The synthesis and properties of bis-1,1′-(porphyrinyl)ferrocenes

Article abstract of DOI:10.1039/b505366h

Ferrocene-bridged bisporphyrins have been synthesized by the condensation of corresponding dipyrromethane-derived diols with a bisdipyrromethane. Purification of the final compounds has been achieved without chromatography. The specific geometry of these

Full text of DOI:10.1039/b505366h

View Article Online / Journal Homepage / Table of Contents for this issue
A R T I C L E
The synthesis and properties of bis-1,1ꢀ-(porphyrinyl)ferrocenes†
Beata Koszarna,a Holger Butenscho¨n*b and Daniel T. Gryko*a
a Institute of Organic Chemistry of the Polish Academy of Science, Kasprzaka 44/52, 01-224
Warsaw, Poland. E-mail: daniel@icho.edu.pl; Fax: 48 22 6326681; Tel: 48 22 6323221
b Universita¨t Hannover, Institut fu¨r Organische Chemie, Schneiderberg 1B, D-30167 Hannover.
E-mail: holger.butenschoen@mbox.oci.uni-hannover.de; Fax: 49 511 762 4616;
Tel: 49 5111 762 4661
Received 18th April 2005, Accepted 25th May 2005
First published as an Advance Article on the web 16th June 2005
Ferrocene-bridged bisporphyrins have been synthesized by the condensation of corresponding
dipyrromethane-derived diols with a bisdipyrromethane. Purification of the final compounds has been achieved
without chromatography. The specific geometry of these bisporphyrins makes them valuable starting points for
building complex molecular and supramolecular structures. In particular it provides a core to which multiple sites of
attractive intermolecular interactions can be attached thereby creating compounds predisposed to form complex
networks by association. We have studied the structure of bis-1,1ꢀ-(porphyrinyl)ferrocenes by 1H NMR, UV-Vis and
electrochemistry. Results have shown that complex dynamic processes occur in these molecules (which may involve
conformers, formation of H-aggregates and tautomers) and that they have non-typical electrochemical behaviour.
to construct an electrochemically tunable ferrocene–porphyrin
Introduction
supramolecular polymeric system. Covalent polymeric systems
The development of supramolecular chemistry in the past years
encompassing ferrocenyl units within photonic crystals have
has relied on the availability of simple components possessing
been recently shown to have interesting material properties.9
suitable molecular architectures.1 Multiporphyrin structures
have recently attracted enormous attention due to their po-
Results and discussion
tential material properties in the fields of sensors, artificial
photosynthesis, etc.2 Their spatial orientation could either be
totally fixed or absolutely flexible. We have become interested in
studying a possible compromise between completely rigid and
flexible spacer linking porphyrin moieties, in particular linkers,
which would allow for limited hinge-like molecular flexibility.
Such molecules bearing various chemical handles in suitable
positions are excellent building blocks for the construction of
elaborate supramolecular assemblies. We have chosen ferrocene
as a candidate for the linker, since the two cyclopentadienyl (Cp)
rings are oriented parallel to each other and rotate almost freely
even at low temperature (an iron atom constitutes a ‘molecular
ball bearing’).3 Ferrocene and its derivatives are also attracting
much attention nowadays from the viewpoint of supramolec-
ular chemistry, e.g. as redox-active ionophores and molecular
receptors,4,5 and 1,1ꢀ-disubstitued ferrocenes have been utilized
to construct several molecular devices of unique functions.6
The specific geometry of the ferrocene system might allow the
adoption of unusual conformations of molecules bearing bulky
groups on their peripheries.7 In particular, a ferrocene moiety
directly attached to the porphyrin ring would cause special
orientations of both fragments. Many examples of this type
of structure have been synthesized within the past 20 years,8
and have found applications, for example, in molecular memory
studies.8h An architectural scheme in which two porphyrins are
connected by a ferrocene hinge is very intriguing and we are
interested in the effect of such a molecular arrangement on
the conformation of these molecules and their properties. The
objective of this work was to develop a efficient synthetic route
to 1,1ꢀ-(porphyrinyl)ferrocenes and to study their fundamental
properties. The ultimate goal of this project is to utilize and
fine tune possible electronic interaction between the electro- and
photo-active subunits by possible p–p stacking interactions with
a specific geometry in molecular electronics and in particular
The simple retrosynthetic analysis revealed that bis-1,1ꢀ-
(porphyrinyl)ferrocenes could be synthesized from the respective
ferrocene-derived bisdipyrromethane (DPM) 2, which in turn
could be synthesized from the respective 1,1ꢀ-diformylferrocene
1
10 using the general procedure of Lindsey and co-workers.11 The
reaction of 1 performed in the presence of 50 equiv. of pyrrole
gave rise to the desired DPM 2 in 40% yield (Scheme 1).
Scheme 1
The following macrocyclization reaction was carried out
using Lindsey’s procedure for the synthesis of meso-substituted
porphyrins bearing up to four different substituents.12 The
reduction of readily available diacyldipyrromethanes12,13 with
NaBH4 afforded unstable diols which could be transformed
into porphyrins using a catalytic amount of trifluoroacetic acid
(TFA).
The first ferrocenylbisporphyrin 5 was synthesized in 18%
yield using the above procedure starting from diketone 4, the
yield of which should be considered as high given that two
porphyrin rings were simultaneously closed (Scheme 2). The
choice of substituents was based on the option to further
functionalise the para position in the C6F5 group.14
During our attempts to purify compound 5 we found that
it behaves in an unusual way during column chromatography.
Compound 5 could not be eluted from the column unless a
small amount of THF was added, although the polarity of 5
is very low. While trying to solve this problem we found that
bisporphyrin 5 could be purified by crystallization directly from
† Electronic supplementary information (ESI) available: 1H NMR
spectra of porphyrins 6 and 7 and molecular modelling of porphyrin
7. See http://www.rsc.org/suppdata/ob/b5/b505366h/
2 6 4 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

View Article Online
In order to check the generality of the procedure for the
synthesis of bisporphyrinylferrocenes we decided to prepare
two additional compounds bearing different substituents. The
simplicity of the purification of 5 provided us with additional
motivation to check if this is a general behaviour for this class
of compounds. Thus, via an analogous process we synthesized
bisporphyrins 6 and 7 (Fig. 1) possessing different substituents.
We found that these compounds strongly resembled porphyrin
5 (both bisporphyrins could not be purified on silica or
alumina), and that both of them were easily purified via double
crystallization. Bisporphyrins were obtained in yields of 17 and
10% respectively. Bisporphyrin 7 was subsequently metallated
with Zn(OAc)2 under standard conditions to afford Zn-7 in 86%
yield (Fig. 1).
Fig. 1 Structure of bisporphyrins 6, 7 and Zn-7.
1
Standard H NMR spectra of all three bisporphyrins 5–7
showed significant line broadening. In particular, signals derived
from b-pyrrole protons and NH protons were broadened. One
has to note that there is no such effect for simple mono-
ferrocenylporphyrins at room temperature.8b,g,16 These intriguing
results, which indicated some complex dynamic processes taking
place, prompted us to study the variable-temperature 1H NMR
spectra. The most interesting regions are shown in Figs. 2 and
3, and full spectra are given in the ESI.† For both porphyrins
studied (6 and 7), coalescence of the NH resonances occurred at
333 K (500 MHz, Dd 0.6–0.8 ppm). For both 6 and 7, the spectra
recorded at 273 K show the presence of two NH signals. The only
difference between 6 and 7 is the peripheral substituents at the
phenyl ring (Me for 6, t-Bu for 7, Fig. 1). Yet, there was a striking
difference in their variable-temperature 1H NMR spectra. While
porphyrin 6 gave narrow lines of the b-pyrrole resonances at
333 K, spectra recorded for porphyrin 7 even at 363 K still had
broad lines. The other striking difference could be found in the
signals of the Fc protons (see ESI†). For compound 6, lines
were pretty narrow even at 273 K, whereas for 7 line broadening
is remarkably significant at this temperature. In general, this
kind of spectrum suggested the presence of an equilibrium
of two conformers with slow exchange relative to the NMR
Scheme 2
the reaction mixture. Double crystallization gave pure materials.
Purification of porphyrins in such a way without at least silica
pad filtration is very rare (generally, chromatographic separation
is the typical bottleneck in the porphyrin synthesis).15
Needless to say that such exceptionally simple purification
procedure greatly expands the preparative possibilities due to
the fact that it allows for increasing the scale of the experiments.
Amounts of bisporphyrin 5 which could be easily obtained in
this manner were in the range 300–500 mg.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5
2 6 4 1

View Article Online
Fig. 3 Variable-temperature 1H NMR spectra of 7 (aromatic and NH
regions).
this bond for bis-1,1ꢀ-(porphyrinyl)ferrocenes. Free rotation of
the ferrocene moiety with the attached porphyrin over the
second porphyrin should be rather difficult. On the other
hand, simple 1,1ꢀ-disubstituted ferrocenes with the possibility
of p-stacking interactions between aromatic substituents can
posses a p-stacking conformation.20 We may assume that for
bis-1,1ꢀ-(porphyrinyl)ferrocenes free rotation of the substituted
cyclopentadienyl ligands is not possible, presumably due to their
restricted conformation (Fig. 1). This complex picture could be
clarified to a certain extent by X-ray analysis. However, so far
it has not been possible to obtain crystals of any bisporphyrins
suitable for an X-ray crystal structure analysis.
UV-Vis data showed a small blue shift for the Soret band
in comparison with directly-bonded mono-ferroceneporphyrins
(410–418 nm vs. 422 nm). A hypsochromic shift of the Soret
band of these porphyrins could result in the formation of
H-aggregates.21 Molecular modelling using Hyperchem was
performed to test this hypothesis (see ESI†). The results obtained
showed a clear preference for a linear monomer (dihedral angle
Por–Cp–Cpꢀ–Porꢀ of 180◦) in comparison to a kinked conforma-
tion (e.g. with a dihedral angle of ca. 104◦). Estimations of dimer
formation again show a strong preference for an ‘open dimer’,22
which as in H-aggregates should have a blue-shifted absorption.
Extension of the open dimers to oligomers readily explains the
broad NMR spectra and the sharpening of the signals upon
increasing the temperature which correlates with deaggregation.
Fig. 2 Variable-temperature 1H NMR spectra of 6 (aromatic and NH
regions).
time scale. In unsubstituted ferrocene, the barrier of internal
rotation of the Cp rings is estimated to be only one third of
that in ethane.17 This means that in the usual temperature range
for NMR investigation the Cp rings rotate freely. It is worthy
1
to emphasize that variable-temperature H NMR experiments
allowed us to observe two distinct conformational processes
for b,bꢀ-fused ferrocene–porphyrins, one of them arising from
ferrocene rotations.18
Additionally, for this type of trans-A2BC-porphyrin the
slowing down of the tautomery should give two distinct N–
Hs with different environments. This process might have an
energy of activation causing a significant deceleration at lower
temperatures. Burrell and Officer’s group have shown that the
presence of b-alkyl substituents hampers the free rotation of
ferrocene around a single bond.8f For such hindered ferrocene–
porphyrins Kim and co-workers showed that coalescence of
two distinct NH signals was unobserved up to the higher
temperature limit of 373 K.19 On the other hand, ferrocene–
porphyrins lacking these substituents can freely rotate. The
question remains if there is still such free rotation around
Electrochemical investigations of bisporphyrin
5 were
carried out in both fast-scan (100 mV s−1) and slow-scan
(10 mV s−1) modes (Figs. 4 and 5). The CV plots significantly
differ from those obtained from ferrocenyl-substituted
2 6 4 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5

View Article Online
is due to the ferrocene moiety, because this value is within the
usual range for substituted ferrocenes.24 The observation, that a
reversible process is seen at the slow scan rate but not at the fast
scan rate deserves some comment. Usually, a reversible process
is observed at a fast scan rate, whereas at a slow scan rate the
system often undergoes an EC process, which is a chemical
reaction following the electron transfer. The latter requires a
certain lifetime of the electrochemically generated species, which
is the case at the slower scan rate. In the case of 5, in contrast to
the usual case, a reversible process assigned to the ferrocene unit
is observed. A possible explanation is that at the slower scan
rate the system has sufficient time to adopt a more coplanar
conformation allowing intramolecular electron transfer from
the porphyrin unit to the ferrocene. Thus, the CV results can
be seen in close connection to the molecular dynamics of 5 and
similar systems. Further investigations along these lines, e.g. CV
measurements at slower scan rates and at variable temperatures,
are currently being pursued in our laboratories. In addition,
similar investigations with metal coordinated di- and tri-metallic
systems are on our agenda.
Fig. 4 Fast-scan (100 mV s−1) voltammetry of porphyrin 5.
In conclusion, a new and interesting type of supramolec-
ular building block, 1,1ꢀ-bis(porphyrinyl)ferrocenes, has been
prepared very efficiently on a large scale avoiding chro-
matographic purification.25 Variable-temperature-dependent 1H
NMR spectra showed that the equilibrium between ‘open
dimers’, oligomers, tautomers and possibly also conformers
is rather complex. The electrochemistry showed that some
kind of conjugative interactions occur between both subunits
which are different from those in directly-bonded mono-
ferroceneporphyrins. These observations suggested that further
exploration of bis-1,1ꢀ-(porphyrinyl)ferrocenes would be highly
productive. Work on the utilization of this scaffold in the
construction of electrochemically tunable ferrocene–porphyrin
supramolecular polymeric systems and metal–organic frame-
works is in progress in our laboratory.
Fig. 5 Slow-scan (10 mV s−1) voltammetry of porphyrin 5.
metalloporphyrins;5,8f ,h the cyclovoltammograms obtained by
Kim’s and other groups for ferrocene-substituted hydropor-
phyrins20,23 also show a shape quite different from that obtained
for 5. This makes us conclude that the substitution of a ferrocene
with porphyrins at either one of the cyclopentadienyl ligands
causes significant differences as compared to the previously
known mono-substituted porphyrinylferrocenes. One aspect in
this context may be the electron transfer between the electrode
and the molecule. In contrast to the mono-substituted ferrocenes
it seems for obvious steric reasaons unlikely for 5 that an
electron transfer directly takes place between the electrode and
the ferrocene moiety. It seems more reasonable that the transfer
occurs via a porphyrin substituent, upon which a transfer to the
ferrocene moiety might occur. This, however, would be highly
dependent on the conformation of the porphyrin substituent
relative to the ferrocene moiety.
Experimental
General
All chemicals were used as received unless otherwise noted.
Reagent grade solvents (CH2Cl2, hexanes) were distilled prior
1
to use. H NMR: Bruker AM 500 MHz or 200 MHz spec-
trometer. J values are given in Hz. UV-VIS spectra were
recorded in toluene (Cary). ESI-MS: (Mariner) the purity of
all new compounds was established based on 1H NMR spectra,
elemental analyses and ESI-MS spectra. All dipyrromethanes,26
1,1ꢀ-diformylferrocene,10 N-methylbenzoylmorpholine13 and
diacyldipyrromethanes12,13 were prepared according to literature
procedures.
The plot obtained for 5 at the fast scan rate (100 mV s−1)
shows three irreversible oxidation potentials at EA = 0.455,
1.059 and 1.272 V (vs. Fc/Fc+). In addition there is possibly
a reversible reduction step at EA = −1.679 V, EK = −1.326 V
(effective potential is the average value, 1.503). However, the
comparatively large difference of 353 mV between these peaks,
which strongly exceeds the theoretical value of 59 mV for a
perfectly reversible process, raises some doubt in the reversibility
of this process. Remarkably, the plot does not show any clearly
reversible redox process for the ferrocene moiety in 5. This
suggests that the processes observed most likely takes place at
the extended porphyrin p-system and that there is only little elec-
tronic communication between these and the ferrocene subunit,
presumably because the porphyrin and ferrocene subunits adopt
a non-coplanar conformation.
1,9-Bis(4-methylbenzoyl)-5-mesityldipyrromethane (8). N-
(4-Methylbenzoyl)morpholine (5.125 g, 25 mmol) and phos-
phorus oxytrichloride (4.66 mL, 50 mmol) were mixed under
an inert atmosphere and kept at 65 ◦C for 3 h. After cooling
to room temperature, the mixture was dissolved in dry 1,2-
dichloroethane (12.5 mL) and 5-mesityldipyrromethane (1.65 g,
6.25 mmol) was added in a single batch. The reaction mixture
was stirred at reflux for 2 h before quenching with saturated
aqueous CH3COONa (50 mL) and heated for an additional hour
at 60 ◦C. The mixture was cooled to 25 ◦C, and the organic layer
was separated. The aqueous layer was extracted with CH2Cl2
and the combined organic phases were extracted with water
to remove CH3COOH, dried (Na2SO4) and chromatographed
(silica; hexane–ethyl acetate, 9 : 1, then 4 : 1). Subsequent
chromatography (silica; hexane–ethyl acetate, 95 : 5, then 9 :
1) afforded a solid which was crystallized (ethyl acetate–hexane,
1 : 4) to give off-white crystals (1.85 g, 59%). All physicochemical
properties concur with literature data.11
The plot obtained at the slow scan rate (10 mV s−1) shows
a reversible oxidation at E1/2 = 0.410 V. In addition there are
less clear signals at EA = 1.045 V and EK = 1.050 V as well as
at EK = 0.923 V. Although an interpretation remains somewhat
speculative, we suggest that the redox process observed at 0.410 V
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5
2 6 4 3

View Article Online
1,1ꢀ-Bis[bis-(2,2ꢀ-pyrryl)methyl]ferrocene (2). A mixture of
pyrrole (20 mL, 0.3 mol) and 1,1ꢀ-diformylferrocene 1 9 (1.40 g,
6.0 mmol) was flushed with argon for 5 min and treated with TFA
(92 lL, 1.2 mmol). The mixture was stirred for 25 min at 25 ◦C,
and triethylamine (170 lL, 1.2 mmol) was added. The excess
pyrrole was removed under reduced pressure. The resulting oil
was dissolved in ethyl acetate, washed with water and then dried
(Na2SO4). The solvent was removed under reduced pressure
to afford a brown oil. The crude product was purified by
column chromatography (silica; hexane–ethyl acetate, 4 : 1).
The resulting solid was crystallized (Et2O–hexane 1 : 1) afforded
crystals (mp 182–184 ◦C) (882 mg, 40%). Rf = 0.55 (silica; ethyl
acetate–hexane, 1 : 4); 1H NMR (200 MHz, CDCl3): d 3.96 (br s,
4H, Fc), 4.05 (br s, 4H, Fc), 5.01 (s, 2H, CH), 5.95 (br s, 4H, CH–
pyrrole), 6.14 (br d, 4H, J = 2.6 Hz, CH–pyrrole), 6.64 (br s, 4H,
CH–pyrrole), 7.86 (br s, 4H, NH); MS(ESI): m/z 474.15 [M +
H+]. A satisfactory elemetal analysis could not be obtained on
this substance.
12H, CH3–Mesyl), 2.52 (s, 12H, CH3), 2.63 (s, 6H, CH3–Mesyl),
4.90 (s, 4H, Fc), 5.65 (s, 4H, Fc), 7.00 (br d, 8H, J = 5.5 Hz
Ar–H), 7.21 (br s, 8H, Ar–H), 7.27 (br d, 8H, Ar–H), 7.93 (br s,
4H, b-H), 8.41 (d, 4H, J = 3.0 Hz, b-H), 8.51 (d, 4H, J =
4.5 Hz, b-H), 9.85 (br s, 4H, b-H); MS(ESI): m/z 1400.6 [M +
H+]. Anal. calc. for C96H78FeN8: C, 82.39; H, 5.62; N, 8.01.
Found: C, 82.54; H, 5.51; N, 7.74%. UV-Vis (toluene): kmax/nm
(e × 10−3/dm3 mol−1 cm−1) 417 (320), 513 (21), 580 (13), 673
(11).
1,1ꢀ -Bis{5,10-bis(4-tert-butylphenyl)-15-mesitylporphyrin-20-
yl}ferrocene (7). The reaction was performed following the
general procedure starting from 1,9-bis(4-tert-butylbenzoyl)-
5-mesityldipyrromethane (702 mg, 1.2 mmol) followed by
condensation with 1,1ꢀ-bis[bis-(2,2ꢀ-pyrryl)methyl]ferrocene 2
(288 mg, 0.6 mmol). The reaction mixture was evaporated
to dryness and crystallized from THF–CH2Cl2–Et2O–hexane
to give dark crystals (37 mg). The residue was crystallized
from THF–ethyl acetate–hexane afforded pure crystals (mp >
360 ◦C) (58 mg). In total, 95 mg of porphyrin were obtained
(10%). Rf = 0.45 (silica; CH2Cl2–hexane, 1 : 1); 1H NMR
(500 MHz, CDCl3): d −2.84 (br s, 4H, NH), 1.43 (s, 36 H,
CH3–t-Bu), 1.73 (s, 12 H, CH3–Mes), 2.62 (s, 6 H, CH3–Mes),
5.01 (s, 4H, Fc), 5.81 (s, 4H, Fc), 6.83 (br s, 16 H, Ar–H), 7.24
(br s, 4 H, Ar–H), 7.65 (br s, 4H, b-H), 8.15 (br s, 4H, b-H),
8.42 (br s, 4H, b-H), 9.72 (br s, 4H, b-H); MS(ESI): m/z 1568.8
[M + H+]. Anal. calc. for C108H102FeN8: C, 82.73; H, 6.56; N,
7.15. Found: C, 82.46; H, 6.42; N, 7.04%. UV-Vis (toluene):
kmax/nm (e × 10−3/dm3 mol−1 cm−1) 410 (245), 513 (18), 580
(11), 673 (8).
General procedure for the preparation of porphyrins
A sample of NaBH4 (1.89 g, 50 mmol) was added in small
portions (every 10 min) to a stirred solution of a diacyl
dipyrromethanes (1 mmol) in THF–methanol (3 : 1, 80 mL)
in a flask open to the atmosphere. The progress of the reduction
was monitored by TLC (alumina; CH2Cl2–ethyl acetate, 3 :
2). After the reaction was completed (about 1 h), the reaction
mixture was poured into a stirred mixture of saturated aqueous
NH4Cl (80 mL) and CH2Cl2 (100 mL). The organic phase was
isolated, washed with water (2 × 100 mL), and dried (Na2SO4).
Removal of the solvent in a rotary evaporator under reduced
pressure (T ꢀ 30 ◦C) yielded the dicarbinol as an oil. Diol
and bisdipyrromethane 2 (240 mg, 0.5 mmol) were dissolved in
acetonitrile (400 mL) and TFA (930 lL, 12 mmol) was added
with vigorous stirring. After 25 min DDQ (680 mg, 3 mmol)
was added. The reaction mixture was stirred for 1 h at room
temperature, triethylamine (1.68 mL, 12 mmol) was added,
before being evaporated and purified by crystallization.
1,1ꢀ-Bis{Zn(II)-5,10-bis(4-tert-butylphenyl)-15-mesitylporphyrin-
20-yl}ferrocene (Zn-7). A solution of 7 (20 mg, 0.013 mmol)
in CHCl3 (20 mL) was treated overnight with a solution of
Zn(OAc)2·2H2O (30 mg, 0.137 mmol) in methanol (5 mL) at
room temperature. The solvent was removed and residue was
filtered through pads of silica (silica; CH2Cl2) to afford a pure
solid which was crystallized from CH2Cl2–hexane to give dark
crystals (19 mg, 86%). Rf = 0.67 (silica; CH2Cl2–hexane, 1 : 1);
1H NMR (200 MHz, CDCl3): d 1.48 (s, 36 H, CH3–t-Bu), 1.83
(s, 12 H, CH3–Mes), 2.65 (s, 6 H, CH3–Mes), 5.00 (s, 4H, Fc),
5.82 (s, 4H, Fc), 6.91 (br s, 8 H, Ar–H), 7.11 (d, 8 H, J = 7.2 Hz,
Ar–H), 7.27 (br s, 4 H, Ar–H), 7.79 (br s, 4H, b-H), 8.37 (d, 4H,
J = 4.2 Hz, b-H), 8.57 (d, 4H, J = 4.6 Hz, b-H), 10.00 (d, 4H,
J = 4.4 Hz, b-H); MS(ESI): m/z 1691.7 [M + H+]. Anal. calc.
for C108H98FeN8Zn2 + 2H2O: C, 74.95; H, 5.94; N, 6.47. Found:
C, 74.87; H, 5.82; N, 6.43%. UV-Vis (toluene): kmax/nm (e ×
10−3/dm3 mol−1 cm−1) 426 (373), 571 (21), 628 (23).
1,1ꢀ -Bis{5,10-bis(4-methylphenyl)-15-(pentafluorophenyl)-
porphyrin-20-yl}ferrocene (5). The reaction was performed
following the general procedure starting from 1,9-bis(4-methyl-
benzoyl)-5-(pentafluorophenyl)dipyrromethane
4 (658 mg,
1.2 mmol) followed by condensation with 1,1ꢀ-bis[bis-(2,2ꢀ-
pyrryl)methyl]ferrocene 2 (288 mg, 0.6 mmol). The reaction
mixture was evaporated to dryness and crystallized from
THF–Et2O to give dark crystals (mp > 360 ◦C). The residue
was crystallized from THF–CH2Cl2–hexane and afforded pure
crystals. In total, 159 mg of porphyrin were obtained (18%).
1
Rf = 0.50 (silica; CH2Cl2–hexane, 1 : 1); H NMR (200 MHz,
Electrochemistry
CDCl3): d −2.82 (br s, 4H, NH), 2.51 (s, 12H, CH3), 4.98 (s,
4H, Fc), 5.65 (s, 4H, Fc), 7.01 (m, 16H, Ar–H), 7.80 (d, 4H,
J = 4.8 Hz, b-H), 8.47 (d, 4H, J = 5.0 Hz, b-H), 8.57 (d, 4H,
J = 4.8 Hz, b-H), 9.77 (d, 4H, J = 5.0 Hz, b-H); MS(ESI):
m/z 1496.4 [M + H+]. Anal. calc. for C90H56F10FeN8: C, 72.29;
H, 3.77; N, 7.49. Found: C, 71.88; H, 4.05; N, 7.23%. UV-Vis
(toluene): kmax/nm (e × 10−3/dm3 mol−1 cm−1) 418 (314), 506
(22), 591 (13.5), 674 (13).
CV measurements were carried out in Hannover and later
confirmed in Heidelberg. The measurements were performed
using three electrodes: the working electrode was a glass-covered
platinum wire (diameter ca. 1 mm), the reference electrode
was Ag/AgCl, and the counter electrode was a platinum
spiral. The supporting electrolyte was tetrabutylammonium
hexafluorophosphate. The oven-dried measurement cell was
◦
cooled to 25 C under argon and then filled with the solution
1,1ꢀ -Bis{5,10-bis(4-methylphenyl)-15-mesitylporphyrin-20-
yl}ferrocene (6). The reaction was performed following the
general procedure starting from 1,9-bis(4-methylbenzoyl)-5-
mesityldipyrromethane 8 (500 mg, 1.0 mmol) followed by
condensation with 1,1ꢀ-bis[bis-(2,2ꢀ-pyrryl)methyl]ferrocene 2
(240 mg, 0.5 mmol). The reaction mixture was evaporated
to dryness and crystallized from ethyl acetate/hexane to
give only impurity. The residue was crystallized from ethyl
acetate/hexane and the resulting crystals were recrystallized
from THF–ethyl acetate–hexane to give dark crystals (mp >
360 ◦C) (115 mg, 17%). Rf = 0.53 (silica; CH2Cl2–hexane, 1 : 1);
1H NMR (500 MHz, CDCl3): d −2.61 (br s, 4H, NH), 1.82 (s,
of the supporting electrolyte and the sample. The solution was
flushed with argon for 5 min. All measurements were performed
at 25 ◦C. A Princeton Applied research potentiostat/galvanostat
model 263A was used in Heidelberg; a HEKA Electronik
potentiostat model PG 284/IEC was used in Hannover. All
potentials are given vs. Fc/Fc+.
Measurement 1: solvent CH2Cl2 (3.0 mL), supporting elec-
trolyte Bu4NPF6 (232.4 mg), sample amount 2.2 mg, sweep
width −2.0 V to +2.0 V, scan rate 100 mV s−1.
Measurement 2: solvent CH2Cl2 (3.0 mL), supporting elec-
trolyte Bu4NPF6 (231.8 mg), sample amount 1.1 mg, sweep
width −1.0 V to +1.3 V, scan rate 10 mV s−1.
2 6 4 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5

View Article Online
Molecular modelling
N. M. Loim, Russ. Chem. Bull., 1999, 48, 1900–1903; (h) D. T. Gryko,
F. Zhao, A. A. Yasseri, K. M. Roth, D. F. Bocian, W. G. Kuhr and
J. S. Lindsey, J. Org. Chem., 2000, 65, 7356–7362; (i) S. J. Narayan,
S. Venkatraman, S. R. Dey, B. Sridevi, V. R. G. Anand and T. K.
Chandrashekar, Synlett, 2000, 1834–1836.
R
Calculations were performed within the HyperChemꢀ Package27
by extensive energy minimizations (Polak–Ribiere conjugate
gradient) alternating between molecular mechanics (MM+ force
field) and semiempirical calculations (PM3).
9 A. C. Arsenault, H. Miguez, V. Kitaev, G. A. Ozin and I. Manners,
Adv. Mater., 2003, 15, 503–507; A. C. Arsenault, H. Miguez,
V. Kitaev, G. A. Ozin and I. Manners, Macromol. Symp., 2003, 196,
63–69; A. C. Arsenault, J. Halfyard, Z. Wang, V. Kitaev, G. A. Ozin,
I. Manners, A. Mihi and H. Miguez, Langmuir, 2005, 21, 499–503.
10 M. A. Carroll, D. A. Widdowson and D. J. Williams, Synlett, 1994,
1025–1026.
11 B. J. Littler, M. A. Miller, C. H. Hung, R. W. Wagner, D. F. O’Shea,
P. D. Boyle and J. S. Lindsey, J. Org. Chem., 1999, 64, 1391–
1396.
12 P. D. Rao, S. Dhanalekshmi, B. J. Littler and J. S. Lindsey, J. Org.
Chem., 2000, 65, 7323–7344; S. Tamaru, L. Yu, W. J. Youngblood,
K. Muthukumaran, M. Taniguchi and J. S. Lindsey, J. Org. Chem.,
2004, 69, 765–777.
13 D. T. Gryko, M. Tasior and B. Koszarna, J. Porphyrins Phthalocya-
nines, 2003, 7, 239–248.
Acknowledgements
We are indebted to Dipl.-Chem. Marc Vollmann (University of
Hannover), Dipl.-Chem. Karin Memminger and Professor Dr
Thomas J. J. Mu¨ller (University of Heidelberg) for their help
with the CV measurements. We thank Dr habil. Teodor Silviu
Balaban (Institute for Nanotechnology, Forschungszentrum
Karlsruhe and DFG-Center for Functional Nanostructures at
the University of Karlsruhe) for discussions and performing the
molecular modelling. This work was kindly supported by the
VolkswagenStiftung (grant I 77750).
14 M. O. Senge and J. Richter, J. Porphyrins Phthalocyanines, 2004, 8,
934.
References and notes
15 J. S. Lindsey and R. W. Wagner, J. Org. Chem., 1989, 54, 828.
16 5,15-Bis(4-methylphenyl)-10-ferrocenyl-20-mesitylporphyrin syn-
thesized by us did not show any line broadening at room temperature.
17 C. Elschenbroich, Organometallchemie, Teibner, Stuttgart, 2003, 4th
edn., p. 458.
1 Comprehensive Supramolecular Chemistry, J. L. Atwood,
J. E. D. Davies, D. D. MacNicol and F. Vogtle, eds., Elsevier,
Oxford, 1996.
2 A. K. Burrell, D. L. Officer, P. G. Plieger and D. C. W. Reid, Chem.
Rev., 2001, 101, 2751–2796; A. Satake and Y. Kobuke, Tetrahedron,
2005, 61, 13–41.
3 E. W. Abel, N. J. Long, K. G. Orrell, A. G. Osborne and V. Sik,
J. Organomet. Chem., 1991, 403, 195.
4 A. E. Kaifer, S. Mendoza, in Comprehensive Supramolecular Chem-
istry, J. L. Atwood, J. E. D. Davies, D. D. MacNicol and F. Vogtle,
eds., Elsevier, Oxford, 1996, vol. 1, pp. 701–732.
18 H. J. H. Wang, L. Jaquinod, D. J. Nurco, M. G. H. Vicente and K. M.
Smith, Chem. Commun., 2001, 2646–2647.
19 S. W. Rhee, B. B. Park, Y. Do and J. Kim, Polyhedron, 2000, 19,
1961–1966.
20 M. Inouye, Y. Hyodo and H. Nakazumi, J. Org. Chem., 1999, 64,
2704–2710.
21 N. C. Maiti, S. Mazumdar and N. Periasamy, J. Phys. Chem. B, 1998,
102, 1528–1538; I. Y. Chan and A. J. Hallock, J. Chem. Phys., 1997,
107, 9297–9301; D. M. Togashi, S. M. B. Costa, A. J. F. N. Sobral and
A. M. D. R. Gonsalves, J. Phys. Chem. B, 2004, 108, 11 344–11 356;
H. Yildirim, E. I. Iseri and D. Gulen, Chem. Phys. Lett., 2004, 391,
302–307.
5 C. Bucher, C. H. Devillers, J.-C. Moutet, G. Royal and E. Saint-
Aman, New J. Chem., 2004, 28, 1584–1589.
6 C. Li, J. C. Medina, G. E. M. Maguire, E. Abel, J. L. Atwood and
G. W. Gokel, J. Am. Chem. Soc., 1997, 119, 1609–1618; T. Muraoka,
K. Kinbara, Y. Kobayashi and T. Aida, J. Am. Chem. Soc., 2003,
125, 5612–5613; M. Vollmann and H. Butenscho¨n, C. R. Chim.,
2005, DOI: 10.1016/j.crci.2005.02.019.
7 C. A. Morrison, S. F. Bone, D. W. H. Rankin, H. E. Robertson, S.
Parsons, R. A. Coxall, S. Fraser, J. A. S. Howell, P. C. Yates and N.
Fey, Organometallics, 2001, 20, 2309–2320.
22 T. S. Balaban, J. Leitich, A. R. Holzwarth and K. Schaffner, J. Phys.
Chem. B, 2000, 104, 1362–1372.
23 S. W. Rhee, Y. H. Na, Y. Do and J. Kim, Inorg. Chim. Acta, 2000,
309, 49–56.
24 P. Zanello, in Ferrocenes: Homogeneous Catalysis, Organic Synthesis,
Materials Science, A. Togni and T. Hayashi, eds., VCH, Weinheim,
1995, p. 317.
8 (a) R. G. Wollmann and D. N. Hendrickson, Inorg. Chem., 1977, 16,
3079–3089; (b) G. B. Maiya, J.-M. Barbe and K. M. Kadish, Inorg.
Chem., 1989, 28, 2524–2527; (c) N. M. Loim, N. V. Abramova and
V. I. Sokolov, Mendeleev Commun., 1996, 46–47; (d) N. M. Loim,
N. V. Abramova, R. Z. Khaliullin and V. I. Sokolov, Russ. Chem.
Bull., 1997, 46, 1193–1194; (e) N. M. Loim, N. V. Abramova, R. Z.
Khaliullin, Y. S. Lukashov, E. V. Vorontsov and V. I. Sokolov, Russ.
Chem. Bull., 1998, 47, 1016–1020; (f) P. D. W. Boyd, A. K. Burrell,
W. M. Campbell, P. A. Cocks, K. C. Gordon, G. B. Jameson, D. L.
Officer and Z. Zhao, Chem. Commun., 1999, 637–638; (g) V. A.
Nadtochenko, N. N. Denisov, V. Y. Gak, N. V. Abramova and
25 When this manuscript was in the final stage of preparation a paper
describing another synthetic route to analogous ferrocene-bridged
trisporphyrins was published: O. Shoji, S. Okada, A. Satake and Y.
Kobuke, J. Am. Chem. Soc., 2005, 127, 2201–2210.
26 J. K. Laha, S. Dhanalekshmi, M. Taniguchi, A. Ambroise and J. S.
Lindsey, Org. Proc. Res. Dev., 2003, 7, 799–812.
27 HyperChemꢀR , Release 7 and Professional Version-Release 6.03,
HyperCube Inc., Gainesville, Florida, 2002.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 6 4 0 – 2 6 4 5
2 6 4 5