A 6,11,16-Triarylbiphenylcorrole with an adj-CCNN Core: Stabilization of an Organocopper(III) Complex

Article abstract of DOI:10.1002/anie.201503347

An adj-dicarbacorrole with CCNN in the core is achieved by replacing the bipyrrole moiety by a simple polycyclic aromatic hydrocarbon, such as biphenyl unit. Spectroscopic studies and structural analyzes confirm the absence of macrocyclic aromatization, thus leading to overall nonaromatic character. The trianionic core is effectively utilized to stabilize a copper(III) ion to form an organocopper complex.

Full text of DOI:10.1002/anie.201503347

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International Edition: DOI: 10.1002/anie.201503347
German Edition: DOI: 10.1002/ange.201503347
Dicarbacorrole
A 6,11,16-Triarylbiphenylcorrole with an adj-CCNN Core:
Stabilization of an Organocopper(III) Complex**
B. Adinarayana, Ajesh P. Thomas, Cherumuttathu H. Suresh, and A. Srinivasan*
Dedicated to Professor T. K. Chandrashekar
Abstract: An adj-dicarbacorrole with CCNN in the core is
achieved by replacing the bipyrrole moiety by a simple
polycyclic aromatic hydrocarbon, such as biphenyl unit.
Spectroscopic studies and structural analyzes confirm the
absence of macrocyclic aromatization, thus leading to overall
nonaromatic character. The trianionic core is effectively
utilized to stabilize a copper(III) ion to form an organocopper
complex.
2) provides information about the nature of porphyrinoids
aromaticity; and 3) generates organometallic complexes with
unusual oxidation states.[2–13] Depending on the nature of the
aromatic subunits in the framework, the degree of aromaticity
varies. For example, benzocarbaporphyrins[7] are highly
aromatic; azuli derivatives[8] are weakly aromatic, whereas
the m-benziporphyrin (2)[4b] is nonaromatic. However, com-
pared to monocarbaporphyrinoids, only limited number of
dicarbaporphyrinoids with cis- or adj-CCNN and trans- or
opp-CNCN in the core is known. This includes aromatic cis-
and trans-doubly N-confused porphyrins, which form organo-
CuIII and AgIII complexes.[14] Among the dicarbaporphyrins
with opp-two indene units,[15] opp-[16a]/adj[16b,c]-azulene and
indene units, and adj-diazuli derivatives,[17] only the last two
macrocycles are stable. Recently reported stable aromatic
adj-dicarbaporphyrins with two indene units forms a tripalla-
dium sandwich complex.[18] The very recently described
phenanthriporphyrin with adj-CCNN in the core is an
antiaromatic aceneporphyrinoid, which affords a hypervalent
organophosphorus(V) complex.[19]
T
he porphyrin 1 is highly aromatic and contains 18p
electrons in the delocalization pathway with a NNNN
core.[1] Carbaporphyrinoid is a porphyrin analogue in which
one or more nitrogen atoms in the porphyrin core is replaced
by carbon atoms and receiving much attention in recent
On the other hand, by removing one of the meso carbon
atoms in the framework of porphyrin 1 leads to contracted
porphyrinoids such as corrole 3 (NNNN), which stabilizes the
unusually high-oxidation-state transition-metal complexes.[20]
As compared to monocarbaporphyrinoids, the number of
monocarbacorroles (CNNN) is fewer, and these include
isocarbacorrole,[21] the series of N-confused corroles,[22] nor-
role, and benzocorrole.[23] The non-aromatic isocarbacorrole
stabilizes organo-CuIII and AgIII complexes,[21] while the
aromatic N-confused corroles bind effectively with
anions.[22] However, the next level in the carbacorrole
chemistry, dicarbacorrole with the core containing adj-
CCNN or opp-CNCN framework is not known to date.
Such a macrocycle would have an ideal platform to stabilize
higher-oxidation-state organometallic complexes, as observed
in the porphyrin analogues. Herein, we wish to report the
synthesis of an adj-dicarbacorrole with CCNN in the core,
years.[2] Research has mainly focused on monocarbaporphyr-
inoids with CNNN in the core, which includes N-confused
porphyrins,[3] benziporphyrins,[4] oxybenziporphyrins,[5] tropi-
porphyrins,[6] benzocarbaporphyrins,[7] azuliporphyrins,[8] N-
confused pyriporphyrins,[9] O- and S-confused heteroporphyr-
ins,[10] pyrazoloporphyrins,[11] napthiporphyrins,[12] and neo-
confused porphyrins.[13] The slight modification in the frame-
work 1) leads to unusual reactivity and spectral properties;
[*] B. Adinarayana, Dr. A. P. Thomas, Dr. A. Srinivasan
School of Chemical Sciences
National Institute of Science Education and Research (NISER)
Bhubaneswar—751005, Odisha (India)
E-mail: srini@niser.ac.in
Dr. C. H. Suresh
termed 6,11,16-triarylbiphenylcorrole
4
or A,d-di-m-
Inorganic and Theoretical Chemistry Section
Chemical Sciences and Technology Division
CSIR-National Institute for Interdisciplinary Science and Technology
Trivandrum—695019, Kerala (India)
benziporphyrin(1.1.1.0). A formal conversion of 3 into 4 is
achieved by introducing a biphenyl unit in place of bipyrrole
unit in 3. Based on the spectral studies and structural
characterization, the macrocycle 4 is found to be nonaromatic
and the trianionic core best suit for the CuIII metal ion to form
the organocopper complex.
The synthesis of the target macrocycle and its metal
complex is outlined in Scheme 1, where the synthesis involved
three steps. The first step is the conversion of biphenyl-3,3’-
dicarbaldehyde (6)[24] to 3,3’-bis(phenylhydroxymethyl)bi-
[**] A.S. thanks NISER, Department of Atomic Energy for financial
support. B.A. thanks CSIR for the fellowship. We thank Pardhasar-
adhi Satha, Giri Teja Illa, and Subba Reddy Marri for solving the
crystal structure of 4 and 5 and useful discussion for synthesis and
crystal analysis. We also thank Dr. Sankar, Department of Chemistry,
IISER, Bhopal for VT-EPR spectral studies.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201503347.
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44 nm (tripyrromethene in 2 vs dipyrromethene in 4); and
2) the absence of an intense Soret band and well-defined Q-
bands and one order of reduction in the e value, as observed in
3,[20c] suggests the macrocycle reported here is not aromatic.
Overall, the electronic absorption spectrum of 4 reflects the
absence of effective p-delocalization and the spectral profile
is similar to 2. Upon protonation of 4 with dilute solution of
TFA in CH2Cl2, the color of the solution changed from blue to
green. The intense band and weak absorption bands are
further red-shifted by 4 nm and 86, 121 nm and observed at
371 and 698, 765 nm, respectively, where the intensity of the
higher energy band is reduced as compared to 4 (Supporting
Information, Figures S7, S8).
Scheme 1. Synthesis of 4 and 5.
1
The H NMR spectrum of 4 was recorded in CD2Cl2 and
phenyl (7) by using freshly prepared Grignard reagent such as
phenylmagnesium bromide in THF to afford 7 in 65% yield.
The key precursor, 3,3’-biphenyl-bis(dipyrromethane) 8, was
synthesized in the second step by condensing 7 with an excess
of pyrrole in presence of BF3·Et2O, where the direct
shown in Figure 2a. There are four doublets in the deshielded
region between 6.23 to 7.77 ppm, where the initial two
doublets at 6.23 (H9,13) and 6.79 ppm (H8,14) are assigned
to the two pyrrolic b-CH protons. The other two doublets at
conversion was not successful, hence, we followed a similar
[25]
´
strategy as reported by Latos-Graz˙ynski et al, where the
mixture was refluxed for 8 h by using 1,2-dichloroethane as
solvent to afford 8 in 42% yield. In the final step, we followed
the Lindsey macrocyclization procedure,[26] where the
BF3·Et2O acid-catalyzed condensation reaction of 8 with
pentafluorobenzaldehyde followed by oxidation with 2,3-
dichloro-5,6-dicyano-p-benzoquinone (DDQ) afforded 4 in
10% yield. The compound was characterized by standard
analytical techniques and further confirmed by single crystal
X-ray diffraction analysis. The electron spray ionization (ESI)
mass spectral analysis of 4 exhibits the molecular ion peak at
m/z 639.1821 [M+1] (Supporting Information, Figure S4) and
is consistent with the exact composition of the macrocycle.
The electronic absorption spectral analysis of 4 in its
freebase and protonated form is shown in Figure 1. The
freebase form exhibits an intense band at 367 nm and broad
absorption bands at 612 nm and 644 nm with the molar
absorption coefficient e of 105. Comparisons of these data
with 2 and 3 reveal the following: 1) the similar intense
absorption band and the e value is in the order of 105, as
observed in 2,[4b] suggests the nonaromatic character in 4;
however reduction in the p-electron delocalization is
observed in 4, where the intense band is blue shifted by
Figure 2. 1H NMR spectrum of a) 4 and b) 5 in CD2Cl2.
6.94 (H4,18) and 7.77 ppm (H2,20) correspond to the
biphenyl CH protons that are on the periphery, where the
remaining outer biphenyl CH (H3,19) proton appears as
a triplet at 7.36 ppm. The inner core biphenyl CH (H22,25) is
a singlet at 9.09 ppm, while the pyrrolic NH (H24) signal is
appeared as a broad singlet at 11.15 ppm, respectively. This
was further confirmed by 2D homonuclear correlation
spectroscopy (COSY) (Supporting Information, Figure S17).
The presence of NH is further confirmed by CD2Cl2/D2O
exchange experiment. The meso-phenyl protons are found as
a multiplet between 7.38 and 7.48 ppm. The chemical shift
difference between the pyrrolic inner NH and outer b-CH
protons (Dd) and the biphenyl inner CH and outer CH (Dd’)
in 4 is 4.64 and 2.15 ppm. Overall, the spectral features and
the chemical shift difference clearly reflect the nonaromatic
features of 4. The results are further compared with 2,[4b] 3,[20c]
and phenanthriporphyrin,[19] where the Dd values are 3.55,
11.84, and 11.86 ppm; on the other hand, the Dd’ values in 2[4b]
and phenanthriporphyrin[19] are 0.4 and 10.76 ppm, respec-
tively. The shift difference (Dd and Dd’) is comparable with 2
further confirms the nonaromatic character in 4. Upon
protonation of 4 with TFA in CD2Cl2, the biphenyl inner-
CH (H22,25) and pyrrolic NH (H23,24) with integration of
two protons are shielded by 0.69 and 1.53 ppm and observed
Figure 1. The electronic absorption spectrum of 4, 4·H+, and 5.
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at 8.40 and 9.62 ppm, respectively, however, the outer core
biphenyl CH and pyrrolic b-CH signals are slightly deshielded
(Supporting Information, Figure S21). The Dd and Dd’ values
are 2.67 and 1.17 ppm, thus indicating no macrocyclic
aromatic ring current in the protonated state.[4e]
porting Information, Figures S31, S32).[19] Overall, the p-
electrons present in the biphenyl unit did not participate in
the macrocyclic aromatization, and thus remain isolated from
the p-electron delocalization of the dipyrromethene unit.
Thus, the absence of diatropic ring current as observed from
the NMR spectral studies, further confirms the overall
nonaromatic character from the crystal analysis. The pyrrole
units in 4 are hardly deviated from the mean plane (contains
the core atoms C6-C12-N1-N2) with the maximum deviation
of 2.938, whereas the m-benzene rings in the biphenyl unit are
deviated by 19.528 and 20.068 which are located above and
below the plane (Figure 3b). Both the molecules in the unit
cell (A and B) are connected individually and combined
together to generate series of 1D arrays, self-assembled
dimers, and tetrameric structures (Supporting Information,
Figures S29, S30).
The final confirmation came from the single-crystal X-ray
structure determination of
4 (Supporting Information,
Table S5). The crystals were grown in a CH2Cl2/n-hexane
solvent mixture. The unit cell contains two molecules of 4 (A
and B; Supporting Information, Figure S28c) and one (A) of
the two crystallographically independent molecules is shown
in Figure 3a. As predicted from the spectroscopic analysis, the
macrocycle contains a biphenyl, meso-pentafluorodipyrrome-
thene units and are connected by two meso-phenyl units. The
crystal analysis reveals that the weak intramolecular hydro-
gen bonding interactions between one of the inner-core
À
À
biphenyl CHs (C6 H6), pyrrolic NH (N1 H1) with pyrrolic
imine nitrogen (N2) with a bond distance and angle of 2.26 Š,
The presence of two inner-core biphenyl CHs and pyrrolic
NH prompted us to carry out metal ion insertion. The
coordination chemistry of 4 was performed by using CuII salts.
When 4 was treated with Cu(OAc)2 in CH2Cl2/CH3OH
mixture, the blue fraction was eluted by neutral alumina
column, affording 5 in 90% yield (Scheme 1). The ESI-MS
spectral analysis of 5 in the solid state showed a molecular ion
peak at 699.0691 [M+1] (Supporting Information, Figure S5),
confirming the exact composition. The electronic absorption
spectrum showed an intense band at 380 nm, which was red-
shifted by 13 nm compared to 4, while the weak bands were
blue-shifted by 27 and 9 nm and observed at 585 and 635 nm,
respectively (Figure 1). The 1H NMR spectrum was recorded
in CD2Cl2 and shown in Figure 2b. The pyrrolic b-CHs are
resonated as two doublets at 6.96 (H9,13) and 7.23 (H8,14);
on the other hand, the outer-core biphenyl CHs are observed
at 7.41 (H4,18), 7.60 (H3,19), and 7.94 ppm (H2,20), respec-
À
À
1238 (N1 H1···N2) and 2.33 Š, 1248 (C6 H6···N2), reflects
the observed deshielding signals of inner NH and biphenyl
CH protons from the NMR spectral analysis. The bond
À
À
À
lengths of C5 C7, C1 C35, and C11 C13 are 1.478 Š,
1.468 Š, and 1.473 Š (Supporting Information, Figure S31),
reflecting that the two m-benzene rings in the biphenyl unit
and also the dipyrromethene and biphenyl units are con-
nected by sp2–sp2 single-bond character.[4b, 19] The carbon–
carbon bond lengths within the biphenyl unit are between
1.366 and 1.408 Š, which have sp2–sp2 double-bond character
and an average angle of 119.9638 (Supporting Information,
Figures S31, S32, Tables S1, S2), confirming that the biphenyl
unit maintains the individual aromatic character as such.[27]
The alternative sp2–sp2 single- and double-bond character
between 1.469 and 1.325 Š in the dipyrromethene moiety
predicts the effective p-delocalization within the unit (Sup-
1
tively. This was further confirmed by H–1H COSY spectral
analysis (Supporting Information, Figure S20). The slightly
deshielded pyrrolic b-CH and outer-core biphenyl CHs and
the disappearance of inner-core biphenyl CHs and pyrrolic
NH signals as compared to 4 confirms the formation of
diamagnetic organometallic CuIII complex 5 and also main-
tains the nonaromatic character as such upon metal ion
insertion. It is pertinent to point out that the reaction of 2 with
CuCl2 forms internal carbon chlorinated mixed-valence (CuI
and CuII) tetranuclear copper complex.[4c] On the other hand,
3 reacts with Cu(OAc)2 to form a higher-oxidation-state CuIII
complex at room temperature.[20b,d]
The explicit structure of organo-CuIII complex of 5 was
unambiguously confirmed by single-crystal X-ray diffraction
analysis (Supporting Information, Table S5). A suitable single
crystal was grown by slow diffusion of n-hexane vapors over
CH2Cl2 solution of 5 and the structure is shown in Figure 4a.
As predicted from the spectral analysis, the CuIII ion is
inserted inside the macrocyclic framework and the geometry
around the metal center is square planar with N1-Cu-N2, N2-
Cu-C6, C6-Cu-C12, and C12-Cu-N1 angles of 93.1758,
À
À
À
91.1708, 82.7068, and 92.2088, and the Cu C6, Cu C12, Cu
À
N2, and Cu N1 bond lengths are 1.946 Š; 1,953 Š; 1.918 Š,
Figure 3. Single-crystal X-ray structure determination of 4.[30] a) Top
view and b) side view. The meso aryl groups are omitted for clarity in
the side view.
and 1.907 Š, respectively (Supporting Information, Fig-
À
À
ure S36, Table S3). As compared to Cu C and Cu N bond
lengths of organo-CuIII complexes of cis-[14a] and trans-
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(Supporting Information, Figure S26, S27). Overall, the
results confirmed the ability of 4 to stabilize the higher
oxidation state CuIII ion. Furthermore, the resolved diamag-
netic spectrum of 5 in [D5]pyridine (Supporting Information,
Figure S25) confirms the absence of axial ligation and thus
that a d8 low-spin configuration is maintained.[29]
In conclusion, we have demonstrated the synthesis,
spectroscopic, and structural characterization of 6,11,16-
triarylbiphenylcorrole and its metal complex. The aromatic
biphenyl unit and the p-delocalized dipyrromethene moiety
were linked together to generate the overall nonaromatic
character. The free ligand with contracted size and trianionic
nature with adj-CCNN core was crucial for the formation of
À
the organocopper complex with two M C bond, which is
diamagnetic and affords square-planar geometry around the
metal center. The chemistry is now being extended to the
pyridine-containing macrocycles and also the exploration of
the possibilities of synthesizing respective aromatic corrole
derivatives, which is currently underway in our research
group.
Figure 4. Single-crystal X-ray structure of 5.[30] a) Top view and b) side
view. The meso aryl groups are omitted for clarity in the side view.
Keywords: copper · dicarbacorrole · nonaromaticity ·
organometallic complexes · porphyrin
doubly[14b] N-confused porphyrins, the Cu C bond lengths of
How to cite: Angew. Chem. Int. Ed. 2015, 54, 10478–10482
Angew. Chem. 2015, 127, 10624–10628
À
[14]
À
5 are larger and Cu N bond lengths are shorter; however
III
À
the latter bond lengths (Cu N) are longer compared to Cu
complexes of 3.[20b,d] The biphenyl and the pyrrole units are
deviated from the mean plane containing the core atoms (C6-
C12-N1-N2-Cu) with the tilt angle between 6.498 and 8.978,
respectively (Figure 4b). As observed in 4, the complex 5
retains the nonaromatic character, the results are reflected
from the crystal analysis, where 1) the biphenyl and dipyrro-
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Received: April 13, 2015
Revised: May 20, 2015
Published online: July 14, 2015
10482 www.angewandte.org
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