New gallium(III) corrole complexes as colorimetric probes for toxic cyanide anion

Article abstract of DOI:10.1016/j.ica.2013.09.049

Demand for new colorimetric sensors for toxic anions has widely increased in the last ten years, because it is an inexpensive technique, in which the analyte is naked-eye detectable. Regarding this issue, two new corrole derivatives 2 and 3 were successfully synthetized and characterized by elemental analysis, ¹H-NMR, MALDI-TOF-MS, UV-Vis absorption and emission spectra. β-Vinyl-corrole 1 was prepared by the Wittig reaction of β-formyl-corrole with phosphorus ylide. Subsequent treatment of β-vinyl-corrole with dimethyl acetylenedicarboxylate afforded compounds 2 and 3. The sensorial ability of the two new corrole derivatives towards fluoride, cyanide, acetate and phosphate anions was carried out by absorption and emission spectroscopy. Compound 2 shows to be colorimetric to cyanide, whereas a change of colour from green to colourless was visualized. In addition the highest association constants were obtained for compounds 2 and 3 in the presence of cyanide that are able to quantify a minor amount of cyanide (ca. 1.00 μM).

Full text of DOI:10.1016/j.ica.2013.09.049

Inorganica Chimica Acta xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
New gallium(III) corrole complexes as colorimetric probes for toxic
cyanide anion
Carla I.M. Santos a,b, Elisabete Oliveira b,c,1, Joana F.B. Barata a,1, M. Amparo F. Faustino a,
José A.S. Cavaleiro a, M. Graça P.M.S. Neves a, , Carlos Lodeiro b,
⇑
⇑
a Chemistry Department and QOPNA, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
b BIOSCOPE Group, REQUIMTE-CQFB, Chemistry Department, Faculty of Science and Technology, University NOVA of Lisbon, 2829-516 Monte de Caparica, Portugal
c Veterinary Science Department, CECAV, University of Trás-os-Montes and Alto Douro, 5001-801 Vila Real, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online xxxx
Demand for new colorimetric sensors for toxic anions has widely increased in the last ten years, because
it is an inexpensive technique, in which the analyte is naked-eye detectable. Regarding this issue, two
new corrole derivatives 2 and 3 were successfully synthetized and characterized by elemental analysis,
1H and 19F-NMR, MALDI-TOF-MS, UV–Vis absorption and emission spectra. b-Vinyl-corrole 1 was
prepared by the Wittig reaction of b-formyl-corrole with phosphorus ylide. Subsequent treatment of
b-vinyl-corrole with dimethyl acetylenedicarboxylate afforded compounds 2 and 3. The sensorial ability
of the two new corrole derivatives towards fluoride, cyanide, acetate and phosphate anions was carried
out by absorption and emission spectroscopy. Compound 2 shows to be colorimetric to cyanide, whereas
a change of colour from green to colourless was visualized. In addition the highest association constants
were obtained for compounds 2 and 3 in the presence of cyanide that are able to quantify a minor amount
Keywords:
Colorimetric
Corrole
Cyanide
Fluorescence
Chemosensor
of cyanide (ca. 1.00 lM).
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
toxicity the highest allowable level of cyanide according to the
World Health Organization in drinking water is around 1.9 lM
Nowadays, a huge number of colorimetric and fluorescent
chemosensors have been developed targeting the anions detection,
which have a widely application on chemical and biological pro-
cesses [1]. Among all anions, fluoride and cyanide are the most
attractive targets, because of their significant importance in health
and environmental matters [2]. Fluoride is an essential anion being
widely used in toothpaste for dental caries prevention and in oste-
oporosis treatment, as well. Like for the other anions, an excess of
fluoride anion could induce several diseases, such as fluorosis,
which might cause nephorotoxic alterations in humans leading
to urolithiasis [3]. The detection and quantification of fluoride an-
ion is often controlled in urine samples, and the standard amount
of this anion in water given by the United States Environmental
[8,9]. There are many techniques to detect cyanide such as spectro-
photometric analysis, electrochemical and optical sensors [10]. The
most inexpensive methods are the use of colorimetric sensors,
which allows the naked-eye detection of cyanide by a change of
colour. As an example, Kang et al. [11] reported a specific naked
eye sensor for cyanide over other competitive anions in protic sol-
vents, whereas a colour change from colourless to yellow in the
presence of cyanide was observed.
Consequently, the search for methods that can rapidly detect
such few amount of anions is a challenge, where the used of high
sensitive techniques as absorption and emission fluorescence spec-
troscopy enable their detection.
The design and synthesis of chemosensors with fluorophores
visible excitable have increased due to their highly application
in vivo and in the environment [12].
Corroles, porphyrins and metalloporphyrins are excellent mul-
tifunctional candidates for a great variety of sensing material
applications.
Protection Agency (EPA) [4] must be around 2 and 4 mg Lꢀ1
.
Cyanide is one of the most poison and toxic anion for the envi-
ronmental and human health [5]. Despite its toxicity cyanide is up
to now applied in industrial fields, such as in gold and silver min-
ing, in nitriles and nylon polymers and in acrylic plastic production
[6,7]. Its quantification is really important and due to its high
Corroles have many advantages such as high radiative rate con-
stants, large Stoke’s shift, absorption and emission bands in the vis-
ible and high luminescent quantum yield [13]. Also, corrole
derivatives are reactive to anions because of their high N–H acidity
[14]. However, most part of the supramolecular interactions be-
tween the fluorophore and the anion are mainly hydrogen bond,
⇑
Corresponding authors. Tel.: +351 21 2948300; fax: +351 21 2948550.
E-mail addresses: gneves@ua.pt (M. Graça P.M.S. Neves), cle@fct.unl.pt (C.
Lodeiro).
1
E. Oliveira and J.F.B. Barata contributed equally to this work.
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.09.049
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C.I.M. Santos et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
acid–base and anion–
p
interactions [15]. The anions used for anal-
From the 1H NMR spectra of compound 3 it was possible to as-
sign in the aromatic region, two singlets at d 10.52 and 9.66 ppm
corresponding to the resonances of protons H-60 and H-2 and a
doublet at d 9.12 ppm due to the resonance of proton H-18. In
the same region, it was also possible to identify four signals, three
doublets at d 8.68, 8.52 and 8.48 ppm and a multiplet at 8.77–
8.73 ppm corresponding to the resonances of the remaining five
b-pyrrolic protons. In the aliphatic region were identified four sing-
lets at d 4.23, 3.95, 3.86 and 3.80 ppm, corresponding to the reso-
nances of the methylester groups.
ysis are highly competitive with water molecules, being their
detection mainly realized in organic solvents [16]. The anions with
the tetrabutylammonium counter ion are the salts commonly used.
Following our interest, on the functionalization of corroles via
cycloaddition rections [17] and the study of fluorescent chemosen-
sors [18], herein we present the synthesis and the sensorial ability
of new corrole derivatives 2 and 3 towards fluoride, cyanide, ace-
tate and phosphate anions by absorption and emission
spectroscopy.
2. Results and discussion
2.2. Photophysical characterization
2.1. Synthesis
The photophysical characterization of compounds 2 and 3 was
performed in toluene solution at 298 K and the main photophysical
data are reported in Table 1. The benzocorrole 2 shows the highly
intense Soret band at 440 nm and two weak Q bands at 590 and
614 nm. The b-substituted corrole 3 exhibits the Soret band at
443 nm and the two weak Q bands at 596 and 616 nm. The emis-
sion bands of highest energy of the compounds 2 and 3 are cen-
tered between 616 and 618 nm, respectively.
As an example, Fig. 1 shows the absorption, emission and exci-
tation spectra in toluene of compound 2. The same photophysical
characterization was performed in toluene for compound 3.
A careful inspection of Fig. 1 rules out for the absence of any
emissive impurity due to the total overlap between the absorption
and excitation spectra. The fluorescence quantum yield of b-substi-
tuted corrole 3 (/ = 0.08) is relatively lower than that obtained
with the benzocorrole 2 (/ = 0.24). The high value shown by deriv-
ative 2, is probably related with conformation issues. Compound 2
is the most planar one having then a major value of fluorescent
quantum yield.
The synthetic route used to prepare the precursors 2 and 3 is
outlined in Scheme 1. The corrole precursors 5,10,15-tris(pentaflu-
orophenyl)corrole and 5,10,15-tris(pentafluorophenyl)corrolato-
gallium(III)(pyridine) were synthesized, according to procedures
described in literature [19,20].
The synthesis of the gallium(III) complex of 3-vinyl-5,10,15-
tris(pentafluorophenyl)corrole 1 involved the Vilsmeier–Haack
formylation
of
5,10,15-tris(pentafluorophenyl)corrolatogalli-
um(III)(pyridine) using POCl3/DMF, followed by a Wittig reaction
using CH3PPh3Br/NaH/THF [15].
The reactivity of the 3-vinyl-corrole 1 as a diene in Diels–Alder
reactions was studied using dimethyl acetylenedicarboxylate as
dienophile. The reaction was carried out by heating corrole 1 with
an excess of the dienophile (2 equiv.) in refluxing toluene, and
were finished when the control by TLC showed the total consump-
tion of the starting reagent. After the usual work up and purifica-
tion, two novel compounds were isolated and identified, as the
benzocorrole 2 ([M+H]+ m/z 1029) obtained in 81% yield and com-
pound 3 ([M+H]+ m/z 1171) obtained in 16% yield (Scheme 1). The
synthesis of compound 2 results from a Diels–Alder reaction fol-
lowed by oxidation. However the formation of compound 3 via a
cyclotrimerization process is quite surprising, since a similar reac-
tion with a b-vinylporphyrin and the same dienophile only affor-
2.3. Sensorial ability towards fluoride, cyanide, acetate and phosphate
anions in toluene
The sensorial ability of compounds 2 and 3 for spherical (Fꢀ),
linear (CNꢀ) and bulky anions (CH3COOꢀ and H2PO4ꢀ) was carried
out by the increasing addition of the tetrabutylammonium salts to
a solution of each corrole derivatives. The titrations were followed
by absorption and emission fluorescence measurements in toluene.
The addition of Fꢀ anion produces spectral changes in the ground
and excited states of compounds 2 and 3. Fig. 2 shows the spectro-
photometric and spectrofluorimetric titrations of compounds 2
ded the expected adduct [21]. This result shows
a clear
difference in the reactivity of porphyrins and corroles, and further
studies will be performed in order to clarify this unexpected
transformation.
The structures of the new compounds were established by spec-
troscopic data, namely NMR, UV–Vis, MS and elemental analysis.
The 1H NMR spectrum of the adduct 2 showed in the aromatic
region two doublets at d 9.46 and d 8.91 ppm due to the resonance
of protons H-18 and H-17, respectively. The multiplet existing at d
8.86–8.67 ppm was attributed to the ressonances of other b-pyrro-
lic protons. The signals at d 8.53 and 8.17 ppm were assigned to the
resonances of the aromatic protons H-50 and H-40.
Table 1
Selected photophysical data of compounds 2 and 3 in toluene.
Compounds
kmax(nm):log
e
kem (nm)
D
k (nm)
U
2
3
590:3.82
596:3.78
616
618
26
22
0.24
0.08
In the aliphatic region were identified two singlets at d 4.58
and 4.09 ppm, that are due to the resonance of the methyl ester
groups.
COOMe
COOMe
MeOOC
18
COOMe
MeOOC
4´
5´
18
2
17
17
COOMe
6´
N
N
N
N
N
Ga
N
N
Ga
MeOOC
COOMe
C6F5
C6F5
C6F5
C6F5
C6 F5
C6F5
Ga
Toluene, reflux, N2
N
py N
N
N
N
py
py
C6F5
C6F5
C6F5
1
2
3
Scheme 1.
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C.I.M. Santos et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
3
tra a red shift from 616 to 630 nm, accompanied by a quenching of
40% is visualized (see Fig. 2B). A similar behaviour was observed for
compound 3. Considering the absorption spectrum of 3 (see
Fig. 2C) the titration with Fꢀ is responsible for a decrease in the
band at 596 nm and an increase in the one at 606 nm, accompanied
by a red-shift from 596 to 606 nm and from 618 to 624 nm. In the
excited state a quenching at 618 nm of ca. 40% occurred, followed
by a red-shift from 618 to 635 nm (see Fig. 2D).
I
norm/a.u.
1
0.06
A
0.4
A
Abs.
0.3
0.2
0.1
0
Abs.
Emis.
Exct.
0.045
0.03
0.015
0
0.8
300 350 400 450 500
Wavelength/nm
0.6
0.4
0.2
0
The most interesting results arise from cyanide interaction,
where the compound 2 shows to be colorimetric, being its interac-
tion with the anions naked-eye detectable.
Fig. 3 shows the absorption (ground state; Q band region) and
emission (excited state) spectra of compounds 2 and 3 with the
increasing amount of cyanide. In all compounds in the ground state
a red shift from ca 440 to 450 nm followed by a decrease in the
absorbance is noticed in the Soret type band. For compound 2 in
the Q band region, a red shift from 590 to 605 nm and from 616
to 630 nm, with an absorbance increased at 630 nm are detected.
These alterations are accompanied by a colour change from green
to colourless (see Fig. 3A). A red shift in the emission spectra of 2
from 616 to 637 nm, and an emission quenching at 616 nm is de-
tected, as well (see Fig. 3B). For compound 3 in the ground state it
is also detected a red shift from 596 to 607 nm (see Fig. 3C). Sub-
sequently, in the excited state a red shift from 618 to 636 nm, is
480 520 560 600 640 680 720 760 800
Wavelength/nm
Fig. 1. Room temperature absorption (bold line), normalized emission (full line,
kexc = 590 nm) and excitation spectra (dotted line, kem = 620 nm) of compound 2 in
toluene. Inset: Absorption spectrum of compound 2.
and 3 in the presence of fluoride anions in toluene. Upon addition
of Fꢀ to derivative 2 a red shift from 590 to 600 nm and from 616 to
620 nm is detected in the absorption, as well as, an increase in the
absorbance at 600 and 620 nm (see Fig. 2A). In the emission spec-
Inorm/a.u.
0.3
0.3
I norm. /a.u.
A
1
0.8
0.6
0.4
0.2
0
A
1
0.8
0.6
0.4
0.2
0
0.2
0.25
616 nm
Fitting
0.1
600 nm
620 nm
0.2
0
0
0.5
1
1.5
2 2.5
[F-]/[2]
0.15
0.1
0.05
0
0
0.5
1
1.5
2
2.5
B
[F-]/[2]
A
600 620 640 660 680 700 720 740
Wavelength/nm
500
550
600
650
700
Wavelength/nm
Inorm/a.u.
1
0.3
A
0.3
I
/a.u.
norm1.
0.8
0.6
0.4
0.2
0
A
0.2
0.25
0.8
0.6
0.4
0.2
0
618 nm
606 nm
624 nm
0.1
0
0.2
0.15
0.1
0
0.5
1
1.5
2
2.5
[F-]/[3]
0
0.2 0.4 0.6 0.8
[F-]/[3]
1
0.05
0
C
D
580 600 620 640 660 680 700 720 740
Wavelength/nm
500
550
600
Wavelength/nm
650
700
Fig. 2. Spectrophotometric (A, C) and spectrofluorimetric (B, D) titration of compounds 2 (A, B) and 3 (C, D) with the addition of Fꢀ in toluene. The inset represents the
absorption at 600, 620 nm (A), 606, 624 nm (C) and the emission intensity at 616 nm (B), 618 nm (D) as a function of [Fꢀ]/[2], [Fꢀ]/[3] ([2] = [3] = 1 ꢁ 10ꢀ5 M, kexc2 = 590 nm,
kexc3 = 596 nm, T = 298 K).
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C.I.M. Santos et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
0.4
A
Inorm/a.u.
0.3
A
2 +CN-
I norm. /a.u.
1
0.8
0.6
0.4
0.2
0
0.2
0.1
0
1
0.8
0.6
0.4
0.2
0
616 nm
637 nm
Fitting
0.3
0.2
0.1
0
605 nm
630 nm
Naked-eye
+CN-
2
0
0.5
1
1.5
[CN-]/[2]
0
0.5
1
1.5
2
2.5
[CN-]/[2]
Under
UV lamp
B
A
600
650
700
750
800
Wavelength/nm
500
550
600
650
700
750
800
850
Wavelength/nm
0.4
A
Inorm/a.u.
1
0.3
A
I norm. /a.u.
0.2
0.1
0
1
0.8
0.6
0.4
0.2
0
0.3
616 nm
Fitting
0.8
0.6
0.4
0.2
0
607 nm
630 nm
0
0.5
1
1.5
2
0.2
0.1
0
[CN-]/[3]
0
0.5
1
1.5
2
[CN-]/[3]
D
C
580 600 620 640 660 680 700 720 740
Wavelength/nm
500
550
600
650
700
750
800
850
Wavelength/nm
Fig. 3. Spectrophotometric (A, C) and spectrofluorimetric (B, D) titration of compounds 2 (A, B) and 3 (C, D) with the addition of CNꢀ in toluene. The inset represents the
absorption at 605, 630 nm (A), 607, 630 nm (C) and the emission intensity at 616, 637 nm (B), 616 nm (D) as a function of [CNꢀ]/[2], [CNꢀ]/[3] ([2] = [3] = 1 ꢁ 10ꢀ5 M,
kexc2 = 590 nm, kexc3 = 596 nm, T = 298 K).
perceived, as well as, a turn-off in the emission intensity at 618 nm
(see Fig. 3D).
amount of cyanide with values of 0.33–0.34
1.01 M, respectively.
lM and of 1.00–
l
The bulky anions as acetate and phosphate can be found in food
additives and in agricultural fertilizers [8]. Their interactions with
corrole 2 did not produce changes in the ground state (see Fig. 4A
and C). However, in the excited state a quenching of ca. 40% at
616 nm was observed for macrocycle 2 in the presence of CH3COOꢀ
and H2PO4ꢀ anions (see Fig. 4B and D). A different situation occurs
with corrole 3 where no changes in the ground and excited state
were observed, during the titrations performed with the anions
above referred.
3. Experimental
3.1. Materials
(CH3CH2CH2CH2)4NF, (CH3CH2CH2CH2)4N(CN), (CH3CH2CH2CH2)4
N(CH3CO2), (CH3CH2CH2CH2)4NCl, (CH3CH2CH2CH2)4N(H2PO4) salts
were purchased from Sigma–Aldrich and dimethyl acetylenedicar-
boxylate were obtained from Alfa Aesar. All these chemicals were
used without further purification. The solvents were obtained from
Panreac and Riedel-de Haen and used as received or distilled and dried
using standard procedures.
The association constants for anions interaction were deter-
mined using the HYPSPEC program [22] and the main results are
gathered in Table 2. For both compounds the highest association
constants were obtained for cyanide anion (corrole
3
LogKass. = 6.82 0.02) and (corrole 2 LogKass. = 6.73 0.02). A stoi-
chiometry of two complexes per anion was postulated for both
derivatives. Concerning the sensorial ability of compounds 2 and
3 studied towards cyanide anion and future application of these
probes, the detection (LOD) and quantification (LOQ) limits for
the analyte (CNꢀ) were also determined (see Table 2). It was found
that compounds 2 and 3 are able to detect and quantify a fewer
3.2. Physical measurements
Elemental analyses were carried out with a Fisons Instruments
EA1108 microanalyser at the University of Vigo (CACTI), Spain. 1H
NMR spectra were recorded on Bruker Avance 300 (at 300 and
75 MHz, respectively) spectrometers. 19F NMR spectra were also
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C.I.M. Santos et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
5
Inorm/a.u.
0.8
A
I norm. /a.u.
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
0.6
0.4
0.2
0
616 nm
0 0.5 1 1.5 2 2.5 3 3.5
[CH3COO-]/[2]
A
B
600 620 640 660 680 700 720 740
Wavelength/nm
400
500
600
700
800
Wavelength/nm
Inorm/a.u.
0.8
A
I norm. /a.u.
1
1
0.8
0.6
0.4
0.2
0
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
616 nm
0 0.5 1 1.5 2 2.5 3 3.5
-
[H2PO4 ]/[2]
D
C
600 620 640 660 680 700 720 740
Wavelength/nm
400 450 500 550 600 650 700 750
Wavelength/nm
Fig. 4. Spectrophotometric (A, C) and spectrofluorimetric (B, D) titration of compound 2 with the addition of CH3COOꢀ and H2PO4 in toluene. The inset represents the
ꢀ
emission intensity at 616 nm for (B) and (D) as a function of [CH3COOꢀ]/[2] and [H2PO4ꢀ]/[2] ([2]=1 ꢁ 10ꢀ5 M, kexc2 = 590 nm, T = 298 K).
Table 2
HORIBA-JY Scientific Fluromax-4. The linearity of the fluorescence
Association constants, detection (LOD) and quantification (LOQ) limits of compounds
2 and 3. [LOD and LOQ were measured at 616 and 618 nm for 2 and 3].
emission versus the concentration was checked out in the concen-
tration used (10ꢀ4–10ꢀ6 M). A correction for the absorbed light was
Compound
Anion
LogKass A:L
LOD (
l
M)
LOQ (lM)
performed when necessary. The spectrometric characterizations
and titrations were performed as follows: the stock solutions of
compounds 2 and 3 (ca. 10ꢀ3 M) were prepared by dissolving an
appropriated amount of each compound in a 10 mL volumetric
flask and diluting it to the mark with toluene. The solutions were
prepared by appropriate dilution of the stock solutions up to
10ꢀ5–10ꢀ6 M. Titrations of compounds 2 and 3 were carried out
by adding microliter amounts of standard solutions of the anions
in DMSO.
Fluorescent quantum yields of compounds 2 and 3 were mea-
sured using a solution of cresyl violet perchlorate in absolute eth-
anol as a standard ([/] = 0.54) [23] and was corrected for different
refraction indexes of solvents. The limit of detection (LOD) and the
limit of quantification (LOQ) for the anions were performed, having
in mind their use for real anion detection and for analytical appli-
cations. For these measurements, ten different analyses for the se-
lected receptor were performed in order to obtain the LOQ. The
LOD was obtained by applying the formula:
2
Fꢀ
5.48 0.02 (1:2)
6.73 0.02 (1:2)
4.28 0.02 (1:2)
3.78 0.02 (1:2)
5.86 0.01 (1:2)
6.82 0.02 (1:2)
–
0.33
–
–
–
–
1.00
–
–
–
CNꢀ
CH3COOꢀ
ꢀ
H2PO4
3
Fꢀ
CNꢀ
0.34
1.01
obtained on a Bruker Avance 300 at 282 MHz. CDCl3 and pyridine-
d5 were used as solvents with tetramethylsilane (TMS) as the inter-
nal reference; the chemical shifts are expressed in d (ppm) with the
coupling constants (J) in Hertz (Hz). Unequivocal 1H assignments
were made using 2D COSY experiments (mixing time of 800 ms).
Preparative thin-layer chromatography (TLC) was carried out on
20 ꢁ 20 cm glass plates coated with silica gel (0.5 mm thick). Ana-
lytical TLC was carried out on precoated sheets with silica gel
(Merck 60, 0.2 mm thick).
3.3. Spectrophotometric and Spectrofluorimetric measurements
Ydl ¼ yblank þ 3std where ydl ¼ signal detection limit and std
¼ standard deviation:
Absorption spectra were recorded on a JASCO V-650 Spectro-
photometer and the fluorescence emission on a Spectrofluorimeter
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C.I.M. Santos et al. / Inorganica Chimica Acta xxx (2013) xxx–xxx
3.4. Synthesis of organic ligands
Ciência e Tecnologia (FCT, Portugal), European Union, QREN, FEDER
and COMPETE for funding the QOPNA research unit (project Pest-C/
QUI/UI0062/2011) and the Portuguese National NMR Network, also
supported by funds from FCT. C.S., E.O and J.F.B.B also thank FCT-
MEC (Portugal) for their doctoral and Post-Doctoral grants, SFRH/
BD/64155/2009, SFRH/BPD/72557/2010 and SFRH/BPD/63237/
2009.
The precursor gallium(III) complex of 3-vinyl-5,10,15-tris(pen-
tafluorophenyl)corrole 1 was synthesized according to the proce-
dures described within the literature [15].
3.5. General procedure for preparing compounds 2 and 3
A solution of 1 (0.025 mmol) and the dienophile (acetylenedi-
carboxylate) (0.050 mmol) in toluene (0.5 mL) was gently refluxed
for 48 h under a nitrogen atmosphere. After cooling to room tem-
perature, the solvent was evaporated and the compounds 2, and
3 were separated and further purified by preparative TLC (silica:
hexane–ethyl acetate–pyridine (15:5:0.1)). Compound 2 and 3
were obtained in 81% and 16% yield and were crystallized from
dichloromethane/methanol.
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(Portugal) for financial support. Thanks to Fundação para
a
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