−zinc or chalcogen−magnesium bind-
ing because of the strong relativistic 6s orbital contraction that
draws the chalcogen charge to the Hg2+ nucleus.25 The greater
stability of phenyl-substituted calixphyrin among those of other
calixphyrins offers the further utilization of these compounds in
the selective detection of mercury. The electronic absorption
spectroscopic titration of 5,10-porphodimethene 5a with a
“soft” Lewis acid, mercuric perchlorate Hg(ClO4)2, was
performed in an acetonitrile/water mixture [6:4 (v/v)] at
room temperature. Calixphyrin 5a gave characteristic absorp-
tion maxima at 339 and 514 nm, and upon addition of Hg2+ in
an acetonitrile/water solution [6:4 (v/v)] of 5a (1:1 complex),
the absorption peak was bathochromically shifted to 415 and
584 nm (shifted by 70 nm) with the increase in relative
intensity (Figure 2). The bright red solution of 5a turned gray
upon complexation with Hg2+, and the color changes were
clearly visible to the naked eye. The binding constant for the
formation of the 1:1 complex from the interaction of 5a and
Hg2+ was calculated from the plot of 1/(A − A0) versus 1/
[Hg2+] using the Benesi−Hildebrand equation26 and was found
to be 1.37 × 107 M−1. The linearity of the plot further
confirmed the 1:1 binding stoichiometry. The UV−vis
absorption response of 5a was also examined in the presence
of 1−100 equiv of various metal ions such as K+, Ag+, Mn2+,
Cu2+, Pb2+, Cr2+, Zn2+, and Cd2+ in an acetonitrile/water
solution [6:4 (v/v)] (Supporting Information). No significant
changes in UV−vis intensity were observed with these metal
ions, which indicated the selective chelation of Hg2+ with 5a
(Figure S15 of the Supporting Information).
The 1H NMR spectrum of selenium calixphyrin with Hg2+ at
298 K was recorded (Figure 5 and Table S1 of the Supporting
Information). A significant downfield chemical shift change was
observed for selenophene protons (conjugated and uncon-
jugated) and pyrrolic protons of 5a. 5a exhibited conjugated
and unconjugated selenophene protons at 7.07 and 6.91 ppm,
respectively, and pyrrolic protons at 6.67−6.71 ppm that were
significantly downfield shifted to 7.45, 7.26, and 6.71−6.74
ppm, respectively. This finding suggests the interaction takes
place through the selenium of selenophene (conjugated and
unconjugated) and nitrogen of the pyrrole ring of 5a. Similar
changes in chemical shifts were also observed in calixphyrin 5b
in which Hg2+ binds with tellurium of tellurophene (conjugated
The fluorescence spectroscopic titration of 5a with Hg2+ was
performed in an acetonitrile/water solution [6:4 (v/v)] at room
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Figure 3. Changes in the fluorescence spectra (λex = 350 nm) of 5a (10 μM) measured upon addition of Hg2+.
of the presence of Hg2+ in solution and inner NH proton
appeared at δ 10.3, and significant downfield chemical shift
changes in selenophene protons and pyrrolic protons were
observed (Figure S64 of the Supporting Information). Titration
of 6a with 1 equiv of Hg2+ resulted in a small decrease in the
absorption at 328 and 440 nm with a 60 nm bathochromic shift
(Figure 7), and the binding constant was calculated to be 16.1
× 104 M−1. The lower binding constants for the interaction of
Hg2+ with porphomethene 6a and porphotrimethene 11a
compared to the binding constant for the interaction with
porphodimethenes 5a and 12a suggest the difference in
macrocycle flexibility and conjugation and the presence of
NH pyrrolic units in 6a and 11a as compared to
porphodimethenes.
CONCLUSIONS
■
In conclusion, the first syntheses of 21,23-diselena/ditellura
core-modified porphomethenes, 5,10-porphodimethenes, 5,15-
porphodimethenes, and porphotrimethenes (phlorins) have
been achieved from easily available precursors. The reaction
approach using readily available conjugated diynes as starting
materials makes this strategy highly attractive in diversity-
oriented synthesis. The different selenium-substituted calix[4]-
phyrins are more stable than tellurium-substituted calix[4]-
phyrins, and these calixphyrins have shown better selectivity for
Hg2+. The binding ability of calixphyrins with Hg2+ ion has
Figure 4. UV−vis titration profile of 5b (4.8 × 10−8 M) with the
gradual addition of Hg2+ in an acetonitrile/water solution [6:4 (v/v)].
The inset shows the Benesis−Hildebrand plot of 5b, assuming a 1:1
stoichiometry for association between 5b and Hg2+.
and unconjugated) and the nitrogen of the pyrrole (Figure S63
of the Supporting Information). The higher binding constant
for mercury with selenium calix[4]phyrins than with tellurium
calix[4]phyrins has been observed by UV−vis spectroscopy.
Stronger inhibition of fluorescence is observed in the case of
different selenium calix[4]phyrins than in the case of tellurium
calix[4]phyrins.
1
been examined by using H NMR, UV−vis, and fluorescence
spectroscopy.
EXPERIMENTAL SECTION
■
The titration profile of 11a (6 × 10−7 M) with Hg2+ was
recorded in an acetonitrile/water solution [6:4 (v/v)] (Figure
6). Upon addition of Hg2+, the intensity of the absorption peak
at 679 nm decreased and a gradual red shift in the spectral
position at 826 nm was observed, along with an increase in the
absorption intensity; the binding constant was calculated to be
General Experimental Details. Melting points were determined
on a capillary melting point apparatus and are uncorrected. The
chemical shifts (δ) are referenced to the respective solvents, and
splitting patterns are designed as s (singlet), d (doublet), t (triplet), m
(multiplet), dt (double triplet), br (broad), and brs (broad singlet).
Coupling constants (J) are reported in hertz. The mass spectra of
selected compounds were recorded on an Agilent Technologies high-
resolution Q-TOF mass spectrometry instrument. Solvents used were
of analytical grade and were dried before being used. Pyrrole was
1
2.3 × 104 M−1. In the H NMR spectra of 11a with Hg2+, the
tautomeric effect of the inner NH proton was restricted because
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1
Figure 5. H NMR spectrum of 5a with Hg2+. (A) 5a (from 6.5 to 7.5 ppm). (B) 5a with Hg2+ (1 equiv) in CDCl3.
Figure 6. UV−vis titration profile of 11a (6 × 10−7 M) with the
Figure 7. UV−vis titration profile of 6a (3.1 × 10−8 M) with the
gradual addition of Hg2+ in an acetonitrile/water solution [6:4 (v/v)].
gradual addition of Hg2+ in an acetonitrile/water solution [6:4 (v/v)].
Synthesis of Unsymmetrical Diynediols (2e). The diynediols
(2e) were synthesized by slightly modifying the literature procedure.21
The solution of TMEDA (46.4 mg, 0.4 mmol), CuI (19.05 mg, 0.1
mmol), and NiCl2·6H2O (23.78 mg, 0.1 mmol) in THF (10 mL) was
stirred at room temperature. A THF (10 mL) solution of 2-methylbut-
3-yn-2-ol 1a (252 mg, 3 mmol) and alkynes (1b) (264 mg, 2 mmol)
were added dropwise with the bubbling of oxygen to the reaction
distilled before being used. All other chemicals were purchased as
reagent quality and used as received. All processes and reactions were
conducted under argon and protected from light.
Synthesis of Symmetrical Diynediols (2a−d). The symmetrical
diynediols (2a−d) were synthesized by slightly modifying our reported
procedure.20
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mixture. The reaction was monitored by TLC. After completion of the
reaction (10 h), the reaction mixture was concentrated under reduced
pressure and purified by column chromatography on silica gel. The
product was eluted with a benzene/acetone solution [97.5:2.5 (v/v)]
to give unsymmetrical diynediols as a pale yellow liquid.
162.41, 140.73, 131.27, 116.91, 107.71, 103.35, 42.04, 31.92. IR (KBr)
νmax: 3367, 2964, 2861, 1559, 1381, 1361, 1254, 1236, 1112, 1037,
1010, 965, 807, 723, 581 cm−1. HRMS (ESI-QTOF): [M + H]+ calcd
for C18H23N2Te m/z 397.0923, found m/z 397.0912. CHN analysis.
Calcd for C18H22N2Te: C, 54.87; H, 5.63; N, 7.11. Found: C, 54.70;
H, 5.82; N, 7.28.
6-Methyl-1-phenylhepta-2,4-diyne-1,6-diol (2e).28 Yellow liquid
1
(227 mg, 53%). H NMR (400 MHz, CDCl3): δ 7.49 (d, 2H, C6H5),
Reaction of Selenophene and Tellurophene Diols (9a and
9b, respectively) with Pyrrole: Synthesis of Unsymmetrical
Selenatripyrrane and Telluratripyrrane (10a and 10b, respec-
tively). Boron trifluoride-etherate (0.3 mmol) was added to the
solution of diols (9a and 9b) (0.7 mmol) in degassed pyrrole (6.5
mL), and the resulting mixture was stirred for 1 h under argon. The
reaction was monitored by TLC. After completion of the reaction, it
was diluted with CH2Cl2 (30 mL) and 40% NaOH (25 mL). The
organic layer was separated and washed with water (3 × 100 mL) and
brine (100 mL). It was dried over MgSO4 and concentrated under
reduced pressure. The product was purified over silica gel (80:20
hexanes/EtOAc) to give 78−91% of 10a and 10b as a yellow oil.
10,10-Dimethyl-5-phenyl-16-selenatripyrromethane (10a). Yel-
low oil (253 mg, 92% yield). Rf = 0.3 [8:2 (v/v) petroleum/
EtOAc]. 1H NMR (400 MHz, CDCl3): δ 7.91 (br, 2H, NH), 7.27 (m,
5H, Ph), 6.73 (s, 2H, selenophene), 6.66 (m, 2H, pyrrole), 6.12−5.92
(m, 4H, pyrrole), 5.55 (s, 1H, CH), 1.67 (s, 6H, CH3). 13C NMR (75
MHz, CDCl3): δ 162.1, 152.2, 143.1, 139.6, 133.3, 128.5, 1287.3,
127.2, 124.3, 117.1, 116.8, 108.3, 107.7, 107.4, 103.5, 48.1, 39.7, 31.6,
30.9, 29.6. HRMS (ESI-QTOF): [M + H]+ calcd for C18H23N2Se m/z
395.1026, found m/z 395.1042. CHN analysis. Calcd for C22H22N2Se:
C, 67.17; H, 5.64; N, 7.12. Found: C, 67.16; H, 5.38; N, 7.51.
10,10-Dimethyl-5-phenyl-16-telluratripyrromethane (10b). Yel-
7.37 (m, 3H, C6H5), 5.50 (s, 1H, CH), 2.37 (brs, 1H, OH), 2.05 (brs,
1H, OH), 1.53 [s (split), 6H, CH3].
Reaction of Diynediols (2a−d or 8) with Selenium and
Tellurium: Synthesis of Symmetrical and Unsymmetrical
Selenophene and Tellurophene Diols (3a−h, 9a, and 9b). A
250 mL three-neck flask equipped with a nitrogen inlet, a reflux
condenser, and a dropping funnel was loaded with selenium/tellurium
(4 mmol), NaBH4 (16 mmol), and distilled water (10 mL). The
reaction mixture was vigorously stirred under nitrogen for 30 min. A
deoxygenated solution of diynediols (2a−d or 8) (3.1 mmol) in
MeOH (12 mL) with AgOAc (50 mg) was added dropwise, and the
reaction mixture was stirred overnight.2 After completion of the
reaction, water (100 mL) was added and the product was extracted
with a benzene/diethyl ether mixture (1:1, 150 mL). The organic layer
was washed with water (2 × 20 mL) and dried over anhydrous
Na2SO4, and the solvent was evaporated under reduced pressure to
give products (3a−h, 9a, and 9b) as an off-white solid (83−94%). All
symmetrical selenophene and tellurophene diols (3a−h) were
characterized, and their values matched the reported values.20
2-{5-[Hydroxy(phenyl)methyl]selenophen-2-yl}propan-2-ol (9a).
Yellow liquid (375 mg, 41%). 1H NMR (400 MHz, CDCl3): δ
7.44−7.28 (m, 5H, C6H5), 6.86 (m, 2H, selenophene), 5.94 (s, 1H,
CH), 2.49 (brs, 1H, OH), 1.59 (s, 6H, CH3). 13C NMR (75 MHz,
CDCl3): δ 161.9, 153.8, 143.4, 128.5, 127.9, 126.3, 126.1, 123.0, 74.2,
72.8, 32.2, 30.9. HRMS (ESI-QTOF): [M + H]+ calcd for C14H17O2Se
m/z 297.0394, found m/z 297.0391. CHN analysis. Calcd for
C14H16O2Se: C, 56.95; H, 5.46. Found: C, 56.99; H, 5.52.
1
low oil (266 mg, 86%). Rf = 0.3 [8:2 (v/v) petroleum/EtOAc]. H
NMR (400 MHz, CDCl3): δ 7.93 (br, 2H, NH), 7.28−7.27 (m, 4H,
Ph), 7.24−7.14 (dd, 2H, tellurophene), 6.65−6.63 (m, 2H, pyrrole),
6.12−6.07 (m, 4H, pyrrole), 5.44 (s, 1H, CH), 1.65 (s, 6H, CH3). 13
C
NMR (75 MHz, CDCl3): δ 151.42, 143.71, 138.6, 132.21, 132.01,
128.2, 127.6, 126.8, 125.3, 124.3, 116.11, 115.8, 107.81, 103.35, 41.04,
39.01, 32.32. IR (KBr) νmax: 3351, 3332, 2901, 2853, 1563, 1389, 1322,
1262, 1202, 1108, 1007, 952, 821, 752 cm−1. HRMS (ESI-QTOF): [M
+ H]+ calcd for C22H23N2Te m/z 445.0923, found m/z 445.0928.
CHN analysis. Calcd for C22H22N2Te: C, 59.78; H, 5.02; N, 6.34.
Found: C, 59.62; H, 5.12; N, 6.48.
2-{5-[Hydroxy(phenyl)methyl]tellurophen-2-yl}propan-2-ol (9b).
1
Yellow liquid (576 mg, 54%). H NMR (400 MHz, CDCl3): δ 7.43
(m, 2H, tellurophene), 7.33−7.20 (m, 5H, C6H5), 5.77 (s, 1H, CH),
2.77 (brs, 1H, OH), 2.34 (brs, 1H, OH), 1.58 [s (split), 6H, CH3]. 13
C
NMR (75 MHz, CDCl3): δ 165.7, 156.6, 146.2, 135.6, 132.0, 130.6,
129.9, 128.0, 78.7, 34.3, 34.2. HRMS (ESI-QTOF): [M + H]+ calcd
for C14H17O2Te m/z 347.0291, found m/z 347.0298. CHN analysis.
Calcd for C14H16O2Te: C, 48.90; H, 4.69. Found: C, 48.96; H, 4.78.
Reaction of Tellurophene and Selenophene Diols (3a and
3b, respectively) with Pyrrole: Synthesis of Symmetrical
Selenatripyrrane (4a) and Telluratripyrrane (4b). Boron
trifluoride-etherate (0.3 mmol) was added to the solution of diols
(3a and 3b) (0.7 mmol) in degassed pyrrole (6.5 mL), and the
resulting mixture was stirred for 1 h under argon. The reaction was
monitored by TLC. After completion of the reaction, it was diluted
with CH2Cl2 (30 mL) and 40% NaOH (25 mL). The organic layer
was separated and washed with water (3 × 100 mL) and brine (100
mL). It was dried over MgSO4 and concentrated under reduced
pressure. The product was purified over silica gel (80:20 hexanes/
EtOAc) to give 78−91% of 4a and 4b as a white solid.
Reaction of Selenophene and Tellurophene Diols (3c and
3d, respectively) with Selena- and Telluratripyrromethane (4a
and 4b, respectively): Synthesis of 5,10-Porphodimethene
5a−d (method A). To a degassed solution of tripyrrane (4a and 4b)
(0.50 mmol) and selenophene and tellurophene diols (3c and 3d,
respectively) (0.50 mmol) in CH2Cl2 (250 mL), BF3·OEt2 (0.091
mmol) was added dropwise and the reaction mixture was stirred for 1
h at room temperature, followed by oxidation with 2.2 equiv of DDQ
(2,3-dichloro-5,6-dicyanobenzoquinone). After 1 h, the solvent was
evaporated under reduced pressure to give a black crude mixture. The
crude was purified by column chromatography on silica gel using
CH2Cl2 as an eluent to afford solid 5a−d (9−11%).
5,5,10,10-Tetramethyl-15,20-bis(phenyl)-21,23-diselenaporpho-
dimethene (5a). Orange solid (32.40 mg, 10% yield). Mp: 173 °C
dec. Rf = 0.5 [5:5 (v/v) petroleum/CHCl3]. UV−vis (CHCl3): 339,
514 nm. 1H NMR (400 MHz, CDCl3): δ 7.38−7.31 (m, 10H, C6H5),
7.07 (s, 2H, selenophene), 6.91 (s, 2H, selenophene), 6.71−6.67 (dd,
4H, pyrrole), 1.78 (s, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ
182.7, 158.7, 158.1, 152.5. 144.8, 137.1, 136.6, 135.3, 130.3, 128.3,
127.6, 125.9, 124.9, 43.0, 29.6, 23.3. HRMS (ESI-QTOF): [M]+ calcd
for C36H30N2Se2 m/z 650.073, found m/z 650.079.
5,5,10,10-Tetramethyl-15,20-bis(phenyl)-21,23-ditelluraporpho-
dimethene (5b). Purple solid (11 mg, 11% yield). Mp: 191 °C dec. Rf
= 0.4 [5:5 (v/v) petroleum/CHCl3]. UV−vis (CHCl3): 356, 554 nm.
1H NMR (400 MHz, CDCl3): δ 7.60 (s, 2H, tellurophene), 7.59 (s,
2H, tellurophene) 7.37−7.33 (m, 10H, Ph), 6.69 (s, 4H, pyrrole),
1.78−1.75 (d, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ 181.8,
161.2, 158.4, 152.6, 150.5, 143.5, 136.6, 135.9, 134.7, 130.2, 128.2,
137.6, 125.4, 45.1, 34.0, 29.6. 26.6, 22.9. HRMS (ESI-QTOF): [M]+
calcd for C36H30N2Te2 m/z 750.053, found m/z 750.051.
5,5,10,10-Tetramethyl-16-selenatripyrromethane (4a).20 White
solid (181 mg, 75% yield). Mp: 97 °C. Rf = 0.2 [8:2 (v/v)
1
petroleum/EtOAc]. H NMR (400 MHz, CDCl3): δ 7.91 (br, 2H,
NH), 6.71 (s, 2H, selenophene), 6.65 (m, 2H, pyrrole), 6.12−6.05 (m,
4H, pyrrole), 1.69 (s, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ
160.94, 139.68, 124.10, 116.78, 107.72, 103.54, 39.68, 31.61. IR (KBr)
νmax: 3372, 3099, 2967, 1559, 1439, 1383, 1312, 1296, 1231, 1112,
1036, 949, 803, 722, 583 cm−1. HRMS (ESI-QTOF): [M + H]+ calcd
for C18H23N2Se m/z 347.1026, found m/z 347.1050. CHN analysis.
Calcd for C18H22N2Se: C, 62.60; H, 6.42; N, 8.11. Found: C, 62.57; H,
6.22; N, 8.41.
5,5,10,10-Tetramethyl-16-telluratripyrromethane (4b).20 White
solid (215 mg, 78% yield). Mp: 148 °C. Rf = 0.2 [8:2 (v/v)
1
petroleum/EtOAc]. H NMR (400 MHz, CDCl3): δ 7.93 (br, 2H,
NH), 7.10 (s, 2H, tellurophene), 6.65 (m, 2H, pyrrole), 6.10−6.03 (m,
4H, pyrrole), 1.66 (s, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ
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5,5,10,10-Tetramethyl-15,20-bis(phenyl)-21-selena-23-tellura-
porphodimethene (5c). Orange solid (31 mg, 9%). Mp: 178 °C dec.
Rf = 0.5 [5:5 (v/v) petroleum/CHCl3]. UV−vis (CHCl3): 343, 520,
CDCl3): δ 7.06 (s, 2H, selenophene), 6.91 (s, 2H, selenophene),
6.72−6.67 (m, 4H, pyrrole), 3.63 (s, 6H, 15,20-meso-CH3), 1.77 (s,
12H, CH3). HRMS (ESI-QTOF): [M]+ calcd for C26H26N2Se2 m/z
526.043, found m/z 526.044.
1
554 nm. H NMR (400 MHz, CDCl3): δ 7.47 (s, 2H, tellurophene),
7.38−7.34 (m, 10H, Ph), 6.89 (s, 2H, selenophene), 6.71−6.65 (dd,
4H, pyrrole), 1.79−1.74 (d, 12H, CH3). 13C NMR (75 MHz, CDCl3):
δ 183.3, 158.2, 152.6, 144.6, 136.8, 135.3, 132.9, 130.3, 128.2, 127.6,
125.9, 45.0, 29.6. HRMS (ESI-QTOF): [M]+ calcd for C36H30N2SeTe
m/z 700.063, found m/z 700.065.
5,5,10,10-Tetramethyl-15,20-bis(phenyl)-21-selena-23-tellura-
porphodimethene (5d). Purple solid (42 mg, 12%). Mp: 189 °C dec.
Rf = 0.5 [5:5 (v/v) petroleum/CHCl3]. UV−vis (CHCl3): 359, 560
nm. 1H NMR (400 MHz, CDCl3): δ 7.62 (s, 2H, tellurophene), 7.37−
7.21 (m, 10H, Ph), 7.18 (s, 2H, selenophene), 6.71−6.68 (m, 4H,
pyrrole), 1.78 (d, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ 181.2,
161.9, 158.0, 152.6, 150.7, 143.4, 136.4, 134.7, 130.2, 128.2, 128.0,
127.6, 125.3, 43.1, 31.1, 27.7. HRMS (ESI-QTOF): [M]+ calcd for
C36H30N2SeTe m/z 700.063, found m/z 700.061.
Reaction of Selenophene and Tellurophene Diols (3e and
3f, respectively) with Selena- and Telluratripyrromethane (4a
and 4b, respectively): Synthesis of 5,10-Porphodimethene 5e
and 5f (method B, isolation of porphyrinogens 7e and 7f and
oxidation with p-chloranil). The methanolic solution (5 mL) of
diol (3e and 3f) (2 mmol) was added to a degassed solution of
tripyrrane (4a and 4b) (2 mmol) in CH2Cl2 (200 mL). The reaction
was conducted at 0 °C in a dark room under argon. After 20 min, a
20% BF3·CH3OH solution (0.4 mmol) was added with a micropipette
and the reaction mixture was stirred for 1 h at 0 °C. The stirring was
continued at room temperature for 1 h. After completion of the
reaction, the solvent was evaporated under reduced pressure and a
viscous colorless oil was obtained, which was purified by column
chromatography on silica gel using CH2Cl2 as an eluent to afford
porphyrinogen (7e and 7f) as a colorless solid in 12−14% yield.
Further, the isolated porphyrinogens were subjected to oxidation.
5,5,10,10,15,20-Hexamethyl-21,23-diselenaporphyrinogen (7e).
White solid (127 mg, 12%). Mp: 169 °C dec. Rf = 0.5 [8:2 (v/v)
petroleum/CHCl3]. IR (KBr) νmax: 3351, 2854, 2821, 1584, 1352,
1198, 969, 796 cm−1. 1H NMR (400 MHz, CDCl3): δ 7.26 (br, 2H, H,
stereoisomer), 7.28 (br, H, NH, stereoisomer), 6.83 (s, H,
selenophene, stereoisomer), 6.86−6.85 (m, H, selenophene, stereo-
isomer), 6.86−6.88 (m, H, selenophene, stereoisomer), 5.87 (m, H,
pyrrole, stereoisomer), 5.86 (m, H, pyrrole, stereoisomer), 4.17 (m,
4H, CH, stereoisomer), 4.16 (m, H, CH, stereoisomer), 1.54 (s, H,
CH3, stereoisomer), 1.56 (s, H, CH3, stereoisomer). 13C NMR (75
MHz, CDCl3): δ 163.01, 157.5, 157.3, 156.4, 155.3, 143.87, 136.2,
136.1, 131.89, 124.6, 124.4, 103.6, 103.2, 103.1, 102.05, 41.36, 37.0,
36.9, 36.5, 22.5, 22.3, 22.2. HRMS (ESI-QTOF): [M]+ calcd for
C26H30N2Se2 m/z 530.073, found m/z 530.071.
5,5,10,10,15,20-Hexamethyl-21,23-ditelluraporphodimethene
(5f). Purple solid (43.50 mg, 7% yield). Rf = 0.5 [5:5 (v/v) petroleum/
CHCl3]. UV−vis (CHCl3): 350, 544 nm. 1H NMR (400 MHz,
CDCl3): δ 7.60 (s, 2H, tellurophene), 7.56 (s, 2H, tellurophene),
6.70−6.62 (m, 4H, pyrrole), 3.69 (s, 6H, 15,20-meso-CH3), 1.78−1.76
(d, 12H, CH3). HRMS (ESI-QTOF): [M]+ calcd for C26H26N2Te2 m/
z 626.022, found m/z 626.021.
Reaction of Selenophene and Tellurophene Diols (3g and
3h, respectively) with Selena and Telluratripyrromethane (4a
and 4b, respectively): Synthesis of 5,10-Porphodimethene (5g
and 5h) (method B, isolation of porphyrinogens 7g and 7h
and oxidation with a 0.1% aqueous FeCl3 solution). To a
degassed solution of tripyrranes (4a and 4b) (1.8 mmol) in CH2Cl2
(200 mL) was added the methanolic solution (4.2 mL) of diols (3g
and 3h) (1.8 mmol). The reaction was conducted at 0 °C in a dark
room under argon. After 20 min, a 20% BF3·CH3OH solution (0.38
mmol) was added with a micropipette and the reaction mixture was
stirred for 1 h. Stirring was continued for 1 h at room temperature.
After completion of the reaction, the solvent was evaporated under
reduced pressure to give a viscous colorless soild. The solid was
purified by column chromatography on silica gel using a petroleum/
CHCl3 mixture as an eluent to afford porphyrinogens (7g and 7h) as a
colorless solid in 10−11% yield.
5,5,10,10-Tetramethyl-15,20-tetrahydro-21,23-diselenaporphyri-
nogen (7g). White solid (99 mg, 11%). Mp: 149 °C dec. Rf = 0.4 [8:2
(v/v) petroleum/CHCl3]. IR (KBr) νmax: 3441, 2941, 1682, 1432,
1
1381, 1233, 1054, 798, 754, 705, 563 cm−1. H NMR (400 MHz,
CDCl3): δ 7.28 (br, 2H, NH), 6.84 (s, 2H, selenophene), 6.82 (s, 2H,
selenophene), 5.86−5.85 (m, 4H, pyrrole), 4.02 (s, 4H, CH2), 1.63 (s,
12H, CH3). 13C NMR (75 MHz, CDCl3): δ 162.74, 151.4, 143.89,
131.02, 130.54, 128.01, 105.64, 102.00, 41.22, 31.79, 31.6. HRMS
(ESI-QTOF): [M]+ calcd for C24H26N2Se2 m/z 502.042, found m/z
502.044.
5,5,10,10-Tetramethyl-15,20-tetrahydro-21,23-ditelluraporphyri-
nogen (7h). White solid (107.50 mg, 10%). Mp: 158 °C dec. Rf = 0.4
[8:2 (v/v) petroleum/CHCl3]. IR (KBr) νmax: 3442, 2957, 2915, 1641,
1422, 1355, 1215, 1041, 788, 741, 723, 591 cm−1. 1H NMR (400 MHz,
CDCl3): δ 7.33 (br, 2H, NH), 7.24 (s, 2H, tellurophene), 7.22 (s, 2H,
tellurophene), 5.82−5.80 (m, 4H, pyrrole), 3.96 (s, 4H, CH2), 1.63 (s,
12H, CH3). 13C NMR (75 MHz, CDCl3): δ 162.6, 150.6, 143.9, 131.1,
130.9, 106.4, 102, 41.2, 32.8. HRMS (ESI-QTOF): [M]+ calcd for
C24H26N2Te2 m/z 602.022, found m/z 602.017.
The isolated porphyrinogens were subjected to oxidation. To a
degassed solution of porphyrinogen (7g and 7h) (1 mmol) in CHCl3
(10 mL) was added a 0.1% aqueous FeCl3 solution at room
temperature, and the mixture was stirred for 10 min. The organic
solvent was separated and evaporated under reduced pressure. The
crude was purified by column chromatography on silica gel using a
petroleum/CHCl3 mixture as an eluent to obtain solid 5g and 5h in
4−5% yield.
5,5,10,10-Tetramethyl-21,23-diselenaporphodimethene (5g).
Red solid (25 mg, 5%). Mp: 134 °C dec. Rf = 0.6 [5:5 (v/v)
petroleum/CHCl3]. IR (KBr) νmax: 2864, 2851 2811, 1531, 1351,
1321, 1184, 1031, 951, 781 cm−1. UV−vis (CHCl3): 331, 528 nm. 1H
NMR (400 MHz, CDCl3): δ 7.103 (s, 2H, selenophene), 6.91 (s, 2H,
selenophene), 6.71 (s, 2H, 15,20-meso-H), 6.67−6.70 (m, 4H,
pyrrole), 1.87 (s, 12H, CH3). HRMS (ESI-QTOF): [M]+ calcd for
C24H22N2Se2 m/z 498.011, found m/z 498.011.
5,5,10,10,15,20-Hexamethyl-21,23-ditelluraporphyrinogen (7f).
White solid (175 mg, 14%). Mp: 153 °C dec. Rf = 0.5 [8:2 (v/v)
petroleum/CHCl3]. IR (KBr) νmax: 3438, 2941, 2868, 1581, 1391,
1
1101, 984, 751 cm−1. H NMR (400 MHz, CDCl3): δ 7.31 (br, 2H,
NH), 7.249 (m, 2H, tellurophene), 7.240 (m, 2H, tellurophene,
isomer), 7.231 (m, 2H, tellurophene), 7.230 (m, 2H, tellurophene,
isomer), 5.85−5.83 (m, 4H, pyrrole), 5.82−5.80 (m, 4H, pyrrole,
isomer), 4.11−4.07 (q, 1H, CH), 4.00−3.95 (q, 1H, CH) 1.63−1.61
(d, 12H, CH3). 13C NMR (75 MHz, CDCl3): δ 163.2, 163.1, 159.0,
157.4, 141.9, 137.6, 137.2, 131.4, 131.1, 130.4, 130.3, 102.6, 102.0,
101.4, 101.3, 42.2, 40.4, 40.0 33.3, 31.2, 30.8, 28.8, 235, 21.9. HRMS
(Q-TOF): m/z 630.051 (M+). HRMS (ESI-QTOF): [M]+ calcd for
C26H30N2Te2 m/z 630.053, found m/z 630.051.
To a degassed solution of porphyrinogen (7e and 7f) (1 mmol) in
CHCl3 (10 mL) was added p-chloranil at room temperature, and the
mixture was stirred for 10 min. The organic solvent was evaporated
under reduced pressure and purified by column chromatography on
silica gel using a petroleum/CHCl3 mixture as an eluent to afford solid
product 5e and 5f in 6−7% yield.
5,5,10,10,15,20-Hexamethyl-21,23-diselenaporphodimethene
(5e). Brick solid (31.50 mg, 6% yield). Rf = 0.45 [5:5 (v/v) petroleum/
CHCl3]. UV−vis (CHCl3): 349, 529 nm. 1H NMR (400 MHz,
5,10-Tetramethyl-21,23-ditelluraporphodimethene (5h). Purple
solid (24 mg, 4%). Mp: 139 °C dec. Rf = 0.7 [5:5 (v/v) petroleum/
CHCl3]. IR (KBr) νmax: 2882, 2841 2801, 1504, 1366, 1358, 1154,
1
1051, 961, 796 cm−1. UV−vis (CHCl3): 346, 554 nm. H NMR (400
MHz, CDCl3): δ 7.68 (s, 2H, tellurophene), 7.32 (s, 2H,
tellurophene), 6.73 (s, 2H, 15,20-meso-H), 6.69−6.67 (m, 4H,
pyrrole), 1.78−1.76 (d, 12H, CH3). HRMS (ESI-QTOF): [M]+
calcd for C24H22N2Te2 m/z 597.991, found m/z 597.994.
3888
DOI: 10.1021/acs.joc.5b00007
J. Org. Chem. 2015, 80, 3880−3890

The Journal of Organic Chemistry
Article
Reaction of Selenophene and Tellurophene Diols (9a and
9b, respectively) with Selena- and Telluratripyrromethane (4a
and 4b, respectively): Synthesis of Porphomethene 6a and 6b.
To a degassed solution of selena- and telluratripyrrane (4a and 4b,
respectively) (3 × 10−4 mol) in DCM (200 mL) were added
selenophene and tellurophene diols (9a and 9b, respectively) (3 ×
10−4 mol), and the reaction was started by the dropwise addition of a
catalytic amount of trifluoroacetic acid (0.020 mL) for 90 min, under a
nitrogen atmosphere. The progress of the reaction was monitored by
TLC. After completion of the reaction, DDQ (3 × 10−4 mol) was
added and the stirring was continued in air for 10 min. The crude
mixture was purified by silica gel column chromatography, and the
separated product was characterized as 6a and 6b in 7−9% yield.
5,5,10,10,15,15-Hexamethyl-20-phenyl-21,23-diselenaporpho-
methene (6a). Brown solid (16 mg, 9%). Rf = 0.6 [5:5 (v/v)
(10a and 10b, respectively) (3 × 10−4 mol) in DCM (200 mL) were
added selenophene and tellurophene diols (9a and 9b, respectively) (3
× 10−4 mol), and the reaction was started by the dropwise addition of
a catalytic amount of trifluoroacetic acid (0.020 mL) for 2 h under a
nitrogen atmosphere. The progress of the reaction was monitored by
TLC. After consumption of the starting material, DDQ (3 × 10−4
mol) was added and stirring was continued in air for 10 min. The
crude mixture was purified by silica gel column chromatography, and
the separated red solid product was characterized as 12a and 12b (12−
18%).
5,5,15,15-Tetramethyl-10,20-diphenyl-21,23-diselenaporphodi-
methene (12a). Red solid (35 mg, 18%). UV−vis (CH2Cl2): 426, 525
1
nm. H NMR (400 MHz, CDCl3): δ 7.52 (d, 2H, β-selenophene),
7.35 (d, 2H, β-selenophene), 7.06−7.28 (m, 10H, C6H5), 6.83 (d, 2H,
β-pyrrole), 6.22 (d, 2H, β-pyrrole), 1.21 (s, 12H, CH3). CHN analysis.
Calcd for C36H30N2Se2: C, 66.67; H, 4.66; N, 4.32. Found: C, 66.46;
H, 4.42; N, 4.28.
1
petroleum/CHCl3]. UV−vis (CHCl3): 328, 440 nm. H NMR (400
MHz, CDCl3): δ 7.85 (brs, 1H, NH), 7.37−7.33 (m, 5H, Ph), 7.04
(m, 2H, selenophene), 6.93 (s, 2H, selenophene), 6.31 (m, 2H,
pyrrole), 6.03 (d, 2H, J = 4.2, pyrrole), 1.74 (s, 6H, CH3), 1.66 (d,
12H, CH3). CHN analysis. Calcd for C32H32N2Se2: C, 63.79; H, 5.35;
N, 4.65. Found: C, 63.93; H, 5.22; N, 4.21.
5,5,15,15-Tetramethyl-10,20-diphenyl-21,23-ditelluraporphodi-
methene (12b). Red solid (18 mg, 8%). UV−vis (CH2Cl2): 443, 536
1
nm. H NMR (400 MHz, CDCl3): δ 7.81 (d, 2H, β-tellurophene),
7.74 (d, 2H, β-tellurophene), 7.08−7.26 (m, 10H, C6H5), 6.85 (d, 2H,
β-pyrrole), 6.26 (d, 2H, β-pyrrole), 1.23 (s, 12H, CH3). CHN analysis.
Calcd for C36H30N2Te2: C, 57.97; H, 4.05; N, 3.76. Found: C, 57.84;
H, 4.18; N, 3.86.
5,5,10,10,15,15-Hexamethyl-20-phenyl-21,23-ditelluraporpho-
methene (6b). Dark purple solid (15 mg, 7%). Rf = 0.6 [5:5 (v/v)
1
petroleum/CHCl3]. UV−vis (CHCl3): 360, 564 nm. H NMR (400
General Procedure for the Sensing of Hg2+ with Calixphyr-
ins. All the experiments were conducted at an ambient temperature of
25 °C. For every experiment, a fresh solution was prepared. The
solution of calixphyrins in acetonitrile (2 mL) was taken in a
spectrophotometer cuvette, and the absorption spectrum was
recorded. A 20 μL stock solution of Hg(ClO4)2 with a similar
concentration was added to the cuvette and mixed well, and the
absorption spectrum was recorded. Similarly, a mercury solution was
added to the cuvette until the absorption spectrum began to change. In
addition, the binding constant was calculated by using the Benesi−
Hilderbrand equation.
MHz, CDCl3): δ 8.01 (brs, 1H, NH), 7.62 (m, 2H, tellurophene), 7.50
(s, 2H, tellurophene), 7.37−7.33 (m, 5H, Ph), 6.35 (m, 2H, pyrrole),
6.02 (m, 2H, J = 4.2, pyrrole), 1.72−1.64 (m, 18H, CH3). HRMS (Q-
TOF): m/z 704.215 (M+). HRMS (ESI-QTOF): [M]+ calcd for
C32H32N2Te2 m/z 704.211, found m/z 704.213. CHN analysis. Calcd
for C32H32N2Te2: C, 54.92; H, 4.61; N, 4.00. Found: C, 54.93; H,
5.02; N, 4.11.
Reaction of Selenophene and Tellurophene Diols (3c and
3d, respectively) with Selena- and Telluratripyrromethane
(10a and 10b, respectively): Synthesis of Porphotrimethene
11a and 11b. The selenophene and tellurophene diols (3c and 3d,
respectively) (3 × 10−4 mol) and selena- and telluratripyrrane (10a
and 10b, respectively) (3 × 10−4 mol) were condensed in 250 mL of
CH2Cl2 under nitrogen in the presence of a catalytic amount of
trifluoroacetic acid (0.020 mL) for 2 h under an inert atmosphere.
DDQ (3 × 10−4 mol) was added, and stirring was continued in air for
an additional 1 h. The crude mixture was purified by silica gel column
chromatography, and the desired 11a and 11b were collected as a
green solid (9−11%).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR, 13C NMR, HRMS, and UV−vis spectra of all new
compounds and UV−vis and fluorescence spectra of Hg2+
titration with newer calix[4]phyrins. This material is available
free of charge via the Internet at http://pubs.acs.org.
5,5′-Dimethyl-10,15,20-triphenyl-21,23-diselenaporphotrime-
thene (11a). Green solid (19 mg, 9%). Rf = 0.6 [5:5 (v/v) petroleum/
CHCl3]. UV−vis (CHCl3): 438, 679 nm. 1H NMR (400 MHz,
CDCl3): δ 12.73 (br s, 1H, NH), 11.32 (br s, 1H, NH), 7.53−7.11 (m,
19H, Ph and β-selenophene), 7.11 (br s, 1H, β-pyrrole), 6.90 (d, 1H,
β-pyrrole), 6.67 (d, 1H, β-pyrrole), 6.28 (d, 1H, β-pyrrole), 1.91 (s,
6H, CH3). 13C NMR (75 MHz, CDCl3): δ 180.1, 179.2, 170.6. 159.3,
155.8, 150.2, 145.7, 137.5 134.2, 132.9, 132.1, 132.0, 131.1, 129.1,
128.6, 122.2, 45.8, 32.1, 31.9. HRMS (ESI-QTOF): [M + H]+ calcd
for C40H31N2Se2 m/z 699.0818, found m/z 699.0748. CHN analysis.
Calcd for C40H30N2Se2: C, 68.97; H, 4.34; N, 4.02. Found: C, 69.03;
H, 4.31; N, 4.03.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: smschauhan@chemistry.du.ac.in.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the DST New Delhi, DU-DST
Purse Grant Delhi, and University of Delhi. S.A., K.K.Y., and
S.B. are also thankful to UGC New Delhi for their senior
research fellowship.
5,5′-Dimethyl-10,15,20-triphenyl-21,23-ditelluraporphotrime-
thene (11b). Green solid (26 mg, 11%). Rf = 0.6 [5:5 (v/v)
1
petroleum/CHCl3]. UV−vis (CHCl3): 362, 583 nm. H NMR (400
MHz, CDCl3): δ 12.20 (br s, 1H, NH), 11.20 (br s, 1H, NH), 7.64 (m,
3H, β-tellurophene), 7.53 (d, 1H, β-tellurophene), 7.43−7.20 (m,
15H, Ph), 7.11 (d, 1H, β-pyrrole), 6.91 (d, 1H, β-pyrrole), 6.66 (d,
1H, β-pyrrole), 6.25 (d, 1H, β-pyrrole), 1.93 (s, 6H, CH3). 13C NMR
(75 MHz, CDCl3): δ 180.6, 179.3, 178.8. 158.4, 155.6, 151.2, 146.5,
136.6, 134.9, 132.7, 132.2, 130.6, 128.6, 128.2,122.4, 45.1, 34.6, 34.5.
HRMS (ESI-QTOF): [M]+ calcd for C40H30N2Te2 m/z 798.052,
found m/z 798.054. CHN analysis. Calcd for C40H30N2Te2: C, 60.52;
H, 3.81; N, 3.53. Found: C, 60.61; H, 3.96; N, 3.63.
Reaction of Selenophene and Tellurophene Diols (9a and
9b, respectively) with Selena- and Telluratripyrromethane
(10a and 10b, respectively): Synthesis of Porphodimethene
12a and 12b. To a degassed solution of selena- and telluratripyrrane
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