Preparation and structures of biferrocenes with alicyclic substituents: Orderedisorder of substituents in the crystal structures of cyclohexenylbiferrocene and its charge-transfer salt

Article abstract of DOI:10.1016/j.jorganchem.2013.05.041

Biferrocene derivatives with cyclohexyl, cyclohexenyl, and cyclopentenyl substituents were prepared and crystallographically characterized. The cyclohexenyl substituents exhibited twofold disorder in the crystals. A charge-transfer salt of 10-cyclohexenylbiferrocene with [Ni(mnt)₂] was prepared. The biferrocenium cation in this salt was in a valence-trapped state owing to electrostatic interactions with the anion. The cyclohexenyl substituent in the [Ni(mnt)₂] salt exhibited no disorder because of closer packing of the salt.

Full text of DOI:10.1016/j.jorganchem.2013.05.041

Journal of Organometallic Chemistry 741-742 (2013) 72e77
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Journal of Organometallic Chemistry
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Preparation and structures of biferrocenes with alicyclic substituents:
Orderedisorder of substituents in the crystal structures of
cyclohexenylbiferrocene and its charge-transfer salt
,
b
,
a
a
Tomoyuki Mochida a , Takashi Kobayashi , Takahiro Akasaka
*
a Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
b Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo 657-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Biferrocene derivatives with cyclohexyl, cyclohexenyl, and cyclopentenyl substituents were prepared and
crystallographically characterized. The cyclohexenyl substituents exhibited twofold disorder in the
crystals. A charge-transfer salt of 10-cyclohexenylbiferrocene with [Ni(mnt)2] was prepared. The bifer-
rocenium cation in this salt was in a valence-trapped state owing to electrostatic interactions with the
anion. The cyclohexenyl substituent in the [Ni(mnt)2] salt exhibited no disorder because of closer packing
of the salt.
Received 1 May 2007
Received in revised form
19 May 2013
Accepted 28 May 2013
Keywords:
Biferrocene
Ó 2013 Elsevier B.V. All rights reserved.
Crystal structures
Redox potentials
Charge-transfer salts
Mixed-valence compound
1. Introduction
substituent into the biferrocenium salts. Cyclopentenyl groups do
not generally show disorder, while disorder is often seen in per-
It is understood that the valence state of the biferrocenium
cation is influenced by its substituents as well as the packing
environment [1]. To investigate this phenomenon, a variety of
substituents has been introduced to biferrocene. In our previous
work, we found an electron-transfer phase transition in the
dineopentylbiferrocenium salt of F1TCNQ [2], in which the bulky
substituent plays an important role. In this study, our aim is to
introduce conformational flexibility to biferrocenium salts. To this
end, we prepared biferrocene derivatives with alicyclic sub-
stituents. Cyclohexane derivatives can adopt various conforma-
tions, and these materials often exhibit glass transitions as well as
phase transitions in the solid state [3]. In crystals of cyclohexene
compounds, conformational disorder is frequently found in the
form of two half-chair conformers (Chart 1), which has been
interpreted as either dynamic or static [4]. In the case of charge-
transfer complexes, conformational flexibility in six-membered
rings allows control of physical properties; in the salts of bis(e-
thylenedithio)tetrathiafulvalene (¼BEDT-TTF), the orderedisorder
of the ethylene groups is reflected in their electrical conductivities
[5]. Because of this, we decided to introduce a cyclohexenyl
fluorocyclopentene derivatives [6].
Here, we report the preparation and properties of 10-(1-
cyclohexenyl)biferrocene (1a), 10,1000-di-1-cyclohexenylbiferrocene
(1b), 10-cyclohexylbiferrocene (2a), 10,1000-dicyclohexylbiferrocene
(2b), 10-(1-cyclopentenyl)biferrocene (3a), and 10,1000-di-1-
cyclopentenylbiferrocene (3b), as shown in Chart 2. We also pre-
pared and structurally characterized a charge-transfer salt, [1a]
[Ni(mnt)2]. The versatile [M(mnt)2] anion (mnt ¼ S2C4N22ꢀ ¼ mal-
eonitriledithiolate) is interesting from the viewpoint of solid-state
physical properties [7,8] and crystal engineering [9] of charge-
transfer salts. [1a][Ni(mnt)2] exhibited a valence-trapped state in
the biferrocenium cation due to electrostatic interactions between
the cation and the anion. The conformational freedom of the
cyclohexenyl substituents in 1a and [1a][Ni(mnt)2] was compared.
2. Results and discussion
2.1. Preparation and properties of 1ae3b
Several methods of introducing alicyclic substituents into
ferrocene have been reported [10], and we chose to adapt the re-
action of lithioferrocene with cyclohexanone [11]. Compounds 1a
and 1b were prepared according to Scheme 1 in 20e30% yield. This
* Corresponding author. Department of Chemistry, Graduate School of Science,
Kobe University, Kobe, Hyogo 657-8501, Japan. Tel./fax: þ81 78 803 5679.
E-mail address: tmochida@platinum.kobe-u.ac.jp (T. Mochida).
procedure gave
a
mixture of mono- and di-substituted
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.041

T. Mochida et al. / Journal of Organometallic Chemistry 741-742 (2013) 72e77
73
Table 1
Melting points (Tm), melting enthalpies (
D
Hm), and melting entropies (
D
Sm) for 1ae
3b.
Compound
1a
1b
2a
2b
3a
3b
Chart 1.
Tm/K
398.9
35.2
87.9
418.3
41.6
99.0
365.0
27.0
73.2
423.5
53.3
125.0
426.4
32.8
75.9
462.1
52.1
112.4
D
D
Hm/kJ molꢀ1
Sm/J Kꢀ1 molꢀ1
asymmetric, bent molecular structure, which prevents crystalliza-
tion. No phase transitions were observed in the solid state in any of
the compounds.
The redox potentials of 1ae3b were measured by means of cy-
clic voltammetry (CV) and are listed in Table 2 (vs. FeCp02/þ). The
first half-wave potentials of these compounds were lower than that
of biferrocene, which indicates that electron-donating ability was
increased by the substituents. No difference was observed between
the redox potentials of the cyclohexyl and cyclohexenyl com-
pounds. The first waves of the compounds containing five-
membered rings (3a and 3b) were slightly higher than those with
six-membered rings (1ae2b). The
DE1/2 value was larger than that
of biferrocene in every case. The
D
E1/2 values of the mono-
substituted compounds were greater than those of the di-
substituted compounds, which is ascribable to the effect of
asymmetry.
2.2. Crystal structures of 1a, 1b, and 2b
The crystal structures of 1a, 1b, and 2b were determined by X-
ray crystallography at 173 K. ORTEP [12] drawings of their molec-
ular structures are shown in Fig. 1. The cyclohexenyl groups in 1a
and 1b are disordered, and are oriented parallel to the adjacent
ferrocenyl moiety within the molecule. In contrast, the cyclohexyl
group in 2a is much bulkier, and extends outside the ferrocenyl
ring.
Chart 2.
In 1a, the average Fe(1)eC(Cp) and Fe(2)eC(Cp) distances are
ꢀ
ꢀ
2.045 A and 2.042 A, respectively. The central CpeCp rings in the
biferrocenyl moiety are twisted by 5.6ꢁ. The cyclohexenyl substit-
uent is nearly planar, and is in a face-to-face orientation with the
other ferrocenyl moiety within the molecule (Fig. 1a). The cyclo-
hexenyl ring exhibits twofold disorder, as shown in Chart 1: the
ethylene carbons (eC23eC24e and eC27eC28e) opposite the
double bond (eC21aC26e) are disordered in a 1:1 ratio. In the
crystal, the molecules form a centrosymmetric dimer via inter-
molecular face-to-face contact between a Cp ring and a cyclo-
hexenyl ring, as shown in Fig. 2a. The centroidecentroid distance
between the neighboring Cp ring and the cyclohexene ring is
biferrocenes, which were separated by gel permeation chroma-
tography (GPC). Compounds 3a and 3b were prepared by the same
method, with yields of about 17%. Alternatively, 1b could be ob-
tained by coupling of bromo-1-cyclohexenylferrocene. Compounds
2a and 2b were readily obtained by hydrogenation of 1a and 1b,
respectively.
The thermal properties of 1ae3b were investigated by means
of differential scanning calorimetry (DSC). Melting points and en-
tropies of melting are listed in Table 1. The melting points of
the cyclopentenyl compounds (3a and 3b) were higher than those
of the cyclohexenyl compounds (1a and 1b), and those of the
di-substituted compounds were higher those of the mono-
substituted compounds. In 2a, melting was not reversible;
melting occurred at 365 K, and a glass transition was observed on
cooling. On heating the material, a glass transition occurred at
245 K, and on further heating, crystallization was observed at 294 K.
The supercooling characteristic of 2a may be attributed to its
ꢀ
4.43 A.
In the crystal of 1b, the molecule is located on the inversion
ꢀ
center. The average FeeC(Cp) distance is 2.050 A. Similarly to 1a,
the cyclohexenyl substituent is nearly planar and exhibits twofold
disorder in a 1:1 ratio (Fig.1b). The substituents are in a face-to-face
orientation with the ferrocenyl moieties in the molecule. In the
crystal, the molecules are arranged almost perpendicular to each
Scheme 1. Preparation of 1a and 1b.

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T. Mochida et al. / Journal of Organometallic Chemistry 741-742 (2013) 72e77
Table 2
Redox potentials of 1ae3b and biferrocene (V vs. FeCp02/þ).
E1/2(Bifcþ/0
)
E1/2(Bifc2þ/þ
)
DE1/2
a
Compound
1a
1b
2a
2b
3a
3b
ꢀ0.17
ꢀ0.19
ꢀ0.17
ꢀ0.19
ꢀ0.15
ꢀ0.17
ꢀ0.11
0.22
0.17
0.22
0.18
0.22
0.19
0.22
0.39
0.36
0.39
0.37
0.37
0.36
0.33
Biferrocene
a
D
E1/2 ¼ E1/2(Bifc2þ/þ) ꢀ E1/2(Bifcþ/0).
other, and no face-to-face intermolecular contacts are present be-
tween the Cp rings and/or the cyclohexene rings.
The molecule of 2b has no inversion symmetry, and the central
CpeCp rings in the biferrocenyl moiety are twisted by 19.4ꢁ. The
ꢀ
average Fe(1)eC(Cp) and Fe(2)eC(Cp) distances are 2.054 A and
ꢀ
2.050 A, respectively. The cyclohexyl group adopts a chair confor-
mation (Fig. 1c), and no disorder was observed. The substituent is
largely twisted with respect to the Cp plane to which it is attached;
the torsion angles are about 58ꢁ and 45ꢁ for the substituents at Fc1
and Fc2, respectively. In the crystal, the molecules are stacked in a
columnar arrangement along the [101] direction. In the column,
each cyclohexyl group faces the Cp ring of an adjacent molecule.
Fig. 2. Structures of the dimer units of 1a in crystals of (a) 1a and (b) [1a][Ni(mnt)2] at
173 K. Interplane distances (A) are also shown. Dashed lines are a guide to the eye.
ꢀ
2.3. Structure and valence states of [1a][Ni(mnt)2]
The charge-transfer salt [1a][Ni(mnt)2] was prepared by react-
ing 1a with [Fe(C5H4Br)2][Ni(mnt)2], followed by vapor diffusion of
pentane into the solution. Attempts to prepare [Ni(mnt)2] salts with
other donors were unsuccessful. TCNQ derivatives afforded no
crystalline charge-transfer complexes.
ꢀ
value: 2.088 A), which is comparable to those in the ferrocenium
ꢀ
cation (2.08 A) [15]. The Fe(2)eC(Cp) distances are within the
ꢀ
ꢀ
range 2.038(2)e2.056(2) A (average value: 2.048 A), which is
comparable to those in neutral ferrocene (2.04 A) [16]. This charge
ꢀ
localization may be ascribed to electrostatic interactions between
the donor and acceptor in the crystal, as seen in other [M(mnt)2]
salts [8]. The local arrangement of the donor and acceptor is
shown in Fig. 3b. The shortest CN.Fe distances around Fe(1) and
Fe(2) are 4.369 A and 4.629 A, respectively. The former, shorter
distance stabilizes the cationic charge on the Fe(1) atom. The
higher electron-donating ability of the Fe(1) site induced by the
cyclohexyl group also favors charge localization on Fe(1). Owing to
the asymmetric crystal environment, it is unlikely that the salt will
exhibit a valence-detrapped state even at higher temperatures.
However, valence-detrapping might occur if non-coordinating
anions are used.
The packing diagram of the complex, as determined by X-ray
crystallography, is shown in Fig. 3a. The crystallographically inde-
pendent unit consists of one biferrocenium cation and one
[Ni(mnt)2] anion. The anions are stacked along the a-axis. The IR
spectrum showed CN stretching bands characteristic of the
[Ni(mnt)2] monoanion [13] at 2208 cmꢀ1. The intramolecular bond
lengths of the anion are virtually identical to those of (NnBu4)
[Ni(mnt)2] [14]; the intramolecular NieS distances are 2.1390(6)e
ꢀ
ꢀ
ꢀ
ꢀ
2.1463(6) A (average: 2.143 A). The anion is not planar, and exhibits
a slight distortion toward a tetrahedral shape, with an angle be-
tween the metallacycle mean planes of 8.1ꢁ around the Ni atom.
The donor molecule was
a mixed-valence cation which
Interestingly, the cyclohexenyl unit is disordered in 1a but not in
[1a][Ni(mnt)2]. The suppression of disorder in the latter compound
exhibited a valence-trapped state. The Fe(1)eC(Cp) distances of
the donors were within the range 2.056(2)e2.153(2) A (average
ꢀ
Fig. 1. Molecular structures of (a) 10-cyclohexylbiferrocene (1a), (b) 10,1000-dicyclohexenylbiferrocene (1b), and (c) 10,1000-dicyclohexylbiferrocene (3b) at 173 K.

T. Mochida et al. / Journal of Organometallic Chemistry 741-742 (2013) 72e77
75
3. Conclusion
In this study, biferrocenes with five- and six-membered alicyclic
substituents were synthesized in order to introduce conforma-
tional freedom into biferrocenium complexes. X-ray structure
analysis revealed that the shapes of the resulting molecules were
significantly influenced by the substituents; cyclohexenyl units
were positioned parallel to the ferrocene moiety, while cyclohexyl
groups were much more bulky and extended outward from the
molecule. In addition, a salt of cyclohexenylbiferrocene with
[Ni(mnt)2] anion was obtained. Here, the donor was a mixed-
valence monocation which exhibited a valence-trapped state due
to electrostatic interactions between the cation and the anion. In
the crystal of cyclohexenylbiferrocene, the substituent exhibited
twofold disorder, but the disorder was suppressed in the [Ni(mnt)2]
salt due to closer packing of the ionic crystal. The introduction of
cyclohexenyl rings was thus shown to be useful in inducing changes
in conformational freedom in the crystal.
4. Experimental
4.1. General methods
1,10-Dibromobiferrocene [17], [Fe(C5H4Br)2][Ni(mnt)2] [8], and 1-
bromo-10-(1-hydroxycyclohexyl)ferrocene [11] were prepared by
literature methods. Other reagents and solvents were commercially
available. All reactionswerecarriedoutunderanitrogenatmosphere.
JAI LC-908 was used for gel permeation chromatography (GPC). NMR
spectrawere recorded ona JEOLJNM-ECL-400 spectrometer. Infrared
spectra were recorded on a JASCO FT-IR 230 spectrometer using KBr
pellets. UVevis spectra were recorded on a JASCO V-570 UVevis/NIR
spectrometer. CyclicvoltammogramswererecordedusinganALS/chi
electrochemical analyzer, model 610C. Redox potentials were
measured at a scan rate of 0.1 V sꢀ1 in acetonitrile containing
0.1 mol dmꢀ3 n-Bu4NClO4 as a supporting electrolyte. An Ag/Agþ
reference electrode anda platinumworkingelectrodewere used, and
the potentials were referenced to a FeCp2/FeCpþ2 couple. Intermo-
lecular overlap integrals were calculated by the extended Hückel
molecular orbital method [18]. Differential scanning calorimetry was
performed on a TA Instruments Q100 calorimeter from 103 K to 473 K
Fig. 3. Crystal structure of [1a][Ni(mnt)2] at 173 K. (a) Packing diagram viewed along
the b-axis; (b) local arrangements of the cation and anion. Intermolecular Ni.Ni and
Fe.NC distances (A) are also shown. Dashed lines are a guide to the eye.
ꢀ
is probably attributed to closer packing in the ionic crystal, caused
by Coulomb attractions. As in the case of 1a (Fig. 2a), the donor
molecules in the salt form centrosymmetric dimers via Cpecyclo-
hexenyl face-to-face contact (Fig. 2b). Comparison of the structures
shows that the Cp ring and the cyclohexene ring face each other
more closely in the salt, which is probably related to suppression of
disorder. The distance from the centroid of the cyclohexene ring to
the mean Cpecyclohexene plane of the neighboring molecule is
at a scan rate of 10 K minꢀ1
.
4.2. 10-Cyclohexenylbiferrocene (1a) and 10,1000
dicyclohexenylbiferrocene (1b)
-
4.2.1. Preparation from 1,10-dibromobiferrocene (Scheme 1)
n-BuLi (4.8 mL, 7.63 mmol, 1.59 mol dmꢀ3 in n-hexane) was
added to a THF (40 mL) solution of 1,10-dibromobiferrocene (2.0 g,
3.79 mmol) in a dropwise manner. The solution was stirred for
30 min, after which cyclohexanone (1.12 mL, 11.9 mmol) was added
slowly. After stirring for 90 min at room temperature, the reaction
was quenched by adding a small amount of water. The solution was
extracted with ether and washed with water, and the organic layer
was separated and dried over anhydrous magnesium sulfate.
Removal of the solvent under reduced pressure afforded a red
oil (2.0 g), which was found to be a mixture of 10,1000-bis(1-
hydroxycyclohexyl)biferrocene and 10-(1-hydroxycyclohexyl)bifer-
rocene. The product was separable by column chromatography
(alumina), but the mixture was subjected to the dehydration re-
action without separation. A toluene solution (40 mL) of p-toluene
sulfonic acid (4.0 mg) was added to the mixture (1.0 g), and the
solution heated at 110 ꢁC for 3 h. The mixture was cooled to room
temperature and washed with water, and the organic layer was
separated and dried over anhydrous magnesium sulfate. The crude
product was a mixture of 1a, 1b, and biferrocene, which were
ꢀ
ꢀ
shorter in [1a][Ni(mnt)2] (3.95 A) than in 1a (4.03 A). Another
difference is the intramolecular CpeCp torsion angle in the fulva-
lenide moiety, which is 5.6ꢁ in 1a and 8.0ꢁ in [1a][Ni(mnt)2]. The
larger angle in the salt may be associated with the fixed confor-
mation of the substituent.
The acceptors form dimers in the column. The intradimer and
ꢀ
ꢀ
interdimer Ni.Ni distances are 4.677 A and 6.241 A, respectively
(Fig. 3a). The shortest Ni.S and S.S distances in the dimer are
ꢀ
ꢀ
4.064 A and 3.769 A, respectively, and those between dimers are
ꢀ
ꢀ
5.230 A and 4.251 A, respectively. Between the molecules, there was
no interatomic distance shorter than the sum of the van der Waals
radii. The overlap integrals between the LUMOs of the acceptors
were S1 ¼ 14.4 ꢂ 10ꢀ3 and S2 ¼ 3.52 ꢂ 10ꢀ3 for the intradimer and
interdimer interactions, respectively; the interdimer value was
about 1/4 of the intradimer one.
DSC measurements of [1][Ni(mnt)2] showed no indication of a
phase transition, and only a broad exothermic peak was observed
above 150 K, which probably corresponds to decomposition.

76
T. Mochida et al. / Journal of Organometallic Chemistry 741-742 (2013) 72e77
separated by gel permeation chromatography (eluent: chloroform).
separated by gel permeation chromatography and recrystallized
Compound 1a was obtained as redeorange crystals, 0.27 g (yield
from chloroform. Compound 3a was obtained as redeorange
31%). 1H NMR (CDCl3)
d
¼ 1.58 (m, 2H), 1.64 (m, 2H), 2.00 (m, 2H),
crystals (yield 17%). 1H NMR (CDCl3)
d
¼ 1.84 (m, 4H), 2.29 (m,
2.13 (m, 2H), 3.97 (s, 5H), 4.00 (s, 2H), 4.12 (s, 4H), 4.15 (t, 2H,
J ¼ 3.6 Hz), 4.23 (s, 2H), 4.31 (t, 2H, J ¼ 3.6 Hz), 5.72 (s, 1H). Anal.
Calcd for C26H26Fe2: C, 69.36; H, 5.82. Found: C, 69.11; H, 5.81.
Compound 1b was obtained as redeorange crystals, 0.20 g (yield
4H), 2.36 (m, 4H), 4.00 (s, 4H), 4.09 (s, 8H), 4.16 (s, 4H), 5.54 (s,
2H). Anal. Calcd for C25H22Fe2: C, 69.10; H, 5.57. Found: C, 68.87;
H, 5.61. Compound 3b was obtained as redeorange crystals (yield
18%). 1H NMR (CDCl3)
d
¼ 1.84 (m, 2H), 2.29 (m, 2H), 2.36 (m, 2H),
20% based on dibromobiferrocene). 1H NMR (CDCl3)
d
¼ 1.64 (m,
3.96 (s, 5H), 4.02 (s, 2H), 4.11 (s, 4H), 4.15 (t, 2H, J ¼ 3.6 Hz), 4.22
(s, 2H), 4.29 (t, 2H, J ¼ 3.6 Hz), 5.57 (s, 1H). Anal. Calcd for
C30H30Fe2: C, 71.73; H, 6.02. Found: C, 71.09; H, 6.12. Biferrocene
was isolated in 18% yield.
8H), 2.13 (m, 8H), 4.01 (s, 4H), 4.13 (s, 8H), 4.22 (s, 4H), 5.68 (s, 2H).
Anal. Calcd for C32H34Fe2: C, 72.47; H, 6.46. Found: C, 72.22; H, 6.52.
Biferrocene was isolated in 15% yield. The products were recrys-
tallized from dichloromethaneehexane (1:1 v/v).
4.5. Charge-transfer salt [1a][Ni(mnt)2]
4.2.2. Preparation of 10,1000-dicyclohexylbiferrocene (1b) via Ullman
coupling
An acetone solution (2 mL) of [Fe(C5H4Br)2][Ni(mnt)2] (3.2 mg,
4.7 mmol) and a dichloromethane solution (2 mL) of 1a (5 mg,
4.7 mmol) were mixed, and pentane vapor was diffused into the
resulting solution at room temperature under a nitrogen atmo-
sphere. Black prismatic crystals of [1a][Ni(mnt)2] formed within a
few days, with a yield of approximately 40%. IR (KBr, cmꢀ1): 2208,
1712, 1620, 1529, 1473, 1417, 1157, 1109, 1039, 850, 821. Anal. Calcd
for C34H26Fe2N4NiS4: C, 51.74; H, 3.32; N, 7.10. Found: C, 51.54; H,
3.49; N, 6.36.
A toluene solution (40 mL) of p-toluene sulfonic acid (7 mg) was
added to 1-bromo-10-(1-hydroxycyclohexyl)ferrocene (1.5 g,
4.1 mmol), and the mixture heated at 80 ꢁC for 2 h. After cooling to
room temperature, the solution was washed with water, and the
organic layer was separated, and dried over anhydrous magnesium
sulfate. Evaporation of the solution afforded 1-bromo-10-cyclo-
hexenylferrocene as a brown oil, 0.86 g (yield 61%). 1H NMR (CDCl3)
d
¼ 1.66 (m, 2H), 1.75 (m, 2H), 2.07 (m, 2H), 2.32 (m, 2H), 4.02 (t, 4H,
J ¼ 3.6 Hz), 4.21 (t, 4H, J ¼ 3.6 Hz), 4.27 (t, 4H, J ¼ 3.6 Hz), 4.33 (t, 4H,
J ¼ 3.6 Hz), 5.95 (q, 1H, J ¼ 9.0 Hz). The 1-bromo-10-cyclo-
hexenylferrocene thus obtained (0.15 g, 4.35 ꢂ 10ꢀ4 mol) was
heated with copper powder (0.28 g, 4.4 ꢂ 10ꢀ3 mol) at 135 ꢁC for
24 h. After cooling to room temperature, the mixture was extracted
with dichloromethane and filtered. The filtrate was evaporated
under reduced pressure, and the residue was purified by column
chromatography (silica gel, hexaneedichloromethane 5:1 v/v) to
give 1b as redeorange crystals (0.027 g, yield 11%).
4.6. X-ray crystallographic analysis
Single crystals of 1a, 1b, and 2b suitable for X-ray structure
analysis were obtained by slow evaporation of acetone solutions.
Single crystals of [1a][Ni(mnt)2] were obtained as described above.
Crystallographic parameters are listed in Table 3. X-ray diffraction
data were collected at 173 K on a Bruker SMART APEX CCD
ꢀ
diffractometer using MoK
a
radiation (
l
¼ 0.71073 A). The data were
corrected for absorption using the SADABS program [19]. The
structures were solved by the direct method (SHELXS 97 [20]) and
expanded using Fourier techniques. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were inserted at the
calculated positions and allowed to ride on their respective parent
atoms.
4.3. 10-Cyclohexylbiferrocene (2a) and 10,1000
dicyclohexylbiferrocene (2b)
-
Palladium carbon (7 mg) was added to an ethanol solution
(15 mL) of 1a (60 mg, 1.34 ꢂ 10ꢀ4 mol), and the solution was
vigorously stirred overnight under an atmosphere of hydrogen.
The reaction was quenched by adding water (3 mL), and the
mixture was filtered to remove insoluble materials. The filtrate
was evaporated under reduced pressure, and passed through a
short column of silica gel (eluent: hexaneedichloromethane 1:1
v/v). Recrystallization from dichloromethane and hexane gave 2a
as redeorange crystals (46 mg, yield 76%). 1H NMR (CDCl3)
Table 3
Crystallographic parameters.
1a
1b
2b
[1b][Ni(mnt)2]
Empirical
C26H26Fe2
C32H34Fe2
C32H38Fe2
C34 H26 Fe2
N4 Ni S4
789.24
173
Formula
Formula weight
T (K)
450.17
173
530.29
173
534.32
173
d
¼ 1.08e1.30 (m, 6H), 1.72 (m, 2H), 1.86 (m, 2H), 2.05 (m, 1H), 3.86
(s, 4H), 3.97 (s, 5H), 4.12 (t, 2H, J ¼ 3.6 Hz), 4.16 (t, 2H, J ¼ 3.6 Hz),
4.28 (t, 2H, J ¼ 3.3 Hz), 4.33 (t, 2H, J ¼ 3.3 Hz). Anal. Calcd for
C26H28Fe2: C, 69.05; H, 6.24. Found: C, 69.30; H, 6.20. Compound
2b was obtained, via the same method, as orange needle crystals
Crystal system
Space group
Monoclinic
P21/c
9.3738(6)
8.0953(5)
Monoclinic
P21/n
9.6398(6)
7.5594(5)
Monoclinic
P21/n
11.3466(12) 10.7386(7)
11.0705(11) 12.9359(9)
Triclinic
P-1
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
25.8271(17) 16.9248(11)
19.538(2)
14.0845(10)
99.0470(10)
109.9100(10)
113.3510(10)
1589.19(19)
2
(32 mg, yield 53%). 1H NMR (CDCl3)
d
¼ 1.08e1.30 (m, 12H), 1.72
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
(m, 4H), 1.85 (m, 4H), 2.04 (m, 2H), 3.85 (s, 8H), 4.12 (t, 4H,
J ¼ 3.6 Hz), 4.26 (t, 4H, J ¼ 3.6 Hz). Anal. Calcd for C32H38Fe2: C,
71.92; H, 7.16. Found: C, 71.07; H, 7.11. These compounds could be
also obtained by reduction of 10,1000-bis(1-hydroxycyclohexyl)
biferrocene and 10-(1-hydroxycyclohexyl)biferrocene by LiAlH4 in
the presence of AlCl3.
91.6510(10) 106.2680(10) 96.916(2)
3
ꢀ
V (A )
1959.0(2)
4
1183.95(13)
2
2436.3(4)
4
Z
Reflections
collected
Independent
reflections
Refl./Parameter
ratio
14168
8492
17748
11940
4869
17.9
2924
17
6039
13.3
7830
19.3
4.4. 10-Cyclopentenylbiferrocene (3a) and 10,1000
dicyclopentenylbiferrocene (3b)
-
Density (g cmꢀ3
)
1.526
1.488
1.457
1.649
R1, Rw (I > 2
s
)
0.0374,
0.1023
0.0459,
0.1089
1.044
0.0330,
0.0987
0.0361,
0.1022
1.024
0.0268,
0.0571
0.0297,
0.0584
1.001
0.0349,
0.0906
0.0439,
0.0963
1.03
These compounds were prepared by the same method as 1a
and 1b, except that twice the amount of cyclopentanone was
used, and the reaction time was prolonged to overnight. The
product was a mixture of 3a, 3b, and biferrocene, which were
R1, Rw (all data)
Goodness-of-fit

T. Mochida et al. / Journal of Organometallic Chemistry 741-742 (2013) 72e77
77
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Acknowledgments
This work was financially supported by KAKENHI (Nos.
23110719 and 18028022). We thank Dr. K. Mitsunaga (Toho Uni-
versity) for elemental analysis. We acknowledge M. Nakama
(Crayonsoft, Co. Ltd.) for providing a Web-based database system.
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Appendix A. Supplementary materials
CCDC 619892e619895 contain the supplementary crystallo-
graphic data for 1a, 1b, 2b, and [1a][Ni(mnt)2]. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre,12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.jorganchem.2013.05.041.
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