Meso-dichlorophenyl substituted Co(III) corrole: A selective electrocatalyst for the two-electron reduction of dioxygen in acid media, X-ray crystal structure analysis and electrochemistry

Article abstract of DOI:10.1142/S1088424614500734

A cobalt(III) corrole, represented as (Cl₂Ph)₃CorCo(PPh₃), where (Cl₂Ph)₃Cor is the trianion of 5,10,15-tri(2,4-dichlorophenyl)corrole, was synthesized and characterized as to its electrochemical and spectroelectrochemical properties. Single-crystal structure analysis showed the corrole to be monoclinic and have a space group P21/c with α = 13.441(3), b = 28.058(6), c = 27.584(6) ?, α = 90, β = 92.75(3), γ = 90°, M_r = 1144.38, V = 1039.1(4) ?³, Z = 8, D_c = 1.463 mg/cm³, μ = 0.816, F(000) = 4644, R_int = 0.0447, R(I > 4σ(I)) = 0.0769, wR(I > 4σ(I)) = 0.2104, R(all data) = 0.1214 and wR(all data) = 0.2705. The compound was also examined as a catalyst for the electroreduction of dioxygen when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO₄. Cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE) or a rotating ring disk electrode (RRDE) were utilized to evaluate the catalytic activity of the corrole and elucidate the products of reduction, H₂O or H₂O₂. Analysis of the data shows exclusively a two-electron transfer process to give 100% H₂O₂ as the product and no H₂O was detectable.

Full text of DOI:10.1142/S1088424614500734

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 1–8
DOI: 10.1142/S1088424614500734
Published at http://www.worldscinet.com/jpp/
Meso-dichlorophenyl substituted Co(III) corrole: A selective
electrocatalyst for the two-electron reduction of dioxygen
in acid media, X-ray crystal structure analysis and
electrochemistry
Jijun Tanga, Zhongping Ou*a◊, LinaYea, MinzhuYuana, Yuanyuan Fangb◊◊,
Zhaoli Xuea◊ and Karl M. Kadish*b◊
a School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China
b Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA
Dedicated to Professor Nagao Kobayashi on the occasion of his 65th birthday
Received 29 July 2014
Accepted 28 August 2014
ABSTRACT: A cobalt(III) corrole, represented as (Cl2Ph)3CorCo(PPh3), where (Cl2Ph)3Cor is
the trianion of 5,10,15-tri(2,4-dichlorophenyl)corrole, was synthesized and characterized as to its
electrochemical and spectroelectrochemical properties. Single-crystal structure analysis showed the
corrole to be monoclinic and have a space group P21/c with a = 13.441(3), b = 28.058(6), c = 27.584(6)Å,
a = 90, b = 92.75(3), g = 90°, Mr = 1144.38, V = 1039.1(4) Å3, Z = 8, Dc = 1.463 mg/cm3, m = 0.816,
F(000) = 4644, Rint = 0.0447, R(I > 4s(I)) = 0.0769, wR(I > 4s(I)) = 0.2104, R(all data) = 0.1214
and wR(all data) = 0.2705. The compound was also examined as a catalyst for the electroreduction
of dioxygen when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO4. Cyclic
voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE) or a rotating ring
disk electrode (RRDE) were utilized to evaluate the catalytic activity of the corrole and elucidate the
products of reduction, H2O or H2O2. Analysis of the data shows exclusively a two-electron transfer
process to give 100% H2O2 as the product and no H2O was detectable.
KEYWORDS: cobalt corrole, crystal structure, electrochemistry, catalytic property for dioxygen
reduction.
Part of our own recent research efforts in this area have
INTRODUCTION
focused on the synthesis, characterization and catalytic
Corroles and metallocorroles have continued to attract
properties of substituted cobalt corroles [9–22]. In the
a great deal of interest [1–5], in part because these
present paper, the synthesis, structural characterization,
compoundshavebeenshowntohavepotentialapplications
electrochemistry and spectroelectrochemistry of a newly
as catalysts for a variety of reactions [6–14]. One of the
synthesized meso-dichlorophenyl substituted cobalt
most frequently studied groups of metallocorroles are
corrole are described. The examined compound is
the cobalt(III) derivatives which have been characterized
represented as (Cl2Ph)3CorCo(PPh3), where (Cl2Ph)3Cor
as to their spectral and electrochemical properties under
is the trianion of 5,10,15-tri(2,4-dichlorophenyl)corrole.
many different solution conditions [1, 2].
Electrochemical and spectroelectrochemical properties
of the compound were examined in dichloromethane,
benzonitrile and pyridine containing 0.1 M TBAP as
◊SPP full and ◊◊ student member in good standing
supporting electrolyte.
When adsorbed on a graphite electrode, cobalt corroles
are able to catalyze the electroreduction of oxygen via a
*Correspondence to: Zhongping Ou, email: zpou2003@yahoo.
com, tel/fax: +86 511-8879-1800; Karl M. Kadish, email: kkadish@
uh.edu, tel: +1 (713)-743-2740, fax: +1 (713)-743-2745
Copyright © 2014 World Scientific Publishing Company

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J. TANG ET AL.
Table 1. Crystal data and structure refinement for
(Cl2Ph)3CorCo(PPh3)
2e or 4e transfer process to produce H2O2 or H2O as a final
product [9–11, 15, 22–24]. We previously demonstrated
that the type and location of substituents on the three
phenyl rings of a triphenylcorrole will significantly
affect the catalytic activity of the compound towards
the reduction of O2 [11, 12, 22]. We also suggested that
bulky substituents at the ortho-positions of the three
meso-phenyl rings of a cobalt corrole would prevent p–p
interactions of the macrocycles on the electrode surface
and thus block dimerization (needed for a 4e reduction
of O2) due to steric hindrance [11, 22]. This is confirmed
in the present paper which reports the electrochemical
properties and catalytic activity of (Cl2Ph)3CorCo(PPh3)
as a catalyst for O2 reduction.
Empirical formula
Formula weight
Temperature
C56.25H35Cl8CoN4O0.25
1144.38
P
173(2) K
Wavelength
0.71073 Å
monoclinic
P 21/c
Crystal system
Space group
Unit cell dimensions
a = 13.441(3) Å a = 90°
b = 28.058(6) Å b = 92.75(3)°
c = 27.584(6) Å g = 90°
Volume
1039.1(4) Å3
Z
8
Density (calculated)
Absorption coefficient
F(000)
1.463 mg/cm3
0.816 mm-1
RESULTS AND DISCUSSION
4644
X-ray structure of (Cl2Ph)3CorCo(PPh3)
Crystal size
0.250 × 0.250 × 0.130 mm3
3.365 to 26.027°
The complex crystalizes in a monoclinic P21/c space
group, with two crystallographically independent cobalt
complex molecules and solvent. An ORTEP plot is
depicted in Fig. 1 where one of the two conformations of
the compound is shown. The structural refinement data
are given in Table 1 and selected bond lengths and angles
are listed in Table 2.
Theta range for data
collection
Index ranges
-16 ≤ h ≤ 14, -29 ≤ k ≤ 33,
-34 ≤ l ≤ 20
Reflections collected
49226
Independent reflections
20215 [R(int) = 0.0447]
Although significant disorder is found for most of the
dichlorophenyl groups and dichloromethane molecules
in the structure, the colbalt-corrole-triphenylphosphine
core is well-defined. The Co–N bond lengths of the two
molecules vary from 1.862(5) to 1.884(5)Å and the Co–P
distances are 2.2167(17) and 2.2158(17) Å, respectively.
It is interesting to note that the dichlorophenyl groups
opposite to the unsubstituted positions of C6H3Cl2 are not
disordered and the chlorine, Cl3 (in Fig. 1) or (Cl9 in the
Completeness to theta =
25.242°
99.0%
Refinement method
full-matrix least-squares on F2
20215/0/1111
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 4s (I)]
R indices (all data)
1.113
R1 = 0.0769, wR2 = 0.2104
R1 = 0.1214, wR2 = 0.2705
0.0018(2)
Extinction coefficient
Largest diff. peak and hole
1.358 and -1.611 eÅ-3
second molecule) is oriented cis to the phosphorus
of the bound PPh3. The triphenylphosphine ligand
is tilted towards the unsubstituted phenyl positions
as evidenced by a smaller angle of 93.5° for N1–
Co1–P1 and N4–Co1–P1 as compared to 103.5° for
N2–Co1–P1 and N3–Co1–P1. The central cobalt ion
is displaced from the corrole mean plane by 0.23 Å.
UV-visible spectra
Electronic absorption spectra of (Cl2Ph)3Cor-
Co(PPh3) in CH2Cl2, PhCN and pyridine are
illustrated in Fig. 2 and a summary of spectral data in
the three solvents is given in Table 3. In CH2Cl2 and
PhCN, neutral (Cl2Ph)3CorCo(PPh3) exhibits a split
Soret band located between 381 and 411 nm and two
weak Q-bands between 554 and 584 nm. However, a
Fig. 1. An ORTEP plot of the complex with thermal ellipsoids at
25% probability level. Hydrogen atoms were omitted for clarity. The
Cl1/Cl2 and Cl5/Cl6 are disordered over at least two positions. The
Cl1 and Cl5 are positioned up or down the corrole mean plane.
The plot represents one of the potential conformations
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MESO-DICHLOROPHENYL SUBSTITUTED CO(III) CORROLE
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Table 2. Selected bond lengths and angles for (Cl2Ph)3CorCo(PPh3)
Molecule 1 Molecule 2
Bond length, Å
1.871 (5)
Bond angle, °
Bond length, Å
Co2-N5 1.864 (5)
Bond angle, °
Co1-N1
Co1-N2
Co1-N3
Co1-N4
Co1-P1
C1-C19
N1-C1
N1-Co1-N2
89.3 (2)
81.3 (2)
N5-Co2-N6
90.0 (2)
80.7 (2)
1.884 (5)
1.875 (5)
1.862 (5)
2.2167 (17)
1.404 (9)
1.368 (7)
1.383 (7)
N1-Co1-N4
N2-Co1-N3
N3-Co1-N4
N1-Co1-P1
N2-Co1-P1
N3-Co1-P1
N4-Co1-P1
Co2-N6
Co2-N7
Co2-N8
Co2-P2
C56-C74
N5-C56
N8-C74
1.882 (5)
1.878 (5)
1.866 (5)
2.2158 (17)
1.412 (10)
1.366 (8)
1.374 (8)
N5-Co2-N8
N6-Co2-N7
N7-Co2-N8
N5-Co2-P2
N6-Co2-P2
N7-Co2-P2
N8-Co2-P2
94.7 (2)
94.5 (2)
89.2 (2)
89.4 (2)
93.54 (15)
103.38 (15)
103.65 (15)
93.53 (15)
92.08 (15)
103.16 (15)
103.76 (15)
95.25 (16)
N4-C19
Fig. 2. UV-visible spectra of the neutral cobalt corrole in CH2Cl2
_____), PhCN (------) and pyridine (……..) containing 0.1 M TBAP
(
Table 3. UV-visible spectral data, lmax, nm (e × 10-4 M-1.cm-1) of
(Cl2Ph)3CorCo(PPh3)
Solvent
Soret region
Visible region
Fig. 3. Cyclic voltammograms of (Cl2Ph)3CorCo(PPh3) in
(a) CH2Cl2, (b) PhCN and (c) pyridine containing 0.1 M TBAP.
Scan rate at 0.10 V/s
CH2Cl2
PhCN
381 (4.05) 409 (3.57) 554 (0.75) 584 (0.60)
383 (3.84) 411 (3.60) 557 (0.75) 580 (0.64)
444 (6.35) 584 (1.16) 614 (2.57)
Pyridine
The first one-electron reduction is irreversible in all
three solvents and located at Epc = -0.65 V in CH2Cl2 or
PhCN and -1.16 V in pyridine. The irreversibility is due
to dissociation of the axially coordinated ligand(s) after
electron transfer to generate a four-coordinate Co(II)
corrole which is then reoxidized to a four-coordinate
Co(III) complex at Epa = -0.05 V in CH2Cl2, -0.12 V
in PhCN and -0.48 V in pyridine as shown in Fig. 3.
The four-coordinate Co(II) corrole can also be reduced
to its Co(I) form at more negative potentials [14, 18, 25]
and this reaction occurs at E1/2 = -1.63 in PhCN, -1.56 V in
pyridine and Epc = -1.56 V in CH2Cl2.
different UV-vis spectrum is exhibited in pyridine where
there is a single sharp Soret band at 444 nm and two well-
defined Q-bands at 584 and 614 nm (see Fig. 2). This
spectrum is consistent with formation of a six-coordinate
cobalt(III)corrole,(Cl2Ph)3CorCo(py)2,wheretheoriginal
axially bound PPh3 group has been displaced by a pyridine
molecule. Similar UV-vis spectra were previously
reported for other six-coordinate cobalt(III) corroles with
two pyridine axial ligands [22].
The second reduction of (Cl2Ph)3CorCo(PPh3) is
reversible in PhCN and pyridine but irreversible in
CH2Cl2 because the electrogenerated Co(I) form of the
corrole rapidly reacts with the solvent to give a transient
Co(III) s-bonded CH2Cl species, as has also been shown
Electrochemistry
Cyclic voltammograms illustrating the oxidations and
reductions of (Cl2Ph)3CorCo(PPh3) in CH2Cl2, PhCN and
pyridine containing 0.1 M TBAP are shown in Fig. 3.
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J. TANG ET AL.
Table 4. Half-wave potentials (V vs. SCE) in different solvents
containing 0.1 M TBAP
with two weak Q-bands at 557 and 583 nm in PhCN. The
singly oxidized corrole, which has an unsplit Soret band
at 383 nm and a new Q-band at 658 nm (Fig. 4a), can be
assigned as a Co(IV) corrole or a Co(III) p-cation radical
[22]. However, DFT calculations at the PCM-B3LYP/
LanL2DZ/6-31G(d) level show that no metal orbital is
involved in the HOMO (Fig. 5a), thus suggesting that the
first oxidation of (Cl2Ph)3CorCo(PPh3) is a macrocycle-
centered electron-transfer. Further oxidation at an applied
potential at 1.30 V then gives the Co(IV) p-cation radical
and the spectral changes associated with this reaction are
shown in Fig. 4a.
Solvent
Oxidation
2nd
Reduction
3rd
1st
1st
2nd
CH2Cl2
PhCN
1.74
1.76
1.13
1.09
0.62
0.63
0.45
-0.65a
-0.65a
-1.16a
-1.56a
-1.63
-1.56
Pyridine
aPeak potential for irreversible reductions at a scan rate of
0.10 V/s.
The first controlled potential reduction at -1.00 V
generates a Co(II) corrole which has a well-defined Soret
band at 428 nm (Fig. 4b). These spectral changes are
reversibleandreoxidationatacontrolledpotentialof0.0V
leads to recovery of the initial Co(III) spectrum in PhCN.
Similar types of spectral changes have been reported
for the Co(III)/Co(II) reaction of other corroles [12, 14,
18, 25] and porphyrins [27, 28] with related structures.
The LUMO orbital calculated by DFT (Fig. 5b) is also
consistent with a metal-centered reduction upon addition
of one electron to the compound.
The second controlled potential reduction of
(Cl2Ph)3CorCo(PPh3) at -1.90 V is accompanied by only
small spectral changes and has been interpreted in terms
of a CoII/CoI electron transfer rather than a corrole ring-
centered process, which would be characterized by a
decreased intensity Soret band and a broad visible band
in the near-IR region of the spectrum.
to occur for other electrogenerated Co(I) corroles [14]
and structurally related Co(I) porphyrins [26] where the
electrochemistry was carried out in dichloromethane.
The first oxidation of (Cl2Ph)3CorCo(PPh3) is
reversible in all three nonaqueous solvents, with E1/2
values ranging from 0.45 V in pyridine to 0.63 V in
PhCN (see Table 4). This one-electron abstraction is
followed by two additional electron abstractions in
CH2Cl2 and PhCN (Fig. 3), but only one oxidation is
observed in pyriding due to the limited positive potential
range of this solvent.
It should be noted that dimerization does not occur
for (Cl2Ph)3CorCo(PPh3) in CH2Cl2 as has been reported
for other b-substituted corroles in this solvent [13, 19],
and this is attributed to the presence of the bulky Cl2Ph
substituents on the meso-positions of the macrocycle,
which prevents dimerization.
The electroreduced and electrooxidized corroles were
characterized by thin-layer spectroelectrochemistry in
PhCN. Examples of the spectral changes are shown in
Fig. 4 during the first and second controlled potential
oxidations and reductions.
Electrocatalytic reduction of O2
Figure 6a illustrates cyclic voltammograms of
(Cl2Ph)3CorCo(PPh3)adsorbedonanEPPGdiskelectrode
in 1.0 M HClO4 under N2 (dashed line) and under air
(solid line). Under N2, there is a small anodic broad
As mentioned above, the neutral Co(III) corrole is
characterizedbyasplitSoretbandat383and411nmalong
Fig. 4. Thin-layer UV-visible spectral changes of (Cl2Ph)3CorCo(PPh3) during controlled potential reductions and oxidations in
PhCN containing 0.1 M TBAP
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MESO-DICHLOROPHENYL SUBSTITUTED CO(III) CORROLE
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Fig. 5. (a) HOMO and (b) LUMO orbitals of (Cl2Ph)3CorCo(PPh3) calculated at the B3LYP/6-31G(d) level
transferred in the catalytic electroreduction of dioxygen.
The RDE response in air-saturated 1.0 M HClO4 is
illustrated in Fig. 7a. The number of electrons transferred
during dioxygen reduction was calculated from the
magnitude of the steady-state limiting currents which
were taken at a fixed potential of -0.10 V on the plateau
of the current-voltage curves. When the amount of O2
reduction at the corrole modified electrode is controlled
by mass transport alone, the relationship between
the limiting current and rotation rate should obey the
Levich equation given in Equation 1 [29], where n is the
number of electrons transferred in the overall electrode
reaction, F is the Faraday constant (96485 C.mol-1), A
is the electrode area (cm2), D is the dioxygen diffusion
coefficient (cm2.s-1), c is the bulk concentration of O2 in
1.0 M HClO4, v is the kinematic viscosity of the solution
and w is the angular rotation rate of the electrode (rad.s-1).
Jlev = 0.62nFAD2/3cv-1/6w1/2
(1)
When the reciprocal of the limiting current density is
plotted against the reciprocal of the square root of the
rotation rate, the resulting straight line (see Fig. 7b) obeys
the Koutecky–Levich equation (Equation 2), where j is
the measured limiting current density (mA.cm-2), jlev is
the Levich current, and jk is the kinetic current which
can be obtained experimentally from the intercept of the
Koutecky–Levich line in Fig. 7b.
Fig. 6. Cyclic voltammograms of (a) (Cl2Ph)3CorCo(PPh3)
absorbed on an EPPG electrode and (b) uncoated bare electrode
in 1.0 M HClO4 under N2 (----) or air (—). Scan rate = 50 mV/s
peak centered at about 0.1 V and no other peaks can
be assigned to the corrole between 0.60 and -0.20 V.
A different situation occurs in 1.0 M HClO4 under air
(solid line in Fig. 6a). Under these conditions, there is
an irreversible but well-defined cathodic reduction peak
at Epc = 0.15 V for a scan rate of 50 mV/s. As will be
shown, this irreversible peak corresponds to the catalytic
reduction of dissolved O2 to give H2O2. The dioxygen in
solution is also reduced at a bare EPPG electrode without
the corrole and this reaction occurs at a more-negative
potential of Epc = -0.13 V for a scan rate of 50 mV/s
(Fig. 6b).
1/j = 1/jlev + 1/jk
jk = 103knFGc
(2)
(3)
The value of k (M-1.s-1) in Equations 2 and 3 is the
second-order rate constant of the reaction which limits
the plateau current, G is the surface concentration of
corroles (mol.cm-2) and the other terms have their usual
significance as described previously. The slope of a
plot obtained by linear regression can then be used to
estimate the average number of electrons (n) involved in
Measurements were also performed at a rotating disk
electrode (RDE) to calculate the number of electrons
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J. TANG ET AL.
Fig. 7. (a) Current-voltage curve with electrode rotating rates (w) indicated on each curve. Potential scan rate = 50 mV/s and (b)
Koutecky-Levich plot for catalytic reduction of O2 in 1.0 M HClO4 saturated with air at a rotating EPPG disk electrode coated with
(Cl2Ph)3CorCo(PPh3)
isreachedatabout0.10V.Theanodicringcurrentincreases
throughout the range of the disk potentials where the disk
current rises. Based on Equation 4 the amount of H2O2
formed upon the reduction of dioxygen was calculated
as 98% under the given experimental conditions. The
value are almost identical to that calculated using the
Koutecky–Levich plot in Fig. 7b. The values of ID and
IR in Equation 4 are the Faradic currents at the disk and
ring electrodes, respectively. The intrinsic value of the
collection efficiency (N) was determined to be 0.24 using
the [Fe(CN)6]3-/[Fe(CN)6]4- redox couple in 1.0 M KCl.
%H2O2 = 100(2IR/N)/(ID+IR/N)
(4)
In earlier studies, we examined the catalytic properties
of several cobalt triarylcorroles containing the Cl, CH3 or
NO2 substituents on the para-position of phenyl rings. For
the catalytsts, the number of electron transferred (n) in the
reduction of O2 ranges form 2.2 to 3.0 depending upon the
type of the substituent [11, 12]. However, in the current
study, the value of n is exactly of 2.0 and the product of
dioxygen reduction in 1.0 M HClO4 is 100% H2O2. This
is because that bulky ortho-Cl substituents on the meso-
phenyl rings of the corrole result in steric hindrance which
would block p–p interactions between macrocycles and
prevent the formation of dimers which would facilite the
4-electron reduction to give an H2O product [11, 22].
Fig. 8. Rotating ring-disk voltammograms of (Cl2Ph)3CorCo-
(PPh3) coated on EPPG electrode in 1.0 M HClO4 saturated with
air and the potential of the ring electrode maintained at 1.0 V.
Rotation rate = 200 rpm and scan rate = 10 mV/s
the catalytic reduction of O2. This analysis was carried
out and the number of electrons transferred per dioxygen
molecule (n) during the catalytic reduction of O2 by the
cobalt corrole was calculated.
Atwoelectrontransfer(n=2)wouldgenerate100%H2O2
while a four electron transfer (n = 4) would give 0% H2O2
and 100% H2O. The Koutecky–Levich plot in Fig. 7b shows
the number of electrons transferred (n) to be 2.0, which
corresponds to 100% H2O2 produced. This indicates that the
catalytic electroreduction of O2 by (Cl2Ph)3CorCo(PPh3) is
a 2e- transfer process, giving H2O2 as the product rather than
a 4e- transfer process to produce H2O.
The catalytic reduction of O2 was also examined at
an RRDE under the same solution conditions. The disk
potential was scanned from 0.5 to -0.1 V at a rotation
speed of 200 rpm while holding the ring potential constant
at 1.0V. This data is shown in Fig. 8 where the disk current
begins to increase at about 0.30 V and a current maximum
EXPERIMENTAL
Chemicals
Dichloromethane (CH2Cl2), benzonitrile (PhCN)
and pyridine (Py) were purchased from Sigma–Aldrich
Co. and used as received for electrochemistry and
spectroelectrochemistry experiments. Tetra-n-butylam-
monium perchlorate (TBAP) was purchased from Sigma
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MESO-DICHLOROPHENYL SUBSTITUTED CO(III) CORROLE
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Chemical or Fluka Chemika Co., recrystallized from
ethyl alcohol, and dried under vacuum at 40°C for at
least one week prior to use.
5,10,15-tris(2,4-Dichlorophenyl)corrole cobalt triph-
enylphoshine, (Cl2Ph)3CorCo(PPh3) was synthesized
according to the procedure described in literature [14, 30].
UV-vis (PhCN): lmax, nm (e × 10-4 M-1.cm-1) 383 (3.84),
411 (3.60), 557 (0.75), 580 (0.64). MS (MALDI-TOF):
m/z 789.294, calcd. for [M – PPh3]+ 789.209.
Theoretical calculations
Density-functional theory (DFT) calculations were
performed with the Gaussian 09 program. Geometry
optimizations were carried out in CH2Cl2 solution
(dielectric constant, e = 8.93) at the PCM-B3LYP/
LanL2DZ functional and 6-31G(d) basis set [34–41]. The
structures were confirmed to be minima by vibrational
frequency analyses. All calculations were implemented
in Gaussian 09, Revision D.01, Graphical outputs of
the computational results were generated with the
GaussView, ver. 5.09.
Instrumentation
UV-visible spectra were recorded with a Hewlett–
Packard Model 8453 diode array spectrophotometer.
Cyclic voltammetry was carried out at 298 K using
an EG&G Princeton Applied Research (PAR) 173
potentiostat/galvanostat or a Chi-730C Electrochemistry
Work Station. A three-electrode system was used for
cyclic voltammetric measurements and rotating disk
voltammetry and consisted of a glassy carbon electrode
or a graphite working electrode (Model MT134, Pine
Instrument Co.), a platinum counter electrode and a
homemade saturated calomel reference electrode (SCE).
The SCE was separated from the bulk of the solution by
a fritted glass bridge of low porosity which contained the
solvent/supporting electrolyte mixture. High purity N2
was used to deoxygenate the solution and kept over the
solution during each electrochemical experiment.
X-ray crystallography of (Cl2Ph)3CorCo(PPh3)
Single-crystals of (Cl2Ph)3CorCo(PPh3) suitable for
X-ray diffraction analysis were obtained in a mixture
of dichloromethane and methanol, mounted on glass
fiber and transferred to a Bruker Smart Apex CCD
diffractometer. The unit cell parameters and crystal-
orientation matrices were determined by least-squares
refinements of all reflections. The intensity data were
recorded as j and w scans with k offsets. The structure
was solved by direct methods and followed by successive
Fourier and difference Fourier syntheses. Refinements
were carried out by full-matrix least-squares on F
using SHELXL-2013 with anisotropic displacement
parameters for all non-hydrogen atoms.
The RRDE was purchased from Pine Instrument
Co. and consisted of a platinum ring and a removable
edge-plane pyrolytic graphite (EPPG) disk (A = 0.196
cm2). A Pine Instrument MSR speed controller was
used for the RDE and RRDE experiments. The Pt ring
was first polished with 0.05 micron a-alumina 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 [31, 32].
CONCLUSION
A cobalt corrole cotaining Cl substituents on ortho-
positions of the three phenyl rings of the macrocycle
was synthesized and the structure determined by X-ray
crystal analysis. The compound is a selective catalyst
for a 2-electron reduction of dioxygen and exclusively
generates H2O2 as the product in acid media.
The corrole catalyst was irreversibly adsorbed on the
electrode surface by means of a dip-coating procedure
described in the literature [9, 33]. The freshly polished
electrode was dipped in a 1.0 mM catalyst solution of
CH2Cl2 for 5 s, transferred rapidly to pure CH2Cl2 for
1–2 s, and then exposed to air where the adhering solvent
rapidly evaporated leaving the corrole catalyst adsorbed
on the electrode surface. All experiments were carried
out under room temperature.
Acknowledgements
This work was supported by grants from the Natural
Science Foundation of China (grants Nos. 21071067,
21301074) and the Robert A. Welch Foundation (KMK,
grant No. E-680). We would like to thank Dr. Ruifa Zong
for his kind help in X-ray crystal analysis.
Thin-layer UV-visible spectroelectrochemical experi-
ments were performed with a home-built thin-layer
cell which has a light transparent platinum net working
electrode. Potentials were applied and monitored with
an EG&G PAR Model 173 potentiostat. Time-resolved
UV-visible spectra were recorded with a Hewlett–Packard
Model 8453 diode array spectrophotometer. High purity
N2 from Trigas was used to deoxygenate the solution and
kept over the solution during each electrochemical and
spectroelectrochemical experiment.
Supporting information
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under
number CCDC-943276. Copies can be obtained on request,
free of charge, via 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: data_request@ccdc.cam.ac.uk).
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 7–8

8
J. TANG ET AL.
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