Ferrocenes bearing highly extended π systems with nitrile, nitro, and dimethylamino end groups

Article abstract of DOI:10.1002/ejoc.201402831

Oligophenylene-ethynylenes are a popular class of molecular wires for molecular electronics. Replacement of some, not all, of the 1,4-phenylene units by 1,1′-ferrocenylene moieties generates less rigid entities with a limited conformational flexibility. Within this concept, the syntheses of some 1,1′-disubstituted ferrocenes that bear arylethynyl or 4-(arylethynyl)phenyl substituents is presented. In contrast to related compounds with sulfur end groups that were prepared previously, the versions presented here have nitrile end groups, which, according to reported precedence, may serve as points of attachment to gold surfaces. A crystal structure analysis of an unusual diferrocenylethyne derivative is included. In addition, one representative with a push-pull disubstitution that has a nitro and a dimethylamino end group is presented. Many of the prepared compounds have been characterized by cyclic voltammetry. New ferrocenes bearing highly extended π systems with nitrile, nitro, and dimethylamino end groups are prepared that include a push-pull-substituted system. The redox properties of the new compounds have been characterized by cyclic voltammetry.

Full text of DOI:10.1002/ejoc.201402831

Job/Unit: O42831
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Date: 01-09-14 11:23:45
Pages: 11
FULL PAPER
DOI: 10.1002/ejoc.201402831
Ferrocenes Bearing Highly Extended π Systems with Nitrile, Nitro, and
Dimethylamino End Groups
Nico Krauße[a] and Holger Butenschön*[a]
Keywords: Sandwich compounds / Redox chemistry / Alkynes / Pi interactions / Conjugation / Cross coupling
Oligophenylene-ethynylenes are a popular class of mo-
lecular wires for molecular electronics. Replacement of some,
not all, of the 1,4-phenylene units by 1,1Ј-ferrocenylene moi-
eties generates less rigid entities with a limited conforma-
tional flexibility. Within this concept, the syntheses of some
1,1Ј-disubstituted ferrocenes that bear arylethynyl or 4-(aryl-
ethynyl)phenyl substituents is presented. In contrast to re-
lated compounds with sulfur end groups that were prepared
previously, the versions presented here have nitrile end
groups, which, according to reported precedence, may serve
as points of attachment to gold surfaces. A crystal structure
analysis of an unusual diferrocenylethyne derivative is in-
cluded. In addition, one representative with a push-pull di-
substitution that has a nitro and a dimethylamino end group
is presented. Many of the prepared compounds have been
characterized by cyclic voltammetry.
used as a standard for cyclic voltammetry.[22,23] There are
many compounds in which an aromatic benzene ring has
Introduction
Since the discovery of ferrocene as the first sandwich com- been replaced by a ferrocene moiety, with examples includ-
plex by Kealy and Pauson[1] more than 60 years ago, this ing topologically remarkable compounds such as su-
compound has formed the basis for many diverse develop- perphane[24] or helicene,[25] medicinally important com-
ments in organometallic chemistry.[2,3] These include cataly- pounds such as tamoxifen,[21,26] or reactions such as the
sis using ferrocene ligands,[4–10] organic synthesis,[11–13] ma- electrophilic acylation, which is nowadays included in basic
terials science,[14–18] molecular devices,[19,20] and biomolec- chemical education.[27] Catalysts such as 4-(dimethyl-
ules.[21] The continued interest in ferrocene chemistry has its amino)pyridine[28] (DMAP) have been modified by anell-
roots in the attractive combination of important properties: ation with a ferrocene unit, rendering the catalyst chiral.[29]
Ferrocene is an electron-rich aromatic compound with a
One class of compounds with relevance for molecular
three dimensional structure. This structure makes it electronics are so-called oligophenylene-ethynylenes (OPE)
stereochemically interesting because unsymmetrically di- such as 1,[30] in which 1,4-phenylene and ethynylene units
substituted cyclopentadienyl ligands cause planar chirality, are combined to give extended π systems that can be used
which is a particularly stable form of chirality. Ferrocene is as molecular wires.[30–33] These molecules form rigid rods,
redox active, indeed, the reversible one-electron oxidation is and the ends are equipped with so-called “alligator clips”,
[a] Institut für Organische Chemie, Leibniz Universität Hannover,
which are functional groups allowing for the attachment of
the molecular wire at a gold surface. These end groups are
usually thioacetyl groups,[30] but tert-butylsulfanyl or nitrile
groups have also been used.[34,35]
Schneiderberg 1B, 30167 Hannover, Germany
E-mail: holger.butenschoen@mbox.oci.uni-hannover.de
http://www.ak-butenschoen.uni-hannover.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402831.
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Our concept in this context is based on the replacement tions using microwave heating. The respective reaction with
of some, not all, of the 1,4-phenylene units in such a molec- 3 afforded [2-(4-cyanophenyl)ethynyl]ferrocene (7) in 98%
ular wire as in 2.[36] In this way, the usually rigid linear wire yield as compared with 84% yield, which had previously
gains some limited conformational flexibility, because the been achieved by using 4-bromobenzonitrile instead.[43] In
ferrocene units act as hinges that can be compared to those
a
similar manner, {4-[(4-cyanophenyl)ethynyl]phenyl}-
of a foldable ruler. In addition, the wire becomes three di- ferrocene (9) was obtained as red crystals from (4-ethyn-
mensional, so that π,π stacking of more than one wire be- ylphenyl)ferrocene[44] (8) in 100% yield. Whereas 7 was
comes less likely.
In compounds such as 2, tert-butylsulfanyl end groups was characterized spectroscopically.
were used because the conditions of the synthesis of 2
1,1Ј-Diiodoferrocene (10)[45] is the starting material of
identified on the basis of its published analytical data,[43]
9
turned out to be incompatible with the more sensitive choice for the bidirectional synthesis of respective 1,1Ј-di-
thioacetal groups. According to a method developed by substituted systems with a ferrocene unit integrated in the
Mayor et al., these groups should be transformed into extended π system. However, to have the option of at-
thioacetyl substituents.[35] However, this method failed with taching two different substituents, we found 1-iodo-1Ј-eth-
ferrocene derivatives. As an alternative, we envisaged the ynylferrocene (11) to be useful. The latter compound is
use of nitrile end groups instead.[34,37] Here, we report the available by a mono Sonogashira coupling of 10 with tri-
synthesis and characterization of some ferrocene derivatives methylsilylethyne, followed by protiodesilylation.[41,46–49]
with arylalkynyl substituents and nitrile or other nitrogen-
containing end groups. The extended π systems make these
compounds interesting with respect to their redox behavior.
Results and Discussion
Treatment of 11 with 3 (2 equiv.) with microwave heating
in a Sonogashira coupling, afforded 1-[(4-cyanophenyl)eth-
The syntheses of ferrocenes with substituents bearing
nitrile end groups can be achieved by coupling of suitable
ynyl]-1Ј-iodoferrocene (12) in 96% yield as an orange-red
ferrocene derivatives with building blocks such as 3–5.
crystalline solid. The corresponding reaction with 4-bromo-
Among these, 4-iodobenzonitrile (3) is commercially avail-
2,6-dimethylbenzonitrile (5; 1.5 equiv.) instead of 3 gave a
able, and 4-ethynylbenzonitrile (4) is easily obtained from 3
less clear result: The isolated product mixture was separated
and trimethylsilylethyne by Sonogashira coupling with mi-
chromatographically, and 16% of starting material 11 was
obtained in addition to 46% unconsumed 5. After Sonoga-
shira coupling, 13 was isolated as the main product in 50%
yield as an orange-red solid. Finally, 14 was isolated as a
crowave heating in a significantly improved yield of
99%,[37,38] followed by quantitative protiodesilylation.[37]
Compound 5 was prepared according to a method devel-
oped by Fuson et al.[39]
side-product in 8% yield as a dark-red solid. Whereas 12
and 13 were easily characterized based on their IR, NMR
(1H, 13C), and MS data, 14 turned out to be an interesting
diyne with two ferrocene units, which was characterized
crystallographically. The reduced chemoselectivity in the
second reaction can be understood by assuming a slower
coupling reaction of the less reactive bromide 5 compared
According to our earlier experience,[36,40,41] ethynylferro- with that of 3. This provides sufficient time for unreacted 11
cene[42] (6) is a suitable starting material for the synthesis to undergo a Sonogashira coupling with 13 that was already
of monosubstituted systems by Sonogashira coupling reac- formed. In principle, this reaction sequence indicates the
2
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Ferrocenes Bearing Highly Extended π Systems
possibility of forming oligo(1,1Ј-ferrocenylidene)ethynyl-
enes directly from 11.
Compound 14 is a diferrocenylethyne derivative with an
unusual substitution pattern: whereas one of the outer cy-
clopentadienyl ligands bears an iodo substituent, the sec-
ond bears a highly unsaturated (3,5-dimethyl-4-cyano-
phenyl)ethynyl group. The structure of 14 is given in Fig-
ure 1. The diferrocenylethyne subunit in 14 adopts the same
conformation as the unsubstituted compound with almost
coplanar cyclopentadienyl ligands at both ends of the triple
bond.[51] As clearly shown in Figure 1, top view, the dialk-
ynylferrocene subunit adopts an intuitively more hindered
syn conformation instead of a less crowded anti conforma-
tion with respect to the alkynyl substituents. This is re-
flected by interatomic distances of C1–C8 (334.9 pm), C11–
C23 (339.3 pm), C12–C24 (347.1 pm), and C13–C25
(363.1 pm), which are in the range of the double van der
Waals radius of carbon.[52] Such a conformation has pre-
viously been observed with 1,1Ј-disubstituted ferrocenes
with aromatic or alkynyl substituents, for example 1,1Ј-
bis[2-(5-ethynyl)thienyl]ferrocene[36] or 1,1Ј-bis(phenyl-
ethynyl)ferrocene.[53] The fact that not only functionalized
compounds such as 14 but also unfunctionalized derivatives
adopt such a conformation, makes intra- or intermolecular
polar interactions between functional groups less likely to
be the reason for this conformation. Although crystal pack-
ing effects have been invoked in the case of 1,1Ј-bis(phenyl-
ethynyl)ferrocene,[53] one might also consider an attractive
π,π interaction between the highly unsaturated substituents.
More extended bidirectional systems were obtained by
Sonogashira coupling in good yields, when 15 or 17 were
Figure 1. Structure of 14 in the crystal;[50] (top) side view (bot-
tom) top view; some atom numbers have been omitted for clarity.
Selected bond lengths [pm], interatom distances [pm], and bond
angles [°]: C1–C2 142.8(7), C1–C5 141.3(8), C1–C11 142.8(7), C2–
C3 139.8(8), C3–C4 142.7(9), C4–C5 140.4(8), C6–C7 143.7(8), C6–
C10 142.9(9), C6–C23 144.4(8), C7–C8 140.5(8), C8–C9 141.6(9),
C9–C10 141.5(8), C11–C12 117.8(7), C12–C13 144.6(7), C13–C14
144.1(7), C13–C17 142.6(8), C14–C15 142.3(7), C15–C16 142.0(8),
C16–C17 140.5(7), C18–C19 142.6(8), C18–C22 140.8(7), C18–I1
208.3(5), C19–C20 142.0(8), C20–C21 140.3(8), C21–C22 142.7(8),
C23–C24 116.0(8), C24–C25 144.1(8), C28–C33 144.3(7), C33–N1
114.1(6); C1–C6 334.9, C11–C23 339.3, C12–C24 347.1, C13–C25
363.1; C1–C11–C12 178.2(6), C11–C12–C13 177.2(6), C6–C23–
C24 176.9(7), C23–C24–C25 177.6(7).
used as starting materials.[36] The coupling of 15 with 4- graphic purification, in 26% yield of 1,1Ј-bis(4-cyanophen-
iodobenzonitrile (3) under conventional reaction conditions ylethynyl)ferrocene (19), which was obtained as a dark-
(95 °C, 44 h) gave 16 in 52% yield, whereas the reaction of orange solid that was barely soluble in common solvents.
17 under microwave heating (100 °C, 30 min) gave 18 in a The corresponding reaction of 13 afforded 20 in only 8%
significantly higher yield of 79%. Compounds 16 and 18 yield, in addition to 80% unconsumed 13. The respective
were characterized spectroscopically, and their spectra were reaction with 1-(tert-butylsulfanyl)-4-ethynylbenzene in-
found to resemble those of the corresponding tert-butyl- stead of 4-ethynylbenzonitrile gave 21 in only 18% yield, in
sulfanyl derivatives.[36]
addition to unconsumed starting materials. All three com-
To obtain compounds with triple bonds directly at the pounds were characterized spectroscopically. The introduc-
ferrocene moiety, 12 was treated with 4-ethynylbenzonitrile tion of a tert-butylsulfanyl substituent proved beneficial for
in a Sonogashira reaction with microwave heating (300 W, the solubility of the compound, and its 13C NMR spectrum
100 °C, 120 min). The reaction resulted, after chromato- could be obtained in CDCl3.
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We then envisaged the synthesis of a push-pull disubsti-
tuted derivative. The synthesis started with 11, from which
In an attempt to prepare derivatives with more than one nitro-substituted compound 24 was obtained in 83% yield
ferrocene moiety, 12 was treated with 1,4-diethynylbenzene as purple crystals by treatment with 4-iodonitrobenzene un-
under the same reaction conditions. However, the double der Sonogashira conditions with microwave heating (300 W,
coupling product 22 was obtained in only 8% yield in ad- 100 °C, 30 min). Subsequent treatment of 24 with 4-ethynyl-
dition to 51% unconsumed 12. Compound 22 was obtained N,N-dimethylaniline[54] afforded the push-pull disubstituted
as an orange-brown solid that was almost insoluble in com- ferrocene 25 in 76% yield; the increased yield compared
mon organic solvents, which prevented 13C NMR spectro- with the preceding reactions might be explained by the elec-
scopic analysis. In a similar way, 23 was obtained in 15% tron-withdrawal exerted by the nitro group in 24. Com-
yield by using 1,4-diethynyl-2,5-dimethoxybenzene instead pound 25 was obtained as an orange powder, and crystalli-
of 1,4-diethynylbenzene. As with 22, compound 23 was not zation from dichloromethane/hexane was achieved; unfor-
sufficiently soluble in any solvent that was suitable for 13C tunately, the crystals were not suitable for a crystal structure
NMR spectroscopy. Compound 23 deserves particular analysis.
interest because of the central hydroquinone derived moi-
A number of the prepared compounds were investigated
ety, which adds another redox-active structure to the two by cyclic voltammetry to assess their redox properties, and
ferrocene units. Compounds 22 and 23 were identified on the results are summarized in Table 1; for comparison the
1
the basis of their H NMR, IR, and mass spectra.
data of 26–28 are also included.[36]
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Ferrocenes Bearing Highly Extended π Systems
Table 1. Cyclovoltammetry. Epc = cathodic peak potential; Epa
=
anodic peak potential; E1/2 = half-wave potential = (Epa + Epc)/2;
potential vs. FcH/FcH+. Solvent CH2Cl2 unless otherwise indi-
cated; 20 °C; 100 mV/s; tetrabutylammonium phosphate. Com-
pound 7 was measured in THF at 25 °C.[43]
Epa [V]
Epc [V]
ΔE [V]
E1/2 [V]
7[43]
9
12
13
14
0.330
0.127
0.493
0.558
0.276
0.447
0.064
0.481
0.178
0.283
0.394
0.006
0.355
0.129
0.141
0.021
0.180
–0.055
0.325
0.417
0.090
0.330
–0.029
0.337
–0.013
0.088
0.241
–0.167
0.187
0.000
0.002
–0.120
0.15
0.255
0.036
0.409
0.488
0.183
0.389
0.018
0.409
0.083
0.186
0.318
–0.081
0.271
0.065
0.072
–0.050
0.182
0.168
0.141
0.186
0.117
0.093
0.144
0.191
0.195
0.153
0.173
0.168
0.129
0.138
0.141
Figure 2. Selected cyclovoltammograms of 18 (A), 14 (B), and 25
(C). Conditions: 100 mV/s, c (TBAF) = 0.1 mol/L in CH2Cl2, c
(ferrocene derivative) = 2 mmol/L, T = 293 K, abscissa: potential
U [V] vs. FcH/FcH+, ordinate: current I [mA].
16
18
20
21
24
25
stituent causes an increase in the half-wave potential of
0.154 V. The iodo-substituted compounds 12–14 and 24
show redox reactions at half-wave potentials of comparable
magnitudes, with the nitro-derivative 24 having the lowest
half-wave potential (0.318 V). Dialkynylferrocenes 20, 21,
and 25 show redox processes between 0.083 and 0.271 V.
26[36]
27[36]
28[36]
With the exceptions of compounds 14 and 25, all com- For 25, a second redox reaction is observed at –0.081 V,
pounds show one reversible wave assigned to the ferrocene/ which is assigned to the dimethylamino group because a
ferrocenium redox processes. Compounds 14 and 25 show corresponding wave was not observed for nitro compound
two reversible waves (Figure 2); these are assigned to the 24. Replacing the nitrile substituents in 16 by tert-butyl-
redox process at the two ferrocene moieties in 14, and at sulfanyl groups as in 26 causes a potential increase from
the ferrocene moiety (0.271 V) and the diemethylamino 0.018 to 0.065 V. Additional attachment of the four meth-
group (–0.081 V) in 25.
oxy groups reverses this, and a half-wave potential of
A comparison of the half-wave potentials obtained does –0.050 V is observed for 28. Remarkably, these changes do
not show a clear correlation with the electron demand of not appear to be of general nature: replacing the nitrile
the substituents of the ferrocene moiety. Going from 7 to 9 groups in 18 by tert-butylsulfanyl groups causes a decrease
shows the effect of a 1,4-phenylene moiety between the tri- of the potential of 0.337 V, which is 0.072 V for 27. Whereas
ple bond and the ferrocenyl part, which causes a reduction 26 and 27 have similar half-wave potentials (0.065 and
of the potential by 0.219 V. A comparison between com- 0.071 V, respectively) these are quite different for 16 and 18
pounds 7 and 12 indicates that the presence of an iodo sub- (0.018 and 0.409 V, respectively).
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otherwise mentioned, the scan rate was 100 mV/s. Freshly sublimed
ferrocene was used for calibration, potentials refer to the FcH/
FcH+ redox couple. Melting points were measured with an Electro-
thermal IA9000 instrument.
Conclusions
A number of new ferrocenes have been prepared in which
the ferrocene moiety is incorporated in an extended π sys-
tem. The compounds resemble oligophenylene-ethynylenes
(OPEs) with nitrile, nitro, or dimethylamino end groups, in
which one of the phenylene moieties has been replaced by
the 1,1Ј-ferrocenylene moiety, thus allowing limited confor-
mational flexibility by rotation around the ferrocene axis.
The syntheses were achieved by Sonogashira coupling reac-
tions with a small number of building blocks. Diferrocenyl
derivative 14 has been characterized crystallographically,
and it adopts a conformation with eclipsed alkynyl substitu-
ents at one of the ferrocene moieties. The cyclovoltammetric
measurements of the ferrocene prepared derivatives do not
allow straightforward correlation between the substitution
patterns and the respective redox potentials.
[(4-Cyanophenyl)ethynyl]ferrocene (7):[43] Ethynylferrocene (6;[42]
0.10 g, 0.5 mmol, 1 equiv.) and 4-iodobenzonitrile (3; 0.11 g,
0.5 mmol, 1 equiv.) were dissolved in degassed (argon) diisopropyl-
amine (20 mL) in a Schlenk flask that was suitable for microwave
irradiation. After addition of [Pd(PPh3)2Cl2] and CuI (2 spatula
tips each, ca. 5 mol-%), the mixture was heated by microwave irra-
diation (300 W, 100 °C, 15 min ramp, 30 min hold) with stirring.
After cooling to 25 °C, the mixture was filtered through a frit cov-
ered with silica gel (10ϫ3 cm), and the red-brown solid obtained
was purified by column chromatography (SiO2; 30ϫ3 cm; petro-
leum ether/dichloromethane, 1:1 to 1:2) to give 7 (0.15 g, 0.5 mmol,
98%) as an orange-yellow solid [Rf = = 0.28 (petroleum ether/
dichloromethane, 1:1)], which was identified by 1H NMR spec-
troscopy.[43]
{4-[(4-Cyanophenyl)ethynyl]phenyl}ferrocene (9): (4-Ethynylphenyl)-
ferrocene (8;[44] 0.040 g, 0.14 mmol, 1 equiv.) and 3 (0.039 g,
0.17 mmol, 1.2 equiv.) were dissolved in degassed (argon) diisopro-
pylamine (40 mL) in a Schlenk flask that was suitable for micro-
wave irradiation. After addition of [Pd(PPh3)2Cl2] and CuI (2 spat-
ula tips each, ca. 5 mol-%), the mixture was heated by microwave
irradiation (300 W, 100 °C, 15 min ramp, 30 min hold) with stirring.
After cooling to 25 °C, the mixture was filtered through a frit cov-
ered with silica gel (10ϫ3 cm), which was then washed with dichlo-
romethane, and the black-red solid obtained was purified by col-
umn chromatography (SiO2; 20ϫ3 cm; petroleum ether/dichloro-
methane, 1:1; Rf = 0.19) to give 9 (0.055 g, 0.14 mmol, 100%) as
Experimental Section
General: All reactions were performed by using Schlenk techniques
with nitrogen or argon as the inert gas. All glassware was heated
at 0.1 mbar or below with a heat gun prior to use to remove any
oxygen or water. Tetrahydrofuran (THF) and toluene were dried
with sodium/potassium alloy/benzophenone and distilled. Pentane
and dichloromethane were dried with CaH2 and distilled. Starting
materials were either commercially acquired or were prepared ac-
cording to published procedures. Ferrocene was obtained as a do-
nation from Innospec Deutschland GmbH.
1
red crystals; m.p. 190 °C (dec.). H NMR (400 MHz, CDCl3): δ =
1H and 13C NMR spectra were obtained with Bruker AVS 200 (1H:
200 MHz) and AVS 400 (1H: 400 MHz, 13C: 100.6 MHz) instru-
ments. Chemical shifts δ refer to TMS (δ = 0 ppm) or to residual
solvent signals. Primary, secondary, tertiary, and quaternary carbon
atom signals were identified as such by APT and DEPT techniques.
In some cases, signal assignments were based on 2D NMR spectra
(HMQC, HMBC). IR spectra were obtained with Perkin–Elmer
instruments FTIR 580 and 1170 using the ATR technique. Signal
characteristics are abbreviated as s (strong), m (medium), w (weak),
and br (broad). Mass spectra were obtained with a Micromass LCT
instrument with lockspray source and direct injection and with a
Q-TOF premier LC-MS/MS instrument with an Ionsabre-APCI-
source (25 μA, 350 °C). In all cases, dichloromethane was used as
the solvent. Analytical TLC was performed with Merck 60F-254
silica gel thin-layer plates. Column chromatography was performed
with J. T. Baker silica gel (60 μm) as the stationary phase using the
flash chromatography method.[55] Elemental analyses were ob-
tained with an Elementar Vario EL instrument. Reactions under
microwave irradiation (μW) were performed with a CEM Discover
Labmate reactor in a nitrogen atmosphere (“open vessel”) in a
100 mL reaction flask using the ChemDriver software. The tem-
perature was monitored by means of an IR sensor. Some reactions
were performed by using the PowerMax method. Cyclic voltamme-
try (CV) measurements were performed in an argon atmosphere
with a Gamry Instrument Reference 600 Potentiostat/Galvanostat/
ZRA. The sample compound (0.02 mmol) was dissolved in freshly
distilled dichloromethane (10 mL), and tetrabutylammonium phos-
phate (TBAP, 0.387 g, 98%) was added corresponding to a concen-
tration of 0.1 mol/L. The reference electrode was a Ag/Ag+
(AgNO3) electrode in acetonitrile with 0.01 mol/L AgNO3 and
0.1 mol/L of TBAP. A 0.25 mm and a 0.1 mm thick platinum wire
were used as the counter and working electrode, respectively. Unless
4.05 (s, 5 H, CpH), 4.38 (m, 2 H, CpH), 4.69 (m, 2 H, CpH),
7.46 (m, 4 H, C6H4), 7.62 (m, 4 H, C6H4-CϵN) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 66.8 (CFcH), 69.8 (CFcH), 70.0 (Cp), 84.0
(CFcC), 88.0 (CϵC), 94.5 (CϵC), 111.4 (CArCϵN), 118.8 (CϵN),
119.3 (FcArCCϵC), 126.1 (CArHCFc), 128.6 (FcArCϵCCAr),
132.0 (CArH), 132.1 (CArH), 132.2 (CArH), 141.2 (CFcCAr) ppm.
IR: ν = 2921 (m, Ar), 2851 (w), 2201 (w, CϵC), 1742 (w), 1590
˜
(m), 1521 (w), 1408 (w), 1280 (w), 1105 (w), 1079 (w), 1032 (w),
999 (w), 883 (w), 833 (s, Ar) cm–1. MS (70 eV): m/z (%) = 388 (54)
[(M + 1)+], 387 (94) [M+], 385 (13), 266 (34), 264 (25), 121 (100)
[FeCp+]. HRMS: m/z calcd. for C25H17FeN 387.0710; found
387.0698.
1-[(4-Cyanophenyl)ethynyl]-1Ј-iodoferrocene (12): 1-Ethynyl-1Ј-
iodoferrocene (11;[40,46–49] 2.84 g, 8.5 mmol, 1 equiv.) and 3 (3.87 g,
16.9 mmol, 2 equiv.) were dissolved in degassed (argon) diisopro-
pylamine (200 mL). Pd(PPh3)2Cl2 and CuI (2 spatula tips each, ca.
5 mol-%) were added and the reaction mixture was heated at 95 °C
oil bath temperature with stirring for 20 h. After cooling to 25 °C,
the mixture was filtered through a frit covered with silica gel
(10ϫ3 cm), which was then flushed with dichloromethane. The
orange-red solid obtained was purified by column chromatography
(SiO2; 30ϫ3 cm; petroleum ether/dichloromethane, 3:1) to give 12
(3.55 g, 8.1 mmol, 96%; Rf = 0.05) as orange-red crystals; m.p.
127–129 °C (dec.). 1H NMR (400 MHz, CDCl3): δ = 4.24 (m, 2 H,
CpH), 4.32 (m, 2 H, CpH), 4.46 (m, 2 H, CpH), 4.49 (m, 2 H,
CpH), 7.60 (m, 4 H, C6H4CϵN) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 41.5 (CFcI), 66.4 (CFcC), 71.0 (HCFcCCϵC or
HCFcCFcCCϵC), 72.6 (HCFcCCϵC or HCFcCFcCCϵC), 74.5
(HCFcCI or HCFcCFcCI), 76.7 (HCFcCI or HCFcCFcCI), 85.8
(CϵC), 92.6 (CϵC), 111.0 (CArCϵN), 118.9 (CϵN), 129.0
(CArCϵC), 132.0 (CArH), 132.2 (CArH) ppm. IR: ν = 2410 (m),
˜
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O42831
/KAP1
Date: 01-09-14 11:23:45
Pages: 11
Ferrocenes Bearing Highly Extended π Systems
2200 (s, CϵC), 2025 (w), 1597 (s, Ar), 1503 (w), 1402 (w), 1156 (m), 6, –31 Յ k Յ 34, –16 Յ l Յ 17), reflections/parameters/restraints
1027 (m), 919 (w), 856 (w), 833 (m, Ar) cm–1. MS (70 eV): m/z (%)
= 438 (12) [M + 1]+, 437 (100) [M]+, 311 (28), 310 (6) [M+ – I],
253 (16), 247 (6), 190 (9), 86 (31), 84 (54), 69 (5). HRMS: m/z calcd.
for C19H12FeIN 436.9364; found 436.9366.
4230/334/0, solution of structure and refinement with SHELXS-97
or SHELXL-97 (Sheldrick, 1997),[56] respectively. Method of re-
finement full-matrix-least-square on F2, numerical absorption cor-
rection, Goodness-of-fit (F2) 1.023, R = 0.0963 (all data), wR =
0.1439 (all data), max./min. residual electron density 1.616,
–1.339 eÅ–3.
1-([4-Cyano-3,5-dimethylphenyl]ethynyl)-1Ј-iodoferrocene (13) and
1-[(4-Cyano-3,5-dimethylphenyl)ethynyl]-1Ј-(1Ј-iodoferrocenyl-
ethynyl)ferrocene (14): 1-Ethynyl-1Ј-iodoferrocene (11; 1.28 g,
3.8 mmol, 1 equiv.) and 5[39] (1.20 g, 5.7 mmol, 1.5 equiv.) were dis-
solved in degassed (argon) diisopropylamine (40 mL) in a Schlenk
flask that was suitable for microwave heating. [Pd(PPh3)2Cl2] and
CuI (2 tips of a spatula each, ca. 5 mol-%) were added and the
mixture was heated by microwave irradiation (300 W, 100 °C,
15 min ramp, 60 min hold). After filtration through a frit covered
with silica gel (10ϫ3 cm) and flushing with dichloromethane, the
dark red-black oil obtained was separated by column chromatog-
raphy (SiO2; 30ϫ2.5 cm; petroleum ether/dichloromethane, 2:1 to
1:6) to give four fractions.
CCDC-1009329 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
1,1Ј-Bis{[4-(4-cyanophenyl)ethynyl]phenyl}ferrocene (16): 1,1Ј-Bis(4-
ethynylphenyl)ferrocene (15;[36] 0.20 g, 0.5 mmol, 1 equiv.) and 3
(0.26 g, 1.1 mmol, 2.2 equiv.) were dissolved in diisopropylamine
(40 mL). After addition of [Pd(PPh3)2Cl2] and CuI (two spatula
tips, each, ca. 5 mol-%), the reaction mixture was heated with stir-
ring at 95 °C oil bath temperature for 44 h. After cooling to 23 °C,
the mixture was filtered through a frit covered with silica gel
(10ϫ3 cm), which was flushed with dichloromethane. The red solid
obtained was separated by column chromatography (SiO2;
12ϫ3 cm; petroleum ether/dichloromethane, 1:2) to give two frac-
tions:
Fraction I [Rf = 0.52 (petroleum ether/dichloromethane, 2:1)]:
Compound 11, yield 0.40 g (0.6 mmol, 16%).
Fraction II [Rf = 0.39 (petroleum ether/dichloromethane, 2:1)]:
Compound 5, yield 0.55 g (2.6 mmol, 46%).
Fraction I (Rf = 0.40): Compound 3, yield 0.14 g (0.6 mmol, 55%
recovered); Rf = 0.40.
Fraction III [Rf = 0.21 (petroleum ether/dichloromethane, 2:1)]:
Compound 13, yield 0.88 g (1.9 mmol, 50%); orange-red solid; m.p.
1
Fraction II (Rf = 0.15): Compound 16, yield 0.16 g (0.3 mmol,
52 %); orange-red solid; m.p. 254–256 °C (dec.). 1H NMR
(200 MHz, CDCl3): δ = 4.32 (m, 4 H, CpH), 4.53 (m, 4 H, CpH),
7.21 (AAЈBBЈ, ΣJ = 8.2 Hz, 4 H, C6H4), 7.34 (AAЈBBЈ, ΣJ =
8.2 Hz, 4 H, C6H4), 7.57 (m, 8 H, C6H4-CϵN) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 68.2 (CFcH), 71.1 (CFcH), 82.8 (CFcC),
88.1 (CϵC), 94.6 (CϵC), 111.4 (CArCϵN), 118.7 (CϵN), 119.4
(FcArCCϵC), 125.9 (CArHCFc), 128.6 (FcArCϵCCAr), 131.96
143–146 °C. H NMR (200 MHz, CDCl3): δ = 2.52 (s, 6 H, CH3),
4.23 (m, 2 H, CpH), 4.30 (m, 2 H, CpH), 4.45 (m, 2 H, CpH), 4.48
1
(m, 2 H, CpH), 7.26 (s, C6H2) ppm. H NMR (200 MHz, C6D6): δ
= 2.09 (s, 6 H, CH3), 3.86 (m, 2 H, CpH), 3.94 (m, 2 H, CpH),
4.27 (m, 2 H, CpH), 4.38 (m, 2 H, CpH), 6.99 (s, 2 H, C6H2) ppm.
13C NMR (100.6 MHz, CDCl3): δ = 20.8 (CH3), 41.4 (CFcI), 66.7
(CFcC), 71.0 (CFcH), 72.5 (CFcH), 74.4 (CFcH), 76.6 (CFcH), 86.1
(CϵC), 91.3 (CϵC), 112.5 (CArCϵN), 117.3 (CϵN), 128.0
(CArH), 132.06 (CArH), 132.14 (CArH), 139.3 (FcCAr) ppm. IR: ν
˜
(CArCϵC), 130.1 (CArH), 142.2 (CArCH ) ppm. IR: ν = 3098 (w),
˜
3
= 2921 (s, Ar), 2852 (s, Ar), 2227 (m), 2213 (m, CϵC), 1599 (m),
1527 (m), 1500 (w), 1457 (m), 1418 (w), 1407 (w), 1378 (w), 1282
(w), 1181 (w), 1138 (w), 1108 (w), 1080 (w), 1035 (w), 892 (m), 836
(s), 834 (s, Ar) cm–1. HRMS: m/z calcd. for C40H24FeN2 588.1289;
found 588.1282.
2920 (s, CH3), 2852 (s, CH3), 2342 (w), 2210 (s, CϵC), 1741 (w),
1593 (s, Ar), 1445 (w), 1382 (m), 1342 (w), 1278 (w), 1122 (w), 1025
(s), 962 (w), 867 (s), 822 (s, Ar) cm–1. MS (70 eV): m/z (%) = 466
(19) [M + 1]+, 465 (100) [M]+, 340 (5), 339 (46), 338 (9) [M+ – I],
322 (5), 282 (6), 267 (6), 111 (5), 97 (10), 85 (11), 71 (18). HRMS:
m/z calcd. for C21H16FeIN 464.9677; found 464.9683.
1,1Ј-Bis[5-(4-cyanophenylethynyl)]thienylferrocen (18): 1,1Ј-Bis[2-(5-
ethynyl)thienyl]ferrocene (17;[36] 0.21 g, 0.5 mmol, 1 equiv.) and 3
(0.26 g, 1.1 mmol, 2.2 equiv.) were dissolved in diisopropylamine
(40 mL) in a Schlenk flask that was suitable for microwave irradia-
tion. Pd(PPh3)2Cl2 and CuI (two tips of a spatula each, ca. 5 mol-
%) were added and the mixture was heated by microwave irradia-
tion (300 W, 100 °C, 15 min ramp, 30 min hold) with stirring. A
saturated aqueous solution of NH4Cl (20 mL) was added and, after
phase separation, the aqueous layer was extracted with dichloro-
methane (3ϫ 20 mL). The collected organic layers were dried with
MgSO4 and, after filtration, the solvent was removed under re-
duced pressure. The red solid obtained was separated by column
chromatography (SiO2; 15ϫ3 cm; petroleum ether/dichlorometh-
ane, 1:2) to give two fractions:
Fraction IV [Rf = 0.16 (petroleum ether/dichloromethane, 2:1)]:
Compound 14, yield 0.21 g (0.3 mmol, 8%); dark-red solid; m.p.
1
130–132 °C. H NMR (400 MHz, CDCl3): δ = 2.47 (s, 6 H, CH3),
4.19 (m, 4 H, CpH), 4.30 (m, 2 H, CpH), 4.33 (m, 2 H, CpH), 4.36
(m, 2 H, CpH), 4.40 (m, 2 H, CpH), 4.51 (m, 2 H, CpH), 4.54 (m,
2 H, CpH), 7.18 (s, 2 H, C6H2) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 20.8 (CH3), 41.1 (CFcI), 66.0 (CFcC), 68.3 (CFcC), 68.4
(CFcC), 70.8 (CFcH), 71.0 (CFcH), 71.4 (CFcH), 71.7 (CFcH), 73.1
(CFcH), 73.4 (CFcH), 74.1 (CFcH), 76.5 (CFcH), 84.05 (CϵC), 84.13
(CϵC), 85.8 (CϵC), 91.7 (CArCϵC), 112.2 (CArCϵN), 117.4
(CϵN), 128.0 (CArCϵC), 130.1 (CArH), 142.1 (CArCH3) ppm. IR:
ν = 2921 (w, CH ), 2334 (w), 2210 (s, CϵC), 1598 (s, Ar), 1380
˜
3
(m), 1348 (w), 1283 (w), 1203 (w), 1125 (w), 1025 (m), 936 (w), 868
(s), 808 (s, Ar) cm–1. HRMS: m/z calcd. for C33H24Fe2IN 672.9652;
found 672.9652.
Fraction I (Rf = 0.37): Compound 3, yield 0.07 g (0.3 mmol, 27%
recovered).
Crystal Structure Analysis of 14:[50] C33H24Fe2IN; dark-red needles;
Mr 673.13 g/mol; crystal system: monoclinic; space group: P21/n; a
= 6.0219(1) Å, b = 29.5044(3) Å, c = 14.7769(1) Å, α = 90.00°, β =
Fraction II (Rf = 0.17): Compound 18, yield 0.25 g (0.4 mmol,
79%); dark-red solid; m.p. 211 °C (dec.). Thp = Thiophenyl. 1H
NMR (400 MHz, CDCl3): δ = 4.30 (m, 4 H, CpH), 4.50 (m, 4 H,
101.2730(10)°, γ = 90.00°; V = 2574.80(3) Å3; Z = 4; dcalcd.
=
CpH), 6.75 (d, J = 3.8 Hz, 2 H, CFc
2 H, CHCThpCϵC), 7.56 (m, 8 H, C6H4-CϵN) ppm. 13C NMR
APEX II; T = –40 °C; Cu-Kα irradiation: 1.54187 Å; θ-range of (100.6 MHz, CDCl3): δ = 68.8 (CFcH), 71.2 (CFcH), 80.6
data collection 3.00–65.32°, measured reflections 13352 (–7 Յ h Յ (FcThpCϵC), 88.2 (CFcC), 92.0 (FcThpCϵC), 111.4 (CArCϵN),
CThpCH), 7.09 (d, J = 3.8 Hz,
1.736 g/cm3; F(000) = 1336; μ = 18.620 mm–1; Bruker KAPPA
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O42831
/KAP1
Date: 01-09-14 11:23:45
Pages: 11
N. Krauße, H. Butenschön
FULL PAPER
118.7 (CϵN), 119.4 (CThpCϵC), 122.8 (CThpHCFc), 128.2 7.11 (s, 2 H, C6H2), 7.43 (m, 2 H, C6H4CϵN), 7.51 (m, 2 H,
(CArCϵC), 131.6 (CArH or CThpH), 132.2 (CArH or CThpH), 134.0
C6H4CϵN) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 20.6 (CH3),
(CArH), 145.4 (CFcCThp) ppm. IR: ν = 2918 (m, Ar), 2850 (m, Ar), 31.9 (CH3), 66.1 (CFcC), 66.5 (CFcC), 71.3 (CFcH), 71.4 (CFcH),
˜
2226 (m), 2186 (s, CϵC), 1729 (w), 1599 (s, Ar), 1539 (m), 1470 73.17 (CFcH), 73.20 (CFcH), 85.6 (CϵC), 86.0 (CϵC), 90.8 (CϵC),
(m), 1424 (m), 1288 (w), 1248 (w), 1217 (w), 1174 (m), 1105 (w), 92.3 (CϵC), 110.7 (CϵN), 112.2 (CϵN), 117.0 (CArCϵN), 118.5
1069 (w), 1040 (m), 974 (m), 832 (s, Ar), 821 (s, Ar), 801 (s, (CArCϵN), 127.7 (CArC), 128.7 (CArC), 129.8 (CArH), 131.6
Ar) cm–1. HRMS: m/z calcd. for C36H20FeN2S2 600.0417; found
600.0406. C36H20FeN2S2 (600.53): calcd. C 72.00, H 3.36, N 4.66;
found C 71.38, H 4.19, N 4.24.
(CArH), 131.8 (CArH), 142.0 (CArC) ppm. IR: ν = 2921 (s, CH ),
˜
3
2852 (m, CH3), 2226 (w), 2209 (CϵC), 1739 (w), 1602 (m),
1510 (w), 1459 (m), 1407 (w), 1378 (w), 1275 (w), 1159 (w), 1124
(w), 1027 (m), 923 (w), 869 (w), 823 (s, Ar), 723 (w), 614 (w) cm–1.
MS (70 eV): m/z (%) = 465 (47) [M + 1]+, 464 (100) [M]+, 449
(12), 218 (12), 203 (7), 190 (24), 189 (5). HRMS: m/z calcd. for
C30H20FeN2 464.0976; found 464.0978.
1,1Ј-Bis(4-cyanophenylethynyl)ferrocene (19): 4-Ethynylbenzonitrile
(4;[37,38] 0.10 g, 0.8 mmol, 1 equiv.) and 12 (0.52 g, 1.2 mmol,
1.5 equiv.) were dissolved in diisopropylamine (40 mL) in a Schlenk
flask that was suitable for microwave irradiation. [Pd(PPh3)2Cl2]
and CuI (2 spatula tips each, ca. 5 mol-%) were added and the
mixture was heated by microwave irradiation (300 W, 100 °C,
15 min ramp, 120 min hold) with stirring. After cooling to 25 °C,
the mixture was filtered through a frit covered with silica gel
(10ϫ3 cm). After flushing with dichloromethane and solvent re-
moval under reduced pressure, the red-brown solid obtained was
separated by column chromatography (SiO2; 30ϫ3 cm; petroleum
ether/dichloromethane, 1:2 to 1:4) to give two fractions:
1-[(4-tert-Butylsulfanyl)phenylethynyl]-1Ј-(4-cyanophenylethynyl)fer-
rocene (21): 1-(tert-Butylsulfanyl)-4-ethynylbenzene[35,57] (0.10 g,
0.5 mmol, 1 equiv.) and 12 (0.28 g, 0.6 mmol, 1.2 equiv.) in an ar-
gon atmosphere were dissolved in diisopropylamine (30 mL) in a
Schlenk flask that was suitable for microwave irradiation. After de-
gassing the solution (FPT, 3 cycles), [Pd(PPh3)2Cl2] and CuI (2
spatula tips each, ca. 5 mol-%) were added. The mixture was heated
by microwave irradiation (300 W, 100 °C, 15 min ramp, 120 min
hold) with stirring. After filtration through a frit covered with silica
gel (10ϫ3 cm), flushing with dichloromethane and solvent removal
under reduced pressure, the obtained dark-red oil was separated by
column chromatography (SiO2; 50ϫ3 cm; petroleum ether/dichlo-
romethane, 1:1) to give three fractions:
Fraction I [Rf = 0.39 (petroleum ether/dichloromethane, 1:2)]:
Compound 12, yield 0.26 g (0.6 mmol, 50% recovered).
Fraction II [Rf = 0.15 (petroleum ether/dichloromethane, 1:2)]:
Compound 19, yield 0.12 g (0.3 mmol, 26%); dark-orange solid;
m.p. 192 °C (dec.). The compound was poorly soluble in common
organic solvents (chloroform, dichloromethane, 1,2-dichloroethane,
dimethyl sulfoxide, benzene, toluene, benzonitrile, acetonitrile,
THF, hexane, diisopropylamine, N,N-dimethylformamide, pyridine,
chlorobenzene), so that it was not possible to obtain a 13C NMR
spectrum.
Fraction I (Rf = 0.54): 1-(tert-Butylsulfanyl)-4-ethynylbenzene,
yield 0.06 g (0.3 mmol, 62% recovered).[35,57]
Fraction II (Rf = 0.21): Compound 12, yield 0.19 g (0.4 mmol, 67%
recovered).
Fraction III (Rf = 0.14): Compound 21: 47 mg (0.09 mmol, 18%);
orange-red solid; m.p. 159–161 °C. 1H NMR (400 MHz, CDCl3): δ
= 1.29 (s, 9 H, tBu), 4.34 (m, 2 H, CpH), 4.38 (m, 2 H, CpH), 4.56
(m, 2 H, CpH), 4.57 (m, 2 H, CpH), 7.37 (m, 4 H, C6H4), 7.48 (m,
4 H, C6H4) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 31.1 (CH3),
46.5 (CCH3), 66.0 (CFcC), 67.4 (CFcC), 71.1 (CFcH), 71.5 (CFcH),
73.2 (CFcH), 73.3 (CFcH), 85.6 (CϵC), 86.6 (CϵC), 88.6 (CϵC),
92.7 (CϵC), 110.8 (CArCϵN), 118.8 (CϵN), 124.2 (FcCϵCCArS),
128.9 (FcCϵCCArCϵN), 131.3 (CArH), 131.8 (CArH), 132.0
1H NMR (400 MHz, CDCl3): δ = 4.38 (m, 4 H, CpH), 4.58 (m, 4
H, CpH), 7.48 (m, 8 H, C H ) ppm. IR: ν = 2921 (w), 2853 (w),
˜
6
4
2202 (s, CϵC), 1738 (w), 1599 (s, Ar), 1510 (m), 1459 (w), 1405
(w), 1378 (w), 1304 (w), 1272 (w), 1157 (m), 1031 (m), 926 (m),
829 (s, Ar) cm–1. MS (70 eV): m/z (%) = 437 (18) [M + 1]+, 436
(100) [M]+, 278 (6), 277 (20), 254 (9), 253 (5), 190 (28), 129 (14),
97 (8), 71 (14). HRMS: m/z calcd. for C28H16FeN2 436.0663; found
436.0663.
(CArH), 132.8 (CArS), 137.3 (CArH) ppm. IR: ν = 2961 (m, CH ),
˜
3
2922 (m, CH3), 2855 (m), 2363 (w), 2201 (m, CϵC), 1738 (w), 1602
(m), 1456 (w), 1390 (w), 1362 (w), 1261 (w), 1160 (m), 1096 (w),
1027 (m), 921 (w), 820 (s, Ar) cm–1. MS (70 eV): m/z (%) = 500 (11)
[M + 1]+, 499 (54) [M]+, 444 (15), 443 (100) [M+ – H2C=C(CH3)2],
442 (8), 352 (8), 335 (12), 285 (9), 277 (16), 219 (14), 190 (8), 169
(47), 131 (17), 119 (19), 100 (8), 69 (48). HRMS: m/z calcd. for
C31H25FeNS 499.1057; found 499.1054.
1-[(4-Cyano-3,5-dimethylphenyl)ethynyl]-1Ј-[4-(cyanophenylethyn-
yl)]ferrocene (20): 1-([4-Cyano-3,5-dimethylphenyl]ethynyl)-1Ј-
iodoferrocene (13; 100 mg, 0.22 mmol, 1 equiv.) and 4[37,38] (42 mg,
0.33 mmol, 1.5 equiv.) were dissolved in diisopropylamine (20 mL)
and THF (20 mL) in a Schlenk flask that was suitable for micro-
wave irradiation. [Pd(PPh3)2Cl2] and CuI (2 spatula tips each, ca.
5 mol-%) were added and the mixture was heated by microwave
irradiation (300 W, 100 °C, 15 min ramp, 120 min hold) with stir-
ring. After cooling to 25 °C, the mixture was filtered through a frit
covered with silica gel (10ϫ3 cm). After flushing with dichloro-
methane and solvent removal under reduced pressure, the reddish
brown solid obtained was separated by column chromatography
(SiO2; 30ϫ3 cm; petroleum ether/dichloromethane, 4:1 to 1:4) to
give three fractions:
1,4-Bis{1Ј-[4-(cyanophenyl)ethynyl]ferrocenylethynyl}benzene (22):
1,4-Diethynylbenzene[58] (50 mg, 0.40 mmol, 1 equiv.) and 12
(260 mg, 0.60 mmol, 1.5 equiv.) were dissolved under argon in di-
isopropylamine (30 mL) in a Schlenk flask that is suitable for mi-
crowave irradiation. After degassing the solution three times (FPT),
[Pd(PPh3)2Cl2] und CuI (two spatula tips each, ca. 5 mol-%) were
added. The mixture was heated by microwave irradiation (300 W,
100 °C, 15 min ramp, 120 min hold) with stirring. After cooling to
25 °C, the mixture was filtered through a frit covered with silica
gel (10ϫ3 cm). After flushing with dichloromethane and solvent
removal under reduced pressure, the orange-red solid obtained was
separated by column chromatography (SiO2; 30ϫ3 cm; petroleum
ether/dichloromethane, 2:1 to 1:4) to give two fractions:
Fraction I [Rf = 0.31 (petroleum ether/dichloromethane, 1:1)]:
Compound 13, yield 80 mg (0.16 mmol, 80% recovered).
Fraction II [Rf = 0.25 (petroleum ether/dichloromethane, 1:1)]:
12 mg; unidentified brown solid.
Fraction III (Rf = 0.09): Compound 20, yield 8 mg (0.02 mmol,
8%); red solid; m.p. 164–167 °C. 1H NMR (400 MHz, CDCl3): δ
= 2.46 (s, 6 H, CH3), 4.37 (m, 4 H, CpH), 4.57 (m, 4 H, CpH),
Fraction I [Rf = 0.50 (petroleum ether/dichloromethane, 1:4)]:
Compound 12, yield 135 mg (0.31 mmol, 51% recovered).
8
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O42831
/KAP1
Date: 01-09-14 11:23:45
Pages: 11
Ferrocenes Bearing Highly Extended π Systems
Fraction II [Rf = 0.45 (petroleum ether/dichloromethane, 1:4)]:
Compound 22, yield 20 mg (0.03 mmol, 8%); orange-brown solid;
m.p. 200 °C (dec.). Compound 22 is poorly soluble in common or-
ganic solvents (chloroform, dichloromethane, 1,2-dichloroethane,
dimethyl sulfoxide, benzene, toluene, benzonitrile, acetonitrile,
THF, hexane, diisopropylamine, N,N-dimethylformamide, pyridine,
H, CpH), 4.34 (m, 2 H, CpH), 4.47 (m, 2 H, CpH), 4.51 (m, 2
H, CpH), 7.63–7.65 (AAЈBBЈ, ΣJ = 8.9 Hz, 2 H, C6H4), 8.19–8.21
(AAЈBBЈ, ΣJ = 8.9 Hz, 2 H, C6H4) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 41.6 (CFcI), 66.2 (CFcC), 71.0 (CFcH), 72.7 (CFcH),
74.5 (CFcH), 76.7 (CFcH), 85.7 (CϵC), 93.9 (CϵC), 123.8
(HCArCNO2), 131.0 (CArCϵC), 132.1 (HCArCCϵC), 146.7
chlorobenzene), so that it was not possible to obtain a 13C NMR
(CArNO ) ppm. IR: ν = 2921 (w), 2363 (w), 2022 (m, CϵC), 1589
˜
2
1
spectrum. H NMR (400 MHz, CDCl3): δ = 4.34 (m, 4 H, CpH), (s, Ar), 1508 (s), 1453 (w), 1403 (w), 1380 (w), 1335 (s), 1164 (m),
4.39 (m, 4 H, CpH), 4.59 (m, 8 H, CpH), 7.20 (m, 4 H, C6H4), 7.45
1106 (m), 1053 (w), 1025 (m), 921 (w), 854 (m), 817 (s, Ar), 745
(m, 8 H, C H -CϵN) ppm. IR: ν = 2922 (s, Ar), 2852 (s, Ar), 2362 (m), 690 (m) cm–1. MS (70 eV): m/z (%) = 458 (17) [M + 1]+, 457
˜
6
4
(w), 2204 (m, CϵC), 1724 (w), 1601 (m), 1515 (w), 1461 (w), 1407
(100) [M]+, 427 (25), 411 (27), 228 (15), 227 (19), 226 (41), 202 (5),
(w), 1377 (w), 1243 (w), 1159 (w), 1032 (w), 928 (w), 828 (s, 183 (10), 163 (12), 86 (8), 84 (16). HRMS: m/z calcd. for
Ar) cm–1. HRMS: m/z calcd. for C48H28Fe2N2 744.0951; found
744.0966.
C18H12FeINO2 456.9262; found 456.9263. C18H12FeINO2 (457.05):
calcd. C 47.30, H 2.65, N 3.06; found C 47.91, H 2.89, N 3.09.
1-[(4-Dimethylaminophenyl)ethynyl]-1Ј-[(4-nitrophenyl)ethynyl]-
ferrocene (25): 4-Ethynyl-N,N-dimethylaniline[54] (0.51 g, 1.1 mmol,
1 equiv.) and 24 (0.63 g, 1.4 mmol, 1.2 equiv.) were dissolved in di-
isopropylamine (40 mL) and THF (30 mL). [Pd(PPh3)2Cl2] and
CuI (two spatula tips each, ca. 5 mol-%) were added and the mix-
ture was heated at 100 °C for 16 h. After cooling to 23 °C, the mix-
ture was filtered through a frit covered with silica gel (10ϫ 3 cm).
After flushing with dichloromethane and solvent removal under
reduced pressure, the obtained black-red solid was separated by
column chromatography (SiO2; 55 ϫ 3.5 cm; petroleum ether/
dichloromethane, 1:1 to 1:9 to dichloromethane) to give two frac-
tions:
1,4-Bis{1Ј-[(4-cyanophenyl)ethynyl]ferrocenylethynyl}-2,5-dimeth-
oxybenzene (23): 1,4-Diethynyl-2,5-dimethoxybenzene[59] (0.10 g,
0.5 mmol, 1 equiv.) and 12 (0.35 g, 0.8 mmol, 1.5 equiv.) were dis-
solved in diisopropylamine (30 mL) in a Schlenk flask that was
suitable for microwave irradiation. After purging argon through the
solution for 20 min, [Pd(PPh3)2Cl2] und CuI (two spatula tips each,
ca. 5 mol-%) were added. The mixture was heated by microwave
irradiation (300 W, 100 °C, 15 min ramp, 120 min hold) with stir-
ring. After cooling to 25 °C, the mixture was filtered through a frit
covered with silica gel (10ϫ3 cm). After flushing with dichloro-
methane and solvent removal under reduced pressure, the red-
brown solid obtained was separated by column chromatography
(SiO2; 40ϫ3 cm; petroleum ether/dichloromethane, 1:4) to give two
fractions:
Fraction I [Rf = 0.45 (petroleum ether/dichloromethane, 1:1)]:
Compound 24, yield 0.20 g (0.4 mmol, 29% recovered).
Fraction II [Rf = 0.36 (petroleum ether/dichloromethane, 1:1)]:
Compound 25, yield 0.40 g (0.9 mmol, 76%); orange powder; m.p.
184–187 °C. Crystallization from dichloromethane/hexane gave
crystals; however, these were unsuitable for crystal structure analy-
sis. 1H NMR (400 MHz, CDCl3): δ = 2.93 (s, 6 H, NCH3), 4.27
(m, 2 H, CpH), 4.36 (m, 2 H, CpH), 4.52 (m, 2 H, CpH), 4.58 (m,
2 H, CpH), 6.45–6.47 (AAЈBBЈ, ΣJ = 9.0 Hz, 2 H, C6H4), 7.16–
7.18 (AAЈBBЈ, ΣJ = 8.9 Hz, 2 H, C6H4), 7.40–7.42 (AAЈBBЈ, ΣJ =
8.9 Hz, 2 H, C6H4), 7.97–8.00 (AAЈBBЈ, ΣJ = 8.9 Hz, 2 H,
C6H4) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 40.2 (CH3), 66.2
(CFcC), 69.9 (CFcC), 70.2 (CFcH), 71.1 (CFcH), 72.6 (CFcH), 73.2
(CFcH), 83.6 (CϵC), 85.9 (CϵC), 88.5 (CϵC), 94.0 (CϵC), 110.5
{CA r [N(CH3 )2 ]CϵC}, 111.7 [C A r HCN(CH 3 )2 ] , 123. 5
(CArHCNO2), 131.2 (O2NCCCC), 131.9 (CArHCCϵC), 132.5
(CArHCCϵC), 146.1 [CArCNO2 or CArCN(CH3)2], 149.8
Fraction I (Rf = 0.40): Compound 12: 114 mg (0.26 mmol, 32%
recovered).
Fraction II (Rf = 0.18): Compound 23, yield 60 mg (0.08 mmol,
15%); red-orange solid; m.p. 245 °C (dec.). Compound 23 is poorly
soluble in common organic solvents (chloroform, dichloromethane,
1,2-dichloroethane, dimethyl sulfoxide, benzene, toluene, benzoni-
trile, acetonitrile, THF, hexane, diisopropylamine, N,N-dimethyl-
formamide, pyridine, chlorobenzene), so that it was not possible to
obtain a 13C NMR spectrum. 1H NMR (400 MHz, CDCl3): δ =
3.78 (s, 6 H, OCH3), 4.34 (m, 4 H, CpH), 4.42 (m, 4 H, CpH), 4.60
(m, 4 H, CpH), 4.61 (m, 4 H, CpH), 6.81 (s, 2 H, C6H2), 7.42–7.52
(m, 8 H, C H ) ppm. IR: ν = 2921 (s, OCH ), 2851 (s, OCH ), 2363
˜
6
4
3
3
(w), 2197 (m, CϵC), 1740 (w), 1598 (m), 1505 (m), 1462 (s), 1389
(m), 1274 (m), 1215 (s), 1180 (m), 1156 (m), 1034 (s), 925 (w), 838
(m), 815 (m) cm–1. HRMS: m/z calcd. for C50H32Fe2N2O2
804.1163; found 804.1147.
[CArCNO2 or CArCN(CH ) ] ppm. IR: ν = 2206 (w, CϵC), 1593
˜
3 2
(m), 1511 (m), 1444 (w), 1360 (m), 1334 (s), 1201 (w), 1159 (w),
1106 (w), 1033 (w), 928 (w), 855 (w), 815 (m) cm–1. MS (70 eV):
m/z (%) = 475 (27) [M + 1]+, 474 (100) [M]+, 444 (16), 413 (8), 208
(5), 192 (8), 163 (9). HRMS: m/z calcd. for C28H22FeN2O2
474.1031; found 474.1031.
1-(4-Nitrophenylethynyl)-1Ј-iodoferrocene (24): 1-Ethynyl-1Ј-iodo-
ferrocene[41,46–49] (11; 0.20 g, 0.6 mmol, 1 equiv.) and 4-iodonitro-
benzene (0.21 g, 0.8 mmol, 1.4 equiv.) were dissolved in diisoprop-
ylamine (30 mL) in a Schlenk flask that was suitable for microwave
irradiation. [Pd(PPh3)2Cl2] and CuI (two spatula tips each, ca.
5 mol-%) were added and the mixture was heated by microwave
irradiation (300 W, 100 °C, 15 min ramp, 30 min hold) with stirring.
After filtration through a frit covered with silica gel (10ϫ3 cm),
flushing with dichloromethane, and solvent removal under reduced
pressure, the obtained red-purple solid was separated by column
chromatography (SiO2; 30ϫ3 cm; petroleum ether/dichlorometh-
ane, 4:1 to 1:4) to give two fractions:
Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectra of all new compounds reported in
this publication.
Acknowledgments
N. K. is indebted to the Leibniz University of Hannover for a grad-
uate fellowship. The authors thank Innospec Deutschland GmbH
for a donation of ferrocene. Dr. Michael Wiebcke, Institut für
Anorganische Chemie, Leibniz University of Hannover, is thanked
for performing the crystallographic analysis.
Fraction I [Rf = 0.22 (petroleum ether/dichloromethane, 4:1)]: 4-
Iodonitrobenzene, yield 0.05 g (0.2 mmol, 25% recovered).
Fraction II [Rf = 0.13 (petroleum ether/dichloromethane, 4:1)]:
Compound 24, yield 0.23 g (0.5 mmol, 83%); purple, glittering so-
1
lid; m.p. 174–176 °C. H NMR (400 MHz, CDCl3): δ = 4.25 (m, 2 [1] T. J. Kealy, P. L. Pauson, Nature 1951, 168, 1039–1040.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
9

Job/Unit: O42831
/KAP1
Date: 01-09-14 11:23:45
Pages: 11
N. Krauße, H. Butenschön
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Received: June 27, 2014
Published Online: ᭿
10
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Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O42831
/KAP1
Date: 01-09-14 11:23:45
Pages: 11
Ferrocenes Bearing Highly Extended π Systems
Ferrocenes
New ferrocenes bearing highly extended π
systems with nitrile, nitro, and dimethyl-
amino end groups are prepared that in-
clude a push-pull-substituted system. The
redox properties of the new compounds
have been characterized by cyclic voltam-
metry.
N. Krauße, H. Butenschön* ............. 1–11
Ferrocenes Bearing Highly Extended π Sys-
tems with Nitrile, Nitro, and Dimethyl-
amino End Groups
Keywords: Sandwich compounds / Redox
chemistry / Alkynes / Pi interactions / Con-
jugation / Cross coupling
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
11