New methodologies for the preparation of porphodimethenes and their conversion to trans-porphyrins with functionalized naphthyl spacers

Article abstract of DOI:10.1021/jo010163l

The MacDonald [2 + 2]-type condensation of readily available 5-aryl-substituted dipyrromethanes with acenaphthenequinone leads to the trans-syn- and anti-porphodimethenes, which in turn can be converted to the α,α- and α,β-porphyrin atropisomers, respectively. Treatment of the metalated or unmetalated porphodimethenes with KOH or NaOMe in THF followed by protonation with HCl results in a ring opening of the acenaphthenone and formation of the trans-8-carboxynaphthylporphyrins or their esters (NaOMe) after oxidation. Alternatively, the porphyrin formation can be accomplished by reaction of the porphodimethenes with acids in the presence of water or methanol. Reaction with NaBH₄ in a THF-methanol mixture yields the corresponding dialcohols in nearly quantitative yields. Sixteen different building blocks were prepared in order to evaluate the generality of this new synthetic approach, with Ar = 2,4,6-Me₃C₆H₂; 2,6-Cl₂C₆H₃; 2,6-F₂C₆H₃; 3,4-tBu₂C₆H₃; 3,4,5-(MeO)₃C₆H₂; 4-BrC₆H₄; 4-MeC₆H₄; and 4-MeOOCC₆H₄ at the meso positions. The synthesized porphodimethenes and porphyrins have been fully characterized, and the X-ray structure analyses of three representative derivatives are presented.

Full text of DOI:10.1021/jo010163l

5374
J . Org. Chem. 2001, 66, 5374-5383
New Meth od ologies for th e P r ep a r a tion of P or p h od im eth en es a n d
Th eir Con ver sion to tr a n s-P or p h yr in s w ith F u n ction a lized
Na p h th yl Sp a cer s
Michael Harmjanz, Hubert S. Gill, and Michael J . Scott*
Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200
mjscott@chem.ufl.edu
Received February 12, 2001
The MacDonald [2 + 2]-type condensation of readily available 5-aryl-substituted dipyrromethanes
with acenaphthenequinone leads to the trans-syn- and anti-porphodimethenes, which in turn can
be converted to the R,R- and R,â-porphyrin atropisomers, respectively. Treatment of the metalated
or unmetalated porphodimethenes with KOH or NaOMe in THF followed by protonation with HCl
results in a ring opening of the acenaphthenone and formation of the trans-8-carboxynaphthylpor-
phyrins or their esters (NaOMe) after oxidation. Alternatively, the porphyrin formation can be
accomplished by reaction of the porphodimethenes with acids in the presence of water or methanol.
Reaction with NaBH4 in a THF-methanol mixture yields the corresponding dialcohols in nearly
quantitative yields. Sixteen different building blocks were prepared in order to evaluate the
generality of this new synthetic approach, with Ar ) 2,4,6-Me3C6H2; 2,6-Cl2C6H3; 2,6-F2C6H3; 3,4-
tBu2C6H3; 3,4,5-(MeO)3C6H2; 4-BrC6H4; 4-MeC6H4; and 4-MeOOCC6H4 at the meso positions. The
synthesized porphodimethenes and porphyrins have been fully characterized, and the X-ray
structure analyses of three representative derivatives are presented.
In tr od u ction
precursors for the synthesis of molecular receptors4 and
for the design of dinuclear complexes.5 In the latter case,
a chelating ligand was bound to the rigid aromatic
system, which provides an additional coordination site
in a predetermined geometry.
The incorporation of a symmetrically or asymmetrically
functionalized linker into the porphyrin backbone is
among the most important steps in these synthetic
approaches. In general, multistep procedures are re-
quired, and in order to vary the type or position of the
functional group at the aromatic spacer, new synthetic
strategies must be developed. So far, no general concept
has been devised to allow for the facile synthesis of
porphyrins bearing rigid aromatic spacers with diverse
functional groups. The ability to anchor various groups
on these rigid spacers offers many exciting opportunities
for engineering porphyrin platforms.
Because of the proximity of the functional groups to
the macrocyclic ring, porphyrins joined at the 1-position
of an 8-substituted naphthalene spacer can be regarded
as superior precursors for the design of artificial molec-
ular receptors, sophisticated oxidation catalysts, or mod-
els for biological porphyrin-based enzymes. While por-
phyrins containing a single 8-functionalized naphthalene
have been prepared and utilized for diverse purposes
including molecular recognition and examination of
electronic porphyrin-quinone interactions,6 we have
recently demonstrated the utility of trans-R,R- and R,â-
Over the past two decades, the preparation of meso-
substituted porphyrins with rigid anthracene, biphe-
nylene, or naphthalene spacers has attracted much
attention, since they provide a useful platform to intro-
duce various functional groups with precise locations and
orientations near the porphyrin backbone. These building
blocks have widely been used to determine the distance
dependence of photoinduced electron-transfer reactions,1
to prepare and examine cofacial diporphyrins,2 and to
synthesize bridged porphyrins with well-defined separa-
tions and varying relative arrangements of the porphyrin
rings.3 In addition, porphyrins with functionalized an-
thracene or naphthalene groups have been used as
* Corresponding author fax: 352-392-3255.
(1) (a) Staab, H. A.; Kratzer, B.; Quazzotti, S. Eur. J . Org. Chem.
1998, 2149, 9. (b) Staab, H. A.; Hauck, R.; Popp, B. Eur. J . Org. Chem.
1998, 631, 1. (c) Staab, H. A.; Feurer, A.; Krieger, C.; Kumar, A. S.
Liebigs Ann. Chem. 1997, 2321. (d) Staab, H. A.; Feurer, A.; Hauck,
R. Angew. Chem., Int. Ed. Engl. 1994, 33, 2428.
(2) For example: (a) Ward, B.; Wang, C.-B.; Chang, C. K. J . Am.
Chem. Soc. 1981, 103, 5236. (b) Chang, C. K.; Abdalmuhdi, I. J . Org.
Chem. 1983, 48, 5388. (c) Collman, J . P.; Bencosme, C. S.; Durand, R.
R.; Kreh, R. P.; Anson, F. C. J . Am. Chem. Soc. 1983, 105, 2699. (d)
Chang, C. K.; Abdalmuhdi, I. Angew. Chem., Int. Ed. Engl. 1984, 23,
164. (e) Chang, C. K.; Liu, H. Y.; Abdalmuhdi, I. J . Am. Chem. Soc.
1984, 106, 2725. (f) Eaton, S. S.; Eaton, G. R.; Chang, C. K. J . Am.
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K.; Anson, F. C. J . Phys. Chem. 1985, 89, 665. (h) Fillers, J . P.;
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112, 8206. (m) Naruta, Y.; Maruyama, K. J . Am. Chem. Soc. 1991,
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10.1021/jo010163l CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/07/2001

Preparation and Conversion of Porphodimethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5375
Sch em e 1. Attem p ted F or m a tion of P or p h yr in s
by Rea ction of 5-Mesityld ip yr r om eth a n e w ith
1,8-Na p h th a ld eh yd ic Acid
8-carboxynaphthylporphyrins bearing two 8-functional-
ized naphthyl moieties.8,11,17 These simple molecules have
the potential to be useful building blocks for numerous
applications, including the preparation of heteronuclear
porphyrin arrays and the development of redox-switch-
able tetrapyrrolic macrocycles.
Given the lack of any suitable procedure, we developed
a general two-step synthesis for the preparation of the
desired porphyrins, and in addition to allowing for the
incorporation of a range of groups on the naphthalene
spacer, the steric and the electronic attributes of the
aromatic substituents at the meso position of the mac-
rocycle can be readily adjusted utilizing this simple
methodology. In sharp contrast to traditional pathways
for the preparation of porphyrins, we initially prepared
and isolated the spiro tricyclic-type porphodimethenes
by acid-catalyzed condensation of commercially available
acenaphthenequinone and readily available 5-aryldipyr-
romethanes. Ring opening and subsequent porphyrin
formation can be induced by either strong bases (KOH,
NaOMe), NaBH4, or acids (H2SO4, TFA). Herein, we
report the details of this synthetic strategy for the
preparation of novel building blocks and discuss the
structural and the spectroscopic properties of both the
porphodimethene precursors and the corresponding por-
phyrins.
Sch em e 2. P r ep a r a tion of th e
5-Acen a p h th en on e-Su bstitu ted Dip yr r om eth a n e 1
a n d Its Rin g Op en in g
Resu lts a n d Discu ssion
Following the [2 + 2] procedures introduced by Lindsey
et al.,7 attempts to react 1,8-naphthalaldehydic acid with
5-aryldipyrromethanes failed to yield the corresponding
porphyrins (Scheme 1). The inactivity of this naphthalene
derivative toward acid-catalyzed porphyrin formation
could possibly be attributed to the strong polar interac-
tions of the adjacent acid function, resulting in a reduced
electrophilicity of the aldehyde group, although this issue
has not been fully explored with other 1-naphthalde-
hydes. Even though formation of the tetrapyrrolic por-
phyrin precursors might be achieved under other condi-
tions, the required oxidation of the porphyrinogens
initially formed in the reaction with oxidants such as
DDQ will likely cause degradation of the macrocycle.8
As demonstrated by Chang and co-workers, acenaph-
thenequinone will condense with 2 equiv of 2-(ethyloxy-
carbonyl)-3-ethyl-4-methylpyrrole to yield the correspond-
ing dipyrromethane, and refluxing the product in 30%
KOH induces the opening of the acenaphthene ring.5a
Following this approach, we reacted acenaphthenequino-
ne with an excess of pyrrole and isolated the â-unsub-
stituted dipyrromethane bearing a 1-acenaphthenone
moiety at the 5-position (Scheme 2). With this precursor,
we reasoned a [2 + 2] condensation with excess aldehyde
might yield a mixture of porphodimethenes (syn and anti)
that could then be converted to the desired porphyrins
following ring opening and oxidation. In comparison to
the acenaphthenone dipyrromethane (1), the predilection
to form the aromatic porphyrin macrocycle should facili-
tate the ring-opening reaction for the porphodimethenes.
Unfortunately, attempts to react the acenaphthenone-
substituted dipyrromethane with various aromatic alde-
hydes resulted in the formation of complicated mixtures
of products, and the desired porphodimethenes were only
obtained as minor products. To overcome this difficulty,
the dipyrromethane (1) precursor was refluxed in 1-pro-
panol in the presence of 30% aqueous KOH to initiate
ring opening (Scheme 2), and the free acid (1a ) was
produced after protonation with HCl(aq). The product
(7) (a) Lindsey, J . S.; Hsu, H. C.; Schreiman, I. C. Tetrahedron Lett.
1986, 27, 4969. (b) Lindsey, J . S.; Schreiman, I. C.; Hsu, H. C.; Kearney,
P. C.; Marguerettaz, A. M. J . Org. Chem. 1987, 52, 827. (c) Lindsey, J .
S.; Wagner, R. W. J . Org. Chem. 1989, 54, 828.
(8) Harmjanz, M.; Gill, H. S.; Scott, M. J . J . Am. Chem. Soc. 2000,
122, 10476.
(9) (a) Buchler, J . W.; Puppe, L. Liebigs Ann. Chem. 1970, 740, 142.
(b) Dwyer, P. N.; Buchler, J . W.; Scheidt, W. R. J . Am. Chem. Soc.
1974, 96, 2789. (c) Buchler, J . W.; Puppe, L. Liebigs Ann. Chem. 1974,
1046. (d) Dwyer, P. N.; Puppe, L.; Buchler, J . W.; Scheidt, W. R. Inorg.
Chem. 1975, 14, 1782. (e) Buchler, J . W.; Lay, K.-L. Z. Naturforsch.,
B: Chem. Sci. 1975, 30, 385. (f) Buchler, J . W.; Lamlay, K.; Smith, P.
D.; Scheidt, W. R.; Rupprecht, G. A.; Kenny, J . E. J . Organomet. Chem.
1976, 110, 109. (g) Buchler, J . W.; Dreher, C.; Lay, K.-L.; Lee, Y. J . A.;
Scheidt, W. R. Inorg. Chem. 1983, 22, 888. (h) Botulinski, A.; Buchler,
J . W.; Lay, K.-L.; Stoppa, H. Liebigs Ann. Chem. 1984, 1259. (i)
Botulinski, A.; Buchler, J . W.; Tonn, B.; Wicholas, M. Inorg. Chem.
1985, 24, 3239. (j) Botulinski, A.; Buchler, J . W.; Abbes, N. E.; Scheidt,
W. R. Liebigs Ann. Chem. 1987, 305. (k) Botulinski, A.; Buchler, J .
W.; Wicholas, M. Inorg. Chem. 1987, 26, 1540. (l) Botulinski, A.;
Buchler, J . W.; Lee, Y. J .; Scheidt, W. R.; Wicholas, M. Inorg. Chem.
1988, 27, 927. (m) Renner, M. W.; Buchler, J . W. J . Phys. Chem. 1995,
99, 8045.
(10) Senge, M. O.; Runge, S.; Speck, M.; Ruhlandt-Senge, K.
Tetrahedron 2000, 56, 8927.
(11) Harmjanz, M.; Scott, M. J . Chem. Commun. 2000, 397.
(12) Kra´l, V.; Sessler, J . L.; Zimmerman, R. S.; Seidel, D.; Lynch,
V.; Andrioletti, B. Angew. Chem., Int. Ed. 2000, 39, 1055.
(13) Bonomo, L.; Solari, E.; Scopelliti, R.; Floriani, C.; Re, N. J . Am.
Chem. Soc. 2000, 122, 5312.
(14) Littler, B. J .; Ciringh, Y.; Lindsey, J . S. J . Org. Chem. 1999,
64, 2864.
(15) Providing further evidence for this flexing, the 1H NMR
spectrum exhibits only two sets of resonances for the pyrrolic protons,
and if the macrocycle were to adopt a single conformation, four pairs
of protons should be inequivalent.
(16) The syn isomers of the porphodimethenes can adopt either an
open or closed confirmation with respect to the carbonyl groups, and
while 4 displays the closed orientation, the open conformer has been
detected in the solid-state structure of a metalated (Zn) syn lactonized
porphodimethene. See ref 8.
(17) Harmjanz, M.; Scott, M. J . Inorg. Chem. 2000, 39, 5428.

5376 J . Org. Chem., Vol. 66, No. 16, 2001
Harmjanz et al.
Ta ble 1. Isola ted Yield s a n d Selected An a lytica l Da ta
5-substituted, â-unsubstituted dipyrromethanes (Table
1) with acenaphthenequinone in the presence of catalytic
amounts of either BF3‚OEt2 or TFA (Scheme 3), and as
outlined in Table 1, the reaction proved to be quite
convenient and versatile. Through simple substitutions
of the aryl groups in the dipyrromethane precursors, this
general pathway allows for the isolation of the por-
phodimethenes with different steric and electronic prop-
erties. Buchler et al. have extensively studied por-
phodimethenes, but the preparation of the macrocycle is
normally achieved by way of the reductive alkylation of
porphyrins,9 prohibiting the synthesis of aryl-substituted
porphodimethenes by this method. Quite recently, several
new procedures for the preparation of porphodimethenes
have been reported, including the condensation of pyrrole
with sterically encumbered aldehydes10 and the reaction
of acetone11 or vicinal diketones12 with 5-aryldipyr-
romethanes. In addition, porphodimethenes can be pre-
pared in convenient quantities by the dealkylation of
porphyrinogens,13 but once again, this methodology can-
not be applied to meso-aryl-substituted macrocycles.
for P or p h od im eth en es 2-17
In the [2 + 2] condensation reactions outlined in
Scheme 3, the overall yields of both isomers (syn and anti)
range from 7 (6 and 7) to 26% (2 and 3), and as witnessed
by Lindsey et al. for the formation of porphyrins by [2 +
2] condensations, the yields7 and the molar ratios of the
atropisomers are strongly dependent on the electronic
and steric nature of the dipyrromethane starting materi-
als as well as the reaction conditions (nature of the acid,
dilution factors, and solvents). Although no concerted
attempt was made to maximize the yields for the respec-
tive porphodimethenes by varying conditions, the proce-
dures optimized for the preparation of porphyrins have
been utilized throughout.14 For the first step in the
purification process, the reaction mixtures were filtered
through a column of neutral alumina, allowing for the
quick isolation of a mixture of the porphodimethenes, syn
and anti. The two isomers can then be separated by
column chromatography (silica gel) with ether (10, 11,
was only slightly soluble in solvents such as methylene
chloride or chloroform, and in order to utilize the mol-
ecule for the preparation of porphyrins, the carboxylic
acid group must be masked to enhance the solubility of
the dipyrromethane in the condensation reaction mix-
ture. In view of the increasing number of synthetic steps
necessary to produce porphyrins from 1, efforts to further
develop methodologies with these precursors were not
undertaken.
With the desire to simplify the procedure, the forma-
tion of porphodimethenes was attempted by treating
Sch em e 3. Gen er a l Tw o-Step Syn th etic P a th w a y for th e P r ep a r a tion of P or p h yr in sa
a
Reagents and conditions: (i) 1, TFA or BF3‚OEt2, CH2Cl2; 2, DDQ. (iia) 30% KOH(aq), reflux (THF), air. (iib) 1, NaOMe (THF/MeOH)
rt; 2, O2. (iic) NaBH4 (THF/MeOH), rt, air.

Preparation and Conversion of Porphodimethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5377
F igu r e 2. Conformational flexing of the porphodimethene
macrocycle.
F igu r e 1. UV-vis spectra of the porphodimethene 3 (Ar )
mesityl), the Zn(II) complex 3d , and the porphyrin-dialcohol
3c within the region of 350-700 nm.
F igu r e 3. ORTEP diagram of the solid-state structure of 4
(30% probability, carbons arbitrary radii). H-atoms omitted
for clarity.
16, and 17), toluene (2, 3, 8, 9, 14, and 15), or a CH2Cl2/
hexanes mixture as the eluting solvent (4-7, 12, and 13);
the anti derivatives are isolated first.
signals for the acenaphthenones insinuate a different
mechanism, and on the basis of these observations, it
appears that the porphodimethenes undergo a fast flex-
ing of the two dipyrromethane units along a line joining
the two saturated meso carbons (Figure 2) in solution.
The respective porphodimethene isomers (syn and anti)
are both bright orange solids and exhibit a characteristic
absorption maxima in the UV-vis spectra ranging from
438 (3) to 446 nm (10) (Figure 1). In comparison to meso-
alkylporphodimethenes (417-426 nm),9g,12 the main ab-
sorption bands are batochromically shifted but exhibit
similar logarithmic extinction (log ꢀ) coefficients ranging
from 4.82 (4, 9) to 4.97 (2, 11) (Table 1).
1
The low temperature H NMR spectrum of the anti-3,5-
tBu2C6H3 derivative 12 reveals significant broadening of
some of the signals for the naphthalene protons as well
as the signals from the pyrrolic and aromatic [3,5-
tBu2C6H3] protons. Even at -80 °C, no splitting of these
broadened peaks could be detected, suggesting a fast
equilibrium between these two possible conformers.15
Further highlighting the flexibility of the porphodimethene
framework, metalation with zinc (3d ) induces significant
flattening of the macrocycle relative to the free por-
phodimethene 3.11 In addition, two conformers can be
envisioned for the syn isomer, each adopting the rooflike
folded structure typical for porphodimethenes.
Figure 3 displays the solid-state structure of the 2,6-
dichlorophenyl-substituted syn-porphodimethene (4). The
two saturated carbon atoms force the tetrapyrrolic mac-
rocycle to adopt a strong rooflike folded structure with
an interplanar roof angle of 123.1°, whereby the two
carbonyl oxygens are pointing toward each other (O‚‚‚O
distance: 2.95 Å). The macrocycle adopts this conforma-
tional arrangement (cis) as it corresponds to the energeti-
cally preferred binding situation of this tricyclic dispiro
conformer in the solid state.16 As expected, the two
dihedral angles at the meso carbons, defined by the five-
membered ring of the acenaphthenone and the adjacent
pyrrole carbons, respectively, deviate only slightly from
90° (90.3 and 88.9°).
Despite the diverse nature of aryl substituents that
have been introduced into the porphodimethene, no
significant correlation was observed between the elec-
tronic and steric properties of the aryl moiety and the
dipyrromethene band in the UV-vis spectra. The two
isomers can easily be distinguished by 1H NMR spec-
troscopy, and the resonances associated with the pyrrolic
protons are compiled in Table 1. All of the porpho-
dimethenes exhibit two sets of doublets for the pyrrolic
C-H protons, typically between 6.0 and 6.5 ppm, in sharp
contrast to the analogous signals for porphyrins normally
found above 8 ppm. This behavior may be attributed to
the disruption of electron delocalization within the mac-
rocycle, increasing the shielding of the pyrrolic protons.
Further highlighting the lack of aromaticity of the
porphodimethenes, the resonances for the N-H protons
appear far downfield shifted [13.79 (5)-14.03 (9) ppm]
1
in the H NMR spectra. Interestingly, the spectra of the
anti isomers consistently display only one set of signals
for the naphthalene and the meso-aryl substituents, even
though the rooflike folded structure with its spiro-locked
acenaphthenenones would implicate two sets of signals.
For instance, the o-methyl and the aromatic (mesityl)
protons of the anti-mesityl derivative 3 each exhibit a
Meta la tion of th e P or p h od im eth en es. The ability
to metalate the porphodimethenes prior to the ring-
opening reactions is an important issue in the design of
novel porphyrin-based ligand systems or cofacial single-
stranded porphyrin arrays.17 In particular, the develop-
ment of heterometallic systems, which involves different
metal ions in the chromophoric backbone and the at-
1
single resonance in the H NMR spectrum. Moreover, in
the aromatic region, the typical two double doublets and
four doublets from two indistinguishable acenaphthenone
moieties are observed. While free rotation about the
Cmeso-Caryl bond could arguably give rise to singlets for
the mesityl substituents, the presence of a single set of

5378 J . Org. Chem., Vol. 66, No. 16, 2001
Harmjanz et al.
Ta ble 2. Isola ted Yield s a n d λm a x for Meta la ted [Zn (II),
Cu (II), a n d Co(II)] P or p h od im eth en es
F igu r e 4. ORTEP diagram of the solid-state structure of 4d
(30% probability, carbons arbitrary radii). H-atoms omitted
for clarity. Selected distances (Å) and angles (deg): Zn(1)-
N(1), 2.071(8); Zn(1)-N(2), 2.069(8); Zn(1)-N(3), 2.037(8); Zn-
(1)-N(4), 2.059(8); Zn(1)-O(1), 2.311(7); N(1)-Zn(1)-N(2),
86.5(3); N(2)-Zn(1)-N(3), 87.9(3); N(3)-Zn(1)-N(4), 86.6(3);
N(1)-Zn(1)-N(4), 88.4(3).
groups situated close to each other above the plane of
the macrocycle, the “closed” arrangement of the porpho-
dimethene does not allow for an interaction of the Zn
center with external ligands, as observed for the related
anti-zinc-mesityl porphodimethene 3d .11 Lacking the
ability to bind to an additional ligand, the Zn is coordi-
nated by the four pyrrolic nitrogens and interacts with
one of the adjacent carbonyl oxygen atoms [Zn-O: 2.311-
(7) Å]. As a consequence of this highly distorted square
pyramidal coordination environment, the Zn-N distances
vary from 2.037(8) to 2.071(8) Å, and the metal resides
0.443 Å above the plane defined by these four pyrrole
donor atoms [0.404 Å (3)].11
F or m a tion of P or p h yr in s. (a ) Rin g-Op en in g Re-
a ction s w ith KOH a n d Na OMe. To generate the
aromatic porphyrin macrocycle, a carbon-carbon bond
in each of the spiro-linked acenaphthenone moieties must
be broken, and as found in our initial studies, refluxing
the respective porphodimethenes (syn and anti) in THF
in the presence of 30% KOH will induce the opening of
this ring. Presumably, the nucleophilic attack of the
hydroxide anion at the carbonyl carbon initiates the ring-
opening reaction, and the resulting species is subject to
oxidation in the presence of dioxygen, rapidly forming
the porphyrin macrocycle. Subsequent protonation with
HCl(aq) yields the corresponding free diacids of the trans-
8-carboxynaphthyl-functionalized porphyrins; in the ab-
sence of acid, the dipotassium salts can be isolated.
Despite these rather harsh reaction conditions, no inter-
conversion between R,R- and R,â-isomers has thus far
been detected. The isolation and purification of the R,â-
free acids have been severely hampered by the insolubil-
ity of these materials in common organic solvents.
Fortunately, these materials can be isolated directly by
precipitation from the reaction mixture as the dipostas-
sium salts, and they can be further purified by recrys-
tallization from methanol/ether solutions. In sharp con-
trast, the R,R-isomers are highly soluble. The insolubility
of the R,â-free acids may be attributed to intermolecular
hydrogen bonding interactions between the acid groups,
which are aligned above and below the porphyrin plane.
On the basis of the rigidly predefined positions of the
functional groups, these compounds have the strong
tached peripheral ligand system, may be envisioned by
metalation of the porphodimethene followed by the
generation of the functionalized porphyrin and the
introduction of the second metal ion.17 Although the
porphodimethenes (2-17) enclose carbonyl groups as
weak peripheral donor functions, only minor coordinative
interactions with metal ions are to be expected due to
their distance and orientation relative to the four nitro-
gen donors. Consequently, the deprotonated porpho-
dimethenes can, in principle, be viewed as tetradentate
macrocycles with two negative charges. As an initial
entry into the chemistry of these macrocycles, the neutral
Cu(II) and Zn(II) complexes of the porphodimethenes 2
and 3 (Ar ) mesityl) and the Co(II) complex of the anti
derivative 11 [Ar ) 3,4,5-(MeO)3C6H2] were prepared.
Metalation was achieved in high yields by refluxing the
porphodimethenes in a chloroform-methanol mixture in
the presence of the respective metal salts [Zn(OAc)2‚2H2O
(2d , 3d , and 4d ), Cu(OAc)2‚H2O (2e, 3e, and 11e), and
Co(OAc)2‚4H2O (11f)] (Table 2). Because the main ab-
sorption band of the porphodimethenes experiences a
significant bathochromic shift after metalation, the reac-
tion progress can easily be monitored by UV-vis spec-
troscopy (Figure 1). Compared to the metal-free por-
phodimethenes [log ꢀ ) 4.97 (2) and 4.93 (3)], a strong
increase [log ꢀ ) 5.13 (2d ), 5.08 (2e), 5.17, (3d ), and 5.09
(3e)] of the extinction coefficient is observed after incor-
poration of Zn(II) or Cu(II) into the chromophoric ligand.
In contrast, complexation of Co(II) by the porphodimethene
(11) induces a considerable decrease of the extinction
coefficient. As a general trend, the separation between
the two doublets arising from the pyrrolic protons in the
1H NMR spectra of the three diamagnetic Zn complexes
(2d -4d ) increases in comparison to the metal-free por-
phodimethenes [0.27 (2d and 4d )-0.44 (3d ) vs 0.1 (3)-
0.23 (2)]. These changes might be traced back to both the
altered electronic situation within the dipyrromethene
halves and the modified structural configuration of the
macrocycle after metalation.
The solid-state structure of the syn-zinc-mesityl por-
phodimethene 4d is outlined in Figure 4.18 Relative to
the unmetalated porphodimethene 4 (123.1°), the inter-
planar angle defined by the dipyrromethene units is
slightly more obtuse (131.3°). With the two carbonyl
(18) Two independent molecules of 4d occur in the asymmetric unit.
Data given and discussed within the text are only for one molecule.
For details, see the Supporting Information.

Preparation and Conversion of Porphodimethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5379
F igu r e 6. UV-vis spectra of 2 upon reaction with 30% KOH
in boiling THF, forming 2d . The arrows indicate the direction
of change in the peaks during porphyrin formation.
Ta ble 3. Isola ted Yield s a n d λm a x for th e P or p h yr in
P r od u cts Dep icted in Sch em e 1
yield UV-vis
atropisomer (%) (λmax)
aryl substituent
M
X, method
F igu r e 5. Temperature-dependent NMR spectra of the pyr-
role protons in 3a .
2,4,6-Me3C6H2
2,4,6-Me3C6H2
2,4,6-Me3C6H2
2,4,6-Me3C6H2
2,4,6-Me3C6H2
3,5-(t-Bu)2C6H3
3,5-(t-Bu)2C6H3
3,4,5-(OMe)3C6H2 Cu COOK, KOH
4-MeC6H4
4-MeC6H4
COOH, KOH
Zn COOH, KOH
COOK, KOH
Zn COOK, KOH
Cu COOK, KOH
COOH, KOH
R,R: 2a
R,R: 2g
R,â: 3a
R,â: 3g
R,â: 3h
R,R: 8a
R,â: 9a
R,â: 11h
R,R: 14a
R,â: 15a
92
75
65
46
65
78
90
45
83
77
432
431
431
430
421
426
427
422
426
432
tendency to form infinite single-stranded porphyrin ar-
rays, as illustrated by the X-ray structure analysis of the
dipotassium salt 3a and by the preparation of several
heterometallic cofacial porphyrin arrays.17 As indicated
by the 1H NMR spectra of the free-base porphyrin
dipotassium salts, the trend toward the formation of
higher aggregates appears to be observable in solution.
While the two peaks for the two chemically distinct
pyrrole protons are significantly broadened at rt, the
splitting of these resonances into two doublets (J ) 4.4
Hz), typical of 2 + 2 porphyrins, is only evident at higher
temperatures (40 °C) (Figure 5). This behavior could be
explained by a back and forward movement of the
naphthalene moiety toward the plane normal to the
porphyrin backbone. At lower temperatures (0 °C), the
doublets merge together, and at -40 °C, a splitting into
three doublets can be observed. As previously witnessed
in the solid-state structure of the dipotassium salt, the
angles between the naphthalene planes and the porphy-
rin ring deviate significantly from 90° (74.8°). Conse-
quently, the formation of higher aggregates in low-
temperature solutions can impose comparable naphthalene
to porphyrin angles, inducing the chemical shifts for the
four pyrrolic protons to be inequivalent. Alternatively,
these findings may also be rationalized by a temperature-
dependent potassium ion migration between the carboxy-
lates and the pyrrolic nitrogens.
Reactions with KOH have also been undertaken with
metalated [Zn(II) and Cu(II)] porphodimethenes to yield
the corresponding metalated porphyrin species. The
overall yields for the ring-opening reaction are highly
dependent on both the properties of the meso-aryl sub-
stituents bound at the porphyrin and the nature of the
metal ions incorporated into the macrocycle (Table 3).
Yields between 45% for the copper derivative 11h (Ar )
3,4,5-(MeO)3C6H2) and 92% for the free-base porphyrin
2a (Ar ) mesityl) have been found. In general, higher
yields are obtained for the unmetalated derivatives, since
the metalated compounds are more prone to undergo ring
closure by oxidative lactonization and formation of
dispiro, tricyclic, meso-C/O bound porphodimethenes.8
Inasmuch as the main absorption bands (Soret band)
of the porphyrins appear at markedly lower wavelengths
COOK, KOH
COOH, KOH
COOK, KOH
2,4,6-Me3C6H2
2,4,6-Me3C6H2
3,5-(t-Bu)2C6H3
3,5-(t-Bu)2C6H3
4-MeC6H4
COOMe, NaOMe R,R: 2b
COOMe, NaOMe R,â: 3b
COOMe, NaOMe R,R: 8b
COOMe, NaOMe R,â: 9b
COOMe, NaOMe R,R: 14b
COOMe, NaOMe R,â: 15b
69
81
71
60
68
60
425
425
426
426
426
426
4-MeC6H4
2,4,6-Me3C6H2
2,4,6-Me3C6H2
3,5-(t-Bu)2C6H3
3,5-(t-Bu)2C6H3
3,4,5-(OMe)3C6H2
3,4,5-(OMe)3C6H2
4-MeC6H4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
CH2OH, NaBH4
R,R: 2c
R,â: 3c
R,R: 8c
R,â: 9c
R,R: 10c
R,â: 11c
R,R: 14c
R,â: 15c
98
98
95
98
97
97
95
97
424
424
426
424
427
424
424
424
4-MeC6H4
with considerably higher intensity as compared to the
metalated porphodimethenes, the progress of the por-
phyrin formation reaction with these compounds can be
easily monitored by UV-vis spectroscopy. Figure 6
depicts the UV-vis spectra of the syn-porphodimethene
2 (Ar ) mesityl and M ) Zn) upon reaction with KOH in
refluxing THF. Besides the aforementioned alteration of
the main absorption band, the formation of the charac-
teristic Q-bands within the region between 540 and 640
nm is evident, concomitant with a color change of the
reaction mixture from dark orange to dark purple.
Other nucleophiles will react with the porpho-
dimethenes, and the ring-opening can be accomplished
with freshly prepared NaOMe in an air- and water-free
THF/methanol mixture to yield the corresponding 8-meth-
oxycarbonylnaphthyl functionalized porphyrins. To avoid
formation of the favored diacid, water must be rigorously
excluded from the reaction mixture, and in contrast to
the hydroxide reaction, the transformation readily occurs
at rt. To provide an oxidant, dry dioxygen is bubbled
through the initially dark green solution prior to the
addition of water or an aqueous NH4Cl solution. The
diesters can typically be obtained in yields from 60 (9b

5380 J . Org. Chem., Vol. 66, No. 16, 2001
Harmjanz et al.
and 15b) to 81% (3b) (Table 3) after column chromatog-
raphy (silica gel, CH2Cl2/hexane mixtures as eluants).
Utilizing the same reaction conditions, less soluble por-
phodimethenes such as the 2,6-dichlorophenyl derivative
cannot be converted to the desired diesters, since the
initially formed porphodimethene disodium salts readily
precipitate from the reaction mixture.
(b) Rin g-Op en in g Rea ction w ith Na BH4. Given
that porphyrins bearing two hydroxymethyl functions at
the 8-position of a naphthalene spacer would be highly
desirable building blocks for the preparation of novel
organic and inorganic compounds, we attempted to
reduce the porphyrin diesters with LiAlH4, but the
reaction produced the desired dialcohols in very poor
yields. Reduction of the 5-acenaphthenone-substituted
dipyrromethane 1 with NaBH4 generates a racemic
mixture of the alcohol without ring opening,21 but in view
of the sensitivity of the porphodimethenes to strong bases
or acids and the considerable driving force toward por-
phyrin formation, we reasoned that the ring opening of
the porphodimethenes might be achieved with simple
reducing agents. Reaction of the porphodimethenes 2, 3,
8-11, 14, and 15 (Table 3) with an excess of NaBH4 in
THF/methanol open to air yields the desired porphyrins
in almost quantitative yields.
F igu r e 7. UV-vis spectrum of the green intermediate formed
from the reaction of 3 with NaBH4 in THF/MeOH and time
course spectra of the reaction mixture after exposure to air.
The arrows indicate the direction of change in peaks during
porphyrin formation.
If the reaction is carried out under rigorous air- and
water-free conditions, a brilliant green solution forms,
which turns dark brown-green after a few minutes. The
UV-vis spectrum of the solution (3 + NaBH4) exhibits
an absorption band at 433 nm with a shoulder at 447
nm, and it also displays an unusual broad band at 820
nm. Although this spectrum is not consistent with the
UV-vis spectra of two-electron-reduced metalated por-
F igu r e 8. ORTEP diagram of the solid-state structure of 2c
(30% probability, carbons arbitrary radii). H-atoms omitted
for clarity. One of the naphthyl groups was disordered across
two positions, each with a site occupancy of 0.5, and only one
orientation has been depicted.
phyrin species such as [TPP-Zn]2- 19
the absence of a
,
metal in the macrocycle may allow for the formation of
the reduced porphyrin sodium salts. When the green
solution is exposed to air, the broad band at 820 nm
slowly decreases while the Soret band (425 nm) and the
characteristic Q-bands grow in, indicating the formation
of the porphyrin (Figure 7). As expected and confirmed
by 1H NMR and X-ray structure analyses of 2c, reactions
of the syn-porphodimethenes with NaBH4 exclusively
produce the R,R-atropisomers, while the analogous reac-
tions of the anti-porphodimethenes yield the R,â-atropi-
somers. Although we restricted our investigation to alkyl-
and methoxy-substituted meso-arylporphyrins, this reac-
tion should be applicable for the preparation of trans-8-
hydroxymethylnaphthylporphyrins containing other sub-
stitution patterns at the meso-aryl substituents. Relative
to the 8-carboxynaphthylporphyrins, the dialcohols ex-
hibit enhanced stability in air; nevertheless, in the
presence of strong oxidants, they also undergo a ring-
closing reaction to form porphodimethenes.8,20
defined by the naphthalene spacer, respectively, deviate
only slightly from 90° (94.0 and 99.5°), and as a result,
the two hydroxymethyl carbons are situated 2.85 Å
[2.793(8) and 2.913 (8), respectively] above the porphyrin
plane with an oxygen-oxygen separation of 7.56 Å. To
minimize electronic repulsion between the electron cloud
of the porphyrin macrocycle and the alcohol groups, the
two hydroxy groups are directed away from the porphyrin
plane with the two oxygen-carbon bonds almost parallel
to the pseudo-C2 axis of the molecule.
(c) Rin g-Op en in g Rea ction s w ith Acid s. Acid-
induced ring opening of the spiro-linked acenaphthene-
ones also affords the aromatic porphyrin macrocycles. As
observed, addition of strong acids such as HCl or H2SO4
to a solution of the porphodimethenes will cause ring
opening at rt. If the reactions are undertaken in the
presence of water, the protonated porphyrin diacid is
obtained and the free-base porphyrin is generated after
washing the product with water. Prior to ring opening,
the N-protonated macrocycle is formed, as demonstrated
by UV-vis spectroscopy and an X-ray structure analysis
of the protonated porphodimethene 8.21 The protonation
induces a split in the primary absorption band of 8 (442
nm) into two bands (411 and 478 nm) with lower and
higher absorptivity (Figure 9). In the solid-state, the
protonated tetrapyrrolic macrocycle severely distorts
from planarity, and presumably, the drive to develop
aromaticity helps induce the ring-opening reaction and
subsequent porphyrin formation.
Figure 8 displays an ORTEP plot of 2c, and in the
solid-state, one of the naphthalene spacers exhibits two
distinct inclinations relative to the porphyrin plane, each
with a site occupancy factor of 0.5. For clarity, only one
position is shown in Figure 8, but for the discussion,
mean values of the two positions are given. Compared
to the R,â-diester 3b (61.8°),11 the porphyrin plane
(defined by the four nitrogen atoms) and the plane
(19) Closs, G. L.; Closs, L. E. J . Am. Chem. Soc. 1963, 85, 818.
(20) Confirmed by cyclic voltammetry: Harmjanz, M.; Gill, H. S.;
Scott, M. J . Manuscript in preparation.
(21) Harmjanz, M.; Gill, H. S.; Scott, M. J . Unpublished results.

Preparation and Conversion of Porphodimethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5381
presented herein to other vicinal diketones as well as the
derivatization of the prepared compounds are currently
underway.
Exp er im en ta l Section
The University of Florida Mass Spectrometry Services
measured all mass spectral data. Elemental analyses were
performed by either Mikroanalytisches Laboratorium H. Kolbe,
Mu¨hlheim a. d. Ruhr, Germany or Atlantic Microlabs, Nor-
cross, GA. All 5-aryldipyrromethanes required for the prepara-
tion of 2-17 have been synthesized according to literature
procedures.22 The dipyrromethane precursors were purified by
the following procedure: After removal of the excess pyrrole,
the crude product mixtures were filtered through neutral
alumina with either CH2Cl2 or a CH2Cl2/hexanes mixture as
the eluant. The solvents were removed in vacuo; the residues
were carefully washed with hexanes, pentane, or cyclohexane
and dried. This methodology allows for the convenient isolation
of the dipyrromethanes in multigram quantities. The products
can be further purified by recrystallization.
F igu r e 9. UV-vis spectra of 8 after addition of TFA. The
arrows indicate the direction of change in the peaks during
protonation.
When BF3‚OEt2 was employed for the formation of the
porphodimethenes, the reactions were carried out under argon
with dried and degassed solvents. The reaction of the por-
phodimethenes (2, 3, 8, 9, 14, and 15) with NaOMe for the
preparation of the diesters 2b, 3b, 8b, 9b, 14b, and 15b and
the acid-catalyzed ring-opening reactions were all performed
under Schlenk conditions with dried and degassed solvents.
Porphyrin diacids, dialcohols, and dipotassium salts have been
found to undergo oxidative ring-closing reactions over time in
the presence of air, and these compounds should be stored
under an inert atmosphere.
Syn th esis of 2,2-Bis-(1H-p yr r ol-2-yl)-2H-a cen a p h th -
ylen -1-on e, 1. A sample of acenaphthenequinone (5 g, 27.4
mmol) was dissolved in 100 mL of freshly distilled pyrrole,
and 1 mL of BF3‚OEt2 (7.90 mmol) was added. After the
reaction mixture was stirred for 45 min, 150 mL of CH2Cl2
was added, and the mixture was subsequently treated with
150 mL of 0.1 N NaOH. The organic layer was washed with
150 mL of water (2×) and dried over NaSO4. The solvent and
the excess pyrrole were removed in vacuo, and the solid was
purified by filtration through neutral alumina (CH2Cl2).
Yield: 3.7 g (45%). UV-vis (CH2Cl2) λmax, nm: 321, 342. 1H
NMR (300 MHz, CDCl3): δ 8.55 (bs, 2H), 8.14 (d, 1H, J ) 7.9
Hz), 8.00 (d, 1H, J ) 6.7 Hz), 7.89 (dd, 1H, J 1 ) J 2 ) 4.5 Hz),
7.69-7.77 (m, 3H), 6.72-6.74 (m, 2H), 6.09 (q, 2H), 5.95-5.97
(m, 2H). HRMS-FAB (m/z): M+ calcd for C20H14N2O, 298.1106;
found, 298.1105.
Syn th esis of 5-(8-Car boxy-1-n aph th yl)dipyr r om eth an e,
1a . A sample of the dipyrromethane 1 (500 mg, 1.68 mmol)
was dissolved in 15 mL of hot 1-propanol, and 1 mL of 30%
KOH(aq) was added. The reaction mixture was refluxed for
45 min, and the solvents were subsequently removed in vacuo.
The brown residue was redissolved in THF and acidified with
10 mL (2 N) of HCl. A 15-mL portion of CH2Cl2 was added,
and the organic phase was separated and subsequently washed
with water (3×). After being dried over Na2SO4, the solvents
were evaporated, and 4 mL of CH2Cl2 was added to the residue.
After being cooled to 5 °C for 1 h, the microcrystalline, colorless
precipitate was filtered off, washed with a small amount of
cold CH2Cl2, and dried in vacuo to yield 170 mg (32%) of 1a .
1H NMR (300 MHz, acetone-d6): δ 9.50 (bs, 2H), 8.05 (dd, 1H,
J 1 ) 1.4, J 2 ) 8.2 Hz), 7.87 (dd, 1H, J 1 ) 2.1, J 2 ) 7.3 Hz),
7.76 (dd, 1H, J 1 ) 1.4, J 2 ) 7.04 Hz), 7.44-7.52 (m, 3 H), 6.66
(q, 2H), 6.44 (s, 1H), 5.91 (q, 2H), 5.57-5.59 (m, 2H). HRMS-
FAB (m/z): MH+ calcd for C20H16N2O2, 316.1211; found,
316.1216.
If methanol is added to the acid-catalyzed reactions
with the exclusion of water, the diester porphyrins are
obtained in high yields [87 (8b), 94 (9), and 85% (15)].
These reactions must be carried out under a dry O2
atmosphere with freshly distilled solvents, and concen-
trated sulfuric acid has been used as the proton source.
No interconversion between the syn and anti derivatives
was observed in this reaction. In comparison to the
methoxide ring-opening reaction discussed above, the
yields for these diesters are higher by the acid-catalyzed
route, and this procedure is ideal for the conversion of
base-sensitive porphodimethene precursors to porphy-
rins.
Con clu sion s
In an effort to prepare a wide range of trans-porphyrins
incorporating two 8-functionalized naphthalene spacers,
a simple, two-step synthetic approach starting from
commercially available acenaphthenequinone and readily
available 5-aryldipyrromethanes has been developed.
This methodology involves the preparation of novel
dispiro tricyclic porphodimethenes employing a [2 + 2]
acid-catalyzed condensation reaction under Lindsey con-
ditions. The porphodimethenes can be metalated [Cu(II),
Zn(II), and Co(II)] in high yields, and both the metal-
bound and free porphodimethenes can be converted to
the corresponding porphyrins. By utilizing KOH, NaOMe,
or NaBH4, the respective 8-carboxynaphthyl-, the 8-
methoxycarbonylnaphthyl-, and the 8-hydroxymethyl-
naphthyl-substituted trans-porphyrins can be prepared.
Alternatively, the porphyrin formation can be achieved
at rt with water or methanol in the presence of strong
acids. With the diverse nature (acid/base) of the ring-
opening reactions and the variety of functionalities that
can be incorporated at both the meso-aryl moieties and
the naphthalene spacer, this work reveals a facile
synthetic approach toward the syntheses of sterically and
electronically diverse porphyrins with functional groups
placed directly above and/or below the macrocycles. The
generality of the synthetic pathways will be quite helpful
for improving existing efforts to establish porphyrin
functionalizations not only in the peripheral surrounding
of the macrocyclic plane but also in well-defined axial
directions. Efforts to extend the synthetic pathways
Gen er a l P r oced u r e for th e P r ep a r a tion of th e P or -
p h od im et h en es (2-17). (a ) Syn t h esis of syn -d isp ir o-
[2H-Acen a p h th ylen -1-on e-2,5′-10′,20′-d im esityld ih yd r o-
p or p h yr in -15′,2′′-2′′H -a cen a p h t h ylen -1′′-on e], 2. a n ti-
(22) (a) Lee, C.-H.; Lindsey, J . S. Tetrahedron 1994, 50, 11427. (b)
Beavington, R.; Burn, P. L. J . Chem. Soc., Perkin Trans. 1 1999, 583.

5382 J . Org. Chem., Vol. 66, No. 16, 2001
Harmjanz et al.
d isp ir o[2H -Acen a p h t h ylen -1-on e-2,5′-10′,20′-d im esit yl-
d ih yd r op or p h yr in -15′,2′′-2′′H-a cen a p h th ylen -1′′-on e], 3.
A portion of 2.064 g of acenaphthenequinone (11.34 mmol) and
3.000 g (11.34 mmol) of 5-mesityldipyrromethane were dis-
solved in 1200 mL of CH2Cl2, and 0.62 mL (4.9 mmol) of BF3‚
OEt2 was added. After 3 h, 2.580 g of DDQ (11.34 mmol) was
added to the greenish-blue solution and the mixture stirred
for 1 h. The volume was reduced by 90%, and the mixture was
loaded onto an alumina column (CH2Cl2, 25 × 4 cm) and slowly
eluted with CH2Cl2. The solvent of the orange fraction was
removed, and the residue was presorbed on silica. The two
isomers (2 and 3) were separated by silica chromatography
(15 × 4 cm, toluene). 2: Yield: 0.534 g (11%). Anal. Calcd for
phodimethene (2) (122 mg, 0.14 mmol) was dissolved in 20 mL
of THF, and 60 mg of NaBH4 (1.58 mmol) dissolved in 2 mL of
MeOH was added. After 3 min, another sample of NaBH4 (50
mg, 1.32 mmol) was added to the reaction mixture, and the
solution was stirred for 1 h. The mixture was treated with 20
mL of 2 N HCl followed by 30 mL of CH2Cl2. The organic phase
was separated, washed with water (3×), and subsequently
dried over anhyd Na2SO4. The solvents were removed under
reduced pressure, and the purple residue was redissolved in
20 mL of CH2Cl2. After addition of 5 mL of hexanes, the CH2-
Cl2 was slowly distilled off, and the remaining light-brown
hexane solution decanted from the microcrystalline material.
Removal of residual hexanes under vacuum yielded analyti-
cally pure 2b. Yield: 120 mg (98%). UV-vis (CH2Cl2) λmax, nm
C
60H44N4O2‚0.25CH2Cl2: C, 82.77; H, 5.13; N, 6.41. Found: C,
1
83.24; H, 5.29; N, 6.32. UV-vis (CH2Cl2) λmax, nm (log ꢀ): 440
(log ꢀ): 424 (5.60). H NMR (300 MHz, CDCl3): δ 8.55 (d, 4H,
1
(4.97). H NMR (300 MHz, CDCl3): δ 14.00 (s, 2H, NH), 8.20
J ) 4.6 Hz), 8.47 (d, 4H, J ) 4.6 Hz), 8.30 (d, 2H, J ) 7.8 Hz),
8.16 (dd, 2H, J 1 ) 6.5, J 2 ) 3.1 Hz), 8.07 (d, 2H, J ) 6.6 Hz),
7.72 (dd, 2H, J 1 ) J 2 ) 7.6 Hz), 7.65-7.60 (m, 4H), 7.21 (s,
4H), 3.24 (s, 4H), 2.56 (s, 6H), 1.85 (s, 6H), 1.78 (s, 6H), 0.21
(bs, 2H), -2.28 (s, 2H). HRMS-FAB (m/z): MH+ calcd for
(d, 2H, J ) 8.1 Hz), 8.15 (d, 2H, J ) 7.0 Hz), 8.04 (d, 2H, J )
8.3 Hz), 7.98 (d, 2H, J ) 7.0 Hz), 7.85 (dd, 2H, J 1 ) 8.2, J 2
)
7.0 Hz), 7.81 (dd, 2H, J 1 ) 8.1, J 2 ) 7.0 Hz), 6.89 (s, 2H), 6.82
(s, 2H), 6.17 (d, 4H, J ) 4.3 Hz), 5.94 (d, 4H, J ) 4.3 Hz) 2.31
(s, 6H), 2.23 (s, 6H), 2.19 (s, 6H). HRMS-FAB (m/z): MH+
calcd for C60H45N4O2, 853.3543; found, 853.3569. 3: The anti
isomer 3 was collected as the first fraction from the silica
column. Yield: 720 mg (15%). Anal. Calcd for C60H44N4O2‚
0.25CHCl3: C, 81.97; H, 5.05; N, 6.35. Found: C, 81.99; H,
5.34; N, 6.26. UV-vis (CH2Cl2) λmax, nm (log ꢀ): 438 (4.93). 1H
C
60H51N4O2, 859.4012; found, 859.4050.
(e) Syn th esis of [syn -d ispir o[2H-Acen a p h th ylen -1-on e-
2,5′-10′,20′-d im e sit yld ih yd r op or p h yr in a t o-15′,2′′-2′′H -
a cen a p h th ylen -1′′-on e]] zin c, 2d . A portion of the por-
phodimethene (2) (100 mg, 0.117 mmol) was dissolved in 25
mL of chloroform, and 2 mL of a saturated solution of
Zn(OAc)2‚2H2O in methanol was added. The reaction mixture
was refluxed for 1 h, cooled to rt, and washed with water (2×).
The organic phase was dried (Na2SO4), and removal of the
solvents yielded 2d as a reddish-brown solid. Yield: 104 mg
NMR (300 MHz): δ 13.92 (s, 2H, N-H), 8.76 (dd, 2H, J 1
)
5.4, J 2 ) 2.4 Hz), 8.22 (d, 2H, J ) 8.1 Hz), 8.17 (d, 2H, J ) 7.1
Hz), 8.03 (d, 2H, J ) 5.4 Hz), 8.01 (d, 2H, J ) 2.4 Hz), 7.82
(dd, 2H, J 1 ) 8.1, J 2 ) 7.1 Hz), 6.85 (s, 4H), 6.21 (d, 4H, J )
4.2 Hz), 6.11 (d, 4H, J ) 4.2 Hz), 2.31 (s, 6H), 2.07 (s, 12H).
HRMS-FAB (m/z): MH+ calcd for C60H45N4O2, 853.3543;
found, 853.3525.
1
(97%). UV-vis (CH2Cl2) λmax, nm (log ꢀ): 477 (5.13). H NMR
(300 MHz): δ 8.19 (dd, 4H, J 1 ) J 2 ) 7.8 Hz), 8.01 (d, 4H, J
) 7.3 Hz), 7.87-7.76 (m, 4H), 6.85 (s, 2H), 6.77 (s, 2H), 6.23
(d, 4H, J ) 4.1 Hz), 5.96 (d, 4H, J = 4.1 Hz), 2.27 (s, 6H), 2.22
(s, 6H), 1.92 (s, 6H). HRMS-FAB (m/z): MH+ calcd for
(b ) Syn t h esis of r,r-5,15-Bis(8-ca r b oxy-1-n a p h t h yl)-
10,20-d im esitylp or p h yr in , 2a . A portion of 0.370 g (0.43
mmol) of the porphodimethene (2) was dissolved in 35 mL of
THF, and 1.3 mL of a 30% aqueous KOH solution was added.
The reaction mixture was refluxed for 3 h and then acidified
with 10 mL of 6 N HCl. After the mixture was stirred for an
additional 5 min, a mixture of 10 mL of H2O and 30 mL of
CH2Cl2 was added. The dark green organic layer was washed
with water (3×) and dried over NaSO4. The solvent was
removed, and the residue was redissolved in a mixture of 15
mL of CH2Cl2 and 10 mL of hexanes. Slow removal of the
solvents under vacuum afforded 2a as a purple microcrystal-
line solid. Yield: 0.355 g (92%). UV-vis (CHCl3) λmax, nm: 432.
1H NMR (300 MHz, CDCl3): δ 8.85 (d, 2H, J ) 7.2 Hz), 8.63
(d, 4H, J ) 4.7 Hz), 8.61 (d, 4H, J ) 4.7 Hz), 8.33 (d, 2H, J )
C
60H43N4O2Zn, 915.2677; found, 915.2678.
(f) Syn th esis of [syn -d ispir o[2H-Acen a p h th ylen -1-on e-
2,5′-10′,20′-d im e sit yld ih yd r op or p h yr in a t o-15′,2′′-2′′H -
a cen a p h th ylen -1′′-on e]] cop p er , 2e. A sample of the por-
phodimethene (2) (79 mg, 0.093 mmol) was dissolved in 20 mL
of CHCl3, and 2 mL of a hot, saturated solution of Cu(OAc)2‚
H2O in MeOH was added. The reaction mixture was heated
under reflux for 1 h. After being cooled to rt, the solvents were
removed, and the residue was redissolved in CHCl3. The
solution was filtered through a short pad of silica gel (CH2-
Cl2). Removal of the solvent yielded 2b as a reddish-brown
solid. Yield: 84 mg (99%). UV-vis (CHCl3) λmax, nm (log ꢀ):
486 (5.08). HRMS-FAB (m/z): MH+ calcd for C60H43N4O2Cu,
914.2681; found, 914.2685.
8.2 Hz), 8.16 (d, 2H, J ) 8.2 Hz), 8.02 (dd, 2H, J 1 ) 7.2, J 2
)
8.2 Hz), 7.41 (dd, 2H, J 1 ) 7.2, J 2 ) 8.2 Hz), 7.24 (s, 2H), 7.18
(s, 2H), 7.06 (d, 2H, J ) 7.2 Hz), 2.56 (s, 6H), 2.01 (s, 6H),
1.67 (s, 6H). HRMS-FAB (m/z): MH+ calcd for C60H47N4O4,
887.3597; found, 887.3595.
(g) Syn th esis of [r,r-5,15-Bis(8-ca r boxy-1-n a p h th yl)-
10,20-d im esitylp or p h yr in a to]zin c, 2g. A portion of 220 mg
(0.240 mmol) of the metalated (Zn) dimesitylporphodimethene
(2d ) was dissolved in 25 mL of THF, and 1 mL of 30% KOH-
(aq) was added. The mixture was refluxed for 3 h, cooled to
rt, and transferred to a separatory funnel. The aqueous
solution was removed, and the organic layer was acidified with
40 mL of 0.1 N aqueous HCl. A total of 80 mL of diethyl ether
was added; the organic layer was separated, immediately
washed with water (2×), and dried over Na2SO4. Removal of
the solvent under reduced pressure afforded 2g as a purple
solid. Yield: 170 mg (75%). UV-vis (CHCl3) λmax, nm (log ꢀ):
(c) Syn t h esis of r,r-5,15-Bis(8-m et h oxyca r b on yl-1-
n a p h th yl)-10,20-d im esitylp or p h yr in , 2b. A total of 50 mg
(2.17 mmol) of Na was added to a mixture of 5 mL of MeOH
and 10 mL of THF. After the sodium had completely reacted,
a portion of 200 mg (0.23 mmol) of the porphodimethene (2)
was added. The solution was stirred for 2 h before oxygen was
bubbled through the reaction mixture. After 5 min, 15 mL of
water and 35 mL of CH2Cl2 were added. The organic layer was
separated and immediately washed with water (3×). The
organic layer was dried (NaSO4), and the solvents were
removed under reduced pressure. Purification was achieved
by column chromatography (silica, CH2Cl2/hexanes, 4:1).
Yield: 145 mg (69%). UV-vis (CH2Cl2) λmax, nm (log ꢀ): 425
1
431 (5.60). H NMR (CDCl3): δ 8.85 (2H, d, J ) 7.3 Hz), 8.61
(8H, s), 8.31 (2H, d, J ) 8.3 Hz), 8.18 (2H, d, J ) 8.3 Hz), 8.02
(2H, dd, J 1 ) J 2 ) 7.7 Hz), 7.40 (2H, dd, J 1 ) J 2 ) 7.7 Hz),
7.20 (2H, s), 7.18 (2H, s), 7.03 (2H, d, J ) 7.3 Hz), 2.56 (6H,
s), 1.94 (6H, s), 1.68 (6H, s). HRMS-FAB (m/z): M+ calcd for
1
(5.67). H NMR (300 MHz): δ 8.57 (d, 4H, J ) 4.8 Hz), 8.52
C
60H44N4O4Zn, 948.2654; found, 948.2677.
(d, 4H, J ) 4.8 Hz), 8.48 (d, 2H, J ) 7.1 Hz), 8.31 (d, 2H, J )
(h ) Syn t h esis of r,â-5,15-Bis(8-ca r b oxy-1-n a p h t h yl)-
8.3 Hz), 8.22 (d, 2H, J ) 8.3 Hz), 7.91 (dd, 2H, J 1 ) 7.1, J 2
)
10,20-d im esitylp or p h yr in Dip ota ssiu m Sa lt, 3a . The por-
phodimethene (3) (150 mg, 176 mmol) was reacted with 30%
KOH(aq) as described for the preparation of 2a . The dipotas-
sium salt formed during the reaction was filtered off and
washed with THF. Recrystallization was achieved by diffusion
of ether to a methanolic solution of the crude product. The
purple crystalline material was collected and dried in vacuo
8.3 Hz), 7.50 (dd, 2H, J 1 ) 7.1, J 2 ) 8.3 Hz), 7.23, 7.22 (br, s
6H), 2.57 (s, 6H), 1.91 (s, 6H), 1.84 (s, 6H), -0.04 (s, 6H), -2.36
(s, 2H). HRMS-FAB (m/z): MH+ calcd for C62H51N4O4,
915.3910; found, 915.3946.
(d ) Syn th esis of r,r-5,15-Bis(8-h yd oxym eth yl-1-n a p h -
th yl)-10,20-d im esitylp or p h yr in , 2c. A portion of the por-

Preparation and Conversion of Porphodimethenes
J . Org. Chem., Vol. 66, No. 16, 2001 5383
to yield 3a (114 mg, 65%). Anal. Calcd for C60H44N4O4K2‚
(5.09). HRMS-FAB (m/z): MH+ calcd for C60H43N4O2Cu,
914.2681; found, 914.2641.
MeOH: C, 73.62; H, 4.86; N, 5.63. Found: C, 73.22; H, 4.77;
1
N, 5.70. UV-vis (MeOH) λmax, nm: 431. H NMR (300 MHz,
(m ) Syn th esis of [r,â-5,15-Bis(8-ca r boxy-1-n a p h th yl)-
10,20-d im esitylp or p h yr in a to]zin c Dip ota ssiu m Sa lt, 3g.
The metalated (Zn) porphodimethene 3d (220 mg, 0.240 mmol)
was reacted with 2 mL of 30% KOH(aq) in 30 mL of THF as
described for 3a . The reaction mixture was refluxed for 3 h.
The volume was subsequently reduced by 60%, and the
precipitated porphyrin dipotassium salt was isolated by filtra-
tion. Slow addition of ether into a methanolic solution of the
crude product gave 3g (115 mg) in 46% yield as a microcrys-
CD3OD): δ 8.54 (br, s, 4H), 8.41 (br, s, 4H), 8.26 (d, 2H, J )
8.2 Hz), 8.11 (d, 2H, J ) 8.2 Hz), 7.99 (d, 2H, J ) 7.1 Hz),
7.76 (dd, 2H, J 1 ) J 2 ) 7.7 Hz), 7.52 (dd, 2H, J 1 ) J 2 ) 7.6
Hz), 7.32 (d, 2H, J ) 7.2 Hz), 7.21 (s, 4H), 2.53 (s, 6H), 1.85 (s,
12 Hz).
(i) Syn t h esis of r,â-5,15-Bis(8-m et h oxyca r b on yl-1-
n a p h th yl)-10,20-d im esitylp or p h yr in , 3b. A portion of the
porphodimethene (3) (200 mg, 0.23 mmol) was reacted with
NaOMe as described for the preparation of 2b, with a reaction
time of 1.5 h. Purification was achieved by column chroma-
tography (silica, CH2Cl2/hexanes, 4:1 to CH2Cl2 gradient).
Yield: 173 mg (81%). UV-vis (CHCl3) λmax, nm (log ꢀ): 425
1
talline solid. UV-vis (MeOH) λmax, nm (log ꢀ): 430 (5.63). H
NMR (MeOD): δ 8.54 (4H, d, J ) 4.6 Hz), 8.42 (4H, d, J ) 4.6
Hz), 8.24 (2H, d, J ) 7.6 Hz), 8.17 (2H, d, J ) 7.6 Hz), 8.08
(2H, d, J ) 7.6 Hz), 7.78 (2H, dd, J 1 ) J 2 ) 7.6 Hz), 7.46 (2H,
dd, J 1 ) J 2 ) 7.6 Hz), 7.19 (6H, m), 2.55 (6H, s), 1.87 (12H, s).
Anal. Calcd for C60.5H44N4O4.5K2Zn (6‚0.5MeOH): C, 69.70; H,
4.25; N, 5.37. Found: C, 69.78; H, 4.24; N, 5.40.
1
(5.53). H NMR (300 MHz): δ 8.61 (d, 4H, J ) 4.8 Hz), 8.57
(d, 4H, J ) 4.8 Hz), 8.40 (d, 2H, J ) 7.1 Hz), 8.34 (d, 2H, J )
8.3 Hz), 8.28 (d, 2H, J ) 8.3 Hz), 7.91 (dd, 2H, J 1 ) 8.3, J 2
)
7.1 Hz), 7.58 (dd, 2H, J 1) 8.3, J 2 ) 7.1 Hz), 7.38 (d, 2H, J )
7.1 Hz), 7.26 (s, 4H), 2.61 (s, 6H), 1.90 (s, 12H), 0.36 (s, 6H),
-2.32 (s, 2H). HRMS-FAB (m/z): MH+ calcd for C62H51N4O4,
915.3910; found, 915.3909.
(n ) Syn th esis of [r,â-5,15-Bis(8-ca r boxy-1-n a p h th yl)-
10,20-d im esitylp or p h yr in a to]cop p er Dip ota ssiu m Sa lt,
3h . Following the procedure described for 3a , 3e was treated
with potassium hydroxide, and the potassium salt was filtered
off and washed with THF. Diffusion of ether into a saturated
solution of the product in MeOH afforded 3h as a microcys-
talline solid. Yield: 61%. UV-vis (MeOH) λmax, nm (log ꢀ): 547
(4.20), 421 (5.28). Anal. Calcd for 3h ‚MeOH (C61H46N4O5K2-
Cu): C, 69.33; H, 4.39; N, 5.30. Found: C, 69.42; H, 4.32; N,
5.32.
(j) Syn th esis of r,â-5,15-Bis(8-h yd r oxym eth yl-1-n a p h -
th yl)-10,20-d im esitylp or p h yr in , 3c. A portion of the por-
phodimethene (3) (108 mg, 0.127 mmol) was reacted with
NaBH4 as described for 2c. Yield: 106 mg (98%). UV-vis (CH2-
Cl2) λmax, (log ꢀ): 424 (5.58). 1H NMR (300 MHz): δ 8.58 (d,
4H, J ) 4.6 Hz), 8.50 (d, 4H, J ) 4.6 Hz), 8.31 (d, 2H, J ) 8.2
Hz), 8.11-8.17 (m, 4H), 7.74 (dd, 2H, J 1 ) J 2 ) 7.6 Hz), 7.60-
7.62 (m, 4H), 7.22 (s, 4H), 3.04 (d, 4H, J ) 5.4 Hz), 2.57 (s,
6H), 1.82 (s, 12H), 0.22 (t, 2H, J ) 5.7 Hz), -2.29 (s, 2H).
HRMS-FAB (m/z): MH+ calcd for C60H51N4O2, 859.4012;
found, 859.3964.
Complete experimental details for 4; 4d ; 5-17; 8a -c; 9a -
c; 10c; 11c,e,f,h ; 14a -c; and 15a -c have been included in
the Supporting Information.
Ack n ow led gm en t. We thank the Research Corpo-
ration (Research Innovation Award 0162), the Deutsche
Forschungsgemeinschaft (postdoctoral fellowship for
M.H.), and the University of Florida (fellowship for
H.S.G.; startup funds for M.J .S.) for financial support.
Support from the National Science Foundation (CA-
REER Award 9874966) is also gratefully acknowledged.
We would also like to express our gratitude to Dr. Khalil
A. Abboud, Dr. Ion Ghiviriga, Dr. Lidia Matveeva, and
Dr. David H. Powell for their assistance.
(k ) Syn th esis of [a n ti-d ispir o[2H-Acen a p h th ylen -1-
on e-2,5′-10′,20′-d im esityld ih yd r op or ph yr in a to-15′,2′′-2′′H-
a cen a p h th ylen -1′′-on e]] zin c, 3d . The porphodimethene (3)
(50 mg, 0.059 mmol) was treated with Zn(OAc)2 as described
for 2d (1.5 h reaction time). Yield: 49 mg (91%). UV-vis (CH2-
1
Cl2) λmax, nm (log ꢀ): 475 (5.17). H NMR (300 MHz): δ 8.19
(dd, 4H, J 1 ) J 2 ) 7.1 Hz), 8.12 (d, 2H, J ) 7.1 Hz), 7.94 (d,
2H, J ) 8.3 Hz), 7.83 (d, 2H, J ) 7.2 Hz), 7.78 (d, 2H, J ) 7.2
Hz), 6.80 (s, 4H), 6.27 (d, 4H, J ) 4.2 Hz), 5.83 (d, 4H, J ) 4.2
Hz), 2.26 (s, 6H), 2.05 (s, 12H). HRMS-FAB (m/z): MH+ calcd
for C60H43N4O2Zn, 915.2677; found, 915.2690.
(l) Syn th esis of [a n ti-d ispir o[2H-Acen a p h th ylen -1-on e-
2,5′-10′,20′-d im e sit yld ih yd r op or p h yr in a t o-15′,2′′-2′′H -
a cen a p h th ylen -1′′-on e]] cop p er , 3e. A portion of the por-
phodimethene (2) (100 mg, 0.117 mmol) was dissolved in 25
mL of CHCl3, and 60 mg (0.305 mmol) of Cu(OAc)2‚H2O
dissolved in 5 mL of MeOH was added. The reaction mixture
was refluxed for 2 h, and the solvents were subsequently
removed under reduced pressure. The residue was redissolved
in CH2Cl2 and filtered through a small pad of silica gel.
Removal of the solvent afforded 3e as a reddish-brown solid.
Yield: 105 mg (98%). UV-vis (CHCl3) λmax, nm (log ꢀ): 483
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
the dipyrromethanes 1 and 2, for all porphodimethenes (2-
17) and their diamagnetic metal complexes (2d , 3d , and 4d ),
for the porphyrin diacids (dipotassium salts) 2a , 8a , 9a , 14a ,
and 15a , and for all porphyrin dialcohols and porphyrin
diesters. Complete experimental details and crystallographic
data (excluding structure factors) for all compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O010163L