BiIII-corroles: A versatile platform for the synthesis of functionalized corroles

Article abstract of DOI:10.1002/ejic.201200697

The Bi^III ion in the center of the corrole macrocyclic ring system was employed to stabilize and protect the corrole inner core during the functionalization at the periphery (meso positions) of the π-conjugated ring system. Moreover, the ease of demetalation makes Bi^III-corroles attractive candidates for functionalization and subsequent demetalation to the free-base corroles. Herein we present examples of possible derivatization reactions of Bi-corroles by employing Suzuki cross-coupling under gentle conditions at ambient temperature. This high-yielding methodology facilitates the design of A₂B corroles that bear elaborate subunits such as the indolyl and pyrenyl group, which are difficult to realize with the synthetic protocols available to date. Later, Pd-catalyzed C-N coupling reactions with the same precursor were tested. To make the corresponding free-base corroles also accessible by means of these new routes, a versatile procedure was developed that allows the subsequent demetalation of the obtained Bi-corroles. Electrochemical characterization was performed with cyclic voltammetry and spectroelectrochemistry to clarify the ring-centred oxidation and reduction processes. Structural considerations of the dome-shaped nature of Bi-corrole derivatives are presented and corroborated by ¹⁹F NMR spectroscopy as well as quantum chemical calculations.

Full text of DOI:10.1002/ejic.201200697

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FULL PAPER
DOI: 10.1002/ejic.201200697
BiIII–Corroles: A Versatile Platform for the Synthesis of Functionalized
Corroles
Lorenz Michael Reith,[a] Michael Koenig,[b] Clemens Schwarzinger,[c] and
Wolfgang Schoefberger*[a]
Keywords: Synthetic methods / Macrocycles / Corrole / Nitrogen heterocycles / Bismuth / Cross-coupling / Demetalation
The BiIII ion in the center of the corrole macrocyclic ring sys-
tem was employed to stabilize and protect the corrole inner
core during the functionalization at the periphery (meso posi-
tions) of the π-conjugated ring system. Moreover, the ease
of demetalation makes BiIII–corroles attractive candidates for
functionalization and subsequent demetalation to the free-
base corroles. Herein we present examples of possible
derivatization reactions of Bi–corroles by employing Suzuki
cross-coupling under gentle conditions at ambient tempera-
ture. This high-yielding methodology facilitates the design of
A2B corroles that bear elaborate subunits such as the indolyl
and pyrenyl group, which are difficult to realize with the syn-
thetic protocols available to date. Later, Pd-catalyzed C–N
coupling reactions with the same precursor were tested. To
make the corresponding free-base corroles also accessible by
means of these new routes, a versatile procedure was devel-
oped that allows the subsequent demetalation of the ob-
tained Bi–corroles. Electrochemical characterization was per-
formed with cyclic voltammetry and spectroelectrochemistry
to clarify the ring-centred oxidation and reduction processes.
Structural considerations of the dome-shaped nature of Bi–
corrole derivatives are presented and corroborated by 19F
NMR spectroscopy as well as quantum chemical calculations.
by means of bromination,[9,10] nitration, or chlorosul-
fonation,[11] whereas reactions performed at the meso sub-
stituents among others include Suzuki,[12,13] Stille,[13] and
Sonogashira coupling reactions,[14] as well as nucleophilic
substitution reactions.[15,16] In the following manuscript, we
mainly focus on the application of Suzuki cross-coupling
and Pd-catalyzed C–N coupling reactions, reasoned by the
large variety of possible substrates that are feasible with
these reaction types. Because most of these reactions can
only be performed with metalated corroles, effective met-
alation and demetalation reactions are of great interest to
open a pathway to obtain more elaborate free-base corroles.
Similar considerations have already been presented for cop-
per corroles, but with a focus on electrophilic substitution
reactions.[17]
Introduction
Corroles are ring-contracted tetrapyrrolic macrocycles
that are one carbon shorter and lack one meso substituent
relative to their parent porphyrins. Since the first corrole
synthesis by Johnson and Kay in 1964,[1] a large variety of
metal atoms were inserted into the macrocycle,[2] and cor-
role-based applications in the fields of catalysis,[3] biomedic-
ine,[4] sensors,[5] and dye-sensitized solar cells[6] have been
presented. Although synthesis of A3 and A2B corroles with
small aromatic side chains at the meso positions is more or
less standard today,[7] the above-mentioned methods show
only a limited applicability for larger and more sophisti-
cated meso substituents, especially for side groups that bear
basic subunits. Consequently, different derivatization strate-
gies have been proposed for free-base and metallocorroles.[8]
Substitution of the β-pyrrole protons has been performed
Results and Discussion
[a] Institute of Inorganic Chemistry, Johannes Kepler University
Linz (JKU),
Preparation of the free-base corrole 1 was performed as
described in the literature[12] by means of condensation of
(pentafluorophenyl)dipyrromethane with 4-bromobenzal-
dehyde in H2O/MeOH under acidic catalysis followed by
subsequent oxidation with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ). As illustrated in Scheme 1, insertion
of bismuth into the corrole macrocycle was achieved by
treatment with Bi{N(SiMe3)2}3 (1.2 equiv.) in dry THF un-
der an inert atmosphere.[18] Reliable indications of the com-
pletion of the metalation reaction are both the characteris-
Altenberger Strasse 69, 4040 Linz, Austria
Fax: +43-732-2468-9681
E-mail: wolfgang.schoefberger@jku.at
Homepage: http://www.anorganik.jku.at/Schoefberger/
Schoefberger.html
[b] Institute of Polymer Chemistry, Johannes Kepler University
Linz (JKU)
Welser Strasse 42, 4060 Linz, Austria
[c] Institute of Chemical Technology of Organic Substances,
Johannes Kepler University Linz (JKU),
Altenberger Strasse 69, 4040 Linz, Austria
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200697.
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tic bathochromic shift of the Soret and Q bands (see Fig-
ure S1 in the Supporting Information) and the complete
disappearance of the intense fluorescence of the free ligand.
Scheme 2. Pd-catalyzed Suzuki cross-coupling reaction of boronic
acid derivatives with the Bi–corrole precursor.
tuted heterocycles (3g–i, 3k). Cross-coupling of substituted
phenyl derivatives could, except for 3g, thoroughly be
Scheme 1. Bismuth metalation reaction of the free-base corrole.
To investigate a route for functionalized Bi–corroles, we achieved in yields in the range of 69 to 87%. In the case of
chose the Suzuki cross-coupling reaction, primarily for the the p-amino-functionalized boronic ester derivative (3g), we
following reasons: nowadays a wide selection of boronic determined a slightly reduced reaction yield. Possible expla-
acid derivatives is easily accessible, which facilitates the as- nations for this are either the coordination of the amine
sembly of a compound library. The same arguments hold group to the palladium catalyst, which eventually affects
true for the catalyst systems available. Elaborate phosphane the catalytic activity, or Pd-catalyzed C–N coupling as a
ligands have been developed that show efficient conversion minor side reaction (though no C–N-coupled product was
even with very low catalyst load,[19] enable reactions of observed). Yields for coupling reactions with larger boronic
quickly deboronating species,[20] and make reactions at am- acid derivatives are in the range of 70% (3d and 3i), which
bient temperature possible.[21]
is still appropriate given their sterically demanding nature.
At this stage, previous experience on Bi–corroles led us As for the practical use of these compounds, the potential
to the assumption that both instability of the macrocycle of Bi–corroles to act as photosensitizer and as catalyst in
on account of ring-centered oxidation reactions, especially oxidation reactions has already been presented elsewhere.[18]
at higher temperatures, and demetalation reactions (see be- Additionally, the introduction of the pyrenyl and indolyl
low) would be the most severe side reactions.[18] As a conse- group as in derivatives 3d and 3i had been of particular
quence, we opted for very mild reaction conditions. The interest as similarly substituted water-soluble porphyrin de-
combination of SPhos (5 mol-%) and Pd(OAc)2 (2.5 mol-%) rivatives have shown promising activity against different
in a THF/H2O mixture with K3PO4 as base, as presented in cancer-cell lines[22] and photonuclease activity.[23]
the literature[21] and employed similarly for the coupling of
The second reaction that was investigated was the Pd-
Cu–corroles,[12] was employed as catalyst system for Suzuki catalyzed C–N coupling reaction (Buchwald–Hartwig cou-
cross coupling (Scheme 2). Treatment of 2 with phenyl and pling reaction). As the system for optimization of the cata-
tolyl boronic acid at room temperature showed very prom- lytic C–N coupling reaction we chose the reaction of 2 with
ising results because the coupled products 3a and 3b could morpholine (2.5 equiv.), catalyzed by XPhos (5 mol-%)/
be isolated in 79 and 87% yield, respectively (Table 1).
[Pd2(dba)3] (dba
=
dibenzylideneacetone; 2.5 mol-%;
Further entries involved the use of bulkier aromatic side Scheme 3). Though primarily developed for the coupling of
groups such as the naphthyl and the pyrenyl groups (3c and aryl tosylates with amines and the amidation of benzensulf-
3d), nitro- (3f), amino- (3g), and aldehyde- (3j) function- onates, C–N coupling of aryl halides with various amines
alized boronic acid derivatives, as well as N- and O-substi- has also been demonstrated with this catalyst setup.[24]
2
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Table 1. Yields for Suzuki cross-coupling reactions of 2 with dif-
ferent boronic acid derivatives and for the subsequent demetalation
reaction.
Scheme 3. Pd-catalyzed C–N coupling reaction of 2 with morph-
oline.
K3PO4 as base was achieved after four hours (entry 5). Both
elongation of the reaction time and subsequent addition of
new catalyst (entry 9) did not lead to an increased yield.
Table 2. Optimization of the reaction conditions for the C–N cou-
pling of 2 with morpholine (2.5 equiv.) and base (2 equiv.) and cata-
lyzed by X-Phos (5 mol-%)/[Pd2(dba)3] (2.5 mol-%).
Entry
Base
Solvent
T [°C]
t [h]
Yield
14[a]
1
2
3
4
5
6
7
8
9
NaOtBu
NaOtBu
NaOtBu
K2CO3
K3PO4
tBuOH
tBuOH
Toluene
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
80
80
70
80
80
80
80
80
80
2
12
2
4
4
8
4
8
11
[b]
–
–
[b]
Not only would the use of higher reaction temperature
facilitate an eventual decomposition of the corrole macro-
cycle, substitution of the para-fluorine atoms with
amines[16] was another potential undesirable side reaction.
Although this substitution reaction predominantly takes
place in polar aprotic solvents (DMF, DMSO) and with a
higher excess amount of amine, we employed rather mild
conditions with 4 equiv. of amine and a reaction tempera-
ture of 80 °C. The influence of different bases and the reac-
tion time is summarized in Table 2. The use of NaOtBu as
inorganic base, which is usually classified as most ef-
–
49
K3PO4
36[c]
47
Cs2CO3
Cs2CO3
Cs2CO3
51
52[d]
[a] 25% of demetalated product were additionally obtained. [b] Par-
tial demetalation of the starting material was observed. [c] 4 equiv.
of morpholine were used. [d] New catalyst was added after half of
the reaction time.
With these optimized reaction conditions (Scheme 4), we
ficient,[25] led to significant demetalation of the Bi species, tested some other amine and aniline derivatives as listed in
in terms of both starting material and the ultimately formed Table 3. Under these conditions, yields are moderate, which
product (Table 2, entries 1–3). Whereas no reaction could is essentially a problem of conversion efficiency and not of
be observed with K2CO3 (entry 4), Cs2CO3 and K3PO4 side-product formation, because it was usually possible to
both showed compatibility with the Bi species and conver- recover most of the unreacted precursor. The aniline deriva-
sion to the C–N coupled product. Eight hours was found tives (5c, 5d) could be coupled with over 50% yield, whereas
to be the optimum reaction time when 2 equiv. of Cs2CO3 those for the reaction with piperidine and pyrrolidine re-
were used (entry 8), whereas the best result with 2 equiv. of mained rather poor. Additionally, reactions with primary
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and secondary aliphatic amines (propylamine, dibu- alation occurs almost instantaneously in solution under
tylamine) as well as the sterically hindered substrate diphe- acidic conditions.[26] Thus, we thought to employ this
nylamine were tested but did not lead to the desired prod- feature to develop a general demetalation method. To avoid
ucts.
potential side reactions such as sulfonation or nitration of
the β-pyrrole positions,[11] we excluded the use of nitric and
sulfuric acid a priori and opted for hydrochloric acid. Thus,
demetalation of the functionalized Bi–corroles was per-
formed as follows: addition of diluted hydrochloric acid to
a solution of the corresponding Bi complex in THF at room
temperature, followed by extraction and chromatography,
yielded the corresponding free-base corroles (Scheme 5). As
outlined above for the metalation reaction, the reaction pro-
gress can be followed by UV/Vis spectroscopy because free-
base corroles show characteristic fluorescence.[27]
Scheme 4. Pd-catalyzed C–N coupling reaction of amines with the
Bi–corrole precursor.
Table 3. Yields for the XPhos/[Pd2(dba)3]-catalyzed C–N coupling
reactions of 2 with different amines and for the subsequent demet-
alation reaction.
Scheme 5. Acid-catalyzed demetalation reaction of the function-
alized Bi–corroles.
We investigated the influence of the acid concentration
on the demetalation of precursor 2 (Table 4). A concentra-
tion of 15 mmolL–1 HCl in the reaction mixture was found
to be sufficient for nearly quantitative demetalation of 2
(1 mmolL–1), whereas higher acid concentrations do not
seem to affect the yield considerably. Later we performed
this demetalation reaction with all Suzuki- and C–N cou-
pled products (3a–k and 5a–e). As a result, excellent yields
(Tables 1 and 3) could be achieved for most of the deriva-
tives.
The formation of isocorrole species from free-base cor-
Although all the prepared complexes are stable as solid roles, which were described as a common side product in
compounds under ambient conditions, previous work on reduction[10] and demetalation reactions,[17] was only ob-
Bi–corrole complexes had already revealed that demet- served to a minor extent by means of ESI-MS in the case of
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BiIII–Corroles
Table 4. Effect of the acid concentration on the demetalation reac-
tion of 2 (1 mmolL–1) in a THF/HCl mixture (10:1).
Entry
C(HCl) [mmolL–1]
Yield [%]
1
2
3
4
15
45
75
92
89
80
88
105
[28]
´
4a and 4g. As discussed by Swider et al. in the literature,
observation of isocorrole species during ESI-MS spec-
troscopy is a common feature and typical for this ionization
method. Although the mechanism of the demetalation is
yet unclear, no prior reduction step for the central metal
atom seems necessary, which is similar to methods proposed
for Mn demetalation.[29] This stands in contrast to the de-
metalation procedures for other metals such as the re-
ductive two-step process for the demetalation of copper cor-
roles,[17] which is SnCl2-mediated, and the different methods
proposed for silver corroles.[30] A plausible reason for the
easier demetalation of Bi–corroles could be the structural
difference between the strongly domed Bi complexes in
which the central metal shows a significant out-of-plane
Figure 1. o-F, m-F, and p-F region of the 19F spectra of (A) 3j and
(B) 4j recorded in [D8]THF at 25 °C.
gen atoms. Indeed, this geometry-optimization procedure
also leads to a dome-shaped structure (Figure S2 in the
Supporting Information) in which the central Bi atom
shows a significant out-of-plane displacement.
displacement (see the discussion below and the literature[18]
Electrochemical characterization of a selection of the
metalated compounds was performed by means of cyclic
voltammetry (Figure 2) and spectroelectrochemistry (Fig-
ure 3). In general, the potentials for first- and second-re-
versible oxidation are almost invariant to the substituent
at the meso-10-position. This also holds true for the first
reduction, with the exception of 3f and 3h, for which the
reduction is an irreversible process (Figures S36 and S37 in
the Supporting Information). In comparison to the pre-
viously published symmetrical derivative Bi(TpFPC), oxi-
dation and reduction potentials experience slight positive
shifts, which can be explained by the weaker electron-with-
drawing effect of the third meso substituent. Consequently,
the electron density within the aromatic π system is en-
larged, which leads to an alleviated oxidation reaction,
whereas the reduction potential is slightly reduced.
[30]
and the more or less planar AgIII
corroles[31]).
–
and saddled CuIII
–
Comparison of the 19F NMR spectra of a metalated (3j)
and nonmetalated derivative (4j) as illustrated in Figure 1
reveals that only one resonance can be observed for the or-
tho- and meta-fluorine atoms in the nonmetalated deriva-
tive (4j), whereas the metalated derivative (3j) shows two
resonances, respectively, which is a characteristic observed
for each pair of metalated and nonmetalated corrole species
3
4
presented above. Detailed analysis of the JF,F and JF,F
coupling constants reveals that the two chemically equiva-
lent pentafluorophenyl meso substituents can be regarded
as an ABCDE-spin system, as already observed for
Bi(TpFPC) [TpFPC = 5,10,15-tris(pentafluorophenyl)cor-
role].[18] Considering not only this NMR spectroscopic fea-
ture but also the size of the central BiIII atom and the facile
demetalation, we suppose that the Bi-A2B corroles should
also display a dome-shaped structure as observed for their
symmetrical A3 counterpart.[18]
Although no X-ray crystal structure of a Bi–A2B corrole
is available to date, we wished to corroborate this hypothe-
sis by quantum chemical calculations. Similar to our recent
work, we employed Gaussian 09 calculations to determine
the geometry-optimized structure of compound 3j.[32]
We first performed a tight structural optimization, which
was checked by a frequency calculation to confirm that the
optimized structure was indeed a minimum (with no imagi-
nary frequencies). Los Alamos National Laboratory 2
(LANL2) relativistic effective core potentials (RECPs)[33]
were used to describe the core electrons of Bi atoms, and
split-valence (double-ζ) basis sets were used to describe s-
and p-valence electrons of Bi. The LANL2DZ basis set was
augmented by adding one set of polarization functions on
Figure 2. Cyclic voltammogram of 3c in MeCN with 0.1 m TBAPF6
all atoms and one set of diffuse functions on all non-hydro- measured with a scanning rate of 100 mVs–1.
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group metallocorroles of the TpFPC ligand, such as
Sn(TpFPC)Cl, Ga(TpFPC)Py, Ge(TpFPC)OH, and
Sb(TpFPC)Py (Py = pyridine), for which values between
2.1 and 2.23 V were determined for the HOMO–LUMO
gap.[34] As already outlined in the literature,[18] the strongly
domed structure of Bi–corrole complexes might be the
reason for the smaller HOMO–LUMO gap of the Bi–cor-
roles studied herein.
Table 5. Summarized electrochemical behavior of selected Bi–cor-
role complexes in MeCN solution with 0.1 m tetrabutylammonium
hexafluorophosphate (TBAPF6) referenced against SCE.
1st oxi-
dation
2nd oxi-
dation
1st re-
duction
Δ(HOMO–
LUMO)
Bi(TpFPC)[18]
2
0.66
0.50
0.46
0.47
0.46
0.49
0.50
0.45
0.48
0.51
0.53
0.52
1.07
0.98
0.94
0.95
0.94
0.95
0.98
0.98
0.95
0.98
0.98
0.97
–1.28
–1.30
–1.35
–1.32
–1.34
–1.31
–1.20[a]
–1.33
–1.38[a]
–1.31
–1.28
–1.30
1.94
1.80
1.81
1.79
1.80
1.80
1.70
1.78
1.86
1.82
1.81
1.82
3a
3b
3c
3d
3f
3g
3h
3i
3j
3k
[a] Denotes irreversible reduction.
Conclusion
In conclusion, we presented a versatile protocol for Su-
zuki cross-coupling on a Bi–corrole complex, whereby a
variety of functional groups and sterically demanding side
Figure 3. Spectral changes during the electrochemical oxidation of
3c at (A) 0.75 and (B) 1.2 V.
Earlier, we hypothesized that the two consecutive electro- groups could be introduced under very mild conditions with
chemical oxidation reactions of Bi(TpFPC) are both ring- good yields. Later, the first examples of Pd-catalyzed C–N
centered processes, reasoned by the rather low oxidation coupling on the same corrole complex were demonstrated
potentials, which would have been quite atypical for an oxi- with different classes of amines and aromatic aniline deriva-
dation of BiIII to BiIV or BiV, especially in terms of the tives. Both Suzuki- and C–N coupled Bi complexes were
strong inert pair effect of the Bi 6s electrons.[18] Thus, to also demetalated by employing a gentle and high-yielding
further clarify the site of electrochemical oxidation, spectro- demetalation procedure.
electrochemical measurements of the multichromophore
With the help of 19F NMR spectroscopy and quantum
compound (3c), which has an attached naphthyl unit, are chemical calculations, dome-shaped structures were pro-
shown in Figure 3. During the first oxidation (Figure 3, A), posed for the Bi-metalated corrole derivatives. The mecha-
the Soret and Q bands decrease significantly as a new band nism of electrochemical oxidation and reduction were
emerges at 750 nm. This behavior is characteristic of the studied with cyclic voltammetry and spectroelectrochemis-
formation of a π-radical cation.[26] The second oxidation is try and were most exclusively found to be reversible ring-
also assigned as a ring-centered process, which leads to a centered processes.
dication as the radical pattern disappears and again only
As a consequence of this study, we have opened up a
the Soret and Q bands are altered. During these reversible synthetic method to insert a chemically and physiologically
processes, the absorption bands of the naphthyl subunit rather inert metal ion into the corrole ring system, which
consequently remain nearly unaltered. Very similar spectro- protects the inner N atoms of the corrole macrocycle during
electrochemical behavior was found for all the Bi–corroles the reaction conditions discussed above. This stabilization
studied herein (Figures S38–S40 in the Supporting Infor- by weak coordination facilitates the functionalization, and
mation), which implies similar oxidation mechanisms. As the weakness of the coordination can be used to sub-
summarized in Table 5, the corresponding HOMO–LUMO sequently demetalate the BiIII–corrole complex in a weak
gap also does not vary significantly within the group of the acidic medium. The ease of this demetalation procedure re-
Bi-metalated A2B corroles and is smaller than for opens possible metalation reactions of the corrole ring cen-
Bi(TpFPC). This stands in contrast to most other main- ter with other more reactive metal ions.
6
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exact initial weight of the starting materials are listed for each prod-
uct).
Experimental Section
General: 10-(4-Bromophenyl)-5,15-bis(pentafluorophenyl)corrole
General Procedure for Demetalation Reactions: The corresponding
Bi-metalated corrole derivative was dissolved in THF (10 mL), and
HCl (1 mL, 0.15 mol) was added dropwise to the solution under
vigorous stirring. After 15 min, dichloromethane (20 mL) was
added to the solution, which was then washed with water twice.
The solution was dried with anhydrous Na2SO4 and the solvent
evaporated. Final purification of the product was achieved by me-
ans of column chromatography (eluents as well as the exact initial
weight of the starting materials are listed for each product).
[35]
(1)[12] and Bi{N(SiMe3)2}3
were prepared according to estab-
lished protocols.
All chemicals were purchased from Sigma Aldrich, Acros chemi-
cals, or Alfa Aesar and used without further purification. Reagent-
grade solvents were purchased from Fischer chemicals and distilled
prior to use. THF was distilled from sodium and benzophenone
under an argon atmosphere and stored over molecular sieves (4 Å)
upon use. TLC was performed by using Fluka silica gel (0.2 mm)
on aluminum plates. Silica-gel columns for chromatography were
prepared with silica gel 60 (0.060–0.20 mesh ASTM) from Acros.
Proton (1H NMR) and carbon (13C NMR) spectra were recorded
with a Bruker DRX 500 spectrometer equipped with a cryogeni-
cally cooled probe (TXI), or with a Bruker Avance 300 MHz spec-
trometer. 19F NMR spectra were recorded with a Bruker Avance
300 MHz spectrometer operating at 282.4 MHz. The chemical
shifts are given in parts per million (ppm) on the delta scale (δ)
and are referenced to the residual nondeuterated solvent for 1H
and TFA for 19F. Mass spectra were collected with a Finnigan LCQ
DecaXPplus ion-trap mass spectrometer with an ESI ion source,
and MALDI-ToF measurements were collected with a Bruker Au-
toflex III Smartbeam spectrometer. UV/Vis absorption spectra
were measured with a Varian CARY 300 Bio spectrophotometer.
Cyclic voltammetry (CV) was carried out under inert conditions in
a glovebox with an Eco Autolab type potentiostat with a home-
made three-electrode cell that consisted of a platinum working elec-
trode, a platinum wire as a counter electrode, and a silver/silver-
chloride pseudoreference electrode. Ferrocene was employed as in-
ternal standard for potential referencing, and the potentials were
subsequently referenced versus SCE accordingly.[36] Spectroelectro-
chemistry was performed in an optically transparent thin-layer elec-
trode (OTTLE) cell[37] with platinum working electrode, a platinum
wire as a counter electrode, and a silver reference electrode. The
corresponding UV absorption spectra were collected with a Jasco
V670 spectrometer.
MALDI-ToF Mass Spectrometry: All spectra were recorded with a
Bruker Autoflex III Smartbeam using the reflectron mode.
Dithranol was used as matrix, and to enable accurate mass determi-
nation an internal standard of polyethylene glycol (PEG) 1000 was
used. Sample preparation was as follows: A solution of PEG
(10 mgmL–1) in THF (5 μL) and a solution of the sample (ca.
10 mgmL–1) in methanol (5–10 μL ) were added to a solution of
dithranol (10 mgmL–1) in THF (50 μL), mixed thoroughly, and
then an aliquot (0.5 μL) was transferred onto a stainless steel tar-
get. For each sample at least 800 spectra were recorded at different
positions and calibration was performed using the sodium ions of
PEG.
Supporting Information (see footnote on the first page of this arti-
cle): Compound data, experimental details, NMR spectra, and cy-
clic voltammogramms.
Acknowledgments
Financial support of this work by the Austrian Science Fund (FWF
project P18384, “Solid state and Liquid NMR of Biomolecular
Metal Complexes”) is gratefully acknowledged. The NMR spec-
trometers were acquired in collaboration with the University of
South Bohemia (CZ) with financial support from the European
Union through the EFRE INTERREG IV ETC-AT-CZ program
(project M00146, “RERI-uasb”). The authors would like to thank
Dr. Manuela List and Dr. Klaus Bretterbauer for the measurement
of ESI-MS and MALDI-MS spectra.
General Procedure for the Suzuki Cross-Coupling Reactions:
Bi-5,15-bis(pentafluorophenyl)-10-(4-bromophenyl)corrole
(2)
(1 equiv.), K3PO4 (2 equiv.), and the corresponding boronic acid or
ester derivative (2.5 equiv.) were placed in a Schlenk tube and dis-
solved in a degassed THF/H2O mixture (2:1) (8 mL). The solution
was purged with N2 for a further 30 min, followed by the addition
of 5 mol-% SPhos and 2.5 mol-% Pd(OAc)2. The Schlenk tube was
sealed, and the reaction mixture was stirred for 24 h (unless not
otherwise noted). After completion, the reaction mixture was ex-
tracted with CH2Cl2, washed with water twice, and dried with an-
hydrous Na2SO4, followed by evaporation of the solvent. The crude
product was purified by means of column chromatography (eluents
as well as the exact initial weight of the starting materials are listed
for each product).
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. M. Reith, M. Koenig, C. Schwarzinger, W. Schoefberger
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Received: June 25, 2012
Published Online: ᭿
8
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Eur. J. Inorg. Chem. 0000, 0–0

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Date: 13-08-12 16:27:31
Pages: 9
BiIII–Corroles
Metallocorroles
L. M. Reith, M. Koenig, C. Schwarzinger,
W. Schoefberger* .............................. 1–9
BiIII–Corroles: A Versatile Platform for the
Synthesis of Functionalized Corroles
Keywords: Synthetic methods
/ Macro-
cycles / Corrole / Nitrogen heterocycles /
Bismuth / Cross-coupling / Demetalation
The BiIII ion in the center of the corrole
macrocyclic ring system was employed to
stabilize and protect the corrole inner core
during the functionalization at the periph-
ery (meso positions) of the π-conjugated
ring system. The ease of demetalation
makes BiIII–corroles attractive candidates
for functionalization and subsequent deme-
talation to the free-base corroles.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
9