Self-assembly of ferrocene-functionalized perylene bisimide bridging ligands with Pt(II) corner to electrochemically active molecular squares

Article abstract of DOI:10.1021/ja029648x

Ferrocenyl-substituted N,N-di(4-pyridyl)perylene bisimide ligands have been synthesized by the coupling reaction of hydroxyphenoxy-perylene bisimides with ferrocenyl carboxylic acids. By means of metallosupramolecular self-assembly, hitherto unprecedented

Full text of DOI:10.1021/ja029648x

Published on Web 07/11/2003
Self-Assembly of Ferrocene-Functionalized Perylene Bisimide
Bridging Ligands with Pt(II) Corner to Electrochemically
Active Molecular Squares
Chang-Cheng You and Frank Wu¨rthner*
Contribution from the Institut fu¨r Organische Chemie, UniVersita¨t Wu¨rzburg, Am Hubland,
97074 Wu¨rzburg, Germany
Received December 9, 2002; Revised Manuscript Received May 30, 2003 ; E-mail: wuerthner@chemie.uni-wuerzburg.de
Abstract: Ferrocenyl-substituted N,N′-di(4-pyridyl)perylene bisimide ligands have been synthesized by the
coupling reaction of hydroxyphenoxy-perylene bisimides with ferrocenyl carboxylic acids. By means of
metallosupramolecular self-assembly, hitherto unprecedented multiredox active dendritic molecular squares
with 16 ferrocene groups positioned in the bridging ligands are prepared from the perylene bispyridyl imide
ligands and [Pt(dppp)][(OTf)2] (dppp ) 1,3-bis(diphenylphosphano)propane; OTf ) trifluoromethanesulfonate)
corner in high yield. The isolated metallosupramolecular squares were characterized by elemental analysis,
1H, 31P{1H} NMR, and UV/vis spectroscopy. The electrochemical properties of the ligands and squares
are investigated by cyclic voltammetry as well as spectroelectrochemistry. The results obtained show that
the redox behavior of ferrocene units is influenced by the square superstructure. Furthermore, redox titration
of free ligand and corresponding molecular square with the one-electron oxidant thianthrenium pentachlo-
roantimonate reveals that ferrocene groups in these structures may be oxidized completely by this oxidant,
and highly charged species generated through oxidation of ferrocenyl groups in molecular square cause
decomposition of the assembly due to pronounced Coulombic repulsion.
Introduction
preparation and reliable characterization but also their useful
applications in molecular recognition,6 catalysis,7 electrochemi-
cal sensing,8 photoluminescence,9 and so forth.
The self-assembly approach based on noncovalent coordina-
tive bonding offers an attractive alternative to the conventional
organic route for the preparation of structurally demanding
functional systems. Thus, in the past decade much attention has
been paid to the transition metal-mediated self-assembling
process to provide diverse functional supramolecular architec-
tures,1 including linear polymers,2 planar grids,3 molecular
cylinders,4 and three-dimensional cages.5 Among the metal-
containingorganic supramolecular systems, molecular squares
produced from metallocorners and linear bridging ligands have
attracted special interests due to not only their convenient
The desired functionality in metallosupramolecular squares
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9716
J. AM. CHEM. SOC. 2003, 125, 9716-9725
10.1021/ja029648x CCC: $25.00 © 2003 American Chemical Society

Ferrocene-Functionalized Molecular Squares
A R T I C L E S
Results and Discussion
may be introduced by employing functional ligands or properly
functionalized metal corners with appropriate size and shape.
To date, considerable efforts have been devoted to the design
and preparation of metal corners, and various functional metal
corners that contain crown ether,10 calixarene,10 and ferrocene11
have been successfully used to provide the respective metallo-
supramolecular squares with organic ligands. In contrast to the
functional metal corners, only few functional bridging ligands
have been reported so far; for example, ditopic porphyrins9b,12
have been used as bridging ligands for photochemically active
metallosupramolecular squares.
Recently, we have successfully prepared molecular squares
with a perylene skeleton, which exhibited excellent fluorescence
properties with quantum yield of almost unity.13 Attractive
opportunities exist to introduce functional groups into the bay
positions of perylene13c to provide bridging ligands for functional
square assemblies. In this regard, the question arises whether,
by introducing electrochemically active groups into perylene-
based bridging ligands, supramolecular squares with novel
electrochemical properties may be accessible. As a stable and
reversibly oxidizable functional organometallic complex, fer-
rocene has been widely used as a redox active building block
in supramolecular chemistry and representatively served as the
core14 or the peripheral moiety15,16 in metallodendrimers. Also
molecular squares in which ferrocenes are positioned at the metal
corners,11 or as linkers,17 have been reported. However,
functional metallosupramolecular squares containing multiple
ferrocenes in bridging ligands are unknown to date. In the
present work, we report on the amplification of a redox
functionality with a factor of 4 × 4 ) 16, which equals to 24 in
conventional dendrimer chemistry, by self-assembly of 4-fold
ferrocene-substituted perylene bisimide dyes with Pt(II) phos-
phine corner to supramolecular squares. Furthermore, the redox
properties of free ligands and the corresponding square as-
semblies have been studied in detail by cyclic voltammetry,
spectroelectrochemistry, and redox titration as well.
Synthesis of Ferrocenyl-Substituted Perylene Bisimides.
Ferrocenyl-substituted N,N′-di(4-pyridyl)perylene bisimide di-
topic ligands 4a and 4b were synthesized according to Scheme
1 in three steps starting from tetra(4-butyloxyphenoxy)perylene
bisanhydride 1.18 In the first step, perylene bisanhydride 1 was
converted to the bisimide derivative 2 by imidization with
4-aminopyridine in quinoline in the presence of catalytic
amounts of zinc acetate. Subsequently, the butyl ether groups
were cleaved by BBr3 to give tetra(4-hydroxyphenoxy)perylene
bisimide 3. The esterification of phenolic groups in substrate 3
with ferrocenylbutyric acid and ferrocenylvaleric acid through
activation of the carboxylic acid function by dicyclohexylcar-
bodiimide (DCC) in the presence of dimethylaminopyridinium
toluenesulfonate (DPTS)19 afforded the corresponding ferroce-
nyl-substituted N,N′-di(4-pyridyl)perylene bisimide ligands 4a
and 4b in moderate yields.
For comparison purposes, the ferrocenyl-substituted N,N′-di-
(2,6-diisopropylphenyl)perylene bisimides 8a,b were prepared
as reference compounds from perylene bisimide 6 according to
the procedures applied for ligands 4a,b by BBr3-promoted ether
cleavage and subsequent esterification (Scheme 2). The 4-bu-
toxyphenoxy perylene bisimide 6 was prepared in turn by the
nucleophilic substitution of the corresponding tetrachloro pre-
cursor 520 with 4-butoxyphenol in N-methylpyrrolidone (NMP)
in the presence of potassium carbonate. The hitherto unknown
dipyridyl ligands 4 and their reference compounds 8 were fully
characterized by 1H NMR and MALDI-TOF mass spectroscopy
and elemental analyses as well (see Experimental Section).
Self-Assembly of Metallosupramolecular Squares. The
metal complex [Pt(dppp)][(OTf)2] (dppp ) 1,3-bis(diphe-
nylphosphano)propane; OTf ) trifluoromethanesulfonate) has
been known to be a versatile 90° corner for the construction of
square supramolecular assemblies with linear bridging ligands.21
Therefore, this Pt(II) complex was chosen as an angular building
block for the metal-mediated self-assembly of newly prepared
ferrocene-functionalized ditopic perylene ligands 4. Indeed, the
treatment of [Pt(dppp)][(OTf)2] with equimolar amounts of
ligand 4a or 4b in dichloromethane at room temperature formed
quantitatively the corresponding molecular squares 9a and 9b
(Scheme 3). Subsequent precipitation with diethyl ether afforded
the analytically pure squares 9a and 9b in 68% and 77% yield.
Besides elemental analysis, NMR studies of the isolated
products suggest the formation of uniform macrocyclic com-
plexes through coordination of perylene ligands 4 with Pt(II)
phosphine corner. As demanded by their highly symmetric
geometry, both squares 9a and 9b display in 31P{1H} NMR
spectra a sharp singlet with appropriate 195Pt satellites21 for the
equivalent phosphorus atoms. The fact that the 31P signals are
shifted upfield by 8.5 ppm relative to that of the precursor
complex [Pt(dppp)][(OTf)2] provides evidence for the ligation
(10) Stang, P. J.; Cao, D. H.; Chen, K.; Gray, G. M.; Muddiman, D. C.; Smith,
R. D. J. Am. Chem. Soc. 1997, 119, 5163-5168.
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1
of Pt(dppp) with 4-pyridine receptors in ligands 4a,b. The H
NMR spectra of squares 9a,b show only a single set of signals
for the ligands and the dppp moieties with significant downfield
(16) (a) Alonso, B.; Cuadrado, I.; Mora´n, M.; Losada, J. J. Chem. Soc., Chem.
Commun. 1994, 2575-2576. (b) Cuadrado, I.; Mora´n, M.; Casado, C. M.;
Alonso, B.; Lobete, F.; Garcia, B.; Ibisate, M.; Losada, J. Organometallics
1996, 15, 5278-5280. (c) Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n,
M.; Losada, J.; Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613-7614. (d)
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J. Angew. Chem., Int. Ed. 2000, 39, 2135-2138.
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Polym. Chem. 2001, 39, 1572-1583.
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771.
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A R T I C L E S
You and Wu¨rthner
Scheme 1 . Synthesis of Ferrocenyl-Substituted N,N′-Di(4-pyridyl)perylene Bisimide Ligands 4
shifts (∆δ ) 0.35 ppm) of the R-pyridyl protons compared to
that of free ligands owing to the metal complexation. Upon
formation of the supramolecular structure, the 1H NMR signals
of ferrocenyl groups were broadened to a single signal with a
slight downfield shift (see Figures S1 and S2 in the Supporting
Information). Variable temperature 1H NMR studies showed that
at lower temperature (278 K) the proton signals are more
broadened, while the signals become notably sharp at higher
temperature (328 K). Because no concentration dependence was
in 4 and 9 did not affect the absorption properties of the perylene
bisimide chromophore, and no additional bands due to charge
transfer were observed, implying that insignificant or no ground-
state electronic interaction between these two chromophores
exists.
In contrast to absorption properties, fluorescence properties
of the perylene bisimide chromophore are strongly affected by
the presence of ferrocenyl substituents. Alkylphenoxy perylene
bisimide ligands and their Pt(II) squares possess high fluores-
cence quantum yields (ΦF ) 0.86-0.94)13b in chloroform or
dichloromethane, while the ferrocene-substituted perylene bi-
simide ligands 4a,b and the corresponding squares 9a,b are poor
fluorescent (ΦF < 0.002) in dichloromethane. The low fluo-
rescence quantum yields of the present compounds are presum-
ably due to the deactivation of the photoexcited singlet state of
perylene bisimide through reductive electron transfer from
ferrocenes, which is supported by the following facts: For these
ferrocene-containing perylene bisimides, the energy level of the
charge-separated state (perylene•--Fc•+) is about 1 eV, as
calculated from cyclic voltammetric reduction and oxidation
potentials (see next section). Because the lowest singlet-excited
state of these perylene bisimides lies ca. 2.15 eV above the
ground state, the photoinduced intramolecular electron-transfer
reaction is exothermic by ca. 1.15 eV (110 kJ mol-1) and,
therefore, thermodynamically feasible. On the other hand, the
singlet-excited state of ferrocene (2.46 eV)22 is above that of
the perylene chromophore (2.15 eV), thus, quenching by the
perylenefferrocene energy transfer would be forbidden due to
1
observed in H NMR measurements, the signal broadening is
not due to some complex association/dissociation processes but
rather is caused by rotational hindrance of the perylene bisimide
moiety imposed by ferrocenyl substituents in molecular squares.
Furthermore, both complexes 9a,b remain highly soluble in
dichloromethane, chloroform, nitromethane, and similar organic
solvents, despite their high molecular weights (over 11 000 Da)
and charges, which is in agreement with the presence of well-
defined assemblies rather than linear oligomeric products.
Optical Properties of Squares 9. The optical properties of
the ferrocene-containing molecular squares 9a,b were investi-
gated by UV/vis spectroscopy and fluorescence measurements.
The UV/vis spectra of these squares in dichloromethane exhibit
intense absorption bands with maxima at 579, 543, and 452
nm, which are characteristic for the perylene bisimide chromo-
phore.13b Compared with the corresponding free ligands 4a,b,
the absorption maxima of 9a,b are bathochromically shifted by
about 5 nm (see Figures S6 and S7 in the Supporting
Information), suggesting coordination of the 4-pyridine group
to Pt(II). As expected, the weak absorption of ferrocene around
440 nm (ꢀ ) 91 dm3 mol-1 cm-1) is hidden by overlapping of
the strong absorption band of perylene. Ferrocenyl substituents
(22) (a) Giasson, R.; Lee, E. J.; Zhao, X.; Wrighton, M. S. J. Phys. Chem. 1993,
97, 2596-2601. (b) Thornton, N. B.; Wojtowicz, H.; Netzel, T.; Dixon,
D. W. J. Phys. Chem. B 1998, 102, 2101-2110.
9
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Ferrocene-Functionalized Molecular Squares
A R T I C L E S
Scheme 2 . Synthesis of Ferrocenyl-Substituted N,N′-Di(2,6-diisopropylphenyl)perylene Bisimides 8
Scheme 3 . Self-Assembly of Metallosupramolecular Squares 9
the endothermic effect by 0.31 eV (30 kJ mol-1). In fact, it has
been reported that covalently linked ferrocenes substantially
quenched the fluorescence emission of other chromophores, for
example, porphyrins, through an intramolecular electron-transfer
process.22
Electrochemical Properties of Perylene Bisimide Ligands.
To assess the effect of redox active ferrocenes on the electro-
chemical properties of perylene bisimide core, first the ferrocene-
containing ligands 4a,b and their reference compounds 8a,b
were investigated by cyclic voltammetry in dichloromethane.
The cyclic voltammograms of 4a and 8a are shown in Figure
1. The cyclic voltammogram of the ferrocene-functionalized
perylene bisimide ligand 4a (Figure 1a) shows two reversible
reduction waves at E1/2 ) -1.00 and -1.16 V (versus Fc/Fc+)
and a 4 times larger reversible oxidation wave at E1/2 ) -0.01
V (versus Fc/Fc+). The two reduction waves are comparable to
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9719

A R T I C L E S
You and Wu¨rthner
Figure 2. Spectroelectrograms of perylene bisimide ligand 4b in CH2Cl2.
Stepwise increasing of the applied potential to (a) the first reduction (radical
anionic perylene bisimide species) and (b) the second reduction of 4b
(dianionic perylene bisimide species).
Figure 1. Cyclic voltammograms of perylene bisimides 4a (a) and 8a (b)
in CH2Cl2, sweep rate 100 mVs-1
.
those of tert-butylphenoxy perylene bisimide,13b which bears
no ferrocene units in the molecule, indicating that ferrocenyl
substituents tethered by flexible propyl chains do not influence
the reduction process of the perylene bisimide moiety. The wave
observed in the oxidation cycle (E1/2 ) -0.01 V) should be
ascribed to the oxidation of four ferrocenyl groups. Further
oxidation of ligand 4a is irreversible, which is attributed to the
oxidation of perylene bisimide involving the lone pairs of pyridyl
nitrogen atoms. As known from our earlier studies, this process
causes adsorption of the ligand on the platinum electrode.13b
Similar electrochemical properties were observed for the ligand
4b where the ferrocenes are tethered to the perylene core by
butyl chains. While the extended oxidation of pyridyl ligands
4a,b is irreversible, the reference compound 8a (Figure 1b), in
which N-pyridine is replaced by a N-phenyl group, shows a
reversible wave at E1/2 ) +0.93 V for the oxidation of perylene
bisimide, in addition to the two reversible reductions at E1/2
)
-1.06 and -1.32 V and the reversible oxidation at E1/2 ) -0.03
V. Clearly, the replacement of nitrogen atoms by carbon atoms
avoids the adsorption of 8a on the platinum working electrode;
thus, the oxidation of perylene core in 8, in contrast to 4,
becomes reversible.
Figure 3. Cyclic voltammograms of metallosupramolecular squares 9a (a)
and 9b (b) in CH2Cl2, sweep rate 100 mV s-1
.
a maximum at 680 nm (Figure 2b), which is characteristic for
perylene bisimide dianionic species.13b These spectroelectro-
chemical results imply that 4b was reduced by two one-electron
reductions through its radical anionic states 4b•- to the dianionic
To obtain further insight into the redox processes of ferrocene-
functionalized perylene bisimides, spectroelectrochemistry of
ligand 4b was studied by recording its UV/vis-NIR absorption
spectra in dichloromethane at different reduction potentials
(Figure 2). Once the applied potential approached the first
reduction potential of 4b, the UV/vis absorption bands of the
neutral species 4b (447, 537 and 575 nm) essentially disap-
peared, while new absorption bands appeared in the NIR region,
one very intense at 784 nm and two weak transitions at 969
and 1073 nm (Figure 2a). These new bands may be attributed
to the generation of radical anionic species 4b•-. When the
potential was increased to the second reduction process, the
absorption bands of 4b•- were completely diminished, ac-
companied by the appearance of a broad absorption band with
species 4b2-
.
Electrochemical Properties of Metallosupramolecular
Squares 9. Once the electrochemical features of ferrocene-
containing free ligands 4 were assessed, the 16-fold ferrocenyl-
substituted molecular squares 9 were investigated by cyclic
voltammetry to elucidate a supramolecular effects on redox
processes. The cyclic voltammogram of square 9a in dichlo-
romethane (Figure 3a) shows two reversible reduction waves
(E1/2 ) -0.98 and -1.13 V). Since similar waves were observed
for the free ligands 4 and their reference compounds 8, these
reversible waves should also be assigned to the reduction of
9
9720 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Ferrocene-Functionalized Molecular Squares
A R T I C L E S
Figure 4. Top (a) and side (b) views of energy minimized structures of
molecular square 9a.
the perylene bisimide skeleton. Interestingly, for the ferrocenium
groups in 9a, peak splitting was observed at E ) -0.06 and
-0.10 V for the reductive wave and at E ) -0.03 V and a
shoulder was observed at E ) -0.01 V for the oxidative wave.
As such a peak splitting was not observed for the corresponding
free ligand 4a, this electrochemical property pinpoints a
supramolecular effect. The square 9b exhibits similar electro-
chemical behavior (Figure 3b). Two “normal” reversible waves
(E1/2 ) -1.01 and -1.18 V) were observed for the perylene
bisimide reduction and peak splitting, however, somewhat less
pronounced, appeared during the reduction of ferroceniums at
E ) -0.13 V and a shoulder appeared at E ) -0.08 V, in
contrast to the one anodic peak at E ) -0.07 V for the oxidation
of ferrocenes.
To understand the observed supramolecular effect on the
reduction process of ferrocenium groups, pertinent structural
features of squares 9 have to be discussed. X-ray analysis and
molecular modeling results revealed that the four substituents
at the 1,6,7,12-positions (bay area) of perylene bisimides lead
to two naphthalene imide half units twisted by ca. 30°.23 The
twisted conformation entails that when ligands 4a or 4b is self-
assembled to a square scaffold, the 16 ferrocene units should
be separated into two groups: one set is pointed toward the
inside of the square cavity, while the other set orients outside.
Indeed, molecular dynamic simulation of square 9a confirms
these structural features (Figure 4). The neutral ferrocene units
are conformationally still flexible due to the presence of an alkyl
linkage; therefore, their oxidation to ferrocenium may not be
affected by the supramolecular organization. However, the
conformation and flexibility of ferroceniums, which are gener-
ated through the one-electron oxidation of ferrocenes, will be
critically restricted because of the electrostatic repulsion between
the adjacent ferrocenium units. The ferrocenium moieties inside
the square are located in a more hydrophobic microenvironment
than the outside ferrocenium groups. Thus, latter ones may be
stabilized by the bulky polar electrolyte, while the inside
ferroceniums are not easily accessible by the polar electrolyte
and, therefore, less stable.24 In addition, the eight counterions
for the four positively charged platinum centers would occupy
at least partially the square cavity, which also prevents the inside
ferroceniums from being stabilized by external counterions.
Figure 5. Spectroelectrograms of metallosupramolecular square 9b in CH2-
Cl2. Stepwise increasing of the applied potential to (a) the first reduction
(radical anionic perylene bisimide species) and (b) the second reduction of
9b (dianionic perylene bisimide species).
Consequently, the inside ferroceniums should be more easily
reduced to ferrocene than the outside ones, i.e., exhibit a higher
E
1/2 value. As a result, two peaks are expected in the reduction
cycle of ferroceniums, which were indeed observed in the cyclic
voltammograms of squares 9 (Figure 3). This interpretation is
also corroborated by the unusual shape of the cyclic voltam-
mogram with a very sharp first reduction peak that points on
different kinetics for the two reduction steps. Thus, while the
inner ferrocenium ions are expected to be easier to reduce from
the thermodynamic point of view, the outer ones are at a close
distance to the electrode leading to faster kinetics. A similar
behavior was observed by Heinze et al. in the cyclic voltam-
metric study on the two-step oxidation of 5,6,-dimethyl-5,6-
dihydrobenzo[c]cinnoline and called the “spike effect”.25
To obtain more information on the redox process, spectro-
electrochemical investigations of metallosupramolecular square
9b were carried out. The successive increase of applied potential
up to the first reduction potential of square 9b resulted in the
disappearance of the UV/vis absorption bands of 9b (452, 543,
and 579 nm), while three new absorption bands (789, 994, and
1093 nm) appeared in the NIR region (Figure 5a). Since identical
spectral changes were observed for the ligand 4b, these new
UV/vis-NIR absorptions are assigned to the perylene bisimide
radical anion. Once the applied potential was further increased
to the second reduction potential of 9b, the absorption bands
for the radical anionic species were diminished and a new broad
band for perylene bisimide dianionic species appeared at 688
nm (Figure 5b), as in the case of ligand 4b. These results imply
that a similar mechanism applies for the reduction of free ligand
4b and metallosupramolecular square 9b and that all of perylene
bisimides in the square assembly are reduced to the radical
anions and the dianions at the respective potentials.
It has been reported that a reversible oxidation wave of the
tetraphenoxyperylene bisimide unit is observable at about 1 V
for simple perylene bispyridyl squares when the nitrogen lone
pairs are blocked by platinum coordination.13b By contrast, at
ca. 1 V the oxidation of squares 9a and 9b remains irreversible,
(23) (a) Wu¨rthner, F.; Sautter, A.; Thalacker, C. Angew. Chem., Int. Ed. 2000,
39, 1243-1245. (b) Hofkens, J.; Vosch, T.; Maus, M.; Ko¨hn, F.; Cotlet,
M.; Weil, T.; Herrmann, A.; Mu¨llen, K.; De Schryver, F. C. Chem. Phys.
Lett. 2001, 333, 255-263.
(24) (a) Pochapsky, S. S.; Mo, H.; Pochapsky, T. C. J. Chem. Soc., Chem.
Commun. 1995, 2513-2514. (b) Beer, P. D.; Graydon, A. R.; Johnson, A.
O. M.; Smith, D. K. Inorg. Chem. 1997, 36, 2112-2118.
(25) Dietrich, M.; Heinze, J.; Krieger, C.; Neugebauer, F. A. J. Am. Chem. Soc.
1996, 118, 5020-5030.
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9721

A R T I C L E S
You and Wu¨rthner
which suggests that ferrocene-functionalized self-assembled
squares are less stable than the previously reported perylene
bisimide-based squares.13b The major difference between these
two perylene bisimide derived molecular squares is that 9a,b
are already highly charged species at the given voltage due to
the ferrocenium units. According to Figure 3, all 16 ferrocene
groups in squares 9 are transformed to ferroceniums at ca. 0 V
to generate supramolecular structures with a total of 24 positive
charges (8 at Pt(II) and 16 by ferrocene one-electron oxidations).
In these highly charged and sterically crowded structures, the
Coulombic repulsion between adjacent ferrocenium groups will
destabilize the assemblies. As a consequence, upon further
oxidation the molecular squares may decompose through rupture
of metal-ligand bonds to form linear oligomeric chains. Indeed,
the characteristic peak split around the redox wave of ferrocene
subunits in the back scan (Figure 3) disappeared after further
oxidation, indicating the loss of the supramolecular effect.
Chemical Oxidation of Ferrocene-Functionalized Perylene
Bisimides and Molecular Squares. Our electrochemical and
spectroelectrochemical studies revealed that all 16 ferrocenyl
groups in molecular squares 9a,b may be oxidized by the one-
electron oxidation process to generate highly charged species.
However, in contrast to the pronounced spectral changes
observed for the perylene bisimides upon reduction (Figures 2
and 5), little spectral changes could be seen upon ferrocene
oxidation owing to the much stronger absorbance of the perylene
chromophores. To shed more light on this oxidation process,
we have extended our investigation to chemical oxidation of
the ferrocene-substituted ditopic ligand 4b and its square
assembly 9b by the thianthrene radical cation (Th•+), a well-
established one-electron oxidant.26 The reduction potential of
Th•+ was determined to be about E1/2 ) +0.85 V versus
Fc/Fc+ couple in dichloromethane (literature value, 1.10 V
versus SCE in acetonitrile27); thus, Th•+ should easily oxidize
ferrocenyl moieties (E1/2 ) 0.0 V) and partly oxidize the
perylene core (E1/2 ) +0.93 V).
Figure 6. Spectral changes of ferrocenylpentanoic acid 4-methoxyphenyl
ester 10 upon oxidation with thianthrenium pentachloroantimonate. (Inset)
The absorption changes are plotted as the function of [Th•+]/[10].
The thianthrene radical cation shows a major UV/vis absorp-
tion at around 550 nm, which disappears upon accepting one
electron to give neutral thianthrene; the latter one has no
absorption over 300 nm. Therefore, the redox process may be
easily monitored by UV/vis spectroscopy. To examine this
possibility, the redox titration of the model compound 5-ferro-
cenylpentanoic acid 4-methoxyphenyl ester (10) with thianthre-
nium pentachloroantimonate was investigated by UV/vis spec-
troscopy (Figure 6). Upon addition of the oxidant to the solution
of 10, two absorption bands, an intense one at 365 nm and a
broad weak one at around 630 nm, appeared due to the oxidation
of the ferrocenyl moiety to ferrocenium.28 The latter one is
responsible for the characteristic blue color of ferrocenium ions.
The intensities of these absorptions increased steadily with the
increasing amount of Th•+ until a 1:1 stoichiometry of Th•+:10
was achieved (Figure 6, inset). The characteristic absorption of
Th•+ became visible at 550 nm when an excess amount of
Figure 7. UV/vis spectra (a) and differential UV/vis spectra (b) of
ferrocenyl-functionalized perylene bisimide 8b upon oxidation with thian-
threnium pentachloroantimonate; the dotted lines indicate that the amount
of thianthrenium pentachloroantimonate is excess. (Inset) The absorption
changes are plotted as the function of [Th•+]/[8b].
thianthrenium was employed. These results demonstrate that
Th•+ is properly suited for the oxidation of ferrocenyl derivatives
and the redox titration can be conveniently followed by simple
UV/vis spectroscopy.
Next, the redox titration of the ferrocenyl-substituted perylene
bisimide 8b with thianthrenium pentachloroantimonate was
performed. From Figure 7, it can be seen that the addition of
Th•+ causes a substantial increase in absorption around 360 and
650 nm. To visualize the spectral changes upon addition of Th•+,
the initial spectrum of 8b was subtracted to obtain the differential
UV/vis spectra (Figure 7b), which are shown to be similar to
the corresponding spectra of model compound 10. Because one
molecule of 8b contains four ferrocenyl units, after oxidation
the molar extinction coefficients of 8b at 365 and 630 nm are
almost 4 times of those for compound 10. In addition, the
absorption of Th•+ at 550 nm appeared once the [Th•+]/[8b]
ratio was over 4. These results clearly demonstrate that all four
(26) (a) Han, D. S.; Shine, H. J. J. Org. Chem. 1996, 61, 3977-3982. (b) van
Harre, J. A. E. H.; Havinga, E. E.; van Dongen, J. L. J.; Janssen, R. A. J.;
Cornil, J.; Bre´das, J.-L. Chem.sEur. J. 1998, 4, 1509-1522. (c) Apperloo,
J. J.; Langeveld-Voss, B. M. W.; Knol, J.; Hummelen, J. C.; Janssen, R.
A. J. AdV. Mater. 2000, 12, 908-911.
(27) Houmam, A.; Shukla, D.; Kraatz, H.-B.; Wayner, D. D. M. J. Org. Chem.
1999, 64, 3342-3345.
(28) (a) Traverso, O.; Scandola, F. Inorg. Chim. Acta 1970, 4, 493-498. (b)
Thander, A.; Mallik, B. Proc. Indian Acad. Sci., Chem. Sci. 2000, 112,
475-485.
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9722 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Ferrocene-Functionalized Molecular Squares
A R T I C L E S
absorption bands has been observed upon protonation of pyridine
units in structural analogues of 4b.30 Thus, thianthrenium
pentachloroantimonate not only oxidizes effectively the ferro-
cenyl units in the ditopic perlyene ligand 4b but also undergoes
complexation processes.
Very similar spectral changes, as in the case of ligand 4b,
were observed in the oxidation of the corresponding molecular
square 9b by thianthrenium pentachloroantimonate (see Figure
S15 in the Supporting Information). Accordingly, the molecular
square 9b behaves like the free ligand 4b upon interaction with
thianthrenium pentachloroantimonate, suggesting that herein
antimony pentachloride replaces Pt(II) corners to coordinate
more strongly to the pyridyl ligand and the square assembly
gets decomposed.
The results of these redox titration studies confirm that
ferrocene-substituted perylene bisimides may be chemically
oxidized by thianthrenium pentachloroantimonate, and the redox
process can be conveniently monitored by UV/vis spectroscopy.
Complete oxidation of ferrocenyl moieties may be achieved in
all ferrocene-functionalized perylene bisimides. In the case of
ligands 4 and squares 9, additional coordination interaction
between the lone pairs of pyridyl and the counterion of oxidant
takes place, while extended oxidation of ferrocenyl functions
in the square causes its rupture. These results again demonstrate
the lability of Pt(II)-based molecular squares that easily
decompose upon oxidative charging of the ferrocene units or
coordinate to a more Lewis acidic metal.
Figure 8. UV/vis spectra (a) and differential UV/vis spectra (b) of ditoptic
perylene ligand 4b upon oxidation with thianthrenium pentachloroanti-
monate. (Inset) The absorption changes are plotted as the function of [Th•+]/
[4b].
ferrocenyl substituents were transformed to ferroceniums by
oxidation with Th•+.
Interestingly, ditopic perylene ligand 4b exhibits more
pronounced spectral changes upon oxidation by thianthrenium
pentachloroantimonate. From Figure 8, it can be seen that the
addition of Th•+ causes a significant bathochromic shift of the
absorption band of ligand 4b. The differential UV/vis spectra
(Figure 8b) show that pronounced changes occurred at around
608, 572, 528, 474, and 365 nm. The absorption changes at
these wavelengthes were plotted as a function of [Th•+]/[4b].
This plot clearly shows that the curves, particularly at 365 nm
(which is inherent for ferrocenium), reach a plateau when the
ratio of [Th•+]/[4b] is about 4. These results suggest that all
four ferrocenyl units in perylene ligand 4b were oxidized.
Because of the large difference in the oxidation potentials of
ferrocene and perylene functions, at the beginning of titration
only the ferrocenyl moieties should be oxidized, though the
perylene core has shown to be oxidizable by Th•+ (see Figures
S11 and S12 in the Supporting Information). However, the
spectrum of compound 4b changed drastically even with the
addition of the first aliquot of Th•+, indicating that an interaction
between the aza perylene lone pairs and thianthrenium pen-
tachloroantimonate takes place. Indeed, a series of control
experiments on redox titrations (see the Supporting Information,
Figures S13 and S14) of 4,4′-bispyridine and N,N′-di(4-pyridyl)-
1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4:9,10-tetracar-
boxylic acid bisimide and its mixture with the model ferrocenyl
derivative 10 revealed that the Lewis acidic SbCl5 generated
from the counterion of the oxidant can interact with the pyridyl
base to form adduct complexes.29 Such complexation of the
pyridine lone pairs of dipyridyl perylene ligand 4b may lead to
the spectral changes observed between 450 and 700 nm (Figure
8), which belong to the absorption bands of the perylene
bisimide chromophore. A similar bathochromic shift of perylene
Conclusion
Through metallosupramolecular coordination strategy, perylene
bispyridyl imides containing four ferrocenyl moieties could be
organized to give molecular squares containing 20 redox active
units. For the inner scaffold of four perylene bisimides, two
reversible four-electron reductive processes that are little
influenced by the supramolecular arrangement could be observed
by cyclic voltammetry. In contrast, it has been found that the
redox properties of the 16 peripheral ferrocenyl subunits are
strongly affected by the sterical constraints imposed by the core
square superstructure. In addition to electrochemical oxidation,
also chemical oxidation of ferrocene-functionalized perylene
bisimides could be realized by using thianthrenium pentachlo-
roantimonate and the redox process could be conveniently
monitored by spectrophotometry. The present study shows that
metal-directed self-assembly of square structures can be used
to organize redox active functional units in three-dimensional
space.31
Experimental Section
Materials and Methods. Solvents and reagents were purchased from
Merck unless otherwise stated and purified and dried according to
standard procedures.32 1,6,7,12-Tetra(4-butyloxyphenoxy)perylene-3,4:
9,10-tetracarboxylic acid bisanhydride (1),18 N,N′-di(2,6-diisopropy-
lphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxylic acid
bisimde (5),20 ferrocenylbutyric acid and ferrocenylvaleric acid,33 [Pt-
(dppp)][(OTf)2]‚2H2O (dppp ) 1,3-bis(diphenylphosphino)propane;
OTf ) trifluoromethanesulfonate),21 and thianthrenium pentachloro-
(30) Sautter, A. Ph.D. Thesis, University of Ulm, 2001.
(31) Grayson, S. M.; Fre´chet, J. M. J. Chem. ReV. 2001, 101, 3819-3868.
(32) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals,
2nd ed.; Pergamon Press: Oxford, 1980.
(33) (a) Rinehart, K. L.; Curby, R. J.; Sokol, P. E. J. Am. Chem. Soc. 1957, 79,
3420-3424. (b) Suzuki, I.; Chen, Q.; Ueno, A.; Osa, T. Bull. Chem. Soc.
Jpn. 1993, 66, 1472-1481.
(29) Antimony pentachloride has been reported to complex with pyridine; for
examples, see: (a) Holmes, R. R.; Gallagher, W. P.; Carter, Jr. R. P. Inorg.
Chem. 1963, 2, 437-441. (b) Lim, Y. Y.; Drago, R. S. Inorg. Chem. 1972,
11, 202-204.
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J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9723

A R T I C L E S
You and Wu¨rthner
antimonate34 were synthesized according to the literature procedure.
Column chromatography was performed on silica gel (Merck Silica
60, particle size 0.04-063 mm). The solvents for spectroscopic studies
were of spectroscopic grade and used as received. NMR spectra were
recorded on a Bruker DRX 400 or AMX 500 spectrometer using TMS
as internal standard. The 31P{1H} NMR spectra were taken at 202 MHz,
and chemical shifts are reported relative to external 85% aqueous H3PO4
(δ ) 0 ppm). MALDI-TOF spectra were recorded on a Bruker Franzen
Reflex III spectrometer.
(pyridyl)perylene 2 (385 mg, 0.32 mmol) in dry CH2Cl2 (250 mL) at
room temperature (ca. 20 °C). After the solution was stirred for an
additional 2 h at room temperature, the solvent was removed by
distillation and the residue was carefully hydrolyzed with ice-cold water
(40 mL). Then methanol (20 mL) was added, and the suspension was
boiled for 1 min. The precipitate was collected by centrifugation, washed
with water (10 mL × 3), and dried in vacuo at 90 °C. Yield 320 mg
1
(92%); mp > 300 °C. H NMR (DMSO-d6): δ 9.47 (br s, 4H, HOH),
3
3
8.78 (d, J ) 6.2 Hz, 4H, HR-py), 7.82 (s, 4H, Hper), 7.54 (d, J ) 6.2
3
3
Hz, 4H, Hâ-py), 6.84 (d, J ) 9.0 Hz, 8H, Har), 6.73 (d, J ) 9.0 Hz,
8H, Har). MS (MALDI-TOF, dithranol): m/z 976.2 [M]+ (calcd for
C58H32N4O12 976.2). Anal. Calcd for C58H32N4O12‚6H2O: C, 64.21; H,
4.09; N, 5.16. Found: C, 64.49; H, 4.07; N, 4.84.
Electrochemistry. Cyclic voltammetry was performed with an
EG&G PAR 273 potentiostat in a three-electrode single-compartment
cell using dichloromethane as solvent (5 mL). Working electrode,
platinum disk; counter electrode, platinum wire; reference electrode,
Ag/AgCl. All potentials were internally referenced to the Fc/Fc+ couple.
The solutions were purged with argon gas prior to use. The supporting
electrolyte was 0.1 M [Bu4N][PF6] (Fluka), which was recrystallized
twice from ethanol/water and dried under high vacuum. The experi-
mental setup for spectroelectrochemistry has been described by
Salbeck.35
N,N′-Di(4-pyridyl)-1,6,7,12-tetra(4-(4-ferrocenyl)butanoyloxy-
phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide (4a). Perylene
bisimide 3 (88.3 mg, 0.081 mmol), ferrocenylbutyric acid (176 mg,
0.65 mmol), DPTS (235 mg, 0.80 mmol), and DCC (206 mg, 1.0 mmol)
were dissolved in a mixture of DMF (4 mL) and CH2Cl2 (10 mL) and
stirred at room temperature (ca. 20 °C) for 3 h. Subsequently, another
portion of DCC (206 mg) and a small amount of molecular sieve
(4 Å) were added, and the mixture was stirred at room temperature for
3 d. Dichloromethane (40 mL) was added to the reaction mixture, and
the undissolved material was removed by filtration. The filtrate was
concentrated to ca. 4 mL, and 40 mL of methanol was added to
precipitate the crude product, which was collected by centrifugation
and washed with methanol. After the sample was dried in air, it was
purified by column chromatography (SiO2) with CH2Cl2/EtOH (95:5)
Redox Titration. UV/vis spectra were measured in a conventional
quartz cell (light path 10 mm) on a Perkin-Elmer Lambda 40P
spectrophotometer at room temperature (ca. 20 °C). For redox-titration
experiments, 2 mL of the sample solution in CH2Cl2 (the concentration
of ferrocenyl moieties is about 0.1 mM) was placed in the cuvette and
the initial spectrum was recorded. Aliquots of a freshly prepared
thianthrenium pentachloroantimonate solution in CH2Cl2 (0.2 mM) were
subsequently added to the sample solution in the cuvette. After each
addition, a UV/vis spectrum was recorded. The spectra obtained were
then normalized based on the concentration of perylene bisimide
samples according to the Beer-Lambert law (ꢀ ) A/c‚l). To visualize
the minor spectral changes, differential UV/vis spectra were also
presented in the results by simply subtracting the initial spectrum.
Molecular Modeling. To get insight into the steric demand and a
possible arrangement of the appendant ferrocenyl substituents within
molecular square 9, molecular modeling and molecular dynamics
simulation (MD-MM2) were carried out by using CAChe 5.0 (Oxford
Molecular 2000). The augmented force field was used with parametri-
zation of transition metals. Molecular dynamics simulations (MD-MM2,
in vacuo at a temperature of T ) 300 K) implemented in the CAChe
5.0 program package were applied.
1
as eluent. Yield 31 mg (19%); mp > 300 °C. H NMR (CDCl3): δ
3
3
8.79 (d, J ) 5.9 Hz, 4H, HR-py), 8.25 (s, 4H, Hper), 7.25 (d, J ) 5.9
3
Hz, 4H, Hâ-py, overlapped with CHCl3 signal), 7.03 (d, J ) 9.1 Hz,
8H, Har), 6.91 (d, 3J ) 9.1 Hz, 8H, Har), 4.12 (s, 20H, Hferro), 4.08 (m,
16H, Hferro), 2.56 (t, 8H, -CH2-), 2.46 (t, 8H, -CH2-), 1.94 (m, 8H,
-CH2-). UV/vis (CH2Cl2): λmax (ꢀ) ) 574 (44 300), 536 (28 700),
448 (17 700), 266 nm (57 300 dm3 mol-1 cm-1). MS (MALDI-TOF,
dithranol): m/z 1992.6 [M]+ (calcd for C114H88Fe4N4O16 1992.4). Anal.
Calcd for C114H88Fe4N4O16: C, 68.69; H, 4.45; N, 2.81. Found: C,
68.67; H, 4.58; N, 2.69.
N,N′-Di(4-pyridyl)-1,6,7,12-tetra(4-(5-ferrocenyl)pentanoyloxy-
phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide (4b). Com-
pound 4b was prepared by the esterification of N,N′-di(4-pyridyl)-
1,6,7,12-tetra(4-hydroxyphenoxy)perylene-3,4:9,10-tetracarboxylic acid
bisimide (3) (109 mg, 0.1 mmol) with ferrocenylvaleric acid (286 mg,
1.0 mmol) according to the above procedure. Yield 54 mg (26%); mp
> 300 °C. 1H NMR (CDCl3): δ 8.79 (d, 3J ) 6.1 Hz, 4H, HR-py), 8.24
(s, 4H, Hper), 7.25 (d, 3J ) 6.1 Hz, 4H, Hâ-py, overlapped with CHCl3
signal), 7.02 (d, 3J ) 9.1 Hz, 8H, Har), 6.91 (d, 3J ) 9.1 Hz, 8H, Har),
4.10 (s, 20H, Hferro), 4.07 (m, 16H, Hferro), 2.55 (t, 8H, -CH2-), 2.40
(t, 8H, -CH2-), 1.78 (m, 8H, -CH2-), 1.62 (m, 8H, -CH2-); UV/
vis (CH2Cl2): λmax (ꢀ) ) 574 (44 800), 537 (29 200), 448 (17 700),
266 nm (57 500 dm3 mol-1 cm-1). MS (MALDI-TOF, dithranol): m/z
2048.4 [M]+ (calcd for C118H96Fe4N4O16 2048.4). Anal. Calcd for
N,N′-Di(4-pyridyl)-1,6,7,12-tetra(4-butyloxyphenoxy)perylene-
3,4:9,10-tetracarboxylic Acid Bisimide (2). A mixture of perylene-
3,4:9,10-tetracarboxylic acid bisanhydride 1 (1.05 g, 1.0 mmol),
4-aminopyridine (0.33 g, 3.5 mmol), and zinc acetate (0.1 g, 0.55 mmol)
in quinoline (30 mL) was stirred under argon at 180 °C for 16 h. After
the solution was chilled, 2 M hydrochloric acid (150 mL) was added
to precipitate the product, which was collected by suction filtration
and washed thoroughly with a large amount of water and dried in a
vacuum. The crude product was purified by column chromatography
(SiO2) with CH2Cl2/CH3OH (98:2) as eluent. After evaporation of the
solvent, the bisimide 2 was obtained as a dark purple powder. Yield
1
3
C118H96Fe4N4O16: C, 69.15; H, 4.72; N, 2.73. Found: C, 69.27; H,
0.65 g (54%); mp > 300 °C. H NMR (CDCl3): δ 8.74 (d, J ) 6.1
3
4.80; N, 2.66.
Hz, 4H, HR-py), 8.07 (s, 4H, Hper), 7.21 (d, J ) 6.1 Hz, 4H, Hâ-py),
6.87 (d, 3J ) 9.1 Hz, 8H, Har), 6.80 (d, 3J ) 9.1 Hz, 8H, Har), 3.91 (t,
8H, -OCH2-), 1.76 (m, 8H), 1.50 (m, 8H), 0.99 (t, 12H, -CH3). MS
(MALDI-TOF, dithranol): m/z 1200.3 [M]+ (calcd for C74H64N4O12
1200.5). Anal. Calcd for C74H64N4O12: C, 73.99; H, 5.37; N, 4.66.
Found: C, 73.70; H, 5.27; N, 4.64.
N,N′-Di(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-butyloxyphenox-
y)perylene-3,4:9,10-tetracarboxylic Acid Bisimide (6). Tetrachlo-
roperylene bisimide 5 (2.55 g, 3.0 mmol), 4-butyloxyphenol (2.50 g,
15.0 mmol), and K2CO3 (2.10 g, 15.0 mmol) were suspended in
N-methyl pyrrolidone (80 mL) and stirred under argon at 160 °C for 6
h. After the solution was cooled to room temperature, dilute HCl (2
M, 100 mL) was added to precipitate the crude product, which was
collected by suction filtration and washed successively with water and
methanol. After the sample was dried in air, it was purified by column
chromatography (SiO2) with dichloromethane as eluent. Yield 1.37 g
N,N′-Di(4-pyridyl)-1,6,7,12-tetra(4-hydroxyphenoxy)perylene-3,4:
9,10-tetracarboxylic Acid Bisimide (3). BBr3 (0.5 mL, 5.3 mmol) in
dry CH2Cl2 (20 mL) was added dropwise to a stirred solution of bis-
(34) (a) Lucken, E. A. C. J. Chem. Soc. 1962, 4963-4965. (b) Kinoshits, M.
Bull. Chem. Soc. Jpn. 1962, 35, 1137-1140. (c) Balch, A. L.; Cornman,
C. R.; Latos-Grazyn˜ski, L.; Olmstead, M. M. J. Am. Chem. Soc. 1990,
112, 7552-7558.
1
(33%); mp > 300 °C. H NMR (CDCl3): δ 8.17 (s, 4H, Hper), 7.42
3
3
(t, 2H, Har), 7.26 (d, J ) 7.7 Hz, 4H, Har), 6.93 (d, J ) 9.1 Hz, 8H,
(35) Salbeck, J. J. Electroanal. Chem. 1992, 340, 169-195.
Har), 6.81 (d, 3J ) 9.1 Hz, 8H, Har), 3.92 (t, 8H, -OCH2-), 2.69
9
9724 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Ferrocene-Functionalized Molecular Squares
A R T I C L E S
(m, 4H, -CH<), 1.75 (m, 8H, -CH2-), 1.49 (m, 8H, -CH2-), 1.11
(d, 3J ) 6.8 Hz, 24H, -CH3), 0.98 (t, 12H, -CH3); UV/vis (CH2Cl2):
λmax (ꢀ) ) 591 (52 700), 548 (30 400), 457 (16 100), 286 (51 200),
268 nm (49 300 dm3 mol-1 cm-1). MS (MALDI-TOF, dithranol): m/z
1367.6 [M + H]+ (calcd for C88H90N2O12 1367.6). Anal. Calcd for
C88H90N2O12: C, 77.28; H, 6.63; N, 2.05. Found: C, 76.90; H, 6.79;
N, 1.90.
mL, and diethyl ether (10 mL) was added to precipitate the product,
which was collected by centrifugation and washed with ether (10 mL
× 2). After the product was dried in a vacuum, a dark red powder was
1
obtained. Yield 20 mg (68%); mp > 300 °C. H NMR (CDCl3): δ
9.14 (br s, 16H, HR-py), 8.15 (s, 16H, Hper), 7.67 (br s, 32H, Hdppp),
7.40 (br m, 48H, Hdppp), 7.11 (br d, 16H, Hâ-py), 6.98 (d, 3J ) 8.9 Hz,
3
32H, Har), 6.86 (d, J ) 8.9 Hz, 32H, Har), 4.25 (br s, 144H, Hferro),
N,N′-Di(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-hydroxyphenox-
y)perylene-3,4:9,10-tetracarboxylic Acid Bisimide (7). Compound
7 was prepared by the reaction of perylene bisimide 6 (0.55 g, 0.40
mmol) with BBr3 (1 M, 20 mL) in dry CH2Cl2 and worked up in the
3.29 (br s, 16H, Hdppp), 2.49 (m, 32H, -CH2-), 2.21 (br s, 40H, Hdppp
+ -CH2-), 1.79 (br s, 32H, -CH2-). 31P{1H} NMR (CDCl3): δ
1
-15.29 (s, JPt-P ) 3084 Hz). UV/vis (CH2Cl2): λmax (ꢀ) ) 579
(186 100), 543 (126 700), 452 nm (67 300 dm3 mol-1 cm-1). Anal.
Calcd for C572H456F24Fe16N16O16P8Pt4S8‚8H2O: C, 58.52; H, 4.05; N,
1.91; S, 2.18. Found: C, 58.41; H, 4.03; N, 1.89; S, 2.30.
1
same way as described for 3. Yield 0.37 g (81%); mp > 300 °C. H
NMR (DMSO-d6): δ 9.49 (s, 4H, OH), 7.88 (s, 4H, Hper), 7.41 (t, 2H,
Har), 7.29 (d, 4H, Har), 6.93 (d, 3J ) 8.8 Hz, 8H, Har), 6.78 (d, 3J ) 8.8
Hz, Har), 2.66 (m, 4H, -CH<), 1.01 (d, 24H, -CH3). UV/vis
(CH3OH): λmax (ꢀ) ) 596 (49 800), 555 (29 500), 459 (14 700), 283
(47 400), 268 nm (48 600 dm3 mol-1 cm-1). MS (MALDI-TOF,
dithranol): m/z 1143.5 [M + H]+ (calcd for C72H58N2O12 1143.4). Anal.
Calcd for C72H58N2O12‚H2O: C, 74.47; H, 5.21; N, 2.41. Found: C,
74.40; H, 5.26; N, 2.28.
Ferrocene-Containing Perylene Bisimide Platinum Square 9b.
N,N′-Di(4-pyridyl)-1,6,7,12-tetra(4-(5-ferrocenyl)pentanoyloxy-phenox-
y)perylene-3,4:9,10-tetracarboxylic acid bisimide (4b) (20.49 mg, 10.0
µmol) and [Pt(dppp)][(OTf)2]‚2H2O (9.42 mg, 10.0 µmol) were reacted
and worked up according to the procedure described for 9a. Yield 23
mg (77%); mp > 300 °C. 1H NMR (CDCl3): δ 9.14 (br s, 16H, HR-py),
8.17 (s, 16H, Hper), 7.66 (br s, 32H, Hdppp), 7.40-7.30 (m, 48H, Hdppp),
7.12 (d, 16H, Hâ-py), 6.97 (d, 3J ) 8.9 Hz, 32H, Har), 6.86 (d, 3J ) 8.9
Hz, 32H, Har), 4.27 (br s, 144H, Hferro), 3.29 (br s, 16H, Hdppp), 2.46 (t,
32H, -CH2-), 2.15 (br s, 40H, Hdppp + -CH2-), 1.70 (m, 32H,
-CH2-), 1.45 (br s, 32H, -CH2-); 31P{1H} NMR (CDCl3): δ -15.33
N,N′-Di(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-(4-ferrocenyl)bu-
tanoyloxy-phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide
(8a). Compound 8a was synthesized by the esterification of N,N′-di-
(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-hydroxyphenoxy)perylene-3,4:
9,10-tetracarboxylic acid bisimide (7) (116 mg, 0.1 mmol) with
ferrocenylbutyric acid (272 mg, 1.0 mmol) in the presence of DCC
and DPTS according to the procedure described for 4a. The product
was purified by column chromatography (SiO2) with chloroform as
1
(s, JPt-P ) 3081 Hz). UV/vis (CH2Cl2): λmax (ꢀ) ) 579 (191 200),
543 (130 500), 452 nm (69 200 dm3 mol-1 cm-1). Anal. Calcd for
C588H488F24Fe16N16O16P8Pt4S8‚8H2O: C, 59.03; H, 4.25; N, 1.87; S, 2.14.
Found: C, 59.22; H, 4.22; N, 1.87; S, 2.26.
1
eluent. Yield 32 mg (15%); mp 170-171 °C. H NMR (CDCl3): δ
5-Ferrocenylpentanoic Acid 4-Methoxyphenyl Ester (10). A
mixture of ferrocenylvaleric acid (572 mg, 2.0 mmol), 4-methoxyphenol
(248 mg, 2.0 mmol), DCC (500 mg, 2.4 mmol), and DMAP (100 mg,
0.8 mmol) was dissolved in dry CH2Cl2 (50 mL) and stirred at room
temperature (ca. 20 °C) for 3 d. After filtration, the filtrate was
concentrated, and the residue was purified by column chromatography
(SiO2) with CH2Cl2 as eluent. The desired eluting band was collected,
and the solvent was evaporated to give a yellow oil, which became a
solid after drying in a vacuum. Yield 520 mg (66%); mp 85-86 °C.
1H NMR (CDCl3): δ 6.98 (d, 3J ) 9.1 Hz, 2H, Har), 6.87 (d, 3J ) 9.1
Hz, 2H, Har), 4.09 (s, 5H, Hferro), 4.07 (m, 2H, Hferro), 4.04 (m,
2H, Hferro), 3.79 (s, 3H, -OCH3), 2.55 (t, 2H, -CH2-), 2.39 (t, 2H,
-CH2-), 1.78 (m, 2H, -CH2-), 1.62 (m, 2H, -CH2-). 13C NMR
(CDCl3): δ 172.49, 157.20, 144.25, 122.29, 114.45, 88.73, 68.49, 68.06,
67.15, 55.59, 34.20, 30.57, 29.29, 24.87. MS (EI, 70 eV): m/z 392.1
[M]+ (calcd for C22H24FeO3 392.1). Anal. Calcd for C22H24FeO3: C,
67.36; H, 6.17. Found: C, 67.10; H, 6.32.
8.28 (s, 4H, Hper), 7.44 (t, 2H, Har), 7.28 (d, 4H, Har), 7.04 (d, 3J ) 9.1
Hz, 8H, Har), 6.94 (d, 3J ) 9.1 Hz, 8H, Har), 4.11 (s, 20H, Hferro), 4.08
(m, 16H, Hferro), 2.70 (m, 4H, -CH<), 2.55 (t, 8H, -CH2CO-), 2.45
(t, 8H, Fc-CH2-), 1.94 (m, 8H, -CH2-), 1.13 (d, 24H, -CH3). UV/
vis (CH2Cl2): λmax (ꢀ) ) 573 (46 500), 535 (29 500), 444 (17 300),
282 (52 600), 264 nm (56 700 dm3 mol-1 cm-1); MS (MALDI-TOF,
dithranol): m/z 2158.6 [M]+ (calcd for C128H114Fe4N2O16 2158.6). Anal.
Calcd for C128H114Fe4N2O16: C, 71.19; H, 5.32; N, 1.30. Found: C,
71.30; H, 5.44; N, 1.23.
N,N′-Di(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-(5-ferrocenyl)pen-
tanoyloxy-phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide
(8b). Compound 8b was synthesized by the esterification of N,N′-di-
(2,6-diisopropylphenyl)-1,6,7,12-tetra(4-hydroxyphenoxy)perylene-3,4:
9,10-tetracarboxylic acid bisimide (7) (116 mg, 0.1 mmol) and
ferrocenylvaleric acid (286 mg, 1.0 mmol) in the presence of DCC
and DPTS according to the procedure described for 4a. Yield 63 mg
(28%); mp 175-176 °C. 1H NMR (CDCl3): δ 8.28 (s, 4H, Hper), 7.44
3
(t, 2H, Har), 7.28 (d, 4H, Har), 7.03 (d, J ) 9.2 Hz, 8H, Har), 6.93 (d,
Acknowledgment. We thank the Alexander von Humboldt
Foundation (fellowship for C.C.Y.) and the Fonds der Chemis-
chen Industrie for financial support and BASF AG and Degussa-
Hu¨ls AG for the donation of chemicals. We are indebted to Dr.
Gu¨nther Go¨tz and Prof. Peter Ba¨uerle (Ulm) for their support
in the electrochemical measurements and helpful discussions.
3J ) 9.2 Hz, 8H, Har), 4.09 (s, 20H, Hferro), 4.06 (m, 16H, Hferro), 2.70
(m, 4H, -CH<), 2.55 (t, 8H, -CH2CO-), 2.42 (t, 8H, Fc-CH2-),
1.78 (m, 8H, -CH2-), 1.62 (m, 8H, -CH2-), 1.13 (d, 24H, -CH3).
UV/vis (CH2Cl2): λmax (ꢀ) ) 573 (47 600), 535 (30 200), 444 (17 500),
282 (53 300), 264 nm (57 400 dm3 mol-1 cm-1). MS (MALDI-TOF,
dithranol): m/z 2214.2 [M]+ (calcd for C132H122Fe4N2O16 2214.6). Anal.
Calcd for C132H122Fe4N2O16: C, 71.55; H, 5.55; N, 1.26. Found: C,
71.44; H, 5.62; N, 1.27.
Supporting Information Available: NMR (1H and 31P) and
UV spectra for molecular squares 9a and 9b and cyclic
voltammograms and UV/vis spectra of redox titrations. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Ferrocene-Containing Perylene Bisimide Platinum Square 9a.
A 1:1 stoichiometric mixture of N,N′-di(4-pyridyl)-1,6,7,12-tetra(4-(4-
ferrocenyl)butanoyloxy-phenoxy)perylene-3,4:9,10-tetracarboxylic acid
bisimide (4a) (19.93 mg, 10.0 µmol) and [Pt(dppp)][(OTf)2]‚2H2O (9.42
mg, 10.0 µmol) in CH2Cl2 (5 mL) was stirred at room temperature (ca.
20 °C) for 24 h. After filtration, the solution was concentrated to ca. 1
JA029648X
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J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9725