A bulky bis-pocket manganese(V)-oxo corrole complex: Observation of oxygen atom transfer between triply bonded MnV≡O and alkene

Article abstract of DOI:10.1021/ja905153r

(Graph Presented) The highly bulky bis-pocket corrole 5,10,15-tris(2,4,6- triphenylphenyl)corrole (H₃TTPPC) has been synthesized. Resonance Raman spectroscopy revealed a triply bonded Mn≡O moiety in its manganese(V)-oxo complex. Direct oxygen atom transfer from (TTPPC)Mn≡O to styrene was confirmed by an ¹⁸O-labeling experiment. The (TTPPC)Mn^III complex also exhibits significant shape selectivity in the catalytic epoxidation of nonconjugated dienes.

Full text of DOI:10.1021/ja905153r

Published on Web 08/19/2009
A Bulky Bis-Pocket Manganese(V)-Oxo Corrole Complex: Observation of
Oxygen Atom Transfer between Triply Bonded MnVt O and Alkene
Hai-Yang Liu,*,†,‡ Fei Yam,†,§ Yu-Tao Xie,† Xiao-Yuan Li,*,† and Chi K. Chang*,†,§
Department of Chemistry, The Hong Kong UniVersity of Science and Technology, Hong Kong, China, Department
of Chemistry, South China UniVersity of Technology, Guangzhou 510641, China, and Department of Chemistry,
Michigan State UniVersity, East Lansing, Michigan 48824
Received June 23, 2009; E-mail: chhyliu@scut.edu.cn; chxyli@ust.hk; changc@msu.edu
Scheme 1
Reactive Mn-oxo species have been implicated as intermediates
in the oxidation of water to oxygen in Photosystem II1 as well as
in certain catalases2 and oxygen atom transfer (OAT) reactions.3
While Mn-catalyzed oxidations of organic substrates4 involving
numerous MnIII-oxo,5a MnIV-oxo,5b,c and MnV-oxo5d,e com-
plexes have been extensively studied, the factors controlling the
reactivity of Mn-oxo complexes are not completely understood,
and the current literature on Mn-oxo chemistry is not without
controversy. An example is MnV-oxo porphyrin,6 which is one of
the most studied MnV-oxo systems but exhibits a wide range of
reactivity in OAT reactions.4b,5e,7 Recently, a definitive character-
ization of the inert trans-dioxo Mn(V) porphyrins has greatly
enhanced our understanding of the structure and properties of
Mn-oxo complexes.8
MnV-oxo complexes are an important mechanistic probe for
OAT reactions in the catalytic oxidation of alkenes. However, the
isolation and identification of OAT-active MnV-oxo complexes
present a considerable challenge. On the one hand, reactive
MnV-oxo species from salen,4a porphyrin,4b triazocyclononane,9
and polyoxometalate10 have only been observed as transient
intermediates. On the other hand, MnV-oxo species from tetraamide
macrocycles11a,b and corrolazine11c are too stable to attack the
olefinic double bond. Corrole is a trianionic ligand bearing a close
resemblance to porphyrin. Manganese corrole is an effective
oxidation catalyst, and its reactivity can be remarkably enhanced
by electron-withdrawing groups.12a,b MnV-oxo corrole was first
prepared with 5,10,15-tris(pentafluorophenyl)corrole (TPFC) and
showed a low reactivity.12a We previously prepared a perfluorinated
2,3,7,8,12,13,17,18-octafluoro-5,10,15-tris(pentafluorophenyl)cor-
role (F8TPFC) and its MnV-oxo complex.13 Kinetic studies implied
that the (F8TPFC)MnV-oxo complex was active for OAT to
cyclooctene. Other studies also indicated that OAT from
(TPFC)MnV-oxo to styrene may be greatly enhanced by N-base
ligation.14 We herein report the synthesis of a highly bulky 5,10,15-
tris(2,4,6-triphenylphenyl)-corrole (H3TTPPC) and its MnV-oxo
complex. Resonance Raman (RR) spectroscopy revealed a triply
bonded MnVt O moiety. The reaction between (TTPPC)MnVt O
and styrene yielded styrene epoxide, providing compelling evidence
of OAT between the MnVt O corrole and the alkene.
achieved by heating with Mn(OAc)2 ·4H2O in DMF. Dark-green
(TTPPC)MnIII was obtained in 88% yield after purification by
chromatography on basic alumina with diethyl ether as the eluent.
Treatment of (TTPPC)MnIII with PhIO in CH2Cl2 resulted in the
formation of (TTPPC)MnVO. Flash chromatography on basic
alumina afforded purified (TTPPC)MnVO. It is a diamagnetic
complex with a low-spin d2 Mn ion as indicated by its highly
resolved 1H NMR spectrum (Figure S5 in the Supporting Informa-
tion). The 18O-labeled isotopologue (TTPPC)MnVO18 was prepared
by the same procedure using PhIO18 as the oxidant,17 and the nature
of (TTPPC)MnVO was characterized by RR spectroscopy (Figure
1). Excitation at 413.1 nm in resonance with the Soret band led to
H3TTPPC was synthesized using the general procedure of
Gryko15 in an isolated yield of 6.5% (Scheme 1). Interestingly,
the corresponding bis-pocket 5,10,15,20-tetra(2,4,6-triphenylphe-
nyl)porphyrin (H2TTPPP)16 could only be obtained in ∼1% yield.
The remarkably higher yield obtained in the H3TTPPC synthesis
may be due to less peripheral steric hindrance without the methine
C-20 in the corrole ring. The insertion of Mn into H3TTPPC was
† The Hong Kong University of Science and Technology.
‡ South China University of Technology.
§ Michigan State University.
Figure 1. Resonance Raman spectra of (a) (TTPPC)MnIII, (b) (TTPPC)MnO16,
and (c) its MnO18 isotopomer in ∼1.0 mM CH2Cl2 solution.
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10.1021/ja905153r CCC: $40.75  2009 American Chemical Society

C O M M U N I C A T I O N S
the appearance of a strongly enhanced Raman peak at 952 cm-1
(Figure 1b). This peak was assigned to the stretching vibration of
the MnV-O unit, as it shifted to 913 cm-1 with 18O substitution
(Figure 1c). The observed isotopic shift of 39 cm-1 is in close
agreement with that calculated for an isolated Mn-O diatomic
oscillator (42 cm-1). The calculated force constant for the 952 cm-1
mode is 6.61 mdyn/Å. This force constant is consistent with that
calculated for triply bonded MnVt O in MnV-oxo corrolazine (for
N-methylimidazole as the axial ligand. A 10:1 alkene/oxidant ratio
was employed in order to suppress double epoxidation. The
regioselectivity for the epoxidation was compared with results
obtained using m-CPBA as a stoichiometric oxidant (Figure 3),
where the more-substituted, electron-rich double bonds are prefer-
ably oxidized. The bulky bis-pocket (TTPPC)MnIII-PhIO system
showed a significantly higher selectivity toward the less-substituted
but more accessible double bond. It is not surprising that the bis-
pocket corrole is more sensitive than the flat corrole (TPFC)MnIII
toward steric crowdedness. The regioselectivty toward 1-methyl-
1,2,4,5-cyclohexadiene and 7,7-dimethyl-1,2,5,6-octadiene displayed
by (TTPPC)MnIII compared favorably with those reported for
encumbered Mn porphyrins.19
In conclusion, this study has presented for the first time direct
evidence of OAT between a corrole MnVt O moiety and an alkene
substrate. This is also the first RR spectroscopic identification of
Mn(V)-oxo corrole. From this work and previously demonstrated
electronic effects,12,13 it is now clear that the corrole Mn-oxo
system possesses a wide range of reactivity rivaling that of the
established porphyrin system. Further study of applications of
Mn-corrole in molecular catalysis is underway.
which νMnt ) 979 cm-1),11c indicating a triply bonded MnVt O
O
in (TTPPC)MnVO. Notably, RR-identified triply bonded MnVt O
complexes are rare.11 The observed MnVt O stretching frequency
of (TTPPC)MnVO is significantly higher than that of doubly bonded
MnVdO porphyrin species such as dioxo OdMnVdO (νMndO
741-743 cm-1),8 and (OH)MnVdO (νMndO ) 791 cm-1).18
)
At 25 °C, the half-life of (TTPPC)MnVO in CH2Cl2 is ∼7 h. In
the presence of excess amounts of styrene substrate, a significant
acceleration of the decay of (TTPPC)MnVO occurred (Figure 2),
indicating direct reaction with styrene. At the end of the reaction,
(TTPPC)MnVO returned to the (TTPPC)MnIII complex. The reaction
yielded styrene oxide, as detected by GC-MS. That OAT occurred
between (TTPPC)MnVt O and styrene was further confirmed by
the stoichiometric reaction between (TTPPC)MnVO18 and styrene,
which afforded 18O-styrene oxide (see the Supporting Information).
Acknowledgment. This work was supported by the NNSFC
(20771039) and by RGC-CERG Grants of Hong Kong (602005,
601706).
Supporting Information Available: Synthesis, selected character-
ization data, and epoxidation and RR experiments. This material is
available free of charge via the Internet at http://pubs.acs.org.
References
(1) Armstrong, F. A. Philos. Trans. R. Soc. London, Ser. B 2008, 363, 1263.
(2) Beyer, W. F.; Fridovich, I. In Oxygen Radicals in Biology and Medicine;
Simic, M. G., Taylor, K. A., Ward, J. F., Von Sanntag, C., Eds.; Plenum:
New York, 1988; p 651.
(3) Rebelo, S. L. H.; Pereira, M. M.; Simo˜es, M. M. Q.; Neves, M. G. P. M.
S.; Cavaleiro, J. A. S. J. Catal. 2005, 234, 76.
(4) (a) Strassner, T.; Houk, K. N. Org. Lett. 1999, 1, 419. (b) Zhang, R.;
Newcomb, M. J. Am. Chem. Soc. 2003, 125, 12418.
(5) Selected examples: (a) Shirin, Z.; Hammes, B. S.; Young, V. G.; Borovik,
A. S. J. Am. Chem. Soc. 2000, 122, 1836. (b) Parsell, T. H.; Yang, M. Y.;
Borovik, A. S. J. Am. Chem. Soc. 2009, 131, 2762. (c) Yin, G. C.;
Buchalova, M.; Danby, A. M.; Perkins, C. M.; Kitko, D.; Carter, J. D.;
Scheper, W. M.; Busch, D. H. J. Am. Chem. Soc. 2005, 127, 17170. (d)
Zhang, R.; Horner, J. H.; Newcomb, M. J. Am. Chem. Soc. 2005, 127,
6573. (e) Jin, N.; Groves, J. T. J. Am. Chem. Soc. 1999, 121, 2923.
(6) Zhang, R.; Newcomb, M. Acc. Chem. Res. 2008, 41, 468.
(7) Song, W. J.; Seo, M. S.; DeBeer George, S.; Ohta, T.; Song, R.; Kang,
M. J.; Tosha, T.; Kitagawa, T.; Solomon, E. I.; Nam, W. J. Am. Chem.
Soc. 2007, 129, 1268.
Figure 2. UV-vis spectral changes of (TTPPC)MnVO in the presence of
excess styrene in CH2Cl2 (scan interval ) 20 min). Inset: absorbance decay
of (TTPPC)MnVO monitored at λ ) 366 nm; the pseudo-first-order rate
constant is 3.8 × 10-4 s-1 (25 ( 0.1 °C).
(8) (a) Jin, N.; Ibrahim, M.; Spiro, T. G.; Groves, J. T. J. Am. Chem. Soc.
2007, 129, 12416. (b) Gross, Z. Angew. Chem., Int. Ed. 2008, 47, 2737.
(9) Gilbert, B. C.; Smith, J. R. L.; Payeras, A. M. I.; Oakes, J. Org. Biomol.
Chem. 2004, 8, 1176.
(10) Khenkin, A. M.; Kumar, D.; Shaik, S.; Neumann, R. J. Am. Chem. Soc.
2006, 128, 15451.
(11) (a) Workman, J. M.; Powell, R. D.; Procyk, A. D.; Collins, T. J.; Bosian,
D. F. Inorg. Chem. 1992, 31, 1548. (b) Collins, T. J.; Powell, R. D.;
Slebodnick, C.; Uffelman, E. S. J. Am. Chem. Soc. 1990, 112, 899. (c)
Mandimutsira, B. S.; Ramdhanie, B.; Todd, R. C.; Wang, H.; Zareba, A. A.;
Czernuszewicz, R. S.; Goldberg, D. P. J. Am. Chem. Soc. 2002, 124, 15170.
(12) (a) Gross, Z.; Golubkov, G.; Simkhovich, L. Angew. Chem., Int. Ed. 2000,
39, 4045. (b) Golubkov, G.; Bendix, J.; Gray, H. B.; Mahammed, A.;
Goldberg, I.; DiBilio, A. J.; Gross, Z. Angew. Chem., Int. Ed. 2001, 40,
2132.
(13) Liu, H.-Y.; Lai, T.-S.; Yeung, L.-L.; Chang, C. K. Org. Lett. 2003, 5, 617.
(14) Liu, H.-Y.; Zhou, H.; Liu, L.-Y.; Ying, X.; Jiang, H.-F.; Chang, C. K.
Chem. Lett. 2007, 36, 274.
(15) Gryko, D. T. J. Porphyrins Phthalocyanines 2008, 12, 906.
(16) Suslick, K. S.; Fox, M. M. J. Am. Chem. Soc. 1983, 105, 3507.
(17) Schardt, B. C.; Hill, G. L. Inorg. Chem. 1983, 22, 1563.
(18) Shimazaki, Y.; Nagano, T.; Takesue, H.; Ye, B.-H.; Tani, F.; Naruta, Y.
Angew. Chem., Int. Ed. 2004, 43, 98.
(19) (a) Lai, T.-S.; Lee, S. K. S.; Yeung, L.-L.; Liu, H.-Y.; Williams, I. D.;
Chang, C.-K. Chem. Commun. 2003, 620. (b) Chang, C. K.; Yeh, C.-Y.;
Lai, T.-S. Macromol. Symp. 2000, 156, 117. (c) Suslick, K. S.; Cook, B. R.
J. Chem. Soc., Chem. Commun. 1987, 200.
Figure 3. Percentage of less-substituted epoxides (formed at the darkened
CdC bonds) produced by epoxidation of dienes using m-CPBA (magenta),
PhIO-(TPFC)MnIII (red), and PhIO-(TTPPC)MnIII (blue).
Shape-selective catalytic epoxidation of nonconjugated dienes
using (TTPPC)MnIII/PhIO was also examined in the presence of
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