Copper β-trinitrocorrolates

Article abstract of DOI:10.1142/S1088424613500120

The β-nitration reaction carried out on the corrole macrocycle has been shown to be extremely regioselective, although the reduced symmetry of the macrocycle could potentially lead to a huge number of possible regioisomers. We recently reported that the careful use of AgNO₂/NaNO₂ as a nitrating system enabled the achievement in good yields of mono- and dinitro-derivatives on both corrole free base and its copper complex, proving to be an efficient and cost-effective method. In this work, we present a detailed study of the scope of this method using TtBuCorrH₃ as a model corrole. A further increase of the oxidant pushes the nitration up to the functionalization of three β-pyrrolic positions, although concomitant decomposition of the macrocycle is also observed. The application of the proven nitration method with a five-fold excess of both silver and sodium nitrites with respect to corrole, afforded the 2,3,17-(NO₂)₃- TtBuPCorrCu as the main product, in 25% yield, together with traces of another compound identified by X-ray crystallographic analysis as the 3,8,17-(NO ₂)₃-TtBuPCorrCu isomer. In light of these recent results, we also reinvestigated the characterization of the nitration products obtained from bis-substitution reactions, allowing among others the identification of the copper 3,8-(NO₂)₂ corrolate.

Full text of DOI:10.1142/S1088424613500120

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2013; 17: 1–7
DOI: 10.1142/S1088424613500120
Published at http://www.worldscinet.com/jpp/
Copper b-trinitrocorrolates
Manuela Stefanellia, Sara Nardisa, Frank R. Fronczekb, Kevin M. Smithb◊
and Roberto Paolesse*a◊
a Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, 00133 Roma, Italy
b Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
Dedicated to Professor Özer Bekaroğlu on the occasion of his 80th birthday
Received 30 November 2012
Accepted 4 February 2013
ABSTRACT: The b-nitration reaction carried out on the corrole macrocycle has been shown to be
extremely regioselective, although the reduced symmetry of the macrocycle could potentially lead to
a huge number of possible regioisomers. We recently reported that the careful use of AgNO2/NaNO2
as a nitrating system enabled the achievement in good yields of mono- and dinitro-derivatives on both
corrole free base and its copper complex, proving to be an efficient and cost-effective method. In this
work, we present a detailed study of the scope of this method using TtBuCorrH3 as a model corrole.
A further increase of the oxidant pushes the nitration up to the functionalization of three b-pyrrolic
positions, although concomitant decomposition of the macrocycle is also observed. The application of
the proven nitration method with a five-fold excess of both silver and sodium nitrites with respect to
corrole, afforded the 2,3,17-(NO2)3-TtBuPCorrCu as the main product, in 25% yield, together with traces
of another compound identified by X-ray crystallographic analysis as the 3,8,17-(NO2)3-TtBuPCorrCu
isomer. In light of these recent results, we also reinvestigated the characterization of the nitration
products obtained from bis-substitution reactions, allowing among others the identification of the copper
3,8-(NO2)2 corrolate.
KEYWORDS: corrole, b-functionalization, nitration, AgNO2.
action can alter some of the macrocycle properties.
INTRODUCTION
The derivatization of the b-positions of corroles with
The definition of corrole as “the little big porphyrinoid”
halogens [4] or boryl groups [5] can be exploited for the
[1a], summarizes in just a few words the peculiar
modification of the corrole moiety by Pd or Ir-catalyzed
properties of this macrocycle, for which the lack of
coupling reactions, while functionalization with
one meso carbon bridge compared with porphyrins, has
charged groups such as carboxylate [6], sulfonate [7] or
interesting repercussions on both coordination properties
pyridinium [8], can enhance the solubility of corroles
and chemical reactivity of the peripheral positions,
in aqueous media, allowing for their investigation in
which can be selectively transformed [1]. All these
biological environments.
feasible manipulations of the corrole skeleton allowed
In the last few years, our efforts have been focused
exploitation of this macrocycle in different applications
on the development of synthetic protocols for the
[2], such as for example the use of a Ga(III)-substituted
introduction of one or more -NO2 groups at the corrole
amphiphilic corrole in anticancer therapy [3].
b-pyrrolic positions [9], the main reason being related
The introduction of specific functionalities at the
with the impressive chemical versatility of this functional
corrole periphery is particularly appealing since this
group. Its transformation into the amino group, with
all the subsequent possible organic reactions, or its
direct involvement in activating aromatic nucleophilic
SPP full member in good standing
substitution at close pyrrolic carbon atoms, are some of
the potential uses of nitrocorroles that are under study
*Correspondence to: Roberto Paolesse, email: roberto.
paolesse@uniroma2.it, fax: +39 06-72594328
Copyright © 2013 World Scientific Publishing Company

2
M. STEFANELLI ET AL.
in our laboratories. For example, we recently reported
the synthesis of b-amino-b-nitrocorrole derivatives
through the nucleophilic attack of 4-amino-4H-1,2,4-
triazole on copper and germanium-b-(NO2) corrolates,
demonstrating the susceptibility of the corrole macrocycle
towards reactions with nucleophiles, regardless of its
high electron-density [9b]. Possessing strong p-acceptor
properties, the nitro group strongly interacts with the
corrole-p-system, altering the spectroscopic and redox
properties of the macrocycle, especially when the
-NO2 is located at the 2-position, where more efficient
conjugation is allowed for steric reasons [9c].
All these aspects prompted us to study the nitration
reaction in depth and, to date, we have provided several
synthetic methodologies, applying various nitrating
systems to achieve b-nitro-derivatives of Cu [9b], Ge
[10], Ag [9a], Fe [11] and Co [12] corrolates. Very
recently, we have reported the preparation of b-nitro-
5,10,15-tritolylcorroles [9c], which represents the first
example of selective b-nitration on the corrole free
base and potentially opens the way to novel complexes
of b-nitrocorroles upon metal insertion. The reaction
of TTCorrH3 with the AgNO2/NaNO2 system afforded
the mono- and di-nitrocorrole derivatives in satisfying
yields when the nature of the oxidant was carefully
chosen. Although the reaction was demonstrated to be
regioselective, giving the 3-NO2 and the 3,17-(NO2)2
isomers as the main reaction products, it was also possible
to identify traces of other regioisomers formed during the
reactions, namely the 2-NO2,2,3-(NO2)2 and 3,12-(NO2)2
compounds. The detection of the latter isomer was
particularly unexpected, because it represented the first
example of bis-functionalization occurring on antipodal
pyrroles A and C while leaving the C17 and C18 carbons
unsubstituted.
We have recently reported the possibility to achieve
tri- and tetra-nitro-derivatives of corroles, using TFA/
NaNO2 as the nitrating system [12]. In this case, the
extreme lability of corrole in acidic media caused both the
degradation of the starting material and the concomitant
formation of the nitroisocorrole species, which was
converted into the aromatic form by metalation with cobalt
salt and PPh3. Considering the moderate yields of such
polynitroderivatives and the presence of a coordinated
cobalt ion which cannot be easily removed from the
inner core, we decided to attempt polynitration of copper
corrolates by using the AgNO2/NaNO2 system, surmising
that a suitable increase of silver nitrite would push the
nitration beyond disubstitution. In particular we intended
to study both the scope of this nitrating system and,
eventually, highlight how pyrrolic sub-units react in the
case of polysubstitution by means of the isolated products.
We report here the nitration of TtBuPCorrCu
performed in DMF using a five molar excess of both
AgNO2 and NaNO2. The synthetic routes towards di- and
tri-nitrocorrole derivatives discussed in the present work
are reported in Scheme 1.
EXPERIMENTAL
General
Silica gel 60 (70–230 mesh, Sigma Aldrich) was used
for column chromatography. Reagents and solvents
(Aldrich, Merck or Fluka) were of the highest grade
1
available and were used without further purification. H
NMR spectra were recorded on a Bruker AV300 (300
MHz) spectrometer. Chemical shifts are given in ppm
relativetoresidualCHCl3 (7.25ppm).UV-visspectrawere
measured on a Cary 50 spectrophotometer. Mass spectra
(FAB mode) were recorded on a VGQuattro spectrometer
in the positive-ion mode using m-nitrobenzyl alcohol
(Aldrich) as a matrix.
X-ray crystallographic data
Crystals of 3,8,12-(NO2)3TtBuPCorrCu for X-ray
crystallographic analysis were grown from CDCl3/
MeOH solution as the chloroform solvate. Diffraction
data for 5 were collected from a very small needle at
low temperature on a Bruker Kappa APEX-II Duo
diffractometer with CuKa radiation (l = 1.54178 Å) and
an Oxford Cryosystems Cryostream chiller. Refinement
was by full-matrix least squares using SHELXL [13],
with H atoms in idealized positions, guided by difference
maps. The chloroform solvent was disordered, and its
electron density was removed using the SQUEEZE [14]
procedure. Crystallographic data: C49H44CuN7O6 . 1.02
CHCl3, monoclinic space group C2/c, a = 23.7684(15),
b = 27.1189(15), c = 19.3749(19) Å, b = 124.292(3)°, V
= 10,317.7(13) Å3, T = 90.0(5) K, Z = 8, rcalcd = 1.303 g
cm-3, μ(CuKa) = 2.49 mm-1. A total of 14,516 data was
collected to q = 55.6°. R = 0.090 for 2458 data with Fo2 >
2s(Fo2) of 6151 unique data and 568 refined parameters,
CCDC 912670.
Preparation of b-nitrocorrole derivatives
Bis-nitrationonTtBuPCorrH3.TtBuPCorrH3(100mg,
0.14 mmol) was dissolved in DMF (10 mL), and the
solution was heated at reflux. Then, NaNO2(79 mg,
1.15 mmol) and AgNO2 (44 mg, 0.28 mmol) were added
and the progress of the reaction was followed by TLC
analysis and UV-visible spectroscopy. The reaction was
complete in 30 min. The reaction mixture was cooled, the
product was precipitated by adding distilled water, and
then filtered. The crude product was taken-up in CH2Cl2
and purified on a silica gel column eluting with CH2Cl2.
After the collection of some brownish compounds eluted
as a first fraction, the two dinitroisomers corresponding
to the 2,3-(NO2)2TtBuPCorrH3 (1) (2 mg, 1.8% yield)
and the 3,12-(NO2)2TtBuPCorrH3 (2) (2 mg, 1.8% yield)
were isolated as green fractions. The last fraction was
collected and crystallized from CH2Cl2/n-hexane giving
the 3,17-(NO2)2TtBuPCorrH3 (3) as a brilliant green
powder (21 mg, 19% yield).
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 2–7

COPPER b-TRINITROCORROLATES
3
tBu
tBu
tBu
O2N
O2N
O2N
O2N
O2N
O2N
N
N
N
NH
NH
NH
NH
NH
i)
+
tBu
tBu
tBu
tBu
tBu
tBu
+
tBu
NH
NH
NH
NH
NO2
tBu
(1)
(2)
(3)
O2N
tBu
tBu
tBu
tBu
tBu
iii)
N
NH
NH
tBu
NH
O2N
N
N
N
N
ii)
N
N
+
Cu
tBu
Cu
N
N
NO2
(4)
O2N
tBu
tBu
tBu
tBu
O2N
O2N
N
N
N
N
N
N
N
N
iv)
+
Cu
Cu
NO2
(5)
(6)
O2N
O2N
tBu
tBu
Scheme 1. Preparation of nitrocorrole derivatives reported in this work. (i) corrole/AgNO2/NaNO2 (1:2:8), DMF, D, 30 min; (ii)
Cu(OAc)2, then Cu-corrole/AgNO2/NaNO2 (1:2:8), DMF, D, 20 min [9b]; (iii) Cu(OAc)2, CHCl3-MeOH, D, 30 min; (iv) Cu(OAc)2,
then Cu-corrole/AgNO2/NaNO2 (1:5:5), DMF, D, 20 min
3,17-(NO2)2-TtBuPCorrH3 (3). mp > 300 °C. UV-vis
(CHCl3): lmax, nm (log e) 434 (4.51), 484 (4.62), 710
yield. The spectroscopic characterization of the product
was fully in agreement with data recently reported in the
literature [9b].
1
(4.50). H NMR (300 MHz, CDCl3): d, ppm 8.81 (s,
2H, b-pyrrole), 8.47 (d, 2H, J = 4.8 Hz, b-pyrrole), 8.19
(d, 2H, J = 4.7 Hz, b-pyrrole), 7.96 (m, 6H, phenyls),
7.74 (m, 6H, phenyls), 1.58 (s, 9H, p-tBu), 1.54 (s, 18H,
p-tBu). Anal. calcd. for C49H48N6O4: C, 75.0; H, 6.2; N,
10.7%. Found: C, 75.1; H, 6.1; N, 10.6%. MS (FAB): m/z
845 [M]+.
Synthesis of 3,12-(NO2)2-TtBuPCorrCu. Compound
(2) was dissolved in CHCl3 and a few drops of a saturated
solution of Cu(OAc)2 in methanol was added. The
solution was refluxing for 30 min, then the solvent was
evaporated. The crude residue was applied to a silica plug
eluting with CH2Cl2 to afford the copper complex as an
orange fraction. Crystallization from CH2Cl2/CH3OH
afforded the title compound (4) in an almost quantitative
3,12-(NO2)2TtBuPCorrCu (4). mp > 300 °C UV-vis
(CHCl3): lmax, nm (log e) 466 (4.37), 652 (4.37). 1H NMR
(300 MHz, CDCl3): d, ppm 8.36 (s, 1H, b-pyrrole), 7.83
(s, 1H, b-pyrrole) 7.68 (m, 8H, b-pyrroles + phenyls),
7.55 (d, 2H, J = 8.2 Hz, phenyls), 7.44 (m, 6H, phenyls),
1.47 (s, 9H, p-tBu), 1.45 (s, 9H, p-tBu), 1.42 (s, 9H,
p-tBu). Anal. calcd. for C49H45CuN6O4: C, 69.6;H, 5.4;
N, 9.9%. Found C, 69.7; H, 5.2; N, 9.7%. MS (FAB): m/z
845 [M]+.
Synthesis of copper(III) b-trinitrocorrolates. To
a refluxing solution of TtBuPCorrH3 (80 mg, 0.11
mmol) in DMF (10 mL) was added Cu(OAc)2 (23 mg,
0.11 mmol). Completion of the metalation process was
monitored by both UV-vis spectroscopy and thin layer
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 3–7

4
M. STEFANELLI ET AL.
chromatography (TLC) analysis. When the copper
complex was quantitatively formed, NaNO2 (40 mg, 0.58
mmol) and AgNO2 (80 mg, 0.58 mmol) were added and
the progress of the reaction was again followed by TLC
analysis and UV-vis spectroscopy. After 20 min TLC
analysis showed major decomposition of the starting
complex together with the formation of a green band. The
reaction product was then precipitated by adding distilled
water, filtered and washed extensively with water. The
crude material was taken-up in CHCl3 and dried over
anhydrous Na2SO4. Chromatographic purification of the
reaction crude was performed on a silica gel column,
eluting with CHCl3. A first orange fraction was isolated
and corresponded to the trinitroisomer 3,8,17-(NO2)3-
TtBuPCorrCu (5) (2 mg, 2%). After collection of traces
of 3,17-(NO2)2-TtBuPCorrCu, the main green band was
isolated and crystallized from CH2Cl2/MeOH giving the
2,3,17-(NO2)3-TtBuPCorrCu (6) as a dark green powder
(24 mg, 25% yield).
3,8,17-(NO2)3-TtBuPCorrCu (5). mp > 300 °C.
UV-vis (CHCl3): lmax, nm (log e) 470 (4.35), 582 (4.14),
704 (4.09). 1H NMR (300 MHz, CDCl3): d, ppm 8.35
(s, 1H, b-pyrrole), 8.23 (s, 1H, b-pyrrole), 7.94 (s, 1H,
b-pyrrole), 7.68 (m, 7H, b-pyrroles + phenyls), 7.48 (m,
7H, b-pyrroles + phenyls), 1.45 (s, 18H, p-tBu), 1.42 (s,
9H, p-tBu). Anal. calcd. for C49H44CuN7O6: C, 66.09; H,
4.98; N, 11.01%. Found: C, 66.18; H, 5.10; N, 11.14%.
MS (FAB): m/z 889 [M]+.
the 3,17-(NO2)2 derivative for bis-nitration [9, 10, 17].
This selectivity has been also observed in the case of
tri-nitration of the gallium complex of F5TPC, which
afforded the 2,3,17-(NO2)3 regioisomer as a single
reaction product [17]. Relying on the effectiveness of the
AgNO2/NaNO2 nitrating system shown in our previous
work [9b, 9c], we decided to test the generality of this
system, investigating the extent to which the nitration
on copper corrole could be performed. Undoubtedly
polysubstitution by such a system requires increased
potential of the oxidant, necessary for the formation
of the p-radical cation forms of the nitro-compounds
produced as the reaction goes along, which become
more resistant to oxidation as the number of NO2 groups
increases. For such a purpose, we performed nitration
on TtBuPCorrH3 similarly to the synthetic protocol
recently reported in literature [9b], using both the silver
and sodium nitrites in a five-molar excess with respect
to the Cu-complex formed in situ. The reaction progress
was monitored by UV-vis spectroscopy, which showed
after 20 min a compound having a broadened Soret band
centered at ca. 450 nm, along with two satellite bands
at about 590 and 720 nm. Chromatographic purification
on silica gel using CHCl3 as eluant firstly afforded traces
of an orange fraction, featuring an intense Soret band
at 470 nm and two absorptions of lower intensity in the
Q-band region at 582 and 704 nm. Even with the small
amount of product obtained, we were able to completely
characterize it by standard spectroscopic methods.
2,3,17-(NO2)3-TtBuPCorrCu (6). mp > 300 °C.
UV-vis (CHCl3): lmax, nm (log e) 454 (4.91), 592 (4.51),
729 (4.14). 1H NMR (300 MHz, CDCl3): d, ppm 8.90 (s,
1H, b-pyrrole), 7.62 (m, 7H, b-pyrroles + phenyls), 7.51
(m, 7H, b-pyrroles + phenyls), 1.46 (s, 18H, p-tBu), 1.44
(s, 9H, p-tBu), 7.43 (br s, 2H, b-pyrroles). Anal. calcd.
for C49H44CuN7O6: C, 66.09; H, 4.98; N, 11.01%. Found:
C, 66.12; H, 5.08; N, 11.10%. MS (FAB): m/z 889 [M]+.
1
The H NMR spectrum revealed the presence of three
different b-pyrrolic protonic resonances at 8.35, 8.23 and
7.94 ppm, respectively, and the integral calculations were
consistent with a copper trinitro-derivative, as was further
confirmed by the molecular peak at m/z 889 provided
by FAB MS analysis. The definitive identification of
this compound was however accomplished by X-ray
crystallographic analysis carried out on crystals
obtained by slow diffusion of methanol into a CDCl3
solution (Fig. 1), which identified the original corrole
derivative 3,8,17-(NO2)3-TtBuPCorrCu 5 bearing three
nitro groups on three different pyrrolic sub-units. The
substitution on carbon C8 of the corrole macrocycle was
not unprecedented, since we have recently reported it in
the case of partial bromination of a Ge complex with a
large excess of Br2. In that case the reaction afforded the
hexabromo-derivative with two Br atoms on carbons C8
and C12, confirming these pyrrolic positions as the more
reactive compared with the C7 and C13 sites [18].
The Cu atom has square-planar coordination geometry
with a slight tetrahedral distortion, with N atoms
alternating above and below their best plane by deviations
in the range 0.141(6)–0.163(6) Å. The Cu atom lies
0.033(1) Å out of this plane and has Cu–N distances in
the range 1.886(6)–1.903(6) Å. The 23-atom corrole core
has a slight saddle conformation, with b carbon atoms
lying an average of 0.314 Å (range 0.147(10)–0.454(10)
Å) out of the corrole best plane. The nitro groups are
RESULTS AND DISCUSSION
The polynitration of metalloporphyrins has been
extensively studied and various nitrating systems for
pernitration of both meso- [15] and b-positions [16]
have been reported in the literature. In the latter case
for example, the rational use of a HNO3/CF3SO3H/
(CF3SO2)2O system generates in high yields a series of
b-polynitroporphyrins bearing from one to eight -NO2
groups, these compounds exhibiting a wide range of
redox potentials exploitable in catalysis. On the other
hand, the substituted products are obtained as a mixture
of isomers, evidencing a poor regioselectivity of the
peripheral functionalization.
In this context corroles have demonstrated their
originality, giving primarily a single isomer of a
b-substituted derivative in spite of their lower symmetry
compared with the porphyrin macrocycle. In the case
of nitration, the 3-NO2 isomer was always obtained in
different conditions for monosubstitution, as well as
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 4–7

COPPER b-TRINITROCORROLATES
5
After traces of copper 3,17-(NO2)2 corrole derivative,
the column chromatographic purification afforded the
main reaction product 6 as a dark green fraction, which
was obtained in 25% yield, and showed optical features
closely reminiscent of the 3,17-dinitroderivative.
Our attempts to pernitrate the copper corrole to the
b-tetranitro level using this oxidizing system were
unsuccessful, since the reaction afforded similar results,
even with an 8-fold excess of AgNO2 reagent. It is also
worth mentioning that the reaction is sensitive to the
nature of the solvent, since in pyridine only bis-nitration
is achieved using five-, eight- or fifty-fold [9b] excess of
the silver salt.
In light of these recent results, we have analysed all
the nitration products obtained both on copper corrolates
[9b] and corrole free base [9c] for mono-, bis- and tri-
substitution by using appropriate amounts of the AgNO2/
NaNO2 system. In both cases reactions demonstrated
to be highly selective, affording the 3-(NO2) and the
3,17-(NO2)2 derivatives as the main products for mono-
and bis-nitration, respectively. While traces of the
monosubstituted isomers 2-(NO2)TTCorrH3 and 2-(NO2)
TtBuPCorrCu were also detected, the dinitro-derivatives
were differently b-substituted. A small amount of a
copper dinitrocorrolate was isolated and tentatively
identified as the 2,17(NO2)2TtBuPCorrCu isomer, on
the basis of its proton NMR spectrum [9b] (Fig. 2). The
presence of two b-pyrrolic singlets at 8.36 and 7.83
ppm and three different tert-butyl proton resonances at
1.47, 1.45 and 1.42 ppm respectively was suggestive of
an asymmetric substitution, which was supposed to be
occurring on C2 and C17 in accordance with the different
reactivity always exhibited by pyrrole A and D subunits
in peripheral reactions. Thus, the identification of the
Fig. 1. Molecular structure of 5, with 50% ellipsoids
rotated out of the planes of their respective pyrroles by
similar amounts, their planes forming dihedral angles
with the corresponding pyrrole planes of 37.5(3)° at C3,
43.2(3)° at C8, and 45.8(3)° at C17.
Fig. 2. 1H NMR spectrum of 2,17-(NO2)2TtBuPCorrCu in CDCl3
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 5–7

6
M. STEFANELLI ET AL.
sites of substitution in such a compound was achieved as
a consequence of NMR data and of similar examples in
the literature.
It is worth discussing the electronic spectral features
of the prepared copper nitro-derivatives, which showed
to be clearly dependent upon which pyrrolic subunit is
subjected to substitution. In recent work reporting b-nitro-
tritolylcorroles, a combination of theoretical studies using
DFT and TDDFT methods with crystallographic data
revealed the influence of the inserted nitro groups upon
the structural, as well as opto-electronic properties of the
corrole macrocycle. In particular, these studies showed
that the conjugation of the NO2 group with the p-aromatic
system of corrole deeply affects some properties of the
nitro-derivative, the effect being more pronounced when
the insertion occurs at carbon C2 and the substituent is
coplanar with the corrole ring.
Considering all the prepared copper nitro-derivatives,
we notice that the UV-vis spectral features of the isomers
bearing the same number of nitro groups are remarkably
different (Fig. 3). In the case of mononitro-derivatives,
the 2-NO2 isomer displays a Soret band centered at
442 nm, red-shifted by ca. 7 nm with respect to the
3-substituted analog and the Q-bands region is almost
featureless; these variations can probably be ascribable
to a strong interaction of the nitro group on C2 with the
p-system as observed for the same 2-isomer of corrole
free base. The difference is more evident for the copper
dinitro-derivatives, wherein the B band of the copper
3,8-(NO2)2corrole is strongly red-shifted by about 17
nm compared to the 3,17-isomer. Moreover, their optical
spectra are completely different in shape, indicating
different electronic transitions occurring in these
compounds. The introduction of the third nitro group
upon the corrole periphery causes a further red-shift of the
Soret band, being located at ca. 454 and 470 nm for the
2,3,17- and 3,8,17- trinitro compounds, respectively. The
more significant differences involve corroles 4 and 5, and
they can probably be ascribable to the functionalization
on the pyrrolenine ring B.
The disubstituted isomers of corrole free base
were fully characterized as the corresponding Co
triphenylphosphine complexes by both traditional
spectroscopic techniques and X-ray crystallographic
analysis [9c]. In this case the substitution occurred on
the same pyrrolic unit, giving the 2,3(NO2)2corrole,
and quite surprisingly, on the opposite pyrroles A
and C, affording the 3,12-dinitroregioisomer. It is
worth mentioning that this compound represents the
first example in which disubstitution does not involve
the usual A and D pyrrolic rings. Tri-nitration gave
mainly the 2,3,17-(NO2)3 complex and traces of the
3,8,17(NO2)3-isomer, the latter showing again the
unusual reactivity of pyrrole subunit B toward the
nitrating system used.
All those considerations led us to revisit our
previous assertion of the 2,17-(NO2)2TtBuPCorrCu as
the minor product of bis-nitration on copper corrole,
and prompted us to find an alternative synthetic route
to this compound allowing for its precise identification.
For such a purpose, we performed nitration on
TtBuPCorrH3 using a corrole/AgNO2 molar ratio of
1:2, obtaining the 3,17-(NO2)2TtBuPCorrH3 (3) in
19% yield together with small amounts of the 2,3- and
3,12-(NO2)2 corroles 1 and 2, similarly to the reported
reaction on TTCorrH3. The last compound was then
metalated with Cu(OAc)2 and the complex 4 obtained
was subjected to spectroscopic characterization.
1
Analyses performed by both UV-vis and H NMR
spectroscopic methods afforded spectra completely in
agreement with those reported for the putative copper
2,17-(NO2)2 corrolate (Figs 2 and 3), indicating C3 and
C12 as the correct sites of subtitution instead of C2
and C17.
Fig. 3. (a) UV-visible spectra of 3,12-(NO2)2TtBuTPCorrCu (full line) and 3,17-(NO2)2TtBuTPCorrCu (dashed line). (b) UV-visible
spectra of 3,8,17-(NO2)3TtBuTPCorrCu (full line) and 2,3,17-(NO2)23TtBuTPCorrCu (dashed line)
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 6–7

COPPER b-TRINITROCORROLATES
7
Mandoj F, Paolesse R and Crociani B. Tetrahedron
Lett. 2004; 45: 5861–5864. c) Nardis S, Mandoj
F, Paolesse R, Fronczek FR, Smith KM, Prodi L,
Montalti M and Battistini G. Eur. J. Inorg. Chem.
2007; 2345–2352.
CONCLUSION
In this work we have demonstrated the feasibility of
the nitrating system, constituted by silver and sodium
nitrites, as a tool for the selective synthesis of copper
b-trinitrocorrole derivatives, one of which represents the
first example of a trisubstituted corrole functionalized on
three different pyrrolic units. The unexpected reactivity
of pyrrole B under these experimental conditions has
prompted us to reconsider our previous results obtained
for bis-nitration.
5. Hiroto S, Hisaki I, Shinokubo H and Osuka A.
Angew. Chem. Int. Ed. Engl. 2005; 44: 6763–6766.
6. a) Saltsman I, Goldberg I and Gross Z. Tetrahedron
Lett. 2003; 44: 5669–5673. b) Stefanelli M, Monti
D, Venanzi M and Paolesse R New J. Chem. 2007;
31: 1722–1725.
7. Mahammed A, Goldberg I and Gross Z. Org. Lett.
2001; 3: 3443–3446.
Acknowledgements
8. Saltsman I, Botoshansky
M and Gross Z.
This research was supported by MIUR Italy (PRIN
project 2009Z9ASCA) and the US National Institutes of
Health (K.M.S. grant CA132861).
Tetrahedron Lett. 2008; 49: 4163–4166.
9. a) Stefanelli M, Mastroianni M, Nardis S, Licoccia
S, Fronczek FR, Smith KM, Zhu W, Ou Z, Kadish
KM and Paolesse R. Inorg. Chem. 2007; 46: 10791–
10799. b) Stefanelli M, Mandoj F, Mastroianni M,
Nardis S, Mohite P, Fronczek FR, Ou Z, Kadish
KM, Xiao X, Ou Z and Paolesse R. Inorg. Chem.
2011; 50: 8281–8292. c) Stefanelli M, Pomarico G,
Tortora L, Nardis S, Fronczek FR, McCandless GT,
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Supporting information
1H NMR spectra of the prepared compounds
(Figs S1– S10) are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under
number CCDC-912670. Copies can be obtained on
request, free of charge, via www.ccdc.cam.ac.uk/data_
request/cif or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223-336-033 or email: deposit@ccdc.cam.ac.uk).
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