Solvent effects on the catalytic activity of manganese(III) corroles

Article abstract of DOI:10.1142/S1088424614500059

Four Mn(III) corroles that differ in their electronic environments based on meso-substitution by pentafluorophenyl and phenyl groups were synthesized and characterized by spectroscopic techniques. Utilization of these Mn(III) corroles for styrene oxidation using iodosylbenzene (PhIO) as oxygen source in toluene, dichloromethane (DCM), DMF, DMAc, THF and DMSO revealed a remarkable effect of solvent on the catalytic activity. Furthermore, the transformation of Mn(III) corroles into their corresponding Mn(V)-oxo corroles, and subsequent treatment with styrene also indicated that more electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in toluene and DCM, while less electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in DMF and DMAc. A significant difference in the observed rates of reaction suggest that the catalytic oxidation of styrene by manganese corroles may proceed through different pathways, and is strongly solvent-dependent.

Full text of DOI:10.1142/S1088424614500059

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 316–325
DOI: 10.1142/S1088424614500059
Published at http://www.worldscinet.com/jpp/
Solvent effects on the catalytic activity of manganese(III)
corroles
Qi Wang,Yang Zhang, LanYu, HongYang, Mian HR Mahmood and Hai-Yang Liu*◊
Department of Chemistry, South China University of Technology, Guangzhou 510640, P.R. China
Received 10 October 2013
Accepted 28 December 2013
ABSTRACT: Four Mn(III) corroles that differ in their electronic environments based on meso-
substitution by pentafluorophenyl and phenyl groups were synthesized and characterized by spectroscopic
techniques. Utilization of these Mn(III) corroles for styrene oxidation using iodosylbenzene (PhIO) as
oxygen source in toluene, dichloromethane (DCM), DMF, DMAc, THF and DMSO revealed a remarkable
effect of solvent on the catalytic activity. Furthermore, the transformation of Mn(III) corroles into their
corresponding Mn(V)-oxo corroles, and subsequent treatment with styrene also indicated that more
electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in toluene and DCM, while less electron-
deficient Mn(V)-oxo corroles exhibit higher reactivity in DMF and DMAc. A significant difference in
the observed rates of reaction suggest that the catalytic oxidation of styrene by manganese corroles may
proceed through different pathways, and is strongly solvent-dependent.
KEYWORDS: manganese, corrole, Mn(V)-oxo, catalysis, solvent effect.
It was found that more electron-deficient b-halogenated
Mn(III) corroles such as Br8Mn(III)(TPFC) (where
TPFC = 5,10,15-trispentafluorophenyl corrole) [22]
and F8Mn(III)(TPFC) [17] exhibit higher reacivity than
comparatively less electron-deficient corrole Mn(III)-
(TPFC) [16] in the epoxidation of alkenes. High-valent
manganese-oxo corroles have been postulated as the key
intermediates in a large number of manganese corroles
catalyzed reactions [1, 9, 23, 24]. DFT calculations
suggested that b-bromination of manganese corroles will
favor oxygen atom transfer to the substrate by inducing
the spin state change in its Mn(V)-oxo complex [25, 26].
The reactivity of Mn(V)-oxo corroles was observed to
be greatly enhanced by axial ligation with imidazole [27,
28]. Mn(V)-oxo corrole was also suggested to undergo
disproportionation to generate Mn(VI)-oxo species,
which then oxidize the substrate in the oxygenation
reaction [16]. Newcomb’s investigations revealed the
possibility of multiple active oxidants in manganese
corroles catalyzed reactions [29], and has recently
been found in case of manganese porphyrin catalyzed
oxidation reactions [30].
INTRODUCTION
Transition metal complexes of corroles have been
implicated as superb catalysts in numerous chemical
reactions[1–6]suchasoxidation[7–10],cyclopropanation
[11], hydroxylation [12], and decomposition of peroxy-
nitrite [13, 14]. Among these catalytic reactions, manga-
nese corroles catalyzed oxidation of organic substrates
have flourished prominently in recent years [1, 8, 9, 15].
Many terminal oxidants, such as iodosylbenzene (PhIO)
[9, 16, 17], m-chloroperbenzoic acid [18], ozone [8] and
hydrogen peroxide [19] have been employed as oxygen
source in the catalytic systems of manganese corroles to
explore their reactivity. More recently, manganese(III)
corroles catalyzed oxidation of alcohols, alkenes and
alkanes by tert-butyl hydroperoxide (t-BuOOH) under
mild condition has been shown to be selective and
efficient [20, 21]. Although a lot of reports have focused
on manganese corroles catalyzed oxidation reactions, the
factors controlling their reactivity are still ambiguous.
◊SPP full member in good standing
The nature of solvent has long been known to play
a crucial role in the oxdiation reactions [31–35], and
*Correspondence to: Hai-Yang Liu, email: chhyliu@scut.edu.
cn, tel/fax: +86 20-2223-6805
Copyright © 2014 World Scientific Publishing Company

SOLVENT EFFECTS ON THE CATALYTIC ACTIVITY OF MANGANESE(III) CORROLES
317
F
F
F
F
R2
F
F15C: R1 = R2 = R3=
N
N
F
F
, R2 =
, R2 =
F10C: R1 = R3=
F
M
R1
R3
F
F
N
N
F
F
F
F
F
F5C: R1 = R3=
Freebase
Mn(III) corrole
Mn(V)-oxo corrole
M= 3H
M= Mn
F0C: R1 = R2 = R3=
Mn
O
M =
Chart 1. Structures of free base corroles and their manganese complexes
has previously been reported in case of chromium-
oxo corrole [36], molybdenum-oxo corrole [37] and
manganese porphyrin catalyzed oxidation reactions
[30, 38]. Our preliminary results showed that the rate
of oxygen atom transference from manganese(V)-oxo
corrole to the substrate is affected by the properties of
the solvent [39]. As a part of our project on the reactivity
of Mn(V)-oxo corroles, we here report the systematic
investigations of the role of solvent on the catalytic
oxidation of styrene by Mn(III) corroles bearing different
electronic features (Chart 1) using PhIO as oxidant. The
plausible mechanism for the oxidation reaction is also
suggested.
The UV-vis spectra of the investigated manganese
corroles in acidic, basic and neutral media are shown
in Fig. 1. It may be concluded from Fig. 1 that F15C-
Mn(III) remains Mn(III) in acidic medium, while the
other manganese(III) corroles are partially transformed
into Mn(IV) corroles. All manganese(III) corroles
exhibit a wider Soret band in acidic medium and split
Soret band along with the increase in the intensity of CT
(charge transfer) band around 480 nm in basic medium.
In order to make sure the trivalent manganese in all
corrole catalysts and to guarantee their studies under the
same conditions, all manganese corroles were dissolved
in dichloromethane and treated with a certain amount
of ammonia prior to use. The solvent was then removed
under vacuum to obtain Mn(III) corrrole catalysts. The
catalytic reactions were carried out in different solvents
and the results are summarized in Table 1.
RESULTS AND DISCUSSION
Under the reaction conditions employed, all the
Mn(III) corroles showed good catalytic activity in
toluene and DCM when using PhIO as oxidant. Styrene
epoxide was the major product along with the formation
of phenyl acetaldehyde and benzaldehyde. A slightly
higher yield was, however, observed in DCM. The
catalytic activity in toluene and DCM followed the
order: F15C-Mn(III) > F10C-Mn(III) > F5C-Mn(III) >
F0C-Mn(III). It is well-known that more electron-
deficient Mn(III) porphyrin exhibits higher activity in
catalytic reaction because it gives more reactive Mn(V)-
oxo intermediate [40]. The same was observed in case
of manganese corroles where the electron-withdrawing
substituents enhanced the reactivity of Mn(V)-oxo
intermediate by lowering the Mn–O bond dissociation
energy [41]. Benzaldehyde was found to be the major
product in the catalytic oxidation of styrene by Mn(III)
corrole using t-BuOOH as oxidant, indicating dioxygen
Catalytic oxidation of styrene
Among the investigated manganese corroles (Chart 1),
F0C-Mn(III) is not sufficiently stable in DCM or toluene
because of its gradual oxidation into Mn(IV) corrole and
may be observed by its color change from green to brown
[1]. However, F0C-Mn(III) is relatively more stable in
alkaline media. For this reason, the stock solution of F0C-
Mn(III) might be kept in dilute ammonia atmosphere to
supress its oxidation and to maintain the typical green
color of manganese corroles. It may be turned brown after
the addition of dilute hydrochloric acid representing a
Mn(IV) corrole. Other Mn(III) corroles also show similar
property, albeit it varies depending on the nature of the
peripheral substituents. The most electron-deficient F15C-
Mn(III) is much more stable in its +3 oxidation state and
the color changes from green to brown in acidic medium
is also much slower than the other Mn(III) corroles.
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318
Q. WANG ET AL.
Fig. 1. The effect of acidic (dilute hydrochloric acid) and basic (ammonia) media on the UV-vis spectra of Mn(III) corroles in
toluene. (a) F15C-Mn(III); (b) F10C-Mn(III); (c) F5C-Mn(III); (d) F0C-Mn(III)
involved free radical mechanism [20]. When the catalytic
reactions were carried out in argon atmosphere, the yield
of benzadehyde was significantly lowered (Table 1, see
yields in parentheses), confirming the role of dioxygen
in the catatlytic reaction under aerobic conditions. As
styrene epoxide was the main product in toluene and
DCM, oxygen atom transfer (OAT) reaction between
Mn(V)-oxo corrole and substrate should be the main
pathway that controls the catalytic reaction. Notably, the
less electron-deficient Mn(III) corroles, F5C-Mn(III) and
F0C-Mn(III), gave higher yields of bezaldehyde. This
implies that when the Mn(V)-oxo corrole intermediate is
less reactive, radical pathway plays more significant role
in the catatlytic system under aerobic conditions. The
different yields of styrene epoxide in toluene and DCM
also indicate that the reactivity of Mn(V)-oxo corrole is
correlated with the nature of the solvent.
the major product, while phenylacetaldehyde could not
be detected. The less electron-deficient Mn(III) corroles
gave higher yields of styrene epoxide and higher total
yields, that is, the most electron-rich F0C-Mn(III)
exhibited the highest catalytic activity [1]. The reactivity
of manganese corroles in basic solvents followed the
order: F15C-Mn(III) < F10C-Mn(III) < F5C-Mn(III) <
F0C-Mn(III). This order is totally reversed compared
with the same catalytic reaction in toluene and DCM.
This may be due to the fact that disproportionation of
Mn(V)-oxo corroles to Mn(VI)-oxo corrole is strongly
favored in electron-rich corrole F0C-Mn(III) [1, 29, 42],
and high-valent Mn(VI)-oxo corrole may be involved
as active intermediate in this case. Interestingly, the
reaction in DMAc favored benzaldehyde rather than
styrene epoxide and only traces of phenyl acetaldehyde
could be observed. The yield of benzaldehyde in DMAc
was sharply decreased from 30.6% under aerobic
conditions to 2.7% under anaerobic conditions (Table 1,
see yields in parentheses), indicating the involvement of
dioxygen. All the investigated Mn(III) corroles exhibited
similar catalytic activity towards epoxide in DMAc
(Table 1). The difference in the catalytic behavior of
The catalytic reactions in basic solvents (DMF and
DMAc) were drastically different from those in toluene
and DCM as expected. In addition to the decrease in
the yield of styrene epoxide and total conversion, the
product distribution was also significantly different. In
DMF, styrene epoxide and benzadehyde were observed
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SOLVENT EFFECTS ON THE CATALYTIC ACTIVITY OF MANGANESE(III) CORROLES
319
Table 1. Mn(III) corrole-catalyzed oxidation of styrene by using PhIO in various solventsa
Solvent
Catalyst
Yield, %b
Benzaldehyde
Phenyl
acetaldehyde
Styrene
oxide
Total
Toluenec
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
F15C-Mn
F10C-Mn
F5C-Mn
F0C-Mn
7.9 (6.9)
11.0 (7.8)
17.5 (8.4)
14.2 (12.2)
4.4
10.9 (15.8)
51.4 (47.0)
45.1 (44.7)
38.2 (41.7)
21.2 (18.1)
59.5
70.2 (69.7)
68.2 (68.6)
61.8 (61.8)
38.3 (35.0)
86.2
12.1 (16.1)
6.1 (11.7)
2.9 (4.7)
DCM
DMF
22.3
2.7
25.2
55.1
83.0
19.8
10.2
42.3
72.4
25.6
7.3
39.1
72.0
11.7
0
16.7
28.4
11.6
0
20.9
32.5
12.7
0
24.1
36.8
22.2
0
25.3
47.5
DMAcc
THF
25.9 (11.4)
20.8 (8.7)
27.1 (5.7)
30.6 (2.7)
11.0
1.6 (1.5)
9.7 (11.8)
14.8 (13.1)
10.9 (14.4)
11.2 (12.0)
3.9
37.2 (24.7)
39.8 (24.9)
40.0 (21.3)
42.7 (15.5)
17.0
4.2 (3.1)
2.0 (1.2)
0.9 (0.8)
2.1
1.7
1.4
1.3
0
11.2
4.4
17.3
12.0
4.8
18.2
17.3
8.4
27.0
DMSO
6.0
1.4
7.4
2.7
0
0
2.7
0.9
0
0
0.9
0.6
0
0
0.6
a The molar ratio of substrate/PhIO/catalyst was 1000:100:1. b Yields based on the amount of oxidant
used. c Yields in parentheses were got in argon atmosphere.
manganese corroles in DMF and DMAc still needs
further exploration.
reactivity [43–46]. To get insights into manganese corroles
catalyzedreactions, wedecidedtoextendourinvestigations
on the kinetics between Mn(V)-oxo corroles and styrene
in different solvents (DCM, toluene, DMF, and DMAc).
THF and DMSO could not be used as solvents for kinetic
studies due to their possible self-oxidation. The manganese
corrole solution (~3 × 10-5 M) was treated with PhIO for
about 5 min followed by flash chromatography on basic
alumina to give Mn(V)-oxo corrole [17].
Owing to the limited stability of Mn(V)-oxo corroles
in solution [1], the self-decay process of Mn(V)-oxo
corroles may easily be traced by UV-vis spectroscopy.
In DMF and DMAc, all Mn(V)-oxo corroles gradually
turned to Mn(III) corroles, while in toluene and DCM
only more electron-deficient F15C-Mn(V)-oxo and F10C-
Mn(V)-oxo returned to their corresponding Mn(III)
corroles during the self-decay process. In contrast,
F5C-Mn(V)-oxo and F0C-Mn(V)-oxo could not return
Manganese(III) corroles exhibited very little catalytic
activity in THF and DMSO because of the susceptible
oxidation of these solvents in the presence of oxidizing
agents. It was found that PhIO can significantly oxidize
DMSO but slightly oxidize THF in 3 h. However, in the
presence of manganese(III) corrole, THF and DMSO
were remarkably oxidized by PhIO within 15 min.
Obviously, Mn(III) corroles could not efficiently catalyze
the epoxidation of styrene in THF and DMSO due to the
involvement of the solvent oxidation.
Kinetics of the reaction between Mn(V)-oxo
corroles and styrene
High-valent metal-oxo species have been extensively
studied in terms of their generation, stability and substrate
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Q. WANG ET AL.
to their corresponding Mn(III) corroles completely due
to their gradual oxidation to Mn(IV) corrole species as
indicated by their UV-vis spectra. Figures 2 and 3 show
the UV-vis spectral changes of four Mn(V)-oxo corroles
in toluene and DMF, respectively. It can be seen that less
electron-deficient F5C-Mn(V)-oxo and F0C-Mn(V)-oxo
exhibit different self-decay pattern in DMF and toluene
compared with the more electron-deficient F15C-Mn(V)-
oxo and F10C-Mn(V)-oxo. The kinetics of the self-decay
of Mn(V)-oxo corroles was monitored by the absorption
at left arm of the Soret-band. The decay was accelerated
remarkably in the presence of large excess of styrene
(Fig. 4), showing that Mn(V)-oxo corroles are reactive
towards styrene substrate. The self-decay rate constants
were calculated by the exponential fit of the kinetic curves
and the data is summarized in Table 2. Interestingly, two
different orders of self-decay rate constants were found
in all these solvents. In toluene and DCM, the self-decay
rate constants decrease with the decreasing electron-
and DMAc the order of self-decay rate constants was
reversed i.e. kF15C-Mn(V)-oxo < kF10C-Mn(V)-oxo < kF5C-Mn(V)-oxo
kF0C-Mn(V)-oxo. As the self-decay rate constants reflect the
reactivity of Mn(V)-oxo corroles, therefore, it may be
concluded that the OAT reaction between Mn(V)-oxo
corroles and substrates is affected significantly by the
nature of the solvent used.
To have a quantitative evaluation of the solvent
effect on the OAT reaction, pseudo-first order reaction
rate constants (kobs, Table 2) of Mn(V)-oxo corroles and
styrene were measured in different solvents (molar ratio:
Mn(V)-oxo/styrene = 1/1000), and the corresponding
bar-graph is shown in Fig. 5. The orders of pseudo-
first-order reaction rates and self-decay rate constants in
different solvents are the same. It may be concluded that
in DCM and toluene, more electron-deficient Mn(V)-oxo
corrole exhibits the higher reactivity, while in DMF and
DMAc more electron-rich Mn(V)-oxo corrole exhibits
the higher reactivity. Such a reversed reactivity order
may be rationalized by the disproportionation of Mn(V)-
oxo corrole into high valent Mn(VI)-oxo corrole in
<
deficient nature of Mn(V)-oxo corrole i.e. kF15C-Mn(V)-oxo
>
kF10C-Mn(V)-oxo > kF5C-Mn(V)-oxo > k F0C-Mn(V)-oxo, while in DMF
Fig. 2. UV-vis spectral changes of manganese(V)-oxo corroles (~3 × 10-5 M) in toluene: F15C-Mn(V)-oxo (a), F10C-Mn(V)-oxo (b),
F5C-Mn(V)-oxo (c) and F0C-Mn(V)-oxo (d)
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SOLVENT EFFECTS ON THE CATALYTIC ACTIVITY OF MANGANESE(III) CORROLES
321
Fig. 3. UV-vis spectral changes of manganese(V)-oxo corroles (~3 × 10-5 M) in DMF: F15C-Mn(V)-oxo (a), F10C-Mn(V)-oxo (b),
F5C-Mn(V)-oxo (c) and F0C-Mn(V)-oxo (d)
Fig. 4. Kinetic curves for the reaction of F15C-Mn(V)-oxo and large excess of styrene in toluene (a) and DMF (b) (25.0 0.1°C)
DMF and DMAc. In such a case, the more electron-rich
Mn(V)-oxo corrole exhibits a higher reactivity due to its
easier disproportionation [1, 16]. These kinetic evidences
suggest that Mn(VI)-oxo corrole may be a possible active
intermediate in manganese corroles catalyzed reactions,
as proposed by Gross et al. [16], and also support the
idea of multiple active oxidants proposed by Newcomb
et al. [29].
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322
Q. WANG ET AL.
Table 2. Self-decay rate constants (k) and pseudo-first-order reaction rate constants (kobs) of Mn(V)-oxo
corroles with styrene in different solvents at 25.0 0.1°Ca,b
Solvent
k/kobs (10-4 s-1)
F5C-Mn(V)-oxo
F15C-Mn(V)-oxo
F10C-Mn(V)-oxo
F0C-Mn(V)-oxo
Toluene
DCM
Self-decay
styrene
9.5084
24.2069
17.3646
29.2546
6.7986
8.0568
17.4945
12.6631
24.9920
9.3212
6.9426
16.1225
5.1967
5.7977
11.5829
2.4992
Self-decay
styrene
19.5378
11.2855
16.6463
13.4097
28.6217
5.7962
DMF
Self-decay
styrene
14.2537
18.7270
23.2774
39.0235
9.5995
13.2886
7.2884
DMAc
Self-decay
styrene
2.2067
12.3047
20.7339
a The reaction was monitored by the absorption at left arm of the Soret band. b The decay rate constants were
calculated by the exponential fit of the kinetic curve.
active specie is mainly Mn(VI)-oxo corrole generated
from Mn(V)-oxo complex by disproportionation reaction.
The catalytic oxidation reaction proceeds through path 3
(Scheme 1), and the more effective catalyst is electron-
rich Mn(III) corrole whose Mn(V)-oxo complex easily
generates Mn(VI)-oxo cation [29]. In all the investigated
solvents, benzaldehyde is formed via dioxygen involved
free-radical mechanism (Scheme 1, path 2). This pathway
is favored in DMAc and is remarkably suppressed under
anaerobic conditions.
EXPERIMENTAL
Reagents
All the solvents, toluene, dichloromethane (DCM),
N,N-dimethylformamide(DMF),N,N-dimethylacetamide
(DMAc), tetrahydrofuran (THF) and dimethyl sulfoxide
(DMSO), as well as the standard samples of the reaction
products and internal standard (chlorobenzene) were
purchased from Sinopharm Chemical Reagent Co. Ltd.
and dried prior to use. Commercial analytical grade
styrene (Aladdin) was passed through silica gel column
prior to use and the purity was tested by GC analysis.
Fig. 5. Self-decay and pseudo-first-order reaction rate constants
of Mn(V)-oxo corroles with styrene in different solvents at
25.0 0.1°C
Mechanistic consideration
By comparing the catalytic activity and the rate
constants of manganese corrole derivatives, we suggest
that catalytic oxidation reaction of styrene by Mn(III)
corroles may proceed via three pathways in different
solvents as shown in Scheme 1 (path 1–3).
In toluene and DCM, the active specie is Mn(V)-oxo
corrole, and the dominant pathway is the electrophilic
reaction between Mn(V)-oxo corrole and styrene (Scheme
1, path 1). In this situation, more electron-deficient Mn(III)
corroles exhibit a higher activity. In DMF and DMAc, the
Apparatus
Electronic absorption measurements were performed
on a Blue Star B UV-vis spectrophotometer connected
with a thermostat at 25.0 0.1°C. Mass spectra (MS)
were recorded on a VG ZAB-HS mass spectrometer
(EI, 70 eV). The product analysis was done by a gas
chromatograph (Echrom A90) equipped with an Agilent
HP-5 capillary column coupled with an FID detector.
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323
subs-O
subs
O
subs
MnV
MnIII
path 1
path 2
path 3
O
MnIV
O
MnIV
O
MnV
O
CHO
O
O
.
O
O
[O]
O2
MnIII
MnV
.
O
MnIV
O
MnV
MnIII
+
O
MnVI
MnIV
subs
subs-O
Scheme 1. Proposed mechanism for oxidation reactions catalyzed by manganese corroles in different types of solvents ([O] = PhIO
and subs = stryene)
Procedure
The catalytic reaction was carried out in six solvents.
5,15-bis(pentafluorophenyl)-10-(phenyl) corrole,
F10C-Mn(III). UV-vis (CH2Cl2): lmax, nm (log e) 308
(4.38), 402 (4.51), 418 (4.50), 581 (4.04), 620 (4.00).
MS (ESI): m/z (%) 758.3 ([M]+, 100). Manganese(III)
5,15-bis(phenyl)-10-(pentafluorophenyl) corrole,
F5C-Mn(III). UV-vis (CH2Cl2): lmax, nm (log e) 308
(4.35), 405 (4.55), 423 (4.54), 583 (3.97), 631 (4.01).
MS (ESI): m/z (%) 668.2 ([M]+, 100). Manganese(III)
5,10,15-triphenylcorrole, F0C-Mn(III). UV-vis
(CH2Cl2): lmax, nm (log e) 402 (4.48), 415 (4.45), 500
(4.13), 640 (3.87). MS (ESI): m/z (%) 578.2 ([M]+, 100).
Preparation of Mn(V)-oxo corroles. Mn(V)-oxo
corroles (Chart 1) were prepared by treating Mn(III)
corrole solution (~3 × 10-5 M) with PhIO (molar ratio
1:10) at room temperature until solution color turns
red. The superfluous PhIO was removed by flash
column chromatography on basic alumina [16, 17].
Manganese(V)-oxo 5,10,15-tris(pentafluorophenyl)
corrole, F15C-Mn(V)-oxo. UV-vis (CH2Cl2): lmax, nm
(log e) 346 (4.56), 408 (4.44), 518 (3.80). MS (ESI):
m/z (%) 864.0 ([M]+, 100), 848.2 ([M+ – O], 95).
Manganese(V)-oxo 5,15-bis(pentafluorophenyl)-10-
(phenyl) corrole, F10C-Mn(V)-oxo. UV-vis (CH2Cl2):
The mixture of catalyst (1 mmol), styrene (1 mmol) and
PhIO (0.1 mmol) in 2 mL of each solvent was stirred for
3.5 h at room temperature. After periodic time interval,
a certain amount of internal standard was added to this
reaction mixture and the aliquot was injected into a
preheated GC.The identification and quantification of the
products were done from the response factors of standard
product sample.
Kinetic studies were carried out in quartz cuvette with
PTFE septa. The freshly synthesized Mn(V)-oxo corrole
solution (~3 × 10-5 M) was taken in the cuvette and placed
immediately in a thermostat cell holder in a UV-vis
spectrophotometer. The absorbance data was collected
over the range of 300–800 nm at 5-sec interval. Each
measurement was repeated three times at 25.0 0.1°C.
Synthesis
Free base corroles (Chart 1) were prepared according
to the previously reported methods [8, 47–49].
Preparation of Mn(III) corroles. All Mn(III) corroles
(Chart 1) were prepared by refluxing the mixture of
corresponding free base corrole and Mn(OAc)2·4H2O
(molar ratio: 1:10) in methanol for 2 h, and the
products were purified by chromatography on silica
gel using dichloromethane as eluent [16, 17]. The
yields of all Mn(III) corroles were above 90%. Manga-
nese(III) 5,10,15-tris(pentafluorophenyl) corrole,
F15C-Mn(III). UV-vis (CH2Cl2): lmax, nm (log e)
308 (4.32), 397 (4.53), 414 (4.55), 593 (4.00). MS
(ESI): m/z (%) 848.2 ([M]+, 100). Manganese(III)
l
max, nm (log e) 347 (4.52), 409 (4.51), 521 (3.82). MS
(ESI): m/z (%) 774.1 ([M]+, 100), 758.3 ([M+ – O], 45).
Manganese(V)-oxo 5,15-bis(phenyl)-10-(pentafluoro-
phenyl) corrole, F5C-Mn(V)-oxo. UV-vis (CH2Cl2):
l
max, nm (log e) 349 (4.54), 421 (4.38), 515 (3.86). MS
(ESI): m/z (%) 684.2 ([M]+, 100), 668.2 ([M+ – O], 42).
Manganese(V)-oxo 5,10,15-triphenyl corrole, F0C-
Mn(V)-oxo. UV-vis (CH2Cl2): lmax, nm (log e) 344
(4.44), 408 (4.30), 525 (3.73). MS (ESI): m/z (%) 595.3
([M]+, 100), 578.2 ([M+ – O], 19).
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014 18: 323–325

324
Q. WANG ET AL.
12. Gross Z, Simkhovich L and Galili N. Chem. Com-
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CONCLUSION
We report the first systematic study of the effect of
solvent on the catalytic oxidation of styrene by four Mn(III)
corroles having different electronic features in the presence
of PhIO as oxidizing agent. We found that the properties of
solvent itself has remarkable effect on the catalytic activity
of Mn(III) corrole catalysts. The transformation of Mn(III)
corroles into their corresponding Mn(V)-oxo corroles,
and their subsequent reaction with styrene in a variety of
solvents was also performed. It was observed that more
electron-deficient Mn(V)-oxo corroles exhibit higher
reactivity towards styrene in DCM and toluene, while
less electron-deficient Mn(V)-oxo corroles exhibit higher
reactivity towards styrene in basic solvents (DMF, DMAc).
A plausible catalytic mechanism is suggested based on the
combined catalytic and kinetic data. It is evident that the
catalytic oxidation of styrene by manganese corroles may
proceed via oxygen atom transfer (OAT) between Mn(V)-
and/or Mn(VI)-oxo corrole intermediate and the substrate,
or via dioxygen involved free radical process, depending
on the solvent used during the catalytic reaction. Further
investigations of solvent effects on the properties of
various Mn(V)-oxo corroles derived from various electron-
donating and -withdrawing substituents and their catalytic
oxidation reactions are currently underway.
Acknowledgements
25. Zhu C, Liang JX, Wang BJ, Zhu J and Cao ZX.
Phys. Chem. Chem. Phys. 2012; 14: 12800–12806.
26. He J, Xu ZG, Xu Xuan, Gong LZ, Mahmood MHR
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The financial support from the National Natural
Science Foundation of China (21171057, 21371059) is
gratefully acknowledged.
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