Synthesis, electrochemical and photophysical properties of β-carboxy triaryl corroles

Article abstract of DOI:10.1016/j.tetlet.2011.12.068

An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III) derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting mild reaction conditions by using hydroxylamin

Full text of DOI:10.1016/j.tetlet.2011.12.068

Tetrahedron Letters 53 (2012) 991–993
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis, electrochemical and photophysical properties of b-carboxy triaryl
corroles
⇑
Kolanu Sudhakar, Veerapandian Velkannan, Lingamallu Giribabu
Inorganic & Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III)
derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting
mild reaction conditions by using hydroxylamine hydrochloride and phthalic anhydride. All these substi-
tuted carboxy corroles were completely characterized by using Mass, CHN analysis, IR, 1H NMR, UV–vis.,
Fluorescence spectroscopies and cyclic voltammetry. Both the absorption maxima and emission maxima
of carboxy corroles were red shifted by 5–13 nm. The LUMO level of these corroles is above the TiO2 con-
duction band and HOMO level was below the redox electrolytes. These b-carboxy corroles confined with
may find applications as sensitizers in dye-sensitized solar cells.
Received 29 October 2011
Revised 14 December 2011
Accepted 16 December 2011
Available online 23 December 2011
Keywords:
Corrole
Porphyrin
Copper
Ó 2011 Elsevier Ltd. All rights reserved.
Sensitizer
Emission
Corrole macrocyle is a contracted analogue of a porphyrin in
>11%.6 However, ruthenium(II) polypyridyl complexes present
two primary drawbacks: (1) rarity of the Ru metal in the earth’s
crust making it very expensive and (2) lack of absorption in red re-
gion of the visible spectrum. As an alternative, tetrapyrrolic com-
pounds, which includes porphyrins and phthalocyanine are
particularly of interest based on their absorption, thermal, photo-
and electrochemical properties.7 Even though, the efficiency of
DSSC devices based on porphyrin sensitizers have shown around
10%, but their durability is low.8 In contrast, phthalocyanine based
sensitizers showed efficiency up to 4.6% but, is not ready for com-
mercialization of technology.9 For this reason, we found corroles
are potential alternative sensitizers for DSSC applications.
which one -meso position has been eliminated, yet possessing
the 18-p
electron aromaticity of porphyrins.1 The structure of cor-
role represents an intermediate between porphyrin and the corrin
ring in the B12 cofactor. The first investigation on corrole was car-
ried out by Johnson and Kay in the late 1960s when the macrocycle
was produced as a by-product during the synthesis of B12.2 Thus,
while corroles have been known for more than 40 years, research
in the field was slow to progress. However, investigations of cor-
roles have recently increased with the synthetic work of the groups
of Paolesse and Gross, with each of the respective groups reporting
a one-pot synthesis of triaryl corroles.3
Unlike porphyrins, corroles are tri-anionic ligands that stabilize
unusual high oxidation states of transition metal centers like Fe(IV),
Cu(III), Co(IV), Ge(IV), Sn(IV), P(V) etc.4 Corrole and its metallo
derivatives are involved in many applications that include a catalyst
in oxidation, reduction and group transfer reactions of many organ-
ic transformations, sensors, in photodynamic therapy, metastasis
and as sensitizers in dye-sensitized solar cells (DSSC) for the gener-
ation of electricity from sunlight.5 Of these, we are particularly
interested in corroles as sensitizers for DSSC applications. DSSC is
a low-cost and environmentally benign technology, an envisaged
alternative to solid-state p–n photovoltaic devices. In these devices
the sensitizer is one of the key component for achieving high effi-
ciency and durability. The widely used sensitizers in DSSC devices
are ruthenium(II) polypyridyl complexes with an efficiency of
Zeev Gross and co-workers have used sulfonated corroles hav-
ing either Ga(III) or Sn(IV) in their central cavity for DSSC applica-
tions.10 Ga(III) complex of corrole has shown an overall conversion
efficiency of up to 1.6%. This is the only example reported in the lit-
erature of corroles as sensitizers for DSSC applications to the best
of our knowledge. However, the sulfonic acid anchoring group does
not strongly bind on to the nanocrystalline TiO2 surface. It is
known from the literature that the carboxylic acid groups bind
more strongly on to the TiO2 surface than sulfonic acid and phos-
phonic acid groups.11 Here in the present manuscript we report
the synthesis and characterization of b-carboxy triaryl corroles
having electron releasing groups on its peripheral positions.
5,10,15-Triaryl substituted corroles and 3-formyl-5,10,15-triaryl
substituted corroles were synthesized as per the methods reported
in the literature.3,12 The Cu(III) metal insertion of 3-formyl-
5,10,15-triaryl substituted corroles was synthesized by a modified
procedure reported in the literature.13 We have initiated the oxida-
⇑
Corresponding author. Tel.: +91 40 27191724; fax: +91 40 27160921.
E-mail address: giribabu@iict.res.in (L. Giribabu).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.12.068

992
K. Sudhakar et al. / Tetrahedron Letters 53 (2012) 991–993
tion of 3-formyl corroles to 3-carboxy corroles using strong oxidiz-
ing agents like KMnO4 and K2Cr2O7, which fails to convert and lead
to a very complex mixture of products. This is true even for the oxi-
dation of 2-formyl tetraarylporphyrins to corresponding 2-carboxy
tetraaryl porphyrins.14 We have adopted a one-pot, mild reaction
condition for the conversion of 3-formyl-5,10,15-triaryl substituted
corroles to the corresponding carboxylic acid corroles using hydrox-
ylamine hydrochloride and phthalic anhydride (Scheme 1). By
implementing this method recently, we have successfully converted
2-formyl-5,10,15,20-tetraaryl-substituted porphyrins to corre-
sponding carboxy substituted porphyrins in quantitative yield.15
We have adopted similar reaction conditions for the oxidation of
3-formyl triaryl substituted corroles to the corresponding carboxy
triaryl substituted corroles. Initially, we have applied this one-pot
oxidation reaction to the conversion of 3-formyl-5,10,15-triaryl cor-
role to the corresponding 3-carboxy corrole in 70–80% yield.16 We
have extendedthismethodologyto other triarylsubstitutedcorroles
having electron releasing groups on phenyl ring viz. 4-methyl phe-
nyl, 4-methoxy phenyl and 3,5-dimethyl phenyl groups and their
copper derivatives. All these carboxy corroles were completely char-
acterized by CHN, Mass, IR, UV–vis., 1H NMR and Fluorescence spec-
troscopies as well as cyclic voltammetry (see Fig. 1).
Figure 1. Absorption and emission spectra of 1 in CH2Cl2.
analogous to those of normal porphyrins, with an intense Soret
band around 420 nm and lower intensity either three (free-base)
or two (copper(III)) Q-bands higher than 500 nm. Both Soret and
Q-bands of free-base and copper(III) carboxy corroles are red
shifted by 5–12 nm, when compared to the corresponding
5,10,15-triaryl corroles. This may be due to the presence of elec-
tron-withdrawing carboxyl group at pyrrole-b position. The Soret
band of copper(III) corroles are red shifted, when compared to the
corresponding free-base corroles expect Cu1, which is blue
The electronic absorption spectra of all free-base and copper(III)
carboxy corroles were measured in dichloromethane solvent. The
absorption spectrum of corrole 1 is presented in Figure 1 and
the corresponding absorption data are presented in Table 1. The
absorption spectrum of corroles are dominated by p–
p⁄ transitions
R1
R1
R4
R4
R2
R2
R3
R5
R3
R5
R2
R4
R3
R5
R3
R2
R4
R4
R3
R5
R4
R2
NH2OH.HCl
N
N
N
N
N
N
N
N
N(C2H5)3
R1
M
R1
R1
R1
M
Phthalic anhydride
R5
OHC
R5
R2
R3
HOOC
R1 = R2 = R3 = R4 = R5 = H; M = 3H; 1; M = Cu(III), 1Cu
R1 = -CH3, R2 = R3 = R4 = R5 = H; M = 3H; 2; M = Cu(III), 2Cu
R1 = -OCH3, R2 = R3 = R4 = R5 = H; M = 3H; 3; M = Cu(III), 3Cu
R1 = R3 = R5 = H, R2 = R4 = -CH3; M = 3H; 4; M = Cu(III), 4Cu
Scheme 1. Synthesis of b-carboxy triaryl corroles.
Table 1
UV–vis., emission and electrochemical dataa
b
c
Compound
kmax, nm (log
e
, Mꢀ1 cmꢀ1
)
kem,max, nm (
U)
E1/2 (V)d
E0–0 (eV)e
Cor0/+
Cu(III)/(II)
Cor0/ꢀ
1
2
3
4
Cu1
Cu2
Cu3
Cu4
421 (4.45), 593 (3.91), 621 (3.87), 653 (3.83)
421 (4.66), 593 (4.04), 627 (4.02), 654 (4.01)
423 (5.04), 590 (4.35), 631 (4.36), 657 (4.34)
421 (4.72), 593 (4.08), 626 (4.05), 653 (4.05)
414 (4.65), 554 (3.83), 639 (3.69)
424 (4.76), 554 (3.97), 643 (3.87)
438 (4.56), 549 (3.89), 638 (3.73)
423 (4.83), 554 (4.01), 642 (3.84)
682 (0.015)
684 (0.269)
694 (0.397)
681 (0.439)
654 (0.012)
647 (0.001)
645 (0.004)
645 (0.104)
0.58
0.57
0.48
0.57
0.80
0.73
0.65
0.72
–
–
–
–
ꢀ1.67
ꢀ1.65
ꢀ1.65
ꢀ1.63
ꢀ1.65
ꢀ1.50
ꢀ1.63
ꢀ1.70
1.88
1.85
1.83
1.86
1.92
1.92
1.93
1.93
ꢀ0.10
ꢀ0.13
ꢀ0.20
ꢀ0.15
a
b
c
Solvent: CH2Cl2.
Error limits, kmax 1 nm, log
10%.
e, 10%.
U,
d
e
0.1 M TBAP, Solvent: CH2Cl2, reference electrode: standard calomel electrode, working: glassy carbon, auxiliary electrode: Pt wire, error limits: E1/2
Error limits, 0.05 eV.
, 0.03 V.

K. Sudhakar et al. / Tetrahedron Letters 53 (2012) 991–993
993
shifted.17 The emission spectra of both free-base and its copper(III)
derivatives of carboxy corroles were measured in CH2Cl2 solvent at
room temperature. The emission maxima of all 3-carboxy corroles
are red shifted by 5–13 nm, when compared to those of its corre-
sponding parent triaryl corroles. The singlet state (E0–0) energies
of free-base carboxy corroles are in the range of 1.85 0.05 eV
and that of its copper derivatives are 1.92 0.05 eV. The redox
potentials of both free-base and Cu(III) carboxy corroles were mea-
sured using cyclic and differential pulse voltammetric techniques.
All new compounds have either reversible or quasireversible three
oxidations. The excited state oxidation potentials (E⁄) of all new
compounds, which correspond to LUMO were found to be above
the TiO2 conduction band and the electron in the excited state
can efficiently inject into the conduction band.18 Both free-base
and Cu(III) carboxy derivatives are having either one or two reduc-
tion potentials. The reduction of Cu(III) carboxy corroles at around
ꢀ0.20 V corresponds to the Cu(III)/(II) redox couple, whereas the
8. (a) Jasieniak, J.; Johnston, M.; Waclawik, E. R. J. Phys. Chem. B 2004, 108, 12962;
(b) Giribabu, L.; Kumar, Ch. V.; Reddy, P. Y. J. Porphyrins Phthalocyanines 2006,
10, 1007; (c) Wang, C.-L.; Chang, Y.-C.; Lan, C.-M.; Lo, C.-F.; Diau, E. W.-G.; Lin,
C.-Y. Energy Environ. Sci. 2011, 4, 1788.
9. (a) Reddy, P. Y.; Giribabu, L.; Lyness, Ch.; Snaith, H. J.; Kumar, Ch. V.;
Chandrasekharam, M.; Kantam, M. L.; Yum, J. –H.; Kalyanasundaram, K.;
Grätzel, M.; Nazeeruddin, M. K. Angew. Chem., Int. Ed. 2007, 46, 373; (b) Mori, S.;
Nagata, M.; Nakahata, Y.; Yasuta, K.; Goto, R.; Kimura, M.; Taya, M. J. Am. Chem.
Soc. 2010, 132, 4054; (c) Giribabu, L.; Singh, V. K.; Kumar, Ch. V.; Soujanya, Y.;
Reddy, P. Y.; Kantam, M. L. Solar Energy 2011, 85, 1204.
10. Walker, D.; Chappel, S.; Mahammed, A.; Brunschwig, B. S.; Winkler, J. R.; Gray,
H. B.; Zaban, A.; Gross, Z. J. Porphyrins Phthalocyanines 2006, 10, 1259.
11. Park, H.; Bae, E.; Lee, J. –J.; Park, J.; Choi, W. J. Phys. Chem. B 2006, 110, 8740.
12. Paolesse, R.; Nardis, S.; Venanzi, M.; Mastroianni, M.; Russo, M.; Fronczek, F. R.;
Vicente, M. G. H. Chem. Eur. J. 2003, 9, 1192.
13. Broring, M.; Bregier, F.; Burghaus, O.; Kleeberg, Ch. Z. Anorg. Allg. Chem. 2010,
636, 1760.
14. (a) Corey, E. J.; Gilman, N. W.; Canem, B. E. J. Am. Chem. Soc. 1968, 90, 5616; (b)
Godfrey, I. M.; Sargent, M. V.; Elix, J. A. J. Chem. Soc., Perkin Trans. 1 1974, 1353.
15. Reeta, P. S.; Kandhadi, J.; Giribabu, L. Tetrahedron Lett. 2010, 51, 2865.
16. Hydroxylamine hydrochloride (0.076 g, 1.1 mmol), triethyl amine (0.15 g,
1.1 mmol) and the corresponding free-base 3-formyl-5,10,15-triaryl
substituted corroles (1 mmol) were added in 60 mL of dry acetonitrile under
nitrogen atmosphere. The resulting reaction mixture was stirred for 30 min. To
this phthalic anhydride (0.015 g, 0.1 mmol) was added and the reaction
mixture was refluxed for 4–5 h. The reaction mixture was filtered under
suction and the solvent was removed under reduced pressure. The obtained
solid material was subjected to silica gel column chromatography and eluted
with CHCl3:CH3OH (92:8) mixture and the green color band was collected and
recrystallized from CH2Cl2:hexane mixture.
reduction at ꢀ1.65 V corresponds to the generation of corrole
p-an-
ion, which is below the reduction potential of redox electrolyte
(Iꢀ=Iꢀ3 ).19 The photovoltaic device studies by using these corrole
sensitizers are currently under progress.
In conclusion, we have used one-pot mild reaction conditions for
the oxidation of 3-formyl-5,10,15-triaryl substituted corroles to the
corresponding 3-carboxy-5,10,15-triaryl substituted corroles. The
singlet state and electrochemical properties of these 3-carboxy cor-
roles suggested that the LUMO of these compounds above the TiO2
conduction band making an efficient electron injection from ex-
cited state of dye to TiO2 conduction band and HOMO is more posi-
tive than the redox couples, which can reoxidize the sensitizer
easily by taking an electron from redox electrolyte. These sensitiz-
ers have potential for applications in dye-sensitized solar cells.
In the case of 3-carboxy-5,10,15-triaryl substituted copper(III) corroles
derivative, we have taken 3-formyl-5,10,15-triaryl copper(III) corroles
instead of corresponding free-base triaryl corroles.
Analytical data: 1: Yield: 70% (0.400 g). Anal. Calcd for C38H26N4O2: C, 79.98; H,
4.59; N, 9.82%. Found: C, 80.00; H, 4.55; N, 9.83%. MS: m/z 570, requires
570.6386. 1H NMR (CDCl3) (300 MHz) d ppm: 10.70 (br, 1H), 9.00 (s, 1H), 8.90
(s, 1H), 8.75 (m, 5H), 8.20 (m, 6H), 7.75 (m, 9H). IR (KBr) cmꢀ1: 3413, 1699,
1549, 1441, 1240, 1054, 970, 701, 572. 2: Yield: 78% (0.478 g). Anal. Calcd for
C41H32N4O2: C, 80.37; H, 5.26; N, 9.14%. Found: C, 80.40; H, 5.25; N, 9.170%.
MS: m/z 612, requires 612.7184. 1H NMR (CDCl3) (300 MHz) d ppm: 10.70 (br,
1H), 8.80 (m, 3H), 8.55 (m, 4H), 8.00 (d, 6H), 7.30 (d, 6H), 2.70 (m, 9H). IR (KBr)
cmꢀ1: 3378, 1716, 1411, 1247, 960, 701, 495. 3: Yield: 75% (0.495 g). Anal.
Calcd for C41H32N4O5: C, 74.53; H, 4.88; N, 8.48%. Found: C, 74.50; H, 4.90; N,
8.50%. MS: m/z 660, requires 660.7166. 1H NMR (CDCl3) (300 MHz) d ppm:
10.70 (br, 1H), 8.80 (m, 3H), 8.55 (m, 4H), 8.05 (d, 6H), 7.30 (d, 6H), 4.05 (m,
9H). IR (KBr) cmꢀ1: 3398, 1719, 1600, 1245, 1171, 790, 597. 4: Yield: 79%
(0.517 g). Anal. Calcd for C44H38N4O2: C, 80.71; H, 5.85; N, 8.56%. Found: C,
80.75; H, 5.85; N, 8.50%. MS: m/z 654, requires 654.7981. 1H NMR (CDCl3)
(300 MHz) d ppm: 10.70 (br, 1H), 8.80 (m, 3H), 8.55 (m, 4H), 8.00 (s, 3H), 7.30
(d, 6H), 2.40 (m, 18H). IR (KBr) cmꢀ1: 3153, 1720, 1464, 1279, 1065, 791, 515
Cu1: Yield: 72% (0.454 g). Anal. Calcd for C38H23N4O2Cu: C, 72.31; H, 3.67; N,
8.88%. Found: C, 72.35; H, 3.69; N, 8.90%. MS: m/z 630, requires 631.1608. 1H
NMR (DMSO-d6) (300 MHz) d ppm: 10.65 (br, H), 8.25 (s, 1H), 7.80 (m, 9H),
7.70–7.20 (m, 6H). IR (KBr) cmꢀ1: 3215, 1697, 1427, 1311, 1068, 792, 578 Cu2:
Yield: 80% (0.538 g). Anal. Calcd for C41H29N4O2Cu: C, 73.14; H, 4.34; N, 8.32%.
Found: C, 73.20; H, 4.40; N, 8.35%. MS: m/z 672, requires 673.2406. 1H NMR
(DMSO-d6) (300 MHz) d ppm: 10.60 (br, 1H), 8.15 (s, 1H), 7.85 (m, 1H), 7.60 (m,
6H), 7.50 (m, 6H), 7.30 (m, 6H), 2.50 (m, 9H). IR (KBr) cmꢀ1: 3285, 1640, 1457,
1312, 1183, 901, 790, 577 Cu3: Yield: 76% (0.548 g). Anal. Calcd for
Acknowledgments
We are thankful to DST for financial supporting this work. The
author K.S. acknowledges CSIR for the research fellowship. The
authors are thankful to Dr. Ravi Kumar for helping with the emis-
sion measurements.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.12.068.
References and notes
C41H29N4O5Cu: C, 68.28; H, 4.05; N, 7.77%. Found: C, 68.30; H, 4.10; N, 7.80%.
MS: m/z 720, requires 721.2388. 1H NMR (DMSO-d6) (300 MHz) d ppm: 12.20
(m, 1H), 8.25 (s, 1H), 7.60 (m, 6H), 7.35–6.85 (m, 9H), 3.98 (m, 9 H). IR (KBr)
cmꢀ1: 3426, 1640, 1471, 1390, 1031, 795. Cu4: Yield: 80% (0.572 g). Anal. Calcd
for C44H35N4O2Cu: C, 73.88; H, 4.93; N, 7.83%. Found: C, 73.85; H, 4.90; N,
7.85%. MS: m/z 715, requires 715.3203. 1H NMR (DMSO-d6) (300 MHz) d ppm:
12.26 (br, 1H), 8.18 (s, 1H), 7.60 (m, 6H), 7.15 (m, 9H), 2.50 (m, 18H). IR (KBr)
cmꢀ1: 3423, 1656, 1425, 1262, 788, 550.
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ox
Eꢁox ¼ E ꢀ E0ꢀ0. It was found that ꢀ1.30, ꢀ1.28, ꢀ1.35 and ꢀ1.29 V for 1, 2, 3
1=2
and 4, respectively, in case of free-base porphyrins whereas in case of copper
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