New riches in carbaporphyrin chemistry: Silver and gold organometallic complexes of benzocarbaporphyrins

Article abstract of DOI:10.1021/ic0400540

The NH-N-NH-N core of the porphyrin system represents one of the best studied and most versatile platforms for coordination chemistry. However, the replacement of one or more of the interior nitrogens with carbon atoms would be expected to diminish the ability of these systems to form metallo derivatives considerably. Despite this expectation, carbaporphyrinoid systems have been shown to form stable organometallic derivatives. Although azuliporphyrins and benziporphyrins act as dianionic ligands, benzocarbaporphyrins are trianionic ligands. Treatment of five different meso unsubstituted benzocarbaporphyrins and two different meso tetraarylbenzocarbaporphyrins with excess silver(I) acetate afforded 65-97% yields of the corresponding silver(III) organometallic derivatives. The insertion of silver metal was confirmed by mass spectrometry and X-ray crystallography. The UV-vis spectra showed a strong Soret band at wavelengths between 437 and 451 nm, together with a series of Q-type bands at longer wavelengths. The new metallo carbaporphyrins demonstrate the presence of a strong diatropic ring current in their proton NMR spectra, and carbon-13 NMR spectroscopy indicates that the derivatives retain a plane of symmetry. The reaction of meso tetraaryl carbaporphyrins with gold(III) acetate afforded the related gold(III) complexes, and these also showed strongly porphyrin-like aromatic characteristics. The UV-vis spectra for the gold complexes again showed a strong Soret band between 437-439 nm, but a secondary band near 400 nm is somewhat intensified for the gold species compared to the spectra for the related silver(III) meso tetrasubstituted carbaporphyrins. The ring currents observed for the gold(Ill) complexes by proton NMR spectroscopy were comparable to those of the silver(Ill) derivatives, implying that both series have similar macrocyclic conformations. Cyclic voltammetry was performed on two different carbaporphyrins, their silver(III) derivatives, and a gold(III) complex. The silver complexes display a reversible cathodic wave that is assigned to the Ag(III/II) couple. However, the gold porphyrinoid gave a value for the reductive wave that could be due to a gold(III/II) couple or a ligand-based process.

Full text of DOI:10.1021/ic0400540

Inorg. Chem. 2004, 43, 5258−5267
New Riches in Carbaporphyrin Chemistry: Silver and Gold
Organometallic Complexes of Benzocarbaporphyrins†
Timothy D. Lash,* Denise A. Colby, and Lisa F. Szczepura
Department of Chemistry, Illinois State UniVersity, Normal, Illinois 61790-4160
Received April 7, 2004
The NH−N−NH−N core of the porphyrin system represents one of the best studied and most versatile platforms
for coordination chemistry. However, the replacement of one or more of the interior nitrogens with carbon atoms
would be expected to diminish the ability of these systems to form metallo derivatives considerably. Despite this
expectation, carbaporphyrinoid systems have been shown to form stable organometallic derivatives. Although
azuliporphyrins and benziporphyrins act as dianionic ligands, benzocarbaporphyrins are trianionic ligands. Treatment
of five different meso unsubstituted benzocarbaporphyrins and two different meso tetraarylbenzocarbaporphyrins
with excess silver(I) acetate afforded 65−97% yields of the corresponding silver(III) organometallic derivatives. The
insertion of silver metal was confirmed by mass spectrometry and X-ray crystallography. The UV−vis spectra showed
a strong Soret band at wavelengths between 437 and 451 nm, together with a series of Q-type bands at longer
wavelengths. The new metallo carbaporphyrins demonstrate the presence of a strong diatropic ring current in their
proton NMR spectra, and carbon-13 NMR spectroscopy indicates that the derivatives retain a plane of symmetry.
The reaction of meso tetraaryl carbaporphyrins with gold(III) acetate afforded the related gold(III) complexes, and
these also showed strongly porphyrin-like aromatic characteristics. The UV−vis spectra for the gold complexes
again showed a strong Soret band between 437−439 nm, but a secondary band near 400 nm is somewhat intensified
for the gold species compared to the spectra for the related silver(III) meso tetrasubstituted carbaporphyrins. The
ring currents observed for the gold(III) complexes by proton NMR spectroscopy were comparable to those of the
silver(III) derivatives, implying that both series have similar macrocyclic conformations. Cyclic voltammetry was
performed on two different carbaporphyrins, their silver(III) derivatives, and a gold(III) complex. The silver complexes
display a reversible cathodic wave that is assigned to the Ag(III/II) couple. However, the gold porphyrinoid gave a
value for the reductive wave that could be due to a gold(III/II) couple or a ligand-based process.
Introduction
ogy3,4,7-9 or by oxidative ring contraction of the related
azuliporphyrins.10-14 Many related porphyrinoids have been
reported in recent years, including benziporphyrins,15-19
Carbaporphyrins (1) are porphyrin analogues where one
of the pyrrolic subunits has been replaced with a cyclopen-
tadiene ring.1-3 The best studied of these remarkable
macrocyclic systems are the benzocarbaporphyrins 2,3-6
which are readily available from the “3 + 1” methodol-
(5) Hayes, M. J.; Spence, J. D.; Lash, T. D. Chem. Commun. 1998, 2409-
2410.
(6) Lash, T. D.; Muckey, M. A.; Hayes, M. J.; Liu, D.; Spence, J. D.;
Ferrence, G. M. J. Org. Chem. 2003, 68, 8558-8572.
(7) Lash, T. D. Chem.sEur. J. 1996, 2, 1197-1200.
(8) Liu, D.; Lash, T. D. J. Org. Chem. 2003, 68, 1755-1761.
(9) Jiao, W.; Lash, T. D. J. Org. Chem. 2003, 68, 3896-3901.
(10) Lash, T. D.; Chaney, S. T. Angew. Chem., Int. Ed. Engl. 1997, 36,
839-840.
* Author to whom correspondence should be addressed. E-mail: tdlash@
ilstu.edu.
† Part 34 in the series “Conjugated Macrocycles Related to the Porphy-
rins”. For part 33, see: Lash, T. D.; Rasmussen, J. M.; Bergman, K. M.;
Colby, D. A. Org. Lett. 2004, 6, 549-552.
(1) Lash, T. D. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000; Vol.
2, pp 125-199.
(11) Lash, T. D. Chem. Commun. 1998, 1683-1684.
(12) Graham, S. R.; Colby, D. A.; Lash, T. D. Angew. Chem., Int. Ed.
2002, 41, 1371-1374.
(2) Lash, T. D. Synlett 2000, 279-295.
(13) Colby, D. A.; Lash, T. D. Chem.sEur. J. 2002, 8, 5397-5402.
(14) Lash, T. D.; Colby, D. A.; Ferrence, G. M. Eur. J. Org. Chem. 2003,
4533-4548.
(3) Lash, T. D.; Hayes, M. J. Angew. Chem., Int. Ed. Engl. 1997, 36,
840-841.
(4) Lash, T. D.; Hayes, M. J.; Spence, J. D.; Muckey, M. A.; Ferrence,
G. M.; Szczepura, L. F. J. Org. Chem. 2002, 67, 4860-4874.
(15) Berlin, K.; Breitmaier, E. Angew. Chem., Int. Ed. Engl. 1994, 33,
1246-1247.
5258 Inorganic Chemistry, Vol. 43, No. 17, 2004
10.1021/ic0400540 CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/27/2004

New Riches in Carbaporphyrin Chemistry
oxybenziporphyrins,16,17,20 tropiporphyrins,21 carbachlorins,22
carbasapphyrins,23,24 oxa- and thiacarbaporphyrins,25 and
dicarbaporphyrins.26 All of these species have a carbocyclic
ring in place of one or more pyrrole units and have a CH
unit lying within the macrocyclic cavity. The latter feature
is also found in the so-called N-confused porphyrins 3,27-29
which can be considered to be “honorary” carbaporphy-
rinoids.2 Porphyrins are extremely versatile ligands because
of their NH-N-NH-N core, but the presence of a carbon
atom within the macrocyclic cavity would be expected to
inhibit the formation of coordination complexes.5,6 Nonethe-
less, N-confused porphyrins have been shown to act as both
dianionic and trianions ligands,28-30 readily forming neutral
organometallic derivatives with divalent and trivalent metal
cations (structures 4 and 5, respectively).30,31 Recently, there
have been a number of reports on the synthesis of organo-
metallic complexes for a variety of carbaporphyrinoid
systems. Of particular note, azuliporphyrins have been shown
to form stable nickel(II), palladium(II), and platinum(II)
organometallic derivatives such as 6,32,33 and similar com-
plexes have been obtained for benziporphyrins18,19 and
oxybenziporphyrins.34 The formation of stable organometallic
derivatives for trivalent metal cations, as exemplified for the
silver(III) N-confused porphyrin 4,30 demonstrates that
systems of this type can stabilize relatively unusual oxidation
states.29,35,36 Indeed, cis doubly N-confused porphyrins have
Chart 1
(16) Lash, T. D.; Chaney, S. T.; Richter, D. T. J. Org. Chem. 1998, 63,
9076-9088.
(17) Richter, D. T.; Lash, T. D.Tetrahedron 2001, 57, 3659-3673.
(18) Stepien, M.; Latos-Grazynski, L. Chem.sEur. J. 2001, 7, 5113-5117.
(19) Szymanski, J. T.; Lash, T. D. Tetrahedron Lett. 2003, 44, 8613-
8616.
(20) Lash, T. D. Angew. Chem., Int. Ed. Engl. 1995, 34, 2533-2535. See
also Lash, T. D.; Chaney, S. T. Chem.sEur. J. 1996, 2, 944-948.
(21) Lash, T. D.; Chaney, S. T. Tetrahedron Lett. 1996, 37, 8825-8828.
(22) Hayes, M. J.; Lash, T. D. Chem.sEur. J. 1998, 4, 508-511.
(23) Lash, T. D.; Richter, D. T. J. Am. Chem. Soc. 1998, 120, 9965-9966.
(24) Richter, D. T.; Lash, T. D. Tetrahedron Lett. 1999, 40, 6735-6738.
(25) Liu, D.; Lash, T. D. Chem. Commun. 2002, 2426-2427.
(26) Lash, T. D.; Romanic, J. L.; Hayes, M. J.; Spence, J. D. Chem.
Commun. 1999, 819-820.
(27) (a) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116,
767-768. (b) Chmielewski, P. J.; Latos-Grazynski, L.; Rachlewicz,
K.; Glowiak, T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779-781.
(c) Liu, B. Y.; Bru¨ckner, C.; Dolphin, D. Chem. Commun. 1996,
2141-2142. (d) Geier, G. R., III; Haynes, D. M.; Lindsey, J. S. Org.
Lett. 1999, 1, 1455-1458. (e) Lash, T. D.; Richter, D. T.; Shiner, C.
M. J. Org. Chem. 1999, 64, 4, 7973-7982.
(28) Latos-Grazynski, L. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, CA,
2000, Vol. 2, pp 361-416.
(29) Furuta, H.; Maeda, H.; Osuka, A. Chem. Commun. 2002, 1795-1804.
(30) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676-2682.
been reported to give silver(III) and copper(III) derivatives,37
and the recently discovered trans doubly confused system
also affords the related copper(III) organometallic complex.38
In a preliminary communication, we reported the synthesis
of silver(III) benzocarbaporphyrins39,40 and have subsequently
shown that many related carbaporphyrinoids with a CH-
NH-N-NH core can also generate silver(III) complexes
(e.g., 7 and 8).35,36 These studies demonstrate that silver(III)
(31) (a) Furuta, H.; Morimoto, T.; Osuka, A. Org. Lett. 2003, 5, 1427-
1430. (b) Maeda, H.; Osuka, A.; Ishikawa, Y.; Aritome, I.; Hisaeda,
Y.; Furuta, H. Org. Lett. 2003, 5, 1293- 1296.
(32) Graham, S. R.; Ferrence, G. M.; Lash, T. D. Chem. Commun. 2002,
894-895.
(33) Lash, T. D.; Colby, D. A.; Graham, S. R.; Ferrence, G. M.; Szczepura,
L. F. Inorg. Chem. 2003, 42, 7326-7338. See also Colby, D. A.;
Ferrence, G. M.; Lash, T. D. Angew. Chem., Int. Ed. 2004, 43, 1346-
1349.
(34) Stepien, M.; Latos-Grazynski, L.; Lash, T. D.; Szterenberg, L. Inorg.
Chem. 2001, 40, 6892-6900. See also Venkatraman, S.; Anand, V.
G.; Pushpan, S. K.; Sankar, J.; Chandrashekar, T. K. Chem. Commun.
2002, 462-463.
(37) Araki, K.; Winnischofer, H.; Toma, H. E.; Maeda, H.; Osuka, A.;
Furuta, H. Inorg. Chem. 2001, 40, 2020-2025.
(38) Maeda, H.; Osuka, A.; Furuta, H. J. Am. Chem. Soc. 2003, 125,
15690-15691.
(35) Lash, T. D.; Rasmussen, J. M.; Bergman, K. M.; Colby, D. A. Org.
Lett. 2004, 6, 549-552.
(39) Preliminary communication: Muckey, M. A.; Szczepura, L. F.;
Ferrence, G. M.; Lash, T. D. Inorg. Chem. 2002, 41, 4840-4842.
(36) Miyake, K.; Lash, T. D. Chem. Commun. 2004, 178-179.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5259

Lash et al.
Scheme 1
is readily stabilized by diverse carbaporphyrinoid systems.
In this paper, we report full details of the synthesis,
spectroscopy, and electrochemistry of a series of silver(III)
benzocarbaporphyrins.39,40 In addition, we report the first
examples of gold(III) complexes for this class of porphyrin
analogues.41
Results and Discussion
Our early metalation studies were conducted on meso
unsubstituted benzocarbaporphyrins 9. These porphyrin
analogues are easily prepared by the “3 + 1” MacDonald
condensation between tripyrranes 10 and diformylindene 11
(Scheme 1).3,4,7-9 Syntheses of carbaporphyrins 9a-c have
been reported elsewhere,3,4,9 but the dipropyl and diisobu-
tylcarbaporphyrins (9d and 9e) represent new compounds.
These were prepared to explore the effect of larger alkyl
chains on the solubility of the metalated carbaporphyrins.
Reaction of diethylpyrrole (12a) with 2 equiv of the known
acetoxymethylpyrroles (13c and 13d)43 in refluxing acetic
acid-ethanol44,45 afforded the new tripyrranes (14d and 14e)
in good yields. The benzyl ester protective groups were then
cleaved by hydrogenolysis over 10% palladium-charcoal
to give the corresponding dicarboxylic acids 10 (quantitative).
Reaction of 10d and 10e with diformylindene46 in TFA-
dichloromethane, followed by neutralization with triethyl-
amine and oxidation with DDQ, afforded the new carbapor-
phyrins 9d and 9e in 46-52% yield. These new compounds
were fully characterized and displayed similar properties to
those of previously described benzocarbaporphyrins3,4 (e.g.,
strong diatropic ring currents by proton NMR spectroscopy,
the presence of a Soret band at ca. 425 nm followed by a
series of Q bands in the UV-vis absorption spectra, etc.).
When solutions of carbaporphyrins 9a-e in dichlo-
romethane-methanol were treated with silver(I) acetate, the
brown mixtures turned orange over a period of several
minutes. Following workup and evaporation of the solvents,
we subjected the residues to chromatography on alumina. A
deep orange-colored fraction eluted that was considerably
(40) The synthesis of silver(III) carbaporphyrin 8a was first disclosed at
the Symposium on NoVel Porphyrinoids and their Metal Complexes
- Chemistry, Photophysical Properties and Biomedical Aspects, 37th
IUPAC Congress/27th Gesellschaft Deutscher Chemiker General
Meeting, Berlin, Germany, August 1999 (Lash, T. D. Book of
Abstracts, Abstract No. MP-2). Additional results were presented at
the following meetings: (a) 221st National ACS Meeting, San Diego,
CA, April 2001 (Muckey, M. A.; Lash, T. D. Book of Abstracts, ORGN
715); (b) Recent AdVances in Heterocyclic Chemistry: Symposia
Honoring Professor B. S. Thyagarajan, Southwest Regional ACS
Meeting, San Antonio, Texas, October 2001. (c) 2nd International
Conference on Porphyrins and Phthalocyanines (ICPP-2), Kyoto,
Japan, July 2002 (Lash, T. D. Book of Abstracts, Abstract No. S-76).
(41) The synthesis of gold(III) tetraarylbenzocarbaporphyrins was first
reported at the 225th National Meeting of the American Chemical
Society, New Orleans, LA, March 2003 (Lash, T. D.; Colby, D. A.;
Muckey, M. A.; Liu, D.; Ferrence, G. M. Book of Abstracts, INOR
672).
less polar than the original carbaporphyrins. Initial studies
were carried out on tetraethylbenzocarbaporphyrin 9a, and
following the reaction with excess AgOAc, chromatography
and recrystallization from chloroform-methanol, silver(III)
complex 15a was isolated in 83% yield. This derivative gave
a porphyrin-like UV-vis spectrum with a strong Soret band
at 437 nm followed by a series of Q bands at 482, 518, 555,
and 593 nm (Figure 1). The incorporation of silver into this
system was easily confirmed by mass spectrometry. Silver
exists as two isotopic forms, 107Ag and 109Ag, in near equal
natural abundance.47,48 The EI MS for the organosilver
derivative gave the expected isotope pattern with two major
(42) Sessler, J. L.; Mozaffari, A.; Johnson, M. R. Org. Synth. 1991, 70,
68-78.
(43) Lash, T. D.; Quizon-Colquitt, D. M.; Shiner, C. M.; Nguyen, T. H.;
Hu, Z. Energy Fuels 1993, 7, 172-178.
(44) Sessler, J. L.; Johnson, M. R.; Lynch, V. J. Org. Chem. 1987, 52,
4394-4397.
(45) Lash, T. D. J. Porphyrins Phthalocyanines 1997, 1, 29-44.
(46) Arnold, Z. Collect. Czech. Chem. Commun. 1965, 30, 2783.
5260 Inorganic Chemistry, Vol. 43, No. 17, 2004

New Riches in Carbaporphyrin Chemistry
evidence for this hypothesis. The spectrum is well resolved
and shows the presence of all of the expected proton
resonances. The meso protons afford two 2H singlets at 9.89
and 10.06 ppm, whereas the benzo protons gave multiplets
at 7.78 and 8.84 ppm. These values are similar to those
observed for the parent carbaporphyrin system 9a, indicating
that the macrocycle supports a comparable diatropic ring
current, and the simplicity of the spectrum also confirms that
the molecule retains a plane of symmetry. The main
difference in the spectra of 9a and 15a is that the upfield
signals corresponding to the internal NH and CH protons
are no longer present for the latter species. Silver(III)
complexes are diamagnetic, whereas silver(II) is a paramag-
netic species, so the absence of line broadening in the proton
NMR spectrum of 9a also provides supporting evidence for
the presence of the metal ion in oxidation state III. A carbon-
13 NMR spectrum could not be obtained for 15a because of
its low solubility in organic solvents. For this reason, we
prepared a series of related silver(III) carbaporphyrins 15b-e
in 65-92% yield from the corresponding benzocarbapor-
phyrins 9b-e. The UV-vis spectra for 15c-e were virtually
identical to the spectrum obtained for 15a; however, diphen-
yl-substituted system 15b showed a slightly red-shifted Soret
band at 441 nm. The strongest Q band for 15b was also
relatively intense and shifted to a longer wavelength (566
nm for 15b compared to 555 nm for 15a). Although the
solubilities of 15b-e were somewhat improved compared
to those of 15a, only 15b gave a good-quality carbon-13
NMR spectrum. These data confirmed that the macrocycle
has a plane of symmetry and gives two resonances for the
meso carbons at 100.4 and 101.1 ppm. Unfortunately, it was
not possible to identify the resonance for the internal carbon
atom. The two silver isotopes both have spin values of I )
1/2; therefore, they might be expected to produce two doublets
for C21,30,48 but the solubility of 15b was still not sufficiently
improved to allow this signal to be observed. However, it
was possible to obtain X-ray-quality crystals of the diphen-
ylcarbaporphyrin complex, and these data confirmed that the
silver cation was present within the macrocyclic cavity. The
silver complex displays a strikingly planar conformation with
only a minor tilting of 5.09° for the indene unit relative to
the mean macrocyclic plane. Full details of this structural
characterization appeared in the preliminary communica-
tion.39
Figure 1. UV-vis spectrum of silver(III) benzocarbaporphyrin 15a in
chloroform.
Figure 2. Electron-impact mass spectum (70 eV) of silver(III) benzocar-
baporphyrin 15a, showing the classic silver isotope pattern for the molecular
ion at m/z 603 and 605.
Recently, we have obtained meso tetraarylbenzocarbapor-
phyrins 16 by oxidative ring contraction of the related meso
tetraarylazuliporphyrins.13,14 These new carbaporphyrins were
also investigated as potential organometallic ligands. The
reaction of 16a and 16b with silver(I) acetate afforded good
yields of the related silver(III) complexes 17a and 17b,
respectively. The best results for the meso substituted
carbaporphyrins were obtained by using pyridine as a solvent
for the metalation reactions. Following chromatography, the
pure silver complexes were obtained as orange powders in
80-97% yield. Both metallo carbaporphyrins were isolated
as fine powders, and it was not possible to obtain crystals
that would be suitable for structural analyses. The UV-vis
spectra for both complexes in chloroform were similar with
molecular ions at m/z 603 and 605 (Figure 2). High-resolution
MS data also confirmed that the molecular formula cor-
responded to C35H34N3Ag. Benzylic fragmentation results in
the loss of a methyl radical to give a smaller silver isotope
pattern at m/z 588 and 590. These results strongly imply that
the macrocycle is intact and that a silver(III) ion has replaced
the three internal carbaporphyrin protons. The proton NMR
spectrum for 15a in CDCl3 provides strong supporting
(47) The natural abundances for 107Ag and 109Ag are 51.82 and 48.18%,
respectively. For this reason, the MS isotope patterns for silver-
containing compounds are very similar to those observed for bromine
derivatives.
(48) Brevard, C.; Granger, P. Handbook of High-Resolution Multinuclear
NMR; Wiley: New York, 1981; pp 162-163.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5261

Lash et al.
Figure 3. (A) UV-vis spectrum of silver(III) tetrakis(4-chlorophenyl)-
carbaporphyrin 17b in chloroform. (B) UV-vis spectrum of the related
gold(III) complex 18b in chloroform.
Figure 4. (A) Proton NMR spectrum (400-MHz) of silver(III) tetrakis-
(4-chlorophenyl)-benzocarbaporphyrin 17b in CDCl3. The pyrrolic protons
near 8.7 ppm show some fine structure due to transannular coupling to the
silver nucleus. (B) Proton NMR spectrum (400-MHz) of the related gold-
(III) complex 18b in CDCl3.
a strong Soret band at 450 nm. A weaker band was observed
near 400 nm, and several Q-type bands are present at longer
wavelengths (Figure 3A). The proton NMR spectra for the
silver complexes were also consistent with the proposed
structures, although the tetraphenylcarbaporphyrin derivative
showed a considerable overlap of the aromatic resonances.
However, tetrakis(4-chlorophenyl)benzocarbaporphyrin com-
plex 17b gave a particularly well-resolved proton NMR
spectrum showing the presence of two sets of para disub-
stitution patterns for the aryl substituents between 7.7 and
8.1 ppm, whereas the benzo protons gave rise to two 2H
multiplets at 7.0 and 7.2 ppm (Figure 4A). The pyrrolic
protons produced a singlet that overlapped with an AB
quartet that showed additional fine structure near 8.7 ppm.
The fine structure associated with the pyrrolic AB quartet is
due to transannular coupling from the silver cation. The
spectroscopic data indicates that the macrocycle retains a
diatropic ring current that is similar to the free base
carbaporphyrins 16 and also confirms the presence of a plane
of symmetry. Although 17b was relatively insoluble and gave
only a noisy carbon-13 NMR spectrum, a good-quality
carbon-13 NMR spectrum could be obtained for 17a. This
showed the presence of the 20 carbon resonances, some of
which showed a small degree of long-range coupling from
the silver metal. However, as was the case for the meso
unsubstituted carbaporphyrin complexes 15, the internal
carbon could not be identified for this system. Silver
complexes 17 could not be analyzed by EI or FAB MS but
gave good results using field desorption mass spectrometry.
The formation of silver(III) complexes from silver(I)
acetate, irrespective of whether the reactions are performed
in the presence of air or under a nitrogen atmosphere,
deserves further comment. In all of these reactions, the
formation of a precipitate or film of metallic silver is always
observed. Although we initially speculated that an oxidative
elimination might be occurring,39 it has been suggested that
a disproportionation of three silver(I) cations to give two
Ag0 and one Ag3+ is involved in the formation of silver(III)
corroles (3Ag+ s> 2Ag0 + Ag3+),49 and it is probable that
this is the origin of the redox chemistry that occurs in our
studies as well.
Although some copper(III) N-confused porphyrin com-
plexes have been reported,37,38 to our knowledge no examples
(49) Bru¨ckner, C.; Barta, C. A.; Brin˜as, R. P.; Krause Bauer, J. A. Inorg.
Chem. 2003, 42, 1673-1680.
5262 Inorganic Chemistry, Vol. 43, No. 17, 2004

New Riches in Carbaporphyrin Chemistry
Scheme 2
ligands to take on similar conformations. Carbon-13 NMR
data was obtained for both gold complexes, but only the more
soluble tetraphenyl complex 18a gave a well-resolved
spectrum. In this case, the internal carbon could be identified
as a small resonance at 115.8 ppm. As was the case for silver
complexes 16, EI MS could not be obtained for the gold
derivatives. The tetraphenyl version 18a gave adequate FAB
MS data, but 18b could only be characterized using FD MS.
All four of the meso substituted complexes (16a, 16b, 18a,
and 18b) gave clean results by field desorption MS; the poor
results using other techniques appear to be due to decom-
position during the analyses.
Our attempts to obtain gold(III) complexes for meso
unsubstituted benzocarbaporphyrins were far less successful.
Trace amounts of metalated products were formed by
reacting carbaporphyrins 9 with Au(OAc)3, but these reac-
tions primarily led to the decomposition of the starting
material. Product 19 from the reaction of diphenylbenzo-
carbaporphyrin (9b) with gold(III) acetate was isolated as
an orange solid in <10% yield. The UV-vis and proton
NMR data for complex 19 were similar to that of the related
silver complexes 15, but the low yields obtained for the
chemistry prevented further investigations.
All of the silver and gold carbaporphyrins are nonpolar
compounds that give deep-orange-colored solutions. The
combined spectroscopic data strongly indicate that these
complexes must be silver(III) or gold(III) complexes because
these are diamagnetic systems that give well-resolved NMR
spectra. The Rf values for the derivatives confirm that the
metalated products are far less polar than corresponding free
base carbaporphyrins 9 and 16. In addition, the three interior
protons residing in the initial carbaporphyrin structures have
all been lost and replaced by a single metal ion. Although
the overall results cannot be adequately explained unless the
metal is in oxidation state III, we performed electrochemical
studies to provide further evidence for these assignments.
These studies were carried out on free base benzocarbapor-
phyrins 9b and 16a, together with related silver complexes
15b and 17a and gold derivative 18a. These specific samples
were primarily selected because of their superior solubility
characteristics.
The cyclic voltammograms for the free base carbapor-
phyrins were measured in dichloromethane under an inert
atmosphere. Starting at -0.10 V and scanning to -1.90 V,
tetraphenylcarbaporphyrin (16a) displays two quasi-reversible
cathodic waves at E1/2 ) -1.51 and -1.81 V (Figure 5a).
Switching potential experiments verified that the small
oxidative waves at -0.53 and -0.16 V are observed only
after accessing the waves at -1.51 and -1.81 V, respec-
tively. Scanning from -0.10 to +1.90 V, we observed five
oxidative waves at Ep,a ) 0.50 V, E1/2 ) 0.62 V, Ep,a ) 1.04
V, and E1/2 ) 1.07 and 1.80 V. Meso unsubstituted
carbaporphyrin 9b also displays two quasi-reversible cathodic
waves when the scan is initiated at 0.0 V, the resting
potential, and scanned in the negative direction. These waves
appear at E1/2 ) -1.58 and -1.88 V, and the small anodic
wave at Ep,a ) 0.72 V is observed only after accessing the
wave at -1.58 V. Five oxidative waves are observed between
of gold(III) derivatives have been described. The reaction
of 16a or 16b with gold(I) iodide in pyridine gave low yields
of the corresponding gold complexes 18, but much better
results could be obtained using gold(III) acetate as the
reagent. In this case, no change in the metal’s oxidation state
is required. Under optimized conditions using pyridine as a
solvent, we could isolate the gold complexes following
column chromatography in 67-83% yield. Again, the gold
derivatives were isolated as fine orange powders. The UV-
vis spectra for 18a and 18b were similar to those of the
corresponding silver derivatives, showing a strong Soret band
at 437 nm and several Q-type bands between 500 and 610
nm (Figure 3B). A medium-sized band just below 400 nm
is also observed in this case. The same absorption is actually
present for silver complexes 17 but is considerably weaker
for these derivatives. The proton NMR spectra for the gold
complexes are also similar to the corresponding silver(III)
derivatives. The best data was obtained for [tetrakis(4-
chlorophenyl)carbaporphyrinato]gold(III) complex (18b), this
confirms the presence of both a plane of symmetry and a
powerful diatropic ring current (Figure 4B). The aryl
substiutents gave rise to the expected signals between 7.7
and 8.1 ppm, whereas the benzo unit produced two 2H
multiplets at 6.9 and 7.1 ppm. The pyrrolic protons gave a
singlet at 8.74 ppm and two 2H doublets at 8.66 and 8.70
ppm (J ) 4.8 Hz). The aromatic character of the silver and
gold complexes appears to be very similar. This is reasonable
given that silver(III) and gold(III) have virtually the same
ionic radii,50 and they presumably allow the porphyrinoid
(50) The ionic radii for four-coordinate square-planar silver(III) and gold-
(III) are reported to be 0.67 and 0.68 Å, respectively. See Shannon,
R. D. Acta Crystallogr. A 1976, 32, 751-767.
Inorganic Chemistry, Vol. 43, No. 17, 2004 5263

Lash et al.
The electrochemical properties of metal complexes 15b,
17a, and 18a were also investigated using cyclic voltam-
metry. Silver complex 17a was scanned between the limits
of +1.90 and -1.90 V versus Ag/AgNO3 (Figure 5b). This
compound displays one reversible cathodic wave at E1/2
)
-1.14 V and three irreversible anodic waves at Ep,a ) 0.62,
1.41, and 1.70 V. Accessing these irreversible waves
generates numerous cathodic waves that are indicative of a
variety of decomposition products. Notably, the reductive
wave in 17a occurs at a potential that is between the first
oxidative and first reductive couples of free base carbapor-
phyrin 16a, indicating that this wave is metal based and not
carbaporphyrin based. Therefore, the wave is assigned to the
Ag(III/II) couple. Meso unsubstituted silver complex 15b
similarly shows a quasi-reversible reductive wave (E1/2
)
-1.24 V) between the first reductive wave (E1/2 ) -1.58
V) and the first oxidative wave (Ep,a ) 0.52 V) of free base
carbaporphyrin 9b, again suggesting that the silver ion is in
the Ag3+ oxidation state. However, the Ag(III/II) redox
couple for complex 17a is 100 mV more positive than that
of complex 15b.
Figure 5. Cyclic voltammograms (200 mV/s) of tetraphenylbenzocarba-
porphyrin 16a (a) and the related silver(III) (b, 17a) and gold(III) (c, 18a)
complexes in anhydrous dichloromethane, 0.2 M Bu4NBF4.
The cyclic voltammogram of gold complex 18a was
qualitatively similar to that of silver(III) carbaporphyrin
complexes 15b and 17a in that there is one reversible
reductive wave and five oxidative waves (Figure 5c). Starting
at -0.20 V and scanning in the negative direction, one
cathodic wave appears at E1/2 ) -1.65 V. Scanning in the
positive direction, we observed the following anodic
waves: E1/2 ) 0.69 and 1.18 V and Ep,a ) 1.32, 1.47, and
1.97 V. Gold(III) porphyrin complexes have long been
thought of as being electrochemically inert.51-53 However,
a recent electrochemical investigation of [5,10,15,20-tetrakis-
(3,5-di-tert-butylphenyl)porphyrinato]-gold(III) hexafluoro-
phosphate provided evidence to the contrary. Kadish, Cross-
ley, and co-workers demonstrated that this gold(III) porphyrin
complex can be electrochemically reduced to its gold(II)
analogue.54 Thus, the reductive wave observed in complex
18a could be the gold(III/II) couple. However, in contrast
to the silver carbaporphyrin complexes, it is difficult to
determine whether the first reductive couple of complex 18a
is metal based or ligand based. In the case of the silver
complexes, the first reductive wave appeared at a potential
that was between the first oxidative and first reductive wave
of the free base carbaporphyrin. However, this is not the
case for the reductive wave of 18a. This single cathodic wave
at E1/2 ) -1.65 V appears at a potential that is more negative
than the first reductive couple of the free base carbaporphyrin
(E1/2 ) -1.51 V). Additional experiments are needed to
determine the exact nature of this electrochemical reduction.
0.0 and 1.90 V. These waves occur at Ep,a ) 0.52 V,
E1/2 ) 0.76 V, Ep,a ) 1.10 V, and E1/2 ) 1.14 and 1.65 V.
The electrochemical properties displayed by 9b and 16a are
similar to those previously reported for 9a,4 in that two quasi-
reversible cathodic waves and five oxidative waves are
observed. The oxidative electrochemistry of these free base
carbaporphyrins is much more complex than that of free base
porphyrins, which typically display two reversible reductive
and two reversible oxidative couples. Focusing on the
cathodic waves of these carbaporphyrins, we found that there
is a noticeable shift in the potentials of the two reductive
couples on comparing the voltammograms of compounds
16a, 9a, and 9b. Both reductive couples of 9b are 70 mV
more cathodic than those of 16a. The reductive couples of
9a are also shifted in the same direction. However, the shifts
for 9a are much greater; that is, the first and second reductive
couples of 9a are 180 and 230 mV more cathodic than those
of 16a, respectively. Because of the quasi-reversible nature
of these waves, it is easier to compare ∆E1/2 values to
determine similarities and differences for these three different
carbaporphyrins. Specifically, we have looked at the differ-
ence between the two quasi-reversible reductive waves
(∆E1/2) as well as the difference between the first reductive
and first oxidative waves (HOMO-LUMO gap). Compounds
16a and 9b both have ∆E1/2 values of 0.30 V, whereas
compound 9a has a ∆E1/2 value of 0.35 V. These values are
all virtually identical to one another but slightly smaller than
those for free base porphyrins and metalloporphyrins, which
have a ∆E1/2 value of 0.42 ( 0.05 V. However, the HOMO-
(51) Antipas, A.; Dolphin, D.; Gouterman, M.; Johnson, E. C. J. Am. Chem.
Soc. 1978, 100, 0, 7705-7709.
(52) 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, CA, 2000; Vol. 8, pp 1-114.
ïx
LUMO gaps (∆E1/2 - ∆E1/2red) for compounds 16a, 9a,
and 9b are 2.02, 2.17, and 2.10 V, respectively. These are
(53) Jamin, M. E.; Iwamoto, R. T. Inorg. Chim. Acta 1978, 27, 135.
(54) Kadish, K. M.; E. W.; Ou, Z.; Shao, J.; Sintic, P. J.; Ohkubo, K.;
Fukuzumi, S.; Crossley, M. J. Chem. Commun. 2002, 356-357.
all comparable to the gap observed for porphyrins and
ïx
red
metalloporphyrins (∆E1/2 - ∆E1/2 ) 2.25 ( 0.15 V).
5264 Inorganic Chemistry, Vol. 43, No. 17, 2004

New Riches in Carbaporphyrin Chemistry
131.9, 132.9, 134.9, 135.1, 135.4, 136.4, 138.6, 140.2, 140.7;
HRMS: calcd for C43H34N3Ag: m/z 699.1787; found: 699.1803.
Anal. Calcd for C43H34N3Ag‚1/2CHCl3: C, 68.72; H, 4.57; N, 5.53.
Found: C, 68.96; H, 4.60; N, 5.62.
Conclusions
Benzocarbaporphyrins readily form silver(III) and gold-
(III) derivatives under mild conditions where the metal ion
is bound within the macrocyclic cavity and forms three
metal-nitrogen bonds and one metal-carbon bond. These
nonpolar diamagnetic complexes were characterized by
spectroscopic and mass spectrometric methods, and a silver-
(III) organometallic derivative was characterized by X-ray
crystallography.39 Electrochemical studies provide additional
support for the oxidation states of the metal ions. This study
demonstrates that carbaporphyrins can act as superior ligands
for the synthesis of organometallic derivatives involving
higher oxidation states that compare favorably with the
results reported for N-confused porphyrins.
[8,17-Di-tert-butyl-12,13-diethyl-7,18-dimethylbenzo[b]-21-
carbaporphyrinato]silver(III) (15c). A solution of di-tert-butyl-
benzocarbaporphyrin (9c) (12 mg) was reacted with silver(I) acetate
(12 mg) under the foregoing conditions. Following chromatography
on grade 3 alumina eluting with dichloromethane, the orange
product fraction was recrystallized from chloroform-methanol to
give the silver(III) complex (9.3 mg, 65%) as orange-red crystals,
mp > 300 °C; UV-vis (CHCl3): λmax (log ꢀ) 385 (4.40), 440 (4.97),
484 (3.67), 520 (3.96), 556 (4.39), 595 nm (3.78); 1H NMR
(CDCl3): δ 1.93 (6H, t, J ) 7.6 Hz), 2.43 (18H, s), 3.89 (6H, s),
4.05 (4H, q, J ) 7.6 Hz), 7.75-7.78 (2H, m), 8.87-8.90 (2H, m),
10.28 (2H, s), 10.67 (2H, s); 13C NMR (CDCl3): δ 15.6, 18.5,
20.2, 35.8, 37.2, 101.0, 102.4, 120.3, 122.0, 126.7, 132.2, 135.8,
136.1, 136.3, 140.2, 141.3, 145.1; FD MS: m/z (rel int) 663.1 (9.6),
662.1 (42), 661.1 (100), 660.0 (49), 659.1 (90, M+). Anal. Calcd
for C39H42N3Ag‚1/4CHCl3: C, 68.27; H, 6.17; N, 6.08. Found: C,
67.96; H, 6.51; N, 5.70.
Experimental Section
Carbaporphyrins 9a-c and 16a and b were prepared as described
previously.3,6,9,13,14 NMR spectra were obtained on a Varian Gemini
400-MHz NMR spectrometer and recorded in ppm relative to CDCl3
(residual chloroform at 7.26 ppm in proton NMR and CDCl3 triplet
at 77.23 ppm in carbon-13 NMR spectra). UV-vis spectra were
recorded on a Varian Cary UV spectrophotometer. EI 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.
[8,12,13,17-Tetraethyl-7,18-dimethylbenzo[b]-21-carbapor-
phyrinato]silver(III) (15a). A solution of benzocarbaporphyrin 9a
(12 mg) in dichloromethane (10 mL) was added to silver(I) acetate
(12 mg) dissolved in methanol (2.5 mL), and the mixture was stirred
at room temperature overnight. The mixture was washed with water,
and the solvent was removed under reduced pressure. The residue
was chromatographed on grade 3 alumina eluting with dichlo-
romethane. A deep red-orange fraction was collected and recrys-
tallized from chloroform-methanol to give the silver(III) complex
(12 mg, 83%) as red crystals, mp > 300 °C dec; UV-vis
(CHCl3): λmax (log ꢀ) 384 (4.44), 437 (5.00), 482 (3.76), 518 (3.98),
2,5-Bis(5-benzyloxycarbonyl-3-methyl-4-propyl-2-pyrrolyl-
methyl)-3,4-diethylpyrrole (14d). A stirred mixture of benzyl
5-acetoxymethyl-4-methyl-3-propylpyrrole-2-carboxylate (13c; 2.67
g) and 3,4-diethylpyrrole (12a; 0.50 g) in acetic acid (2 mL) and
ethanol (30 mL) was heated under reflux under a nitrogen
atmosphere for 16 h. The solution was cooled to room temperature
and further chilled in an ice bath. The resulting precipitate was
suction filtered, washed with cold ethanol, and dried in vacuo to
give the tripyrrane dibenzyl ester (1.96 g; 73%) as an off-white
1
powder, mp 180-181.5 °C; H NMR (400 MHz, CDCl3, 20 °C):
δ 0.79 (6H, t, J ) 7.4 Hz), 1.08 (6H, t, J ) 7.6 Hz), 1.39 (4H,
sextet), 1.89 (6H, s), 2.42 (4H, q, J ) 7.5 Hz), 2.61 (4H, t, J ) 7.6
Hz), 3.64 (4H, br s), 4.54 (4H, br s), 7.08-7.12 (4H, m), 7.21-
1
7.34 (6H, m), 8.53 (1H, br s), 10.42 (2H, br s); H NMR (400
MHz, CDCl3, 40 °C): δ 0.82 (6H, t, J ) 7.2 Hz), 1.08 (6H, t, J )
7.4 Hz), 1.43 (4H, sextet), 1.89 (6H, s), 2.42 (4H, q, J ) 7.5 Hz),
2.61 (4H, t, J ) 7.6 Hz), 3.69 (4H, s), 4.77 (4H, br s), 7.17-7.21
(4H, m), 7.25-7.31 (6H, m), 8.04 (1H, br s), 9.75 (2H, br s); 13C
NMR (CDCl3): δ 9.0, 14.4, 16.9, 17.9, 22.5, 24.5, 27.9, 65.8, 116.2,
117.0, 119.4, 122.3, 127.3, 127.5, 128.3, 132.4, 133.1, 136.9, 162.7.
Anal. Calcd for C42H57N3O4: C, 78.95; H, 6.49; N, 5.76. Found:
C, 78.98; H, 6.43; N, 5.89.
2,5-Bis(5-benzyloxycarbonyl-4-isobutyl-3-methyl-2-pyrrolyl-
methyl)-3,4-diethylpyrrole (14e). Benzyl 5-acetoxymethyl-4-meth-
yl-3-isobutylpyrrole-2-carboxylate (13d; 1.39 g) was reacted with
12a (0.25 g) under the foregoing conditions. The tripyrrane (0.84
g, 60%) was isolated as a pink powder, mp 171.5-173 °C; 1H NMR
(400 MHz, CDCl3, 20 °C): δ 0.72 (12H, d, J ) 6.4 Hz), 1.04 (6H,
t, J ) 7.6 Hz), 1.65-1.76 (2H, m), 1.88 (6H, s), 2.40 (4H, q, J )
7.5 Hz), 2.47 (4H, br d, J ) 6 Hz), 3.67 (4H, s), 4.49 (4H, br s),
7.08-7.11 (4H, m), 7.21-7.30 (6H, m), 8.66 (1H, br s), 10.57 (2H,
br s); 13C NMR (CDCl3): δ 9.4, 16.4, 16.7, 17.9, 22.6, 22.9, 30.4,
34.5, 65.9, 117.0, 117.4, 120.3, 122.0, 127.9, 128.1, 128.4, 131.9,
132.4, 136.7, 162.4. Anal. Calcd for C44H55N3O4: C, 76.60; H,
8.03; N, 6.09. Found: C, 76.21; H, 7.87; N, 6.15.
1
555 (4.46), 593 (3.70); H NMR (CDCl3): δ 1.85 (6H, t, J ) 7.6
Hz), 1.90 (6H, t, J ) 7.6 Hz), 3.57(6H, s), 4.03 (8H, q, J ) 7.4
Hz), 7.78 (2H, m), 8.84 (2H, m), 9.89 (2H, s), 10.06 (2H, s). HRMS
(EI): calcd for C35H34N3Ag: m/z 603.1803; found: 603.1803. Anal.
Calcd for C35H34N3Ag: C, 69.54; H, 5.63; N, 6.95. Found: C,
69.02; H, 5.72; N, 6.91.
[8,17-Diethyl-7,18-dimethyl-12,13-diphenylbenzo[b]-21-car-
baporphyrinato]silver(III) (15b). A solution of diphenylbenzo-
carbaporphyrin 9b (12 mg) in dichloromethane (10 mL) was added
to silver(I) acetate (12 mg) dissolved in methanol (2.5 mL), and
the mixture was stirred at room temperature overnight. The mixture
was washed with water, and the solvent was removed under reduced
pressure. The residue was chromatographed on grade 3 alumina
eluting with dichloromethane. A deep red-orange fraction was
collected and recrystallized from chloroform-methanol to give the
silver(III) complex (13 mg, 92%) as red crystals, mp > 300 °C;
UV-vis (CHCl3): λmax (log ꢀ) 380 (4.40), 393 (4.43), 441 (5.11),
12,13-Diethyl-7,18-dimethyl-8,17-dipropylbenzo[b]-21-car-
baporphyrin (9d). Tripyrrane dibenzyl ester 14d (1.50 g) was
dissolved in freshly distilled THF (225 mL) in a hydrogenation
vessel, methanol (75 mL) and triethylamine (20 drops) were added,
and the air was flushed out with a stream of nitrogen. Palladium-
charcoal (10%; 200 mg) was added, and the resulting mixture was
shaken under a hydrogen atmosphere at 40 psi overnight. The
1
529 (3.98), 566 nm (4.63); H NMR (CDCl3): δ 1.70 (6H, t, J )
7.5 Hz), 3.24 (6H, s), 3.73 (4H, q, J ) 7.5 Hz), 7.61 (2H, m), 7.66
(2H, t, J ) 7.4 Hz), 7.76 (4H, t, J ) 7.4 Hz), 8.05 (4H, d, J ) 6.8
Hz), 8.32 (2H, m), 9.22 (2H, s), 9.82 (2H, s); 13C NMR (CDCl3):
δ 11.4, 17.3, 20.2, 100.4, 101.1, 119.7, 121.2, 126.4, 127.4, 128.8,
Inorganic Chemistry, Vol. 43, No. 17, 2004 5265

Lash et al.
catalyst was filtered off, and the solvent was removed under reduced
pressure. The resulting residue was taken up in 3% aqueous
ammonia and neutralized with acetic acid 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 drying overnight in vacuo, the dicarboxylic
acid 24b (1.07 g; 98%) 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 (36 mg) was immediately added, and the solution
stirred in the dark under N2 for an additional 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
was removed under reduced pressure. The residue was chromato-
graphed on grade 3 alumina eluting with dichloromethane, and the
product was collected as a brown band. Recrystallization from
chloroform-methanol gave the dipropylcarbaporphyrin (57 mg;
52%) as fluffy copper-bronze crystals, mp > 300 °C; UV-vis
(1% Et3N-CHCl3): λmax (log ꢀ) 376 (4.62), 425 (5.23), 511 (4.25),
545 (4.18), 603 (3.80), 662 nm (3.37); UV-vis (0.05% TFA-CHCl3;
monocation): λmax (log ꢀ) 401 (4.75), 439 (5.00), 474 (4.51), 548
(4.09), 586 (3.94), 612 nm (3.93); UV-vis (50% TFA-CHCl3):
mg, 46%) as reddish-purple crystals, mp > 300 °C; UV-vis (1%
Et3N-CHCl3): λmax (log ꢀ) 377 (4.60), 425 (5.17), 511 (4.25), 545
(4.15), 603 (3.80), 663 nm (3.41); UV-vis (0.05% TFA-CHCl3;
monocation): λmax (log ꢀ) 395 (4.41), 440 (4.95), 474 (4.48), 549
(4.08), 588 (3.94), 610 nm (3.93); UV-vis (50% TFA-CHCl3):
1
λmax (log ꢀ) 345 (4.53), 425 (5.17), 614 (3.94), 669 nm (4.37); H
NMR (400 MHz, CDCl3): δ -6.79 (1H, s), -4.08 (2H, br s), 1.27
(12H, d, J ) 6.4 Hz), 1.85 (6H, t, J ) 7.8 Hz), 2.66 (2H, m), 3.56
(6H, s), 3.89-3.97 (8H, m), 7.73-7.77 (2H, m), 8.80-8.83 (2H,
m), 9.75 (2H, s), 10.03 (2H, s);1H NMR (400 MHz, trace TFA-
CDCl3; monocation): δ -6.73 (1H, s), -4.25 (1H, br s), -2.85
(2H, br s), 1.16 (12H, d, J ) 6.8 Hz), 1.87 (6H, t, J ) 7.6 Hz),
2.48 (2H, m), 3.56 (6H, s), 3.91 (4H, d, J ) 7.6 Hz), 4.10 (4H, q,
J ) 7.6 Hz), 7.71-7.74 (2H, m), 8.67-8.70 (2H, m), 10.04 (2H,
s), 10.28 (2H, s);1H NMR (400 MHz, 50% TFA-CDCl3; di-
cation): δ -5.05 (2H, s), -1.33 (3H, br s), 1.28 (12H, d, J ) 6.8
Hz), 1.73 (6H, t, J ) 7.8 Hz), 2.59 (2H, m), 3.58 (6H, s), 3.91
(4H, d, J ) 7.2 Hz), 4.06 (4H, q, J ) 7.6 Hz), 8.95-8.98 (2H, m),
10.13-10.16 (2H, m), 10.49 (2H, s), 11.03 (2H, s);13C NMR
(CDCl3): δ 11.8, 18.7, 20.1, 23.5, 32.3, 35.8, 95.6, 99.1, 109.3,
120.6, 126.6, 131.7, 133.7, 135.5, 136.2, 137.2, 141.4, 144.4, 152.8;
13C NMR (CDCl3, trace TFA-CDCl3; monocation): δ 12.2, 17.8,
19.9, 23.3, 32.1, 35.9, 94.7, 104.9, 119.8, 121.5, 128.1, 134.8, 137.0,
137.4, 138.3, 139.1, 141.1, 141.5, 142.2; 13C NMR (CDCl3, 50%
TFA-CDCl3; dication): δ 12.1, 17.3, 20.2, 22.8, 32.4, 33.1, 35.8,
108.4, 125.0, 134.8, 140.2, 140.6, 142.4, 145.3, 145.9, 146.7, 151.4,
151.7; HRMS (EI): calcd for C39H45N3, 555.3613; found, 555.3619.
Anal. Calcd for C39H45N3.0.6CHCl3: C, 75.81; H, 7.46; N, 6.70.
Found: C, 75.96; H, 7.42; N, 6.71.
1
λmax (log ꢀ) 344 (4.56), 425 (5.24), 615 (3.92), 668 nm (4.42); H
NMR (400 MHz, CDCl3): δ -6.84 (1H, s), -4.07 (2H, br s), 1.29
(6H, t, J ) 7.4 Hz), 1.85 (6H, t, J ) 7.6 Hz), 2.29 (4H, sextet),
3.56 (6H, s), 3.93 (4H, q, J ) 7.6 Hz), 4.01 (4H, t, J ) 7.8 Hz),
7.74-7.77 (2H, m), 8.81-8.84 (2H, m), 9.73 (2H, s), 10.04 (2H,
s);1H NMR (400 MHz, trace TFA-CDCl3; monocation): δ -6.76
(1H, s), -4.52 (1H, br s), -3.09 (2H, br s), 1.19 (6H, t, J ) 7.4
Hz), 1.86 (6H, t, J ) 7.8 Hz), 2.13 (4H, sextet), 3.55 (6H, s), 4.01
(4H, t, J ) 7.4 Hz), 4.10 (4H, q, J ) 7.7 Hz), 7.71-7.74 (2H, m),
8.68-8.71 (2H, m), 10.04 (2H, s), 10.29 (2H, s);1H NMR (400
MHz, 50% TFA-CDCl3; dication): δ -5.06 (2H, s), -1.40 (3H,
br s), 1.34 (6H, t, J ) 7.4 Hz), 1.76 (6H, t, J ) 7.6 Hz), 2.28 (4H,
sextet), 3.60 (6H, s), 4.04 (4H, t, J ) 8 Hz), 4.09 (4H, t, J ) 7.8
Hz), 8.96-9.00 (2H, m), 10.17-10.20 (2H, m), 10.54 (2H, s), 11.10
(2H, s); 13C NMR (CDCl3): δ 11.5, 14.7, 18.7, 20.1, 26.2, 28.6,
95.5, 98.8, 109.4, 120.6, 126.5, 131.2, 133.8, 135.1, 136.3, 137.9,
141.5, 144.4, 152.8; 13C NMR (CDCl3, trace TFA-CDCl3; mono-
cation): δ 11.9, 14.6, 17.7, 19.9, 25.8, 28.7, 94.5, 104.6, 119.6,
121.5, 128.1, 134.5, 137.0, 137.6, 138.4, 140.0, 141.1, 141.2, 142.1;
HRMS (EI): calcd for C37H41N3, 527.3300; found: 527.3292. Anal.
Calcd for C37H41N3‚1/20CHCl3: C, 83.38; H, 7.75; N, 7.87. Found:
C, 83.35; H, 7.76; N, 7.92.
[12,13-Diethyl-7,18-dimethyl-8,17-dipropylbenzo[b]-21-car-
baporphyrinato]silver(III) (15d). A solution of dipropylbenzo-
carbaporphyrin (9d) (12 mg) was reacted with silver(I) acetate under
the conditions used to prepare 9a. Following chromatography on
grade 3 alumina eluting with dichloromethane, the orange product
fraction was recrystallized from chloroform-methanol to give the
silver(III) complex (10.7 mg, 75%) as orange-red crystals, mp >
300 °C; UV-vis (CHCl3): λmax (log ꢀ) 383 (4.42), 437 (4.98), 483
1
(3.71), 518 (3.94), 555 (4.43), 594 nm (3.62); H NMR (CDCl3):
δ 1.33 (6H, t, J ) 7.4 Hz), 1.90 (6H, t, J ) 7.6 Hz), 2.29-2.37
(4H, m), 3.63 (6H, s), 4.00-4.08 (8H, overlapping t and q), 7.79-
7.82 (2H, m), 8.92-8.95 (2H, m), 10.00 (2H, s), 10.22 (2H, s);
HRMS (EI): calcd for C37H38N3Ag, 631.2117; found, 631.2107.
Anal. Calcd for C37H38N3Ag‚1/8CHCl3: C, 68.63; H, 5.93; N, 6.49.
Found: C, 68.61; H, 5.90; N, 6.36.
[12,13-Diethyl-8,17-diisobutyl-7,18-dimethyl-benzo[b]-21-car-
baporphyrinato]silver(III) (15e). The silver complex was prepared
from 9e (12 mg) by the procedure reported above. Recrystallization
from chloroform-methanol gave the silver(III) complex (11.9 mg,
83%) as orange-red crystals, mp > 300 °C; UV-vis (CHCl3):
λmax (log ꢀ) 384 (4.47), 438 (5.03), 483 (3.77), 519 (4.01), 555
(4.49), 594 nm (3.72); 1H NMR (CDCl3): δ 1.30 (12H, d, J ) 6.4
Hz), 1.89 (6H, t, J ) 7.4 Hz), 2.63-2.73 (2H, m), 3.58 (6H, s),
3.89 (4H, d, J ) 7.2 Hz), 4.01 (4H, q, J ) 7.4 Hz), 7.79-7.82
(2H, m), 8.88-8.91 (2H, m), 9.94 (2H, s), 10.13 (2H, s); FD MS:
m/z (rel int) 663.1 (9.8), 662.0 (40), 661.0 (100, M+), 660.0 (43),
659.0 (99, M+). Anal. Calcd for C39H42N3Ag: C, 70.90; H, 6.41;
N, 6.36. Found: C, 70.72; H, 6.11; N, 6.09.
12,13-Diethyl-8,17-diisobutyl-7,18-dimethyl-benzo[b]-21-car-
baporphyrin (9e). Tripyrrane dibenzyl ester (14e) (200 mg) was
hydrogenolysed by the procedure described above to give the
corresponding dicarboxylic acid 10e (145 mg, quantitative) as a
pink powder. Tripyrrane 10e (100 mg) was stirred with TFA (2
mL) in a pear-shaped flask for 2 min under nitrogen, the solution
was diluted with dichloromethane (200 mL), and diformylindene
(33.8 mg) was immediately added. The resulting solution was stirred
in the dark under N2 for an additional 16 h. The mixture was
neutralized by the dropwise addition of triethylamine, DDQ (46
mg) was added, and the resulting solution was stirred for an
additional 30 min. The mixure was washed with water, and the
solvent was removed under reduced pressure. The residue was
chromatographed on grade 3 alumina eluting with dichloromethane,
and the product was collected as a brown band. Recrystallization
from chloroform-methanol gave the diisobutylcarbaporphyrin (50
[5,10,15,20-Tetraphenylbenzo[b]-21-carbaporphyrinato]silver-
(III) (17a). Nitrogen was bubbled through a solution of tetraphen-
ylbenzocarbaporphyrin (16a) (14.8 mg, 0.0223 mmol) in pyridine
(15 mL) for 10 min. Silver acetate (17.4 mg, 0.104 mmol) was
added, and the resulting mixture was stirred under nitrogen for 24
h. The solution was diluted with chloroform, washed with water,
5266 Inorganic Chemistry, Vol. 43, No. 17, 2004

New Riches in Carbaporphyrin Chemistry
the organic layer dried over sodium sulfate, and the solvent removed
under reduced pressure. The residue was chromatographed on a
silica column eluting with 20% hexanes-dichloromethane, and the
metalated product was collected as an orange band. Evaporation
of the solvent under reduced pressure gave 17a (13.7 mg, 0.0178
mmol, 80%) as an orange powder, mp > 350 °C; UV-vis
(CHCl3): λmax (log ꢀ) 396 (4.57), 450 (5.29), 525 (4.31), 566 (4.09),
mg, 0.0749 mmol) in pyridine (15 mL). Following chromatography
on silica eluting with 20% hexanes-dichloromethane, we isolated
gold(III) derivative 18b (16.7 mg, 0.0168 mmol, 83%) as an orange
powder, mp > 350 °C; UV-vis (CHCl3): λmax (log ꢀ) 397 (4.81),
439 (5.14), 520 (4.31), 563 (4.09), 612 nm (3.00); 1H NMR
(CDCl3): δ 6.86-6.90 (2H, AA′XX′ system), 7.05-7.08 (2H,
AA′XX′ system), 7.74 (4H), 7.76 (4H), 7.95 (4H), 8.05 (4H), 8.66
(2H, d, J ) 4.8 Hz), 8.70 (2H, 2H, d, J ) 4.8 Hz), 8.74 (2H, s);
13C NMR (CDCl3): δ 119.1, 124.9, 125.0, 126.6, 125.5, 127.7,
127.8, 128.1, 128.4, 129.5, 133.7, 135.0, 135.1, 136.2, 138.3, 140.2,
141.3, 143.5; FD MS: m/z (% rel int) 999.1 (15), 998.1 (28), 997.1
(60), 996.2 (47), 995.2 (100), 994.1 (39), 993.2 (66).
1
610 nm (3.19); H NMR (CDCl3): δ 6.91-6.94 (2H, AA′XX′
system), 7.08-7.11 (2H, AA′XX′ system), 7.71-7.86 (12H, m),
8.06-8.09 (4H, m), 8.14-8.18 (4H, m), 8.69-8.73 (6H, m); 13C
NMR (CDCl3): δ 120.8, 123.1, 125.1, 125.2, 126.3, 127.2, 127.9,
128.1, 128.2, 128.3, 129.1, 129.7, 132.8, 134.2, 138.5, 138.6, 139.7,
141.9, 142.4, 142.9; FD MS: m/z (rel int) 771.1 (12), 770.2 (50),
769.2 (100), 768.2 (49), 767 (93).
[8,17-Diethyl-7,18-dimethyl-12,13-diphenylbenzo[b]-21-car-
baporphyrinato]gold(III) (19). The reaction of diphenylbenzo-
carbaporphyrin 9b (10 mg) with gold(III) acetate (7 mg) under the
foregoing conditions afforded the gold complex (0.9 mg, 7%) as
an orange solid, mp > 300 °C; UV-vis CHCl3): λmax (rel int) 375
(0.41), 390 (0.45), 430 (1.00), 452 (0.39), 524 (0.13), 560 (0.41),
[5,10,15,20-Tetrakis(4-chlorophenyl)benzo[b]-21-carbapor-
phyrinato]silver(III) (17b). Using the foregoing procedure, 16b
(15.0 mg, 0.0188 mmol) was reacted with silver(I) acetate (22 mg,
0.132 mmol)) in pyridine (15 mL). Following chromatography on
silica eluting with 20% hexanes-dichloromethane, we isolated the
metalated product 17b (16.4 mg, 0.0181 mmol, 97%) as an orange
powder, mp > 350 °C; UV-vis (CHCl3): λmax (log ꢀ) 398 (4.57),
451 (5.25), 526 (4.29), 566 (4.07), 614 nm (3.12); 1H NMR
(CDCl3): δ 6.98-7.02 (2H, AA′XX′ system), 7.14-7.17 (2H,
AA′XX′ system), 7.74 (4H), 7.77 (4H), 7.99 (4H), 8.07 (4H), 8.66
1
594 nm (0.01); H NMR (CDCl3): δ 1.74 (6H, t, J ) 7.6 Hz),
3.47 (6H, s), 3.86 (4H, q, J ) 7.6 Hz), 7.62-7.75 (8H, m), 8.03
(4H, d, J ) 7 Hz), 8.62-8.65 (2H, m), 9.90 (2H, s), 9.96 (2H, s);
HRMS (FAB): calcd for C43H34N3Au, 789.2418; found, 789.2416.
Cyclic Voltammetry. The electrochemical studies were carried
out in anhydrous dichloromethane using a BAS CV-27 potentiostat
equipped with an x-y recorder or a BAS CV-50W. A conventional
three-electrode cell consisting of a platinum disk working 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 +1.7 to -1.9 V
versus Ag/AgNO3, and the ferrocene/ferrocenium couple appeared
at +0.22 V versus the Ag/AgNO3 reference. All potentials are
reported versus the Ag/AgNO3 reference electrode.
3
4
(2H, dd, JHH ) 5 Hz, JAgH ) 1.6 Hz), 8.69-8.71 (4H, s
overlapping with dd); 13C NMR (CDCl3): δ 119.7, 122.1, 123.3,
123.8, 125.2, 126.7, 127.6, 128.3, 128.4, 129.2, 129.8, 134.0, 134.9,
135.0, 135.2, 138.6, 139.7, 140.6, 141.2, 141.7; FD MS: m/z (rel
int) 911, 910, 909, 908, 907, 907, 906, 905 (100), 904, 903.
[5,10,15,20-Tetraphenylbenzo[b]-21-carbaporphyrinato]gold-
(III) (18a). Using the foregoing conditions, 16a (15.4 mg, 0.0232
mmol) was reacted with gold(III) acetate (33.0 mg, 0.0882 mmol))
in pyridine (15 mL). Following chromatography on silica eluting
with 20% hexane-dichloromethane, we obtained gold(III) complex
18a (13.4 mg, 0.0156 mmol, 67%) as an orange powder, mp >
350 °C; UV-vis (CHCl3): λmax (log ꢀ) 395 (4.76), 437 (5.14), 519
Acknowledgment. This material is based upon work
supported by the National Science Foundation under grant
nos. CHE-0134472 (to T.D.L.) and CHE-0239805 (to L.F.S.),
and the donors of the Petroleum Research Fund, administered
by the American Chemical Society. D.A.C. received ad-
ditional funding from the Barry M. Goldwater Foundation,
the Johnson and Johnson Travel Award Program, and Pfizer
Incorporated.
1
(4.28), 561 (4.07), 608 nm (3.03); H NMR (CDCl3): δ 6.81-
6.85 (2H, AA′XX′ system), 7.00-7.04 (2H, AA′XX′ system),
7.72-7.82 (12H, m), 8.04-8.07 (4H, m), 8.12-8.15 (4H, m),
8.69-8.73 (4H, AB quartet, J ) 5 Hz), 8.75 (2H, s); 13C NMR
(CDCl3): δ 115.8, 120.2, 125.0, 126.1, 126.2, 127.2, 127.3, 127.7,
127.9, 128.1, 128.2, 128.3, 129.4, 132.6, 134.1, 136.3, 137.8, 138.3,
142.0, 143.1, 143.7; FD MS: m/z (% rel int) 859, 858, 857 (100);
HRMS (FAB): calcd for C49H30N3Au + H, 858.2183; found,
858.2182.
1
Supporting Information Available: UV-vis, H NMR, 13C
NMR, and mass spectra for selected compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
[5,10,15,20-Tetrakis(4-chlorophenyl)benzo[b]-21-carbapor-
phyrinato]gold(III) (18b). Using the foregoing procedure, 16a
(16.1 mg, 0.0201 mmol) was reacted with gold(III) acetate (28.0
IC0400540
Inorganic Chemistry, Vol. 43, No. 17, 2004 5267