Conjugated macrocycles related to the porphyrins. 21. Synthesis, spectroscopy, electrochemistry, and structural characterization of carbaporphyrins

Article abstract of DOI:10.1021/jo020267b

The "3 + 1" variant of the MacDonald condensation has been shown to be an excellent methodology for synthesizing carbaporphyrins. In particular, 1,3-indenedicarbaldehyde condenses with tripyrranes in the presence of TFA to give, following oxidation with DDQ, a series of benzocarbaporphyrins in excellent yields. Triformylcyclopentadienes also afford carbaporphyrin products, albeit in low yields ranging from 5 to 8%. These hybrid bridged annulene structures have porphyrin-like electronic absorption spectra with strong Soret bands near 420 nm and a series of Q-bands through the visible region. The proton NMR spectrum confirms the presence of a strong diamagnetic ring current, and the meso-protons show up at 10 ppm, while the internal CH is shielded to approximately -7 ppm. Carbaporphyrins undergo reversible protonation with TFA. Initial addition of acid affords a monocation, although mixtures of protonated species are observed in the presence of moderate concentrations of TFA. However, in the presence of 50% TFA a C-protonated dication is generated. The dications relocate the π-delocalization pathway through the benzo moiety of benzocarbaporphyrins, and these therefore represent bridged benzo[18]annulenes, although they nevertheless retain powerful macrocyclic ring currents. Carbaporphyrins with fused acenaphthylene and phenanthrene rings have been prepared, and the former demonstrated significantly larger bathochromic shifts in UV-vis spectroscopy that parallel previous observations for acenaphthoporphyrins. A diphenyl-substituted benzocarbaporphyrin 19b was also characterized by X-ray crystallography, and these data show that the macrocycle is reasonably planar although the indene subunit is tilted out of the mean macrocyclic plane by 15.5°. The structural data indicates that the preferred tautomer in the solid state has the two NH's flanking the pyrrolene unit in agreement with previous spectroscopic and theoretical studies. Cyclic voltammetry for carbaporphyrin 19a was more complex than for true porphyrins, showing five anodic waves and two quasi-reversible reductive couples.

Full text of DOI:10.1021/jo020267b

Con ju ga ted Ma cr ocycles Rela ted to th e P or p h yr in s. 21.† Syn th esis,
Sp ectr oscop y, Electr och em istr y, a n d Str u ctu r a l Ch a r a cter iza tion
of Ca r ba p or p h yr in s
Timothy D. Lash,* Michael J . Hayes, J ohn D. Spence,‡ Melanie A. Muckey,
Gregory M. Ferrence, and Lisa F. Szczepura
Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160
tdlash@ilstu.edu
Received April 15, 2002
The “3 + 1” variant of the MacDonald condensation has been shown to be an excellent methodology
for synthesizing carbaporphyrins. In particular, 1,3-indenedicarbaldehyde condenses with tripyr-
ranes in the presence of TFA to give, following oxidation with DDQ, a series of benzocarbaporphyrins
in excellent yields. Triformylcyclopentadienes also afford carbaporphyrin products, albeit in low
yields ranging from 5 to 8%. These hybrid bridged annulene structures have porphyrin-like electronic
absorption spectra with strong Soret bands near 420 nm and a series of Q-bands through the visible
region. The proton NMR spectrum confirms the presence of a strong diamagnetic ring current,
and the meso-protons show up at 10 ppm, while the internal CH is shielded to approximately -7
ppm. Carbaporphyrins undergo reversible protonation with TFA. Initial addition of acid affords a
monocation, although mixtures of protonated species are observed in the presence of moderate
concentrations of TFA. However, in the presence of 50% TFA a C-protonated dication is generated.
The dications relocate the π-delocalization pathway through the benzo moiety of benzocarbapor-
phyrins, and these therefore represent bridged benzo[18]annulenes, although they nevertheless
retain powerful macrocyclic ring currents. Carbaporphyrins with fused acenaphthylene and
phenanthrene rings have been prepared, and the former demonstrated significantly larger
bathochromic shifts in UV-vis spectroscopy that parallel previous observations for acenaphtho-
porphyrins. A diphenyl-substituted benzocarbaporphyrin 19b was also characterized by X-ray
crystallography, and these data show that the macrocycle is reasonably planar although the indene
subunit is tilted out of the mean macrocyclic plane by 15.5°. The structural data indicates that the
preferred tautomer in the solid state has the two NH’s flanking the pyrrolene unit in agreement
with previous spectroscopic and theoretical studies. Cyclic voltammetry for carbaporphyrin 19a
was more complex than for true porphyrins, showing five anodic waves and two quasi-reversible
reductive couples.
CHART 1. Ca r ba p or p h yr in s
In tr od u ction
The porphyrin macrocycle 1 (Chart 1), which serves
as one of Nature’s most versatile ligand systems, at-
tracted considerable attention throughout the 20th cen-
tury.1 The robust characteristics associated with the
porphyrins are due in part to the fully π-delocalized
nature of these systems and their associated aromatic
character.2 Aromaticity in porphyrins can be inferred
from X-ray crystallography (lack of bond length alterna-
tion),3 calorimetry,4 and NMR spectroscopy.5 In particu-
lar, porphyrins show powerful diatropic ring currents by
proton NMR spectroscopy and this property leads to the
external methine or meso-protons being shifted downfield
to approximately 10 ppm while the internal NHs resonate
upfield near -4 ppm.6 The origin of aromaticity in the
porphyrins is often attributed to the presence of an 18π-
electron delocalization pathway (indicated in bold)7 and
indeed the porphyrins have been termed the [18]annu-
lenes of Nature.8 Another view suggests that the “lone
pair” electrons of the two pyrrole type nitrogens are also
crucial to the aromatic character of porphyrins and that
* To whom correspondence should be addressed.
† Part 20: Graham, S. R.; Ferrence, G. M.; Lash, T. D. Chem.
Commun. 2002, 894.
‡ Present address: Department of Chemistry, Trinity University,
715 Stadium Drive, San Antonio, TX 78212-7200.
10.1021/jo020267b CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/31/2002
4860
J . Org. Chem. 2002, 67, 4860-4874

Conjugated Macrocycles Related to the Porphyrins
the system should be considered a 22π-electron aromatic
system.9 Clearly the nitrogen electrons must have an
important influence on the electronic structure of the
porphyrins, but it is less obvious how significant the [18]-
annulene substructure is in relation to the macrocycle’s
chemical, physical, and spectroscopic properties. Porphy-
rin analogues with one or more chalcogen element (O, S,
Se, or Te) in place of the usual nitrogen atoms have been
known for many years7,10 but these atoms also provide
the equivalent lone pair electrons and so do not allow
the two factors to be disentangled. Recently, the possibil-
ity of replacing one or more of the nitrogen atoms in the
porphyrin macrocycle with carbons has been explored.8
This approach, in principle, may allow the significance
of the 18π-electron core delocalization pathway to be
ascertained. The long-term goal of this work is the
synthesis of the hypothetical hydrocarbon analogue of the
porphyrins 2 which has been named tetracarbaporphyrin
or quatyrin (Chart 1).8 The synthesis of monocarbapor-
phyrins 311 and an example of an opp-dicarbaporphyrin
412 have been previously noted, but the quatyrin system
and other intermediary macrocyclic structures such as
5 and 6 are presently unknown (Chart 1).8 In this paper,
the full details of our synthetic studies on monocarba-
porphyrins11,13 and their spectroscopic and electrochemi-
cal characterization are reported. In addition, the first
structural characterization of a carbaporphyrin by single-
crystal X-ray diffraction is described.
(1) (a) Willstatter, R.; Stoll, A. Untersuchungen uber Chlorophyll;
Springer: Berlin, 1913. (b) Fischer, H.; Orth, H. Die Chemie des
Pyrrols; Akademische Verlag: Leipzig, 1934; Vol. I. (c) Ibid., Vol. II
(i), 1937. (d) Fischer, H.; Stern, H., ibid., Vol. II (ii), 1940. (e) Lemberg,
R.; Legge, J . W. Haematin Compounds and Bile Pigments; Inter-
science: New York, 1949. (f) Vannotti, A. Porphyrins; Hilger & Watts,
1954. (g) Falk, H. Porphyrins and Metalloporphyrins; Elsevier: Am-
sterdam, 1964. (h) The Chlorophylls; Vernon, L. P.; Seely, G. R., ed.;
Academic Press: New York, 1966. (i) Goodwin, T. W. Porphyrins and
Related Compounds; Academic Press: London, 1968. (j) Marks, G. S.
Heme and Chlorophyll; Van Nostrand: London, 1969. (k) J ackson, A.
H.; Smith, K. M. The Total Synthesis of Pyrrole Pigments. In The Total
Synthesis of Natural Products; ApSimon, J ., Ed.; 1973; Wiley: New
York; Vol. 1, pp 143-234. (l) The Chemical and Physical Behavior of
Porphyrin Compounds and Related Structures. In Annals of the New
York Academy of Sciences; Adler, A. D., Ed.; 1973; Vol. 206, pp 1-761.
(m) Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier:
Amsterdam, 1975. (n) The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vols. 1-7. (o) Porphyrin Chemistry Advances;
Longo, F. R., Ed.; Ann Arbor Science: Ann Arbor, MI, 1979. (p)
Lavallee, D. K. The Chemistry and Biochemistry of N-Substituted
Porphyrins; VCH: New York, 1987. (q) Chlorophylls; Scheer, H., Ed.;
CRC Press: Boca Raton, FL. 1991. (r) Milgrom, L. R. The Colours of
Life; Oxford University Press: New York, 1997. (s) Sessler, J . L.;
Weghorn, S. J . Expanded, Contracted & Isomeric Porphyrins; Perga-
mon: Oxford, U.K., 1997. (t) The Porphyrin Handbook; Kadish, K. M.;
Smith, K. M.; Guilard, R., Eds.; Academic Press: San Diego, 2000;
Vols. 1-10.
Resu lts a n d Discu ssion
Monocarbaporphyrins possess an inner core arrange-
ment of three nitrogen atoms and one carbon atom. This
CNNN arrangement is also found in the so-called N-
confused porphyrins 7 (Chart 2), porphyrin isomers that
were originally obtained as byproducts in the Rothemund
reaction.8a,14,15 The incorporation of carbacyclic units into
porphyrin-like ring systems required a more directed
synthetic approach and a “3 + 1” variant on the Mac-
Donald condensation has been found to be a superior
route to systems of this type.16 The “3 + 1” strategy for
porphyrin synthesis involves the condensation of a dial-
dehyde 8 with a tripyrrolic intermediate 9 known as a
tripyrrane (Scheme 1).16 This methodology has been very
effective in the synthesis of porphyrins and has been
adapted as a high yielding rational synthesis of alkyl-
substituted N-confused porphyrins 10.17,18 Porphyrins
(2) Vogel, E. J . Heterocycl. Chem. 1996, 33, 1461.
(3) Senge, M. O. In The Porphyrin Handbook; Kadish, K. M.; Smith,
K. M.; Guilard, R., Eds.; Academic Press: San Diego, 2000; Volume
10.
(4) Stern, A.; Klebs, G. Ann. Chem. 1932, 500, 91; 1933, 504, 287;
1933, 505, 295.
(5) J anson, T. R.; Katz, J . J . In The Porphyrins; Dolphin, D., Ed.;
Academic Press: New York, 1978; Vol. 4, pp 1-59. Scheer, H.; Katz,
J . J . In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.;
Elsevier: Amsterdam, 1975; pp 399-524. Medforth, C. J . In The
Porphyrin Handbook; Kadish, K. M.; Smith, K. M.; Guilard, R., Eds.;
Academic Press: San Diego, 2000; Vol. 5, pp 1-80. Chakraborty, S.;
Clezy, P. S.; Sternhell, S.; van Thuc, L. Aust. J . Chem. 1982, 35, 2315.
Crossley, M. J .; Harding, M. M.; Sternhell, S. J . Am. Chem. Soc. 1992,
114, 3266.
(6) Smith, K. M. in Porphyrins and Metalloporphyrins; Smith, K.
M., Ed.; Elsevier: New York, 1975; pp 3-28.
(7) Vogel, E.; Haas, W.; Knipp, B.; Lex, J .; Schmickler, H. Angew.
Chem., Int. Ed. Engl. 1988, 27, 406.
(8) (a) Lash, T. D. Synlett 2000, 279. (b) Lash, T. D. In The Porphyrin
Handbook; Kadish, K. M.; Smith, K. M.; Guilard, R., Eds.; Academic
Press: San Diego, 2000; Vol. 2, pp 125-199.
(9) Cyranski, M. K.; Krygowski, T. M.; Wisiorowski, M.; Hommes,
N. J . R. van E.; Schleyer, P. von R. Angew. Chem., Int. Ed. 1998, 37,
177.
(10) J ohnson, A. W. in Porphyrins and Metalloporphyrins; Smith,
K. M., Ed.; Elsevier: Amsterdam, 1975; pp 729-754. Latos-Grazynski,
L. In The Porphyrin Handbook; Kadish, K. M.; Smith, K. M.; Guilard,
R., Eds.; Academic Press: San Diego, 2000; Vol. 2, pp 361-416.
Broadhurst, M. J .; Grigg, R.; J ohnson, A. W. J . Chem. Soc. (C) 1971,
3681. Ulman, A.; Manassen, J . J . Am. Chem. Soc. 1975, 97, 6540. Ibid.,
J . Chem. Soc., Perkin Trans. 1 1979, 1066. Lash, T. D.; Motta, Y. G.
Heterocycles 1983, 20, 2343. Haas, W.; Knipp, B.; Sicken, M.; Lex, J .;
Vogel, E. Angew. Chem., Int. Ed. Engl. 1988, 27, 409. Vogel, E.; Rohrig,
P.; Sicken, M.; Knipp, B.; Herrmann, A.; Pohl, M.; Schmickler, H.; Lex,
J . Angew. Chem., Int. Ed. Engl. 1989, 28, 1651. Lash, T. D.; Armiger,
Y. L. S.-T. J . Heterocycl. Chem. 1991, 28, 965. Vogel, E.; Pohl, M.;
Herrmann, A.; Wiss, T.; Ko¨nig, C.; Lex, J .; Gross, M.; Gisselbrecht, J .
P. Angew. Chem., Int. Ed. Engl. 1996, 35, 1520. Chmielewski, P. J .;
Latos-Grazynski, L.; Olmstead, M. M.; Balch, A. L. Chem. Eur. J . 1997,
3, 268. Gross, Z.; Saltsman, I.; Pandian, R. P.; Barzilay, C. M.
Tetrahedron Lett. 1997, 38, 2383.
(11) Preliminary communication: Lash, T. D.; Hayes, M. J . Angew.
Chem., Int. Ed. Engl. 1997, 36, 840.
(12) Lash, T. D.; Romanic, J . L.; Hayes, M. J .; Spence, J . D. Chem.
Commun. 1999, 819.
(13) These results were presented, in part, at the following meetings
and symposia: Symposium on Advances in Natural Products Synthe-
sis, 28th Central Regional Meeting of the American Chemical Society,
Dayton, OH, J une 1996 (Lash, T. D. Program and Abstracts, Abstract
No. 201); 89th Annual Meeting of the Illinois State Academy of Science,
Illinois Wesleyan University, Bloomington, IL, October 1996 (Hayes,
M. J .; Lash, T. D. Transactions of the Illinois State Academy of Science,
1996, Supplement to Volume 89, p 55, Abstract No. 46); 213th National
Meeting of the American Chemical Society, San Francisco, CA, April
1997 (Lash, T. D. Book of Abstracts, ORGN 14 and Hayes, M. J .; Lash,
T. D. Book of Abstracts, ORGN 297); 30th Great Lakes Regional
Meeting of the American Chemical Society, Loyola University, Chicago
IL, May 1997 (Hayes, M. J .; Lash, T. D. Program and Abstracts,
Abstract No. 128; Lash, T. D. Program and Abstracts, Abstract No.
142); 5th Chemical Congress of North America, Cancun, Mexico,
November 1997 (Lash, T. D.; Chaney, S. T.; Hayes, M. J .; Petryka, J .
C.; Richter, D. T. Book of Abstracts, Abstract No. 1154); 221st National
Meeting of the American Chemical Society, San Diego, CA, April 2001
(Muckey, M. A.; Lash, T. D. Book of Abstracts, ORGN 715).
A
popularized account of these studies and related work also appeared:
Freemantle, M. Porphyrin Route Revival: Aromatic Porphyrinoids
Synthesized by ‘3 + 1’ Condensation. Chem. Eng. News 1997, 75 (35),
31-33.
(14) (a) Chmielewski, P. J .; Latos-Grazynski, L.; Rachlewicz, K.;
Glowiak, T. Angew. Chem. Int. Ed. Eng. 1994, 33, 779. (b) Furuta, H.;
Asano, T.; Ogawa, T. J . Am. Chem. Soc. 1994, 116, 767.
(15) Geier, G. R., III; Haynes, D. M.; Lindsey, J . S. Org. Lett. 1999,
1, 1455. Geier, G. R., III; Ciringh, Y.; Li, F.; Haynes, D. M.; Lindsey,
J . S. Org. Lett. 2000, 2, 1745.
(16) Lash, T. D. Chem. Eur. J . 1996, 2, 1197. Lin, Y.; Lash, T. D.
Tetrahedron Lett. 1995, 36, 9441. Lash, T. D. J . Porphyrins Phthalo-
cyanines 1997, 1, 29.
J . Org. Chem, Vol. 67, No. 14, 2002 4861

Lash et al.
CHART 2. Ca r ba p or p h yr in oid s a n d Rela ted
Ma cr ocyclic System s
SCHEME 2
by oxidation with chloranil (Scheme 2).25 In surprising
contrast, Lash and Chaney found that 16 and 17 con-
densed in the presence of TFA in dichloromethane to give,
following oxidation with DDQ, the cross-conjugated por-
phyrinoid macrocycle azuliporphyrin (18) in 28% yield.26
This system was quite stable and showed a degree of
aromatic character due to zwitterionic canonical forms
such as 18a .26 Subsequently, Lash demonstrated that
azuliporphyrin rearranged under basic oxidative condi-
tions with tert-butyl hydroperoxide to give benzocarba-
porphyrins 15 and a mechanism to explain this unusual
rearrangement was proposed.27 In independent work, we
developed a rational synthesis of benzocarbaporphyrins
19 using indene dialdehyde 20 as the key precursor
(Scheme 3).11 Tripyrrane dibenzyl esters 21 are easily
prepared by condensing 2,5-unsubstituted pyrroles 22
with 2 equiv of an acetoxymethylpyrrole 23 in the
presence of an acid catalyst.16,28 Hydrogenolysis of the
benzyl esters over 10% Pd/C affords the corresponding
relatively unstable dicarboxylic acids 24 in quantitative
yields.16,28 Treatment of tripyrranes 24 with TFA, fol-
lowed by dilution with dichloromethane, reaction with
20 under N2 and subsequent neutralization with triethyl-
amine and dehydrogenation with DDQ affords the ben-
zocarbaporphyrins 19 in 43-51% yield. Most of our early
studies were carried out on tetraethylcarbaporphyrin
19a 11,29 and the discussion on the properties of carba-
porphyrins will mostly focus on this compound. However,
unless otherwise noted, the spectroscopic properties of
the other monocarbaporphyrins presented in this paper
were similar to those for 19a .
SCHEME 1
with carbacyclic rings are easily prepared by this ap-
proach: for instance, isophthalaldehyde affords benzi-
porphyrin 11,19,20 5-formylsalicylaldehyde gives oxyben-
ziporphyrin 12,20-22 1,6-diformyl-1,3,5-cycloheptatriene
yields tropiporphyrin 13,23 and bicyclo[3.3.0]octane dial-
dehydes produced carbachlorins 1424 (Chart 2). Complex
mixtures of true carbaporphyrins 15 were first obtained
by the “3 + 1” condensation of 1,3-azulenedicarbaldehyde
(16) with tripyrrane 17 in the presence of HBr, followed
(17) Lash, T. D.; Richter, D. T.; Shiner, C. M. J . Org. Chem. 1999,
64, 7973.
(18) For a “2 + 2” MacDonald synthesis of N-confused porphyrins,
see: Liu, B. Y.; Bru¨ckner, C.; Dolphin, D. Chem. Commun. 1996, 2141.
(19) Berlin, K.; Breitmaier, E. Angew. Chem., Int. Ed. Engl. 1994,
33, 1246.
(20) Lash, T.D.; Chaney, S. T.; Richter, D. T. J . Org. Chem. 1998,
63, 9076.
(25) (a) Berlin, K.; Steinbeck, C.; Breitmaier, E. Synthesis 1996, 336.
(b) Berlin, K. Angew. Chem. Int. Ed. Engl. 1996, 35, 1820.
(26) Lash, T. D.; Chaney, S. T. Angew. Chem., Int. Ed. Engl. 1997,
36, 839. Graham, S. R.; Colby, D. A.; Lash, T. D. Angew. Chem., Int.
Ed. 2002, 41, 1371.
(21) Lash, T. D. Angew. Chem., Int. Ed. Engl. 1995, 34, 2533. See
also: Lash, T. D.; Chaney, S. T. Chem. Eur. J . 1996, 2, 944
(22) Richter, D. T.; Lash, T. D. Tetrahedron 2001, 57, 3659.
(23) Lash, T. D.; Chaney, S. T. Tetrahedron Lett. 1996, 37, 8825.
(24) Hayes, M. J .; Lash, T. D. Chem. Eur. J . 1998, 4, 508.
(27) Lash, T. D. Chem. Commun. 1998, 1683.
(28) Sessler, J . L.; J ohnson, M. R.; Lynch, V. J . Org. Chem. 1987,
52, 4394.
(29) Hayes, M. J .; Spence, J . D.; Lash, T. D. Chem. Commun. 1998,
2409.
4862 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
SCHEME 3
Cl2), benzocarbaporphyrin 19a gave rise to another
green colored species that showed multiple peaks in the
Soret band region. This was attributed to the monocation
27 (Scheme 4).
Proton NMR spectroscopy provided strong support for
the porphyrin-like nature of carbaporphyrins 19. The
powerful diatropic ring current in 19a is evident in the
proton NMR spectrum (Figure 3) as the bridging methine
or meso-protons were shifted downfield to 9.8 and 10.1
ppm, while the internal CH shifted upfield to near -7
ppm (this value varied slightly with concentration). The
NHs were also strongly shielded and gave a broad
resonance near -4 ppm. As is the case for porphyrins,
the alkyl substituents were also strongly effected by the
aromatic ring current with the methyl groups showing
up at 3.6 ppm while the ethyl methylenes resonated near
4 ppm. The protons on the benzo moiety adjacent to the
porphyrinoid macrocycle were also strongly influenced
and resonated near 8.8 ppm. In independent work by
Breitmaier and co-workers, low yields of carbaporphyrins
were obtained using related chemistry.25 In these samples,
the presence of tautomers (e.g., 28, Scheme 5) that did
not interconvert on the NMR time scale were postulated
on the basis of additional peaks that were present in the
proton NMR spectra.25 We deacidify the CDCl3 for our
studies by running the solvent through a small amount
of basic alumina. If the solvent is not pretreated, ad-
ditional peaks may show up due to the presence of
protonated species. However, using deacidified CDCl3 we
have never seen any of the extra peaks that were noted
by this group. While it is possible that the extra peaks
observed by Breitmaier and co-workers25 may have arisen
due to spurious protonation, we have suggested previ-
ously that they are most likely due to isomeric impuri-
ties.11,20 Under certain acid-catalyzed conditions, the
tripyrrane intermediates may undergo acidolysis and
subsequent recombination of the resulting fragments can
lead to isomeric tripyrroles which in turn would give rise
to mixtures of macrocyclic products. A more detailed
discussion on this issue has been published elsewhere,20
and in the absence of evidence to the contrary it is
assumed that this is the correct interpretation of the
available data.
Porphyrins have characteristic UV-vis absorption
spectra that show a strong Soret band near 400 nm
followed by a series of four Q-bands through the visible
region. If carbaporphyrins retain porphyrin-like proper-
ties, one would expect that they would also have the same
type of electronic absorption spectra. This is evidently
the case, as 19a shows a Soret band at 424 nm (log ꢀ )
5.25) and four Q-bands at 510, 544, 602, and 662 nm
(Figure 1A). These bands have undergone small batho-
chromic shifts compared to the related benzoporphyrin
25 (Chart 3) which shows the Soret absorption at 404
nm (log ꢀ ) 5.46) and Q-bands at 504, 542, 574, and 628
nm (Figure 2A).30 The Soret band of 19a is less intense,
and a secondary band is also evident at 376 nm. Diphen-
ylcarbaporphyrin 19b gave slightly red-shifted absorp-
tions compared to 19a , and the Soret band was somewhat
intensified. On the other hand, butanocarbaporphyrin
19c gave a virtually identical spectrum to 19a .
Addition of TFA to solutions of 19a leads to protona-
tion, but mixtures of species appear to be present and
the results are of little diagnostic value at moderate
concentrations of TFA. However, in 50% TFA-CHCl3 a
deep green colored diprotonated species 26 was gener-
ated, and this showed a moderate band at 348 nm, a
Soret absorption at 426 nm (log ꢀ ) 5.27) and weaker
absorptions at 614 and 662 nm (Figure 1B). Not sur-
prisingly, the UV-vis spectrum for the diprotonated form
of benzoporphyrin 25 in 5% TFA-CHCl3 is quite differ-
ent, showing a far stronger Soret band at 414 nm, and
weaker absorptions at 562 and 612 nm (Figure 2B). At
very low concentrations of TFA (0.005-0.1% TFA-CH2-
Although two similar tautomers can be considered for
19a (Scheme 5), theoretical studies suggest that tautomer
19a with two NHs flanking the imine nitrogen is favored
over 28a by 6 kcal/mol.33 This is primarily due to the
presence of more favorable hydrogen bonding interactions
as the three inner hydrogens have similar steric interac-
tions in both forms. Our NMR data is consistent with
the presence of either a single tautomer 19a with a plane
of symmetry, or with the presence of mixed tautomers
that rapidly interconvert on the NMR time scale. In
variable temperature studies, little change was observed
between the room-temperature spectrum and the spectra
at -50 or -75 °C apart from a sharpening up of the NH
resonance (Figure 3). The CH proton does shift slightly
(31) Lash, T. D. Energy Fuels 1993, 7, 166.
(32) (a) Clezy, P. S.; Fookes, C. J . R.; Mirza, A. H. Aust. J . Chem.
1977, 30, 1337. (b) Clezy, P. S.; Mirza, A. H. Aust. J . Chem. 1982, 35,
197. (c) Clezy, P. S.; Leung, C. W. F. Aust. J . Chem. 1993, 46, 1705.
(33) Ghosh, A.; Wondimagegn, T.; Nilsen, H. J . J . Phys. Chem. B
1998, 102, 10459. See also: Nilsen, H. J .; Ghosh, A. Acta Chem. Scand.
1998, 52, 827. Ghosh, A. Angew. Chem. Int. Ed. Engl. 1995, 34, 1028.
Ghosh, A. Acc. Chem. Res. 1998, 31, 189.
(30) Hayes, M. J . M. S. Thesis, Illinois State University, 1997.
J . Org. Chem, Vol. 67, No. 14, 2002 4863

Lash et al.
F IGURE 1. UV-vis spectra of benzocarbaporphyrin 19a . A. Free base in 1% triethylamine-chloroform. B. Dication 26 in 50%
TFA-chloroform.
tautomer with an external NH in DMF solution.34
Density functional theory indicates that these two forms
only differ in stability by 5.7 kcal/mol.33,35 We took the
opportunity to examine the previously synthesized hep-
taalkyl N-confused porphyrin 10a .17 Interestingly, the
proton NMR spectrum for 10a in d7-DMF at 21 °C
showed the presence of two tautomeric forms in an
approximately 1:1 ratio (Figure 4A). The aromatic form
10a was evident from the four downfield singlets between
9.8 and 10.2 ppm corresponding to the meso-protons and
the upfield resonances at -6.29, -3.61, and -3.71 ppm
due to the internal CH and two nonequivalent NH
protons. The cross-conjugated tautomer 29 (Chart 4) gave
three singlets for the meso-protons at 8.53, 8.80, and 9.12
ppm in the ratio of 2:1:1 and a broad singlet at 13.57 ppm
for the external NH. The inner CH resonated at -0.07
ppm, a value that is comparable to the resonance
observed by Furuta for the corresponding CH in 7 at
+0.76 ppm.34 Tautomer 29 is clearly stabilized by dipolar
contributors such as 30 that provide a degree of aromatic
character to the system.36 The balance is further influ-
enced by favorable hydrogen bonding between the DMF
and the external NH of 29. It is noteworthy that the rate
of interconversion between 10 and 29 must be relatively
slow. In addition, the two inner NHs of the aromatic form
CHART 3
upfield, but this is also observed at higher concentrations
and is most likely due to aggregation effects. While these
data do not distinguish between a preference for a single
tautomer vs rapid exchange, it nonetheless limits the
possibilities. Carbon-13 NMR spectroscopy also confirms
that 19a has a plane of symmetry with 5 sp3 carbon
resonances between 11.7 and 20.3 ppm, two meso-carbons
appearing at 95.1 and 100.2 ppm (these values are
similar to those observed for true porphyrins), and the
11 other types of sp2 carbons expected based on symmetry
considerations produced 10 resonances between 109 and
146 ppm. The internal CH is present at 109.7 ppm. Again
no evidence for the presence of tautomers was found in
any of the carbon-13 spectra that were run on these
compounds. The structures of carbaporphyrins 19 were
further confirmed by mass spectrometry.
(34) Furuta, H.; Ishizuka, T.; Osuka, A.; Dejima, H.; Nakagawa, H.;
Ishikawa, I. J . Am. Chem. Soc. 2001, 123, 6207.
(35) Ghosh, A. In The Porphyrin Handbook; Kadish, K. M.; Smith,
K. M.; Guilard, R., Eds.; Academic Press: San Diego, 2000; Vol. 7, pp
1-38.
Recently, Furuta has demonstrated that meso-tet-
raphenyl N-confused porphyrin exists as the aromatic
tautomer 7 in CDCl3, but prefers a cross-conjugated
(36) In this respect, the system resembles azuliporphyrin 18.26
4864 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
F IGUR E 2. UV-vis spectra of benzoporphyrin 25. A. Free base in 1% triethylamine-chloroform. B. Dication in 5% TFA-
chloroform.
SCHEME 4
slight downfield shift for the meso- and benzo-protons
(Figure 4B).
Addition of trace amounts of TFA to NMR solutions of
19a in CDCl3 afforded the monocation 27 where the first
protonation has occurred as expected at the pyrrolene
nitrogen (Scheme 4). The proton NMR spectrum for 27
showed the inner CH at -6.75 ppm, while the NHs gave
two broadened singlets at -4.61 (1H) and -3.22 ppm
(2H). The plane of symmetry for the macrocycle in the
monocation was retained as judged by the simplicity of
the proton NMR spectrum, and the meso-protons gave
rise to two 2H singlets at 10.06 and 10.33 ppm. Addition
of further amounts of TFA produced complex proton NMR
spectra showing the presence of mixtures of different
species. However, in 50% TFA-CDCl3 a single species
was observed that could be assigned as the C-protonated
dication 26 (Scheme 4). The proton NMR spectrum shows
that 26, like 27, retains a strong diamagnetic ring current
(Figure 5). The meso-protons resonated at 10.45 and
11.05 ppm while the internal CH2 was shifted upfield to
-5.14 ppm, and the NH protons were observed at -1.4
ppm. The benzo-protons adjacent to the macrocyclic ring
were shifted downfield to 10.13 ppm compared to 8.83
ppm in the free base and 8.69 for the monocation, while
the remaining benzo-protons resonated at 8.94 ppm
compared to 7.74 for 19a and 7.72 ppm for 27. These
shifts cannot be simply due to the dicationic nature of
this species and are instead consistent with the 18π-
electron delocalization pathway having been relocated
10 are well resolved at 21 °C, indicating that only one
aromatic tautomer is favored and that the NH exchange
rate within the macrocyclic cavity is also slow on the
NMR time scale. At 50 °C, the spectrum was little
effected, and no indication of coalescence for any of these
processes was observed. The proton NMR spectrum of
benzocarbaporphyrin 19a in d7-DMF, on the other hand,
gave much the same results as in CDCl3, although the
NH resonance was relatively sharp and there is a
J . Org. Chem, Vol. 67, No. 14, 2002 4865

Lash et al.
F IGURE 3. 400 MHz proton NMR spectrum of benzocarbaporphyrin 19a in deuteriochloroform at 25 °C. A. Upfield region at
-25 °C; B. -50 °C; C. -75 °C. At low temperatures some peak broadening occurs due to precipitation of the sample.
SCHEME 5
C-protonation in the presence of trace amounts of TFA
to give the fully aromatic benzo[18]annulene monocation
33 (Chart 5).12 In this case, C-protonation occurs more
easily as this results in only one delocalized positive
charge.12,38 At room temperature the NH protons pro-
duced a broad peak that only integrated for 2H, but at
-10 °C the 2H resonance sharpened up and an additional
broad signal for 1H can be discerned. These data indi-
cates that one proton for the internal NH’s undergoes
intermolecular exchange while the other two are held
more firmly. A similar phenomenon was also observed
for the dication of N-confused porphyrin 10a .17 Addition
of 50% d-TFA to NMR solutions of 19a in CDCl3 resulted
in a slow deuterium exchange of the meso-protons (ap-
proximately 20-30% loss of signal intensity after 16 h
at room temperature). Similar exchange rates at the
meso-positions were noted in the presence of trace d-TFA,
and these data suggest that the monocation 27 is in
equilibrium with C-protonated species such as 34 and
35 (Scheme 4). It is possible that similar diprotonated
species are also present in these equilibria. However,
under both sets of conditions, exchange at the C-10 and
C-15 positions occurred approximately 50% faster than
at the C-5 and C-20 positions. As would be expected,
rapid exchange of the NH and inner CH protons is also
through the benzene ring (see bold pathway for structure
26). The dication is, therefore, an example of a bridged
benzo[18]annulene. Benzo[18]annulene 31 (Chart 5) has
a weakly diatropic nature, and the difference in chemical
shifts (∆δ) between the inner and outer macrocyclic ring
protons is only 3.3 ppm.37 In complete contrast, the ∆δ
for the internal vs external CH resonances of 26 are on
the order of 16 ppm! Therefore, the characteristics of 26
are quite different from the parent system, and this can
be attributed to the enhanced charged delocalization that
is only possible in the fully delocalized aromatic struc-
ture. Dicarbaporphyrin 32 has been shown to undergo
(37) Meissner, U. E.; Gensler, A.; Staab, H. A. Tetrahedron Lett.
1977, 18, 3.
(38) C-protonation is also observed for carbasapphyrins: Lash, T.
D.; Richter, D. T. J . Am. Chem. Soc. 1998, 120, 9965.
4866 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
F IGURE 4. (A) Upfield and downfield regions of the 400 MHz proton NMR spectrum for N-confused porphyrin 10a in d7-DMF.
The presence of two tautomers, 10a and 29, are evident. The sample shows signs of significant degradation on standing in this
solvent. (B) Upfield and downfield regions of the 400 MHz proton NMR spectrum for benzocarbaporphyrin 19a in d7-DMF.
observed in these experiments. The carbon-13 NMR
spectrum of 26 in 50% TFA-CDCl3 shows the presence
of a plane of symmetry with five sp3 carbon resonances
between 11 and 21 ppm, the internal CH2 at 32.9 ppm,
and two meso-carbons near 108 ppm; nine additional sp2
signals were observed for the 10 remaining carbons
between 125 and 152 ppm.
ically, the introduction of fused benzene (e.g., 25)31,32 or
phenanthrene rings (e.g., 36, Chart 6)40 onto the porphy-
rin chromophore resulted in only small bathochromic
(39) Lash, T. D. J . Porphyrins Phthalocyanines 2001, 5, 267.
(40) Lash, T. D.; Novak, B. H. Ang. Chem. Int. Ed. Engl. 1995, 34,
683. Novak, B. H.; Lash, T. D. J . Org. Chem. 1998, 63, 3998.
(41) Lash, T. D.; Chandrasekar, P.; Osuma, A. T.; Chaney, S. T.;
Spence, J . D. J . Org. Chem. 1998, 63, 8455.
(42) Lash, T. D.; Chandrasekar, P. J . Am. Chem. Soc. 1996, 118,
8767. Spence, J . D.; Lash, T. D. J . Org. Chem. 2000, 65, 1530-1539.
In other work, we have examined the effects of fusing
aromatic rings onto the porphyrin nucleus.31,39-43 Specif-
J . Org. Chem, Vol. 67, No. 14, 2002 4867

Lash et al.
CHART 4
porphyrin-type electronic spectrum (Figure 6). At low
concentrations of TFA (0.01%), a new species is observed
that shows a series of moderate absorptions through the
Soret band region; this species was assigned as the
monocation 46. In 40% TFA-chloroform, the correspond-
ing dication 47 was generated. This shows a split Soret
band at 410 and 426 nm and three smaller absorptions
at 548, 600, and 664 nm. The yields for porphyrinoids
44 were low, generally 5-8%, most likely due to the
unwanted reactivity of the third formyl moiety. Attempts
to improve these yields were not successful. We have
found that in some reactions substituting a wash with
dilute aqueous ferric chloride solution for the oxidation
step with DDQ can give much improved yields,17,45 but
this procedure gave essentially the same results in the
present case.
shifts in UV-vis spectroscopy, but acenaphthylene-fused
porphyrins (e.g., 37, Chart 6) gave rise to greatly altered
UV-vis spectra that showed much larger shifts toward
longer wavelengths.41,42 It was therefore of some interest
to see whether these trends also held for the carbapor-
phyrin series. Dibenzocarbaporphyrin 38 was easily
prepared by dehydrogenating the butano derivative 19c
with 2 equiv of DDQ in refluxing toluene (Scheme 3).31
The addition of a second fused benzene ring causes the
Soret band for 38 to shift to 432 nm from 424 nm for
19a . This contrasts to dibenzoporphyrin 3930,44 which
shows a Soret band at 410 nm compared to a value of
404 nm in the case of monobenzoporphyrin 25 (Chart 3).
Reaction of the known acenaphthotripyrranes 4041 with
diformylindene 20 under standard “3 + 1” conditions gave
the corresponding acenaphthocarbaporphyrins 41 in 18-
29% yield, while phenanthrotripyrrane 42 gave the
corresponding phenanthrocarbaporphyrin 43 in 28% yield
(Scheme 6). The spectroscopic properties of 38, 41, and
43 are fully consistent with the assigned structures.
Dibenzocarbaporphyrin 38 shows a Soret band at 432
nm, while the value for 43 is 442 nm and for acenaph-
thocarbaporphyrin 41a the absorption appears at 456
nm. The longest wavelength Q-band absorptions for 19a ,
38, 43, and 41a are 662, 672, 677, and 688 nm (this band
is very weak for 41a ), respectively, again showing the
largest effects for the acenaphthylene-fused porphy-
rinoids. The trend is more gradual in the carbaporphyrin
series than has been observed for true porphyrins,39
although it is comparable to the results for oxybenzi- and
oxypyriporphyrins.20 The same trends are observed for
the corresponding dications in 50% TFA-chloroform and
the Soret band for 41a under these conditions shifts to
474 nm.
Triformylcyclopentadienes 44 have also been reported
to react with tripyrrane 24a to give low yields of carba-
porphyrins (Scheme 7).25b In the initial publication, these
porphyrinoids also showed additional peaks that were
attributed to tautomers. We have synthesized formyl-
carbaporphyrins 45a and 45b under our reaction condi-
tions and find no sign of the extra resonances in any of
the NMR spectra. In addition, the UV-vis absorptions
for our samples gave molar extinction coefficients for the
major absorptions that were nearly 3 times larger than
those in the earlier report. The UV-vis spectrum of 45a
is substantially different from benzocarbaporphyrin 19a ,
showing a weaker broadened Soret band at 436 nm, but
this nonetheless retains the essential features of a
The proton NMR spectra for 45a and 45b in CDCl3
demonstrated the same large diatropic ring currents that
were observed for 19, with the internal CH showing up
near -7 ppm (again some variation was noted with
changes in concentration). Three of the meso-protons
were observed as singlets between 9.4 and 9.7 ppm, but
CH-20 was further deshielded by the proximate formyl
moiety and resonated near 10.7 ppm. The proton NMR
spectrum of 45a in d7-DMF showed some small downfield
shifts for the external protons, but otherwise was similar
to the spectrum obtained in CDCl3. However, the external
cyclopentadiene proton CH-3 did show coupling to the
internal CH under these conditions and gave a doublet
4
with a coupling constant J ) 1.2 Hz. Addition of trace
amounts of TFA to NMR solutions of 45a in CDCl3
afforded the corresponding monocation 46a (Scheme 7).
This retained the macrocyclic ring current with the
interior CH at -5.83 ppm, while the NH’s gave rise to
three separate resonances at -3.4, -2.3, and -2.2 ppm.
Three of the meso-protons gave singlets between 9.7 and
10.1 ppm, while the fourth meso-proton, CH-20, was
again further deshielded and resonated at 10.54 ppm.
The external cyclopentadiene proton, CH-3, showed up
slightly downfield compared to the free base 45a at 8.94
ppm. In 50% TFA-CDCl3, the dication 47a (Scheme 7)
was generated and this showed significant differences
from the diprotonated forms in the benzocarbaporphyrin
series. The internal CH2 of 47a gave a resonance at -7.4
ppm, compared to a value of -5.15 for 26a , and this
result suggests that the macrocyclic ring current is
significantly larger for this species. The outer cyclopen-
tadiene proton, CH-3, is also deshielded to 11 ppm, while
the meso-protons show substantial downfield shifts.
These data indicate that the fused benzo unit interferes
with the macrocyclic ring current in the doubly proto-
nated species giving a greater than 2 ppm upfield shift
to the internal methylene group compared to 47, although
macrocyclic aromaticity still dominates the spectroscopic
properties for 26 (Scheme 4). Trimethylcarbaporphyrin
45b shows similar trends to 45a upon protonation. Of
particular note, the cyclopentadiene methyl group of 45b
is observed near 3.5 ppm in the proton NMR spectra for
the free base and monocation, but this resonance is
deshielded to 4.5 ppm in the dication 47b. Again, the
interior methylene of 47b is strongly deshielded and
resonates at -7.3 ppm. Addition of d-TFA to 45a gave
(43) Lash, T. D.; Denny, C. P. Tetrahedron 1995, 51, 59. Lash, T.
D.; Gandhi, V. J . Org. Chem. 2000, 65, 8020-8026. Lash, T. D.;
Werner, T. M.; Thompson, M. L.; Manley, J . M. J . Org. Chem. 2001,
66, 3152.
(44) See also: Nguyen, L. T.; Senge, M. O.; Smith, K. M. J . Org.
Chem. 1996, 61, 998.
(45) Richter, D. T.; Lash, T. D. Tetrahedron Lett. 1999, 40, 6735.
4868 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
F IGURE 5. 400 MHz proton NMR spectrum of benzocarbaporphyrin 19a in 50% TFA-CDCl3 at 21 °C. The data shows that
C-protonation has occurred to give the dication 26.
CHART 5
CHART 6
ever, the diphenyl-substituted carbaporphyrin 19b gave
crystals that were suitable for analysis by X-ray diffrac-
tion, and the first carbaporphyrin solid state structure
is reported below. The molecular structure (Figure 7)
shows that the porphyrinoid is reasonably planar as
evidenced by the minimal pyrrole to mean macrocycle
plane tilts of 2.5°, 4.4°, and 4.9°. The indene subunit,
however, is significantly tilted 15.5° out of the mean
macrocyclic plane. This presumably relieves steric crowd-
ing in the central cavity due to the presence of three
hydrogen atoms. All C-N bond distances are equivalent
with an average length equal to 1.371(4) Å. The C(6)-
N(22)-C(9) and C(16)-N(24)-C(19) bond angles, 111.2-
(3)° and 110.9(3)°, respectively, are similarly equivalent;
however, the 105.3(3)° C(11)-N(23)-C(14) bond angle is
significantly compressed, and this may be attributed to
the presence of the nonbonding pair of electrons on N(23).
Thus, the three hydrogen atoms, H21, H22, and H24,
located in the carbaporphyrin cavity, are attached to the
rapid exchange for the NH and internal CH protons. Slow
exchange was also observed for the meso-protons at
positions 10 and 15. In 50% d-TFA-CDCl3, after 3 days
at room temperature, the resonances for these positions
showed a 57-70% loss in intensity, although none of the
remaining resonances showed any measurable exchange
under these conditions. These results suggest that non-
aromatic C-protonated species such as 48 or 49 (or
perhaps the related dications) are present in solution in
equilibrium with monocation 46 (Scheme 7).
Up to this point, the carbaporphyrin system had not
been examined by X-ray crystallographic analysis. How-
J . Org. Chem, Vol. 67, No. 14, 2002 4869

Lash et al.
SCHEME 6
remained associated with their respective parents, lend-
ing further support for the structural assignment. Both
solution NMR data and solid-state diffraction data are
consistent with tautomer 19b, which has two NHs
flanking the pyrrolene nitrogen, rather than tautomers
such as 27b (Chart 4). This result is in agreement with
theoretical studies by Ghosh and co-workers that indicate
that tautomers such as 19b are favored over the alterna-
tive forms by approximately 6 kcal/mol.33 As would be
expected, the phenyl groups are tilted 58° out of the
carbaporphyrin plane and therefore do not significantly
contribute their π systems to the macrocycle.
Electrochemical studies were also performed on car-
baporphyrin 19a . The cyclic voltammogram 19a is shown
in Figure 8. Starting at -0.2 V and scanning in a
negative direction, two cathodic waves were observed
corresponding to quasi-reversible couples at E1/2 ) -1.69
V and -2.04 V. Scanning positively, five anodic waves
were observed, corresponding to irreversible peaks at Ep,a
) 0.48 and 0.68 V, quasi-reversible couples at E1/2 ) 0.77
V and E1/2 ) 1.17 V, as well as a reversible couple at E1/2
) 1.49 V. These data indicate more complex redox
behavior than has been observed for the well studied
tetraphenylporphyrin or H2OEP.46,47 For example, por-
phyrins such as H2OEP display four reversible couples,
two oxidative and two reductive couples,46,47 whereas 19a
displays at least five oxidative and two reductive couples.
Due to the complexity of these data, we decided to focus
on the reductive processes.
SCHEME 7
As mentioned above, the free base carbaporphyrin
displays two quasi-reversible reductive couples in the
cyclic voltammogram at E1/2 ) -1.69 V and -2.04 V
(∆E1/2 ) 0.35 V). Reductively 19a looks most similar to
porphyrins and metalloporphyrins which display two
reversible reductive couples with ∆E1/2 ) 0.42 ( 0.05
V.46,47 The cyclic voltammogram of N-confused porphyrin
contains only one irreversible reductive wave in the
region scanned.48 Notably, the difference between the
first oxidative couple and the first reductive couple of the
free base carbaporphyrin, typically referred to as the
HOMO-LUMO gap, falls within the range of free base
porphyrins. Compound 19a has a HOMO-LUMO gap of
2.17 V, whereas an average HOMO-LUMO gap of 2.25
( 0.15 V for porphyrin and metalloporphyrin complexes
has been reported.46,47
Con clu sion s
The synthesis of nine examples of monocarbaporphy-
rins by the “3 + 1” version of the MacDonald condensa-
tion has been completed. These porphyrin analogues
retain porphyrin-like electronic spectra and show strong
diamagnetic ring currents by proton NMR spectroscopy.
Ring fusion of benzo, phenanthro, and acenaphtho units
produce increasing bathochromic shifts in that order for
UV-vis absorption spectra in parallel with previous
results for tetrapyrrolic porphyrins. In addition to spec-
troscopic characterization, carbaporphyrins have been
parent atoms C(21), and N(22) and N(24), the pyrrole
nitrogens cis to C(21). Located by a difference Fourier
immediately following anisotropic refinement of all non-
hydrogen atoms, H21, H22, and H24 were allowed to
freely refine through the remainder of the structure
refinement procedure. The three core hydrogen atoms
(46) Kadish, K. M.; Van Caemelbecke, E.; Royal, G. In The Porphyrin
Handbook; Kadish, K. M.; Smith, K. M.; Guilard, R., Eds.; Academic
Press: San Diego, 2000; Vol. 8, pp 1-114.
(47) Davis, D. G. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. 5.
(48) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem.
1999, 38, 2676.
4870 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
F IGURE 6. UV-vis spectra of formylcarbaporphyrin 45a . A. Free base in 1% triethylamine-chloroform. B. Dication 47 in 50%
TFA-chloroform.
8,12,13,17-Tet r a et h yl-7,18-d im et h ylb en zo[b]-21-ca r -
ba p or p h yr in (19a ). Tripyrrane dicarboxylic acid 20a (100
mg) was stirred with TFA (1 mL) under an atmosphere of
nitrogen for 10 min. Dichloromethane (19 mL) was added,
followed immediately by 1,3-diformylindene (38 mg), and the
mixture was stirred under nitrogen for a further 2 h. The
mixture was neutralized by the dropwise addition of triethy-
lamine, DDQ (50 mg) was added, and the resulting solution
was stirred for an additional 1 h. The mixture was washed
with water and chromatographed on neutral Grade 3 alumina
eluting with dichloromethane, and a dark brown fraction was
collected. Further chromatography on a silica column, eluting
with dichloromethane, gave the product as a broad brown
band. Recrystallization from chloroform-methanol afforded
the carbaporphyrin 19a (47 mg; 43%) as fluffy copper-bronze
colored crystals, mp >270 °C; UV-vis (1% Et3N-CHCl3): λmax
(log ꢀ) 376 (4.63), 424 (5.25), 510 (4.27), 544 (4.21), 602 (3.79),
662 nm (3.25); UV-vis (CH2Cl2): λmax (log ꢀ) 375 (4.66), 423
(5.23), 510 (4.21), 544 (4.21), 604 (3.77), 662 nm (3.28); UV-
vis (0.01% TFA-CH2Cl2; monocation 27a ): λmax (log ꢀ) 307
(4.54), 399 (4.80), 437 (5.03), 473 (4.56), 550 (4.09), 586 (3.935),
611 nm (3.96); UV-Vis (50% TFA-CHCl3; dication 26a ): λmax
(log ꢀ) 348 (4.54), 426 (5.27), 462 (sh) (4.47), 614 (3.91), 662
characterized electrochemically and by X-ray crystal-
lography for the first time. Further, protonation studies
demonstrate that monoprotonation occurs at low concen-
trations of TFA, but complex mixtures of different species
are generated above 0.1% TFA-CH2Cl2. At much higher
acid concentrations (50% TFA-chloroform) C-protonated
dications are favored. This study provides the foundations
for detailed investigations into the synthesis and chem-
istry of carbaporphyrin systems.
Exp er im en ta l Section
Triformylcyclopentadienes 44 were synthesized according
to the procedure of Hafner et al.;49 tripyrranes 24a , 24c, 40,
and 42 were prepared as described previously.16,41 EI and FAB
mass spectral determinations were made at the Mass Spectral
Laboratory, School of Chemical Sciences, University of Illinois
at Urbana-Champaign, supported in part by a grant from the
National Institute of General Medical Sciences (GM 27029).
Elemental analyses were obtained from the School of Chemical
Sciences Microanalysis Laboratory at the University of Illinois.
1,3-Difor m ylin d en e (20). Prepared by the procedure of
Arnold.50 Recrystallization from acetonitrile-water gave the
dialdehyde as brown crystals, mp 198-200 °C (lit. mp 198-
200 °C); 1H NMR (d6-DMSO): δ 7.22 (2H, m), 7.76 (1H, s),
7.96 (2H, m), 9.08 (2H, br s); EI MS (70 eV): m/z (rel int.) 172
(M+; 64%), 171 (14%), 144 (39%), 115 (100%); HRMS: Calcd
for C11H8O2: 172.0524. Found: 172.0524.
1
nm (4.42); H NMR (500 MHz, CDCl3): δ -6.74 (1H, s), -4.0
(2H, v br), 1.85 (6H, t), 1.87 (6H, t), 3.68 (6H, s), 3.97 (4H, q),
4.07 (4H, q), 7.74 (2H, m), 8.83 (2H, m), 9.82 (2H, s), 10.10
(2H, s); 1H NMR (400 MHz, d7-DMF): δ -6.78 (1H, s), -3.92
(2H, br s), 1.83-1.88 (12H, 2 overlapping triplets), 3.73 (6H,
s), 4.04 (4H, q, J ) 7.5 Hz), 4.17 (4H, q, J ) 7.5 Hz), 7.77-
7.80 (2H, m), 9.14-9.17 (2H, m), 10.04 (2H, s), 10.51 (2H, s);
1H NMR (400 MHz, trace TFA-CDCl3, monocation 27a : δ
-6.75 (1H, s), -4.61 (1H, s), -3.22 (2H, s), 1.69 (6H, t, J )
7.6 Hz), 1.85 (6H, t, J ) 7.6 Hz), 3.57 (6H, s), 4.03-4.14 (8H,
(49) Hafner, K.; Vo¨pel, K. H.; Ploss, G.; Ko¨nig, C. Liebigs Ann. Chem.
1963, 661, 52.
(50) Arnold, Z. Coll. Czech. Chem. Commun. 1965, 30, 2783.
J . Org. Chem, Vol. 67, No. 14, 2002 4871

Lash et al.
M+), 498 (3.4), 497 (3.7) 496 (9.1), 484 (6.4), 469 (3.4), 454 (3.5),
249.8 (17; M2+); HRMS (EI): calcd for C35H37N3: m/z 499.29795;
found: 499.29875. Anal. Calcd for C35H37N3‚H2O: calcd C,
83.38; H, 7.49; N, 8.33. Found: C, 83.31; H, 7.29; N, 8.19.
8,12,13,17-Tet r a et h yl-2-for m yl-7,18-d im et h yl-21-ca r -
ba p or p h yr in (45a ). Formylcarbaporphyrin 45a was prepared
by the procedure outlined above from tripyrrane 24a (100 mg)
and triformylcyclopentadiene 44a (33 mg). Recrystallization
from chloroform-methanol yielded the title porphyrinoid (7
mg; 7.7%) as purple crystals, mp >240 °C. UV-vis (1% Et3N-
CH2Cl2): λmax (log ꢀ) 364 (4.67), 436 (4.99), 524 (4.09), 566
(4.18), 640 (3.42), 710 nm (3.50); UV-vis (CH2Cl2): λmax (log
ꢀ) 362 (4.71), 434 (4.99), 524 (4.085), 564 (4.16), 643 (3.37),
707 nm (3.44); UV-vis (0.01% TFA-CH2Cl2; monocation 46a ):
λmax (log ꢀ) 316 (4.53), 394 (4.775), 424 (4.84), 434 (4.84), 445
(4.86), 491 (4.15), 550 (4.01), 591 (3.72), 713 nm (3.20); UV-
vis (50% TFA-CHCl3; dication 47a ): λmax (log ꢀ) 410 (5.16),
426 (5.02), 548 (3.79), 600 (4.07), 664 nm (3.50); 1H NMR (500
MHz, CDCl3): δ -6.80 (1H, s), -3.80 (2H, v br), 1.79 (12H,
m), 3.43 (3H, s), 3.53 (3H, s), 3.81 (4H, q), 3.92 (4H, 2
overlapping quartets), 8.60 (1H, s), 9.40 (1H, s), 9.46 (1H, s),
1
9.48 (1H, s), 10.66 (1H, s), 10.69 (1H, s); H NMR (400 MHz,
d7-DMF): δ -6.49 (1H, s), -3.47 (2H, s), 1.79-1.84 (12H, 2
overlapping triplets), 3.59 (3H, s), 3.60 (3H, s), 3.96 (4H, q, J
) 7.7 Hz), 4.10 (4H, q, J ) 7.7 Hz), 9.11 (1H, d, J ) 1.2 Hz),
9.85 (1H, s), 9.87 (1H, s), 10.17 (1H, s), 10.82 (1H, s), 10.85
(1H, s); 1H NMR (400 MHz, trace TFA-CDCl3, monocation
46a ): δ -5.83 (1H, s), -3.38 (1H, br), -2.31 (1H, s), -2.23
(1H, s), 1.66 (6H, t), 1.80 (6H, t), 3.48 (3H, s), 3.50 (3H, s),
3.93-4.04 (8H, m), 8.94 (1H, s), 9.77 (1H, s), 9.81 (1H, s), 10.06
F IGURE 7. (A) Aerial view ORTEP drawing with shaded
ellipsoids of 19b showing the atom labeling scheme. Non-
hydrogen atoms are represented by Gaussian ellipsoids at the
50% probability level. Hydrogen atoms have been omitted for
clarity with the exception of the carbaporphyrin core hydrogen
atoms that have been drawn arbitrarily small. (B) Edge view
ORTEP drawing of 19b.
1
(1H, s), 10.54 (1H, s), 10.96 (1H, s); H NMR (400 MHz, 50%
TFA-CDCl3, dication 47a ): δ -7.42 (2H, s), -3.67 (2H, br),
1.77-1.85 (12H, m), 3.76 (3H, s), 3.77 (3H, s), 4.20-4.28 (8H,
m), 10.99 (1H, s), 11.05 (1H, s), 11.50 (1H, s), 11.60 (1H, s),
11.92 (1H, s), 12.12 (1H, s); 13C NMR (CDCl3): δ 11.2, 11.4,
17.1, 17.2, 18.3, 19.4, 19.9, 94.3, 95.0, 104.1, 106.8, 108.4, 132.7,
133.0, 134.9, 135.3, 135.7, 135.9, 136.7, 137.7, 137.8, 138.5,
138.9, 143.3, 145.3, 145.6, 155.5, 155.8, 189.3; EI MS: m/z (rel
int.) 479 (8), 478 (37), 477 (100; M+), 476 (2.4), 462 (4.2), 238.8
(11.5; M2+); HRMS (EI): calcd for C32H35N3O: 477.2780 m/z;
found: 477.2780.
8,12,13,17-Tetr a eth yl-2-for m yl-3,7,18-tr im eth yl-21-ca r -
ba p or p h yr in (45b). Carbaporphyrin 45b was prepared as
outlined for 19a from tripyrrane 24a (100 mg) and methyl-
triformylcyclopentadiene 44b (33 mg). Recrystallization from
chloroform-methanol gave formylcarbaporphyrin 45b (7.0 mg,
6.5%) as purple crystals, mp > 240 °C. UV-vis (1% Et3N-
CH2Cl2): λmax (log ꢀ) 368 (4.69), 438 (4.89), 528 (4.09), 566
(4.12), 642 (3.43), 710 nm (3.30); UV-vis (0.01% TFA-CH2Cl2;
monocation 46b): λmax (log ꢀ) 321 (4.49), 401 (4.84), 428 (4.79),
447 (sh, 4.72), 500 (sh, 4.01), 551 (3.96), 593 (3.77), 647 (3.58),
708 nm (3.31); UV-vis (50% TFA-CHCl3; dication 47b): λmax
(log ꢀ) 414 (5.26), 428 (5.07), 554 (3.73), 604 (4.04), 664 nm
(3.75); 1H NMR (400 MHz, CDCl3): δ -6.62 (1H, s), -3.52 (2H,
br s), 1.77-1.85 (12H, m), 3.51 (3H, s), 3.56 (3H, s), 3.57 (3H,
s), 3.87 (4H, q), 3.94-4.01 (4H, 2 overlapping quartets), 9.54
(1H, s), 9.61 (1H, s), 9.71 (1H, s), 10.78 (1H, s), 11.00 (1H, s);
1H NMR (400 MHz, trace TFA-CDCl3, monocation 46b): δ
-6.07 (1H, s), -3.27 (1H, br s), -1.99 (1H, s), -1.91 (1H, s),
1.62-1.68 (6H, 2 overlapping triplets), 1.81 (6H, t), 3.47 (6H,
s), 3.59 (3H, s), 3.92-4.03 (8H, m), 9.74 (1H, s), 9.82 (1H, s),
10.04 (1H, s), 10.75 (1H, s), 10.99 (1H, s); 1H NMR (400 MHz,
50% TFA-CDCl3, dication 47b): δ -7.28 (2H, s), -3.48 (2H,
br), 1.76-1.85 (12H, m), 3.73 (3H, s), 3.75 (3H, s), 4.15-4.27
(8H, m), 4.53 (3H, s), 10.86 (1H, s), 10.97 (1H, s), 11.46 (1H,
s), 11.97 (1H, s), 12.05 (1H, s); 13C NMR (CDCl3): δ 11.3, 11.5,
17.2, 17.3, 18.4, 19.5, 19.9, 94.3, 95.5, 102.2, 103.7, 107.9, 131.6,
133.8, 134.0, 134.6, 135.2, 135.4, 135.6, 137.5, 137.8, 138.7,
145.0, 145.5, 152.9, 154.9, 155.6, 188.2; EI MS: m/z (rel int.)
493(9), 492 (35), 491 (100; M+), 490 (2.8), 476 (4.2) 464 (3.5),
463 (6.3), 462 (5.1), 245.7 (6.9; M2+); HRMS (EI): calcd for
F IGURE 8. Cyclic voltammogram of 19a in 0.2 M Bu4NBF4/
CH2Cl2.
2 overlapping quartets), 7.71-7.74 (2H, m), 8.68-8.71 (2H,
m), 10.06 (2H, s), 10.33 (2H, s); 1H NMR (400 MHz, 50% TFA-
CDCl3, dication 26a , 20 °C): δ -5.15 (2H, s), -1.47 (2H, br s),
1.74 (6H, t, J ) 7.8 Hz), 1.78 (6H, t, J ) 7.8 Hz), 3.60 (6H, s),
4.02-4.10 (8H, m), 8.94-8.98 (2H, m), 10.15-10.18 (2H, m),
1
10.45 (2H, s), 11.10 (2H, s); H NMR (400 MHz, 50% TFA-
CDCl3, dication 26a , -10 °C): δ -5.21 (2H, s), -1.6 (1H, vb),
-1.55 (2H, s), 1.67 (6H, t, J ) 7.6 Hz), 1.73 (6H, t, J ) 7.8
Hz), 3.57 (6H, s), 4.00-4.08 (8H, m), 8.94-8.96 (2H, m), 10.14-
10.17 (2H, m), 10.46 (2H, s), 11.07 (2H, s); 13C NMR (CDCl3):
δ 11.4, 17.4, 18.6, 19.6, 20.0, 95.5, 98.8, 109.7, 120.6, 126.6,
132.5, 133.9, 135.6, 137.8, 141.6, 144.6, 152.9; 13C NMR (50%
TFA-CDCl3, dication 26a ): δ 11.1, 16.1, 17.2, 20.1, 20.3, 32.9,
107.8, 108.2, 125.2, 134.9, 138.0, 139.5, 140.6, 146.0, 146.5,
150.9, 151.7; EI MS: m/z (rel int.) 501 (7.5), 500 (41), 499 (100;
C
33H37N3O: m/z 491.2937. Found: 491.2937.
4872 J . Org. Chem., Vol. 67, No. 14, 2002

Conjugated Macrocycles Related to the Porphyrins
12,13-Bu t a n o-8,17-d iet h yl-7,18-d im et h ylb en zo[b]-21-
ca r ba p or p h yr in (19c). Butanobenzocarbaporphyrin 19c was
prepared in the same procedure as 19a from tripyrrane 24c
(200 mg) and 1,3-diformylindene (75 mg). Recrystallization
from chloroform-methanol afforded 19c (104 mg; 50.5%) as
purple-colored crystals, >300 °C; UV-vis (1% Et3N-CH2Cl2):
λmax (log ꢀ) 376 (4.63), 426 (5.24), 512 (4.26), 544 (4.16), 602
(3.71), 662 nm (3.28); UV-vis (50% TFA-CHCl3; 26c): λmax
(log ꢀ) 346 (4.56), 424 (5.27), 616 (3.92), 672 nm (4.47); 1H NMR
(300 MHz, CDCl3): δ -6.80 (1H, s), -4.0 (2H, v br), 1.83 (6H,
t), 2.47 (4H, m), 3.61 (6H, s), 4.04 (8H, m), 7.75 (2H, m), 8.82
134.7, 137.8, 137.9, 139.4, 145.4, 145.7, 150.9, 151.7; HRMS
(FAB): calcd for C41H33N3 + H: m/z 568.2753; found: 568.2753.
8,17-B is (2-m e t h o x y c a r b o n y le t h y l)-7,18-d im e t h y l-
a cen a p h th o[b]ben zo[l]-21-ca r ba p or p h yr in (41b). The title
carbaporphyrin was prepared by the foregoing procedure from
tripyrrane 40b (100 mg), 20 (23 mg), and DDQ (30 mg).
Recrystallization from chloroform-methanol gave the carba-
porphyrin (26 mg; 29%) as a dark blue solid, mp > 300 °C;
UV-vis (1% Et3N-CHCl3): λmax (log ꢀ) 343 (4.23), 395 (4.57),
454 (5.02), 509 (4.00), 544 (3.96), 587 (4.49), 624 nm (3.99);
UV-vis (50% TFA-CHCl3): λmax (log ꢀ) 307 (4.20), 371 (4.42),
476 (5.13), 640 (4.08), 702 nm (4.22); 1H NMR (400 MHz,
CDCl3): δ -7.67 (1H, s), -5.2 (2H, br s), 3.07 (4H, t, J ) 7.6
Hz), 3.42 (6H, s), 3.60 (6H, s), 4.11 (4H, t, J ) 7.6 Hz), 7.83-
7.85 (2H, m), 7.97 (2H, t, J ) 7 Hz), 8.06 (2H, d, J ) 8.5 Hz),
8.66 (2H, d, J ) 6.7 Hz), 8.78-8.81 (2H, m), 9.46 (2H, s), 9.70
1
(2H, m), 9.64 (2H, s), 10.06 (2H, s); H NMR (300 MHz, 50%
TFA-CDCl3; dication 26c): δ -5.12 (2H, br s), -1.20 (2H, br
s), 1.77 (6H, t), 2.49 (4H, br m), 3.59 (6H, s), 4.05 (8H, m),
8.96 (2H, m), 10.16 (2H, m), 10.41 (2H, s), 11.11 (2H, s); 13C
NMR (CDCl3): δ 11.4, 17.3, 19.6, 23.8, 24.2, 95.2, 98.9, 109.8,
120.7, 126.7, 132.6, 133.9, 135.5, 135.8, 137.7, 141.8, 141.9,
153.3; 13C NMR (50% TFA-CDCl3; dication 26c): δ 11.1, 16.1,
20.3, 22.6, 23.5, 32.8, 107.7, 108.3, 125.2, 135.0, 138.4, 139.7,
141.1, 143.7, 146.2, 151.0, 151.4 (2); EI MS: m/z (rel int.) 499
(8), 498 (38), 497 (100; M+), 496 (3.0), 482 (8.0; [M - CH3]+),
469 (1.6; [M - CH2dCH2]+), 454 (2.4), 248.8 (18; M2+); HRMS
(EI): calcd for C35H35N3: m/z 497.2831. Found: 497.2827.
1
(2H, s); H NMR (400 MHz, 50% TFA-CDCl3): δ -4.97 (2H,
br s), 3.34 (4H, t, J ) 7.6 Hz), 3.65 (6H, s), 3.81 (6H, s), 4.51
(4H, br t), 8.16 (2H, t, J ) 7 Hz), 8.38 (2H, d, J ) 7.9 Hz), 8.97
(2H, m), 9.18 (2H, d, J ) 6.7 Hz), 10.14 (2H, m), 11.04 (4H, s);
HRMS (FAB): calcd for C45H37N3O4 + H: m/z 684.2862;
found: 684.2861.
8,17-Dieth yl-7,18-d im eth ylben zo[b]p h en a n th r o[l]-21-
ca r ba p or p h yr in (43). The title compound was prepared from
tripyrrane 42 (100 mg), 20 (26 mg) and DDQ (35 mg) by the
foregoing procedure. Chromatography on Grade III alumina,
eluting with CH2Cl2, followed by chromatography on silica
eluting with CH2Cl2, gave the product as a brown fraction.
Recrystallization from chloroform-methanol gave the phenan-
throcarbaporphyrin (25 mg; 28%) as a flaky dark burgandy-
colored solid, mp > 300 °C; UV-vis (1% Et3N-CHCl3): λmax
(log ꢀ) 390 (4.64), 442 (5.30), 496 (4.26), 529 (4.13), 568 (4.49),
618 (3.93), 677 nm (3.44); UV-vis (50% TFA-CHCl3): λmax
(log ꢀ) 355 (4.45), 462 (5.08), 606 (3.94), 638 (4.07), 698 nm
(4.34); 1H NMR (400 MHz, CDCl3): δ -7.12 (1H, s), -4.8 (2H,
br s), 1.74 (6H, t, J ) 7.6 Hz), 3.46 (6H, s), 3.90 (4H, q, J ) 7.6
Hz), 7.77-7.79 (2H, m), 7.92 (2H, t, J ) 7.3 Hz), 8.10 (2H, t,
J ) 7.3 Hz), 8.74-8.76 (2H, m), 9.09 (2H, d, J ) 8.5 Hz), 9.73
8,17-Diet h yl-7,18-d im et h yld ib en zo[b,l]-21-ca r b a p or -
p h yr in (38). Butanobenzocarbaporphyrin 19c (11 mg) and
DDQ (11 mg) were stirred under reflux with 10 mL of toluene
for 2 h. The solvent was removed under reduced pressure and
the residue dissolved in CH2Cl2. The solution was washed with
water and chromatographed on a silica column eluting with
CH2Cl2. Recrystallization from chloroform-methanol gave 38
(8.0 mg; 46%) as fluffy copper-bronze-colored crystals, mp >
300 °C; UV-vis (1% Et3N-CH2Cl2): λmax (log ꢀ) 386 (4.66), 432
(5.27), 452 (sh) (4.49), 518 (4.24), 552 (4.43), 610 (3.86), 672
nm (3.91); UV-vis (50% TFA-CHCl3): λmax (log ꢀ) 370 (4.57),
438 (5.08), 486 (sh) (4.43), 728 nm (4.43); 1H NMR (300 MHz,
CDCl3): δ -6.59 (1H, s), -4.02 (2H, br s), 1.87 (6H, t), 3.61
(6H, s), 4.07 (4H, q), 7.76 (2H, m), 8.06 (2H, m), 8.81 (2H, m),
9.26 (2H, m), 10.04 (2H, s), 10.06 (2H, s); 1H NMR (300 MHz,
TFA-CDCl3): δ -6.01 (2H, br s), -2.30 (3H, v br s, 3 x NH),
1.83 (6H, t), 3.72 (6H, s), 4.18 (4H, q), 8.55 (2H, m), 9.01 (2H,
m), 9.60 (2H, m), 10.29 (2H, m), 11.03 (2H, s), 11.40 (2H, s);
13C NMR (CDCl3): δ 11.9, 16.5, 20.3, 96.2, 96.6, 123.7, 123.8,
131.6, 131.6, 134.0, 134.1, 137.5, 139.4, 139.5, 141.9, 142.7,
144.0; EI MS: m/z (rel int.) 495 (7.4), 494 (39), 493 (100; M+),
492 (3.7), 491 (3.6), 478 (20; [M - CH3]+); 463 (3.4), 462 (3.3),
247 (16; M2+); HRMS (EI): calcd for C35H31N3: m/z 493.2518.
Found: 493.2517.
1
(2H, d, J ) 8.5 Hz), 9.77 (2H, s), 10.36 (2H, s); H NMR (400
MHz, 50% TFA-CDCl3): δ -4.40 (2H, s), 0.05 (2H, br s), 1.76
(6H, t, J ) 7.6 Hz), 3.51 (6H, s), 4.01 (4H, q, J ) 7.6 Hz), 8.20
(2H, t, J ) 7.3 Hz), 8.28 (2H, t, J ) 7.3 Hz), 8.91-8.93 (2H,
m), 9.25 (2H, d, J ) 8.5 Hz), 9.58 (2H, d, J ) 7.9 Hz), 10.06-
10.08 (2H, m), 10.86 (2H, s), 11.10 (2H, s); 13C NMR (50%
TFA-CDCl3): δ 11.0, 15.9, 20.3, 33.7, 107.9, 108.7, 124.9,
125.2, 126.6, 127.2, 129.7, 130.3, 133.7, 134.5, 136.4 (2), 137.1,
139.7, 145.4, 149.8, 152.1, 152.6; HRMS (FAB): calcd for
C
43H35N3 + H: m/z 594.2909; found: 594.2910.
8,17-Diet h yl-7,18-d im et h yla cen a p h t h o[b]b en zo[l]-21-
ca r ba p or p h yr in (41a ). Tripyrrane 40a was stirred with TFA
(1.0 mL) for 10 min under nitrogen. Dichloromethane (19 mL)
was added, followed immediately by diformylindene 20 (27
mg), and the resulting solution was stirred under N2 in the
dark for a further 2 h. The solution was neutralized with
triethylamine, DDQ (36 mg) was added, and the mixture
stirred for 1 h. The mixture was diluted with dichloromethane,
washed with water, and evaporated under reduced pressure.
The residue was columned on Grade III neutral alumina,
eluting first with dichloromethane, and then chloroform with
increasing amounts of methanol (0-5%). The product fraction
was recrystallized from chloroform-methanol to give the
acenaphthocarbaporphyrin (16 mg; 18%) as a dark blue solid,
mp > 300 °C; UV-vis (1% Et3N-CHCl3): λmax (log ꢀ) 402
(4.63), 456 (5.07), 511 (4.00), 546 (4.01), 590 (4.60), 624 (4.10),
688 nm (3.21); UV-vis (50% TFA-CHCl3): λmax (log ꢀ) 307
(4.24), 368 (4.53), 474 (5.23), 632 (4.17), 691 nm (4.35); 1H NMR
(400 MHz, 50% TFA-CDCl3): δ -4.64 (2H, br s), -1.0 (2H,
br s), 1.90 (6H, t, J ) 7.6 Hz), 3.63 (6H, s), 4.15 (4H, q, J ) 7.6
Hz), 8.16 (2H, t, J ) 7 Hz), 8.38 (2H, d, 7.9 Hz), 8.96 (2H, m),
9.07 (2H, d, J ) 6.7 Hz), 10.14 (2H, m), 10.89 (2H, s), 11.02
(2H, s); 13C NMR (50% TFA-CDCl3): δ 11.0, 16.1, 20.3, 33.1,
107.8, 109.6, 124.9, 126.8, 129.5, 130.3, 131.5, 131.7, 134.6,
2,5-Bis(5-ben zyloxyca r bon yl-3-eth yl-4-m eth yl-2-p yr r o-
lylm eth yl)-3,4-d ip h en ylp yr r ole (21b). A stirred mixture of
benzyl 5-acetoxymethyl-4-ethyl-3-methylpyrrole-2-carboxy-
late51 (1.45 g) and 3,4-diphenylpyrrole52 (0.50 g) in acetic acid
(2 mL) and ethanol (300 mL) was heated under reflux under
a nitrogen atmosphere for 16 h. The solution was cooled to
room temperature and further chilled with an ice bath. The
resulting precipitate was suction-filtered, washed with cold
ethanol, and dried in vacuo to give the tripyrrane dibenzyl
ester (1.21 g; 73%) as an off-white powder, mp 135 °C; 1H NMR
(400 MHz, CDCl3): δ 0.74 (6H, t, J ) 7.4 Hz), 2.01 (4H, q),
2.21 (6H, s), 3.75 (4H, br s), 4.52 (4H, br s), 7.05-7.08 (8H,
m), 7.16 (2H, t, J ) 7.2 Hz), 7.22 (4H, d, J ) 7.6 Hz), 7.25-
7.27 (6H, m), 9.39 (1H, br s), 11.35 (2H, br s); 13C (CDCl3): δ
11.2, 15.7, 17.1, 22.8, 65.6, 117.6, 120.1, 123.9, 125.3, 125.4,
126.8, 127.0, 127.6, 128.0, 128.3, 128.5, 130.5, 132.7, 136.5,
137.0, 163.1. Anal. Calcd for C48H47N3O4: calcd C, 78.95; H,
6.49; N, 5.76. Found: C, 78.98; H, 6.43; N, 5.89.
8,17-Dieth yl-7,18-d im eth yl-12,13-d ip h en ylben zo[b]-21-
ca r ba p or p h yr in (19b). The foregoing dibenzyl ester (1.52 g)
(51) J ohnson, A. W.; Kay, I. T.; Markham, E.; Price, R.; Shaw, K.B.
J . Chem. Soc. 1959, 3416.
(52) Friedman, M. J . Org. Chem. 1965, 30, 859.
J . Org. Chem, Vol. 67, No. 14, 2002 4873

Lash et al.
was dissolved in freshly distilled THF (225 mL) in a hydro-
genation vessel, methanol (75 mL) and triethylamine (20
drops) were added, and the air was flushed out with a stream
of nitrogen. Palladium-charcoal (10%, 300 mg) was added and
the resulting mixture shaken under a hydrogen atmosphere
at 40 psi overnight. The catalyst was filtered off and the
solvent removed under reduced pressure. The resulting residue
was taken up in 3% aqueous ammonia and neutralized to a
litmus end point while maintaining the temperature of the
solution between 0 and 5 °C with the aid of a salt-ice bath.
The resulting precipitate was suction-filtered and washed
repeatedly with water to remove all traces of water. After being
dried overnight in vacuo, the dicarboxylic acid 24b (1.065 g;
93%) was obtained as a pink powder that was used without
further purification. Tripyrrane 24b (100 mg) was stirred with
TFA (2 mL) in a pear-shaped flask for 10 min under nitrogen.
The solution was diluted with dichloromethane (38 mL),
diformylindene (31 mg) was immediately added, and the
solution was stirred in the dark under N2 for a further 2 h.
The solution was neutralized by the dropwise addition of
triethylamine, DDQ (50 mg) was added, and the resulting
solution was stirred for an additional 1 h. The mixure was
washed with water and the solvent removed under reduced
pressure. The residue was chromatographed on Grade 3
alumina, eluting with dichloromethane, and the product
collected as a brown band. Recrystallization from chloroform-
methanol gave the diphenylcarbaporphyrin (53 mg; 51%) as
shiny purple crystals, mp > 300 oC; UV-vis (CHCl3): λmax (log
ꢀ) 430 (5.59), 518 (4.20), 555 (4.36), 605 (3.83), 665 (2.97);
UV-vis (CH2Cl2): λmax (log ꢀ) 385 (4.71), 429 (5.325), 517 (4.27),
553 (4.39), 605 (3.93), 666 nm (3.51); UV-vis (0.01% TFA-
CH2Cl2; monocation 27b): λmax (log ꢀ) 310 (4.435), 402 (4.75),
443 (5.14), 476 (4.51), 555 (4.03), 595 (4.02), 617 (sh, 3.92),
679 nm (3.29); UV-vis (50% TFA-CHCl3; dication 26b): λmax
19b was found to crystallize in the triclinic crystal system with
the following cell parameters: a ) 10.7457(8) Å, b ) 11.8726-
(9) Å, c ) 14.160(1) Å, R ) 66.692(2)°, â ) 76.363(1)°, and γ )
83.235(2)°, Z ) 2. A total of 8081 reflections were collected, of
which 6489 were unique, and 3473 were observed F2
>
o
2σ(F2o). Data reduction was accomplished using SAINT.53b The
data were corrected for absorption through use of the SADABS
procedure.53c
Solution and data analysis was performed using the WinGX
software package.55 The structure of 19b was solved using the
direct method program SHELXS-97 and the refinement com-
pleted using the program SHELXL-97.56 With the exception
of the three core hydrogen atoms, hydrogen atoms were
assigned positions based on the geometries of the attached
carbon atoms and were given thermal parameters of 20%
greater than the attached atoms. Ethyl carbons, C8b1 and
C8b2, represent the same atom disordered over two occupancy
sites, 60% and 40%, respectively. Both were, nonetheless,
refined anisotropically. The three core hydrogen atoms, H21,
H22, and H24, were located by a difference Fourier im-
mediately following anisotropic refinement of all non-hydrogen
atoms and were allowed to freely refine through the re-
mainder of the process. Full-matrix least-squares refinement
on F2 led to a convergence with R1 ) 0.065 and wR2 ) 0.141
for 3473 data with F2 > 2σ(F2o). A final difference Fourier
o
synthesis showed features in the range of + 0.334 to -0.294
e-/Å3. An ORTEP55b drawing of the refined structure is shown
in Figure 7.
Complete X-ray structural data have been deposited at the
Cambridge Crystallographic Data Center CCDC no. 184698.
Copies of this information can be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: + 44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
Cyclic Volta m m etr y. The electrochemical studies were
carried out in anhydrous dichloromethane using a BAS
CV-27 potentiostat equipped with an x-y recorder. A conven-
tional three-electrode cell consisting of a platinum disk work-
ing electrode, a platinum wire auxiliary electrode, and a
Ag/AgNO3 (0.01 M) reference electrode was used. The cyclic
voltammograms were run in a 0.2 M Bu4NBF4 solution in an
inert atmosphere glovebox at a scan rate of 200 mV/s. The
scanning limits were +2.2 V and -1.9 V vs Ag/AgNO3.
1
(log ꢀ) 435 (5.30), 607 (4.01), 661 (4.39); H NMR (400 MHz,
CDCl3): δ -6.91 (1H, s), -4.07 (2H, br s), 1.75 (6H, t, J ) 7.5
Hz), 3.59 (6H, s), 3.91 (4H, q, J ) 7.5 Hz), 7.60 (2H, t, J ) 7.2
Hz), 7.68 (4H, t, J ) 7.4 Hz), 7.73 (2H, m), 7.97 (4H, d, J )
7.6 Hz), 8.78 (2H, m), 9.86 (2H, s), 10.03 (2H, s);1H NMR (400
MHz, trace TFA-CDCl3; monocation 27b): δ -6.71 (1H, s),
-4.29 (1H, br), -3.23 (2H, br), 1.60 (6H, t, J ) 7.5 Hz), 3.56
(6H, s), 3.91 (4H, q, J ) 7.5 Hz), 7.66-7.75 (8H, m), 7.97 (4H,
d, J ) 6.8 Hz), 8.68-8.70 (2H, m), 10.11 (2H, s), 10.34 (2H, s);
1H NMR (400 MHz, 50% TFA-CDCl3; dication 26b): δ -4.67
(2H, s), -0.84 (2H, br s), 1.66 (6H, t, J ) 7.6 Hz), 3.53 (6H, s),
3.85 (4H, q, J ) 7.6 Hz), 7.72-7.74 (3H, m), 7.79-7.81 (2H,
m), 8.89-8.94 (2H, m), 10.07-10.12 (2H, m), 10.31 (2H, s),
10.94 (2H, s); 13C (CDCl3): δ 11.6, 17.3, 19.7, 98.5, 99.1, 110.0,
120.6, 126.8, 127.2, 128.5, 132.5, 132.7, 134.6, 135.6, 136.1,
137.0, 138.7, 141.4, 144.3, 151.1; HRMS (EI): calcd for
C43H37N3: 595.2984; found: 595.2987. Anal. Calcd for C43H37N3‚
H2O: calcd C, 84.14; H, 6.40; N, 6.84. Found: C, 84.57; H,
6.13; N, 6.95.
Cr ysta l Str u ctu r e Deter m in a tion of 19b. X-ray quality
crystals were obtained by the addition of methanol to a hot
chloroform solution. A dark blue plate thereby obtained of
approximate dimensions 0.34 × 0.16 × 0.10 mm was mounted
on a glass fiber with super-glue and transferred to a Brucker
P4/R4/SMART 1000 CCD diffractometer.53 The X-ray diffrac-
tion data were collected at -80 °C using Mo KR radiation. Data
collection and cell refinement were performed using SMART.53a
The unit cell parameters were obtained from a least squares
refinement of 2778 centered reflections. The systematic ab-
sences indicated the space group P-1 (no. 02).54 Carbaporphyrin
Ack n ow led gm en t. This material is based upon
work supported by the National Science Foundation
under Grant Nos. CHE-9732054 and CHE-0134472, the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, and the Camille and Henry
Dreyfus Scholar/Fellow Program. We thank Dr. Robert
McDonald and The University of Alberta Structure
Determination Laboratory for collecting the experimen-
tal data set for the X-ray structure of 19b and for useful
discussions.
1
Su p p or tin g In for m a tion Ava ila ble: UV-vis, H NMR,
13C NMR, and mass spectra for selected compounds are
provided. Tables of crystallographic details, atomic coordinates,
bond lengths and angles, critical angle planes, torsional angles,
anisotropic thermal parameters and hydrogen atom param-
eters for carbaporphyrin 19b are also available. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O020267B
(53) (a) Brucker SMART 1000 CCD software package; Brucker
Advanced X-ray Solutions: Madison, WI, 1999. (b) Brucker SAINT
Integration Software for Single-Crystal Data frames - h, k, l, intensity;
Brucker Advanced X-ray Solutions: Madison, WI, 1999. (c) Brucker
SADABS-Empirical adsorption correction procedures; Brucker Ad-
vanced X-ray Solutions: Madison, WI, 1999.
(55) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837. b. Farrugia,
L. J . J . Appl. Crystallogr. 1997, 30, 565.
(56) (a) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (b)
Sheldrick, G. M. SHELXS-97; 97-2 ed.; University of Goettingen:
Goettingen, Germany, 1997. (c) Sheldrick, G. M. SHELXL-97; 97-2
ed.; University of Goettingen: Goettingen, Germany, 1997.
(54) McArdle, P. J . Appl. Crystallogr. 1996, 29, 306.
4874 J . Org. Chem., Vol. 67, No. 14, 2002