High-Valent Manganese Corroles and the First Perhalogenated Metallocorrole Catalyst

Full text of DOI:10.1002/1521-3773(20010601)40:11<2132::AID-ANIE2132>3.0.CO;2-5

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result of the introduction of the electron-poor 5,10,15-
tris(pentafluorophenyl)corrole (H3(tpfc),[10] tpfc ˆ the trian-
ion). The iron, manganese, and rhodium complexes of
H3(tpfc) have been shown to be potent catalysts for the
oxygen and carbene transfer to olefins and alkanes,[11] with a
readily observed (oxo)manganese(v) intermediate in epox-
idation catalyzed by [Mn(tpfc)] (1).[11b] In addition, the
FeIV(Cl), RhIII(PPh3), CrV(O), and MnIII(OPPh3) complexes
have been fully characterized by a combination of spectro-
scopic methods and X-ray crystallography.[12] In all these
complexes there were no indications for oxidation of the
corrole, as opposed to the ambiguity in the case of the iron
and manganese octaalkylcorroles.[8, 9, 13] We now show that 1
can be functionalized at both the metal and the corrole
centers, which leads to the isolation and full characterization
of two manganese(iv) corroles, a stable (nitrido)manganese(v)
High-Valent Manganese Corroles and the First
Perhalogenated Metallocorrole Catalyst**
Galina Golubkov, Jesper Bendix, Harry B. Gray,*
Atif Mahammed, Israel Goldberg,* Angel J. DiBilio,
and Zeev Gross*
Two major goals of research on the manganese(iii) porphyr-
in catalyzed oxygenation of hydrocarbons are improved
activity/lifetime profiles and the identification of reaction
intermediates.[1] Increasingly more active catalysts have been
obtained by replacing tetraphenylporphyrin with halo-phenyl
analogues, and then with derivatives in which the b-pyrrole
carbons are halogenated as well.[2] Interestingly, this effect is
more pronounced for manganese than for iron porphyrin-
s.[1a, 2b] Spectroscopic identificationÐparticularly by NMRÐ
of proposed manganese(v) intermediates should be relatively
straightforward, since d2 metalloporphyrins with strong p-
donor ligands are expected to be diamagnetic. The first
1H NMR spectroscopic characterization of a (nitrido)manga-
nese(v) complex indeed dates from 1983,[3] but the spectrum
of an (oxo)manganese(v) porphyrin was obtained only very
recently.[4] Manganese(iv) porphyrins are more stable: X-ray
structures have been reported for several [Mn(por)(OR)2]
complexes (e.g., R ˆ CH3, C6H5I, porˆ porphyrin);[5] but so
far the characterization of high-valent manganese porphyrins
with oxo or halo ligands is limited to spectroscopic methods.[6]
Corroles are known to be superior to porphyrins in
stabilizing high oxidation states of various transition metals,[7]
but until recently only trivalent complexes were reported for
manganese.[8, 9] Furthermore, the oxidation state assignment
of the formally manganese(iii) and manganese(iv) complexes
of octaalkylcorroles remained ambiguous because of some
indications that the corrole is oxidized.[8, 9] In addition,
octaalkylcorrole metal complexes have never been examined
in oxidation catalysis, probably because meso aryl substitution
is almost always required in the related porphyrin-based
catalysts. However, this situation is changing dramatically as a
corrole, and
a perhalogenated manganese(iii) corrole
(Scheme 1). Preliminary results for the perhalogenated man-
ganese(iii) corrole demonstrate its superior activity as an
oxidation catalyst.
C6F5
N
N
N
N
C6F5
MnV
N
C6F5
F
F
F
F
F
4
C6F5
F
F
F
F
a
c
X
N
MnIV
N
N
N
N
N
N
MnIII
b
F
C6F5
C6F5
N
F
F
F
F
2: X = Br
3: X = Cl
C6F5
Br
Br
F
Br
Br
C6F5
Br
N
N
N
MnIII
N
1
C6F5
Br
[*] Prof. Dr. Z. Gross, G. Golubkov, Dr. A. Mahammed
Department of Chemistry and Institute of Catalysis Science and
Technology
Br
Br
5
Scheme 1. a) NaN3, hn, b) 1/2X2 (X ˆ Cl, Br), c) excess Br2/MeOH.
TechnionÐIsrael Institute of Technology
Haifa 32000 (Israel)
Fax : (‡972)4-8233735
Cyclic voltammetry of 1 reveals a redox potential of 0.71 V
(vs. standard calomel electrode (SCE)), suggesting that mild
oxidants could be used for the isolation of novel high-valent
manganese corroles. Indeed, treating a green hexane solution
of the highly soluble 1 with bromine or tris(4-bromophenyl)-
aminium hexachloroantimonate results in the immediate and
quantitative precipitation of [Mn(tpfc)(Br)] (2) and
[Mn(tpfc)Cl] (3), respectively.[14, 15] The electronic spectra of
these complexes (each exhibits a single Soret band) are very
similar to those of manganese(iv) porphyrins,[4±6] suggesting
that the oxidations are metal rather than corrole centered.
Reduction of 2 (Figure 1) produces a UV/Vis spectrum that is
E-mail: chr10zg@tx.technion.ac.il
Prof. Dr. H. B. Gray, Dr. J. Bendix, Dr. A. J. DiBilio
Beckman Institute
California Institute of Technology
Pasadena, CA 91125 (USA)
Fax : (‡1)6264494159
E-mail: hgmc@its.caltech.edu
Prof. Dr. I. Goldberg
School of Chemistry
Tel Aviv University
Tel Aviv 69978 (Israel)
Fax : (‡972)3-6409293
E-mail: goldberg@chemsg7.tau.ac.il
[**] This research (No. 368/00) was supported by the Israel Science
Foundation (Z.G.), the US National Science Foundation (H.B.G.), and
the Fund for the Promotion of Research at the Technion (Z.G.).
‡
identical to that obtained by adding n-Bu4N Br to 1,
corresponding to the metal-centered couple [MnIV Br]/
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nese atom. Corresponding deviations from the N4 and corrole
planes are 0.42 and 0.47 Š in 2, 0.43 and 0.58 Š in 3, but only
0.29 and 0.29 Š in [MnIII(tpfc)(OPPh3)].[12c] Interestingly, the
Mn Cl and Mn N bond lengths in 3 and [Mn(oec)(Cl)] are
very similar,[9] despite the large structural and electronic
differences between the corroles.
In the course of these studies, we noted two other unique
features of 1, both of which could be exploited for preparation
of novel manganese corroles. First, the aforementioned high
affinity of 1 for Br was also applied to N3 , which led to a
one-pot version of the known protocol for preparation of
(nitrido)metal complexes:[19] irradiation of a mixture of 1 and
NaN3 in CH3CN resulted in very clean conversion into
Figure 1. Spectroelectrochemical reduction of 2 at 0.4 V and a plot of the
magnetic moment versus T for 2.
‡
[MnV(tpfc)(N)] Na (4). This complex, which is stable at
room temperature in solution or as a solid, was identified by a
combination of spectroscopic methods (Figure 3). Both the
sodium ion and the nitrido ligand are apparent in the mass
spectrum (MS); sharp resonance signals in the NMR spectrum
are consistent with a diamagnetic manganese(v) center; and
the UV spectrum of 4 is very similar to that of analogous
neutral (nitrido)manganese(v) porphyrins.[3]
[MnIII Br] . Also consistent with the reduction of the metal
center is the large dependence of the reduction potential on
axial ligation; E1/2 ˆ 0.69 and 0.41 V for 2 and 3, respectively.
This proposal was further supported by magnetic suscepti-
bility measurements (SQUID, Figure 1, inset) on 2 and its
EPR spectra (not shown, frozen CH2Cl2 at 130 K; solid at
room temperature). The magnetic moment of 3.80 mB and the
EPR data (broad g ˆ 4.3 signal and a g ˆ 1.99 signal with
resolved Mn hyperfine structure, aMn ˆ 85 G) confirm an
isolated S ˆ 3/2 system, in line with the electronic structure of
other manganese(iv) complexes.[16] The alternative formula-
tion of 2 and 3 as manganese(iii) corrole radical complexes is
expected to result in much more complex magnetic data and
EPR spectra.[6b]
X-ray crystallographic analysis of 2 and 3 (Figure 2) reveals
a pronounced doming of the corrole framework in both
structures, with all four pyrrole nitrogens lying significantly
Figure 3. 1H NMR and UV/Vis spectra of 4 in CD3CN at room temper-
ature.
Second, we noticed remarkably facile pyrrole-substitution
during the aforementioned metal-based oxidation of 1. In fact,
the first two crystal structures of 2 and 3 were obtained with
partially halogenated (Br, Cl) corroles. This phenomenon was
exploited by treating 1 with an excess of Br2 in MeOH, which
allowed isolation of the fully brominated complex,[20]
[Mn(Br8tpfc)] (5), in high yield. In contrast, the preparation
of analogous porphyrins requires four synthetic steps: metal-
lation of the porphyrin by zinc, bromination of the zinc
complex with NBS (1-bromo 2,5-pyrrolidinedione), not Br2 as
with the corrole, removal of the zinc, and metallation by
manganese.[2] The transformation of 1 to 5 causes a 0.37 V
shift of the MnIII/MnIV couple in the cyclic voltammogram
(Figure 4), which is the reason that 5 is isolated in the
manganese(iii) oxidation state, despite the fact that the first
equivalent of bromine oxidizes 1 to 2. To assess differences in
reactivity between the ªsecond and third generationº man-
ganese(iii) corroles,[2a] 1 and 5 were compared as catalysts for
oxygenation of three representative substrates (Scheme 2).
Both complexes catalyze the oxidation of styrene by iodosyl-
benzene in very high yield, but with a very large difference in
reaction time: 10 h with 1 compared to 15 min with 5. These
differences were amplified with the less reactive substrates:
yields of 100% versus 40% for trans-stilbene and 100%
versus only 11% for cyclohexene catalyzed by 5 (15 min) and
Figure 2. ORTEP views of [Mn(tpfc)(Br)] (2; top) and [Mn(tpfc)(Cl)] (3;
bottom).
above the 19-membered carbon ring (average out of plane
distance of 0.065 Š in 2 and 0.21 Š in 3). As expected, the
manganese(iv) ± halide bond lengths of 2.428 and 2.312 Š in 2
and 3, respectively, are shorter (by approximately 0.05 Š)
than those found in analogous manganese(iii) porphyrin
complexes.[17, 18] The average Mn N bond lengths in 2
(1.925 Š) and 3 (1.932 Š) are longer than those in [MnIII(tpf-
c)(OPPh3)] (1.916 Š),[12c] but this is because of very large
differences in the out of plane displacements of the manga-
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tracted & Isomeric Porphyrins (Eds.: J. L. Sessler, S. J. Weghorn),
Pergamon, UK, 1997, chap. 1.
[8] a) S. Licoccia, E. Morgante, R. Paolesse, F. Polizio, M. O. Senge, E.
Tondello, T. Boschi, Inorg. Chem. 1997, 36, 1564; b) R. Paolesse, L.
Jaquinod, M. O. Senge, K. M. Smith, J. Org. Chem. 1997, 62, 6193;
c) K. M. Kadish, V. A. Adamian, E. Van Caemelbecke, E. Gueletii, S.
Will, C. Erben, E. Vogel, J. Am. Chem. Soc. 1998, 120, 11986.
[9] For data on manganese(iv) complexes of 2,3,7,8,12,13,17,18-octaethyl-
corrole (H3(oec)) see: C. Erben, S. Will, K. M. Kadish in The
Porphyrin Handbook, Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R.
Guilard), Academic Press, New York, 2000, chap. 12.
[10] a) Z. Gross, N. Galili, I. Saltsman, Angew. Chem. 1999, 111, 1530;
Angew. Chem. Int. Ed. 1999, 38, 1427; b) Z. Gross, N. Galili, L.
Simkhovich, I. Saltsman, M. Botoshansky, D. Bläser, R. Boese, I.
Goldberg, Org. Lett. 1999, 1, 599.
[11] a) Z. Gross, L. Simkhovich, N. Galili, Chem. Commun. 1999, 599. b) Z.
Gross, G. Golubkov, L. Simkhovich, Angew. Chem. Int. Ed. 2000, 39,
4045; c) L. Simkhovich, A. Mahammed, I. Goldberg, Z. Gross, Chem.
Eur. J. 2001, 7, 1041.
Figure 4. Cyclic voltammetry of [Mn(tpfc)] (1) and [Mn(Br8tpfc)] (5), in
CH2Cl2 with 0.1m TBAP.
Ph
Ph
Ph
O
+
[12] a) L. Simkhovich, N. Galili, I. Saltsman, I. Goldberg, Z. Gross, Inorg.
Chem. 2000, 39, 2704; b) A. E. Meier-Callahan, H. B. Gray, Z. Gross,
Inorg. Chem. 2000, 39, 3604; c) J. Bendix, H. B. Gray, G. Golubkov, Z.
Gross, Chem. Commun. 2000, 1957.
O
20.8%
45.0%
1:
5:
78.0%
53.7%
Ph
[13] S. Cai, F. A. Walker, S. Licoccia, Inorg. Chem. 2000, 39, 3466
[14] 2: A hexane solution of 1 (10 mg, 11.8 mmol) was treated with a hexane
solution of Br2 (5.9 mmol), which resulted in quantitative precipitation
of 2 as a red-brown solid. MS : e/z (%): 927 (40) [M ], 848 (100)
Ph
Ph
Ph
+
O
O
Ph
Ph
1:
5:
40%
87%
0%
13%
[M
Br], UV/Vis (CH2Cl2) lmax [nm] (lg e) 368 (4.63), 416 (4.72), 582
(3.74); elemental analysis (%) calcd for C37H8BrF15MnN4 ´ 2H2O: C
46.08, H 1.25, N 5.81; found: C 45.76, H 1.38, N 6.20. Recrystallization
from benzene/heptane resulted in X-ray quality crystals.
O
OH
[Mn(tpfc)(Br)],
crystallized
as
benzene
hemi-solvate
O
+
+
(C37H8BrF15MnN4) ´ 1ꢁ2 (C6H6): formula weight 967.38, monoclinic,
space group P21/c, a ˆ 13.425(1), b ˆ 23.629(1), c ˆ 11.208(1) Š, b ˆ
0.3%
32%
1.6%
32%
1:
5:
9.3%
36%
3
98.38(1)8, Vˆ 3517.5(2) Š3, Z ˆ 4, Tˆ 110 K, 1calcd ˆ 1.827 gcm
,
m(MoKa) ˆ 1.63 mm 1, 6636 unique reflections, R1 ˆ 0.053 for 4854
Scheme 2. 1 and 5 as oxygenation catalysts, reaction conditions: substrate
(1.2 mmol), iodosylbenzene (0.12 mmol), catalyst (1.2 mmol), benzene
(1 mL) at room temperature under Ar, for 15 min with 5 and 10 ± 12 h with
1.
observations with Fo > 4s(Fo), R1 ˆ 0.082 (wR2 ˆ 0.148) for all unique
3
data, jD1 jˆ 1.31 eŠ
.
[15] 3: A hexane solution of 1 (2.5 mg, 3 mmol) was treated with a
dichloromethane solution of tris(4-bromophenyl)aminium hexachloro-
antimonate (2.5 mg, 3 mmol), which resulted in quantitative precip-
itation of 3 as a red-brown solid. MS : e/z (%): 883 (25) [M ], 848
1 (12 h), respectively. Most significantly, 5 was not bleached at
the end of all reactions, while this is only true for 1 in the
reaction with styrene.
In conclusion, we have demonstrated that functionalization
of the manganese(iii) complex of H3(tpfc) provides a facile
route to various high-valent manganese corroles and to the
first perhalogenated corrole-based catalyst, all in very simple
one-pot syntheses. The very large increase in catalytic activity
upon b-pyrrole bromination of 1 to 5 will be fully investigated.
(100) [M
Cl]; UV/Vis (CH2Cl2) lmax [nm] 362, 414 (Soret), 582
(Q band). Recrystallization from benzene/heptane resulted in X-ray
quality crystals. [Mn(tpfc)(Cl)], crystallized as dibenzene solvate
(C37H8ClF15MnN4) ´ 2(C6H6): formula weight 1040.08, triclinic, space
Å
group P1, a ˆ 8.547(1), b ˆ 13.488(1), c ˆ 19.675(1) Š, a ˆ 71.08(1),
b ˆ 85.59(1), g ˆ 73.88(1)8, Vˆ 2061.1(2) Š3, Z ˆ 2, Tˆ 110 K, 1calcd
ˆ
3
1
1.676 gcm
,
m(MoKa) ˆ 0.50 mm
,
7056 unique reflections, R1 ˆ
0.062 for 4274 observations with Fo > 4s(Fo), R1 ˆ 0.128 (wR2 ˆ
0.147) for all unique data, jD1 jˆ 0.55 eŠ 3. Crystallographic data
(excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-147467 (2) and
CCDC-147468 (3). Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[16] M. J. Camenzind, F. J. Hollander, C. L. Hill, Inorg. Chem. 1983, 22,
3776.
Received: January 17, 2001 [Z16442]
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[17] A. Tulinsky, B. M. L. Chen, J. Am. Chem. Soc. 1977, 99, 3647.
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[2] a) D. Mansuy, Coord. Chem. Rev. 1993, 125, 129; b) Z. Gross, L.
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[19] J. DuBois, C. S. Tomooka, J. Hong, E. M. Carreira, Acc. Chem. Res.
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[20] [Mn(Br8tpfc)] 5: A solution of bromine (5 mL, 0.2 g, 1.2 mmol) and 1
(10 mg, 12 mmol) in methanol was stirred overnight, after which the
methanol and excess bromine were removed under vacuum. Recrys-
tallization from ethanol/water afforded 14.8 mg (85% yield) of 5.
[3] J. T. Groves, T. Takahashi, J. Am. Chem. Soc. 1983, 105, 2073.
[4] N. Jin, J. T. Groves, J. Am. Chem. Soc. 1999, 121, 2923.
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therein.
[6] a) Y. Watanabe, H. Fujii, Struct. Bonding 2000, 97, 61; b) L. Kaustov,
M. E. Tal, A. I. Shames, Z. Gross, Inorg. Chem. 1997, 36, 3503.
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Haubtmann, M. Bernard, M. Gross, Angew. Chem. 1997, 109, 367;
Angew. Chem. Int. Ed. Engl. 1997, 36, 357, and refs therein;
b) Tetrahedron Organic Chemistry Series, Vol. 15: Expanded, Con-
MS : e/z (%): 1479 (100) [M ], 1399 (10) [M
Br]; UV/Vis (CH2Cl2)
lmax [nm] 402 (4.73), 422 (4.70), 490 (4.38), 612 (4.24); 19F NMR
(CDCl3): d ˆ 138 (two overlapping brs, 6F), 152.3 (brs, 1F),
153.2 (brs, 2F), 160.5 (brs, 2F), 161.4 (brs, 4F).
2134
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