5,10,15-Triphenylcorrole: A product from a modified Rothemund reaction

Article abstract of DOI:10.1039/a903247i

One-pot synthesis of 5,10,15-triphenylcorrole has been achieved by reaction of benzaldehyde with an excess of pyrrole; the triphenylphosphinocobalt complex of 5,10,15-triphenylcorrole has been structurally characterized using X-ray crystallography.

Full text of DOI:10.1039/a903247i

5,10,15-Triphenylcorrole: a product from a modified Rothemund reaction
Roberto Paolesse,*a Laurent Jaquinod,b Daniel J. Nurco,b Sonia Mini,a Francesco Sagone,a Tristano Boschia
and Kevin M. Smithb
a
Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, 00133 Roma, Italy.
E-mail: roberto.paolesse@uniroma2.it
Department of Chemistry, University of California, Davis, CA 95616, USA. E-mail: kmsmith@ucdavis.edu
b
Received (in Corvallis, OR, USA) 23rd April 1999, Accepted 1st June 1999
One-pot synthesis of 5,10,15-triphenylcorrole has been
achieved by reaction of benzaldehyde with an excess of
pyrrole; the triphenylphosphinocobalt complex of
5,10,15-triphenylcorrole has been structurally characterized
using X-ray crystallography.
additional pigments were observed but in very low yield and
therefore were not characterized.9
During our studies on the chemistry of corrole, we reported
the formation of a meso-phenyl-b-substituted corrole from the
cobalt catalyzed cyclization of a hydroxybenzylpyrrole,10 the
first intermediate in the condensation of pyrrole and benzalde-
hyde. This result, and knowledge that the ring-expanded
sapphyrin system was also isolated,7 caused us to suspect that
5,10,15-triphenylcorrole 4 might also be another, albeit dimin-
utive, product of the Rothemund reaction. Two examples of
meso-substituted corroles have since been reported in the
literature;11,12 these corroles were obtained as by-products of
the expected porphyrins in the reaction of pyrrole and
aldehydes. These examples further supported our hypothesis
that corroles might be obtained from the condensation of
pyrrole and aldehydes, but because of the low yields and the
particular aldehydes used, these results cannot be generalized.
Here we report that, under certain defined conditions, triphe-
nylcorrole 4 is formed in reasonable yield from the Rothemund
reaction;† cobalt was easily inserted into 4 and the correspond-
ing triphenylphosphino complex 5 was structurally charac-
terized.
5,10,15,20-Tetraphenylporphyrin 1 is probably the most ubiqui-
tous synthetic porphyrin and it has often been utilized to study
biomimetic and/or catalytic systems.1,2 Its success in these roles
is probably due to the relatively easy synthetic approach to 1,
which is obtained by condensation of pyrrole and benzalde-
Ph
Ph
N
NH
N
N
NH
N
Ph
Ph
Ph
Ph
HN
HN
Ph
Ph
Ph
1
2
Pyrrole and benzaldehyde (3+1 molar ratio) were reacted in
refluxing AcOH for 4 h with spectrophotometric monitoring.
Following work-up and chromatographic separation on alu-
mina, triphenylcorrole 4 was obtained in 6% yield (un-
optimized) as red–green crystals. The expected tetraphenylpor-
phyrin 1 was also obtained from this reaction in yields
comparable with those of 4, indicating that under these modified
conditions the ring closure to corrole is competitive with the
formation of the larger porphyrin macrocycle; trace amounts of
NC-TPP were also observed. 5,6 When the reaction was carried
out in propionic acid14 (for 2 h) the yields of corrole were
slightly lower. The choice of reaction conditions is critical for
the formation of useful amounts of 4.
NH HN
Ph
Ph
NH HN
N
N
Ph
NH
N
H
N
Ph
Ph
Ph
4
3
Ph
PPh3
The 1H NMR spectrum of 4 shows broad AB patterns for the
b-pyrrolic protons because of the reduced symmetry of the
corrole ring. Spectrophotometry of 4 provided the optical
spectrum shown in Fig 1. The Soret band appears at 416 nm (e
101 000), without significant shift with respect to that of 1; three
N
N
Co
Ph
Ph
N
N
5
hyde.3 Since the first synthetic approach reported by Rothe-
mund,4 a huge number of studies related to the synthetic aspects
of 1 have been reported in the literature.3 Different reaction
conditions have been utilized and the reaction mechanism has
been minutely discussed, but until recently5–9 the possibility
that other macrocycles might be generated from this reaction
had been ignored. This aspect has now been investigated and
different macrocycles have been isolated and characterized
from the Rothemund reaction; these include the ‘N-confused’-
porphyrin 2 (NC-TPP)5,6 and 5,10,15,20-tetraphenylsapphyrin
3 (TPS)7 from the standard pyrrole/benzaldehyde condensation,
and a meso-hexa(pentafluorophenyl)hexaphyrin, in low yield,
from a related reaction.8 While a study by Lindsey and Geier
established the scope of the formation of NC-TPP and TPS,
Fig. 1 Optical spectra of 4 in CH2Cl2 (solid line), in DMF (dotted line) and
in AcOH (dashed line). Absorbances are normalized to their maxima.
Chem. Commun., 1999, 1307–1308
1307

Notes and references
† After the present paper had been submitted and reviewed, a report of the
synthesis of 5,10,15-tris(pentafluorophenyl)corrole from pyrrole and penta-
fluorobenzaldehyde appeared (ref. 13). These authors showed that using
their conditions with pyrrole and benzaldehyde does not afford 5,10,15-tri-
phenylcorrole (4). We thank a reviewer for informing us of the imminent
publication of this article.
‡ Crystal data for 5: Crystals were grown by slow diffusion of MeOH into
a CH2Cl2 solution of 5 (C55H38N4PCo). The selected crystal (0.28 3 0.52 3
¯
0.54 mm) had a triclinic unit cell, space group P1 and cell dimensions a =
8.5269(8), b = 13.1028(13), c = 18.161(2) Å, a = 94.284(8), b =
92.308(8), g = 97.677(8)°, V = 2002.6(3) Å3 and Z = 2 (FW = 844.8).
Data were collected on a Siemens R3 m/V diffractometer with a sealed tube
Fig. 2 Molecular structure of 5; hydrogen atoms have been omitted for
clarity.
source [l(Mo-Ka) = 0.71073 Å] at 130(2) K in w scan mode to 2qmax
=
broad Q bands are present in the 570–650 nm region. It is
interesting to note that 4 is more acidic than the corresponding
b-octaalkyl analogues15 because DMF is sufficiently basic to
give the corresponding monoanion derivative without addition
of bases, as evidenced by the visible spectrum (Fig. 1) recorded
in DMF. The same spectrum is obtained by addition of a few
drops of base (NaOH 10% in water) to a methanolic solution of
4. The monocation of 4 was formed in AcOH, as is also shown
in Fig. 1. Addition of increasing amounts of H2SO4 to the AcOH
solution of 4 led to further changes in the visible absorption
spectrum; these indicated additional protonation processes
which have not yet been characterized, but which do not involve
disruption of the conjugated pathway (i.e. no removal of the
Soret band). In the case of b-octaalkylcorroles16,17 protonation
at the 5-position in H2SO4 has been proposed on account of the
disappearance of the Soret band in the electronic absorption
spectrum.
55.0°. Of 9795 reflections measured (+h, ±k, ±l) all were independent and
7351 had I > 2s (Tmin = 0.78, Tmax = 0.89, rcalc = 1.40 g cm23, m =
0.515 m21). The structure was solved by direct methods and refined (based
on F2 using all data except for three suppressed reflections) by full-matrix
least-squares methods with 550 parameters (Siemens SHELXTL ver. 5.03).
Hydrogen atom positions were generated by their idealized geometry and
refined using a riding model. An empirical absorption correction was
applied (ref. 19). Final R factors were R1 = 0.041 (observed data) and wR2
= 0.112 (all data). CCDC 182/1277.
1 R. A. Sheldon, in Metalloporphyrins in Catalytic Oxidations, ed. R. A.
Sheldon, Marcel Dekker, New York, 1994, p. 1.
2 B. Morgan and D. Dolphin, Struct. Bonding (Berlin), 1987, 64, 115.
3 J. S. Lindsey, in The Porphyrin Handbook, ed. K. Kadish, K. M. Smith
and R. Guilard, Academic Press, San Diego, 1999, Book 1, ch. 2.
4 P. Rothemund, J. Am. Chem. Soc., 1939, 61, 2912.
5 P. J. Chmielewski, L. Latos-Grazynski, K. Rachlewicz and T. Glowiak,
Angew. Chem., Int. Ed. Engl., 1994, 33, 779.
The insertion of the cobalt(iii) ion into 4 was performed by
reaction of corrole and Co(OAc)2 in refluxing MeOH in the
presence of PPh3 to give the corresponding complex 5 in 88%
yield. The 1H NMR spectrum of 5 is similar to that of 4, but with
more resolved resonances. The axial phosphine ligand shows
three sets of resonances for the ortho, meta and para protons, in
accord with observations in the corresponding b-octaalkyl-
corrole complexes,10,18 indicating that the PPh3 ligand does not
suffer from steric interactions with the meso-phenyl groups.
The electronic spectrum of 5 shows a Soret band at 385 nm (e
51 000) and a Q band centered at 561 nm (e 11 500). Its EI mass
spectrum shows an [M 2 PPh3]+ ion, while use of the FAB
technique allowed observation of the molecular ion without loss
of the axial ligand.
The structure of 5 was determined by X-ray crystallography.‡
Compound 5 was slightly non-planar with a 0.069 Å mean
deviation of the macrocyclic atoms from the corrole mean
plane. The conformation observed resembles the porphyrin-
type dome conformation.20 The central CoIII ion featured M–N
bond lengths of 1.863(2), 1.891(2), 1.886(2) and 1.867(2) Å; the
two shortest of these bonds involved the nitrogens adjacent to
the Ca–Ca linkage. This is typical of metallocorroles and has
been observed in the crystal structures of other corroles.10,21 In
5, the CoIII ion is displaced from the corrole mean plane by
0.389 Å and the Co–P bond length is 2.201(1) Å.
6 H. Furuta, T. Asano and T. Ogawa, J. Am. Chem. Soc., 1994, 116,
767.
7 P. J. Chmielewski, L. Latos-Grazynski and K. Rachlewicz, Chem.
Eur. J., 1995, 1, 68.
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A. M. S. Silva, V. Felix, M. G. B. Drew and J. A. S. Cavaleiro, Chem.
Commun., 1999, 385.
9 G. R. Geier III and J. S. Lindsey, J. Org. Chem., 1999, 64, 1596.
10 R. Paolesse, S. Licoccia, G. Bandoli, A. Dolmella and T. Boschi, Inorg.
Chem., 1994, 33, 1171.
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1427.
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L. J. Korsakoff, J. Org. Chem., 1967, 32, 476.
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Soc., Perkin Trans. 1, 1972, 143.
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Elson, J. Chem. Soc., Perkin Trans. 1, 1973, 2281.
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In conclusion, we have shown that the synthesis of 4, even at
only 6% yield, permits the corrole field to utilize and exploit a
direct analogue of tetraphenylporphyrin; this should provide a
starting point for further development of the comparative
chemistry of this contracted macrocyclic system.
This work was supported by grants from CNR-Italy (MA-
DESS II project no. 97.01380.PF48) and the US National
Science Foundation (CHE-96-23117) and National Institutes of
Health (HL-22252).
20 W. Jentzen, X.-Z. Song and J. A. Shelnutt, J. Phys. Chem. B, 1997, 101,
1684.
21 S. Will, J. Lex, E. Vogel, H. Schmickler, J.-P. Gisselbrecht, C.
Haubtmann, M. Bernard and M. Gros, Angew. Chem., Int. Ed. Engl.,
1997, 36, 357; E. Vogel, S. Will, A. S. Tilling, L. Neumann, J. Lex, E.
Bill, A. X. Trautwein and K. Wieghardt, Angew. Chem., Int. Ed. Engl.,
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Chem. Commun., 1999, 1307–1308