Tetraaryltetraanthra[2,3]porphyrins: Synthesis, structure, and optical properties

Article abstract of DOI:10.1021/jo302135q

A synthetic route to symmetrical tetraaryltetraanthra[2,3]porphyrins (Ar₄TAPs) was developed. Ar₄TAPs bearing various substituents in meso-phenyls and anthracene residues were prepared from the corresponding pyrrolic precursors. The synthesized porphyrins possess high solubility and exhibit remarkably strong absorption bands in the near-infrared region (790-950 nm). The scope of the method, selection of the peripheral substituents, choice of the metal, and their influence on the optical properties are discussed together with the first X-ray crystallographic data for anthraporphyrin.

Full text of DOI:10.1021/jo302135q

Article
pubs.acs.org/joc
Tetraaryltetraanthra[2,3]porphyrins: Synthesis, Structure, and
Optical Properties
Mikhail A. Filatov,*,† Stanislav Baluschev,†,‡ Iliyana Z. Ilieva,‡ Volker Enkelmann,† Tzenka Miteva,§
Katharina Landfester,† Sergey E. Aleshchenkov,∥ and Andrei V. Cheprakov*,∥
†Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
‡Optics and Spectroscopy Department, Faculty of Physics, Sofia University “St. Kliment Ochridski”, 5 James Bourchier, 1164 Sofia,
Bulgaria
§Materials Science Laboratory, Sony Deutschland GmbH, Hedelfingerstrasse 61, 70327 Stuttgart, Germany
∥Department of Chemistry, Moscow State University, Moscow 119899, Russia
S
* Supporting Information
ABSTRACT: A synthetic route to symmetrical tetraaryltetra-
anthra[2,3]porphyrins (Ar4TAPs) was developed. Ar4TAPs bearing
various substituents in meso-phenyls and anthracene residues were
prepared from the corresponding pyrrolic precursors. The
synthesized porphyrins possess high solubility and exhibit
remarkably strong absorption bands in the near-infrared region
(790−950 nm). The scope of the method, selection of the
peripheral substituents, choice of the metal, and their influence on
the optical properties are discussed together with the first X-ray
crystallographic data for anthraporphyrin.
a useful level of emissivity upon distortion of the system.14
Moreover, the distortion at the same time dramatically
improves the solubility and processability of such porphyrins,
making such huge polyaromatic compounds conveniently
INTRODUCTION
■
The fusion of aromatic rings to porphyrin cores received much
attention because such modification was expected to have a
strong influence on electronic properties of core motifs,
handled and modified in contrast to practically insoluble planar
particularly reducing HOMO−LUMO gap and shifting the
annelated porphyrins. Symmetric tetraaryl derivatives are
absorption and emission into near-IR. Because of these
additionally the easiest for synthesis. Such a unique
properties, such porphyrins are attractive for numerous
applications, such as NIR photodetectors,1 photovoltaics,2
combination of useful properties makes tetraaryl derivatives
semiconductors,3 and two-photon absorbing materials.4
A
of linearly annelated extended porphyrins and their metal
complexes promising models for materials research,15 research
on biomedical imaging and sensing,16 triplet−triplet annihila-
tion photon upconversion,17 and photodynamic and boron
neutron-capture therapy.18 Recently, a far less well-studied
representative of this class, tetraanthra[2,3]porphyrins (TAP,
Figure 1), was also shown to possess valuable optical properties
with respect to upconversion of noncoherent NIR light (800
nm) into visible light (550 nm)19 and fabrication of organic
light emitting diodes.20
variety of π-extended porphyrins have been synthesized by
fusing benzene,5 naphthalene,6 pyrene,7 azulene,8 anthracene,9
corannulene,10 and other aromatic moieties across the meso-
and β-positions of porphyrins. Among the π-extended
porphyrins, the linear fusion of aromatic rings results in
particularly strong red-shift and intensification of Q-band.11 So
far, the best known and most useful representatives of this class
are tetrabenzoporphyrins (TBPs, Figure 1) and tetranaphtho-
[2,3]porphyrins (TNPs).12 The effect is manifested only when
all four aromatic residues, which can be different (e.g., mixed
benzo-naphthoporphyrins reported by Niedermair and co-
workers13), are linearly annelated to β-positions of porphyrin
macrocycle (discussion of annelation modes12a). Moreover,
linearly annelated extended porphyrins exhibit another
important and very interesting trend revealed in their tetra-
meso-aryl derivatives: the steric repulsion of aryl rings and
annelated residues results in a strong distortion of the system.
In the domain of regular porphyrins, the distortion inevitably
leads to dramatic deterioration of emissive properties. Linearly
annelated extended porphyrins, however, were shown to retain
Comparison of absorption spectra of TBP, TNP, and TAP
(Figure 2) demonstrates the trend of changing the optical
properties in this series. Annelation of each extra layer of
benzo-rings to the porphyrin core has a strong and cumulative
effect on the energies of S1 state of the molecule, similar to
what is observed for linear polybenzenoid hydrocarbons
(acenes).21 It is seen from the pronounced red shift of the
Q-bands by about 100 nm for each additional ring. On the
Received: October 15, 2012
Published: December 3, 2012
© 2012 American Chemical Society
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Figure 1. Linearly annelated π-extended porphyrins.
are crucial if such photonic application as photon up-
conversion is targeted.23
Despite promising properties, tetraanthraporphyrins have
until this time been little studied. As was theoretically predicted,
π-extension results in the case of TAPs in the destabilization of
the third LUMOs and the first HOMOs that makes it unstable
against oxidation and reduction.24 The first representative of
the TAP family was prepared by Kobayashi and co-workers,25
using the Luk’yanets−Kopranenkov high-temperature template
condensation method,26 which resembles the classical proce-
dures of phthalocyanine chemistry. Melting of anthracene-2,3-
dicarboxyimide with sodium biphenylacetate in the presence of
zinc acetate (Scheme 1, route A) resulted in the formation of
zinc complex of triarylsubstituted TAP (aryl = p-phenylphenyl).
The synthesis of both meso-unsubstituted and meso-aryl-
substituted TAPs was very recently reported by Ono and co-
workers using a common approach to extended porphyrins
relying on thermal retro-Diels−Alder extrusion of ethylene
from bicyclo[2.2.2]octadiene-annelated porphyrins (Scheme 1,
route B).27 Thus obtained materials were reported to be poorly
soluble and unstable toward photooxidation.
Figure 2. UV−vis absorption spectra of free base Ar4TBP (black),
Ar4TNP (red), and Ar4TAP (blue). Ar = 4-MeO2C−C6H4.
An obvious drawback of reported syntheses of TAPs is a
need for harsh conditions of condensation or aromatization
steps, which are poorly compatible with the emerging huge and
fragile TAP system. This results in low yields and poor quality
of the obtained materials and limits opportunities of
introducing functionality to improve solubility and stability or
to modulate optical properties.
As an advanced method delivering tetraanthraporphyrins, the
dihydroisoindole method based on an oxidative aromatization
of the closest partially hydrogenated porphyrin precursor can
be applied. It warrants that the conditions of aromatization of
the annelated system are as soft as possible and occur
spontaneously along with the aromatization of the porphyri-
nogen intermediates. The method was earlier optimized for the
other hand, the effect on S2 state energies is much less
pronounced: the Soret band is shifted only by 20−30 nm. As a
result, a “spectral window” between Soret and Q-bands
increases from TBP through TNP to TAP, despite bandwidth
broadening due to increased molecular size. Moreover, the
relative intensity of the Q-band also increases and in the case of
TAPs becomes as strong as the Soret band (extinction
coefficients ∼105 cm mol L−1). These spectral features make
TAP a unique representative of π-extended porphyrins.
Although some of the reported molecular systems, designed
by annelation or fusion of aromatic fragments to the porphyrin
core, reach absorptions at as far as 1500 nm,22 none of them
exhibit narrow and symmetrical bands along with a broad
“spectral window” in the visible region. These characteristics
Scheme 1. Reported Approaches toward the Synthesis of TAP
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Scheme 2. Retrosynthetical Analysis of TAP Precursors
synthesis of various derivatives of tetrabenzo- and tetranaph-
thoporphyrin.28 A key feature of the approach is the use of a
common line of synthons, dihydroisoindole derivatives, which
(i) can be prepared from readily available starting materials by
well-established methods, (ii) upon condensation with
aldehydes form porphyrins that are then easily oxidized by
DDQ or chloranil to corresponding annelated porphyrins using
the same Lindsey’ protocol as broadly applied to regular
porphyrins,29 only with an extra amount of aromatizing agent
added. However, in the application of this methodology to the
TAP system notorious for its high sensitivity toward oxidation,
severe if not fatal complications could have been expected. To
our delight, however, we have succeeded in preparing TAP
derivatives from the corresponding naphtho-annelated dihy-
droisoindole precursor,19,30 which was then successfully
reproduced by Schanze et al.31 Herein, we report a detailed
account of this methodology, describing the synthesis of
Ar4TAP with both substituted and unsubstituted anthracene
subsystem. In addition, we present basic optical properties of
new TAPs and report the first X-ray crystallographic structure
of a free base of tetraanthraporphyrin.
can be accessed from 1,4-dihydroanthracenes by analogy with
previously developed syntheses of dihydroisoindole and
dihydrobenzoisoindoles. In the case of TAPs with unsubstituted
anthracene rings, the corresponding precursor is 1,4-dihydroan-
thracene (Scheme 2, route A), which is readily accessible by the
reported procedures.33 For the synthesis of TAPs with
substituted anthracene rings, two pathways can be regarded.
The precursors of the corresponding dihydronaphthoisoindoles
bearing substituents in the outermost rings can be obtained
through a sequential construction of polycyclic system using
Diels−Alder reactions starting from the readily available adduct
of benzyne and furan (Scheme 2, route B). The precursors
bearing substituents in the inner ring of anthracene system are
accessible from Diels−Alder adducts of 1,4-naphthoquinone
(Scheme 2, route C). Both routes present broad opportunities
for varying substituents and utilizing conventional well-
established procedures, capable of upscaling.
The synthesis of TAPs 5a−d bearing no substituents on the
anthracene rings is shown in Scheme 3.
The synthesis started from 1,4-dihydroanthracene 1, which
was prepared by a three-step procedure described by Dehaen et
al.33 Compound 1 was then transformed into allylic sulfone 2
using the procedure reported in the synthesis of TBP and TNP
derivatives.28 The latter was subjected to the Barton−Zard
reaction with ethyl isocyanacetate, delivering naphthoisoindo-
lecarboxylate 3. Obtained naphthoisoindolecarboxylate 3 was
cleanly transformed into 4,11-dihydro-2H-naphtho-[2,3-f ]-
isoindole 4, which was introduced into Lindsey’s porphyrin
synthesis.34 MALDI spectra of the samples of the reaction
mixtures obtained after quenching with DDQ showed
appreciable amounts of partially dehydrogenated intermediate
porphyrins, with one, two, or three anthracene residues.
Without separation of the individual components, the mixture
was further treated with additional portion of DDQ at room
temperature for 30 min to achieve complete aromatization of
the fused rings. After chromatographic purification, the target
TAPs 5a−c were obtained in good yields.
This scheme was applied also for the synthesis of TAPs
bearing alkoxy-substituents in the outermost rings (Scheme 4).
The corresponding benzyne dienophile was generated from
4,5-dibromo-1,2-di-n-butoxybenzene 8, which was obtained by
bromination of o-dibutoxybenzene 7, produced by alkylation of
catechol. The adduct of Diels−Alder reaction between
dibutoxybenzyne and furan 9 was further introduced into
second Diels−Alder reaction with butadiene. Because of the
RESULTS AND DISCUSSION
■
Synthesis. The known attempts to synthesize TAPs, as well
as our first experiments, made us to suspect that such a huge
extension of porphyrin system would render the materials
extremely prone to aggregation via strong π−π stacking
interactions between molecules, to result in a miserable
solubility and difficulties in isolation, purification, and
characterization. Therefore, we initially planned, besides
attempting the synthesis of the core TAP system, to introduce
solubilizing bulky substituents not only at the meso-phenyls, but
also into the annelated anthracene residues, similar to what was
earlier done with tetrabenzo- and tetranaphthoporphyrins.6e
Introduction of substituents to anthracene rings may also
provide the means for additional shifting of the absorption and
the emission bands further into NIR. Medium-size alkoxy
groups (e.g., n-butyloxy) are an obvious first choice for such
modification, as the introduction of a pair of such into each
anthracene residue would be expected to render adequate
solubility in common organic solvents, besides offering red-
shifting auxochromic effect due to strong electron donation.
The oxidative aromatization approach regards the corre-
sponding dihydronaphthoisoindoles as the most suitable
synthons for the synthesis of TAP.32 These pyrrolic precursors
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a
Surprisingly, the exact procedure for laboratory-scale synthesis
of 18 has not been so far published in the literature, although
the adduct 18 is mentioned in the original paper by Diels and
Alder but without any experimental details.35 In this case, 3-
sulfolene as 1,3-butadiene synthetic equivalent cannot be used,
because the liberated SO2 can be expected to reduce the
quinone moiety. In our work, we succeeded to prepare the
adduct 18 by two different methods: (i) long (45 days)
exposure of naphthoquinone in neat liquid butadiene taken in
huge excess at room temperature in a thick-wall glass tube and
(ii) fast catalyzed cycloaddition36 at low temperature in the
presence of 1 equiv of Lewis acid (SnCl4). The first method
was found to provide high yields, although it took a very long
reaction time. The second method allows for almost immediate
reaction, but the yield of target product is substantially lower
probably due to competitive cationic polymerization of
butadiene. Adduct 18 upon treatment with bases irreversibly
forms deprotonated hydroquinone, which was used for
alkylation reaction without isolation to give diether 19. The
attempt to perform the acid-catalyzed rearrangement of
diketone 18 into the respective enol form (hydroquinone)
was abandoned because of extensive formation of dark
byproducts. The substituted 1,4-dihydroanthracene 19 was
next used in a series of transformations analogous to those
shown in Schemes 3 and 4 to obtain corresponding
dihydronaphthoisoindole 23, which was then used for the
preparation of anthraporphyrin 24. The latter was obtained in
lower yield as compared to porphyrins 5a−d, which is probably
due to the steric hindrance effect on the macrocyclization
process.
Scheme 3. Synthesis of Anthra-Unsubstituted Porphyrins 5
The products 5a−d, 16, and 24 were additionally purified by
recrystallization and characterized by NMR and mass spectros-
copy (see the Supporting Information). To our utmost surprise,
instead of the envisaged problems with aggregation and poor
solubility of these huge compounds supposedly prone to π-
stacking, we observed rather good solubility (as compared to
previously studied tetranaphtho[2,3]porphyrins) of obtained
products in common organic solvents (chlorohydrocarbons,
aromatics, THF) even in the case of porphyrins 5a−d having
no solubilizing substituents on the anthracene rings. The
observed solubility was comparable or even higher than that of
the corresponding TBP and TNP ancestors. Moreover, unlike
in the case of TBP and TNP, 1H NMR spectra of 5a−d can be
obtained for their free base forms without the need of running
the spectra at elevated temperatures, adding coordinating
solvents or conversion into protonated forms or metal
complexes. Free base forms of nonplanar tetraaryl derivatives
of extended porphyrins are known to exhibit complex fluxional
behavior due to simultaneous occurrence of several dynamic
processes such as tautomerization and macrocycle inversion,37
additionally complicated by aggregation. In the case of tetraaryl
TBP and TNP, this fluxionality causes a severe broadening of
NMR spectra, particularly in the region of resonances of
annelated rings, the signals of which are usually not resolved.
Therefore, the spectra were registered for diprotonated forms
of higher symmetry and lesser tendency toward aggregation. In
the case of TAP, the spectra of free base forms are quite
adequately resolved, although the broadening and coalescence
of some lines are still observed, and the spectra are improved
upon protonation (Figure 3, porphyrin 5b). Running spectra
for diprotonated forms is a common trick used to improve the
resolution of the spectra of tetraannelated porphyrins. Usually it
is performed by just adding a drop of TFA to samples.
a
Reagents and conditions: (a) (i) PhSCl, CH2Cl2, rt, 1 h; (ii) oxone,
MeOH−H2O (2:1), rt, 7 days (78%); (b) DBU, CH2Cl2, rt, 1 h
(90%); (c) CNCH2CO2Et, tBuOK, THF (80−90%), rt, 4 h; (d)
KOH, (CH2OH)2, reflux, 30 min (70−85%); (e) (i) Y2XC6H4CHO,
BF3·Et2O, CH2Cl2, rt, 2 h; (ii) DDQ, rt, 30−60 min (15−40%).
rather low reactivity of this dienophile, the cycloaddition
requires prolonged heating above 100 °C, which is a rather
dangerous procedure requiring special equipment for work
under elevated pressure, if neat butadiene is used. Therefore,
we used butadiene generated in situ by thermal sulfur dioxide
extrusion from 3-sulfolene, in which case no buildup of
butadiene pressure could be expected as the liberated diene is
consumed in the cycloaddition, and therefore the equilibrium
of the reversible extrusion reaction acts as an internal “safety
valve”. The reaction was performed in the presence of
NaHCO3 in pyridine, used as a scavenger of liberated SO2 to
prevent uncontrolled increase of pressure. It allowed us to use a
high-pressure thick-wall glass tube instead of an autoclave even
for syntheses on a tens-of-grams scale. The obtained adduct 10
is smoothly transformed into 1,4-dihydroanthracene 11 by mild
acid-catalyzed dehydration. Further transformation (steps f, g,
h, and i in the Scheme 4) of the synthesis leading to
corresponding pyrrole 15 follows the previously established
approach. Lindsey’s condensation followed by subsequent
additional treatment with DDQ successfully delivered the
corresponding porphyrin 16.
The synthesis of porphyrins 24, bearing butoxy-groups in the
middle ring (Scheme 5), was performed according to route C
shown in Scheme 2. The preparation of corresponding butoxy-
substituted 1,4-dihydroanthracenes makes use of the Diels−
Alder adduct of 1,4-naphthoquinone 17 with butadiene.
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a
Scheme 4. Synthesis of Octabutoxyporphyrin 16
a
Reagent and conditions: (a) n-BuI, K2CO3, acetone, reflux, 2 days (92%); (b) Br2, CH2Cl2, rt, 3 h (90%); (c) furan, n-BuLi, THF, −50 °C, 1 h
(91%); (d) sulfolene, NaHCO3, Py, 120 °C (58%); (e) HCl, EtOH, reflux, 24 h (61%); (f) (i) PhSCl, CH2Cl2, rt, 1 h; (ii) oxone, MeOH−H2O
(2:1), rt, 7 days (78%); (g) DBU, CH2Cl2, rt, 1 h (90%); (h) CNCH2CO2R, tBuOK, THF, rt, 4 h, R = tBu (80%), R = Et (85%); (i) for R = tBu,
TFA, Ar, rt, 30 min (60%); for R = Et, KOH, (CH2OH)2, reflux, 30 min (85%); (j) (i) p-MeOOCC6H4CHO, BF3·Et2O, CH2Cl2, rt, 2 h; (ii) DDQ,
rt, 1 h (18% for two steps); (k) PdCl2, PhCN, reflux, 30 min (88%).
However, in the case of TAP, severe broadening took place if
the sample would contain even traces of free acid, probably
because the extended aromatic system can undergo reversible
protonation at carbon atoms, which adds yet another process to
the already complex fluxional behavior of these molecules. In
fact, we earlier noted the same behavior already for some
tetranaphthoporphyrins. However, if the dication salt is isolated
in crystalline form and redissolved in NMR solvents, well-
resolved spectra of dicationic forms are observed. This trick
like benzonitrile, was found to proceed smoothly at room
temperature. Upon stirring TAPs with Pd(OAc)2 in dioxane for
24−48 h at rt, high conversion (70−80%) of free base into
metalloporphyrin was observed, although quantitative trans-
formation takes place only upon heating.
Structural Aspects. A good solubility of the obtained TAPs
enabled us to obtain crystals suitable for X-ray diffraction
analysis and determination of structure for porphyrin 5d free
base as shown in Figure 4. This structure completes the series
of structures of linearly annelated extended porphyrins
obtained by us6e,14,28 and others.6c,37
The geometry of porphyrin 5d like all known geometries of
tetraaryl derivatives of tetraannelated porphyrins is distorted to
take a very characteristic “saddle” shape. The degree and main
mode of distortion obtained by applying Shelnutt’s normal-
coordinate structural decomposition38 show that total out-of-
plane distortion Doop is equal to 2.81 Å, in which saddle
distortion B2u is a main component (2.73 Å), with a very slight
contribution of the ruffling mode evident from a slight tilt of
bonds between β-carbons of pyrrolic residues relative to mean
plane of the porphyrin core (cf., Figure 5C). By comparing all
known structures of tetraaryl derivatives of tetraannelated
generally worked well for recording 1H NMR spectra. With 13
C
NMR, the approach is less efficient. An increase of sample
concentrations, necessary to warrant reasonable acquisition
times, resulted in broadening of spectral lines, particularly in the
aromatic portion of spectra, taking place because of either
spontaneous deprotonation or aggregation (cf., Supporting
Information).
The solubility of substituted porphyrins 16 and especially 24
is particularly high, justifying the efforts for their synthesis. The
other gratifying and intriguing feature probably at least partly
associated with good solubility of obtained TAPs is an
unprecedented ease of metalation. Particularly, Pd insertion,
which usually requires prolonged reflux in high boiling solvents
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a
Scheme 5. Synthesis of Butoxy-Substituted Anthtaporphyrins 24
a
Reagents and conditions: (a) 1,3-butadiene (neat), rt, 45 days (98%) or 1,3-butadiene, SnCl4, CH2Cl2, −50 °C, 1.5 h (45%); (b) n-BuI, K2CO3,
acetone, reflux, 2 days (84%); (c) (i) PhSCl, CH2Cl2, rt, 1 h; (ii) oxone, MeOH−H2O (2:1), rt, 7 days (82%); (d) DBU, CH2Cl2, rt, 1 h (95%); (e)
CNCH2CO2R, tBuOK, THF (72% (R = tBu), 83% (R = Et)); (f) for R = tBu, TFA, Ar, rt, 30 min (56%); for R = Et, KOH, (CH2OH)2, reflux, 30
min (90%); (g) (i) 4-MeO2CC6H4CHO, BF3·Et2O, CH2Cl2, rt, 2 h; (ii) DDQ, rt, 1 h (12% for two steps); (h) PdCl2, PhCN, reflux, 30 min (80%).
annelated rings (for distortion analysis, see red 14). No
intermediate forms with noticeably weaker or stronger saddle-
type of distortion have been observed, although if the steric
repulsion would be the main factor determining the distortion,
a wider range of distortion degrees could be expected to meet
the particular internal interaction profile of each of such
molecules. Indeed, a broad variation of distortion degrees has
been revealed for a large body of saddle distorted
dodecasubstituted porphyrins,39 interpreted by Rosa et al.40
as a consequence of softness of the porphyrin core toward
deformation, thus making each particular porphyrin molecule
seek its own balance of steric repulsion, distortion, and
stabilization due to improved conjugation with meso-aryls.
1
Certainly, in the known annelated porphyrins, steric repulsion
Figure 3. H NMR spectra comparison of free base (black line) and
can be regarded to be mainly localized in the interaction of the
meso-aryl ring with the CH-site of the first annelated ring, which
are likely to be roughly the same in all published structures, and
so far no annelated porphyrins bearing substituents at this site,
or ortho-substituted meso-aryls have appeared. There is,
however, an important and intriguing exclusion explicitly
showing that steric repulsion cannot be the main factor
defining the geometry of saddling distortion. Krautler and co-
workers described a planar structure for tetraaryl derivatives of
tetraannelated porphyrin with annelated naphthoquinone
dication (red line) of 5b.
porphyrins, we see that both the degree and the mode of
distortion are practically conserved along the series with total
out-of-plane distortion Doop staying within very close range of
2.7−3.0 Å and dominated by saddle B2u mode. Noteworthy,
such a practically invariant geometry was recorded both for free
porphyrins and their metal complexes, and not only for π-
extended molecules (TBP, TNP, TAP) but also for
tetracyclohexeno derivatives with partially flexible saturated
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Figure 5. Main structural features of tetraarylTAP as seen from the X-
ray structure of 5b. (A) Bond alternation in anthracene residues; (B)
effective planarity of the macrocyclic core (marked red); (C) the same,
but including pyrrolic rings (blue); (D) the angle between the
macrocyclic core mean plane and the annelated residue (green); and
(E) the angle between the macrocyclic core mean plane and meso-aryl
(blue).
Figure 4. X-ray structure of 5d: top and side views. Alkyl chains of
alkoxycarbonyl groups are omitted for clarity.
residues,41 thus being structurally very close (in what concerns
the spatial arrangement and thus the steric interaction of meso-
aryls and annelated fragments) to the tetraaryl TNP series.
Thus, the observed trends (“a bewildering variation”40a of
distortion degrees reported for dodecasubstituted porphyrins vs
practically invariant distortion degree and core geometry of the
tetraannelated tetraarylporphyrins) suggest that the config-
uration of the porphyrin core in the latter is defined not only by
variable balance of steric repulsion between meso-aryls and
annelated rings and stabilizing factors such as the conjugation
with meso-aryl rings. Rather, the repulsion very likely acts as a
weak push, which brings the geometry out of equilibrium, and a
new equilibrium is sought and attained. This new equilibrium,
saddle-shaped with out-of-plane B2u distortion of about 2.7 Å, is
likely to be an interesting compromise between the
destabilization of aromatic macrocyclic core and stabilization
due to increased conjugation with meso-aryl groups.
When discussing the structures of tetraryl derivatives of
tetraannelated porphyrins, both we and others referred to their
characteristic structure as “heavily saddle-distorted”, and the
side view of the new representative of the series (Figure 4)
seems to justify such an epithet. However, a closer scrutiny of
the structures shows that such a way of describing the character
of geometry is an exaggeration, hiding really important features
of such geometry. Indeed, if the mean plane of the porphyrin
core is drawn in these structures (shown in Figure 5B,C for
TAP, but similar pictures drawn for all other known structures
of such porphyrins are virtually indistinguishable from the one
shown), it becomes evident that the inner macrocyclic ring (the
inner 18e-contour) remains practically planar with the largest
deviation from the plane measured for α-pyrrolic atoms being a
meager 0.3 Å (Figure 5B). Importantly, all four nitrogen atoms
and all four meso-carbons lie in a plane with negligible
deviations from it. Thus, from the point of view of macrocyclic
aromaticity, the core of saddle-shaped porphyrins can be
regarded as effectively planar, not much different from the
geometry of the core in regular porphyrins; thus, it is not
surprising that the position of Soret bands in a very long list of
tetraarylporphyrins from TPP to TAP stay within a narrow
range of less than 40 nm. The only part of the core that
substantially deviates from the plane includes β-pyrrolic atoms
and the connecting bond to which the annelated rings are
attached. However, even these atoms deviate only by 0.7−1.0 Å
(the largest values are in TBP, while in TNP and TAP the
deviations are smaller), which is less than the van der Waals
radii of these atoms. It should be noted that the main
contribution to the overall stabilization of porphyrin molecules
is believed, at least in the frames of model advocated by Aihara
and coauthors,42 to be due to aromatic stabilization of 6-
electron circuits of pyrrolic/pyrrolenic fragments, which is not
likely to be dependent on the deviation of these fragments from
the plane. The annelated rings form acute angles with the mean
plane (Figure 5D) of only 23−26°, being within a very short
range in all of the known structures, and in TAP the angle is
among the smallest. Thus, the saddled geometry of the
annelated porphyrins including TAP benefits from the
conservation of aromatic stabilization in both almost planar
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Figure 6. Comparison of the UV−vis absorption spectra for free base porphyrins 5a−d (A), free base, dication, and metalated porphyrin 5a (B), free
base porphyrins 5a, 16, and 24 (C), and Pd-24 and the product of its photooxidation (D).
inner macrocyclic core and annelated pyrrolic/pyrrolenic
fragments.
(b) the arrangement of annelated residues and meso-aryls
enforcing the highest possible degree of conjugation of the
latter with the core. The conservation of geometric parameters
along the series tentatively identifies this as a discrete structural
type in the porphyrin chemistry, and high-level theoretical
treatment and more of resolved structures are required to
enforce or refute this hypothesis.
In TAP and all other known structures of β-annelated
tetraarylporphyrin, the meso-aryls are tilted relative to the
macrocyclic mean plane with angles of ca. 55° (Figure 5E).
These angles are substantially smaller than the tilt angles of
meso-aryls known for planar tetraarylporphyrins,43 in which the
degree of conjugation between the aryls and the core is largely
disrupted. Therefore, the structure of the saddled porphyrins
implies a substantially better conjugation of meso-aryls to the
core. Such a small tilt angle is accounted for by the
checkerboard pattern of deviation of annelated rings to the
opposite directions from the plane, which enables the aryl to
rotate deeper inward at the side where the annelated ring bends
out (Figure 4 side view and Figure 5E) until a close van der
Waals contact of ortho-carbon of meso-aryl and the first atom of
the annelated ring is reached. Interestingly, the conjugation of
meso-aryl rings with the core defined by the tilt angle was earlier
shown by Rosa et al.,4044 to counterbalance the distortion in
both dodecasubstituted porphyrins, and protonated forms of
regular porphyrins in a synergic fashion to generate a
continuum of variable saddled geometries.
TetraarylTAP thus can be considered as regular members of
large class of saddle-shaped tetraannelated porphyrins.
Anthracene residues annelated to the core interact very tightly
with it. The strong interaction is well manifested by bond
alternation in the residues. In fact, the alternation of bonds is a
well-known feature of linear polybenzenoid hydrocarbons
(acenes), being the result of the impossibility to localize
favorable aromatic sextets in such an arrangement of benzene
rings. Therefore, the acenes behave as integral conjugated
systems, the aromaticity of which is rapidly declining with the
addition of each new benzene ring, which in its turn leads to
destabilization of the frontier energy levels and huge red-
shifting of the absorption bands. In TAP molecule, the degree
of bond alternation (Figure 5A) is unprecedented, with some of
the bonds reaching 1.48−1.49 Å, which is close to the regular
single C−C bond length. Bond alternation in TAP is thus more
manifested than that in either TBP or TNP analogues, but this
is not only in free anthracene, but also for higher acenes at least
Thus, the saddled geometry of an important class of
porphyrins (tetraaryl derivatives of tetraannelated porphyrins)
is characterized by (a) practically planar macrocyclic core, and
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up to pentacene.45 This observation shows that porphyrin core
annelated to anthracene residues very strongly interacts with
the latter, which results in a large extent of bond localization in
the rings belonging to these residues. This mode of annelation
creates a sort of huge heteroacene.
UV−Vis Spectra. Electronic absorption properties of
anthraporphyrins prepared are presented in Figure 6. All
TAPs showed a rather broad Soret band with a shoulder at the
hypsochromic side. Because of extension of π-system and
acene-type destabilization of one of the orbitals of the
Gouteman’s model (b1 (a1u) HOMO) leading to the lift of
pseudodegeneracy (this effect was computationally predicted
for lower members of the family46), TAPs exhibit strongly red-
shifted and hyperchromic Q-bands. The maximum of
absorption is about 830 nm for 5a−d. The molar extinction
coefficients of both Soret and Q-bands reach 105 scale. As is
seen from Figure 6A, the nature of aryl substituent has only a
weak effect on absorption properties. In contrast, protonation
and metal insertion were found to have a profound effect. The
comparison of absorption spectra of 5a in free base and
protonated forms, as well as for Zn and Pd-complexes, is shown
in Figure 6B. Very strong red-shift by about 90 nm upon
protonation and blue-shift by 20−40 nm upon metal insertion
are observed. Surprisingly, the introduction of electron donor
substituents into anthra rings was found to have an effect on the
absorption properties only in the case of porphyrin 24, bearing
butoxy-groups in the middle rings. Its Soret and Q-bands are
shifted into red by 20 and 30 nm, respectively. In contrast, the
absorption of porphyrin 16, bearing butoxy-groups in the
outmost rings, is almost identical to that of parent porphyrin 5a
(Figure 6C).
In the course of synthetic procedures and purification of
obtained products 5a−d, 16, and 24, special attention was paid
to protection of the products from the light as the instability
toward photooxidation was noted in previous works.25
However, in the course of experiments, no reasonable
decomposition or impurities formation derived from photo-
degradation was observed upon protecting the working
solutions of porphyrins with foil. In contrast, diluted solutions
of TAPs were found to be sensitive to photooxidation. Air-
exposed solutions with a concentration in a range of 10−4−10−5
M undergo complete photooxidation under ambient light in
10−15 min, while the same solutions are stable in the dark.
Deoxygenated solutions are not sensitive to the light.
Absorption spectra of the oxidized solutions show the
disappearance of the intensive near-IR absorption accompanied
by the appearance of new Q-bands in the visible. The effect is
much stronger pronounced for corresponding metallo-com-
plexes, especially with palladium, then for free base porphyrins.
As an example, a transformation of absorption spectra of
oxygenated solution of Pd-24 upon exposition to light is shown
in Figure 6C. Such transformation of absorption spectra is likely
to be accounted for by addition of singlet dioxygen formed
upon sensibilization of its triplet form by excited state of the
porphyrin, know to be quite efficient.47 From Figure 6C it
becomes clear that the spectra of the oxidized solution closely
resemble the spectra of tetrabenzoporphyrin system both by
position and by relative intensities of B- and Q-bands.
Therefore, we can tentatively suppose that the photooxidation
probably leads to the addition of singlet oxygen across the
diene system of inner rings similarly to what happens with
anthracene and higher acenes in the cycloaddition reactions
(Figure 7, the addition of from 1 to 4 oxygen molecules can be
Figure 7. Probable structure of the product of TAP system
photooxidative bleaching.
hypothesized to result in the loss of TAP long-wavelength
intense bands). Such self-sensitized photoreaction with oxygen
forming macrocycle with four endoperoxide bridges was
previously described by Freyer et al. for tetraanthraporphyr-
azinato palladium.48 The ease of addition is likely to correlate
with the destabilization of anthracene residues as was discussed
above. Currently, we are working on the isolation and
characterization of such adducts, which are of considerable
interest as potentially reversible photoactivated singlet oxygen
reservoirs.
CONCLUSIONS
■
In summary, we have developed a reliable and effective method
for the preparation of tetraanthraporphyrins bearing functional
substituents in meso-positions of the core or on the anthracene
rings. A series of new TAPs were synthesized, and the structure
of a representative molecule was identified by single crystal X-
ray diffraction. The analysis of the structure of representative
tetraarylTAP molecule shows that it has the same structure as
all other known tetraaryl derivatives of tetraannelated
porphyrins, which are characterized by saddle-type out-of-
plane distortion of porphyrin system. The degree of distortion
quantitatively characterized by normal-coordinate structure
decomposition along with such basic geometric parameters as
the deviation of atoms belonging to the macrocyclic system
from the mean plane of the macrocycle, the dihedral angles
between this plane and annelated rings and meso-aryl rings,
show that saddle distortion, a robust arrangement of
constituents of such systems, is reproduced with a substantial
degree of accuracy in practically all of the representatives of the
series including TAP. This type of distortion allows for
practically full conservation of planarity of the internal
macrocyclic 18-electron aromatic core and higher extent of
conjugation between the core and meso-aryls than that
occurring in planar porphyrins of the common TPP type. On
the other hand, the linear fusion of anthracene residues and
porphyrin core enables a very strong interaction between these
aromatic moieties to elicit the behavior known for linearly fused
acenes. This interaction leads to strong destabilization of
frontier orbitals manifested in huge red shift of absorption
bands. The new porphyrins were shown to be soluble in
common organic solvents showing only marginal tendency for
aggregation, and to exhibit strong absorption in the near-IR,
which makes them promising materials for various applications
in biological and materials fields.
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131.1, 128.0, 125.2, 124.7, 107.2, 77.5, 77.0, 76.5, 68.5, 31.2, 29.9, 19.3,
13.9. Anal. Calcd for C22H28O2: C, 81.44; H, 8.70. Found: C, 81.17; H,
8.91.
1,4,4a,9a-Tetrahydroanthraquinone-9,10 (18). Method 1.
Naphthoquinone (20 g, 126 mmol) was added at 0 °C to 1,3-
butadiene (50 mL), and the mixture was stirred for 45 days at room
temperature in a high-pressure glass tube in the dark. The excess
amount of butadiene was evaporated, and the residue was recrystal-
lized from methanol. 18: 26.3 g (98%), white powder, mp 102 °C
(lit.35 102 °C).
Method 2. Synthesis was performed following a modified literature
procedure.36 A solution of naphthoquinone (20 g, 126 mmol) in dry
CH2Cl2 (500 mL) was cooled to 0 °C, and 1,3-butadiene (40 mL) was
added. The mixture was cooled to −60 °C, and 43 mL of SnCl4 (95.7
g, 367 mmol) was added dropwise over 30 min, keeping the
temperature between −60 and −50 °C. The resulting solution was
stirred at −50 °C for 1 h, then warmed to room temperature, and 200
mL of water was added. Organic phase was separated, washed with
water, dried with Na2SO4, and evaporated in vacuum. Solid residue
was recrystallized from ethanol. 18: 12 g (45%), white powder, mp 102
°C (lit.35 102 °C).
EXPERIMENTAL SECTION
■
o-Dibutoxybenzene (7). A mixture of catechol (27.5 g, 0.25 mol),
n-butyliodide (138 g, 0.75 mol), anhydrous K2CO3 (75.9 g, 0.55 mol),
and acetone (200 mL) was refluxed for 48 h. The resulting mixture
was filtered, concentrated by evaporation, and the residue was distilled
in vacuum: yield 51 g (92%), colorless oil, bp 155−161 °C at 16 mm/
Hg (lit.49 149−157 °C at 149−157 mm/Hg).
1,2-Dibromo-4,5-di-n-butoxybenzene (8). The title compound
was prepared following a modified literature procedure.50 To a
solution of o-dibutoxybenzene (20 g, 90 mmol) and I2 (0.5 g, 2 mmol)
in CH2Cl2, distilled over CaH2, was added 11.6 mL of Br2 (36 g, 225
mmol) dropwise over a period of 30 min. The solution was stirred at rt
for 3 h, then evaporated in vacuum. Residual dark-brown oil was
diluted with 150 mL of ethanol and kept in a fridge at −20 °C for 12 h.
Formed crystals were filtered and dried in vacuum. 8: 30.8 g (90%),
colorless easily melting (∼20 °C) crystals; 1H NMR (400 MHz,
CDCl3) δ 7.05 (d, J = 3.8 Hz, 2H), 3.95 (t, J = 6.5 Hz, 4H), 1.79 (dt, J
= 14.5, 6.7 Hz, 4H), 1.59−1.38 (m, 4H), 0.97 (t, J = 7.3 Hz, 6H); 13C
NMR (100 MHz, CDCl3) δ 149.2, 118.1, 114.8, 77.7, 77.2, 76.6, 69.4,
31.2, 19.3, 13.9. Anal. Calcd for C14H20Br2O2: C, 44.24; H, 5.30.
Found: C, 43.87; H, 5.48.
1,4-Dihydro-9,19-di-n-butoxyanthracene (19). Synthesis gen-
erally followed the procedure described for the synthesis of o-
dibutoxybenzene (7). Crude product was purified by recrystallization
6,7-Di-n-butoxy-1,4-epoxy-1,4-dihydronaphthalene (9). The
title compound was prepared following a modified literature method.51
1,2-Dibromo-4,5-di-n-butoxybenzene 8 (28.5 g, 75 mmol) and 27.3
mL of freshly distilled furan (25.5 g, 375 mmol) were dissolved in
THF (75 mL), freshly distilled from LiAlH4. The solution was cooled
to −50 °C under Ar, and 46.8 mL (75 mmol) of 1.6 M n-BuLi solution
in hexane was added dropwise over a period of 30 min. After the
addition was complete, the mixture was stirred for 1 h at −30 °C.
Next, 5 mL of water was added, and the reaction mixture was allowed
to warm to room temperature. The solvent was evaporated in vacuum,
residual oil was dissolved in CH2Cl2 (100 mL), washed with water,
dried with Na2SO4, and evaporated in vacuum. Resulting product was
used in the next step without additional purification. 9: 20.6 g (91%),
1
from methanol. 19: 84%, colorless crystals, mp 80−81 °C; H NMR
(400 MHz, CDCl3) δ 7.95 (dd, J = 6.4, 3.3 Hz, 2H), 7.35 (dd, J = 6.4,
3.2 Hz, 2H), 5.93 (s, 2H), 3.86 (t, J = 6.6 Hz, 4H), 3.47 (s, 4H), 1.96−
1.73 (m, 4H), 1.55 (dq, J = 14.4, 7.1 Hz, 4H), 0.96 (t, J = 7.3 Hz, 6H);
13C NMR (100 MHz, CDCl3) δ 148.0, 127.4, 125.1, 124.3, 122.1, 77.5,
77.0, 76.5, 73.5, 32.7, 24.6, 19.5, 14.1. Anal. Calcd for C22H28O2: C,
81.44; H, 8.70. Found: C, 81.25; H, 8.88.
6,7-Di-n-butoxy-2-chloro-3-phenylsulfonyl-1,2,3,4-tetrahy-
droanthracene (12) and 9,10-Di-n-butoxy-2-chloro-3-phenyl-
sulfonyl-1,2,3,4-tetrahydroanthracene (20). Synthesis was per-
formed following a previously published general procedure for the
preparation of α-chlorosulfones.52 Thiophenol (2 mL, 2.2 g, 20 mmol)
was added dropwise to a suspension of N-chlorosuccinimide (2.14 g,
16 mmol) in CH2Cl2 (20 mL). The mixture was stirred for 1 h, then
filtered from the white precipitate of succinimide. The orange filtrate
was added dropwise to a stirred solution of corresponding
dihydroanthracene (20 mmol) in CH2Cl2 (50 mL) at 0 °C. The
mixture was stirred at room temperature for 2 h and evaporated in
vacuum. The residue was dissolved in methanol (60 mL), and a
suspension of oxone (12.3 g, 20 mmol) in water (30 mL) was added
under vigorous stirring. The mixture was stirred at room temperature
for 7 days, diluted with water (100 mL), and extracted with CH2Cl2.
The combined organic layers were dried with Na2SO4 and evaporated
to dryness. Solid residue was recrystallized from MeOH. 12: 7.8 g
(78%), beige crystals, mp 135−136 °C; 1H NMR (250 MHz, CDCl3)
δ 8.01−7.91 (m, 2H), 7.76−7.53 (m, 3H), 7.43 (s, 2H), 7.04 (d, J =
4.5 Hz, 2H), 4.89 (q, J = 4.4 Hz, 1H), 4.09 (t, J = 6.6 Hz, 4H), 3.81−
3.65 (m, 1H), 3.53−3.09 (m, 4H), 1.96−1.79 (m, 4H), 1.65−1.45 (m,
4H), 1.01 (dd, J = 7.7, 6.9 Hz, 6H); 13C NMR (63 MHz, CDCl3) δ
149.6, 137.9, 134.3, 129.5, 129.3, 129.0, 128.7, 128.6, 125.6, 124.9,
107.5, 77.7, 77.2, 76.6, 68.7, 67.9, 53.3, 37.9, 31.2, 26.9, 19.4, 14.0.
Anal. Calcd for C28H33ClO4S: C, 67.12; H, 6.64. Found: C, 66.80; H,
1
pale-yellow oil; H NMR (400 MHz, CDCl3) δ 7.02 (d, J = 0.8 Hz,
2H), 6.95 (s, 2H), 5.65 (s, 2H), 4.01−3.90 (m, 4H), 1.79−1.70 (m,
4H), 1.54−1.42 (m, 4H), 0.96 (m, 6H); 13C NMR (100 MHz, CDCl3)
δ 146.3, 143.4, 142.0, 110.0, 82.7, 77.7, 77.2, 76.6, 70.0, 31.7, 31.5,
19.3, 14.0. Anal. Calcd for C18H24O3: C, 74.97; H, 8.39. Found: C,
74.78; H, 8.57.
1,4,4a,9,9a,10-Hexahydro-6,7-di-n-butoxy-9,10-epoxyan-
thracene (10). The title compound was prepared following a
modified literature method.20 A mixture of 6,7-di-n-butoxy-1,4-epoxy-
1,4-dihydronaphthalene 9 (15.1 g, 50 mmol), 3-sulfolene (1.5 g, 13
mmol), NaHCO3 (2.5 g, 30 mmol), and pyridine (30 mL) was placed
into a high-pressure glass tube and heated at 120−125 °C for 18 h.
During this time, 5.0 g of 3-sulfolene was added to the reaction
mixture in five portions. The resulting mixture was filtered and
evaporated in vacuum. The residue was purified on a silica gel column
(eluent: CH2Cl2). After evaporation of the solvent, the product was
crystallized from methanol. 10: 10.1 g (59%), beige crystals, mp 31−
1
33 °C; H NMR (400 MHz, CDCl3) δ 6.77 (s, 2H), 5.91−5.79 (m,
2H), 4.84 (s, 2H), 3.97−3.80 (m, 4H), 2.38 (dd, J = 7.7, 5.8 Hz, 2H),
2.03−1.61 (m, 8H), 1.42 (dq, J = 14.4, 7.3 Hz, 4H), 0.89 (t, J = 7.3 Hz,
6H); 13C NMR (100 MHz, CDCl3) δ 147.9, 138.5, 129.2, 106.8, 85.2,
77.5, 77.0, 76.5, 69.7, 42.9, 31.5, 27.5, 19.2, 13.9. Anal. Calcd for
C22H30O3: C, 77.16; H, 8.83. Found: C, 76.87; H, 8.98.
1
6.89. 20: 8.2 g (82%), biege crystals, mp 99−101 °C; H NMR (250
MHz, CD2Cl2) δ 8.10−8.01 (m, 2H), 8.00−7.93 (m, 2H), 7.78−7.57
(m, 3H), 7.54−7.45 (m, 2H), 5.00 (q, J = 4.3 Hz, 1H), 3.99−3.84 (m,
4H), 3.75 (tt, J = 9.2, 4.6 Hz, 1H), 3.59−3.33 (m, 3H), 3.18 (dd, J =
16.5, 7.3 Hz, 1H), 1.97−1.75 (m, 4H), 1.70−1.43 (m, 4H), 1.10−0.96
(m, 6H); 13C NMR (63 MHz, CD2Cl2) δ 149.3, 148.6, 138.1, 134.7,
129.9, 129.7, 129.2, 128.4, 126.2, 125.7, 123.2, 122.7, 122.6, 75.2, 75.0,
66.9, 54.7, 54.28, 53.8, 53.4, 53.0, 52.8, 32.9, 32.9, 31.9, 21.5, 19.8,
19.8, 14.2. Anal. Calcd for C28H33ClO4S: C, 67.12; H, 6.64. Found: C,
66.87; H, 6.86.
6,7-Di-n-butoxy-1,4-dihydroanthracene (11). The title com-
pound was prepared following a modified literature method.33
1,4,4a,9,9a,10-Hexahydro-6,7-di-n-butoxy-9,10-epoxyanthracene 10
(8.55 g, 25 mmol) was dissolved in ethanol (100 mL), then
concentrated HCl solution (10 mL) was added, and the resulting
mixture was refluxed in Ar for 24 h. The reaction mixture was allowed
to cool to room temperature, and the resulting precipitate was filtered
and recrystallized from methanol. 11: 4.9 g (61%), colorless crystals,
mp 112−113 °C; 1H NMR (400 MHz, CDCl3) δ 7.43 (s, 2H), 7.03 (s,
2H), 6.01 (t, J = 1.4 Hz, 2H), 4.10 (t, J = 6.6 Hz, 4H), 3.52 (d, J = 0.8
Hz, 4H), 1.89 (dt, J = 14.5, 6.7 Hz, 4H), 1.55 (dq, J = 14.4, 7.3 Hz,
4H), 1.01 (t, J = 7.4 Hz, 6H); 13C NMR (63 MHz, CDCl3) δ 149.1,
2-Benzenesulfonyl-6,7-dibutoxy-1,2-dihydro-anthracene
(13) and 2-Benzenesulfonyl-9,10-dibutoxy-1,2-dihydro-an-
thracene (21). Synthesis was performed following a modified
literature procedure.52 To a solution of corresponding α-chlorosulfone
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(15 mmol) in CH2Cl2 (30 mL) was added 1,8-diazabicycloundec-7-
ene (2.2 mL, 2.3 g, 15 mmol) dropwise over a period of 10 min at 0
°C. The mixture was stirred for 1 h at room temperature, washed with
water, dried with Na2SO4, and evaporated in vacuum. Solid residue
was recrystallized from MeOH. 13: 6.3 g, 90%, colorless crystals, mp
7,8-Dibutoxy-4,11-dihydro-2H-naphtho[2,3-f ]isoindole (15)
and 5,10-Dibutoxy-4,11-dihydro-2H-naphtho[2,3-f ]isoindole
(23). Method 1. tert-Butyl esters 14a or 22a (1 mmol) were dissolved
in TFA (10 mL), and the solution was stirred for 30 min under Ar at
room temperature. After the addition of CH2Cl2 (20 mL), the mixture
was washed with water, then with 10% solution of Na2CO3, dried with
Na2SO4, and evaporated in vacuum. The residue was passed through a
layer of silica using CH2Cl2 as eluent. The solvent was evaporated to
1
116−118 °C; H NMR (250 MHz, CD2Cl2) δ 7.64 (dd, J = 5.3, 3.3
Hz, 2H), 7.29−7.06 (m, 4H), 6.99 (s, 1H), 6.90 (s, 1H), 6.86 (s, 1H),
6.64 (d, J = 9.7 Hz, 1H), 5.94 (dd, J = 9.6, 5.0 Hz, 1H), 4.13−3.86 (m,
5H), 3.54−3.16 (m, 2H), 1.90−1.69 (m, 4H), 1.58−1.35 (m, 4H),
0.94 (td, J = 7.4, 3.0 Hz, 6H); 13C NMR (63 MHz, CDCl3) δ 150.0,
149.4, 136.4, 134.4, 133.5, 129.7, 129.4, 128.3, 128.2, 127.2, 125.0,
124.5, 118.4, 108.0, 107.5, 77.7, 77.2, 76.6, 68.7, 61.7, 31.3, 28.6, 19.4,
14.1. Anal. Calcd for C28H32O4S: C, 72.38; H, 6.94. Found: C, 72.61;
1
give a product. 15: 0.218 g (60%), gray powder, mp 74−76 °C; H
NMR (250 MHz, CD2Cl2) δ 7.56 (s, 1H), 7.56 (s, 2H), 7.08 (s, 2H),
6.67 (d, J = 2.5 Hz, 2H), 4.09 (t, J = 6.6 Hz, 4H), 3.99 (s, 4H), 1.95−
1.77 (m, 4H), 1.66−1.45 (m, 4H), 1.11−0.94 (m, 6H); 13C NMR (63
MHz, CD2Cl2) δ 149.7, 134.6, 128.4, 125.5, 119.9, 112.9, 107.8, 69.1,
54.9, 54.4, 54.0, 53.6, 53.1, 31.9, 28.6, 19.9, 14.3. Anal. Calcd for
C24H29NO2: C, 79.30; H, 8.04; N, 3.85. Found: C, 79.12; H, 8.30; N,
1
H, 7.22. 21: 6.6 g, 95%, colorless crystals, mp 86−87 °C; H NMR
(250 MHz, CDCl3) δ 7.96 (ddt, J = 11.6, 7.0, 3.5 Hz, 2H), 7.81−7.73
(m, 2H), 7.52−7.39 (m, 2H), 7.33−7.09 (m, 3H), 6.15 (dd, J = 9.9,
5.2 Hz, 1H), 4.18−4.07 (m, 1H), 4.01−3.80 (m, 4H), 3.70 (qt, J = 9.3,
6.6 Hz, 2H), 3.22 (dd, J = 17.4, 7.9 Hz, 1H), 1.99−1.78 (m, 4H),
1.72−1.50 (m, 4H), 1.06 (td, J = 7.3, 4.4 Hz, 6H); 13C NMR (63
MHz, CDCl3) δ 147.8, 147.8, 136.6, 133.4, 129.4, 129.3, 128.5, 128.2,
128.0, 126.4, 125.8, 122.6, 122.2, 121.2, 120.3, 119.1, 77.6, 77.0, 76.5,
75.8, 73.9, 60.7, 32.5, 32.4, 22.4, 19.5, 19.4, 14.1, 14.0. Anal. Calcd for
C28H32O4S: C, 72.38; H, 6.94. Found: C, 72.33; H, 7.34.
1
3.59. 23: 203 g (56%), gray powder, mp 89−90 °C; H NMR (250
MHz, CD2Cl2) δ 8.23−7.92 (m, 3H), 7.57−7.32 (m, 2H), 6.70 (d, J =
2.5 Hz, 2H), 4.06 (s, 4H), 3.97 (t, J = 6.6 Hz, 4H), 1.97 (ddd, J = 14.6,
9.5, 6.5 Hz, 4H), 1.67 (tdd, J = 14.5, 8.5, 6.3 Hz, 4H), 1.08 (dd, J = 9.2,
5.5 Hz, 6H); 13C NMR (63 MHz, CD2Cl2) δ 148.6, 128.3, 127.8,
125.5, 122.5, 118.8, 113.1, 74.1, 54.7, 54.2, 53.8, 53.4, 52.9, 33.0, 22.3,
19.9, 14.3. Anal. Calcd for C24H29NO2: C, 79.30; H, 8.04; N, 3.85.
Found: C, 79.03; H, 8.35; N, 3.40.
Method 2. A mixture of ethyl ester 14b or 22b (1 mmol) and
potassium hydroxide (0.56 g, 10 mmol) in ethylene glycol (10 mL)
was heated at reflux under an atmosphere of Ar for 30 min. The
mixture was cooled to room temperature, and CH2Cl2 (100 mL) was
added. The solution was washed with water and brine, dried with
Na2SO4, and the solvent was evaporated in vacuum. The residue was
passed through a layer of silica using CH2Cl2 as eluent, and the
resulting solution was evaporated to give a product. 15, 0.31 g (85%);
23, 0.326 g (90%).
7,8-Dibutoxy-4,11-dihydro-2H-naphtho[2,3-f ]isoindole-1-
carboxylates (14a,b) and 5,10-Dibutoxy-4,11-dihydro-2H-
naphtho[2,3-f ]isoindole-1-carboxylates (22a,b). Barton−Zard
syntheses of pyrroles 14 and 22 were performed following a previously
published general procedure.28 A solution of corresponding iso-
cyanoacetate (10 mmol) in THF (10 mL) was dropwise over a period
of 10 min to a stirred suspension of potassium tert-butoxide (1.12 g, 10
mmol) at 0 °C. The resulting mixture was stirred for 30 min, and then
a solution of corresponding allyl sulfone (10 mmol) in THF (20 mL)
was added dropwise over a period of 30 min. The reaction mixture was
stirred at room temperature for 4 h, then evaporated in vacuum,
dissolved in CH2Cl2 (50 mL), washed with water, dried with Na2SO4,
and evaporated in vacuum. Solid residue was recrystallized from
Tetraanthroporphyrins 5a−d, 16, 24. Naphthoisoindole 4, 15,
or 23 (1 mmol) and the corresponding aldehyde (1 mmol) were
dissolved in freshly distilled CH2Cl2 (100 mL), and the mixture was
kept under continuous stirring in the dark under Ar for 10 min.
BF3·Et2O (8.5 μL, 0.014 g, 0.1 mmol) was added in one portion, and
the mixture was left to react at rt under Ar for 2 h. A solution of DDQ
(0.17 g, 0.75 mmol) in THF (10 mL) was added, and the mixture was
allowed to stir for another 1 h. The resulting green solution was
washed with 10% solution of Na2SO3 (100 mL), dried with Na2SO4,
and evaporated in vacuum. The residue was dissolved in THF (20
mL), DDQ (0.17 g, 0.75 mmol) was added, and the mixture was
stirred in the dark under Ar for 30 min then evaporated in vacuum.
The resulting material was washed again with the solution of Na2SO3,
dried with Na2SO4, and evaporated to dryness. The residue was
purified on a silica gel column twice (eluent: CH2Cl2, then CH2Cl2−
THF, 10:1). Each time, a purple band eluting with CH2Cl2−THF was
collected, and the solvent was removed in a vacuum. All manipulations
were performed either in the dark or in vessels covered by aluminum
foil. The remaining green solid was purified by recrystallization from
CH2Cl2−diethyl ether mixture (4:1). The crystals that formed after 1−
2 days were centrifuged, washed by ether, and dried in a vacuum.
Palladium complexes were obtained by heating of a mixture of
porphyrin, excess Pd(OAc)2 (2 equiv), and Et3N (1−2 drops) in
benzonitrile at 160 °C for 0.5−3 h (control by UV−vis spectroscopy),
with subsequent filtration through a layer of silica (eluent CH2Cl2) and
evaporation of filtrate.
1
methanol. 14a: 3.7 g (80%), colorless crystals, mp 158−160 °C; H
NMR (400 MHz, CDCl3) δ 8.98 (br s, 1H), 7.63 (s, 1H), 7.57 (s,
1H), 7.10 (s, 1H), 7.08 (s, 1H), 6.82 (d, J = 2.40 Hz, 1H), 4.31 (s,
4H), 4.13 (t, 4H), 4.03 (s, 4H), 1.91 (m, 4H), 1.66 (s, 9H), 1.58 (m,
4H), 1.04 (t, 6H); 13C NMR (100 MHz, CDCl3) δ 161.1, 149.2,
132.2, 128.1, 128.0, 125.6, 125.2, 121.2, 117.1, 107.2, 80.6, 68.5, 31.2,
29.7, 28.6, 27.5, 19.3, 14.0. Anal. Calcd for C29H37NO4: C, 75.13; H,
8.04; N, 3.02. Found: C, 74.88; H, 8.34; N, 2.70. 14b: 3.7 g (85%),
yellowish crystals, 126−128 °C; 1H NMR (250 MHz, CD2Cl2) δ 9.01
(br s, 1H), 7.59 (d, J = 15.9 Hz, 2H), 7.08 (d, J = 2.9 Hz, 2H), 6.86 (d,
J = 2.7 Hz, 1H), 4.43−4.22 (m, 4H), 4.19−3.96 (m, 6H), 1.95−1.77
(m, 4H), 1.65−1.47 (m, 4H), 1.42 (t, J = 7.1 Hz, 3H), 1.03 (dd, J =
9.7, 5.0 Hz, 6H); 13C NMR (63 MHz, CD2Cl2) δ 161.6, 149.6, 132.7,
132.6, 128.4, 128.4, 127.2, 125.8, 125.5, 121.7, 118.1, 117.8, 107.5,
107.4, 68.9, 60.3, 54.7, 54.2, 53.8, 53.4, 52.9, 31.7, 28.8, 27.7, 19.7,
14.8, 14.1. Anal. Calcd for C27H33NO4: C, 74.45; H, 7.64; N, 3.22.
Found: C, 74.10; H, 8.02; N, 2.85. 22a: 3.34 g (72%), colorless
1
crystals, mp 129−130 °C; H NMR (400 MHz, CDCl3) δ 9.41 (br s,
1H), 8.12 (m, 2H), 7.49 (m, 2H), 6.89 (d, J = 2.78 Hz, 1H), 4.37 (s,
4H), 4.10 (s, 4H), 4.03 (m, 4H), 2.01 (m, 4H), 1.72 (s, 9H), 1.68 (m,
4H), 1.10 (t, 3H), 1.09 (t, 3H); 13C NMR (100 MHz, CDCl3) δ 161.6,
148.7, 148.4, 127.5, 127.4, 126.4, 126.2, 125.2, 124.8, 122.22, 122.16,
120.17, 119.0, 117.7, 80.7, 73.8, 32.74, 32.69, 28.7, 23.0, 21.7, 19.5,
14.1. Anal. Calcd for C29H37NO4: C, 75.13; H, 8.04; N, 3.02. Found:
C, 74.97; H, 8.22; N, 2.59. 22b: 3.61 g (83%), yellowish crystals, 138−
5a: 0.145 g (40%), green powder, analytical data are in
correspondence to those described previously.20
5b: 0.062 g (15%), green powder. 1H NMR (250 MHz, CD2Cl2) δ
8.69 (d, J = 1.5 Hz, 8H), 8.33 (s, 8H), 8.25 (s, 8H), 8.19 (t, J = 1.7 Hz,
4H), 8.02 (dd, J = 6.6, 3.2 Hz, 8H), 7.48 (dd, J = 6.7, 3.1 Hz, 8H), 1.52
(s, 72H). UV/vis for free base (toluene) λmax (log ε) 467 (4.82), 507
(5.0), 749 (4.23), 807 (4.91), 823 (5.0); diprotonated form (toluene,
CF3COOH) 535 (4.74), 575 (4.74), 797 (4.19), 884 (4.68). HRMS
(ESI): m/z found 1663.9368, calcd for [M+] C124H118N4 1663.9390.
1
140 °C; H NMR (250 MHz, CD2Cl2) δ 9.05 (br s, 1H), 8.20−8.05
(m, 2H), 7.59−7.42 (m, 2H), 6.95 (d, J = 2.9 Hz, 1H), 4.47−4.33 (m,
4H), 4.17−3.91 (m, 6H), 2.10−1.90 (m, 4H), 1.84−1.62 (m, 4H),
1.48 (t, J = 7.1 Hz, 3H), 1.11 (td, J = 7.3, 2.8 Hz, 6H); 13C NMR (63
MHz, CDCl3) δ 181.7, 161.8, 148.7, 148.4, 127.5, 127.4, 126.2, 126.1,
125.8, 125.28, 122.2, 122.2, 120.4, 118.2, 117.7, 77.6, 77.0, 76.5, 73.8,
73.8, 60.1, 32.7, 32.7, 22.9, 21.7, 19.6, 19.5, 14.6, 14.2, 14.1. Anal.
Calcd for C27H33NO4: C, 74.45; H, 7.64; N, 3.22. Found: C, 74.18; H,
7.24; N, 2.96.
1
5c: 0.073 g (20%), green powder. H NMR (500 MHz, CD2Cl2) δ
8.54 (s, 8H), 8.42 (s, 8H), 8.06 (dt, J = 11.1, 5.5 Hz, 8H), 7.88 (d, J =
2.1 Hz, 8H), 7.52 (dd, J = 6.7, 3.0 Hz, 8H), 7.25 (t, J = 2.1 Hz, 4H),
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Article
4.02 (s, 24H), 1.85 (d, J = 68.3 Hz, 4H). UV/vis for free base
(CH2Cl2) λmax (log ε) 472 (4.82), 507 (4.92), 753 (4.14), 813 (4.76),
827 (4.79); diprotonated form (CH2Cl2, CF3COOH) 534 (4.78), 647
(4.28), 788 (4.1), 881 (4.7). HRMS (ESI): m/z found 1455.5211,
calcd for [M+] C100H70N4O8 1455.5227.
(2) Tokuji, S.; Takahashi, Y.; Shinmori, H.; Shinokubo, H.; Osuka, A.
Chem. Commun. 2009, 1028.
(3) Sayyad, M. H.; Saleem, M.; Karimov, K. S.; Yaseen, M.; Ali, M.;
Cheong, K. Y.; Noor, A. F. M. Appl. Phys. A: Mater. Sci. Process. 2009,
98, 103.
5d: 0.098 g (19%), green powder. 1H NMR (250 MHz, CD2Cl2) δ
9.54−9.46 (m, 4H), 9.45−9.36 (m, 8H), 8.45−8.20 (m, 8H), 8.11−
7.94 (m, 8H), 7.93−7.56 (m, 8H), 7.55−7.42 (m, 8H), 4.41 (t, J = 6.7
Hz, 16H), 1.77 (dt, J = 14.4, 6.7 Hz, 16H), 1.40 (dd, J = 15.0, 7.5 Hz,
16H), 0.85 (t, J = 7.4 Hz, 24H). UV/vis for free base (toluene) λmax
(log ε) 468 (5.08), 518 (5.27), 757 (4.49), 833 (5.26); diprotonated
form (toluene, CF3COOH) 537 (5.15), 821 (4.41), 911 (5.08).
HRMS (ESI): m/z found 2015.8512, calcd for [M+] C132H118N4O16
2015.8576.
(4) Kurotobi, K.; Kim, K. S.; Noh, S. B.; Kim, D.; Osuka, A. Angew.
Chem., Int. Ed. 2006, 45, 3944.
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Org. Chem. 2004, 69, 522. (e) Filatov, M. A.; Cheprakov, A. V.;
Beletskaya, I. P. Eur. J. Org. Chem. 2007, 2468. (f) Filatov, M. A.;
Lebedev, A. Y.; Vinogradov, S. A.; Cheprakov, A. V. J. Org. Chem.
2008, 73, 4175.
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Fujimoto, T.; Nakamura, K.; Kaneda, T.; Sakata, Y.; Yamashita, M.
Chem. Lett. 2004, 33, 40. (b) Gandhi, V.; Thompson, M. L.; Lash, T.
D. Tetrahedron 2010, 66, 1787.
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Chem., Int. Ed. 2006, 45, 3944.
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10, 3945. (b) Davis, N. K. S.; Pawlicki, M.; Anderson, H. L. Org. Lett.
2010, 12, 2124. (c) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L.
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(b) Spence, J. D.; Lash, T. D. J. Org. Chem. 2000, 65, 1530. (c) Xu, H.-
J.; Mack, J.; Descalzo, A. B.; Shen, Z.; Kobayashi, N.; You, X. Z.;
Rurack, K. Chem.-Eur. J. 2011, 17, 8965.
16: 0.091 g (18%), green powder. 1H NMR (250 MHz, CD2Cl2) δ
8.65 (dd, J = 24.3, 8.0 Hz, 16H), 8.49−7.34 (m, 16H), 7.20 (s, 8H),
4.24 (s, 12H), 4.17 (t, J = 6.5 Hz, 16H), 2.00−1.80 (m, 16H), 1.67−
1.47 (m, 24H), 1.05 (t, J = 7.4 Hz, 24H). UV/vis for free base
(toluene) λmax (log ε) 471 (4.98), 523 (5.17), 748 (4.39), 830 (5.2);
diprotonated form (toluene, CF3COOH) 535 (4.74), 575 (4.74), 797
(4.19), 884 (4.68). HRMS (ESI): m/z found 2023.9203, calcd for
[M+] C132H126N4O16 2023.9202.
Pd-16: 88%, brown solid. 1H NMR (500 MHz, d8-toluene, 223 K) δ
9.53−7.66 (m, 24H), 3.76−2.79 (m, 28H), 1.85−1.11 (m, 26H),
1.04−0.58 (m, 26H). UV/vis (toluene) λmax (log ε) 469 (4.88), 710
(4.23), 789 (4.93). HRMS (ESI): m/z found 2127.8067, calcd for
[M+] C132H124N4O16Pd 2127.8081.
1
24: 0.06 g (12%), green powder. H NMR (400 MHz, CD2Cl2) δ
8.85−7.35 (m, 40H), 4.20 (s, 12H), 3.87 (m, 4H), 1.84 (m, 16H),
1.62 (m, 16H), 1.11 (m, 24H). UV/vis for free base (toluene) λmax
(log ε) 501 (5.0), 539 (5.11), 785 (4.36), 859 (5.04); diprotonated
form (toluene, CF3COOH) 446 (4.83), 560 (5.1), 850 (4.42), 953
(4.93). HRMS (ESI): m/z found 2024.9242, calcd for [MH+]
C132H127N4O16 2024.9281.
1
Pd-24: 80%, brown solid. H NMR (250 MHz, CD2Cl2) δ 8.82−
8.56 (m, 16H), 8.42−7.96 (m, 18H), 7.59−7.35 (m, 10H), 4.25−4.12
(m, 12H), 3.96−3.76 (m, 16H), 3.74−3.62 (m, 6H), 1.88−1.75 (m,
12H), 1.70−1.52 (m, 24H), 1.15−1.02 (m, 24H). UV/vis (toluene)
λmax (log ε) 477 (4.69), 643 (3.69), 726 (4.18), 815 (4.65). HRMS
(ESI): m/z found 2127.8047, calcd for [M+] C132H124N4O16Pd
2127.8081.
(12) (a) Cheprakov, A. V. In The Synthesis of π-Extended Porphyrins.
Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M., Guilard,
R., Eds.; World Scientific: Singapore, 2011; Vol. 13. (b) Ono, N.;
Yamada, H.; Okujima, T. In Synthesis of Porphyrins Fused with Aromatic
Rings. Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M.,
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Weber, H.; Saf, R.; Klimant, I. Inorg. Chem. 2010, 49, 9333.
(14) Lebedev, A. Y.; Filatov, M. A.; Cheprakov, A. V.; Vinogradov, S.
A. J. Phys. Chem. A 2008, 112, 7723.
ASSOCIATED CONTENT
* Supporting Information
■
S
Details of X-ray structure determination and copies of the
NMR spectra of newly synthesized compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
(15) (a) Shea, P. B.; Chen, C.; Kanicki, J.; Pattison, L. R.; Petroff, P.;
Yamada, H.; Ono, N. Appl. Phys. Lett. 2007, 90, 233107. (b) Borek, C.;
Hanson, K.; Djurovich, P. I.; Thompson, M. E.; Aznavour, K.; Bau, R.;
Sun, Y.; Forrest, S. R.; Brooks, J.; Michalski, L.; Brown, J. Angew.
Chem., Int. Ed. 2007, 46, 1109. (c) Sun, Y.; Borek, C.; Hanson, K.;
Djurovich, P. I.; Thompson, M. E.; Brooks, J.; Brown, J. J.; Forrest, S.
R. Appl. Phys. Lett. 2007, 90, 213503. (d) Sommer, J. R.; Farley, R. T.;
Graham, K. R.; Yang, Y.; Reynolds, J. R.; Xue, J.; Schanze, K. S. ACS
Appl. Mater. Interfaces 2009, 1, 274.
(16) (a) Esipova, T. V.; Karagodov, A.; Miller, J.; Wilson, D. F.;
Busch, T. M.; Vinogradov, S. A. Anal. Chem. 2011, 83, 8756.
(b) Lebedev, A. Y.; Cheprakov, A. V.; Sakadzic, S.; Boas, D. A.; Wilson,
D. F.; Vinogradov, S. A. ACS Appl. Mater. Interfaces 2009, 1, 1292.
(c) Finikova, O. S.; Galkin, A.; Rozhkov, V.; Cordero, M.; Hagerhall,
C.; Vinogradov, S. A. J. Am. Chem. Soc. 2003, 125, 4882. (d) Wilson,
D. F.; Lee, W. M. F.; Makonnen, S.; Finikova, O. S.; Apreleva, S.;
Vinogradov, S. A. J. Appl. Physiol. 2006, 101, 1648.
AUTHOR INFORMATION
Corresponding Author
*E-mail: filatov@mpip-mainz.mpg.de (M.A.F.); avchep@elorg.
chem.msu.ru (A.V.C.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.A.F. acknowledges the EU-founded FP-7 project EphoCell
(no. 227127) for financial support. S.B. acknowledges
Reintegration Grant RG-09-0002(DRG-02/2) Bulgarian Na-
tional Science Fund for financial support. A.V.C. acknowledges
financial support from Russian Foundation of Basic Research
grant RFBR 10-03-01122.
(17) (a) Baluschev, S.; Yakutkin, V.; Miteva, T.; Avlasevich, Y.;
Chernov, S.; Aleshchenkov, S.; Nelles, G.; Cheprakov, A.; Yasuda, A.;
Mullen, K.; Wegner, G. Angew. Chem., Int. Ed. 2007, 46, 7693.
(b) Baluschev, S.; Yakutkin, V.; Wegner, G.; Miteva, T.; Nelles, G.;
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