Corroles: The Hitherto Elusive Parent Macrocycle and its Metal Complexes

Article abstract of DOI:10.1002/anie.202110964

Corroles, macrocycles that owe their name to the cobalt-chelating prosthetic group of vitamin B12 and share numerous features with the iron-chelating porphyrin present in heme proteins/enzymes, constantly cross new boundaries ever since stable derivatives became easily accessible. Particularly important is the increasing utilization of corroles and the corresponding metal complexes for the benefit of mankind, in terms of new drug candidates for treating various diseases and as catalysts for sustainable energy relevant processes. One challenge is to gain access to the plain macrocycle, as to allow for full elucidation of the most fundamental properties of corroles. We have obtained the substituent-free corrole by several surprising and conceptually different pathways. Selected features of the corresponding metal complexes are illuminated, for pointing towards unique phenomena that are anticipated to largely expand the horizon regarding their utilization for contemporary catalysis.

Full text of DOI:10.1002/anie.202110964

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Corroles: The Hitherto Elusive Parent Macrocycle and its Metal
Complexes
Authors: Zeev Gross, Amit Kumar, Pinky Yadav, Mahmoud
Majdoub, Irena Saltsman, Natalia Fridman, Anil Kumar, Atif
Mahammed, and Sachin Kumar
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Angewandte Chemie International Edition
RESEARCH ARTICLE
Corroles: The Hitherto Elusive Parent Macrocycle and its Metal
Complexes
Amit Kumar,[a],# Pinky Yadav,[a],# Mahmoud Majdoub,[a],# Irena Saltsman,[a] Natalia Fridman,[a] Sachin
Kumar,[a] Anil Kumar, [a],[b] Atif Mahammed,*[a] and Zeev Gross*[a]
[a]
Dr. A. Kumar, Dr. P. Yadav, M. Majdoub, Dr. I. Saltsman, Dr. N. Fridman, S. Kumar, Prof. Dr. A. Kumar, Dr. A. Mahammed, Prof. Dr. Z. Gross
Schulich Faculty of Chemistry
Technion – Israel Institute of Technology
Haifa 32000 (Israel)
E-mail: chatif@technion.ac.il; chr10zg@technion.ac.il
Prof. Dr. A. Kumar
Department of Applied Chemistry
Delhi Technological University
Delhi 110042 (India)
[b]
[#]
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.
catalysts for clean and renewable energy processes.[4] Regarding
the last aspects, we became increasingly involved in the design
of optimally performing corroles by focusing on affecting
Abstract: The science and technology of corroles, macrocycles that
owe their name to the cobalt-chelating prosthetic group of Vitamin B12
and share numerous features with the iron-chelating porphyrin
present in heme proteins/enzymes, constantly crosses new
boundaries ever since stable derivatives became easily accessible.
Particularly important is the increasing utilization of corroles and the
corresponding metal complexes for the benefit of mankind, in terms
of new drug candidates for treating various diseases and as catalysts
for sustainable energy relevant processes. One still unmet challenge
is to gain access to the plain macrocycle, as to allow for a full
elucidation of the most fundamental properties of corroles. We now
report the success in obtaining the substituents-free corrole, by
several surprising and conceptually different pathways. Selected
features of the corresponding metal complexes are illuminated, for
pointing towards unique phenomena that are anticipated to largely
expand the horizon regarding their utilization for contemporary
catalysis.
photophysical and electrochemical properties via hypothesis-
5]
driven approaches.[4f,
Our current motivation for preparing
minimally substituted corroles is that while the meso-aryl groups
present in the traditionally used derivatives (H3(tArc) in Scheme
1) are extremely important for homogeneous catalysis, that is not
necessarily the case for heterogenous catalysis. This may be
exemplified by the procedure required for preparation of
metal/nitrogen doped carbon electrodes that are almost as
efficient as non-sustainable platinum in catalyzing the oxygen
reduction reaction of fuel cells. Both natural and synthetic
porphyrins are commonly used as precursors for the pyrolysis
process, during which their substituents are removed at about 600
˚C. Such treatment is obligatory for carbonization, the process
upon which the metal-chelating N4 coordination becomes part of
the porous carbon material that is used for catalysis.[6] Our
hypothesis was that starting with substituent-free corrole would
eliminate the need of pyrolysis and eventually allow for a much
better control of the number and identity of catalytically active
sites. We note that the cobalt(III) complex of plain corrole was
reported almost 50 years ago but never used for any application
and that surprisingly little has been done with the substituent-free
porphyrin (porphine), focusing mainly on electroplymerization.[7]
Last, but certainly not least, is the scientific curiosity of studying
the fundamental properties of the parent corrole, i.e., with no
substituents whatsoever on the macrocycle.
Introduction
Corroles were first introduced in the early 1960’s, coinciding with
Dorothy C. Hodgkin being awarded the Noble Prize that
recognized her achievement in determining the structure of
Vitamin B12.[1] That raised the interest in corroles, which may be
considered the aromatic version of the cobalt-chelating
macrocycle corrin that serves as the prosthetic group of this
vitamin or, alternatively, as porphyrin analogs with a contracted
and tri- rather than di-anionic N4 coordination core. Hodgkin was
in fact the person who reported the first X-ray structure
determination of a metal-free corrole; and this remained the sole
example for more than 30 years.[2] This does not reflect lack of
interest in this class of compounds, since there was never any
doubt that the photophysical properties of corroles and the unique
redox reactions of the corresponding metal complexes are of high
relevance for numerous applications. It rather serves as a
testimony for how severe obstacles regarding the synthesis of
corroles limited development to two annual publications by
average, zero patents and no utilization in any practical field. The
situation improved dramatically only in 1999, upon the disclosure
of facile one-pot syntheses of 5,10,15-triarylcorroles (H3(tArc),
Scheme 1) from obvious building blocks.[3] This initiated
worldwide efforts in introducing such molecules and their
corresponding metal chelates as key elements for the most urgent
needs of modern society. Representative examples are corrole
metal complexes for bioimaging and agriculture, as potential drug
candidates for many diseases, and as photo- and electro-
1
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metallated corroles requires good access to (tcc)M complexes,
which is not always the case; and c) both routes rely on two-steps
procedures from stable starting compounds (e.g., H3(tcc) or
(tcc)Ga). Of particular relevance regarding the need for an
alternative approach is that (tfc)Co and (tfc)Re(O) could actually
not be hydrolyzed to (tcc)Co and (tcc)Re(O).[9]
Scheme 1. Structures of the longest known octaalkylcorroles H3(oRc), the most
intensively investigated meso-triarylcorroles H3(tArc), and the most recently
introduced tris-carboxylated corrole H3(tcc) that served as one synthetic
precursor for accessing the completely non-substituted corrole H3(cor) that is
reported only now. All these corroles efficiently chelate elements in their +3 or
higher oxidation state via their deprotonated N4 coordination core, forming
(oRc)M, (tArc)M, (tcc)M) and (cor)M complexes. Representative examples for
M are manganese(III), iron(III), cobalt(III), gallium(III), (oxo)molybdenum(V),
and (oxo)rhenium(V).
Scheme 2. The synthetic approaches towards the non-substituted corrole
H3(cor) and its corresponding metal complexes (cor)M, wherein M stands for
either gallium(III), (oxo)rhenium(V) or (oxo)molybdenum(V). Chemical yields
are only reported for the last two metal complexes.
Considering all the above, efforts were first devoted to the
preparation the low-spin d2 (oxo)rhenium(V) and d6 cobalt(III)
corroles. Characterization of such diamagnetic complexes may
safely be expected to be easier; and the latter complex is of large
relevance for alternative-energy related catalysis. The first
approach was to heat H3(tcc) in the inert and high boiling solvent
decalin, in the presence of Re2(CO)10. The hypothesis was that
decarboxylation will take place at elevated temperature and that
the thus produced H3(cor) will undergo metalation in situ. This was
the case indeed, as was first easily evaluated by naked eye. The
initially colorless solution, due to insolubility of H3(tcc) in decalin,
started to become colored within 30 minutes at 150 ˚C and
Re2(CO)10 was added 1 hour later when all solid material
dissolved. The targeted complex, isolated in 18% yield, was easily
identified as (cor)Re(O) by its 1H NMR spectrum (Figure 1B) and
it appeared to be completely stable when stored at ambient
conditions in both the solid state and in solution. Encouraged by
the simplicity of that approach, the (oxo)molybdenum(V) corrole
(cor)Mo(O) was obtained in a similar fashion (in 26% yield), with
Mo(CO)6 as the metal source.
A conceptually different approach was developed for the
preparation of the cobalt(III) complex, relying on the quite good
access to non-substituted oligopyrromethanes (tri-, tetra- and
penta-pyrromethanes) via the microwave-assisted reaction
between pyrrole and formalin.[12] While the ultimate goal of those
earlier studies was to use these compounds as precursors to
H3(cor), only porphine (the trivial name of the parental (i.e., non-
substituted) porphyrin) and a meso-pyrrole-substituted porphyrin
were obtained.[12] We have now upscaled the reaction conditions
of the first step as to obtain the non-substituted tetrapyrromethane
(TPM, Scheme 3) in larger amounts (about 1.3 gram per day).
This allowed for the renewed efforts of using TPM for the
synthesis of the non-substituted corrole, while considering the
instability of the target free-base H3(cor) under the oxidizing
conditions that are essential for its formation from TPM. The
approach adopted for resolving this synthetic problem was to
perform oxidation and metallation in a one-pot fashion. On top of
profiting from the much higher stability of metallocorroles towards
oxidants, a possible template effect for the cyclization by the
cobalt ion was also considered. These investigations started with
Results and Discussion
We have most recently introduced a largely improved synthesis
of the corrole substituted by only CF3 substituents on the three
meso-C atoms (5,10,15-tris(trifluoromethyl)corrole, H3(tfc)),[8]
followed by discovering its highly facile hydrolysis to the water-
soluble tris-carboxylated derivative H3(tcc) (Scheme 1).[9] The
same route worked equally well for the corresponding
manganese(III), iron(III), gallium(III) and phosphorous(V)
complexes. Given these developments, we have now decided to
check decarboxylation of H3(tcc) and/or its metal complexes as a
viable route to the yet elusive H3(cor) (Scheme 1) and a large
variety of its corresponding metal complexes.
The rather unsophisticated approach of subliming H3(tcc) for
inducing decarboxylation was met with success, as may be
appreciated by the UV-vis spectrum of the thus produced H3(cor)
(Figure S7). However, while the good news is that the elusive
parent corrole was finally obtained and by a facile pathway,
H3(cor) appeared to be of quite limited stability to ambient
humidity and light exposure. This came as no surprise,
considering that electron-withdrawing substituents are required
for reducing the π-system electron richness of the corrole
macrocycle.[4c] Bearing in mind that metal chelation stabilizes
corroles very much,[10] the analogous procedure was performed
on the gallium(III) complex of H3(tcc). Sublimation of (tcc)Ga
produced (cor)Ga indeed (Scheme 2), which was characterized
as the mono-pyridine complex by dissolving the sublimed material
in pyridine-containing benzene. Its 1H NMR spectrum (Figure 1A)
clearly discloses all CH protons of the corrole: 2 meso-H’s at 9.8
and 9.6 ppm in the proper 2:1 respective ratio and the four
couples of β-pyrrole H’s as doublets with corrole-characteristic J-
coupling constants of 3.7 – 4.2 Hz.[11] The stability to ambient
conditions of (cor)Ga was much larger than that of the free-base
H3(cor), as long as pyridine (or other ligands) are bound to the
gallium(III) center. These encouraging achievements also
exposed the limitations that must be resolved for gaining access
to a large variety of other metal complexes, considering that: a)
metallation of preformed H3(cor) is problematic because of its
limited stability; b) performing decarboxylation on the already
2
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cobalt, the perfect match for corroles,[7d] by treating TPM with
cobalt acetate in pyridine, which is the best solvent for metallation
of corroles and stabilizes metallocorroles by serving as ligand for
saturating the coordination sphere of the central metal ion. In
terms of chemical yield from very simple and cheap starting
material and the amount of isolated material this approach was
most rewarding, providing 22 mg (cor)Co(py)2 from 90 mg TPM
within a few hours. Cyclization of TPM was performed both with
and without adding mild oxidizing agents, revealing that the
desired product was formed even in the latter case, albeit in only
3% chemical yield (most of the TPM remained unreacted). Using
3
mol/equivalents of either (diacetoxy)iodobenzene or the
fluorinated analog [bis(trifluoroacetoxy)iodo]benzene (PIFA)
induced a significant increase in the yields. In the latter case, the
target complex was isolated in its 6-coordinate form with two axial
pyridine ligands, i.e., (cor)Co(py)2, in a chemical yield of 15%. All
the starting TPM was consumed in this reaction, but the many
other byproducts were not analyzed yet. The axial pyridines could
easily be replaced by triphenylphosphine, either before or after
purification of (cor)Co(py)2, leading to the 5-coordinate
(cor)Co(PPh3) in 8% yield relative to TPM in the latter case. The
1H NMR spectra of (cor)Co(py)2 and (cor)Co(PPh3) are presented
in Figures 1C and 1D, respectively, with a full analysis for the
latter complex as described later.
Scheme 3. One-pot synthesis of (cor)Co and (cor)Mn via one-pot oxidative
cyclization of TPM and metalation by cobalt(II) or manganese(II) acetate
tetrahydrate; and the preparation of the diamagnetic (cor)Mn(N) by nitrogen
atom transfer from (salen)Mn(N) to the paramagnetic (cor)Mn.
Figure 1. 1H NMR spectra (400 MHz, in C6D6) of the meso and β-pyrrole
protons of A) (cor)Ga(py); B) (cor)Re(O); C) (cor)Co(py)2; D) (cor)Co(PPh3),
including the complete assignment of the 1H chemical shifts of the corrole
macrocycle; and E) (cor)Mn(N).
Scheme 4. Preparation of (dfc)Ga(py)2 by metalation of H3(dfc) with
a
reasonable excess of GaCl3 (route i) and of (cor)Ga(py) by either treating H3(dfc)
with large excess of GaCl3 (route ii) or by heating a pyridine solution of (tcc)Ga
(route iii). The X-ray crystal structure of (dfc)Ga(py)2 is also presented (all H
atoms have been omitted for clarity).
Similar success was obtained in the oxidative cyclization of TPM
in the presence of manganese(II) acetate in pyridine, affording
(cor)Mn in 8% yield (Scheme 3). Its electronic spectrum revealed
the characteristic of MnIII corroles: strongly split near UV (Soret)
bands and a charge-transfer band at 478 nm (in EtOAc, Fig. S14).
Considering the difficulties in characterization of the d4 (cor)Mn
complex[13], it was converted to the MnV (low-spin d2) oxidation
state via treatment with (salen)Mn(N) in methanol solution
(Scheme 3).[14] This very effective nitrogen atom transfer reaction
yielded the diamagnetic (nitrido)Mn(V) corrole, (cor)Mn(N),
characterized by 1H NMR spectroscopy [(Figure 1E).
3
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radiative decay rates of the singlet-excited state is less large for
(tpfc)Ga.
1
One outstanding feature of the new complexes is that all the H
NMR resonances could be assigned with full confidences, as
exemplified for (cor)Co(PPh3) (Figure 1D and S23). In short, the
C10-H atom (Hf) experiences long range 4J coupling with the C8-
H/C12-H (He) atoms, which are strongly coupled to their vicinal
C7-H/C13-H (Hd) atoms. All other resonances were similarly
assigned to specific H atoms, an achievement for which is hardly
any prior art in the field and none for corroles with a C2 symmetry
axis.[15]
Figure 2. 1H NMR spectra (400 MHz, in C6D6) of the meso and β-pyrrole protons
of A) H3(dfc); B) (dfc)Ga(py)2, which was obtained by reacting H3(dfc) with small
excess of GaCl3; and C) (cor)Ga(py), which was obtained by reacting H3(dfc)
with large excess of GaCl3.
Still another route was discovered when the recently reported
5,15-bis-CF3-substituted corrole H3(dfc)[9] was treated with GaCl3.
The expected (dfc)Ga(py)2 (1H NMR and X-ray structure
displayed in Figure 2 and Scheme 4) was obtained when a
reasonable excess (10 equivalents) of GaCl3 was used, but
(cor)Ga(py) was formed when a very large excess of the metal
salt was utilized (Scheme 4, routes i and ii, respectively). Clues
for the origin of this surprising phenomenon were obtained by the
following experiments: a) heating of the gallium complex of the
tris-carboxylated corrole (tcc)Ga in pyridine or decalin did provide
(cor)Ga(py) even in the absence of GaCl3 (Scheme 4, route iii);
treatment of either H3(tfc) or (tfc)Ga with excess GaCl3 in hot
pyridine did not lead to (cor)Ga(py); and c) the same holds true
when already isolated (dfc)Ga(py)2 was treated under the same
conditions that were successful for the free-base H3(dfc) (Scheme
4, route ii). These results suggest that the one-pot C-CF3 to C-H
transformation requires hydrolysis to proceed prior to metalation.
This is apparently more facile for the bis-CF3 substituted corrole,
likely because its non-substituted C10 position increases the
chance for hydrolysis via attack on the remote (from CF3) carbon
atom.[9]
Figure 3. The X-ray structures of the (oxo)molybdenum(V), (oxo)rhenium(V),
(pyridine)gallium(III), (bis-pyridine)cobalt(III) and (triphenylphosphine)cobalt(III)
complexes of the completely non-substituted corrole (All H atoms have been
omitted for clarity).[16]
The stability of the (cor)M complexes allowed for their full
characterization by X-ray crystallography (Figure 3 and Table S2).
The trans-bis-pyridine coordinated (cor)Co(py)2 displays
a
practically planar corrole, in which the cobalt ion deviates only
0.003 and 0.002 Å from the planes defined by the four chelating
nitrogen atoms and by the 23-core atoms, respectively. This is
distinctively different from the 5-coordinate (cor)Co(PPh3),
(cor)Ga(py), (cor)Re(O) and (cor)Mo(O) complexes wherein the
corrole is domed and the out of the N4 plane displacements of the
metal ion towards the single axial ligand are 0.278, 0.391, 0.688
and 0.736 Å, respectively. Inspection of Table S3, wherein data
from the same metal ions chelated by the corroles with either CF3,
C6F5, or H on the meso-C atoms is compiled, does disclose similar
structural features for all of them. That comparison also reveals
that the average metal-Npyrrole bond lengths in (cor)M are shorter
by 0.002 - 0.024 Å, relative to those present in the CF3- and C6F5-
substituted corroles. This finding testifies for stronger metal
chelation by the less electron-withdrawing corrole. Supporting
and independent evidence for the last conclusion is provided by
cyclic voltammetry, exemplified by the redox potentials of
(cor)Co(PPh3), (tpfc)Co(PPh3) (tfc)Co(PPh3) being -2.04, -1.74,
and -1.55 V vs. Fc/Fc+, respectively. This data is not of pure
scientific interest only, but also of large potential relevance for
electrocatalysis.
Bearing in mind that porphyrins are considered as the pigments
of life, and also that corroles are actually more fluorescent than
porphyrins, raised the interest in examining the effect of H vs. CF3
vs. C6F5 meso-C-substituents on the absorption and emission
spectra of (cor)Ga, (tfc)Ga and (tpfc)Ga. These comparisons,
performed in pyridine as solvent for assuring that all complexes
will be 6-coordinate with two trans-pyridine ligands (Fig. S16),
uncovered that: a) the largest differences appear in the near-UV
absorbances (termed Soret bands), which appear at highest
energy (max = 407 nm) for (cor)Ga, followed by (tfc)Ga and
(tpfc)Ga which are significantly more red-shifted (max = 426 and
428 nm, respectively); b) the differences are smaller regarding the
Considering the vast knowledge accumulated in the last two
decades regarding the advantages of (much larger) porphyrinoids
as molecular catalysts, whose activity is boosted by annealing
them onto carbon material by very high temperature pyrolysis, we
predicted that the current synthetic breakthrough might be
transformative regarding electrocatalysis and related applications.
Preliminary results supportive of these expectations were
obtained by adsorbing the (cor)M complexes, with M= Co(PPh3),
Co(py)2, Re(O), or Mo(O), onto Vulcan XC72R carbon by adding
the latter to isopropanol solutions of the former. In all cases, the
(cor)M complexes were adsorbed faster and to much larger
lowest-energy electronic transitions (termed Q bands), with max
=
596, 594, and 610 nm for (cor)Ga, (tfc)Ga and (tpfc)Ga,
respectively; c) the maximum fluorescence wavelengths of
(cor)Ga and (tfc)Ga are almost identical (longer by 2 nm for the
former) and shorter by about 20 nm relative to (tpfc)Ga; and d)
the relative fluorescence quantum yields are 1.00, 0.38, and 0.50
for (tpfc)Ga, (tfc)Ga and (cor)Ga, respectively (Fig. S16 and Table
S1). This data allows for the conclusion that the HOMO-LUMO
gap in (cor)Ga is higher than that of (tpfc)Ga and similar to that of
(tfc)Ga; and that, quite surprisingly, the ratio of radiative vs. non-
4
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RESEARCH ARTICLE
degree compared to the C6F5- and CF3- reported corroles (Figure
4 for M = Mo(O) and Figs. S17-S19 for other metal complexes).
The adsorbed amounts of the catalysts were calculated by
comparing the UV-Vis spectra of their original solutions before
and after the addition of the carbon, revealing that all the (cor)M
were totally adsorbed on the Vulcan XC72R carbon. In fact, the
intensively colored (cor)M solutions became completely colorless
within < 30 minutes after the addition of the carbon nanoparticles.
Figure 5. A) Cyclic voltammograms of Vulcan XC72R carbon only (red),
(cor)Mo(O) adsorbed onto Vulcan XC72R carbon (blue), and 20% Pt adsorbed
onto Vulcan XC72R carbon (pink) as the solid support, in 0.5 M H2SO4 solution
and under nitrogen. Scan rate: 50 mV/s, Ag/AgCl and Pt wire were used as
reference and counter electrodes, respectively. B) Charge curve of (cor)Mo(O)
adsorbed onto Vulcan XC72R carbon during 15 hr of bulk electrolysis at applied
potential of −0.8 V. C) H2 generation in the form of bubbles on the surface of
glassy carbon electrode modified by (cor)Mo(O) after 10 min of bulk electrolysis
at applied potential -0.8 V.
Figure 4. Results obtained by spontaneous adsorption (examined after 30 min
for (cor)(Mo(O), and after 12 hr. for the others) from solutions of (tfc)Mo(O),
(tpfc)Mo(O), or (cor)Mo(O) (0.8 mg each, in 1 mL isopropanol), checked by
recording the UV-vis spectra of the solutions before (blue) and after (red) the
addition of a Vulcan XC72R carbon (10 mg) (A-C).
The carbon modified by (cor)Mo(O) was adsorbed on the surface
of glassy carbon electrodes in order to check its ability to reduce
protons to hydrogen. Figure 5A shows the performance of Vulcan
XC72R carbon only (red) relative to (cor)Mo(O) and 20% Pt
adsorbed onto XC72R (blue and pink, respectively) as the solid
support, in 0.5 M H2SO4 solution and under nitrogen. (cor)Mo(O)
Conclusion
We introduce the parent corrole with no substituents whatsoever,
as well as several elemental ions chelated by it. This dream come
true triumph became permissible due to a combination of several
novel discoveries that include -CF3 hydrolysis, facile
decarboxylation reactions, and metal-assisted cyclization. Also
presented are some of the many predictable advantages of these
compounds/complexes: extremely strong bonding to solid
surfaces, excellent performance as electrocatalysts for proton to
hydrogen reduction, and the facile sublimation of the metal
complexes of unsubstituted corrole.
shows very good catalytic activity with only
a 280 mV
overpotential (Figure 5A), and electrocatalytic stability for more
than 15 hours (Figure 5B). Clearly visible bubbles of H2 gas were
generated on the surface of the electrode upon bulk electrolysis
at applied potential of -0.8 V (vs. Ag/AgCl) (Figure 5C).
Quantification of the thus generated hydrogen gas was performed
by gas chromatography, leading to the conclusion that (cor)Mo(O)
is a very effective catalysts for proton reduction with a Faradaic
efficiency (FE) of 92%.
Another aspect, which is predicted to become important in future
utilization of (cor)M complexes for electrocatalysis and many
other purposes, was briefly addressed by heating solid
(cor)Co(PPh)3 in a simple Kugelrohr apparatus under the quite
weak vacuum of 40 mTorr. This revealed that it was sublimed
without decomposition at 220 ℃, in sharp contrast with both
porphyrins and phthalocyanines for which much higher
temperatures and ultrahigh vacuum (10-5-10-9 Torr) are normally
applied.[17] The combination of low molecular weight and absence
of macrocycle substituents in (cor)M complexes are the apparent
reasons for this feature; and this paves the way for introducing
such complexes for many advanced applications.
Acknowledgements
This research was supported by the Israel Science Foundation (to
Z.G.).
Conflict of interest
The authors declare no conflict of interest.
Keywords: corroles • molybdenum • cobalt • one-put-synthesis •
hydrogen-evolution-reaction
5
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6
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10.1002/anie.202110964
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
11.062 Å
17.887 Å
8.508 Å
1999
2018
2021
Following the impact of the previous century’s latest year discovery of triarylcorroles and the more recently described CF3-substituted
corroles, is the now described development of three synthetic routes to the completely unsubstituted corrole. This already allowed for
the introduction of five fully characterized metal complexes chelated by this corrole, which were used for starting to uncover unique
beneficial features that are relevant to clean energy catalysis and many other purposes.
7
This article is protected by copyright. All rights reserved.