Porphyrin-o-quinones as model systems for electron transfer and catecholase reactions

Article abstract of DOI:10.1002/1099-0690(200006)2000:12<2303::AID-EJOC2303>3.0.CO;2-U

Various porphyrin-o-quinones 1-8 were prepared as model compounds for electron transfer reactions. The synthesis of these compounds could only be accomplished by using o-quinone components stabilized by sterically demanding substituents in the o,o'-positions and by using protected catechol aldehydes for the initial porphyrin condensation step. The stability of the target compounds strongly depends on the steric influence of substituents on the o- quinone, which are necessary to stabilize the o-quinones. To test this steric influence we synthesized the porphyrin-o-quinones both without and with methyl and tert-butyl groups and investigated the influence of the bridging position on the reactivity. The ¹H and ¹³C-NMR spectroscopic characteristics of all compounds are given: The electron transfer properties were determined using optical spectroscopy and cyclic voltammetry. The free base porphyrin-o-quinone 1 with two tert-butyl groups in the o,o'-positions of the quinone readily underwent degradation reactions to muconic acid derivatives similar to those observed in catecholase reactions. Nevertheless, this is the first report of such reactions that do not involve the addition of metal-containing-catalysts. The respective zinc(II) complex 6 and the two separated components tetraphenylporphyrin 26 and 3,6-di-tert-butyl-o-quinone (27) did not undergo this reaction, and we surmise a photochemical mechanism that depends on the steric demand of the o-quinone.

Full text of DOI:10.1002/1099-0690(200006)2000:12<2303::AID-EJOC2303>3.0.CO;2-U

FULL PAPER
Porphyrin-o-quinones as Model Systems for Electron Transfer and Catecholase
Reactions
Marcus Speck,[a] Harry Kurreck,[a] and Mathias O. Senge*[a]
Keywords: Porphyrinoids / Photosynthesis / Quinones / Electron transfer / Oxygenations
Various porphyrin-o-quinones 1−8 were prepared as model
compounds for electron transfer reactions. The synthesis of
these compounds could only be accomplished by using o-
quinone components stabilized by sterically demanding sub-
are given. The electron transfer properties were determined
using optical spectroscopy and cyclic voltammetry. The free
base porphyrin-o-quinone 1 with two tert-butyl groups in the
o,oЈ-positions of the quinone readily underwent degradation
stituents in the o,oЈ-positions and by using protected catechol reactions to muconic acid derivatives similar to those ob-
aldehydes for the initial porphyrin condensation step. The
stability of the target compounds strongly depends on the
served in catecholase reactions. Nevertheless, this is the first
report of such reactions that do not involve the addition of
steric influence of substituents on the o-quinone, which are metal-containing catalysts. The respective zinc(II) complex 6
necessary to stabilize the o-quinones. To test this steric influ-
and the two separated components tetraphenylporphyrin 26
ence we synthesized the porphyrin-o-quinones both without and 3,6-di-tert-butyl-o-quinone (27) did not undergo this re-
and with methyl and tert-butyl groups and investigated the action, and we surmise a photochemical mechanism that de-
influence of the bridging position on the reactivity. The 1H-
and 13C-NMR spectroscopic characteristics of all compounds
pends on the steric demand of the o-quinone.
Introduction
The preparation of model compounds for photosynthesis
[(D)Ϫ(B)Ϫ(A)], consisting of a porphyrin donor (D) and a
quinone acceptor (A), has been pursued for more than 20
years and has been described in several comprehensive re-
views.[1] Many hundreds of compounds have been described
that contain porphyrins and quinones linked by amide
bridges, ester functions,[2] or CϪC bonds.[3] Although nu-
merous compounds are known in which porphyrin and qui-
none are linked by covalent linkages (B ϭ bridge), only a
limited number of directly linked porphyrin quinones (B ϭ
no bridge) have been synthesized.[4]
Many such systems have been prepared by cross con-
densation and often the 10,15,20-triphenylporphyrin-5-yl
system has been used as porphyrin donor component
(Scheme 1). Recently, we also described the use of porphy-
rins with various meso-alkyl groups for the preparation of
porphyrin-quinones (PϪQ) with Q ϭ p-benzoquinone.[5]
All these studies have exclusively utilized p-benzoquinones
or their substituted analogs (anthraquinone, naphthoqui-
none, and triptycene quinone) as the quinone component.[6]
The potential use of o-quinones in electron transfer
chains was first demonstrated by Giangiacomo and Dut-
ton.[7] They modified native photosystems by exchanging
the second quinone (QB) in the photosynthetic reaction
center of the purple bacterium Rhodobacter sphaeroides
with an o-quinone to utilize the significantly higher reduc-
Scheme 1
tion potential of o-quinone. The synthesis of model systems
containing o-quinones is of interest in connection with
compounds that, according to the theory of electron trans-
fer (ET), have a high |∆GET|. In addition, the reduction po-
tential of the o-quinones may be further increased through
formation of metal chelates with metals from the first and
second main group.[8] Otherwise a similarly drastic increase
of the reduction potential is possible only by introduction
of strong electron-withdrawing substituents in p-quinones.
[a]
Institut für Chemie, Organische Chemie, Freie Universität
Berlin,
Takustrasse 3, 14195 Berlin, Germany
Fax: (internat.) ϩ 49-30/838-55163
E-mail: mosenge@chemie.fu-berlin.de
Eur. J. Org. Chem. 2000, 2303Ϫ2314
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/0612Ϫ2303 $ 17.50ϩ.50/0
2303

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
Since then we have successfully connected the more un-
Initially we tested the use of dihydroxybenzaldehydes in
stable o-quinones with porphyrins and have gained access mixed porphyrin condensation reactions. Only in the case
to a new class of model compounds for ET studies.[9] Sub- of the dimethyl compound 23 was the target compound ob-
sequent to our first report on porphyrin-o-quinones,[9b] tained, and even then only small amounts were formed. At-
D’Souza and co-workers published the synthesis of a por- tempts to synthesize porphyrins with dihydroxyaldehydes
phyrin-o-quinone without additional substituents on the that contained more than one free aromatic position gave
quinone.[10]
complex, fluorescing mixtures of porphyrins in all cases.
In the present work we describe the complete synthesis Even after oxidation with silver(I) oxide the formation of
and spectroscopic characterization of porphyrin-o-quinones porphyrin-o-quinones was not observed by NMR spectro-
as model compounds for ET and various reactions and scopy.
their dependence on the steric demand of substituents on
Thus, the 3,4-dimethoxybenzaldehydes 21 and 22 were
the o-quinone. These reactions include the unexpected utilized for the porphyrin condensation. Both aldehydes
formation of muconic acid derivatives, which are of rele- were prepared by Rieche formylation[13] from the respective
vance for natural catecholase systems.
1,4-dialkyl-2,3-dimethoxybenzenes (Scheme 3). Despite the
high steric demand in the veratrol, aldehyde 21 was ob-
tained in 60% yield.
Results and Discussion
Tetra-meso-substituted porphyrins are normally prepared
by mixed condensation of pyrrole and the respective substi-
tuted aldehydes. In order to control the high reactivity of o-
quinones, we targeted porphyrins with o-quinone units that
carry substituents with various degrees of steric demand in
the o,oЈ-positions (Scheme 2). In contrast to the preparation
of some porphyrin-p-quinones,[6b,11] the synthesis of por-
phyrin-o-quinones can only be accomplished by condensing
an aldehyde bearing protected o-dihydroxy functions with
pyrrole 9 and benzaldehyde 10 to give the desired porphy-
rins 11Ϫ15.[12]
Scheme 3. a: Cl2CHϪOMe, TiCl4, CH2Cl2, 0 °C
The protected porphyrin catechols were prepared using
these aldehydes and this was followed by demethylation
with boron tribromide. Subsequent oxidation of the por-
phyrin catechols with silver(I) oxide gave the target com-
pounds as shown in Scheme 4.
Scheme 4. General reaction scheme for the porphyrin synthesis us-
ing the dimethyl compound 12 as an example; a: BBr3, CH2Cl2,
Ϫ80 °C; b: Ag2O; c, d: Zn(ac)2, MeOH
Porphyrin-o-quinone 1, which has the highest steric de-
mand on the quinone, showed side reactions (vide supra)
and thus we attempted to decrease the steric demand in the
Scheme 2. a: BF3Et2O/CH2Cl2, room temp., DDQ
2304
Eur. J. Org. Chem. 2000, 2303Ϫ2314

Porphyrin-o-quinones
FULL PAPER
porphyrin-o-quinones. Accordingly, the two stable porphy- nances of six-membered cyclic ketones.[15] The assignment
rin-o-quinones 2 and 4, with methyl groups on the o-qui- of the individual resonances in the 1H- and 13C-NMR spec-
none fragment, were synthesized. Subsequently, the consti- tra was performed using 2D NMR methods. The strong
tutional isomers of the unsubstituted porphyrin-o-quinones high-field shift of the signal for one of the methyl groups in
3 and 5 were prepared to investigate whether the electronic compound 2 is particularly noteworthy. This group lies over
and steric influence of the porphyrin alone is sufficient for the porphyrin plane and is strongly influenced by the ring
the formation of stable porphyrin-o-quinones. In principle, current of the porphyrin.[16]
o-quinones with only one additional substituent are quite
The direct linkage of porphyrin and o-quinone results in
unstable, with the relative position of the substituent also strong electronic interactions, whose magnitude correlates
influencing the stability. With regard to the electron transfer with the dihedral angle due to the fact that orbital overlap
in model systems, different dihedral angles between the por- between donor and acceptor is possible.[17] In the case of
phyrin and quinone will be obtained as a result of the steric the unsubstituted porphyrin-o-quinone 3, this results in an
demand of the substituent.
additional band in the UV/Vis spectrum that tails up to
Isolation and purification of the unsubstituted porphy- 900 nm (Figure 1). This is the first report on such strong
rin-o-quinones 3 and 5 proved to be extremely difficult. electronic interactions in synthetic porphyrin donor-ac-
Both the initial porphyrin catechols 24 and 25 (Scheme 5) ceptor systems. The zinc(II) complex of 3 has been used by
and the expected porphyrin-o-quinones are sensitive to D’Souza and co-workers as a fluorescence sensor, although
humidity and light. Even small impurities resulted in the they did not mention any additional band in the visible
immediate formation of numerous degradation products. spectrum.[10] Some of the NMR assignments do not agree
Thus, these compounds were prepurified by column chro- with our values and this may be due to impurities.
matography (silica gel, dichloromethane, column with cool-
ing mantle, 5 °C). In order to prevent reduction reactions,
activated lead dioxide and sodium sulfate (anhydrous)
needed to be added to the column head. Only under these
conditions was a crude purification possible at all. Sub-
sequently, all porphyrins were purified by preparative
HPLC. Assessment of the purity was performed by 1H-
NMR spectroscopy (500 MHz). Highly purified fractions
of the unsubstituted porphyrin-o-quinones 3 and 5 can be
stored for several weeks at Ϫ20 °C if light and air are ex-
cluded. The metalloporphyrins formed by reaction of the
unsubstituted porphyrin-o-quinones 3 and 5 with ZnO and
TFA could only be obtained with a purity of Ͻ 50% and
were not characterized further. Use of the method described
recently by D’Souza for related zinc(II) complexes did not
Figure 1. Electronic absorption spectrum of the porphyrin-o-qui-
lead to an improvement in the degree of purity.[10]
none 3 in dichloromethane
1
We were able to measure the H-NMR spectra of both
unsubstituted porphyrin-o-quinones and completely assign
all signals (Figure 2). The chemical shifts of the quinone
protons are of special importance for the relative assign-
ment of the two different constitutional isomers. For ex-
Scheme 5
For spectroscopic studies in connection with the investi- ample, compound 3 gave two doublets with large couplings,
gation of the theory of the electron transfer, all free bases with the signal at low field (30-H) showing an additional
4
were converted into the respective zinc(II) complexes (6Ϫ8, splitting. Due to the J coupling with 30-H the signal for
16Ϫ20) and characterized spectroscopically. While this is 26-H is split further. In contrast, for compound 5 a doublet
normally easily achieved using zinc(II) acetate,[14] we used of doublets with two large couplings is detected for 29-H.
a treatment of the free bases with zinc(II) oxide under the The two remaining quinone protons, 28-H and 30-H, each
catalytic influence of TFA.[6a] This procedure prevents the exhibit only one coupling with 29-H. As the signal for 30-
occurrence of addition reactions at the o-quinone fragment. H is obscured by the m- and p-phenyl protons, no further
1H- and 13C-NMR spectra were recorded for all com- interpretation is possible for this signal. The exact chemical
pounds in order to obtain complete characterization of the shift of this proton was determined from an HMQC spec-
porphyrin-o-quinones. 13C-NMR spectroscopy is especially trum.[16]
suited to the task of checking for the formation of the iso-
To test the utility of the porphyrin-o-quinones as model
meric p-quinones or the reduced porphyrin catechols during compounds for the photoinduced ET, the redox potentials
the purification steps. Investigations by Hollenstein and von of the various compounds were determined. In a first
Philippsborn showed that the carbonyl resonances of o-qui- approximation the redox potentials of the model com-
nones are the strongest high-field shifted carbonyl reso- pounds are the sum of the two potentials Ϫ oxidation po-
Eur. J. Org. Chem. 2000, 2303Ϫ2314
2305

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
chelation of the porphyrin-o-semiquinone anion radicals
with various counterions has been reported elsewhere.[9a,16]
We expected porphyrin-o-quinone 1 to be a stable com-
pound as, in contrast to other o-quinones, the 3,6-di-tert-
butyl-o-quinone 27 (Scheme 6) is a chemically and ther-
mally stable product. Nevertheless, compound 1 immedi-
ately decomposed under the influence of light and air with
initial formation of an olefinic diketone 32. During the
course of further purification attempts (column chromato-
graphy and preparative HPLC) the porphyrin quinone 1
also reacted to give the muconic acid derivative 33, whose
constitution was confirmed by a single crystal X-ray struc-
ture determination (Scheme 7).[9b] In order to elucidate the
mechanism of these reactions, additional experiments were
performed. Under standard conditions (room temperature,
air) only partial decomposition of 1 is observed. When the
sample is also irradiated with a 1000-W lamp,[21] decom-
position is complete within 3 min. When a mixture of the
two individual compounds 5,10,15,20-tetraphenylporphyrin
(26) and 3,6-di-tert-butyl-o-quinone (27) (1:5) was irradi-
ated under oxygenating conditions, the formation of the de-
composition products was not observed. Similarly, neither
28 or 29 underwent photooxygenation in the presence of
26. In addition, neither the metal complex 6 nor the homo-
logous dimethyl compound 2 showed similar reactions.
Thus, the observed side reactions are a consequence of both
the steric demand of the two tert-butyl groups and the steric
and electronic influence of the covalently linked porphyrin
system.
1
Figure 2. H-NMR spectra of the two unsubstituted porphyrin-o-
quinone isomers 3 and 5
tential of the porphyrin and reduction potentials of the qui-
none. Hence, the oxidation potentials of the porphyrin-o-
quinones do not differ significantly from the known values
of 5,10,15,20-tetraarylporphyrins.
The experimental results in Table 1 indicate that the re-
duction potentials of the porphyrin-o-quinones are approx-
imately 200 mV higher than the isomeric porphyrin-p-qui-
nones.[18] Thus, according to the RehmϪWeller equation
[Equation (1)], a greater |∆GET| is found for the porphyrin-
o-quinones compared to the respective p-quinone com-
pounds.[19]
Scheme 6. o-Quinones with high steric demand and their corres-
ponding pyrocatechols
0
∆GET ϭ e(E0D /D Ϫ EA/A ) Ϫ ∆E (S0 S1) ϩ wP Ϫ wR
(1)
ϩ
Ϫ
The applicability of Equation (1) has been discussed with
great controversy in the literature.[20] In the present case,
this equation is solely used to indicate the magnitude of
the differences in ∆GET for porphyrin-o-quinones and the
isomeric porphyrin-p-quinones. An EPR and ENDOR in-
vestigation of the changes in spin density distribution upon
Table 1. Redox potentials of the model compounds in dichlorome-
thane vs. SCE, working electrode Pt, conducting salt 0.1  TBAP
OX
OX
RED
RED
Compound E2 [V] E1 [V] ϪE1
[V] ϪE2
[V]
1
4
5
2
3
6
8
1.16
1.13
1.18
1.13
1.17
0.82
0.88
0.52
0.23
0.22
0.27
0.36
0.58
0.42
1.27
Scheme 7
1.36
1.31
1.35
1.25
Formation of the oxidation products must occur inde-
pendently from each other by two different routes, as first
the diketone 32 is formed and the formation of the muconic
1.18
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Eur. J. Org. Chem. 2000, 2303Ϫ2314

Porphyrin-o-quinones
FULL PAPER
acid anhydride 33 from 32 is not possible for stoichiometric
reasons. Nevertheless, both reactions appear to be mutually
interconnected. The more slowly proceeding formation of
the muconic acid derivatives depends on the reactivity of
the o-quinones and is an example of the degradation of ca-
techols under the influence of catecholases. Catecholases
are nonheme iron oxygenases that catalyze the degradation
of aromatic compounds through activation of molecular
oxygen.[22]
The known degradation reactions in microorganisms in-
volve the formation of substituted catechols and protocate-
chuic acid derivatives from aromatic amino acids and car-
bohydrates. During the last four decades several groups
have investigated the nonenzymatic reaction of oxygen with
aromatic compounds to obtain information about the pos-
sible reaction products and their distribution.[23] To coun-
teract the high reactivity of the initial reaction products,
tert-butylated catechols were used in most model reactions.
Despite their lower symmetry, which results in a larger
number of possible reaction products, most catecholase
model studies utilized 3,5-di-tert-butylcatechol (31) rather
than the 3,6-isomer 30, which is more difficult to prepare.
All known reactions required the addition of metal oxide
containing catalysts for chelation of the 1,2-dioxo function,
or the use of a peroxide-containing oxidant. Depending on
the modification of the reaction conditions the product dis-
tribution varied considerably in the published reactions.[24]
Of special environmental relevance is the degradation reac-
tion of halogenated catechols recently described by Funa-
biki et al.[25] This involves oxidation with molecular oxygen
by catalysis with a nonheme iron(III) complex.
As a result of the groundbreaking work of Que Jr. and
co-workers the basic mechanism of the intradiol cleaving
catechol dioxygenase is known.[26] Interestingly, one inter-
mediate of this mechanism is a muconic acid anhydride that
subsequently decomposes. This reaction is a result of the
chelation of the catechol by an iron-containing catalyst, the
latter being capable of activating molecular oxygen for initi-
ation of an intradiol cleavage. In contrast to this, the oxida-
Scheme 8. Possible mechanism for the formation of the muconic
acid derivative 33
tive cleavage of the catechol 34 described in this paper pro- significantly higher reactivity. This assumption is confirmed
ceeds without additional catalyst. by the observation that an acidic solution of 1 decomposes
In agreement with other known reactions of o-quinones completely within a few minutes.
we suggest the following mechanism (Scheme 8).[27Ϫ29] The
The ϩI effect of the tert-butyl groups as well as the ϩM
peroxide 35 as well as bisketene 36 are possible interme- effect of the porphyrin unit will determine the reactivity of
diates in a complex mechanism for the formation of the the whole system. Accordingly no reaction is observed in
muconic anhydride 33. The discussion of a radical mecha- the case when the separated porphyrin 26 and o-quinone 27
nism starting from catechol 34 presents an explanation for are irradiated. A photochemical oxidation may also provide
the different reactivity of the homologous dimethyl com- a possible explanation and the different photochemical be-
pound 2, which will form a more stable benzyl radical. As havior of the free base and metalloporphyrins can have a
the formation of muconic acid from the respective o-qui- determining influence on the reactivity of the various por-
nones can successfully be accomplished only with a phyrins.
BaeyerϪVilliger oxidation, we favor a reaction mechanism
In contrast to the known catecholase model reactions, we
that occurs via the catechol 34.
found the olefinic diketone 32 to be the first degradation
The stability of the metalloporphyrin 6 can be explained product. Similar to related reactions in the literature we
in terms of the influence of the porphyrin chromophore; propose the formation of an endo-peroxide and subsequent
metal insertion results in a formally higher nucleophilicity decarbonylation as the key steps for the formation of 32. A
of the porphyrin. In contrast, protonation should result in prerequisite for the formation of an endo-peroxide 40 is the
an increase in electrophilicity that, in turn, will lead to a generation of the required singlet oxygen by reaction of at-
Eur. J. Org. Chem. 2000, 2303Ϫ2314
2307

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
mospheric oxygen with sensitizers such as, for example, metallated with dilute hydrochloric acid in the cold and un-
tetraphenylporphyrin or chlorophyll.[30]
der an inert gas and was immediately characterized spectro-
Investigations by Wasserman and Scheffer showed that scopically.
the reactivity of the 1,3-diene in the middle ring of substi-
tuted anthracenes is dependent on the electron density at
the 9- and 10-positions.[31] An increase of the electron den-
sity at both positions resulted in a higher reactivity with
oxygen and gave a higher yield in the generation of singlet
oxygen from the endo-peroxides formed.[32] These differ-
ences in reactivity might explain the fact that neither the
metalloporphyrin 6 nor the homologous dimethyl com-
pound 2 reacts according to the sequence given in
Scheme 9. According to studies by Wilcox and Stevens, ox-
idation of cyclic ketones with singlet oxygen also yields sub-
sequent decarbonylations, resulting in open-chain dike-
tones.[33] Twofold cleavage of carbon monoxide from the
endo-peroxide 40 will result in formation of the diketone as
the thermodynamically more stable (E) compound 32.
Conclusion
According to the properties established here, the porphy-
rin-o-quinones present a new, interesting class of com-
pounds for studying electron transfer processes. Although
o-quinones are often highly unstable, this can be counter-
acted in porphyrin-o-quinones by using sterically de-
manding substituents. For example, compound 2 showed
stability comparable to that of porphyrin-p-quinones and
thus could be used for initial studies on their ET properties.
All porphyrin-o-quinones showed the typical quenching of
the porphyrin fluorescence by the o-quinone fragment. The
two porphyrin-o-quinones 3 and 5, without any additional
substituents on the quinone fragment, exhibited a much
lower stability but could be obtained in their pure form and
characterized by NMR spectroscopy. As shown, the steric
demand of additional substituents in the quinone fragment
should not be too high. Thus, in contrast to our expecta-
tions, compound 1 was not a stable porphyrin-o-quinone.
Instead, the formation of the various oxidation products is
mainly a consequence of the photophysical properties of 1
combined with the covalent linkage of the donor and ac-
ceptor systems. As formation of a diketone during the ox-
idation of catechols has not been described under biological
conditions, further studies are needed to address the ques-
tion of whether diketones can also be formed under these
conditions from other catechols, e.g. 3,5-di-tert-butylcate-
chol. As this is the first catecholase model reaction not in-
volving additional metal catalysts, further studies are re-
quired. In addition, interesting synthetic possibilities reside
in the 1,2-dicarbonyl function of the porphyrin-o-quinones
that might allow the formation of higher porphyrin aggre-
gates. Olefinic diketones like 32 have potential as synthetic
building blocks, e.g. for the formation of bis(porphyrins).
Scheme 9. Putative formation of the porphyrin diketones 32, 43
and 44
Treatment of the porphyrin mixture formed after de-
methylation with zinc(II) acetate results in an isomerization
of the 1,4-diketone. The (E)-diketone 32 is converted into a
3:1 (Z)/(E) mixture of the respective metal complexes 43
and 44. Analogous observations were also made during
treatment of the pure (E) isomer 32. A reinvestigation of
the mixture of metal complexes after four weeks revealed
Experimental Section
General Remarks: All chemicals used were of analytical grade and
were purchased from Aldrich Co. unless stated otherwise. Ϫ Melt-
ing points were measured with a Büchi melting point apparatus
and are uncorrected. Ϫ Silica gel 60 (Merck) was used for column
chromatography. Analytical thin-layer chromatography (TLC) was
only the pure cis isomer 44. The metal complex of the (E) carried out using Merck silica gel 60 plates (precoated sheets,
0.2 mm thick, fluorescence indicator F254). Ϫ 1H-NMR spectra
isomer 43 could not be obtained in its pure form. Neverthe-
were recorded at frequencies of 500 MHz (Bruker, AMX 500), 13C-
less, the spectroscopic data were unambiguously assigned
NMR spectra at 126 MHz. All chemical shifts are given in ppm,
from the mixture with 2D NMR experiments and are in
referenced on the δ scale downfield from the TMS signal. CDCl3
agreement with expected values.[34] Formation of the (Z)-
was used as internal standard. Ϫ Electronic absorption spectra
diketone during the metallation is the result of a photoiso-
were recorded with a Specord S10 (Carl Zeiss Jena) spectrophoto-
merization, similar to the observations made for (E)-2,2,7,7-
meter using dichloromethane as solvent. Ϫ Mass spectra were re-
tetramethyl-4-octene-3,6-dione by Rassat and co-
corded with a Varian MAT 711 mass spectrometer using EI tech-
workers.[35]
nique with a direct insertion probe and, if not otherwise noted,
In order to obtain a pure sample of the porphyrin-o-qui-
none 1, the stable metal complex 6 was carefully de- formed with a PerkinϪElmer 240 Analyzer. Ϫ HPLC Columns:
with an excitation energy of 80 eV. Ϫ Elemental analyses were per-
2308
Eur. J. Org. Chem. 2000, 2303Ϫ2314

Porphyrin-o-quinones
FULL PAPER
Nucleosil 50 SiO2 (5µ), 300 mm ϫ 5 mm i.d. and 107 mm ϫ 32 mm
i.d.; HPLC instrumentation: Knauer HPLC pump 64 high pres-
sure, Knauer MPLC pump and variable-wavelength monitor UV/
Vis detector from Knauer; all chromatograms were taken at ambi-
ent temperature with the detector wavelength fixed at λ ϭ 420 nm.
8.27Ϫ8.22 (1 H, m, o-phenyl), 8.19Ϫ8.13 (3 H, m, o-phenyl),
7.80Ϫ7.68 (9 H, m, m- and p-phenyl), 7.47 (1 H, s, arom.), 4.15 (3
H, s, ϪOMe), 4.13 (3 H, s, ϪOMe), 1.35 (9 H, s, tBu), 0.81 (9 H,
s, tBu), Ϫ2.67 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 153.55,
153.30, 142.86, 142.25, 142.12, 137.07, 134.57, 134.45, 134.37,
134.11, ca. 131, 130.15, 127.62, 126.64, 123.77, 119.92, 119.71,
59.80, 59.52, 37.77, 34.63, 32.59, 30.59. Ϫ UV/Vis (CH2Cl2): λmax
(lg ε) ϭ 420 (5.6), 517 (4.3), 552 (3.8), 592 (3.7), 649 nm (3.6). Ϫ
MS; m/z (%): 787 [M ϩ 1]•ϩ (15), 786 [M]•ϩ (100), 729 [M Ϫ
C4H9]•ϩ (12), 699 [M Ϫ C5H12]•ϩ (4), 671 [M Ϫ C6H13]•ϩ (6), 57
[C4H9]ϩ (11). Ϫ HRMS: calcd. for C54H50O2N4 786.39338; found
786.39300.
3,4-Dimethoxy-2,5-dimethylbenzaldehyde (22): To a magnetically
stirred solution of the corresponding veratrol, prepared at 0 °C
from 3.32 g (20 mmol) of 3,6-dimethylpyrocatechol dimethyl
ether[36] in 100 mL of dichloromethane, was added 4.74 g
(25 mmol) of titanium(IV) chloride and, dropwise, 3.45 g
(30 mmol) of freshly distilled dichloromethyl methyl ether. The re-
action mixture was allowed to warm up to room temperature and
stirred for 1 h before it was poured into ice/water. Extraction was
effected with dichloromethane. The combined organic layers were
washed with 5% aqueous NaHCO3 and dried with sodium sulfate.
Evaporation of the solvent and vacuum distillation gave 3.5 g (87%)
of 22 as a colorless liquid, b.p.003 114 °C. Ϫ 1H NMR (CDCl3):
δ ϭ 10.11 (1 H, s, ϪCHO), 7.38 (1 H, s, arom.), 3.89 (3 H, s,
ϪOMe), 3.77 (3 H, s, ϪOMe), 2.51 (3 H, s, ϪMe), 2.25 (3 H, s,
ϪMe). Ϫ 13C NMR (CDCl3): δ ϭ 191.45, 156.12, 151.19, 132.86,
129.94, 129.69, 129.47, 59.87, 59.72, 15.38, 10.54. Ϫ MS (70 eV);
m/z (%): 195 [M ϩ 1]•ϩ (12), 194 [M]•ϩ (100), 179 [M Ϫ CH3]•ϩ
(47), 91 [C7H7]ϩ (17). Ϫ HRMS: calcd. for C11H14O3 194.09430;
found 194.09428.
5-(2,5-Dimethyl-3,4-dimethoxyphenyl)-10,15,20-triphenylporphyrin
(12): According to the general procedure 0.78 g (4 mmol) of 2,5-
dimethyl-3,4-dimethoxybenzaldehyde (22) was allowed to react and
gave 351 mg (12.4%) of purple crystals, m.p. 204Ϫ208 °C. Ϫ
1
HPLC: n-hexane/ethyl acetate ϭ 94:6. Ϫ H NMR (CDCl3): δ ϭ
3
8.85 (4 H, s, β-pyrrole), 8.84 (2 H, d, J ϭ 4.6 Hz, β-pyrrole), 8.78
(2 H, d, 3J ϭ 4.6 Hz, β-pyrrole), 8.27Ϫ8.22 (3 H, m, o-phenyl),
8.22Ϫ8.18 (3 H, m, o-phenyl), 7.80Ϫ7.72 (9 H, m, m- and p-
4
phenyl), 7.63 (1 H, q, J ϭ 1.9 Hz, arom.), 4.17 (3 H, s, ϪOMe),
4.08 (3 H, s, ϪOMe), 2.48 (3 H, s, ϪMe), 1.92 (3 H, s, ϪMe),
Ϫ2.75 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 151.39, 150.51,
142.19, 142.06, 137.50, 134.54, 134.51, 134.46, 132.02, 131.72, ca.
131, 127.68, 127.23, 126.67, 120.11, 119.95, 118.71, 60.52, 60.50,
15.94, 14.55 . Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 418 (5.61), 514
(4.24), 548 (3.84), 589 (3.74), 645 nm (3.57). Ϫ MS: m/z (%): 703
[M ϩ 1]•ϩ (54), 702 [M]•ϩ (100), 687 [M Ϫ CH3]•ϩ (8), 672 [M Ϫ
2CH3]•ϩ (8), 657 [M Ϫ 3 CH3]•ϩ (8), 644 [M Ϫ 4 CH3]•ϩ (3). Ϫ
HRMS: calcd. for C48H38O2N4 702.29948; found 702.29870.
2,5-Di-tert-butyl-3,4-dimethoxybenzaldehyde (21): According to the
above procedure the aldehyde 21 was obtained as a colorless solid,
2.8 g (52%), m.p. 67Ϫ68 °C. For further purification the product
1
was sublimated. Ϫ H NMR (CDCl3): δ ϭ 10.65 (1 H, s, ϪCHO),
7.35 (1 H, s, arom.), 3.87 (3 H, s, ϪOMe), 3.77 (3 H, s, ϪOMe),
1.55 (9 H, s, tBu), 1.36 (9 H, s, tBu). Ϫ 13C NMR (CDCl3): δ ϭ
193.95, 157.33, 153.53, 142.62, 141.67, 133.01, 122.94, 59.92, 59.53,
37.10, 34.83, 33.58, 30.19. Ϫ MS; m/z (%): 279 [M ϩ 1]•ϩ (7), 278
[M]•ϩ (37), 263 [M Ϫ CH3]•ϩ (100), 91 [C7H7]ϩ (4), 57 [C4H9]ϩ
(14). Ϫ HRMS: calcd. for C17H26O3 278.18820; found 278.18811.
5-(3,4-Dimethoxyphenyl)-10,15,20-triphenylporphyrin (13): As de-
scribed above, 0.42 g (2.5 mmol) of 3,4-dimethoxybenzaldehyde
(Fluka) was condensed with pyrrole and benzaldehyde to give the
porphyrin. Ϫ Yield: 189 mg (11%) of purple crystals, m.p. Ͼ 330
°C. Ϫ 1H NMR (CDCl3): δ ϭ 8.97 (2 H, d, 3J ϭ 4.5 Hz, β-pyrrole),
8.94Ϫ8.87 (6 H, AB, β-pyrrole), 8.30Ϫ8.27 (3 H, m, o-phenyl),
Synthesis of the Porphyrins
General Procedure According to Lindsey Conditions:[12] Pyrrole
(0.8 mL, 7.5 mmol), benzaldehyde and 2.5 mmol of a second alde-
hyde were dissolved in 1 L of CH2Cl2 (ϩ 7.5 mL of anhydrous eth-
anol) under Ar. Condensation was initiated by addition of 4 mmol
of a 25% BF3Ϫdiethyl ether solution in the dark. After stirring
for 1 h, the porphyrinogen formed was oxidized with p-chloranil
followed by stirring for about 12 h. The reaction mixture was neut-
ralized with triethylamine[37] and the product extracted. Purifica-
tion was achieved by repeated column chromatography on silica gel
followed by preparative HPLC.
4
8.27Ϫ8.25 (3 H, m, o-phenyl), 7.85 (1 H, d, J ϭ 2.0 Hz, arom.),
7.84Ϫ7.76 (9 H, m, m- and p-phenyl), 7.76 (1 H, dd, arom.), 7.25
3
(1 H, d, J ϭ 8.5 Hz, arom.), 4.18 (3 H, s, ϪOMe), 4.03 (3 H, s,
ϪOMe), Ϫ2.70 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 148.89,
147.08, 142.17, 134.80, 134.53, ca. 131, 127.69, 127.44, 126.67,
120.13, 120.09, 119.93, 118.34, 109.45, 56.12. Ϫ UV/Vis (CH2Cl2):
λmax (lg ε) ϭ 417 (5.59), 514 (4.26), 548 (3.84), 589 (3.73), 646 nm
(3.60). Ϫ MS; m/z (%): 675 [M ϩ 1]•ϩ (50), 674 [M]•ϩ (100), 659
[M Ϫ CH3]•ϩ (7), 614 [M Ϫ C2H6O2]•ϩ (12), 337 [M]•ϩϩ (4). Ϫ
HRMS: calcd. for C46H34O2N4 674.26818; found 674.26835.
5-(2,5-Di-tert-butyl-3,4-dimethoxyphenyl)-10,15,20-triphenylpor-
phyrin (11): 2,5-Di-tert-butyl-3,4-dimethoxybenzaldehyde (21)
(1.04 g, 3.75 mmol) was treated according to the general procedure.
For purification the crude reaction mixture was concentrated after
separation of the polypyrrole condensates. Due to the excellent
solubility of 11 in n-hexane the product was separated almost com-
pletely from TPP by extraction in a Soxhlet extractor. Despite a
starting material ratio of pyrrole/benzaldehyde/aldehyde 21 ϭ 8:7:1,
HPLC/UV coupling detected high molecular mass porphyrins,
which were identified as di- and trimeric products by preliminary
NMR investigations. The low polarity of the porphyrins made puri-
fication of the crude product with preparative HPLC quite difficult.
Porphyrin 11 was obtained as purple crystals (4%), m.p. Ͼ 330 °C.
5-(2,3-Dimethoxy-4-methylphenyl)-10,15,20-triphenylporphyrin (14):
0.45 g (2.5 mmol) of 2,3-Dimethoxy-4-methylbenzaldehyde[38] was
allowed to react to give porphyrin 14. Ϫ Yield: 190 mg (11%) of
purple crystals, m.p. 308Ϫ310 °C. Ϫ HPLC: n-hexane/ethyl ace-
1
tate ϭ 92:8. Ϫ H NMR (CDCl3): δ ϭ 9.08 (2 H, AB, β-pyrrole),
9.06 (6 H, s, β-pyrrole), 8.48Ϫ8.40 (3 H, m, o-phenyl), 8.40Ϫ8.32
(3 H, m, o-phenyl), 7.94Ϫ7.81 (9 H, m, m- and p-phenyl), 7.80 (1
3
3
H, d, J ϭ 7.8 Hz, arom.), 7.35 (1 H, d, J ϭ 7.8 Hz, arom.), 4.24
(3 H, s, ϪOMe), 3.41 (3 H, s, ϪOMe), 2.74 (3 H, s, ϪMe), Ϫ2.49
(2 H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 153.36, 150.97, 142.20,
142.13, 134.56, 134.52, 134.48, 134.29, 132.93, ca. 131.1, 130.48,
127.68, 126.66, 124.03, 120.33, 120.00, 115.66, 60.81, 60.57, 16.36.
Ϫ HPLC: n-hexane/diisopropyl ether ϭ 99:1. Ϫ 1H NMR (CDCl3): Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 417 (5.52), 514 (4.18), 549 (3.80),
3
δ ϭ 8.82 (4 H, s, β-pyrrole), 8.80 (2 H, d, J ϭ 4.6 Hz, β-pyrrole),
589 (3.69), 645 nm (3.49). Ϫ MS: m/z (%): 689 [M ϩ 1]•ϩ (53), 688
8.75 (2 H, d, 3J ϭ 4.6 Hz, β-pyrrole), 8.32Ϫ8.27 (2 H, m, o-phenyl), [M]•ϩ (100), 673 [M Ϫ CH3]•ϩ (6), 658 [M Ϫ 2 CH3]•ϩ (5), 344
Eur. J. Org. Chem. 2000, 2303Ϫ2314 2309

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
[M]•ϩϩ (10). Ϫ HRMS: calcd. for C47H36O2N4 688.28383; found
688.28403.
quinoid), 1.19 (9 H, s, tBu), 0.78 (9 H, s, tBu), Ϫ2.68 (2 H, s,
ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 185.24, 181.71, 148.98, 147.90,
143.42, 142.66, 141.83, 141.58, 134.52, 134.44, 134.35, 127.95,
127.89, 126.83, 126.80, 126.74, 121.09, 120.64, 117.73, 37.88, 34.72,
31.17, 29.11. Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 416 (5.41), 516
(4.15), 550 (3.87), 595 (3.84), 652 nm (3.67). Ϫ MS; m/z (%): 759
[M ϩ 2 H ϩ 1]•ϩ (17), 758 [M ϩ 2 H]•ϩ (29), 728 [M Ϫ 2 CH3]•ϩ
(7), 716 [M Ϫ C3H6]•ϩ (9), 700 [M ϩ 2 H Ϫ C4H8]•ϩϩ (41), 644
[M ϩ 2 H Ϫ 2 C4H8]•ϩϩ (68), 157 (100). Ϫ HRMS: calcd. for
C52H46O2N4 758.36208; found 758.36227 as pyrocatechol.
5-(2,3-Dimethoxyphenyl)-10,15,20-triphenylporphyrin (15): 0.42 g
(2.5 mmol) of 2,3-Dimethoxybenzaldehyde was treated with pyrrole
and benzaldehyde following the general procedure. Ϫ Yield: 136 mg
(8%) of purple crystals, m.p. Ͼ 330 °C. Ϫ HPLC: dichloromethane.
Ϫ 1H NMR (CDCl3): δ ϭ 8.98 (2 H, d, β-pyrrole), 8.97 (6 H, s, β-
pyrrole), 8.39Ϫ8.35 (2 H, m, o-phenyl), 8.34 (1 H, m, o-phenyl),
8.32 (1 H, m, o-phenyl), 8.32Ϫ8.27 (2 H, m, o-phenyl), 7.88Ϫ7.78
(9 H, m, m- and p-phenyl), 7.77 (1 H, dd, 3J ϭ 7.5 Hz, 4J ϭ 1.5 Hz,
arom.), 7.43 (1 H, dd, 3J ϭ 8.3 Hz, 3J ϭ 7.5 Hz, arom.), 7.37 (1 H,
(E)-2,2,7,7-Tetramethyl-4-(10,15,20-triphenylporphyrin-5-yl)-oct-4-
3
4
1
dd, J ϭ 8.3 Hz, J ϭ 1.5 Hz, arom.), 4.14 (3 H, s, ϪOMe), 3.31
(3 H, s, ϪOMe), Ϫ2.59 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3):
δ ϭ 152.46, 149.66, 142.27, 142.19, 136.35, 134.56, ca. 131, 128.02,
127.68, 126.67, 122.05, 120.34, 120.03, 115.49, 112.67, 60.83, 56.04.
Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 417 (5.64), 513 (4.30), 547 (3.85),
589 (3.76), 645 nm (3.57). Ϫ MS; m/z (%): 675 [M ϩ 1]•ϩ (50), 674
[M]•ϩ (100), 659 [M Ϫ CH3]•ϩ (6), 337 [M]•ϩϩ (6). Ϫ HRMS:
calcd. for C46H34O2N4 674.26818; found 674.26834.
ene-3,6-dione (32): Purple crystals, m.p. 248Ϫ250 °C Ϫ H NMR
3
(500 MHz, CDCl3): δ ϭ 9.59 (2 H, d, J ϭ 4.8 Hz, β-pyrrole), 8.92
(2 H, d, 3J ϭ 4.8 Hz, β-pyrrole), 8.83 (4 H, AB, 3J ϭ 4.6 Hz, β-
pyrrole), 8.40Ϫ8.34 (2 H, m, o-phenyl), 8.34Ϫ8.28 (1 H, m, o-
phenyl), 8.09Ϫ8.01 (3 H, m, o-phenyl), 7.84Ϫ7.68 (9 H, m, m- and
p-phenyl), 7.50 (1 H, s, olef.), 1.44 (9 H, s, tBu), 0.85 (9 H, s, tBu),
Ϫ2.79 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 213.42, 205.39,
156.85, 141.91, 141.62, 135.72, 134.46, 127.90, 126.78, 126.73,
126.70, 121.51, 120.83, 113.05, 45.67, 43.71, 27.08, 26.33. Ϫ UV/
Vis (CH2Cl2): λmax (rel. int.) ϭ 423 (1.000), 520 (0.050), 557 (0.032),
595 (0.018), 650 nm (0.017). Ϫ MS; m/z (%): 733 [M ϩ 1]•ϩ (15),
732 [M]•ϩ (27), 716 [M Ϫ O]•ϩ (100), 676 [M Ϫ C4H8]•ϩ (75), 647
[M Ϫ C4H9 Ϫ CO]•ϩ (32), 563 (81). Ϫ HRMS: calcd. for
C50H44O2N4 732.34643; found 732.34621.
Demethylation of the Dimethoxyporphyrins
General Procedure: For demethylation 0.1 mmol of the porphyrin
was dissolved in 50 mL of dichloromethane and treated dropwise
(1 h) under Ar at Ϫ80 °C under vigorous stirring with 15 mL of
BBr3. The reaction mixture was warmed to room temperature,
poured onto ice and adjusted to pH ϭ 7.0 with NaHCO3. The
combined dichloromethane extracts were dried with Na2SO4 and
purified as described below.
3,6-Di-tert-butyl-4-(10,15,20-triphenylporphyrin-5-yl)-2,7-dihydro-
oxepin-2,7-dione (33): Purple crystals, m.p. 260Ϫ262 °C Ϫ 1H
3
NMR (CDCl3): δ ϭ 9.12 (2 H, br. s, β-pyrrole), 8.95 (2 H, d, J ϭ
3,6-Di-tert-butyl-4-(10,15,20-triphenylporphyrin-5-yl)-1,2-benzo-
quinone (1): For synthesis of the porphyrin-o-quinone 1 79 mg of
the protected porphyrin pyrocatechol 11 was demethylated as de-
scribed above. After warming the reaction mixture to room temper-
ature, stirring was continued under Ar for 12 h. The initially
formed catechol was oxidized by atmospheric oxygen during the
column chromatographic workup (silica; n-hexane/CH2Cl2 ϭ 1:4,
v/v). During workup two additional porphyrins were formed, a
substituted muconic anhydride 33 and an olefinic 1,4-diketone 32.
In contrast to 1, both porphyrins 32 and 33 are stable to light and
air. Due to this phenomenon, only the decomposition products 32
and 33 could be separated in pure form by preparative HPLC. De-
pending on the conditions (air, light) the o-quinone 1 formed and
slowly decomposed. The relative composition of the reaction mix-
ture was determined by 1H-NMR spectroscopy directly after col-
umn chromatography and found to be: muconic acid anhydride 33/
o-quinone 1/1,4-diketone 32 ϭ 1:13:3.7. For purification of 1 the
reaction components were first converted into the respective
zinc(II) complexes and the stable zinc(II) complex 6 of the o-qui-
none 1 was separated. Then 50 mg of 6 was dissolved in 10 mL of
degassed deuteriochloroform[39] and stirred for 1 h with 1 mL of
HCl (20%) under Ar and with exclusion of light. The reaction mix-
ture was neutralized under Ar with a saturated solution of sodium
hydrogen carbonate. The organic phase was separated and dried
with Na2SO4. Subsequently, the solution was used for NMR stud-
ies. Both NMR and HPLC/UV coupling showed only one product.
The complete workup must be performed in the dark. Ϫ HPLC:
n-hexane/diisopropyl ether ϭ 97:3.
4.4 Hz, β-pyrrole), 8.84 (4 H, s, β-pyrrole), 8.35Ϫ8.29 (2 H, m, o-
phenyl), 8.29Ϫ8.25 (1 H, m, o-phenyl), 8.14Ϫ8.08 (3 H, m, o-
phenyl), 7.83Ϫ7.70 (9 H, m, m- and p-phenyl), 7.17 (1 H, s, arom.),
1.21 (9 H, s, tBu), 0.79 (9 H, s, tBu), Ϫ2.79 (2 H, s, ϪNH). Ϫ 13C
NMR (CDCl3): δ ϭ 163.84, 162.28, 147.24, 141.84, 141.59, 141.46,
136.78, 134.55, 134.47, 134.33, 127.92, 127.87, 126.80, 126.72,
121.24, 120.57, 112.69, 37.58, 36.15, 30.45, 28.99. Ϫ UV/Vis
(CH2Cl2): λmax (lg ε) ϭ 419 (5.52), 515 (4.14), 550 (3.72), 590
(3.62), 646 nm (3.39). Ϫ MS; m/z (%): 773 [M ϩ 1]•ϩ (56), 772
[M]•ϩ (100), 728 [M Ϫ C2H4O]•ϩ (51), 716 [M Ϫ C4H8]•ϩ (49), 671
[M Ϫ C4H9 Ϫ C2H4O]•ϩ (94), 656 (55), 84 (52). Ϫ HRMS: calcd.
for C52H44O3N4 772.34134; found 772.34160.
3,6-Dimethyl-4-(10,15,20-triphenylporphyrin-5-yl)-1,2-benzoquinone
(2): The dimethoxyporphyrin 12 (67 mg) was treated according to
the general procedure. For complete oxidation the dried (Na2SO4)
solution was stirred for 20 min with 500 mg of PbO2.[40] Ϫ Yield:
37 mg (58%) of reddish brown crystals, m.p. 310Ϫ312 °C (dec.). Ϫ
1
HPLC: n-hexane/diisopropyl ether ϭ 85:15. Ϫ H NMR (CDCl3):
δ ϭ 9.23 (2 H, d, 3J ϭ 4.6 Hz, β-pyrrole), 9.00 (2 H, d, 3J ϭ 4.6 Hz,
β-pyrrole), 8.87 (4 H, s, β-pyrrole), 8.29Ϫ8.25 (2 H, m, o-phenyl),
8.25Ϫ8.22 (1 H, m, o-phenyl), 8.22Ϫ8.16 (3 H, m, o-phenyl),
4
7.84Ϫ7.73 (9 H, m, m- and p-phenyl), 7.66 (1 H, q, J ϭ 1.8 Hz,
quinoid), 2.15 (3 H, s, ϪMe), 1.82 (3 H, s, ϪMe), Ϫ2.68 (2 H, s,
ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 182.12, 181.03, 149.71, 142.56,
141.76, 141.56, 137.56, 134.48, 134.41, 132.79, ca. 131.6, 127.97,
127.92, 126.84, 126.80, 126.74, 121.58, 120.80, 113.71, 15.35, 14.45.
Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 414 (5.53), 512 (4.19), 550 (3.80),
593 (3.81), 654 nm (3.57). Ϫ MS; m/z (%): 675 [M ϩ 2 H ϩ 1]•ϩ
(47), 674 [M ϩ 2 H]•ϩ (100), 658 [M Ϫ O]•ϩ (4), 328 (7), 149 (93).
Ϫ HRMS: calcd. for C52H44O3N4 674.268177; found 674.268177.
3,6-Di-tert-butyl-4-(10,15,20-triphenylporphyrin-5-yl)-1,2-benzo-
quinone (1): Reddish brown crystals, m.p. 78Ϫ81 °C (dec.) Ϫ 1H
3
NMR (CDCl3): δ ϭ 9.22 (2 H, d, J ϭ 4.5 Hz, β-pyrrole), 8.97 (2
3
H, d, J ϭ 4.5 Hz, β-pyrrole), 8.84 (4 H, s, β-pyrrole), 8.33Ϫ8.28 3-Methyl-6-(10,15,20-triphenylporphyrin-5-yl)-1,2-benzoquinone (4):
(2 H, m, o-phenyl), 8.26Ϫ8.22 (1 H, m, o-phenyl), 8.17Ϫ8.11 (3 H,
According to the general procedure 69 mg of the dimethoxy com-
m, o-phenyl), 7.83Ϫ7.71 (9 H, m, m- and p-phenyl), 7.47 (1 H, s, pound 14 was demethylated. After oxidation with 500 mg of active
2310
Eur. J. Org. Chem. 2000, 2303Ϫ2314

Porphyrin-o-quinones
FULL PAPER
PbO2 and purification by column chromatography and preparative
HPLC, the substituted 3-methyl-o-quinone 4 was obtained as red
possible only under Ar in sealed tubes. Compound 38 was oxidized
with 500 mg of AgI oxide for 3 d at Ϫ20 °C to the unsubstituted
brown crystals. Ϫ Yield: 28 mg (43%), m.p. 293 °C (dec.). Ϫ HPLC: porphyrin-o-quinone 3; water formed during the reaction was
1
n-hexane/ethyl acetate ϭ 88:12. Ϫ H NMR (CDCl3): δ ϭ 8.98 (2
bound with Na2SO4. After an initial purification step (silica,
CH2Cl2) the porphyrin was purified by preparative HPLC. In solid
form the o-quinone is stable at room temperature, while a solution
H, d, 3J ϭ 4.4 Hz, β-pyrrole), 8.87 (2 H, d, 3J ϭ 4.4 Hz, β-pyrrole),
8.82 (4 H, AB, 3J ϭ 4.5 Hz, β-pyrrole), 8.22Ϫ8.15 (6 H, m, o-
3
phenyl), 7.78Ϫ7.68 (9 H, m, m- and p-phenyl), 7.50 (1 H, d, J ϭ in dichloromethane can be stored at Ϫ20 °C for several weeks.
6.3 Hz, quinoid), 7.07 (1 H, dq, 3J ϭ 6.3 Hz, 4J ϭ 1.7 Hz, quinoid),
5-(3,4-Dihydroxyphenyl)-10,15,20-triphenylporphyrin (24): HPLC:
n-hexane/ethyl acetate ϭ 88:12. Ϫ Yield: 59 mg (46%) of purple
2.21 (3 H, s, ϪMe), Ϫ2.80 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3):
δ ϭ 181.07, 180.97, 142.54, 141.88, 141.85, 141.23, 140.66, 136.05,
134.55, 134.48, ca. 131.2, 129.3, 127.78, 126.78, 126.70, 126.63,
121.33, 120.55, 109.82, 15.93. Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ
416 (5.48), 512 (4.28), 545 (3.81), 589 (3.76), 646 nm (3.49). Ϫ MS;
m/z (%): 661 [M ϩ 2 H ϩ 1]•ϩ (49), 660 [M ϩ 2 H]•ϩ (100), 659
[M ϩ 1]•ϩ (47), 658 [M]•ϩ (54), 330 [M]•ϩϩ (7), 156 (32). Ϫ HRMS:
calcd. for C45H30O2N4 658.23688; found 658.23624.
1
crystals, m.p. Ͼ 330 °C. Ϫ H NMR ([D]6acetone): δ ϭ 9.01 (2 H,
d, β-pyrrole), 8.84 (6 H, s, β-pyrrole), 8.26Ϫ8.21 (6 H, m, o-phenyl),
4
7.86Ϫ7.78 (9 H, m, m- and p-phenyl), 7.74 (1 H, d, J ϭ 2.2 Hz,
arom.), 7.56 (1 H, dd, 3J ϭ 8.2 Hz, 4J ϭ 2.2 Hz, arom.), 7.26 (1
H, d, 3J ϭ 8.2 Hz, arom.), Ϫ2.74 (2 H, s, ϪNH). Ϫ 13C NMR
([D]6acetone): δ ϭ 146.15, 144.22, 142.74, 142.71, 135.10, 135.03,
134.94, 134.21, 131.2, 130.9, 128.62, 127.54, 122.83, 121.45, 120.75,
120.59, 114.46. Ϫ UV/Vis (CH2Cl2): λmax (rel. int.) ϭ 418 (1.000),
515 (0.043), 550 (0.020), 588 (0.015), 647 nm (0.011). Ϫ MS; m/z
(%): 647 [M ϩ 1]•ϩ (48), 646 [M]•ϩ (100), 323 [M]•ϩϩ (7), 110 (4).
Ϫ HRMS: calcd. for C44H30O2N4 646.23688; found 646.23691.
3-(10,15,20-Triphenylporphyrin-5-yl)-1,2-benzoquinone (5): For syn-
thesis of the porphyrin-o-quinone 134 mg of the dimethoxy com-
pound 15 was demethylated. As unsubstituted porphyrin-o-qui-
nones are unstable compounds for characterization, the analogous
porphyrin catechols were first isolated and analyzed spectrosco-
pically. This is a purple, stable compound. Purification was
achieved by column chromatography (dichloromethane/meth-
anol ϭ 20:1, v/v). The relatively low yield can be explained by
formation of other polar products, which were not characterized
further. The NMR studies on the catechol were performed in a
sealed (Ar) NMR tube. Subsequently, the catechol formed was
treated with AgI oxide in the NMR solvent according to the general
procedure. Addition of water-free Na2SO4 ensured complete reac-
tion. Column chromatographic purification (silica, CH2Cl2) was
possible only on a small scale using a cooled column. NMR studies
were performed at Ϫ20 °C.
4-(10,15,20-Triphenylporphyrin-5-yl)-1,2-benzoquinone (3): HPLC:
n-hexane/ethyl acetate ϭ 92:8. Ϫ M.p. 295Ϫ300 °C (dec.). Ϫ 1H
3
NMR (CDCl3): δ ϭ 9.22 (2 H, d, J ϭ 4.8 Hz, β-pyrrole), 8.95 (2
3
H, d, J ϭ 4.8 Hz, β-pyrrole), 8.81 (4 H, s, β-pyrrole), 8.22Ϫ8.16
(6 H, m, o-phenyl), 8.09 (1 H, dd, 3J ϭ 10.0 Hz, 4J ϭ 2.0 Hz,
4
quinoid), 7.82Ϫ7.70 (9 H, m, m- and p-phenyl), 7.14 (1 H, d, J ϭ
2.0 Hz, quinoid), 6.61 (1 H, d, 3J ϭ 10.0 Hz, quinoid), Ϫ2.59 (2
H, s, ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 180.23, 179.86, 153.35,
145.36, 141.57, 140.66, 134.49, 133.38, 131.6, 128.6, 128.06, 126.86,
126.80, 126.10, 122.36, 121.52, 113.24. Ϫ UV/Vis (CH2Cl2): λmax
(rel. int.) ϭ 415 (1.000), 512 (0.049), 544 (0.023), 591 (0.020),
651 nm (0.015). Ϫ MS; m/z (%): 647 [M ϩ 2 H ϩ 1]•ϩ (33), 646
[M ϩ 2 H]•ϩ (63), 644 [M]•ϩ (13.8), 628 [M Ϫ O]•ϩ (7), 323 [M]•ϩϩ
(9), 247 (16), 157 (100), 91 [C7H7]ϩ (60).
5-(2,3-Dihydroxyphenyl)-10,15,20-triphenylporphyrin (25): HPLC:
dichloromethane/ethyl acetate ϭ 96:4. Ϫ Yield: 36 mg (28%), m.p.
Ͼ 330 °C. Ϫ H NMR (CDCl3): δ ϭ 8.86 (8 H, 2 AB, β-pyrrole),
1
Preparation of the (Porphyrinato)zinc(II) Complexes
8.24Ϫ8.17 (6 H, m, o-phenyl), 7.82Ϫ7.72 (9 H, m, m- and p-
3
4
phenyl), 7.55 (1 H, dd, J ϭ 7.5 Hz, J ϭ 1.5 Hz, arom.), 7.25 (1
H, dd, 3J ϭ 8.3 Hz, 4J ϭ 1.5 Hz, arom.), 7.18 (1 H, dd, 3J ϭ 8.3 Hz,
3J ϭ 7.5 Hz, arom.), Ϫ2.81 (2 H, s, ϪNH). Ϫ 13C NMR (CDCl3):
δ ϭ 143.79, 143.23, 141.93, 141.76, 134.57, 134.55, 134.52, 131.5,
131.2, 128.09, 127.84, 126.75, 126.71, 121.10, 120.49, 119.62,
115.57, 111.31. Ϫ UV/Vis (CH2Cl2): λmax (rel. int.) ϭ 417 (1.000),
513 (0.053), 548 (0.021), 589 (0.017), 645 nm (0.013). Ϫ MS; m/z
(%): 647 [M ϩ 1]•ϩ (48), 646 [M]•ϩ (100), 323 [M]•ϩϩ (12), 86 (44).
Ϫ HRMS: calcd. for C44H30O2N4 646.23688; found 646.23632.
General Procedure: In all dimethoxy-protected porphyrin pyrocate-
chols and in the porphyrin-quinone 1, insertion of zinc(II) was
achieved by Method A. Free base porphyrins with more than one
proton on the quinone fragment were converted into the metallo-
porphyrins by Method Β.
Insertion of Zinc with Zinc(II) Acetate (Method A): For preparation
of the zinc(II) complexes 0.05 mmol of the free base porphyrins
was dissolved in 20 mL of dried dichloromethane and treated with
10 mL of a saturated solution of zinc(II) acetate. After 60 min, ex-
cess zinc acetate and acetic acid were extracted with water. After
drying with Na2SO4, the solvent was removed in vacuo and the
product purified by column chromatography and HPLC. The reac-
tion is quantitative.
3-(10,15,20-Triphenylporphyrin-5-yl)-1,2-benzoquinone (5): Brown
1
crystals, m.p. 230Ϫ235 °C (dec.). Ϫ H NMR (CDCl3): δ ϭ 8.94
(2 H, d, 3J ϭ 4.6 Hz, β-pyrrole), 8.83 (2 H, d, 3J ϭ 4.6 Hz, β-
3
pyrrole), 8.76 (4 H, AB, J ϭ 4.4 Hz, β-pyrrole), 8.17Ϫ8.09 (6 H,
m, o-phenyl), 7.74Ϫ7.65 (9H, m, m- and p-phenyl), 7.75 (1 H, d,
3
3
quinoid), 7.58 (1 H, dd, J ϭ 10.2 Hz, J ϭ 6.1 Hz, quinoid), 6.87
Insertion of Zinc with Zinc(II) Oxide and Trifluoroacetic Acid
(1 H, dd, 3J ϭ 10.2 Hz, 3J ϭ 1.5 Hz, quinoid), Ϫ2.87 (2 H, s, (Method B): In this case 0.05 mmol of the free base porphyrins
ϪNH). Ϫ 13C NMR (CDCl3): δ ϭ 180.93, 180.62, 144.15, 141.84, was dissolved in 20 mL of dried dichloromethane and treated with
141.79, 141.27, 140.35, 134.57, 134.49, 131.17, 127.83, 126.80, 200 mg of zinc oxide. After the addition of 4 drops of TFA, the
126.66, 121.12, 120.68, 109.50. Ϫ UV/Vis (CH2Cl2): λmax (rel.
int.) ϭ 417 (1.000), 512 (0.052), 544 (0.023), 589 (0.019), 649 nm
(0.015).
reaction mixture turned green. A color change back to red indic-
ated completion of the reaction. The product was separated from
ZnO and most of the TFA by filtration through a short silica col-
umn. Further purification was performed according to Method A.
4-(10,15,20-Triphenylporphyrin-5-yl)-1,2-benzoquinone (3): As de-
scribed for 5 134 mg of 13 was demethylated with BBr3 followed
by a similar purification procedure. The porphyrin pyrocatechol
24 is an extremly air-sensitive substance. NMR investigations were
{5-(2,5-Di-tert-butyl-3,4-dimethoxyphenyl)-10,15,20-triphenyl-
porphyrinato}zinc(II) (16): Using Method A 39 mg of the free base
11 was converted into the zinc(II) complex. Ϫ HPLC: dichlorome-
Eur. J. Org. Chem. 2000, 2303Ϫ2314
2311

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
thane/n-hexane ϭ 70:30. Purple crystals, m.p. Ͼ 330 °C. Ϫ 1H 585 nm (3.52). Ϫ MS; m/z (%): 752 [M ϩ 2]•ϩ (1), 751 [M ϩ 1]•ϩ
3
NMR (CDCl3): δ ϭ 8.92 (4 H, AB, J ϭ 4.6 Hz, β-pyrrole), 8.89
(2 H, d, 3J ϭ 4.7 Hz, β-pyrrole), 8.85 (2 H, d, 3J ϭ 4.7 Hz, β-
pyrrole), 8.33Ϫ8.29 (2 H, m, o-phenyl), 8.28Ϫ8.25 (1 H, m, o-
phenyl), 8.19Ϫ8.13 (3 H, m, o-phenyl), 7.78Ϫ7.69 (9 H, m, m- and
p-phenyl), 7.59 (1 H, s, arom.), 4.14 (3 H, s, ϪOMe), 4.13 (3 H, s,
ϪOMe), 1.39 (9 H, s, tBu), 0.72 (9 H, s, tBu). Ϫ 13C NMR
(CDCl3): δ ϭ 153.50, 153.19, 151.26, 150.08, 150.00, 149.99,
142.88, 142.83, 142.81, 136.92, 134.78, 134.50, 134.45, 134.36,
134.28, 132.16, 131.82, 131.72, 129.83, 127.42, 126.52, 126.50,
124.64, 120.96, 120.76, 59.80, 59.54, 37.73, 34.67, 32.38, 30.69. Ϫ
UV/Vis (CH2Cl2): λmax (lg ε) ϭ 422 (5.59), 513 (3.41), 551 (4.27),
591 nm (3.50). Ϫ MS; m/z (%): 850 [M ϩ 2]•ϩ (83), 849 [M ϩ 1]•ϩ
(73), 848 [M]•ϩ (100), 791 [M Ϫ Zn]•ϩ (6), 57 [C4H9]ϩ (9). Ϫ
HRMS: calcd. for C54H48O2N4Zn 848.30687; found 848.30662.
(1), 750 [M]•ϩ (1), 44 [C2H4O]ϩ (100). Ϫ HRMS: calcd. for
C47H34O2N4Zn 750.19732; found 750.19744.
{5-(2,3-Dimethoxyphenyl)-10,15,20-triphenylporphyrinato}zinc(II)
(20): Free base 15 (34 mg) was treated according to Method A and
gave red-purple crystals. Ϫ HPLC: n-hexane/ethyl acetate ϭ 85:15.
1
Ϫ M.p. Ͼ 330 °C. Ϫ H NMR (CDCl3): δ ϭ 8.95, 8.92 (8 H, AB,
β-pyrrole), 8.28Ϫ8.18 (6 H, m, o-phenyl), 7.80Ϫ7.71 (9 H, m, m-
and p-phenyl), 7.67 (1 H, dd, 3J ϭ 7.5 Hz, 4J ϭ 1.5 Hz, arom.),
7.38 (1 H, dd, 3J ϭ 8.4 Hz, 3J ϭ 7.5 Hz, arom.), 7.32 (1 H, dd,
3J ϭ 8.4 Hz, 4J ϭ 1.5 Hz, arom.), 4.09 (3 H, s, ϪOMe), 3.21 (3 H, s,
ϪOMe). Ϫ 13C NMR (CDCl3): δ ϭ 152.20, 150.24, 150.16, 149.98,
149.46, 142.85, 142.81, 136.88, 134.45, 134.42, 132.16, 131.92,
131.84, 131.66, 127.86, 127.41, 126.50, 121.92, 121.24, 120.96,
116.25, 112.44, 60.80, 56.02. Ϫ UV/Vis (CH2Cl2): λmax (rel. int.) ϭ
419 (1.000), 511 (0.006), 547 (0.039), 584 nm (0.007). Ϫ MS; m/z
(%): 738 [M ϩ 2]•ϩ (68), 737 [M ϩ 1]•ϩ (50), 736 [M]•ϩ (100), 721
[M Ϫ CH3]•ϩ (7). Ϫ HRMS: calcd. for C46H32O2N4Zn 736.18167;
found 736.18196.
{5-(2,5-Dimethyl-3,4-dimethoxyphenyl)-10,15,20-triphenyl-
porphyrinato}zinc(II) (17): Free base porphyrin 12 (35 mg) was
treated according to Method A and yielded the zinc(II) complex as
red-purple crystals. Ϫ HPLC: n-hexane/ethyl acetate ϭ 92:8, m.p.
Ͼ 330 °C. Ϫ 1H NMR (CDCl3): δ ϭ 8.92 (4 H, AB, β-pyrrole),
3
8.90 (2 H, d, 3J ϭ 4.7 Hz, β-pyrrole), 8.84 (2 H, d, J ϭ 4.7 Hz, β-
Synthesis of the Zinc(II) Complexes of the Demethylation Products
of 11: For preparation of larger amounts of the zinc(II) complexes
of the tert-butylated porphyrin-o-quinone 1 and its decomposition
products 32 and 33, the mixture resulting from the demethylation
of 11 was treated with zinc(II) acetate according to Method A. As
all products were stable compounds, the individual zinc(II) com-
plexes could be separated from each other by HPLC. Ϫ The zinc-
(II) complexes could also be prepared from the individual free base
porphyrins. During metallation of the diketone 32 two different
metal complexes [the (E) and (Z) stereoisomers] were formed (1:3.2
ratio). The (Z) isomer 43 could be obtained in its pure form by
treating the mixture with light for 2 d.[41] HPLC: n-hexane/ethyl
acetate ϭ 90:10.
pyrrole), 8.25Ϫ8.17 (6 H, m, o-phenyl), 7.78Ϫ7.70 (9 H, m, m- and
p-phenyl), 7.60 (1 H, q, 4J ϭ 1.9 Hz, arom.), 4.14 (3 H, s, ϪOMe),
4.06 (3 H, s, ϪOMe), 2.44 (3 H, s, ϪMe), 1.89 (3 H, s, ϪMe). Ϫ
13C NMR (CDCl3): δ ϭ 151.19, 150.42, 150.22, 150.16, 150.14,
150.12, 142.80, 142.75, 138.14, 134.43, 134.37, 132.11, 131.91,
131.83, 131.65, 131.55, 127.45, 127.04, 126.52, 120.10, 120.94,
119.73, 60.51, 60.49, 15.92, 14.63. Ϫ UV/Vis (CH2Cl2): λmax (lg
ε) ϭ 419 (5.69), 510 (3.46), 548 (4.32), 584 nm (3.52). Ϫ MS; m/z
(%): 766 [M ϩ 2]•ϩ (73), 765 [M ϩ 1]•ϩ (59), 764 [M]•ϩ (100), 749
[M Ϫ CH3]•ϩ (6), 719 [M Ϫ 3 CH3]•ϩ (10), 662 (20), 530 (23),
382 (9), 57 (45). Ϫ HRMS: calcd. for C48H36O2N4Zn 764.21297;
found 764.21557.
{5-(3,6-Di-tert-butyl-1,2-dioxocyclohexa-3,5-dien-4-yl)-10,15,20-
triphenylporphyrinato}zinc(II) (6): Reddish brown crystals, m.p.
{5-(3,4-Dimethoxyphenyl)-10,15,20-triphenylporphyrinato}zinc(II)
(18): The zinc(II) complex was prepared using 34 mg of the dime-
thoxyporphyrin 13 and following Method A. HPLC: n-hexane/
3
183Ϫ185 °C. Ϫ 1H NMR (CDCl3): δ ϭ 9.30 (2 H, d, J ϭ 4.5 Hz,
β-pyrrole), 9.05 (2 H, d, 3J ϭ 4.5 Hz, β-pyrrole), 8.94 (4 H, AB,
3J ϭ 4.5 Hz, β-pyrrole), 8.34Ϫ8.29 (2 H, m, o-phenyl), 8.28Ϫ24 (1
H, m, o-phenyl), 8.18Ϫ8.10 (3 H, m, o-phenyl), 7.83Ϫ7.70 (9 H,
m, m- and p-phenyl), 7.58 (1 H, s, quinoid), 1.22 (9 H, s, tBu), 0.69
(9 H, s, tBu). Ϫ 13C NMR (CDCl3): δ ϭ 185.26, 181.80, 150.61,
150.56, 150.32, 148.72, 148.67, 147.01, 143.47, 142.44, 142.33,
142.32, 134.42, 134.35, 134.26, 133.21, 132.39, 129.72, 127.71,
127.64, 126.69, 126.64, 126.61, 121.98, 121.57, 118.73, 37.82, 34.70,
30.98, 29.16. Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ 418 (5.42), 553
(3.99), 597 nm (3.42). Ϫ MS; m/z (%): 820 [M ϩ 2]•ϩ (6), 819 [M
ϩ 1]•ϩ (1), 818 [M]•ϩ (2), 792 [M Ϫ CO]•ϩ (22), 708 [M Ϫ 2 CO
ϪC4H8]•ϩ (12), 191 (100). Ϫ HRMS: calcd. for C52H42O2N4Zn
818.25992; found 818.25968.
1
ethyl acetate ϭ 84:16. Purple crystals, m.p. Ͼ 330 °C. Ϫ H NMR
3
(CDCl3): δ ϭ 8.92 (2 H, AB, J ϭ 4.7 Hz, β-pyrrole), 8.89Ϫ84 (6
H, AB, s, β-pyrrole), 8.16Ϫ8.10 (6 H, m, o-phenyl), 7.72 (1 H, d,
3J ϭ 2.0 Hz, arom.), 7.70Ϫ7.62 (9 H, m, m- and p-phenyl), 7.69 (1
H, arom.), 7.13 (1 H, d, 3J ϭ 8.1 Hz, arom.), 4.06 (3 H, s, ϪOMe),
3.87 (3 H, s, ϪOMe). Ϫ 13C NMR (CDCl3): δ ϭ 150.44, 150.18,
150.15, 148.55, 146.80, 142.75, 135.36, 134.38, 131.98, 127.47,
127.16, 126.53, 121.12, 121.10, 120.88, 118.09, 109.23, 56.08, 56.04.
Ϫ UV/Vis (CH2Cl2): λmax (rel. int.) ϭ 420 (1.000), 511 (0.008), 547
(0.050), 586 nm (0.010). Ϫ MS; m/z (%): 738 [M ϩ 2]•ϩ (72), 737
[M ϩ 1]•ϩ (51), 736 [M]•ϩ (100), 721 [M Ϫ CH3]•ϩ (5), 368 [M]•ϩϩ
(8).
Ϫ HRMS: calcd. for C46H32O2N4Zn 736.18167; found
736.18153.
{5-(2,3-Dimethoxy-4-methylphenyl)-10,15,20-triphenyl-
porphyrinato}zinc(II) (19): The substituted dimethoxyporphyrin
(34 mg) was treated with zinc(II) acetate according to Method A.
Ϫ HPLC: n-hexane/ethyl acetate ϭ 90:10. Red-purple crystals, m.p.
{5-(3,6-Di-tert-butyl-2,7-dihydro-2,7-dioxooxepin-4-yl)-10,15,20-
triphenylporphyrinato}zinc(II) (39): Purple crystals, m.p. Ͼ 330 °C.
Ϫ H NMR (CDCl3): δ ϭ 9.20 (2 H, br. s, β-pyrrole), 9.04 (2 H,
1
3
3
d, J ϭ 4.7 Hz, β-pyrrole), 8.94 (4 H, AB, J ϭ 4.7 Hz, β-pyrrole),
Ͼ 330 °C. Ϫ 1H NMR (CDCl3): δ ϭ 8.95 (8 H, AB, β-pyrrole), 8.35Ϫ8.30 (2 H, m, o-phenyl), 8.30Ϫ8.26 (1 H, m, o-phenyl),
8.26Ϫ8.21 (3 H, m, o-phenyl), 8.21Ϫ8.17 (3 H, m, o-phenyl),
7.75Ϫ7.66 (9 H, m, m- and p-phenyl), 7.76 (1 H, d, arom.), 7.20 (1 phenyl), 7.26 (1 H, s, olef.), 1.23 (9 H, s, tBu), 0.71 (9 H, s, tBu).
H, d, 3J ϭ 7.6 Hz, arom.), 4.01 (3 H, s, ϪOMe), 3.20 (3 H, s, 13C NMR (CDCl3): δ ϭ 163.97, 162.35, 150.51, 150.34, 150.13,
ϪOMe), 2.55 (3 H, s, ϪMe). Ϫ 13C NMR (CDCl3): δ ϭ 153.29, 146.91, 142.45, 142.30, 141.13, 137.36, 134.44, 134.41, 134.35,
8.15Ϫ8.09 (3 H, m, o-phenyl), 7.84Ϫ7.69 (9 H, m, m- and p-
Ϫ
150.81, 150.45, 150.22, 150.19, 150.06, 142.80, 134.82, 134.42,
134.40, 132.65, 132.23, 131.95, 131.91, 131.67, 130.25, 127.46,
134.35, 134.25, 133.24, 132.36, 132.25, 130.09, 127.69, 127.63,
126.65, 126.59, 122.13, 121.50, 113.67, 37.53, 36.14, 30.31, 29.01.
126.52, 123.84, 121.27, 121.03, 116.57, 60.76, 60.47, 16.30. Ϫ UV/ Ϫ UV/Vis (CH2Cl2): λmax (rel. int.) ϭ 421 (1.000), 513 (0.006), 549
Vis (CH2Cl2): λmax (lg ε) ϭ 419 (5.76), 511 (3.46), 547 (4.34),
(0.041), 588 nm (0.007). Ϫ MS; m/z (%): 836 [M ϩ 2]•ϩ (1), 835 [M
2312
Eur. J. Org. Chem. 2000, 2303Ϫ2314

Porphyrin-o-quinones
FULL PAPER
ϩ 1]•ϩ (1), 834 [M]•ϩ (2), 806 [M Ϫ CO]•ϩ (2), 790 [M Ϫ CO
ϪO]•ϩ (100), 733 [M Ϫ CO Ϫ O Ϫ C4H9]•ϩ (96), 718 [M Ϫ 2
122.24, 121.53, 110.75, 16.09. Ϫ UV/Vis (CH2Cl2): λmax (lg ε) ϭ
419 (5.46), 510 (3.57), 547 (4.22), 585 nm (3.52). Ϫ MS; m/z (%):
C4H9]•ϩ (56). Ϫ HRMS: calcd. for C52H42O3N4Zn 834.25484; 724 [M ϩ 2 H ϩ 2]•ϩ (3), 723 [M ϩ 2 H ϩ 1]•ϩ (2), 722 [M ϩ 2
found 834.25478.
H]•ϩ (4), 157 (48), 44 [C2H4O]ϩ (100). Ϫ HRMS: calcd. for
C45H30O2N4Zn 722.16602; found 722.16766 as pyrocatechol.
[5-{(E)-2,2,7,7-Tetramethyl-3,6-dioxooct-4-en-4-yl}-10,15,20-tri-
phenylporphyrinato]zinc(II) (43): 1H NMR (CDCl3): δ ϭ 9.70 (2 H,
d, 3J ϭ 4.7 Hz, β-pyrrole), 9.03 (2 H, d, 3J ϭ 4.7 Hz, β-pyrrole),
8.93 (4 H, AB, 3J ϭ 4.6 Hz, β-pyrrole), 8.38Ϫ8.34 (2 H, m, o-
phenyl), 8.17Ϫ8.13 (1 H, m, o-phenyl), 8.12Ϫ8.05 (3 H, m, o-
phenyl), 7.82Ϫ7.69 (9 H, m, m- and p-phenyl), 7.53 (1 H, s, olef.),
1.45 (9 H, s, tBu), 0.81 (9 H, s, tBu). Ϫ 13C NMR (CDCl3): δ ϭ
213.28, 205.65, 157.43, 150.51, 150.16, 149.06, 142.66, 142.42,
135.37, 134.42, 134.25, 132.90, 132.41, 132.13, 131.48, 127.67,
126.64, 126.52, 122.39, 121.72, 114.19, 45.65, 43.72, 27.03, 26.37.
Acknowledgments
This work was generously supported by grants from the Deutsche
Forschungsgemeinschaft (Se543/2-4, SFB 337, and Heisenberg fel-
lowship Se543/3-1) and the Fonds der Chemischen Industrie.
[1] [1a]
D. Gust, T. A. Moore, Adv. Photochem. 1991, 16, 1Ϫ65. Ϫ
[1b] M. R. Wasielewski, Chem. Rev. 1992, 92, 435Ϫ461. Ϫ [1c] H.
Kurreck, M. Huber, Angew. Chem. 1995, 107, 929Ϫ947; Angew.
[1d]
Chem. Int. Ed. Engl. 1995, 34, 849Ϫ866. Ϫ
J. S. Connolly,
[5-{(Z)-2,2,7,7-Tetramethyl-3,6-dioxooct-4-en-4-yl}-10,15,20-tri-
phenylporphyrinato]zinc(II) (44): Purple crystals, m.p. Ͼ 330 °C. Ϫ
J. R. Bolton, in: Photoinduced Electron Transfer Part D (Eds.:
M. A. Fox, M. Chanon), Elsevier, Amsterdam, 1988, p.
303Ϫ393.
3
1H NMR (CDCl3): δ ϭ 9.32 (2 H, d, J ϭ 4.7 Hz, β-pyrrole), 8.95
[2] [2a]
J. L. Y. Kong, P. A. Loach, J. Heterocycl. Chem. 1980, 17,
(2 H, d, 3J ϭ 4.7 Hz, β-pyrrole), 8.89 (4 H, AB, 3J ϭ 4.5 Hz, β-
pyrrole), 8.30Ϫ8.24 (3 H, m, o-phenyl), 8.17Ϫ8.13 (2 H, m, o-
phenyl), 8.12Ϫ8.05 (1 H, m, o-phenyl), 8.08 (1 H, s, olef.),
7.83Ϫ7.69 (9 H, m, m- and p-phenyl), 1.16 (9 H, s, tBu), 0.78 (9
H, s, tBu). Ϫ 13C NMR (CDCl3): δ ϭ 209.63, 204.98, 154.03,
150.33, 150.03, 149.97, 148.77, 142.66, 142.42, 134.48, 134.35,
132.72, 132.06, 131.89, 130.65, 130.54, 127.48, 126.52, 126.48,
121.92, 121.26, 112.87, 45.90, 44.63, 27.75, 26.16. Ϫ UV/Vis
(CH2Cl2): λmax (rel. int.) ϭ 422 (1.000), 518 (0.014), 553 (0.060),
594 nm (0.016). Ϫ MS; m/z (%): 796 [M ϩ 2]•ϩ (20), 795 [M ϩ 1]•ϩ
(15), 794 [M]•ϩ (26), 778 [M Ϫ O]•ϩ (11), 709 [M Ϫ CO ϪC4H9]•ϩ
(18), 624 [M Ϫ 2 CO Ϫ 2 C4H9]•ϩ (31), 149 (100), 57 [C4H9]ϩ (29).
Ϫ HRMS: calcd. for C50H42O2N4Zn 794.25992; found 794.25972.
[2b]
737Ϫ744. Ϫ
D. Gust, T. A. Moore, P. A. Liddell, G. A.
Nemeth, L. R. Makings, A. L. Moore, D. Barrett, P. J. Pessiki,
´
R. V. Bensasson, M. Rougee, C. Chachaty, F. C. De Schryver,
M. van der Auweraer, A. R. Holzwarth, J. S. Connolly, J. Am.
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[3] [3a]
J. von Gersdorff, M. Huber, H. Schubert, D. Niethammer,
B. Kirste, M. Plato, K. Möbius, H. Kurreck, R. Eichberger,
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[3b]
Angew. Chem. Int. Ed. Engl. 1990, 29, 670Ϫ672. Ϫ
H. A.
Staab, J. Weiser, M. Futscher, G. Voit, A. Rückemann, C. An-
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J. Dalton, L. R. Milgrom, J. Chem. Soc., Chem. Commun.
[4b]
1979, 609Ϫ610. Ϫ
R. A. Cormier, M. R. Posey, W. L. Bell,
H. N. Fonda, J. S. Connolly, Tetrahedron 1989, 45, 4831Ϫ4843.
[4c]
Ϫ
J. L. Sessler, M. R. Johnson, Recl. Trav. Chim. Pays-Bas
1987, 106, 222.
[5]
[6]
S. Runge, M. O. Senge, Z. Naturforsch. 1998, 53b, 1021Ϫ1030.
{5-(3,6-Dimethyl-1,2-dioxocyclohexa-3,5-dien-4-yl)-10,15,20-tri-
phenylporphyrinato}zinc(II) (7): 34 mg of the free base was treated
in dichloromethane with a methanol solution of zinc(II) acetate. Ϫ
HPLC: n-hexane/diisopropyl ether ϭ 80:20. Reddish brown crys-
tals, m.p. 320 °C (dec.). Ϫ 1H NMR (CDCl3): δ ϭ 9.20 (2 H, d,
[6a] H. Dieks, M. O. Senge, B. Kirste, H. Kurreck, J. Org. Chem.
[6b]
1997, 62, 8666Ϫ8680. Ϫ
R. A. Cormier, M. R. Posey, W.
L. Bell, H. N. Fonda, J. S. Connolly, Tetrahedron 1989, 45,
[6c]
4831Ϫ4843. Ϫ
M. R. Wasielewski, M. P. Niemczyk, D. G.
Johnson, W. A. Svec, D. W. Minsek, Tetrahedron 1989, 45,
3
3J ϭ 4.6 Hz, β-pyrrole), 8.97 (2 H, d, J ϭ 4.6 Hz, β-pyrrole), 8.86
4785Ϫ4806.
[7]
[8]
K. M. Giangiacomo, P. L. Dutton, Proc. Natl. Acad. Sci. USA
1989, 86, 2658Ϫ2662.
(4 H, s, β-pyrrole), 8.18Ϫ8.14 (2 H, m, o-phenyl), 8.14Ϫ8.07 (4 H,
m, o-phenyl), 7.73Ϫ7.62 (9 H, m, m- and p-phenyl), 7.57 (1 H, q,
4J ϭ 1.4 Hz, quinoid), 2.02 (3 H, s, ϪMe), 1.70 (3 H, s, ϪMe). Ϫ
13C NMR (CDCl3): δ ϭ 182.22, 181.09, 150.69, 150.56, 150.43,
150.41, 146.58, 142.69, 142.36, 142.27, 137.11, 134.35, 134.31,
133.42, 132.54, 132.39, 132.39, 129.35, 127.73, 127.68, 126.69,
126.65, 126.61, 122.44, 121.73, 114.82, 15.31, 14.55. Ϫ UV/Vis
(CH2Cl2): λmax (lg ε) ϭ 415 (5.62), 488 (sh), 548 (4.14), 620 nm
(3.61). Ϫ MS; m/z (%): 737 [M ϩ 2 H ϩ 1]•ϩ (53), 736 [M ϩ 2
H]•ϩ (100), 694 [M Ϫ CO, Ϫ CH3]•ϩ (33), 207 (82), 156 (68), 156
(78). Ϫ HRMS: calcd. for C46H32O2N4Zn 736.18167; found
736.16638 as pyrocatechol.
T. Nagaoka, S. Okazaki, T. Fujinaga, J. Electroanal. Chem.
1982, 133, 89Ϫ99.
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H. Kurreck, S. Aguirre, S. N. Batchelor, H. Dieks, J. von
Gersdorff, C. V. M. Kay, H. Mößler, H. Newman, D. Niet-
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[9b]
1995, 38, 91Ϫ110. Ϫ
M. Speck, M. O. Senge, A. Schäfer,
H. Kurreck, Bioorg. Med. Chem. Lett. 1997, 7, 2589Ϫ2592.
G. R. Deviprasad, B. Keshavan, F. D’Souza, J. Chem. Soc.,
Perkin Trans. 1 1998, 3133Ϫ3135.
[10]
[11]
[12]
[13]
J. von Gersdorff, B. Kirste, H. Kurreck, Liebigs Ann. Chem.
1993, 897Ϫ903.
J. S. Lindsey, I. C. Schreiman, H. C. Hsu, P. C. Kearney, A.
M. Marguerettaz, J. Org. Chem. 1987, 52, 827Ϫ836.
A. Rieche, H. Gross, E. Höft, Chem. Ber. 1960, 93, 88Ϫ94.
{5-(3-Methyl-1,2-dioxocyclohexa-3,5-dien-6-yl)-10,15,20-triphenyl-
porphyrinato}zinc(II) (8): For the synthesis of the zinc(II) complex
33 mg of the respective free base porphyrin-o-quinone 4 was treated
according to Method B. Ϫ HPLC: dichloromethane/ethyl acetate ϭ
98:2. Reddish brown crystals, m.p. 305Ϫ308 °C (dec.). Ϫ 1H NMR
[14] [14a]
H. Fischer, W. Neumann, Justus Liebigs Ann. Chem. 1932,
[14b]
494, 225Ϫ245. Ϫ
J. W. Buchler, L. Puppe, Justus Liebigs
Ann. Chem. 1970, 740, 142Ϫ163.
[15]
[16]
R. Hollenstein, W. von Philipsborn, Helv. Chim. Acta 1973,
56, 320Ϫ322.
3
(CDCl3): δ ϭ 9.13 (2 H, AB, J ϭ 4.6 Hz, β-pyrrole), 8.98 (2 H,
The complete assignment of all resonances can be found in:
M. Speck, Synthese, Reaktionen und Strukturanalyse kovalent
verknüpfter Porphyrin-o-chinone als Modellverbindungen für die
Photosynthese, Shaker Verlag, 1999, p. 334, ISBN 3-8265-
4600-8.
The dihedral angles were determined from a single crystal X-
ray structure analysis of the the protected porphyrin catechols.
M. O. Senge, M. Speck, A. Wiehe, S. Aguirre, H. Dieks, H.
Kurreck, Photochem. Photobiol. 1999, 70, 206Ϫ216.
AB, 3J ϭ 4.6 Hz, β-pyrrole), 8.92 (4 H, AB, 3J ϭ 4.6 Hz, β-pyrrole),
8.24Ϫ8.14 (6 H, m, o-phenyl), 7.80Ϫ7.68 (9 H, m, m- and p-
phenyl), 7.72 (1 H, quinoid), 7.36 (1 H, dq, 3J ϭ 6.6 Hz, 4J ϭ
1.6 Hz, quint), 2.33 (3 H, s, ϪMe). Ϫ 13C NMR (CDCl3): δ ϭ
181.34, 181.24, 150.50, 150.17, 150.15, 149.40, 142.54, 142.52,
142.03, 142.01, 140.60, 136.32, 134.51, 134.41, 134.33, 134.29,
132.90, 132.32, 132.07, 130.14, 127.59, 126.66, 126.59, 126.50,
[17]
Eur. J. Org. Chem. 2000, 2303Ϫ2314
2313

M. Speck, H. Kurreck, M. O. Senge
FULL PAPER
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Y. Tatsuno, C. Nakamura, T.
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The assignment of the isomers was confirmed by non broad-
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Received June 7, 1999
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2314
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