Synthesis, structure and electrochemistry of new diferrocenyl pyridine derivatives

Article abstract of DOI:10.1016/j.poly.2013.02.043

Four diferrocenyl pyridine derivatives, 4,6-diferrocenyl-2-phenylpyridine (1), 3,6-diferrocenyl-2-phenylpyridine (2), 4,6-diferrocenyl-2-methylpyridine (3) and 3,6-diferrocenyl-2-methylpyridine (4) were synthesized via dicarbonylcyclopentadienylcobalt or

Full text of DOI:10.1016/j.poly.2013.02.043

Polyhedron 54 (2013) 221–227
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure and electrochemistry of new diferrocenyl pyridine derivatives
⇑
Ya-Qi Wang, Li-Min Han, Quan-Ling Suo , Ning Zhu, Jian-Min Hao, Rui-Jun Xie
Chemical Engineering College, Inner Mongolia University of Technology, Hohhot 010051, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four diferrocenyl pyridine derivatives, 4,6-diferrocenyl-2-phenylpyridine (1), 3,6-diferrocenyl-2-phenyl-
pyridine (2), 4,6-diferrocenyl-2-methylpyridine (3) and 3,6-diferrocenyl-2-methylpyridine (4) were
Received 12 December 2012
Accepted 9 February 2013
Available online 26 February 2013
synthesized via dicarbonylcyclo pentadienylcobalt or Co2(CO)6(l2-g
2-ferrocenylacetylene) mediated
[2+2+2] cycloaddition reaction and characterized by FT-IR, NMR, MS, CV, elemental analysis and X-ray
single crystal diffraction analysis (1, 2, 3). Compounds 1, 2, 4 are new diferrocenyl pyridine derivatives
and the molecular structures of 1, 2, 3 have been determined for the first time. It has been shown that
cobalt-mediated [2+2+2] cycloaddition reaction is an efficient, simple new method to prepare diferroce-
nyl pyridine derivatives. The electrochemistry results reveal that the electronic communication between
the two nonequivalent ferrocenyl units in 1–4 is electrostatic interactions.
Keywords:
Diferrocenyl pyridine derivative
Carbonyl cobalt catalyst
Cycloaddition reaction
Molecular structure
Electrochemistry
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
cycloaddition reactions of nitriles with Fc-C„CH (Fc = ferrocenyl)
to prepare diferrocenyl pyridine derivatives. Four diferrocenyl pyr-
The ferrocenyl-substituted pyridines with perfect redox-active
termini have attracted considerable attention due to their high
thermal stability and excellent electrochemical reversibility of FeII/
FeIII redox couple in ferrocene [1–5]. They can be applied to the de-
sign of liquid crystal materials and molecular devices [6–8]. It is
known from the literature that C–C cross-coupling reaction is a
classic method in the synthesis of ferrocenyl-containing pyridines,
such as Suzuki, Nigishi and Stille coupling reaction [9–16]. These
coupling reactions could prepare the pyridine derivatives bearing
ferrocenyl groups in certain positions by reacting appropriate pyr-
idylhalides with ferrocenyl metal-salt intermediates which require
laborious preparation. However, the vast majority of known ferr-
ocenyl pyridines only contain a single ferrocenyl unit, and a few
of them have two or more ferrocenyl units [17]. The studies on
the chemical, physical, and electrochemical properties of diferroce-
nyl pyridines are relatively rare, especially for the diferrocenyl pyr-
idines with other substituents. Therefore, an efficient method to
synthesize diferrocenyl pyridines would be helpful in the deeper
research of these compounds.
idine derivatives 1–4 were obtained when Co2(CO)6(l2
FcC„CH) was used as catalyst in [2+2+2] cycloaddition
reactions of ferrocenylacetylene with benzonitrile or acetonitrile.
In this paper, the synthesis, molecular structure and electro-
chemical property of 1–4 are reported.
- -
g2
a
2. Experimental
2.1. General procedures
All reactions and operations were carried out under an atmo-
sphere of purified argon using standard Schlenk techniques.
Solvents and reagents were purified, dried or distilled prior to
use. Fc-C„CH and Co2(CO)6(l2-g
2-FcC„CH) were prepared using
the reported literature procedures [22,23]. CpCo(CO)2 (Cp =
cyclopentadienyl) was purchased from Alfa-Aesar Chem. and used
as received. All reactions were monitored with thin-layer chroma-
tography (TLC). Column chromatographic separations and purifica-
tions were performed on 200–300 mesh silica gel or neutral
alumina.
[2+2+2] Cycloaddition reaction is an atom-efficient, powerful
and straightforward route to substituted pyridine derivatives
[18–20]. Our research team has reported a new method to synthe-
size diferrocenyl benzene derivatives through the cycloaddition
1H and 13C NMR were recorded on a Bruker Avance-500 MHz
spectrometer. FT-IR spectra were recorded on a Nicolet FT-IR spec-
trometer using KBr discs. Elemental analyses were carried out on
an Elementar var III-type analyzer. Mass spectra were determined
using a Shimadzu LCMS-2020 instrument.
reactions of alkynes with cobalt cluster Co2(CO)6(ll
2-alkyne)
[21], which the substituted positions of ferrocenyl groups in the
benzene ring could be effectively controlled. It inspired us to try
Cyclic voltammetry was performed on a CHI-760C electrochem-
ical analyzer using a platinum disk working electrode, an Ag|AgCl
reference electrode and a platinum wire auxiliary electrode. The
⇑
Corresponding author. Tel./fax: +86 471 6575675.
E-mail addresses: szj010062@163.com, szj@imut.edu.cn (Q.-L. Suo).
working electrode surface was polished with 0.05 lm alumina
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.043

222
Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
Table 1
Optimization results of cycloaddition reaction via cobalt catalysts.
Entry
Catalyst
Conversion (%)
Yield (%)d
Selectivity (%)
Fc-C„CH
1
2
5
1
2
5
1a
2a
3a
4a
5a
6b
7b
8c
CpCo(CO)2
Co2(CO)6(l2
Co2(CO)8
CoCl2
Cobalt powder
CpCo(CO)2
48.0
55.5
100
0
13.9
7.2
0
0
0
51.3
8.4
0
6.2
3.4
0
0
0
21.6
4.1
0
23.7
34.8
55.3
0
28.9
12.8
0
0
0
51.3
9.9
0
12.7
6.1
0
0
0
21.6
4.9
0
49.6
62.9
55.3
0
-
g
2-FcC„CH)
0
0
0
100
85.1
100
10.3
38.2
94.9
10.3
44.9
94.9
Co2(CO)6(l2
Co2(CO)6(l2
-
-
g
g
2-FcC„CH)
2-FcC„CH)
a
b
c
Fc-C„CH:PhCN = 1:1.
The reaction was carried out under the optimized conditions; Fc-C„CH:PhCN = 1:6.
Co2(CO)6(l2
2-FcC„CH) as reactant reacted with PhCN; Co2(CO)6(l2 2-FcC„CH):PhCN = 1:12.
-
g
-g
d
Isolated yield.
before each run. The samples of 1–4 were dissolved in a mixture of
CH3CN and CH2Cl2 with concentration 5.0 Â 10À4 M. The support-
ing electrolyte was tetra-n-butylammonium hexafluorophosphate
(TBAHFP, 0.01 M). The scan rate was 0.1 V/s. Oxygen was purged
from the one-compartment cell before each electrochemical run.
Chromatographic analyses were realized by a Shimadzu SLC-
10A High Performance Liquid Chromatography with a C18 column
(methanol used as the mobile phase) and an UV–Vis detector.
(dCH, Cp), 821 (c
CH, Cp); ESI-MS (CH2Cl2): m/z: 524.10 [M+1]+; Anal.
Calc. for C31H25Fe2N: C, 71.16; H, 4.82; N, 2.68. Found: C, 70.85; H,
5.05; N 2.57%.
2.2.2. Synthesis of compounds 3, 4
2.2.2.1. Method III. Fc-C„CH (150 mg, 0.71 mmol, 1 equiv.), CH3CN
(375 lL, 7.2 mmol, 10 equiv.), CpCo(CO)2 [10 lL, 0.07 mmol, Co
(10 mol.%)] and toluene (10 mL) were placed in a Schlenk flask,
then the reaction mixture was refluxed for 5 h.
2.2. Synthesis
2.2.2.2. Method IV. Fc-C„CH (100 mg, 0.48 mmol, 1 equiv.), CH3CN
2.2.1. Synthesis of compounds 1, 2
2.2.1.1. Method I. Fc-C„CH (100 mg, 0.48 mmol, 1 equiv.), benzoni-
trile (300 lL, 3.0 mmol, 6 equiv.), CpCo(CO)2 [10 lL, 0.07 mmol, Co
(15 mol.%)] and toluene (10 mL) were placed in a Schlenk flask,
(250 lL, 4.8 mmol, 10 equiv.) and Co2(CO)6(l2-g
2-FcC„CH)
[10 mg, 0.02 mmol, Co (8.2 mol.%)] were dissolved in toluene
(10 mL). The reaction mixture was stirred for 5 h at a temperature
of reflux.
then the reaction mixture was refluxed for 5 h.
In a general procedure, the solvent was removed under reduced
pressure and the residue was purified by silica gel column chroma-
tography. Elution with a mixture of petroleum ether and ethyl ace-
tate (20:1, V/V) afforded compounds 3, 4 and 5. The fuscous red
crystals of 3 and 4 were obtained by recrystallizing technique.
Compound 3 has been prepared by a different synthetic route
[24], however its molecular structure has not been reported to
date.
Compound 3: 26 mg (yield, 16%, Method III) and 10 mg (yield,
9%, Method IV). M.p. 191–192 °C; 1H NMR (500 MHz, CDCl3): d
7.31 (s, 1H, pyridyl), 6.99 (s, 1H, pyridyl), 4.94–4.07 (m, 18H, Fc),
2.56 (s, 3H, CH3); 13C NMR (500 MHz, CDCl3): d 158.27, 157.59,
148.01, 117.18, 114.37 (pyridyl), 84.59, 81.88, 69.90, 69.84,
69.59, 67.47, 66.80 (Fc), 24.75 (CH3); FT-IR (KBr disk, cmÀ1):
2.2.1.2. Method II. Fc-C„CH (100 mg, 0.48 mmol, 1 equiv.), benzo-
nitrile (300 lL, 3.0 mmol, 6 equiv.) and Co2(CO)6(l2-g
2-FcC„CH)
[18 mg, 0.035 mmol, Co (15 mol.%)] were dissolved in toluene
(10 mL). The reaction solution was stirred for 5 h at 110 °C.
In a general procedure, the solvent was removed under vacuum
and the residue was purified by silica gel column chromatography
using a mixture of petroleum ether and ethyl acetate (20:1, V/V) as
eluent. The 1:1 co-crystals (I) of compound 1 and compound 2, the
byproduct 1,2,4-triferrocenylbenzene (5), were obtained. The co-
crystals I was further separated by PTLC (a mixture of petroleum
ether and ethyl acetate, 200:1, V/V) to give the pure 1 and 2. The
orange crystals of co-crystals I and compounds 1, 2 were obtained
by recrystallizing technique.
3083 (
m
CH, Cp), 1599, 1549 (
mC=C, pyridyl), 1407 (mC=C, Cp), 1105,
Compound 1: 64 mg (yield, 51%, Method I) and 10 mg (yield, 8%,
Method II). M.p. 171–172 °C; 1H NMR (500 MHz, CDCl3): d 8.16 (s,
1H, pyridyl), 8.15 (s, 1H, pyridyl), 7.59–7.40 (m, 5H, Ph = phenyl),
5.07–4.08 (m, 18H, Fc); 13C NMR (500 MHz, CDCl3): d 158.70,
156.35, 148.72, 115.35, 114.35 (pyridyl), 139.88, 128.74, 128.59,
126.93 (Ph), 84.51, 82.03, 69.96, 69.74, 69.65, 67.58, 66.92 (Fc);
999 (dCH
,
Cp), 818 (cCH, Cp); ESI-MS (CH2Cl2, m/z): 462.05
[M+1]+; Anal. Calc. for C26H23Fe2N: C, 67.72; H, 5.03; N, 3.04.
Found: C, 67.54, H, 5.14, N, 2.88%.
Compound 4: 8 mg (yield, 5%, Method III) and 3 mg (yield, 3%,
Method IV). M.p. 182–183 °C; 1H NMR (500 MHz, CD3OD): d 8.04
(d, J = 6.5 Hz, 1H, pyridyl), 7.49 (d, J = 8.0 Hz, 1H, pyridyl), 4.99 (s,
2H, Fc), 4.60–4.09 (m, 16H, Fc), 2.61 (s, 3H, CH3); 13C NMR
(500 MHz, CDCl3): d 155.79, 154.78, 137.32, 129.81, 117.47 (pyri-
dyl), 85.57, 84.55, 69.56, 69.47, 68.36, 67.31 (Fc), 24.48 (CH3);
FT-IR (KBr disk, cmÀ1): 3131 (
m
CH, Cp), 1598, 1549 (
mC=C, Ph),
1401 (mC=C, Cp), 1107, 1003 (dCH, Cp), 820 (cCH, Cp); ESI-MS (CH2Cl2,
m/z): 524.10 [M+1]+; Anal. Calc. for C31H25Fe2N: C, 71.16; H, 4.82;
N, 2.68. Found: C, 71.33; H, 4.78; N, 2.67%.
FT-IR (KBr disk, cmÀ1): 3112 (
mCH, Cp), 1583, 1560 (mC=C, pyridyl),
Compound 2: 27 mg (yield, 22%, Method I) and 5 mg (yield, 4%,
Method II). M.p. 180–182 °C; 1H NMR (500 MHz, CDCl3): d 8.02 (d,
J = 8.0 Hz, 1H, pyridyl), 7.38 (d, J = 8.0 Hz, 1H, pyridyl), 7.43–7.40
(m, 2H, Ph), 7.31–7.29 (m, 3H, Ph), 4.98–4.05 (m, 18H, Fc); 13C
NMR (500 MHz, CDCl3): d 156.16, 156.03, 138.78, 129.37, 117.90
(pyridyl), 141.01, 129.95, 127.57, 127.53 (Ph), 85.47, 84.32, 70.02,
69.72, 69.60, 69.53, 68.12, 67.52 (Fc); FT-IR (KBr disk, cmÀ1):
1401 (mC=C, Cp), 1104, 1000 (dCH, Cp), 820 (cCH, Cp); ESI-MS (CH2Cl2,
m/z): 462.05 [M+1]+; Anal. Calc. for C26H23Fe2N: C, 67.72; H, 5.03;
N, 3.04. Found: C, 67.45; H, 4.88; N, 2.97%.
Compound
5 (red-orange byproduct 1,2,4-triferrocenylben-
zene): M.p. 255–257 °C; 1H NMR (500 MHz, CDCl3): d 7.88–7.34
(m, 3H, Ph), 4.73–4.04 (m, 27H, Cp); 13C NMR (500 MHz CDCl3): d
136.85, 136.10, 134.96, 131.18, 128.90, 123.64 (Ph), 88.05, 87.46,
85.40, 70.81, 70.48, 69.65, 69.60, 69.45, 69.43, 68.88, 67.29,
3123 (mCH, Cp), 1582, 1544 (mC=C, Ph), 1402 (mC=C, Cp), 1106, 1002

Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
223
Table 2
Crystal data and relevant structural parameters for co-crystals I and compounds 2, 3.
Identification code
I
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
31H25Fe2N
C62H50Fe4N2
1046.44
93(2)
0.71073
monoclinic
P21/c
21.767(6)
18.312(5)
12.329(4)
90.00
C26H23Fe2N
461.15
93(2)
0.71073
monoclinic
P21
10.3883(8)
27.875(2)
10.9964(9)
90.00
523.22
93(2)
0.71073
orthorhombic
Pca21
10.539(4)
18.598(8)
23.381(10)
90.00
b (Å)
c (Å)
a
(°)
b (°)
90.00
90.00
4583(3), 8
1.517
1.287
105.078(4)
90.00
4745(2), 4
1.465
1.243
2160
0.20 Â 0.05 Â 0.05
2.04–28.48
À29 6 h 6 27
0 6 k 6 24
0 6 l 6 16
12574
106.882(2)
90.00
3047.0(4), 6
1.508
1.440
1428
0.20 Â 0.05 Â 0.05
2.05–25.00
À12 6 h 6 7
À33 6 k 6 33
À12 6 l 6 13
16142
c
(°)
Volume (Å3), Z
Density (calculated) (Mg mÀ3
)
)
Absorption coefficient (mmÀ1
F(000)
2160
Crystal size (mm3)
0.20 Â 0.05 Â 0.05
1.09–24.48
À12 6 h 6 12
À21 6 k 6 21
À17 6 l 6 27
22132
h Range for data collection (°)
Limiting indices
Reflections collected
Independent reflections
Completeness to h (%)
6106
100
12574
99
10663
99.8
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.9385/0.7829
6106/883/614
0.941
0.9405/0.7892
12574/0/613
1.114
0.9315/0.7616
10663/1210/788
1.113
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0685, wR2 = 0.1448
R1 = 0.1881, wR2 = 0.2007
0.458/À0.617
R1 = 0.0663, wR2 = 0.1369
R1 = 0.1427, wR2 = 0.1633
0.727/À0.777
R1 = 0.0602, wR2 = 0.1260
R1 = 0.1028, wR2 = 0.1428
0.660/À0.439
Largest difference peak and hole (e ÅÀ3
)
Fe
Fe
Fe
Fe
Fe
Fe
Fe
Fe
C
CH
Catalyst
toluene,reflux
+
R
C N
Fe
+
+
+
+
R
R
N
N
N
R
R
N
Fe
R=Ph, CH3
Fe
Fe
5
B
C
D
A
Catalyst = CpCo(CO)2 ; Co (CO) (μ2-η2-FcC≡CH)
A = compound 1 or 3; R = Ph or CH3
B = compound 2 or 4; R = Ph or CH3
2
6
Scheme 1. The possible products of ferrocenylacetylene-nitrile cycloaddition reaction.
67.26, 66.25 (Fc); FT-IR (KBr disk, cmÀ1): 3089 (
mCH, Cp), 1605,
monochromated Mo-K
a
(k = 0.71073 Å) radiation. All data was
-scan techniques. The molecular con-
1523 (
m
C=C, Ph), 1106, 1002 (dCH, Cp), 817 (
c
CH, Cp); ESI-MS (CH2Cl2,
collected using the - and x
u
m/z): 630.05 [M]+; Anal. Calc. for C36H30Fe3: C, 68.61; H, 4.79.
figurations were solved by direct methods and refined by full-
matrix least squares on F2 using SHELXL-97 [25]. All non-hydrogen
atoms were refined anisotropically. All hydrogen atoms were
added on calculated positions. The bond lengths were restrained
with DFIX, and then the additional refinements were performed.
Crystal data and relevant structural parameters are given in
Table 2.
Found: C, 68.49; H, 4.84%.
2.3. Optimization of synthetic condition
The optimization of cycloaddition reaction focused on the prep-
aration of 1 and 2. The synthesis details are similar to Section 2.2.1.
The influence of reactant ratio, solvent, reaction temperature and
time on the activity and selectivity of five cobalt catalysts, Co,
3. Results and discussion
CoCl2, Co2(CO)8, CpCo(CO)2 and Co2(CO)6(l2-g
2-FcC„CH), was
investigated.
3.1. Synthesis of compounds 1–4
The optimal reactions were obtained with 15% (mol) catalyst
concentration, 1:6 ratio of Fc-C„CH to PhCN, toluene used as sol-
vent, 5 h reaction time and reflux reaction temperature. The opti-
mal results are listed in Table 1.
The [2+2+2] cycloaddition reaction is a simple atom-economical
method for producing six-membered hetero cyclic compounds. We
found that Co2(CO)6(l2-g
2-FcC„CH) could catalyze the cycloadd-
dition reaction of ferrocenylacetylene with benzonitrile or acetoni-
trile. Although the yield of pyridine derivatives is not high, this is
the first time to report the synthesis of diferrocenyl pyridines using
Co2(CO)6(l2
also have investigated other cobalt catalysts, Co, CoCl2, Co2(CO)8,
2.4. X-ray crystallography study
All measurements for co-crystals I, compounds 2 and 3 were
made on a Bruker SMART APEX CCD diffractometer with graphite
-g
2-FcC„CH) as a catalyst (see Methods II and IV). We

224
Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
Fig. 1. The molecular structures of 1 and 2 in their 1:1 co-crystals I.
Fig. 2. The molecular structures of compound 2.
CpCo(CO)2, using the cycloaddition reaction of ferrocenylacetylene
with benzonitrile as a model reaction in order to find an efficient
catalyst for this type of reaction. The results in Table 1 (entries
pyridine derivatives. It also could be deduced from Table 1 (entries
1 and 6) that the use of a large excess of benzonitrile appears to be
the most critical factor for the conversion and selectivity of the
synthesis of pyridine derivatives.
1–5) show that only CpCo(CO)2 and Co2(CO)6(l2-g
2-FcC„CH)
could give pyridine products (1, 2); Co2(CO)8 has better catalytic
activity for the synthesis of ferrocenyl benzene derivative (5).
The optimal catalytic activity and selectivity for the cycloaddi-
tion reaction are demonstrated in Table 1 (entries 6 and 7). The re-
sults exhibit that CpCo(CO)2 is an efficient catalyst for preparing
Although the diversified diferrocenyl pyridine derivatives were
expected from the [2+2+2] cycloaddition of two ferrocenylacetyl-
enes with one nitrile (Scheme 1), only two derivatives (A, B) were
successfully detected and separated. The products C and D have
not been detected by either TLC or HPLC method in our work.
The substituted position of ferrocenyl groups in 1–4 demonstrates
the two ferrocenyl groups in pyridine ring always adopt meta-po-
sition (A) or para-position (B). However, the ferrocenyl units in
benzene ring of 5 can choose ortho-position. The compound A is
the main pyridine product owing to the steric bulk of the ferroce-
nyl groups in pyridine rings [26].
diferrocenyl pyridines (1, 2) and Co2(CO)6(l2-g
2-FcC„CH) is a bet-
ter catalyst for preparing triferrocenyl benzene (5).
Only the cyclotrimerization byproduct 1,2,4-triferrocenylben-
zene (5) was obtained when using Co2(CO)6(l2-g
2-FcC„CH) as
starting material reacted with benzonitrile without the raw mate-
rial Fc-C„CH (Table 1, entry 8). It reveals that the ligand Fc-C„CH
in catalyst Co2(CO)6(l2
-g
2-FcC„CH) has contributed to the forma-
We provided a new simple method to synthesize the diferroce-
nyl pyridine derivatives, in which ferrocenylacetylene was used di-
rectly without the preparation of metal-salt intermediates, and the
tion of 5. The data in Table 1 suggest that the carbonyl cobalt frag-
ment and the reactant Fc-C„CH are essential to the synthesis of

Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
225
Fig. 3. The molecular structures of compound 3.
pyridines bearing two ferrocenyl groups at 2,4- and 2,5- positions
were obtained simultaneously by a single step with the best yield
of 51% and 22%, respectively.
tuted pyridines (1, 3) are the main products in our cycloaddition
reactions.
3.3. Electrochemistry study
3.2. Molecular structures of co-crystals I and compounds 2, 3
The electrochemical properties of compounds 1–4 were investi-
gated by cyclic voltammetry (Table 3). The 1–4 display two redox
waves in À0.1 to 0.6 V scan range, which are assigned to two FeII/
FeIII redox couples from two ferrocenyl units. From Ipa/Ipc value
(ꢀ1) of each couple, it is obvious that the redox processes are
chemically reversible [30–32].
The ferrocenyl units present in 1–4 could be oxidized sepa-
rately. The two ferrocenyl groups of 1–4 are chemically nonequiv-
alent, therefore, the first ferrocenyl unit of 1–4 is oxidized at
distinct potentials due to its different chemical environment
The molecular structures of co-crystals I, compounds 2 and 3
were determined by X-ray single crystal diffraction analysis. Crys-
tal data and relevant structural parameters are enumerated in Ta-
ble 2. The very thin natures of the crystals lead to the poor values
of R (Table 2). The molecular structures with the atom numbering
scheme are shown in Figs. 1–3 and the unit cell of co-crystals I is
demonstrated in Fig. 4.
There are two or three molecules in one unit cell of co-crystals I,
compounds 2 and 3, respectively. The formation of C–HÁ Á Á
p hydro-
gen bonds (Fig. 5) is the main reason of this conformation phenom-
enon [27]. The bond lengths and angles of 1–3 are within the
normal range of ferrocenyl-substituted pyridine derivatives
[28,29].
Although the single crystal of compound 1 has not been ac-
quired yet, the single crystal of the 1:1 co-crystals I of compound
1 and compound 2 was fortunately obtained (Fig. 1). The one unit
cell of co-crystals I contains four molecules of 1 and 2, respectively
(Fig. 4). The molecular structures in Fig. 1 show that 1 and 2 are
two isomeric twin molecules with different substitution pattern
of ferrocenyl groups on the central pyridine ring. The two ferroce-
nyl groups of 1 are at meta-position in the pyridine ring and adopt
a cis conformation. The two ferrocenyl groups of 2 adopt para-po-
sition and a trans conformation. The two Cp rings from the two
ferrocenyl groups and the phenyl ring of 1 are almost coplanar
with the central pyridine ring, whereas the two Cp and phenyl
rings of 2 are significantly tilted out of planarity (Figs. 1 and 2).
The coplanar situation of Cp rings with the central pyridine ring
in 3 is similar to 1. Whether the molecule of 3 (Fig. 3) is a cis or
trans conformation, the connected two Cp and pyridine rings are
nearly coplanar.
The molecular structures of 1–3 show that the steric hindrance
in 1 and 3 is much smaller than that in 2, therefore 2,4,6-substi-
Fig. 4. The unit cell showing packing of molecules 1 and 2 in their 1:1 co-crystals I.

226
Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
Fig. 5. C–HÁ Á Á
p
hydrogen bonds in compound 3.
Table 3
CV data of compounds 1–4 and ferrocene.
1
2
Compound
Epa1 (mV)
Epc1 (mV)
E1/2 (mV)
Epa2 (mV)
Epc2 (mV)
E1/2 (mV)
D
E1/2 (mV)
Ipa1/Ipc1
Ipa2/Ipc2 (fitting)
1
2
3
4
213
176
187
184
200
108
98
107
87
160.5
137
147
135.5
111
332
288
327
306
227
210
207
189
279.5
249
267
119
112
120
112
1.26
0.97
0.96
1.00
1.18
1.07
0.96
1.04
247.5
FcH
22
(Table 3). For example, the effect of the phenyl or methyl on the
first ferrocenyl unit of 1 or 3 is different, hence the first oxidation
potentials (Epa1) of 1 and 3 are 213 mV and 187 mV, respectively. It
is noteworthy that comparing with the first oxidation potential
(Epa1) of ferrocene, the Epa1 is higher for 1 and is lower for the other
pyridine compounds (2–4), which can be ascribed to the better
coplanar effect of the four connected rings (pyridine, phenyl and
two Cp rings) of 1 leads to the stronger conjugated effect on the
ferrocenyl groups.
1 ꢀ 3 > 2 = 4, which means that interactions between the two ferr-
ocenyl groups of meta-substituted pyridines are slightly larger
than those of para-substituted pyridines. This phenomenon is con-
sistent with the shorter metal–metal distances in 1, 3. The same
ferrocenyl substituted pattern has almost the same
DE1/2 value,
which indicates that E1/2 of 1–4 is not affected by other elec-
D
tron-withdrawing or electron-donating substituent, such as phenyl
or methyl group. The electronic communication between the two
ferrocenyl substituents of 1–4 can be attributed to electrostatic
interactions, and belongs to a behavior of the class I according to
Robin and Day [1,17,33–35].
The oxidation potential differences (
120 and 112 mV, respectively. The
D
D
E1/2) of 1–4 are 119, 112,
E1/2 order of 1–4 is

Y.-Q. Wang et al. / Polyhedron 54 (2013) 221–227
227
[2] D. Braga, M. Polito, D. D’addario, E. Tagliavini, D.M. Proserpio, F. Grepioni, J.W.
Steed, Organometallics 22 (2003) 4532.
4. Conclusion
[3] C.D. Nunes, T.M. Santos, H.M. Carapuça, A. Hazell, M. Pillinger, J. Madureira,
W.M. Xue, F.E. Kühn, I.S. Gonçalves, New J. Chem. 26 (2002) 1384.
[4] J.A. Mata, S. Uriel, R. Llusar, E. Peris, Organometallics 19 (2000) 3797.
[5] O. Carugo, G. De Santis, L. Fabbrizzi, M. Licchelli, A. Monichino, P. Pallavicini,
Inorg. Chem. 31 (1992) 765.
[6] T.M. Keller, S.B. Qadri, Chem. Mater. 16 (2004) 1091.
[7] S. Kume, K. Nomoto, T. Kusamoto, H. Nishihara, J. Am. Chem. Soc. 131 (2009)
14198.
[8] J.D. Crowley, I.M. Steele, B. Bosnich, Chemistry 12 (2006) 8935.
[9] B.H. Long, Y.B. Yang, L.X. Wang, W.M. He, J.N. Xiang, Synth. Commun. 40 (2010)
1202.
[10] R. Knapp, M. Rehahn, J. Organomet. Chem. 452 (1993) 235.
[11] K. Sünkel, S. Weigand, Inorg. Chim. Acta 370 (2011) 224.
[12] V.C. Gibson, J.L. Nicholas, J.O. Philip, A.J.P. White, D.J. Williams,
Organometallics 25 (2006) 1932.
The synthesis of three new diferrocenyl pyridine derivatives (1,
2, 4) was accomplished via [2+2+2] cycloaddition reaction using
CpCo(CO)2 or Co2(CO)6(l2-g
2-FcC„CH) as a catalyst. The molecu-
lar and crystal structures of 1–3 have been determined by X-ray
single crystal diffraction analysis. CpCo(CO)2 is an efficient catalyst
for preparing diferrocenyl pyridine derivatives and Co2(CO)6(l2
g
-
2-FcC„CH) is a better catalyst for preparing triferrocenyl ben-
zene derivatives. The electrochemistry results of 1–4 reveal that
the interactions between the two ferrocenyl substituents are elec-
trostatic interactions and the oxidation potential difference (DE1/2)
between the two ferrocenyl units is only affected by the substi-
tuted position of ferrocenyl groups in the central pyridine ring.
[13] C.M. Liu, B.H. Chen, W.Y. Liu, X.L. Wu, Y.X. Ma, J. Organomet. Chem. 598 (2000)
348.
[14] C.M. Liu, Y.L. Guo, X. Wu, Y. Liang, Y.X. Ma, J. Organomet. Chem. 612 (2000)
172.
[15] I.P. Beletskaya, A.V. Tsvetkov, G.V. Latyshev, V.A. Tafeenko, N.V. Lukashev, J.
Organomet. Chem. 637 (2001) 653.
Acknowledgments
We are grateful to the Program for New Century Excellent Tal-
ents in University (NCET-08-858), the Natural Science Foundation
of China (NSFC 21062011, NSFC 21266019), the Natural Science
Foundation of the Inner Mongolia (20080404MS020), the Scientific
Research Program of Higher Education Institutions of Inner Mon-
golia Autonomous Region (NJZY12053) and the Research Fund for
Project of Inner Mongolia University of Technology (X201208).
[16] J. Rajput, J.R. Moss, A.T. Hutton, D.T. Hendricks, C.E. Arendse, C. Imrie, J.
Organomet. Chem. 689 (2004) 1553.
[17] J.R. Wright, K.J. Shaffer, C.J. Mcadam, J.D. Crowley, Polyhedron 36 (2012) 73.
[18] P.R. Chopade, J. Louie, Adv. Synth. Catal. 348 (2006) 2307.
[19] J.A. Varela, C. Saá, Synlett 17 (2008) 2571.
[20] C.X. Wang, X.C. Li, F. Xu, B.S. Wan, Prog. Chem. 22 (2010) 610.
[21] R.J. Xie, L.M. Han, N. Zhu, H.L. Hong, Q.L. Suo, P. Fu, Polyhedron 38 (2012) 7.
[22] J. Polin, H. Schottenberger, Org. synth. 73 (1996) 262.
[23] C.U. Pittman, J. Smith, L.R. Smith, J. Organomet. Chem. 90 (1975) 203.
[24] K. Shibata, I. Katsuyama, H. Izoe, M. Matsui, H. Muramatsu, J. Heterocycl.
Chem. 30 (1993) 277.
Appendix A. Supplementary data
[25] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures,
University of Göttingen, Göttingen, Germany, 1997.
[26] J.A. Varela, C. Saá, Chem. Rev. 103 (2003) 3787.
[27] M.H. Luo, L.M. Han, N. Zhu, H.L. Hong, R.J. Xie, Q.L. Suo, L.H. Weng, J. Coord.
Chem. 63 (2010) 3805.
[28] J.G. Seitzberg, C. Dissing, I. Søtofte, P.O. Norrby, M. Johannsen, J. Org. Chem. 70
(2005) 8332.
[29] J. Rajput, A.T. Hutton, J.R. Moss, H. Su, C. Imrie, J. Organomet. Chem. 691 (2006)
4573.
[30] C. Patoux, C. Coudret, J.P. Launay, C. Joachim, A. Gourdon, Inorg. Chem. 36
(1997) 5037.
CCDC 888003, 888584, 888583 contain the supplementary crys-
tallographic data for co-crystals I, compounds 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2013.02.043.
[31] M.C.P. Wang, Y.C. Li, N. Merbouh, H.Z. Yu, Electrochim. Acta 53 (2008) 7720.
[32] P. Huang, B. Jin, P. Liu, L. Cheng, W. Cheng, S. Zhang, J. Organomet. Chem. 697
(2012) 57.
[33] M. Iyoda, T. Kondo, T. Okabe, H. Matsuyama, S. Sasaki, Y. Kuwatani, Chem. Lett.
(1997) 35.
References
[34] K. Kowalski, R.F. Winter, J. Organomet. Chem. 694 (2009) 1041.
[35] M.B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 10 (1967) 247.
[1] U. Pfaff, A. Hildebrandt, D. Schaarschmidt, T. Hahn, S. Liebing, J. Kortus, H. Lang,
Organometallics 31 (2012) 6761.