Synthesis and electrochemical properties of tetrasubstituted tetraphenylethenes

Article abstract of DOI:10.1002/ejoc.200600123

Tetrakis(4-acetoxyphenyl and 4-benzoyloxyphenyl)ethenes 1f and 1g were obtained by acylation of tetrakis(4-hydroxyphenyl)ethene 1b. Ullmann etherification of 4,4′-dihydroxybenzophenone 2b and subsequent McMurry coupling yielded tetrakis(phenoxyphenyl)ethe

Full text of DOI:10.1002/ejoc.200600123

FULL PAPER
DOI: 10.1002/ejoc.200600123
Synthesis and Electrochemical Properties of Tetrasubstituted
Tetraphenylethenes
Alina Schreivogel,[a] Jörg Maurer,[b] Rainer Winter,*[b,c] Angelika Baro,[a] and
Sabine Laschat*[a]
Keywords: Cyclic voltammetry / McMurry reaction / Spectroelectrochemistry / Tetraphenylethenes
Tetrakis(4-acetoxyphenyl and 4-benzoyloxyphenyl)ethenes
1f and 1g were obtained by acylation of tetrakis(4-hy-
droxyphenyl)ethene 1b. Ullmann etherification of 4,4Ј-dihy-
quent McMurry coupling. Compounds 1f–l were investigated
by cyclic voltammetry. While the phenyl ether derivative 1i
displays single-electron processes during oxidation, a two-
droxybenzophenone 2b and subsequent McMurry coupling electron process was discovered for trifluoroacetamide 1j as
yielded tetrakis(phenoxyphenyl)ethene 1i. The tetrakis(acet-
amidophenyl)ethene 1h was prepared in three steps from tet-
raphenylethene 1c by nitration, Raney-Ni reduction and sub-
sequent acetylation. Alternatively, trifluoroacetamide 1j, 2-
methylhexanamide 1k and 2,4-dimethylbenzamide 1l, with
less tendency to form 2D hydrogen bonding networks and
thus increased solubility as compared to 1h, were prepared
by acylation of 4,4Ј-diaminobenzophenone 2a and subse-
was also supposed for the esters 1f and 1g. In addition, com-
proportionation constants were shown to be dependent on
the solvent. In situ IR spectroelectrochemistry provided evi-
dence for quinoidal type substructures in the dioxidized
forms of tetraphenylethenes 1.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
to look for the redox properties of much simpler model sys-
tems. The unsubstituted tetraphenylethene,[6,12,13] as well as
the substituted analogues with methyl,[5,6,12] trifluoro-
methyl,[12] phenyl,[12] hydroxy,[14] methoxy,[5,6,12] amino,[12]
N,N-dimethyl-,[12,14,15] and diphenylamino,[16] halogen,[12]
nitro,[12] cyano[6] and acetyl[17] were investigated by cyclic
voltammetry, spectroelectrochemistry and EPR in great de-
tail.[18]
According to these studies, tetraphenylethenes are gen-
erally oxidized and reduced in two successive one-electron
steps. Functional groups at the para positions strongly in-
fluence the redox potentials and good correlations between
the average reduction potential and the sum of the σ– coeffi-
cients of the individual substituents have been observed.[2]
The arene substituents also affect the overall chemical sta-
bilities of the oxidized and the reduced forms. Resonance
stabilization by strongly electron-donating alkoxy groups
has even allowed for the preparation and structural charac-
Introduction
Tetraphenylethenes display interesting chemical and
physical properties. For example, they can undergo photo-
cyclization to the corresponding diphenylphenan-
threnes.[1–4] Upon oxidation tetraphenylethenes easily form
radical cations and dications, respectively,[5–7] while re-
duction with alkali metals leads to dianions. Both di-
anions[8] and dications[5,9] can be characterized by crystal-
lography. Furthermore, tetraarylethenes provide three dif-
ferent conjugation modes: diagonal, lateral and cross conju-
gation and they may be used as two-dimensional molecular
scaffolds for bichromophoric donor-acceptor dyads for en-
ergy transfer.[10] Recently we have described novel liquid
crystalline tetraphenylethene derivatives which form colum-
nar mesophases.[4,11] In an attempt to understand the redox
properties of these compounds in solution, cyclic voltam-
metric (CV) studies were performed. However, preliminary
results revealed a complex behavior. We therefore decided
[a] Institut für Organische Chemie der Universität Stuttgart,
Pfaffenwaldring 55, 70569 Stuttgart, Germany,
Fax: +49-711-68564285
E-mail: sabine.laschat@oc.uni-stuttgart.de
[b] Institut für Anorganische Chemie der Universität Stuttgart,
Pfaffenwaldring 55, 70569 Stuttgart, Germany
[c] Institut für Anorganische Chemie der Universität Regensburg,
Universitätsstrasse 31, 93040 Regensburg, Germany
E-mail: rainer.winter@chemie.uni-regensburg.de
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Scheme 1. Tetraphenylethene derivatives 1.
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FULL PAPER
terization of the mono- and di-oxidized forms of tetra(4- mon organic solvents, thus, suitable NMR spectra were ob-
anisyl)ethene (1a), giving valuable insight into the structural tained in DMSO only at 60 °C. Presumably, extensive hy-
changes induced by electron transfer.[5] Surprisingly, no in- drogen bonding of the four amide groups leads to a two
formation was available about tetraphenylethenes 1 with dimensional network with very low solubility.[25] As further
either acyloxy, acetamido, aryloxy or related substituents in solubility problems were expected for tetrakis(benzamido-
the para position (Scheme 1).
phenyl)ethene, this target compound was completely aban-
As these derivatives 1, however, are particularly interest- doned and we looked for alternative amides. Trifluoroacetic
ing precursors for the synthesis of liquid crystalline com- acid derived amides are assumed to be less prone to hydro-
pounds, we investigated their preparation and redox behav- gen bonding. As depicted in Scheme 3, 4,4Ј-diaminobenzo-
ior. The results of this study are reported below.
phenone 2a was treated with (CF3CO)2O in pyridine at
room temperature to give the bisamide 3b in 82% yield.
The latter was converted via McMurry coupling to the tet-
raphenylethene derivative 1j (43%), which, indeed displays
a much better solubility than the acetamide 1h.
Additionally, based on previous observations with
branched side chains,[26] 4,4Ј-diaminobenzophenone 2a was
N-acylated with 2-methylhexanoyl chloride and 2,4-dimeth-
ylbenzoyl chloride to give the corresponding amides 3c and
3d in 47% and 99% yield, respectively. Coupling of 3c and
3d under the usual McMurry conditions[19] gave the desired
tetraphenylethenes 1k and 1l in 26% and 29% yields,
respectively (Scheme 3). The rather low yields result from
difficulties encountered in their chromatographic purifica-
tion.
Results and Discussion
Synthesis of Tetraphenylethenes 1
As shown in Scheme 2, tetrahydroxytetraphenylethene
1b, which was obtained from tetrakis(4-methoxyphenyl)eth-
ene 1a,[11,19] was acetylated with acetic anhydride in pyri-
dine at 30 °C according to the procedure by Cid[20] to
cleanly afford the tetraacetate 1f in 74% yield. Treatment
of 1b with benzoyl chloride in the presence of triethylamine
in CH2Cl2 following a procedure by Lee[21] yielded the tet-
rabenzoate 1g in 91%.
Scheme 3 shows the synthesis of the tetrakis(4-phen-
oxyphenyl)ethene 1i, which was obtained from 4,4Ј-dihy-
Surprisingly no conversion was observed upon nitration droxybenzophenone 2b which underwent an Ullmann
of tetraphenylethene 1c in neat conc. HNO3 and HOAc or etherification[27] in the presence of bromobenzene, CuO and
H2SO4.[22] In contrast, 1c was easily nitrated in CH2Cl2 to K2CO3 in pyridine to give the benzophenone derivative 3a
afford the desired tetrakis(nitrophenyl)ethene 1d in 60% in 29% yield. Subsequent McMurry coupling under the us-
(Scheme 2). Attempts to reduce the nitro groups by using ual conditions[19] yielded the target ether 1i in 34%. Alter-
Pd/C, hydrazine,[23] Sn/HCl or SnCl4 and NaBH4 in EtOH natively, in order to improve the overall yield, hydroxy-sub-
all failed.[24] After considerable experimentation, reduction stituted phenylethene 1b was directly converted into the tet-
was successfully carried out using Raney-Ni in CH2Cl2/ raphenyl ether 1i under Ullmann etherification conditions
MeOH to give the tetraamine 1e in 79% yield. The latter albeit with a lower overall yield (19%). The long reaction
was treated with acetic anhydride in the presence of DMAP times of 7 days may be taken as evidence that the fourfold
and NEt3 to provide the acetamide derivative 1h (82%). etherification suffers from increasing steric hindrance dur-
Unfortunately, the acetamide 1h was insoluble in most com- ing the course of the reaction.
Scheme 2. Preparation of tetraphenylethene derivatives 1b,[11] 1d,e using slightly modified known protocols and preparation of novel
derivatives 1f–h.
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Synthesis and Electrochemical Properties of Tetrasubstituted Tetraphenylethenes
FULL PAPER
Scheme 3. Preparation of ethene derivatives 1i–l starting from benzophenones 2a,b.
Electrochemistry of Tetraphenylethenes 1
Table 1. Electrochemical data for the oxidation of substituted tetra-
phenylethenes 1 at 295 K. Potentials are calibrated against the in-
ternal ferrocene/ferrocenium standard. NBu4PF6 (0.2 ) was used
as supporting electrolyte.
We studied the electrochemical properties of the new tet-
raphenylethenes 1f–l, along with those of reference com-
pounds 1d and tetrakis(bromophenyl)ethene (1-Br) in dif-
ferent solvents than in the original report.[12] The known
behavior of tetra(4-anisyl)ethene (1a) in CH2Cl2/
0/+
+/2+
[28]
Entry
Compd. Solvent E1/2
E1/2
∆E1/2
Kcomp
[V]
[V]
[V]
1
2
3
4
5
6
7
8
1-Br[a]
1a
CH3CN 1.08
1.25[b]
0.53[c]
2.02
0.18
0.12
n. a.
0.12
0.13
n. a.
n. a.
0.07[h]
975
112
n. a.
935
136
n. a.
n. a.
13
[5]
NBu4PF6 was completely reproducible under our condi-
CH2Cl2 0.41
CH2Cl2 1.72
CH2Cl2 0.93
CH2Cl2 0.93
CH3CN 0.56[f]
1d
tions. As all other previously reported tetraphenylethenes,
compounds 1f–l undergo at least two sequential one-elec-
tron oxidation and reduction events. The first oxidation and
reduction potentials differ by more than 3 V. Therefore,
most compounds require different solvents for monitoring
the anodic and the cathodic processes. The data are summa-
rized in Table 1 and Table 2.
The chemical stabilities of the electrogenerated oxidized
forms of the tetraarylethenes depend on both the para-sub-
stituents and the solvent. The best anodic responses were
usually obtained when using the CH2Cl2/NBu4PF6 electro-
lyte system. As can be seen from Table 1, in this medium
ethers 1a, 1i and benzoate 1g (entries 2, 5 and 8) display
chemically reversible waves even at sweep rates as low as
0.05 V s–1 and at room temperature. Their oxidized forms
1f[d]
1g
1.05
1.06[e]
n. a.
1h
1h
1i
1i
DMF
CH2Cl2 0.58
0.47[g]
n. a.
0.65
9
DMF
0.68[i]
0.59[i]
0.86[i]
Ͻ0.53
Ͻ0.48
n. a.
–0.09[h] 0.03
10
11
12
13
14
1j
CH3CN 0.84[i]
CH3CN 0.53
0.02[h]
Ͻ0[h]
Ͻ0[h]
n. a.
2.70
Ͻ1
Ͻ1
n. a.
n. a.
1k
1k
1k
1l
THF
0.48
DMF
0.56[g]
CH3CN 1.15[g]
n. a.
n. a.
[a] Tetrakis(4-bromophenyl)ethene. [b] Second wave is associated
with a significantly larger ∆Ep than the first one (quasireversible
behavior); additional irreversible oxidation at 1.63 V. [c] Additional
irreversible multi-electron oxidation peak at 1.73 V. [d] At 195 K.
[e] Additional irreversible oxidation at 1.94 V. [f] Potential of a par-
tially reversible wave at 233 K. See text for behavior at 295 K.
are thus chemically stable, at least on the time scale of the [g] Irreversible peak under all conditions employed. [h] E1/2 and
∆E1/2 values are based on digital simulations. [i] Irreversible peak.
Partially reversible at 233 K. n. a. = not applicable.
voltammetric experiments. The amides, however, were insol-
uble in CH2Cl2. Thus, the more polar CH3CN and/or DMF
had to be used. In order to probe for solvent effects on
the voltammetric behavior, amide 1k was studied in three temperature and sweep rate. Compound 1j displayed reverse
different electrolyte systems. While in THF/NBu4PF6 and to forward peak current ratios ip,rev/ip,forw, slightly lower
CH3CN/NBu4PF6 a single, chemically reversible anodic than unity at low sweep rates and at room temperature. The
wave was observed (entries 11, 12), 1k showed irreversible underlying chemical process is suppressed at higher sweep
behavior in DMF/NBu4PF6 (entry 13). The oxidation of rates or by lowering the temperature resulting in full chemi-
1l is completely irreversible in CH3CN/NBu4PF6 under all cal reversibility (entry 10).
conditions (entry 14). For amides 1j and 1h and for the
For ester 1f and amide 1h (entries 4, 6, 7) temperature
ester 1f voltammetric responses were found to depend on effects are even more pronounced. At room temperature
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Table 2. Peak potentials of the main feature for the reduction of
substituted tetraphenylethenes 1 at 295 K, sweep rate v = 0.1 V s–1.
Potentials are calibrated against the internal ferrocene/ferrocenium
standard. NBu4PF6 (0.2 ) was used as the supporting electrolyte.
Entry
Compd. Solvent E [V] (n)
1-Br[a] DMF –2.45 (2e–, irrev.)[b]
CH2Cl2 –1.33 (2e–, rev.); –1.61 (2e–, qua-
1
2
1d
sirev.)
3
4
1f
1g
THF
THF
–2.69[c] (2e–, irrev.)
–2.62[d] (1e–, p.rev.); –2.73[d] (1e–,
irrev.)
5
6
7
1h
1i
1l
DMF
DMF
DMF
–2.39 (2e–, irrev.)
–2.55 (2e–, p.rev.)
–2.80 (2e–, irrev.)
[a] Tetrakis(4-bromophenyl)ethene. For comparison see ref.[12]
[b] CVs show a discernible shoulder at ca. –2.26 V. Digital simula-
tions indicate a peak composed of two individual reduction pro-
cesses with a difference of intrinsic half-wave potentials of about
150 +/– 30 mV; additional partially reversible reduction peak at
–2.57 V. [c] Additional peaks due to the formation of electroactive
products following reduction: Ep,c = –3.04 V, Ep,a = –0.92, –0.53,
–0.135, and –0.015 V. [d] Data by digital simulation of voltammo-
grams recorded at 273 K. n. a. = not applicable, irrev. = irreversible,
rev. = reversible, quasirev. = quasireversible and p.rev. = partially
reversible.
amide 1h is oxidized in a single irreversible wave at 0.485 V
(peak A in Figure 1, parts a and b). The corresponding oxi-
dized form rapidly converts to a secondary species which
undergoes further oxidation at a more anodic potential
(Figure 1, parts a and b). The symmetric shape of this ad-
Figure 1. Cyclic voltammetric studies of compound 1h in CH3CN/
NBu4PF6 (0.2 ). a) At v = 0.1 V s–1 (295 K), b) at v = 0.8 V s–1
(295 K), and c) at v = 0.1 V s–1 (233 K).
ditional anodic peak (peak B) suggests an adsorption of the formed electroactive products. These newly formed species
underlying species onto the surface of the working elec- collect in the vicinity of the working electrode upon repeti-
trode. Upon reversal of the initial sweep direction a cath- tive scanning. This is accompanied by a decrease of the
odic return peak associated with the secondary oxidation height of peak A during the second scan (see Figure 2, b).
product (peak C) and the absence of such a return peak for At 195 K under identical conditions two fully reversible,
the primary one indicates that this transformation is com- consecutive one-electron oxidation waves are observed in-
plete even on the voltammetric time scale. The half-wave stead (c in Figure 2, Table 1, entry 4).
potential of this secondary couple was determined as
The appearance of two consecutive one-electron oxi-
0.535 V. As the sweep rate is increased, the peak current of dation waves in CH2Cl2/NBu4PF6 is typical of the tetra-
peak B diminishes with respect to peak A but still no fur- phenylethene derivatives in our study (see also part c in Fig-
ther return peak as peak C is observed (Figure 1, parts a ure 2, part a in Figure 3, and part a in Figure 4). Wave split-
[28]
and b). However, upon cooling to 233 K the primary oxi- tings, ∆E1/2
,
were either determined from the voltammo-
dation wave is observed as a partially reversible couple at grams or were simulated on the basis of the peak-to-peak
E1/2 = 0.56 V with a peak current ratio of about 0.55 along separations and the half-widths of the forward waves when
with a small peak due to the subsequently formed product the individual anodic peaks were too close to be sufficiently
(c in Figure 1 and Table 1, entry 6).
resolved. Values of ∆E1/2 in CH2Cl2/NBu4PF6 vary between
When the sweep rate is increased above 0.4 V s–1, the 70 and 130 mV (Table 1) and show that the intermediate
reverse peak continuously broadens with a concomitant de- monocations are only moderately stable with respect to dis-
crease in the reverse to forward peak current ratio, obvi- proportionation. The redox splittings reflect, at least on a
ously as a result of slow electron transfer kinetics. In DMF/ qualitative level, trends in the relative thermodynamic sta-
NBu4PF6 the behavior of amide 1h was qualitatively sim- bilities of the monocations as the supporting electrolyte and
ilar. However, the cathodic return peak was absent even at temperature are kept constant in this series. Medium and
low temperature (Table 1, entry 7).
ion pairing have also a strong bearing on ∆E1/2 and thus
The room temperature oxidation of acetate 1f in CH2Cl2/ on the relative stabilities of the monooxidized vs. the dioxid-
NBu4PF6 occurs as a broad irreversible composite peak ized and the neutral forms. The phenyl ether 1i provides an
(Figure 2, part b, peak A). The appearance of additional instructive example for such medium effects.
anodic (peak B) and cathodic (couples C/CЈ and D/DЈ) fea-
Whereas Kcomp assumes a value of 13 in CH2Cl2/
tures of the immediate oxidation peak indicates that the de- NBu4PF6 (Table 1, entry 8, Figure 3, a), it is even lower
gradation of the oxidized form(s) gives rise to subsequently than 1 in the more polar DMF/NBu4PF6 system (Table 1,
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Synthesis and Electrochemical Properties of Tetrasubstituted Tetraphenylethenes
FULL PAPER
Figure 2. Cyclic voltammetric studies of compound 1f in CH2Cl2/
NBu4PF6 (0.2 ). a) At v = 0.05 V s–1 (295 K), b) two repetitive
scans at v = 0.1 V s–1 (295 K), and c) at 0.1 V s–1 (195 K).
Figure 4. Cyclic voltammetry of benzoate 1g. a) In CH2Cl2/
NBu4PF6 (0.2 ), v = 0.1 V s–1 (295 K), b) in THF/NBu4PF6
(0.2 ), v = 0.05 V s–1 (273 K), and c) v = 0.6 V s–1 (273 K).
The two-electron nature of the oxidation wave of the
amide 1j in CH3CN/NBu4PF6 (Table 1, entry 10) was first
established using the Baranski method,[29] which gave an
estimate of 1.7 electrons vs. the ferrocene standard. Bulk
coulometry on a 0.05 m solution of 1j in CH3CN/
NBu4PF6 at ambient temperature finally confirmed the
two-electron process. Upon electrolysis the solution turned
intense purple-blue in color while 2.03 equivalents of charge
were released. However, when the oxidation was complete,
the color quickly faded along with the disappearance of the
corresponding voltammetric wave of the 1j2+/1j couple. This
indicates that the dication has only limited stability on a
more extended time-scale.
In CH2Cl2/NBu4PF6 the nitro derivative 1d is oxidized
in two consecutive largely irreversible peaks close to the sol-
vent discharge limit (Table 1, entry 3). Both peaks are asso-
ciated with about the same peak currents as the reduction
waves and, with reference to the known cathodic behavior
of 1d,[12] are thus assigned as two-electron processes. Under
Figure 3. Cyclic voltammograms of the phenyl ether 1i in
a) CH2Cl2/NBu4PF6 (0.2 ) and b) in DMF/NBu4PF6 (0.2 ) at v
= 0.05 V s–1 (295 K).
entry 9, Figure 3, b). Hence, in the DMF-based electrolyte the same conditions, 1d is reduced at considerably less cath-
system the dication is thermodynamically more favoured odic potentials than the other tetraphenylethene derivatives
than the monooxidized form. Such a situation may be en- 1 (see below). This is because the reductions of 1d involve
countered when the higher oxidized form enjoys some ad- the nitro substituents and not the tetraphenylethene core
ditional stabilization, e.g. by resonance. Similar observa- itself, as it has already been pointed out.[12,30] As a conse-
tions are made for the amide 1k in CH3CN/NBu4PF6 or quence, two cathodic waves are observed as perfectly revers-
THF/NBu4PF6 solutions (Table 1, entries 11 and 12).
ible and quasireversible features (Table 2, entry 2).
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For all other tetraphenylethene derivatives described the reduction steps, the substituent effects on the reduction
herein, the reductions are outside the potential window of potentials are less clear cut as is the case for the oxidations.
the CH2Cl2/NBu4PF6 electrolyte but were monitored in
The presence of charge-sensitive IR labels in the benzo-
THF and DMF owing to their superior cathodic discharge ate 1g and trifluoroacetamide 1j[32] paired with the chemi-
limits (Table 2). For every new amide studied, ether and es- cally reversible nature of their first and second oxidations
ter-substituted tetraphenylethene reductions are followed by in cyclic voltammetry prompted us to study these processes
chemical reactions, which are so fast under all conditions under the conditions of in situ IR spectroelectrochemistry.
that the reductions appear as chemically irreversible com- As is shown in part a of Figure 5 for the amide 1j, the
posite peaks in their cyclic voltammograms. This prevents CONH band, which is originally located at 1730 cm–1,
us from determining individual E1/2 values.[31] In most gradually splits into two separate features at 1753 and
cases, a discernible shoulder at the anodic side of the main 1733 cm–1, respectively. From this observation we conclude
peak indicates the presence of separate redox processes and that there are two kinds of differently charged amide groups
stepwise reduction to the mono- and dianions. Similar at the dication stage. This finding nicely parallels the results
behavior has been reported for the tetraphenylethene of a structural study on the tetra(4-anisyl)ethene 1a, where
itself and its methyl, tert-butyl, phenyl and amino substantially different degrees of quinoidal distortions have
derivatives.[12]
been observed for the two geminal anisyl groups at each
In the case of benzoate 1g and phenyl ether 1i, a small carbon atom.[5] Such charge localization, on mainly one of
anodic reverse peak was detected in DMF and THF, respec- the arenes at each of the central carbon atoms, is expressed
tively. For 1i the partially reversible wave broadened con- by resonance form B in part b of Figure 5. The prominent
siderably as the sweep rate was increased or the temperature feature that grows in at 1570 cm–1 is probably related to the
lowered, indicating that the reduction also suffers from slow quinone iminium type substructures of the dioxidized form
electron transfer kinetics. In the case of 1g the return peak (Figure 5, a). The subsequent reduction at a potential cath-
intensified at higher sweep rates and lower temperatures odic of the composite wave gave the reduced parent in
(Table 2, entry 4, Figure 4, b and c). Monitoring this couple nearly quantitative spectroscopic yield.
as a function of sweep rate allows us to derive the rate and
equilibrium constants for the subsequent processes and reli-
able estimates of the ∆E1/2 of the first and second re-
ductions. Although the values for the equilibrium constants
and the rates of the subsequent processes may only be qual-
itatively correct, it is still clear that both the reduction steps
are followed by chemical reactions and that the second re-
duction accelerates the rate of the subsequent process(es)
by about a factor of 1000 with respect to the first one. There
is also an additional, largely irreversible composite wave at
more cathodic potentials. On the basis that the peak cur-
rents increase with increasing sweep rate and with decreas-
ing temperature (see Figure 4, b and c), this wave is assigned
to further reductions of the dianion of 1g to the tri- and
tetraanions with half-wave potentials of ca. –3.085 and
–3.145 V, respectively. Additional peaks on the reverse scan
after traversing the third and fourth reduction waves are
attributed to the oxidations of the products of the subse-
quent reaction (Figure 4, c).
A comparison of the data listed in Table 1 and Table 2
demonstrates the influence of the para substituents on the
oxidation and reduction potentials with the phenyl ether 1i
and nitro derivative 1d as the extremes. Thus, 1i displays
the lowest oxidation potentials of all compounds in this
study. Its reduction potential is even more negative than the
cathodic discharge limit of the THF/NBu4PF6 electrolyte
system. Even within a series of chemically similar systems
such as the ethers and amides, the influence of remote sub-
stituents is clearly observed. Replacing the methoxy by the
Figure 5. a) IR spectroelectrochemical traces recorded upon step-
wise oxidation of the amide 1j. The down and up arrows at 1730,
1733, and 1753 cm–1 indicate the CONH bands of the neutral start-
ing material and of the dication, respectively, while the up arrow at
1570 cm–1 may indicate a quinoidal type substructure of the dioxid-
ized form. b) Possible resonance forms of the trifluoroacetamide
phenoxy group (1a vs. 1i) shifts the oxidation potentials to dication 1j2+
.
about 180 mV higher in value (Table 1, entries 2, 8). Substi-
tution of CH(Me)C4H9 by the CF3 or by the 2,4-Me2C6H3
Qualitatively similar results were obtained for the benzo-
group in the amides 1j–l has an even larger effect (Table 1, ate 1g, where the dioxidized form is of only fleeting exis-
entries 10, 11, 14). Owing to the chemical irreversibility of tence and substantial degradation to a new species is ob-
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Eur. J. Org. Chem. 2006, 3395–3404

Synthesis and Electrochemical Properties of Tetrasubstituted Tetraphenylethenes
FULL PAPER
screw valves and allowed experiments to be performed under an
atmosphere of argon with approximately 2.5 mL of analyte solu-
tion. Bulk electrolysis was performed in a vacuum type “H-cell”
with a large surface Pt gauze working and a smaller size Pt gauze
counter electrode and a silver wire as the reference directly welded
into the side walls of the individual cell compartments. The com-
partments are separated from each other by medium porosity frits.
The OTTLE cell was also home built following the design of Hartl
and co-workers[33] and comprises a Pt-mesh working and counter
electrode and a thin Ag wire as a pseudo-reference electrode sand-
wiched between the CaF2 windows of a conventional liquid IR cell.
The working electrode was positioned in the center of the spec-
trometer beam. In all experiments NBu4PF6 (0.2  in the respective
solvent) was used as the supporting electrolyte. For each compound
cyclic voltammograms were run at sweep rates from 0.05 V s–1 to
10 V s–1 at both room temperature and at low temperature (195 K
in CH2Cl2, 233 K in CH3CN or DMF, 213 K in THF). Scans re-
corded at high sweep rates suffer, however, from distortions owing
to Ohmic drop and somewhat slow electron transfer kinetics, espe-
cially at low temperatures.
served during the time required to effect complete con-
sumption of the neutral starting compound (for details see
Figure S1 in the Supporting Information).
Conclusions
We have synthesized novel tetraphenylethenes 1f–l with
various substituents in para positions and studied their elec-
trochemical behavior by cyclic voltammetry. Our investi-
gations extend the range of tetraphenylethenes studied by
electrochemistry to amide, ester and phenyl ether function-
alized derivatives 1f–l. Additional studies include the nitro
and bromo derivatives as references in solvents other than
those employed in the previous work, such that the oxi-
dation potentials of the nitro derivative 1d are also avail-
able. This work also demonstrates the medium effects on
the comproportionation constants. The two electron nature
of the composite wave of a prototype amide derivative 1j
has been probed by a comparison of the results of potential
sweep and potential step methods and finally by bulk elec-
trolysis. In situ IR spectroelectrochemistry served to ident-
ify the presence of two differently charged (and thus struc-
turally different) aryl groups at each of the central carbon
atoms and has provided spectroscopic evidence for quino-
idal type substructures in the dioxidized forms of tetraphen-
ylethenes 1.
Tetrakis(4-acetoxyphenyl)ethene (1f): Acetic anhydride (1.27 g,
1.17 mL, 12.4 mmol) was added to a solution of pyridine (3 mL)
and 1b (420 mg, 1.10 mmol) and the reaction mixture stirred at
room temperature for 15 h. The solvent was removed under vac-
uum, the residue dissolved in CH2Cl2 (20 mL) and washed with
diluted HCl (3×10 mL). Recrystallization from methanol gave
compound 1f as fine colorless crystals (457 mg, 0.8 mmol, 74%).
M.p. 221 °C. 1H NMR (300 MHz, CDCl3): δ = 2.25 (s, 12 H, CH3),
3
3
6.85 (d, J = 8.7 Hz, 8 H, 3-H, 5-H), 7.01 (d, J = 8.7 Hz, 8 H, 2-
H, 6-H) ppm. 13C NMR (75 MHz, CDCl3): δ = 21.5 (CH3), 121.3
(C-3, C-5), 132.7 (C-2, C-6), 140.0 (C=C), 140.9 (C-1), 149.7 (C-
4), 169.5 (C=O) ppm. FTIR (ATR): ν = 3068 (w), 1750 (vs), 1600
˜
Experimental Section
(m), 1501 (s), 1367 (s), 1185 (vs), 1009 (s), 908 (m), 850 (m) cm–1.
UV/Vis (toluene) λmax = 314 nm. MS (EI): m/z (%) = 654 (100)
[M+], 522 (59), 480 (57), 438 (41), 396 (70), 43 (56). C34H28O8
(564.58): calcd. C 72.33, H 5.00; found C 72.11, H 5.10.
General: The following tetraphenylethenes 1a–e are known in the
literature.[6,11–14,18] Melting points were measured using a differen-
tial scanning calorimeter Mettler–Toledo DSC 822. 1H NMR spec-
tra were recorded using a Bruker ARX 300 and ARX 500 with
tetramethylsilane as the internal standard. 13C NMR multiplicities
were assigned by DEPT experiments. IR spectra were recorded
using a Bruker Vector 22 FT-IR spectrometer with ATR technique.
Mass spectrometry was performed using a Varian MAT 711 mass
spectrometer with EI ionization (70 eV). UV/Vis spectra were re-
corded using a Perkin–Elmer Lambda7 spectrometer. Column
chromatography was performed using silica gel 60 (Fluka, mesh
40–63 µm) with hexanes (boiling range 30–75 °C). Electrochemical
data were acquired with a computer controlled EG&G model 273
potentiostat utilizing the EG&G 250 software package. Digital sim-
ulations of experimental CVs were performed with DigiSim® soft-
ware (version 2.1) available from BAS. CH2Cl2 and 1,2-Cl2C2H4
(Fluka, Burdick&Jackson Brand) for electrochemical work and
CH3CN (Roth) were freshly distilled from CaH2 prior to use. DMF
(Fluka, Burdick&Jackson Brand) was stored over molecular sieves
(4 Å) and purged with argon prior to use. THF was dried with
potassium and freshly distilled from potassium/benzophenone.
Tetrakis(4-benzoyloxyphenyl)ethene (1g): Benzoyl chloride (0.59 g,
0.49 mL, 4.20 mmol) was added dropwise over 20 min to a solution
of 1b (414 mg, 1.00 mmol) and triethylamine (430 mg, 0.59 mL,
4.20 mmol) in CH2Cl2 (5 mL) at 0 °C. Then the reaction mixture
was stirred at room temperature for 2 h and washed with 1  HCl
(3×2 mL). After removal of the solvent under vacuum, the residue
was recrystallized from methanol/hexane (1:1) to give 1g as fine
colorless crystals (743 mg, 0.92 mmol, 91%). M.p. 306 °C. 1H
3
NMR (500 MHz, CDCl3): δ = 7.05 (d, J = 8.6 Hz, 8 H, 3-H, 5-
3
3
H), 7.16 (d, J = 8.6 Hz, 8 H, 2-H, 6-H), 7.50 (t, J = 7.8 Hz, 8 H,
3
3
3Ј-H, 5Ј-H), 7.63 (t, J = 7.4 Hz, 4 H, 4Ј-H), 8.19 (d, J = 7.3 Hz,
8 H, 2Ј-H, 6Ј-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 121.2
(C-3, C-5), 128.6 (C-2Ј, C-6Ј), 129.6 (C-1Ј), 130.2 (C-3Ј, C-5Ј),
132.5 (C-2, C-6), 133.6 (C-4Ј), 139.9 (C=C), 140.9 (C-1), 149.1 (C-
4), 165.0 (C=O) ppm. FTIR (ATR): ν = 3161 (w), 1730 (vs), 1598
˜
(w), 1503 (m), 1260 (s), 1199 (s), 1163 (s), 1059 (s), 700 (vs) cm–1.
UV/Vis (toluene): λmax = 308 nm. MS (EI): m/z (%) = 812 (47)
[M+], 105 (100). C54H36O8 (812.86): calcd. C 79.79, H 4.46; found
C 80.12, H 4.48.
Electrochemical Experiments: All electrochemical experiments were
performed in a home-built cylindrical vacuum-tight one-compart-
ment cell. A spiral shaped Pt wire and a Ag wire as the counter
and reference electrodes, respectively, were sealed directly into op-
posite sides of the glass wall while the respective working electrode
[Pt or glassy carbon, 1.1 mm, polished with 0.25 µm diamond paste
(Buehler–Wirtz) before each experiment] was introduced via a tef-
lon screw cap with a suitable fitting. The cell was attached to a
conventional Schlenk line via two side arms equipped with teflon
Tetrakis(4-acetylaminophenyl)ethene (1h): A solution of 4-(dimeth-
ylamino)pyridine (6.10 mg, 0.05 mmol), triethylamine (47 mg,
0.07 mL, 0.47 mmol) and acetic anhydride (130 mg, 0.12 mL,
1.30 mmol) in CH2Cl2 (5 mL) was added dropwise to a suspension
of 1e (61 mg, 0.16 mmol) in CH2Cl2 (5 mL) and the reaction mix-
ture was stirred at room temperature for 16 h. A 0.1  solution of
NaOH (10 mL) was then added, the layers were separated and the
Eur. J. Org. Chem. 2006, 3395–3404
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3401

A. Schreivogel, J. Maurer, R. Winter, A. Baro, S. Laschat
FULL PAPER
aqueous layer was extracted with CH2Cl2 (3×2 mL). The com-
bined organic layers were washed with brine (3×5 mL). The sol-
vent was removed under vacuum and the residue was washed with
CH2Cl2 and dried to give 1h as orange powder (71 mg, 0.13 mmol,
4,4Ј-Bis(trifluoroacetylamino)benzophenone (3b): Trifluoroacetic an-
hydride (0.6 mL, 4 mmol) was slowly added dropwise to a solution
of 2a (200 mg, 0.93 mmol) in pyridine (15 mL) and the reaction
mixture was stirred at room temperature for 30 min (tlc control).
82%). M.p. Ͼ230 °C (dec.). 1H NMR (500 MHz, [D6]DMSO, Pyridine was removed, the residue dissolved in CHCl3 (10 mL) and
3
60 °C): δ = 1.99 (s, 12 H, CH3), 6.86 (d, J = 7.7 Hz, 8 H, 3-H, 5-
H), 7.32 (d, 3J = 7.7 Hz, 8 H, 2-H, 6-H), 9.71 (s, 4 H, NHCO)
ppm. 13C NMR (125 MHz, [D6]DMSO): δ = 23.5 (CH3), 118.1,
successively washed with 1  HCl (10 mL) and a satd. solution of
NaHCO3 (2×5 mL). After removal of the solvent, the residue was
purified by flash chromatography with hexanes/acetone (5:1) and
130.7 (C-2, C-3, C-5, C-6), 137.2, 138.0 (C-1, C-4), 138.8 (C=C) recrystallized from hexanes/acetone to give 3b as white crystals
1
ppm. FTIR (ATR): ν = 3249 (m), 3102 (w), 3035 (w), 1663 (s),
1593 (s), 1511 (vs), 1403 (m), 1370 (m), 1313 (s), 1017 (m), 839 (s)
(300 mg, 0.74 mol, 82%). M.p. 241 °C. H NMR (500 MHz, [D6]-
acetone): δ = 7.90 (d, J = 8.7 Hz, 4 H, 2-H, 6-H), 7.96 (d, J =
˜
cm–1. UV/Vis (CH3CN): λmax = 273 nm. MS (EI): m/z (%) = 560 8.7 Hz, 4 H, 3-H, 5-H), 10.59 (s, 2 H, NHCO) ppm. 13C NMR
(1), 518 (2), 476 (3), 434 (3), 393 (1), 58 (30), 43 (100).
(125 MHz, [D6]acetone): δ = 116.81 (q, 1J = 288.1 Hz, CF3),
121.10, 131.85 (C-2, C-3, C-5, C-6), 135.43, 141.15 (C-1, C-4),
155.10 (q, 2J = 37.6 Hz, CF3CO), 194.21 (C=O) ppm. FTIR
Bis[4-(phenyloxy)phenyl] Ketone (3a): Potassium carbonate (1.94 g,
14 mmol) was dried in a Schlenk flask, and in a N2 atmosphere 2b
(1.50 g, 7.00 mmol), bromobenzene (2.20 g, 1.48 mL, 14.0 mmol),
CuO (1.68 g, 21 mmol) and pyridine (30 mL) were added. The reac-
tion mixture was stirred at 150 °C for 7 d. After cooling to room
temperature, CH2Cl2 (200 mL) was added and the solid filtered off.
The filtrate was vigorously stirred with 10% HCl (2×200 mL) for
1 h, washed with a satd. solution of NaHCO3 and H2O (200 mL
each) and dried (MgSO4). The solvent was removed under vacuum
and the residue purified by chromatography on SiO2 with CH2Cl2/
EtOAc (10:1) to give 3a as yellowish crystals (700 mg, 2.00 mmol,
(ATR): ν = 3279 (s), 1707 (s), 1642 (m), 1600 (m), 1536 (s), 1150
˜
(s), 927 (m), 856 (m), 676 (s) cm–1. UV/Vis (CH3CN): λmax
=
291 nm. MS (EI): m/z (%) = 404 (76) [M+], 292 (5), 216 (100), 168
(4), 146 (6), 28 (11). C17H10F6N2O3 (404.27): calcd. C 50.51, H
2.49, N 6.93; found C 50.40, H 2.56, N 6.70.
4,4Ј-Bis(2-methylhexylamino)benzophenone (3c): 2-Methylhexanoyl
chloride (2.1 g, 14 mmol) was added dropwise to a solution of 2a
(849 mg, 4 mmol) in pyridine (50 mL) and the reaction mixture
stirred at room temperature for 2 h. Pyridine was removed, the resi-
due dissolved in CHCl3 (20 mL) and successively washed with 1 
HCl (10 mL) and a satd. solution of NaHCO3 (2×10 mL). After
removal of the solvent, the residue was purified by flash chromatog-
raphy with hexanes/acetone (3:1) and recrystallized from hexanes/
acetone to give 3c as white crystals (825 mg, 1.9 mmol, 47%). M.p.
1
29%). H NMR (300 MHz, CDCl3): δ = 7.01–7.04 (m, 4 H, 3-H,
5-H), 7.08–7.43 (m, 10 H, 3-H, 2Ј-H, 3Ј-H, 4Ј-H, 5Ј-H, 6Ј-H), 7.78–
7.81 (m, 4 H, 2-H, 6-H) ppm. 13C NMR (75 MHz, CDCl3): δ =
117.5 (C-3Ј, C-5Ј), 120.5 (C-2Ј, C-6Ј), 124.9 (C-4Ј), 130.4 (C-3, C-
5), 132.5 (C-1), 132.6 (C-2, C-6), 155.9 (C-1Ј), 161.8 (C-4), 188.4
(C=O) ppm.
1
163 °C. H NMR (300 MHz, [D6]acetone): δ = 0.90 (t, J = 7.1 Hz,
6 H, 5Ј-H), 1.20 (d, J = 6.8 Hz, 6 H, 6Ј-H), 1.27–1.58 (m, 9 H, 3Ј-
H, 4Ј-H, 2Ј-H), 1.66–1.86 (m, 1 H, 2Ј-H), 2.55 (sext, J = 6.8 Hz, 1
H, 1Ј-H), 7.76 (d, J = 8.8 Hz, 4 H, 3-H, 5-H), 7.86 (d, J = 8.9 Hz,
4 H, 2-H, 6-H), 9.41 (s, 2 H, NHCO) ppm. 13C NMR (75 MHz,
[D6]acetone): δ = 13.88 (C-5), 17.08 (C-6), 22.14 (C-4), 29.10 (C-
3), 33.42 (C-2), 40.70 (C-1), 118.29, 130.84 (C-2, C-3, C-5, C-6),
131.71, 143.09 (C-1, C-4), 175.41 (NHCO), 193.39 (C=O) ppm.
Tetrakis(4-phenyloxyphenyl)ethene (1i): a) In a Schlenk flask in an
inert gas atmosphere TiCl4 (390 mg, 0.23 mL, 2.00 mmol) was
added to abs. THF (20 mL) at 0 °C. Then Zn powder (265 mg),
pyridine (0.14 mL) and a suspension of 3a (690 mg, 1.90 mmol) in
THF (10 mL) were slowly added and the reaction mixture stirred
at 60 °C for 18 h. A solution of K2CO3/H2O (10%, 20 mL) and
H2O (20 mL) were added, the layers were separated and the aque-
ous layer was extracted with CH2Cl2 (3×20 mL). The combined
organic layers were dried (MgSO4) and concentrated. The residue
was purified by chromatography on SiO2 with hexanes/EtOAc
(15:1) to give 1i as colorless crystals (460 mg, 0.60 mmol, 34%).
FTIR (ATR): ν = 3248 (s), 2926 (s), 2856 (w), 1651 (s), 1592 (s),
˜
1521 (s), 1406 (m), 1306 (m), 1250 (m), 937 (m), 855 (m), 758 (w),
665 (w) cm–1. UV/Vis (CH3CN): λmax = 306, 231 nm. MS (CI):
m/z (%) = 437 (100) [M+], 380 (28), 324 (47), 268 (7), 232 (8), 212
(22), 183 (5), 120 (5), 85 (16), 43 (16). C27H36N2O3 (436.59): calcd.
C 74.28, H 8.31, N 6.42; found C 74.02, H 8.19, N 6.32.
b) In a Schlenk flask K2CO3 (710 mg, 5.00 mmol) was dried and
in an inert gas atmosphere 1b (500 mg, 1.26 mmol), CuO (605 mg,
7.60 mmol) and bromobenzene (801 mg, 0.54 mL, 5.00 mmol) were
added. The reaction mixture was stirred at 150 °C for 7 d and then
cooled to room temperature. After addition of CH2Cl2 (50 mL),
the reaction mixture was filtered. The filtrate was vigorously stirred
with diluted HCl (2×50 mL) for 1 h, washed with a satd. solution
of NaHCO3 and H2O (2×30 mL each) and dried (MgSO4). The
solvent was removed under vacuum and the residue was purified
by flash chromatography on SiO2 with CH2Cl2/EtOAc (15:1) to
4,4Ј-Bis(2,4-dimethylbenzylamino)benzophenone (3d): 2,4-Dimeth-
ylbenzoyl chloride (2.3 g, 13.6 mmol) was added dropwise to a
solution of 2a (724 mg, 3.4 mmol) in pyridine (40 mL) and the reac-
tion mixture stirred at room temperature for 2 h. Pyridine was re-
moved, the residue dissolved in CHCl3 (50 mL) and successively
washed with 1  HCl (25 mL) and a satd. solution of NaHCO3
(2×25 mL). After removal of the solvent, the residue was purified
by flash chromatography with hexanes/acetone (3:1) and recrys-
give 1i (166 mg, 0.24 mmol, 19%). M.p. 196 °C. 1H NMR tallized from hexanes/acetone to give 3d as white crystals (1.6 g,
1
(500 MHz, CDCl3): δ = 6.77–6.78 (m, 8 H, 3Ј-H, 5Ј-H), 6.96–7.03
3.5 mmol, 99%). M.p. 235 °C. H NMR (500 MHz, [D6]DMSO):
(m, 20 H, 3-H, 5-H, 2Ј-H, 4Ј-H, 6Ј-H), 7.30–7.32 (m, 8 H, 2-H, 6- δ = 2.34 (s, 6 H, 4Ј-CH3), 2.38 (s, 6 H, 2Ј-CH3), 7.10–7.20 (m, 4 H,
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 118.4 (C-3Ј, C-5Ј), 6Ј-H, 3Ј-H), 7.41 (d, J = 7.5 Hz, 2 H, 5Ј-H), 7.76 (d, J = 8.7 Hz, 4
119.2 (C-3, C-5), 123.6 (C-4Ј), 130.6 (C-2, C-6), 133.1 (C-2Ј, C- H, 2-H, 6-H), 7.92 (d, J = 8.8 Hz, 4 H, 3-H, 5-H), 10.59 (s, 2 H,
6Ј), 139.1 (C-1), 139.3 (C=C), 156.1 (C-1Ј), 157.4 (C-1) ppm. FTIR
(ATR): ν = 3032 (w), 2963 (w), 1586 (s), 1503 (m), 1485 (vs), 1227
NHCO) ppm. 13C NMR (125 MHz, [D6]DMSO): δ = 19.33 (4Ј-
CH3), 20.80 (2Ј-CH3), 118.82, 130.78 (C-2, C-3, C-4, C-5), 126.10,
˜
(vs), 1167 (m), 1158 (m), 1095 (m), 1070 (m), 1011 (m), 858 (m), 127.48, 131.24 (C-3Ј, C-5Ј, C-6Ј), 132.13, 133.89, 135.54, 139.59,
844 (m), 793 (s), 749 (s), 689 (s) cm–1. UV/Vis (THF): λmax = 324,
143.15 (C-1, C-4, C-1Ј, C-2Ј, C-4Ј), 168.27 (NHCO), 193.48 (C=O)
263, 259 nm. MS (EI): m/z (%) = 700 (100) [M+], 514 (4), 350 (6), ppm. FTIR (ATR): ν = 3298 (s), 2964 (w), 2923 (w), 1707 (s), 1666
˜
28 (8), 18 (27). HRMS for C50H36O4 (EI): calcd. 700.2614; found (w), 1600 (w), 1586 (s), 1507 (s), 1403 (m), 1309 (m), 1246 (m), 928
700.2616.
(w), 855 (w), 832 (w) cm–1. UV/Vis (CH3CN): λmax = 309 nm. MS
3402
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 3395–3404

Synthesis and Electrochemical Properties of Tetrasubstituted Tetraphenylethenes
(EI): m/z (%) = 404 (76) [M+], 292 (5), 216 (100), 168 (4), 146 (6), 28 (s) cm–1. UV/Vis (CH3CN): λmax = 265 nm. C62H56N4O4 (921.15):
FULL PAPER
(11). C31H28N2O3 (476.57): calcd. C 78.13, H 5.92, N 5.88; found C
77.91, H 5.95, N 5.83.
calcd. C 80.84, H 6.13, N 6.08; found C 75.36, H 6.09, N 5.57.
Supporting Information (see also the footnote on the first page of
this article): IR spectroelectrochemical spectra recorded during the
oxidation of tetrakis(4-benzoyloxyphenyl)ethene (1g).
General Procedure for the Preparation of Tetrakis(4-amidophenyl)-
ethenes 1j–k: In a Schenk flask TiCl4 was added to abs. THF in a
N2 atmosphere at 0 °C. Then Zn powder and pyridine were added
followed by dropwise addition of a solution of the respective 3b–d
in THF/CH2Cl2. The reaction mixture was stirred at 60 °C for 20 h,
cooled to room temperature and filtered through Celite. The filtrate
was washed once with K2CO3/H2O (10%) and H2O. The aqueous
layer was extracted three times with CHCl3, and the combined or-
ganic layers were dried (MgSO4) and concentrated under vacuum.
The residue was purified by flash chromatography with hexanes/
acetone (3:1) and recrystallized from acetone/hexanes to give the
products 1j–k as yellowish solid.
Acknowledgments
Generous financial support by the Deutsche Forschungsgemein-
schaft, the Fonds der Chemischen Industrie and the Ministerium
für Wissenschaft, Forschung und Kunst des Landes Baden-
Württemberg is gratefully acknowledged. We would like to thank
Prof. Jürgen Heinze, University of Freiburg, for helpful discussions
and initial experiments.
Tetrakis(4-trifluoroacetamidophenyl)ethene (1j): According to the
General Procedure from 3b (0.606 g, 1.5 mmol) in THF (10 mL)
and CH2Cl2 (5 mL), TiCl4 (0.2 mL, 1.8 mmol), Zn (0.210 g,
3.2 mol), pyridine (0.11 mL, 1.4 mol), THF (15 mL). Yield:
0.257 mg, 0.32 mmol, 43%. M.p. 357 °C. 1H NMR (500 MHz, [D6]-
acetone): δ = 6.97 (d, J = 8.7 Hz, 8 H, 2-H, 6-H), 7.42 (d, J =
8.7 Hz, 8 H, 3-H, 5-H), 10.09 (s, 4 H, NHCO) ppm. 13C NMR
(75 MHz, [D6]acetone): δ = 116.88 (q, 1J = 287.9 Hz, CF3), 120.99,
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ell, L. Mazuch, B. Shell, P. R. West, Can. J. Chem. 1978, 56,
1246–1252; f) M. V. Sargent, C. J. Timmons, J. Chem. Soc.
1964, 5544–5552.
132.70 (C-2, C-3, C-5, C-6), 136.07, 141.67 (C-1, C-4), 140.96
2
(C=C), 155.55 (q, J = 37.2 Hz, CF CO) ppm. FTIR (ATR): ν =
˜
3
3306 (s), 3127 (w), 2934 (w), 1703 (vs), 1596 (m), 1537 (s), 1279
(m), 1242 (m), 1186 (s), 1156 (vs), 915 (m), 823 (m) cm–1. UV/Vis
(CH3CN): λmax = 272 nm. MS (DEI): m/z (%) = 776 (100) [M+],
706 (3), 338 (6). C34H20F12N4O4 (776.53): calcd. C 52.59, H 2.60,
N 7.22; found C 52.84, H 2.88, N 7.21.
Tetrakis[4-(2-methylhexylamido)phenyl]ethene (1k): According to
the General Procedure from 3c (0.5 g, 1.1 mmol) in THF (10 mL)
and CH2Cl2 (3 mL), TiCl4 (0.14 mL, 1.3 mmol), Zn (0.157 g,
2.4 mmol), pyridine (0.08 mL, 1 mol), THF (15 mL). Yield:
120 mg, 0.143 mmol, 26%. M.p. 296 °C. 1H NMR (500 MHz, [D6]-
DMSO): δ = 0.86 (t, J = 7.1 Hz, 12 H, 5Ј-H), 1.06 (d, J = 6.8 Hz,
12 H, 6Ј-H), 1.27–1.58 (m, 9 H, 3Ј-H, 4Ј-H, 2Ј-H), 1.16–1.35 (m,
20 H, 2Ј-H, 3Ј-H, 4Ј-H), 1.55 (m, 4 H, 2Ј-H), 2.39 (sext, J = 6.6 Hz,
4 H, 1Ј-H), 6.87 (d, J = 8.6 Hz, 8 H, 3-H, 5-H), 7.38 (d, J = 8.6 Hz,
4 H, 2-H, 6-H), 9.77 (s, 4 H, NHCO) ppm. 13C NMR (125 MHz,
[D6]DMSO): δ = 11.54 (C-5Ј), 15.57 (C-4Ј), 19.82 (C-6Ј), 26.82 (C-
3), 31.10 (C-2), 38.22 (C-1), 116.14, 128.84 (C-2, C-3, C-5, C-6),
135.18, 136.02 (C-1, C-4), 136.04 (C=C), 172.33 (HNC=O) ppm.
FTIR (ATR): ν = 3296 (s), 2928 (s), 2187 (w), 1979 (w), 1658 (vs),
˜
1589 (s), 1511 (vs), 1402 (s), 1306 (m), 1242 (m), 1180 (m), 825 (s)
cm–1. UV/Vis (CH3CN): λmax = 338, 275, 240 nm. MS (EI): m/z (%)
= 840 (100) [M+], 729 (12), 616 (2), 112 (2), 85 (6), 74 (10), 43 (14).
[4] A. Schultz, S. Laschat, S. Diele, M. Nimtz, Eur. J. Org. Chem.
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[5] R. Rathore, S. V. Lindeman, A. S. Kumar, J. K. Kochi, J. Am.
Chem. Soc. 1998, 120, 6931–6939.
[6] a) W. J. Leigh, D. R. Arnold, Can. J. Chem. 1981, 59, 3061–
3075; b) V. D. Parker, K. Nyberg, L. Eberson, J. Electroanal.
Chem. Interfacial Electrochem. 1969, 22, 150–152.
Tetrakis[4-(2,4-dimethylbenzamido)phenyl]ethene (1l): According to
the General Procedure from 3d (1 g, 2.1 mmol) in THF (15 mL)
and CH2Cl2 (10 mL), TiCl4 (0.26 mL, 2.4 mmol), Zn (0.312 g,
4.8 mmol), pyridine (0.16 mL, 2 mmol), THF (20 mL). Yield:
1
210 mg, 0.23 mmol, 29%. M.p. 333 °C. H NMR (300 MHz, [D6]- [7] F. Barbosa, V. Peron, G. Gescheidt, A. Fürstner, J. Org. Chem.
1998, 63, 8806–8814.
DMSO): δ = 3.37 (br. s, 12 H, 2Ј-CH3), 3.38 (br. s, 12, 4Ј-H), 7.09–
7.13 (m, 8 H, 6Ј-H, 3Ј-H), 7.33 (d, J = 7.5 Hz, 4 H, 5Ј-H), 7.46 (d,
J = 8.5 Hz, 8 H, 3-H, 5-H), 7.54 (d, J = 8.5 Hz, 8 H, 2-H, 6-H)
ppm. 13C NMR (125 MHz, [D6]DMSO): δ = 19.29 (4Ј-CH3), 20.76
(2Ј-CH3), 119.44, 127.25, 128.16 (C-3Ј, C-5Ј, C-6Ј), 125.95, 131.05
(C-2, C-3, C-5, C-6), 134.39, 135.27, 136.84, 139.02, 139.83 (C-1,
C-4, C-1Ј, C-2Ј, C-4Ј), 167.54 (NHCO) ppm. (The C=C signal was
[8] H. Bock, K. Ruppert, D. Fenske, Angew. Chem. 1989, 101,
1717–1719; Angew. Chem. Int. Ed. Engl. 1989, 28, 1685–1688.
[9] a) H. Bock, C. Näther, Z. Havlas, J. Chem. Soc., Chem. Com-
mun. 1995, 1111–1112; b) T. Suzuki, H. Shiohara, M. Monobe,
T. Sakimura, S. Tanaka, Y. Yamashita, T. Miyashi, Angew.
Chem. 1992, 104, 454–456; Angew. Chem. Int. Ed. Engl. 1992,
31, 455–458; c) N. C. Baenziger, R. E. Buckles, T. D. Simpson,
J. Am. Chem. Soc. 1967, 89, 3405–3408.
not detected.) FTIR (ATR): ν = 3295 (s), 2921 (s), 1656 (vs), 1596
˜
(s), 1512 (vs), 1409 (s), 1319 (s), 1231 (s), 1081 (s), 818 (m), 778
[10] S. Sengupta, Synlett 2004, 1191–1194.
Eur. J. Org. Chem. 2006, 3395–3404
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3403

A. Schreivogel, J. Maurer, R. Winter, A. Baro, S. Laschat
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oxidized forms according to the equation:
Kcomp = [A+]2/[A]·[A2+] = exp{(nF/RT)·∆E1/2
}
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Received: February 12, 2006
Published Online: May 30, 2006
3404
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 3395–3404