From diferrocenyl-cyclopropenone to diferrocenyl-cyclopropenylium cations and triferrocenylpropenones: An electrochemical study

Article abstract of DOI:10.1016/j.jorganchem.2017.03.018

The reaction of 2,3-diferrocenylcyclopropenone (1) with the electrophiles H[BF₄] and [Et₃O][BF₄], respectively, produced the corresponding cyclopropenylium cations [Fc₂C₃OH][BF₄] (2) and [Fc₂C₃OEt][BF₄] (3) (Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅)). Reacting 3 with HNEt₂ afforded the NEt₂-functionalized species [Fc₂C₃NEt₂][BF₄] (4). However, when 2 was reacted with nucleophiles such as FcLi a ring opening of the C₃ cycle was observed and E- and Z-1,2,3-triferrocenylpropenones Z-5 and E-5 were formed. Crystallization of a dichloromethane solution containing 3, layered with hexane, gave the BF₃ adduct of diferrocenylcyclopropenone 6 at the interphase. The molecular solid state structures of Z-5, E-5 and 6 were determined by single crystal X-ray diffraction. Compound E-5 possesses a helical chirality and crystallizes in an enantiopure form. The electronic properties of the ferrocenyl-substituted cyclopropenylium cations 2–4 and of the triferrocenyl-α,β-unsaturated ketones Z-5 and E-5 were studied by cyclic voltammetry and square wave voltammetry. In comparison to the cyclopropenone derivative 1, the ferrocenyl oxidation processes of the cyclopropenylium cations 2 and 3 are shifted towards higher potentials, which is caused by the lower electron density of the strained C₃ rings. Compound 4 decomposes during the electrochemical measurements. Furthermore, it could be shown that E/Z isomerism has only small effects on the electronic properties of the triferrocenyl-α,β-unsaturated ketones. Spectroelectrochemical UV–Vis/NIR measurements carried out on 1 and Z-5 and E-5 confirmed electron-transfer interactions within the 2,3-diferrocenylcyclopropenone and the 1,2,3-triferrocenyl-α,β-unsaturated ketones. However, the cyclopropenylium cations 2 and 3 show no long time stability under oxidative conditions.

Full text of DOI:10.1016/j.jorganchem.2017.03.018

Journal of Organometallic Chemistry xxx (2017) 1e9
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
From diferrocenyl-cyclopropenone to diferrocenyl-cyclopropenylium
*
cations and triferrocenylpropenones: An electrochemical study
*
Steve W. Lehrich, Alexander Hildebrandt, Marcus Korb, Heinrich Lang
Technische Universit a€ t Chemnitz, Fakult a€ t für Naturwissenschaften, Institut für Chemie, Anorganische Chemie, D-09107 Chemnitz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 January 2017
Received in revised form
The reaction of 2,3-diferrocenylcyclopropenone (1) with the electrophiles H[BF ] and [Et O][BF ],
4
3
4
respectively, produced the corresponding cyclopropenylium cations [Fc
2
C
3
OH][BF
afforded the NEt
] (4). However, when 2 was reacted with nucleophiles such as FcLi a ring opening of the
cycle was observed and E- and Z-1,2,3-triferrocenylpropenones Z-5 and E-5 were formed. Crystalli-
zation of a dichloromethane solution containing 3, layered with hexane, gave the BF adduct of difer-
4
] (2) and [Fc
2
C
3
OEt]
5
5
[
[
BF
Fc
4
] (3) (Fc ¼ Fe(
h
-C
5
H
4
)(
h
-C
5
H
5
)). Reacting 3 with HNEt
2
2
-functionalized species
7
March 2017
2
C
3
NEt ][BF
2
4
Accepted 8 March 2017
Available online xxx
C
3
3
rocenylcyclopropenone 6 at the interphase. The molecular solid state structures of Z-5, E-5 and 6 were
determined by single crystal X-ray diffraction. Compound E-5 possesses a helical chirality and crystallizes
in an enantiopure form. The electronic properties of the ferrocenyl-substituted cyclopropenylium cations
2e4 and of the triferrocenyl-a,b-unsaturated ketones Z-5 and E-5 were studied by cyclic voltammetry
and square wave voltammetry. In comparison to the cyclopropenone derivative 1, the ferrocenyl
oxidation processes of the cyclopropenylium cations 2 and 3 are shifted towards higher potentials, which
Keywords:
Ferrocenyl
Cyclopropenone
Cyclopropenylium
Solid state structure
(
Spectro)Electrochemistry
is caused by the lower electron density of the strained C
electrochemical measurements. Furthermore, it could be shown that E/Z isomerism has only small effects
on the electronic properties of the triferrocenyl- -unsaturated ketones. Spectroelectrochemical UV
eVis/NIR measurements carried out on 1 and Z-5 and E-5 confirmed electron-transfer interactions
within the 2,3-diferrocenylcyclopropenone and the 1,2,3-triferrocenyl- -unsaturated ketones. How-
ever, the cyclopropenylium cations 2 and 3 show no long time stability under oxidative conditions.
2017 Elsevier B.V. All rights reserved.
3
rings. Compound 4 decomposes during the
a,b
a,b
©
1. Introduction
heterocycles [6,7]. Cyclopropenones can also act as a three-carbon
building block to elongate the nucleophiles added [8].
Since the first preparation of triphenylcyclopropenylium
perchlorate [1], cyclopropenylium cations as the smallest member
of Hückel aromatic systems have been studied intensively [2].
Cyclopropenylium ions possess a high reactivity due to their
strained ring system. On the other hand, the aromatic stabilization
induces a considerable thermodynamic stability [2,3]. The chem-
istry of cyclopropenones is follows by the presence of zwitterionic
mesomeric structures that contain the aromatic cyclopropenylium
motif (Fig. 1), which causes the high polarity of the molecule and
enhances the stability of the strained system [2,4,5]. Thermolysis or
Ferrocenyl-substituted cyclopropenones allow to introduce iron
atoms in a large number of different organic compounds [8]. In this
respect, especially extended conjugated metal-containing systems
are of great interest because they can be used as model compounds
for molecular wires [8e12]. Furthermore, the electron-donating
nature of ferrocenyl functionalities on the cyclopropenone system
enhances their stability by delocalizing the positive charge
[3,13,14]. Another benefit of using ferrocenyls in cyclopropenone
chemistry is the in situ generation of mixed-valent compounds
through oxidation of one of the two ferrocenyl units and hence the
possibility to study the charge transfer behaviour through the ar-
nucleophilic attack at the C
3
(¼O) ring cause ring opening, allowing,
for example, to prepare five- or six-membered nitrogen-containing
3
omatic C framework. This family of compounds can be considered
as enrichment of well-studied diferrocenyl-functionalized 5-
membered heterocycles [15e24].
*
Herein, we report the charge transfer between ferrocenyl/fer-
rocenium moieties via 2p-aromatic strained C ring systems in
3
Dedicated to Prof. Dr. John A. Gladysz on the occasion of his 65th birthday.
Corresponding author.
*
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
http://dx.doi.org/10.1016/j.jorganchem.2017.03.018
022-328X/© 2017 Elsevier B.V. All rights reserved.
0
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S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
respective mixed-valent compounds. In addition, the reaction
chemistry of diferrocenylcyclopropenone towards FcLi to give 1,2,3-
triferrocenylprop-2-enones and their electrochemical and spec-
troelectrochemical characteristics are discussed.
2.2. Characterization
The identity of organometallic compounds 1e5 was confirmed
1
13
1
by IR and NMR ( H, C{ H}) spectroscopy. The observed infrared
ꢀ
1
ꢀ1
ꢀ1
bands of 1 at 1849 cm , 1817 cm and 1614 cm are diagnostic
for the cyclopropenone structure motif [3]. The change of the
characteristic carbonyl stretching vibrations in 1 as well as the
ꢀ1
occurrence of
could be used to monitoring the progress of the reactions.
,2,3-Triferrocenylprop-2-enones Z-/E-5 were additionally
nB-F vibrations (1060 - 1170 cm ) in IR spectroscopy
1
characterized by high resolution mass spectrometry, elemental
analysis (Materials and Methods) and single crystal X-ray structure
analysis (Fig. 2).
Fig. 1. Mesomeric structures of cyclopropenones [2].
2
. Results and discussion
The electrochemical behavior of 1e5 was studied by cyclic vol-
tammetry (CV) and square wave voltammetry (SWV). In addition,
for compounds 1 and Z-/E-5 in situ UVeVis/NIR spectroelec-
trochemistry measurements were carried out.
2.1. Synthesis
Diferrocenylcyclopropenone (1) (Scheme 1) was prepared by
The molecular structures of Z-5 and E-5 (Fig. 2) in the solid state
have been determined by single crystal X-ray diffraction analysis.
Suitable crystals of Z-/E-5 were obtained by solvent evaporation at
ambient temperature. They crystallize in the non-centrosymmetric
Friedel-Crafts alkylation of ferrocene with tetrachlorocyclopropane
in the presence of AlCl [3,13]. The synthesis of the cyclo-
3
propenylium salts 2e4 (Scheme 1) was performed according to
published procedures [4,5,25]. During crystallization of 3 from a
hexane/dichloromethane mixture at ambient temperature it was
observed that at the hexane ad-layer a minor number of single
orthorhombic space group Pca2
eter [27] ¼ 0.022(16)) and the non-centrosymmetric Sohncke space
group [28] P2
1
(Z-5) (absolute structure param-
1
(E-5) (absolute structure parameter [27] ¼ 0.06(4))
crystals of 6 grew, most likely due to a trace of BF
3
present in the
with one molecule in the asymmetric unit.
Et OBF reagent. The solid state molecular structure of 6 is dis-
3
4
The ferrocenyl groups of Z-5 and E-5 are attached to the carbonyl
cussed in the Supporting Information (Fig. SI5). To prepare 6 in a
straightforward manner, diferrocenylcyclopropenone (1) was sub-
sequently treated with trifluoroborane etherate in tetrahydrofuran.
carbon atom and the a- and b-position of the ethylene unit (Fig. 2,
Scheme 1). The C1eO1, C1eC2 and C2eC3 bond lengths are in the
range for related compounds, i. e. 2,3-diferrocenyl-1-phenyl-prop-
2-enone or [Fc-COCH¼CH-Anth] derivatives (Anth ¼ antracenyl)
[29e41]. Due to the steric interaction for a cis-substitution pattern,
the ferrocenyls at the olefin group resulted in an increased bending
However, instead of neutral 1,BF
), tracing the in situ formation of HBF
Klimova et al. described the nucleophilic attack of phenyl- or
3
, cationic 2 was isolated (Scheme
1
4
.
ꢁ
ꢁ
methyl-lithium on diferrocenyl-substituted cyclopropenes [26]. In
this respect, compound 1 was treated with ferrocenyllithium,
producing Z- and E-1,2,3-triferrocenylprop-2-enone (Z-5, E-5)
out of the vinylic plane by 10.5(7) for Z-5, in contrast to 173.2(19)
for E-5, as evidenced by the C14eC2eC3eC24 torsion angle. To
avoid an interaction of the hydrogen atoms of the Fe2-and Fe3-
labeled ferrocenyls in Z-5, they are rotated out of plane of the
(Scheme 1).
ꢁ
ꢁ
Compounds 1 and Z-/E-5 are stable towards air, light and
CeC¼C vinyl unit by 31.9(5) for the Fe2 entity and by 47.2(4) for
the Fe3 moiety. For E-5, the trans-substitution avoids the steric
interaction between the two ferrocenyls and reduces the rotation
moisture both in the solid state and in solution. The cyclo-
propenylium cations 2e4 are best isolated using anhydrous sol-
vents under inert conditions and are preferably stored under argon
atmosphere, whereas aerobic conditions led to a slow decomposi-
tion of the respective compounds.
ꢁ
out of the olefin plane to 22.8(14) and 21.3(17) , respectively. In
contrast to Z-5 with an anti-orientation, the ferrocenyls in E-5 are
rotated in a syn-coplanar fashion towards each other with a plane
3
Scheme 1. Synthesis of cyclopropenylium salts 2e4, diferrocenylcyclopropenone BF complex 6 and 1,2,3-triferrocenylprop-2-enones Z-5 and E-5.
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S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
3
Fig. 2. ORTEPs (50% probability level) of the molecular structure of Z-5 (left) and E-5 (right) with the atom numbering scheme. Left (Z-5): Hydrogen atoms and a disordered C
5
H
5
ꢁ
ring (0.43:0.57 occupancy ratio) have been omitted for clarity. Selected bond distances (Å) and torsion angles ( ): C1¼O1 1.218(5), C1eC2 1.502(6), C2¼C3 1.343(6), O1eC1eC2eC3
ꢁ
1
32.2(4). Right (E-5): Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and torsion angles ( ): O1¼C1 1.231(14), C1eC2 1.514(17), C2¼C3 1.295(17),
O1eC1eC2eC3 123.2(13).
ꢁ
ꢀ1
intersection of 5.0(7) . The Fe1 cyclopentadienyls are rather
C
5
H
5
)
2
) redox couple [47]. The CV data at a scan rate of 100 mV s
ꢁ
coplanar with the attached O¼CeC moiety with 3.0(5) for Z-5 and
are summarized in Table 1.
ꢁ
1
2.5(7) for E-5.
The ferrocenyl units in 1, 2, Z-5 and E-5 can be oxidized sepa-
rately. Compounds 1 and 2 show two and Z-5 and E-5 three
consecutive reversible one-electron redox processes for the redox
active termini in the CV as well as in the SWV (Fig. 5). While for 3 in
the initial scans two reversible oxidation events are characteristic,
multi-cyclic experiments demonstrated the low electrochemical
stabilities of [3] /[3] . The two ferrocenyl-related oxidation events
are in close proximity and therefore the better resolved SWV data
are given in Table 1 (Supporting Information, Fig. SI10). Compound
4 was not stable in electrochemical measurements and hence after
the first cycle no defined redox processes could be detected, which
is most probably caused by a contamination of the electrode surface
with decomposition products. The low electron density and the
chemically less stable amine functionality in 4 might be responsible
for rapid decomposition after oxidation.
Regarding the
a,b-unsaturated moiety, a trans orientation of
both double bonds is observed, whereas the interactions of the
attached ferrocenyls rotate the C¼O and C¼C bonds out of co-
ꢁ
planarity around the C1eC2 single bond by 47.8(4) to avoid in-
teractions of the C8 and C3 hydrogen atoms in Z-5. For E-5, the
torsion angle increases to 56.8(13) to avoid the interaction of the
C28 und C5 hydrogen atoms.
The C4eC1eC2eC3eC24 atoms of E-5 form a helical structural
motif in the solid state (Fig. SI8). The crystallization in the non-
centrosymmetric Sohncke space group P2 , which does not contain
1
the respective enantiomer, allows the assigned of the absolute
conformation to be the M isomer within the used single crystal [42].
ꢁ
þ
2þ
2.3. Electrochemistry
Compound 1 shows under the applied measurement conditions
a half-wave potential separation of 250 mV. Klimova et al.
n
The electrochemical properties of 1e4, Z-5 and E-5 were
investigated by cyclic voltammetry (CV) and square-wave voltam-
metry (SWV) (Fig. 3; for data of 3 see Supporting Information
described that 1 absorbs on the platinum electrode, when [N Bu ]
4
[PF ] in dichloromethane was used as electrolyte. However, by
changing the electrolyte from [N Bu ][PF ] to weakly coordinating
[ Bu N][B(C F ) ], two reversible one-electron processes with a
4 6 5 4
redox separation of 260 mV were found, which is in agreement
with our measurements [25].
The cyclopropenylium species 2 showed higher redox potentials
in comparison with neutral 1, which is caused by the electron-
p aromatic C3 ring system.
The separation between the 1st and 2nd redox event is decreased
6
n
4
6
þ
þ/2þ
þ/
n
Fig. SI10). The charge transfer behavior of [1] , [Z-5]
and [E-5]
was additionally studied by in situ UVeVis/NIR spectroelec-
trochemistry (Figs. 4e7, and Figs. SI12eSI13), while it was found
2
þ
þ
þ
þ
that [2] , [3] and [4] were not stable under oxidative conditions
in multi-cyclic measurements. The electrochemical studies were
carried out in anhydrous dichloromethane solutions containing
] (0.1 mol$L ) as supporting electrolyte under
inert conditions (Materials and Methods) [43]. The weak coordi-
withdrawing effect of the cationic 2
n
ꢀ1
[
Bu
4
N][B(C
6
F
5
)
4
ꢁ
by 35 mV (
D
E ' ¼ 215 mV) (Table 1). The trend that a lower electron
n
nating electrolyte [ Bu
4
N][B(C
6
F
5
)
4
] was used, since it is known to
density within the bridging system often corresponds to a lower
electronic coupling has been established on various examples of
bridged diferrocenes [16,19,51,52], i. e. in a series of 2,5-
stabilize highly charged species and minimize ion pairing effects
44e46]. The cyclic voltammetry measurements were performed at
5 C. All potentials are referenced to the FcH/FcH (FcH ¼ Fe(
p
-
[
2
ꢁ
þ
5
h -
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S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
Z-5
1
ia
ia
ic
E-5
2
ic
-200
0
200 400 600 800 1000 1200
-1200 -800 -400
0
400
800 1200
+
+
E vs FcH/FcH (mV)
E vs FcH/FcH (mV)
Fig. 3. Cyclic voltammograms (solid lines: scan rate 100 mV sꢀ1) and square-wave voltammograms (dotted lines: step-height 25 mV, pulse-width 5 s, amplitude 5 mV) of 1 and 2
ꢀ
1
ꢁ
ꢀ1
n
(
[
left) and Z-5 and E-5 (right) in dichloromethane solutions (1.0 mmol L ) at 25 C measured with glassy carbon working electrode. Supporting electrolyte 0.1 mol L of [N Bu
B(C ]).
4
]
6 5 4
F )
ꢀ
1
ꢁ
ꢀ1
Fig. 4. Left: UVeVis/NIR spectra of Z-5 in dichloromethane solution (2.0 mmol L ) at rising potentials (ꢀ200 mVe1300 mV vs Ag/AgCl) at 25 C; supporting electrolyte 0.1 mol L
n
þ
2þ
.
of [N Bu
4
][B(C
F
6 5
)
4
]. Right: UVeVis/NIR spectral changes of Z-5 to in situ generated [Z-5] and [Z-5]
þ
2þ
Fig. 5. Three band Gaussian deconvolution of the NIR absorption envelope of [Z-5] (left) and [Z-5] (right) obtained by spectroelectrochemistry in an OTTLE cell.
diferrocenyl-1-phenyl-1H-pyrroles [51] and in 3,4-di-N-substituted
,5-diferrocenyl thiophenes [19]. For the -unsaturated carbonyl
stabilization in
enhanced electron density at the
electron deficient [53]. Following this principle, we assume that the
1st oxidation takes place at the ferrocenyl unit in -position to the
a
,
b
-unsaturated carbonyl compounds leads to an
2
a,
b
a
carbon, while the ß-position is
compounds Z-5 and E-5 the assignment of the individual oxidation
processes of the three ferrocenyls could be achieved by comparison
with similar building blocks from literature (Chart 1). A comparison
of various vinylferrocenes with acylferrocenes shows that the
electron-withdrawing effect of the carbonyl group leads to a
decreased electron density at the CO-bonded ferrocenyl and hence
this unit is oxidized at higher potentials (see, for example, ace-
a
carbonyl functionality, while the ß-ferrocenyl is oxidized
subsequently.
1
Paramagnetic H NMR studies on partially oxidized analytes can
be used to determine the sequence of the ferrocenyl oxidations
1
[54,55]. Therefore, H NMR studies of E-5 were carried out by
ꢁ
0
tylferrocene 10,
E
E
¼
280 mV; vinyl ferrocenes 11e13,
z ꢀ75 mV). Therefore, it is reasonable to assume that the CO-
bonded ferrocenyl termini in Z/E-5 are oxidized last. Mesomeric
subsequent dropwise addition of a solution of “Magic Blue” (¼ tris-
ꢁ
0
(4-bromophenyl)aminium hexachloroantimonate; 20 mmol in
3
CH CN) as oxidant (Supporting Information, Fig. SI11). From these
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S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
þ/2þ
5
5]
typical absorptions in the UVeVis (inner ferrocenyl related
MLCT/DMSO-d
region (IVCT ¼ inter valence charge transfer) could be detected
Figs. 4e7 and Figs. SI12eSI13). A spectral simulation of the NIR
absorptions with three Gaussian-shaped functions was performed
to determine the physical parameters (wavenumber (~
extinction coefficient (εmax) and full width at half maximum (
)) of the charge transfer excitations (Figs. 5 and 7 and Fig. SI12,
Table 2).
Cyclopropenone 1 shows a weak IVCT absorption at 5300 cm
6
and p*-p* transitions) [19,57,58] and in the NIR
(
nmax),
Dn
~
1/
2
ꢀ1
ꢀ
1
ꢀ1
ꢀ1
(
D
ε
max ¼ 220 L mol cm
,
Dn1/2 ¼ 4750 cm ). The redox separation
ꢁ
E ' of 250 mV for 1 seems to be mainly a result of electrostatic
interactions.
Organometallic compounds [Z-5]
þ/2þ
þ/2þ
showed
and [E-5]
IVCT transitions in both oxidation states þ and 2þ (Figs. 4 and 6 and
Fig. SI13). The IVCT absorption after mono-oxidation was found at
ꢀ
1
ꢀ1
ꢀ1
Fig. 6. UVeVis/NIR spectra of E-5 in dichloromethane solution (2.0 mmol Lꢀ1) at rising
6060 cm
(¼ 1650 nm) (εmax ¼ 400 L mol
cm
, Dn1/
ꢁ
ꢀ1
ꢀ1
þ
ꢀ1
potentials (ꢀ200 mVe1200 mV vs Ag/AgCl) at 25 C; supporting electrolyte 0.1 mol L
¼ 4560 cm ) for [Z-5] and 4810 cm
(¼ 2079 nm)
2
n
of [N Bu
4
][B(C
F
6 5
)
4
.
þ
2þ
Fig. 7. Three band Gaussian deconvolution of the NIR absorption envelope of [E-5] (left) and [E-5] (right) obtained by spectroelectrochemistry in an OTTLE cell.
1
ꢀ1
ꢀ1
þ
measurements it can be concluded that the carbonyl bound ferro-
cenyl is oxidized last, while a distinction between the - and
ferrocenyl was not possible, which might be due to partial charge
delocalization between those two ferrocenyl units. This result
confirms the statement made earlier.
The Z/E isomerism seems to have no significance for the first two
consecutive oxidation processes, which is in accordance with the
vinylferrocenes 11e13 (Chart 1) [50]. However, the closer proximity
of the E-ß-ferrocenyl unit toward the CO-bonded ferrocenyl leads to
higher electrostatic repulsion in the E-isomer and hence, the 3rd
redox potential is increased from 490 mV (Z-5) to 560 mV (E-5).
While for other examples an oxidation-mediated isomerization of
vinyl ferrocenes is reported [50], we found no evidence for such
behavior in our electrochemical measurements.
(εmax ¼ 870 L molꢀ cm
,
Dn1/2 ¼ 4170 cm ) for [E-5] . After
a
b
-
subsequent oxidation to the dicationic mixed-valent species, a
ꢀ
1
bathochromic shift of the IVCT band to 5130 cm (¼ 1949 nm)
(εmax ¼ 540 L molꢀ cm
1
ꢀ1
,
Dn1/2 ¼ 4970 cm ) for [Z-5] and a
1
ꢀ1
2þ
ꢀ
hypochromic
shift
to
6000
cm
(¼
1667
nm)
(εmax ¼ 190 L molꢀ cm
1
ꢀ1
,
Dn1/2 ¼ 5690 cm ) for [E-5] was
ꢀ1
2þ
observed. Since the first oxidation takes place at the ferrocenyl in a-
position, two electron-transfer pathways from the two other fer-
rocenyls are possible. It could be shown that the electronic coupling
in E-vinyl-diferrocenes is stronger than in the corresponding Z-
isomers [50]. The same result was observed of [E-5] and [Z-5] ,
since the oscillator strength of the IVCT absorption (f), which rep-
þ
þ
þ
resents the strength of the charge transfer, for mono-cationic [E-5]
is higher than for [Z-5] (Table 2). However, after the second
þ
In order to get a deeper insight into the charge transfer behavior
in 1, Z-5 and E-5, in situ UVeVis/NIR spectroelectrochemical mea-
surements were performed (Figs 4 and 6, Figs. SI12 and SI13) in an
optically transparent thin-layer electrochemical [56] (¼ OTTLE) cell
oxidation only the transfer path from the CO-ferrocenyl is possible.
In this case the enhanced steric strain for the E-isomer, as evinced
by the higher torsion between the carbonyl and the vinyl func-
tionality (see X-ray discussion), hinders the conjugation between
the redox active termini. As a result, only a very weak IVCT band
was observed for the E-isomer, while strong electronic coupling
was found in the Z-analog (Figs. 4e7, Table 2). The relatively weak
bands at ca. 4000 cm can be assigned to interconfigurational (IC)
transition bands, which are normally forbidden, but gain intensity
through spin-orbit coupling and metal-ligand mixing. This obser-
vation is often found in ferrocenium complexes [19,59,60].
ꢀ
1
ꢀ1
n
4
containing 2.0 mmol$L of the analyte and 0.1 mol$L of [ Bu N]
6 5 4
[B(C F ) ] as supporting electrolyte with a stepwise increase of the
applied potential from ꢀ200 to 1200 mV vs Ag/AgCl. The sequential
in situ generation of the mixed-valent species was performed by
increasing potentials using varying step heights of 25, 50 and
ꢀ
1
100 mV. In the homo-valent neutral state, molecules 1, Z-5 and E-5
are, as expected, transparent in the near infrared (NIR). During in
þ
þ/2þ
and [E-
situ generation of the mixed-valent species [1] , [Z-5]
Please cite this article in press as: S.W. Lehrich, et al., Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.03.018

6
S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
Table 1
showed for E-5 a helical chirality crystallizing in an enantiopure
form. In addition, from a dichloromethane solution of 3, which was
layered with hexane, single crystals of 6, a cyclopropenone species
Cyclic Voltammetry Data of 1e3, Z-5, E-5 and 7e13 for comparison. All potentials are
given in (mV).
ꢁ
'a
ꢁ
'b
)d
ꢁ
'c
ꢁ
e
D
Compd.
E
(
1
E
(
2
E
3
E '
3
complexing one molecule of BF , could be obtained. The electro-
D
E
p
)d
DE
p
(DE
p
)d
chemical behavior of 1e5 have been determined by cyclic vol-
tammetry and square wave voltammetry. It was found that the
redox splitting between the ferrocenyl units is decreased for the
cyclopropenylium compounds 2 and 3, when compared with
cyclopropenone 1. All cyclopropenylium molecules decompose
upon oxidation in multi-cyclic experiments and hence are not
1
1
255 (64)
330 (91)
425 (62)
420
505 (70)
590 (115)f
640 (95)
510
250
260
215
90
f
f
2
3
g
Z-5
E-5
ꢀ75 (70)
ꢀ60 (60)
110h
290 (71)
275 (60)
490 (73)
560 (75)
365/200
335/285
stable under oxidative conditions. The well-resolved three
h
235h
430 (72)
125h
495
7
8
9
1
1
1
1
ꢁ0
ferrocenyl-centered oxidations of E-5 (E
1
¼
ꢀ60 mV,
i
ꢀ65 (70)
ꢁ
ꢁ
0
0
ꢁ0
ꢁ0
j
E
E
2
¼ 275 mV and E
3
¼ 560 mV) and Z-5 at (E
1
¼ ꢀ75 mV,
ꢀ55
ꢁ0
0j
1
2
3
¼ 290 mV and E
¼ 490 mV) allowed for an assignment of the
280
2
3
k
k
89k
159k
ꢀ67
individual redox events to the respective ferrocenyl units by com-
parison with similar literature known compounds (Chart 1, Elec-
trochemistry). It is shown that solely the 3rd oxidation process is
influenced in a significant way by the E/Z isomerism, whereby the
k
k
k
k
k
ꢀ77
93
82
170
k
k
172k
ꢀ90
Potentials vs FcH/FcH (FcH ¼ Fe(h5-C
þ
H ) ), scan rate 100 mV s at a glassy-
ꢀ1
5 5 2
ꢀ
1
carbon electrode of 1.0 mmol L solutions in anhydrous dichloromethane con-
closer proximity of the b-ferrocenyl and the CO-ferrocenyl in E-5
led to an increase of electrostatic interactions and hence the 3rd
ꢀ
1
n
ꢁ
taining 0.1 mol L of [N Bu
4
][B(C
6
F
5
)
4
] as supporting electrolyte at 25 C.
a
b
c
d
e
f
ꢁ
ꢁ
ꢁ
E
E
E
D
D
1
2
3
' ¼ formal potential of 1st redox process.
' ¼ formal potential of 2nd redox process.
' ¼ formal potential of 3rd redox process.
ꢁ
oxidation is shifted towards higher potentials (Z-5, E
3
' ¼ 490 mV;
ꢁ
E-5, E
3
' ¼ 560 mV). In situ UVeVis/NIR spectroelectrochemical
E
p
ꢁ
¼ difference between oxidation and reduction potentials.
measurements on compounds 1 and Z-/E-5 evince the charge
transfer behavior between the ferrocenyls. The analysis of the IVCT
bands allowed the classification of these two compounds as weakly
coupled Robin and Day class II systems [62].
E ' ¼ potential difference between the two ferrocenyl-related redox processes.
þ
Data taken from literature, potentials converted to FcH/FcH by adding ꢀ0.42 V
[
25].
g
Potentials from square-wave voltammogram (dotted line: step-height 25 mV,
pulse-width 5 s, amplitude 5 mV).
h
n
ꢀ1
Electrolyte [N Bu
4
][B(3,5-C
H
6 3
(CF
3
)
2
)
4
], scan rate 50 mV s , reference elec-
4. Materials and methods
þ
trode Ag/AgI, potentials vs FcH/FcH [11].
i
From reference [48].
From reference [49].
In nitrobenzene, electrolyte [N Bu
j
4.1. General data
k
n
ꢀ1
4
][PF
6
], scan rate 200 mV s , reference
þ
electrode Ag/AgCN, potentials converted to FcH/FcH by adding of ꢀ125 mV [50].
All reactions were carried out under an atmosphere of argon
using standard Schlenk techniques. Tetrahydrofuran was purified
by distillation from sodium/benzophenone ketyl. Hexane was pu-
rified with a MBRAUN SBS-800 purification system. Dichloro-
2
methane was purified by distillation from CaH . For column
chromatography alumina with a particle size of 90
Merck KgaA) or silica with a particle size of 40e60
mesh (ASTM), Fa. Macherey-Nagel) were used. As filtration support
celite (Riedel de H a€ en) was applied.
m
m
m (standard,
m (230e400
7
[11]
8
[48]
4.2. Instrumentation
9
[49]
10 [49]
Infrared spectra were recorded with a FT-Nicolet IR 200 equip-
1
ment. The H NMR spectra were recorded with a Bruker Avance III
5
00 spectrometer operating at 500.303 MHz in the Fourier trans-
13
1
form mode; the
C{ H} NMR spectra were recorded at
1
1 [50]
12 [50]
13 [50]
1
25.800 MHz. Chemical shifts are reported in ppm downfield from
1
tetramethylsilane with the solvent as reference signal ( H NMR:
d
1
3
1
(CDCl
3
) ¼ 7.26 ppm; C{ H} NMR:
d
(CDCl
3
) ¼ 77.16 ppm). The
melting points were determined with
a
Gallenkamp MFB
595 010 M melting point apparatus. Elemental analyses were per-
formed with a Thermo FlashEA 1112 Series instrument. High res-
olution mass spectra were recorded using a micrOTOF QII Bruker
Daltonite workstation.
Chart 1. Selected ferrocene species for comparison of the electrochemical data.
1
3
. Conclusion
Paramagnetic H NMR studies were performed in CDCl with
3
dropwise adding of “Magic Blue” (tris-(4-bromophenyl)aminium
Cyclopropenylium cations 2e4 have been prepared starting
hexachloroantimonate; 20 mmol in CH CN) as oxidant and
3
1
from 2,3-diferrocenylcyclopropenone (1) [4,5,25]. The strained C
3
measuring a H NMR spectra after each drop.
ring system in 1 could be cleaved by a nucleophilic attack of fer-
rocenyl lithium at the carbonyl carbon atom. The ring opened
products were obtained as separable isomeric mixtures of 1,2,3-
triferrocenylpropenones E-5 and Z-5. Both the E- and Z-isomer
could be crystallized and the molecular solid-state structures were
determined by single crystal X-ray diffraction. The single crystals
4.3. X-ray diffraction
Data were collected with an Oxford Gemini S diffractometer at
120 K for E-5, Z-5 and at 110 K for 6 (for more details for 6 see
Supporting Information) using Mo Ka (
l
¼ 0.71073 Å) radiation. The
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j.jorganchem.2017.03.018

S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
þ/2þ a
7
Table 2
þ
þ/2þ
NIR data of the absorptions of [1] , [E-5]
and [Z-5]
.
max (cm 1)
ꢀ
D
n
ꢀ1
1/2 (cm
)
(
D
n
)
theo (cm
b
ꢀ1
)
f $ 10
ꢀ3c
ꢀ1
(cm )
Compd.
~
n
~
~
1/2
ꢀ ꢀ1
1
(
ε (L mol cm ))
þ
[
[
[
[
[
1]
IVCT
IC
IVCT
IC
IVCT
IC
IVCT
IC
5300 (220)
3710 (40)
6060 (400)
3860 (80)
5130 (540)
3770 (130)
4810 (870)
3640 (340)
6000 (190)
3800 (80)
4750
360
4560
660
4970
640
4170
740
3500
3740
3440
3330
3720
4.8
þ
Z-5]
8.4
Z-5]2
þ
12.3
16.7
5.0
þ
E-5]
E-5]2
þ
IVCT
IC
5690
720
a
b
c
ꢀ1
1/2
n
ꢁ
6 5 4
F ) ] as supporting electrolyte at 25 C.
In dichloromethane solutions containing 0.1 mol L of [N Bu
4
][B(C
Calculated with equation (
D
~
n
1/2
)
theo ¼ (2310 ~
n max) according to the Hush relationship for weakly coupled systems [61].
ꢀ9
Calculated with equation f ¼ 4.6 · 10 $ ε $
1/2
Dn .
~
þ
structures were solved by direct methods and refined by full-
matrix least square procedures on F with SHELXL-2013 [63,64].
All non-hydrogen atoms were refined anisotropically, and a riding
model was employed in the treatment of the hydrogen atom po-
sitions. Graphics of the molecular structures have been created by
using ORTEP [65].
220 mV vs Ag/Ag (
D
E
p
¼ 61 mV) within the measurements [72,73].
2
The cyclic voltammograms, which are depicted in Fig. 5, Fig. SI9 and
Fig. SI10 were taken after typically three scans and are considered
to be steady state cyclic voltammograms in which the signal pattern
differs not from the initial sweep.
UVeVis/NIR measurements were carried out in an OTTLE (¼
Crystal Data for E-5: C33
H
28Fe
3
O, M
r
¼ 608.10 g molꢀ1, mono-
optically thin-layer electrochemical) cell with quartz windows
clinic, P2
1
, a ¼ 12.890(11) Å, b ¼ 5.805(5) Å, c ¼ 17.414(16) Å,
similar to that described previously [56] in anhydrous dichloro-
ꢁ
3
ꢀ3
ꢀ1
b
m
¼ 109.071(9) , V ¼ 1231.5(2) Å , Z ¼ 2,
r
calcd ¼ 1.640 g m
,
methane solutions containing 2.0 mmol$L
analyte and
ꢀ
1
ꢁ
ꢀ1
n
¼ 1.770 mm , T ¼ 120(1) K,
q
range 3.345e24.991 , 3800 re-
0.1 mol$L of [N Bu
4
][B(C
6
F
5
)
4
] as supporting electrolyte using a
ꢁ
flections collected, 3800 independent reflections (Rint ¼ 0.0463),
Varian Cary 5000 spectrophotometer at 25 C. The working elec-
trode Pt-mesh, the AgCl coated Ag wire for reference and the Pt-
mesh auxiliary electrode are melt-sealed into a polyethylene foil.
The values obtained by deconvolution could be reproduced within
R1 ¼ 0.0636, wR2 ¼ 0.1513 (I > 2
Crystal Data for Z-5: C33
rhombic, Pca2
V ¼ 2445.2(15) Å , Z ¼ 4,
T ¼ 120 K,
s
(I)).
O, M
H
28Fe
3
r
¼ 608.10 g molꢀ1, ortho-
1
, a ¼ 23.167(11) Å, b ¼ 5.811(2) Å, c ¼ 18.164(16) Å,
3
ꢀ3
ꢀ1
ꢀ1
ꢀ1
ꢀ1
ꢀ1
.
r
calcd ¼ 1.652 g m
,
m
¼ 1.783 mm
,
ε
max ¼ 100 L$mol $cm
,
n
max ¼ 50 cm and Dn1/2 ¼ 50 cm
ꢁ
q
range 3.506e24.997 , 3141 reflections collected, 3141
Between the spectroscopic measurements the applied potentials
have been increased step-wisely using step heights of 25, 50 or
100 mV. At the end of the measurements the analyte was reduced
at ꢀ400 mV for 30 min and an additional spectrum was recorded to
prove the reversibility of the oxidations.
independent reflections (Rint ¼ 0.0383), R1 ¼ 0.0250, wR2 ¼ 0.0543
(
I > 2 (I)).
s
4.4. Electrochemistry
Electrochemical measurements on 1.0 mmol Lꢀ1 solutions of the
4.5. Reagents
analyte in anhydrous, air free dichloromethane containing
n
ꢀ1
n
[N( Bu)
4
][B(C
6
F
5
)
4
] was prepared by metathesis of lithium tet-
0
.1 mol$L
of [N Bu
4
][B(C
6
F
5
)
4
] as supporting electrolyte were
rakis(pentafluorophenyl)borate etherate (Boulder Scientific) with
tetra-n-butylammonium bromide according to reference [45]. All
other chemicals were purchased from commercial suppliers and
were used without further purification. Compounds 1e4 were
synthesized according to published procedures [3e5,13,25].
ꢁ
conducted under a blanket of purified argon at 25 C utilizing a
Radiometer Voltalab PGZ 100 electrochemical workstation com-
bined with a personal computer [66e68]. A three electrode cell,
which utilized a Pt auxiliary electrode, a glassy carbon working
electrode (surface area 0.031 cm ) and an Ag/Ag (0.01 mol$L
AgNO ) reference electrode mounted on a Luggin capillary was
used. The working electrode was pretreated by polishing on a
Buehler microcloth first with a 1 m and then with a 1/4 m dia-
mond paste. The reference electrode was constructed from a silver
2
þ
ꢀ1
3
4.6. Synthesis
m
m
Z- and E-1,2,3-triferrocenylprop-2-enone (Z-5/E-5). Ferrocene
(0.4 g, 2.13 mmol) and KO Bu (30 mg, 0.27 mmol) were dissolved in
ꢀ1
t
wire inserted into a solution of 0.01 mol$L
[AgNO
] in acetonitrile in a Luggin capillary
with a CoralPor tip. This Luggin capillary was inserted into a second
3
] and
ꢀ
1
n
ꢁ
0
.1 mol$L [N Bu
4
][B(C
6
5
F )
4
40 mL of tetrahydrofuran and the mixture was cooled to ꢀ80 C.
t
BuLi (2.2 mL, 4.26 mmol, 1.9 M solution in pentane) was added
ꢀ
1
Luggin capillary with a CoralPor tip filled with a 0.1 mol$L
dropwise via a syringe and the reaction mixture was stirred for 1 h
during warming up to 0 C. Then compound 1 (0.9 g, 2.13 mmol)
n
ꢁ
[
N Bu
4
][B(C
6
F
5
)
4
] solution in dichloromethane. Successive experi-
ments under the same experimental conditions showed that all
formal reduction and oxidation potentials were reproducible
within 5 mV. Experimentally, potentials were referenced against an
dissolved in 20 mL of tetrahydrofuran was added dropwise via a
syringe and the reaction solution was stirred at ambient tempera-
ture for 12 h. After evaporation of all volatiles in vacuum, 20 mL of
water and 60 mL of dichloromethane were added and the organic
phase was extracted twice each with 40 mL of water. The resulting
þ
Ag/Ag reference electrode but results are presented referenced
against ferrocene as an internal standard as required by IUPAC [69].
When decamethylferrocene was used as an internal standard, the
experimentally measured potentials were converted into E vs FcH/
4
organic phase was dried over MgSO and all volatiles were
removed. The crude product was purified by column chromatog-
raphy (column size: 20 ꢂ 3 cm, silica) using a hexane-
dichloromethane mixture of ratio 1:1 (v/v) as eluent. The third
þ
þ
5
FcH by setting the Fc*/Fc* (Fc* ¼ Fe(ƞ -C
5 5 2
Me ) ) potential
to ꢀ614 mV [70,71]. Ferrocene itself showed a redox potential of
Please cite this article in press as: S.W. Lehrich, et al., Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.03.018

8
S.W. Lehrich et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
[4] T. Klimova Berestneva, E.I. Klimova, J.M. M
eꢀ ndez Stivalet, S. Hern ꢀa ndez-
fraction was (E)-1,2,3-triferrocenylprop-2-enone (E-5) and the
fourth fraction (Z)-1,2,3-triferrocenylprop-2-enone (Z-5).
Removing of all volatiles under reduced pressure gave dark red
solids. The isomeric ratio is 1:1.
Ortega, M. Martínez García, Eur. J. Org. Chem. (2005) 4406.
5] E.I. Klimova, T.K. Berestneva, S.H. Ortega, D.M. Iturbide, A.G. Marquez,
M.M. García, J. Organomet. Chem. 690 (2005) 3333.
[
[6] T. Eicher, D. Lerch, Tetrahedron Lett. 21 (1980) 3751.
[
[
7] S. Yoneda, H. Hirai, Z. Yoshida, Chem. Lett. 46 (1976) 1051.
8] T. Berestneva, E. Klimova, M. Flores-Alamo, L. Backinowsky, M. García, Synth.
(E)-1,2,3-triferrocenylprop-2-enone (E-5): Yield of E-5: 135 mg
(
(
(
0.22 mmol, 10% based on 1). Anal. Calcd. for C33H28Fe O
3
(Stuttg) (2006) 3706.
ꢀ
1
M ¼ 608.11 g$mol ): C 65.18, H 4.64; found: C 64.41, H 4.93
[9] U. Pfaff, A. Hildebrandt, D. Schaarschmidt, T. Rüffer, P.J. Low, H. Lang, Organ-
ometallics 32 (2013) 6106.
10] F. Paul, C. Lapinte, Coord. Chem. Rev. 178e180 (1998) 431.
11] Y. Li, M. Josowicz, L.M. Tolbert, J. Am. Chem. Soc. 132 (2010) 10374.
Although these results are outside the range viewed as establish-
[
[
ing analytical purity, they are provided to illustrate the best values
ꢁ
ꢀ1
obtained to date.). Mp.: >200 C decomposition. IR (KBr, in cm ):
088 (m, CꢀH), 2954 (w), 1635 (s, ), 1615 (m), 1450 (m), 1410
w), 1374 (m), 1265 (w), 1244 (m), 1105 (m), 1094 (m), 1048 (m),
029 (m), 1000 (m, ), 821 (s, ), 516 (s, C ring
in ppm): 4.01 (s, 5 H, C ), 4.17 (s, 5 H, C ),
), 4.24 (s, 5 H,
), 4.31 (pt, JHH ¼ 1.9 Hz, 2 H,
), 4.46 (pt, JHH ¼ 1.9 Hz, 2 H,
[12] M.D. Ward, Chem. Soc. Rev. 24 (1995) 121.
[
[
[
13] I. Agranat, E. Aharon-Shalom, Tetrahedron 35 (1979) 733.
14] R. Hauser, D. Lednicer, Angew. Chem. Int. Ed. Engl. 11 (1972) 1025.
15] A. Hildebrandt, H. Lang, Organometallics 32 (2013) 5640.
[16] A. Hildebrandt, U. Pfaff, H. Lang, Rev. Inorg. Chem. 31 (2011) 111.
17] S.W. Lehrich, A. Hildebrandt, T. Rüffer, M. Korb, P.J. Low, H. Lang, Organo-
metallics 33 (2014) 4836.
18] D. Miesel, A. Hildebrandt, M. Korb, P.J. Low, H. Lang, Organometallics 32
(2013) 2993.
[19] J.M. Speck, M. Korb, A. Schade, S. Spange, H. Lang, Organometallics 34 (2015)
3788.
3
n
C O
n ]
(
1
d
CꢀH, C
d
5
H
4
p
CꢀH, C
5
H
5
5
H
4
1
[
[
tilt). H NMR (CDCl
3
,
5
H
5
5 5
H
4
C
C
C
.17 (pt (¼ pseudo triplett), JHH ¼ 1.9 Hz, 2 H, C
5 4
H
H
5 5
H
5 4
H
5 4
), 4.28 (pt, JHH ¼ 1.9 Hz, 2 H, C
), 4.36 (pt, JHH ¼ 1.9 Hz, 2 H, C
5 4
H
5 4
H
1
3
1
), 4.60 (pt, JHH ¼ 1.9 Hz, 2 H, C
5
H
H
4
), 6.70 (s, 1 H, C¼CH). C{ H}
), 68.6 (C ), 69.3 (C ), 69.4
), 70.6 (C ), 71.9
), 124.6 (C¼CH),
[
20] D. Miesel, A. Hildebrandt, M. Korb, H. Lang, J. Organomet. Chem. 803 (2016)
NMR (CDCl
3
,
d
in ppm): 66.5 (C
5
4
5
H
4
5 4
H
104.
(
(
C
C
5
5
H
H
5
), 69.5 (C ), 69.9 (C
5
H
4
5
H
5
), 70.2 (C
5
H
5
5
H
4
[21] K. Kaleta, A. Hildebrandt, F. Strehler, P. Arndt, H. Jiao, A. Spannenberg, H. Lang,
U. Rosenthal, Angew. Chem. - Int. Ed. 50 (2011) 11248.
22] K. Kaleta, F. Strehler, A. Hildebrandt, T. Beweries, P. Arndt, T. Rüffer,
A. Spannenberg, H. Lang, U. Rosenthal, Chem. Eur. J. 18 (2012) 12672.
[23] B. van der Westhuizen, J.M. Speck, M. Korb, D.I. Bezuidenhout, H. Lang,
i
i
i
4
), 80.3 ( C-C
5
H
4
), 82.0 ( C-C
5
H
4
), 85.1 ( C-C
5
H
4
[
1
36.3 (C¼CH), 202.5 (C¼O). HRMS (ESI-TOF, m/z): calcd. for
þ
C
33
H
28Fe
3
O: 608.0188; found 608.0135 [M] .
Z)-1,2,3-triferrocenylprop-2-enone (Z-5): Yield of Z-5: 135 mg
0.22 mmol, 10% based on 1). Anal. Calcd. for C33
J. Organomet. Chem. 772e773 (2014) 18.
24] S.W. Lehrich, A. Hildebrandt, M. Korb, H. Lang, J. Organomet. Chem. 792
(
[
(
(
H28Fe
3
O
(2015) 37.
ꢀ
1
M ¼ 608.11 g$mol ): C 65.18, H 4.64; found: C 64.65, H 4.99. Mp.:
[25] E.I. Klimova, T. Klimova Berestneva, L.R. Ramirez, A. Cinquantini, M. Corsini,
ꢁ
ꢀ1
P. Zanello, S. Hern ꢀa ndez-Ortega, M.M. García, Eur. J. Org. Chem. (2003) 4265.
1
76 C. IR (KBr, in cm ): 3093 (m,
w), 1635 (s, ), 1615 (m), 1439 (m), 1410 (w), 1376 (m), 1272
m), 1246 (m), 1106 (m), 1094 (m), 1046 (m), 1031 (m), 1001 (m,
nCꢀH), 2959 (w), 2923 (w), 2852
[
26] E.I. Klimova, T. Klimova, S.H. Ortega, M.E. Rabell, L.R. Ramírez, M.M. García,
(
(
C O
n ]
J. Organomet. Chem. 689 (2004) 2395.
[27] H.D. Flack, Acta Crystallogr. Sect. A 39 (1983) 876.
€
28] J.J. Burckhardt, R. Haüy, Die Symmetrie Der Kristalle, Birkhauser, Basel,
1
[
d
CꢀH, C
5
H
d
4
), 820 (s,
in ppm): 3.92 (s, 5 H, C
HH ¼ 1.9 Hz, 2 H, C ), 4.25 (pt, JHH ¼ 1.9 Hz, 2 H, C
), 4.35 (s, 5 H, C
), 4.41 (pt, JHH ¼ 1.9 Hz, 2 H,
), 4.61 (pt, JHH ¼ 1.9 Hz, 2 H, C ), 4.94 (pt, JHH ¼ 1.9 Hz, 2 H,
in ppm): 68.3
), 70.1 (C ), 70.2
p
CꢀH, C
5
H
5
), 526 (w, C
5
H
4
ring tilt). H NMR
), 4.20 (pt,
), 4.30 (pt,
Schweiz, 1988.
(
CDCl
3
,
5
H
5
), 4.13 (s, 5 H, C
5 5
H
H
5 4
[
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J
J
C
C
5
H
4
HH ¼ 1.9 Hz, 2 H, C
5
H
4
5
H
5
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9
5
H
H
4
5 4
H
[
1
3
1
5
4
), 7.28 (s, 1 H, ¼CH). C{ H} NMR (CDCl
3
, d
907, University of Southampton, 2002.
(
(
C
C
5
5
H
H
4
), 69.2 (C
), 70.3 (C
), 80.1 ( C-C
5
H
5
), 69.3 (C
5
H
4
), 69.5 (C
5
H
5
5
H
4
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4
5
H
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), 71.3 (C
5
H
4
), 72.2 (C ), 79.1 ( C-C H ), 79.2 ( C-
5
H
4
5 4
[
[
i
C
H
5 4
5
H
4
), 131.0 (C¼CH), 136.2 (C¼CH), 200.6 (C¼O).
HRMS (ESI-TOF, m/z): calcd. for C33
H28Fe
3
O: 608.0188; found 608
þ
0
.0148 [M] .
[
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[
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We thank Julia A. Kronawitt for her support in lab. We are
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financial support. M.K. thanks the Fonds der Chemischen Industrie
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Appendix A. Supplementary data
€
[
[
Figures, Tables, and CIF files giving further (spectro)electro-
chemical spectra, NMR spectra, and crystallographic data. This
material is available free of charge via the Internet at http://dx.doi.
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Crystallographic data of Z-/E-5 and 6 are also available from the
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