Soluble synthetic multiporphyrin arrays. 1. Modular design and synthesis

Article abstract of DOI:10.1021/ja961611n

A set of porphyrin building blocks has been developed for the construction of light-harvesting model compounds and related molecular photonic devices. The porphyrins are facially encumbered to enhance solubility in organic solvents, are employed in a defi

Full text of DOI:10.1021/ja961611n

11166
J. Am. Chem. Soc. 1996, 118, 11166-11180
Soluble Synthetic Multiporphyrin Arrays. 1. Modular Design
and Synthesis
Richard W. Wagner, Thomas E. Johnson, and Jonathan S. Lindsey*
Contribution from the Department of Chemistry, North Carolina State UniVersity,
Raleigh, North Carolina 27695-8204
ReceiVed May 14, 1996X
Abstract: A set of porphyrin building blocks has been developed for the construction of light-harvesting model
compounds and related molecular photonic devices. The porphyrins are facially encumbered to enhance solubility
in organic solvents, are employed in a defined metalation state (free base (Fb) or zinc chelate), and bear peripheral
functional groups such as iodo or ethyne for joining the porphyrins via covalent bonds. The coupling of an
iodophenylporphyrin and an ethynylphenylporphyrin via mild Pd-mediated reactions (2-4 mM of each porphyrin in
toluene/triethylamine (5:1) with Pd2(dba)3 and AsPh3 at 35 °C for 2 h) yields the corresponding diphenylethyne-
linked multiporphyrin array in 70-80% yield. The arrays are easily purified by a sequence of flash silica
chromatography, preparative size exclusion chromatography, and gravity elution silica chromatography. The
diphenylethyne linkers give a center-to-center separation of the porphyrins of ∼20 Å. Model light-harvesting
compounds are easily prepared using Zn and Fb porphyrin building blocks. In order to investigate the role of the
linker in through-bond electronic communication, and the effect of through-bond electronic communication on the
rates and yields of photoinduced energy transfer in the arrays, four ZnFb dimers have been prepared that have a
systematic increase in steric hindrance in the diphenylethyne unit. The presence of steric hindrance inhibits rotation
of the phenyl group toward coplanarity with the porphyrin, thereby modulating the electronic communication. A
linear ZnFbZn trimer and a right-angle ZnFbZn trimer have been prepared to probe the effects of geometry on
electronic communication pathways. A linear ZnZnFb trimer has been synthesized to investigate the photodynamics
of energy migration among isoenergetic zinc porphyrins. These multiporphyrin arrays have sufficient solubility
(∼5 mM) for routine handling in organic solvents such as toluene, CH2Cl2, or CHCl3, and can be examined
spectroscopically (1-10 µM) in diverse solvents such as tetrahydrofuran, acetone, dimethyl sulfoxide, and castor
oil. This building block approach should make diverse multiporphyrin arrays readily available.
Introduction
harvesting systems highlights a broader range of unknowns: (1)
What types of pigments are appropriate and how do their
electronic, photophysical, and photochemical properties affect
light-harvesting efficiency? (2) How does energy migration
depend on the 3-dimensional organization (distance, orientation,
and packing patterns) of the pigments? (3) What are the
mechanisms of electronic communication among pigments, how
is electronic communication affected by the local medium, and
how is electronic communication altered in synthetic arrays that
have covalent connections between pigments versus those with
strictly non-covalent interactions? Most importantly, what types
of interactions provide efficient excited-state energy transfer
while simultaneously avoiding electron-transfer quenching
processes? (4) How many pigments in an array can function
as an antenna, and over what molecular distances can energy
migration occur? (5) Can energy-migration efficiency be
improved by structural alterations or energy gradients, and what
are the design constraints for achieving vectorial energy
migration? These questions are central to an understanding of
light-harvesting processes in photosynthetic organisms and to
realizing the objective of harnessing solar energy. Addressing
these questions can best be accomplished with synthetic model
systems. Furthermore, the ability to control and manipulate
energy-transfer processes in synthetic systems may also form
the basis for the design of a variety of molecular photonic
devices whose properties transcend photosynthesis. The de-
velopment of molecular-scale wires, gates, switches, sensors,
energy funnels, and related devices utilizing energy transfer may
lay the foundation for molecular-scale information-processing
systems.
Natural photosynthetic systems employ elaborate light-
harvesting antenna complexes, which absorb low intensity
sunlight (∼280-900 nm) and funnel energy to the reaction
centers. The light-harvesting complexes consist of large
numbers of chlorophylls (or bacteriochlorophylls) and accessory
pigments held in close proximity, usually in association with
protein scaffoldings. The absorption of a photon by a pigment
in the antenna complexes is followed by migration of the excited
state among the pool of pigments until a reaction center is
reached. Energy transfer can occur over long distances and
involve large numbers of chromophores, yet is extraordinarily
rapid (<100 ps) and has high quantum efficiency. An in-depth
understanding of the molecular origins of light-harvesting
phenomena has been difficult to acquire, mainly because the
natural antenna complexes encapsulate large numbers of several
types of pigments in self-assembling proteins that in turn are
embedded in membranes.1
Many issues concerning the origins of efficient light-
harvesting phenomena in natural systems remain unclear.
Consideration of the de noVo molecular design of light-
X Abstract published in AdVance ACS Abstracts, November 1, 1996.
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S0002-7863(96)01611-3 CCC: $12.00 © 1996 American Chemical Society

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11167
The challenge of creating model systems for energy-transfer
studies has led to many different approaches. Energy transfer
in assemblies of porphyrins has been studied in lipid bilayers,2
amorphous films,3 monolayers,4 coated microspheres,5 and
Langmuir-Blodgett multilayers.6 These non-covalent assem-
blies are synthesized easily, involve large numbers of visible-
absorbing chromophores, but often afford insufficient structural
control. Energy-transfer processes among pendant chro-
mophores in polymers have been characterized.7 Covalently-
linked systems for tests of the Forster theory of resonance energy
transfer have been developed that involve two UV-absorbing
chromophores held at defined distances.8 A synthetic hemo-
globin has been prepared containing four zinc-chlorophyllide
molecules at defined locations in place of the hemes.9 An ideal
model system would afford the dual capabilities of incorporating
a large and exact number of visible-absorbing pigments of
known photophysical properties, and exercising precise struc-
tural control over the entire ensemble of pigments.
Two promising approaches for achieving this ideal and
thereby addressing the issues outlined above are the self-
assembly of pigments bearing molecular recognition units and
the synthesis of covalent arrays of pigments. Balzani and co-
workers have pioneered the self-assembly of visible-absorbing
metal coordination compounds.10 A few energy transfer model
systems have been prepared involving the self-assembly of
porphyrins11 or porphyrins with other chromophores such as
sapphyrins12 or dansyl amides.13 Far more covalent arrays
containing two or more porphyrins have been prepared and their
energy transfer properties characterized.14-16 In addition,
covalent systems have been prepared containing porphyrins and
energy transfer donors such as anthracenyl polyenes,17 boron-
dipyrromethenes,16,18 carbocyanines,19 carotenoids,20 polyynes,21
and ruthenium coordination complexes (triplet transfer),22 as
have covalent systems containing porphyrins and energy transfer
acceptors such as tricarbocyanines,19 carotenoids (triplet trans-
fer),20 chlorins,23 phthalocyanines,24 and sapphyrins.25 A recent
system describes chlorin-chlorin energy transfer.26 Moore has
devised a dendritic antenna that is architecturally defined with
a vectorial organization of numerous phenylethyne-based chro-
mophores, though the absorption is predominantly in the
ultraviolet.27 In order to investigate visible light-harvesting
phenomena in a systematic manner, we have developed a
covalent building block approach for the synthesis of multi-
porphyrin arrays.
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Molecular Design
Synthetic porphyrins share many of the general structural,
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11168 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Wagner et al.
occurring chlorophylls and bacteriochlorophylls. A chief dif-
ference, however, is that porphyrins absorb strongly only in the
blue while chlorins and bacteriochlorins absorb strongly both
in the blue and in the red regions of the solar spectrum. This
distinction arises from the differing symmetries of the metal-
loporphyrin (D4h), chlorin (C2V), or bacteriochlorin (D2h) mac-
rocycles (considered for the unsubstituted planar chromophores).
In addition to the enhanced absorption in the red, the symmetry
of the hydroporphyrins also may facilitate vectorial energy
transfer. Though hydroporphyrins ultimately are more desirable
for incorporation in light-harvesting arrays, the more readily
accessible synthetic porphyrins are suitable for beginning to
investigate a number of issues concerning light-harvesting
phenomena.
Our building block approach was designed with the goal of
constructing arrays composed of large numbers of porphyrins
in defined geometries.28,29 Two anticipated problems that we
sought to avoid included insolubility of the multiporphyrin arrays
and photoinduced electron transfer quenching reactions among
the porphyrins. The solubility problem can be acute; indeed,
one early pentameric porphyrin array was practically insoluble,30
and some architecturally elegant arrays made more recently also
have been plagued by poor solubility.31-33 Approaches to
impart solubility to multiporphyrin arrays include incorporation
of long alkyl groups at the â-pyrrole positions,14v incorporation
of a variety of groups at the more accessible meso-positions
including alkyl groups,34 3,5-di-tert-butylphenyl groups,14j,35
4-alkoxycarbonylphenyl groups with long-chain alkyl units at
the ester,31,33 and introduction of ortho-disubstituted phenyl
groups.15,16,28,36 A deep understanding of the factors that favor
energy transfer over electron transfer is not available, however
one approach for limiting electron transfer is to arrange the
porphyrins at fixed, substantial distances where the electronic
interactions are relatively weak. Gaining a deeper understanding
of the design of energy transfer systems is a central goal of this
work.
The porphyrin building blocks we have devised incorporate
several distinctive features (Figure 1). Each porphyrin is in a
defined metalation state (metal or free base), has meso-phenyl
groups which can be substituted in the ortho positions, and bears
one or more peripheral iodo or ethyne groups. The use of free
base or metalloporphyrin building blocks enables the fabrication
of arrays with predesignation of the metalation state of each
porphyrin. The introduction of ortho-substituents such as
methyl, methoxy or benzyloxy36 is based on the notion that such
facially-encumbered porphyrins are less able to undergo cofacial
aggregation and hence should have greater solubility in organic
solvents. Though it is often difficult to pinpoint the structural
origins of why some compounds have high solubility and others
do not, most of these facially encumbered porphyrins have
Figure 1. Schematic of a linear porphyrin building block.
sufficient solubility in a variety of organic solvents for routine
synthesis, manipulation, and characterization. Using ortho-
substituents leaves the para-positions unhindered, where the
peripheral functional groups provide sites for joining the
porphyrins in a covalent manner. The use of iodophenyl and
ethynylphenyl groups yields a diphenylethyne linker when
porphyrins are joined, causing the porphyrins to be separated
by ∼20 Å center-to-center. In principle, the synthesis of diverse
arrays can be done by rational combination of a small set of
different building blocks, in the same way that diverse proteins
are available from a basis set of amino acids. The modular
nature of this building block approach has been discussed in
depth.29
The synthetic methods that make this building block approach
possible include (1) a synthesis of meso-porphyrins that is
compatible with a wide variety of precursor aldehydes,37
including the ortho-disubstituted benzaldehydes that yield
facially-encumbered porphyrins,38 (2) a one-flask synthesis of
meso-dipyrromethanes that enables a simple synthesis of trans-
substituted porphyrins39 and also boron-dipyrromethene dyes,40
(3) general methods for preparing metalloporphyrins,41 and (4)
Pd-mediated coupling reactions that are optimized for joining
the free base and metalloporphyrin building blocks under mild
conditions in dilute solution without altering the metalation state
of each porphyrin.42 Powerful analytical methods that are
invaluable for carrying out this synthesis program include the
ability to separate the larger arrays by size exclusion chroma-
tography (SEC) and to characterize them by laser desorption
mass spectrometry. The mild, neutral to slightly basic nature
of all experimental conditions in this approach ensures the
integrity of each free base or metalloporphyrin in the array.
This modular approach has been used to construct a star-like
array of five porphyrins (1)15 as well as a linear array of four
porphyrins and one accessory pigment (Figure 2). The latter
functions as a molecular photonic wire (2).16 A photon of light
is absorbed at the input end and a photon of light is then emitted
(28) Lindsey, J. S.; Prathapan, S.; Johnson, T. E.; Wagner, R. W.
Tetrahedron 1994, 50, 8941-8968.
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W. Tetrahedron Lett. 1989, 30, 1129-1132.
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pp 49-86. Lindsey, J. S.; MacCrum, K. A.; Tyhonas, J. S.; Chuang, Y.-Y.
J. Org. Chem. 1994, 59, 579-587.
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Ed.; Elsevier: Amsterdam, 1975; pp 157-231. Buchler, J. W. In The
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pp 389-483.
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1995, 60, 5266-5273.
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Turowska-Turk, I.; Scheidt, W. R. Tetrahedron 1994, 50, 11097-11112.

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11169
Figure 2. Light-harvesting array and a molecular photonic wire.
at the opposite (output) end of the same molecule. The quantum
efficiency of energy migration from input to output is 76%.
More recently two molecular optoelectronic gates have been
devised based on the same general molecular architecture as
the wire, and these also have been constructed using the same
building block approach.18 These porphyrin arrays have
controlled inter-porphyrin distances yet exhibit high solubility
in good organic solvents (5 mM in toluene or CH2Cl2). This
building block approach is not restricted to the synthesis of
hydrophobic compounds and has recently been applied to the
synthesis of amphipathic dimeric and trimeric arrays for
incorporation in lipid bilayer assemblies.43
In designing the diphenylethyne-linked multiporphyrin arrays
we attempted to place methyl groups at all ortho-phenyl
positions allowable by the available synthetic methods with the
sole aim of increasing the solubility of the arrays. In resonance
Raman experiments of various arrays, however, Seth et al.
observed an enhanced band due to the ethyne unit in the linker.44
Further studies showed that the enhanced band was present with
those diphenylethyne linkers (or monomers bearing the ethyne
substituent) lacking ortho-phenyl substitution (3), but was absent
with those diphenylethyne linkers substituted with 2,6-dimethyl
groups (4). These studies suggested that the diphenylethyne
unit mediates electronic communication between the porphyrins,
and that rotation toward a more coplanar geometry of the
diphenylethyne with the porphyrin(s) would enhance the com-
munication and thereby increase the energy-transfer rate (Figure
3). Conversely, phenyl rings that have constrained rotation due
to ortho-dimethyl substitution would have diminished electronic
communication and should exhibit slower rates of energy
transfer.
We selected the diphenylethyne linker at the outset of this
work because we felt it would provide ample distance of
separation (20 Å center-to-center) to avoid competing electron
transfer quenching reactions while still permitting energy transfer
among the porphyrins. Indeed, the diphenylethyne linker affords
a weakly coupled system where the absorption bands of the
porphyrin arrays are only slightly perturbed from those of the
component porphyrins, yet single-step energy-transfer efficien-
cies are g90% with no discernible electron-transfer quenching.
More recently we have learned that in spite of the large distance
and the relatively unchanged absorption spectra, the diphenyl-
ethyne linker provides some through-bond electronic com-
munication between the attached porphyrins.44 Other porphyrin
arrays have been prepared with ethyne or butadiyne linkages
attached directly to the porphyrins, and these show profound
shifts in the optical spectra.31,45
To investigate this hypothesis concerning structural control
of energy transfer, we have prepared a set of dimeric arrays
with a progressive increase in the steric hindrance in the
diphenylethyne linkers. This set of dimers allows systematic
probing of the effects of linker structure on the rates and yields
of energy transfer. Zinc and free base porphyrins are employed
in the arrays. Zinc porphyrins are used as they exhibit
photophysical properties similar to those of magnesium por-
phyrins but have been more easily synthesized than magnesium
porphyrins. Free base porphyrins absorb and emit at longer
wavelengths than zinc porphyrins and serve as a convenient
low-energy trap to which excited-state energy flows. Two
trimers have been prepared to examine the role of geometry
(linear, right-angle) on electronic communication among por-
phyrins. An additional trimer has been designed to investigate
the rate of energy transfer among isoenergetic zinc porphyrins
in an array. Finally we summarize the solubility properties of
this family of arrays and related compounds. This paper
describes the synthesis of these arrays, and the two companion
papers investigate the photophysical properties46 and the modes
(43) Nishino, N.; Wagner, R. W.; Lindsey, J. S. J. Org. Chem. In press.
(44) Seth, J.; Palaniappan, V.; Johnson, T. E.; Prathapan, S.; Lindsey, J.
S.; Bocian, D. F. J. Am. Chem. Soc. 1994, 116, 10578-10592.
(45) Arnold, D. P.; Johnson, A. W.; Mahendran, M. J. Chem. Soc., Perkin
Trans. 1 1978, 366-370. Arnold, D. P.; Nitschinsk, L. J. Tetrahedron 1992,
48, 8781-8792. Arnold, D. P.; Nitschinsk, L. J. Tetrahedron Lett. 1993,
34, 693-696. Arnold, D. P.; James, D. A.; Kennard, C. H. L.; Smith, G. J.
Chem. Soc., Chem. Commun. 1994, 2131-2132. Anderson, S.; Martin, S.
J.; Bradley, D. D. C. Angew. Chem., Int. Ed. Engl. 1994, 33, 655-657.
Anderson, H. L. Inorg. Chem. 1994, 33, 972-981. Gosper, J. J.; Ali, M. J.
Chem. Soc., Chem. Commun. 1994, 1707-1708. Lin, V. S.-Y.; DiMagno,
S. G.; Therien, M. J. Science 1994, 264, 1105-1111. Lin, V. S.-Y.; Therien,
M. J. Chem. Eur. J. 1995, 1, 645-651.

11170 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Wagner et al.
Figure 3. Effect of ortho-dimethyl groups on linker rotation.
Chart 1. Aldehyde Precursors to Porphyrins
Chart 2. Porphyrin Bulding Blocks
of electronic communication47 in the same set of arrays. The
results from these studies provide fundamental information for
guiding the design of more sophisticated synthetic light-
harvesting model compounds. This work is a prelude to
addressing higher order organizational issues in light-harvesting
systems, such as the 3-dimensional organization of pigments,
channeling of energy migration, the role of energy gradations,
and required photophysical properties of the pigments.
Results and Discussion
Synthesis of Porphyrin Building Blocks. The preparation
of the porphyrin building blocks depends on the availability of
the corresponding functionalized benzaldehydes. For preparing
diphenylethyne linked arrays, the key benzaldehydes bear
ethynes or iodo groups (Chart 1). 4-Iodobenzaldehyde (5) is
commercially available, and 4-[2-(trimethylsilyl)ethynyl]ben-
zaldehyde (6) is readily derived from 5 or from 4-bromoben-
zaldehyde. We have refined the syntheses of aldehydes 7 and
8.28 An improved diazotization of 2,6-dimethyl-4-iodoaniline
afforded 2,6-dimethyl-4-iodobenzonitrile, the precursor to 7, in
42% yield compared with 11% previously. Ethynylation of 2,6-
dimethyl-4-bromobenzaldehyde via Pd-mediated coupling con-
ditions under mild conditions (55 °C for 36 h) gave cleaner
reaction mixtures with less higher-molecular weight material,
affording 8 in 85% yield upon recrystallization from 2-propanol.
These aldehydes enable the synthesis of a variety of porphyrin
building blocks. In order to pinpoint the effects of substituents
on the porphyrin ring, diphenylethyne carboxaldehydes (9, 10)
were prepared for the synthesis of the corresponding porphyrin
model compounds.
Porphyrin building blocks bearing one functional group
provide the basis for the synthesis of dimeric arrays. These
types of porphyrins (Chart 2) can be obtained through mixed-
aldehyde condensations using the two-step one-flask room
(46) Paper 2 of this series: Hsiao, J.-S.; Krueger, B. P.; Wagner, R. W.;
Johnson, T. E.; Delaney, J. K.; Mauzerall, D. C.; Fleming, G. R.; Lindsey,
J. S.; Bocian, D. F.; Donohoe, R. J. J. Am. Chem. Soc. 1996, 118, 11181-
11193.
(47) Paper 3 of this series: Seth, J.; Palaniappan, V.; Wagner, R. W.;
Johnson, T. E.; Lindsey, J. S.; Bocian, D. F. J. Am. Chem. Soc. 1996, 118,
11194-11207.
(48) Little, R. G.; Anton, J. A.; Loach, P. A.; Ibers, J. A. J. Heterocycl.
Chem. 1975, 12, 343-349.

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11171
temperature synthesis of porphyrins.37,38 The method of mixed-
aldehyde condensations with pyrrole affords a mixture of six
porphyrins.48 This approach is not elegant but is expedient if
the desired porphyrin can be easily separated by chromatogra-
phy. In general, the separability of these mixtures of porphyrins
by adsorption chromatography depends on the different polarities
of peripheral substituents, the different polarity of ortho-
substituents, and the different amounts of facial encumbrance
due to the presence of ortho-substituents.28 In performing
numerous mixed-aldehyde condensations, we have made the
following observations:
Scheme 1. Scheme for Preparing Porphyrin Building Blocks
(1) Condensation of 4-[2-(trimethylsilyl)ethynyl]benzaldehyde
(6) and benzaldehyde with pyrrole affords a mixture of
porphyrins that cannot be separated easily as the peripheral
substituents (H, trimethylsilylethyne) have nearly identical
polarities and neither aldehyde has ortho-substituents.
(2) Condensation of 6 and mesitaldehyde with pyrrole affords
a mixture of porphyrins where each porphyrin (except the cis
and trans) has different amounts of facial encumbrance; the
components of this mixture closely chromatograph but separa-
tion can be achieved with repetitive column chromatography.
The mono-ethynyl porphyrin 11 was obtained with some
difficulty in this manner.28
(3) Condensation of 4-iodobenzaldehyde (5) and mesitalde-
hyde with pyrrole affords a mixture that is easily separable on
a single adsorption column, due both to the differing degrees
of facial encumbrance of the porphyrins and the slightly different
polarities of the iodo and methyl groups. This approach readily
afforded the mono-iodo porphyrin 14, and other more highly
iodinated porphyrins also can be obtained easily, such as the
cis-diiodo-substituted porphyrin 15 (7% yield). The latter is
the key building block for the synthesis of a right-angle trimeric
array of porphyrins.
(4) Condensation of the ortho-dimethyl substituted benzal-
dehyde 7 (or 8) and mesitaldehyde with pyrrole yields an
inseparable mixture as each porphyrin has eight ortho-methyl
groups. In contrast, condensation of 7 (or 8) and benzaldehyde
with pyrrole yields a separable mixture as each porphyrin (except
the cis and trans) has different degrees of facial encumbrance.
Thus condensation of benzaldehyde, 8, and pyrrole gave 16 in
17% yield, while condensation of benzaldehyde, 7, and pyrrole
gave 19 in 13.5% yield. In each case one flash silica column
was used to separate the porphyrins from unwanted side
products, and a second flash silica column afforded separation
of the various porphyrins. Porphyrins 16 and 19 each eluted
as the fifth of the six porphyrin components in their respective
mixtures.
(5) Condensation of 4-[2-(trimethylsilyl)ethynyl]benzaldehyde
(6) and 2,6-dimethoxybenzaldehyde with pyrrole yields a crude
reaction mixture from which the desired porphyrin (20) was
isolated in 8% yield via a single flash silica chromatography
column (similar results were obtained upon condensation with
4-iodobenzaldehyde and 2,6-dimethoxybenzaldehyde).28 The
polarity imparted by the ortho-methoxy groups dramatically
eases the separation of this mixture of porphyrins.
(6) Condensation of the ortho-dimethyl substituted benzal-
dehyde 7 (or 8) and 2,6-dimethoxybenzaldehyde with pyrrole
yields a crude reaction mixture from which the desired porphyrin
can be isolated via a single flash silica chromatography column.
Although each porphyrin has substituents at all eight ortho-
positions, the different polarity of the methoxy and methyl
groups affords facile separation. Thus the mono-iodo porphyrin
26 and the mono-ethynyl porphyrin 23 were isolated in 4.8%
and 4.4% yield, respectively.
tions where both aldehydes have identical ortho-substituents
(either all substituted or all unsubstituted) and nonpolar
peripheral substituents (e.g., iodo or ethyne groups). Porphyrins
that bear one iodo or ethyne group and three sites of facial
encumbrance (11 or 14, derived from three mesitaldehyde
molecules, and 6 or 5) yet with similar polarity can be separated
by repetitive chromatography. Porphyrins bearing only one site
of facial encumbrance (16 or 19, derived from three benzalde-
hyde molecules and 8 or 7) are more easily separated. Por-
phyrins that bear one ethyne (or iodo) group and three sites of
facial encumbrance (20, derived from three 2,6-dimethoxyben-
zaldehyde molecules, and 6) with polar groups can be separated
easily by chromatography. Porphyrins with sets of ortho-
substituents of considerably different polarity, as in the case of
the methoxy-substituted porphyrins (23, 26), also are separated
with great ease.
The ortho-methoxy-substituted porphyrins were initially the
most attractive as their separation is most straightforward.
Though the ZnFb dimers exhibited good solubility in CH2Cl2
and other solvents, we subsequently found that the Zn2 dimer
having a hindered linker (prepared from 25 and 26) had poor
solubility in some electrochemical studies (Vide infra). The
family of ortho-methoxy-substituted porphyrins was abandoned
for these studies and the more soluble mesityl-substituted
porphyrin dimers were pursued. The desired mono-ethynyl
porphyrin 11 is obtained with difficulty, however, and we sought
a method to overcome this bottleneck.
To prepare the ZnFb dimers, one of the porphyrins is required
as the zinc porphyrin. We found that metalation of the mixture
of six porphyrins afforded the zinc porphyrins which could be
easily separated via column chromatography (Scheme 1). Thus
the crude mixture from a 2-L scale reaction of mesitaldehyde,
aldehyde 6, and pyrrole was concentrated and then passed over
a flash silica column, yielding the mixture of free base
porphyrins freed from reagents, byproducts, and open-chain
oligopyrromethenes. This mixture was metalated with zinc. The
resulting zinc porphyrins were separated on a single flash silica
column, affording 280 mg of zinc mono-ethynyl porphyrin 12
in 12.4% overall yield. Given the two aldehydes the desired
porphyrin can be obtained in ∼2 days by this approach. The
zinc mono-ethynyl porphyrin 12 can be demetalated to afford
In summary, it is not possible to easily obtain a mono- or
trifunctionalized porphyrin building block via mixed condensa-

11172 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Wagner et al.
Scheme 2. Synthesis of a Porphyrin Building Block for
Preparing Linear Arrays
Scheme 3. Pd(0)-Catalyzed Synthesis of an Ethyne-Linked
Porphyrin Dimer
have refined the synthesis of porphyrin 27 by separating the
zinc porphyrins rather than the free base porphyrins. Thus the
mixture of three porphyrins obtained from the 500-mL scale
reaction of 2.5 mmol 8, 2.5 mmol 4-iodobenzaldehyde (5), and
5 mmol meso-(mesityl)dipyrromethane was subjected to zinc
insertion conditions and then chromatographed on flash silica
gel. The three zinc porphyrins afforded distinct, non-overlap-
ping chromatographic bands that were easily separated on a
single flash silica column, and 280 mg (11%) of the zinc chelate
28 was obtained in a straightforward manner. Demetalation
(0.03 M TFA in CH2Cl2) of 28 at room temperature afforded
the free base porphyrin 27.
In preparation for the coupling reactions the trimethylsilyl-
protected porphyrins were deprotected at room temperature with
tetrabutylammonium fluoride on silica, or with K2CO3 in THF/
methanol. The use of K2CO3 is cleaner and generally gives
higher yields than tetrabutylammonium fluoride on silica, though
tetrabutylammonium fluoride on silica is used more frequently
as most of these porphyrins lack adequate solubility in THF/
methanol.
Synthesis of Dimeric Arrays. Porphyrin-porphyrin dimers
are of interest for investigating the pairwise interactions of
porphyrins in larger arrays. The preparation of the dimeric
arrays relies on Pd-mediated coupling reactions of ethynyl
porphyrins and iodo porphyrins (Scheme 3). Pd-mediated
coupling reactions have often been performed at high concentra-
tions and elevated temperatures with a copper reagent as a
cocatalyst. To meet the constraints of porphyrin chemistry we
refined this key Pd-mediated coupling reaction so that the
porphyrins can be joined at modest temperature, in dilute
solution of equimolar porphyrin reactants, in the absence of any
copper reagents.42 Thus the reaction of a free base iodopor-
phyrin (14, 5 mM) and a zinc ethynylporphyrin (13, 5 mM)
with the Pd(0) reagent Pd2(dba)3 and AsPh3 in toluene/
triethylamine (5:1) at 35 °C under argon in standard glassware
afforded the diphenylethyne-linked dimer 29 in 2 h in >70%
yields. These conditions generate the Pd(0) reagent in situ and
avoid the use of any copper cocatalysts. These conditions
represent the outcome of a lengthy optimization study42 and
are superior to the more forcing conditions (Pd(PPh3)4 at g50
°C for 24 h) that we employed earlier.28
the corresponding free base porphyrin 11 or can be deprotected
forming 13 for use in the syntheses of arrays. In general, this
approach is applicable for porphyrins that have peripheral and
ortho-substituents that are nonpolar. The introduction of zinc
imparts a polar site which enhances the affinity of the porphyrins
for silica gel. The effects of facial encumbrance are accentuated
as the interaction of the face of the zinc porphyrin with the
chromatographic medium determines the affinity and the elution
order of these otherwise nonpolar porphyrins. We find that even
if the free base porphyrin 11 is desired, the separation of the
zinc porphyrins and subsequent demetalation is the preferred
route. The zinc porphyrins typically have the added advantage
of higher solubility than the free base porphyrins.
In order to prepare linear arrays containing two or more
porphyrins, as in the molecular wire 2, a porphyrin building
block with two different substituents in a trans-configuration
is required. The iodo-ethynyl porphyrin 27, which we previ-
ously synthesized,39 meets these needs (Scheme 2). In the
separation of the free base porphyrins on silica, the bis-ethyne
and mono-ethyne porphyrins are not completely resolved and
one or more alumina columns are required to isolate 27. We
During the course of this work we sought to make sure that
the Pd-coupling conditions were not inadvertently yielding any
Pd porphyrins. Excess phenylacetylene and iodobenzene (0.01
M each) were subjected to these mild Pd-coupling conditions
in the presence of meso-tetraphenylporphyrin (TPP, 0.001 M).

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11173
No PdTPP was observed by TLC analysis (silica, hexanes/CH2-
Cl2 (1:1), PdTPP Rf 0.7, TPP Rf 0.4) with calibrated standards
of PdTPP; given the limits of detection the yield of PdTPP must
be e0.05%. Preparative chromatography of this reaction
mixture in an effort to isolate PdTPP (based on its known
chromatographic retention factor) gave no PdTPP, indicating
the yield of any Pd insertion into TPP is e0.0003%. Thus these
Pd coupling conditions are compatible with free base porphyrins.
Chart 3. Zn-Fb Porphyrin Dimers with Different Sites of
o-Methyl Substitution
In the synthesis of ZnFb-dimer 29, the milder coupling
conditions give cleaner reaction mixtures with lesser amounts
of high molecular weight materials and no detectable diphen-
ylbutadiyne-linked dimer. The crude reaction mixture consists
of small amounts of (uncharacterized) high molecular weight
materials, desired diphenylethyne-linked ZnFb dimer (29),
monomeric porphyrin starting materials or byproducts, reagents,
and other byproducts. The progress of the reaction can be
assessed by silica TLC or by analytical SEC. For preparative
purification, initially we employed a single flash silica column
with hexanes/CH2Cl2 (2:1). Upon performing time-resolved
fluorescence measurements, we observed a multiphasic decay
with a single component constituting 95% of the decay and two
other components constituting the remaining 5%. The latter
two components gave lifetimes characteristic of monomeric zinc
and free base porphyrins.46 Thus the single flash silica column
afforded dimer having purity of 95%. To achieve higher levels
of purity as required for photochemical studies, we devised a
better purification scheme.
The improved purification scheme involves a sequence of
three chromatography procedures. First, the concentrated crude
reaction mixture is passed over a short flash silica column,
eluting AsPh3 first followed by the mixture of porphyrin
components, leaving the Pd species bound to the top of the
column. The porphyrin mixture then is passed over a prepara-
tive SEC column in toluene, which affords separation of higher
molecular weight material, desired dimer, and most monomeric
porphyrins. The fraction containing the desired dimer then is
passed over a silica column using gravity elution with hexanes/
CH2Cl2 (2:1), which removes a small amount of monomeric
zinc porphyrin byproduct that co-chromatographed with the
dimer fraction via preparative SEC. The purity of fractions can
be assessed by analytical SEC at all stages of the purification.
For example, the dimer fraction obtained from preparative SEC
columns consists of dimer (99%) and residual monomeric zinc
porphyrin (1%) based on integrated peak areas; upon the final
silica column the dimer is the only integrated peak (100%) in
the analytical SEC. The fluorescence lifetimes of these dimers
were monophasic with amplitude g99%, reflecting the much
cleaner samples which contained e1% zinc porphyrin mono-
mer.46
but upon attempted insertion of zinc into the free base porphyrin
unit, a relatively insoluble Zn2 dimer (37) was obtained. The
insolubility of this dimer shows that extensive facial encum-
brance alone, at least when groups of differing polarity are
employed, is insufficient to ensure solubility in all cases.
Synthesis of Trimeric Arrays. A linear trimer and a right-
angle trimer were prepared to investigate the influence of
geometry on electronic communication among porphyrins. We
have previously described the synthesis of the linear ZnFbZn-
trimer 38 (Chart 4).42 The corresponding right-angle trimer 40
was prepared in analogous fashion (Scheme 4). The reaction
of the cis-diiodo free base porphyrin 15 and the zinc ethynyl
porphyrin 13 under the Pd-mediated coupling reactions (Pd(0)
reagent Pd2(dba)3 and AsPh3 in toluene/triethylamine (5:1) at
35 °C under argon for 2 h) afforded a mixture consisting of
higher molecular weight material, trimer 40, dimer, and a
monomeric zinc porphyrin, from which the desired right-angle
trimer was obtained in 90% yield. Metalation of these trimers
with zinc afforded the Zn3 trimers 39 and 41.
The natural light-harvesting complexes exhibit rapid energy
migration among isoenergetic pigments. The molecular wire
2 includes an array of three zinc porphyrins, implying a
minimum of two energy transfer steps between zinc porphyrins
as energy flows from the boron-dipyrromethene dye to the free
base porphyrin. In principle energy transfer can occur in either
direction among the zinc porphyrins. To investigate the
dynamics of energy migration, including the possibility of
reversible energy transfer among zinc porphyrins, we prepared
the linear ZnZnFb-trimer 44 shown in Scheme 5.
The dimers 29-32 were obtained in 69-86% yields (Chart
3). This three-column chromatography sequence is applicable
to all dimers (and the trimer) bearing mesityl substituents. The
ZnFb diphenylethyne-linked dimers are easily identified because
the visible absorption spectra (450-700 nm) of the dimers are
the sum of the spectra of the component (zinc porphyrin, free
base porphyrin) parts. No demetalation of the zinc porphyrin,
transmetalation of the zinc porphyrin, or metalation of the free
base porphyrin occurs during the synthetic reactions or the
purification, as all the conditions to which the building block
porphyrins and arrays are treated involve mild temperatures and
neutral to slightly basic solvents. These coupling reactions are
highly reproducible. The all-zinc dimers 33-35 were prepared
by treatment of the appropriate ZnFb dimers with methanolic
zinc acetate. Zinc insertions were generally quantitative. The
methoxy-substituted bis-hindered dimer 36 also was obtained,
The reaction of the zinc ethynyl porphyrin 13 with the zinc
iodo ethynyl porphyrin building block 28 via the Pd-coupling
conditions afforded the porphyrin dimer 42 in 68% yield. This
reaction proceeded like the previous syntheses of porphyrin
dimers. Deprotection of 42 in CHCl3 with tetrabutylammonium
fluoride on silica gel afforded the monoethyne-substituted ZnFb-
dimer 43 in 90% yield. Reaction of 43 with the free base iodo

11174 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Chart 4. Linear Porphyrin Trimers
Wagner et al.
Scheme 4. Synthesis of Right-Angle Porphyrin Trimers
ethyne unit, exhibit characteristic features in the covalently-
linked arrays. For example, in monomer 13 (or 14) the
â-pyrrole protons that are flanked by the mesityl groups (distal
from the para-substituted phenyl unit) give an unresolved
singlet, while AB doublets are observed for the â-pyrrole protons
that are situated between the mesityl group and the substituted
phenylene unit. The protons on the phenylene group yield an
AA′BB′ pattern. Upon coupling of 13 and 14 to form the ZnFb-
dimer 29, the observed splitting pattern due to the â-pyrrole
protons is the sum of the splitting patterns of the component
parts. The signals from the meta-phenylene protons of 13 and
14 shift downfield by ∼0.2 ppm upon formation of the
diphenylethyne linkage in 29. This change in chemical shift is
observed in all the arrays (dimers, trimers, pentamer) and is a
diagnostic for the formation of the diphenylethyne linkage.
Formation of the symmetric Zn2-dimer 33 caused simplification
of the 1H NMR spectrum (CDCl3), giving â-pyrrole and
phenylene splitting patterns identical with zinc porphyrin
monomer 13.
Similar features were observed in the larger arrays. The
ZnFbZn-trimer 38 showed resonances from the â-pyrrole
protons that are the sum of the spectra of the component parts,
and the phenylene protons (8.33-8.06 ppm) exhibited, as
expected, two sets of AA′BB′ patterns. In the pentamer 1, the
four-fold symmetric substitution causes the â-pyrrole protons
of the core free base porphyrin to give a singlet (9.097 ppm).
A detailed NMR study of the conformational mobility of these
types of multiporphyrin arrays has been performed.49
Solubility. High solubility of the arrays in a variety of
solvents is essential for synthesis, manipulation, chemical
characterization, and spectroscopic analysis. Because of the
high extinction coefficients of porphyrins, spectroscopic studies
are usually performed at concentrations of 1-10 µM, but for
synthesis, purification, and manipulation, higher solubility is a
necessity. Here we delineate some of the operational solubilities
we have observed. The ZnFb-dimers 29-32 are soluble in
toluene/triethylamine (5:1) used in the Pd-coupling reactions
(a convenient concentration of 1.8-4.3 mM), can be dissolved
in hexanes/CH2Cl2 (1:1 or 2:1) for preparative chromatography
(maximum solubility corresponds to ∼4.7-7.8 mM), are soluble
in CHCl3 for conversion to the bis-zinc chelates (1.9-3.4 mM),
and can be dissolved in a minimal amount of CDCl3 for NMR
spectroscopy (6.4-7.3 mM). For these dimers a concentration
of 5 mM corresponds to ∼8 mg/mL. Similar solubility
properties also were observed for the larger arrays. Thus the
ZnZnFb-trimer 44 was soluble at 2.4 mM in toluene/triethyl-
amine (5:1) and at 4.2 mM in CDCl3 (10 mg/mL). The
molecular wire 2 was soluble at 1.5 mM in toluene/triethylamine
(5:1) and at 2 mM in CDCl3 (7 mg/mL).
porphyrin 14 via the same Pd-mediated coupling reactions
afforded the ZnZnFb-trimer 44. The formation of the trimer
was easily detected by analytical SEC (but not by TLC). This
compound could be purified exclusively by preparative SEC,
but the improved chromatography procedures developed for the
dimers 29-32 provided the highest quality purification. The
ZnZnFb-trimer 44 was isolated in 80% yield. The identification
of this trimer is facilitated as the visible absorption bands are
the sum of the spectra of the component parts, showing two
zinc porphyrins and one free base porphyrin. The yields in the
synthesis of the trimer 44 (coupling 68%, deprotection 90%,
coupling 80%) are consistently high, indicating the applicability
of this approach for the synthesis of linear multiporphyrin arrays.
This stepwise elongation process is the same strategy employed
in the preparation of the molecular wire 2.16 The synthesis of
the molecular wire will be described elsewhere.
Synthesis of a Pentameric Array. A pentamer was prepared
by coupling tetrakis(4-iodophenyl)porphyrin28 with the zinc
monoethynyl porphyrin 22. These methoxy-substituted por-
phyrins are not adequately soluble in toluene/triethylamine (5:
1) thus pyridine/triethylamine (5:1) was employed as coupling
solvent. We have not optimized the coupling conditions in this
solvent, and use of Pd(PPh3)4 required reaction at 100 °C for
12 h to form the pentamer. The products of the reaction were
easily separable by silica chromatography, however, and the
Zn4Fb pentamer was obtained in 50% yield. The architecture
of the pentamer resembles a four-fold dimer as the core free
base porphyrin is attached to four zinc porphyrins via diphen-
ylethyne linkers. This pentamer was used in prior studies of
electronic communication among the porphyrins.44
In addition, the dimers and trimers have been examined for
analytical and spectroscopic purposes in dilute solution in a
variety of solvents, though the upper solubility limits in these
solvents have not been established. The absorption bands hardly
1H NMR Features. The phenyl- or mesityl-substituted
1
monomers and arrays were readily characterized by H NMR
spectroscopy in CDCl3 or toluene-d8, while the methoxy-
substituted pentamer was examined in CD2Cl2. The resonances
from the â-pyrrole protons, and from the protons flanking the
(49) Bothner-By, A. A.; Dadok, J.; Johnson, T. E.; Lindsey, J. S. J. Phys.
Chem. In press.

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11175
Scheme 5. Synthesis of the ZnZnFb Trimeric Porphyrin Array
shift across a change of solvent polarity from toluene to dimethyl
sulfoxide (Table 1). Absorption and fluorescence spectroscopy
of the dimers and trimers has been performed at 1-20 µM in
solvents such as acetone, dimethyl sulfoxide, and the very
viscous medium, castor oil. In addition, the purity of each of
the arrays has been assessed by analytical SEC in THF
(convenient concentration of 10-5 to 10-4 M).
The mesityl- or phenyl-substituted porphyrin arrays are
soluble in a range of solvents, particularly toluene. The
methoxy-substituted porphyrin arrays are soluble in CH2Cl2,
CHCl3, or pyridine, but are rather insoluble in toluene. The
methoxy-substituted dimer 36 (Chart 3) was less soluble than
the mesityl and phenyl arrays and surprisingly, the bis-zinc
derivative 37 was found to be nearly insoluble. In general the
highest solubilities of the methoxy-substituted arrays in the best
solvents (CH2Cl2, CHCl3, or pyridine) are less than that of the
mesityl- or phenyl-substituted porphyrin arrays in toluene or
CH2Cl2. Accordingly we shifted our focus toward the mesityl-
substituted building block porphyrins and have used these in
the preparation of the light harvesting model compounds
described here, the molecular wire,16 and molecular optoelec-
tronic gates.18
Conclusions
Modular porphyrin building blocks can be used to construct
a variety of synthetic multiporphyrin arrays. The multiporphyrin
arrays are soluble in various organic solvents, have controlled
interporphyrin distances, incorporate porphyrins in predeter-
mined metalation states, and have visible absorption spectra that
are nearly the sum of spectra of the component parts. The
straightforward synthesis of these porphyrin building blocks and
arrays should facilitate investigation of issues underlying light-
harvesting phenomena and also allow the creation of a wide
variety of molecular photonic devices.
Experimental Section
General. 1H NMR spectra (300 MHz, IBM FT-300), absorption
spectra (HP 8451A, Cary 3), and fluorescence spectra (Spex FluoroMax)
were collected routinely. Porphyrins were analyzed by laser desorption
(LD-MS) or plasma desorption mass spectrometry (PD-MS).50 Pyrrole
was distilled at atmospheric pressure from CaH2. Commercial sources
provided trimethylsilylacetylene (Janssen Chimica), pyridine (Fluka),
(50) Lindsey, J. S.; Chaudhary, T.; Chait, B. T. Anal. Chem. 1992, 64,
2804-2814.

11176 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Table 1. Absorption Maxima in Different Solventsa
Wagner et al.
dimer. In prior work we have determined the yield of particular
components by injecting precise amounts of known concentrations of
authentic samples. We also have obtained working curves that establish
the linearity of Beers law for the concentrations of the samples
investigated. We use analytical SEC primarily to monitor the progress
of the reaction in a semiquantitative way, and then to check that the
purified product is truly free of higher molecular weight material (which
typically appears at the leading edge of the array), starting porphyrins,
and intermediates.
sample
toluene acetone acetonitrile DMSO castor oil
monomers
TPP
420
548
420
548
420
551
424
550
423
550
423
550
414
545
414
545
415
545
422
554
422
554
424
556
414
546
414
547
414
546
423
556
422
556
424
558
419
549
420
549
419
548
428
561
427
560
430
562
419
549
420
549
419
548
427
557
426
556
428
558
FbU (11)
FbH (16)
ZnH (17)
ZnTPP
Solvents. CH2Cl2 (Fisher, reagent grade) and CHCl3 (Fisher certified
A.C.S.) were subjected to simple distillation from K2CO3. The
commercially-available CHCl3 contained ethanol (0.75%) as a stabilizer.
All references to CHCl3 in this paper pertain to CHCl3 containing 0.75%
ethanol. Simple distillation does not significantly alter the ethanol
content. THF (Fisher certified A.C.S.) and toluene (Fisher certified
A.C.S.) were distilled from LiAlH4 and triethylamine (Fluka puriss)
was distilled from CaH2. Other solvents were used as received.
Methoxy-Substituted Zn4Fb-Pentamer 1.15 A sample of tetrakis-
(4-iodophenyl)-porphyrin28 (25 mg, 22.4 µmol) was added to a solution
of zinc ethynyl porphyrin (22, 80 mg, 90.8 µmol) in 15 mL of pyridine-
triethylamine (5:1) and the mixture was deaerated with argon for 1 h.
The Pd(0) catalyst (Pd(PPh3)4, 10 mg, 8.7 µmol) was added and
deaeration was continued for 15 min. Then the flask was immersed in
an oil bath at 100 °C. The reaction mixture became homogeneous
within 30 min and remained homogeneous for the duration of the
reaction. At 7.5 h the product distribution consisted of pentamer, zinc
monomer, and several intermediates as determined by analytical SEC.
Additional samples of 22 (20 mg) and Pd(PPh3)4 catalyst (2 mg) were
added at this time and again at 10 h. At 12 h the product distribution
consisted of lesser quantities of intermediates and increased amounts
of pentamer and butadiyne-linked dimer. Solvent was removed under
reduced pressure and the residue was treated with 1 mL of methanol
and then dissolved in CH2Cl2. The solution was washed with H2O
and brine and then dried (Na2SO4). Column chromatography (2 cm
diameter × 22 cm) over flash silica gel with CH2Cl2/ethyl acetate (96:
4) yielded three major components (in order of elution): monomeric
zinc porphyrin, butadiyne-linked dimer, and the pentamer 1. The
pentamer containing fractions were rechromatographed similarly,
affording 45.6 mg (50%) of pure 1. PD-MS C252H182N20O24Zn4 calcd
mass 4135.8, obsd 4136.0; λabs (CH2Cl2) 428, 519, 550, 590, 649 nm;
1H NMR (300 MHz) (CD2Cl2) δ -2.7 (s, 2 H, NH), 3.548 (s, 24 H,
OCH3), 3.606 (s, 48 H, OCH3), 7.060 (m, 8 H, J ) 8.47, Hz, o-ArH),
7.095 (m, 16 H, J ) 8.47 Hz, o-ArH), 7.767 (m, 4 H, J ) 8.52 Hz,
p-ArH), 7.795 (m, 8 H, J ) 8.47 Hz, p-ArH), 8.101 (AA′BB′, 8 H, J
) 8.30 Hz, ArH), 8.177 (AA′BB′, 8 H, J ) 8.30 Hz, ArH), 8.316
(AA′BB′, 8 H, J ) 8.30 Hz, ArH), 8.405 (AA′BB′, 8 H, J ) 8.30 Hz,
ArH), 8.763 (d, 8 H, J ) 4.54 H, â-pyrrole peripheral porphyrins),
8.795 (d, 8 H, J ) 4.54 H, â-pyrrole peripheral porphyrins), 8.884 (d,
8 H, J ) 4.54 H, â-pyrrole peripheral porphyrins), 8.941 (d, 8 H, J )
4.54 H, â-pyrrole peripheral porphyrins), 9.097 (bs, 8 H, â-pyrrole core
porphyrins).
ZnU (12)
dimers
ZnFbU (29) 426
426
555
424
553
425
555
423
553
428
557
426
556
424
553
425
556
423
554
429
558
431
562
429
559
429
556
429
556
550
ZnFbP (31) 426
551
ZnFbD (30) 426
550
ZnFbB (32) 425
550
419, 431 429
562
429
559
433
562
556
428
556
428
558
Zn2U (33)
427
551
trimers
ZnZnFb (44) 422, 430 423, 431
550 556
423, 431 424, 432
550 558
b
b
435
563
427, 434
557
Zn3L (39)
426, 436 426, 435
563 558
a The compounds were dissolved in CH2Cl2 and 2-5 µL was added
to 3 mL of solvent. The spectra were collected with 0.25 nm spectral
resolution (slit width ) 1 nm). The absorption maxima of the Soret
band and the the principal visible band are shown. b The samples
aggregated in this solvent.
4-iodobenzaldehyde (5, Karl Industries, Inc.), and all other reagents
and starting materials (Aldrich).
Chromatography. Adsorption column chromatography was per-
formed using flash silica (Baker) or alumina (Fisher A540, 80-200
mesh). Porphyrins were dissolved in CH2Cl2 (for silica) or toluene
(for alumina) at high concentration and then hexanes was added to
achieve a nonpolar loading solvent.
Preparative scale size exclusion chromatography (SEC) was per-
formed using BioRad Bio-Beads SX-1. A preparative scale glass
column (4.8 × 60 cm) was packed using BioRad Bio-Beads SX-1 in
toluene. The chromatography is performed with gravity flow (∼4 mL/
min). A typical separation requires ∼3 h. Following purification, the
SEC column is washed with two volume equivalents of toluene. Unlike
adsorption columns, these SEC columns can be used repeatedly although
with continued use for porphyrin separations the columns become
uniformly slightly pink-brown. We have used some preparative SEC
columns for more than 50 separations over as long as one year with
no noticeable decline in fractionation capability.
Analytical scale SEC was performed to assess the purity of the array-
forming reactions and to monitor the preparative purification of the
arrays.42 Analytical SEC columns (styrene-divinylbenzene copolymer)
were purchased from Hewlett Packard and Phenomonex. Analytical
SEC was performed with a Hewlett-Packard 1090 HPLC using 500 Å
(300 × 7.8 mm), 500 Å (300 × 7.5 mm), and 100 Å (300 × 7.5 mm)
columns (5 micron) in series eluting with THF (flow rate ) 0.8 mL/
min; void volume ∼ 18.0 min). Reaction monitoring was performed
by removing aliquots from the reaction mixture and diluting with THF
(Fisher, HPLC grade). Sample detection was achieved by absorption
spectroscopy using a diode array detector with quantitation at 420 nm
((10 nm band width), which best captures the peaks of monomeric
porphyrins and the multiporphyrin arrays. The dimers elute at 25.5
min and the trimer elutes at 23.9 min. Spectroscopic quantitation of
the products of the reaction mixture is difficult because the monomers,
dimers, trimers, and higher oligomers have different extinction coef-
ficients, and the value of these often is not known. Furthermore, the
dimer peak can consist of ethyne-linked dimer and butadiyne-linked
Molecular Photonic Wire 2. See ref 16.
Zinc(II) 5,10,15-Tris[2,6-dimethoxyphenyl]-20-{4-(phenylethynyl)-
phenyl}porphyrin (3). Samples of zinc porphyrin 2228 (50 mg, 57
µmol) and iodobenzene (6.5 µL, 57 µmol) were dissolved in 5.7 mL
of toluene/triethylamine (5:1). The solution was purged with argon
for 30 min, then Pd(PPh3)4 (2 mg, 1.4 µmol) was added and the solution
was heated to reflux. After stirring for 4 h, the mixture was cooled,
filtered, and concentrated to dryness. Chromatography on silica (CH2-
1
Cl2/hexanes, 10:1) yielded 37 mg (69%) of the desired porphyrin. H
NMR (CDCl3) δ 3.52 (s, 6 H, OCH3), 3.55 (s, 12 H, OCH3), 7.00 (d,
J ) 8.4 Hz, 6 H, ArH), 7.41, 7.45 (m, 3 H, ArH), 7.68, 7.73 (m, 5 H,
ArH), 7.89 (AA′BB′, 2 H, ArH), 8.20 (AA′BB′, 2 H, ArH), 8.81 (s, 4
H, â-pyrrole), 8.84, 8.86 (m, 4 H, â-pyrrole); PD-MS C58H44N4O6Zn
calcd mass 956.3, obsd 957.6; λabs (CH2Cl2) 422, 548 nm.
Zinc(II) 5,10,15-Tris[2,6-dimethoxyphenyl]-20-{2,6-dimethyl-4-
(phenylethynyl)phenyl}porphyrin (4). Samples of aldehyde 8 (468
mg, 2.0 mmol), 2,6-dimethoxybenzaldehyde (996 mg, 6 mmol), and
pyrrole (555 µL, 8 mmol) were dissolved in 800 mL of CHCl3, then
.
1.06 mL of BF3 O(Et)2 (2.5 M in CHCl3) was added and the mixture
was stirred at room temperature. After 60 min the yield determined
by spectroscopic monitoring was 24%. Then 1.36 g of DDQ was added

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11177
and the mixture was stirred at room temperature for a few minutes.
The reaction mixture was concentrated to dryness, and the residue was
chromatographed on flash silica gel, eluting with CH2Cl2/hexanes (10:
1). The desired porphyrin was isolated in about 90% purity from the
first column. The compound was rechromatographed on a second
column in identical manner, affording 97 mg (5.0%) of the desired
porphyrin. 1H NMR (CDCl3) δ -2.65 (br s, 2 H, NH), 1.90 (s, 6 H,
ArCH3), 3.55 (s, 6 H, OCH3), 3.60 (s, 12 H, OCH3), 7.05, 7.10 (m, 6
H, ArH), 7.40, 7.50 (m, 3 H, ArH), 7.65, 7.70 (m, 4 H, ArH), 7.73,
7.80 (m, 3 H, ArH), 8.60 (d, 2 H, â-pyrrole), 8.67-8.75 (m, 6 H,
â-pyrrole); λabs (CH2Cl2) 418, 514, 544, 588, 644 nm. A sample of
this porphyrin (20 mg, 0.021 mmol) was metalated using 1.5 equiv of
Zn(OAc)2‚2H2O in CH2Cl2/methanol (9:1). Metal insertion was
monitored spectroscopically and the reaction was complete in 2 h. The
reaction mixture was poured into CH2Cl2 and extracted with 5%
NaHCO3 and water, and then the organic layer was dried (Na2SO4).
Evaporation of the solvent afforded the zinc porphyrin in >95% yield.
1H NMR (CD2Cl2) δ 1.81 (s, 6 H, ArCH3), 3.48 (m, 18 H, OCH3),
6.98 (m, 6 H, ArH), 7.35, 7.40 (m, 3 H, ArH), 7.57, 7.62 (m, 4 H,
ArH), 7.66, 7.72 (m, 3 H, ArH), 8.62 (d, 2 H, â-pyrrole), 8.70, 8.78
(m, 6 H, â-pyrrole); PD-MS C60H48N4O6Zn calcd mass 984.3, obsd
984.3; λabs (CH2Cl2) 420, 548 nm.
4-[2-(Trimethylsilyl)ethynyl]benzaldehyde (6). See ref 51.
2,6-Dimethyl-4-iodobenzaldehyde (7). A sample of 2,6-dimethyl-
4-iodoaniline52 (12.0 g, 48.6 mmol) was suspended in a mixture of 12
mL of concentrated HCl and 50 g of crushed ice. The mixture was
cooled to 0 °C. A 10-mL aqueous solution of NaNO2 (3.41 g, 49.4
mmol) was added over 10 min to the mixture, maintaining a temperature
of 0-5 °C. After the addition the reaction was allowed to proceed for
30 min. When the presence of free nitrous acid was confirmed (starch-
iodine paper), the diazonium salt mixture was carefully neutralized with
anhydrous Na2CO3.
solution was purged with argon for 30 min, then Pd2(dba)3 (107 mg,
0.12 mmol) was added and the flask was placed in an oil bath at 55
°C. After stirring for 24 h, trimethylsilylacetylene (2.0 mL, 14.1 mmol),
tri-2-furylphosphine (223 mg, 0.96 mmol), and Pd2(dba)3 (107 mg, 0.12
mmol) were added. The reaction was judged to be complete at 36 h
by GC-MS. At this point the mixture was cooled and filtered. The
filtrate was concentrated to dryness, yielding a light brown solid. The
residue was dissolved in diethyl ether, washed with brine, dried (Na2-
SO4), filtered, and concentrated to a light brown oil that solidified upon
standing at 0 °C. Recrystallization from 2-propanol yielded 4.6 g (85%)
of a light yellow powder: mp 62-63 °C; 1H NMR (CDCl3) δ 0.20 (s,
9 H, SiCH3), 2.45 (s, 6 H, ArCH3), 7.05 (s, 2 H, ArH), 10.43 (s, 1 H,
CHO). Anal. (C14H18OSi) C, H.
4-(Phenylethynyl)benzaldehyde (9). see ref 53.
2,6-Dimethyl-4-(phenylethynyl)benzaldehyde (10). Samples of
2,6-dimethyl-4-bromobenzaldehyde52 (1 g, 4.7 mmol) and phenylacety-
lene (1.3 mL, 12 mmol) were dissolved in 10 mL of triethylamine at
room temperature. The solution was deaerated with argon for 30 min.
Pd2(dba)3 (43 mg, 47 µmol) and AsPh3 (115 mg, 376 mmol) were added
and the reaction vessel was placed in an oil bath at 90 °C. After
refluxing for 4 h the reaction mixture was cooled to room temperature
and then vacuum filtered. The remaining off-white precipitate was
washed with hexanes. The filtrate was rotary evaporated to an oil.
Flash column chromatography (silica, hexanes/CH2Cl2, 4:1) gave 760
1
mg (70%) of an off-white powder: mp 63-64 °C; H NMR (CDCl3)
δ 2.61 (s, 6 H, ArCH3), 7.27 (s, 2 H, ArH), 7.37, 7.38 (m, 3H, ArH),
7.53, 7.55 (m, 2H, ArH), 10.60 (s, 1 H, CHO). Anal (C17H14O) C, H.
5,10,15-Trimesityl-20-{4-[2-(trimethylsilyl)ethynyl]phenyl}-
porphyrin (FbU)46 (11). A sample of zinc porphyrin 12 (200 mg,
0.22 mmol) was dissolved in 25 mL of CH2Cl2 and treated with TFA
(68 µL, 0.88 mmol). The demetalation was complete after 10 min as
evidenced by silica TLC, absorption, and fluorescence excitation
spectroscopy. Triethylamine (184 µL, 1.32 mmol) was added and the
reaction mixture was stirred for another 10 min. The solution was
then washed three times with 10% NaHCO3 and once with H2O, dried
(Na2SO4), filtered, and rotary evaporated to give 182 mg (100%) of a
purple solid. The analytical data were consistent with an authentic
sample.28
A cuprous cyanide mixture was prepared in the following manner.
Cuprous cyanide (5.45 g, 60.9 mmol) was suspended in 25 mL of H2O.
Aqueous NaCN (12 mL, 7.6 g, 155 mmol) was added and the mixture
was stirred at room temperature until the CuCN dissolved. Toluene
(100 mL) was then added to the cuprous cyanide solution and the
mixture was cooled to 0 °C.
The diazonium salt mixture was then added to the cuprous cyanide-
toluene mixture with vigorous stirring, maintaining a reaction temper-
ature of 0-5 °C. When the addition was complete, the mixture was
stirred at 0 °C for 1 h and at room temperature for 4 h, then heated to
50 °C without stirring. The mixture was then allowed to cool to room
temperature, the layers were separated, and the aqueous layer was
extracted with toluene (2 × 100 mL). The organic layers were
combined, washed with H2O (1 × 50 mL), dried (Na2SO4), and
concentrated to dryness, giving a dark green solid. The crude product
was chromatographed on silica (4.8 × 18 cm, CH2Cl2/hexanes (1:1), 3
columns), affording 5.14 g (42%) of light yellow crystals. mp 113-
114 °C; 1H NMR (CDCl3) δ 2.46 (s, 6 H, ArCH3), 7.55 (s, 2 H, ArH).
Anal. (C9H8IN) C, H, N.
A sample of 2,6-dimethyl-4-iodobenzonitrile (3.3 g, 12.8 mmol) was
dissolved in 10 mL of CH2Cl2 (distilled from CaH2) and the solution
was cooled to 0 °C. A 15.4-mL solution of a diisobutylaluminum
hydride (1 M in CH2Cl2, 15.4 mmol) was added dropwise. After the
addition was complete, the reaction was allowed to warm to room
temperature and stirred for 30 min. The reaction mixture was then
poured into a beaker containing 40 g of crushed ice and 50 mL of 6 N
HCl. After stirring for 1 h, the aqueous phase was separated and
extracted with CH2Cl2 (2 × 50 mL). The organic layers were combined,
washed with 5% NaHCO3 (25 mL) and brine (25 mL), dried (Na2-
SO4), and concentrated to dryness affording 2.95 g (88%) of a white
solid: mp 68-69 °C; 1H NMR (CDCl3) δ 2.50 (s, 6 H, ArCH3), 7.48
(s, 2 H, ArH), 10.52 (s, 1 H, CHO). Anal. (C9H9IO) C, H.
2,6-Dimethyl-4-[2-(trimethylsilyl)ethynyl]benzaldehyde (8). Sam-
ples of 2,6-dimethyl-4-bromobenzaldehyde52 (5.0 g, 23.5 mmol),
trimethylsilylacetylene (4.0 mL, 28.2 mmol), and tri-2-furylphosphine
(223 mg, 0.96 mmol) were dissolved in 50 mL of triethylamine. The
Zinc(II) 5,10,15-Trimesityl-20-{4-[2-(trimethylsilyl)ethynyl]phenyl}-
porphyrin (ZnU)46 (12). The crude reaction mixtures from several
mixed aldehyde condensations (totaling 2 L) of 20 mmol of pyrrole,
15 mmol of mesitaldehyde, and 5 mmol of 4-[2-(trimethylsilyl)ethynyl]-
benzaldehyde (6) were combined. This mixture was passed over a silica
column (CH2Cl2/hexanes, 1:1) affording the six porphyrins (900 mg)
free from dark pigments and quinone species. The mixture of six
porphyrins (450 mg, half of the original mixture) was dissolved in 100
mL of CHCl3, and metalated with Zn(OAc)2‚2H2O (219 mg, 1 mmol,
10 mL methanol). After metalation was complete the reaction mixture
was washed with 10% NaHCO3, dried (Na2SO4), filtered, and rotary
evaporated to a purple solid. The product mixture was dissolved in
10 mL of CH2Cl2 and then 20 mL of hexanes was added. The solution
was loaded onto a silica column (6.8 × 12 cm, hexanes/CH2Cl2, 2:1).
The six porphyrin products were clearly visible on the column as the
separation proceeded. The title porphyrin comprised the second band,
affording 280 mg (12.4%). 1H NMR (CDCl3) δ 0.39 (s, 9 H), 1.83 (s,
12 H, ArCH3), 1.84 (s, 6 H, ArCH3), 2.63 (s, 9 H, ArCH3), 7.27 (s, 6
H, ArH), 7.89 (AA′BB′, 2 H, ArH), 8.19 (AA′BB′, 2 H, ArH), 8.70 (s,
4 H, â-pyrrole), 8.77 (d, J ) 4.5 Hz, 2 H, â-pyrrole), 8.83 (d, J ) 4.5
Hz, 2 H, â-pyrrole); LD-MS C58H54N4SiZn calcd av mass 900.6, obsd
900.3; λabs (toluene) 423, 550 nm.
Zinc(II) 5,10,15-Trimesityl-20-(4-ethynylphenyl)porphyrin (13).
See ref 42.
5,10,15-Trimesityl-20-(4-iodophenyl)porphyrin (14). See ref 28.
5,10-Dimesityl-15,20-bis{4-iodophenyl}porphyrin (15). Samples
of mesitaldehyde (1.1 mL, 7.5 mmol), 4-iodobenzaldehyde (580 mg,
2.5 mmol), and pyrrole (694 µL, 10 mmol) were condensed in 1 L of
CHCl3 with BF3‚O(Et)2 (1.32 mL of 2.5 M stock solution, 3.3 mM) at
room temperature for 1 h. Then DDQ (1.7 g, 7.5 mmol) was added
and after 1 h of stirring at room temperature the reaction mixture was
(51) Austin, W. B.; Bilow, N.; Kelleghan, W. J.; Lau, K. S. Y. J. Org.
Chem. 1981, 46, 2280-2286.
(52) Kajigaeshi, S.; Kakinami, T.; Yamasaki, H.; Fujisaki, S.; Okamoto,
T. Bull. Chem. Soc. Jpn. 1988, 61, 600-602.
(53) Dieck, H. A.; Heck, F. R. J. Organomet. Chem. 1975, 93, 259-
263.

11178 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Wagner et al.
worked up in the standard way.28 One column (silica, CH2Cl2/hexanes,
2:1) was used to remove the non-porphyrinic components from the
crude reaction mixture. The mixture of six porphyrins was chromato-
graphed on neutral alumina (hexanes/toluene, 4:1) yielding 166 mg
(7.0% yield) of the desired porphyrin, which eluted as the fourth
porphyrin component. 1H NMR (CDCl3) δ -2.69 (bs, 2 H, NH), 1.84
(s, 12 H, ArCH3), 2.63 (s, 6 H, ArCH3), 7.27 (s, 4 H, ArH), 7.93
(AA′BB′, 4 H, ArH), 8.08 (AA′BB′, 4 H, ArH), 8.65 (s, 2 H, â-pyrrole),
8.70 (d, J ) 5.1 Hz, 2 H, â-pyrrole), 8.76 (d, J ) 5.1 Hz, 2 H,
â-pyrrole), 8.81 (s, 2 H, â-pyrrole); PD-MS C50H40I2N4 calcd av mass
950.1, obsd 950.3; λabs 420, 516, 552, 590, 648 nm.
5,10,15-Triphenyl-20-{2,6-dimethyl-4-[2-(trimethylsilyl)ethynyl]-
phenyl}-porphyrin (FbH)46 (16). Samples of benzaldehyde (514 µL,
5.06 mmol), aldehyde 8 (389 mg, 1.69 mmol), and pyrrole (468 µL,
6.75 mmol) were condensed in 675 mL of CHCl3 with BF3‚O(Et)2 (891
µL of 2.5 M stock solution, 3.3 mM) at room temperature for 1 h.
Then DDQ (1.149 g, 5.06 mmol) was added and after 1 h of stirring
at room temperature the reaction mixture was worked up in the standard
way.28 Chromatography on silica (CH2Cl2/hexanes (1:1), 6.8 × 7 cm)
gave the six porphyrins eluting as one band. Subsequent chromatog-
raphy on alumina (hexanes/toluene (2:1), 6.8 × 10 cm) yielded the
desired porphyrin (217 mg, 17%) from the mixture as the fifth porphyrin
band. 1H NMR (CDCl3) δ -2.72 (s, 2 H, NH), 0.37 (s, 9 H, SiCH3),
1.85 (s, 6 H, ArCH3), 7.63 (s, 2 H, ArH), 7.71, 7.80 (m, 9 H, PhH),
8.20, 8.23 (m, 6 H, PhH), 8.63 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.81,
8.83 (m, 6 H, â-pyrrole); LD-MS C51H42N4Si calcd av mass 739.0,
obsd 739.9; λabs (toluene) 420, 514, 551, 592, 648 nm.
Zinc(II) 5,10,15-Triphenyl-20-{2,6-dimethyl-4-[2-(trimethylsilyl)-
ethynyl]phenyl}porphyrin (ZnH)46 (17). A sample of porphyrin 16
(150 mg, 0.20 mmol) was metalated in 50 mL of CHCl3 with
Zn(OAc)2‚2H2O (88 mg, 0.4 mmol, 5 mL methanol) over 2.5 h,
affording 160 mg (100%) of the zinc chelate as a purple solid. 1H
NMR (CDCl3) δ 0.37 (s, 9 H, SiCH3), 1.84 (s, 6 H, ArCH3), 7.63 (s,
2 H, ArH), 7.73, 7.76 (m, 9 H, PhH), 8.21, 8.24 (m, 6 H, PhH), 8.72
(d, 2 H, J ) 4.8 Hz, â-pyrrole), 8.91 (d, 2 H, J ) 4.8 Hz, â-pyrrole),
8.94 (s, 4 H, â-pyrrole); LD-MS C51H40N4SiZn calcd av mass 802.4,
obsd 802.2; λabs (toluene) 424, 550 nm.
Zinc(II) 5,10,15-Triphenyl-20-{2,6-dimethyl-4-ethynylphenyl}-
porphyrin (18). A sample of porphyrin 17 (150 mg, 0.11 mmol) was
dissolved in 26.5 mL of THF/methanol (3:1). K2CO3 (53 mg, 0.39)
was added and the reaction mixture was stirred at room temperature
for 4 h. The reaction mixture was concentrated to dryness and then
the purple solid was redissolved in 50 mL of CHCl3. The organic
solution was washed with H2O, dried (Na2SO4), filtered, and concen-
trated to dryness. Column chromatography on silica (CH2Cl2/hexanes
(1:1), 4.8 × 7 cm) afforded 130 mg (95%). 1H NMR (CDCl3) δ 1.85
(s, 6 H, ArCH3), 3.25 (s, 1 H, CCH), 7.64 (s, 2 H, ArH), 7.74, 7.79
(m, 9 H, PhH), 8.21, 8.24 (m, 6 H, PhH), 8.73 (d, 2 H, J ) 4.2 Hz,
â-pyrrole), 8.91 (d, 2 H, J ) 4.2 Hz, â-pyrrole), 8.94 (s, 4 H, â-pyrrole);
LD-MS C48H32N4Zn calcd av mass 730.2, obsd 730.1; λabs (toluene)
423, 550 nm.
Zinc(II) 5,10,15-Tris(2,6-dimethoxyphenyl)-20-{4-ethynylphenyl}-
porphyrin (22). See ref 28.
5,10,15-Tris(2,6-dimethoxyphenyl)-20-{2,6-dimethyl-4-[2-(tri-
methylsilyl)ethynyl]phenyl}porphyrin (23). Samples of 2,6-dimethoxy-
benzaldehyde (2.24 g, 13.5 mmol), aldehyde 8 (1.04 g, 4.5 mmol),
and pyrrole (1.25 mL, 18 mmol) were condensed in 1.8 L of CHCl3
with BF3‚O(Et)2 (2.4 mL of 2.5 M stock solution, 3.3 mM) at room
temperature for 1 h. Then DDQ (3.06 g, 13.5 mmol) was added and
after 1 h of stirring at room temperature the reaction mixture was
worked up in the standard way.28 Chromatography (one column, silica,
CH2Cl2) gave the first four porphyrins eluting as one band and the
title porphyrin as the second porphyrin band, affording 180 mg (4.4%)
of porphyrin. 1H NMR (CDCl3) δ -2.53 (s, 2 H, NH), 0.36 (s, 9 H,
SiCH3), 1.86 (s, 6 H, ArCH3), 3.47 (s, 6 H, OCH3), 3.48 (s, 12 H,
OCH3), 6.96 (d, 6 H, J ) 6 Hz, ArH), 7.59 (s, 2 H, ArH), 7.67 (t, 3 H,
J ) 8.4 Hz, ArH), 8.50 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.65, 8.68 (m,
6 H, â-pyrrole); LD-MS C57H54N4O6Si calcd av mass 919.2, obsd 920.9;
λabs (toluene) 420, 514, 548, 592, 646 nm.
Zinc(II) 5,10,15-Tris(2,6-dimethoxyphenyl)-20-{2,6-dimethyl-4-
[2-(trimethylsilyl)ethynyl]phenyl}porphyrin (24). A sample of por-
phyrin 23 (155 mg, 0.17 mmol) was dissolved in 50 mL of CHCl3,
then a methanolic solution of Zn(OAc)2‚2H2O (75 mg, 0.34 mmol, 5
mL of methanol) was added. The reaction mixture was stirred at room
temperature and was monitored by fluorescence excitation spectroscopy.
After stirring overnight the reaction mixture was washed with 10%
NaHCO3, dried (Na2SO4), filtered, and concentrated affording 167 mg
(100%) of the zinc chelate as a purple solid. 1H NMR (CDCl3) δ 0.36
(s, 9 H, SiCH3), 1.84 (s, 6 H, ArCH3), 3.49 (s, 6 H, OCH3), 3.50 (s, 12
H, OCH3), 6.98 (d, 6 H, J ) 7.8 Hz, ArH), 7.58 (s, 2 H, ArH), 8.75 (t,
3 H, J ) 9.6 Hz, ArH), 8.58 (d, 2 H, J ) 4.2 Hz, â-pyrrole), 8.74 (d,
2 H, J ) 4.2 Hz, â-pyrrole), 8.77 (m, 4 H, â-pyrrole); LD-MS
C57H52N4O6SiZn calcd av mass 982.5, obsd 983.3; λabs (toluene) 425,
549 nm.
Zinc(II) 5,10,15-Tris(2,6-dimethoxyphenyl)-20-{2,6-dimethyl-4-
ethynylphenyl}porphyrin (25). A sample of zinc porphyrin 24 (167
mg, 0.17 mmol) was dissolved in 10 mL of anhydrous THF. Upon
addition of 340 mg of tetrabutylammonium fluoride on silica (1.0-
1.5 mmol F-/g) a precipitate was observed. CHCl3 (2 mL) was added
to redissolve the starting porphyrin. After 30 min further aggregation
was noted and 50 mL of CHCl3 was added. After 1 h the deprotection
1
was complete as evidenced by H NMR spectroscopy. The reaction
mixture was concentrated to dryness and then redissolved in 50 mL of
CHCl3. The organic layer was washed with 50 mL of 10% NaHCO3
and 50 mL of H2O, dried (Na2SO4), filtered, and concentrated to
dryness. Column chromatography on silica (CH2Cl2, 4.8 × 7 cm)
afforded 130 mg (82%) of porphyrin. 1H NMR (CDCl3) δ 1.86 (s, 6
H, ArCH3), 3.22 (s, 1 H, CCH), 3.49 (s, 6 H, OCH3), 3.50 (s, 12 H,
OCH3), 6.95, 6.99 (m, 6 H, ArH), 7.64 (s, 2 H, ArH), 7.64, 7.69 (m,
3 H, ArH), 8.60 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.76 (d, 2 H, J ) 4.5
Hz, â-pyrrole), 8.78 (s, 4 H, â-pyrrole); LD-MS C54H44N4O6Zn calcd
av mass 910.3, obsd 911.0; λabs (toluene) 424, 550 nm.
5,10,15-Triphenyl-20-{2,6-dimethyl-4-iodophenyl}porphyrin (19).
Samples of benzaldehyde (1.45 mL, 14.25 mmol), aldehyde 7 (1.235
g, 4.75 mmol), and pyrrole (1.32 mL, 19 mmol) were condensed in
1.9 L of CHCl3 with BF3‚O(Et)2 (2.51 mL of 2.5 M stock solution, 3.3
mM) at room temperature for 1 h. Then DDQ (3.235 g, 14.25 mmol)
was added and after 1 h of stirring at room temperature the reaction
mixture was worked up in the standard way. Chromatography (silica,
CH2Cl2/hexanes (1:1), 6.8 × 7 cm) gave the five porphyrins eluting as
one band. The 5,10,15,20-tetrakis{2,6-dimethyl-4-iodophenyl}porphyrin
did not elute because of limited solubility. Chromatography on alumina
(hexanes/toluene (2:1), 6.8 × 10 cm) afforded the desired porphyrin
(492 mg, 13.5%) as the last band in the porphyrin mixture. 1H NMR
(CDCl3) δ -2.72 (s, 2 H, NH), 1.85 (s, 6 H, ArCH3), 7.73, 7.79 (m, 9
H, PhH), 7.85 (s, 2 H, ArH), 8.19, 8.23 (m, 6 H, PhH), 8.66 (d, 2 H,
J ) 4.5 Hz, â-pyrrole), 8.82, 8.84 (m, 6 H, â-pyrrole); LD-MS
C46H33N4I calcd av mass 768.7, obsd 770.0; λabs (toluene) 419, 514,
548, 592, 646 nm.
5,10,15-Tris(2,6-dimethoxyphenyl)-20-{2,6-dimethyl-4-iodophenyl}-
porphyrin (26). Samples of 2,6-dimethoxybenzaldehyde (1.246 g, 7.5
mmol), aldehyde 7 (650 mg, 2.5 mmol), and pyrrole (694 µL, 10 mmol)
were condensed in 1 L of CHCl3 with BF3‚O(Et)2 (1.32 mL of 2.5 M
stock solution, 3.3 mM) at room temperature for 1 h. Then DDQ (1.70
g, 7.5 mmol) was added and after 1 h of stirring at room temperature
the reaction mixture was worked up in the standard way.28 Chroma-
tography (one column, silica, CH2Cl2) gave the first four porphyrins
as one band and the desired product as the second band, yielding 110
mg (4.8%) of porphyrin. 1H NMR (CDCl3) δ -2.53 (s, 2 H, NH),
1.84 (s, 6 H, ArCH3), 3.45 (s, 6 H, OCH3), 3.49 (s, 12 H, OCH3), 6.95,
6.99 (m, 6 H, ArH), 7.69 (t, 3 H, J ) 8.4 Hz, ArH), 7.80 (s, 2 H,
ArH), 8.52 (d, 2 H, J ) 4.2 Hz, â-pyrrole), 8.66, 8.68 (m, 6 H,
â-pyrrole); LD-MS C52H45N4IO6 calcd av mass 948.9, obsd 949.2; λabs
(toluene) 420, 514, 550, 591, 651 nm.
5,15-Bis(mesityl)-10-(4-iodophenyl)-20-[2,6-dimethyl-4-(2-(tri-
methylsilyl)ethynyl)phenyl]porphyrin (27). A sample of zinc por-
phyrin 28 (200 mg, 0.20 mmol) was dissolved in 25 mL of CH2Cl2
and treated with TFA (62 µL, 0.80 mmol). The demetalation was
complete after 10 min as evidenced by silica TLC, absorption, and
fluorescence excitation spectroscopy. Triethylamine (167 µL, 1.20
5,10,15-Tris(2,6-dimethoxyphenyl)-20-{4-[2-(trimethylsilyl)ethynyl]-
phenyl}porphyrin (20). See ref 28.
5,10,15-Tris(2,6-dimethoxyphenyl)-20-{4-ethynylphenyl}-
porphyrin (21). See ref 28.

Soluble Synthetic Multiporphyrin Arrays. 1
J. Am. Chem. Soc., Vol. 118, No. 45, 1996 11179
mmol) was added and the reaction mixture was stirred for another 10
min. The solution was then washed three times with 10% NaHCO3
and once with H2O, dried (Na2SO4), filtered, and rotary evaporated to
give 188 mg (100%) of a purple solid. The analytical data were
consistent with an authentic sample.39
coupling reaction at half this scale.28 The duration of these chromato-
graphic procedures is as follows: flash silica column (30 min),
preparative SEC (2 h), final silica column (2 h). 1H NMR (CDCl3) δ
-2.73 (bs, 2 H, NH), 1.83 (s, 12 H, ArCH3), 1.90 (s, 24 H, ArCH3),
2.45 (s, 6 H, ArCH3), 2.49 (s, 12 H, ArCH3), 7.19 (s, 4 H, ArH), 7.29
(s, 8 H, ArH), 8.06 (AA′BB′, 4 H, ArH), 8.30 (AA′BB′, 4 H, ArH),
8.65, 8.94 (m, 16 H, â-pyrrole); LD-MS C108H92N8Zn calcd av mass
1567.4, obsd 1568.4; λabs (toluene) 426, 515, 550, 592, 650 nm.
Zinc(II) 5,10,15-Triphenyl-20-{4-[4-(5,10,15-triphenyl-20-por-
phinyl)phenylethynyl]-2,6-dimethylphenyl}porphyrin (ZnFbD)46 (30).
Samples of free base iodo porphyrin 19 (52 mg, 68 µmol) and zinc
ethynyl porphyrin 13 (68 mg, 82 µmol) were coupled, affording 69
mg (69%) following chromatographic workup. 1H NMR (CDCl3) δ
-2.67 (bs, 2 H, NH), 1.87 (s, 18 H, ArCH3), 1.96 (s, 6 H, ArCH3),
2.64 (s, 3 H, ArCH3), 2.65 (s, 6 H, ArCH3), 7.29 (s, 6 H, ArH), 7.76,
7.80 (m, 9 H, PhH), 7.84 (s, 2 H, ArH), 8.04 (AA′BB′, 2 H, ArH),
8.21, 8.24 (m, 6 H, PhH), 8.30 (AA′BB′, 2 H, ArH), 8.73 (s, 4 H,
â-pyrrole), 8.76 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.81 (d, 2 H, J ) 4.5
Hz, â-pyrrole), 8.86, 8.89 (m, 6 H, â-pyrrole), 8.94 (d, 2 H, J ) 4.8
Hz, â-pyrrole); LD-MS C101H78N8Zn calcd av mass 1469.2, obsd
1472.1; λabs (toluene) 426, 515, 550, 591, 648 nm.
Zinc(II) 5,10,15-Triphenyl-20-{4-[4-(5,10,15-triphenyl-20-por-
phinyl)(2,6-dimethylphenyl)ethynyl]phenyl}porphyrin (ZnFbP)46
(31). Samples of zinc ethynyl porphyrin 18 (60 mg, 82 µmol) and
free base iodo porphyrin 14 (59 mg, 68 µmol) were coupled, affording
86 mg (86%) following chromatographic workup. 1H NMR (CDCl3)
δ -2.55 (bs, 2 H, NH), 1.87 (s, 18 H, ArCH3), 1.95 (s, 6 H, ArCH3),
2.63 (s, 3 H, ArCH3), 2.64 (s, 6 H, ArCH3), 7.28 (s, 2 H, ArH), 7.30
(s, 4 H, ArH), 7.75, 7.78 (m, 9 H, PhH), 7.84 (s, 2 H, ArH), 8.05
(AA′BB′, 2 H, ArH), 8.22, 8.28 (m, 8 H, ArH), 8.65 (s, 4 H, â-pyrrole),
8.74 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.84, 8.87 (m, 4 H, â-pyrrole),
8.94, 8.98 (m, 6 H, â-pyrrole); LD-MS C101H78N8Zn calcd av mass
1469.2, obsd 1468.8; λabs (toluene) 426, 516, 551, 592, 650 nm.
4-[Zinc(II) 5,10,15-triphenyl-20-porphinyl]-4′-[5,10,15-triphenyl-
20-porphinyl]di(2,6-dimethylphenyl)ethyne (ZnFbB)46 (32). Samples
of zinc ethynyl porphyrin 18 (58 mg, 79 µmol) and free base iodo
porphyrin 19 (55 mg, 72 µmol) were coupled, affording 68 mg (69%)
following chromatographic workup. 1H NMR (CDCl3) δ -2.67 (bs,
2 H, NH), 1.96 (s, 12 H, ArCH3), 7.73, 7.79 (m, 18 H, PhH), 7.82 (s,
4 H, ArH), 8.20, 8.27 (m, 12 H, PhH), 8.76 (d, 4 H, J ) 4.8 Hz,
â-pyrrole), 8.86, 8.89 (m, 6 H, â-pyrrole), 8.96, 8.98 (m, 6 H, â-pyrrole);
LD-MS C94H64N8Zn calcd av mass 1371.0, obsd 1372.5; λabs (toluene)
425, 515, 550, 590, 648 nm.
Zinc(II) 5,15-Bis(mesityl)-10-(4-iodophenyl)-20-[2,6-dimethyl-4-
(2-(trimethylsilyl)ethynyl)phenyl]porphyrin (28). Samples of alde-
hyde 8 (576 mg, 2.5 mmol), 4-iodobenzaldehyde (580 mg, 2.5 mmol),
and meso-(mesityl)dipyrromethane39 (1.322 g, 5 mmol) were dissolved
in 500 mL of CHCl3. BF3‚O(Et)2 (660 µL of 2.5 M stock solution,
3.3 mM) was then added and the solution was stirred at room
temperature for 45 min. Then DDQ (1.70 g, 7.5 mmol) was added
and stirring was continued at room temperature for 1 h. Flash
chromatography (silica, CH2Cl2/hexanes, 1:1) gave the mixture of three
porphyrins (800 mg). To facilitate the purification, the mixture of three
porphyrins was dissolved in 100 mL of CHCl3 and metalated with Zn-
(OAc)2‚2H2O (373 mg, 1.7 mmol, 10 mL methanol). After metalation
was complete the reaction mixture was washed with 10% NaHCO3,
dried (Na2SO4), filtered, and rotary evaporated to a purple solid. The
product mixture was dissolved in 15 mL of CH2Cl2 and then 30 mL of
hexanes was added. The solution was loaded onto a silica column
(6.8 × 12 cm, hexanes/CH2Cl2, 2:1). The three porphyrin products
were clearly visible as distinct bands on the column as the separation
proceeded. The desired zinc porphyrin was the second band off of the
column, affording 280 mg (11%). 1H NMR (CDCl3) δ 0.37 (s, 9 H,
SiCH3), 1.84 (s, 12 H, ArCH3), 1.85 (s, 6 H, ArCH3), 2.63 (s, 6 H,
ArCH3), 7.29 (s, 4 H, ArH), 7.62 (s, 2 H, ArH), 7.94 (AA′BB′, 2 H,
ArH), 8.08 (AA′BB′, 2 H, ArH), 8.58 (d, 2 H, J ) 4.5 Hz, â-pyrrole),
8.65 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.70 (d, 2 H, J ) 4.5 Hz,
â-pyrrole), 8.77 (d, 2 H, J ) 4.5 Hz, â-pyrrole); LD-MS C57H51N4-
ISiZn calcd av mass 1012.4, obsd 1011.1; λabs (toluene) 423, 550 nm.
Exemplary Procedure for Performing Pd-Coupling Reactions:
4-[Zinc(II) 5,10,15-trimesityl-20-porphinyl]-4′-[5,10,15-trimesityl-
20-porphinyl]diphenylethyne (ZnFbU)46 (29). Samples of free base
iodo porphyrin 14 (82 mg, 95 µmol) and zinc ethynyl porphyrin 13
(84 mg, 100 µmol) were added to a 100-mL one-neck round-bottom
flask containing 40 mL of toluene/triethylamine (5:1). The flask was
heated to 35 °C and was fitted with a 15 cm reflux condenser through
which a drawn glass pipet was mounted for deaeration with argon. The
reaction vessel headspace including the condenser was deaerated with
a high flow rate of argon for 5 min. The solution was then deaerated
by immersing the pipet in the solution and gently bubbling argon for
30 min. The condenser was then elevated, leaving the pipet in the
solution, and Pd2(dba)3 (12.8 mg, 14 µmol) and AsPh3 (34 mg, 110
µmol) were added. The condenser was replaced and argon was bubbled
through the solution for another 5 min. At this point the pipet was
removed from the reaction mixture and positioned about 2 cm above
the solution. The argon flow rate was turned up slightly and the reaction
was allowed to proceed. After 2 h the reaction mixture was
concentrated to dryness, redissolved in 9 mL of hexanes/CH2Cl2 (2:1),
and poured on top of a flash silica chromatography column (4.8 × 5
cm; poured dry and then washed with hexanes/CH2Cl2, 2:1). Elution
with ∼200 mL hexanes/CH2Cl2 (2:1) with gentle application of air
pressure caused rapid elution of AsPh3 with only slight movement of
the porphyrin components which remained bound at the top of the
column. TLC analysis (silica, hexanes/CH2Cl2, 2:1) of the eluant
confirms the complete elution of AsPh3. Then the column was washed
with 300 mL of hexanes/CH2Cl2 (1:1), eluting zinc monomeric
porphyrin, desired dimer, and higher molecular weight material. The
Pd species remained bound to the top of the column, forming a black
layer while the lower portion of the column was white. The mixture
of porphyrins was then concentrated to dryness, dissolved in 2 mL of
toluene, and then placed on top of a preparative SEC column (Bio-
Beads SX-1 poured in toluene). Gravity elution afforded three major
components (in order of elution): higher molecular weight material,
desired dimer, and monomeric zinc porphyrin. The dimer-containing
fraction was concentrated to dryness, dissolved in 15 mL of hexanes/
CH2Cl2 (2:1), and chromatographed on silica (4.8 cm diameter × 10
cm, poured in hexanes/CH2Cl2, 2:1) with gravity elution. A small
amount of monomeric zinc porphyrin eluted quickly, followed by the
desired dimer. Concentration of the appropriate fractions gave 115
mg (77%). We previously prepared this dimer in 82% yield in a 24 h
Zinc(II) 5,10,15-Trimesityl-20-{4-[4-(5,10,15-trimesityl-20-por-
phinyl)phenylethynyl]phenyl}zinc(II) Porphyrin (Zn2U)46,47 (33). See
ref 28.
Zinc(II) 5,10,15-Triphenyl-20-{4-[4-(5,10,15-triphenyl-20-por-
phinyl)(2,6-dimethylphenyl)ethynyl]phenyl}zinc(II) Porphyrin
(Zn2M)46,47 (34). A sample of ZnFb-dimer 31 (25 mg, 0.017 mmol)
was dissolved in 5 mL of CHCl3, then a methanolic solution of Zn-
(OAc)2‚2H2O (7.5 mg, 0.034 mmol, 500 µL methanol) was added. The
reaction mixture was stirred at room temperature and was monitored
by fluorescence excitation spectroscopy. After 1 h the reaction mixture
was washed with 10% NaHCO3, dried (Na2SO4), filtered, and concen-
trated affording 26 mg (100%) of the zinc chelate as a purple solid. 1H
NMR (CDCl3) δ 1.87 (s, 18 H, ArCH3), 1.96 (s, 6 H, ArCH3), 2.64 (s,
3 H, ArCH3), 2.65 (s, 6 H, ArCH3), 7.28 (s, 2 H, ArH), 7.30 (s, 4 H,
ArH), 7.77, 7.89 (m, 9 H, PhH), 7.84 (s, 2 H, ArH), 8.05 (AA′BB′, 2
H, ArH), 8.25, 8.31 (m, 8 H, ArH), 8.73 (s, 4 H, â-pyrrole), 8.81 (d,
2 H, J ) 4.5 Hz, â-pyrrole), 8.85 (d, 2 H, J ) 4.5 Hz, â-pyrrole),
8.94, 8.97 (m, 8 H, â-pyrrole); LD-MS C101H76N8Zn2 calcd av mass
1532.5, obsd 1531.8; λabs (toluene) 427, 551 nm.
4,4′-Bis[zinc(II) 5,10,15-triphenyl-20-porphyrinyl]di(2,6-dimeth-
ylphenyl)ethyne (Zn2B)46,47 (35). A sample of ZnFb-dimer 32 (20
mg, 0.014 mmol) was metalated in 5 mL of CHCl3 with a methanolic
solution of Zn(OAc)2‚2H2O (7.9 mg, 0.036 mmol, 500 µL methanol)
over 1 h, affording 20 mg (100%) of the zinc chelate as a purple solid.
1H NMR (CDCl3) δ 1.95 (s, 12 H, ArCH3), 7.76, 7.79 (m, 18 H, PhH),
7.82 (s, 4 H, ArH), 8.20, 8.27 (m, 12 H, PhH), 8.86 (d, 4 H, J ) 4.5
Hz, â-pyrrole), 8.95, 8.98 (m, 12 H, â-pyrrole); LD-MS C94H62N8Zn2
calcd av mass 1434.3, obsd 1434.3; λabs (toluene) 427, 550 nm.

11180 J. Am. Chem. Soc., Vol. 118, No. 45, 1996
Wagner et al.
4-[Zinc(II) 5,10,15-tris(2,6-dimethoxyphenyl)-20-porphinyl]-4′-
[5,10,15-tris(2,6-dimethoxyphenyl)-20-porphinyl]di(2,6-dimethyl-
phenyl)ethyne (Methoxy-Based ZnFbB) (36). A deaerated solution
of the zinc ethynyl porphyrin 25 (39 mg, 4.3 µmol), free base iodo
porphyrin 26 (49 mg, 5.2 µmol), and tri-2-furylphosphine (5 mg, 2.1
µmol) in 12 mL of pyridine/triethylamine (5:1) was treated with 2.4
mg (2.6 µmol) of Pd2(dba)3 under argon in a one-neck round-bottom
flask fitted with a reflux condenser. Deaeration was achieved by
passing argon through a syringe needle immersed in the solution. The
mixture was heated to 80 °C for 48 h. At this point the reaction mixture
was cooled to room temperature and concentrated to dryness under
reduced pressure. The crude material was dissolved in CH2Cl2 and
purified on three consecutive chromatographic columns (first column,
silica, CH2Cl2 enriched steadily with ethyl acetate; second column,
silica, CH2Cl2 enriched steadily with ethyl acetate; third column, silica,
CH2Cl2 enriched steadily with ethyl acetate), affording 16 mg (21%)
of the dimer. 1H NMR (CDCl3 containing 5% pyridine-d5) δ -2.47
(s, 2 H, NH), 2.07 (s, 12 H, ArCH3), 3.50 (s, 18 H, OCH3), 3.52 (s, 18
H, OCH3), 6.94, 7.02 (m, 12 H, ArH), 7.63, 7.76 (m, 12 H, ArH),
8.54, 8.62 (m, 4 H, â-pyrrole), 8.69, 8.75 (m, 12 H, â-pyrrole); LD-
MS C106H90N8O12Zn calcd av mass 1733.3, obsd 1730.8; λabs (CH2Cl2)
422, 514, 548, 588, 642 nm.
8.86 (d, 4 H, J ) 4.5 Hz, â-pyrrole), 8.90 (d, 2 H, J ) 4.5 Hz,
â-pyrrole), 8.97 (s, 2 H, â-pyrrole); LD-MS C160H128N12Zn3 calcd av
mass 2415.0, obsd 2414.9; λabs (toluene) 428, 512, 550, 592 nm.
4-[Zinc(II) 5,10,15-trimesityl-20-porphyrinyl]-4′-[zinc(II) 5,15-
dimesityl-10-{2,6-dimethyl-4-[2-(trimethylsilyl)ethynyl]phenyl}-20-
porphinyl]diphenylethyne (Mono-Trimethylsilylethyne Dimer for
ZnZnFb Trimer) (42). Samples of zinc iodo ethynyl porphyrin 28
(95 mg, 94 µmol) and zinc ethynyl porphyrin 13 (91 mg, 110 µmol)
were coupled, affording 110 mg (68%) following chromatographic
workup. 1H NMR (CDCl3) δ 0.37 (s, 9 H, SiCH3), 1.86 (s, 36 H,
ArCH3), 2.63 (s, 3 H, ArCH3), 2.64 (s, 12 H, ArCH3), 7.30 (s, 10 H,
ArH), 7.62 (s, 2 H, ArH), 8.06 (AA′BB′, 4 H, ArH), 8.30 (AA′BB′, 4
H, ArH), 8.66 (d, 2 H, J ) 4.5 Hz, â-pyrrole), 8.72, 8.74 (m, 6 H,
â-pyrrole), 8.80, 8.83 (m, 4 H, â-pyrrole), 8.93, 8.95 (m, 4 H, â-pyrrole);
LD-MS C112H96N8SiZn2 calcd av mass 1712.9, obsd 1710.5; λabs
(toluene) 427, 551 nm.
4-[Zinc(II) 5,10,15-trimesityl-20-porphyrinyl]-4′-[zinc(II) 5,15-
dimesityl-10-{2,6-dimethyl-4-ethynylphenyl}-20-porphinyl]di-
phenylethyne (Mono-Ethyne Dimer for ZnZnFb Trimer) (43). A
sample of 42 (100 mg, 0.058 mmol) was dissolved in 10 mL of CHCl3.
Tetrabutylammonium fluoride on silica gel (116 mg, 1.0-1.5 mmol
F-/g) was added and the reaction mixture was stirred at room
temperature for 30 min. The organic layer was washed with 10%
NaHCO3, dried (Na2SO4), filtered, and rotary evaporated to dryness.
Column chromatography on silica (CH2Cl2/hexanes (1:1), 4.8 × 7 cm)
afforded 86 mg (90%). 1H NMR (CDCl3) δ 1.86 (s, 36 H, ArCH3),
2.63 (s, 3 H, ArCH3), 2.64 (s, 12 H, ArCH3), 3.25 (s, 1 H, CCH), 7.28
(s, 4 H, ArH), 7.30 (s, 6 H, ArH), 7.63 (s, 2 H, ArH), 8.06 (AA′BB′,
4 H, ArH), 8.30 (AA′BB′, 4 H, ArH), 8.67 (d, 2 H, J ) 4.5 Hz,
â-pyrrole), 8.72, 8.75 (m, 6 H, â-pyrrole), 8.80, 8.83 (m, 4 H, â-pyrrole),
8.93 (d, 2 H, J ) 3.3 Hz, â-pyrrole), 8.95 (d, 2 H, J ) 3.3 Hz,
â-pyrrole); LD-MS C109H88N8Zn2 calcd av mass 1640.7, obsd 1637.1;
λabs (toluene) 427, 551 nm.
ZnZnFb Trimer (ZnZnFb)46 44. Samples of mono-ethynyl por-
phyrin dimer 43 (50 mg, 30 µmol) and free base iodo porphyrin 14
(29 mg, 33 µmol) were coupled in 12.6 mL of toluene/triethylamine
(5:1) using Pd2(dba)3 (4.6 mg, 5 µmol) and AsPh3 (12.2 mg, 40 µmol)
in a 50-mL one-neck round-bottom flask at 35 °C for 2 h under
anaerobic conditions (following the general conditions for ZnFbU
dimer), affording 57 mg (80%) following chromatographic workup.
1H NMR (CDCl3) δ -2.55 (bs, 2 H, NH), 1.87 (s, 36 H, ArCH3), 1.89
(s, 12 H, ArCH3), 1.98 (s, 6 H, ArCH3), 2.64 (s, 9 H, ArCH3), 2.65 (s,
9 H, ArCH3), 2.66 (s, 6 H, ArCH3), 7.28 (s, 6 H, ArH), 7.30 (s, 6 H,
ArH), 7.32 (s, 4 H, ArH), 7.84 (s, 2 H, ArH), 8.04, 8.09 (m, 6 H,
ArH), 8.26, 8.32 (m, 6 H, ArH), 8.65 (s, 4 H, â-pyrrole), 8.75 (s, 8 H,
â-pyrrole), 8.79, 8.89 (m, 8 H, â-pyrrole), 8.95 (d, 2 H, J ) 4.5 Hz,
â-pyrrole), 8.97 (d, 2 H, J ) 4.5 Hz, â-pyrrole); LD-MS C162H134N12-
Zn2 calcd av mass 2379.7, obsd 2374.4; λabs (toluene) 425, 431, 516,
552, 593, 651 nm.
Methoxy-Based Zn2B 37. Attempts to prepare this dimer led to
an insoluble porphyrin product.
ZnFbZn Linear Trimer (ZnFbZn-L)47 38. See ref 42.
Zn3 Linear Trimer (Zn3L)46,47 39. Zinc was inserted into 15 mg
of 38 using the standard conditions of zinc acetate dihydrate and CHCl3/
methanol (10:1). The reaction mixture was stirred for 16 h at room
temperature. 1H NMR (CDCl3) δ 1.87 (s, 36 H, ArCH3), 1.89 (s, 12
H, ArCH3), 2.64 (s, 6 H, ArCH3), 2.65 (s, 12 H, ArCH3), 2.67 (s, 6 H,
ArCH3), 7.28 (s, 4 H, ArH), 7.30 (s, 8 H, ArH), 7.33 (s, 4 H, ArH),
8.06, 8.10 (m, 8 H, ArH), 8.30, 8.35 (m, 8 H, ArH), 8.73 (s, 8 H,
â-pyrrole), 8.82 (d, 4 H, J ) 4.2 Hz, â-pyrrole), 8.86 (d, 4 H, J ) 4.5
Hz, â-pyrrole), 8.95 (d, 4 H, J ) 4.2 Hz, â-pyrrole), 8.99 (d, 4 H, J )
4.5 Hz, â-pyrrole); LD-MS C160H128N12Zn3 calcd av mass 2415.0, obsd
2407.9; λabs (toluene) 429, 550 nm.
ZnFbZn Right-Angle Trimer (ZnFbZn-R)47 40. Samples of free
base diiodo porphyrin 15 (25 mg, 26.2 µmol) and zinc ethynyl porphyrin
13 (65 mg, 78.9 µmol) were coupled in 21 mL of toluene/triethylamine
(5:1) using AsPh3 (6.4 mg, 21.0 µmol) and Pd2(dba)3 (2.4 mg, 2.6 µmol)
at 40 °C under anaerobic conditions (following the general conditions
for ZnFbU dimer), affording 56 mg (90%) following chromatographic
workup. 1H NMR (toluene-d8) δ -2.45 (s, 2 H, NH), 1.82 (s, 48 H,
o-ArCH3), 2.58 (s, 24 H, p-ArCH3), 7.30 (s, 12 H, ArH), 7.35 (s, 4 H,
ArH), 8.06 (AA′BB′, 4 H, ArH), 8.12 (AA′BB′, 4 H, ArH), 8.31
(AA′BB′, 4 H, ArH), 8.35 (AA′BB′, 4 H, ArH), 8.63, 8.71 (m, 12 H,
â-pyrrole), 8.73 (d, 2 H, J ) 4.7 Hz, â-pyrrole), 8.86 (m, 6 H,
â-pyrrole), 8.91 (d, 2 H, J ) 4.7 Hz, â-pyrrole), 8.98 (s, 2 H, â-pyrrole);
LD-MS C160H130N12Zn2 calcd av mass 2351.6, obsd 2350.3; λabs
(toluene) 424, 519, 550, 590, 648 nm.
Zn3 Right-Angle Trimer (Zn3R)47 41. 41 was prepared at the
analytical scale by zinc insertion with 40 following the general
metalation procedure described above. 1H NMR (toluene-d8) δ 1.86
(s, 12 H, o-ArCH3), 1.88 (s, 24 H, o-ArCH3), 1.89 (s, 12 H, o-ArCH3),
2.60 (s, 6 H, p-ArCH3), 2.62 (s, 12 H, p-ArCH3), 2.60 (s, 6 H, p-ArCH3),
7.29 (s, 8 H, ArH), 7.31 (s, 4 H, ArH), 7.33 (s, 4 H, ArH), 8.05, 8.10
(m, 8 H, ArH), 8.24, 8.34 (m, 8 H, ArH), 8.63 (m, 8 H, â-pyrrole),
8.66, 8.70 (m, 4 H, â-pyrrole), 8.74 (d, 4 H, J ) 4.5 Hz, â-pyrrole),
Acknowledgment. This work was supported by the NIH
(GM36238). We thank Dr. Walter Svec at Argonne National
Laboratory for performing laser desorption mass spectrometry,
and Prof. Aksel A. Bothner-By for assistance with NMR
spectroscopy.
JA961611N