Mass spectrometry studies on meso-substituted corroles and their photochemical decomposition products

Article abstract of DOI:10.1002/jms.1860

Corroles, ring-contracted analogs of porphyrins, are an important class of compounds which have attracted the attention of many researchers in the fields of organic, coordination and physical chemistry. In the present work, the stability and the decomposition pathways of a diverse set of meso-substituted corroles have been studied using mass spectrometry (MS), UV-Vis absorption and preparative methods combined with NMR spectroscopy. Four different ionization methods (electrospray ionization, field desorption, atmospheric pressure photoionization and atmospheric pressure chemical ionization) were utilized to investigate light- and oxygen-induced decomposition in various solvents. It was found that the rate of decomposition in MeCN is significantly higher than in CH₂Cl₂, hexane, MeOH and ethyl acetate. HR-MS combined with CID-MS/MS enabled us to identify the products of initial decomposition. Surprisingly, numerous smaller open-chain compounds were also detected. Large-scale decomposition of a corrole bearing sterically hindered substituents at positions 5 and 15 allowed us to isolate mg quantities of three decomposition products: isocorrole and isomeric biliverdin-type species. These are formed as a result of oxygen attack on the meso-10 position. Copyright

Full text of DOI:10.1002/jms.1860

Research Article
Received: 29 July 2010
Accepted: 13 October 2010
Published online in Wiley Online Library: 6 December 2010
(wileyonlinelibrary.com) DOI 10.1002/jms.1860
Mass spectrometry studies on
meso-substituted corroles and their
photochemical decomposition products
a
a
a
´
´
Paweł Swider, Agnieszka Nowak-Krol, Roman Voloshchuk,
Jan P. Lewtak,a Daniel T. Grykoa∗ and Witold Danikiewicza∗
Corroles, ring-contracted analogs of porphyrins, are an important class of compounds which have attracted the attention
of many researchers in the fields of organic, coordination and physical chemistry. In the present work, the stability and the
decomposition pathways of a diverse set of meso-substituted corroles have been studied using mass spectrometry (MS), UV–Vis
absorption and preparative methods combined with NMR spectroscopy. Four different ionization methods (electrospray
ionization, field desorption, atmospheric pressure photoionization and atmospheric pressure chemical ionization) were utilized
to investigate light- and oxygen-induced decomposition in various solvents. It was found that the rate of decomposition in
MeCN is significantly higher than in CH2Cl2, hexane, MeOH and ethyl acetate. HR-MS combined with CID–MS/MS enabled us
to identify the products of initial decomposition. Surprisingly, numerous smaller open-chain compounds were also detected.
Large-scale decomposition of a corrole bearing sterically hindered substituents at positions 5 and 15 allowed us to isolate mg
quantities of three decomposition products: isocorrole and isomeric biliverdin-type species. These are formed as a result of
c
oxygen attack on the meso-10 position. Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: corroles; mass spectrometry; photochemistry; electrospray ionization; field desorption; photoionization
Introduction
is clearly a need for a comprehensive understanding on this topic.
(3) The detailed data on the routes and rates of decomposition of
corroles with diverse patterns of substituents in various solvents
should be helpful in choosing the right pattern of substituents
to perform further reactions with these molecules. MS is a very
powerfulandsensitiveanalyticalmethod. However, thenumberof
publicationsrelatedtotheanalysisofcorrolesusingMStechniques
is limited.[18–20] Obviously, there are many examples in the
literature regarding the use of various MS ionization techniques
[EI, ESI, FAB, field desorption (FD), MALDI][4,21] to confirm the
molecular weight of prepared corroles. Additionally, MALDI-time
of flight (TOF) has been used to monitor the conversion reaction
of corrole to porphyrin.[10] One of the aims of our study was to
apply MS techniques to monitor processes that occur in solutions
containing corroles. Four ionization techniques were used: FD, ESI,
atmospheric pressure photoionization (APPI) and atmospheric
pressure chemical ionization (APCI).
Corroles, porphyrin analogs contracted by one carbon, emerged
a few years ago as an independent area of research.[1] Their
coordination chemistry,[2] photophysics,[3] synthesis,[4] chemical
transformations,[5] electrochemistry[6] andotherproperties[7] have
recently been studied in great detail. One of the crucial factors
governing the use of these molecules is their stability. Corroles
have the same 18-π electron system as porphyrins but have one
less atom in the core, which results in greater electron density. This
inturnisresponsiblefortheirlowerstabilityonexposuretooxygen
in air. The lower stability of corroles versus porphyrins has been
described in a number of papers[8–16] and various decomposition
products were identified: biliverdin,[8–11,14,15] isocorroles[13] and
β –β linked dimers and trimers.[16] As expected, the oxygen
stability of meso-substituted corroles increases when electron-
withdrawing substituents are placed on the periphery of the
macrocycle.[17] This can be correlated with their first oxidation
potential values.[6a] Here we present the first comprehensive
study on the stability and light-induced decomposition of corroles
in solutions utilizing mass spectrometry (MS) as the primary
analytical tool. The motivation to perform this study came from
the several directions: (1) previous electrospray ionization (ESI)-MS
data collected by us suggested the presence of additional signals
in the samples of pure, freshly prepared corrole solutions, which
we need to identify and characterize. We also need to investigate
the potential of MS as a quick and reliable tool for examining
the purity of corroles. (2) In-depth analysis of the literature reveals
that various authors describe different decomposition products of
rather similar corroles. This effect remains unexplained and there
∗
Correspondence to: Daniel T. Gryko, Institute of Organic Chemistry, Polish
Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
E-mail: daniel@icho.edu.pl
Witold Danikiewicz,InstituteofOrganicChemistry,PolishAcademyofSciences,
Kasprzaka 44/52, 01-224 Warsaw, Poland. E-mail: witold@icho.edu.pl
a
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52,
01-224 Warsaw, Poland
c
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´
P. Swider et al.
CN
CN
F3C
CF3
F3C
F3C
CF3
CF3
N
HN
N
HN
N
HN
NC
CN
NH HN
1 (635)
NH HN
2 (601)
NH HN
3 (934)
OMe
HN
OMe
CN
MeO
OMe
F
F
F
F
F
F
F
MeO
MeO
MeO
OMe
OMe
OMe
N
HN
N
N
HN
F
F
NH HN
5 (579)
NH
HN
NH HN
F
4 (796)
6 (736)
Chart 1. The structures and nominal molecular masses of corroles studied.
Results and Discussion
whereas CH3CN does not dissolve molecular oxygen particularly
well.
Mass spectrometry studies in various solvents
The intriguing results obtained for acetonitrile solutions led us
to focus on this solvent for further experiments. It was found that
all six corroles undergo oxidation but at different rates and to
different extents. Our study showed that corrole 6 was clearly the
most stable. This can be attributed to the electron-withdrawing
effect of the pentafluorophenyl group in the meso-positions. The
relative stability of corroles in MeCN can be estimated on the basis
of the ratio of isocorrole and biliverdin versus corrole over time.
Based on relative intensities of peaks corresponding to a corrole
anditsoxidationproductsasafunctionoftime, therankof stability
is: 6 > 3 > 1∼2 > 4∼5. In the case of corrole 2, the isocorrole
formed is rapidly decomposed.
TheresultsobtainedbyESI, APCIandAPPIionizationtechniques
show some important differences (Fig. 2). Spectra acquired using
APCI and APPI methods differ only slightly in the relative peak
intensities which can be attributed to the different ionization
efficiencies of these methods for molecules with different
structural features. In the ESI spectrum, however, an additional
[M + 15]+ peak appears while the intensity of the [M + 17]+ peak
is quite low. Additionally, the relative intensity of the [M + H]+
peak is much higher compared to the APCI and APPI spectra. This
may reflect the higher ability of milder ESI ionization to generate
stable [M + H]+ ions compared to APCI and APPI methods which
prefer the formation of M+• ions due to the higher energy transfer
during the ionization process.
As the stability of corroles strongly depends on the type of
substituents located on the periphery of the macrocycle, we
identified a diverse set of meso-substituted corroles bearing
electron-withdrawing, electron-donating and sterically hindered
substituents for our study (Chart 1). These compounds were syn-
thesized according to the well-established literature procedures
just before investigation.[12,22,23]
The stability of corroles in the solution was tested in the
following solvents: methanol (ESI, APPI), acetonitrile (ESI, APPI),
ethyl acetate (APPI), dichloromethane (FD) and hexane (APCI,
APPI). In all cases, corroles were dissolved in a drop of CH2Cl2
and diluted with the appropriate non-degassed solvent. Samples
were kept at ambient light in contact with air. Mass spectra were
recorded immediately after the dilution, after 30 min and after 1 h
(sometimes also after a longer period of time). All experiments
showed that the mass spectra of the corrole solutions change
over time. The intensity of additional peaks corresponding to
decomposition products increased continuously with time. The
decomposition of corroles was the most rapid in acetonitrile. We
observed slower decomposition in methanol and ethyl acetate. In
CH2Cl2 andhexane,corroleswererelativelystable.Typicalchanges
that were observed in the mass spectra of corrole solutions are
presented in Fig. 1. APCI was used because ESI does not have a
possibility to measure spectra in hexane and ethyl acetate. The
spectra in methanol, hexane and ethyl acetate recorded after
1 h show additional peaks of lower intensity in comparison with
the spectrum in acetonitrile recorded after 5 min. The correlation
of the rate of corrole decomposition and oxygen solubility in the
solventsusedwasinvestigated(TableS2, SupportingInformation).
Surprisingly, we found that the stability of corroles in solvents
which contain the highest amount of oxygen is rather high,
Besides the M+• molecular ion and the protonated molecule
([M + H]+ ion), additional ions are observed in the spectra of all
corroles: [M − 1]+, [M + 15]+ (usually observed in ESI-MS spectra),
[M + 17]+, [M + 33]+ and rarely [M + 49]+.
As expected, the [M − 1]+ ion corresponds to [M − H]+
species. We observed [M − H]+ ion in spectra recorded using all
ionization techniques and its abundance did not increase during
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Mass spectrometry studies on meso-substituted corroles
Figure 1. Light-induced decomposition of corrole 1 (M = 635 Da) in various solvents studied by APCI-MS. The [M + 15]+, [M + 17]+ and [M + 33]+ ions
were assigned to [M − H + O]+, [M + O + H]+ and [M + 2O + H]+ species, respectively. See text for more details.
measurement. In the spectra recorded for methanolic solution,
[M − H]+ ion was present at very low intensity or was not observed
at all (Fig. 1). The addition of triethylamine to the acetonitrile
solutions of corroles 1, 3 and 4 led to an increase in the abundance
of [M − H]+ ion (FD ionization). This ion was most likely formed
from the radical cation of corrole by the loss of a hydrogen atom
during the ionization. Alternatively, it can be formed by the anodic
two-electron oxidation of the [M − H]− anion on the surface of
the ESI capillary (Scheme 1).
The [M + 15]+ and [M + 17]+ ions were assigned to [M − H +
O]+ and [M + O + H]+ species, respectively. The presence of both
ions is related to the oxidation of corrole. Therefore, the [M + O +
H]+ ion corresponds to the protonated [M + O] molecule with the
structure of isocorrole (formula 7 in Scheme 2). This assignment
was confirmed by HR-MS and in the preparative decomposition
experiment with corrole 1 (vide infra). The [M − H + O]+ ion is
observed mainly in ESI ionization and is most likely the oxidized
[M − H]+ ion. The origin of the [M + 33]+ ion can be explained by
the addition of two oxygen atoms and a proton to the molecule
of corrole: [M + 2O + H]+. The presence of this ion suggests that
biliverdin-like species are formed in the oxidation process. This
assumption has been supported by MS/MS experiments of the
[M + 2O + H]+ ions (Fig. 3). The presence of the biliverdin-like
species was further confirmed in the preparative decomposition
experiment with corrole 1 (described below). A comparison of
various techniques clearly shows that FD is the method of choice
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P. Swider et al.
Figure 2. ESI, APCI, APPI and FD mass spectra of compound 3 in acetonitrile recorded 30 min after the preparation of the solution. The [M + 15]+, [M +
17]+ and [M + 33]+ ions were assigned to [M − H + O]+, [M + O + H]+ and [M + 2O + H]+ species, respectively. See text for more details.
for studying corrole decomposition as it reveals all impurities
present but does not induce any reactions in the spectrometer.
In contrast, corrole oxidation in the ion-source during ESI-MS can
lead to the wrong conclusion about corrole purity: [M + 15] and
[M + 17] peaks are always present.
S6(c), Supporting Information). This is in line with the oxidation
product observed by Paolesse et al.[13] with DDQ in MeOH of
5,10,15-tris(p-tolyl)corrole. The next oxidation product observed is
the [M + 3O] compound. The presence of an [M + 3O] compound
was also observed in our preparative decomposition experiment
with corrole 1 (described below). In ESI and APCI ionization
techniques, it appears as the protonated ion [M + 3O + H]+,
but in FD as a radical cation [M + 3O]+•. Both signals appeared
after a longer reaction time in MeCN but their abundances were
always low.
In the course of our research, we noticed more signals related
to oxidation processes. During APCI experiments we observed
additional ions with m/z lower than the molecular ion. Figure 4(a)
and (b) shows APCI mass spectra of corrole 2 and possible
structures of the oxidation product observed at m/z 569 in positive
mode and at m/z 567 in negative mode. We acquired the product
ion spectrum of the m/z 569 and on the basis of this we were
able to determine a possible structure of the oxidation product
(Fig. 5). This is the most probable structure based on the presence
of m/z 439 and 309 peaks in the product ion spectrum. A similar
oxidation product was observed in the preparative decomposition
experiment with corrole 1 (vide infra). Additionally, we observed
that corroles and their oxidation products in negative mode
ionized very abundantly. Spectra recorded in negative mode were
similartothoseinpositiveionmodeandcontainanalogoussignals.
It was observed that the oxidation process does not take place
in the absence of light even if oxygen is present. Similarly, when
we add formic acid to the sample, we did not observe additional
In order to establish the structures of the oxidation products,
we performed a number of MS/MS experiments (Figs 3 and S6,
Supporting Information). The results show that for trans-A2B
corroles, it is possible to determine which isomers with the mass
[M + 16] and [M + 32] are formed in the oxidation process. Even
if the acylium cation of an appropriate aldehyde is difficult to
detect or observe, it is possible to observe an elimination of a
neutral molecule or the respective radical in the product spectra.
On the basis of these results, it is possible to determine the
position of the hydroxyl group in the molecule of isocorrole [M +
O] and, consequently, in which position the macrocyclic ring has
opened. For obvious reasons, the determination of the side of the
ring-opening is impossible for A3-corroles.
Scheme 1. Possible mechanisms of [M − H]+ formation in ion sources.
The lack of sterically hindered substituents at meso-positions
results in oxidative attack both at positions 5 and 10 (Figs 3(c) and
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Mass spectrometry studies on meso-substituted corroles
Figure 3. CID spectra of the [M + 2O + H]+ ions of corroles 4(a), 1(b), 5(c) and 6(d) in MeCN.
signals in the mass spectra of corroles. These results clearly show
that the presence of an acid as well as the absence of light inhibits
the oxidation of the studied compounds. Interesting results were
obtained after triethylamine addition. Under such conditions, the
[M + 32] product was formed in small amounts.
60 h. TLC analysis revealed that after this time corrole 1 had
decomposed almost completely into a number of products, of
which only three were isolated in sufficient amounts. Compounds
7, 8 and 9 were purified and characterized by NMR (1D and
2D experiments, Figs S7–S18, Supporting Information), MS and
UV–Visspectra(Fig.S5,SupportingInformation).Compound7was
relatively stable, although it decomposed partially into a navy blue
compound during chromatography, significantly in methylene
chloride/hexane. In contrast, compounds 8 and 9 turned out to
be stable for at least 15 h in the chloroform solution used for
NMR analysis. Additionally, the fractions containing compounds
formed in trace amounts were analyzed with the use of MS (Table
S1, Supporting Information).
Synthetic and UV–Vis studies
In order to fully characterize the oxidation products observed,
we carried out the preparative scale decomposition of one
corrole. The aim was to isolate and elucidate the structures
of the compounds observed in MS. The electron-rich corrole 1
was selected for the preparative scale decomposition reaction.
Based on MS experiments, acetonitrile was selected as the
solvent to provide the most rapid decomposition. A sample
of 1 was dissolved in acetonitrile and exposed to sunlight for
Among the three decomposition products, isocorrole 7 was
the easiest to identify. Its structure was fully confirmed by NMR
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CN
N
HN
NH HN
1
hv, MeCN, 60 h
NC
OH
N
N
NH HN
7 (8%)
+
NC
O
O
Figure 4. Positive (a) and negative (b) APCI spectra of compound 2 in
MeCN recorded 30 min after the preparation of the solution.
N
HN
H
N
H
N
a tilted pyrrole ring (E/Z isomers). This assignment is supported
by DFT calculations of NMR spectra (Figs S19–S21, Supporting
Information). Such compounds have not been reported in the
literature up to now. The most characteristic feature of their
absorption spectrum is a strong signal at 555 nm. Both 8 and
9 form complexes with Zn2+, whereby the complex with 8 is
distinctly green in solution.
Our results strongly suggest that the position of the initial attack
of oxygen on the corrole core is governed by both electronic and
steric factors. According to Paolesse, the chemical oxidation of a
meso-substituted corrole possessing both electron-withdrawing
and sterically hindered groups in the meso-position does not
occur, whereas in the case of unhindered ones, oxidation occurs
at position 5.[13–15] Our ketone is regioisomeric to that which
Paolesse reported to be formed during chemical oxidation of
triaryl corroles.[13–15] Surprisingly, the A2B-porphyrin observed
by Guilard et al.[10] for structurally similar 5,15-bismesityl-10-(4-
nitrophenyl)corrole was neither observed by MS nor via isolation
of the products in our experiments.
The stability of a solution of corrole 1 was studied using
UV spectrophotometry. Measurements were performed both in
CH3CN and CH2Cl2 in the presence and absence of light (Figs
S1–S4, Supporting Information). No changes were observed in
the absence of light. On the other hand, in the presence of
light, the intensity of the Soret band quickly decreased and the
formation of a broadband around 550 nm, corresponding to the
formation of ketones 8 and 9, was observed. These spectroscopic
8 (51%)
+
NC
O
O
NH
N
H
N
H
N
9 (28%)
Scheme 2. Proposed structures for the main products of the photochemi-
cal oxidation of corrole 1.
and comparison with Paolesse’s compounds.[13,15] The remaining
two products were more difficult to identify. HR-MS revealed that
they have the same molecular masses which correspond to the
open-chain ketones depicted in Scheme 2. Detailed NMR analysis
showed that in both compounds the decomposition site is the
carbon–carbon bond in the meso-10 position. The identical CID
massspectrasuggestthatthesecompoundsdifferonlyslightlyand
are most likely geometrical isomers. A shifted NH proton signal for
9 eventually allowed us to identify it as an open-chain ketone with
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Mass spectrometry studies on meso-substituted corroles
Figure 5. Product ion spectrum of m/z 569 ion of one of the products resulting from the oxidative decomposition of corrole 2.
studies confirm that the decomposition in the presence of light is
faster in CH3CN than in CH2Cl2. The origin of this phenomenon is
unclear at this point.
(Waters/Micromass). The IR spectra were recorded in the film and
the wavenumbers are expressed in cm−1. Corroles 1(a–f) were
prepared according to the literature procedures.[12,22,23]
Corrole 1 (160 mg, 0.25 mmol) was dissolved in MeCN (1000 ml)
and the solution was exposed to sunlight for 60 h. Subsequently,
the reaction mixture was evaporated to the dryness and the
resulting solid was preliminarily chromatographed (DCVC, silica
gel, hexanes/ethylacetate19 : 1to4 : 1, thenhexanes/acetone4 : 1,
thenacetone,thenMeOH)toaffordseveralcontaminatedproducts
of decomposition. Fractions containing compounds formed in
trace amounts were analyzed with the use of MS. The rest were
submitted to further purification.
Chromatography of the first main fraction (DCVC, silica gel,
hexanes/acetone 97 : 3) followed by the second chromatography
(DCVC, silica gel, hexanes/methylene chloride 3 : 2) furnished
compound 7 (13 mg, 8%), which was then suspended in hexanes
and filtered to afford green crystals.
Summary and Conclusions
The following conclusions can be drawn: (1) MS was found to
be useful not only in the analysis of the purity of corroles
but also in the detection and structure determination of the
oxidative decomposition products of corroles. (2) FD is the most
suitable ionization method to evaluate the purity of corroles.
(3) Electrospray induces oxidation that results in the detection
of the [M + 15] signal (isocorrole), even if a corrole sample is
pure. (4) The rate of light and oxygen-induced decomposition
decreases when the corrole possesses electron-withdrawing
substituents. (5) Decomposition of corroles bearing sterically
hindered substituents at positions 5 and 15 leads to attack at
position 10 and results in the formation of isocorrole and ketones
in substantial yield as well as more than 15 other open-chain
products.
Rf = 0.43 (silica gel, acetone/hexane, 1 : 3); m.p. >330 ◦C; 1H
NMR (600 MHz, CDCl3, 25 ◦C, TMS): δ = 2.12 (s, 6H, CH3), 2.15 (s,
6H, CH3), 2.34 (s, 6H, CH3), 2.84 (s, 1H, OH), 6.30 (d, J(H,H) = 4.3 Hz,
2H, β-H), 6.34 (d, J(H,H) = 4.3 Hz, 2H, β-H), 6.48 (d, J(H,H) = 4.1 Hz,
2H, β-H), 6.61 (d, J(H,H) = 4.1 Hz, 2H, β-H), 6.92 (s, 4H, mesityl), 7.55
(m, AAꢁ part of the AAꢁXXꢁ system, 2H, NC-C6H4), 7.83 (m, AAꢁ part
of the AAꢁXXꢁ system, 2H, NC-C6H4), 15.5 ppm (bs, 2H, NH); 13C
NMR (150 MHz, CDCl3, 25 ◦C, TMS): δ = 20.0, 20.1, 21.1, 74.9, 111.1,
116.2, 117.4, 118.8, 126.8, 127.8, 127.9, 128.0, 128.1, 132.2, 132.4,
136.5, 136.9, 137.8, 140.6, 140.8, 141.4, 146.4, 147.0, 162.2 ppm; IR
(film): ν bar = 808, 824, 1033, 1353, 1559, 1603, 1739, 2229 (CN),
2923, 3193 (N–H), 3433 cm−1 (O–H); UV–Vis (CH2Cl2): λ (ε) = 428
(31 600), 348 (11 400), 666 nm (4200 M−1 cm−1); HRMS (FD): m/z
calcd. for C44H37N5O: 651.2998; found: 651.2990, isotope profiles
match.
The next fraction, consisting of two isomeric compounds 8
and 9, was submitted to chromatography (DCVC, silica gel,
hexane/ethyl acetate 93 : 7 to 3 : 1) followed by three consecutive
chromatographies (DCVC, silica gel, hexanes/acetone 23 : 2 to
4 : 1), which provided the contaminated compound 8, and
the chromatographically pure compound 9 (47 mg, 28%). Two
subsequent chromatographies of the product 8 (DCVC, silica gel,
hexanes/acetone 23 : 2 to 9 : 1) furnished the pure isomer 8 (85 mg,
51%). Both compounds were suspended in hexane and filtered to
afford navy blue crystals, which were submitted to analyses.
Experimental Section
General methods
All chemicals were used as received unless otherwise noted.
Reagent grade solvents (CH2Cl2, hexane, ethyl acetate) were
1
distilled prior to use. All reported H NMR and 13C NMR spectra
were recorded using a Varian VNMRS 600 MHz spectrometer.
Chemical shifts (δ ppm) were determined with TMS as the internal
reference; J values are given in Hz. The UV–Vis absorption
spectra were recorded in CH2Cl2. The absorption wavelengths
are reported in nm with the extinction coefficient in M−1 cm−1
in brackets. Melting points were determined using a Boetius-type
apparatus. Chromatography was performed on silica (200–400
mesh) or alumina. Dry column vacuum chromatography (DCVC)
was performed on preparative thin-layer chromatography silica.
Mass spectra were recorded using ESI, APCI, APPI and FD
ionization methods. ESI, APCI and APPI mass spectra were
recorded on 4000 QTrap triple quadrupole/linear ion trap
mass spectrometer (Applied Biosystems) and FD spectra were
recorded on GCT Premier high resolution TOF mass spectrometer
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´
P. Swider et al.
Compound 8: Rf = 0.56 (silica gel, ethyl acetate/hexanes, 3 : 2),
0.48 (silica gel, acetone/hexanes, 2 : 3); m.p. 201.3–203.7 ◦C; 1H
NMR (600 MHz, CDCl3, 25 ◦C, TMS): δ = 2.08 (s, 6H, CH3), 2.12 (s,
6H, CH3), 2.20 (s, 3H, CH3), 2.36 (s, 3H, CH3), 6.02 (d, J(H,H) = 4.1 Hz,
1H, β-H), 6.05 (d, J(H,H) = 5.5 Hz, 1H, β-H), 6.52 (m, 1H, β-H), 6.57
(d, J(H,H) = 5.5 Hz, 1H, β-H), 6.61 (d, J(H,H) = 4.1 Hz, 1H, β-H),
6.68 (d, J(H,H) = 4.7 Hz, 1H, β-H), 6.94 (s, 2H, mesityl), 6.96 (d,
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∼
J(H,H) = 4.7, 1H, β-H), 6.97 (s, 2H, mesityl), 6.98 (d, J(H,H) 4.2 Hz,
=
1H, β-H), 7.75 (d, J(H,H) = 8.1 Hz, 2H, NC-C6H4), 7.98 (d, J(H,H) =
8.1 Hz, 2H, NC-C6H4), 9.0 ppm (bs, 3H, NH); 13C NMR (150 MHz,
CDCl3, 25 ◦C, TMS): δ = 20.0, 20.1, 21.10, 21.13, 115.1, 116.3, 117.3,
117.8, 118.2, 119.6, 122.9, 126.4, 128.1, 128.9, 129.3, 130.6, 131.5,
132.2, 132.7, 132.8, 134.4, 134.5, 134.7, 135.8, 137.0, 137.4, 137.8,
137.9, 138.1, 138.2, 142.1, 154.3, 160.9, 173.1 and 182.0 ppm; IR
(film): ν bar = 804, 1285, 1603, 1681, 2230 (CN), 2919, 3264 cm−1
(N–H); UV–Vis (CH2Cl2): λ (ε) = 396 (36 800), 557 (26 800), 757 nm
(400 M−1 cm−1); HRMS (FD): m/z calcd. for C44H37N5O2: 667.2947;
found: 667.2953, isotope profiles match.
Compound 9: Rf = 0.49 (silica gel, ethyl acetate/hexanes, 3 : 2),
0.42 (silica gel, acetone/hexanes 2 : 3); m.p. 127.5–128.3 ◦C; 1H
NMR (600 MHz, CDCl3, 25 ◦C, TMS): δ = 2.10 (s, 6H, CH3), 2.15 (s,
6H, CH3), 2.27 (s, 3H, CH3), 2.36 (s, 3H, CH3), 6.08 (d, J(H,H) = 4.1 Hz,
1H, β-H), 6.24 (d, J(H,H) = 4.0 Hz, 1H, β-H), 6.52 (dd, J(H,H) = 5.8 Hz,
1.9 Hz, 1H, β-H), 6.70 (3H, three overlapping signals of two β-H
and one amide NH), 6.84 (d, J(H,H) = 4.0 Hz, 1H, β-H), 6.90 (d,
J(H,H) = 4.7 Hz, 1H, β-H), 6.96 (s, 2H, mesityl), 6.99 (s, 2H, mesityl),
7.83 (m, AAꢁ part of the AAꢁXXꢁ system, 2H, NC-C6H4), 8.02 (m,
AAꢁ part of the AAꢁXXꢁ system, 2H, NC-C6H4), 8.08 ppm (dd, J(H,H)
= 5.8 Hz, 1.9 Hz, 1H, β-H); 13C NMR (150 MHz, CDCl3, 25 ◦C, TMS):
δ = 19.6, 20.1, 21.1, 21.2, 115.3, 115.9, 116.7, 117.2, 117.9, 118.1,
119.8, 124.8, 126.1, 126.4, 128.1, 129.2, 129.3, 130.7, 131.2, 132.4,
132.6, 132.7, 134.3, 134.5, 134.6, 135.0, 136.1, 136.8, 137.0, 138.0,
138.5, 138.7, 142.0, 154.3, 160.9, 170.4 and 182.2 ppm; IR (film): ν
bar = 805, 1283, 1604, 1686, 2230 (CN), 2923, 3239 and 3440 cm−1
;
UV–Vis (CH2Cl2): λ (ε) = 398 (36 900), 565 nm (17 900 M−1 cm−1);
HRMS (FD): m/z calcd. for C44H37N5O2: 667.2947; found: 667.2921,
isotope profiles match.
[9] R. Paolesse, F. Sagone, A. Macagnano, T. Boschi, L. Prodi,
M. Montalti, N. Zaccheroni, F. Bolletta, K. M. Smith. Photophysical
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J. Porphyrins Phthalocyanines 1999, 3, 364.
Acknowledgements
This work has been supported by the Polish Ministry of Science
and Higher Education (Grant No. N N204 263837). Authors thank
Prof. Justin Youngblood and Dr. David Will for amending this
manuscript.
[10] C. P. Gros, J.-M. Barbe, E. Espinoza, R. Guilard. Room-temperature
autoconversion of free-base corrole into free-base porphyrin.
Angew. Chem. Int. Ed. 2006, 45, 5642.
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III,
J. F. B. Chick,
J. B. Callinan,
C. G. Reid,
W. P. Auguscinski.
A
survey of acid catalysis and oxidation
conditions in the two-step, one-flask synthesis of meso-substituted
corroles via dipyrromethanedicarbinols and pyrrole. J. Org. Chem.
2004, 69, 4159.
Supporting information
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corroles in a H2O-MeOH mixture. J. Org. Chem. 2006, 71, 3707.
[13] S. Nardis, G. Pomarico, F. R. Fronczek, M. G. H. Vicente, R. Paolesse.
One-step synthesis of isocorroles. Tetrahedron Lett. 2007, 48, 8643.
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M. Montalti, G. Battistini. Synthesis and functionalization of
germanium triphenylcorrolate: the first example of a partially
brominated corrole. Eur. J. Inorg. Chem. 2007, 2345.
[15] F. Mandoj, S. Nardis, G. Pomarico, M. Stefanelli, L. Schiaffino,
G. Ercolani, L. Prodi, D. Genovese, N. Zaccheroni, F. R. Fronczek,
K. M. Smith, X. Xiao, J. Shen, K. M. Kadish, R. Paolesse. 6-
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Supporting information may be found in the online version of this
article.
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