Acid-mediated migration of bromide in an antiaromatic porphyrinoid: Preparation of two regioisomeric Ni(II) bromonorcorroles

Article abstract of DOI:10.1021/acs.joc.7b01899

The regioselective halogenation of porphyrinoids is critical for their selective functionalization, which enables the fine tuning of their electronic and optical properties. Here we report the synthesis of two regioisomeric Ni(II) bromonorcorroles on the

Full text of DOI:10.1021/acs.joc.7b01899

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Article
Acid-Mediated Migration of Bromide in an Antiaromatic Porphyrinoid:
Preparation of Two Regioisomeric Ni(II) Bromonorcorroles
Hiroyuki Kawashima, Satoru Hiroto, and Hiroshi Shinokubo
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01899 • Publication Date (Web): 13 Sep 2017
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Acid-Mediated Migration of Bromide in an
Antiaromatic Porphyrinoid: Preparation of Two
Regioisomeric Ni(II) Bromonorcorroles
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Hiroyuki Kawashima, Satoru Hiroto, and Hiroshi Shinokubo*
Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering,
Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
ABSTRACT: Regioselective halogenation of porphyrinoids is critical for their selective
functionalization, which enables fine-tuning of their electronic and optical properties. Here we
report the synthesis of two regioisomeric Ni(II) bromonorcorroles on the basis of acid-induced
migration of the bromo substituent. Treatment of Ni(II) dimesitylnorcorrole with N-
bromosuccinimide (NBS) selectively afforded Ni(II) 3-bromonorcorrole, which was further
converted into Ni(II) 2-bromonorcorrole upon treatment with hydrogen bromide. In addition, the
reaction of Ni(II) dimesitylnorcorrole with an excess amount of NBS afforded the
octabrominated product. The reaction mechanism of the bromination reaction of Ni(II)
dimesitylnorcorrole was investigated by theoretical calculations.
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Introduction
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A halogen dance reaction of halogenated aromatic compounds is a powerful methodology to
effectively expand the diversity of aryl halides, thus enabling a variety of regioselective
functionalizations of aromatic compounds (Scheme 1).1 Generally, the halogen dance reaction
occurs under basic conditions involving migration of the halogen atom to a highly reactive
anionic carbon center via a lithium–halogen exchange reaction. In contrast, rearrangement of a
halogen atom has been rarely observed under acidic conditions and regioselective halogen
migration has not been well documented.2
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Scheme 1. A representative halogen dance reaction of 2,5-dibromothiophene.
Li
Br
Br
LDA
Br
Br
Br
Br
Br
Br
Li
S
S
S
S
Peripheral functionalization of porphyrins is essential to modulate their electronic and
photophysical properties.3 To achieve site-specific functionalization of porphyrins, a halogen
substituent at the porphyrin periphery is often employed as a foothold to introduce various
functionalities at the desirable position of porphyrins. Consequently, regioselective halogenation
of porphyrins has been extensively investigated.4 However, the regioselectivity in electrophilic
halogenation of porphyrins is determined by the electron density of the peripheral positions. It is
difficult to override the inherent selectivity by other factors. In addition, porphyrinoids have
many similar reactive sites on the pyrrole subunits. It is generally difficult to prepare different
types of halogenated products regioselectively depending on the reaction conditions.
Norcorrole is a ring-contracted porphyrin with a 16π-antiaromatic conjugation system, which
lacks two meso-carbons from a regular porphyrin.5,6 Recently, we have synthesized an
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antiaromatic Ni(II) norcorrole complex 1.7 The reactivity of 1 has been explored in several types
of reactions such as oxidation, reduction, nucleophilic substitution, and silylene-insertion.8
Recently, Li, Chmielewski, and co-workers have also reported intriguing reactions of 1 with
several reagents.9
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Here we wish to disclose a method to prepare two regioisomeric brominated norcorrole Ni(II)
complexes selectively depending on the reaction conditions. We have found that electrophilic
brominating reagents delivered a bromine atom selectively at the C3 position of Ni(II)
dimesitylnorcorrole 1. Interestingly, Ni(II) 3-bromonorcorrole selectively rearranged into 2-
bromonorcorrole under acidic conditions. These two bromonorcorroles were transformed to
functionalized norcorroles through cross-coupling reactions, which elucidate the substituent
effect at the 2- and 3-positions to the antiaromatic 16π-electronic system. In addition, treatment
of 1 with an excess amount of N-bromosuccinimide (NBS) resulted in formation of
octabrominated product, which was transformed through Migita–Kosugi–Stille coupling to Ni(II)
octaalkynylnorcorrole with substantially enhanced near IR absorption property.
Results and Discussion
Bromination of Ni(II) dimesitylnorcorrole
Bromination of Ni(II) dimesitylnorcorrole 1 with several electrophilic brominating reagents
was investigated. We found that treatment of 1 with 1.1 equiv of NBS in THF at –60 °C
furnished 3-brominated product 2a in 72% yield regioselectively (Scheme 2). None of other
isomeric bromonorcorroles was detected in the reaction mixture. The regioselectivity for 3-
substituted norcorrole is the same as that observed in nitration of 1, reported by Li and
Chmielewski.9a Compound 2a was fully characterized by its NMR and MS analysis. The
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position of the bromine atom in 2a was unambiguously determined by the X-ray diffraction
analysis (Figure 1a and Figure S20). The use of N-bromophthalimide (NBP) also afforded 2a in
a comparable yield (69% yield). The use of bromine and bis(sym-collidine)bromide
hexafluorophosphate10 as brominating reagents at –60 °C also exhibited the same regioselectivity
to furnish only 2a in 53% and 61% yields, respectively.
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Scheme 2. Bromination of norcorrole 1 with NBS and bromine.
Mes
5
Mes
Br
3
1
4
2
N
N
NBS (1.1 equiv)
THF, –60 °C, 2 h
N
N
N
Ni
Ni
N
N
N
1
Mes
2a
Mes
72%
Figure 1. X-Ray crystal structures of 2a and 2b. a) Top and b) side views of 2a and c) top and d)
side views of 2b. Atomic displacement parameters are set at 50% probability and mesityl groups
are omitted for clarity.
Interestingly, 2-brominated product 2b was selectively obtained in 27% yield with bromine at
room temperature. The slightly domed structure of 2b was elucidated by single crystal X-ray
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analysis (Figure 1c and Figure S21). Unfortunately, however, the reaction with bromine lacked
in reproducibility, and the observed regioselectivity for 2a vs. 2b was sensitive to the reaction
conditions such as reaction temperatures and the workup procedures.
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It prompted us to examine the reaction conditions to understand the key factor for the
ambiguous selectivity for 2b. While the bromination reaction with NBS is almost neutral,
hydrogen bromide should be formed as a byproduct in the reaction with Br2. We eventually
revealed that hydrogen bromide was essential for the formation of 2b (Scheme 3). In fact,
treatment of 2a with an excess amount of hydrogen bromide in THF at room temperature
induced migration of the 3-bromo group to the 2-position, furnishing 2-brominated product 2b in
52% yield along with recovery of 2a in 9% yield. Importantly, migration of the bromine atom is
reversible at room temperature: The reaction of 2a with HBr under the same reaction conditions
provided 2a and 2b in 58% and 12% yields, respectively, along with 1 in 15% yield. These
results indicate the existence of equilibrium between 2a and 2b under acidic conditions at room
temperature. In addition, partial debromination also occurred under these conditions.
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Scheme 3. Rearrangement of bromonorcorroles 2a and 2b.
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Mes
Mes
Br
8
9
Br
+ 2a
9%
N
N
N
N
N
N
HBr/AcOH
Ni
Ni
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THF, rt, 30 min
N
N
2b
2a
52%
Mes
Mes
Mes
Mes
Br
Br
HBr/AcOH
N
N
N
N
N
N
+ 2b
58%
Ni
Ni
THF, rt, 30 min
N
N
2b
2a
12%
Mes
Mes
Reaction mechanism of bromination of Ni(II) norcorrole
Li, Chmielewski, and co-workers have investigated the origin of the 3-position selectivity in
nitration of 1 on the basis of the density functional theory (DFT) calculations.9a They concluded
that the stability of arenium type cation intermediates is essential in determining the major
nitration product. In the case of bromination of 1, we also consider the relative stability of
brominated arenium cations governs the regioselectivity for 3-brominated norcorrole 2a. Then,
the issue is the reason for the 2-position selectivity in the reaction of 2a with HBr to form 2b.
Scheme 4. Proposed reaction mechanism for bromine migration.
Mes
Ni
Mes
Ni
Br
H
H
H
H
–H+
H+
H+
Br
N
N
N
N
N
N
N
N
2a
2b
–H+
2a+
2b+
Mes
Mes
Because bromination of 1 with either NBS or Br2 selectively afforded the same product 2a at
low temperatures, the key factor should be the reaction temperature and the amount of hydrogen
bromide in the reaction mixture. On the basis of the finding that the HBr-induced migration
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reaction is reversible, we propose the following reaction mechanism (Scheme 4). Protonation of
2a with HBr provides cationic intermediate 2a+, which is in equilibrium with 2b+. Deprotonation
of cationic intermediate 2b+ yields 2b as a more stable product. At low temperatures under
neutral conditions, the reaction selectively furnished 2a, indicating that 2a is a kinetically
favorable product. In contrast, 2b is thermodynamically more stable due to its less sterically
demanding nature.
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To verify the proposed mechanism, we conducted DFT calculations on the reaction products,
arenium cation intermediates, and transition states at the B3LYP/6-31+G(d,p)+SDD level
(Figure S24 and Table S1).11,12 The solvent effect of THF was considered with the polarizable
continuum model (PCM) method.13 The cationic intermediate 2a+ is more stable by 1.27 kcal
mol–1 than 2b+ (Figure 2a). The origin of the relative stability of 2a+ over 2b+ is not clear at this
moment but we now speculate that the cationic charge is more effectively delocalized in 2a+ than
in 2b+ as indicated in the resonance structures of 2a+ over 2b+ (Figure S29 and S30). For the
migration process between 2a+ and 2b+, a three-membered ring bromonium species TS1 was
located as a transition state. The activation barrier from 2a+ to 2b+ via TS1 is 24.4 kcal mol–1.
The deprotonation processes from the cationic intermediates 2a+ and 2b+ with a bromide anion
were also calculated and transition states TS2 and TS3 were found, respectively. The activation
energies for deprotonation of 2a+ and 2b+ are 5.8 and 3.6 kcal mol–1, respectively (Figure 2b,c).
Considering the substantially higher activation barrier of the migration process, the bromination
reaction and the subsequent deprotonation at low temperatures should occur under kinetic control,
yielding 3-brominated product 2a through more stable intermediate 2a+. On the other hand,
protonation processes of 2a and 2b require 8.6 and 8.0 kcal mol–1 of activation energies,
respectively. This result indicates that re-protonation of 2a and 2b is facile at high temperatures
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under highly acidic conditions in the presence of an excess amount of HBr. In this situation, the
whole processes are reversible at high temperatures, favoring the formation of more
thermodynamically stable 2b, which is thermodynamically more stable by 3.6 kcal mol–1 than 2a.
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a)
TS1
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Ea = 24.4
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2b+
2a+
1.27
Mes
Br
N
N
N
N
Ni
TS1
Mes
TS2
Ea = 5.8
2.9
b)
2a+ + Br–
2a + HBr
TS2
Br–
c)
2b+ + Br–
Ea = 3.6
4.4
2b + HBr
TS3
Br–
Figure 2. Calculated energy profiles and activation energies for a) migration between 2a+ and
2b+, b) deprotonation of 2a+, and c) deprotonation of 2b+. Calculations were performed at the
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B3LYP/6-31+G(d,p)+SDD level. The solvent effect of THF was included by the PCM method.
Energy values are shown in kcal mol–1.
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Suzuki–Miyaura Cross-coupling of bromonorcorroles and their properties
While several 3-functionalized norcorrole Ni(II) complexes have been reported, none of 2-
functionalized norcorrole is precedent. With two different regioisomers of Ni(II)
bromonorcorroles 2a and 2b in hand, we then introduced several functionalities on the periphery
of norcorrole to investigate their substituent effect. Electron-rich and electron-deficient aryl
groups were readily installed under the standard Suzuki–Miyaura coupling reaction conditions
(Scheme 5). Arylated norcorroles were fully characterized by high-resolution mass and NMR
spectra. In addition, the structure of 3ab was clearly determined by the X-ray analysis (Figure
S22). The introduced 3-dimethylaminophenyl group is titled by 48.7° with respect to the
adjacent pyrrole ring.
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Scheme 5. Suzuki–Miyaura coupling of 2a and 2b with 4-nitrophenyl- and 4-
dimethylaminophenylboronic acids.
R
(HO)2B
Pd(PPh3)4
R
Mes
K3PO4
N
N
N
2a
3aa: R = NO2 56%
3ab: R = NMe2 57%
Ni
THF, 70 °C, 2 h
N
Mes
Mes
(HO)2B
R
Pd(PPh3)4
K3PO4
R
N
N
2b
Ni
3ba: R = NO2 46%
3bb: R = NMe2 81%
N
N
THF, 70 °C, 2 h
Mes
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The UV/vis absorption spectra of arylated products in dichloromethane are shown in Figure 3
along with that of the parent Ni(II) norcorrole 1. The absorption spectra of 3aa and 3ba were
similar to that of 1 except small red-shifts of the absorption bands around 500 nm. In contrast, 3-
dimethylaminophenyl-substituted norcorroles 3ab and 3bb exhibited novel broad absorption
bands around 660 nm. The broad band in 3ab was more evident than that in 3bb but disappeared
upon the addition of trifluoroacetic acid to the solution (Figure S23). These results imply the
existence of intramolecular charge transfer interactions between the electron-donating
aminophenyl group and the norcorrole core. Time-dependent (TD)-DFT calculations of 3ab and
3bb indicate that these absorption bands are originated from the HOMO–3 to LUMO transition
with significant charge transfer character (Figure S25). LUMO of 3bb has a nodal position at the
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2-position so that the intensity of this band was weaker than that in 3ab.
5.0
4.0
1
3aa
3ab
3ba
3.0
2.0
1.0
0
3bb
ε
300
400
500
600
700
800
900 1000
wavelength/nm
Figure 3. UV/vis/NIR absorption spectra of 3aa, 3ab, 3ba, and 3bb in dichloromethane.
To obtain further insights on the substituent effect, the electrochemistry of arylated norcorroles
was examined with cyclic voltammetry (Figure S27). Oxidation and reduction potentials of 3aa
and 3ba were shifted anodically with respect to those of 1 due to the electron-withdrawing
nitrophenyl group. The electrochemical HOMO–LUMO gap was almost same as that of 1. In
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contrast, introduction of the dimethylaminophenyl group resulted in cathodic shifts in oxidation
and reduction potentials of 3ab and the oxidation potential of 3bb. However, the reduction
potential of 3bb was unchanged from that of 1, resulting in smaller HOMO–LUMO gap of 3bb.
This is because the effect of the π-donating dimethylaminophenyl group on the LUMO level is
marginal because of the nodal position of LUMO at the 2-position of norcorrole.8e
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Alkynylation of Ni(II) norcorrole
Peripheral alkynyl moieties of porphyrinoids often enable efficient expansion of their π-
conjugation systems. Consequently, we attempted alkynylation of brominated norcorroles
through Sonogashira coupling. However, the reaction of 2a with ethynylbenzene under standard
Sonogashira conditions (PdCl2(PPh3)4, CuI, Et3N/THF) afforded a complex mixture of many
products. We then found that Migita–Kosugi–Stille coupling with an alkynylstannane reagent
was quite effective to introduce a phenylethynyl groups to brominated norcorroles. The reaction
of 2a and 2b with tributyl(phenylethynyl)tin afford 2- and 3-phenylethynylnorcorroles 3ac and
3bc in excellent yields (Scheme 6).
Scheme 6. Migita–Kosugi–Stille coupling of 2a and 2b with tributyl(phenylethynyl)stannane.
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Mes
7
8
9
Bu3Sn
N
N
N
Pd(PPh3)4
2a
Ni
dioxane, 70 °C, 5 h
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N
3ac
84%
Mes
Mes
Bu3Sn
N
N
N
N
Pd(PPh3)4
2b
Ni
dioxane, 70 °C, 5 h
3bc 78%
Mes
We also attempted exhaustive bromination of norcorrole 1. Treatment of 1 with an excess
amount of NBS (20 equiv) afforded octabromonorcorrole 4 along with octabromooxacorrole 5
(Scheme 7). Probably octabromooxacorrole was formed through oxidation of norcorrole 1 and
brominated norcorroles with dioxygen in air.7 Because the low solubility of 4 hampered the
purification with silica-gel column chromatography, we employed the mixture of these
compounds for further functionalization without separation. Coupling of the mixture with an
excess amount of tributyl(phenylethynyl)tin under the standard conditions provided
octa(phenylethynyl)norcorrole 6 in 8% yield after purification. Although the alkynylated
oxacorroles
were
detected
in
the
reaction
mixture
by
MS
analysis,
octa(phenylethynyl)oxacorrole could not be isolated because of difficult purification.
Scheme 7. Octabromination and octaalkynylation of 1.
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Mes
Br
Br
Mes
Br
Br
Br
Br
Br
Br
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8
Br
Br
N
N
N
N
N
NBS (20 equiv)
CH2Cl2, rt, 2 h
N
1
+
Ni
O
Ni
N
N
Br Br
9
Br
Br
44%
Br
Mes
Mes
Br
15%
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Ph
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Bu3Sn
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N
N
Pd(PPh3)4
Ni
dioxane, 70 °C, 5 h
N
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Ph
Mes
8%
6
Ph
Ph
Figure 4 shows absorption spectra of series of alkynylated norcorroles 3ac, 3bc, and 6 along
with that of 1 for comparison. While introduction of one phenylethynyl unit to 1 induced
relatively small red shift (ca. 10 nm) in the absorption spectra, 6 exhibited substantially red-
shifted and intensified absorption spectrum with broad absorption bands in the NIR region from
800 to 1600 nm. This NIR absorption band was characterized as HOMO–2→LUMO and
HOMO–1→LUMO transitions on the basis of TD-DFT calculation (Figure S26). These
molecular orbitals are substantially perturbated by the alkynyl substituents. While degenerate
HOMO–2 and HOMO–1 are delocalized over the norcorrole core and all of eight phenylethynyl
units, LUMO is located on the norcorrole core and four ethynyl moieties at 3-, 7-, 12-, 16-
positions (Figure S26b).
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ε
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Figure 4. UV/vis/NIR absorption spectra of 1, 3ac, 3bc, and 6 in dichloromethane.
The electrochemistry of alkynylated norcorroles 3ac, 3bc, and 6 was also investigated (Figure
S28). Introduction of phenylethynyl groups induced anodic shifts due to the electron-
withdrawing alkynyl substituents. In particular, octa(phenylethynyl)norcorrole 6 showed a rather
high reduction potential, resulting in a small electrochemical HOMO–LUMO gap of 0.906 V.
This result as well as the red-shifted broad NIR absorption band and the MO calculations
indicate the effective expansion of π-conjugation over phenylethynyl substituents.
Conclusions
We have found hydrogen bromide-induced migration of the bromo substituent on norcorrole
and developed a synthetic procedure for preparation of two regioisomeric Ni(II)
bromonorcorroles. Treatment of Ni(II) dimesitylnorcorrole with NBS selectively afforded Ni(II)
3-bromonorcorrole, which was further converted into Ni(II) 2-bromonorcorrole upon treatment
with hydrogen bromide. In addition, the reaction of Ni(II) norcorrole with an excess amount of
NBS afforded the octabrominated product. The reaction mechanism of the bromination reaction
of Ni(II) dimesitylnorcorrole was investigated by theoretical calculations. At low temperatures,
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the electrophilic bromination reaction of norcorrole 1 selectively provides 3-bromonorcorrole 2a
through more stable cationic intermediate 2a+. Under highly acidic conditions at higher
temperatures, the whole processes are reversible, thus favoring the formation of
thermodynamically more stable product 2-bromonorcorrole 2b. The brominated norcorroles
were employed for palladium-catalyzed cross-coupling reactions to provide a variety of
functionalized Ni(II) norcorroles. The optical and electrochemical properties of these substituted
Ni(II) norcorroles were investigated experimentally and theoretically. The present procedure for
selective bromination of Ni(II) norcorroles should be useful to prepare redox active and near IR
absorbing norcorrole derivatives.
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Experimental Section
Instrumentation and Materials: 1H NMR (500 MHz) and 13C NMR (126 MHz) spectra were
recorded on a Bruker AVANCE III HD spectrometer, and chemical shifts were reported as the
1
delta scale in ppm relative to CHCl3 (δ = 7.260 ppm) for H NMR and CDCl3 (δ = 77.16 ppm)
for 13C NMR. UV/vis/NIR absorption spectra were recorded on a Shimadzu UV-2550 or JASCO
V670 spectrometer. High-resolution mass spectra were recorded on a Bruker microTOF using
positive mode ESI-TOF method for acetonitrile solutions. X-ray diffraction data were taken on
a Bruker D8 QUEST X-ray diffractometer with ImS microfocus X-ray source and a large area
(10 cm × 10 cm) CMOS detector (PHOTON 100). Unless otherwise noted, materials obtained
from commercial suppliers were used without further purification.
Synthesis of 2a: A solution of Ni(II) dimesitylnorcorrole 1 (116 mg, 201 μmol) in THF (80
mL) was cooled to –60 °C. A solution of N-bromosuccinimide (37.8 mg, 212 μmol) in THF (20
mL) was added dropwise and the mixture was stirred at –60 °C for 1.5 h. Acetone (10 mL) was
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then added and the mixture was warmed to room temperature. An aqueous NaHCO3 solution was
added and the mixture was extracted with ethyl acetate (20 mL × 3). The combined organic
layers were washed with water and brine, and dried over Na2SO4. After removing the solvent, the
residue was purified by silica-gel column chromatography (hexane/CH2Cl2 = 4/1 as an eluent).
The product was further purified by recrystallization (CH2Cl2/MeOH) to afford Ni(II) 3-bromo-
5,14-dimesitylnorcorrole 2a (94.1 mg, 143 μmol) as black crystals in 72% yield. Mp > 300 °C.
1H NMR (500 MHz, CDCl3): δ = 6.27 (s, 2H, Mes), 6.27 (s, 2H, Mes), 2.87 (s, 6H, ortho-Mes),
2.86 (s, 6H, ortho-Mes), 1.87 (d, J = 4.5 Hz, 1H, β-CH), 1.84 (s, 3H, para-Mes), 1.83 (s, 3H,
para-Mes), 1.76 (d, J = 4.5 Hz, 1H, β-CH), 1.73 (d, J = 4.5 Hz, 1H, β-CH), 1.69 (d, J = 4.0 Hz,
1H, β-CH), 1.69 (s, 1H, β-CH), 1.66 (d, J = 4.0 Hz, 1H, β-CH), 1.60 (d, J = 4.5 Hz, 1H, β-CH)
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ppm. C NMR (500 MHz, CDCl3): δ = 170.2, 169.7, 166.8, 165.5, 159.4, 158.4, 148.6, 148.1,
148.0, 142.8, 137.2, 137.1, 133.8, 133.5, 131.6, 131.0, 128.9, 128.2, 128.0, 125.8, 124.9, 116.8,
116.0, 115.2, 114.9, 20.8, 20.7, 17.8, 17.8 ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 431 (45000),
480 (18000), 518 (20000) nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for C36H29BrN4Ni 656.0903;
Found 656.0873.
Synthesis of 2b: To a solution of 2a (98.4 mg, 150 μmol) in dry THF (15 mL) was added a
solution of HBr in acetic acid (190 mg) under N2 atmosphere. The mixture was stirred at room
temperature for 30 min. A NaHCO3 solution was added to quench the reaction and the mixture
was extracted with ethyl acetate (20 mL × 3). The combined organic layers were washed with
water and brine, and dried over Na2SO4. After removing the solvent, the residue was purified by
silica-gel column chromatography (hexane/CH2Cl2 = 9/1 as an eluent). The product was further
purified by recrystallization (CHCl3/MeOH) to afford Ni(II) 2-bromo-5,14-dimesitylnorcorrole
1
2b (51.3 mg, 78.1 μmol) as black crystals in 52% yield. Mp > 300 °C. H NMR (500 MHz,
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CDCl3): δ = 6.27 (s, 4H, Mes), 2.89 (s, 6H, ortho-Mes), 2.88 (s, 6H, ortho-Mes), 1.83 (s, 3H,
para-Mes), 1.83 (s, 3H, para-Mes), 1.82 (d, J = 4.5 Hz, 1H, β-CH), 1.78 (d, J = 4.5 Hz, 1H, β-
CH), 1.72 (d, J = 4.5 Hz, 1H, β-CH), 1.64 (d, J = 4.0 Hz, 1H, β-CH), 1.59 (d, J = 4.0 Hz, 1H, β-
CH), 1.56 (d, J = 4.0 Hz, 1H, β-CH), 1.56 (s, 1H, β-CH) ppm. 13C NMR (500 MHz, CDCl3): δ =
172.5, 169.2, 165.3, 162.7, 159.0, 158.2, 148.3, 148.2, 147.2, 137.3, 137.1, 133.4, 132.6, 131.7,
128.3, 128.3, 128.2, 126.7, 125.8, 125.4, 116.5, 116.2, 114.9, 100.1, 20.7, 17.7, 17.7 ppm.
UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 432 (42000), 480 (18000), 519 (20000) nm. HRMS (ESI-
TOF) m/z: [M]+ Calcd for C36H29BrN4Ni 656.0903; Found 656.0928.
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Synthesis of 3aa: A Schlenk flask containing 2a (13.8 mg, 21.0 μmol), 4-nitrophenylboronic
acid (43.9 mg, 263 μmol), Pd(PPh3)4 (4.81 mg, 4.16 μmol), and K3PO4 (109 mg, 513 μmol) was
filled with N2 and dry THF (2.0 mL) was added. The solution was stirred at 70 °C for 2 h. After
cooling down, the resulting mixture was passed through a short pad of silica-gel with CHCl3 and
the solution concentrated in vacuo. The residue was purified by silica-gel column
chromatography (hexane/CH2Cl2 = 7/3 as eluent). The product was further purified by
recrystallization (CHCl3/MeOH) to afford Ni(II) 3-(4-nitrophenyl)-5,14-dimesitylnorcorrole 3aa
(8.19 mg, 11.7 μmol, 56%) as dark brown crystals. Mp > 300 °C. 1H NMR (500 MHz, CDCl3): δ
= 7.10 (pseudo-d, J = 8.5 Hz, 2H, Ph), 6.28 (s, 2H, Mes), 5.88 (s, 2H, Mes), 5.54 (pseudo-d, 2H,
J = 8.5 Hz, Ph), 2.90 (s, 6H, ortho-Mes), 2.74 (s, 6H, ortho-Mes), 1.84 (d, J = 4.5 Hz, 1H, β-CH),
1.84 (d, J = 4.0 Hz, 1H, β-CH), 1.84 (s, 3H, para-Mes), 1.77 (d, J = 4.0 Hz, 1H, β-CH), 1.71 (d,
J = 4.5 Hz, 1H, β-CH), 1.66 (d, J = 4.0 Hz, 1H, β-CH), 1.63 (d, J = 4.5 Hz, 2H, β-CH), 1.61 (s,
3H, para-Mes), 1.60 (s, 1H, β-CH) ppm. 13C NMR (500 MHz, CDCl3): δ = 170.7, 170.0, 166.0,
164.9, 159.1, 157.6, 148.4, 148.0, 148.0, 145.2, 144.3, 143.8, 138.9, 138.0, 137.1, 133.6, 133.5,
132.4, 131.4, 128.7, 128.2, 127.9, 125.8, 125.8, 125.1, 121.3, 116.2, 115.4, 114.9, 114.8, 20.7,
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20.3, 17.9, 17.8 ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 433(40000), 529(21000) nm. HRMS
(ESI-TOF) m/z: [M]+ Calcd for C42H33N5NiO2 697.1982; Found 697.1980.
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Synthesis of 3ab: A Schlenk flask containing 2a (13.1 mg, 20.0 μmol), 4-N,N-
dimetylaminophenylboronic acid (40.0 mg, 243 μmol), Pd(PPh3)4 (5.21 mg, 4.50 μmol), and
K3PO4 (107 mg, 502 μmol) was filled with N2 and dry THF (2.0 mL) was added. The solution
was stirred at 70 °C for 2 h. After cooling down, the resulting mixture was passed through a
short pad of silica-gel with CHCl3 and the solution concentrated in vacuo. The residue was
purified by silica-gel column chromatography (hexane/CH2Cl2 = 7/3as eluent). The product was
purified by recrystallization (CHCl3/MeOH) to afford Ni(II) 3-(4-N,N-dimetylaminophenyl)-
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5,14-dimesitylnorcorrole 3ab (7.84 mg, 11.3 μmol, 57%) as black crystals. Mp > 300 °C. H
NMR (500 MHz, CDCl3): δ = 6.29 (s, 2H, Mes), 5.93 (s, 2H, Mes), 5.57 (pseudo-d, J = 9.0 Hz,
2H, Ph), 5.29 (pseudo-d, J = 9.0 Hz, 2H, Ph), 2.89 (s, 6H, ortho-Me), 2.72 (s, 6H, ortho-Me),
2.53 (s, 6H, Me), 1.88 (d, J = 4.5 Hz, 1H, β-CH), 1.84 (s, 3H, para-Me), 1.73 (d, J = 4.0 Hz, 1H,
β-CH), 1.71 (d, J = 4.0 Hz, 1H, β-CH), 1.68 (d, J = 4.0 Hz, 1H, β-CH), 1.67 (s, 1H, β-CH), 1.66
(d, J = 4.0 Hz, 1H, β-CH), 1.59 (d, J = 4.0 Hz, 1H, β-CH) ppm. 13C NMR (500 MHz, CDCl3): δ
= 170.1, 170.4, 164.0, 162.4, 157.7, 156.9, 153.6, 149.4, 148.4, 147.7, 147.2, 144.8, 136.9, 136.3,
133.7, 133.7, 131.7, 128.1, 127.7, 127.1, 127.0, 126.6, 126.2, 125.1, 120.0, 115.6, 115.5, 114.0,
113.7, 109.7, 40.3, 20.7, 20.5, 17.9, 17.8 ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 430 (34000),
523 (20000), 665 (5800) nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for C44H39N5Ni 695.2554;
Found 695.2528.
Synthesis of 3ba: A Schlenk flask containing 2-bromo-5,14-dimesitylnorcorrole 2b (13.4 mg,
20.5 μmol), 4-nitrophenylboronic acid (41.7 mg, 250 μmol), Pd(PPh3)4 (5.66 mg, 4.90 μmol),
and K3PO4 (108 mg, 508 μmol) was filled with N2 and dry THF (2.0 mL) was added. The
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solution was stirred at 70 °C for 2 h. After cooling down, the resulting mixture was passed
through a short pad of silica-gel with CHCl3 and the solution was concentrated in vacuo. The
residue was purified by silica-gel column chromatography (hexane/CH2Cl2 = 7/3as eluent). The
product was further purified by recrystallization (CHCl3/MeOH) to afford Ni(II) 2-(4-
nitrophenyl)-5,14-dimesitylnorcorrole 3ba (6.67 mg, 9.55 μmol, 46%) as dark brown crystals.
Mp > 300 °C. 1H NMR (500 MHz, CDCl3): δ = 7.42 (pseudo-d, J = 9.0 Hz, 2H, Ph), 6.35 (s, 2H,
Mes), 6.31 (s, 2H, Mes), 5.36 (pseudo-d, 2H, J = 9.0 Hz, Ph), 2.88 (s, 6H, ortho-Mes), 2.86 (s,
6H, ortho-Mes), 2.09 (d, J = 4.5 Hz, 1H, β-CH), 1.98 (s, 1H, β-CH), 1.97 (d, J = 4.0 Hz, 1H, β-
CH), 1.94 (d, J = 4.5 Hz, 1H, β-CH), 1.93 (d, J = 4.5 Hz, 1H, β-CH), 1.88 (s, 3H, para-Mes),
1.87 (d, J = 4.0 Hz, 1H, β-CH), 1.86 (s, 3H, para-Mes), 1.83 (d, J = 4.5 Hz, 1H, β-CH) ppm. 13C
NMR (500 MHz, CDCl3): δ = 171.6, 169.0, 166.0, 162.9, 159.5, 158.9, 148.3, 148.1, 147.9,
147.7, 145.1, 137.8, 137.4, 137.3, 133.6 133.5, 132.3, 131.5, 129.3, 129.1, 128.4, 128.3, 125.9,
125.8, 124.3, 123.3, 121.7, 116.9, 116.4, 115.3, 20.7, 20.7, 17.9, 17.8 ppm. UV/vis (CH2Cl2) λmax
(ε [M–1 cm–1]): 433 (39000), 542 (32000) nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for
C42H33N5NiO2 697.1982; Found 697.1958.
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Synthesis of 3bb: A Schlenk flask containing 2b (13.4 mg, 20.5 μmol), 4-N,N-
dimetylaminophenylboronic acid (40.3 mg, 244 μmol), Pd(PPh3)4 (5.63 mg, 4.87 μmol), and
K3PO4 (108 mg, 508 μmol) was filled with N2 and dry THF (2.0 mL) was added. The solution
was stirred at 70 °C for 2 h. After cooling down, the resulting mixture was passed through a
short pad of silica-gel with CHCl3 and the solution was concentrated in vacuo. The residue was
purified by silica-gel column chromatography (hexane/CH2Cl2 = 7/3 as eluent). The product was
further purified by recrystallization (CHCl3/MeOH) to afford Ni(II) 3-(4-N,N-
dimetylaminophenyl)-5,14-dimesitylnorcorrole 3bb (7.84 mg, 11.3 μmol, 81%) as black crystals.
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Mp > 300 °C. H NMR (500 MHz, CDCl3): δ = 6.25 (s, 2H, Mes), 6.24 (s, 2H, Mes), 5.57
(pseudo-d, J = 9.0 Hz, 2H, Ph), 5.29 (pseudo-d, J = 9.0 Hz, 2H, Ph), 2.89 (s, 6H, ortho-Me), 2.72
(s, 6H, ortho-Me), 2.53 (s, 6H, Me), 1.88 (d, J = 4.5 Hz, 1H, β-CH), 1.84 (s, 3H, para-Me), 1.73
(d, J = 4.0 Hz, 1H, β-CH), 1.71 (d, J = 4.0 Hz, 1H, β-CH), 1.68 (d, J = 4.0 Hz, 1H, β-CH), 1.67
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(s, 1H, β-CH), 1.66 (d, J = 4.0 Hz, 1H, β-CH), 1.59 (d, J = 4.0 Hz, 1H, β-CH) ppm. C NMR
(500 MHz, CDCl3): δ = 170.1, 170.4, 164.0, 162.4, 157.7, 156.9, 153.6, 149.4, 148.4, 147.7,
147.2, 144.8, 136.9, 136.3, 133.7, 133.7, 131.7, 128.1, 127.7, 127.1, 127.0, 126.6, 126.2, 125.1,
120.0, 115.6, 115.5, 114.0, 113.7, 109.7, 40.3, 20.7, 20.5, 17.9, 17.8 ppm. UV/vis (CH2Cl2) λmax
(ε [M–1 cm–1]): 431 (44000), 537 (25000) nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for C44H39N5Ni
695.2554; Found 695.2548.
Synthesis of 3ac: A Schlenk flask containing 2a (13.2 mg, 20.1 μmol) and Pd(PPh3)4 (5.0 mg,
4.3 μmol) was filled with N2 and dry dioxane (4.0 mL) was added and stirred at room
temperature for 15 min. Tributyl(phenylethynyl)tin was added dropwise (25 μL) and the mixture
was stirred at 70 °C for 5 h. After cooling down, the resulting mixture was passed through a
short pad of silica-gel with CH2Cl2 and the solution concentrated in vacuo. The residue was
purified by silica-gel column chromatography (10% w/w anhydrous K2CO3/silica-gel;
hexane/CH2Cl2 = 7/3 as eluent) to afford Ni(II) 3-(phenylethynyl)-5,14-dimesitylnorcorrole 3ac
1
(11.4 mg, 16.9 μmol, 84%) as black crystals. Mp > 300 °C. H NMR (500 MHz, CDCl3): δ =
6.97–6.93 (m, 1H, Ph), 6.89–6.86 (m, 2H, Ph), 6.29 (s, 2H, Mes), 6.29–6.27 (m, 2H, Ph), 6.25 (s,
2H, Mes), 2.91 (s, 6H, ortho-Me), 2.86 (s, 6H, ortho-Me), 2.53 (s, 6H, Me), 1.92 (d, J = 4.5 Hz,
1H, β-CH), 1.85 (d, J = 4.5 Hz, 1H, β-CH), 1.85 (s, 3H, para-Me), 1.83 (s, 1H, β-CH), 1.80 (d, J
= 4.5 Hz, 1H, β-CH), 1.76 (s, 3H, para-Me), 1.76 (d, J = 4.0 Hz, 1H, β-CH), 1.72 (d, J = 4.0 Hz,
1H, β-CH), 1.71 (d, J = 4.5 Hz, 1H, β-CH) ppm. 13C NMR (500 MHz, CDCl3): δ = 170.4, 169.8,
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166.1, 165.0, 159.0, 157.7, 148.6, 147.9, 147.8, 147.3, 137.1, 137.0, 134.2, 133.6, 131.7, 131.3,
131.0, 128.5, 128.2, 128.0, 27.6, 127.4, 26.0, 125.6, 123.4, 122.8, 118.0, 116.0, 15.3, 114.9, 95.1,
80.9, 21.0, 20.6, 27.8, 17.8 ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 435(33000), 533(28000),
578(2300) nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for C44H34N4Ni 676.2137; Found 676.2137.
Synthesis of 3bc: A Schlenk flask containing 2b (13.4 mg, 20.4 μmol) and Pd(PPh3)4 (4.8 mg,
4.2 μmol) was filled with N2 and dry dioxane (4.0 mL) was added and stirred at room
temperature for 15 min. Tributyl(phenylethynyl)tin was added dropwise (25 μL) and the mixture
was stirred at 70 °C for 5 h. After cooling down, the resulting mixture was passed through a
short pad of silica-gel with CH2Cl2 and the solution concentrated in vacuo. The residue was
purified by silica-gel column chromatography (10% w/w anhydrous K2CO3/silica-gel;
hexane/CH2Cl2 = 7/3 as eluent) to afford Ni(II) 2-(phenylethynyl)-5,14-dimesitylnorcorrole 3bc
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(10.8 mg, 16.0 μmol, 78%) as black crystals. Mp > 300 °C. H NMR (500 MHz, CDCl3): δ =
7.01–6.98 (m, 1H, Ph), 6.96–6.92 (m, 2H, Ph), 6.64–6.62 (m, 2H, Ph), 6.30 (s, 2H, Mes), 6.29 (s,
2H, Mes), 2.89 (s, 6H, ortho-Me), 2.89 (s, 6H, ortho-Me), 1.94 (d, J = 4.5 Hz, 1H, β-CH), 1.89
(d, J = 4.5 Hz, 1H, β-CH), 1.86 (d, J = 4.5 Hz, 1H, β-CH), 1.85 (s, 6H, Me), 1.85 (s, 3H, para-
Me), 1.82 (s, 1H, β-CH), 1.77 (d, J = 4.5 Hz, 1H, β-CH), 1.72 (d, J = 4.0 Hz, 1H, β-CH), 1.69 (d,
J = 4.0 Hz, 1H, β-CH) ppm. 13C NMR (500 MHz, CDCl3): δ = 171.5, 169.3, 166.2, 165.4, 158.9,
158.4, 148.5, 148.0, 147.8, 146.8, 137.2, 137.1, 133.6, 132.2, 131.6, 130.7, 129.3, 128.6, 128.3,
128.2, 128.0, 127.5, 126.0, 125.7, 123.0, 116.5, 116.3, 114.9, 109.6, 90.1, 79.8, 20.7, 17.8, 17.8
ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]): 432 (36000), 498 (20000), 531 (32000), 646 (5100)
nm. HRMS (ESI-TOF) m/z: [M]+ Calcd for C44H34N4Ni 676.2137; Found 676.2138.
Synthesis of 4: To a solution of 1 (35.2 mg, 60.9 μmol) in dry CH2Cl2 (15 mL) was added a
solution of N-bromosuccinimide (214 mg, 1.20 mmol) in CH2Cl2 (30 mL) under argon
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atmosphere in a glovebox. The mixture was stirred at room temperature for 2 h. After removing
the solvent, the residue was purified by silica-gel column chromatography (CHCl3 as eluent).
The product was further purified by recrystallization (CHCl3/MeOH). Ni(II) octabromo-5,14-
dimesitylnorcorrole 4 and Ni(II) octabromo-5,15-dimesityl-10-oxacorrole 5 were obtained as an
inseparable mixture as a black solid. The yield of 4 was determined on the basis of the NMR
analysis. Mp > 300 °C. 1H NMR (500 MHz, CDCl3): δ = 6.31 (s, 4H, Mes), 2.81 (s, 12H, ortho-
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Me), 1.89 (s, 6H, para-Me) ppm. The C NMR spectrum of 4 was difficult to be measured due
to the low solubility. HRMS (ESI-TOF) m/z: [M]+ Calcd for C36H22Br8N4Ni 1207.4587; Found
1207.4585.
Synthesis of 6: A Schlenk flask containing a mixture of octabromonorcorrole 4 and
octabromooxacorrole 5 (25.3 mg, 4:5 = 3:1) and Pd(PPh3)4 (9.76 mg, 8.44 μmol) was filled with
N2 and dry dioxane (15 mL) was added and stirred at room temperature for 15 min.
Tributyl(phenylethynyl)tin was added dropwise (170 μL) and the mixture was stirred at 70 °C
for 5 h. After cooling down, the resulting mixture was passed through a short pad of silica-gel
with CH2Cl2 and the solution concentrated in vacuo. The residue was purified by silica-gel
column chromatography (10% w/w anhydrous K2CO3/silica-gel; hexane/CH2Cl2 = 3/2 as eluent)
to afford Ni(II) octa(phenylethynyl)-5,14-dimesitylnorcorrole 6 (1.81 mg, 1.31 μmol, 8%) as
1
dark purple crystals. Mp > 300 °C. H NMR (500 MHz, CDCl3): δ = 7.05–7.02 (m, 4H, Ph),
6.97–6.90 (m, 12H, Ph), 6.75–6.72 (m, 8H, Ph), 6.68–6.66 (m, 8H Ph), 6.49–6.48 (m, 4H, Ph),
13
6.40 (s, 4H, Mes), 2.91 (s, 12H, ortho-Me), 1.86 (s, 6H, para-Me) ppm. C NMR (500 MHz,
CDCl3): δ = 166.1, 157.1, 146.2, 138.0, 135.2, 131.5, 131.2, 129.4, 128.2, 127.8, 127.7, 125.1,
122.7, 122.6, 116.3, 102.4, 96.2, 80.8, 79.1, 20.8, 18.2 ppm. UV/vis (CH2Cl2) λmax (ε [M–1 cm–1]):
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345 (38000), 583 (39000), 633 (56000), 1104 (1700), 1234 (1700) nm. HRMS (ESI-TOF) m/z:
[M]+ Calcd for C100H62N4Ni 1377.4355; Found 1377.4342.
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X-ray diffraction analysis: X-ray data for 2a and 2b were obtained using a Rigaku CCD
diffractometer (Saturn 724 with MicroMax-007) with Varimax Mo optics using graphite
monochromated Mo-Kα radiation (λ = 0.71075 Å). X-ray data for 3ab were obtained using a
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Bruker D8 QUEST X-ray diffractometer with an IµS microfocus X-ray source and a large area
CMOS detector (PHOTON 100). Crystallographic data for 2a, 2b, and 3ab have been deposited
with the Cambridge Crystallographic Data Centre.
Crystallographic data for 2a (CCDC-1516103): Single crystals were obtained by vapor
diffusion of methanol into a chloroform solution. C36H29BrN4Ni, Mw = 656.25, monoclinic, P21/c,
a = 13.1619(8) Å, b = 13.8635(4) Å, c = 8.2762(3) Å, β = 101.230(5)°, V = 1481.24(12) Å3, Z =
2, R1 = 0.0608 (I > 2.0 σ(I)), Rw = 0.1702 (all data), GOF = 1.087.
Crystallographic data for 2b (CCDC-1516102): Single crystals were obtained by vapor
diffusion of methanol into a chloroform solution. C36H29BrN4Ni, Mw = 656.25, monoclinic, P21/c,
a = 12.6966(3) Å, b = 27.8406(7) Å, c = 8.1912(2) Å, β = 98.977(2)°, V = 2859.97(12) Å3, Z = 4,
R1 = 0.0445 (I > 2.0 σ(I)), Rw = 0.1403 (all data), GOF = 1.272.
Crystallographic data for 3ab (CCDC-1516104): Single crystals were obtained by vapor
diffusion of methanol into a dichloromethane solution. C45H41Cl2N5Ni, Mw = 781.44, monoclinic,
P21/c, a = 9.7230 (4) Å, b = 25.486(11) Å, c = 15.9516(5) Å, β = 106.565(4)°, V = 3788.8(3) Å3,
Z = 4, R1 = 0.0596 (I > 2.0 σ(I)), Rw = 0.1504 (all data), GOF = 1.065.
Cyclic Voltammetry: Cyclic voltammograms of compounds were recorded on ALS
electrochemical analyzer 612C. Measurements were performed in freshly distilled
dichloromethane with tetrabutylammonium hexafluorophosphate as electrolyte. A three-
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electrode system was used and consisted of a grassy carbon working electrode, a platinum wire
and Ag/AgClO4 as the reference electrode. All potentials are referenced to the potential of
ferrocene/ferrocenium cation couple.
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Theoretical calculations: All calculations were carried out using the Gaussian 09 program.14
Full optimizations were performed with Becke’s three-parameter hybrid exchange functional and
the Lee–Yang–Parr correlation functional (B3LYP)and a basis set consisting of SDD for Ni and
6-31G(d) for the rest. Geometries of 2a and 2b were obtained from their X-ray crystal structures.
For the calculation of the reaction pathway, rough transition state geometries were obtained
using the Reaction plus Pro software package,15 based on the nudged elastic band method.16 The
ground and transition state geometries were fully optimized at the B3LYP/6-31+G(d,p)+SDD
level without any symmetry restriction. The solvent effect of THF was included on the basis of
the PCM method using the scrf = iefpcm keyword. Zero-point energy and thermal energy
corrections were conducted for all optimized structures, and the sums of electronic and thermal
free energies were obtained. The zero-point energies were not scaled, and the enthalpic
corrections were made at 298.150 K. The transition states gave single imaginary frequency. The
calculated absorption wavelengths and oscillator strengths were obtained with the TD-DFT
method at the B3LYP/6-31G(d)+SDD level for the optimized structures at the same level of
theory.
ASSOCIATED CONTENT
Supporting Information.
The Supporting Information is available free of charge on the ACS Publications website at DOI:
xxxxx.
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Crystallographic data for 2a (CIF)
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Crystallographic data for 2b (CIF)
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Crystallographic data for 3ab (CIF)
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NMR spectra, UV/vis absorption spectra, cyclic voltammograms, and results of DFT calculations
(PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: hshino@chembio.nagoya-u.ac.jp
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by JSPS KAKENHI Grant Numbers JP26102003 and JP17H01190.
H.S. gratefully acknowledges the Murata Science Foundation for financial support.
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SYNOPSIS
R
Ni
R
R
Ni
R
R
Ni
R
Br
Br
N
N
N
N
N
N
N
N
N
N
N
N
HBr
NBS
Selective Bromination
and Migration
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