Electrochemical properties and catalytic reactivity of cobalt complexes with redox-active meso -substituted porphycene ligands

Article abstract of DOI:10.1142/S1088424619500780

The cobalt complexes of meso-aryl substituted porphycenes were synthesized and characterized. The reduction potentials of the complexes were shifted to the positive side depending on the strength of the electron-withdrawing properties of the meso-substituents, while the optical properties, such as the absorption spectra of these complexes, were similar. This suggests that the energy levels of the molecular orbitals of the complexes were changed by the meso-substituents while the gaps of the orbitals were not significantly changed. The one-electron reduction of the complex did not afford the Co(I) species, but the ligand-reduced radical anion, which was characterized by electrospectrochemistry. The generated ligand-reduced species reacted with alkyl halides to form the Co(III)-alkyl complex. As a result, the reduction potential of the electrolytic reaction could be directly controlled by the substituents of the porphycene. The catalytic reaction with trichloromethylbenzene was also performed and it was found that the ratio of the obtained products was changed by the reduction potentials of the catalyst, i.e. the cobalt porphycenes.

Full text of DOI:10.1142/S1088424619500780

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1–8
DOI: 10.1142/S1088424619500780
Published at http://www.worldscinet.com/jpp/
Electrochemical properties and catalytic reactivity of cobalt
complexes with redox-active meso-substituted porphycene
ligands
Taro Koidea, Zihan Zhoua, Ning Xua, YoshioYanoa, Toshikazu Onoa,b,
Zhongli Luoa, Hisashi Shimakoshia andYoshio Hisaeda*a,b
a Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Moto-oka 744,
Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan
b Center for Molecular Systems (CMS), Kyushu University, Moto-oka 744, Nishi-ku, Fukuoka-shi,
Fukuoka 819-0395, Japan
Dedicated to Professor Atsuhiro Osuka on the occasion of his 65th birthday.
Received 23 April 2019
Accepted 13 June 2019
ABSTRACT: The cobalt complexes of meso-aryl substituted porphycenes were synthesized and
characterized. The reduction potentials of the complexes were shifted to the positive side depending on
the strength of the electron-withdrawing properties of the meso-substituents, while the optical properties,
such as the absorption spectra of these complexes, were similar. This suggests that the energy levels of
the molecular orbitals of the complexes were changed by the meso-substituents while the gaps of the
orbitals were not significantly changed. The one-electron reduction of the complex did not afford the
Co(I) species, but the ligand-reduced radical anion, which was characterized by electrospectrochemistry.
The generated ligand-reduced species reacted with alkyl halides to form the Co(III)-alkyl complex. As a
result, the reduction potential of the electrolytic reaction could be directly controlled by the substituents
of the porphycene. The catalytic reaction with trichloromethylbenzene was also performed and it was
found that the ratio of the obtained products was changed by the reduction potentials of the catalyst, i.e.
the cobalt porphycenes.
KEYWORDS: cobalt complex, porphycene, ligand reduction, dehalogenation reaction.
using metal complexes with redox active ligands depend
INTRODUCTION
on the electronic state of both the central metal and the
Redox-active ligands and/or redox non-innocent
ligand. Collaboration between ligands and central metals
ligands for ligand-centered reactions have attracted
offers new types of reactions.
considerable attention since new reactivity and new
As has been previously reported, the Co(III)-alkyl
reaction mechanisms can be developed by using these
complex is a key intermediate of the reaction of cobalt
ligands [1–3]. While the classic reactions using transition
complexes and light irradiation leads to homolytic
metal complexes were metal-centered, which highly
bond cleavage, which affords the Co(II) complex and
depend on the valence of the central metals, reactions
an alkyl radical [4–9]. Generally, the reactivity of the
cobalt complex could be classified by the valence of the
*Correspondence to:Yoshio Hisaeda, Department of Chemistry
cobalt. Lower-valence cobalt has a higher reactivity: for
and Biochemistry, Graduate School of Engineering, Kyushu
example, in the case of cobalt porphyrin, the Co(I) species
generated by one-electron reduction is sufficiently
reactive to react with alkyl halides to form Co(III)-alkyl
University, Moto-oka 744, Nishi-ku, Fukuoka-shi, Fukuoka
819-0395, Japan. tel.: +81-92-802-2826, fax: +81-92-802-
2827, email: yhisatcm@mail.cstm.kyushu-u.ac.jp.
Copyright © 2019 World Scientific Publishing Company

2
T. KOIDE ET AL.
complexes [10–15]. However, the Co(II) species is less
reactive and cannot react with alkyl halides, but can react
with an alkyl radical to afford the Co(III)-alkyl complex
[16, 17]. There have been several reports of cobalt
complexes using redox-active ligands [3, 18–23].
RESULTS AND DISCUSSION
Synthesis and characterization
The meso-substituted porphycenes, 9,10,19,20-tetra-
phenylporphycene 1, 9,10,19,20-tetrakis(3,5-difluoro-
phenyl)porphycene 2, and 9,10,19,20-tetrakis(3,5-bis(tri-
fluoromethyl)phenyl)porphycene 3, were synthesized by
following earlier reported procedures [33]. The cobalt
complexes 4, 5, and 6 were prepared by the metallation
of each porphycene, i.e. 1, 2, and 3, with cobalt acetate
in phenol under refluxing conditions for 3 h. The yields
of the cobalt complexes 4, 5, and 6 were 96%, 72%, and
83%, respectively (Scheme 1). The structure of 5 was
revealed by a single crystal X-ray diffraction analysis
[34]. The cobalt ion was inserted into the central cavity
and the porphycene skeleton had a planar structure with a
mean plane deviation of 0.016Å for the twenty carbon and
four nitrogen atoms of the porphycene macrocycle. The
meso-3,5-difluorophenyl substituents were perpendicular
to the porphycene plane, indicating that there might be
no π-extension effect by the introduction of the meso-aryl
substituents (Fig. 1). The UV-vis absorption spectra of 4,
5, and 6 exhibited similar shapes with the Soret band and
Q band at 390 and 625 nm, 390 and 618 nm, and 392 and
619 nm, respectively, indicating that the corresponding
band gaps of the MOs of each complex are almost the
same (Fig. 2).
Recently, we reported the cobalt–carbon bond
formation of cobalt porphycene with alkyl halides trig-
gered by the reduction of a ligand [24]. In this reaction
system, the electronic state of the ligand, porphycene,
changes from an 18π aromatic to an open-shell 19π
radical anion due to the low-lying LUMO of the
porphycene [24–27]. Of course, the reactivity of the
ligand increases, but the reaction occurs at the cobalt
center, indicating the activation of the central metal by
reduction of the ligand. Using a combination of both
experimental and theoretical methods, we revealed
the reaction mechanism: the porphycene ligand works
as a non-innocent ligand and the cobalt reacts with an
alkyl halide via the SN2-type transition state. This result
encouraged us to further investigate the porphycene
ligand for application to the catalytic reaction. We
also reported the effect of peripheral modification of
the ligand. The hydrogenation of the b position of the
porphycene caused a change in the reduction site from
the ligand to central cobalt to afford the Co(I) species
by one-electron reduction [28]. However, the synthesis
and peripheral modification of porphycene are rather
difficult compared to porphyrin [29, 30]. For a better
understanding of the effect of the electronic state of the
ligand, systematic tuning of the redox potentials by the
introduction of substituents is important.
Electrochemistry
The electronic effect of the meso-substituents was
confirmed by electrochemical analysis; i.e. cyclic
voltammetry (CV). The electrochemical analyses were
all performed under nitrogen in a glove box. As
expected, both reduction potentials and oxidation
potentials were shifted to the positive side in the order
of 4<5<6. All of them showed two reversible reduction
processes. The first reduction potentials of 4, 5, and 6
were exhibited at -0.623, -0.525, and -0.454 V (vs. Ag/
Ag/Cl), respectively, which were shifted depending on
In this study, for the efficient modification of
cobalt porphycene, we selected the meso-substituted
porphycenes, which can be prepared in shorter steps
with a high yield [31–33]. We synthesized several Co(II)
complexes with the periphery modified porphycenes and
carried out electrochemical experiments and catalytic
dehalogenation reactions. Since the one-electron
reduction of the ligand promotes the reaction, it could
be expected that the modification of the ligand directly
affects the reactivity of the complex.
R
R
R
R
N
H
N
N
H
N
N
N
Co(OAc)2
R
R
R
R
R
R
R
R
Co
phenol
reflux, 3 h
N
N
R
R
R
R
1: R = H
2: R = F
4: R = H
5: R = F
96%
72%
83%
3: R = CF3
6: R = CF3
Scheme 1. Synthesis of Co(II) porphycenes with meso-aryl substituents
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 2–8

ELECTROCHEMICAL PROPERTIES AND CATALYTIC REACTIVITY OF COBALT COMPLEXES
3
Fig. 3. Cyclic voltammograms of 4, 5, and 6 in DMF
Fig. 1. X-Ray crystal structures of 5. Thermal ellipsoids are
drawn at the 50% probability level. Solvent melecules were
omitted for clarity
Fig. 2. UV-vis absorption spectra of 4, 5, and 6 in CH2Cl2
Fig. 4. Time-resolved UV-vis absorption spectra for the
reduction of 4 in DMF + 0.1 M TBAClO4 at a controlled
potential of -0.8 and -1.2 V for the 1st and 2nd reduction steps,
respectively. WE: Pt mesh, CE: Pt, RE: Ag/AgCl
the strength of the electron-withdrawing properties of
the substituents (Fig. 3). This result indicates that the
meso-aryl substituents do not affect to the HOMO–
LUMO energy gaps but do affect the energy levels of the
molecular orbitals.
after the second reduction step at -1.20 V (vs. Ag/AgCl)
(Fig. 4). Similar spectral changes were observed for 5
and 6 under the reduction potential of -0.70 and -1.1 V
and -0.60 and -1.0 V (vs. Ag/AgCl), respectively (Figs
S1 and S2). The dramatic change in these absorption
spectra indicated that the one-electron reduction did not
occur at the cobalt center but at the porphycene ligands
to afford the radical anion species by the first reduction
step and that the radical anion species disappeared by
the second reduction (Scheme 2a) [24–26]. The electron
Electrospectrochemistry
To confirm the generation of radical anion species of
the cobalt porphycenes 4, 5, and 6, the absorption spectra
and ESR spectra were measured. In the case of 4 in DMF,
the original absorptions at 390 and 635 nm became weaker
and new absorption bands at 755 and 880 nm appeared
under the reduction potential of -0.80 V (vs. Ag/AgCl).
The absorption bands at 755 and 880 nm disappeared and
a broad absorption between 250–500 nm was observed
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 3–8

4
T. KOIDE ET AL.
hyperfine coupling signal, the g values of the signals
were 2.0031 and 2.0030, respectively, suggesting the
generation of a ligand-reduced species of the cobalt
complexes (Figs S3 and S4).
Reaction with alkyl halide and characterization
of cobalt-alkyl complex
Next, the reactivities of the cobalt porphycenes with
alkyl halides were explored. After the addition of 50
equivalents of iodomethane to the solution, the cyclic
voltammograms of 4, 5, and 6 were changed. In the case
of 4, a new reduction wave appeared at -0.735 V, shifted
to the negative side compared to the original reduction
wave, suggesting the reaction of the one-electron
reduced species with iodomethane in the system. The
new reduction processes observed at -0.709 and -1.007 V
after the addition of iodomethane could be assigned to the
reduction potential from the neutral state to the radical
anion state and from the radical anion to dianion species
of the Co(III)–CH3 complex (Fig. 6). This phenomenon
is the same for the other cobalt complexes, 5 and 6. The
reduction potentials observed by CV in the presence
of iodomethane for 5 and 6 were –0.614, -0.889 V and
-0.534, -0.782 V (vs. Ag/AgCl), respectively (Figs S8
and S9). The newly appearing redox waves were also
reversible, indicating the stability of the generated
Co(III)–CH3 complexes under the reductive conditions.
The Co(III)-CH3 complexes 7, 8, and 9 were pre-
pared by bulk electrolysis using carbon felt as the
working electrode in an undivided cell in DMF with 50
equivalents of iodomethane and purified by filtration
after adding water to the reaction mixture to obtain the
Fig. 5. ESR spectrum of the one-electron reduced species of 4
after the electrolysis at -0.8V for 1 h and the simulated spectrum
spin resonance (ESR) spectrum of 4 after the electrolysis
showed a signal at g = 2.0071 with complicated hyperfine
couplings, which could be assigned to the organic radical
delocalized on the macrocyclic conjugation system of
the porphycene ligand. Based on the simulation of the
spectrum, the hyperfine coupling constants (A values)
were 0.741 (4H), 0.709 (4H), 0.640 (8H), 0.639 (8H)
and 0.600 (4H) G, indicating that the unpaired electron
is delocalized not only on the porphycene skeleton, but
also on the phenyl rings at the meso-positions (Fig. 5).
Although the ESR signal observed for the one-electron
reduced species of 5 and 6 did not show an assignable
–
2–
+ e–
+ e–
R’
R’
R’
R’
R’
R’
R’
R’
R’
R’
R’
R’
N
N
N
N
N
N
N
N
N
N
N
CoII
CoII
CoII
– e–
DMF
– e–
DMF
N
4: R’ = Ph
5: R’ = 3,5-F2Ph
6: R’ = 3,5-(CF3)2Ph
(a)
CH3
–
+ e–
DMF
R’
R’
R’
R’
CH3I
DMF
R’
R’
R’
R’
R’
R’
R’
N
N
N
N
N
N
N
N
N
N
CoII
CoIII
CoII
N
N
R’
4: R’ = Ph
5: R’ = 3,5-F2Ph
6: R’ = 3,5-(CF3)2Ph
7: R’ = Ph
8: R’ = 3,5-F2Ph
9: R’ = 3,5-(CF3)2Ph
(b)
Scheme 2. (a) Two step one-electron reduction of 4, 5, and 6 and (b) electrolytic synthesis of Co(III)-CH3 complexes 7, 8, and 9
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 4–8

ELECTROCHEMICAL PROPERTIES AND CATALYTIC REACTIVITY OF COBALT COMPLEXES
5
changes the first reduction potential of the cobalt
porphycene, which corresponds to the energy
level of the LUMO, and the reaction via the
ligand-reduced species of the cobalt porphycene
proceeds under a controlled reduction potential.
Catalytic properties
For further application of this reactivity, we
performed a catalytic reaction using trichloro-
methylbenzene as a substrate, which had been
reported for the system using a vitamin B12 deriva-
tive as a catalyst [35]. The electrolytic reaction of
cobalt porphycene with trichloromethylbenzene
was first monitored by a CV measurement in
DMF. For complex 4, the catalytic current was
observed at around -0.6 V (vs. Ag/AgCl) and the
reduction process became irreversible, indicating
the formation of the Co(III)-alkyl complex
Fig. 6. Comparison of the cyclic voltammograms of 4, 4 with CH3I
(50 equiv.), and 7 in DMF
product as a precipitate. The obtained solid was washed
and the fast cleavage of the cobalt–carbon bond in the
system. The bond dissociation gave the alkyl radical,
the porphycene cobalt complex returned to the Co(II)
neutral state and the catalytic reaction proceeded. For
complexes 5 and 6, the cyclic voltammograms also
showed similar behaviors with the catalytic current at
positively shifted potentials compared to that of 4. For
a better understanding of this reaction, bulk electrolysis
in an undivided cell using carbon felt as the working
electrode, 200 equivalents of trichloromethylbenzene
as the substrate, biphenyl as the internal standard was
done to analyze the product by GC-MS. The reaction
of each cobalt complex, 4, 5, and 6, was carried out at
-0.80 V, -0.70 V, and -0.60 V (vs. Ag/AgCl), respectively,
for 3 h and the resulting products were analyzed by
GC-MS after the purification by short silica gel column
chromatography. The electrolysis potentials were selected
to be able to generate the one-electron reduced species
of each complex. The same reaction was performed
using b-tetrapropyl porphycene Co(II) complex 12 [24]
at -1.20 V (vs. Ag/AgCl) for the comparison. From the
GC-MS analysis, there were two main products: one was
1,2-diphenyl-1,1,2,2-tetrachloroethane 10 and the other
was dichloromethylbenzene 11 (Scheme 3). In the case
of complex 4, 5, and 6, the main product was 10 and only
a little amount of 11 was observed, while the conversion
rate, yield and turnover number (TON) decreased as
with methanol/water in the dark (Scheme 2b). From
the H NMR spectrum of 7, the signal of the methyl
1
proton was observed at -4.16 ppm (Fig. S5). The high
field shift of the methyl proton indicated the shielding
effect by the ring current of the porphycene since the
methyl group is located on the central cobalt as the axial
ligand. Focusing on the signals of the phenyl groups,
signals of ortho- and meta- protons were exhibited as
two signals for each, indicating that the protons of upper
side and lower side against the porphycene plane were
distinguishable because of the existance of the methyl
group as the axial ligand. These features of the 1H NMR
spectrum were similar for those of 8 and 9 (Figs S6 and
S7). The reduction potentials of the isolated Co–CH3
complex were -0.733 and -1.022 V (vs. Ag/AgCl), which
are consistent with the observed reduction potentials of
4 with CH3I (Fig. 6). The cyclic voltammogram of 8 and
9 also exhibited two reversible reduction processes at
-0.604 and -0.870 V and -0.534 and -0.785 V (vs. Ag/
AgCl), respectively, which showed good agreement with
the results of the CVs of 5 and 6 with iodomethane (Figs
S8 and S9). Based on the above results, the reaction
mechanism could be proposed in which the one-electron
reduced anion radical species of the Co(II) porphycene
reacts with the alkyl halide to form the Co(III)-alkyl
complex. Thus, it could be said that the introduction of
meso-substituents to the porphycene skeleton effectively
n-Pr
n-Pr
Cl
H
Cl
Cl
Co catalyst
Cl
Cl
Cl Cl
Cl Cl
10
N
N
N
N
(4 or 5 or 6 or 12)
Co
+
DMF
electrolysis
n-Pr
n-Pr
11
12
Scheme 3. Catalytic dehalogenation and dimerization reaction of trichloromethylbenzene using Co(II) porphycenes as a catalyst
under electrochemical reductive conditions. 12 is the previously reported complex
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 5–8

6
T. KOIDE ET AL.
Table 1. The yields of the products of the catalytic reaction
checked by GC-MS analysis
electrode and a platinum wire counter electrode in
dehydrated solvents containing 0.1 M Bu4NClO4 as a
supporting electrolyte under a nitrogen atmosphere at
room temperature. In the experiment, we employed a
Ag/10 mM AgCl reference electrode. The reference
electrode was separated from the bulk solution by a
fritted-glass bridge filled with 0.1 M NaCl aqueous
solution.
Data from X-ray diffraction were collected on a Rigaku
XtaLAB mini diffractometer at 123(2)K using Mo Ka
radiation (l = 0.71073Å). Collected data were integrated,
corrected, and scaled using the program CrysAlisPro.
The structures were refined using SHELXT (Sheldrick,
2015) Intrinsic Phasing and SHELXL (Sheldrick, 2015).
The program Olex2 was used as a graphical interface.
All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were located at calculated positions.
The gas chromatography-mass spectra (GC-MS) were
obtained using a Shimadzu GCMS-QP 2010 equipped
with an Agilent J&W DB-1 column (length:30 m; ID:
0.25mm, film:0.25mm)withheliumasthecarriergas. For
the measurement, the injector and detector temperatures
were 250°C, the oven temperature was initially held at
100°C for 2 min, then increased to 240°C at the rate of
10°C/min.
Catalyst Electrolysis Conversion
potential/V
10
11
TON
4
5
-0.8
-0.7
-0.6
-1.2
62%
50%
37%
28%
53%
2%
110
94
47% <1%
21% <1%
15% 12%
6
42
12
54
the electrolysis potential become more positive (Table
1). TON is calculated from the yield of the products
against the catalyst, cobalt porphycene. The results were
different from that using the complex 12 as a catalyst.
When 12 was used as a catalyst, a considerable amount
of the simply reduced species (dechlorinated species) 11
was also observed along with the dimer 10. The generated
alkyl radical is more easily reduced at a more negative
potential and gave the anion species, which became a
dehalogenated product of the substrate 11, suggesting
that the peripheral modification of the porphycene ligand
is effective to control the reduction potentials, reactivity,
and the products of the catalytic reaction.
Synthesis
Synthesis of freebase porphycenes, 1, 2 and 3. Meso-
substituted porphycenes 1, 2 and 3 were synthesized as
described in the literature [33].
EXPERIMENTAL
Synthesis of meso-tetraphenylporphycene cobalt
complex 4: Synthesis of the cobalt complex 4 is described
in another paper [34].
General
Reagents and solvents of best grade available were
purchased from commercial suppliers and were used
without further purification unless otherwise noted. Dried
dichloromethane (CH2Cl2) was obtained by distillation
from CaH2 under a N2 atmosphere.
Synthesis of meso-tetrakis(3,5-difluorophenyl)por-
phycene cobalt complex 5. A mixture of tetrakis(3, 5-
difluorophenyl)porphycene 2 (10.0 mg, 0.013 mmol),
cobalt(II) acetate tetrahydrate (32.0 mg, 0.13 mmol) and
phenol (5 mL) were reflux at 170°C for 3 h. After cooling
to room temperature, the mixture was dissolved using
CH2Cl2. The organic layer was washed with water once,
with a 5% NaOH solution 10 times and with water again
once, then dried over anhydrous Na2SO4 and purified
by a silica gel column with CH2Cl2. After evaporation
the main aquamarine band was collected. The solvent
Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker Avance 500MHz NMR spectro-
meter. The resonance frequencies were 500 MHz for
1H. Chemical shifts were reported as d values in ppm
relative to tetramethylsilane. High-resolution fast atom
bombardment mass spectra (HR-FAB-MS) were mea-
sured with 3-nitrobenzyl alcohol (NBA) as a matrix and
recorded on a JMS-700 spectrometer (JEOL, Japan).
Ultraviolet–visible-near infrared (UV-vis-NIR) absorption
spectra were recorded on U-3310 spectrometer (Hitachi,
Japan) and V-670KS spectrometer (JASCO, Japan).
Electron spin resonance (ESR) measurement was carried
out with a Bruker EMX 8/2.7. The simulation of the ESR
spectrum was carried out using Bruker WinEPR SimFonia
software.
was evaporated to yield 5 as purple solid (7.70 mg,
-1
72%). UV-vis (CH2Cl2): lmax, nm (e/M-1 cm ) = 323
.
(29700), 390 (98500), 617 (53600). HR-MS (FAB): m/z
815.0894 (calcd. for [M]+ 815.0892). Anal. calc. for:
C44.5H21CoN4Cl (C44H20CoN4 + 0.5 CH2Cl2): C, 62.29; H,
2.47; N, 6.53%. Found: C, 62.26; H, 2.45; N, 6.65.
Synthesis of meso-tetrakis(3,5-bis(trifluoromethyl)
phenyl)porphycene cobalt complex 6. A mixture of
tetrakis(3, 5-bis(trifluoromethyl)phenyl)porphycene 3
(23.0 mg, 0.0189 mmol), cobalt(II) acetate tetrahydrate
(50.0 mg, 0.201 mmol) and phenol (10 mL) were refluxed
at 170°C for 3 h. After cooling to room temperature, the
Redoxpotentialsweremeasuredbycyclicvoltammetry
method on an ALS electrochemical analyzer model 630C
in a glove box. Cyclic voltammetric measurements were
carried out using a 1.6 mm diameter platinum working
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 6–8

ELECTROCHEMICAL PROPERTIES AND CATALYTIC REACTIVITY OF COBALT COMPLEXES
7
mixture was dissolved by CH2Cl2. The organic layer
electrospectrochemistry and ESR measurements after
electrolysis. The ligand-reduced species could react
with alkyl halides to afford Co(III)-alkyl complexes
and their reduction potentials and reactivity could be
controlled by the substituents at the meso positions. The
Co(III)–CH3 complexes 7, 8 and 9 were synthesized and
was washed with water once, with 5% NaOH solution
10 times, and with water for once, then dried over
anhydrous Na2SO4 and purified by silica gel column with
CH2Cl2. After evaporation, the main aquamarine band
was collected. The solvent was evaporated to yield 6
1
as purple solid (20.0 mg, 83%). UV-vis (CH2Cl2): lmax
,
characterized by H NMR and MS. Catalytic reactions
nm (e/M-1 cm ) = 299 (21500), 336 (sh, 28500), 392
(108000), 619 (58900). HR-MS (FAB): m/z 1215.0623
([M]+ 1215.0637). Anal. calc. for: C52H20CoF24N4: C,
51.38; H, 1.66; N, 4.61%; Found C, 51.56; H, 1.80;
N, 4.56.
using the cobalt porphycenes were also performed
and the product ratio of the dimer and dechlorinated
form of the substrate were found to be changed by the
catalyst and reduction potential. The ligand reduction
mechanism for the formation of the Co(III)-alkyl
complex became more useful for easier synthesis of the
cobalt porphycenes and it also enabled easier control of
the reduction potential of the ligand.
-1
.
Synthesis of porphycene cobalt-methyl complexes
7–9. The controlled-potential electrolysis of porphycene
cobalt complex 4–6 (2 × 10-3 mmol) was dissolved in
DMF (5 mL) with 0.1 M n-Bu4NClO4. The solution was
carried out in a one-compartment cell with a zinc plate
anode as a sacrificial electrode and a carbon felt cathode
and electrolysis at -0.8, -0.7, or -0.6V vs. Ag/AgCl in
glove box at room temperature. The zinc electrode was
used as a sacrificial anode. Electrolysis for one hour and
then 50 equiv. CH3I was added, continue stirring for 5 min
under electrolysis conditions. The solution was diluted
with water and the solvent was removed by filtration,
then the solid was washed with a 50% methanol aqueous
solution, and dried under reduced pressure to afford
the porphycene cobalt methyl complexes 7–9 as purple
solids in about 100% yield.
Acknowledgments
This work was partially supported by JSPS KAKENHI
Grant Number 18H04265 in Precisely Designed
Catalysts with Customized Scaffolding, Grant Number
JP16H04119 (Grant-in-Aid for Scientific Research for
Y. H.), and Grant Number JP17H04875 (Grant-in-Aid
for Young Scientists (A) for T. O.), and by JSPS and
PAN under the Research Cooperative Program Grant
Number AJ179063(29-9111-t11). T. K. is grateful for the
financial support from the Toyota Physical and Chemical
Research Institute, Tonen General Sekiyu, Casio Science
Promotion Foundation and Kyushu University QR
program.
Compound 7. Electrolysis at -0.8V vs. Ag/AgCl for
1
1 h. H NMR (500 MHz, CDCl3): dH, ppm 9.14 (4H, d,
b-H), 8.29 (4H, d, b-H), 7.83 (4H, m, Ph), 7.23–7.35
(16H, m, Ph), -4.16 (3H, s, CH3). UV-vis (CH2Cl2): lmax
,
Supporting information
nm 291 (sh), 390, 626.
Spectroelectrochemical measurements, ESR spectra,
1H NMR spectra, cyclic voltammetry and UV-vis
absorption spectra are given in the supplementary
material. This material is available free of charge via
the Internet at http://www.worldscinet.com/jpp/jpp.
shtml. Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under
numbers CCDC 1910791 (5). Copies can be obtained on
request, free of charge, via http://www.ccdc.cam.ac.uk/
data_request/cif or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44 1223-336-033 or email: deposit@ccdc.cam.
ac.uk).
Compound 8. Electrolysis at -0.7V vs. Ag/AgCl for
1 h. H NMR (500 MHz, CDCl3): dH, ppm 9.21 (4H,
1
d, b-H), 8.33 (4H, d, b-H), 7.39 (4H, d, Ar), 6.98 (4H,
d, Ar), 6.91 (4H, m, Ar), -4.16 (3H, s, CH3). UV-vis
(CH2Cl2): lmax, nm 288, 390, 618.
Compound 9. Electrolysis at -0.6V vs. Ag/AgCl for
1
1 h. H NMR (500 MHz, CDCl3): dH, ppm 9.29 (4H, d,
b-H), 8.25 (4H, d, b-H), 8.20 (4H, s, Ar), 7.90 (4H, s, Ar),
7.85 (4H, s, Ar), -3.95 (3H, s, CH3). UV-vis (CH2Cl2):
l
max, nm 277, 392, 620.
CONCLUSION
The cobalt complexes of the meso-aryl substituted
porphycenes, 4, 5, and 6, were synthesized and
characterized by MS, UV-vis absorption, elemental
analysis and X-ray diffraction analysis. Their
electrochemical properties were explored by CV
and DPV. The reduction potentials of each complex
were shifted in the order of 4<5<6, depending on
the strength of the electron-withdrawing effect of
the meso-substituents. The one-electron reduction of
these Co(II) porphycenes produced the ligand-reduced
radical anion species, which were confirmed by
REFERENCES
1. van der Vlugt JI. Chem. — Eur. J. 2019; 25:
2651–2662.
2. Luca OR and Crabtree RH. Chem. Soc. Rev. 2013;
42: 1440–1459.
3. Lyaskovskyy V and de Bruin B. ACS Catal. 2012;
2: 270–279.
4. Shimakoshi H and Hisaeda Y. Current Opinion in
Electrochemistry 2018; 8: 24–30.
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 7–8

8
T. KOIDE ET AL.
5. Tahara K, Pan L, Ono T and Hisaeda Y. Beilstein J.
Org. Chem. 2018; 14: 2553–2567.
6. Morita Y, Oohora K, Sawada A, Kamachi T,
Yoshizawa K and Hayashi T. Inorg. Chem. 2017;
56: 1950–1955.
25. Gisselbrecht JP, Gross M, Kocher M, Lausmann
M and Vogel E. J. Am. Chem. Soc. 1990; 112:
8618–8620.
26. Bernard C, Gisselbrecht J, Gross M and Vogel E.
Inorg. Chem. 1994; 33: 2393–2401.
7. Giedyk M, Goliszewska K and Gryko D. Chem.
Soc. Rev. 2015; 44: 3391–3404.
8. Lexa D and Saveant J-M. Acc. Chem. Res. 1983; 16:
235–243.
9. Wayland BB, Gridnev AA, Ittel SD and Frydlc M.
Inorg. Chem. 1994; 33: 3830–3833.
27. Kadish KM, Boulas PL, Kisters M, Vogel E,
Aukauloo AM, D’Souza F and Guilard R. Inorg.
Chem. 1998; 37: 2693–2700.
28. Hashimoto K, Koide T, Okawara T, Shimakoshi H,
Hori Y, Shiota Y, Yoshizawa K and Hisaeda Y. Dal-
ton Trans. 2019; 48: 872–881.
10. Ogoshi H, Watanabe E, Koketsu N and Yoshida Z.
Bull. Chem. Soc. Jpn. 1976; 49: 2529–2536.
11. Zheng GD,YanY, Gao S, Tong SL, Gao D and Zhen
KJ. Electrochim. Acta 1996; 41: 177–182.
12. Zhu W, Fang Y, Shen W, Lu G, Zhang Y, Ou Z and
Kadish KM. J. Porphyrins Phthalocyanines 2011;
15: 66–74.
13. Maiya GB, Han BC and Kadish KM. Langmuir
1989; 5: 645–650.
14. Lexa D, Saveant J-M, Su K-B and Wang D-L. J.
Am. Chem. Soc. 1988; 110: 7617–7625.
29. Sánchez-Garcia D and Sessler JL. Chem. Soc. Rev.
2008; 37: 215–232.
30. Anguera G and Sánchez-Garcia D. Chem. Rev.
2017; 117: 2481–2516.
31. Anju KS, Ramakrishnan S, Thomas AP, Suresh E
and Srinivasan A. Org. Lett. 2008; 10: 5545–5548.
32. Ganapathi E, Chatterjee T and Ravikanth M. Eur. J.
Org. Chem. 2014; 6701–6706.
33. Ono T, Xu N, Koga D, Ideo T, Sugimoto M and
Hisaeda Y. RSC Adv. 2018; 8: 39269–39273.
34. Sakakibara E, Shisaka Y, Onoda H, Koga D, Xu N,
Ono T, Hisaeda Y, Sugimoto H, Shiro Y, Watanabe
Y and Shoji O. RSC Adv. 2019; 9: 18697–18702.
35. Shimakoshi H, Luo Z, Inaba T and Hisaeda Y. Dal-
ton Trans. 2016; 45: 10173–10180.
15. Kadish KM, Lin XQ and Han BC. Inorg. Chem.
1987; 26: 4161–4167.
16. Wayland BB, Gridnev AA, Ittel SD and Frydlc M.
Inorg. Chem. 1994; 33: 3830–3833.
17. Glod G, Angst W, Holliger C and Schwarzenbach
R. Environ. Sci. Technol. 1997; 31: 253–260.
18. Smith AL, Hardcastle KI and Soper JD. J. Am.
Chem. Soc. 2010; 132: 14358–14360.
19. Dzik WI, van der Vlugt JI, Reek JNH and de Bruin
B. Angew. Chem., Int. Ed. 2011; 50: 3356–3358.
20. Paul GC, Ghorai S and Mukherjee C. Chem. Com-
mun. 2017; 53: 8022–8025.
21. Bowman AC, Milsmann C, Atienza CCH, Lob-
kovsky E, Wieghardt K and Chirik PJ. J. Am. Chem.
Soc. 2010; 132: 1676–1684.
22. Semproni SP. Milsmann C and Chirik PJ. J. Am.
Chem. Soc. 2014; 136: 9211–9224.
36. Crystal data for
5
(from CH2Cl2/hexane):
C90H44Cl3Co2F16N8, Fw 1765.54, monoclinic, space
group P21/c, a = 8.7161 (4), b = 12.4531 (6), c =
18.1269 (8) Å, b = 99.414 (4), V = 1941.04 (16) Å3,
Z = 1, T = 123 K, d = 1.51 gcm-3, GOF = 1.071, R1
(I > 2s (I)) = 0.0573 and wR2 = 0.1780 (all data),
CCDC 1910791.
37. The cobalt-methyl complexes 7–9 were unsta-
ble to light and heat and the corresponding mass
peaks were not obseaved by ESI-TOF MS. In the
observerd absorption spectra of 7, 8 and 9, the
absorption bands around 330 nm, which are char-
acteristic to the Co(II) species, were weaker than
those of 4, 5, and 6, indicating the valence of the
central cobalt was mainly +3 (Fig. S10) [38].
38. HayashiT, Okazaki K, Shimakoshi H, Tani F, Naruta
Y and Hisaeda Y. Chem. Lett. 2000; 2: 90–91.
23. Shiga T, Kumamaru R, Newton GN and Oshio H.
Dalton Trans. 2018; 47: 7804–7811.
24. Koide T, Aritome I, Saeki T, Morita Y, Shiota Y.
Yoshizaw K, Shimakoshi H and Hisaeda Y. ACS
Omega 2018; 3: 4027–4034.
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 8–8