Manganese as a template: A new synthesis of corrole

Article abstract of DOI:10.1039/b107362c

The reaction of 2,2′-bisdipyrrins 1, 2, and 3 with manganese(II) acetate tetrahydrate and molecular dioxygen yields the manganese(III)corroles 4, 5 and 6, which are readily demetalated to the respective free-base corroles.

Full text of DOI:10.1039/b107362c

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Manganese as a template: a new synthesis of corrole
Martin Bröring* and Christian Hell
Institut für Anorganische Chemie, Universität Würzburg, Am Hubland D-97074. Würzburg, Germany.
E-mail: Martin.Broering@mail.uni-wuerzburg.de
Received (in Cambridge, UK) 14th August 2001, Accepted 2nd October 2001
First published as an Advance Article on the web 22nd October 2001
The reaction of 2,2A-bisdipyrrins 1, 2, and 3 with man-
ganese(II) acetate tetrahydrate and molecular dioxygen
yields the manganese(III)corroles 4, 5 and 6, which are
readily demetalated to the respective free-base corroles.
octaethylcorrole 8 quantitatively within 10 min (Scheme 3).7
This clean demetalation protocol makes the newly found
manganese induced cyclization a useful synthetic tool towards
The chemistry of corrole, the one-carbon short analogue of
porphyrin, is currently one of the most flourishing fields in the
porphyrin area.1 Ever since the unexpected observation by
Vogel et al. in 1994, that this trisanionic ligand stabilises
unusually high oxidation states of transition metal centers like
Fe(IV), Cu(III), and Co(IV),2 the interest in this particular
macrocycle has continuously increased. The synthetic pathways
leading to corroles, however, are still rather small in number,
albeit a large body of work has been conducted in recent years
towards general approaches to differently substituted corroles,
mainly by the groups of Paolesse3 and Gross.4 Very recently,
the first applications of corroles as ligands in catalytically active
transition metal complexes have appeared in the literature,5 and
the first multi-macrocyclic architectures using corroles as
building blocks have also been achieved.6 Today, the major
methods used for the preparation of corroles are the oxidative
cyclization of a,w-didesoxybiladienes-a,c as described by
Murakami,7 and the strategy of Gross et al., who developed the
non-catalysed condensation of pyrrole and aromatic aldehydes
as a one step procedure.4 In the course of studies towards a
synthetic entry into the corrole and corrin field, Johnson et al.
attempted to cyclize 2,2A-bisdipyrrin complexes of Pd(II) as
early as 1960, but received a palladium(II)-10-oxacorrole
instead.8 Here we report, that by simply changing the metal ion
to manganese the desired formation of corroles from 2,2A-
bisdipyrrins9 can in fact be observed.
As 3,3A,4,4A,8,8A,9,9A-octaethyl-10,10A-dimethyl-2,2A-bisdi-
pyrrin 1 is treated with manganese(II) acetate tetrahydrate under
aerobic conditions in boiling DMF, varying amounts of 4 build
up over the course of several hours. Purging the hot reaction
mixture with dioxygen accelerates the reaction significantly, so
that within five minutes the cyclization is complete. After
chromatography and recrystallization from diethyl ether–n-
hexane, 4 is obtained as violet crystals in 23% yield (Scheme 1).
The material obtained this way is identical in every respect with
the manganese(III)octaethylcorrole reported earlier.10 When
applying the very same conditions to other a,w-dimethyl-2,2A-
bisdipyrrins,9 substituted manganese(III)corroles can be pre-
pared. For example, meso-diphenyl- and meso-di-p-tolyl-2,2A-
Scheme 1
bisdipyrrins
2
and
3
are
cyclized
to
the
Scheme 2
manganese(III)-5,15-diarylcorroles 5 and 6 in 18 and 19% yield,
respectively.11,12
As we experienced at an initial stage of the project, the
manganese(III)corroles appear remarkably prone to oxidation by
chlorinated solvents (Scheme 2). Thus, simply performing the
chromatographic work-up of 4 on silica with a dichloro-
methane–methanol mixture as the eluent directly gave the
known chloro-manganese(IV) complex 71b as the only product,
albeit in diminished yield (17%). This observation provides yet
another example for the ease of stabilisation of high oxidation
states through the trisanionic corrole ligand.
Free base corroles are readily released from the manganese
complexes by simple acid induced demetallation. For example,
treatment of 4 with HBr in acetic acid yields the well-known
Scheme 3
2336
Chem. Commun., 2001, 2336–2337
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b107362c

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Handbook, ed. K. M. Kadish, K. M. Smith and R. Guilard, Academic,
San Diego, CA, 2000, vol. 2, ch. 12, p. 233–300.
2 E. Vogel, S. Will, A. Schulze-Tilling, L. Neumann, J. Lex, E. Bill, A. X.
Trautwein and K. Wieghardt, Angew. Chem., Int. Ed. Engl., 1994, 33,
731; S. Will, J. Lex, E. Vogel, V. A. Adamian, E. Van Caemelbecke and
K. M. Kadish, Inorg. Chem., 1996, 35, 5577; S. Will, J. Lex, E. Vogel,
H. Schmickler, J.-P. Gisselbrecht, C. Haubtmann, M. Bernard and M.
Gross, Angew. Chem., Int. Ed. Engl., 1997, 36, 357.
3 R. Paolesse, S. Licoccia, M. Fanciullo, E. Morgante and T. Boschi,
Inorg. Chim. Acta, 1993, 203, 107; R. Paolesse, S. Licoccia, G. Bandoli,
A. Dolmella and T. Boschi, Inorg. Chem., 1994, 33, 1171; V. A.
Adamian, F. D’Souza, S. Licoccia, M. L. Di Vona, E. Tassoni, R.
Paolesse, T. Boschi and K. M. Smith, Inorg. Chem., 1995, 34, 532; R.
Paolesse, L. Jaquinod, D. J. Nurco, S. Mini, F. Gagone, T. Boschi and
K. M. Smith, Chem. Commun., 1999, 1307.
4 Z. Gross, N. Galili and I. Saltsman, Angew. Chem., Int. Ed., 1999, 38,
1427; Z. Gross, N. Galili, L. Simkhovich, I. Saltsman, M. Botoshansky,
D. Blaser, R. Boese and I. Goldberg, Org. Lett., 1999, 1, 599; for related
work, see also:; D. T. Gryko, Chem. Commun., 2000, 2243; R. Paolesse,
S. Nardis, F. Sagone and R. G. Khoury, J. Org. Chem., 2000, 66, 550;
D. T. Gryko and K. Jadach, J. Org. Chem., 2001, 66, 4267; C. V.
Asokan, S. Smeets and W. Dehaen, Tetrahedron Lett., 2001, 42,
4483.
5 Z. Gross, L. Simkhovich and N. Galili, Chem. Commun., 1999, 599; Z.
Gross, G. Golubkov and L. Simkhovich, Angew. Chem., Int. Ed., 2000,
39, 4045; G. Golubkov, J. Bendix, H. B. Gray, A. Mahammed, I.
Goldberg, A. J. DiBilio and Z. Gross, Angew. Chem., Int. Ed., 2001, 40,
2132.
6 R. Paolesse, R. K. Pandey, T. P. Forsyth, L. Jaquinod, K. R. Gerzevske,
D. J. Nurco, M. O. Senge, S. Licoccia, T. Boschi and K. M. Smith, J.
Am. Chem. Soc., 1996, 118, 3869; F. Jérome, C. P. Gros, C. Tardieux,
J.-M. Barbe and R. Guilard, Chem. Commun., 1998, 2007; R. Paolesse,
A. Macagnano, D. Monti, P. Tagliatesa and T. Boschi, J. Porph. Phthal.,
1998, 2, 501; F. Jérome, C. P. Gros, C. Tardieux, J.-M. Barbe and R.
Guilard, New J. Chem., 1998, 1327; R. Paolesse, F. Sagone, A.
Macagnano, T. Boschi, L. Prodi, L. Mantalti, N. Zaccheroni, F. Boletta
and K. M. Smith, J. Porph. Phthal., 1999, 3, 364.
Scheme 4
substituted corrole ligands, some which are hardly or not at all
accessible by any other of the corrole forming reactions known
today.
Although the mechanistic details of the Mn(II)–O2 induced
cyclization of 2,2A-bisdipyrrins are still in question, the
formation of 4–6 points to an analogous oxidative transforma-
tion in the porphyrin field, namely the reaction of a,c-biladienes
9 with several metal salts or oxidants to yield porphyrins 10
(Scheme 4). This valuable transformation, initially found by
Johnson et al.,13 has been thoroughly investigated and mecha-
nistically explained by Smith.14 It appears highly probable, that
a related sequence of steps occurs also in the case of 2,2A-
bisdipyrrin cyclization. As a major difference to the macro-
cyclization of a,c-biladienes we believe, that in our case a
templating action of the metal ion—prior to or after partial
oxidation—is crucial to the reaction. Most probably, the 2,2A-
bisdipyrrin unit will not stabilise the tense, helical conformation
necessary for ring closure on its own, but rather retain the ability
of an almost free rotation around the central pyrrole–pyrrole
axis. Additionally, it is quite questionable, whether the terminal
methyl groups of a 2,2A-bisdipyrrin in a closed, quasi-
macrocyclic conformation would have sufficient overlap with-
out being forced by a central metal ion.
Further studies towards an understanding of the C1 extrusion,
the use of other metal ions and/or co-oxidants, and the
application of the new macrocyclization in the synthesis of
tailor-made and functionalized corroles and metallocorroles are
currently in progress.
This work was funded by the Deutsche Forschungsge-
meinschaft (Emmy-Noether-Programm) and the Fonds der
Chemischen Industrie. We thank Professor Helmut Werner for
his generous support.
7 Y. Murakami, Y. Matsuda, K. Sakata, S. Yamada, Y. Tanaka and Y.
Aoyama, Bull. Chem. Soc. Jpn., 1981, 54, 163.
8 A. W. Johnson and R. Price, J. Chem. Soc., 1960, 1649; A. W. Johnson
and I. T. Kay, Proc. Chem. Soc., 1961, 168.
9 M. Bröring, Synthesis, 2000, 1291; M. Bröring, D. Griebel, C. Hell and
A. Pfister, J. Porph. Phthal., 2001, 5, 708.
10 K. M. Kadish, V. A. Adamian, E. Van Caemelbecke, E. Gueletii, S.
Will, C. Erben and E. Vogel, J. Am. Chem. Soc., 1998, 120, 11986.
11 Spectroscopic data for 5: mp. 252 °C (decomp.); MS (FAB): m/z 726.4,
M+; calc. for C47H51N4Mn: C 77.66, H 7.07, N 7.71; found: C 77.21, H
7.25, N 7.53%.
12 Spectroscopic data for 6: mp. 294 °C (decomp.); MS (FAB): m/z 754.5,
M+; calc. for C49H55N4Mn: C 77.96, H 7.34, N 7.42; found: C 77.97, H
7.52, N 7.44%.
13 A. W. Johnson and I. T. Kay, J. Chem. Soc. C, 1961, 2418.
14 K. M. Smith, in The Porphyrin Handbook, ed. K. M. Kadish, K. M.
Smith and R. Guilard, Academic, San Diego, CA, 2000, vol. 1, ch. 3, p.
119–148.
Notes and references
1 (a) R. Paolesse, in The Porphyrin Handbook, ed. K. M. Kadish, K. M.
Smith and R. Guilard, Academic, San Diego, CA, 2000, vol. 2, ch. 11,
p. 201–232 ; (b) C. Erben, S. Will and K. M. Kadish, in The Porphyrin
Chem. Commun., 2001, 2336–2337
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