Functionalization of corroles: The nitration reaction

Article abstract of DOI:10.1021/ic7014572

The reaction of meso-triarylcorroles with AgNO₂ proceeds with concomitant metalation and peripheral substitution to give the corresponding nitro-substituted silver(III) corrole complex. The substitution is highly regioselective, giving only the

Full text of DOI:10.1021/ic7014572

Inorg. Chem. 2007, 46, 10791−10799
Functionalization of Corroles: The Nitration Reaction
Manuela Stefanelli,† Marco Mastroianni,† Sara Nardis,† Silvia Licoccia,† Frank R. Fronczek,‡
Kevin M. Smith,‡ Weihua Zhu,§ Zhongping Ou,§ Karl M. Kadish,§ and Roberto Paolesse*,†
Dipartimento di Scienze e Tecnologie Chimiche, UniVersita` di Roma Tor Vergata, Via della
Ricerca Scientifica, 1, 00133 Rome, Italy, Department of Chemistry, Louisiana State UniVersity,
Baton Rouge, Louisiana 70803, and Department of Chemistry, UniVersity of Houston,
Houston, Texas 77204-5003
Received July 23, 2007
The reaction of meso-triarylcorroles with AgNO2 proceeds with concomitant metalation and peripheral substitution
to give the corresponding nitro-substituted silver(III) corrole complex. The substitution is highly regioselective, giving
only the corresponding 3-nitro derivative, among the different possible isomers. The results obtained indicate that
the reaction intermediate is the
proven by the reaction of the copper corrole complexes with NaNO2: in this case, the nitration reaction proceeded
without the addition of an oxidant, because of the -cation radical character of the copper complex. The reaction
π-cation radical of the complex, which is then attacked by nitrite ion. This was
π
is also successful in the case of 2,3,17,18-tetraethyl-8,12-diacetoxymethyl-7,13-dimethylcorrole (AMCorH3), with
the formation of the meso-substituted silver corrole derivative (NO2)3AMCorAg (fully characterized by X-ray
crystallography), the first of its kind to be reported. Two of the corroles are characterized by cyclic voltammetry and
spectroelectrochemistry in dichloromethane, and the site of electron transfer is elucidated.
Introduction
macrocycle-specific reactivity and coordination chemistry,3
which has led in some cases to applications of these
compounds in the field of sensors or as catalysts.4 The
publication of new synthetic routes for preparation of meso-
aryl-substituted corroles from commercially available re-
agents5 has also facilitated a ready access to these com-
pounds, which has led to rapid and impressive advancements
in the field of corrole chemistry. Indeed, the previously
lengthy and laborious synthetic routes to obtain â-alkylcor-
roles6 had represented a formidable obstacle to the study and
use of these macrocycles.
The rich properties of porphyrins and related macrocycles
make these compounds of interest for a wide range of
disciplines, ranging from medicine to material science.1 In
all of these fields, the synthetic versatility of porphyrinoids
is of fundamental importance, in part because it allows for
fine-tuning of the macrocyclic properties and in part because
it makes possible the construction of supramolecular archi-
tectures; this in turn can induce additional properties via
cooperative interaction of the different macrocycles, often
mimicking the complex structures of biological systems.2
Among the porphyrinoids, the corroles have assumed in
recent years an increasingly important role because of their
(3) Erben, C.; Will, S.; Kadish, K. M. In The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San
Diego, 2000; Vol. 2, p 233.
* To whom correspondence should be addressed. E-mail: kmsmith@
lsu.edu (K.V.M.); kkadish@uh.edu (K.M.K.); roberto.paolesse@uniroma2.it
(R.P.).
(4) (a) Gross, Z.; Gray, H. B. AdV. Synth. Catal. 2004, 346, 165. (b) Aviv,
I.; Gross, Z. Chem. Commun. 2007, 1987. (c) Barbe, J.-M.; Canard,
G.; Brande`s, S.; Je´rome, F.; Dubois, G.; Guilard, R. J. Chem. Soc.,
Dalton Trans. 2004, 1208. (d) Paolesse, R.; Mandoj, F.; Marini, A.;
Di Natale, C. In Encyclopedia of Nanoscience and Nanotechnology;
Nalwa, H., Ed.; American Science Publishers: Valencia, CA, 2004;
Vol. 9, p 21.
(5) (a) Gross, Z.; Galili, N.; Saltsman, I. Angew. Chem., Int. Ed. 1999,
38, 1427. (b) Paolesse, R.; Jaquinod, L.; Nurco, D. J.; Mini, S.; Sagone,
F.; Boschi, T.; Smith, K. M. Chem. Commun. 1999, 1307. (c) Paolesse,
R.; Nardis, S.; Sagone, F.; Khoury, R. J. Org. Chem. 2001, 66, 550.
(d) Koszarna, B.; Gryko, D. T. J. Org. Chem. 2006, 71, 3707.
(6) Paolesse, R. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 2, p
201.
† Universita` di Roma Tor Vergata.
‡ Louisiana State University.
§ University of Houston.
(1) (a) Chou, J.-H.; Nalwa, H. S.; Kosal, M. E.; Rakow, N. A.; Suslick,
K. In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard,
R., Eds.; Academic Press: San Diego, 2000; Vol. 6, p 43. (b) Pandey,
R. K.; Zheng, G. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 6,
p 157. (c) Malinski, T. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000;
Vol. 6, p 231.
(2) Balaban, T. S. Acc. Chem. Res. 2005, 38, 612.
10.1021/ic7014572 CCC: $37.00
Published on Web 11/07/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 25, 2007 10791

Stefanelli et al.
Chart 1. Molecular Structures of the Corroles Studied
While the preparative chemistry of corroles is now well-
advanced, functionalization of the â-pyrrole positions of these
macrocycles still represents a significant synthetic challenge,
as indicated by the fact that there are only a few examples
of â-pyrrole-substituted corroles in the literature.7 The
â-functionalization of corroles is particularly troublesome,
not only because the macrocycle shows in some cases an
unpredictable reactivity8 but also because of its lower
symmetry compared with porphyrins, which can potentially
lead to the formation of difficult to separate regioisomers.9
In the compendium of aromatic macrocycle â-function-
alizations, nitration is particularly appealing because the nitro
group is a useful staging point for further transformations.10
To the best of our knowledge, there is only one example in
the literature of the nitration of a corrole.9 This reaction was
carried out on a Ga complex of tri(pentafluorophenyl)corrole
and has never been shown to work for a â-substituted
alkylcorrole.
free-base corroles is more challenging because metal-free
corroles have, in the past, shown an intriguing and erratic
reactivity. For example, in the case of bromination, a
corrole-isocorrole tautomeric equilibrium is observed,5c
while hydroformylation affords an inner-core ethane-bridged
macrocycle in the case of triphenylcorrole8b and an ami-
nomethene derivative in the case of â-alkylcorroles.8a Finally,
the reaction with CI4 gave the corresponding hemiporphycene
by macrocyclic ring expansion.8c
In the present paper, we report the nitration reaction carried
out on free-base meso-triarylcorroles and â-alkylcorroles and
characterization of the resulting silver and copper nitro
derivatives (Chart 1). Our results give useful information on
the mechanism of synthesis as well as provide a facile
approach to the preparation of nitro-substituted corroles. We
also report the first electrochemistry of silver corroles. The
oxidation and reduction potentials were measured by cyclic
voltammetry, and the UV-vis spectra of the electrogenerated
species were characterized by thin-layer spectroelectrochem-
istry.
The substitution reactions of metal-free corroles are of
potentially more general scope because the demetalation of
corroles is difficult. On the other hand, functionalization of
Experimental Section
(7) Nardis, S.; Monti, D.; Paolesse, R. Mini-ReV. Org. Chem. 2005, 2,
546.
General Procedure. Reagents and solvents (Sigma-Aldrich,
Fluka, and Carlo Erba Reagenti) were of synthetic grade and used
without further purification. Silica gel 60 (70-230 mesh) and neutral
alumina (Brockmann Grade III) were used for chromatography.
1H NMR spectra were recorded on Bruker AV300 (300 MHz)
or AM400 (400 MHz) spectrometers. Chemical shifts are given in
ppm relative to tetramethylsilane (TMS). UV-vis spectra were
measured on a Cary 50 spectrophotometer; more precise measure-
ments were performed on a Perkin-Elmer λ18 spectrophotometer
(8) (a) Paolesse, R.; Jaquinod, L.; Senge, M. O.; Smith, K. M. J. Org.
Chem. 1997, 62, 6193. (b) Paolesse, R.; Nardis, S.; Venanzi, M.;
Mastroianni, M.; Russo, M.; Fronczek, F. R.; Vicente, M. G. H.
Chem.sEur. J. 2003, 9, 1192. (c) Paolesse, R.; Nardis, S.; Stefanelli,
M.; Fronczek, F. R.; Vicente, M. G. H. Angew. Chem., Int. Ed., 2005,
44, 3047.
(9) Saltsman, I.; Mahammed, A.; Goldberg, I.; Tkachenko, E.; Botoshan-
sky, M.; Gross, Z. J. Am. Chem. Soc. 2002, 124, 7411.
(10) Jaquinod, L. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M.. Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 1, p
201.
10792 Inorganic Chemistry, Vol. 46, No. 25, 2007

Functionalization of Corroles
equipped with a temperature-controlled cell holder. IR spectra were
recorded with a Perkin-Elmer 983G spectrometer. Mass spectra
(FAB mode) were recorded on a VGQuattro spectrometer in the
positive-ion mode using m-nitrobenzyl alcohol (Aldrich) as a matrix.
Cyclic voltammetry was carried out at 298 K by using an EG&G
Princeton Applied Research (PAR) 173 potentiostat/galvanostat. A
homemade three-electrode cell was used for cyclic voltammetric
measurements and consisted of a platinum button or glassy-carbon
working electrode, a platinum counter electrode, and a homemade
saturated calomel reference electrode (SCE). The SCE was separated
from the bulk of the solution by a fritted glass bridge of low
porosity, which contained the solvent/supporting electrolyte mixture.
Thin-layer UV-visible spectroelectrochemical experiments were
performed with a homebuilt thin-layer cell which has a light
transparent platinum net working electrode.11 Potentials were
applied and monitored with an EG&G PAR Model 173 potentiostat.
Time-resolved UV-vis spectra were recorded with a Hewlett-
Packard Model 8453 diode array spectrophotometer. High purity
N2 from Trigas was used to deoxygenate the solution and kept over
the solution during each electrochemical and spectroelectrochemical
experiment.
C, 84.7; H, 7.2; N, 8.1. UV-vis: λmax (CHCl3): 418 (ꢀ 130 000),
573 (17 700), 619 (16 700), 651 (13 700) nm. 1H NMR (300 MHz,
CDCl3): δ 8.94 (br s, 4H, â-pyrr), 8.63 (br s, 4H, â-pyrr), 8.33 (br
d, 4H, phenyl), 8.13 (br d, 2H, phenyl), 7.84 (br d, 4H, phenyl),
7.79 (br d, 4H, phenyl), 1.61 (s, 27H, p-tBu). LRMS (FAB): m/z
695 (M+).
5,10,15-Tris(3,5-Difluorophenyl)corrole [T(3,5-F2)PCorH3].
T(3,5-F2)PCorH3 was prepared following a literature method6
(yield 16%). Found: C, 69.8; H, 3.0; N, 8.5. Anal. Calcd for
C37H20F6N4: C, 70.0; H, 3.2; N, 8.8. UV-vis: λmax (CHCl3): 416
(ꢀ 149 000), 574 (23 400), 615 (14 000), 647 (8700) nm. 1H NMR
(300 MHz, CDCl3): δ 9.06 (s, 2H, â-pyrr), 8.97 (s, 2H, â-pyrr),
8.67 (s, 4H, â-pyrr), 7.92 (m, 6H, phenyl), 7.75 (m, 3H, phenyl).
LRMS (FAB): m/z 635 (M+).
5,10,15-Tris[(4-tert-butylphenyl)corrolato]silver(III)
[(TtBuPCor)Ag]. TtBuPCorH3 (70 mg, 0.1 mmol) was dissolved
in pyridine (10 mL), and silver(I) acetate (55 mg, 0.33 mmol) was
added. The resulting solution was heated at 80 °C, and the progress
of the reaction was monitored by thin-layer chromatography (TLC)
or UV-vis spectroscopy. The color of the solution changed from
green to dark red as the reaction proceeded. Upon completion, the
reaction mixture was filtered through a Celite plug, the solvent was
removed under vacuum, and the residue was purified by column
chromatography on silica gel (CH2Cl2 as eluent). The first red-
violet fraction was isolated and crystallized from CH2Cl2/MeOH,
affording 52 mg (0.065 mmol, 65% yield) of (TtBuPCor)Ag as
dark red crystals. Found: C, 73.4; H, 6.1; N, 6.9. Anal. Calcd for
C49H47AgN4: C, 73.6; H, 5.9; N, 7.0. UV-vis: λmax (CHCl3): 427
Anhydrous dichloromethane (>99.8%) was obtained from Al-
drich Co. and used as received for electrochemistry and spectro-
electrochemistry experiments. Tetra-n-butylammonium perchlorate
(TBAP) was purchased from Sigma Chemical or Fluka Chemika
Co., recrystallized from ethyl alcohol, and dried under vacuum at
40 °C for at least one week prior to use.
X-ray Crystal Data. Intensity data were collected for compound
[(NO2)3AMCor]Ag at T ) 90 K using graphite-monochromated
Mo KR radiation (λ)0.71073 Å) on a Nonius KappaCCD diffrac-
tometer fitted with an Oxford Cryostream cooler. Multiscan
absorption corrections led to transmission coefficients 0.837-0.935.
The structure was solved by direct methods and refined by full-
matrix least squares, using SHELXL97.12 H atoms were visible in
difference maps, but were placed in idealized positions and treated
as riding. Crystal data: C35H36AgN7O10, fw ) 822.58, dark red
needle, triclinic space group P1h, a ) 9.7991(10) Å, b ) 13.8489-
(16) Å, c ) 14.166(2) Å, R ) 62.170(4)°, â ) 76.617(7)°, γ )
88.069(7)°, V ) 1647.7(3) Å3, Z ) 2, θmax ) 30.0°, 41 575
measured reflections, 9611 independent reflections, Rint ) 0.038,
8062 with I > 2σ(I), R ) 0.032, GOF ) 1.030, 487 refined
parameters, ∆Fmax ) 0.77, ∆Fmin ) -0.93 e‚Å-3, deposition no.
CCDC 651146.
Rotating-Frame Overhauser Enhancement Spectroscopy
(ROESY) Experiment. The ROESY NMR experiment was
recorded with an 80 ms spin-lock period. The 2D data sets were
typically acquired with 2048 points in t2, 380 points in t1, and 48
scans. Data were processed and analyzed using XWinNMR and
Topspin 1.2 software (Bruker Biospin). Shifted sine-bell apodization
and zero-filling (1024 _ 380 real points) were applied prior to
Fourier transformation, and subsequent baseline corrections were
applied in one or both dimensions.
1
(ꢀ 72 400), 562 (11 000), 589 (22 400) nm. H NMR (300 MHz,
CDCl3): δ 9.15 (d, 2H, J ) 4.35 Hz, â-pyrr), 9.00 (d, 2H, J ) 4.7
Hz, â-pyrr), 8.77 (dd, 4H, â-pyrr), 8.27 (d, J ) 8.2 Hz, 4H, phenyl),
8.17 (d, J ) 8.2 Hz, 2H, phenyl), 7.85 (d, 4H, J ) 8.2 Hz, phenyl),
7.81 (d, 2H, J ) 8.2 Hz, phenyl),1.62 (s, 18H, 5,15-p-tBu), 1.58
(s, 9H, 10-p-tBu). LRMS (FAB): m/z 800 (M+).
3 - N i t r o - 5 , 1 0 , 1 5 - t r i p h e n y l c o r r o l a t o s i l v e r ( I I I )
[(NO2TPCor)Ag]. TPCorH3 (53 mg, 0.1 mmol) was dissolved in
CH3CN (10 mL), and AgNO2 (1.54 g, 10 mmol) was added. The
mixture was stirred at room temperature and the progress of the
reaction was monitored by UV-vis spectroscopy. The reaction was
complete in about 30 min. The reaction mixture was filtered through
a Celite plug, the solvent was removed on a rotary evaporator, and
the residue was chromatographed on silica gel. The column was
eluted with CH2Cl2/hexane (3:1) to afford two main fractions: the
first, red-violet in color, was crystallized from CH2Cl2/MeOH to
give (TPCor)Ag as red crystals (5 mg, 8% yield) and had
spectroscopic and analytical data in good agreement with those
reported in the literature.14 The second brilliant green fraction, after
evaporation, was crystallized from CH2Cl2/MeOH to give crystals
of (NO2TPCor)Ag (20 mg, 30% yield). Found: C, 65.6; H, 3.3;
N, 10.2. Anal. Calcd for C37H22AgN5O2: C, 65.7; H, 3.3; N, 10.4.
UV-vis: λmax (CHCl3): 433 (ꢀ 50 700), 448 (sh, 48 900), 591
1
(28 800), 611 (26 400) nm. H NMR (400 MHz, CDCl3): δ 9.51
Synthesis. TPCorH3, TTCorH3, and TF5PCorH3 were prepared
as previously reported.13 AMCorH3 was prepared by cyclization
of the corresponding a,c-biladiene following literature methods.6
(s, 1H, â-pyrr), 8.95 (s, 1H, â-pyrr), 8.75 (s, 1H, â-pyrr), 8.66 (s,
1H, â-pyrr), 8.57 (s, 1H, â-pyrr), 8.52 (s, 2H, â-pyrr), 8.24 (m,
2H, phenyl), 8.13 (m, 4H, phenyl), 7.77 (m, 9H, phenyl). LRMS
(FAB): m/z 676 (M+).
5,10,15-Tris(4-tert-butylphenyl)corrole
(TtBuPCorH3).
TtBuPCorH3 was prepared following a literature method6 (yield
3-Nitro-5,10,15-tris[(4-methylphenyl)corrolato]silver(III)
[(NO2TTCor)Ag]. TTCorH3 (74 mg, 0.13 mmol) was reacted as
above to give 5 mg (0.007 mmol, 6% yield) of (TTCor)Ag14 and
43 mg (46% yield) of (NO2TTCor)Ag as green crystals. Found:
15%). Found: C, 84.6; H, 7.3; N, 7.9. Anal. Calcd for C49H50N4:
(11) Lin, X. Q.; Kadish, K. M. Anal. Chem. 1985, 57, 1498-501.
(12) Sheldrick, G. M. SHELXL97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(13) Paolesse, R.; Froiio, A.; Nardis, S.; Mastroianni, M.; Russo, M.; Nurco,
D. J.; Smith, K. M. J. Porphyrins Phthalocyanines 2003, 7, 585.
(14) Bru¨ckner, C.; Barta, A. C.; Brin˜as, R. P.; Krause Bauer, J. A. Inorg.
Chem. 2003, 42, 1673-1680.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10793

Stefanelli et al.
C, 66.6; H, 3.8; N, 9.9. Anal. Calcd for C40H28AgN5O2: C, 66.9;
NaNO2 (390 mg, 5.7 mmol); the chromatographic separation was
carried out on a silica gel column, using CH2Cl2/hexane 3:1 as
eluent. (NO2TtBuPCor)Cu (15 mg, 33% yield) was isolated as the
second fraction, and a trace of the dinitrated complex was isolated
as the third fraction. Found: C, 73.6; H, 6.1; N, 8.9. Anal. Calcd
for C49H47CuN5O2: C, 73.4; H, 5.9; N, 8.7. UV-vis: λmax
(CHCl3): 370 (ꢀ 28 400), 435 (62 000), 573 (11 700), 672 (6900)
H, 3.9; N, 9.7. UV-vis: λmax (CHCl3): 433 (ꢀ 52 700), 452 (sh,
1
48 200), 594 (28 800), 616 (sh, 28 000) nm. H NMR (400 MHz,
CDCl3): δ 9.36 (s, 1H, â-pyrr), 8.77 (d, 1H, J ) 4.36 Hz, â-pyrr),
8.67 (d, 1H, J ) 4.72 Hz, â-pyrr), 8.61 (d, 1H, J ) 4.96 Hz, â-pyrr),
8.45 (m, 3H, â-pyrr), 8.10 (d, 2H, J ) 7.8 Hz, phenyl), 8.00 (d,
2H, J ) 7.8 Hz, phenyl), 7.96 (d, 2H, J ) 7.8 Hz, phenyl), 7.64
(d, 2H, J ) 7.8 Hz, phenyl), 7.59 (d, 2H, J ) 7.8 Hz, phenyl),
7.55 (d, 2H, J ) 7.8 Hz, phenyl), 2.69 (s, 3H, p-CH3), 2.66 (s, 3H,
p-CH3), 2.62 (s, 3H, p-CH3). LRMS (FAB): m/z 718 (M+).
3-Nitro-5,10,15-tris[(4-tert-butylphenyl)corrolato]silver(III)
[(NO2TtBuPCor)Ag]. TtBuPCorH3 (180 mg, 0.26 mmol) was
reacted as above to give 16 mg (0.020 mmol, 8% yield) of
(TtBuPCor)Ag and 92 mg (42% yield) of (NO2TtBuPCor)Ag as
green crystals. Found: C, 69.6; H, 5.3; N, 8.0. Anal. Calcd for
C49H46AgN5O2: C, 69.7; H, 5.5; N, 8.3. UV-vis: λmax (CHCl3):
431 (ꢀ 46 500), 455 (sh, 41 800), 591 (sh, 23 900), 613 (24 500)
nm. 1H NMR (300 MHz, CDCl3): δ 9.44 (s, 1H, â-pyrr), 8.86 (d,
1H, J ) 4.3 Hz, â-pyrr), 8.74 (d, 1H, J ) 4.7 Hz, â-pyrr), 8.63 (d,
1H, J ) 4.9 Hz, â -pyrr), 8.54 (d, 1H, J ) 4.3 Hz), 8.51 (m, 2H,
â -pyrr), 8.18 (d, 2H, J ) 8.2 Hz, phenyl), 8.09 (d, 2H, J ) 8.2
Hz, phenyl), 8.03 (d, 2H, J ) 8.2 Hz, phenyl), 7.84 (d, J ) 8.2
Hz, 2H, phenyl) 7.79 (d, J ) 8.2 Hz, 2H, phenyl), 7.75 (d, J ) 8.2
Hz, 2H, phenyl), 1.61 (s, 9H, p-tBu), 1.60 (s, 9H, p-tBu), 1.58 (s,
9H, p-tBu). LRMS (FAB): m/z 845 (M+).
1
nm. H NMR (300 MHz, CDCl3): δ 8.34 (s, 1H, â-pyrr), 7.78 (s
,1H, J ) 4.9 Hz, â-pyrr), 7.35-7.70 (m, 17H, â-pyrr and phenyl),
1.46 (s, 9H, p-tBu), 1.44 (s, 9H, p-tBu), 1.43 (s, 9H, p-tBu). LRMS
(FAB): m/z 801 (M+).
(5,10,15-Trinitro-2,3,17,18-tetraethyl-8,12-diacetoxymethyl-
7,13-dimethylcorrolato)silver(III) [(NO2)3AMCor]Ag. AMCorH3
(52 mg, 0.1 mmol) was dissolved in CH3CN (10 mL), and
AgNO2 (1.54 mg, 10 mmol) was added. The mixture was stirred
at room temperature, and the progress of the reaction was moni-
tored by UV-vis spectroscopy. The reaction was complete in
about 10 min. The reaction mixture was filtered through a plug of
Celite, the solvent was removed using a rotary evaporator, and the
residue was purified by chromatography on neutral alumina
(Brockman grade III, CH2Cl2 eluant). The first brilliant orange
fraction was collected and crystallized with MeOH, affording
[(NO2)3AMCor]Ag as red crystals (40 mg, 49% yield). Found: C,
50.9; H, 4.3; N, 11.9. Anal. Calcd for C35H36AgN7O10: C, 51.1;
H, 4.4; N, 11.9. UV-vis: λmax (CH2Cl2): 421 (ꢀ 78 400), 533
1
(15 800), 564 (24 600) nm. H NMR (400 MHz, CDCl3): δ 4.59
5,10,15-Tris[(4-tert-butylphenyl)corrolato]copper(III)
(TtBuPCor)Cu. TtBuPCorH3 (100 mg, 0.14 mmol) was dissolved
in CHCl3 (100 mL), and then a solution of copper(II) acetate (60
mg, 0.33 mmol) in MeOH was added. The mixture was heated to
reflux for about 2 h, and the progress of the reaction was monitored
by UV-vis spectroscopy. Upon completion, the solvent was
concentrated and 87 mg (80% yield) of dark brown crystals of
(TtBuPCor)Cu were obtained. Found: C, 77.9; H, 6.5; N, 7.3. Anal.
Calcd for C49H47CuN4: C, 77.9; H, 6.3; N, 7.4. UV-vis: λmax
(s, 4H, -CH2CO2CH3), 4.05 (q, 4H, -CH2CH3, J ) 7.5 Hz), 3.83
(s, 6H, -CH2CO2CH3), 3.66 (q, 4H, -CH2CH3, J ) 7.5 Hz), 3.23
(s, 6H, CH3), 1,81 (t, 6H, -CH2CH3, J ) 7.5 Hz), 1.67 (t, 6H,
-CH2CH3, J ) 7.5 Hz). LRMS (FAB): m/z 823 (M+).
Results and Discussion
A wide range of different nitrating systems has been
successfully used for the preparation of â-nitro derivatives
of tetra-arylporphyrins.10 This is not the case for corroles
since special attention must be paid to the maintenance of
the integrity of the macrocycle under the same reaction
conditions. For this reason, we did not utilize harsh nitrating
systems, such as HNO3/H2SO4, considering the high sensitiv-
ity of the corrole macrocycle toward oxidation. Taking into
account the good results obtained in the case of porphyrins,15
we first tried using N2O4 for the nitration of TPCorH3 (which
was chosen as a reference system). However, no reaction
was observed, and the starting material remained unchanged.
We then investigated Cu(NO3)2 in acetic anhydride as the
nitrating system; in this case, a Cu corrole complex was
obtained in very low yield but there was also extensive
decomposition of the starting material. The 1H NMR
spectrum of the isolated product indicated a â-monosubsti-
tuted derivative, but because of the low yield, we did not
attempt further characterization of this compound. Reaction
with BF4NO2 was also investigated, but these conditions led
to complete decomposition of the starting material.
1
(CHCl3): 421 (ꢀ 47 700), 539 (8300), 627 (4800) nm. H NMR
(300 MHz, CDCl3): δ 7.92 (s, 2H, â-pyrr), 7.75 (m, 6H, â -pyrr
and phenyl), 7.67 (s, 2H, phenyl) 7.50 (m, 6H â-pyrr and phenyl),
7.43 (m, 2H -pyrr and phenyl), 7.35 (m, 2H â -pyrr and phenyl),
1.56 (s, 18H, 5,10-p-tBu), 1.44 (s, 9H, 15-p-tBu). LRMS (FAB):
m/z 755 (M+).
3-Nitro-5,10,15-tris[(4-methylphenyl)corrolato]copper(III)
[(NO2TTPCor)Cu]. (TTPCor)Cu (110 mg, 0,17 mmol) was
dissolved in dimethylformamide (DMF) (30 mL), and NaNO2
(1.2 g, 17 mmol) was added. The mixture was stirred at 80 °C; the
progress of the reaction was followed by examining the optical
spectrum, in the Soret region, of aliquots of solution and after 90
min, the mixture was allowed to cool to room temperature and the
solvent was removed using a rotary evaporation. The residue was
taken up in CHCl3 and washed with H2O (3 × 50 mL portions),
reduced to a small volume, and purified by chromatography on a
silica gel column using CH2Cl2 as eluent, affording (NO2TTPCor)-
Cu (25 mg, 22% yield) as a reddish powder. Found: C, 71.1; H,
4.3; N, 10.2. Anal. Calcd for C40H28CuN5O2: C, 71.3; H, 4.2; N,
10.4. UV-vis: λmax (CHCl3): 372 (ꢀ 25 000), 435 (56 000), 577
(10 300), 672 (7100) nm. 1H NMR (300 MHz, CDCl3): δ 8.40 (s,
1H, â-pyrr), 7.87 (s, 1H, J ) 4.1 Hz, â-pyrr), 7.63 (m, 7H, â-pyrr
and phenyl), 7.47 (d, 1H, J ) 4.7 Hz, â-pyrr), 7.42 (s, 2H, â-pyrr),
7.34 (s, 1H, â-pyrr), 7.32 (m, 4H, â-pyrr and phenyl), 2.48 (s, 3H,
p-CH3), 2.44 (s, 3H, p-CH3), 2.39 (s, 3H, p-CH3). LRMS (FAB):
m/z 674 (M+).
Our attention therefore turned to different nitrating sys-
tems, and more satisfying results were obtained when
TPCorH3 was reacted with AgNO2/I2. In this case, some
decomposition of the starting material was still observed,
but two reaction products were isolated in moderate yields
3-Nitro-5,10,15-tris[(4-tert-butylphenyl)corrolato]cop-
per(III) [(NO2TtBuPCor)Cu]. The reaction was carried out as
above, starting from (TtBuPCor)Cu (43 mg, 0.057 mmol) and
(15) Jaquinod, L.; Gros, C.; Olmstead, M. M.; Antolovich, M.; Smith, K.
M. Chem. Commun. 1996, 1475.
10794 Inorganic Chemistry, Vol. 46, No. 25, 2007

Functionalization of Corroles
Figure 1. ROESY NMR experiment on (NO2TTCor)Ag.
Table 1. Influence of the Corrole Structure on the Reaction Productsa
we obtained good yields of the corresponding mononitro
derivatives (NO2TTCor)Ag and (NO2TtBuPCor)Ag, with
traces of the nonsubstituted complexes (TTCor)Ag and
(TtBuPCor)Ag; with T(3,5-F2)PCorH3 and TF5PCorH3, we
observed mostly decomposition of the corrole ring.
substrate
TPCorH3
reaction products
(TPCor)Ag + (NO2TPCor)Ag + open chain
(TTCor)Ag + (NO2TTCor)Ag
(TtBuPCor)Ag + (NO2TtBuPCor)Ag
traces of Ag complex + open chain
open chain
TTCorH3
TtBuPCorH3
T(3,5-F2)PCorH3
TF5PCorH3
It is interesting to note at this point that I2 is not necessary
for the success of nitration. When the reaction was carried
out on corrole TtBuPCorH3, we observed that I2 in-
creased the rate of the reaction, which was complete in about
5 min, but without I2 the reaction gave the same products in
25 min. Furthermore, in the latter case, better yields of
(NO2TtBuPCor)Ag were observed, with no significant
decomposition of the starting corrole. This intriguing result
led us to further investigate the influence of specific reagents
in the reaction. The silver complex (TtBuPCor)Ag was
reacted with NaNO2 under the same conditions, to check
whether the presence of the silver(I) ion is necessary for the
success of the reaction, but no reaction was observed, at
either room temperature or under reflux in DMF, while the
desired product was immediately formed when AgNO2 was
added to the reaction mixture. The same result was obtained
when I2 was added to solution instead of AgNO2.
a Reaction conditions: AgNO2/I2 in CH3CN, RT, 5-20 min under N2.
after chromatographic separation. The first red band, obtained
in the smallest amount, was the corresponding complex
(TPCor)Ag, as indicated by spectroscopic characterization
and comparison with an authentic specimen of the compound
prepared according to literature methods.14 The second green
band was characterized as the complex (NO2TPCor)Ag
where coordination of the silver ion was accompanied
by concomitant â-nitration of the corrole ring. This reaction
seems to be regioselective, because only one product was
formed; attempts to obtain single crystals of this compound
were unsuccessful. The p-CH3 derivative (NO2TTCor)Ag
is more soluble and was obtained in better yields than
(TPCor)Ag, and we therefore carried out a ROESY ex-
periment on the structurally similar corrole complex
(NO2TTCor)Ag to establish the site of the substitution. The
spectrum obtained for (NO2TTCor)Ag was shown in Figure
1 and is consistent with substitution having occurred at
position 3 of the macrocycle.
The above results support the proposed reaction pathway
-
shown in Scheme 1 where the nitrating agent is the NO2
ion which attacks the π-cation radical of the Ag(III) corrole
that is formed by reaction with excess Ag+ ion. At this point,
a second one-electron oxidation takes place at the macrocycle
and the loss of a proton restores the corrole aromaticity. The
role of the silver(I) ion in macrocycle oxidation has earlier
been reported for the nitration of â-octaalkylporphyrins at
the meso position using AgNO2.16
This result is also in agreement with previous examples
reported in the literature where the â-pyrrole position 3 is
usually observed to be the most reactive site on the meso-
triarylcorroles.7
With this promising result, we investigated the generality
of the reaction, studying the influence of the corrole struc-
ture on the reaction products; these results are reported
in Table 1. Nitration of the macrocycle is clearly favored
by the presence of electron-releasing groups on the three
phenyl rings. In the case of both TTCorH3 and TtBuPCorH3,
A potential alternative to this pathway would be the
possible oxidation of nitrite ion, instead of the corrole and a
subsequent attack of the resulting NO2 to give the substituted
(16) Smith, K. M.; Barnett, G. H.; Evans, B.; Martynenko, Z. J. Am. Chem.
Soc. 1979, 101, 5953-5961.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10795

Stefanelli et al.
Scheme 1. Reaction Pathway to 3-Nitro Corroles
corrole, as proposed by Gross and co-workers for a reaction
involving the Ga complex of TF5PCorH3.9 However, this
hypothesis was ruled out in the present case for two rea-
sons. The first is that the corrole is stable in the presence of
N2O4, and the second reason is when the reaction is carried
out under the same conditions but in the presence of urea
(known to be a •NO2 radical trap17), the same product
(NO2TtBuPCor)Ag was isolated in good yield.
The presence of π-cation radical species is quite common
in the coordination chemistry of corroles due to their easy
oxidation and the reported “noninnocence” of the corrole
macrocyclic ligand for many metal derivatives.18 One of the
first reports of these radicals was by Vogel and co-workers
for copper corroles;19 in this case, a temperature-dependent
equilibrium, as shown in eq 1, was characterized for such
species. This finding was later confirmed for corroles with
triaryl substitution,20 and although doubts have occasionally
been raised about the correct assignment of the Cu(III)
oxidation state, the presence of a radical species for the
neutral corrole was recently confirmed.21 The presence of a
radical species has also been invoked for intermediates in
the spontaneous formation of dimeric corroles in solution.22
temperature.19 This reaction was successful, and the mono-
substituted product (NO2TTCor)Cu was obtained along with
the starting complex (TTCor)Cu and traces of a disubstituted
species.
This result supports the presence of a corrole π-cation
radical as the reactive species in the nitration as well as
providing a convenient and facile route for the nitration
reaction of corroles. It is worth mentioning that to the best
of our knowledge, this is the first nonspectroscopic evidence
for the π-radical cation nature of such a complex.
To further examine the scope of the reaction, we examined
nitration of the â-alkylcorroles, a reaction that had not before
been reported. We first reacted AMCorH3 with AgNO2 in
CH3CN and after 10 min observed complete disappearance
of the starting corrole; TLC showed the formation of a
single reaction product, and spectroscopic characterization
indicated complete substitution at the meso position to give
[(NO2)3AMCor]Ag. The structural identity was confirmed
by single-crystal X-ray crystallography (Figure 2).
The Ag atom has square-planar coordination, with Ag-N
distances in the range of 1.9478(15)-1.9752(15) Å, those
to the directly linked pyrroles shorter than the other two by
0.025 Å. Likewise, the N1-Ag-N4 bite angle in the five-
membered chelate ring is 79.95(7)°, while those in the six-
membered chelate rings are in the range of 92.10(7)-
95.62(6)°. The corrole ring deviates slightly from planarity,
with a small saddle distortion. Opposite peripheral C atoms
C2, C3, C12, and C13 lie out of the best plane of the 23
corrole atoms by an average of 0.253 Å, while the other four,
C7, C8, C17, and C18, lie out-of-plane by an average of
-0.238 Å. The Ag atom is nearly in the plane, with a
deviation of -0.0195(2) Å.
(OEC)CuIII / (OEC‚+)CuII
(1)
The earlier finding that a π-radical cation species is an
intermediate in the nitration reaction suggests the possibility
that the reaction might be carried out, in this case, without
the addition of an oxidant; were this to be true, it would
further support the proposed reaction pathway. We therefore
reacted the copper complex (TTCor)Cu with NaNO2 in
CH3CN, heating the mixture to 80 °C, to shift the equilibrium
in eq 1 toward the π-cation radical species at higher
Electrochemistry in CH2Cl2. Two representative Ag(III)
corroles, (TtBuPCor)Ag and (NO2TtBuPCor)Ag, were elec-
trochemically investigated to determine the ease of oxidation/
reduction, the stability of electrogenerated products, and the
effect of nitration on the redox reactions. (TtBuPCor)Ag
undergoes two oxidations, and a single well-defined reduction
in CH2Cl2 containing 0.1 M TBAP, as seen in Figure 3a.
All three reactions involve reversible one-electron transfers
located at E1/2 ) 0.72, 1.20, and -0.87 V vs SCE.23
(17) Shine, H. J.; Padilla, A. G.; Wu, S. J. Org. Chem. 1979, 44, 4069.
(18) Ghosh, A.; Wondimagegn, T.; Parusel, A. B. J. J. Am. Chem. Soc.
2000, 122, 5100.
(19) Vogel, E.; Will, S.; Tilling, A. S.; Neumann, L.; Lex, J.; Bill, E.;
Trautwein, A. X.; Wieghardt, K. Angew. Chem., Int. Ed. Engl. 1994,
33, 731-735.
(20) (a) Wasbotten, I. H.; Wondimagegn, T.; Ghosh, A. J. Am. Chem. Soc.
2002, 124, 8104. (b) Bru¨ckner, C.; Brin˜as, R. P.; Krause Bauer, J. A.
Inorg. Chem. 2003, 42, 4495-4497. (c) Guilard, R.; Gros, C. P.; Barbe,
J.-M.; Espinosa, E.; Je´roˆme, F.; Tabard, A. Inorg. Chem. 2004, 43,
7441-7455. (d) Luobeznova, I.; Simkhovich, L.; Goldberg, I.; Gross,
Z. Eur. J. Inorg. Chem. 2004, 1724-1732.
(21) Bro¨ring, M.; Bre´gier, F.; Consul Tejero, E.; Hell, C.; Holthausen, M.
C. Angew. Chem., Int. Ed. 2007, 46, 445.
(22) Luobeznova, I.; Simkhovich, L.; Goldberg, I.; Gross, Z. Eur. J. Inorg.
Chem. 2004, 8, 1724.
(23) Experiments were also carried out in pyridine, but a quite different
electrochemical behavior was observed due to demetalation and
formation of the free-base corrole in the more basic solvent.
10796 Inorganic Chemistry, Vol. 46, No. 25, 2007

Functionalization of Corroles
Figure 2. X-ray molecular structure of [(NO2)3AMCor]Ag with 50% ellipsoids.
corresponding porphyrins, so they have almost identical
Soret band maxima. For example, the corroles (TPCor)Ag,
(TtBuPCor)Ag and (TTCor)Ag have a Soret band at 423-
424 nm, while the porphyrins (TPP)Ag and (TTP)Ag have
a Soret band at 422-423 nm.24 Porphyrins and related
macrocycles with silver(IV) are unknown, and the two
reversible oxidations of (TtBuPCor)AgIII can be reasonably
assigned as generating a Ag(III) corrole π-cation radical and
dication. The ∆E1/2 value of 480 mV between the two oxida-
tions is larger than that observed for most porphyrins25 but
smaller than what has been reported for other corroles that
are oxidized at the conjugated π-ring system, for example,
the metal derivatives of Cu(III),26 Sn(IV),27 and P(V).28
(NO2TtBuPCor)Ag also undergoes a reversible one-
electron reduction at -0.63 V and three oxidations at 0.93,
1.35, and 1.51 V as seen in Figure 3b. The second oxidation
of (NO2TtBuPCor)Ag is coupled to a chemical reaction
following electron abstraction, as shown by the dashed line
in the cyclic voltammogram. The product of the doubly
oxidized corrole may be an isocorrole, as indicated by the
reversible third oxidation at E1/2 ) 1.51 V and the new re-
reduction peak at Epc ) 0.36 V, but this was not investigated
in the current study.
Figure 3. Cyclic voltammograms of (TtBuPCor)AgIII and (NO2TtBuPCor)-
AgIII in CH2Cl2 containing 0.1 M TBAP at a scan rate of 0.1 V/s.
The electrochemical data in Figure 3a can be compared
to results obtained for (TPP)AgII under similar solution
conditions,24 where TPP ) the dianion of tetraphenylpor-
phyrin. The (TPP)AgII complex is reduced to its Ag(I) form
at -1.01 V vs SCE in CH2Cl2 and oxidized to [(TPP)AgIII]+
at 0.59 V. Both reactions of the porphyrin occur at more
negative potentials than those for the reduction and oxidation
of (TtBuPCor)AgIII, but the HOMO-LUMO gap of 1.60 V
for (TPP)AgII is identical within experimental error to the
1.59 V gap observed in the case of (TtBuPCor)AgIII. The
HOMO-LUMO gap is the same for silver corroles and the
The addition of an NO2 group to one of the â-pyrrole
positions of (TtBuPCor)Ag was expected to result in a
(25) Kadish, K. M.; Van Caemelbeck, E.; Royal, G. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: New York, 2000; Chapter 55, pp 1-114.
(26) Ou, Z.; Shao, J.; Zhao, H.; Ohkubo, K.; Wasbotten, I. H.; Fukuzumi,
S.; Ghosh, A.; Kadish, K. M. J. Porphyrins Phthalocyanines 2004, 8,
1236-1247.
(27) Kadish, K. M.; Will, S.; Adamian, V. A.; Walther, B.; Erben, C.; Ou,
Z.; Guo, N.; Vogel, E. Inorg. Chem. 1998, 37, 4573-4577.
(28) Kadish, K. M.; Ou, Z.; Adamian, V. A.; Guilard, R.; Gros, C. P.;
Erben, C.; Will, S.; Vogel, E. Inorg. Chem. 2000, 39, 5675-
5682.
(24) Kadish, K. M.; Lin, X. Q.; Ding, J. Q.; Wu, Y. T.; Araullo, C. Inorg.
Chem. 1986, 25, 3236-3242.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10797

Stefanelli et al.
Figure 5. UV-vis spectral changes of (NO2TtBuPCor)AgIII obtained
during (a) the first reduction at -0.85 V and (b) the first oxidation at
1.10 V in CH2Cl2, 0.1 M TBAP.
combined with the above-described results for the reduction
of the two corroles, provides strong indirect evidence for
the electron-transfer reactions given in eqs 2-4, and this
was confirmed by thin-layer UV-vis spectroelectrochem-
istry.
Figure 4. UV-vis spectral changes of (TtBuPCor)AgIII obtained during
controlled potential electrolysis at (a) -1.10 V, (b) 0.90 V, and (c) 1.40 V
in CH2Cl2, 0.1 M TBAP.
(Cor)AgIII + e / [(Cor)AgII]-
(Cor)AgIII / [(Cor)AgIII] + e
[(Cor)AgIII]+ / [(Cor)AgIII]2+ + e
(2)
(3)
(4)
positive shift of E1/2 for both the oxidation and reduction,
with the difference in potentials between the nitrated and
non-nitrated compounds depending upon the site of electron
transfer. A shift in E1/2 of 300-400 mV has often been
observed for ring-centered reductions of TPP complexes upon
nitration,29 but the shift in E1/2 is less for metal-centered
reductions, for example, the MIII/II reductions of porphyrins
with Au (260 mV)30 or Co (190 mV)31 metal centers. Thus,
the 240 mV difference in E1/2 between the reduction of
(TtBuPCor)Ag and (NO2TtBuPCor)Ag is quite consistent
with the expected AgIII/AgII reaction of the corrole.
The 210 mV separation in E1/2 between the first oxidation
of (TtBuPCor)Ag (0.72 V) and (NO2TtBuPCor)Ag (0.93 V)
is also consistent with what has been reported for porphy-
rin ring-centered oxidations, example being given for deriva-
tives with Cu, Zn, and Mg central metal ions.29 This fact,
Examples of the spectral changes which occur during
the reduction and oxidation of (TtBuPCor)Ag and
(NO2TtBuPCor)Ag are illustrated in Figures 4 and 5,
respectively. The initial (TtBuPCor)Ag complex in CH2Cl2
has a Soret band at 424 nm and two visible bands at 560
and 586 nm. Upon the first reduction at -1.10 V, the Soret
band shifts to 441 nm and an intense visible band grows in
at 636 nm (Figure 4a). There are no characteristic π-anion
radical bands in the spectrum of the singly reduced species,
and the spectral changes are consistent with the AgIII/AgII
process shown in eq 2. The spectra of the singly and doubly
oxidized corrole are also consistent with the stepwise
formation of a π-cation radical and dication, the former being
characterized by a decreased intensity Soret band and a broad
band between 700 and 850 nm. The spectrum of the neutral
corrole could be fully recovered when the potential was set
back to 0.0 V, thus indicating a reversibility of the processes
and a good stability of the singly and doubly oxidized forms
of the corrole in CH2Cl2.
(29) Binstead, R. A.; Crossley, M. J.; Hush, N. S. Inorg. Chem. 1991, 30,
1259-1264.
(30) Ou, Z.; Kadish, K. M.; E, W.; Shao, J.; Sintic, P. J.; Ohkubo, K.;
Fukuzumi, S.; Crossley, M. J. Inorg. Chem. 2004, 43, 2078-
2086.
(31) Kadish, K. M.; Ou, Z.; Tan, X.; Boschi, T.; Monti, D.; Fares, V.;
Tagliatesta, P. J. Chem. Soc., Dalton Trans. 1999, 10, 1590-
1602.
10798 Inorganic Chemistry, Vol. 46, No. 25, 2007

Functionalization of Corroles
Similar spectral changes were seen during the first
reduction and first oxidation of (NO2TtBuPCor)Ag in
CH2Cl2. The spectrum of neutral (NO2TtBuPCor)Ag differs
from that of neutral (TtBuPCor)Ag under the same experi-
mental conditions (Figure 5), but the spectra of the singly
reduced and singly oxidized forms of the corrole are
consistent with electrogeneration of [(NO2TtBuPCor)AgII]-
and [(NO2TtBuPCor)Ag]+, respectively, as shown in eqs 2
and 3.
This was proven by reaction of the copper corrole complexes
with NaNO2; in this case, the nitration reaction proceeded
without the addition of an oxidant, because of the π-cation
radical character of the copper complex.
This Article presents also the first study on electrochem-
istry and spectroelectrochemistry of silver corrole complexes,
and elucidates the site of electron transfer and the influence
of the nitro group. The nitro-substituted complexes represent
useful intermediates for the construction of more complex
molecular architectures based on corroles, a topic of ongoing
research in our laboratories.
Conclusions
We have reported a general method for the nitration of
corroles both at the â and meso positions of the macrocycle
by reaction of the free-base corrole with AgNO2. The reaction
proceeds with high selectivity for substitution on the meso-
triarylcorroles, and it is also successful in the case of
â-alkylcorroles. Although the reaction was carried out on
the free-base corrole, the reaction product was always the
corresponding substituted silver(III) complex. The results
obtained indicate that the reaction intermediate is the π-cation
radical of the complex, which is then attacked by nitrite ion.
Acknowledgment. This research was supported by the
Italian MUR (FIRB project RBNE01KZZM), the U.S.
National Science Foundation (K.M.S. Grant CHE-0296012),
and the Robert A. Welch Foundation (K.M.K. Grant E-680).
Supporting Information Available:
CIF file of
[(NO2)3AMCor]Ag. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC7014572
Inorganic Chemistry, Vol. 46, No. 25, 2007 10799