Solvent effects on oxygen atom transfer reaction between manganese(V)-oxo corrole and alkene

Article abstract of DOI:10.1016/j.cclet.2013.03.029

Pseudo-first order reaction rate constants of 5,10,15- tris(pentafluorophenyl)corrole Mn(V)-oxo (F₁₅CMn(V)-oxo), 5,15-bis(pentafluorophenyl)-10-(phenyl)corrole Mn(V)-oxo (F₁₀CMn(V)- oxo), 5,15-bis(phenyl)-10-(pentafluorophenyl)corrole Mn(V)-oxo (F ₅CMn(V)-oxo) and 5,10,15-tris(phenyl)corrole Mn(V)-oxo (F ₀CMn(V)-oxo) with a series of alkene substrates in different solvents were determined by UV-vis spectroscopy. The results indicated that the oxygen atom transfer pathway between Mn(V)-oxo corrole and alkene is solvent-dependent.

Full text of DOI:10.1016/j.cclet.2013.03.029

Chinese Chemical Letters 24 (2013) 447–449
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Solvent effects on oxygen atom transfer reaction between manganese(V)-oxo
corrole and alkene
Lan Yu a, Qi Wang a, Lu Dai a, Wei-Ying Li a, Rong Chen a, Mian HR Mahmood a, Hai-Yang Liu a,
,
*
Chi-Kwong Chang b,
*
a Department of Chemistry, South China University of Technology, Guangzhou 510640, China
b Department of Chemistry, Michigan State University, E. Lansing, MI 48824, USA
A R T I C L E I N F O
A B S T R A C T
Article history:
Pseudo-first order reaction rate constants of 5,10,15-tris(pentafluorophenyl)corrole Mn(V)-oxo
(F15CMn(V)-oxo), 5,15-bis(pentafluorophenyl)-10-(phenyl)corrole Mn(V)-oxo (F10CMn(V)-oxo), 5,15-
bis(phenyl)-10-(pentafluorophenyl)corrole Mn(V)-oxo (F5CMn(V)-oxo) and 5,10,15-tris(phenyl)corrole
Mn(V)-oxo (F0CMn(V)-oxo) with a series of alkene substrates in different solvents were determined by
UV–vis spectroscopy. The results indicated that the oxygen atom transfer pathway between Mn(V)-oxo
corrole and alkene is solvent-dependent.
Received 16 January 2013
Received in revised form 28 February 2013
Accepted 3 March 2013
Available online 19 April 2013
Keywords:
ß 2013 Hai-Yang Liu, Chi-Kwong Chang. Published by Elsevier B.V. on behalf of Chinese Chemical
Society. All rights reserved.
Corrole
Mn(V)-oxo corrole
Oxygen atom transfer reaction
Solvent effect
1. Introduction
the reactivity of b-brominated Mn(V)-oxo corrole is more related
to the spin state changes [12]. It is well-known that solvent plays
important role in the catalytic oxidation reactions [13] and solvent
effects have previously been observed in chromium-oxo corroles
[14] and molybdenum-oxo corroles [15] Herein, we wish to report
the solvent effects on the OAT reaction between manganese(V)-
oxo corroles and alkenes. The investigated manganese(V)-oxo
corrole species are shown in Scheme 1.
Many biological reactions involve oxygen atom transfer (OAT)
from a transition metal active center to the substrates [1]. High-
valent metal–oxo complexes are critical to a large class of
metalloenzymes involved in OAT reaction [2,3]. Manganese(V)-
oxo porphyrins have long been recognized as an active species in
OAT reactions [4]. Corrole is an aromatic 18-p electron macrocycle
that bears a close resemblance with porphrin [5]. Compared to the
transient Mn(V)-oxo porphyrin [6], Mn(V)-oxo corrole is more
stable and thus provides an ideal mechanistic probe for the
catalytic oxidation of organic substrates.
2. Experimental
Mn(III) corroles were prepared according to our previously
reported procedure [16]. The corresponding Mn(V)-oxo corroles
were also prepared according to reported method [7,9]. Typically,
iodosobenzene (PhIO) was added to a solution of Mn(III) corrole
(ꢀ3.0 Â 10À5 mol/L) (Mn(III) corrole/PhIO molar ratio is 1:10), and
the solution color turned into red gradually. After reaction,
superfluous PhIO was removed by flash chromatography on basic
alumina. It is noteworthy that Mn(V)-oxo corroles could not be
prepared by the same method in THF or DMSO.
The first synthesis of manganese(V)-oxo was achieved by
oxidation of manganese 5,10,15-tris(pentafluorophenyl)corrole
[(TPFC)Mn(III)] with iodosylbenzene (PhIO) or ozone as an oxidant
[7], albeit laser flash photolysis may also be used [8]. Electron-
deficient perfluorinated Mn(V)-oxo corrole was found to be more
reactive towards a cyclooctene substrate [9], and the presence of
an axial ligand also enhanced the reactivity of Mn(V)-oxo corrole
[10]. The direct evidence of OAT between Mn(V)-oxo and alkene
came from the 18O-labeling experiments using a highly bulky
Mn(V)-oxo corrole complex [11]. DFT calculations indicated that
3. Results and discussion
Mn(V)-oxo corroles are unstable and will gradually decompose
and finally return to the corresponding Mn(III) corrole in general.
However, the more electron-rich F5CMn(V)-oxo and F0CMn(V)-
oxo will gradually change to Mn(IV) corrole in toluene and
* Corresponding authors.
E-mail addresses: chhyliu@scut.edu.cn (H.-Y. Liu), changc@msu.edu
(C.-K. Chang).
1001-8417/$ – see front matter ß 2013 Hai-Yang Liu, Chi-Kwong Chang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.03.029

[
L. Yu et al. / Chinese Chemical Letters 24 (2013) 447–449
50
40
30
20
10
0
50
F15CMn(V)-oxo
F10CMn(V)-oxo
F5CMn(V)-oxo
F0CMn(V)-oxo
F15CMn(V)-oxo
F10CMn(V)-oxo
F5CMn(V)-oxo
F0CMn(V)-oxo
40
30
20
10
0
α
β
α
β
50
50
F15CMn(V)-oxo
F10CMn(V)-oxo
F5CMn(V)-oxo
F0CMn(V)-oxo
F15CMn(V)-oxo
F10CMn(V)-oxo
F5CMn(V)-oxo
F0CMn(V)-oxo
40
40
30
20
10
0
30
20
10
0
α
α
β
β
Fig. 1. Self-decay and pseudo-first-order reaction rate constants of manganese-oxo corroles with substrates (25.0 8C Æ 0.1 8C) in different solvents.
dichloromethane (DCM), as indicated by UV–vis spectra. These
two Mn(V)-oxo species could only return to Mn(III) corrole in DMF
or DMAc solutions, which may be related to the stability of
electron-rich Mn(III) corrole in these solvents. It was also
observed that these electron-rich Mn corroles prefer to exhibit
Mn(IV) complex in DCM [17]. The self-decay rate constants (k) of
Mn(IV) corroles were determined by monitoring the absorption
maximum of Soret band (left arm) at (25.0 Æ 0.1) 8C and the data
are shown in Fig. 1. It can be seen that in toluene and DCM, the self-
decay rate constants follow the order: F15CMn(V)-oxo > F10CMn(V)-
oxo > F5CMn(V)-oxo > F0CMn(V)-oxo. In contrast, self-decay rate
constants follow a reversed order: F15CMn(V)-oxo < F10CMn(V)-
oxo < F5CMn(V)-oxo < F0CMn(V)-oxo in DMF, DMAc. This indicates
that solvent has a significant effect on the self-decay process of
Mn(V)-oxo corroles.
Pseudo-first order reaction rate constants (kobs) between Mn(V)-
oxo corroles and alkene substrates in different solvents are also
shown in Fig. 1. Here, kobs was measured by the reaction of Mn(V)-
oxo corrole and a large excess of substrates ([substrate]/[Mn-
oxo] = 1000). In all these cases, the addition of alkene substrate was
found to accelerate the decay of Mn(V)-oxo corrole significantly.
This is caused by the OAT reaction between Mn-oxo corrole and
electron-rich alkene double bond (Fig. 1). The difference in rate
constants between limonene, -pinene and -pinene are consistent
withtheenhancedreactivity ofMn(V)-oxotriphenylcorroletowards
the less-substituted and electron-rich alkene [11]. In toluene and
DCM, pseudo-first order rate constants (kobs) follow the order:
a
b
F15CMn(V)-oxo > F10CMn(V)-oxo > F5CMn(V)-oxo > F0CMn(V)-
oxo. This is in accordance with the electronic demand of Mn(V)-oxo
corroles. As the OAT reaction between Mn(V)-oxocorrole and alkene
is an electrophilic reaction, it is expected that more electron-
deficient Mn(V)-oxo corroles would be more reactive. This means a
direct OAT reaction between Mn(V)-oxo corrole and alkene
substrates could have occurred in this case. Interestingly, in DMF
and DMAc, the pseudo-first order rate constants (kobs) follow a
reversed order:
F15CMn(V)-oxo < F10CMn(V)-oxo < F5CMn(V)-
oxo < F0CMn(V)-oxo. This is contradictory to the reactivity of
Mn(V)-oxo corroles based on electronic demand. Similar phenome-
non was also observed by Mn(V)-oxo corroles generated by laser
flash photolysis [8]. It was rationalized by the generation of a higher
valent Mn(VI)-oxo species via a disproportionation process of the
Mn(V)-oxo corrole. The more electron-rich Mn(V)-oxo corroles
undergo the disproportionation reaction more easily. In DMF and
DMAc, electron-rich F0CMn(V)-oxo exhibited the largest reaction
rate constants to all examined substrates, and the kobs of alkene with
electron-rich double bonds are also much higher. This indicates the
formation of new reactive F0CMn-oxo species in these solvent
systems. These observations also suggested that OAT reaction of
Mn(V)-oxo corrole and alkene substrates may proceed via different
mechanisms in different solvents.
alkene. The rate constants of limonene,
a-pinene and b-pinene are
much larger than that of styrene due to the presence of more
[(Scheme_1)TD$FIG]
4. Conclusion
In conclusion, we report the first observation of solvent effect on
the OAT reaction between Mn(V)-oxo corroles and alkene sub-
strates. The reaction may proceed either through a direct OAT
between Mn(V)-oxo and alkene or through a high-valent Mn-oxo
Scheme 1. Structures of free base corroles and their Mn complexes.

L. Yu et al. / Chinese Chemical Letters 24 (2013) 447–449
449
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solvent-dependent. Further investigations on how the solvent
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Acknowledgment
The financial support from the National Natural Science
Foundation of China (Nos. 20971046 and 21171057) is gratefully
acknowledged.
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