Amination reaction on copper and germanium β-nitrocorrolates

Article abstract of DOI:10.1021/ic2008073

Copper and germanium complexes of β-substituted nitrocorroles were reacted with 4-amino-4H-1,2,4-triazole to give the corresponding β-amino-β-nitro derivatives, in moderate to good yields. This is the first successful example of a vicarious nucleophilic substitution performed on corrole derivatives, because the same reaction carried out on silver complexes afforded the corresponding 6-azahemiporphycenes by way of corrole ring expansion. The first step of this work is related to the modification of a synthetic protocol for preparation of the β-substituted nitro corroles. The nitration reaction was carried out on a copper corrole using NaNO₂ as the primary source of NO₂^- coupled with AgNO ₂ used as oxidant. By variation of the molar ratio of the reagents it was possible to direct the product distribution toward mono- and dinitro derivatives. The reaction between mono- and dinitro derivatives of (TtBuCorrCu) with 4-amino-4H-1,2,4-triazole gave good results, leading to the isolation of 2-(NH₂)-3-(NO₂)-TtBuCorrCu and 2,18-(NH₂) ₂-3,17-(NO₂)₂-TtBuCorrCu in moderate yields. To elucidate factors that influence the reaction, and to highlight the different behavior observed for different metal complex substrates, the electrochemistry of three copper complexes, TtBuPCorrCu, (NO₂)TtBuPCorrCu, and (NO₂)₂TtBuPCorrCu, was studied by cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry. The nitro groups on (NO ₂)_xTtBuPCorrCu are highly electron-withdrawing, which leads not only to a substantial positive shift of all redox potentials but also to a unique redox behavior and UV-vis spectrum of the singly reduced product as compared to the parent compound, TtBuPCorrCu. Finally, the amination reaction was carried out on a Ge(IV) nitrocorrolate, giving in good yield the 2-amino-3-nitroderivative, which was structurally characterized by single crystal X-ray crystallography.

Full text of DOI:10.1021/ic2008073

ARTICLE
pubs.acs.org/IC
Amination Reaction on Copper and Germanium β-Nitrocorrolates
Manuela Stefanelli,† Federica Mandoj,† Marco Mastroianni,† Sara Nardis,† Pruthviray Mohite,†
Frank R. Fronczek,‡ Kevin M. Smith,*,‡ Karl M. Kadish,*,§ Xiao Xiao,§ Zhongping Ou,§ Ping Chen,§
and Roberto Paolesse*,†
†Dipartimento di Scienze e Tecnologie Chimiche, Universitꢀa di Roma Tor Vergata, via della Ricerca Scientifica, 1, 00133 Rome, Italy
‡Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
§Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States
S Supporting Information
b
ABSTRACT: Copper and germanium complexes of β-substi-
tuted nitrocorroles were reacted with 4-amino-4H-1,2,4-triazole
to give the corresponding β-amino-β-nitro derivatives, in
moderate to good yields. This is the first successful example
of a vicarious nucleophilic substitution performed on corrole
derivatives, because the same reaction carried out on silver
complexes afforded the corresponding 6-azahemiporphycenes
by way of corrole ring expansion. The first step of this work is
related to the modification of a synthetic protocol for prepara-
tion of the β-substituted nitro corroles. The nitration reaction
was carried out on a copper corrole using NaNO2 as the primary source of NO2ꢀ coupled with AgNO2 used as oxidant. By variation
of the molar ratio of the reagents it was possible to direct the product distribution toward mono- and dinitro derivatives. The reaction
between mono- and dinitro derivatives of (TtBuCorrCu) with 4-amino-4H-1,2,4-triazole gave good results, leading to the isolation
of 2-(NH2)-3-(NO2)-TtBuCorrCu and 2,18-(NH2)2-3,17-(NO2)2-TtBuCorrCu in moderate yields. To elucidate factors that
influence the reaction, and to highlight the different behavior observed for different metal complex substrates, the electrochemistry
of three copper complexes, TtBuPCorrCu, (NO2)TtBuPCorrCu, and (NO2)2TtBuPCorrCu, was studied by cyclic voltammetry
and thin-layer UVꢀvisible spectroelectrochemistry. The nitro groups on (NO2)xTtBuPCorrCu are highly electron-withdrawing,
which leads not only to a substantial positive shift of all redox potentials but also to a unique redox behavior and UVꢀvis spectrum of
the singly reduced product as compared to the parent compound, TtBuPCorrCu. Finally, the amination reaction was carried out on a
Ge(IV) nitrocorrolate, giving in good yield the 2-amino-3-nitroderivative, which was structurally characterized by single crystal
X-ray crystallography.
’ INTRODUCTION
In this latter case the reaction with a variety of nucleophiles3 such
as alkoxides, cyanide, hydride, or active methylene compounds
yields 2-substituted, 2-nitro-3-substituted porphyrins, or stable
chlorins as products, depending on the experimental conditions
and the nature of the nucleophile. Furthermore, starting from
2-nitroporphyrins, it is possible to introduce useful functional-
ities on the porphyrin β-pyrrolic positions, namely, pyrrole4 and
di- or tetraone respectively,5 allowing for the construction of
elaborated β-fused oligoporphyrin architectures in which the
extended aromatic system could potentially be exploited in
molecular electronics.
In the case of corroles, peripheral functionalizations of the
macrocycle have been far less explored compared to the dramatic
development observed for synthesis of the macrocycle itself. The
quite original chemistry shown by the corroles has led to the first
seminal exploitations of corroles in different fields,6 and for this
reason the modulation of corrole properties by synthetic
The development of new and efficient routes for functionali-
zation of the porphyrinoid skeleton represents a mandatory task
for researchers interested in both investigating the macrocycle
reactivity and exploring potential uses of these compounds in a
variety of practical applications, from molecular materials and
catalysts to sensors and medical uses. Among the known pyrrolic
macrocycles, porphyrins have been the most intensively studied,
and different examples of macrocycle “decoration by introduc-
tion of peripheral groups” have been reported in the literature.1
As expected for an aromatic ring, the porphyrin β-pyrrolic
positions can undergo attack by both electrophilic and nucleo-
philic agents, although reactions with electrophiles are more
common. It is important to note that the macrocyclic reactivity
can be finely tuned by the presence of other substituents and/or
by the nature of the inner core coordinated metal ion. From this
point of view one of the most useful peripheral substituents is the
nitro group, and the electron withdrawing character of such a
substituent has been used to direct the orientation of further
functionalizations2 or to facilitate aromatic nucleophilic substitution.
Received: April 19, 2011
Published: July 28, 2011
r
2011 American Chemical Society
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Scheme 1. Conversion of σ-Adducts: (a) the Oxidative
Nucleophilic Substitution (ONSH) and (b) the Vicarious
Nucleophilic Substitution (VNS) Pathways
and dinitro derivatives in good yields. The Cu(III) β-dinitro-
corrolate was prepared for the first time and the influence of the
nitro group on corrole redox behavior is investigated in nonaqu-
eous solvents. The synthesized β-nitrocorrole copper complexes
were reacted with 4-amino-4H-1,2,4-triazole to obtain the corre-
sponding difunctionalized β-amino-β-nitrocorrole derivatives.
The reaction was also carried out in the case of a Ge(IV)
complex, so as to study the influence of the coordinated metal
ion and its oxidation state on the nucleophilic aromatic substitu-
tion reaction.
Structures of the novel corroles presented in this work are
illustrated in Chart 1.
’ EXPERIMENTAL SECTION
Reagents and solvents (Sigma-Aldrich, Fluka, and Carlo Erba Re-
agenti) for synthesis and purification were of synthetic grade and used as
received. AgNO2 reagent (Sigma-Aldrich) should be of high purity grade
(99.98%) and freshly used. Chromatography was performed on silica gel
1
60 (70ꢀ230 mesh) and neutral alumina (Brockmann grade III). H
NMR spectra were recorded on a Bruker AV300 (300 MHz) spectro-
meter. Chemical shifts are given in parts per million (ppm) relative to
tetramethylsilane (TMS). UVꢀvis spectra were measured on a Cary 50
spectrophotometer. Mass spectra were recorded on a VG Quattro
spectrometer in the positive-ion mode, using m-nitrobenzyl alcohol
(NBA, Aldrich) as a matrix (FAB), or on a Voyager DE STR Biospec-
trometry workstation in the positive mode, using R-cyano-4-hydroxy-
cinnamic acid as a matrix (MALDI). Electron spin resonance (ESR)
spectra were obtained on an IBM model ESP 300 apparatus. Low
temperature measurements were carried out using a liquid-nitrogen
finger dewar.
Diffraction data were collected at T = 90K on a Bruker Kappa Apex-II
diffractometer equipped with graphite-monochromated CuKR radiation
(λ = 1.54178 Å) and an Oxford Cryostream low temperature device.
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 mea-
surements and consisted of a glassy carbon working electrode, a
platinum counter electrode, and a homemade saturated calomel refer-
ence electrode (SCE). The SCE was separated from the bulk of the
solution by a fritted glass bridge of low porosity that contained the
solvent/supporting electrolyte mixture.
manipulations has become an attractive task for many research-
ers. However, only a few examples of corrole functionalizations
have so far been reported in the literature,7 in part because of the
inherent lower stability of corroles compared with porphyrins.
This problem of decreased compound stability is evident in
the case of β-nitrocorroles, where efficient routes for preparation
of the free-base macrocycles has been limited by the facile
oxidation of the macrocycle which occurs under the utilized
reaction conditions. For this reason, the preparation of β-nitro-
corroles has been limited to the synthesis of metal derivatives,8,9
using a variety of reaction conditions and nitrating agents.
We have been particularly interested in elucidating new
synthetic routes to β-nitrocorroles, with the aim of both inves-
tigating the macrocycle reactivity and using these derivatives as a
starting point for the preparation of covalently linked corrole
units. Since the preparation of disubstituted corroles is the first
necessary step toward new chromophores as well as highly
conjugated fused oligomeric systems, we have investigated the
role of the β-nitro group in activating nucleophilic substitution
on the vicinal positions of the corrole ring. The role of the nitro
group in the nucleophilic aromatic substitution has been detailed
in the literature;10 in each reaction, formation of the nitronate
σ-adduct is followed by an elimination step that necessarily
involves release of a hydride anion that is not a spontaneous
event. The Hꢀ departure requires additional factors to favor its
removal from the negative adduct after which conversion into the
product of nucleophilic substitution can occur. The σH-adduct
can be transformed according to different pathways depending
on the substrates and the reaction conditions, as described by an
exhaustive review on the nucleophilic substitution of hydrogen in
heterocyclic chemistry.11 The fate of the σH-complex is strictly
related to two distinctive outcomes; one is the susceptibility
toward oxidation of the adduct (the so-called ONSH path) and
the other the presence on the reacting nucleophile of a leaving
groupX assisting the base-inducedelimination ofHꢀ asHX. Inthe
latter case, the reaction is called vicarious nucleophilic substitution
of hydrogen (VNS) thanks to the supporting action of the
nucleophile (Scheme 1).
Thin-layer UVꢀvisible spectroelectrochemical experiments were
performed with a home-built thin-layer cell, which has a light transparent
platinum net working electrode. Potentials were applied and monitored
with an EG&G PAR Model 173 potentiostat. Time-resolved UVꢀ
visible 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.
Synthesis. TtBuPCorrH3 and 3NO2-TPCorrGe(OCH3) were pre-
pared as previously described.8a,b
3,17-(NO2)2-TtBuPCorrCu. Method A: CorrCu/AgNO21:50. TtBuP-
CorrH3 (100 mg, 0.14 mmol) was dissolved in pyridine (15 mL), and
Cu(OAc)2 (29 mg, 0.14 mmol) was added. The mixture was stirred at
reflux, and the progress of the reaction was monitored by UVꢀvis
spectroscopy. When the metal insertion was complete AgNO2 (1.1 g, 7.1
mmol) was added. After 20 min the starting material was all consumed,
as indicated by this UVꢀvis spectrum and thin layer chromatography
(TLC) analysis, and a more polar green band was observed as the major
product. The reaction mixture was precipitated by adding distilled water
(20 mL), then filtered and washed extensively with water. The crude
residue was taken up in CHCl3 and filtered again through Na2SO4. The
solvent was evaporated under vacuum, the residue was dissolved in
In present paper, we first describe an improved route for the
nitration of copper meso-triarylcorroles, which affords mono-
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Chart 1. Molecular Structures of the Synthetized Corroles
CH2Cl2 and purified by chromatography on a silica gel column using
CH2Cl2 as eluent. Traces of 3-(NO2)-TtBuPCorrCu were isolated as a
first brownish band, and successively traces of 2,17-(NO2)2-TtBuP-
CorrCu were also collected as orange rust fractions. The third dark green
fraction was eluted with CHCl3 and corresponded to 3,17-(NO2)2-
TtBuPCorrCu. Crystallization from CH2Cl2/MeOH, gave 62 mg (52%
yield) as a dark green powder. Anal. Calcd for C49H45CuN6O4: C, 69.6;
H, 5.4; N, 9.9%. Found C, 69.9; H, 5.2; N, 9.8%. λmax(CHCl3)(log ε) nm
370 (4.58), 449 (4.89), 594 (4.46), 699 (4.18). 1HNMR δH(CDCl3, J
[Hz]): 8.29 (s, 2H, β-pyrrole), 7.67 (m, 6H, β-pyrrole+phenyls), 7.48
(m, 10H, phenyls), 1.45 (s, 9H, p-tBu), 1.44 (s, 18H, p-tBu). MS
(MALDI): m/z 845 (M+).
2,17-(NO2)2TtBuPCorrCu. Anal. Calcd for C49H45CuN6O4: C, 69.6;
H, 5.4; N, 9.9%. Found C, 69.7; H, 5.2; N, 9.7%. λmax(CHCl3)(log ε) nm
466 (4.37), 652 (4.37). 1HNMR δH(CDCl3, J [Hz]): 8.36 (s, C18 1H,
β-pyrrole), 7.83 (s, C3 1H, β-pyrrole) 7.68 (m, 8H, β-pyrrole+phenyl),
7.55 (d, 2H, J = 8.2 Hz, phenyl), 7.44 (m, 6H, phenyl), 1.47 (s, 9H, p-
tBu), 1.45 (s, 9H, p-tBu), 1.42 (s, 9H, p-tBu). MS (MALDI): m/z 845
(M+).
Method B: CorrCu/AgNO2/NaNO2 1:2:8. TtBuPCorrH3 (100 mg,
0.14 mmol) was dissolved in dimethylformamide (DMF) or pyridine
(15 mL), and Cu(OAc)2 (29 mg, 0.14 mmol) was added. The mixture
was stirred at reflux, and the progress of the reaction was monitored by
UVꢀvis spectroscopy. When the metal insertion was complete AgNO2
(45 mg, 0.29 mmol) and NaNO2 (83 mg, 1.2 mmol) were added. After
20 min the starting material was all consumed as indicated by UVꢀvis
spectroscopy and TLC analysis that showed a more polar green band as
the major product. The product was precipitated by adding distilled
water (30 mL), then filtered and washed extensively with water. The
crude residue was taken up in CHCl3 and filtered again through Na2SO4.
The solvent was evaporated under vacuum, and the residue dissolved in
CH2Cl2 and purified by chromatography on a silica gel column using
CH2Cl2 as eluent. Traces of the 3-mononitro derivative and the 2,17-
dinitrocorrole regioisomer were also detected as the first and the second
fraction, respectively. The third dark green fraction corresponding to
3,17-(NO2)2-TtBuPCorrCu was eluted with CHCl3, isolated and crys-
tallized from CH2Cl2/MeOH, to give 60 mg (51% yield) as a dark green
powder.
of lower grade reagent, or one having a clearly gray solid color, the molar
proportions of the TtBuCorrCu, AgNO2 and NaNO2 reagents reported
in Method B must be changed to 1:5:5, respectively, to achieve
comparable results.
3-(NO2)TtBuPCorrCu. TtBuPCorrH3 (100 mg, 0.14 mmol) was
dissolved in DMF or pyridine (15 mL), and Cu(OAc)2 (29 mg, 0.14
mmol) was added. The mixture was stirred at reflux, and the progress of
the reaction was monitored by UVꢀvis spectroscopy. When the metal
insertion was complete, AgNO2 (22 mg, 0.14 mmol) and NaNO2 (89
mg, 1.3 mmol) were added, and the reaction mixture, following the
above-mentioned experimental procedure, afforded in 20 min the
copper mono- and dinitro compounds. In particular, purification on a
silica column eluting with a CH2Cl2/hexane (7:3) solvent mixture
afforded the first brownish fraction corresponding to 3-(NO2)-
TtBuPCorrCu (86 mg) and second green fraction of 3,17-(NO2)2-
TtBuPCorrCu (18 mg) in 75 and 15% yields, respectively. Spectroscopic
data for the copper 3-nitrocorrolate were in full agreement with those
previously reported in the literature8a
Note: The scale-up of the reaction, typically starting from 300 mg of
TtBuPCorrH3, afforded as a first fraction a small amount of the
2-(NO2)TtBuPCorrCu regioisomer, just enough for complete spectro-
scopic characterization:
2-(NO2)TtBuPCorrCu. Anal. Calcd for C49H46CuN5O2: C, 73.5; H,
5.8; N, 8.7. % Found: C, 73.6; H, 6.0; N, 8.7. UVꢀvis: λmax(CHCl3)(log ε)
nm: 370 (4.40), 442 (4.82), 636 (3.96). 1HNMR δH(CDCl3, J [Hz]):
7.91 (s, 1H, β-pyrrole), 7.80 (d, 1H, J = 4.1 Hz, β-pyrrole), 7.73 (m, 6H,
β-pyrrole+phenyl), 7.64 (d, 1H, J = 4.3 Hz, β-pyrrole), 7.58 (m, 7H,
β-pyrrole+ phenyl), 7.43 (d, 1H, J = 4.6 Hz, β-pyrrole), 7.38 (d, 2H, J =
8.2 Hz, phenyl), 1.49 (br s, 18H, p-tBu), 1.41 (br s, 9H, p-tBu). MS
(MALDI): m/z 801 (M+).
2-NH2-3NO2-TtBuPCorrCu. 3NO2-TtBuPCorrCu (253 mg, 0.32
mmol) was dissolved in 132 mL of toluene/ethanol (120:12) solvent
mixture and then NaOH (63 mg, 1.58 mmol) and 4-amino-4H-1,2,4-
triazole (319 mg, 3.8 mmol) were added. The reaction mixture was
stirred at room temperature and monitored by TLC. The reaction was
complete after 45 min. The solvent was then removed under vacuum, the
residue dissolved in CHCl3, washed twice with the aqueous Na2S2O3,
and dried over Na2SO4. Thecrudemixturewaspurifiedbychromatography
on silica gel eluting with CHCl3. The first red-brown fraction was
collected and crystallized from CH2Cl2/MeOH, affording the title
Note: It is important to underline that high purity grade AgNO2
should be used; the color of the reagent should be pale yellow; in the case
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compound as a brown-reddish powder (47 mg, 18% yield). Anal. Calcd
for C49H47CuN6O2: C, 72.2; H, 5.8; N, 10.3%. Found C, 72.4; H, 3.9; N,
11.9%. UVꢀvis: λmax(CHCl3) (log ε) nm 440 (4.52), 579 (3.99)
1HNMR δH(CDCl3, J [Hz]): 7.56 (d, 2H, J = 7.6 Hz, phenyls), 7.42
(m, 12H, β-pyrrole+phenyls), 7.03 (m, 3H, β-pyrrole), 6.96 (d, 1H, J =
4.3 Hz, β-pyrrole), 6.04 (s, 2H, -NH2), 1.44 (s, 9H, p-tBu), 1.41 (s, 9H,
p-tBu),1.40 (s, 9H, p-tBu). MS (MALDI): m/z 815 (M+).
2,18-(NH2)2-3,17-(NO2)2-TtBuPCorrCu. 3,17-(NO2)2-TtBuPCorrCu
(160 mg, 0.19 mmol) was dissolved in 33 mL of a toluene/ethanol
(30:3) solvent mixture and then NaOH (38 mg, 0.95 mmol) and
4-amino-4H-1,2,4-triazole (191 mg, 2.27 mmol) were added. The
reaction mixture was stirred at room temperature and monitored by
TLC. All of the starting material was consumed in 20 min, as indicated by
TLC analysis, which showed a more polar olive green band together with
decomposition products. The solvent was then removed under vacuum,
the residue dissolved in CHCl3, washed twice with aqueous Na2S2O3,
and dried over Na2SO4. The crude mixture was purified by chromatog-
raphy on silica gel. Traces of the starting material were eluted with
CH2Cl2. Then the use of CHCl3 as eluent afforded a dark green fraction
which was collected and crystallized from CH2Cl2/MeOH, giving the
title compound as a greenish powder (50 mg, 30% yield). Anal. Calcd for
C49H47CuN8O4: C, 67.2; H, 5.3; N, 12.8%. Found C, 67.4; H, 5.4; N,
12.7%. UVꢀvis: λmax(CHCl3) (log ε) nm 366 (4.67), 465 (4.84), 604
(4.23).
the corresponding free-base corrole with AgNO2 as nitrating
agent.8a Although this approach leads to formation of the silver
corrole complex, the low stability of these compounds under
both acidic and basic conditions allowed us to define efficient
demetalation procedures,13 which opened the way to preparation
of otherwise unavailable novel 3-(NO2)metallocorrolates using
other nitration methods, the exception being the gallium9 and
germanium8b corrole complexes. In this case, reductive demeta-
lation in basic conditions (DBU/THF) was particularly useful to
obtain the corresponding free-base macrocycle, while acidic
conditions led to the formation of isocorrole species, in which
oxidation regioselectively occurred at the 5-position of the ring.
In light of such a finding, we were able to identify as a byproduct
of the nitration reaction8a a [3-(NO2)5-(OH)] isocorrole spe-
cies, which was previously supposed to be an open chain
compound. The formation of such a compound, both during
the reaction with AgNO2 and during chromatographic purifica-
tion on silica gel, represents the main drawback of the nitration
reaction, causing a substantial decrease in the yield of the silver
3-nitrocorrolate. This drawback could be addressed by subse-
quent reduction of the isocorrole to the corresponding corrole14
or by the direct application of the demetalation protocol to the
crude mixture of the nitration reaction, which reduced the
isocorrole formation. We therefore decided to follow an alter-
native route, which can use the same reaction protocol on corrole
metal complexes, with the aim to improve the reaction yields by
completely avoiding the isocorrole formation. Copper was the
metal ion of choice, since it has the double advantage of being
readily inserted and removed from the macrocyclic core,15 and its
corrole complexes are diamagnetic at room temperature, hence
easy to characterize.
1HNMR δH(CDCl3, J [Hz]): 7.41 (d, 2H, J = 8.0 Hz, phenyl), 7.29
(m, 6H, phenyl), 7.14 (d, 4H, J = 7.6 Hz, phenyl), 6.86 (d, 2H, J = 4.4 Hz,
β-pyrrole), 6.72 (d, 2H, J = 4.2 Hz, β-pyrrole), 5.66 (s, 4H, -NH2), 1.45
(s, 9H, p-tBu), 1.37 (s, 18H, p-tBu). MS (MALDI): m/z 876(M+).
2-NH2-3-NO2-TPCorrGe(OCH3). 3-NO2-TPCorrGe(OCH3) (40 mg,
0.06 mmol) and 4-amino-4H-1,2,4-triazole (50 mg, 0.6 mmol) were
dissolved in toluene/ethanol (20:1) (32 mL), and the solution was
stirred at room temperature until complete dissolution of all reagents.
The temperature was then raised to 80 °C, and NaOH (24 mg, 0,60
mmol) was added. After 1 h the reaction mixture was cooled, the solvent
removed, and the residue was taken up in CH2Cl2 and washed with H2O.
The organic phase was dried over anhydrous Na2SO4, concentrated, and
then purified using an alumina Brockmann grade IV column eluted with
CHCl3. The major green fraction, after adding few drops of MeOH, was
precipitated from CH2Cl2/hexane, affording the title compound as a
dark green powder (20 mg, yield 50%). Anal. Calcd for C38H26GeN6O3:
C, 66.4; H, 3.8; N, 12.2%. Found C, 66.5; H, 3.8; N, 12.0%. UVꢀvis:
λmax(CHCl3) (log ε) nm 384 (4.64), 448 (5.01), 624 (4.36). HNMR
δH(CDCl3, J [Hz]): 9.21 (d, 1H, J = 3.8, β-pyrrole), 9.10 (m, 2H, β-
pyrrole), 9.02 (d, 1H, J = 4.8, β-pyrrole), 8.83 (d, 2H, J = 3.8, β-pyrrole),
7.5ꢀ8.5 (br, m, 15H, phenyl), 7.22 (br. s, 2H, -NH2), ꢀ0.77 (s, 3H, -
OCH3). MS (FAB): m/z 687 (M+). Crystal data: C38H26GeN6O3,
monoclinic, space group P21/c, a = 10.6310(5), b = 18.9383(10), c =
15.0218(9) Å, β = 92.646(5)°, V = 3021.2(3) Å3, Z = 4, Dcalc = 1.511
g cmꢀ3, μ = 1.797 mmꢀ1, T = 90 K, 23268 reflections collected with θmax
< 68.9°, 5398 independent reflections (Rint = 0.033) which were used in
all the refinements, using SHELXL.12 An electron-density peak 1.1 Å
from the Ge position, slightly out of the corrole plane opposite Ge,
was interpreted as an alternate position for Ge, and was included in
the refinement with 2.0% occupancy. All H atoms were visible in
difference maps. Coordinates for NH2 hydrogen atoms were refined,
while all other H atoms were in idealized positions, with a torsional
parameter refined for the Me group. Final residuals (for 445 para-
meters) were R1 [I >2σ(I)] = 0.031, wR2 (all data) = 0.083, max. resid.
We have earlier reported the preparation of copper 3-nitro-
corrolates by reacting Cu triarylcorroles with a large excess of
NaNO2 in refluxing DMF or CH3CN.8a Evidence for the
π-radical cation nature of copper corrolates was obtained,
although the synthetic relevance of this route was lessened by
the low yields obtained. To reduce the reaction steps in
preparation of the corrole nitro derivatives, we decided to study
the feasibility of a one-pot reaction, starting from the free-base
corrole TtBuCorrH3 (Chart 2).
The corrole was first reacted with Cu(OAc)2 in refluxing
pyridine to obtain the metal complexes. When the metalation
was complete a 50-fold excess of AgNO2 was added and the
reaction progress was monitored by UVꢀvis spectroscopy. After
20 min, the color of the solution changed from brownish to dark
green, and the UVꢀvis spectrum showed a novel compound
having a Soret band which was red-shifted by about 25 nm
compared with the starting copper complex, along with two new
bands at about 591 and 690 nm. Chromatographic purification
afforded traces of the Cu 3-mononitrocorrole, followed by an
orange rust fraction having a peculiar UVꢀvis spectrum, char-
acterized by an intense Soret band at 465 nm and broadened
absorptions in the Q-band region. Although only traces of such a
1
product were isolated, we were able to identify it by H NMR
spectroscopic analysis. The proton spectrum revealed the pre-
sence of two proton singlets at 8.36 and 7.83 ppm and three
different tert-butyl proton signals of equal intensity at 1.47, 1.45,
and 1.42 ppm, respectively, indicating an asymmetric product
(Supporting Information, Figure S1). Furthermore, the integral
calculations are consistent with a disubstituted compound, and
the MALDI mass spectrum affording a molecular peak at m/z
845 led us to identify the compound as 2,17-(NO2)2TtBuCorr
density 0.40 e Åꢀ3
.
’ RESULTS AND DISCUSSION
Synthesis of (NO2)xTtBuPCorrCu. We recently reported the
preparation of [3-(NO2)triarylcorrolato]Ag(III) by reaction of
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Chart 2. Synthesis of (NO2)xTtBuPCorrCu
Cu. The main reaction product was isolated in 52% yield and fully
characterized as 3,17-(NO2)2TtBuCorrCu. The 3,17-substitu-
tion pattern observed is in fact identical with that recently
reported by us and others for the selective nitration of a Ge
triphenylcorrole8b and a gallium(III) 5,10,15-tris(pentafluorophenyl)-
corrole, respectively.9 Introduction of the second nitro group at
the C17 position restored the molecular symmetry, as reflected
by the proton resonance distribution in the 1H NMR spectrum:
the number of signals decreases and the tert-butyl protons return
to a 2:1 ratio, as found for the starting Cu complex. (Supporting
Information, Figure S2).
Although the above-mentioned conditions are convenient for
preparation of 3,17-(NO2)2-5,10,15-triarylcorrolato Cu complexes
in satisfactory yield starting from the corresponding corrole
free-base macrocycles, it should be noted that a large excess of
the quite expensive AgNO2 reagent was necessary. For this
reason we decided to decrease the amount of silver nitrite,
further surmising that formation of the mononitroderivative
would be favored; when we employed from 1.2- up to a 5-fold
molar excess of AgNO2 relative to the copper complex, we
generally obtained a mixture of three products; these were the
starting Cu complex, and the mono- and dinitro derivatives,
with relative yields of each depending on the molar excess of
AgNO2 used.
AgNO2 was used. However, it is worth mentioning that the yields
of the nitration reaction are remarkably affected by the purity
grade of the silver nitrite reagent utilized. We found that when
the color of the salt is quite gray, indicative of a less pure grade of
AgNO2, the TtBuCorrCu/AgNO2/NaNO2 molar ratio needed
to be scaled up to obtain similar results as described in the
Experimental Section.
The encouraging results led us to explore the possible forma-
tion of a mononitro product by modification of the AgNO2/
NaNO2 ratio. It was found that a Cu complex/silver nitrite/
sodium nitrite molar ratio of 1:1:9 was the best choice to obtain
3-(NO2)TtBuCorrCu as the main product, together with the
corresponding 3,17-dinitroderivative, in 75 and 15% yields,
respectively.
It is worth mentioning that the scale-up of the reaction under
these conditions led us to detect, during purification on chro-
matography columns, traces of a less polar compound having
similar UVꢀvis spectral features to that of the 3-nitro derivative,
(see Experimental Section); the identity of this compound was
1
established by mass spectrometry and H NMR spectroscopy.
The MALDI mass spectrum showed the new compound to
have a molecular peak at m/z 801, as found for 3-(NO2)-
TtBuCorrCu, and the proton NMR spectrum (Supporting
Information, Figure S3) was consistent with a monosubstituted
product. The presence of a singlet at 7.91 ppm allowed us to identify
this new compound as the isomer, 2-(NO2)TtBuCorrCu, in
which nitro substitution had occurred at position 2 of the
macrocycle.
Amination Reaction on (NO2)xTtBuPCorrCu. The establish-
ment of these synthetic procedures for preparation of nitrocor-
role copper derivatives allowed us to explore their possible
further functionalization. Among possible peripheral functiona-
lizations we were most interested in the amination reaction, with
the aim to use the resulting difunctionalized corroles as building
blocks for the preparation of oligomeric species, following an
approach reported by Crossley, who utilized 2-amino-3-nitropor-
phyrin derivatives as excellent starting compounds for the con-
struction of elaborated laterally bridged oligoporphyrin arrays.5
We had previously studied the amination of 3-(NO2)TtBu-
CorrAg using 4-amino-4H-1,2,4-triazole, an aminating reagent
introduced by Katritzky16 for introduction of an NH2 group onto
electron-deficient arenes, and recently used for the synthesis of
2-amino-3-nitroporphyrins.17 In this case the reaction failed, and
we observed the unexpected formation of 6-azahemiporphycene,
a novel porphyrin analogue, arising from macrocyclic ring
These results indicate that an excess of nitrite ion is necessary
for completion of the reaction, and for this reason we turned our
attention toward other nitrating systems that would combine the
oxidation properties of AgNO2, allowing also the required nitrite
excess.
The first system investigated utilized NaNO2 as the nitrite
source and I2 as oxidant, but the results were not satisfying since
only the complete decomposition of the macrocycle was ob-
served. Considering this failure we decided to use AgNO2 as
oxidant, mixing it in appropriate amounts with NaNO2, to ensure
the nitrite ion excess. The first attempt was carried out in
refluxing DMF or pyridine and made use of a TtBuCorrCu/
AgNO2/NaNO2 molar ratio of 1:2:8. After formation of the
copper complex, silver and sodium nitrite were added, and in
20 min formation of the copper 3,17-dinitroderivative was observed
by TLC analysis and UVꢀvisible spectroscopy. Chromato-
graphic purification afforded the same fractions as when using
the previous method, namely, traces of the 3-mononitro deriva-
tive and the 2,17-dinitro regioisomer along with a main green
fraction corresponding to the Cu 3,17-dinitrocorrole in 52%
yield. This latter value is similar to what was obtained when only
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expansion.18 In our studies we demonstrated that formation of
the 6-azahemiporphycene species is not dependent on the
presence of the nitro group because the same corrole ring-
expansion was observed when the reaction was carried out on
unsubstituted corroles. We discovered that the macrocycle
oxidation is a key step for the reaction, considering that 5- and
a 10-hydroxyisocorrole could be used as starting materials.19 In
this case, silver corroles are not useful as starting materials,
because they are readily demetalated under the basic conditions
necessary for the reaction. For this reason copper corroles seem
Chart 3. Amination Reaction of (NO2)xTtBuPCorrCu
Figure 1. 1H NMR spectrum of 2,18-(NH2)2-3,17-(NO2)2-TtBuPCorrCu.
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to be more promising for the reaction, providing that their
stability would allow the vicarious substitution to occur instead
of the azahemipophycene ring expansion.
2 and 18 β-pyrrole positions of the macrocycle results in a
deshielding of both the aromatic and the pyrrolic proton signals.
The effect is particularly pronounced for the β-hydrogens of the
B and C pyrroles that resonate at 6.86 and 6.72 ppm, uncom-
monly low values for such resonances.
It is worth mentioning that when 4-amino-4H-1,2,4-triazole
was reacted with an unsubstituted copper corrolate TtBuCorr-
Cu, the copper 6-azahemiporphycene was obtained as the
main product, and was identified by comparison with the same
compound prepared by metalation of [6-Aza-5,11,16-tris(4-tert-
butylphenyl)hemiporphycene] with Cu(OAc)2.19
To investigate in greater detail the different reactivity shown
by the unsubstituted copper complex with respect to the
corresponding 3-nitro- and 3,17-dinitro- derivatives, we decided
to study the electrochemistry of the species. This is described on
the following pages.
The amination on 3-(NO2)TtBuCorrCu was performed
using 4-amino-4H-1,2,4-triazole and NaOH as reagents, in
the molar ratio of 1:12:5 following the same protocol employed
for the preparation of 2-amino-3-nitroporphyrins (Chart 3).
When we carried out the reaction at reflux temperatures, rapid
decomposition of the starting complex was observed, as shown
by both TLC analysis and UVꢀvis spectroscopy. When all of
the reagents were stirred at room temperature, TLC analysis
showed after a few minutes the formation of a second band
having a lower Rf value with respect to the starting complex.
After 45 min the copper 3-nitrocorrolate was completely
consumed, and the crude reaction mixture was subjected to
purification on a chromatography column. A single brownish
1
fraction was isolated and analyzed by UVꢀvis and H NMR
spectroscopies. The UVꢀvis spectral features are quite similar
to those of the starting material, although a slight red-shift of the
Soret band is clearly visible.
Table 1. Half-Wave Potentials (V vs SCE) of
(NO2)xTtBuPCorrCu in CH2Cl2 or PhCN Containing 0.1 M
TBAP
The 1H NMR spectrum (Supporting Information, Figure S4)
showed a disappearance of the proton singlet of the β-pyrrolic
carbon 2 and an upfield shifting of some pyrrolic resonances
below about 7 ppm. Furthermore, the presence of a broad singlet
at 6.04 ppm can be ascribed to the amino group, the correspond-
ing proton signal of which is strongly deshielded by the presence
of the adjacent nitro group, as recently reported in the case of
2-amino-3-nitroporphyrins. The MALDI mass spectrum shows a
molecular peak at 815 m/z, enabling unambiguous identification
of the product as the desired 2-NH2-3-NO2-TtBuCorrCu.
The reaction was performed on 3,17-(NO2)2TtBuCorrCu
under the same experimental conditions, affording, after 20 min
the tetra-substituted 2,18-diamino-3,17-dinitrocorrole copper
oxidation
reduction
# of NO2
Solvent groups, x third second first
first
second
third
CH2Cl2
0
1
2
0
1
2
1.75a
1.31
1.50
1.61
1.39
1.58
1.65
0.71 ꢀ0.17
0.90
1.11
0.00 ꢀ1.34 ꢀ1.74a
0.20 ꢀ1.11 ꢀ1.44
PhCN
1.69a
1.86a
0.74 ꢀ0.18
0.92
0.04 ꢀ1.40
0.24 ꢀ1.12 ꢀ1.47
1.12
a Irreversible peak potential at a scan rate of 0.10 V/s.
1
complex, whose aromatic region of the H NMR spectrum is
presented in Figure 1. Introduction of the two NH2 groups at the
Figure 3. Correlation between (a) E1/2 for the first reduction of
(NO2)xTtBuPCorrCu in PhCN and (b) the Soret band maximum of
the neutral compounds.
Figure 2. Cyclic voltammograms of (NO2)xTtBuPCorrCu in CH2Cl2,
0.1 M TBAP.
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Electrochemistry. Since the seminal paper by Vogel, Kadish,
and collaborators on electrochemical and spectroscopic studies
of (OECorr)Cu,20 different triphenylcorroles (TPCorr) contain-
ing electron-donating or electron-withdrawing substituents on
the meso and/or β-pyrrole positions of the macrocycle have been
investigated in detail.20ꢀ29
While the early characterization of copper corrole complexes
proposed an equilibrium between the two forms reported in eq 1,
subsequent investigations now favor the formulation of the
complex as a copper(II) corrole π cation radical rather than as
a metal(III) corrole with an unoxidized π ring system. Such an
assignment has been discussed in the literature in light of the
noninnocent nature of the corrole macrocycle.20,27ꢀ32
solvent limit (∼+1.80 V in CH2Cl2 or PhCN) and one
additional ring centered reduction process under the same
solution condition.
In the absence of nitro substituents, TtBuPCorrCu undergoes
a reversible reduction process located at E1/2 = ꢀ0.17 V in
CH2Cl2 and ꢀ0.18 V in PhCN, both containing 0.1 M TBAP. A
similar redox behavior has been reported for copper triphenyl-
corrole, TPCorrCu and 17 related corroles29 containing elec-
tron-donating or electron-withdrawing substituents on the meso
and/or β-pyrrole positions of the macrocycle. The parent
triphenylcorrole is reduced at ꢀ0.16 V in CH2Cl2 while the
same process for the other corroles varied from E1/2 = ꢀ0.22 to
+0.64 V, depending upon the type and position of the electron-
withdrawing or electron-donating substituents.
As described below, this behavior differs from what is seen for
the currently investigated nitrocorroles in nonaqueous media.
Cyclic voltammograms of the three (NO2)xTtBuPCorrCu com-
plexes are illustrated in Figure 2 (CH2Cl2) and Supporting
Information, Figure S12 (PhCN), and a summary of half-wave
and peak potentials are given in Table 1. The nitro groups on
(NO2)xTtBuPCorrCu are highly electron-withdrawing, and this
leads to a substantial positive shift of all redox potentials as
compared to the parent compound, TtBuPCorrCu. Two one-
electron reductions, not observed for TtBuPCorrCu, are also
seen for the mono- and dinitrocorrole, and these are located
ðCorrÞCuIII h ðCorrþ:ÞCuII
ð1Þ
Previous electrochemical characterization of Cu corroles with
a variety of structures have shown up to six different redox
reactions to occur for these complexes, with the number of
processes and half-wave potentials being dependent upon the
solvent and specific electron-donating or electron-withdrawing
properties of the substituents. For example, TPCorrCu under-
goes three ring-centered oxidations in CH2Cl2, with only one
reduction process,29 while corroles with electron-withdrawing
substituents on the meso and/or β-pyrrole positions undergo
a maximum of two ring centered oxidations within the potential
Figure 4. (a) Cyclic voltammograms of (NO2)xTtBuPCorrCu in
PhCN, 0.1 M TBAP and (b) plots of half wave potential for the first
oxidation and first reduction of the corrole vs the Soret band maximum
of (NO2)xTtBuPCorrCu in wavenumbers. Values of λmax are given in
Table 2.
Figure 5. Spectra changes during first reduction of (NO2)xTtBuPCorrCu
in PhCN, 0.1 M TBAP.
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at E1/2 = ꢀ1.11 and ꢀ1.44 V versus SCE for the case of
(NO2)xTtBuPCorrCu in CH2Cl2.
Plots of E1/2 for first reduction and first oxidation versus the
reduced products of TFPCorrCu and Br8TPCorrCu exhibit only
one additional reduction at E1/2 = ꢀ1.70 and ꢀ1.48 V, respec-
tively, in CH2Cl2 as compared to two reversible one-electron
reductions for [(NO2)2TtBuPCorrCu]ꢀ which are located at
number of NO2 groups on the molecule are linear (ΔE1/2
/
ΔNO2 ≈ 200 mV) indicating a similar redox mechanism for all
three compounds. A linear correlation also exists between the
number of NO2 groups and λmax for the Soret band of the neutral
compound (Figure 3) or between E1/2 and the Soret band λmax
when plotted in wavenumbers (Figure 4).
E
1/2 =ꢀ1.11 and ꢀ1.44 V under the same solution conditions. Two
well-defined reductions are also seen for singly reduced (NO2)-
TtBuPCorrCu in CH2Cl2 (Figure 3) or PhCN (Supporting
Information, Figure S12) and this occurrence is unprecedented
in the literature of copper corroles. It is also markedly different
from what is seen in the case of TtBuPCorrCu, TFPCorrCu, and
all previously investigated corroles with electron-withdrawing
substituents, which exhibit UVꢀvisible spectra for the electro-
reduced product that are characteristic of a Cu(II) corrole with
an unreduced π ring system.29 UVꢀvisible spectra obtained in a
thin-layer cell during controlled potential reduction of the
currently investigated compounds in PhCN are shown in
Figure 5; UVꢀvisible spectra of the singly oxidized species were
also obtained in PhCN, and examples of thin-layer spectra are
given in Supporting Information, Figure S13. A summary of the
spectral data is given in Table 2.
The above linear correlations suggest the same initial electron
transfer site for reduction of all three compounds but, as earlier
indicated, the redox properties of the singly reduced product
are quite different in the case of (NO2)TtBuPCorrCu and
(NO2)2TtBuPCorrCu as compared to all previously investigated
triphenylcorroles with electron-withdrawing Br, F, or CF3 sub-
stituents. For example, TFPCorrCu and Br8TPCorrCu are
reduced at 0.21 and 0.19 V versus SCE in CH2Cl2,29 which are
potentials almost identical to those of (NO2)2TtBuPCorrCu,
where the first reduction occurs at 0.20 V (see Table 1). The
oxidation potentials of these three compounds are also similar,
being 1.12 V for TFPCorrCu, 1.16 V for Br8TPCorrCu, and 1.11
V for (NO2)2TtBuPCorrCu in CH2Cl2. In contrast, the singly
In summary, electrochemistry and thin-layer spectroelectro-
chemistry of the investigated (NO2)xTtBuPCorrCu derivatives
Table 2. Absorption Maximum (λmax, nm) and Molar Absorptivities (log ε in Parentheses) of [(Corr)Cu]n Where
Corr = (NO2)xTtBuPCorr and n = 0, ꢀ1, and +1
(Corr)
solvent
x
Cu
[(Corr)Cu]ꢀ1
[(Corr)Cu]+1
CH2Cl2
0
1
2
0
1
2
418 (5.08) 547 (4.02) 636 (3.74)
371 (4.73) 436 (5.05) 578 (4.33) 682 (4.03)
372 (4.59) 450 (4.88) 594 (4.45) 700 (4.34)
422 (4.96) 548 (3.84) 640 (3.52)
428 (5.08)
613 (4.22)
418 (4.97)
446 (4.82)
450 (4.82)
422 (4.65)
438 (4.46)
453 (4.29)
378 (4.78) 408 (4.81) 477 (4.74) 616 (4.58) 682 (4.39)
397 (4.62) 450 (4.78) 594 (4.40) 700 (4.41)
PhCN
435 (5.03)
614 (4.26)
377 (4.33) 438 (4.69) 575 (4.00) 686 (3.77)
377 (4.40) 408 (4.45) 480 (4.42) 618 (4.27) 686 (4.03)
377 (4.17) 453 (4.49) 596 (4.08) 703 (3.82) 327 (4.23) 356 (4.23) 399 (4.24) 508 (4.17) 636 (4.12) 703 (4.15)
Figure 6. (a) UVꢀvis spectra of (NO2)xTtBuPCorrCu before (black dashed lines) and after (red solid lines) reduction with 1000 eqs DBU in PhCN,
0.1 M TBAP and (b) ESR spectra of singly reduced (NO2)xTtBuPCorrCu in the same solution at 77 K.
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are self-consistent in indicating the same initial site of electron
transfer for all three compounds, although they show very
different UVꢀvisible changes. The peripheral nitro groups are
responsible for this different behavior, but the mechanism of their
influence should be clarified. While the initial product of the one
electron addition is assigned as (Corr)CuII for all three com-
pounds, some contrasting results make difficult to elucidate the
nature of the final electroreduced products in the case of
(NO2)TtBuPCorrCu and (NO2)2TtBuPCorrCu (see Figure 5).
For example it is interesting to note that the same UVꢀvisible
changes were obtained by addition of DBU to the (NO2)x-
TtBuPCorrCu solutions; this DBU influence is similar to what
observed in the case of silver corrole complexes, which are
reductively demetalated by addition of DBU.13 These UVꢀvis
spectra are also shown in Figure 6 and closely resemble spectra
reported for structurally similar Ge(IV) corroles after a one-
electron reduction,8b where only a corrole π-anion radical is
possible. However low temperature electron spin resonance
(ESR) characterization of singly reduced (NO2)xTtBuPCorrCu
shows clear signatures of a Cu(II) corrole (Figure 6) and does
not support this hypothesis; the above conflicting results in the
case of singly reduced (NO2)xTtBuPCorrCu may be related to
the effect of temperature, but we were unable to obtain room
temperature ESR measurements to resolve this point. Further-
more, the peculiar spectra for the singly reduced corroles with
nitro groups might be ascribed to a mesomeric rather than an
inductive electron-withdrawing effect of the β-pyrrole NO2
substituents, which would stabilize the anion by delocalization
of the negative charge via conjugation with the aromatic corrole
ring, thus resulting in the significant UVꢀvisible changes.33
In any event, the observed behavior is very specific to the
currently investigated nitrocorroles and does not seem to occur
for other related corroles having Br, F, or CF3 substituents on the
macrocycle. These highly electron-withdrawing groups will lead
Chart 4. Amination Reaction of 3-NO2-TPCorrGe(OCH3)
Figure 7. Molecular Structure of 2-NH2-3-NO2-TPCorrGe(OCH3).
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in some cases to more positive redox potentials than in the case of
(NO2)TtBuPCorrCu or (NO2)2TtBuPCorrCu, but despite the
more facile reduction, the currently investigated nitrocorroles
appear to be unique in their redox behavior and in the UVꢀvis
spectrum of the singly reduced product.
carried out on a corrole ring. To investigate in detail the influence
of the coordinated metal on the reaction pathway, an electro-
chemical characterization of the copper corrole nitro derivatives was
carried out. The highly electron-withdrawing character of the nitro
groups leads to a substantial positive shift of all redox potentials
of (NO2)xTtBuPCorrCu as compared to the parent compound,
TtBuPCorrCu, inducing also unique UVꢀvis spectra of the
singly reduced products. The scope of the reaction was tested
on the Ge(IV) corrole complex, which afforded higher yields of the
amino-derivative than with the copper analogue; the obtained
Ge(IV) product was characterized by X-ray crystallography. A
synthetic route to these bis-functionalized corroles, which are
promising building blocks for the development of more complex
molecular architectures based on corroles, has been defined.
Amination Reaction on 3-NO2-TPCorrGeOCH3. Finally, we
have also investigated the role of the corrole central metal ion on
the reaction with 4-amino-4H-1,2,4-triazole, with the intention
to increase the moderate yields obtained in the case of copper
derivatives (18 and 30% for the mono- and dinitro compounds,
respectively). According to the similar redox behavior, we
decided to carry out the same reaction on germanium(IV) 3-(NO2)-
triphenylcorrolate, which was recently prepared and characterized
in our laboratories.8b In this complex the Ge ion is in a high
oxidation state (+4), so it can inductively cooperate with the
electron-withdrawing character of the nitro groups for the amina-
tion reaction, without the strong electronic interaction with the
π-system of the corrole ring.
’ ASSOCIATED CONTENT
Supporting Information. 1H NMR spectra, UVꢀvis,
S
b
3-NO2-TPCorrGe(OCH3) was reacted with 4-amino-4H-
1,2,4-triazole following a slightly modified amination protocol
(see Experimental Section), and a single fraction was isolated in
good yield (50%) (Chart 4).
mass spectra, cyclic voltammograms, and CIF of 2-NH2-3-
NO2-TPCorrGe(OCH3). This material is available free of charge
via the Internet at http://pubs.acs.org.
The isolated compound displayed a UVꢀvis spectrum similar
’ AUTHOR INFORMATION
in shape to that of the starting complex, although the absorbances
1
were red-shifted. The H NMR spectrum are consistent with a
Corresponding Author
*E-mail: roberto.paolesse@uniroma2.it (R.P.), kkadish@uh.edu
(K.M.K.), kmsmith@lsu.edu (K.M.S.).
disubstituted germanium complex, showing in particular the
disappearance of the singlet at 9.71 ppm corresponding to the
proton on C2 of the starting compound and a broad singlet at
7.22 ppm ascribable to the amino group (Supporting Informa-
tion, Figure S5). The FAB mass spectrum indicated a molecular
peak at m/z 687, confirming the identity of this compound as the
difunctionalized β-amino-β-nitro-corrole derivative. In this
case we were able to grow single crystals by slow diffusion of
hexane into a diluted dichloromethane solution of the product.
The X-ray crystal structure determination unambiguously con-
firmed it to be 2-NH2-3-NO2-TPCorrGe(OCH3). (Figure 7).
The Ge atom has square-pyramidal coordination geometry,
lying 0.4323(2) Å out of the N4 plane. The apical GeꢀO distance
is 1.7879(14) Å, and the GeꢀN distances range from 1.8923(16)
to 1.9463(16) Å, averaging 1.913 Å, with GeꢀN2 the shortest
and GeꢀN1 the longest. The O-Me bond is nearly eclipsed with
GeꢀN4, forming a NꢀGeꢀOꢀC torsion angle of 9.89(13)°.
The NO2 group is twisted by 28° out of the plane of the pyrrole
to which it is bonded and accepts an intramolecular hydrogen
’ ACKNOWLEDGMENT
We gratefully acknowledge the support of MIUR, Italy (PRIN
project 2007C8RW53), the Robert A. Welch Foundation (K.M.K.,
Grant E-680), and the U.S. National Institutes of Health (K.M.S.,
Grant CA 132861).
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’ CONCLUSIONS
Modification of the reaction protocol established for the
preparation of 3-nitro- and 3,17-dinitro-corrole copper com-
plexes allows for modulation of the number of the peripheral
substituents while also leading to an increase in the reaction
yields and a reduction in the quantity of the expensive AgNO2
reagent utilized. These complexes were reacted with 4-amino-
4H-1,2,4-triazole to obtain the corresponding amino-nitrocor-
role derivatives. This is the first successful preparation of such
derivatives, because corrole ring expansion was observed to give
the corresponding 6-azahemiporphycene in the case of the
corresponding silver complexes. To the best of our knowledge,
this is also the first example for nucleophilic aromatic substitution
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Inorganic Chemistry
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