Investigation of two rational routes for preparing p-phenylene-linked porphyrin trimers

Article abstract of DOI:10.1016/S0040-4020(01)00928-0

Multiporphyrin arrays with p-phenylene linkers, aryl groups at the non-linking meso positions, and no β-substituents are attractive constructs for light-harvesting applications. Condensation of a free base porphyrin-benzaldehyde and 5-mesityldipyrromethane (10 mM each) in CH₂Cl₂ containing 100 mM TFA at room temperature for 30-40 min followed by oxidation with DDQ afforded a p-phenylene-linked porphyrin trimer in 36% yield. Suzuki coupling of an iodo-porphyrin and a bis(dioxaborolane)-porphyrin (20 and 10 mM, respectively) in toluene/DMF (2:1) containing K₂CO₃ (8 equiv.) at 90-95°C for ～20 h afforded the same trimer in 66% yield. The former route was used to prepare a diethynyl substituted p-phenylene-linked porphyrin trimer. While the two routes are somewhat complementary in scope, both are convergent and proceed in a rational manner.

Full text of DOI:10.1016/S0040-4020(01)00928-0

TETRAHEDRON
Pergamon
Tetrahedron 57 *2001) 9285±9298
Investigation of two rational routes for preparing
p-phenylene-linked porphyrin trimers
Lianhe Yu and Jonathan S. Lindseyp
Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA
Received 8 August 2001; accepted 10 September 2001
AbstractÐMultiporphyrin arrays with p-phenylene linkers, aryl groups at the non-linking meso positions, and no b-substituents are
attractive constructs for light-harvesting applications. Condensation of a free base porphyrin-benzaldehyde and 5-mesityldipyrromethane
*10 mMeach) in CH Cl2 containing 100 mMTFA at room temperature for 30±40 min followed by oxidation with DDQ afforded a
2
p-phenylene-linked porphyrin trimer in 36% yield. Suzuki coupling of an iodo-porphyrin and a bis*dioxaborolane)-porphyrin *20 and
10 mM, respectively) in toluene/DMF *2:1) containing K2CO3 *8 equiv.) at 90±958C for ,20 h afforded the same trimer in 66% yield.
The former route was used to prepare a diethynyl substituted p-phenylene-linked porphyrin trimer. While the two routes are somewhat
complementary in scope, both are convergent and proceed in a rational manner. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
5,15-positions) takes advantage of methodology for the
synthesis of meso-substituted porphyrin building blocks.5
Biomimicry: the photosynthetic antenna complexes are
composed of domains of pigments, with stronger inter-
actions within domains and weaker interactions between
domains.6 An architecture with domains of p-phenylene-
linked trimers interspersed by diphenylbutadiyne or
diphenylethyne linkers would provide a primitive model
for the ¯ow of energy in photosynthetic antenna complexes.
Photophysics: excited-state energy transfer in covalently
linked porphyrin arrays occurs predominantly via a linker-
mediated through-bond mechanism.1 The rate of energy
transfer ꢀkZn!Fb† depends both on the distance of separation
of the porphyrins and the electron density of the porphyrin
frontier molecular orbitals at the position of linker attach-
ment. Dyads comprised of a zinc tetraarylporphyrin and a
free base tetraarylporphyrin *Chart 1) exhibit an energy-
transfer rate that depends on the nature of the linker in the
following way: *38 ps)21, 4,40-diphenylbutadiyne linker;4
*24 ps)21, 4,40-diphenylethyne linker;3 *3.5 ps)21, p-phenyl-
ene linker.2 The porphyrins in these dyads are linked at the
meso-positions, bear mesityl groups at the non-linking
meso-positions, and have no b-substituents. Analogous
dyads with a full complement of substituents at the eight
b-positions on each porphyrin exhibit rates of *417 ps)21
As part of a program in arti®cial photosynthesis, we have
been working to construct multiporphyrin light-harvesting
arrays in which the porphyrins are weakly coupled elec-
tronically.1 Weakly coupled arrays exhibit absorption
spectra and electrochemical potentials that are essentially
the sum of the features observed for the corresponding
monomers, thereby facilitating molecular design. Studies
of meso-substituted *b-unsubstituted) porphyrin dyads
have shown that p-phenylene,2 diphenylethyne3 and diphe-
nylbutadiyne4 linkers afford differing extents of interpor-
phyrin communication, though each remains within the
weak coupling regime. A particularly attractive construct
is a linear trimeric porphyrin building block with the follow-
ing features: *1) p-phenylene linkers across the meso-posi-
tions to join the porphyrins, *2) electron-rich substituents at
the non-linking meso-positions, *3) no substituents at the
b-positions of the porphyrins, and *4) iodophenyl or
ethynylphenyl substituents at the termini of the trimer
for extension to larger multiporphyrin constructs via
Sonogashira or Glaser coupling *affording diphenylethyne
or diphenylbutadiyne linkers, respectively).
The motivation for this molecular design stems from
synthetic, biomimetic, and photophysical considerations.
Synthesis: the use of multimeric building blocks provides
greater ef®ciency in the construction of large arrays
compared with monomeric building blocks. Moreover,
attachment of linkers at the porphyrin meso-positions *i.e.
7
*4,40-diphenylethyne) or *10 ps)21 *p-phenylene linker).8
The difference in rate is attributed to the characteristics of
the porphyrin frontier molecular orbitals in the different
systems. A tetraarylporphyrin with electron-rich sub-
,8
²
stituents at the meso-positions has an a2u*p) HOMO,
²
Keywords: porphyrins and analogues; pyrroles; Suzuki reactions; alkynes.
Corresponding author. Tel.: 11-919-515-6406; fax: 11-919-513-2830;
e-mail: jlindsey@ncsu.edu
The presence of strongly electron-withdrawing groups *e.g. penta¯uoro-
phenyl) at the meso-positions results in the a1u HOMO, hence the require-
ment for electron-rich groups at the non-linking meso-positions.1,7
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020*01)00928-0

9286
L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
Scheme 2.
With one exception,9 all p-phenylene-linked porphyrin
trimers synthesized to date have incorporated the linker
across the meso-positions of porphyrins bearing alkyl
groups at all eight b-positions.10±15 No trimers have
included synthetic handles at the termini of the trimer.
The syntheses of p-phenylene linked trimers generally
have employed reaction of a porphyrin-benzaldehyde with
a b-substituted dipyrromethane thereby creating the inner
porphyrin macrocycle. The reaction proceeds via acid-
catalyzed condensation followed by quinone-mediated
oxidation. In any acid-catalyzed reaction with a dipyrro-
methane, acidolysis can occur yielding fragments that
upon undesired recombination afford a mixture of porphyrin
species *i.e. scrambling).16 While b-substituted *meso-
unsubstituted) dipyrromethanes are quite stable toward
acidolysis,17 the stability of meso-substituted *b-unsubsti-
tuted) dipyrromethanes depends on the nature of the group
attached to the meso-position: a sterically hindered group
*e.g. mesityl) provides resistance while an unhindered group
*e.g. phenyl) results in susceptibility to acidolysis.16 Indeed,
in the only prior example of the synthesis of a p-phenylene-
linked porphyrin trimer lacking b-substituents, a complex
mixture of porphyrins was obtained upon reaction of a
porphyrin-benzaldehyde with 5-*p-tolyl)dipyrromethane,
while with 5-pentyldipyrromethane the desired trimer was
obtained in 12% yield.9 Accordingly, the acid-catalyzed
condensations studied herein have employed 5-mesityl-
dipyrromethane to minimize scrambling processes.
Chart 1.
which has electron density at the meso-position *thereby
enhancing through-bond energy transfer); a b-substituted
octaalkylporphyrin has an a1u*p) HOMO, which has a
node at the meso-position. Thus, achieving the fastest possible
rate of energy transfer requires the avoidance of b-alkyl
groups in arrays with linkers attached to the meso-positions.
An alternative approach for preparing p-phenylene-linked
trimers employs the Suzuki coupling of a dialkoxyboryl-
porphyrin and a halo-porphyrin. Suzuki coupling has been
employed for *1) attaching diverse groups to porphyrins,18±21
and *2) preparing porphyrin dimers with a phenylene unit
across the b,meso-positions,21,22 a direct C±C bond across
the b,b-positions,23 and a carbazole unit across the
Scheme 1.

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9287
Scheme 3.
meso,meso-positions.20 However, to our knowledge Suzuki
coupling has not been employed previously to prepare
trimers or larger multiporphyrin arrays.
2. Results and discussion
2.1. 5-Substituted dipyrromethanes
In this paper, we report a comparison of two routes for
preparing b-unsubstituted p-phenylene-linked porphyrin
trimers. We ®rst synthesized several porphyrin building
blocks in a rational manner. With these building
blocks, the condensation of a porphyrin-benzaldehyde
and 5-mesityldipyrromethane was investigated to identify
optimal acid-catalysis conditions. Suitable conditions were
also examined for the Suzuki coupling of a meso-iodo-
substituted porphyrin and a meso-substituted porphyrin
bearing two dioxaborolane groups in a trans architecture
*porphyrin 5,15-positions). In all cases, free base porphyrins
were employed, no statistical reactions were performed, and
potential scrambling processes were investigated.
Dipyrromethanes bearing a wide variety of substituents at the
5-position are readily available, including mesityl *3a),24 4-[2-
*trimethylsilyl)ethynyl]phenyl *3b),25 no substituent *3d),24
and 4-formylphenyl *3e).5 The synthesis of the dioxaboro-
lane-dipyrromethane 3c is shown in Scheme 1. The syn-
thesis of aldehyde 2 has been reported but without a
detailed procedure or characterization data.26 To facilitate
eventual puri®cation of the porphyrin, the boronic acid group
was employed as the dioxaborolane derivative. Aldehyde 2 was
obtained in 90% yield by treatment of 1 with pinacol in dry
ethyl ether followed by column chromatography. The reaction
of aldehyde 2 with pyrrole under TFA catalysis in a one-¯ask
process24 afforded the desired dipyrromethane 3c in 32% yield.

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L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
2.2. Porphyrin building blocks
To pursue the two routes for forming p-phenylene-linked
porphyrin trimers, porphyrins bearing 4-formylphenyl,
4-[2-*trimethylsilyl)ethynyl]phenyl or 4-*1,3,2-dioxaboro-
lan-2-yl)phenyl substituents were prepared via rational
procedures. The method of synthesis depends on the pattern
of substituents at the perimeter of the porphyrin. For
these applications, AB2C-porphyrins5 and trans-A2B2-por-
phyrins16 were prepared bearing 3,5-di-tert-butylphenyl or
mesityl *rather than phenyl) groups at non-linking positions
to enhance the solubility of the corresponding porphyrin
trimers.
For the synthesis of AB2C-type porphyrins *6a±d), treat-
ment of dipyrromethane 3 *A component) with 5 equiv. of
EtMgBr followed by 2.5 equiv. of acid chloride 4 *B
component) in toluene *Scheme 2) afforded diacyldipyrro-
methane 5a or 5b *BAB component) in 51 or 35% yield,
respectively. Reduction of diacyldipyrromethane 5 with
NaBH4 in THF/methanol afforded the corresponding dipyr-
romethane-dicarbinol *5-OH), which was condensed
directly with another dipyrromethane 3 *C component) in
acetonitrile containing TFA followed by oxidation with
DDQ *Scheme 3). The dipyrromethane1dipyrromethane-
dicarbinol reaction gave yields ranging from 13 to 23%.
Several observations are noteworthy: *1) the dipyrro-
methane with a free formyl group *3e) gave a somewhat
low yield *13%) in two cases examined; *2) puri®cation of
dioxaborolane-porphyrin 6b could not be achieved by
chromatography on alumina due to the signi®cant loss of
product incurred.
Scheme 4.
The trans-A2B2-type porphyrin 7 was prepared by the
condensation of 5-mesityldipyrromethane *3a) and the
dioxaborolane-benzaldehyde 2 as shown in Scheme 4. The
acid catalysis conditions *BF3´O*Et)2 in CHCl3)27 employed
in this reaction are now known to afford a small amount of
scrambling.16 However, porphyrin 7 was readily isolated in
pure form *27% yield) after silica column chromatography.
Iodo-porphyrin 8 was prepared as shown in Scheme 5.
Treatment of porphyrin 6c with bis*tri¯uoroacetoxy)iodo-
benzene and iodine in CHCl3/pyridine19,28 at room tempera-
ture afforded 8 in 80% yield after column chromatography.
1
No b-iodinated products were observed upon H NM R
analysis.
2.3. Synthesis of p-phenylene-linked porphyrin trimers
by condensation/oxidation of a porphyrin-benzalde-
hyde1dipyrromethane
We previously studied the reaction of an aldehyde and a
dipyrromethane leading to a trans-A2B2-porphyrin.16 We
found that the condensation of sterically hindered dipyrro-
methanes and an aryl aldehyde catalyzed by TFA gave no
scrambling for all reactions examined, regardless of the acid
catalyst concentration, reaction solvent, reagent concen-
tration, reaction temperature, presence of catalytic salts or
reagent ratio. The optimum conditions that emerged from
this study were as follows: 5-mesityldipyrromethane
*10 mM) and aryl aldehyde *10 mM) in reagent-grade
CH2Cl2 containing TFA *17.8 mM) at room temperature
Scheme 5.

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9289
Scheme 6.
followed by oxidation with DDQ. Under these conditions,
seven porphyrins were prepared in 28±48% yield.16
Second, because the benzaldehyde bears a porphyrin, the
inevitable polypyrrolic byproducts each incorporate one or
more porphyrins, which can complicate identi®cation and
isolation of the desired trimer.
Two issues arise for the reaction of a porphyrin-benz-
aldehyde and a dipyrromethane. First, the porphyrin can
buffer the acid employed for catalysis of the condensation.
The trimer-forming reaction *Scheme 6) was performed
under the standard conditions for an aldehyde1dipyrro-
methane condensation *10 mMreactants and 17.8 mM
TFA in CH2Cl2 at room temperature) followed by oxidation
with DDQ.16 However, analysis of the crude reaction
mixture by TLC or LD-MS showed no detectable trimer
*9) was observed, even with reaction times of up to 2.5 h.
We therefore investigated the condensations at different
TFA concentrations as shown in Fig. 1. The data show the
isolated yield obtained upon workup of the reaction mixture
after 40 min. The yield peaked with reactions at 100 mM
TFA. The reactions performed with the higher TFA con-
centrations *56.2, 100, 178 mM) were rapid. Indeed, after
40 min no starting porphyrin was detected upon TLC or
LD-MS analysis. In addition, LD-MS analysis of oxidized
reaction aliquots showed no peaks due to the formation
of scrambled porphyrin products. Thus, suitable con-
ditions for the trimer-forming reaction are as follows:
porphyrin-benzaldehyde
*10 mM),
5-mesityldipyrro-
methane *10 mM), and TFA *100 mM) in CH2Cl2 at room
temperature for 30±40 min followed by oxidation with
DDQ. Under these conditions, the desired trimer 9 was
obtained in 36% yield. The crude product contained a
chlorin contaminant, which upon oxidation with DDQ in
re¯uxing toluene29 yielded the desired porphyrin trimer.
Figure 1. Isolated yield of trimer 9 as a function of the concentration
of TFA. The condensation was performed in CH2Cl2 at room temperature
for 40 min with constant amounts of porphyrin-benzaldehyde 6a and
5-mesityldipyrromethane *3a) *10 mMeach). Oxidation was performed
with DDQ and the product isolated for yield determination.

Scheme 7.

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9291
Scheme 8.
The concentration of acid is substantially higher than that
for the normal synthesis of trans-A2B2-porphyrins, but the
data show that 100 mMTFA with a porphyrin-benz-
aldehyde and 5-mesityldipyrromethane does not result in a
mixture of scrambled products.
for 1 h) to convert trace amounts of chlorin to the porphyrin;
*4) ®ltration through a silica pad; *5) size exclusion
chromatography *SEC)30 and *6) a ®nal silica gel chroma-
tography. Trimer 10 was obtained in 32% yield. A ®nal
oxidation was a necessary step because of the presence of
chlorin contamination; chlorin formation is a common
byproduct in the synthesis of trans-porphyrins by the
reaction of a dipyrromethane and an aldehyde.16 Deprotec-
tion of the TMS groups with tetra-n-butylammonium
¯uoride *TBAF) in CHCl3/THF gave the diethynyl
substituted trimer 11 in 90% yield.
Prior studies of the reaction of a porphyrin-benzaldehyde
and a b-substituted dipyrromethane have led to different
®ndings concerning the amount of acid required for reac-
tion. Nagata et al. found an increased concentration of
trichloroacetic acid in acetonitrile was required compared
with that for a reaction with an aldehyde without an attached
12
porphyrin *37 mMtrichloroacetic acid; 9 mMreactants),
giving yields of 35±47%.12±15 On the other hand, Sessler et
al. employed a slightly lower concentration of TFA
*10 mM; 10 mM reactants) in dichloromethane than would
2.4. Synthesis of p-phenylene-linked porphyrin dimers
and trimers via Suzuki coupling
be used for the reaction of an aryl aldehyde and pyrrole
10,11
The use of Pd-coupling methods for joining porphyrins
often requires conditions that are substantially different
from those employed in mainstream organic chemistry for
coupling small molecules.30 The chief difference stems from
the fact that porphyrins typically have low solubility and
require reactions to be performed with 1±10 mMporphyrin
concentrations. Consequently, many coupling methods that
work very well under mild conditions with small molecules
at high concentration *0.1 to 1 M) give poor results or fail
altogether in more dilute solution. One objective of our
study of the Suzuki coupling was whether the milder con-
ditions31 reported quite recently could be applied to the
synthesis of trimeric porphyrin building blocks.
*20±50 mMTFA), obtaining yields of 60.4
and
81.6%.11 Comparative studies of acid catalysis indicate
that b-substituted dipyrromethanes and meso-substituted
dipyrromethanes have quite different reactivity.17
We applied the re®ned acid-catalysis conditions employed
for the synthesis of 9 to prepare a p-phenylene-linked
porphyrin trimer bearing two TMS-protected ethynyl
groups as shown in Scheme 7. The puri®cation of the trimer
from this method involved: *1) ®ltration of the crude
reaction mixture through alumina; *2) silica gel chroma-
tography; *3) re-oxidation with DDQ in toluene *re¯uxing

9292
L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
the desired dimer *6.4%) and monomeric porphyrins
*93.5%) by integrated intensities *uncorrected). Therefore,
additional K2CO3 *6 molar equiv.) and Pd*PPh3)4 *15 mol%)
were added and the temperature was raised to 908C. The
analytical SEC trace showed that most of the starting
porphyrins were consumed after stirring for 15 h at 908C
*Fig. 2C). Puri®cation of the crude product involved *1)
silica gel chromatography to remove the inorganic salt
and Pd species, *2) preparative SEC *THF) and *3) a ®nal
silica gel chromatography, affording the desired porphyrin
dimer 12 in 70% yield *Fig. 2D).
We applied the conditions for the Suzuki coupling of an
iodo-porphyrin and a dioxaborolane-porphyrin yielding
the dimer *8 molar equiv. of K2CO3 and 30 mol% of
Pd*PPh3)4 at 908C for several hours) to prepare the phenyl-
ene-linked trimer 9 as shown in Scheme 9. In this two-site
coupling reaction, the concentrations were as follows:
iodoporphyrin 8, 20 mM; bis*dioxaborolane)porphyrin 7,
10 mM; K2CO3, 16 molar equiv. relative to porphyrin 7;
Pd*PPh3)4, 30 mol% relative to porphyrin 7. Analytical
SEC indicated that most of the starting porphyrins remained
unreacted even after 6 h at 908C *Fig. 3). Therefore, an
additional amount of Pd*PPh3)4 *30 mol%) was added and
the reaction was allowed to proceed for 18 h at 90±958C.
Analytical SEC showed complete consumption of the
starting porphyrins.
The puri®cation of the crude reaction mixture by silica
column chromatography [CHCl3/hexanes *2:1)] afforded
four fractions *in order of elution): *1) the desired trimer
9; *2) byproduct I *dimers); *3) byproduct II *dimer); and *4)
monomeric species. Further puri®cation of the trimer by
preparative SEC *toluene) followed by ®nal silica gel
chromatography gave 9 in 66% yield *Fig. 3D). Preparative
SEC puri®cation *THF) of fraction 2 afforded one band as
evidenced by analytical SEC; however, ®nal silica column
chromatography [CHCl3/hexanes *2:1)] afforded clearly two
bands, which were collected separately, affording dimer 13
*®rst purple band) and 14 *second purple band) in 8.0 and
6.5% yield, respectively. Similar puri®cation of fraction 3
by preparative SEC *THF) and silica column chroma-
tography [CHCl3/hexanes *2:1)] afforded dimer 15 in
6.1% yield. In summary, the Suzuki coupling afforded a
direct synthesis of the desired trimer *or dimer) upon
reaction at the low concentrations typical in porphyrin
Figure 2. SEC traces of the crude reaction mixture from the formation of
dimer 12 via Suzuki coupling. *A) Reaction mixture before adding the
catalyst. *B) Reaction mixture after 3 h at 708C. *C) Reaction mixture
after 15 h at 90±958C. The integrated intensities *uncorrected) were as
follows: the desired dimer *tRˆ10.75 min), 73.4%; monomeric porphyrins
*tRˆ11.28 min), 26.5%. *D) Puri®ed dimer 12.
The syntheses of porphyrin dimers joined across the meso-
position and b-position by a p-phenylene unit has been
achieved by Suzuki coupling of a b-substituted bromo-
porphyrin and
a
meso-substituted dioxaborinane-
porphyrin.21 These reaction conditions employed a 3.4:1
ratio of the dioxaborinane-porphyrin/bromo-porphyrin
with 10±15 mol% of Pd*PPh3)4 and 8 equiv. of K2CO3 in
toluene for 48 h at 90±1008C, affording the desired
porphyrin dimer in 88% yield. We investigated the Suzuki
coupling reactions using stoichiometric amounts of the two
porphyrins, because both porphyrin components are
valuable and chromatographic workup is simpli®ed if an
excess of starting material is not present.30,32 As shown in
Scheme 8, equimolar amounts of dioxaborolane-porphyrin
6b and iodo-porphyrin 8 were coupled in toluene/DMF *2:1)
using Pd*PPh3)4 *15 mol%) and K2CO3 *2 molar equiv. rela-
tive to the porphyrin). We chose the mixture of toluene and
DMF because tetraarylporphyrin monomers have good
solubility in toluene, while K2CO3 has good solubility in
DMF. The concentration of each porphyrin was 10 mM.
The reaction was followed by analytical SEC *Fig. 2).
After 3 h at 758C, the reaction mixture consisted of
³
chemistry. The requirement to use high-temperature con-
ditions in the presence of base, as employed in the synthesis
of trimer 9, precluded the use of the Suzuki reaction to
prepare diethynyl-substituted or other trimeric porphyrin
building blocks.
³
Fu and co-workers recently reported extremely mild conditions for the
Suzuki coupling of arylboronic acids with aryl halides.31 Under their
conditions, an aryl iodide and an aryl boronic acid *,1 Meach) were
coupled in excellent yield *94±98%) with Pd2*dba)3 *0.5 mol%), P*t-Bu)3
*1.2 mol%) and KF *3.3 equiv.) in THF at room temperature for 3±20 h.
Application of these conditions to prepare porphyrin dimer 12 using
10 mMof each porphyrin was not successful. A 10-fold increase in the
loading of Pd2*dba)3 *5 mol%) and P*t-Bu)3 *12 mol%) also gave no
dimer. A reasonable interpretation is that the low solubility of porphyrinic
substrates limits the types of Pd-mediated coupling conditions that can be
employed.

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9293
Scheme 9.
2.5. Electronic spectra of p-phenylene-linked arrays
porphyrin trimers.9,12,14,15 The ¯uorescence emission spec-
trum and emission intensity of 9 in toluene *lexcˆ520 nm,
ffˆ0.13) closely resembled that of meso-tetraphenyl-
porphyrin *ffˆ0.11), with peak emission wavelengths of 9
within 3 nm of those of meso-tetraphenylporphyrin. Nearly
identical behavior was observed for the diethynyl-trimer 10.
In contrast, the p-phenylene linked trimer composed of
b-substituted free base porphyrins gave a slightly broadened
emission spectrum,11 and the zinc chelates of the same type
of trimer gave quite red-shifted and broadened emission
spectra.14,15 The essentially unaltered ¯uorescence spectrum
and intensity compared with that of a monomeric free base
The absorption spectrum of the trimer 9 shows broadening
and splitting of the Soret *B) band compared with that of the
monomer 6b, but the visible *Q) bands are essentially
unchanged *Fig. 4). Dimer 12 exhibits broadening and split-
ting of the Soret band intermediate between that of a trimer
and monomer 6b. The unchanged visible bands are consis-
tent with an excited singlet state that is unaffected by the
juxtaposition of the three porphyrins via the
p-phenylene bridges. These absorption spectral features
resemble those observed previously for p-phenylene linked

9294
L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
Figure 4. UV±Vis absorption spectra *normalized) of monomer *6b),
dimer *12) and trimer *9) in toluene at room temperature: *A) Soret band
region. *B) Q-band region.
Figure 3. SEC traces of the crude reaction mixture from the formation of
trimer 9 via Suzuki coupling. *A) Reaction mixture before adding the
catalyst. *B) Reaction mixture after 6 h at 90±958C. *C) Reaction mixture
after 18 h at 90±958C. The integrated intensities *uncorrected) were as
follows: desired trimer *tRˆ10.38 min), 49.0%; dimer species *tRˆ
10.84 min), 39.4%; monomeric species *tRˆ11.26±11.48 min), 11.05%.
*D) Puri®ed trimer 9.
to survive these mild conditions.16 The latter route offered
higher yield *66%) but required more forcing conditions
*90±958C, 24 h in the presence of K2CO3). Functional
groups such as the TMS-protected ethynyl unit are not
expected to survive these conditions. Puri®cation of the
p-phenylene-linked porphyrin trimer was somewhat simpler
in the Suzuki route.
tetraarylporphyrin indicates the integrity of the excited
singlet state in the p-phenylene linked trimers, a desirable
attribute of weakly coupled systems for photochemical
applications.
4. Experimental
4.1. General
3. Conclusions
1H NMR spectra *300 MHz) and 13C NMR spectra
*75 MHz) were collected in CDCl3 unless noted otherwise.
Absorption and ¯uorescence spectra were collected in
toluene at room temperature. Mass spectra of porphyrins
were obtained via laser desorption mass spectrometry
*LD-MS) in the absence of an added matrix,33 or by high
resolution fast atom bombardment mass spectrometry
*FAB-MS) using a matrix of nitrobenzyl alcohol and
polyethylene glycol. Fluorescence quantum yields were
determined in toluene at room temperature using chlorin-
free meso-tetraphenylporphyrin *Ffˆ0.11;34 lemˆ652,
718 nm) as a standard as described previously.3 Anhydrous
K2CO3, tetrabutylammonium ¯uoride *TBAF) *1.0 M
Linear porphyrin trimers joined via p-phenylene linkers
across the respective porphyrin meso-positions were
successfully prepared both by condensation of
a
porphyrin-benzaldehyde1dipyrromethane and by Suzuki
coupling of an iodo-porphyrin and a bis*dioxaborolane)-
porphyrin. Both routes are convergent and proceed in a
rational manner but employ conditions of somewhat
complementary scope. The former route gave a lower
yield *36%) but the reaction proceeded under mild con-
ditions and a short time course *room temperature,
30±40 min). Diverse functional groups *e.g. iodo,
trimethylsilylethynyl, triisopropylsilylethynyl) are known

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9295
solution in THF), tetrakis*triphenylphosphine)palladium*0)
*Pd*PPh3)4), mesitaldehyde, 4-formylphenylboronic acid,
and pinacol were used as received from Aldrich. The syn-
thesis of the porphyrin monomers was performed without
degassing.
4.3.3. 1,9-Bis13,5-di-tert-butylbenzoyl)-5-mesityldipyrro-
methane 15a). Following the general diacylation pro-
cedure,5 a solution of 5-mesityldipyrromethane *2.64 g,
10.0 mmol) in toluene *200 mL) was treated with EtMgBr
*50.0 mL, 50.0 mmol, 1.0 Min THF) for 30 min at room
temperature followed by addition of 3,5-di-tert-butyl-
benzoyl chloride *6.33 g, 25.0 mmol, 2.5 equiv.). The
mixture was stirred for 20 min at room temperature.
Standard workup and chromatography [silica, CH2Cl2]
followed by precipitation from methanol afforded a brown
solid *3.55 g, 51%): mp .2408C *dec); 1H NM Rd 11.28 *s,
br, 2H), 7.56 *s, 4H), 7.53 *s, 2H), 6.92 *s, 2H), 6.61 *s, 2H),
6.24 *s, 1H), 5.96 *s, 2H), 2.31 *s, 3H), 2.29 *s, 6H), 1.29 *s,
36H), 13C NM Rd 184.4, 150.0, 140.0, 137.9, 136.6, 133.9,
130.4, 130.0, 125.2, 124.0, 121.0, 110.0, 39.2, 34.8, 31.3,
21.1, 20.8. Calcd for C48H60N2O2: C, 82.71; H, 8.68; N,
4.02. Found: C, 82.66; H, 8.81; N, 4.00.
4.2. Solvents
All solvents were dried by standard methods. Triethylamine
and toluene were distilled from CaH2. Anhydrous DMF
*Aldrich), CH2Cl2 and CHCl3 *Fisher, certi®ed ACS
grade, stabilized with 0.8% ethanol) were used as received.
4.3. Chromatography
Adsorption column chromatography was performed using
¯ash silica gel *Baker, 60±200 mesh) or alumina *Fisher).
Preparative-scale SEC was performed using BioRad Bio-
beads SX-1 in THF or in toluene *Fisher HPLC grade).
Analytical scale SEC *ldetectionˆ420 nm) was performed as
described previously to monitor the progress of the coupling
reactions and assess the purity of the porphyrin oligomers.35
4.3.4. 1,9-Bis13,5-di-tert-butylbenzoyl)-5-{4-[2-1trimethyl-
silyl)ethynyl]phenyl} dipyrromethane 15b). Following the
general diacylation procedure,5 a solution of dipyrro-
methane 3b *1.57 g, 4.93 mmol) in toluene *90 mL) was
treated with EtMgBr *24.7 mL, 24.7 mmol, 1.0 M in THF)
for 30 min at room temperature followed by addition of
3,5-di-tert-butylbenzoyl chloride *3.12 g, 12.3 mmol,
2.5 equiv.). The mixture was stirred for 40 min at room
temperature. Standard workup and chromatography [silica,
CH2Cl2!CH2Cl2/ethyl acetate *98:2)] followed by precipi-
tation *from a methanol solution upon addition of water)
gave an amorphous solid *1.30 g, 35%): mp 168±1708C;
1H NM Rd 11.97 *s, br, 2H), 7.58 *d, Jˆ8.1 Hz, 2H), 7.54
*s, 6H), 7.48 *d, Jˆ8.1 Hz, 2H), 6.54±6.52 *m, 2H), 5.94
*m, 2H), 5.71 *s, 1H), 1.29 *s, 36H), 0.25 *s, 9H); 13C NM R
d 185.5, 150.2, 141.5, 137.8, 132.4, 131.1, 128.9, 125.4,
124.2, 122.1, 120.9, 111.1, 105.0, 94.1, 45.2, 34.8, 20.1;
Anal. Calcd for C50H62N2O2Si: C, 79.95; H, 8.32; N, 3.73.
Found: C, 79.75, H, 8.34, N, 3.73.
The known compounds 5-mesityldipyrromethane *3a),24
5-[4-*trimethylsilylethynyl)phenyl]dipyrromethane *3b),25
dipyrromethane *3d),24 5-*4-formylphenyl)dipyrromethane
*3e),5 and 3,5-di-tert-butylbenzoyl chloride *4)5 were
prepared according to literature procedures.
4.3.1. 4-14,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-
benzaldehyde 12). To a suspension of 4-formylphenyl-
boronic acid *5.02 g, 33.4 mmol) in dry ethyl ether
*50 mL) was added pinacol *4.70 g, 40.1 mmol, 1.2
equiv.), causing the reaction mixture to turn to a clear solu-
tion after 30 min. After stirring for 15 h at room tempera-
ture, ethyl ether *100 mL) was added and the mixture was
washed with H2O. The organic layer was dried *MgSO4) and
chromatographed *silica, CH2Cl2), affording a slightly
yellow oil. Trituration with hexanes gave a solid, which
was ®ltered and dried affording a colorless solid *6.98 g,
4.3.5.
5,15-Bis13,5-di-tert-butylphenyl)-10-14-formyl-
phenyl)-20-mesitylporphyrin 16a). Following a standard
procedure,5 reduction of 5a *2.79 g, 4.00 mmol) with
NaBH4 *7.60 g, 200 mmol) in THF/methanol *320 mL,
3:1) yielded the dipyrromethane-dicarbinol. Condensation
of the latter with dipyrromethane 3e *1.00 g, 4.05 mmol)
in CH3CN *1600 mL) containing TFA *3.70 mL, 30 mM)
for 5 min, followed by oxidation with DDQ *2.72 g, 12.0
mmol) and standard workup gave a purple solid *467 mg,
1
90%): mp 58±598C; H NM Rd 10.05 *s, 1H), 7.96 *d,
Jˆ8.1 Hz, 2H), 7.87 *d, Jˆ8.1 Hz, 2H), 1.36 *s, 12H); 13C
NMR d 192.5, 138.0, 135.1, 128.6, 84.2, 24.8. Anal calcd
for C13H17BO3: C, 67.28; H, 7.38. Found: C, 67.42; H, 7.47.
4.3.2. 5-[4-14,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-
phenyl]dipyrromethane 13c). Following a general pro-
cedure,24 a mixture of pyrrole *35 mL, 0.50 mol) and
aldehyde 2 *4.64 g, 20.0 mmol) was ¯ushed with argon for
5 min and treated with TFA *154 mL, 2.00 mmol). The
mixture was stirred for 5 min at room temperature and
then quenched with triethylamine. Ethyl acetate *100 mL)
was added and the mixture was washed with H2O and dried
*Na2SO4). Removal of solvent and excess pyrrole followed
by chromatography [silica, CH2Cl2!CH2Cl2/ethyl acetate
*95:5)] gave a slightly yellow oil. Trituration with hexanes
afforded a colorless solid *2.50 g, 32%): mp 129±1308C; 1H
NMR d 7.91 *s, br, 2H), 7.77 *d, Jˆ8.1 Hz, 2H), 7.24 *d,
Jˆ8.1 Hz, 2H), 6.70±6.69 *m, 2H), 6.17±6.14 *m, 2H), 5.91
*s, br, 2H), 5.49 *s, 1H), 1.34 *s, 12H); 13C NM Rd 145.1,
135.0, 132.0, 127.7, 117.2, 108.2, 107.1, 83.7, 44.0, 24.8;
Anal calcd for C21H25BN2O2: C, 72.43; H, 7.24; N, 8.04.
Found: C, 72.06; H, 7.34; N, 7.97.
1
12.8%): H NM Rd 10.38 *s, 1H), 8.90 *d, Jˆ4.5 Hz, 2H),
8.86 *d, Jˆ4.5 Hz, 2H), 8.75 *d, Jˆ5.1 Hz, 2H), 8.71 *d,
Jˆ5.1 Hz, 2H), 8.41 *d, Jˆ8.1 Hz, 2H), 8.27 *d, Jˆ8.1 Hz,
2H), 8.08 *s, 4H), 7.80 *s, 2H), 7.28 *s, 2H), 2.63 *s, 3H),
1.87 *s, 6H), 1.52 *s, 36H), 22.65 *s, br, 2H); LD-MS obsd
908.8; FAB-MS obsd 908.5387, calcd 908.5393
*C64H68N4O).
4.3.6. 5,15-Bis13,5-di-tert-butylphenyl)-10-mesityl-20-[4-
14,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-
porphyrin 16b). Following a standard procedure,5 reduction
of 5a *0.697 g, 1.00 mmol) with NaBH4 *1.90 g, 50.0 mmol)
in THF/methanol *80 mL, 3:1) yielded the dipyrromethane-
dicarbinol. The latter was condensed with 3c *0.348 g,
1.00 mmol) in CH3CN *400 mL) containing TFA *0.92
mL, 30 mM) for 5 min followed by oxidation with DDQ

9296
L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
*0.68 g, 3.0 mmol). Filtration through a pad of silica and
chromatography *silica, CH2Cl2) afforded a purple solid
*162 mg, 16%): H NM Rd 8.87±8.84 *m, 4H), 8.80 *d,
6H), 1.83 *s, 12H), 1.50 *s, 24H), 22.65 *s, br, 2H); LD-MS
obsd 949.2; FAB-MS obsd 950.5137, calcd 950.5114
*C62H64B2N4O4).
1
Jˆ4.5 Hz, 2H), 8.69 *d, Jˆ4.5 Hz, 2H), 8.23 *d, Jˆ
7.2 Hz, 2H), 8.18 *d, Jˆ7.2 Hz, 2H), 8.08 *s, 4H), 7.78 *s,
2H), 7.27 *s, 2H), 2.62 *s, 3H), 1.86 *s, 6H), 1.53±1.50 *m,
48H), 22.66 *s, br, 2H); LD-MS obsd 1007.9; FAB-MS
obsd 1007.6398, calcd 1007.6374 *C69H79BN4O2); labs
422, 517, 552, 593, 648 nm; lem *lexˆ520 nm) 651,
720 nm.
4.3.10.
5,15-Bis13,5-di-tert-butylphenyl)-10-iodo-20-
mesitylporphyrin 18). Following a general procedure,19,28
a stirred solution of porphyrin 6c *201 mg, 0.249 mmol)
and I2 *44.5 mg, 0.175 mmol, 0.7 equiv.) in CHCl3 *30
mL) was treated with a solution of [bis*tri¯uoroacetoxy)-
iodo]benzene *86 mg, 0.20 mmol, 0.8 equiv.) in CHCl3
*5 mL) followed by pyridine *10 drops). The mixture was
stirred at room temperature. TLC [silica, CH2Cl2/hexanes
*1:2)] showed iodination was complete after 40 min. The
reaction mixture was diluted with CH2Cl2, washed with
aqueous Na2S2O3 and dried *Na2SO4). Chromatography
[silica, CH2Cl2/hexanes *1:2)] afforded a purple solid
which was washed with methanol *sonicated), ®ltered and
4.3.7. 5,15-Bis13,5-di-tert-butylphenyl)-10-mesitylpor-
phyrin 16c). Following a standard procedure,5 reduction
of 5a *1.04 g, 1.49 mmol) with NaBH4 *2.78 g, 75.0
mmol) in THF/methanol *120 mL, 3:1) yielded the dipyrro-
methane-dicarbinol. The latter was condensed with dipyrro-
methane 3d *219 mg, 1.50 mmol) in CH3CN *600 mL)
containing TFA *1.39 mL, 30 mM) for 5 min followed by
oxidation with DDQ *1.02 g, 4.49 mmol). Standard workup
and chromatography *silica, CH2Cl2) gave a purple solid
1
dried *187 mg, 80%): H NM Rd 9.68 *d, Jˆ4.2 Hz, 2H),
8.90 *d, Jˆ5.1 Hz, 2H), 8.79 *d, Jˆ5.1 Hz, 2H), 8.65 *d,
Jˆ4.2 Hz, 2H), 8.06 *s, 4H), 7.80 *s, 2H), 7.25 *s, 2H), 2.60
*s, 3H), 1.85 *s, 6H), 1.53 *s, 36H), 22.61 *s, br, 2H); LD-
MS obsd 928.2; FAB-MS obsd 931.4209, calcd 931.4176
*C57H63IN4).
1
*280 mg, 23%): H NM Rd 10.20 *s, 1H), 9.33 *d, Jˆ
4.5 Hz, 2H), 9.05 *d, Jˆ4.5 Hz, 2H), 8.91 *d, Jˆ4.5 Hz,
2H), 8.74 *d, Jˆ4.5 Hz, 2H), 8.12 *s, 4H), 7.80 *s, 2H),
7.27 *s, 2H), 2.62 *s, 3H), 1.84 *s, 6H), 1.55 *s, 36H),
22.82 *s, br, 2H); LD-MS obsd 803.9; FAB-MS obsd
804.5177, calcd 804.5131 *C57H64N4).
4.3.11. Trimer 9 1via the condensation/oxidation pro-
cedure). A solution of 6a *36.4 mg, 0.0401 mmol) and
5-mesityldipyrromethane *10.6 mg, 0.0401 mmol) in
CH2Cl2 *4.0 mL) was ¯ushed with argon for 5 min; then
TFA *30.9 mL, 100 mM) was added. The mixture was
stirred for 40 min at room temperature. Analysis of an
oxidized aliquot by LD-MS showed a signi®cant peak at
m/zˆ2305, corresponding to the desired trimer; no starting
porphyrin peak was seen at this point. DDQ *13.6 mg,
0.060 mmol, 1.5 equiv.) was added and the mixture was
stirred for 1 h at room temperature. Triethylamine *56 mL,
100 mM) was added. The mixture was ®ltered through a pad
of alumina and washed with CH2Cl2. Chromatography
[silica, CH2Cl2/hexanes *1:1)] gave a purple solid. The latter
was dissolved in toluene *10 mL), treated with DDQ
*13.6 mg, 0.060 mmol) and the mixture was re¯uxed for
1 h. After cooling to room temperature, the reaction mixture
was ®ltered through a pad of silica *CH2Cl2). Further
puri®cation by chromatography [SEC *THF); silica
4.3.8.
5,15-Bis13,5-di-tert-butylphenyl)-10-14-formyl-
phenyl)-20-{4-[2-1trimethylsilyl)ethynyl]phenyl}porphyrin
16d). Following the general procedure for the preparation of
trans-AB2C-porphyrins,5 a sample of 5b *1.46 g, 1.95
mmol) was reduced in THF/methanol *88 mL, 10:1) with
NaBH4 *1.52 g, 39.0 mmol, 20 equiv.). The resulting dipyr-
romethane-dicarbinol was condensed with dipyrromethane
3e *488 mg, 1.95 mmol) in CH3CN *800 mL) containing
TFA *1.9 mL, 30 mM) for 5 min followed by oxidation
with DDQ *1.36 g, 5.99 mmol). Standard workup and
puri®cation by chromatography *silica, CH2Cl2) afforded
a purple solid *254 mg, 13.6%): 1H NM Rd 10.38 *s,
1H), 8.92±8.90 *m, 4H), 8.82 *d, Jˆ5.1 Hz, 2H), 8.78 *d,
Jˆ5.1 Hz, 2H), 8.41 *d, Jˆ8.1 Hz, 2H), 8.28 *d, Jˆ8.1 Hz,
2H), 8.17 *d, Jˆ8.1 Hz, 2H), 8.07 *m, 4H), 7.87 *d,
Jˆ7.8 Hz, 2H), 7.81 *m, 2H), 1.52 *s, 36H), 0.37 *s,
9H), 22.74 *s, br, 2H); LD-MS obsd 961.7; FAB-MS
obsd 963.5427, calcd 963.5397 *C66H70N4OSi); labs
423, 517, 553, 593, 650 nm; lem *lexˆ520 nm) 653,
720 nm.
1
*CH2Cl2)] afforded a purple solid *16.8 mg, 36.4%): H
NMR d 9.33±9.31 *m, 8H), 9.10 *d, Jˆ4.5 Hz, 4H),
8.97±8.94 *m, 8H), 8.77 *d, Jˆ4.5 Hz, 4H), 8.68 *s, 8H),
8.20 *m, 8H), 7.86 *m, 4H), 7.40 *s, 4H), 7.33 *s, 4H), 2.72
*s, 6H), 2.66 *s, 6H), 2.01 *s, 12H), 1.93 *s, 12H), 1.60 *s,
72H), 22.30 *s, br, 2H), 22.47 *s, br, 4H); LD-MS obsd
2301.4, calcd avg. mass 2305.1; labs *log 1) 419 *5.76), 434
*5.83), 518 *4.80), 554 *4.57), 593 *4.32), 649 nm *4.24);
lem *lexˆ520 nm) 653, 720 nm *Ffˆ0.13).
4.3.9. 5,15-Dimesityl-10,20-bis[4-14,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)phenyl]porphyrin 17). Following
an early procedure27 now known to give a small amount
of scrambling,16 a solution of 5-mesityldipyrromethane
*1.05 g, 3.98 mmol) and aldehyde 2 *952 mg, 4.01 mmol)
in CHCl3 *500 mL) was treated with BF3´O*Et)2 *210 mL,
3.3 mM) for 30 min at room temperature under argon.
DDQ *1.36 g, 5.99 mmol) was added and the mixture was
stirred for 1 h at room temperature. Triethylamine *230 mL,
3.3 mM) was added and the mixture was ®ltered through
a pad of silica and washed with CHCl3. Removal of
solvent and chromatography *silica, CH2Cl2) afforded a
purple solid *516 mg, 27%): 1H NM Rd 8.78 *d,
Jˆ4.5 Hz, 4H), 8.67 *d, Jˆ4.5 Hz, 4H), 8.24 *d, Jˆ
8.1 Hz, 4H), 8.18 *d, Jˆ8.1 Hz, 4H), 7.28 *s, 4H), 2.63 *s,
4.3.12. Trimer 10. Following the general procedure
described for the preparation of 9, a solution of 6d
*250.4 mg, 0.260 mmol) and 5-mesityldipyrromethane
*68.7 mg, 0.260 mmol) in CH2Cl2 *26 mL) was ¯ushed
with argon for 5 min. TFA *201 mL, 100 mM) was added
and the mixture was stirred for 40 min at room temperature.
Analysis of an oxidized aliquot by LD-MS showed a signi®-
cant peak at m/zˆ2412, corresponding to the desired trimer;
no starting porphyrin peak was seen at this point. DDQ
*88.4 mg, 0.389 mmol, 1.5 equiv.) was added and

L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
9297
the mixture was stirred for 1 h at room temperature.
Triethylamine *362 mL, 100 mM) was added. After stirring
for 5 min, the mixture was ®ltered through a pad of alumina
and washed with CH2Cl2. Chromatography *silica, CH2Cl2)
gave a purple solid. The purple solid was dissolved in
toluene *50 mL). DDQ *88.4 mg, 0.389 mmol) was added
and the mixture was re¯uxed for 1 h, then the mixture was
cooled to room temperature and ®ltered through a pad of
silica *CHCl3). Further chromatography [SEC *THF); silica
12, samples of 8 *55.9 mg, 0.0600 mmol), 7 *28.5 mg,
0.0300 mmol), K2CO3 *66.2 mg, 0.480 mmol) and Pd*PPh3)4
*10.4 mg, 9.0 mmol) were weighed into a 10 mL Schlenk
¯ask. The ¯ask was pump-purged with argon three times.
Toluene/DMF *3.0 mL, 2:1) was added and the mixture was
stirred at 90±958C. Analytical SEC indicated incomplete
consumption of the starting porphyrins after 6 h, therefore
an additional amount of Pd*PPh3)4 *10.4 mg, 9.0 mmol)
was added and the reaction mixture was stirred for 18 h at
90±958C *total reaction timeˆ24 h). Analytical SEC
showed complete consumption of the starting materials at
this point. The solvent was removed and the residue was
chromatographed [silica, CHCl3/hexanes *2:1)], affording
four major bands *in order of elution): the desired
trimer *®rst purple band, tRˆ10.41 min); byproduct
dimer *second purple band, tRˆ10.77 min); byproduct
dimer *third purple band, tRˆ10.84 min) and monomeric
porphyrin species *fourth purple band, tRˆ11.28 min).
The trimer fraction was further puri®ed by chromatography
[preparative SEC *toluene); silica *CHCl3/hexanes, 2:1)]
affording a purple solid *45.6 mg, 66%). The analytical
data *1H NMR, LD-MS, UV±Vis, ¯uorescence) were
identical with those obtained from the porphyrin-benzalde-
hyde1dipyrromethane condensation route.
1
*CH2Cl2)] afforded a purple solid *101.4 mg, 32.3%): H
NMR d 9.32±9.30 *m, 8H), 9.09 *d, Jˆ4.5 Hz, 4H),
8.98±8.94 *m, 8H) 8.86 *d, Jˆ5.1 Hz, 4H), 8.69±8.63 *m,
8H), 8.22 *d, Jˆ8.1 Hz, 4H), 8.18±8.17 *m, 8H) 7.90 *d,
Jˆ7.2 Hz, 4H), 7.86 *s, br, 4H), 7.39 *s, 4H), 2.71 *s, 6H),
2.00 *s, 12H), 1.58 *s, 72H), 0.29 *s, 18H), 22.32 *s, br, 2H),
22.58 *s, br, 4H); LD-MS obsd 2408.0, calcd avg. mass
2413.4; labs *log 1) 420 *5.58), 435 *5.68), 519 *4.37),
555 *4.18), 594 *3.86), 650 nm *3.80); lem *lexˆ520 nm)
654, 721 nm *Ffˆ0.15).
4.3.13. Trimer 11. A solution of trimer 10 *97 mg,
0.040 mmol) in CHCl3/THF *16 mL, 1:1) was treated with
tetrabutylammonium ¯uoride *TBAF) *88 mL, 0.088 mmol,
2.2 equiv., 1.0 Min THF) for 20 min at room temperature.
Standard workup and chromatography [silica, CHCl3/
1
hexanes *2:1)] afforded a purple solid *82 mg, 90%): H
The dimer fraction *the second purple band) was further
puri®ed by preparative SEC *THF); however, TLC analysis
showed two spots after the preparative SEC column
chromatography. Silica chromatography [CHCl3/hexanes
*2:1)] afforded two purple bands *in order of elution):
dimer 13 *3.8 mg, 8.0%); dimer 14 *3.2 mg, 6.5%). The
dimer fraction *the third purple band) was further puri®ed
by chromatography [preparative SEC *THF); silica *CHCl3/
hexanes, 2:1)] to afford a purple solid: dimer 15 *2.8 mg,
6.1%).
NMR d 9.33±9.30 *m, 8H), 9.10 *d, Jˆ4.5 Hz, 4H), 8.98
*d, Jˆ4.2 Hz, 4H), 8.95 *d, Jˆ4.5 Hz, 4H), 8.87 *d, Jˆ
4.2 Hz, 4H), 8.66 *s, 8H), 8.24 *d, Jˆ8.1 Hz, 4H), 8.18
*m, 8H), 7.92 *d, Jˆ8.1 Hz, 4H), 7.86 *s, 4H), 7.39 *s,
4H), 3.33 *s, 2H), 2.71 *s, 6H), 2.00 *s, 12H), 1.58 *s,
72H), 22.32 *s, br, 2H), 22.57 *s, br, 4H); LD-MS obsd
2264.3, calcd avg. mass 2269.0 *C162H154N12); labs 419,
434, 518, 554, 593, 649 nm; lem *lexˆ520 nm) 654,
721 nm.
1
4.3.16. Dimer 13. H NM Rd 9.28±9.26 *m, 4H), 9.06 *d,
4.3.14. Dimer 12 1via Suzuki coupling). Samples of 6b
*27.9 mg, 0.0300 mmol),
*30.2 mg, 0.0300 mmol),
8
Jˆ4.5 Hz, 2H), 8.94±8.88 *m, 6H), 8.78±8.74 *m, 4H) 8.62
*s, 4H), 8.34 *d, Jˆ8.1 Hz, 2H), 8.01 *d, Jˆ8.1 Hz, 2H),
7.95 *d, Jˆ7.2 Hz, 2H), 7.84 *m, 2H), 7.62 *t, Jˆ7.2 Hz,
2H), 7.49 *t, Jˆ7.2 Hz, 1H), 7.34 *s, 4H), 7.30 *s, 2H), 2.67
*s, 6H), 2.64 *s, 3H), 1.92±1.91 *m, 18H) 1.57 *s, 36H),
22.45 *s, br, 2H), 22.50 *s, br, 2H); LD-MS obsd 1577.4,
calcd avg. mass 1578.1 *C113H108N8).
anhydrous K2CO3 *8.3 mg, 0.060 mmol) and Pd*PPh3)4
*5.2 mg, 4.5 mmol, 15 mol%) were weighed into a 10 mL
Schlenk ¯ask. The ¯ask was pump-purged with argon three
times. Toluene/DMF *3.0 mL, 2:1) was added and the
mixture was heated to 758C under argon. Analytical SEC
showed only 6% of product formation after 3 h. Additional
amounts of K2CO3 *49.8 mg, 0.36 mmol) and Pd*PPh3)4
*5.2 mg, 4.5 mmol) were added and the mixture was stirred
for 15 h at 908C. Analytical SEC indicated that most of the
starting porphyrins were consumed. Chromatography
[silica, CHCl3/hexanes *3:2)] removed most of the
unreacted porphyrin monomeric species. Preparative SEC
*THF) removed the trace amount of remaining monomeric
porphyrins. A ®nal silica gel column [CHCl3/hexanes *2:1)]
1
4.3.17. Dimer 14. H NM Rd 9.28±9.25 *m, 4H), 9.06
*d, Jˆ4.2 Hz, 2H), 8.92 *d, Jˆ4.5 Hz, 2H), 8.88 *d,
Jˆ5.1 Hz, 2H), 8.83 *d, Jˆ5.1 Hz, 2H), 8.75±8.73 *m,
4H), 8.62 *s, 4H), 8.28 *d, Jˆ8.1 Hz, 2H), 8.20 *d,
Jˆ8.1 Hz, 2H), 8.17 *m, 4H), 7.83 *m, 2H), 7.33 *s, 4H),
7.30 *s, 2H), 2.67 *s, 6H), 2.64 *s, 3H), 1.91 *s, 18H), 1.57 *s,
36H), 1.51 *s, 12H), 22.48 *s, br, 2H), 22.50 *s, br, 2H);
LD-MS obsd 1625.9, calcd avg. mass 1628.0
*C113H115N8BO2).
1
afforded a purple solid *35.5 mg, 70.2%): H NM Rd 9.30
*d, Jˆ4.2 Hz, 4H), 9.07 *d, Jˆ5.4 Hz, 4H), 8.92 *d, Jˆ
5.4 Hz, 4H), 8.75 *d, Jˆ4.2 Hz, 4H), 8.62 *s, 4H), 8.18
*m, 8H), 7.84 *m, 4H), 7.31 *s, 4H), 2.64 *s, 6H), 1.91 *s,
12H), 1.57 *s, 72H), 22.50 *s, br, 4H); LD-MS obsd 1683.0,
calcd avg. mass 1684.0 *C120H130N8); labs *log 1) 422*5.67),
430 *5.72), 518 *4.55), 553 *4.28), 594 *4.02), 649 nm
*3.96); lem *lexˆ 520 nm) 652, 720 nm *Ffˆ0.10).
1
4.3.18. Dimer 15. H NM Rd 9.28±9.24 *m, 4H), 9.06 *d,
Jˆ4.2 Hz, 2H), 8.92 *d, Jˆ4.5 Hz, 2H), 8.88±8.86 *m, 4H),
8.74 *d, Jˆ5.1 Hz, 4H), 8.62 *s, 4H), 8.17 *m, 2H), 8.12 *d,
Jˆ8.7 Hz, 2H), 7.84 *m, 2H), 7.33 *s, 4H), 7.30 *s, 2H),
7.23±7.16 *m, 4H) 2.67 *s, 6H), 2.64 *s, 3H), 1.91 *s,
18H), 1.57 *s, 36H), 22.47 *s, br, 2H), 22.50 *s, br, 2H);
LD-MS obsd 1517.9, calcd avg. mass 1518.0
*C107H104N8O).
4.3.15. Trimer 9 1via Suzuki coupling). Following the
general procedure described for the preparation of dimer

9298
L. Yu, J. S. Lindsey / Tetrahedron 57 02001) 9285±9298
18. *a) Zhou, X.; Zhou, Z.-Y.; Mak, T. C. W.; Chan, K. S. J. Chem.
Acknowledgements
Soc., Perkin Trans. 1 1994, 2519±2520. *b) Chan, K. S.; Zhou,
X.; Luo, B.-S.; Mak, T. C. W. J. Chem. Soc., Chem. Commun.
1994, 271±272. *c) Zhou, X.; Tse, M. K.; Wan, T. S. M.;
Chan, K. S. J. Org. Chem. 1996, 61, 3590±3593. *d) Yoshida,
N.; Shimidzu, H.; Osuka, A. Chem. Lett. 1998, 55±56.
*e) Kimura, M.; Shiba, T.; Muto, T.; Hanabusa, K.; Shirai,
H. Macromolecules 1999, 32, 8237±8239. *f) Muzzi, C. M.;
Medforth, C. J.; Voss, L.; Cancilla, M.; Lebrilla, C.; Ma, J.-G.;
Shelnutt, J. A.; Smith, K. M. Tetrahedron Lett. 1999, 6159±
6162. *g) Tse, M. K.; Zhou, Z.-Y.; Mak, T. C. W.; Chan, K. S.
Tetrahedron 2000, 56, 7779±7783.
This research was supported by the Division of Chemical
Sciences, Of®ce of Basic Energy Sciences, Of®ce of Energy
Research, US Department of Energy. Mass spectra were
obtained at the Mass Spectrometry Laboratory for Biotech-
nology at North Carolina State University. Partial funding
for the Facility was obtained from the North Carolina
Biotechnology Center and the NSF. We acknowledge
those individuals in our lab *Dr Toru Arai, Dr Polisetti
Dharma Rao, Professor Chang-Hee Lee, Mr Christopher
Wack) who performed early exploratory work on syntheses,
primarily statistical in nature, of p-phenylene-linked arrays.
19. Shultz, D. A.; Gwaltney, K. P.; Lee, H. J. Org. Chem. 1998,
63, 769±774.
20. Hyslop, A. G.; Kellett, M. A.; Iovine, P. M.; Therien, M. J.
J. Am. Chem. Soc. 1998, 120, 12676±12677.
References
21. Zhou, X.; Chan, K. S. J. Org. Chem. 1998, 63, 99±104.
22. Zhou, X.; Chan, K. S. J. Chem. Soc., Chem. Commun. 1994,
2493±2494.
1. Holten, D.; Bocian, D. F.; Lindsey, J. S. Acc. Chem. Res., in
press.
2. Yang, S. I.; Lammi, R. K.; Seth, J.; Riggs, J. A.; Arai, T.; Kim,
D.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Phys. Chem.
1998, 102, 9426±9436.
23. Deng, Y.; Chang, C. K.; Nocera, D. G. Angew. Chem., Int. Ed.
Engl. 2000, 39, 1066±1068.
24. Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.;
O'Shea, D. F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem.
1999, 64, 1391±1396.
3. 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.
25. Cho, W.-S.; Kim, H.-J.; Littler, B. J.; Miller, M. A.; Lee,
C.-H.; Lindsey, J. S. J. Org. Chem. 1999, 64, 7890±7901.
26. *a) Nicolas, M.; Fabre, B.; Marchand, G.; Simonet, J. Eur. J.
Org. Chem. 2000, 1703±1710. *b) Ishiyama, T.; Itoh, Y.;
Kitano, T.; Miyaura, N. Tetrahedron Lett. 1997, 38, 3447±
3450.
4. Youngblood, W. J.; Gryko, D. T.; Lammi, R. K.; Bocian, D.
F.; Holten, D.; Lindsey, J. S. Manuscript in preparation.
5. Rao, P. D.; Dhanalekshmi, S.; Littler, B. J.; Lindsey, J. S.
J. Org. Chem. 2000, 65, 7323±7344.
6. *a) McDermott, G.; Prince, S. M.; Freer, A. A.;
Hawthornthwaite-Lawless, A. M.; Papiz, M. Z.; Cogdell,
R. J.; Isaacs, N. W. Nature 1995, 374, 517±521. *b) Pullerits,
27. Ravikanth, M.; Strachan, J.-P.; Li, F.; Lindsey, J. S.
Tetrahedron 1998, 54, 7721±7734.
28. Shanmugathasan, S.; Johnson, C. K.; Edwards, C.; Matthews,
E. K.; Dolphin, D.; Boyle, R. W. J. Porphyrin Phthalo-
cyanines 2000, 4, 228±232.
È
T.; Sundstrom, V. Acc. Chem. Res. 1996, 29, 381±389.
7. Strachan, J. P.; Gentemann, S.; Seth, J.; Kalsbeck, W. A.;
Lindsey, J. S.; Holten, D.; Bocian, D. F. J. Am. Chem. Soc.
1997, 119, 11191±11201.
29. *a) Barnett, G. H.; Hudson, M. F.; Smith, K. M. Tetrahedron
Lett. 1973, 2887±2888. *b) Rousseau, K.; Dolphin, D.
Tetrahedron Lett. 1974, 4251±4254. *c) Barnett, G. H.;
Hudson, M. F.; Smith, K. M. J. Chem. Soc., Perkin Trans. 1
1975, 1401±1403.
8. Cho, H. S.; Jeong, D. H.; Yoon, M.-C.; Kim, Y. H.; Kim,
Y.-R.; Kim, D.; Jeoung, S. C.; Kim, S. K.; Aratani, N.;
Shinmori, H.; Osuka, A. J. Phys. Chem. A 2001, 105, 4200±
4210.
30. *a) Wagner, R. W.; Johnson, T. E.; Li, F.; Lindsey, J. S. J. Org.
Chem. 1995, 60, 5266±5273. *b) Wagner, R. W.; Ciringh, Y.;
Clausen, P. C.; Lindsey, J. S. Chem. Mater. 1999, 11, 2974±
2983.
9. Hammel, D.; Erk, P.; Schuler, B.; Heinze, J.; MuÈllen, K. Adv.
Mater. 1992, 4, 737±739.
10. Sessler, J. L.; Capuano, V. L. Angew. Chem., Int. Ed. Engl.
1990, 29, 1134±1137.
31. Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122,
4020±4028.
11. Sessler, J. L.; Capuano, V. L.; Harriman, A. J. Am. Chem. Soc.
1993, 115, 4618±4628.
32. Wagner, R. W.; Johnson, T. E.; Lindsey, J. S. J. Am. Chem.
Soc. 1996, 118, 11166±11180.
12. Nagata, T.; Osuka, A.; Maruyama, K. J. Am. Chem. Soc. 1990,
112, 3054±3059.
33. *a) Srinivasan, N.; Haney, C. A.; Lindsey, J. S.; Zhang, W.;
Chait, B. T. J. Porphyrins Phthalocyanines 1999, 3, 283±291.
*b) Fenyo, D.; Chait, B. T.; Johnson, T. E.; Lindsey, J. S.
J. Porphyrins Phthalocyanines 1997, 1, 93±99.
34. Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31,
1±13.
13. Osuka, A.; Liu, B.-L.; Maruyama, K. Chem. Lett. 1993, 949±
952.
14. Osuka, A.; Tanabe, N.; Zhang, R.-P.; Maruyama, K. Chem.
Lett. 1993, 1505±1508.
15. Osuka, A.; Tanabe, N.; Nakajima, S.; Maruyama, K. J. Chem.
Soc., Perkin Trans. 2 1996, 199±203.
35. Li, J.; Ambroise, A.; Yang, S. I.; Diers, J. R.; Seth, J.; Wack,
C. R.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Am. Chem.
Soc. 1999, 121, 8927±8940.
16. Littler, B. J.; Ciringh, Y.; Lindsey, J. S. J. Org. Chem. 1999,
64, 2864±2872.
17. Geier, III, G. R.; Littler, B. J.; Lindsey, J. S. J. Chem. Soc.,
Perkin Trans. 2 2001, 701±711.