Synthesis and electrochemistry of cobalt tetrabutanotriarylcorroles. Highly selective electrocatalysts for two-electron reduction of dioxygen in acidic and basic media

Article abstract of DOI:10.1142/S1088424616500280

Three β,β'-tetrabutano-substituted cobalt(III) triarylcorroles were synthesized and characterized by UV-vis, ¹H NMR spectroscopy and mass spectrometry as well as electrochemistry and spectroelectrochemistry. The examined compounds are represented as butano-(YPh)₃CorCo(PPh3), where Cor represents the core of the corrole and Y is a CH₃, H or Cl group on the para-position of each meso-phenyl ring of the macrocycle. Each corrole undergoes two stepwise cobalt-centered reductions leading to formation of Co(II) and Co(I) derivatives in CH₂Cl₂ containing 0.1 M TBAP. Three reversible one-electron oxidations were observed within potential, ranging from 0.16 to 1.40 V in CH₂Cl₂. The first oxidation generates a mixture of Co(III) cation radical and Co(IV), while the second oxidation is metal-centered to give the Co(IV) corrole. Each cobalt corrole was examined as a catalyst for electroreduction of O₂ when coated on an edge-plane pyrrolytic graphite electrode in acidic and basic solutions. The results indicate that the cobalt tetrabutanotriarylcorroles can act as selective catalysts for the 2e reduction of molecular oxygen to give H₂O₂ as the final product under the given solution conditions.

Full text of DOI:10.1142/S1088424616500280

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2016; 20: 1–9
DOI: 10.1142/S1088424616500280
Published at http://www.worldscinet.com/jpp/
Synthesis and electrochemistry of cobalt tetrabutanotriaryl-
corroles. Highly selective electrocatalysts for two-electron
reduction of dioxygen in acidic and basic media
a
a◊
a
a◊
a
Jing Sun , Zhongping Ou* , Rui Guo , Yuanyuan Fang , Minyuan Chen ,
b
b◊
Yang Song and Karl M. Kadish*
a
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013, China
Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA
b
Dedicated to Professor Kevin M. Smith on the occasion of his 70th birthday
Received 14 December 2015
Accepted 23 January 2016
ABSTRACT: Three b,b′­tetrabutano­substituted cobalt(III) triarylcorroles were synthesized and
1
characterized by UV­vis, H NMR spectroscopy and mass spectrometry as well as electrochemistry
and spectroelectrochemistry. The examined compounds are represented as butano­(YPh) CorCo(PPh ),
3
3
where Cor represents the core of the corrole and Y is a CH , H or Cl group on the para­position of each
3
meso­phenyl ring of the macrocycle. Each corrole undergoes two stepwise cobalt­centered reductions
leading to formation of Co(II) and Co(I) derivatives in CH Cl containing 0.1 M TBAP. Three reversible
2
2
one­electron oxidations were observed within potential, ranging from 0.16 to 1.40 V in CH Cl . The first
2
2
oxidation generates a mixture of Co(III) p­cation radical and Co(IV), while the second oxidation is metal­
centered to give the Co(IV) corrole. Each cobalt corrole was examined as a catalyst for electroreduction
of O when coated on an edge­plane pyrrolytic graphite electrode in acidic and basic solutions. The
2
results indicate that the cobalt tetrabutanotriarylcorroles can act as selective catalysts for the 2e reduction
of molecular oxygen to give H O as the final product under the given solution conditions.
2
2
KEYWORDS: cobalt corroles, butano­substitution, electrochemistry, dioxygen reduction.
triarylcorroles or tetraarylporphyrins containing iron,
INTRODUCTION
cobalt or manganese central metal ions can significantly
affect the catalytic activity of the compound to act as
an electrocatalyst for reduction of dioxygen [18–24].
However, to the best of our knowledge, it is still not
known how the addition of butano­groups on the b,b′­
pyrrole positions of a cobalt corrole will affect the
electrocatalyticactivityofthesetypesofcompoundswhen
adsorbed on an electrode surface. This is investigated
in the present paper where we have synthesized three
cobalt corroles containing four b,b′­butano substituents
and characterized them as to their catalytic activity
for reduction of molecular oxygen in acidic and basic
solutions when adsorbed the corrole catalyst on an
electrode surface. The number of electron transferred
and the percentage of H O produced in the catalytic
Cobalt corroles can have potential applications as
catalysts for a variety of reactions [1–10]. In this regard,
part of our own research efforts have been directed
towards the synthesis [6–8, 11–16] and characterization
of substituted cobalt corroles as catalysts for the
electroreduction of O in acid media [8, 15–18].
2
We have demonstrated that the addition of substi­
tuents on meso­phenyl and/or b­pyrrole positions of
◊
SPP full member in good standing
*
Correspondence to: Zhongping Ou, email: zpou2003@yahoo.
com, tel: +86 511­8879­1800, fax: +86 0511­8879­1800; Karl
M. Kadish, email: kkadish@uh.edu, tel: +1 (713)­743­2740,
fax: +1 (713)­743­2745
2
2
Copyright © 2016 World Scientific Publishing Company

2
J. SUN ET AL.
(a) Butano-cobalt corroles
CH3
Cl
N
N
CoIII
N
N
CoIII
N
N
CoIII
H3C
CH3
Cl
Cl
N
N
N
N
N
N
PPh3
PPh3
PPh3
1
a-CH Ph
2a-Ph
3a-ClPh
3
(b) Non-butano-cobalt corroles
CH3
Cl
N
N
CoIII
N
N
CoIII
N
N
CoIII
H3C
CH3
Cl
Cl
N
N
N
N
N
N
PPh3
PPh3
PPh3
1
b-CH Ph
2b-Ph
3b-ClPh
3
Chart 1. Structures of (a) butano­cobalt corroles and (b) non­butano­cobalt corroles
reduction of oxygen were calculated from cyclic and
linear sweep voltammetry coupled with measurements at
a rotating disk electrode (RDE).
is shown in Scheme 1. The functionalized pyrrole ring,
4,5,6,7­tetrahydroisoindole, which was synthesized
according to a procedure described in the literature
[26], was used as starting material to react with a
corresponding arylaldehyde. The aldehyde and pyrrole
(ratio 1/2) were dissolved in CH OH/H O and stirred
The investigated compounds are represented as
butano­(YPh) CorCo(PPh ), where Cor is the core of the
3
3
corrole and Y is CH , H or Cl group on the para­position
3
3
2
of the phenyl rings of the compound, as seen in Chart 1
which also includes the structure of the related non­
butano­substituted cobalt corroles.
for 15 min under N before the addition of HCl as
catalyst, and the resulting mixture was stirred for 3 h.
2
The reaction mixture was extracted by CHCl and then
3
Reduction/oxidation potentials and UV­visible spectra
of each neutral, oxidized and reduced species were also
measured in dichloromethane (CH Cl ) containing 0.1 M
tetra­n­butylammonium perchlorate. The effect of the
butano substituents on redox potentials and the site of
electron transfer is also discussed.
oxidized by p­chloranil in this solvent to give a mixture
including the free­base tetrabutanocorrole. The free­
base tetrabutanotriarylcorroles have been synthesized
previously by Paolesse and co­workers [27], but due to
their poor stability they were immediately oxidized to the
corresponding tetrabenzocorroles. Our attempts to purify
the mixture by chromatographic separation also failed.
To avoid decomposition of the free­base corrole during
the purification process, the mixture was directly utilized
to react with the salt of cobalt acetate and the yield of
cobalt tetrabutanocorroles 1a–3a was 7–8%.
2
2
RESULTS AND DISCUSSION
Synthesis and characterization
1
H NMR spectra of butano­(YPh) CorCo(PPh ) 1a–3a
3
3
Synthesis of the free­base butano­triarylcorroles
was carried out in a mixture of CH OH/H O [25]. The
were measured in CDCl . As an example, the spectrum
2
3
2
of butano­(CH Ph) CorCo(PPh ) 1a is shown in Fig. S1,
3
3
3
III
synthetic route of butano­(YPh) CorCo (PPh ) 1a–3a
whichalsoincludesthespectrumof(CH Ph) CorCo(PPh )
3
3
3 3 3
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 2–9

SYNTHESIS AND ELECTROCHEMISTRY OF COBALT TETRABUTANOTRIARYLCORROLES
3
R
CH3OH, H2O, HCl
N2, rt, dark, 3 h
CHCl3, chloranil
rt, 1.5 h
Co(OAc)2, PPh3
+
1a-3a
CH3OH, reflux, 1 h
N
H
CHO
Scheme 1. Synthesis routes for compounds 1a–3a
1b for a comparison.As seen in Fig. S1a, the resonances at
d = 7.73, 7.10 and6.55 pmare assigned tothe meso-phenyl
protons while the resonances of the triphenylphosphine
protons appear at 7.26, 6.72 and 5.07 ppm for 1a. The
resonances of protons on the para­position of the meso-
phenyl appear at 2.51 ppm, while the signals at 3.42 and
2
.10–1.12 ppm are attributed to the b­butano protons of
1
a. The d of triphenylphosphine protons for 1a are shifted
downfield, as compared to the d values of PPh (7.06, 6.71
3
and 4.70 ppm) for (CH Ph) CorCo(PPh ) 1b (Fig. S1b),
3
3
3
indicating an effect of the b­butano­substituents on the
chemical shifts of 1a. The mass spectra of 1a–3a display
m/z peaks at 838.890, 798.433 and 900.609, respectively,
+
which correspond in each case to [M­PPh ] species.
3
The electronic absorption spectra of the butano­
substituted corroles 1a–3a and the related non­butano­
substituted compounds 1b–3b are illustrated in Fig. 1.
As seen in the figure, one sharp single Soret band and
one weak Q­band were observed for compounds 1b–3b
in CH Cl . Compounds 1a–3a also exhibit a sharp Soret
2
2
band and a weak Q­band in the same solvent. However,
a shoulder peak at 408–414 nm can also be observed for
1
a–3a, as seen from the solid lines in Fig. 1. The Soret
band of 1a–3a was blue­shifted by 10–15 nm while the
Q­band was red­shifted by 13–14 nm, as compared to the
non­butano­substituted cobalt corroles 1b–3b.
Fig. 1. UV­vis spectra of cobalt butano­corroles and non­
butano­corroles in CH Cl
Electrochemistry
2
2
Electrochemistry of compounds 1a–3a were carried
out in CH Cl containing 0.1 M TBAP as supporting
dissociation of the axialy bound PPh to give four­
2
2
3
II ­
electrolyte. Cyclic voltammograms showing the
reductions and oxidations are illustrated in Figs 2 and 3,
respectively, while the redox potentials of 1a–3a are
summarized in Table 1, which also includes the potentials
of 1b–3b obtained under the same experimental
conditions.
coordinate [butano­(YPh) CorCo ] . The four coordinate
3
Co(II) species can be further reduced to its Co(I) form
at more negative potentials or reoxidized at E = ­0.38,
pa
­0.37 and ­0.29 V to give the neutral cobalt(III) corroles.
A similar reduction mechanism was previously proposed
for other related cobalt(III) triarylcorroles [16].
As seen in Fig. 2, each compound undergoes two
irreversible reductions in CH Cl . The first reduction peak
Three reversible one­electron oxidations are observed
for compounds 1a–3a in CH Cl containing 0.1 M TBAP
2
2
2
2
potentials (E ) of 1a–3a range from ­1.09 to ­0.97 V,
and examples of cyclic voltammograms are illustrated in
Fig. 3, which also includes a cyclic voltammogram of 3b
under the same solution conditions. The first oxidation of
1a–3a is located at E1/2 = 0.16–0.26 V, while the second
pc1
while the second peak potentials (E ) range from ­2.03
pc2
to ­1.93 V vs. SCE. The difference in peak potentials
between the first and the second reductions is listed in
Table 1 as DE(1r–2r), which ranges from 0.92 to 0.96 V. The
values are 60–100 mV larger than the DE(1r–2r) for 1b–3b.
and third are located at E = 0.78–0.81V and 1.38–1.40V,
1/2
respectively.
III
The first reductions of butano­(YPh) CorCo (PPh )
The difference in half­wave potentials between the
first two oxidations and the second and third oxidations
are listed as DE1/2(2o–1o) and DE1/2(3o–2o) in Table 1. Both sets
of separations are close to 0.60 V for 1a–3a.
3
3
1
a–3a are assigned to metal­centered processes which
involve an electrochemical EC mechanism to generate
II
­
[
butano­(YPh) CorCo (PPh )] , which undergoes a rapid
3 3
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4
J. SUN ET AL.
Fig. 2. Cyclic voltammograms showing the reductions of butano­(YPh) CorCo(PPh ) 1a–3a in CH Cl containing 0.1 M TBAP
3
3
2
2
Easier oxidations are observed in CH Cl for 1a–3a,
2
2
as compared to 1b–3b in the same solvent. For example,
the first oxidation of 3a is shifted negatively by 0.31 V,
while the second and third oxidations are negatively
shifted by 0.17–0.19 V, as compared to 3b (see Figs 3c
and 3d). This result is consistent with an effect of the
four electron­donating butano groups on the b,b′­pyrrole
positions of compounds 1a–3a.
Spectroelectrochemistry
The singly and doubly reduced corroles in CH Cl
2
2
containing 0.1 M TBAP were characterized by thin­
layer spectroelectrochemistry. The spectral changes of
compounds 1a, 2a and 3a during the first and second
controlled potential reductions are shown in Fig. 4. The
first controlled potential reduction gives a product with a
Soret band at 413–418 nm and two Q­bands at 544–547
and 610–626 nm. Generation of the first one­electron
reduced product, a Co(II) corrole, in the thin­layer cell
is accompanied by a decrease in intensity of the neutral
Soret band as a new band grows in, which is red­shifted
by 37–42 nm. The intensity of the Soret band for the first
reduced corrole was slightly increased, while the peak
is blue­shifted during the second controlled potential
reduction to give a final Co(I) corrole product with an
intense Soret band at 410–419 nm (Fig. 4).
Thin­layer UV­visible spectral changes were also
measured for each Co(III) corrole during the first, second
and third controlled potential oxidations in CH Cl
Fig. 3. Cyclic voltammograms showing the oxidations of butano­
(YPh) CorCo(PPh ) 1a–3a and (ClPh) CorCo(PPh ) 3b in CH Cl
containing 0.1 M TBAP
3
3
3
3
2
2
2
2
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J. Porphyrins Phthalocyanines 2016; 20: 4–9

SYNTHESIS AND ELECTROCHEMISTRY OF COBALT TETRABUTANOTRIARYLCORROLES
5
Table 1. Half­wave potentials (V vs. SCE) of compounds 1a–3a and 1b–3b in CH Cl containing 0.1 M TBAP
2
2
a
Compound
Oxidation
2nd
Reduction
Ref.
III
II
II
I
DE1
/2(3o–2o)
3rd
1st
DE1/2(2o–1o)
0.62
Co /Co
Co /Co
DEpc(1r–2r)
0.94
1
2
3
1
2
a­CH Ph
0.60
1.38
1.39
1.40
1.54
1.56
1.59
0.78
0.80
0.81
0.94
0.92
0.98
0.16
0.20
0.26
0.52
0.51
0.57
­1.09
­1.05
­0.97
­0.81
­0.75
­0.65
­2.03
­1.97
­1.93
­1.65
­1.61
­1.54
tw
tw
tw
16
16
16
3
a­Ph
0.59
0.59
0.60
0.64
0.61
0.60
0.92
a­ClPh
0.55
0.96
b­CH Ph
0.42
0.84
3
b­Ph
0.41
0.86
3
b­ClPh
0.41
0.89
a
Irreversible peak potentials at a scan rate of 0.10 V/s. tw = this work.
Fig. 4. Thin­layer UV­vis spectral changes of cobalt butano­corroles 1a–3a during the controlled potential reductions in CH Cl
2
2
containing 0.1 M TBAP
containing 0.1 M TBAP. These spectral changes are
shown in Fig. 5. As seen in the figure, the initial Soret
bands of 1a–3a decrease in intensity and blue­shifted
during the first controlled potential oxidation at 0.50 V.
The spectral data suggests that a mixture of Co(III) cation
radical and Co(IV) are generated after a one­electron
abstraction in the thin­layer cell.
changes can be interpreted in terms of a corrole ring­
centered process.
Electrocatalytic reduction of O2
The catalytic activity of 1a–3a towards the reduction
of O was examined by cyclic voltammetry and rotating
2
The spectral changes shown in the middle of Fig. 5
suggest that a Co(IV) corrole was generated during the
second controlled potential oxidation of the Co(III)
corrole at 1.10 V. The third controlled potential oxidation
at 1.60 V shows that the Soret band decreases in intensity
as the oxidation proceeds, but the wavelengths of
maximum absorption do not change upon generation
of the triply oxidized species. These types of spectral
ring­disk electrode voltammetry in aqueous solutions
containing 1.0 M HClO . As an example, Fig. 6a
4
illustrates cyclic voltammograms for 2a adsorbed on an
EPPG disk electrode in 1.0 M HClO under N (dashed
4
2
line) and under air (solid line). Two quasi­reversible
reductions are observed under both solution conditions;
the first reduction is located at 0.64 V (N ) and 0.60 V
2
(air) while the second located at 0.21 V under both N2
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J. SUN ET AL.
Fig. 5. Thin­layer UV­vis spectral changes of cobalt butano­corroles during the controlled potential oxidations in CH Cl containing
2
2
0
.1 M TBAP
­
1
and air within the potential window of 0.9~ ­0.20 V.
Similar behavior was previously reported for a cobalt
b­brominated triarylcorrole [28]. As will be shown, the
second reduction has a higher peak current in HClO4
under air, which corresponds to the catalytic reduction of
dissolved O to give H O as the product.
The number of electrons transferred in the catalytic
electroreduction of dioxygen was calculated at a rotating
disk electrode (RDE). Each compound has similar RDE
the Faraday constant (94,685 C.mol ), A is the electrode
2
2
­1
area(cm ),Disthedioxygendiffusioncoefficient(cm .s ),
c is the bulk concentration of O (M) in 1.0 M HClO ,
v is the kinematic viscosity of the solution, and w is the
angular rotation rate (rad.s ) of the electrode.
2
4
­1
2
2
2
1
/j = 1/jlev + 1/jk
(1)
(2)
2
/3
-1/6 1/2
jlev = 0.62nFAD cn
w
responses in air­saturated 1.0 M HClO and an example
The plot shown in Fig. 6c for 2a indicates that
the number of electrons transferred to O2 in the
electroreduction process is 2. The same values of n
are also obtained for compounds 1a and 3a, which are
consistent with the catalytic electroreduction in a two­
electron process by using these corroles as catalysts.
Dioxygen can be cathodically reduced to give H O or
4
of the linear sweep voltammograms is shown in Fig. 6b.
From the magnitude of the steady­state limiting current
values which was taken at a fixed potential (­0.10 V) on
the catalytic wave plateau of the current­voltage curve.
The slope of the diagnostic Koutecky–Levich plot [29]
(
Fig. 6c) obtained by linear regression was then used to
2
2
­
­
estimate the average number of electrons (n) involved in
the catalytic reduction of O2.
H O in acidic media, which is 2e or 4e transfer process.
2
In the current study, the number of electron transferred
(n) is 2 for all three compounds, proving that the catalytic
reduction of O gives H O under the given experimental
The Koutecky−Levich plots are interpreted on the
basis on Equation 1, where j is the measured limiting
lim
2
2
2
−2
current density (mA.cm ), j is the kinetic current, and
conditions. This is consistent with the effect of the
electron­donating and steric interactions involving the
b,b­butano­substituents of the corrole.
k
jlev is the Levich current which is used to measure the rate
of the current­limiting chemical reaction as defined by
Equation 2. The value of n in Equation 2 is the number of
electrons transferred in the overall electrode reaction, F is
H O was the final product formed in the reduction of
2
2
oxygen and it cannot be further electroreduced to H O
2
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SYNTHESIS AND ELECTROCHEMISTRY OF COBALT TETRABUTANOTRIARYLCORROLES
7
_____
Fig. 6. (a) Cyclic voltammorgams under N (­ ­ ­ ­) and air ( ),
2
(b) linear sweep voltammograms at different rotating rate and
(
c) Koutecky–Levich plot for catalyzed reduction of O in 1.0 M
2
HClO saturated with air at a rotating EPPG disk electrode coated
4
with compound 2a at a potential scan rate of 50 mV/s
using the corrole as a catalyst. This was confirmed by
recording cyclic voltammograms with and without added
Fig. 7. (a) Cyclic voltammograms, (b) linear sweep
voltammograms at different rotating rate and (c) Koutecky−
0
.2 mM H O in acidic solution under N using 2a as the
2
2
2
Levich plot for catalyzed reduction of O in pH10 solution
2
catalyst (Fig. S2).
saturated with air at a rotating EPPG disk electrode coated with
Oxygen reduction was also carried out in a basic
solution (pH = 10) using compound 2a as catalyst which
was adsorbed on an EPPG disk electrode. As seen in
Fig. 7a, an irreversible reduction peak was observed
at Epc = ­0.35 V for both solutions saturated with
nitrogen or air. However, a higher peak current is
seen in the solution saturated with air, indicating that
compound 2a at a potential scan rate of 50 mV/s
transferred (n) for O electroreduction process is 2 in
2
the basic solution.
a catalytic reduction of dissolved O occurred under
the given solution conditions. The RDE responses for
EXPERIMENTAL
2
2
a adsorbed on the electrode in air­saturated pH10
Instrumentation
solution are shown in Fig. 7b and were used to calculate
the number of electron transferred during oxygen
reduction. The slope of the Koutecky–Levich plot for
Thin­layer UV­visible spectroelectrochemical experi­
ments were performed with a home­built thin­layer
cell which has a light transparent platinum net working
2
a (Fig. 7c) indicates that the number of electrons
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8
J. SUN ET AL.
electrode. Potentials were applied and monitored with
an EG&G PAR Model 173 potentiostat or a BiStat
electrochemistry station. Time­resolved UV­visible
spectra were recorded with a Hewlett­Packard Model
added into the solutions. The mixture was stirred under
nitrogen for 3 h at room temperature and then extracted
with CHCl . The organic layer was collected, washed
3
twice with H O and dried with Na SO . After filtered
2
2
4
8
453 diode array spectrophotometer. High purity N2
and diluted to 300 mL with CHCl , p­chloranil (4 mmol)
3
from Trigas was used to deoxygenate the solution and
kept over the solution during each electrochemical and
spectroelectrochemical experiment.
was added into the mixture and stirred for 1.5 h at room
temperature.After evaporating the mixture to dryness, the
residue containing the free­base tetrabutanocorrole was
dissolved in a solution of CH OH with Co(OAc) ·4H O
1
All reported H NMR spectra were recored on a Bruker
3
2
2
Avanc II 400 MHz instrument. Chemical shifts (d ppm)
were determined with TMS as the internal reference.
MALDI­TOF mass spectra were taken on a Bruker
BIFLEX III ultra­high resolution instrument using alpha­
cyano­4­hydroxy­cinnamic acid as the matrix.
All electrochemical measurements were carried
out at 298 K using an EG&G Princeton Applied
Research (PAR) 173 potentiostat/galvanostat or a CHI­
and triphenylphosphine. After refluxed for 1 h, the
solvent was removed under vacuum, and the mixture
was flash chromatographed using neutral alumina
column (200~300 mesh) and dichloromethane/hexane
(v/v = 1) as eluent. The red fraction was collected and
evaporated to dryness. Pure compound was obtained
after re­crystallizing in the mixed solvents of methanol
and chloroform.
7
30C Electrochemistry Work Station. A three­electrode
Butano-(CH Ph) CorCo(PPh ) 1a. Yield 112 mg
3
3
3
1
system was used and consisted of a graphite working
electrode (Model MT134, Pine Instrument Co.) for
cyclic voltammetry and rotating disk voltammetry. A
platinum wire served as the auxiliary electrode and a
home­made saturated calomel electrode (SCE) as the
reference electrode, which was separated from the bulk
of the solution by means of a salt bridge. The RRDE
was purchased from Pine Instrument Co. and consisted
of a platinum ring and a removable edge­plane pyrolytic
(7%). UV­vis (CH Cl ): l , nm 378, 413, 572. H NMR
2
2
max
(400 MHz, CD Cl ): d, ppm 7.73 (br, 3H), 7.26 (s, 3H),
2
2
7.10 (br, 7H), 6.72 (t, 6H), 6.55 (s, 2H), 5.07 (t, 6H),
3.42 (br, 6H), 2.51 (d, 9H), 2.08–1.66 (m, 8H), 1.59 (br,
12H), 1.24 (s, 6H). MS (MALDI­TOF): m/z calcd. for
+
[M – PPh ] 838.890, found: 840.360.
3
Butano-(Ph) CorCo(PPh ) 2a. Yield 122 mg (8%).
3
3
1
UV­vis (CH Cl ): l , nm 376, 408, 572. H NMR (400
MHz, CD Cl ): d, ppm 8.14 (s, 2H), 7.79 (s, 2H), 7.63 (s,
2
2
max
2
2
2
graphite (EPPG) disk (A = 0.196 cm ). A Pine Instrument
2H), 7.59–7.45 (br, 4H), 7.39 (d, 3H), 7.21 (s, 5H), 6.77
(s, 6H), 5.54 (s, 6H), 3.58 (br, 4H), 1.85 (brm, 14H), 1.47
MSR speed controller was used for the RDE and RRDE
experiments. The Pt ring was first polished with 0.05
micron a­alumina powder and then rinsed successively
with water and acetone before being activated by cycling
the potential between 1.20 and ­0.20 V in 1.0 M HClO4
until reproducible voltammograms are obtained [30, 31].
The corrole catalysts were irreversibly adsorbed on the
electrode surface by means of a dip­coating procedure
described in the literature [32]. The freshly polished
electrode was dipped in a 1.0 mM catalyst solution of
CH Cl for 5 s, transferred rapidly to pure CH Cl for
(br, 10H), 1.26 (s, 4H). MS (MALDI­TOF): m/z calcd.
+
for [M – PPh ] 798.313), found: 798.433.
3
Butano-(ClPh) CorCo(PPh ) 3a. Yield 112 mg
3
3
1
(7%). UV­vis (CH Cl ): l , nm 376, 414, 574. H NMR
2
2
max
(400 MHz, CD Cl ): d, ppm 8.07 (s, 2H), 7.64 (br, 6H),
2
2
7.43 (br, 4H), 7.22 (s, 3H), 6.75 (s, 6H), 5.46 (s, 6H), 3.56
(br, 4H), 1.95 (br, 8H), 1.74 (br, 10H), 1.48 (br, 10H).
+
MS (MALDI­TOF): m/z calcd. for [M – PPh ] 900.609,
3
found: 900.196.
2
2
2
2
1
–2 s, and then exposed to air where the adhering solvent
CONCLUSION
rapidly evaporated leaving the corrole catalyst adsorbed
on the electrode surface. All experiments were carried
out at room temperature.
Three cobalt b,b′­butano­substituted triarylcorroles
were synthesized and characterized as to their
electrochemistry and spectroelectrochemistry. The
butano­groups lead to easier oxidations and harder
reductions of the compound as compared to the related
non­butano corroles. The studied compounds are highly
selective electrocatalysts for two­electron reduction of
dioxygen in both acidic and basic solutions.
Chemicals
Dichloromethane (CH Cl ) was purchased from
2
2
Sinopharm Chemical Reagent Co. or Aldrich Chemical
Co. and used as received for electrochemistry and
spectroelectrochemistry experiments. Tetra­n­butylam­
monium perchlorate (TBAP) was purchased from Sigma
Chemical or Fluka Chemika and used as received.
Supporting information
1
H NMR spectra for compound 1a, 1b and cyclic
Synthesis
voltammorgams of compound 2a absorbed on an EPPG
_
__
The 4,5,6,7­tetrahydroisoindole (8 mmol) and
electrode in 1.0 M HClO with ( ) or without 0.2 mM
4
aldehyde (4 mmol) were dissolved in 200 mL CH OH/
H O (­ ­ ­) under N (Figs S1 and S2) are given in the
3
2
2
2
H O (v/v = 1:1) and then HCl (36%, 2.5 mL) was
supplementary material. This material is available free of
2
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J. Porphyrins Phthalocyanines 2016; 20: 8–9

SYNTHESIS AND ELECTROCHEMISTRY OF COBALT TETRABUTANOTRIARYLCORROLES
9
charge via the Internet at http://www.worldscinet.com/
14. Paolesse R, Licoccia S, Fanciullo M, Morgante
jpp/jpp.shtml.
E and Boschi T. Inorg. Chim. Acta 1993; 203:
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07–114.
Acknowledgements
15. Guilard R, Jerome F, Gros CP, Barbe JM, Ou ZP,
Shao JG and Kadish KM. C.R. Acad, Sci. Series
IIC: Chimie. 2001; 4: 245–254.
We gratefully acknowledge support from the Natural
Science Foundation of China (Grant No. 21071067,
1
6. Huang S, Fang YY, Ou ZP and Kadish KM. J. Por-
phyrins, Phthalocyanines 2012; 12: 958–967.
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1501070), Jiangsu University Foundation (Grant
No. 05JDG051) and the Robert A. Welch Foundation
K.M.K., E­680).
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K, Fukuzumi S, El Ojaimi M, Gros CP, Barbe JM
and Guilard R. Inorg. Chem. 2009; 48: 2571–2582.
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J. Porphyrins Phthalocyanines 2016; 20: 9–9